Theoretical and Experimental Investigations into Composite Cathode Architectures for Solid-State Batteries

Abstract

Solid-state batteries (SSB) are promising technologies for high energy density storage for automotive applications. Materials selection, property optimizations, architecture design and effective component integration are key parameters for successful applications of SSB. Material families that can meet ion transport criteria comparable to the state-of-the-art liquid electrolytes have been identified for solid ion conductors[1]. Integration of these materials into a high-performance battery stack is still far from realization[2]. The primary limitation is the lack of fundamental understanding of the interplay between charge transfer kinetics and transport within the system, specifically at the electrode | electrolyte interfaces[3]. A key challenge with SSB is the low areal capacity and the long-term stability of high voltage cathodes with areal capacities excess of 5 mAh cm-2 required for techno-economic feasibility. However, current SSBs only employ cathodes with loadings up to 0.5-2 mAh cm-2. Poor cathode architecture, improper utilization and cathode degradation are key factors that contribute to low areal capacity. In this work, the authors discuss a theoretical modeling framework for establishing solid electrolyte packing around a primary particle. Subsequently, this local architecture is used to estimate upper-bounds of the cell-level energy density. The developed model suggests an order of magnitude variation in the particle size of active material and the solid electrolyte in the composite cathode to achieve effective packing. In addition, the model predictions will be validated by experimental investigation using NMC622 based composite cathodes with a PEO-LLZO hybrid solid electrolyte. Initial experimental results indicate that the differential particle sizing for the components of composite electrodes leads to denser composite cathodes.[1] A. Manthiram, X. Yu, S. Wang, Nat. Rev. Mater. 2017, 2.[2] S. Randau, D. A. Weber, O. Kötz, R. Koerver, P. Braun, A. Weber, E. Ivers-Tiffée, T. Adermann, J. Kulisch, W. G. Zeier, F. H. Richter, J. Janek, Nat. Energy 2020, 5, 259.[3] K. B. Hatzell, X. C. Chen, C. Cobb, N. P. Dasgupta, M. B. Dixit, L. E. Marbella, M. T. McDowell, P. Mukherjee, A. Verma, V. Viswanathan, A. Westover, W. G. Zeier, ACS Energy Lett. 2020, 5, 922. Figure 1