Preparation And Lithium/sodium Storage Properties Of Spherical Nickel-based Anode Materials

Lithium-ion batteries（LIBs）have been widely used in portable storage systems and electric vehicles.Besides LIBs,sodium has similar properties to lithium,and has the advantages of abundant reserves,low cost,and environmental friendliness,which make the sodium-ion batteries（SIBs）are expected to become an important supplement for large-scale energy storage systems.The anode is a critical component of the batteries,and its electrochemical performance has a direct impact on the overall performance of the battery.Therefore,the development of efficient anode materials is crucial to improve the performance and cycle life of LIBs.Nickel-based compounds are widely used in the energy storage field due to their low cost,high capacity,and excellent safety.However,they still suffer from inherent issues such as low intrinsic conductivity and capacity decrease caused by volume expansion.This thesis focuses on how to improve the conductivity of nickel-based compounds and reduce their volume expansion,so as to improve their lithium/sodium storage performance.Spherical nickel-based composites including Co_0.5Ni_0.5Fe₂O₄nanospheres,Ni_0.5Zn_0.5Fe₂O₄@NC nanospheres with adjustable shell thickness,hollow four-shell Ni_0.5Mn_0.5Co₂O₄@NC microspheres and hierarchical mesoporous Ni_0.33Co_0.67Se₂nanospheres were prepared and applied to LIBs and SIBs anode materials to explore and improve the lithium/sodium storage performance.The specific research contents are as follows:Part Ⅰ Preparation and lithium storage of rambutan-like Co_0.5Ni_0.5Fe₂O₄nanospheresIn this part,the rambutan-like trimetallic compound Co_0.5Ni_0.5Fe₂O₄was synthesized by self-template solvothermal method with the metal elements doping strategy.The prepared Co_0.5Ni_0.5Fe₂O₄nanospheres are assembled by a plurality of nanosheets,and their special structure can effectively buffer the volume change during charge and discharge.The rambutan-like structure also increases the specific surface area of the sample and provides more reactive sites.Cobalt ions are doped in the reverse spinel Ni Fe₂O₄lattice,the coexistence of nickel and cobalt components provides a richer redox reaction,and the synergistic effect between several metals enhances the conductivity of the electrode material.The kinetic studies show that the ternary metal compound Co_0.5Ni_0.5Fe₂O₄has higher pseudocapacitance contribution and ion diffusion coefficient than Ni Fe₂O₄and Co Fe₂O₄.Theoretical calculation shows that the Co_0.5Ni_0.5Fe₂O₄electrode has better adsorption energy.As anode material of LIBs,at the current density of 0.5 A g^-1,after 200 cycles,the specific capacity of Co_0.5Ni_0.5Fe₂O₄can reach 963 m Ah g^-1,even at the high current density of 2.0 A g^-1,the specific capacity can reach 763 m Ah g^-1.Its rate performance and long cycle performance are significantly better than those of Ni Fe₂O₄and Co Fe₂O₄electrodes.In this work,polymetallic compounds with unique structure were prepared by a simple solvothermal method through metal element doping strategy,which significantly improved the electrochemical performance of electrode materials.The method is simple and effective,and can be extended to the preparation of other polymetallic compounds to develop more potential applications of LIBs anode materials.Part Ⅱ Preparation and lithium storage properties of Ni_0.5Zn_0.5Fe₂O₄@NC nanospheres with adjustable shell thicknessA trimetallic compound Ni_0.5Zn_0.5Fe₂O₄nanospheres was prepared by introducing Zn into Ni Fe₂O₄through a simple solvothermal method.Then,Ni_0.5Zn_0.5Fe₂O₄@NC composites with nitrogen-doped carbon shells with different thicknesses（about 5,15 and 30 nm）were prepared by coating with polydopamine and regulating the content of dopamine.Subsequently,the lithium storage properties of Ni_0.5Zn_0.5Fe₂O₄@NC composite were investigated,and the effect of the thickness of the N-doped carbon shell on electrode properties was discussed.The results show that Ni_0.5Zn_0.5Fe₂O₄@NC with thickness of N-doped carbon shell of 15 nm has high reversible capacity and excellent lithium storage properties.The reversible capacity reaches 1124.3 m Ah g^-1at 0.1 A g^-1current density.At 1.0 A g^-1current density,the specific capacity is 953.6 m Ah g^-1after 400 cycles.The synergistic effect of polymetallic components can provide more redox active sites and increase reaction pathways,thus enhancing the adsorption of Li⁺.At the same time,the appropriate thickness of the NC shell can not only improve the conductivity of the material,but