research group Tohoku University has developed a prototype metal-calcium (Ca) battery that can withstand 500 charge-discharge cycles, a benchmark for practical use. The breakthrough was reported on May 19, 2023 in the journal Advanced Science.
With the increasing use of electric vehicles and large energy storage systems, the need to explore alternatives to lithium-ion batteries is greater than ever. One such replacement is calcium-based metal batteries. The fifth most abundant element in the earth’s crust, calcium is widely available and inexpensive, and has a higher energy density potential than lithium. It’s also believed that its properties help accelerate ion transport and diffusion in electrolytes and cathode materials, giving it an advantage over other lithium-ion battery alternatives such as magnesium and zinc.
However, many obstacles still stand in the way of the commercial use of calcium-metal batteries. The main obstacle proved to be the lack of efficient electrolyte and cathode materials with satisfactory storage conditions for the cells. Already in 2021, members of the current research group found a solution to the first problem by developing a new fluorine-free electrolyte based on a hydrogen cluster (monocarborane). The electrolyte showed significantly improved electrochemical performance such as high conductivity and high electrochemical stability.
“In our current study, we tested the long-term performance of a calcium-based metal battery with a copper sulfide (CuS) nanoparticle cathode and carbon composite with a hydride-based electrolyte.said Kazuaki Kisu, associate professor at the Institute of Materials Research (IMR) at Tohoku University. As a natural mineral, CuS has favorable electrochemical properties. Its layered structure allows for the storage of various cations, including lithium, sodium and magnesium. Its theoretical capacity is 560 mAh per gram, two to three times that of current cathode materials for lithium-ion batteries.
Thanks to nanoparticles and a composite with carbon materials, Keys and his colleagues managed to create a cathode that can accumulate a large amount of calcium ions. Using a hydride-type electrolyte, they created a battery with very stable cycle performance. The prototype battery retains 92% capacity after 500 cycles.
The group is confident that their discovery will help advance research into cathode materials for calcium-based batteries.