Abstract
In situ electrochemical electron paramagnetic resonance (EPR) spectroscopy is used to understand the mixed lithiation/deposition behavior on graphite anodes during the charging process. The conductivity, degree of lithiation, and the deposition process of the graphite are reflected by the EPR spectroscopic quality factor, the spin density, and the EPR spectral change, respectively. Classical over‐charging (normally associated with potentials ≤0 V vs. Li+/Li) are not required for Li metal deposition onto the graphite anode: Li deposition initiates at ca. +0.04 V (vs. Li+/Li) when the scan rate is lowered to 0.04 mV s−1. The inhibition of Li deposition by vinylene carbonate (VC) additive is highlighted by the EPR results during cycling, attributed to a more mechanically flexible and polymeric SEI layer with higher ionic conductivity. A safe cut‐off potential limit of +0.05 V for the anode is suggested for high rate cycling, confirmed by the EPR response over prolonged cycling.
Highlights
Li ion batteries (LIBs) play an increasingly important role in the energy system, so the development of an understanding of their degradation mechanisms is a pre-requisite to extending battery life.[1]
The solid electrolyte interface (SEI) interface takes more time to form without the vinylene carbonate (VC), which is deduced from the slower rate of change in the background response
In situ Electron paramagnetic resonance (EPR) spectroscopy has been used to understand the electrochemical behavior, including lithiation and the Li deposition, of the graphite anode upon voltammetric cycling in a bespoke three-electrode EPR cell operated at room temperature
Summary
Li ion batteries (LIBs) play an increasingly important role in the energy system, so the development of an understanding of their degradation mechanisms is a pre-requisite to extending battery life.[1]. Angewandte Chemie International Edition published by Wiley-VCH GmbH A concentric geometry, three-electrode in situ EPR cell was designed with a metallic Li cathode and graphitic anode to study (de-)lithiation of the LIB anode at room temperature. We use this approach to assess the formation of the solid electrolyte interface (SEI) layer on the 1st potential cycle, which is based on the change in microwave skin depth via its effect on the conductivity of whole cell. The inhibition of the anode degradation by the VC electrolyte additive is confirmed by the decrease in the Li signal during long-term cycling
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