Ultrafast and Persistent Electrolyte Acid Scavenger for Stable High‐Voltage Lithium Batteries

ABSTRACT

Hydrofluoric acid (HF) generation in carbonate‐based electrolytes with LiPF₆ is a primary failure cause in high‐voltage lithium‐ion batteries. Here, a new dual‐functional additive 5‐trimethylsilanylthiazole (5‐SiTZ) is developed by rational molecular design for ultrafast and persistent acid scavenging. Siloxane group in 5‐SiTZ reacts spontaneously with HF, while its thiazolyl moiety acts as a secondary Lewis base scavenger and chelates PF₅ to suppress further HF generation. This synergistic action achieves ultrafast (<1 s) and complete HF removal for over 200 days upon open‐air exposure. Furthermore, 5‐SiTZ promotes the formation of a robust, inorganic‐rich cathode electrolyte interphase. The combined effect of persistent HF removal and interface stabilization enables commercial graphite||NCM811 pouch cells to deliver outstanding capacity retention of 92.1% after 700 cycles at 4.6 V. This work establishes a paradigm of synergistic molecular design for multi‐functional additives, providing a practical route to durable high‐energy batteries.

A rationally designed dual‐functional additive integrating siloxane and thiazolyl groups achieves ultrafast (<1s) and persistent (>200 days) acid scavenging in commercial carbonate electrolytes. This molecular design simultaneously neutralizes HF and sequesters PF₅, suppressing parasitic reactions and promoting robust interphases that enable durable high‐voltage cycling in practical lithium batteries.

1. Introduction

Nickel‐rich layered cathodes, such as LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811), are pivotal for developing high energy‐density (>400 Wh kg^{− 1}) lithium‐ion batteries (LIBs) [1, 2], yet their performance is severely compromised under high‐voltage (≥4.4 V) and long cycling operation [3, 4, 5]. The aggressive electrochemical environment at these potentials intensifies parasitic reactions with carbonate‐based electrolytes, leading to rapid structural degradation and capacity decay during cycling [6, 7]. A critical failure mechanism involves trace moisture, which reacts with the LiPF₆ salt to generate hydrofluoric acid (HF) [8, 9, 10]. This highly corrosive HF attacks the cathode, causing transition metal (TM) dissolution, oxygen loss, and corrosion of the aluminum current collector, ultimately resulting in irreversible phase transitions and a compromised cathode–electrolyte interphase (CEI) [11, 12].

Incorporating functional additives into the electrolyte represents a promising strategy to mitigate HF‐induced degradation. Several classes of additives have been explored. The cyanogroup‐based additives, such as trimethylsilyl isocyanate (SiNCO) [13] and 3‐isocyanatopropyltrimethoxysilane (PTTSNCO) [14], utilize isocyanate groups to neutralize acidic species. Silane‐based additives, valued for their thermal stability and non‐toxicity (e.g., vinyl‐triethoxy‐silane (VTEO) [12] and vinyl‐trimethyl‐silane (VTMS) [15]), react with fluoride ions (F⁻) in hydrogen fluoride to form stable silicon–fluorine compounds. Similarly, phosphorus‐based additives (e.g., ethoxy (pentafluoro) cyclotriphosphazene (PFPN) [16] and tripropargyl phosphate (TPP) [17]) and amide‐based additives (e.g., N, O‐bis(trimethylsilyl) trifluoroacetamide (BSTFA) [18]) rely on their phosphorus atoms and amide groups, respectively, to interact with HF. While effective, these approaches are inherently limited by their dependence on a single functional group, which often results in incomplete acid removal and compromised performance under demanding high‐voltage, long‐term cycling conditions [19, 20]. This limitation underscores the need for multifunctional additives that can remove acidic species through cooperative mechanisms. Such multifunctionality not only enhances HF removal efficiency but can also promote the formation of robust, multi‐element‐containing CEI layers, thereby improving interfacial stability [21]. Thiazole, a five‐membered aromatic heterocycle containing nitrogen and sulfur, presents an attractive molecular scaffold for this purpose [22, 23]. Its inherent Lewis basicity enables it to neutralize acids, while its structure allows for facile functionalization with other active moieties, such as siloxane groups. This design can yield a synergistic, dual‐function additive capable of both rapid HF chemical capture and the introduction of beneficial heteroatoms for CEI engineering.

