碳原子线的磁学、电学性质

【作者】 尹寿银；

【导师】 薛宽宏；

【作者基本信息】 南京师范大学 ， 应用化学， 2005， 硕士

【摘要】 本文报告碳原子线（CAW）的磁学性质以及作为锂电池负极材料的电化学性能的研究结果。运用振动样品磁强计（VSM）和电子顺磁共振仪（EPS）等设备对碳原子线的磁学性质进行研究,并定量计算了碳原子线上每个碳原子的未成对电子的数目;通过红外、环伏安、充放电、交流阻抗等方法,研究锂离子二次电池的碳原子线负极的电化学特性以及硝酸处理对碳原子线电极充放电性能的影响。 我们对碳原子线的磁学行为进行研究时,发现在室温下碳原子线的磁滞回线为“S”形。随着磁场强度的增加,磁化强度渐渐趋于饱和,但其饱和磁化强度比通常的铁磁性材料小很多,故碳原子线具有类铁磁性。至今,已有C₆₀在低温下呈现类铁磁行为的报道,而碳原子线却能在室温下显示出类铁磁性。这种特殊的磁学性能很可能与碳原子线的特殊的sp杂化结构有关。通过电子顺磁共振,我们定量测量了碳原子线中未成对电子的数目,结果显示碳原子线中有大量的未成对电子,此结果同碳原子线的分子结构是基本一致的。 作为锂离子二次电池负极材料,碳原子线首次充放电容量分别为369.5mAh/g和999.4mAh/g,从第2次循环起,充放电效率开始提高,第10次达到94.3%,不可逆容量逐渐降低,可逆容量基本维持在约300mAh/g左右。显示出碳原子线负极具有良好的循环性能和可逆容量。 此外,当对碳原子线进行硝酸处理后,红外光谱表明在碳原子线上产生了更多的羟基、羧基等基团。一般认为,表面形成的这些基团在锂插入过程中有助于形成致密钝化膜,可减少溶剂分子的共插入,从而抑制电解液的分解,这样可使可逆比容量明显提高。处理后的碳原子线首次充放电容量分别为1618.6mAh/g和741.7mAh/g,和未处理的碳原子线相比首次充放电容量、充放电效率都有很大程度的提高。更多还原

【Abstract】 This dissertation reports the preliminary experimental results of magnetic properties of carbon atom wires (CAWs) and their electrochemical features demonstrated in the anode of lithium-ion secondary batteries A vibrating sample magnetometer (VSM) and an electron paramagnetic resonance (EPR) spectrometer were used in the magnetic investigation and the number of unpaired electrons in CAWs was evaluated. The electrochemical features of the CAW anode for lithium-ion secondary batteries were studied by use of the cyclic voltammetry, constant-current charging-discharging experiments and the AC impedance method. In addition, the effects of nitric acid treatment applied on CAWs were also tested.By a vibrating sample magnetometer, we discovered that magnetic hysteresis loop of CAW in the shape of "S" at the room temperature. The intensity of magnetization increased with the applied magnetic field until saturation, but whose value was much smaller than those of ordinary ferromagnetic materials. The experimental results showed CAWs to be a kind of alike ferromagnetic substance. The abnormal magnetic behaviors probably came from the particular structure of sp hybridization. By means of EPR, we estimated the number of unpaired electrons of CAW and a plenty of unpaired electrons existed in CAWs, as shown in the experiments, in agree with their structure proposed.In the constant-current charging-discharging experiment for a battery composed of a CAW electrode and a piece of Li electrode, the discharging capacity in the first cycle was as great as 999.4mAh/g and the corresponding charging capacity was 369.5mAh/g,.The charging-discharging efficiency began to increase from the 2nd cycle and reached 94.3% at the 10th cycle. The irreversible capacity was reduced gradually and the reversible capacity maintained to be about 300mAh/g finally. From the results, CAWs have a potential application used as an anode in the lithium-ion secondary batteries.Treated by concentrated nitric acid, some carboxylic acid groups on CAWs were produced, which could help to form a solid film arising from the reduction of thesolvent and the electrolyte on the interphase between the electrode and electrolyte solution in the process along with the lithium-ion intercalation. The solid film can reduce the co-intercalation of solvent molecules and inhibit their decomposition. Therefore, the nitric acid treatment can reduce the irreversible capacity and increase the reversible capacity of the CAW electrode.更多还原