Synthesis And Regulation Of Mn/Ni-based Layered Compounds And Its Application In Supercapacitor

Layered transition metal compounds are a large family of inorganic materials.The special arrangement of atomic layers and polyhedral structural units with transition metals as centers endow the layered transition metal compounds with variable properties such as phase structure,electronic structure,interlayer spacing and chemical bonding effect and so on.Many important applications of layered transition metal compounds have blossomed in energy storage and conversion,biological medicine,artificial intelligence,nano sensor and other emerging science and technology fields,among which the excellent performance of supercapacitor has attracted increasing attention.However,there are still many scientific problems to be solved,such as the mechanism of interlayer spacing on electrochemical performance,the relationship between two-dimensional atomic arrangement and mechanical stability,the relationship between d-band electron states of transition metals and electrochemical performance,and the influence of the variability for local coordination environment on functional units.These problems limit the deep application of layered transition metal compounds to a certain extent.Structure determines the properties of compounds,and chemical synthesis can effectively regulate the structure,including the macro phase structure and micro electronic structure.Therefore,from the perspective of synthetic chemistry,it is of great significance to precisely regulate the microstructure of layered transition metal compounds,optimize the performance of supercapacitor,and clarify the structure-activity relationship,so as to push the application of layered transition metal compounds in new fields more than supercapacitors.This dissertation takes Mn/Ni-based layered compounds as the main research object.The phase structure,electronic structure,interlayer spacing and chemical bonding effect of Mn/Ni-based layered compounds were regulated by chemical synthesis,and the accompanying electrochemical performance changes were studied,so as to reveal the microstructural effect and energy storage mechanism in Mn/Ni-based layered compounds.On this basis,the supercapacitor performance was optimized,and the application in new-type flexible supercapacitor was realized to some extent.Four main results obtained are as follows:1.Hydrothermal phase engineering of layered Cu_xMn_2-xO₂ and its optimized supercapacitor performance:the phase structure of layered Cu_xMn_2-xO₂ is regulated by accurately controlling the reaction conditions of a template-free hydrothermal method,such as the ratio of transition metal precursor（Cu and Mn）,the range of synthetic temperature and the concentration of mineralizer.The phase diagram of layered Cu_xMn_2-xO₂ under hydrothermal condition was determined for the first time.The results show that the concentration ratio of Cu to Mn has an important influence on the formation of layered phase.When n _Cu/n_（Cu+Mn）=0.45,0.5.and 0.55,the pure phase of layered structure can be obtained in the temperature range of 85（？）C to 175（？）C.The effect of nonstoichiometric occupation between Cu and Mn on magnetic susceptibility and d-electron state was also found in layered Cu_xMn_2-xO₂.The test of supercapacitor performance shows that the electrochemical performance of n _Cu/n_（Cu+Mn）=0.55 samples are generally better when the reaction temperature is fixed.When n _Cu/n_（Cu+Mn）=0.55 is further fixed,the sample obtained at the lowest temperature has the best performance.From the particularity of magnetic susceptibility and d-electron state,the optimization of supercapacitor performance is explained.2.Solvothermal synthesis and supercapacitor performance of layered CuMnO₂with controllable electronic structure:Based on the hydrothermal phase engineering of Cu_xMn_2-xO₂,a cetyltrimethylammonium bromide（CTAB）assisted solvothermal method was developed to synthesize a series of oriented layered crednerite CuMnO₂.On the premise of keeping the monoclinic layered structure of CuMnO₂ stabled,the3d electronic structure of transition metals（Cu and Mn）was regulated.The results show that the high aspect ratio CuMnO₂ nanowires synthesized at 160（？）C preferentially grow along（002）crystal plane,and the transition metals exist in the form of mixed valence states of Cu⁺/Cu²⁺and Mn³⁺/Mn²⁺.When used in supercapacitor for the first time,the nanowires exhibit a high specific capacitance of921 F/g at a current density of 1 A/g.The synergistic effect between special redox equilibrium and one-dimensional crystal architecture in CuMnO₂ with controllable electronic structure is the mechanism of electrochemical energy storage optimization.This study provides a new idea for precise regulation of electronic structure in layered transition metal compounds.3.Effect of regulating interlayer spacing in layered Ni（OH）_xCl_2-x on supercapacitor performance:nickel hydroxychloride was selected as the model layered material with heteroanionic coordination to study the mechanism of changed interlayer spacing on electrochemical performance.The nickel hydroxychloride composed of neutral layers of[Ni（OH）_3/3Cl_3/3]octahedral was synthesized by a template-free solvothermal method.Then,Cl^-deintercalation and OH^-intercalation from crystal lattice were accomplished by a long-time water stirring method.The precise regulation of interlayer spacing was realized,and a series of layered Ni（OH）_xCl_2-x with different stoichiometric ratio of anions.The result shows that Ni（OH）_0.99Cl_1.01 with a maximum Cl^-ion content has the largest interlayer spacing of0.57 nm,when first used in supercapacitor,delivered an ultra-high specific capacitance of 3831 F/g at a current density of 1 A/g.The Ni（OH）_2.18（H₃O）_0.18 fully embedded with OH^-ions and trace amount of H₂O molecules,exhibited a specific capacitance of 1489 F/g at a current density of 1 A/g.This work clarified the regulation mechanism of coordinated anions de-/intercalation in layered nickel hydroxychloride on interlayer spacing shrinkage/expansion and supercapacitor performance.4.Synthesis of Carbon cloth@Ni（OH）Cl@Ni O composite electrode with stable interfacial chemical bonds and its farbrication for flexible supercapacitor:Based on the study of the relationship between coordinated anions in layered Ni（OH）_xCl_2-x and supercapacitor performance,we designed a strategy that uses interface structure to regulate chemical bonding effect by a solvothermal,chemical bath,and subsequent annealing method with conductive carbon cloth（CC）as the template.CC/Ni（OH）Cl and Ni（OH）Cl/Ni O interfaces were successfully synthesized.The composite flexible electrode,double-interface CC@Ni（OH）Cl@Ni O,was constructed.The electrochemical results show a remarkable areal capacitance of 8290 m F/cm² at a current density of 30 m A/cm² and a high rate performance（3580 m F/cm²）at an ultra-high current density of 120 m A/cm².More importantly,its cycling stability is nearly doubled compared with that of single-interface CC@Ni（OH）Cl electrode.A flexiblequasi-solid-stateasymmetricsupercapacitordevice,CC@Ni（OH）Cl@Ni O//graphene,was assembled,which achieved favorable energy storage ability and splendid flexibility as well as mechanical stability.Combined with the synchrotron radiation analysis,it is found that the synergistic double interfaces by chemical construction afford the benefits of stable Ni-O covalency during the electrochemical cycles,meanwhile bring about more octahedral distortion and stimulate activity of surface electrons,which improves capacitance and stability of the electrode.This study provides a new insight for regulation design of chemical bonding effect in layered transition metal compounds.