(Industrial Electrochemistry and Electrochemical Engineering Division New ElectrochemicalTechnology (NET) Award) Development and Commercialization of Rechargeable Zinc Manganese Alkaline Batteries to Enable a Sustainable Low-Carbon Energy Future

Abstract

Urban Electric Power Inc. (UEP), a 2013 spinoff from the City University of New York Energy Institute (CUNY-EI), manufactures and markets rechargeable large-format zinc manganese dioxide (Zn-MnO2) alkaline battery cells in Pearl River, NY. The active materials in the UEP rechargeable cells are Zn and MnO2, both of which have high energy density, low cost, good safety characteristics, and are readily available with abundant supplies. These materials are key components of primary (non-rechargeable) alkaline batteries that presently dominate the disposable battery market, showing established commercial acceptability. This technology holds enormous potential to address a variety of energy storage applications, however the traditional chemistries used in primary alkaline batteries lead to irreversible degradation of the electroactive components which makes them unsuitable for the thousands of charge/discharge cycles desired for rechargeable grid-scale energy storage systems. UEP and the CUNY-EI have achieved several breakthroughs in addressing these challenges, utilizing chemical dopants and additives to stabilize both the Zn and MnO2 electrodes, which allow for more complete utilization of the battery capacity while maintaining hundreds to thousands of cycles.MnO2 and Zn deliver theoretical capacities, respectively, of 617mAh/g and 820mAh/g through a two-electron reaction in alkaline electrolyte (Figure 1). The theoretical energy density of this cell can be >400Wh/L, which is higher than many varieties of lithium-ion batteries. The Zn delivers its capacity through a dissolution-precipitation reaction, while MnO2 can exhibit solid-state proton insertion and dissolution-precipitation reactions depending on the type of MnO2 polymorph used. Electrolytic manganese dioxide (EMD, γ-MnO2), which is electrochemically synthesized in large quantities and used in primary batteries, exhibits proton insertion and dissolution-precipitation reactions. In batteries consisting of EMD, these two mechanisms each provide part of the two-electron capacity, where proton insertion delivers the first electron reaction (308mAh/g), and dissolution-precipitation delivers the second electron reaction. In contrast, birnessite(δ-MnO2), which has a layered crystal structure and is most commonly found in soils, exhibits only dissolution-precipitation reactions to deliver the two-electron capacity.The CUNY-EI made a breakthrough in 2014 and accessed the 2nd e- capacity of MnO2 reversibility. This was the first report of its complete reversibility for >6,000 cycles. EMD was used to make birnessite electrochemically in-situ, and also, because of ease of manufacturing, materials logistics and economic reasons. The additives, when mixed with EMD in the first discharge-charge formation process to make δ-MnO2, stabilized the layered cathode structure and prevented Mn3O4 formation. Bi2O3 prevented Mn3O4 formation electrochemically by complexing with the dissolved Mn(OH)6 3- and Mn(OH)4 2- ions. It also promoted δ-MnO2 formation in the charging process. The main discovery made at CUNY-EI involved recognizing that intercalating the MnO2 layers with Cu ions stabilized the cathode crystal structure and reduced the charge transfer resistance during the δ-MnO2’s electrochemical reactions. It was shown for the very first time in alkaline battery literature that energy densities approaching to 200Wh/L could be accessed from δ-MnO2 when paired with highly utilized Zn anodes.UEP’s current proton intercalation chemistry utilizes about 120-140 mAh/g-MnO2 and >160-200mAh/g-Zn. This creates an energy density of the cell of 150 Wh/L, which is comparable to existing lead-acid batteries, meaning UEP is competitive in many stationary battery applications including renewable integration, grid energy storage, backup power, including uninterruptible power supply (UPS), and residential backup applications. The company established a pilot scale manufacturing plant in Pearl River, NY with current production capacity of 100 MWh per year. Early production runs have gone to support battery systems for grid applications, backup power, and renewable integration projects. The batteries can be produced at cost lower than lead acid and lithium-ion batteries of comparable performance. Zn and MnO2 make up a small fraction of the cost per unit of storage capacity compared with costly or less environmentally friendly materials like cobalt, nickel, lithium, and lead that are used in other batteries. When manufactured in large volumes, UEP anticipates that its battery packs will cost less than $50’P3/kWh allowing building energy storage systems with a levelized cost of energy (LCOE) below the $0.05/kWh that ARPA-E has identified as the target for widespread adoption of energy storage on the electric grid. At $50/kWh, the technology becomes competitive for wide range grid applications including demand charge reductions, renewable load shifts and transmission and distribution upgrades. Moreover, these batteries offer a new level of inherent safety and environmental friendliness as they contain none of the flammable, toxic, or volatile electrolytes that have plagued other batteries considered for grid-scale storage. Figure 1