Sanyo Electric Introduces Improved NiMH Rechargeables
FlashlightNews.org - 01/20/2006
OSAKA, Japan. -- Japan's Sanyo Electric Co Ltd., has developed a new NiMH rechargeable battery which can retain a charge after a year of sitting on a shelf. In contrast, previously available NiMH rechargeables have no meaningful charge left when subjected to such long storage times.
Sanyo Electric claims that battery self-discharge and operating voltage loss have been reduced so that the batteries keep about an 85% charge, even one full year after an initial full charge. The new technology, which is referred to as eneloop, was initially available in a AA size cell which was released in Japan in late 2005, and Sanyo Electric says the AAA size cell will ship on January 21, 2006.
The corporate goal with the new battery technology is to replace disposable batteries that utilize older chemistries like alkali and manganese dry cells. Because the new cells have shelf-storage profiles that are similar to dry cells, Sanyo can ship and market the batteries fully charged, enabling instant use, just like conventional batteries.
Charging time for the AA battery is 230 minutes, when charged with Sanyo's NC-MDR02 charger. The AA batteries are rated at a nominal capacity of 2000mAh. The AAA battery has a claimed charge time of 135 minutes and a nominal capacity of 800mAh. The new batteries are priced competitively with existing NiMH cells, but are more cost efficient due to their higher number of recharge cycles (1000).
Self-discharge was reduced through improvements in the anode and the electrolyte. Principally, an additive was added to the Ni(OH)2 anode, and the ratio of KOH, NaOH, LiOH and other substances was optimized in the electrolyte. Also, the composition of the hydrogen-absorbing alloy in the cathode, was changed to minimize the drop in operating voltage after discharge.
In addition, the amount of chemically active materials in the batteries was increased to help suppress self-discharge, while at the same time maintaining capacity at 2000mAh. In the past it has been problematic to both suppress self-discharge and maintain capacity, because controlling self-discharge tends to weaken the chemical reactions at discharge.
The new Sanyo batteries will compete against a Matsushita Battery NiMH rechargeable with reduced self-discharge, to be released in February. After a full charge, Matsushita claims their new cells can maintain 80% capacity after six to 12 months. However, the Matsushita cells require storage off the charger at temperatures of less than +20¢. The capacities of the Matsushita AA and AAA cells are 2000mAh and 750mAh, respectively. They are also rated for abpproximately 1,000 discharge/recharge cycles.
Sanyo Global Web Site