Research On Controllable Synthesis And Energy Storage Performance Of Metal Sulfide Electrode Materials

Vigorously developing green new energy is the main way to solve environmental pollution and energy crisis.Lithium-ion batteries are widely used in power and energy storage fields due to their high energy density.However,the continuous consumption of lithium resources and safety issues has become a bottleneck restricting the development of lithium-ion batteries.Metal sodium has received extensive attention due to its abundant resources and similar physical and chemical properties to lithium.However,the large Na⁺radius makes it difficult to deintercalate quickly and reversibly in traditional graphite anodes.On the other hand,metallic magnesium has good characteristics such as higher capacity,lower reduction potential,abundant reserves,and no dendrites,and has also attracted attention.However,due to the strong polarization of Mg²⁺in magnesium ion batteries,it is difficult for Mg²⁺to be transported in the electrode material,resulting in poor capacity and cycle stability,which limits the large-scale application of magnesium ion batteries.Aiming at the problems of sodium ion batteries and magnesium ion batteries,this thesis selects metal sulfides as the research object,and systematically studies its sodium or magnesium storage performance.The main contents are as follows:(1)In Chapter 3,we designed a three-dimensional(3D)hierarchical structure CuS-Cu@CNTs composite material with excellent reversible sodium storage performance by using the electroplating-vulcanization method.First:The reversible capacity of 512.5 mAh g^-1can be maintained after 1100 cycles at a current density of 2.4 A g^-1,which corresponds to a capacity retention rate of 87.5%(capacity decay rate?0.0113%);second,The CuS-Cu@CNTs composite exhibits excellent rate performance,with a capacity of 439.9 mAh g^-1 even at 3.2 A g^-1.The excellent rate performance of the CuS-Cu@CNTs electrode is attributed to the Cu nano particles,carbon nanotubes and pseudocapacitance in the electrochemical process in the3D electrode.Third,the CuS-Cu@CNTs composite material also has excellent low temperature performance.At-20?,a high capacity of 413.6 mA h g^-1 can still be obtained under the condition of 100 mA g^-1.Finally,we use constant current intermittent titration technique(GITT),electrochemical impedance spectroscopy(EIS)and ex-situ XRD to study the mechanism of performance improvement.(2)In view of the shortcomings of lithium-ion batteries prone to produce dendrites and poor dynamic performance of magnesium-ion batteries,this chapter has carried out research on magnesium-lithium hybrid-ion batteries.In Chapter 4,we applied natural chalcopyrite to the magnesium-lithium hybrid ion battery for the first time.When the current density of is 50mA g^-1,the first discharge capacity of the natural chalcopyrite cathode is as high as 383.3mAh g^-1;further more,the introduction of carbon nanotubes builds a flexible,binder-free self-supporting chalcopyrite/carbon nanotube composite film(F-CuFeS₂-CNTs),and shows more excellent electrochemical performance.When the current density is 1000 mA g^-1,the capacity is still as high as 89.5 mAh g^-1,and the capacity is 102.3 mAh g^-1 after 300 cycles.The unique porous network structure of F-CuFeS₂-CNTs thin-film electrodes facilitates the rapid transfer of carriers(lithium ions and electrons)and buffers the large volume changes of CuFeS₂.(3)In Chapter 5,we used a simple hydrothermal method to synthesize CuFeS₂@CNTs nanospheres in one step,and further studied its electrochemical properties.The CuFeS₂@CNTs composite material has a first coulombic efficiency of 87.3%,and it still has a reversible capacity of 444.5 mAh g^-1 after 300 cycles at 60 mA g^-1.The analysis of EIS,GITT and ex-situ SEM shows that,compared with pure CuFeS₂,CuFeS₂@CNTs has a more stable material structure,lower charge transfer resistance and higher ion transfer rate.