Cell Gasket Research Articles

A Guide to Choosing Polymers for Use in Lithium-Ion Cells

Every commercial lithium-ion cell made by winding or stacking electrodes uses tape to secure the jelly roll. Recently, it has been shown that lithium-ion cell jelly roll tape is often made out of polyethylene terephthalate (PET)1 and can dissolve into dimethyl terephthalate (DMT), a redox shuttle capable of inducing self-discharge unless effective electrolyte additives are present.2 This is due to ester bonds in PET that are susceptible to methanolysis via methanol and lithium methoxide. that are created in situ during battery operation from dimethyl carbonate (DMC), a ubiquitous solvent used in lithium-ion battery cells’ electrolytes. Effective electrolyte additives suppress the production of methanol and lithium methoxide from DMC, reducing the depolymerization of PET. However, the quantity of electrolyte additives used in commercial cells is low (1-3 wt%), and it has been shown that when ≤2 wt% of vinylene carbonate (VC) is used, most of it will be consumed during the first 200 h of operation.3 Thus, PET and any other polymer with a similar structure could become susceptible to methanolysis over long-term cycling.Other polymers with a similar chemical structure to PET are also often used in battery manufacturing. Examples include polybutylene terephthalate (PBT) or polyethylene naphthalene (PEN), used in cylindrical cell gaskets4 or metalized polymer current collectors5–7, respectively. Due to their chemical structure being similar to PET, it is reasonable to assume that these polymers might also be susceptible to depolymerization during battery operation, if no effective additives are used. However, in these two use cases, the risk of depolymerization does not only affect self-discharge but also cell safety. If a cell gasket or current collector dissolves during battery operation, this could lead to serious battery safety hazards, e.g., leaks or internal shorts.This study investigates the chemical stability of the most common polymers used in inactive components of commercial lithium-ion cells, e.g., pouch foils, adhesive tapes1, separators8, gaskets4, and metalized polymer current collectors5–7. The chemically stable and safe polymers to use in batteries are shown. In addition, the potential hazards of using chemically unstable polymers are demonstrated, and possible alternatives for battery manufacturers are proposed. References A. Adamson et al., Nat. Mater. (2023) https://www.nature.com/articles/s41563-023-01673-3.S. Buechele et al., J. Electrochem. Soc., 170, 010511 (2023).R. Petibon, J. Xia, J. C. Burns, and J. R. Dahn, J. Electrochem. Soc., 161, A1618–A1624 (2014).H. Kondo and T. Yamada, (2000) https://patents.google.com/patent/US6025091A/en.https://metamaterial.com/solutions/battery-materials/.https://soteriabig.com/technology/.http://www.dupontteijinfilms.com/.S. S. Zhang, Journal of Power Sources, 164, 351–364 (2007).

Mitigation of Silicon Contamination in Fuel Cell Gasket Materials through Silica Surface Treatment.

Gaskets and seals are essential components in the operation of proton exchange membrane (PEM) fuel cells and are required for keeping hydrogen and air/oxygen within their individual compartments. The durability of these gaskets and seals is necessary, as it influences not only the lifespan but also the electrochemical efficiency of the PEM fuel cell. In this study, the cause of silicon leaching from silicone gaskets under simulated fuel cell conditions was investigated. Additionally, to reduce silicon leaching, the silica surface was treated with methyltrimethoxysilane, vinyltriethoxysilane, and (3,3,3-trifluoropropyl)trimethoxysilane. Changes in the silica surface chemistry were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, elemental analysis, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Inductively coupled plasma-optical emission spectroscopy analysis revealed that surface-treated silica was highly effective in reducing silicon leaching.

