Supercapacitors are highly attractive for a large number of emerging mobile devices for addressing energy storage and harvesting issues. This mini review presents a summary of recent developments in supercapacitor research and technology, including all kinds of supercapacitor design techniques using various electrode materials and production methods. It also covers the current progress achieved in novel materials for supercapacitor electrodes. The latest produced EDLC/hybrid/pseudo-supercapacitors have also been described. In particular, metal oxides, specifically ZnO, used as electrode materials are in focus here. Eventually, future developments, prospects, and challenges in supercapacitor research have been elaborated on.

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Current progress achieved in novel materials for supercapacitor electrodes: mini review

Multi-colored, water soluble fluorescent carbon nanodots (C-Dots) with quantum yield changing from 4.6 to 18.3% were synthesized in multi-gram using dated cola beverage through a simple thermal synthesis method and implemented as conductive and ion donating supercapacitor component. Various properties of C-Dots, including size, crystal structure, morphology and surface properties along with their Raman and electron paramagnetic resonance spectra were analyzed and compared by means of their fluorescence and electronic properties. α-Manganese Oxide-Polypyrrole (PPy) nanorods decorated with C-Dots were further conducted as anode materials in a supercapacitor. Reduced graphene oxide was used as cathode along with the dicationic bis-imidazolium based ionic liquid in order to enhance the charge transfer and wetting capacity of electrode surfaces. For this purpose, we used octyl-bis(3-methylimidazolium)diiodide (C8H16BImI) synthesized by N-alkylation reaction as liquid ionic membrane electrolyte. Paramagnetic resonance and impedance spectroscopy have been undertaken in order to understand the origin of the performance of hybrid capacitor in more depth. In particular, we obtained high capacitance value (C = 17.3 μF/cm2) which is exceptionally related not only the quality of synthesis but also the choice of electrode and electrolyte materials. Moreover, each component used in the construction of the hybrid supercapacitor is also played a key role to achieve high capacitance value.

/pdf/high-capacitance-hybrid-supercapacitor-based-on-multi-3mx8ay6dpw.pdf

High-Capacitance Hybrid Supercapacitor Based on Multi-Colored Fluorescent Carbon-Dots

Activated biomass carbon made from bamboo as electrode material for supercapacitors

Sate of charge (SOC) accurate estimation is one of the most important functions in a battery management system for battery packs used in electrical vehicles. This paper focuses on battery SOC estimation and its issues and challenges by exploring different existing estimation methodologies. The key technologies of lithium-ion battery state estimation methodologies of the electrical vehicles categorized under five groups, such as the conventional method, adaptive filter algorithm, learning algorithm, nonlinear observer, and the hybrid method, are explored in an in-depth analysis. Lithium-ion battery characteristic, battery model, estimation algorithm, and cell unbalancing are the most important factors that affect the accuracy and robustness of SOC estimation. Finally, this paper concludes with the challenges of SOC estimation and suggests other directions for possible research efforts.

https://www.mdpi.com/1996-1073/11/7/1820/pdf

State of the Art of Lithium-Ion Battery SOC Estimation for Electrical Vehicles

From last few decades, piezoelectric materials have played a vital role as a mechanism of energy harvesting, as they have the tendency to absorb energy from the environment and transform it to electrical energy that can be used to drive electronic devices directly or indirectly. The power of electronic circuits has been cut down to nano or micro watts, which leads towards the development of self-designed piezoelectric transducers that can overcome power generation problems and can be self-powered. Moreover, piezoelectric energy harvesters (PEHs) can reduce the need for batteries, resulting in optimization of the weight of structures. These mechanisms are of great interest for many researchers, as piezoelectric transducers are capable of generating electric voltage in response to thermal, electrical, mechanical and electromagnetic input. In this review paper, Fluid Structure Interaction-based, human-based, and vibration-based energy harvesting mechanisms were studied. Moreover, qualitative and quantitative analysis of existing PEH mechanisms has been carried out.

https://www.mdpi.com/1996-1073/11/7/1850/pdf

A Review on Mechanisms for Piezoelectric-Based Energy Harvesters

In this work, reduced graphene oxide (rGO) based electrode materials were developed to achieve a hybrid supercapacitor (SC) function. Therefore, several synthesis methods were developed to prepare a cost effective and environmentally friendly rGO. Additionally, to maintain the high surface area, spinel lithium titanate (sLTO) nanoparticles (NPs) were synthesized and deposited on the rGO surface to inhibit the restacking of the rGO layers on graphite. Furthermore, the adequate Fe-doping of sLTO increased the ionic conductivity and the intercalation capacity, which is necessary for a SC performance. The sLTO/rGO-composites were electrochemically analysed by chronopotentiometry and electrochemical impedance spectroscopy (EIS) to determine the stability during charge/discharge cycling and the capacity, respectively. To overcome the drawback of LTO's low conductivity values, its value has been drastically increased by Fe-doping. The results demonstrated the remarkable cycling performance of the Fe:LTO/rGO composite as well as a higher capacity compared to LTO/rGO and pure rGO-electrodes. The thermal stability, degradation and weight loss of the sLTO/rGO in the temperature range between 20 °C and 800 °C were investigated by thermogravimetry (TG)/DTA. As a conclusion, it can be stated that, increasing the ionic conductivity by Fe-doping drastically increases the hybrid capacity of the SC electrodes.

Synergetic effects of Fe3+ doped spinel Li4Ti5O12 nanoparticles on reduced graphene oxide for high surface electrode hybrid supercapacitors

Nanocrystalline ZnO particles were prepared using the high-energy ball milling technique and investigated with electron paramagnetic resonance (EPR), impedance, and Raman spectroscopy to reveal the origin of surface and core defects. We observed two distinct EPR signals with different g-factors, g ∼ 2.0 and ∼1.96, indicating EPR-active defects on the surface and core, respectively. Using the semi-empirical core-shell model, we identified that sufficiently small nanocrystals (below 30 nm) can show p-type character. The model can also explain the origin of the non-linearity of the U-I behaviour in nanocrystalline ZnO.

Investigation of intrinsic defects in core-shell structured ZnO nanocrystals

ZnO quantum dots with relatively narrow size distribution were produced by the presented precipitation method. Theoretical results from the literature were correlated to Zn-rich and O-rich preparations of ZnO. The investigation of the defect evolution was performed by photoluminescence (PL) measurements and electron paramagnetic resonance (EPR). By a deconvolution of PL spectra, the often mentioned defect-related green luminescence with line centers between 2.72 and 2.26 eV was observed. Since all defect centers have different defect formation enthalpies, additional information on the formation of these centers via annealing was collected. This data led us to the conclusion that VZn shows more prominent properties than usually reported. The VO defect is assigned to be responsible for the blue-light emission. The investigation of nonstoichiometric ZnO including its annealing revealed that the EPR signal at g = 1.959 can be assigned to core defects with a weak coupling to remote hydrogens from water molecul...

Sergej Repp

Papers

High-Capacitance Hybrid Supercapacitor Based on Multi-Colored Fluorescent Carbon-Dots

Synergetic effects of Fe3+ doped spinel Li4Ti5O12 nanoparticles on reduced graphene oxide for high surface electrode hybrid supercapacitors

Investigation of intrinsic defects in core-shell structured ZnO nanocrystals

Defect Evolution of Nonstoichiometric ZnO Quantum Dots

Controlling the exciton energy of zinc oxide (ZnO) quantum dots by changing the confinement conditions.