Properties and Structure of the LiCl-films on Lithium Anodes in Liquid Cathodes

Lithium anodes passivated by LiCl layers in different types of liquid cathodes (catholytes) based on LiAlCl4 in SOCl2 or SO2 have been studied by means of impedance spectroscopy. The impedance spectra have been fitted with two equivalent circuits using a nonlinear least squares fit program. Information about the ionic conductivity and the structure of the layers has been extracted. A new physical description, which is able to explain the circuit parameters, is proposed. It assumes that the LiCl-layer contains a large number of narrow tunnels and cracks filled with liquid catholyte. It is explained why such tunnels probably are formed, and for a typical case it is shown that tunnels associated with most of the LiCl grain boundaries of the fine crystalline layer near the Li surface are requested in order to explain the impedance response. The LiCl production rate and through this, the growth rate of the LiCl-layer, is limited by the electron conductivity of the layer. Micro-calorimetry data parallel with impedance spectra are used for determination of the electron conductivity of the LiCl-layer.