Study on low temperature and durability characteristics of gasket for polymer electrolyte membrane fuel cell (PEMFC) depending on cross-sectional geometry

This study investigates the low-temperature and durability characteristics of fuel cell gaskets based on their cross-sectional geometry. Samples of rectangular, half-circular, and mountain shapes produced by injection molding are introduced. Experiments are conducted at −40 °C, near the glass transition temperature of EPDM (Ethylene-propylene-diene monomer), to elucidate the differences in airtightness. The maximum pressures capable of maintaining airtightness at −40 °C are 1.5, 2.1, and 2.6 barg initially for the rectangular, half-circular, and mountain shapes, respectively. After degradation for 28 days at 120 °C, these pressures drop by 0.4, 0.6, and 1.1 barg. Simulations suggest that enhancing sealing performance relies on increasing contact pressure via a smaller contact area but it causes rapid degradation due to the internal stress concentration. Hence, achieving an optimal design balancing airtightness and durability under high pressure is crucial. In this study, it is concluded that the half-circular shape demonstrates the most stable structural performance in this regard.

FEA Assessment of Contact Pressure and Von Mises Stress in Gasket Material Suitability for PEMFCs in Electric Vehicles

Ensuring the safety of electric vehicles is paramount, and one critical concern is the potential for hazardous hydrogen fuel leaks caused by the degradation of Proton-Exchange Membrane Fuel Cell (PEMFC) gasket materials. This study employs advanced techniques to address this issue. We leverage Finite Element Analysis (FEA) to rigorously assess the suitability of gasket materials for PEMFC applications, focusing on two crucial conditions: ageing and tensile stress. To achieve this, we introduce a comprehensive “dual degradation framework” that considers the effects of contact pressure and von Mises stress. These factors are instrumental in evaluating the performance and durability of Liquid Silicon Rubber (LSR) and Ethylene Propylene Diene Monomer (EPDM) materials. Our findings reveal the Yeoh model as the most accurate and efficient choice for ageing simulations, boasting a minimal Mean Absolute Percentage Error (MAPE) and computational time of just 0.27 s. In contrast, the Ogden model, while accurate, requires more computational resources. In assessing overall model performance using MAE, Root Mean Square Error (RMSE), and R-squared metrics, both LSR and EPDM materials proved promising, with LSR exhibiting superior performance in most areas. Furthermore, our study incorporates uniaxial tensile testing, which yields RMSE and MAE values of 0.30% and 0.40%, respectively. These results provide valuable insights into material behaviour under tensile stress. Our research underscores the pivotal role of FEA in identifying optimal gasket materials for PEMFC applications. Notably, LSR is a superior choice, demonstrating enhanced FEA modelling performance under ageing and tensile conditions. These findings promise to significantly contribute to developing safer and more reliable electric vehicles by advancing gasket material design.

Changes in Compression Characteristics with Accelerated Aging of Fuel Cell Gasket

Changes in Compression Characteristics with Accelerated Aging of Fuel Cell Gasket

Finite Element Analysis of Surface Pressure of Hydrogen Fuel Cell Gasket

Finite Element Analysis of Surface Pressure of Hydrogen Fuel Cell Gasket

Discharge State of Layered P2-Type Cathode Reveals Unsafe than Charge Condition in Thermal Runaway Event for Sodium-Ion Batteries.

A sol-gel process followed by heat treatment derived a layered P2-type NaCoO2 cathode, which depicted unit cell parameters values of a = 2.8389 Å, c = 10.9899 Å, and V = 76.71 Å3 in powder X-ray diffraction pattern. The synthesized cathode exhibited hexagonal, 2D platelets with an ∼300 nm thickness. During the anodic and cathodic sweeps, the cyclic voltammograms revealed multiple redox peaks with the same current densities, shapes, and peak positions, associated with the highly reversible phase transition mechanism of the layered P2-type NaCoO2 cathode. The sodium cells yielded the capacities of 93/92 mAh g-1 at 0.5 C and 87/87 mAh g-1 at 1 C for the 50th charge-discharge cycles. The in situ multimode calorimetry (MMC) studies of sodium cells demonstrated a thermal explosion event, which occurred by sodium melting, short-circuit, electrode decomposition reaction, gas generation, exothermic reaction, released heat energy ,and cell gasket melting. Ultimately, the calculated released total heat energies of ∼550/740 J g-1 for in situ MMC studies and ∼312/594 J g-1 for ex situ DSC analyses (charge state at 4 V and discharge state at 2 V) show that the discharged state of sodiated layered P2-type NaCoO2 cathode material is more unsafe than the charge state. Furthermore, the ex situ differential scanning calorimetry (DSC) spectrum of a discharge state at 2 V of layered P2-type NaCoO2 revealed a decreased onset temperature (DOT) at 141 °C with two pronounced exothermic peaks at 197 and 266 °C with a released higher total heat energy of 594 J g-1 than the charge state heat energy at 312 J g-1, attributed to the higher charge onset temperature (COT) at 191 °C. Thus, the observed higher heat energy and decreased onset temperature for the discharge state at 2 V is associated with the higher Na+ ion in the discharge state of the layered P2-type NaxCoO2 cathode than that of the pristine cathode, showcasing that the layered P2-type NaCoO2 cathode is unsafe at the discharged condition for sodium-ion batteries.

