Dead lithium

Many studies have been undertaken with a view to improving lithium anode performance to obtain a practical cell. This section will describe recent progress in the study of lithium-metal anodes and the cells. Sections 3.2 to 3.7 describe studies on the surface of uncycled lithium and of lithium coupled with electrolytes, methods for measuring the cycling efficiency of lithium, the morphology of deposited lithium, the mechanism of lithium deposition and dissolution, the amount of dead lithium, the improvement of cycling efficiency, and alternatives to the lithium-metal anode. Section 3.8 describes the safety of rechargeable lithium-metal cells. 

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,... 

We believe that (3) is the main reason for the low cycling efficiency. The thermal stability of lithium-metal cells decreases with cycling [30] and the dead lithium may be the cause of this reduction. This indicates that the cycling efficiency is strongly affected by the morphology of the lithium surface. 

There are four possible ways of explaining [45] why a higher current discharge creates a smaller amount of dead lithium. 

A lithium anode mixed with conductive particles of Cu or Ni was studied by Saito et al. they obtained an improvement in the cycling efficiency (Fig.6) [80]. Their idea is based on the recombination of dead lithium and formation of many active sites for deposition. 

It is worthwhile attempting to develop a rechargeable lithium metal anode. This anode should have a high lithium cycling efficiency and be very safe. These properties can be realized by reducing the dead lithium. Practical levels of lithium cycling efficiency and safety could be achieved... 

De Wolff model, manganese oxides 89 dead lithium 344 ff Debye length... 

In particular, in lithium metal polymer batteries, dendritic growth of lithium on a lithium anode, formation of dead lithium, interfacial phenomenon between the lithium anode and the polymer electrolyte, etc., adversely affects the stability and cycle characteristics of the batteries. In view of these problems, various polymer electrolytes have been developed. 

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. 

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