Carbon-wrapped four-component Na–Ni–Ti–Co oxides via sol–gel process for NIB anode material with superior cycling stability

An easy sol–gel method was devised to synthesize the carbon-wrapped Na 0.67 Ni 0.17 Ti 0.67 Co 0.17 O 2 nanoparticles (NNTC/C), which served as anode material in the new type of sodium-ion batteries. Functioned as the sodium storage medium, the NNTC/C exhibited initial discharge/charge capacities of 122/110 mA h g −1 at the rate of 0.2 C in the voltage range of 0.2–2.5 V with capacity retention of almost 82% of its initial capacity after 500 cycles. It is indicated that among the component metals, redox association only exists between the Ti 4+ /Ti 3+ couple and the Na + insertion and extraction during the charge/discharge process. In addition, ex situ X-ray diffraction analysis illustrated a small fluctuation of cell volume in the cycling, suggesting a high level of reversible structural changeability and stability of the NNTC/C. The characterization results demonstrate that the NNTC/C is an ideal candidate as anode material for high-performance sodium-ion batteries. Graphical Abstract