Study of the Li / Li3 N  Electrode in an Organic Electrolyte

Abstract

Lithium nitride has been studied as a possible solid-electrolyte interphase between the lithium electrode and an organic electrolyte. The Li/Li.,N electrode has been obtained by exposing lithium to a pure nitrogen atmosphere at ambient temperature. This procedure is found to lead to the formation of a porous lithium nitride film, resulting from a decrease in the molar volume during the reaction. The impedance behavior of the Li/Li:~N electrode can be interpreted by a porous-film model deduced from a transmission-line model. The slow filling of the micropores of the film and reaction of lithium with the electrolyte at the pore bases are responsible for changes of impedance and open-circuit potential with time and under cycling.When a lithium electrode is stored in an organic electrolyte, a surface layer is usually formed, due to the decomposition products of the solvent and salt in the presence of lithium (1, 2). This surface layer inhibits the successful cycling of the lithium electrode. One possible way to limit the formation of the surface layer is to place an ionic conductor that is less reactive than lithium between the electrode and the electrolyte. A survey of the literature suggests that lithium nitride may be an excellent candidate for this purpose because it is a solid dec'-trolyte with a high ionic conductivity (3-5). The use of a lithium nitride film to protect lithium against chemical corrosion in organic electrolytes has been proposed earlier by Muller and Schwager (6). The purpose of this paper is to analyze the morphological and kinetic properties of lithium nitride, formed by exposure of lithium at ambient temperature to a nitrogen atmosphere, as a possible interphase between lithium and a propylene carbonate-based electrolyte. TheoreticalThe impedance behavior of the metal/film/solution system is primarily determined by the morphological and kinetic properties of the film. Because this film between the metal and the solution is polycrystalline, it can be compact or porous. The models described in detail below take into account the structure of the film for an analysis of the equivalent circuit of the system. The impedance spectrum is deduced under the assumption that only ionic conduction is involved in the film.Model of a compact film.--For a polycrystalline material, as shown in Fig. la, the transcrystalline and intercrystalline conduction processes can be represented by different equivalent circuits (5). The transcrystalline resistance Rt and the capacitance Ct are related to the conductivity inside each particle, while the intercrystalline resistance R~ and the capacitance C~ are related to the conductivity between two adjacent particles. The resulting circuit is a series of RJCt and RJC~ circuits as shown in Fig. lb. A large dispersion of time constants for the intercrystalline conduction is due to different causes among them the random orientation of anisotropic particles. The impedance of each circuit is defined by the Cole-Cole formula (7) and the total impedance for a radial frequency 0~...

Diffusion-Controlled Porous Crystalline Silicon Lithium Metal Batteries

“…Li—F bonds are also observed in the cycled electrode due to surface-adsorbed LiF as a standard inorganic SEI component ( Yan et al., 2018 ). However, the lithium composition is dominated with lithium nitride species ( Yan et al., 2018 ), due to N 2 exposure when utilizing an N 2 atmosphere glove box to deconstruct the post-cycled cells—thereby forming Li 3 N at ambient temperature and obscuring the surface analysis of native lithium species ( Thevenin and Muller, 1987 ). Oxygen comprises a significant atom % on the as-fabricated anode ( Figure 5 ) due to the presence of silicon surface oxides ( Figure S6 ).…”