Autocatalytic Eutectic Gel Electrolyte for Quasi‐Solid State Zn‐Ion Cells

Hydrated eutectic electrolytes offer immense application potential for zinc‐ion batteries. However, the high reactivity between the electrodes and hydrated eutectic electrolytes causes dendrite growth and cathode dissolution owing to the unstable and adverse interface layer formation. Although gelation of the eutectic electrolyte can mitigate the reactivity, the traditional polymerization initiation strategy still leads to severe residual monomers and initiators. These highly chemically and electrochemically reactive residual monomers/initiators can further react with the electrodes, deteriorating the electrode interface and ultimately leading to battery performance degradation. Herein, we designed an initiator‐free acrylamide eutectogel electrolyte featuring autocatalysis, wherein polymerization is spontaneously driven by its own components, which reduces residual monomer and in situ converts residual acrylamide into a nitrogen‐containing protective interphase during cycling, thereby suppressing the hydrogen evolution reaction, harmful chlorinated by‐products, and cathode dissolution. As a result, the Zn||NaV 3 O 8 ·1.5H 2 O cells deliver a capacity of 172.7 mAh g −1 with 98.5% retention over 2450 cycles at 1.0 A g −1 , and can also cycle stably at −20°C and 65°C. This autocatalytic polymerization strategy holds great promise for other polymer monomers and Lewis acid salts, and may offer a scalable approach to developing long‐life quasi‐solid zinc batteries.