Herein, we report a new dual‐function additive, 5‐trimethylsilanylthiazole (5‐SiTZ), engineered with cooperative siloxane and thiazolyl groups to achieve ultrafast and persistent acid scavenging for carbonate electrolyte with LiPF₆. The trimethylsilyl (TMS) groups react rapidly with HF to form stable fluorinated silicon species, accomplishing primary HF elimination. Concurrently, the thiazolyl groups act as Lewis basic sites, neutralizing residual HF via acid–base interactions for advanced acid removal. This concerted action enables an exceptional HF scavenging rate of less than 1 s and maintains electrolyte stability for over 200 days upon open‐air exposure. Furthermore, as an N/S/Si‐rich molecule, 5‐SiTZ facilitates the construction of a multicomponent‐doped CEI rich in protective inorganic phases, endowing exceptional high‐voltage tolerance. As a result of this synergistic functional evolution and sustained HF depletion, the Li||NCM811 battery exhibited excellent capacity retention of 83.5% after 300 cycles at 4.6 V and 80% after 240 cycleseven at 4.8 V, the graphite||NCM811 commercial pouch cell employing the modified electrolyte achieves an outstanding capacity retention of 92.1% over 700 cycles at 4.6 V.

2. Results and Discussion

2.1. Thiazole and Its Derivatives for HF Removal

Thiazole is a five‐membered aromatic heterocycle containing sulfur and nitrogen heteroatoms (Figure 1a). The sp²‐hybridized nitrogen atom possesses a lone pair of electrons that can accept a proton (H⁺), which confers weak basicity to the thiazole molecule [24]. This property allows thiazole to act as a Lewis base to develop an HF scavenger in electrolytes, achieving a moderate degree of acid removal (Table S1). To enhance this acid‐scavenging performance, a trimethylsilyl group (TMS) is introduced at different positions on the thiazole ring (Figure 1a). The TMS is an electron‐withdrawing substituent, and its position can induce significant electronic perturbations. These effects can alter the electron density on the nitrogen lone pair (impacting basicity) [25, 26] and the conjugated π‐system of the thiazole ring (influencing stability) [27]. Therefore, the strategic placement of the silicon group is critical for optimizing performance (Figure S1).

FIGURE 1.

Acid scavenging performance and stability of 5‐SiTZ in the electrolyte. (a) Molecular structure of thiazole and substituted derivatives, with π‐electron distribution mapping. (b) Electron localization function (ELF) analysis for 2‐SiTZ and 5‐SiTZ. (c) Long‐term storage test (200 days) under open‐air exposure for pure EMC, base electrolyte (1 M LiPF₆ in EC/EMC, 3:7 vol.), and electrolyte with 1 vol %5‐SiTZ. (d) Formation charge–discharge curve of a cell using base electrolyte after one day of open‐air exposure. (e) Formation charge–discharge curve of a cell using 5‐SiTZ‐containing electrolyte after 200 days of open‐air exposure. (f) Cycling performance of open‐air assembled graphite||NCM811 cells at 4.3 V. (g) Comparative chart of open‐air‐stability duration for 5‐SiTZ versus other HF‐scavenging additives reported in the literature (Table S2) [14, 15, 16, 18, 21, 28, 29, 30, 31, 32, 33]. (h) HF removal mean time of 5‑SiTZ, thiazole (TZ), 2‑SiTZ, hexamethyldisilazane (HMDS), tris(trimethylsilyl) phosphate (TMSP), vinyltrimethylsilane (VTMS), vinyltriethoxysilane (VTEO), ethoxy(pentafluoro)cyclotriphosphazene (PFPN), and toluene‑2,4‑dTiisocyanate (TDI) (Table S3). (i) ¹⁹F NMR spectra of the base electrolyte after 7 days and 5‐SiTZ electrolyte after 7 and 30 days of storage.

To guide this molecular design, theoretical calculations and electron localization function (ELF) analysis were employed to map the electron cloud distribution of TMS‐substituted thiazole derivatives. As illustrated in Figures 1b and S2, the substitution of a silicon‐based group at the 2‐ or 4‐position, due to proximity to the electronegative nitrogen, exerts a strong electron‐withdrawing effect. This depletes electron density from the nitrogen, diminishing its basicity. In contrast, substitution at the 5‐position is electronically decoupled from the nitrogen due to steric hindrance, resulting in minimal disturbance to both the nitrogen's lone pair and the aromatic π‐electron distribution. This theoretical predication was confirmed experimentally by measuring the pH of solutions containing the 2‐ and 5‐substituted isomers (2‐SiTZ and 5‐SiTZ) (Table S1). The 5‐SiTZ exhibits a higher pH (8.02) than 2‐SiTZ (7.21), confirming its superior basicity and, consequently, its greater potential for acid scavenging. Furthermore, frontier molecular orbital analysis was conducted to assess the CEI‐forming potential of the additives (Figure S3). Among the isomers, 5‐SiTZ exhibits a higher highest occupied molecular orbital (HOMO) level, indicating a thermodynamic tendency to be preferentially oxidized on the cathode surface to form a protective interphase. This theoretical advantage translates to superior electrochemical performance, as shown in Figure S4, 5‐SiTZ enables significantly better cycling stability at a high voltage of 4.6 V.

