The effect of dimethyl pyrocarbonate on electroanalytical behavior and cycling of graphite electrodes

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Abstract
The addition of small concentrations of dimethyl pyrocarbonate (DMPC), about 5% by volume, to a standard solution of 1 M LiPF6/ethylene carbonate+dimethyl carbonateLiPF6/ethylene carbonate+dimethyl carbonate (1:1) was shown to improve substantially the cycling behavior of graphite electrodes. A combination of fast and slow scan rate cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), Fourier transform infrared, 1H,1H, and 13C13C nuclear magnetic resonance spectroscopy were applied to understand the nature of the stabilizing effect caused by the presence of DMPC. DMPC was shown to increase impregnation of the active mass of the porous electrodes with solution (thus increasing the specific electrode capacity), and facilitates the rate of Li-ion migration across the surface films around the graphite particles and across the surface film/particle interface. Based on a combination of fast- and slow-scan rate CV and EIS, a convenient procedure allowing for an intermittent monitoring of the kinetic and thermodynamic characteristics of the Li-insertion process into graphite in the course of long-term electrode cycling was elaborated. We show that a simple procedure consisting of the application of a series of consecutive fast- and slow-scan rate CVs can be conveniently used for a systematic search and optimization of electrolyte solutions suitable for long-term cycling of graphite electrodes in lithium-ion cells. © 2004 The Electrochemical Society. All rights reserved.

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