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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).

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

We present a nanomesh material that is widely applicable in a variety of sustainable-applications requiring high surface area electrodes such as batteries, electrocatalytic convertors, fuel cells and hydrogen production. The nanomesh material is a three-dimensional nanowire (metal) grid structure with highly regular internal dimensions. The hexagonally organized vertical nanowires are horizontally interconnected to its three neighboring nanowires. As a result, it combines high porosity with an unprecedented surface-to-volume ratio. For each micrometer thickness, there is a 26-fold increase of available surface area. To visualize this: when filling a volume of a small can of soda, it would remain 75% empty while containing a surface area equal to the size of a football field. On top of that, the internal and external dimensions can be tuned to almost any specification, making it potentially compatible with a multitude of application requirements. The material can be quite easily manufactured through cheap anodization and electroplating processes. First, a mold is formed by anodization of aluminum foil as for the well-known Anodic Aluminum Oxide (AAO) process. The secret for the regular horizontal perforation at the nanoscale lays in the controlled doping of the aluminum metal with copper. The resulting 3D nanoporous structure acts as a mold in which a large variety of metal (compounds) can be electrodeposited. After consecutive chemical dissolution of the alumina template, a mechanically rigid nanomesh structure remains. The nanomesh can be detached from the substrate as a free-standing flexible nanomesh foil. We will show that a 3 micron thick nanomesh easily outperforms a 400 micron thick foam in surface area and electrochemical performance for hydrogen evolution reaction.

Solid-state batteries are considered to reach the high energy densities needed for our emerging sustainable energy society. Recently, solid electrolytes (SE) with ion conductivities equalling or even surpassing that of liquid electrolyte solution are already available. However, the rigid nature of the SE powder materials caused poor interface contacts between individual electrolyte particles and with the active electrode particles. To solve this issue, a solid composite electrolytes (SCE) composed of ionic liquid (IL) and Li-salt supported on a porous inorganic matrix have been explored. [1] These composite electrolytes were prepared by sol-gel methods. The low viscous liquid sol-gel precursor can be impregnated into the porous powder electrodes and gelled in the electrodes, thus resulting in good interfacial contacts between the active electrode and the electrolyte. Further drying and curing make the composite electrodes compact, which results in high energy density. However, the ionic conductivity was typically lower than that of pure ionic liquid electrolyte (ILE) used in SCE. This is due to the increase of the IL viscosity in the nano-sized pores, which is known as IL confinement effect. [2] To overcome this problem, our group developed a new type of SCE with water-based sol-gel process, which is named “nano-SCE”. [3] We demonstrated systematic promotion of the Li-ion conductivity by controlling the IL molecules ordering on the silica pore surface with an functional adsorbed ice-water layer. The strong hydrogen bonding between the ice-water and the IL molecules induces the ordering of IL anions and cations on the silica surface. This interfacial interaction weakens the association between the Li-ion and its anion, thus enhancing the ion conductivity well beyond that of pure ILE. Further control of the porous structures will make the conductivity go higher, and thus can be a breakthrough technology to develop the high-conductive SEs. For designing the ideal porous structure and control the synthesis process of nano-SCEs, the silica nanoporous structure must be clarified. However, so far, it is difficult to characterize the silica matrix structure because the silica structure collapsed by the surface tension when the ILE is removed by rinsing with solvents such as ethanol and acetone and after drying both in ambient and vacuum. In this paper, we applied the CO2 supercritical drying method to extract ILE. A careful drying above CO2 super critical point enabled to keep the original structure avoiding the collapse due to the surface tension. The porous silica matrix was successfully obtained without damage or shrinkage. The porous structures of nano-SCEs with different IL/SiO2 material ratio were analysed by SEM, TEM, N2 adsorption/desorption and positron annihilation spectroscopy (PALS) technique. SEM and N2 adsorption/desorption analysis revealed that there are > 10 nm pores distributed, and their size and number were increased with ILE/SiO2 molar ratio. Our measurements confirmed that the IL confinement effect, that is, the conductivity of nano-SCE with smaller pore-size was lower due to the increasing of the viscosity of ILE filled in pores. In contrast, the surface area was decreased with ILE/SiO2 ratio due to the reduction of 5 nm size pores, which is characterized by PALS analysis. From the relationship between surface area and surface enhancement factor (sice-water/sdried) in Fig. 1, the surface conduction was verified to be increased with the surface area, indicating the conduction promotion effect was clearly related with the surface chemistry. A nano-SCE with higher conductivity can be realized by designing the pore structure with high surface area and optimized pore size. [1] J. Le Bideau, J. B. Ducros, P. Soudan and D. Guyomard, Solid-state electrode materials with ionic-liquid properties for energy storage: The lithium solid-state ionic-liquid concept, Adv. Funct. Mater., 2011, 21, 4073–4078. [2] S. Zhang, J. Zhang, Y. Zhang and Y. Deng, Nanoconfined Ionic Liquids, Chem. Rev., 2017, 117, 6755–6833. [3] P. M. Vereecken, X. Chen, K. B. Gandrud, B. Put, A. Sagara, M. Murata, M. Tomiyama, Y. Kaneko, M. Shimada, J. Steele, M. Roeffaers, M. Debucquoy and M. J. Mees, "Mechanism Analysis of Enhanced Li-Ion Conductivity in Mesoporous Silica-Based Solid Nano-Composite Electrolytes," ECS Meeting Abstracts, 2018, 470, MA2018-02. Fig. 1 The relationship between surface enhancement factor of nano-SCEs and BET surface area of porous silica matrix. The surface enhancement factor was defined as the ratio of the conductivity with and without functional ice-water layer on the silica surface. Porous silica was obtained by removal of ILE from nano-SCE with ethanol soaking for 36 hours at 40 oC and subsequent drying by CO2 super critical dryer. Figure 1

