Structure Of Current Collector Research Articles

Thermal stress and contact analysis utilizing tested temperature data in a kW-class external-manifold solid oxide fuel cell stack

Thermal stress and contact are two pivotal factors influencing the operational lifespan and performance of solid oxide fuel cell (SOFC) stacks. In practical kW-MW SOFC systems, stack boxes are typically constructed using kW-class stack blocks comprising dozens of cells. Temperature distribution affects the thermal stress distribution, thus affecting the contact of the stack. In this work, the thermal stress distribution and contact of a 2.5 kW external-manifold stack composed of 60 repeat units are investigated by using finite element analysis (FEA). To get a more accurate and realistic results, temperature data of a stack measured in an ongoing SOFC system is incorporated into the computational model. The influences of the clamp loads from manifolds, the structure of current collectors, the number of spacer plates, and the thickness of interconnects on the thermal stress distribution and contact of the stack are investigated. In the basic stack, the tensile stress induced by the temperature gradient appears to be the primary cause of the high thermal stress in the air inlet region of top cells. Due to the high-temperature strength of the seal material and endplates, the contact is inferior in cells near endplates. Increasing the clamp loads of manifolds within specified limits leads to a reduction in both the magnitude and area of high thermal stress, concurrently enhancing the stack contact. Strengthening the current collector structure induces more high-stress regions and simultaneously increases the stack contact. The introduction of overmuch spacer plates results in more high stress regions and a deterioration in stack contact. Moreover, increasing the thickness of interconnects introduces more high stress regions, negatively impacting stack contact.

Bipolar Current Collectors of Cu/polymer/Al Composite for Anode‐Free Batteries

AbstractThe all‐in‐one design of cathode and anode is a promising strategy to improve energy density and assembly efficiency for lithium batteries. However, it is an important prerequisite to combine negative and positive current collectors in a single sheet. Here, an asymmetric structure of bipolar composite current collector (BCCC), thin copper (Cu) and aluminum (Al) metal layers respectively deposited on each side of a thin polyethylene terephthalate (PET) polymer substrate is developed. Unlike conventional metal foils, the electronically insulative polymer blocks electron transfer between the cathode and anode coated on each side of BCCC. Buckling‐based mechanics measurement and molecular simulation are conducted to quantitatively evaluate the interfacial strength of metal/polymer, which is enhanced by introducing an intermediate chromium (Cr) layer. For applications in anode‐free wound batteries, the integrated sheet of separator/cathode/BCCC can simplify the alignment of the electrodes during the winding process. Without special surface and electrolyte optimizations, a higher Coulombic efficiency (99.1%) and larger capacity retention (50.0%) are achieved after 100 cycles in the LiNi0.8Co0.1Mn0.1O2 anode‐free battery than the battery using Cu foils.

Ultra-Thick Cathodes for High-Energy Lithium-Ion Batteries Based on Aluminium Foams—Microstructural Evolution during Densification and Its Impact on the Electrochemical Properties

Using three-dimensional (3D) metal foams as current collectors is considered to be a promising approach to improve the areal specific capacity and meet the demand for increased energy density of lithium-ion batteries. Electrodes with an open-porous metal foam as current collector exhibit a 3D connected electronic network within the active mass, shortening the electron transport pathways and lowering the electrodes’ intrinsic electronic resistance. In this study, NMC622 cathodes using an aluminium foam as current collector with a measured areal capacity of up to 7.6 mAh cm−2 were investigated. To this end, the infiltrated foams were densified to various thicknesses between 200 µm and 400 µm corresponding to an electrode porosity between 65% and 30%. The microstructural analysis reveals (i) the elimination of shrinking cavities and a decrease in the porosity of the infiltrated active mass, (ii) an improved contact of active mass to the current collector structure and (iii) a pronounced clogging of the surface pores. The electrochemical properties such as capacity and rate capability are correlated to the electrode’s microstructure, demonstrating that densification is necessary to improve active material utilization and volumetric capacity. However, strong densification impairs the rate capability caused by increased pore resistance and hindered electrolyte accessibility.

