Electrochemical Properties Of Lithium Storage And Sodium Storage Based On Iron-based Sulfides

With the rapid development of society,non-renewable resources are becoming less and less,such as coal,oil,natural gas and so on.Currently,non-renewable energy has been difficult to satisfy our future living requirements,so the development of green and sustainable energy is imminent.Rechargeable batteries,supercapacitors,solar cells and other high-efficiency energy storage and conversion devices have attracted people's attention and are expected to become alternatives to non-renewable energy.Lithium/sodium ion batteries in energy storage devices are widely used in power grids and various portable electronic products due to their low cost/high energy density.In this paper,research on iron based sulfides are used as anode materials for lithium/sodium.On the one hand,iron-based sulfide materials have been extensively studied because of their abundant resources,low price,green,non-toxic and high specific capacity.On the other hand,compared with metallic oxides with high specific capacity,they have higher conductivity and smaller volume expansion during cycling.Therefore,we choose FeS₂ as the negative electrode material to study.However,iron-based sulfides has many merits in practical application,such as complex synthesis process and large volume expansion during lithium/sodium ion battery cycle.In order to solve these problems,we control the different synthetic temperatures and cooling methods in the reaction process and test the electrochemical performance of FeS₂.Finally,we obtain that FeS₂ exhibits excellent electrochemical performance when it is quenched in ice water and the reaction temperature is 180?C.At a current density of 200 mA·g^-1,the capacity can still be maintained at 384 mAh·g^-1 after 200 cycles.In order to further overcome the capacity attenuation caused by volume expansion in the process of sodium storage,the FeS₂ material was calcined at 500?C for 4 hours in argon atmosphere to induce partial phase transformation and led to Fe₇S₈ phase.Finally,the FeS₂/Fe₇S₈ composite was formed and the electrochemical performance is improved.The introduction of Fe₇S₈ phase can effectively reduce particle size and volume expansion,and synergize with FeS₂ phase to improve its electrochemical performance.At a current density of 200 mA·g^-1,the specific capacity of sodium ion batteries increased significantly and reached 609 mAh·g^-11 after 200 cycles.Reduced graphene oxide has high conductivity,specific surface area,flexible structure and stable chemical performance,and can significantly improve the electrochemical performance of the batteries.In this paper,FeS₂/RGO was synthesized by a simple oil bath thermal method,and calcined at 500?C for 4 hours to obtain FeS₂/Fe₇S₈/RGO material.FeS₂/Fe₇S₈/RGO maintained a capacity of 640 mAh·g^-1 after200 cycles at a current density of 200 mA·g^-1 in sodium ion batteries.The specific discharge capacity of the material remained at 1044 mAh·g^-1 after 300 cycles at a current density of 500 mA·g^-1.Even at a high current density 2 A·g^-1,the capacity remained at492 mAh·g^-1 after 3000 cycle in lithium ion batteries.