Cathode Active Layer Research Articles

A Discrete Element Analysis of the Mechanical Properties of Lithium-Ion Electrode Layers Linked to Mechanical Degradation

Lithium-ion batteries are a key player in the electrification of the transport sector. One of the main challenges of today’s lithium-ion batteries is the degradation of charge capacity over time. This capacity degradation stems from several phenomena, and chemical degradation has historically been the main focus of investigation. However, the mechanical degradation of the cell also contributes considerably to the charge degradation and is, therefore, a topic of interest. In this work, a framework for modelling the mechanical behaviour of a positive electrode layer within a lithium-ion battery cell has been developed. This framework uses the discrete element method (DEM), which accurately resolves the granular microstructure of the electrode's active layer. This study aims to characterize the electrode layer’s mechanical response, stemming from the active particles’ elastic-plastic nature and the viscoelastic binder domain. The DEM framework links the local contact behaviour of the particles and the binder and the global mechanical response of the full electrode layer. Understanding this link between length scales is a central first step to fully understanding the mechanical degradation behaviours of the electrode. The model is verified against experimental measurements of the electrode layers’ mechanical properties, measured through U-shape bend tests, by Gupta et al. [1]. The in-plane unloading stiffness and the relaxation of the layer were determined in the experiments, both in compression and tension. The experiments indicated that the in-plane stiffness of the layer differed in compression and tension, with an increasing stiffness at increased compression levels. The relaxation of the layer is also measured over a six-hour period. Through our modelling framework, we were able to capture the pressure-sensitive in-plane stiffness and relaxation of the electrode layer. This work lays an excellent foundation for further investigations of the mechanical properties of the active layer and its mechanical degradation mechanisms, such as swelling and fracture of the active particles due to charge cycling.[1] P. Gupta, I. B. Üçel, P. Gudmundson, and E. Olsson, “Characterization of the Constitutive Behavior of a Cathode Active Layer in Lithium-Ion Batteries Using a Bending Test Method,” Exp. Mech., vol. 60, no. 6, pp. 847–860, 2020, doi: 10.1007/s11340-020-00613-5.

Designer Electrocatalysts for the Oxygen Reduction Reaction with Controlled Platinum Nanoparticle Locality

AbstractFor global deployment of proton exchange membrane fuel cells, achieving optimal interaction between the components of the cathode active layer remains challenging. Studies addressing the effect of nanoparticle location (inside vs outside of pores) on performance and durability mostly compare porous and nonporous carbon supports, thus coming short of decoupling nanoparticle locality from carbon support effects. To address the influence of nanoparticle locality on performance and durability, new carbon‐supported electrocatalysts with designed and distinct nanoparticle localities are presented. The developed methodology allows to place Pt nanoparticles preferentially inside or outside of the mesopores of conductive carbon supports from materials under development at Cabot Corporation. Synthesis protocols are tuned to control nanoparticle size, crystallinity, and loading; this way the effect of Pt locality can be studied for two experimental carbon supports in isolation from all other parameters. For one carbon support, Pt active surface area and activity are significantly lower when nanoparticles are placed inside the pores. In contrast, for another, more graphitic carbon support, placing nanoparticles inside or outside of the carbon pores produces no appreciable difference in active surface area and performance rotating disk electrode measurements. Given their carefully tailored structure, these catalysts provide a framework for evaluating locality‐performance‐durability relationships.

Infiltrated nano-CeO2 and inserted Ni-Fe active layer in a tubular cathode substrate for high temperature CO2 electrolysis on solid oxide cells using La0.9Sr0.1Ga0.8Mg0.2O3−δ thin film electrolyte

A tubular type solid oxide cell which consists of a NiO-Y 2 O 3 stabilized ZrO 2 (YSZ) tubular cathode substrate, a La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3−δ (LSGM) electrolyte film and a Sm 0.5 Sr 0.5 CoO 3-δ (SSC) anode was prepared by dip-coating for CO 2 electrolysis at 800 °C. Since Ni in Ni-YSZ substrate is easily re-oxidized under a pure CO 2 electrolysis atmosphere, co-feeding a reductive gas was essential for avoiding Ni re-oxidation and achieving a stable and large CO 2 electrolysis current under high temperature operation. It was found that co-feeding H 2 is more effective for preventing re-oxidation of Ni compared with CO, however, the CO formation rate was slightly lower than that estimated amount by Faraday`s law due to a water shift reaction when H 2 was used as a reductive gas. Deposition of a thin Ni-Fe cathode active layer and CeO 2 nano-particles obtained by infiltration were effective for increasing the CO 2 electrolysis current because of the decrease in the cathodic overpotential. In spite of the low concentration of Ce was infiltrated by using a 1 M solution with a dip process, the volume change in substrate caused by the CO 2 oxidant was also measured. The CO formation rate almost corresponded to the amount estimated by Faraday`s law and the coke deposition was hardly observed in Ni-YSZ substrate after CO 2 electrolysis, when 10% or 5% of CO was co-fed.

