Electrode Binder Research Articles

High-Rate Lithium-Ion Cell with Dihexyl-Substituted Poly(3,4-Propylenedioxythiophene) Mixed Conductive Polymer As Electrode Binder

The utilization of conductive polymers as electrode additives/binders for lithium-ion batteries has been reported by several authors.1–3 Specifically, it has been shown that the utilization of p-dopable conductive polymers improves cycle stability and rate capability in Li-NCA cells. 4,5 The enhanced performance and cell stability over cycling are attributed to the conductivity of the electronic/ionic network of conducting polymer through all the lithium intercalating active material particles that reduces the electrode resistance. Furthermore, the conductive polymer serves as a protective coating for the NCA particles, creating a thin, smooth, and high conducting solid electrolyte interface. Here we present the benefits of Dihexyl-Substituted Poly(3,4-Propylenedioxythiophene) (PProDOT-Hx2) as an electrode additive in Li-NCA cells. We have compared the rate capability and cycle life of NCA-PProDOT-Hx2 electrodes versus NCA-PVDF electrodes. In addition, we have characterized the impedance response as function of state of charge of the NCA electrodes to identify the internal resistances involved during lithiation/delithiation and for monitoring the accessible electroactive surface area. The study shows that the NCA-PProDOT-Hx2 electrodes had three times lower resistance compared to the NCA-PVDF electrodes suggesting a three times higher interfacial surface area for charge transfer and diffusion. At the rate of 6C, the NCA-PProDOT-Hx2 electrodes were capable of delivering a specific capacity of 111 mAh g-1. V. A. Nguyen and C. Kuss, J. Electrochem. Soc., 167, 065501 (2020).S. N. Eliseeva, O. V. Levin, E. G. Tolstopyatova, E. V. Alekseeva, and V. V. Kondratiev, Russ. J. Appl. Chem., 88, 1146–1149 (2015).T. M. Higgins et al., ACS Nano, 10, 3702–3713 (2016).C.-H. Lai et al., Chem. Mater., 30, 2589–2599 (2018).P. Das et al., Chem. Mater., acs.chemmater.0c02601 (2020).

Effect of Water Management for Membranes and Catalyst Layers Using an In-House Developed Polymer Electrolyte on Cell Performance Hysteresis in Anion Exchange Membrane Fuel Cells

In this work, we focus on the water management challenges and report on the improvements of cell performance for anion exchange membrane fuel cells (AEMFCs) using an in-house-developed anion exchange ionomer (quaternized poly(arylene perfluoroalkylene), i.e., QPAF-4, developed in this laboratory (Figure 1).1 Previously, we investigated the I-V hysteresis observed in cells using the non-precious metal catalyst Fe-N-C and found the importance of water management. 2A thinner electrolyte membrane facilitates the diffusion of water due to OH⁻ movement, such as the use of back-diffusing water to the cathode, and is effective for water management in AEMFCs. As the electrolyte membrane, QAPF-4 (ion exchange capacity: IEC = 2.0 meq g-1) membranes with film thicknesses of ca. 10, 20 and 30 μm were used. Since this membrane is soluble in methanol, it is also suitable for use as an electrode binder. An MEA in which platinum was loaded (0.20 mgPt cm-2) on both the anode and cathode was prepared. Pt loaded on carbon black (Pt/CB, TEC10E50E), supplied from TKK Japan, was used as the platinum electrocatalyst.Figure 2 shows a comparison of the I-V performances for cells utilizing the various membrane thicknesses at 60 oC, 100% RH, 0 kPag; anode H2 (100 mL min-1); cathode O2 (100 mL min-1). The cells all exhibited I-V hysteresis, i.e., a large difference in potential between increasing and decreasing current densities (CDs) as the membrane thickness decreased. From Figure 3a-b, as a result of confirming the potential change between the anode and the cathode using a cell with a reversible hydrogen electrode (RHE) provided on the cathode side, we conclude that this hysteresis phenomenon mainly occurs at the anode. We are exploring the contributing factors and will provide further details in the presentation. From these results, we found that there is an important factor in the relationship between the anode and the electrolyte membrane in the development of high performance AEMFCs with efficient water management capability. Acknowledgement This project was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) Japan through funds for the “Advanced Research Program for Energy and Environmental Technologies,” by the Japan Society for the Promotion of Science (JSPS) and the the Swiss National Science Foundation (SNSF) under the Joint Research Projects (JRPs) program, and by the Japan Science and Technology (JST) through the Strategic International Collaborative Research Program (SICORP). References Ono, T. Kimura, A. Takano, K. Asazawa, J. Miyake, J. Inukai, K. Miyatake, Robust anion conductive polymers containing perfluoroalkylene and pendant ammonium groups for high performance fuel cells, J. Mater. Chem. A 5 (2017) 24804–24812, https://doi.org/10.1039/c7ta09409d.Otsuji, Naoki Yokota, D. A. Tryk, K. Kakinuma, K. Miyatake, M. Uchida, Performance hysteresis phenomena of anion exchange membrane fuel cells using an Fe–N–C cathode catalyst and an in-house developed polymer electrolyte, Journal of Power Sources, 487 (2021) 229407, https://doi.org/10.1016/j.jpowsour.2020.229407 Figure 1

