Investigation of Electronic and Ionic Structures of Selected High Entropy Chlorides for Application as an Electrode in Batteries

Abstract

The integration, growth, and penetration of renewable energy requires durable, cost-effective, and sophisticated materials for energy storage. Current Lithium-ion batteries (LIBs) are the major players due to their longer cycle life, high energy density, and other advantages; however, their performance is limited by the materials used for the cathodes, namely the common transition oxides. High-entropy materials (HEMs) and high-entropy chlorides (HECls) are promising alternatives due to their entropy stability and optimised transport properties. This work explores electronic and ionic structures of such systems as Li2[Me2+]Cl4 where Me is Zn, Mn, Co, Mg, and Fe to crown their potential as cathode materials. Density functional theory (DFT) calculations using the Quantum ESPRESSO package were done by including both constant and element-dependent Hubbard U corrections to consider the present correlation effects due to transition-metal d-orbitals suitably. From the analysis, the density of states (DOS), band structure, and the spin polarisation in single-component as well as multi-component chlorides were focused on. Binary chlorides such as, FeCl4, MnCl4, and CoCl4 exhibit an insulating nature through intense spin polarisation, while ZnCl4 and MgCl4 are wide-bandgap non-magnetic insulators. Multi-component high-entropy chlorides exhibit a broader electronic-state distribution across the Fermi surface, characterised by d-bands, resulting in a range of semiconductor or insulating properties. The results show that the entropy effect found in high-entropy chlorides results in substantial electronic changes, which can potentially enhance the conductivity and cycling stability of the single-component counterparts. The electronic density of states computed here will facilitate and help to explain the subsequent experimental results (XANES, EXAFS) from Forschungszentrum Jülich colleagues. This work maps out a pathway to developing high-entropy halide cathodes and suggests Li2[Me2+]Cl4 as potential materials for next-generation rechargeable batteries.