Recent advances on biopolymer fiber based membranes for lithium-ion battery separators

Separator, as one of the key components to isolate the cathode and anode in the cell, heavily influences the safety, life-span and energy density of lithium ion batteries (LIBs). Currently, most widely used separators in LIBs are polyethylene (PE) or polypropylene (PP) based porous membranes due to their good chemical/electrochemical stabilities and high ionic conductivities. However, the raw materials for these polyolefin-based separators are produced by a petrochemical process, which is not eco-efficient, environmentally friendly, and sustainable. In order to meet the requirements of sustainable development, using biopolymer fibers to fabricate separators for LIBs has attracted intensive attention owing to their excellent thermal stability, low cost, biodegradable and renewable benefits. Here, we present the recent progress of biopolymer fiber based membranes applied as separators in LIBs. In this review, we begin with a brief introduction of LIB separators with the basic requirements for the membranes to be used as separators. Then, we highlight several typical biopolymer fiber based membranes recently reported for the separators of LIBs. In this section, the main focus is put on the integration of biopolymer microfibril based membranes, biopolymer microfibril based composite membranes, biopolymer nanofiber based membranes and biopolymer nanofiber based composite membranes. Finally, we provide the perspectives on several issues that need further exploration in this active research field in the future.