Copper foil, electrodes containing the same, a secondary battery containing the same, and a method for manufacturing the same.

Abstract

The present invention provides copper foil, an electrode containing the same, a secondary battery containing the same, and a method for manufacturing the same. [Solution] One embodiment of the present invention provides a copper foil comprising a copper film having a matte surface and a shiny surface, and a protective layer on the copper film, wherein the compressive elastic strain index is 10 to 30 GPa. The compressive elastic strain index is measured using a nano indenter.

Description

[Technical Field]

[0001] The present invention relates to copper foil, an electrode containing the same, a secondary battery containing the same, and a method for manufacturing the same. Specifically, the present invention relates to copper foil with improved corrosion resistance, an electrode containing the same, a secondary battery containing the same, and a method for manufacturing the same. [Background technology]

[0002] Secondary batteries are a type of energy conversion device that stores electrical energy as chemical energy and generates electricity by converting the chemical energy back into electrical energy when needed. They are used in portable electronic devices such as mobile phones and laptops, as well as as an energy source for electric vehicles. Because secondary batteries can be recharged, they are also called rechargeable batteries.

[0003] Compared to disposable primary batteries, secondary batteries offer economic and environmental advantages, including lead-acid batteries, nickel-cadmium secondary batteries, nickel-metal hydride secondary batteries, and lithium-ion secondary batteries.

[0004] In particular, lithium-ion batteries can store a relatively large amount of energy relative to their size and weight compared to other rechargeable batteries. Therefore, lithium-ion batteries are suitably used in the field of information and communication equipment where portability and mobility are important, and their application range is expanding to energy storage devices for hybrid and electric vehicles.

[0005] Lithium-ion secondary batteries are used repeatedly, with each cycle consisting of charging and discharging. To power any device using a fully charged lithium-ion secondary battery, the battery must have a high charge / discharge capacity to increase the device's operating time. Therefore, research is constantly needed to meet the ever-increasing expectations (needs) of consumers regarding the charge / discharge capacity of lithium-ion secondary batteries.

[0006] In particular, in order to increase the capacity of a lithium secondary battery, it has been proposed to use a composite active material in which Si or Sn is added to a carbonaceous active material as the negative electrode active material. However, such a composite active material has a relatively large thermal expansion rate compared to a normal negative electrode active material. The composite active material during charge and discharge of a lithium secondary battery causes rapid contraction and expansion, which promotes the separation of the electrolytic copper foil and the negative electrode active material and reduces the charge and discharge capacity retention rate of the lithium secondary battery. Further, when drying at a high temperature after coating the electrolytic copper foil with the negative electrode active material, the surface of the electrolytic copper foil is oxidized, which promotes the desorption of the negative electrode active material. The weaker the adhesion strength between the copper foil and the negative electrode active material, the more significantly the charge and discharge capacity retention rate of the lithium secondary battery decreases.

[0007] As the charge and discharge cycles are repeated, when the charge and discharge capacity of the secondary battery decreases rapidly (that is, when the capacity retention rate is low or the life is short), the consumer needs to replace the secondary battery frequently, which causes inconvenience to the consumer and waste of resources.

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, the present invention relates to a copper foil that can prevent problems caused by the limitations and disadvantages of the related art as described above, an electrode including the same, a secondary battery including the same, and a method for manufacturing the same.

[0009] One embodiment of the present invention aims to provide a copper foil having a compressive elastic strain index of 10 to 30 GPa and improved adhesion to an active material.

[0010] One embodiment of the present invention aims to provide a copper foil having a compressive elastic strain index of 10 to 30 GPa and excellent charge and discharge characteristics.

[0011] Another embodiment of the present invention aims to provide an electrode for a secondary battery including such a copper foil, and a secondary battery including such an electrode for a secondary battery.

[0012] A further embodiment of the present disclosure provides a method for manufacturing copper foil with improved adhesion to an active material. The method includes the steps of preparing an electrolyte containing copper ions, forming a copper film, and forming a protective layer on the copper film, wherein the step of forming the copper film includes showering the surface of a rotating anode drum with a cleaning agent and forming a copper film on the rotating anode drum by passing an electric current between a positive electrode plate and a rotating anode drum, which are spaced apart from each other in an electrolyte in an electrolytic cell. The electrolyte comprises 70-150 g / L of copper ions, 80-130 g / L of sulfuric acid, 15-25 ppm of chlorine (Cl), and an organic additive. The organic additive comprises a brightener (component A), a moderator (component B), and a roughness modifier (component C). The brightener (component A) comprises sulfonic acid or a metal salt thereof with a concentration of 1-15 ppm. The moderator (component B) comprises a nonionic water-soluble polymer with a concentration of 0.1-15 ppm. The roughness modifier (component C) comprises a nitrogen-containing heterocyclic quaternary ammonium salt or a derivative thereof with a concentration of 1-15 ppm.

[0013] According to yet another embodiment of the present disclosure, the cleaning agent comprises 8% (w / w) to 12% (w / w) sulfuric acid and 0.1% (w / w) to 0.3% (w / w) a polishing agent (component A), wherein the polishing agent (component A) in the cleaning agent comprises sulfonic acid or a metal salt thereof.

[0014] In addition to the aspects of the present invention mentioned above, other features and advantages of the present invention are described below, or can be clearly understood from such description to a person with ordinary skill in the art to which the present invention pertains. [Means for solving the problem]

[0015] One embodiment of the present invention provides a copper foil comprising a copper film having a matte surface and a shiny surface, and a protective layer on the copper film, wherein the compressive elastic strain index is 10 to 30 GPa. The compressive elastic strain index is measured using a nano indenter. [Effects of the Invention]

[0016] A copper foil according to one embodiment of the present invention can improve adhesion to an active material by having a compressive elastic strain index of 10 to 30 GPa.

[0017] A copper foil according to one embodiment of the present invention can have excellent charge-discharge characteristics by having a compressive elastic strain index of 10 to 30 GPa. [Brief explanation of the drawing]

[0018] [Figure 1] This is a cross-sectional view of copper foil according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view of copper foil according to another embodiment of the present invention. [Figure 3] This is a cross-sectional view of an electrode for a secondary battery according to another embodiment of the present invention. [Figure 4] This is a cross-sectional view of an electrode for a secondary battery according to yet another embodiment of the present invention. [Figure 5] This is a schematic cross-sectional view of a secondary battery according to yet another embodiment of the present invention. [Figure 6] This is a copper foil manufacturing apparatus according to yet another embodiment of the present invention. [Modes for carrying out the invention]

[0019] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the embodiments described below are presented only for illustrative purposes to aid in a clear understanding of the present invention and do not limit the scope of the invention.

