Interfacial Chemistry in High‐Voltage Ni–Mn‐Based Cathodes: Understanding and Controlling Degradation Pathways

ABSTRACT

Owing to its high energy density, environmental friendliness, and low cost, the high‐voltage Ni–Mn‐based oxides material has emerged as a highly promising cathode candidate. Nevertheless, such kind of material faces significant limitations including hydrofluoric acid (HF) corrosion, transition metal dissolution, and the Jahn–Teller effect, which substantially hinder its large‐scale commercialization. This review comprehensively introduces the fundamental characteristics and limitations of LiNi_0.5Mn_1.5O₄ (LNMO) and LiNi_xCo_yMn_zO₂ (NCM), followed by state‐of‐the‐art mitigation approaches of CEI regulation encompassing electrolyte additives, synergistic additive combinations, doping modifications, surface coating engineering, and particle design optimization. Future research could explore the synergistic combination of these modification approaches, potentially sparking novel research avenues.

This review discusses interfacial chemistry in understanding the failure mechanisms of high voltage metal oxide cathode (HVMOC) and elaborates comprehensive strategies to control the degradation pathways of the battery, providing assistance for the realization of the application of high voltage lithium metal batteries.

1. Introduction

Since their commercial emergence in the 1990s, lithium‐ion batteries have been rapidly adopted across various fields due to their advantages of compact size, absence of memory effect, and relatively long cycle life. However, rising living standards have placed greater demands on the energy density of lithium‐ion batteries, particularly within the electric vehicle power battery sector, which increasingly demands higher energy density batteries to meet volumetric constraints. Given that cathode materials account for approximately 40% of the total battery cost, the development of high‐energy‐density, low‐cost cathode materials has become a prevailing research trend [1].

Currently, commercial lithium‐ion battery cathode materials include LiFePO₄ [2], LiCoO₂ [3], LiMn₂O₄ [4], and LiNi_xCo_yMn_zO₂. Among these, LiCoO₂ and LiNi_xCo_yMn_zO₂ meet the requirements for high energy density. However, the toxicity and high cost of cobalt constrain their commercial viability [5, 6]. Consequently, a cobalt‐free, high‐voltage spinel cathode material, LiNi_0.5Mn_1.5O₄ (LNMO), has emerged as a highly promising candidate. Its high operating voltage of 4.7 V enables a theoretical energy density of up to 650 Wh kg⁻¹. Furthermore, its abundant raw material resources and suitable cost position LNMO as one of the most promising cathode materials for next‐generation lithium‐ion batteries [7, 8, 9, 10].

The term “high‐voltage” is frequently used in the lithium‐ion battery literature but often lacks a precise operational definition, which can hinder direct comparison between studies. In this review, we adopt a multi‐faceted definition to provide clarity. “high‐voltage” is defined as charging to an upper cut‐off voltage (UCV) of ≥ 4.4 V (vs. Li/Li⁺). This threshold is selected for two primary reasons. First, it marks the practical stability limit of conventional carbonate‐based electrolytes (e.g., EC/EMC with LiPF₆), beyond which oxidative decomposition at the cathode surface becomes kinetically significant and necessitates advanced interfacial stabilization strategies. Second, this voltage regime encompasses the operating conditions relevant to the two cathode families central to this review: the high‐voltage spinel LNMO, which exhibits a characteristic plateau near 4.7 V, and Ni‐rich layered oxides (e.g., NMC811), which are commonly charged to 4.4–4.5 V to maximize energy density.

Structural studies on LNMO reveal two distinct space group configurations. In one form, Ni atoms partially and orderly substitute for Mn atoms, occupying the 4a sites while Mn resides on the 12d sites, forming distinct Ni─O and Mn─O bonds; this ordered phase crystallizes in the P4₃32 space group [11]. The other form features Ni atoms statistically substituting for Mn atoms on the 16d sites, resulting in average M(Ni, Mn)─O bonds. This disordered structure, analogous to LiMn₂O₄, belongs to the Fd3m space group and represents a non‐stoichiometric LiNi_0.5Mn_1.5O_4−δ compound, where δ denotes the oxygen deficiency content [8, 12]. Comparatively, the disordered Fd3m structure facilitates superior lithium‐ion diffusion kinetics, whereas the ordered P4₃32 structure exhibits enhanced thermal stability. The transition between these two structural types is governed by the interplay of synthesis temperature and oxygen partial pressure, which together control the oxygen non‐stoichiometry and the associated Mn^{3 +} content [13]. The oxygen deficiency determines the concentration of Mn^{3 +} in the structure, as charge compensation for oxygen vacancies requires the reduction of Mn^{4 +} to Mn^{3 +}. A higher oxygen deficiency promotes the disordered Fd3m structure, whereas a lower oxygen deficiency favors the ordered P4₃32 structure. Synthesis under high oxygen partial pressure (e.g., pure O₂ atmosphere) suppresses oxygen vacancy formation, yielding a low oxygen deficiency material with minimal Mn^{3 +} content. Under such conditions, the ordered P4₃32 phase is stabilized even at elevated temperatures. Conversely, synthesis under low oxygen partial pressure (e.g., air or inert atmosphere) promotes oxygen loss from the lattice, increasing oxygen deficiency and generating higher concentrations of Mn^{3 +} [14, 15, 16]. This reduction process destabilizes the ordered cation arrangement and induces the transformation to the disordered Fd3m structure. The influence of temperature is mediated through its effect on the equilibrium oxygen non‐stoichiometry: higher temperatures favor oxygen release, thereby increasing oxygen deficiency and promoting the disordered phase, while lower temperatures favor oxygen retention, reducing oxygen deficiency and stabilizing the ordered phase.

Importantly, the ordered–disordered transition is reversible and can be controlled by post‐synthesis annealing under controlled oxygen partial pressure. Subjecting a disordered Fd3m material to annealing under oxygen‐rich conditions at moderate temperatures (600°C–700°C) promotes oxygen uptake, re‐oxidizes Mn^{3 +} to Mn^{4 +}, reduces oxygen deficiency, and restores the ordered P4₃32 structure. Thus, the final phase composition of LNMO is not determined by a simple temperature rule but rather by the coupled effects of synthesis temperature and, more critically, the oxygen chemical potential that governs oxygen non‐stoichiometry during synthesis and post‐treatment [17].

LNMO is formed by substituting one‐quarter of the Mn in LiMn₂O₄ with Ni. The introduction of Ni²⁺ elevates the valence state of Mn, which theoretically exists entirely as Mn⁴⁺. Since Mn⁴⁺ is electrochemically inert, it enhances the cycling stability of LNMO and mitigates significant Mn³⁺ dissolution [18]. However, this ideal state remains theoretical. In practice, trace amounts of Mn³⁺ persist in LNMO, inducing Jahn–Teller distortion and compromising structural integrity [19, 20]. The impact of Mn³⁺ on electrochemical performance remains debated, as its presence increases structural disorder while concurrently improving electronic conductivity and facilitating Li⁺ diffusion at high rates [21, 22, 23]. Consequently, optimizing the Mn³⁺ content is critical for achieving superior electrochemical performance. Furthermore, the high operating voltage of 4.7 V triggers electrolyte decomposition, generating HF that degrades the LNMO crystal structure [24, 25, 26]. In summary, despite its considerable advantages, these unresolved challenges have hindered the commercialization of LNMO. Substantial efforts are therefore directed toward material modification (e.g., doping, coating) and advanced electrolyte formulations to overcome these limitations [27].

While investigating methods to enhance the electrochemical performance of LNMO, we observed that high‐nickel ternary cathode materials (e.g., NCM811, NCM622), which similarly feature high operating voltage and high energy density, face challenges analogous to those encountered by LNMO. Both material systems suffer from detrimental interfacial side reactions and the corrosive impact of hydrofluoric acid (HF) generated by electrolyte decomposition, along with the issue of transition metal ion dissolution [28]. Although the primary issue of high‐nickel NCM stems from the poor thermal stability induced by high nickel content, the problems ultimately manifest as an unstable interface and compromised crystal structure. For both types of batteries, the challenge lies not merely in a breakthrough within a single material system, but rather in the synergistic advancement of electrode materials, electrolytes, and interface engineering [29, 30]. Consequently, their solutions share common ground in this regard. Consequently, strategies for mitigating these problems share common ground. For instance, Wang et al. demonstrated remarkable improvements in LiNi_1/3Co_1/3Mn_1/3O₂/graphite pouch cells by incorporating lithium difluoro phosphate (LiDFP) as an electrolyte additive [31]. Several years later, Hai et al. successfully applied the same LiDFP additive to LNMO batteries [32]. Other additives, such as lithium tetrafluoroborate (LiBF₄), provide further examples of this cross‐applicability. This observation indicates that certain electrolyte additives proven effective for NCM ternary batteries can also be beneficially applied to LNMO systems. Given that NCM ternary cathode materials are commercially established and extensively researched, this article elaborates on improvement strategies relevant to both LNMO and NCM‐based batteries [33, 34]. This comparative approach aims to identify shared characteristics and provide insights for future research directions.

Across the spectrum of strategies employed to enhance the performance of LNMO and NCM‐based batteries, the regulation of the cathode electrolyte interphase (CEI) represents a central objective, whether pursued through electrolyte modification or cathode doping/coating [35, 36, 37]. The formation of a thin yet robust CEI is widely recognized as a critical factor in improving battery electrochemical performance, as such an optimized interphase minimizes cathode degradation, hinders transition metal dissolution, and typically results in a LiF‐rich layer that enhances ionic conductivity [38]. It is important to note, however, that CEI properties do not operate in isolation. The overall electrochemical performance of high‐voltage cathodes is governed by the complex interplay of multiple factors, including bulk structural stability, surface reconstruction phenomena, chemo‐mechanical degradation (e.g., microcrack propagation), and transport limitations, with CEI characteristics serving as one essential component within this interconnected system. Recognizing this multifaceted nature, the present review focuses on recent progress in CEI regulation, specifically through electrolyte modification and cathode doping/coating, as applied to LNMO and NCM ternary batteries, while acknowledging that these interfacial strategies must be considered alongside other complementary approaches to achieve comprehensive performance optimization.

