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Quantum Mechanics Simulations Aid the Identification of Candidate Cathode Materials for Calcium-Ion Batteries

Low-cost and high-performing calcium batteries will help streamline the transition from traditional gas cars to more environmentally-friendly electric cars.

Across the globe, governments and automakers have been shifting gears to promote electric vehicles as a key technology to end our dependence on fossil fuels, fight climate change, and reduce air pollution. As their name suggests, purely electric cars are powered exclusively by electricity. With neither combustion engines nor tailpipes, pure electric cars are significantly cleaner and safer for the environment compared to traditional gas cars since they do not produce carbon dioxide emissions when driven. However, there remains a major obstacle in the widespread adoption of electric cars – the limited availability of lithium to produce all these car batteries.

The best rechargeable batteries today are primarily based on chemical reactions that involve lithium, hence its use extensive use in portable electronic gadgets. Unfortunately, the earth is not rich in lithium, with its reserves representing only 0.002 per cent of the earth’s crust. As electric cars become more commonly used, the demand for lithium will quickly overtake the available supply. A possible solution to this problem is designing new types of batteries that rely on other alkaline metals that are more abundant than lithium. Calcium, for instance, offers promising potential as a rechargeable battery as it is 10,000 times more abundant than lithium and could theoretically yield a comparable battery performance. Unfortunately, scientists have yet to determine suitable cathode materials that can efficiently and reversibly store and release calcium.

Addressing this problem, Assistant Professor Haesun Park of Chung-Ang University, Korea, and his team have adopted a systematic approach that can help identify the best candidate for cathode materials for calcium batteries. By running high-throughput quantum mechanical simulations based on density functional theory (DFT), the scientists successfully predicted battery-relevant properties of various layered materials that combine calcium and transition metal oxides.

In the study, Park and colleagues selected seven transition metal ions and four types of layered structures to develop 28 potential cathode candidates. Through DFT calculations, the team analysed numerous features including but not limited to their energy density, electronic structure, calcium mobility, synthesisability, and thermodynamic stability, to help them identify the most suitable materials for developing calcium-based batteries.

Their findings revealed that cobalt may serve as a well-rounded transition metal for a layered calcium-based cathode with the formula CaCo2O4. They also demonstrated that combining different transition metals in the cathode can help to improve upon certain desired properties. Given these hopeful results, their experimental works are expected to pave the way for the development of low-cost and high-performing calcium ion batteries.

“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 [calcium] cathodes,” highlighted Prof. Park. “The promising candidate structures and chemical compositions we found will hopefully encourage further experiments on these materials.” [APBN]

Source: Park et al. (2021). Layered Transition Metal Oxides as Ca Intercalation Cathodes: A Systematic First-Principles Evaluation. Advanced Energy Materials, 11, 2101698.