Foam Current Collector Research Articles

Self-supported Co-Ni-P ternary nanowire electrodes for highly efficient and stable electrocatalytic hydrogen evolution in acidic solution

Self-supported electrodes comprising densely-packed, vertically-aligned Co-Ni-P ternary nanowire arrays supported on a nickel foam current collector (Co-Ni-P/NF) have been fabricated through hydrothermal growth of Co-Ni precursor nanowires on nickel foam, followed by a facile phosphorization treatment using low-cost red phosphorous. The morphology, crystal structure, microstructure and chemical composition of the as-fabricated Co-Ni-P nanowires are comprehensively investigated using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. The as-obtained Co-Ni-P nanowires are porous and composed of polycrystalline solid solution, and Co, Ni and P are uniformly distributed over nanowires. Moreover, these nanowires are firmly adhered to the nickel foam with excellent structural robustness, forming an integrated electrode. The self-supported integrated electrode exhibits outstanding catalytic activity towards the hydrogen evolution reaction (HER), which can deliver current densities of −10, −20 and −100mAcm−2 at small overpotentials of 68, 94 and 134mV, respectively. Furthermore, it is able to sustain continuous galvanostatic electrolysis at −10mAcm−2 for 40h without obvious degradation, showing good long-term stability. The excellent electrocatalytic performance can be attributed, on the one hand, to the intrinsically high catalytic activity of Co-Ni-P ternary nanowires; on the other hand, to the unique porous nanowire morphology and monolithic electrode structure that not only offer appreciable electrocatalytically active sites, but also provide efficient conductive paths and facilitate mass transport of electrolyte and release of the generated gas bubbles.

3D flower-like CoNi2S4 grown on graphene decorated nickel foam as high performance supercapacitor

3D Flower-like CoNi2S4 is in situ grown on 3D graphene decorated nickel foam current collector as high performance supercapacitor. After the nickel foam is decorated by graphene using CVD method, then the flower-like CoNi2S4 is grown using two step hydrothermal processes. The structural characterizations indicate a uniform and numerous 3D flower-like CoNi2S4 anchored on graphene decorated nickel foam. The flower-like CoNi2S4 directly grown on graphene decorated nickel foam avoids the use of polymer or conductive additive binder which commonly adds in extra contact resistance and dead sites. In addition, the presence of graphene between CoNi2S4 and nickel foam can effectively improve ion/electron transportation and also provide large surface area with regular frame work for anchoring of flower-like CoNi2S4. Using these advantages the as-synthesized electrode exhibits a high areal capacitance of 6.528F/cm2 at current density of 6mA/cm2; excellent cycling stability of 85% after 3500cycles of charge discharge by applying current density of 20mA/cm2 and good rate capability of 71% as current increased from 6 to 60mA/cm2. Such impressive results suggest promising applications of flower-like CoNi2S4 supported on graphene decorated nickel foam as high-performance electrodes for supercapacitors.

Simulation-Supported Analysis of Calendering Impacts on the Performance of Lithium-Ion-Batteries

