Nickel-Based Batteries

Electric vehicles (HOUSE) and portable electronic devices like have become indispensable parts of daily life, increasing the demand for high-energy-density and environmentally friendly energy storage solutions. In this context, Nickel-Metal Hydride (NiMH) batteries were developed primarily to replace Nickel-Cadmium (Ni-Cd) batteries and have gained a significant important share in recent years. NiMH batteries stand out due to their high energy density, environmentally friendly composition, and longer cycle life.

History and Market Share of NiMH Batteries

Ni-Cd batteries have been in use since the early 20th century and dominated battery technologies for approximately four decades. However, recent environmental concerns, the need for longer-lasting batteries, and the pursuit of higher-capacity energy storage solutions have accelerated the development of NiMH technology. From the mid-1980s onward, NiMH batteries rapidly spread into products such as portable devices, laptop computers, mobile phones, and video camera batteries. Today, NiMH batteries hold a significant market share of around 35 percent in the rechargeable (charge) battery market, a share that continues to grow annually.

NiMH batteries are used in numerous industrial applications, including electric vehicles and sun energy systems, among others. These batteries are preferred primarily because of their high load capacity and lack of environmental harm.

Chemical Structure and Design Features

The fundamental materials used in the design of NiMH batteries are nickel (Ni) and metal hydride compounds. These batteries consist primarily of a cathode (negative electrode) and an anode (positive electrode). The cathode is made from hydride electrodes formed by the accumulation of metal hydride compounds, while the anode is produced from nickel oxyhydroxide (NiOOH). These batteries utilize metallic alloys capable of storing hydrogen gas. The most commonly used alloys are AB5 (LaNi5) and AB2 (TiNi2).

• AB5 Alloys: This alloy type has a weight capacity of 1.5% for hydrogen storage and an energy density of approximately 8–8.5 g/cm³. AB5 alloys are suitable for smaller, compact batteries requiring high energy density. They are particularly preferred in applications such as electric vehicles that demand compact battery designs.
• AB2 Alloys: AB2 alloys offer a weight capacity of 2% for hydrogen storage and possess higher hydrogen storage capacity. However, this increased capacity leads to larger battery dimensions, which is a disadvantage in compact EV designs. Therefore, AB2 alloys are suitable for larger battery systems but are less preferred in small portable devices.

The cathode electrodes of NiMH batteries are produced by compacting metallic alloy particles with hydride electrodes to enhance energy density. The ability to store hydrogen is very high, and the hydrogen atom is easily absorbed into the interstitial regions of the electrodes. This feature enables the battery to achieve high energy densities of up to 1,800 mAh/cm³.

NiMH Battery. Generated by artificial intelligence.

Advantages of NiMH Batteries

The key advantages of NiMH batteries are as follows:

1. High Energy Density: NiMH batteries provide 25–30 percent higher energy density compared to Ni-Cd batteries. This is a significant advantage in applications requiring high energy, such as portable devices and electric vehicles.
2. Environmentally Friendly: NiMH batteries do not contain harmful substances like cadmium, reducing the risk of environmental damage and facilitating recycling.
3. Longer Cycle Life: NiMH batteries offer a longer cycle life and can withstand more charge-discharge cycles. This provides a distinct advantage in applications requiring deep discharges.
4. High Load Capacity: NiMH batteries deliver high load capacities even at high discharge rates, making them ideal for applications with high power demands such as electric vehicles.

Disadvantages of NiMH Batteries

NiMH batteries also have certain disadvantages:

1. High Production Cost: The production of NiMH batteries is costly, particularly due to the complex and expensive processes involved in processing AB5 alloys. The traditional manufacturing method requires a four-stage process, which can limit commercial viability. However, new production techniques such as high-pressure gas atomization have been developed to reduce these costs.
2. Limited Thermal Stability: NiMH batteries may experience performance degradation under extreme temperature conditions, both high and low. Increased temperature can reduce battery capacity and affect discharge behavior.
3. Self-Discharge Rate: The self-discharge rate of NiMH batteries can increase, particularly under elevated temperatures. This can lead to performance loss during long-term storage.

Production Process and Recent Developments

The traditional production process for NiMH batteries is highly complex and generally consists of four stages:

1. Melting and Rapid Cooling: Melting large metal masses and rapidly cooling them.
2. Thermal Treatment: Applying thermal treatment to eliminate microscopic compositional heterogeneities.
3. Hydrogenation and Dehydrogenation: Using hydrogenation and dehydrogenation processes to break down metal masses into smaller particles.
4. Milling: Grinding processed metal particles to produce high-quality powders.

However, instead of this four-stage process process, AB5 alloys can be produced more efficiently using the solidification processing method combined with high-pressure gas atomization. This method improves hydrogen absorption and desorption behavior, thereby enhancing battery efficiency.

NiMH batteries play a critical role in future energy storage solutions across numerous fields, including electric vehicles, portable devices, and renewable energy systems. With their high energy density, long cycle life, and environmentally friendly properties, NiMH batteries have successfully replaced Ni-Cd batteries and have been further strengthened by technological advancements. However, challenges such as production costs and thermal stability issues remain still areas that require further resolution. Future research and developments will continue to improve the performance of NiMH batteries, delivering even more economical and efficient battery solutions.