Lithium insertion in carbons prepared from phosphorus-containing polymers

Phosphorus-containing carbon has been prepared by the pyrolysis of phenolic resin containing chemically bonded phosphorus atoms, which is synthesized through the esterification of phenolic hydroxyl group by phosphoric acid. T he electrochemical insertion of lithium in as-prepared carbon is also inves tigated. II is found that, at a pyrolysis temperature of 500 degreesC, the addition of phosphoric acid in the precursor lowers the reversible capacity of the resultant carbon, but at 900 degreesC, the addition of phosphoric a cid in the precursor resin increases the reversible capacity of resultant c arbon. Especially, the phosphorus-containing carbon prepared by the above m ethod at 900 degreesC gives a capacity beyond the theoretical value of grap hite and reasonable discharge/charge curves. The phosphorus-containing carb on prepared by the pyrolysis at 500 degreesC shows a similar electrochemica l behavior to that of pure carbon and the effect of phosphorus atoms is lit tle. Its reversible capacity is mainly determined by the content of hydroge n atoms rather than phosphorus atoms. However, at a relatively high pyrolys is temperature, 900 degreesC, more phosphorus atoms are bonded with carbon atoms and are introduced to the microcrystallite structure of carbon. Hence , phosphorus element exerts a strike effect on the electrochemical behavior of carbon and, because of its different electronic effect from carbon elem ent, more lithium species are inserted into carbon matrix. (C) 2001 Elsevie r Science B.V. All rights reserved.