钠离子电池用膨胀石墨的电化学法制备及性能探究

摘要

In order to investigate the properties for sodium-ion storage of expanded graphite,an expanded graph-ite was prepared by electrochemical method.The structure of the samples were characterized by X-ray diffrac-tion (XRD)and the electrochemical behaviors were studied using galvanostatic charge/discharge test,cyclic voltammogram,and electrochemical impedance spectra.The results indicated that the modified flake graphite still kept the layer structure after electrochemical oxidation and expansion,while the average interlayer distance expanded slightly.Using diethylene glycol dimethyl ether (DEGDME)as the solvent,the capacity of sodium-ion insertion and extraction of the expanded graphite as well as the the rate performance and cycling behavior were improved significantly.A high reversible capacity of 110.9 mAh/g could be obtained at 700 mA/g,which was 66.8% of the capacity at 10 mA/g.After cycling over 100 charge/discharge cycles at 100 mA/g,the ex-panded graphite still maintained the high capacity of 154.8 mAh/g,with a capacity retention ration ratio of 114.8%.A study of potentiostatic intermittent titration technique(PITT)yield that the mean Na-ion diffusion coefficient,was 7.7×10-8 cm2/s.%为了探究膨胀石墨的储钠性能,利用电化学法制备了膨胀石墨,采用 XRD对其结构进行了表征,并利用恒电流充放电、循环伏安(CV)、电化学阻抗谱(EIS)对其储钠性能进行了分析.结果表明,鳞片石墨经过电化学氧化再经过高温瞬时膨胀之后,层间距略微增大,但依然保持着石墨的层状结构.以二乙二醇二甲醚(DEG-DME)为电解液,膨胀石墨对钠离子表现出较好的嵌/脱钠容量、倍率性能和循环性能：当电流密度为700 mA/g时,其可逆比容量为110．9 mAh/g,是10 mA/g时容量的66．8％.在100 mA/g电流密度下循环100次时,其第100次循环时的放电比容量为154．8 mAh/g,第一次循环时的放电比容量为134．8 mAh/g,容量保持率为114．8％.通过PITT测试,得出钠离子在膨胀石墨中的化学扩散系数为DNa＋＝7．7×10－8 cm2/s.