Copper foil, secondary battery including copper foil, and method of manufacturing the same

Abstract

The present invention relates to a treated copper foil for use in a secondary battery, the treated copper foil having a first side and a second side opposite the first side. The treated copper foil includes a copper foil having two opposing surfaces and a treatment stack disposed on each one of the copper foils, the side of the treated copper foil corresponding to the surface of the copper foil with its respective treatment stack. The treatment stack includes a structured layer and at least one functional layer. Each of the first and second sides has an Rz between 1.0 and 3.0 μm, preferably between 1.5 and 2.5 μm, and an Sk between 1.0 and 3.0 μm.

Description

[Technical Field]

[0001] The present invention relates generally to the field of copper foil, and more particularly to silicon secondary batteries including current collectors, electrodes, and copper foil. [Background technology]

[0002] Energy storage devices, including batteries and capacitors, are used in a variety of applications. Advanced rechargeable batteries are desirable for a wide range of consumer electronics, electric vehicles, grid storage, and other important (future) applications due to their relatively high energy density, relatively high energy per mass, light weight, and potential long life. However, despite increasing commercial adoption of lithium (Li)-ion batteries, these batteries require further development, particularly for potential applications in low- or zero-emission, hybrid-electric, or fully-electric vehicles, drones, home appliances, energy-efficient cargo ships and locomotives, aerospace applications, and power grids.

[0003] Currently, graphite is commonly used commercially as an anode material for rechargeable Li-ion batteries due to its large volume (approximately 10%) and reversible Li-ion intercalation without morphology change. The main drawback of graphite is its relatively low specific capacity (370 mAh / g), which limits the specific capacity of Li-ion batteries. Silicon is considered a promising alternative to carbon-based anodes for various types of rechargeable batteries due to its high theoretical Li-ion storage specific capacity of approximately 3,579 mAh / g compared to other materials. In practice, lower capacities have been achieved. Although alternative manufacturing methods for silicon-based and carbon-free anodes have been developed over the past few years, silicon has so far primarily been commercialized as a strengthening additive for carbon-based anodes. For example, WO 2021 / 029769 A1 discloses a battery containing a silicon anode and a method for manufacturing the anode using chemical vapor deposition.

[0004] One of the barriers to fully implementing silicon-based electrodes is the fact that Li-Si electrodes experience significant shattering and spalling during lithiation and an unstable solid-electrolyte interface (SEI). The breakdown of the active silicon material can shorten the battery's lifespan and create safety issues due to short-circuiting. Another barrier is that, while carbon-based anodes undergo only a 10% volume change during charge and discharge, silicon-based anodes undergo a significant volume change of up to 300%. This volume change can lead to delamination of the silicon-based anode from the current collector, resulting in a loss of electrochemical contact. When the silicon particles no longer contact the current collector, electron transfer is no longer possible and the silicon particles become dead mass, thus reducing the battery's overall capacity.

[0005] Current collectors often comprise copper foil. Treatments have been proposed to enhance the adhesion of copper foil to silicon anodes, such as coating the copper foil with a layer containing zinc and / or tin oxide, as proposed in WO 2021 / 029769 A1. While this known treatment allows the battery to maintain its capacity for 20 charge-discharge cycles, a satisfactory first step in the right direction, silicon-based anodes are not yet powerful enough to achieve what carbon-based anodes currently achieve, i.e., to maintain battery capacity for hundreds of charge-discharge cycles. Therefore, there is a need for improved current collectors with higher resistance to delamination, which would enable an increased number of charge-discharge cycles. OBJECTIVES OF THE INVENTION

[0006] An object of the present invention is to provide an improved copper foil for use as a current collector in a secondary battery that does not suffer from the above-mentioned problems. Summary of the Invention

[0007] To achieve the above object, the present invention proposes a treated copper foil for use in a secondary battery, comprising a copper foil having a first side and a second side opposite the first side, and having two opposing surfaces, and a treatment stack disposed on each of the surfaces of the copper foil, the sides of the treated copper foil corresponding to the surfaces of the copper foil with its respective treatment stack, the treatment stack including a structuring layer for controlling / creating surface roughness and at least one functional layer for imparting one or more optimized functions.

[0008] In accordance with the present invention, the treated copper foil provides the following surface roughness characteristics, one on each of the first and second sides: - Surface roughness Rz (ISO) comprised between 1.0 and 3.0 μm, preferably between 1.5 and 2.5 μm; and - Surface roughness Sk, also known as core height, between 1.0 and 3.0 μm.

[0009] In other words, both treated sides of the treated copper foil of the present invention exhibit a surface roughness that meets the specified ranges for the roughness parameters Rz and Sk.

[0010] Ideally, the Rz and Sk values ​​are the same on both sides, or at least as similar as possible. However, in practice, manufacturing tolerances can result in differences in the Rz and / or Sk values ​​from one side to the other. Furthermore, in the case of electrodeposited copper foil, the matte (electrolyte) side and the drum side can have different initial roughness profiles, which will affect the roughness of the treated side.

[0011] In practice, both surfaces of a copper foil may be subjected to the same treatment. However, the two sides of the treated copper foil may exhibit different surface roughnesses within the specified range due to the variation in the initial surface roughness of the (untreated) copper foil. Note that this difference primarily reflects initial variations unrelated to the structuring treatment performed to form the structured layer.

[0012] In summary, a treatment stack is applied to the surface of a base copper foil to achieve a desired surface roughness characteristic, and this can be done using conventional techniques and processes for both the structured and functional layers.

[0013] The present invention is based on the inventor's conclusion that a particular surface roughness profile or particular surface condition of the treated copper foil is desirable for use in a secondary battery, particularly as a current collector in the battery, and the identification of the corresponding surface roughness characteristics.

