Lithium spinels

James Hunter of Eveready Battery Co. was the first to patent spinel cathode material. The application of material to Li-ion system has been developed by J. M. Tarascon [59] and extensively studied by M. Thackeray [60]. Generally, lithium spinel oxides suitable for the cathode are limited to those with a normal spinel in which the lithium ions occupy the tetrahedral (8a) sites and the transition-metal ions reside at the octahedral (16d) sites. Currently, spinel is the center of much interest as the cathode material for large format lithium-ion cell for hybrid electric vehicle applications where high power, safety, and low cost are the strongly required features. 

The lithium spinels, Li[6,]04, are particularly attractive electrode materials because they offer the possibility of both lithium insertion (e.g., Li, JMn2]04... 

Good results are obtained with oxide-coated valve metals as anode materials. These electrically conducting ceramic coatings of p-conducting spinel-ferrite (e.g., cobalt, nickel and lithium ferrites) have very low consumption rates. Lithium ferrite has proved particularly effective because it possesses excellent adhesion on titanium and niobium [26]. In addition, doping the perovskite structure with monovalent lithium ions provides good electrical conductivity for anodic reactions. Anodes produced in this way are distributed under the trade name Lida [27]. The consumption rate in seawater is given as 10 g A ar and in fresh water is... 

These batteries are new systems which use a lithium-manganese composite oxide for the active material of the positive electrode a lithium-titanium oxide with a spinel... 

The lithium-titanium oxides are prepared by heating a mixture of anatase (Ti02) and LiOH at a high temperature. The product heated at 800-900 °C has a spinel structure of Li4/3Ti5y304. When the charge and discharge cycles are performed... 

In contrast, LiMn204 has a spinel structure. This material has the space group Fd3m in which the transition-metal and lithium ions are located at octahedral 8(a) and tetrahedral 16(d) sites, respectively, and the oxygen ions are at 32(e) sites. There are octahedral 16(c) sites around the 8(a) sites and lithium ions can diffuse through the 16(c) and 8(a) sites. As this structure contains a diffusion path for the lithium ions, these ions can be deinter-calated and intercalated in these compositions. 

Figure 11. The [B2]X4 framework of an v4[B 2X4 spinel, e.g. A - MnO, with three dimensional pathways for lithium-ion transport. (The direction of transport perpendicular to the plane of the paper has not been marked by an arrow).

The composition of lithium-manga-nese-oxide spinel electrodes that are of interest for lithium battery applications fall within the Li[Mn2]04 - Li4Mn5Ot2 -Li2[Mn4]0() tie-triangle of the Li-Mn-0... 

By contrast, lithium extraction from the tetrahedral sites in Li[Mn2]04, i.e., for 0cubic symmetry of the spinel structure [105, 114, 120]. It is difficult to extract all the lithium electrochemi-cally from Li[Mn2]04, at least at practical voltages, without causing decomposi-... 

It is possible that all three phenomena contribute to the capacity loss of 4V Lix[Mn2]04 electrodes. Nonetheless, all three can be at least partly circumvented by slightly modifying the composition of the spinel electrode. For example, cell performance can be improved by increasing the amount of lithium in the spinel structure [107, 123, 130] and, in particular, by substituting a small amount of manganese on the B sites with lithium [107], which drives the composition a small way down the stoichiometric spinel tie-line, towards... 

Some cations with an octahedral-site preference (such as Ni2+, Co3+, and Cr3+) are expected to occupy the 16d sites of the spinel with Mn, whereas cations with a strong tetrahedral-site preference (such as Zn2+) are expected to occupy the 8a sites and to dislodge corresponding lithium ions into the 16d sites. In cases where Mn is substituted by transition metal ions (such as Co, Ni, and Cr) that can partake in the electrochemical reaction, voltage plateaus between 4 and 5V have been observed [135, 136],... 

It is worthwhile to point out that lithium extraction from inverse spinels V[LiM]04, such as V[LiNi]04 and V[LiCo]04 takes place at high voltage, typically between 4 and 5V [153]. Lithium is extracted from the octahedral 16d sites of these spinels with a concomitant oxidation of the divalent nickel or cobalt ions. From a structural point of view, this can be readily understood because lithium must be dislodged from the 16d octahedral sites, which are of low-energy, into neighboring energetically unfavorable 8b tetrahedra, which share all four faces with 16d sites that are occupied by nickel or cobalt and by lithium. Lithium extraction reactions... 

Electrodes that are prepared from acid-leached LT-LiCo, xNix02 compounds (0< x<0.2) show significantly enhanced electrochemical behavior over the parent LT-LiCo1 xNix02 structure. The improved performance has been attributed to the formation of compounds with a composition and cation arrangement close to the ideal Li[B2]04 spinel structure (B = Co, Ni) [62]. These spinel-type structures have cubic symmetry, which is maintained on lithiation the unit cells expand and contract by only 0.2 percent during lithium insertion and extraction. 

Lithium-titanium-oxide spinels provide a relatively low voltage of 1.5V vs. lithium. They are, therefore, of interest as possible negative electrode materials for lithium-ion cells [161-163] they can be coupled, for example, to Li[Mn2104 (4V vs. Li) to yield a 2.5V lithium-ion cell, or to LixMn02 (3V vs. Li) to yield a 1.5V lithium-ion cell. Although these cells have a voltage lower than that of commercial... 

LixC/Li, xCo02 cells (3.5V), they are attractive from a safety point of view because the titanium spinel operates at a potential significantly far away from that of metallic lithium. 

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