High Active Mass Loading Research Articles

Polypyrrole-Carbon Nanotube-FeOOH Composites for Negative Electrodes of Asymmetric Supercapacitors

For the first time, polypyrrole (PPy) coated carbon nanotubes (CNT) were combined with FeOOH to fabricate negative supercapacitor (SCP) electrodes. The synergistic effects of PPy-CNT and FeOOH resulted in enhanced electrochemical performance at high active mass loading of 37 mg cm−2 in a voltage window of −0.8–+0.1 V versus a saturated calomel electrode. Particle extraction through liquid-liquid interface (PELLI) was utilized for the agglomerate-free processing of FeOOH, which improved FeOOH mixing with PPy-CNT and contributed to the enhanced capacitive behavior of the composite. Tetradecylamine (TA) was found to be an efficient extractor for FeOOH. Cyclic voltammetry and impedance spectroscopy data at different electrode potentials provided an insight into the synergistic effects of PPy-CNT and FeOOH, and influence of PELLI on electrode performance. An areal capacitance of 4.5 F cm−2 and nearly ideal capacitive behavior were achieved at a low electrode impedance. The important finding was that capacitances of the negative PPy-CNT-FeOOH and positive MnO2-CNT electrodes can be matched in different voltage windows to fabricate advanced asymmetric devices, which exhibited promising electrochemical performance in a voltage window of 1.6 V at high active mass.

Facile synthesis of B/N co-doped 2D porous carbon nanosheets derived from ammonium humate for supercapacitor electrodes

In this work, we report a facile method for preparing the B/N co-doped 2D porous carbon nanosheets (BNHCs) with high contents of boron (3.41–3.96 at.%) and nitrogen (5.1–6.09 at.%) via annealing the mixtures of ammonium humate and H3BO3. The ammonium humate is used as nitrogen-containing carbon precursor, and H3BO3 acts as boron source and pore-forming agent. Moreover, we demonstrate firstly that the existence of H3BO3 can enhance the graphitization degree of BNHCs by inducing the conversion of BCO2 to BC3 with increasing the H3BO3/ammonium humate mass ratio to 2. BNHC-1.5 exhibits the highest specific surface area of 592 m2 g−1 among all the samples, and BNHC-2 shows the enhanced graphitization degree and highest mesopore ratio (60.5%). In a three-electrode system, the BNHC-1, BNHC-1.5 and BNHC-2 exhibit high specific capacitances of 305 F g−1, 311 F g−1 and 225 F g−1 at 0.2 A g−1, and 64 F g−1, 125 F g−1 and 120 F g−1 at ultrahigh current density of 100 A g−1, respectively. Moreover, as assembled symmetric supercapacitor electrodes with high active material mass loading (∼180 μm, ∼13 mg cm−2), BNHCs deliver high specific capacitances of 170–210 F g−1 at 0.05 A g−1, and BNHC-2 presents an outstanding cyclic stability (94.8% capacitance retention after 10,000 cycles), making them promising candidates for practical supercapacitor application.

Surface modification and dispersion of ceramic particles using liquid-liquid extraction method for application in supercapacitor electrodes

Particle extraction through liquid-liquid interface (PELLI) was used for the extraction of MnO2, Mn3O4, FeOOH and ZnO particles from an aqueous synthesis medium to the n-butanol phase. The benefits of PELLI were demonstrated by the fabrication of supercapacitor electrodes, which showed good electrochemical performance at high active mass loadings. Octyl gallate (OG) was found to be an efficient and versatile extractor for the ceramic particles. The phase transfer of the particles resulted in reduced agglomeration, which allowed for improved electrolyte access to the particle surface and facilitated their mixing with conductive multiwalled carbon nanotube (MWCNT) additives. It was shown that OG is a promising extractor material for the fabrication of ceramic-ceramic, ceramic-metal and ceramic-MWCNT nanocomposites. The strong adsorption of OG on the particle surface involved bridging or chelating bidentate bonding of the catechol group to the metal atoms. The capacitive properties of FeOOH-MWCNT electrodes were tested in the negative potential window. MnO2-MWCNT and Mn3O4-MWCNT electrodes were investigated for charge storage in the positive potential window. The highest capacitance of 5.7 F cm−2 for positive electrodes was achieved using MnO2-MWCNT composites with active mass loading of 36 mg cm−2. The Mn3O4-MWCNT electrodes exhibited improved capacitance retention at high charge-discharge rates.

Toward Mechanically Stable Silicon-Based Anodes Using Si/SiO x@C Hierarchical Structures with Well-Controlled Internal Buffer Voids.