2. Challenges Toward High‐Voltage Ni–Mn‐Based Oxides

To discuss improvement methods for high‐voltage Ni–Mn‐based oxides including LNMO and ternary NCM batteries, it is first necessary to identify their existing problems. This section now addresses both the shared and unique issues of these high‐voltage cathode materials. Although LNMO and NCM have distinct crystal structures, both cathode materials exhibit highly convergent degradation pathways when subjected to high‐voltage operation. A primary shared failure mechanism is the aggressive parasitic reactions at the CEI. Under high states of charge (high potential), both materials catalyze the oxidative dehydrogenation of carbonate‐based electrolytes. The generated protons (H⁺) readily react with trace moisture or fluoride salts (e.g., LiPF₆), yielding hydrofluoric acid. This HF generation initiates a cascade of degradation events common to both LNMO and NCM: (i) Surface Etching and Transition Metal Dissolution: HF leaches transition metals from the lattice, destroying the structural integrity of the surface. (ii) Surface Phase Reconstruction: The loss of oxygen and TM dissolution drive a phase transition from the pristine layered/spinel structure to a rock‐salt phase (e.g., NiO‐like), which densifies the surface and impedes lithium‐ion transport. (iii) Anode‐Cathode Crosstalk: The dissolved TM ions migrate through the electrolyte to the anode, where they disrupt the solid electrolyte interphase and accelerate active lithium loss. Therefore, the degradation of both LNMO and NCM should be viewed not as isolated material failures, but as a coupled chemical‐structural instability driven by synchronized interfacial side reactions.

2.1. LNMO

Spinel LNMO is regarded as one of the most promising cathode materials for batteries, it suffers from numerous drawbacks that hinder its commercialization [39]. Primarily, the high operating voltage of LNMO (∼4.7 V vs. Li/Li⁺) imposes severe stability demands on all internal battery components, such as the electrolyte, current collectors, binders, and conductive additives. The high voltage induces complex decomposition of the electrolyte. The resulting decomposition products deposit onto the cathode surface, forming an inhomogeneous and poorly conductive CEI that impedes Li⁺ transport during lithiation/de‐lithiation cycling. Concurrently, trace water present in the electrolyte reacts with the LiPF₆ salt, generating hydrofluoric acid (HF), which corrodes both the cathode and anode, inducing detrimental effects such as intergranular stress, phase boundary movement, and particle cracking (Figure 1).

FIGURE 1.

Schematic of the space group structure and challenges in LNMO.

Secondly, transition metal dissolution presents a major challenge for LNMO. Mechanistic studies specifically addressing metal ion dissolution in LNMO remain relatively scarce. Current understanding of Mn dissolution in LNMO largely relies on findings from research on LiMn₂O₄ spinel, given their shared spinel structure. During high‐temperature sintering, partial reduction of Mn⁴⁺ to Mn³⁺ occurs in LNMO to maintain charge neutrality. It has been established that Mn on the (111) facets primarily exist in the +3‐oxidation state and exhibits a higher propensity for dissolution. Furthermore, Mn ions within distorted octahedral sites on these (111) facets are more susceptible to generating lattice stress, leading to microcrack formation within the crystal [40, 41, 42]. Additionally, the presence of Mn³⁺ triggers Jahn–Teller distortion, which destabilizes the LNMO structure. Under elevated temperatures, Mn³⁺ readily undergoes a disproportionation reaction (2Mn³⁺ → Mn²⁺+ Mn⁴⁺) [43]. Beyond degrading the cathode structure, dissolved Mn species migrate and deposit onto the anode, blocking Li⁺ diffusion pathways and exacerbating capacity fading. Pieczonka et al. investigated the mechanisms and impacts of transition metal dissolution in LNMO/graphite full cells at varying states of charge (SOC) [39]. Their findings revealed increasing dissolution rates with higher SOC, exhibiting significant acceleration at 100% charge. The study demonstrated that elevated SOC promotes electrolyte decomposition at the LNMO cathode, generating HF which attacks the cathode structure and facilitates metal dissolution. Post‐cycling analysis via transmission electron microscopy (TEM) after 100 cycles detected substantial Mn deposits but minimal Ni accumulation on the graphite anode. This preferential Mn deposition is attributed to both the higher reduction potential of Ni²⁺ ions and the greater Mn content within LNMO compared to Ni. These metallic Mn deposits accelerate solid electrolyte interphase (SEI) layer growth, consume active lithium inventory, and consequently exacerbate capacity fade in full cells.

2.2. NCM

High nickel layered oxide cathodes (e.g., NCM811, NCM622) present compelling prospects for electric vehicle batteries owing to their competitive cost structure and exceptional high energy density, driving their widespread adoption in the premium electric vehicle (EV) segment. Nevertheless, these high‐Ni cathode systems exhibit persistent limitations. In NCM811, for instance, the near‐identical ionic radii of Ni²⁺ (0.069 nm) and Li⁺ (0.076 nm) promote the undesired migration of Ni²⁺ ions into lithium‐layer vacancies [44, 45]. The cation mixing (or disordering) detrimentally compromises the material's electrochemical functionality [46]. Furthermore, oxygen vacancies develop during high‐temperature sintering as the material loses lattice oxygen, resulting in progressively lower oxygen occupancy [47]. These vacancies lower the activation barrier for Ni²⁺/ Li⁺ disordering, thereby exacerbating the cation mixing phenomenon. Concurrently, higher nickel content intensifies structural degradation during lithium (de)intercalation. The resulting anisotropic lattice strain generates microcracks within individual grains (intragranular) and along grain boundaries (intergranular), which significantly increases the electrochemically active surface area exposed to the electrolyte. Consequently, thicker and more heterogeneous CEI forms, substantially impairing ionic transport kinetics and overall electrode performance (Figure 2).

FIGURE 2.

Schematic diagram of the degradation mechanism of NCM cathode.

Additionally, inherent lithium volatilization occurs during the high‐temperature solid‐state reaction between precursors and lithium sources in NCM811 synthesis [48]. To compensate for this stoichiometric loss, lithium excess is routinely employed. Nevertheless, it will result in residual lithium compounds persisting on particle surfaces, which exhibit high reactivity toward ambient oxygen, carbon dioxide, and moisture. Consequently, surface contaminants such as lithium carbonate (Li₂CO₃) and lithium hydroxide (LiOH) form. During electrode fabrication using N‐methyl‐2‐pyrrolidone (NMP) as the processing solvent, these impurities undergo solvation‐induced polymerization, rapidly generating highly viscous gel complexes. This phenomenon disrupts slurry rheology, yielding inhomogeneous cathode coatings with poor adhesion to current collectors. These electrochemically inactive deposits remain on active material surfaces, impeding Li⁺ diffusion kinetics during cycling and degrading rate capability and cycle life. Electrochemical interrogation further reveals this finding. Surface lithium residues act as nucleation sites. They initiate deleterious interfacial reactions with conventional electrolytes, such as LiPF₆ hydrolysis. This process generates HF. Notably, this degradation pathway is analogous to that observed in high‐voltage spinel cathodes like LNMO. Moreover, the highly oxidized transition metal species (Ni⁴⁺, Co⁴⁺) present at upper cutoff voltages catalytically promote electrolyte oxidative breakdown and lattice oxygen evolution [48]. Liberated gaseous oxygen substantially elevates safety risks, potentially instigating cascading exothermic reactions, venting, thermal runaway, or catastrophic cell failure. The above intrinsic thermal instability is critically exacerbated above ∼55°C, underscoring the imperative for developing advanced stabilization strategies for Ni‐rich layered oxide cathodes.

2.3. Industrial Challenges

From an industrial standpoint, the challenges of Ni‐rich NCM and LNMO transcend electrochemical cycling; they begin during the electrode slurry preparation. The high surface alkalinity of Ni‐rich materials (due to residual LiOH and Li₂CO₃) acts as a base catalyst that can trigger the dehydrofluorination of PVDF binders, leading to the notorious “slurry gelation” or the “jelly effect.” This significantly complicates the high‐speed coating process, resulting in inconsistent electrode loading and poor adhesion. While most laboratory studies utilize pristine materials in controlled environments, the industry requires modification strategies that can enhance the “ambient stability” of these powders during storage and handling to reduce the exorbitant costs of ultra‐dry room operations.

3. CEI Regulation

To address the critical issues faced by high‐voltage Ni–Mn‐Based Oxides in terms of LNMO and NCM ternary batteries (e.g., NCM811), such as unsatisfying cycling performance, capacity retention, specific capacity, and even performance under extreme temperatures, researchers commonly employ strategies including electrolyte additive incorporation, cathode material modification, and the application of artificial CEI layers. A summary of comparison based on the above‐mentioned strategies is listed in Table 1.

TABLE 1.

Summary of Representative Modification Strategies for Ni–Mn‐Based Cathodes and Corresponding Electrochemical Performance.

Additive/Modifier	Cathode	Anode	Electrolyte base	Voltage range	Temp.	Rate	Cycle number	Capacity retention	Ref.
Electrolyte additives
LiDFP (1 wt.%)	NCM111	Graphite	1 M LiPF6 in EC/EMC (3/7, v/v)	3.0–4.5	25°C	1C	100	92.6%	[31]
LiDFP (1 wt.%)	NCM111	Graphite	1 M LiPF6 in EC/EMC (3/7, v/v)	3.0–4.5	25°C	1C	200	78.2%	[31]
LiDFP (0.1 M)	LNMO	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	2.3–5.0	25°C	0.5C(1st)‐1C	300	82.8%	[32]
LiBF4 (1 wt.%)	LNMO	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	3.0–5.0	25°C	0.1C	200	93%	[49]
LiBF4 (1 wt.%)	LNMO	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	3.0–5.0	55°C	1C	200	72%	[49]
B(OCH2CHF2)3 (1 wt.%)	NCM811	Cu(anode‐less)	1 M LiPF6 in EC/EMC (3/7, v/v)	2.8–4.5	25°C	1C	120	80.1%	[50]
LBTA (0.03 M)	NCM811	Graphite	1 M LiPF6in EC/DMC/EMC (1/1/1, v/v/v)	3.0–4.5	25°C	1C	200	60%	[51]
LTFMP‐TMB (0.2 wt.%)	LNMO	Graphite	1 M LiPF6 in EC/DEC/EMC (3/2/5, wt.%)	3.5–4.8	25°C	0.5C	150	80%	[52]
LiDFTFSI (0.8 M)	NCM811	Graphite	1 M LiPF6 in EC/EMC (3/7,v/v)	3.0–4.4	25°C	1C	500	77.9%	[53]
TFPMDS (1 wt.%)	LNMO	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	3.5–5.0	25°C	1C	400	90.8%	[54]
APTS (0.5 wt.%)	LNMO	Li	1 M LiPF6in EC/DMC/EMC (1/1/1, v/v/v)	3.5–5.0	25°C	1C	350	92%	[55]
APTS (0.5 wt.%)	LNMO	Li	1 M LiPF6in EC/DMC/EMC (1/1/1, v/v/v)	3.5–4.9	55°C	1C	300	71%	[55]
SN2BF3 (1 wt.%)	NCM811	Graphite	1 M LiPF6in EC/DMC/EMC (1/1/1, v/v/v)	3.0–4.5	25°C	1C	300	77.05%	[56]
FS (1 wt.%)	LNMO	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	3.5–4.9	25°C	1C	600	84%	[57]
GT (0.5 wt.%)	LNMO	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	3.5–4.9	25°C	1C	400	84.9%	[58]
GT (0.5 wt.%)	LNMO	Graphite	1 M LiPF6 in EC/DMC (1/1, v/v)	3.5–4.9	25°C	1C	300	93.12%	[58]
M‐3FEn‐IO (0.2 vol%)	NCM622	Li	1 M LiPF6in EC/DMC/EMC (1/1/1, v/v/v)	3.0–4.6	30°C	1C	600	84.07%	[59]
M‐3FEn‐IO (0.2 vol%)	NCM622	Li	1 M LiPF6in EC/DMC/EMC (1/1/1, v/v/v)	3.0–4.6	60°C	2C	400	73.8%	[59]
TMSOTf (0.5 wt.%)	NCM622	Li	1 M LiPF6in EC/DMC/EMC (1/1/1, v/v/v)	3.0–4.6	25°C	1C	150	81.1%	[60]

