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Nickel nanowire mesh electrodes offer great potential for water electrolysis in alkaline environment, given their high internal surface area, mechanical strength, and alkaline resistance. Here we use a nickel nanowire mesh with a specific area of 26 m2/cm3, resulting in ~100-fold area enhancement for a 4µm thick nanowire mesh, compared to planar nickel. This highly benefits geometric current density, potentially into a regime where mass transport is the main limiting factor. Therefore, we performed a systematic study of electrode behaviour under various mass transport conditions to decouple kinetic and mass transfer related contributions to electrode voltage losses. An electrochemical flow cell was designed to measure the nanowire mesh electrode performance under optimal mass transport conditions. The cell provided electrolyte flow through the nanomesh, enabling convective supply of reagent into the nanopores as well as convective removal of reaction products. Facilitated by the inherent strength of the nanowire mesh, superficial flow velocities up to 1 cm/s could be obtained, with which geometric current densities as high as 320 mA/cm2 could be measured in the kinetically limited (flowrate independent) regime. Internal mass transport limitations were isolated by use of an inverted rotating disk electrode (iRDE). Koutecky-Levich analysis was performed to compensate for external mass transfer contributions on both nanowire mesh electrodes and planar electrodes. The nanowire mesh as iRDE resembles operating conditions in an electrolyzer, whereas the planar electrode provides a well-defined benchmark area for the electrode surface activity. For both the oxygen evolution reaction as the hydrogen evolution reaction, mass transport limitations were studies as function of current density and electrolyte (NaOH) concentration. Nanowire mesh electrode operation in the presence of internal mass transport limitations was compared to the non-limited condition and planar benchmark, from which the electrode effectiveness factor could be calculated. A 1-d simplified model of the electrode was used to explain the observed phenomena and to provide guidance for design optimization.

Over the past decades the use of renewable energy for the conversion of readily available resources to valuable chemicals (power-to-X) was found to be a key factor in enabling the transition to a more sustainable future. This can for example be the reduction of CO2 or N2 to CO, synthetic fuels, formic acid, alcohols, ammonia, and other more complex chemicals. The most prominent type of reaction, however, is the electrolysis of water for the formation of H2, which can serve as a medium for energy storage or as building block for the further conversion to a variety of different molecules. While serving different purposes, all these reactions share the general requirement of an energy efficient conversion to be economically viable. In many areas where green electricity is inexpensive, increasing gas prices already make green hydrogen (from electrolysis) cheaper than grey hydrogen (from steam reforming of methane). In order to reach Europe’s ambitious goal of 2251 TWh of energy consumption that could be covered by hydrogen in 2050 (24% of the total), however, current electrolysis technology is in need of improvements. As in any electrochemical system, the electrodes play an essential role in the efficiency of an electrolysis cell. Some factors that influence the performance of an electrolytic cell are the catalytic activity of the electrodes to reduce the overpotential, the electrochemically active surface area (ECSA), and mass transport of electrolyte and produced gases through the electrodes. The mass transport becomes especially detrimental in polymer electrolyte membrane electrolysis (PEM) and hydroxyl exchange membrane electrolysis (HEM). A zero-gap architecture in these types of cells demands electrodes with an open porosity. HEM allows furthermore the use of more cost-efficient materials, such as nickel, and can thus facilitate the transition to green hydrogen. To meet the above-mentioned requirements for a new generation of electrode materials, we developed 3D nano-porous electrodes with an ECSA of about 26 m2/cm3, leading to an area enhancement of about 130x compared to the geometric electrode area over an electrode thickness of only 5µm. Furthermore, these electrodes offer a tunable high porosity of more than 75% and mechanical stability as a fully freestanding electrode that is given through interconnected nanowires and an integrated porous support structure. We were able to demonstrate the drastically improved performance as compared to classical Ni-foam electrodes in HEM-type electrolyzers. The surface area enhancement in combination with a porosity and tortuosity that facilitate mass transport leads to a low overpotential, even without the application of additional catalytic coatings. While the improved electrochemical behavior is fundamental for the application of novel electrode materials, it alone is not sufficient for their successful application in real systems. Also scalability is an important factor, which can often be difficult to reach when nanomaterials are involved. Especially electrochemical processes, such as anodization of the templates and electrodeposition of the nano-structured electrodes, have to be carefully controlled. Here, we were able to leave the typical lab-scale and bring the 3D nano-porous nickel electrodes to an industrially relevant size. Figure 1

