Multi-Scale Electrochemo-Mechanical Experiments on Thin Film Battery Materials

The application of a solid-electrolyte may enable the use of certain high energy density anodes like Li and Si and also circumvents the flammable liquid-electrolyte. However, all solid components introduce multiple solid-solid interfaces whose responses are strongly affected by the mechanical state of the region on both sides, which can be affected by a combination of applied stack pressure and cycling induced volumetric change1. Electrochemo-mechanical coupling (ECM) studies2 are a relatively new area for this society, especially with thin film structures,3 which provide high purity, uniformity, and controlled geometries for the reaction to take place. However, correctly interpreting ECM experimental results as well as explaining the fundamental failure mechanisms (i.e. cracking and dendrite propagation) requires careful experimental study of material mechanical properties and how electrochemical characteristics change with mechanical state4. In this work, we describe two experimental studies on sputter-deposited thin-film LixV2O5 electrodes, with a thickness of 1 µm on a Si wafer. A lateral cell design that has the two electrodes on a single plane on a substrate, is described to focus on a single electrode. An ionic liquid electrolyte (ILE) on the Si substrate is used instead of a solid electrolyte pellet to avoid high ohmic losses , and to focus on the mechanics of the LixV2O5. The ILE covers the two electrodes and serves as the ionic pathway. Lithium foil (or vapor-deposited Li metal) is placed on the wafer and serves as the Li source. The first study is conducted with a liquid electrolyte and compares the cell behaviors between stressed and unstressed states. An external mechanical load is applied to the whole electrode surface for a uniform force distribution. An important thermodynamic contribution of stress is the change in equilibrium potential, which can be measured as a function of applied stress on the electrode and may also affect charge transfer kinetics at the interface. The second experiment will focus on the composition modulated mechanical properties of LixV2O5 which is crucial for ECM modeling work. Here, we lithiate V2O5 electrodes to different amounts, remove the electrolyte to stop ionic transport, and then perform nanoindentation in an inert argon environment. The correlation between elastic moduli and x in LixV2O5 as well as the variation of equilibrium potential provide important parameters for building accurate ECM numerical models. Pasta, M., Armstrong, D., Brown, Z.L., Bu, J., Castell, M.R., Chen, P., Cocks, A., Corr, S.A., Cussen, E.J., Darnbrough, E., et al. (2020). 2020 roadmap on solid-state batteries. JPhys Energy 2, 032008. Wan, T.H., and Ciucci, F. (2020). Electro-chemo-mechanical modeling of solid-state batteries. Electrochim. Acta 331, 135355. Spencer Jolly, D., Ning, Z., Darnbrough, J.E., Kasemchainan, J., Hartley, G.O., Adamson, P., Armstrong, D.E.J., Marrow, J., and Bruce, P.G. (2020). Sodium/Na β″ Alumina Interface: Effect of Pressure on Voids. ACS Appl. Mater. Interfaces 12, 678–685. Cao, D., Sun, X., Li, Q., Natan, A., Xiang, P., and Zhu, H. (2020). Lithium Dendrite in All-Solid-State Batteries: Growth Mechanisms, Suppression Strategies, and Characterizations. Matter 3, 57–94.