Chemomechanical Behaviors Research Articles

Model-free chemomechanical interfaces: History-dependent damage under transient mass diffusion

This paper presents a data-driven framework based on distance functional for chemo-mechanical cohesive interfaces to capture transient diffusion and resulting interfacial damage evolution. The framework eliminates reliance on complex constitutive models and phenomenological assumptions, especially avoiding the coupling tangent terms with a given material database. The interfacial chemical potential and its jumps are used to expand the phase space for describing the chemical states of interfaces. Subsequently, a novel chemo-mechanical distance norm, including traction-separation pair, interfacial chemical potential-concentration pair and corresponding chemical potential jump-flux pair, is presented. Momentum conservation law for interfacial tractions and mass conservation law for interfacial concentration are enforced via Lagrange multipliers. For tracking the history-dependent state of the interface damage, an internal variable, termed interface integrity, is introduced to condition the interfacial database and manage the subsets mapping strategies, following physically motivated evolution constraints. Numerical examples are conducted to investigate the efficiency and capability of the present framework. A monotonic loading test validates a good numerical convergence relative to the number of data points. Subsequent cyclic loading simulations, compared with the reference solutions, show that the algorithm is well suitable to predict the history-dependent interface damage evolution under complex loading paths. Finally, the chemo-mechanically coupled examples capture phenomena such as interfacial swelling and interface degradation induced by transient diffusion and stress-driven diffusion. The current work provides a promising tool for understanding chemo-mechanical behaviors of interfaces within heterogeneous composites.

Coupled modeling of thermal-fluid-solid and chemo-mechanical behaviors in thermal barrier coatings under flowing gas environment

This study proposes a modeling approach to simulate the thermo-chemo-mechanical responses of thermal barrier coatings (TBCs) exposed to flowing high-temperature gas. A thermal-fluid-solid analysis was performed to simulate temperature fields of the coatings under flowing gas environment, while finite element analysis was carried out to study the oxidation and stress evolutions of the coatings using a developed chemo-mechanical constitutive model. Thermal loads from thermal-fluid-solid analysis were imposed on the finite element model, by which the factors associated with flowing gas were incorporated into the thermo-chemo-mechanical modeling. The study systematically investigated the effects of flowing gas and coolant on the chemo-mechanical responses of the coatings. The results revealed that the enhanced gas factors (temperature, velocity, angle of attack, and pressure) and coolant temperatures accelerate oxidation and induce higher residual stresses, while higher coolant velocity mitigates both oxidation and stresses. The volume fraction of oxygen in the gas was found to have a negligible influence. Dimensional analysis and multiple regression were performed to derive mathematical expressions for assessing out-of-plane stress and oxidation dynamics. Design maps were proposed to guide the durable design of the coatings.

In situ enzymatic control of colloidal phoresis and catalysis through hydrolysis of ATP.

The ability to sense chemical gradients and respond with directional motility and chemical activity is a defining feature of complex living systems. There is a strong interest among scientists to design synthetic systems that emulate these properties. Here, we realize and control such behaviors in a synthetic system by tailoring multivalent interactions of adenosine nucleotides with catalytic microbeads. We first show that multivalent interactions of the bead with gradients of adenosine mono-, di- and trinucleotides (AM/D/TP) control both the phoretic motion and a proton-transfer catalytic reaction, and find that both effects are diminished greatly with increasing valence of phosphates. We exploit this behavior by using enzymatic hydrolysis of ATP to AMP, which downregulates multivalent interactivity in situ. This produces a sudden increase in transport of the catalytic microbeads (a phoretic jump), which is accompanied by increased catalytic activity. Finally, we show how this enzymatic activity can be systematically tuned, leading to simultaneous in situ spatial and temporal control of the location of the microbeads, as well as the products of the reaction that they catalyze. These findings open up new avenues for utilizing multivalent interaction-mediated programming of complex chemo-mechanical behaviors into active systems.