Next Generation Low-Cost NMP/PVDF-Free Fast-Charging Ni-Rich NMC Cathode Electrodes for High Power Energy Storage Device Applications

Longer range, faster charging, safer, and more durable and affordable batteries are required in order to promote the shift to an EV society powered by renewable energy. However, the current battery performance is limited by the conventional PVDF-NMP processing based cathode, which has lower electrical and ionic conductivity. The high molecular weight PVDF binders are the main cause of non-uniform porosity distribution, material agglomeration in active layer, and poor electrical conductivity. This problem is more prominent in high mass loading thick cathodes (>5 mg/cm2) that are required in high energy density battery designs. For examples, these cathode electrodes are not compatible with fast charging as they have high impedance and do not allow moderate to high C-rates in both charge and discharge.Nanoramic has re-invented how electrodes are manufactured by completely removing high molecular weight polymers such as PVDF and the toxic NMP solvent from the active layer of electrode. This dramatically improves Li-ion battery and Li-metal battery cell performance while decreasing the cost of manufacturing and the capital expenditures related to mixing, coating and drying, NMP solvent recovery, and calendering. In the Neocarbonix™ electrodes, a 3D nanocarbon matrix works as a mechanical scaffold for the electrode active material and mimics the polymer chain entanglement. The engineered surface chemistry of the nanocarbon materials, active materials (NMC), and the current collector promotes excellent mechanical stability for the resulting electrode architecture. As opposed to PVDF polymer, the 3D nanocarbon matrix is highly electrically conductive, allows for significantly thicker cathode active layer while improving the electrical conductivity of the electrode. By using eco-friendly solvents that are easily evaporated, the electrode throughput is higher, and more importantly, the energy consumption from electrode drying process is reduced by 30% due to reduction of temperature from 150 ⁰C-180 ⁰C required by the NMP to 60-70 ⁰C.In the Neocarbonix cathode electrodes the 3D carbon matrix is formed during a proprietary slurry preparation: high aspect ratio 1D and 2D carbon materials are properly dispersed and chemically functionalized using a 2-step proprietary slurry preparation process. The chemical functionalization is designed to form an organized self-assembled structure with the surface of active material particles (e.g. NMC particles). The so formed slurry is usually based on low-boiling point environmental green solvents for Ni-Rich NMC cathodes and are very easily evaporated and handled.After coating and drying, the electrodes undergo a calendering to control the density and porosity of the active material. In NMC811 cathode electrodes, densities of ≥3.6 g/cc and ≤20% porosity can be achieved. Depending on mass loading and battery cell requirements, the porosity can be optimized. Nanoramic projects a reduction in $/kWh of up to 20% with such cathode design. Figure below displays the preliminary results comparing the Neocarbonix (NX) NMP-PVDF free Ni-Rich NMC cathode electrodes with the conventional PVDF based NMC cathode electrodes in Li-Metal based half pouch cells (Li metal is the counter electrodes). Preliminary data shows that NX electrodes can maintain 62-66% capacity retention under 7C-Rate while the PVDF based electrodes can only maintain ~39% of initial capacity, which proves 27% improvement under high C-Rate discharge power performance. Also the NX NMC622 electrodes shows excellent fast-charging capability with 87.1% charge capacity within 15 mins constant current (CC) region fast-charge. Even for the higher areal loading NMC811 cathode (5.2-5.6 mAh/cm2) under 3.4C-Rate fast-charging, NX NMC811 displays 77.3% capacity retention within 17 mins CC region fast-charge, while the PVDF NMC811 control electrode only shows 35.9% capacity retention under 3.4C-Rate fast-charging, which proves that high capacity loading ~5.6 mAh/cm2 Neocarbonix Ni-rich NMC cathode can improve >2X in high-rate 15mins fast-charging capability compared with conventional PVDF electrodes in the electric vehicle (EV) applications. Figure 1

