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

Abstract

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 °C were monitored using X-ray diffraction and X-ray photoelectron spectroscopy. The intrinsic boron acts effectively as a catalyst of graphitization above 2100 °C. 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 °C, 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 °C, X irr decreases to about 0.1 in the graphitic carbons, while X rev reaches a minimum of 0.4–0.5 at 1700 °C and next increases to a value close to 1 at 2500 °C. 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.