Dendrite Growth Rate Research Articles

Chemo-Mechanical Model for Internal Stress Impact on Lithium Dendrite Growth

Lithium-ion batteries have the potential for greater efficiency and lifetime than current commercial options. However, there are operational and safety concerns that must be addressed before expanding their applications. During charge-discharge cycles lithium dendrites form within the battery due to plating on Li-electrolyte surface inhomogeneities. Full penetration through the electrolyte to the cathode leads to a short-circuit, resulting in battery failure and sometimes fire. Thus, controlling the rate of lithium dendrite growth is imperative for creating safer and longer-lasting batteries. Dendrite growth occurs when the lithium deposition rate exceeds the stripping rate and increases when the current density at the peak of a surface inhomogeneity is greater than at the valley. Addition of mechanical stress due to both internal and external pressures can decrease the propensity for dendrite growth; for various system conditions, a critical pressure exists above which formation is suppressed. However, mechanical pressure also leads to other complications, including inhomogeneous transport through the separator caused by nonuniform contact of a rough Li surface. Pressure-driven creep of the Li surface additionally evolves the contact and mechanical landscape. In this work, we present a mesoscale model and parametrically study the effect of internal stress and material properties on dendrite growth. The model couples mechanical deformation in both Li and the separator with the electrochemical response during the charging phase. Both the effects of mechanical and transport properties of the liquid electrolyte are investigated. Phase maps of the conditions for which dendrite formation is encouraged or suppressed are created and can be used to inform battery manufacturing and material choices.This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525.

In situ study of the electrochemical migration of tin in the presence of H2S

The electrochemical migration of tin in the presence of H2S was in situ investigated using optical and electrochemical techniques. The results show that dendrites co-exist with precipitates at H2S concentration range from 0 to 1000 ppmv; furthermore, the time to short circuit decreases with increasing H2S concentration. The essential reason is that higher H2S concentration increases the conductivity of electrolyte, resulting in a higher growth rate of dendrite. As the H2S concentration further increases up to 10,000 ppmv or 100,000 ppmv, no dendrites but precipitates can be observed. This can be attributed to that large amount of tin hydroxides and tin sulfides are produced quickly at the beginning of electrochemical migration test, which act as a barrier to hinder the arrival of Sn2+/Sn4+ to the cathode. Thus, no dendrites but precipitates can be found. Under square wave electric field with a time period of 1 s, it is observed that there are no dendrites but some precipitates. This is because there is a circulation between metal tin deposition during the first 0.5 s and its dissolution in the next 0.5 s. Therefore, the occurrence of short circuit in the presence of H2S is semi-cycle dependent.

Simulating dendrite growth in lithium batteries under cycling conditions

Studies have shown that the lifetime and performance of lithium batteries are greatly influenced by the charge/discharge cycles of the battery. The number of cycles over which a battery operates depends on the rate and depth of charge/discharge. Degradation in battery performance over multiple cycles is directly related to dendrite growth at the electrode-electrolyte interface in the battery. Understanding how cycling effects dendrite growth rates and morphology requires resolution of the chemical-physical processes at the electrode-electrolyte interface. In this study, a numerical model of dendrite growth at this electrode-electrolyte interface over multiple charge/discharge cycles is presented. In this work, dendrite growth over multiple charge/discharge cycles is simulated at the interfacial level where the effects on dendrite growth rate and morphology can be resolved. The simulations are able to predict qualitative dendrite morphologies presented in experimental studies, and the effects of fast charging scenarios on dendrite growth rate and morphology are discussed.

Controlling dendrite growth in lithium metal batteries through forced advection

Instabilities during metal electrodeposition create dendrites on the plating surfaces. In high energy density lithium metal batteries (LMBs) dendrite growth causes safety issues and accelerated aging. In this paper, analytical models predict that dendrite growth can be controlled and potentially eliminated by small advective flows normal to the surface of lithium metal electrode. Electrolyte flow towards the Li metal electrode lowers the dendrite growth rate, overpotential, and impedance. Flow in the opposite direction, however, enhances the dendrite growth. For every current density, there exists a critical velocity above which dendrite growth can be totally eliminated. The critical velocity increases almost linearly with increasing current density. For typical current densities and inter-electrode separation, the critical velocity is very small, indicating the potential for practical application.

