Supercapacitor and supercapattery as emerging electrochemical energy stores

Abstract

This article reviews critically selected recent literature on electrochemical energy storage (EES) technologies, focusing on supercapacitor and also supercapattery which is a generic term for various hybrid devices combining the merits of rechargeable battery and supercapacitor. Fundamentals of EES are explained, aiming at clarification of some literature confusions such as the differences between capacitive and non-capacitive Faradaic charge storage mechanisms, and between cathode and positive electrode (positrode), and between anode and negative electrode (negatrode). In particular, the concept and origin of pseudocapacitance are qualitatively correlated with the band model for semiconductors. Strategies for design and construction of supercapattery are discussed in terms of both the materials structures and device engineering. Selection of materials, including electrolytes, is another topic reviewed selectively. Graphenes and carbon nanotubes are the favourable choice to composite with both capacitive and non-capacitive redox materials for improved kinetics of charge storage processes and charge-discharge cycling stability. Organoaqueous electrolytes show a great potential to enable EES to work at sub-zero temperatures, while solid ion conducting membranes and ionic liquids can help develop high voltage (>4.0 V) and hence high energy supercapatteries. ARTICLE HISTORY

Quantum‐Chemical Study of the FeNCN Conversion‐Reaction Mechanism in Lithium‐ and Sodium‐Ion Batteries

“…The quantum-chemical bonding analysis in Figure S8 also indicates that the FeÀN bonds in the Li 2 Fe 2 (NCN) 3 structure derived from the Li 2 NCN supercell possess a more negative ICOHP value (meaning stronger bonding, À1.84 eV) than the ones in the FeNCN supercell (À1.46 eV). In other words, the good agreement of the DFT-predicted structure with the experimental spectra confirms the formation of an intermediate yet amorphous phase compatible with the local structure of Li 2 Fe 2 (NCN) 3 during the conversion reaction of FeNCN vs. Li. Unravelling such transient phases in complex reaction mechanisms is a valuable asset of the MCR-ALS approach, was recently shown for sodiation of SnSb.…”

“…[31] The EXAFS spectra indicate that component 1 and component 3 can be easily fitted with the structure of pristine FeNCN and the iron nanoparticles, as shown in Figure S6 and S7, respectively. Component 2 represents the ternary intermediate, which reaches its maximum concentration at about one third of the first discharge (Figure S5 b), and can therefore be successfully fitted by the theoretical structure of Li 2 Fe 2 -(NCN) 3 , in line with the amount of reacted lithium. The compound Li 2 Fe 2 (NCN) 3 , structurally derived from Li 2 NCN, yields satisfactory results, as shown in Figure 5 b and Table 2.…”

Construction of symmetric supercapacitors using anhydrous electrolytes containing heterocyclic oligomeric structures

“…Nowadays, the focus is more on hybrid polymer electrolyte membranes (HPEMs), which could provide lightweight thin films, high ionic conductivity, wide electrochemical window, and operational safety for the development and production of energy storage systems. HPEMs are fabricated by incorporating inorganic particles into an ion‐conductive polymer matrix or by chemical modification of inorganic/organic hybrid matrix by various chemical units …”

“…HPEMs are fabricated by incorporating inorganic particles into an ion-conductive polymer matrix or by chemical modification of inorganic/organic hybrid matrix by various chemical units. 7 To date, heterocyclic aromatic structures, such as triazole, imidazole (Imi), and benzimidazole (BnIm), indicating high ionic conductivity in the anhydrous state have been used in designing electrolytes. These protonconducting electrolytes are synthesized by an alternative fundamental method where heterocyclic units are immobilized by covalent bonding.…”

Determination of accurate electrode contribution during voltammetry scan of electrochemical capacitors

“…In case when the electrode contains the species which are able to undergo redox reaction, the charge is consumed for the chemical potential change, and in turn, the counter electrode needs to balance the charge by accelerated increase of its electric potential. Finally, the cell voltage is governed by electrical double-layer (EDL) polarizable electrode, while the redox one is responsible for the increased cell capacitance as it can be found in hybrid capacitors [5][6][7]. In real capacitors utilizing electrode materials of high surface area, these two limiting conditions occur simultaneously and the final cell voltage is an outcome of partial chemical and electrical potential changes of the electrodes.…”