Real-Time Reservoir Balancing and Leak-Free Nonaqueous Cell Design for Flow Batteries

Benchtop-scale testing of redox flow batteries presents numerous operational challenges related to electrolyte imbalance, leakage, and chemical compatibility. Electrolyte imbalance creates a capacity-limiting reservoir and necessitates manual or automatic transfer of electrolyte between reservoirs to rebalance. Leakage of electrolyte in the cell, often at tubing connections or interfaces between the graphite plates, gaskets, and membrane, also reduces capacity and experimental repeatability. The testing of increasingly common nonaqueous electrolytes requires not only strict wetted material compatibility across a range of solvents but also greater resistance to leaks – the lower surface tensions of many organic solvents (vs. water) makes them more prone to leakage. The above issues are more easily dealt with in large-scale, permanent installations that do not have the benchtop-scale requirements of manual assembly/disassembly, modularity, and configurational simplicity. Additionally, benchtop flow batteries often use peristaltic pumps, a type of positive displacement pump which create large pressure and flowrate pulsations compared to the continuous output of centrifugal pumps commonly used in large scale systems. The use of individual peristaltic pumps for each side of the flow battery can create an electrolyte imbalance when an asymmetric pressure drop occurs across the cell, causing a Darcy flow of electrolyte through the membrane separator. Other aspects of the flow battery can exacerbate this imbalance, such as using porous separators which are more permissive to electrolyte crossover, or more viscous electrolytes which create higher pressure differentials in the hydraulic circuit at a given flowrate. A new pump control strategy for flow batteries is designed and implemented which controls the speed and flowrate of the pumps in real time in response to the reservoir levels, as shown in Figure 1. This control scheme maintains balanced electrolyte reservoirs by minimizing the average differential pressure across the membrane. Minimal pressure drops are achieved by effectively matching the pressures in each half-cell of the battery by adjusting each pump’s speed and flowrate independently, so that both pumps are operating at the same pressure on their respective fluid mechanical system curves. Additionally, a more leak-resistant cell gasket design shown in Figure 2 is developed, while maintaining chemical compatibility for nonaqueous systems. These two developments are employed in a long-term cycling experiment using a nonaqueous disproportionation electrolyte. Figure 1

Design optimization through thermomechanical finite-element analysis of a hybrid piston-clamped anvil cell for nuclear magnetic resonance experiments.

The investigation of materials under extreme pressure conditions requires high-performance cells whose design invariably involves trade-offs between the maximum achievable pressure, the allowed sample volume, and the possibility of real-time pressure monitoring. With a newly conceived hybrid piston-clamped anvil cell, we offer a relatively simple and versatile system, suitable for nuclear magnetic resonance experiments up to 4.4 GPa. Finite-element models, taking into account mechanical and thermal conditions, were used to optimize and validate the design prior to the realization of the device. Cell body and gaskets were made of beryllium-copper alloy and the pistons and pusher were made of tungsten carbide, while the anvils consist of zirconium dioxide. The low-temperature pressure cell performance was tested by monitoring in situ the pressure-dependent 63Cu nuclear-quadrupole-resonance signal of Cu2O.