Over the last two decades, post lithium ion battery chemistries with even higher power and energy density, compared to those of conventional lithium ion batteries with intercalation hosts, have been widely researched for application in large scale energy storage. Among various candidates, Li-O2 battery is one of the most promising alternative chemistries, having a theoretical energy of 3505 Wh kg-1 via plating and stripping of Li2O2 with an average working potential of 3 V vs. Li+/Li. However, Li-O2 battery often shows insufficient areal capacity due to the insulating properties of thick Li2O2 layer. Previously, our group reported the fabrication of a novel 3.3 μm thick 3D Ni nanomesh current collector, which shows excellent surface area to geometric footprint area ratio (100 cm2/1 cm2) and high theoretical porosity (76 %) with systematically controlled nanowire thickness via anodization of aluminum alloys (Fig. 1) [1, 2]. Thanks to its unique properties, the 3D Ni nanomesh qualifies as an excellent current collector candidate for reversible Li2O2 plating and stripping performance over large surface area with the enhanced areal capacity. In this study, we aimed to introduce amorphous carbon, one of the most studied electrode materials for Li-O2 battery, as a coating material for 3D Ni nanomesh via low temperature PECVD technique. To investigate its potential application as an electrode for Li-O2 battery, the galvanostatic charge and discharge profiles of glassy carbon and carbon-coated 3D Ni nanomesh are recorded with the discharging current rate of 0.1 mA cm-2 and the balanced charging current rate of 0.05 mA cm-2 under pure O2 atmosphere. During the preliminary electrochemical measurement, we observed that the carbon-coated 3D Ni nanomesh showed greatly increased discharge and charge areal capacity than those of glassy carbon (102 and 563 times higher than those of glass carbon). In addition to the above-mentioned findings, the ex-situ STEM images of carbon-coated 3D Ni nanomesh after charging and discharging processes will further be discussed. References [1] J. Vanpaemel, A. Abd-Elnaiem, S. De Gendt, and P.M. Vereecken, J. Phys. Chem. C, 2015, 119, 2105-2112. [2] S.P. Zankowski and P.M. Vereecken, ACS Appl. Mater. Interfaces, 2018, 10, 44634-44644. Fig. 1. Brief description of 3D Ni nanomesh fabrication process and SEM images of as-prepared 3.3 μm thick 3D Ni nanomesh current collector template. Figure 1

