Morphology of lithium

Figure 1. Morphology of lithium deposited on stainless steel, 3 mAcm 2, 3 mAh cm 2, 1.5 molL 1 LiAsF6 - EC/2MeTHF (1 1), v/v.

The morphology of lithium deposits from 1-3 M LiC10.,-EC/PC-ethylene oxide (EO)/ propylene oxide (PO) copolymer electrolytes was investigated." It... 

A new measurement technique, in-situ AFM combined with XPS, scanning AES, and continuous argon sputtering reveals that the films are not uniform. Nanostructures at the lithium surface consisting of grain boundaries, ridge-lines, and flat areas control the morphology of lithium electrodeposition [381, 382, 395]. 

Films on lithium play an important part in secondary lithium metal batteries. Electrolytes, electrolyte additives, and lithium surface treatments modify the lithium surface and change the morphology of the lithium and its current efficiency [93],... 

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. 

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 have been many reports on the morphology of the lithium that is electrochemically deposited in various kinds of organic electrolyte [32-39]. 

A possible mechanism for lithium deposition based on our observations of lithium morphology in LiAsFb-EC/ 2MeTHF electrolyte is described below [31], Figure 2 (left-hand panel) shows our image of the mechanism. 

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]. 

Naoi and co-workers [55], with a QCM, studied lithium deposition and dissolution processes in the presence of polymer surfactants in an attempt to obtain the uniform current distribution at the electrode surface and hence smooth surface morphology of the deposited lithium. The polymer surfactants they used were polyethyleneglycol dimethyl ether (molecular weight 446), or a copolymer of dimethylsilicone (ca. 25 wt%) and propylene oxide (ca. 75 wt%) (molecular weight 3000) in LiC104-EC/DMC (3 2, v/v). 

Figure 4. Morphology of deposited lithium on lithium, after five cycles with 1 mAcm 2,2 mAh cm 2 in 1 mol L-1 LiPF6 - PC. ...

These compounds may reduce the reactivity of lithium and make the lithium deposition morphology smoother as a result of the spontaneous electrochemical alloy formation during the charging of lithium on the anode. The lithium was plated on... 

Desjardins and MacLean [79] studied a composite of lithium and Li3N named "Linode". Their research cell showed improvements in cycle life, shelf life, and electrode morphology after cycling. 

The quality and quantity of sites which are capable of reversible lithium accommodation depend in a complex manner on the crystallinity, the texture, the (mi-cro)structure, and the (micro)morphology of the carbonaceous host material [7, 19, 22, 40-57]. The type of carbon determines the current/potential characteristics of the electrochemical intercalation reaction and also potential side-reactions. Carbonaceous materials suitable for lithium intercalation are commercially available in many types and qualities [19, 43, 58-61], Many exotic carbons have been specially synthesized on a laboratory scale by pyrolysis of various precursors, e.g., carbons with a remarkably high lithium storage capacity (see Secs. 

The chemical composition of the SEI formed on carbonaceous anodes is, in general, similar to that formed on metallic lithium or inert electrodes. However some differences are expected as a result of the variety of chemical compositions and morphologies of carbon surfaces, each of which can affect the i() value for the various reduction reactions differently. Another factor, when dealing with graphite, is solvent co-intercalation. Assuming Li2C03 to be a major SEI building material, the thickness of the SEI was estimated to be about 45 A [711. 

JThe effect of the substituent on the properties of the polyphosphazenes is not fully understood. For instance, [NP(OCH ) ]n and [NP C CH. homopolymers are elastomers (8,29). Synthesis using lithium, in contrast to sodium, salts is claimed to produce rubber-like fluoroalkoxyphosphazene polymers (30). The presence of unreacted chlorine or low molecular weight oligomers can affect the bulk properties (31,32). Studies with phosphazene copolymers both in solution and in the bulk state (29,33-38) indicate a rather complex structure, which points out the need for additional work on the chain structure and morphology of these polymers. 

---