Beyond Lithium: A Search for Candidate Materials for Calcium-Ion Batteries

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Scientists conduct quantum mechanics simulations to identify a promising class of materials for new types of rechargeable battery that go beyond lithium.

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Editor’s note: There is some misinformation about lithium in the article below. Lithium is quite abundant on Earth. What are indeed limited are lithium mining operations and lithium production facilities. That can be solved over time, but it doesn’t mean that diversity of options beyond lithium couldn’t be useful. Generally speaking, diversity of options is preferred and helps economically. So, the research below seems interesting and noteworthy despite some of the common counterproductive claims included in the article.

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By Chung-Ang University

The scarcity of lithium has led scientists to look for other alkaline metals to produce rechargeable batteries. In a recent study, Assistant Professor Haesun Park of Chung-Ang University, Korea, and his colleagues, conducted computational simulations of various calcium (Ca)-based cathode materials to pinpoint the most promising ones for Ca-ion batteries. Their findings will help guide future experimental efforts and accelerate the development of new batteries, paving the way to the widespread adoption of electric cars.

Electric cars are the future; they will help reduce air pollution and end our dependence on fossil fuels. However, there is one glaring problem with this potentially disruptive technology: the availability of sufficient lithium (Li) to produce all these car batteries. The best rechargeable batteries we currently have are based on chemical reactions involving Li, which is why one finds Li-ion batteries in most portable electronic gadgets. Unfortunately, Li is not abundant on earth, and its reserves represent as little as 0.002% of the earth’s crust. Once electric cars become more widespread, the demand for Li will start exceeding the supply.

A possible way out of this conundrum is to design new types of batteries that rely on more abundant alkaline metals instead of Li. Out of several candidates that could replace Li, calcium (Ca) stands out as a promising metal for rechargeable batteries. Not only is Ca 10,000 times more abundant than Li, but it can also yield a similar battery performance in theory. However, there still remains some major hurdles to the development of Ca-based batteries, one of them being a lack of knowledge on suitable cathode (negative terminal) materials that can efficiently store and release Ca in a reversible manner.

In an effort to help identify the best candidate cathode materials for Ca-batteries, Assistant Professor Haesun Park of Chung-Ang University, Korea, and his colleagues adopted a systematic approach. By running high-throughput quantum mechanical simulations based on density functional theory (DFT), the team predicted battery-relevant properties of various layered materials combining Ca and transition metal oxides.

Most of this work was conducted at Argonne National Lab and in a Joint Center for Energy Storage Research (JCESR) project supported by the US Department of Energy. “Research on calcium batteries constitutes one of JCESR’s major ongoing efforts,” remarks Prof. Park. “The stable support from Argonne and the JCESR project allowed us to tackle the challenges in Ca-ion batteries, and their inclusive environments set the stage for synergetic collaborations.” The associated paper was made available online on November 6, 2021, and was published in Volume 11, Issue 48 of Advanced Energy Materials on December 23, 2021.

The scientists considered seven transition metal ions and four types of layered structures for a total of 28 candidate cathodes. Through DFT calculations, they assessed many important characteristics, including their thermodynamic stability, energy density, synthesizability, Ca mobility, and electronic structure. In turn, this allowed them to pinpoint promising materials for developing Ca-based batteries.

In particular, the scientists identified cobalt (Co) as a well-rounded transition metal for a layered Ca-based cathode with the formula CaCo₂O₄. Moreover, they also showed that combining different transition metals in the cathode can be a viable strategy to improve upon certain desired characteristics. “We managed to show that layered transition metal oxides, which are widely used in lithium, sodium, and potassium batteries, can be a promising class of materials for Ca cathodes,” highlights Prof. Park. “The promising candidate structures and chemical compositions we found will hopefully encourage further experiments on these materials.”

The successful development of low-cost and high-performance Ca-ion batteries will certainly help in the necessary transition away from traditional cars and towards electric vehicles, which will be more environmentally friendly in many regards. Let us hope experimental works cement the findings of this study and pave the way to a greener future.

Reference

Title of original paper: Layered Transition Metal Oxides as Ca Intercalation Cathodes: A Systematic First-Principles Evaluation

Journal: Advanced Energy Materials

DOI: https://doi.org/10.1002/aenm.202101698

About Chung-Ang University: Chung-Ang University is a private comprehensive research university located in Seoul, South Korea. It was started as a kindergarten in 1918 and attained university status in 1953. It is fully accredited by the Ministry of Education of Korea. Chung-Ang University conducts research activities under the slogan of “Justice and Truth.” Its new vision for completing 100 years is “The Global Creative Leader.” Chung-Ang University offers undergraduate, postgraduate, and doctoral programs, which encompass a law school, management program, and medical school; it has 16 undergraduate and graduate schools each. Chung-Ang University’s culture and arts programs are considered the best in Korea.