Anvil cell gasket design for high pressure nuclear magnetic resonance experiments beyond 30 GPa

Nuclear magnetic resonance (NMR) experiments are reported at up to 30.5 GPa of pressure using radiofrequency (RF) micro-coils with anvil cell designs. These are the highest pressures ever reported with NMR, and are made possible through an improved gasket design based on nano-crystalline powders embedded in epoxy resin. Cubic boron-nitride (c-BN), corundum (α-Al2O3), or diamond based composites have been tested, also in NMR experiments. These composite gaskets lose about 1/2 of their initial height up to 30.5 GPa, allowing for larger sample quantities and preventing damages to the RF micro-coils compared to precipitation hardened CuBe gaskets. It is shown that NMR shift and resolution are less affected by the composite gaskets as compared to the more magnetic CuBe. The sensitivity can be as high as at normal pressure. The new, inexpensive, and simple to engineer gaskets are thus superior for NMR experiments at high pressures.

Effects of curing systems on the mechanical and chemical ageing resistance properties of gasket compounds based on ethylene-propylene-diene-termonomer rubber in a simulated fuel cell environment

Ethylene-propylene-diene-termonomer (EPDM) rubber based fuel cell gasket compounds have been designed and explored the effects of various vulcanization systems on different properties. Three types of sulphur-accelerated vulcanization systems such as conventional vulcanization (con), semi-efficient vulcanization (sev) and efficient vulcanization (ev) and also a peroxide vulcanization system were employed in this study. The curing characteristics, tensile, hardness and compression set properties of the cured compounds were evaluated. The crosslink density was assessed by equilibrium swelling method in dodecane. The chemical stability of the cured EPDM compounds was also evaluated through an accelerated durability test (ADT) using a solution (1 M H2SO4 + 10 ppm HF) very close to the fuel cell atmosphere. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM) were employed to investigate the chemical and physical changes of the cured EPDM compounds before and after exposure to the ADT solution over time. The results indicate that the EPDM compounds cured with peroxide exhibit the highest crosslink density with lowest compression set value at both room temperature and at elevated temperature. The FTIR and the corresponding SEM results show no significant chemical degradation of the peroxide cured EPDM compounds due to ADT ageing.

Focusing polycapillary to reduce parasitic scattering for inelastic x-ray measurements at high pressure.

The double-differential scattering cross-section for the inelastic scattering of x-ray photons from electrons is typically orders of magnitude smaller than that of elastic scattering. With samples 10-100 μm size in a diamond anvil cell at high pressure, the inelastic x-ray scattering signals from samples are obscured by scattering from the cell gasket and diamonds. One major experimental challenge is to measure a clean inelastic signal from the sample in a diamond anvil cell. Among the many strategies for doing this, we have used a focusing polycapillary as a post-sample optic, which allows essentially only scattered photons within its input field of view to be refocused and transmitted to the backscattering energy analyzer of the spectrometer. We describe the modified inelastic x-ray spectrometer and its alignment. With a focused incident beam which matches the sample size and the field of view of polycapillary, at relatively large scattering angles, the polycapillary effectively reduces parasitic scattering from the diamond anvil cell gasket and diamonds. Raw data collected from the helium exciton measured by x-ray inelastic scattering at high pressure using the polycapillary method are compared with those using conventional post-sample slit collimation.

The laser micro-machining system for diamond anvil cell experiments and general precision machining applications at the High Pressure Collaborative Access Team.

