Photopolymerizable Ionogel with Healable Properties Based on Dioxaborolane Vitrimer Chemistry

Abstract

Ionogels are solid polymer gel networks loaded with ionic liquid (IL) percolating throughout each other, giving rise to ionically conducting solid electrolytes. They combine the mechanical properties of polymer networks with the ionic conductivity, non-volatility, and non-flammability of ILs. In the frame of their applications in electrochemical-based flexible electronics, ionogels are usually subjected to repeated deformation, making them susceptible to damage. It appears critical to devise a simple and effective strategy to improve their durability and lifespan by imparting them with healing ability through vitrimer chemistry. In this work, we report the original in situ synthesis of polythioether (PTE)-based vitrimer ionogels using fast photopolymerization through thiol-acrylate Michael addition. PTE-based vitrimer was prepared with a constant amount of the trithiol crosslinker and varied proportions of static dithiol spacers and dynamic chain extender BDB containing dynamic exchangeable boronic ester groups. The dynamic ionogels were prepared using 50 wt% of either 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide or 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate, both of which were selected for their high ionic conductivity. They are completely amorphous (Tg below −30 °C), suggesting they can be used at low temperatures. They are stretchable with an elongation at break around 60%, soft with Young’s modulus between 0.4 and 0.6 MPa, and they have high ionic conductivities for solid state electrolytes in the order of 10−4 S·cm−1 at room temperature. They display dynamic properties typical of the vitrimer network, such as stress relaxation and healing, retained despite the large quantity of IL. The design concept illustrated in this work further enlarges the library of vitrimer ionogels and could potentially open a new path for the development of more sustainable, flexible electrochemical-based electronics with extended service life through repair or reprocessing.

Healable Ionoelastomer Designed from Polymeric Ionic Liquid and Vitrimer Chemistry

“…The washability of the ionoelastomer has been considered for further use in possible applications such as smart electrochemical devices and wearables. Taking advantage of the “dry” nature of the synthesized ionoelastomers, with ions grafted directly on the polymer backbone, is especially promising since these ionic materials do not contain any dispersed salt ,, or ionic liquid − that can be extracted in the presence of a solvent. The washability of PIL-BDB25-PEGSH samples has been evaluated in immersing them in a classical dry-cleaning solvent (C 2 Cl 4 ) at ambient temperature for 1 h. PIL-BDB25-PEGSH25 demonstrates a very limited swelling ratio of 5.6 wt % and an ionic conductivity of 1.5 × 10 –6 S·cm –1 after the dry washing test, which is very similar to its ionic conductivity before immersion (1.7 × 10 –6 S·cm –1 ).…”

“…These examples of all-solid electrolytes, based on the dispersion of lithium salt in a polymer network, have an extended lifetime and improved cycling stability after deformation or even cracks. Ionically conducting materials with dynamic covalent bonds based on ionogels were also reported . Healable and reprocessable gelatin ionogels due to the reversible exchange of imine bonds have been designed for flexible supercapacitors .…”

“…Ionically conducting materials with dynamic covalent bonds based on ionogels were also reported. 42 Healable and reprocessable gelatin ionogels due to the reversible exchange of imine bonds have been designed for flexible supercapacitors. 43 These dynamic ionogels demonstrated an ionic conductivity higher than 1 mS·cm –1 at room temperature, thanks to the use of 1-ethyl-3-methylimidazolium acetate.…”

Catalyst-Free, Mechanically Robust, and Ion-Conductive Vitrimers for Self-Healing Ionogel Electrolytes

“…Such external catalysts, often Lewis or Bro̷nsted acids, strong bases, transition metals, or nucleophilic reagents, can result in catalyst aging, oxidation, or even degradation under charging and discharging-cycles. ,,− Therefore, there is a high demand for catalyst-free vitrimers in PE applications. Successful attempts have been made using disulfide bonds ,, and boric esters − for generating self-healing all-solid-state polymer electrolytes. , However, there are very few reports on vitrimer-based self-healable GPEs, placing the application of vitrimers into mechanically robust and self-healable GPEs that can withstand fragmentation during charging and discharging still as a major challenge.…”

Gels: Synthesis, Characterization and Applications in High Performance Chemistry

“…They display dynamic properties typical of the vitrimer network, such as stress relaxation and healing, retained despite the large quantity of IL. The design concept illustrated in this work further enlarges the library of vitrimer ionogels and could potentially open a new path for the development of more sustainable, flexible electrochemical-based electronics with extended service life through repair or reprocessing [ 13 ].…”