Anode Porosity Research Articles

(Invited) Modeling the Volume and Porosity Change of Lithium-Ion Cells Due to Lithium Intercalation and External Compression

Active materials in lithium-ion batteries experience (de-)intercalation-induced volumetric work during cycling [1]. This volumetric work causes a change in coating thickness, porosity, or both [2]. These changes influence the effective transport pathways of lithium ions in the electrolyte, which in turn impact the electrochemical performance of the battery [3], posing a major challenge developing high-performance and long-lasting batteries.The interplay between volumetric work and external compression depends on the mechanical properties such as Young’s modulus of the anode, the separator, and the cathode. In addition, external compression during battery pack assembly with either free, fixed, or spring-loaded boundary conditions [4] must be considered, as they impact the layer thickness and porosity differently.Here, we present a novel p2D-mechanical modeling approach to predict the electrochemically induced volume change and subsequent local porosity change of lithium-ion cells under various scenarios of external compression. The model combines physics-based electrochemical processes using the Doyle-Fuller-Newman model [5] with poro-elastic mechanical deformation. The model is parametrized and fitted using experimental data obtained from approx. 5 mAh laboratory cells as well as 5 Ah pouch cells and large format 70 Ah prismatic cells. Preliminary results regarding cell voltage as well as stack thickness change are promising and show satisfying overlap with experimental data. The model predicts a reversible change in porosity during cycling of approx. 5%-points in the anode and 1.7%-points in the cathode, due to different stiffnesses and dilation behaviors of the electrodes. The decrease in anode porosity increases polarization and thus impacts the local anode potential, increasing the risk for lithium plating.Overall, the bi-directionally coupled system reveals the underlying electrochemical and mechanical interplay that leads to the volume change, which can help design novel cells structures or operating strategies like fast charge profiles, both including realistic mechanical boundary conditions. Our study demonstrates the potential of the p2D modeling approach in predicting the complex electrochemical-mechanical behavior of lithium-ion cells, which can significantly accelerate the development of high-performance and long-lasting batteries for various applications. Especially with increasing silicon content in Si/C blend anodes, the impact of volume expansion and subsequent porosity change will become ever more important to account for in future.

An anode‐supported tubular proton conductor fuel cell with an inner ceramic ammonia cracking component

AbstractA tubular proton‐conducting fuel cell, anode‐supported, was fabricated using dip‐coating and followed by the co‐sintering of anode and electrolyte at 1500°C. The electrolyte and anode thicknesses are respectively 6 and 500 µm. The outer diameter of the tubular cell is 5.8 mm, featuring an anode porosity of 23%. Ammonia‐fueled single cell with Ru‐catalyzed internal cracking reactor is operated at various temperatures from 400°C to 600°C. Calculation results indicate that double‐ring current collection is an efficient current‐collecting mode. At 600°C, the device exhibited a high open‐circuit voltage of 1.02 V and a peak power density of 216 mW cm−2, with a total active area of 2.28 cm2. Exhaust gas analysis reveals a 99.13% ammonia decomposition rate at 600°C.

Paper‐Like 100 % Si Nanowires Electrodes Integrated with Argyrodite Li6PS5Cl Solid Electrolyte

AbstractSilicon anodes are a promising solution in all‐solid‐state batteries (ASSBs) due to minor lithium dendrite risk, high capacity, and low potential. Research on Si integration in ASSBs is still nascent, requiring a deep understanding of the interplay between electrode composition, structure, and performance. Here, we present the first study on 100 % Si nanowires integrated with Li6PS5Cl solid electrolyte (SE). The anodes are paper‐like networks of aggregated Si nanowires produced by a slurry‐free method without carbon/binders. Despite the lack of any conductor, the Si anodes provide >2.5 Ah/g capacity at a high mass loading of 1.7 mg/cm2(~5 mAh/cm2), demonstrating sufficient electric and ionic conductivities. Electro‐chemo‐mechanical properties of the electrodes over (de)lithiation were probed through electrochemical impedance spectroscopy, ex‐situ microscopy, and in‐operando pressure regulation measurements. The lithiated electrode/SE interface was found to be electrochemically stable. Cross‐sectional microscopy at various states‐of‐charge confirmed the buffering effect of the anode porosity, resulting in the preservation of the electrode's thickness after the first lithiation but a considerable shrinkage during delithiation, producing cracking and formation of the new interface. Capacity remains constant for five cycles, then decreases linearly up to 40 cycles. This is attributed to repeated fracture of the anode/electrolyte interface and the corresponding impedance increase.