Synergistic multi‐additive formulation
FEC (10 wt.%) + LiDFOB (1 wt.%) + HN (2 wt.%)	LNMO	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	3.5–5.0	25°C	1C	500	>88%	[61]
FEC (10 wt.%) + LiDFOB (1 wt.%) + HN (2 wt.%)	LNMO	Graphite	1 M LiPF6 in EC/DMC (1/1, v/v)	3.5–5.0	25°C	1C	300	90.3%	[61]
Li2TB (2 wt.%) + FBP (0.25 wt.%)	NCM622	Li	1 M LiPF6 in EC/EMC (3/7, wt.)	2.7–4.5	−10°C	1C	200	100%	[62]
Li2TB (2 wt.%) + FBP (0.25 wt.%)	NCM622	Li	1 M LiPF6 in EC/EMC (3/7, wt.)	2.7–4.5	25°C	1C	200	99%	[62]
Li2TB (2 wt.%) + FBP (0.25 wt.%)	NCM622	Li	1 M LiPF6 in EC/EMC (3/7, wt.)	2.7–4.5	55°C	1C	100	83%	[62]
PFTFA (2 wt.%) + LiDFOB (2 wt.%)	NCM811	Li	1 M LiPF6 in FEC/DMC (1/1, v/v)	3.0–4.4	25°C	1C	420	80%	[63]
PFTFA (2 wt.%) + LiDFOB (2 wt.%)	NCM811	Li	1 M LiPF6 in FEC/DMC (1/1, v/v)	3.0–4.8	25°C	0.5C	200	77.8%	[63]

Second‐phase additive blending
LLZT (5 wt.%)	NCM622	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	3.0–4.5	25°C	C/3	150	∼170 mAh g− 1	[64]
LLZT (5 wt.%)	LNMO	Graphite	1 M LiPF6 in EC/EMC (3/7, v/v)	3.0–4.7	25°C	0.5C	100	∼87%	[65]

Doping
KPBS (1.0 wt.‰)	LNMO	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	3.5–4.9	25°C	1C	1000	Negligible decay	[66]
Fe‐Ti co‐doping + Li3PO4 additive	LNMO	Graphite	1 M LiPF6 in EC/DMC (1/1, v/v)	3.5–4.9	25°C	1C	1000	>90%	[67]
Sb‐F co‐doping	LNMO	Graphite	1 M LiPF6 in EC/DMC (1/1, v/v)	3.0–4.9	25°C	1C	300	96.9%	[68]
La‐Mg co‐doping	NCM	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	2.7–4.5	25°C	1C	100	95%	[69]
W‐Nb co‐doping	NCM811	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	3.0–4.3	25°C	5C	400	54.9%	[70]
Ascorbic Acid (AA)	LNMO	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	3.5–4.9	25°C	1C	1000	87.4%	[71]

Coating
Li4TeO5	S‐NCM955	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	3.0–4.5	25°C	1C	200	82.12%	[72]
LiCoPO4 (LCP, 3 wt.%)	LNMO	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	3.0–4.9	25°C	1C	600	90.8%	[73]
LiCoPO4 (LCP, 3 wt.%)	LNMO	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	3.0–4.9	50°C	1C	200	84.9%	[73]
0.25‐B2O3	LNMO	Graphite	1 M LiPF6 in EC/EMC (3/7, v/v)	3.5–4.9	25°C	1C	1000	62.5%	[74]
LiBO2 (LBO)	LNMO	Graphite	1 M LiPF6 in EC/EMC (3/7, v/v)	3.5–4.9	25°C	0.5C	50	∼92%	[75]

Engineering
Magnetic field induction (Fe3O4 shell)	LNMO	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	3.5–4.9	25°C	0.5C	500	85%	[76]
Sintering temperature optimization (850°C)	LNMO	Li	1 M LiPF6 in EC/DMC (1/1, v/v)	3.5–5.0	25°C	0.2C	100	∼96%	[77]
Al(H2PO4)3 wet impregnation	NCM811	Li	1 M LiPF6 in EC/EMC (3/7, v/v)	2.7–4.5	25°C	1C	200	90%	[78]

3.1. Electrolyte Modification

The strategy of incorporating electrolyte additives into the industry‐proven electrolyte system, which uses LiPF₆ as the lithium salt and carbonate esters as solvents, is widely recognized as an effective approach for enhancing battery performance. These additives function by preferentially decomposing before the solvent, thereby participating in the formation of robust and stable CEI or SEI that protect electrode materials [79]. To fulfill this dual functionality, additives must satisfy two fundamental requirements. First their highest occupied molecular orbital (HOMO) energy level must be marginally higher than that of electrolyte solvent molecules, enabling prior oxidative decomposition at the cathode surface to form a protective film and modify the cathode interface. Second, they should effectively modulate lithium‐ion solvation structures, specifically by coordinating within the Li⁺ solvation sheath. The coordination allows their transportation with Li⁺ ions to electrode surfaces, facilitating direct participation in CEI/SEI formation processes at both anodic and cathodic interfaces [80].

While electrolyte additives are indispensable for enabling stable high‐voltage operation, it is important to recognize that their beneficial effects often come with trade‐offs. The same oxidative decomposition that forms protective CEI layers can also generate unwanted byproducts or lead to unintended consequences. A balanced assessment of additive performance must therefore consider not only their protective functions but also potential drawbacks, including parasitic oxidation, gas evolution, impedance rise, and coulombic efficiency loss. Additives are designed to decompose preferentially at the cathode surface, forming a protective interphase. However, their oxidation products are not necessarily inert; residual or continuously generated species may contribute to ongoing parasitic reactions over extended cycling, particularly once the additive reservoir is depleted. This phenomenon is especially pronounced for additives that undergo non‐passivating decomposition pathways or form soluble products that do not effectively incorporate into the CEI.

A well‐documented side effect of many effective additives is the generation of gaseous byproducts during formation and, in some cases, during prolonged cycling. Azam et al. systematically quantified gas evolution for three generations of additives in NMC442/graphite pouch cells [81]. Their results revealed that while certain additives (e.g., 2% PES in FEC:TFEC) produced minimal gas, particularly the Generation 2 Li‐salt additives such as LiDFDOP, exhibited substantial gassing during formation. LiDFDOP, containing two oxalate groups, decomposes to release CO₂, and even the addition of co‐additives like FEC or LFO could not suppress this excessive gas evolution. Such gassing poses practical challenges for cell manufacturing, necessitating degassing steps and potentially compromising cell integrity if not properly managed. Azam et al. reported that the formation of a robust, highly passivating CEI often comes at the cost of increased interfacial resistance. Additives such as PES, TAP, and certain nitrile‐containing compounds exhibit high charge‐transfer resistance after formation. While this passivation effectively suppresses further electrolyte decomposition, it can severely limit rate capability, particularly at low temperatures. In extreme cases, the resulting voltage polarization can induce lithium plating on the anode, leading to premature rollover failure. The temperature‐dependent performance of additives directly reflects this trade‐off between passivation quality and kinetic accessibility.

Additives that undergo inefficient or non‐passivating decomposition can contribute to first cycle irreversibility and long‐term coulombic inefficiency. Shkrob et al. observed that the in situ conversion of TMS‐based additives to oxalato‐fluorophosphates, while highly effective for cathode protection, also introduced additional reduction peaks during the first lithiation of graphite, indicating that these additives or their decomposition products interfere with SEI formation [82]. Collectively, these observations highlight that additive selection involves navigating a complex multi‐objective optimization space. An additive that excels in one metric, such as suppressing transition metal dissolution, may underperform in another, such as gas evolution or rate capability. No single additive formulation simultaneously optimizes all performance metrics; the optimal choice depends on the specific application requirements, operating temperature, and voltage window. Recognizing these trade‐offs is essential for rational design of next‐generation high‐voltage electrolytes.

3.1.1. Lithium Salt Modification

It is well‐established that LiPF₆ has been widely adopted in commercial lithium‐ion battery electrolytes due to its superior overall performance. However, it still suffers from several drawbacks. For instance, trace water present in the electrolyte can react with LiPF₆ to generate HF, which corrodes the cathode. Although LiPF₆ exhibits limited stability under high voltage conditions, it is critical for inhibiting aluminum foil corrosion. While replacing LiPF₆ with more stable lithium salts could potentially reduce transition metal dissolution, this approach is not employed due to the severe aluminum corrosion it would incur. Consequently, instead of complete substitution, lithium salts are utilized as additives to function synergistically with LiPF₆. These lithium salt additives can be categorized into inorganic and organic types. Regarding inorganic lithium salts, several salts commonly used in commercial lithium‐ion batteries have also been found to be highly effective as additives. Examples include lithium phosphate salts and lithium borate salts. Research has demonstrated that, when employed as additives, these inorganic salts can preferentially decompose to form a thin yet robust CEI, thereby significantly enhancing the electrochemical performance.

In the realm of lithium salt additives, many additives proven effective for improving NCM ternary batteries have also been found to be beneficial when applied to LNMO batteries. Wang et al. pioneered the investigation of LiDFP as an additive in NCM ternary batteries [31]. Their research revealed that H(PO₂F₂), a hydrolysis product of LiPF₆, negatively impacts battery cycling performance. Phosphate‐based electrolyte additives can effectively control the formation of H(PO₂F₂). Notably, LiDFP shares the same anion ([PO₂F₂]⁻) as H(PO₂F₂), enabling it to suppress both LiPF₆ hydrolysis and H(PO₂F₂) generation [83]. As illustrated in Figure 3a, LiDFP additionally facilitates the formation of a uniform and intact CEI, effectively inhibiting oxidative decomposition of the electrolyte at the electrode/electrolyte interface. Simultaneously, on the anode side, it participates in constructing a stable and compact SEI, further enhancing overall stability. For the electrolyte with 1 wt.% LiDFP addition, decomposition initiates at 4.3 V, earlier than that of the baseline electrolyte at 4.7 V, suggesting that LiDFP may preferentially decompose to participate in the formation of the CEI. (Figure 3b) Experimental results demonstrate that incorporating 1 wt.% LiDFP into LiNi_1/3Co_1/3Mn_1/3O₂/graphite pouch cells yielded outstanding performance. A capacity retention of 92.6% was maintained after 100 cycles, significantly surpassing that of additive‐free cells (only 36% retention). Even after 200 cycles, the capacity retention remained as high as 78.2% (Figure 3c).

