2006 Fiscal Year Final Research Report Summary
Structure - Electrode Activity Relationship in Triphyllite - Related Compounds
| Project/Area Number |
16350108
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Inorganic industrial materials
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
YAMADA Atsuo Tokyo Institute of Technology, Interdiciplinary Graduate School of Science and Engineering, Department of Electronic Chemistry, Associate Professor, 大学院総合理工学研究科, 助教授 (30359690)
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| Co-Investigator(Kenkyū-buntansha) |
KANNO Ryoji Tokyo Institute of Technology, Interdiciplinary Graduate School of Science and Engineering, Department of Electronic Chemistry, Professor, 大学院総合理工学研究科, 教授 (90135426)
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| Project Period (FY) |
2004 – 2006
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| Keywords | Lithium Battery / Large Battery / Iron / Cathode / Olivine |
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| Research Abstract |
A series of synthetic (Mn_yFe_<1-y_)PO_4(y<0.8) phases were obtained by chemical oxidation of crystallized isotypic Li(Mn_yFe_<1-y>)PO_4 under optimized conditions. All samples exhibit antiferromagnetism but the decrease in Neel temperature is more than 7 times larger in (Mn_yFe_<1-y>)PO_4 than in Li(Mn_yFe_<1-y>)PO_4. This was discussed in terms of the asymmetric superexchange interaction by an unusual synergetic effect of Jahn-Teller distortion and edge-shared interconnection with PO_4 tetrahedra.
We provide firm experimental evidence that Li_xFePO_4 at room temperature can be described as a mixture of the Fe^<3+>/Fe^<2+> mixed-valent intermediate Li_αFePO_4 and Li_<1-β>FePO_4 phases with surprisingly large values of α and β. Using powder neutron diffraction, the site occupancy numbers for lithium in each phase were refined to be α=0.05 and 1-β=0.89. The corresponding solid solution ranges outside the miscibility gap (0<x<α, 1-β<x<1) were detected by the anomaly in the configurational
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entropy and also by the deviation of the open-circuit voltage from the constant equilibrium potential. These findings encourage further improvement of this important class of compounds at ambient temperatures.
Rietveld analysis for the powder neutron diffraction profile for LiFePO_4 was performed. Tensor elements of the unisotropic thermal factor showed the principal axis of the lithium vibration is toward the face shared vacant tetrahedral space. This is consistent with the theoretical prediction ; lithium ions diffuse along curved one-dementional chain along b-axis. Impact of temperature on the phase diagram of LixFePO_4 with > 200nm particle size was slight under the unmixing line around 200 C. While the reduction in particle size down to <100 nm seems to have significant effect to the room temperature miscibility gap. The thermodynamic concepts for the extended solution in smaller particles are discussed, followed by a very high rate capability observed for the small spherical particles <80nm. Less
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