Akiyoshi Morita

High voltage, rechargeable lithium batteries using newly-developed carbon for negative electrode material

Abstract Carbon is a good candidate for negative electrodes because it can take the form of lithium intercalation compounds. We discussed the characteristics of typical carbon materials which have been studied as negative electrode materials. We have found that the mesophase pitch-based carbon microbead (MCMB) of high graphitization stage which have been graphitized at a high temperature such as 2800 °C gives good characteristics as a negative electrode for rechargeable lithium batteries. The cylindrical ‘AA-size’ batteries of our trial products using LiCoO2 as the positive electrode and the MCMB graphitized at 2800 °C as the negative electrode have been found to provide large capacities of 500 mA h and high voltages of 3.7 V with high energy densities of 240 W h/l, 100 W h/kg.

Evaluation of cathode materials for the lithium/ carbonmonofluoride battery

Abstract The lithium—carbonmonofluoride (CF)n system is one of the most promising systems for high energy density primary batteries and is described in this paper. In this system, discharge performances mainly depend on cathode materials, (CF)n, prepared by fluorinating various carbon materials at moderate temperatures. Two kinds of active carbons, graphite and coke, were chosen and tested in cells to determine the best carbon material for the carbonmonofluoride cathode. The (CF)n cathode made of coke has been shown to have excellent discharge performances, good storage behavior, and an energy density of 140 W h/kg in small button cell sizes.

Effects of an additive material, CuFeS2, on Li/CuO battery performance

Abstract The discharge characteristics of the Li/CuO system have been improved by adding chalcopyrite (CuFeS x , 1.6 x ≤ 2) to the cathode. The chalcopyrite was thermally prepared from iron disulfide and cuprous sulfide. The open-circuit voltage of synthetic chalcopyrite was ∼ 0.2 V lower than that of cupric oxide. Chalcopyrite shows no voltage depression when discharged and only causes a relatively small increase in the cell thickness on its discharge. Both chalcopyrite and cupric oxide have a low solubility in the organic electrolyte. In summary, a cathode system composed of cupric oxide and chalcopyrite has the following properties: a brief excursion to the plateau voltage, no voltage depression at the beginning of discharge, only a small increase in the cell thickness, and a good storage life. Button cells using this system have been successfully developed for electronic devices.