Low conductivity and structural degradation of silicon-based anodes lead to severe capacity fading, which fundamentally hinders their practical application in Li-ion batteries. Here, we report a scalable Si/SiO x@C anode architecture, which is constructed simultaneously by sintering a mixture of SiO/sucrose in argon atmosphere, followed by acid etching. The obtained structure features highly uniform Si nanocrystals embedded in silica matrices with well-controlled internal nanovoids, with all of them embraced by carbon shells. Because of the improvement of the volumetric efficiency for accommodating Si active spices and electrical properties, this hierarchical anode design enables the promising electrochemical performance, including a high initial reversible capacity (1210 mAh g-1), stable cycling performance (90% capacity retention after 100 cycles), and good rate capability (850 mAh g-1 at 2.0 A g-1 rate). More notably, the compact heterostructures derived from micro-SiO allow high active mass loading for practical applications and the facile and scalable fabrication strategy makes this electrode material potentially viable for commercialization in Li-ion batteries.

Phase transfer of oxide particles using hydroxamic acid derivatives and application for supercapacitors

Particle extraction through liquid-liquid interface (PELLI) methods are developed for the colloidal processing of ZnO, CeO2 and FeOOH particles. The direct transfer of the particles from an aqueous synthesis medium to a device processing medium allows for reduced nanoparticle agglomeration, because drying and re-dispersion processes are avoided. Different PELLI methods are developed, which are based on the use of chelating hydroxamates molecules, such as octanohydroxamic acid (OCHA) and bufexamac (BFXM) as extractors. OCHA and BFXM show strong adsorption on the ZnO, CeO2 and FeOOH particles due to chelating bonding mechanisms and allow for efficient particle extraction from water to organic solvents. Bottom–up and top-down methods are used, depending on the density of the organic solvents. OCHA shows improved extraction of particles, compared to BFXM due to the difference in the chemical structure. The unique feature of hydroxamates is related to their pH-dependent solubility and their strong adsorption on particles at high pH, despite the electrostatic repulsion of the negatively charged particles and dissociated hydroxamic acids. It is found that OCHA can be used as a capping agent for particle synthesis and an extractor for their extraction to an organic phase. The advantages of PELLI methods are demonstrated by the fabrication and testing of FeOOH-carbon nanotube electrodes for supercapacitors, which show enhanced performance and high capacitance at high active mass loading. The enhanced electrochemical performance is achieved due to reduced particle agglomeration, which allows improved particle mixing with conductive carbon nanotubes. The capacitive properties are investigated at different charge-discharge rates. The impedance spectroscopy data shows dependence of capacitance on electrode potential and provides an insight into the strategies for further improvement of electrode performance.

A Flexible Supercapacitor with High True Performance

SummaryThe demand for better “true performance” of supercapacitors, which is defined as the energy density based on the packaged cell with high active mass loading, is spurred by the ever-increasing energy storage market. The true performance of present supercapacitors is unsatisfactory, greatly limited by the currently used current collectors. Here, we develop a through-pore structured nickel current collector with excellent flexibility by electrodepositing nickel on laser-drilled stainless steel sheets filled with epoxy resin. Based on the new current collector, the electrodes possess higher performance than those fabricated by employing conventional current collectors. At a high active mass loading, the assembled supercapacitors show superior flexibility and high energy densities of 50.4 W hr L−1 and 30.1 W hr kg−1, respectively, based on the packaged cell, outperforming the present supercapacitors. Our strategy provides a new opportunity for promoting the further development of supercapacitors by enhancing the true performance.

A Flexible Supercapacitor with High True Performance

The demand for better “true performance” of supercapacitors, which is defined as the energy density based on the packaged cell with high active mass loading, is spurred by the ever-increasing energy storage market. The true performance of present supercapacitors is unsatisfactory, which is greatly limited by the currently used current collectors. Here, we develop an ultrathin ultralight through-pore structured nickel current collector with excellent flexibility by electrodepositing nickel on laser drilled stainless steel sheets filled with epoxy resin. Based on the new current collector, the electrodes possess higher performance than those fabricated by employing conventional current collectors. At a high active mass loading, the assembled supercapacitors show superior flexibility and high energy densities of 50.4 W hr L−1 and 30.1 W hr kg−1 based on the packaged cell, outperforming the present supercapacitors. Our strategy provides a new opportunity for promoting the further development of supercapacitors by enhancing the true performance.

