Thickness-Dependent Creep in Lithium Layers of All-Solid-State Batteries under Stack Pressures

Area of Science:

• Materials Science
• Electrochemistry
• Mechanical Engineering

Background:

• Stack pressure is crucial for optimizing lithium metal-solid-state electrolyte interfaces in all-solid-state lithium-metal batteries (ASSLBs).
• The accommodation of lithium metal under pressure is time-dependent and influenced by confinement.
• Understanding lithium mechanics under these conditions is vital for ASSLB performance.

Purpose of the Study:

• To investigate the mechanical behavior of pressed lithium layers under confined conditions using a continuum modeling framework.
• To analyze the impact of lithium layer thickness and aspect ratio on plastic accommodation.
• To determine the interplay between power-law creep and diffusion in lithium deformation.

Main Methods:

• Developed a continuum modeling framework coupling power-law creep and diffusion.
• Simulated the mechanical behavior of lithium layers with varying thicknesses and aspect ratios (D/H).
• Theoretically determined and validated a critical thickness for diffusion dominance over creep.

Main Results:

• Lateral shear stress from confinement significantly retards plastic accommodation in thinner lithium layers (higher D/H).
• The required stack pressure scales with (D/H)^{(1 + m)/m} for high D/H ratios.
• Diffusion enhances lithium deformability by reducing shear stress and promoting creep.

Conclusions:

• Findings provide fundamental insights into the mechanics of confined lithium.
• Quantitative guidelines are offered for the structural design and pressure management of ASSLBs.
• Optimizing lithium layer geometry and understanding diffusion-creep interplay are key for ASSLB development.