Spinel electrodes

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... 

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... 

A clear advantage of alkaline electrolysers is the use of nickel-based electrodes, thus avoiding the use of precious metals. Catalytic research is aimed at the development of more active anodes and cathodes, primarily the development of high surface area, stable structures. Nickel-cobalt spinel electrodes for oxygen evolution and high surface area nickel and nickel cobalt electrodes for hydrogen evolution have been shown at the laboratory scale to lead to a decrease in electrolyzer cell voltage [47]. More active electrodes can lead to more compact electrolysers with lower overall systems cost. 

Figure 13.27 Outputs of NO, sensors with spinel electrodes [29, 275, 309, 313, 320, 324, 325, 327-330],...

This change in b can be either due to a change in the surface oxide-layer composition or due to a change in the active site characteristics caused by the surface interactions. Otherwise, the change in b reported for crystalline Ni-Co alloys in alkaline solutions has also been explained by the different nature of the surface oxides [27]. It is also important to say that the nickel and cobalt-spinel voltammetric behavior is attained after potential cycling at a low scan rate, where b = 0.04 V decade-1. However, a pre-anodization at 1.8 V vs. RHE led to a Co304 spinel electrode for which b = 0.06 V decade-1. 

J. S. Gnanaraj, V. G. Pol, A. Gedanken, D. Aurbach, Improving the high-temperature performance of LiMn204 spinel electrodes by coating the active mass with MgO via a sonochemi-cal method, Electrochem. Commun. 2003, 5, 940-945. 

Thackeray MM (1999) Spinel electrodes for lithium batteries. J Am Ceram Soc 82 337-3354... 

Thackeray MM, de Kock A, Rossouw MH, Liles D, Bittihn R, Hoge D (1992) Spinel electrodes from the Li-Mn-O system for rechargeable lithium battery applications. J Electrochem Soc 139 363-366... 

Chen CH, Vaughey JT, Jansen AN, Dees DW, Kahaian AJ, Goacher T, Thackeray MM (2001) Studies of Mg-substituted Li4 xMgxTi50i2 spinel electrodes (0x1) for lithium batteries. J Electrochem Soc 148 A102... 

Figure 1 XPS spectra for a spinel electrode after 50 cycles at C/3 electrolyte EC/DMC-LiPF solid line prior to Ar-ion sputtering dotted line after 60 s Ar-ion sputtering. Reproduced from [31] with permission from The Electrochemical Society Inc.

Nevertheless, the impression remains that a more detailed understanding of surface-related processes is the key to improving spinel-electrode stability. This is especially true at slightly elevated temperatures, where capacity-fade effects are known to be larger a major area of application for Li-ion batteries is in electronic circuits, e.g., cell-phones and lap-tops, where considerable heat is generated. Tarascon and co-workers have, in fact, shown that the mechanisms responsible for capacity fade at moderate elevated temperatures are essentially the same as those at ambient temperature. Let us proceed then by describing... 

The example serves to show an interesting feature the relative amounts of the various elements in the two surface films formed (under electrochemical cycling and chemical storage) are essentially identical. A small increase in the amount of Li and F is observed just below the surface, while the C content is seen to decrease. This gives us the first indication of the existence of a layered structure in the surface film. As we move into the sample, the F, O, P and Li concentrations decrease, while the relative amounts of Mn and C increase, as more of the bulk spinel electrode is exposed. The amount of surface material present is also found to increase with cycle number and storage time, suggesting that the layer formed on the LiMUjO., cathode is not sufficiently dense to serve as a barrier between the electrolyte and the oxidising environment close to the cathode surface. Fresh electrolyte can be transported to the electrode surface. 

However, studies of the material losses from spinel electrodes, and the resulting Mn concentration in the electrolyte, found dissolution can account for only a fraction of the capacity fade observed in spinel cells." For example, when spinel cells were cycled at 50°C, analysis of the electrolyte for manganese found spinel dissolution could account for only 34% of the capacity fade observed." ... 

The alcohol can then react at the positive electrode where it is oxidized to H2O and CO2, the spinel electrode serving as a source of oxygen ... 

Fey GTK, Huang DL (1999) Synthesis, characterization and cell performance of inverse spinel electrode materials for lithium secondary batteries. Electrochim Acta 45 295-314... 

Chung, K.Y. and Kim, K.-B. (2002) Investigation of structural fatigue in spinel electrodes using in situ laser probe beam deflection technique. J. Electrochem. Soc., 149 (1), A79. 

Spinel electrode from the Li-Mn-O system for rechargeable lithium battery applications. 139 363-366. 

Ortiz, J., Puelma, M. and Gautier, J.L. Indirect oxidation of phenol on graphite on Nio.3C02.7O4 spinel electrodes in alkaline medium , J. Chil. Chem. Soc., 48 (2003) 67-71. 

R.M. Darling, "Lithium Manganese Oxide Spinel Electrodes." Ph.D. Dissertation, University of California, Berkeley, 1998. 

Thackeray MM, Shao-Hom Y, Kahaian AJ, Kepler KD, Skinner E, Vaughey JT, Hackney S A (1998) Structural fatigue in spinel electrodes in high voltage (4 V) Li/LixMn204 cells. Electrochem Solid State Lett 1 7-9... 

Fig. 9.19 The voltage composition profile for a Li//LiMii204 using a spinel electrode synthesized by the combustion urea-assisted method. The cell was charged and discharged at current density 0.05 mA/cm ...

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