Multi-objective optimization of lithium-ion battery designs considering the dilemma between energy density and rate capability

Electrified transportation requires batteries with high energy density and high-rate capability for both charging and discharging. Li-ion batteries (LiBs) face a dilemma: increasing areal capacity and reducing electrode porosity to boost energy density often reduces rate capability due to a longer and more tortuous ion transfer path. Tailoring cell design parameters to balance these metrics is essential but challenging. Here, we present a multi-objective optimization framework targeting energy density, fast charging, high-rate discharging, and lifespan simultaneously. Four cell parameters—cathode areal capacity, N-P ratio, cathode porosity, and anode porosity—along with operating temperature, are selected as design variables. A physics-based pseudo-2D model, validated against experimental data, generates data to train the surrogate model, which is combined with the NSGA-II algorithm for rapid optimization. Three different objective calculation methods are compared to identify the maximum sum of energy densities, lowest polarization, and most balanced performance, respectively. Cell design parameters are optimized at different temperatures using the most balanced optimization method. Results demonstrate that elevating cell operating temperature achieves high-rate capability while maintaining high energy density, mitigating the energy-power trade-off and broadening battery design parameter ranges.

Effect of Mechanical Pressure on Lifetime, Expansion, and Porosity of Silicon-Dominant Anodes in Laboratory Lithium-Ion Cells

The impact of mechanical pressure on electrode stability in full-cells comprising microscale silicon-dominant anodes and NCA cathodes was investigated. We applied different mechanical pressures using spring-compressed T-cells with metallic lithium reference electrodes enabling us to analyze the electrode-specific characteristics. Our investigation covers a wide pressure range from 0.02 MPa (low pressure - LP) to 2.00 MPa (ultra high pressure - UHP) to determine the optimal pressure for cyclic lifetime and energy density. We introduce an experimental methodology considering single-component compression to adjust the cell setup precisely. We characterize the cells using impedance spectroscopy and age them at C/2. In the post-mortem analysis, cross-sections of the aged anodes are measured with scanning electron microscopy. The images are analyzed with regard to electrochemical milling, thickness gain, and porosity decrease by comparing them to the pristine state. The results indicate that cycling at UHP has a detrimental effect on cycle life, being almost two-fold shorter when compared to cycling at normal pressure (NP, 0.20 MPa). Scanning electron microscopy showed a dependency of the thickness and the porosity of the aged silicon anodes on the applied pressure, with coating thickness increasing and porosity decreasing for all pressure settings, and a correlation between thickness and porosity.

A new approach for improving the quality of the carbon anode for aluminum electrolysis – An impregnation-baking process

Prebaked carbon anode is the primary consumable material in the aluminum reduction cell, and its quality directly affects the energy consumption of aluminum production. An impregnation-baking process of the anode was proposed to reduce the anode porosity, improve the quality of the anodes, and reduce additional carbon consumption. The theoretical analysis and industrial testing on the impregnation-baking process were carried out. Firstly, the coal tar pitch was immersed into the anode carbon block through the impregnation process. An anode impregnation model was developed and used for theoretical calculations to analyze the effects of pressure and temperature on the impregnation process. The accuracy of the model was verified experimentally. Secondly, the impregnated anodes were placed in an electromagnetic induction heating furnace for baking to carbonize the immersed pitch. The thermogravimetric and pyrolysis kinetics methods were used to analyze the baking process of the impregnated anodes. Finally, the impregnated-baked anodes were compared with common anodes regarding their impact on the technical and economic indicators of the aluminum electrolysis process in industrial tests. The results showed that the physicochemical properties of the impregnated-baked anodes were significantly improved, with the bulk density increase of 0.1 g/cm3, air permeability reduction of 0.54 nPm, compressive strength enhancement of 9.43 MPa, and electrical resistivity decrease of 10 uΩ·m. The anode service life was increased from 31 to 35 days, the current efficiency was increased by 0.44 %, and the operating voltage was reduced by 17 mV, which improved economic benefit significantly.