Homogenization-based chemomechanical properties of dissipative heterogeneous composites under transient mass diffusion

The chemomechanical properties of heterogeneous composites under mass diffusion are of significance in modern advanced technology and engineering applications. A homogenization-based two-scale chemomechanical model is developed for heterogeneous composites undergoing chemical mass diffusion. A two-scale incremental variational formulation is established for heterogeneous composites consisting of multiconstituents featuring local dissimilar diffusion-deformation properties. The minimization problems for coupled chemomechanical behaviors are solved for both macrostructure and microstructure contexts, where the macroscopic material properties are extracted from the results of local boundary value problem on the nested representative volume elements (RVEs). Through a staggered finite element method (FEM) implementation procedure, the proposed homogenization-based two-scale solution algorithm is implemented in the FEM package ABAQUS (V6.14). The developed variational model and tangential algorithm is checked by solving chemomechanical properties of particles enforced composite, where several numerical examples are conducted applying two-scale solution algorithm and validated by full-scale simulations. Parametric studies are carried out on the size effects of RVEs, with respect to the ‘inertia effect’ associated with ‘moment of mass concentration’, and the coupling mechanisms are discussed for mechanical and chemical solutions. To the end, the inelastic dissipations are solved on subscale BVPs and their effects on the mechanical deformation and chemical mass diffusion are checked. The contributions of this work are mainly two-folds. One is the theoretical advance for self-consistent homogenization modeling of the coupled multi-physics of heterogeneous composites, and a rigorous FE2 solution procedure. The other is providing numerical reference for evaluation of approximation algorithm as well as advanced data-driven method, which is needed for high-efficient material design.

High-Spatial-Resolution Quantitative Chemomechanical Mapping of Organic Composite Cathodes for Sulfide-Based Solid-State Batteries

Understanding the chemomechanical behaviors of electrodes, particularly at electrode/electrolyte interfaces, is critical for improving the performance of all-solid-state batteries. However, due to the instability of electrolyte materials under ambient conditions, such characterizations are challenging, particularly for sulfide-based all-solid-state batteries. Herein, by combining time-of-flight secondary-ion mass spectroscopy (ToF-SIMS) and in-SEM nanoindentation measurements, a systematic quantitative investigation of the chemomechanical behaviors of pyrene-4,5,9,10-tetraone (PTO)/Li6PS5Cl composite cathodes is carried out. Chemical and quantitative mechanical information on the composite cathode was collected with high spatial resolution after developing and implementing an air-free characterization protocol. By directly connecting the Young’s modulus and hardness with the Li distribution in the composite cathode, a comprehensive chemomechanical mapping of the PTO/Li6PS5Cl composite cathode has been established. This work improves our knowledge of the critical chemomechanical phenomena that occur at the cathode/electrolyte interfaces in all-solid-state batteries.

Probing intraparticle heterogeneity in Ni-rich layered cathodes with different carbon black contents using scanning probe microscopy

Much effort has been made to improve the electrochemical performance of Ni-rich layered cathodes toward high-energy density of Li-ion batteries. Nonetheless, capacity fading and chemo-mechanical behaviors during charge/discharge processes have not been fully understood yet. Herein, we report microstructural changes and capacity degradation of a polycrystalline LiNi0.88Co0.09Al0.03O2 (NCA) cathode during repeated cycles using electron microscopy and scanning probe microscopy. By varying the content of carbon black (CB; 1–4 wt%) in the NCA cathode, we evaluated cycle performance, capacity-fading, and structural degradation by scanning electron microscopy, scanning spreading resistance microscopy, and Kelvin probe force microscopy based on atomic force microscopy. CB content at 1 wt% in the NCA cathode resulted in a significant increase of electrode resistance and hence a severe capacity decay of full cells. Microscopic analyses for cycled cathode particles surrounded by different CB contents confirmed that the lack of CB around particles developed secondary particle microcracking, local heterogeneity of capacity fading, and formation of NiO-like phase, which could be responsible for degradation of the cathode during repeated cycles. Our results offer a new way to diagnose chemo-mechanical changes of Ni-rich cathodes with different electrochemical properties and highlight the significance of electrode engineering for ensuring effective charge-transport pathways.