Controlling solid-liquid interfacial energy anisotropy through the isotropic liquid

Although the anisotropy of the solid-liquid interfacial free energy for most alloy systems is very small, it plays a crucial role in the growth rate, morphology and crystallographic growth direction of dendrites. Previous work posited a dendrite orientation transition via compositional additions. In this work we examine experimentally the change in dendrite growth behaviour in the Al-Sm (Samarium) system as a function of solute concentration and study its interfacial properties using molecular dynamics simulations. We observe a dendrite growth direction which changes from langle 100rangle to langle 110rangle as Sm content increases. The observed change in dendrite orientation is consistent with the simulation results for the variation of the interfacial free energy anisotropy and thus provides definitive confirmation of a conjecture in previous works. In addition, our results provide physical insight into the atomic structural origin of the concentration dependent anisotropy, and deepen our fundamental understanding of solid-liquid interfaces in binary alloys.

The Marangoni convection effects on directional dendritic solidification

The Pore Formation and Mobility Investigation (PFMI) experiments conducted on the International Space Station revealed that Marangoni convection caused by the presence of bubbles could affect the microstructure formation. The experiment provided information on the bubble movement and morphological evolution during remelting and directional solidification under microgravity condition for a succinonitrile (SCN)-water binary alloy. In this work, a three-dimensional lattice Boltzmann (LB)-Cellular automaton (CA) model was utilized to study the effects of Marangoni convection on the solidification microstructure. The results reveal that the induced convection is strong enough to bend dendrites from their preferential crystallographic direction and can affect the dendrite growth rate.

Binary alloy dendrite growth in presence of shrinkage induced convection

In this paper, the effect of shrinkage induced flow on binary alloy dendrite growth is investigated. The standard enthalpy model for dendritic solidification is modified to incorporate unequal phase densities and coupled with a flow solver to simulate shrinkage driven flow. Simulations show that shrinkage induced convection towards the solidification interface leads to increased solute accumulation at the interface resulting in reduced solidification rate. Thus even if the change in volume due to density difference is considered, the predicted growth rate will not be accurate unless shrinkage driven convection is incorporated in the model. The effect of Lewis number on shrinkage is also investigated and it is found that the relative decrease in dendrite growth rate due to shrinkage induced flow is not affected significantly by change in Lewis number.

The effect of local thermo-solutal convection on dendrite fragments at variable cross section

The dendrite fragments formation process of hypoeutectic Al–Cu alloy at variable cross section was observed by synchrotron radiation imaging. The results show that the variable cross section structure causes a series of chain reactions among the solidification parameters and dendrite characteristic parameters. It can induce the sudden decrease of concentration gradient, constitutional undercooling and dendrite growth rate. The solute enrichment process at the variable cross section can be divided into two stages: the rapid solute enrichment stage and the slow solute enrichment stage. The dendrite fragments occur in the rapid solute enrichment stage is satisfying the Rayleigh number based fragmentation criterion. The purpose of establishing the relationship between Rayleigh number and dendrite growth rate is to optimize the single crystal production process window.

Effect of Organic Acids on the Electrochemical Migration of Tin in Thin Electrolyte Layer

Background and Objective: The effects of representative solder flux residue weak organic acids on electrochemical migration (ECM) of tin in thin electrolyte layer were studied using a technique based on the coupling of in situ electrochemical measurements and optical observations, as well as ex situ characterizations. Methods and Results: The results showed that the increasing amount of weak organic acid decreased the probability of ECM and dendrites formed were mainly composed of metallic tin. Tin ions reacted with organic compound ions from hydrolysis of weak organic acids to form complexes with electronegativity, which retarded the transfer of tin ions. Some complexes can be oxidized to the insoluble tin oxides on the anode surface and blocked the dissolution of anode during tin ECM. Conclusion: The growth rate of tin dendrite was found to be limited by the dissociation of complexes. Mechanisms involved were proposed to explain the role of weak organic acid in the tin ECM.

