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

Abstract

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. A new type of CQD is synthesized by pyrolysis, and the corresponding SLIC-SPEs is also developed. The large size of CQD anions makes their migration in the polyethylene oxide (PEO) matrix difficult. The SPE possesses a high lithium ion transport number (0.9446) and room-temperature ionic conductivity of 2.02 × 10 −4 S cm −1 . This material shows outstanding power performance and cycling stability in a battery prototype. • A new approach to fabricate SLIC-SPEs based on CQDs was reported. • Addition of PLSSCQD ensured superior stretching and puncture resistance properties of SPE. • PLSSCQD/PEO SPE exhibited a high room-temperature ion conductivity and Li + transport number of 2.02 × 10 −4 S cm −1 and 0.9446, respectively. • The cell using PLSSCQD/PEO SPE exhibited a dendrite-free morphology during repeated discharge–charge, excellent cycling stability and capacity retention.