Future energy reserves: analysis of nickel-metal hydride battery technology

The positive electrode of the battery is composed of nickel hydride material, and the negative electrode is composed of cobalt hydride or other alloy materials. The electrolyte inside the battery is usually a potassium hydroxide solution. During the discharge process, the nickel hydride of the positive electrode releases hydrogen ions, and the hydride of the negative electrode absorbs these hydrogen ions and transfers them between the positive and negative electrodes through the electrolyte. When charging, the reaction process is reversed, hydrogen ions migrate from the negative electrode to the positive electrode, and nickel hydride is converted into nickel hydride again. This back-and-forth electrochemical reaction makes nickel-metal hydride batteries rechargeable.

Advantages of NiMH batteries
NiMH batteries have some significant advantages in multiple aspects:

High energy density: Compared with nickel-cadmium batteries, nickel-metal hydride batteries have a greater energy density, that is, they store more energy per unit volume or mass.

Environmentally friendly: Compared with lead-acid batteries and nickel-cadmium batteries, nickel-metal hydride batteries do not contain the heavy metal lead or the toxic substance cadmium, so they have less impact on the environment and are easier to recycle and dispose of when disposing of used batteries.

Long life: Ni-MH batteries have a long charge-discharge cycle life, usually up to 500-1000 times. This means it can be recharged and discharged multiple times, giving it a longer lifespan.

Low self-discharge rate: NiMH batteries have a low self-discharge rate compared to other rechargeable batteries. The battery maintains a high charge level even when not used for long periods of time.

Wide temperature range: Ni-MH batteries generally have a wide operating temperature range and can adapt to lower temperature conditions and are suitable for various environments.

Disadvantages and limitations
However, NiMH batteries also have some limitations and disadvantages:

Low voltage: Compared to lithium-ion batteries, nickel-metal hydride batteries have a lower standard voltage. This means that in order to provide the same power, more battery cells need to be used to form the battery pack, increasing the size and weight.

Slow charging speed: Compared to lithium-ion batteries, nickel-metal hydride batteries charge slowly. It usually takes longer to fully charge the battery, which may not be ideal in some use cases.

Higher self-discharge rate: Although relatively low, NiMH batteries still have a certain self-discharge rate. This means that even when not in use, the battery's charge gradually decreases and requires regular recharging to maintain battery performance.

Larger volume and weight: Compared with lithium-ion batteries, nickel-metal hydride batteries have larger volume and weight. This limits its application in certain lightweight devices, especially those that require a compact and thin design.

Limited performance at low temperatures: The performance of nickel-metal hydride batteries in low temperature environments will be affected to a certain extent. In extreme cold conditions, battery power output and capacity may be significantly reduced.

Application scenarios
Although nickel-metal hydride batteries have some disadvantages, they are still widely used in many fields due to their several advantages:

Consumer electronics: such as mobile phones, digital cameras, and portable audio devices.

Hybrid vehicles: Nickel metal hydride batteries are used as energy storage systems in hybrid and electric vehicles.

Energy storage systems: Nickel metal hydride batteries play an important role in storage systems for renewable energy sources such as solar and wind energy.

Lighting equipment: such as emergency lighting, flashlights and stage lights.

As a rechargeable battery type, nickel-metal hydride batteries have the advantages of high energy density, environmental protection, long life and low self-discharge rate. Despite some disadvantages, such as lower voltage, slow charging speed, and temperature limitations, nickel-metal hydride batteries are still widely used in consumer electronics, hybrid vehicles, and energy storage systems.