[0014] Thus, one advantage of the present invention is the identification of specific surface conditions represented by 2D and 3D surface roughness parameter ranges, and more specifically, by the conventional roughness parameter Rz in combination with Sk, that are suitable for accurately characterizing the surface roughness of treated copper foils, particularly, but not exclusively, for use as current collectors in batteries, particularly rechargeable Li-ion batteries. The conclusions about 3D surface roughness characterization in relation to this application are particularly relevant. Indeed, 3D surface roughness characterization, sometimes known in the art as "non-contact" because it is determined by microscope, provides more accurate information about surface roughness compared to contact measurements such as Rz.

[0015] In other words, one of the advantages of the present invention is the identification of a particular surface roughness, characterized by the herein-specified values ​​of surface roughness Rz and Sk, that is suitable for treated copper foils used as anode current collectors in electrode assemblies, particularly anode assemblies.

[0016] It will be appreciated that the inventors have surprisingly discovered that the copper foils of the present invention used as electrodes provide improved behavior in charge-discharge cycling. Indeed, the inventors have discovered that such a surface roughness profile can ensure good adhesion of the treated copper foil to electrode materials attached to or coated thereon, such as, but not limited to, Si-based electrode materials.

[0017] More specifically, the inventors have discovered that having an Rz within the specified range of 1.0 to 3.0 μm is necessary but not sufficient to ensure satisfactory behavior in charge-discharge cycling, and that only copper foils exhibiting a surface roughness of both Rz and Sk within the specified range of 1.0 μm to 3.0 μm can achieve the desired improved behavior when used in electrode assemblies.

[0018] According to the present invention, the first and second sides of the treated copper foil exhibit, in use, an Rz between 1.0 and 3.0 μm and an Sk between 1.0 and 3.0 μm, and an electrode material, such as a silicon layer, is formed on each one of the two sides of the copper foil.

[0019] For Si-based anodes containing the present copper foils, initial testing has shown that the treated copper foils of the present invention provide greater resistance to delamination and allow for an increased number of charge and discharge cycles.

[0020] The defined roughness profile of the treated copper foil is primarily influenced by the structured layer, which largely controls the overall roughness.

[0021] While Rz has always been the primary parameter for characterizing the roughness of copper foils in the industry, the inventors have discovered that it can be advantageously complemented by other surface roughness parameters, such as Sk, to adequately and reproducibly characterize the surface of the treated copper foils of the present invention, where defined values ​​of Rz and Sk provide enhanced charge / discharge behavior not previously achievable with conventional copper foils for electrodes.

[0022] The inventors have identified a suitable value of Sk for the treated copper foil to be between 1 and 3 μm. At lower Sk, the treated copper foil may be too smooth to properly adhere to another layer of material, while at higher Sk, corresponding to a very rough foil, this may prevent the formation of a continuous and / or uniform layer thereon.

[0023] Surface roughness Sk- or simply Sk-, also called core roughness depth or core height, is a measure of the core roughness (peak to valley) of a surface excluding the extreme peaks and valleys (maximum height peaks and minimum height valleys) and is derived from the areal material ratio curve.

[0024] Because Sk is affected by both texture (number and size of peaks and valleys) and the spatial arrangement and spacing of peaks and valleys, this parameter can advantageously further distinguish surfaces with similar roughness as those described using 2D parameters such as Rz. Typically, Sk increases with the spatial complexity of the texture, regardless of whether Rz varies.

[0025] In an embodiment, the treated copper foil is between 50 and 190 g / m 2 The processed copper foils have areal weights between 100 and 150. It is desirable for the processed copper foil to be as uniform as possible, with little to no variation in thickness. In this context, referring to areal weight to characterize the copper foil is similar to referring to foil thickness, since foil thickness is fairly constant. The processed copper foils with the highest areal weights are the thickest, and the processed copper foils with the lowest areal weights are the thinnest.

[0026] The treated copper foil is thin enough to be cost-effectively manufactured and exhibit the desired conductive properties for use in rechargeable or secondary batteries, where thinner copper foils result in higher gravimetric energy densities.

[0027] Preferably, the treated copper foil has a strength of 30 and 100 kgf / m 2 The treated copper foil can advantageously resist elongation caused by the surface increase of a layer attached to or coated thereon, such as a silicon layer, which expands or contracts due to the insertion or desorption of Li ions during charging and discharging of a battery containing such treated copper foil as a current collector and a silicon layer as an anode.

[0028] Preferably, the treated copper foil has an elongation between 3 and 30%. Thus, the treated copper foil can advantageously stretch enough to accommodate the surface increase of a layer (such as an electrode layer) attached to or coated thereon, but on the other hand, the stretchability is insufficient to form buckles when the layer attached to or coated thereon undergoes a surface decrease, thereby preventing the formation of areas on the copper foil that are not attached to or coated with the (e.g., electrode) layer.

[0029] In an embodiment, the copper foil is an electrolytic copper foil, i.e., the copper foil is produced by copper electrodeposition / electroplating. As is known in the art, the surface roughness of the untreated copper foil affects the surface roughness of the treated copper foil. Preferably, the base copper foil (especially the electrolytic copper foil) has a surface roughness Rz (ISO) of 1.0 to 2.5 μm, preferably 1.3 to 2.4 μm, more preferably 1.5 to 2.2 μm on both surfaces.

[0030] In embodiments, the structured layer is formed directly on the untreated side of the copper foil by electrodeposition of a structured copper layer with a predetermined roughness. The structured layer is generally formed by adjacent deposits of copper masses / shapes that provide controlled alternating peaks and valleys on the surface.

