Preparation And Lithium-ion Battery Performance Of Cobalt Selenide Based Anode Materials

With the increasing development of society,the problems of energy consumption and environmental pollution have attracted widespread attention from all walks of life.In recent years,researchers around the world have devoted to the development of high-performance,sustainable,green and low-cost new energy storage devices.Lithium-ion battery is currently the most widely studied energy storage device,and it has the advantages of long cycle life,high specific energy and good safety.As an important part of battery,anode material has become a bottleneck restricting the development and application of high-performance lithium-ion batteries.Transition metal compounds,as a kind of high-performance anode materials of transformation-type anode materials,have achieved many remarkable research results.Cobalt selenide which is a typical kind of transition metal compound is called metal conductor and exchange-enhanced pauli paramagnetism.Its excellent electrical conductivity and high specific capacity have attracted wide attention from researchers.However,it is still a challenge to effectively suppress the irreversible Se/Co dissolution and rapid capacity decay caused by severe volume changes during the cycles.This paper mainly focuses on the preparation process of the cobalt selenide-based material,different characterization and various electrochemical tests to analyze the influences of the designed hollow nanostructures,composite systems and other factors to suppress the irreversible Se/Co dissolution and volume change during the cycle,and achieve high lithium storage performance.The main work content and research results are as follows:1.The preparation of Co_0.85Se@NCMT composite material and its lithium storage performance.A facilitate and efficient self-generated sacrificial template method is used to prepare Co_0.85Se nanoparticles encapsulated in the inner wall of N-doped carbon matrix nanotubes(Co_0.85Se@NCMT).In this strategy,the formation of stable Co-N/C and Se-C as well as enhancing the mechanical strength between active materials and N-doped carbon matrix nanotubes can critically affect the performance through suppressing the dissolution of Se/Co increasing conductivity,promoting the shuttling of the ions/e^-moving and mitigating the volume expansion during charge-discharge process,which play a key role in improving the structure stability and electrochemical performance;Co_0.85Se nanoparticles encapsulated in the robust carbon matrix inner wall can ensure good electron transfer and prevent to aggregating together of nanoparticles,leading to superior electrochemical reversibility;carbon matrix nanotube can provide sufficient space to effective in accommodating the volume changes of encapsulated Co_0.85Se nanoparticles,thereby improving the cyclic stability.Based on the above advantages,as expected,the electrochemical investigations exhibited that the Co_0.85Se@NCMT anode performs a stable reversible capacity of 462.9 mAh g^-1 at a large current density of 5 A g^-1 and a remarkable capacity retention of 99.5%after 800cycles,suggesting its promising potential for the anode of LIBs.2.The preparation of Co_0.85Se/Ni_0.85Se@PPy composite material and its lithium storage performance.Designing and synthesizing a compound Co_0.85Se and Ni_0.85Se spherical shell structure uniformly coated by conductive polymer polypyrrole(Co_0.85Se/Ni_0.85Se@PPy)through simple hydrothermal method,calcination and polymerization process.In this strategy,the hollow spherical shell structure can provide a reasonable volume expansion space for the process of lithium insertion and extraction,and provide a fast channel for ions and electrons,thereby improving the reaction kinetics during the charging and discharging process,and improving the cycle life and stability;the coating of conductive polymer polypyrrole can effectively prevent the Co_0.85Se/Ni_0.85Se spheres from pulverizing during the cycles and protect the original morphology;the synergistic effect formed between the two components of Co_0.85Se and Ni_0.85Se reduces activation energy of the reaction and further improves the cycle life and stability.This well-designed structure can provide a stable capacity of 612.9 mAh g^-1 after 300 cycles at a high current density of 2 A g^-1,and has a high capacity-upgrade rate of nearly 194.6%,making Co_0.85Se/Ni_0.85Se@PPy expected to become one of the promising anode materials for lithium-ion batteries.