Metal Current Collectors Research Articles

Front Cover: Stability of Metallic Current Collectors in Acidic Ionic Liquid for Rechargeable Aluminum‐Ion Batteries (ChemElectroChem 22/2018)

The Front Cover illustrates the concept of finding the last piece of the puzzle to complete rechargeable aluminum-ion batteries as one of the future advanced energy storage systems. More information can be found in the Communication by Y. Oh et al. on page 3348 in Issue 22, 2018 (DOI: 10.1002/celc.201800892).

Stability of Metallic Current Collectors in Acidic Ionic Liquid for Rechargeable Aluminum‐Ion Batteries

AbstractInvited for this month's cover picture is the group of Prof. Gibaek Lee (Yeungnam University, Republic of Korea) and Prof. Yongsug Tak (Inha University, Republic of Korea). The cover picture shows the concept of finding the last piece to complete rechargeable aluminum‐ion batteries as one of the advanced energy storage systems. Read the full text of the Communication at 10.1002/celc.201800892.

Sb2S3-rGO for high-performance sodium-ion battery anodes on Al and Cu foil current collector

Sodium-ion batteries (SIBs) have recently drawn great interest as an alternative due to their lower cost compare to lithium-ion batteries (LIBs). As in the practical application in LIBs manufacturing, Cu and Al foils are generally used as the current collectors for the anode and cathode of SIBs respectively. The concern for amorphous Li-Al alloy formation at ∼0.2 V is the main reason for selecting a different metallic (i.e. Cu) current collector. However, it is not the case for the SIBs since Na-Al alloys are formed at much lower potentials. In this paper, we demonstrate that the electrochemistry of SIBs allows an Al current collector to be used for the SIB anode without any adverse effect. The cell performance using a high capacity Sb2S3-reduced graphene oxide (Sb2S3-rGO) composite anode is undistinguishable between the use of Cu and Al current collectors. The reversible storage of Na+ in this Sb2S3-rGO composite is evaluated on both Cu-foil and Al-foil current collectors and comparable results are obtained: high desodiation specific capacities of ∼555 mAh g−1 (on Al-foil current collector) and 537 mAh g−1 (on Cu-foil current collector) for 70 cycles at 100 mA g−1. Therefore, the Al current collector can replace Cu in SIBs, which simplifies the construction of SIB cells and reduces the material cost in SIB production.

Automated Scalpel Patterning of Solution Processed Thin Films for Fabrication of Transparent MXene Microsupercapacitors.

A simple and generic strategy is proposed to pattern thin films deposited by a solution processable route. A soft approach based on an automated scalpel technique is developed to engrave thin films in a single step for sculpting functional planar devices. MXenes-the emerging family of 2D transition metal carbides and nitrides-combine metallic conductivity and hydrophilicity, enabling solution processing of transparent conducting electrodes (TCEs) under ambient conditions. Scalable dip coating is employed to process titanium carbide, Ti3 C2 , MXene thin films with excellent optoelectronic properties, achieving electrical Figure of merit up to 14. Automated scalpel engraving is adopted to fabricate transparent and semi-transparent MXene microsupercapacitors in a single step, hitherto not reported. Combining TCE and pseudocapacitive characteristics, MXene devices show excellent capacitive storage capabilities at high rates, without the aid of external metal current collectors. This technique allows for maskless patterning of solution processed thin films without losing intrinsic physicochemical properties and can be extended to fabricate heterostructured hybrid devices out of solution processable materials.

Self-Supporting Hybrid Supercapacitor Electrodes Based on Carbon Nanotube and Activated Carbons

Self-supporting AC (activated carbon)-FWCNT (few-wall carbon nanotubes) hybrid electrodes were fabricated by mixing of ACs with high specific surface area (SSA) and sub-millimeter-long FWCNTs. In order to fabricate the hybrid electrodes, AC and FWCNT were mixed in a weight ratio of 9:1, dispersed by bath-sonication and vacuum-filtrated on a membrane filter. The addition of FWCNTs gives conductivity and mechanical strength, and replace metallic current collectors in thick (0.1 mm) electrodes. For making an electrode, three different ACs that derived from walnut shell (WS), that from apricot stones (AS), and that commercially used for capacitors (YP-80F, Kuraray Chemical Co., Osaka Japan), were used with FWCNT in weight ratio of AC:FWCNT = 9:1. An electrode based only on FWCNT was also prepared as a reference for comparison. Electrochemical properties of the obtained electrodes were investigated by the cyclic voltammetry method (CV). Electrochemical characteristics were measured using the three-electrode cell contained of YP80F-FWCNT, AS-FWCNT, WS-FWCNT as a working electrode, a YP-80F-FWCNT counter electrode and a Ag/AgCl reference electrode with an electrolyte of 1 M Na2SO4 aqueous solution. Also, the morphological properties of obtained electrodes were studied using scanning electron microscope (SEM), the SSA was investigated by the Brunauer-Emmett-Teller analysis. SSA, conductivity, and resistivity of AS-FWCNT and WS-FWCNT electrodes were summarized. Both the AS-FWCNT and WS-FWCNT hybrid electrodes showed specific capacitances of about 140 F/g at 1 mV/s and about 100 F/g at 100 mV/s, which are similar or even better than the AC-CNT hybrid electrode made of commercialized AC (YP-80F).

