As potential alternatives to lithium-ion batteries, rechargeable calcium (Ca) metal batteries offer advantageous features such as high energy density, cost-effectiveness, and natural elemental abundance. Its properties are also thought to help accelerate ion transport and diffusion in electrolytes and cathode materials, giving it an edge over other lithium-ion battery alternatives such as magnesium and zinc.
However, many challenges impede the development of practical Ca metal batteries. The challenges include the lack of an efficient electrolyte and the absence of cathode materials with sufficient Ca2+ storage capabilities.
Now, Tohoku University researchers have developed a prototype calcium metal rechargeable battery capable of 500 cycles of repeated charge-discharge – the benchmark for practical use.
In their previous research, the team provided a solution to the above-mentioned challenges when they developed a new fluorine-free calcium (Ca) electrolyte based on a hydrogen (monocarborane) cluster. The electrolyte showed 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).
Copper sulfide has favorable electrochemical properties. Its layered structure enables it to store a variety of cations, including lithium, sodium, and magnesium. Also, it has a large theoretical capacity of 560 mAh g−1 – two to three times higher than present cathode materials for lithium-ion batteries.
Researchers were able to create a cathode capable of storing large amounts of calcium ions through nanoparticulation and compositing with carbon materials. When employed with the hydride-type electrolyte, they produce a battery with highly stable cycling performance. The prototype battery maintained 92% capacity retention with a long-life cycle of over 500 cycles based on the capacity of the 10th cycle.
Based on the results, researchers are confident that their breakthrough will help advance research into cathode materials for Ca-based batteries.
“Our study confirms the feasibility of Ca metal anodes for long-term operations, and we are hopeful the results will expedite the development of Ca metal batteries,” says Kisu.
- Kazuaki Kisu, Rana Mohtadi, Shin-ichi Orimo. Calcium Metal Batteries with Long Cycle Life Using a Hydride-Based Electrolyte and Copper Sulfide Electrode. Advanced Materials, 2023; DOI: 10.1002/advs.202301178