New Insight into Desodiation/Sodiation Mechanism of MoS2: Sodium Insertion in Amorphous Mo-S Clusters.

Molybdenum disulfide (MoS2) is a promising anode material for sodium batteries due to its high theoretical capacity. While significantly improved electrochemical performance has been achieved, the reaction mechanism is still equivocal. Herein, we applied electron pair distribution function and X-ray absorption spectroscopy to investigate the desodiation/sodiation mechanism of MoS2 electrodes. The results reveal that Mo-S bonds are well preserved and dominant in the sodiation product matrix but do not convert to metallic Mo and Na2S even at deep sodiation. The MoS2 multilayer sheets break into disordered MoSx clusters with modified octahedral symmetry during discharging. The long-range order was not rebuilt during subsequent charging but with partial recovery of the Mo-S coordination symmetry. The mechanism of the reaction is independent of the carbon matrix, although it prevents the MoSx clusters from leaching into the electrolyte and thus contributes to an extended cycle life. This work refreshes the fundamental understanding of the desodiation/sodiation mechanism of MoS2 materials.