Electrochemical capacitors, also called supercapacitors, store energy using either ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudo-capacitors). They can complement or replace batteries in electrical energy storage and harvesting applications, when high power delivery or uptake is needed. A notable improvement in performance has been achieved through recent advances in understanding charge storage mechanisms and the development of advanced nanostructured materials. The discovery that ion desolvation occurs in pores smaller than the solvated ions has led to higher capacitance for electrochemical double layer capacitors using carbon electrodes with subnanometre pores, and opened the door to designing high-energy density devices using a variety of electrolytes. Combination of pseudo-capacitive nanomaterials, including oxides, nitrides and polymers, with the latest generation of nanostructured lithium electrodes has brought the energy density of electrochemical capacitors closer to that of batteries. The use of carbon nanotubes has further advanced micro-electrochemical capacitors, enabling flexible and adaptable devices to be made. Mathematical modelling and simulation will be the key to success in designing tomorrow's high-energy and high-power devices.

https://hal.archives-ouvertes.fr/hal-02417326/document

Materials for electrochemical capacitors

There is intense interest in graphene in fields such as physics, chemistry, and materials science, among others. Interest in graphene's exceptional physical properties, chemical tunability, and potential for applications has generated thousands of publications and an accelerating pace of research, making review of such research timely. Here is an overview of the synthesis, properties, and applications of graphene and related materials (primarily, graphite oxide and its colloidal suspensions and materials made from them), from a materials science perspective.

/pdf/graphene-and-graphene-oxide-synthesis-properties-and-2q80uaujok.pdf

Graphene and Graphene Oxide: Synthesis, Properties, and Applications

In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

/pdf/a-review-of-electrode-materials-for-electrochemical-2cok5em0bo.pdf

A review of electrode materials for electrochemical supercapacitors

Electrochemical energy storage technology is based on devices capable of exhibiting high energy density (batteries) or high power density (electrochemical capacitors). There is a growing need, for current and near-future applications, where both high energy and high power densities are required in the same material. Pseudocapacitance, a faradaic process involving surface or near surface redox reactions, offers a means of achieving high energy density at high charge–discharge rates. Here, we focus on the pseudocapacitive properties of transition metal oxides. First, we introduce pseudocapacitance and describe its electrochemical features. Then, we review the most relevant pseudocapacitive materials in aqueous and non-aqueous electrolytes. The major challenges for pseudocapacitive materials along with a future outlook are detailed at the end.

https://hal.archives-ouvertes.fr/hal-01171774/document

Pseudocapacitive oxide materials for high-rate electrochemical energy storage

Since the discovery of mechanically exfoliated graphene in 2004, research on ultrathin two-dimensional (2D) nanomaterials has grown exponentially in the fields of condensed matter physics, material science, chemistry, and nanotechnology. Highlighting their compelling physical, chemical, electronic, and optical properties, as well as their various potential applications, in this Review, we summarize the state-of-art progress on the ultrathin 2D nanomaterials with a particular emphasis on their recent advances. First, we introduce the unique advances on ultrathin 2D nanomaterials, followed by the description of their composition and crystal structures. The assortments of their synthetic methods are then summarized, including insights on their advantages and limitations, alongside some recommendations on suitable characterization techniques. We also discuss in detail the utilization of these ultrathin 2D nanomaterials for wide ranges of potential applications among the electronics/optoelectronics, electrocat...

Recent Advances in Ultrathin Two-Dimensional Nanomaterials

Traditional positive electrode materials such as transition metal oxides/hydroxides/sulfides exhibit high capacitances for asymmetric supercapacitors. However, their rate performance and cycling stability are rather poor. Herein, we develop a novel strategy for the design of Fe(CN)63− ions confined into porous pillared-carbon nanosheets (F–OPPCNs) as a positive electrode material for high energy density asymmetric supercapacitors. As a result, the specific capacitance of the F–OPPCNs (363 F g−1) is about three times higher than that of pillared-porous carbon nanosheets (PPCNs, 126 F g−1) due to the existence of the additional faradaic reaction. Benefiting from the high performances of the positive electrode, the as-assembled asymmetric supercapacitor delivers a high energy density of 48 W h kg−1 at 960 W kg−1, much higher than those of previously reported asymmetric supercapacitors in neutral aqueous electrolytes, as well as excellent cycling stability with 91% capacitance retention over 10 000 cycles. Therefore, the introduction of a redox mediator into porous carbons is a versatile approach for constructing high-performance asymmetric supercapacitors.

