Negative electrode for lithium-free secondary battery, method for manufacturing the same, and lithium-free secondary battery containing the same

Abstract

The present invention relates to a negative electrode for a lithium-free secondary battery, a method for manufacturing the same, and a lithium-free secondary battery, which can be made lighter and thinner while reducing side reactions on the negative electrode and improving the electrochemical properties and lifespan characteristics of the lithium-free secondary battery.

Description

Technical Field

[0001] [Cross-reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0168063 filed on November 28, 2023 and Korean Patent Application No. 10-2024-0165866 filed on November 20, 2024, and all the contents disclosed in the documents of the Korean patent applications are included as part of this specification.

[0002] The present invention relates to a negative electrode for a lithium-free secondary battery, a method for manufacturing the same, and a lithium-free secondary battery, which can be lightweight and thin, reduce side reactions on the negative electrode, and improve the electrochemical characteristics and life characteristics of the lithium-free secondary battery.

Background Art

[0003] A lithium metal battery is a battery that applies a negative electrode active material made of a lithium metal (Li-metal) material, and has the advantage of having a theoretically high energy density and capacity compared to a battery that applies a conventional graphite-based negative electrode. Therefore, research and development related to applying such a lithium metal battery to a battery that requires a high energy density have been continuously conducted.

[0004] However, problems such as large side reactions and low reversibility of lithium metal batteries have not yet been solved. Therefore, in an attempt to compensate for the low reversibility of lithium metal batteries, excessive lithium has been previously stored in the negative electrode and an attempt has been made to drive the lithium metal battery. However, as the N / P ratio (N / P ratio) of the secondary battery increases, the energy density of the lithium metal battery may be significantly reduced, and problems of cost and safety due to excessive lithium may also occur, so such attempts are facing limitations.

[0005] Therefore, in recent years, there has been increasing interest in so-called lithium-free secondary batteries or anode-free secondary batteries, which are secondary batteries without a negative electrode. Such lithium-free secondary batteries refer to secondary batteries in which, in the manufacturing process, a separate lithium metal layer is not formed on the negative electrode current collector, and the negative electrode current collector itself is included as the negative electrode. Such lithium-free secondary batteries can be defined as batteries in which lithium metal is electrodeposited onto the negative electrode current collector during charging, and this lithium metal is used as the negative electrode active material. The aforementioned lithium-free secondary batteries can maximize the use of the high energy density of lithium metal while mitigating safety issues such as those caused by the storage of excess lithium.

[0006] However, in the case of such lithium-free secondary battery negative electrodes, the negative electrode current collector is not completely covered by a lithium metal layer, and only a limited amount of lithium metal is used as the negative electrode active material. This can lead to numerous side reactions in the negative electrode, including galvanic corrosion, and rapid capacity loss. Furthermore, the lithium metal can be unevenly electrodeposited and grown on the negative electrode current collector, resulting in the formation of lithium dendrites.

[0007] Previously, in order to induce uniform growth of lithium on the negative electrode current collector and suppress the formation of lithium dendrites, methods were studied to increase the surface area of ​​the negative electrode by forming a three-dimensional porous microstructure on the negative electrode current collector.

[0008] However, conventional negative electrodes for lithium-free secondary batteries almost always had large thickness and weight in order to form a three-dimensional porous microstructure on the metal current collector. Therefore, when applied to such lithium-free secondary battery negative electrodes, there was a disadvantage in that the energy density per unit volume of the battery was significantly reduced.

[0009] Furthermore, the large surface area of ​​the negative electrode can lead to increased side reactions between the current collector and the lithium metal and electrolyte deposited during charging, significantly reducing the initial capacity of the secondary battery. This can also accelerate galvanic corrosion, resulting in a decrease in the lifespan characteristics of the secondary battery, among other drawbacks. [Overview of the project] [Problems that the invention aims to solve]

[0010] Therefore, the object of the present invention is to provide a negative electrode for a lithium-free secondary battery that can be made lighter and thinner, while reducing galvanic corrosion and side reactions on the negative electrode and enabling uniform electrodeposition of lithium metal, and a method for manufacturing the same.

[0011] Another object of the present invention is to provide a lithium-free secondary battery that includes the negative electrode and exhibits improved safety, electrochemical properties, and lifespan characteristics. [Means for solving the problem]

[0012] According to one embodiment of the present invention, a porous metal layer having a three-dimensional microstructure; and a conductive carbon nanostructure formed on the porous metal layer, The porous metal layer includes a metal mesh layer in which fibrous metal having a diameter on the micron (μm) scale forms a network structure, and a metal nanostructure formed on the fibrous metal. At least a portion of the metal nanostructures are interconnected, providing a negative electrode for a lithium-free secondary battery that defines a plurality of pores on the porous metal layer.

[0013] In such a negative electrode, the metal nanostructure may include metal nanorods or metal nanofibers, and the conductive carbon nanostructure may include carbon nanotubes.

