Lithium negative electrode

This is a common problem when using elemental lithium negative electrodes in contact with electrolytes containing organic cationic groups, regardless of whether the electrolyte is an organic liquid or a polymer [4]. 

Cases exist, however, where for fundamental reasons aqueous solutions cannot be used. One such case is that of devices in which electrochemical processes take place at elevated temperatures (above 180 to 200°C) for example, the electrowinning of aluminum performed at temperatures close to 1000°C. Another case is that of devices in which electrodes consisting of alkali metals are used, which are unstable in aqueous solutions, such as batteries with a lithium negative electrode. 

SOME THERMODYNAMICS AND KINETICS ASPECTS OF THE GRAPHITE-LITHIUM NEGATIVE ELECTRODE FOR LITHIUM-ION BATTERIES... 

Cells were manufactured at AA size with a rated capacity of 0.6 Ah. Fig. 7.25 shows a cut-away drawing of a Molicel battery, and Fig. 7.26 shows a typical cycling performance. Despite a cycle life of over 400 and an energy density of 50 Wh/kg, safety hazards were identified which were associated with the lithium negative electrode, especially when the cell was abused. 

Morita M, Matsuda Y. Effects of alloying substrates on the characteristics of the lithium negative electrode. J Power Sources 1989 26 573-578. 

F yrolysis of gaseous hydrocarbons at 1000-1700 °C is a common route (cf. Nos. 6 and 7 in Table 9, where two examples involving benzene are considered [441, 442]). The substrate was nickel, and dense black layers were obtained to serve as a host lattice for the lithium negative electrode. The pyrolytic carbon from benzene at 1000 °C gave a lithium GIC (CeLi) and could be cycled at 99% current efficiency [407]. Pyrolysis of epoxy Novolac resin and epoxy-functionalized silane gave a material containing silicon with a capacity of 770 mAh/g for the lithiated form [443]. 

The highest energy density could be achieved with lithium-metal electrodes. The first section (a) of Table 10 is devoted to such systems. It should be mentioned that the examples given there are partly a matter of historical development, e.g., earlier r.b.s with a lithium negative electrode would be built today with the more stable negative electrodes of the LiAl or LiCg type cf. sections (b) and (c) of Table 10. 

Polyaniline is frequently used in r.b.s with lithium negative electrodes. However, in the course of the development of a commercialized system (Seiko/Bridgestone), there have only been a few examples with true lithium-metal negative electrodes, but many for the more practical LiAl alloy electrodes. The redox processes of RANI are basically the same in aqueous electrolytes and in Li -containing organic solutions. 

Most proposed battery types employed lithium-negative electrodes. In such batteries the electrolyte must contain a lithium salt and the electrode processes on the lithium electrode consist of simple transfer of the lithium ions from the crystal lattice of the metal to the melt and back. 

Figure 2.2 shows the discharge of a test secondary battery with capacity 2.5 mAh with a Li2Ti30y positive electrode facing a metal lithium negative electrode. Discharge takes place with a C/5 current with a one-hour pause every 4.76% of discharge. 

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). 

For the last quarter century, almost every battery company in the world has conducted an R and D programme targeted to the development of batteries with a lithium negative electrode. This very high level of activity resulted from the... 

Solid-cathode cells using intercalation compounds for the positive electrode, a liquid organic electrolyte, and a metallic lithium negative electrode. 

The capacity of a thin-film LiCo02 battery with an in-situ electroplated lithium negative electrode cycled at high rate (4C charge, 20C discharge) is illustrated in Fig. 35.114. As shown, the fade rate was 0.02%/cycle, comparable to that typical for cylindrical C/LiCo02 batteries cycled at the 1C rate. 

FIGURE 35.112 Battery voltage for a solid-state thin-film LiCoOj battery with an in-situ electroplated lithium negative electrode. Courtesy of Oak Ridge National Laboratory. Reproduced by permission of The Electrochemical Society, Inc. From Ref. 100.)... 

The term lithium battery is now used to describe a large family of batteries whose only common feature is the lithium negative electrode. The major differences involve the choice of the electrolyte medium and of the positive electrode chemistry but there is also a range of designs, sizes and materials of construction which use a variety of separators. 

Additives such as methyl acetate (MA), toluene, and y-butyrolactone (GBL) have been studied for their effects on capacity and cycleabiUty [17, 129]. Only toluene improves both the initial capacity and cycleability owing to its capabiHty of forming a stable electrode/electrolyte interface [124, 129]. ImidazoHum salts, when introduced into the mixed DME-DOL electrolytes, are reported to improve the cycleability by enhancing the electrochemical reaction of polysulfides and improving the stability of the lithium negative electrode [122]. Addition of tetrabutylam-monium hexafluorophosphate (TBAPFg) into the electrolyte shows a comparable effect [113]. 

---