Ultrahigh Volumetric Capacitance Research Articles

Ultrafine Ti3C2 MXene Nanodots-Interspersed Nanosheet for High-Energy-Density Lithium-Sulfur Batteries.

Nanostructured carbon materials have been extensively used for encapsulating sulfur and improving cyclic stability of lithium-sulfur (Li-S) batteries, but high carbon content and low packing density greatly limit their volumetric energy density. Herein, we present MXene-based Ti3C2T x (T x stands for the surface terminations) nanodots-interspersed Ti3C2T x nanosheet (TCD-TCS) to accomplish spatial immobilization and conversion of high-loaded sulfur species. Rich surface polar sites in TCD-TCS enhance structural integrity of the resultant electrode, while the absence of the carbon-based materials and conductive additives results in high tap density of the cathode materials. The TCD-TCS/S electrode exhibits an almost theoretical discharge capacity at a medium sulfur loading of 1.8 mg cm-2. Notably, ultrahigh volumetric capacity (1957 mAh cm-3) and high areal capacity (13.7 mAh cm-2) are synchronously achieved at a high sulfur loading of 13.8 mg cm-2. The mechanism study of sulfur evolution during discharge process highlights the importance of the integration of MXene-based nanodots and nanosheets in Li-S batteries. This proposed methodology holds great promise for the development of various high-performance energy storage materials.

Synchronous Gains of Areal and Volumetric Capacities in Lithium-Sulfur Batteries Promised by Flower-like Porous Ti3C2T x Matrix.

The areal and volumetric capacities are important metrics in practical deployment of advanced energy storage systems with the imposed constraints of device volume and chip area. Conductive carbons are promising sulfur host materials for improving areal capacity in lithium-sulfur (Li-S) batteries, but they face a few congenital deficiencies, such as low tap density and weak polysulfide entrapment ability, resulting in poor volumetric performance. Here, we report one type of cathode system based on flower-like porous Ti3C2T x (FLPT) without the incorporation of any carbon hosts or conductive additives. The resultant FLPT-S electrode synchronously acquires a high areal capacity of 10.04 mAh cm-2 and ultrahigh volumetric capacity of 2009 mAh cm-3. Furthermore, ex situ electron paramagnetic resonance and UV-visible spectra have demonstrated that FLPT enables a fast dynamic equilibrium between S62- anion and S3•- radical during cycling, which promotes the redox reactions of sulfur species.

N-doped hollow carbon spheres intercalated graphene film induced macroporous frameworks for ultrahigh volumetric energy density supercapacitor

Ideal electrodes should hold well-defined pore size distribution, high electrical conductivity and superior compatibility. Herein, we present a scalable strategy for the design and generation of macroporous frameworks based on N-doped hollow carbon spheres intercalated graphene film (GNC). In the unique structure, hollow carbon spheres separate the graphene nanosheets and provide convenience for ion entering the film and maximize the ion-accessible surface area. In situ deposition high performance MnO2 on the surface of GNC film can help to enhance the specific capacity of the compounds. The obtained GNC/MnO2 binder-free supercapacitor electrode exhibits ultrahigh volumetric capacitance 532.7 F cm−3 at 2 mV s−1. An asymmetric supercapacitor based on GNC/MnO2//GNC shows an ultrahigh volumetric energy density of 45.9 Wh L−1 at 1024 W L−1, which is much higher than the reported carbon based materials in aqueous electrolytes. The device also shows an excellent cycling stability with 93.1% initial capacitance after 5000 charge/discharge cycles. The device can light two LEDs, which indicates the potential of the composite for practical application.

Nitrogen-doped highly dense but porous carbon microspheres with ultrahigh volumetric capacitance and rate capability for supercapacitors

Controlling the dosage ratio of KOH to samples for an optimized porous structure with both high gravimetric capacitance and high volumetric capacitance.

Thickening and Homogenizing Aqueous Electrolyte towards Highly Efficient and Stable Zn Metal Batteries

Rechargeable Zn metal aqueous batteries featuring low cost, superior safety, and ultrahigh volumetric capacity are of great interest for large-scale applications. However, their practical implementation is hindered by poor reversibility and short cycling stability, which fundamentally result from the corrosion and the dendritic growth of the Zn metal anode in the aqueous electrolyte. Stabilization of Zn metal is therefore essential to achieve satisfactory performances. Here, we report a new electrolyte system containing a thickening agent (fumed silica) that can immobilize the water molecules and a homogenizing agent (fatty methyl ester ethoxylate) that assists in smoothing the Zn2+ cations deposition, which effectively alleviates the water-induced corrosion reaction and suppresses the Zn dendrite formation. Zn/Zn symmetric cells in the new electrolyte, therefore, show extraordinary reversibility with a coulombic efficiency of 99.5% that is the highest among those of the reported symmetric cells and a long cycling stability of 1500 h. Furthermore, the Zn-MnO2 full cell in this work exhibits equally excellent cycling stability with low capacity loss of 0.002% per cycle, which is superior to those of previously developed Zn metal batteries. This study offers a promising approach to stabilize Zn metal and enable high-performance Zn metal aqueous battery.

