What's Inside: Rechargeable Batteries

Mardi, 26 Juillet 2011 18:00

What's Inside: Rechargeable Batteries

E-mail

Rate this item

(0 Votes)

Energizer rechargeable nickel metal hydride (NiMH) battery.
Photo: Jamie Chung

Potassium Hydroxide
A battery works by converting chemical energy into free electrons; some of the electrons get used, and the rest return to the cell. The battery needs a way to move the current internally. Enter potassium hydroxide, an alkaline electrolyte consisting of potassium and negatively charged hydroxyl (-OH) ions in water. The OH carries electrons, creating current inside the battery.
Nickel Hydroxide
Every battery has a positive and a negative electrode. In an NiMH cell, the positive one is primarily nickel hydroxide. While the battery is charging, this compound surrenders hydrogen atoms and becomes nickel oxyhydroxide and water, which frees up electrons. When discharging, the process is reversed.
Misch Metal
The negative electrode. German for “mixed metal,” this is a mischmash of rare earth elements, including lanthanum, cerium, praseodymium, and neodymium. It can suck up hydrogen atoms (about 1,000 times its own volume!), which makes it an electron storehouse. (Hydrogen-absorbing alloys like misch metal are called metal hydrides, and this ingredient is the MH in NiMH.) When the battery is discharging, the electrolyte’s OH hydroxyl reacts with the hydrogen from the metal hydride, producing water and a stream of free electrons. During a recharge, the incoming electrons reverse that process.
Lithium Hydroxide
Charging NiMH batteries is most efficient at room temperature. By adding LiOH to the electrolytes, the batteries can be charged at temperatures of up to 120 degrees Fahrenheit, meaning they’ll work in photovoltaic and industrial settings.
Zinc
When nickel oxyhydroxide is charged too frequently, it can become oversaturated with electrons, which can reduce storage capacity. Adding zinc prevents this from happening.
Aluminum
Scattered throughout and on the surface of the negative electrode. Some patents claim that Al keeps hydrogen production under control; others offer AI as a sacrificial lamb, because it limits corrosion of the electrode by corroding itself first. Either way, adding Al increases the battery’s lifespan.
Cobalt
Alkaline electrolytes found in batteries can easily damage most metals. Adding Co to the metal hydride increases the battery’s thermodynamic stability and protects the electrode from corrosion. Coating the positive nickel electrode with cobalt also increases the battery’s discharge efficiency, allowing you to squeeze out those last few electrons.
Manganese
This element and its fellow alloy additives help keep the electrode from becoming brittle during repeated charge cycles. In some alloys, it helps the battery hold a charge and improves performance at low temperatures.