bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Internal Short Circuit and Thermal Runaway of Li-Ion Battery Due to Mechanical Abuse
Authors: Sheikh Muhammad , Rashid Muhammad
Published: February 2024

Due to the growing electric vehicle market and new trends to reduce fuel consumption for a healthy environment, safe and reliable vehicles are desirable for reasons beyond EV and new technology. Although certain safety standards and legislation are in place and continuously improving but several concerns including battery safety, battery performance, vehicle structure, and battery design to be considered as these affect the overall reliability of Electric vehicles (EVs). Lithium-ion battery technology is considered a good solution to power electric vehicles but potential overheating due to stressful conditions such as mechanical abuse, overcharge, over-discharge, short circuit, and excessive heat from external environment gives rise to safety issues and the occurrence of one or more than one of these can lead to thermal runaway. In most cases, an electric short circuit is a necessary but not sufficient condition for the occurrence of thermal runaway after mechanical abuse. Chemistry of the cell, the resistance of separator to heat, size of the fractured part, and rate of heat transfer all play a role in processes leading to a thermal runaway, if the cell has not gone to thermal runaway right away it can still go into a slow process of electrochemical reaction, releasing gases that eventually could lead to a catastrophic event. This abstract investigates the mechanical behaviour of the separator in the LiCoO2/Graphite cylindrical 18650 cells. Internal short circuit (ISC) behaviour, strain rate dependency, and electrochemical status of the cells (i.e. SOC dependency) are studied to understand failure patterns. Furthermore, a simple and effective constitutive model for the separator layer is formed, facilitating further mechanical analysis and numerical simulation of lithium-ion battery study. The occurrence of ISC is investigated by jellyroll deformation where the casing is removed, and quasi-static load is applied. The numerical simulation model is developed to further investigate sequential structural failures and temperature changes. Simulation results showed good accuracy with experimental results and are useful to predict structural failure of cells. The number of failures including electrolyte leakage, change in shape, sudden voltage drop/temperature rise, and gas venting are observed.
Failure Modes in Sulfide-Based All Solid-State Batteries (ASSB) Investigated By Operando SEM
Authors: Davoisne Carine , Yadav Neelam , Morcrette Mathieu
Published: February 2024

Studies on solid state batteries (ASSB) which began back in 190’s has seen a tremendous growing interest for multiple reasons such as the safety and the ability to use the metallic anodes for enhancing the gravimetric energy density. However, it exists different issues linked with poor performance of the batteries, which could be the results of interfacial challenges such as poor ion transport, dendrite formation, electrochemical degradation and chemo-mechanical degradation[1]. Among the potential parameters impacting the cycling process, the influence of the particle size of solid electrolyte is not well studied.

In this study, we focused on sulfide-based SEs particle size distribution and its impact on electrochemical performance by investigating from the morphological point of view via operando SEM. A batch of Argyrodite (Li6PS5Cl (LPSCl)) was sieved to obtain two batches of particles range (0,5-20µm and 50-150µm). The AASBs were prepared using the two particles size distribution while keeping the anode (lithium metal), cathode (MA: NMC) composite formation and the fabrication process constant. The different morphological and chemical evolutions were monitored in real time by scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDX) to obtain a complete of the different modification throughout the battery components and their interfaces. To do so, a home-made electrochemical cell was developed to perform in-situ and operando cycling in the SEM.

From the two particles sized distribution, the one with the large particles have better electrochemical performance. From morphological point of view at the cathode composite electrode, the formation of a cathode electrolyte interface is visible in the different batteries but is more developed in the case of small sized particles. In the solid electrolyte, the type of cracks differs with relatively strait feature for small particles and sinuous one for large one. At the anodic interface, a lost in contact between the SE separator and the lithium is observed and increased with the cycling process with a higher impact for the small particles (Figure 1.a and b). By investigating further, the formation of dendrites with different morphologies are visible at the anodic interfaces (Figure1.c).

We categorized the observed changes into three modes: (i) electrical failure by the formation of lithium dendrites of different morphologies following the ES going up to short circuit in the case of small particles, (ii) mechanical failure by the formation of cracks in the electrolyte whose shape and propagation strongly depend on the distribution particles size and (iii) electrochemical failure with the formation of solid electrolyte interphases on the surface of the active material. The main obstacles for the use of lithium metal are related to the propagation of lithium dendrites and thus to the mechanical instability of solid electrolytes.
(Invited) Safety and Performance Testing of Commercial Sodium-Ion Batteries
Authors: Carter Rachel Elizabeth , Waller Gordon Henry , Love Corey T.
Published: February 2024

