Advances in Alkaline Secondary Batteries for Grid Storage Applications

Rechargeable Zn/MnO2 batteries have recently become a strong candidate for electrical grid storage applications due to their established materials supply chain, high energy density, and low cost. Such cells could rival Li-ion systems in terms of theoretical specific energy and, when produced at scale, could cost as little as $50/kWh (S. Banerjee et al.). Yadav and coworkers have developed a MnO2 cathode stabilized by Bi and Cu, which can reversibly access the full 2e– capacity of MnO2, but pairing this electrode with Zn is still met with a number of issues, deeming the long cycle lives (e.g. ≥ 5000 cycles) necessary for grid storage currently unobtainable. Over repeated charge–discharge cycles in alkaline conditions, Zn anodes undergo numerous dissolution/re-precipitation reactions, resulting in irreversible shape change, redistribution of active material, and eventual electrode passivation, limiting the achievable capacity and lifetime. Recently, our group examined pre-saturation of the electrolyte with zincate (Zn(OH)4 2 –), which forms when ZnO is dissolved in strong base, as a potential solution to this problem, showing a 110-235% improvement in cycle life of Zn/Ni cells at increased Zn depth-of-discharge (DOD) (14-35% DOD) (M. Lim et al.). Unfortunately, these benefits are nullified when a MnO2 cathode is used, because the cell shorts and (Zn(OH)4 2 –) further reacts with soluble Mn(III) species, causing the formation of insoluble and/or electrochemically inactive side products, such as ZnMn2O4. Thus, the development of a zincate-blocking, yet hydroxide and/or cation-conducting separator, which could isolate the zincate-saturated electrolyte within only the anode was undertaken in order to enable longer cycle lives of higher DOD Zn/MnO2 cells. As a result, we have now developed several permselective polymeric separators for use in higher depth-of-discharge Zn/MnO2 batteries at enhanced rates (Kolesnichenko et al.). After synthesis and characterization, the functionalized separators were screened for hydroxide and zincate crossover, using pH measurements and our newly-developed anodic stripping voltammetry assay (Duay et al.), respectively. Several separators showed a strong selectivity for hydroxide over zincate, while ionic conductivity measurements were comparable to those of commercial CelgardTM 3501 and Cellophane 350P00 separators. This presentation will discuss various aspects of improving Zn anode performance at higher depths-of-discharge and implementation of functionalized polymeric separators into Zn/MnO2 batteries to isolate the cathode from zincate. This work was supported by the U.S. Department of Energy, Office of Electricity, and the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program 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-NA-0003525. Dr. Imre Gyuk, Director of Energy Storage Research at the U.S. Department of Energy Office of Electricity, is 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. References [1] S. Banerjee 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 [2] G. G. Yadav, J. W. Gallaway, D. E. Turney, M. Nyce, J. Huang, X. Wei, and S. Banerjee, Nat. Commun., 8, 14424 (2017). [3] M. B. Lim, T. N. Lambert, and E. I. Ruiz manuscript submitted. [5] I. V. Kolesnichenko, D. J. Arnot, M. B. Lim, and T. N. Lambert manuscript in final preparation. [6] J. Duay, T. N. Lambert, and R. Aidun Electroanal 29, 2261-2267 (2017).