The ability of fast and safe charging is critical for the further success of lithium ion batteries in automotive applications. In state-of-the-art lithium ion batteries, the charging rate is limited by the onset of lithium plating on the graphite anode. Despite its high importance, so far no analytical technique has been available for directly measuring lithium plating during battery charge. Herein, we introduce operando electron paramagnetic resonance (EPR) spectroscopy as the first technique capable of time-resolved and quantitative detection of lithium metal plating in lithium ion batteries. In an exemplary study, the C-rate dependence of lithium metal plating during low-temperature charging at -20?°C is investigated. It is possible to quantify the amount of ‘dead lithium’ and observe the chemical reintercalation of plated lithium metal. In this way, it is possible to deconvolute the coulombic inefficiency of the lithium plating/stripping process and quantify the contributions of both dead lithium and active lithium loss due to solid electrolyte interphase (SEI) formation. The time-resolved and quantitative information accessible with operando EPR spectroscopy will be very useful for the optimization of fast charging procedures, testing of electrolyte additives, and model validation.

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DOI: 10.1016/j.mattod.2017.11.001