[0031] In particular, the structured layer may comprise or consist of copper nodules deposited directly on the (untreated) side of the copper foil, preferably covered with a copper plating layer for fixing / encapsulating the nodules to the surface of the copper foil in a conventional manner. In other words, the structured layer may be present directly on the side of the untreated copper foil and may comprise copper nodules, and preferably may comprise a continuous copper layer on the copper nodules. The deposition of copper nodules is well known in the art. The copper nodules generally have a spherical and / or elliptical shape.

[0032] Preferably, the copper nodules are ellipsoidal in shape (with their main extensions substantially perpendicular to the surface of the copper foil), have a height between 1.2 and 3.0 μm, preferably between 1.8 and 2.4 μm, and a diameter between 0.6 and 1.1 μm, preferably between 0.7 and 0.9 μm. One advantage of depositing ellipsoidal copper nodules is that the developed surface area can be increased relative to the same foil with spherical copper nodules, and therefore the surface roughness of Sk can be increased. Indeed, ellipsoidal nodules are taller than spherical nodules of the same diameter, resulting in higher peaks and valleys per unit surface area and, consequently, larger interfaces.

[0033] In an embodiment, the processing stack includes at least one functional layer selected from the following: a heat-resistant layer containing mainly zinc and / or nickel, -Anti-corrosion layers containing mainly chromium, and an adhesion-promoting layer comprising a silane compound, for example an aminosilane.

[0034] The term should be understood here to include predominantly more than 50% by weight of the compound, preferably more than 60%, 70% or 80% by weight.

[0035] In an embodiment, the heat resistant layer comprises zinc and / or nickel in a total amount of up to 60 mg / m 2 where the nickel and zinc concentrations are 0 and 30 mg / m, respectively. 2 However, the minimum amount of nickel and / or zinc in this layer is 3 mg / m 2 In some embodiments, the heat-resistant layer contains zinc and / or nickel in a total amount of 22 to 32 mg / m 2 include.

[0036] In an embodiment, the corrosion protection layer is between 2 and 10 mg / m 2 between 1000 and 15000 mg / m², preferably ... 2 As in, 4 and 8 mg / m 2 Contains between 0.01 and 0.1% chromium.

[0037] In an embodiment, the adhesion promoting layer is between 3 and 20 mg / m 2between 10 mg / m and 100 mg / m. 2 As in, 5 and 15 mg / m 2 The amount of silane is between 100 and 1500 mg / L.

[0038] In an embodiment, the structure layer is between 5 and 20 g / m 2 Between 8 and 12 g / m 2 Contains copper in amounts between 0.1 and 0.2%.

[0039] Preferably, the treatment stack includes all three layers: an inner layer (over the structured layer) that is a heat resistant layer, an intermediate corrosion protection layer, and an outer layer that is an adhesion promoting layer.

[0040] Alternatively, the functional layer may be formed as a combination of zinc, nickel and / or chromium covered by an adhesion promoting layer.

[0041] The functional layer is generally a continuous layer and may be formed by any suitable / known process.

[0042] Preferably, the processing stack, and in particular the structured layers, exhibit a thickness that is determined by the nature and number of the processing layers, regardless of the thickness of the (untreated) copper foil: the thickness of the processing stack is determined primarily by the thickness of the structured layers, which in embodiments is determined by the dimensions of the copper nodules.

[0043] According to another aspect, the present invention relates to the use of the treated copper foil of the present invention as a current collector for a secondary battery. Advantageously, and as mentioned above, the inventors have discovered that such treated copper foil of the present invention exhibits suitable mechanical properties and surface roughness for attachment to electrodes, preferably in secondary batteries, and particularly for use as a current collector.

[0044] According to yet another aspect, the present invention also relates to an electrode assembly comprising a current collector comprising the treated copper foil according to the first aspect of the invention, and an electrode comprising a silicon layer (greater than 50% Si by weight).

[0045] This copper foil was specifically developed to support a Si-based layer. Depending on the manufacturing method, the amount of silicon in the silicon layer can be at least 90%, usually at least 95%, and possibly at least 99%. The electrode is a silicon-based electrode and not a Si-doped carbon-based electrode. The electrode preferably contains primarily silicon. However, it is still within the scope of this disclosure that the electrode may contain other chemical components as doping elements, such as hydrogen (since the silicon is amorphous silicon) or trace amounts of nitrogen, phosphor, bore, aluminum, and / or carbon, to enhance electrical conductivity and / or improve the crystalline structure of the silicon. Those skilled in the art will understand that electrodes containing silicon layers can be formed by any suitable process, such as physical or chemical vapor deposition, sputtering, electron beam evaporation, or application and calcination of a silicon-containing slurry. These are particularly suitable for high Si content. In a preferred embodiment, the silicon layer may be formed by chemical vapor deposition of silicon, more preferably by low-pressure plasma-enhanced chemical vapor deposition. One advantage of this formation method is that the silicon formation process is a self-organizing and spontaneous process to form a continuous layer of silicon. According to the same or other embodiments, the silicon layer has a thickness between 5 and 30 μm.

[0046] However, more conventional methods can be used to form silicon layers, such as conventional wet slurry coating, but with a lower Si content (still above 50 wt%).

[0047] In an embodiment, a silicon layer is formed on each one of the first and second sides of the treated copper foil.

[0048] According to yet another aspect, the present invention also relates to a secondary battery comprising an electrolyte, a cathode assembly, an anode assembly, a separator layer, and a lithium salt compound (conventionally with an associated electrolyte additive), wherein the anode assembly comprises the treated copper foil of the present invention or is an electrode assembly according to the present invention.

[0049] According to yet another aspect, the present invention also relates to a method for producing a copper foil as defined in claim 16.

[0050] The resulting treated copper foil contains a treatment stack on both surfaces, the exposed sides of which exhibit a surface roughness Rz between 1.0 and 3.0 μm, preferably 1.5 and 2.5 μm, and Sk between 1.0 and 3.0 μm, respectively.