[0014] Furthermore, the porous metal layer can have a thickness of 10 μm to 30 μm and a concentration of 4.0 mg / cm³. 2 ~10.0 mg / cm³ 2 It can have a mass per unit area. Furthermore, the porous metal layer can have a porosity of 55% to 70%.

[0015] According to another embodiment of the invention, a method for manufacturing a negative electrode for a lithium-free secondary battery of the first embodiment is provided, comprising the steps of: electrochemical etching a metal mesh containing a conductive metal; re-depositioning the conductive metal onto the electrochemically etched metal mesh to form a porous metal layer on which metal nanostructures are formed on a fibrous metal having a network structure; and forming carbon nanostructures on the porous metal layer while supplying a gaseous carbon source containing aliphatic hydrocarbons and a reducing gas in the presence of a metal catalyst.

[0016] In this manufacturing method, the electrochemical etching step and the re-deposition step of the conductive metal can be carried out sequentially in situ within the same electrolytic cell containing a working electrode with the metal mesh, a counter electrode with the same conductive metal as the metal mesh, and an electrolyte containing ions of the conductive metal and an acid.

[0017] Furthermore, the manufacturing method of the other embodiment may further include a step of heat-treating the metal mesh or porous metal layer in the presence of hydrogen gas before the electrochemical etching step or after the re-deposition step of the conductive metal.

[0018] On the other hand, according to an additional embodiment of the invention, a lithium-free secondary battery is provided comprising a positive electrode containing a positive electrode active material; a negative electrode of the first embodiment; and a separation membrane or electrolyte layer interposed between the positive electrode and the negative electrode.

[0019] In this type of lithium-free secondary battery, a lithium metal layer is electrodeposited onto the porous metal layer of the negative electrode during the charging process, and acts as the negative electrode active material. [Effects of the Invention]

[0020] One embodiment of a lithium-free secondary battery negative electrode includes a porous metal layer formed by electrochemical etching and re-deposition of a conductive metal onto a metal mesh containing a conductive metal, and a carbon nanostructure on such a porous metal layer.

[0021] Our experiments have confirmed that such a porous metal layer for the negative electrode has a relatively thin thickness and small mass per unit area, yet possesses a well-developed three-dimensional porous microstructure and relatively high porosity suitable for uniform electrodeposition of lithium.

[0022] Furthermore, in one embodiment of the negative electrode, carbon nanostructures such as carbon nanotubes can be formed on the porous metal layer. Such carbon nanostructures can exhibit low reactivity and inattention to lithium metal (lithiophobicity). By forming such carbon nanostructures, lithium metal can be electrodeposited more uniformly within the porous metal layer, and the uneven growth of lithium metal outside the porous metal layer, which can lead to the formation of lithium dendrites and the like, can be suppressed.

[0023] Furthermore, when the negative electrode of the above embodiment is applied to a lithium-free secondary battery, it is possible to reduce the weight and thickness of the negative electrode while significantly reducing galvanic corrosion and side reactions on the negative electrode. In addition, it is possible to induce uniform lithium electrodeposition on the negative electrode and suppress the growth of lithium dendrites, thereby contributing to the provision of a lithium-free secondary battery exhibiting high energy density, improved electrochemical properties, and long life characteristics. [Brief explanation of the drawing]

[0024] [Figure 1] This is a schematic diagram illustrating the configuration of a negative electrode for a lithium-free secondary battery according to one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating the cross-sectional shape of a negative electrode for a lithium-free secondary battery according to one embodiment of the present invention. [Figure 3a]This is a schematic diagram illustrating, step by step, a method for manufacturing a negative electrode for a lithium-free secondary battery according to another embodiment of the present invention. [Figure 3b] Figure 3a above shows a schematic diagram illustrating the changes in the object before and after each manufacturing step, and an electron microscope image of an example of the object. [Figure 4] These are electron microscope images of the porous copper layers formed during the manufacturing process of the negative electrodes in Examples 1 to 6. [Figure 5] These are electron microscope images of the porous copper layers formed during the manufacturing process of the negative electrodes in Examples 7-9. [Figure 6] The results of XRD analysis of the porous copper layers of Examples 1, 4, and 7-9 are shown. [Figure 7] The results of evaluating the change in current density over time by performing galvanic charge and discharge on half-cells manufactured using the negative electrodes of Comparative Example 1, Comparative Example 2, and Example 4 are shown. [Figure 8] The following shows the results of evaluating the change in discharge capacity over each cycle by conducting charge-discharge tests on batteries manufactured using the negative electrodes of Comparative Example 1, Examples 4 and 8. [Modes for carrying out the invention]

[0025] In this specification, when a part is said to "include" a component, it means that it may include other components rather than excluding them, unless otherwise specified.