Sodium-ion batteries (SIBs) have emerged on the global market and are poised to complement the ubiquitous li-ion battery (LIB). SIBs deliver a lower energy density than LIBs but utilize more globally abundant materials and boasts a higher degree of safety. These batteries possess similarities to LIBs but contain a wider range of materials due to the different size and reactivity of the alkali ion. Herein we utilize accelerating rate calorimetry (ARC) and electrochemical analysis to characterize the safety and performance of two cell types. The Cell A contains an aqueous electrolyte and has power capability (up to 80 C or 200 A) but low energy density (~30 Wh/kg), while the Cell B cell is non-aqueous and delivers higher energy density (~80 Wh/kg). ARC reveals benign failure modes compared to LIBs for single cells and 3 cells touching. Calorimetry also reveals minimal self-heating during charge/discharge, mitigating need for pack thermal management. Electrochemical analysis identifies impressive rate capability (tested up to 20 A) and a wide range of ambient temperatures (-20 to 45 °C). Both cells utilize aluminum for both positive and negative current collectors, since sodium and aluminum do not alloy. This is unique in comparison to LIBs, that require a copper current collector at the anode, preventing low voltage storage, where the copper reduces and dissolves. Therefore we investigated “de-energized” or 0 V storage of both SIBs. Cell A proved robust to these excursions, while Cell B exhibited capacity loss but maintained a high degree of safety.
Development of Multi-Physical Simulation Models for Quasi-Static Load Analysis to Predict the Behavior of Li-Ion and Na-Ion Batteries Under Different Mechanical Abuse Loadings
Authors: Cabello Moreno Noelia , Vicente Lopez Ana Maria
Published: February 2024

There are lot of studies on understanding the short-circuit phenomena at cell component level and how to address the thermal management at module and pack level to avoid overheating. However, it is also very important, in terms of safety, to evaluate the response and failure of cells during abuse tests as this can promote the thermal runaway event. Safety of metal ion batteries under mechanical loadings is currently one of the most challenging and urgent issues face in the Electric Vehicle (EV) industry. In the battery manufacturing community, the property of strength and resistance of batteries to external loading has never been a design consideration. However, under local mechanical loading, batteries are prone to developing a internal short circuit (ISC), which may lead to the generation of smoke, fire, and possible explosion.

This work is focused on the metal ion batteries safety studies (lithium and sodium) including the investigation of predictive models to determine the critical parameters that would lead to potential failure and provide critical insights to understand the mechanical and ISC behaviors of cells under mechanical abuse. Having a numerical model that correctly represents the cells and its response under different abuse tests could allow identifying main issues and helping on the cell design and chemistries to be used. To develop these models using LS-Dyna, it has been necessary to carry out studies of mechanical deformation on cell components and the complete cells. These studies have offered a better knowledge of the deformation of the inner components of the battery, being useful to identify the mechanism that initiate short circuits under mechanical misuse conditions. Building numerical models for batteries requires experimental work that provides not only the data for mechanical behavior of individual components (anode, cathode, separator, etc.), but also validation data for simulations of internal short circuit induced by mechanical abuse.

Figure 1
Non-Flammable Ether and Phosphate-Based Liquid Electrolytes for Sodium-Ion Batteries
Authors: van Ekeren Wessel Willem Andries , Mogensen Ronnie , Younesi Reza
Published: February 2024

The demand on the lithium reserves has been increasing rapidly due to the continuous growth in energy storage devices. Since the lithium reserves are limited and only accessible at certain geographical areas, the costs of lithium precursors are increasing significantly.1 Therefore, alternative battery chemistries need to be investigated. One of the next generation battery solutions is sodium-ion batteries (SIBs).2 However, current commercial electrolytes in SIBs are based on highly flammable carbonate-based solvents, such as ethylene carbonate, propylene carbonate, diethyl carbonate and dimethyl carbonate.3 To enhance the safety of SIBs, it is of utmost importance to develop non-flammable electrolytes. In this work, NaPF6 and NaBF4 salts are used in combination with a solvent mixture of ethers (diglyme, tetraglyme) and phosphates (triethylphosphate, trimethylphosphate) to obtain non-flammable liquid electrolytes. The electrolytes are evaluated in terms of physicochemical properties and electrochemical performance full-cells using high-mass loading Prussian White (12 mg/cm2) and Hard Carbon (7 mg/cm2). Flammability tests have shown that at least 70% of phosphate co-solvents are required to make the glyme based electrolyte non-flammable. In summary, the combination of glymes and phosphates provide promising electrolyte formulations in terms of non-flammability characteristics and ionic conductivities, but still lack long-term cycling stability. This work opens avenues to optimizing non-flammable electrolytes for high-performing and safe SIBs.

References

1 R. Schmuch, R. Wagner, G. Hörpel, T. Placke and M. Winter, Nat. Energy, 2018, 3, 267–278.

2 H. S. Hirsh, Y. Li, D. H. S. Tan, M. Zhang, E. Zhao and Y. S. Meng, Adv. Energy Mater., 2020, 10, 1–8.

3 R. Gond, W. Van Ekeren, R. Mogensen, A. J. Naylor and R. Younesi, Mater. Horizons, 2021, 8, 2913–2928.

Acknowledgement

The authors would like to acknowledge the financial support by the Swedish Energy Agency via project no. 50177-1, VINNOVA via projects no. 2022-01465 and 2019-00064 (Batteries Sweden), and SuSaNa project under M-ERA-Net call 2021 (G.A. no 958174).
(Invited) The Path to Vapour Cloud Explosions and Lithium-Ion Batteries
Authors: Christensen Paul A.
Published: February 2024