The Effect of Structure and Mechanical Properties Change of Current Collector during Cycling on Sb-Based Lithium-Ion Batteries’ Performance

Here, we investigate structure and mechanical change of Cu and Al current collector during cycling and analyze the contribution to capacity attenuation of Sb-based lithium-ion batteries (LIBs). There exists migration of C, Sb, and Li atoms to the inside of Cu current collector, and diffusion of Li, Co, and O atoms to the inside of Al current collector during cycling, which results in the formation of a porous film of Li2SbCu (with the thickness of 21 µm after 100 cycles) and a relatively dense film of Al2O3 (with the thickness of 23 µm after 100 cycles) on the surface of Cu and Al current collector, respectively. The formation of films results in a weak bond between active layer and current collector, and the increase of hardness of 0.84 GPa and modulus of 22.5 GPa for Cu current collector after 100 cycles, which is adverse to the charge capacity and cycling stability. Nevertheless, Al2O3 films caused hardness decrease of 0.53 GPa and modulus decrease of 18.93 GPa of Al current collector after 100 cycles, which contributes to the improvement of cycling stability and charge capacity. This study provides an understanding of the capacity loss of Sb-based LIBs from the perspective of structural degradation of current collectors.

Stable Li deposition of 3D highstrength-lithiophilicity-porous CuZn current collector with gradient structure

The growth and volume changes of dendrites caused by irregular Li deposition hinder the commercial application of Li metal anodes. Here, we design a bottom-up current collector with a gradient layered structure to fabricate dendrite-free Li metal anode and achieve high stability of the cycle. The high strength support layer stabilizes the volume change of the repeated Li plating/stripping process, and the lithiophilic CuZn alloy layer and porous Cu surface enable Li to uniformly nucleate and stably deposit inside the pore structure, thus efficiently suppressing the growth of Li dendrites. Due to the unique gradient structure of current collector, the symmetrical cell achieved a long cycle life of over 560 h at Li plating/stripping capacity of 1 mAh cm−2 and a current density of 1 mA cm−2, approximately four times and twice as long as plane Cu and porous Cu. In the full cells with LiFePO4 cathode, the capacity retention increased from 33.2 % (plane Cu) to 80 % after 200 cycles, and achieved excellent rate performance. This gradient design deepens the understanding of the nucleation and growth of Li in the integrated lithiophilic matrix and 3D porous structure, and provides an optional idea for the development of high-performance Li metal anode.

Advances in research on the inhibitory effect of 3D current collector structures for lithium dendrites

The structural advantages and disadvantages of various 3D current collectors are summarized to provide suggestions for the future development of anode in lithium metal batteries.

Insights on the work function of the current collector surface in anode-free lithium metal batteries

We demonstrate the relationship between the work function of current collector and electrolyte decomposition. This work can give an insight into how to design the electronic structure of current collector for advanced anode-free LMBs.

EGaIn coated 3D-Cu foam as a self-healing current collector for lithium ion batteries

Traditional lithium-ion batteries are prone to cracks and perforations in extreme environments, which could cause electrochemical performance degradation or even safety problems. Here, based on the alloying reaction of liquid metal, through the adjustment of alloying temperature and reaction time, a uniform and stable dispersion of eutectic gallium indium liquid metal (EGaIn) on the surface and internal structure of the micro-etched 3D-Cu current collector (EGaIn@3D-Cu) is obtained. Furthermore, the graphite anode prepared with the EGaIn@3D-Cu current collector (the self-healing graphite anode) shows an excellent self-healing performance. Namely, the specific capacities of the self-healing graphite anode before and after scratch damage are 327.4 mA h g−1 and 309.6 mA h g−1, respectively, which is significantly better than that of the graphite anode assembled with 2D-Cu foil current collector. Therefore, the EGaIn@3D-Cu current collector prepared by a simple manufacturing process could effectively realizes the self-healing function, prevent the capacity degradation and improve the stability of the battery.

