Synthesis of amorphous carbon materials for lithium secondary batteries.

A new and effective approach to enhance electrochemical properties of amorphous carbons is presented. Phosphorus-doped amorphous carbons have been prepared by incorporating a phosphorus compound into petroleum cokes and carbonizing them at 850 degrees C for 1 h. It was observed that reversible capacity of amorphous carbons was greatly improved by incorporating a very small amount of phosphorus (around 1%), implying that extra lithium-storage-sites were created by phosphorus doping. In addition, the phosphorus-doped amorphous carbons showed outstanding rate capability (205 mA h/g at 5 C) and excellent capacity retention of about 90% after 50 cycles, comparable to that of undoped carbons. Very interestingly, a trade-off relation between capacity and cycle property, which is very common in electrode materials, was not found in the phosphorus-doped amorphous carbons.