Investigation Of Silicon/carbon And Li₄Ti₅O₁₂ Anode Materials

With rapid development of hybrid electric vehicle and electric vehicle, electrodematerials of lithium-ion batteries with high energy density, high safity and long cyclic lifetimeare necessary. Silicon/carbon and carbon-coated Li₄Ti₅O₁₂composites were prepared bysolid-state reaction method. The structure and morphology of the composites were studied byXRD, SEM and TEM. Also, the electrochemical performance was investigated by constantcurrent charge/discharge test, cyclic voltammetry and electrochemical impedancespectroscopy.Silicon/carbon composites were fabricated using mesophase pitch as carbon source bysolid-reaction method. The silicon particles of the composites were coated by amorphouscarbon layers. In addition, some bulk amorphous carbon was formed and its content increasedwith increase of the mesophase pitch content in the starting materials. The silicon/carboncomposite obtained from the mass ratio of Si: mesophase pitch=1:3shows the bestelectrochemical properties with the first-cycle discharge/charge capacities of1468.4/1157.4mAh/g and the first-cycle coulombic efficiency of78.8%. The reversible specific capacity canremain656.6mAh/g after30cycles. The capacity retention is56.7％（Silicon+graphite）/carbon composites were prepared by solid-state reaction method. The（silicon+graphite）/carbon composite obtained from the mass ratio of Si: mesophase pitch:graphite=1:2:2exhibits the best electrochemical properties with the first-cycledischarge/charge capacities of924.5/798.6mAh/g and the first-cycle coulombic efficiency of86.1%. The reversible specific capacity can remain653.4mAh/g with the capacity retentionof82.1％after40cycles.Carbon-coated Li₄Ti₅O₁₂composites were fabricated using H2TiO3, Li₂CO₃andmesophase pitch as starting materials by solid-state reaction method. Carbon-coated Li₄Ti₅O₁₂composite without any other impurity phases and displaying the best electrochemicalproperties could be obtained when the excess of Li₂CO₃was3％in the starting materials.The first-cycle discharge capacity of the pure carbon-coated Li₄Ti₅O₁₂composite is161.1mAh/g with the first-cycle coulombic efficiency of98.3％. The reversible specific capacitycan remain156.6mAh/g with the capacity retention of98.9％after70cycles, which showexcellent cyclic performance. The first-cycle discharge capacity of the pure carbon-coatedLi₄Ti₅O₁₂composite is136.6mAh/g at0.5C and the discharge capacity can remain132.2mAh/g after50cycles at the rates of0.5C,1C,1.5C,2C and5C. The capacity retention is96.8%, exhibiting good rate capability.