Researchers extend NiMH battery life by adding oxygen

Swedish researchers at the University of Stockholm have developed a method that makes it possible to significantly extend the life of nickel-metal hydride batteries. This is achieved by adding oxygen.

The scientists report that they can counteract the aging process of NiMH batteries by adding oxygen. In this aging process, the battery dries out as the metal alloy corrodes, ‘consuming’ the water-based electrolyte. In addition, the corrosion affects the internal balance between the electrodes. The addition of oxygen appears to restore the balance between the electrodes and replace the electrolyte, as it were.

According to the researchers, this process of adding oxygen can easily be applied to an existing NiMH battery construction from the Swedish company Nilar, which has been producing NiMH batteries for many years. The company’s battery construction used for the research has cells that all have the same volume, which simplifies the application of the oxygen method. The scientists state that with the right balance of oxygen and hydrogen, it is possible to exceed the lifespan of all existing mainstream battery types.

NiMH batteries are characterized by the use of moist electrolytes, which are safe and not harmful to the environment. In these batteries, the hydrogen is bonded to the metal alloy. NiMH batteries originate from NiH2 batteries; these nickel-hydrogen batteries have a relatively long lifespan, which is why they have been used, for example, in space probes and in the Hubble telescope. However, the disadvantage of these nickel-hydrogen batteries is that the necessary hydrogen has to be stored in special gas tanks, which is not practical for smaller technology applications. NiMH batteries are much more compact, because the hydrogen is incorporated in the metal alloy, where the hydrogen density is comparable to that of liquid hydrogen. Compared to NiH2 batteries, however, this does reduce the lifespan and that problem is now being combated by adding oxygen.

According to the researchers, their discovery allows the batteries to go through a large number of additional charging cycles without losing any capacity. Once worn out, the new method would also make it possible to easily recover the batteries, so they don’t have to be melted down for recycling. The find could be of significance not only for the energy sector, as storage for solar and wind energy, but also for the car industry. Toyota, for example, uses NiMH batteries in its hybrid Prius cars. The research is published under the title Development of metal hydride surface structures for high power NiMH batteries.