[0020] The shapes, sizes, proportions, angles, numbers, etc., disclosed in the drawings illustrating embodiments of the present invention are illustrative, and the present invention is not limited to those shown in the drawings. The same components throughout the specification may be referred to by the same reference numerals. When describing the present invention, if a specific explanation of related prior art is deemed likely to unnecessarily obscure the gist of the invention, such detailed explanation will be omitted.

[0021] Wherever "includes," "has," "consists of," etc., as used herein, other parts may be added unless the expression "only" is used. Wherever a component is expressed singularly, it includes multiple components unless otherwise explicitly stated. Furthermore, in the interpretation of a component, it shall be interpreted as including a margin of error, even without further explicit statement.

[0022] When describing spatial relationships, for example, when the relationship between two parts is described using phrases such as "on top," "above," "below," or "beside," one or more other parts may be located between the two parts, unless the expressions "immediately" or "directly" are used.

[0023] Spatially relative terms such as "below" or "beneath," "lower," "above," and "upper" can be used to easily describe the correlation between one element or component and another, as shown in the drawing. Spatially relative terms should be understood as terms that include different directions of elements in use or operation, in addition to the directions shown in the drawing. For example, if elements shown in the drawing are flipped over, an element described as "below" or "beneath" of another element may be positioned "above" of the other element. Thus, the exemplary term "below" may include both the downward and upward directions. Similarly, the exemplary terms "up" or "above" may include both the upward and downward directions.

[0024] When describing temporal relationships, for example, when a temporal sequence is described using phrases such as "after," "following," "next," or "before," it may include non-continuous events unless expressions like "immediately" or "directly" are used.

[0025] While terms such as "first," "second," etc., are used to describe various components, these components are not limited by these terms. These terms are simply used to distinguish one component from others. Therefore, the first component referred to below may be the second component within the technical concept of the present invention.

[0026] The term "at least one" should be understood to include all possible combinations of one or more related items. For example, "at least one of items 1, 2, and 3" could mean not just each of items 1, 2, or 3 individually, but all possible combinations of items that could be presented from two or more of items 1, 2, and 3.

[0027] The terms "matte side" and "shiny side" can refer to a side that is relatively matte and a side that is relatively glossy, respectively, when comparing the two sides.

[0028] Each of the various embodiments of the present invention is partially or entirely combinable or combined with one another, enabling a variety of technically diverse interlocking and driving processes. Each embodiment may be implemented independently of the others or together in relation to one another.

[0029] Figure 1 is a cross-sectional view of copper foil 110a according to one embodiment of the present invention.

[0030] Referring to Figure 1, the copper foil 110a of the present invention includes a copper film 111 containing 99.9% by weight or more of copper. Referring to Figure 1, the copper foil 110a of the present invention includes the copper film 111 and a protective layer 112 on the copper film 111. Figure 1 shows a configuration in which the protective layer 112 is arranged on one surface of the copper film 111. However, the present invention is not limited thereto, and the protective layer 112 may be arranged on both surfaces of the copper film 111 (see Figure 2).

[0031] The copper film 111 may be formed on the rotating anode drum through electroplating, and may have a shiny surface that is in direct contact with the rotating anode drum during the electroplating process and a matte surface on the opposite side.

[0032] The protective layer 112 is formed by electrodepositing an anticorrosion material onto the copper film 111. The anticorrosion material may contain at least one of chromium compounds, silane compounds, and nitrogen compounds. The protective layer 112 prevents oxidation and corrosion of the copper film 111 and improves heat resistance, thereby extending the lifespan of the copper foil 110 itself, as well as the lifespan of the final product containing it.

[0033] The copper foil 110 described later can correspond to the copper foils 110a and 110b shown in Figures 1 and 2.

[0034] According to one embodiment of the present invention, the copper foil 110 has a compressive elastic strain index (E) of 10 to 30 GPa. IT ) may have. Specifically, the compressive elastic strain index (E) of the copper foil 110. IT When the pressure is 10-30 GPa, the copper foil 110 can be stable under external pressure and can have excellent adhesion to the active material.

[0035] The compressive elastic strain index (EIT) can be considered as the bulk modulus. The compressive elastic strain index (EIT) is a material property that indicates the degree to which copper foil resists volume deformation within its elastic range when external pressure is applied. In other words, the compressive elastic deformation index (EIT) can be described as the degree to which copper foil resists deformation when compressed within its elastic range. The compressive elastic deformation index is proportional to the ratio (dP / dV) of the rate of change of volume (dV) to the rate of change of pressure (dP). More specifically, the compressive elastic strain index (EIT) corresponds to the value (dP / dV) obtained by dividing the rate of change of pressure within the elastic deformation range by the rate of change of volume in a specific volume of copper foil.

[0036] Compressive elastic strain index of copper foil (E ITWhen the value is less than 10 GPa, when an external force is applied to the copper foil, the copper foil 110 can be excessively deformed, which can reduce the mechanical stability of the copper foil. Also, in a lithium secondary battery, physical changes repeatedly occur during the charge and discharge process, but when the compressive elastic strain index (E IT ) is less than 10 GPa, the adhesive force with the active material may decrease.

[0037] Also, when the compressive elastic strain index (E IT ) exceeds 30 GPa, there may occur a problem that the copper foil hardly elastically deforms against an external pressure. For example, a copper foil with a compressive elastic strain index (E IT ) exceeding 30 GPa hardly undergoes deformation, so when pressure or impact is continuously applied, there is a high possibility that fine cracks or peeling may occur in the copper foil. This may cause mechanical defects in the copper foil during long-term use.

[0038] According to the present invention, the compressive elastic strain index (E IT ) is measured by a nano indenter.

[0039] According to the present invention, the compressive elastic strain index (E IT ) is measured under the following conditions. - Temperature: 23 ± 2 °C - Humidity: 45 ± 5% R.H. - Manufacturer: Helmut Fischer - Model name: HM2000 - Load: 8 mN - Load Increase Time: 10 sec - Unload Increase Time: 10 sec - Creep Time: 3 sec - Indenter Type: Vickers Indenter (Correction Factor: 0.75)

[0040] According to the present invention, the compressive elastic strain index (E ITThis may be related to the elastic properties of the copper foil 110, among its elasticity and plasticity.