Activated carbon fibres as high performance supercapacitor electrodes with commercial level mass loading

Turning waste cotton into useful energy storage device shows great scientific and industrial importance due to the sustainability, abundance, low-cost and environmental friendliness. This study delineates the fabrication and electrochemical performances of activated porous carbon fibres used as high performance supercapacitor electrodes with commercial level mass loading (150 ± 10 μm thickness, 10 ± 1 mgcm−2). The fabricated supercapacitor electrodes showed combination of high gravimetric and volumetric capacitances in three different electrolytes 6 M KOH (0–1 V), 0.5 M Na2SO4 (0–1.8 V) and 1 M TEABF4/AN (0–2.7 V) due to the thick electrodes (high active mass loading). Particularly, the electrodes in organic electrolyte TEABF4 at 2.7 V exhibited excellent gravimetric and volumetric capacitances of 112 Fg-1 and 74 Fcm−3 at 1 Ag-1, respectively with long life cycle (87% capacitance retention after 10,000 cycles). Hence, it delivers maximum gravimetric and volumetric energy density of 29.50 Whkg−1 and 19.42 WhL−1, respectively. A practical approach to combine the supercapacitor (4 coin cells in series, 2.7 V x 4) with commercial solar lantern to integrate self-sustaining power pack is demonstrated. It is evidently proved that activated carbon fibres with high areal capacitance delivered high volumetric energy to the device which is prime requisite for practical implementation.

Supercapacitor electrodes with high active mass loading

Abstract

(Invited) Synthesis of 3D Network Graphene Based on Physical Metallurgy

As a new nanocarbon material with excellent mechanical, physical and chemical performances, graphene has been attracted wide attentions for the applications in many field, especially for the electrode materials of energy storage devices. The high quality, controllable and effective synthesis of GN are main issues for its application. A 3D network structural graphene is promising for increase the electrochemical properties. We report a synthesis strategy by combining chemical method with physical metallurgy，achieving high quality and effective synthesis of 3D network graphene from powder, sheet to bulk foam. Chemical vapor deposition, de-alloying and powder metallurgy methods have been successfully used for the synthesis. Furthermore, carbon nanotubes(CNTs) was introduced in the 3D graphene for increasing the strength and conductivity. The processes and effects of chemical and physical process on the graphene structure are introduced and investigated, and the performance of the 3D-GN as the electrode materials in supercapacitor and lithium ion battery are explored. Without any current collectors and binder employed, a lithium ion capacitor (LIC) was assembled by 3D graphene reinforced by CNTs, which can achieve a high active materials mass loading per area, a large operating voltage window (0.01-4.2 V), current density per area (> 3 mA cm-2) and comparable energy density per mass (32 Wh kg-1), as well as excellent long cycling performance. Therefore, the 3D graphene are expected to be ideal electrode materials in high-performance electrochemical energy storage devices.

Influence of molecular structure of extractor molecules on liquid-liquid extraction of oxide particles and properties of composites

Interest in particle extraction through liquid-liquid interface (PELLI) technology is motivated by the need to transfer particles directly from the synthesis medium to the device processing medium. This method avoids the difficulty encountered by conventional re-dispersion methods where particles agglomerate during the drying stage. We develop PELLI strategies to transfer MnO2, ZnO and CeO2 particles that are synthesized in aqueous media into 1-butanol using extractors containing phosphonate and carboxylic groups. We demonstrate that, in addition to head-tail (HT) surfactants, molecules containing two hydrophilic end groups (HTH) can also be employed as extractors, a finding that opens new PELLI applications. We demonstrate this new approach using multifunctional HTH molecules as both PELLI extractors, and charged dispersing agents for the electrophoretic deposition (EPD) of particles that are transferred to an EPD processing medium. Using the HTH extractors for PELLI, we fabricate MnO2-based bulk electrodes for electrochemical supercapacitors (ES) that exhibit superior electrochemical performance. These high active mass loading ES electrodes have a capacitance of 5.7 F cm−2 (157 F g−1) and 2.5 F cm−2 (67 F g−1) at 2 and 100 mV s−1 scan rates, respectively, with low impedance. In another strategy, the use of HTH extractor for particle transfer to screen printing processing medium facilitates the fabrication of efficient thin film SC electrodes. Measurements provide insight into the influence of anchoring groups and extractor molecule structure on the extraction efficiency and electrochemical performance.