Vertically constructed monolithic electrodes for sodium ion batteries: toward low tortuosity and high energy density

A vertically aligned architecture for an electrode is constructed through physical vapor deposition which benefits the charge transport kinetics and leads to an ultrahigh volumetric capacity for sodium ion batteries.

Scalable Water‐Based Production of Highly Conductive 2D Nanosheets with Ultrahigh Volumetric Capacitance and Rate Capability

Adv. Energy Mater. 2018, 8, 1800227 The measurement methods (i.e., changing the techniques and parameters) used to evaluate the electrochemical performance of the electrode materials could also affect the reported results depending on whether CV or GCD techniques are used.7, 8 In the original article, the specific capacitance values of the electrode materials were reported using the GCD technique only. Here, data on the volumetric capacitance and rate capability of the electrode materials using the CV technique are provided (Table 2). CV and GCD measurements were performed using a VersaSTAT 4 instrument (Princeton Applied Research) equipped with a power booster (specification of ± 20 A and ± 20 V). Although there is a small difference between the capacitance values of the CV and GCD methods, the decreasing tendency of the capacitances as the Gr loading increases are similar for both techniques. The rate capabilities of the electrode materials obtained from the GCD technique are also very close to those of the CV method. A scalable water-based fluid dynamic exfoliation process was reported for preparing highly conductive metallic phase MoS2 and graphene sheets and then free-standing flexible hybrid films were fabricated for the high-volumetric performance of flexible supercapacitor devices. Additional studies on hybrid films were also conducted using organic electrolytes of 1-ethyl-3-methylimidazoluim tetrafluoroborate ([EMIM][BF4]) dissolved in acetonitrile (ACN) to increase the energy density. The energy density value of 564.91 W h kg−1 (1.14 W h cm–3), which was based on the organic electrolytes reported in the original article, resulted from an error in the calculation of the energy density using overcharged GCD curves. A cell voltage of 1 V was used for the aqueous electrolyte instead of 3.5 V for the energy density calculation of the organic electrolyte, thus leading to the incorrect energy density value in the original article. To address this error, the GCD of the supercapacitors was retested (Figure 5f) and the energy densities were recalculated using an integral equation instead of a linear equation (Figures 5g,h). The newly obtained CV and GCD data show stable cell voltages of ≈3.2 V. Based on these new results, the maximum energy density is 122.2 W h kg−1 at 1.4 kW kg−1 (246.9 mW h cm−3 at 2.97 W cm−3). The corrected Figure 5f–h are shown here: The authors apologize for these errors and any confusion they may have caused.

Recent Progress of MXene‐Based Nanomaterials in Flexible Energy Storage and Electronic Devices

The increasing demands for wearable electronics have stimulated the rapid development of flexible energy storage devices. MXenes are considered as promising flexible electrodes due to the ultrahigh volumetric specific capacitance, metallic conductivity, superior hydrophily, and rich surface chemistry. This work reviews, for the first time, the recent advances of MXene‐based nanomaterials in flexible energy storage devices, including pure MXenes, MXene‐carbon composites, MXene‐metal oxide composites, and MXene‐polymer composites. Applications of MXenes in flexible electronics such as sensors, nanogenerators, and electromagnetic interference shielding are also included. Then, properties of stress, strain, conductivity, and capacitance are compared to help researchers to keep balance between mechanical and electrochemical performances in designing flexible devices. Finally, challenges together with the possible solutions related to the application of MXenes in flexible devices and outlook to future directions are provided.

