Ionic liquid integrated high-voltage polymer gel electrolyte to improve the capacitance and cyclic stability of supercapacitors

Abstract

With the rapidly increasing demand for the most promising electrical energy storage devices, supercapacitors (SCs) have attracted widespread interest due to their high capacity, specific power density and long cyclic performance. To date, symmetric electrodes made of various types of porous carbons such as activated carbon (AC), carbon nanofibers, carbon nanotubes (CNT), and graphene/reduced graphene oxide (rGO) are commonly used for commercial electrical double layer capacitors (EDLCs) or supercapacitors [1]. Electrolytes also play an important role for supercapacitor devices through their physical, thermal and electrochemical properties. Because of high ionic conductivity, simple processing, low cost and good interfacial (electrode/electrolyte) properties of aqueous electrolytes and organic liquid-based electrolytes have been widely used for SCs. However, lower voltage windows, lower cycle life, corrosion, leakage problem, flammability and safety issues limit their commercialization [2]. To address the above-mentioned issues, ionic liquids (ILs) integrated solid/semi-solid polymer electrolytes have attracted wide interest as an alternative electrolyte in electrochemical energy storage due to their wide potential windows (≥3V), high ionic conductivity (10−4Ω−1 cm−1 ), leakage free, low flammability, good thermal stability, flexibility, tunable chemical functionalities and self-healing capabilities [3,4]. Significant efforts have also been devoted to integrating various ionic liquids (ILs) into solid/semi-solid polymer electrolytes for emerging SCs. In this work, 1-Ethyl-3- Methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSI] ionic liquid embedded in Polypropylene Carbonate (PPC) and Polycarbonate (PC) based polymer gel electrolyte has been developed by entrapping the IL in the polymer network for activated carbon (AC) electrode-based pouch cell SC and laser induced graphene (LIG) electrode micro-supercapacitors (MSCs) applications. The electrochemical performance of this [EMIM][TFSI]/ PPC/PC polymer gel electrolyte has been evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) (Figure 1a), electrochemical impedance spectroscopy (EIS) and long cycle charge-discharge (CCD) analysis. Relying on the combined effect of IL, this novel semi-solid electrolyte improves the capacitance (0.94 mF/cm2 @ 2V), electrode/electrolyte interface compatibility, voltage windows (≥2.0V), ionic conductivity and long cycle stability (≥ 50000 cycles) making it a potential electrolyte for next-generation supercapacitors. Acknowledgment The authors A. Ray and B. Saruhan would like to acknowledge GRAPHERGIA (grant agreement No. 101120832), supported by the European Union’s Horizon Europe research and innovation programme, for financial support. References [1] W. Wu, S. Dong, X. Zhang, J. Hao, Chemical Engineering Journal 446 (2022) 137328. [2] S. Pan, M. Yao, J. Zhang, B. Li, C. Xing, X. Song, P. Su and H. Zhang, Frontiers in Chemistry 8 (2020) 261. [3] B. Saruhan and A. Ray, Materials Research Bulletin 180 (2024), 113052. [4] W. Chen, Z. Xing, Y. Wei, X. Zhang, Q. Zhang, Polymer 268 (2023) 125727.