Designing network solid polymer electrolytes for all-solid-state lithium metal batteries

Abstract

Solid polymer electrolytes (SPEs) present a compelling pathway for developing safer and higher-performance lithium metal batteries (LMBs). However, practical implementation faces challenges related to electrolyte conductivity, lithium dendrite formation, and interfacial stability. This research systematically investigates branched polyethyleneimine-polyethylene oxide (bPEI- PEO)-based comb-chain SPEs (ConSPEs), beginning with evaluating solvent and crosslinker effects on polymer electrolyte performance. Selection of suitable solvents and precise crosslinker content significantly influenced membrane homogeneity, structural stability, and salt-polymer interactions, forming the foundation for optimized electrolyte architectures. To directly address dendrite growth, two-dimensional MXene nanocomposite coatings were integrated into optimized bPEI-PEO ConSPE frameworks. These nanocomposites effectively regulated lithium-ion deposition and significantly improved electrode-electrolyte interface stability, with MXene demonstrating outstanding performance due to superior ionic transport and enhanced mechanical robustness. Lastly, polymer-in-salt bPEI-PEO comb-chain SPEs (ConSPEs) were explored, identifying a critical EO/Li transition at a 2:1 ratio, where extensive LiTFSI amorphization enhanced ionic conductivity but simultaneously induced polymer rigidity and salt aggregation. Molecular weight analyses further revealed lower molecular weight PEO2k as notably superior to higher molecular weight PEO300k in facilitating salt dissolution and ionic mobility at elevated salt contents. Collectively, this study establishes critical design principles and demonstrates effective material strategies for advancing SPEs towards safe, reliable, and high-performance lithium metal battery technologies.