UC Berkeley

A key challenge for energy storage and conversion technologies is finding simple, reliable methods that can identify device failure and prolong lifetime. Lithium plating is a well-known degradation process that prevents Li-ion battery fast charging, which is essential to reduce electric vehicle ‘range anxiety’ and enable emerging technologies such as aerial drones and high-performance portable electronics. The ability to detect the initial onset of lithium plating from easily accessible voltage measurements would greatly improve battery safety and feedback controls modeling. In this work, we first highlight the application of a differential open-circuit voltage analysis (dOCV) to detect when Li plating begins during a single charge for room temperature fast charging. We also show that dOCV can identify the Li plating onset during cycling with sensitivity of 1 mg plated Li per gram graphite, equivalent to 1% of the graphite capacity, indicating that this method has commercial promise for on-line Li detection.

Next, we demonstrate the power of simple, accessible, and high-throughput cycling techniques to quantify irreversible Li plating spanning data from over 200 cells. We first observe the effects of energy density, charge rate, temperature, and State-of-Charge (SOC) on lithium plating, use the results to refine mature physics-based electrochemical models, and provide an interpretable empirical equation for predicting the plating onset SOC. We then explore the reversibility of lithium plating and its connection to electrolyte design for preventing irreversible Li accumulation. Finally, we design a method to quantify in-situ Li plating for commercially relevant Graphite|LiNi0.5Mn0.3Co0.2O2 (NMC) cells and compare with results from the experimentally convenient Li|Graphite configuration. The hypotheses and abundant data in this section were generated primarily with equipment universal to the battery researcher, encouraging further development of innovative testing methods and data processing that enable rapid battery engineering.

Finally, we consider the challenge of highly variable charging conditions possible in commercial cells. We combine pseudo-2D electrochemical modeling with data visualization methods to reveal important relationships between the measurable cell voltage and difficult-to-predict Li plating onset criteria. An extensively validated model is used to compute lithium plating for thousands of multistep charging conditions spanning diverse rates, temperatures, states-of-charge (SOC), and cell aging. We observe an empirical cell operating voltage limit below which plating does not occur across all conditions, and this limit varies with battery state-of-charge and aging. A model sensitivity analysis also indicates that when comparing two charging voltage profiles, the capacity difference at 4.0V correlates well with the difference in the plating onset capacity. These results encourage simple strategies for Li plating prevention that are complementary to existing battery controls.