Analysis of growth dynamics of dendrite copper deposit in copper sulfate solutions under the galvanostatic conditions

It is shown that, under certain conditions, the dynamics of dendrite copper deposit formation in the galvanostatic electrolysis may be analyzed using the model of cylindrical electrode, which was developed for the systems with a single cathodic reaction. The model enables one to estimate the structural parameters of the deposit (the radii of dendrite tips at the growth front r _tip and their location density N). The deposit growth dynamics was studied experimentally in the laboratory conditions by combining the recording of electrical parameters with video recording of dendrite deposit growth. An analysis of spectral density of measured chronopotentiograms is proposed as an additional way of following the formation dynamics of dendrite deposit, which is meant for the production of powder with prescribed structure.     

Structural Changes in Dendrite Deposits during Galvanostatic Electrolysis: A Calculation

Modeling concepts on the growth dynamics of dendrite deposits are used to design a technique for calculating distributions of a dendrite deposit by its structural parameters (radius of a dendrite apex r _aand density of distribution of growing apices at the deposit growth front). The r _adistribution correlates with that of the dry powder by particle size. The reciprocal of the average density of apices distribution correlates with the filling density of the dry powder. The model comprises a set of differential equations that describe time variations in the dendrite deposit height, r _a, the kinetic density of the metal reduction current at apices, and the hydrogen discharge current density. The equations are solved by numerical integration inside the Mathcad Plus 6 package. The growth dynamics and structural characteristics of a growing deposit are calculated as functions of the metal ion concentration in solution and the hydrogen exchange current.     

Morphology, internal structure and growth mechanism of electrodeposited Ni and Co powders

In this paper the morphology (SEM analysis), the internal structure (cross-section analysis) and the growth mechanism of Ni and Co powders electrodeposited from ammoniacal electrolyte are investigated. It is shown that morphology and the internal structure of those powders are quite different. For Ni powder, all particles are of the same morphology, cauliflower-like type. In the case of Co powder, generally two types of particles are detected: (1) dendrite particles and (2) different types of agglomerates, compact, spongy-like and ball-like ones. The growth mechanism for all agglomerates is based on the fact that with the time of growth the disperse (dendrite) agglomerate is branching in different directions and at the tip of each branch spherical diffusion takes over the planar one, providing conditions for the growth of compact deposit. After some time, these branches form compact deposit all over the agglomerate surface and the same agglomerate further grows as a compact one, until it falls off from the electrode surface. Characteristic of all agglomerates is the presence of deep cavities on their surface and the fern-like dendrites on the bottom for most of these cavities.     

Electroconvective dendrites in nematic phases having short range smectic order exhibited by the 4,n-alkoxybenzoic acids

Electroconvective (EC) dendrites (parabolic type) in nematic (N) liquid crystals with short range smectic order shown by 4,n-octyloxybenzoic acid (8-OBA) were observed. The driving of the dendrites by lateral d.c. and a.c. electric field parameters in the nematic temperature range was carried out. The dynamics of dendrite growth were studied and analysed by the Ivantsov two-dimensional solution for the diffusion equation. Using various combinations of blocked and unblocked electrodes, we studied dependences between the dimensionless electric field parameter and product of the dendrite parabolic radius and the velocity of the dendrite growth and found that the type of electrode significantly modifies these basic dependences. We attribute this effect possibly to the opposing ion propagation, i.e. gradient of electric field in direction opposite to that of the charge injection. A possible mechanism of EC dendrite growth is suggested. A comparison with thermal dendrites in liquid crystals is presented.     

Dendrite structure of electrolytic gold deposited from molten chlorides

The structure of gold deposits produced by electrolysis of molten eutectic NaCl-KCl-CsCl at 500–700°C in an inert atmosphere is studied. The initial process on the gold cathode is the epitaxial growth of a layer up to 3 μm thick with a smoothed surface and a considerably later growth of grain boundaries. Gradually, on the protruding parts of deposit, the growth of dendrites starts. The dendrites are the major form of gold deposits. Typical gold dendrites are two-dimensional 2D〈112〉 and 2D〈112〉–〈110〉 and three-dimensional 3D〈100〉. Upon supplying air into the atmosphere above the melt at high current densities at the initial period there appears a powder comprising particles of a rounded twisted shape. Probable mechanisms leading to the formation of the “rounded” powder are discussed.     

