High-performance Polymer Electrolyte Research Articles

Polysilaketals: High‐Performance Polyether‐Based Electrolytes with Tunable Disubstituted Silane Linkers

Polymer electrolytes exhibit higher energy density and improved safety in lithium‐ion batteries relative to traditionally used liquid electrolytes but are currently limited by their lower electrochemical performance. Aiming to access polymer electrolytes with competitive electrochemical properties, we developed the anionic ring‐opening polymerization (AROP) of cyclic silaketals to synthesize amorphous silicon‐containing polyether‐based electrolytes with varying substituent bulk of the general formula [OSi(R)2(CH2CH2O)2]n (R = alkyl, phenyl). As opposed to previously reported uncontrolled polycondensation routes toward low molecular weight polysilaketals, AROP allows access to targeted molecular weights above the entanglement threshold of the polymers. The polysilaketal with the lowest steric bulk (P(OSiMe,Me‐2EO)) exceeds the conductivity of poly(ethylene oxide) (PEO), a leading polymer electrolyte. To the best of our knowledge, this is the first solid polymer electrolyte to achieve this benchmark. Steric bulk in polysilaketals was found to impart stability and two bulkier polysilaketals, P(OSiEt,Et‐2EO) and P(OSiMe,Ph‐2EO), exhibited higher current fractions than PEO over a wide range of salt loadings. Moreover, the efficacy of P(OSiEt,Et‐2EO) was competitive with that of PEO. Taken together, the tunable and competitive electrochemical properties of polysilaketals validate the systematic incorporation of silyl groups as a strategy to access high performance polymer electrolytes.

Polysilaketals: High-Performance Polyether-Based Electrolytes with Tunable Disubstituted Silane Linkers.

Polymer electrolytes exhibit higher energy density and improved safety in lithium-ion batteries relative to traditionally used liquid electrolytes but are currently limited by their lower electrochemical performance.Aiming to access polymer electrolytes with competitive electrochemical properties, we developed the anionic ring-opening polymerization (AROP) of cyclic silaketals to synthesize amorphous silicon-containing polyether-based electrolytes with varying substituent bulk of the general formula [OSi(R)2(CH2CH2O)2]n(R = alkyl, phenyl).As opposed to previously reported uncontrolled polycondensation routes toward low molecular weight polysilaketals, AROP allows access to targeted molecular weights above the entanglement threshold of the polymers. The polysilaketal with the lowest steric bulk (P(OSiMe,Me-2EO)) exceeds the conductivity of poly(ethylene oxide) (PEO), a leading polymer electrolyte. To the best of our knowledge, this is the first solid polymer electrolyte to achieve this benchmark. Steric bulk in polysilaketals was found to impart stability and two bulkier polysilaketals, P(OSiEt,Et-2EO) and P(OSiMe,Ph-2EO), exhibited higher current fractions than PEO over a wide range of salt loadings. Moreover, the efficacy of P(OSiEt,Et-2EO) was competitive with that of PEO. Taken together, the tunable and competitive electrochemical properties of polysilaketals validate thesystematic incorporation of silyl groups as a strategy to access high performance polymer electrolytes.

Synthesis of poly(terphenyl-co-dibenzo-18-crown-6 methylimidazole) copolymers for high-performance high temperature polymer electrolyte membrane fuel cells

