New potential substitute of PVDF binder: poly(propylene carbonate) for solvent-free manufacturing high-loading cathodes of LiFePO4|Li batteries

For decades, the slurry coating has been used to manufacture lithium-ion battery electrodes. The process involves toxic and expensive organic solvents, followed by time- and energy-consuming vacuum drying. Herein, a solvent-free method for LiFePO4 cathode preparation using lithium-ion conductive and biodegradable poly(propylene carbonate) (PPC) as a binder is proposed. The cathode is prepared by simple ball milling and hot-pressing method. PPC with a glass transition temperature of 36.5 celcius is processed at a rubbery state and PPC work as a binder at glassy state while battery running. Microscopically, amorphous PPC contains more polar carbonate groups that coordinate lithium ion at a medium strength to absorb and desorb lithium-ion, which is good for lithium-ion migration. PPC with good mechanical strength as the binder and artificial cathode electrolyte interface in LiFePO4 cathode reduces the internal resistance of the battery effectively and protects LiFePO4 from deformation, realizing the remarkable improvement of electrochemical performance of battery. The mass loading for the LiFePO4 cathode with PPC binder is up to 20 mg/cm(2) and the initial discharge capacity of LiFePO4|Li batteries reach 141.9 mAh/g at 0.5 C, and the capacity retention is 79.1% after 800 cycles. Replacing high-cost and environment-polluting PVDF with low-cost and environment-friendly PPC, this solvent-free method will largely reduce the cost and emission of the lithium-ion battery industry.