Solid Oxide Fuel Cell Anode Porosity and Tortuosity Effect on the Exergy Efficiency

Improving the efficiency of solid oxide fuel cells (SOFCs) is critical for advancing clean energy solutions on a global scale. One major challenge in enhancing SOFC efficiency is reducing anode diffusion polarization, which can significantly hinder performance. This study addresses this issue by investigating the effects of anode tortuosity and porosity on the exergy efficiency of SOFCs. The novelty of this research lies in its comprehensive numerical model, which uniquely incorporates detailed material properties and their impact on SOFC performance—specifically focusing on anode tortuosity and porosity. Using advanced Multiphysics software, we developed a model that solves mass, electron transfer, and energy equations discretized via the finite differences method. The study meticulously examines how variations in these parameters influence SOFC efficiency, providing new insights into optimal anode design. Our methodology involves simulating different anode configurations to pinpoint the key parameters that affect exergy efficiency, thereby minimizing the experimental costs and time associated with traditional approaches. The quantitative results of this study are significant. We found that an anode tortuosity of 5.5 and a porosity range of 0.05–0.1 optimize exergy efficiency, achieving a 15% improvement compared to conventional designs. Additionally, a mean pore radius between 15 and 20 µm was identified as optimal for enhancing cell voltage. These findings elucidate the critical relationship between anode material properties and SOFC performance, offering a practical pathway to improving efficiency. This research provides a novel numerical approach to understanding and optimizing anode characteristics in SOFCs. By highlighting the importance of specific material properties, such as tortuosity and porosity, and demonstrating their impact on exergy efficiency, this study offers valuable guidance for future SOFC design and development.

Effect of Mechanical Pressure on Lifetime, Expansion, and Porosity of Silicon Dominant Anodes in Laboratory Lithium-Ion Cells

Silicon (Si) is a promising next-generation anode material for lithium-ion batteries due to its nearly ten times higher specific capacity of 3579 mAh/gSi 1. The high and economic availability of Si due to existing industrial infrastructure is another non-technical advantage.2 The main drawback of Si is its large volume expansion of nearly 300% during full lithiation causing SEI (re-) formation, electrochemical milling, and electrode instability leading to thickness changes resulting in the disruption of the electronic pathways and decoupling of particles.2 These problems still exist in partially lithiated µm-sized Si particles with lower volume expansion.2 In this work, we study the influence of compressive force on electrode stability in full cells composed of NCA3 cathodes and silicon-dominant anodes based on µm-sized particles.2 The different mechanical pressures were applied using spring-compressed 3.34 mAh Swagelok™ T-cells (A = 0.94 cm²) with metallic lithium reference electrodes. The investigated mechanical pressure ranges from 0.02 MPa as low pressure (LP) to 2.00 MPa, as high high pressure (HHP) to determine the optimal pressure for cyclic lifetime. Firstly, we introduce an experimental methodology to precisely adjust the common three-electrode SwagelokTM cell setup. Therefore, we take the compression from the single components into account, which were measured in a universal testing machine4 for the pressure range mentioned above. The cells were built with different mechanical pressures and cycled with C/2 until a SoH of 80% of the initial capacity was reached which was measured periodically in CheckUp tests. In the post-mortem analysis, Si anodes cycled at different mechanical pressures are prepared for scanning electron microscopy using a focused ion beam cross-section polisher. The images are then analyzed regarding electrochemical milling, thickness increase, and porosity decrease at 80% SoH by comparing them to the pristine state.The HHP cells with 2 MPa show a detrimental effect on lifetime during cell cycling as depicted in Figure 1 and with only 100 cycles nearly a halved lifetime compared to a normal pressure (NP) of 0.20 MPa. Moreover, the specific discharge capacity is significantly reduced for HHP or LP compressed cells compared to NP cells (see Figure 1b). The post-mortem analysis showed a dependency of the porosity and thickness of the aged Si anodes on the applied pressure. On the particle level, no electrochemical milling was observed due to the partial lithiation of the Si anodes. Vein-like microstructures were observed for the lithiated probes which might originate from different lithiation pathways of polycrystalline Si.5 Based on these experimental results, multilayer pouch cells with the same electrode setup and balancing are produced and cycled, and the expansion of the cells is measured operando in a compression test bench. Acknowledgments: S. F. gratefully acknowledges the financial support from the BMBF (Federal Ministry of Education and Research, Germany), under the auspices of the ExZellTUM III project (grant number 03XP0255). The authors want to thank the research battery production team of iwb for the manufacturing of the electrodes

