Unraveling high efficiency multi-step sodium storage and bidirectional redox kinetics synergy mechanism of cobalt-doping vanadium disulfide anode

Sodium-based storage devices based on conversion-type metal sulfide anodes have attracted great atten-tion due to their multivalent ion redox reaction ability.However,they also suffer from sodium polysul-fides(NaPSs)shuttling problems during the sluggish Na^(+) redox process,leading to"voltage failure"and rapid capacity decay.Herein,a metal cobalt-doping vanadium disulfide(Co-VS_(2))is proposed to simulta-neously accelerate the electrochemical reaction of VS_(2) and enhance the bidirectional redox of soluble NaPSs.It is found that the strong adsorption of NaPSs by V-Co alloy nanoparticles formed in situ during the conversion reaction of Co-VS_(2) can effectively inhibit the dissolution and shuttle of NaPSs,and ther-modynamically reduce the formation energy barrier of the reaction path to effectively drive the complete conversion reaction,while the metal transition of Co elements enhances reconversion kinetics to achieve high reversibility.Moreover,Co-VS_(2) also produce abundant sulfur vacancies and unsaturated sulfur edge defects,significantly improve ionic/electron diffusion kinetics.Therefore,the Co-VS_(2) anode exhibits ultrahigh rate capability(562 mA h g^(-1) at 5 A g^(-1)),high initial coulombic efficiency(~90%)and 12,000 ultralong cycle life with capacity retention of 90%in sodium-ion batteries(SIBs),as well as impressive energy/power density(118 Wh kg^(-1)/31,250 W kg^(-1))and over 10.000 stable cycles in sodium-ion hybrid capacitors(SIHCs).Moreover,the pouch cell-type SIHC displays a high-energy density of 102 Wh kg^(-1) and exceed 600 stable cycles.This work deepens the understanding of the electrochemical reaction mechanism of conversion-type metal sulfide anodes and provides a valuable solution to the shuttlingofNaPSs inSIBsandSIHCs.

Metallic few-layered 1T-VS_(2)nanosheets for enhanced sodium storage

Metallic few-layered 1T phase vanadium disulfide nanosheets have been employed for boosting sodium ion batteries.It can deliver a capacity of 241 mAh∙g^(−1)at 100 mA∙g^(−1)after 200 cycles.Such long-term stability is attributed to the facile ion diffusion and electron transport resulting from the well-designed two-dimensional(2D)electron-electron correlations among V atoms in the 1T phase and optimized in-planar electric transport.Our results highlight the phase engineering into electrode design for energy storage.

Boost VS_(2) electrochemical reactive kinetics by regulating crystallographic planes and coupling carbon matrix for high performance sodium-ion storage

Vanadium disulfide(VS_(2)) as a typical two-dimensional transition metal chalcogenide has excellent competitiveness for sodium-ion storage due to its wide layer spacing(0.575 nm),high theoretical capacity of 932mAh·g^(-1) originating from multi-electron electrochemical redox.However,continuous sodiation process accompanied by crystal structural evolution and collapse cause rapid capacity decaying.Herein,novel few-layer VS_(2)nanosheets with open(001) crystal planes are in-situ constructed on reduced graphene oxide to solve these issues mentioned above.It indicates that few-layer VS_(2)provides more Na^(+) storage activity due to the low Na^(+)surface migration energy barrier on exposed crystal(001)planes.The flexible and high electronic conductivity of carbon matrix also effectively builds multi-level buffer structure and electron transport kinetics to boost the Na^(+)insertion/conversion reactive activity on VS_(2) as well as Na^(+) pseudocapacitance storage kinetics on edges and defects of nano sheets.Those coupling effects result in high rate capability and long cycling stability as a battery/capacitor anode.It delivers conspicuous high energy density of 81 and 40 Wh·kg^(-1) at power density of 118 and 10,286W·kg^(-1),as well as 80% energy retention rate after 5000cycles,confirming its great application potential in sodiumbased storage devices.