Supercapatteries as High-Performance Electrochemical Energy Storage Devices

Abstract: The development of novel electrochemical energy storage (EES) technologies to enhance the performance of EES devices in terms of energy capacity, power capability and cycling life is urgently needed. To address this need, supercapatteries are being developed as innovative hybrid EES devices that can combine the merits of rechargeable batteries with the merits of supercapacitors into one device. Based on these developments, this review will present various aspects of supercapatteries ranging from charge storage mechanisms to material selection including electrode and electrolyte materials. In addition, strategies to pair different types of electrode materials will be discussed and proposed, including the bipolar stacking of multiple supercapattery cells internally connected in series to enhance the energy density of stacks by reducing the number of bipolar plates. Furthermore, challenges for this stack design will also be discussed together with recent progress on bipolar plates. Graphic Abstract: Supercapattery is an innovated hybrid electrochemical energy storage (EES) device that combines the merit of rechargeable battery and supercapacitor characteristics into one device. This article reviews supercapatteries from the charge storage mechanisms to the selection of materials including the materials of electrodes and electrolytes. Strategies for pairing different kinds of electrode materials and device engineering are discussed.[Figure not available: see fulltext.

Research Progress and Perspectives on High Voltage, Flame Retardant Electrolytes for Lithium-Ion Batteries

© 2017 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. The electrolyte is an indispensable constituent in lithium ion batteries, and its role conducts electricity by means of the transportation of charge carries between the pair of electrodes. Its properties directly affect the energy density, cycle life and safety of the battery. However, there are two major challenges to using carbonate-based electrolytes in recent lithium ion batteries (LIBs) to further increase the energy density of the devices without compromising the safety. One is that carbonate- based electrolytes are not sufficiently stable at the positive electrode, and the other is their relatively high flammability. Therefore, developing high voltage and flame retardant electrolytes for LIBs is highly desired. Herein, we review the recent progress and challenges in new electrolytes, focusing on high-voltage electrolytes, flame retardant electrolytes and highly concentrated electrolytes. Among the reported electrolytes, highly concentrated electrolytes are worth a special attention, showing various unusual functionalities, for example, high oxidative stability, low volatility, high reductive stability, and non-corrosive to Al. These special properties are totally different from that of the conventional 1 mol•L-1 LiPF6/EC-based electrolytes, which are result from solution structures. A discussion is also provided in this review on the prospects of further development of new electrolytes for LIBs

Cryo-solvatochromism in ionic liquids

Cryo-solvatochromism (blue to green) in response to cooling from room temperature to well below 0 °C can have many applications, and has been achieved in an ionic liquid, 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate, containing di-(1-butyl-3-methylimidazolium) tetrachloro-nickelate and excess 1-butyl-3-methylimidazolium chloride

Electrolytes for electrochemical energy storage

An electrolyte is a key component of electrochemical energy storage (EES) devices and its properties greatly affect the energy capacity, rate performance, cyclability and safety of all EES devices. This article offers a critical review of the recent progress and challenges in electrolyte research and development, particularly for supercapacitors and supercapatteries, rechargeable batteries (such as lithium-ion and sodium-ion batteries), and redox flow batteries (including fuel cells in a broad sense). The review will focus on liquid electrolytes, including aqueous and organic electrolytes, ionic liquids and molten salts. The influence of electrolyte properties on the performances of different EES devices is discussed in detail

A Robust Alumina Membrane Reference Electrode for High Temperature Molten Salts

A new reference electrode for high temperature molten salts (except for fluorides) was conveniently fabricated by sealing the Ag|Ag+ (AgCl) couple in a commercial alumina tube whose closed end was ground into a membrane (ca. 0.1 mm in thickness) to facilitate ion conduction. Repeated (>15 times) and prolonged continuous (7 days) tests of this reference electrode in molten chloride and carbonate salts confirmed highly satisfactory and robust performance in terms of stability, reproducibility and reusability over a wide range of temperatures (500∼900°C) without any noticeable deterioration. It exhibited ionic resistance (<4 kΩ) decreasing with temperature, but changing insignificantly with the composition of all molten salts tested. A linear relation of potential versus logarithm of mole fraction of NaCl was observed in mixed NaCl-CaCl2 (slope: 0.1603 V/decade). Salt penetration into the membrane was confirmed by scanning electron microscopy, although no through-pores were observed. These findings are discussed in terms of the membrane and liquid junction potentials, and a mechanism of ion conduction through semi-closed pores (fast and ion-non-selective) and grain boundaries (slow and cation-selective) in series