An attractive solution towards net-zero carbon emission is the electrocatalytic CO2 reduction with its ability to convert the greenhouse gas CO2 with renewable electricity and appropriate catalytic materials to useful chemicals and fuels to store energy. Depending on the number of electrons transferred a variety of oxygenates and hydrocarbons can be obtained. Among used catalytic materials, such as metals, alloys or composites, copper has shown the unique property to electrocatalytically convert CO2 into a wide variety of valuable C2+ products such as ethylene or alcohols. Apart from the high potential to reshape our carbon economy the electrocatalytic CO2 reduction is still in its early development stage compared to the more mature water electrolysis, with high-throughput operation at practical current densities as well as long-term stability of the catalysts being only scarcely demonstrated. Additionally, selectivity towards high-value (beyond C1) products using copper catalysts has proven to be challenging and many research efforts are directed towards improving product selectivity. For this purpose, mainly nanostructured porous Cu electrodes either based on randomly ordered nanoparticles loaded on porous (carbon-based) supports or low-surface area metal foams, meshes or felts with high porosity are commonly used. While the former electrode architecture typically shows poor long-term stability with often weak adhesion between the nanoparticles and the porous support, the latter electrodes have a low electrochemical surface area and hence are not suitable for high-throughput CO2 reduction at high current densities. In this work we present novel high-surface area porous copper electrodes, so-called copper nanomeshes, that are regular 3D-networks of interconnected Cu nanowires. These unique few µm-thin electrodes show a large surface area enhancement (compared to planar Cu) by a factor of ~80, while providing a high porosity of ~70% together with sufficient mechanical stability, an important aspect towards their practical implementation in electrocatalytic flow cells. Cu nanomesh electrodes with a thickness of 4µm were fabricated through electrochemically plating in 3D-porous anodic aluminum oxide templates and show a mixed surface texture of (111), (100) and (110) Cu. We demonstrate the high potential toward high-throughput CO2 electrolysis of these novel electrodes in comparison to planar copper electrodes in various CO2-containing electrolyte solutions. The CO2 reduction product analysis showed a significant difference in selectivity between planar (polycrystalline or with preferential 111 or 200 texture) and the polycrystalline Cu nanomesh electrodes with CO or C2H4 as major reduction products depending on the potential applied. The beneficial effect of the high electrochemical surface area was demonstrated by a significant increase in the current density on the nanostructured Cu electrodes. Additionally, we characterized the copper nanomesh electrodes before, during and after CO2 reduction with complementary techniques to gain insights on the reaction mechanism and on the electrode stability. Figure 1

