Phase Interface Research Articles

Composite catalysts based on the CaO‒Fe2O3 system for the oxidative conversion of methane

The catalysts of the CaO‒Fe2O3 system with Fe2O3 content in the range of 0‒100 wt.% were synthesized by the solid state method at 900 and 1000 °C. The catalysts were characterized by XRD and SEM‒EDX methods, and their activity in the oxidative conversion of methane at 750 °C was studied. The phase composition of the catalysts corresponds to the CaO‒Ca2Fe2O5, Ca2Fe2O5‒CaFe2O4 and CaFe2O4‒a-Fe2O3 regions of the phase diagram. The specific catalytic activity dependence on the Fe2O3 content has an extremum. The CaO‒Ca2Fe2O5 catalysts have the highest reactivity and the active centers in them are localized at the phase interface. The activity of Ca2Fe2O5–CaFe2O4 samples decreases with an increase in the CaFe2O4 content. The CaFe2O4‒a-Fe2O3 catalysts have a core-shell structure and exhibit the least activity, which is determined by the CaFe2O4 shell.

Remediation of seawater polluted by oil spills via integrating porous materials with phase-change materials

The cleanup of viscous oil spills, especially in frigid regions, presents significant challenges due to the low fluidity of the oil. While the integration of absorption materials with photo/electric thermal conversion has shown significant promise, its effectiveness can be greatly influenced by environmental factors. To address these challenges, this study introduces an innovative solution: three-dimensional porous materials (3D-PMs) combined with phase change materials (PCMs). By utilizing energy pre-stored in PCMs through sunlight irradiation or electric heating, heat can be efficiently released when 3D-PMs come into contact with crude oil. A novel superhydrophobic melamine sponge (PPCPP@MS), composed of polypyrrole (PPy) and polyethylene glycol (PEG), has been developed for this purpose. The PPy polymerization layer reliably converts light/electricity into heat, while the PEG‑carbon nanotube (CNT) composite coating layer facilitates heat storage and release. This innovative design significantly enhances safety, energy utilization efficiency, and operational effectiveness. Furthermore, COMSOL simulation was employed to the interfacial heat transfer and phase transformation process of PPCPP@MS during crude oil absorption. Demonstrating stable heat release and oil-adsorbing performance in simulated low-temperature marine environments, PPCPP@MS exhibits great potential for addressing oil spills in extreme climates. The innovative design of PPCPP@MS offers crucial insights for managing viscous oil spills, particularly in frigid regions, providing a promising approach in environmental protection and remediation efforts.

The wetting of H2O by CO2.

Biphasic interfaces are complex but fascinating regimes that display a number of properties distinct from those of the bulk. The CO2-H2O interface, in particular, has been the subject of a number of studies on account of its importance for the carbon life cycle as well as carbon capture and sequestration schemes. Despite this attention, there remain a number of open questions on the nature of the CO2-H2O interface, particularly concerning the interfacial tension and phase behavior of CO2 at the interface. In this paper, we seek to address these ambiguities using abinitio-quality simulations. Harnessing the benefits of machine-learned potentials and enhanced statistical sampling methods, we present an abinitio-level description of the CO2-H2O interface. Interfacial tensions are predicted from 1 to 500 bars and found to be in close agreement with experiment at pressures for which experimental data are available. Structural analyses indicate the buildup of an adsorbed, saturated CO2 film forming at a low pressure (20 bars) with properties similar to those of the bulk liquid, but preferential perpendicular alignment with respect to the interface. The CO2 monolayer buildup coincides with a reduced structuring of water molecules close to the interface. This study highlights the predictive nature of machine-learned potentials for complex macroscopic properties of biphasic interfaces, and the mechanistic insight obtained into carbon dioxide aggregation at the water interface is of high relevance for geoscience, climate research, and materials science.

