Fiber-like lithium

Deposited lithium is isolated from the base anode [30, 31]. When a cell is charged, lithium is deposited on the lithium substrate of the anode. Sometimes, the plated lithium is not flat but fiber-like. When the cell is discharged, the lithium anode dissolves, and sometimes the fiber-like lithium is cut and becomes isolated from the anode substrate [31]. This isolated lithium is called "dead lithium", and it is electochemically inactive but chemically active. During cycling,... 

The protective film is broken in certain places on the lithium surface by the stress. Fiber-like lithium grows, like an extrusion of lithium, through these broken holes in the film. If the deposition current is small enough and the stress is therefore small, the protective film will probably not break. In this case, the deposited lithium may be particle-like or amorphous. 

After the fiber-like lithium has grown, lithium is still deposited on the lithium substrate that is not at the tip of the fiber-like lithium. If the deposition continues for a long time, the lithium electrode becomes covered with long, fiber-like lithium. In this situation, lithium-ion transport in the electrolyte to the lithium electrode surface is hindered by the fiber-like lithium. Then, lithium begins to be deposited on the tip and on kinks of the fiber-like lithium, where there are crystalline defects. The morphology of the deposited lithium is particle-like or amorphous. As there are many kinks, the current density of the lithium deposition becomes very low. This low current density may create particle-like, rather than fiber-like, lithium. Thus the morphology of the lithium as a whole becomes mushroom-like [31]. 

The dissolution process of plated lithium may be the reverse of the plating process (Figure 13.2b). At first, the parHcle-like lithium on the kinks is dissolved. Then, the fiber-like lithium at the base is dissolved. During this process, fiber-like lithium is sometimes cut from the lithium substrate and becomes dead lithium. There is a large amount of dead lithium when the diameter of the fiber-like lithium is small under conditions of high-rate and/or low-temperature deposition, because the whiskers are easily cut. 

When the discharge current is high, transport of lithium ions becomes difficult and stripping occurs from the particle-like lithium on the tip and on the kinks of the fiber-like lithium. In this case, the fiber-like lithium rarely breaks and the efficiency increases. 

The contribution by Rouzaud et al. teaches to apply a modified version of high resolution Transmission Electron Microscopy (TEM) as an efficient technique of quantitative investigation of the mechanism of irreversible capacity loss in various carbon candidates for application in lithium-ion batteries. The authors introduce the Corridor model , which is interesting and is likely to stimulate active discussion within the lithium-ion battery community. Besides carbon fibers coated with polycarbon (a candidate anode material for lithium-ion technology), authors study carbon aerogels, a known material for supercapacitor application. Besides the capability to form an efficient double electric layer in these aerogels, authors... 

Kanno et al. studied less crystalline carbons like pyrolyzed polymers and commercial carbon fibers. They reported an irreversible charge capacity in the first cycle related to the carbon surface. However, the reversible charge capacity which they could observe over several cycles was independent of the surface reaction.106 Mohri et al.107 demonstrated only 20% capacity fading over 500 cycles with a lithium-ion cell containing a lithium metal oxide and low crystallinity pyrolytic carbon electrode. 

Aramid polymers have high melting points or melt with decomposition that makes fiber processing by melt spinning impractical [1] . Fibers are therefore spun from polymer solutions. These polymers not only do not melt but also are not easy to dissolve. Highly polar solvents, with or without the aid of inorganic salts such as lithium chloride or calcium chloride, or acids like concentrated sulfuric add have to be used [88]. 

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