Anthony Valero

While playing a pivotal role in battery performance, affecting energy density, cycling life, and safety, the anodic current collector of lithium‐ion batteries (LIBs) is largely overlooked in the literature. Copper, the dominant material for anode current collectors, contributes to approximately 8.1% of the battery weight yet does not participate in energy storage, limiting overall energy density. Reducing weight and thickness of copper foils optimizes the gravimetric energy density of LIBs, but challenges in processability hinder the production of thinner foils. This study presents a novel fabrication method to integrate multi‐walled carbon nanotubes (MWCNTs) inside copper to potentially develop a lightweight, thin, and efficient current collector. The composite is fabricated by coating MWCNTs with polydopamine (PDA), spray‐depositing onto an industrial support layer, and infilling the porous nanostructure via copper electroplating. This process enables the production of composite foils with surface areas up to 400 cm ² —potentially addressing industry needs for scalable, high‐performance current collectors—and achieves a thickness of 4.5 µm and density of 6.4 g cm ⁻³ . Moreover, electrochemical performance of the material as anode current collector in half‐cell battery architecture showed improvements in gravimetric capacity of up to 7.3%, with stable cycling and efficiency.

Ces dernières années, l’électronique portable connait un véritable essor, et envahit notre environnement. Le progrès technologique dans le domaine de la microélectronique a permis la réduction conséquente des dimensions des composants électroniques et ouvert des possibilités de mise en réseau et de contrôle jusqu’alors impossible. La question de l’alimentation en énergie est primordiale pour ces réseaux et leur déploiement n’est possible à condition de garantir leur autonomie énergétique. La production autonome d’énergie est souvent privilégiée pour que les microsystèmes soient capables de s’alimenter librement en énergie d’origine mécanique, thermique ou solaire. De telles sources de production restent intermittentes et c’est en miniaturisant les dispositifs de stockage que leur autonomie réelle leur sera envisageable. Pour répondre à ces besoins en sources d’énergie stables et miniaturisables, des micro-batteries ont été développées en parallèle des progrès conséquents du domaine des accumulateurs électrochimiques secondaires. Les micro-batteries souffrent néanmoins de limitations intrinsèques qui se voient exacerbées à échelle micrométrique. Elles se voient donc peu à peu remplacées ou combinées ces dernières années avec des unités de stockage de type supercondensateur désigné sous le terme « micro-supercondensateur » (souvent abrégé MSC) car utilisé à l’échelle microscopique. Ces travaux de thèse proposent de confronter une solution pour micro-supercondensateurs, les nanostructures de silicium aux nouveaux enjeux du stockage de l’énergie. Un état des lieux de la technologie sera tout d’abord proposé avec la mise en évidence de faiblesses majeures. Une étude électrique fondamentale permettra ensuite de comprendre le fonctionnement d’une protection électrochimique mise en place historiquement. Les nanostructures de silicium seront ensuite ouvertes au fonctionnement en électrolyte aqueux, l’une de leur faiblesse principale. Ces avancées permettront la résiliation d’un matériau composite capable de performances capacitives jamais atteintes pour un polymère conducteur. Enfin, la collaboration avec le groupe Elkem Silicon Materials permettra de préparer cette technologie aux nouveaux enjeux du stockage en micro-dispositifs avec l'augmentation substantive des capacités de production disponibles à l'échelle laboratoire.