This study focuses on the development of high temperature polymer electrolyte membranes (HT-PEMs), which are essential components for HT-PEM fuel cells (HT-PEMFCs). While phosphoric acid (PA) doped polybenzimidazole (PBI) has been recognized as a successful HT-PEM, it faces several challenges, including the use of carcinogenic monomer, complex synthesis processes, and poor solubility in organic solvents. To produce more cost-effective, easily synthesized, and high-performance alternatives, this study utilizes a straightforward superacid-catalyzed Friedel-Crafts reaction to synthesize a series of poly(terphenyl-co-dibenzo-18-crown-6 methylimidazole) copolymers, referred to as Co-x%TP-y%CE-Im, using p-terphenyl, dibenzo-18-crown-6 and 1-methyl-1H-imidazole-2-formaldehyde as monomers. The copolymerized hydrophilic and bulky crown ether units introduce substantial free volume and multiple interaction sites with PA molecules, as indicated by theoretical calculations. Additionally, the formation of microphase separation structures, confirmed by atomic force microscope (AFM) and transmission electron microscope (TEM), contributes to the enhanced performance of these membranes. For instance, after immersion in 85 wt% and 75 wt% PA solutions, the Co-90%TP-10%CE membrane achieves PA doping contents of 200 % and 169 %, achieving high conductivities of 0.092 S cm−1 and 0.054 S cm−1 at 180 °C, while maintaining tensile strengths of 6.5 MPa and 7.5 MPa at room temperature. Without the need for humidification or backpressure, the peak power density of an H2-O2 cell equipped with Co-90%TP-10%CE/169%PA membrane with a thickness of 79 μm reaches an impressive 1018 mW cm−2 at 210 °C. These results demonstrate new materials and insights for the development of high-performance HT-PEMs.

Porous Wood Composite as a Green Approach for Enhancing Electrochemical Performance of Gel Polymer Electrolytes for Supercapacitors.

Delignified wood (DW) is a kind of environment-friendly porous material, and its unique hierarchical orous structure and excellent wettability are conducive to the rapid transfer and storage of ions, which can be used as electrolyte matrix of supercapacitors. In order to solve the deficiency of mechanical properties of DW as electrolyte materials, a novel cross-linked polyurethane (CPU) with high water absorption is designed as a reinforced matrix to improve the mechanical properties of electrolytes while maintaining high ionic conductivity. First, DW is immersed in CPU precursor solution, and the DW/CPU composite (W-CPC) is obtained by thermal crosslinking. Finally, W-CPC is soaked in 1 M LiClO4 aqueous electrolyte to obtain the composite gel polymer electrolyte (W-CPC-GPE). Benefiting from the good hydrophilicity of W-CPC, the anisotropic vertical channels inside the DW, and the synergism of hydrogen bond and covalent bond. The highest ionic conductivity and mechanical strength of W-CPC-GPE are 3.5×10-2 S cm-1 and 0.67 MPa, respectively. The W-CPC-5-G based supercapacitor exhibits a high specific capacitance of 146.52 F g-1 and favorable capacitance retention rate of 90.7 % after 5000 cycles. The results show that compounding with DW is an efficient and green way to develop high-performance gel polymer electrolytes for supercapacitors.

Binary solvent-reinforced poly (vinyl alcohol)/sodium alginate double network hydrogel as a highly ion-conducting, resilient, and self-healing gel polymer electrolyte for flexible supercapacitors

We present a reliable approach for producing high-performance ion-conducting gel polymer electrolytes (GPEs) based on the sodium chloride (NaCl)-integrated dual network hydrogel of poly (vinyl alcohol)/sodium alginate (PVA/SA) using a binary solvent system of ethylene glycol (EG) and water, providing exceptional ionic conductivity, mechanical strength, and self-healing properties. Different GPEs were produced via the freezing-thawing method using different v/v% of EG and water (named PVA/SA/EG). The best PVA/SA/EG GPE provided a maximum ionic conductivity of 25 mS cm−1, astonishing mechanical strength of 0.42 MPa, exceptional stretchability of 462 %, and remarkable self-healing properties. The binary solvent system- and water-based GPEs were utilized in the construction of symmetric supercapacitors (SSCs) using carbon cloth electrodes and their electrochemical performance were compared. At a current density of 0.5 mA cm−2, the SSC prepared using the best PVA/SA/EG GPE demonstrated a high specific capacity of 577.21 mF cm−2, maintained 94.5 % capacitance after 5000 cycles at 1 mA cm−2, and provided an energy density of 80.14 mWh cm−2 while operating at a power density of 293.3 mW cm−2. The flexible SSC prepared based on this GPE demonstrated outstanding flexibility, while no significant decline in capacitive performance and ionic conductivity was detected when it was bent.

