Manganese Dioxide (MnO₂) is one of the cheapest and most abundant materials available on earth. It is used in a number of applications like catalysis, water purification, lithium-ion batteries and many more. However, it is commonly known to most as a AA primary battery, where it is used to power remote controls, clocks, etc. MnO₂ is used as a cathode in these primary batteries because of its high theoretical capacity of 617mAh/g, where it is delivered through a two electron reaction mechanism in alkaline electrolyte. The first electron reaction has been known to deliver ~308mAh/g through a solid-state proton insertion, while the second electron reaction has been known to deliver the remaining half through a dissolution-precipitation reaction. For many years MnO₂ was considered to be electrochemically irreversible because of the breakdown of the crystal structure during the first electron reaction and the deleterious side-reactions during the second electron reaction that resulted in the formation of an inactive substance called hausmannite (Mn₃O₄).^1,2 These major problems relegated this energy dense cathode to the realm of primary batteries, which otherwise would have been used for many important applications like grid energy storage.

In this talk, we will present different ways of accessing the theoretical second electron capacity (617mAh/g) of MnO₂ for over 3000 cycles, where the use of dopants like bismuth oxide and copper, removal of hydrophobic binders like Teflon, use of high surface area carbon and maintaining a porous electrode architecture are extremely important.^3-5 We will present the diverse and complex electrochemistry of MnO₂ that take place with the addition of bismuth oxide and copper as complexation and intercalation reactions are added with the solid-state and dissolution-precipitation reactions on the account of the tendency of bismuth and copper to enhance the redox activity of MnO₂.⁶ We will also show comprehensive combinatorial cyclic voltammetry and impedance analysis, where the roles of bismuth and copper will be further elucidated, and remark on the potential regions where the complexation and intercalation regions exist in the MnO₂ electrochemistry. For the first time we will show real time microscopy images and video of the formation and deformation of MnO₂ through dissolution-precipitation reactions.^5,6 We will also report on the role of high surface area carbon and binder on MnO₂ electrochemistry, where we find that they affect the electrode architecture and porosity, which turn out to be very important for the dissolution-precipitation reactions. Finally, we will present our perspective on the current understanding of MnO₂ electrochemical reactions based on the aforementioned and other advanced characterizations that we have performed.

Funding:

This work was supported by the New York State Research and Development Authority (NYSERDA) under Project Number 58068 and US Department of Energy ARPA-E under award number DE AR0000150.

References:

1] Gallaway, J. W.; Hertzberg, B. J.; Zhong, Z.; Croft, M.; Turney, D. E.; Yadav, G. G.; Steingart, D. A; Erdonmez; C. K.; Banerjee, S. Journal of Power Sources, 2016, 321, 135-142

2] Huang, J.; Yadav, G. G.; Gallaway, J. W.; Wei, X.; Nyce, M.; Banerjee, S., Electrochemistry Communications, 2017, 81, 136-140

3] Yadav, G. G.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Huang, J.; Wei, X.; Banerjee, S., Nat. Commun., 2017, 8, 14424

4] Yadav, G. G.; Wei, X.; Huang, J.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Secor, J.; Banerjee, S., J. Mater. Chem. A, 2017, 5 (30), 15845-15854

5] Yadav, G. G.; Wei, X.; Gallaway, J. W.; Chaudhry, Z.; Shin, A.; Huang, J.; Yakobov, R.; Nyce, M.; Vanderklaauw, N.; Banerjee, S. Materials Today Energy, 2017, 6, 198-210.

6] Yadav, G. G.; Wei, X.; Huang, J.; Turney, D.; Nyce, M.; Banerjee, S. International Journal of Hydrogen Energy, 2018, https://doi.org/10.1016/j.ijhydene.2018.03.061

Figure. Potentiodynamic cycling of MnO₂ showing its diverse and complex electrochemistry. Top part is the cyclic voltammetry (CV) scan of the first cycle which shows the conversion of γ-MnO₂ to δ-MnO₂. Bottom part is the CV scan after the first cycle, which shows the electrochemistry of δ-MnO₂ with Bi and Cu additives.