Enhanced thermal stability and lithium ion conductivity of polyethylene separator by coating colloidal SiO2 nanoparticles with porous shell.

Electric vehicles have very strict requirements for lithium ion batteries (LIBs). However, the commercial polyethylene (PE) separators cannot meet the demands of high safety and electrochemical performance for LIBs. This work aims to enhance the electrochemical and safety performance of LIBs by coating the separator with multifunctional particles. First, the colloidal SiO2 nanoparticles were etched by LiOH to form porous shell and lithium silicate (LSO) species simultaneously. Then, the SiO2 nanoparticles with porous shell were coated on PE separator by dip-coating method in the presence of binder. The experiment results indicate that SiO2 nanoparticles with porous shell can endow PE separator excellent thermal stability (thermal shrinkage is almost 0% at 150 ℃ for 30 min) and electrochemical properties (improved ionic conductivity and Li+ ion transference number). Moreover, the Li/LiCoO2 cell employing the PE separator coated by SiO2 with porous shell exhibits the best cycle life and C-rate performance. The discharge capacity retention of the cell assembled with LSO-SiO2@PE separator increase from 69% (cells assembled with pristine PE separator) to 86% after 100 cycles at 0.2C.