Dendrite-like texture growth in the nematic liquid crystal phase of 4-n-heptyl- and 4-n-octyl-oxybenzoic acids aligned by a polyimide coating

An oriented dendrite-like texture is reported, appearing at a definite temperature in the nematic phase range of 4-n-heptyl- and 4-n-octyl-oxybenzoic acids (HOBA and OOBA), aligned by rubbed polyimide and preceding the smectic C phase, on cooling. Two preferred directions with respect to the 'easy' axis are indicated in the dendrites grown of HOBA and OOBA. We discuss a possible mechanism, at molecular and supramolecular levels, for this dendrite growth; and assume that the building 'blocks' of the dendrites are oligomers, or mixture of oligomers with 'free' closed and open dimers, constituting a detached crystalline layered state (named by us SmX, a smectic state intermediate between the N₁ ordinary nematic and SmC phases). The study of the dynamics of the dendrite growth demonstrates a scaling relationship typical for non-equilibrium systems. The observed dendrites can be considered as patterns formed in complex non-linear dissipative systems, driven outside of equilibrium.     

Dendrite-like texture growth in the nematic liquid crystal phase of 4-n-heptyl- and 4-n-octyl-oxybenzoic acids aligned by a polyimide coating

An oriented dendrite-like texture is reported, appearing at a definite temperature in the nematic phase range of 4-n-heptyl- and 4-n-octyl-oxybenzoic acids (HOBA and OOBA), aligned by rubbed polyimide and preceding the smectic C phase, on cooling. Two preferred directions with respect to the ‘easy’ axis are indicated in the dendrites grown of HOBA and OOBA. We discuss a possible mechanism, at molecular and supramolecular levels, for this dendrite growth; and assume that the building ‘blocks' of the dendrites are oligomers, or mixture of oligomers with ‘free’ closed and open dimers, constituting a detached crystalline layered state (named by us SmX, a smectic state intermediate between the N₁ ordinary nematic and SmC phases). The study of the dynamics of the dendrite growth demonstrates a scaling relationship typical for non-equilibrium systems. The observed dendrites can be considered as patterns formed in complex non-linear dissipative systems, driven outside of equilibrium.     

Crystallization and morphology of poly(vinylidene fluoride)/poly(3‐hydroxybutyrate) blends. I. Spherulitic morphology and growth by polarized microscopy

The development of the poly(3‐hydroxybutyrate) (PHB) morphology in the presence of already existent poly(vinylidene fluoride) (PVDF) spherulites was studied by two‐stage solidification with two separate crystallization temperatures. PVDF formed irregular dendrites at lower temperatures and regular, banded spherulites at elevated temperatures. The transition temperature of the spherulitic morphology from dendrites to regular, banded spherulites increased with increasing PVDF content. A remarkable amount of PHB was included in the PVDF dendrites, whereas PHB was rejected into the remaining melt from the banded spherulites. When PVDF crystallized as banded spherulites, PHB could consequently crystallize only around them, if at all. In contrast, PHB crystallized with a common growth front, starting from a defined site in the interfibrillar regions of volume‐filling PVDF dendrites. It formed by itself dendritic spherulites that included a large number of PVDF spherulites. For blends with a PHB content of more than 80 wt %, for which the PVDF dendrites were not volume‐filling, PHB first formed regular spherulites. Their growth started from outside the PVDF dendrites but could later interpenetrate them, and this made their own morphology dendritic. These PHB spherulites melted stepwise because the lamellae inside the PVDF dendrites melted at a lower temperature than those from outside. This reflected the regularity of the two fractions of the lamellae because that of those inside the dendrites of PVDF was controlled by the intraspherulitic order of PVDF, whereas that from outside was only controlled by the temperature and the melt composition. The described morphologies developed without mutual nucleating efficiency of the components. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 873–882, 2003     

Special fractal growth of dendrite copper using a hydrothermal method

Special fractal dendrite Cu nanostructures have been synthesized through a simple hydrothermal method, and the effects of the volume ratio between glycerol and water and the concentration of H₃PO₃ on the morphologies of dendrite Cu have been studied in detail. The Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM) and X-ray diffraction (XRD) have been used to characterize these Cu products. The results indicate that rhombic diamond and different morphologies of fractal dendrite were prepared because of the accumulation of Cu nuclei based on the diffusion-limited aggregation (DLA) and the nucleation-limited aggregation (NLA) model. Fortunately, symmetrical leaf-like dendrite Cu nanostructures different from Cu dendrites reported before have been obtained. Additionally, an explanation for the growth of fractal dendrite Cu has been discussed carefully.     

