Half-Heusler Alloy CoMnZ (Z = Sb/Sn): Electrode Material for Lithium-Ion Batteries

Heusler alloys (HAs) are a well-known family of compounds generating promising interest due to their robust structure, ease of tailoring their unique properties, and potential applications. The investigations in the direction of the electrochemical performance of these materials as electrodes for rechargeable lithium-ion batteries (LIBs) have been established theoretically and experimentally. Alloying of alkali metal ions into half-HAs unit cells can be another route to improve LIBs performance. This work presents our investigations on thermodynamically stable half-HAs CoMnZ (Z: Sb/Sn) as electrode materials for rechargeable LIBs using the first-principle calculations based on the density functional theory. The negative formation energies validate the thermodynamic stability of the alloys considered in this study. With increasing Li doping, a structural change from cubic to tetragonal and orthorhombic phase is observed in the host structure, and upon full lithiation (LiMnZ), a cubic structure is attained. The band structure calculations of the host structure and its lithiated phase indicate a metallic nature in these alloys. The calculations are also performed to investigate the structural stability of parent alloys and corresponding lithiated phases. We calculated a storage capacity of around 14.5 Ah/kg for 0.125 atomic fraction of Li atoms, which is increased by nearly 10 times upon full lithiation. A maximum open circuit voltage of around 9.8 V is calculated for Li0.125Co0.875MnSb and CoLi0.125Mn0.875Sb. Thus, all these remarkable results suggest that these intermetallic compounds have a strong potential as the cathode material for LIBs with a robust life and a large capacity.