A phosphorylated nanocellulose/hydroxypropyl methylcellulose composite matrix: A biodegradable, flame-retardant and self-standing gel polymer electrolyte towards eco-friendly and high safety lithium ion batteries

Abstract

Gel polymer electrolyte (GPE) is considered as a midway solution of liquid electrolyte and solid polymer electrolyte. Nowadays, the biodegradable and renewable cellulose based GPEs are adopted as promising substitutes for GPEs based on other polymers like PVDF and PMMA. However, the safety concerns derived from the flammability of cellulose still hinders the practical application of the cellulose based GPEs. Simultaneously, the conventional methods to improve the flame-resistance of the host membranes are either unreliable or often invalidate the biodegradability of the GPEs based on cellulose. To achieve the unique combination of biodegradability and high safety, we report the preparation of composite GPEs with flame-retardancy resulted from hydrolysis between phosphorylated nanocellulose (PNC) and hydroxypropyl methylcellulose (HPMC). Besides, the present GPEs are demonstrated to be self-standing and mechanically robust with the advent of PNC. In comparison of the GPEs with various content of PNC, MPC50%/GPC50% are considered as the suitable options thanks to the high tensile strength, satisfactory electrochemical performances and good flame-retardancy. Finally, the LiFePO4/GPC50%/Li coin battery performs a remarkable cycling performance with a high capacity retention of 88.9% at 0.2C and a good rate capability in the battery test. It is anticipated that the as-constructed GPE can contribute to the design on the eco-friendly and high safety batteries in the future.