Suitability of Ethyl Cellulose As a Binder in Positive Electrode of Aqueous Battery

Novel materials for energy storage devices need to be affordable, durable, safe and environmentally friendly. PVDF, which is the most popular polymer used as a binder in battery cathode electrodes, requires the use of and toxic solvents for processing, such as N-methyl-pyrrolidone (NMP).1 Ethyl cellulose is a biodegradable and water-insoluble polymer. Ethyl cellulose based slurry can be prepared using ethanol as solvent, which makes the process cheaper and more sustainable. Replacing PVDF with more environmentally friendly binder like ethyl cellulose in positive electrode of aqueous battery systems would be beneficial in many ways. It would shorten the assembly procedure due to high speed of solvent evaporation, there are no strict requirements for humidity control and the recycling procedure is easier as there are no fluorinated compounds.2 Therefore, this replacement would enable to produce safer and cheaper energy storage devices.In this work electrodes with different composition have been described using galvanostatic charging-discharging and cyclic voltammetry. LiMn2O4 (LMO) has been used as active material for cathode, carbon black Super P as conductive additive and PDVF or ethyl cellulose as a binder. The electrodes were prepared using different mass ratios of conductive additive and binder to evaluate the performance of this sustainable polymer. Using ethyl cellulose as a binder, discharge capacity 100 mAhg− 1 was achieved at 0.2C rate for LMO cathode which is comparable to the results obtained with PVDF as a binder. 500 cycles at the rate of 1C showed somewhat better capacity retention for electrodes prepared using PVDF. However, the results show that ethyl cellulose is a promising option to replace PVDF as cathode binder in aqueous systems. This binder promising option in the application of aqueous redox flow battery with solid boosters, where large amount of solid charge storage material is used in thanks to increase the capacity of the system.The research was supported by the Estonian Research Council grant PUTJD956 and Magnus Ehrnrooth Foundation.

Conductive Geopolymers as Low-Cost Electrode Materials for Microbial Fuel Cells.

Geopolymer (GP) inorganic binders have a superior acid resistance compared to conventional cement (e.g., Portland cement, PC) binders, have better microbial compatibility, and are suitable for introducing electrically conductive additives to improve electron and ion transfer properties. In this study, GP–graphite (GPG) composites and PC–graphite (PCG) composites with a graphite content of 1–10 vol % were prepared and characterized. The electrical conductivity percolation threshold of the GPG and PCG composites was around 7 and 8 vol %, respectively. GPG and PCG composites with a graphite content of 8 to 10 vol % were selected as anode electrodes for the electrochemical analysis in two-chamber polarized microbial fuel cells (MFCs). Graphite electrodes were used as the positive control reference material. Geobacter sulfurreducens was used as a biofilm-forming and electroactive model organism for MFC experiments. Compared to the conventional graphite anodes, the anode-respiring biofilms resulted in equal current production on GPG composite anodes, whereas the PCG composites showed a very poor performance. The largest mean value of the measured current densities of a GPG composite used as anodes in MFCs was 380.4 μA cm–2 with a standard deviation of 129.5 μA cm–2. Overall, the best results were obtained with electrodes having a relatively low Ohmic resistance, that is, GPG composites and graphite. The very first approach employing sustainable GPs as a low-cost electrode binder material in an MFC showed promising results with the potential to greatly reduce the production costs of MFCs, which would also increase the feasibility of MFC large-scale applications.

