Enhancing the Discharge Capacity and Rechargeability of Zn-MnO2 Alkaline Batteries through Partial Inclusion of Al into Zn

Abstract

Zn-MnO2 alkaline batteries have been a reliable primary battery system for several decades due to their inherent safety, low cost and acceptable performance at low current densities 1. However, the discharge capacity and energy density of primary Zn-MnO2 alkaline batteries has plateaued and there is a high desire to improve these performance metrics to broaden the applications of alkaline batteries. One possible way to enhance the discharge capacity of alkaline batteries is to replace Zn anodes with other anode materials that possess a higher theoretical capacity. Among different elements that could be used in battery systems, Al can offer high theoretical gravimetric and volumetric capacity compared to Zn (2980 mAh g-1 vs. 820 mAh g-1 and 8.05 Ah cm-3 vs. 5.85 Ah cm-3, respectively) 2. Al is also highly naturally abundant and low cost. However, Al is fundamentally more unstable than Zn in alkaline media due to high rates of corrosion and passivation 3. Therefore, the complete replacement of Zn with Al anodes would not be viable and practical.In this work, partial inclusion of Al in Zn anodes was explored through synthesizing hexagonal-shaped Zn-rich electrolytic Zn/Al (e-Zn/Al). In three-electrode cells with excess electrolyte, it was shown that the Al capacity was accessible within these morphologies resulting in higher discharge capacities compared to pure electrolytic Zn (e-Zn) 4. The corrosion of e-Zn and e-Zn/Al was controlled by including ZnO and Al(OH)3 as electrolyte additives. Moreover, the fundamental effects of the two electrolyte additives on corrosion and passivation of Zn surfaces were investigated using an electrochemical quartz crystal microbalance. Finally, in cylindrical full cells with limited volume (i.e. more realistic conditions), it was found that the discharge capacity and energy density of e-Zn were increased by 53% (581 mA g-1 anode) and 56% (~784 Wh kg-1 anode), accordingly, through partial Al inclusion (e-Zn/Al anodes). This was accompanied by a superior cycle performance in secondary full cells (>800 h ~ 200 cycles at C/20 and 10% depth of discharge). References Faegh, E.; Omasta, T.; Hull, M.; Ferrin, S.; Shrestha, S.; Lechman, J.; Bolintineanu, D.; Zuraw, M.; Mustain, W. E., Understanding the Dynamics of Primary Zn-MnO2 Alkaline Battery Gassing with Operando Visualization and Pressure Cells. Journal of The Electrochemical Society 2018, 165 (11), A2528.Faegh, E.; Ng, B.; Hayman, D.; Mustain, W. E., Practical assessment of the performance of aluminium battery technologies. Nature Energy 2020. https://doi.org/10.1038/s41560-020-00728-yFaegh, E.; Shrestha, S.; Zhao, X.; Mustain, W. E., In-depth structural understanding of zinc oxide addition to alkaline electrolytes to protect aluminum against corrosion and gassing. Journal of Applied Electrochemistry 2019, 49 (9), 895-907.Faegh, E.; Ng, B.; Hayman, D.; Mustain, W. E., Design of Highly Reversible Zinc Anodes for Aqueous Batteries Using Preferentially Oriented Electrolytic Zinc. Batteries & Supercaps 2020, 3 (11), 1220-1232.