简易法制备孔隙可调的三维石墨烯宏观体及锂电池性能的研究

Simple preparation of three-dimensional graphene with adjustable pore structure and performance of lithium batteries

石墨烯宏观体具有大的比表面积和丰富的相互连接的内部孔道结构,广泛应用于锂离子电池、超级电容器等领域.现阶段多采用将石墨烯水凝胶进行冷冻干燥或二氧化碳超临界干燥的方法制备石墨烯宏观体,该方法具有一次成型、耗时短等优点,但是存在孔隙大小无法调控、设备昂贵等不足.本文以氧化石墨烯(GO)为原料制备得到石墨烯水凝胶,仅利用室温干燥和冰箱冷冻相协同的简单方法制备孔隙可调的三维石墨烯宏观体(GM).研究发现经室温部分干燥后的石墨烯水凝胶经冰箱冷冻后再进行室温完全干燥其体积几乎不发生变化,因此通过调控首次室温干燥的时间调变石墨烯宏观体的孔隙大小.此方法具有操作简单、造价低廉的优点.将所制备的GM作为锂离子电池负极材料,表现了良好的储锂性能.结果表明:首次室温干燥3h的石墨烯水凝胶再经过冰箱冷冻和第二次室温完全干燥所获得的GM(GM-3h)在0.1A·g^-1电流密度下其比容量高达1039mAh·g^-1远高于传统石墨负极372mAh·g^-1的比容量;在0.5A·g^-1的电流密度下经100次循环后,其比容量降低到504mAh·g^-1,保持率为73.1%,表现了良好的循环稳定性.

Graphene macrostructure (GM) has large specific surface area and abundant interconnected internal pore structure,which is widely used in lithium ion batteries,supercapacitors and other fields.At present,freeze-drying of graphene hydrogel or supercritical drying of carbon dioxide are often used to prepare GM.This method has the advantages of one-time forming and time-economical,but there are some shortcomings such as uncontrollable pore size and using expensive equipment.In this paper,graphene hydrogels were prepared from graphene GO,followed by drying at room temperature and freezing in refrigerators.At last,the three-dimensional GM with adjustable pore size were synergistically prepared.It was found that the volume of graphene hydrogel dried at room temperature hardly changed after freezing in refrigerator and then drying at room temperature.Therefore,the pore size of GM could be adjusted by adjusting the time of first drying at room temperature.This method has the advantages of simple operation and low cost.The prepared GM was used as negative electrode material of lithium ion batteries and showed good lithium storage performance.The results show that the specific capacity of GM (GM-3 h) obtained from graphene hydrogels dried at room temperature for 3 hours,refrigerated in refrigerator and dried at room temperature for the second time is 1 039 mAh g^-1 at 0.1 A·g^-1,which is much higher than that of 372 mAh·g^-1 of traditional graphite anode.After 100 cycles at 0.5 A·g^-1,the specific capacity decreases to 504 mAh·g^-1 with a retention rate of 73.1%,which shows good cycle stability.