Abstract
The rechargeable lithium-ion cell is an advanced energy-storage system. However, high cost, safety hazards, and chemical instability prohibit its use in large-scale applications. An alternative cathode material, LiFePO4, solves these problems, but has a kinetic problem involving strong electron/hole localization1. One reason for this is believed to be the limited carrier density in the fixed monovalent Fe3+PO4/LiFe2+PO4 two-phase electrode reaction in LixFePO4. Here, we provide experimental evidence that LixFePO4, at room temperature, can be described as a mixture of the Fe3+/Fe2+ mixed-valent intermediate LiαFePO4 and Li1−βFePO4 phases. 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 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.
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References
Padhi, A. K., Nanjundaswamy, K. S. & Goodenough, J. B. Phospho-olivines as positive-electrode materials for rechargeable lithium batteries. J. Electrochem. Soc. 144, 1188–1194 (1997).
Yamada, A. & Yamahira, T. Cathode for nonaqueous electrolyte lithium battery. European patent 1150368 (2001).
Yamada, A., Chung, S.-C. & Hinokuma, K. Optimized LiFePO4 for lithium battery cathode. J. Electrochem. Soc. 148, A224–A229 (2001).
Chung, S. Y., Bloking, J. T. & Chiang, Y. M. Electronically conductive phospho-olivines as lithium storage electrode. Nature Mater. 1, 123–128 (2002).
Subramanya Herle, P., Ellis, B., Coombs, N. & Nazar, L. Nano-network electronic conduction in iron and nickel olivine phosphates. Nature Mater. 3, 147–152 (2004).
Dahn, J. R. & McKinnon, W. R. Phase diagram of LixMo6Se8 for 0<x<1 from in situ x-ray studies. Phys. Rev. B 32, 3003–3005 (1985).
Dahn, J. R. et al. Entropy of the intercalation compound LixMo6Se8 from calorimetry of electrochemical cells. Phys. Rev. B 32, 3316–3318 (1985).
Delmas, C., Nadiri, A. & Soubeyroux, J. L. The NASICON-type titanium phosphates ATi2(PO4)3 (A=Li,Na) as electrode materials. Solid State Ionics 28–30, 419–423 (1988).
Delacourt, C., Poizot, P., Tarascon, J. M. & Masquelier, C. The existence of a temperature-driven solid solution in LixFePO4 for 0<x<1 . Nature Mater. 4, 254–260 (2005).
Andersson, A. S., Kalska, B., Häggström, L. & Thomas, J. O. Lithium extraction/insertion in LiFePO4: an X-ray diffraction and Mössbauer spectroscopy study. Solid State Ionics 130, 41–52 (2000).
Yamada, A., Koizumi, H., Sonoyama, N. & Kanno, R. Phase change in LixFePO4 . Electrochem. Solid State Lett. 8, A409–A413 (2005).
Kobayashi, Y. et al. Precise electrochemical calorimetry of LiCoO2/graphite lithium-ion cell—Understanding thermal behavior and estimation of degradation mechanism. J. Electrochem. Soc. 149, A978–A982 (2002).
Kobayashi, Y. et al. Electrochemical and calorimetric approach to spinel lithium manganese oxide. J. Power Sources 81, 463–466 (1999).
Reynier, Y. et al. Entropy of Li intercalation in LixCoO2 . Phys. Rev. B 70, 174304 (2004).
Srinivasan, V. & Newman, J. Existence of path-dependence in the LiFePO4 electrode. Electrochem. Solid State Lett. 9, A110–A114 (2006).
Morgan, D., Van der Ven, A. & Ceder, G. Li conductivity in LixMPO4 (M=Mn,Fe,Co,Ni) olivine materials. Electrochem. Solid State Lett. 7, A30–A32 (2004).
Zhou, F., Marianetti, C. A., Cococcoini, M., Morgan, D. & Ceder, G. Phase separation in LixFePO4 induced by correlation effects. Phys. Rev. B 69, 201101 (2004).
Yamada, A., Kudo, Y. & Liu, K. Y. Phase diagram of Lix(MnyFe1−y)PO4 (0<x,y<1) . J. Electrochem. Soc. 148, A1153–A1158 (2001).
Yamada, A., Kudo, Y. & Liu, K. Y. Reaction mechanism of the olivine-type Lix(Mn0.6Fe0.4)PO4(0<x<1) . J. Electrochem. Soc. 148, A747–A754 (2001).
Yamada, A. & Chung, S.-C. Crystal chemistry of the olivine-type Li(MnyFe1−y)PO4 and (MnyFe1−y) PO4 as possible 4 V cathode materials for lithium batteries. J. Electrochem. Soc. 148, A960–A967 (2001).
Yamada, A. et al. Electrochemical, magnetic, and structural investigation of the Lix(MnyFe1−y)PO4 phases. Chem. Mater. 18, 804–813 (2006).
Acknowledgements
The authors would like to thank H. Miyashiro, S. Seki and Y. Ohno for enlightening discussions. This work was financially supported by the TEPCO Research Foundation, the Murata Science Foundation, Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, No. 16350108, and the New Energy and Industrial Technology Development Organization (NEDO).
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Yamada, A., Koizumi, H., Nishimura, Si. et al. Room-temperature miscibility gap in LixFePO4. Nature Mater 5, 357–360 (2006). https://doi.org/10.1038/nmat1634
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DOI: https://doi.org/10.1038/nmat1634
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