Differential Analysis of Galvanostatic Cycle Data from Li-Ion Batteries: Interpretative Insights and Graphical Heuristics

Abstract

Differentiation of a Li-ion battery cycling profile (galvanostatic voltage vs charge) yields a pair of complementary measures: differential capacity (dQ/dV vs voltage, also called incremental capacity) and differential voltage (dV/dQ vs charge). These metrics, especially when obtained under experimental conditions approximating cell equilibrium, are widely used to diagnose cell state and mechanisms related to cell aging. Central to the resulting diagnosis is the understanding of how the chemistry of individual electrode materials manifests in the full-cell differential plots. In this article, a fundamental theory of differential analysis is advanced from the starting point of idealized single electrode (half-cell) measurements, building up to the nontrivial translation to full cell data, with consideration of cell balancing and degradation. Various complementary approaches from the existing literature are harmonized with the aid of a novel graphical heuristic in which cell voltage and differential capacity data are superimposed on a 2D representation (“square plot”) of the cell thermodynamic state. Interpretative analysis based on the new approach is demonstrated using data from a commercial pouch cell with the well-characterized LiCoO2|graphite chemistry. A brief review of current literature on practical uses of differential analysis is also provided.

Quantification of Electrode Pulverization Enabled through Operando Video Microscopy of an Electrodeposited Antimony Anode

“…In addition to examining the voltage profile, more information can be gathered when incorporating differential capacity analysis to correlate electrochemical events to pulverization events. In a voltage versus time plot (Figure A), electrochemical events appear as plateaus where the capacity changes a large amount for a small change in voltage. , In Figure A, it is evident that significant electrochemical event(s) may be occurring between −3 and −3.25 V. However, if plateaus from different electrochemical events overlap, then it is not possible to deconvolute the contributions of multiple events. Figure B shows a differential capacity plot for the discharge (delithiation) step referenced in Figures E and A with peaks of interest identified (Table ).…”

Differential voltage analysis for battery manufacturing process control

“…Near-equilibrium (i.e., slow-rate) full cell voltage curves have been widely used to understand dominant cell degradation modes such as loss of active material (LAM) and loss of lithium inventory (LLI) (Bloom et al, 2005;Dubarry et al, 2012;Birkl et al, 2017;Olson et al, 2023). The appeal of these techniques is easy to appreciate: full cell data is easier and faster to collect than materials-level characterization data which often requires cell tear-down and electrode harvesting.…”

Ageing of High Energy Density Automotive Li-ion Batteries: The Effect of Temperature and State-of-Charge

“…The capacity of the graphite part of the active material was partitioned into three segments based on the sharp differential voltage peaks N1 and N3, illustrated in Figure 12 a. If kinetic limitations can be reasonably neglected (i.e., if cycling sufficiently slowly), the resulting segments a (𝑄 𝑁1 − 0), b (𝑄 𝑁3 − 𝑄 𝑁1 ), and c (𝑄 𝑑 − 𝑄 𝑁1 ) contain 50, 38, and 12 % of the graphite capacity, respectively [58,77,78]. The observed capacities in each region, as well as the total electrode delithiation capacity, 𝑄 𝑑 , is presented for each cycling condition in Figure 12 and Table S 6 (shown in SI) as the averages from multiple harvested electrodes from various regions within each test cell.…”