In situ construction of 3D crossing-linked gel polymer electrolyte toward high performance and safety lithium metal batteries

Our study focuses on developing high-performance gel polymer electrolytes (GPEs) tailored for lithium metal batteries (LMBs), harnessing the combined benefits of high conductivity of liquid electrolytes and the enhanced safety of solid electrolytes. To this end, we engineered an in situ polymerized GPE (PMIA- TP) that integrates trifluoroethyl methacrylate (TFMA) and pentaerythritol triacrylate (PETA) monomers within an electrospun poly (m-phthaloyl-m-phenylenediamine) (PMIA) supporting membrane. In addition to high ionic conductivity, high lithium ion transference number, enhanced tensile strength and good thermal stability, the resulting PMIA-TP GPE exhibits satisfactory electrochemical stability against lithium electrodes, enabling long-term and stable lithium plating/stripping in symmetric Li//Li cells, and good rate capability and prolonged cycle life for LiFePO4//Li cells. Further X-ray photoelectron spectroscopy analysis and density functional theory calculations revealed that the electrochemical stability of the PMIA-TP GPE towards lithium metal electrode is due to the formation of a fluorine-rich solid electrolyte interphase (SEI) layer facilitated by reactions involving the –CF3 groups in TFMA, which is beneficial for the effective Li+ transport and lithium dendrite suppression. In summary, our study offers a promising approach to fabricating GPEs that offer high safety and high performance for LMBs.

A Facile Strategy for Constructing High-Performance Polymer Electrolytes via Anion Modification and Click Chemistry for Rechargeable Magnesium Batteries.

Polymer electrolytes play a crucial role in advancing rechargeable magnesium batteries (RMBs) owing to their exceptional characteristics, including high flexibility, superior interface compatibility, broad electrochemical stability window, and enhanced safety features. Despite these advantages, research in this domain remains nascent, plagued by single preparation approaches and challenges associated with the compatibility between polymer electrolytes and Mg metal anode. In this study, we present a novel synthesis strategy to fabricate a glycerol α,α'-diallyl ether-3,6-dioxa-1,8-octanedithiol-based composite gel polymer electrolyte supported by glass fiber substrate (GDT@GF CGPE) through anion modification and thiol-ene click chemistry polymerization. The developed route exhibits novelty and high efficiency, leading to the production of GDT@GF CGPEs featuring exceptional mechanical properties, heightened ionic conductivity, elevated Mg2+ transference number, and commendable compatibility with Mg anode. The assembled modified Mo6S8||GDT@GF||Mg cells exhibit outstanding performance across a wide temperature range and address critical safety concerns, showcasing the potential for applications under extreme conditions. Our innovative preparation strategy offers a promising avenue for the advancement of polymer electrolytes in high-performance rechargeable magnesium batteries, while also opens up possibilities for future large-scale applications and the development of flexible electronic devices.

The High-Performance Polymer Electrolytes Based on Agarose–Mg(ClO4)2 for Application in Electrochemical Energy Storage Devices

Electrochemical energy storage devices (EES) such as batteries and supercapacitors depend significantly on electrolytes, which have properties that significantly impact their energy capacity, rate performance, cyclability, and safety. Agarose–Mg(ClO4)2–based polymer electrolyte was prepared using the solution casting method by incorporating various amounts of Mg(ClO4)2 from 0 – 35 wt%. The presence of Mg(ClO4)2 as the dopant in agarose-matrix enhanced the ionic conductivity of the system from 1.796 × 10-8 S∙cm-1 to 6.247 × 10-4 S∙cm−1 in the composition of 30 wt% Mg(ClO4)2 due to the production of free ions. This system obeys the Arrhenius rule as it records the conductivity increment when temperature increases. This increment shows the amorphous nature of electrolytes, which XRD analyses by determining the crystallite size and degree of crystallinity of agarose–Mg(ClO4)2 polymer electrolyte. High ionic conductivity at room temperature has increased attention to this polymer electrolyte based on agarose–Mg(ClO4)2.