FIGURE 3.

(a) The mechanism diagram of LiDFP inhibiting HF generation and participating in CEI formation. (b) Electrochemical window of baseline electrolyte without and with 1 wt.% LiDFP employing linear sweep voltammetry at Pt electrode. (c) The discharge capacity retention of the LiNi_1/3Co_1/3Mn_1/3O₂/graphite pouch cells without and with different amount of LiDFP operated under the voltage ranges of 3.0–4.5 V [31]. Copyright 2018, American Chemical Society. (d) Schematic diagram illustrating the role of LiDFP in the formation mechanism of the CEI. (e) Cycling performance of LNMO‐Li batteries with different LiDFP additive amounts [32]. Copyright 2024, John Wiley and Sons. (f) Comparative analysis of HOMO‐LUMO levels for BF⁴⁻ and species present in electrolytes. (g) Cycling performance comparison of LNMO batteries with the additive versus baseline electrolyte at 0.1C [49]. Copyright 2024, John Wiley and Sons.

Building upon the mechanistic understanding of LiDFP, Hai and colleagues explored its application as an electrolyte additive in LNMO batteries, observing similarly beneficial effects [32]. During cycling of the LNMO cells, LiDFP effectively suppressed transition metal dissolution(Figure 3d). Furthermore, the two electron‐rich oxygen atoms within the DFP⁻ anion possess strong chelating ability, enabling them to compete with solvent molecules (EC and DMC) for Li⁺ coordination. This competition facilitates the incorporation of DFP⁻ into the Li⁺ solvation sheath. Consequently, the additive participates in forming a thin and dense CEI. This mechanism underpins the enhanced performance of LNMO cells containing 0.1 m LiDFP, which maintained 82.8% capacity retention after 300 cycles (Figure 3e).

Similarly, lithium tetrafluoroborate (LiBF₄) serves as a highly effective additive in both LNMO and NCM batteries. Ahuja et al. investigated the incorporation of LiBF₄ into a baseline carbonate‐based electrolyte (1 M LiPF₆ in EC:DMC 3:7 v/v) for LNMO cathodes [49]. Density functional theory (DFT) and molecular dynamics (MD) simulations revealed that the BF₄ ⁻ anion undergoes preferential oxidative decomposition (Figure 3f). This process contributes to the formation of a thin and uniform CEI enriched with inorganic components, including LiF, Li₂CO₃, B─O, and B─F species. This inorganic‐rich interphase enhances electrochemical cycling stability through multiple mechanisms, such as mitigating HF generation and suppressing transition metal dissolution. Notably, additive concentration significantly influences performance. An optimal loading of 1 wt.% LiBF₄ delivers the most favorable outcomes, with deviations (either higher or lower concentrations) diminishing their efficacy. Electrochemical testing confirmed that cells containing 1 wt.% LiBF₄ in the baseline electrolyte retained 93% capacity retention after 200 cycles at 0.1C rate (Figure 3g).

In summary, inorganic lithium salt additives play a crucial role in enhancing electrochemical performance. Analysis of the CEI formed on LNMO in baseline electrolytes reveals a predominantly organic composition, characterized by species such as C─O, O─C═O, and Li_xPF_yO. This organic‐rich CEI lacks mechanical resilience and is susceptible to degradation by HF, leading to fracture and deterioration during extended cycling. Inorganic lithium salt additives address this limitation by preferentially forming a robust, inorganic‐rich CEI that provides effective cathode protection. Furthermore, the salt additive concentration requires careful optimization. Insufficient loading fails to establish a stable, resilient CEI, while excessive amounts promote passivation through an overly thick interphase. Too much increase elevates interfacial impedance, ultimately compromising electrochemical performance.

Organic lithium salts are also widely employed. Chen et al. proposed an organic fluoroborate, tris(2,2‐difluoroethyl) borate (B(OCH₂CHF₂)₃), as an electrolyte additive for NCM811 batteries to promote CEI formation [50]. While traditional organic borates like LiDFOB and LiBOB can passivate the cathode surface, they concurrently increase interfacial resistance, hindering lithium‐ion transport. In contrast, the B(OCH₂CHF₂)₃ additive facilitates lithium‐ion transfer via an O─Li─F binding effect (Figure 4a). It simultaneously provides superior passivation, enabling stable operation at high voltage (4.5 V) and elevated temperature (60°C). Specifically, an anode‐free NCM811 pouch cell operating at 4.5 V and delivering 410 Wh kg^{− 1} exhibited an 80.1% capacity retention after 120 cycles.

FIGURE 4.

(a) Organic fluoroborates promote lithium‐ion transfer through O─Li─F binding effects [50]. Copyright 2025, Elsevier. (b) LBTA, DMC, EC, and EMC binding energy with Co₄ ⁺. (c) Binding energy with Li⁺ [51]. Copyright 2025, Elsevier. (d) Mechanism diagram of LTFMP‐TMB for improving the cyclability of LNMO/graphite batteries. (e) Cyclability and corresponding coulombic efficiency of LNMO/Graphite coin cells at room temperature at 0.2C for initial three cycles and 0.5 C for the subsequent cycles between 3.5 and 4.8 V in baseline and 0.2% LTFMP‐TMB electrolytes [52]. Copyright 2024, Elsevier. (f) The ionic conductivity and Arrhenius relationship of various electrolyte samples with different molar ratios LiTFSI to Pyr_1,3FSI [86]. Copyright 2018, Elsevier. (g) Cycling performance of NMC811@CE andNMC811@PC over 200 cycles at 0.2C [87]. Copyright 2023, American Chemical Society. (h) Comparative cycling performance of NMC811||graphite batteries with BE, BE with individual additives, and BE with synergistic additives [53]. Copyright 2023, John Wiley and Sons.

The nitrile group and boron‐oxygen (B─O) functional group exhibit high prevalence as components in high‐voltage cathode electrolyte additives. However, additives combining both functionalities are rare. Li et al. successfully synthesized a novel organic lithium salt integrating these two groups: 4‐benzonitrile‐1,3‐double (trimethylboric acid) lithium (LBTA) [51]. The nitrile group contributes excellent electrochemical performance and robust thermal stability, while the B─O group is indispensable for forming a stable and compact CEI. Furthermore, boron‐containing decomposition products can interact with PF₆ ⁻ anions, thereby reducing HF generation. Comparative analysis of the binding affinity between LBTA and other solvent molecules towards Co⁴⁺ revealed that LBTA addition also suppresses transition metal dissolution (Figure 4b). The low binding energy between LBTA and Li⁺ indicates that Li⁺ ions can effectively facilitate the migration of LBTA between the electrodes, enabling its participation in the formation of both the CEI and the SEI (Figure 4c).

Organic borate lithium salt additives also demonstrate efficacy in LNMO batteries. Xia et al. synthesized a multifunctional additive, lithium 5‐Trifluoromethylpyridine‐trimethyl lithium borate (LTFMP‐TMB) [52]. During operation, its anion accumulates at the cathode interface, where it preferentially oxidizes to generate trimethyl borate (TMB) and the TFMP radical. The TFMP radical effectively scavenges HF, mitigating its detrimental effects, while TMB undergoes preferential oxidation on the cathode surface. This process contributes to the formation of a protective CEI (Figure 4d). Experimental results indicate that minimal incorporation of LTFMP‐TMB (0.5 wt.%) into the baseline electrolyte substantially enhances the cycling stability of LNMO/graphite full cells. Specifically, capacity retention increased from 52% to 80% after 150 cycles at 0.5C (Figure 4e).

Regarding organic lithium salts, bis(trifluoromethanesulfonic)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI) represent prominent candidates [84, 85]. These salts exhibit superior thermal stability and broad electrochemical stability windows. Despite challenges such as current collector corrosion and moderate ionic conductivity, they remain highly promising electrolyte materials. Their commercial viability has already been demonstrated in advanced electrolyte formulations. Zhang et al. proposed an electrolyte comprising LiTFSI salt dissolved in the ionic liquid Pyr_1,3FSI at a 1:1 molar ratio(Figure 4f) [86]. Leveraging the synergistic interaction between the TFSI⁻ and FSI⁻ anions, this electrolyte demonstrates exceptional cycling durability and superior rate capability in lithium‐ion batteries employing high‐voltage cathode materials. Jabeen et al. employed C₂mpyr[FSI]:[LiFSI] (1:1 mol) as the electrolyte for NCM811 batteries [87]. This highly viscous liquid exhibits an ionic conductivity of 2.3 × 10⁻³ S cm⁻¹ at room temperature and demonstrates exceptional rate capability and cycling performance in NCM811 cells (Figure 4g).

Building upon LiTFSI, Yan et al. proposed a novel organic lithium salt, lithium (difluoromethanesulfonyl)(trifluoromethanesulfonyl)imide (LiDFTFSI), as an electrolyte additive [53]. In contrast to LiTFSI that corrodes current collectors above 3.8 V, LiDFTFSI demonstrates effective corrosion‐inhibiting behavior toward aluminum current collectors under high‐voltage operation. Coupled with its inherent thermal stability, LiDFTFSI enables the formation of a high‐quality CEI, significantly enhancing cycling performance. Experimental findings revealed that incorporating a 2 wt.% concentration of the film‐forming additive vinylene carbonate (VC) further synergizes with LiDFTFSI. This optimized electrolyte system delivered 87.1% capacity retention in NMC811||graphite full cells after 500 cycles (Figure 4h).

