Solvation Chemistry Reimagined: LiPF6‐Enabled Suppression of Gas Evolution for Ultra‐Stable 200 Ah Anode‐Free Lithium‐Metal Batteries

ABSTRACT

Anode‐free lithium‐metal batteries (AFBs) offer an attractive pathway to achieve cell‐level energy densities >500 Wh kg⁻¹ but suffer from rapid degradation driven by parasitic electrolyte decomposition, gas evolution, and unstable interphases. Here, we report a solvation‐structure engineering strategy using trace LiPF₆ additive in localized high‐concentration electrolytes (LHCEs) to regulate homogeneous Li deposition and stabilize electrode‐electrolyte interfacial chemistry. Molecular dynamics simulations and spectroscopic analyses reveal a synergistic PF₆ ⁻–FSI⁻ coordination that dramatically enriches aggregate (AGG) species in the Li⁺ solvation sheath, increasing AGG populations from 17% to 93% with only 1 wt.% LiPF₆. Owing to its persistent stability, this LiPF₆‐derived AGG‐dominated solvation suppresses ether‐solvent reduction and CH₄ generation, forming an inorganic‐rich solid–electrolyte interphase/cathode‐electrolyte interphase. AFBs with optimized electrolyte achieve substantially improved performance, including a significant reduction in high‐temperature gas evolution alongside increases in cycle life of 64% at 45°C and 28% at 25°C. When scaled to 240 Ah blade cells, this optimized electrolyte delivers stable cycling for nearly 100 cycles at 80% DOD and 45°C with negligible swelling and >1260 Wh L⁻¹ volumetric energy density. This study demonstrates a practical and scalable electrolyte design principle that overcomes the key barriers to commercial deployment of large‐format AFBs.

LiPF₆ enables persistent solvation‐structure regulation in LHCEs, suppressing gas evolution and stabilizing large‐format anode‐free lithium‐metal batteries with 1260 Wh L^{− 1} energy density.

1. Introduction

Achieving next‐generation lithium‐metal batteries (LMBs) with energy densities exceeding 500 Wh kg⁻¹ requires disruptive design strategies. As a compelling candidate for high‐energy‐density LMBs, the anode‐free configuration, which features a bare current collector with no excess lithium, provides exceptional gravimetric energy and simplified manufacturing compared with conventional battery systems [1, 2, 3]. However, practical adoption of anode‐free lithium‐metal batteries (AFBs) remains hindered by their intrinsically limited cycle life. The absence of a host anode amplifies the irreversible loss of active lithium (Li) during deposition/stripping on Cu current collectors and causes severe instability at the electrolyte‐electrode interfaces. Because charge transfer across electrolyte/electrode boundaries governs the kinetics and reversibility of electrochemical reactions, rational design of interfacial chemistry is indispensable [4]. In AFBs, interphase formation is particularly complex due to the hybrid mechanism combining the gradual solid–electrolyte interphase (SEI) formation of Li‐ion batteries (LIBs) and the spontaneous interphase evolution characteristic of LMBs [5]. This complexity poses unique challenges in controlling interfacial reactions and ensuring long‐term stability. Beyond dendritic growth and unstable SEI layers, gas generation has recently emerged as an equally critical and underexplored failure mode in anode‐free systems. While ether‐based electrolytes are favored for Li metal compatibility, they suffer severe decomposition, such as producing CH₄ at the anode and CO₂/CO at the cathode under elevated temperatures (>45°C) [6]. Unlike CO₂/CO, which can partially participate in SEI formation, CH₄ continuously accumulates without contributing to protective interphase chemistry [7, 8]. Persistent gas buildup accelerates interfacial degradation, elevates internal pressure, compromises cycling stability, and may trigger catastrophic safety hazards such as thermal runaway [9]. Suppressing parasitic gas evolution while stabilizing the interphase is therefore essential for the commercialization of AFBs.

