Heterostructures of 2D Molybdenum Dichalcogenide on 2D Nitrogen-Doped Carbon: Superior Potassium-Ion Storage and Insight into Potassium Storage Mechanism

Constructing 2D heterostructure materials by stacking different 2D materials can combine the merits of the individual building blocks while eliminating their shortcomings. Dichalcogenides are attractive anodes for potassium-ion batteries (KIBs) due to their high theoretical capacity. However, the practical application of dichalcogenide is greatly hampered by the poor electrochemical performance due to sluggish kinetics of K+ insertion and the electrode structure collapse resulting from the large K+ insertion. Herein, heterostructures of 2D molybdenum dichalcogenide on 2D nitrogen-doped carbon (MoS2, MoSe2-on-NC) are prepared to boost their potassium storage performance. The unique 2D heterostructures possess built-in heterointerfaces, facilitating K+ diffusion. The robust chemical bonds (C-S, C-Se, C-Mo bonds) enhance the mechanical strength of electrodes, thus suppressing the volume expansion. The 2D N-doped carbon nanosheets interconnected as a 3D structure offer a fast diffusion path for electrons. Benefitting from these merits, both the MoS2-on-NC and the MoSe2-on-NC exhibit unprecedented cycle life. Moreover, the electrochemical reaction mechanism of MoSe2 is revealed during the process of potassiation and depotassiation.