(Invited) Ionomer Adhesives, Coatings, and Membranes for Electrochemical Separations

A growing population striving for higher standards of living are stressing water resources around the globe. Because of the anticipated water scarcity and security challenges, water futures began trading as a commodity, like gold, oil and other precious commodities, on the stock market in late 2020. Ensuring water security necessitates water treatment and remediation technologies that are low cost, scalable, and energy efficient. Furthermore, advances in electrochemical separations technologies have been useful for targeted nutrient recovery, carbon valorization, and pollutant removal from liquids. In this talk, I will present our group’s work on addressing ohmic related resistances in membrane capacitive deionization and electrodeionization with new membrane and porous ion conducting materials. Borrowing from advances in fuel cell electrode binder technology, we show that solution processable ionomers are versatile for arriving at a new class of porous ionic conductors that address spacer channel resistances in the said deionization platforms under low TDS (total dissolved solids) concentrations. The new materials improve the separation efficiency and energy efficiency of deionization processes.

A straightforward fabrication of solid-state lithium secondary batteries based on multi-functional poly(arylene ether sulfone)-g-poly(ethylene glycol) material

Lithium ion conductive poly(arylene ether sulfone)-g-poly(ethylene glycol) (PAES-g-PEG) is synthesized for the application of solid state electrolyte membrane and electrode binder. The solid polymer electrolyte (SPE) system prepared from PAES-g-PEG and 1-butyl-1-methylpyrrollidum bis(fluoromethane sulfonyl) (PYR-1,4-TFSI) ionic liquid illustrates high ion conductivity of 8.48 × 10−4 S cm−1 and low interfacial resistance at room temperature, along with excellent thermal and mechanical stability (degradation temperature > 180 °C and tensile strength > 0.8 MPa). As the PAES-g-PEG containing lithium bis (fluoromethane sulfonyl) (LiTFSI) salt exhibits not only such high conductivity of 2.11 × 10−4 S cm−1 but also excellent adhesive strength (>23 MPa), it plays an important role as a binder for the electrode. As the active electrode materials such as LiCoO2 (LCO) and LiNi0.6Mn0.2Co0.2O2 (NMC 622) are quite well compatible with PAES-g-PEG, the battery cells fabricated by binding the synthesized SPE and cathode layer show excellent cell performance of 139.01 mAh g−1 (LCO) and 158.15 mAh g−1 (NMC 622) at 0.1C. When this multi-functional PAES-g-PEG material is applied to the lithium sulfur battery system, the resulting cell discharge capacity is even higher than 925 mAh g−1 at 0.1C with long term cyclic stability.

Redox behavior and surface morphology of polystyrene thermoplastic electrodes

Carbon composite electrodes consisting of graphite and a non-conductive binder are widely used due to their low cost and ease of fabrication but often suffer from slow electrode kinetics and high capacitance relative to traditional electrode materials such as gold and glassy carbon. Modifiers including metallic nanoparticles and carbon nanotubes are used to enhance electrode performance, but this complicates electrode preparation, increases cost, and limits reusability. Our group recently reported a new type of carbon composite electrodes called thermoplastic electrodes (TPEs) that use common thermoplastics mixed with graphite in a solvent processing system that give enhanced electrochemical performance. The polymers reported to date include polymethylmethacrylate, cyclic olefine copolymer, polycaprolactone (PCL), and blends of these materials. Polystyrene (PS) is an inexpensive and commonly used thermoplastic substrate, however, there are only several reports incorporating PS as a binder in carbon composite electrodes. Here, we report the first PS TPEs and show their unique electrochemical behavior relative to electrodes made with other binders. These unmodified composite materials surpass the performance of traditional electrode materials and show similar behavior to nanomaterial-modified electrodes. The capacitance and conductivity were measured for PS and PS-polycaprolactone (PCL) blends using PCL TPEs as a reference. Even small additions of PS to PCL electrodes substantially lowered capacitance and increased conductivity. The electrochemistry of PS and PS-PCL TPEs was investigated using cyclic voltammetry with various common and biologically relevant redox probes. The effect of differing molecular weight and the use of waste expanded polystyrene (EPS) were explored as well, and all PS binder TPEs were found to exhibit similar redox behavior. Optical profilometry (OP) and scanning electron microscopy (SEM) were used to examine morphological characteristics. OP showed lower surface roughness for PS electrodes than for PCL ones, explaining the lower capacitance. SEM data suggests the source of this enhanced redox behavior stems from the edge-plane rich PS TPE surfaces.

