Robust asymmetric gel polymer electrolytes with 2D h-BN as protective layer for highly stable solid-state lithium metal batteries

Abstract

Gel polymer electrolytes (GPEs) have emerged as a highly promising alternative to conventional liquid electrolytes for stable lithium-metal batteries (LIBs). However, their inherent poor mechanical properties and limited interfacial compatibility with lithium metal usually lead to unexpected growth of lithium dendrites, hindering commercial viability. Herein, an asymmetric polymer electrolyte with h-BN (HGPE) as protective layer was fabricated via a facile one-step coating strategy. Compared to pure GPE, the asymmetric polymer electrolytes exhibit significantly enhanced mechanical strength from 4.4 MPa to 7.4 MPa, effectively suppressing lithium dendrite growth. Furthermore, the HGPE improves interfacial compatibility with the anodes by preventing direct contact between GPE and lithium metals. The addition of h-BN also enhances the lithium-ion transfer number (tLi+), reaching 0.87 compared to 0.53 for pure GPE, attributed to the hindrance of anion movement by the protective layer. Consequently, the Li symmetric battery assembled with HGPE demonstrate exceptional long-term stability, maintaining performance over 1600 h at 0.1 mA cm−2. Furthermore, the assembled Li|LiFePO4 battery can deliver a high-capacity retention rate of 93.8 % after 500 cycles at room temperature, showcasing the promising potential of asymmetric polymer electrolytes for high-performance LMBs.