Chemomechanical behaviors of particle enforced heterogeneous composites with chemical interfacial jumps

Deep understanding of mass diffusion controlled chemomechanical behaviors of composites with local mass flux discontinuities between inclusions and matrixes are of great significance in modern advanced technology and engineering applications. This work develops a finite-deformation chemomechanical model for particle-enforced composites when under mass diffusion. A general chemomechanical cohesive model is developed for chemo-mechanically imperfect interfaces between the inclusions and matrixes. In the developed cohesive model, both of the displacement jump, the chemical potential jump as well as the mass flux jump are considered. A interfacial potential is developed upon the consideration that the diffusant permeation deteriorate interfacial fracture and degrade the interface strength. Applying standard variations procedure on total energy of the coupled chemomechanical system, the associated weak formulations are developed, and then implemented in finite element method software ABAQUS through subroutine UELs. To validate the proposed cohesive model, the mass-diffusion-driven crack propagation is simulated and compared with the published works. A series of numerical examples are conducted to elucidate the key features of chemo-mechanically imperfect interface model. The results show that the jump of mass flux across interface results in a normal swelling of interface even no mechanical load is applied. An increase of interface diffusion coefficient causes a lower chemical potential jump. Parametric analysis show that the interface properties, such as the cohesive strength, fracture energy and degradation parameter, affect the diffusion rate through controlling the mechanical performance of interface. A strong interface can restrict effectively the mass spread across the interface. This research provides a theoretical reference for a wide applications of particle-reinforced composites in chemical environment.

Heterogeneous Effects on Chemo-Mechanical Coupling Behaviors at the Single-Particle Level

Understanding and alleviating the chemo-mechanical degradation of silicon anodes is a formidable challenge due to the large volume change during operations. Here, for a comprehensive understanding of heterogeneous effects on chemo-mechanical behaviors at the single-particle level, in situ observation of single-crystalline silicon micropillar electrodes under the inhomogeneous extrinsic conditions, taken as an example, was made. The observation shows that the anisotropic deformation patterns and fracture starting sites are reshaped with the combination of the inhomogeneous electrochemical driving force for charge transfer at the interface between the silicon micropillar and the electrolyte, and crystal orientation-dependent lithiation dynamics. Also, the numerical simulation unravels the underlying mechanisms of deformation and fracture behaviors, and well predicts the relative depth of lithiation at the time of crack initiation under heterogeneous conditions. The results show that heterogeneities arising from extrinsic conditions may induce inhomogeneous mechanical damage and tailor lithiation degree at an active particle level, offering insights into designing large-volume-change battery particles with good mechanical integrity and electrochemical performance under heterogeneous impacts.

Multiphase, Multiscale Chemomechanics at Extreme Low Temperatures: Battery Electrodes for Operation in a Wide Temperature Range (Adv. Energy Mater. 37/2021)

Lithium-Ion Batteries In article number 2102122, Peter Cloetens, Kejie Zhao, Feng Lin, Yijin Liu and co-workers systematically elucidate multiphase, multiscale chemomechanical behaviors of composite lithium-ion battery cathodes under low-temperature conditions. Their results suggest that, in order to design batteries for use in a wide temperature range, it is critical to develop electrode components that are structurally and morphologically robust when the temperature is switched.