Thirty years after the release of the first commercial lithium-ion battery, capacity fading due to complex ageing mechanisms remains one of the major concerns in lithium-ion battery research. Lithium-ion battery cathodes age due to phenomena as transition metal dissolution, electrolyte oxidation and volume expansions.[1] To suppress these effects, a protective coating can be applied to the cathode’s surface to avoid direct contact with the liquid electrolyte. Many studies exist in literature, showing the protective effect of conformal and pinhole-free Atomical Layer Deposited (ALD) coatings. However, the inorganic coatings deposited by ALD are rigid and will crack upon volume expansion of the cathode.[2] Molecular Layer Deposition (MLD) offers the same benefits as ALD but can be used to deposit hybrid inorganic/organic flexible films that can accommodate potential volume expansions of the cathode. To our knowledge, apart from ‘metalcones’ i.e. MLD films grown using a metal containing precursor and an alcohol, MLD films remain to be explored as protective and flexible coatings for lithium-ion batteries.[3] In this work, hybrid MLD titanium carboxylate thin films are deposited using tetrakis(dimethylamido)titanium (TDMAT) and various dicarboxylic acid precursors: oxalic acid, malonic acid, succinic acid, glutaric acid and 3,6-dioxaoctanedioic acid. The latter containing two ethylene oxide units per molecule, potentially increasing the lithium-ion conductivity.[4] The growth of the titanium carboxylate MLD processes is studied using in situ ellipsometry at a substrate temperature of 100 °C and 160 °C. Only the TDMAT/oxalic acid process is found to display good saturation behavior, while a parasitic CVD component is present during the TDMAT pulse for the other processes. The structure of the as-deposited films is physically characterized using Fourier Transform IR spectroscopy (FTIR) and X-Ray Photoelectron Spectroscopy (XPS), confirming the successful deposition of titanium carboxylate films. The films are found to be stable in air up to 50 days as shown by FTIR. This is in contrast to many metalcone MLD films which are considered to be air sensitive as the organic backbone degrades upon air exposure. In addition, FTIR, X-Ray Reflectivity (XRR) and X-Ray Fluorescence (XRF) measurements show that the titanium carboxylate films remain intact upon immersion into a solution of 1 M LiClO4 in propylene carbonate, the liquid electrolyte used for electrochemical characterization. The electrochemical properties of a 5 nm TDMAT/oxalic acid, TDMAT/3,6-dioxaoctanedioic acid and TDMAT/glycerol film (conventional titanicone film [5]) are tested on top of three ideal electrode systems: anatase TiO2, TiN and LiMnO2 (LMO). The titanium carboxylate films are observed to have little to no effect on the lithium-ion kinetics of the TiO2 electrode system compared to the uncoated electrode. This is in contrast to the titanicone film displaying a detrimental effect on the kinetics. All films are observed to effectively suppress electrolyte oxidation when exposing the TiN electrode system to elevated potentials. On the LMO electrode an activation step is necessary for all films, after which a good lithium-ion mobility through the titanium carboxylate films is observed without the severe irreversible reactions detected in the potential profile for the titanicone films. Overall, the explorative tests on thin film electrodes in this work indicate that the electrochemical properties of the titanium carboxylate films seem promising candidates as protective and flexible coating of lithium-ion battery cathodes. [1] Vetter, J., Novák, P., Wagner, M. R., Veit, C., Möller, K. C., Besenhard, J. O., ... & Hammouche, A. (2005). Ageing mechanisms in lithium-ion batteries. Journal of power sources, 147(1-2), 269-281. [2] Ban, C., & George, S. M. (2016). Molecular layer deposition for surface modification of lithium‐ion battery electrodes. Advanced Materials Interfaces, 3(21), 1600762. [3] Zhao, Y., Zhang, L., Liu, J., Adair, K., Zhao, F., Sun, Y., ... & Sun, X. (2021). Atomic/molecular layer deposition for energy storage and conversion. Chemical Society Reviews, 50(6), 3889-3956. [4] Xue, Z., He, D., & Xie, X. (2015). Poly (ethylene oxide)-based electrolytes for lithium-ion batteries. Journal of Materials Chemistry A, 3(38), 19218-19253. [5] Van de Kerckhove, K., Mattelaer, F., Deduytsche, D., Vereecken, P. M., Dendooven, J., & Detavernier, C. (2016). Molecular layer deposition of “titanicone”, a titanium-based hybrid material, as an electrode for lithium-ion batteries. Dalton Transactions, 45(3), 1176-1184.

