Salicylic acid treated Li7La3Zr2O12 achieves dual functions for a PEO-based solid polymer electrolyte in lithium metal batteries

Abstract

The Li₇La₃Zr₂O₁₂ (LLZO) electrolyte is typically introduced as an inorganic filler into poly(ethylene oxide) (PEO) to enhance the performance of batteries. However, LLZO particles inevitably come into contact with air and produce a Li₂CO₃ layer. The low ionic conductivity of Li₂CO₃ is not conducive to the conduction of Li⁺. Herein, LLZO particles were treated with salicylic acid (SA) to achieve dual functions. First, SA is used to effectively remove the Li₂CO₃ layer of the LLZO particles, which improves Li⁺ mobility at the interface of LLZO and the PEO matrix. Furthermore, SA treatment favors the uniform dispersion of LLZO and the positively charged SA-treated LLZO facilitates the immobilization of anions in LiTFSI, both of which promote the fast transport of Li⁺ in the PEO matrix. Therefore, the modified composite electrolyte exhibits an improved ionic transference number (0.63) and ionic conductivity (1.21 × 10⁻⁴ S cm⁻¹ at 30 °C). The Li/Li symmetric battery can operate over 1300 h. Furthermore, the Li/LiFePO₄ battery exhibits an impressive discharge capacity of 142.8 mA h g⁻¹ after 150 cycles at 0.2C. These results indicate that SA treatment is a useful method for enhancing the electrochemical properties of the LLZO/PEO solid electrolyte.