Up to now, copper is an essential material for lithium-ion battery industry as preferential candidate for anode current collectors due to its high electrical conductivity, low price, and electrochemical stability in the working potential range of the anodic electroactive materials. However, such component, accounting for 8.1% of the battery total weight, does not participate in any energy storage processes. [1] Thus, the trend in this industry is to decrease the weight as well as the thickness of the collector foil to optimize the gravimetric energy of the whole lithium-ion battery system. It is therefore of interest to explore the development of lighter current collectors with equal/improved mechanical and electrical properties. Nanocarbon materials such as Multi-Wall Carbon Nanotubes (MWCNTs) and Single-Wall Carbon Nanotubes (SWCNTs) display a combination of performances, namely high electrical conductivity, low density and high mechanical stability, of a high interests to be combined with copper as innovative lightweight current collectors. Such nanocarbon/copper composite represents a valid alternative to foster the rapid change the battery technology is undergoing. In 2013, Subramaniam et al. [2] reported the fabrication of a Copper /Carbon nanotubes (Cu-CNTs) composites with a similar specific conductivity than copper and an ampacity increased by two orders of magnitude. Moreover, Arai et al. have shown, by electrochemical impedance analysis, that MWCNTs additive in a copper matrix can serve as preferential electron conduction pathway inside a Lithium-ion battery anode. [3]. Nanocarbon/copper composite therefore represents a valid alternative to foster the rapid change the battery technology is undergoing. Recently, a new promising and scalable way to fabricate nanocarbon/copper composite has been demonstrated by our team. The process involved the coating of MWCNTs by a dispersing agent, namely the Polydopamine biopolymer, their spraying, and finally the electrochemical plating of metallic copper inside the porosity of the MWCNTs network.[4] The present work exhibits the fabrication of a free standing MWCNTs/Copper composite current collector foil of a thickness of 9 µm with surface area reaching up to 300 mm² via a process inspired by the Copper foil industrial production techniques with the use of a Copper carrier foil. Such areal dimensions, unprecedented for a copper/carbonaceous composite, are prerequisites for a potential market deployment since Lithium-ion battery manufacturers deposit electrode materials on large scale collector foils. In addition, the density of the as-synthetised composite was shown to be 10% lower than that of typical Copper battery foil while the material retains intrinsic mechanical and electrical properties required for Energy storage technologies. With a view of decreasing the weight of the overall battery packs by 10 to 20% following the guidelines of the HORIZON-CL5-2024-D2-02-03 Eu-funding 2024 call for proposals, such improvements on a non-electrochemically active part of the battery represents a major step forward. [5] In order to study the mechanical impact of the addition of MWCNTs in a copper collector foil Nanoindentation technique and electromechanical tensile testing bench were combined. The composite current collector was shown to display mechanical performances on par with that of battery Copper foil with Young Modulus and Hardness of 114.5 GPa and 3.25 GPa respectively. Value reaching the industrial standards required by the Lithium-ion battery market players for the next generation cells.[6] A combination of 4-points probe measurement and Conductive Atomic Force Microscopy (C-AFM) showed an improvement of the electrical conductivity of the material with the addition of MWCNTs compared to the Battery Copper with sheet resistance decreasing to 2.670 mΩ.sq^-1. Finally, electrochemical performances of the composite as anode battery collector were tested into 2-electrode cells with Lithium metal as counter electrodes. In this regard, Copper/MWCNTs composites with a protrusion of the carbon nanotubes were produced and tested with typical anodic graphitic slurries. A focus was made on the impact of the use of this new collector material on the cycling stability of typical Lithium-ion battery commercial mixture. Preliminary results indicate that the Cu/MWCNT composite displays an increase up to 30% of the volumetric capacity compared to that of pure copper collector. [1] Zhu, P. Gastol, D. Marshall, J. Sommerville, R. Goodship, V. Kendrick, E. J Power Sources, 485, 229321 (2021) [2] Subramaniam, C. Yamada, T. Kobashi, K. Sekiguchi, A. Futaba, Yumura, D. N. Hata, K. Nat Commun,4, 2202 (2013). [3] Shimizu, M. Ohnuki, T. Ogasawara, T. Banno, Arai, S., RSC Advances, 9(38), 21939-21945 (2019) [4] Duhain, A. Guillot, J. Lamblin, G. Lenoble, D., RSC Advances,11(63), 40159-40172 (2020) [5] Eu Funding & Tenders Portal: https://www.horizon-europe.gouv.fr/size-weight-reduction-cell-and-packaging-batteries-system-integrating-lightweight-and-functional [6] Copper Foil Market, Straits Research, 9.5.2.3.(2022) Figure 1

