Structure- and porosity-tunable, thermally reactive metal organic frameworks for high-performance Ni-rich layered oxide cathode materials with multi-scale pores

Abstract

We describe for the first time molecular rearrangements in a highly stable and porous Ni-rich layered oxide cathode material (LiNi0.80Co0.15Mn0.05O2, Ni-rich NCM) using a thermally reactive, Co-embedded metal-organic framework (MOF). The thermal decomposition of the MOF on the surface of the active material forms a molecular-level thin layer of CoOx species, which are thought to act as seeds for the dramatic transformation of the surface of the Ni-rich NCM from a layered oxide (R3m) to a more stable spinel-like phase (Fd3m) before cycling and the formation of multi-scale (nano-to-micro) pores in the active particles. These phase transformations and morphology changes are associated with a galvanic replacement reaction between Co ions from the MOF and Ni ions near the surface of Ni-rich NCM, where some of the Ni ions migrate to the neighboring vacant Li sites by the diffusion of Co ions through melted residual lithium. Therefore, the resultant Co-/Ni-rich surface domains with a more stable spinel-like phase as well as a porous microstructure improve the cyclability and thermal stability of the MOF-inspired Ni-rich NCM.