Observing the Growth of Metal Dendrites in Specimens Prepared by Fabricating Galvanic Cells and Electrolytic Cells

This paper introduces a safe, interesting, convenient, and low-cost experiment. The products of galvanic cells and electrolytic cells are compressed into specimens that are placed on a slide to stretch the metal dendrites in one plane and ensure they are not easily destroyed by external factors. The details and growth process of the metal dendrites can be clearly observed with the naked eye and optical microscopy, which arouses interest from students and allows them to enjoy the beautiful images while obtaining a large amount of macroscopic information. By allowing the students to observe the macroscopic phenomena and the corresponding microscopic changes among the microparticles, it is possible for them to explain the morphological origins and growth rates of the metal dendrites, which deepens their understanding of the reactions that occur in galvanic and electrolytic cells.

ELECTROCHEMICAL MIGRATION BEHAVIOR OF Sn-3.0Ag-0.5Cu SOLDER ALLOY UNDER THIN ELECTROLYTE LAYERS

The electrochemical migration (ECM) behavior of Sn-3.0Ag-0.5Cu solder alloy under thin electrolyte layers was investigated using a technique based on the coupling of in situ electrochemical measurements and optical observation. Results showed that the mean time to failure first increased and then decreased as thickness of the electrolyte layer increased, the maximum value was present at 200[Formula: see text][Formula: see text]m. The higher the bias voltage applied, the faster was the rate of dendrite growth. And, Sn leaded the ECM of SAC305 solder alloy. Mechanisms relevant have been proposed to explain the ECM behavior of Sn-3.0Ag-0.5Cu solder alloy.

Computational Study of Cycling Effects on Dendrite Growth in Lithium Metal Batteries

Dendrite growth is an ongoing challenge on the anode surface in lithium metal batteries. Over multiple charge and discharge cycles dendritic growth leads to a decrease in battery performance and increased safety issues due to short circuiting. The morphology and growth rate of dendrites depend on a number of factors including the rate and depth of charge/discharge. In this work a computational model of dendrite growth at the interface is used to investigate the effects of cycling on dendrite growth rate and morphology. The model resolves the interfacial chemical-physical processes and simulates multiple charge and discharge cycles. Results show that dendrite growth depends on both the charging and discharging cycles, which can lead to heterogeneous growth patterns based on the levels of deposition and dissolution of lithium during the cycles.

Modeling the Effects of Cycling on Dendrite Growth in Lithium Batteries

Dendrite growth is an ongoing challenge in lithium batteries. Over multiple charge and discharge cycles dendritic growth leads to a decrease in battery performance and increased safety issues due to short circuiting. The morphology and growth rate of dendrites depend on a number of factors including the rate and depth of charge/discharge. In this work a computational model of dendrite growth at the interface is used to investigate the effects of cycling on dendrite growth rate and morphology. The model resolves the interfacial chemical-physical processes and simulates multiple charge and discharge cycles. Results show that dendrite growth depends on both the charging and discharging cycles, which can lead to heterogeneous growth patterns based on the levels of deposition and dissolution of lithium during the cycles.

Effects of Porous Separators on Dendrite Growth in Lithium Batteries

Dendrite growth on the surface of the anode in lithium batteries can diminish their energy storage capacity and increase safety concerns, i.e. risks of a short circuit. Dendrite growth consists of two stages, nucleation and growth. Favorable sites for the nucleation of dendrites are difficult to avoid and so suppressing dendrites after nucleation is a promising research direction. Previous work has suggested that the local mass transport in the electrolyte is closely related to the structure of dendrites. In this research, a mesoscale diffusion-reaction model is used to study the effects of various porous separator geometries and configurations on dendrite formation. The porous separators act to restrict the local mass transport near the anode surface, which effects dendrite structure and growth rates. The porous separator structures considered in this study highlight the importance of both porosity and tortuosity. These attributes are often simplified when reporting characteristics in experimental tests or ignored in other simulations. In this study, we directly observe the impact of separator characteristics on the local mass transport gradient through the separator and the subsequent dendrite growth. By taking into account the impact of both overall and local porosity and tortuosity on dendrite growth, battery design can be improved.

