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....

Protocol

1. Synthesis of PVA- and PVDF-HFP polymer-matrix-based electrolytes

NOTE: When handling methanol, it is best to avoid direct exposure as much as possible.

1. PVA polymer-matrix-based electrolyte synthesis
   1. Dissolve PVA (1 g) (Mw 146,000-186,000)in double-distilled water (10 mL) in a water bath at 90 °C and stir at 500 rpm until a clear solution is obtained. Then, add H₃PO₄ (1 mL) to the hot solution with constant stirring at RT for 24 h.
   2. Pour the stretchable polymer electrolyte into a glass Petri dish and dry it overnight in a vacuum oven at 40 °C.
      NOTE:....

Results

PVA was widely applied as a polymer-matrix-based electrolyte for SCs because it is biodegradable, inexpensive, chemically stable and non-toxic, has a wide operating temperature range, and has a transparent-film forming capability^10,11. PVA enhances ionic conductivity due to its hydroxyl groups which absorb water¹². In this study, we prepared the PVA-based gel electrolyte by mixing H₃PO₄/H₂O, which served as.......

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.

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Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
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