Several liquid electrolyte engineering strategies have been explored, including: (1) increasing salt concentration to reinforce interphase stability, albeit at the expense of viscosity and wettability [10, 11, 12]; (2) constructing artificial SEI layers with limited durability and scalability [13]; (3) solvent fluorination in localized high‐concentration electrolytes (LHCEs) to enhance oxidative stability [14, 15, 16]; and (4) additive engineering to regulate interfacial reactions [8]. However, progressing beyond empirical optimization requires a mechanistic understanding of electrolyte solvation structures and their influence on interphase chemistry and gas evolution [8, 17]. According to the formation mechanism, it is generally accepted now that the solvation structure in liquid electrolyte plays a critical role in both ionic conductivity and anodic interfacial reactions [4]. Electrolyte solvation, dictated by cation‐anion‐solvent interactions, determines the distribution of solvent‐separated ion pairs (SSIPs), contact ion pairs (CIPs), and ion aggregate (AGG) species. These species regulate ionic conductivity, viscosity, reductive stability, and the SEI/cathode‐electrolyte interphase (CEI) composition [18]. In particular, AGG‐rich solvation promotes anion‐derived interphases such as LiF‐enriched SEI layers, which is key to mitigating parasitic reactions and stabilizing Li deposition [19, 20, 21]. Consequently, high‐concentration electrolytes (HCEs: >3.5 mol L⁻¹) and LHCEs, which inherently favor AGG formation, outperform conventional liquid electrolytes (e.g., Li salt concentration of 1 mol L⁻¹) in interfacial protection [22]. Yet, HCEs suffer from high cost, increased viscosity, and limited wettability. LHCEs alleviate these drawbacks by introducing chemically inert diluents while retaining HCE‐like coordination structures that minimize free‐solvent activity and suppress gas evolution. Despite this progress, achieving simultaneously high ionic conductivity, robust interphase stability, and AGG‐dominated solvation remains challenging [23]. Additive‐assisted solvation engineering thus provides a promising pathway. For instance, molecules capable of hydrogen‐bond regulation (e.g., triformylphloroglucinol) or anion modification (e.g., Br⁻, NO₃ ⁻) have been shown to strengthen interphases and reduce solvent degradation [24, 25, 26].

Motivated by these advances, we demonstrate a designated additive strategy for LHCEs that addresses the coupled challenges of unstable electrolyte/electrode interphases and CH₄ gas evolution in an anode‐free configuration. By systematically tuning lithium bis(fluorosulfonyl) imide (LiFSI) concentration and incorporating LiPF₆ as a solvation‐modulating additive, we enable AGG‐dominated coordination structures suitable for hundred‐ampere‐hour blade‐type NCM7/Cu AFBs (200 Ah @80%DOD). Remarkably, LHCEs with optimized LiPF₆ content achieve cycling stability comparable to LHCE with 2 m LiFSI (2m‐LHCE), while offering superior cost‐effectiveness. Molecular dynamics simulations and Raman spectroscopy reveal that PF₆ ⁻ participates synergistically (rather than competitively) with FSI⁻ in Li⁺ solvation, significantly increasing anion coordination numbers and boosting AGG populations from 17% to 95%. These AGG clusters effectively suppress solvent decomposition, promote FSI⁻‐derived electrolyte/electrode interphases, enable dense Li deposition, and critically reduce CH₄ generation during cycling [27, 28]. This low‐cost, solvation‐structure engineering strategy unlocks notable improvements in room‐temperature and high‐temperature cycling performance for industrial‐scale AFBs, offering a practical and scalable route toward safe, high‐energy anode‐free battery commercialization.

2. Results and Discussion

2.1. Influence of Li⁺ Solvation Structure

The reversibility of Li⁺ plating/stripping on copper current collectors is strongly governed by the structure and stability of Li⁺ solvation sheath in liquid electrolytes. To simultaneously achieve high energy density, long cycling life, and high safety in large‐format LMBs, we developed a targeted additive strategy for localized high‐concentration electrolytes (LHCEs). This design maximizes the benefits of group functionality while mitigating intrinsic trade‐offs. The synergistic interactions among LiFSI, LiPF₆ (additive), and solvent molecules enable low‐salt LHCEs to deliver performance comparable to high‐salt versions, while additionally suppressing gas evolution, facilitating uniform and dense Li deposition, and forming mechanically robust interphases (Scheme 1). Solvation structure is a key determinant of interphase chemistry in AFB [24]. Conventional electrolytes are dominated by solvent‐separated ion pairs (SSIPs). In this case, excessive free solvent molecules undergo parasitic decomposition, generating a thick yet unstable SEI and severe gas evolution, which ultimately compromises coulombic efficiency, cycling stability, and safety. In contrast, LHCEs favor CIPs and ion AGGs, which promote the formation of anion‐derived, LiF‐rich SEI layers with enhanced stability. Incorporating LiPF₆ additive into LiFSI‐based LHCEs further strengthens AGG formation [29, 30], reducing free solvent activity while simultaneously inhibiting gas evolution and enabling denser Li deposition.