The lecture will cover the research that led to the realisation that vapour cloud explosion was and is the understated hazard of lithium-ion batteries, commencing with work in January and March 2020 and leading up to the present day. The research was initiated with an exploration of the effect of various abuse methods on 1.7 kWh Envision-AESC modules, followed by investigating the effect of State-of-Charge on the manifestation of thermal runaway, the latter leading to the realisation of the vapour cloud and its potential consequences. This was followed by experiments on the larger scale to analyse the vapour cloud composition and to trigger deflagration: these suggested the possibility that arc plasma may have a role in the production of the vapour cloud. Later, experiments on the suppression of thermal runaway clearly showed the risks associated with the suppression of fire without the suppression of thermal runaway, as the hazard flips from fire to explosion. This was a key finding, as was the large volume of vapour cloud produced by lithium-ion batteries (i.e. at least 500 L/kWh and up to 5500 L/kWh), causing the routinely observed rocket-like flames when the cloud ignites immediately, and the fact that even small lithium-ion batteries (e-bikes, e-scooters) are causing vapour cloud explosions.

As well as academic research, the concepts and ideas discussed will be illustrated with information and videos from a wide range of sources including first responder reports from across the world.

Finally, the possible risks and hazards of the use of electric vehicle batteries in 2nd life applications will be addressed
Increasing Battery Safety of Lithium-Ion Batteries by Using Cell-Internal Glass Fiber Sensors for in-Situ Temperature Monitoring
Authors: Burger Alexandra , Krause Florian , Bausch Bruno , Böse Olaf , Ophey Jannes , Wuersig Andreas , Sauer Dirk Uwe , Kapels Holger
Published: February 2024

Lithium-ion batteries (LIB), featuring high energy density and power density, are used in a wide range of applications. One of the most important requirements for their application is to ensure their safety and continuous performance under different operating conditions. In order to ensure the afore mentioned factors, in-situ monitoring of internal cell parameters, such as temperature, state-of-charge, and state-of-health of LIB is essential. The cell temperature is a critical factor for both the safety and the LIB’s health. Not only the average temperature, but also the temperature distribution within the cell must be considered. However, common battery management systems mostly rely on monitoring the surface temperature of the cells, while neglecting changes of the internal parameters. This is where the integration of optical glass fiber sensors into battery cells, which allow direct monitoring of internal temperature changes during operation, makes a significant contribution.

In this work, different approaches for the integration of optical glass fiber sensors into battery cells have been evaluated. The focus was set on the complete integration of the glass fiber at specific positions within the LIB, while ensuring that both, the glass fiber, and the battery components remain intact. Furthermore, the influence of the integrated glass fibers on the performance of the LIB was investigated. Finally, their functionality as temperature sensors was evaluated.

In a second step, temperature measurements were performed on LIB during operation, using both internal and external sensors. The results obtained clearly reveal an early detection of temperature changes by internal glass fibers compared to external sensors. This not only confirms the efficiency of the internal sensors, but also leads the path to improved battery safety by early detection of critical temperatures within the cell.
Design of Novel Types of Phosphorus-Containing Flame-Retardant Hybrid Solid Electrolytes with Enhanced Ionic Conductivities
Authors: Zhang Yinghui , Gohy Jean-François
Published: February 2024

Hybrid polymer/inorganic solid electrolytes have been considered one of the promising routes toward improved safety and higher energy density compared to today’s liquid electrolytes. Herein, flame-retardant phosphorus-containing random copolymers, namely poly(oligo(ethylene glycol) methyl ether methacrylate)-co-(dimethyl(methacryloyloxy)methyl phosphonate) (P(xPEGMA-co-yMAPC1)), were synthesized with different ratio of monomer compositions and further used as the polymer matrix. By mixing P(xPEGMA-co-yMAPC1) with lithium perchlorate (LiClO4) and acetonitrile (ACN), the solid polymer electrolytes were obtained after vacuum evaporation of ACN. Among the P(xPEGMA-co-yMAPC1) copolymer electrolytes, the P(9PEGMA-co-1MAPC1) with 10wt% LiClO4 presented an ionic conductivity of 1.0×10-4 S cm-1 at 60℃ and 3.1×10-5 S cm-1 at 30℃ and showed good flame-retardant performance compared to pure PPEGMA. The increase in MAPC1 content upgraded the flame-retardant performances but enhanced the glass transition temperature (Tg) of the copolymers, leading to a decrease in ionic conductivity. To further enhance the ionic conductivity of the copolymer electrolytes, hybrid polymer/inorganic solid electrolytes are synthesized by adding Li1.3Al0.3Ti1.7(PO4)3 (LATP) and SiO2 inorganic fillers, respectively. P(9PEGMA-co-1MAPC1) with 10wt% LATP exhibits a higher ionic conductivity of 1.4×10-4 S cm-1 at 60℃, while P(9PEGMA-co-1MAPC1) with SiO2 fillers show a lower ionic conductivity of 8.5×10-5 S cm-1 at 60. Finally, the cycling performances of hybrid solid electrolytes containing LiFePO4|P(9PEGMA-co-1MAPC1) + LiClO4 + LATP/SiO2|Li batteries were tested. The capacity reaches 164.2 mAh g−1 at 0.05 C, and the capacity retention reaches 90% after 200 cycles at 0.1 C.

