Polyether sulfone and Li6.4La3Zr1.4Ta0.6O12 based polymer-in-ceramic electrolyte with enhanced conductivity at low temperature for solid state lithium batteries

Developing solid state lithium batteries (SSLBs) is an essential step to overcome current safety and energy density issues of traditional Li-ion batteries. As the core component of SSLBs, a solid electrolyte with high ionic conductivity, great physical and chemical properties is still under exploration. Herein, a novel “polymer in ceramic” composite polymer-ceramic electrolytes (CPEs) is reported, which is composed of a polyether sulfone (PESF) polymer and cubic Li6.4La3Zr1.4Ta0.6O12 (LLZTO) ceramic with high contents (up to 80 wt. %). The as-prepared PESF-LLZTO CPEs possess good heat resistance and high mechanical strength to maintain structural integrity. The optimized 0.2PESF-0.8LLZTO CPEs exhibits an excellent ionic conductivity of 4.13×10−4 S cm−1 with a tLi+value as high as 0.64 at 20 °C after wetted by trace wetting agent (6.0 ul cm−2). More impressively, the ionic conductivity is still reached 1.49×10−4 S cm−1 at -10 °C and 9.42×10−4 S cm−1 at 80oC. Meanwhile, the 0.2PESF-0.8LLZTO CPEs shows a broad electrochemical window (≤4.8 V vs. Li+/Li) and an excellent compatibility with Li metal. Density functional theory calculations and 6Li solid-state NMR characterizations suggest that strong interactions among LLZTO, PESF and wetting agents contribute to the enhanced conductivity. As a proof for practical application, the Li||0.2PESF-0.8LLZTO CPEs||LiFePO4 full cells deliver a specific discharge capacity of 133.2 mAh g−1 at 2.0 C, and successfully run over 80 cycles at 0.5 C without capacity attenuation at 20 °C. The full cell also demonstrates a possibility for the application at low temperature down to -10oC and high temperature up to 60oC. This work brings a new perspective for high-performance SSLBs.