Probing the interplay between chain diffusion and polymer crystal growth under nanoscale confinement: a study by single molecule fluorescence microscopy

Motions of single poly(ε-caprolactone) (PCL) molecules during the formation of the dendrite crystals in ultrathin films are captured by single molecule fluorescence microscopy. The relationship of single molecule diffusion coefficient with the crystal growth rate, together with radius curvature, side-branch spacing of dendrite crystal and morphology are examined. The results support Mullins-Sekerka (MS) instability as the origin of lamellar branching induced by a diffusion field generated by a gradient of polymer segment density ahead of the crystal. Further analysis of the molecular trajectories has recognized different types of motions, depending on the distance to the crystal front: Fickian diffusion in regions far away from the crystal, sub-diffusion in regions adjacent to the crystal, and directed motion between these two regions. Anti-correlation of successive steps is discovered accompanying the sub-diffusion, providing a clear signature of macromolecule crowding at the crystal growth front. This anomalous diffusion process in polymer ultrathin films presents a new insight into the understanding of the retarded dynamics of interfacial mass transport towards the crystal front. It is considered to play a decisive role in controlling the crystal growth and evolution of crystal morphology.     

电极界面浓差极化对锂金属沉积的影响

锂金属作为下一代高能量密度电池的理想负极材料受到研究人员广泛关注。然而,锂枝晶生长引起的安全隐患和循环寿命短等问题严重影响了锂金属电池的实用化进程。本文以电化学现象和理论为依据,从浓差极化角度详细分析锂金属电沉积过程中枝晶生长、死锂形成和全电池失效机制,并对目前研究较多的多孔宿主电极中的浓差极化及枝晶抑制进行分析,提出锂金属界面浓差电池现象。本文得到的结论为研究人员更深入地探究锂金属保护策略提供了理论依据。     

脉冲电沉积抑制锂枝晶生成的研究

采用脉冲充电方法替代传统充电方法,研究了在有机电解液 0.5 mol·L^-1 LiBr/PC (碳酸丙烯酯)中,在铜电极上沉积锂的表面变化. 扫描电镜观测结果显示,在传统直流充电时电极表面明显地出现了枝晶,而使用脉冲充电时能够抑制枝晶的生长. 交流阻抗测试结果显示,在占空比为 0.5 时,沉积锂表面固体电解质界面(solid electrolyte interphase,SEI)膜电阻最大,沉积锂表面枝晶较少;单次脉冲电沉积时间过长,会使沉积锂表面 SEI 膜电阻减小,沉积锂表面枝晶增加;电流密度大于等于 2 mA·cm^-2时,脉冲电沉积可有效抑制枝晶生长.     

四方相钛酸钡纳米枝晶阵列的水热合成

采用水热法,在表面活性剂十六烷基三甲基溴化铵(CTAB)和合适的矿化剂NaOH的作用下,得到具有新颖结构的钛酸钡纳米枝晶阵列。X射线衍射(XRD)和拉曼光谱(Raman)结果分析显示该枝晶为四方相,随着时间的延长其结晶性增强、四方相更加明显。利用扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)和电子衍射(ED)研究了该枝晶的生长特点和生长机理,结果表明该枝晶其各枝均沿着[111]方向生长,并且同级枝相互平行形成阵列;在枝晶阵列的外侧部分会有2级子枝长出,中间部位由于空间阻碍没有子枝形成。同时探讨了CTAB和NaOH在枝晶形成过程中的作用机理,以及枝晶产品的介电性能。     

Advances in Artificial Layers for Stable Lithium Metal Anodes

Lithium (Li) metal is considered as the most promising anode material for rechargeable high-energy batteries. Nevertheless, the practical implement of Li anodes is significantly hindered by the growth of Li dendrites, which can cause severe safety issues. To inhibit the formation of Li dendrites, coating an artificial layer on the Li metal anode has been shown to be a facile and effective approach. This review mainly focuses on recent advances in artificial layers for stable Li metal anodes. It summarizes the progress in this area and discusses the different types of artificial layers according to their mechanisms for Li dendrite inhibition, including regulation of uniform deposition of Li metal and suppression of Li dendrite growth. By doing this, it is hoped that this contribution will provide instructional guidance for the future design of new artificial layers.     

添加剂在KOH溶液中对锌电极枝晶的影响

采用电流-时间曲线研究了6-硝基苯并咪唑、苯并咪唑和Pb2+在KOH（4 mol/L）溶液中对锌枝晶的影响。 结果表明,6-硝基苯并咪唑、苯并咪唑以及Pb2+能有效抑制锌枝晶的形成,从而提高锌电极的充电性能;当0.05 g/L Pb2+分别与6-硝基苯并咪唑和苯并咪唑在阴极过电位η=-200 mV进行充电实验时,具有较高的充电效率并能有效的抑制锌枝晶的生长。     

Crystallization of amorphous colloids: an effective approach for the rapid and large-scale preparation of antimony sulfide dendrites