Figure 1
Using Artificial Solid-Electrolyte Interphase Coatings for Enhancing Safety of High-Energy Li-Ion Batteries from Material Level
Authors: Wu Nae-Lih (Nick) , Chang Shu Jui , Chen Hsi
Published: February 2024

The development of high-energy-density Li-ion batteries (LIBs) to meet the demand for electric vehicles and sustainable energy storage applications simultaneously brings about more safety issues. On the anode side, graphite has been a major anode material for high-energy LIBs and is anticipated to continuously play an important role even for the high-capacity Si-graphite (Si-Gr) composite anodes in the near future. The low lithiation electrochemical potential of graphite enables a lower anode potential allowing higher energy for a full cell but is vulnerable to the plating of metallic Li dendrite, which could easily arise from either over-lithiation, due to heterogeneity in the negative electrode, or fast charging. Li dendritic deposits could penetrate through the separator to trigger cell short-circuit and eventually thermal runaway. On the cathode side, the high surface reactivity and low oxygen lattice stability of the Ni-rich layered oxide cathodes lower the thermal stability. This study focuses on enhancing the safety of LIB full-cells by modifying the properties and stability of the solid-electrolyte interphases (SEIs) respectively on the anode and cathode electrodes. A polymeric artificial SEI for the anode is developed not only to improve the electrode performance but also effectively suppress SEI and Li dendrite formation. Meanwhile, a composite coating for the cathode is derived to simultaneously enhance the cycle stability and thermal stability, due to the altered thermal decomposition pathway, of an NCM811 cathode. The overall enhanced safety of the full cells is illustrated with the nail penetration test, and the safety-enhancing mechanisms are revealed by conducting post-mortem and synchrotron-based operando studies.
Experimental Analysis of Thermal Runaway Energy Release of an Automotive Li-Ion Battery Cell
Authors: Novotny Frederik , Köhler Jürgen , Golubkov Andrey
Published: February 2024

Thermal runaway (TR) reactions of lithium ion cells pose a particular risk to the safety of battery systems. Beside the energy remaining in the cell body, particles and gases exiting the cell during the venting process cause major thermal load for adjacent cells and further system components [1]. In addition, high energy particles can act as an ignition source in the presence of ignitable venting gases and oxygen [2]. Therefore, measurements minimizing the risk of thermal propagation (TP) caused by venting ejecta material and the ignition of combustible gases are introduced on system level. For the dimensioning of the measures, the energy transported by venting particles and gases is identified as a crucial parameter. Depending on the amount of transported energy, the gas cooling distance as well as the complexity of the particle separation structure differ. Simulation methods are used to evaluate the effectiveness of such system measures. More information is needed regarding energy release to accurately predict the system behavior in simulations and to use them as a tool for design.

Introducing a novel approach for TR tests enables the determination of the energy remaining in the cell body, separated from the energy transported by venting ejecta. The test setup combines a calorimeter combined with a cyclone separator placed inside an autoclave reactor. The TR energy release of 156 Ah prismatic lithium ion cells have been analyzed using the setup. Venting particles and gases transported a main part of the released energy out of the cell during the TR. Using an analytical approach, the energy transferred to the calorimeter is calculated. The obtained data can be used for validating simulation models for predicting the impact of venting reactions on TP.

References

[1] W. Walker, J. Darst, D. Finegan, G. Bayles, K. Johnson, E. Darcy, S. Rickman, J. Power Sources 2019, 415, 207-218

[2] H. Wang, H. Xu, Z. Zhao, Q. Wang, C. Jin, Y. Li, J. Sheng, K. Li, Z. Du, C. Xu, X. Feng, Appl. Therm. Eng. 2022, 211, 118418.
Developing an Apparatus to Analyze Volume Changes in a Pouch Battery Cell
Authors: Kim Dongchan , Choi Sung Hwan , Sim Gyu Jang , You Jehyun , Choi In-Suk
Published: February 2024

Recently, there has been a significant increase in demand for lithium-ion batteries due to the growing demand for eco-friendly mobility. However, to ensure the stability of electric vehicles during operation, research on the structural and material characteristics of batteries is essential. The Battery Management System (BMS), responsible for managing battery degradation and performance, is directly impacted not only by the electrochemical characteristics but also by the structural and material stability of the battery. As the demand for high-density battery modules increases, the volume change of batteries after degradation can generate significant internal stresses, making it crucial to develop the vehicle's BMS in relation to this issue. Therefore, this study aims to measure the characteristics of batteries volume changes during degradation under various pressure conditions from the cell level. Ultimately, we propose a homogenized model that can predict the degradation characteristics of a battery pack subjected to pressure during charging and discharging. An apparatus capable of measuring the volume changes of batteries is developed for the modelling.