SCHEME 1.

Schematic diagram of gas evolution, ionic solvation, and SEI formation behaviors in the base electrolyte with and without additives.

Suppressing gas evolution is vital for advancing practical AFBs. Ether solvents such as DME undergo reductive decomposition at the anode, generating CH₄, while producing CO₂/CO at the cathode [6]. Although CO₂/CO can participate in SEI formation, CH₄ remains chemically inert, accumulating at the anode interface and exacerbating internal pressure buildup. To investigate the origin of gas formation, we systematically studied LiFSI‐based LHCEs with LiFSI concentrations ranging from 0.8 to 2.2 m in DME/TTE (20:80 vol/vol) mixture, denoted as X m‐LHCE (where X represents the molarity of LiFSI). The 1 m‐LHCE served as a baseline for comparative analysis. Differential electrochemical mass spectrometry (DEMS) measurements reveal pronounced CH₄ generation during cycling at 45°C in cells with 1 m‐LHCE (Figure 1a and Figure S1). Correspondingly, the pouch‐type NCM7/Cu AFB using 1 m‐LHCE exhibits rapid gas accumulation and severe swelling, while increasing Li salt concentration (over 2 m) significantly enhances gas suppression capability (Figures S1 and S2). With the increasing salt concentration, the pouch‐type AFB displays markedly improved cycling life (e.g., 80% capacity retention after 85 cycles for 2 m‐LHCE vs. 58 cycles for 1 m‐LHCE) at elevated temperature (45°C), confirming that solvation engineering plays a decisive role in mitigating electrolyte decomposition (Figure 1b,c, and Figure S2). As the performance with even higher concentrations (2.2 m‐LHCE) was similar to that of the 2 m‐LHCE system, 2 m‐LHCE was selected for subsequent experimental studies to investigate the composition of the solvated structure.

FIGURE 1.

(a) The possible CH₄ evolution pathway for DME decomposition. (b) Cycling performance and (c) gas evolution at 45°C for electrolytes with various concentrations in NCM7/Cu AFBs. (d) Quantified results of the decomposition species’ relative ratios in SEI of the discharged Li anode for 1 m‐ and 2 m‐LHCE after the first and 15^th cycles. (e) TOF‐SIMS depth profiles of C₂H₃O‐ in the discharged Li anode for 1 m‐ and 2 m‐LHCE after the first and 15^th cycles. (f) 3D reconstructions via TOF–SIMS with a detection area. (g) Schematic illustration of SEI formation process derived from 2 m electrolyte.

To establish mechanistic links, we characterized the chemical composition of SEI in cells cycled with 1 m‐ and 2 m‐LHCE using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). In the baseline electrolyte (1 m‐LHCE), C _1s analysis shows substantial accumulation of Li₂CO₃ (Figure 1d), likely attributed to CO₂/CO formation from DME decomposition at the cathode, followed by crossover and reaction at the anode [6]. In stark contrast, the 2 m‐LHCE maintains stable and minimal Li₂CO₃ content throughout over 15 cycles, suggesting suppressed gas evolution and reduced parasitic solvent oxidation. TOF‐SIMS analysis further supports these trends: increasing C₂H₃O⁻ signal in the 1 m‐LHCE (Figure 1e,f) reflects ongoing DME decomposition, whereas 2 m‐LHCE exhibits negligible gas evolution, confirming improved solvent stability. Raman spectroscopy (Figure S3) identifies significantly enriched AGG species at higher LiFSI concentration in LHCE. Notably, a strong negative correlation emerges between AGG population and measured gas evolution (Figure 1g), establishing that AGG‐dominated solvation robustly suppresses side reactions. Collectively, these results demonstrate that tailoring the solvation environment to favor AGG structures effectively mitigates parasitic gas generation, stabilizes interphase chemistry, and improves battery cycling performance, laying a mechanistic foundation for scalable high‐performance AFBs.

2.2. Modulating the Solvation Structure With LiPF₆

To elucidate how solvation‐structure modifications suppress gas evolution and interfacial degradation, we performed molecular dynamics (MD) simulations and density functional theory (DFT) calculations. As shown in Figure 2a, SSIP structures exhibit the highest occupied molecular orbital (HOMO) energy level, indicating their vulnerability toward oxidative decomposition at the cathode interface. In contrast, the lowest unoccupied molecular orbital (LUMO) energy levels decrease sharply when transitioning from isolated FSI⁻ to CIP and AGG configurations, with no further reduction upon AGG growth. These results highlight that optimizing solvation structure (rather than solely relying on interphase chemistry) is the dominant factor in electrolyte stabilization.

