Increased driving voltage and energy density with redox flow batteries
A research team led by Professor Heetak Kim of the Department of Biological and Chemical Engineering at KAIST announced on the 5th that they have succeeded in developing the longest-lasting aqueous zinc-bromine redox flow battery.

Recently, energy storage system (ESS) technology, which can increase energy efficiency, is gaining attention.

Currently, most ESS systems adopt the inexpensive 'lithium-ion battery' technology, but it has been pointed out that it is unsuitable for ESS due to inherent fire risks. In fact, there were 33 ESS fire accidents caused by lithium-ion batteries in Korea over the two years from 2017 to 2019. This accounts for 35% of the total, and the total loss, including damages incurred from shutdowns, is estimated to exceed 700 billion won.

Therefore, redox flow batteries using water-based electrolytes that can fundamentally prevent battery overheating are receiving great attention. In particular, zinc-bromine redox flow batteries using ultra-low-cost zinc bromide (ZnBr2) as an active material have been developed for ESS since the 1970s because they have the advantage of being able to increase energy density along with high operating voltage compared to other aqueous redox flow batteries, and are inexpensive.

The problem is that commercialization is being delayed due to the short lifespan of zinc anodes. In particular, the formation of uneven, protruding dendrites on zinc metal during the charging and discharging process is pointed out as a major cause of shortened lifespan by inducing internal short circuits in the battery.

Professor Heetak Kim's research team focused on the fact that "self-agglomeration" through "surface diffusion" of zinc nuclei occurs at carbon electrode interfaces with low surface energy. Through quantum mechanics-based computer simulations and transmission electron microscopy analysis, they succeeded in identifying self-agglomeration as the primary cause of zinc dendrite formation. In addition, the team discovered that dendrites did not form in specific carbon defect structures because the surface diffusion of zinc nuclei was suppressed.

"Professor Kim Hee-tak stated, 'The achievement of this research is the presentation of a new technology to overcome the lifespan limitations of next-generation aqueous batteries.' He added, 'Not only is it cheaper than existing lithium-ion batteries, but it can also operate for over 5,000 cycles at an energy efficiency of over 80%, which will contribute to the expansion of renewable energy and the revitalization of the ESS market.'"