also serve as a protective shell to effectively buffer the volume change.Furthermore,Li Co O₂//Ni_0.5Zn_0.5Fe₂O₄@NC lithium-ion full cells are successfully assembled,and the electrochemical evaluation results demonstrate that they exhibit excellent lithium storage performance and promising application prospect.This work provides a feasible optimization strategy for the construction of polymetallic compound/carbon-based composites,which can be extended to the preparation of other metal compound/carbon-based electrode materials.Part Ⅲ Preparation and lithium storage properties of hollow four-shell Ni_0.5Mn_0.5Co₂O₄@NC microspheresA ternary metal compound Ni_0.5Mn_0.5Co₂O₄with complex hollow four-shell structure was prepared by using PVP as the structure guide agent and doping Mn into Ni Co₂O₄through solvothermal and further calcination treatment.Subsequently,the Ni_0.5Mn_0.5Co₂O₄@NC composite with nitrogen-doped carbon shells of different thicknesses（about 5,15 and 30 nm）were constructed by coating with polydopamine and further heat treatment.As an anode material for LIBs,Ni_0.5Mn_0.5Co₂O₄@NC with a nitrogen-doped carbon shell thickness of 15 nm exhibits remarkably high reversible capacity.At a current density of 0.1 A g^-1,the specific capacity remains at 1204.5 m Ah^-1after 100 cycles.In addition,it has excellent long-term cycle stability and rate performance.At the current density of 1.0 A g^-1,its specific capacity can remain at721.1 m Ah^-1after 500 cycles,and at a current density of 2.0 A g^-1,its capacity can reach 715.1m Ah g^-1.Its excellent lithium storage performance is mainly attributed to its unique hollow multi-shell structure,which can effectively alleviate the volume expansion/contraction effect during the charge and discharge process,shorten the ion diffusion path,and provide enough active sites.The polymetallic synergies enhance the chemical reaction efficiency,increase the reactive site,and enhance the capacitance effect by introducing more oxygen vacancies.The nitrogen-doped carbon shell further improves the conductivity and structural stability of the material.The theoretical calculation also further shows that the coating of nitrogen-doped carbon shell is beneficial to reduce the diffusion energy barrier of Li⁺.In this work,Li Co O₂//Ni_0.5Mn_0.5Co₂O₄@NC lithium-ion battery was successfully assembled,tested and evaluated,indicating its excellent electrochemical lithium storage performance and potential application prospects.This work provides a simple,effective and universal preparation strategy for constructing novel metal compound composites with special structures,which is expected to play an important role in the field of energy storage and conversion.Part Ⅳ Preparation and sodium storage properties of hierarchical mesoporous Ni_0.33Co_0.67Se₂nanospheresA self-template solvothermal method with Co doped strategy was proposed to synthesize nickel-cobalt glycerate nanosphere precursors.Subsequently,through a simple solvothermal selenization strategy and further heat treatment,a series of Ni_xCo_1-xSe₂compounds were successfully synthesized by regulating the Ni/Co ratios.The sodium storage performance of the synthesized Ni_xCo_1-xSe₂compounds were investigated.It was found that the morphologies of the Ni_xCo_1-xSe₂compounds vary with different Ni/Co ratios.The uniform Ni_0.33Co_0.67Se₂nanospheres with hierarchical mesoporous structures exhibited excellent cycle life and rate performance.After 1300 cycles at 1.0 A g^-1,the capacity of Ni_0.33Co_0.67Se₂remained at 301.9m Ah g^-1.When the current density reached 8.0 A g^-1,the capacity of Ni_0.33Co_0.67Se₂could reach314.5 m Ah g^-1.The unique hierarchical mesoporous nanostructure increased the specific surface area of the samples,facilitating rapid electrolyte infiltration and providing more reactive sites and ion/electron transport paths.The synergistic effect of nickel-cobalt binary metal components also significantly enhancing the electrochemical activity of the Ni_0.33Co_0.67Se₂electrode materials.Additionally,kinetic analysis showed that the Ni_0.33Co_0.67Se₂electrode exhibited pseudocapacitive behavior and ion diffusion coefficients.These factors synergistically contribute to the excellent sodium ion storage performance of Ni_0.33Co_0.67Se₂.In this work,the proportion of elements is regulated on the basis of element doping,which provides a new idea for the design and optimization of metal compound composite materials,and is expected to further develop polymetallic compound composite electrode materials with more optimized structure and better performance.