Polyimide/cellulose composite membrane with excellent heat-resistance and fast lithium-ion transport for lithium-ion...

Polyimide membranes have long been of great interest in the battery industries due to their outstanding thermal stability and flame retardancy. However, the preparation of polyimide membranes with ideal pore structure and excellent lithium-ion transference remains a challenge. In this study, we reported for the first time, that a nano-porous fluorinated and partially carboxylated polyimide/cellulose composite membrane was successfully synthesized by selected monomers and prepared by thermal imidization, phase separation, and alkaline hydrolysis method. Particularly, an appropriate addition of cellulose acetate (CA) during the synthesis process can optimize the pore structure of the membrane. Besides, CA was converted to cellulose after alkaline hydrolysis, further enhancing the electrolyte affinity and lithium-ion transference of the membrane. Hence, this composite membrane exhibited distinct heat-resistance, high porosity (78 %), electrolyte absorption (344 %), and lithium-ion transfer number (0.84). Most importantly, thanks to the above characteristics of the membrane, the assembled LiFePO₄/Li cells demonstrated excellent cycling stability compared with the cell with PP membrane, showing a capacity retention rate of as high as 93 % after 500 cycles at 1C. We anticipate that this composite membrane with superior physical and electrochemical properties would shed light on the development of next-generation membranes for high-power and high-safety batteries.