Metal-Ion Batteries and Supercapacitors: Uses of Pi-Conjugated Polymers

By Akhlaqul KaromahNov 11 2021Reviewed by Skyla Baily

The world wants high energy density, low cost, environmentally friendly, and sustainable electrical energy storage systems to tackle the future difficulties of energy storage of portable and flexible cutting-edge electronics, (ESS) motivating the research in the journal Royal Society Open Science.

Study: A review of π-conjugated polymer-based nanocomposites for metal-ion batteries and supercapacitors. Image Credit: Fishman64/Shutterstock.com

The ever increasing demand for energy and the depletion of fossil fuels has underlined the need for energy generation from renewable sources. Energy storage is just as important as energy generation for industrial progress and human well-being.

Supercapacitors and Battery

Consumers' principal power sources for portable electronics are currently batteries and supercapacitors (SCPs). The lithium-ion battery (LIB) and lead-acid battery (LAB) are both completely commercialized. Both of these batteries have their own set of drawbacks and advantages.

Because of the use of dangerous and prohibited lead as an electrode material, as well as the lower volumetric energy density of lead-acid batteries, they are not a viable option for future sustainable energy management.

(a) Schematics of electro-polymerization of poly-PNBTH-Boc from monomer PNBTH-Boc, (b) three-electrode electro-polymerization reactor, and (c) photo of poly-PBNTH-Boc film on the ITO electrode [43]. Images reproduced with permission. Image Credit: Uke, S., et al, Royal Society Open Science

Furthermore, due to their remarkable properties such as low price, relatively high energy density, high specific capacitance, high retention in capacitance, and renewability, SCPs are also attractive and mature electrochemical energy storage systems. Energy density, power density, capacitance, cycle life, and shelf life are critical criteria for the commercial viability of any electrical energy system, and they further drive the efficiency of these ESS.

Organic Materials for Making Electrodes

Organic materials have recently received a lot of attention as electrode materials for a variety of energy storage technologies. Organic polymers have remarkable qualities such as ease of synthesis, low production costs, lightweight, environmental compatibility, processability, and molding ability, among others.

The utilization of -conjugated polymers (π-CPs) for energy storage applications has skyrocketed among the various organic polymers. Interestingly, the π-CPs offer a number of qualities that make them appealing for energy storage applications, including good electrical conductivity, cost-effectiveness, lightweight, and environmental friendliness.

There are numerous reviews in the literature at the moment that illustrate the recent progress of organic materials as active electrode materials for energy storage applications. Many of them are concentrated on the application and development of organic materials, metal oxides, and carbon-based materials as active electrode materials for energy storage.

 Electrochemical performance of the t-CNTs–PA–PE cathode in ZIBs. (a) CV curves; (b) GCD curves; (c) and (d) rate performance; (e) cyclic performance at 10 A g⁻¹ [47]. Images reproduced with permission. Image Credit: Uke, S., et al, Royal Society Open Science

Special Types of Organic Materials

In this respect, the study extensively examined the special types of organic material, i.e. π-CPs as electrode material for versatile ESS, in the current analysis to enlighten the positive advancements and innovation in electrode materials.

We began by providing a quick overview of the various π-CPs, as well as their essential inherent features relevant to energy storage applications. Furthermore, the research concentrated on the synthesis of π-CPs and recent advances in various synthesis techniques.

Chemical oxidative polymerization is a two-electron exchange technique, which necessitates the use of an oxidant to oxidize monomers. Electro-polymerization is the second most advantageous synthesis method after oxidative polymerization.

The polymerization takes place on the working electrode when an external voltage is applied. In most cases, the synthesis takes place inside the glove box. ITO-coated slides or gold-coated glass, for example, are employed as working electrodes in electropolymerization.

Battery Electrodes Using Conjugate Polymer

With the rising environmental problems linked with internal combustion engines, as well as breakthroughs in wearable and portable electronic gadgets, electrochemical energy storage batteries are becoming increasingly popular.

Batteries with low cost, high power density, lightweight, high safety, long life, and environmental friendliness are in high demand for applications such as electric vehicles (EVs), portable electronics, and frequency regulation, among others.

The electroactive organic chemical has several advantages over inorganic compounds, including lightweight and increased safety. Furthermore, the electroactive organic compound can be produced with the necessary structure and functional group, resulting in more redox-active sites for increased electrolyte ion exchange during charging and discharging.

(a) Schematic of hydrogel skeleton, porous network and PEDOT sheets containing PANI. (b) SEM micrographs of lyophilized PEDOT/PANI hydrogel at different magnification. The rough surface of the sheet evidences the inlay of PANI particles in each PEDOT sheet. Images reproduced with permission. Image Credit: Uke, S., et al, Royal Society Open Science

In versatile ESS, π-CPs, their modifications, and composites with nanostructured metal oxides as well as carbon-based materials have indeed been widely employed as electrode materials.

CPs are highly valued materials and potential candidates for SCPs and MIBs because of their flexibility, cheap cost, environmentally friendly nature, structural variety, and ease of derivatization through nano-structured engineering. Low capacity, a sloping plateau, and poor stability are some of the key drawbacks of using π-CPs as electrode material in storage devices.

Furthermore, the breakdown of the π-CPs electrode in aprotic electrolytes causes rapid capacity fading during the battery and SCP discharge. To date, various solutions for overcoming such obstacles have been published in the literature. These include making a salt of π-CPs using organic carbonyl compounds, building covalent compounds of π-CPs using conductive materials, and using non-covalent techniques to make composites with nanostructured carbon/metal oxides.

Because the lone pair seems to have high electron mobility, it has been discovered that π-CPs, which include lone pairs including heteroatoms (such as oxygen, nitrogen, sulfur, and others), have high electrical conductivity and redox activity, further improving the energy and power density of ESS.

References

Uke, S., et al. (2021). A review of π-conjugated polymer-based nanocomposites for metal-ion batteries and supercapacitors. Published:20 October 2021. https://royalsocietypublishing.org/doi/10.1098/rsos.210567

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