CoF2-modified PEO-LLZTO composite polymer electrolyte to optimize Li+ transport pathway

Abstract

Solid-state lithium metal batteries face challenges when utilizing polymer solid-state electrolytes based on poly(ethylene oxide) (PEO), primarily because these materials exhibit low ionic conductivity at room temperature. A common method of modifying polymer electrolytes is to add LLZTO inorganic powder to a PEO matrix to form a composite polymer electrolyte (CPEs). However, PEO-LLZTO CPEs still suffer from ionic conductivity as well as lithium dendrite penetration problems. Therefore, constructing an ideal artificial interfacial layer is crucial to solve the above problems. In this paper, a bilayer heterogeneous SEI layer enriched with LiF inorganic components and Li-Co lithophilic alloys is constituted by adding CoF₂ commercial solid-state electrolyte additive to optimize the lithium homogeneous deposition behavior and accelerate the migration of lithium ions. The CoF₂@CPEs prepared in the paper have an ionic conductivity of 5.10 × 10⁻⁴ S·cm⁻¹, a Li⁺ ions migration of 0.32, and an electrochemical window of >4 V. In addition, the Li|CoF₂@CPEs|Li symmetric cell can be stably cycled at a current density of 0.2 mA·cm⁻² for 1200 h. And the LFP|CoF₂@CPEs|Li cell formed by pairing with LiFePO₄ (LFP) has good multiplication capability and cycling stability. The initial discharge specific capacity of the cell was 130.07 mAh·g⁻¹ at 0.5C, with 78.81 % capacity retention and 99.15 % average Coulombic efficiency after 200 cycles.