Electrodeposition is typically associated with the electroreduction of metal ions for the deposition of metals, alloys or semiconductors. Compounds can be electrodeposited when the metal ions form an insoluble compound upon change of its valence state at the electrode surface. A well-known example is the anodic deposition of MnO2, where aqueous solvated Mn2+ ions are oxidized to the insoluble Mn(IV) in acid sulfate solutions. Alternatively, the precipitation of a compound or oxide can be triggered by changing the local pH at the electrode by a suitable electrochemical reaction. The use of electrochemical formed base from so-called probase molecules has found applications in formation of oxides, phosphates but also organic materials such metal organic frameworks (MOFs). Nitrate was one of the first pro-bases suggested for the electrochemical precipitation of ZnO. An alternate electrochemical approach for depositing compounds and oxides is the electrochemical initiation of a sol-gel reaction first developed for the silica sol-gel process by Shacham et al. [1] During deposition, an electrode is submerged into a precursor solution followed by the application of a cathodic current. The chemical reaction is triggered by electro-generating the OH- catalyst that is required for the polycondensation of the silica precursor. Since this occurs near the surface, the method results in silica thin films deposited only on the electrode surface. Finally, also electro-polymerization can lead to thin insulating films. In this paper, several of these reaction paths will be explored. The initial stages of MnO2 electrodeposition are strongly dependent on the starting surface and determines the adhesion and attainable film thickness [2]. The relationship between (intentionally) introduced meso-porosity, growth rate and film thickness will be discussed. The poor electronic conductivity of oxides makes that the reaction is maintained by ionic conduction through the films, similar as for oxide formation by anodization. For the formation of micron thick oxide films, also good control of hydrodynamic conditions is essential. [3] The resistive nature of the layers typically allows also for good conformality over high aspect ratio substrates. Conformal deposition of oxide thin-film coatings on high aspect ratio structures is typically claimed by Atomic Layer Deposition. Inorganic-organic hybrid films such as metal cones can be similarly deposited by Molecular Layer Deposition (MLD). [4] The nature of the surface limited reactions of these vapor-phase methods allows for the formation of continuous sub-nanometer to a few tens of nanometer thin films with uniform thickness over the most complex architectures. The accuracy of the technique goes at the cost of long deposition cycles especially when very large surface areas with extreme aspect ratios (>100) are involved. The intrinsic resistive nature of the electrodeposited oxide and insulator films allows for excellent conformal coatings with growth rates much more suited for thicker films without loss in conformality or uniformity. In this paper, we will show examples where electrochemical induced deposition process are used also to coat nano-architectures such as our nanomesh with very large surface area (100 cm2 per planar cm2) and aspect ratio (100x). [1] Shacham, B. R., Avnir, D. & Mandler, D. Electrodeposition of Methylated Sol-Gel Films on Conducting Surfaces. Adv. Mater. 384–388 (1999). [2] "Electrodeposition of Adherent Submicron to Micron Thick Manganese Dioxide Films with Optimized Current Collector Interface for 3D Li-Ion Electrodes" Marina Timmermans, Nouha Labyedh, Felix Mattelaer, Stanislaw Zankowski, Stella Deheryan, Christophe Detavernier, and Philippe M. Vereecken, J. Electrochem. Soc. 164, 14, D954-D963 (2017). [3] Aggregate-Free Micrometer-Thick Mesoporous Silica Thin Films on Planar and Three-Dimensional Structured Electrodes by Hydrodynamic Diffusion Layer Control during Electrochemically Assisted Self-Assembly”, G Vanheusden, H Philipsen, SJF Herregods, PM Vereecken, Chemistry of Materials (2021). [4] “Molecular Layer Deposition of "Magnesicone", a Magnesium-based Hybrid Material" Jeroen Kint, Felix Mattelaer, Sofie S. T. Vandenbroucke, Arbresha Muriqi, Matthias M. Minjauw, Mikko Nisula, Philippe M. Vereecken, Michael Nolan, Jolien Dendooven, and Christophe Detavernier, Chem. Mater. 32, 11, 4451–4466, (2020).

This paper asserts that the development of continuum-scale mathematical models utilizing John Newman’s BAND subroutine can be simplified through the use of dual number automatic differentiation. This paper covers the salient features of the BAND algorithm as well as dual numbers and how they can be leveraged to algorithmically linearize systems of partial differential equations; these two concepts can be combined to produce accurate and computationally efficient models while significantly reducing the amount of personnel time necessary by eliminating the time-consuming process of equation linearization. As a result, this methodology facilitates more rapid model prototyping and establishes a more intuitive relationship between the numerical model and the differential equations. By utilizing an existing and validated programming module, dnadmod, these advantages are achieved without burdening the general user with significant additional programming overhead.

Three-dimensional (3D) configuration of high-performance energy storage devices has been the subject of ongoing investigations targeting their integration in autonomous microelectronic systems. In this study we demonstrate a route toward the realization of high capacity cathode material for 3D thin-film lithium-ion (Li-ion) batteries. Electrolytic manganese dioxide (EMD) film can be applied as a Li-ion intercalation electrode upon its conversion to lithium manganese dioxide (LiMn2O4 or LMO) by solid-state reaction. The main challenges of depositing thicker EMD film directly on the current collector often lay in achieving a good film adhesion and preventing oxidation of non-noble current collectors such as TiN, Ni. To improve the adhesion of the EMD films we modify the surface of the current collector by means of thin-film or seed layer coatings, which also prevent the oxidation of the underlying current collector substrate during the anodic deposition process. As a result submicron to micron thick EMD films with good adhesion were deposited on various current collectors. The acidity of the electrolyte solutions was varied depending on the type of the surface coating or current collector used. The mechanism of the EMD film growth and morphology on different substrates was examined. Compatibility of the proposed current collector interface modification for the electrodeposition of conformal thick EMD films on high-aspect ratio microstructures was demonstrated. A method of EMD film conversion to LMO at low-temperature on different substrates was shown as the path toward their application in 3D Li-ion batteries. ispartof: Journal of the Electrochemical Society vol:164 issue:14 pages:D954-D963 status: published