[0026] Terms such as “about” and “substantially” used throughout this specification are used either numerically or in a sense close to numerically, when they indicate manufacturing and material tolerances inherent to the meaning referred to, and are used to facilitate understanding of this application and to prevent unscrupulous infringers from unfairly exploiting disclosures that refer to precise or absolute numerical values. For example, when it is stated that the porous metal layer of the negative electrode of one embodiment is “substantially” free of conductive metal oxides, this can be interpreted to mean that, considering the detectable limits of an analytical instrument such as XRD, when the components of the porous metal layer are analyzed with said analytical instrument, the conductive metal oxides are not detected above the noise level of the analysis result, and this can be interpreted to include detection at the noise level of the analysis result.

[0027] As used throughout this specification, the terms "step" or "step of" do not mean "step for".

[0028] Throughout this specification, terms indicating a scale such as “diameter” or “thickness” of a component can be interpreted as meaning the “maximum diameter” or “maximum thickness” of that component. For example, the “diameter” range of metallic nanostructures such as metallic fibers, metallic nanorods, or metallic nanofibers contained in a porous metal layer of a negative electrode in one embodiment can be defined as the range relative to the “maximum diameter” of the thickest part of a single strand of nanorod or (nano)fiber.

[0029] Furthermore, when we say that a layer, film, region, plate, or other part is "on top of" another part, this includes not only the case where it is "directly above" the other part, but also the case where there is yet another part in between. Moreover, a portion of the film, region, plate, or other part that is "on top of" the other part may overlap with a portion of the other part in the thickness direction.

[0030] Furthermore, throughout this specification, "lithium-free secondary battery" can refer to a secondary battery in which, in its pre-charge / discharge state, for example, immediately after manufacture, there is no separate negative electrode active material layer, such as a separate lithium metal layer or lithium alloy layer, on the negative electrode or negative electrode current collector (for example, a negative electrode in one embodiment that includes a conductive metal layer such as copper, a porous metal layer, and a carbon nanostructure). Thus, the "lithium-free secondary battery" can be defined as one that, in its pre-charge / discharge state, does not contain a separate negative electrode active material layer (for example, a lithium metal layer) on the negative electrode or negative electrode current collector. However, it goes without saying that the addition of a separate insulating layer or functional layer other than the negative electrode active material layer is not restricted. Moreover, the term "lithium-free secondary battery" cannot be interpreted as restricting the presence of lithium-containing positive electrode active material or the presence of a lithium metal layer or lithium-containing compound that is electrodeposited on the negative electrode by charging and discharging.

[0031] The embodiments of the invention will be described in detail below, based on the definitions described above and with reference to the attached drawings. However, these are presented as examples only and do not limit the invention; the invention is defined solely by the claims described later.

[0032] Figure 1 is a schematic diagram illustrating the configuration of a negative electrode for a lithium-free secondary battery according to one embodiment of the present invention, and Figure 2 is a schematic diagram illustrating the cross-sectional shape of a negative electrode for a lithium-free secondary battery according to one embodiment of the present invention.

[0033] As also shown in Figures 1 and 2, the negative electrode for a lithium-free secondary battery according to one embodiment of the present invention includes a porous metal layer having a three-dimensional microstructure; and a conductive carbon nanostructure formed on the porous metal layer. The porous metal layer includes a metal mesh layer in which fibrous metal having a diameter on the micron (μm) scale forms a network structure, and metal nanostructures formed on the fibrous metal, wherein at least a portion of the metal nanostructures are interconnected and define a plurality of pores on the porous metal layer.

[0034] The negative electrode of the above embodiment, as will be described in more detail below, includes, for example, a porous metal layer formed by electrochemical etching and re-deposition of a conductive metal onto a metal mesh layer containing a conductive metal, and a carbon nanostructure on such a porous metal layer.

[0035] During the electrochemical etching and re-deposition process, the conductive metal contained in the metal mesh layer is etched, reducing the diameter of the fibrous metal, while the conductive metal is re-deposited onto the fibrous metal. As a result, metal nanostructures having shapes such as metal nanorods or metal nanofibers with nanoscale diameters are formed and grown on the metal mesh layer. At least some of these metal nanostructures are interconnected, defining fine pores on the porous metal layer. In particular, as can be seen in the following examples, the porous metal layer can have a three-dimensional microstructure containing multiple pores defined by the metal nanostructures, while having a thinner thickness and smaller mass per unit area than conventionally known lithium-free secondary battery negative electrodes (or negative electrode current collectors).

[0036] Therefore, the negative electrode of one embodiment can be made thinner and lighter than conventional negative electrodes for lithium-free secondary batteries, while uniformly electrodepositing lithium metal within the three-dimensional porous microstructure during battery charging, thereby suppressing the uneven growth of lithium metal outside the negative electrode to form lithium dendrites, as well as side reactions between the negative electrode and electrolyte, or galvanic corrosion of the negative electrode.

[0037] Furthermore, in one embodiment of the negative electrode, carbon nanostructures such as carbon nanotubes can be formed on the porous metal layer. Such carbon nanostructures can exhibit low reactivity and inattention to lithium metal (lithiophobicity). The formation of such carbon nanostructures allows for more uniform electrodeposition of lithium metal within the porous metal layer, and the degree of aggregation of such lithium metal is controlled to an appropriate size. Therefore, it is possible to suppress the non-uniform growth of lithium metal outside the porous metal layer, which can lead to the formation of lithium dendrites and the like, thereby suppressing volume changes of the negative electrode during the battery operation process.