Research Progress of Pt-Based Catalysts toward Cathodic Oxygen Reduction Reactions for Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) have been considered by many countries and enterprises because of their cleanness and efficiency. However, due to their high cost and low platinum utilization rate, the commercialization process of PEMFC is severely limited. The cathode catalyst layer (CCL) plays an important role in manipulating the performance and lifespan of PEMFCs, which makes them one of the most significant research focuses in this community. In the CCL, the intrinsic activity and stability of the catalysts determine the performance and lifetime of the catalyst layer. In this paper, the composition and working principle of the PEMFC and cathode catalyst layer are briefly introduced, focusing on Pt-based catalysts for oxygen reduction reactions (ORRs). The research progress of Pt-based catalysts in the past five years is particularly reviewed, mainly concentrating on the development status of emerging Pt-based catalysts which are popular in the current research field, including novel concepts like phase regulation (intermetallic alloys and high-entropy alloys), interface engineering (coupled low-Pt/Pt-free catalysts), and single-atom catalysts. Finally, the future research and development directions of Pt-based ORR catalysts are summarized and prospected.

A quantitative theory and atomistic simulation study on the soft-sphere crystal-melt interfacial properties. I. Kinetic coefficients.

By employing non-equilibrium molecular dynamics (NEMD) simulations and time-dependent Ginzburg-Landau (TDGL) theory for solidification kinetics [Cryst. Growth Des. 20, 7862 (2020)], we predict the kinetic coefficients of FCC(100) crystal-melt interface (CMI) of soft-spheres modeled with an inverse-sixth-power repulsive potential. The collective dynamics of the local interfacial liquid phase at the equilibrium FCC(100) CMIs are calculated based on a recently proposed algorithm [J. Chem. Phys. 157, 084 709 (2022)] and are employed as the resulting parameter that eliminates the discrepancy between the predictions of the kinetic coefficient using the NEMD simulations and the TDGL solidification theory. A speedup of the two modes of the interfacial liquid collective dynamics (at wavenumbers equal to the principal and the secondary reciprocal lattice vector of the grown crystal) is observed. With the insights provided by the quantitative predictive theory, the variation of the solidification kinetic coefficient along the crystal-melt coexistence boundary is discussed. The combined methodology (simulation and theory) presented in this study could be further applied to investigate the role of the inter-atomic potential (e.g., softness parameter s = 1/n of the inverse-power repulsive potential) in the kinetic coefficient.

Construction of a durable, halogen-free, and phosphorus-free flame retardant cotton fabric system with hydrophobic properties by phase separation and interface polymerization

Inspired by the synthesis of polyurethane, a multifunctional fabric with hydrophobic and long-lasting flame retardancy was prepared through the phase separation and interfacial reaction process between PEI (polyethyleneimine)/BX (borax) aqueous solution and isocyanate terminated polydimethylsiloxane (PDMS-NCO) in tetrahydrofuran solution. The limit oxygen index of the treated fabric increased from 18.0 % to 33.7 %, and the total heat release decreased by 34.2 %. The enhancement of flame retardant performance and thermal stability is attributed to the enhanced char-forming capacity. After 50 cycles of water washing, the cotton fabric can still pass the vertical flammability test because of the curing effect of PDMS-NCO on functional additives. Furthermore, SEM analysis revealed that the formation of nano-rough structures on the fibers was promoted by phase separation, thus leading an increased water contact angle of sample to 139°. The materials utilized in this modified process do not contain elements such as F, Cl, Br, and P, indicating its potential as an environmentally friendly methodology for fabric functionalization.

