A Review of Current Trends on Polyvinyl Alcohol (PVA)-Based Solid Polymer Electrolytes

Abstract

Presently, the rising concerns about the fossil fuel crisis and ecological deterioration have greatly affected the world economy and hence have attracted attention to the utilization of renewable energies. Among the renewable energy being developed, supercapacitors hold great promise in broad applications such as electric vehicles. Presently, the main challenge facing supercapacitors is the amount of energy stored. This, however, does not satisfy the increasing demand for higher energy storage devices, and therefore, intensive research is being undertaken to overcome the challenges of low energy density. The purpose of this review is to report on solid polymer electrolytes (SPEs) based on polyvinyl alcohol (PVA). The review discussed the PVA as a host polymer in SPEs followed by a discussion on the influence of conducting salts. The formation of SPEs as well as the ion transport mechanism in PVA SPEs were discussed. The application and development of PVA-based polymer electrolytes on supercapacitors and other energy storage devices were elucidated. The fundamentals of electrochemical characterization for analyzing the mechanism of supercapacitor applications, such as EIS, LSV and dielectric constant, are highlighted. Similarly, thermodynamic transport models of ions and their mechanism about temperature based on Arrhenius and Vogel-Tammann-Fulcher (VTF) are analyzed. Methods for enhancing the electrochemical performance of PVA-based SPEs were reported. Likely challenges facing the current electrolytes are well discussed. Finally, research directions to overcome the present challenges in producing SPEs are proposed. Therefore, this review is expected to be source material for other researchers concerned with the development of PVA-based SPE material.

Keywords: ionic conductivity; polyvinyl alcohol; solid polymer electrolytes; supercapacitors.

Figure 1

Ragone plot comparing main energy storage devices of fuel cells, batteries, supercapacitors and capacitors [2].

Figure 2

Schematic summary of the article.

Figure 3

Schematic illustration of a typical charged EDLC [20,21].

Figure 4

Block diagram for types of supercapacitors.

Figure 5

Schematic diagram of (A) an electrostatic capacitor, (B) an electric double-layer capacitor and (C) a pseudocapacitor [17].

Figure 6

The three major constituents of a supercapacitor.

Figure 7

Li-ion battery charge–discharge process [31].

Figure 8

Block diagram for types of Li-ion batteries.

Figure 9

Type of electrolytes used for supercapacitors.

Figure 10

Chemical structures of important polymers mostly applied for solid electrolytes (a) PS, (b) PVP, (c) PVC, (d) PVDF, (e) PMMA, (f) PVA, (g) PCL and (h) PEO [27].

Figure 11

Possible structure for the synthesized PVA-K₂CO₃ composite electrolyte [66].

Figure 12

Possible structure of the synthesized PVA-K₂CO₃-SiO₂ composite PE [75].

Figure 13

Schematic diagram of lithium-ion conduction mechanism of polymer-based polymer electrolyte [80].

Figure 14

Ion transport by hopping and segmental motion in SPE [85].

Figure 15

The schematic diagram of the PVA-BC-KOH electrolyte membrane structure [54].

Figure 16

Cole–Cole plots of (a) P-10, P-20, P-30, P-40 and P-50 films; and (b) P-40-5, P-40-10, P-40-15, and P-40-20 films [88].

Figure 17

Cole–Cole plot for pure PVA and PVA-K₂CO₃ SPEs [66].

Figure 18

The impedance spectra of the PVA-BC-KOH electrolyte membranes with different contents of BC filler; the inset of b for the high-frequency area [54].

Figure 19

Variation of conductivity of chitosan–PVA on (a) NH₄NO₃ and (b) EC concentrations at room temperature [69].

Figure 20

Effect of salt concentration on the ionic conductivity of PVA-K₂CO₃ at ambient temperature [66].

Figure 21

The conductivity of the PVA-based electrolytes with different amounts of BC [54].

Figure 22

ESW for EDLC cell with PVA-LiCLO₄-TiO₂ electrolyte [90].

Figure 23

LSV plots of the synthesized PE PK0 (pure PVA) and PVA-K₂CO₃ composites [66].

Figure 24

LSV for the PVA-based electrolyte [103].

Figure 25

LSV plots of the synthesized PVA (a) un-plasticized and (b) plasticized PEs [75].

Figure 26

Dielectric constant as a function of frequency at various temperatures of (a) pure MC-PVA polymer blend and (b) MC-PVA doped with NH₄NO₃ [114].

Figure 27

The plots of (a) ε_r and (b) ε_i against frequency for PVA-K₂CO₃ electrolytes [113].

Figure 28

Conductivity versus temperature of PEs (PVA-K₂CO₃) electrolytes [66].

Figure 29

Variation of conductivity of chitosan–PVA on (a) NH₄NO₃ and (b) EC concentrations at room temperature [69].

Figure 30

FTIR spectra of pure PVA (PK0), PK10, PK20, PK30, PK40 and PK50 polymer electrolytes [66].

Figure 31

Morphological images of different electrolytes: (a) pure PVA, (b) P-40, (c) P-40-5, (d) P-40-10, (e) P-40-15 and (f) cross-section of P-40-10 [88].

Figure 32

X-ray diffraction patterns of pure Mg(NO₃)₂ and PVA:Mg(NO₃)₂ complexes [39].

Figure 33

Digital photographs of (A) PVA electrolyte, (B) flexibility of PVA electrolyte by bending in circular arc and (C) PVA electrolyte stretched to check its elastic ability [70].

Figure 34

(A) The CV curves of fabricated supercapacitor with the developed electrolytes based on PVA, CMC and PEO at a scan rate of 100 mV s⁻¹, (B) Galvanostatic charge–discharge curves at a current density of 2 A g⁻¹ [70].

Figure 35

Electric field vs. conductivity of PVA-based electrolyte at different temperatures [99].

Figure 36

SEM images of pure chitosan–PVA films at (a) surface and (b) cross-section [69].

Figure 37

The schematic diagram for the preparation of PVA/PVP by blending and chemical cross-linking [128].