Annealing environment effects on the electrochemical behavior of supercapacitors using Ni foam current collectors

Nickel (Ni) foam-based symmetric/asymmetric electrochemical supercapacitors benefit from a randomly 3D structured porous geometry that functions as an active material support and as a current collector. The surface composition stability and consistency of the current collector is critical for maintaining and consistency supercapacitor response, especially for various mass loading and mass coverage. Here we detail some annealing environment conditions that change the surface morphology, chemistry and electrochemical properties of Ni foam by NiO formation. Air-annealing at 400 and 800 °C and annealing also in N2 and Ar at 800 °C result in the in situ and ex situ formation of NiO on the Ni foam (NiO@Ni). Oxidation of Ni to NiO by several mechanisms in air and inert atmospheres to form a NiO coating is subsequently examined in supercapacitors, where the electrochemical conversion through Ni(OH)2 and NiOOH phases influence the charge storage process. In parallel, the grain boundary density reduction by annealing improves the electronic conductivity of the foam current collector. The majority of stored charge occurs at the oxidized Ni-electrolyte interface. The changes to the Ni metal surface that can be caused by chemical environments, heating and high temperatures that typically occur when other active materials are grown on Ni directly, should be considered in the overall response of the electrode, and this may be general for metallic current collectors and foams that can oxidize at elevated temperatures and become electrochemically active.

Stability of Metallic Current Collectors in Acidic Ionic Liquid for Rechargeable Aluminum‐Ion Batteries

AbstractHerein, we investigate the stability of current collectors for aluminum‐ion batteries employing aluminum chloride in 1‐ethyl‐3methylimidazolium chloride as the electrolyte under severe environments, confirming that nickel metal is electrochemically and chemically unstable in the expanded operating potential window, thus leading to the failure of cell operation and maintenance. The molybdenum current collector exhibits fairly stable and reversible redox cycling in the expanded potential window without any side effects or reactions, thus leading to the enhanced capacity of approximately 85 mAh g−1 at an extremely high current density of 4000 mA g−1.

Improved safety and mechanical characterizations of thick lithium-ion battery electrodes structured with porous metal current collectors

Porous metal current collectors enable the fabrication of thick electrode structures with improved safety margins and unique mechanical properties. Interpenetrating phase composite LiCoO2 cathodes and graphite anodes with large active material loadings are formed using advanced slurry processing techniques with a submersible ultrasonic horn. Full cells with 600 μm thick electrodes demonstrate high aerial capacity of 16.7 mAh.cm−2, improving energy density by 22% with respect to volume versus reference cells using traditional laminate composite electrode stacks. External shorting and nail penetration testing show notably suppressed joule heating currents, limiting peak temperature accrued to just 25% of the reference. Shear testing and three-point bending of individual electrodes and stack assemblies elucidate the greater role of the binder phase in the mechanical response, and that extensive characteristics such as thickness can be more influential than the intensive properties of the materials. Optimization of electrode thicknesses to balance rate capability with abuse safety is discussed, and opportunities for multifunctional application as load-bearing structural components are considered. Improved battery safety characteristics are demonstrated by reorienting the inherent components of the cell, without altering the chemical make-up, emphasizing the profound influence of structural design.

