Synthesizing a Gel Polymer Electrolyte for Supercapacitors, Assembling a Supercapacitor Using a Coin Cell, and Measuring Gel Electrolyte Performance
Summary
We present a protocol to test the electrochemical and physical properties of a supercapacitor gel polymer electrolyte using a coin cell.
Abstract
Supercapacitors (SC) have attracted attention as energy storage devices due to their high density and long cycle performance. SCs used in devices operating in stretchable systems require stretchable electrolytes. Gel polymer electrolytes (GPEs) are an ideal replacement for liquid electrolytes. Polyvinyl alcohol (PVA) and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) have been widely applied as a polymer-matrix-based electrolytes for supercapacitors because of their low cost, chemically stable, wide operating temperature range, and high ionic conductivities. Herein, we describe the procedures for (1) synthesizing a gel polymer electrolyte with PVA and PVDF-HFP, (2) measuring the electrochemical stability of the gel polymer electrolytes by cyclic voltammetry (CV), (3) measuring the ionic conductivity of the gel polymer electrolytes by electrochemical impedance spectroscopy (EIS), (4) assembling symmetric coin cells using activated carbon (AC) electrodes with the PVA- and PVDF-HFP-based gel polymer electrolytes, and (5) evaluating the electrochemical performance using galvanostatic charge-discharge analysis (GCD) and CV at 25 °C. Additionally, we describe the challenges and insights gained from these experiments.
Introduction
Flexible SCs have grown rapidly in recent years for the fabrication of electronics with stretchable displays and wearable energy devices. Flexible SCs typically consist of flexible electrodes1, separators2, and the electrolyte3 in a flexible assembly. Therefore, GPEs are the most effective structure owing to their flexibility4, separator-free nature, relatively high ionic conductivity5, and thin-film forming ability6.
To prepare the polymer matrices of GPEs, materials such as polymethylmethacrylate (PMMA), PVDF-HFP, and PVA have been developed in recent years. PVA and PVDF-HFP have especially been widely applied as polymer-matrix-based electrolytes for SCs due to their low cost, chemically stable, wide operating temperature range, and high ionic conductivities at room temperature (RT).
Herein, we describe a synthetic method for two representative polymer-matrix materials-PVA7 and PVDF-HFP-and the electrochemical characterization of the polymer-matrix material-based gel electrolyte. In summary, we illustrate the general synthesis, material processing methods, and performance evaluation methods employed to fabricate stretchable SCs.
For application in flexible SCs, polymer electrolytes should exhibit the following properties: (1) high ionic conductivity at ambient temperature, (2) high chemical and electrochemical stability, (3) good mechanical properties of dimensional stability, and (4) sufficient thin film processability. These features were confirmed using EIS, CV, and tensile tests. The EIS and CV measurements were conducted using a coin cell. First, the ionic conductivity of the polymer-matrix-based electrolyte was estimated according to the equation using impedance. Second, the chemical and electrochemical stabilities of the polymer-matrix-based electrolyte were estimated by the CV and GCD tests. The stabilities of the polymer-matrix-based electrolytes were demonstrated by controlling the voltage range tested by the CV. Third, the mechanical properties of the polymer-matrix-based electrolytes were evaluated by conducting tensile tests.
A coin cell was fabricated using PVA- and PVDF-HFP polymer-matrix-based electrolytes with AC symmetric cells. The supercapacitor performances of the two different coin cell supercapacitors were evaluated at 25 °C. Because this work mainly involves PVA- and PVDF-HFP polymer-matrix-based electrolytes, the remainder of this paper focuses on these electrolytes. The detailed procedures of these experiments, difficulties in execution, and insights gained from these experiments are described as below.
Protocol
Representative Results
Discussion
Our approach for developing stretchable SCs involved the synthesis of GPEs and their subsequent evaluation in prototypical coin cells. In particular, the PVA- and PVDF-HFP-based GPEs were tested in coin cells with symmetric AC electrodes or SUS plates. The critical steps in this approach include 1) preventing bubble generation during the preparation of GPEs, 2) developing a cell assembly procedure that accords with a working supercapacitor, and 3) setting an appropriate experimental range.
Pol…
Divulgaciones
The authors have nothing to disclose.
Acknowledgements
The research was supported by the Competency Development Program for Industry Specialists of the Korean MOTIE operated by KIAT (No. P0012453, Next-generation Display Expert Training Project for Innovation Process and Equipment, Materials Engineers), and the Chung-Ang University Research Scholarship Grants in 2021.
Materials
| 1 M LiPF6 in EC/DMC=1/1, v/v | Sigma aldrich | 746738 | Electrolyte for pvdf-hfp polymer based gel electrolyte |
| Activated carbon | Sigma aldrich | 902470 | Active material |
| Ag/AgCl electrode | BASi | RE-5B | Reference electrode |
| Carbon black | Sigma aldrich | 699632 | Conductive material |
| Diamino-poly (propylene oxide) (DPPO) | Sigma aldrich | 80506-64-5 | corss linking material for pvdf-hfp polymer based gel electrolyte |
| Diglycidyl ether of bisphenol-A (DEBA) | Sigma aldrich | 106100-55-4 | corss linking material for pvdf-hfp polymer based gel electrolyte |
| Dimethylformamide (DMF) | Samchun | D0551 | |
| Electrode pressing machine | Rotech | MP200 | |
| Extractor | WonA Tech | Convert program (raw data to Excel ) | |
| Isopropanol(IPA) | Samchun | I0346 | Solvent to melt the binder |
| Phosphoric acid | Samchun | 00P4277 | |
| poly (ethylene glycol) diglycidyl ether (PEGDE) | Sigma aldrich | 475696 | corss linking material for pvdf-hfp polymer based gel electrolyte |
| Polytetrafluoroethylene(PTFE) | Sigma aldrich | 430935 | Binder |
| polyvinyl alcohol (PVA) | Sigma aldrich | 9002-89-5 | |
| Polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) | Sigma aldrich | 427160 | |
| Potentiostat | WonA Tech | Zive SP1 | |
| Pt electrode | BASi | MW-018122017 | Counter electrode |
| Smart management 6(SM6) | WonA Tech | Program of setting sequence and measuring electrochemical result | |
| Sulfuric acid | Samshun | S1423 | Electrolyte |
| Tensile testing machine | Nanotech | NA-50K | tensile testing machine |
| Zman | WonA Tech | EIS program |
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