Electrochemical Characterization of Intermediate-Temperature Solid Oxide Fuel Cells with PVD-Coated Electrolyte

Intermediate temperature solid oxide fuel cells (SOFCs) working in the range of 600–800°C are interesting because they allow the expansion of the choice of materials that can be used, decrease system cost, and reduce the corrosion rate of system components [1]. The thickness of the electrolyte should be reduced, so reducing the area-specific resistance of the fuel cell for working in this temperature range. Physical vapor deposition methods, such as magnetron sputtering are used to produce thin-film electrolytes [2]. This work is an extension of our previous efforts focusing on scaling the technology of magnetron deposition of electrolyte to large-area cells [3]. It is known that area-specific resistance of small button cells is much less than that of industrial-sized planar anode-supported SOFC cells (10 cm×10 cm or greater). Such difference in ASR is due to large ohmic losses in a SOFC stack that are highly dependent on contact resistance at the cathode/bipolar plate interface. For example, the power density of our 10 cm×5 cm cell with magnetron sputtered yttria-stabilized zirconia (YSZ)/gadolinium-doped ceria (GDC) bilayer electrolyte and La0.6Sr0.4Co0.2Fe0.8O3/Gd0.1Ce0.9O1.95 (LSCF/GDC) cathode was 430 mW/cm2 at 0.7 V and at 750°C [4]. This value was about 40% of that of the 2 cm diameter button cell (1025 mW/cm2) with a similar structure and composition. The area-specific resistance of the former cell was 0.54 Ohm·cm2, while it was 0.2 Ohm·cm2 for the latter one. The goal of this work is to increase the performance of the large-area cell with PVD-deposited electrolyte by improving the structure and composition of the cathode active and contact layers. 4-µm-thick YSZ electrolyte and 2-µm-thick GDC barrier layer were deposited on the 5 cm×5 cm commercial NiO/10ScCeSZ anodes (KCERACELL CO., Korea) by means of reactive magnetron sputtering. LSCF/GDC cathode active layer with an active area of 4 cm×4 cm was screen printed onto the electrolyte. Electrochemical investigations were performed in the temperature interval of 600–800 °С. Figure shows the resulting performance – I–V–P curves of the large-area (5 cm×5 cm) cell with PVD-deposited electrolyte. High power densities of 0.29, 0.55, 0.83, 1.16 и 1.4 W/cm2 were achieved at 0.7 V and at 600, 650, 700, 750 and 800°C, respectively. Acknowledgements. This work was funded by the Russian Science Foundation (Grant No. 17-79-30071).[1] D. J. L. Brett et al., Chem. Soc. Rev., 37, 1568 (2008)[2] S. Sønderby et al., Surf. Coat. Technol., 240, 1 (2014)[3] A. Solovyev et al., J. Electrochem. En. Conv. Stor., 15(4), 044501 (2018)[4] A. Solovyev et al., Fuel Cells, 17(3), 378 (2017) Figure 1: I–V–P curves of the large-area (5 cm×5 cm) cell with PVD-deposited electrolyte. Figure 1

Stability against Degradation and Activity of Catalysts with Different Platinum Load Synthesized at Carbon Nanotubes

Platinum catalysts synthesized at carbon nanotubes with the noble metal content of 20 and 40 wt % are studied under model conditions and in cathodes of membrane-electrode assemblies (MEA) of hydrogen–air fuel cells with proton-conducting polymer electrolyte. The effect of the cathode active layer and MEA overall composition on the activity and operation stability of the synthesized catalytic systems is elucidated. Stability against degradation is studied by using the accelerated stress-testing method by the cathode potential repeated cycling over the 0.6–1.3 V range. The synthesized catalysts were shown to possess higher stability against degradation as compared to the commercial 60Pt/C catalysts (HiSPEC). Contribution of the electrochemical, Ohmic, and transport components into the overall voltage losses depends on the total platinum surface area in the active layers, which determines the polarization current density, and on the Pt mass at the support. The higher Ohmic and transport losses in the case of the catalyst with the Pt content of 40 wt %, as compared to the catalyst containing 20 wt % of platinum, are due to the structural characteristics, namely, a decrease in the carbon nanotubes’ pore volume and size when a greater metal load is applied.

