Syntheses And Performances Of Novel Electrode Materials For Lithium/Nickel-ion Batteries With Multi-Electron Reaction

With rapid economic development,there is an increasing societal demand and an urgent requirement for sustainable sources of energy.Secondary batteries have become important for smart grid,electric vehicle applications and consumer electronics industries,and designed novel electrode materials and battery systems are of obvious interest to meet the increasing requirements of electric devices.The energy density of the batteries depends on the number of electrons that can be transferred per unit weight of the electrode materials.The multi-electronic has broken the obstacles in traditional battery research and application,providing new ideas for increasing energy density of battery.Where,developing multi-electronic reaction electrode materials and new secondary multivalent ion battery systems with high energy density may meet the future demand for large-scale energy storage.Based on the charge transfer mechanism of multi-electronic response,on the one hand,we study the electrochemical properties of the transition metal oxides as novel lithium-ion battery anode materials,and use surface coating and structural design to modify and optimize;on the other hand,we successfully explored a reversible organic secondary nickel ion battery system for the first time,and deeply explored its electrochemical properties and energy storage mechanism.The specific contents are as follows:Firstly,rare-earth metavanadates CeVO₃with the zircon type perovskite structures,is considered promising to apply as electrode materials due to its unique electronic structures and the high-valence state of vanadium.Use the simple sol-gel method,we successfully synthesized the novel CeVO₃anode material for lithium ion battery and the electrochemical performances of it are studied for the first time.The crystal structure of CeVO₃is determined by the X-ray diffraction（XRD）measurement.Interesting,the CeVO₃possesses a stable framework and a good lithium-ion migration pathway.In our electrochemical measurement,the pure CeVO₃shows a low reversible discharge capacity and poor rate performance due to the low electronic conductivity.In order to improve the electrochemical properties,the CeVO₃/C samples are prepared choosing sucrose as carbon source,where the carbon content is 9.5%.The added carbon inhibits the particle growth and increases the conductivity,which increased the corresponding electronic conductivity and the lithium diffusion coefficient of the CeVO₃/C by one order of magnitude.By carbon-coating,the discharge specific capacity and rate performance are great improvement.In addition,we determine that the Li ions insertion/extraction mechanism of the CeVO₃/C material by In-situ XRD method.It can be interpreted as a solid-solution behavior with minimal electrode material volume change and extremely high cycle stability.And this is relatively rare in common metal oxides.Secondly,based on the multiple valence states of Mo and Fe,Li₃Fe（MoO₄）₃,can be used as a high-capacity multi-electron reaction anode material in Li-ion battery.We successfully rapidly synthesized coral-shaped nanoporous structure Li₃Fe（MoO₄）₃nanoparticles by a glycine-assisted sol-gel combustion method at lower temperatures,and investigated its electrochemical performances for the first time.Attributed to the large amount of gas generated in the combustion reaction,the morphology of the sample exhibits a fluffy porous nature like a coral.The special morphology is helpful for buffering the volume expansion in the cycle and improving the structural stability of the electrode material.The Li₃Fe（MoO₄）₃anode exhibits an excellent cycle performance because the realization of a multielectron reaction.It can present a high reversible capacity of 988.2 m Ah g^-1at a current density of 100m A g^-1.Based on the fluffy porous nature morphology,Li₃Fe（MoO₄）₃material exhibits excellent cycling performance,where a stable capacity of 622 m Ah g^-1can be maintained even after 450 cycles.In addition,we firstly discussed the complex reaction mechanism of Li₃Fe（MoO₄）₃during the charge/discharge process by in situ X-ray diffraction and high-resolution transmission electron microscopy technologies.In addition,the reversible reaction mechanism of Li₃Fe（MoO₄）₃is a typical conversion reactions between the metal element and the corresponding oxide amorphous phase.We also studied the practical application of Li₃Fe（MoO₄）₃as anode material by combining with a layered structure Li Ni_0.8Co_0.1Mn_0.1O₂cathode in full cells,which presents a good capacity and cycling stability.Thirdly,multivalent metal ion batteries as the most expected"surpassing lithium-electric"battery,has attracted wide attention in recent years.Organic nickel ion battery using Ni²⁺as a charge carrier has yet to be explored due to the lack of workable electrolytes and high-performing Ni²⁺storage cathode materials to couple with the nickel metal anode.Herein,a feasible rechargeable organic nickel ion battery with an ether base electrolyte is demonstrated for the first time,in which Li₃V₂（PO₄）₃and nickel foam as cathode and anode materials,respectively.The Li₃V₂（PO₄）₃can demonstrate a high reversible specific capacity of 124 m Ah g^-1at the rate of 1 C and a stable cycle performance with 84%capacity retention after 50 cycles.In addition,a reversible insertion and extraction of Ni²⁺ions into the cathode structure is confirmed by XRD,XPS,and EDX studies.Finally,using in-situ X-ray diffraction technology and Rietveld refinement,the reaction mechanism and structural changes during the cycle process are analyzed in detail.Therefore,the results provide an avenue to explore the organic nickel ion battery as a novel energy storage technique for renewable energies.Fourthly,based on the studies of previous work,we successfully explored a similar polyanionic compound Na₃V₂（PO₄）₃as cathode material for nickel ion battery,and studied its different electrochemical properties in water and organic electrolyte.Our test results show that since the water-based electrolyte has a higher ion mobility,Na₃V₂（PO₄）₃with aqueous electrolyte represents a better rate performance and lower polarization.However,the battery presents a poor long cycle stability and a rapid attenuation capacity,which may be due to the unstable structure of Na₃V₂（PO₄）₃in the water system.In contrast,Na₃V₂（PO₄）₃positive electrode using an organic electrolyte not only has a higher capacity,but also express a great advantage in stability.After 1000 cycles,it can still work properly and maintain most capacity at large current,which indicates that Na₃V₂（PO₄）₃is more suitable as a cathode material of nickel ion battery with organic electrolyte.The rate CV and GITT tests present that the battery capacity is basically contributed by diffusion control and the nickel ion diffusion coefficient is between 10^-13cm²s^-1to 10^-11cm²s^-1.By in situ X-ray diffraction technology and structural refinement,we analyzed the reaction mechanism and the structural information of full discharge product in detail.In addition,the XPS and EDX results demonstrated that the nickel ion can be used as charge carrier reversible insert into the host structure,which confirming the rocking chair mechanism of Ni²⁺ions in nickel ion battery.