[0051] Step b) corresponds to a structuring process, or structuring treatment, or roughening treatment, and can also be called electrodeposition of fine copper particles or copper nodules. This method is very effective in obtaining a copper foil surface with a desired texture (or 3D structure or roughness).

[0052] The copper concentration and bath temperature of the structuring process are usually lower than the corresponding parameters specified for electroplating copper foil, resulting in the formation of discrete copper particles or nodules instead of a continuous layer. The structuring process of step b) is followed by a subsequent step (step c) of conventional copper plating, which forms a continuous copper layer on the nodules on each side of the copper foil. The formed copper nodules are thus firmly adhered to the copper foil. Step c) can be performed directly after step b by passing the foil through a further plating bath containing a high concentration of copper.

[0053] In steps c) and d), continuous layers are formed on the copper foil surface, which are relatively thin compared to the structured layer. Therefore, these layers tend to follow / replicate the surface roughness of the structured layer. In other words, the functional layer is a fairly thin layer that does not noticeably change the surface roughness of the treated copper foil, which is mainly determined by the initial roughness of the base copper foil and the structured layer.

[0054] The production of the treated copper foil according to the invention can generally be carried out using conventional techniques. Electrolytic baths / solutions for structuring (deposition of nodules) and deposition of functional layers (passivation / adhesion) are known in the art. They can be used in the context of the present invention. The production parameters are adjusted by the skilled worker to provide the desired roughness profile, in particular to control the shape of the nodules, more particularly their height and diameter.

[0055] In particular, those skilled in the art of metal electrodeposition are familiar with the theory of Winand and Fischer (Reference 1), who explained the type of electrodeposition as the ratio of current density to two main parameters: diffusion-limited current density (i.e., metal concentration) and inhibition strength (e.g., temperature / agitation).

[0056] However, it should be appreciated that the present invention advantageously provides for the production of ellipsoidal nodules, which is a particularly convenient method of optimizing surface roughness to achieve a desired roughness profile, i.e., a roughness profile with a desired Rz and Sk range.

[0057] A preferred electroplating bath for step b) is 15-30 g / L of copper, preferably copper ions, Cu 2+ and 50-150 g / L of sulfuric acid. An alternative and equally preferred electroplating bath for step b) comprises 5-25 g / L of copper, preferably copper ions, Cu 2+ and 30-90 g / L, preferably 40-80 g / L, of sulfuric acid. The applied current densities are between 15 and 30 A / dm 2 , preferably 20 and 30A / dm 2The bath is preferably kept at a temperature between 20 and 30° C. The deposition time (immersion length) can be between 5 and 10 s (seconds).

[0058] The electroplating bath allows the production of a structured layer of copper nodules with dimensions suitable for achieving the desired roughness parameters, in particular the desired Rz and Sk.

[0059] A preferred electroplating bath for step c) is a bath containing 60-100 g / L of copper, preferably copper ions, Cu 2+ and 30-90 g / L, preferably between 40 and 80 g / L, of sulfuric acid. The applied current density is between 15 and 30 A / dm 2 The bath is preferably kept at a temperature between 40 and 60° C. The deposition time (immersion length) can be between 5 and 10 s.

[0060] Preferably, the ellipsoidal copper nodules are grown by a two-step process in which steps b) and c) are repeated. That is, a first layer of copper nodules is formed and covered with a continuous copper layer. Next, a second layer of copper nodules is formed, followed by the deposition of a continuous copper layer. Experience has shown that the second layer of copper nodules tends to form on the nodules of the first layer. Thus, as a result of the shape combination, an ellipsoidal shape is formed. These steps are preferably performed sequentially on both sides of the copper foil, but may be performed simultaneously.

[0061] It is believed that one iteration is sufficient to obtain an ellipsoid (due to the combination of two overlapping nodules), however this should not be construed as limiting and more iterations may be envisaged.

[0062] The base copper foil, nodules, and covering / encapsulating copper foils are formed by electrodeposition and therefore consist of pure copper, i.e., pure copper with a copper content of at least 99% by weight, or even 99.9% by weight.

[0063] Further details and advantages of the invention will become apparent from the following detailed description of some non-limiting embodiments, with reference to the accompanying drawings. [Brief explanation of the drawings]

[0064] The invention will now be described, by way of example only, with reference to the accompanying drawings in which: [Figure 1] 1 is a schematic cross-sectional view of a treated copper foil according to the present invention. [Figure 2] 1A-1C are SEM (scanning electron microscope) views of a copper foil according to the present invention at different magnifications. [Figure 3] 1A-1C are SEM (scanning electron microscope) views of a copper foil according to the present invention at different magnifications. [Figure 4] 1A-1C are SEM (scanning electron microscope) views of a copper foil according to the present invention at different magnifications. [Figure 5] This is an SEM image of a comparative copper foil. [Figure 6] This is an SEM image of a comparative copper foil. [Figure 7] This is an SEM image of a comparative copper foil. [Figure 8] This is an SEM image of a comparative copper foil. [Figure 9] 1 is a schematic curve showing the area material ratio curve and the determination of the parameter Sk. [Figure 10] FIG. 1 is a schematic diagram of a structured copper foil illustrating how the nodule height is estimated. [Figure 11] FIG. 1 illustrates deposition of ellipsoidal copper nodules according to one embodiment. DESCRIPTION OF THE PREFERRED EMBODIMENT

[0065] As described above, the present invention provides a treated copper foil with a specific surface roughness. The treated copper foil of the present invention will be described with reference to Figure 1. The treated copper foil 1 includes a copper foil 2 having a first side 1a and a second side 1b opposite the first side, and having two opposite surfaces 2a and 2b. The copper foil 2 alone may also be referred to as a base copper foil, and the two surfaces 2a and 2b may be referred to as untreated surfaces.

