Developing Quasi‐Solid‐State Ether‐Based Electrolytes with Trifluorotoluylation Ionic Liquids for High Voltage Lithium Metal Batteries

Abstract

The practical application of quasi‐solid‐state ether‐based electrolytes is hindered by lithium dendrite formation and poor oxidation stability, which reduce the cycle life and energy density of the battery. Here, taking advantage of the ionic liquids’ high ionic interactions and structural flexibility in forming an optimized electrode/electrolyte interface, a pyrrolidinium‐based ionic liquids with trifluorotoluylation cationic segment is designed and developed. The oxidation of anions in the electrolytes is induced to form a robust inorganic LiF‐rich interphase at the cathode, thereby effectively achieving high oxidation stability and suppressing the dissolution of transition metal ions. In addition, the LiF interphases derived from the trifluorotoluylation cations increase the modulus of the anode interface and suppress the growth of lithium dendrites. Therefore, the Li‐LiFePO₄, Li‐LiCoO₂, and Li‐LiNi_0.8Co_0.1Mn_0.1O₂ full cells with the optimized electrolytes demonstrate remarkable performance improvements at high current density (10 C), a wide voltage range of 4.5 V, a high mass loading of 11.1 mg cm⁻², and a wide temperature range of −20–80 °C. Furthermore, a 2.66 Ah‐level pouch cell with a high‐energy‐density of exceeding 356 Wh kg^‒1 and excellent cyclic stability demonstrates the potential of the strategy in providing a path for the practical application of quasi‐solid‐state ether‐based electrolytes in high‐energy‐density batteries.

This study proposes molecular design strategies to develop trifluorotoluylation ILs that enable quasi‐solid‐state ether‐based electrolytes for high‐voltage LMBs. The designed ILs greatly enhance the oxidative stability of the electrolyte and effectively suppress the dissolution of transition metal ions, facilitating the formation of a LiF‐rich interfacial layer on the lithium anode, promoting uniform distribution of Li⁺ and regular deposition of lithium.

1. Introduction

Solid‐state lithium metal batteries (LMBs) have garnered significant attention over recent years due to their high energy density and safety, and are regarded as the next‐generation rechargeable batteries.^{[ 1 ]} Solid‐state polymer electrolytes, especially ether‐based, have demonstrated superior practical industrialization potential compared to ceramic electrolytes, attributed to their high flexibility and processability.^{[ 2 ]} Further, there has been a close focus on integrating polymer electrolytes with high‐capacity and high‐potential‐difference electrodes, such as lithium metal anodes and high‐nickel layered oxide cathodes (LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) and LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622)), to attain higher energy densities.^{[ 3 ]} Although considerable progress has been made by designing quasi‐solid‐state ether‐based electrolytes to enhance the interface contact and the cycle life of the cell of LiFePO₄/Li, achieving high‐voltage tolerance and interface stability remains challenging.^{[ 4 ]} Specifically, the inevitable decomposition of the polymer electrolyte constitutes the primary factor contributing to battery failure.^{[ 5 ]} The generation of rich organic side products forms a rough cathode electrolyte interphase (CEI), which leads to the continuous consumption of the electrolyte and excessive dissolution of transition metal ions. These ions migrate and deposit on the surface of the lithium metal anode, augmenting the interface impedance.^{[ 6 ]} In response to the aforementioned issues, many scholars have conducted extensive research on the design of high‐voltage electrolytes, such as adding inorganic fillers,^{[ 7 ]} covalent organic framework,^{[ 8 ]} nitrile,^{[ 9 ]} ionic liquids^{[ 10 ]} (ILs, e.g., Py₁₃TFSI and EMIMTFSI) to extend the operating voltage window of solid‐state LMBs. Nevertheless, the application of quasi‐solid‐state ether‐based electrolytes in high‐voltage (e.g., 4.5 V) NCM811 cathode still faces significant limitations.

The lifetime of lithium metal batteries also hinges on the uniformity and stability of the solid electrolyte interphase (SEI).^{[ 11 ]} The uneven interface layer is caused by the poor mechanical strength and electrical insulation, which leads to repeated rupture and regeneration of the SEI. Consequently, this process accelerates the rapid depletion of active lithium and the electrolyte, resulting in low coulombic efficiency and shortened working life of the battery.^{[ 12 ]} Additionally, the compatibility of quasi‐solid‐state ether‐based electrolytes with lithium metal awaits improvement due to the unstable SEI and low shear modulus, allowing only for low current densities (such as 0.1 mA cm⁻²).^{[ 13 ]}

Typically, the ideal SEI/CEI should be lithiophobic and weakly bound to the electrode to mitigate the stress caused by electrode volume changes, and the CEI should also be stable under high voltage.^{[ 14 ]} Lithium fluoride (LiF), owing to its high lithiophobic and anode stability, can serve as the electrode interphase to achieve uniform lithium deposition and better cycling performance.^{[ 15 ]} Therefore, simultaneously constructing the CEI and SEI with rich‐LiF interphase is crucial for achieving the long‐term cycling of high‐voltage quasi‐solid‐state ether‐based LMBs. To achieve this herculean task, ILs with high ionic conductivity, wide electrochemical window, and good electrochemical stability are considered potential electrolyte additives.^{[ 16 ]} However, LMBs based on high voltage/energy density cathodes in electrolytes with ILs have only achieved Li plating/stripping at low current densities and low cathode mass loadings due to the high viscosity and poor electrode material compatibility.^{[ 17 ]} Importantly, ILs, with their inherent safety and flexibility in structural design, are expected to achieve an optimized SEI which can promote uniform lithium deposition, thus preventing the formation of dendrites and inactivated lithium, and establish a stable charge transfer interface on the cathode surface.^{[ 18 ]}

