Study On Preparation And Performance Of Silica-Graphite Composite Anode Material

Industrial raw material silicon oxide(Si O_x,O<x<2)has attracted people's attention due to its high theoretical specific capacity(?2500 m Ah/g)and relatively excellent cycle performance.The most common one is silicon oxide(Si O,x=1),it has been used as anode material for lithium-ion batteries and has shown its great potential.When lithium is inserted for the first time,Si O_x generates inert phases Li₂O and Li₄Si O₄,which can effectively buffer it's volume expansion effect.Compared with silicon anode materials,its cycle stability is improved,but specific capacity and initial coulomb efficiency is reduced.In the application of commercial anode materials,the cycle stability of Si O_x is much lower than that of graphite anode materials,so it cannot be used as anode material independently.Si O_x is usually prepared as a high specific capacity anode material(specific capacity reached 1500 m Ah/g?1600 m Ah/g),then mixed with graphite in a certain proportion to make a composite high specific capacity anode material.In this paper,commercial silicon oxide anode materials,graphite and carbon microspheres are used as raw materials to prepare high-capacity Composite anode materials.The following three aspects are studied:(1)The silicon oxide was mixed with artificial graphite A616KE,ZH-9X,natural graphite N9,and carbon microspheres PG11 through a drum mixer to prepare a composite anode material with a design specific capacity of 430 m Ah/g.Among them,the composite anode material consist of silicon oxide and artificial graphite A616KE has the best electrochemical performance.Under 0.1 C(1 C=430 m A)charge and discharge conditions,the first reversible specific capacity is 432 m Ah/g,the initial coulomb efficiency is 90%,and the capacity retention is 88%after 50 cycles.(2)The material mixing and dispersing process of artificial graphite A616KE and silicon oxide is studied by using roller ball mill,V-type mixer,and VCH high-efficiency mixer.The composite anode material obtained by mixing materials in VCH high-efficiency mixer at 800 r/min for 1 hour has the best electrochemical performance.Under 0.1 C charge and discharge conditions,the first reversible specific capacity is431.5 m Ah/g,the the initial coulomb efficiency is 90.06%,and the capacity retention is 92.3%after 50 cycles.(3)Aiming at the problem that composite material composed of artificial graphite A616KE and silicon oxide has a low initial coulomb efficiency(only 90%),the effect of lithium carbonate(Li₂CO₃)on improving the initial coulomb efficiency of composite materials is studied.The study find that after adding Li₂CO₃ at 2%,2.5%,and 3%of the mass of silicon oxide,the initial coulomb efficiency of the composite materials are increased from 90.06%to 91.3%,92.11%,91%respectively.The 2.5%Li₂CO₃modified composite anode material has the highest initial coulomb efficiency,reached92.11%.Under 0.1 C charge and discharge conditions,the reversible specific capacity drops to 429.3 m Ah/g,and the capacity retention is 92%after 50 cycles.