Keywords: Battery volume changes, pouch cell, modeling, mechanical properties, compression test, apparatus
Monitoring Lithium Metal Plating in Battery Modules: Insights from NMR and Electrochemical Analysis
Authors: Mohrhardt Marvin , Brunklaus Gunther , Brake Tobias , Ulrich Julian
Published: February 2024

Current interest in and projected demands for large-scale batteries are constantly expanding. In particular, envisioning batteries as power source for electric vehicles, it is important to move scientific research beyond individual cells to much larger units such as battery pack level. Marginal differences inside a battery pack may have strong impact on the achievable battery performance and cycle life. Hence, safer and more efficient management of battery modules and packs is emphasized. This talk highlights aspects of undesirable lithium metal plating in lithium-ion batteries and the importance of detecting such deposits based on electrochemical methods. The study involved cycling of model battery modules comprised of up to four cells and monitoring the evolution of lithium metal deposits by 7Li NMR, where various operational conditions to induce lithium metal plating were applied to individual cells. After deposition, the cells were continuously cycled within a battery pack to evaluate the effects of the lithium metal deposits on the achievable performance. Electrochemical methods, such as impedance measurements, were invoked to detect faulty cells, and corresponding fractions of lithium metal deposits were quantified by NMR and GC-MS measurements. Malfunctioning cells exhibited unfavourable impact on all the surroundings cells, as monitored by electrochemical methods without disassembly of considered modules. The insights of this study are significant for designing strategies for better safety and overall efficiency of large-scale battery packs.
Three-Dimensional Modeling of Dendrite Formation during Automotive Relevant Cycling
Authors: Teel Hunter , Lopata Joseph Steven , Garrick Taylor R. , Shimpalee Sirivatch
Published: February 2024

Dendrites commonly form during rapid charging of lithium-ion batteries when plating is favored over intercalation. If not mitigated, the potential exists for dendrites to growth through the separator and short the anode and cathode. One metric for diagnosing plating conditions in a computational model is the minimum local potential at the anode, where plating is seen to be thermodynamically favorable below 0.0 V with respect to Li metal.1, 2 Three-dimensional (3D) models can offer insight to predict the possibility of local lithium plating and can be used as a tool to detect possible global lithium plating onset, so it follows that 3D microstructure models can be used to predict dendrite formation and propagation as well. The moving boundary technique with mesh motion can be utilized to separate the electrolyte region into a liquid phase and a dendrite phase.3

This strategy is implemented in a 3D microstructure model of a lithium-ion battery to observe the growth of dendrites at the anode during rapid charging. Under onset conditions at the solid/electrolyte interface (SEI), the solid metal phase is deposited at the SEI. Upon growth, the overall electrolyte resistance at the tip of the metal phase is reduced, leading to dendrite growth. The 3D model provides valuable insight into various conditions that may cause plating, if dendrites are formed due to plating, and whether the dendrites formed may proceed to a shorting effect.

References

T. R. Garrick, J. Gao, X. Yang and B. J. Koch, J Electrochem Soc, 168, 010530 (2021).

U. Janakiraman, T. R. Garrick and M. E. Fortier, J Electrochem Soc, 167, 160552 (2020).

T. Jang, L. Mishra, S. A. Roberts, B. Planden, A. Subramaniam, M. Uppaluri, D. Linder, M. P. Gururajan, J.-G. Zhang and V. R. Subramanian, J Electrochem Soc, 169, 080516 (2022).
(Invited) Effect of Oxygen on Activation Annealing of Mg-Doped GaN
Authors: Kumar Ashutosh , Wang Qin , Ramvall Peter
Published: February 2024

The effects of N2 and O2:N2 (1:1) as ambient gases during activation annealing of Mg as p-type doping of GaN grown by MOCVD are investigated. The purpose is to understand the mechanisms involved and especially the impact of O2 on the resulting free hole concentration and hole mobility. The addition of O2 to the ambient gas during annealing is very effective in reducing the H level of the Mg-doped GaN layer, especially at lower activation temperatures, but the maximum achievable hole concentration and mobility, as determined by Hall characterization, is still higher with pure N2.

The difference between activation in pure N2 or O2:N2 (1:1) ambient a is explained by an in-diffusion of O to the GaN layer acting as n-dopant and thus giving rise to a compensation effect. It is found that to a large degree only the Mg-H complexes at substitutional (MgGa), i.e., the electrically active acceptor sites that provide free holes, are activated by annealing with N2 only as ambient gas, while annealing with O2:N2 (1:1) also dissociates electrically inactive Mg-H complexes resulting in much less residual H. Thus, the residual H level in relation to the Mg level after activation annealing with N2 only may provide a representative measure of the resulting free hole concentration of the Mg-doped GaN layer.

An additional factor to be taken into account for in order to maximize the hole concentration is the growth pressure. At the lower growth pressure of 150 mbar compared to higher growth pressure of 300 mbar, an increasing carbon incorporation leads to a compensation effect drastically reducing the free hole concentration while the mobility is unaffected.

Conclusions

Addition of O2 during RTP is very effective in reducing the H level however, the maximum hole concentration and mobility are still higher with pure N2.

