Lithium-Ion Transport In Li4ti5o12 Epitaxial Thin Films Vs. State Of Charge

We investigate the electrochemical lithiation of epitaxial Li4Ti5O12 thin-film model electrodes grown on epitaxial platinum current collectors. Structure and composition of Li4Ti5O12 films are confirmed by out-of-plane and in-plane X-ray diffraction and elastic recoil detection analysis. Employing different cell configurations, we deconvolute electrochemical impedance spectra and extract for the first time the lithium-ion conductivity as a function of electrochemical lithiation. Lithium-ion conductivity increases monotonously by more than two orders of magnitude from 2.6.10(-9) S/cm in Li4Ti5O12 to above 3 . 10(-7) S/cm between Li4.5Ti5O12 and Li6Ti5O12 and drops again to 1.3.10(-9) S/cm in Li7Ti5O12. We discuss our results in light of nuclear magnetic resonance studies and theoretical models reported previously and derive important implications for fast-charging applications of lithium-ion batteries with Li4Ti5O12 anodes.