Preparation And Study Of Lithium Storage Performance About Transition Metal Oxide And Selenide-based Anode Materials

In recent years,with the continuous growth of energy demand and the increasing consumption of fossil fuels,the application and development of global new energy has entered a critical stage,which also means that an era dominated by fossil energy development is gradually withdrawn,and an era of transition to non-fossil energy has arrived.Energy is the core issue of the survival and development of human society,especially in the context of"carbon neutrality and emission peak",how to exploit and develop new energy and corresponding materials is an important issue to be urgently solved.At present,the clean and environmentally friendly renewable energies,such as wind energy,solar energy,tidal energy,hydro energy,and biomass energy,have hindered their practical application and development in many fields,due to its shortcomings such as unpredictable energy,unstable and intermittent supply.Scientists are committed to exploring green and advanced energy conversion and storage devices to use these clean energy sources more efficiently.Among many energy storage devices,lithium-ion batteries have become one of the most widely used and potential energy storage devices owing to their excellent electrochemical performance such as high energy density,long cycle life,and no memory effect.Among them,due to the rapid development of 3C consumer electronics and electric vehicles,the market has put forward ultra-high requirements for power storage systems with high energy and power densities,and long cycle life.However,the graphite anode commercially used can only provide a specific capacity of 372 m Ah g^-1,which is far lower than the market expectation.Therefore,researchers have begun to explore the development of lithium-ion battery anode materials with higher lithium storage performance.Transition metal-based compounds have attracted extensive research by virtue of their advantage over the theoretical specific capacity of graphite.Among them,transition metal oxides and selenides are potential substitutes for lithium ion battery anode materials due to their adjustable morphology and structure,large specific surface area,abundant reserves,and environmental friendliness.However,the commercial application of these transition metal-based compounds is far from being expected.Specifically,there are limitations such as low electronic conductivity,large volume expansion during charging and discharging,and potential hysteresis between discharge and charging at high operating potential.In view of the above problems,the researchers found that through material structure regulation,nanotechnology,and compounding with carbonaceous materials,electrode pulverization can be effectively alleviated,and composite anode materials with high specific capacity and long cycle life can be obtained.Based on this,two composite materials of metal oxide/selenide and carbon with unique structure were designed and prepared,the structure,composition,and morphology of the material were determined by various characterization techniques,their electrochemical lithium storage performance as the anode of lithium-ion battery were tested,and the lithium storage mechanism of the composites and the reasons affecting the excellent lithium storage performance were analyzed.The main content includes the following two aspects:（1）Preparation and lithium storage performance of oxygen vacancy-enriched Zn Mn₂O₄nanoparticles anchored on reduced graphene oxide composites.By using a simple solvothermal method,uniformly dispersed zinc manganate（Zn Mn₂O₄）nanoparticles were grown in situ on graphene oxide（GO）substrate,and then a pyrolysis strategy under a reducing atmosphere was adopted to obtain the composite of oxygen vacancy-enriched Zn Mn₂O₄nanoparticles anchored on reduced graphene oxide（O-Zn Mn₂O₄/r GO）.An increasing electrochemical reactive site and the rich pore structure between r GO substrate and Zn Mn₂O₄nanoparticles together endow the as-prepared O-Zn Mn₂O₄/r GO with excellent specific capacity,rate performance,and cycle stability when it was used as an anode material for lithium-ion batteries.Compared to pure Zn Mn₂O₄,its inherent defects and shortcomings have been effectively improved,successfully alleviates the expansion and crushing of the electrode structure during the cycling process.Besides,by changing the solvent concentration and reaction temperature,the size of the nanoparticles can be adjusted controllably,which further increases the specific surface area of the material,reduces the possibility of particle accumulation,promotes the charge transport rate,and improves the kinetic process of the electrode material.The results show that the O-ZMO/r GO electrode has a reversible capacity of 1272.1 m Ah g^-1after 100charges and discharges at a current density of 0.2 A g^-1,and its specific capacity can still maintain 780.0 m A h g^-1after 700 cycles at a high current density of 1.0 A g^-1.（2）Preparation and lithium storage performance of spherical Mo Se₂/Zn Se@NC composite with core-shell structure.In this part,a core-shell nitrogen-doped carbon-coated molybdenum diselenide and zinc selenide composite（Mo Se₂/Zn Se@NC）was synthesized by surface coating technique.Typical process was as follows:a metal-organic framework was firstly covered on the surface of MOG nanospheres,and then the Mo Se₂/Zn Se@NC with unique structure and morphology was obtained by selenization treatment.This unique core-shell structure not only effectively buffers the internal volume expansion of the electrode material generated during the cycling and improves the structural stability,but also changes the electronic structure inside the transition metal selenium compound through interface coupling,and promotes the electron transport capacity inside the material.By investigating the influence of selenidation temperature on battery performance of Mo Se₂/Zn Se@NC,it was found that it had a significant impact on the morphology,structure,and electrochemical performance of the composite,and the appropriate selenidation temperature was helpful to improve the structural stability and lithium storage performance of the material.The results show that optimal Mo Se₂/Zn Se@NC-700 composite delivers the best electrochemical performance as an electrode material for lithium-ion batteries.Its specific capacity can be stable at 1298.2m Ah g^-1after 100 cycles at a constant current density of 0.2 A g^-1,and it also shows good rate capability and cycle stability.