Differential voltage analysis for battery manufacturing process control

Abstract

Voltage-based battery metrics are ubiquitous and essential in battery manufacturing diagnostics. They enable electrochemical “fingerprinting” of batteries at the end of the manufacturing line and are naturally scalable, since voltage data is already collected as part of the formation process which is the last step in battery manufacturing. Yet, despite their prevalence, interpretations of voltage-based metrics are often ambiguous and require expert judgment. In this work, we present a method for collecting and analyzing full cell near-equilibrium voltage curves for end-of-line manufacturing process control. The method builds on existing literature on differential voltage analysis (DVA or dV/dQ) by expanding the method formalism through the lens of reproducibility, interpretability, and automation. Our model revisions introduce several new derived metrics relevant to manufacturing process control, including lithium consumed during formation and the practical negative-to-positive ratio, which complement standard metrics such as positive and negative electrode capacities. To facilitate method reproducibility, we reformulate the model to account for the “inaccessible lithium problem” which quantifies the numerical differences between modeled versus true values for electrode capacities and stoichiometries. We finally outline key data collection considerations, including C-rate and charging direction for both full cell and half cell datasets, which may impact method reproducibility. This work highlights the opportunities for leveraging voltage-based electrochemical metrics for online battery manufacturing process control.

Accurate LLI and LAMPE Estimation Using the Mechanistic Modeling Approach with Layered Oxides

“…Equations for the correct accommodation for lithiation-based models are already available in the literature. 38,39 The following section is more focused on a mechanistic discussion of the impact of the electrode size. Before getting into the details, it is important to first discuss what SOC scale to use to avoid any possible confusion.…”

“…Most of the pioneering models [2][3][4][5][6][7] were Q/SOC-based and relied on at minimum two parameters to match the electrodes, the ratio of capacity between PE and NE (LR) and their offset or slippage (OFS). The lithiation-based models [23][24][25][26][27][28][29][30][31][32][33][34]38,39 relied on a minimum of four parameters, the minimum and maximum lithiation operation values for each electrode. To best of our knowledge, both approaches have always been considered equivalent.…”

“…40,41 While both approaches are equivalent when used with materials using 100% of their lithium, this is not the case for materials which do not because of the presence of inaccessible lithium. 38,39,42 This will affect lithium cobalt oxide (LCO), nickel cobalt aluminum oxide (NCA), and nickel manganese cobalt oxide (NMC) that typically display lithiations between 0.33 and 0.5 in the 4.2 to 4.3 V window. This work complements previous descriptions of the issue 38,39 to illustrate that the usage of only a portion of the available lithium ions induces different issues in both categories of mechanistic models in their current implementations.…”

“…38,39,42 This will affect lithium cobalt oxide (LCO), nickel cobalt aluminum oxide (NCA), and nickel manganese cobalt oxide (NMC) that typically display lithiations between 0.33 and 0.5 in the 4.2 to 4.3 V window. This work complements previous descriptions of the issue 38,39 to illustrate that the usage of only a portion of the available lithium ions induces different issues in both categories of mechanistic models in their current implementations. The Q/SOC-based models are able to correctly quantify and simulate the voltage response induced by LAM PE but are overestimating LLI.…”

Modeling Battery Formation: Boosted SEI Growth, Multi-Species Reactions, and Irreversible Expansion

“…Electrode capacities. Electrode capacities Q p and Q n were initialized using a differential voltage fitting procedure outlined in Weng et al 65 This method uses a C/20 charge voltage curve to extract information about electrode-specific capacities. The voltage curve used for this analysis was taken at the end of the two-week formation aging step.…”