[0041] According to one embodiment of the present invention, the copper foil 110 has a Martens hardness of 600 to 1,000 MPa (H M ) may have. Specifically, the Martens hardness (H) of the copper foil 110. M When the pressure is between 600 and 1,000 MPa, the copper foil 110 can be stable under external pressure and can have excellent adhesion to the active material.

[0042] Marten hardness (HM), also known as Martens hardness, comprehensively represents the elastic and plastic properties of a material with respect to indentations. Marten hardness (HM) is determined by the value obtained from the load / indentation depth curve in a test in which an indenter is used to indent a copper foil until a predetermined test load is reached. Marten hardness (HM) may also correspond to the value obtained by dividing the load (or force) applied to the copper foil when the predetermined test load is reached during the indentation test by the indentation area formed in the copper foil.

[0043] Martens hardness of copper foil (H M If the Martens hardness (H) is less than 600 MPa, when an external force is applied to the copper foil, the copper foil 110 can deform excessively, reducing the mechanical stability of the copper foil. Also, in lithium secondary batteries, physical changes occur repeatedly during the charge and discharge process, but the Martens hardness (H) of the copper foil is less than 600 MPa. M If the pressure is less than 600 MPa, the adhesion to the active material may decrease.

[0044] Also, the Martens hardness of copper foil (H M When the compression Martens hardness (H) exceeds 1,000 MPa, a problem may occur where the copper foil hardly deforms elastically under external pressure. For example, M Copper foil with a pressure exceeding 1,000 MPa experiences very little deformation, but if subjected to sustained pressure or impact, it is highly likely that microscopic cracks or delamination will occur in the copper foil. This can lead to mechanical defects in the copper foil during long-term use.

[0045] According to the present invention, the Martens hardness (H M ) is measured by a nano indenter. Martens hardness (H) according to the present invention M ) is the compressive elastic strain index (E IT It is measured using the same measurement method as ).

[0046] According to the present invention, the Martens hardness (H M The higher the value, the greater the ability of the copper foil 110 according to the present invention to resist press-fitting, and the Martens hardness (H M A lower value may indicate that the copper foil 110 according to the present invention is easily deformed during press-fitting.

[0047] The Martens hardness (H) according to the present invention M ) is Martens hardness, which can represent a composite property of elasticity and plasticity against press-fitting.

[0048] According to one embodiment of the present invention, the copper foil 110 may have a plastic hardness (HIT) in the range of 1,000 to 1,500 MPa. Specifically, when the plastic hardness (HIT) of the copper foil 110 is 1,000 to 1,500 MPa, the copper foil 110 can be stable under external pressure and can have excellent adhesion to the active material.

[0049] In detail, plastic deformation refers to the phenomenon in which a material undergoes a permanent change in shape when an external force is applied, and does not return to its original state. In this invention, hit hardness (HIT) is a characteristic that indicates how well the copper foil resists permanent deformation (plastic deformation) when force or pressure is applied. Hit hardness (HIT) is evaluated by measuring the depth to which the indenter is pressed into the surface of the copper foil or the size of the indentation. In this invention, hit hardness (HIT) may be expressed as the pressure (expressed in MPa) at which the copper foil undergoes plastic deformation in the process of applying pressure to the copper foil using a nanoindenter and measuring the degree of plastic deformation.

[0050] Plastic hardness of copper foil (H IT If the plastic hardness (H) is less than 1,000 MPa, when an external force is applied to the copper foil, the copper foil 110 can deform excessively, reducing the mechanical stability of the copper foil. Also, in lithium secondary batteries, physical changes occur repeatedly during the charge and discharge process, but the plastic hardness (H) of the copper foil is important. IT If the pressure is less than 1,000 MPa, the adhesion to the active material may decrease.

[0051] Also, the plastic hardness of copper foil (H IT When the plastic hardness (H) exceeds 1,500 MPa, a problem may occur where the copper foil hardly deforms elastically against external pressure. For example, IT Copper foil with a pressure exceeding 1,500 MPa experiences very little deformation, but if subjected to sustained pressure or impact, it is highly likely that microscopic cracks or delamination will occur in the copper foil. This can lead to mechanical defects in the copper foil during long-term use.

[0052] According to the present invention, the plastic hardness (H IT ) is measured by a nano indenter. Plastic hardness (H) according to the present invention IT ) is the compressive elastic strain index (E IT It is measured using the same measurement method as ).

[0053] According to the present invention, the plastic hardness (H IT The higher the value, the greater the ability of the copper foil 110 according to the present invention to resist permanent deformation, and the plastic hardness (H IT A lower value may indicate that the copper foil 110 according to the present invention is more likely to undergo permanent deformation.

[0054] The plastic hardness (H) according to the present invention IT This may be related to the plasticity among the elasticity and plasticity of the copper foil 110.

[0055] According to one embodiment of the present invention, the copper foil 110 has a Vickers hardness (H) in the range of 80 to 150 Hv. V ) may have. Specifically, the Vickers hardness (H) of the copper foil 110. V When the temperature is between 80 and 150 Hv, the copper foil 110 can be stable under external pressure and can have excellent adhesion to the active material.

[0056] Vickers hardness (HV) is an index used to determine the deformation limit when scratching or compressive force is applied to copper foil. Vickers hardness (HV) is evaluated based on the surface area of ​​the indentation formed by pressing an indenter (e.g., a square pyramidal diamond indenter) against the copper foil. Vickers hardness (HV) is calculated by dividing the applied test load (F) by the indentation area. An example of the measurement method is as follows: 1) Using an indenter (e.g., a square pyramidal diamond indenter with a principal angle of 136°), press the copper foil with a predetermined load (F) for a certain period of time. 2) After removing the load, observe the indentation (square pyramidal indentation mark) formed on the copper foil under a microscope. 3) Measure the diagonal length of the indentation to calculate the residual indentation area, and divide the test load (F) by this indentation area to obtain the Vickers hardness (HV) value.

[0057] Vickers hardness of copper foil (H V If the Vickers hardness (H) is less than 80Hv, when an external force is applied to the copper foil, the copper foil 110 can deform excessively, reducing the mechanical stability of the copper foil. Also, in lithium secondary batteries, physical changes occur repeatedly during the charge and discharge process, but the Vickers hardness (H) of the copper foil is less than 80Hv. V If the temperature is below 80Hv, the adhesion to the active material may decrease.