Lithium-Ion-Batteries (LIB) are promising energy storages for electric vehicles. However, to realize driving ranges equivalent to ones of combustion engine powered vehicles they need increased energy densities. The cells could be improved by targeted optimization of certain electrode manufacturing parameters, such as the calendering strenght [1]. However, calendering does not only affect several geometric parameters of the LIB, like electrode thicknesses and porosities, which can experimentally be measured. Calendering also affects other parameters, such as effective electronic and ionic conductivities and solid-liquid interfacial area [1, 2, 3]. The latter parameters are more complex to investigate, and exclusively experimental or exclusively simulative methods which are usually applied, are not sufficient to understand calendering impacts on battery behaviour. Therefore in this talk we introduce a method where experimental and simulative methods are combined in order to improve the understanding of calendering impact. For the experimental part inhouse made pouchcells were examined by measuring capacity, discharge curves at 1 C and electrochemical impedance spectroscopy. To investigate calendering impacts, these experiments were carried out for cells containing non-calendered NMC cathodes and ones containing cathodes calendered to a degree of 22% compaction of their original thickness, which is a moderate calendering strenght where no electrode damage by compression forces is expected, respectively. Additionally the samples' electronic conductivity was measured. To achieve consistency between experiments and simulation we implemented a pseudo 2D physico-chemical model [4, 5] which enables to simulate discharge curves and Li transport within solid and liquid during discharge process. This model was parameterized [6] and validated to achieve agreement between experimental and simulated discharge curves of pouchcells. Then impacts of the particular parameters affected by calendering (Figure 1 a) were simulated and evaluated stepwisely. With the aid of simulation-supported analysis we show to what extend each of the particular parameters described above contributes to the impact of calendering (Figure 1 b). Geometric parameters, being namely electrode thickness and porosity contribute relatively sparsely, whereas the most significant impact is caused as calendering improves effective ionic and electronic conductivities and solid-liquid interfacial area. Larger electrode thickness and porosity in non-calendered electrodes only cause a slight voltage loss, whereas lower effective ionic and electronic conductivities in non-calendered electrodes not only cause additional voltage losses but also lead to capacity losses due to kinetic limitations of electron and Li ion transport at 1 C discharge. Furthermore the effective solid-liquid interfacial area where electrons and Li ions are exchanged between electrolyte and active material particles appears to be reduced in non-calendered electrodes. Contributions of these effects can be quantified and corresponding cell internal correlations can be analyzed by additionally investigating simulated Li transport within electrolyte and active material. Especially for LIB, where electrodes are complex particle-pore networks with solid and liquid diffusion in addition of binder and carbon black, simulation-supported investigation is shown to yield physically sound correlations between calendering and battery performance. The method presented in this work is also a useful approach to achieve a targeted optimization of LIB manufacturing parameters in order to improve crucial performance quantities, such as the energy density of automotive batteries. Figure 1: Parameters affected by calendering and their particular impacts on electrochemical performance at 1 C [1] W. Haselrieder, S. Ivanov, D. K. Christen, H. Bockholt, A. Kwade, Impact of the Calendering Process on the Interfacial Structure and the Related Electrochemical Performance of Secondary Lithium-Ion Batteries, ECS Transactions 50 (26) (2013) 59-70. [2] G.-F. Yang, S.-K. Joo, Calendering effect on the electrochemical performances of the thick Li-ion battery electrodes using a three dimensional Ni alloy foam current collector, Electrochimica Acta 170 (2015) 263-268. [3] H. Zheng, L. Tan, G. Liu, X. Song, V.S. Battaglia Calendering effects on the physical and electrochemical properties of Li[Ni1/3Mn1/3Co1/3]O2cathode, Journal of Power Sources 208 (2012), 52-57. [4] J. Newman, W. Tiedemann Porous-Electrode Theory with Battery Applications, AlChE Journal 21(1) (1975) 25-41. [5] N. Legrand, S. Rael, B. Knosp, M. Hinaje, P. Desprez, F. Lapicque, Including double-layer capacitance in lithium-ion battery mathematical models, Journal of Power Sources 251 (2014) 370-378. [6] G. Lenze, N. Lin, U. Krewer, Analysis of Parameterization Steps for a Physico-Chemical Lithium-Ion-Battery Model, ModVal12, Freiburg, Germany, Mar. 31 – Apr. 1, 2015. Figure 1

Production of Ni(OH)2 Nanosheets By Liquid Phase Exfoliation: High Performance Oxygen Evolution Catalysts and Supercapacitor Electrodes