The key figures of merit for batteries are Energy density, charging time (C-rate) and cycling Life time. In this invited talk we will focus on the application of continuous closed thin films as artificial interfaces in large capacity batteries or for the fabrication of functional battery components in micro-batteries. We will deal mostly with the perspective of device performance where the ALD and MLD processes merely provide the films and enable their ultrathin, continuous and conformal nature. Nanoscale film thickness allows for low interface and cell resistance even when the materials themselves are poor conductors. For example. LiPON (N-doped Li3PO4) is a solid electrolyte interesting because it is stable against metallic lithium but, because of its poor ionic conductivity (-6 S/cm) only practically useful for thicknesses under few hundred nanometers. Even further, materials which are not solid electrolytes by their own merit (e.g. TiO2) still have ion-transparent properties up to several tens of nanometer and can be used as ion transparent artificial interfaces in contrast to alumina which is an insulator for Li-ions. For coating of individual particles, ideally coatings which have both electronic and ionic conducting (or transparent) properties. Doping is one approach to enhance either conductivity. When scaling down of the film thickness also finite size effects have to be considered, for example, the thickness of the electrical double layer, diffusion layer thickness and the electric field over the dielectric. ALD and MLD can be used also to fabricate functional nanomaterials; i.e. by harvesting nanoscale effects. For example, nanocomposite solid electrolyte films of a few tens of nanometers were fabricated by a combination of MLD of inorganic-organic hybrid alucone thin-films, etching the organic fraction in water and functionalization by ALD of Li2CO3 and Li3PO4. For the first time, enhanced ion conductivity is shown by harvesting the enhanced ion conductivity at oxide/ion conductor interfaces. Finally, volume changes during charge and discharge are limiting the cycle life-time of batteries, especially for rigid solid-state batteries. Also ALD thin-films suffer from the mechanical strain and the benefits of the “closed” protective film are lost. Therefore, MLD of hybrid organic/inorganic coatings is explored to enable more elastic coatings for improved cycle life time.

Recently, our group reported a novel solid-state electrolyte material which is constituted of a nano-porous SiO2 monolith and an ionic liquid electrolyte (ILE) which occupies the pores. The unique feature of this solid nano-composite electrolyte (nano-SCE) is its ion conductivity which is higher than that of the ILE itself [1]. Here, we report a direct measurement of this enhanced ion conductivity by measuring the ion conductivity of a thin-film ILE on a planar SiO2 substrate. The enhanced ion conductivity is directly measured with interdigitated electrode arrays deposited on a planar SiO2 substrate, as shown in Figure 1. By depositing a thin-film ILE film on these electrodes, the impedance response of the ILE/SiO2 interface could be measured by impedance spectroscopy (IS). The ion conductivity on the ILE/SiO2 interface could subsequently be quantified by analysis of the equivalent circuit model and by measuring the ILE film thickness. The ILE film thickness is scaled down to the nanometer regime. This is the first time that such thin ILE films could be deposited using liquid processing techniques. The enhanced ion conductivity is revealed when the ILE film thickness is reduced to 20 nm thicknesses and below. The ion conductivity of the ILE films with a thickness around 80 nm have a similar conductivity compared to the bulk ILE. Enhanced ion conductivity along interfaces has been observed before and is typically referred to as heterogenous doping [2]. The mechanism that governs the enhanced conductivity in the nano-SCE are similar to those described by heterogenous doping. However, the ion conductivities measured in this work are many times higher compared to those reported before. In conclusion, for the first time ILE thin-films with thicknesses in the nanometer regime are deposited with liquid processing. Moreover, the ion conductivity at the ILE/SiO2 interface could be quantified and showed an increased conductivity compared to the bulk ILE value. References [1] P. M. Vereecken, X. Chen, K. B. Gandrud, B. Put, A. Sagara, M. Murata, M. Tomiyama, Y. Kaneko, M. Shimada, J. Steele, M. Roeffaers, M. Debucquoy and M. J. Mees, "Mechanism Analysis of Enhanced Li-Ion Conductivity in Mesoporous Silica-Based Solid Nano-Composite Electrolytes", ECS Meeting Abstracts, vol. 470, pp. MA2018-02, 2018. [2] N.F. Uvarov, “Composite Solid Electrolytes: Recent Advances and Design Strategies”, J. Solid State Electrochem., 15 (2), 367–389, 2011. Figure 1