Here, we designed and synthesized a trifluorotoluyl‐functionalized pyrrolidine ILs, 1‐methyl‐1‐(4‐(trifluoromethyl)phenyl)pyrrolidin‐1‐ium bis(triffuoromethanesulfonyl)imide (Py₁₁₄TFSI), for Li/NCM811 high‐voltage quasi‐solid‐state ether‐based lithium metal batteries (Figure 1a). Py₁₁₄TFSI exhibits the following characteristics: i) The prepared quasi‐solid‐state electrolytes demonstrate improved Li salt dissociation. Specifically, Py₁₁₄TFSI weakens Li⁺‐O (polymer) interactions, which favors the free movement of Li⁺ ions and enhances the anion‐polymer interactions, leading to a high lithium‐ion transference number and ionic conductivity. ii) On the cathode side, Py₁₁₄TFSI greatly enhances the structural stability of the cathode material, which forms a robust cathode passivation layer rich in LiF through anion oxidation, achieving high oxidation stability. iii) When Py₁₁₄TFSI is adsorbed on the lithium anode, the C─F bonds in Py₁₁₄TFSI show a distinct dissociation tendency on the lithium surface, conducive to the formation of beneficial SEI components. Thus, a SEI with enhanced interfacial mechanical properties can be formed, significantly improving the anti‐lithium dendrite ability. These prominent advantages of Py₁₁₄TFSI facilitate the stable cycling of the lithium metal batteries with quasi‐solid‐state ether‐based electrolyte and high‐voltage cathodes (200 cycles at 4.5 V NCM811/Li; 350 cycles at 4.3 V NCM811/Li; 700 cycles at 4.3 V NCM622/Li), even in the presence of unavoidable polymer decomposition. Also, a remarkable reversible capacity of 172.5 mAh g⁻¹ after 300 cycles at 0.2 C with an excellent capacity retention of 94.6% can be achieved in the cell with NCM811 cathode. Additionally, the assembled 2.66 Ah quasi‐solid‐state NCM811/Li pouch battery achieves a high energy density of 356 Wh kg⁻¹. Furthermore, the assembled lithium symmetric battery maintains a high critical current density of up to 2.6 mA cm⁻² and provides a long operating time of over 1500 h at 0.5 mA cm⁻²/0.5 mAh cm⁻². Moreover, the assembled LFP/Li quasi‐solid‐state LMBs exhibit stable operation within the temperature range of −20 to 80 °C and can even reliably operate for over 1300 cycles at 2 C and 30 °C. The same structural modification method is also demonstrated in electrolytes with imidazole‐based ILs, showing both high ionic conductivity and high voltage stability.

Figure 1.

Design of quasi‐solid‐state electrolytes with trifluorotoluylation ILs and Li⁺ transfer mechanisms. a) Design of ILs structure and associated properties. b) Calculated HOMO and LUMO energy levels of PDOL(n = 3), FEC, DEC, Py₁₃TFSI and Py₁₁₄TFSI. c) The immobilization mechanism of anion with Py₁₁₄TFSI. d) Illustration of the interaction between Py₁₁₄TFSI and LiTFSI, LiDFOB in the as‐prepared QSSE@Py₁₁₄TFSI. e) Binding energy values. f,g) The radial distribution functions and coordination numbers in QSSE@Py₁₃TFSI and QSSE@Py₁₁₄TFSI. h,i) Percentages of four types of TFSI⁻ and DFOB⁻ coordination environments. j) Mean‐square displacement for lithium atoms. k) Arrhenius plot. l) ⁷Li solid‐state NMR spectra. m) Comparisons of ${\sigma }_{L{i}^{+}}$ and $t_{L{i}^{+}}$ between QSSE, QSSE@Py₁₃TFSI and QSSE@Py₁₁₄TFSI.

2. Results and Discussion

2.1. Design of Quasi‐Solid‐State Electrolytes with Trifluorotoluylation ILs and Li⁺ Transfer Mechanisms

Trifluorotoluylation pyrrolidine ILs (Py₁₁₄TFSI) were successfully synthesized and their molecular structure was confirmed by NMR spectroscopy (Figure S1, Supporting Information). To delineate the effect of Py₁₁₄TFSI on the electrode compatibility and battery life of quasi‐solid‐state electrolytes, reference electrolytes (QSSE, 1 m LiTFSI (Lithium bis(triffuoromethanesulfonyl)imide) and LiDFOB (Lithium difluoro(oxalato)borate) in DOL (1,3‐Dioxolane)/FEC (Fluoroethylene carbonate)/DEC (Diethyl carbonate)) were prepared by in situ ring‐opening polymerization method. LiDFOB was used as an initiator, and FEC was added to the solvent to induce the formation of a fluorine‐rich interfacial to improve the interfacial stability. The QSSE@Py₁₃TFSI electrolyte (Py₁₃TFSI (N‐Propyl‐N‐methylpyrrolidinium bis(trifluoromethanesulfonyl)imide) ILs in QSSE) and the QSSE@Py₁₁₄TFSI electrolyte (Py₁₁₄TFSI ILs in QSSE) were compared and investigated (see Supporting Information for details). The in situ polymerization of DOL was studied by Fourier transform infrared (FTIR) spectroscopy (Figure S2, Supporting Information) and visual observation (Figure S3a,b, Supporting Information), which showed a significant reduction in the intensity of the C─H out‐of‐plane bending vibration of DOL (913 cm⁻¹) and the vibration of the long‐chain species (862 cm⁻¹)after in situ polymerization.^{[ 19 ]} Figure S4a,b (Supporting Information) showed the surface and cross‐sectional morphology of the QSSE@Py₁₁₄TFSI films in the disassembled cells, and the results indicated that the voids in the glass fibers were filled by the polymer electrolyte after in situ polymerization of the precursors.

