Nickel metal hydride (NiMH) batteries are a type of rechargeable alkaline battery commonly used in modern devices. First introduced in 1989 by Sony, NiMH batteries have since replaced NiCd batteries in many applications due to their higher energy density and reduced toxicity. This article will provide an overview of NiMH battery chemistry, performance advantages over other battery types, historical applications, and current uses.
Battery Chemistry
NiMH batteries use nickel oxide hydroxide as the positive electrode and a hydrogen-absorbing alloy as the negative electrode. The electrolyte used is potassium hydroxide, similar to NiCd batteries. During discharge, hydrogen atoms are stripped from the negative electrode and combine with oxygen from the positive electrode to form water.
When charging, an electric current causes the hydrogen atoms to return to the negative electrode, recharging the battery. NiMH batteries can reach 1.2 volts per cell when fully charged, which is higher than NiCd batteries. Their chemistry allows them to store more energy in smaller packages compared to NiCd cells.
Performance Benefits Over Other Batteries
Some key advantages that made Nickel Metal Hydride Battery popular include higher energy density, reduced memory effect, and lack of toxicity compared to NiCd cells. NiMH batteries were able to store 35-50% more energy in the same size package as NiCd cells. They also do not develop a "memory effect" where performance decreases if a partial discharge/charge cycle is used frequently.
Additionally, NiMH batteries are safer and more environmentally friendly than NiCd batteries. Cadmium used in NiCd batteries is toxic, whereas NiMH batteries use less hazardous materials. They do not pose the same environmental disposal concerns as NiCd or lead-acid batteries.
The higher energy density of NiMH batteries allowed them to power devices for longer periods compared to alkaline batteries. Initially used in remote controls, calculators, and toys, the higher performance made them well-suited to power early portable electronics like camcorders, cordless power tools, and laptops.
Historical Applications
One of the first major applications of NiMH batteries was in camcorders during the 1990s, where they provided extended battery life compared to previous battery technologies. Sony and Panasonic were early adopters for camcorder batteries using NiMH chemistry.
In the late 1980s and 1990s, Nickel Metal Hydride Battery began replacing alkaline batteries in remote controls and toys that saw high drain. Devices like remote controls could be made much smaller and last longer with NiMH technology. Toys also benefitted from longer run times between charges or battery replacements.
Laptop computers were another huge early application for NiMH batteries starting in the 1990s. Early portable PCs lasted only 1-2 hours on lead-acid or alkaline batteries. NiMH chemistry provided 4-8 hours of runtime, revolutionizing laptop computer usage. This helped catalyze mass adoption of portable computers.
Although NiMH was used in early consumer electronics like mobile phones, their relatively high cost limited widespread adoption. NiMH batteries consolidated their role powering high-drain devices like power tools, where their resistance to memory effect and greater cycle life provided advantages over NiCd alternatives.
Modern Applications and Outlook
Today, the primary applications of NiMH batteries are in portable power tools, scooters, hybrid electric vehicles, and other niche areas. Their energy density has been surpassed by lithium-ion batteries for most consumer electronics. However, NiMH still provides advantages for some use cases.
Power tools demand quick charging and highly reproducible battery performance over hundreds of charge cycles. With its resistance to memory effect and tolerance to partial discharges, NiMH excels compared to lithium alternatives. Many power tool manufacturers still utilize NiMH battery packs for this reason.
The same durability has made Nickel Metal Hydride Battery suitable for electric scooters and low-speed electric vehicles. Their lower cost also makes NiMH competitive for smaller EV applications compared to lithium-ion. Some hybrid electric vehicles still employ NiMH as the main traction battery for its tolerance to rapid charging.
Going forward, NiMH will likely remain an important battery choice where robust cycling performance and abuse tolerance are priorities over the highest energy density. Industry experts predict portable power tools and certain EV roles will remain their core domains. However, lithium-ion continues to capture most new applications as costs decline.
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