Interfacial fusion-enhanced 11 μm-thick gel polymer electrolyte for high-performance lithium metal batteries

In the pursuit of ultrathin polymer electrolyte (< 20 μm) for lithium metal batteries, achieving a balance between mechanical strength and interfacial stability is crucial for the longevity of the electrolytes. Herein, 11 μm-thick gel polymer electrolyte is designed via an integrated electrode/electrolyte structure supported by lithium metal anode. Benefiting from an exemplary superiority of excellent mechanical property, high ionic conductivity, and robust interfacial adhesion, the in-situ formed polymer electrolyte reinforced by titanosiloxane networks (ISPTS) embodies multifunctional roles of physical barrier, ionic carrier, and artificial protective layer at the interface. The potent interfacial interactions foster a seamless fusion of the electrode/electrolyte interfaces and enable continuous ion transport. Moreover, the built-in ISPTS electrolyte participates in the formation of gradient solid-electrolyte interphase (SEI) layer, which enhances the SEI's structural integrity against the strain induced by volume fluctuations of lithium anode. Consequently, the resultant 11 μm-thick ISPTS electrolyte enables lithium symmetric cells with cycling stability over 600 h and LiFePO4 cells with remarkable capacity retention of 96.6% after 800 cycles. This study provides a new avenue for designing ultrathin polymer electrolytes towards stable, safe, and high-energy-density lithium metal batteries.