As shown in Figure 1b, the HOMO value of Py₁₁₄TFSI (−9.28 eV) was lower than that of PDOL (−9.00 eV) and Py₁₃TFSI (−8.94 eV), indicating that Py₁₁₄TFSI showed a better antioxidant capability. Also, the LUMO value of Py₁₁₄TFSI (−1.68 eV) was lower than that of PDOL (0.70 eV) and Py₁₃TFSI (−0.58 eV), suggesting that Py₁₁₄TFSI could preferentially lead to a reduction reaction at the anode side and generate an interfacial layer rich in inorganic components. This calculation provided a theoretical basis for the Py₁₁₄TFSI to induce stable interfaces with NCM811 cathode and lithium anode. The linear sweep voltammetry (LSV) curves (Figure S5, Supporting Information) showed that the electrochemical stability window of QSSE@Py₁₁₄TFSI was as high as 4.8 V at room temperature (RT), which was consistent with the results of theoretical calculations (frontline orbital theory). Notably, the Li⁺ transference number ($t_{L{i}^{+}}$, 0.72) of QSSE@Py₁₁₄TFSI was significantly higher than that of QSSE@Py₁₃TFSI (0.45) and QSSE (0.36). This might be attributed to the anion anchoring effect of Py₁₁₄ ⁺ on TFSI⁻/DFOB⁻, which restricted the movement of anions in the electrolyte (Figure S6, Supporting Information). The DFT calculations revealed that the Gibbs free energy of anion substitution was 0.1 eV (Figure 1c; Table S1, Supporting Information), while the Gibbs free energy of simultaneous capture of TFSI⁻ and DFOB⁻ was −1.01 eV. The results indicate that the pathway of capturing DFOB⁻ with Py₁₁₄TFSI was energetically favorable. To gain a deeper insight into the effect of Py₁₁₄TFSI on the dissociation of lithium salts, as shown in Figure 1d and Table S2 (Supporting Information), the energies required for the dissociation of LiTFSI and LiDFOB into free anions and cations were 5.42 and 5.01 eV, respectively. In contrast, the dissociation energies of LiTFSI (3.72 eV) and LiDFOB (2.85 eV) were reduced when Py₁₁₄TFSI is added, meaning that lithium salts in the QSSE@Py₁₁₄TFSI system were more easily dissociated. Particularly, Py₁₁₄TFSI facilitated the release of more free lithium ions and improved ion transport kinetics, which was consistent with the measured Li⁺ conductivity results. The binding energy of Li⁺‐Py₁₁₄TFSI (−2.40 eV) was much higher than those of Li⁺‐PDOL (−2.17 eV), Li⁺‐FEC (−1.62 eV) and Li⁺‐DMC (−1.42 eV) (Figure 1e), indicating that Py₁₁₄TFSI tended to bind to lithium ions and preferentially participate in the interfacial reaction, achieving a robust interface passivation layer.

The radial distribution function (g(r), solid line) and coordination number (CN, dashed line) of Li⁺‐O (PDOL) and Li⁺‐O (TFSI⁻/DFOB⁻) were calculated using molecular dynamics (MD) to explore the coordination of Li⁺ in different electrolytes (Figure 1f,g; Figure S7 and Table S3, Supporting Information). The CN of Li⁺‐O (PDOL) in QSSE@Py₁₁₄TFSI electrolyte was smaller than that of QSSE@Py₁₃TFSI electrolyte, which suggested that the structure of Py₁₁₄TFSI weakens Li⁺‐O (polymer) interactions. This weakening of interactions was beneficial because it allowed the lithium ions to move more freely. Additionally, it enhanced the interactions between anions and the polymer. Consequently, more anions could be involved in the solvation structure, which contributed to the formation of an interfacial layer that was rich in inorganic components. Figure 1h,i and Figure S8 (Supporting Information) showed the percentage of TFSI⁻ and DFOB⁻ coordination environments in the two electrolyte systems. 55% of TFSI⁻ had a common coordination environment with Li and other components, which was much higher than 46.7% in QSSE@Py₁₃TFSI system. Similarly, the coordination ratio of DFOB‐ anions with lithium and other components was 74%, which was also higher than 53.1% in QSSE@Py₁₃TFSI system. This solvation structure dominated by cation‐X‐anion aggregates (X = PDOL/PDOL‐Py₁₁₄ ⁺/PDOL‐TFSI⁻) was conducive to the formation of LiF‐rich electrode interface layers. Meanwhile, as shown in Figure 1j, the self‐diffusion coefficient and mean‐square displacement (MSD) of lithium ions in the QSSE@Py₁₁₄TFSI system was 6 × 10⁻⁹ cm² s⁻¹, which was higher than that in the QSSE@Py₁₃TFSI system (5 × 10⁻⁹ cm² s⁻¹), indicating that the addition of Py₁₁₄TFSI was more favorable to enhance the dissociation of lithium ions and the ionic conductivity of the quasi‐solid‐state electrolyte. The temperature‐dependent ionic conductivities of the different electrolytes were compared in Figure 1k. The ionic conductivity (${\sigma }_{L{i}^{+}}$) of the QSSE@Py₁₁₄TFSI was 0.84 mS cm⁻¹ at 25 °C, which was higher than that of the QSSE@Py₁₃TFSI (0.60 mS cm⁻¹) and QSSE (0.28 mS cm⁻¹). Also, the activation energy E_a of the QSSE@Py₁₁₄TFSI was calculated to be 0.16 eV, which was much lower than the QSSE@Py₁₃TFSI (0.22 eV) and QSSE (0.26 eV), suggesting a much better temperature adaptability of the Li⁺ transport. The charge atmosphere of lithium ions in quasi‐solid‐state electrolytes was investigated using ⁷Li solid‐state NMR.^{[ 20 ]} As shown in Figure 1l, the ⁷Li chemical shift of QSSE@Py₁₁₄TFSI was significantly downfield shifted compared to QSSE and QSSE@Py₁₃TFSI, indicating a lower density of the electron cloud around the Li ions and looser coordination with the lithium‐salt anions, which further confirmed that Py₁₁₄TFSI played an important role in dissociating the lithium salts and contributing to fast Li⁺ kinetics. Overall, as depicted in Figure 1m, the aforementioned analyses indicated that, compared with QSSE@Py₁₃TFSI and QSSE in quasi‐solid‐state LMBs, the designed QSSE@Py₁₁₄TFSI exhibited higher values of ${\sigma }_{L{i}^{+}}$ and $t_{L{i}^{+}}$.

2.2. The Li Plating/Stripping Behaviors and Characterizations of Anode Interface

In order to assess the stability of the lithium metal anode, lithium symmetric cells with different electrolytes were constructed and a series of tests aimed at investigating the lithium stripping/plating behavior were performed. The critical current density (CCD) test was carried out in the symmetrical cell with each cycle lasting for 2 h. The results indicated that the battery employing QSSE@Py₁₁₄TFSI achieved a remarkable CCD of up to 2.6 mA cm⁻² (Figure 2a). The Tafel curve results showed that the exchange current density (ECD) of the lithium symmetric battery with QSSE@Py₁₁₄TFSI (0.116 mA cm⁻²) was much higher than those with other electrolytes, presenting the effectively enhanced the ion transfer kinetics between the electrolyte and lithium anode (Figure S9, Supporting Information). We further performed EIS tests on lithium symmetric batteries with different electrolytes (Figure 2b), and the results showed that the impedance of Li|QSSE@Py₁₁₄TFSI|Li cells was significantly lower than that of Li|QSSE|Li and Li|QSSE@Py₁₃TFSI|Li cells, indicating a fast Li⁺ transport and excellent interface compatibility of QSSE@Py₁₁₄TFSI. As depicted in Figure 2c, the adsorption energy (−4.34 eV) presented by Py₁₁₄ ⁺ was higher than that of Py₁₃ ⁺ (−1.59 eV). Interestingly, when Py₁₁₄ ⁺ was adsorbed parallelly on the Li (100) metal surface, it presented a state of dissociative adsorption and the C‐F bond in Py₁₁₄ ⁺ displayed a significant dissociation tendency on the lithium atom. In other words, the QSSE containing Py₁₁₄TFSI suppressed the side reactions with lithium anode and enhanced the stability of the Li/electrolyte interface.

