Alternative materials for negative electrodes in lithium systems

There is interest in the feasibility of the replacement of the lithium-carbons that are currently employed as negative electrode reactants in lithium systems. Possible improvements might involve the ability to operate safely at higher current densities, less first cycle irreversible capacity loss, better cycling behavior, reduced specific volume, and lower cost. The surprise announcement by Fujifilm on the use of convertible oxide materials in lithium negative electrodes a few years ago has led to growing interest in possible alternative materials. In addition to oxides, other convertible precursors are being considered for this purpose, including metal alloys and semiconductors, A disadvantage of this approach is the need for extra internal lithium-containing material within the cell, However, it is also possible to do the conversion of these precursors outside of the electrochemical cell to alleviate this problem. Binary and ternary metal-metal alloys are also being considered as negative reactants, with efforts to reduce volume changes that contribute to capacity losses during cycling. A recent model explains the mechanism of decrepitation and the observation of a critical minimum particle size. This helps explain one of the advantages of the use of very fine particles. A different approach is the consideration of metal-metalloid alloys, including nitrides, borides, and silicides. In some cases, their relatively light weight mean that it is not necessary that they react with large amounts of lithium to achieve attractive specific capacities. This leads to less mechanical distortion, and potentially to better behavior upon cycling. The advantages and disadvantages of these several approaches will be discussed, and an overview of the critical parameters of some of the more attractive candidates is presented. (C) 2002 Elsevier Science B.V. All rights reserved.