3.1.2. Electrolyte Additives

Beyond lithium salt additives, researchers are also exploring the synthesis of new organic compounds, leveraging their functional groups or specific properties to enhance battery cycling performance. Among these, organics containing silicon‐oxygen (Si─O) bonds have garnered significant interest. Li et al. proposed a novel silane coupling agent‐type electrolyte additive, 3, 3, 3‐trifluoropropylmethyldimethoxysilane (TFPMDS) [54]. This additive not only possesses the dual bond character of the Si─O bond, enabling it to maintain high ionicity (40%–50%), but also benefits from the unique advantage of coupling agents to establish “molecular bridges” at interfaces, effectively connecting inorganic and organic components. The Si─O group exhibits a strong affinity for harmful HF in the electrolyte, while the excellent stability of the Si─O bond makes it an ideal constituent for the CEI (Figure 5a). Furthermore, the presence of molecular bridges enhances the robustness and compatibility of the Si─O bond‐containing CEI. Experiments demonstrate that adding 1 wt.% TFPMDS can increase the capacity retention of LNMO after 400 cycles at 1C from 29.6% to 90.8% (Figure 5b). Notably, TFPMDS also exerts a positive effect on the graphite anode. Adding 1 wt.% TFPMDS improves the capacity retention of a graphite/Li half‐cell from 68.1% to 98.3% after 200 cycles. The outstanding performance far surpasses that of other additives. Nguyen et al. introduced a novel 3‐aminopropyltriethoxysilane (APTS) electrolyte additive featuring silane and amine functional groups [55]. The silane moiety in APTS enhances interfacial stability by neutralizing detrimental hydrofluoric acid (HF) and water in the electrolyte, while its amine group facilitates the formation of a protective cathode layer. LNMO||Li half‐cells incorporating 0.5 wt.% APTS demonstrated exceptional cycling stability, achieving 92% capacity retention after 350 cycles at room temperature (Figure 5c) and 71% retention after 300 cycles at 55°C (1C rate) (Figure 5d). To elucidate the amine group's critical role, the authors designed a control additive, 3‐glycidyloxypropyltrimethoxysilane (GLYMO), which lacks the amine functionality (Figure 5e). Remarkably, LNMO||Li cells with 0.5 wt.% GLYMO exhibited only 73% capacity retention after 350 cycles at room temperature, highlighting the amine group's indispensable contribution to performance enhancement.

FIGURE 5.

(a) The mechanism of TFPMDS involvement in constructing protective CEI on LNMO surfaces. (b) Comparative analysis of cycle stability in LNMO batteries with and without additives [54]. Copyright 2024, John Wiley and Sons. (c) Comparison of cycling stability of LNMO half‐cells at room temperature (d) at 55°C. (e) Mechanisms of APTS and GLYMO as functional additives [55]. Copyright 2025, Royal Society of Chemistry. (f) CEI images of NCM811 cathode with different electrolytes. (g) Cycling performance of NCM811||Graphite full cells [56]. Copyright 2025, Elsevier.

Silicon‐containing organic additives are also frequently employed in high‐nickel ternary NCM batteries. Wu et al. proposed an organosilicon zwitterionic liquid, trimethylsilyl trifluoroborate (SN₂BF₃), containing a trifluoroborate anion [56]. Unlike TFPMDS, which builds “molecular bridges” at the interface, SN₂BF₃ primarily functions by preferentially participating in the formation of a dense CEI layer containing B─O and Si─O bonds. It also leverages the inherent advantages of ionic liquids, such as non‐flammability and a wide operating temperature range. Comparing TEM images of cycled batteries with and without SN₂BF₃ reveals that the CEI formed with SN2BF3 is thin and uniform (Figure 5f). Adding SN₂BF₃ improves the capacity retention after 300 cycles for NCM811||graphite full cells from 58.52% (baseline electrolyte) to 77.05% (Figure 5g).

Apart from silicon‐oxygen bond‐containing additives, Hou et al. developed a novel electrolyte additive, 2,2‐difluoroethyl methyl sulfone (FS), which operates through a distinct mechanism compared to conventional additives [57]. FS selectively adsorbs onto Mn/Ni transition metal sites of LNMO cathodes, forming an antioxidant buffer layer that effectively isolates carbonate solvent molecules from the electrode surface. This physical barrier prevents solvent decomposition and associated detrimental side reactions. Concurrently, the weak C─C bond in FS facilitates dissociation of the CF₂H group upon adsorption, enabling preferential formation of a LiF‐rich CEI. Incorporating FS into the electrolyte significantly enhances the cycle life of LNMO/Li cells, achieving 84% capacity retention after 600 cycles. Notably, Li/LNMO pouch cells with FS‐additive electrolytes demonstrated over 150 cycles. Their finding represents a substantial advancement compared to previously reported carbonate‐based electrolytes.

Tan et al. proposed glyceryl triacetate (GT, triacetin) as an electrolyte additive. GT possesses multiple hydroxyl groups [58]. During its preferential oxidation to form the CEI film, electrons from its carboxyl groups occupy the d‐orbitals of the transition metals (TMs). The activity of LNMO was effectively reduced and the dissolution of TM ions was suppressed. Concurrently, under electrochemical influence, GT can form complexes with dissolved TM ions, thereby capturing them during the initial cycles. Furthermore, GT reacts rapidly with trace amounts of water (H₂O), preventing the reaction between H₂O and LiPF₆ that generates HF. The glycerol produced by the reaction between GT and H₂O can, through hydrogen‐bonding interactions, trap both HF and H₂O molecules. This further enhances electrolyte stability and protects the LNMO cathode (Figure 6a). Consequently, an LNMO/Li cell with 0.5 wt.% GT additive exhibited a capacity retention of 84.9% after 400 cycles at 1C. Similarly, an LNMO/graphite cell demonstrated a retained capacity of 93.12% after 300 cycles at 1C. These results indicate that GT substantially improves the stability of LNMO‐based batteries.

FIGURE 6.

(a) The cyclic performance of LNMO/Li cells [58]. Copyright 2023, Elsevier. (b) Mechanism diagram of the multifunctional effect of DFBN additives [88]. Copyright 2025, Elsevier. (c) Comparative study on cycle performance at 1C rate with/without synergistic additive addition. (d) TEM images of LNMO cathode electrode from Li||LNMO full cells after 50 cycles in EDFBH [61]. Copyright 2024, John Wiley and Sons. (e) Oxidation Potentials of EC, EMC, Li₂TB, and FBP with/without PF Combination [62]. Copyright 2023, Elsevier. (f) Comparative study on cycling performance of NCM811 at 4.4 V cut‐off voltage with individual vs. synergistic additive addition [63].

Recent organic additives for NCM ternary batteries have diversified significantly, particularly fluorine‐containing variants. Zhu et al. proposed a novel additive, 2,5‐difluorobenzonitrile (DFBN) [88], which scavenges HF and participates in forming a robust cyanide‐rich (─C≡N) CEI while effectively binding active Ni⁴⁺ to suppress side reactions, substantially enhancing the high‐temperature cycling performance of NCM811/Li batteries (Figure 6b). Zeng et al. introduced a novel fluorinated additive, 1‐methyl‐3‐(2,2,2‐trifluoroethyl)‐1,3‐dihydro‐2Himidazol‐2‐one (M‐3FEn‐IO) [59], which functionally resembles the film‐forming agent vinylene carbonate but substitutes oxygen with nitrogen and incorporates fluorine groups at nitrogen sites. Their molecular design enables effective electrode passivation, dramatically improving cycle performance in Li‖NCM622 cells. Jing et al. employed trimethylsilyl trifluoromethanesulfonate (TMSOTf) as an electrolyte additive to address challenges in Li||NCM622 systems [60]. TMSOTf modifies the Li⁺ solvation structure and contributes to forming a mechanically stable CEI enriched with LiF and Li₂SO _x (x = 0,3,4), while simultaneously scavenging HF from the electrolyte to mitigate electrode corrosion. Li||NCM622 cells with TMSOTf exhibit superior cycling stability and rate capability.

3.1.3. Synergistic Multi‐Additive Formulation

Distinct from the limited functionality of single additives, the synergistic addition of multiple additives can yield more efficient cooperative effects. Zhang et al. first proposed a strategy incorporating three additives synergistically [61]. They added 10 wt.% fluoroethylene (FEC), 1 wt.% lithium difluoro (oxalato) borate (LiDFOB), and 2 wt.% adiponitrile (HN) to the conventional 1 M LiPF₆/EC‐DMC (1:1 vol%) electrolyte. Among them, HN suppresses transition metal dissolution, while the fluorine‐containing additives participate in forming a thin yet robust cathode electrolyte interphase (CEI) film, rich in LiF and Li₃N. (Figure 6f) Through a series of characterizations and electrolyte behavior simulations, the changes in the solvation structure upon additive incorporation were revealed. Unlike the traditional solvent‐separated ion pairs (SSIPs)‐dominant model, this Li⁺ solvation sheath facilitates the formation of a robust CEI derived from HN and a LiF‐rich CEI originating from the LiDFOB and FEC on the LNMO cathode. The synergistic action of the additives endowed the Li/LNMO cell with exceptional electrochemical performance, demonstrating unprecedented cycling stability with a capacity retention exceeding 88% after 500 cycles (Figure 6c).

The synergistic addition of multiple electrolytes can also construct unique multi‐layered CEIs. Xie et al. proposed the co‐addition of lithium tetraborate (Li₂TB) and 2,4‐difluorobiphenyl (FBP) [62]. Due to its higher oxidation activity than FBP, Li₂TB oxidizes preferentially during cycling. Subsequently, FBP undergoes two consecutive oxidative decomposition steps by losing two electrons. Consequently, the CEI layer on the NCM cathode surface is constructed through the sequential oxidation of Li₂TB followed by FBP, forming a robust bilayer CEI (Figure 6e). This significantly enhances the wide‐temperature performance of the NCM cathode. Using this dual‐additive synergistic strategy, the NCM||Li cells achieved remarkable capacity retention: 100% after 200 cycles at 10°C, 99% after 200 cycles at 25°C, and 83% after 100 cycles at 55°C. In stark contrast, the benchmark electrolyte delivered only 63%, 69%, and 45% retention under the same respective conditions. Undoubtedly, this synergistic strategy for constructing a bilayer CEI substantially expands the operational temperature range of the battery, making significant contributions toward the practical application of all‐climate NCM batteries.

The synergistic additive strategy has also been applied to NCM811‐based batteries. As HF is a major contributor to capacity fade, Dai et al. proposed the combined use of pentafluoro phenyl trifluoroacetate (PFTFA) and lithium difluoro(oxalate)borate (LiDFOB) additives [63]. The synergistic pairing enables simultaneous chemical HF scavenging and physical barrier formation against HF penetration. The optimized electrolyte system not only promotes the formation of a robust cathode‐electrolyte interphase (CEI) layer rich in LiF and lithium borate (LiB_xO_y) compounds but also effectively scavenges HF via coordination with PFTFA. Consequently, the cathode stability was significantly enhanced. As a result, Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cells employing this electrolyte demonstrated capacity retention of 80% after 420 cycles at a 1C rate with a cutoff voltage of 4.4 V. In stark contrast, cells using a conventional carbonate‐based electrolyte retained only 54.8% capacity after 150 cycles under identical conditions. Furthermore, even under high‐voltage operation (4.8 V cutoff at 0.5C rate), the developed electrolyte enabled a capacity retention of 77.8% after 200 cycles (Figure 6f).