Figure 2.

The Li plating/stripping behaviors and characterizations of anode interface. a) Rate performance test of the Li|QSSE@Py₁₁₄TFSI|Li batteries to determine their critical current density with a stripping/plating period of 2 h. b) EIS of symmetrical lithium metal batteries with QSSE, QSSE@ Py₁₃TFSI and QSSE@ Py₁₁₄TFSI. c) DFT calculations of the adsorption energies of the Li/Py₁₃ ⁺ and Li/Py₁₁₄ ⁺ interfaces. Color code: Li (green), C (brown), N (deep silver), H (light pink), F (light silver). d) Galvanostatic cycling curves of different electrolytes symmetric cells at 0.5 mA cm⁻², 0.5 mAh cm⁻², and 30 °C. inset: enlarged profiles of various electrolytes. e) Operando OM observation of Li plating behavior on stainless steel electrode with QSSE, QSSE@ Py₁₃TFSI and QSSE@ Py₁₁₄TFSI. f) SEM images of lithium metal surface with SSEs after cycling. g) AFM images of Li metal anodes in QSSE, QSSE@Py₁₃TFSI and QSSE@Py₁₁₄TFSI symmetric cells after cycling.

As shown in Figure 2d, the Li|QSSE@Py₁₁₄TFSI|Li cells could stably cycle for more than 1500 h at 0.5 mA cm⁻²/0.5 mAh cm⁻² with a small polarization voltage (≈0.1 V). In particular, the voltage curves throughout the process were smooth and symmetrical, indicating that QSSE@Py₁₁₄TFSI batteries exhibited stable lithium deposition/stripping behavior and lower electrochemical polarization (see the inset in Figure 2d). In contrast, the QSSE and QSSE@Py₁₃TFSI batteries exhibited relatively large polarization voltages and drastic fluctuations, with obvious polarization increases at the initial moment and after 300 h, respectively. More impressively, the Li|QSSE@Py₁₁₄TFSI|Li could maintain a low polarization voltage of ≈0.19 V even at higher current density and areal capacity (1.0 mA cm ⁻² and 1.0 mAh cm ⁻²) (Figure S10, Supporting Information). In order to further reveal the interfacial stability with QSSE, QSSE@ Py₁₃TFSI and QSSE@Py₁₁₄TFSI, we performed in situ optical microscopy (OM) observations to directly visualize the lithium deposition behavior in Li|SSEs|SS (stainless steel) transparent cells (Figure 2e). After 0.5 h of operation at the current density of 3 mA cm ⁻² and RT, significantly uneven lithium deposition and dendrite growth were observed at the QSSE/SS and QSSE@Py₁₃TFSI/SS interfaces during plating. On the contrary, the lithium deposition at the QSSE@Py₁₁₄TFSI/SS interface was very uniform and eventually formed a uniform and dense lithium layer with less dendrite lithium. This dynamic deposition behavior provided strong evidence that QSSE@Py₁₁₄TFSI could effectively regulate lithium deposition, thereby inhibiting the formation of lithium dendrites.^{[ 21 ]} The excellent ability of QSSE@Py₁₁₄TFSI to regulate lithium deposition can be explained by its close interfacial contact and the formation of a SEI layer with good modulus (described below).

In addition, the surface morphology of lithium anode after 50 cycles was examined by SEM (Figure 2f). The lithium anode in the Li|QSSE@Py₁₁₄TFSI|Li battery exhibited a relatively flat surface and no dendritic protrusions, indicating consistent and dense lithium deposition. In contrast, the lithium anode surface in QSSE and QSSE@Py₁₃TFSI batteries showed many irregular bumps and rough lithium dendrite growth. The denser morphology limited parasitic side reactions between the electrolyte and the lithium metal, further reducing the consumption of active lithium. Notably, Atomic Force Microscope (AFM) results showed that cycled lithium anode in Li|QSSE@Py₁₁₄TFSI|Li cells presented a more uniform and smooth morphology (Figure 2g; Figure S11, Supporting Information). At the same time, the Young's modulus of SEI was also as high as 8.82 GPa with QSSE@Py₁₁₄TFSI, which was 3.8 times of the value of QSSE (2.28 GPa) and 2.1 times of the value of QSSE@Py₁₃TFSI (4.11 GPa). The difference is attributed to the fact that QSSE@Py₁₁₄TFSI electrolyte forms a dense SEI layer rich in inorganic substances through the contribution of Py₁₁₄ ⁺, thereby achieving uniform lithium deposition behavior.

2.3. The Performance of Quasi‐Solid‐State Lithium Metal Full Cells

To demonstrate the enhanced long‐term cycling performance of cells using trifluorotoluylation ILs, LMBs with NCM811/Li cells were fabricated with QSSE, QSSE@Py₁₃TFSI and QSSE@Py₁₁₄TFSI and cycled at 30 °C. The EIS of the full cell was conducted to characterize the Li⁺ and electron transfer resistance (Figure S12, Supporting Information). In comparison with QSSE and QSSE@Py₁₃TFSI, the battery employing QSSE@Py₁₁₄TFSI demonstrated smaller charge transfer resistance, which was mainly attributed to the enhanced conductivity of the electrolyte and the superior electrode interface. To further investigate ion transport in the batteries, the Li⁺ diffusion coefficient (Figure 3a) of QSSE@Py₁₁₄TFSI was calculated to be 1.11 × 10⁻¹³ cm² s⁻¹, which was higher that of QSSE@Py₁₃TFSI (5.81 × 10⁻¹⁴ cm² s⁻¹) and QSSE (2.68 × 10⁻¹⁴ cm² s⁻¹). The higher Li⁺ diffusion coefficient of QSSE@Py₁₁₄TFSI promoted the transportation of lithium ions within the batteries, thereby improving the discharge capacity and rate performance of quasi‐solid‐state LMBs. Figure S13 (Supporting Information) illustrated a comparison of the rate capabilities among the three cells across a current density range of 0.1 C from 2.0 C. The cell utilizing QSSE@Py₁₁₄TFSI electrolyte demonstrated consistently higher specific capacity than that with QSSE@Py₁₃TFSI and QSSE at all current densities. Moreover, it maintained excellent specific capacity even after reverting the current density back to 0.2 C, showcasing exceptional reversible capacity recovery ability.