Combined Effect of Thermal Anisotropy and Forced Convection on the Growth of Binary Alloy Equiaxed Dendrites

A numerical model has been developed to simulate the growth of an equaixed binary alloy dendrite under the combined effect of thermal anisotropy and forced convection. A semi implicit–explicit approach is used where the velocity and pressure fields are solved implicitly using the SIMPLER algorithm, while energy and species conservation equations are treated explicitly. The effect of thermal anisotropy present in the solid crystal is implemented by the addition of a departure source term in the conventional isotropic heat transfer based energy equation. The departure source represents the anisotropic part of the diffusive term in the isotropic heat transfer based energy equation. Simulations were performed to find the relative effect of convection strength and thermal anisotropy on the growth rate and morphology of a dendrite. Subsequently, parametric studies were conducted to investigate the effect of thermal anisotropy ratio, inlet flow velocity, undercooling temperature, and the relative strength of the thermal to mass diffusivity ratio by analyzing the variation of the equilibrium tip velocity of the top and left arms, the arm length ratio (ALR), and the equivalent grain radius. Based on simulations, a chart has been developed, which demarcates different regimes in which convection or thermal anisotropy is the most dominant factor influencing the dendrite growth rate. The model has also been extended to study the growth of multiple dendrites with random distribution and orientation. This can be useful for the simulation of microstructure evolution under the combined effect of convection and thermal anisotropy.

Plasticized Hybrid Network Solid Polymer Electrolytes for Lithium‐Metal Batteries

AbstractIncorporating solid polymer electrolyte (SPE) into lithium metal batteries has the benefit of employing the electrolyte as the electrode separator while inhibiting the growth of lithium dendrites. The two main models on lithium dendrite growth show that either ionic conductivity or mechanical property affect lithium dendrite nucleation and growth rate. In this work, with a well‐controlled hybrid network SPE as the model system, the modulus and conductivity of the hybrid SPEs are systematically tuned by plasticizing the network with low molecular with diluents. This systematic property control allows for establishing the correlation between mechanical/electrochemical properties of the SPEs with their propensity of lithium dendrite resistance using galvanostatic polarization and cycling experiments. It is further demonstrated that lithium metal batteries can be operated at 30 °C for the plasticized SPEs due to the dramatically improved conductivity.

DSCAM differentially modulates pre- and postsynaptic structural and functional central connectivity during visual system wiring

BackgroundProper patterning of dendritic and axonal arbors is a critical step in the formation of functional neuronal circuits. Developing circuits rely on an array of molecular cues to shape arbor morphology, but the underlying mechanisms guiding the structural formation and interconnectivity of pre- and postsynaptic arbors in real time remain unclear. Here we explore how Down syndrome cell adhesion molecule (DSCAM) differentially shapes the dendritic morphology of central neurons and their presynaptic retinal ganglion cell (RGC) axons in the developing vertebrate visual system.MethodsThe cell-autonomous role of DSCAM, in tectal neurons and in RGCs, was examined using targeted single-cell knockdown and overexpression approaches in developing Xenopus laevis tadpoles. Axonal arbors of RGCs and dendritic arbors of tectal neurons were visualized using real-time in vivo confocal microscopy imaging over the course of 3 days.ResultsIn the Xenopus visual system, DSCAM immunoreactivity is present in RGCs, cells in the optic tectum and the tectal neuropil at the time retinotectal synaptic connections are made. Downregulating DSCAM in tectal neurons significantly increased dendritic growth and branching rates while inducing dendrites to take on tortuous paths. Overexpression of DSCAM, in contrast, reduced dendritic branching and growth rate. Functional deficits mediated by tectal DSCAM knockdown were examined using visually guided behavioral assays in swimming tadpoles, revealing irregular behavioral responses to visual stimulus. Functional deficits in visual behavior also corresponded with changes in VGLUT/VGAT expression, markers of excitatory and inhibitory transmission, in the tectum. Conversely, single-cell DSCAM knockdown in the retina revealed that RGC axon arborization at the target is influenced by DSCAM, where axons grew at a slower rate and remained relatively simple. In the retina, dendritic arbors of RGCs were not affected by the reduction of DSCAM expression.ConclusionsTogether, our observations implicate DSCAM in the control of both pre- and postsynaptic structural and functional connectivity in the developing retinotectal circuit, where it primarily acts as a neuronal brake to limit and guide postsynaptic dendrite growth of tectal neurons while it also facilitates arborization of presynaptic RGC axons cell autonomously.

