Lewis-acid-engineered polymer electrolytes for all-solid-state lithium batteries

Abstract

Poly(ethylene oxide) (PEO)-based solid-state polymer electrolytes are promising for all-solid-state lithium metal batteries owing to their intrinsic flexibility, cost-effectiveness, and facile processability. However, their practical application is hindered by low ionic conductivity and insufficient oxidative stability toward high-voltage cathodes. Herein, Zn(BF4)2 is introduced as a Lewis acid additive into the PEO-based solid-state electrolytes. The incorporation of Zn(BF4)2 suppresses PEO crystallization and enlarges the free volume for Li+ migration. Meanwhile, Lewis-acidic Zn2+ ions interact with TFSI− anions and ether oxygen (EO) groups of PEO, synergistically enhancing lithium salt dissociation and facilitating Li+ transport. The optimized electrolyte achieves an ionic conductivity of 3.98 × 10−4 S cm−1 at 60 °C. Furthermore, Zn(BF4)2 promotes the formation of a LiF-rich solid electrolyte interphase, enabling uniform lithium deposition and suppressing dendrite growth, with stable cycling over 1400 hours in Li symmetric cells at 0.1 mA cm−2. In addition, the Zn2+−EO coordination enhances oxidative stability, ensuring compatibility with high-voltage cathodes. As a result, LiNi0.8Co0.1Mn0.1O2 and LiFePO4 cathodes deliver 80% capacity retention after 145 cycles and stable operation over 700 cycles, respectively.