Rational design of Co-free layered cathode material for sodium-ion batteries

The effect of Ti substitution on the structure and electrochemical properties of O3-type Na[(Mn0.4Fe0.3Ni0.3)1−xTix]O2 (x = 0, 0.1) is investigated. The initial capacities of the Ti-free and Ti-doped materials are 167 and 151 mAh g−1 (24 mA g−1), respectively, and improved capacity retention is observed for the Ti-substituted material. Operando X-ray diffraction analysis reveals that both materials undergo a O3→P3→OP2 phase transition during Na+ extraction and an OP2→OP→P3→O3 phase transition upon Na+ insertion, with suppressed volume change observed for the Ti-substituted material. The improved electrode performance is likely associated with suppression of the interlayer distance and volume changes, resulting from the presence of the strong Ti−O bond in Na[(Mn0.4Fe0.3Ni0.3)0.9Ti0.1]O2. To evaluate the long-term electrode performance, Na[(Mn0.4Fe0.3Ni0.3)0.9Ti0.1]O2 is paired with a hard-carbon anode; excellent cyclability and retention (∼70%) are achieved for 300 cycles at a rate of 0.5C (120 mA g−1). Our findings provide insight for the future design of high-performance cathode materials from abundant and environmentally friendly elements for sodium-ion batteries.