The acid‐scavenging efficacy of 5‐SiTZ was first evaluated through a long‐term storage test under ambient conditions in open air (Figures 1c and S5). Upon adding an acid–base mixed indicator, the pristine electrolyte immediately turned pink, confirming its inherent acidity. However, the introduction of just 1% 5‐SiTZ induced an instantaneous color change to yellow within 1 s, indicating rapid HF removal. This stability proved to be remarkably persistent in the next storage experiment. After 200 days of open‐air storage, the base electrolyte significantly degraded due to the decomposition of lithium salts. In contrast, the 5‐SiTZ‐containing electrolyte retained its yellow color and HF‐free state. Electrochemical validation confirmed this stark contrast. Electrolytes stored for 200 days with 5‐SiTZ remained functionally intact, supporting full charge–discharge cycles, whereas the unmodified base electrolyte failed after only one day of exposure (Figure 1d,e). Given its superior air stability, experiments were conducted to assemble graphite||NCM811 pouch cells under ambient air conditions. As shown in Figure 1f, the cell containing 5‐SiTZ operated stably even when assembled in air, whereas the cell using the base electrolyte failed to complete the formation stage (Figure S6). The same conclusion was obtained in repeated tests at 4.6 V (Figure S7), further demonstrating the reliable air stability of 5‐SiTZ. A survey of reported acid scavengers confirms that the 200‐day stability enabled by 5‐SiTZ significantly surpasses the performance of existing additives (Figure 1g and Table S2). To further demonstrate the acid‐removal speed, we introduced 2000 ppm of water into a fresh electrolyte and allowed it to hydrolyze for 8 h, generating substantial amounts of HF (evidenced by a bright red indicator color). Subsequent addition of 5‐SiTZ caused the solution to revert to yellow in less than 1 s (Video S1), visually confirming its ultrafast HF scavenging kinetics. Commonly available acid scavengers were tested for comparison with 5‐SiTZ. Benefit from the molecular design with siloxane and thiazole groups, 5‐SiTZ achieves ultrafast acid removal (0.68s, Figure 1h), which is significantly superior to the other silicon‐based or cyano‐based additives. ¹⁹F nuclear magnetic resonance (NMR) spectroscopy was employed to quantitatively monitor HF and LiPF₆ decomposition products in the electrolytes (Figure 1i). The spectra of the base electrolyte exhibit characteristic peaks for PO₃F²⁻ (−60 ppm), PO₂F⁻ (−90 ppm), and HF (−120 ppm), which are decomposition products of LiPF₆ [34, 35]. In contrast, the electrolyte with 1% 5‐SiTZ shows a complete absence of these characteristic peaks even after 30 days of air exposure. This conclusively proves that 5‐SiTZ not only removes HF but also effectively suppresses the decomposition cascade of LiPF₆, ensuring long‐term electrolyte stability. This long‐term stability underscores the potential of 5‐SiTZ as a reliable additive for maintaining the chemical integrity of electrolytes over extended periods. Finally, Fourier transform infrared spectroscopy (FTIR) was employed to evaluate the ability of the additive to mitigate moisture. The O─H stretching vibration of water exhibits a broad and strong absorption band in the 3200–3600 cm^{− 1} region, the intensity of which is proportional to its content. Figure S8 shows that the 5‐SiTZ additive can effectively mitigate the impact of water at 500 ppm. The reduction of trace water content is effective in resisting its reaction with LiPF₆, and this also reduces the generation of subsequent HF, ensuring the long‐term stability of the electrolyte. The HF scavenging performance of 5‑SiTZ under real operating conditions was verified by cycling Li||NCM811 cells at 4.6 V for 100 cycles (room temperature and 45°C). ¹⁹F NMR of the post‑cycle electrolytes (Figures S9 and S10) shows that 5‑SiTZ nearly eliminates the HF signal, in contrast to the base electrolyte, confirming its efficient HF removal even under harsh cycling conditions.

2.2. Mechanism of Hydrofluoric Acid Scavenging by 5‐SiTZ

The HF‐scavenging of 5‐SiTZ involves synergistic chemical reactions. The multiple reaction pathways of HF generation are illustrated in Figure 2a [8, 9, 10]. Trace amounts of H₂O initiate multiple decomposition pathways of LiPF₆, leading to the accumulation of HF and PF₅ in the electrolyte. Upon introduction, 5‐SiTZ engages HF through two sequential, cooperative steps (Figure 2b). First, the TMS group reacts rapidly and spontaneously with HF (ΔG = −29.6 kcal/mol) to form fluorotrimethylsilane (FTMS, confirmed by a ^{1 9}F NMR peak at −160 ppm in Figure S11) and releases free thiazole [15]. Subsequently, both the integral thiazole moiety of 5‐SiTZ and the liberated thiazole act as Lewis bases, neutralizing residual HF via acid–base interactions to form thiazolium salts, thereby accomplishing thorough acid removal.

