Metallic lithium anode

Positive intercalation electrode-lithium anode (lithium-metal) with a dry polymer electrolyte layer. 

One criterion for the anode material is that the chemical potential of lithium in the anode host should be close to that of lithium metal. Carbonaceous materials are therefore good candidates for replacing metallic lithium because of their low cost, low potential versus lithium, and wonderful cycling performance. Practical cells with LiCoOj and carbon electrodes are now commercially available. Finding the best carbon for the anode material in the lithium-ion battery remains an active research topic. 

The cathode of coin-type batteries consists of Mn02 with the addition of a conductive material and binder. The anode is a disk made of lithium metal, which is pressed onto the stainless steel anode can. The separator is nonwoven cloth made of polypropylene, which is places between the cathode and the anode. 

The Li-SOCl2 battery consists of a lithium-metal foil anode, a porous carbon cathode, a porous non-woven glass or polymeric separator between them, and an electrolyte containing thionyl chloride and a soluble salt, usually lithium tetrachloro-aluminate. Thionyl chloride serves as both the cathode active material and the elec-... 

Secondary lithium-metal batteries which have a lithium-metal anode are attractive because their energy density is theoretically higher than that of lithium-ion batteries. Lithium-molybdenum disulfide batteries were the world s first secondary cylindrical lithium—metal batteries. However, the batteries were recalled in 1989 because of an overheating defect. Lithium-manganese dioxide batteries are the only secondary cylindrical lithium—metal batteries which are manufactured at present. Lithium-vanadium oxide batteries are being researched and developed. Furthermore, electrolytes, electrolyte additives and lithium surface treatments are being studied to improve safety and recharge-ability. 

One of the most important factors determining whether or not secondary lithium metal batteries become commercially viable is battery safety, which is affected many factors insufficient information is available about safety of practical secondary lithium metal batteries [91]. Vanadium compounds dissolve electrochemi-cally and are deposited on the lithium anode during charge-discharge cycle. The... 

Table 3). However, their cycle life depends on the discharge and charge currents. This problem results from the low cycling efficiency of lithium anodes. Another big problem is the safety of lithium-metal cells. One of the reasons for their poor thermal stability is the high reactivity and low melting point (180 °C) of lithium. 

These values are poor compared with lithium-ion cells, whose corresponding values are 500 cycles and above 130 °C. This poor performance is explained mainly by the characteristics of the lithium-metal anode, and specifically its low cycling efficiency. 

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. 

Lithium metal is chemically very active and reacts thermodynamically with any organic electrolyte. However, in practice, lithium metal can be dissolved and deposited electrochemically in some organic electrolytes [5]. It is generally believed that a protective film is formed on the lithium anode which prevents further reaction [6, 7]. This film strongly affects the lithium cycling efficiency. 

There have been many attempts to improve the cycling efficiency of lithium anodes. We describe some of them below, by discussing electrolytes, electrolyte additives, the stack pressure on the electrode, composite anodes, and alternatives to the lithium-metal anode anode. 

An Alternative to the Lithium-Metal Anode (Lithium-Ion Inserted Anodes)... 

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... 

Little work has been done on bare lithium metal that is well defined and free of surface film [15-24], Odziemkowski and Irish [15] showed that for carefully purified LiAsF6 tetrahydrofuran (THF) and 2-methyltetrahydrofuran 2Me-THF electrolytes the exchange-current density and corrosion potential on the lithium surface immediately after cutting in situ, are primarily determined by two reactions anodic dissolution of lithium, and cathodic reduc-... 

Today we have some understanding of the first lithium intercalation step into carbon and of the processes taking place on the lithium metal anode. A combination of a variety of analytical tools including di-latometry, STM, AFM, XPS, EDS, SEM, XRD, QCMB, FTIR, NMR, EPR, Raman spectroscopy, and DSC is needed in order to understand better the processes occurring at the anode/electrolyte interphase. This understanding is crucial for the development of safer and better lithium-based batteries. 

As to anodes, in most of the research work a generously dimensioned sheet of lithium metal has been used. Such an electrode is rather irreversible, but this is not noticed when a large excess of lithium is employed. Li-Al alloys and carbon materials inserting lithium cathodically during recharging can be used as anodes in nonaqueous solutions. Zinc has been used in polymer batteries with aqueous electrolyte (on the basis of polyaniline). 

The Li-Ion system was developed to eliminate problems of lithium metal deposition. On charge, lithium metal electrodes deposit moss-like or dendrite-like metallic lithium on the surface of the metal anode. Once such metallic lithium is deposited, the battery is vulnerable to internal shorting, which may cause dangerous thermal run away. The use of carbonaceous material as the anode active material can completely prevent such dangerous phenomenon. Carbon materials can intercalate lithium into their structure (up to LiCe). The intercalation reaction is very reversible and the intercalated carbons have a potential about 50mV from the lithium metal potential. As a result, no lithium metal is found in the Li-Ion cell. The electrochemical reactions at the surface insert the lithium atoms formed at the electrode surface directly into the carbon anode matrix (Li insertion). There is no lithium metal, only lithium ions in the cell (this is the reason why Li-Ion batteries are named). Therefore, carbonaceous material is the key material for Li-Ion batteries. Carbonaceous anode materials are the key to their ever-increasing capacity. No other proposed anode material has proven to perform as well. The carbon materials have demonstrated lower initial irreversible capacities, higher cycle-ability and faster mobility of Li in the solid phase. 

An overview about more than 10 years of R D activities on solid electrolyte interphase (SEI) film forming electrolyte additives and solvents at Graz University of Technology is presented. The different requirements on the electrolyte and on the SEI formation process in the presence of various anode materials (metallic lithium, graphitic carbons, and lithium storage metals/alloys are particularly highlighted. 

Figure 20. SEI formation on different anodes for rechargeable Li batteries (A) lithium metal, (B) graphitic carbon, and (C) metals and intermetallics. Different colors of the SEI indicate SEI products formed at different stages of charge and discharge (and do not indicate different composition) [42],...

Figure 1. Discharge curves for 2325 coin cells with lithium metal anodes and electrolytic (crystalline) vs amorphous manganese oxide-based cathodes.

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