Surfaces lithium foil

Lithium foil is commercially available. Its surface is covered with a "native film" consisting of various lithium compounds [Li0H,Li20,Li3N, (Li20-C02) adduct, or Li2C03], These compounds are produced by the reaction of lithium with 02, H20, C02, or N2. These compounds can be detected by electron spectroscopy for chemical analysis (ESCA) [2], As mentioned below, the surface film is closely related to the cycling efficiency. 

Fig. 14. Schematic illustration for native surface film on lithium foil.

A reversible lithium-air system was first implemented on a laboratory scale in 1996. In this cell, the gel-polymer electrolyte was pressed between lithium foil on the one side and an air electrode on the other. (Later, usual liquid electrolyte in a porous, for example, glass fabric, separator was often used in lithium-air batteries). The whole cell was sealed into a plastic container ( coffee bag ) and small holes were made in the container wall adjacent to the air electrode to supply air under discharge and remove oxygen under charging. The air electrode was made of a mixture of particles of polymer electrolyte and carbon black with the catalyst supported on its surface (cobalt phthalocyanine). 

SEI 2-5nm thick. When lithium is cut while immersed in the electrolyte, the SEI forms almost instantaneously (in less than 1ms [15,16]). On continuous plating of lithium through the SEI during battery charge, some electrolyte is consumed in each charge cycle in a break-and-repair process of the SEI [1,2] and this results in a faradaic efficiency lower than 1. When a battery is made with commercial lithium foil, the foil is covered with a native surface film. The composition of this surface film depends on the environment to which the lithium is exposed. It consists of Li20, LiOH, Li2C03, U3N, and other impurities. When this type of lithium is immersed in the electrolyte, the native surface film may react with the solvent, salts, and impurities to form an SEI, whose composition may differ from that of elec-trodeposited lithium in the same electrolyte. The formation of SEI on carbonaceous anodes is discussed in Sec. 6.3. 

Surface of Uncycled Lithium Foil 379 Table 13.3 Prototype AA-size rechargeable lithium-metal cells. 

Two companies (Eveready and venture Technology) have been involved in the development of these cells. The venture Technology AAA type bobbin cell introduced in 1982 has a stainless steel can with lithium foil in contact with the inner surface. The positive electrode is a composite of iron disulphide (FCS2), graphite and PTFE binder on an aluminium grid. The separator is porous polypropylene and the electrolyte a solution of lithium perchlorate in a 1 1 v/v propylene carbonate 1 2 dimethoxyethane mixture. 

Instead of hydrous aluminum oxide, aluminum foils have very recently been proposed for the extraction of lithium from sea water. However, not the aluminium metal itself, but its corrosion product hydrous aluminum oxide formed in sea water on the metal surface was found to be the effective lithium binding agent15) thus, there seems to be no fundamental difference compared to the direct application of pure hydrous aluminum oxide. 

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