Electronically conductive MXene clay-polymer composite binders for electrochemical double-layer capacitor electrodes

Electrochemical double-layer capacitors recently attract strong attention because of their fast and stable charge/discharge characteristics and their high-power density. To improve the performance of EDLCs, it is necessary to conduct comprehensive studies on electrode, including the binder. An ideal binder for an EDLC must have high adhesion ability to the electrode components and should be electronically conductive. Here, we synthesize a composite binder consisting of MXene clay and poly(acrylonitrile-co-butyl acrylate) using an in-situ emulsion polymerization. This is a first report of an in-situ polymerization method to make a conducting composite binder with good mechanical, adhesion, and electronic conducting properties. An EDLC containing electrodes of activated carbon and MXene clay/poly(acrylonitrile-co-butyl acrylate) composite binder shows a high specific power of 8510 W kg−1 with a high specific energy of 23.6 Wh kg−1. This is a significant improvement over EDLC electrodes containing only activated-carbon and poly(acrylonitrile-co-butyl acrylate). The excellent performance is attributable to the binder's high conductivity and toughness due to improved interactions among the electrode components.

(Invited) Electrode Binder As an Enabling Material for Si Based Electrode

Silicon (Si) is an attractive candidate for lithium-ion batteries because it delivers 10 times greater theoretical (∼4200 mAh/g) specific capacity than that of a traditional graphite anode (∼370 mAh/g). However, the widespread application of silicon materials has remained a significant challenge because of the large volume changes during lithium insertion and extraction processes disrupt both the Si electrode surface and electrode mechanical integrity. This large volume change causes electrode failure, leading to loss of the electrical contact and drastic capacity fading. Functional electrode binders can play multiple functions for Si electrode, including improved adhesion, lithium ion compensation, better ion and electric conductivity as well as surface and interface modification. Organic and polymer chemistry have provided almost infinity possibilities to modify the polymeric binders to include the desired functionalities. This presentation will discuss the specific molecular design principles and synthetic steps to realize the structures and functionalities of the binders, how these binders interact with different Si materials, and the electrochemical performances of the electrodes based on these binders.

High Adhesive Polyimide Binder for Silicon Anodes of Lithium Ion Batteries

Silicon has been extensively studied as an anode material in lithium-ion batteries due to its extremely high theoretical specific capacity of 3578 mAh/g (assuming Li15Si4 as intermediate product). However, silicon undergoes huge volume variations during repeated discharge and charge, leading to poor electrode mechanical integrity, continual electrolyte decomposition and fast capacity decay. Developing high strength binders in silicon anodes have been considered as an efficient pathway to alleviate various capacity decay pathways.Currently, lithiated poly acrylic acid (LiPAA) is mostly used as the binder for silicon electrodes due to its strong binding capability and (electro)chemical compatibility with Si and electrolyte. However, cracks at the electrode level can still be observed for the cycled electrodes, which suggests that a stronger binder is required to mitigate volume expansion of Si electrode and hold the particles together. Herein we study the polyimide (PI) materials as the binders for Si anode in an attempt to achieve stable cycling performance. With PI binder, the silicon electrode exhibits a higher tensile strength than that of conventional PAA binder. The strong adhesion of the PI binder suppresses the structural collapse of the Si negative electrode during lithiation/delithiation, enabling high capacity retention and stable cycle life. However, the PI crosslinking process requires high temperature and inert atmosphere, which is a challenge for its practical application. In this work, we explore various PI crosslinking conditions and their effects on electrochemical performance. This work offers us an alternative binder material with high tensile strength for the Si electrode.AcknowledgementWe gratefully acknowledge the support from the U.S. Department of Energy's Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. Argonne National Laboratory is operated for DOE office of Science by UChicago Argonne, LLC, under contract number DE-AC02-06CH11357.