High Energy Density and Stable Three‐Dimensionally Structured Se‐Loaded Bicontinuous Porous Carbon Battery Electrodes

3D‐structured Se‐loaded bicontinuous porous carbon (BPC) electrodes are fabricated through colloidal templating of BPC followed by pulsed‐voltage Se electrodeposition. The resultant electrodes are found to deliver a specific capacity of 665 mAh g−1 at a rate of 0.1 C, near the theoretical value for Se. When a vinylene carbonate (VC) containing electrolyte is utilized, the capacity fade over 500 cycles at 1 C rate is as small as a few percent. Impedance measurements and physical characterization of cycled electrodes indicate the exceptionally stable cycling performance is possibly due to VC resulting in the formation of a stable solid electrolyte interface (SEI) during cycling. Along with the cycling stability, the rate performance of the 3D Se/BPC electrodes is also good. Due to the bicontinuous structure of carbonaceous current collector at rates as high as 5 C, the deliverable capacity is about 300 mAh g−1.

Degradation of MCFC Materials in a 81 cm2 Single Cell Operated Under Alternated Fuel Cell/Electrolysis Mode

The possibility of producing hydrogen from molten carbonate steam electrolysis using the well-established Molten Carbonate Fuel Cell (MCFC) technology was explored in this work. For this purpose, a 81 cm2MCFC single cell assembled with conventional cell materials was operated under alternated fuel cell/electrolysis conditions at 650°C in a binary eutectic Li2CO3-K2CO3electrolyte for about 400 h after an initial period of 650 h in which the cell worked only in the usual MCFC mode. A rapid cell performance loss in terms of cell internal resistance and electrode polarization was observed as soon as the cell started to work in the alternated fuel cell/electrolysis mode. After test completion, a post-mortem analysis was conducted to correlate the electrochemical response with cell materials degradation. Cell materials of the reverse cell were compared against a reference single cell that was assembled with the same materials and operated only in the fuel cell mode under comparable experimental conditions. Post-mortem analysis allowed to identify several serious stability issues of conventional MCFC materials when used in alternated operation modes. Thus, although the electrolyte matrix appeared almost unaffected, a significant amount of dissolved nickel was found in the matrix indicating that electrolysis operations promote an increasing chemical instability of the NiO oxygen electrode. A serious reduction of electrode porosity was also observed in both NiO oxygen and Ni metal fuel electrodes, which could explain the higher polarization resistance of the reversible cell in comparison to the reference MCFC cell. Furthermore, the oxygen current collector made with conventional 316L stainless steel was found to be seriously corroded under the alternated operation modes. Thus, the observed rapid increase in internal resistance in the reverse cell could be caused, at least in part, by an increased contact resistance between the oxygen electrode and the corroding current collector structure. Possible solutions for improving stability of electrodes and of the oxygen current collector in reverse MCFC cells were proposed and discussed in the final part of the work.

Nanoscale Wrinkled Cu as a Current Collector for High-Loading Graphite Anode in Solid-State Lithium Batteries.

Solid-state lithium batteries have been intensively studied as part of research activities to develop energy storage systems with high safety and stability characteristics. Despite the advantages of solid-state lithium batteries, their application is currently limited by poor reversible capacity arising from their high resistance. In this study, we significantly improve the reversible capacity of solid-state lithium batteries by lowering the resistance through the introduction of a graphene and wrinkle structure on the surface of the copper (Cu) current collector. This is achieved through a process of chemical vapor deposition (CVD) facilitating graphene-growth synthesis. The modified graphene/wrinkled Cu current collector exhibits a periodic wrinkled pattern 420 nm in width and 22 nm in depth, and we apply it to a graphite composite electrode to obtain an improved areal loading average value of ∼2.5 mg cm-2. The surface-modified Cu current collector is associated with a significant increase in discharge capacity of 347 mAh g-1 at 0.2 C when used with a solid polymer electrolyte. Peel test results show that the observed enhancement is due to the improved strength of adhesion occurring between the graphite composite anode and the Cu current collector, which is attributed to mechanical interlocking. The surface-modified Cu current collector structure effectively reduces resistance by improving adhesion, which subsequently improves the performance of the solid-state lithium batteries. Our study can provide perspective and emphasize the importance of electrode design in achieving enhancements in battery performance.

