Hobbies And Interests
Home  >> Science & Nature >> Science

How Are NiMH Batteries Made?

NiMH stands for "Nickel Metal Hydride," a rechargeable battery technology invented by American inventor Stanford R. Ovshinsky in the late 1980s. NiMH batteries are a variation on earlier NiCd, or "Nickel Cadmium," batteries and are made in much the same way. However, NiMH batteries don't contain toxic cadmium metal and are less damaging to the environment.
  1. Construction

    • NiMH batteries consist of a positive electrode containing nickel hydroxide as its main active ingredient and a negative electrode composed mainly of hydrogen-absorbing alloys. The two electrodes are wound together into a coil and inserted into a metal case, which is sealed with a sealing plate after a small amount of an alkaline, electrically-conducting solution -- known as an electrolyte -- has been injected. The sealing plate contains a self-sealing safety vent, and the finished battery cell may be shrink-wrapped with plastic to provide electrical insulation between cells.

    Negative Electrode

    • The negative electrode, or cathode, of a NiMH battery is made from nickel mixed with another element, such as iron, lanthanum or magnesium, to produce an alloy -- also known as a Misch metal -- capable of absorbing and releasing about 1,000 times its own volume of hydrogen. During charging of the battery, the metal hydride electrode absorbs and stores hydrogen and, during discharging, releases it into the electrode, where it reacts to form water.

    Positive Electrode

    • The design of the positive electrode, or anode, of a NiMH battery draws heavily on that of the anode in NiCd batteries. The anode consists of the nickel hydroxide, in the form of spherical nickel hydroxide powder with additives, such as calcium or cobalt compounds, to improve its charging capacity. During charging, the nickel hydroxide reacts with hydroxide ions from the electrolyte to form nickel oxyhydroxide, water and one free, negatively charged particle, called an electron. The water and electron react with the metal alloy in the cathode to produce metal hydride and hydroxide. During discharging, the reactions occur in the opposite direction.

    Other Components

    • The anode and cathode of a NiMH battery are immersed in a dilute solution of potassium hydroxide, which contains small concentrations of other constituents to improve the performance of the battery. The idea is that hydrogen moves from the anode to the cathode during charging and vice versa during discharging, but the electrolyte takes no part in the reaction, so does not increase or decrease in volume. The electrodes themselves are separated by a nylon separator, which prevents physical contact between them, but allows charged particles -- in other words, ions and electrons -- to pass.


https://www.htfbw.com © Hobbies And Interests