[0066] A processing stack 3 is formed on each one of the two untreated surfaces 2 a, 2 b. The processing stack 3 includes a structured layer 4 and at least one functional layer 5. In the described embodiment, the structured layer includes nodules 6 or fine copper particles covered by a continuous layer of copper 7. Note that in FIG. 1 , for illustrative purposes, layer 7 is represented with a significant height; in reality, copper layer 7 is rather thin and follows the shape of the nodules, as shown in FIG. 11 . The roughness characterization of the processed copper foil 1 corresponds to the roughness of the sides 1 a, 1 b of the copper foil 2, i.e., the roughness of the surfaces 2 a, 2 b, as modified by the processing stack 3, and in particular by the structured layer 4.

[0067] This treated copper foil is produced by subjecting untreated copper foil, produced by rolling (rolled copper foil) or electrodeposition (electrodeposited copper foil), to at least a structuring (i.e., roughening) process, which in an embodiment consists of growing or forming fine copper nodules, also called grains, on the two sides (i.e., surfaces) of the untreated copper foil.

[0068] The electrodeposited copper foil (or electrolytic copper foil) selected as the starting / base copper foil is produced using an electroforming cell (known in the industry as a plating machine). In the electroforming cell, an electrolyte solution is passed through a device containing a rotating drum-shaped cathode (surfaced with stainless steel or titanium) and a stationary anode (a lead or titanium electrode coated with a noble metal oxide) located opposite the cathode. An electric current is passed through both electrodes, depositing copper to the desired thickness on the surface of the cathode, thus forming the electrodeposited copper foil. The electrodeposited copper foil is then peeled from the surface of the cathode and wound onto a storage reel. The foil prepared in this manner is commonly referred to as untreated copper foil.

[0069] Rolled copper foil can be produced to a predetermined thickness by, for example, performing known processes of hot rolling, cold rolling, homogenizing, and degreasing of an ingot obtained by melting and casting a pure copper material.

[0070] In a subsequent step, the untreated copper foil is subjected to a surface structuring (i.e. roughening) process / treatment, in which fine copper particles, i.e. copper nodules, are preferably produced (by electrolysis) on the surface 2a, 2b of the copper foil by reduction of copper ions, the size of the nodules typically depending on the duration of the electrolysis.

[0071] An exemplary electrolyte for nodular treatment (called a nodular bath) is 20 g / L of copper ions, Cu 2+ and 60 g / L of sulfuric acid. The electrolyte can be kept at room temperature (e.g., about 20°C). The electrolysis is carried out at a current density slightly higher than that typically used to produce electrodeposited copper foil, e.g., about 30 A / dm 2 Fine copper particles, i.e., copper nodules, are produced on the surface of the copper foil by the reduction of copper ions and grow depending on the duration of the electrolysis (e.g., 6 seconds).

[0072] Immediately after the copper nodules have formed on the untreated side, a conventional copper plating step is carried out using an electrolyte with a high copper concentration at a higher temperature and a higher current density to form a continuous copper layer on the nodules on each side of the copper foil, which are thus firmly attached to the copper foil, a step also known as encapsulation.

[0073] An exemplary electrolyte for copper plating (called an encapsulated bath) contains 60 g / L of copper ions, Cu 2+ , and 60 g / L sulfuric acid. The electrolyte may be maintained at 50° C. The electrolysis may be performed at a current density slightly higher than that typically used to produce electrodeposited copper foil, e.g., about 15 A / dm 2The duration of the electrolysis may be, for example, 6 seconds.

[0074] Although those skilled in the art of metal electrodeposition are aware of the conditions necessary for the formation of particulate metal deposits, the present invention relies on the discovery of a specific relationship between surface conditions during battery charge-discharge cycling, as described by Rz and Sk.

[0075] In particular, the inventors have discovered a particularly advantageous method for structuring copper layers with ellipsoidal copper nodules, which in principle can be formed as a single metal deposition layer by selecting appropriate deposition parameters and adapting the deposition / dwell time to the growth of oval grains.

[0076] Preferably, in the interest of industrialization, and in particular for productivity, the spheroidal nodules are formed in a two-stage process, i.e., the nodule treatment and copper plating steps can be repeated on each side, as disclosed in Figure 11. The process is suitable for forming spheroidal copper nodules on copper foil moving at conventional speeds, i.e., about 15-30 m / min.

[0077] As can be seen from FIG. 11, the untreated copper foil 2 is subjected to a first structuring treatment on one of its sides 2a or 2b, and a first layer of copper nodules 10 is deposited in a nodule bath; subsequently, a thin copper layer 11 is deposited in an encapsulation bath. In this first step, the nodules 10 are rather round / spherical. The same steps are then carried out, for example using the same nodule bath and encapsulation bath: a second layer of copper nodules 12—also generally round / spherical—is formed, which are then encapsulated by a thin continuous layer of copper 7. The other side 2b or 2a of the copper foil 2 is then subjected to a similar process.

[0078] As can be seen, the nodules of the second layer are generally deposited onto the nodules of the first layer, the combination of which forms a general elliptical shape.

[0079] Without being bound by any theory, it is believed that the second layer of nodules forms preferentially on the first layer of nodules when the current peaks and because the copper concentration in the nodule bath is not sufficient for copper ions to reach the valleys between the already deposited copper nodules.

[0080] In a subsequent step, the structured copper foil is subjected to an electrochemical or chemical surface treatment to form at least one functional layer on the structured layer containing copper nodules. The surface treatment can be, for example, a bonding enhancement and / or passivation treatment.