FIGURE 2.

Mechanism of hydrofluoric acid scavenging and solvation structure regulation by 5‐SiTZ. (a) Multiple reaction pathways for HF generation via LiPF₆ hydrolysis, initiated by trace H₂O. (b) Reaction pathway of 5‐SiTZ with HF and the pathway of neutralization reaction between thiazole and HF. (c) Reaction transition state energy barrier analysis with initial state (IS), transition state (TS), intermediate state (INT), final state (FS) of PF₅+H₂O, PF₅ +H₂O with TZ, and PF₅ +H₂O with 5‐SiTZ. (d) Binding energy of 5‐SiTZ, TZ, EMC, EC with HF and PF₅. Radial distribution functions (RDFs) and coordination numbers of Li⁺ in the (e) base electrolyte and (f) 5‐SiTZ electrolyte. (g) Statistical analysis of AGGs (aggregated clusters), CIPs (contact ion pairs), and SSIPs (solvent–solvent interaction pairs) in the electrolytes.

Beyond direct reaction, 5‐SiTZ actively suppresses HF generation at its source by inhibiting the pathway of LiPF₆ decomposition. Reaction transition state energy barrier analysis (Figure 2c) reveals that the decomposition of PF₅ and H₂O to PF₃O and 2HF is thermodynamically favorable (final state (FS): −0.26 eV), which is a main pathway leading to the deterioration of the electrolyte [35]. When TZ or 5‐SiTZ is added, the energy barrier at the transition state TS1 increases, making it more difficult for PF₅ and water to form the intermediate INT1. Furthermore, the reaction with 5‐SiTZ exhibits a significantly higher TS2 barrier for INT2 formation than the reaction with TZ, suggesting that the TMS group effectively increases the energy barrier during PF₂OH‐HF formation. The TS3 stage presents the highest energy barrier in the profile, identifying it as the rate‐determining step. Notably, the presence of 5‐SiTZ significantly increases this barrier, indicating its crucial role in stabilizing reaction intermediates and thereby inhibiting the reaction's spontaneous progression. This inhibitory effect is attributed to the strong binding affinity of 5‐SiTZ for key decomposition species. As shown in Figure 2d, the thiazole nitrogen, with its sp² hybridized lone pair, coordinates strongly with both PF₅ (−0.994 eV) and HF (−0.521 eV). These binding energies are substantially higher than those with the carbonate solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC), indicating that 5‐SiTZ preferentially sequesters PF₅, preventing it from initiating further hydrolysis and HF generation.

Molecular dynamics (MD) simulations were performed to understand the Li⁺ solvation structure (Figures 2e,f and S12). The introduction of 5‐SiTZ induces a new, strong Li‐N(5‐SiTZ) coordination peak at ∼1.65 Å, indicating preferential interaction between Li⁺ and the thiazole nitrogen. This preferential interaction modifies the solvation structure, decreasing Li⁺ coordination with EC/EMC while increasing association with PF₆ ⁻ anions. Consequently, the population of contact ion pairs (CIPs) and aggregates (AGGs) increases, as statistically shown in Figure 2g, indicating an enhanced weak solvation effect. This restructured environment effectively facilitates Li⁺ transportation, evidenced by a significant increase in the Li⁺ transference number from 0.423 (base electrolyte) to 0.511 (5‐SiTZ electrolyte, Figure S13). This enhancement confirms the effectiveness of 5‐SiTZ in facilitating Li⁺ transport through its unique coordination chemistry [31]. In summary, 5‐SiTZ operates through a multifunctional mechanism: (1) ultrafast and spontaneous silylation for primary HF removal, (2) secondary acid–base neutralization, (3) suppression of HF generation by sequestering PF₅ and stabilizing hydrolysis intermediates, and (4) optimization of the Li⁺ solvation structure to enhance ion transport.

2.3. Electrochemical Performance Enhancement Enabled by 5‐SiTZ

The positive impact of 5‐SiTZ on electrochemical performance was systematically evaluated across multiple cell configurations. Linear sweep voltammetry (LSV) reveals its role in enhancing the electrochemical window of the electrolyte (Figure 3a). Electrolytes containing 1% or 2% 5‐SiTZ show a distinct oxidation peak at 4.3–4.5 V prior to solvent decomposition, which corresponds to the preferential oxidation of the additive on the cathode surface. This sacrificial decomposition effectively passivates the NCM811 cathode, extending the electrolyte's practical anodic stability to ∼5 V.

FIGURE 3.

