Dual-network bacterial cellulose-based separators with high wet strength and a dual ion transport mechanism for uniform lithium deposition

Abstract

Inherently insulating and thermally stable nanocellulose membranes are prone to forming a three-dimensional porous structure, which is conducive to storing large amounts of electrolyte and providing ion migration pathways. However, the infiltration of polar electrolytes can compromise the mechanical strength of the nanocellulose membrane by disrupting hydrogen bonding, leading to a suboptimal interface and cycling stability of the batteries. This study effectively improves the mechanical strength and electrochemical performance of bacterial cellulose (BC) based separators by in situ constructing a dual-network structure polymerized from poly(ethylene glycol) diacrylate (PEGDA) and acrylic acid (AA). The distinctive dual-network structure not only significantly enhances the wet strength of the BC separator but also introduces a polymer-coordination transport mechanism, building upon the original lithium-ion pore transport system. The transport of lithium ions is regulated by the ether, ester and carboxyl groups in the polymer network, so that they are uniformly deposited on the surface of the lithium metal negative electrode, and finally form an SEI layer dominated by LiF, which greatly reduces the side reactions between the electrolyte and the electrode. The assembled lithium symmetric battery exhibits stable lithium deposition/stripping behavior, and the cycle stability and rate performance are far superior to those of commercial PP separators.