[0081] According to non-limiting embodiments, the at least one functional layer is formed by subjecting the structured copper foil to at least one of the following processing steps: Electroplating a layer of zinc. By way of example, this may be done using a bath containing 0.80 g / L zinc and 0.95 g / L CrO3 at pH 3.8 at 4 A / dm² for a length of time depending on the desired deposition amount. 2 This can be done using a current density of . Electroplating a layer of nickel. By way of example, this may be done using a bath containing 5.0 g / L nickel and 40.0 g / L H3BO3 at pH 3.5, at 1.5 A / dm for a length of time depending on the desired deposition rate. 2 This can be done using a current density of Electroplating a layer of chromium. By way of example, this can be done using a bath containing 0.95 g / L CrO3 at pH=2.0 at 1 A / dm² for a length of time depending on the desired deposition amount. 2 This can be done using a current density of

[0082] Zinc passivation and nickel passivation are usually considered alternatives: the zinc or nickel passivation layer is formed first, followed by the chromium layer.

[0083] Typically, zinc and / or plating is 30 mg / m 2 The minimum amount of this passivation layer is 3 mg / m².2 Chromium plating is 2 to 10 mg / m 2 This can be carried out to deposit chromium.

[0084] Finally, a silane compound layer can be applied as an outer layer for adhesion promotion purposes. The silane compound layer can be applied by passing a bath of 0.4 g / L of Si (as aminosilane). This optional layer can be applied in a concentration of 3 to 20 mg / m 2 The silane compound may include:

[0085] example Electrodeposited copper foils with an initial surface roughness Rz between 1.0 and 3.0 μm were produced by methods well known in the art. The untreated copper foils were then subjected to a structuring process according to the invention (Examples 1 to 3) or not (Comparative Examples 1 and 2, not part of the invention) during production.

[0086] The copper foils (Examples 1 to 3) having the structured layer according to the invention were then subjected to a functional treatment to deposit three functional layers in succession: a layer containing zinc, a layer containing chromium, and a layer containing a silane compound, each of which was a continuous layer, with a total thickness of the functional layers between 5 and 50 nm.

[0087] Comparative example copper foils, either structured or unstructured, were subjected to either no nodule treatment, no functional treatment other than chromium passivation (Comparative Examples 1 and 2), nodule and functional treatment similar to one of the copper foils according to the invention (Comparative Example 3), and a different nodule treatment with the same functional treatment (Comparative Example 4).

[0088] The surface roughness observed under an SEM microscope is shown in Figures 2 to 8: 2 to 4 correspond to Examples 1, 2 and 3, respectively. 5 to 8 correspond to counterexamples 1 to 4, respectively.

[0089] The copper foils thus obtained were then analyzed to determine surface properties such as surface roughness (such as Rz and Sk, all according to ISO standards) and mechanical properties such as areal weight, tensile strength, elongation, etc.

[0090] A secondary battery comprising a silicon anode according to Examples 1-3 or Comparative Examples 1-4 and the treated copper foil as an anode current collector is then manufactured according to methods known in the art and will not be further detailed herein.

[0091] The copper foil is analyzed as follows: Determination of surface roughness Rz The Rz roughness of copper foil is measured with a contact profilometer, which consists of a diamond stylus sliding across the surface. From this measurement, a 2D profile of the surface is created, and Rz is calculated as the average distance between the highest peak and the lowest valley across the entire eight sample lengths. Here, surface roughness Rz refers to ISO 4287:1997.

[0092] Determination of surface roughness Sk The Sk parameter (core height) is measured using a non-contact 3D white light interference microscope, where the surface roughness Sk refers to ISO 25178-2 dated 2021.

[0093] The SK core height is calculated as the difference between the heights at 0% and 100% areal material ratio values ​​on the equivalent line. Specifically, it is the maximum height minus the minimum height of the core surface. The determination of SK is shown in Figure 9.

[0094] The area-area ratio represents the area above a certain height c. The area-area ratio curve is the curve that represents the height at which the area-area ratio changes from 0% to 100%. The equivalent line is the line where the sum of the squares of the deviations in the direction of the vertical axis is the smallest at the center. The center of the area-area ratio curve is defined as the location where the secant line has the smallest slope (inflection point).

[0095] The area between the two height positions on the equivalent line where the area material ratio is 0% and 100% is called the core surface. A peak with a height above the core surface is called a reduced peak, and a valley below the core surface is called a reduced valley. Sk is calculated as the difference in height between the area material ratio values ​​of 0% and 100% on the equivalent line: specifically, it is the value obtained by subtracting the minimum height from the maximum height of the core surface.

[0096] The principle of white light interference microscopy is to split a light beam into two paths, one directed towards a reference mirror and the other towards the sample surface. This measurement beam travels different distances depending on the surface profile. The two waveforms are then recombined, creating specific interference patterns depending on the phase difference. These patterns are then analysed to calculate the height of the sample at each scanned point (pixel). This is then typically measured over a distance of 155 μm x 116 μm (i.e., approximately 18,000 μm). 2 ) measured at the sample surface, and the area material ratio curve is calculated from this 3D profile.

[0097] In the context of the present invention, a Keyence microscope model VK-X100 has been used to measure Sk for examples and counterexamples.

[0098] The area-material ratio curve shows the height as a function of the area-material ratio. Neither the measurement device (interferometer) nor the mathematical calculation method or model used to determine the area-material ratio curve affects the curve. In other words, the same curve is obtained regardless of the measurement device or mathematical method; the only possible variability is related to the sensitivity of the measurement device and, therefore, the accuracy of the obtained values. On the obtained area-material ratio curve, a tangent line at the inflection point is determined. The maximum and minimum heights of the core surface are defined as the intersection points of the tangent line and the height axis at area-material ratios of 0% and 100%, respectively. Sk is then calculated by subtracting the minimum height from the maximum height of the core surface.