High Energy Density Lithium Secondary Battery with S Cathode and Si Anode Based on Carbon Nanotube Sponge

The lithium secondary batteries with higher energy density is strongly required for electric vehicle application. The sulfur cathode and silicon anode show high theoretical capacity (1675 mAh gsulfur -1 and 3580 mAh gsilicon -1). Nevertheless, both active materials change their volume during charge-discharge cycles, which leads to pulverization of electrodes. Therefore, it is difficult to load large amount of active material in the electrode. Limited values of active material results in low capacity in total system of batteries due to the large mass of metal current collector (Al and Cu). To solve the problem, self-supporting, sponge-like paper of carbon nanotubes (CNTs) can be a candidate for non-metal based 3D current collector, which can reduce the mass of current collector. It also accommodates large amount of active material due to high porosity. Previously, we have developed S-CNT cathode and Si-CNT anode [1] and demonstrated high capacity for their individual half cells [1]. In this work, we combined them to achieve higher energy density full cell without any metal current collector. Submillimeter-long few-wall CNTs produced by fluidized-bed chemical vapor deposition method [2] were used for the 3D current collector. 30-μm-thick CNT paper was fabricated via dispersion and filtration of the CNTs, and the S-CNT cathode was fabricated by sublimation of sulfur into the CNT paper. The Si-CNT anode was fabricated by co-dispersion and co-filtration of Si nanoparticles (50, 100, and 150 nm in diameter) and the CNTs followed by carbon coating by chemical vapor deposition. Lithium was pre-doped to the Si-CNT anode either by contacting it with Li foil in electrolyte or by electrochemically using Li foil as counter electrode. The full cell of the S-CNT cathode (58 mass% S) and the LixSiy-CNT anode (70 mass% Si) showed a high initial discharge capacity and energy density of over 320 mAh/g and 540 Wh/kg based on the total mass of the cathode and anode. [1] T. Kowase, et al, J. Power Sources, 363, 450 (2017). [2] Z. Chen, et al., Carbon, 80, 339, (2014)

A 1D Mathematical Model to Study the Effects of Adhesive Strength on the Electrochemical Performance of Silicon Electrodes for Advanced Lithium Ion Batteries

In recent times, commercially available lithium ion batteries (LIBs) employ graphite, with a theoretical capacity of 372 mAh g-1, as their anode material. To enhance the energy density of LIBs, alternative anode materials with higher capacities, such as Li metal, Si, and various alloys, have been extensively exploited. With its advantages of a higher theoretical capacity (4200 mAh g-1), environmental friendliness, and terrestrial abundance, Si is particularly well-suited as an anode material for this purpose. Nevertheless, Si suffers from large volume variations (up to 300%) during lithiation/delithiation processes, leading to pulverization, low cycling efficiency, unstable solid electrolyte interphases (SEI), and permanent capacity losses. There have been several scientific investigations and strategies to solve the issues related to the large volume changes in Si. Relevant breakthroughs have been made with the help of advanced nanotechnologies in terms of enhancing the cycle life and improving the cycle rate performance. Notable among them is the use of binding materials with improved adhesive properties, such as copolyimide, alginate, poly(acrylic acid) (PAA), carboxymethyl cellulose, polyamide-imide, polyimide, and polymers that form cross-linked networks. Moreover, enhancing the adhesive strength between the Si composite electrode and Cu current collector by coating the latter’s surface with a very thin polymeric layer has significantly enhanced the electrochemical performance of Si anodes. However, the mechanism underlying this improvement in performance was not clearly addressed. In this presentation, a coupled chemo-mechanical model which considers the contact resistance as well as the influence of the attractive forces inside the contact area between the electrode and current collector was developed to study the effects of the adhesive strength of a binding material on the electrochemical performance of silicon-based lithium-ion batteries. The model predictions were validated with experimental data from coin-type half-cells composed of Li metal, Si electrodes, and Cu current collectors coated with binding materials with different adhesive strengths. The proposed model was used to investigate the effects of the adhesive strength and various cell design parameters on the specific capacity of the Si-based Li-ion cells.

Micropatterned arrays of vertically-aligned CNTs grown on aluminum as a new cathode platform for LiFePO4 integration in lithium-ion batteries

The conventional lithium-ion battery fabrication process involves mixing of the active cathode material with additives and tape casting on metallic current collectors. The thickness of this layer limits the performance of the cathode. In this work, a novel cathode platform is presented consisting of a micropatterned array of vertically aligned carbon nanotubes (CNTs) on aluminum (Al) foil that serves as host for active cathode powders. This highly conductive three-dimensional structure provides a high specific surface area to support greater mass loading capable of achieving high energy and power densities. The feasibility of this structure was demonstrated by using commercially available lithium iron phosphate (LFP) powder which was processed and dispersed using two different techniques—vibration-assisted drip-coating and electrophoretic deposition. A high specific capacity of 143 mAh/g at 3.4 V was achieved at C/20 rate for the novel cathode fabricated using electrophoretic deposition, which seemed superior to vibration-assisted drip coating with its easier application, more uniform particle coating, stronger particle attachment to the CNTs, and better electrochemical performance. In addition, CNT array on Al has been demonstrated to be a viable candidate for fabricating cathodes for energy storage applications without the need for any additives and/or binders.

