Role of coupled electrochemistry and stress on the Li-anode instability: A continuum approach

TL;DR

A fully coupled electro-chemo-mechanical continuum framework is developed to study Li-metal anode instability and SEI wrinkling under plating/stripping, incorporating Li viscoplasticity, SEI swelling, surface energy, and stress-driven Butler–Volmer kinetics. The model is implemented in Abaqus/Standard via a user element and used to generate stability maps across SEI modulus, thickness, and surface tension. Key findings show Li viscoplasticity as a major driver of instability, and that optimized artificial SEIs, including bilayer designs with appropriate thickness and modulus, can enhance stability by delaying deformation and distributing stress. The work provides design criteria for artificial SEI configurations and emphasizes the importance of treating stress and electrochemistry jointly to suppress dendrite growth in liquid-electrolyte Li-metal batteries.

Abstract

We present a coupled mechanistic approach that elucidates the intricate interplay between stress and electrochemistry, enabling the prediction of the onset of instabilities in Li-metal anodes and the solid electrolyte interphase (SEI) in liquid-electrolyte Li-metal batteries. Our continuum theory considers a two-way coupling between stress and electrochemistry, includes Li and electron transport through SEI, incorporates effects of Li viscoplasticity, includes SEI and electrolyte interface surface energy and evaluates crucial roles of these mechanistic effects on the continuously evolving anode surface due to the viscoplastic deformation of lithium. In the model, spatial current density evolves with the stress-induced potential across the deformed anode/SEI interface. We assume SEI as a homogeneous, artificial layer on the Li-anode, which allows the investigation of the mechanical and electrochemical properties of the SEI systematically. Subsequently, we solve a set of coupled electrochemistry and displacement equations within the SEI and anode domains. The model is implemented numerically by writing a user element subroutine in Abaqus/Standard. We conduct numerical simulations under various galvanostatic conditions and SEI properties and predict conditions for anode instability. We find that Li viscoplasticity is one of the key attributes that drives instability in the Li-anode and show that applying a soft artificial SEI layer on the Li-anode to minimize viscoplastic deformation can be an effective method. We also report the role of artificial SEI elasticity and thickness on anode stability. Selected stability maps are provided as a design aid for artificial SEI.

Figures (19)

• Figure 1: Finite element model setup for Li-anode and SEI: Li is plated and stripped at the interphase I
• Figure 2: Geometry of a Li anode with a 5$\mu m$ thick SEI
• Figure 3: Contour plots of (a) Normalized Li-ion concentration; (b) displacement in $\mu m$; (c) Stress-induced potential in J/mol plated at (left) $2.5~\textrm{mA}/{\textrm{cm}}^2$ for 1 hr; (right) plated at $0.5~\textrm{mA}/{\textrm{cm}}^2$ for 1 hr
• Figure 4: Contour plots of (a) Stress T11 in MPa; and (b) Plastic strain (left) plated at $2.5~\textrm{mA}/{\textrm{cm}}^2$ for 1 hr; (right) plated at $0.5~\textrm{mA}/{\textrm{cm}}^2$ for 1 hr
• Figure 5: Contour plots of vertical displacement in $\mu m$(left) and bending stress, T11 in MPa (right) for perturbation wavelengths 10, 100, and 500 $/ \mu m$ when plated at $0.5~\textrm{mA}/{\textrm{cm}}^2$ for 1 hour.