Study of phase transformations in Co/CoCo2O4 nanowires

The paper presents the results of a systematic study of the influence of thermal annealing on changes in the structural properties and phase composition of metallic nanostructures based on cobalt, as well as the possibilities of using an anode material for lithium ion batteries. It was established that as a result of thermal annealing, a four-stage phase transition of nanowires (Co-C/Co-H) -> (Co-C) -> (Co-C/CoCo2O4) -> (CoCo2O4) is observed, accompanied by a rearrangement of the crystal structure, coarsening of the crystallites and the formation of oxide growths on the surface of nanowires. It has been established that with an increase in temperature up to 700 degrees C, a partial destruction of the oxide layer occurs, which confirms the results of a decrease in the degree of crystallinity and an increase in stresses and strains in the structure. In the course of life tests, the prospect of using nanostructures as the basis for anode materials of lithium-ion batteries has been established. For the initial sample, the number of cycles is about 300 cycles. For oxide nanostructures, an increase in the amount of the resource lifetime of the anode material is observed and in the case of annealed at 500 degrees C, the resource lifetime exceeds 500 cycles. That corresponds to the average lifetime of the anode materials based on silicon or carbon nanostructures. The dependences of degradation rate of nanostructures in highly concentrated solutions of sulfuric acid were obtained. That will later make it possible to predict the amorphization rate and oxidation of nanowires. (C) 2019 Elsevier B.V. All rights reserved.