A transparent, anti‐blue‐light, and high strength nylon/nickel phosphate oligomer nanocomposite formed via intermolecular hydrogen bond crosslinking

AbstractPolymer/transition metal inorganic salts nanocomposites are promising engineering materials in automotive, electronics, aerospace and smart wearables fields. However, the interfacial incompatibility always causes agglomeration and phase separation, constraining their further application. Inspired by inorganic oligomers' polymerization, nylon/nickel phosphate oligomer (NPO) nanocomposite (ENCC) was prepared via hydrogen bond crosslinking method. Due to the formation of hydrogen bonds between PO43− end groups of NPO with an average diameter of 6.5 ± 1.2 nm and NH groups on the nylon molecular chain, the phase compatibility is greatly improved. Hence, NPO was uniformly nano‐dispersed and had no obvious agglomerate in ENCC, inducing an invisible phase interface at nano‐micro scale. Nylon/nickel phosphate oligomer showed an excellent reinforcing effect on nylon, the tensile strength and elongation of ENCC reached 28 ± 0.8 MPa and 585 ± 26% at a high loading of 20 wt%, increased by 155% and 92%, compared with pure matrix, respectively. Furthermore, ENCC was still optically transparent and had excellent anti‐blue‐light performance (up to 96.6%).Highlights Novel inorganic/nylon composite prepared by hydrogen bond crosslinking method. Phase separation and aggregation problems were solved remarkably. Inorganic metal phosphate dispersed with a diameter of 6.5 ± 1.2 nm. The composite was still transparent at 20 wt% loading of metal phosphate. Tensile strength and elongation increased by 155% and 92%, respectively.

Nano-sulfur decorated graphene oxide to improve the mechanical properties of natural rubber by interfacial participate in the vulcanization reaction

As a new material with excellent comprehensive properties, graphene is an excellent reinforcing agent for natural rubber (NR). However, how to improve the interface performance between graphene and NR, and at the same time be practical, is still a great challenge. In this study, nano-sulfur decorated graphene oxide materials (GO-S) were prepared by in-situ loading nano-sulfur on the surface of graphene oxide (GO). Nano-surface cross-link with NR in the vulcanization process, acts as a bridge to anchor GO and NR molecular chains and improve the interface bonding strength of GO and NR. The AFM results show that the interfacial phase thickness of NR-GO-S composites increased from 135 ± 18 nm to 245 ± 28 nm after in-situ loading modification. The tensile strength and tear property of NR-GO-S composites modified by sulfur loading reach 30.3 MPa and 40.0 kN⋅m−1, respectively, which are 31.1 % and 12.8 % higher than those of NR-GO composite. Nano-sulfur form O–S and C–S covalent bonds with GO, and form more efficient covalent crosslinking networks with NR molecules in the vulcanization process, thus improving the interfacial compatibility between GO and NR and making the load transfer in rubber matrix more effective. This work provides a new idea and method to improve the interface property between rubber and inorganic nanomaterials.

Accelerated hydrolytic degradation of poly(l-lactide) by blending with poly(ether-block-amide)

A continuing challenge in the most common biodegradable polyester of poly(l-lactide) (PLLA) is to improve the degradation rate in the environment, though it has been widely used in packaging and medical applications. In this study, PLLA/poly(ether-block-amide) (PEBA) blends are prepared by melt blending to investigate the effect of PEBA component on the phase morphology, thermal behavior, mechanical properties, and hydrolytic degradation of the blends. The incorporation of PEBA component is beneficial to the improved toughness and increased water absorption of the blends, and accelerated hydrolytic degradation of PLLA. The blend exhibits the optimal mechanical and hydrolytic degradation properties when the blend mass ratio of PLLA/PEBA is 80/20. The toughness of the blend is increased by 390 % compared to that of pure PLLA. After being hydrolyzed at 58 °C for 240 h, the water absorption, the mass loss and the decrease of molecular weight of the blend is increased by 138 %, 160 % and 40 %, respectively, indicating faster hydrolytic degradation rate of the blend than that of pure PLLA. Furthermore, the accelerated hydrolytic degradation mechanism of PLLA in the blend is revealed. The amorphous region of PLLA is hydrolyzed initially at the phase interface of the blend, and subsequently the crystalline structure of PLLA is degraded. The hydrolysis process causes a change in the relative content of crystalline regions in the system, resulting in an increase in crystallinity of PLLA first and then decrease. These findings provide a new strategy for the design of novel degradable PLLA materials for practical applications.