2D materials have generated much excitement in recent years.1-2 Although these can now be produced in a number of ways, many applications, particularly in the energy arena, require liquid dispersions of 2D nanosheets. Liquid phase exfoliation3-4(LPE) is a very simple processing method which allows layered crystals to be exfoliated in liquids to give suspensions of good quality nanosheets. One strength of this process is its versatility. It has been used to exfoliate graphene and a number of inorganic 2D materials such as BN, MoS2 and GaS. Another is its simplicity – it is straightforward and easy to replicate. Here we bring together these two strengths by demonstrating that LPE can be used to exfoliate a new family of 2D materials, the layered double hydroxides (LDHs). This family of materials have been exfoliated previously using chemical exfoliation techniques. These techniques work well but are time consuming, take multiple steps and use harsh chemicals. Here, LPE method method involves sonication of commercially available powders in aqueous surfactant solutions and so is mild and potentially scalable. More specifically, we demonstrate that LPE can be used to convert layered crystals of nickel hydroxide into Ni(OH)2 nanosheets in relatively large quantities. TEM, XPS and Raman spectroscopy show the exfoliated nanosheets to be relatively thin and of good quality. Size selection allowed the production of samples with mean nanosheet lengths ranging from 55 to 195 nm. Optical measurements showed the optical absorption coefficient spectra to be relatively invariant with nanosheet size while the scattering coefficient spectra varied strongly with size. The resulting strong size dependence allows the extinction spectra to be used to estimate nanosheet size as well as concentration. We used the exfoliated nanosheets to prepare thin film electrodes for use in supercapacitors and as oxygen evolution catalysts. Prior to use we perfomed an activation procedure of polarising the electrode at 10 mA/cm2 in 1 M NaOH which significantly increased both the capacitance and catalytic activity towards the oxygen evolution reaction (OER). While the resultant capacitance was reasonably high at ~1200 F/cm3 (20 mV/s), the catalytic performance was exceptional. We observed currents of 10 mA/cm2 at overpotentials as low as 297 mV for the OER, which is close to the state of the art. Fig 1 (a) A) Structure of nickel hydroxide, Ni(OH)2. Blue, Ni; yellow, O; silver, H. B) Photograph of typical Ni(OH)2 dispersion in surfactant solution (H2O + sodium cholate) showing distinctive green colour. C) Representative low resolution TEM image of Ni(OH)2 nanosheets (b) Polarisation curves, 1 M NaOH (1 mV/s), for OER from Ni(OH)2 electrodes fabricated from Ni(OH)2films on Ni foam current collector before and after activation with the equivalent curve for the bare Ni foam shown for comparison. 1. Chowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H., The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nature Chemistry 2013,5, (4), 263-275. 2. Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S., Electronics and optoelectronics of two-dimensional transition metal dichalcogenides. Nature Nanotechnology 2012,7, (11), 699-712. 3. Hernandez, Y.; Nicolosi, V.; Lotya, M.; Blighe, F. M.; Sun, Z.; De, S.; McGovern, I. T.; Holland, B.; Byrne, M.; Gun'ko, Y. K.; Boland, J. J.; Niraj, P.; Duesberg, G.; Krishnamurthy, S.; Goodhue, R.; Hutchison, J.; Scardaci, V.; Ferrari, A. C.; Coleman, J. N., High-yield production of graphene by liquid-phase exfoliation of graphite. Nature Nanotechnology 2008,3, (9), 563-568. 4. Coleman, J. N.; Lotya, M.; O'Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.; Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.; Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J. C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen, K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V., Two-Dimensional Nanosheets Produced by Liquid Exfoliation of Layered Materials. Science 2011, 331, (6017), 568-571. Figure 1

High-Energy Laminated-Type Li-S Batteries Using High-Sulfur Loading Positive Electrode on Aluminum Foam

