Unveiling Surface Reconstruction as the Primary Trigger for Capacity Loss in Ultra-High Nickel Cathodes.

Mechanical failures, such as cracks and nanopores, along with the associated surface reconstruction, have long been regarded as the primary causes of capacity decay in ultra-high Ni layered oxides. However, the impact of these failures on performance degradation has not yet been effectively elucidate and distinguished. Herein, we develop ultra-high Ni cathodes with tailored morphological structures by incorporating B and Mo to optimize lithiation kinetics, which can suppress lattice strain, particle cracking, and surface reconstruction during charging/discharging. And the role of chemo-mechanical failures in capacity loss is systematically investigated. Surprisingly, contrary to the traditional view, structural and electrochemical characterizations of the cycled cathodes demonstrate that intragranular cracks, intergranular cracks, and nanopores are not the primary contributing factors of capacity loss. Instead, surface reconstruction triggers rapid capacity decay. Notably, compared to nanopores, intragranular cracks expose a significantly larger quantity of active substances, thereby promoting interfacial side reactions and accelerating surface structural reconstruction during cycling.