Pulse Voltammetric and ac Impedance Spectroscopic Studies on Lithium Ion Transfer at an Electrolyte/Li4/3Ti5/3O4 Electrode Interface

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Abstract
Pulse voltammetry and ac impedance spectroscopy were used to study the lithium ion kinetics at a lithium ion insertion electrode consisting of Li4/3Ti5/3O4 thin films in an organic electrolyte. In the cyclic voltammogram, two redox peaks appeared at around 1.56 V vs Li/Li+ due to the insertion and extraction of lithium ion at the electrode. Differential pulse voltammetry gave a large reduction current at ∼1.56 V during a cathodic scan due to lithium ion insertion into the electrode. From the peak current and potential, the charge-transfer resistance was evaluated by quantitative analysis using approximate equations for irreversible reactions. In the Nyquist plot, one semicircle was observed at 1.56 V, which was assigned to the charge-transfer resistance due to lithium ion transfer at the electrode/electrolyte interface. The value of the charge-transfer resistance at 1.56 V was almost identical to that evaluated by differential pulse voltammetry with an identical characteristic relaxation time. This result shows that both dc differential pulse voltammetry and ac impedance spectroscopy are useful for elucidating the phase transfer kinetics of lithium ion at insertion electrodes.