[Introduction]Interesting in Li-S batteries has been accelerated because it is expected to realize Li ion batteries delivering high energy density. Moreover, its poor cycle stability caused by severe dissolution of sulfur active material in organic carbonate electrolyte has been much improved by introducing novel materials such as Li ion selective separators [1] and Li salt solvate ionic liquid as insoluble electrolyte [2]. Hence, many researches have recently performed to enhance specific energy density. Although, Al foil, in general, has been widely used as a cathode current collector so far, it has not easy with increase in the loading amount of active material, in particularly S/KB composite. When the S/KB loading amount increases on the conventional Al foil, the cathode is suffered from difficulty in Li ion path into bulk active material and large internal resistance with reduced electrical conductivity. To solve such drawbacks, 3D mesh structured metallic foams have been researched and used as a current collector, which reported stable cycle performances with even 10 times larger sulfur loading amount than conventional Al foil [3]. In this report, we enlarged sulfur loading amount by introducing the 3D mesh structured Al foam as a current collector of cathode. Furthermore, optimization of the solvate ionic liquid was also investigated. Herein, it is suggested development on high energy density laminated Li-S battery delivering 200 wh kg-1. [Experimental]S/KB composite was obtained by mixing sulfur and KB in the weight ratio of 5:5, followed by heating at 155 degree C for 12 hours under N2 atmosphere. Cathode slurry was prepared in the weight ratio of S/KB (1/1) : KB : PVdF = 60 : 30 : 10. The sulfur amount of 1 – 12 mg cm-2 was loaded on 3D mesh structured Al foam (1mm in thickness). Laminated cells with 70 x 70 mm in size were prepared by assembling the prepared S/KB cathode, Li metal anode, separator (UPORE) and solvate ionic liquid (either G3 : LiTFSI : HFE = 1 : 1 : 4 or G1 + G3 : LiTFSI : HFE = 1 : 1 : 4). Cycle performances were tested between 1.5 V – 3.3 V with 16.7 mA g-1-S after 2 cycles of activation process. [Results and discussion]Both areal and specific discharge capacity of the laminated Li-S batteries are shown in Fig. 1a dependent for sulfur loading amount on 3D mesh structured Al foam, i.e., 1.3, 6.2 and 8.6 mg cm-2. Same values of specific discharge capacity delivering ca. 1400 mAh g-1-S were obtained from the different three samples. It revealed that sulfur was efficiently utilized compared to the previous report. This result assumed that loading S/KB on the 3D mesh structured Al foam enhanced Li ion and electron path in comparison to the conventional Al foil. Moreover, since the areal discharge capacity increased linearly with increase in sulfur loading amount, it is considered that stable Li ion and electron path would be maintained within this sulfur loading range.The laminated Li-S battery containing 11.5 mg cm-2 of sulfur loading was successfully prepared (see its picture in Fig.1b) and cycled with solvate ionic liquid (G1 + G3 : LiTFSI : HFE = 1 : 1 : 4). Fig.2 shows its charge-discharge potential profile. It attained specific discharge capacity delivering 1400 mA h g-1-S and areal discharge capacity delivering 15 mAh cm-2. Furthermore, the laminated Li-S battery achieved 735 mA h of cell capacity with a pair of electrode 70 x 70 mm in size. [Conclusion]We developed Li-S batteries composed of S/KB cathode with 3D mesh structured Al foam current collector, Li metal anode and Li salt solvate ionic liquid as electrolyte. The Li-S battery containing 11.5 mg cm-2 of sulfur achieved high specific and areal discharge capacity delivering 1400 mA h g-1-S and 15 mA cm-2, respectively. These results suppose that laminated batteries with high energy density delivering 200 Wh kg-1would be realized by efficiently laminating the electrode material and optimizing Li anode. [Acknowledgement] This work is supported by Advanced Low Carbon Technology Research and Development Program (JST-ALCA) Special Priority Research Area "Next-generation Rechargeable Battery". [References] [1]N. Nakamura, Y. Wu, T. Yokoshima, H. Nara, T. Momma, T. Osaka, J.Electrochem. Soc., 163, A683 (2016). [2]K. Yoshida, M. Nakamura, Y. Kazue, N. Tachikawa, S. Tsuzuki, S. Seki, K.Dokko, and M. Watanabe, J. Am. Chem. Soc., 133, 13121 (2011). [3]G. Zhou et al., Nano Energy(2015) 11, 356–365. Figure 1

Control Synthesis of Nitrogen Doped Carbon Nanotubes and Their Application in Energy Storage

Considerable progress has been made in investigating the carbon nanotubes (CNTs), which possess many desirable properties, including high mechanical strength and flexibility, excellent electrical conductivity and conductivity. Although the properties of CNTs are nothing short of exceptional, there are many areas in nano- and molecular-electronics, optics, electromechanics or chemistry where pristine tubes are not the appropriate. Substitutional doping of CNTs can lead to chemical activation of the passive surface of the CNTs and adds additional electronic states around Fermi level. This disrupts the smooth, largely chemically inert, p-bond and makes the tubes more chemically active. Correspondingly, the mechanical, thermal and transport properties will be changed by the doping of CNTs. For this reason, extrinsically doped tubes should make excellent starting candidates for a new generation of controlled chemically functionalized nanotube based materials. Nitrogen atoms substituting carbon atoms in the graphite matrix are electron donors and promote n-type conductivity. It was shown by tunneling microscopy that nitrogen–doped carbon nanotubes (CNx-NTs) have metallic properties independent of the structural parameters and are characterized by the presence of a donor state close to the Fermi level. The increase of the localized density of states at the Fermi level results in larger emission currents at lower voltages. Due to the metal-type conductivity and stable emission characteristics at low voltages, CNx-NTs are promising materials for field emitters and conducting coatings and composites. Furthermore, the enhancement of the donor properties and electrical conductivity of CNx-NTs after doping with nitrogen increases the activity of the carbon material in electron-transfer reactions. In this presentation, we will firstly give a straight forward illustration of the control synthesis of nitrogen doped carbon nanotubes on Ni foam current collector for afterward application, in which CNx-NTs were prepared using a floating catalyst chemical vapor deposition method and the nitrogen content can be controlled by precursor amount. Considering the increase of the surface activity of the tubes’ surface after nitrogen doping, the dispersion and distribution of metal oxides on CNx-NTs might be improved when they were grown on CNx-NTs. Hence, a series of compositing materials was synthesized including MoO3, ZnO, NiCo2O4, etc. were composed with CNx-NTs. Thanks to the following merits, the composites present very good performance in both lithium ion batteries and supercapacitors. (1) the 3D conducting network of CNx-NTs not only offers a strong skeleton for homogeneous deposition of metal oxides, but also provides a good electrical conducting pathway for ion and electron transportation and redox kinetics; (2) the large void space between CNx-NTs and metal oxides allows electrolyte easily penetrate into the inner-space and can endure the volume change during electrochemical measurement; (3) the direct deposition of metal oxides on CNx-NTs could ensure good mechanical adhesion and decrease the contact resistance between the composites and the current collectors; (4) the ultrathin and interconnected nanostructure of metal oxides possess numerous active sites for the redox reaction, the short diffusion path and fast ion transport; (5) the high conductive CNx-NTs directly grown on the Ni foam current collector benefit the fast electron transfer and avoid the use of polymer binder and conductive additives.