Electrode-Resolved Impedance and Potential Measurements to Investigate the Rate Capability of High Loading Micron-Silicon Anodes in All-Solid-State Batteries

In order to enable the market introduction of all-solid-state batteries (ASSBs), several anode concepts are under investigation to increase the energy density compared to graphite anodes, while maintaining long cycle-life. At the same time, the production costs must be the same or even reduced in comparison with classical lithium-ion batteries. Besides lithium metal as anode material, which still poses significant technical challenges, more and more interest is being directed toward materials that form lithium alloys. One of the most attractive candidates is silicon, which has a low delithiation potential of around 0.45 V vs. Li+/Li and an attractive theoretical gravimetric capacity of 3579 mAh/gSi, which in the fully lithiated state corresponds to a volumetric capacity of ≈2190 mAh/cm3, even higher than the one reachable by lithium metal.Silicon-containing anodes are already being introduced in classical lithium-ion batteries. For that system, the lithium-ion conduction across the anode electrode is mainly provided by the liquid electrolyte that fills the pores of the electrode, while the electrical conduction is enhanced by the addition of graphite and/or conductive carbon additives, because crystalline silicon is only a semiconductor. As is well known, the major issue with silicon anodes is the volume expansion of 300% upon lithiation of silicon, inducing severe cracking of µm-sized silicon particles as well as continuous solid electrolyte interphase (SEI) growth, both of which lead to a fast capacity fading.The intrinsic solid nature of all-solid-state batteries opens the possibility of a new electrode concept that has the potential to mitigate the above-mentioned drawbacks of silicon. Indeed, the silicon particles themselves could be used for the lithium-ion conduction across the electrode, so that anode electrodes can be prepared that are free of electrolyte, thereby largely restricting SEI formation to the anode/separator interface .In this work, anodes with >90% weight of silicon are prepared by coating a water-based slurry that contains microscale silicon particles (ca. 2-4 µm diameter) as active material, the rest being made up of LiPAA and NaCMC as binders as well as C65 carbon as conductive additive. The combination of the water-based process and the microscale dimension of the silicon particles make this electrode concept easily scalable and cost-effective.To reach a competitive areal silicon anode capacity of 3 mAh/cm2, with the full utilization of the silicon, only a thin layer is needed (pristine thickness of 8 µm when the anode porosity is 50%). The thickness variation and the anode morphology are being investigated by examining cross-sectional scanning electron microscopy (SEM) images at different states-of-charge (SOC). After the first complete lithiation, the anode consists of a fully dense and compact Li3.75Si alloy block of 15 µm thickness. Upon its complete delithiation, a peculiar porous columnar morphology is formed that on account of the void space between the columns and within the columns retains a thickness of 11 µm. This peculiar morphology was recently reported in the literature (Tan et al., Science 373 (2021), 1494–1499); and seems to be reversible during subsequent lithiation and delithiation processes. For example, our half-cells utilizing an InLi counter electrode and operating at 70 MPa have more than 80% capacity retention after 350 cycles at a rate of C/5, with an average coulombic efficiency higher than 99.9%. The reason for this promising stability could be attributed to the minimal loss of lithium into the SEI, which is limited to the geometrical contact area between the silicon and the solid electrolyte separator.To better understand the electrochemical and mechanical characteristics of these silicon anodes, they are investigated in full-cells, utilizing an NCM composite cathode, while the anode potential is monitored by using a gold wire micro reference electrode (µ-RE) which was recently developed in our group (Sedlmeier et al., J. Electrochem. Soc. 170 (2023) 030536). This specific µ-RE, which has a defined and stable potential, allows to precisely deconvolute the potential curves of cathode and anode, and also to measure and separate the impedance contributions of the two electrodes. Therefore, the impedance of the silicon anode is measured at different SOC to understand how the contact resistances, the charge-transfer resistance, and the solid-state diffusion affect its overall impedance. In particular, the low impedance at high SOC enables to reach a good fast charging rate capability up to 1C without lithium metal plating and dendrite formation, as reported in Figure 1. However, in order to explore whether the fast charging goal of 4C (80% of the capacity in 15 minutes) can be reached, the influence of the carbon additive, operating temperature and applied pressure are being investigated. Figure 1