The synthesis of ordered nanocomposite or nanoporous silica thin films by template-assisted sol-gel processes offers interesting applications in various fields including catalysis, sensors, membranes and energy. The electrochemically assisted self-assembly method allows the growth of highly ordered vertically aligned nanoporous silica thin films on conductive substrates. This orientation, optimized for high mass-transport capabilities, is difficult to obtain by classical approaches. The method involves submerging the conductive substrate in a pre-hydrolyzed precursor liquid followed by the application of a cathodic potential, thereby causing the electrogeneration of hydroxide ions. The pH increase in the diffusion layer near the electrode surface catalyzes the sol-gel formation and the result is a silica thin film that grows on the conductive substrate. The addition of cetyltrimethylammonium bromide (CTAB) micelle templates leads to the formation of a highly ordered nanostructure. A fundamental limitation of the method as reported in the literature is that the maximum layer thickness which can be obtained is rather limited due to the formation of aggregate by-products. In our contribution we show that diffusion layer thickness control is essential to obtain aggregate-free layers. Silica formation is catalyzed by OH- formed in the electrode’s diffusion layer, which quickly grows up to hundreds of microns under stationary conditions, thereby leading to composite thin films as well as precipitation of aggregates. By using a rotating disc electrode, the hydrodynamic layer is controlled, enabling aggregate-free film growth over a wide thickness range. Additionally, thin film coatings on high aspect ratio micropillar structures were demonstrated. Parameters such as precursor age, deposition temperature and deposition current were systematically investigated and the deposits were characterized using SEM, ellipsometry, TEM, FT-IR and an electrochemical redox probe. Using these techniques, we demonstrated the controlled growth of aggregate-free, uniform and nanostructured thin films with high mass-transport capabilities and thicknesses of 20 nm up to 15 µm, thereby significantly expanding the range of 50-150 nm as reported in literature. These results are explained using a single hydrodynamic layer model. Figure 1

Welcome to E01: Electrodeposition for Energy Applications 5! Take a moment to listen to welcome remarks from the lead organizer, Philippe Vereecken.

The transformation from liquid-based Li-ion batteries to solid-state Li-metal batteries is a necessary step to achieve beyond energy densities of 1000 Wh/L. However, the commercial widespread application of the solid-state Li-metal batteries has been hindered by several electrolyte constraints, among which narrow electrochemical window and low compatibility against metallic lithium as negative electrode. Among the various solid-state electrolytes, nitrogen doped lithium phosphate glass or LiPON is a well-known material with an excellent electrochemical stability above 5 V and a good compatibility against metallic lithium [1]. However, owing to its low ionic conductivity (~10-6 S/cm), application of LiPON is limited for thin-film batteries in medical implants and various sensor systems. For thin-film batteries, because the path length for Li+ ion diffusion is in the order of few 100 nm or less, low conductivity of LiPON is enough for application. LiPON has also been evaluated as solid-electrolyte coatings on electrode particles as buffer layer between active material and the bulk electrolyte. In a thin-film stack, it is an ideal model system for electrochemical study. Previously, we investigated detailed electrochemistry of RF-sputtered LiPON thin films with different thickness [2]. We demonstrated formation of an electronically insulating LiPON films down to 15 nm with a maximum conductivity of 1×10-6 S/cm. We have also formulated a breakdown mechanism for LiPON layer based on experimental measurements and thermodynamic considerations. In the present work, we investigated LiPON thin-films as artificial solid-electrolyte interphase for lithium plating and stripping on copper current collectors. The stability of 100 nm down to 10 nm LiPON thin-films was evaluated by electrochemical galvanostatic cycling test of Li plating/stripping with carbonate-based electrolyte. The LiPON thin-film with 100 nm showed reversible plating/stripping of Li with an overpotential of only ~40 mV for current density of 0.1 mA/cm2 for over 100 cycles, indicating formation of a uniform Li layer in-between substrate and LiPON without breaking of LiPON layer during the cycles. Furthermore, even with the thickness of only 10 nm, LiPON thin-film demonstrated significant improvement of coulombic efficiency of Li plating/stripping compared to without LiPON layer. In the presentation, thickness-dependence of LiPON on growth behavior of Li will be further discussed. Reference [1] X. Yu, J. B. Bates, G. E. Jellison, Jr., and F. X. Hart, J. Electrochem. Soc., 144 (1997) 524-532. [2] B. Put; P.M. Vereecken; J. Meersschaut; A. Sepúlveda; A. Stesmans, ACS Appl. Mater. Interfaces., 8 (2016) 7060-7069.

