Researchers evaluated battery chemistries best suited for grid-level storage

Researchers applied rough set theory to rank some of the most commonly used battery chemistries according to parameters deemed important for grid-level storage applications. The team gave a score in each category and determined a winner, and it isn't lithium-ion.

The battery in a combustion engine car is usually a lead-acid battery, while the battery in a laptop is a lithium-ion battery. The different battery types offer unique advantages and disadvantages that make them more or less suitable for a particular application, which is why the industry prefers using one type over another in these examples.

With grid-level storage just making a market entry, that level of experience and learning has not yet been made, so a question for developers is which chemistry to use. A team of researchers from China’s Tianjin University has attempted to make the answer to this question somewhat easier. The team examined lead-acid(LAB), lithium-ion(LIB), zinc-air(ZAB), nickel/metal-hydrogen (Ni-MH), and sodium-sulfur batteries (Na-S), for their properties in terms of round-trip efficiency, specific energy, specific capacity, operating voltage, cycling life, self-discharge, cost, environmental impact, and safety.

Leading the pack, according to this study, are zinc-air batteries. In their findings, the team noted that zinc-air batteries have a relatively high specific energy and specific capacity.

Furthermore, the chemistry is based on zinc electrodes and free-oxygen fuel from the atmosphere. This composition makes these batteries comparatively low cost, environmentally friendly, and safe.

Despite these advantages, the researchers did point out that a broad commercial roll-out of ZABs has been hampered by the technology’s issues related to electrodes and electrolytes. “For example, air cathodes suffer from sluggish reaction kinetics due to four-electron oxygen reactions, which leads to low discharge voltages, high charge voltages, and low energy efficiency,” the researchers write in their paper. Additionally, the team notes that using alkaline electrolytes in ZABs causes passivation and dendrite growth, significantly shortening battery life. Other known problems of this chemistry are carbonation and water loss during charge and discharge cycling, caused by the half-open structure.

Coming second in the ranking are LIBs. They are already widely used in the industry and appeal with high operating voltages, high efficiency, and a very long cycle life. Concerns over raw material sourcing, costs, and safety, however, have downgraded the industry’s chemistry of choice. The team noted that for LIBs to be used at scale in stationary storage applications, optimal management of the battery and a sophisticated recycling route are required.

“Ni-MHs demonstrate great promise in power grid applications due to their relatively high energy density, high specific capacity, long cycling life, and environmental friendliness,” the team writes about its third-ranked battery chemistry. High costs and low energy efficiency have taken their toll on the chemistry’s overall rating. Especially at lower temperatures, there are a lot of problems associated with these battery types.

LABs meanwhile have a range of promising properties the team identified in terms of cycling durability and energy efficiency. On the downside, the use of lead is dangerous for human health and the environment. Also, these types of battery don’t perform well on the specific energy, specific capacity, and operating voltage metrics.

Coming in last are the Na-SBs. Sodium-sulfur batteries have been used in small-scale storage applications in the past, the team writes, and they have shown some good performances in terms of high efficiency, operating voltage, and cycle life. What makes them complicated to use in large-scale storage is the comparatively high operating temperature, which raises safety concerns and needs to be managed, at more considerable effort than is the case with rival chemistries.

“Although a large number of battery technologies has been reported, the fabrication of low-cost, high-performance batteries with excellent power and energy densities, operating safety, and cycle stability remains a great challenge,” the researchers conclude in their publication.

“In-depth investigations of high-performance and novel battery systems are necessary. Many efforts, for example, to investigate high-performance potassium-ion batteries with relatively high energy density but lower cost compared with LIBs, are ongoing.”

Additionally, the team pointed out that standardized methods to evaluate battery performance are desirable at this stage. With this suggestion, they pointed to the methodology they had to use. As the team reviewed an existing body of literature about the various chemistries, they were prompted with somewhat hard to compare data. Therefore, the team chose Rough Set Theory as a methodology to process the data sets. Rough set theory is a mathematical approach to solve vague and uncertain issues. “Rough set theory expresses uncertainty and imprecision by a boundary region of a set. The rough set refers to the process of topological operations, also known as approximations,” the authors define.

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