CAO An-Min lab from the Institute of Chemistry of the Chinese Academy of Sciences revealed the enormous potential of molecular engineering on cellulose biopolymers to develop new kinds of solid-state electrolytes (SSEs) through a green and scalable process. High-performance solid-state electrolytes (SSEs) lies at the heart of the solid-state battery for developing the next-generation rechargeable batteries.

Abundant hydroxyl groups on the cellulose skeleton provide a versatile platform for molecular design. However, the ion-insulating nature of cellulose limits their usages in SSEs largely as inactive supporting materials. The introduction of phthalate group onto the cellulose skeleton not only enables multi-coordination with Li+ to facilitate the coupling/decoupling of lithium salt, but also generate strong hydrogen-bond network between cellulose chains.

The prepared CP-SSE displayed a high Li⁺ conductivity of 1.09×10^-3 S cm^-1 with a transference number of 0.81 while maintained a high mechanical strength of 12 MPa. The assembled solid-state batteries (SSBs) showed extraordinary capability in high reversible capacity (158.5 mAh g^-1, 0.1 C) and cycling capability (87% capacity retention, 1000 cycles). Furthermore, the wide electrochemical window of CP-SSE allows for the utilization of other high-voltage cathodes such as LiCoO₂ (LCO), LiMn₂O₄ (LMO) and LiNi_0.9Co_0.1O₂ (NC), showing the high-voltage electrochemical stability of the CP-SSE across different configurations of cathode materials.

      Schematic diagram for the fabrication of cellulose phthalate (CP) based solid state electrolyte (SSE)

This work has been published in Nature Sustainability. The research was supported by the National Natural Science Foundation of China, the Key Research Program of Frontier Sciences, , the Beijing National Laboratory for Molecular Sciences), the RGC General Research Fund, Seed Fund of the University of Hong Kong and Hong Kong Quantum AI Lab Limited, Air @ InnoHK of Hong Kong Government.