Enthalpy-mediated local structural ordering stabilizes O3-type layered cathode for sodium-ion batteries

Abstract

O3-type Na_0.9Ni_0.4Fe_0.1Mn_0.5O₂ (NFM) is a promising candidate material for sodium-ion batteries (SIBs) because of high theoretical capacity (220 mAh g⁻¹), but largely suffers from rapid capacity decay due to severe phase transition caused by unstable transition metal (TM) layer gliding and anisotropic lattice strain accumulation upon cycling. Herein, we propose an enthalpy-doping strategy to precisely manipulate the local coordination ordering structure, thereby stabilize the TMO₆ octahedral framework in the O3-type Na_0.9Ni_0.35Zn_0.05Fe_0.1Mn_0.3Ti_0.2O₂ (NZFMT). Our findings demonstrate that the negative enthalpy characteristics of dopants reduce the ΔH_mix of TM layers, thereby strengthening cation-anion interactions and promoting the formation of an ordered lattice structure. As anticipated, this tailored structure strategy favorably stabilizes layered structure to resist severe phase transition, leading to remarkable electrochemical improvements. The optimized NZFMT delivers a high capacity of 162.3 mAh g⁻¹ with a prominent capacity retention of 96.3% after 100 cycles at 1 C (vs. 62.5% for NFM). Furthermore, the practical feasibility of an Ampere-hour-scale NZFMT||HC pouch cell is demonstrated by an energy density of 148 Wh kg⁻¹, along with outstanding cycling stability (80.5% retention after 200 cycles at 0.5 C), outperforming many state-of-the-art O3-type cathodes. This work provides a universal enthalpy-mediated stabilization approach for designing high-energy-density SIB cathodes.