An advanced Fe/Ti substituted tunnel-type cathodes for high-performance sodium-ion batteries

Although lithium-ion batteries (LIBs) offer high energy density and long cycle life, their large-scale application is hindered by the scarcity and high cost of lithium resources. sodium-ion batteries (SIBs) have emerged as a promising alternative for large-scale energy storage due to the abundance and low cost of sodium. However, the development of high-performance SIBs is impeded by structural instability in cathode materials, primarily caused by the relatively large ionic radius of Na + , which induces lattice strain and phase transitions during cycling. In this work, a Fe/Ti co-doped tunnel-type sodium manganese oxide cathode material, Na 0.55 Mn 0.9 Fe 0.05 Ti 0.05 O 2 (NaMO55-FT5), was successfully synthesized via a high-temperature solid-state method. The structural evolution and electrochemical behavior of the material were systematically investigated. It was found that synergistic Fe/Ti doping effectively expanded Na + interlayer spacing, mitigated Jahn-Teller distortion through Mn 3+ stabilization, and disrupted Na + /vacancy ordering, thereby enhancing both Na content and structural integrity. As a result, the NaMO55-FT5 material delivered an initial discharge capacity of 98.5 mAh g −1 at 0.5C, retains 72.0% of its capacity after 300 cycles, and maintained a reversible capacity of 55.2 mAh g −1 at a high rate of 5C, demonstrating outstanding cycling stability and superior rate capability. This study presented a rational design strategy based on dual-metal co-doping for developing high-sodium-content, structurally robust tunnel-type cathode materials, offering valuable insights for advancing the practical deployment of SIBs in grid-scale energy storage applications.