Halloysite nanotube coated-separator enhances the safety and electrochemical performance of lithium-ion battery

The high-temperature resistance and Li+ transmission ability of separator are the key factors to determine the safety and electrochemical performance of lithium-ion battery. Herein, halloysite with hollow nanotube structure (HNTs) is used as coating, and polyvinyl alcohol-phosphate organic-inorganic composite binder is applied to bond the coating on polyethylene substrate (HAB-PE). Results showed that the high-temperature resistance of HAB-PE was significantly improved with the shrinkage rate decreasing from 79.75 % to 0.6 % at 220 degrees C. And the separator retains complete HNTs coating structure after combustion which enables excellent safety for the LiCoO2/HAB-PE/Li battery. Secondly, the hollow nanotube structure of HNTs shows a strong adsorption for the liquid electrolyte, which significantly improves the separator wettability. And the porous structure formed by interlaced HNTs greatly increasing the electrolyte uptake. More importantly, the Li+ transference number is significantly increased from 0.37 to 0.59, which are mainly due to the opposite charge properties of the inner and outer surfaces of HNTs. Since the negatively charged outer surface can adsorb Li+, which partially remove ethylene-carbonate (EC) and dimethyl-carbonate (DMC) solvent molecules due to the electrostatic adsorption. While the positively charged inner surface can adsorb and fix the PF6- anionic, thereby enhancing the dissociation degree of LiPF6.