The Impact of the Interface Layer on Li Plating and Stripping Morphology

A reversible Li-metal electrode, paired with a solid electrolyte, is critical for attaining higher energy density and safer batteries beyond the current lithium-ion cells. Multiple interface design strategies are explored by multiscale electro-chem-mechanical coupled models.
To block lithium filament growth into the solid electrolytes, we introduced residual in-plane compressive stresses at the surface of the solid electrolyte by exchanging lithium ions (Li⁺) with larger isovalent ions such as Na⁺, Ag⁺, and K⁺. A multiscale modeling approach was developed to optimize the macroscopic compressive stress due to the ion-exchange species, concentration, and depth profile based on density function theory (DFT) and molecular dynamics (MD) computed chemical strain and diffusion coefficients, respectively. Among the isovalent dopants, the Ag ion-exchanged lithium lanthanum zirconium oxide (LLZO) is shown to induce compressive stress and improve the critical current density (CCD) in symmetric Li cells.
Comparing the plating, a stable stripping process may be even harder to attain as the stripping process will remove Li-atoms from the surface. Here, we capture the mechanisms occurring at multiple length- and time- scales, i.e., interface interactions, vacancy hopping, and plastic deformation, by integrating DFT simulations, kinetic Monte Carlo (KMC), and continuum finite element method (FEM). By assuming the self-affine nature of multiscale contacts, we predict the steady-state contact area as a function of stripping current density, interface wettability, and stack pressure. We further define a “tolerable steady-state” contact area loss for maintaining stable stripping as estimated at 20 %, corresponding to a 10 % increase in overpotential. We demonstrate that a lithiophilic interface requires less stack pressure to constrain contact loss within the tolerance. The modeling results agree with experiments on the impact of stack pressure quantitatively, while the discrepancy in stripping rate sensitivity is attributed to ignoring interface degradations in our simulations.