Reversible six-electron tellurium redox enabled by selenium-modulated hypervalent activation in aqueous sodium/zinc hybrid batteries

Aqueous hybrid sodium-ion batteries hold promise as next-generation electrochemical storage due to intrinsic safety and low cost. However, they are limited by specific energy and cycle lifespans. Here, we unlock multielectron tellurium redox chemistry in the aqueous system by coupling in situ hypervalent oxidation with selenium solid-solution modulation. In a sodium acetate electrolyte, the Te₄O₉^2- ↔ Te ↔ Te^2- sequence enables a highly reversible six-electron reaction distinct from conventional tellurium chemistry. Selenium withdraws electron density from neighbouring tellurium, promotes oxidation, stabilizes high-valence intermediates and accelerates Na⁺ diffusion. As a result, Te_0.85Se_0.15 delivers 95.8% utilization of the theoretical six-electron capacity (~1217 mAh g^-1 at 0.1 A g^-1) and operates for 2000 cycles at 10 A g^-1. Furthermore, a pouch cell achieves an active-material-level specific energy of approximately 114.3 Wh kg^-1 at 0.33 A g^-1. These findings outline a practical route to high-energy, high-power, and intrinsically safe aqueous sodium/zinc hybrid batteries for grid-scale deployment.