Toshimi Takada

Novel synthesis process and structure refinements of Li4Mn5O12 for rechargeable lithium batteries

Well-crystallized Li 4 Mn 5 O 12 powder with grain size of 0.1-0.4 μm was prepared by heating a eutectic mixture of lithium acetate (LiOAc), and manganese nitrate (Mn(NO 3 ) 2 ), in an oxygen atmosphere. The structure of Li 4 Mn 5 O 12 crystallites was found to be a cubic spinel using Rietveld refinement of both neutron and X-ray powder diffraction data. We confirmed that lithium ions occupy both the tetrahedral 8a sites, and part of the octahedral 16d sites, but not the 16c sites in the space group Fd3m, while all the manganese ions occupy the 16d sites. The lattice parameter was found to be sensitive to the synthesis temperature as a result of the variation in manganese valence. Samples prepared at 500 °C showed better electrode performance. A rechargeable capacity of about 135 mAh/g for the cell Li/Li 4 Mn 5 O 12 was obtained in the 25 -3.6 V range of cell voltages.

Structure and electrochemical characterization of Li1+xMn2-xO4 spinels for rechargeable lithium batteries

Abstract Neutron and X-ray powder diffraction and Rietveld refinements have been carried out for the well-crystallized samples with a homogeneous composition Li 1+ x Mn 2− x O 4 (0≤ x ≤0.125). The lattice parameter of these spinels changes with both the composition and the synthesis temperature. SEM and TEM micrographs show that the crystallites appear as single crystals with a size of 0.1–2 μm. The phase transition from cubic Fd 3 m to orthorhombic Fddd around 280 K of samples Li 1+ x Mn 2− x O 4 ( x ≤0.04) was observed using low temperature XRD and DSC. The orthorhombic phase further converts to a single tetragonal phase I 4 1 / amd around 65 K. The charge/discharge capacity, and cyclability of these samples were examined in both the 3 V and the 4 V regions. We found that the discharge capacity as well as the cyclability of the cell Li/Li 1+ x Mn 2− x O 4 change largely with not only the value of x but also the crystal structure which depends on the synthesis conditions.

Crystallographic data of new superlattice phases for spinel LiMn 2 O 4 at low temperatures

Extensive analyses of low-temperature powder x-ray diffraction data for spinel LiMn 2 O 4 ( Fd 3¯ m at room temperature) make it clear that two structural phase transitions occur: first around 285 K from cubic to orthorhombic, second around 65 K from orthorhombic to tetragonal. At temperatures under 285 K, superlattice peaks appear in the diffraction pattern that were successfully indexed by tripling the a and b axes of the spinel unit cell. At 250 K, the unit cell is face-centered orthorhombic, Fddd , F 2 dd , or Fd 2 d , with a =24.855(1), b =24.755(2), c =8.2014(3) A, V =5046.1(4) A 3 , D x =4.284 g / cm 3 , Z =72. The unit cell at 30 K was confirmed to be body-centered tetragonal I 4 1 / amd or I 4 1 / a , with a =17.5176(3), c =8.1961(2) A, V =2515.1(1) A 3 , D x =4.298 g / cm 3 , Z =36.