How does a NiMH battery work?

Although lithium batteries are in the spotlight, NiMH (nickel-metal hydride) batteries remain an essential solution. Renowned for their robustness and safety, they are used in everyday objects as well as in the most famous hybrid cars.

What is a NiMH battery?

A NiMH battery is a rechargeable battery that stores energy through a chemical reaction between nickel and hydrogen. Unlike older cadmium batteries (NiCd), it is more environmentally friendly because it does not contain highly toxic heavy metals.

Strategic applications in hybrid mobility

In the automotive sector, and more specifically for non-rechargeable hybrid vehicles (HEVs), NiMH technology is favored for its “energy buffer” function.

Regenerative braking management: During deceleration phases, kinetic energy is converted into electricity. NiMH chemistry is particularly effective at absorbing these high, intermittent charging currents without the risk of thermal overload.

Optimization of engine torque: During acceleration, the battery instantly releases stored energy to assist the combustion engine, thereby reducing fuel consumption and CO2 emissions.

Industrial example: In a benchmark model such as the Toyota Prius, the NiMH battery is not designed to offer extended electric range. Its role is to maximize overall energy efficiency by systematically recovering energy that would otherwise be dissipated as heat during braking.

Formats and architecture: Cylindrical vs. Prismatic

The physical architecture of NiMH cells is adapted according to integration and power constraints:

• Cylindrical format: robustness and performance

The cylindrical format of battery cells, largely derived from standard rechargeable batteries, is characterized by excellent mechanical strength and very good heat dissipation. Its geometry allows it to effectively withstand vibrations, shocks, and stresses associated with frequent charge and discharge cycles, making it a particularly suitable solution for electric micro-mobility applications such as electric bicycles, scooters, and kick scooters.

In the automotive sector, this format is also used for applications requiring rapid and repeated charging, as its consistent thermal management helps to limit cell heating and reduce premature wear during intensive urban use.

• Prismatic format: energy density and space optimization

The prismatic format prioritizes volume optimization and energy density thanks to its rectangular shape, which reduces wasted space when assembling battery packs. This format has become standard in the automotive industry for hybrid and electric vehicles, as it facilitates the design of compact, high-capacity, high-voltage batteries that integrate perfectly into modern chassis. Beyond mobility, prismatic cells are also widely used in stationary urban applications, such as energy storage for smart buildings or charging stations, where their compactness and modularity contribute to the stabilization of the power grid and better integration of renewable energies.

Toyota (Yaris, Prius, Auris, Rav4, Corolla) – Lexus

Prismatic module battery

Resilience in urban environments and extreme conditions

NiMH technology offers decisive advantages for autonomous public facilities (solar bus shelters, signage) and mobility.

High thermal stability and maximum safety in public environments

NiMH (Nickel Metal Hydride) technology is establishing itself as the benchmark solution for autonomous public equipment, such as solar bus shelters and urban signage, thanks to its exceptional thermal stability. Unlike lithium, its aqueous electrolyte is non-flammable, making the risk of thermal runaway virtually zero. This feature ensures maximum safety in high-traffic areas, where energy storage systems must meet extremely rigorous civil protection standards without requiring complex cooling devices.

Cool resistance and service continuity at low temperatures

In addition, NiMH ensures unfailing continuity of service in the face of adverse weather conditions thanks to its remarkable resistance to cold. While lithium batteries see their conductivity drop and their recharge capacity freeze below 0°C, NiMH chemistry maintains excellent ionic mobility at low temperatures. This thermal resilience allows urban infrastructure to remain operational throughout the winter, ensuring the proper functioning of security lighting and connected services, even in extreme weather conditions.