Fabrication and Characterization of Pitch/Cokes/Natural Graphite Composites as Anode Materials for High-Power Lithium Secondary Batteries

In order to prepare anode materials for high power lithium ion secondary batteries, carbon composites were fabricated with a mixture of petroleum pitch and coke (PC) and a mixture of petroleum pitch, coke, and natural graphite (PC-NG). Although natural graphite has a good reversible capacity, it has disadvantages of a sharp decrease in capacity during high rate charging and potential plateaus. This may cause difficulties in perceiving the capacity variations as a function of electrical potential. The coke anodes have advantages without potential plateaus and a high rate capability, but they have a low reversible capacity. With PC anode composites, the petroleum pitch/cokes mixture at 1: 4 with heat treatment at 1000 degrees C (PC14-1000C) showed relatively high electrochemical properties. With PC-NG anode composites, the proper graphite contents were determined at 10 similar to 30 wt.%. The composites with a given content of natural graphite and remaining content of various petroleum pitch/cokes mixtures at 1: 4 similar to 4: 1 mass ratios were heated at 800 similar to 1200 degrees C. By increasing the content of petroleum pitch, reversible capacity increased, but a high rate capability decreased. For a given composition of carbonaceous composite, the discharge rate capability improved but the reversible capacity decreased with an increase in heat treatment temperature. The carbonaceous composites fabricated with a mixture of 30 wt.% natural graphite and 70 wt.% petroleum pitch/cokes mixture at 1: 4 mass ratio and heat treated at 1000 degrees C showed relatively high electrochemical properties, of which the reversible capacity, initial efficiency, discharge rate capability (retention of discharge capacity in 10 C/0.2 C), and charge capacity at 5 C were 330 mAh/g, 79 %, 80 %, and 60 mAh/g, respectively.