While a plethora of functional additives are effective in scavenging HF or stabilizing the CEI in coin cells, their real‐world application must navigate the trade‐off between performance and “Formation” efficiency. For large‐scale pouch cells, additives that undergo slow or continuous decomposition may lead to persistent gas evolution during the first few cycles, necessitating expensive degassing and resealing steps. Furthermore, the “cost‐benefit ratio” is a decisive factor for mass‐produced EVs. A high‐performance additive that increases the electrolyte cost by more than 10% is rarely viable unless it provides a disproportionate increase in cycle life or safety. We argue that future research should prioritize additives that can form a stable CEI within a short formation window (fast‐charging compatible) to maximize production throughput.

3.1.4. Solid‐State Electrolytes

The transition from liquid to solid‐state electrolytes (SSEs) provides a fundamental solution to the interfacial instability of high‐voltage cathodes by eliminating the volatile and acid‐generating carbonate solvents. While LNMO and Ni‐rich NCM belong to different structural families, they share a common failure root in liquid systems: the “electrolyte oxidation to HF formation to TM dissolution” cascade. SSEs break this chain by providing a wider electrochemical stability window and a physical barrier against acid corrosion.

Recent studies highlight that a stable interface requires both electrochemical passivity and structural intimacy. Shimizu et al. investigated a 5 V‐class thin‐film battery using a spinel LNMO cathode and a solid LiPON electrolyte [89]. Their work, utilizing neutron depth profiling (NDP) and cryo‐TEM, revealed that while the LNMO surface undergoes a slight “overlithiation” and Jahn‐Teller distortion during deposition, the interface remains remarkably stable over 600 cycles. Unlike liquid systems where Mn dissolution is rampant, the solid LiPON prevents the catalytic decomposition of electrolytes and maintains an intimate, crack‐free contact with LNMO even at 5 V. Complementary to inorganic SSEs, in situ polymerization offers a more scalable “drop‐in” technology for NCM systems. Zhang et al. demonstrated an in situ polymerized poly‐1,3‐dioxolane (PDOL) electrolyte for NCM811 batteries [90]. By introducing a sacrificial additive, diethyl (2,2,2‐trifluoroethyl) phosphite (DETFPi), they engineered a uniform CEI rich in pentavalent phosphorus and LiF. Scientifically, this highlights the importance of HOMO/LUMO level tailoring: the additive oxidizes preferentially to form a protective layer, which not only inhibits the pervasive HF generation typical of LiPF6 hydrolysis but also accommodates the volume expansion of the layered NCM811, reducing interfacial impedance to half that of unmodified PDOL.

From an industrial perspective, a clear gap exists between the precision of thin‐film models and the requirements of mass production. While the LiPON/LNMO system offers a “gold standard” for interfacial stability, its reliance on physical vapor deposition (PVD) limits its application to micro‐batteries due to low throughput and high equipment costs. Conversely, the in situ polymerization approach is highly compatible with current slurry‐casting infrastructure. However, for large‐scale manufacturing, the challenges shift toward the control of polymerization kinetics across thick electrodes and the potential for “slurry gelation” if the acidic/basic nature of the cathode surface is not neutralized. Future industrial implementation must prioritize solvent‐free processing and ensure that solid‐state interfaces can withstand high‐pressure calendering without losing the “conformal contact” that is so effectively demonstrated in laboratory‐scale thin‐film models.

3.2. Cathode Modification

In the lithium metal batteries with LNMO cathode, interfacial stability at both the LNMO/current collector and LNMO/electrolyte interfaces critically governs electrochemical performance. Consequently, surface modification, morphological optimization, and structural ordering control represent essential strategies for mitigating transition metal dissolution and enhancing lithium nickel manganese oxide functionality. Research demonstrates that selected metal ion doping not only modulates structural ordering and morphology but also induces nickel‐depleted surface layers through elemental segregation. The surface reconstruction strategy effectively reduces interfacial oxidative reactivity [48]. Analogous modification approaches prove equally beneficial for NCM cathodes, where surface coating serves as an effective barrier technology, which enhancing lithium‐ion diffusion kinetics, suppressing transition metal dissolution, and minimizing parasitic side reactions. Conversely, bulk doping constitutes a structural stabilization technique that inhibits cationic disordering and subsequent phase transitions by introducing foreign ions into the NCM lattice. The doping mechanism alleviates lattice strain propagation, thereby preventing microcrack formation and improving cycling stability. While recent advances highlight coating with thin metal oxide or phosphate layers as a promising approach for parasitic reaction suppression at CEI interfaces, it faces inherent limitations including complex processing requirements, elevated costs, and compromised discharge capacities due to the intrinsically poor lithium conductivity of many coating materials [91].

3.2.1. Second‐Phase Additive Blending

Second‐phase additive blending is an emerging strategy that has gained attention in recent years which involves the physical mixing of functional inorganic additives directly into the cathode slurry. These additives do not enter the crystal lattice and they do not form a continuous shell around the active particles. Instead, they exist as a discrete second phase distributed among the active material particles. Representative examples such as Yu et al. investigated lithium garnet‐type Li_6.7La₃Zr_1.7Ta_0.3O₁₂ (LLZT), which noted for its wide electrochemical stability window, favorable mechanical properties, and moderate ionic conductivity, as a dopant in NCM622 cathodes [64]. Optimal performance emerged at 5 wt.% LLZT incorporation. XPS analysis revealed that LLZT not only serves as an ion‐conducting barrier within the CEI but also functions as an effective scavenger for protons and trace water, significantly mitigating parasitic reactions at the electrode/electrolyte interface. Remarkably, stabilization persists even under moisture‐contaminated cell conditions. EIS measurements demonstrated that 5.0 wt.% LLZT optimally balances ionic and electronic transport properties (Figure 7a,b), reducing interfacial resistance by 50% during cycling up to 4.5 V while enhancing coulombic efficiency. Consequently, the 5 wt.% LLZT‐NMC cathodes retained a specific capacity of 170 mAh/g after 150 cycles at C/3 rate, substantially outperforming the undoped control (146 mAh/g).

FIGURE 7.

EIS of (a) bare NCM and (b) 5 wt.% LLZT‐modified cathodes at 50% SOC [64]. Copyright 2022, Elsevier. (c) cycle performance at different rate of bare LNMO, 2.5 wt.% LLZT‐LNMO, 5 wt.% LLZT‐LNMO and 10 wt.% LLZT‐LNMO. [65] Copyright 2023, Elsevier.(d) Raman spectra of benchmark sample and (e) LNMFTO sample [67]. Copyright 2022, Royal Society of Chemistry. (f) Schematic illustration of Li⁺ migration in LNMO‐SbF material. (g) Diffusion energy barriers of Li⁺ in LNMO vs. LNMO‐SbF [68]. Copyright 2024, John Wiley and Sons. (h) Cycling performance of benchmark LNMO and doped LNMO at 5C and (i) 10C rates under room temperature [70]. Copyright 2025, John Wiley and Sons. (j) Mechanism illustration of AA additive function in LNMO||Li battery [71]. Copyright 2024, American Chemical Society.

Given the methodological parallels between LNMO and NCM cathode modifications, numerous research groups have successfully translated NCM optimization approaches to LNMO systems. Recently, Jiao et al. extended the LLZT doping strategy to LNMO cathodes to evaluate its efficacy in high‐voltage systems (operating up to 4.7 V vs. Li⁺/Li) [65]. Incorporating varying LLZT concentrations (2.5, 5, and 10 wt.%) into LNMO electrodes revealed consistent performance optimization at 5 wt.% loading. XPS analysis indicates that 5% LLZT‐modified LNMO develops a superior CEI (Figure 7c). Mechanistic analysis established that LLZT particles construct direct interfacial contact with active material, significantly enhancing lithium‐ion transport kinetics across the CEI. This interfacial modification was quantitatively verified through electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis. Furthermore, LLZT functions as an effective scavenger of electrolyte decomposition by product while simultaneously mitigating CEI and SEI degradation during extended cycling.

3.2.2. Doping

Doping technology is frequently characterized as an ‘atomic scalpel’ for its ability to perform precise lattice surgery. By introducing trace amounts of foreign elements without compromising the integrity of the host structure, it achieves disproportionate enhancements in electrochemical performance. Furthermore, the doping strategy offers distinct competitive edges in terms of processing compatibility, energy efficiency, and overall cost‐effectiveness for large‐scale manufacturing. To enhance interfacial stability and structural integrity of cathode materials, numerous researchers have explored cationic doping by substituting Ni or Mn with elements such as Cu²⁺, Fe³⁺, Ga³⁺, Co³⁺, Al³⁺, Cr³⁺, Zn²⁺, Mg²⁺, Ru⁴⁺, and Ti⁴⁺ [66, 67]. Extensive experimental evidence confirms that such metal ion doping improves structural stability and facilitates the formation of disordered spinel phases. Zhang et al. proposed a novel approach involving trace incorporation of potassium hexafluoro‐1‐butanesulfonate (KPBS) dissolved in N‐methyl‐2‐pyrrolidone during electrode slurry processing [66]. The K⁺, Rb⁺, and Cs⁺ cations from KPBS play crucial roles in forming a homogeneous and stable CEI enriched with KF and LiF. The as‐prepared fluoride‐rich interphase generates abundant grain boundaries that accelerate lithium‐ion diffusion. Furthermore, the sulfonate functional groups in KPBS establish strong coordination bonds with Ni²⁺ and Mn³⁺ ions, effectively suppressing transition metal dissolution. The robust interaction between ‐SO₃ ⁻ groups and Ni/Mn ions promotes targeted deposition of KPBS derivatives precisely onto LNMO particle surfaces, enabling exceptional effectiveness at minimal dosages. Electrochemical testing demonstrated that LNMO cathodes incorporating merely 1.0 wt.‰ KPBS exhibited negligible capacity decay after 1,000 cycles at 1C rate, highlighting remarkably enhanced cycling stability achieved through this ultra‐low additive concentration.

Stuble et al. developed a Fe–Ti co‐doping strategy for Mn substitution, synthesizing LiNi_0.5Mn_1.37Fe_0.1Ti_0.03O_3.95 (LNMFTO) via two‐step spray‐drying synthesis [67]. Raman spectroscopy analysis confirmed effective suppression of ordered crystalline domain formation and reduced Mn³⁺ content through Ti–Fe co‐doping (Figure 7d,e), correlating with enhanced cycling robustness. Building upon this foundation, the researchers introduced Li₃PO₄ as a secondary dopant [92]. The creative modification significantly reduced transition metal deposition on graphite anodes while concomitantly supplying supplemental lithium ions that mitigated active lithium depletion. Electrochemical evaluation revealed that LNMFTO cathodes incorporating 1 wt.% Li₃PO₄demonstrated exceptional capacity retention exceeding 90% after 1,000 cycles at 1C rate in full‐cell configuration, highlighting the synergistic benefits of this dual modification approach.

