Solid-state batteries use solid-state electrolyte (SE); they are among the future energy technologies due to their promise of high capacity and high thermal stability. However, poor physical and electrical contact at the anode-SE-cathode interfaces can cause high interfacial resistance. Both space and time domains are multiscale for the multifield mechano-electrochemical problems of solid-state batteries.
Computational Interfacial Mechanics and Electrochemical Kinetics for Solid-State Lithium Batteries
The development of solid-state Li batteries has encountered a number of problems due to the complex contact conditions and imperfect interface between the Li metal and solid-state electrolyte (SSE). Professor Wang pointed out that the key issues are interfacial resistance, Li yield, and, Li creep in the presence and change of surface roughness in chemomechano-electrical field. Professor Wang’s group has developed the first 3D, multifield, time-evolution, rough-surface contact model for all solid-state Li-metal battery interfaces in charge-discharge cycling under stacking pressure by using the continuous convolution and FFT algorithm for spatial scale extension, together with the Laplace transform for time-domain charging/discharging simulations. The model can simulate charge/discharge for multiple hours with surface roughness tracking under a stacking pressure, The model considers the surface roughness of the Li and the SSE, Li elastoplasticity, Li creep, and the Li metal plating/stripping processes. It has been validated by simulating several a set of published data for the variation of electrical potential during 60 hrs of stripping under varying pressure. The simulation using this model reveals that the Li-SSE projected contact area depends primarily on the ratio between stack pressure and Li yield strength. This work is the first that reveals the mechanisms how a proper stacking pressure improves the Li-SSE interface and prevents Li dendrite/void via asperity elastoplastic deformation and creep during charge/discharge cycling. It also found that there is a competition between Li plating/stripping and creep, where the latter gradually results in a more conformal Li-SE contact and more uniform contact stresses. The results suggest that the effective yield strength of the Li used in these experiments is between 14 and 18 MPa, with the medium at 16 MPa, well agreeing with recently published experimental measurement results. The research on symmetric cells also found that a ceramic electrolyte needs P>10~12.5 MPa, a polymer electrolyte needs P>2 MPa, and the LLZO-polymer composite electrolyte needs P> 1~2 MPa to maintain stable charge/discharge and high ionic conductivity. This model has also been used to determine the hardness, or yield strength, of the Li thin film without conducting a mechanical test like indentation. A method for determining the Li-SSE interfacial resistance is suggested.
Related publications
- Zhang, X., Wang, Q., Harrison, K. L., Roberts, S. A, and Harris, S. J., 2020, “Pressure-Driven Interface Evolution in Solid State Lithium Metal Batteries,” Cell Reports Physical Science, Vol. 1 (2), 100012, https://doi.org/10.1016/j.xcrp.2019.100012.
- Zhang, X., Wang, Q., Harrison, K., Roberts, S., Harris, S. J., 2019, “Rethinking How External Pressure Can Suppress Dendrites in Lithium Metal Batteries,” Journal of the Electrochemical Society, Vol. 166, pp. A3639-A3652. https://iopscience.iop.org/article/10.1149/2.0701914jes
- Zhao, L., Wang, Q., Zhang, X., Hatzell, K., Zaman, W., Martin, T., Wang, Z., 2022, “Laplace-Fourier Transform Solution to the Electrochemical Kinetics of a Symmetric Lithium Cell Affected by Interface Conformity,” Journal of Power Sources, Vol. 531, 231305. https://authors.elsevier.com/a/1eoEF1M7w0X8SE
- Zaman, W., Zhao, L., Martin, T., Zhang, X., Wang, Z., Wang, Q., Harris, S., and Hatzell, 2023, “Temperature and Pressure Impacts on Unrecoverable Voids in Li 2 Metal Solid-State Batteries,” ACS Applied Materials and Interfaces, https://doi.org/10.1021/acsami.3c05886
Computational Interfacial Mechanics and Electrochemical Kinetics for Solid-State Sodium Batteries
All-solid-state batteries using an alkali metal anode and a solid-state electrolyte face several problems due to poor physical and electrical contact. The mechanical properties of Na metal are different from those of Li metal, leading to differences in the mechanisms of the pressure-dependent interface evolution. This work has resulted a three-dimensional time-dependent model for tracking the evolution of interfaces formed between Na metal and Na-β″-alumina SE. The results show that Na metal contacts more conformally with the SE, providing a lower interfacial resistance, compared with Li metal, assuming equal resistance due to contamination. The differences are due more to contact elastoplasticity than to differences in metal creep effects. The data reveal the effective hardness of Na in the Na-SE batteries to be 15 MPa. The results further indicate that the pressure dependence of void suppression is dominated by contact elastoplasticity.
Related publication
Zhang, X., Wang, Q., Peng, B., and Wu, Y., 2021, “Pressure-Driven and Creep-Enabled Interface Evolution in Sodium Metal Batteries,” ACS Applied Materials and Interfaces, Vol. 13, pp. 26533−26541.