Mg-H complexes at substitutional (MgGa) electrically active acceptor are preferentially dissociated by annealing with N2 as ambient gas.

By employing a higher growth pressure, carbon incorporation that leads to a compensation effect drastically reducing the free hole concentration can be minimized.

By activation annealing with N2 the residual H level provides a measure of the free hole concentration.

Figure 1
(Invited) Selective Area Growth, Etching, and Doping of GaN By MOCVD for Power Electronics
Authors: Li Bingjun , Han Jung
Published: February 2024

Gallium Nitride (GaN) possesses a wide band gap and excellent transport properties, making it a highly promising material for high-power and high-frequency applications. Microwave power amplification for commercial and military purposes has already benefited from GaN-based high electron mobility transistors (HEMTs). However, currently available GaN optoelectronic and electronic devices use planar junctions and heterostructures prepared by epitaxy, typically via metalorganic chemical vapor deposition (MOCVD). To enable more sophisticated device configurations, in-plane lateral junctions are necessary. The most effective method for achieving this is through selective area etching (SAE) followed by selective area growth (SAG). In this talk, we will discuss the progress made at Yale in the selective-area etching, growth, and doping of GaN.

Selective-area etching of GaN is the most challenging and critical step in this process. Instead of using conventional ICP etching, we have employed tertiarybutylchloride (TBCl) as an in-situ chemical etchant of GaN in MOCVD to create smooth trenches and remove plasma etching-generated damages on the surface. With electrical and material characterizations, we have confirmed that TBCl etching is a low-damage and clean etching process. We will also describe our recent efforts to bypass the constraint of dielectric masking during in-situ etching and perform maskless selective area etching (SAE) to create low-defect lateral p-n junctions for GaN power electronics. Additionally, we will discuss non-planar selective-area growth and doping, including the principles of growth evolution, non-uniform Mg distribution, and parasitic impurities.

This work is supported by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. DOE, under DE-AR0000871 as part of the PNDIODES program managed by Dr. Isik Kizilyalli.
(Invited) Growth and Characterization of 200 mm SiC Crystals and Substrates
Authors: Carria Egidio , Sörman Erik , Thörnberg Jimmy , Ellison Alexandre , Magnusson Bjorn , Riva Carlo
Published: February 2024

SiC power device technology has over the past years continued to gain massive interest in automotive and industrial applications. The majority of devices is today fabricated on 150 mm diameter substrates while the 200 mm diameter substrates still is at early stage in both development and in terms of mass production. An increase of 50 mm in the wafer diameter corresponds to a 78% larger area and then a corresponding increase of the number of devices per wafer. This change impacts on the productivity of a production line and therefore the cost of the final device can be reduced. Higher production volume and lower cost will lead to a further massive implementation of SiC based power devices in the automotive industry that today is rushing on the path of electrification.

At STMicroelectronics we are an early adopter of 200 mm substrates since the first substrate was demonstrated in 2021. Development of 200 mm device quality substrates have progressed well and defect density are today in same range as for 150 mm substrates. The ramp up of production is now made in the new STMicroelectronics plant in Catania while R&D unit in Norrköping Sweden continue to further push the limits of the technology.

In this paper, we report the latest progress on STMicroelectronics 200 mm diameter crystals and substrates. We will discuss the most suitable characterization routes available and how we can detect device affecting defects at an early stage. In particular we will start by describing the mechanism that is behind the crystal growth process together with the characterization methods that allow to control the quality of the ingot by monitoring the relevant properties (i.e. bulk defectivity, polytype composition, internal stress). We will then describe the main key parameters to be controlled on the substrate to be sure it is suitable for device making (i.e. mechanical behavior, resistivity, surface roughness, effectiveness of the surface preparation). We will also describe the CVD process that is used to grow on top of the substrate an epitaxial layer with proper resistivity and thickness tailored on the device we need to produce for specific applications. In conclusion we will show some data about the correspondence in between device failure and defectivity on both substrate and epitaxial layer. A comparison of the results collected on both 6” and 8” substrates will be reported to show the excellent job performed in our R&D department in Norrköping to increase the wafer size maintaining the same level of quality. On the other side, our production line in Catania is going to be the first of this kind in Europe with a vertical integration that guarantee process control from the SiC powder to the design and characterization of the final power device.
Fabrication of Chiral Plasmonic Photocatalyst By Circularly Polarized Light and Enantioselective Hydrogen Generation Activity
Authors: Kang Haeun , Won Dong Il , Kim Dong Ha
Published: February 2024