Multiphase, Multiscale Chemomechanics at Extreme Low Temperatures: Battery Electrodes for Operation in a Wide Temperature Range

AbstractUnderstanding the behavior of lithium‐ion batteries (LIBs) under extreme conditions, for example, low temperature, is key to broad adoption of LIBs in various application scenarios. LIBs, poor performance at low temperatures is often attributed to the inferior lithium‐ion transport in the electrolyte, which has motivated new electrolyte development as well as the battery preheating approach that is popular in electric vehicles. A significant irrevocable capacity loss, however, is not resolved by these measures nor well understood. Herein, multiphase, multiscale chemomechanical behaviors in composite LiNixMnyCozO2 (NMC, x + y + z = 1) cathodes at extremely low temperatures are systematically elucidated. The low‐temperature storage of LIBs can result in irreversible structural damage in active electrodes, which can negatively impact the subsequent battery cycling performance at ambient temperature. Beside developing electrolytes that have stable performance, designing batteries for use in a wide temperature range also calls for the development of electrode components that are structurally and morphologically robust when the cell is switched between different temperatures.

Modeling Electro-Chemo-Mechanical Behaviors within the Dense BaZr0.8Y0.2O3-δ Protonic-Ceramic Membrane in a Long Tubular Electrochemical Cell.

This paper reports an extended Nernst–Planck computational model that couples charged-defect transport and stress in tubular electrochemical cell with a ceramic proton-conducting membrane. The model is particularly concerned with coupled chemo-mechanical behaviors, including how electrochemical phenomena affect internal stresses and vice versa. The computational model predicts transient and steady-state defect concentrations, fluxes, stresses within a thin (BZY20) membrane. Depending on the polarization (i.e., imposed current density), the model predicts performance as a fuel cell or an electrolyzer. A sensitivity analysis reveals the importance of thermodynamic and transport properties, which are often not readily available.

Li-ion distribution and diffusion-induced stress calculations of particles using an image-based finite element method

The realistic particles in lithium batteries have unique microstructures, which should be determined in the analysis of chemo-mechanical behaviors during charge/discharge cycles. In this paper, an image-based finite element method (IBFEM) is developed to investigate the volume expansion, Li-ion distribution, and diffusion-induced stress (DIS) of a realistic particle. A threshold-based segmentation method is proposed to improve the segmentation accuracy based on the improved threshold of each phase. Based on the IBFEM, the active material phase, conductive additive and binder phase, and pore space are segmented and reconstructed using microstructural images. The volume expansion, Li-ion distribution, and DIS of an image-based SnO2 nanoparticle are simulated under galvanostatic/potentiostatic charging process. The predicted lithiation that induced the volume expansion of the SnO2 nanoparticle is approximately coincided with the experiment result observed by TEM. The realistic particle shape and size have a significant impact on the Li-ion distribution and DIS. The concentration profile is analogous to the boundary of the realistic particle at the early stage of lithiation and gradually disappears with further lithiation. The von Mises stress near a concave region is higher than that near a convex region. The maximum von Mises stress in the realistic particle with a larger equivalent radius is higher than that in the smaller particle with the same state of charge. By considering the comprehensive effect of particle shape and size, the size can be increased appropriately while guaranteeing the particle mechanical integrity. These results will contribute to understanding DIS evolution in a realistic particle and can be used to guide the selection of active particles for electrode preparation.

Quantifying the equilibrium swelling responses and swelling-induced snap-through of heterogeneous spherical hydrogels

We employ the finite deformation theory to analyze the inhomogeneous large deformation of a heterogeneous spherical hydrogel subjected to chemo-mechanical loadings. The heterogeneous spherical hydrogel is composed of two concentric spherical hydrogel layers with different material properties. The Gent model is employed for the free energy function of the polymer stretching part in order to tackle the effect of the limiting chain extensibility. The heterogeneous spherical hydrogel is assumed to be perfectly bonded at the interface and is traction free at the external surface. At the internal surface, two boundary conditions are considered: one is internally fixed and the other is internally pressurized. Numerical examples are performed to describe the nonlinear behaviors of a heterogeneous spherical hydrogel when subjected to the swelling and mechanical loadings. For internally fixed case, numerical results show that the limiting chain extensibility and the initial swelling ratio have significant effect on the actuation deformation of a heterogeneous spherical hydrogel. For internally pressurized case, we find that the swelling-induced snap-through instability can be triggered under specified conditions. It is shown that the chemo-mechanical behaviors of the heterogeneous spherical hydrogels can be adjusted by tuning the material properties and the initial swelling ratios.

