First principles study of layered scandium disulfide for use as Li-ion and beyond-Li-ion batteries.

The growing demand for high efficiency portable batteries has prompted a deeper exploration for alternative cathode materials. Due to low Earth abundance, scandium has not received much attention, however its low atomic mass makes it ideal for high gravimetric capacity electrodes. Here we have performed a comprehensive first-principles study to assess the performance of layered ScS 2 as a potential cathode for lithium-ion and beyond-lithium-ion batteries. We have explored the configuration space of ScS 2 and its intercalated compounds using a mix of machine learning and ab initio techniques, finding the ground state geometry to be layered in nature. This layered structure is found to have a high voltage, reaching above 4.5 V for Group I intercalants, ideal volume expansions below 10% for lithium and magnesium intercalation, is electronically conductive, and is ductile once intercalated. Of the intercalants considered, we find that lithium is the best choice for cathode applications, for which we have used a combination of thermodynamic phase diagrams, ab intio phonon calculations, and evaluation of the elastic tensor to conclude that ScS 2 possesses a reversible capacity of 182.99 mA h g -1 , on par with current state of the art cathode materials such as LiCoO 2 , NMC, and NCA. Finally, we substitute foreign metal species into the ScS 2 material to determine their effect on key cathode properties, but find that these are overall detrimental to the performance of ScS 2 . This does, however, highlight the potential for improvement if scandium were mixed into other layered systems such as the layered transition metal oxides.