Up to now, copper is an essential material for lithium-ion battery industry as preferential candidate for anode current collectors due to its high conductivity, low price, and electrochemical stability in the working potential range of the anodic electroactive material. However, such component, accounting for 8.1% of the battery total weight, does not participate in any energy storage processes. [1] Thus, the trend is in this industry is to decrease the weight as well as the thickness of the collector foil to optimize the gravimetric energy of the whole lithium-ion battery system. It is therefore of interest to explore the development of lighter current collectors with equal/improved mechanical and electrical properties. Nanocarbon materials such as Multi-Wall Carbon Nanotubes (MWCNTs) and Single-Wall Carbon Nanotubes (SWCNTs) display a combination of performances, namely high electrical conductivity, low density and high mechanical stability, of a high interests to be combined with copper as innovative lightweight current collectors. Such nanocarbon/copper composite represents a valid alternative to foster the rapid change the battery technology is undergoing. In 2013, Subramaniam et al. [2] reported the fabrication of a Copper /Carbon nanotubes (Cu-CNTs) composites with a similar specific conductivity than that of copper and an ampacity increased by two orders of magnitude. Moreover, Arai et al. have shown, by Electrochemical impedance analysis, that MWCNTs additive in a copper matrix can serve as preferential electron conduction pathway inside a Lithium-ion battery anode. [3] Recently, a new promising and scalable way to fabricate nanocarbon/copper composite has been demonstrated by our team. The process involved the coating of MWCNTs by a dispersing agent, namely the Polydopamine biopolymer, their spraying, and finally the electrochemical plating of metallic copper inside the porosity of the MWCNTs network.[4] Following similar approach, the present work exhibits the fabrication of a free standing MWCNTs/ Copper composite current collector foil of a thickness of 9 µm, a value reaching the industrial standards required by the Lithium-ion battery market players for the next generation cells.[5] Scanning Electron Microscopy and Transmission Microscopy have been used to investigate the interaction between the copper matrix and the carbonaceous reinforcement additive. Figure 1. displays a cross section of nanocarbon/copper composite obtain via Focused Ion Beam slicing, where homogeneous mixing of copper and carbon phases down to nanoscale is highlighted. Such experiments contribute to the understanding of the copper nucleation mode on modified MWCNTs which remains insufficiently controlled to this day. Nanoindentation technique and electromechanical tensile testing bench were combined to study the mechanical properties of such material to be used under mechanical stress as battery collector. In contrary to conventional indentation technique where the mechanical properties of micro-size area are probed, indentation at nanoscale allow the probing of the local mechanical heterogeneity of a composite material. Using such technique, the fabricated self-standing nanocarbon/copper composite was shown to display average hardness and Young modulus close to those of pure carbon (3.5 GPa and 152 GPa respectively). Electrochemical performances of the composite as anode battery collector are under test into pouch and coin-cells battery architecture. The adhesion strength between the electrode slurry and the nanocomposite substrate material is expected to be reinforced by the addition of a nanocarbon. A focus was made on the impact of the use of this new collector material on the cycling stability of typical Lithium-ion battery commercial mixture. Preliminary results indicate that the Cu/MWCNT composite is a promising current collector material to withstand the expansion/contraction imposed by the working cycles of a rechargeable Lithium-ion battery. [1] Zhu, P. Gastol, D. Marshall, J. Sommerville, R. Goodship, V. Kendrick, E. J Power Sources, 485, 229321 (2021) [2] Subramaniam, C. Yamada, T. Kobashi, K. Sekiguchi, A. Futaba, Yumura, D. N. Hata, K. Nat Commun,4, 2202 (2013). [3] Shimizu, M. Ohnuki, T. Ogasawara, T. Banno, Arai, S., RSC Advances, 9(38), 21939-21945 (2019) [4] Duhain, A. Guillot, J. Lamblin, G. Lenoble, D., RSC Advances,11(63), 40159-40172 (2020) [5] Copper Foil Market, Straits Research, 9.5.2.3.(2022) Figure 1. Scanning Electron Microscopy imaging of the cross section of MWCNTs/Copper composite with a thickness lower than 3 µm – 7kV acceleration, 45° tilt. . Figure 1

