The Effect of Mechanical State on the Equilibrium Potential of Alkali Metal/Ceramic Single‐Ion Conductor Systems

Abstract

The relationship between mechanical stress states and interfacial electrochemical thermodynamics of Li metal/Li6.5La3Zr1.5Ta0.5O12 and Na metal/Na‐β”‐Al2O3 systems are examined in two experimental configurations with an applied uniaxial load; the solid electrolytes are pellets and the metal electrodes high‐aspect‐ratio electrodes. The experimental results demonstrate that 1) the change in equilibrium potential at the metal/electrolyte interface, when stress is applied to the metal electrode, is linearly proportional to the molar volume of the metal electrode, and 2) the mechanical stress in the electrolyte has a negligible effect on the equilibrium potential for an experimental setup in which the electrolyte is stressed and the electrode is left unstressed. Solid mechanics modeling of a metal electrode on a solid electrolyte pellet indicates that pressure and normal stress are within ≈0.5 MPa of each other for the high aspect ratio (≈1:100 thickness:diameter in our study) Li metal electrodes under loads that exceed yield conditions. This work should aid in advancing the quantitative understanding of alkali metal dendrite formation within incipient cracks and their subsequent growth, and pore formation upon stripping, both situations where properly accounting for the impact of mechanical state on the equilibrium potential is of critical importance for calculating the current distribution.

Multi‐Physical Field Simulation: A Powerful Tool for Accelerating Exploration of High‐Energy‐Density Rechargeable Lithium Batteries

“…Besides the instinct stress evolution of Li metal along with the electrodeposition processing, the extra stress can also come from SEI film. The stress evolution inside the Li metal can also impact the electrochemical reaction kinetics of Li metal, which can be given as: [ 43 ] $$$$\begin{equation}{U}_{{\mathrm{eq}}} = \frac{1}{F}\ \left( {\Delta {G}_{{\mathrm{Ref}}} + {{{\Omega}}}_{{\mathrm{Li}}}{\sigma }^M + {{{\Omega}}}_ + {p}^ + } \right)\end{equation}$$$$with electrochemical reaction equilibrium potential ( U eq ), reference state Gibbs free energy difference between the Li anode and the electrolyte (Δ G Ref ), Faraday's constant partial molar volume ( F ), normal stress (σ M ), pressure ( p + ). When the stress relaxation caused by material yielding is not considered, the change in stress (1.0–100 MPa) can cause a shift in equilibrium potential of 0.1–10 mV, which in turn affects the speed of electrochemical kinetics.…”

“…Besides the instinct stress evolution of Li metal along with the electrodeposition processing, the extra stress can also come from SEI film. The stress evolution inside the Li metal can also impact the electrochemical reaction kinetics of Li metal, which can be given as: [43] U eq = 1 F…”

Progress and Perspective of Controlling Li Dendrites Growth in All‐Solid‐State Li Metal Batteries via External Physical Fields

“…The molecular dynamics calculations conducted by them showed that even the application of very high residual compressive stresses had only a small impact on the kinetics of Li + ion transport, which was experimentally validated by a recent study. [ 146 ] Ultimately, they recommended that although several commercial methods can be employed to introduce compressive residual stresses, ion implantation appears to be the most suitable approach for achieving this goal, as it may provide a novel path for creating controllable, high‐performance, and mechanically stable SEs.…”

Vertically Heterostructured Solid Electrolytes for Lithium Metal Batteries

“…The mechanical pressure applied to the inorganic solid electrolytes plays a role in maintaining the close interface contact, and in the meantime, affects the decomposition pathway and the electrochemical stability of the inorganic solid electrolytes, [ 21c,36,122 ] as discussed in Section 2. Thus, the origin of the wide stability induced by the applied pressure is summarized: 1) minimized exposed surface that is vulnerable to chemical and electrochemical attack; 2) mechanically induced kinetical stability by the curbed ionic interdiffusion among the decomposition zones; 3) reversible decomposition via an indirect pathway.…”