High-capacity disordered carbons derived from peanut shells as lithium-intercalating anode materials

We report for the first time initial lithium intake capacities for pyrolytic carbonaceous materials far exceeding even the theoretical value for metallic lithium. The carbonaceous materials were synthesized by pyrolysis of peanut shells under argon. Thermal conditions for the pyrolysis were optimized in order to obtain materials with desirable electrochemical properties. Peanut shells carbonized in a two-step process that occurred between 300 and 600 degreesC. The shells were also treated with a proprietary porogenic agent with the goal of altering the pore structure and surface area of the pyrolysis products. Both the untreated and the porogen-treated shells yielded carbons with poor crystallinity, although the surface area and the pore diameter of the latter registered a 66-fold and two-fold increase, respectively, over the former. Both the carbons had a predominance of non-parallel single sheets of carbons, as determined by the values of their R factors. Charge-discharge studies showed that although the capacities registered with carbons from the untreated shells varied with the H/C ratio, it was generally reasonable to relate the high initial capacities (in some cases as much as 4765 mAh/g) to the extra surface area of unorganized single layers of carbon and nanoscopic cavities generated by the pore-former. It is also believed that the 'extra' capacity may stem from lithium interaction with surface groups and from lithium plating on the carbon surface and subsequent passivation. (C) 2003 Elsevier Science B.V. All rights reserved.