Effective Current Collector Research Articles

Synergising hard-carbon and soft-carbon interactions for delivering metal-free microscale supercapacitors with high specific energy and rapid power delivery

Overcoming the limitations of low energy density and efficiency is a pertinent challenge for the continued development of micro-supercapacitive (MSC) energy storage devices. Traditional metal-thin film-based current collectors suffer from improper interfacial contact with the active material leading to rapid decay in cyclability, while carbon based current collectors underperform in energy density and energy efficiency. In this submission, we design multiscale hierarchical carbon nanostructures and achieve synergistic interactions between them that overcome these limitations. Specifically, the highly conductive (0.2 S/cm) laser-induced-carbon (LIC) acts as an effective current collector with negligible iR drop and simultaneously establishes robust interface with multidimensional nanostructured carbons made-up of (a) porous nanostructured hardcarbon florets (NCF) with high surface area (948 m2/g), open-ended framework and graded porosity and (b) conventional soft-nanocarbons such as one-dimensional single wall carbon nanotubes (CNT) and two-dimensional-graphene (Gr). Consequently, the binder-free MSC resulting from the combination of LIC, NCF and CNT exhibits outstanding high specific capacitance (18 mF/cm2), energy density (10 μWh/cm2), and relaxation time constant (67 ms) without sacrificing power density (1.66 mW/cm2). This is clearly reflected in the unique solitary position achieved by the MSC in the Ragone plot. Fundamentally, the addition of CNT and its integration with non-graphitizable, hard-carbon NCF mimics a ball-net structure that facilitates the ion-migration pathways and thereby delivers the combination of highest energy density and scan rate capability (12,000 mV/s) among all MSCs reported.

Electrosynthesis of Vertically Aligned Zinc Oxide Nanoflakes on 3D Porous Cu Foam Enables Dendrite-Free Li-Metal Anode.

Three dimensional (3D) hosts have been recognized as effective current collectors for Li metal anodes because of their physical suppression of the lithium dendrites growth. A lithiophilic surface layer on them could increase the Li metal nucleation sites, further regulating the genuine plating of Li metal. The current strategies to construct this lithiophilic layer on 3D structure is complex and not suitable for the scalable fabrication of Li metal anode. In this work, we developed a facile method to grow vertically aligned ZnO nanoflakes on the surface of 3D Cu foam through an electrochemical synthetic process, which physically suppressed the Li dendrites growth due to the unique structure during the Li plating/stripping process. Moreover, these lithiophilic flakes effectively increase the specific surface area of the anode and Li metal nucleation sites number, which reduces the local current densities, leading to the formation of a robust SEI and further suppressing the Li dendrites growth. Consequently, the performances of the symmetric Li plated Cu foam/Li cell and the Li plated Cu foam/LiFePO4 full cell have been greatly enhanced after the growth of vertically aligned ZnO nanoflakes on the Cu foam surface, including capacity, cycling stability, overpotential, and rate capability.

Porous Carbon Nanosheets Armoring 3D Current Collectors toward Ultrahigh Mass Loading for High-Energy-Density All-Solid-State Supercapacitors.

The in situ growth of active materials on 3D current collectors (such as Ni foams) presents facile and efficient access to high-performance supercapacitors. However, the low surface area of current collectors limits the mass loading, microstructure, and capacitive performance of active materials thereon. Herein, we develop a novel surface modification with hierarchical N-rich carbon nanosheets on Ni foams via a simple sol-gel method. At the same time, its favorable effects on mass loading and utilization are demonstrated using NiCoMn-carbonate hydroxide (NCM) as a model active material. Specifically, the carbon modification greatly boosts the current collector's specific surface area and enables the growth of dense NCM nanoneedles with controllable mass loading ranging from 5.2 to 23.1 mg cm-2. Meanwhile, the correlation between mass loading and utilization is systematically studied, which shows the well-maintained energy storage efficiency due to the conducive surface modification. As a result, excellent performance with the ultrahigh area-specific capacity of 19.36 F cm-2 at 2 mA cm-2 in the three-electrode configuration and remarkable area-specific energy density of 1352 μW h cm-2 in the solid-state asymmetric device can be achieved, demonstrating a prospective pathway toward facile and effective current collector designs for high-energy/power-density supercapacitors.

