| With the rapid development of portable electronic devices and new energy vehicles,there is an increasing need for energy storage systems that possess both high power density and high energy density.Despite the widespread commercial use of lithium-ion batteries,their power density remains suboptimal.Additionally,the further large-scale application of lithium-ion batteries is confronted with challenges due to limited resources,uneven distribution,and escalating mining expenses of lithium.Compared to lithium,sodium resources are abundant,inexpensive,and easily accessible.And the physical and chemical properties of sodium are similar to those of lithium.Therefore,the development of low-cost energy storage devices for sodium holds significant importance in both basic science and engineering.In recent years,sodium ion capacitors have garnered significant attentions due to their high energy and power densities,which are assembled by a battery-type negative electrode and a capacitor-type positive electrode.The capacitive cathode typically employs activated carbon materials with high specific surface areas.However,the commercialization of sodium ion capacitors still faces a critical challenge in developing battery-type anode materials with high specific capacity,high rate capability,and long cycle stability.Among various negative electrode materials,molybdenum disulfide（Mo S2）has garnered significant attention and extensive research due to its large layer spacing of 0.62 nm and high theoretical specific capacity of 670 m Ah g-1.However,Mo S2 still faces problems in practical applications due to its poor intrinsic conductivity and structural fragility during long-term cycling,resulting in unsatisfied rate capability and poor cycle stability.In view of these issues,this paper modifies the surface and interlayer of Mo S2 with carbon materials of different dimensions based on interfacial structure design,constructing a series of Mo S2/carbon composites with"face-to-face"stacking,strong interfacial Mo-N bonding,and high packing density.Those approaches achieve excellent electrochemical sodium storage performance in terms of high capacity,high power density,and high cycle stability.The sodium ion capacitor was assembled using the prepared materials and commercial activated carbon,exhibiting remarkable properties of high energy density and high power density.The primary contents of this paper are shown as follows:（1）The“face-to-face”overlapped single-layer Mo S2 and nitrogen-doped carbon（Mo S2/NG）were successfully synthesized by utilizing the complexation between hexamethyltetramine and Mo7O246-as well as employing glucose as carbon source.The morphology with crosslinked nanosheets provides abundant mesoporous structures and channels for ion diffusion.The carbon layer embedded between the Mo S2 layers not only enhances the conductivity and interfacial charge transfer,but also effectively suppresses volume expansion and structural damage during sodium storage.Therefore,Mo S2/NC exhibits excellent rate performance and cycle stability when used for electrochemical sodium storage,delivering specific capacities of 521 and 294 m Ah g-1 at 1 and 10 A g-1,respectively,and a capacity retention up to 95.5%after 1000 cycles at a current density of 1 A g-1.Finally,the sodium-ion capacitor utilizing Mo S2/NC as the negative electrode and activated carbon as the positive electrode exhibits energy densities of up to 122 and 44 Wh kg-1 at power densities of79 and 11500 W kg-1,and the capacity retention of 85.2%even after 1600 cycles at a current density of 5 A g-1.（2）By coating positively charged polyaniline on graphene oxide（PANI@GO）,Mo7O246-were adsorbed on the PANI@GO surface by electrostatic attraction,and then forming Mo S2/nitrogen-doped graphene composites（E-Mo S2/NG）with high-loading（90 wt%）,strong bonding（Mo-N bond）,and expanded layer spacing after hydrothermal treatment and calcination.High Mo S2 load characteristic is conducive to deliver high capacity.The interfacial Mo-N bond not only facilitates rapid charge transfer but also effectively prevents detachment of Mo S2 from the graphene surface.Additionally,increased layer spacing promotes rapid ion diffusion between layers and buffers volume expansion during sodium storage.E-Mo S2/NG exhibits outstanding specific capacity(620 m Ah g-1 at 0.1 A g-1),ultrahigh rate capability(201m Ah g-1 at 50 A g-1),and excellent cycling stability(390 m Ah g-1 after 1000 cycles at 1 A g-1).Furthermore,the sodium-ion capacitor constructed with E-Mo S2/NG as the negative electrode and activated carbon as the positive electrode demonstrates superior energy density and power density,delivering an energy density of 143 and 82 Wh kg-1 at power densities of 68 and 14421W kg-1,respectively.After 1500 cycles at a current density of 10 A g-1,the capacity retention remains at 78.1%.（3）The ordered compact self-assembly was achieved through electrostatic adsorption between Mo7O246-and PANI@GO,resulting in the formation of DNG/Mo S2 composite structure with ultra-small Mo S2 size,porous architecture,and strong interfacial bonding after calcination.The ultra-small size of Mo S2 facilitates the provision of abundant sodium storage active sites and interfaces with nitrogen-doped graphene,ensuring high conductivity and rapid charge transfer.The pore structure between dense graphene layers not only provides channels for ion diffusion,but also offers buffering space for the volume expansion of Mo S2 upon sodium insertion.Based on the above merits,DNG/Mo S2 exhibits high gravimetric/volumetric capacity(514 m Ah g-1/1439 m Ah cm-3 at 0.1 A g-1),high rate performance(290 m Ah g-1 and 811 m Ah cm-3 at 10 A g-1),and excellent cyclic stability(82.4%capacity retention rate after 2000 cycles at 1 A g-1)when applied to electrochemical sodium storage.Combining DNG/Mo S2 as the negative electrode and activated carbon as the positive electrode,the assembled sodium ion capacitor demonstrates high energy/power density and long cycle stability,delivering an energy density of 129 Wh kg-1 at a power density of 79 W kg-1,and a capacity retention of 81.8%after1600 cycles. |
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