石墨烯-Li2MnSiO4复合正极材料的合成与电化学性能研究

Synthesis and Electrochemical Performance of Graphene-Li_2MnSiO_4 Composite

采用水热辅助溶胶凝胶法成功合成了石墨烯-Li2MnSiO4锂离子电池复合正极材料.利用XRD,SEM及TEM等手段表征了复合正极材料的组成和形貌,并测试了不同氧化石墨烯复合量正极材料样品(质量分数为2%,4%,6%,8%,10%,及未复合氧化石墨烯)的电化学性能.研究结果表明,石墨烯与Li2MnSiO4材料均匀地复合在一起;添加适量的氧化石墨烯能促使Li2MnSiO4粒子的分布趋向疏松,并形成微孔结构;氧化石墨烯复合量为6%时形成的石墨烯-Li2MnSiO4样品电化学性能最佳,扣除碳含量后,以10 mA/g为电流密度,首周放电比容量为166 mAh/g,循环20周后放电比容量仍保持在101 mAh/g.此外,与石墨烯复合后的Li2MnSiO4材料倍率性能也得到了明显的改善.石墨烯的存在提高了复合材料的导电性,提升了Li2MnSiO4正极材料的可逆嵌脱锂容量.

Graphene-Li2MnSiO4 composite cathodes for lithium ion batteries were successfully synthesized by hydrothermal assisted sol-gel method.XRD(X-ray diffraction),SEM(scanning electron microscope) and EIS(electrochemical impedance spectroscopy) were used to characterize the component,structure and morphology of the obtained composite materials.Electrochemical performance of the as-prepared materials was tested when composited with different amount of graphene oxide(2%,4%,6%,8%,10% and without graphene oxide).The experiment results indicated that composite materials belong to the orthorhombic Pmn21 space group and the addition of graphene oxide did not change the structure of the materials.Graphene and Li2MnSiO4 material were homogeneously composited with each other and it could be clearly observed the relatively transparent and thin layer graphene in the edges of the materials.The micro-scale particle of all the samples was agglomeration of nano-crystallites.When composited with appropriate amount of the graphene oxide,the particles became loose and some micropore structure was formed.The conductive network graphene could greatly promote the liquid electrolyte to pass through particles,facilitate the electron transport and restrain particles agglomeration.The sample with 6% graphene oxide yielded the best electrochemical performance in all the samples(the carbon content is 8.25%).Without calculating the carbon mass,this material delivered an initial discharging capacity of 166 mAh/g,and retained 101 mAh/g after 20 cycles at 1.5~4.8 V with a current density of 10 mA/g.Besides,compared with the pristine,the graphene-Li2MnSiO4 composite materials delivered an excellent rate performance.The improvement of specific capacity and rate performance was due to that the interconnected network structure of graphene oxide acted a key role in stabilizing the structure of composite materials and inhibiting structural damage in the charge-discharge process.Moreover,the surface charge transfer resistance of the Li2MnSiO4 was significantly decreased when composited with graphene oxide.It means that the enhancement of electronic conduction ability is one of the main reasons that contribute to improvement of the electrochemical performance of composite materials.Thus,the graphene is considered to be of significance in improving material electronic conductivity and enhancing the reversible lithium intercalation/deintercalation capacity of Li2MnSiO4 cathode materials.