Abstract:

Magnetron sputtering technology was used to deposit SiO₂ and AlF₃ ceramic particle layers with a thickness of 200 nm on both sides of a polypropylene (PP) separator. The preparation of a SiO₂/PP/AlF₃ functional separator prevents the pitfalls of increased thickness and decreased porosity caused by traditional coating methods. In general, SiO₂ and AlF₃ ceramic particles have excellent mechanical properties and chemical stability, properties which can improve the heat resistance of a polyolefin (PP) separator. In addition, the nonpolar SiO₂ and AlF₃ can synergistically improve the affinity of the separator to the electrolyte, thereby promoting the conductivity of lithium ions and reducing the internal resistance of the battery. In addition, the strong Lewis acidity and low surface energy of AlF₃ effectively suppresses the decomposition of the electrolyte and the growth of lithium dendrites, improving the electrochemical performance and safety of lithium-ion batteries. The modified separator was characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), differential scanning calorimetry (DSC), and X-ray photoelectron spectroscopy (XPS). The porosity, electrolyte affinity, and electrochemical performance were also measured. The results show that magnetron sputtering has little impact on the thickness and porosity of the modified separator. The lithium-ion battery with a SiO₂/PP/AlF₃ separator has an initial discharge specific capacity of 164.98 mA·h/g at 0.2 C, a specific capacity of 154.87 mA·h/g after 50 cycles, and a cycle decay rate of 0.12%. The battery prepared with a SiO₂/PP/AlF₃ separator has a discharge specific capacity of 102.07 mA·h/g at a high current density of 5.0 C. Overall, the cycle and rate performance were significantly better than batteries with a traditional PP separator. The application of a SiO₂/PP/AlF₃ functional separator has the potential to inform the development of high-performance lithium-ion batteries.

Key words: magnetron sputtering, battery separator, coating, SiO₂, AlF₃, lithium ion battery