锂离子蓄电池碳负极嵌锂过程的研究

Study on the lithium intercalation in carbon anodes for lithium ion battery

用交流阻抗法对ＰＡＮ基碳纤维、石油焦、沥青焦、针状焦进行了嵌锂过程的研究。ＰＡＮ基碳纤维的阻抗图谱由高频区ＳＥＩ膜容抗半圆、中频区电化学反应容抗半圆、低频区垂直线组成，低频部分为典型的固相有限扩散有效层效应。焦碳电极的阻抗图谱与ＰＡＮ基碳纤维相似，只是低频部分为４５°斜线，具有半无限扩散特征，表明嵌锂过程是由固相扩散和电化学步骤混合控制。石油焦随准稳态电位（开路电位）的升高，Ｒｃｔ值、Ｗａｒｂｕｒｇ 系数σ、固相扩散系数Ｄ均增大，反映了高电位下的电化学极化增加，扩散极化也增大了，嵌锂反应难以进行，嵌锂量减少。石油焦和沥青焦在不同循环次数的Ｒｆ、Ｃｆ、Ｃｄ、Ｒｃｔ、σ的变化说明了电极性能不变，阻抗图谱基本不变。若Ｒｆ、Ｒｃｔ、σ增大，则放电容量衰减。

Electrochemical intercalation of lithium into PAN based carbon fibers, petroleum coke, pitch coke and needle coke were studied by AC impedance method. The impedance spectrum of PAN based carbon fibers consisted of the SEI film condensive reactance semicircle in high frequency range, the electrochemical reaction condensive reactance semicircle in medium frequency range and the straight line in low frequency. The low frequency showed typical solid diffusion effective layer effect. The impedance spectrum of coke was similar to that of carbon fibers except that it showed a oblique line with the angle of 45° to the real axes, which revealed the intercalation process was controlled by both solid diffusion and electrochemical stage. The R ct value, Warburg coefficient σ and solid diffusion coefficient D increased along with the raise of quasi steady potential. It indicated that under high voltage, the chemical polarization of charge transfer and diffusion increased so that lithium intercalation was hard to react and the quantity of intercalation decreased. The change of R f,C f,C d,R ct and σ of petroleum coke and pitch coke at different cyclic numbers showed that the performance of electrode and the impedance spectrum did not change. If R f,R ct and σ increased,the discharge capacity would decrease and the internal structure of carbon would change.