Preparation And Electrochemical Behavior Characterization Of Transition Metal Oxide Anode Materials

The transition metal oxide material has high specific capacity,abundant resources,and low economic cost.So,it is very promising to become the nextgeneration high-performance lithium-ion battery anode material.However,the practical application of transition metal oxide anode materials is limited by poor cycle stability and low electronic conductivity.Researchers have adopted a variety of methods to solve this problem.However,the real electrochemical process,electrochemical reaction mechanism,cause of capacity decay and microstructure change process of transition metal oxide anode materials need to be further studied.Among the many transition metal oxides,Co₃O₄ has extremely high theoretical capacity and excellent physical properties.Through the study of Co₃O₄ electrode,we found that the specific capacity of Co₃O₄ electrode was very high in the first few cycles,but the specific capacity decreased rapidly after 30 cycles.The phenomenon indicated that the cycling performance of Co₃O₄ electrode was poor.Compared with previous studies,it can be known that the low conductivity and volume expansion of Co₃O₄ are the main reasons for poor cycling performance.Therefore,a Co₃O₄ polyhedron was prepared in this paper based on the ZIF-67 metal organic framework as the precursor system.The metal organic frame can effectively inhibit the volume expansion of Co₃O₄.At the same time,carbon materials with excellent conductivity were compounded with Co₃O₄ to improve the conductivity of Co₃O₄.The C coated Co₃O₄ and CNTs/Co₃O₄ obtained in this paper showed a unique dodecahedral structure.It has a three-dimensional pore structure,which can inhibit the volume expansion of Co₃O₄ in the charging and discharging process.Based on the synergistic effect of carbon nanotubes?or conductive carbon coating?and metal organic framework structure,C coated Co₃O₄ and CNTs/Co₃O₄ electrodes show excellent electrochemical performance.After 500 cycles at a high current density of 1 C,they maintained the reversible capacities of 391.7 and 309.4 m Ah g-1,respectively,with an average coulomb efficiency of nearly 100%.We prepared NiO nanostructures with different morphologies in this paper.And the morphology evolution,phase transformation,electrochemical reaction and valence state changes of NiO during lithiation process have been probed in real time by in situ TEM.The results show that NiO is reduced to Ni,and Li₂ O is formed during the first lithium charging process.We found that NiO has a huge volume expansion during lithiation.In addition,some lithium ions cannot be extracted from the NiO electrode after lithium charging,which will lead to poor cycling performance of NiO.We assembled half-cell using metallic Li as anode and NiO nanoparticles as the working electrode.Studied the electrochemical performance of the NiO electrode.The results of the cyclic voltammetry curve showed that the discharge / charge reaction of the NiO electrode.The results confirm the conclusions obtained in the in-situ TEM.It is worth noting that that the specific capacity of the NiO electrode is high and stable around the 25 cycles.After that,the specific capacity quickly dropped.Combined with the in-situ TEM results,we believe that the rapid decrease in specific capacity is because of the loss of active material.Owing to the poor conductivity of Li₂ O,some lithium ions cannot be extracted.Moreover,the continuous accumulation of Li₂ O on the NiO electrode causes the conductivity of the NiO electrode to become worse and worse,and part of the specific capacity will also be lost.