Study on fatigue properties with composite waveform and variable amplitude of TC21 titanium alloy pulsed laser-arc hybrid welded joints

TC21 titanium alloy is widely used in the manufacturing of key components such as aerospace industry, its welded structure in actual service is often subjected to the cyclic loading with composite waveform and variable amplitude and leads to fatigue failure. Therefore, in this work, the composite waveform and variable amplitude fatigue properties of TC21 titanium alloy pulsed laser-arc hybrid welded joints were investigated in this paper, and the micro-deformation mechanism and crack initiation mechanism of welded joints under different initial maximum cyclic stresses were revealed. The results indicated that the micro-deformation mechanism was the competition between twinning and dislocation slip in the α′ phase at low stress. When the initial maximum cyclic stress increased, the generation and slip of dislocation dominated, and the main distribution of dislocations gradually transitioned from the α′ phase to the β phase. This caused the phase transition in the β phase to the α phase, which increased the energy at the α/β phase interface and reduced the resistance of fatigue microcrack initiation accordingly, thus promoting fatigue failure. In addition, pores were the main factor of fatigue failure for welded joints. Therefore, in this work, the influence of defect size, location and shape on the fatigue life of welded joints was considered to develop a fatigue life prediction model based on the control parameter Z-parameter and equivalent stress amplitude. The predicted composite waveform and variable amplitude fatigue life of TC21 titanium alloy welded joints was within the triple error band.

Optimization design and interface characteristics research of high damping NiTi - Nickel-Aluminum Bronze functional gradient composite coating additively manufactured by high-speed laser-directed energy deposition

The near-equatomic NiTi shape memory alloy demonstrates exceptional damping performance due to its distinctive low-temperature self-cooperative martensitic internal friction. This study successfully fabricated NiTi-NAB (Nickel-Aluminium bronze shape memory alloy) functionally graded composite coatings with excellent metallurgical bonding between layers on Q235 steel substrates by designing an appropriate interlayer structure and employing the high-speed laser-directed energy deposition (LDED). Through comprehensive evaluation of the composite coating's performance and the numerical simulations of heat transfer within the molten pool, we elucidated the impact of process parameter levels on the microstructure and phase transformation characteristics of the NiTi alloy coating (NTC). The phase composition and phase interface characteristics of the NTC surface and bonding interface were analyzed using an electron probe microanalyzer and transmission electron microscopy, while dynamic thermomechanical analysis was employed to evaluate the damping performance of the NTC. The results indicate that an optimal parameter combination area still exists within the NTC-LDED process parameter window, even with equal laser energy density. Insufficient parameter levels can lead to an increase of micro-defects within the NTC, consequently causing a deterioration in both the cohesion and deformation resistance of the coating. Excessively high parameter levels can lead to significant element loss and residual stress, which in turn contributes to an increase in microcracks within the coating. A considerable quantity of reaction product mixture phases was formed at the interface between NTC and NAB, tending to align coherently with the NAB phase interface. The NTC, prepared with optimal process parameters, exhibits exceptional damping performance with a damping ratio of 0.498 at internal friction equilibrium, rendering it highly promising for applications in surface erosion protection for fluid machinery.

