MnO2-Zn batteries once dominated the energy storage market, but their application was limited to use as primary batteries. A new generation of rechargeable MnO2-Zn batteries is poised to compete with Li-ion and Pb-acid batteries on cost, safety, and energy density.
Lithium-ion (Li-ion) batteries dominate the rechargeable battery landscape because of their favorable energy densities and power characteristics. High voltages make Li-ion technology ideal for portable electronics and battery electric vehicles, and their relatively flat discharge rates contribute to energy-efficient systems (1).
However, Li-ion technology has been developed to near maturity, and only incremental improvements in energy density and cost are expected. In addition, the chemistry is inherently flammable. Scientific literature as well as the media have widely reported on the flammability dangers of Li-ion batteries. The electrolyte, the unstable nature of the cathodes, and the cobalt (Co) content in the cathodes make the battery very flammable, and exothermic side reactions at high temperatures can become violent. Grid-scale storage applications require large safety systems, which greatly reduce the volumetric energy density of the system.
The human cost of Li-ion batteries also cannot be ignored. The cobalt used in the cathode is mined primarily from the Democratic Republic of Congo by miners, some of them children, using their bare hands. Cobalt is a known toxin that produces harmful effects, including breathing problems and birth defects (2). Cobalt is the key to Li-ion power and energy density, and will likely remain in the cathode for the foreseeable future. Efforts are underway to reduce the amount of cobalt in the battery, with a goal to transition to manganese (Mn)-rich cathodes in the next few years.
Despite their drawbacks, Li-ion batteries have become the favorite, but lead (Pb)-acid batteries are still a dominant battery storage system because of their low cost and historical legacy. They are perhaps one of the oldest rechargeable battery technologies and boast the most established chemistry. Pb-acid batteries are used in several applications and markets, including uninterruptible power supplies (UPS) for backup power, grid energy storage, electric vehicle batteries, and automobile starting, lighting, and ignition (SLI).
In the developing world, Pb-acid batteries are the most widely used energy storage device because of their low cost — economics supported in part by illegal lead recycling. Recycling is often done illegally in small shops, frequently by children without the use of proper safety equipment. Battery manufacturers buy the illegally recycled lead at a fraction of the cost of virgin material.
Because they require expensive materials, Li-ion and other modern battery designs have trouble competing on cost with Pb-acid technology. Batteries capable of challenging the market dominance of Li-ion and Pb-acid batteries will need to be low cost, safe, and energy dense. This article presents a possible challenger that meets these criteria — an aqueous-based manganese dioxide (MnO2)-zinc (Zn) battery.
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