Introducing chirality in nanostructures has been explored actively in various field, such as sensing, optoelectronics and catalysts, due to its unique chiroptical properties. Especially in photochemistry, considering the synergistic interaction between chiral plasmonics and polarized light, they can be utilized to improve efficiency and selectivity of catalytic reaction. In this work, we synthesized chiral plasmonic photocatalysts, (R)-,(L)- Au/C3N4, through photoreduction of gold precursor on C3N4 substrate under the irradiation of circularly polarized light (CPL) as a means to induce chirality. Then, we demonstrated that the efficiency of hydrogen generation can be increased by matching the chirality of the CPL with the photocatalyst, which was 2-fold enhanced than chiral mismatching conditions. This can be explained by the asymmetric hot carrier formation of chiral plasmonic structures under CPL excitation. Also, the reactivity of water molecule with photocatalyst surface was confirmed through in-situ FT-IR, showing the enhanced interaction under chiral matching conditions. This study could pave the way for advancing chiral light-matter interactions and explore the application of novel device, particularly toward chiral-induced photocatalytic performance.
Open-Source and Multi-Fluid Numerical Modeling of Proton Exchange Membrane Fuel Cell
Authors: Liu Wei , Olesen Anders Christian , Liso Vincenzo , Berning Torsten
Published: February 2024

Numerical modeling is a powerful tool for the virtual design and optimization of the next-generation proton exchange membrane fuel cells (PEMFC). While almost all of them are not open-source, which causes inconvenience and limits. In this paper, a three-dimensional, multi-component, multi-fluid, open-source model developed in the commercial CFD package (CFX) is used to investigate the species’ transport in a proton exchange membrane fuel cell. The model includes a complete fuel cell with both the seven-layer membrane-electrode-assembly and the gas flow channels and bipolar plates, which account for all major transport phenomena. In the porous medium, liquid water transport is dominant by the capillary pressure gradient; momentum loss describes the Darcy equation; and mass transfer between phases by a nonequilibrium phase change model. Multi-component gas phases are governed by convection and diffusion. Moreover, diffusion is the predominant transport mechanism for dissolved water between the membrane and catalyst layers. Consequently, the code of this model is shared on GitHub to provide a starting point and inspire further development and optimization.
Parameterization and Validation of a 2-Dimensional, Transient, Two-Phase MEA Model Capable of Simulating Electrochemical Impedance Spectra
Authors: Eppler Michael , Hanauer Matthias , Gerling Christophe , Berner Ulrich , Eikerling Michael
Published: February 2024

Proton exchange membrane fuel cells (PEMFC) are promising energy converters, offering both sustainability and efficiency. Achieving optimal performance, however, requires a deep understanding of the underlying cause-effect relationships within the functional layers. One effective approach for validating models that capture the complex physics of PEMFC is through differential cells, which reduce computational effort by allowing along-the-channel-effects to be discarded [1,2].

In this study, we present a 2-dimensional, transient, non-isothermal PEMFC model that enables the disentanglement of loss contributions, facilitating effective material screening. Our model accounts for multiphase transport to provide insights into water management and mass transport. To ensure robust parameterization, we conducted a multitude of both ex-situ and in-situ experiments, reducing our reliance on often-contradictory literature data [3].

We fitted our model to a wide range of polarization curves obtained under operating conditions spanning temperatures of 50-80 °C and relative humidities of 40-100 %. Notably, our model is able to simulate impedance spectra, which enables the disentanglement of processes with different time constants [4]. This approach provides a unique opportunity to study the electrochemical behavior and offers a more profound understanding of PEMFC performance limitations. The thorough parameterization process and validation against a broad range of operating conditions and impedance spectra render our model reliable and effective for industry professionals and researchers. We also highlight shortcomings and physics aspects that require further research to deepen insights and enable faster industrialization cycles.

References

[1] Gerling, C., Hanauer, M., Berner, U., & Friedrich, K. A. (2022). PEM single cells under differential conditions: full factorial parameterization of the ORR and HOR kinetics and loss analysis. Journal of The Electrochemical Society, 169(1), 014503.

[2] Pant, L. M., Stewart, S., Craig, N., & Weber, A. Z. (2021). Critical Parameter Identification of Fuel-Cell Models Using Sensitivity Analysis. Journal of the Electrochemical Society, 168(7), 074501.

[3] Vetter, R., & Schumacher, J. O. (2019). Experimental parameter uncertainty in proton exchange membrane fuel cell modeling. Part I: Scatter in material parameterization. Journal of Power Sources, 438, 227018.

[4] Gerling, C., Hanauer, M., Berner, U., & Friedrich, K. A. (2023). Experimental and Numerical Investigation of the Low-Frequency Inductive Features in Differential PEMFCs: Ionomer Humidification and Platinum Oxide Effects. Journal of The Electrochemical Society.

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Investigating the Applicability of Rotating Disk Electrode Measurements for Determining Catalyst Activity in Fuel Cells
Authors: Müller Marcel , Melke Julia , Kintzel Birgit
Published: February 2024

Currently, the mass production of fuel cells is mainly limited by the availability and the price of platinum, which is typically used as the catalyst for the hydrogen oxidation reaction (HOR) as well as for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). To eliminate or at least reduce this limitation, it is necessary to develop new catalytic systems, which are based on other, cheaper active components or at least require less platinum. For the characterisation of catalysts, many different methods are in use for the physical and the chemical part. For example, the rotating disk electrode (RDE) is a widely used method for characterizing catalysts in electrochemistry. However, RDE measurement does not reflect the same reaction conditions as exist in a fuel cell. Nevertheless, characterisation by RDE tests is often used for pre-selection at an early stage of catalyst development. In later stages of development, catalyst investigations are carried out by full-cell or half-cell tests.

