Key Findings
A study conducted by researchers from Argonne National Laboratory, the University of Wisconsin-Madison, the National Laboratory of the Rockies, and the University of Chicago Pritzker School of Molecular Engineering reveals that silicon anodes drive calendar aging in lithium-ion batteries. By monitoring three-electrode cells with NMC811 cathodes and milled silicon anodes over 11 months of open-circuit storage, the team determined that degradation is caused by interfacial reactions and the resulting loss of cyclable lithium, not by the extensive loss of active electrode material.
Technical Details
The researchers utilized a combination of capacity measurements, voltage-relaxation analysis, impedance evaluation, and post-test characterization to isolate the contributions of each electrode. The results showed that the silicon anode governed the full cell’s discharge impedance and voltage relaxation throughout the aging process. As parasitic reactions consumed the lithium inventory, the operating windows of both electrodes shifted, forcing the NMC811 cathode into higher states of delithiation to compensate for the lithium lost at the silicon interface.
Voltage-relaxation analysis served as a key non-destructive diagnostic tool, identifying two kinetically distinct equilibration processes. The longer-timescale process evolved systematically during each month of storage and partially reset after reference performance test (RPT) cycling, indicating a strong dependence on the silicon electrode’s electrochemical history.
Background & Context
Calendar aging occurs due to parasitic side reactions that continue inside a battery even when no current flows. These reactions erode the energy a cell can deliver by consuming cyclable lithium and altering electrode behavior. Post-test characterization confirmed that while the NMC811 and Si electrodes showed only minor capacity loss, there was a significant increase in anode impedance, pointing to the evolution of the solid electrolyte interphase (SEI) and the silicon interfacial environment.
Significance & Outlook
The findings, published in Frontiers in Batteries and Electrochemistry, emphasize that the silent chemistry occurring at the silicon interface during storage is the primary factor limiting capacity retention over time for silicon-containing cells.
Source: https://bioengineer.org/silicon-anode-drives-calendar-aging-in-lithium-ion-cells-study-finds/
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