Fresh Lithium Surface

According to the depth profile of lithium passivated in LiASFg/dimethoxyethane (DME), the SEI has a bilayer structure containing lithium methoxide, liOH, IJ2O, and LiF [19]. The oxide-hydroxide layer is close to the Hthium surface, and there are solvent-reduction species in the outer part of the film. The thickness of the surface film formed on lithium freshly immersed in liAsFg/DME solutions is of the order of 100 A. 

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Lithium is consumed by reaction with the electrolyte which forms a protective film [6]. During the deposition and stripping of lithium, the surface shape changes and a fresh lithium surface is formed, with a new protection film on it lithium is consumed in the process. 

Fresh Lithium Surface The stracture and composition of the lithium... 

In a modified preparation of phenyllithium, bromobenzene was added to finely powdered lithium (rather than coarse particles) in ether. The reaction appeared to be proceeding normally, but after about 30 min it became very vigorous and accelerated to explosion. It was thought that the powdered metal may have been partially coated with oxide or nitride which abraded during stirring, exposing a lot of fresh metal surface on the powdered metal. 

Alkaline, alkaline earth metals and aluminum are naturally covered with anodic films. The removal of these native films, even in the best glove box atmosphere, exposes the fresh metal to reactive atmospheric contaminants at a high enough concentration and quickly cover the metal with new surface films. As discussed above, even the glove box atmosphere of an inert gas containing atmospheric components at the ppm level should be considered as being quite reactive to active metals such as lithium. Therefore, anyone intending to study the intrinsic behavior of active metal electrodes in solution must prepare a fresh electrode surface in solution. 

There are reports on the preparation of lithium electrodes in which Li wires [17,23-25] and Li rods have been embedded in glass or plastic materials, and fresh Li surfaces have been prepared in solutions by shearing off the edges of the metal [17,23,24], An example of such an approach was noted in the discussion on the construction of various cells. It should be mentioned that the plastics that can be used with metals such as lithium are highly pure (low plasticizer content) polyethylene and propylene. 

Electrochemical deposition of lithium usually forms a fresh Li surface which is exposed to the solution phase. The newly formed surface reacts immediately with the solution species and thus becomes covered by surface films composed of reduction products of solution species. In any event, the surface films that cover these electrodes have a multilayer structure [49], resulting from a delicate balance among several types of possible reduction processes of solution species, dissolution-deposition cycles of surface species, and secondary reactions between surface species and solution components, as explained above. Consequently, the microscopic surface film structure may be mosaiclike, containing different regions of surface species. The structure and composition of these surface films determine the morphology of Li dissolution-deposition processes and, thus, the performance of Li electrodes as battery anodes. Due to the mosaic structure of the surface... 

Physical Properties.—Lithium is a white metal with silver-like lustre. It remains untarnished in dry air,12 but a freshly cut surface develops a yellow tinge if moisture is present. In extremely thin layers it is translucent, the transmitted light having a dark, reddish-browm colour.13 It is harder than caesium, rubidium, sodium, or potassium, but softer than lead, the degree of hardness on Rydberg s14 scale being 0 6. In ductility it resembles lead, and can be drawn into wire or rolled into thin... 

The processes on the metallic lithium electrode are simple anodic dissolution with the formation of Li" " ions under discharge and cathodic deposition under charging. In a freshly assembled battery, the lithium surface is covered by SEI (see Chapter 11) that includes the products of interaction between lithium and components of electrolyte. Under cycling, the SEI composition changes in the course of the first several... 

Figure 20 FTIR spectra obtained from lithium surfaces freshly prepared and stored in PC solutions. The surfaces were protected with KBr windows and measured using external reflectance mode at a grazing angle, (a) Pure solvent, (b) LiClO IM solutions, (c) liBF, IM solutions. Sohd line, 2 h of storage. Dashed line, 2 days of storage. Reprinted with copyright from The Electrochemical Society Inc. (See [92].)...

Figure 16.15 [6] schematically represents the li/PE interphase. Solid PEs have a rough surface, so when they are in contact with lithium, some spikes, like 2 in Figure 16.15, penetrate the oxide layer and the lithium metal, and a fresh SEI is formed at the Li/PE interface. In other parts of the interface, softer contacts between the PE and lithium are formed ( 1 and 3 in Figure 16.15). Here the fresh SEI forms on the native oxide layer or, as a result of the retreat of lithium during its corrosion, the native oxide layer breaks and the gap is filled by a fresh SEI ( 1 in Figure 16.15). The net result is that only a fraction 9) of the lithium surface is in intimate contact with the PE. The situation in composite solid electrolytes (CPEs) is more severe because of their greater stiHhess. This complex morphology of the Li/PE and li/CPE interfaces causes difficulties in measuring SEI and PE...

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