Electrochemical-Mechanical Coupled Modeling of Thin-Film Solid-State Energy Storage Devices

The application of solid electrolytes not only provides opportunities to solve the safety issues of lithium-ion batteries with flammable organic electrolytes but also enables the application of thin-film techniques in battery fabrication processes that can develop high surface-to-volume ratio structures which may further improve the performance of solid-state batteries [1]. Thin-film structures are potentially good candidates for fundamental electrochemistry studies considering their high purity and structural control. However, the cyclic volume change of an all-solid-state cell may introduce significant stresses, altering thermodynamics, kinetics and even induce mechanical degradation and failure [2]. Due to the difficulties in conducting mechanics-related experiments with thin-film batteries, developing multi-physics-based models that couple electrochemistry and solid mechanics will not only help in understanding how mechanics affects battery performance mechanisms but can also provide useful information for fabrication and experiment design strategies. <br/>The present work incorporates intercalation-induced stress and stress-driven diffusion to the standard battery FEA model in COMSOL [3]. We choose to simulate an AAO 3D thin-film battery (TiO₂/LiPON/V₂O₅) as a representative and experimentally achievable device that highlights the impact of electrochemical-mechanical coupling (ECM) on battery performance and potential device failure modes. Both electrode regions are modeled as a continuum intercalation-type material with constant expansion rates as a function of lithium content. The single-ion conductor assumption is utilized to annihilate composition variations in the solid electrolyte region. Simulation results show a significant amount of stress can be introduced by joint influences from lithium transport-induced volume expansion tendency and mechanical boundary conditions. The stress gradient provides an additional transport mechanism to redistribute the lithium content to a more uniform pattern which improves the capacity behavior. However, the induced stress on the interface could lead to mechanical-related degradation mechanisms including interfacial decohesion and yielding or cracking of the solid electrolytes. The induced stress will also change the thermodynamic state of the lithium atom along the interface which has been incorporated into the Butler-Volmer equation to capture mechanics-modified interfacial kinetics. This study shows multiple electrochemical-mechanical coupling mechanisms have collective influences on the battery performance and structural integrity. The consistency and inheritance of concepts and assumptions from classic electrochemistry formulation greatly reduces the gaps between experimental and simulation works.<br/> <br/><b>References: </b><br/>[1] A. Talin et al., “Fabrication, Testing, and Simulation of All-Solid-State Three-Dimensional Li-Ion Batteries,” ACS Appl. Mater. Interfaces, vol. 8, no. 47, pp. 32385–32391, Nov. 2016, doi: 10.1021/acsami.6b12244.<br/>[2] Y. Song, B. Bhargava, D. M. Stewart, A. A. Talin, G. W. Rubloff, and P. Albertus, “Electrochemical-mechanical coupling measurements,” Joule, vol. 7, no. 4, pp. 652–674, Apr. 2023, doi: 10.1016/j.joule.2023.03.001. <br/>[3] X. Zhang, W. Shyy, and A. M. Sastry, “Numerical Simulation of Intercalation-Induced Stress in Li-Ion Battery Electrode Particles,” J. Electrochem. Soc., vol. 154, no. 10, p. A910, Jul. 2007, doi: 10.1149/1.2759840.