[0038] On the other hand, the negative electrode for a lithium-free secondary battery according to the first embodiment may include the porous metal layer as its substrate, and may further include a conductive metal layer supporting the porous metal layer if applicable. In this case, the porous metal layer and the conductive metal layer selectively supporting it may be formed using any conductive metal known to be usable as a negative electrode current collector, as a metal that does not cause chemical changes in the lithium-free secondary battery and has high conductivity while having relatively low reactivity.

[0039] Specific examples include metals such as stainless steel, aluminum, nickel, titanium, or copper, or copper, aluminum, or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. However, considering the excellent conductivity and lightweight nature of the negative electrode in one embodiment, and the ease of manufacturing the porous metal layer, the porous metal layer may contain copper.

[0040] On the other hand, the porous metal layer can have a thickness of 10 μm to 30 μm, or 12 μm to 25 μm, or 14 μm to 20 μm, and its mass per unit area is 4.0 mg / cm². 2 ~10.0 mg / cm³ 2 , or 4.5 mg / cm³ 2 ~9.0 mg / cm³ 2 , or 5.0 mg / cm³ 2~8.0 mg / cm³ 2 This may also be the case. As described above, the porous metal layer included in the negative electrode of one embodiment can have a porous three-dimensional microstructure developed by metallic fibers and metal nanostructures grown therefrom, despite having such a thin thickness and small mass per unit area. In this way, lithium metal can be uniformly electrodeposited within the pores of the thin and lightweight three-dimensional microstructure, and the formation of lithium dendrites and the like can be suppressed, making it possible to provide a lithium-free secondary battery with higher energy density and capacity.

[0041] In such a porous metal layer, the fibrous metal can have a diameter on a micron (μm) scale, based on the fibrous structure of a single strand, for example, 5 μm to 15 μm, 7 μm to 13 μm, or 8 μm to 12 μm, and a metal mesh layer can be formed by creating a network structure such that the distance between opposing fibrous metals is 30 μm to 80 μm, 40 μm to 75 μm, or 50 μm to 70 μm. Furthermore, metal nanostructures in the shape of metal nanorods or metal nanofibers formed on the fibrous metal can have a diameter of 100 nm to 700 nm, 150 nm to 650 nm, or 200 nm to 550 nm, respectively.

[0042] The metal nanostructures grown on the fibrous metal can be connected or intertwined with each other to define a large number of open pores in the porous metal layer, and lithium metal is uniformly electrodeposited in such pores during the charging of the lithium-free secondary battery. At this time, the porous metal layer can have a porosity of, for example, 55% to 70%, or 56% to 67%, or 57% to 63%. When the porosity is higher than this, lithium electrodeposition may be performed unevenly, or lithium may aggregate unevenly in the negative electrode, resulting in an increase in lithium metal desorption, lithium dendrite formation, or side reactions. Conversely, when the porosity is excessively low, lithium electrodeposition cannot be correctly performed, lithium grows unevenly outside the negative electrode, and problems such as an increase in the volume of the negative electrode may occur, and the characteristics of the secondary battery may deteriorate.

[0043] On the other hand, in the negative electrode of the above-described embodiment, the porous metal layer contains a conductive metal such as copper, and more specifically, it is composed of a reduced form of the conductive metal. At this time, the phrase "composed of the reduced form of the conductive metal" can mean that the porous metal layer does not substantially contain an oxide of a conductive metal such as, for example, copper oxide (Cu x O). More specifically, when the porous metal layer is analyzed by XRD, peaks derived from copper oxide, for example, peaks detected at 2θ of 60° to 63°, may not be detected with an intensity higher than noise.

[0044] As will be explained in more detail below, in the manufacturing process of the negative electrode in one embodiment, the porous metal layer or the metal mesh that serves as its raw material can be heat-treated in a reducing atmosphere (hydrogen atmosphere) at a high temperature, for example, 300°C or higher, or 500°C or higher. The porous metal layer that has undergone such heat treatment contains substantially no oxides of conductive metals such as copper oxide, and the porous metal layer consists of a reduced form of conductive metal (for example, reduced copper itself). In addition, during the heat treatment process, some of the metal nanostructures aggregate and their diameter is adjusted, and the size of the pores defined between the metal nanostructures is also adjusted. As a result, lithium metal can be electrodeposited more uniformly on the negative electrode in one embodiment, and the conductivity of the negative electrode can be further improved. Furthermore, because the porous metal layer contains substantially no oxides of conductive metals, galvanic corrosion or side reactions of the negative electrode can be suppressed.

