Dual-Anion-Rich Polymer Electrolytes for High-Voltage Solid-State Lithium Metal Batteries

Solid polymer electrolytes (SPEs) are promising candidates for lithium metal batteries (LMBs) owing to their safety features and compatibility with lithium metal anodes. However, the inferior ionic conductivity and electrochemical stability of SPEs hinder their application in high-voltage solid-state LMBs (HVSSLMBs). Here, a strategy is proposed to develop a dual-anion-rich solvation structure by implementing ferroelectric barium titanate (BTO) nanoparticles (NPs) and dual lithium salts into poly(vinylidene fluoride) (PVDF)-based SPEs for HVSSLMBs. The BTO NPs regulate the spatial structure of PVDF segments, enhancing the local built-in electric field in the SPEs, which, in turn, facilitates the dissolution and dissociation of lithium salts. This contributes to the dual-anion-rich solvation structure with an enhanced steric effect, which significantly improves Li⁺ transport kinetics and electrochemical stability. The designed PVDF-based SPE achieves a high ionic conductivity of 4.1 × 10^-4 S cm^-1 and a transference number of 0.70 at 25 °C. The Li//Li symmetric cells deliver an excellent critical current density of 2.4 mA cm^-2 and maintain a stable Li plating/stripping process for over 5000 h. After 1000 cycles at 2C, the LiFePO₄//Li cells achieve a discharge capacity of 108.3 mAh g^-1. Furthermore, the LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811)//Li cells present high capacity retention after 300 cycles at 1C with a cutoff voltage of 4.4 V. The NCM811/Graphite pouch batteries exhibit excellent cycling and safety performance. This work illustrates that the synergistic integration of functional nanoparticles with multiple lithium salts holds significant potential for the development of high-voltage SPEs.