Overcharging effects

The effect of these ferrocene-based additives on overcharge protection is shown in Figure 44, where AA cells based on lithium, LhMn02, and electrolytes with or without additives were overcharged. In the absence of these redox shuttles (A), the cell voltage continues to rise, indicating the occurrence of major irreversible decompositions within the cell whereas the presence of shuttle agents (B—E) locks the cell potential in the vicinity of their redox potentials... 

Overcharge tests were carried out in LiCo02 cathode half-cells that contained these additives, and a redox shuttle effect was observed between 4.20 and 4.30 V, close to the redox potentials of these additives. The same shuttling effect was observed even after 2 months of storage for these cells, indicating the stability and redox reversibility of these additives. A closer examination of the capacity retention revealed that 4-bromo-l,2-dimethoxybenzene seemed to have the best shuttle-voltage performance for the 4.0 V lithium cell used." The stability of these additives against reductive decomposition was also tested by the authors on metallic lithium as well as on carbonaceous anodes, and no deterioration was detected. 

Zebra batteries have been subjected to a series of tests to demonstrate their ruggedness and safety. These include overcharge, short circuit, overheating and vibration and shock. Drop testing to simulate the effect of a... 

Integral equations theories are another approach to incorporate higher order correlations, and consequently also lead to lowered osmotic coefficients. There are numerous variants of these theories around which differ in their used closure relations and accuracy of the treatment of correlations [36]. They work normally very well at high electrostatic coupling and high densities, and are able to account for overcharging, which was first predicted by Lozada-Cassou et al. [36] and also describe excluded volume effects very well, see Refs. [37] for recent comparisons to MD simulations. 

Applications of Ni/MH batteries include computers, camcorders, cellular phones, communication equipment, variety of cordless consumer products, high rate long cycle life applications, electric vehicles (under development), and so on. Ni/MH batteries are more environmental friendly than Ni/Cd batteries, and they are easy to dispose. Disadvantages of Ni/MH batteries include lower rate capability, poorer charge retention, and less tolerance for overcharge than Ni-Cd batteries. Like Ni/Cd batteries, Ni/MH batteries are also subject to the memory effect a description of this phenomenon can be found in Sect. 7.9.2.2. 

Nickel batteries use P-Ni(OH)2 as electrode material. This material converts to P-NiOOH during the charging process and this rearranges to y-NiOOH when it is overcharged. This last process is accompanied by a significant expansion, because of the difference in density between P-NiOOH and y-NiOOH, which may result in poor electric contact between the current collector and P-Ni(OH)2/p-NiOOH, with concomitant decrease in the discharge capacity of the battery. Among others, layered double hydroxides of Ni and other metals, often termed stabilized a-Ni(()H), or doped Ni(0H)2, have been tested as electrode materials (Bernard et al., 1996). The effect of the interlayer anions on the electrochemical performance of layered double hydroxide electrode materials has been recently studied by Lei et al. (2008) (see Chapter 6). 

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