Design And Electrochemical Performance Of X₂S₃（X=Sb,Bi） As Potassium-ion Battery Anode

Potassium ion batteries（PIBs）have attracted much attention of researchers due to the abundant resource of potassium in the earth’s crust（2.09 wt%）,low cost and wide distribution.In addition,the lower oxidation-reduction potential（-2.93 V）also guarantees a higher operating voltage and a higher energy density,which makes potassium ion batteries a powerful alternative to lithium ion batteries（LIBs）.Compared to the LIBs,however,the electrode material system of PIBs is not yet perfect.Therefore,the development of suitable electrode materials,especially negative electrode materials,has become an urgent task for the development of PIBs.This paper mainly includes the following aspects:Due to the large ionic radius of potassium,electrode materials will suffer from the huge volume changes during the potassiation/depotassiation process.Therefore,Surface carbon coating is an efficient strategy to improve the cyclability of electrode materials for potassium-ion batteries by alleviating the volume changes during the charge-discharge process.In this strategy,the realization of a high-quality carbon layer is crucial and generally relies on the post-annealing process.Nevertheless,the optimum of annealing temperatures should not only consider the graphitization degree of the carbon layer but also take into account the electrode materials.Herein,the variations in the morphology,composition and electrochemical properties of core-shell Sb₂S₃@C composites as PIBs anode are studied in detail when being annealed at and above the sublimation/melting point of Sb₂S₃.Due to the sublimation and melting of,the nanorods Sb₂S₃@C is changed to sphere-like shape,the content of Sb₂S₃ is decreased,and the thickness and doping of carbon shell are varied.The Sb₂S₃core is completely evaporated to form a homogenous carbon sphere when the annealing temperature is700°C.Among all annealed samples,Sb₂S₃@C annealed at 600°C exhibits the most stable cycle performance and remarkable rate capability.The thermal annealing strategy at the critical temperature range of core materials would offer an avenue for optimizing the properties of core-shell composites for device applications.For a specific or a certain type of electrode material,the key points to be considered when selecting a suitable electrolyte are electrochemical/chemical/thermal stability,voltage window range,good ionic conductivity,electronic insulation,non-toxic and low cost,etc.Herein,Bi₂S₃ nano-flower were prepared by low-cost solvothermal method and then as a case study to explore the effect of different electrolytes on its electrochemical performance.Compared to the hexafluorophosphate（KPF6）,the experimental results indicates that the electrolyte using Bis（fluorosulfonyl）imide potassium salt（KFSI）as the solute,can obtained more stable cyclic voltammetry curve and significantly improve the cycling performance of Bi₂S₃ nano-flower materials in potassium ion batteries.