Enhanced Performance of PTB7:PC71BM Based Organic Solar Cells by Incorporating a Nano-Layered Electron Transport of Titanium Oxide

The performance improvement of PTB7:PC71BM based organic solar cells was achieved and optimized by using a very thin layer of TiO as electron transporting layer (ETL) between the cathode electrode (Al) and active layer of the devices. Different thicknesses of TiO ETL were thermally deposited onto the solution-processed active layers followed by aluminium deposition and device encapsulation under glovebox. Results showed that with the use of 5 nm TiO the power conversion efficiency was improved from 5.6% to 9.63%. This interesting enhancement was attributed to various effects of TiO ETL at the boundary/interface of the semiconductor-metal component. Furthermore, high photosensitivity and fast photo-response for the investigated devices with the presence of TiO indicated their viable use as light photodetector.

Efficiency enhancement in polymer solar cells using combined plasmonic effects of multi-positional silver nanostructures

Abstract Achieving high absorption enhancement in a broad wavelength range without increasing the thickness of active layer is essential for improving the performance of polymer solar cells. In this work, we report efficiency enhancement in poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno [3,4-b]thiophenediyl}): [6,6]-phenyl C71-butyric acid methyl ester active layer based polymer solar cells by incorporating silver nanostructures simultaneously in cathode buffer layer and active layer. Efficiency of the device was increased from 6.53% to 7.53% after incorporating the nanostructures. The plasmonic devices exhibited superior performance in a broad wavelength range from 450 nm to 750 nm. Photoluminescence measurements were carried out to confirm the improvement in light harvesting capability of the devices. Finite-difference time-domain simulations and Raman spectroscopy were employed to verify the electric field intensity enhancement around the nanostructures. The performance enhancement mechanism was realized based on theoretical simulations and optical measurements.

A Regular Biporous Model of the Cathode Active Layer Structure of a Lithium-Oxygen Battery. Calculation of Overall Characteristics of the Cathode Active Layer

The active layer of a lithium-oxygen battery (LOB) cathode must have a complex structure consisting of two types of pores (macropores and mesopores). For successful operation of the cathode active layer during the LOB discharge, attempts are being made to create two types of pore clusters: a macropore cluster that provides the transport of oxygen to a zone, where the final product, lithium peroxide, is formed, and a mesopore cluster that guarantees the delivery of lithium ions. The structure of the cathode active layer composed of two types of clusters is optimized in model calculations. However, it from the experimental data, even after the actual implementation of these theoretical recommendations, that the LOB dimensional characteristics during the discharge (in particular, current density I, mA/cm2, and cathodic capacitance C, C/cm2) remain low. In the present work, a new type of cathode active layer structure was suggested: a regular biporous model. In this model, the channels for the supply with oxygen and lithium ions are separated from each other. This fact allows one to simultaneously and independently improve the operation of each of the two channels. The calculations showed a clear advantage of the active layers with this new structure. In particular, the current density i and cathode capacitance С raised to tens of mA/cm2 and about of a thousand of C/cm2.

Electrochemical cleaning: An in-Situ method to reverse chromium poisoning in solid oxide fuel cell cathodes

Chromium poisoning is one of the primary factors that affect solid oxide fuel cell (SOFC) durability. In this study, an electrochemical cleaning method has been employed to reverse the effects of chromium poisoning. Two cells were fabricated and poisoned under identical conditions by operating them at 800 °C in the presence of a Cr source. Both poisoned cells exhibited a significant reduction in maximum power density and an increase in polarization resistance. One of the poisoned cells, designated as the baseline cell, was cooled to room temperature after poisoning. Microstructural observation of the baseline cell showed significant contamination of the cathode active layer by chromium oxide and (Cr,Mn) spinel deposits. The other poisoned cell was electrochemically cleaned for 2 h under a mild electrolytic condition. As a result of the electrochemical cleaning process, the chromium oxide deposits were substantially removed leading to a significant reduction of Cr concentration in the cathode, especially at the cathode/electrolyte interface. A substantial fraction of the cell performance loss was also reversed. To the best of our knowledge, this is a first demonstration of reversing the effects of chromium poisoning using a rapid in-situ process.