[0058] Also, the Vickers hardness of copper foil (H V If the Vickers hardness (H) exceeds 150 Hv, a problem may arise where the copper foil hardly deforms elastically under external pressure. For example, if the Vickers hardness (H) exceeds 150 Hv, VCopper foil with a hardness exceeding 150 Hv is highly susceptible to deformation, but if subjected to sustained pressure or impact, it is likely to develop microscopic cracks or delamination. This can lead to mechanical defects in the copper foil during long-term use.

[0059] According to the present invention, the Vickers hardness (H V The Vickers hardness (H) is measured by a nano indenter. V ) is the compressive elastic strain index (E IT It is measured using the same measurement method as ).

[0060] According to the present invention, the Vickers hardness (H V A higher Vickers hardness (HV) value indicates a greater ability of the copper foil 110 according to the present invention to resist press-fitting, while a lower Vickers hardness (HV) value may indicate that the copper foil 110 according to the present invention is easily deformed during press-fitting.

[0061] When copper foil is used as a current collector in a secondary battery, the copper foil needs to expand and contract in response to the heat generated inside the battery and the expansion and contraction of the electrode active material. If the copper foil can easily expand and contract, it can prevent peeling or separation from the active material. If the copper foil does not peel or separate from the active material, the performance of the secondary battery, such as the charge / discharge capacity retention rate, can be maintained. In addition, the copper foil is required to have a certain strength in order to support the active material and ensure durability.

[0062] This invention introduces the following criteria for determining whether copper foil is sufficiently expandable and expandable for secondary battery applications and possesses the durability and strength necessary to support the active material. Specifically, the compressive elastic strain index (EIT), marten hardness (HM), press-fit hardness (HIT), and Vickers hardness (HV) are introduced as criteria for determining whether the copper foil has the expandability suitable for secondary battery applications and simultaneously possesses sufficient durability and strength to support the active material. Each of the above characteristics functions as a criterion for identifying the properties of copper foil, and by combining them, it is also possible to provide a criterion for comprehensively determining the properties of copper foil.

[0063] A copper foil 110 according to one embodiment of the present invention has a thickness of 3 to 35 μm. When the copper foil 110 is used as a current collector for electrodes in a secondary battery, the thinner the copper foil 110, the more current collectors can be accommodated in the same space, which is advantageous for increasing the capacity of the secondary battery. However, manufacturing copper foil 110 with a thickness of less than 3 μm causes a decrease in workability.

[0064] On the other hand, when manufacturing secondary batteries with copper foil 110 exceeding 35 μm in thickness, the thick copper foil 110 makes it difficult to achieve high capacity.

[0065] The following describes in detail the electrode 100 containing the copper foil 110 of the present invention and the secondary battery containing the electrode 100.

[0066] Figure 3 is a cross-sectional view of electrode 100a for a secondary battery according to one embodiment of the present invention. Figure 4 is a cross-sectional view of electrode 100b for a secondary battery according to another embodiment of the present invention.

[0067] As shown in Figure 3, an electrode 100a for a secondary battery according to one embodiment of the present invention includes one of the copper foils 110 and active material layer 120 from the embodiments of the present invention described above.

[0068] Figure 3 shows a configuration in which the active material layer 120 is formed on one surface of the copper foil 110. However, the present invention is not limited to this, and referring to Figure 4, the active material layer 120 can also be formed on both sides of the copper foil 110.

[0069] In lithium secondary batteries, aluminum foil is commonly used as the positive electrode current collector that bonds with the positive electrode active material, and copper foil 110 is commonly used as the negative electrode current collector that bonds with the negative electrode active material.

[0070] According to one embodiment of the present invention, the electrode 100 for the secondary battery is a negative electrode, the copper foil 110 is used as a negative electrode current collector, and the active material layer 120 contains a negative electrode active material.

[0071] To ensure the high capacity of the secondary battery, the active material layer 120 of the present invention may be formed of a carbon-metal composite. The metal may include, for example, at least one of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, and Fe, preferably Si and / or Sn.

[0072] Figure 5 is a schematic cross-sectional view of a secondary battery according to one embodiment of the present invention.

[0073] Referring to Figure 5, the secondary battery includes a cathode 370, a negative electrode 340, an electrolyte 350 placed between the cathode 370 and the negative electrode 340 to provide an environment in which ions can move, and a separator 360 that electrically insulates the cathode 370 and the negative electrode 340. Here, the ions that move between the cathode 370 and the negative electrode 340 are, for example, lithium ions. The separator 360 separates the cathode 370 and the negative electrode 340 to prevent the charge generated at one electrode from being wasted by moving to the other electrode through the interior of the secondary battery. Referring to Figure 5, the separator 360 is placed within the electrolyte 350.

[0074] The positive electrode 370 includes a positive electrode current collector 371 and a positive electrode active material layer 372, and aluminum foil can be used as the positive electrode current collector 371.

[0075] The negative electrode 340 includes a negative electrode current collector 341 and a negative electrode active material layer 342, and copper foil 110 can be used as the negative electrode current collector 341.

[0076] According to one embodiment of the present invention, the copper foil 110 shown in Figures 1 and 2 can be used as the negative electrode current collector 341. In addition, the secondary battery electrodes 100a and 100b shown in Figure 3 or Figure 4 can be used as the negative electrode 340 of the secondary battery shown in Figure 5.

[0077] The method for manufacturing the copper foil 110 of the present invention will be specifically described below with reference to Figure 6.

[0078] The present invention provides a method for manufacturing copper foil 110, which includes the steps of forming a copper film 111 and forming a protective layer 112 on the copper film 111.

[0079] The method of the present invention includes the step of forming a copper film 111 on a rotating negative electrode drum 40 by energizing a positive electrode plate 30 and a rotating negative electrode drum 40 that are arranged spaced apart from each other in an electrolyte 20 in an electrolytic cell 10.

[0080] As shown in Figure 6, the positive electrode plate 30 may include first and second positive electrode plates 31 and 32 that are electrically insulated from each other.

[0081] The copper film 111 formation step can be carried out by forming a seed layer by energizing the first positive electrode plate 31 and the rotating negative electrode drum 40, and subsequently growing the seed layer by energizing the second positive electrode plate 32 and the rotating negative electrode drum 40.

[0082] The current densities supplied by the first and second anode plates 31 and 32, respectively, are 40 to 130 A / dm². 2 (ASD) is also acceptable.

[0083] If the current densities provided by the first and second positive electrode plates 31 and 32, respectively, are less than 40 ASD, the surface roughness of the copper foil 110 may be low, and the adhesion between the copper foil 110 and the active material layer 120 may not be sufficient.

