Heterogeneities Propagation and Homogenization Methods for Li Metal Anodes in Pouch Cells

Li metal batteries (LMBs) are promising candidates for next generation energy storage with the potential to reach 500 Wh/kg specific energy due to the use of high capacity Li metal anodes. Despite the high promise, Li metal anodes are unstable during cycling. The formation of detrimental microstructures, including excess solid electrolyte interphase (SEI), dendrites, and dead Li all introduce heterogeneities on the anode and compromise cell lifetime. Such heterogeneities originate from the native passivation layer and surface microstructures formed naturally after Li manufacturing and storage [1, 2]. As LMB cycles, the non-uniformities at the Li surface accumulate and propagate, eventually manifesting at the electrode and cell levels, causing uneven Li utilization [3] and cell-to-cell variations that will reduce consistency in battery manufacturing and hinder LMB commercialization.

In this presentation, we investigate the formation and propagation of non-uniformities on commercially available Li sheets used in Li-NMC811 and Li-SPAN (sulfurized polyacrylonitrile) pouch cells. We discover that local heterogeneities appear as early as when the Li anode is plated or stripped during cell formation process. The localized Li aggregation sites and pit holes distribute unevenly across the electrode active area and are the root cause of cell variations and failures. The heterogeneities are furthermore amplified under lean electrolyte conditions for realistic cells [4], in which uneven wetting and electrolyte deprivation on the anode accelerate cell degradation. To homogenize Li surface and enhance cell performance consistency, we introduce mechanical and chemical etching methods that remove the surface passivation layer and reveal the Li underneath. Moving forward, the methods for Li surface homogenization and evaluation of cell-to-cell consistency will establish a solid foundation for the commercialization of LMBs.


[1] Otto, Svenja-K., et al. "In-depth characterization of lithium-metal surfaces with XPS and ToF-SIMS: toward better understanding of the passivation layer." Chemistry of Materials 33.3 (2021): 859-867.
[2] Hatzell, Kelsey, et al. "Aligning lithium metal battery research and development across academia and industry." Joule (2024).
[3] Kim, Sangwook, et al. "Calendar life of lithium metal batteries: Accelerated aging and failure analysis." Energy Storage Materials 65 (2024): 103147.
[4] Niu, Chaojiang, et al. "Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries." Nature Energy 6.7 (2021): 723-732.