Electrochemical performance enhancement enabled by 5‐SiTZ. (a) Linear sweep voltammetry curves of the base electrolyte and electrolytes with 1%, 2% 5‐SiTZ. (b) Cycling performance and coulombic efficiency (CE) of Li||NCM811cells at of 3–4.6 V for the base and 1% 5‐SiTZ‐containing electrolytes. (c) Voltage curves at 1–120 cycles of Li||NCM811 cells with base and 5‐SiTZ electrolytes. (d) Differential capacity curves at the 10–100 cycle of Li||NCM811 cells with base and 5‐SiTZ electrolytes. (e) Electrochemical impedance spectroscopy Nyquist plots of Li||811 cells after 50 cycles with base and 5‑SiTZ electrolytes, measured from 1 MHz to 0.005 Hz with an AC amplitude of 5 mV. (f) Rate performance of Li||NCM811 cells with base and 5‐SiTZ electrolytes. (g) Cycling performances of commercial graphite||NCM811pouch cells, and inset images show ultrasonic images of pouch cells after 12 h of electrolyte immersion. (h) Comparative cycling performance of 5‐SiTZ against reported HF‐scavenging additives in commercial graphite||NCM811 pouch cells (corresponding data in Table S4) [17, 19, 35, 36, 37, 38].

Optimization studies identified 1% as the ideal additive concentration for cycling performance (Figure S14). The cycling performance of Li||NCM811cells (Figure 3b) reveals substantial improvements by 5‐SiTZ in cycle life and capacity retention. The cell with the base electrolyte suffers rapid degradation, losing nearly all capacity within 100 cycles at 4.6 V. In contrast, the cell with 1% 5‐SiTZ electrolyte demonstrates remarkable stability, maintaining 83.5% of its initial capacity even after 300 cycles. This improvement is attributed to reduced polarization, as evidenced by the well‐maintained charge/discharge voltage profiles over 120 cycles, and enhanced structural reversibility of the cathode (Figure 3c). The differential capacity plots (Figure 3d) show that characteristic phase transition peaks, especially the H2↔H3 transition near 4.2 V, remain stable and highly reversible with 5‐SiTZ, while they shift and diminish rapidly in the base electrolyte. This indicates improved structural integrity of the cathode in the modified electrolyte [39]. At 45°C and 4.6 V, Li || NCM811 cells cycling with the additive maintain stable capacity over 150 cycles, whereas the baseline exhibits rapid decay to below 50 mAh g⁻¹(Figure S15). Notably, the 5‐SiTZ electrolyte can still maintain an 80% retention rate of 240 cycles even at an extremely high voltage of 4.8 V (Figure S16). Those stark contrasts confirm the additive's ability to suppress parasitic reactions and acid‐induced cathode degradation under high‐temperature, high‐voltage conditions.

The enhanced kinetics afforded by 5‐SiTZ were quantified through impedance and diffusion analyses. Electrochemical impedance spectroscopy (EIS) after 50 cycles shows a marked reduction in overall impedance for the 5‐SiTZ containing cell (Figure 3e), signifying a more conductive and stable interface. This is corroborated by galvanostatic intermittent titration technique (GITT) analyses, which reveal an order of magnitude increase in the average Li⁺ diffusion coefficient (D_Li ⁺), from 6.32×10^{− 11} (base) to 3.16×10^{− 10} cm² s^{− 1} (5‐SiTZ) (Figure S17). Consequently, the rate capability is significantly improved (Figure 3f), with the 5‐SiTZ cell delivering notably higher capacities at high currents (5C and 10C), underscoring its superior ability to support rapid charge–discharge. Furthermore, Li||Li symmetric cell testing confirms enhanced interfacial stability at the lithium metal anode, with 5‐SiTZ significantly postponing the onset of polarization (Figure S18). Using Aurbach's method, the Li||Cu cell with the 5‑SiTZ electrolyte achieves a Coulombic efficiency (CE) of 99.28% (Figure S19), far exceeding the 97.51% of the base electrolyte. Moreover, the 5‑SiTZ electrolyte enables stable Li||Cu cycling with a high CE over 80 cycles (Figure S20), confirming its excellent compatibility with Li anodes.

To validate performance under practical conditions, high‐loading Li||NCM811 pouch cells (1000 mAh, 4.3 mAh cm^{− 2} cathode, 50 µm Li anode) were assembled. The pouch cell with 5‐SiTZ electrolyte retains 80.5% capacity after 100 cycles at 4.6 V, while the base cell fails rapidly, retaining only 20% after 30 cycles (Figures S21 and S22). Most compellingly, in commercial graphite||NCM811 full pouch cells cycled at a high cutoff voltage of 4.6 V, the addition of 1% 5‐SiTZ enables an exceptional capacity retention of 92.1% after 700 cycles, far surpassing the rapid degradation of the base electrolyte (Figures 3g, S23 and S24). Beyond electrochemical stabilization, 5‐SiTZ improves electrolyte wettability, which is highly important for large cell assembly. Contact angle measurements show enhanced spreading on the separator (Figure S25), a property attributed to the surfactant‐like behavior of its siloxane group [40]. Ultrasonic imaging of a pouch cell after 12 h of electrolyte immersion (Figure 3g, inset) visually confirms the superior and uniform wetting enabled by 5‐SiTZ, which promotes homogeneous electrode/electrolyte contact. A benchmark comparison of reported HF‐scavenging additives in pouch cells (Figure 3h and Table S2) highlights the superior practicality of 5‐SiTZ. Its unique combination of ultrafast and persistent acid removal, coupled with beneficial interfacial modification and improved wettability, establishes it as a pivotal enabler of long‐term cycling stability under aggressive high‐voltage conditions.