High energy supercapattery with an ionic liquid solution of LiClO4

A supercapattery combining an ideally polarized capacitor-like electrode and a battery-like electrode is demonstrated theoretically and practically using an ionic liquid electrolyte containing 1-butyl-1-methylpyrrolidinium tri(pentafluoroethyl)trifluorophosphate (BMPyrrFAP), gamma-butyrolactone (γ-GBL) and LiClO4. The electrochemical deposition and dissolution of lithium metal on a platinum and glass carbon electrode were investigated in this ionic liquid solution. The CVs showed that the fresh electrochemically deposited lithium metal was stable in the electrolyte, which encouraged the investigation of this ionic liquid solution in a supercapattery with a lithium battery negative electrode. The active material counted specific energy of the supercapattery based on a lithium negative electrode and an activated carbon (Act-C) positive electrode could reach 230 W h kg−1 under a galvanostatic charge–discharge current density of 1 mA cm−2. The positive electrode material (Act-C) was also investigated by CV, AC impedance, SEM and BET. The non-uniform particle size and micropores dominated porous structure of the Act-C enabled its electric double layer capacitor (EDLC) behavior in the ionic liquid solution. The measured specific capacitance of the Act-C in this ionic liquid solution is higher than the same Act-C in aqueous solution, which indicates the Act-C can also perform well in the ionic liquid electrolyte

Mechano‐fenton–piranha oxidation of carbon nanotubes for energy application

Emission of nitrogen oxides (NOx) from chemical processing of materials is a serious environmental concern, frustrating the development of many innovative technologies. For example, sulfonitric oxidation is the most widely used method for processing carbon nanotubes (CNTs), producing a large amount of NOx. As a result, large scale applications of CNTs for downstream purposes remain challenging. Herein, a NOx-free oxidation method is proposed for CNTs processing. It starts with mechanically grinding, and then oxidizing the CNTs by hydroxyl radicals in sealed reactors. Such processed CNTs are shorter, possess balanced surface oxygen containing groups without compromising the original CNT integrity, and can disperse readily in water. These are desirable for making various CNT composites, including those with conducting polymers for supercapacitors. The reactors in the process are industrially adoptable, promising a great technological and commercial future

Optimal Utilization of Combined Double Layer and Nernstian Charging of Activated Carbon Electrodes in Aqueous Halide Supercapattery through Capacitance Unequalization

Charge storage through electric double layer (EDL) charging of activated carbon (AC) and redox reactions of iodide and bromide ions in aqueous electrolytes and at the AC | electrolyte interface has been investigated by cyclic voltammetry and galvanostatic charging and discharging. Electrochemical experiments were carried out in both the three-electrode and two-electrode cells with the latter resembling the so-called supercapacitor-battery hybrid or simply supercapattery. By comparing the electrochemical behavior of bromide and iodide ions used as dissolved redox species (DRS), some observed features of the supercapattery are described and analyzed from the standpoint of the EDL charging of the AC electrodes, the thermodynamics and kinetics of the electrode reactions of the DRS, and the adsorption and transport of the charging reaction products. Furthermore, the effect of capacitance unequalization was explored for the adequate utilization of the charge storage from both the DRS and EDL contributions. It is also shown that counter-electrode oversizing has to be critically appraised for the design of optimal devices

Physicochemical and Electrochemical Properties of 1,1,2,2-Tetrafluoroethyl-2,2,3,3-Tetrafluoropropyl Ether as a Co-Solvent for High-Voltage Lithium-Ion Electrolytes

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Although high-voltage positive electrode materials for high energy density lithium-ion batteries have gained a great attention, the lack of compatible electrolytes with sufficiently high oxidative stability to deliver an excellent cycling ability restricts their practical application. Fluorinated solvents are considered as promising candidates for high-voltage electrolyte solvents. In this study, we select 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) with a high boiling point, low cost, and good SEI-filming ability as a co-solvent of fluoroethylene carbonate-based electrolytes and extensively investigate its physicochemical and electrochemical properties for applications in high-voltage lithium-ion batteries. Our experimental results show that the TTE-containing electrolyte exhibits not only a high oxidative stability up to 5.5 V (vs. Li/Li+), but also excellent wettability with the separator. In addition to high discharge capacity and increased coulombic efficiency of the Li/LiNi0.5Mn1.5O4 half-cell assembled with the TTE-containing electrolyte cycled between 3.0 and 4.9 V, the cell also displays a high rate capability. This work shows that partially fluorinated ethers, e. g., TTE, are promising co-solvents for high-voltage electrolytes that can enable commercial development of high energy density lithium-ion batteries

Redox electrode materials for supercapatteries

Redox electrode materials, including transition metal oxides and electronically conducting polymers, are capable of faradaic charge transfer reactions, and play important roles in most electrochemical energy storage devices, such as supercapacitor, battery and supercapattery. Batteries are often based on redox materials with low power capability and safety concerns in some cases. Supercapacitors, particularly those based on redox inactive materials, e.g. activated carbon, can offer high power output, but have relatively low energy capacity. Combining the merits of supercapacitor and battery into a hybrid, the supercapattery can possess energy as much as the battery and output a power almost as high as the supercapacitor. Redox electrode materials are essential in the supercapattery design. However, it is hard to utilise these materials easily because of their intrinsic characteristics, such as the low conductivity of metal oxides and the poor mechanical strength of conducting polymers. This article offers a brief introduction of redox electrode materials, the basics of supercapattery and its relationship with pseudocapacitors, and reviews selectively some recent progresses in the relevant research and development