We have designed and constructed a new system for micro-machining parts and sample assemblies used for diamond anvil cells and general user operations at the High Pressure Collaborative Access Team, sector 16 of the Advanced Photon Source. The new micro-machining system uses a pulsed laser of 400 ps pulse duration, ablating various materials without thermal melting, thus leaving a clean edge. With optics designed for a tight focus, the system can machine holes any size larger than 3 μm in diameter. Unlike a standard electrical discharge machining drill, the new laser system allows micro-machining of non-conductive materials such as: amorphous boron and silicon carbide gaskets, diamond, oxides, and other materials including organic materials such as polyimide films (i.e., Kapton). An important feature of the new system is the use of gas-tight or gas-flow environmental chambers which allow the laser micro-machining to be done in a controlled (e.g., inert gas) atmosphere to prevent oxidation and other chemical reactions in air sensitive materials. The gas-tight workpiece enclosure is also useful for machining materials with known health risks (e.g., beryllium). Specialized control software with a graphical interface enables micro-machining of custom 2D and 3D shapes. The laser-machining system was designed in a Class 1 laser enclosure, i.e., it includes laser safety interlocks and computer controls and allows for routine operation. Though initially designed mainly for machining of the diamond anvil cell gaskets, the laser-machining system has since found many other micro-machining applications, several of which are presented here.

Two and Three Electrode Electrochemical Cells for Ambient and High Temperature Battery Materials Research

Introduction Coin cells and Swagelok cells are typically used for two and three electrode electrochemical testing of metal ion battery materials. Commercial three electrode laboratory cells are also available, but are typically expensive and often use elastomeric seals, which react with electrolyte and are not compatible with high temperatures. The use of traditional 2325 coin cell hardware at high temperature applications is limited by the 60°C softening temperature of the cell gasket. At 60°C, the pressure generated by highly volatile solvents can cause the cell to rupture. This is especially troublesome for Mg battery research where volatile solvents are generally used and high temperatures are needed for better intercalation kinetics. Two and three electrode Swagelok cells are more difficult to prepare than standard coin cells. They typically use PTFE ferrules, and care must be taken as PTFE is reactive with electrolyte at low potentials. Here we describe cell hardware based on Conflat vacuum fittings. Typically Conflat vacuum fittings use copper or Viton gaskets. These can either cause a short circuit between two Conflat fittings or react with electrolyte. We have found gasket materials made from stable polymers form effective insulating, electrolyte resistant and high temperature seals in laboratory test cells. Experimental Conflat cells were constructed using standard 2.125" Conflat blank and bored flanges. HDPE or PTFE gaskets were punched from 0.125" sheets using a circular die press. Two electrode cells used the same inner cell stack as a two electrode coin cell (spring, spacer, electrodes, separator). Three electrode cells included a Li or Mg ring reference electrode. 2325 coin cell hardware was used for comparative testing. Results and Discussion Figure 1 shows the cycling performance of a LiFePO4 (LFP) vs Li two electrode Conflat cell using 1M LiTFSI in PC at 30oC. It shows no capacity fade and identical performance as coin cells.Figure 2 shows the cycling of a two electrode Li4Ti5O12 (LTO)/Li Conflat cell tested at high temperatures. No capacity fade was detected below 110oC. As the temperature is increased, reactions with the electrolyte caused the capacity to fade due to increased impedance from electrolyte decomposition reactions.Figure 3 shows the cycling performance of a Mo6S8/Mg/Mg three electrode Conflat cell containing a highly volatile tetrahydrofuran (THF) based electrolyte at 60°C. We have found that three electrode cells using such volatile electrolytes at this temperature are extremely unreliable and difficult to make using coin cell hardware. The conflat cell, on the other hand cycled reversibly, during which time the voltages of the Mg counter and Mo6S8working electrode were accurately measured without electrolyte polarization using the third electrode.Conflat cells are excellent low cost cell hardware that use readily available parts. They are simple to assemble can be made into two and three electrode cell configurations and particularly useful for high temperature studies. We consider Conflat cells an excellent alternative to coin and Swagelok cell hardware especially in Mg battery research where the electrolyte is volatile and moderately high temperatures are used. Three electrode measurements at high temperature of Li and Mg battery materials and further details regarding Conflat cell design will be discussed.