Characterization of the Constitutive Behavior of a Cathode Active Layer in Lithium-Ion Batteries Using a Bending Test Method

Presently used experimental techniques for the characterization of tensile and compressive behavior of active layers in lithium-ion batteries have limitations of different kinds. This is particularly true for measurements of compressive properties. Furthermore, the characterizations of time-dependent stress-strain behavior are largely missing. In order to characterize the stress-strain relationship for a dry cathode active layer in lithium-ion batteries, a mechanical testing method is presented that previously has been applied to the testing of optical fibers. The method is based on U-shaped bending of single-side coated aluminum foils, which enables separate measurements of tensile and compressive properties. In particular, the method has clear advantages for measurements of compressive properties in comparison to previously reported techniques. Relaxation experiments are also conducted in order to characterize the time-dependent properties of the dry active layer and to check if these effects could explain the measured hysteresis. It is found that the elastic modulus in compression is significantly larger than the elastic modulus in tension and that the compressive modulus increases with strain level. Contrary, the tensile modulus is approximately independent of strain. Furthermore, hysteresis effects are present at loading-unloading measurements, both for tension and compression. The low values of the measured elastic moduli show that the electrode properties are largely controlled by the binder and carbon additives. It is concluded that the development of particle-particle contacts most likely is the reason for the higher modulus in compression in comparison to tension. The time-dependent effects are significant, primarily for shorter time scales, which explains the relaxation behavior, but they cannot fully explain the hysteresis effects. Most likely non-linear micro-mechanisms do contribute as well.

Computer Simulation of the Structure and Operation Mechanisms for the Active Layer of Lithium–Oxygen Battery Cathode

Currently, the development of lithium–oxygen (air) battery became a hot topic. It is recognised that its specific energy will exceed that of traditional lithium-ion batteries by order of magnitude. The principal element of the lithium–oxygen battery, that is, the active layer of the cathode constitutes a layer of material with a complicated pore structure. During discharge, some electrochemical and chemical processes therein result in the accumulation of lithium peroxide that eventually has been used in the lithium–oxygen battery charging. This power source still suffers from disadvantages, indeed. In this work, computer simulation is used in the elucidating of the effects of the cathode active layer structure on the lithium–oxygen battery overall characteristics during its charging and discharging. A set of obstacles on the way to improvement of the lithium–oxygen battery overall characteristics has been revealed. The obstacles are shown being crucial, they cannot be overcome in terms of current practice of the designing of the lithium–oxygen battery cathode. Therefore, new approaches to the manufacturing of lithium–oxygen battery cathode have to be sought for.

Interface and grain boundary degradation in LSM-YSZ composite Solid Oxide Fuel Cell cathodes operated in humidified air

The interfaces between the different phases and the associated triple phase boundaries (TPBs) in solid oxide fuel cell (SOFC) cathodes are critical for the oxygen reduction reaction, and their degradation impacts SOFC performance and durability. This work examines nanostructure degradation of composite LSM/YSZ cathodes induced by electrochemical operation in humidified air. Three commercial button cells operated in humidified air for various durations at 800 °C exhibited more severe performance degradation than the cell operated in dry air. Microscopy imaging reveals nanostructure degradation within the cathode active layer, especially in the regions nearest to the electrolyte. Newly formed Mn-enriched nano-precipitates accompanied by nano-voids initiate at the original TPBs and propagate along the LSM/YSZ interface. The abundance of the nano-precipitates at LSM/YSZ interfaces increases with operation time, and prolonged operation in humidified air further promotes the formation of the Mn-enriched precipitates along YSZ/YSZ grain boundaries. The formation mechanism of those precipitates and their influence on the cathode performance are discussed.

Interface and Grain Boundary Degradation of Cathode from Commercial Cells Induced By Electrochemical Operation in Humidified Air

Electrode performance degradation is a major obstacle for the development of SOFC technologies. Among different causes of electrode performance degradation, variation of operating gas environment could impact durability of SOFCs and lead to degradation. For the cathode, certain degree of humidity is always present in ambient air. It has been consistently reported that the degradation rate is accelerated when the cell is operated in the humidified air. This work presents nanostructure analyses of operated commercial SOFCs with either LSM/YSZ cathode or with mixed conducting LSCF/SDC cathode exposed to humidified air. For the cell with LSM/YSZ cathode, three commercial button cells were operated in humidified air for various time at 800 °C. Microscopy work reveals nanostructure degradation occurred within the cathode active layer, and it is most pronounced in the region next to the electrolyte. Newly grown Mn-rich nano-precipitates accompanied with nano-voids and cracking propagate at the LSM/YSZ interface. Additionally, prolonged operation in humidified air promotes the formation of the Mn-enriched precipitates at the YSZ/YSZ grain boundaries. By contrast, for the cell with LSCF/SDC cathode, upon long term operation of 2600 hours, Co and Fe enriched Spinel nano-grains were found accumulated at the original pore region of the cathode. The formation mechanism of Mn-enriched nano-precipitates and Co-enriched nanograins for the LSM/YSZ and LSCF/SDC cathode are discussed.