[0045] On the other hand, in the negative electrode of the embodiment described above, a conductive carbon nanostructure made of carbon nanotubes or carbon nanofibers is formed on the porous metal layer, for example, the metal mesh layer containing the fibrous metal. As mentioned above, due to the lithium-inafflement of the carbon nanostructure, lithium metal can be electrodeposited more uniformly within the porous metal layer, and the growth of lithium dendrites by such lithium metal outside the negative electrode can be suppressed. Furthermore, due to the low reactivity of carbon nanotubes and the like, side reactions between the negative electrode of the embodiment, the electrodeposited lithium metal layer and the electrolyte can be further reduced, and the negative electrode can exhibit improved electrochemical properties.

[0046] Such conductive carbon nanostructures, such as carbon nanotubes, can be directly synthesized and grown on the porous metal layer during the manufacturing process of the negative electrode. For this purpose, a thin layer of metal catalysts for the synthesis of carbon nanotubes, such as aluminum oxide and iron, is coated onto the porous metal layer, and a gaseous carbon source is applied onto this metal catalyst layer to synthesize the carbon nanotubes.

[0047] In one embodiment of the negative electrode, for example, a catalyst layer containing aluminum, iron, or ions derived from the metal catalyst is further formed on the porous metal layer, and conductive carbon nanostructures such as carbon nanotubes are formed on such a catalyst layer. In this case, the catalyst layer may have a thickness of, for example, 10 nm to 50 nm or 15 nm to 30 nm. In this configuration, the conductive carbon nanostructures are formed uniformly with a thin thickness near the surface of the porous metal layer. As a result, the lithium metal layer is electrodeposited and formed on the negative electrode more uniformly and with an appropriate size.

[0048] On the other hand, according to another embodiment of the present invention, a method for manufacturing a negative electrode as described above is provided. Such a method for manufacturing a negative electrode may include, for example, the steps of: electrochemical etching a metal mesh containing a conductive metal; re-depositioning the conductive metal onto the electrochemically etched metal mesh to form a porous metal layer on which metal nanostructures are formed on a fibrous metal having a network structure; and forming carbon nanostructures on the porous metal layer while supplying a gaseous carbon source containing aliphatic hydrocarbons and a reducing gas in the presence of a metal catalyst.

[0049] Figure 3a schematically shows a method for manufacturing a negative electrode for a lithium-free secondary battery according to another embodiment of the invention, step by step. Figure 3b schematically shows the changes in the object before and after each manufacturing step, while the lower section shows an example of an electron microscope photograph showing the changes in the object.

[0050] Referring to Figures 3a and 3b, the manufacturing method involves electrochemical etching and re-deposition of the conductive metal using a metal mesh containing a conductive metal, such as copper. This process involves etching and then re-deposition of the conductive metal with the fibrous metal of the metal mesh, thereby growing and forming a large number of metal nanostructures, such as metal nanorods or bundles of metal nanofibers, on the fibrous metal. Such metal nanostructures can be linked at least partially to define a large number of pores, forming a porous metal layer of the negative electrode in one embodiment.

[0051] Subsequently, a metal catalyst, for example, containing aluminum oxide and iron, is added to the porous metal layer. At the same time, heat treatment is performed on such a metal catalyst while supplying a gaseous carbon source containing aliphatic hydrocarbons and a reducing gas to synthesize and grow carbon nanostructures such as carbon nanotubes. This makes it possible to manufacture an anode of one embodiment that is thin and lightweight while containing a developed three-dimensional porous microstructure and carbon nanostructures.

[0052] On the other hand, in this manufacturing method, a commercially available conductive metal mesh with an appropriate mesh size and scale can be used as the metal mesh used in the raw materials, taking into consideration the porosity and thickness of the porous metal layer to be ultimately manufactured. As a specific example, the metal mesh can include metal wires (or fibrous metals) having a diameter of 20 μm to 40 μm, 22 μm to 35 μm, or 23 μm to 30 μm, and the metal wires can form a mesh structure with a mesh size of 200 mesh to 500 mesh, or 300 mesh to 400 mesh. This forms a negative electrode of one embodiment having appropriate porosity and a porous three-dimensional microstructure.

[0053] Furthermore, as shown in the first drawing of Figure 3a, the electrochemical etching step and the re-deposition step of the conductive metal can be carried out sequentially within the same electrolytic cell. In a more specific example, the electrolytic cell can be the same electrolytic cell containing a working electrode including the metal mesh, a counter electrode including the same conductive metal as the metal mesh, such as a conductive metal sheet such as copper foil, and an electrolyte containing ions of the conductive metal and an acid.

[0054] In this case, the electrolyte may, for example, contain copper ions and sulfuric acid, and in a more specific example, it may be an aqueous electrolyte containing copper sulfate (CuSO4) and sulfuric acid. In one embodiment, the electrolyte may be an aqueous electrolyte containing copper sulfate (CuSO4) at a concentration of 20 mM to 100 mM, or 30 mM to 80 mM, and sulfuric acid at a concentration of 100 mM to 300 mM, or 150 mM to 250 mM. If the concentration of sulfuric acid, etc., is excessively low, the re-deposition of conductive metals such as copper may not be performed uniformly.

