Ramadoss, Ananthakumar
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Binder-free TiN/graphite based thin film negative electrode for flexible energy storage devices
Transition metal nitrides are trustworthy electroactive materials due to their merits like good electrical conductivity, wettability, multi-oxidation state, and higher specific capacity than metal oxides and carbon materials. In the present work, titanium nitride is deposited over a highly flexible graphite substrate using physical vapour deposition process. The physiochemical studies confirmed the formation of TiN film over the graphite substrate and also exhibited flexible characteristics. The nitrogen content of the electrode provides considerable wettability to the electrode surface while having better conductivity. Noticeably, the as-fabricated negative electrode showed pseudocapacitive property with a good specific capacitance of 86 mF cm−2 at 1 mA cm−2 and stable cycling performance with 80% capacitance retention even after 3000 cycles at 3 mA cm−2 . The results of this study demonstrate that these metal nitrides can be considered as an alternative negative electrode for supercapacitor applications.
Hierarchical carbon coated vertically aligned α-MoO3 nanoblades anode materials for supercapacitor application
Molybdenum oxide (MoO3) is an appropriate electrode material for vast applications such as gas sensing, catalyst, and energy storage devices. Its high oxidation states provide the possibility for ion intercalation and de-intercalation to the electrode material, which is truly advantageous for supercapacitor application. Herein, we report about reduced vertically aligned α-MoO3 nanoblades on conducting substrates via a post-treatment in reduced gas environments (H2, N2 and vacuum) to tune their conductivity by introducing oxygen vacancies. These α-MoO3 nanoblades were further carbonized through decomposition of glucose as a carbohydrate material to obtain binder-free carbon coated vertically aligned α-MoO3 electrode. As a binder-free supercapacitor negative electrode, the vacuum treated α-MoO3 electrode showed the highest specific capacitance (39.8 mF cm−2), as compared to that achieved by N2 and H2 treated samples (29.2 mF cm−2 and 24.5 mF cm−2, respectively). Besides, the vacuum annealed electrode also maintained around 76.4% of its initial specific capacitance value after 10,000 cycles indicating a more stable electrochemical performance of such electrode. An asymmetric device 3D-MnO2//α-MoO3 was assembled and it attained maximum specific capacitance value of 37.5 mF/cm2 at current density value 1.5 mA cm− 2 and maximum energy density value of 16.875 µWh cm-2 at power density value of 675 µW cm-2. The results demonstrate that the proposed hybrid synthesis approach is very promising for preparation of binder-free materials for high-performance supercapacitors.
Titanium oxynitride coated graphite paper electrodes for light-weight supercapacitors
The rapid development of smart electronics devices has stimulated intensive research on flexible supercapacitors with high mechanical tolerance and energy density. Up to date, most of the asymmetric devices are fabricated using carbon-based materials as negative electrode materials. However, the lower capacitance of carbon-based materials limited its applicability widely. Also, the device unavoidably carries unnecessary mass and volume, leads to poor contact and performance to repeated bending of devices, and occupies more space in the electronics devices. Herein, we prepared flexible, light-weight, and thin graphite paper current collectors to fabricate flexible supercapacitors. Further, the titanium oxynitride (TiOxNy) coatings were deposited by DC magnetron sputtering over a flexible and light-weight graphite substrate as a potential negative electrode. The presence of nitrogen content in transition metal oxynitrides adds wettability to the material; hence more electrolyte ions get adsorps onto the surface of the electrode owing to their hydrophilic nature. The resultant TiOxNy/graphite electrode exhibited a high areal capacitance of 62 mF cm−2 and also showed 100% capacitance retention even after 1500 GCD cycles. The results of a series of tests indicated that the flexible electrode has better capacitive performance, suggesting that as-prepared film is a favorable candidate for light-weight and flexible supercapacitors.
An extensive review on three dimension architectural Metal-Organic Frameworks towards supercapacitor application
Metal-organic frameworks (MOFs) are evolving as emerging materials for application in supercapacitors on account of their inherent porous characteristics, which can be suitably controlled with molecular engineering. This allows suitable attributes to MOFs such as multiple dimensionalities, high surface area and additional aspect ratio compared to traditional materials. Secondary building units (SBUs) are the milestones that allow immense structural diversity, thermodynamic stability, and mechanical/architectural stability to demonstrate materials on-demand with predetermined topologies in the synthesis of MOFs through stronger bonding between the constituent metals and organic linkers. Despite these advancements, the usage of pristine MOFs is lagging in the area of supercapacitor, majorly due to their insulating nature. As smart avenues, hybridization of MOFs or using MOFs as templates for deriving metal oxide, carbon or hydroxides etc., are being proved as hugely successful. This review is directed towards the utilization of MOFs, specifically three-dimensional MOFs as a platform for utilization in supercapacitor. Extensive discussion is developed on divergent methods related to the synthesis of MOFs, their performance in supercapacitor application and various strategies adopted to enhance their functionality. Finally, the future prospective and possible research proceedings in this field are described briefly.
