Bioinspired Ultrastrong and Ion‐Selective Gel Electrolytes by Interfacial Coacervation for High‐Performance Lithium‐Metal Batteries

ABSTRACT Coupling lithium metal with gel polymer electrolytes (GPEs) has been demonstrated as an effective strategy to enable stable lithium metal batteries (LMBs). However, the current design of GPEs faces difficulties in simultaneously achieving satisfactory mechanical properties and efficient and selective ion transport. Here, we present the fabrication of ultrastrong and hierarchically nanoporous cellulose gel electrolytes via poly(ionic liquid)‐induced interfacial coacervation of cellulose nanofibrils. The nanofibrils GPE with a cascade ion‐conduction network spanning from molecular‐scale channels to mesopores enables dual‐mode Li⁺ transport through nanoconfinement and interstitial ion hopping. This mechanism effectively blocks anion movement while achieving selective Li⁺ transport with a high transference number of 0.7 and a high ionic conductivity of 0.65 mS cm −1 . The GPE enables stable cycling of high mass loading (LiFePO₄, 16 mg cm⁻²) LMBs and high‐temperature (80°C) LMBs. Specifically, the LMB with a high LiFePO₄ loading of 12 mg cm⁻² delivers stable cycling life over 600 cycles, maintaining 87% capacity retention. Furthermore, the assembled 635 mAh pouch full cell demonstrates excellent stability with a high capacity retention of 91.7% after 1500 cycles. This study offers a novel strategy for the development of robust and ion‐selective GPEs for stable LMBs.