How Observable Is Lithium Plating? Differential Voltage Analysis to Identify and Quantify Lithium Plating Following Fast Charging of Cold Lithium-Ion Batteries

Abstract

Fast charging of batteries is currently limited, particularly at low temperatures, due to difficulties in understanding lithium plating. Accurate, online quantification of lithium plating increases safety, enables charging at speeds closer to the electrochemical limit and accelerates charge profile development. This work uses different cell cooling strategies to expose how voltage plateaus arising from cell self-heating and concentration gradients during fast charging can falsely indicate plating, contrary to prevalent current assumptions. A solution is provided using Differential Voltage (DV) analysis, which confirms that lithium stripping is observable. However, scanning electron microscopy and energy-dispersive X-ray analysis are used to demonstrate the inability of the plateau technique to detect plating under certain conditions. The work highlights error in conventional plating quantification that leads to the dangerous underestimation of plated amounts. A novel method of using voltage plateau end-point gradients is proposed to extend the sensitivity of the technique, enabling measurement of lower levels of lithium stripping and plating. The results are especially relevant to automotive OEMs and engineers wishing to expand their online and offline tools for fast charging algorithm development, charge management and state-of-health diagnostics.

The influence of surface inhomogeneity on the overcharge and lithium plating of graphite electrodes

“…Of note, the ANL authors found that Li plating did not cause measurable discharge capacity loss for currents up to 6C for the conditions studied (see their discussion associated with figure 5 of [7]), despite the fact that their reference electrode measurement confirmed Li plating at the graphite electrode. Recent analyses [7][8][9][10][11][12] of lithium plating underscore its technological relevance. In [13], the authors developed a set of equations that can be used to treat Li plating and subsequent electro-dissolution in the context of a porous electrode, and simulations were provided for a single-particle model, which ignores all impedances associated with the electrolyte phase and considers each particle in the porous electrode to be identically spherical and isolated.…”

Voltage Relaxation to Detect the Onset of Lithium Plating on Graphite for Fast Charging

“…This explanation would be consistent with other groups that have observed , to decrease with slower discharge rates after the same amount of Li plating. 15,32 Considering these effects, we consider the 72% SE value associated with the smallest , to be the most accurate estimate, as it would be the least affected by the underestimation. This value is near the 70% SE's reported from overlithiation studies that we used previously to estimate the Li recovery factor η in the main text.…”

“…This effect has been observed by other groups, which caution that , estimates decrease when using slower discharge rates after the same amount of Li plating. 15,32,18 The higher temperatures used in this work (23°C vs. ≤ 0°C) appear to exacerbate the effect. Another observation consistent with these statements is that the dV/dQ maxima peak times during discharge (Fig.…”

“…reported technique for electrochemical Li detection is differential voltage analysis of the discharge profile (dV/dQ), which detects a plateau feature corresponding to Li stripping -the reverse of the Li plating reaction -and can estimate the amount of plated Li based on the length of the plateau. 15,[30][31][32] This technique, however, can give false positive plating signals, 32 fail to identify plating when it occurs, 32 and requires a constant-current battery discharge immediately following the fast charge, which may be challenging to implement given the fluctuating power demand for vehicles. We assert dOCV as the more commercially feasible technology but nonetheless believe it important to understand its detection capabilities relative to dV/dQ.…”

“…It was our intention to use the dV/dQ peak positions to quantify the capacity of reversible Li plating, 15,19,30,32 , , and combine that information with CE data to estimate Li stripping efficiencies (SE), the fraction of plated Li that is stripped during discharge. This method, however, yields SE values that decrease systematically from 72% to 50% for the charge cycles ranging 50-65%.…”