Simultaneous control of crystallite size and interlayer spacing of MoS2 to achieve pseudocapacitive lithium intercalation

The functional properties of molybdenum disulfide (MoS2) are highly dependent on its structure. Here, we present a one-pot hydrothermal synthesis approach allowing to simultaneous control MoS2 structure over several length scales. Lowering the pH of the hydrothermal precursor solution leads to smaller crystallite sizes of the pristine MoS2 formed. Moreover, the addition of alkyldiamines to the same precursor solution leads to their physical confinement between the forming MoS2 layers without the formation of covalent bonds, yielding interlayer-expanded MoS2. Controlling alkyldiamine precursor concentration can vary the number of confined structural pillars in interlayer-expanded MoS2. Electrochemical lithium intercalation is tested as a function of MoS2 structural properties. It is revealed that both smaller crystallite sizes and expanded interlayer-spacing lead to an increasingly pseudocapacitive lithium intercalation signature. The number of lithium that is reversibly stored in interlayer-expanded MoS2 is increased to almost 1.5 per formula unit. The results provide a facile synthesis approach to simultaneously control MoS2 crystallite size and d-spacing, which may be of interest for applications beyond lithium intercalation, such as multivalent ion intercalation or electrocatalytic hydrogen evolution.