Computational Investigation of Halide Solid Electrolytes for Na-Based Batteries

Abstract

Significant scientific and economic challenges are presented by developing battery systems with increased energy storage capacity. Geopolitical issues might pose supply chain risks for lithium (Li)-ion batteries, which are frequently used in portable electronics. As an alternative, sodium-ion batteries (NIBs), have drawn attention from researchers all over the world due to the perspective of being lower cost systems[1]. In comparison to lithium-ion batteries, solid-state sodium-ion batteries (SSSBs) promise as a safe, scalable, and environmentally friendly alternative. For the production of robust and adaptable SSSBs, the development of highly conductive, electrochemically stable, and chemically stable solid electrolytes (SEs) is essential [2]. With greater durability, adaptability, and safety, solid-state batteries with inorganic solid electrolytes are being heavily investigated as safer and perhaps more energy-dense alternatives to liquid electrolyte cells.Sulfides solid electrolytes have been extensively investigated due to their mechanical softness and high ionic conductivity. However, the electrochemical oxidation stability of those materials are as low as 2 V (vs. Na+/Na)[3]. Alternatively, the excellent ion conductivities and stability at high potentials have made halide compounds, intriguing candidates for solid electrolytes in batteries. These compounds offer fast ion transport, good stability at highly oxidative potentials, and are easily processed. A wide range of chemistries, such as A3MX6 (A = Li, Na; M = Sc, In, Y, Yb, Er, Hf, Ho, Dy, Al, Zr; X = F, Cl, Br, I), have been synthesized with tunable properties and the characterizations of those materials shows relevant electrochemical proprieties [2].In our work, we investigate different Na-based chloride compounds by Density Functional Theory (DFT). We expand beyond the reported compositions to consider possible cation-substituted compounds. Here, we report on the structures, ionic conduction pathways and ionic conductivity (computed by molecular dynamics methods) expected for such compounds. In the next months, we will also evaluate the compounds´ chemical and electrochemical stability. Our work moves us one step closer towards the development of stable and highly conductive solid electrolytes for Na-based solid-state batteries.References :[1] J. Mater. Chem. A, 2021,9, 281-292[2]J. Mater. Chem. A, 2022,10, 21565-21578[3] ACS Energy Lett. 2022, 7, 10, 3293–3301