Electrochem Seminar - Detecting the onset of Li plating during fast charging of Li-ion batteries using operando electrochemical impedance spectroscopy
Li-ion batteries (LIBs) offer a very promising avenue for the necessary decarbonization of the transportation industry via the broad adoption of electric vehicles (EVs). However, current EVs are plagued by long charging times, on the order of thirty minutes to an hour or longer at their fastest charging rates. The U.S. Department of Energy has set a goal to develop LIB battery packs that can achieve a 200-mile charge in 15 minutes or less, termed extreme fast charging (XFC). XFC is currently not viable, because it induces detrimental electrochemical plating of Li metal on the graphite negative electrode. Li plating, a partially irreversible process, can cause significant capacity fade over the cycle life of the LIB, or if enough Li is plated, it can cause the LIB to short and the non-aqueous liquid electrolyte to combust. Given these concerns, there is great interest in developing techniques that can detect the onset of Li plating on graphite during XFC. Our group has previously shown the ability to quantify Li plating on graphite using destructive, post-mortem mass spectrometry titrations (MST) and, separately, by using differential analysis of the graphite relaxation voltage for Gr/Li half-cells after XFC cycling (dOCV). In this talk, I will discuss our work using operando impedance spectroscopy to clearly show that the onset of Li plating can be detected via a rise in the graphite SEI impedance during XFC in three-electrode full cells. This signal is cross-validated with MST and shows improved detection resolution for Li plating over dOCV analysis. I will also demonstrate that this technique can be applied to more commercially-relevant two-electrode cells. And lastly, I will discuss possible physical explanations for the impedance behavior observed. This technique represents, to the best of our knowledge, the first truly operando electrochemical method for Li plating detection in LIBs during XFC.