Lithium plating and dendrite formation are critical challenges in lithium-ion batteries, particularly under fast-charging conditions or low-temperature operation. These phenomena degrade battery performance, reduce lifespan, and pose safety risks by increasing the likelihood of internal short circuits. Accurate modeling of these processes is essential for developing mitigation strategies and improving battery designs. This article explores phase-field models, kinetic theories, and their integration with electrochemical models to simulate lithium plating and dendrite growth, along with implications for fast-charging and safety.
Lithium plating occurs when lithium ions, instead of intercalating into the anode, deposit as metallic lithium on the anode surface. This is driven by overpotentials that exceed the thermodynamic stability window of the electrolyte, often exacerbated by high charging currents or insufficient ion transport. Dendrites are needle-like lithium structures that grow from plated lithium, penetrating the separator and causing internal shorts. Modeling these processes requires capturing the interplay between electrochemical reactions, ion transport, and mechanical deformation.
Phase-field models are widely used to simulate dendrite growth due to their ability to handle complex interfacial dynamics without explicitly tracking the interface. The phase-field variable distinguishes between the electrolyte and lithium metal phases, with evolution governed by free energy minimization. The model incorporates electrochemical potentials, ion concentration gradients, and mechanical stresses. Key parameters include the interfacial energy between lithium and electrolyte, the mobility of lithium ions, and the overpotential driving deposition. Phase-field simulations reveal that dendrite growth is highly sensitive to local current density inhomogeneities, which arise from electrode roughness or uneven separator contact.
Kinetic theories complement phase-field models by describing the nucleation and growth of lithium deposits at atomic or mesoscopic scales. These models often rely on Butler-Volmer kinetics to describe charge transfer reactions, coupled with diffusion equations for ion transport. The nucleation rate of lithium is influenced by the local overpotential, with higher overpotentials leading to more frequent nucleation and finer lithium deposits. Growth kinetics depend on the competition between ion reduction and surface diffusion of deposited lithium atoms. Kinetic models show that slow surface diffusion promotes dendritic growth, while fast diffusion leads to smoother deposits.
Coupling these models with electrochemical frameworks, such as the Doyle-Fuller-Newman model, enables a comprehensive description of battery behavior under plating conditions. The coupled approach solves for ion concentrations, potentials, and reaction rates across the cell while incorporating phase-field or kinetic descriptions of lithium deposition. This integration allows for the prediction of plating onset, dendrite morphology, and their impact on cell voltage and capacity fade. For example, simulations demonstrate that plating initiates at the anode-separator interface where local current density peaks, and dendrites propagate along paths of least mechanical resistance.
The implications for fast-charging are significant. Models predict that increasing charging rates elevates the risk of lithium plating due to higher overpotentials and concentration gradients. At low temperatures, reduced ion mobility further exacerbates plating. Strategies to mitigate plating include optimizing electrode porosity to homogenize current distribution, designing electrolytes with higher lithium transference numbers, and applying pulse charging protocols to relax concentration gradients. Simulations suggest that anode coatings with high surface energy can also suppress dendrite growth by promoting lateral lithium spreading.
Safety concerns arise from dendrite-induced short circuits, which can lead to localized heating and cell failure. While thermal runaway is a separate topic, modeling dendrite formation helps identify conditions that increase short-circuit risks. For instance, repeated fast-charging cycles accelerate dendrite accumulation, raising the probability of separator penetration. Mechanical models coupled with electrochemical simulations show that dendrites are more likely to pierce separators under mechanical stress, such as in flexible or compressed cells.
Recent advancements in modeling include incorporating solid-electrolyte interphase (SEI) dynamics, which influence plating behavior. The SEI acts as a resistive layer that modifies local overpotentials, and its fracture during plating exposes fresh lithium to further reactions. Multiscale models that account for SEI formation, lithium deposition, and mechanical stresses provide a more holistic view of degradation mechanisms.
In summary, modeling lithium plating and dendrite formation requires a multidisciplinary approach combining phase-field methods, kinetic theories, and electrochemical models. These tools enable the prediction of plating onset, dendrite growth patterns, and their effects on battery performance and safety. Insights from these models guide the development of fast-charging protocols and safer battery designs, ultimately enhancing the reliability of lithium-ion batteries. Future work may focus on integrating machine learning for parameter optimization and exploring novel materials that inherently resist dendrite formation.