Biomass-derived robust three-dimensional porous carbon for high volumetric performance supercapacitors

The inherent low volumetric performance of two-dimensional (2D) carbon materials hinders their practical usage in portable devices. Three-dimensional (3D) carbon materials derived from sustainable biomass have been widely investigated but also suffer from the moderate volumetric performance. In this work, using biomass (jujube) as carbon precursor, robust 3D porous carbon with a high particle density of 1.06 gcm−3 is synthesized through high-temperature carbonization and subsequent activation. In three-electrode system, the electrode exhibits an ultrahigh volumetric capacitance of 476 Fcm−3 in 6 M KOH electrolyte, which is much higher than previously reported results. The symmetrical two-electrode supercapacitor delivers excellent rate capability (75% capacitance retention at 20 Ag−1) as well as superior cycle stability (91% capacitance retention after 10,000 cycles) in 1 M H2SO4 electrolyte. Furthermore, an energy density as high as 13 WhL−1 at a power density of 477 WL−1 is demonstrated in 1 M Li2SO4 electrolyte. The high volumetric performance of our biomass-derived porous carbon meets the requirements of portable devices and the fabrication process can be scaled up easily to industrial levels.

A facile synthesis of self-assembling reduced graphene oxide/cobalt carbonate hydroxide papers for high-performance supercapacitor applications

Electrode materials as an important component for the supercapacitors (SC) mainly undertake energy storage. Hence, the research hotspots in the SC fields are focused on the active materials of the electrode. In this study, we have provided a facile synthesis method to prepare reduced graphene oxide (RGO) and cobalt carbonate hydroxide (Co(CO3)0.5(OH)0.11·H2O) nanorod composites. The RGO films were obtained by vacuum filtration of GO papers and hydrothermal method. And during this hydrothermal, Co(CO3)0.5(OH)0.11·H2O nanorods also grow on the surface of RGO films. The as-fabricated RGO/Co(CO3)0.5(OH)0.11·H2O composites are characterized by SEM, EDS, XRD measurement. According to the electrochemical research results, the RGO/Co(CO3)0.5(OH)0.11·H2O electrodes own an ultrahigh volumetric capacitance of 1627 F cm−3 at a current density of 0.5 A g−1. Besides, the energy density of the symmetrical supercapacitor (SSc) assembled with the RGO/Co(CO3)0.5(OH)0.11·H2O electrode material is 9.22 mW h cm−3, and the capacity can be maintained 100.0% after 10,000 cycles when the composite material at the current density of 1 A g−1, these promote an efficient electrode material for electrochemical supercapacitor applications.

Densely pillared holey-graphene block with high-level nitrogen doping enabling ultra-high volumetric capacity for lithium ion storage

Developing high volumetric capacity and long cycle-life anode materials for high-performance lithium-ion batteries (LIBs) still remains a great challenge. Herein, densely pillared holey-graphene block with high N-doping (P-NHG) has been successfully synthesized through thermal decomposition of (NH4)6Mo7O24 in-between stacked GO sheets. The dense graphene building block processes a high packing density of 2.53 g cm−3, high nitrogen doping (19.2 at%), numerous holes on the graphene sheet, and ∼5 nm Mo2C nanoparticles as the pillars in-between the graphene sheets, facilitating rapid ion diffusion and storage and ensuring structural stability during Li ion storage. As a result, the P-NHG electrode can deliver high gravimetric capacity of 1221 mAh g−1 and ultrahigh volumetric capacity of 3089 mAh cm−3 at 0.1 A g−1, as well as excellent cyclability (713 mAh g−1/1803 mAh cm−3 after 300 cycles at 0.5 A g−1). The novel design of densely pillared holey-structure materials represents greatly improved properties such as superior cyclability, and high volumetric capacity for LIBs.

Surface modified MXene film as flexible electrode with ultrahigh volumetric capacitance

In recent years, the rapid development of portable equipment and flexible wearable devices urgently requires supercapacitor electrode material with high volumetric capacitance. Ti3C2Tx, a member of MXenes family, is one of the most promising supercapacitor electrode material candidates. However, how to further enhance the volumetric capacitance of the Ti3C2Tx is still a great challenge at present. In this paper, a simple and eco-friendly method is presented by preparing flexible Ti3C2Tx supercapacitor electrode using self-assembly of few-layer Ti3C2Tx followed by alkalinizing and annealing treatment. The alkalinized and annealed Ti3C2Tx film (denoted as ak-Ti3C2Tx film-A) exhibits an ultrahigh volumetric capacitance of 1805 F cm−3 at 1 A g−1, and an impressive cycling stability up to 98% capacitance retention after 8000 cycles. The significant improvement in volumetric capacitance performance is mainly due to the increase of redox-active sites exposed by removal of surface terminal groups during alkalinizing and annealing, and the enhancement in conductivity of the film owing to the annealing induced increase of crystalline order. Moreover, the supercapacitor fabricated with ak-Ti3C2Tx film-A displays an outstanding volumetric energy density of 45.2 Wh L−1. This work provides a new strategy for design and development of other MXenes-based materials with high volumetric capacitance performance for flexible and highly integrated supercapacitors.