2.4. Structural Preservation of the Cathode by 5‐SiTZ

The beneficial role of 5‐SiTZ in preserving cathode structural integrity was elucidated through in situ and post‐mortem analyses. In situ x‐ray diffraction (XRD) analysis (Figure 4a,b) reveals that during the delithiation process, the (003) peak initially shifts to lower 2θ angles, indicating lattice expansion along the c‐axis. This is followed by a rapid shift to higher angles upon the H2–H3 phase transition, signifying lattice shrinkage. The incorporation of 1% 5‐SiTZ in the electrolyte results in a reduced peak shift of 0.20° at a high state of charge compared to the baseline group, suggesting enhanced structural stability. Furthermore, the (104) peak shift to higher angles during delithiation, the difference of peak shift between the 5‐SiTZ and baseline is 0.12°, showing the effective regulation of lattice shrinkage, thereby demonstrating the beneficial role of 5‐SiTZ in maintaining the structural integrity of the NCM811 cathode [33]. Post‐cycling XRD confirms that the layered crystal structure of NCM811 remains intact after cycling with 5‐SiTZ, unlike the baseline sample, which shows structural degradation with a greatly reduced I(003)/I(104) ratio (Figure S26).

FIGURE 4.

Structural Preservation of the NCM811 Cathode by 5‐SiTZ. In situ XRD characterization for NCM811 cathode and the evolution of (003) peaks and (104) peaks during the initial charge–discharge (0.3C‐rate) using base electrolyte (a) and 5‐SiTZ electrolyte (b). Post‐cycling structural analysis (100 cycles, 4.6 V) for cathode cycled in base electrolyte: SEM image (c), TEM image of CEI layer (d), and high‐resolution TEM image with lattice fringes (e). Post‐cycling structural analysis (100 cycles, 4.6 V) for cathode cycled in 5‐SiTZ electrolyte: SEM image (f), TEM image of CEI layer (g), and high‐resolution TEM image with lattice fringes (h).

This macroscopic structural stability is reflected in the cathode particle morphology. Scanning electron microscopy (SEM) image of the cathodes after 100 cycles shows severe microcracking in the baseline sample (Figure 4c), a common failure mode driven by anisotropic lattice strain and HF attack. In contrast, the cathode cycled with 5‐SiTZ electrolyte (Figure 4f) displays a significantly preserved surface with minimal cracks, directly linking structural integrity to the superior cycling stability observed in Figure 3g. Transmission electron microscopy (TEM) images further reveal the nanoscale interfacial and crystallographic improvements. The cathode–electrolyte interphase formed in the baseline electrolyte is thick and non‐uniform (2.1–3.6 nm, Figure 4d). In contrast, 5‐SiTZ electrolyte results in a much thinner and more uniform CEI layer (∼1.6 nm, Figure 4g), suggesting enhanced electrolyte stability and reduced decomposition. Simultaneously, the high‐resolution TEM images provide atomic‐scale evidence of bulk structural preservation. The baseline cathode (Figure 4e) exhibits extensive surface reconstruction into a rock‐salt phase (0.24 nm, (101) plane), an irreversible degradation that impedes Li⁺ transport [41]. The cathode cycled with 5‐SiTZ (Figure 4h) maintains sharp lattice fringes of the layered phase (0.48 nm, (003) plane). Collectively, these multi‐scale characterizations demonstrate that the 5‐SiTZ additive comprehensively protects the NCM811 cathode: it regulates bulk lattice strain, prevents particle microcracking, forms a thin and stable CEI, and inhibits surface phase transformation. This multifaceted structural preservation is the fundamental origin of the enhanced long‐term cycling performance under high‐voltage operation.

2.5. Enhanced Cathode–Electrolyte Interface by 5‐SiTZ

The 5‐SiTZ additive fundamentally improves interfacial stability by directing the formation of a robust, inorganic‐rich cathode–electrolyte interphase (CEI). Atomic force microscopy (AFM) reveals a drastically smoother and mechanically stronger cathode surface after cycling with 5‐SiTZ (Figure 5a,b). The surface roughness of cycled NCM811 decreases from 319 to 114 nm, while the Young's modulus increases from 7.7 to 13.2 GPa upon the incorporation of the 5‐SiTZ additive. This indicates the formation of a uniform, compact, and mechanically robust CEI layer, which mitigates surface‐initiated degradation and particle cracking [42]. Density functional theory (DFT) calculations provide the molecular‐scale rationale for this improvement. 5‐SiTZ exhibits a significantly stronger adsorption energy on the NCM811 surface (−1.77 eV) than the solvent molecules EC and EMC (Figure 5c). This preferential adsorption, consistent with its high HOMO energy, ensures that 5‐SiTZ decomposes sacrificially prior to the bulk electrolyte, forming the foundational CEI matrix.