Hybrid supercapacitors, formation, and new advances with different electrochemical electrodes based on layered double hydroxides (LDHs), metal–organic framework (MOF) materials, smart supercapacitors
Hybrid supercapacitors (HSCs) are made by the combination of electric double-layer capacitor (EDLC) materials, various types of pseudocapacitive, and battery-type materials. The progress made on the improvement of energy density without sacrificing the power density attracted the researchers to move toward HSC. The specific capacitance of the HSC showed a superior value than the EDLC or pseudocapacitance-based supercapacitors. Numerous advancements have been made on the HSCs with the development in preparation of electrode materials, electrolyte, formation of component, device structure, and the new mechanisms for the improvement of electrochemical characteristics. This chapter specifically emphasis the new development made on the HSCs based on the layered double hydroxides, metal–organic frameworks (MOFs), MOF-derived materials and their composites. The specific characteristics requirement of the electrode material, electrolyte, the substrate in support of electrode materials, and the progress made on them for smart supercapacitors are discussed.
Flexible, Lightweight, and Ultrabendable RuO2–MnO2/Graphite Sheets for Supercapacitors
In the present work, we have introduced lightweight, ultrabendable, rough graphite sheets on a polyimide tape substrate as a current collector. The flexible current collector was fabricated by the peel-off method. The as-prepared graphite-sheet-coated polyimide substrate is ultraflexible (bendable, rollable, and twistable), thin, and lightweight, has better conductivity, high mechanical durability, and ease of fabrication, and is cost-effective, rough, and environment friendly. The fabricated flexible current collector could be directly used as the substrate for constructing RuO2–MnO2/graphite flexible supercapacitors. The as-prepared electrode delivered a maximum gravimetric capacitance of 183 F g–1 (73.5 mF cm–2) at a current density of 1 A g–1 with better rate capability and 96% capacitance retention (after 5000 cycles). The better electrochemical performance of the electrode is due to the rough surface and good electrical conductivity of the current collector leads to the better attachment of active material and rapid ions/electron transfer.
A brief review on stretchable, compressible, and deformable supercapacitor for smart devices
In the modern phase of electricity and global connectivity, a supercapacitor plays an eye-catching role by overcoming the detrimental of capacitors and batteries. Imagining an advanced smartphone, a miniature, light-weight, flexible electronic device with good power and energy capability, large-scale stretchability, and self-healing property is one step ahead of becoming a reality in innovations. To facilitate the sustainable operation and ensure the reliability of the obtained electronic system, it is desirable to obtain satisfactory performance under certain conditions like bending, stretching, compressing, deforming and twisting, etc. However, multifunctional integrity remains a challenge in a single system. The stable and insistent output can only be possible by choosing the proper electrode design and material selection. This review discusses the recent trends in different categories of stretchable materials used for supercapacitor applications, various architectures influencing their stretchability, their mechanical properties like strain, pre-stretchability and healability, etc. and the usability of these stretchable materials in smart and wearable devices.
Construction of light-weight and flexible vanadium nitride coated graphite paper electrodes for supercapacitors
The energy storage devices for flexible/wearable and portable electronics are on immediate requirement demanding for high-performance flexible supercapacitors. Nevertheless, the real-time application of advanced electronics necessitates supercapacitors to own admirable mechanical properties to endure rigorous straining environments. Also, it is necessary to reduce the mass and volume of the whole device. Therefore, constructing a high-performance flexible supercapacitor based on better electrochemical and significant mechanical properties is still a formidable task. Herein, we have successfully fabricated a vanadium nitride thin film electrode onto the flexible, thin, and light-weight graphite paper substrate via reactive direct current (DC) magnetron sputtering method. The as-fabricated graphite sheets current collector is flexible, thin, light-weight, electrically conductiviting, cost-effective, and easy to fabricate. Furthermore, the as-prepared binder-free flexible negative electrode displayed better supercapacitor performance in terms of specific capacitance and cycle stability. The negative electrode exhibited an areal capacitance of 91 mF cm−2 and better cycling stability with > 64% capacitance retention after 2000 cycles. Moreover, the flexible hybrid supercapacitor is fabricated with NiCo hydroxide and VN films and showed a maximum energy density of 1.80 μWh cm−2 and power density of 387.5 μW cm−2 and good stability. These results propose that the fabricated electrode has great prospective as a power source for flexible, wearable, and portable electronic devices.
Recent trends in template assisted 3D porous materials for electrochemical supercapacitors
Supercapacitors have emerged as an outstanding candidate among numerous energy storage devices because of their long-term cycle life, high power density, and minimal safety concerns. As we know, the lower energy density of supercapacitors hindered their practical applications. Therefore, extensive research efforts have been devoted to exploring various nanostructured three-dimensional electrode materials to overcome this obstacle. To achieve a larger surface area, shorter ion-diffusion path, faster ion accessibility, and higher conductivity, most researchers developed template-assisted 3D architecture designed electrodes. Based on the current research trends, we have reviewed recent advances in the fabrication of hierarchically three-dimensional porous materials via various experimental strategies for supercapacitors. Particularly, hydrogen bubble dynamic template (HBDT), anodic aluminium oxide (AAO), and metal–organic framework (MOF) based approaches have been extensively reviewed. Various experimental parameters, which control the morphology of 3D structures, are summarized. Moreover, the electrochemical performance analysis of template-assisted 3D architecture electrodes for supercapacitor applications with their pros and cons is discussed. Various research studies have showed that higher energy and power performance can be achieved based on a conductive network, shorter diffusion path length, large active surface area, tuneable morphological, 3D porous network, etc. Therefore, the 3D template approach could lead to positive steps towards higher energy and power performance. Also, the present review demonstrates that binder and conductive additive-free 3D porous electrodes open up a new avenue to fabricate high surface area electrodes for improved charge storage performance. Finally, the challenges and future direction of 3D porous-based electroactive materials for supercapacitors were also discussed.