Exploiting Super-Lithiation in 3D Mesostructured Polyimide Electrodes: Towards Practical Organic Batteries

Recent developments in redox-active organic molecules appear to be providing sustainable and cost-effective electrode materials as potential alternatives to conventional metal-based electrodes for lithium-ion batteries (LIBs). However, utilization of the organic battery electrodes in practical applications has been quite limited. The rational design principles of the electrode structure would be beneficial in concurrently achieving practical performance demands of high energy, fast charging rate, and long-term cyclability. In this work, we conceive a lithographic fabrication strategy for realizing a 3D mesostructured organic electrode that exploits a ‘super-lithiation’ phenomenon of nearly all unsaturated C=C bonds in multi-carbonyl polyimide. The polyimide layer grown on the ordered porous nickel current collector which is prepared via proximity-field nanopatterning (PnP), generates promoted super-lithiation and shows a much higher specific capacity of 1300 mAh g−1 compared to that of the 2D electrode (270 mAh g−1). We attribute the high electrochemical activity to fast reaction kinetics through the efficient pathways for Li-ions and electrons within the electrode, as well as pathways for rapid transport of ions within the interconnected, electrolyte-filled porous network. The effect of the 3D structure is further corroborated by the unprecedented high-rate capability (achieved rates up to 400 C) and 83% capacity retention at 10 C (15 A g−1) after 250 cycles. Finally, the full electrode-basis capacity reaches 2800 mAh cm−3, surpassing the target lines required to meet the energy density target of 1500 Wh L−1 (on half-cell level) for hybrid electric vehicles. Our findings suggest that our strategic electrode design may contribute to spurring the commercialization of organic electrodes for practical systems in near future. Furthermore, the 3D nickel with the continuous, periodic porous network used in this study is expected to accommodate the severe volume expansion and induce uniform Li deposition as an effective current collector. It could be further studied for the development of Si- and Sn-based anodes for advanced LIBs or dendrite-free Li anode for lithium-metal batteries.

Autonomously Adhesive, Stretchable, and Transparent Solid‐State Polyionic Triboelectric Patch for Wearable Power Source and Tactile Sensor

AbstractRobust power supplies and self‐powered sensors that are extensible, autonomously adhesive, and transparent are highly desirable for next‐generation electronic/energy/robotic applications. In the work, a solid‐state triboelectric patch integrated with the above features (≈318% elongation, >85% average transmission, ≈44.3 N m−1 adhesive strength) is developed using polyethylene oxide/waterborne polyurethane/phytic acid composite (abbreviated as PWP composite) as an effective current collector and silicone rubber as tribolayer. The PWP composite is optimized systematically and corresponding single‐electrode device can supply a power density of 2.3 W m−2 at 75% strain. The triboelectric patch is capable of charging capacitors and powering electronics by efficiently harvesting biomechanical energies. Moreover, it can be autonomously attached to nonplanar skin or apparel substrates and used as a tactile sensor or an epidermal input touchpad for physiological motion detection and remote control of appliances, respectively. Even after dynamic deformation, tailoring, and prolonged use, the patch can maintain good stability and reliability of electrical outputs. This work provides a novel solid‐state and liquid‐free polyionic electrode‐based triboelectric nanogenerator integrated with adhesiveness, stretchability, and transparency, which can meet wide application needs from transparent electronics, artificial skins, to smart interfaces.

Enhancing electrochemical performance of thin film lithium ion battery via introducing tilted metal nanopillars as effective current collectors

Novel Li2MnO3 (LMO)-Au nanocomposite thin film with tilted Au pillars has been synthesized by using an oblique angle deposition technique (OAD) in pulsed laser deposition. The tilt angle and dimension of the Au nanopillars can be tuned by varying the inclination angle of the incoming flux and the growth rate. The obtained LMO-Au nanocomposite structure exhibits an initial volumetric discharge capacity of 35.78 μAh cm−2 μm−1 for the 1st cycle but increases to 62.32 μAh cm−2 μm−1 at the 100th cycle. Such an increase in discharge capacity upon cycling is attributed to significantly increased reaction depth upon cycling, indicating that Au pillars function as effective current collectors and the LMO-Au interfaces improve the cycling stability. In addition, the LMO-Au nanocomposites display highly anisotropic optical complex dielectric function in-plane and out-of-plane, reduced bandgap, and high hardness of 10 GPa which almost doubled that of pure Li2MnO3. This study presents a novel approach for processing nanocomposite thin films with tunable tilted current collectors towards advanced thin film battery cathode, nanoscale plasmonic systems, and other oxide-metal hybrid electrochemical systems.

