Revealing the Link between Morphological Heterogeneity and Reaction Behavior of Cathode in Solid-State Batteries

Abstract

Structural heterogeneity within solid-state electrodes can have a significant impact on material utilization and reaction rates. This reaction heterogeneity is greater in solid state systems in comparison to conventional liquid electrolytes because it requires exquisite solid-solid contact between the active energy storage materials and the solid ion conducting phase (e.g. solid electrolyte) [1]. Electrode reaction behaviors encompass electrochemical lithiation and delithiation dynamics and chemo-mechanical processes such as volume change and fracture [2]. Understanding the connection between structural heterogeneity and reaction behavior is crucial for understanding degradation mechanisms and optimizing solid state battery architectures. Herein, we examine the implications of reaction heterogeneity in an additive-free, crystallographically textured electroplated lithium cobalt oxide (LCO) cathode [3]. The electroplated dense cathode alleviates the need for any solid electrolyte material in the cathode. A diverse set of synchrotron-based operando and ex situ experiments are combined with modeling to uncover the relationship between structural heterogeneity and reaction behavior. Operando energy dispersive X-ray diffraction and ex situ 3D XANES are used to identify reaction heterogeneity and X-ray nanotomography is used to probe nano-scale structural heterogeneity. Nanoindentation is utilized to determine the mechanical properties of LCO. To validate the results, we combine these experimental results with transport and mechanics modeling. Through this comprehensive characterization approach, we confirm that the reaction behavior of cathode in our model is mainly determined by the morphological heterogeneity rather than the Li diffusion within the electrode. Structural heterogeneity causes localized high stress and leads to fracture, which in turn limit the full utilization of the cathode. Reference [1] Jung, S.H., Kim, U.H., Kim, J.H., Jun, S., Yoon, C.S., Jung, Y.S. and Sun, Y.K., 2020. Ni‐rich layered cathode materials with electrochemo‐mechanically compliant microstructures for all‐solid‐state Li batteries. Advanced Energy Materials, 10(6), p.1903360.[2] Liu, X., Zheng, B., Zhao, J., Zhao, W., Liang, Z., Su, Y., Xie, C., Zhou, K., Xiang, Y., Zhu, J. and Wang, H., 2021. Electrochemo‐mechanical effects on structural integrity of Ni‐rich cathodes with different microstructures in all solid‐state batteries. Advanced Energy Materials, 11(8), p.2003583.[3] Zahiri, B., Patra, A., Kiggins, C., Yong, A.X.B., Ertekin, E., Cook, J.B. and Braun, P.V., 2021. Revealing the role of the cathode–electrolyte interface on solid-state batteries. Nature Materials, 20(10), pp.1392-1400. Figure 1