Minerals As Electrode Materials for Ca-Based Rechargeable Batteries: Evaluation of the Pyroxene, Garnet, Melilite and Double Carbonate Groups

Abstract

Rechargeable lithium-ion batteries dominate the consumer electronics and electric vehicle markets. However, concerns on Li availability have prompted the development of alternative high energy density electrochemical energy storage systems. Rechargeable batteries based on a Ca metal anode can exhibit advantages in terms of energy density, safety and cost. The development of rechargeable Ca metal batteries requires the identification of suitable high specific energy cathode materials. This work focuses on Ca-bearing minerals because they represent stable and abundant compounds. Suitable minerals should contain a transition metal able of being reversibly reduced and oxidized, which points to several major classes of silicates and carbonates. A recent work [1] discusses their electrode characteristics based on crystal chemistry analysis and density functional theory (DFT) calculations. The results indicate that upon Ca deintercalation, compounds such as pyroxene, garnet and double carbonate minerals could display high theoretical energy densities (ranging from 780 to 1500 Wh/kg) with moderate structural modifications. As a downside, DFT calculations indicate a hampered Ca mobility in their crystal structures with energy barriers for Ca migration exceeding 2 eV. More recent investigations found a lower energy barrier of 1 eV in the group of melilite with formula Ca2MSi2O7, where Ca ions are in a square antiprism coordination polyhedron and M is a transition metal ion in tetrahedral coordination.Acknowledgements: Authors are grateful for financial support from European Union H2020-FETOPEN funded project CARBAT-766617.[1] Torres, Luque, Tortajada, Arroyo-de Dompablo, Scientific Reports 9, 9644 (2019).