FIGURE 2.

(a) Frontier orbital energies of selected AGG clusters. Specifically, AGG2 indicates an aggregate with two anions, AGG3 indicates an aggregate with three anions, and AGG4 indicates an aggregate with four anions. The (b) average AGG size distribution and (c) AGG charge distribution for the 1 m‐LHCE and 1 m‐LHCE with the same amount of LiFSI and LiPF₆ additives. (d) Raman spectra of 1 m‐LHCE and 1 m‐LHCEs with various LiPF₆ contents. (e) Proportions of different solvation structure models (SSIP, CIPs, and AGGs) as a function of LiPF₆ content from Raman spectra. (f) ⁷Li NMR spectra of the base electrolytes and electrolytes with 1 and 2 wt.% of LiPF₆ content.

Radial distribution function (RDF) analysis reveals a strong enhancement in FSI⁻ coordination around Li‐ions with increasing LiFSI concentration, accompanied by pronounced weakening of DME solvation (Figure S4a). A detailed quantitative assessment further confirms that concentrated LHCEs effectively promote AGG formation (Figure S3). However, this approach comes with significant drawbacks: increasing salt content elevates viscosity, which in turn reduces ionic conductivity, leading to pronounced rate performance degradation in 2 m‐LHCEs (Figures S5 and S6). Consequently, the most pronounced effect is observed in the rate capability. Thus, although higher LiFSI concentration maintains AGG‐rich environments, it compromises ion mobility and salt dissociation, which is a critical limitation for practical high‐power applications. Achieving both anion‐dominated solvation (i.e., AGG) and high ionic conductivity in liquid electrolytes requires a strategy that enhances AGG formation without increasing viscosity. Inspired by prior studies on solvation‐regulating additives [27, 28], we systematically screened a broad set of Li salts and solvents as electrolyte additives (Figures S4, S7 and S8). RDF analysis shows that most additives (e.g., LiDFOB, LiTFSI, LiBF₄, or FEC, etc) compete for Li⁺ coordination, reducing the population of both FSI⁻ and coordinated DME. Surprisingly, LiPF₆ uniquely strengthens FSI⁻ coordination while simultaneously suppressing DME binding, thereby synergistically increasing AGG density (Figure S4b,c and S7). No other additive exhibited such a distinct solvation effect, indicating that LiPF₆ restructures Li⁺ solvation sheaths. Electrochemical screening confirms LiPF₆ as the most effective additive, enabling 80% capacity retention after 82 cycles, superior to all other candidates tested (Figure S8). To isolate cation‐specific effects, we compared with sodium salts (Figure S4d). NaPF₆ displays only a marginal influence, emphasizing that the regulation arises from the Li⁺‐PF₆ ⁻ interaction, not simply PF₆ ⁻ presence (Figures S7 and S8). Remarkably, just 1 wt.% LiPF₆ additive achieved Li⁺ solvation characteristics comparable to those in 2 m‐LHCE (Figure S7) without a significant increase in viscosity (Figures S6 and S10), underscoring its unique efficacy in modulating the coordination environment.

AGG cluster distribution analysis (Figure 2b) further validates this effect for LiPF₆ additive. The addition of LiPF₆ to 1 m‐LHCE electively shows higher content of 5–10 anion‐based AGG compared to others. Meanwhile, 1 m‐LHCEs with additional 1 wt.% LiFSI are predominantly positively charged, confirming FSI⁻‐dominant coordination (Figure 2c). When LiPF₆ is introduced, slight negative charging emerges within SSIPs (on average) and CIPs, implying weaker PF₆ ⁻ binding and increased availability of PF₆ ⁻ as a spectator anion in AGG coordination [21]. This subtle asymmetry enhances the reducibility of AGG, promoting FSI⁻‐derived, LiF‐rich interphases that protect both Li deposition and solvent stability. The small‐angle X‐ray scattering (SAXS) analysis shows that the trace LiPF₆ additive alters the local solvation environment around the Li⁺ clusters, leading to a more pronounced signal from ion clusters of a specific size within the solvation sheath (Figure S9).

