| As a typical layered metal selenide,tin selenide(SnSe)has been widely studied in photovoltaic(PV)applications because of its excellent photoelectric properties,non-toxicity and abundance.At the same time,the thermoelectric and optoelectronic properties of SnSe can be regulated by structural transformation and appropriate doping.In addition,in terms of secondary battery energy storage,SnSe has a high sodium/potassium storage specific capacity(780 mAh g-1),which is a suitable anode material for sodium-ion batteries(SIBs)and potassium-ion batteries(KIBs).However,SnSe has poor conductivity as a semiconductor material and faces poor charge-discharge cycle stability and highcurrent charge-discharge ability during electrochemical sodium/potassium storage.To solve the above problems and obtain high-performance SnSe-based anode materials,this paper synergistically improves the sodium/potassium storage performance of SnSe from the aspects of multi-dimensional carbon structure enhancement,doping and defect control and nano-hollow composite structure design.At the same time,the electrochemical reaction process is elucidated and the electrochemical enhancement mechanism in the sodium/potassium storage cycle is revealed.The specific research results are as follows:(1)The SnSe-based multidimensional carbon structure was designed to enhance sodium storage performance.In this structure,SnSe nanoparticles are supported by an "inner" sandwich-like RGO and an "outer" nitrogen-doped carbon(SnSe/RGO@NC).These "inner" and "outer" structures could work together to form a multidimensional charge transfer path.The "inner" RGO constructs a fast charge migration path as a "highway".The "outer" nitrogendoped carbon provides a stable and strong interaction as a "ramp" for charge transfer between SnSe and RGO.First principle calculations show that nitrogendoped carbon can stabilize the SnSe/RGO@NC structure and enhance interfacial charge transfer through electrochemical interactions.The above behavior realizes the efficient kinetic performance of SnSe in sodium-ion batteries(small charge migration resistance and high sodium ion diffusion rate).Based on this,the composite electrode exhibits excellent charge-discharge cycle reversibility(448 mAh g-1 reversible sodium storage capacity after 500 reversible cycles,capacity attenuation is only 12.7%)and good rate performance(306 mAh g-1 at 5 A g-1).The design of multi-dimensional charge transfer path provides an idea for synergistic improvement of electrochemical performance in energy storage.(2)An SnSe-based multidimensional carbon structure that enhances potassium storage performance by synergistic reaction on a single electrode was designed.In this structure,SnSe nanoparticles are co-coated with "inner" 3D graphene aerogels and "outer" nitrogen-doped carbon(SnSe/3DRGO@NC).The"outer" nitrogen-doped carbon can provide stronger adsorption affinity for reaction products and improve potassium energy storage."Inner" and "outer"carbon materials can synergistically improve conductivity,promote the redox kinetics of Se,and realize K-Se energy storage.The results of the in situ test showed that a K-Sn reaction and a redox reaction of Se were formed in the electrode.Finally,the electrode has good potassium storage reversibility(312 mAh g-1 after 350 cycles,0.016%capacity attenuation per cycle)and good rate performance(196 mAh g-1 at 5 A g-1)during the K-Sn and K-Se reactions.This study can provide ideas for the structural design of monomer battery systems using synergistic reactions to enhance electrochemical performance.(3)Nb/In bimetallic doped SnSe/3DRGO composites were obtained by solvothermal method,and the doping ratios with the best performance were obtained by exploring different doping ratios.When the doping ratio of Nb and In is 1:1,the obtained Nb/In(1:1)-SnSe/3D RGO composite electrode has good potassium storage performance.After 300 cycles of reversible cycling,the specific potassium storage capacity was still 336.7 mAh g-1(tested at a current density of 0.2 A g-1).At a current density of 0.1-5A g-1,the reversible specific capacity of the Nb/In(1:1)-SnSe/3D RGO electrode can reach 495.5,406.6,333.5,279.3,216.4 and 130.2 mAh g-1,respectively.It was found that the Nb/In(1:1)-SnSe/3D RGO electrode exhibited a higher potassium ion diffusion coefficient and smaller charge transfer resistance,which may be due to the equal amount of heterogeneous metal atom doping of the composite electrode to maximize the number of exposed active sites,optimize reaction kinetics,and improve reactivity.Moreover,the two-ion doping strategy significantly expands the crystal structure layer spacing,which is conducive to the reversible intercalation of potassium ions in charging and discharging,and realizes highperformance potassium storage.(4)F-SnSe/3D RGO complexes with different doping concentrations were obtained by solvothermal method.After the potassium storage performance test,it is found that when the fluorine source:tin source is 2:1(wt%),the obtained electrode material has the best electrochemical performance.By testing its potassium storage performance,it was found that the specific potassium storage capacity of F/2-SnSe/3D RGO electrode material was still 410.3 mAh g-1 after 350 cycles,which was much higher than that of other doped samples and undoped samples.At current densities of 0.1,0.2,0.5,1,2,5A g-1,the reversible specific capacity of F/2-SnSe/3D RGO electrodes can reach 407.6,379.5,303.3,258.6,219.3 and 151.8 mAh g-1,respectively.Subsequently,the current density is gradually changed to small,and the storage capacity of the F/2-SnSe/3D RGO electrode material increases rapidly with the decrease of current density,which indicates that it has a fast reaction kinetics during the discharge/charge cycle.Furthermore,by studying the kinetics of potassium storage during the reaction,it was found that it had a fast potassium ion diffusion coefficient.The good cycle stability and rate performance are due to this suitable fluoroanion doping concentration in this electrode.(5)Using nano-SiO2 as a template,SiO2/SnSe complexes were prepared by a simple one-step solvothermal method,and then SnSe/HC complexes with nano-hollow structures were obtained by subsequent experimental steps.SiO2/SnSe complexes with different growth amounts were obtained by controlling the amount of raw material added,and the best growth control amount was obtained through test performance.Through the potassium storage performance test,the nano-hollow structure SnSe/HC electrode has better cycling performance and rate performance than the SnSe/C electrode and the pure phase SnSe electrode.After 280 cycles of reversible potassium storage,the specific capacity is still 376.3 mAh g-1,while the specific capacity of SnSe/C electrode and pure phase SnSe electrode rapidly decays to 156.3 mAh g-1 and 132.9 mAh g-1 after 80 cycles,which indicates that the nano-hollow structure can effectively improve the potassium storage cycle stability of the material.In addition,the reversible specific capacities of the SnSe/HC electrode at current densities of 0.1,0.2,0.5,1,2,and 5 A g-1 are 500.4,473.7,355.1,245.8,168.8,and 90 mAh-1,respectively.When the current density is gradually reduced after testing at a high current density of 5A g-1,the specific capacity of potassium storage of SnSe/HC electrode can be rapidly increased,indicating that the electrode has an effective charge transfer process.Through the capacity contribution analysis and kinetic characterization test of the electrode,the specific capacity of the nano hollow structure SnSe/HC electrode was maintained well in the alloying reaction stage and the transition reaction stage.At the same time,the fast and high potassium ion diffusion coefficient and small charge migration impedance of the electrode indicate that the electrode can achieve rapid charge transfer.This may be due to the large specific surface area of the nano hollow structural complex,which can expose more active sites and increase their utilization.At the same time,the nano-hollow structure has a unique anti-deformation internal cavity structure,which can provide an effective relief space for the volume expansion phenomenon caused by the charging and discharging of potassium ions.The construction of nanocomposite hollow structures is an effective strategy to improve the conductivity of materials. |
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