Solid electrolytes with a Li-ion conductivity exceeding 1 mS/cm are a prerequisite to enable solid-state Li-ion batteries. In solid composite electrolytes (SCEs), the interface between an ionic conductor and a dielectric matrix can be engineered to enhance this ionic conductivity. The solid composite electrolyte developed at imec contains a monolithic, mesoporous, silica matrix filled with a non-volatile ionic liquid and an organic Li-salt. This composite material is made by a sol-gel process, similar to that for ionogels, with that difference that no acid is used but water. The resulting aqueous gel is carefully dried from water and solvents, resulting in the solid nano-composite electrolyte where the ionic liquid and the lithium salt are confined in the pores and channels of the mesoporous silica matrix. The slow sol-gel reaction and drying allows the adsorption of an ordered molecular layer on the fully hydrolyzed silica surface. Interfacial ice layers induce strong adsorption and ordering of the ionic liquid molecules through H-bonding, rendering them immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate results in solvation of the Li+ ions for enhanced conduction. We demonstrate that when the silica surface is appropriately hydroxylated, the Li-ion conductivity of the nano-SCE can be several times higher than that of the pure ionic liquid electrolyte itself. By this process solid nano-SCEs with conductivities between 0.4 and 8 mS/cm have been synthesized, using TFSI- and FSI-based ionic liquid electrolytes. Battery cells can be made by impregnating the liquid sol-gel precursor solution inside the powder-based electrodes, very similar to the application of liquid electrolytes. As our precursor solution does not contain corrosive acid compounds such as formic acid, which is typically proposed as catalyst in literature recipes, we can deposit the solution directly on and into the porous electrodes. The sol-gel reaction and drying take place in-situ inside the electrodes allowing the nano-SCE to fill the empty spaces and providing an all-around contact with the active material. As such, we are able to realize functional solid-state cells with the TFSI- and FSI-based nano-SCE. Not only low voltage cells with LFP and LTO electrodes, but also high voltage cells with NCA and Li metal or Li alloy electrodes are demonstrated (Fig 1a and b). C-rate and cycling performance of these solid-state cells with the nano-SCE are given. Figure 1

The transition to solid-state Li-ion batteries requires solid electrolytes with Li-ion conductivity exceeding 1 mS/cm. Solid composite electrolytes or SCEs consisting of an ionic conductor and a dielectric matrix offers an elegant strategy to enhance the ionic conductivity of electrolytes by engineering the interface conduction. Composite electrolyte materials with inorganic oxide matrixes such as silica, alumina or titania with, for example, inorganic or polymer electrolytes have indeed shown enhancements in ion conductivity, however, the total ion conductivity was still well below 1mS/cm due to the low conductivity of the starting individual electrolytes used. Also composites of mesoporous oxide matrix filled with non-volatile ionic liquid electrolyte (ILE) fillers have been explored as solid electrolyte option. The advantage is that ILE can already have quite high ionic conductivity as individual electrolyte component. However, simple confinement of an electrolyte solution in nanometer size pores results in lower conductivity as its effective viscosity increases. The decrease in ion conductivity is expected the worse for mesoporous channels (~10nm in diameter) where the ionic liquid can even turn solid. To achieve higher ion conductivity, interface enhancement has to exceed the decrease in conductivity by confinement. Monolithic nanoporous silica with ILE confined in the porous structures, also named “ionogels” have shown ion conductivities approaching that of the ILE bulk conductivity, indeed, indicating the presence of interface enhancement in these materials. However, so far, the ionic conductivity of the confined ILE in the nanoporous oxide has never exceeded that of the ILE conductivity itself. These ionogels are fabricated by a sol-gel process e.g. by hydrolysis-condensation reaction with tetra-ethylorthosilicate (TEOS) precursor and typically formic acid where the ILE is added in the solution as the template for the silica to grow around. In this paper we demonstrate that the Li-ion conductivity of nano-composites consisting of a mesoporous silica monolith with an ionic liquid electrolyte as filler can be several times higher than that of the pure ionic liquid electrolyte itself when the silica surface is appropriately hydroxylated. Interfacial ice layers induce strong adsorption and ordering of the ionic liquid molecules through H-bonding rendering it immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate results in solvation of the Li+ ions for enhanced conduction. The existence of an interfacial mesophase layer is proven by Infrared and Raman spectroscopy. Higher Li-ion diffusion coefficients for the nanocomposite compared to the pure ionic liquid electrolyte reference is shown by Pulsed-Field-Gradient NMR. The principle of ion conduction enhancement is generic and could be applied to different ion systems. The concept also allows for further (nano)engineering towards specific properties of ion conduction, transport number, electrochemical window, safety and cost for future battery cell generations. The nano-SCE was fabricated in a similar way as the ionogels: a single-step sol-gel process with a TEOS precursor and with the ionic liquid electrolyte in the homogeneous precursor solution, except we did not use formic acid but water. We will focus on systematic study of our nano-SCE model system with (N-butyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl) imide ([BMP]TFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI). Figure caption: Ball-and-stick model for the adsorbed mesophase layer on silica with an interfacial ice water layer. The strong H-bonding between TFSI anions and OH surface groups result in polarization of the adsorbed ILE layer and the dissociation of Li+ from TFSI- anion. The free Li-ions can move faster through the liquid-like layer just above the adsorbed mesophase layer resulting in enhanced ion conductivity. Figure 1