Effect of Surface Roughness Evolution of a Metal Current Collector Using a Pulse-Reverse Polarization Method on the Stability of the Anode-Free Lithium Metal Batteries

Recently, Lithium(Li) metal has been considered as a “ideal” anode material due to the extra-high capacity (3,860 mAh g-1), the lowest electrochemical equilibrium potential (-3.040 VSHE) and low density (0.534 g cm-3). Despite its ideal characteristics, Li metal anode(LMA) has a critical drawback that Li deposits grow in the form of dendrite due to its ununiform plating/stripping behaviors. The undesired dendritic growth of Li results in the detrimental effects on the cell performance, such as cell short-circuit, low coulombic efficiency(CE), and dead lithium, which have hampered widespread exploits of lithium metal-based batteries. Therefore, in recent years, numerous strategies to prevent or mitigate the problematic dendrite growth, including construction of artificial solid electrolyte interphase (SEI), lithiophilicity/morphology control of current collector, modification of electrolyte, and so forth [1,2].Meanwhile, by virtue of quite successful improvement in performance of LMAs, the battery system using in-situ formed LMAs, called anode-free lithium metal batteries (AFLMBs) have gained much interests [3]. In AFLMBs, the anode compartment has only a current collector at the initial state and then lithium metal anode is formed by electroplating with lithium ions provided from the cathode through initial charging step. The absence of corrosive/reactive Li metal in assembly process decreases the production cost and the energy density of a full-cell can be increased due to additional loading of cathode active materials. However, the dendritic growth of lithium could become more problematic because the cyclable lithium ions are fully limited to those provided from the cathode active materials. For solving notorious dendrite problem in AFLMBs, many strategies such as a use of highly concentrated salt electrolytes [3], the addition of functional electrolyte additives [4] and the introduction of lithiophilic elements on the current collector have been reported [5]. Unfortunately, however, it still seems difficult to nurture all strengths of AFLMBs related to the cost-effectiveness, simple cell design and high-energy density.One of the effective ways to regulate electroplating behavior of lithium is to introduce the surface-roughed metal current collector. Using such the structures, the charge accumulation sites on the microscopic structure of current collector can be randomly distributed, resulting in uniform electric field on the surface of current collector. Additionally, the localized current density can be reduced, and problematic volume changes of lithium can be buffered [2].In this context, we introduced the surface-roughed metal current collector as a substrate of AFLMBs to improve their stability. The surface roughness was controlled by an electrochemical method using a pulse-reverse polarization [6]. In particular, we focused on studying the effect of various pulse parameters on the morphological evolution of a metal current collector. To investigate their effects on the stability of AFLMBs, the CR 2032-type coin cells composed of the roughly surface-treated metal foil as a current collector and high-loading Li-Ni0.5Co0.2Mn0.3 (≈ 12.1 mg/cm2) as a cathode were assembled in an Ar-filled glove box. Figure 1-(a) presents an example of pulse signal used to modify roughness of metal surfaces. First, to investigate effect of pulse current density(iox=ire=i), we fixed the amount of metals, which were electrochemically oxidized and reduced by giving different pulse duration time (tox = tre = t,). Figure 1-(b) presents the effect of pulse current on the morphology of metal foils. After pulse with 0.5 mA/cm2, the surface of metal foil is covered by the clusters of metal/metal oxide particles. With increasing current density, the diameter of the clusters decreased and the number of clusters increased. Figure 2 shows the effect of surface-roughed metal surface on the electroplating behavior of lithium metals. As can be seen in Figure 2-(a), the morphology of electrodeposited lithium on the surface-treated metal foil has a denser and flatter Li deposit than that on pristine metal foil, where a needle-like dendritic structure is shown. Figure 2-(b) presents the CE of the repeated plating/stripping process of lithium metal. All the cells adopting the surface-treated foils showed a higher cycling stability compared to a pristine metal foil.Additionally, in this presentation, the correlation between pulse-reverse parameters and morphological evolution of a metal current collector, and the effect on the electrochemical long-term stability of AFLMBs will be discussed in more detail References [1] X.-B. Cheng et al., Chem. Rev, 117, 10403, 2017.[2] J. Zheng et al., Chem. Soc. Rev., 49, 2701, 2020.[3] J. Qian et al., Adv. Funct. Mater., 26, 7094, 2016.[4] N. A. Sahalie et al., J. Power Sources, 437, 226912, 2019.[5] S. S. Zhang et al., Electrochimica Acta, 258, 1201, 2017.[6]M. S. Chandrasekar and M. Pushpavanam, Eletrochimica Acta, 53, 3313, 2008 Figure 1

