Semi-Spontaneous Post-Crosslinking Triblock Copolymer Electrolyte for Solid-State Lithium Battery

Abstract

The solid polymer electrolyte is a promising candidate for solid-state lithium battery because of favorable interfacial contact, good processability and economic availability. However, its application is limited because of low ionic conductivity and insufficient mechanical strength. In this study, the delicate molecular structural design was realized via controlled / “living” radical polymerization in order to decouple the trade-off between ionic conductivity and mechanical strength. The random and triblock copolymer electrolytes were designed and synthesized to investigate the influence of molecular structure on ionic conduction, while a chemical cross-linking network was constructed via a semi-spontaneous post-crosslinking reaction. Compared with a random counterpart, the triblock copolymer electrolyte presented stronger chain segment motion and a liquid-like mechanical response due to the independent ion-conducting block, resulting in significantly improved ionic conductivity (from 6.29 ± 1.11 × 10−5 to 9.57 ± 2.82 × 10−5 S cm−1 at 60 °C) and cell performance. When assembled with LiFePO4 and lithium metal electrodes, the cell with triblock copolymer electrolyte showed significantly improved rate performance (150 mAh g−1 at 1 C) and cycling life (200 cycles with 92.8% capacity retention at 1 C). This study demonstrates the advantages of molecular structure regulation on ionic conduction and mechanical support, which may provide new insights for the future design of solid polymer electrolytes.