Lead Acid Batteries
The Pb-acid battery chemistry is an established technology that was invented in 1859 making it the oldest rechargeable battery. The Pb-acid battery can be found in various aerospace applications. The components of the Pb-acid battery cell include a cathode comprised of lead peroxide, an anode made of sponge lead, electrolyte of sulfuric acid, and a fiberglass separator.
The advantages of the Pb-acid battery are its manufacturing simplicity, mature technology, dependable service, low maintenance requirements, and low cost. Additionally, processes have been established to make the Pb-acid battery highly recyclable. It is estimated that 95 percent of all Pb-acid batteries produced are recycled, and new Pb-acid battery materials range from 60 to 80 percent recycled content.
Nickel Cadmium Batteries
Although the basic chemistry for NiCd batteries has been used for some time, there has been continuous development on the electrode, electrolyte and packaging technologies to enable a wide range of applications. The components of the NiCd battery cell include a cathode composed of nickel hydroxyl oxide, an anode made of metallic cadmium, and an electrolyte of potassium hydroxide.
NiCd cells come in all forms for many applications such as small cylindrical cells for lower power, pocket-plate for high mechanical and electrical abuse, and sintered plate for higher-rate discharge. The flexibility of NiCd batteries is why it is used on many Boeing defense and commercial products with specific power requirements. Besides the wide range of applications that NiCd batteries have, other advantages include reliability, long battery cell life, low maintenance, long storage life, and a wide range of operating temperatures.
Nickel Metal Hydride Batteries
NiMH batteries are commercially available batteries that are widely used in hybrid vehicles and portable electronics. The NiMH battery originated as the successor to the NiCd battery, and exhibits a higher energy density and specific energy when compared to Pb-acid and NiCd. The components of the NiMH battery cell include a cathode composed of nickel hydroxyl oxide, an anode of mischmetal (Me) hydrides, electrolyte of potassium hydroxide, and a separator of a porous polypropylene membrane.
Recyclable materials are used in the construction, and the battery does not contain hazardous materials such as cadmium, mercury or lead. The batteries are also maintenance free, and are safe during charging and discharging.
NiMH batteries are not historically used as a primary source of power in aircraft applications, although the NiMH cells are used within other aircraft equipment or systems, such as the emergency door and floor escape path lighting, as well as portable entertainment devices and electronic flight bags.
Lithium Ion Batteries
Li-ion batteries provide energy on a vast array of programs across Boeing. The designs for each of these platforms include either small- or large-cell formats making up the battery pack. Small cell batteries offer many advantages over large cells, including high reliability, high-volume manufacturing, high-volumetric efficiency, and reduced likelihood of cell-to-cell thermal runaway propagation.
A Li-ion cell comprises a cathode that contains lithium composite oxide materials (LiMnO, LiCoO2, etc.), while the anode is graphite-based composite. The electrolyte varies in composition but is commonly a combination of ethylene carbonate [solvent], diethyl carbonate [solvent], and lithium hexaflurophosphate [salt]. Li-ion batteries are sealed cells, requiring no maintenance and the chemistry offers high specific energy and low discharge rates, thus providing an extended cell life cycle.
Environmental impacts are minimal in the production of lithium and extraction processes are not energy-intensive. However, recycling standardization is challenging due to the variation in materials within the cathode, anode and electrolyte used to construct Li-ion batteries, as well as diversity in shapes and sizes.
Lithium Sulfur Batteries
The Li-S battery is capable of revolutionizing the battery industry. With a theoretical energy capacity of 2600 Wh/kg, it has an energy capacity five times higher than Li-ion batteries. The battery is lightweight, inherently safe (doesn’t make use of flammable solvents), durable and maintenance-free. The battery has a low cost in comparison to anode- and cathode-based materials such as graphite and LiCoO2, respectively. For comparison, the cost per capacity ($/kAh) is 110 (LiCoO2) vs. 1.9 (graphite) vs. 1x10-3 (Sulfur).
As with all lithium battery chemistries, there is a risk of combustion if lithium is exposed to the air. The primary weaknesses of the cell chemistry is the formation of lithium dendrites and dissolution of sulfur active materials from the polysulfide shuttle effect, ultimately limiting the charge-discharge cycle life.
Advancement in this technology is showing the likelihood of the Li-S battery becoming the battery of the future. The current industry leader in Li-S technology is Oxis Energy, which currently produces the rechargeable Li-S Rack Mounted Battery for European consumers.
Lithium Air Batteries
Li-air, also called a Li-oxygen battery, is typically designed using a lithium metal anode, a porous carbon cathode and an electrolyte (typically lithium salt). Metal-air batteries have the highest energy density because the cathode active material (oxygen) is not stored in the battery, but can be accessed from the environment. Currently lithium batteries are the subject of ARPA-E efforts, but are not mass produced commercially. The theoretical capacity of Li-air batteries makes them very attractive for aerospace and automotive applications, however several technical challenges need to be overcome.
One of the major drawbacks of this technology is current Li-air batteries lose 25 percent of their original capacity after only 50 discharge cycles. Charge efficiency with a carbon cathode is only 57 percent, which falls well short of the typical aerospace efficiency of >90 percent. Use of platinum or gold catalysts can improve this to 73 percent, however, this is not likely to be a commercial solution due to the cost of platinum and gold.
Zinc Air Batteries
As mentioned earlier, the greatest benefit provided by metal-air batteries is their high energy density, as compared to other battery chemistries. The Zn-air configuration represents a safe, environmentally responsible and potentially inexpensive option for the storage of electrical power. Because of this fact, a recent surge in research efforts has developed in Zn-air battery chemistries for potential usage in both portable (cell phones, laptops) and stationary devices (power grid), as well as electric vehicles.
Zn-air batteries are composed of three main components: a zinc anode, an alkaline electrolyte (potassium hydroxide), and an air cathode, usually made of a porous and carbonaceous material.
When comparing Zn-air batteries to other metal-air chemistries, there are several potential advantages that can be exploited in the battery manufacturing process. One example is the abundance of zinc metal as a raw material. This key benefit potentially provides an advantage in the hypothetical expense of the mass production of zinc-air batteries. With respect to the environment, zinc, as a raw metal, is a safer material than lithium and can be fully recycled.