[0099] Imaging of treated copper foil The treated copper foils produced according to the present invention and comparative examples are imaged using a scanning electron microscope (SEM) THERMAFISHER, PrismaE, at a voltage of 20 kV and a tilt of 30° at magnifications between 1000 and 6000.

[0100] Determination of nodule height and diameter As can be seen from the SEM images, the nodules tend to grow as round (spherical) particles or, particularly in Examples 1-3, as more elongated (ellipsoidal) particles in a direction fairly perpendicular to the surface of the copper foil.

[0101] An approach has been proposed to characterize the dimensions of the nodules, i.e., diameter and height.

[0102] The diameter of the nodules was determined from the SEM images. The diameters of 10 nodules were measured, and the arithmetic mean and standard deviation were calculated from the measurements and are shown in Table 1.

[0103] The nodule height is evaluated as follows: the weight area of ​​the structured copper foil is measured, and the weight area of ​​the untreated copper foil is subtracted from the weight area of ​​the structured copper foil to evaluate the weight area of ​​the structured layer (or treated copper foil, since the weight of the functional foil is relatively negligible). The theoretical thickness of a plain and smooth structured layer is then determined as follows: Thickness of structured layer = Weight of structured layer / Area of ​​copper foil × Copper density

[0104] The height of the nodules is then estimated to be twice the theoretical thickness by the hypothesis that the nodules form a pyramidal pattern on the surface of the copper foil, as shown in Figure 10.

[0105] Determination of mechanical properties Tensile strength and elongation are determined in accordance with IPC TM 650 2.4.18.

[0106] Tensile strength and elongation at break were determined by mechanical force testing at ambient temperature at a drawing rate of 2.0 inches / minute using 6 x 1 / 2 inch cut specimens of (treated) copper foil as test samples. The elongation is determined as follows: Elongation = ((length at break - original length) / original length) x 100

[0107] The tensile strength is determined as follows: Tensile strength = load used to break sample / average cross-sectional area. Here, the average cross-sectional area is determined as follows: Average cross-sectional area = sample weight / sample area x copper density

[0108] The area weight is determined by weighing the test specimen and calculating the area weight as follows: Area weight = weight of sample / area of ​​sample

[0109] Five measurements were made for each example and comparative example, and the arithmetic mean values ​​for elongation, tensile strength, and area weight are shown in Table 1.

[0110] Determining the number of cycles that will retain more than 80% of the original capacity A cell containing the treated copper foil as the anode current collector and a silicon anode was cycled at an irreversible capacity of approximately 600 mAh per gram of silicon, and the retention capacity was measured after each cycle.

[0111] The last column in Table 1 shows the number of cycles achieved at this ratio. QN / Q1×100≧80% where Q1 is the initial discharge capacity and QN is the discharge capacity at the Nth cycle. This test is common in the art.

[0112] Discussion of examples and counterexamples Table 1 shows the surface properties, mechanical properties, and number of cycles for the treated copper foils according to the present invention and comparative examples that retain more than 80% of their original capacity.

[0113] All copper foils are 50 and 190 g / m 2 They have approximately the same areal weight and tensile strength (Table 1).

[0114] Furthermore, all treated copper foils according to the present invention (Examples 1 to 3) have Sk between 1.0 and 3.0 μm and Rz between 1.0 and 3.0 μm, as well as elongation between 3 and 30%.

[0115] Comparing the results obtained in Examples 2 and 3 with those obtained in Comparative Examples 1 and 2, it should be noted that although these four copper foils have very similar areal weights and tensile strengths (Table 1), the batteries containing the treated copper foils according to the present invention retained more than 80% of their original capacity for a much greater number of cycles than the batteries containing the comparable copper foils (Table 1). Unlike the foils of Comparative Examples 1 and 2 (see Figures 5 and 6), Examples 2 and 3 were subjected to a structuring process (see Figure 3 corresponding to Example 2 and Figure 4 corresponding to Example 3). The presence of nodules (or fine copper particles) on the surface of the copper foil and the resulting higher surface roughness, particularly the higher Sk, enabled the treated copper foils to adhere better to the silicon anode and retain a higher battery capacity. As is evident from Comparative Examples 1 and 2, the specified Rz range of 1.0 to 3.0 μm alone is insufficient to ensure a satisfactory number of cycles with retention of more than 80% of the original capacity. If Sk is less than 1.0 μm, a battery containing this copper foil will lose more than 20% of its original capacity after less than 10 cycles.

[0116] Referring now to Comparative Examples 3 and 4, the formation of nodules on the copper foil alone is insufficient to ensure satisfactory battery capacity retention during charge-discharge cycling. If the treated copper foil is too rough (Comparative Example 3) or too smooth (Comparative Example 4), performance is not optimal. Capacity loss is more rapid than in batteries containing treated copper foils according to the present invention (see Table 1, Comparative Examples 3 and 4, and e.g., Example 1).

[0117] Also, Comparative Examples 1, 2, and 4 exhibit surface roughness, in terms of Rz, very similar to that of one of the treated copper foils according to the present invention. However, the capacity retention of Comparative Example 4 is lower than that achievable with the copper foil according to the present invention. One explanation is that the comparative foil is not actually rough enough, and certainly not as rough as the inventive foil when non-contact parameters such as 3D and Sk are considered. Characterizing the roughness of treated copper foils primarily by contact parameters such as 2D and Rz does not provide sufficient sensitivity to evaluate the actual roughness of the foil and to explain the performance achieved. Thus, an advantage of the present invention is the ability to identify surface roughness conditions, as described above, that can be characterized with greater sensitivity by their Rz and also by the parameter Sk, which improve the performance of the copper foil as an anode current collector and the capacity retention of batteries containing the copper foil.

