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Dynamics of Lithium Insertion in Electrochromic Titanium Dioxide Nanocrystal Ensembles

preprint
submitted on 05.10.2020 and posted on 06.10.2020 by Clayton Dahlman, Sungyeon Heo, Youtian Zhang, Lauren C. Reimnitz, daniel he, Ming Tang, Delia Milliron
Nanocrystalline anatase TiO2 is a robust model anode for Li-insertion in batteries. The influence of nanocrystal size on the equilibrium potential and kinetics of Li-insertion is investigated with in operando spectroelectrochemistry of thin film electrodes. Distinct visible and infrared responses correlate with Li-insertion and electron accumulation, respectively, and these optical signals are used to deconvolute Li-insertion from other electrochemical responses, such as double-layer capacitance and electrolyte leakage. Electrochemical titration and phase-field simulations reveal that a difference in surface energies between anatase and lithiated phases of TiO2 systematically tunes Li-insertion potentials with particle size. However, particle size does not affect the kinetics of Li-insertion in ensemble electrodes. Rather, Li-insertion rates depend on applied overpotential, electrolyte concentration, and initial state-of-charge. We conclude that Li diffusivity and phase propagation are not rate-limiting during Li-insertion in TiO2 nanocrystals. Both of these processes occur rapidly once the transformation between the low-Li anatase and high-Li orthorhombic phases begins in a particle. Instead, discontinuous kinetics of Li accumulation in TiO2 particles prior to the phase transformations limits (dis)charging rates. We demonstrate a practical means to deconvolute non-equilibrium charging behavior in nanocrystalline electrodes through a combination of colloidal synthesis, phase field simulations and spectroelectrochemistry.

History

Email Address of Submitting Author

claytondahlman@ucsb.edu

Institution

University of Califonia, Santa Barbara

Country

United States

ORCID For Submitting Author

0000-0002-4555-4846

Declaration of Conflict of Interest

The authors declare the following competing financial interests: D.J.M. has a financial interest in Heliotrope Technologies, a company pursuing commercial development of electrochromic devices.

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