High-performance Copper-based Sulfide-based For Energy Storage

With the increasing of global energy shortage and environmental pollution problems,it is urgent to build a clean and efficient energy storage system.Since the first generation of commercial lithium batteries developed by Sony in 1991,lithiumion batteries have been rapidly developed and widely used in the past three years.However,with the increasing demands for energy in society,the energy storage of lithium resources on earth is difficult to support its sustainable supply and large-scale energy storage.In contrast,sodium and potassium have similar physical and chemical properties with lithium,but they are rich in reserves and thus resulting in low cost.More importantly,sodium and potassium ion batteries have the same "rocking chair" working principle as lithium ion batteries,which means that the rich knowledge on lithium ion batteries and their electrode materials might be effective to sodium and potassium ion batteries.However,due to larger ionic radii of sodium and potassium ions,their requirements for host materials are more stringent.Therefore,the developing of suitable anode materials with high theoretical specific capacity and energy density has become one of the most important challenge for secondary batteries.Among many over-anode materials,transition metal chalcogenides have attracted much attention due to their high theoretical specific capacity,which are considered to be one of the most promising anode materials.However,such materials have fatal shortcomings,such as low electronic conductivity,poor kinetic performance,huge reaction volume expansion,poor cycle performance,etc.,which are more serious for sodium ions and potassium ions with larger radii.In view of the above problems,this thesis takes transition metal chalcogenides as the research object,and proposes targeted optimization and modification of different materials from the perspective of functional design of materials,so as to provide theoretical support for the subsequent research and application of secondary battery anodes and ideas for reference.The conclusions of this paper are as followsFirst,we selected metallic Cu Se anode with high volume energy density as the research object.In view of its large volume expansion and slow ion transport in the material,we prepared the self-assembled crystal columnar morphology of nanosheets via wet chemical synthesis as a negative electrode material for sodium ion and potassium ion batteries.Benefiting from the unique morphological design,the material exhibits excellent sodium and potassium storage properties.At current densities of 10 A g-1 and 5A g-1,the material could provide a specific capacity of 295 m A h g-1 for sodium storage and 280 m A h g-1 for potassium storage,respectively.And the retention rate of sodium storage capacity was 95.6% after 1200 cycles at 5 A g-1,and the retention rate of potassium storage capacity was 92.6% after 360 cycles at 2 A g-1.The dynamic properties of the material were analyzed,and it was found that the excellent rate performance of the material was derived from the extrinsic pseudocapacitive behavior,and the in-situ XRD results showed that the material’s sodium and potassium storage processes were highly reversible.Second,we functionally design the material from the perspective of ion doping.Cu S0.8Se0.2 materials with hexagonal nanosheet morphology were prepared by wet chemical synthesis.On the premise that ion doping does not change the morphology and crystal structure,the introduction of Se brings a huge improvement to the electrochemical performance of the material.With a voltage range of 0.01-3 V,the Cu S0.8Se0.2 material exhibits a specific capacity of 423 m A h g-1 at a current density of0.1 A g-1,which is much higher than that of the undoped material.The material can achieve a reversible specific capacity of 374 m Ah g-1 at a large current density of 5 A g-1,and the capacity retention rate is still as high as 96% after 2000 cycles,while the undoped material is difficult to maintain stable cycling.The phase evolution process of the reaction process was revealed by in-situ XRD,and it was found that the electrochemical reactions were highly reversible due to the presence of S-Se.And the material also exhibits excellent potassium storage performance.At a current density of2 A g-1,the capacity retention rate is 96% after 600 cycles.Subsequently,Cu FeS2 microcurds were prepared by self-assembled nanosheets via a hydrothermal method,and the material was then coated with graphene by a photoreduction method to obtain Cu FeS2@RGO.This "hierarchical" structure of nanocomposite has a larger specific surface area and a shorter ion migration path,thereby realizing the material’s superior kinetic properties.Benefiting from the unique morphology design and graphene coating,the Cu FeS2@RGO anode could provide a specific capacity of 599 m A h g-1 at room temperature with a voltage range of 0.01-3 V(at a current density of 0.1 A g-1).In addition,the material can be cycled for 4800 times at a current density of 5A g-1with a capacity retention rate of 98.7%,which is far superior to similar anode materials.Moreover,the material still show a good electrochemical performance at a low temperature of 0 °C due to the excellent kinetic properties.At a current density of 0.1A g-1,it exhibited a reversible specific capacity of463 m A h g-1 after 40 cycles,and the capacity retention rate is 79.0% after 810 cycles at a current density of 2A g-1.The high reversibility of the reaction was further demonstrated by means of in-situ XRD and ex-situ XPS.Finally,we extended the idea of functional design to a new materials,and prepared nano-sized Cu2 SnS3 materials on graphene sheets via a one-step hydrothermal method.Benefiting from the nanometer size of Cu2 SnS3 and the construction of a threedimensional conductive network of graphene,the composite material exhibited excellent kinetic properties and excellent cycling stability.At a current density of 0.1 A g-1,the material could provide a reversible specific capacity of 432 m A h g-1.At a large current density of 2 A g-1,the capacity retention rate was 100% after 260 cycles.The construction of a three-dimensional conductive network enables excellent rate performance.The specific phase transformation processes of the material were further studied by in-situ XRD.In sum,in this thesis,we have prepared a variety of transition metal chalcogenide materials with excellent performance from the perspective of functional design of materials,and systematically explored the energy storage mechanisms of the materials by using a variety of characterization methods.Poor conductivity for such materials.Due to the huge volume expansion and other problems,we have optimized them through functional design of material structure,nanoscale regulation,carbon material composite,etc.,and applied the materials to sodium ion and potassium ion batteries.The research results lay a fundamental principles for the application and development of transition metal chalcogenides as anodes for batteries.