Design of networked solid-state polymer as artificial interlayer and solid polymer electrolyte for lithium metal batteries

Abstract

• Using low energy polymer to completely cover Li anode and regulate Li + transport. • Using low energy polymer to form Li−F bonds facilitating uniform Li deposition. • Using high elasticity polymer to accommodate Li anode volume changes. • Being used as an artificial interlayer or solid electrolyte in lithium batteries. • Enabling solid batteries to retain 86% capacity after 750 cycles at 30 °C. Major challenges in the development of lithium metal batteries (LMBs) are nonuniform Li deposition and substantial variation in Li volume, resulting in Li dendrite growth and Li consumption. A networked solid-state polymer electrolyte (NSPE) that comprises poly(ethylene oxide- co -propylene oxide) (P(EO- co -PO)) and poly(dimethylsiloxane) diglycidyl ether (PDMSDGE) chains and a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is developed for resolving the Li deposition challenges. The methyl pendants on P(EO- co -PO) and PDMSDGE chains render the NSPE a low-surface-energy film for complete coverages on the high-energy Li electrode and regulating Li + transport. The low-surface-energy characteristics induces overspreading of the highly lithiophilic C-F ends of the TFSI − anion at the Li electrode–NSPE interface, forming Li−F bonds and facilitating uniform Li deposition. The elastic PDMS chains enable the NSPE to accommodate Li volume changes. Liquid-phase Li||LiFePO 4 and Cu||LiFePO 4 cells with the NSPE as an artificial interface or a solid-state Li||LiFePO 4 cell with the NSPE as solid electrolyte had uniform anodic Li deposition, resulting in long cycle life and high coulombic efficiency. Our study demonstrated that (a) low surface energy to completely cover the Li anode and (b) the presence of interfacial Li − F bonds are two essential requirements for uniform Li deposition in LMBs.