Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 143, Issue 22, Pages 8278-8294Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.0c10628
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Funding
- National Science Foundation [CHE-1905263]
- Companhia Brasileira de Metallurgia e Mineracao (CBMM) [UTA16-000941]
- Welch Foundation [F-1848]
- DOE Basic Energy Sciences Office [DE-SC0019111]
- Lockheed Martin [UTA19-000624]
- U.S. Department of Energy (DOE) [DE-SC0019111] Funding Source: U.S. Department of Energy (DOE)
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The study reveals that the equilibrium potential and kinetics of Li insertion in nanocrystalline anatase TiO2 are mainly influenced by the nanocrystal size. The rate of Li insertion depends on the applied overpotential, electrolyte concentration, and initial state of charge, while Li diffusivity and phase propagation are not rate limiting factors.
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 bulk Li insertion from other electrochemical responses, such as double-layer capacitance, pseudocapacitance, 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 the Li-insertion potentials with the particle size. However, the particle size does not affect the kinetics of Li insertion in ensemble electrodes. Rather, the Li-insertion rates depend on the 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 the nonequilibrium charging behavior in nanocrystalline electrodes through a combination of colloidal synthesis, phase field simulations, and spectroelectrochemistry.
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