Enhanced thermostability and electrochemical performance of separators based on an organic-inorganic composite binder composed of polyvinyl alcohol and inorganic phosphate for lithium ion batteries

The present ceramic-coated separator has poor thermostability above 140 °C since the application of organic binders. Herein, an organic-inorganic composite binder composed of phosphate inorganic binder (PIB) and polyvinyl alcohol (PVA) organic binder is applied, which greatly improves the thermostability of separator and also enhances the electrochemical performance of battery. Results show that the thermal shrinkage of separator with 0.5%PVA+ 0.5%PIB binder at 140 °C is only 0.86% compared to that of 48% of polyethylene (PE) and 5.2% of separator with 1% PVA. And the thermal shrinkage is low of 3.9% at 200 °C, which is much lower than that of the separator with 1% PVA binder (70%). An interpenetrating porous structure is formed by the "clustered" Al2O3 ceramic with 0.5%PVA+ 0.5%PIB which improves the porosity, electrolyte uptake and conductivity of the separator. Both the OCV-temperature curve and the constant-voltage charging indicates that the separator based on 0.5%PVA+ 0.5%PIB has better safety performance. The battery with 0.5%PVA+ 0.5%PIB separator has higher capacity retention of 91.5% after 100 cycles than that of the PE (82.2%) and separator with 1% PVA (62.8%). And the discharge capacity at 1 C, 2 C and 5 C is 98.4%, 94.3% and 86.1% of the theoretical capacity.