Preparation Of Silicon/Carbon/Graphite Composite Particles And Its Performance In Batteries

With the promotion of the concept of sustainable development and the rise of the new energy vehicle industry,the development direction of lithium-ion battery anode materials tends to be high capacity,high rate and high stability.Silicon is considered to be one of the most promising anode materials.Most research focus is on improving the damage of electrode structure caused by the volume change in the process of lithium embedding and release,and preventing the recombination of SEI membrane caused by expansion and contraction and the continuous consumption of electrolyte and lithium source.In this paper,the composite of silicon/carbon and graphite materials with various morphologies are prepared by different methods,and the influence of graphite on properties of silicon particles with bigger size as the anode of lithium-ion batteries is studied.The main work included:(1)Silicon/carbon/graphite composite particles were prepared by combining chitosan solution with four different types of graphite using cutting waste of crystal silicon photovoltaic cells as silicon raw material.The effects of graphite type on the morphologies and electrochemical performance of the composite were compared and analyzed.After the combination of graphite and silicon particles,the specific chargedischarge capacity of the anode is significantly higher than that of graphite anode.The charge and discharge characteristics of silicon particles composited with artificial graphite G-A are the most stable,and the specific capacity retention rate can reach 81%after 100 cycles.(2)Silicon/carbon/graphite composite particles SCGP and SPG are prepared by spray granulation using chitosan and water-based polyurethane resin as bonding carbon between G-A graphite and silicon particles.The effect of the bonded carbon on the morphology and electrochemical stability of composite particles is investigated.The results show that the charge-discharge stability of submicron silicon particles is significantly improved under the coating and support of carbon and graphite.After the addition of graphite,the charging and discharging capacity of SCGP2(550-580 m Ah/g)is similar to that of SCP without graphite,and the capacity retention rate increases from 45.82% to 87.94% after 100 cycles.The viscosity of water-based polyurethane resin is low to form a thin carbon layer on the surface of silicon,so that the charge and discharge specific capacity of SPU is higher and even to 1018.4 m Ah/g after 100 cycles.Meanwhile,the charge and discharge capacity retention rate is below76.1% due to the lower adhesion between silica and graphite based on thin carbon layer.(3)Silicon/carbon/graphite composite SCG is prepared by hydrothermal method using chitosan as bonding carbon between G-A graphite and silicon particle.Under the action of high temperature and high pressure,the connection between silicon and graphite is strengthened by the pyrolytic carbon,so as to improve the specific capacity and electrochemical stability of the silicon-based composite anode.The first chargedischarge specific capacity of SC(without graphite)can reach 1081.9 m Ah/g and1163.6 m Ah/g,and its initial coulombic efficiency(ICE)is 92.98%.The specific capacity of SC can maintain 67.52% after 100 cycles.The charge specific capacity of SCG0.25(with a small amount of graphite)can maintain to 747.7 m Ah/g after 100 cycles,whose capacity retention rate is up to 90.88%.As a result,the silicon particles of big size coated by pyrolytic carbon adhere to the surface of the graphite particles,which can alleviate the stress caused by the expansion of silicon during the alloying process of lithium-silicon,and effectively improve the cycle performance of the battery.