Study On Preparation And Lithium Storage Performance Of Multi–shelled Metal Oxide Composites

The latest research topic in efficient electrode materials for lithium–ion batteries（LIBs）is the development of multi–metal oxide composites with complex structures.Metal oxides,particularly multi–metal oxides,are widely utilized in energy storage due to their affordability,high capacity,and safety.However,low intrinsic conductivity and capacity attenuation remain significant challenges.Metal oxide/carbon composites with complex hollow structures and heterostructures have garnered significant interest thanks to their increased specific surface area,electrical conductivity,and stable framework based on a hierarchical structure.This structure helps to reduce the transmission distance of ions/electrons and mitigate volume changes during cycling.Additionally,the introduction of foreign metal cations into the crystal structure can provide more redox active sites for Li⁺adsorption,thereby further improving the electrochemical performance of LIBs.The composites,yolk–double–shell NiFe₂V₂O₈@NC and hollow four–shell Zn_0.5Mn_0.5Co₂O₄/RGO,were prepared using a combination of solvothermal and ion exchange methods.Both composites demonstrated excellent electrochemical lithium storage performance.The specific research contents are detailed below:（1）Preparation and lithium storage properties of yolk–double–shell NiFe₂V₂O₈@NC nanocomposites.The yolk–double–shell NiFe₂V₂O₈@NC nanocomposites were created using a straightforward self–template method and precise temperature control during the calcination process.This material was assessed as a effective anode material for LIBs.During the preparation process,the yolk–shell NiFe₂V₂O₈ was formed through an anion exchange reaction between Ni–Fe glycinate spheres and VO₃^–.This reaction took place in a condensation reflux environment and was followed by heat treatment.Then,the yolk–double–shell NiFe₂V₂O₈@NC nanocomposites were synthesized by coating PDA and carbonization in argon atmosphere.Benefiting from the unique yolk–double–shell structure,the electrode impressively achieves a high reversible capacity of 1347.6 m A h g^–1 after 200 charge–discharge cycles at a current density of 0.2 A g^–1 without significant degradation,with ideally stable rate performance(726.1 m A h g^–1 at 5 A g^–1),and superior cycling stability(75.6%capacity retention after 300 cycles at 1 A g^–1).This excellent electrochemical lithium–ion storage capacity is thought to be caused by the rapid ion diffusion kinetics achieved by synergistic redox of anions,cations,and oxygen,due to the introduction of vanadium redox pairs,which can be further enhanced by capacitance led surface electrochemical reactions(pseudocapacitance contributes up to89.6%at a sweep speed of 1.0 m V s^–1).Finally,Li Co O₂//NiFe₂V₂O₈@NC full cell were assembled and the electrochemical performance of the whole battery was evaluated,showing great potential for practical applications.This work will provide enlightening insights for the well–designed and controlled construction of complex porous yolk–shell like nanostructures for efficient lithium storage.（2）Preparation and lithium storage properties of hollow four–shell Zn_0.5Mn_0.5Co₂O₄/RGO composites.Zn_0.5Mn_0.5Co₂O₄/RGO composites featuring a hollow four–shell structure was prepared using an efficient and versatile synthesis strategy.The study aims to explore the application of these composites as high–performance anode materials in LIBs.First,Zn–Mn–Co precursors were prepared by solvothermal method,followed by the calcination method of programmed temperature control,and finally the Zn_0.5Mn_0.5Co₂O₄ sample powder was dispersed into graphene aqueous dispersion and hydrothermal reduction to prepare Zn_0.5Mn_0.5Co₂O₄/RGO heterostructural composites with hollow four–shell structure.When the lithium storage performance of the anode material of LIBs is explored,the Zn_0.5Mn_0.5Co₂O₄/RGO electrode has a significantly high reversible capacity(current density of 0.1 A g^–1,100 cycles,specific capacity of1173.4 m A h g^–1)and excellent long–cycle stability(specific capacity of 623.6 m A h g^–1after 2 A g^–1,500 cycles).In addition,the Zn_0.5Mn_0.5Co₂O₄/RGO electrode also has stable high–rate performance,and its discharge specific capacity can be as high as 446.8m A h g^–1 when the current density is 5 A g^–1.The exceptional lithium storage performance of the subject material can be attributed to its distinctive hollow multi–shell and heterostructure design.These structures are capable of effectively mitigating the significant volume changes that occur during the cycling process,shortening the ion diffusion path,and facilitating rapid diffusion of Li⁺ions,ultimately resulting in high–rate performance.Furthermore,we have successfully assembled a full cell using Li Co O₂//Zn_0.5Mn_0.5Co₂O₄/RGO and conducted various tests and evaluations.Our results indicate exceptional rate performance,cycle stability,and potential for practical applications.This work offers a straightforward and effective approach to synthesizing metal oxide/RGO composites with intricate hollow structures,along with useful guidelines for their construction.