Li-insertion in hard carbon anode materials for Li-ion batteries.

'Non-graphitizable' or 'hard' carbon anode materials for Li-ion batteries have many advantages and disadvantages when compared to graphitic materials such as mesocarbon micro-beads (MCMB). The advantages include higher capacity (per unit mass) [Yamada et al., United States Patent No. 5,834,138 (1998); Buiel et al., J. Electrochem. Sec. 147(2) (1988) 2252-2257; Buiel and Dahn, J. Electrochem. Sec. 145(6) (1998) 1977-1981], higher cycle life [Omaru et al., United States Patent No. 5,451,477 (1995)], good rate capabilities [Rakotondrainibe et al., In: Proceedings of the 194th Meeting of the Electrochemical Society. Abstract No. 83. 1-6 November 1998] and lower cost of production. The disadvantages that must be resolved before a successful material can be commercialized are the low density, incompatibility with current coating technologies, larger irreversible capacity and hysteresis in the voltage profile [Buiel and Dahn, J. Electrochem. Sec. 145(6) (1998) 1977-1981]. Some reports have suggested that the problem of low density can be solved using composite anode materials consisting of a mixture of hard carbon and MCMB. These composites also boast higher rate capabilities and longer cycle life when compared to pure MCMB. In this paper, reducing the hysteresis in the voltage profile and reducing the irreversible capacity of hard carbons is the primary focus. In order to achieve this goal, a study of the electrochemistry and structure of promising hard carbon materials is presented and correlated to various parameters that can be adjusted during synthesis. (C) 1999 Elsevier Science Ltd. All rights reserved.