Li/LiClO_4-碳酸丙烯酯体系的交流阻抗研究

INVESTIGATION OF Li/LiCIO_4-PROPYLENE CARBONATE SYSTEM BY A. C. IMPEDANCE

结合扫描电子显微镜,用交流阻抗法对Li/LiClO_4-碳酸丙烯酯锂电极体系的研究表明,锂电极表面膜层的生长分三个阶段,相当于两个紧密层和一个疏松层。里紧密层由Li_2CO_3组成,厚度约10~2A,是Li^+导体和电子绝缘体,电阻率为1.4×10~8Ωcm,对锂电极的充放电无不利影响。外紧密层由Li_2CO_3和有机物组成。疏松层是在外紧密层表面不断破裂和修复中形成的。它们都不利于锂电极的充放电。

Li/LiClO_4-Propylene Carbonate is one of lithium electrode systems studied often. In this article we present some new findings obtained with a. c. impedance and SEM methods. The variation of R_p×C_p with logarithm of time shows three distinct periods, corresponding to three different stages of growth of the film on lithium surface. In the initial period of film growth R_p×C_p is constant, corresponding to growth of primary compact layer consisting of Li_2CO_3, an ionic conductor. Resistivity of film was calculated to be 1.4×10~8Ω·cm. and the thickness of film is several hundred angstrons. In the second period of film growth the product of R_p and C_p varies linearly was logarithm of time, corresponding to growth of another compact layer, which consists of Li_2CO_3 and organic compounds including organic polymers. Because of inclusion of organic components, the conductivity of the film decreases and it is difficult to calculate the thickness of film. The third period is charactered by chaotic vibration, which is probably caused by periodic breaking and resealing of the compact layer and the growth of a porous layer. Upon polarization the primary compact layer probably undengoes no significant change and has no effect on the reversibility of the electrode system, while the outer compact layer and porous layer definitely have unfavourable influence on the revesihility of charging and discharging processess.