Grid Storage Batteries from Earth Abundant Elements

Over the last 3 decades, Li ion battery (LIB) production has grown rapidly driven by the mobile device applications and rapid expansion of electric vehicles. Along with these expansions of LIB production, large scale energy storage demands are also rapidly increasing, driven by the increasing renewable energy generation by solar and wind farms. . Recent projections of the global energy trends by the US National Academies require replacing the currently growing fossil fuel consumption by renewable energy sources (mainly solar and wind): 30% in 2030 and 50% in 2040. The intermittent and seasonal nature of solar/wind energy generation will require unusually large-scale energy storage capacity for long durations of 4-10 hours or longer. The global energy infrastructure is under rapid transition away from the fossil fuel economy toward renewable energy economy, and there are multiple challenges and opportunities for the current and emerging energy storage technologies. For the large-scale energy storage applications, fundamentally different electrochemistry with intrinsic safety is required based on earth-abundant elements (e.g., Na, K, Zn, Mg, Ca, Al, Fe, Mn) to avoid the competing demands of LIBs for mobile and EV battery applications<br/>Among many emerging beyond LIB chemistries, aqueous zinc ion battery (AZIB) has recently attracted increasing research attentions due to high Zn energy density (5854 Ah l^-1 and 820 Ah kg⁻¹), nonflammable nature, good durability, and low cost. Due to the water stability limits, the operating voltage of AZIB is lower that LIB (1.7 V vs. 4 V), but the overall theoretical energy densities are comparable to high ends of LIBs (300 Wh/kg and 500 Wh/L). With further research and development for performance improvements, AZIBs are very promising candidate for grid scale energy storage. The AZIB can be classified based on the electrolyte pH: strongly acidic electrolyte through acid addition, strongly basic electrolyte with alkaline solution, and mild acidic electrolyte with Zn salt solution. Different electrolyte pH leads to different proton electrochemical activity that leads to different electrolyte-electrode interactions, thus fundamental battery operation and degradation mechanism. AZIB with mild acidic electrolyte is an advantageous option due to better safety, lower corrosivity, higher durability, etc. While as both proton and OH- can be active at neutral pH, the fundamental chemistry tends to be more complex. In this work, combined modeling and experimental research progresses are presented to help deepen the understanding on AZIB systems.