Nickel–metal hydride battery

Nickel–metal hydride battery (NiMH or Ni–MH) is a type of rechargeable battery that uses nickel oxide hydroxide and metal hydride as electrodes. NiMH batteries have replaced nickel-cadmium batteries (NiCd) in many applications due to their higher capacity and lack of memory effect. However, they are somewhat less energy-dense than lithium-ion batteries, which limits their use in lightweight devices such as smartphones and laptops.

History

The development of NiMH technology began in the 1960s and 1970s as part of efforts to find more efficient and durable power storage solutions. The first commercial NiMH batteries were available in the late 1980s. They were initially used in high-end consumer electronics and electric vehicles.

Chemistry

NiMH batteries operate on the principle of electrochemical reactions between nickel oxide hydroxide (NiOOH) in the positive electrode and a hydrogen-absorbing alloy in the negative electrode. During charging, electrical energy is used to generate hydrogen in the form of metal hydride in the negative electrode, while the positive electrode is converted to nickel oxyhydroxide. The process is reversed during discharge.

Advantages

NiMH batteries offer several advantages over other types of rechargeable batteries:

• Higher energy density compared to NiCd batteries.
• Lack of memory effect, which allows for partial discharges and charges without loss of capacity.
• A more environmentally friendly option, as they contain no cadmium, which is toxic.

Disadvantages

Despite their advantages, NiMH batteries also have some limitations:

• Lower energy density compared to lithium-ion batteries.
• Higher self-discharge rate than NiCd and lithium-ion batteries.
• Performance can be affected by extreme temperatures.

Applications

NiMH batteries are used in a wide range of applications, including:

• Consumer electronics such as digital cameras, portable music players, and handheld gaming devices.
• Electric vehicles (EVs) and hybrid electric vehicles (HEVs), although they are increasingly being replaced by lithium-ion batteries in this application.
• Medical devices, emergency lighting, and other applications where reliable rechargeable power is needed.

Recycling and Environmental Impact

NiMH batteries are more environmentally friendly than NiCd batteries due to the absence of toxic cadmium. They are also recyclable, and many countries have established recycling programs to recover valuable materials from used batteries.

Future Developments

Research into NiMH technology continues, with a focus on increasing energy density, reducing self-discharge rates, and improving performance at extreme temperatures. Advances in electrode materials and electrolyte formulations are expected to lead to the next generation of NiMH batteries with improved overall performance.