桉木基硬碳用作钠离子电池负极材料

Eucalyptus-based hard carbon as anode material for sodium ion battery

受到较低的初始库仑效率以及不同制备方法导致的储钠机制仍不清楚的限制,硬碳负极的在钠离子电池中的实际使用受到了较大限制。硬碳负极的储钠行为对于开发高效的钠离子电池很重要。利用裂解法合成了产碳率较高的桉木基硬碳材料,运用扫描电镜、高分辨率透射电镜、拉曼光谱、X射线衍射和氮气吸脱附探究了材料的表面形貌、物相结构以及孔径分布;通过恒电流充放电和循环伏安测试考察了材料的电化学性能。实验结果表明:随着碳化温度的升高,桉木硬碳的比表面积和层间距下降,有序度增加,电化学性能提高,裂解温度1100℃时,可以提供224 mA·h/g的比容量,初始库伦效率高达81%,0.1 A/g的电流密度下循环200次后的容量保持率高达96%,5 A/g电流密度下的可逆容量达164 mA·h/g。结果显示桉木硬碳负极储钠的方式主要是由钠离子在表面和缺陷处的吸附和石墨烯层间的嵌入共同决定的。

The practical use of hard carbon anodes is largely limited by low initial Coulombic efficiency(ICE)and the elusive sodium storage mechanism.The sodium ion behaviour in hard carbon anodes is crucial to develop more efficient sodium ion batteries.Eucalyptus-based hard carbon with high carbon yield was synthesized by pyrolysis method.The surface morphology,phase structure and pore size distribution of the material were studied by scanning electron microscopy(SEM),high resolution transmission electron microscopy(HR-TEM),Raman spectroscopy,X-ray diffraction(XRD),and nitogen absorption and desorption.The electrochemical perfomance was explored by galvanostatic charge-discharge and cyclic voltammetry tests.The results show that with the increase of carbonization temperature,the specific surface area and the spacing of hard carbon layers decrease,but degree of order of hard carbon is improved,which are conducive to the charge-discharge specific capacity and rate performance.When the pyrolysis temperature is 1100℃,the specific capacity of 224 mA·h/g can be delivered at a current density of 0.03 A/g,and the initial coulombic efficiency is 81%.After 200 cycles at a current density of 0.1 A/g,the capacity retention rate is up to 96%,and the reversible capacity at a current density of 5 A/g is 164 mA·h/g.The sodium storage mode is mainly determined by both the adsorption of sodium ions on the surface and defects and the embedding between graphene layers.