In this work, we will compare the oxygen reduction reaction (ORR) properties of Pt/C catalysts from RDE measurements with those from CCM measurements in half-cell and full-cell configurations to determine what correlations can be made between the different type of investigations.
Neutron Nanomediators for Non-Invasive Temperature Mapping of Fuel Cells
Authors: Ruffo Antonia , Strobl Markus , Kenzelmann Michel , Boillat Pierre
Published: February 2024

Polymer electrolyte fuel cells (PEFCs) have gained significant attention in the past century for their ability to convert hydrogen chemical energy into electrical energy. However, the technology still requires refinement due to losses in polarization, ohmic resistance, and mass transport that result in heat generation, negatively affecting the device water management and durability. To better understand these processes, researchers initiate studies to improve knowledge of the temperature at the cell structure core. However, current methods using micro-thermocouples [1] are highly invasive, impeding cell operation and limiting data accuracy.

The project aims to overcome the latter problem using ferromagnetic nanoparticles for non-invasive temperature mapping on these devices. A key part of this novel method is the application of Neutron Imaging through a polarized beam [2], which allows to detection of the temperature distribution on the surrounding nanosensors. The dispersed ferromagnetic nanomediators, in these conditions, depolarize the incoming neutron beam due to the random magnetic field produced by the nanoparticles themselves. Furthermore, as the temperature rises toward the Curie temperature (Tc), the nanosensors tend to lose their magnetic preferential orientation, influencing the neutron beam polarization gradually less as the ambient temperature increases.

This project includes identifying a suitable material, synthesizing nanoparticles through solution techniques [3], and performing physical and magnetic ex-situ characterizations. By dispersing them in Polytetrafluoroethylene micro-powders, nickel, iron, and Nd2Fe14B alloys were initially studied at different concentrations, grain sizes, and magnetic environments, showing promising signal detection (η) and absolute thermal variation (Δη) results.

References

[1] S.-K. Lee, et al., Electrochemical and Solid-State Letters, 12, B126 (2009).

[2] M. Strobl, et al., Journal of Physics D: Applied Physics, 52, 123001 (2019).

[3] Couto GG, et al. Journal of Colloid and Interface Science. 311 (2007)

Figure 1
Electrospun Fuel Cell Electrodes and Their Behavior Under Hydrogen/Air Start-up/Shut-Down Conditions
Authors: Kallina Valentina , Oezaslan Mehtap , Hasche Frederic
Published: February 2024

Affordable and clean energy is one of the 17 sustainable development goals proposed by the United Nations in 2015. [1] In this context, polymer electrolyte membrane fuel cells (PEMFCs) are a promising renewable and clean energy conversion technology. The large implementation of PEMFCs, however, is hindered by high loading of very costly and scarce platinum group metals (PGM) and insufficient long-term durability. Most of the cathode catalysts are suffering from hydrogen/air start-up/shut-down (SUSD) conditions. [2, 3] Generally, the performance of the PEMFC is controlled by the utilization of the catalytically active sites and the mass transport properties within the porous catalyst layers (CL) in particular operating at high current density. New strategies in the design of functional porous catalyst layers are needed to overcome these challenges. As a very promising strategy, nanometer-sized fibers prepared by electrospinning can be used as a backbone to improve the utilization and accessibility of catalytically active sites by maintaining the PGM loading. [4, 5]

In this work, a nozzle-free electrospinning machine by Elmarco S.R.O. (Liberec, Czech Republic) was employed to design and nano-engineer advanced catalyst layers with improved catalytic as well as mass transport properties. Thereby, several highly homogeneous catalyst layers deposited on gas diffusion layer with controlled platinum loading of up to 0.1 mg/cm2 were prepared and characterized by scanning electron microscope (SEM) and micro X-ray fluorescence spectroscopy (μ-XRF). The structural information such as morphology and chemical distribution was correlated with the electrochemical data obtained from the single cell measurements in a fuel cell test station. Additionally, the durability of the as-prepared nanofiber-based catalyst layers was studied under real hydrogen/air SUSD conditions.

Our results show the impact of different nanostructured catalyst layers prepared by electrospinning process on the long-term performance of the PEMFC. Here, we will present the great advantages of the electrospun catalyst layers over the classical catalyst layers prepared by decal transfer process.

References

[1] https://sdgs.un.org/goals/goal7 (date 26 March 2023).

[2] Mittermeier et al., J. Electrochem. Soc. 2017, 164 (2) F127-F137. DOI: https://doi.org/10.1149/2.1061702jes

[3] Mittermeier et al., J. Electrochem. Soc. 2018, 165 (16) F1349-F1357. DOI: https://doi.org/10.1149/2.0931816jes

[4] M. Brodt et al., J. Electrochem. Soc. 2013, 160 (8), F744-F749. DOI: https://doi.org/10.1149/2.008308jes

[5] W. Zhang et al., ChemSusChem 2011, 4 (12), 1753-1757. DOI: https://doi.org/10.1002/cssc.201100245