Electrochemical Properties of High-Temperature Polymer Electrolyte Thin Films

Electrode binders based on ionomer chemistries have a profound impact on the performance of polymer electrolyte membrane (PEM) fuel cells. High temperature PEM fuel cells (HT-PEMFCs) typically use phosphoric acid (H3PO4) imbibed polymers or polymers without ionic moieties as the binder (e.g., PTFE). The former materials hinder gas reactant transport and compromise electrode kinetics, while the latter materials suffer from severe ohmic penalties in the electrode layers. The ionomer binder limitations for HT-PEMFCs stymie power density and lead to poor utilization of the costly platinum catalyst. This talk presents our work probing the electrochemical properties of high-temperature ionomer thin films. The polymer electrolytes investigated are phosphoric acid imbibed polycations as well as phosphonated polymers. Thin films are examined because they mimic the structure found in electrode layers and they can be interrogated with interdigitated electrode (IDE) arrays featuring nanoscale electrocatalysts. The IDE platform is useful for drawing definitive conclusions about the electrochemical behavior of ionomer binder materials without being muddled by the complexity of bulk electrodes. Our work has shown that phosphonated ionomers display better hydrogen diffusivity and hydrogen oxidation reaction kinetics than acid imbibed polycations. The phosphonated ionomers can match the anhydrous proton conductivity of acid imbibed polymers provided they contain electron withdrawing moieties in the polymer. The final part of the talk presents Machine Learning (ML) tools (e.g., support vector regression, density-based clustering, and self-organized maps) that use data from IDEs and single-cell polarization. The ML bridges materials properties to device performance and is poised to accelerate the timeline for realizi

MXene (Ti3C2Tx) anodes for asymmetric supercapacitors with high active mass loading

MXene (Ti3C2Tx) is an emerging material choice for advanced energy storage. However, the relatively low areal capacitance is a bottleneck in developing asymmetric supercapacitors with enhanced energy-power characteristics in large voltage windows. A simple and straightforward approach is proposed to design and fabricate Ti3C2Tx-multiwalled carbon nanotube (Ti3C2Tx-CNT) composite electrodes. Polymethylmethacrylate (PMMA) is used as a binder for electrodes with 40 mg cm−2 high active mass loadings (AML); meanwhile, both multilayered Ti3C2Tx and CNT are efficiently dispersed in PMMA solution. The fabricated Ti3C2Tx-CNT electrodes with different CNT contents are tested in a −1.1~-0.3 V negative potential window and analyzed by different electrochemical techniques. The optimization of Ti3C2Tx-CNT-PMMA composition facilitates the design of anodes with capacitance of 2.26 F cm−2 in Na2SO4 electrolyte, which is essentially higher than literature results for Ti3C2Tx. The ability to obtain high capacitance in the Na2SO4 electrolyte is a crucial result, which facilitates the fabrication of asymmetric aqueous devices operating at 1.6 V. The Ti3C2Tx-CNT anode is combined with a MnO2-CNT cathode in an asymmetric cell, which shows a 1.24 F cm−2 capacitance at 3 mA cm−2.

Communication—Functional Conductive Polymer Binder for Practical Si-Based Electrodes

Multifunctional conductive binders represent an emerging class of polymer materials to address inherent challenges of Si electrodes for high capacity lithium-ion batteries. Advanced binders with oriented functionalities are greatly desired to facilitate the battery chemistry. We here report stable capacity cycling of a practical composite anode comprising industrial available SiOx (>60 wt%), carbon materials and a conductive polymer binder—poly(9,9-dioctylfluorene-co-fluorenonecomethylbenzoic ester) (PFM). This multifunctional polymer functions as both an interface modifier and an electrode binder for high-performing SiOx composite electrodes. The viability of multifunctional conductive polymer binders was further validated in a practical full cell.

Sodium Alginate Binders for Bivalency Aqueous Batteries.