Identifying ultrathin dielectric nanosheets induced interface polarization for high-performance solid-state lithium metal batteries

Solid-state lithium metal batteries (SSLMBs) with polymer electrolytes are promising due to enhanced safety and high energy density, but the low ionic conductivity of polymer electrolytes and the unstable interface of lithium metal anode hinder the development of SSLMBs. Herein, we propose a unique strategy to address these challenges by coupling ultrathin high-dielectricity Ca2Nb3O10 (CNO) nanosheets with PEO-based electrolyte. The interfacial polarization originating from the distortion of NbO6 octahedra along the vertical direction of CNO nanosheets is maximized and so the interaction between CNO and LiTFSI, which greatly supports the dissociation of LiTFSI and improves the ionic conductivity (2.0 × 10−4 S cm−1) of the composite polymer electrolyte, compared to that without CNO. The optimized interfacial polarization effect is thoroughly demonstrated by theoretical calculation and experimental results. Moreover, due to a homogeneous, robust and LiF-rich solid electrolyte interphase film with promoted Li ion transport being formed at the lithium metal interface, the superior cycling stability (90 % capacity retention after 440 cycles at 0.5 C) and rate capability for LFP||Li full batteries are achieved. This design of composite polymer electrolyte with ultrathin dielectric nanosheet fillers demonstrates a new approach to the development of high-performance polymer electrolytes for SSLMBs.

Multiple Na+ transport pathways and interfacial compatibility enable high-capacity, room-temperature quasi-solid sodium batteries

Sodium-metal batteries (SMBs) are ideal for large-scale energy storage due to their stable operation and high capacity. However, they have safety issues caused by severe dendrite growth and side reactions, particularly when using liquid electrolytes. Therefore, it is critically important to develop electrolytes with high ionic conductivity and improved safety that are non-flammable and resistant to dendrites. Here, we developed polymerized polyethylene glycol diacrylate (PEGDA)-modified poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) electrolytes (PPEs) with highly conductive sodium bis(trifluoromethanesulfonyl)imide and corrosion-inhibitive sodium bis(oxalato)borate salts for SMBs. Well-complexed PEGDA not only increases the amorphicity of the PVDF matrix, but also offers numerous Lewis basic sites through the polar groups of carbonyl and ether groups (i.e., electron donors). The presence of the Lewis basic sites facilitates the dissociation of sodium salt and transportation of Na+ within the PVDF matrix. This results in the generation of additional Na+ transport pathways, which can enhance the performance of the battery. Among PPEs, the optimized PPE-50 exhibits a high ionic conductivity of 3.42 × 10–4 S cm−1 and a mechanical strength of 14.0 MPa. A Na||Na symmetric cell with PPE-50 displays high stability at 0.2 mA cm−2 for 800 h. PPE-50 further displays high capacity, e.g., a Na3V2(PO4)3|PPE-50|Na battery delivers a decent discharge capacity of 101.5 mAh g−1 at 1.0C after 650 cycles. Our work demonstrates the development of high-performance quasi-solid polymer electrolytes with multiple transport pathways suitable for room-temperature SMBs.

Lithium Superionic Conductive Nanofiber-Reinforcing High-Performance Polymer Electrolytes for Solid-State Batteries.

Although composite solid-state electrolytes (CSEs) are considered promising ionic conductors for high-energy lithium metal batteries, their unsatisfactory ionic conductivity, low mechanical strength, poor thermal stability, and narrow voltage window limit their practical applications. We have prepared a new lithium superionic conductor (Li-HA-F) with an ultralong nanofiber structure and ultrahigh room-temperature ionic conductivity (12.6 mS cm-1). When it is directly coupled with a typical poly(ethylene oxide)-based solid electrolyte, the Li-HA-F nanofibers endow the resulting CSE with high ionic conductivity (4.0 × 10-4 S cm-1 at 30 °C), large Li+ transference number (0.66), and wide voltage window (5.2 V). Detailed experiments and theoretical calculations reveal that Li-HA-F supplies continuous dual-conductive pathways and results in stable LiF-rich interfaces, leading to its excellent performance. Moreover, the Li-HA-F nanofiber-reinforced CSE exhibits good heat/flame resistance and flexibility, with a high breaking strength (9.66 MPa). As a result, the Li/Li half cells fabricated with the Li-HA-F CSE exhibit good stability over 2000 h with a high critical current density of 1.4 mA cm-2. Furthermore, the LiFePO4/Li-HA-F CSE/Li and LiNi0.8Co0.1Mn0.1O2/Li-HA-F CSE/Li solid-state batteries deliver high reversible capacities over a wide temperature range with a good cycling performance.