New Methods for the Fabrication of Composites for Supercapacitor Electrodes with High Active Mass Loading

ABSTRACTMnO2-multiwalled carbon nanotube (MWCNT) supercapacitor electrodes with active mass loading of 30-45 mg cm-2 were prepared. In method 1, MnO2 and MWCNT were dispersed using 3,4-dihydroxybenzaldehyde (DHB) and toluidine blue (TD), respectively. The Schiff base formation between amino group of TD and aldehyde group of DHB facilitated improved mixing of MnO2 and MWCNT. In method 2, gallocyanine (GC) was used as a co-dispersant for MnO2 and MWCNT. The catecholate type bonding of DHB and GC allowed for adsorption of the dispersant molecules on MnO2 nanoparticles. The electrodes, prepared by method 1 showed higher capacitance, compared to the electrode, prepared by method 2. The highest capacitance of 7.8 F cm-2 (173 F g-1, 139 F cm-3) was obtained at a scan rate of 2 mV s-1 and active mass loading of 45 mg cm-2.

Paper-like TiO2/graphene-carbon nanotube hybrid electrode with high mass loading: Toward high-performance lithium ion battery

One key challenge in flexible batteries lies in the development of deformable/flexible electrode with high active materials mass loading and good electronic conductivity. Herein, we report such a paper-like TiO2/graphene-carbon nanotube hybrid electrode by a facile vacuum filtration approach. In this electrode, titania nanoparticles with uniform size (9 nm) and carbon nanotubes are embedded into graphene sheet homogeneously, forming a peculiar 3D conducting network. This feature ensures 1) a high TiO2 mass loading (77.3 wt %, 2.93 mg cm−2); 2) good electric conductivity (∼1000 S m−1); and 3) good flexibility. Benefiting from these, the electrode delivers a high specific capacity (214 mAh g−1), excellent rate capability, and up to 700 cycles stability at a high rate of 1000 mA g−1. This fabrication strategy demonstrates great practical potential and opens up new idea for high-performance self-supported electrode design.

High areal capacitance of Mn3O4-carbon nanotube electrodes

This paper reports the fabrication of Mn3O4-multiwalled carbon nanotube (MWCNT) electrodes for supercapacitors with a high active mass loading of 35 mg cm−2, which showed high capacitance of 3.5 F cm−2, good capacitance retention at high charge-discharge rates and low impedance. Good electrochemical performance was achieved using non-covalent modification of MWCNT with an anionic steroid dispersant, which allowed excellent MWCNT dispersion and facilitated the fabrication of Mn3O4-MWCNT nanocomposites with uniform distributions of individual components. The electrodes showed activation behavior, related to capacitance increase, impedance reduction and enrichment of the Mn3+ and Mn4+ oxidation states.

Fabrication of Mn3O4–carbon nanotube composites with high areal capacitance using cationic and anionic dispersants

Mn3O4-multiwalled carbon nanotube (MWCNT) electrodes for supercapacitors with high active mass loadings have been fabricated with the goal of achieving a high area normalized capacitance (CS) and enhanced capacitance retention at high charge-discharge rates. Poly(4-styrenesulfonic acid-co-maleic acid) sodium salt P(SSA-MA) was used as a charging and dispersing agent for the fabrication of Mn3O4. The unique bonding properties of the MA monomers allowed efficient P(SSA-MA) adsorption on Mn3O4, whereas SSA monomers imparted a negative charge. Cationic ethyl violet (EV) and pyronin Y (PY) dyes were used for dispersion and charging of MWCNT. Good dispersion of the individual components and their electrostatic heterocoagulation facilitated efficient mixing, which allowed enhanced capacitive behavior at mass loadings of 28.4 mg cm−2, which meet requirements for practical applications. The highest capacitance of 2.8 F cm−2 was obtained at a scan rate of 2 mV s−1 for the composites, prepared using PY. However, the composites, prepared using EV showed better capacitance retention of 88% in the scan rate range of 2–100 mV s−1 and the capacitance of 2.1 F cm−2 was obtained at a scan rate of 100 mV s−1. The composites showed activation behavior during cycling, which resulted in a capacitance increase and electrical resistance reduction. The results of this investigation showed that Mn3O4–MWCNT composites, prepared by new colloidal methods are promising materials for practical applications in electrochemical supercapacitors.

