Abstract
Ni-rich layered oxide cathode materials are promising candidates for high-specific-energy battery systems owing to their high reversible capacity. However, their widespread application is still severely impeded by severe capacity loss upon long-term cycling. It has been proven that the cyclic stability of Ni-rich cathode materials is closely related to their microstructure and morphology. Despite this, the influence of the microstructure of primary particles on the fatigue mechanism of Ni-rich cathode materials during prolonged cycling has not been fully understood. Here, two Ni-rich layered spherical agglomerate oxides consisting of the primary particle with different length/width ratios are successfully synthesized. It is found that the long-term structural stability of both materials strongly depends on the microstructure of primary crystallites, although there is no significant difference between the electrochemical and crystalline characteristics during the initial cycle. A higher primary particle length/width ratio could effectively inhibit the accumulation of microcracks and chemical degradation during long-term cycling, thereby promoting the electrochemical performance of the cathode materials (80% capacity retention after 200 cycles at 1 C compared to the 55% of the counterpart with a lower primary particle length/width ratio). This study highlights the structure-activity relationship between the primary particle microstructure and fatigue mechanisms during long-term cycling, thereby advancing the development of Ni-rich cathode materials.