Onion-like carbon microspheres as long-life anodes materials for Na-ion batteries

Room-temperature Na-ion batteries have been widely used as promising energy storage systems for large-scale storage due to the nature abundance and low cost of Na. However, the search for an anode with appropriate Na storage and high structural stability still remains challenging. In this work, the carbon microsphere films-coated Ni foam is prepared by a simple chemical vapor deposition method and is used as a novel anode for the long-lifespan Na-ion batteries. These carbon microspheres possess special onion-like structures that enhance the Na-ions intercalation and exhibit excellent Na storage properties. In addition, directly coating the carbon microsphere films on Ni foam current collectors without binders and conductive additives results in an integrated electrode structure, which avoids the undesirable interfaces and reduces the packaging volume. Compared to the common used hard carbon anode with long discharge plateau and short lifespan, this integrated electrode exhibits a slope discharge profile with higher security and demonstrates a long lifespan of 700 cycles with a high capacity retention of 83%. Furthermore, the storage mechanism of sodium ion is also investigated in detail by ex situ Raman, X-ray diffraction and nuclear magnetic resonance techniques in this study.