Preparation And Energy Storage Properties Of High-performance Metal Chalcogenides

Energy storage has become a growing global concern due to increasing energy demand for energy,rising prices of fossil fuels,and the adverse impacts of their use on the environment.The high efficiency,flexibility and sustainability of secondary battery energy storage can meet different grid functions.Lithium-ion batteries(LIBs)developed in recent years cannot meet the demands of large-scale energy storage due to cost constraints.Therefore,the development of new low-cost,environment-friendly,and high-performance secondary ion batteries is of great significance to achieve highefficiency energy storage.Sodium-ion(SIBs)and potassium-ion batteries(PIBs),which have a similar working principle to LIBs,have broad development prospects and application potential because of their abundant raw material and low price.As one of the important components of the battery,the performance of electrode materials has a decisive impact on the battery.The exploitation and design of high-performance anode materials is a necessary means to promote the development of SIBs and PIBs.Among numerous anode materials,metal chalcogenides have attracted extensive attention due to their variety,abundance,low cost,stable properties and high theoretical capacity.However,there are also serious volume expansion,slow kinetics,and side reactions during the electrochemical process.This thesis is mainly aimed at the problem of slow dynamic properties,taking copper based and iron based metal chalcogenides as the research object,several different copper based and iron based metal chalcogenides materials have been designed and synthesized from the characteristics and existing problems of the materials themselves,and a variety of optimization strategies have been developed to obtain a series of anode materials with excellent performance.Meanwhile,combined with different testing methods and characterization methods,the structureactivity relationship between material properties and performance was deeply analyzed.The main conclusions are listed as follows:First,a chemically in situ fabrication method is proposed to prepare the integrated cuprous selenide(Cu2Se)electrode by means of directly chemical selenization ofthe copper(Cu)current collector with commercial selenium powder.During in situ selenization,the composition of the electrolyte plays a key role in the formation of polyselenide intermediates and the further selenization of Cu current collectors.The obtained self-assembled Cu2 Se electrode with interconnected nanosheet morphology not only facilitates the ion transport kinetics but also alleviates the volume expansion during the conversion reaction of selenium-based materials.In addition,the strong interaction between selenium species and the current collector is conducive to inhibiting the loss of active materials.Benefiting from the above advantages,the in situ fabricated Cu2 Se electrode demonstrated superior potassium ion storage performance(462 m A h g-1 at 2 A g-1 for 300 cycles)and sodium ion storage performance(775 m A h g-1 at 2A g-1 for 4000 cycles).Next,Secondly,based on the above simple in situ preparation strategy,we prepared copper sulfide(Cux S)again through the spontaneous sulfidation process of sulfur powder and Cu current collector.However,the reaction kinetics of a single Cux S electrode is sluggish,leading to a lower reversible capacity.Here,we select Fe2O3 material with low cost and ultra-high theoretical specific capacity(1007 m A h g-1),and first melt it with sulfur to obtain Fe2O3@S composite,and the Fe2O3@Cux S heterostructure is then obtained by the sulfurization reaction of S and Cu current collector through the battery resting process.The built-in electric field of the p-n heterostructure formed when a p-type semiconductor(Cux S)and an n-type semiconductor(Fe2O3)are coupled promotes ion/electron transport and electrode activity for efficient energy storage.As a result,the Fe2O3@Cux S heterostructure achieves ultra-high specific capacity(1089 m A h g-1 at 0.2 A g-1)and high first Coulombic efficiency(96%),which is the highest level of metal compounds heterostructure materials in current sodium-ion batteries.Finally,in view of the slow dynamic properties caused by the poor intrinsic electronic conductivity of metal chalcogenides,we started from the intrinsic properties of materials,regulate the energy band structure through Se doping,so that the semiconductor Fe S material was transformed into a metallic Fe S0.5Se0.5 material.Benefiting from the inherent high electronic conductivity of Fe S0.5Se0.5 and the high tap density of the bulk material,the conducting-additive-free(CA-free)electrodes are fabricated with high volumetric capacity of 933 m A h cm-3 in SIBs.Meanwhile,Fe S0.5Se0.5 material with layered structure exhibits a rare intrinsic intercalation pseudocapacitive behavior and fast kinetic properties even if it is crystallized into a micron-scale bulk,achieves excellent rate performance(273 m A h g-1 at 50 C rate).This strategy of optimizing the intrinsic properties of materials can effectively guide the development of electrode materials in the future.To sum up,in this thesis,to solve the slow dynamic properties of metal chalcogenides,three strategies are employed including morphology design,heterostructure construction and energy band structure regulation to optimize the energy storage properties of electrodes.The structure-activity relationship between electrode properties and energy storage performance was revealed by combining various characterization methods,which provided a new idea for the synthesis and optimization of electrode materials in the future.