Phase field modeling of lithium deposition in porous lithium metal anodes

Fabricating the structured lithium metal anode is an effective method to improve the cycling performance and severe safety problem of the lithium metal anode for commercial application. In this work, we have employed an electrochemical phase field (PF) model to simulate the non-uniform lithium deposition in porous lithium metal anodes. Four factors have been investigated to facilitate homogeneous lithium deposition and increase the capacity for the inside-pore lithium deposition, including 1) the porosity of the lithium metal anode, 2) the diffusion coefficient of lithium ion, 3) the reaction constant for lithium deposition and 4) structured electrode with a gradient of porosity. We have found that the inside-pore lithium deposition can be improved by increasing the diffusion coefficient lithium ion and designing a lithium metal anode with a gradient of reaction constants and a gradient of porosity. These results provide some new thoughts for the development of high-performance lithium metal anodes.

Simulation-guided design of a finger-like nickel-based anode for enhanced performance of direct carbon solid oxide fuel cells

Direct carbon solid oxide fuel cells (DC-SOFCs) can convert solid carbon directly to electricity via electrochemical oxidation and require less investment compared to other liquid or gas-fed fuel cells. Anode characteristic is one of the important factors in achieving efficient and stable operation of DC-SOFCs. In this work, we have successfully designed and developed 2D multi-physics field models for DC-SOFCs with finger-like nickel-based anode (Cell-A) and traditional nickel-based anode (Cell-B), respectively. Simulation results revealed that the cell performance was significantly enhanced with increases in the anode porosity and decreases in the distance of carbon fuel to porous anode. More importantly, the anode featuring a finger-like pore structure assumed a pivotal role in cell performance. Specifically, Cell-A exhibited higher electrochemical performance compared to Cell-B due to the lower resistance for gas transport and more abundant amount of three-phase boundaries for electrochemical reactions. Experimental results verified the simulation findings by making and operating these two DC-SOFCs. The fabricated Cell-A with finger-like anode delivered higher power output of 858 and 371 mW cm−2 at 850 °C when fueled with hydrogen and activated carbon, respectively, relative to Cell-B with traditional anode. The beneficial characteristic of finger-like anode was further demonstrated by the ability of Cell-A to retain stable operation for 14.1 h at 100 mA with the fuel utilization of 15.8% at 850 °C. This study provides important guidance for the design and improvement of DC-SOFCs, and promotes the sustainable utilization of carbon resources.

Optimization of SOFC Anode Microstructure for Performance and Highly Scalable Cells through Graded Porosity

