Understanding of TiO₂/Co₃O₄-modified configuration strategy for stabilizing O3-type NaNi_0.4Fe_0.2Mn_0.4O₂ cathodes with enhanced long-term and rate performance

Sodium-ion batteries (SIBs) have recently gained wildly interest due to the abundance of sodium, lower production costs, and better low-temperature performance compared to lithium-ion batteries (LIBs). Among various cathode materials of SIBs, O3-type NaNi_0.4Fe_0.2Mn_0.4O₂ (NFM424) demonstrates high capacity and ease of synthesis, yet suffers from structural degradation and sluggish Na⁺ kinetics caused by large ionic radius and strong electrostatic interactions. To overcome these issues, a configuration strategy combined with TiO₂ and Co₃O₄ by a simple solid-state reaction method was introduced to improve structural and electrochemical stability. XRD, SEM, TEM, and various electrochemical characterizations as well as TGA/DSC tests were conducted. The resulting NaNi_0.4Fe_0.2Mn_0.3Co_0.05Ti_0.05O₂ (NFMCT) cathode mitigated Jahn-Teller distortions and Na⁺/vacancy ordering while enhancing phase integrity and diffusion pathways. The obtained NFMCT maintained 93.7 mAh·g⁻¹ after 550 cycles at 1 C, with superior rate capabilities at 2 C and 5 C. These findings deepen the understanding of configuration strategy by using multi-element oxide and highlight a practical strategy for designing high-performance SIB cathodes.