Preparation And Properties Of Composite Separator Modified By Nano-BaSO₄ For Lithium-ion Batteries

As one of the key components of lithium-ion batteries, the separator has a major influence on the production cost, performance and safety of batteries. In this paper, two kinds of modified separator were prepared by introducing nano-BaSO4 particles which was synthesized by liquid precipitation with stearic acid as surface modifiers. The main contents and results are summarized as follows:(1) The nano-sized BaSO4 particle modified by stearic acid was prepared in ethanol and water reaction system and then characterized by Transmission Electron Microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray Diffraction (XRD), thermal gravimetric analysis (TGA) and other methods. The results indicate that the smallest nano-BaSO4 particles can be obtained when the reaction temperature is 25℃, the concentration of the reactants is 0.5mol/L and the dropping speed of NaSO4 solution is 2mL/min. Furthermore, under above conditions, some mesoporous is formed in the interior of the resulting nano-BaSO4 and the resulting nano-BaSO4 is not easy to deposit when self-dispersed in the ionized water.(2) The composite separator for lithium-ion battery was prepared by coating nano-BaSO4 upon porous polyolefin membrane (Celgard 2325) with polyimide (PI) as binder. The physical and electrochemical properties of composite separator were tested. The results show that nano-BaSO4 can be well distributed in the coating surface of the separator. The coating of BaSO4 on separator can effectively improve the thermal dimensional stability and enhance the electrolyte uptake. Moreover, it can reduce the interfacial resistance between the separator and Li electrode. Meanwhile, the good cycling performance was proved by the coin cells assembled with the composite separator.(3) The composite gel electrolyte separator was prepared by coating nano-BaSO4 powder upon the surface of Celgard 2325 separator with PVDF-HFP copolymer as binder, then soaked in the solution of ethanol/water. The test results of thermal shrinkage, electrolyte uptake, stretching, AC impedance show that the properties of PVdF-HFP composite separators were significantly enhanced by the addition of nano-BaSO4 particles. The electrochemical measurements demonstrate that the cycling performance and c-rate performance of the PVDF-HFP gel electrolyte separator containing nano-BaSO4 particles were much better than those of PVDF-HFP gel electrolyte separator without nano-BaSO4 particles.