Synthesis And Electrochemical Performance Of Metal Selenides As Anode Materials For Potassium Ion Batteries

Limited by the lack of lithium resources,lithium-ion batteries can not meet the needs of large-scale energy storage in the future;potassium is regarded as a good substitute for lithium-ion batteries because of its high crustal abundance.The weak metal selenium bond in metal selenide makes the conversion reaction easy.In addition,its unique layered structure is conducive to ion diffusion.The above advantages make the metal selenides have better cycle stability.When the metals are germanium,antimony and tin,the material has both alloying and conversion reactions,and has a high theoretical capacity.In this paper,Sb2Se3,Ge Se2 and Sn Se2 are selected as the specific research objects,which are compounded with carbon materials to solve the inherent problems of poor conductivity and large volume expansion.The following researches were carried out.（1）Sb2Se3@N-C was prepared by chelation reaction and catechol formaldehyde resin modified by ethylenediamine was used as carbon source.The nano-sized Sb2Se3particles are tightly coated by nitrogen doped carbon.The material exhibits excellent cyclic stability Sb2Se3@N-C After 40 cycles at 0.1 A g^-1 current density,the capacity is403.5 m Ah g^-1;after 1000 cycles at 1.6 A g^-1 current density,the capacity is still 180m Ah g^-1.The good stability of Sb2Se3 can be attributed to the synergistic effect between the nanocrystallization of Sb2Se3 and the coating of nitrogen doped carbon,which effectively alleviates the volume change of Sb2Se3 during the charge discharge process.（2）The agglomerated Ge Se2/N-C spherical materials and well dispersed Ge Se2/C spherical materials were obtained by adjusting the morphology of Ge Se2/N-C with organic amine and ammonia.The electrochemical performance of Ge Se2/C spherical materials was tested as anode materials for potassium ion batteries for the first time.The results show that Ge Se2/C has poor cycle stability,while Ge Se2/N-C has excellent cycle stability.The charging capacity of Ge Se2/C is 354.5 m Ah g^-1 at 0.2 A g^-1 current density,and it will be below 100 m Ah g^-1 after 10 cycles;the charging capacity of Ge Se2/N-C is 430.5 m Ah g^-1 at 0.2 A g^-1 current density,the capacity of Ge Se2 is 350.2 m Ah g^-1 after 140 cycles.The capacity of Ge Se2 is still 192.7 m Ah g^-1 at high current density of 5 A g^-1 and above 200 m Ah g^-1 at high current density of 3 A g^-1 after 1500 cycles.The results show that the agglomeration of good carbon layer can improve the cycle stability,which is probably since there are other electron channels to maintain the redox reaction even if one or several spherical structures are broken or broken.Moreover,nitrogen doping can enhance the chemical binding force between carbon layer and Ge Se2,which can improve the rate performance and cycle stability of the material.（3）A three-dimensional conductive network was synthesized by solvothermal method to improve the electrochemical performance of Sn Se2.The results show that Sn Se2/C exhibits excellent electrochemical performance,and its capacity remains at113.2 m Ah g^-1 after 1000 cycles at a current density of 0.5 A g^-1;in contrast,the capacity of pure Sn Se2 decreases to zero after 30 cycles at a current density of 0.1 A g^-1.The results show that the construction of stable conductive structure can effectively improve the cyclic stability of the material.