Dual functional effect of the ferroelectricity embedded interlayer in lithium sulfur battery

A carbon nanotube sheet having homogeneously distributed BaTiO3 is applied to the Li-S cell system as a pseudo-current collector between the cathode and separator. This interlayer serves as a site distributor, where polysulfide eluted from the cathode continuously reacts, and it is expected to play a role as a more effective current collector by mixing the ferroelectric material. A cell utilizing a ferroelectricity embedded interlayer exhibits a higher capacity (908 mAh g−1) at 0.2C than that of carbon alone (740 mAh g−1) at 200th cycle. This result corresponds to a capacity retention ratio enhancement from 67.5% to 75.6%. Furthermore, it is confirmed that the retention of the coulombic efficiency is effectively maintained in long cycles at 0.5C (94.5%–99.6%). This is not only because the modified interlayer functions as an effective current collector owing to the high affinity of the ferroelectric material to polysulfide, but also because ferroelectricity in the interlayer acts as a polysulfide anchor. The evenly distributed polarization leads to a uniform deposition of sulfur, which results in the prevention of inactive sulfur agglomeration and dissolution of polysulfide. Thus, the utilization of active material can be improved with stabilized reaction.

Free-Standing Sandwich-Type Graphene/Nanocellulose/Silicon Laminar Anode for Flexible Rechargeable Lithium Ion Batteries.

Freely deformable and free-standing electrodes together with high capacity are crucial to realizing flexible Li-ion batteries. Herein, a lamellar graphene/nanocellulose/silicon (GN/NC/Si) film assembled by interpenetrated GN nanosheets is synthesized via a facile vacuum-assisted filtration approach accompanied by the covalent cross-linking effect of glutaraldehyde. The hybrid film consists of the highly conductive GN matrix as an effective current collector, hydroxylated silicon nanoparticles (Si NPs) embedded uniformly within GN interlayer and NC as adhesive to cross-link GN and Si NPs. When applied as anode, the GN/NC/Si film exhibits a high reversible capacity of 1251 mA h g-1 at 100 mA g-1 after 100 cycles and superior rate capability. More importantly, in the stress-strain test, this film represents robust mechanical strength, which not only provides good flexibility but also accommodates volume change of Si during cycling. By coupling with lithium cobalt oxide as the cathode, the full cell successfully powers a light-emitting diode, even bended and folded, indicating the deformation-tolerant GN/NC/Si film electrode for flexible Li-ion batteries. Therefore, the design of layered nanocomposites will offer the possibility closer to the application of flexible batteries.

Metal-free, flexible triboelectric generator based on MWCNT mesh film and PDMS layers

We demonstrate a metal-free triboelectric energy harvester consisted of MWCNT mesh film and PDMS layer. Upon touch from a finger, the single electrode-mode energy harvester generates up to 27.0 W/m2 output power at 10 MΩ matched impedance. The device generates stable power upon touch by bare fingers or gloved fingers. Using copper counter electrode results in decreased power output, due to the weaker tendency in triboelectrification. The power output also scales with the pressure applied by the finger. The intertwined, condensed MWCNT network acts as a flexible yet effective current collector, with resistance across the device less than 10 Ω. This current collector possesses strong corrosion resistance and stability against potential oxidation, while its metal counterpart may undergo oxidation over extended exposure to air or frequent fracture upon straining. The flexible device form may be applied to various curved or irregular surfaces that undergo frequent human touches.

Effects of Current Collector Materials on Performances of Micro-Tubular Solid Oxide Electrolysers for Splitting CO2

Specific surface areas of micro-tubular solid oxide electrolysers (MT-SOEs) increase with the reciprocal of their lumen diameters. However, this benefit over planar counterparts may be offset by difficulties in fabricating effective current collectors for < 1 mm diameter inner electrodes, causing significant potential losses, decreasing their performance. Hence, the effects were investigated of different current collector materials for the inner cathodes of such SOEs for splitting CO2. Ohmic area-specific resistances were lowest for silver wire-based compared to nickel wire-based current collectors, due to silver’s higher electronic conductivity. However, silver’s lower mechanical strength required addition of silver paste for effective connections, but the paste interfered with the electrode process, increasing the area-specific electrode polarization at 1.5 V by > 300% at 700 and 800 °C. Microstructural analysis suggested the silver paste caused partial blockage of surface pores. MT-SOEs with only nickel wire current collectors achieved 1 A cm-2 at 1.5 V.