Synergistic effect of 3D current collector structure and Ni inactive matrix on the electrochemical performances of Sn-based anodes for lithium-ion batteries

A three-dimensional (3D) architecture design of the battery electrodes is believed to enhance the energy and power densities of conventional lithium-ion batteries. In this paper, we report a unique 3D architecture anode fabricated by electrodeposition of ultrathin Ni3Sn4 intermetallic alloy onto a commercially available nickel foam current collector from an aqueous electrolyte. Along with 3D nickel foam, planar (2D) copper current collector was also electrodeposited at the same deposition conditions to compare the effect of architecture. The X-ray diffraction results obtained from three-dimensional and planar anode electrodes indicated that the main phase of electrodeposited alloys for both substrates was Ni3Sn4. The designed three-dimensional electrode demonstrated a high discharge capacity of 843,75 mAh g−1 during initial cycles and an improved cycle performance over 100 cycles in contrast with the same alloy electrodeposited onto planar substrate. The high surface area of the electrode and short Li+-ions diffusion paths along with suppression of volume expansion provided by the proposed 3D structure and Ni inactive matrix play a key role in improving the performance of the electrode.

Electro-deposition of the lithium metal anode on dendritic copper current collectors for lithium battery application

Lithium metal is a promising material for high-energy density lithium battery application because of its high theoretical capacity value. However, during the cycling process, growth of lithium dendrites and change in volume are the two major issues lead to uncontrollable lithium deposition. These problems are directly linked to safety hazards and poor cycle stability. Here, we report the formation of dendritic copper current collectors by hydrogen evolution reactions for lithium metal anodes. The high-surface structure of the dendritic copper current collector facilitates the easy transfer of lithium ions and suppresses lithium dendrite formation. Compared to planar copper foil, the dendritic copper showing good cycling performance and cycle stability because of its low interfacial resistance and stable lithium electrode deposition. Lithium anode with the dendritic copper current collector showed low voltage hysteresis with stable performance without any short circuit problem. A long cycle life of 500 h was achieved in a symmetric cell which also showed excellent performance in full cell cycling performance.

