Performance Advances of Industrial-Design Rechargeable Zinc Alkaline Anodes via Low-Cost Additives

Abstract

Cost and safety are emerging as paramount considerations for grid-scale energy storage and often limit battery technology from practical deployment. Zinc alkaline is under renewed interest due to opportunity for lowered cost and improved fire safety. Nominal industrial-design zinc alkaline electrodes need improvement on their ∼100 cycle life when cycled at significant zinc utilization. Here, we analyze a collection of 72 practical paste Zn alkaline electrodes at 15 or 30% utilization of zinc’s 820 mAh/g Zn, with and without additives, and compare the resulting performance, industrial cost, and material evolution. Additives comprising calcium hydroxide [Ca(OH)2], bismuth oxide (Bi2O3), cetyltrimethyl ammonium bromide (CTAB), and/or a synthetic layered silicate (Laponite) were chosen to reduce shape change, mitigate gassing, reduce zincate migration, and alter the ionic environment, respectively. The concentration of potassium hydroxide (KOH) was also varied (10, 20, and 37 wt % KOH). We find performance that surpasses the best values in the literature for practical, real-world, industrially relevant zinc alkaline electrodes: Ca(OH)2 with Bi2O3 increased cycle life to ∼1200 cycles in 20% KOH (150 Ah/mL anode volume); CTAB with Bi2O3 and Laponite in 10 wt % KOH achieved slightly higher than ∼1200 cycles (∼210 Ah/mL anode volume) and pure-ZnO electrodes in 10 wt % KOH cycled ∼1000 times at 15% Zn utilization (240 Ah/mL anode volume). XRD, SEM, and EDS characterization reveals an altered microstructure when the additives are used. The first direct observation of calcium zincate cycling is collected by in situ XRD. The characterization data suggest that the mechanism for increased cycle life is capture and localization of the soluble zincate that forms during discharge, thereby reducing zinc material dispersal and shape change and increasing cycle life. Another important feature is pore geometry. When Bi2O3 is added, the electrode microstructure switches from a “closed cell” pore geometry with large ZnO flakes locking up pores to a more “open cell” geometry when small amounts of Bi2O3 are present.