2D transition metal carbides and nitrides, named MXenes, are attracting increasing attentions and showing competitive performance in energy storage devices including electrochemical capacitors, lithium- and sodium-ion batteries, and lithium-sulfur batteries. However, similar to other 2D materials, MXene nanosheets are inclined to stack together, limiting the device performance. In order to fully utilize MXenes' electrochemical energy storage capability, here, processing of 2D MXene flakes into hollow spheres and 3D architectures via a template method is reported. The MXene hollow spheres are stable and can be easily dispersed in solvents such as water and ethanol, demonstrating their potential applications in environmental and biomedical fields as well. The 3D macroporous MXene films are free-standing, flexible, and highly conductive due to good contacts between spheres and metallic conductivity of MXenes. When used as anodes for sodium-ion storage, these 3D MXene films exhibit much improved performances compared to multilayer MXenes and MXene/carbon nanotube hybrid architectures in terms of capacity, rate capability, and cycling stability. This work demonstrates the importance of MXene electrode architecture on the electrochemical performance and can guide future work on designing high-performance MXene-based materials for energy storage, catalysis, environmental, and biomedical applications.

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1393wileyonlinelibrary.com the practical applications of SIBs have been hamstrung by the lack of suitable anode materials to host Na + , which has a larger radius than that of Li + . Graphite with a highly ordered structure is considered to be not suitable to accommodate Na + because Na hardly forms staged intercalation compounds with graphite. [ 2 ] Twodimensional layered metal sulfi des (LMSs) with analogous structures to graphite, such as MoS 2 , [ 3 ] WS 2 , [ 4 ] SnS, [ 5 ] and SnS 2 , [ 6 ] have been reported as potential electrode materials for SIBs. The open framework of these types of materials allows Na + to insert reversibly with acceptable mobilities. However, the further application of 2D LMSs is impeded by their inherent limitations. First, these semiconductor metal sulfi des have inherently low electronic conductivity, which affects their electrochemical performances for Na + storage. Second, owing to the high surface energy and interlayer van der Waals attractions, [ 7 ] these thermally unstable 2D nanomaterials have a tendency to restack to minimize the surface energy. Furthermore, the signifi cant volume change and mechanical stress as a concomitant of sodium-ion insertion and extraction can induce the failure of the electrode and the loss of contact between active materials and the current collector, resulting in poor cycling stability.Graphene has established itself as a promising candidate to circumvent these challenges. For example, WS 2 /graphene, [ 4 ] SnS/graphene, [ 5b ] and SnS 2 /graphene [ 6 ] nanocomposites have already been successfully applied as anode materials for SIBs, showing a synergistic effect for sodium-ion storage, including improved capacity, rate capability, and cycling stability. In these reports, it is generally recognized that the enhanced electrochemical performances are attributed to the good electronic conductivity and mechanical resilience of graphene as 2D conformal building blocks for these layered sulfi des. However, a fundamental understanding of the exact interaction mechanism between LMSs and graphene for improving Na + storage performance is still not clear. The heterointerface between LMSs and graphene has been proven to contribute to novel properties and new functionalities that cannot be achieved by individual constituting materials. [ 8 ] Therefore, investigations Graphene has been widely used as conformal nanobuilding blocks to improve the electrochemical performance of layered metal sulfi des (MoS 2 , WS 2 , SnS, and SnS 2 ) as anode materials for sodium-ion batteries. However, it still lacks in-depth understanding of the synergistic effect between these layered sulfi des and graphene, which contributes to the enhanced electroactivity for sodium-ion batteries. Here, MoS 2 /reduced graphene oxide (RGO) nanocomposites with intimate two-dimensional heterointerfaces are prepared by a facile one-pot hydrothermal method. The heterointerfacial area can be effectively tuned by changing the ratio of MoS 2 to RGO. When used as anode materials for sodiu...