Effects of phosphorus content and operating temperature on the electrochemical performance of phosphorus-doped soft carbons

A series of high capacity soft carbons with different phosphorus contents were successfully prepared by carbonizing petroleum cokes treated with hypophosphorous acid at $900^\circC$. The effect of phosphorus content on the electrochemical performance of the soft carbons was extensively investigated. The P-doped soft carbons exhibited greatly enhanced discharge capacities and outstanding rate capabilities with increasing phosphorus content. In addition, the influence of temperature on the electrochemical behaviors of the soft carbons was investigated in a wide temperature range of $25^\circC$ to $50^\circC$. Surprisingly, the electrochemical properties of the pristine and P-doped soft carbons were highly sensitive to the operating temperature, unlike conventional graphite. The pristine and P-doped soft carbons exhibited significantly high discharge capacities of 470 and 522 mAh/g, respectively, at a high temperature of $50^\circC$.