Porous polymer electrolytes for long-cycle stable quasi-solid-state magnesium batteries

Abstract

A flexible porous polymer electrolyte (PPE) was creatively designed for quasi-solid magnesium battery. The MoS 2 /C//PPE//Mg battery exhibited high reversible capacity and unprecedentedly long cycling life. The development of applicable electrolytes is the key point for high-performance rechargeable magnesium batteries (RMBs). The use of liquid electrolyte is prone to safety problems caused by liquid electrolyte leakage. Polymer-based gel electrolytes with high ionic conductivity, great flexibility, easy processing, and high safety have been studied by many scholars in recent years. In this work, a novel porous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane is prepared by a phase inversion method. By immersing porous PVDF-HFP membranes in MgCl 2 -AlCl 3 / TEGDME (Tetraethylene glycol dimethyl ether) electrolytes, porous PVDF-HFP based electrolytes (PPEs) are formed. The PPE exhibits a high ionic conductivity (4.72 × 10 −4 S cm −1 , 25 °C), a high liquid electrolyte uptake of 162%, as well as a wide voltage window (3.1 V). The galvanostatic cycling test of Mg//Mg symmetric cell with PPE reveals that the reversible magnesium ion (Mg 2+ ) plating/stripping occurs at low overpotentials (~0.13 V). Excellent long cycle stability (65.5 mAh g −1 over 1700 cycles) is achieved for the quasi-solid-state RMB assembled with MoS 2 /C cathode and Mg anode. Compared with the liquid electrolyte, the PPE could effectively reduce the side reactions and make Mg 2+ plating/stripping more uniformly on the Mg electrode side. This strategy herein provides a new route to fabricate high-performance RMB through suitable cathode material and polymer electrolyte with excellent performance.