Polyurethane/LLZTO solid electrolyte with excellent mechanical strength and electrochemical property for advanced lithium metal battery

Liquid electrolytes are prone to leaks and fires, which is exacerbated in Li metal batteries (LMBs) because of dendrite formation. Solid polymer electrolytes (SPEs) with their tunable mechanical properties and easy manufacturability, are increasingly becoming the preferred choice to address the interface issues in LMBs. However, their electrochemical instability against lithium-metal, mediocre conductivity and poorly interphases between Li and SPEs have prevented extensive application in LMBs. In this study, guided by theoretical calculations, an organic–inorganic composite solid-state polymer electrolyte (LPCU) based on Polyurethane (PU) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) was designed, and showed no lithium dendrite penetration after 500 h of cycling. The addition of LLZTO makes up for the deficiency of lithium ion coordination environment in PU matrix and improve electrochemical performances of LPCU electrolytes. Owing to the room-temperature ionic conductivity of 2.22 × 10−4 S cm−1, the transference number of 0.55 and the improved contact interface of Li-SPE, the optimized LPCU with a LLZTO content of 4% could achieve 150.0 mAh/g with 90% retention capacity after 150 cycles at 1C rate and 60 °C for Li||LiFePO4 full batteries. This composite solid polymer electrolyte (LPCU) presents a powerful strategy for enabling the stable operation of LMBs.