In situ grown cockscomb flower-like nanostructure of NiCo2S4 as high performance supercapacitors

Cockscomb flower-like NiCo2S4 composite material is made for supercapacitor application by using two step hydrothermal processes. The cockscomb flower-like NiCo2S4 architecture contains numerous ultrathin folded nanosheets which increases the active areas of the electrode and the three dimensional open space between the flower sheets facilitates the easy flow of electrolyte ions and leads to efficient utilization of active materials even at high current densities. Two kinds of composite electrodes were fabricated by coating and in situ growing a cockscomb flower-like of NiCo2S4 on nickel foam current collector. The in situ grown cockscomb flower-like NiCo2S4 showed superior performance compared to cockscomb flower-like of NiCo2S4 coated on nickel foam by avoiding the uses of polymer binders which adds dead areas and increase resistance on the electron and ion diffusion. Using this advantage the in situ grown cockscomb flower-like of NiCo2S4 showed high specific capacitance of 1707 F/g at current density of 1 A/g and areal capacitance of 4.1 F/cm2 at current density of 2.4 mA/cm2 with good rate capability of 65.12 % as current increases from 2.4 to 80 mA/cm2. Such excellent conductive and stable structure may find potential application in future energy storage devices.

Electrochemical reaction of sulfur cathodes with Ni foam current collector in Li-S batteries

The electrochemical properties of sulfur cathode with Ni foam current collector are investigated in detail. Different from sulfur cathode with stain steel current collector, it is interesting found that novel redox peaks at 1.95 V/1.35 V are observed for sulfur cathode with Ni foam. The electrochemical behavior is further verified by ex-situ XRD, SEM and XPS analyses. The results indicate that Ni foam current collector is involved in the redox reaction in Li/S rechargeable battery, and NiS forms at the surface of the Ni foam. These results demonstrate that the sulfur electrode is transformed into NiS.

