Nickel-hydrogen batteries for large-scale energy storage
Large-scale energy storage is of significance to the integration of renewable energy into electric grid. Despite the dominance of pumped hydroelectricity in the market of grid energy storage, it is limited by the suitable site selection and footprint impact. Rechargeable batteries show increasing interests in the large-scale energy storage; however, the challenging requirement of low-cost materials with long cycle and calendar life restricts most battery chemistries for use in the grid storage. Recently we introduced a concept of manganese-hydrogen battery with Mn<sup>2+</sup>/MnO<sub>2</sub> redox cathode paired with H<sup>+</sup>/H<sub>2</sub> gas anode, which has a long life of 10,000 cycles and with potential for grid energy storage. Here we expand this concept by replacing Mn<sup>2+</sup>/MnO<sub>2</sub> redox with a nickel-based cathode, which enables ∼10× higher areal capacity loading, reaching ∼35 mAh cm<sup>−2</sup>. We also replace high-cost Pt catalyst on the anode with a low-cost, bifunctional nickel-molybdenum- cobalt alloy, which could effectively catalyze hydrogen evolution and oxidation reactions in alkaline electrolyte. Such a nickel-hydrogen battery exhibits an energy density of ∼140 Wh kg<sup>−1</sup> (based on active materials) in aqueous electrolyte and excellent rechargeability with negligible capacity decay over 1,500 cycles. The estimated cost of the nickel-hydrogen battery based on active materials reaches as low as ~$83 per kilowatt-hour, demonstrating attractive characteristics for large-scale energy storage.