Without the assistance of any templates and organic additives, orthorhombic antimony sulfide (Sb₂S₃) dendrites were obtained rapidly (3 h) through the crystallization of amorphous colloidal microspheres. The top view of dendrites reveals that their side branches are tetragonal prisms with a smooth face and nearly uniform breadth. The investigations on the growth mechanism demonstrated that the intermediate steps in the formation of dendrites are the rods and the structures with tip splitting. The kinetics of crystal growth, the anisotropic crystal structure and H⁺ ions in the solution are believed to be responsible for the tip splitting. The structures with tip splitting subsequently grew and developed into dendrites eventually. A prolonged crystallization time (10 h) was found to be unfavorable to the further increase of dendrite size but led to its fragmentation.     

Bio‐Inspired Stable Lithium‐Metal Anodes by Co‐depositing Lithium with a 2D Vermiculite Shuttle

Progress in lithium‐metal batteries is severely hindered by lithium dendrite growth. Lithium is soft with a mechanical modulus as low as that of polymers. Herein we suppress lithium dendrites by forming soft–hard organic–inorganic lamella reminiscent of the natural sea‐shell material nacres. We use lithium as the soft segment and colloidal vermiculite sheets as the hard inorganic constituent. The vermiculite sheets are highly negatively charged so can absorb Li⁺ then be co‐deposited with lithium, flattening the lithium growth which remains dendrite‐free over hundreds of cycles. After Li⁺ ions absorbed on the vermiculite are transferred to the lithium substrate, the vermiculite sheets become negative charged again and move away from the substrate along the electric field, allowing them to absorb new Li⁺ and shuttling to and from the substrate. Long term cycling of full cells using the nacre‐mimetic lithium‐metal anodes is also demonstrated.     

An Interfacial Layer Based on Polymers of Intrinsic Microporosity to Suppress Dendrite Growth on Li Metal Anodes

The performance and safety of lithium (Li) metal batteries can be compromised owing to the formation of Li dendrites. Here, the use of a polymer of intrinsic microporosity (PIM) is reported as a feasible and robust interfacial layer that inhibits dendrite growth. The PIM demonstrates excellent film-forming ability, electrochemical stability, strong adhesion to a copper metal electrode, and outstanding mechanical flexibility so that it relieves the stress of structural changes produced by reversible lithiation. Importantly, the porous structure of the PIM, which guides Li flux to obtain uniform deposition, and its strong mechanical strength combine to suppress dendrite growth. Hence, the electrochemical performance of the anode is significantly enhanced, promising excellent performance and extended cycle lifetime for Li metal batteries.     

聚ε-己内酯结晶形态的研究

采用DSC测试了聚ε-己内酯(PCL)的结晶温度(TC)和熔融温度(Tm)。同时采用偏光显微镜(POM)探讨了结晶时间的影响,发现结晶时间的改变只能够改变其晶体的尺寸,对其结晶形态并没有太大的影响。最后采用原子力显微镜(AFM)讨论了基底材料、溶剂和过冷度对PCL结晶形态的影响。结果表明:基底材料对PCL结晶形态的影响是比较显著的,PCL在硅片上呈棒状,在云母和涂有碳膜的云母上呈树枝状。溶剂对PCL结晶形态的影响明显,其结晶形态的差别与蒸汽压有关。在不同的温度下PCL结晶形态都成树枝状晶体,且分枝宽度随着过冷度的降低而增加。     

The mechanism of silver granular electrodeposits formation

Granules as a possible form of metal electrodeposit can be formed during deposition of metals, such deposition processes being characterized by large exchange current density values. Because of this, zero nucleation zones around growing grains are formed, permitting granular metal growth. In some cases of prolonged deposition, macro-crystalline deposits can be formed as well as granular ones, e.g. in the case of silver deposition at overpotentials lower than the critical value for dendrite growth initiation. The mechanism of granular deposit growth as a final form of metal electrocrystallization is proposed. Silver boulders were deposited on␣platinum and silver substrates. At low deposition potentials, various crystallographic forms, some of them ideal or derived from cube-octahedron-type morphology, were obtained as a result of independent grain growth inside zones of zero nucleation. In addition to cube-octahedra, twinned and multiply twinned silver particles were also observed. The nucleation density was found (1) to increase with increasing deposition overpotential, (2)␣to decrease with increasing silver concentration, and (3) to be greater on Ag than on Pt for the same deposition overpotential and dendrite precursors. Increasing overpotential leads to increase of density of twinned grains. The grain growth at greater overpotentials from more concentrated solution is less ideal, producing a granular deposit on prolonged deposition. Received: 21 April 1997 / Accepted: 18 September 1997