Computer Simulation of the Cathode Active Layer in Hydrogen–Oxygen Fuel Cell with Polymer Electrolyte: The Nature of the Overall Current Variations

Full computer simulation of the cathode structure in hydrogen–oxygen fuel cell with polymer electrolyte is performed. Both transport, support grains (agglomerates of carbon particles onto whose surface Pt-catalyst is deposited), and the current generation in active layer are simulated. The active layer operation in potentiostatic mode is studied. The effect of variations of the active layer and the fuel cell temperature (Ts and Т, respectively) on the cathode overall current I and the support grain flooding with water is calculated. The changes in the temperature difference Ts–Т was shown for the first time, experimentally and by the simulation, to generate variations of I and the degree of the support grain flooding with water. In particular, with the increasing of Ts–Т the current I increased, whereas the support grain flooding with water decreased; and vice versa, with the decreasing of Ts–Т the current I drops down, while, the support grain flooding with water grows. An explanation of the phenomena is presented, which takes account of structure of the support grains in which О2 reduction and Н2О generation occur. There exist intrinsic channels for protons and О2 molecules transportation to the catalyst. Water releasing in the support grains is able to fill partially or even entirely the gas pores through which oxygen is supplied to the platinum. As a result, the current generated in the support grains can drop down significantly; at the same time, the value of I also drops down. The degree of the support grainfilling with water is determined by two processes, namely, the flooding and draining. The source of flooding is the current generation; that of draining, the water saturated vapor diffusion and water filtration in nanopores. The lower cathode potential, the higher the flooding rate, whereas the water removal rate grows or drops down with the increasing of decreasing of the temperature difference Тs–Т, respectively. Thus, the temperature difference variations naturally lead to those of the quantity I.

Resistance Reduction Effect by SDX® in Lithium-Ion Batteries

1. Introduction Practical uses of lithium-ion batteries(LIB) are rapidly growing especially in large batteries for full electric vehicle(EV), plug-in hybrid electric vehicle(PHEV) and so on, but improvements of their characteristics(“high-energy density”, “high power”, “long cycle-life”, “safety” and “lower cost”) are still strongly demanded. SDX® is a surface coated aluminum current collector(AL) with carbon black(CB) and organic binder, and the thickness of the coated layer is about 1μm, and SDX®makes a cell internal resistance lower and adhesion between cathode active materials and AL stronger, so as to improve battery performance dramatically[1,2]. The control of the internal resistance of LIB by the clarification of the mechanism is one of the biggest key items to improve them. So the mechanisms of the interface resistance between cathode active material layer and AL have been investigated and discussed[3]. In general, cell internal resistance is separated simply into electronic resistance and ionic resistance. We successfully separated the electronic resistance into material resistance and interface resistance between cathode active material layer and AL. And then we independently measured the material resistance and the interface resistance by Electrode Resistance Meter(HIOKI E.E. CORPORATION) which can separate electrode resistance into material and interface resistance. In the battery which used LFP as cathode active material, the quantitative investigation of the contribution of SDX® and conducting additives to the electronic resistance reduction was provided by the result of measurement using Electrode Resistance Meter(Fig.1). The interface resistance of the cathode with AL was higher than the material resistance of that by almost one order of magnitude. The interface resistance of the cathode with SDX® was lower than that with AL by almost one order of magnitude. It is not only presumed that the interface resistance is dominant in the electronic resistance but confirmed that the interface resistance is maintained at lower level by SDX®. Because the interface resistance was reduced by SDX®, it has been reported that conducting additives could be reduced much in cathode[4]. By application of SDX®, it was confirmed that the interface resistance of LFP could be decreased largely irrespective of a distribution state of conducting additives. As a result, cell internal resistance and discharge capacity retention of LFP was constant irrespective of coating speed[5]. In this paper, more detailed examination will be carried out, and resistance reduction effect by SDX®in LIB will be tried to be clarified. 2. Experiment Firstly, the preparation of electrode slurry was carried out by dispersing LFP as a cathode active material, CB as a conducting additive and polyvinylidene difluoride(PVdF) as binder into N-methylpyrrolidone(NMP). The compounding ratio of LFP, CB and PVdF was set to 90:5:5 as a solid mass ratio. Secondly, cathode electrodes were prepared by coating the slurry onto AL or SDX®and dried, before they were pressed at several conditions(e.g. 1.6, 2.0 or 2.5g/cc). By laminating one sheet of anode and one sheet of cathode, pouch type cell was assembled. 3. Results and discussion The material resistance and the interface resistance of the cathode were measured by Electrode Resistance Meter(Fig.2). The interface resistance of the cathode with AL increased as the electrode density lowered and finally the interface resistance of the cathode of electrode density of 1.6g/cc with AL could not be measured because of high resistance. On the other hand, it was confirmed that the interface resistance of the cathode with SDX®was constant irrespective of the electrode density. Cell internal resistance(DCR) were measured(Fig.3). The cell DCR with AL increased when the electrode density lowered, and the cell of the cathode of electrode density of 1.6g/cc with AL did not work because of high resistance. It was confirmed that the cell DCR with SDX® was constant irrespective of the electrode density showing similar behavior to the interface resistance of the cathode with SDX®. Cell discharge performance was also evaluated(Fig.4). It confirmed that the cell discharge performance of the cathode of electrode density of 2.5g/cc with AL was almost same as that with SDX®. But when the electrode density with SDX® lowered, especially at high rate(10, 20C), the cell capacity retention with SDX®was improved.

