High rate capability of carbonaceous composites as anode electrodes for lithium-ion secondary battery

Anode materials with high rate capability for Li-ion secondary batteries were investigated by using the mixture of graphite, cokes, and petroleum pitch. Since obvious potential plateaus were obtained at graphite contents above 40 wt.%, which would cause difficulties in perceiving the capacity variations as a function of electrical potential, the graphite content were determined at 20–30 wt.%. The composites with a given content of graphite and remaining content of petroleum pitch/cokes mixtures at 1:4, 1:1, and 4:1 mass ratios were heated at a temperature range of 800–1200 ${^{\circ}C}$. For a given composition of carbonaceous composite, the discharge rate capability improved but the reversible capacity decreased with increasing the heat treatment temperature. Although the reversible capacity increased with increasing content of the petroleum pitch for given graphite content and heat treatment temperature, the discharge rate capability decreased. The carbonaceous composites prepared by the mixture of 30 wt.% graphite and 70 wt.% petroleum pitch/cokesmixture at 1:4 mass ratio with the heat treatment at 800 ${^{\circ}C}$ showed relatively high electrochemical properties, of which reversible capacity, initial efficiency, discharge rate capability (retention of discharge capacity in 5 C/0.2 C) and charge capacity at 5 C were 312 mAh/g, 79%, 89% and 78 mAh/g, respectively.