UC Berkeley

Promising sulfur spinel systems with facile cation mobility are revealed for multivalent cathode applications based on systematical calculation and screening.

The rapid growth of portable consumer electronics and electric vehicles demands new battery technologies with greater energy stored at a reduced cost. Energy storage solutions based on multivalent metals, such as Mg, could significantly increase the energy density as compared to lithium-ion based technology. In this paper, we employ density functional theory calculations to systematically evaluate the performance, such as thermodynamic stability, ion diffusivity and voltage, of a group of 3d transition-metal sulfur-spinel compounds (21 in total) for multivalent cathode applications. Based on our calculations, Cr ₂ S ₄ , Ti ₂ S ₄ and Mn ₂ S ₄ spinel compounds exhibit improved Mg ²⁺ mobility (diffusion activation energy <650 meV) relative to their oxide counterparts, however the improved mobility comes at the expense of lower voltage and thereby lower theoretical specific energy. Ca ²⁺ intercalating into Cr ₂ S ₄ spinel exhibits a low diffusion activation barrier of 500 meV and a voltage of ∼2 V, revealing a potential cathode for use in Ca rechargeable batteries.