Figure 3.

The performance of quasi‐solid‐state lithium metal full cells. a)The Li⁺ diffusion coefficient with different electrolytes. b) Cycling performance at 0.2 C. c) The corresponding charge and discharge voltage profiles of cells with different SSEs at a cutoff voltage of 4.3 V during the first cycle. d) Charge–discharge curves of the first five cycles for NCM811|QSSE@Py₁₁₄TFSI|Li batteries at a cutoff voltage of 4.5 V. e)Long‐term cycling performances with different electrolytes in NCM811/Li cells at 1 C. f) Cycling performance of NCM811/NCM622/LCO batteries with QSSE@Py₁₁₄TFSI under different cut‐off voltage. g,h) Long cycling performances of LFP batteries with QSSE@Py₁₁₄TFSI under different current rates at 30 °C. i,j) Cycling performance and charge–discharge curves of the NCM811/Li pouch cell. k) The performance comparison between this work and reported PDOL‐based electrolytes in terms of cut‐off voltage and cycle number.

As illustrated in Figure 3b, the NCM811|QSSE@Py₁₁₄TFSI|Li cell obtained a reversible capacity of 172.5 mAh g⁻¹ after 300 cycles at 0.2 C with an excellent capacity retention of 94.6%, indicating excellent long‐term cycling stability and could be successfully applied in quasi‐solid‐state LMBs. Furthermore, the NCM811|QSSE@Py₁₁₄TFSI|Li battery delivered a high discharge capacity of 115.6 mAh g⁻¹ after 350 cycles at 1 C and a cutoff voltage of 4.3 V. In contrast, the cells with QSSE@Py₁₃TFSI and QSSE suffered rapid capacity decay after 100 cycles (Figure 3e). The first cycle coulomb efficiency of the battery with QSSE@Py₁₁₄TFSI was ≈86%, which was an improvement compared to the cells with other electrolytes. This may be due to the decomposition of QSSE@Py₁₁₄TFSI on the anode surface to form SEI and the consumption of lithium ions, and the irreversible phase transition of the cathode material, which lead to the loss of capacity and the decrease of coulomb efficiency (Figure 3c). Even at a cutoff voltage of 4.5 V, the NCM811/Li battery still exhibited outstanding cycling stability after 200 cycles at 1.0 C with a capacity retention of 81.3% (from 157.7 to 128.2 mAh g⁻¹). Besides, the NCM622/Li (cutoff voltage of 4.3 V, 700 cycles) and LCO/Li batteries (cutoff voltage of 4.2 V, 400 cycles), also showed excellent cycling stability (Figure 3f), confirming the adaptability of the QSSE@Py₁₁₄TFSI electrolyte to various cathode materials. In addition, Figure 3d showed that the cell with QSSE@Py₁₁₄TFSI (NCM811|QSSE@Py₁₁₄TFSI|Li) exhibited a stable charge–discharge profile and lower polarization during battery operation at a cutoff voltage of 4.5 V. The electrolyte was also tested under various conditions in the LPF cell. The LFP|QSSE@Py₁₁₄TFSI|Li battery delivered an initial discharge capacity of 140.8 mAh g⁻¹ with a capacity decay of 0.023% per cycle after 1300 cycles at 2 C and 30 °C (Figure 3g). Even at the relatively high charge–discharge rates of 5 C and 10 C, the battery still demonstrated an excellent initial capacity and a stable reversible capacity, with 120.2 mAh g⁻¹ at 5 C and 106.9 mAh g⁻¹ at 10 C, as depicted in Figure S14 (Supporting Information). Notably, QSSE@Py₁₁₄TFSI cells with high LFP loading (11.1 mg cm⁻²) also exhibited a high‐capacity retention of 81.8% (from 155.7 to 127.4 mAh g⁻¹) after 120 cycles with 0.5 C (Figure 3h). When the NCM622 mass loading was increased to 10 mg cm⁻², the NCM622|QSSE@Py₁₁₄TFSI|Li battery still provided an average CE of ≈99.5% with a discharge capacity of 152.2 mAh g⁻¹ at 0.5 C after 60 cycles (Figure S15, Supporting Information). Moreover, the outstanding working temperature stability of QSSE@Py₁₁₄TFSI enabled the battery to function within a broad temperature range from −20 to 80 °C. As depicted in Figure S16 (Supporting Information), the stable discharge capacity was 108.9 mAh g⁻¹after more than 100 cycles at 0.1 C, suggesting that the battery could operate properly in an environment as low as −20 °C. The LFP/Li full cells with QSSE@Py₁₁₄TFSI obtained a high initial capacity of 151.1 mAh g⁻¹ at 1 C and 80 °C (Figure S17, Supporting Information), as well as the batteries at 50 °C (at 1 C for 550 cycles) and 60 °C (at 1 C for 450 cycles) also exhibited excellent cycle performance (Figure S18, Supporting Information). These excellent properties may be due to the excellent interfacial stability and good ionic conductivity of QSSE@Py₁₁₄TFSI.

Impressively, the 5.0 mAh cm⁻² NCM811/Li pouch cell with QSSE@Py₁₁₄TFSI (N/P≈2.8) exhibited a discharge capacity of 2.66 Ah at a current of 300 mA, and the energy density reached 356 Wh kg⁻¹ in the initial cycle (Figure 3i,j; Table S4, Supporting Information). Collectively, QSSE@Py₁₁₄TFSI simultaneously achieved the construction of stable SEI/CEI interfaces by the structural design of trifluorotoluylation ILs and further exerted excellent electrochemical performance in PDOL‐based LMBs. For this reason, we made a comparison of the performance of reported PDOL‐based electrolytes in terms of cut‐off voltage and cycle number (Figure 3k; Table S5, Supporting Information).^{[ 4} , ¹⁹ , ^{22 ]} Our work enables the QSSE@Py₁₁₄TFSI to achieve 200 cycles at a high voltage of 4.5 V and 700 cycles at 4.3 V, which shows a significant improvement over previous work and provides a new and more effective research idea for the high energy density research of quasi‐solid‐state electrolytes.