The transition to solid-state Li-ion batteries requires solid electrolytes with Li-ion conductivity exceeding 1 mS/cm. Solid composite electrolytes or SCEs consisting of an ionic conductor and a dielectric matrix offers an elegant strategy to enhance the ionic conductivity of electrolytes by engineering the interface conduction. At imec, we have developed a ternary nano-composite electrolyte composed of a non-volatile ionic liquid and organic Li-salt confined in mesoporous silica. The material is made by a one-step sol-gel process whereby the ionic liquid acts as template for the hydrolysis and polycondensation reaction leading to an aqueous gel. The process is similar to that for ionogels with that difference that no acid is used but water. The water and solvents are subsequently carefully removed to form a solid nano-composite electrolyte. The slow sol-gel reaction and drying allows the adsorption of an ordered molecular layer on the fully hydrolyzed silica surface. In this way, several nano-SCE with conductivities between 0.3 and 3 mS/cm have been synthesized, using TFSI-based ionic liquid electrolytes (ILE). We demonstrate that the Li-ion conductivity of nano-composites consisting of a mesoporous silica monolith with an ionic liquid electrolyte as filler can be several times higher than that of the pure ionic liquid electrolyte itself when the silica surface is appropriately hydroxylated. Interfacial ice layers induce strong adsorption and ordering of the ionic liquid molecules through H-bonding rendering it immobile and solid-like as for the interfacial ice layer itself. The dipole over the adsorbate results in solvation of the Li+ ions for enhanced conduction. We will show that the ice layer is electrochemically inactive, in contrast with water-in-salt electrolytes. Functional cells with LFP, LMO and NCA cathodes with Li, Li-alloy and LTO electrodes are demonstrated. As the ice-water layer was confirmed to be electrochemically inactive, it doesn’t cause degradation during cycling of the batteries. Furthermore, damage to the active electrode materials is avoided as our water-based sol-gel precursor does not contain corrosive acid compounds such as formic acid typically proposed as catalyst in literature. The cells are made by impregnation of the liquid sol-gel precursor solution inside the porous electrodes, very similar to how liquid cells are made. The sol-gel reaction and solidification is done in-situ inside the electrodes. By careful drying, the nano-SCE contracts the electrodes together and the electrolyte fills the spaces in the porous electrodes, providing an all around contact with the active material. As such, we have shown high capacity cells at C-rates up to 0.5C. C-rate and cycling performance of the solid-state cells with nano-SCE is shown. Figure caption: Functionality of nano-SCE as Li-ion electrolyte up to 4.3V: galvanic charge/discharge curves of Li/nano-SCE/ LiMn2O4 cell for 5 cycles at each C-rate of 1 C, 5 C, and 20 C. Figure 1

