The Advent of Aqueous >2.85V Zn-MnO₂ Batteries: Uncovering Novel Mechanisms in This New High Voltage Chemistry

Alkaline zinc (Zn)-manganese dioxide (MnO2) batteries are ubiquitous, safe, cheap and used in several applications that require only a single discharge. Its impact in the developing world has been significant where its affordability has helped consumers with low to medium economic background power several of their household devices and flashlights when grid reliability has been poor. Its single discharge is enough to deliver an energy density of ~400Wh/L. However, its promising characteristics are outweighed by its limited use in the next generation of green energy technologies because of the irreversibility of its active materials and its low nominal voltage of ~1.3V. The application of battery energy storage in these next generation of technologies like grid-storage, electric vehicles and personal electronics is extremely vital to decarbonize our future. Currently, expensive, toxic and flammable lithium-ion and lead acid batteries dominate these fields. If Zn-MnO2 batteries could be made rechargeable with an increase in its nominal voltage and capacity utilized, it could be serious contender to the dominant lithium-ion and lead acid batteries. In this presentation, we report on an innovative approach where we solve the two aforementioned issues by redesigning the battery system to have two electrolytes that are decoupled from each other(1). The two electrolytes are aqueous-based, where the cathode and anode are immersed in mildly acidic solutions and alkaline solutions, respectively. Operating in decoupled electrolytes allows the chemistry to widen its potential window and access voltages of >2.85V, while also allowing the respective electrodes operate efficiently and reversibly in their respective electrolyte system. The neutralization of these electrolytes is prevented by gelation of the alkaline electrolyte, which removes the need of expensive ion-exchange membranes. As a demonstration of this concept, we have developed Zn-MnO2 batteries reaching voltages >2.85V that are able to access the theoretical capacity (617mAh/g) of MnO2. This translates to energy densities 2 to 3 times greater than the commercially available alkaline batteries that can be recharged multiple times at costs that are comparable to primary batteries (~$20-30/kWh). G. Yadav et al., ACS Energy Lett. 2019, 4(9), 2144-2146.