Claudette Audry

Effect of Yttria Content on Corrosion of AB 5-Type Alloys for Nickel-Metal Hydride Batteries

Adding Y 2 O 3 in a metal hydride (MH) electrode diminishes the corrosion rate. Yttria dissolves in the electrolyte and then precipitates as hydroxide on the alloy surface. Alloy corrosion inhibition has been quantified for Y 2 O 3 contents varying between 0 and 2 wt % in the negative electrode. The amount, structure, and morphology of corrosion products depend on the content of added Y 2 O 3 in the MH electrode. A change in the effect was observed for 0.7 wt % Y 2 O 3 . It corresponds to a morphological and structural change in the corrosion scale. When the amount of Y 2 O 3 is lower than or equal to 0.7 wt %, corrosion products with an Mm 1 - x Y x (OH)3-type composition are formed that adopt a structure similar to that of Mm(OH) 3 (Mm = mischmetal, mixture of La, Ce, Nd, and Pr) and crystallize as hexagonal platelets. Below this limit, yttrium is incorporated in the corrosion scale as Mm 1 - x Y x (OH) 3 and strongly diminishes the corrosion kinetics of the AB 5 alloy. In contrast, beyond 0.7 wt % of Y 2 O 3 , corrosion products are rich in yttrium: a Y 1 - z Mm z (OH) 3 -type composition adopts a structure similar to that of Y(OH) 3 and crystallizes as spherical grains. For Y levels above 0.7 wt %, yttrium precipitates as Y 1 - z Mm z (OH) 3 between alloy particles and becomes less efficient as a corrosion inhibitor.

A Conductive Additive for Positive Electrodes of Alkaline Batteries Structural, Physicochemical, and Electrochemical Evaluation of Li Co O 2

For the first time, LiCoO 2 materials were synthesized at a very low temperature, below 100°C. The influence of synthesis parameters, such as temperature and time of reaction, on the structure and conductivity of the material was investigated. It was shown that these materials contain structural defects, such as stacking faults and lithium vacancies, which lead to a good electronic conductivity of these materials as compared to classical high-temperature materials. The time and temperature of reaction decrease the amounts of stacking faults in the materials. However, lithium intercalation can occur during a long-time synthesis, leading to a decrease in conductivity of the material. If process parameters are conveniently chosen, a LiCoO 2 material with a conductivity of around 10 - 1 S cm - 1 can be obtained and used with success as a conductive additive in positive electrodes of alkaline batteries. The major advantage of this new additive is that LiCoO 2 prevents the loss of capacity of alkaline cells at low voltage, in the whole potential window of the positive electrode in alkaline batteries.