Solid electrolytes are considered a necessary step for Li-ion ions to surpass the practical limit of 800Wh/L. Next to safety aspects, solid-state electrolytes could enable more compact batteries thus increasing their volumetric storage capacity. A main driver, however, is the potential for solid-electrolytes to increase the electrochemical window to accommodate high voltage positive electrodes (5V cathodes) and stability against metallic lithium as negative electrode. As such, solid-state batteries could enable high energy density through increased cell voltage. Numerous Li-ion conducting solids are known today, however most do not have the broad electrochemical window and stability against lithium yet. Nitrogen doped lithium phosphate glass or LiPON is a well known solid electrolyte material attributed with excellent electrochemical stability above 5V and stable against metallic lithium [1]. However, due to its limited ionic conductivity (~10-6 S/cm) it is only applicable in thin-film batteries for use for medical implants and various sensor systems. It 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. In this paper, we report on the electrochemistry of RF-sputtered LiPON thin films and studied the out plating of lithium until break down. The LiPON thin-films had ionic conductivities ranging between 1x10-7 and 1x10-6 S/cm [2]. The decomposition potential was calculated from basic thermodynamic quantities and was linked to current-voltage (I-V) measurements with great consistency. The reported I-V measurements were conducted on metal-electrolyte-metal or MEM structures. The decomposition of LiPON was shown to occur at a potential of 4.8 V and proceeds in a diffusion limited way. It could be shown that LiPON breakdown is rather determined by the time needed for the decomposition reactions to complete, rather than being solely driven by the electric field. From the diffusion limited Li-ion current, the Li+ diffusion coefficient was extracted and found to be 2x10-11 cm2/s. This value is in excellent agreement with literature reports [3]. Ultimately hard breakdown was shown by TOF-SIMS imaging experiments and occurs through the formation of metallic lithium filaments. In the present work, we have for the first time formulated a breakdown mechanism for LiPON layers based on experimental measurements and thermodynamic considerations. The presented work provides a detailed evaluation of a solid electrolyte's breakdown and stability using I-V measurements. As such these measurements allow determination of ion transport phenomena as well as of the electrochemical stability window. It can also provide insight in the breakdown mechanism of RRAM devices. References [1] J. Bates; N. Dudney; G. Gruzalski; R. Zuhr; A. Choudhury; C. Luck; J. Robertson, Solid State Ionics, 52-53 (1992) 647-654. [2] B. Put; P.M. Vereecken; J. Meersschaut; A. Sepúlveda; A. Stesmans, ACS Appl. Mater. Interfaces., 8 (2016) 7060-7069. [3] X. Yu; J. Bates; G. Jellison; F. Hart, A stable thin-film lithium electrolyte: Lithium phosphorus oxynitride. J Electrochem Soc., 144 (1997), 524-532.

Solid electrolytes with Li-ion conductivity higher than 1 mS/cm are required for the development of high capacity solid-state Li-ion batteries. In the past decade, several studies were done on the improvement of ion conductivity in composite materials by employing interface enhanced ion conduction at inorganic oxide surfaces such as silica, alumina or titania added to, for example, inorganic or polymer electrolytes. Also, composites of nanoparticles and mesoporous microparticles mixed with ionic-liquid electrolyte (ILE) have been proposed to promote the Li-ion conductivity along the particle or pore surface. However, so far the ionic conductivity was always lower than that of the original ILE due to the interrupted ionic paths by percolation from particle to particle. Monolithic nanoporous silica with ILE confined in the porous structures, also named “ionogels” have shown ion conductivities approaching the ILE bulk conductivity. These ionogels are fabricated by a sol-gel process e.g. by hydrolysis-condensation reaction with tetraethylorthosilicate (TEOS) precursor and typically formic acid where the ILE is added in the solution as the template for the silica to grow around. So far, the ionic conductivity of the confined ILE in the standard nanoporous oxide has never exceeded that of the ILE conductivity itself. By introduction of a surface functional group, an ion conductivity slightly higher than that of the bulk ILE was obtained, showing that surface interactions can be used to tailor the ion conductivity in these materials. In this paper, we show nanocomposite electrolyte (nano-SCE) materials with enhancements in ion conductivity exceeding 200% and ion conductivities up to 3mS/cm. The nano-SCE was fabricated in a similar way as the ionogels: a single-step sol-gel process with a TEOS precursor and with the ionic liquid electrolyte in the homogeneous precursor solution. The processing conditions were such that molecular ordering of the IL molecules was favored and the adsorbed interface layers provided free Li+ ions for enhanced Li-ion conductivity along the surface. Figure 1 shows the ion conductivity of the obtained solid pellet for a model system with (N-butyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl) imide ([BMP]TFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI). Importantly, the graph shows the difference between an ionogel material with a confined ILE and our nano-SCE. For the ionogels, the conductivity versus temperature behavior is the same as that for the bulk ILE, albeit with lower conductivity due to the fraction of inactive silica. Both the ionogel composites and the bulk ILE show the melting point of the ILE with a lower conductivity for the solid phase. For the nano-SCE, however, the melting point is no longer observed and the slope indicates that the formed nanocomposite material has a lower activation energy for diffusion than that of the bulk ILE and of the ionogels with the confined ILE. In this paper, we propose a mechanism for the observed behavior based on adsorption of the TFSI anion and subsequent molecular ordering and layering of the BMP cation and TFSI anions. The adsorbed layer has a solid-state like character and is therefore named as the mesophase layer. We will present experimental evidence for the interface interactions from FTIR spectra. Raman measurements confirm that the fraction of free Li+ ions increases in the composites. NMR measurements show that similar enhanced surface diffusion happens at nanoparticle systems but the interconnected pores in the SCE provide continuous pathways throughout the solid electrolyte nanostructure, ensuring the full effect of the surface enhancement is observed in contrast to analogous nanoparticle-ILE composites. To demonstrate the functionality of the nano-SCE as Li-ion electrolyte, cells with LFP cathodes were prepared. A technologically distinguishing feature of the nano-SCE, as for ionogels, is that it is applied as a liquid – via wet chemical coating – and only afterwards is converted into a solid. That way it is perfectly suited to be casted into dense powder electrodes where it fills all cavities and makes maximum contact, just as a liquid electrolyte does. A cell with 200Wh/L at 0.5C is demonstrated by casting of the nano-SCE precursor solution into the electrodes. The possibility of wet application of the nano-SCE precursor makes this technology also compatible with current Li-ion battery fabrication processes. Fig. 1 Temperature dependence of the ion conductivity for the ionic liquid electrolyte (ILE) with Li-TFSI and BMP-TFSI, for two silica ionogels with changing ILE content (x refers to the ratio of ILE to silica) and for our nano-SCE showing different behavior between the nano-SCE and the ILE it contains as a result of the mesophase layer formed on the silica pore surface. Figure 1