Environmental friendly sodium alginate (SA) cannot be used as a binder in aqueous batteries due to its high solubility in water. A water-insoluble polyvinylidene difluoride (PVDF) binder has been widely applied for an aqueous battery, in which the toxic and expensive organic solvent of N-methy-2-pyrrolidone (NMP) is required during the coating process. Herein, we report that the water-soluble SA can be utilized as a binder in aqueous Zn batteries because SA could cross-link with the Zn2+ ion to form a water-insoluble and mechanically super strong binder for electrodes. Aqueous Zn||LiFePO4 cells are assembled to demonstrate the performance of the SA binder for LiFePO4 cathodes. Due to the high adhesion strength of cross-linked Zn-SA, LiFePO4 with the SA binder displays a high capacity retention of 93.7% with a high Coulombic efficiency of nearly 100% after 100 cycles at a 0.2 C rate, while the capacity of LiFePO4 with the PVDF binder quickly decays to 84.7% after 100 cycles at 0.2 C. In addition, the LiFePO4 cathode with the SA binder also has smaller redox polarization, faster ion diffusion rate, and more favorable electrochemical kinetics than that with the PVDF binder.

Comparing the effects of polymer binders on Li+ transport near the liquid electrolyte/LiFePO4 interfaces: A molecular dynamics simulation study

Various functional polymers as electrode binders with enhanced lithium ion conductivity have been proposed recently to improve the overall performance of high-power lithium ion battery (LIB). To identify the critical features of polymer binders, we utilized molecular dynamics (MD) simulations to systematically examine and compare the molecular effects of poly(vinylidene fluoride) (PVDF), poly(ethylene oxide) (PEO), polyacrylonitrile (PAN), poly(N-vinylformamide) (PNVF), and poly(styrene sulfonate) (PSS) binders on lithium ion transports at liquid electrolyte/LiFePO4 (LFP) cathode interface. Compared with conventional PVDF, all tested functional polymers have higher Li+ affinity and can disrupt the electric double layer structure. As a binder, PEO can form stable coordination complex with Li+ to effectively lower the free energy of Li+ at interface, resulting in a significantly reduction of interfacial impedance Rint. Both PAN and PNVF have polar side-chains where the PNVF formamide groups has higher Li+ affinity than PAN nitrile. PNVF can further enhance the Li+ mobility near the LFP surface and lower the total Rint. In contrast, rigid PAN has minor effects on Li+ free energy at interface, giving little impacts toward the total Rint. Finally, the negatively charged PSS can significantly reduce the surface electric potential and lower the Li+ free energy over a wide range near the interface, which greatly reduces the total Rint. The combined results suggest that improving the Li+ affinity and the local mobility at interface are important factors for a good binder, where the free energy variations play more dominant effects. The presented molecular mechanisms of various functional polymer binders provide valuable insights for novel binder design.

Fluorinated (Nano)Carbons: CFx Electrodes and CFx‐Based Batteries

Fluorine‐based chemistry is widely used in commercial battery technology, from primary batteries consisting of Li/CFx to binders for electrodes in secondary lithium‐ion batteries. Fluorine‐based compounds are also formed during operation for both battery configurations as discharge products such as LiF or as components of the solid electrolyte interface (SEI) layers on electrodes. Herein, the fluorinated carbons or CFx detailing the commercialization of the first Li/CFx cells are discussed‐ the understanding of how performance is correlated to composition or x, the various methods to synthesize CFx compounds, the correlation between the nature of the CF bonds and electrochemical performance, the role of theoretical studies in such endeavors, the use of CFx in alternative battery chemistries and the wide range of techniques available to probe either CFx compounds individually or CFx compounds in devices under electrochemical conditions. A picture of the field from which future directions can be derived is provided.

Correlating high temperature thin film ionomer electrode binder properties to hydrogen pump polarization

Influence of ionomer electrode binders thin film properties on electrochemical hydrogen pump (ECHP) polarization.

Полимерные связующие для электродов литиевых аккумуляторов. Часть 2. Синтетические и природные полимеры

The second part of the review describes the prospects of using alternative polymer binders for composite electrodes of lithium electrochemical systems. Possible options having been taken into account, the most popular commercially-available synthetic polymers with functional group (the ones forming aqueous solutions or dispersions predominantly) and water-soluble polymers of natural origin are considered. The versatility of such materials is their distinctive feature. The availability of salt forms for natural and synthetic polymers, many of which are polyelectrolytes, makes it possible to significantly affect the ion transfer in the composite electrode mass, reducing the polarization of the electrodes and improving the power characteristics of batteries. The ability to form “artificial SEI” and / or form a three-dimensional network with self-healing cross-links between macromolecules allows long-term safe cycling, the latter being especially important for active materials with very large volume changes during lithium intercalation / deintercalation (e.g. silicon).

