Preparation And Performance Research Of Silicon Carbon Negative Electrode Surface Modified Film

With the rapid development of electric vehicles(EVs)and smart grids,higher requirements have been placed on next-generation lithium-ion batteries with high energy / power density,long cycle life,and low manufacturing costs.Silicon-based anode materials have been considered one of the most promising alternatives to commercial graphite anodes,which have ultra-high theoretical specific capacities and low operating potentials.However,the inherent poor conductivity of silicon-based anode materials,unstable solid electrolyte membrane,and volume expansion problem of up to 300% have restricted the widespread application of silicon-based anode batteries.In this dissertation,the problem of volume expansion of silicon-based batteries is alleviated by constructing a surface modification layer on the silicon carbon negative electrode sheet.The effects of two different modified films on silicon-based batteries were studied.The electrochemical performance and structural performance were characterized.The results show that the development of modified interface films can improve the stability of silicon-based batteries to a certain extent.The modified layer of dopamine was obtained on the silicon carbon negative electrode sheet through a simple infiltration process,and different modified electrode sheets were prepared by controlling the reaction time of self-polymerization.Electrochemical test results show that when the self-polymerization reaction time is 40 minutes,its long-cycle stability,rate performance and impedance performance are optimal.X-ray photoelectron spectroscopy,transmission electron microscopy,and scanning electron microscopy characterization also prove that the modified dopamine layer promoted the formation of a uniform and dense SEI film,and reduced cracks on the electrode surface,thereby reducing electrode crushing.Different modified electrodes were obtained by spin coating a mixed solution of PEO and LiTFSI with different mass fractions on the surface of the silicon carbon negative electrode sheet.The comparison of the electrochemical performance of the blank electrode sheet and the modified electrode sheet assembled battery shows that the electrochemical performance of the modified electrode is better than that of the blank electrode,and the performance is best when the mixed solution has a mass fraction of 3%.On this basis,the structure morphology and elemental analysis were performed on it.The polymer modified membrane of the modified electrode can buffer the volume expansion during battery cycling,greatly reduce the volume effect,and can form a stable SEI membrane.