To increase the energy densities of batteries beyond 800Wh/L determined by the currently available cathode and anode materials used in combination with liquid type electrolytes, next generations solid-state electrolytes are investigated. Combined with the Li metal anode, they should enable safe (i.e. free of dendrites), long life (i.e. low to no consumption of Li metal during cycling) and high-performance solid-state batteries reaching energy density above 1000Wh/L. Over the last years, an increasing number of studies have been dedicated to the research and development of various classes of solid-state electrolytes. New materials have emerged enriching the diversity of the type of solid-state battery concepts. Indeed, besides the classical sulfidic, oxidic and polymer type solid-state battery systems, several concepts based on hybridization of materials and technologies have been proposed [1, 2]. While obviously the ionic conductivity of the Li-ion conductor is a pre-requisite to enable all solid-state battery, other criteria such as stability and compatibility of electrode materials and their integration in the cell are also needed. Our group recently reported a novel class of nano-composite electrolytes (nano-SCEs) for which ion conductivity values are obtained higher than those seen in conventional liquid electrolytes. These nano-SCEs constitute a nano-porous SiO2 monolith that encloses an adsorbed ionic liquid electrolyte. Different from to so-called ionogel electrolytes – which follow a similar approach in that they confine an ILE in a porous oxide matrix [3] – our electrolytes feature the unique property that the ionic conductivity of the composite ( ) is higher than to that of the ionic liquid electrolyte ( ) [4]. The high ion conductivity and enhancement factor were established by engineering the surface chemistry in the nano-SCE. In this presentation, novel solid-state nano-composite electrolytes are reported having the unique feature of enhanced ion conductivity. Along the pore walls of the oxide matrix, the ionic liquid electrolyte is organizing itself such that “highway” conduction paths are created for fast Li-ion transport. The exact nature of these highway conduction paths strongly depends on the chemistry of the ionic liquid electrolyte. Reference s : [1] Z. Zhang, Y. Shao, B. V. Losch, Y. Hu, H. Li, J. Janek, C. Nan, L. Nazar, J. Maier, M. Armand, L. Chen, Energy Environ. Sci. 2018, DOI: 10.1039/C8EE01053F [2] M. Keller, A. Verzi, S. Passerini, DOI: 10.1016.j.powsour.2018.04.0999 [3] N. Chen, H. Zhang, L. Li, R. Chen and S. Guo, Advanced Energy Materials, vol. 8, p. 1702675, 2018. [4] X. Chen, B. Put, A. Sagara, K. B. Gandrud, M. Murata, J. Steele, H. Yabe, T. Hantschel, M. Roeffaers, M. Tomiyama, Y. Kaneko, M. Shimada, M. J. Mees, P. M. Vereecken, Sci . Adv . 2020; 6: eaav3400