Gao et al. developed a co‐modification strategy for LNMO cathodes through antimony (Sb) and fluorine (F) dual incorporation [68]. Sb doping homogenizes high‐voltage phase behavior by converting detrimental two‐phase transitions into solid‐solution reactions, effectively suppressing Mn dissolution. Concurrent F substitution facilitates partial Mn⁴⁺ to Mn³⁺ reduction within the spinel lattice, expanding crystallographic metrics and improving Li⁺ diffusion kinetics (Figure 7f). The synergistic approach remarkably enhances cycling stability and rate performance. Analogous to synergistic electrolyte formulations, cationic‐anionic co‐doping compensates for inherent limitations of single‐element modifications. Electrochemical benchmarking of LNMO‐Sb, LNMO‐F, and co‐doped LNMO‐SbF revealed superior performance in the Sb–F system. Specifically, LNMO‐SbF || graphite full cells demonstrated exceptional capacity retention (96.9%) after 300 cycles at 1C. The attractive performance is ascribed from reduced Li⁺ diffusion barriers through optimized crystallochemistry, which suppressed interfacial side reactions at electrode‐electrolyte junctions, as well as structural consolidation of the spinel framework inhibiting Mn dissolution‐mediated irreversible phase transformations during cycling (Figure 7g).

The co‐doping approach is similarly prevalent in NCM cathode optimization. For instance, Li et al. demonstrated La/Mg co‐doping in layered NCM cathodes [69], where La³⁺ ions facilitate formation of perovskite‐like protective surface structures during calcification, effectively shielding active materials from electrolyte corrosion. Mg²⁺ doping enhances electronic conductivity, collectively achieving 95% capacity retention after 100 cycles. Yang et al. implemented W/Nb co‐doping in NCM811 cathodes [70], revealing that dual modification substantially reduces system energy compared to individual W or Nb doping, thereby stabilizing the host structure. The co‐doping derived passivation layer concurrently mitigates parasitic reactions and suppresses microcrack propagation. Synergistic W‐Nb interaction further inhibits bulk oxygen vacancy formation and surface Li₂CO₃ generation. Electrochemical validation showed co‐doped NCM811 maintains 54.9% capacity retention after 400 cycles at 5C and 52.3% after 500 cycles at 10C (Figure 7h,i). These exemplars collectively affirm co‐doping as a straightforward and effective cathode modification strategy.

Beyond the doping of metal cations, many researchers have found that doping with specific material properties can also yield highly beneficial effects. Since carbonate solvents generate alkyl radicals during the charging process, suppressing the formation of these alkyl radicals and the ensuing chain reactions aids in inhibiting electrolyte decomposition. Inspired by the radical‐scavenging antioxidant properties of ascorbic acid (AA), Shen et al. attempted to incorporate AA into the cathode fabrication process [71]. Comparative analysis of the electrolyte decomposition residues on the cycled LNMO cathodes, with and without AA addition, revealed obviously fewer electrolyte decomposition byproducts in the AA‐containing cells. This indicates that AA substantially suppresses the radical reactions within the LNMO electrolyte. Due to its high HOMO energy, AA is preferentially oxidized and loses electrons (Figure 7j). Consequently, the radicals generated from carbonate solvent oxidation receive electron compensation, forming anions or molecules, thus terminating the radical chain reactions and inhibiting vigorous electrolyte decomposition. This process leads to the formation of a robust and stable CEI. LNMO||Li half‐cells incorporating AA exhibited a capacity retention of 87.4% after 1000 cycles at a 1C rate. Even under high rates (5C, 10C), the capacity retention remained above 80%.

3.2.3. Coating

Coating represents an effective strategy in optimizing the surface of high‐voltage cathode materials like LNMO to enhance their electrochemical performance. To date, various coating materials applied to such high‐voltage cathodes include oxides (e.g., Al₂O₃, ZnO, SnO₂, SiO₂, ZrO₂, phosphates (e.g., AlPO₄, Li_xFePO₄, ZrP₂O₇, and lithium‐ion‐conducting solid electrolytes (e.g., LiPON, Li₇La₃Zr₂O₁₂ (LLZO)) [93, 94, 95, 96]. The primary mechanisms through which these surfaces coatings improve the material performance are: (i) suppressing electrolyte decomposition by blocking electron transfer across the electrode‐electrolyte interface; (ii) inhibiting the dissolution of transition metals from the cathode structure; and (iii) mitigating the generation of HF within the electrolyte.

Nevertheless, the interfacial impedance increase induced by coating materials remains a significant challenge, as poor compatibility between the coating and the LNMO cathode can also compromise rate capability and long‐term cycling stability. Coherent interfacial coating has emerged as a promising strategy to mitigate such interfacial incompatibility. Ding et al. proposed a coherent Li₂ZnSiO₄ (LZSO) coating to protect LNMO from HF corrosion and electrolyte decomposition [97]. This ion‐conducting LZSO exhibits a high ionic conductivity of 3.1 mS cm⁻¹ at 300 K [98]. Critically, the coherent interface formed between LZSO and LNMO enhances interfacial stability and suppresses transition metal dissolution (Figure 8a). Beyond functioning as a physical barrier, the coherent‐derived Si atoms from LZSO penetrate the LNMO surface, creating a near‐surface gradient Si doping. The strong oxygen affinity of Si induces modifications in the Mn─O bonds of the MnO₆ octahedra, counteracting the Jahn–Teller distortion direction (Figure 8b). This alleviates both Jahn–Teller distortion and Mn dissolution, thereby further bolstering the stability of the LNMO crystal structure and the LNMO‐LZSO interface. Experimental results demonstrate a substantially improved capacity retention of 95.47% for the LZSO‐coated LNMO after 200 cycles at 0.5C and 25°C.

FIGURE 8.

(a) Mechanism of LZSO coating on the structural stability of LNMO. (b) Mechanism of gradient Si doping in alleviating crystal distortion of LNMO [97]. Copyright 2025, Elsevier. (c) Respective Young's modulus values for NCM and (d) LTeO‐1.0 materials [72]. Copyright 2025, Elsevier. (e) Mechanism of the Inner Helmholtz Plane (IHP) [73]. Copyright 2025, Elsevier. (f) coulombic efficiencies of the bare LNMO and 0.250‐B₂O₃‐LNMO materials during cycling. (g) Cycling (2nd cycle) of bare LNMO and 0.250‐B₃O₃‐LNMO in half‐cell for reference and reconstructed half cells [74]. Copyright 2024, Elsevier. (h) Schematics of performance improvement by LBO‐coated LNMO in LNMO/Gr full cell [75]. Copyright 2023, John Wiley and Sons.

The combined strategy of applying a surface coating while incorporating gradient elemental doping is also evident in NCM ternary cathode development. Wang et al. proposed utilizing a Li₄TeO₅ coating on the surface of single‐crystal, Ni‐rich LiNi_0.90Co_0.05Mn_0.05O₂ (S‐NCM955) cathodes, integrated with gradient Te⁶⁺ doping [72]. The gradient Te⁶⁺ doping facilitates the formation of robust Te─O bonds, effectively suppressing the detrimental H2 to H3 phase transition and reinforcing the cathode's lattice framework. Atomic force microscopy (AFM) analysis of the modified material (designated LTeO‐1.0) revealed enhanced mechanical properties, with the average Young's modulus increasing by 34.1 GPa (Figure 8c,d). Coatings with enhanced mechanical strength exhibit superior resilience against stress‐induced fatigue during prolonged electrochemical cycling, effectively mitigating the delamination of the interphase from the active material surfaces to ensure long‐term interfacial integrity. Such robust encapsulation maintains a stable physical barrier even in highly de‐lithiated states, significantly suppressing persistent parasitic reactions at the interface. Therefore, this leads to a marked reduction in internal pressure buildup and capacity attenuation within the full cell. The synergistic effect of the Li₄TeO₅ coating and the doping dramatically strengthened the mechanical robustness and structural stability of the CEI. Consequently, the LTeO‐1.0 cell demonstrated markedly improved cycling stability, achieving a capacity retention of 82.12% after 200 cycles at a 1C rate.

To circumvent limitations of conventional coatings [99], Fan et al. devised a strategy combining olivine‐type LiCoPO₄ (LCP) surface modification with targeted Helmholtz plane manipulation on LNMO cathodes (denoted LCP‐LNMO) [73]. This approach stabilizes interfacial electrochemistry through controlled ion adsorption at the electrode‐electrolyte boundary. The specific chemisorption behavior at the Inner Helmholtz Plane (IHP) governs initial interfacial architecture, while solvation sheath restructuring provides fundamental building blocks for CEI formation during cycling [100, 101]. Owing to strong F‐Co interactions within the cathodically polarized LCP framework, anions preferentially adsorb onto transition metal sites, displacing organic solvent species from the IHP (Figure 8e). This anion‐enriched IHP configuration facilitates the development of an ultrathin yet mechanically robust inorganic‐rich CEI. Meanwhile, the LCP coating physically isolates LNMO from direct electrolyte contact, effectively mitigating HF corrosion. Electrochemical validation revealed that 3 wt.% LCP‐LNMO achieves exceptional capacity retention (90.8%) after 600 cycles at 1C. The modified cathode also demonstrates remarkable thermal resilience, maintaining 84.9% capacity after 200 cycles at 50°C, highlighting the effectiveness of this dual‐function interfacial engineering strategy.

Although numerous successful coating materials have been proposed, many of these surface modification techniques involve complex chemical processes that often lack cost‐effectiveness and present challenges for scalable industrial production. For practical industrial adoption, coating strategies must prioritize both performance and considerations of cost‐efficiency and scalability. Addressing this need, Nisar et al. developed a borate coating suitable for large‐scale applications [74]. To ensure uniform borate coverage on the LNMO surface, a wet‐coating process was employed. Post‐cycling X‐ray photoelectron spectroscopy (XPS) analysis revealed significantly reduced electrolyte decomposition byproducts on the borate‐coated LNMO electrode (Figure 8f). Furthermore, scanning electron microscopy (SEM) examination of the graphite cathode demonstrated that the SEI became thinner and more robust in cells utilizing the borate‐coated LNMO. As a result, the 0.25‐B₂O₃‐LNMO || graphite full cell exhibited a capacity retention of 62.50% after 1000 cycles, substantially outperforming the uncoated LNMO counterpart, which retained only 41.20% capacity (Figure 8g). Similarly, Park et al. employed lithium metaborate (LiBO₂, denoted as LBO) as a surface coating for LNMO cathodes [75]. Utilizing a dry‐coating process, they achieved nanoscale LBO particles uniformly dispersed on the LNMO surface. During electrochemical cycling, the LBO coating gradually dissolved into the electrolyte, generating BF₄ ⁻species (Figure 8h) . This reaction mitigated the dissolution of transition metals from LNMO and prevented excessive thickening of the SEI on the anode. Consequently, these synergistic effects substantially enhanced the cycling stability of the full cell.

