A novel method to prepare a highly porous separator based on nanocellulose with multi-scale pore structures and its application for rechargeable lithium ion batteries

Nanocellulose has been adopted to fabricate renewable and thermally stable separators for lithium ion batteries (LIBs). However, the nanofibrils tend to form dense network because of the capillarity during drying, consequently limiting the electrolyte retention capability of the membrane and blocking the migration of ions. To tackle the problems, a novel method is presented to fabricate a nanocellulose based separator with high porosity and multiscale pore structure. The micro-sized pores derived from the dissolution of PS spheres can assure a highly porous feature of the separator. The nano-sized pores fabricated from the ethanol bath further increase the porosity and improve the permeability of the separator. Although the resultant pores weaken the mechanical strength of the separator, the electrochemical performances including the ionic conductivity, interfacial resistance and electrochemical window are ameliorated due to the distinctive microstructures. Moreover, the battery performances, containing capacity retention and rate capability, of the coin battery assembled with the as-constructed separator are proven to be agreeable by the battery test.