Controllable Preparation And Sodium/Potassium Storage Performance Research Of MoS₂/C Nanocomposites

Compared with that of lithium-ion batteries,sodium-/potassium-ion batteries have been the most promising in large-scale energy storage device application due to the advantages of abundant resources,low cost,and suitable redxo potential of Na⁺/Na and K⁺/K.Graphite,as commercial anode material for LIBs,is unsuitable for Na⁺/K⁺with large ionic radius accommodation due to the narrow interlayer spacing(0.335 nm)delivering low reversible capacity.MoS₂owns high theoretical capacity(670 mAh g^-1)based on the insertion/conversion type reaction.However,the intrinsic low electrical conductivity and structural instability lead to sluggish electrochemical reaction dynamics and poor cycle life,which has seriously impeded their practical application for sodium/potassium-ion batteries anode materials.Carbon is a kind of material with excellent conductivity and structural stability.Therefore,the scientific and effective design of MoS₂and carbon composite can solve the above problems.Details are as following:First,the composites of carbon-encapsulating flower spherical MoS₂tightly connected with carbon nanotubes was successful synthesized via hydrothermal and carbonization methods.The retention rate of sodium storage capacity achieved 82.8%at 1.0 Ag^-1after 1200 cycles.Carbon and carbon nanotubes can improve high electronic conductivity of MoS₂,enhance the wettability of electrolyte to electrode materials,shorten the Na⁺diffusion distance,and improve the stability of MoS₂structure.Second,a controllable and simple strategy to fabricate tunable few-layered MoS₂materials strongly chemically bonding(C-S)with in situ conversion nitrogen-doped carbon as an advanced anode for SIBs and KIBs.The C-S bond ensures that the close link between nitrogen-doped carbon and MoS₂,which prevent MoS₂materials falling off the foreign carbon substrate especially at large currents.Few-layered MoS₂shortens the diffusion distance of Na⁺/K⁺,facilitates the energy storage reaction to be carried out on the surface,which shows a high proportion of pseudocapacitance behavior(92%and 84%at 1.0 mV s^-1for SIBs and KIBs,respectively),thus ensuring the high rate performance of electrode.At the same time,the phase change of MoS₂electrode material during sodium/potassium storage process are studied in detail by ex-situ XRD.Third,the core-shell structure of dopamine hydrochloride coated hydrothermal products in second part.The capacity can get to 220 mAh g^-1as sodium anode materials at 1.0 Ag^-1after 1200 cycles.The excellent electrochemical performance proves that the double-layer carbon composite greatly limits the volume change of internal MoS₂in the process of charging/discharging,which thus improves the stability of structure.Moreover,the double carbon also further makes up for poor conductivity.