We assessed the impact of LiPF₆ concentration on the solvation behaviors of electrolytes using Raman spectroscopy. The Raman peaks of free and solvated DME are located at 830–850 and ∼870 cm⁻¹, respectively [31], while the vibrational peaks of FSI⁻ are ∼720 cm⁻¹ for SSIPs, ∼735 cm⁻¹ for CIPs, and ∼750 cm⁻¹ for AGGs [32]. Raman analysis of DME shows that the addition of LiPF₆ led to an intensity reduction and broadening of the ∼870 cm⁻¹ peak for solvated DME and a shift of the ∼830 cm⁻¹ peak for free DME (Figure 2d). The results indicate reduced DME participation in solvation and enhanced anion‐rich coordination, which is a critical step toward stabilizing high‐order AGGs. Meanwhile, the FSI⁻ vibrational region evolves from SSIP‐/CIP‐dominated profiles (∼720–735 cm⁻¹) toward AGG‐dominated spectra (∼750 cm⁻¹) with increasing LiPF₆ content (Figure 2e and Figure S11). Peak‐area analysis quantifies an increase in AGG fractions rising from 17% (1 m‐LHCE) to 93% (1 wt.% LiPF₆‐doped 1 m‐LHCE), and further to 95% (2 wt.% LiPF₆‐doped 1 m‐LHCE), respectively. Such near saturation at minimal additive loading underscores the exceptional efficacy of LiPF₆ in restructuring Li⁺ solvation chemistry. Although strictly speaking the SSIP population cannot be absolutely zero, its detectable abundance can be considered negligible given the simulation time scale and statistical error. Temperature‐dependent Raman spectroscopy analysis is also employed to evaluate the thermal stability of these electrolytes (Figure S12). The solvation structure of the LiPF₆‐modified electrolytes remains nearly unchanged across 25°C, 45°C, and 60°C, indicating its excellent thermal stability under demanding operating temperatures. The influence of LiPF₆ on Li⁺ solvation is further corroborated by ⁷Li NMR spectroscopy. As shown in Figure 2f, the addition of LiPF₆ induces a pronounced upfield shift in the ⁷Li NMR signal, indicative of strengthened anion coordination and increasing AGG/CIP populations in the solvation structure. The consistent trends across MD, Raman, XPS, and NMR analyses confirm that LiPF₆ fundamentally reconfigures Li⁺ solvation structure into a highly anion‐coordinated regime, while preserving electrolyte fluidity. As depicted in Figure S13, the pouch‐type NCM7/Cu AFBs employing 1 m‐LHCE doped with 1% or 2% LiPF₆ exhibit superior rate performance compared with both the 2 m‐LHCE and the baseline (1 m‐LHCE). This electrolyte formulation with 1 m LiFSI maintains the high interfacial stability of an AGG‐rich environment without sacrificing ionic mobility. Meanwhile, the LiPF₆‐derived AGG‐rich environment has improved high‐current tolerance, thereby unlocking enhanced rate performance alongside excellent cycle life.

2.3. Influence on SEI and CEI

To elucidate how AGG‐dominated solvation structures regulate interfacial chemistry, we examined cycled electrodes using depth‐profiling XPS. The SEI formed in 1 wt.% LiPF₆‐modified 1 m‐LHCE exhibits significantly reduced C–F signal intensity from TTE decomposition (CF₃ peak at 291.2 eV) (Figure 3a,b and Figure S14), confirming that AGG enrichment effectively suppresses diluent breakdown at the anode. Depth profiling further reveals that LiPF₆ additive significantly reduce carbon (C) and oxygen (O) in the anode SEI after sputtering, signifying suppressed decomposition of DME and TTE under AGG‐rich conditions (Figure 3e–h). By contrast, increased sulfur (S) and nitrogen (N) signals confirm that FSI⁻ becomes the primary precursor to SEI formation. Importantly, even after etching to a depth of 80 nm following formation, no characteristic signal of phosphorus (P) is detected, demonstrating that the main components of the solid electrolyte interphase (SEI) are derived from the decomposition of LiFSI and the solvent during initial cycling. Cryo‐TEM results corroborate these findings (Figure 3i,j). The LiPF₆‐derived AGG‐rich electrolytes yield a significant increase in Li₂S content, consistent with XPS and TOF‐SIMS characterization (Figures S15 and S16). The resulting SEI enriched in inorganic Li₂S/LiF species is mechanically resilient and ionically conductive. Meanwhile, the corresponding CEI displays reduced Li₂CO₃ and enhanced LiF and SO _x signals (Figure 3c,d and Figure S16). These trends indicate preferential FSI⁻‐derived CEI formation and mitigated solvent degradation at the cathode/electrolyte interface. To further investigate the evolution of electrolytes, we conducted ion chromatography (IC) analysis of the pristine and cycled electrolytes (Figure S17). It reveals LiPF₆ remaining largely unconsumed after the formation cycle, exhibiting a lower consumption rate than that of LiFSI. These results support a mechanism in which LiPF₆ functions as a stable solvation‐structure regulator, rather than a sacrificial additive, showing its potential in enabling long‐term interfacial stability.

