Synthesis and Electrochemical Performance of High-Entropy Spinel-Type Oxides Derived from Multimetallic Polymeric Precursors

High-entropy spinel-type oxides are synthesized by a modified Pechini process, wet chemistry approach, and solid-state synthesis method and characterized as anode materials for Li-ion batteries. The Pechini process that involves chelation and polyesterification reactions facilitates the formation of high-entropy spinel-type oxides without compositional segregation at ≈600 °C as confirmed by in situ and ex situ XRD. XAFS analysis and the Rietveld refinement of room-temperature neutron diffraction data suggest the composition (Mn_0.05Fe_0.48Co_0.47, tetrahedral)(Cr_0.61Mn_0.52Fe_0.11Co_0.09Ni_0.68, octahedral)O₄ for phase-pure specimens. Compared to high-entropy spinel-type oxides synthesized by the solid-state method, the precursor-derived materials demonstrate higher specific capacity as anodes, in which the materials without citric acid addition exhibit low capacity fading at high current densities and maintained a capacity of ≈200 mAh g⁻¹ after 1000 cycles. The generation of a rock-salt-type phase during cycling is confirmed for the first time by in situ charging–discharging XRD. The charging–discharging of this anode material is achieved mainly through the embedding–disembedding of lithium ions in the lattice of the generated rock-salt-type phase.