TiN hollow multishelled structure as separator modification material for enhanced lithium-sulfur battery performance
Lithium-sulfur(Li-S)batteries have garnered extensive attention due to their high theoretical capacity and cheap sulfur cathodes.However,sulfur has quite poor conductivity and exhibits large volume change during lithiation-delithiation processes,inducing poor structure stability.Moreover,intermediate products released during discharge,i.e.,lithium polysulfides,tend to dissolve in the electrolyte and pass through the separator to the anodic side,resulting in a severe"shuttle effect".Hence,the cyclic stability and rate capability of Li-S batteries are poor,hindering their commercialization.Several approaches have been developed to address the above challenges,mainly including an S host construction,electrolyte modification,separator modification,and so on.Among them,separator modification has been widely explored because it is simple to process and economical while effectively improving the Li-S battery performance.However,due to the nonideal composition and structure design,the Li-S battery performance remains undesirable.Herein,to simultaneously address the above issues,a titanium nitride hollow multishelled structure(TiN HoMS)was designed and employed for preparing different separator modification materials.TiN exhibits remarkable electrical conductivity and can catalyze the redox conversion of sulfur and polysulfides.HoMS can not only offer multiple physical barriers and abundant adsorption sites to inhibit the"shuttle effect"but also reduce the charge diffusion path.TiN HoMS was synthesized using a modified sequential templating approach followed by a nitridation of TiO2 HoMS.Using the hydrothermal method and sucrose as the carbon source,uniform carbon sphere templates were obtained by controlling the temperature and duration of the hydrothermal method.Subsequently,TiCl4 solution was adsorbed by these templates to yield titanium-rich composite spheres.Further,TiO2 HoMS with relatively uniform size was obtained by controlling the temperature and duration of calcination.Finally,TiO2 HoMS was nitrided in an argon atmosphere using melamine as the nitrogen source to obtain TiN HoMS,and the TiN HoMS modified separator was obtained via filtering.The electrochemical properties of various separator modification materials,including 3s-TiO2 HoMS,3s-TiN HoMS,TiN HS,and TiN-NP,were investigated and compared.The results revealed that the 3s-TiN HoMS modified separator displayed the best performance.The initial specific discharge capacities of batteries using PP/3s-TiO2 HoMS,PP/3s-TiN HoMS,PP/TiN HS,PP/TiN-NP,and PP separators at 1 C were 750,1134,875,788,and 642 mAh/g,respectively.After 300 cycles,their specific capacities remained at 522,792,704,640,and 469 mAh/g,respectively.This indicates that 3s-TiN HoMS can enhance the battery performance more effectively than other modification materials.Based on the above results,TiN HoMS,which combines the advantages of TiN and HoMS structures,can not only effectively inhibit the shuttle effect of lithium polysulfide and reduce the charge transport path but can also catalyze the redox reaction between sulfur and lithium polysulfide.Our proposed material design could provide a solution for addressing the bottlenecks of other high-energy-density rechargeable batteries.
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