Nature of extra capacity in MoS2 electrodes: Molybdenum atoms accommodate with lithium

Two-dimensional (2D) layered transition metal sulfide based materials are promising candidates for electrodes of lithium ion batteries (LIBs). As one of the representatives, molybdenum disulfide (MoS2), exhibits additional reversible capacity beyond their theoretical value although the lithium storage mechanism is still poorly understood. In this report, we developed a highly conducting metallic phase 1T(octahedral)-MoS2 based electrode with metal Mo atoms confined in "graphene nanoreactor" of abnormal lithium-storage sites, which delivered a high specific capacity of similar to 1800 mAh g(-1) at 1 A g(-1), about 2.6 times of its intercalation reactions value. Contrary to previous reports, a new lithium-storage mechanism for the high and ever-increasing capacity was proposed. The theoretical calculations and experiments show that a major contribution to the extra capacity in MoS2 anodes is due to Mo atoms accommodate with Li+. The Mo precipitates and their full contact with Li2S matrix enabled the reversible Mo -> LixMo -> Mo -> 1T-MoS2 reaction during charging/discharging processes. Over prolonged cycling, per Mo atomic could accommodate six Li+ ions. This new proposal could help to establish an accurate electrochemical reaction mechanism of MoS2 LIBs, which may lead to inspiration on new methods to greatly improve the performance of the MoS2 anode.