Cellulose-based membrane with ion regulating function for high-safety lithium-ion battery at low temperature enabled by grafting structural engineering

Abstract

The separator plays an important role in determining the performance and cost of lithium-ion battery (LIBs). Biomass cellulose has been considered as a promising candidate to substitute the petroleum-based materials due to its biodegradability, high thermal stability and favorable wettability. However, the physical entanglement, hydrogen bonds and van der Waals force between the cellulose fibers results in small porosity and pore size, which make obstacles for electrolytes uptaking and Li⁺ migrating. Here the mesoporous cellulose-based membrane with ions regulating effect was designed by an approach of grafting structural engineering. The cross linking between the polymer with big molecules and the cellulose could effectively alleviate the aggregation of the cellulose fibers with the effect of steric hindrance. The grafted polymer with abundant –NH₂ functional groups have higher binding energy with the anions in the electrolyte as proved by DFT (density functional theoretical) calculation, which can restrict the movement of anions and accelerate Li⁺ transfer. The results indicate that the membrane has fast Li⁺ conductivity of 2.069 mS cm⁻¹. As separator for LIBs, it exhibits wide electrochemical stability window (up to 4.8 V) and enhanced rate/cycling performance even at extra low temperature (−30^oC).