Lithium-ion batteries (LIB) are now considered as standard power storage units in laptops, mobile phones, and electric cars. Yet, they trigger important and constant R&D efforts to improve their energy density, lifespan, safety, and cost efficiency. Among LIB components, anodic copper current collector contributes to 8.1% of the total LIB weight [1]. In their ongoing quest to reduce the thickness of the anodic electrode foils, manufacturers face now a 6 µm thickness limitation due to mechanical issues (wrinkling and tearing) complicating their processing. In this context, using lighter materials with improved mechanical properties (with equal or improved thermal and electrical conductivity) compared to pristine copper is considered as an interesting solution to contribute to a further improvement of Lithium-Ion Batteries energy density. Owing to its high mechanical properties, high electrical and thermal conductivity, and low density [2], graphene and its derivates could be considered as promising materials to fabricate graphene / copper composites and achieve thinner / lighter current collectors. Such composites have already been successfully synthetised using copper electroplating with clear thermal and mechanical improvement [3]. The work to be presented in this talk will describe a new and simple route for the fabrication of graphene nanoplatelets (GNPs) or graphene oxide (GO) / copper composites consisting of : (i) the dispersion of graphene derivates in ethanol, (ii) their spraying onto Titanium substrate, (iii) a post electroplating on the sprayed graphene materials. In case of GNPs, a prior functionalization by polydopamine biopolymer is performed to increase their hydrophilicity and allow their dispersion. The polydopamine polymerization mechanism is known in literature to be complex and not extensively understood. The investigations done to understand the functionalization of GNPs by polydopamine using different techniques like Transmission Electron Microscopy (TEM) and X-ray Photoemission Spectroscopy (XPS) will be shared. Moreover, the use of Helium Ions Microscopy coupled with Secondary Ions Mass Spectrometer (HIM-SIMS) has been chosen as an original and powerful technique to further study the conformation of polydopamine onto GNPs. Finally, we will present the fabrication of thin graphene oxide copper composite foils and their characterization using Scanning Electron Microscope (SEM). A special focus will be given on the comprehension of copper nucleation behaviour on Graphene materials that remains not well studied. Electrochemical techniques such as impedance and current transient nucleation and growth analysis is currently under testing. [1] Zhu, P. Gastol, D. Marshall, J. Sommerville, R. Goodship, V. Kendrick, E. J Power Sources, 485, 229321 (2021) [2] Fatemeh Farjadian et al. Recent Developments in Graphene and Graphene Oxide: Properties, Synthesis, and Modifications: A Review 5,10200-10219, Chemistry Europe (2020) [3] Song, G. et al.. One-step synthesis of sandwich-type Cu/graphene/Cu ultrathin foil with enhanced property via electrochemical route. Materials and Design, 191, 108629. (2020)

This work deals with electroactive conducting polymers (ECPs) used as a complementary component on purely capacitive silicon nanowires protected by a 3 nm alumina layer. Accordingly, in this work, we use a fast and simple deposition method to create a pseudocapacitive material based on the electropolymerization in aqueous micellar media (SDS and SDBS 0.01 M) of hydroxymethyl-EDOT (EDOT-OH) onto 3 nm alumina-coated silicon nanowires (Al₃@SiNWs). The composite material displays remarkable capacitive behavior with a specific capacitance of 4.75 mF·cm⁻² at a current density of 19 µA·cm⁻² in aqueous Na₂SO₄ electrolyte.

Silicon nanowires were coated by a 1–5 nm thin alumina layer by atomic layer deposition (ALD) in order to replace poorly reproducible and unstable native silicon oxide by a highly conformal passivating alumina layer. The surface coating enabled probing the behavior of symmetric devices using such electrodes in the EMI-TFSI electrolyte, allowing us to attain a large cell voltage up to 6 V in ionic liquid, together with very high cyclability with less than 4% capacitance fade after 10⁶ charge/discharge cycles. These results yielded fruitful insights into the transition between an electrochemical double-layer capacitor behavior and an electrolytic capacitor behavior. Ultimately, thin ALD dielectric coatings can be used to obtain hybrid devices exhibiting large cell voltage and excellent cycle life of dielectric capacitors, while retaining energy and power densities close to the ones displayed by supercapacitors.