Lithium-Loss Mechanisms Driving Rate-Dependent Practicable Capacity in Metal Electrodes

The dependence of practicable lithium-storage capacity on the charge-discharge rate is crucial for deploying lithium-ion batteries in energy-intensive applications that demand high current densities and short recharge times. Under high-current operation, where most electrode materials fail, Ag stands out as a benchmark for systems where metal electrodes function both as an anode and current collector, increasing its practicable capacity at elevated rates. This performance arises from the rapid formation of γ-brass-type alloy phases, which enable intercalation-solid-solution-like lithium storage with fast kinetics, high capacity, and suppressed lithium loss even at high rates. This behavior is directly resolved by combining electrochemistry with ion beam analysis, which provides quantitative lithium concentration profiles and depth-resolved coulombic efficiency across current densities. The results reveal that Ag maintains efficient lithium utilization by minimizing irreversible trapping and surface-driven loss pathways. In contrast, Mg and Al exhibit pronounced rate-dependent irreversibility due to diffusion-limited lithiation and Li trapping in structural defects, while Cu shows the most severe degradation, dominated by porous, highly reactive Li plating. These findings establish Ag as a model system for high-rate metal electrodes and demonstrate that controlling lithiation behavior is key to enabling stable anode-free battery operation under demanding conditions.