Droplet-based microfluidics for engineering shape-controlled hydrogels with stiffness gradient

Current biofabrication strategies are limited in their ability to replicate native shape-to-function relationships, that are dependent on adequate biomimicry of shape, size and spatial heterogeneity, within cell-laden hydrogels. In this study, a diffusion-based microfluidics platform is presented that meets these needs in a two-step process. In the first step, a hydrogel-precursor solution is dispersed into a continuous oil phase within the microfluidics tubing. By adjusting the dispersed and oil phase flow rates, the physical architecture of hydrogel-precursor phases can be adjusted to generate spherical and plug-like structures, as well as continuous meter-long hydrogel-precursor phases (up to 1.75 m). The second step involves the controlled introduction a small molecule-containing aqueous phase through a T-shaped tube connector to enable controlled small molecule diffusion across the interface of the aqueous phase and hydrogel-precursor. Application of this system is demonstrated by diffusing co-initiator sodium persulfate (SPS) into hydrogel-precursor solutions, where the controlled SPS diffusion into the hydrogel-precursor and subsequent photo-polymerization allows for the formation of unique radial stiffness patterns across the shape- and size-controlled hydrogels, as well as allowing the formation of hollow hydrogels with controllable internal architectures. Mesenchymal stromal cells are successfully encapsulated within hollow hydrogels and hydrogels containing radial stiffness gradient. The cells are observed to respond to the microscale spatial heterogeneity as evidenced by increased cell elongation in softer core regions of the hydrogel as compared to the peripheral stiffer hydrogel regions, as well as stiffness-dependent nuclear accumulation of the yes-associated protein mechano-regulator. Finally, breast cancer cells are found to phenotypically switch in response to stiffness gradients, causing a shift in their ability to aggregate, which may have implications for metastasis. The diffusion-based microfluidics will mimic native shape-to-function relationship and provides a platform to further study the roles of micro- and macroscale architectural features that exist within native tissues.

Tutorials: Physics-informed machine learning methods of computing 1D phase-field models

Phase-field models are widely used to describe phase transitions and interface evolution in various scientific disciplines. In this Tutorial, we present two neural network methods for solving them. The first method is based on physics-informed neural networks (PINNs), which enforce the governing equations and boundary/initial conditions in the loss function. The second method is based on deep operator neural networks (DeepONets), which treat the neural network as an operator that maps the current state of the field variable to the next state. Both methods are demonstrated with the Allen–Cahn equation in one dimension, and the results are compared with the ground truth. This Tutorial also discusses the advantages and limitations of each method, as well as the potential extensions and improvements.

Thermal and hydraulic characteristics of a single reverse nanofluid jet in a double-wall cooling configuration

AbstractThis work investigates the thermo-hydraulic characteristics of a novel reverse jet impingement cooling 3-D module for high-power systems, entailing a single jet impinging upon a concave hemispherical surface within a double-wall cooling configuration. Water-based nanofluids, with Al2O3 and multi-wall carbon nanotubes (MWCNT), were subject to a comprehensive examination at a range of Reynolds numbers from 10,000 to 40,000. The computational framework utilized the volume of fluid (VOF) model for precise phase interface tracking, along with the $$k-\omega$$ k - ω SST turbulence model. The results demonstrated that nanofluids have remarkable heat transfer enhancement, compared to water. The maximum Nusselt number augmentation reached 61.76% and 77.47% for 2.0% Al2O3 and 0.04% MWCNT nanofluids, respectively. The thermal performance improved when escalating nanoparticle concentration and Reynolds numbers, reaching a cooling module’s thermal resistance of only 0.0266 K W−1. However, mild increments in pressure drop of up to 7.80 and 3.04% were noticed at the lowest Reynolds number for the two nanofluids, respectively. MWCNT nanofluids exhibited superior thermal enhancement over their Al2O3 counterparts despite their lower concentrations. The greatest combined thermo-hydraulic performance was attained with a 0.04% MWCNT nanofluid at a Reynolds number of 20,000, where the energy performance was boosted by 77%, compared to water. The study identified significant conjugate heat transfer effects, demonstrating how temperature gradients within the solid walls directly influenced heat transfer coefficients and thermal resistances within the fluid phase. These findings provide a deeper understanding of thermal management strategies for high-power systems. Graphic abstract

Polymer-modified nanofillers for enhancing CO2 separation performance of MMMs: A comparative study on the role of bridging ligands

