Lattice-Matched Epitaxial Growth Enabling High-Entropy-Doped Single-Crystal Ni-Rich Oxide Cathodes.

Abstract

The synergistic effects of a single-crystal structure and high-entropy doping are expected to enhance the structural and thermal stability of high-capacity Ni-rich cathodes. Nonetheless, the pinning effect caused by heavy-mass dopants and surface phase segregation induced by the thermodynamic immiscibility of dissimilar elements hinder atomic diffusion and crystal fusion, making it extremely difficult to synthesize single crystals with high-entropy doping. In this study, density functional theory calculations confirm that effective diffusion is achievable within a grain-boundary-free single-crystal matrix at elevated temperatures, even for heavy-mass dopants with high valence states. A lattice-matched epitaxial growth approach is proposed to enable the synthesis of single-crystal Ni-rich oxides with high-entropy doping. The synergistic effects of high-entropy doping and single crystals within a Ni-rich cathode exhibit significantly reduced changes in the lattice volume and Ni-O/TM coordination distance and the absence of intragranular cracks upon Li⁺ de/intercalation, presenting highly improved cyclic and thermal stabilities compared with the high-entropy-doped polycrystal counterpart and single-crystal counterpart without high-entropy doping. This integration not only addresses the inherent limitations of Ni-rich compositions but can also be expanded to the design of other electrode materials, where entropy-driven stabilization and single crystals can work together to enhance cathode performance.