Preparation Of Electrospun Tin-based Chalcogenides Composite Nanofibers And Their Performances Of Sodium/potassium Storage

At present,although lithium-ion batteries（LIBs）havs realized commercialization,safety,high cost and resource shortage of lithium have become key factors restraining its further development.Sodium/potassium-ion batteries（SIBs/PIBs）are expected to become strong competitor of the next generation of novel rechargeable batteries due to their lower cost,abundant reserves of sodium/potassium resources.Nevertheless,compared with Li-ion,the radius of Na/K-ion is larger,causing severe volume variations during Na/K-ion intercalation,and then inducing poor cyclic stability and sluggish reaction kinetics,which restrains the practical application.In this situation,it’s crucial to design state-of-the-art SIBs/PIBs anode materials with high energy density,long-service life and high rate characteristic,synchronously.Considering the unique layered structure,profoundly high theoretical capacity and large interlayer distance,the tin-based chalcogenides（such as Sn S₂and Sn Se₂）has a wide application foreground in SIBs/PIBs.However,as a conversion and alloy reaction-type anode material,the major issues of pure Sn S₂/Sn Se₂including indigenous low conductivity,the intermediate products are easily soluble in the electrolyte and inescapable volume distention during the cycle,resulting in the unsatisfactory cycle durability.Therefore,it is of great significance to design high performance Sn S₂-based and Sn Se₂-based electrode materials for sodium/potassium storage.In recent years,electrospun sulfurized/selenided polyacrylonitrile（SPAN/Se PAN）fibers are poised to become candidate materials to supersede carbon nanofibers substrate.SPAN/Se PAN possess the stable three-dimensional network structure and serviceable electrochemical properties,which are favorable to restrain the clustering of the active materials and the dissolution of intermediate products,buffer volume expansion,induce more active sites as well.Inspired by these advantages of SPAN/Se PAN,applying SPAN/Se PAN as a substrate to confine active constituent,aiming at innovating and developing anode materials with high capacity,long cycle stability and high rate characteristics,for SIBs/PIBs.Additionally,as a sustainable,environmentally friendly and affluent biomasses,the waste chlorella contains the plentiful N and P elements.N/P dual doping can facilitate ions transfer and induce sufficient defect sites,thus providing more active sites.Therefore,in this dissertation,a series of Sn S₂-SPAN,Sn S₂-N/P-SPAN and Sn Se₂-Se PAN composites were fabricated via the electrospinning combined with calcination treatment,and used as anodes of sodium/potassium-ion batteries.The research contents are as below:Firstly,utilizing SPAN fibers as a substrate to confine ultra-small Sn S₂nanocrystals,the Sn S₂-SPAN composites was synthesized by an electrospinning combined with sulfuration treatment.The combination of ultra-small Sn S₂nanocrystals and SPAN fibers enhanced structure stability of composite materials,thus improved the electrochemical properties of Na/K storage.Additionally,density functional theory（DFT）calculation results demonstrate that SPAN fiber is expected to afford a short-range diffusion path and additional storage sites for Na⁺/K⁺.As a consequence,Sn S₂-SPAN composite manifests excellent sodium/potassium-storage performances(SIBs:613 m Ah g^-1/100 cycles/0.1 A g^-1,328 m Ah g^-1/10000 cycles/5 A g^-1,261 m Ah g^-1/30000 cycles/10 A g^-1;PIBs:565m Ah g^-1/50 cycles/0.05 A g^-1,221 m Ah g^-1/2000 cycles/5 A g^-1).Surprisingly,when paired with Na₃V₂（PO₄）₃cathode,Sn S₂-SPAN//NVP Na-ion full cell maintains a capacity of 253 m Ah g^-1under 0.5 A g^-1after 50 cycles.Secondly,we dexterously utilize chlorella as the source of N/P element,designing Sn S₂nanocrystals confined on N/P co-doped SPAN fiber.N/P co-doping can not only promote the migration rate of ions but also provide more active sites.As expected,compared with Sn S₂-SPAN,Sn S₂-N/P-SPAN composite possesses more superior specific capacity,rate performance and cycle life(SIBs:570 m Ah g^-1/100 cycles/0.5 A g^-1,267m Ah g^-1/20000 cycles/10 A g^-1,229 m Ah g^-1/30000 cycles/15 A g^-1;PIBs:578 m Ah g^-1/100 cycles/0.05 A g^-1,178 m Ah g^-1/10000 cycles/5 A g^-1).Identically,when paired with Na₃V₂（PO₄）₃cathode,Sn S₂-N/P-SPAN//NVP Na-ion full battery retains a stable capacity of 265 m Ah g^-1under 0.5 A g^-1after 50 cycles.Finally,considering Se has higher conductivity than S,we designed a novel composite material（denoted as Sn Se₂-Se PAN）,that is,Sn Se₂nanoparticles uniformly encapsulated in the Se PAN matrix.Se PAN fiber is not only advantageous to restrain the aggregation of Sn Se₂nanoparticles but also eliminate the dissolution and shuttle problem of polyselenide.In addition,the combination of Sn Se₂and Se PAN efficiently reinforces the structural stability of the composite.Experimental results show that the Sn Se₂-Se PAN electrode manifests exceedingly excellent performance in storing Na/K(SIBs:429 m Ah g^-1/100 cycles/0.1 A g^-1,283 m Ah g^-1/10000 cycles/5 A g^-1,192 m Ah g^-1/66000 cycles/15A g^-1;PIBs:380 m Ah g^-1/2000 cycles/0.5 A g^-1,142 m Ah g^-1/12000 cycles/5 A g^-1).Identically,Sn Se₂-Se PAN was applied as anode to assemble the Na-ion full cell,which displays excellent electrochemical performance(222 m Ah g^-1/50 cycles/0.5 A g^-1).