Yolk-shell, hollow, and single-crystalline ZnCo₂O₄ powders: Preparation using a simple one-pot process and application in lithium-ion batteries

The electrochemical properties of yolk-shell-structured, multi-component, transition-metal oxides have not yet been properly compared to those of hollow-structured or nanoscale powders. In this study, yolk-shell, hollow, and single-crystalline ZnCo₂O₄ powders with uniform compositions are prepared by using simple gas-phase reaction methods. Double-shelled ZnCo₂O₄ yolk-shell powder is prepared directly from the spray solution by using spray pyrolysis. Single-crystalline ZnCo₂O₄ nanopowder is prepared by means of flame spray pyrolysis. The yolk-shell ZnCo₂O₄ powder shows higher charge and discharge capacities than the hollow and single-crystalline powders. The yolk-shell, hollow, and single-crystalline ZnCo₂O₄ powders deliver discharge capacities of 753, 586, and 206mAh g^-1, respectively, after 200 cycles at a charge/discharge rate of 3A g^-1, and the corresponding capacity retentions measured after the first cycle are 99, 74, and 27 %, respectively. The yolk-shell ZnCo₂O₄ powders are structurally stable during cycling and have good electrochemical properties even at high current densities. Heroes in a double shell: Double-shelled ZnCo₂O₄ yolk-shell powder with a complex composition is prepared directly from the sucrose-containing spray solution by using spray pyrolysis within a short residence time. The yolk-shell ZnCo ₂O₄ powder displayed better cycling and rate performances than those of the hollow and single-crystalline powders, and have good electrochemical properties even at high current densities.