A Polymer-in-Salt Electrolyte Enables Room Temperature Lithium Metal Batteries

Abstract

The lithium metal battery with solid-state polymer electrolyte (SPE) is a promising candidate for solid-state batteries with high safety and high energy density. However, the low room temperature ionic conductivity and poor electrolyte/electrode interfacial stability of the SPEs seriously hinder the practical application. Herein, we adopt a polymer-in-salt electrolyte (PISE) strategy on the comb-like polycaprolactone (PCL) to circumvent the low ionic conductivity and poor interfacial stability of the conventional SPE, thus enabling the full function of room temperature lithium metal batteries. The all-solid-state PISE exhibits a high ionic conductivity of 3.9 × 10−4 S cm−1 at 30 °C, a superior lithium-ion transference number of 0.61 and an improved oxidative stability of ∼4.8 V vs Li/Li+. Due to the ultra-stable interface generated by the superconcentrated lithium salt, the all-solid-state LiFePO4∣∣Li cells exhibit prominent high cycling stability, with high capacity retention (92%) after 300 cycles at ambient temperature. The full function of the ambient temperature PISE offers a promising pathway towards high energy density and high safety room temperature LMBs.