Distribution In Electrodeposition Research Articles

Inhibiting Dendritic Growth Using Additives: Efficacy of Deposit-Incorporating Additives vs. Additives Accumulating on the Electrode

Electrodeposition, particularly when carried under transport limitations, may result in rough surface texture. The roughness elements often evolve into dendrites which may cause internal shorts in batteries, leading to catastrophic failure. Since just about all commercial electroplating processes use additives to control the texture and distribution of electrodeposits, it has been suggested to use similar additives to eliminate or minimize dendritic growth. Strickler and Landau presented an analysis1 showing that if inhibiting additives were to preferentially adsorb on the tips of the roughness elements, dendritic growth could indeed be suppressed. However, these authors also argued that any additive that adsorbs and accumulates on the surface will eventually cover the entire electrode, eliminating the preferential inhibition at the tips and thus negating the beneficial effects. In order to maintain the preferential tip coverage, additive removal mechanism must be provided, e.g., by additive incorporation into the deposit. A correct balance of additive transport, adsorption, and incorporation could maintain the tips preferentially covered while the remainder of the electrode can stay essentially free of inhibiting additives, leading to level deposition1. We report here the results of an experimental study that was conducted in order to test this hypothesis. Although copper is not used in advanced batteries, it was selected as a model system because the interaction of different additives in the copper system is well-characterized2,3. Copper was plated from acidified copper sulfate (0.1 M) solution onto a rotating disk electrode, in the presence of different additives. In order to accelerate roughness evolution and increase the number of roughness elements to yield reliable statistics, deposition was conducted close to the limiting current (i/iL=0.95). Following deposition (209 coulomb/cm2), the height of the roughness elements (0-200 mm) was measured by focusing on the roughness elements tips an optical microscope objective with calibrated stage elevation. Two additives were compared: polyethylene glycol (PEG) and polyethyleneimine (PEI). PEG adsorbs weakly on copper (through its polyether oxygen) and is known to remain on the electrode. By contrast, the stronger adsorbing PEI (due to its nitrogen moiety) is incorporated within the deposit. Results, summarized in Fig. 1, indicate, as expected, only small reduction in number and height of the roughness elements in the presence of PEG as compared to the pure copper system. Two PEG systems were compared: PEG 4000 (100 ppm) by itself, and PEG 4000 (100 ppm) in the presence of chloride (70 ppm), which is known to enhance the PEG adsorption2. Both PEG systems reduced the number of large (150 – 200 mm) roughness elements by only about 14% as compared to the pure copper system. By contrast, the PEI (10 ppm), which is known to incorporate within the deposit, reduced the number of large roughness elements by a significant amount (42%). These results give credence to the hypothesis that incorporating additives should be effective in inhibiting roughness evolution and dendritic growth, while additives that remain on the electrode are expected to have little effect. However, in order to irrevocably validate the hypothesis, more studies, encompassing additional additives, with precise control of the additives transport and incorporation balance, should be conducted. Acknowledgements This research was conducted as part of the NSF/DOD funded Research Experience for Undergraduates (REU) program on Electrochemical Engineering at Case Western Reserve University. NSF/DOD stipend to K.G. is gratefully acknowledged. References Alaina Strickler and Uziel Landau, “Arresting Dendritic growth during electrodeposition using special additives”, # 993, 223rd, Electrochemical Society Meeting, Toronto, Canada, May 15, 2013.Rohan Akolkar and Uziel Landau, Electrochem. Soc., 151, C702 (2004).Julie Mendez, Rohan Akolkar and Uziel Landau, Electrochem. Soc. 156, (11), D474-D479 (2009). Figure 1

Structure and distribution of electrodeposits on anodic aluminium films by electrolytic colouring in zinc sulphate solution

Electrolytic colouring of aluminium was carried out by anodising in sulphuric acid, re-anodising in phosphoric acid followed by AC electrolytic colouring in zinc sulphate solution. The films produced by this three step electrolytic colouring method were examined using electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Element line scan analysis indicated that the electrodeposits were distributed almost to the base of the alumina pores with dimensions of 2 μm. The XRD pattern showed the material deposited in the AC anodising layer to be metallic Zn. The main reactions during the cathodic half cycle are discussed based on the structure and distribution of the electrodeposits formed during the colouring process. An increase in concentration polarisation was also observed during the AC colouring treatment. The relationship of this increased film resistivity to the limited amount of metallic Zn deposited in the alumina pores is discussed.