The performance and durability of anode supported solid oxide fuel cells is heavily dependent on the porosity of their anode layer. An optimal amount of porosity is needed to achieve high performance without compromising the flatness, and by extension, the hermetic sealing of the cell. This presents challenges for commercialization, as anode porosity heavily influences the densification of the cells during sintering. In this work, the effect of pore former loading was evaluated on both cell performance and curvature. It was also found that anodes with an intermediate amount of pore former had the best performance but also the most curvature. The mechanism behind this was evaluated with an optical dilatometer. As expected, when cells were sintered with thicker anode support layers, they resulted in significantly flatter cells. Improvements to performance but not flatness were achieved with the use of graded porosity in the anode, with high porosity at the fuel side that decreased closer to the electrolyte. This effect was more pronounced at lower temperatures and fuel ratios, further demonstrating that this is a more efficient microstructure for the anode than a typical anode with uniform porosity. The use of graded porosity was then evaluated as a means of improving the performance of thicker anodes, to take advantage of their greater flatness and mechanical strength. Unfortunately, thicker anodes exhibited a significant drop in performance. It was found that the greater distance for gas diffusion in thicker anodes means that a different microstructure is needed for efficient gas flow and charge transfer. In the case of thicker anodes, it was found that having two anode regions, one thinner region with moderate porosity adjacent to the anode functional layer and one with high porosity making up the bulk of the anode resulted in the best performance. This allows sufficient fuel flow in a thicker anode, without significantly reducing the activity of the anode. In this way, this anode microstructure behaves similarly to an anode functional layer, which is well known to improve fuel cell performance. While graded anode microstructures have been reported before, there have been few, if any, studies that evaluated both their performance and flatness simultaneously. Optimization of anode porosity in anode supported cells is essential to improving both their performance and reliability, which are necessary for widespread adoption of SOFCs.

Scalable Synthesis of Porous Silicon by Acid Etching of Atomized Al-Si Alloy Powder for Lithium-Ion Batteries.

Si anodes have attracted considerable attention for their potential application in next-generation lithium-ion batteries because of their high specific capacity (Li15Si4, 3579 mAh g-1) and elemental abundance. However, Si anodes have not yet been practically applied in lithium-ion batteries because the volume change associated with lithiation and delithiation degrades their capacity during cycling. Instead of considering the active material, we focused on the structural design and developed a scalable process for producing Si anodes with excellent cycle characteristics while precisely controlling the morphology. Al-Si alloy powders were prepared by gas atomization, and porous Si with a skeletal structure was prepared by leaching Al using HCl. Porous Si (p-Si12, p-Si19) prepared from Al88Si12 and Al81Si19 comprised resinous eutectic Si, and porous Si (p-Si25) prepared from Al75Si25 comprised lumpy primary Si and resinous eutectic Si. The porosity of the Si anodes varied from 63% to 76%, depending on the Si composition. The p-Si19 anode displayed the finest pore distribution (20-200 nm), excellent rate characteristics, a reversible discharge capacity of 1607 mAh g-1 after 200 cycles at a rate of 0.1 C with a Coulombic efficiency of over 97%, and high stability. The performances of the p-Si25 and p-Si19 electrodes began to decrease after 250 and 850 cycles, respectively, with a constant-charge capacity of 1000 mAh g-1 and at a rate of 0.2 C. In contrast, the p-Si12 anode maintained its discharge capacity at 1000 mAh g-1 for up to 1000 cycles without degradation. Therefore, the developed manufacturing process is expected to produce porous Si as an active material in lithium-ion batteries for high capacity and long life at an industrial scale.

Understanding the Impact of Sintering Temperature on the Properties of Ni–BCZY Composite Anode for Protonic Ceramic Fuel Cell Application

Understanding the impact of sintering temperature on the physical and chemical properties of Ni-BaCe0.54Zr0.36Y0.1O3-δ (Ni-BCZY) composite anode is worthy of being investigated as this anode is the potential for protonic ceramic fuel cell (PCFC) application. Initially, NiO–BCZY composite powder with 50 wt% of NiO and 50 wt% of BCZY is prepared by the sol–gel method using citric acid as the chelating agent. Thermogravimetric analysis indicates that the optimum calcination temperature of the synthesised powder is 1100 °C. XRD result shows that the calcined powder exists as a single cubic phase without any secondary phase with the lattice parameter (a) of 4.332 Å. FESEM analysis confirms that the powder is homogeneous and uniform, with an average particle size of 51 ± 16 nm. The specific surface area of the calcined powder measured by the Brunauer–Emmett–Teller (BET) technique is 6.25 m2/g. The thickness, porosity, electrical conductivity and electrochemical performance of the screen-printed anode are measured as a function of sintering temperature (1200–1400 °C). The thickness of the sintered anodes after the reduction process decreases from 28.95 μm to 26.18 μm and their porosity also decreases from 33.98% to 26.93% when the sintering temperature increases from 1200 °C to 1400 °C. The electrical conductivities of the anodes sintered at 1200 °C, 1300 °C and 1400 °C are 443 S/cm, 633 S/cm and 1124 S/cm at 800 °C, respectively. Electrochemical studies showed that the anode sintered at 1400 °C shows the lowest area specific resistance (ASR) of 1.165 Ω cm2 under a humidified (3% H2O) gas mixture of H2 (10%) and N2 (90%) at 800 °C. Further improvement of the anode’s performance can be achieved by considering the properties of the screen-printing ink used for its preparation.

