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The formation of LiOH and Li 2 CO 3 impurities on high Ni content LiNi 0.83 Co 0.15 Al 0.02 O 2 powders due to H 2 O and CO 2 absorption from the air can be reduced without structural degradation by washing in water. Although the as-synthesized sample had a moisture content of 570 ppm immediately after firing, this level increased rapidly to 1270 ppm in air with a relative humidity of 50%. However, its content was decreased to 210 ppm after washing twice in water, followed by heat-treatment at 700°C. It is believed that this improvement was due to the decreased level of Li 2 CO 3 and LiOH impurities on the particles. This was highlighted by the decreasing swelling of the Li-ion cell at 90°C, and the thickness of the cell containing the washed samples was decreased by 50% compared with the bare sample.Since the 1200 mAh Li-ion cell in a cylindrical 18650R size was developed in 1991, its capacity has been increasing by 7-10% each year, and a 2400 mAh Li-ion cell was commercialized in 2004. Despite the fact that the electrode materials used were graphite and LiCoO 2 , the capacity has increased by 100% compared with the capacity 12 years ago. The achievement of such a high capacity was made possible by the maximum utilization of the dead spaces within the cell, decreasing the amount of binder and conducting agents, and using LiCoO 2 with a high electrode density 3.7 g/cm 3 . However, increasing the capacity beyond 2400 mAh can only be made possible using new high capacity active materials, such as Si, Sn, or LiNi 1−x−y Co x Mn y O 2 with a 4.2 V cutoff. 1-5 One of the fundamental problems of the LiNi 1−x−y Co x Mn y O 2 , where 1 − x − y is Ͼ0.8 ͑high Ni content͒ is the rapid reaction with air resulting in the formation of Li 2 CO 3 and LiOH on the surface. 6-8 Zhuang et al. reported the presence of Li 2 CO 3 on the surface of LiNi 0.8 Co 0.15 Al 0.05 O 2 powder exposed to air, and the long-term exposure of the cathode produced a dense Li 2 CO 3 coating, approximately 10 nm in thickness, which severely reduces the capacity and increased the irreversible capacity, according to the following equation LiNi 0.8 Co 0.15 Al 0.05 O 2 + 4xO 2 + 2xCO 2 → Li 1−x Ni 0.8 Co 0.15 Al 0.05 O 2 + 2xLi 2 CO 3 . Moshtev et al. also reported the formation of LiOH on the LiNiO 2 as a result of oxygen evolution: LiNiO 2 + yH 2 O → Li 1−y NiO 2−y/2 + yLiOH. 8 In addition, the extraction of Li from Li 1.1 NiO 2 in water led to a rapid decrease in capacity, and the discharge capacity of the washed powder was reduced to 150 mAh/g from 181 mAh/g. 9 Recently, Yang et al. reported that surface-active oxygen O 2− from an impurity NiO phase that combined with CO 2 and H 2 O in air to form CO 3 2− and OH − , and suggested the following surface reaction mechanism: 2Li + + CO 3 2− /2 OH − → Li 2 CO 3 /2LiOH. 10 The presence of such impurities led to severe cell swelling during the formation process in the Li-ion cell manufacturing and at 90°C storage at the 4.2 V charged state. Therefore, this study investigated the effect of washing on an air-expo...

The effect of organic solvents on horseradish peroxidase structure and function has been studied. Some, but not complete, enzyme denaturation occurs even in low volumes of water-miscible organic solvents (e.g., greater than 30% v/v dioxane, greater than 50% v/v methanol, and greater than 20% v/v acetonitrile) as determined by the decreased difference between the fluorescence of peroxidase's sole tryptophan residue and free L-tryptophan in solution. Absorbance and electron paramagnetic resonance spectroscopies indicate exposure of peroxidase's active site to the organic solvent. This reduces the local polarity in the enzyme's active site and results in stronger hydrogen bonding of phenolic substrates to the enzyme. In extreme cases (e.g., 95% v/v dioxane, 90% v/v acetonitrile, and ethyl and butyl acetate containing 2 and 1% v/v aqueous buffer, respectively), the transition state of the enzymic reaction is sufficiently perturbed so as to alter the magnitude of the Hammett rho value. This is most likely the result of the increased strength of hydrogen bonding between electron-donating alkoxyphenols (negative sigma values) and an electrophilic group in the enzyme's active site, thereby reducing catalytic efficiencies for such substrates relative to alkyl- and chlorophenols. Perhaps the most important effect of the organic solvent, however, is the significant ground-state stabilization of phenolic substrates in organic media as opposed to aqueous buffer. This stabilization can account for nearly 4 orders of magnitude in reduction of catalytic efficiency and is manifested in increased Km's. This study indicates that enzymes can maintain much of their native active-site structure in organic media and that the effect of solvent on substrate thermodynamics must be considered.

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