Electrolytic Solution of Anion Exchange Membrane Electrolyzer

In the promotion of the use of renewable energy, the role of hydrogen (H2) as the energy carrier is a key for buffering the fluctuating and/or intermittent power from renewable energy sources. As the hydrogen production device from renewable energy, a water electrolyzer is the simplest and most realistic. Among several options, PEM water electrolysis is suitable for intermittent power input, and also capable of operation at higher current density (> 3 A cm-2). However, a major drawback of PEM electrolysis is its high capital cost per power input compared to conventional alkaline electrolysis. The acidic environment of PEM limits the type of material that can be used for cell components (i.e., bipolar plates and current collectors) to titanium (Ti) and that of the catalyst to platinum-group metals (PGMs). The use of these precious materials is a major reason for the high stack cost of a PEM electrolyzer. When a membrane performing under alkaline (basic) conditions is applied to the electrolyte, the material restriction for the cell components can be relaxed. In particular, the material Ti of the bipolar plates can replaced by a cheaper material such as stainless steel, which would significantly reduce the stack cost, because the cost share of Ti-bipolar plates is significant in the total stack cost of PEM electrolyzer. An alternative material for the electrolyte is an anion exchange membrane (AEM) that has high internal pH. When such an AEM is applied as the electrolyzer based on the same structure as the PEM electrolyzer, a low-capital-cost device is possible and still retain the advantages of PEM electrolysis. In this study, in order to confirm the potential of AEM electrolysis under mild alkaline conditions (pH ≤ 12), the effect of species and concentration of electrolytic solution on the performance of AEM electrolysis was experimentally examined, where DI water, KOH (10mM), and K2CO3 of different concentrations (0.1, 1, and 10 wt. %) were applied for the electrolytic solution. In the cell, Pt/C was used as the cathode catalyst and CuCoOx as the anode catalyst. Furthermore, to examine the effect of structure of anode current collector (i.e., gas diffusion layer; GDL) on the performance, either nickel (Ni)-foam or Ni-felt was applied to the cell. In addition to current-voltage (i-V) characteristics, the Faraday (current) efficiency and hydrogen cross-permeation was also evaluated based on the experimental data.

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.

Silicon thin film on graphene coated nickel foam as an anode for Li-ion batteries

In this study, we propose a 3D structured composite anode containing silicon thin film on graphene coated Ni foam prepared using chemical vapor deposition and magnetron sputtering techniques. The electrochemical test results show that 3D structure of current collector is capable to effectively suppress/diminish the volume changes of the anode upon cycling. Along with this, graphene serves as an additional electrochemically active component and provides improved conductivity. Designed anode exhibits a high areal capacity of around 75 μAh cm−2 upon 500 cycles with the coulombic efficiency of around 99%.

Study on the effect of current collector structures on the performance of MCFCs using three-dimensional fluid dynamics analysis

Abstract The effect of current collectors of molten carbonate fuel cells (MCFCs) was studied through three-dimensional computational fluid dynamics and experiments. Three types of current collectors such as a sheet with sheared protrusions and perforated sheets were employed and performances of MCFCs were compared. A current collector structure with a large gas open area to electrodes improves diffusion characteristics between electrodes and gas flow channels. As a result, differences of gas mole fractions between gas flow channels and electrodes were decreased. Finally, Nernst loss and cathode polarization loss decreased, and the performance was enhanced. Using these results, current collector structures for improved performance and long-term operation were discussed.

Architectural modifications for flexible supercapacitor performance optimization

We have developed material and architectural alternatives for flexible supercapacitors and investigated their effect on practical performance. The substrate alternatives include paperboard as well as various polyethylene terephthalate (PET) films and laminates, with aqueous NaCl electrolyte used in all devices. In all the supercapacitors, activated carbon is used as the active layer and graphite ink as the current collector, with various aluminium or copper structures applied to enhance the current collectors’ conductivity. The capacitance of the supercapacitors was between 0.05 F and 0.58 F and their equivalent series resistance (ESR) was from <1 Ω to 14 Ω, depending mainly on the current collector structure. Furthermore, leakage current and selfdischarge rates were defined and compared for the various architectures. The barrier properties of the supercapacitor encapsulation have a clear correlation with leakage current, as was clearly shown by the lower leakage in devices with an aluminium barrier layer. A cycle life test showed that after 40000 charge-discharge cycles the capacitance decreases by less than 10%.

Fault Tree Analysis of Pantograph Type Current Collector Based on Ontology Modeling

Complex mass faults diagnosis of the pantograph type current collector was difficult. Based on the analysis of the structure, working principle and failure mode of the pantograph type current collector, fault tree of the pantograph was established. A lot of expert knowledge has been collected to support this diagnose process. Some serious problems such as ambiguity, uncertainty and inconsistency exist in the knowledge. Focused on the deficiencies, ontology modeling was proposed in this paper. StrOnto, FaultOnto and FTOnto were established to standardize the knowledge and to improve the efficiency of fault diagnosing. Finally, combined with the example of the pantograph type current collector of CRH2 EMU-train, the proposed algorithms proposed in this paper were proved reasonable and effective.