Communication—O3-Type Layered Oxide with a Quaternary Transition Metal Composition for Na-Ion Battery Cathodes: NaTi_0.25Fe_0.25Co_0.25Ni_0.25O₂

NaTi<sub>0.25</sub>Fe<sub>0.25</sub>Co<sub>0.25</sub>Ni<sub>0.25</sub>O<sub>2</sub> is explored as a cathode material for Na-ion batteries. Synthesized by a solid-state reaction, the compound is phase-pure with the O3-type layered structure and consists of Ti<sup>4+</sup>, Fe<sup>3+</sup>, Co<sup>3+</sup>, and Ni<sup>2+</sup> according to X-ray absorption spectroscopy. The cathode delivers 163 mAh/g and 504 Wh/kg at C/20 in the first discharge with 89% capacity retention after 20 cycles and demonstrates superior rate capability with micron sized particles, in which discharge capacity at 30 C is 80mAh/g. Our results indicate that the Ti-containing quaternary material can be a potential cathode composition for Na-ion batteries.