The role of zwitterionic crosslinks in facilitating ion conduction, lithium deposition, and stable interface formation for polymer electrolyte-based lithium metal batteries

Abstract

Developing flexible polymer electrolytes that can concurrently promote ion conduction, uniform Li deposition, and robust solid electrolyte interphase (SEI) formation is promising for the development of next-generation lithium metal batteries (LMBs). Herein, a new polymeric zwitterionic electrolyte with a glass fiber support was investigated. A sulfobetaine zwitterionic crosslinker participated in in situ UV-triggered photopolymerization with a carbonate monomer and ether type dimethacrylate. The zwitterionic gel electrolyte (ZGE) demonstrated a high ionic conductivity exceeding 1 × 10⁻³ S cm⁻¹ and electrochemical oxidative stability (>5 V vs. Li⁺/Li). The zwitterionic crosslinker in the ZGE was able to mediate homogeneous Li⁺ flux toward the lithium anode and suppress lithium dendrites (the Li/ZGE/Li cell can cycle stably for more than 1400 h with a current density of 0.1 mA cm⁻²). The ZGE also helped construct a LiF-rich SEI favorable for dendrite suppression. A Li/ZGE/LiFePO₄ (LFP) cell demonstrated excellent long-term cycling stability (>600 cycles with a capacity retention of 92%, high discharge capacity of 155 mA h g⁻¹, and coulombic efficiency of >99.5%). The ZGE could also support a Li/Ni_0.815Co_0.15Al_0.035O₂ (NCA) cell to operate with a high specific capacity of 232 mA h g⁻¹. The flexible ZGE made it possible for a pouch-type Li/LFP cell to cycle and function well in a flat and bending state. This polymer electrolyte holds great promise for the exploration of high-energy polymeric LMBs.