Out of several candidates that could replace Li in rechargeable batteries, calcium (Ca) stands out as a promising metal. Not only is Ca 10,000 times more abundant than Li, but it can also yield—in theory—similar battery performance. However, there still remain some major hurdles to the development of Ca-based batteries, one of them being a lack of knowledge on suitable cathode materials that can efficiently store and release Ca in a reversible manner.

Now, researchers from Chung-Ang University, Korea; UC Berkeley; and Argonne National Laboratory have used first principles calculations to demonstrate that layered calcium transition metal (TM) oxide materials (CaTM₂O₄) with a range of TM substitutions (TM = Ti, V, Cr, Mn, Fe, Co, and Ni) have excellent battery-related properties including thermodynamic stability, average voltage, energy density, synthesizability, ionic mobility, and electronic structure.

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.

In a paper published recently in the journal Advanced Energy Materials, they report that the thermodynamic stability of the charged phase and TM redox activity are sensitive to TM selection, with CaCo₂O₄ having the best balance of all considered properties.

The scientists considered seven transition metal ions and four types of layered structures for a total of 28 candidate cathodes. In addition to identifying 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. The promising candidate structures and chemical compositions we found will hopefully encourage further experiments on these materials.

—Prof. Haesun Park, Chung-Ang University, co-corresponding author

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.

Resources

• Haesun Park, Christopher J. Bartel, Gerbrand Ceder, Peter Zapol (2021) “Layered Transition Metal Oxides as Ca Intercalation Cathodes: A Systematic First-Principles Evaluation” Advanced Energy Materials doi: 10.1002/aenm.202101698