FIGURE 5.

Enhanced cathode–electrolyte interface by 5‐SiTZ. The AFM image of NCM811 cathode after 100 cycles in (a) base electrolyte and (b) 5‐SiTZ electrolyte. Corresponding root‐mean‐square (RMS) roughness and Young's modulus values are indicated. (c) Calculated adsorption energies of EC, EMC, and 5‐SiTZ on the NCM811 (001) surface. (d) F 1s x‐ray photoelectron spectroscopy spectra of NCM811 cathode after 100 cycles in base and 5‐SiTZ electrolytes. (e) TOF‐SIMS visualization distribution of C₂HO⁻, LiF²⁻, S⁻, CN⁻, and Si⁻ within the CEI formed in base and 5‐SiTZ electrolytes. (f) ICP‐OES analysis of transition metal dissolution into the electrolyte after cycling. (g) In situ DEMS measurement of gas (O₂, CO₂, and H₂) evolution rates during the first formation cycle for cells with the base and 5‐SiTZ electrolytes.

Thus, XPS measurement was performed to analyze the surface chemical composition of the CEI on the NCM811 cathode. The C 1s spectra (Figure S27) shows reduced organic carbonates (C═O, C─O) and increased carbonate species, indicating less solvent‐derived decomposition in 5‐SiTZ electrolyte [43]. Concurrently, the F 1s spectra (Figure 5d) is more dominated by a strong LiF peak (685.0 eV) with decreased C─F component. These results point to an inorganic‐rich CEI where LiF, a key component for Li⁺ conductivity and chemical stability, is prevalent [44]. Time of flight secondary ion mass spectrometry (TOF‐SIMS) depth profiling (Figure 5e) provides three‐dimensional insights into the composition of the CEI. The CEI formed with 5‐SiTZ shows a suppressed C₂HO⁻ (organic fragments) and a significantly enhanced LiF²⁻ signal (inorganic LiF), suggesting the formation of a more inorganic‐rich CEI. Additionally, the depth profiles confirm the uniform incorporation of heteroatoms—nitrogen (N), sulfur (S), and silicon (Si)—from the decomposed additive throughout the CEI. XPS analysis (Figure S28) identifies these as beneficial species, including Li₃N, Li₂SO_x, Li₂S, and Si─O compounds, which are known to enhance interfacial Li⁺ transport and passivate the cathode surface [41, 45, 46]. This high‐quality, multifunctional CEI delivers direct protective benefits. Inductively coupled plasma (ICP) analysis (Figure 5f) confirms that the 5‐SiTZ cell exhibits dramatically suppressed dissolution of transition metals (Ni, Co, Mn), particularly nickel, which is a major contributor to capacity fade.

Finally, in situ differential electrochemical mass spectrometry (DEMS) directly correlates the improved interface with suppressed parasitic reactions during operation (Figure 5g). The cell with 5‐SiTZ shows markedly reduced gas evolution at the first formation process (up to 4.8 V). O₂ evolution is minimized, indicating effective suppression of irreversible lattice oxygen release at high voltages [47]. Carbon dioxide (CO₂), associated with the EC decomposition at high voltages [48] and the HF‐induced carbonate corrosion [28], is significantly lower, confirming both enhanced electrolyte stability and effective HF scavenging. Moreover, 5‑SiTZ scavenges trace water, thereby suppressing H₂ generation and preventing the formation of acidic species (such as HF) throughout the cell, further evidencing its role in maintaining electrolyte stability [49, 50]. In summary, the 5‐SiTZ additive orchestrates the formation of a thin, smooth, inorganic‐rich, and heteroatom‐doped CEI. This engineered interface simultaneously passivates the cathode surface, suppresses transition metal dissolution, inhibits gas evolution, and facilitates Li⁺ transport, collectively underpinning the exceptionally high‐voltage cycling stability.

