Submolecular Selenium Enables Low‐Pressure and Recyclable All‐Solid‐State Li–Se Batteries

All‐solid‐state lithium‐selenium (Li–Se) batteries offer high energy density and intrinsic safety, but their practical deployment is hindered by sluggish solid‐state redox kinetics, large volume fluctuations, and unstable solid‐solid interfaces, particularly under low stack pressure. Here we report a submolecular Se x cathode by converting crystalline cyclo‐Se 8 into amorphous single‐atom and short‐chain Se (Se x , x < 4) species anchored on graphene (Se x @G), which increases the electronic conductivity from 6.3 × 10 −5 to 13 S cm −1 and Li + diffusivity from 1.7 × 10 −14 to 2.0 × 10 −11 cm 2 s −1 . Meanwhile, a Li 2 O‐nanoshell‐modified sulfide solid electrolyte is designed to stabilize the interface against both Li metal and Se cathode. As a result, all‐solid‐state Li–Se batteries deliver the theoretical capacity of 673 mAh g −1 at 0.1 C and retain 86% capacity over 2800 cycles at 3 C under 8 MPa, with stable operation down to −30°C. All‐solid‐state Li–Se pouch cells further achieve an energy density of 420 Wh kg −1 and 94% capacity retention after 300 cycles under 2.5 MPa. Post‐mortem analysis reveals that the submolecular Se x species are not only structurally preserved but also recyclable after electrochemical cycling within the solid‐state reaction environment. This work establishes submolecular chalcogen chemistry as a new design paradigm for low‐pressure, recyclable, and high‐energy all‐solid‐state batteries.