Modeling the Mechanical and Electrochemical Response of All-Solid-State Lithium-Ion Batteries

All-solid-state rechargeable lithium-ion batteries have attracted much interest recently for applications of much larger scale than previous thin-film batteries.  The replacement of an organic liquid electrolyte with a non-flammable inorganic solid electrolyte (SE) may simplify battery design and improve safety and durability [2]. However, in all-solid cells, the battery life depends in large measure on the mechanical integrity of the composite system [1]. A suitable theory to identify the electro-chemo-mechanical limits of Li-ion batteries performance in realistic electrode-electrolyte configurations is therefore required. In this work, a fully coupled electro-chemo-mechanical model is developed to facilitate the mesoscale optimization of such composite microstructures.

A key development in all-solid-state batteries has been the discovery of solid electrolytes with high Li+  ion conductivity at room temperature comparable to that of organic liquid electrolytes [3, 4, 5]. These have been tested with numerous electrode active materials.The durability of a coherent solid-solid interface between electrode and electrolyte is likely to be an important consideration. Notwithstanding the several techniques investigated to increase the contact area at the interface [6], interface cohesion and its effects on the rate capability and the overall performance throughout the expected life cycles needs to be maintained.

In the present research, we develop a nonlinear continuum model able to account for the combined effects of Li diffusion and for the consequent volumetric expansion of the hosting material. The electrode and electrolyte are idealized as elastic materials with elastic properties varying with lithium concentration.  The complexity and the multi-physical nature of the problem require numerical modeling strategies and pose several challenges. To address this, we have established a computational framework based on large deformation kinematics and posed in a thermodynamically consistent fashion. The model is implemented in an in-house, object oriented C++ numerical code that incorporates three-dimensional finite element calculations. The numerical analysis allows for delamination at the interface between electrode particles and solid electrolyte. Crack formation and propagation is predicted by means of a cohesive zone model extended to include decreased Li flux across interfaces due to their loss of mechanical integrity.

Our simulations indicate trends of mechanical reliability of all-solid state batteries realized with some of the most promising solid electrolyte materials (e.g. Li2S-P2S5 [1], LIPON [3], garnet SE [7]), using mechanical properties available in literature. When physical values for the solid electrolyte’s mechanical behavior are not available, the simulations indicate trends of how mechanical reliability correlates with the battery design and operating conditions (i.e., charging rate).

Acknowledgments

The work was supported by the grant DE-SC0002633 funded by the U.S. Department of Energy, Office of Science.

Keywords 

Lithium ion batteries, All-solid-state batteries, Nonlinear continuum mechanics; Diffusion; Thermodynamics

References

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Figure 1: Simulation  of a composite all-solid Li-ion battery microstructure upon lithiation. The diffusion fronts (white lines) appear perturbed due to partial delamination of the interface between electrode particles and solid electrolyte.