Advanced CO2 separation technology is one of the key technologies for reducing carbon emissions and can make significant contributions to reducing the negative impact of the greenhouse effect on human survival. Membrane separation technology is regarded as a new generation of carbon capture technology because of its great potential to reduce carbon capture energy consumption and improve net carbon capture efficiency. Mixed matrix membranes (MMMs) can break through the performance limit of traditional polymer membranes, but the influence of bridging agents for post-modifying nanofillers on membrane structure and properties needs further systematic investigation. In this work, four types of ligands were selected for synthesizing polymer-modified nanofillers and then incorporated into poly (vinylamine) (PVAm) to prepare MMMs. The comparative analysis results indicate that bridging ligands with superior flexibility are conducive to enhancing the gas permeability within the pores by diminishing the compactness of the polymer shell. The constructed phase interface transition area with uniformly enhanced mechanical strength demonstrates the improved interface compatibility between the matrix and nanofillers bridged via the flexible ligand. Techno-economic evaluation verifies the industrial application potential of the optimal MMMs targeting CO2 capture from post-combustion gas.

A unified FFT framework with coupled gradient damage model and phase-field method for the failure analysis of composites

A unified FFT framework coupling the Gradient Damage Model (GDM) and the Variational Phase-Field Model (PFM) for failure analysis of composites is proposed. GDM and PFM are used to simulate the failure of the matrix and the interphase, respectively. Based on the similarity of the damage evolution equations (elliptic partial differential equations) of GDM and PFM, a unified iterative solution and numerical implementation based on fast Fourier transform (FFT) are derived, and simultaneously applied to a computational model. In addition, the high computational efficiency of the FFT method is used to solve the mechanical equilibrium problem. The complete form of the PFM is introduced to avoid erroneous damage diffusion at the different phase interfaces of the composites, and a stress decomposition-based PFM is formulated. 2D and 3D computational examples are established to investigate the mesh insensitivity of the damage models used and the erroneous damage diffusion at interfaces. The applicability of the stress decomposition-based PFM at interphase is discussed in the context of single-edge notched specimens under tension and fiber-reinforced composites with interfacial phases under transverse tension. Finally, the performance of the unified computational framework is evaluated using two simple numerical examples, and the mechanical behavior of unidirectional CF/PEEK composites under transverse tensile loading is simulated based on the unified framework. The results are compared with experiments to evaluate the computational accuracy and practical applicability of the proposed framework.

Synthesis of multicomponent boron nitride/carbon nanotube conjugated hybrid composite nanosol aqueous sizing agent to improve mechanical properties and thermal conductivity of carbon fiber composites

AbstractInterfacial and thermal conductivity issues of carbon fiber composites pose key challenges that restrict their application in the industry. Hence, we prepared an aqueous sizing agent modified with nanosol of boron nitride (BN) and carbon nanotube (CNT) hybrids using sol–gel method to synergistically enhance the interfacial performance and thermal conductivity of carbon fiber (CF) composites. Compared to the unsized CF composites, the interlaminar shear strength (ILSS), interfacial shear strength (IFSS), flexural strength and thermal conductivity of the sized composites were increased by 47.0%, 41.4%, 51.0% and 49.5%, respectively. This was attributed to the fact that the BN/CNT nanoparticles contained in the sizing agent increased the specific surface area of the fibers, enlarged the interfacial phase region for stress transfer, and facilitated the formation of strong chemical/physical interactions among the fibers and resin. Additionally, BN and CNT nanoparticles formed a three‐dimensional thermally conductive network on the fiber surface, which promoted the formation of a good heat transfer path between the fibers and resin. This work presents an effective strategy for fabricating CF composites with exceptional mechanical performance and thermal conductivity.Highlights A BN/CNT nanohybrid sol is prepared by sol–gel method. A sizing agent is fabricated by modifying WEP through BN/CNT nanohybridised sols. Sizing agent promotes a good thermal conductivity path between CF and resin. Sizing agent enhances the mechanical properties of CF composites.

