  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.
