Lithium insertion into boron containing carbons prepared by co-pyrolysis of coal-tar pitch and borane-pyridine complex

Carbon materials of boron content ranging from 0.6 to 4 wt.% were synthesized by co-pyrolysis of QI-free coal-tar pitch with the borane-pyridine complex. The growing amount of boron introduced into the carbonaceous material is associated with an increase in nitrogen content and a progressive degradation of structural and textural ordering. The structural variations of the boron-doped materials on heat treatment up to 2500 degreesC were monitored using X-ray diffraction and X-ray photoelectron spectroscopy. The intrinsic boron acts effectively as a catalyst of graphitization above 2100 degreesC. The carbonaceous material with boron content of about 1.5 wt% shows the highest degree of structural ordering after thermal treatment. A high amount of oxygen was found in the graphitized boronated carbons, proving that the incorporated boron induces a strong chemisorption activity of the material when exposed to air. For a series of cokes calcined at 1000 degreesC, the most striking effect of increasing the boron content is an increase of irreversible capacity X-irr from 0.2 to 0.7. The reversible capacity (X-rev) amounts to about 1, with a slight tendency to decrease with the boron content. Upon increasing the temperature up to 2500 degreesC, X-irr decreases to about 0.1 in the graphitic carbons, while X-rev reaches a minimum of 0.4-0.5 at 1700 degreesC and next increases to a value close to 1 at 2500 degreesC. In the boron doped graphite, X-irr has a slight tendency to increase with the boron content, due to the simultaneous presence of nitrogen in these materials and their strong affinity for oxygen from the atmosphere. (C) 2003 Elsevier Ltd. All rights reserved.