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Nat Commun. 2015 Sep 8;6:8169. doi: 10.1038/ncomms9169.

Combined operando X-ray diffraction-electrochemical impedance spectroscopy detecting solid solution reactions of LiFePO4 in batteries.

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Paul Scherrer Institute, Electrochemical Energy Storage Section, 5232 Villigen PSI, Switzerland.
ETH Zurich, Department of Chemistry and Applied Biosciences, Laboratory of Inorganic Chemistry, 8093 Zurich, Switzerland.
Toyota Central R&D Labs., Inc., Battery Laboratory, Nagakute, Aichi 480-1192, Japan.


Lithium-ion batteries are widely used for portable applications today; however, often suffer from limited recharge rates. One reason for such limitation can be a reduced active surface area during phase separation. Here we report a technique combining high-resolution operando synchrotron X-ray diffraction coupled with electrochemical impedance spectroscopy to directly track non-equilibrium intermediate phases in lithium-ion battery materials. LiFePO4, for example, is known to undergo phase separation when cycled under low-current-density conditions. However, operando X-ray diffraction under ultra-high-rate alternating current and direct current excitation reveal a continuous but current-dependent, solid solution reaction between LiFePO4 and FePO4 which is consistent with previous experiments and calculations. In addition, the formation of a preferred phase with a composition similar to the eutectoid composition, Li0.625FePO4, is evident. Even at a low rate of 0.1C, ∼20% of the X-ray diffractogram can be attributed to non-equilibrium phases, which changes our understanding of the intercalation dynamics in LiFePO4.

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