NiCo2O4 nanosheets in-situ grown on three dimensional porous Ni film current collectors as integrated electrodes for high-performance supercapacitors

Three dimensional interconnected hierarchical porous Ni films are easily fabricated as effective current collectors through hydrogen bubble template electrochemical deposition. The binder-free integrated electrodes of spinel NiCo2O4 nanosheets directly coated the three dimensional porous Ni films are facilely obtained through successively electrochemical co-deposition of Ni/Co alloy layer then followed by subsequent annealing at 350 °C in air. Compared with NiCo2O4 nanosheets on smooth Ni foil or porous NiO/Ni film electrodes, the porous NiCo2O4/Ni integrated film electrodes for supercapacitors demonstrate remarkably higher area specific capacitance. The porous NiCo2O4/Ni film electrodes also exhibit excellent rate capability and cycling stability. The super electrochemical capacitive performances are attributed to the unique integrated architecture of NiCo2O4 nanosheets in-situ grown on three dimensional continuous hierarchical porous Ni collector collectors, which could provide large electrode-electrolyte interface area, high active sites, low contact resistance between current collector and active materials, fast electron conduction and ion/electrolyte diffusion.

Investigation of sheet resistance in thin-film mixed-conducting solid oxide fuel cell cathode test cells

Patterned and thin-film electrode experiments are effective in isolating or separating the complex charge and mass transport processes involved in the oxygen reduction reaction within and on the surface of a mixed-conducting solid oxide fuel cell cathode, making it possible to correlate electrochemical performance with electrode geometry, reaction pathway, and limiting steps. Very little information about either the impact of sheet resistance on global response or on effective design of current collector configuration to avoid sheet resistance has been reported to date, however. In this contribution, an empirical numerical model is presented to simulate sheet resistance under various material and catalytic parameters, current collector configurations, and other experimental factors in thin-film, mixed-conducting working electrodes. This model is used to provide general guidance for effective current collector placement by mapping in parameter space. In general, continuous crisscrossing metal lines, deposited through e.g. photolithography, provide the best intra-film current collection while small, regularly spaced discrete contacts, provided by e.g. a metal mesh, provide less efficient intra-film current collection. Most thin-film aspect ratios and current collector configurations can be accommodated without severe intra-film sheet resistance limitation provided the current collectors are spaced appropriately.

Co(OH) 2-combined carbon-nanotube array electrodes for high-performance micro-electrochemical capacitors

We have investigated binder-free Co(OH) 2-combined carbon-nanotube (CNT) array electrodes using anodized aluminum oxide (AAO) templates for micro-electrochemical capacitors. It is shown that compared to the capacitors fabricated with CNT only electrodes (6.3 F/cm 3 at 100 mV/s), those with the Co(OH) 2-combined CNT array electrodes produce much higher capacitance (12.74 F/cm 3 at 100 mV/s) together with superior high-rate capacitance. The improved electrochemical behavior is explained in terms of high capacitance of amorphous Co(OH) 2 electrode and the use of CNT arrays as effective current collector.

Analysis of chamber simulations of long collecting probes in high-speed dense plasmas

Chamber tests of simulated electrodynamic tethers (EDTs) of different geometries operating in a dense high-speed plasma are described. The geometries tested and described here are cylindrical and flat-ribbon tape. By moving the probe samples relative to the plasma source it was possible to vary the density and therefore the effective width over a range of approximately 1 to 2 Debye lengths (/spl lambda//sub D/) for the cylinder sample and 6 to 19 /spl lambda//sub D/ for the tape samples. Several important conclusions can be drawn from the tests. 1) The current-voltage characteristics of the cylinder behave as predicted by orbital-motion-limited (OML) current collection theory in the saturation region. 2) The tape tether had comparable current levels to a theoretical equal area OML cylinder up to an effective width of at least /spl sim/11/spl lambda//sub D/ and possibly wider. 3) Orienting the tape samples parallel or perpendicular to the plasma flow yielded different current responses (perpendicular is larger) above a bias potential that is near the estimated energy of the incoming beam ions. The observed difference was generally more pronounced at larger effective widths (higher densities). 4) It was also necessary to be above this bias potential to have a V/sup 0.5/ current-voltage character appropriate for an ideal cylinder in the OML regime. It is concluded that wide ribbon-like tape tethers can be effective current collectors but that velocity effects will be a factor to consider, especially as relative width of the tape tether (with respect to /spl lambda//sub D/) grows.