FIGURE 3.

The high‐resolution XPS profiles of the initial SEI and CEI after formation. The initial SEI component from (a) 1 m‐LHCE and (b) 1 m‐LHCE with 1 wt.% LiPF₆, as well as the initial CEI from (c) 1 m‐LHCE and (d) 1 m‐LHCE with 1 wt.% LiPF₆. The XPS depth profiles of (e) SEI and (f) CEI from 1 m‐LHCE after formation. The XPS depth profiles of (g) SEI and (h) CEI from 1 wt.% LiPF₆‐doped 1 m‐LHCE after formation. Cryo‐TEM images of the Li‐metal anode after 1 mAh cm⁻² deposition followed by 0.5 mAh cm⁻² stripping in (i) the 1 m‐LHCE and (j) the 1 wt.% LiPF₆‐doped 1 m‐LHCE.

2.4. Battery Performance

The electrochemical performance of pouch‐type AFBs was systematically evaluated at both room temperature (25°C) and elevated temperature (45°C). Under an 80% depth‐of‐discharge (DOD) protocol at 25°C, the addition of 1 and 2 wt.% LiPF₆ in 1 m‐LHCE extends the cycle life by 28% and 40%, respectively, demonstrating significantly improved long‐term cycling stability (Figure 4a,b). The improvement becomes even more pronounced at 45°C, where both 1 wt.% LiPF₆‐doped and 2 wt.% LiPF₆‐doped 1 m‐LHCE achieve 64% and 85% longer cycle life compared to the baseline, respectively. These results highlight the superior thermal resilience imparted by AGG‐regulated solvation.

FIGURE 4.

The cycling performance of NCM7/Cu batteries at (a) 25°C and (b) 45°C. The (c) surface and (d) cross‐section of the Li deposition from 1 m‐LHCE. The (e) surface and (f) cross‐section of the Li deposition from 1 m‐LHCE with 1 wt.% LiPF₆. (g) Cycling performance of the hundred‐Ah‐level blade battery at 45°C with 80% DOD. (h) The gas evolution of the battery after the battery SOC dropped to 80% at 45°C. (i) The photos and ultrasonic characterization images of the blade battery before and after cycling. (j) Comparison of the volumetric energy density of various batteries with different anode thicknesses (details see Table S1).

The beneficial effects persist under 100% DOD conditions. The pouch‐type NCM7/Cu AFBs with baseline (1 m‐LHCE) retains 80% of its initial capacity for only 60 cycles, whereas cells with baseline containing 1 wt.% LiPF₆ and 2 wt.% LiPF₆ endure 82 and 85 cycles, respectively, before reaching the same capacity‐fade threshold (Figure S18). Such robust stability under high‐utilization conditions directly demonstrates the capability of AGG engineering to suppress active Li consumption and parasitic gas evolution. To correlate performance with interfacial behavior, Li deposition morphology after the initial charging process was examined (Figure 4c–f). The 1 m‐LHCE with 1 wt.% LiPF₆ yields denser and more cohesive mossy Li deposition compared to the baseline. As shown in Figure 4d,f, the cross‐sectional thickness measurements confirm a reduction in Li plating thickness, decreasing from an average of 28.1 to 23.9 µm. This indicates that the 1 wt.% LiPF₆‐doped 1 m‐LHCE enables more compact and efficient Li utilization during the cycling. Furthermore, porosity distribution analysis of the Li deposits (Figure S19) reveals that the modified electrolyte yields a denser structure with minimal voids of Li deposition. This densification helps to mitigate parasitic reactions and maintains intimate Li─Cu interfacial contact, whereas the baseline electrolyte exhibits significant interfacial delamination.