Diffusion kinetics of water in graphite anodes for Li-ion batteries

Since the loading of electrodes for Li-ion batteries with an excessive amount of moisture affects the performance of the cells, the moisture is partly removed in a post-drying process step. The drying time is thereby controlled by the amount of moisture that has to be removed as well as the mass transport kinetics of water. This mass transport kinetics is limited by various mass transport resistances, which in turn can be influenced by individual dryer settings. In this paper, we investigate water-based anodes for Li-ion batteries as well as selected materials, and distinguish between different possible mass transport resistances that affect the drying time. Determined diffusion coefficients can be used in future modeling of the post-drying process. Special consideration needs to be bestowed upon the mass transport of water in the polymeric binders, since earlier investigations revealed that the moisture uptake of the anodes is particularly caused by sodium carboxymethyl cellulose (Na-CMC). This high water uptake by the binder in water-based electrodes leads to a polymer film drying process within the porous structure of the electrode. The diffusion of water in layers of binder is particularly dependent on the concentration as well as the temperature of the binder.

(Invited) Effect of Water Management for Cathode Catalyst Layers Using a Non-Noble Metal Catalyst and a Novel Polymer Electrolyte on Cell Performance Hysteresis in Anion Exchange Membrane Fuel Cells

In this work, we examined the cell performance of membrane-electrode assemblies (MEAs), for anion exchange membrane fuel cells (AEMFCs), using a non-noble metal catalyst and a novel polymer electrolyte. The chemical structure of quaternized poly(arylene perfluoroalkylene), i.e., QPAF-4 (ion exchange capacity: IEC = 2.1 meq g-1) developed in this laboratory1 is shown in Figure 1. Since this membrane is soluble in methanol, it is also suitable for use as an electrode binder. The non-precious metal catalyst cell was loaded with 0.45 mg cm-2 Fe-N-C catalyst supplied by Pajarito Powder on the cathode and 0.20 mgPt cm-2 platinum catalyst on the anode. An MEA in which platinum was loaded (0.20 mgPt cm-2) on both the anode and cathode was prepared for comparison. Pt loaded on carbon black (Pt/CB, TEC10E50E), supplied from TKK Japan, was used as the platinum electrocatalyst. Figure 2 shows a comparison of Fe-N-C and Pt/CB for their I-V performances at 60 oC, 100% RH, 0 kPag; anode H2 (100 mL/min); cathode O2 (100 mL/min). The cell using the Fe-N-C catalyst exhibited large hysteresis in the I-V curve, i.e., a large difference in potential between increasing and decreasing current. Figure 3 shows a comparison of Fe-N-C and Pt/CB for their I-V performances at 60 oC, 100% RH, 100 kPag; anode H2 (100 mL/min); cathode O2 (100 mL/min). The hysteresis of the I-V performance for the cell using the Fe-N-C cathode decreased with increasing back pressure. The cell exhibited slightly lower open circuit voltage and similar IV performance compared with those using Pt/CB. At the present stage, the loading amount of Fe-N-C catalyst, ionomer content, and porosity of the catalyst layer have not yet been optimized. We investigated whether the hysteresis originates from the anode or cathode. Based on the results of various I-V measurements, we conclude that the hysteresis is related to water supplied to the cathode using the Fe-N-C catalyst. Further details will be given in this presentation. We found from these results that the water management is essential, due to its requirement for the cathode reaction, for high-performance AEMFCs. Finally, these results demonstrate the viability of the use of low-cost materials such as non-noble metal catalysts for the AEMFC.Acknowledgement This project was partly supported by NEDO Japan through funds for the “Advanced Research Program for Energy and Environmental Technologies” and the Japan Society for the Promotion of Science (JSPS) and the Swiss National Science Foundation (SNSF) under the Joint Research Projects (JRPs) program.