[0084] On the other hand, if the current densities provided by the first and second positive plates 31 and 32, respectively, exceed 130 ASD, the surface of the copper foil 110 may become rough, and the coating of the active material may not be carried out smoothly.

[0085] The surface properties of the copper film 111 can be changed by the degree of surface buffing or polishing of the rotating anode drum 40. For example, the surface of the rotating anode drum 40 can be polished with an abrasive brush having a grit size (Grit) of #800 to #3000.

[0086] During the formation of the copper film 111, the electrolyte 20 is maintained at a temperature of 40-65°C. More specifically, the temperature of the electrolyte 20 can be maintained at 45°C or higher. In this process, the physical, chemical, and electrical properties of the copper film 111 can be controlled by adjusting the composition of the electrolyte 20.

[0087] According to one embodiment of the present invention, the electrolyte 20 may contain copper ions, sulfuric acid, chlorine, and organic additives.

[0088] To facilitate the formation of the copper film 111 by copper electrodeposition, the concentrations of copper ions and sulfuric acid in the electrolyte 20 are adjusted to 70-150 g / L and 80-130 g / L, respectively.

[0089] In one embodiment of the present invention, chlorine (Cl) is a chloride ion (Cl - This includes all chlorine atoms present in the molecule. Chlorine (Cl) can be used, for example, to remove silver (Ag) ions that flow into the electrolyte 20 during the process of forming the copper film 111. Specifically, chlorine (Cl) can precipitate silver (Ag) ions in the form of silver chloride (AgCl). Such silver chloride (AgCl) can be removed by filtration.

[0090] If the chlorine (Cl) concentration is less than 15 ppm, the removal of silver (Ag) ions will not proceed smoothly. On the other hand, if the chlorine (Cl) concentration exceeds 25 ppm, unwanted reactions may occur due to an excess of chlorine (Cl). Therefore, the chlorine (Cl) concentration in the electrolyte 20 is controlled within the range of 15 to 25 ppm.

[0091] According to one embodiment of the present invention, the electrolyte 20 may contain organic additives.

[0092] The organic additives contained in the electrolyte 20 include a brightener (component A), a moderator (component B), and a roughness modifier (component C).

[0093] The glossing agent (component A) contains sulfonic acid or a metal salt thereof. The glossing agent (component A) may have a concentration of 1 to 15 ppm in the electrolyte 20.

[0094] The brightener (component A) can increase the charge of the electrolyte 20, increase the electrodeposition rate of copper, improve the curl characteristics of the copper foil, and increase the gloss of the copper foil 110. If the concentration of the brightener (component A) is less than 1 ppm, the gloss of the copper foil 110 will decrease, and if it exceeds 15 ppm, problems such as changes in the weight or surface roughness of the copper foil 110 after immersion may occur.

[0095] The glossing agent may include, for example, at least one of the following: bis-(3-sulfopropyl)-disulfide disodium salt, 3-mercapto-1-propanesulfonic acid, 3-(N,N-dimethylthiocarbamoyl)-thiopropanesulfonate sodium salt, 3-[(amino-iminomethyl)thio]-1-propanesulfonate sodium salt, o-ethyldithiocarbonate-S-(3-sulfopropyl)-ester sodium salt, 3-(benzothiazolyl-2-mercapto)-propyl-sulfonate sodium salt, and ethylenedithiodipropylsulfonic acid sodium salt.

[0096] The moderator (component B) contains a nonionic water-soluble polymer. The moderator (component B) may have a concentration of 0.1 to 15 ppm in the electrolyte 20.

[0097] The moderator (component B) reduces the electrodeposition rate of copper, preventing a rapid increase in the roughness and decrease in strength of the copper foil 110. Such a moderator (component B) is also called an inhibitor or suppressor.

[0098] If the concentration of the moderator (component B) is less than 0.1 ppm, the roughness of the copper foil 110 increases rapidly, and a problem may arise where the surface condition of the copper foil 110 changes. On the other hand, even if the concentration of the moderator (component B) exceeds 15 ppm, there is almost no change in the physical properties of the copper foil 110, such as appearance, gloss, roughness, strength, and elongation. Therefore, the concentration of the moderator (component B) can be adjusted within the range of 0.1 to 15 ppm without unnecessarily increasing the concentration of the moderator (component B), thereby increasing manufacturing costs and wasting raw materials.

[0099] The moderator (component B) may include, for example, at least one nonionic water-soluble polymer selected from polyethylene glycol (PEG), polypropylene glycol, polyethylene polypropylene copolymer, polyglycerin, polyethylene glycol dimethyl ether, hydroxyethylene cellulose, polyvinyl alcohol, polyglycol stearate ether, and stearyl alcohol polyglycol ether. However, the type of moderator is not limited to these, and other nonionic water-soluble polymers that can be used in the production of high-strength copper foil 110 can be used as moderators.

[0100] The roughness modifier (component C) includes nitrogen-containing heterocyclic quaternary ammonium salts or their derivatives.

[0101] The roughness modifier (component C) improves the glossiness and flatness of the copper foil 110. The roughness modifier (component C) may have a concentration of 1 to 15 ppm in the electrolyte 20.

[0102] If the concentration of the roughness modifier (component C) is less than 1 ppm, a problem occurs where the improvement in gloss and flatness of the copper foil 110 does not occur. On the other hand, if the concentration of the roughness modifier (component C) exceeds 15 ppm, a problem occurs where the surface gloss of the copper foil 110 becomes uneven and the surface roughness increases rapidly.

[0103] The roughness modifier (component C) may contain at least one of the compounds represented by the following chemical formulas 1 to 5. [ka] [ka] [ka] [ka] [ka]

[0104] In chemical formulas 1-5, l1-l4, m1-m4, and n1-n5 each represent repeating units, are integers greater than or equal to 1, and may be the same or different from one another.

[0105] According to one embodiment of the present invention, the compounds represented by chemical formulas 1 to 5 each have a number average molecular weight of 500 to 12,000.

[0106] If the number-average molecular weight of the compounds represented by chemical formulas 1-5 used as roughness modifiers is less than 500, the monomer ratio is high, resulting in high surface roughness of the copper foil 110. If the roughness modifier content is low, the surface roughness of the copper film 111 increases, and its gloss and flatness may decrease.

[0107] When the number-average molecular weight of the compounds represented by chemical formulas 1-5 exceeds 12,000, the deviation in the surface roughness of the copper foil 110 increases. In this case, even by adjusting the concentrations of other additives, it is difficult to suppress the increase in the deviation in the surface roughness of the copper foil 110.

