Construction Of Tin-based Compound/Carbon Composite And Its Electrochemical Potassium Storage Performance

The development of Lithium-ion batteries（LIBs）in large-scale energy storage is seriously resteicted by the high cost,low reserve,as well as uneven distribution of lithium resources.Compared with lithium,potassium has the advantages of abundant resources and lower raw material price,so that potassium-ion batteries（PIBs）has attracted great attention as an alternative choice of LIBs.One of the keys to the large-scale application of PIBs lies in the development of high-performance potassium storage materials.As for the anode,due to the combination of conversion and alloying reaction,tin-based compounds have a high theoretical specific capacity,which is expected to be a promising anode material for PIBs.However,the severe volume effects can destroy electrode integrity and cause electrode pulverization,causing further serious side reactions.Therefore,it is important for the development of PIBs to find a suitable electrode material and its matching electrolyte.In this work,a stable SEI layer was constructed on the surface of Sn S/r GO composites by using the co-interface engineering of KFSI electrolyte and ultra-thin Ti O₂ coating.Moreover,the introduction of oxygen vacancy in Sn P₂O₇/NC composite provides additional reaction sites,enhances the electrical conductivity,promotes ion transport and alleviates the structure deformation,thus greatly improves the electrode performance.It is a great significance for tin-based composite in the practical application of PIBs.Firstly,TiO₂ coating with uniform and controllable thickness was coated on the surface of Sn S particles by atomic layer deposition technology.It is found that the performance of Sn S/r GO could be significantly improved by a synergistic interface engineering of using potassium bis（fluorosulfonyl）imide（KFSI）electrolyte and ultrathin Ti O₂ coating.The Sn S/r GO@Ti O₂-20 electrode in KFSI electrolyte delivers ultra-stable cycling performance(450 m Ah g^-1 at 0.2 A g^-1 over 400 cycles)and outstanding rate capability(233 m Ah g^-1 at 5 A g^-1).The reversible potassiation/depotassiation processes of Sn S and Ti O₂ are experimentally demonstrated for the first time.The potassiation K_xTi O₂ coating layer is found to benefit the formation of ultrathin inorganic compound-rich solid electrolyte interphase（SEI）layer,both of which boost the Coulombic efficiency,charge transfer and K-ion diffusion kinetics of Sn S/r GO electrode.Then,SnP₂O₇/NC composites with high performance and rich oxygen vacancies were prepared in one step by using the method of carbonization of tin salt and organics containing phosphous at high temperature to create anoxic environment.By adjusting the calcination temperature,the concentration of oxygen vacancies in the composite was adjusted flexibly.The Sn P₂O₇/NC-400 composite delivers stable cycling performance of 190.5 m Ah g^-1 at 2 A g^-1 over5000 cycles.Moreover,the experimental results further exhibit that the Sn P₂O₇/NC electrode with higher oxygen vacancies can increase the conductivity and K⁺diffusion coefficient compared with the electrode with less oxygen vacancies,showing excellent electrochemical performance.