Lithium Ionic Conductive Mechanism in PEO Polymer Electrolytes Enhanced by Nano/Micron Size LLZO Fillers

Abstract

Solid polymer electrolytes (SPEs) incorporating inorganic ceramic fillers are key solutions of all solid-state lithium battery technology applications. At present, the conductive mechanism of LLZO-PEO electrolyte is still controversial. Herein, the effect of nano and micron LLZO on the conductive mechanism of PEO matrix with different molecular weight is studied. The low molecular weight PEO electrolyte (LSPEs) containing nano LLZO exhibit higher conductivities than those with the micron ones, which is primarily caused by the percolation effect resulting from the difference in specific surface area. However, for high molecular weight PEO electrolytes (HSPEs), the addition of nano LLZO ceramic fillers can mainly lead to reduce the crystallinity of HSPEs to enhance the motion of polymer segment. Thus, compared with HSPEs alone, the nano LLZO-HSPEs show conductivities one order of magnitude larger. Besides, the discharge capacity of nano LLZO-HSPEs based LiFePO4/Li batteries at 1 C is around 131 mAh g−1 at 60 °C, as well as discharge specific capacity holds 99.2% after 200 cycles. Notably, nano LLZO ceramic fillers will enhance cyclic performance of LiFePO4/Li batteries at 0.2 C and 40 °C, which still maintain 126.7 mAh g−1 after 50 cycles.