Self-discharge of a hybrid supercapacitor with incorporated galvanic cell components

Supercapacitors can provide a high specific power and long cycle life but suffer a significant self-discharge limiting their application as a stand-alone energy storage device. A new hybrid supercapacitor with incorporated galvanic cell components was proposed to mitigate the self-discharge problem. The hybrid supercapacitor was similar to a conventional supercapacitor with two active carbon electrodes separated by a polymer electrolyte membrane containing 1.5 M zinc sulfate. However, a zinc foil and a copper foil were used as the current collectors for the negative and the positive electrodes respectively, which can provide a micro-current to compensate the self-discharge current. The hybrid supercapacitor exhibited a maximum specific capacitance of 55 F g− 1 and specific energy of 4.51 Wh kg−1 with a charge efficiency of 90%. The capacitance retention of the hybrid supercapacitor was 80% after 2000 cycles. The open circuit voltage of the charged hybrid supercapacitor was stable and declined slightly from initial 0.90 V–0.85 V in a month. The results demonstrate that via replacement of a pair of conventional metal current collectors with a galvanic couple the ubiquitous self-discharge problem can be significantly mitigated and the storage time can be prolonged to meet the requirement for stand-alone applications.

A coupled chemo-mechanical model to study the effects of adhesive strength on the electrochemical performance of silicon electrodes for advanced lithium ion batteries

A coupled chemo-mechanical model which considers the contact resistance as well as the influence of the attractive forces inside the contact area between the electrode and current collector was developed to evaluate the effects of the adhesive strength of a binding material on the electrochemical performance of silicon-based lithium-ion batteries. The increase in contact resistance between the electrode and current collector was introduced as a factor that reduces the electrochemical performance of the cell. The model predictions were validated with experimental data from coin-type half-cells composed of Li metal, Si electrodes, and Cu current collectors coated with binding materials with different adhesive strengths. The contact resistance increased with an increasing number of cyclic current rate. The adhesive strength decreased with cyclic current rate. The proposed model was used to investigate the effects of adhesive strength and various cell design parameters on the specific capacity of the Si-based Li-ion cells.

A current collector covering nanostructured villous oxygen-deficient NiO fabricated by rapid laser-scan for Li-O2 batteries

Non-aqueous Li-O2 batteries attract extensive attention because of their ultra-high theoretical specific energy density. However, the high charge potential, which induces severe parasitic reactions such as the corrosion of carbon-based catalysts and metal current collectors, is one of the biggest challenges currently. Herein, a current collector of Ni foam covering nanostructured villous NiO with oxygen vacancies (NiO1-δ) was fabricated by a fast laser-scan technique. The modified NiO1-δ based current collector presented superior stability and comparable electrocatalytic activity. It delivered a discharge capacity of about 500 mAh g−1 and a low charge potential of 3.84 V in a Li-O2 cell in the absence of catalysts. And this cell could maintain 73.5% of the initial capacity after 100 full discharge-charge cycles. Density functional theory (DFT) calculations verified that the improved electrocatalytic activity mainly derived from the introduction of oxygen vacancies in NiO1-δ. It improved the electronic conductivity for rapid electron transfer as well as served as active sites to bind O2 and oxygen-containing intermediates (eg. LiO2) for electrochemistry reactions. This work gives a rapid and easily mass-produced method to fabricate a stable and activated current collector for Li-O2 batteries.

Effects of wire-type and mesh-type anode current collectors on performance and electrochemistry of microbial fuel cells

Carbon-based material is commonly used for anodes in MFCs, but its low conductivity often limits anodic performance. Application of corrosion-resistive current collector to carbon-based anode can be a promising strategy for increasing the anodic performance. In this study, it was hypothesized increasing metal current collector improved anodic performance. Two different carbon-felt anodes with titanium wires (CF-W) or stainless steel mesh (CF-M) as a current collector were tested in a single chamber MFC. In the short-term tests such as polarization and impedance tests, CF-M with the larger current collector area (21.7 cm2) had 33% higher maximum power (2311 mW/m2), 81% lower anodic resistance (3 Ω), and 92% lower anodic impedance (1.1 Ω). However, in the long-term tests, CF-W with the smaller current collector area (0.6 cm2) showed higher performance in power and current generation, COD removal, and CE (51%, 10%, 11%, and 5% higher, respectively) and produced 41% higher net current in cyclic voltagramm (20.0 mA vs. 14.2 mA). This result shows that larger current collector is advantageous in short-term performance and disadvantageous in long-term performance, because the larger current collector is good for current collection, but interferes with mass transfer and microbial growth.