The emerging 3-dimensional integration relies on components such as through-silicon vias (TSVs) and micro-bumps for vertical stacking [1, 2]. In a typical micro-bump fabrication process, a thin Cu seed layer is coated with a thick layer of photoresist. After exposure and development, cylindrical openings are formed in the photoresist layer. Depending on the application, bumps with single or multiple metal layers, one of them typically being Cu, are deposited. The removal of photoresist is followed by wet etch of the Cu seed, revealing individual micro-bumps. While Cu in the ‘body’ of the micro-bump is deposited electrochemically, the Cu seed layer is typically fabricated using physical vapor deposition (PVD). As the plated Cu etches up to 30% faster than PVD Cu [3], the Cu part of the bumps may suffer from significant radial etch before the seed is removed completely. Figure 1 shows the post-etch SEM image of a micro-bump with Cu-Ni-Sn metal stack. For 4 µm micro-bumps plated on a 200 nm Cu seed, the contact area with the pad will be reduced by about 25 % after seed etch. In order to minimize the ‘under-etch’ of the micro-bumps, the thickness of the Cu seed layer should be reduced. However, the reduction of Cu seed layer thickness leads to the well-known ‘terminal effect’ on the wafer scale [4]. Figure 2 illustrates the cross-section of a plating cell. Due to the potential drop along the radial direction, the plating current density decreases from the wafer edge to the wafer center, resulting in the micro-bump height decreasing from the wafer edge to the wafer center. In this study a quick and cost-effective approach was developed to evaluate the micro-bump height uniformity on wafer level. We studied dependency of micro-bump height uniformity on Cu seed thickness using 300 mm wafers and demonstrated the impact of terminal effect on height variation along the radial direction. By using only the experimentally measured i-ηcurve for the kinetics, numerical simulation of the wafer-scale plating uniformity was significantly simplified. As the proposed methodology required no explicit knowledge of the plating bath composition and only involved coupon-scale experiments, it provided a fast and cost-effective way to evaluate the effectiveness of proprietary plating chemistries with respect to wafer-scale height uniformity of micro-bumps. The usefulness of the proposed approach was supported by the good match between simulation results and the corresponding experimental measurement. Although the simulation capability was only demonstrated for Cu, the same approach can be applied to other layers deposited for micro-bumps. The overall uniformity can be readily calculated through summation of all the layers involved. The simulation program can also be modified to address different profile control approaches such as additional current collectors or anodes with modified geometry. References: [1] Y. Civale, D. S. Tazcan, H. G. G. Philipsen, P. Jaenen, R. Agarwal, F. Duval, P. Soussan, Y. Travely, E. Beyne, Die stacking using 3D-wafer level packaging copper/polymer through-Si via technology and Cu/Sn interconnect bumping,” IEEE International 3D System Integration Conference, 2009. [2] R. Agarwal, W. Zhang, P. Limaye, R. Labie, B. Dimcic, A. Phommahaxay, P. Soussan, Cu/Sn microbumps interconnect for 3D TSV chip stacking, IEEE Electronic Components and Technology Conference (ECTC), 858 (2010). [3] Wet etch rate PVD Cu vs ECD Cu is internal imec data for a given specific process. [4] S. Armini, P.M. Vereecken, Impact of terminal effect on Cu plating: theory and experimental evidence, ECS Transactions 25 (2010) 185. Figure 1

A nanocomposite electrolyte composed of a non-volatile ionic liquid, organic Li-salt and porous-inorganic material can be a promising option as a solid electrolyte material. We present a high-rate performance in solid-state lithium metal and Li-ion batteries using a silica-gel solid nanocomposite electrolyte (nano-SCE) made by the sol-gel method with a bis(fluorosulfonyl)imide (FSI)-based ionic liquid. The nano-SCE, composed of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMI-FSI) and Li-FSI confined in the mesoporous silica matrix, exhibits an ionic conductivity of 6.2 mS cm−1 at room temperature. The capacity of the Li-LiFePO4 cell using the EMI-FSI based nano-SCE reaches 150 mAh g−1 at 0.1C and 113 mAh g−1 at 1C, which is higher than that achieved by the other reported batteries that use a similar composite electrolyte. The C-rate performance of the prepared solid batteries is comparable to that of cells with the conventional lithium hexafluorophosphate (LiPF6) electrolyte. Our results show that impregnation of a liquid precursor is an efficient approach for an excellent electrode/electrolyte interface contact in the solid composite electrode as the reaction kinetics at the interface of the active mass and nano-SCE are sufficiently fast, and thus is advantageous compared with the other types of solid electrolytes.

In this study, we apply the economically feasible liquid ALD process to deposit a 2 nm amorphous MnO2 thin-film on our high surface-area 3D Ni nanomesh substrate, which shows a high surface to footprint area ratio (30 cm2:1 cm2 for 1 μm thick Ni nanomesh), and demonstrate its preliminary electrochemical activity as a cathode under N2 and O2. The excellent footprint charge density and faradaic efficiency can be attributed to the catalytic oxygen reduction reaction, followed by Li-intercalation thus forming a hybrid combination of Li-ion and Li-O2 activity, alleviating the detrimental deactivation process of pristine MnO2.