Electrodeposition is a prevailing method in fabrication of Cu interconnects in microelectronics due to its ability to fill complex structures having a wide range of critical dimensions. A typical acidified Cu electrolyte contains a number of additives, organic and inorganic species in ppm amounts, with a specific role in the plating process. The additives in Cu plating have been extensively studied in the past couple of decades, and grouped according to their role in filling/creating features for microelectronics applications. This categorization is not a uniform one, and it might differ from author to author. In one popular convention, organic additives in the so-called three-component plating bath are named accelerator, suppressor and leveler, with their names hinting at how they influence Cu deposition. Ultimately, it is thanks to these additives that defect-free Cu features ranging from tens of nanometers to hundreds of micrometers can be economically fabricated. However, it is not enough to successfully fill a given single feature. The same has to be done for all the features on a 300 mm wafer, and then performed reproducibly over and over again. So, one needs to monitor the state of the electrolyte, i.e. of all the bath constituents, and either replace or replenish the electrolyte when the need arises. Additives could also have a strong influence on the physical properties of the deposit and therefore have a strong influence on the post-plating processing results. An additive that promotes void-free deposition of Cu structures in the end might not be used in a production line if it creates issues in the processing steps following electrodeposition. In our presentation we focus on a number of specific examples showing the effect of additives on nucleation and growth of Cu, propagation of Cu fronts on resistive substrates, post-plating processing, and their use in substrate surface modifications. A closer look is taken into in situ microscopic and electrochemical techniques and their use in studies of electrochemical nucleation and growth of Cu. We discuss advantages and drawbacks of potential step and galvanostatic deposition techniques in determining nucleation and growth parameters, and selection criteria for additive sets for a given plating task. We demonstrate that substrate surface modifications prior to plating could help simplify bath composition, i.e. eliminate need for some additives in the electrolyte, or improve the filling performance of the given plating bath. We also give examples of additives that promoted void-free filling of features but also influenced physical/mechanical properties of the final product in such a way that rendered it unusable in a specific application.

