Ionic Conductivity and Cycling Performance in PEO Polymer Electrolyte Enhanced by Non-Milled In Situ Nano-LLZO Powders

High Li + conductivity, good interfacial compatibility, and nano-scale particle size have always been essential conditions for selecting inorganic fillers in high-performance composite solid electrolytes. In this study, non-milled in situ LLZO fillers with nanosize was synthesized via the sol–gel method by rapid heating sintering, which resulted in more surface defects and fewer impurities in LLZO. Compared with milled LLZO fillers, these non-milled LLZO fillers with more surface defects and fewer impurities can effectively reduce the crystallinity of PEO and agglomeration in PEO, which can form composite electrolytes with high Li + conductivity. Most importantly, the discharge capacity of the 7.5% non-milled LLZO–PEO-based LiFePO 4 /Li battery is about 135.5 mA h g –1 at 1C and 60 °C. After 100 cycles, the discharge specific capacity remains at 99%. It is worth noting that nano-sized non-milled LLZO will improve the discharge capacity of LiFePO 4 /Li batteries to 122.1 mA h g –1 at 0.2C and 30 °C.