On-demand capacity extraction through thermo-electrochemical hysteresis in metastable Li-Cu alloy

Metastable states provide unique opportunities to access functional materials inaccessible through conventional equilibrium pathways. Here, we employ this path dependency to enable safe storage and supplementation of capacity in lithium (Li) batteries, compensating for irreversible loss of Li caused by its high reactivity. We introduce a strategy of storing Li as a metastable Li-Cu alloy phase with characteristic thermo-electrochemical hysteresis—the phase is accessible only through a thermal process, inhibiting electrochemical re-alloying with Cu during cycling. The Li-Cu current collector (CC) demonstrates on-demand capacity extraction of up to 2 mAh cm⁻² for extended cycle life in Li batteries. The high extraction potential of the Li-Cu alloy (1.2 V vs. Li/Li⁺) allows intentional activation by a designed protocol while otherwise remaining inactive within the conventional operating window. This approach transforms CCs into a Li reservoir with on-demand capability via hysteretic pathways, offering a promising design platform for high-energy-density batteries.