Operando Electrochemical Pressiometry Using Three-Electrode Cells Probing (Electro)Chemo-Mechanics for All-Solid-State Lithium-Ion Batteries

Due to the nonflammability of inorganic solid electrolytes (SEs) and the wide operation temperature ranges, bulk-type all-solid-state lithium or lithium-ion batteries (ASLBs) have been emerged as a promising power source. In particular ASLBs using sulfide SEs, such as Li10GeP2S12 (LGPS, 1.2 × 10-2 S cm-1) and Li3P7S11 (1.7 × 10-2 S cm-1), are attractive because of the extremely high ionic conductivities of sulfide SE materials, which are comparable to those of conventional organic liquid electrolytes used for lithium-ion batteries.For the success of practical ASLBs, however, a current level of understanding and development on the electrode microstructure and interfacial (electro)chemistry is insufficient. While ASLBs consist of all the solid-state components (i.e., electrode active materials, SEs, conducting additives such as carbon, binders), volumetric strains of electrode active materials upon repeated charge-discharge cycles cause a serious deterioration of the performances. Thus, (electro)chemo-mechanics have been emerging as the critical issue. However, the relevant reports are scarce to date. Moreover, complex interfacial evolutions which could also contribute to the (electro)chemo-mechanical behaviors have been overlooked.In this work, we first report an operando pressiometry using three-electrode cells to enable deconvolution of voltages and volumetric strains of positive and negative electrodes in-situ. Figure 1 shows the result of Li[Ni,Co,Mn]O2/Li6PS5Cl/graphite all-solid-state full cells cycled at 30 °C. The pressiometry profiles reveal signatures of phase transitions of electrode active materials, providing valuable information in terms of the assessment of the electrochemical performances and/or the management of battery system. More details will be discussed in the presentation. Figure 1

Superstrong Noncovalent Interface between Melamine and Graphene Oxide.

There have been growing academic interests in the study of strong organic molecule-graphene [or graphene oxide (GO)] systems, owing to their essential noncovalent nature and the consequent chemomechanical behavior within the interface. A more recent experimental measurement [ Chem 2018, 4, 896-910] reported that the melamine-GO interface exhibits a remarkable noncovalent binding strength up to ∼1 nN, even comparable with typical covalent bonds. But the poor understanding on the complex noncovalent nature in particular makes it challenging to unveil the mystery of this high-performance interface. Herein, we carry out first-principles calculations to investigate the atomistic origin of ultrastrong noncovalent interaction between the melamine molecule and the GO sheet, as well as the chemomechanical synergy in interfacial behavior. The anomalous O-H···N hydrogen bonding, formed between the triazine moiety of melamine and the -OH in GO, is found cooperatively enhanced by the pin-like NH2-π interaction, which is responsible for the strong interface. Following static pulling simulations validates the 1 nN level rupture strength and the contribution of each noncovalent interaction within the interface. Moreover, our results show that the -OH hydrogen bonding will mainly augment the interfacial adhesion strength, whereas the -NH2 group cooperating with the -OH hydrogen bonding and conjugating with the GO surface will greatly improve the interfacial shear performance. Our work deepens the understanding on the chemomechanical behaviors within the noncovalent interface, which is expected to provide new potential strategies in designing high-performance graphene-based artificial nacreous materials.

