Zwitterionic Cellulose‐Based Polymer Electrolyte Enabled by Aqueous Solution Casting for High‐Performance Solid‐State Batteries

Abstract Polyethylene oxide (PEO)‐based solid‐state batteries hold great promise as the next‐generation batteries with high energy density and high safety. However, PEO‐based electrolytes encounter certain limitations, including inferior ionic conductivity, low Li + transference number, and poor mechanical strength. Herein, we aim to simultaneously address these issues by utilizing one‐dimensional zwitterionic cellulose nanofiber (ZCNF) as fillers for PEO‐based electrolytes using a simple aqueous solution casting method. Multiple characterizations and theoretical calculations demonstrate that the unique zwitterionic structure imparts ZCNF with various functions, such as disrupting PEO crystallization, dissociating lithium salts, anchoring anions through cationic groups, accelerating Li + migration by anionic groups, as well as its inherent reinforcement effect. As a result, the prepared PL‐ZCNF electrolyte exhibits remarkable ionic conductivity (5.37×10 −4 S cm −1 ) and Li + transference number (0.62) at 60 °C without sacrificing mechanical strength (9.2 MPa), together with high critical current density of 1.1 mA cm −2 . Attributed to these merits of PL‐ZCNF, the LiFePO 4 |PL‐ZCNF|Li solid‐state full‐cell delivers exceptional rate capability and cycling performance (900 cycles at 5 C). Notably, the assembled pouch‐cell can maintain steady operation over 1000 cycles with an impressive 93.7 % capacity retention at 0.5 C and 60 °C, highlighting the great potential of PL‐ZCNF for practical applications.