Intercalation compounds lithium

The properties of lithium intercalation compounds depend in a decisive manner on the nature of the host material. If oxides of metals with varying valency are used instead of TiSj, the potential of the electrode (consequently also, the battery voltage) will increase to 3 V. Even higher values (up to 4 V) are obtained when as host material... 

The intercalation compounds of lithium with graphite are very different in their behavior from intercalation compounds with oxides or halcogenides. Intercalation processes in the former compounds occur in the potential region from 0 to 0.4 V vs. the potential of the lithium electrode. Thus, the thermodynamic activity of lithium in these compounds is close to that for metallic lithium. For this reason, lithium intercalation compounds of graphite can be used as negative electrodes in batteries rather than the difficultly of handling metallic lithium, which is difficult to handle. 

Due to its high energy density (3,860 mAh/g) and low voltage, lithium is the most attractive metal of the periodic table for battery application. Unfortunately lithium metal, and most of its alloys cannot be used in rechargeable batteries because of their poor cyclability. Therefore, lithium intercalation compounds and reversible alloys are among today s materials of choice for subject application. The most common active materials for the negative electrodes in lithium-ion battery applications are carbonaceous materials. The ability of graphitized carbonaceous materials to... 

Billaud D., Henry F.X. and Willmann P. Electrochemical Synthesis of Binary Graphite-Lithium Intercalation Compounds. Mat. Res. Bull., 28, 477-483 (1993). 

Perhaps the most well known of the lithium intercalation compounds is Li jTiSj. Both Li (for x < 1) and Ti are octahedrally coordinated by S (Fig. 7.1) in the ABC notation, the structure is AbC(b)AbC, where the letter in parentheses denote lithium atoms. This structure is also called the IT form, because of its trigonal (T) symmetry and the single layer per unit cell. The electrochemical behaviour of Li in TiSj is described below in connection with staging. 

Many of the intercalation batteries being studied now are so-called rocking chair or lithium ion cells, in which both electrodes are lithium intercalation compounds. Thus there is a need for electrodes with a low voltage vs lithium (for the anode) as well as those with a high voltage (for the cathode). Early studies of intercalation compounds for electrodes were part of a search for cathodes, not anodes, and may have passed over materials suitable for anodes. 

It is believed that the discharge mechanism involves the formation of an intermediate lithium intercalation compound in which both lithium and fluorine are situated between the carbon layers of the graphitic structure. The carbon formed is graphitic and improves the cell performance as the discharge progresses, leading to a high cathode utilization - close to 100% for low currents. The lithium fluoride precipitates. 

Historically the most commonly used lithium intercalation compound was titanium disulphide, TiS2- This compound has a layered structure of covalently bound S-Ti-S stacks held together by weak van der Waals forces. Each stack is formed by a layer of titanium atoms between two layers of sulphur atoms in a hexagon ally close packed arrangement, Lithium ions can be readily intercalated between the stacks, and if the intercalation level x is maintained below unity, the process induces only a modest and reversible expansion along the c axis (Fig. 7.13). The electrochemical reaction of the Li/TiS2 couple... 

This is the change in the active masses volume (active mass breathing). Oxidized and reduced forms do not usually have the same volumetric density. This may cause a defect in electronic percolation and loss of active mass. The lower the difference in density, the higher the cyclability. Usually, proton and lithium intercalation compounds have low volumetric variation on cycling. 

If the formed intercalation compound is crystallographically stable, that is, if no significant change in the elementary cell volume occurs under lithium intercalation, then such a compound is the actual discharge product. An example of such a process is reaction (11.5). Active substances forming stable lithium intercalation compounds can be the basis of not only primary cells, but also rechargeable cells. 

Lyness C, Delobel B, Aimstrong AR, Brace PG (2007) The lithium intercalation compound Li2CoSi04 and its behaviour as a positive eleetrode for lithium batimies. J Chem Soc Chem Commun 46 4890-4892... 

ABSTRACT. A layer structured crystal 3-ZrNCl forms a lithium intercalation compound Li ZrNCl. The upper limit for x determined on the compound prepared by the n-butyl lithium technique is %0.29. In the electrochemical process, a pressed 3 ZrNCl cathode is further reduced up to x=... 

The lithium intercalation compound of 3 ZrNCl was prepared by the n-butyl lithium technique the powder sample of 3 ZrNCl was dispersed into a n-butyl lithium solution (15w/o in hexane) under a dry argon atmosphere. The sample was immediately colored black in the solution. 

Since the lithium intercalation compound was very labile to water and oxygen, all the manipulations were done in a glove box filled with circulated and purified argon (< 20 ppm O2 and H2O contaminations). Separate samples of the lithium intercalated 3-ZrNCl were dispersed in... 

To improve the safety of secondary lithium batteries, the metallic lithium is replaced by another intercalation compound such as graphite. In addition, the cathode would contain ionic lithium in its structure, which is intercalated in the anode or the cathode depending on the direction of the current. Lithium-ion cells are the most advanced batteries now in the market. These cells supply up to 4 volts, have an energy density close to 120 Wh/kg, and have a long life at room temperature. The technology is based on the use of appropriate lithium intercalation compounds as electrodes. Normally a lithium transition metal oxide is used as the cathode and carbonaceous materials serve as the anode. 

Because of the large area of electrodes so obtained, it is possible to achieve the current density necessary to produce a useful battery. The cathode is usually constructed by impregnation of carbon films with LiCo02 LiMn04 and the anode is a carbon-lithium intercalation compound. 

Lithium intercalation compounds are preferably suitable for use as cathodes. The tiny lithium ion is easily inserted into and released from a certain number of inorganic solids at a potential that lies at positive values on the electrochemical series far away from the Li/Li electrode. The lithium ion s small volume affects the host structure only slightly. The intercalation is merely not hindered so that this process is mostly reversible and hence suitable for rechargeable batteries. 

The load levels or phases of the lithium intercalation compound are called step F to step IV depending on the number of carbon layers between adjacent interlayers loaded with lithium. 

---