Ti-doped NaCrO2 as cathode materials for sodium-ion batteries with excellent long cycle life

Different content of Ti4+ has been successfully doped into the lattice sites of Cr3+ in NaCrO2 by the two step solid-state reaction. The analysis results of crystal structure demonstrate that the interslab (NaO2) spacing is increased with Ti doping content, which contributes to widening the sodium ion migration channel and then facilitating the rapid (de)intercalation capability of sodium ions. During charge-discharge processes, these O3-Na1-xCr1-xTixO2 (x = 0.03, 0.05, 0.1) layered oxides exhibit delayed O3-P3 phase transition and increased average discharge voltage due to stronger Ti-O bond relative to Cr-O bond. In particular, the Na0.95Cr0.95Ti0.05O2 shows the optimal electrochemical performance which releases a discharge specific capacity of 96.7 mAh g−1 at 1 C (100 mA g−1) with 80.1% capacity retention after 800 cycles. Even under the high rate of 30 C, it can deliver a discharge specific capacity of 67 mAh g−1.