A general transmission line model that is able to describe accurately the measured impedance spectra of uncycled and cycled lithium electrodes is introduced. The model has all the essential features that are contained in analytical solutions for determining the impedance response of porous electrodes. In addition to that, it allows easy coupling between the various phenomena met in lithium anodes in contact with a separator: transport through a solid electrolyte interphase film, transport across "live lithium dendrites", reaction inside "live lithium dendrites", transport across "dead dendrites", diffusion in a porous separator, and so forth. The model is used for quantitative analysis of measured impedance spectra collected at different C-rates and after different numbers of charge−discharge cycles. Further, combining impedance spectroscopy with scanning electron microscopy, several unique correlations between the morphological development of lithium anodes and development of impedance spectra are identified and discussed. Finally, several simplified schemes that allow identification of the main degradation or failure mechanism(s) occurring in cycled lithium anodes are presented.

Metallic lithium is considered to be one of the most promising anode materials since it offers high volumetric and gravimetric energy densities when combined with high-voltage or high-capacity cathodes. However, the main impediment to the practical applications of metallic lithium is its unstable solid electrolyte interface (SEI), which results in constant lithium consumption for the formation of fresh SEI, together with lithium dendritic growth during electrochemical cycling. Here we present the electrochemical performance of a fluorinated reduced graphene oxide interlayer (FGI) on the metallic lithium surface, tested in lithium symmetrical cells and in combination with two different cathode materials. The FGI on the metallic lithium exhibit two roles, firstly it acts as a Li-ion conductive layer and electronic insulator and secondly, it effectively suppresses the formation of high surface area lithium (HSAL). An enhanced electrochemical performance of the full cell battery system with two different types of cathodes was shown in the carbonate or in the ether based electrolytes. The presented results indicate a potential application in future secondary Li-metal batteries.

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Lithium (Li) metal has been considered as an important anode candidate to reach more powerful energy storage devices with higher gravimetric and volumetric capacities. Nevertheless, the growth of high surface area lithium (HSAL) and dendrites during the stripping/deposition of Li causes safety concerns and a low cycle life of Li metal batteries. Here, we report the obtained results for protection of metallic lithium surface by using a gel polymer ionic liquid cross-linked by activation with UV radiation (UV-PIL). The UV-PIL protects Li against the constant degradation caused by the formation of unstable lithium metal–electrolyte interphase and cell dry out due to continuous electrolyte consumption. We observed retarded growth of dendrites when lithium metal was protected with UV-PIL, and due to the lower ionic conductivity of UV-PIL, some differences of mass transport are present compared to carbonate-based liquid electrolyte. Nevertheless, the UV-PIL@Li negative electrode was successfully applied in a Li-ion battery with a lithium iron phosphate (LFP) positive electrode, showing similar behavior compared to the bare Li surface.