PNNL

Abstract

Chemical short-range order (SRO) has been widely noticed to dictate the electrochemical properties of Li-excess cation-disordered rocksalt oxides, which are extensively studied as cathode based on earth abundant elements for next-generation high-energy-density batteries. Existence of SRO is normally evidenced by a diffused intensity pattern in reciprocal space, however, derivation of local atomic arrangements of SRO in real space is hardly possible. Here, by a combination of aberration-corrected scanning transmission electron microscopy, electron diffraction, and cluster-expansion Monte Carlo simulations, we reveal, for the first time, that the SRO in cation-disordered rocksalt oxides is a convolution of three basic types of SRO: tetrahedron, octahedron, and cube. We discover that SRO directly correlates with Li percolation channels, which correspondingly affects Li transport behavior. We further demonstrate that the cation SRO can be effectively manipulated by anion doping or post-synthesis thermal treatment, creating new avenues for tailoring the electrochemical properties of cation-disordered rocksalt cathodes by tuning their SRO parameters. Our results provide fundamental insights into ways of decoding the complex relationship between local chemical ordering and properties of crystalline compounds.