[0055] Furthermore, in the manufacturing method of the other embodiment described above, the electrochemical etching step is 30 mA / cm 2 ~60mA / cm 2 , or 35mA / cm 2 ~55mA / cm 2 The etching may be performed by constant current etching under constant current application at the specified current density. If the current density is excessively low, the conductive metal may not be etched correctly from the metal mesh, and if the current density is excessively high, the conductive metal may be etched unevenly, potentially causing the three-dimensional microstructure of the porous metal layer to collapse at the final negative electrode.

[0056] On the other hand, in the electrochemical etching step, the etched conductive metal ions, such as copper ions, move to the counter electrode, which then act as a source of conductive metal in the re-deposition step. In such a re-deposition step, the conductive metal ions move from the counter electrode to the working electrode and are deposited onto the metal wire (fibrous metal) of the metal mesh, forming a metal nanostructure of metal nanorods or metal nanofibers.

[0057] Such a re-deposition step may be performed under an applied voltage of 2.2V to 2.7V, or 2.3V to 2.5V. However, if the applied voltage is excessively low, uniform deposition of conductive metal onto a large-area metal mesh layer may be difficult.

[0058] On the other hand, in the manufacturing method of the other embodiments described above, a further step may be taken to heat-treat the metal mesh or porous metal layer at 300°C or higher in a reducing gas atmosphere (for example, in the presence of hydrogen gas) before the electrochemical etching step or after the re-deposition step of the conductive metal. As a specific example, the heat treatment may be performed on the porous metal layer after the re-deposition step.

[0059] As a result of this heat treatment, residual conductive metal oxides on the porous metal layer are reduced, and the porous metal layer can be substantially free of conductive metal oxides and composed of a reduced form of conductive metal. This allows the porous metal layer and the negative electrode containing it to exhibit improved conductivity and lower resistance.

[0060] Furthermore, by performing heat treatment at an appropriate temperature and time, some of the metal nanostructures formed on the porous metal layer aggregate, and the distribution and size of the pores defined between them are adjusted. As a result, lithium metal is electrodeposited more uniformly on the negative electrode in one embodiment, and the formation of lithium dendrites is suppressed.

[0061] The heat treatment step can be carried out at a temperature of 300°C or higher for 5 minutes or more to reduce the oxide of the conductive metal, and it is even more preferable to carry it out at a temperature of 500°C or higher to optimize the pore distribution and size for proper aggregation of the metal nanostructure and uniform electrodeposition of the lithium metal. Furthermore, if the heat treatment temperature is excessively high or the heat treatment time is excessively long, the metal nanostructure will aggregate excessively and the pore size and other properties will be excessively reduced, so the heat treatment step can be carried out at a temperature of 300°C to 800°C, or 500°C to 800°C, for 5 minutes to 1.5 hours.

[0062] On the other hand, the heat treatment step may be carried out continuously in the same reactor as the subsequent carbon nanostructure formation step. For such continuous operation, after heat treatment at a temperature of 600°C to 800°C for 5 to 20 minutes, the subsequent carbon nanostructure synthesis steps may be carried out continuously in the same reactor.

[0063] On the other hand, after the re-deposition step of the conductive metal or the selective heat treatment step, for example, a metal catalyst containing aluminum oxide and iron is added to the porous metal layer, and heat treatment is carried out in the presence of such a metal catalyst while supplying a gaseous carbon source containing aliphatic hydrocarbons and a reducing gas to synthesize carbon nanostructures such as carbon nanotubes. As a result, the carbon nanostructures grow on the porous metal layer, more specifically on the metal mesh layer and the metal nanoprecursor, and a negative electrode of one embodiment is manufactured.

[0064] In this case, the gaseous carbon source may include, for example, an aliphatic hydrocarbon having 1 to 5 carbon atoms, such as ethylene gas, and the reducing gas may include hydrogen gas. Furthermore, in the metal catalyst containing aluminum oxide and iron, the aluminum oxide is added to a thickness of 10 nm to 25 nm, while the iron is added to a thickness of 1 nm to 5 nm. If the thickness of the added metal catalyst is excessively thin, the metal catalyst may be contaminated by the diffusion of conductive metals such as copper, or sufficient carbon nanostructures such as carbon nanotubes may not be formed. In addition, the metal catalyst containing aluminum oxide and iron may be deposited on the porous metal layer under irradiation with an E-beam.

[0065] Furthermore, the heat treatment step for synthesizing the carbon nanostructure can be carried out at a temperature of 600°C to 800°C for 5 to 20 minutes, or 10 to 20 minutes, depending on the synthesis conditions for general carbon nanotubes, thereby allowing the carbon nanoprecursors to grow sufficiently.

[0066] On the other hand, according to an additional embodiment of the invention, a lithium-free secondary battery is provided which includes the negative electrode of the embodiment described above. Such a lithium-free secondary battery may include, for example, the negative electrode of the embodiment described above; a positive electrode facing the negative electrode and containing a positive electrode active material; and a separation membrane or electrolyte layer interposed between the positive electrode and the negative electrode. Furthermore, the lithium-free secondary battery may further include an electrolyte containing a lithium salt and a non-aqueous organic solvent, together with the separation membrane.

