(1. 中南大学 冶金与环境学院,长沙 410083;
2. 长沙理工大学 物理与电子科学学院,长沙 410004)
摘 要: 以硫酸为表面修饰剂,采用浸渍法对天然石墨进行表面修饰改性。傅里叶变换红外光谱仪(FTIR)分析结果表明,硫酸表面修饰的天然石墨表面—OH和C=C消失,—COO-数量增多。电化学性能测试结果表明,经硫酸表面修饰的天然石墨的循环性能和倍率性能均得到提高。经3 mol/L H2SO4处理12 h的天然石墨(NGS3)在0.5C下20次循环后脱锂容量为320.5 mA?h/g;而未经表面修饰的天然石墨(NG)在相同条件下的脱锂容量仅为299.9 mA?h/g。采用交流阻抗谱对石墨进行嵌脱锂动力学研究,结果显示,经硫酸表面修饰的天然石墨膜电阻(RSEI)和电荷转移电阻(Rct)均减小,膜电容(CSEI)和双电层电容(CCPE)增加,多次循环后RSEI保持稳定,NG的活化能(Ea)为87.7 kJ/mol,NGS3的Ea为77.2 kJ/mol,表明 H2SO4修饰有利于锂离子去溶剂化能力的提高,并有利于形成稳定的固体电解质界面(Solid electrolyte interface,SEI)。
关键字: 天然石墨;表面修饰;负极;固体电解质界面;交流阻抗;活化能
(1. School of Metallurgy and Environment, Central South University, Changsha 410083, China;
2. School of Physics and Electronic Science, Changsha University of Science and Technology, Changsha 410004, China)
Abstract:The natural graphite was modified by impregnation method with sulfuric acid as surface modification agent. FTIR results show that —OH and C=C bonds on the surface of natural graphite disappear while the number of —COO- increases after sulfuric acid surface-modification. The electrochemical performance reveals that the cycle performance and ratio performance are improved. The lithium-deinsertion capacities of natural graphite impregnated by 3 mol/L H2SO4 for 12 h (NGS3) and unmodified natural graphite (NG) are respectively 320.5 and 299.9 mA?h/g after 20 cycles at 0.5C. AC impedance was used to investigate kinetics on lithium ion insertion/ deinsertion. It is found that the membrane resistance (RSEI) and charge transfer resistance (Rct) decrease, while the membrane capacitance (CSEI) and extracted capacitance (CCPE) increase. Moreover, RSEI keeps constant after several cycles. The activation energies of NG and NGS3 are 87.7 and 77.2 kJ/mol, respectively, which indicates that sulfuric acid treatment is beneficial to the improvement of the desolvation of lithium ion from solvent molecules and the formation of a stable solid electrolyte interface (SEI).
Key words: natural graphite; surface-modification; anode; solid electrolyte interface; alternating impedance; activation energy