Porous and electrically conductive materials having extended surface area are attractive for wide range of applications, such as catalysis, sensing or energy storage. High surface area of the material provides higher reaction rates and lower electrode resistance. For instance, metallic sponges such as Raney nickel, having surface areas up to 100 m2/g show high catalytic activity during water electrolysis or heterogenous organic synthesis. However, low porosity and small average pore diameter limit their application for devices utilizing additional functional layers (e.g. active electrode materials in batteries). On the other hand, highly porous nickel foams are commonly used as current collectors for Ni- and Zn-based batteries, where sufficient loading of active material can be realized inside of the porous network. However, the surface area of such foams is more than three orders of magnitude smaller than that of the metallic sponges, lowering the potential for e.g. high rate operations of their parent devices. In this talk we will present a recently developed material composed of interconnected nickel nanowires of controllable diameter and distance. The nanowires assembly offers a unique combination of high surface area of metallic sponges and high porosity of metallic foams. The material is conveniently obtained by cheap and up-scalable electrochemical techniques. The unique nanostructural properties of the interconnected nanowires allow for high flexibility of the material and applications in e.g. flexible electronics or wearable sensors. As a proof-of-concept, we will present the performance of our structure for hydrogen generation during water electrolysis. Compared to nickel foams, the high surface area interconnected nanowires offers significantly higher hydrogen evolution currents, showing their potential for next generation electrolyzers and energy devices. Figure 1

A pressing issue in flip-chip and stacked integrated circuit (SIC) technology is the breakdown of microbumps over time. These microbumps are the physical and electrical connections between the chips. They consist out of Cu stages on both chips which are typically soldered together by Sn. Due to diffusion and electromigration, Cu and Sn form two intermetallic phases of which Cu3Sn induces microvoids at the Cu3Sn/Cu interface causing in turn breakdown of the microbump. Chemical modelling shows that a CuNi alloy, with an approximate 9:1 Cu:Ni ratio, together with Sn doesn’t form the Cu3Sn intermetallic compound thus tremendously improving the stability of the microbumps, and therefore the chip. By far the most feasible method to manufacture microbumps is galvanostatic electrochemical deposition. However, electrochemical CuNi co-deposition from a single deposition bath requires current densities higher than the limiting current density of copper causing rough, uncontrolled dendritical growth of Cu. Existing CuNi baths are citrate based but citrates can corrupt other features of the chip manufacturing process. In this work the possibility of smooth, solid solution electrodeposition of CuNi in a 9:1 ratio using benzotriazole (BTA) is investigated. Benzotriazole is a well-known corrosion inhibitor for copper. Here we show that BTA has a tremendous potential for suppressing Cu2+ reduction and limiting the uncontrolled mass-transfer limited Cu growth. First we demonstrate with a RDE voltammetric investigation, together with viscosimetry, the effects of the combination of an existing CuSO4 and a NiSO4 bath on Cu2+ reduction. Then, we introduce BTA and show the large difference between the working of BTA in the combined bath and in a CuSO4 only bath. Later, we improve the working of BTA by increasing the pH thus defining a parameter window for which we’re able to deposit CuNi with a maximum suppressing effect of BTA. CuNi deposits on metal pellets with a Cu substrate layer are investigated by SEM and EDX to evaluate the morphology and elemental composition of the deposit. We were able to demonstrate the change in CuNi morphology upon increasing the BTA concentration from 0 to 1000 ppm. No distinction could be made in Cu or Ni rich areas over different deposit areas indicating that we’re able to deposit CuNi as a solid solution. Figure 1

Three-dimensional (3D) architectures for high-performance energy storage devices has been the subject of ongoing investigations targeting their integration in autonomous microelectronic systems. In this paper we present a route toward the realization of high capacity LiMn2O4 (LMO) cathode films for 3D thin-film lithium-ion batteries. One of the critical steps in the process is the electrodeposition of MnO2 coatings also known as electrolytic manganese dioxide (EMD) films. The main challenges of depositing thick enough EMD films directly on the current collector often lay in achieving a good film adhesion and preventing oxidation of non-noble current collectors such as TiN and Ni. Indeed, whereas EMD is typically used as powder for primary MnO2 based batteries and thus delamination from the current collector is desired, well adherent films are required for 3D thin-film batteries. To improve the adhesion of the EMD films we modify the surface of the current collector by means of nanometer thin 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 adjusted depending on the type of the surface coating or current collector used. The mechanism of the EMD film growth and morphology on different substrates will be discussed. Compatibility of the proposed current collector interface modification for the electrodeposition of conformal thick EMD films on high-aspect ratio microstructures was demonstrated. Finally, conversion of the EMD to LMO films is shown at low enough temperatures to be compatible with the underlying substrates. The functionality and high rate performance of the 3D LMO electrodes in Li-ion cell is demonstrated. Figure: Electrolytic manganese dioxide (EMD) films coated conformally on high aspect ratio pillar arrays for 3D thin-film batteries. Figure 1