Abstract:

Concentrated sulfuric acid and concentrated nitric acid were used as oxidants to oxidize the surface of hard carbon by ultrasonic oxidation, and its electrochemical performance as a negative electrode material for lithium ion supercapacitors was studied. The influence of ultrasonic oxidation treatment on the morphology, structure and relative content of oxygen-containing functional groups on the surface were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical performance of hard carbon before and after treatment was studied by means of galvanostatic charge and discharge, cyclic voltammetry and AC impedance. The results showed that ultrasonic oxidation treatment can introduce appropriate amount of oxygen-containing functional groups on the hard carbon surface, add additional active sites, improve the electron mobility, and then improve the electrochemical performance of hard carbon materials. In the half-cell test, at a high current density of 2 A·g^-1, the specific capacity of oxidized hard carbon is twice that of untreated hard carbon, and it has excellent rate performance. Lithium ion capacitors were fabricated with oxidized hard carbon anode and activated carbon cathode. The energy density is 37.6 W·h·kg^-1, and the power density is 9415 W·kg^-1, the capacity retention rate was 99.1% after 4000 cycles at a current density of 1.0 A·g^-1, showing good cyclic stability.

Key words: lithium ion capacitors, anode materials, hard carbon, surface, oxidation, electrochemical

摘要：

以浓硫酸和浓硝酸为氧化剂，采用超声氧化法对硬碳进行表面氧化处理，并研究其作为锂离子超级电容器负极材料的电化学性能。采用扫描电镜、X射线衍射和X射线光电子能谱等表征手段研究了超声氧化处理对硬碳形貌、结构以及表面含氧官能团相对含量的影响。采用恒电流充放电、循环伏安法及交流阻抗法等电化学测试手段对处理前后硬碳的电化学性能进行研究。结果表明：超声氧化处理能在硬碳表面引入适量的含氧官能团，添加额外的活性中心，提高电子迁移率，进而提高硬碳材料的电化学性能。半电池测试中，在2 A·g^-1的高电流密度下，氧化硬碳的比容量是未处理硬碳的2倍，具有优秀的倍率性能。以氧化硬碳负极和活性炭正极制备出锂离子电容器，能量密度为37.6 W·h·kg^-1，功率密度可达9415 W·kg^-1，在1.0 A·g^-1电流密度下，经过4000次充放电循环后，容量保持率为99.1%，具有良好的循环稳定性。

关键词: 锂离子电容器, 负极材料, 硬碳, 表面, 氧化, 电化学