Rechargeable batteries for military aircraft

Rechargeable batteries for military aircraft

① Nickel metal hydride rechargeable batteries used in military aircraft
Research on rechargeable batteries has shown that nickel metal hydride (Ni-MH) batteries may achieve higher performance due to unique electrochemical technology and prismatic bipolar design. According to the vice president of development at Electro Energy Corp, this special battery design can improve battery performance by about 20% and reduce production costs by 25%.

Nickel metal hydride (Ni-MH) batteries can carry out certain overcharge and overdischarge reactions on the positive electrode and the negative electrode. The battery capacity is limited by the positive electrode, and the ratio of negative to positive is 1.5 to 2.0. When overcharged, oxygen is formed on the positive electrode and diffuses to the negative electrode to generate water (H2O). During overdischarge, hydrogen is formed at the positive electrode and water is again generated at the negative electrode. Hydrogen and oxygen recombine to form water, thereby ensuring the sealing operation of nickel metal oxide (Ni-MH) batteries. Interestingly, the hydrogen ions move back and forth between the two electrodes during charging and discharging.

Materials scientists have found that appropriate use of alloys containing rare earth materials, such as lanthanum nickel (LaNi5) alloy, zirconium vanadium (ZrV2), will significantly improve the performance of nickel metal hydride (Ni-MH) batteries, such as widening the temperature range and extending cycle life , Improve power and energy capacity, enhance electrochemical activity, increase hydrogen diffusion rate, low cost, and environmentally friendly operation. The step-by-step optimization steps of a hydrogen storage alloy (LaNi5) for the negative electrode of a sealed nickel metal hydride (Ni-MH) battery are shown in Figure 1. The currently used components, namely mixed rare earth (Mm), nickel-cobalt-manganese-aluminum (Ni-Co-Mn-AI), provide a discharge capacity of 330 mA·h/g, which is 10% higher than LaNi5. This special alloy works better than ZrV2 alloy at low temperature, high temperature and required discharge rate. In addition, this alloy is cheaper and works better. Therefore, LaNi5 alloy is suitable for nickel metal hydride (Ni-MH) rechargeable batteries.

Rechargeable batteries for military aircraft
Figure 1 Progressive optimization steps of LaNis alloy-based sealed nickel-metal hydride rechargeable batteries (Mm: Mischmetal)

The performance of nickel metal hydride (Ni-MH) batteries also depends on the cathode formulation and the characteristics of the separator. The use of high-performance rare earth elements may achieve a higher capacity of 700 ~ 1000 A·h/kg. Preliminary studies on various rare earth materials have shown that a V3Ti is composed of vanadium V3, 4, 5 and titanium Ti2, 3, 4. The capacity of the alloy is twice that of LaNi5 alloy. Materials scientists believe that adding cobalt hydroxide [Co(OH)2] to the cathode will produce a more conductive cobalt oxide than nickel hydroxide (Ni-OOH). Any oxygen generated by overcharging on the positive electrode may oxidize the surface of the separator, and to avoid the formation of such oxides, a chemical separator such as sulfonated polypropylene is necessary.

②The key role of nickel-cadmium rechargeable batteries in military aircraft
Utah’s Acme Electronic Research and Development Corporation, Eagle Pitcher Industries, and several other companies are producing sealed nickel-cadmium rechargeable batteries. The sealed nickel-cadmium battery developed by cutting-edge electronics is currently used in the flight of some commercial aircraft, including the commercial transportation of MD-80, MD-90, DC-9, and Boeing 777. In addition, some F-16 fighter jets and Apache helicopters also use these rechargeable batteries. Maintenance-free sealed nickel-cadmium batteries have been approved for use in F-16, F-18, B-52, and E-8 advanced airborne early warning and control systems (AWACS). The typical energy comparison chart of lithium, nickel metal hydride batteries and nickel cadmium batteries is shown in Figure 2. These charts are very useful in choosing the right battery to meet the specific requirements of mass energy density (W·h/kg) and power density (W/L).

Rechargeable batteries for military aircraft
Figure 2 Typical energy ratio of mass energy density and volume energy density of various rechargeable batteries widely used in automobiles

Market research shows that no one can compare with the high power density of vented nickel-cadmium rechargeable batteries, which can start aircraft engines at a temperature of -45°C. There are reasons to believe that in the next 10-15 years, both commercial and military aircraft will still rely on high-power sealed lead-acid and sealed nickel-cadmium rechargeable batteries.