Thin hybrid electrolyte based on garnet-type lithium-ion conductor Li7La3Zr2O12 for 12 V-class bipolar batteries

Thin hybrid electrolytes based on lithium-ion conducting ceramics with a few micrometers thickness have been studied in order to be practically applied to 12 V-class bipolar battery with liquid-free and separator-free. A cubic garnet-type Li7La3Zr2O12 (LLZ)-based hybrid electrolyte composed of LLZ particles coated with 4 wt% polyacrylonitrile (PAN)-based gel polymer electrolyte was prepared as the thin electrolyte layer, which reduced the internal resistance of LiMn0.8Fe0.2PO4(LMFP)/Li4Ti5O12(LTO) cells and enabled discharge at low temperatures. The conductivity of the LLZ-based hybrid electrolyte at 25°C was one order of magnitude higher than that of the LLZ solid electrolyte and comparable to that of the PAN-based gel polymer. The activation energy for ionic conductivity of the hybrid electrolyte was significantly smaller than that of the gel polymer electrolyte. The fabricated 12 V-class bipolar LMFP/LTO battery using the thin LLZ-based hybrid electrolyte layer exhibited good performance in terms of discharge rate capability, operating in the wide temperature range of −40°C to 80°C, and charge–discharge cycling comparable to those of conventional lithium-ion batteries.