XRD Observation on Fully-Charged Li[Li_yMn_2−y]O₄ in Nonaqueous Lithium Cells

Abstract

Li[Li_yMn_2−y]O₄ (0≦y<1/3) having a spinel-framework structure was prepared and examined in nonaqueous lithium cells in wide voltage range of 1.0 to 5.2 V. Li[Li_yMn_2−y]O₄ can be used as a positive electrode with rechargeable capacities of 50-120 mAh/g depending on y in Li[Li_yMn_2−y]O₄ for 4-volt class of lithium-ion batteries with a graphite negative-electrode. A redox signal at 5.0 V was observed for all samples except stoichiometric LiMn₂O₄. The X-ray examinations on the charged samples at 5.2 V vs. Li gave a structural parameter of 8.04-8.05 Å regardless of y in Li[Li_yMn_2−y]O₄. In addition to the redox potentials of 3.0, 4.0 and 5.0 V, we found a redox potential of about 1.8 V at which one-phase reaction proceeded in a tetragonal phase.