Study On Preparation And Electrochemical Performance Of Si/C Composite Anode Materials For Lithium Ion Batteries

Silicon is considered to be one of the most promising anode materials for the next-generation lithium-ion batteries due to its high theoretical specific capacity and suitable potential for lithium insertion/extraction.However,there are also some disadvantages of silicon material such as the huge volume effect during the charging/discharging process,which will lead to the broken of silicon particles and the result in the poor electrical connection between active material and substrate.The reversible specific capacity and the performance of the electrode will decrease rapidly.Moreover,the low electronic conductivity of the silicon material will result in poor rate performance.To solve the above-mentioned problems,several specific methods are proposed in the paper to prepare Si/C composite with excellent performances.Si/C composite was prepared by mechanical ball milling combained high-temperature pyrolysis using nano-silicon,flake graphite and phenolic resin as raw materials.The influence of pyrolysis temperature,ball milling time,ball milling speed and silicon content on the properties of the composites was investigated.The test results show that the composite exhibit the superior properties when the pyrolysis temperature is 750?,the milling time is 8 h,the milling speed is 300 r/min,and the silicon content is 10%.Under optimized conditions,the first reversible capacity of Si/C composites is 743.7 mAh·g^-1,and the reversible capacity remains 569.2 mAh·g^-1after 50 cycles with a capacity retention of 76.5%.The composite also show good rate performance,exhibiting a reversible capacity of 662.9 mAh·g^-1 under a current density of 500 mA·g^-1.Annealing treatment was introduced to improve the performance of Si/C composite.SEM results show that a more dense morphology and complete structure were obtained after 50 cycles.Electrochemical test results show that the cyclic stability of the composites was improved after annealing.The initial charge capacity is 717.3 mAh·g^-1 and maintains 615.8 mAh·g^-1 after 50 cycles with the capacity retention up to 85.8%.In addition,the effect of different binders on the properties of Si/C composites was also studied.SEM results show that the structure of the electrode is more stable before and after the cycle when using LA133 as the binder.Electrochemical test results show that the composite with LA133 as a binder exhibits the best electrochemical performance.The initial reversible capacity of Si/C composites is 660.4 mAh·g^-1,and a reversible capacity of 613.9 mAh·g^-1 with a capacity retention of 92.9%was obtained after 50 cycles.Based on the previous studies,Si/SiO₂/C composite anode materials were prepared by mechanical ball milling combained high temperature pyrolysis.The effect of different types of SiO₂ and different SiO₂ addition on the properties of the composites was investigated.The results illustrate that the as-prepared Si/SiO₂/C composites exhibit good electrochemical performance while adding 5%SiO₂ with the diameter of 30 nm.The cycle performance of the composite is very stable.The first reversible capacity is 634.6 mAh·g^-1,and the reversible capacity of the composite is698.4 mAh·g^-1 after 50 cycles.The EIS impedance test shows that the charge transfer impedance of the composite does not change significantly with the circulation,indicating that the structure of the composite is very stable.