Water covers about 70 percent of the Earth’s surface, but only 3 percent of it is freshwater that’s suitable for drinking. The remaining 97 percent is seawater, which is too salty for consumption. However, what if we could tap into its potential as a new renewable energy source?
A team of researchers, led by Professor Changshin Jo and Ph.D. candidate Hyebin Jeong from POSTECH’s Graduate Institute of Ferrous & Energy Materials Technology and Department of Chemical Engineering, respectively, has made significant progress in this field. They’ve confirmed the exceptional performance of seawater batteries (SWBs) that incorporate chelating agents, publishing their results in the Chemical Engineering Journal.
While lithium-ion batteries are widespread in portable electronics and automotive batteries, they have limitations, such as the risk of explosions and unusability if lithium supplies become depleted. To address these challenges, the development of next-generation batteries is underway.
Seawater batteries are one promising option, using Na-ions present in seawater to produce energy. These batteries offer easy accessibility to resources and are eco-friendly as they require no separate treatment processes.
Seawater’s high salinity comes from Na-ions that seawater batteries use to create and store electrical energy as they move between the cathode and anode.
The utilization of nickel hexacyanoferrate (NiHCF) as an intercalation cathode material in seawater batteries poses a challenge due to the high likelihood of defects during fabrication. To overcome this issue, the research team developed NiHCF with a chelating agent (Sample A) and compared its effectiveness to untreated NiHCF (Sample B).
Under a microscope, the two samples differed greatly in shape and structure. Sample B was composed of aggregated nanosized primary particles, while Sample A consisted of individual cubic-shaped particles that were 200-300 nanometers in size. Although Sample B had smaller individual particles, the aggregation of multiple particles into larger cohesive structures was less advantageous for battery production.
The electrochemical performance of both samples was also assessed. Sample A had lower water content, which typically impedes electrochemical performance, and showed higher energy efficiency and capacity based on current and voltage measurements.
The research team achieved a groundbreaking milestone by performing 2,000 cycles of charging and discharging on batteries using the two samples. Sample A demonstrated a remarkable capacity retention rate of approximately 92.8% and a decrease in the defect generation rate, a previous drawback of NiHCF, to 6%.
These findings demonstrate the superior performance of adding a chelating agent to nickel hexacyanoferrate and using it as a cathode material in seawater batteries. This discovery has the potential to advance seawater batteries as a viable candidate for next-generation energy storage systems.