High thermal stability and low impedance polypropylene separator coated with aluminum phosphate

Separators with low ionic impedances and high thermal/electrochemical stability are desirable for high-performance Li-ion batteries. Herein, a composite layer consisting of AlPO4, poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and polymethyl methacrylate (PMMA) is coated on the polypropylene (PP) separator matrix. The coated PP exhibits an electrolyte uptake of 2.28%, leading to improved ionic conductivity and Li-ion diffusion coefficient. In addition, this separator has a wide electrochemical stability window, high peeling strength of 111.2 N m−1 and superior thermal stability at 170 °C. By applying this coated separator in the cell with LiNi0.5Co0.2Mn0.3O2 cathode, excellent cycling stability and rate performance can be also obtained. The improved electrochemical performances can be attributed to that AlPO4 in the coating layer exhibits high electrolyte uptake and firmly combines with the PP matrix.