Comparative characteristics of cathodes with different catalytic systems in hydrogen–oxygen and hydrogen–air fuel cells with proton-conducting polymer electrolyte

The characteristics of low-temperature hydrogen–oxygen (air) fuel cell (FC) with cathodes based on the 50 wt % PtCoCr/C and 40 wt % Pt/CNT catalysts synthesized on XC72 carbon black and carbon nanotubes (CNT) are compared with the characteristics of commercial monoplatinum systems 9100 60 wt % Pt/C and 13100 70% Pt/C HiSPEC. It is shown that the synthesized catalysts exhibit a high mass activity, which is not lower than that of commercial Pt/C catalysts, a high selectivity with respect to the oxygen reduction to water, and a significantly higher stability. The characteristics of PtCoCr/C and Pt/CNT were confirmed by testing in the hydrogen—oxygen FCs. However, when air was used at the cathode, especially in the absence of excessive pressure, a voltage of FC with the cathode based on PtCoCr/XC72 is lower as compared with the commercial systems. Probably, this is associated with the transport limitations in the structure of trimetallic catalyst synthesized on XC72 carbon black due to the absence of mesopores. This drawback was eliminated to a large extent by raising the volume of mesopores as a result of application of mixed support (XC72 + CNT) and the use of only CNT for the synthesis of the monoplatinum catalyst. However, this did not eliminate another drawback, namely, a low platinum utilization coefficient in the cathode active layer as compared with that measured under the model conditions in the 0.5 M Н2SO4 solution. Therefore, further research is required to improve the structure of the catalytic systems, which are synthesized both on carbon black and nanotubes, while maintaining their high stability and selectivity.

Chromium Poisoning of Cathodes in Solid Oxide Fuel Cells and its Mitigation Employing CuMn1.8O4 Spinel Coatings on Interconnects

