Gravity-driven Poly(ethylene glycol)@Li1.5Al0.5Ge1.5(PO4)3 asymmetric solid polymer electrolytes for all-solid-state lithium batteries

An asymmetric solid polymer electrolyte (ASPE) is designed as two-in-one layered structure driven by gravity and in-situ polymerization. The rigid layer composed of polymer embedded three-dimensional continuous Li1.5Al0.5Ge1.5(PO4)3 (LAGP) framework improves the Li+ transference number and critical current densities. The soft poly(ethylene glycol) (PEG) layer prepared via thermal polymerization by poly(ethylene glycol) methyl ether methacrylate (PEGMEM) makes good interfacial contact with cathodes. Driven by gravity, the two layers are automatically stratified during the polymerization. By virtue of this structural merit, the Li+ transference number of PEG@LAGP ASPE extends to 0.144 (vs. 0.083 of PEG SPE), and symmetric Li/PEG@LAGP ASPE/Li cells can stably cycle over 400 h at current density of 0.5 mA cm−2 under 60 °C. LiFePO4/PEG@LAGP ASPE/Li cell exhibits excellent electrochemical performance at 2.5 C (0.5 mA cm−2) under 60 °C, reaching to a maximum specific capacity of 130.8 mA h g−1 and a capacity retention of 87.2% after 1000 cycles. Furthermore, the cells operating at high rates or high temperatures also have been demonstrated. This work provides a promising electrolyte design strategy for all-solid-state batteries with superior interface compatibility and long cycle life.