Improving Cycle Life and Active Materials Utilization for Rechargeable Alkaline Zn–MnO2 Batteries

Abstract

The increasing utilization of renewable power sources has highlighted the need for inexpensive and safe energy storage systems in the electrical grid to stabilize the inherent fluctuations of such sources. Rechargeable alkaline Zn–MnO2­ batteries are an especially promising candidate for grid-scale storage, with high theoretical volumetric energy density rivaling Li-ion systems, environmentally compatible materials, and a safe non-flammable aqueous chemistry. Historically, conventional Zn–MnO2 batteries have been limited to only tens of cycles due to formation of irreversible manganese oxide and zinc-manganese oxide species in the cathode, along with shape change and passivation of Zn in the anode. Ingale et al. [1] first showed that practical electrodes could obtain ~1000–3000 cycles when only a small fraction of the theoretical capacity of MnO2 and Zn was accessed during each cycle (e.g. ≤ 20% of the first MnO2 electron and ≤ 2.5% of Zn capacity). Due to the inexpensiveness of the materials and ease of manufacturing, these limited depth of discharge (DOD) Zn–MnO2 cells have already been commercialized at overall costs of ~$150-250/kWh.[2] This presentation will cover ongoing efforts to improve the cycle life and active materials utilization (i.e. energy density) in limited DOD Zn–MnO­2­ cells[3,4,5] using additives and alternatives to conventional electrode, electrolyte, and separator materials. Initial work in increasing cycle life has focused on the use of electrolyte additives and zincate blocking separators. For example, the electrolyte additive triethanolamine (TEA) demonstrated an almost 300% improvement in cycle life with higher average energy efficiency,[3] while increased cycle life was also obtained by using a zincate-impermeable ceramic NaSICON membrane.[4] More recent work has focused on improving the overall energy density of the system, such as by increasing the loading of active materials in the cathode and by attempting to increase the DOD of the Zn anode through the use of electrode formulations along with the application of zincate-blocking polymers. Various aspects of this work will be presented. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. Dr. Imre Gyuk, Energy Storage Program Manager, Office of Electricity Delivery and Energy Reliability is also thanked for his financial support of this project. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government. [1] N.D. Ingale, J.W. Gallaway, M. Nyce, A. Couzis, S. Banerjee, J. Power Sources 276 (2015) 7–18. [2] S. Banerjee, Alkaline Zn-MnO2 Battery Development: A University-Private-Public Partnership, in Department of Energy Office of Electricity and Energy Reliability Peer Review, Santa Fe, NM, September 25-27th, 2018. https://eesat.sandia.gov/wp-content/uploads/2018/10/1_SanjoyBanerjee_Presentation.pdf [3] M. Kelly, J. Duay, T.N. Lambert, R. Aidun, J. Electrochem. Soc. 164 (2017) A3684–A3691. [4] J. Duay, M. Kelly, T.N. Lambert, J. Power Sources 395 (2018) 430–438. [5] I. Vasiliev, B.A. Magar, J. Duay, T.N. Lambert, B. Chalamala, J. Electrochem. Soc. 165 (2018) A3517–A3524.