Polyimide binder by combining with polyimide separator for enhancing the electrochemical performance of lithium ion batteries

Lithium ion battery (LIB) has been assembled by a polyimide (PI) binder, which is prepared by one-pot solution polycondensation, and PI non-woven separator. Compared to the cell using the traditional PVDF binder and polyethylene (PE) separator, the cell with PI binder and PI separator (PI-PI) not only has a better thermal stability but also displays significantly improved electrochemical performance, especially rate performance and cycling behavior. The thermogravimetric analysis (TGA) shows that the temperature of the weight loss of 10% of PVDF and PI is 464.6 °C and 525.9 °C, respectively. The properties of the separator, including wettability, electrolyte uptake and mechanical performance are tested. Owing to the hydrophilic imide group and the rigid aromatic nucleus. These properties make a possibility of a battery to meet higher requirements. In the terms of electrochemistry, when the current density over 1C, the cell with PVDF binder and PE separator (PVDF-PE) only retains no more than 61% of its capacity at a rate of 0.05C. However the cell that based on PI-PI still maintains 72.6%. Besides, the cycle performance of PI-PI gains a significant improvement. It can stay over 85% capacitance retention ratio after 200 cycles at a rate of 1C, while the PVDF-PE is only 57.68%. The outstanding improvement of the rate capability is due to the reduction of internal resistance of the battery.