Single-Crystalline High-Entropy Oxide Particles Synthesized via Coordination Polymerization

High-entropy oxides (HEOs) have attracted increasing attention due to their extreme chemical disorder incorporated in long-range structural order. Various single-phase HEOs have been successfully fabricated through solid-state synthesis, yet the resulting materials are often bulky aggregates. Solution-based chemical reactions can be applied to prepare HEO particles. However, the co-precipitation of multiple metal ions is practically challenging, given that the composition of a precipitated HEO can deviate significantly from an equimolar ratio. Here, coordination polymerization has been coupled with solid dispersant-assisted annealing, producing single-crystalline HEO rods with uniform dispersion. The stepwise polymerization of cations into metal-organic chains (MOCs) enables homogeneous deposition of different metals into submicron-sized particles. Owing to this pre-mixing feature of oxalate precursors, single-phase HEOs can be obtained through short annealing. While this deposition method extends the compositional spectrum of rocksalt HEO to other metals and simplifies the production of HEO particles with single-crystalline structures, solid dispersants enable the retention of the morphology and dispersity of precursor particles after annealing. The resulting HEO single crystals demonstrate impressive cycle performance in half-cell and full-cell configurations.