Modification And Electrochemical Performance Of MoSe₂ Anode Materials

Sodium-ion batteries are considered as one of the electrochemical energy storage technologies to replace lithium-ion batteries and achieve large-scale energy storage due to their abundant resource reserves and excellent energy storage performance.Molybdenum selenide（MoSe₂）has the characteristics of large interlayer space and high theoretical capacity,which is suitable for the anode electrode of sodium ion battery which is restricted by large ion radius and slow ion diffusion kinetics.However,due to the weak intrinsic electron transmission ability and volume expansion during sodium insertion,the rate performance and cycle performance of MoSe₂ cannot meet actual needs.In this paper,MoSe₂ is used as the research object.With the help of a simple one-step hydrothermal method,the molybdenum selenide anode material is modified by sulfur doping and carbon coating.The effect of doping and carbon coating on molybdenum selenide is systematically studied.Meanwhile,the enhanced mechanisms are thoroughly discussed,and provide an optimized parameter to explore the potential of MoSe₂ anode.The specific research content is as follows:A simple one-step hydrothermal method is used to prepare sulfur-doped molybdenum selenide anode material,namely MoS_xSe_2-x,using thiourea as a sulfur source.The electrochemical performance test shows that when the S/Se ratio in MoS_xSe_2-x is 0.61(MoS_0.76Se_1.24),the sodium ion storage performance of the material is the best.As for the rate performance,the MoS_0.76Se_1.24 electrode possesses superior specific capacity retention of 60%when the current rate increase from 0.1 A/g to 4 A/g,showing excellent rate capability.When the current density is 0.5 A/g,the specific discharge capacity of MoS_0.76Se_1.24 after 50 cycles is 368.82 m Ah/g,and the coulombic efficiency is 98.35%,showing excellent cycle stability.The excellent sodium storage performance of MoS_0.76Se_1.24 can be attributed to rational S doping.A proper amount of S doping can create anion vacancies in MoSe₂,improve its conductivity and reactivity,and improve the material’s sodium ion storage performance.Based on the preparation process of MoS_0.76Se_1.24,a carbon-coated MoS_0.76Se_1.24@C composite material was prepared by one-step hydrothermal method and annealing.Carbon materials can not only improve the electron transport ability of MoS_0.76Se_1.24,but also suppress the volume change of the composite material during charging and discharging.When the carbon mass ratio in the composite material is12.85 wt.%,MoS_0.76Se_1.24@C has the best sodium storage performance.At a high current density of 4 A/g,the capacity retention rate of MoS_0.76Se_1.24@C after 600cycles is as high as 83.9%.The results demonstrate that insufficient carbon coating fail to inhibit the volume expansion of MoS_0.76Se_1.24 significantly,leading to continuous loss of active materials and the continuous formation of solid electrolyte interphase（SEI）.Furthermore,excess carbon coating will extend the diffusion pathway of ions to MoS_0.76Se_1.24,reducing the ion diffusion capacity of the composite electrode.