Universal-neural-network-potential molecular dynamics for lithium metal and garnet-type solid electrolyte interface

All-solid-state Li-metal batteries can conceivably improve the safety and extend the driving ranges of electric vehicles. In this regard, the garnet-type solid electrolyte Li7La3Zr2O12 (LLZ) has garnered considerable attention because of its high Li-ion conductivity and nonreactivity towards molten Li metal. Here, we perform molecular dynamics (MD) simulations using a universal neural network potential (UNNP) to analyse the Li-ion exchange at the LLZ/Li interface at the atomic scale. The UNNP-MD calculations show that Li ions traverse the LLZ/Li interface and that excess Li ions relative to the stoichiometric composition accumulate in an approximately 1 nm-thick zone near the LLZ phase interface, signifying the formation of a space-charge layer. Electronic structural analysis of the UNNP-MD-derived configuration, performed using density functional theory calculations, reveals band bending near the LLZ phase interface and the simultaneous suppression of Li metal reduction. These findings can help expedite the development of rationally designed all-solid-state Li-metal batteries.

(Digital Presentation) The Effects of Heat Treatment on Electroreduction of Tungsten (VI) Oxide

According to the classic scheme of the FFC Cambridge process, oxides of refractory metals are reduced in the solid state. Before electrolysis, oxides are shaped into cylindrical preforms and annealed at high-temperatures (~1000 °С). Therefore, the purpose of this study is to establish the effect of heat treatment of the initial sample of tungsten trioxide on its electrochemical reduction on a solid cathode in a CaCl2–NaCl melt.There are two types of tablets (preforms) were used for research: non-sintered (only compressed) WO3 and annealed at a temperature of 1000 °C. The surface of a pelletized tungsten trioxide sample without sintering is characterized by a uniform distribution of particles, shown in the SEM image (Fig. a). The particles agglomeration is characteristic for the sample WO3 after heat treatment (1000 °С) (Fig. b), which leads to a decrease in the area and an increase in the size of the voids. The unsintered sample has a larger surface area between the particles due to their dispersed state, which facilitates the penetration of the melt compared to the annealed sample.Electrochemical reduction of pressed WO3 samples (d=0.8 cm, h=0.15±0.20 cm, m=0.45–0.50 g) was carried out under galvanostatic conditions (800 °С) with using steel as the cathode and graphite as the anode. It was established that preliminary heat treatment of WO3 does not contribute to its electrochemical reduction. After applying 1.20 A·h of electricity, the porous granules of unsintered WO3 were completely transformed into metallic tungsten (W), which is shown in Fig. c, line 1. However, sintered samples after electrolysis (quantity of electricity is 1.42 A·h) reduced only partially: W – 74.1%; CaWO4 – 25.9% (Fig. c, line. 2).The results show that the reduction occurs more intensively in samples with more micropores, through which mass transfer occurs at the phase interface: tungsten compound to be reduced molten electrolyte mixture. That is why in the unsintered WO3 sample, the electrochemical reduction is faster. It can be assumed that the degree of reduction of WO3 on a solid electrode in CaCl2–NaCl also depends on its crystal structure. The annealed sample (tetragonal structure) is less susceptible to electrochemical reduction compared to the unannealed sample of tungsten trioxide (monoclinic structure). This is due to the fact that tetragonal WO3 (above 740 °C) is resistant to chemical attack, a poor conductor of electricity and has a low surface area. Monoclinic WO3 (from 17 to 330 °C) is more reactive, a better conductor of electricity and has a higher surface area. Figure 1

Electro-Chemo-Mechanical Modeling of Composite Cathodes in All-Solid-State Li-Ion Batteries

