Chemical Pre-Processing of Transition Metal Chalcogenide Electrode Materials

We have identified H_xCrS₂, which is produced through proton exchange of NaCrS₂, as a new sodium ion battery electrode with improved performance over its parent material. H_xCrS₂ sees a measured capacity of 728 mAhg^-1 and an improvement in diffusion constant of three orders of magnitude better than NaCrS₂. Notably, the structure of H_xCrS₂ consists of an alternating crystalline/amorphous motif as a result of Cr migration during desodiation which is seemingly responsible for the improvement in performance. The alternating structure enables access to reversible Cr redox in the material which supports the high capacities. A range of techniques is used to study the mechanism by which the presence of the amorphous phase allows for these improvements. We then apply similar synthetic conditions to a library of other materials in which removal of the alkali ion results in transition metal migration to identify candidates which may feature similar structural motifs and study their electrochemical behavior. Through the development of pre-processing techniques such as proton exchange, we can re-explore electrode chemistries which may have previously been rejected due to migration of the transition metal in the absence of capacity limiting side reactions.