[0108] Compounds represented by chemical formulas 1 to 5 can be prepared, for example, by polymerization or copolymerization using DDAC (Diallyl dimethyl ammonium chloride).

[0109] Examples of compounds represented by chemical formula 1 include PAS-2451 (Mw 30,000, Nittobo).

[0110] Examples of compounds represented by chemical formula 2 include PAS-84 (Mw20,000, Nittobo).

[0111] Examples of compounds represented by chemical formula 3 include PAS-2351 (Mw 25,000, Nittobo).

[0112] Examples of compounds represented by chemical formula 4 include PAS-A-1 (Mw 5,000, Nittobo) and PAS-A-5 (Mw 4,000, Nittobo).

[0113] Examples of compounds represented by chemical formula 5 include PAS-J-81 (Mw 180,000, Nittobo).

[0114] When the copper film 111 is formed, the flow rate of the electrolyte 20 supplied into the electrolytic cell 10 is 41-45 m / s. 3 / hour is also acceptable.

[0115] According to one embodiment of the present invention, before immersing the rotating anode drum 40 in the electrolyte 20 manufactured as described above to form a copper film 111 on the rotating anode drum 40, the surface of the rotating anode drum 40 can be showered or washed with a cleaning agent.

[0116] According to the present invention, the cleaning agent is an aqueous solution containing 8% (w / w) to 12% (w / w) sulfuric acid and a glossing agent (component A) in the range of 0.1% (w / w) to 0.3% (w / w). In this case, the glossing agent (component A) may contain any one of the types of glossing agents (component A) described above.

[0117] According to the present invention, when the surface of the rotating anode drum 40 is showered with a cleaning agent, the sulfuric acid in the cleaning agent reacts with oxides present on the surface of the rotating anode drum 40, which is effective in dissolving or removing the oxides.

[0118] Furthermore, titanium (Ti) may be present on the surface of the rotating anode drum 40 from which the oxides have been removed. If the titanium (Ti) present on the surface of the rotating anode drum 40 is exposed to air, an oxide film may form on the surface of the rotating anode drum 40. Since such a titanium oxide film has insulating properties, it can obstruct the flow of current, which can make it difficult to achieve a uniform current distribution in the electroplating process. Also, if the titanium oxide film becomes thick, the surface of the rotating anode drum 40 becomes irregular, and the desired thickness and flatness may not be maintained during the plating process.

[0119] In this case, the brightener (component A) in the cleaning agent can coat the surface of the rotating anode drum 40 before the titanium (Ti) present on the surface of the rotating anode drum 40 is exposed to the air. As a result, it is possible to prevent the formation of a titanium oxide film on the surface of the rotating anode drum 40.

[0120] In other words, if the surface of the rotating anode drum 40 is not showered or washed with a cleaning agent before immersing the rotating anode drum 40 in the electrolyte 20 to form a copper film 111 on the rotating anode drum 40, the surface of the manufactured copper foil may become irregular, and the copper foil may have more defects. As a result, the copper foil may have a compressive elastic strain index outside the range of 10 to 30 GPa.

[0121] Therefore, in order for the copper foil 110 to have a compressive elastic strain index in the range of 10 to 30 GPa, it is necessary to shower or wash the surface of the rotating anode drum 40 with a cleaning agent before immersing the rotating anode drum 40 in the electrolyte 20 to form a copper film 111 on the rotating anode drum 40.

[0122] According to the present invention, in order for the copper foil 110 to have a compressive elastic strain index in the range of 10 to 30 GPa, the concentration of the brightener (component A) in the cleaning agent must be maintained in the range of 0.1% (w / w) to 0.3% (w / w).

[0123] If the concentration of the brightener (component A) in the cleaning agent is less than 0.1% (w / w), the amount of brightener (component A) in the cleaning agent may be insufficient, and the pretreatment effect of the rotating negative electrode drum 40 may be inadequate. As a result, the copper foil may have more defects, and the copper foil may have a compressive elastic strain index outside the range of 10 to 30 GPa.

[0124] Furthermore, if the concentration of the brightener (component A) in the cleaning agent exceeds 0.3% (w / w), the brightener (component A) can be excessively adsorbed onto the rotating anode drum 40. When a large amount of brightener (component A) is adsorbed onto the rotating anode drum 40 in this way, it occupies sites on the rotating anode drum 40 where other organic additives are adsorbed, thus reducing the opportunity for other organic additives to be adsorbed onto the rotating anode drum 40. If an appropriate adsorption balance is maintained among the organic additives, the physical properties of the copper foil 110 according to the present invention can be obtained. However, if the brightener (component A) is excessively adsorbed onto the rotating anode drum 40, this balance may be disrupted. That is, the gloss of the copper foil may become even better, but the decelerator (component B) and roughness modifier (component C), which improve the surface properties of the copper foil, may not be sufficiently adsorbed onto the rotating anode drum 40, resulting in a problem where the surface properties of the copper foil deteriorate. As a result, the copper foil may have more defects, and the copper foil may have a compressive elastic strain index outside the range of 10 to 30 GPa.

[0125] According to the present invention, in order for the copper foil 110 to have a compressive elastic strain index in the range of 10 to 30 GPa, the sulfuric acid in the cleaning agent needs to be maintained at a concentration in the range of 8% (w / w) to 12% (w / w).

[0126] If the concentration of sulfuric acid in the cleaning agent is less than 8% (w / w), it may react with oxides present on the surface of the rotating negative electrode drum 40, potentially resulting in insufficient dissolution or removal of the oxides. This can lead to an irregular surface on the manufactured copper foil, potentially resulting in more defects in the copper foil. Consequently, the copper foil may have a compressive elastic strain index outside the 10-30 GPa range.

[0127] Furthermore, if the concentration of sulfuric acid in the cleaning agent exceeds 12% (w / w), a high concentration of sulfuric acid is present on the surface of the rotating negative electrode drum 40, which excessively increases the current density and makes it difficult to obtain copper foil of the desired quality. In addition, if the concentration of sulfuric acid in the cleaning agent is excessive, it may cause non-uniform defects on the surface of the copper foil, making it difficult to obtain the physical properties of the copper foil 110 according to the present invention. As a result, the surface of the manufactured copper foil becomes irregular, and the copper foil may have more defects. Consequently, the copper foil may have a compressive elastic strain index outside the range of 10 to 30 GPa.