2.4. Cathode Cycling Stability and Lithiation Dynamics of NCM811 Particles

As depicted in Figure 4a, the TEM image indicated that the CEI film of QSSE@Py₁₁₄TFSI was uniform and thin (≈4 nm), while the CEI films of QSSE and QSSE@Py₁₃TFSI were inhomogeneous and ≈32 and 13 nm thick respectively, implying that an optimized ionic liquid system could efficiently alleviate electrolyte degradation and enhance the structural stability of NCM811 cathode. To fully understand the evolution of the chemical environment of CEI, X‐ray photoelectron spectroscopy (XPS) analysis was performed on electrodes subjected to cycling of QSSE, QSSE@Py₁₃TFSI and QSSE@Py₁₁₄TFSI electrolytes. The C─C, C─O─C, CO₃2⁻, and C─F signals could be clearly observed in C ls spectra, which corresponded to the decomposed products of the electrolytes (Figure 4b). In the O1s spectra (Figure 4c), the NCM811 cathode cycled in QSSE@ electrolyte exhibited weaker C─O (535.8 eV) and C─O (533.2 eV) signal and stronger B─O (534.1 eV) signal compared to QSSE and QSSE@Py₁₃TFSI, indicating Py₁₁₄TFSI efficiently inhibited the decomposition of the SSEs and facilitated the dissociation of the LiDFOB salt. Moreover, the metal‐O peak (M─O) at 530.6 eV could be regarded as the evidence of the dissolution of transition metal ions.^{[ 23 ]} A significantly weaker M─O peak appeared in NCM811 cathode cycled in QSSE@Py₁₁₄ electrolyte compared with QSSE and QSSE@Py₁₃TFSI electrolyte. The results indicate that the CEI derived from Py₁₁₄TFSI can effectively isolate the cathode and electrolyte, reducing the corrosion of the electrolyte on the cathode and the dissolution of the Ni element. According to the Ni 2p XPS spectra in Figure 4d and the corresponding statistical results in Figure 4f, the Ni²⁺ proportions of NCM811 after cycling with QSSE, QSSE@Py₁₃TFSI, and QSSE@Py₁₁₄TFSI were 20.6%, 18.1%, and 15.36%, respectively. The results meant that the formation of NiO rock salt phase in QSSE@Py₁₁₄TFSI electrolyte was inhibited, thereby improving the capacity and prolonging the cycling performance of NCM cathode. A peak of LiF phase could be detected in F ls spectra (Figure 4e), which was attributed to the decomposition of anions of ILs and lithium salt. The existence of LiF in CEI could improve fast Li‐ions transportation between the electrolyte and cathode. The effect of Py₁₁₄TFSI on the stability of the cathode crystal structure was analyzed using X‐ray diffraction (XRD). The cation ordering degree is usually expressed by the intensity ratio R of the diffraction peak (003)/(104).^{[ 24 ]} As shown in Figure 4g, the cathode cycled with QSSE@Py₁₁₄TFSI showed a significantly higher R value (1.26) after 20 cycles compared to other SSEs, indicating that the cation ordering of the NCM811 cathode was significantly enhanced and the CEI could effectively inhibit the dissolution of transition metal ions. Therefore, the introduction of trifluorotoluylation ILs can obtain a robust CEI film, thereby inhibiting the irreversible oxidative decomposition of quasi‐solid‐state ether‐based electrolytes and further improving its high‐voltage resistance and the operation life of NCM811/Li full battery.

Figure 4.

Cathode cycling stability and lithiation dynamics of NCM811 particles. a) TEM images of cycled NCM811 cathode with QSSE, QSSE@ Py₁₃TFSI and QSSE@ Py₁₁₄TFSI. (b) b–e) The C 1s, O 1s, Ni 2p and F 1s XPS of cycled NCM811 cathode with different SSEs. f) The quantified atomic ratios of M‐O, Ni²⁺, and LiF in O 1s, Ni 2p and F 1s spectra from cathode. g) XRD patterns of pristine and cycled NCM811 cathodes. h) Finite element analysis simulating the lithiation behavior of different electrolytes in the NCM811 cathode at the current density of 1 C. i) Evolution of Li⁺ concentration in the QSSE, QSSE@ Py₁₃TFSI and QSSE@ Py₁₁₄TFSI.

Reasonable electrolyte structure design that enables NCM electrodes with fast Li⁺ and electron transfer kinetics is a key strategy to improve the performance of quasi‐solid‐state LMBs. Numerical simulation was used to perform electrochemical simulations of Li⁺ insertion into NCM811 particles in different electrolytes at the same current density (Figure 4h).^{[ 25 ]} As the depth of lithiation increased, lithium ions diffused from the surface to the inside, and the Li⁺ concentration in the NCM811 particles gradually increased from the outside to the inside. It showed that the solid sphere particles with QSSE and QSSE@Py₁₃TFSI exhibited an uneven Li⁺ concentration distribution at the end of discharging. This was due to the poor interface contact between the electrolytes and NCM811 cathode, and the limited Li⁺ migration channel leaded to slow Li⁺ diffusion kinetics. However, the NCM811 particles with QSSE@Py₁₁₄TFSI showed a more uniform Li⁺ concentration distribution throughout the discharge process, effectively shortening the diffusion distance of lithium ions and accelerating Li⁺ transmission. Meanwhile, with the extension of discharge time, the inhomogeneity of the NCM811 particles caused by different electrolytes was more obvious. The evolution of the Li⁺ concentration distribution achieved along the radial direction further verified these results (Figure 4i). These simulation results highlight that QSSE@Py₁₁₄TFSI electrolytes show better ion diffusion and interface contact, and are expected to achieve superior high‐energy‐density quasi‐solid‐state battery performance.

