Design,Preparation And Electrochemical Properties Of Multi-component Molybdenum-based Composite Energy Storage Materials

With the development of science and technology in today’s world,people’s demand for energy is increasing,and as environmental pollution and other issues continue to emerge,lithium-ion batteries have attracted much attention as one of the important energy storage devices.As one of the important components of lithium-ion batteries,anode materials have always been an important research direction in the field of energy storage.At present,the main commercial anode material is graphite,which has excellent electrical conductivity and high cycle stability,but its low theoretical specific capacity limits the further application of this material.In recent years,multi-transition metal compound lithium-ion battery anode materials have received more and more attention.Such compounds have higher specific capacities,resulting in higher energy densities.Compared with graphite,it has a higher discharge potential and is safe as a negative electrode material for lithium-ion batteries.However,these compounds have poor electrical conductivity,which affects the rate performance capability of the material.At the same time,as a conversion material,there is a volume effect,and the cycle performance is poor.Based on the above problems,the first work of this thesis prepared a solid electrolyte coated with high-valence molybdenum-based transition metal compounds to solve the problem of poor rate performance,and further studied the kinetic mechanism;The carbon-coated transition metal compounds with morphological appearance can be used to solve the problems such as the decrease of cyclability caused by the volume effect.Some high-valence oxides are not suitable for modification with conventional carbon materials,and Li2SiO3 solid electrolyte coating is an effective technology to improve the electrochemical performance of high-valence oxides.The electrochemical performance was successfully improved by surface modification of the high-valent oxide MnTeMoO6 anode material with solid electrolyte Li2SiO3.By analyzing the dQ/dV curve,the reasons for the improved performance of the MnTeMo6@Li2SiO3 composite were further analyzed,and it was found that the peak shift of the discharge voltage was different for different samples.The activation energy(Ea)was calculated using the temperature-variable AC impedance test results.Studies have shown that compared with bare MnTeMoO6,Li2SiO3-coated MnTeMoO6 composites have higher electrochemical performance,lower activation energy,and higher discharge platform under rate performance.The effect of solid electrolyte coating on enhanced performance is revealed.Mo/Fe organic microsphere intermediate was successfully synthesized by using FeCl3 which is also lewis acid instead of NbCls.MoS2/FeS2/C microsphere composites with regular morphology were successfully prepared by pyrolysis and vulcanization.The electrochemical properties of MoS2/FeS2/C microspheres were characterized,and it was proved that they have the potential to be used as anode materials for lithium ion batteries.At a current density of 100 mA g-1,the material can maintain the capacity of 1089.2 mAh g-1 after 50 cycles.Rate performance tests show that the capacity can reach 550 mAh g-1 at a large current density of 1200 mA g-1.By analyzing the dQ/dV curve,it is found that the reason for the slow decrease of the capacity during the cycle is mainly the refinement of the particles inside the material and the generation of metal particles.