[0128] According to the present invention, even if the surface of the rotating negative electrode drum 40 is showered with a cleaning agent, the brightener (component A) in the electrolyte 20 may have a concentration of 1 to 15 ppm, and the sulfuric acid may have a concentration of 70 to 150 g / L.

[0129] To ensure the cleanliness of the electrolyte 20, the copper wire (Cu wire) that is the raw material for the electrolyte 20 can be washed.

[0130] According to one embodiment of the present invention, the steps for producing the electrolyte 20 may include a step of heat-treating a copper wire, a step of pickling the heat-treated copper wire, a step of washing the pickled copper wire with water, and a step of putting the washed copper wire into sulfuric acid for the electrolyte.

[0131] More specifically, in order to maintain the cleanliness of the electrolyte 20, copper for the production of the electrolyte 20 can be produced by sequentially following the steps of: heat-treating high-purity (99.9% or higher) copper wire (Cu wire) in an electric furnace at 750°C to 850°C to burn off various organic impurities attached to the copper wire; pickling the copper wire that has been heat-treated with a 10% sulfuric acid solution for 10 to 20 minutes; and rinsing the pickled copper wire with distilled water. The rinsed copper wire can then be added to sulfuric acid for the electrolyte to produce the electrolyte 20.

[0132] The copper film 111 manufactured in this manner can be washed in a washing tank.

[0133] For example, acid cleaning can be performed sequentially to remove impurities on the surface of the copper film 111, such as resin components or natural oxide films, followed by water cleaning to remove the acidic solution used in acid cleaning. The cleaning step may be omitted.

[0134] Next, a protective layer 112 is formed on the copper film 111.

[0135] Referring to Figure 6, the step may further include immersing the copper film 111 in an anticorrosion solution 60. When the copper film 111 is immersed in the anticorrosion solution 60, it may be guided by a guide roll placed in the anticorrosion solution 60.

[0136] As mentioned above, the rust-preventive liquid 60 may contain at least one of a chromium compound, a silane compound, and a nitrogen compound. For example, the copper film 111 can be immersed in a 1-10 g / L potassium dichromate solution at room temperature for 1-30 seconds.

[0137] Furthermore, the protective layer 112 may contain silane compounds obtained by silane treatment, or nitrogen compounds obtained by nitrogen treatment.

[0138] The copper foil 110 is produced by forming such a protective layer 112.

[0139] The electrode for a secondary battery (i.e., a negative electrode) of the present invention can be manufactured by coating one or more negative electrode active materials selected from the group consisting of carbon; metal (Me) of Si, Ge, Sn, Li, Zn, Mg, Cd, Ce, Ni, or Fe; alloys containing the metal (Me); oxides (MeOx) of the metal (Me); and composites of the metal (Me) and carbon onto one or both sides of the copper foil 110 of the present invention manufactured by the method described above.

[0140] For example, 100 parts by weight of carbon for the negative electrode active material is mixed with 1 to 3 parts by weight of styrene-butadiene rubber (SBR) and 1 to 3 parts by weight of carboxymethylcellulose (CMC), and then a slurry is prepared using distilled water as a solvent. Next, the slurry is applied to the copper foil 110 to a thickness of 20 to 60 μm using a doctor blade, and heated at 110 to 130°C for 0.5 to 1.5 ton / cm². 2 Press with this pressure.

[0141] A secondary battery can be manufactured using the electrode (negative electrode) for the secondary battery of the present invention, manufactured by the method described above, along with a conventional positive electrode, electrolyte, and separator membrane.

[0142] The present invention will be described in detail below with reference to examples and comparative examples. However, the following examples are provided to aid in understanding the present invention, and the scope of the present invention is not limited to these examples.

[0143] Examples 1-4 Copper foil was manufactured using a foil-making machine that included an electrolytic cell 10, a rotating negative electrode drum 40 positioned in the electrolytic cell 10, and a positive electrode plate 30 positioned away from the rotating negative electrode drum 40. The electrolyte 20 was a copper sulfate solution. The concentration of copper ions in the electrolyte 20 was set to 87 g / L, the concentration of sulfuric acid to 110 g / L, the temperature of the electrolyte to 55°C, and the current density to 60 ASD.

[0144] Furthermore, the concentration of chlorine (Cl) in the electrolyte solution 20 was maintained at 20 ppm, and the concentrations of the organic additives were as shown in Table 1 below.

[0145] Among the organic additives, bis-(3-sulfopropyl)-disulfide disodium salt (SPS) is used as the brightener (component A), polyethylene glycol (PEG) is used as the moderator (component B), and diallylmethylethylammonium ethyl sulfate maleic acid copolymer (PAS-2451) is used as the roughness modifier (component C). TM Nittobo (MW30,000) was used.

[0146] Before immersing the rotating anode drum 40 in the electrolyte solution 20, the surface of the rotating anode drum 40 was cleaned using a cleaning agent. The cleaning agent used was an aqueous solution containing sulfuric acid and a polishing agent (component A). Bis-(3-sulfopropyl)-disulfide disodium salt (SPS) was used as the polishing agent (component A) in the cleaning agent. The concentrations of sulfuric acid and polishing agent (component A) in the cleaning agent are shown in Table 1 below.

[0147] A copper film 111 was manufactured by applying a current at a current density of 60 ASD between the rotating negative electrode drum 40 and the positive electrode plate 30. Next, copper foil was manufactured by immersing the copper film 111 in a rust-preventive solution for about 2 seconds and applying a chromate treatment to both sides of the copper film 111 to form a protective layer 112. A rust-preventive solution mainly composed of chromic acid was used, and the concentration of chromic acid was 5 g / L.

[0148] As a result, copper foils of Examples 1 to 4 were manufactured. The thickness of the manufactured copper foil was 8 μm.

[0149] Comparative Examples 1-2 The concentrations of organic additives, whether or not drum cleaning was performed, and the concentrations of polishing agents in the cleaning agent are as shown in Table 1 below.

[0150] Comparative Examples 1 and 2 were manufactured using the same method as in Examples 1 to 4. In this case, the thickness of the manufactured copper foil was 8 μm.

[0151] Comparative Examples 3-4 The concentration of organic additives and whether or not drum cleaning was performed are as shown in Table 1 below.

[0152] The copper foil was manufactured in the same manner as in Examples 1 to 4, except that the surface of the rotating anode drum 40 was showered with a cleaning agent before immersing the rotating anode drum 40 in the electrolyte 20 to form a copper film 111 on the rotating anode drum 40. In this case, the thickness of the manufactured copper foil was 8 μm.