In situ catalytic polymerization of LiNO3-containing PDOL electrolytes for high-energy quasi-solid-state lithium metal batteries

1,3-Dioxolane (DOL) can be induced to form polymer electrolytes by in situ ring opening polymerization at Lewis acid salts. However, the presence of ion–dipole interactions between NO3− and DOL suppresses this polymerization behavior. Herein, we report that the use of Sc(OTf)3 as an initiator can well disrupt this ion–dipole interaction. The in situ ring-opening polymerization of DOL is achieved to form a LiNO3-modified polyDOL-based electrolyte. New mechanism of Li migration in polymer electrolytes have been revealed by molecular dynamics modeling and constructed molecular interface models. It is found that the electrolyte interior is affected by the ion–dipole interactions of Li+ by NO3−, which made it easier for Li+ to be released from the polar ether-oxygen ligands on the polymer chain for rapid migration, thus exhibiting an ionic conductivity of 1.8 mS cm−1 and tLi+ of 0.78. In addition, NO3− preempts the binding sites around Li+, improves the coordination environment, and prioritizes the formation of a kinetically stable anion-derivative interface, which effectively mitigates the interfacial side reactions between the electrodes and the electrolytes. As a result, the assembled solid-state Li||LiFePO4 cell exhibits an impressive 152.3 mAh/g discharge capacity at 0.5C and maintains 80.3 % of the capacity after 450 cycles at 50 °C. This work not only opens a new avenue for designing high-performance gel polymer electrolytes for more metal-based batteries, but also provides valuable insights into understanding the ion migration mechanism.

High-performance and robust high-temperature polymer electrolyte membranes with moderate microphase separation by implementation of terphenyl-based polymers

Acid loss and plasticization of phosphoric acid (PA)-doped high-temperature polymer electrolyte membranes (HT-PEMs) are critical limitations to their practical application in fuel cells. To overcome these barriers, poly(terphenyl piperidinium)s constructed from the m- and p-isomers of terphenyl were synthesized to regulate the microstructure of the membrane. Highly rigid p-terphenyl units prompt the formation of moderate PA aggregates, where the ion-pair interaction between piperidinium and biphosphate is reinforced, leading to a reduction in the plasticizing effect. As a result, there are trade-offs between the proton conductivity, mechanical strength, and PA retention of the membranes with varied m/p-isomer ratios. The designed PA-doped PTP-20m membrane exhibits superior ionic conductivity, good mechanical strength, and excellent PA retention over a wide range of temperature (80–160 °C) as well as satisfactory resistance to harsh accelerated aging tests. As a result, the membrane presents a desirable combination of performance (1.462 W cm−2 under the H2/O2 condition, which is 1.5 times higher than that of PBI-based membrane) and durability (300 h at 160 °C and 0.2 A cm−2) in the fuel cell. The results of this study provide new insights that will guide molecular design from the perspective of microstructure to improve the performance and robustness of HT-PEMs.

