Study On The Synthesis And Sodium Ion Storage Properties Of Ultralight Flexible SnS₂@Graphene Fiber Fabric Anode

With the increasing market share of portable electronic devices,the manufacturing of flexible,portable and cost-effective electronic devices has become one of the most concerned issues for electronic equipment manufacturers.The portable electronic devices have great applications in fields of not only smart phones and tablet computers,but also health,aerospace and advanced manufacturing.With the rapid development of flexible electronic touch screens and flexible micro-nano devices,flexible energy storage devices have gradually become the key technical challenge for the flexibility of electronic devices.Previous studies have shown that the traditional battery systems such as lithium ion batteries,sodium ion batteries and supercapacitors have great limitations in portable energy storage devices.For example,when the device is bent,the structure of the powder electrode film is prone to be destroyed,leading to battery failure and safety risks.Therefore,this paper will focus on the study of the flexible negative electrode of the emerging sodium-ion battery,discuss the challenges of sodium-ion battery in flexible electronic devices,and how to solve these problems by using graphene fiber fabrics.In this paper,we designed a novel flexible SnS₂@graphene fiber fabric to solve the following problems that exist in the traditional slurry-coating electrode:first,the mass ratio of active material in the traditional SnS₂ electrode?SnS₂+copper foil/aluminum foil/nickel foam current collectors+conductive additives+polymer binder?is very low,which will further affect the enhancement of the overall specific capacity of the electrode.Second,serious volume expansion of the SnS₂ material will occur during the discharge-charge cycles.Thus,the traditional slurry-coating electrode will easily cause material pulverization,finally resulting in rapid capacity fading.Another concern is that the conductivity of SnS₂ is very low.If the active material is separated from the conductive additive,the energy density will decrease quickly,resulting in the ineffective utilization of the active material.Therefore,we chose tin disulfide as the active material and graphene fiber fabric as the flexible conductive framework,to construct the tin disulfide@graphene fiber fabric?SnS₂@rGF?composite electrode with light weight,porosity and excellent flexibility.As SnS₂ nanocrystals are obtained by in-situ sulfuration of SnO₂ nanocrystals,it can preserve the strong interface binding effect of in-situ nucleation of nanocrystals,which endows the SnS₂ nanocrystals with good interfacial carrier migration efficiency with graphene fiber skeleton and improving the structural stability of the electrode.As a result,the mass proportion of SnS2 active materials in the SnS₂@rGF can reach up to 67.2wt%,which is much higher than that of electrode by using metal foils as the current collectors.Moreover,the constructed SnS₂@rGF electrode can be bent at will,showing more flexibility than that of copper,aluminum and nickel current collectors and active materials.The specific capacities of the constructed SnS₂@rGF electrode at the second cycle were 836,818,706,593 and 492mAh/g at current densities of 0.1,0.2,0.5,1.0 and 2.0A/g,while the specific capacity was very close to the theoretical value of low current density.During long-term cycles,the capacity retentions were 95.89%?677mAh/g?,82.57%?583mAh/g?,76.20%?538mAh/g?and70.82%?500mAh/g?at 50th,100th,200th and 500th cycles,with a coulomb efficiency of 100%,respectively.It can be seen that the SnS₂@rGF electrode system designed in this paper delivered a practical capacity larger than most values of in literatures.In summary,we firstly adopted the ultralight graphene fiber fabric as the flexible current collector to solve the problems of low mass proportion of active materials and poor electrode stability in the traditional slurry-coating electrode,further leading to the improvement of sodium ion storage properties.The reported design concept of flexible electrode and electrode materials could provide some guides for future research of high-performance flexible sodium-ion batteries.