Abstract:

Hard carbon material is an ideal anode for sodium-ion batteries due to its stable structure， high specific capacity， and good safety. Biomass and its derivatives can be used as a green and cost-effective carbon source for the production of hard carbon due to their abundant reserves and low prices. However， it is difficult to precisely control the microstructure of hard carbon materials using the traditional direct carbonization strategy， which is not conducive to improve the specific capacity and rate performanceof the materials. In this paper， porous carbon microspheres （PCGS） have been successfully prepared by spray freeze drying and low-temperature pyrolysis technique. The relationship between the structure and the electrochemical properties of the materials has been systematically investigated using characterization methods， including scanning electron microscopy （SEM）， transmission electron microscopy （TEM）， X-ray diffraction （XRD）， and Raman spectroscopy， combined with electrochemical tests. The results show that the sodium storage property of PCGS with average diameter of 10~60 μm is much better than that of the hard carbon materials obtained by direct carbonization method. The reversible specific capacity of PCGS was as high as 280 mA·h/g at 0.1 C， and the specific capacity remained at 230 mA·h/g at 0.2 C even after 100 cycles， with a capacity retention of 92%. In addition， the sodium storage mechanism of porous carbon microspheres has been investigated in this work using the in-situ Raman technique. The results of this work provide experimental references and guidance for structure modulation and performance optimization of high-performance hard carbon materials.

Key words: Sodium-ion battery, Anode, Porous carbon microspheres, Starch, Graphene