A robust inorganic coated separator enabled by polyacrylate-modified microsphere binders for high safe lithium-ion batteries

Polyethylene separators (PE) are widely used in lithium-ion batteries due to their good electrochemical stability and low cost. However, PE separators have issues including high-temperature shrinkage and poor electrolyte wettability, which reduce the safety and electrochemical performance of batteries. In this work, we synthesized a large-sized microsphere binder (SNE) and designed an inorganic ceramic/polymer composite coating strategy. The prepared single-layer PE/SNE separator exhibits a unique micro-convex structure, where microspheres with diameters slightly larger than the thickness of the ceramic layer are partially exposed outside the composite coating. The electrodes and separators are hot-pressed to make the microspheres viscoelastic, which effectively bonds the electrodes, prevents sliding, and strengthens the interface to reduce interface impedance. Compared to traditional PVDF-coated ceramic separators, PE/SNE separators feature simple production processes, lower cost, and environmental friendliness. The ceramic-coated optimized PE/SNE separator can maintain shrinkage of <1% at 130 °C/0.5 h and improves the ionic conductivity (0.83 mS/cm) and lithium-ion transference number (t Li +  = 0.62). Due to the optimized hot-pressed interface and improved overall performance of the PE/SNE separator, the NCM622//Li cell has a discharge capacity of 118 mAh/g at 5C, and the NCM622//graphite full cell has a capacity retention rate of 81% after stable cycling for 1500 cycles at 2C. This approach offers a promising method for developing lithium-ion battery separators with enhanced safety and cycling performance.