2.5. Characterizations of Derived SEI

In order to demonstrate the improved mechanism and study the chemical environment of SEI films, XPS and Time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS) analysis were performed on the lithium anode interface of Li|QSSE|Li, Li|QSSE@Py₁₃TFSI|Li and Li|QSSE@Py₁₁₄TFSI|Li batteries after 50 cycles at 0.5 mA cm⁻². The C1s XPS spectroscopy revealed that the SEI layer consists of both organic and inorganic compounds, with a much lower proportion of Li₂CO₃ on QSSE@Py₁₁₄TFSI compared to QSSE and QSSE@Py₁₃TFSI (Figure S19a–c, Supporting Information). Generally, the SEI produced by Li₂CO₃ was poor in stability due to its low conductivity, which was not conducive to the long‐term operation of the battery. With the increase of sputtering depth, the ratios of inorganic component (Li₂CO₃) and organic component in the SEI of Li|QSSE@Py₁₁₄TFSI|Li cells were generally lower than those of Li|QSSE|Li and Li|QSSE@Py₁₃TFSI|Li cells, suggesting that the SEI in QSSE@Py₁₁₄TFSI was a gradient interfacial layer with a surface organic‐rich and inner inorganic‐rich layer (Figure S20, Supporting Information). On the one hand, the organic component‐rich interface in contact with the electrolyte shows better flexibility, which greatly improves the interfacial compatibility. On the other hand, the inorganic component‐rich interface in contact with lithium metal shows better mechanical properties, effectively stopping the disordered growth of lithium dendrites. As the F1s spectrum showed, the three peaks corresponded to C─F, B─F and LiF (Figure 5a–c). The LiF signal peak could be attributed to the efficient decomposition of lithium salts and Py₁₁₄TFSI, while the B─F signal peak may be due to the presence of residual LiDFOB salts in the SSEs. With the increase of etching time, the strength of C─F group in QSSE@Py₁₁₄TFSI gradually decreased, while the strength of LiF was opposite (Figure 5d). The polar C─F bond functions as Lewis's base site to adsorb lithium ions on the surface, forming homogeneous stripping/plating of lithium metal. Further, LiF, due to its strong electronic insulation and low Li diffusion barrier, can inhibit electrons at the interface and accelerate Li⁺ transfer to the lithium anode.^{[ 26 ]} Therefore, the excellent cycling stability of quasi‐solid‐state LMBs containing the Py₁₁₄TFSI electrolyte can 5be attributed to this unique gradient SEI layer structure with a outer layer rich in C─F bonds and a inner layer rich in LiF, which is conducive to inhibit the formation of lithium dendrites at the interface and the decomposition of the electrolyte. The chemical composition of the anode interface was further analyzed using TOF‐SIMS. The distributions of LiF₂ ⁻, LiB₂O₄ ⁻, LiCO₃ ⁻, and CH₂O⁻ in 3D views (Figure 5e,g) clearly indicated that the cycled lithium anode surface of the Li|QSSE@Py₁₁₄TFSI|Li cells was rich in LiF and scarce in Li₂CO₃ compared to QSSE and QSSE@Py₁₃TFSI, consistent with the XPS results. The chemical composition depth profiles (Figure 5f,h) show that the lithium anode surface of QSSE@Py₁₁₄TFSI exhibits a high content of LiB₂O₄ ⁻ and a lower content of organic components (CH₂O⁻). The results indicate that QSSE@Py₁₁₄TFSI facilitates the decomposition of LiDFOB, which leads to the formation of more LiF to achieve a dense and stable SEI interface.

Figure 5.

Characterizations of derived SEI. a–c) XPS spectra at different sputtering times of F 1s after 50 cycles in Li||Li cells with different electrolytes in F 1s. d) The quantified atomic ratios of LiF in F 1s spectra from anode with different electrolytes. Corresponding 3D reconstruction and TOF‐SIMS negative ion depth profiles (LiF₂ ⁻, LiB₂O₄ ⁻, LiCO₃ ⁻, and CH₂O⁻) of Li anode with e,f) QSSE@Py₁₃TFSI and g,h) QSSE@Py₁₁₄TFSI. i) Cryo‐TEM images of cycled Li anode with different SSEs. j) Finite element simulation of lithium dendrite growth in QSSE, QSSE@Py₁₃TFSI and QSSE@Py₁₁₄TFSI.

SEI on the lithium anode was also detected using cryo‐TEM and the schematic diagram of sample preparation process was shown in Figure S21 (Supporting Information). A thin passivation layer of SEI ≈25.3 nm was observed on the surface of the lithium particles with QSSE@Py₁₁₄TFSI. In sharp contrast, thick and uneven SEI layers formed on the surface of recycled lithium using QSSE and QSSE@Py₁₃TFSI were clearly visible, with local thicknesses of 93.9 and 71.9 nm, respectively (Figure 5i). The crystal structures of the main components in the interface layer were characterized by high‐resolution TEM (HRTEM) images. The corrected interplanar spacing was 0.20 nm, which corresponded well to the (200) plane of LiF (Figure S22, Supporting Information). This enables Li⁺ ions to diffuse through the grain boundaries, thereby achieving a highly reversible plating/stripping process. Overall, the cryo‐TEM analysis offers valuable insights into the morphology and composition of the Li/QSSE@Py₁₁₄TFSI interface, highlighting the beneficial effect of LiF in improving battery performance. As shown in Figure 5j and Figure S23a,b and Table S6 (Supporting Information), QSSE@Py₁₁₄TFSI showed a faster Li⁺ ion transport rate and transference number, which promoted the formation of bulk Li during deposition. In contrast, in the QSSE and QSSE@Py₁₃TFSI systems, the Li⁺ ion transport rate was slower and tended to form rod‐like Li structures, which was consistent with the AFM, SEM, and cryo‐TEM results. In summary, the Py₁₁₄TFSI ILs exhibit a stronger Li⁺ binding affinity and participates in the solvation structure under the action of electric field as a Li⁺ transport site, which enhances the Li⁺ ion transport and the construction of a stable interface.

