Research

A research group has developed a prototype calcium (Ca) metal rechargeable battery capable of 500 cycles of repeated charge-discharge - the benchmark for practical use.

The breakthrough was reported in the journal Advanced Science on May 19, 2023.

With the use of electric vehicles and grid-scale energy storage systems on the rise, the need to explore alternatives to lithium-ion batteries (LIBs) has never been greater. One such replacement is Ca metal batteries. As the fifth most abundant element in earth’s crust, calcium is widely available and inexpensive, and has higher energy density potential than LIBs. Its properties are also thought to help accelerate ion transport and diffusion in electrolytes and cathode materials, giving it an edge over other LIB-alternatives such as magnesium and zinc.

But many hurdles remain in the way of Ca metal batteries’ commercial viability. The lack of an efficient electrolyte and the absence of cathode materials with sufficient Ca²⁺ storage capabilities have proved to be the main stumbling blocks.

Back in 2021, some members of the current research group provided a solution to the former problem when they realized a new fluorine-free calcium (Ca) electrolyte based on a hydrogen (monocarborane) cluster. The electrolyte demonstrated markedly improved electrochemical performances such as high conductivity and high electrochemical stabilities.

“For our current research, we tested the long-term operation of a Ca metal battery with a copper sulfide (CuS) nanoparticle/carbon composite cathode and a hydride-based electrolyte,” says Kazuaki Kisu, assistant professor at Tohoku University’s Institute for Materials Research (IMR).

Schematic of a prototype Ca metal battery. The battery comprises a Ca²⁺ storing positive electrode containing the CuS cathode and Ca metal anode with a hydrogen cluster electrolyte. Cycling performance of the Ca–CuS battery. ©Kazuaki Kisu

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