Pendulum-swing coordination boosting “liquid-like” Li-ion conduction within asymmetric lamellar fillers for solid polymer electrolytes

Solid polymer electrolytes have shown great prospect in high-energy lithium-metal batteries, yet the most critical challenge is their unsatisfactory ionic conductivity. A common strategy involves the incorporation of symmetric lamellar fillers with ions/molecules fixed in interlayers. However, because of strong fixation, it sacrifices “liquid-like” flow properties as small-molecular solvents in polymer matrices. Herein, a novel concept of pendulum-swing coordination within interlayers is proposed to integrate advantages from both scenarios, based on the design of one-side fixation of solvents in asymmetric lamellar fillers. This delicate modulation of the coordination environment ensures the weakened Li+-solvent interaction and the strengthened anion-cation dissociation of lithium salts. More importantly, it enhances dynamic motion of the “hanged” solvents in highly-confined space, activating “liquid-like” Li-ion conduction. Meanwhile, the confined solvent does not plasticize polymer matrices, thus excellent mechanical property maintains. As a result, the developed electrolyte exhibits an impressive ionic conductivity of 1.35 × 10−4 S/cm at room temperature and exceptional anodic stability with stable Li stripping/platting cycles for over 2000 h. Solid-state Li-LiFePO4 batteries exhibit good rate behavior and remarkable capacity retention of 85.4% after 400 cycles at 0.5C. This work provides enlightening ideas for continuous development of high-performance polymer electrolytes towards real applications of lithium-metal batteries.

Long-stable lithium metal batteries with a high-performance dual-salt solid polymer electrolyte

A high-performance dual-salt solid polymer electrolyte, consisting of cross-linked NPGDA-VEC copolymer interpenetrated in a PVDF-HFP nanofiber matrix, with LiTFSI and LiBOB as Li+ sources, was prepared for lithium metal battery applications.

Novel PEO-based composite solid electrolytes for All-Solid-State Li-S battery

Solid polymer electrolytes (SPEs) were investigated for several decades due to their good compatibility with electrodes. However, meeting the essential requirements for solid polymer electrolytes, including enhanced ionic conductivity, superior solubility with conductive lithium salts, and robust interface stability when in contact with a Li anode, remains a formidable challenge. In our work, we found that transition metal carbides (NiNbCeC) over mesoporous silica (SBA-15) can be filled into the Polyethylene Oxide (PEO) matrix to form composite solid electrolytes which can greatly improve the ionic conductivity of PEO. We investigate a series of transition metal carbides with varying mass ratios of Cerium (5%, 10%, and 20%) to fabricate All-Solid-State Li-S batteries (ASSLi-S). Our results demonstrate that different mass ratios of Cerium play a pivotal role in enhancing the ionic conductivity of the composite solid electrolytes, reducing impedance levels from 9150 O (20% Ce) to 4000 O (5% Ce) to 1730 O (10% Ce). At room temperature, the high initial specific capacity at 1C and reversible specific capacity after 100 cycles are 525 and 363 mAh/g, 605 and 403 mAh/g, 246.3 mAh/g and 63.28 mAh/g for 5% Ce, 10%, and 20%, respectively. Furthermore, long-term cycling tests of ASSLi-S cells at 0.5C reveal promising performance, with the cell containing 10% Ce solid electrolytes delivering an initial specific capacity of 1165.7 mAh/g and maintaining 335 mAh/g after 200 cycles. This represents a significant breakthrough, demonstrating that PEO-based solid electrolytes can achieve impressive electrochemical results at room temperature. SEM characterization was employed to assess the volume change in the solid electrolyte layer and elemental distribution of solid electrolyte materials through cross-sectional analysis. This analysis revealed that the failure modes of solid-state Li-S cells can also be attributed to the migration of sulfur elements from the cathode to the solid electrolyte layer during the cycling process. XRD was utilized to study the crystallinity of composite solid electrolytes. This study represents a significant stride in the progress of high-performance solid polymer electrolytes for All-Solid-State Li-S batteries, shedding light on the failure modes of such batteries. It underscores the potential of composites based on transition metal carbides in addressing crucial challenges for their practical implementation in Solid-State Lithium-Sulfur Batteries.