[0067] In such a lithium-free secondary battery, the negative electrode does not contain a separate negative electrode active material layer, such as a lithium metal layer, before charging and discharging. However, as charging and discharging of the lithium-free secondary battery progresses, lithium ions that have migrated from the positive electrode are electrodeposited onto the porous metal layer of the negative electrode, forming a lithium metal layer or lithium alloy layer, and such a lithium metal layer can act as a negative electrode active material.

[0068] On the one hand, in the lithium-free secondary battery of the additional embodiment, the positive electrode can include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

[0069] Such a positive electrode can be manufactured by mixing an active material, a binder, and optionally a conductive material, a filler, etc. in a solvent to produce a positive electrode slurry composition, and applying this to the positive electrode current collector.

[0070] The positive electrode current collector can generally have a thickness of 3 μm to 500 μm. Also, the positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. The current collector can also form fine irregularities on its surface to enhance the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc. are possible.

[0071] And in the case of the positive electrode active material, as a compound capable of reversible intercalation and deintercalation of lithium, specifically, it can include a lithium metal oxide containing one or more metals such as iron, cobalt, manganese, nickel or aluminum and lithium.

[0072] Specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1O2 (where 0 < Y1 < 1), lithium-manganese-cobalt-based oxides (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), lithium-nickel-manganese-cobalt-based oxides (e.g., Li(Ni p Co q Mn r )O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), lithium-nickel-cobalt-transition metal (M) oxides (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are the atomic fractions of independent elements, respectively, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is one or more selected from Al, Mg and Ti, X is one or more selected from F, S and N, -0.5 ≦ a ≦ +0.5, 0 ≦ x ≦ 0.5, 0 ≦ b ≦ 0.1), etc., and any one or two or more of these compounds may be included.

[0073] In particular, the positive electrode active material includes a lithium metal oxide containing lithium and two or more metals selected from the group consisting of nickel, manganese, cobalt, and aluminum, and the lithium metal oxide may contain 50 mol% or more, or 60 mol% to 99 mol%, or 70 mol% to 95 mol%, of nickel relative to the total metal content excluding lithium. Such a lithium metal oxide is, for example, represented by the following chemical formula 1: [Chemical formula 1] Li x Ni a Co b M 1 c M 2 d O2 In the above chemical formula 1, the above M 1 M may be one or more selected from Mn and Al, or a combination thereof. 2 a may be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and may be 0.90≦x≦1.1, or 0.95≦x≦1.08, or 1.0≦x≦1.08, and may be 0.50≦a<1.0, or 0.60≦a≦0.99, or 0.70≦a≦0.95. Also, 0 <b≦0.3であり、0<c≦0.3であり、0≦d≦0.1であってもよい。

[0074] By using a lithium metal oxide containing such a high nickel content as the positive electrode active material and combining it with the negative electrode of one embodiment, the output, capacity characteristics, and lifespan characteristics of a lithium-free secondary battery can be further improved.

[0075] The positive electrode active material described above may be included in an amount of 60% to 99% by weight, 70% to 99% by weight, or 80% to 98% by weight, based on the total weight of the positive electrode active material layer.

[0076] On the other hand, the conductive material contained in the positive electrode active material layer is a component for further improving the conductivity of the positive electrode active material. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. Examples include carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives. In particular, the conductive material may include conductive nanomaterials such as carbon nanotubes or carbon nanofibers, which can further reduce the resistance of the lithium-free secondary battery and further improve its output characteristics.

[0077] Typically, the conductive material is included in an amount of 1% to 20% by weight, or 1% to 15% by weight, or 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0078] The binder selectively included in the positive electrode active material layer is a component that assists in the bonding of the positive electrode active material to conductive materials and to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber. A mixture or copolymer of two or more of these can also be used.

[0079] Typically, the binder is included in an amount of 1% to 20% by weight, or 1% to 15% by weight, or 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0080] Furthermore, a filler may be selectively added to the positive electrode as a component to suppress its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing a chemical change in the battery, and for example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. can be used.

[0081] The positive electrode described above can be manufactured by dispersing and mixing the positive electrode active material, binder, and conductive material in a dispersion medium (solvent) to create a slurry, applying this slurry to a metal current collector, and then drying and rolling it. In this process, the dispersion medium can be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof, but is not necessarily limited to these.

[0082] On the other hand, the lithium-free secondary battery of the other embodiment may further include an electrolyte comprising a non-aqueous organic solvent and a lithium salt.

[0083] The lithium salt contained in the electrolyte is used as a medium for transferring ions within the secondary battery. The lithium salt is, for example, Li as a cation. + Includes F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6- CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - , C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CF3(CF2)7SO3 - and SCN - It can also include anions selected from the group consisting of the following.

[0084] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 It may contain one or more selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBF2 (C2O4), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2, and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2).

