| Graphite anode materials occupy almost the whole field of anode materials for lithium-ion batteries because of their high capacity,stable cycling performance,close to lithium metal’s lithium-ion separation platform and low cost,however,its poor rate performance limits its further development and utilization.Therefore,the key to maintain the dominant position of graphite in the field of anode materials is to develop anode materials suitable for fast charge discharge lithium-ion batteries.On the other hand,the theoretical specific capacity of graphite material is gradually unable to meet the requirements of the constantly developing new high energy density lithium-ion batteries.Therefore,the development of new anode materials with high specific capacity is another important development direction of the current lithium-ion anode materials.The theoretical specific capacity of silicon-based anode is much higher than that of graphite anode,which is a promising direction to develop high energy density anode materials.Therefore,starting from the preparation process of artificial graphite,this paper explored the influence of many factors in the preparation process on its performance,and finally modified by nano carbon conductive agent,graphite anode material with excellent performance was obtained.In the second step,the anode material with high specific capacity was prepared by combining it with silicon-carbon material,and the following results were obtained:（1）Using needle coke as main raw material,pitch as binder and nano carbon material as additive,the artificial graphite was obtained by dry powder granulation in high temperature coating kettle,carbonization and graphitization.The effects of graphitization temperature,carbonization temperature,carbonization time,the ratio of raw material and pitch,the particle size of artificial graphite and the addition of different kinds of nano carbon conductive agent on the properties of artificial graphite were investigated.Finally,when the mass ratio of needle coke to pitch is 0.85:0.15,1.5%CNTs+1.5%Li435 is added,carbonized at 1100℃for 12 h and graphitized at 2900℃,the artificial graphite anode with particle size of 14～15μm has the best performance.The first charge specific capacity is 333.19 m Ah g-1,the first coulomb efficiency is90.11%,the cycle retention rate is 100.3%after 100 cycles,and the rate performance is improved by 5～10%.（2）The anode material of lithium-ion battery obtained by combining silicon material with the artificial graphite and coating it with asphalt and glucose has higher specific capacity,better ratio and cycling performance.After characterization,it is found that the thin carbon layer obtained by carbonization on the surface of the composite material can improve the electrical conductivity of the material,and is beneficial to weaken the expansion of particles,and help improve the performance of lithium insertion and delithium properties of the silicon carbon material.At the same time the artificial graphite occupies the main body of the composite material has better rate and cycling properties.The composite material test results obtained under different conditions found that when the adding mass of asphalt accounted for 15%show that the silicon carbon composite obtained at 900℃has the best electrical properties,and the experiment shows that the interface resistance of silicon carbon material is the lowest at this temperature.The first reversible capacity of the current is 436.42 m Ah g-1,and the capacity retention rate of60 weeks is 89.99%.The addition of asphalt can modify the surface of silicon carbon material and improve the electrochemical properties of the material effectively.In addition,in this paper,silicon,graphite and glucose as raw materials,through high temperature carbonization,preparation of surface coating modified silicon-amorphous carbon-graphite composite material and carbonization at high temperature,TEM,SEM and cyclic charge discharge were used to test the structure and electrical properties of the composites.The results show that the hard carbon layer obtained by carbonization can modify the surface of the material to improve the properties of the material.When the mass of glucose is 10%of the mixture and the carbonization temperature is 700℃,the electrochemical performance is the best.The reversible capacity is456.96 m Ah g-1,the first coulomb efficiency is 79.15%,after 40 weeks of constant current charging and discharging,the capacity retention rate was 88.69%.In order to optimize the properties of the silicon-carbon material,artificial graphite with matching particle size is used to composite with silicon carbon,using asphalt to knead and glucose to coat,silicon-carbon-graphite composites with more stable properties were obtained.The specific capacity of the first discharge reaches more than 600 m Ah g-1,excellent rate performance and the capacity retention rate is more than 80%after 300 weeks of 3C cycle. |