Crystal structure refinement of MgSiO3high temperature C2/c clinoenstatite

The high-temperature clinoenstatite (HT-CEn) is one of the important MgSiO3 pyroxene polymorph. The single-crystal of C2/c HT-CEn endmember is firstly synthesized by rapid pressure-temperature quenching from 15-16 GPa and 900-19000C [1]. No report that it is produced as single crystal or large domain has been made on the MgSiO3 endmember. The HT-CEn-type modifications are observed in Ca-poor Mg-Fe clinoenstatite and pigeonite and are always found to be unquenchable in rapid cooling. The high pressure and high temperature experiments of MgSiO3 composition were carried out with a Kawai-type multi-anvil apparatus. The samples were quenched by rapidly releasing the oil pressure load and/or by blow out of anvil cell gasket. The space group of C2/c is strictly determined by Rigaku RAPID Weissenberg photographs and synchrotron radiation. Single-crystal X-ray diffraction experiments were performed at ambient conditions using a Rigaku AFC-5 four circle diffractometer. A total of 9383 reflections was measured and averaged in Laue symmetry 2/m to give 766 independent reflections used for the structure refinements. Final reliability factors converged smoothly to R = 0.029. The single-crystal diffraction analysis shows that the unusual bonding distances frozen in this metastable structure. The degree of kinking of the silicate tetrahedral chains is 1750for HT-CEn. The chain angle for HP-CEn is substantially smaller (1350) and the angle for L-CEn turned to the opposite direction at -1600(=2000). The degree of kinking increases by being curved in more than 1800in the transition from HT-CEn to L-CEn. As for the reverse change from the expansion to the stretch, a potential barrier exists in the point of the continuity. It is suggested that the reason which can quench structure under ambient conditions is the present HT-CEn single crystal was formed by the isosymmetric phase transition from HP-CEn. HT-CEn type single-crystals cannot be frozen without pressure.

Assessing the Tearing Energy of a Hydrocarbon Elastomeric Seal Material for Fuel Cell Applications

AbstractElastomeric gaskets are commonly used between cells within a fuel cell stack to ensure that the reactant gases are isolated. Failure of a fuel cell gasket can cause the reactant gases to mix and can lead to failure of the fuel cell. An investigation of the durability of a hydrocarbon elastomeric seal material developed for proton exchange membrane fuel cells was performed by comparing the tearing energy required for crack propagation of as‐received and environmentally aged samples. Tear force was recorded as a function of crosshead displacement rate and the critical strain energy release rate was calculated and plotted against crack growth rate. Data obtained at different temperatures were then used to generate a fracture energy master curve. Additional samples were aged in selected relevant environments and compared to the as‐received material to study the effect of environmental aging on tear energy master curves. Comparison of tearing energy master curves for different test conditions showed an increase in the tearing energy for all aging environments. The tear energy master curve for testing carried out in water suggested that the crack propagation rates as low as of 10–8 ms–1 can be seen as the fracture energy approaches 80 Jm–2.

スメクタイトを主成分とする膜材料の開発

Smectite-based film “Claist®” was developed. Layered smectite crystals are orderly densely stacked and added organic polymer acts as a binder. Purified bentonite, and synthetic smectite were used because of their good film formability. The film has superior heat-resistance and gas barrier performance. Transparent films were also successfully made from synthetic smectite and transparent organic polymer. The films are hopeful for electric devices including display, hydrogen gas tight sheet, solar cell back sheet, gasket and packing, functional wallpaper, and so on.

Fuel cell gasket testing started

Fuel cell gasket testing started

Integral moulding method of fuel cell gasket

Integral moulding method of fuel cell gasket

Attainment of near-hydrostatic compression conditions using the Paris–Edinburgh cell

By means of a straightforward modification to the Paris–Edinburgh cell gasket configuration, it is now possible to utilize fluid pressure-transmitting media up to at least 9 GPa. Test data on various representative samples are presented, discussed and contrasted with typical results obtained using the earlier gasket arrangement and Fluorinert pressure-transmitting medium. For the case of deuterated urea, the significant improvement in compression conditions revealed the existence of two new structural phases (IV and V) which are first observed at 3.0 GPa and 7.5 GPa. Future development possibilities for the technique of sample encapsulation are presented and discussed.