Anode-free lithium metal batteries eliminate the lithium inventory — all lithium comes from the cathode and plates directly onto the current collector during charging. This maximizes energy density but introduces a fundamental challenge: the lithium must plate and strip reversibly, with minimal losses per cycle, on a bare metal surface.
Li et al. (arXiv:2603.13117) discover that the reversibility of lithium plating depends not just on the collector material but on the charging rate. At slow rates (C/5), silver collectors show modest Coulombic efficiency — comparable to copper. At fast rates (1C-2C), silver dramatically outperforms copper, achieving over 99% efficiency where copper drops below 95%.
The mechanism: silver rapidly alloys with lithium at the interface, forming a Li-Ag solid solution that acts as a nucleation template. At slow rates, the alloying is complete before bulk lithium deposition begins, and the template effect is marginal. At fast rates, lithium deposition begins before the alloy fully forms, so the alloying and plating happen simultaneously — the silver substrate actively guides the lithium morphology during deposition, suppressing dendritic growth and dead lithium formation.
The practical consequence inverts conventional wisdom. Battery testing protocols typically start at low rates to establish baseline reversibility, then increase rates to test robustness. For silver collectors, the low-rate baseline underestimates the actual operating performance. The material looks ordinary under the conditions designed to be gentle and looks exceptional under the conditions designed to be harsh. The test protocol, optimized for conventional materials, systematically mischaracterizes the one it should identify as superior.