Fe(CN)63− ions confined into porous pillared-carbon nanosheets for high energy density supercapacitors

This chapter will focus mainly on functional carbon nanotubes (CNTs) and their applications in property enhancement of various hybrids and composites In principle, three parts are included in the chapter In Section 8172, the general methods for CNT preparation are briefly introduced In Section 8173, the functionalization of CNTs, particularly via chemical approaches, is summarized; the application of these functionalized CNTs is also discussed In Section 8174, the interaction of CNTs with various polymers, the formation of CNT–polymer nanocomposites, and their property and applications are discussed

Functionalized Carbon Nanotubes and Their Enhanced Polymers

Metal oxides/hydroxides have attracted great attention as battery‐type electrodes for supercapacitors due to their high theoretical capacitance. However, their poor electrical conductivity and ion transport kinetic severely limit their rate performance, hindering the practical application for high power devices. Herein, a simple co‐precipitation method to synthesize partial substitution of OH– with Cl– in Co, Ni layered hydroxide in saturated NaCl solution is reported. The Cl– substitution significantly increases the interlayer H2O content from 5.3% to 10.2% by changing the polarity of the hydroxide layers, leading to ultrafast ion transport through the Grotthuss behavior. Moreover, the Cl– substitution also changes the electron configuration of Ni and Co, enhancing the electrical conductivity and redox activity. Thanks to the robust electrochemical kinetics, the Ni0.85Co0.15(OH)1.77Cl0.23 shows well‐maintained redox peaks at an ultrahigh scan rate up to 500 mV s–1 and an outstanding rate performance (1076.3 C g–1 at 1 A g–1 and 333.6 C g–1 at 100 A g–1), which are among the best in the previously reported Ni(OH)2 based electrodes. Therefore, this simple anion substitution strategy opens up a new concept for achieving ultrahigh rate battery‐type electrodes.

Ni, Co Hydroxide Modified by Partial Substitution of OH– with Cl– for Boosting Ultra‐Fast Redox Kinetics up to 500 mV s−1 in Supercapacitors

To improve wettability between electrode material and electrolyte for high-rate supercapacitor application, the surfaces of graphite nanoplatelets (GNPs) were chemically modified by concentrated acids. The functional groups were confirmed by Fourier transform infrared spectra (FTIR) and zeta potential measurement. The microstructures and morphology of composites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrochemical properties of the composites were characterized by cyclic voltammograms (CV), galvanostatic charge/discharge and electrochemical impedance spectroscopy (EIS). At high discharge rates, the increase of specific capacitance of electrode material was primarily attributed to the improvement in wettability between electrode material and electrolyte, which came from the attached hydrophilic functional groups, resulting in rapid proton transport and more ion-accessible surface area.

https://link.springer.com/content/pdf/10.1007%2Fs10854-009-9966-4.pdf

Effect of chemical modification of graphite nanoplatelets on electrochemical performance of MnO2 electrodes

The preparation method of carbon/ceramics composite material includes the following steps: firstly, mixing petroleum coke or asphalt coke, doping particles and adhesive for 10-15 min, in high-speed mixing machine to obtain premixed powder, placing the premixed powder its ball grinding machine, adding solvent and dispersing agent, grinding for 5-100 hr., making the ground mixture undergo the process of reduced pressure distillation treatment, breaking it to 60-100 meshes, finally hot-pressing and forming so as to obtain the invented product with high strength, high heat-conductivity and low electric resistance.

Zhuangjun Fan

Papers

Fe(CN)63− ions confined into porous pillared-carbon nanosheets for high energy density supercapacitors

Functionalized Carbon Nanotubes and Their Enhanced Polymers

Ni, Co Hydroxide Modified by Partial Substitution of OH– with Cl– for Boosting Ultra‐Fast Redox Kinetics up to 500 mV s−1 in Supercapacitors

Effect of chemical modification of graphite nanoplatelets on electrochemical performance of MnO2 electrodes

Preparation method of carbon/ceramic composite material