Performance investigation and effect of temperature on a passive μDMFC with stainless steel mesh

In this paper, we provide a novel type of micro-direct methanol fuel cell (μDMFC) fabricated with two stainless steel plates as metal current collectors. In order to improve cell performance, two sheets of stainless steel mesh (SSM) are added between the membrane electrode assembly (MEA) and current collectors. To avoid electrochemical corrosion, titanium nitride (TiN) layers with thickness of 500 nm are deposited onto the surface of current collectors and stainless steel mesh. The results show that the embedded stainless steel mesh can remarkably reduce the interior impedance of the μDMFC. Moreover, compared with μDMFC without SSM, the novel cell exhibits a more outstanding performance, yielding a maximum power density of 54.4 mW cm−2 at 80 °C.

MOF-derived Cobalt Sulfide Grown on 3D Graphene Foam as an Efficient Sulfur Host for Long-Life Lithium-Sulfur Batteries

SummaryLithium-sulfur (Li-S) batteries are an appealing candidate for advanced energy storage systems because of their high theoretical energy density and low cost. However, rapid capacity decay and short cycle life, mainly resulting from polysulfide dissolution, remains a great challenge for practical applications. Herein, we present a metal-organic framework (MOF)-derived Co9S8 array anchored onto a chemical vapor deposition (CVD)-grown three-dimensional graphene foam (Co9S8-3DGF) as an efficient sulfur host for long-life Li-S batteries with good performance. Without polymeric binders, conductive additives, or metallic current collectors, the free-standing Co9S8-3DGF/S cathode achieves a high areal capacity of 10.9 mA hr cm−2 even at a very high sulfur loading (10.4 mg cm−2) and sulfur content (86.9 wt%). These results are attributed to the unique hierarchical nanoarchitecture of Co9S8-3DGF/S. This work is expected to open up a promising direction for the practical viability of high-energy Li-S batteries.

Thermal Conductivity Changes Due to Degradation of Cathode Film Subjected to Charge–Discharge Cycles in a Li Ion Battery

A battery device with graphene platelets as anode, lithium nickel manganese oxide as cathode, and solid-state electrolyte consisting of layers of lithium phosphorous oxynitride and lithium lanthanum titanate is assembled on the stainless steel substrate. The battery in a polymer enclosure is subjected to several electrical tests consisting of charge and discharge cycles at different current and voltage levels. Thermal conductivity of the cathode layer is determined at the end of charge-discharge cycles using transient thermoreflectance. The microstructure and composition of the cathode layer and the interface between the cathode, the anode, and the electrolyte are characterized using scanning electron microscopy and elemental mapping. The decrease in the thermal conductivity of the same cathode observed after each set of electrical test cycles is correlated with the volume changes and formation of low ionic and thermal conductivity lithium oxide and lithium oxychloride at the interface and along porous regions. The interface between the metal current collector and the cathode is also found to be responsible for the increase in thermal resistance. The results indicate that changes in the thermal conductivity of the electrodes provide a measure of the resistance to heat transfer and degradation of ionic transport in the cathode accompanying the charge–discharge cycles in the batteries.

Nano-porous copper metal current collector for lithium ion batteries

A low-cost and scalable ultrasonic synthetic method to produce copper metal current collector with uniform nanopores on the surface is achieved for the first time. A layer of silicon active material was sputtered on the surface of as-prepared metal current collector (vs. metal lithium) as an innovative current collecting material for lithium ion battery. The assembled battery with this current collector showed an areal capacity of 2.2 mAh/cm2, comparable to that of commercially available lithium ion batteries. Due to the nano-porous structure of current collector, the silicon active material electrochemical capacity retention and cycling stability also improved significantly.

Three-dimensional graphene as gas diffusion layer for micro direct methanol fuel cell

The gas diffusion layer (GDL), as an important structure of the membrane electrode assembly (MEA) of the direct methanol fuel cell (DMFC), provides a support layer for the catalyst and the fuel and the product channel. Traditionally, the material of GDL is generally carbon paper (CP). In this paper, a new material, namely three-dimensional graphene (3DG) is used as GDL for micro DMFC. The experimental results reveal that the performance of the DMFC has been improved significantly by application of 3DG. The peak powers increase from 25 mW to 31.2 mW and 32 mW by using 3DG as the anode and cathode GDL instead of CP, respectively. The reason may be the decrease of charge and mass transfer resistance of the cell. This means that the unique 3D porous architecture of the 3DG can provide lower contact resistance and sufficient fuel diffusion paths. The output performance of the cell will be further improved when porous metal current collectors is used.