Scientific literature frequently highlights Atomic Layer Deposition (ALD) for its precision; however, its low throughput and high vacuum requirements represent a significant barrier to industrial scalability. In contrast, “One‐pot” wet‐chemical coatings or solvent‐free “Dry‐coating” methods are much more compatible with the current gigafactory infrastructure. However, wet‐chemical methods often involve secondary calcination, which may cause unwanted cation mixing if the temperature is not precisely controlled. The industry is currently gravitating toward “Dry‐coating” or “Gas‐phase surface modification” during the final lithiation stage, as these routes minimize energy consumption and eliminate the need for extra solvent recovery systems. Any new coating material must not only be ionically conductive but also mechanically robust enough to withstand the high‐pressure calendering process without cracking.

3.2.4. Engineering

Beyond doping and coating modifications, researchers have explored various engineering techniques, such as sintering temperature adjustments and magnetic field induction, to enhance cathode materials. Sun et al. successfully employed a local magnetic field to induce a transformation of LNMO from an ordered to a disordered structure [76]. Their approach involved applying a localized magnetic field via a magnetic Fe₃O₄ shell deposited on the surface of ordered‐phase LNMO particles. During the coating process at 300°C, this local field promoted spin‐selective electron transfer (Figure 9a). This process led to the loss of triplet oxygen, consequently increasing the concentration of oxygen vacancies. These oxygen vacancies, in turn, facilitated the disordering of transition metal ions, ultimately yielding disordered LNMO. Crucially, the authors ruled out potential confounding influences from interfacial effects or shell‐induced stress. Compared to alternative methods for inducing disorder, this magnetic induction approach achieved the structural transformation without concomitantly increasing the Mn³⁺ content, thereby pioneering a novel pathway for manipulating material phases using magnetic effects. Electrochemical evaluation confirmed the effectiveness of this strategy. The battery based on LNMO cathode transformed via magnetic induction retained 85% of its initial capacity after 500 cycles, outperforming the control sample, which exhibited a reduced capacity retention of only 78% after just 200 cycles (Figure 9b).

FIGURE 9.

(a) Schematic illustration of magnetic field‐induced order‐disorder transition in LNMO. (b) Comparison of cycling performance at 0.5C under the voltage range of 3.5–4.9 V [76]. Copyright 2024, John Wiley and Sons. (c) Regulating oxygen defects via different sintering temperatures to tailor material performance [77]. Copyright 2023, Elsevier. (d) Schematic illustration of the wet impregnation process for fabricating a beneficial surface coating composed of Li₃PO₄ and aluminum phosphate compounds [78]. Copyright 2023, John Wiley and Sons.

The electrochemical performance of the LNMO cathode is intrinsically linked to its oxygen stoichiometry and surface structure, highlighting that optimizing the material synthesis process itself represents an effective route for LNMO improvement. Wang et al. demonstrated that controlling the sintering temperature significantly alters LNMO properties, with the optimal temperature determined experimentally [77]. Their findings reveal that increasing the sintering temperature not only enhances the material's crystallinity and thermal stability but also elevates the concentration of oxygen vacancies (Figure 9c). These oxygen vacancies segregate at the LNMO crystal surface, leading to the formation of thin surface reconstruction layers. These spinel‐deficient surface layers compromise the structural stability of the LNMO surface, ultimately contributing to diminished cycling performance. Besides, while higher sintering temperatures yield greater crystallinity, they also promote detrimental oxygen vacancy formation, resulting in poorer stability. This interplay establishes a competing mechanism between crystallinity and oxygen vacancies within LNMO. Through systematic investigation, 850°C was identified as the optimal sintering temperature, producing LNMO material that exhibited superior capacity retention.

Similar strategies for surface modification have also been extended to high‐nickel NCM cathodes. For example, Xie et al. proposed a wet impregnation method to transform detrimental surface impurities into beneficial functional coatings [78]. Rather than employing washing steps to remove residual lithium carbonate (Li₂CO₃), which triggers parasitic reactions on the cathode surface, their approach utilizes a specialized solution to convert this impurity into a protective layer, offering a dual‐purpose solution. Recognizing that phosphate species (PO₄3⁻) can preemptively occupy active sites and enhance the electrochemical performance of Ni‐rich cathodes, they treated the cathode surface with an Al(H₂PO₄)₃ solution (Figure 9d). This treatment successfully converted residual Li₂CO₃ into Li₃PO₄ and AlPO₄, both recognized as effective coating materials for high‐voltage cathodes. Experimental characterization confirmed that the wet impregnation process resulted in a protective layer composed of Li₃PO₄ and AlPO₄. This layer effectively suppressed detrimental side reactions between the electrolyte and cathode, mitigated the harmful phase transformation from a layered structure to rock‐salt structure on the Ni‐rich cathode surface, and consequently led to a significant enhancement in the capacity retention of LiNi_0.83Mn_0.1Co_0.07O₂.

4. Summary and Outlook

Overall, both LNMO and Ni‐rich NCM cathodes represent high‐voltage material systems with broad application prospects. However, their large‐scale commercialization remains hindered by persistent challenges, including HF corrosion, transition metal dissolution, structural degradation, and interfacial instability. This review has analyzed the specific degradation mechanisms of each material, for LNMO, the critical roles of Mn^{3 +} disproportionation and Jahn–Teller distortion, and for Ni‐rich NCM, the dominant effects of cation mixing, oxygen vacancy formation, and anisotropic lattice strain‐induced microcracking. Despite these differences, both systems share common interfacial issues, including parasitic electrolyte decomposition and transition metal crossover, which suggests that modification strategies developed for one material can often be adapted for the other.

Significant progress has been made in stabilizing these cathodes through various approaches. Electrolyte engineering, including lithium salt additives (e.g., LiDFP, LiBF₄), organic additives (e.g., Si–O‐containing compounds, fluorinated species), and synergistic multi‐additive formulations, has enabled the formation of robust, ion‐conductive CEI layers that suppress HF attack and transition metal dissolution. Cathode modification strategies ranging from lattice doping (e.g., Ti, Zr, Nb, or co‐doping schemes) that reinforce the crystal framework and suppress oxygen evolution, to surface coating (e.g., oxides, phosphates, Li‐ion conductors) that physically isolate the cathode from electrolyte corrosion, and second‐phase additive blending (e.g., LLZT) that introduces functional particles to enhance interfacial Li⁺ transport and scavenge harmful species, which have collectively contributed to improved cycling stability and rate capability. Engineering approaches, such as morphology control and sintering optimization, further complement these strategies.

Looking forward, the research focus for both LNMO and NCM systems is expected to converge toward the synergistic optimization of full‐cell configurations rather than isolated material‐level modifications. Several key directions merit particular attention: First, the development of advanced electrolyte systems represents a critical pathway for substantially mitigating parasitic decomposition at high voltages of 4.4 V or above. This includes both wide‐potential‐window liquid formulations and solid‐state electrolytes. It is important to recognize, however, that solid‐state electrolytes, while offering improved oxidative stability, introduce their own interfacial challenges. These include poor solid–solid contact, interfacial side reactions, and lithium dendrite penetration. Future efforts must therefore focus on integrated interface engineering that addresses both the bulk stability of the electrolyte and the compatibility of electrode–electrolyte contacts. No single electrolyte system can be expected to eliminate all decomposition pathways. Instead, a combination of molecular design, interfacial modification, and cell engineering will be required. A second promising avenue lies in multifunctional interphase design. Building on insights from additive synergies and composite cathode strategies, future work should prioritize the construction of adaptive, self‐healing, or functionally graded interphases that can dynamically respond to electrochemical and mechanical stresses. The integration of in situ characterization techniques, such as operando spectroscopy and synchrotron‐based X‐ray imaging, with theoretical modeling will be essential for unraveling the complex interplay among interfacial chemistry, mechanical integrity, and transport phenomena under multi‐physics field coupling. Equally important is the consideration of industrial scalability and sustainable materials. While many modification strategies have demonstrated laboratory‐scale success, their translation to industrial production requires careful attention to cost, process complexity, and environmental impact. The development of single‐crystalline cathode morphologies, multi‐element co‐doping, and dry‐coating or additive‐blending methods that are compatible with existing manufacturing infrastructure will be pivotal for enabling the large‐scale commercialization of high‐voltage cathodes for long range electric vehicles and other high‐energy applications. Finally, cross system learning and synergy will continue to play a vital role. Given the mechanistic commonalities between LNMO and Ni‐rich NCM, future research should leverage insights across these material families. Approaches that prove effective in one system, such as the use of LLZT as a second‐phase additive or the deployment of silane‐based electrolyte additives should be systematically evaluated for their transferability to the other. Such evaluation must be conducted with careful attention to the distinct degradation drivers of each material.

In summary, achieving stable high‐voltage operation of Ni–Mn‐based cathodes requires moving beyond single component optimization toward a holistic strategy that integrates electrolyte engineering, cathode modification, and interfacial design. By embracing this systems level perspective and leveraging advances in characterization and manufacturing, the field is well positioned to overcome the remaining barriers and realize the full potential of these high energy density cathode materials.

Conflicts of Interest

The authors declare no conflicts of interest.

Biographies

Lili Liu obtained her Ph.D. degrees in physical chemistry from Fudan University in 2015 and in engineering from University of Wollongong in 2017. From 2017 to 2019, she was supported by the Alexander von Humboldt Foundation for postdoc research in the University of Freiburg, Germany. Currently she is a professor in Nanjing Tech University. Her research interest mainly focuses on Li metal batteries.

Xinhai Yuan, Associate Professor at Nanjing Tech University, primarily focuses on high‐energy‐density aqueous batteries and novel energy storage materials, including magnesium, aluminum, zinc, and lithium‐ion batteries. He has published over 50 papers in journals such as Advanced Energy Materials and Advanced Science, and is the principal investigator of a National Natural Science Foundation Youth Program.

Xiangwen Gao obtained his Ph.D. degree in University of Oxford in 2018. Form then, he conducted his postdoctoral research in Austin and Oxford until 2022. From 2023, he was employed as a Tenure‐Track Associate Professor in Puyuan Future Technology School, Shanghai Jiao Tong University. His research is foused on solid‐state lithium metal batteries and Li‐air batteries.

Yuping Wu, full professor, Fellow of RSC. In 2003, he was promoted to full professor at Fudan University, China. In 2015 he moved to Nanjing Tech University as a Distinguished Professor. He was selected as Most Influential Minds over the World from Highly Cited Researchers in 2015 by Thomas Reuter. He is the main inventor of 2^nd and 3^rd generations of aqueous rechargeable lithium batteries, and pore‐free separators for lithium batteries.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.