Single Li ion conducting solid-state polymer electrolytes based on carbon quantum dots for Li-metal batteries

Single Li ion conducting solid-state polymer electrolytes (SLIC-SPEs) can effectively inhibit the growth of Li dendrites in Li-metal batteries. However, SLIC-SPE synthesis using traditional polymerization methods yields electrolytes with insufficient conductivity, which limits their practical application. Herein, a novel Li+ conductor based on carbon quantum dots (CQDs) is fabricated via the pyrolysis of poly(lithium 4-styrene sulfonate) and citric acid. The large CQD anionic size and hydrogen bonding interaction with matrix hinder anion migration in the polyethylene oxide matrix and thereby grants a high Li+ transport number of 0.9446. Moreover, CQD incorporation improves the mechanical properties and ionic conductivity of the SPEs. The as-prepared SPE membrane demonstrates a high room-temperature ionic conductivity of 2.02 × 10−4 S cm−1. All-solid-state Li-metal batteries fabricated with these SPEs show good cycling stability, rate performance, and capacity retention over 1000 cycles at 2 C and 60 °C. The SPEs also withstand deformations such as bending and twisting.