Effect of deviation from Ni/Mn stoichiometry in Li[Ni1/2Mn3/2]O4 upon rechargeable capacity at 4.7 V in nonaqueous lithium cells

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Lithium nickel manganese oxides having 20% nickel excess and deficient with respect to the stoichiometric Li[Ni1/2Mn3/2]O4 having a space group symmetry of P4332 were prepared and examined in nonaqueous lithium cells. Rechargeable capacity observed for the 20% nickel excess sample in voltage above 4.5 V is larger than that for the 20% nickel deficient sample. The effect of deviation from Ni/Mn stoichiometry from the ideal composition of Li[Ni1/2Mn3/2]O4 upon the rechargeable capacity at 4.7 V is described in terms of the solid solution, phase separation, and superstructural Li[Ni1/2Mn3/2]O4. From the results, the composition preferable to the five-volt lithium insertion material of Li[Ni1/2Mn3/2]O4 is discussed. The cycling stability of Li[Ni1/2Mn3/2]O4 in the cell with the Li[Li1/3Ti5/3]O4-negative electrode is also examined in voltages ranging from 1.5 to 3.6 V at 25°C for 250 cycles and shown that the capacity fading of the cell is negligibly small below 4% even after 250 cycles.
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