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Vol. 18 (2026)

Anion–Diluent Decoupled Solvation Chemistry in Ionic Liquid-Based Localized High-Concentration Electrolytes Toward High-Voltage Lithium Metal Batteries

https://doi.org/10.1007/s40820-026-02242-4
Guangye Wu
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China
Haifeng Tu
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Zhicheng Wang
Tianmu Lake Institute of Advanced Energy Storage Technologies Co., Ltd., Liyang 213300, People’s Republic of China
Yiwen Gao
School of Materials Science and Engineering, Shanghai University, Shanghai 200444, People’s Republic of China
Peng Ding
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Yi Yang
College of Material Science and Engineering, Hohai University, Changzhou 213022, Jiangsu, People’s Republic of China
Lingwang Liu
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Suwan Lu
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Farwa Mushtaq
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Guochao Sun
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Hexiang Chen
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Haiyang Zhang
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Jiangyan Xue
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China
Jingjing Xu
College of Material Science and Engineering, Hohai University, Changzhou 213022, Jiangsu, People’s Republic of China
Hong Li
Tianmu Lake Institute of Advanced Energy Storage Technologies Co., Ltd., Liyang 213300, People’s Republic of China
Xiaodong Wu
i‑Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, Jiangsu, People’s Republic of China

Corresponding Author: Xiaodong Wu

xdwu2011@sinano.ac.cn

Nano-Micro Letters, Vol. 18 (2026), Article Number: 394

Abstract

Ionic liquid-based localized high-concentration electrolytes (IL-based LHCEs), derived from non-solvating diluents and ionic liquid electrolytes (ILEs), are promising candidates for long-life and safe lithium metal batteries (LMBs). However, conventional understanding holds that diluents merely reduce electrolyte viscosity and enhance ionic conductivity at the macroscopic level, overlooking their influence on the solvation structure at the molecular scale. Herein, we propose an anion–diluent decoupled solvation structure that is more conducive to stable cycling of high-voltage LMBs. Specifically, diluents with weak interactions toward FSI− anions effectively promote coordination between FSI− anions and Li+, leading to a solvation structure dominated by contact ion pairs (CIPs). The small anionic clusters within CIPs in IL-based LHCEs further facilitate Li+ ion transport. Moreover, compared to aggregate (AGG)-dominated solvation structures rich in anions and electrons, the CIPs exhibit superior oxidation resistance, contributing to the formation of a thin and compact cathode electrolyte interphase (CEI). As a proof, an IL-based LHCE incorporating 1,1,2,2-tetrafluoroethyl methyl ether (TFE) as the diluent (TFE-LHCE) was developed. A Li||TFE-LHCE||NCM523 (LiNi0.5Mn0.3Co0.2O2) cell cycled at 4.3 V achieves a capacity retention of 70% after 600 cycles, while a Li||NCM811 (LiNi0.8Mn0.1Co0.1O2) cell at 4.5 V retains 88% capacity after 200 cycles. Furthermore, a 2.6 Ah Li||NCM83 (LiNi0.83Mn0.1Co0.07O2) pouch cell demonstrates stable cycling over 40 cycles and successfully passes a nail penetration safety test. This work elucidates the critical mechanism by which non‑solvating diluents reconstruct the Li+ ion solvation structure, establishing a theoretical foundation for the rational screening and design of high‑performance electrolyte diluents.


Highlights:
1 Weak diluent-anion interactions decouple FSI⁻ from diluent molecules, promoting a contact ion pair (CIP)-dominant solvation structure in IL-based localized high-concentration electrolytes.
2 The CIP-dominant solvation sheath exhibits intrinsically higher oxidation stability and facilitates faster Li⁺ desolvation and interfacial charge transfer kinetics.
3 The designed TFE-LHCE enables 600 stable cycles for 4.3 V Li||NCM523 cells and 200 cycles for 4.5 V Li||NCM811 cells, with a 2.6 Ah pouch cell passing nail penetration tests.

Keywords

Lithium metal batteries Ionic liquid Localized high-concentration electrolytes Solvation structure Diluent High-voltage LMBs
Wu, Guangye, Haifeng Tu, Zhicheng Wang, Yiwen Gao, Peng Ding, Yi Yang, Lingwang Liu, Suwan Lu, Farwa Mushtaq, Guochao Sun, Hexiang Chen, Haiyang Zhang, Jiangyan Xue, Jingjing Xu, Hong Li, and Xiaodong Wu. 2026. “Anion–Diluent Decoupled Solvation Chemistry in Ionic Liquid-Based Localized High-Concentration Electrolytes Toward High-Voltage Lithium Metal Batteries”. Nano-Micro Letters 18 (June):394. https://doi.org/10.1007/s40820-026-02242-4.
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