Deciphering the Impact of the Active Lithium Reservoir in Anode-Free Pouch Cells

Anode-free batteries, which revolutionize energy storage by discarding traditional anodes in favor of copper foil to plate lithium directly from the cathode, offer increased energy densities and better safety than conventional lithium metal cells. However, their advantage is tempered by a significantly reduced cycle life, attributed to lithium loss through parasitic reactions. Comprehending the lithium inventory evolution under diverse conditions is vital for developing strategies to improve their performance. Herein, using coulometry, titration gas chromatography, and cryogenic scanning electron microscopy, we analyze the evolution of active and inactive lithium in NMC622||Cu pouch cells. Our results reveal the mechanism of lithium reservoir formation due to cathode irreversibility and its subsequent impact on cell performance across various electrolytes. Our findings not only highlight the significance of the lithium reservoir for anode-free cells' cycle life but also explore its modulation through charge/discharge rates, offering new opportunities to understand and enhance anode-free cells' cycle life.