A model-based understanding can assist and accelerate developing all-solid-state batteries (ASSB). In addition to chemo-mechanical influences within electrode particles (e.g., NMC) [1-2], a solid electrolyte (e.g., argyrodites) introduces additional interfacial interactions between electrode and electrolyte phases [3-5]. The present research derives and implements a coupled multi-physics finite-element model that captures electrochemical, transport, and structural behaviors of composite electrode structures. The models incorporate concentration-dependent and anisotropic material properties that are based on previously published combinations of experiment and density functional theory (DFT). These include stiffness and fracture toughness, porosity and crystallographic orientation, and operating conditions such as charge/discharge rates and external pressure.Figure 1 illustrates predicted stresses developed during electrode manufacturing. The relatively complex cathode microstructure is based on replicating scanning electron microscopy (SEM) images [6]. The composite electrode consists of electrode, electrolyte, and pore phases (Fig. 1a). As illustrated in Fig. 1b, the ASSB synthesis process involves applying and removing high compressive pressure, which causes plastic deformation and introduces residual stresses. Figure 1c shows residual von Mises stresses near electrode-electrolyte interfaces that can be on the order of a gigapascal. The synthesis-generated residual stresses serve as initial conditions for modeling the chemo-mechanics during battery cycling.During cell operation, spatially varying Li concentrations cause material deformation and associated stresses. Figure 1d shows predicted crack nucleation and growth during operation. Depending on the stress levels, crack nucleation and growth leads to cell degradation and capacity fade. The models predict interfacial fracture and phase separations using phase-field fracture theory. In phase-field formulation, the sharp cracks are approximated as diffuse cracks using a process-zone. High values of the phase parameter ξ (Fig. 1d) represent cracked surfaces. The structural disintegration and loss of active surface areas increase the tortuous path for Li/Li-ion transport, which eventually manifests as capacity-fade.The simulations are validated using published experimental work. The modeling approach, which combines phase-field and finite-element algorithms, is implemented using the COMSOL Multiphysics software. The models are expected to inform microstructure/manufacturing design and optimal operating conditions that improve cycling performance and limit/prevent mechanical damage.[1] K. Taghikhani, P.J. Weddle, J.R. Berger, and R.J. Kee. Modeling coupled chemo-mechanical behavior of randomly oriented NMC811 polycrystalline Li-ion battery cathodes. J. Electrochem. Soc., 168(8):080511, 2021.[2] R. Xu, Y. Yang, F. Yin, P. Liu, P. Cloetens, Y. Liu, F. Lin, and K. Zhao, Heterogeneous damage in Li-ion batteries: experimental analysis and theoretical modeling. J. Mech. Phys. Solids, 129, 160, 2019.[3] K. Taghikhani, P.J. Weddle, R.M. Hoffman, J.R. Berger, and R.J. Kee. Electro-chemo-mechanical finite-element model of single-crystal and polycrystalline NMC cathode particles embedded in an argyrodite solid electrolyte. Electrochim. Acta, 460:142585, 2023.[4] A. Bielefeld, D.A. Weber, R. Rueß, V. Glavas, and J. Janek. Influence of lithium ion kinetics, particle morphology and voids on the electrochemical performance of composite cathodes for all-solid-state batteries. J. Electrochem. Soc., 169(2):020539, 2022.[5] P. Minnmann, F. Strauss, A. Bielefeld, R. Ruess, P. Adelhelm, S. Burkhardt, S.L. Dreyer, E. Trevisanello, H. Ehrenberg, T. Brezesinski, F.H. Richter, and J. Janek. Designing cathodes and cathode active materials for solid-state batteries. Adv. Energy Mater., 12(35):2201425, 2022.[6] C. Doerrer, I. Capone, S. Narayanan, J. Liu, C.R.M. Grovenor, M. Pasta, and P.S. Grant. High energy density single-crystal NMC/Li6PS5Cl cathodes for all-solid-state lithium-metal batteries. ACS Appl. Mater. & interfaces, 13(31):37809–37815, 2021. Figure 1