Phase transfer of oxide particles for application in thin films and supercapacitors

This paper reports efficient liquid-liquid extraction strategies for concentrated suspensions of oxide particles and demonstrates the benefits of using such strategies for thin film applications and the fabrication of supercapacitor electrodes. We performed materials synthesis in an aqueous phase and achieved efficient materials transfer to an organic phase, avoiding agglomeration during the drying stage. The metal oxides, suspended in an organic solvent were used directly for the deposition of polymer-titania composite films and fabrication of Mn3O4-carbon nanotube composite electrodes for supercapacitors. Strategy E1 involved the modification of particles in-situ during synthesis and a Schiff base reaction with an extractor at the liquid-liquid interface. In the one-step E2 procedure the interface reactions were used for the extraction. We discuss advantages of the E1 and E2 strategies. Both strategies featured a biomimetic approach for the surface modification of the particles, which allowed for strong adsorption of the extractors. The ability to perform efficient extraction using concentrated suspensions allowed for the fabrication of Mn3O4–carbon nanotube electrodes with high active mass loading. The electrodes showed a capacitance of 2.63 F cm−2, good capacitance retention at high charge-discharge rates and low impedance. The results of this investigation pave the way for the agglomerate free processing of various functional materials for applications in advanced films, coatings and devices

Liquid–liquid extraction of oxide particles and application in supercapacitors

Abstract

Honeycomb-like Nitrogen and Sulfur Dual-Doped Hierarchical Porous Biomass-Derived Carbon for Lithium-Sulfur Batteries.

Honeycomb-like nitrogen and sulfur dual-doped hierarchical porous biomass-derived carbon/sulfur composites (NSHPC/S) are successfully fabricated for high energy density lithium-sulfur batteries. The effects of nitrogen, sulfur dual-doping on the structures and properties of the NSHPC/S composites are investigated in detail by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and charge/discharge tests. The results show that N, S dual-doping not only introduces strong chemical adsorption and provides more active sites but also significantly enhances the electronic conductivity and hydrophilic properties of hierarchical porous biomass-derived carbon, thereby significantly enhancing the utilization of sulfur and immobilizing the notorious polysulfide shuttle effect. Especially, the as-synthesized NSHPC-7/S exhibits high initial discharge capacity of 1204 mA h g-1 at 1.0 C and large reversible capacity of 952 mA h g-1 after 300 cycles at 0.5 C with an ultralow capacity fading rate of 0.08 % per cycle even at high sulfur content (85 wt %) and high active material areal mass loading (2.8 mg cm-2 ) for the application of high energy density Li-S batteries.

High Areal Capacitance of V2O3–Carbon Nanotube Electrodes

V2O3-multiwalled carbon nanotube (MWCNT) electrodes with active mass loading of 30 mg cm−2 and ratio of active material mass to current collector mass of 33% have been developed for charge storage in electrochemical supercapacitors. Good electrochemical performance at high active mass loading allowed for an electrode areal capacitance as high as 4.4 F cm−2 and low electrode resistance. This high performance was, in part, achieved using an advanced colloidal processing method, which involved the use of lauryl gallate (LG) as a dispersant. It was demonstrated that LG allowed for good dispersion of both V2O3 and MWCNT and facilitated their mixing. An electrode activation procedure (AP) was also developed, and contributed to the high capacitance and low resistance at high active mass loadings. To further understand the AP, as received and ball milled V2O3 electrodes were investigated using cyclic voltammetry and impedance spectroscopy before and after activation, as well as with cycling stability. This, coupled with XRD, XPS and SEM data provided an insight into the composition and morphology changes of the active material. The influence of particle size on electrode capacitance, cyclic stability and capacitance retention at high charge-discharge rates has been analyzed. The results of this investigation showed that V2O3-MWCNT composites are promising for practical applications in electrochemical supercapacitors.

MnO2-Carbon Nanotube Electrodes for Supercapacitors with High Active Mass Loadings

MnO2-carbon nanotube electrodes with high active mass loadings for supercapacitors have been fabricated with the goal of achieving a high area normalized capacitance, low impedance and enhanced capacitance retention at high charge-discharge rates. Interface synthesis and liquid-liquid extraction of MnO2 particles produced non-agglomerated MnO2 particles which allowed the fabrication of electrodes with good dispersion of carbon nanotubes in the MnO2 matrix. This strategy was used to fabricate electrodes with active mass loadings in the range of 21–50 mg cm−2 and mass ratios of active material to the nickel foam current collector of 0.33–0.78. The comparison of the experimental data for different extractor molecules provided an insight into the influence of the molecular structure, adsorption mechanism and interface phenomena on particle size and electrode performance. The analysis of capacitance data at different charge-discharge rates and different mass loadings was utilized to optimize electrode performance. The highest capacitance of 7.52 F cm−2 was achieved at a scan rate of 2 mV s−1 and active mass loading of 47 mg cm−2. Electrodes with mass loading of 35 mg cm−2 showed improved capacitance retention at high scan rates and the highest capacitance of 2.63 F cm−2 at a scan rate of 100 mV s−1.