Preparation And Properties Of MoS₂/C Composites For Sodium-ion Battery Anode Materials

The excessive use of traditional fossil fuels has brought about increasingly serious environmental problems.To develop new clean energy that can replace the traditional fossil energy and seek the harmonious development between man and environment is the focus of attention of the scientific community and the governments of various countries.As a new type clean energy,lithium ion battery has the advantages of high specific energy,long cycle life,high working voltage and environmental friendliness,which has obtained irreplaceable important applications in electric vehicles,electronic product driving power and so on.However,with the development and utilization of lithium resources,the amount of lithium on the earth cannot meet the rapid growth of people's demand for lithium,thus limiting the development and use of lithium ion batteries.Lithium and sodium are located in the same main group and have similar physical and chemical properties.Compared with lithium metal,sodium ion has the advantages of low cost and abundant reserves.Therefore,sodium-ion battery?SIB?has been widely studied.Sodium-ion battery has been considered one of the most promising alternatives to lithium ion batteries as the next-generation rechargeable energy storage devices.However,it remains a great challenge to exploit suitable anode electrode materials for sodium storage owing to relatively large radius of Na⁺.Molybdenum disulfide has been considered as a promising anode material for sodium-ion batteries due to its suitable layer spacing and high theoretical specific capacity.But the low electronic conductivity and large volume change during sodiation/desodiation processes limit its wide application.In the present study,firstly,a single-layer MoS₂ embedded in amorphous carbon nanofibers is fabricated by electrospinning.The obtained MoS₂/carbon nanofibers?MoS₂/CNFs?have unique hierarchical structure incorporating 2D single-layer ultrasmall MoS₂,1D carbon continuous phase and 3D interconnected porous network.When employed as anode material in sodium-ion battery,this hierarchical structure can enlarge accessible surface area of MoS₂,accelerate ion diffusion speed,shorten ion transfer length and improve the bulk conductivity,and then endow MoS₂/carbon nanofibers composite with high capacity and superior cycling stability.The electrochemical results show that the initial discharge and charge capacities of MoS₂/carbon nanofibers can reach 921 and 665 m Ah g^-1.After repeated charge-discharge test for 100 cycles,a stable capacity of 485 m Ah g^-1 is achieved,demonstrating a very low capacity loss of 0.05%per cycle.Secondly,on the basis of above,a novel 1D fiber-like electrode material integrating few-layer MoS₂,ultrathin carbon continuous framework,doped N atoms and well-defined3D connected macropores is developed by electrospinning?MoS₂/NCF-MP?.When used as anode in sodium ion battery,its unique structural hierarchy is able to maximumly diminish the solid-state diffusion length,lower electrochemical resistance,accelerate Na⁺transfer from bulk to electrode,and relieve the volume variation during sodiation/desodiation process,thus displays highly reversible capacity,long-term durability,along with ultrafast sodium storage capability.The stable reversible capacity of MoS₂/NCF-MP reaches 480 m Ah g^-1 at0.1 A g^-1 after 100 cycles,and undergoes a long cycling life of 300 cycles at 1 A g^-1,no visible capacity degradation is observed.More importantly,even under a very high current density of 30 A g^-1,the MoS₂/NCF-MP can deliver a commendable capacity of 217 m Ah g^-1,which means the charge/discharge step can be completed within a very short time of 26 s.Thirdly,MoS₂/honeycomb carbon?MoS₂/Hc C?composites were synthesized by usingpolyvinylidene fluoride as carbon source,ammonium tetrathiocarbolybdate as precursor of molybdenum disulfide,and polystyrene nanospheres?PS?as soft template agent.MoS₂/Hc C showed excellent electrochemical performance:the first coulomb efficiency is 72%;the reversible capacity of MoS₂/Hc C reaches 480 m Ah g^-1 at 0.1 A g^-1 after 100 cycles;the capacity of MoS₂/Hc C displays 270 m Ah g^-1 at a high current density of 1 A g^-1 after 100cycles;even at high current density of 5 A g^-1,the MoS₂/Hc C can deliver capacity of 203m Ah g^-1.The reported in situ pyrolytic and nano-space confined methods provide a new way for the design of high-performance SIBs anode,which may provide valuable reference for the future development of SIBs.