Ultrahigh volumetric capacitance and cycle stability via structure design and synergistic action between CoMoO4 nanosheets and 3D porous Ni-Co film

The rational design of the composites constituted by active materials and self-supported conductive current collectors has been turned out to be an effective way to achieve excellent electrochemical performance of supercapacitors. In this work, the 3D network-like continuous porous Ni-Co film (3DNC) with high conductivity and controllable porous structure was obtained through simple de-alloying and annealing processes, and then ultrathin CoMoO4 nanosheets were homogeneously grown onto skeleton of 3DNC film by hydrothermal and low-temperature annealing processes. The 3DNC film exhibits considerable electrochemical performance, whose controllable pore structure insures optimized mass loading of CoMoO4 and maximized space utilization of integrated electrode. The highly interconnected porous channels among the ultrathin CoMoO4 nanosheets provide high ion-accessible effective surface area and fast ion diffusion path, which significantly increases the reaction kinetics of the CoMoO4 nanosheets. Such outstanding structural advantages and the synergistic effect between CoMoO4 nanosheets and 3DNC film result in desired electrochemical performance with an extremely high volumetric capacitance of 2601.3 F cm−3 (325.2 mAh cm−3), excellent rate performance and superior cycle stability up to 20,000 cycles. The impressive results open an avenue toward the rational design of free-standing composites with high-performance electrochemical performance through both structure design and the synergistic action between active materials and conductive current collectors.

Efficient and scalable synthesis of highly aligned and compact two-dimensional nanosheet films with record performances

It is crucial to align two-dimensional nanosheets to form a highly compact layered structure for many applications, such as electronics, optoelectronics, thermal management, energy storage, separation membranes, and composites. Here we show that continuous centrifugal casting is a universal, scalable and efficient method to produce highly aligned and compact two-dimensional nanosheets films with record performances. The synthesis mechanism, structure control and property dependence of alignment and compaction of the films are discussed. Significantly, 10-μm-thick graphene oxide films can be synthesized within 1 min, and scalable synthesis of meter-scale films is demonstrated. The reduced graphene oxide films show super-high strength (~660 MPa) and conductivity (~650 S cm−1). The reduced graphene oxide/carbon nanotube hybrid-film-based all-solid-state flexible supercapacitors exhibit ultrahigh volumetric capacitance (407 F cm−3) and energy density (~10 mWh cm−3) comparable to that of thin-film lithium batteries. We also demonstrate the production of highly anisotropic graphene nanocomposites as well as aligned, compact films and vertical heterostructures of various nanosheets.

Modified MXene/Holey Graphene Films for Advanced Supercapacitor Electrodes with Superior Energy Storage.

MXene films are attractive for advanced supercapacitor electrodes requiring high volumetric energy density due to their high redox capacitance combined with extremely high packing density. However, the self‐restacking of MXene flakes unavoidably decreases the volumetric performance, mass loading, and rate capability. Herein, a simple strategy is developed to prepare a flexible and free‐standing modified MXene/holey graphene film by filtration of the alkalized MXene and holey graphene oxide dispersions, followed by a mild annealing treatment. After terminal groups (—F/—OH) are removed, the increased proportion of Ti atoms enables more pseudocapacitive reaction. Meanwhile, the embedded holey graphene effectively prevents the self‐restacking of MXene and forms a high nanopore connectivity network, which is able to immensely accelerate the ion transport and shorten transport pathways for both ion and electron. When applied as electrode materials for supercapacitors, it can deliver an ultrahigh volumetric capacitance (1445 F cm−3) at 2 mV s−1, excellent rate capability, and high mass loading. In addition, the assembled symmetric supercapacitor demonstrates a fantastic volumetric energy density (38.6 Wh L−1), which is the highest value reported for MXene‐based electrodes in aqueous electrolytes. This work opens a new avenue for the further exploration of MXene materials in energy storage devices.

Scale-up production of high-tap-density carbon/MnOx/carbon nanotube microcomposites for Li-ion batteries with ultrahigh volumetric capacity

Electrode materials with high tap density are important for their practical application to achieve high volumetric energy density Li-ion batteries. In this work, large-scale fabrication of microsized carbon/MnOx/carbon nanotube composites by a low-cost spray-drying method is reported. The carbon/MnOx/carbon nanotube is characteristic of microspherical morphology consisting of interconnected carbon nanotubes and nano-MnOx with an exterior carbon coating. The micropacking enables the composite to exhibit a tap density as high as 2.54 g cm−3. When evaluated as anode materials for Li-ion batteries, the high-tap-density carbon/MnOx/carbon nanotube electrode delivers a specific capacity of 927 mAh g−1 after 100 cycles, corresponding to an ultrahigh volumetric capacity of 2355 mAh cm−3. The carbon network also has dual-functions of excellent electrical conductivity and good mechanical elasticity for the MnOx to sustain superior rate and cycling properties. The scale-up production method provides a reliable practical avenue of fabricating high-tap-density metal-oxide materials for high-performance Li-ion batteries.