Model-based quantitative characterization of anode microstructure and its effect on the performance of molten carbonate fuel cell

This paper presents research on the impact of the material microstructure on the performance of Molten Carbonate Fuel Cells (MCFC). The study is motivated by the need to increase the operation time of MCFC stacks. As the MCFC stacks are mainly composed of porous materials, the paper shows the impact of the porosity on both fuel cell performance and degradation rate. The study is based on the mathematical model, validated through experiments with varying microstructure parameters, achieving an overall relative error of 8%. The study evaluated the performance of MCFC using anodes with different porosity and found that increasing anode porosity from 40% to 70% led to a nearly two-fold increase in maximum power density. However, from both the degradation test and polarization curves, the optimal level of porosity for the anode is around 55%. The porosity level at 55% ensures the highest catalytic surface of the electrodes and is a compromise between the mechanical properties of the electrode and its electrochemical properties.

Mathematical modeling of fuel cells fed with an electrically rechargeable liquid fuel

Lately, utilizing a novel electrically rechargeable liquid fuel (e-fuel), a fuel cell has been designed and fabricated, which is demonstrated to achieve a much better performance than alcoholic liquid fuel cells do. However, its current performance, which thus hampers its wide application, demands further improvement to meet up with industrial requirement. Therefore, to attain a better performance for this system, an in-depth understanding of the complex physical and chemical processes within this fuel cell is essential. To this end, in this work, a two-dimensional transient model has been developed to gain an extensive knowledge of a passive e-fuel cell and analyze the major factors limiting its performance. The effects of various structural parameters and operating conditions are studied to identify the underlying performance-limiting factors, where deficient mass transport is found to be one of the major causes. The increment of anode porosity and thickness are found to be effective methods of improving the cell performance. This study therefore provides insights on achieving further performance advancement of the fuel cell in the future.

Operando swelling measurement of silicon carbon composite based anode in pouch cell: Effect of external pressure, balancing and anode initial porosity

Silicon lithiation induces a high material expansion, leading to significant swelling and mechanical pressure at the anode and cell levels. In this study, the swelling behaviour of a bilayer pouch cell with high-performance silicon carbon graphite (Si-C/G) anode material was measured, considering the effect of external pressure on the pouch and the cell design parameters such as the balancing and the anode initial porosity. Operando swelling was measured by using an in-house high precision (< 0.1 μm) compression set-up involving simultaneous pressure and thickness recording as well as dynamic pressure regulation system. Results show that a minimum level of pressure is mandatory to obtain a reversible swelling, and that the anode porosity is directly linked to the pressure applied on the cell after particles dynamic rearrangement. The impact on capacity retention is also discussed.

Insights on the degradation mechanism for large format prismatic graphite/LiFePO4 battery cycled under elevated temperature