Towards Conformally Grafted Thin Film Ionomers for High Performance Polymer Electrolyte Fuel Cells

The development of the next generation of polymer electrolyte fuel cells has become a major focus in the decarbonization of heavy-duty transportation, such as public transport, land, aviation, and maritime freight1. Specifically, there is a need for improved catalyst layers with lower amounts of expensive platinum group metals2, as well as improved mass transport characteristics at high current densities, fluorine-free ionomers, and increased durability3. Achieving an optimal electrode microstructure is crucial in this process, as it influences the mass transport of reactant gases and products2. The chemistry and morphology of the ionomer film determine proton availability and affect oxygen transport and overall catalyst utilization. Thus, it is critical to maintain a delicate balance between the transport of reactants, products, protons, and electrons to ensure optimal cell performance. Traditional catalyst layers are fabricated using catalyst ink dispersions which limits the control over the triple-phase boundary microstructure4. This is problematic as poor distribution of the ionomer has been shown to have a negative impact on fuel cell performance5. It has been observed that some catalytic sites are inundated with ionomer, leading to a high oxygen transport resistance, while other uncoated sites may experience a lack of protons. Moreover, research has shown that the catalyst's active sites can be poisoned by the adsorption of sulfonic acid moieties present in commonly used ionomers. Motivated by these challenges, and the negative environmental impact of conventional fluorinated ionomers, it is essential to develop alternative ionomer chemistries and coating techniques6.To address these challenges, our research focuses on developing innovative synthetic methods that leverage both electrochemical and chemical principles to enable local control of ionomer coating in the catalyst layer. Our interest in these methods originates from their scalability and ability to control the morphology of coatings (e.g. thickness, conformality, porosity and polymer length). We employ grafting techniques based on radical mechanisms to covalently graft conformal ionomer thin films onto conventional Pt/C catalysts to produce improved triple phase boundaries. A vast array of monomers with different kinds of functionalities (e.g. amines, vinylics, diazo-compounds, carboxylates) can be used for grafting, including fluorine-free systems7. In this presentation, I will first describe the synthetic procedure to produce ionomer thin films. Second, we perform ex-situ characterization including electron microscopy, porosimetry and wettability measurements. Furthermore, we study the ionomeric nature of the films by its ion exchange capacity. Subsequently, we screen the most promising samples in single cell tests and compare them against a state-of-the-art benchmark. By combining potentiostatic and impedance-based techniques, we seek to gain insight into the in-operando characteristics of these new electrode materials. Through this comprehensive set of experiments, we aim to elucidate morphology – property – performance relationships for these ionomer thin films to further guide optimization of catalyst microstructures. Acknowledgement: This publication is part of the project 3D-FCoat (3-Dimensional structures for Fuel Cells through advanced Coating techniques) of the research program LIFT which is (partly) financed by the Dutch Research Council (NWO) and Nedstack Fuel Cell Technology B.V.

(Digital Presentation) Modeling the Effect of Membrane Electrode Assembly Microstructure on Thermal and Water Transport in Polymer Electrolyte Fuel Cells

