Preparation And Electrochemical Properties Of SnO₂ And SnS₂ Anode Materials

With the consumption of nonrenewable energy sources along with environmental pollution,it is extremely urgent to design efficient energy storage devices.Lithium-ion batteries(LIBs)and sodium-ion batteries(SIBs)are two of high-efficient energy storage devices that have been investigated widely,and the electrode materials with high reversible capacity,long cycle life,and excellent rate capability are the key to advanced LIBs/SIBs.SnO₂ and SnS₂ anode materials have attracted extensive research in virtue of earth abundance and high theoretical capacity.However,the low conductivity and huge volume expansion of SnO₂ and SnS₂ would lead to poor electrochemical performance.Combining nanosized SnO₂(SnS₂)with carbon materials can effectively improve the electronic conductivity and alleviate the volume expansion.Therefore,we designed and prepared the composite materials of nitrogen-doped porous carbon nanofiber encapsulated nano SnO₂ and the composite materials of SnS₂ quantum dots uniformly anchored on dispersed sulfur-doped graphene,and effectively improved the reversible capacity,rate capability,and cycle stability.Details are as following:First,SnO₂ nanoparticles encapsulated in nitrogen doped porous carbon nanofibers were prepared by electrospinning and selective etching strategy(SnO₂/CNF).Nitrogen-doped porous carbon nanofibers can also improve the conductivity and accelerate the electronic/Li⁺transportation,and nanosized SnO₂ can shorten the diffusion distance of Li⁺.Furthermore,porous carbon nanofibers can prevent the agglomeration of SnO₂nanoparticles and inhibit the volume expansion of SnO₂ nanoparticles in the electrochemical reactions,and the chemical bonding between SnO₂ and carbon nanofiber is conducive to electron transport and structural stability.Therefore,when examined as an anode material for LIBs,the SnO₂/CNF electrode exhibits excellent rate capability and cycle stability.After 600 cycles at the current density of 1 A g^-1,the capacity of Li storage was 568.7 m Ah g^-1.Second,in view of its excellent electrochemical performance in LIBs,the sodium-storage performance of SnO₂/CNF in SIBs was also studied.Compared with pure SnO₂,SnO₂/CNF shows a higher capacity and longer cycle life.After 1000 cycles at the current density of 1 A g^-1,the Na-storage capacity of the SnO₂/CNF electrode was 172.2m Ah g^-1,indicating that nitrogen-doped porous carbon nanofiber can significantly enhance the structural stability of electrode materials.Third,SnS₂ quantum dots uniformly anchored on dispersed sulfur-doped graphene were designed and synthesized via a low-temperature hydrothermal method with the addition of KCl(K-SnS₂@SG).Dispersed sulfur-doped graphene can increase the conductivity and accelerate the electronic/ionic transportation.The abundant voids around SnS₂ quantum dots can relieve much of volume expansion and keep SnS₂ from aggregating.Therefore,K-SnS₂@SG shows superior rate capability.The K-SnS₂@SG electrode can deliver high capacity of 236 m Ah g^-1 at the current density of 27 A g^-1.Furthermore,the kinetic analyses demonstrate that the dominant capacitive behaviors account for excellent rate capability.