Post‐mortem analysis after 20 cycles further clarifies the morphological evolution at the anode and the electrolyte/electrode interphase composition. The baseline electrolyte develops highly fragmented, powdered Li with sparse active regions, indicating persistent pulverization and loss of active Li. In contrast, LiPF₆‐modified cells maintain >80% coverage of dense mossy Li deposits, even at 100% state‐of‐charge (SOC), confirming sustained structural integrity (Figure S20). The morphology of Li deposition after 20 cycles aligns with the corresponding SEI composition analyzed by XPS (Figure S21). Depth profiles of the deposition from the LiPF₆ modified 1 m‐LHCE show minimal Li composition change (Δ<0.5 at%) and persistently undetectable P content, demonstrating that LiPF₆ neither incorporates into nor destabilizes the anode SEI during extended cycling. In contrast, CEI evolution on the cathode surface exhibits systematic depletion of C, O, N, and S components along with increasing Li/F signals with sputtering depth, demonstrating a densified, FSI⁻‐derived CEI structure (Figure S22). Consistent with this, in situ gas monitoring reveals a monotonic decrease in CH₄ generation with increasing LiPF₆ concentration, approaching negligible gas evolution at 1 wt.% (Figure 4h). To validate scalability and practical relevance, the optimized electrolyte with 1 wt.% LiPF₆ was deployed in 240 Ah blade‐type NCM7/Cu AFBs. These large‐format cells retained 80% capacity for nearly 100 cycles at 80% DOD and 45°C, which is a performance level not previously demonstrated in anode‐free chemistries (Figure 4g). Post‐cycling ultrasonic imaging reveals no external swelling or internal gas‐bubble signatures, confirming outstanding structural and electrochemical stability (Figure 4i). Beyond cycling durability, the optimized electrolyte system enables the NCM7/Cu blade battery to maintain a discharge capacity of about 200 Ah (80% DOD) and achieve an exceptional volumetric energy density exceeding 1260 Wh L⁻¹, surpassing state‐of‐the‐art lithium battery systems (Figure 4j, Figure S23 and Table S1). This anode‐free blade battery used in this work (Figure S24) represents a new benchmark for practical high‐energy AFBs compatible with industrial‐scale pack integration.

3. Conclusions

In summary, this work reveals a unique and highly effective role of LiPF₆ as a solvation‐regulating additive in LHCEs. Through comprehensive investigation of salt chemistry, solvation behavior, and interfacial evolution, we demonstrate that both increased LiFSI concentration and trace LiPF₆ incorporation promote the formation of AGG‐dominated solvation structures in classical LHCEs (LiFSI in DME/TTE). Remarkably, only 1 wt.% LiPF₆ elevates AGG populations from 17% to 93% while significantly reducing SSIP, achieving the benefits of high‐salt formulations without viscosity penalties. When implemented in NCM7/Cu blade batteries, this solvation‐structure engineering strategy reduces the CH₄ evolution under high‐temperature (45°C) and extends the batteries’ cycle life by 64% at 45°C and 28% at room temperature. Molecular dynamics simulations and spectroscopic analyses confirm a synergistic PF₆ ⁻–FSI⁻ interaction within the Li⁺ solvation sheath, enhancing anion coordination without competitive interference. The resulting AGG‐rich environment suppresses solvent decomposition, a LiFSI‐derived LiF/Li₂S‐rich SEI and CEI, and enables denser and more uniform Li deposition on Cu. Overall, this study establishes a rational and scalable electrolyte design principle, which lies in the persistent solvation‐structure regulation via non‐consumptive additives. The approach delivers substantial improvements in large‐format blade‐type AFBs, offering a viable path toward safe, high‐energy‐density lithium‐metal battery commercialization.

4. Experimental Section/Methods

4.1. Electrolyte Preparation

Lithium bis(fluorosulfonyl) imide (LiFSI) (99.99%, Capchem Co., Ltd), 1,2‐dimethoxyethane (DME) (99.95%, J&K Co., Ltd), and 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether (TTE) (99.5%, Aladdin Co., Ltd) were used for the electrolyte solutions. Electrolytes with LiFSI concentrations ranging from 0.8 to 2.2 m (0.8, 1, 1.3, 1.8, 2, 2.2 m) were formulated in DME/TTE (20:80 vol%). Among them, the 1 m LiFSI in DME/TTE (20:80 vol%) electrolyte was denoted as the base electrolyte. The base electrolytes containing corresponding additives (LiPF₆) were prepared and used as the research subject of this manuscript. All preparations were conducted in an Ar‐filled glove box (H₂O < 0.1 ppm, O₂< 0.1 ppm). For cell assembly, the electrolytes were injected into dry cells in a dry room with a relative humidity of < 1%.