[0153] [Table 1]

[0154] [Table 2]

[0155] [Table 3]

[0156] For the copper foils of Examples 1-4 and Comparative Examples 1-4 manufactured in this manner, (i) compressive elastic strain index, (ii) Martens hardness, (iii) plastic hardness, (iv) Vickers hardness, (v) peel strength, and (vi) volume retention rate were confirmed.

[0157] The copper foil was cut to obtain a 10cm x 10cm sample.

[0158] (i) Compressive elastic strain index (E IT ) Compressive elastic strain index (E IT ) is measured by a nano indenter.

[0159] The specific measurement conditions are as follows: -Temperature: 23±2℃ -Humidity: 45±5%RH -Manufacturer: Helmut Fischer -Model name: HM2000 -Load:8mN - Load Increase Time: 10 sec -Unload Increase Time: 10 sec -Creep Time: 3 sec -Indenter Type:Vickers Indenter(Correction Factor:0.75)

[0160] (ii) Martens hardness (H M ) Martens hardness (H M The compressional strain index (E) is measured by a nano indenter. The specific measurement conditions are as follows: IT The measurement conditions are the same as those used for )

[0161] (iii) Plastic hardness (H IT ) Plastic hardness (H IT The compressional strain index (E) is measured by a nano indenter. The specific measurement conditions are as follows: IT The measurement conditions are the same as those used for )

[0162] (iv) Vickers hardness (H V ) Vickers hardness (H V The compressional strain index (E) is measured by a nano indenter. The specific measurement conditions are as follows: IT The measurement conditions are the same as those used for )

[0163] (v) Peel strength For the negative electrode active material, 100 parts by weight of commercially available carbon was mixed with 2 parts by weight of SBR (styrene-butadiene rubber) and 2 parts by weight of CMC (carboxymethylcellulose). Next, distilled water was added to this mixture as a solvent to produce a slurry. Using a doctor blade, the slurry was applied to the surface of copper foil (width: 10 cm) to a thickness of approximately 60 μm, dried at 120°C for 10 minutes, and then subjected to a pressing process (pressure: 1 ton / cm²). 2 The negative electrode was manufactured by performing the following procedure.

[0164] After attaching the active material-laid surface of the negative electrode sample (width: 12.7 mm) with double-sided tape, the peel strength between the copper foil and the active material was measured using a universal testing machine (UTM) while peeling the copper foil at a 90° angle according to the IPC-TM-650 standard (measurement speed: 50 mm / min).

[0165] (vi) Capacity retention rate For the negative electrode active material, 100 parts by weight of commercially available carbon was mixed with 2 parts by weight of SBR (styrene-butadiene rubber) and 2 parts by weight of CMC (carboxymethylcellulose). Next, distilled water was added to this mixture as a solvent to produce a slurry. Using a doctor blade, the slurry was applied to the surface of electrolytic copper foil (width: 10 cm) to a thickness of approximately 60 μm, dried at 120°C for 10 minutes, and then subjected to a pressing process (pressure: 1 ton / cm²). 2 The negative electrode was manufactured by performing the following procedure.

[0166] Lithium manganese oxide (Li 1.1 Mn 1.85 Al 0.05 A positive electrode active material was prepared by mixing O4 and orthorhombic lithium manganese oxide (o-LiMnO2) in a weight ratio of 90:10. A slurry was prepared by mixing the positive electrode active material, carbon black, and polyvinylidene fluoride (PVDF) with NMP as an organic solvent in a weight ratio of 85:10:5. The positive electrode was prepared by coating both sides of a 20 μm thick aluminum foil with the slurry and then drying it.

[0167] Furthermore, a basic electrolyte was prepared by dissolving 1 M of LiPF6 as a solute in a non-aqueous organic solvent, which was a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 1:2 weight ratio. This basic electrolyte was then mixed with 0.5% by weight of succinic anhydride to produce another electrolyte.

[0168] A secondary battery was manufactured using the negative electrode, positive electrode, and electrolyte produced in this manner.

[0169] Next, the capacity per g of the positive electrode was measured for the secondary batteries manufactured in this manner at a charging operating voltage of 4.3V and a discharging operating voltage of 3.4V. A charge-discharge experiment was performed 50 times at a charge-discharge rate of 0.2C at 50°C, and the capacity retention rate of the secondary batteries was calculated using Equation 1 below. [Formula 1] Capacity retention rate (%) = (Discharge capacity at 50th discharge / Discharge capacity at 1st discharge) × 100

[0170] Referring to Tables 1 to 3, the copper foils from Examples 1 to 4 met the compressive elastic strain index range of 10 to 30 GPa and achieved a secondary battery capacity retention rate of 90% or more. However, the copper foils from Comparative Examples 1 to 4 did not meet the compressive elastic strain index range of 10 to 30 GPa and had a peel strength of 13 N / mm². 2 The peel strength between the copper foil and the active material was so low that it could not be achieved, resulting in the secondary battery's capacity retention rate not meeting the industry requirement of 90%.

[0171] The present invention, as described above, is not limited by the embodiments and examples and accompanying drawings, and it will be apparent to those with ordinary skill in the art to which the present invention pertains that various substitutions, modifications, and alterations are possible without departing from the technical matters of the present invention. Accordingly, the scope of the present invention is expressed by the claims described below, and it should be understood that all modified or altered forms derived from the meaning, scope, and equivalent concepts of the claims are included within the scope of the present invention. [Explanation of symbols]

[0172] 100 Electrodes for Secondary Batteries 110, 110a, 110b copper foil 111 Copper Film 112 Protective Layer 120 living matter layer 10 Electrolytic Cells 20 Electrolyte

Claims

1. A copper film having a matte surface and a shiny surface, The protective layer on the copper film includes, Copper foil with a compressive elastic strain index of 10-30 GPa: The compressive elastic strain index is measured using a nanoindenter.

2. The copper foil according to claim 1, having a Martens hardness in the range of 600 to 1,000 MPa: The aforementioned Martens hardness is measured using a nanoindenter.

3. The copper foil according to claim 1, having a plastic hardness in the range of 1,000 to 1,500 MPa: The aforementioned plastic hardness is measured using a nanoindenter.

4. The copper foil according to claim 1, having a Vickers hardness in the range of 80 to 150 Hv: The Vickers hardness is measured using a nanoindenter.

5. The copper foil according to claim 1, wherein the protective layer comprises at least one of a chromium compound, a silane compound, and a nitrogen compound.

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