Surface Functionalization of Electrodes and Synthesis of Dual-Phase Solid Electrolytes for Structural Supercapacitors

Abstract

The interface between structural electrodes and solid electrolytes plays a key role in the electrical−mechanical properties of energy storage structures. Herein, we present a surface functionalization method to improve the ion conduction efficiency at the interface between a structural electrode and a solid electrolyte that consists of a bicontinuous network of epoxy and ionic liquid (IL). Composite supercapacitors made with this electrolyte and carbon fiber (CF) electrodes coated with manganese dioxide (MnO 2 ) demonstrate that treating the electrodes with the silane can increase the areal capacitance by 300% without degrading the tensile strength. The dual-phase electrolyte containing 40 wt % IL and 60 wt % epoxy exhibits the highest multifunctional performance, measured by the product of stiffness and ionic conductivity. The outstanding mechanical and energy storage properties demonstrate that the silane treatment of MnO 2 -coated CF fabric structural electrodes is a promising method for future high-performance structural composite supercapacitors.

A critical review of structural supercapacitors and outlook on future research challenges

“…There is a large body of work using WCF decorated with metal oxides or metal chalcogenides to imbue pseudocapacitance to the structural supercapacitor. The most widely used additive is manganese dioxide (MnO 2 ) [56,[65][66][67][68][69]. Carbon fibres decorated with MnO 2 nanowires in 1M Na 2 SO 4 liquid electrolyte gave an almost four-fold (41.3 F/g, normalised by active mass) improvement in capacitance over pristine WCFs [65].…”

“…The tensile performance of the device with the structural electrolyte was twice that with the 'semi-solid' electrolyte. WCF coated with MnO 2 and silane sizing in a structural electrolyte (epoxy/BMIMTFSI) achieved a capacitance (normalised by active mass) of 10.5 F/g and tensile moduli and strength of 14 GPa and 397 MPa, respectively [69]. Other approaches include using WCF decorated with NiCo nanowires (Fig.…”

“…Due to their wide usage in conventional composites, the structural phase in electrolytes synthesised using RIPS has mainly comprised of epoxy resin. The composition of the ion conducting phase has varied and has included ionic liquids (ILs) [69,[104][105][106][107], lithium salt solutions in organic solvents [108,109]; their combination [106,110] as well as other systems [111]. The addition of ILs to epoxy resin has resulted in electrolytes with the most promising combination of properties.…”

“…The addition of ILs to epoxy resin has resulted in electrolytes with the most promising combination of properties. An addition of 37% of BMIM-TFSI to epoxy has resulted in a structural electrolyte with a Young's modulus of 962 MPa and an ionic conductivity of 0.07 mS/cm [69]. The addition of a similar proportion (35%) of EMIM-TFSI to DGEBA led to a structural electrolyte with a slightly lower Young's modulus of 800 MPa but significantly higher ionic conductivity of 0.28 mS/cm [105].…”

Concepts and Emerging Trends for Structural Battery Electrolytes

“…[60] The ratio of the filler/matrix and the uniform distribution of the filler is important in securing a positive effect. Another approach that has proven effective in designing structural electrolytes while maintaining a desirable ionic conductivity is simultaneous copolymerization of robust structural motifs, [61,62] such as epoxy [24][25][26][27]63,64] or porous methacrylate polymer [12,16] with a high ion conducting phase, such as ionic liquid, to form a bi-continuous structural electrolyte system. Using this approach, the performance is highly dependent on the presence of a homogenous framework.…”