A sustainable seven-electron cascade battery via orchestrated gas-liquid-solid triphase redox reactions

The quest for high-energy-density batteries has spurred interest in multielectron chemistry beyond conventional two-electron reactions. Here, we report a cascade battery that synergistically integrates gas-phase (Cl₂ ↔ Cl^-), liquid-phase (Cu²⁺ ↔ Cu⁺), and solid-phase (S ↔ CuS ↔ Cu₂S) redox reactions within a deep eutectic solvent (DES) electrolyte. This unique gas-liquid-solid triphase coupling strategy unlocks a seven-electron transfer process. In particular, the chloride-rich DES electrolyte fundamentally alters the copper (Cu) redox thermodynamics, enabling a reversible liquid-phase Cu²⁺/Cu⁺ couple via the formation of stable [CuCl₃]^2- complexes, which prevents disproportionation. The resulting cascade cell delivers an ultrahigh specific capacity of 4426.4 milliampere hours per gram [based on sulfur (S)] and exceptional cycling stability (88.5% capacity retention after 2000 cycles at 10 C). Furthermore, a practical pouch cell configuration achieves a high operating voltage of 1.5 volts and a remarkable energy density of 6917 watt-hours per kilogram (based on S; 2767 watt-hours per kilogram based on the total mass of the cathode), substantially surpassing most aqueous S-based systems. Ultimately, this work underscores that the strategic integration of orchestrated gas-liquid-solid triphase chemistry transcends the capacity limits of conventional single-phase reactions, demonstrating a viable pathway toward a next-generation paradigm for ultrahigh-energy-density storage.