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

The study establishes a unique ruthenium/carbon nanotube (Ru/CNT) cathode coupled with an electrospun quasi-solid-state electrolyte (E-QSSE), achieving 115 cycles, among the longest reported for secondary magnesium-oxygen (Mg–O₂) batteries. This sandwich structure that ensures stable electrochemical reactions and effective magnesium-ion transport between the anode and cathode.

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(NO₃)₂ salt, and Pyr₁₄TFSI ionic liquid (IL), exhibits high Mg²⁺ 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-O₂ 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-O₂ 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 MgF₂ contributing to stable solid electrolyte interphase. This E-QSSE design promotes efficient Mg²⁺ ion migration and stable electrochemical reactions. This work advances the development of stable, high-capacity Mg-O₂ batteries and can open up avenues for quasi-solid-state electrolytes in post-lithium metal-air battery technologies.