Lithium-passivation phenomena

It seems clear that in PEs, especially in the gel types, lithium-passivation phenomena are similar to those commonly occurring in liquid electrolytes. The crucial role played by the nature and composition of the PE in controLHng electron transfer has been described by several authors [3-6, 41-43]. It is postulated that at least two separate competitive reactions occur simultaneously to form the passive layer. The first is the reaction of lithium with contaminants. The second reaction is that... 

One may then conclude that, the gel-type electrolytes, and the PAN-based ones in particular, have electrochemical properties that in principle make them suitable for application in versatile, high-energy lithium batteries. In practice, their use may be limited by the reactivity towards the lithium electrodes induced by the high content of the liquid component. Indeed, severe passivation phenomenon occurs when the lithium metal electrode is kept in contact with the gel electrolytes [60, 69]. This confirms the general rule that if from one side the wet-like configuration is essential to confer high conductivity to a given polymer electrolyte, from the other it unavoidably affects its interfacial stability with the lithium metal electrode. 

Work has therefore been devoted by a number of developers to improving the cyclability of the lithium metal electrode. Since passivation of lithium is an unavoidable phenomenon, one approach has been directed to the promotion of uniform and smooth surface passivation layers, for example by selecting the most appropriate combination of solvents and electrolyte salts. An example is the inclusion of 2-methyltetrahydrofuran (2-Me-THF), since the presence of the methyl group slows down the reactivity towards the lithium metal. The selection of fluorine-based elec-... 

This inter-layer separation remains slight (which is an essential condition for the battery to woik) because the lithium is inserted without its solvation shell formed by the organic molecules from the electrolyte. This phenomenon of desolvation takes place when lithium ions are diffused in an interfacial passivation layer present between the electrode and the... 

In addition, the volumetric expansion of the lithiated particle is such that a phenomenon of electrochemical prrlverization occurs, whereby large particles crumble into smaller particles. Unpassivized active surfaces are thus created during the cotrrse of cycling, leading to the continuous formation of a passivation film, which consiunes electrolyte and electrons (irreversible capacity). This is particularly true for metals accepting lithium insertion below 0.8 V versus aHA such as Sn, Al, Si, etc. 

P2S5 passivates the surface of lithium metal and therefore eliminates the polysulfide shuttle phenomenon. 

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