The effect of water management on oxygen transport plays a critical role in the design of high-performance polymer electrolyte fuel cells (PEFCs) for the automotive industry, especially at low cathode platinum loading [1,2]. In this regard, optimizing the hierarchical pore structure of the membrane electrode assembly (MEA) is crucial to alleviate cathode flooding while ensuring good membrane hydration [3]. However, this task is complicated due to the small dimensions involved in the problem. Mathematical modeling has turned out to be a key tool to understand transport in the thin layered assembly used in PEFCs, including the catalyst layer (CL), microporous layer (MPL) and gas diffusion layer (GDL).In this work, oxygen, heat and two-phase water transport in the MEA are examined by means of a 1-dimension continuum bundle of capillary tubes model. Experimental pore size distributions (PSDs) are considered for the GDL/MPL/CL assembly. The model takes especial care in analyzing thermal and water behavior in catalyst layer by considering micro (< 20 nm of pore radius), meso (between 20 and 300 nm) and macroscale (> 300 nm) structures as different interconnected domains, each with their own effective thermal conductivity and water saturation. In this aspect, taking into account pore hydrophilicity or hydrophobicity is determinant as water behavior is extremely different.The model predictions are validated against previous experimental data for various operating conditions and pore structures (Figure 1a). The results offer precise information on the coupling between heat and water transport in both liquid and gas phases, and the impact of operating conditions and transport properties on the saturation distribution through the MEA layers (Figure 1b). Then the continuum bundle of capillary tubes model is also used to run a parametric analysis centered on the obtention of optimal PSD-dependent effective transport properties to produce improved MEA microstructures.[1] A. Sánchez-Ramos, J.T. Gostick, P.A. García-Salaberri, Modeling the Effect of Low Pt loading Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells: Part I. Model Formulation and Validation, Journal of the Electrochemical Society 168 (2021) 124514.[2] A. Sánchez-Ramos, J.T. Gostick, P.A. García-Salaberri, Modeling the Effect of Low Pt loading Cathode Catalyst Layer in Polymer Electrolyte Fuel Cells: Part II. Parametric Analysis, Journal of the Electrochemical Society 169 (2022) 074503.[3] M. Gomaa, A. Sánchez-Ramos, N. Ureña, M.T. Pérez-Prior, B. Levenfeld, P.A. García-Salaberri, M. Rabeh, Characterization and modelling of free volume and ionic conduction in copolymer proton exchange membranes, Polymers 14(9) (2022) 1688. Figure 1

Unveiling Local Aging Patterns Following Accelerated Stress Testing of High-Performance Polymer Electrolyte Fuel Cells.

This study presents an in-depth analysis of heterogeneous aging patterns in membrane electrode assemblies (MEAs) subjected to diverse accelerated stress test (AST) conditions, simulating carbon corrosion (CC AST) and Pt particle size growth in fully humidified (Pt AST-Wet) and underhumidified (Pt AST-Dry) H2/N2 atmospheres. Multimodal characterization techniques are used to focus on heterogeneous aging patterns, primarily examining the variations in current distributions and Pt particle size maps. The findings reveal distinct characteristics of current distributions for all the AST cases, with substantial changes and strong current gradients in the CC AST case, indicative of severe performance degradation. Notably, despite significant differences in Pt particle size growth at the end-of-life (EOL), the Pt AST-Wet and Pt AST-Dry cases show minor changes in spatial current distributions. Moreover, a preferential growth of Pt particles under serpentine flow field bends in the Pt AST-Wet case is observed for the first time. This study provides crucial insights into the role of mass transport properties in shaping fuel cell performance, and highlights the need to consider factors beyond electrochemically-active surface area (ECSA) when assessing fuel cell durability.

Room-temperature solid-state metallic lithium batteries based on high-content boron nitride nanosheet-modified polymer electrolytes

Polyethylene oxide (PEO)-based solid-state electrolytes have great potential in the development of solid-state metallic lithium batteries. However, it is difficult to apply them in metallic lithium batteries at room temperature because of the poor ionic conductivity and the lithium dendrite-induced safety problem. Herein, high-performance composite polymer electrolytes (CPEs) are developed by filling high-content boron nitride (BN) nanosheets with well dispersity in the PEO-LiTFSI matrices. Theoretical calculations and experimental characterizations reveal that the BN nanofillers with a strong Lewis acid property can capture TFSI− to release more free Li+, reduce the polymer crystallinity, and facilitate the generation of rich BN/PEO-LiTFSI fast-ion interfaces. Thus, the ionic conductivity and the Li+ transference number of the CPEs at room temperature greatly increase to 4 and 2 times those of the pristine electrolyte, respectively. Hence, the Li/CPE/Li batteries can operate steadily at 0.05 mA/cm2 (0.05 mAh/cm2) and 30 °C for 1200 h. Furthermore, the LiFePO4/CPE/Li batteries show higher initial capacity of 132 mAh/g and capacity retention of 84 % after 90 cycles at 0.3C and 30 °C than the pristine electrolyte-based batteries (29 %). This study provides a feasible case to prepare excellent-performance CPE films containing high nanofiller content for room-temperature solid-state metallic lithium batteries.