2.6. Expanded Applications on Imidazolium ILs and Full Battery Performance

The concept of constructing functional groups of trifluorotoluene can be applied to other ionic liquids, such as commonly used imidazolium ILs, using a similar preparation process. The synthesized electrolytes were named QSSE@EMIMTFSI and QSSE@MTPITFSI, respectively (Figure S24, Supporting Information). The trifluorotoluylation ILs added to PDOL‐based electrolytes (QSSE@MTPITFSI) not only solves the contact problem of electrode interface, but also helps to reduce interface impedance and improve lithium‐ion diffusion. Therefore, the modification of ionic liquids in ether‐based quasi‐solid‐state electrolytes is very important to improve the interface compatibility and ionic conductivity of quasi‐solid‐state batteries (Figure 6a,b). The HOMO and LUMO energy levels of different molecules were depicted in Figure 6c. MTPITFSI exhibited lower LUMO/HOMO energy, indicating its advantageous reaction potential in SEI formation and effectively improving the oxidation stability of electrolytes. QSSE@MTPITFSI revealed a higher electrochemical stability up to 4.7 V and is suitable for pairing with most high voltage cathodes compared to QSSE@EMIMTFSI (Figure S25, Supporting Information). Moreover, as shown in Figure 6d,e, Li|QSSE@MTPITFSI |Li cells exhibited lower interfacial impedance and higher adsorption energy compared to QSSE@EMIMTFSI, suggesting that EMIMTFSI is conducive to the migration of lithium ions and improve the stability of SSEs/Li interface. The ECD value measured in the cell with QSSE@EMIMTFSI was 0.093 mA cm⁻², whereas it increased significantly to 0.143 mA cm⁻² in the cell with QSSE@MTPITFSI, indicating that MTPITFSI enhanced the charge transfer capability in the flat and homogeneous lithium plating layer and facilitated the uniform deposition of lithium (Figure 6f). Compared to the 0.22 eV of QSSE@EMIMTFSI, The QSSE@MTPITFSI exhibited the lowest ion transport barrier of 0.20 eV calculated by the Arrhenius equation, meaning fast Li ion transport kinetics in the QSSE@MTPITFSI (Figure 6g). As displayed in Figure 6h and Figure S26 (Supporting Information), the QSSE@MTPITFSI exhibited a significantly higher $t_{L{i}^{+}}$ and ${\sigma }_{L{i}^{+}}$ value of 0.63 and 0.76 mS cm⁻¹ at 25 °C compared to 0.44 and 0.46 mS cm⁻¹ for QSSE@EMIMTFSI, respectively, evidencing that MTPITFSI enhanced Li⁺ transport dynamics.

Figure 6.

Expanded applications on imidazolium ILs and full battery performance. a,b) Schematic illustration of Li⁺ transport and electrolytes/Li interfacial evolution in quasi‐solid‐state LMBs with QSSE@EMIMTFSI and QSSE@MTPITFSI. c) Calculated HOMO and LUMO energy levels of EMIMTFSI and MTPITFSI. d) DFT calculations of the adsorption energies. e) EIS of symmetrical lithium metal batteries. f) Tafel curves. g) Arrhenius plot. h) Comparisons of ${\sigma }_{L{i}^{+}}$ and $t_{L{i}^{+}}$ between QSSE@EMIMTFSI and QSSE@MTPITFSI. i) Long‐term charge and discharge cycling of NCM811 batteries with QSSE@EMIMTFSI and QSSE@MTPITFSI under 1 C at 30 °C. j) Long cycling performances of LFP batteries with QSSE@MTPITFSI at 5 C.

To further determine the role of trifluorotoluylation ILs in simultaneously improving ion conductivity and interfacial compatibility, QSSE@EMIMTFSI and QSSE@MTPITFSI with NCM811/Li cells were assembled and tested. As displayed in Figure S27 (Supporting Information), the 4.3 V NCM811|QSSE@MTPITFSI|Li cell achieved discharge capacities of 187.0, 179.9, 164.9, and 144.1 mAh g⁻¹ under 0.2, 0.5, 1, and 2 C, respectively, which were also higher than that of the QSSE@EMIMTFSI with 179.9, 172.0, 157.1, and 135.7 mAh g⁻¹ at the same rates. The NCM811|QSSE@MTPITFSI|Li cell exhibited very high cycling stability at 1 C, providing a high initial discharge capacity of 165.8 mAh g⁻¹. In contrast, the NCM811|QSSE@EMIMTFSI|Li battery showed a significant and sharp capacity drop at 20 cycles (Figure 6i). Furthermore, the quasi‐solid‐state LMBs utilizing QSSE@MTPITFSI electrolyte matched LFP achieved a high reversible capacity with a capacity decay of only 0.02% per cycle (from 119.3 to 83.8 mAh g⁻¹) under 5 C after 1500 cycles at 30 °C, as shown in Figure 6j. These results indicate that the strategy of designing quasi‐solid‐state ether‐based electrolyte with trifluorotoluylation to construct a stable electrode interface can be widely used in interface modification engineering of various types of ILs.

3. Conclusion

In this work, a unique molecular design strategy is proposed to design trifluorotoluylation ILs that enable quasi‐solid‐state ether‐based electrolytes for high voltage lithium metal batteries. The results demonstrate that Py₁₁₄TFSI greatly enhances the oxidative stability of the electrolyte, facilitating the formation of a robust cathode passivation layer rich in LiF, and effectively suppresses the dissolution of transition metal ions. In addition, Cryo‐TEM, XPS etching, and TOF‐SIMS analyses confirmed the formation of a LiF‐rich interfacial layer on the lithium anode, promoting uniform distribution of Li⁺ and regular deposition of lithium. Consequently, Py₁₁₄TFSI significantly improves the cycling stability of the NCM811/Li full cell at a high cut‐off voltage of 4.5 V and the reversibility of lithium deposition/stripping in lithium symmetric batteries (at 0.5 mA cm ⁻² for 1500 h). Furthermore, a 2.66 Ah quasi‐solid‐state NCM811/Li pouch cell achieves an impressive energy density value of 356 Wh kg⁻¹. These findings underscore the effectiveness of trifluorotoluylation structure within ionic liquids regarding their tolerance toward high voltages and compatibility with lithium metal as applied to quasi‐solid‐state ether‐based electrolytes, which provides valuable insights into designing effective interfacial layers between polymer electrolytes and electrodes for quasi‐solid‐state LMBs while enhancing overall performance in terms of high energy density.

Conflict of Interest

The authors declare no conflict of interest.

Author Contributions

T.S.Z. supervised this work. J.L. and J.S. conducted the concept design. J.L. provided material characterizations and conducted the experiments and simulations. J.L., J.J.C., B.L.H., and X.X.X. did the data analysis. J.L. wrote the paper. T.S.Z., J.J.C., B.L.H., X.X.X., J.D.S., Z.Y.W., Z.X.G., P.Z.L., and J.S. revised the manuscript. All authors commented on the final manuscript.

Supporting information

Supporting Information

Li J., Chen J., Xu X., Shen J., Wang Z., Guo Z., Lin P., Sun J., Huang B., Zhao T., Developing Quasi‐Solid‐State Ether‐Based Electrolytes with Trifluorotoluylation Ionic Liquids for High Voltage Lithium Metal Batteries. Adv. Mater. 2025, 37, 2501006. 10.1002/adma.202501006

Data Availability Statement

The data that support the findings of this study are available in the supplementary material of this article.