4.2. Battery Preparation and Test

All dry cells were manufactured on BYD's cell stacking production line, employing a double‐sided coated Ni‐rich LiNi_0.72Co_0.05Mn_0.23O₂ (NCM7) cathode (design capacity: 2.6 Ah), the copper foil anode (8 µm thickness), and a ceramic‐coated polyethylene (PE) separator (10 µm thickness). After electrolyte injection, cells were stored at room temperature for 12 h to ensure complete electrolyte wetting. All cells were set to 350 kPa initial pressure with a home‐made fixture to maintain stable electrode contact for proceeding cycling test. Following one formation cycle (0.05 C, 3.6–4.3 V), all cells were cycled at 0.2 C (charge)‐0.5 C (discharge) between 0% and 100% state‐of‐charge (SOC) (3.0–4.3 V) by using a Neware CT‐4008Tn‐5V6A‐S1 (Neware Technology Co., Ltd).

4.3. Characterizations

SEM images of Li anodes were acquired by a cold‐field emission scanning electron microscope (Hitachi NX5000). The porosity of Li anodes was analyzed using cryo‐focused ion beam‐scanning electron microscopy (Cryo‐FIB‐SEM, Helios 5 Hydra CX) through reconstructing the 3D structure by stacking sequential cross‐sectional images. Before the characterization test, these anodes extracted from cycled cells at corresponding stages were rinsed by soaking twice in DME (5 min each) and then thoroughly dried within the glove box. To preserve native Li morphology, Li electrodes were plunge‐frozen in liquid nitrogen slush (−210 C) and transferred to a Leica VCT500 cryo‐stage. Cross‐sections were milled using Ga⁺ ions (30 kV, 1 nA initial current, final polish at 100 pA). Samples were imaged at −170°C to prevent beam‐induced artifacts. Cryo‐TEM characterization is performed using a JEOL JEM‐ARM300F Grand ARM microscope equipped with a cold‐field emission gun (CFEG) and a Gatan K3‐IS direct electron detector. The solvation structures within various electrolytes were analyzed using a Renishaw inVia confocal microscope (759 nm laser, 0.5 mW power). The ¹H, ⁷Li, and ¹⁹F NMR spectra were obtained on the Bruker Avance III HD 600 MHz using samples dissolved in DMSO‐d₆. X‐ray photoelectron spectroscopy (XPS) analysis of the SEI composition was performed using a Thermo Scientific K‐Alpha+ spectrometer with Al Kα radiation (1486.6 eV). High‐resolution spectra of the C 1s, F 1s, Li 1s, O 1s, and P 2p regions were collected. Depth profiling was achieved through Ar⁺ sputtering (500 eV, 30 s intervals). Gas evolution during cycling was monitored using a Hiden HPR‐20 mass spectrometer coupled to a custom‐designed electrochemical cell. The system tracks masses 2 (H₂), 28 (CO), 44 (CO₂), and 15 (CH₄) with Faraday cup detection. Calibration curves were generated using certified gas standards (5–100 ppm). For investigating the surface/interface chemistry, time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) was conducted with PHI nanoTOF 3.

4.4. DFT Calculation

Molecular dynamics (MD) simulations were performed using OpenMM with the OPLS‐AA force field. Partial atomic charges for the solutes were derived from the RESP charge fitting scheme implemented in LigParGen. The simulations employed a Nose‐Hoover thermostat and Monte Carlo barostat with a coupling constant of 0.1 ps. Temperature and pressure were maintained at 298.15 K and 1 atm, respectively, unless otherwise specified. The system was first equilibrated in a stepwise manner: 0.5 ns of NVT equilibration, followed by 1.0 ns of NPT equilibration, a 1.6 ns annealing phase at 500 K, an additional 2.0 ns of NPT equilibration, and finally 1.0 ns of NVT equilibration. The production run was carried out for 5 ns under NVT conditions with a time step of 1 fs.

The simulation box had dimensions of 59 × 59 × 59 ų and contained 180 molecules of DME and 480 molecules of TTE as solvents, along with varying concentrations of Li salts and additives. Long‐range electrostatic interactions were treated using Particle Mesh Ewald (PME) with a cutoff distance of 1.0 nm. Bond constraints were applied to hydrogen‐containing bonds using the SHAKE algorithm. Further details on the force field parameterization and system setup were inferred from standard OpenMM protocols for nonbonded interactions and constraints.

Conflicts of Interest

The authors declare no conflicts of interest.

Supporting information

Supporting File: adma73946‐sup‐0001‐SuppMat.docx.

Data Availability Statement

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