Equilibrium and non-equilibrium free carrier dynamics in 2D Ti3C2Tx MXenes: THz spectroscopy study

MXenes is an emerging class of 2D transition metal carbides, nitrides and carbonitrides which exhibit large conductivity, ultrahigh volumetric capacitance, high threshold for light-induced damage and nonlinear optical transmittance, making them attractive candidates for a variety of optoelectronic and electrochemical applications. Here, we report on equilibrium and non-equilibrium free carrier dynamics of Ti3C2Tx gleaned from THz spectroscopic studies for the first time. Ti3C2Tx showed high (~2 × 1021 cm−3) intrinsic charge carrier density and relatively high (~34 cm2 V−1 s−1) mobility of carriers with an exceptionally large, ~46 000 cm−1 absorption in the THz range, which suggests that Ti3C2Tx is well suited for THz detection. We also demonstrate that Ti3C2Tx conductivity and THz transmission can be manipulated by photoexcitation, as absorption of near-infrared, 800 nm pulses is found to cause transient suppression of the conductivity that recovers over hundreds of picoseconds. The possibility of control over THz transmission and conductivity by photoexcitation suggests the promise for application of Ti3C2Tx Mxenes in THz modulation devices and variable electromagnetic shielding.

Spatially confined synthesis of vanadium nitride nanodots intercalated carbon nanosheets with ultrahigh volumetric capacitance and long life for flexible supercapacitors

High volumetric capacitance electrode materials are highly desirable for miniaturized and portable capacitive storage devices. Herein, a spatially confined strategy to prepare 0D-in-2D pillared lamellar hybrid comprising vanadium nitride nanodots intercalated carbon nanosheets (VNNDs/CNSs) is proposed for promising capacitive material with high volumetric capacitance. The VNNDs/CNSs shows an ultrahigh volumetric capacitance of 1203.6 F cm−3 at 1.1 A cm−3 and rate capability of 703.1 F cm−3 at 210 A cm−3 surpassing those of carbon, transition metal oxides/nitrides. Even the 150 μm-thick film electrode comprising VNNDs/CNSs has a volumetric capacitance of 867.1 F cm−3. Moreover, the VNNDs/CNSs electrode exhibits extraordinary cycling stability with 90% capacitance retention after 10,000 cycles. The all-solid-state symmetric flexible supercapacitor based on VNNDs/CNSs electrodes boasts a high volumetric energy density/power density of 30.9 Wh L−1/64,500 W L−1 with 91% capacitance retention after 10000 cycles, rendering promising applications in high-performance flexible supercapacitors. The strategy provides an insight into the rational design of compact, robust and highly conductive electrode materials with high volumetric capacitances and long life.

Supercapacitors: Scalable Water‐Based Production of Highly Conductive 2D Nanosheets with Ultrahigh Volumetric Capacitance and Rate Capability (Adv. Energy Mater. 18/2018)

Supercapacitors: Scalable Water‐Based Production of Highly Conductive 2D Nanosheets with Ultrahigh Volumetric Capacitance and Rate Capability (Adv. Energy Mater. 18/2018)

Nanotubular Ni-supported graphene @ hierarchical NiCo-LDH with ultrahigh volumetric capacitance for supercapacitors

The design of the electrode materials for supercapacitors with high volumetric utilization and excellent capacitance is in high demand. In this study, the three dimensional porous hierarchical nickel cobalt layered double hydroxides (NiCo-LDH) grown on the nanotubular Ni supported N-doped graphene (ntN-NG) matrix are fabricated via chemical vapor deposition process combined with hydrothermal method. The ntN-NG substrate with low void content, high specific surface area, appropriated pore size and a hydrophilic surface facilitates the effective nucleation and robust growth of hierarchical NiCo-LDH, and thus, ensures high material loading in a limited space and the structure stability of the composite. The hybrid exhibits a record high volumetric capacitance of 867 F/cm3 at 1 mA/cm2 and remarkable cycling stability of 89.4% retention after 10,000 cycles, which holds great promising application as the miniaturized energy storage and conversion devices in the future.