Spinel LiMn

In spinel LiMn O, the light element, lithium, occupies the tetrahedral 8a site and the heavy metal element, manganese, occupies the octahedral 16d site (32e site) forms the cubic close packing. The spinel of such a construction is called a... 

It can be understood that the temperature of the exothermic peak with oxygen evolution increased from 200°C of LiNiO to 310°C of LiNi gCo j Al due to the decrease in the nickel content and the aluminum doping. The thermal stability of this compound has been considerably improved. The oxygen evolution was not observed below 300°C. On the whole, the thermal stabihty of this is more excellent than that of LiCoO and comparable to that of spinel LiMn O. hi addition, the SEM image of this material is shown in Fig. 2.23. It would be possible to control the powder characteristics the same as the co-precipitation method. It is clear from Table 2.5 that this material has a larger capacity than that of the cobalt-based cathode. This cathode delivers more than 180 mAh/g for 4.3 V charge, as shown in Fig. 2.24. 

Spinel LiMn O is one of the most promising cathode materials due to low cost, abundance, and nontoxicity. It is well known that the spinel LiMn O electrode shows good stability during cycling at room temperature, but a poor cychng behavior at elevated temperature, e.g., 50-80°C, which prevents its wider use as cathode materials for lithium secondary batteries. ... 

Yue Z, Zhou J, Wang X, Gui Z, Li L (2001) Low temperature sintered Mg-Zn-Cu ferrite prepared by auto-combustion of citrate-nitrate gel. J Mater Sci Lett 20 1327-1329 Du K, Zhang H (2003) Preparation and performance of spinel LiMn O, by a citrate route... 

In the case of spinel compounds prepared at about 1,000°C with this method, the concentration of manganese ion is roughly 3 ppm even when spinels are stored in the electrolyte at 60°C for 4 weeks. Such value is significantly lower than 100 ppm of LiMn O prepared at 800°C. Finally, manganese dissolution from spinel can be reduced about 1/30 by the introduction of the initial heating process. As a result, the elevated temperature characteristics of the lithium-ion battery composed of the spinel cathode synthesized by this method and graphite anode are considerably improved, as shown in Fig. 2.10. 

Fig. 2.14 Lattice parameters of delithiated stoichiometric LiMn O (a), oxygen stoichiometric spinel (b), and oxygen-deficient spinel (c)...

The stoichiometric composition of LMO is LiMn O. It has a cubic spinel structure with a lattice constant of 0.8248 mn. Lithium and manganese reside in the 8a tetrahedral site and 16d octahedral site in lattice positions of the Fd3m space group, respectively. The 8a site is located next to and shares a plane with the 16c octahedral site it is assumed that lithium ions move along 8a, 16c, and 8a sites. ... 

Once formed, HF attacks LiMn O and the spinel is dissolved... 

To improve the cyclability of LiMn O in the 4-V region, many studies have been made using doped manganese-substituted spinels such as LiM n O (M = Co, Ni, Cr, Al,. ..). It has been reported that the capacity failure was suppressed by the replacement of a part of manganese with another metal ion because of the doped manganese-substituted spinels inhibited the decay of its original structure in lithium insertion/extraction process. Next we show our investigation of the LiM n O compound (M = Co, Ni, X is from 0.0 to 0.5). 

VlCo VCo ) 4.2 V and V (Ni /Ni ) 4.8 V. Orthorhombic LiVtMn]04 was transformed to the spinel V[LiMn]04 under pressure of 55 kbar at 850°C [61] electrochemical delithiation gave V°(Mn /Mn ) 3.8 V aU vv. Li. These values represent a remarkable stabilization of the redox energies compared to their values with Li in the 8a sites. However, these spinels are not of interest as battery cathodes as the Li -ion mobility is reduced by its coexistence with M atoms on the octahedral 16d sites. 

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