High-entropy engineering enables O3-type layered oxide with high structural stability and reaction kinetic for sodium storage

Abstract

O3-type layered oxides are considered promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical capacity, but they often face issues with structural instability and poor sodium-ion diffusion, leading to rapid capacity fading. In this work, we introduce a high-entropy approach combined with synergistic multi-metal effects to address these limitations by enhancing both the structural stability and reaction kinetics. A novel O3-type layered high-entropy cathode material, Na_0.9Fe_0.258Co_0.129Ni_0.258Mn_0.258Ti_0.097O₂ (TMO5), which was synthesized via a straightforward solid-phase method for easy mass production. Experimental analysis combined with in/ex-situ characterization verifies that high-entropy metal ion mixing contributes to the improved reversibility of the redox reaction and O3-P3-O3 phase transition behaviors, as well as the enhanced Na⁺ diffusivity. Benefit from the advantage of structure and composition, the TMO5 exhibits a higher initial specific capacity of 159.6 mAh g⁻¹ and an impressive capacity retention of 85.6 % after 100 cycles at 2 C with the specific capacity of 110.1 mAh g⁻¹. This work showcases high-entropy O3-type layered oxides as a promising pathway for achieving robust, high-performance SIB cathodes.