Advanced Alkaline MnO2-Zn Batteries: Accessing the Second Electron Capacity
Authors: Yadav Gautam Ganapati , Gallaway Joshua W , Nyce MIchael , Banerjee Sanjoy 
Published: February 2020

Manganese dioxide (MnO2) and zinc (Zn) are one of the most abundant, safest and cheapest materials available. Together, they are found in common household batteries like Duracell, Energizer, etc. as small cylindrical alkaline cells. These cells or batteries are used as primary batteries, i.e., as single use batteries, where the entire capacity of the battery is delivered once and then discarded. The disadvantage of primary batteries is that it takes a lot of energy to produce the battery than the energy that can be actually obtained from it, and also, it creates environmental waste. However, the manufacturing of primary cells has still been rampant due to the cost of manufacturing MnO2-Zn cells being very cheap. In terms of improving the overall energy efficiency, reducing waste and maintaining its cost advantage, it makes good sense, economically and environmentally, to make MnO2-Zn cells rechargeable. However, the main deterrent to this direction has been the fundamental material and chemical problems of the main raw components, i.e., MnO2and Zn.

Manganese dioxide can theoretically deliver a capacity of approximately 617mAh/g. It delivers this capacity through a 2 electron electrochemical reaction (each electron providing around 308mAh/g). MnO2has been found to be rechargeable when the capacity has been limited to around 5-10% of the 617mAh/g. It suffers a crystal structure breakdown as more of the capacity is accessed, and it inherently forms electrochemical irreversible phases. If the entire 2 electron capacity can be accessed then theoretically it can reach energy density numbers near lithium-ion batteries. Similar problems are associated with the zinc electrode, where higher utilization of its capacity causes dendrite formation, shape change and formation of inactive zinc oxides that ultimately lead to electrode failure. These are the main deterrent to a cheap and safe battery that could be a disruptive technology in the energy storage field.

At the CUNY Energy Institute, we have made a breakthrough in accessing the second electron capacity by altering the crystal structure of manganese dioxide.through dopants and novel and cheap synthesis routes. We have cycled the MnO2 electrode to well over 3000 cycles at rates that are of interest in the battery community. Characterization techniques have shown that the CUNY modified MnO2 is able to maintain its crystal structure and limit the formation of inactive phase hausmannite (Mn3O4) which makes it cycle for thousands of cycles. A 50Ah CUNY modified MnO2 –Zn cell has also been built and cycled well beyond 50 cycles (still running). The cell demonstrates that by accessing the full second electron capacity we can achieve high energy density’s that are theoretically possible of alkaline battery technology. Also, in this talk I will go through the various breakthroughs that have been made at the CUNY Energy Institute with regards to solving other fundamental problems and the scope of these batteries in the current market.

Figure 1