Development and Testing of Innovative Carbon Nanotubes/ Copper Composite Foils, Towards Lighter and Mechanically Improved Anode Current Collector for Lithium-Ion Batteries

Abstract

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