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 ZnCo2 O4 powders with uniform compositions are prepared by using simple gas-phase reaction methods. Double-shelled ZnCo2 O4 yolk-shell powder is prepared directly from the spray solution by using spray pyrolysis. Single-crystalline ZnCo2 O4 nanopowder is prepared by means of flame spray pyrolysis. The yolk-shell ZnCo2 O4 powder shows higher charge and discharge capacities than the hollow and single-crystalline powders. The yolk-shell, hollow, and single-crystalline ZnCo2 O4 powders deliver discharge capacities of 753, 586, and 206 mAh g(-1) , respectively, after 200 cycles at a charge/discharge rate of 3 A g(-1) , and the corresponding capacity retentions measured after the first cycle are 99, 74, and 27 %, respectively. The yolk-shell ZnCo2 O4 powders are structurally stable during cycling and have good electrochemical properties even at high current densities.