A Comparison of the Electrical Properties of Gel Polymer Electrolyte-Based Supercapacitors: A Review of Advances in Electrolyte Materials

Abstract

Flexible solid-state-based supercapacitors are in demand for the soft components used in electronics. The increased attention paid toward solid-state electrolytes could be due to their advantages, including no leakage, special separators, and improved safety. Gel polymer electrolytes (GPEs) are preferred in the energy storage field, likely owing to their safety, lack of leakage, and compatibility with various separators as well as their higher ionic conductivity (IC) than traditional solid electrolytes. This review covers the classification, properties, and configurations of different GPE-based supercapacitors and recent advancements that have occurred in this area of energy storage. Ionic liquid (IL)-based materials are popular GPEs for electrochemical energy storage and can be used to prepare unprecedented flexible supercapacitors due to their great IC and wide potential range. A comparative assessment of the GPEs-based supercapacitors reveals that in a majority of them, the value of specific capacitance is generally under 1000 F g^-1, energy density reaches around 125 Wh kg^-1, and the power density is seen to be less than 1500 W kg^-1. The results of this research serve as an essential reference for upcoming scholars, and could significantly improve our comprehension of the efficacy of GPE-containing supercapacitors.

Keywords: PVA; gel polymer electrolytes; ionic liquids; supercapacitor.

Figure 1

The schematic representation of (a) abundancy of publications, (b) the contributions on gel based supercapacitors in different fields, and (c) increasing trends toward gel electrolytes (from Google trends).

Figure 2

A comparative schematic of keywords extracted from reported publications on gel-based supercapacitors indexed in Scopus.

Figure 3

(a) Fabrication procedure for MnMoS₄@CNF, and SEM images of (b,c) CNF, (d,e) MnMo@CNF, (f,g) MnMoS₄-@CNF, and (h–m) electrochemical characteristics of the supercapacitor [48].

Figure 4

(a) The fabrication methodology for ZnCo₂O₄@LDH, SEM images of (b,c) ZnCo₂O₄ nanowires, (d,e) ZnCo₂O₄@Ni–Al LDH (f,g) ZnCo₂O₄@Co–Al LDH, and (h–n) electrochemical properties of the supercapacitor [51].

Figure 5

(a) Chemical structure of different IL-b-PE electrolytes, (b–e) electrical characterization of supercapacitors, (f) Nyquist plot, and (g) Ragone plot of the supercapacitors [68].

Figure 6

(a) Carboxylate chitosan solution; (b) schematic of assembled EDLC device; (c–g) electrochemical properties of GPE-based supercapacitor [83].

Figure 7

(a) Comparison of the specific capacitance and (b) Ragone plot of the GPE-based supercapacitors from Table 1, Table 2 and Table 3 [40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87].

Figure 8

A Ragone plot of the comparison of GPE-based supercapacitors, batteries, and fuel cells.