Lithium positive insertion materials

Beginning in the early 1980s [20, 21] metallic lithium was replaced by lithium insertion materials having a lower standard redox potential than the positive insertion electrode this resulted in a "Li-ion" or "rocking-chair" cell with both negative and positive electrodes capable of reversible lithium insertion (see recommended papers and review papers [7, 10, 22-28]). Various insertion materials have been proposed for the anode of rechargeable lithium batteries,... 

There are two main kinds of rechargeable battery based on lithium chemistry the lithium-metal and the lithium-ion battery. In both the positive electrode is a lithium insertion material the negative in the former is lithium metal and in the latter it is a lithium insertion host. The reason for the application in lithium batteries of insertion electrode materials, which are electronic and ionic conductive solid matrixes (inorganic and carbon-based), is that electrochemical insertion reactions are intrinsically simple and highly reversible. 

Among the transition metal oxides, mention should also be made of the vanadium oxides, the most studied as positive electrode materials being V2O5, V Oii, and LiV30g, which insert lithium in the potential domain of 3 V vs. Li/Li+. For the vanadium oxides, too, doping and suitable structure have been shown to improve their electrochemical performance, and recently a sol-gel process has yielded high-capacity (500-600 Ah kg ) materials delivering 500 Wh kg at 4 mA cm" [137]. 

Research has also focused on the study of highly reversible negative lithium insertion materials. Transition metal oxides and chalcogenides, such as M0O2, WO2, and TiS2, if combined with a metal oxide positive electrode material yield cells with low OCV values (ca. 1.5-2 V) [111]. 

Lithium insertion and extraction into/from the positive electrode material must occur at a higher potential and the same reactions on the negative electrode material must occur at the maximum negative potential. The difference between the lithium insertion and extraction potentials for the same material must be... 

While the development of primary cells with a lithium anode has been crowned by relatively fast success and such cells have filled their secure rank as power sources for portable devices for public and special purposes, the history of development of lithium rechargeable batteries was full of drama. Generally, the chemistry of secondary batteries in aprotic electrolytes is very close to the chemistry of primary ones. The same processes occur under discharge in both types of batteries anodic dissolution of lithium on the negative electrode and cathodic lithium insertion into the crystalline lattice of the positive electrode material. Electrode processes must occur in the reverse direction under charge of the secondary battery with a negative electrode of metallic lithium. Already at the end of the 1970s, positive electrode materials were found, on which cathodic insertion and anodic extraction of lithium occur practically reversibly. Examples of such compounds are titanium and molybdenum disulfides. 

Under discharge of the battery, deintercalation of lithium from the carbon material occurs on the negative electrode and lithium is inserted into the oxide on the positive electrode. Under charging, the processes are reversed. Thus, there is no lithium metal in the whole system and the discharge and charging processes are reduced to the... 

Although the two redox couples are not identical, as regards the electrolyte both redox reactions involve a supply or consumption of Li with the same stoichiometry. This applies to a Li-ion battery with two insertion materials or to a Li-polymer battery with Li as the negative electrode and an insertion material at the positive electrode. When a lithium battery is in operation, one must take into account simultaneously the migration and diffusion of the ions in the electrolyte, however, this makes no change in qualitative terms to what has just been illustrated. 

Some positive electrode materials have three-dimensional rather than layered structures. LiMn204 and LiFeP04 are in this category. Lithium ions are inserted in tunnels rather than between layers. 

Their positive electrode materials are lithium intercalation (insertion) compounds such as... 

Figure 2.5 shows the evolution of the SOH of a lithium-ion device comprising two insertion materials (graphite for the negative electrode and mixed cobalt/nickel oxide for the positive electrode). Cycling was performed to a DOD of 75% for a C/5 charge/discharge current amplitude. 

Figure 5.5 represents the three types of crystalline structure which characterize the insertion materials presented herein LiM02 (M=Co, Ni), LiMn204 and LiFeP04. The structures are drawn by linking the atoms to form planes, thereby helping to visualize the available spaces, the cavities, in which the lithium ions (represented by little spheres) can position themselves. At each vertex of the polyhedra there is an oxygen atom the iron or phosphorus are at the center of the polyhedron. 

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