Is Incremental Capacity Useful for Characterizing Anode Degradation in Lithium Metal Batteries?

Quantification of the anode degradation with charge/discharge cycling is a primary requirement to develop lithium metal batteries (LMBs) with improved battery lifetime. Although the physical characterization such as scanning electron imaging, gas chromatography, and nuclear magnetic resonance, etc., can provide valuable insights into the anode degradation, these invasive techniques are not convenient for real-time degradation diagnostics during the cycling measurements. Here we show that the degradation diagnostics for LMBs can be greatly facilitated with non-invasive electrochemical voltage (EVS) spectroscopy. Though widely explored for conventional lithium-ion batteries, EVS techniques such as incremental capacity (IC), i.e., the derivative (
$dQ/dV$
) of the capacity vs. voltage response are not well understood for anode degradation in LMBs. We quantify the signatures of anode degradation in IC features as a function of cell design variations including anode thickness, electrolytes, E/C ratio, and C-rate and relate these with capacity loss and physical characterization results. We show that the polarization effects due to dead (inactive) lithium and depleted electrolyte which are not visible in the capacity loss during early cycles can reveal a prominent signature in the IC features including the peak height and its location. The evolution of these features shows consistent trends for different experimental datasets comprising a variety of electrolytes and cell design parameters. These findings suggest that IC can be a powerful approach for health diagnostics and lifetime prediction for LMB which can aid the ongoing research on further optimization of the anode and the electrolyte materials for enhancing the battery lifetime.