Anode property of boron-doped graphite materials for rechargeable lithium-ion batteries

Anode properties of boron-doped graphites were investigated by means of electrochemical measurements. A discharge capacity of about 315 mAh/g was obtained for 3.8 mass% boron-doped pitch coke-derived graphite in galvanostatic measurements. Increased discharge capacity for boron-doped graphite compared with boron-free one was considered to be mainly due to the enhanced graphitization by boron. Also, in this measurements, a shoulder was observed at 1.3 V (vs. Li/Li+) in boron-doped graphites. This peculiar reaction was confirmed to be the diffusion control and reversible process by the cyclic-voltammogram measurements, and it occurred before intercalation of lithium-ion into graphite-layers in charge process and after deintercalate of lithium-ion from graphite layers in discharge process. These phenomena are inferred to be explained as that the lithium atom can be trapped easily to boron solid-solution phase due to the valence band hole created by boron. This capacity existed at high potential is probably worthwhile for the utilization as the signal of the ending of discharge process to prevent over-discharging in rechargeable lithium-ion batteries.