锂离子在石墨负极材料中扩散系数的测定

锂离子电池是以各种碳材料为负极而起来的一 种新型电池，成功地解决了以 为负极瓣锂可充电电池的安全性问题，已经应用于锂离子电池的负极材料有石墨和石油焦炭，正在研究的负极材料有热解碳，石墨化碳纤维，硼炭或硼炭氮化合物以及锡基氧化物等1]，石墨的比容量要比石油焦炭的比容量高一倍左右，其理论比容量372mA.h.g^-1，但锂离子在石墨材料中的扩散系数比较低，限制了以其为负极材料的电池的大电流充放电能力，锂离子在电极材料中的扩散系数可以用多种电化学方法测量得到，主要有：电位间歇滴定方法（PITT）（Potentiostatic Intermittent Titratiobn Technique)^2,3,4,6]，恒电流间歇滴定法（GITT）（Galvanostatic Intermittent Titration Technology)^6],电流脉冲松弛法（CPR）（Current Pulse Relaxation Method)^3,6]和交流阻抗法（A－C Technology)^4,5,6],GITT,CPR,A-C等方法测定锂离子扩散系数时，由于相变发生处dE/dy值不容易准确得到（相变时，dE/dy→0），此时测得的扩散系数误差比较大，PITT方法测定锂离子扩展系统，不存在这个问题，能比较准确地测定整个嵌入组成范围内的锂离子扩散系数。

Determination of the Lithium Ion Diffusion Coefficient in Graphite Anode Material

Two expressions are introduced to calculate the lithium ion diffusion coefficients in graphite anode as a function of potentials when potentiostatic intermittent titration technique(PITT) is used. The lithium ion diffusion coefficients in graphite derived from effective surface area, which is measured by electrochemical method, are more reliable than those derived simply from radius of graphite particles(calculated from equation (3) and equation (2) respectively). The curves of dQ/dE vs E demonstrate that there are three reversible phase transitions during intercalation or deintercalation of lithium ion in graphite. In the vicinity of the potentials where phase transitions take place, the lithium ion diffusion coefficients in graphite material have three minima in the potential range 10～ 600 mV.