Intermediate temperature solid oxide fuel cells (IT-SOFCs) enable the use of chromia-forming alloys in interconnects and balance-of-plant (BoP) materials. However, depending on the SOFC operating conditions, the chromium (Cr) containing species can transport and deposit in the SOFC cathodes and deteriorate their performances. In order to investigate the Cr-poisoning phenomena, anode-supported planar SOFCs with Sr-doped LaMnO3 (LSM) + yttria-stabilized zirconia (YSZ) cathode active layer and LSM cathode current collector layer were fabricated and electrochemically tested in contact with Crofer interconnect at 800 °C. The cathode atmosphere (dry air or 10% humidified air) and current condition (no current or constant cathodic current) were varied in tests on identical cells, and the performance degradations under different test conditions were compared. It was found that both humidity and cathodic current can promote Cr poisoning. Microstructure characterizations also confirmed major amounts of Cr-containing deposits at the cathode/electrolyte interfaces of the cell tested with cathodic current and/or humidity. Free energy minimization calculations and thermogravimetric experiments were performed to determine the chromium vapor species that form over the chromia-forming alloy interconnect and result in the chromium deposition. Based on these results, the roles of humidity and cathodic current in chromium poisoning are evaluated, and a performance degradation mechanism associated to chromium vapor species dissociation at the cathode/electrolyte interface is proposed. In order to mitigate the effect of Cr-poisoning, a protective Cu-Mn spinel coating was applied on the interconnect surface. The Cu-Mn spinel coating has good thermal compatibility, high stability and electronic conductivity at the SOFC operating temperature. The candidate interconnect material (Crofer22H meshes) with no protective coating, those with commercial CuMn2O4 spinel coating and the ones with lab-developed CuMn1.8O4spinel coating were investigated. The lab-developed CuMn1.8O4spinel coating was deposited on the Crofer22H mesh by electrophoretic deposition and densified by a reduction and re-oxidation process. Anode-supported SOFCs with LSM based cathode with different Crofer22H meshes (bare, commercially coated CuMn2O4, and lab-coated CuMn1.8O4) were electrochemically tested at 800 °C with a constant cathodic current (0.5 A/cm2) for total durations of up to 216 hours, and the cell performances were characterized by current-voltage measurements every 24 hours. Cross sections of the Crofer22H meshes and the SOFC cathodes were examined before and after the cell tests by scanning electron spectroscopy and energy dispersive X-ray spectroscopy. The results of the mitigating effects of the two types of Cu-Mn spinel interconnect coatings on Cr-poisoning of the SOFC cathodes were compared. It was observed that the performance of the denser lab-developed Cu-Mn spinel coating was distinctly better showing significantly less chromium containing deposits at the cathode/electrolyte interface after the test.

Effect of Humidity and Cathodic Current on Chromium Poisoning of Sr-Doped LaMnO3-Based Cathode in Anode-Supported Solid Oxide Fuel Cells

Anode-supported solid oxide fuel cells (SOFCs), which were comprised of a Sr-doped LaMnO3 (LSM) + yttria-stabilized zirconia (YSZ) cathode active layer and a LSM cathode current collector layer, were fabricated. Electrochemical performance tests of the cells with and without chromia-forming alloy interconnect at 800 °C were conducted, under different cathode atmospheres (dry air or 10% humidified air) and current conditions (no current or 0.75 A/cm2). It was found that both humidity and cathodic current promote chromium (Cr) poisoning which has a detrimental effect on cathode performance. Major amounts of Cr-containing deposits were observed at the cathode/electrolyte interfaces of the cells tested with cathodic current and/or humidity. Based on the experimental results and free energy minimization calculations, a mechanism associated to Cr vapor species dissociation at the cathode/electrolyte interface is proposed.

Chromium Poisoning Effects on Performance of (La,Sr)MnO3-Based Cathode in Anode-Supported Solid Oxide Fuel Cells

Chromium (Cr) vapor species from chromia-forming alloy interconnects are known to cause cathode performance degradation in solid oxide fuel cells (SOFCs). To understand the impact of Cr-poisoning on cathode performance, it is important to determine its effects on different cathode polarization losses. In this study, anode-supported SOFCs, with a (La,Sr)MnO3 (LSM) + yttria-stabilized zirconia (YSZ) cathode active layer and a LSM cathode current collector layer were fabricated. At 800°C, cells were electrochemically tested in direct contact with Crofer22H meshes, under different cathode atmospheres (dry air or humidified air) and current conditions (open-circuit or galvanostatic). Significant performance degradation was observed when cell was tested under galvanostatic condition (0.5 A/cm2), which was not the case under open-circuit condition. Humidity was found to accelerate the performance degradation. By curve-fitting the experimentally measured current-voltage traces to a polarization model, the effects of Cr-poisoning on different cathodic polarization losses were estimated. It is found that, under normal operating conditions, increase of activation polarization dominates the cathode performance degradation. Microstructures of the cathodes were characterized and Cr-containing deposits were identified. Higher concentrations of Cr-containing deposits were found at the cathode/electrolyte interface and the amounts directly correlated with the cell performance degradations.