Poly(ethylene oxide)‐based block copolymer electrolytes for lithium metal batteries

AbstractNanostructured block copolymer electrolytes (BCEs) based on poly(ethylene oxide) (PEO) are considered as promising candidates for solid‐state electrolytes in high energy density lithium metal batteries (LMBs). Because of their self‐assembly properties, they confer on electrolytes both high mechanical strength and sufficient ionic conductivity, which linear PEO cannot provide. Two types of PEO‐based BCEs are commonly known. There are the traditional ones, also called dual‐ion conducting BCEs, which are a mixture of block copolymer chains and lithium salts. In these systems, the cations and anions participate in the conduction, inducing a concentration polarization in the electrolyte, thus leading to poor performances of LMBs. The second family of BCEs are single‐lithium‐ion conducting BCEs (SIC‐BCEs), which consist of anions being covalently grafted to the polymer backbone, therefore involving conduction by lithium ions only. SIC‐BCEs have marked advantages over dual‐ion conducting BCEs due to a high lithium ion transference number, absence of anion concentration gradients as well as low rate of lithium dendrite growth. This review focuses on the recent developments in BCEs for applications in LMBs with particular emphasis on the physicochemical and electrochemical properties of these materials. © 2018 Society of Chemical Industry

Influence of impurities, strontium addition and cooling rate on microstructure evolution in Al-10Si-0.3Fe casting alloys

The effect of impurities, Sr additions and cooling rate on the microstructural evolution of high-purity Al-10Si-0.3Fe and corresponding impure commercial alloys is examined by optical microscopy and in situ by X-ray synchrotron 3D tomography. At fast cooling rate (∼470 K min−1) the presence of impurities decreases the growth rate of primary Al dendrites and enables formation of the β phase. Besides a modification of the eutectic Si, the addition of Sr prevents the formation of the β phase and increases the growth rate of Al dendrites. A low cooling rate (∼1 K min−1) leads to the formation of α, γ, δ and β intermetallic phases. In all four alloys, the dominant phase is the δ phase, regardless of commercial impurities or the Sr level. Intermetallic phases formed during slow cooling rates are much coarser than those formed during fast cooling and they have different morphologies. Our results suggest that the velocity of growth and the final morphology and size of the intermetallic phases are mainly determined by diffusional processes which in turn are controlled by the cooling rate.

Study on the Thermal Contraction Behaviors of Mg and Al

By using a device which could achieve the 1-Dimensional shrinkage instead of 3D shrinkage of the casting during the solidification and cooling, the cooling curves and the relationship between the shrinkage / temperature and time were investigated. Then, the thermal shrinkage behaviors of pure Mg and Al ingots were obtained. As a result, the characterization of the thermal shrinkage behavior of Mg and Al was systematically investigated. The results indicate that the contraction rate of pure Mg ingot increases with the increase of growth rate of dendrites in quantity during solidification. The maximum contraction rate νl, max will be reached when the formationof primary dendrite ends, and the value of νl, max is 1.12×10-2 mm·s-1. However, the shrinkage will not be present until the solid state cooling starting for the pure Al ingot. The contraction of pure Mg ingot in solid state can be divided into two stages: high temperature solid shrinkage stage and low temperature solid shrinkage stage. And the rate of shrinkage firstly increases then decreases with the temperature dropping at the stage of high temperature solid shrinkage. The rate of solid shrinkage of pure Al ingot is present at the beginning of solid-state cooling. And its value is 9.69×10-3 mm·s-1, which is more than 3 times of that of pure Mg ingot. The shrinkage behaviors of both pure Mg and Al ingots tend to be uniform shrinkage when the temperature is below 400°C.