Lithium-carbon negative electrodes

Whereas there had been a significant amount of work on the properties of lithium alloys in the research community for a number of years, this alternative did not receive much attention in the commercial world until about 1990, when Sony began producing batteries with lithium-carbon negative electrodes. Since then, there has been a large amount of work on the preparation, structure, and properties of various carbons in lithium cells. 

In the lithium-ion secondary battery, which was put on the market in 1990, the difficulty of the Li+/Li electrode was avoided by use of a carbon negative electrode Cy), which works as a host for Li+ ions by intercalation. The active material for the positive electrode is typically LiCo02, which is layer-structured and also works as a host for Li+ ions. The electrolyte solutions are nearly the same as those used in the primary lithium batteries. A schematic diagram of a lithium-ion battery is shown in Fig. 12.2. The cell reaction is as follows ... 

Switching to lithium-alloy negative electrodes, some voltage loss must be noted. LiAl has Uu = -1-385 mV, Li4.5Pb has Uu = 388 mV. Entries 18-20 in Table 10(b) represent three examples of rechargeable cells, which have been, at least temporarily, commercialized. The first (No. 18) is due to a lithium alloy/carbon black battery conunercialized by the Matsushita Co. [248]. The lithium alloy components are Pb -I- Cd -I- Bi -h Sn (Wood s alloy). Button cells in the range 0.3 to 2.5 mAh were offered. The electrolyte was LiC104 in an unknown solvent. The practical energy densities, 2Wh/kg, were rather low. The c.b. positive electrode acts as a double... 

Ishikawa M, Sugimoto T, Kikuta M, et al. Pure ionic liquid electrolytes compatible with a graphitized carbon negative electrode in rechargeable lithium-ion batteries. J. Power Sources. 2006. 162, 658-662. 

V versus Lf/Li (case of a metal lithium negative electrode) or 4.18V versus C/LiCg (case of a lithiated carbon negative electrode in lithium-ion secondary batteries). 

As with primary lithium batteries, a number of different approaches have been taken in the chemistry and design of rechargeable lithium batteries to obtain the desired performance characteristics. These are summarized in Fig. 34.1a for batteries with lithium metal negative electrodes (the anode during discharge) and in Fig. 34.1fc for batteries with other materials, such as lithium alloys and lithiated carbon. ... 

FIGURE 34.1 Lithium rechargeable batteries (a) with metalUc lithium as negative electrode, (b) with lithium alloys or lithiated carbon negative electrode. 

Carbon materials which have the closest-packed hexagonal structures are used as the negative electrode for lithium-ion batteries carbon atoms on the (0 0 2) plane are linked by conjugated bonds, and these planes (graphite planes) are layered. The layer interdistance is more than 3.35 A and lithium ions can be intercalated and deintercalated. As the potential of carbon materials with intercalated lithium ions is low, many studies have been done on carbon negative electrodes [69-72]. 

For graphitic carbon, as mentioned in Section Z4.2.2, PC is usually not regarded as an ideal electrolyte solvent therefore, EC-based electrol5de solution is commonly used. However, the melting point of PC (-49°C) is lower than that of EC (38°C) [1]. In order to broaden the application fields of liquid electrolyte-based lithium-ion batteries, one should try to improve their performance at low temperatures such as -30°C. One may achieve this by coating with additional carbon. There is still some room for the enhancement of the reversible capacity of carbon negative electrode materials, and coating with additional carbon is one possible choice. 

Wu, YP, Rahm, E., Holze, R. 2003. Carbon negative electrode materials for lithium ion batteries. 1. Power Sources 114 228-236, and references therein. 

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