An Ionic Liquid/Poly(vinylidene fluoride‐co‐hexafluoropropylene) Gel‐Polymer Electrolyte with a Compatible Interface for Sodium‐Based Batteries

Abstract

Ionic liquid gel-polymer electrolytes (GPEs) have attracted increasing attention, owing to their merits of safety and reliability. However, the high viscosity of ionic liquid requires better transmission channels for the polymer. Exploration of ionic liquid GPEs with high ionic conductivity and excellent transmission channels is a possible strategy to optimize the practicability of sodium-based technology. A flexible GPE with high ionic conductivity and excellent transmission channels is synthesized with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDFÀ HFP) as the base material blended with the waterinsoluble ionic liquid N-methyl-N-butyl piperidine difluorome-thylimide ([PP 14 ][TFSI]) by using a phase-inversion technique. A polydopamine coating is then introduced into the GPE to improve wettability and compatibility. The thermal decomposition temperature of the prepared gel-polymer films is greater than 450°C. Our activated GPE achieves good safety, a wide electrochemical window, and high ionic conductivity. When testing a sodium-ion battery with Prussian blue as the cathode, the batteries show good cycling performance. Our results suggest that the as-prepared GPE can be efficiently and safely used in sodium-ion batteries.[a] Dr. photoelectron spectra (XPS) using PHI Quantera-II scanning XPS microprobe. The contact angle of the membranes were conducted on a JY-82B contact angle apparatus. Electrochemical CharacterizationThe galvanostatic charge-discharge tests were performed on a LAND cycler (Wuhan Kingnuo Electronic Co.) at room temperature. Linear sweep voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy were carried out on a CHI 660e electrochemical workstation (ChenHua Instruments Co.).

Recent Advances and Perspectives on the Polymer Electrolytes for Sodium/Potassium‐Ion Batteries

“…Ionic liquids, with the merits of nonflammability, high ionic conductivity, and good electrochemical stability, are suitable plasticizers for preparing GPEs. [ 137,145–148 ] Pyrrolidinium‐based ionic liquids combining with TFSI − or FSI − were widely applied owing to their high antireducibility. It has been demonstrated that the Pyr 13 TFSI or Pyr 13 FSI ionic liquids could suppress the crystallization of PEO, [ 149–152 ] which had a distinct plasticizing effect on the polymer, but the plasticizing mechanism was seldom discussed.…”

“…As a PE matrix, it exhibits excellent properties, including high mechanical strength, electrochemical stability, thermal stability, etc. [ 147,153–155 ] Lately, Janakiraman et al. [ 156 ] prepared a PVDF‐based GPE for SIBs by electrospinning method with a nanofibers structure, which exhibited a wide voltage window (0–5 V vs Na + /Na) and high ionic conductivity of 1.08 × 10 −3 S cm −1 .…”

Gel–Polymer Electrolytes Based on Poly(Ionic Liquid)/Ionic Liquid Networks

“…A particular advantage of IL-based GPEs is the high thermal stabilities of the membranes that can be obtained. For example, Xie and co-workers incorporated the IL N-methyl-N-butylpiperidine difluoromethylimide into poly­(vinylidene fluoride-co-hexafluoropropylene) membranes to make GPEs for Na-ion batteries that were thermally stable up to 450 °C . Zheng and co-workers formed poly­(vinyl alcohol)-based membranes containing ammonium-based ILs for use as proton exchange membranes, which were stable up to 160 °C, considerably higher than that achievable using conventional membranes (∼80 °C) .…”

“…For example, Xie and co-workers incorporated the IL N-methyl-Nbutylpiperidine difluoromethylimide into poly(vinylidene fluoride-co-hexafluoropropylene) membranes to make GPEs for Na-ion batteries that were thermally stable up to 450 °C. 13 Zheng and co-workers formed poly(vinyl alcohol)-based membranes containing ammonium-based ILs for use as proton exchange membranes, which were stable up to 160 °C, considerably higher than that achievable using conventional membranes (∼80 °C). 14 Langevin and co-workers synthesized proton-conductive GPEs that could operate at 130 °C, by incorporating triethylmethylammonium trifluoromethanesulfonate into polyimide membranes.…”

Zwitterionic Copolymer-Supported Ionogel Electrolytes Featuring a Sodium Salt/Ionic Liquid Solution

“…However, safety concerns can arise from the flammability of such organic solvents and the potential hazards of electrolyte leakage. One of the most promising methods to mitigate such safety risks would be to adopt a nonflammable liquid electrolyte or a solid-state electrolyte for SIBs. − …”