Electrochemical Energy Storage Of Transition Metal Oxide Electrode Materials

Properties of electrode materials can exert significant influence on performance of elelctrchemical energy storage devices.A brief introduction of working mechanism of lithium-ion battery was presented in the first section.In the following section,we tracked the study of intercalation-type,alloying-type,and conversion-type electrode,respectively.And in the final part of introduction,we made a minireview on the study of lithium-ion capacitors.Selecting conversion reaction-based transition metal oxide electrode materials as target,we conducted a comprehensive study on the electrochemical energy storage performance of tricobalt tetroxide(Co3OO),nickel cobaltate(NiCo2O4),trimanganese tetroxide(Mn3O4)and manganese monoxide(MnO),respectively.Defect engineering,anion doping,hybridization and structural design were applied to modified Co3O4,NiCo2O4,Mn3O4 and MnO,respectively.Electrochemical energy storage performance and electrochemical reaction mechanism of these above electrode materials were studied by systematic characterizations and tests.Oxygen-defective Co3O4 nanobelts were prepared via a typical two-step strategy,including an initial CTAB-mediated coordination reaction at room temperature and a subsequent thermal treatment at low temperature.The existence of oxygen vacancy in Co3O4 was verified by XPS,Raman,HR-TEM and EPR.Content of oxygen vacancy was further measured via a redox titration.Ex-situ XRD and ex-situ FE-SEM were applied to study the phase transition and morphological evolution of Co3O4 during the charge/discharge process.Increased electron transfer and accelerated Li+ion diffusion induced by oxygen vacancies were unveiled by the analysis of AC-EIS.P-doped NiCo2O4 microspheres were prepared via a tri-step method,including an initial hydrothermal preparation,a subsequent annealing in ambient atmosphere and a final phosphating treatment in N2.Experimental results showed that P-doping could effectively improve the electrochemical performance of NiCo2O4,leading to enhanced rate capacities and cycling stability.Further kinetics analysis revealed that pseudocapacitance played a major role in the lithium storage of P-doped NiCo2O4.Yolk-shell structure formed during the phosphating treatment was also believed to make a contribution to the improved electrochemical performance.Porous carbon encapsulated Mn3O4 nanoparticles(Mn3O4@C)were obtained by annealing Mn-based metal organic framework precursor in N2.The confinement of Mn3O4 in porous carbon layer lead to improved cycling stability,and the conductive nature of porous carbon is beneficial to an enhanced rate performance.Therefore,the Mn3O4@C anode showed attractive performance in both half cells and full cells.And the electrochemical reaction mechanism of Mn3O4 anode had been verified by XPS characterizations at different states of charge/discharge.Core-shell structured MnO@C microspheres were prepared by thermal treatment of PDA-coated MnCO3 precursor in N2 atmosphere.The introduction of carbon layer can not only inhibit side reactions between MnO and electrolyte,but also improve the electrical conductivity of electrode material.Benefited from the protective coating layer,the MnO@C exhibited attractive performance in half cell LIBs and lithium-ion capacitors.Structural and morphological evolution of the MnO@C anode during the charge/discharge process had been investigated by ex-situ characterizations.AC-EIS was applied to study the variation of impedance and Li+ion diffusion coefficient during initial cycles.