Potential of Zinc-ion Batteries for Grid Storage
Researchers say that zinc-ion batteries for electrical grid storage are overestimated and still face many challenges.
For the last few decades, there have been many advancements in sustainable electrical grids that can charge electric vehicles and power homes and industries. However, due to the intermittence of renewable energy sources like solar or wind, the transition to sustainable grids depends on energy storage technologies.
Batteries are promising candidates for grid storage due to their modularity, and they are practical for scaling capacities.
Energy storage technologies are crucial to the transition to sustainable grids. Image used courtesy of Pixabay
Currently, lithium-ion batteries dominate the battery market due to their high energy density and long cycle life. Although energy and power density are key factors in batteries for many applications, they are relatively less crucial for grid applications. Cost, safety, and sustainability are far more significant due to the scale of storage required.
Lithium-ion batteries (LiBs) exhibit many safety concerns due to flammable electrolytes. Moreover, the scarcity of lithium means high costs. One of the promising candidates for this sort of application is an aqueous zinc-ion battery (AZiB). It maximizes the advantages of renewable energy sources.
Compared to lithium, zinc is more naturally abundant, translating to lower costs. But the main advantage of this battery chemistry lies in the compatibility of zinc with water, which allows for developing low-cost, non-flammable, aqueous electrolytes.
Battery energy storage. Image used courtesy of Adobe Stock
Zinc-ion batteries (ZiBs) are considered an exciting alternative to lithium-ion batteries as the zinc anodes allow for high volumetric capacity, low-cost, inherent safety due to lack of toxic and flammable solvents in the electrolyte, and practical advantages that make these batteries easy to manufacture on large-scale. Some lifecycle assessments suggest that the carbon footprints of ZiBs are up to 80% lower than LiBs.
However, in a new study published in Joule, the researchers at the University of Waterloo and the U.S. Department of Energy's (DOE) Argonne National Laboratory pointed out numerous claims in many open works of literature that have been overestimated. They further report that zinc-ion batteries still face many challenges associated with their practical applications.
Challenges of Zinc-ion Batteries
Zinc anode leads to high safety and low cost for ZiBs. However, zinc tends to grow spiky crystals called dendrites that can short-circuit the batteries. The dendrites form due to uneven deposition of zinc in the charging process. Many studies have focused on tackling this issue. However, only a few can meet the requirements for practical applications.
There are also issues with the cathode. The water molecules in the aqueous electrolyte can split into hydroxide ions and protons. The protons compete with zinc ions to move between the electrodes, while the hydroxide ions combine with zinc. Therefore, the electrolyte reduces the effect of zinc ions and insulates the surface. This process is known as intercalation. University of Waterloo Professor Linda Nazar, lead author of the study, suggests that electrolytes have proven effective in ensuring that zinc ions dominate the chemistry.
Another challenge the researchers identified was that the ZiBs running at high cycling rates experienced much more zinc intercalation. Therefore, high cycling rates would not be beneficial for large-scale grid storage. The researchers are trying to cycle at moderate rates and perform electrolyte engineering to prevent water separation.