Degradation of lithium metal batteries due to dead lithium accumulation under ultrasound

Lithium metal batteries (LMBs) have emerged as promising alternatives to conventional lithium-ion batteries (LIBs) due to their superior capacity and energy density. However, practical applications are hindered by challenges such as dendritic lithium growth and the accumulation of dead lithium, which severely impact performance and safety. To address these issues, ultrasound has been proposed as a physical method to mitigate dendrite formation. In this study, we investigate the effects of real-time ultrasound application on LMBs and their subsequent electrochemical performance. Interestingly, our findings reveal that contrary to the intended effect, ultrasound accelerates the accumulation of dead lithium, worsening with continued cycling. Mechanical simulations indicate that the stress induced by ultrasound causes fragmentation and further dead lithium accumulation. This accumulation not only hinders reaction kinetics but also disrupts plating/stripping processes, leading to significant capacity retention issues. Consequently, ultrasound-treated cells exhibit higher over potential, lower coulombic efficiency, and faster capacity fade compared to untreated cells across half-cells, symmetric cells, and full cells. These results underscore that ultrasound negatively impacts the lifespan of LMBs, highlighting its critical adverse effects on the porous, dendritic structure of LMBs. Therefore, this provides a novel insight that these dynamics are crucial for optimizing the application of ultrasound in future LMBs technologies.