Synergistically tailoring Kongming-lock morphology and Li⁺/Ni²⁺ intermixing to achieve ultrahigh-volumetric-energy-density layered Li-rich oxide cathodes

The rapid growth of energy storage systems demands higher-performance lithium-ion batteries (LIBs). However, state-of-the-art polycrystalline (PC) LIB cathodes struggle with low compaction density, limiting their use in volume-constrained applications. While single-crystal (SC) materials such as LiCoO₂ suffer from low gravimetric energy density. Inspired by the traditional Chinese puzzle, we propose a lithium-rich manganese-based (LMR) cathode with a Kongming lock (KML)-like morphology that optimally regulates Li⁺/Ni²⁺ intermixing. Cross-sectional scanning electron microscopy (SEM) confirms enhanced compaction density contributed by the micron-sized primary particles. High-resolution transmission electron microscopy (HRTEM) then shows Li⁺ diffusion-favorable {010} planes on the secondary particle surfaces, improving Li⁺ transport. As a result, electrochemical testing demonstrates an initial discharge capacity of 253 mAh g^-1, with 96.3 % capacity retention after 100 cycles at 0.1C, and an ultra-high volumetric energy density of approximately 3050 Wh L^-1, surpassing that of SC-LiCoO₂. Synchrotron-based characterizations, combined with wide-angle X-ray scattering (WAXS), density functional theory (DFT), and finite element analysis, confirm the local structural, crystalline, and morphological stability of KML. This study underscores the importance of morphology design in cathode materials and advances the development of high gravimetric and volumetric energy density LMR cathodes for next-generation LIBs.