Virus-Based Metal Nanofoams As Scalable Three-Dimensional Current Collectors

In this work, we demonstrate the use of M13 virus to produce metal nanofoams that can be used as current collectors in lithium ion battery electrodes. Metal foam current collectors have been demonstrated to promote rapid electronic conduction in battery electrodes while maintaining a high active material mass fraction. An ideal three dimensional metal current collector comprises a nanofoam, with pore size on the order of one lithium diffusion distance through the active material on the timescale of one (dis)charge. In such a structure, the high specific surface area of a metal nanofoam allows deposition of large quantities of active material, while a continuous metal network embedded within the electrode provides an electronically conductive pathway. However, unlike macroscopic metal foams, metal nanofoams are not widely available because robust and scalable synthetic routes for their production are difficult to achieve. Our lab has taken steps toward this by producing metal nanofoams using M13 virus as a biological template, and showing that these materials can be used as 3D current collectors. M13 is a filamentous virus that has been used as a template for nanomaterials for both electronic and non-electronic applications. Its utility arises from its nanoscale dimensions, as well as the fact that its surface chemistry and morphological properties can be controlled genetically. To fabricate metal nanofoams, we treat the M13 virus capsid as a high aspect ratio nanoparticle and use it to assemble a template. The process uses amino acid residues at three positions on the pVIII major capsid protein: the lysine residue located at position 14 (L14), a glutamic acid fusion to the protein’s N terminus (EEAE), and a tyrosine to methionine point mutation at site 21 (Y21M). The first step in nanofoam fabrication uses glutaraldehyde to crosslink a concentrated virus solution, making use of the lysine residues exposed on the virus capsid. This facile crosslinking process results in a hydrogel. These hydrogels can be formed on a wide range of substrates, and freestanding hydrogels can be produced. The virus used for this process is genetically modified with an EEAE amino acid fusion that increases its negative surface charge. That surface charge is used to bind a palladium-based catalyst, which is then used for electroless deposition of nickel onto the hydrogel. The resulting open-cell nanofoam comprises struts that are templated onto the filamentous virus. As such, modifying the morphology of the virus particles was expected to affect the foam morphology. Because virus genes encode the amino acid sequence of the proteins forming the virus capsid, this can be done genetically. We demonstrate this control using the Y21M mutation, a point mutation shown to increase the persistence length of the virus. Using a Y21M variant as a genetically programmable control, we are able to lower the relative density of our foams. We also demonstrate control over foam morphology using virus concentration, and by controlling immersion time in the electroless bath. Lithium ion battery active materials were deposited on the nanofoam surface using electrodeposition. This technique is employed to deposit a controllable thickness of manganese oxide onto the surface of our biologically derived metal nanofoams. The resulting foams are then assembled into half cells. Using pulsed electrodeposition, the active material thickness was controlled by varying the number of pulses. By depositing thin active materials, we demonstrate that it is possible to produce ‘capacitor-like’ biotemplated electrodes with excellent rate capability. Thicker active material layers are used to produce more energy-dense electrodes with lower rate capability. Beyond the use of virus to synthesize three-dimensional current collectors for coin cells, we demonstrate that the biological templating method allows scale-up of the nanofoams to produce larger batteries. As the foams are based on self-assembling virus nanoparticles, it is possible to obtain large quantities of the template through biological amplification. Unlike a process employing extensive top-down fabrication techniques, genetically programmable templates provide a facile route toward large-format electrodes with control over nanoscale morphology. Through amplification of the virus and scale-up of the nanofoam production process, we demonstrate 4”x3” pouch cells. These electrodes are shown to be flexible, allowing compatibility with a wide range of systems. This demonstrates our biological templating method as an advance toward practical metal nanofoam engineering materials. Figure: an M13-templated nickel nanofoam before active material deposition. Figure 1

Hierarchical Co3O4 Nanowires as Binder Free Electrodes for Reversible Lithium Storage

AbstractTo develop a long cycle life and good rate capability electrode, tricobalt tetraoxide (Co3O4) nanowires with hierarchical structure composed of ultra‐small nanoparticles are directly grown on nickel foam current collector. The size of the nanoparticles is about 10 nm. They are synthesized via a facile hydrothermal route followed by calcination and evaluated as an anode of binder‐free lithium‐ion batteries. The concentration of reactant and duration of reaction are considered as important synthesis parameters. Co3O4 nanowires electrode exhibits excellent electrochemical performance including outstanding cycling performance, a high reversible discharge capacity and good rate capability, owing to the hierarchical architecture composed of micro‐/nanostructures. After rate capacity performance measurements, a capacity of 1060.1 mAh·g−1 is retained. At a rate of 500 mA·g−1, a reversible capacity remains stable as high as 957 mAh·g−1. The enhanced performance is owing to the hierarchical structure of the nanowires and good contact with the substrate which can make electrons efficiently transport from Co3O4 nanowires to the current collectors. The mesoporous structure may facilitate the lithium ion diffusion and mitigate the internal mechanical stress induced by volume variations of the electrode upon cycling, which lead to outstanding electrochemical performance.