A non-equilibrium thermodynamic model for tumor extracellular matrix with enzymatic degradation

The extracellular matrix (ECM) of a solid tumor not only affords scaffolding to support tumor architecture and integrity but also plays an essential role in tumor growth, invasion, metastasis, and therapeutics. In this paper, a non-equilibrium thermodynamic theory is established to study the chemo-mechanical behaviors of tumor ECM, which is modeled as a poroelastic polyelectrolyte consisting of a collagen network and proteoglycans. By using the principle of maximum energy dissipation rate, we deduce a set of governing equations for drug transport and mechanosensitive enzymatic degradation in ECM. The results reveal that osmosis is primarily responsible for the compression resistance of ECM. It is suggested that a well-designed ECM degradation can effectively modify the tumor microenvironment for improved efficiency of cancer therapy. The theoretical predictions show a good agreement with relevant experimental observations. This study aimed to deepen our understanding of tumor ECM may be conducive to novel anticancer strategies.

Computational analysis of chemomechanical behaviors of composite electrodes in Li-ion batteries

Abstract

Lithiation of ZnO nanowires studied by in-situ transmission electron microscopy and theoretical analysis

Transition-metal oxides constitute an important family of high-capacity anodes for Li-ion batteries. ZnO is a model material due to the high theoretical capacity and its representative reaction mechanism upon lithiation. We investigate the structural evolution, mechanical degradation, and stress-regulated electrochemical reactions of ZnO nanowires during the first lithiation through coordinated in-situ transmission electron microcopy experiments, continuum theories, and first-principles computation. Lithiation induces a field of stress in ZnO nanowires. The stress field mediates the electrochemical reaction and breaks the planar solid-state reaction front into a curved interface. The tensile stress in the lithiated shell causes surface fracture in the basal plane of nanowires. The compressive stress in the unlithiated core retards local reactions and results in an uneven lithiation on a given basal plane. We also observe that metallic Zn nanoparticles aggregate in the amorphous matrix of the reaction products. At a critical size, Zn nanoparticles impede the propagation of the reaction front due to the thermodynamically unfavorable lithiation reaction. The results provide fundamental perspectives on the chemomechanical behaviors of oxides for the next-generation Li-ion batteries.

Lithiation of SiO2 in Li-ion batteries: in situ transmission electron microscopy experiments and theoretical studies.

Surface passivation has become a routine strategy of design to mitigate the chemomechanical degradation of high-capacity electrodes by regulating the electrochemical process of lithiation and managing the associated deformation dynamics. Oxides are the prevalent materials used for surface coating. Lithiation of SiO2 leads to drastic changes in its electro-chemo-mechanical properties from an electronic insulator and a brittle material in its pure form to a conductor and a material sustainable of large deformation in the lithiated form. We synthesized SiO2-coated SiC nanowires that allow us to focus on the lithiation behavior of the sub-10 nm SiO2 thin coating. We systematically investigate the structural evolution, the electronic conduction and ionic transport properties, and the deformation pattern of lithiated SiO2 through coordinated in situ transmission electron microcopy experiments, first-principles computation, and continuum theories. We observe the stress-mediated reaction that induces inhomogeneous growth of SiO2. The results provide fundamental perspectives on the chemomechanical behaviors of oxides used in the surface coating of Li-ion technologies.

Hydrogels with the ordered structures

A water-swollen hydrogel with a molecularly-ordered structure was prepared by copolymerizing acrylic acid and acrylic monomer containing hydrophobic long alkyl or mesogenic moiety. The gels with a long alkyl side chain formed the crystalline structure and undergo the reversible order–disorder transition with change in temperature or solvent composition which accompanied a dramatic change in Young’s modulus. These gels exhibited such chemomechanical behaviors as the shape memory and the rotational motility on the water surface. On the other hand, the gels with the mesogenic side chain formed the liquid crystalline structure with polymorphism in water, and mesophase diagram was established by changing copolymer composition and water content. Mechanism of these structural and chemomechanical behaviors has been explained in terms of order–disorder transition.