In the last years, concerns on Li availability have aroused the search for suitable alternatives to rechargeable Li-ion batteries. An attractive alternative is to combine sustainability with prospects of high energy density and develop metal anode technologies based on multivalent abundant elements such as Ca. The development of the Ca-ion technology requires technical advances to overcome the existing hurdles concerning electrolytes, electrodes and cell design^1-3. Identifying cathode materials enabling effective diffusion of Ca²⁺ ions is far from being evident and, to the date, none of the investigated materials develops a stable high specific capacity with cycling ^1-3.

In order to identify potential cathode materials for the Ca batteries, we have carried out a Density Functional Theory investigation to quickly screen a variety of structures and compositions. The screening started with a pre-selection of candidate compounds from the Inorganic Crystal Structure Database (ICSD). For the selected compounds, the general strategy is firstly to calculate average voltage and volume changes associated to the redox reaction. In a second step, DFT calculations for the promising materials are performed to gain information of electronic and ionic conductivities, crystal structure of reduced/oxidized phases and possible phase transformations. Fifty Ca-transition metal compounds including oxides, sulphides, nitrides, carbonates and phosphates were preselected from the ICSD. Out of this set, 25 ternary oxides and the minerals belonging to the pyroxene, garnet and double carbonates groups have been analysed in deep. The results will be discussed in this communication.

Acknowledgments: Authors are grateful for financial support from European Union H2020-FETOPEN funded project CARBAT-766617.

References:

1. A. Ponrouch and M. R. Palacin, Current Opinion in Electrochemistry, 2018, 9, 1-7.
2. R. J. Gummow, G. Vamvounis, M. B. Kannan and Y. He, Advanced Materials, 2018, 30, e1801702.
3. P. Canepa, G. S. Gautam, D. C. Hannah, R. Malik, M. Liu, K. G. Gallagher, K. A. Persson and G. Ceder, Chemical Reviews, 2017, 117, 4287-4341.