Photoassisted Control of Pt Electrodeposition on p-Type Si

A new method to control the size and distribution of electrodeposited metal on a semiconductor was investigated, using a system of Pt deposition on p-type Si. Pt is a noble metal, and electrodeposition is possible on p-type Si through hole injection to the valence band. When the Si surface is illuminated, an additional charge-transfer path becomes possible utilizing electrons photoexcited to the conduction band. The two pathways give different morphologies for the deposits. Fine and dispersed particles were electrodeposited under illumination, indicating the nucleation process was prevailing; in the dark, grown deposits were observed and the dominant process was crystal growth. We used the different deposition behavior to control the size and distribution of electrodeposits by the illumination-modulated method. Initial illumination gives nuclei of electrodeposits, and the adjustment of the duration can control the number of electrodeposits. The following electrolysis in the dark grows the deposits and can control the size. The method showed the possibility of controlling the size and distribution of Pt electrodeposits on p-type Si without changing applied potential.

Erratum: “Three‐Dimensional Calculation of Current Distribution in Electrodeposition on Patterned Cathode with Auxiliary Electrode” [J. Electrochem. Soc., 143, 480 (1996)

not Available.

Three‐Dimensional Calculation of Current Distribution in Electrodeposition on Patterned Cathode with Auxiliary Electrode

A three‐dimensional model has been developed to predict the current distribution on a patterned cathode with an auxiliary electrode. The solution for the three‐dimensional Laplace equation has been obtained by a boundary element method using a linear element of trigonal type. Integrals with singularity due to the fundamental solution have been analytically computed. This model suggests the optimum size of an auxiliary electrode, which minimizes the thickness variation through the entire area of the rectangular cathode for electrodeposition onto a lithographically patterned substrate.

The Influence of Lithographic Patterning on Current Distribution in Electrodeposition: Experimental Study and Mass‐Transfer Effects

The effect of lithographic patterning on electrodeposit thickness uniformity was investigated in a series of experiments. Copper was electrodeposited from an acid‐sulfate solution onto a specially patterned cathode under controlled agitation provided by a reciprocating paddle. The thickness nonuniformity resulting from a difference in “active‐area‐density” between adjacent zones was measured by profilometry. At current densities far below the mass‐transfer limit, the thickness distributions agreed well with predictions from a recently developed secondary‐current‐distribution model, in which each zone is treated as a continuum. Since this “secondary” model was found to be insufficient to describe behavior at higher current densities, it was extended to include a simple treatment of mass transfer. The resulting “tertiary” model better described the observed behavior. It was discovered that the influence of mass transfer can either decrease or increase the nonuniformity, depending on the importance of radially enhanced diffusion at individual features.

The Influence of Lithographic Patterning on Current Distribution: A Model for Microfabrication by Electrodeposition

A model has been developed to predict current distribution in electrodeposition onto substrates that contain lithographic patterns. The aim of the work was to understand the strong effects that substrate patterning can exert on the thickness distribution of plated films. Based on the familiar potential‐theory model for secondary current distribution in electrochemical cells, the model is applicable at length scales that are large compared to the individual features of a pattern. The pattern is described entirely as a continuous distribution of “active‐area density,” a property that reflects any relative change in the electroactive area of the substrate due to the pattern. The active‐area density enters the expression that relates the surface overpotential to the current density. An implementation of the model, using the boundary‐element method, has been applied to several problems that illustrate the effects of substrate patterning on current distribution. For each example, the dimensionless groups that characterize the current distribution have been identified, general solutions have been obtained over wide parameter ranges, and behavioral trends have been interpreted.

Computation of current distribution in electrodeposition, a review

Computation of current distribution in electrodeposition, a review

Devices for Controlling the Distribution of Electrodeposits

Devices for Controlling the Distribution of Electrodeposits