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我们通过包覆炭化的方法制备得到了石墨烯包覆的天然球形石墨(G/SG)材料,并使用扫描电子显微镜、X射线衍射仪以及多种电化学测试手段考察了不同石墨烯含量的复合材料的形貌结构及电化学性能.我们发现,在不添加乙炔黑(AB)的情况下,G/SG复合材料表现出较高的首次库伦效率,很好的循环稳定性和高倍率性能.当石墨烯包覆量为1％时,材料50次循环后的可逆容量可与添加10％AB的天然石墨电极(SG)等同;当石墨烯包覆量为2.5％时,材料的比容量完全高于添加10％AB的石墨电极.材料电化学性能的改善归因于石墨烯的包覆.一方面,石墨烯的柔软可变性可以保证天然石墨颗粒在充放电过程中的结构完整性,从而有效改善材料的循环稳定性;另一方面,石墨烯的存在提高了电极的导电性,促进更好导电网络的形成.因此,石墨烯包覆天然球形石墨材料中,石墨烯不仅是活性物质,也发挥导电剂的作用.当添加5％的乙炔黑时,在50 mA·g-1电流循环50次后,5％G/SG电极的可逆容量从381.1 mAh·g-1提高到404.5 mAh·g-1,在1A·g-1电流时可逆容量从82.5 mAh·g-1提高到101.9 mAh·g-1,这表明G/SG电极仍然需要乙炔黑导电剂.乙炔黑颗粒填充在复合材料的空隙中,通过点接触的形式连接到G/SG颗粒,与石墨烯协同作用形成了更加有效的导电网络.尽管石墨烯包覆和乙炔黑添加对天然石墨电极具有积极的影响,例如增加了天然石墨电极的导电性和储锂性能(包括可逆容量,倍率性能和循环性能),但随着石墨烯或乙炔黑的增加,电极密度通常会降低.因此,在实际应用中应考虑石墨负极材料的质量和体积容量的平衡.这些结果对天然石墨的进一步商业应用具有重要意义.我们的工作为天然石墨电极在锂电池中的电化学行为提供了一种新的认识,并且有助于制备更高性能的负极材料.“,”Graphene-wrapped natural spherical graphite (G/SG)composites were prepared using the encapsulation-carbonization approach.The morphology and structure of the composites were characterized by scanning electron microscopy and X-ray diffraction analysis.The electrochemical performance of the composites with different graphene contents as anode materials for lithium-ion batteries was investigated by various electrochemical techniques.In the absence of acetylene black (AB),the G/SG composites were found to exhibit high specific capacity with high first-cycle coulombic efficiency,good cycling stability,and high rate performance.Compared with the natural spherical graphite (SG) electrode,the G/SG composite electrode with 1％ graphene exhibited higher reversible capacity after 50 cycles;this capacity performance was equal to that of the SG + 10％AB electrode.Moreover,when the addition of 2.5％ graphene,the composite electrode exhibited higher initial charge capacity and reversible capacity during 50 cycles than the SG+10％AB electrode.The significant improvement of the electrochemical performance of the G/SG composite electrodes could be attributed to graphene wrapping.The graphene shell enhances the structural integrity of the natural SG particles during the lithiation and delithiation processes,further improving the cycling stability of the composites.Moreover,the bridging of adjacent SG particles allows the formation of a highly conductive network for electron transfer among SG particles.Graphene in the composites serves as not only an active material but also a conductive agent and promotes the improvement of electrochemical performance.When 5％AB was added,the reversible capacity of the 5％G/SG electrodes significantly increased from 381.1 to 404.5 mAh·g-1 after 50 cycles at a rate of 50 mA·g-1 and from 82.5 to 101.9 mAh·g-1 at 1 A·g-1,suggesting that AB addition improves the performance of the G/SG composite electrodes.AB particles connect to G/SG particles through point contact type and fill the gaps between G/SG.A more effective conductive network is synergistically formed via graphene-AB connection.Although graphene wrapping and AB addition improve the performance of natural graphite electrodes,such as through increase in electrical conductivity and enhancement of Li-storage performance,including improvement of reversible capacity,rate performance,and cycling stability,electrode density typically decreases with graphene or AB addition,which should consider the balance between the gravimetric and volumetric capacities of graphite anode materials in practical applications.These results have great significance for expanding the commercial application scope of natural graphite.Our work provides new understanding and insight into the electrochemical behavior of natural SG electrodes in lithium-ion batteries and is helpful for the fabrication of high-performance anode materials.