[0118] Treated copper foils according to the present invention, i.e., foils exhibiting an Rz between 1 and 3 μm plus an Sk between 1 and 3 μm, allow for the desired retention of battery capacity during charge-discharge cycling to be achieved. Reference 1

[0119] R. WINAND, "Electrocristalisation.Theorie et applications", JOURNAL DE PHYSIQUE IV Colloque C1, supplement au Journal de Physique III, Volume 4, January 1994, C1-55 ~ C1-73

[0120] [Table 1]

Claims

1. A treated copper foil (1) for use in a secondary battery having a first side (1a) and a second side (1b) opposite to the first side, wherein the treated copper foil includes a copper foil (2) having two opposite surfaces (2a, 2b) and a treatment stack (3) disposed on one of each of the surfaces (2a, 2b) of the copper foil (2), the side of the treated copper foil corresponding to the surface of the copper foil having each of the treatment stacks; The processing stack comprises a structured layer (4) and at least one functional layer (5), wherein one of each of the first side (1a) and the second side (1b) has an Rz between 1.0 and 3.0 μm, preferably between 1.5 and 2.5 μm, and a Sk between 1.0 and 3.0 μm. Processed copper foil (1) for use in secondary batteries.

2. The treated copper foil according to claim 1, wherein the copper foil is an electrolytic copper foil, and both surfaces thereof exhibit a surface roughness Rz of 1.0 and 2.5 μm, preferably 1.3 and 2.4 μm, more preferably 1.5 and 2.2 μm.

3. The treated copper foil according to claim 1 or 2, wherein the structured layer is a structured copper layer having a predetermined roughness that is directly formed on each surface of the copper foil by electrodeposition.

4. The treated copper foil according to claim 3, wherein the structured layer comprises copper nodules (6) directly deposited on the surface (2a, 2b) of the copper foil.

5. The treated copper foil according to claim 4, wherein the copper nodules are ellipsoidal and have a height between 1.2 and 3.0 μm, preferably between 1.8 and 2.4 μm, and a diameter between 0.6 and 1.1 μm, preferably between 0.7 and 0.9 μm.

6. The treated copper foil according to claim 1 or 2, wherein the treatment stack comprises at least one of a heat-resistant layer containing zinc or nickel, a corrosion-resistant layer containing chromium, and an adhesion-promoting layer containing a silane compound.

7. The treated copper foil is 50 to 190 g / m². ２ A treated copper foil according to claim 1 or 2, having the area weight of the specified value.

8. The treated copper foil can withstand temperatures of 30 and 100 kgf / mm² at 20°C. ２ A treated copper foil according to claim 1 or 2, having a tensile strength between the specified values.

9. The treated copper foil according to claim 1 or 2, wherein the treated copper foil has an elongation between 3 and 30%.

10. Use of the treated copper foil described in claim 1 or 2 as a current collector for a secondary battery.

11. An electrode assembly including a current collector, comprising a treated copper foil according to claim 1 or 2, which supports an electrode having a silicon layer in which the amount of silicon in the silicon layer is greater than 50%, preferably at least 90%, more preferably 95% or greater.

12. The electrode assembly according to claim 11, wherein the silicon layer is formed by chemical vapor deposition of silicon, preferably by low-pressure plasma-enhanced chemical vapor deposition.

13. The electrode assembly according to claim 12, wherein the silicon layer has a thickness between 5 and 30 μm.

14. The electrode assembly according to claim 11, wherein a silicon layer is formed on each side surface of the treated copper foil.

15. A secondary battery comprising an electrolyte, a cathode assembly, an anode assembly, a separator layer, and a lithium salt compound, wherein the anode assembly comprises the treated copper foil described in claim 1 or 2, or the anode assembly is the electrode assembly described in claim 11.

16. a) Providing an untreated copper foil (2) having a first surface (2a) and a second surface (2b) opposite to the first surface, preferably having a surface roughness Rz between 1.0 and 2.5 μm on both surfaces of the electrolytic copper foil; b) In order to provide a predetermined surface roughness on both sides, the copper foil is immersed in an electroplating bath and a structuring treatment (3) is performed on each surface of the copper foil. c) Electroplating an additional continuous layer of copper (7) onto the nodule-containing layer; and d) Forming at least one functional layer (5) on an additional continuous layer of copper, A method for producing the treated copper foil according to claim 1 or 2, comprising the steps described above.

17. Step b) The copper foil is coated with 5 to 25 g / L of copper, preferably copper ions (Cu) ２＋ The process involves passing copper in a form and sulfuric acid at a concentration of 30 to 90 g / L, preferably between 40 and 80 g / L, through an electroplating bath, in which case the current flow rate is 15 to 30 A / dm². ２ Preferably 20 to 30 A / dm ２ The method according to claim 16, wherein the current density is applied and the immersion time is between 5 and 10 s.

18. The method according to claim 17, wherein the bath is maintained at a temperature between 20 and 30°C.

19. The method according to claim 17, wherein steps b) and c) are repeated on each surface to produce an ellipsoidal copper nodule having a height between 1.2 and 3.0 μm, preferably between 1.8 and 2.4 μm, and a diameter between 0.6 and 1.1 μm, preferably between 0.7 and 0.9 μm.

20. Step c) is 60 to 100 g / L of copper, preferably copper ions Cu ２＋ The process involves passing the plated copper through an electroplating bath containing copper in a specific form, sulfuric acid at a concentration of 30 to 90 g / L, preferably between 40 and 80 g / L, and in this case, at a rate of 15 to 30 A / dm ２ Preferably 15 to 25 A / dm ２ The method according to claim 16, wherein the current density is applied and the immersion time is between 5 and 10 s.

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