稳定界面助力石墨实现超长储钾性能

Stable Graphite Interface for Potassium Ion Battery Achieving Ultralong Cycling Performance

石墨作为锂离子电池的商业阳极材料,由于其高丰度、低成本和低电位的优势,在K离子电池中也显示出了的巨大潜力。然而,K离子半径(0.138 nm)大于Li离子半径(0.076 nm),会造成的明显结构损伤导致明显的容量衰减和不稳定的循环寿命。在这里,我们用简单有效的微波方法通过石墨烯涂层设计了石墨阳极的稳定界面。微波还原可以在10 s内有效地去除氧化石墨烯的氧基,这一点得到了X射线光电子能谱(XPS)的证实。石墨烯涂层不仅可以缓冲石墨的体积膨胀以抑制结构崩溃,还可以加速电子传输以提高倍率性能。石墨烯涂层负极(GCG)在3000次循环后表现出262 m Ah·g^(-1)的超级循环稳定性。与石墨相比GCG的倍率性能也更加优异(500 m A·g^(-1)的电流密度下容量为161.2 m Ah·g^(-1))。相反,在相同的电流密度下,石墨的容量在150次循环后衰减到小于150m Ah·g^(-1)。进一步的电化学阻抗(EIS)和恒电流间歇滴定(GITT)测试表明,与石墨相比,GCG表现出更快的电导率和离子扩散。循环后的拉曼光谱、扫描电镜(SEM)和透射电镜(TEM)图像验证了石墨烯作为缓冲界面有利于电极结构的完整性和固体电解质膜(SEI)的稳定性。这项工作为钾离子电池的大规模应用提供了新的希望。

Graphite has been extensively employed as commercial anode material in Li-ion batteries due to its high abundance,low cost,and negative electrode potential.Furthermore,it has demonstrated significant potential for use in Kion batteries.However,distinct structural damage caused by the larger radius of K-ion(0.138 nm)compared to that of Li-ion(0.076 nm)leads to obvious capacity decay and unstable cycle life.It is crucial to improve the cycling stability of graphite in potassium ion batteries(PIBs).Herein,we design a stable interface of graphite anode by graphene coating with a simple and efficient microwave method.According to X-ray photoelectron spectroscopy(XPS),microwave reduction can effectively remove the oxygen group of graphene oxide(GO)within 10 s.The graphene coating can buffer the volume expansion of the graphite to suppress structural collapse;it can also accelerate electronic transmission to improve rate performance.As a result,the graphenecoating graphite anode,named GCG,exhibits super cycling stability with a capacity of 262 mAh∙g^(-1) after 3000 cycles at a current density of 0.2 A∙g^(-1),which means it can operate smoothly for one year.In contrast,at the same current density,graphite exhibits capacity fading to less than 150 mAh∙g^(-1) after 150 cycles.Moreover,compared to graphite,GCG demonstrates better rate performance achieving a capacity of 161.2 mAh∙g^(-1) at 500 mA∙g^(-1).Further electrochemical impedance spectroscopy(EIS)and galvanostatic intermittent titration technique(GITT)tests show that GCG exhibits faster electrical conductivity and ion diffusion compared to graphite.Raman spectroscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM)images after cycling verify that the graphene buffer interface benefits the integrity of the electrode structure and improves the stability of the solid electrolyte interphase(SEI).Compared to graphite,the GCG anode exhibits better performance,as follows:1)The graphene coating inhibits exfoliation of graphite during cycling,solving the problem of graphite anode’short cycling life,and 2)the graphene protective layer improves the ion diffusion rate,resulting in better rate performance of the GCG.In addition,this approach offers the advantages of simple operation and low cost,hopefully enabling large-scale applications of potassium-ion batteries.