Assessing Charge Contribution from Thermally Treated Ni Foam as Current Collectors for Li-Ion Batteries

In this report we have investigated the use of Ni foam substrates as anode current collectors for Li-ion batteries. As the majority of reports in the literature focus on hydrothermal formation of materials on Ni foam followed by a high temperature anneal/oxidation step, we probed the fundamental electrochemical responses of as received Ni foam substrates and those subjected to heating at 100°C, 300°C and 450°C. Through cyclic voltammetry and galvanostatic testing, it is shown that the as received and 100°C annealed Ni foam show negligible electrochemical activity. However, Ni foams heated to higher temperature showed substantial electrochemical contributions which may lead to inflated capacities and incorrect interpretations of CV responses for samples subjected to high temperature anneals. XRD, XPS and SEM analyses clearly illustrate that the formation of electrochemically active NiO nanoparticles on the surface of the foam is responsible for this behavior. To further investigate the contribution of the oxidized Ni foam to the overall electrochemical response, we formed Co3O4 nanoflowers directly on Ni foam at 450°C and showed that the resulting electrochemical response was dominated by NiO after the first 10 charge/discharge cycles. This report highlights the importance of assessing current collector activity for active materials grown on transition metal foam current collectors for Li-ion applications.

Inexpensive electrochemical synthesis of nickel iron sulphides on nickel foam: super active and ultra-durable electrocatalysts for alkaline electrolyte membrane water electrolysis

The inexpensive fabrication of nano-honeycomb structured nickel iron sulphides on a nickel foam current collector is described and used as both anode and cathode in the alkaline membrane water electrolysis.

Facile synthesis of MnO2/rGO/Ni composite foam with excellent pseudocapacitive behavior for supercapacitors

In this study, the MnO2/reduced graphene oxide/Ni (MnO2/rGO/Ni) composite foam as a binder-free supercapacitor electrode was prepared by a facile method. The rGO film has been firstly coated on the skeletons of Ni foam current collectors by chemical deposition method and that have been used as substrates for preparation of a novel three dimensional rGO/Ni composite foam-supported porous MnO2 film by the hydrothermal method. The structure of MnO2/rGO/Ni composite foam was characterized by Raman spectra, IR spectra and Scanning electron microscopy. It indicated that the high-quality rGO film have been coated on skeletons of Ni foam current collectors and the MnO2 film had a 3D network microstructure, consisting of interlaced nanosheets. Furthermore, the binder-free MnO2/rGO/Ni composite foam electrode has been characterized by the cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectra. It exhibited excellent pseudocapacitive behavior with specific capacitance of 479.0 F/g. The capacitance could retain about 83.5% after 1000 charge–discharge cycles. This simple synthetic approach provides a convenient route for the large scale preparation of 3D porous MnO2/rGO/Ni composite foam for lots of applications in future.

Partial conversion of current collectors into nickel copper oxide electrode materials for high-performance energy storage devices.

A novel substrate sacrifice process is proposed and developed for converting part of a current collector into supercapacitor active materials, which provides a new route in achieving high energy density of supercapacitor device. Part of a copper foam current collector is successfully converted into highly porous nickel copper oxide electrode for light- and high-performance supercapacitors. Remarkably, this strategy circumvents the problem associated with poor contact interface between electrode and current collector. Meanwhile, the overall weight of the supercapacitor could be minimized. The charge transfer kinetics is improved while the advantage of the excellent mechanical properties of metal current collector is not traded off. By virtue of this unique current collector self-involved architecture, the material derived from the current collector manifests large areal capacitance of 3.13 F cm(-2) at a current density of 1 A g(-1). The capacitance can retain 2.97 F cm(-2) at a much higher density (4 A g(-1)). Only a small decay of 6.5% appears at 4 A g(-1) after 1600 cycles. The strategy reported here sheds light on new strategies in making additional use of the metal current collector. Furthermore, asymmetric supercapacitor using both solid-state gel electrolyte and liquid counterpart are obtained and analyzed. The liquid asymmetric supercapacitor can deliver a high energy density up to 0.5 mWh cm(-2) (53 Wh kg(-1)) at a power density of 13 mW cm(-2) (1.4 kW kg(-1)).

Calendering effect on the electrochemical performances of the thick Li-ion battery electrodes using a three dimensional Ni alloy foam current collector