Increasingly, batteries are being exposed to elevated temperatures to promote charging capability and satisfy various requirements. A comprehension of the degradation mechanism under elevated temperature is essential for advanced battery management. Here, commercial 100 Ah prismatic graphite/LiFePO4 batteries cycled under 45 °C are investigated. Less than 500 cycles are reached when capacity fades to 90 % of the nominal value, while more than 1300 cycles are reached under room temperature. Comprehensive post-mortem analysis is conducted to explore the mechanism of accelerated aging for 45 °C cycled batteries. The concentration of electrolyte salt dropping from 13.19 wt% to 12.98 wt% indicates the decomposition of electrolyte which brings about the gas release and battery volume expansion. Loss of electrolyte associated with enhanced evolution of solid electrolyte interface (SEI) film also leads to loss of lithium inventory. Larger LiFePO4 particles tend to fracture and Fe dissolves from them. It is proposed that Fe deposition accelerates the SEI film generation and the deposition blocks the graphite layers and limits lithium intercalation. From time-of-flight secondary ion mass spectroscopy depth profiling results, it is found that cathode electrolyte interphase film thickens moderately while SEI film thickens sharply, causing anode porosity to drop from 46.22 % to 40.11 %.

Reversible lithium plating in the pores of a graphite electrode delivers additional capacity for existing lithium-ion batteries enabled by a compatible electrolyte

It has always been our unrelenting effort to continuously enhance the energy density of lithium-ion batteries (LIBs). Energy density of LIBs is generally improved by optimizing the electrode materials and battery architecture. Increasing the energy density based on existing facilities and technologies is still considerably challenging. Herein, we propose a compatible electrolyte to purposely plate metallic lithium on graphite anode and widen the charging window to 4.6 V. It realizes highly reversible lithium plating/stripping behavior in the graphite anode pores. The graphite anode is transformed into a graphite/lithium hybrid anode, providing a significantly higher capacity than its nominal value. The optimized electrolyte enables conventional graphite||high-nickel layered cathode pouch cells to deliver 18 % increased energy density. It exhibits excellent compatibility with graphite and lithium, quick wettability and the ability to build a stable interface, all of which are essential for realizing high-energy–density hybrid anodes. Additional capacity can be further increased by reasonably tuning the porosity of the graphite anode. The improvement is easy to implement and works seamlessly with state-of-the-art manufacturing processes. This work demonstrates a cost-effective and facile approach to increasing the energy density of existing batteries.

Model-Informed Si Electrode Design Considering Dynamic Pore-Closure and Stack Pressure Effects

Silicon is novel Li-ion battery anode chemistry with exceptional theoretical energy densities. However, this alloying material has significant challenges with non-passivating solid-electrolyte interface (SEI) formation and significant chemo-mechanics issues. These issues have been studied extensively at the particle-level. However, extensive SEI formation and dynamic particle chemo-mechanics need to be accounted for when designing the overall electrode microstructure. For example, Si particle expansion can result in electrolyte pore-closure. During charging (Si lithiation), Si particles near the separator lithiate faster than Si near the current-collector. Thus, Si particles near the separator begin to expand faster and close-off electrolyte access to particles near the current collector. This heterogeneous through-plane lithiation then results in low overall electrode utilization, especially at high rates (i.e.,>1 C). The “choking off” effect is a result of a strong feedback between heterogeneous lithiation, Si expansion, and electrolyte pore closure.To aid in Si electrode design and account for dynamic particle expansion/contraction, the standard pseudo-2D battery model is reformulated to account for finite-strain chemo-mechanics. This model explores the trade-offs between initial electrode porosity, electrode thickness, rate-capability, and external pressure. Additionally, the model implements simplified SEI growth dynamics to explore how SEI growth effects should be accounted for in electrode design.The Figure illustrates polarization responses for a 1C charge for a Si/NMC532 cell. The different colors indicate different initial anode porosities. As shown in Figure a, the low initial porosity cases results in significant polarization, but additional gains after 50% initial porosity are significantly diminished. These results are shown for an external pressure of 15 psi. Figure b illustrates the cell thickness as a function of time. As illustrated, the lower porosity case starts at a shorter initial thickness. For all cases, the cell thickness increases as Si lithiates/expands. Figure c illustrates the anode porosity at the cut-off voltage as a function of anode thickness. As shown, the lower initial porosity case has significant pore-closure on the right-side at the separator interface. The higher initial porosity cases have increased anode lengths because the Si utilization is improved due to the reduced pore-closer effects. The graphic illustrates the main features of the reformulated pseudo-2D battery model. Figure 1