Preparation Of Silicon/Graphite/Carbon Composite Material And Its Application In Full Lithium-ion Batteries

With the high speed development of electronic devices and new energy vehicles, the need of Li-ion batteries with high energy density is growing with each passing day. Silicon-based material has super high energy density, thus it is the perfect material to enhance the anode capacity and full cell capacity.In this paper, we use ball-milling and liquid coating to fabricate the silicon/graphite/carbon composite material. Firstly, we reaserch several types of graphite and their influence towards the composite in small-scale.The reversible specific capacity of battery for the first time is 823 m Ah/g, the initial Coulomb efficiency is 80.4%, and the capacity retention remains 83% after 210 cycles under 0.1C. After changing the stirring equipment, optimizing the ball-milling process and adjusting the program of chamber heater, we amplify the composite fabrication procedure to 1.5 kg. The material of mass production has a more stable property.The reversible specific capacity for the first time is 812 m Ah/g,the initial Coulomb efficiency is 81.6%, and the capacity retention remains 90% after 80 cycles under 0.2C.In this paper, we also prepare silicon/graphite/carbon@graphite composite whichis the combination of silicon/graphite/carbon composite material and commercialized graphite.This material shows great electrochemical properties, the reversible specific capacity of half-cell is 423 m Ah/g, and the capacity retention remains 98.4% after 230 cycles under 0.2C. This material is used as anonde inthe full cell, and its property is studied through dismantling batteries. It is found that one of the main reasons of battery aging is the volume effect of silicon and continuously forming of SEI filmwhich leads to the drying of electrolyte and bulging of batteries. Another reason is that negative electrode can not display its full capacity,and lots of Li dendritic crystal has formed to cause an insufficiency of active Li. After optimization, silicon/graphite/carbon @graphite composite displays a great cycling propertyandthe initial Coulomb efficiency is 90%. This material is also used in the full batteries which has a better cycling performance than commercialized material batteries.Beyond that, we research the solid recombination method to fabricate silicon/graphite/carbon composite, so the dissolving of asphalt is removed to save the cost of time and money. The reversible specific capacity is 774.2m Ah/g and the capacity retention remains 99.98% after 150 cycles under 0.2C.