High surface area and a three dimensional NiCrAl alloy foam current collector was used for two kinds of thick lithium iron phosphate electrodes. One kind of electrodes were compressed after the slurry of active material in the metal foam was dried and then annealed at 140°C for half a day whereas the other kind of electrodes were prepared without pressing. When the addition of carbon black was 4wt% for the two kinds of electrodes, a charge-discharge test revealed that the capacity of the cell using the pressed electrode faded much more although the voltage-drop was much smaller at the plateau region. For example, the capacity of the pressed electrode exhibited 85mAhg−1, while it was 135mAhg−1 for the unpressed electrode although the voltage-drop at the plateau region was 250mV higher at 0.5C-rate for the unpressed electrode. The AC impedance analysis showed that the charge transfer resistance of the pressed electrode was only 15Ω whereas it was 4 times higher for the unpressed electrode. The results illustrated that the effective redox area was much larger for the unpressed electrode since the cell using the unpressed electrode exhibited much higher capacity even at the condition of poor electronic conductivity. To solve the low electronic conductivity issue for the unpressed electrode, the addition of carbon black was further increased to 14 wt% and as a result, there was almost no difference in voltage drop at plateau region or charge transfer resistance between the two kinds of electrodes. Obviously, the capacity of unpressed electrode exhibited much higher at higher current rate due to the larger effective redox area.

MnOx nanosheets for improved electrochemical performances through bilayer nano-architecting

A new bilayer nanostructure of manganese oxide is developed by two-step hydrothermal reactions. Much higher mass loading of manganese oxide is successfully maintained (∼2.4 mg cm−2) through this new type of nanoarchitecture. In the meanwhile, the desired high specific surface area, good conductivity and ion accessibility are obtained, therefore giving rise to significantly improved electrochemical performance for manganese oxide (e.g., specific capacitance of 559.5 F g−1 and excellent cycle ability). By growing the second layer of MnOx on the Ni foam current collector that is pre-covered by a MnO2 substrate layer, uniformly thin and continuous nanosheets from the second layer MnOx with excellent surface coverage and open mesoporous structure are obtained, leading to large surface area and fast charge transfer. This novel architecting explores the new potential of manganese oxides as high performance supercapacitor electrodes.

Research and analysis on electrochemical performances of α-Fe2O3 electrode in Li-ion battery with different current collectors

In this work, we reported a simple synthesis of submicron α-Fe2O3 with rod-like structure. When it evaluated as electrode material for lithium ion battery, comparing with Cu foil and Ni foam, the as-prepared α-Fe2O3 electrodes with Cu foam current collector exhibited higher reversible capacity of 415mAhg−1 and more stable cycle performance after 30 cycles. Comparative researches on electrochemical performances of the α-Fe2O3 employing different current collectors (Cu foil, Cu foam and Ni foam) were discussed here in detail. According to our results, the improved electrochemical behaviors of α-Fe2O3 electrode with Cu foam current collector could be attributed to its particular electrode structure, i.e., porous, good electric conductivity, closed adhere to the electrode materials. Just because of that, it may make sure an easy accessibility of electrolytes and fast transportation of lithium ions, importantly, it could avoid the active materials falling off from the current collector on account of volume expansion.

Binder-free electrodes consisting of porous NiO nanofibers directly electrospun on nickel foam for high-rate supercapacitors

Porous NiO nanofibers (NFs) with an average diameter of 280-400nm have been fabricated directly on nickel foam current collector (NiO-NFs/Ni) by a simple electrospinning technique followed by appropriate heat treatment. The as-obtained NiO-NFs/Ni is used as a binder-free electrode in supercapacitors and its electrochemical performance is evaluated by cyclic voltammetry, galvanostatic charge/discharge test and electrochemical impedance spectroscopy. The results reveal that the binder-free NiO-NFs/Ni electrode can offer reasonably high specific capacitance (737Fg−1 at 2Ag−1), excellent rate capability with capacitance retention as high as 570Fg−1 even at 40Ag−1, and very good cycling stability at various rates up to 8000 cycles. The excellent performance can be attributed to the porous nature of both the NiO-NFs and Ni foam current collector as well as the binder-free feature of the electrode, which greatly facilitate the ion and electron transport in the electrode.

Integration of Si in a metal foam current collector for stable electrochemical cycling in Li-ion batteries

We improve the electrochemical performance of Li-ion batteries by trapping micron-sized silicon particles inside a metal foam current collector in Li-ion batteries.

Direct solvothermal phosphorization of nickel foam to fabricate integrated Ni2P-nanorods/Ni electrodes for efficient electrocatalytic hydrogen evolution.

We report an easy one-step approach for fabricating integrated Ni2P-nanorods/Ni (Ni2P-NRs/Ni) electrodes by direct phosphorization of a commercially available nickel foam current collector under solvothermal conditions. The resulting self-supported Ni2P-NRs/Ni composite electrode exhibits high electrochemical performance towards hydrogen evolution reaction in acidic medium.