High‐Performance Mg–O₂ Batteries Enabled by Electrospinning PVDF‐HFP‐Based Quasi‐Solid‐State Polymer Electrolyte

Abstract This article reports a high‐performance rechargeable battery enabled by an electrospun quasi‐solid‐state electrolyte (E‐QSSE). The E‐QSSE, composed of Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP), Mg(NO 3 ) 2 salt, and Pyr 14 TFSI ionic liquid (IL), exhibits high Mg 2+ ion transport and interfacial stability. A unique sandwich structure coupling the E‐QSSE with a Ruthenium nanoparticles decorated multi‐walled carbon nanotubes (Ru/CNT) cathode catalyst on carbon paper significantly augments electrochemical reversibility. The optimized E‐QSSE with a 1:1 molar ratio of salt and IL achieves a high room temperature ionic conductivity of 6.39 mS cm −1 . The E‐QSSE's electrochemical stability window extends up to 3.95 V, showcasing its potential for high‐energy‐density applications. The Mg‐O 2 cell, with the optimized E‐QSSE, delivers 115 discharge/charge cycles at 100 mA g −1 , one of the longest reported cycle‐lives for secondary Mg‐O 2 batteries. The battery exhibits a maximum discharge capacity of 9305 mAh g −1 with 100% Coulombic efficiency. X‐ray photoelectron spectroscopy and absorption near‐edge structure analyses reveal MgO as the primary discharge product, with MgF 2 contributing to stable solid electrolyte interphase. This E‐QSSE design promotes efficient Mg 2+ ion migration and stable electrochemical reactions. This work advances the development of stable, high‐capacity Mg‐O 2 batteries and can open up avenues for quasi‐solid‐state electrolytes in post‐lithium metal‐air battery technologies.