Controllable Preparation Of Marcasite-type FeS₂ And Electrochemical Properties Research

The current social energy and environmental issues need to be resolved urgently.This is not only current situation that China needs to face but also the all country of the earth.Therefore,researchers are committed to the development of environmentally friendly and efficient renewable energy devices for alleviating the pressure of the energy crisis in some way.Transition metal sulfides can be used not only as electrode materials for high-performance lithium-ion batteries,but also as excellent electrode materials for sodium ion batteries.Among them,FeS₂ has been widely concerned because of the low cost and environmental friendliness.The type that most researches focus on are pyrite-type FeS₂ at present,and there is less research on another type of marcasite-type FeS₂.marcasite-type FeS₂,which has a smaller forbidden band width,stronger Fe-S and weaker S-S bond than pyrite,is expected to be an excellent electrochemical storage material.However,this is still a challenge that the preparation of high-purity marcasite-type FeS₂ micro/nano materials using a simple synthetic way.In this paper,the metastable phase FeS₂ with special morphological structure was prepared by simple hydrothermal method.At the same time,we explore the synthesis mechanism of the sample by X-ray diffraction,scanning electron microscopy,transmission electron microscopy and so on.The electrochemical properties of metastable phase FeS₂ as anode electrode materials for lithium ion/sodium batteries were investigated.The main conclusions are as follows:?1?In order to solve the problem of poor capacity and cycle performance degradation of FeS₂,and improve the electrochemical performance of FeS₂,these problems are more dependent on the morphology of the material,so the topography needs to be considered.This experiment explores the appropriate parameters through a series of hydrothermal experiments,using the common deionized water as a solvent to synthesize the desired metastable phase FeS₂ by simple hydrothermal method.The sample is composed of micron-sized particles and has a special hollow spherical structure.And for the first time through the time evolution experiment,it is concluded that the synthesis mechanism of ferrous sulfide meets the Ostwald ripening effect.The hollow spherical structure composed of micron-sized particles has a large specific surface area and can have more lithium/sodium intercalation sites,thereby improving the lithium/sodium storage properties of the material.In addition,in the charging and discharging process,the volume expansion and contraction of FeS₂ affects the battery performance,and the hollow sphere structure can largely alleviate this negative effect.?2?We have a lithium storage electrochemical performance test about metastable phase FeS₂.The synthesized material has a high specific capacity,and the metastable phase FeS₂ with a hollow ball special structure has good lithium storage performance and cycle performance.After 100 charge-discharge cycles at a current density of 500mA g^-1,the discharge specific capacity of metastable phase FeS₂ still is 430.2 mAh g^-1,and the capacity retention rate is 69.8%;The current density is from high(10A g^-1)to low(100mA g^-1),metastable phase FeS₂ still has a capacity retention rate of86.8%.?3?With the development of sodium ion batteries,sodium ion anode materials have also received increasing attention.The metastable phase FeS₂ with special structure as the anode material of sodium battery and had electrochemical performance test.It was found that the metastable phase FeS₂ with a hollow sphere structure has a high first charge-discharge specific capacity of 449.2 mAh g^-1 and420.7 mAh g^-1,and after 300 cycles,the material still has a capacity retention rate of79.6%.After a high current density cycle test of 10 A g^-1 and returning to a low current density of 100 mA g^-1,it can still reach 357.3 mAh g^-1,and the capacity retention rate is as high as 79.8%.