2.6. Discussion on Mechanism of Synergistic Acid Scavenging and Interfacial Stabilization by 5‐SiTZ

Based on the above analyses, the mechanism of ultrafast and persistent electrolyte acid scavenging of the 5‐SiTZ additive is schematically summarized in Figure 6. This mechanism operates through three synergistic pillars: (1) direct and persistent HF elimination, (2) suppression of HF generation at its source, and (3) the formation of stabilized electrode interfaces. LiPF₆ spontaneously decomposes into PF₅ in the presence of trace amounts of H₂O, which in turn triggers the formation of HF, exacerbating degradation reactions. HF attacks components such as lithium carbonate, alkyl carbonates, and lithium metal in the CEI, causing degradation of both the anode and cathode. First, 5‐SiTZ achieves ultrafast and thorough acid scavenging via a sequential dual‐action chemical process. The trimethylsilyl (TMS) group reacts spontaneously with HF to form stable fluorosilane and thiazole, providing rapid primary removal. Simultaneously, the inherent thiazole moiety—both from the original molecule and generated in situ—acts as a Lewis base to neutralize residual HF through acid–base interactions, ensuring comprehensive cleanup. Second, 5‐SiTZ actively suppresses the generation of HF by intercepting its precursor, PF₅. The nitrogen atom in the thiazole ring, with its lone pair of electrons, strongly coordinates with PF₅, preventing further side reactions and inhibiting the production of HF. This dual capability—scavenging existing HF while inhibiting its formation—confers the observed ultrafast HF removal within 1 s and persistent electrolyte stability over 200 days (as shown in Figure 1).

FIGURE 6.

Schematic illustration of synergistic acid scavenging and interfacial stabilization by 5‐SiTZ additive in electrolytes.

Moreover, by effectively HF scavenging, the additive directs the formation of robust, protective interphases on both cathode and anode, which is crucial for battery stability during long‐term cycling. 5‐SiTZ's high HOMO enables its preferential oxidation on the cathode, leading to a thin, inorganic‐rich, and heteroatom‐doped high‐quality CEI (Figures 4 and 5). This CEI mitigates oxygen loss, suppresses transition metal dissolution, and prevents particle cracking. Concurrently, 5‐SiTZ also participates in the Li⁺ solvation sheath (Figure 2), allowing more anions in the solvation shell. It promotes the formation of an inorganic‐rich SEI on the anode, which is further shielded from HF attack (Figures S29 and S30). In essence, 5‐SiTZ functions as a molecular regulator that breaks the vicious side reaction of LiPF₆ hydrolysis and HF‐driven degradation. Thus, this additive enhances battery performance by ultrafast and persistently removing HF and promoting the formation of high‐quality interfacial layers on both electrodes, resulting in high‐voltage stability and prolonged cycling life.

3. Conclusion

In summary, we presented a newly designed dual‐functional additive, 5‐SiTZ, which integrates cooperative siloxane and thiazolyl units to achieve ultrafast acid scavenging kinetics and exceptional durability. The synergy between these moieties facilitates a two‐stage mechanism. The siloxane group rapidly reacts with HF through fluorination, while the thiazolyl groups acts as persistent Lewis base that not only remove residual HF and suppress HF regeneration by capturing PF₅ continuously. This dual action enables ultrafast HF scavenging (< 1s) and long‐term electrolyte stability for over 200 days in open air. Furthermore, the additive promotes the formation of a robust, inorganic‐rich CEI enriched with N, S, and Si, providing exceptional stability under high‐voltage operation. The modified electrolyte successfully mitigates oxygen loss, suppresses transition metal dissolution, and prevents particle cracking at the cathode side. At the anode side, this additive also promotes the formation of a stable SEI film, inhibiting the growth of dendrites and ensuring the stability of the cycle. Consequently, the Li||NCM811 battery exhibited excellent capacity retention, maintaining 83.5% after 300 cycles at 4.6 V and 80% after 240 cycles even at an extremely high voltage of 4.8 V. In practical graphite||NCM811 pouch cells, 5‐SiTZ enables a remarkable 92.1% capacity retention after 700 cycles at 4.6 V. This work establishes a rational molecular design strategy for multifunctional additives that combine rapid, persistent acid scavenging with advanced interfacial engineering, offering a critical pathway toward stable, high‐energy lithium‐ion batteries.

Author Contributions

Jiachao Duan: conceptualization, methodology, investigation, validation, writing – review and editing, writing – original draft, formal analysis, data curation. Guohuang Kang: software, conceptualization, methodology, resources. Qi Liu: conceptualization, investigation, formal analysis. Yue Cao: formal analysis, investigation, conceptualization. Yuanyuan Zhang: formal analysis, investigation, conceptualization. Manxue Zhang: formal analysis, investigation. Feiyu Kang: project administration, supervision. Yidan Cao: conceptualization, methodology, funding acquisition, project administration, supervision, writing – review and editing.

Conflicts of Interest

The authors declare no conflicts of interest.

Funding

National Natural Science Foundation of China (22379084), Shenzhen Science and Technology Program (KJZD20240903101303005)

Supporting information

Supporting File: anie72774‐sup‐0001‐SuppMat.docx.

Supporting File: anie72774‐sup‐0002‐VideoS1.mp4.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.