[0085] The concentration of the lithium salt can be appropriately changed within a range that is normally usable, and is included in the electrolyte at a concentration of 0.4 M to 6 M, or 0.5 M to 5 M.

[0086] In a more specific embodiment, the electrolyte may contain lithium salt at a relatively low concentration of 0.4 M to less than 2 M, or 0.5 M to 1.5 M, but it may also contain lithium salt at a high concentration of 2 M to 6 M, or 2.5 M to 5.5 M. By using an electrolyte containing such a high concentration of lithium salt, the output characteristics of the secondary battery can be further improved.

[0087] On the other hand, the type of non-aqueous organic solvent included in the electrolyte is not particularly limited, and any organic solvent that has been known to be applicable to electrolytes for lithium-ion batteries can be used. Examples of such organic solvents include one or more selected from the group consisting of carbonate-based solvents, ether-based solvents, nitrile-based solvents, phosphate-based solvents, and sulfone-based solvents. However, considering the stability of the lithium metal layer electrodeposited on the lithium electrodeposition induction layer, it is preferable that the non-aqueous organic solvent includes a carbonate-based solvent or an ether-based solvent.

[0088] More specifically, the carbonate-based solvent can be dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, or methyl (2,2,2-trifluoroethyl) carbonate, and the phosphate-based solvent can be trimethyl phosphate, triethyl phosphate, or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide.

[0089] Furthermore, as the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, or tetrahydrofuran derivatives such as 2-methyltetrahydrofuran can be used, and as the nitrile-based solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. Furthermore, as the sulfone-based solvent, dimethyl sulfone, ethyl methyl sulfone, or sulforane can be used.

[0090] On the other hand, the lithium-free secondary battery described above may further include a porous separation membrane interposed between the positive electrode and the negative electrode.

[0091] Such porous separation membranes can be made from olefin polymers such as polyethylene and polypropylene, glass fibers, etc., in the form of sheets, multilayer membranes, fine porous films, woven fabrics, and nonwoven fabrics, but are not necessarily limited to these forms. However, it is preferable to use porous polyethylene or porous glass fiber nonwoven fabric (glass filter) as the separation membrane, and it is even more preferable to use a porous glass filter (glass fiber nonwoven fabric) as the separation membrane. The separation membrane may be a thin insulating film with high ion permeability and mechanical strength, and the pore diameter of the separation membrane is generally in the range of 0.01 μm to 10 μm, and the thickness is generally in the range of 5 μm to 300 μm, but is not limited to these.

[0092] Furthermore, in another example of the lithium-free secondary battery, the separation membrane may be integrated with the electrolyte and interposed between the positive and negative electrodes in the form of an electrolyte layer or electrolyte film. For example, the electrolyte layer or electrolyte film may be in a form in which the above-mentioned lithium salt and non-aqueous organic solvent are contained within a polymer matrix, or in a form in which a solid electrolyte is contained. In addition, widely known polymer-based solid electrolytes can be used as the polymer matrix.

[0093] The lithium-free secondary battery of the above-described embodiment can be a semi-solid battery using a liquid electrolyte and a solid electrolyte in combination, or a fully solid battery having a solid electrolyte layer, depending on the presence and form of the electrolyte layer.

[0094] On the other hand, lithium-free secondary batteries of the other embodiments described above can be manufactured by conventional methods of the art. For example, they can be manufactured by a method in which an electrode assembly including a positive electrode, a negative electrode and a separator membrane is housed in a case and the electrolyte described above is injected and impregnated, or by a method in which an electrode assembly including a positive electrode, a negative electrode and an electrolyte layer is housed in a case.

[0095] Such lithium-free secondary batteries can be applied not only to battery cells used as power sources for small devices, but also to units of battery modules that power medium to large devices.

[0096] The following describes preferred embodiments of the invention, comparative examples, and experimental examples for evaluating them. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to these embodiments.

[0097] Comparative Example 1: A copper foil with a thickness of 9 μm was used as the negative electrode for the lithium-free secondary battery in Comparative Example 1.

[0098] Comparative Example 2: Manufacturing of a negative electrode for lithium-free secondary batteries A copper mesh with a wire diameter of 25 μm and a mesh size of 300 to 400 mesh was used. An electrolytic cell was also used, comprising a working electrode containing such copper mesh, a counter electrode made of copper foil with a thickness of 9 μm, and an aqueous electrolyte containing 50 mM copper sulfate and 200 mM sulfuric acid.

[0099] In the electrolytic cell, a constant voltage of 2.4V was applied for 720 seconds to deposit copper from the copper foil onto the copper mesh. This deposition formed a copper nanostructure in the form of nano-protrusions on the copper mesh, which was then used as the negative electrode for the lithium-free secondary battery in Comparative Example 2.

[0100] Examples 1-6: Manufacturing of negative electrodes for lithium-free secondary batteries A copper mesh with a wire diameter of 25 μm and a mesh size of 300 to 400 mesh was used. An electrolytic cell was also used, which contained a working electrode with such copper mesh, a counter electrode with a copper foil thickness of 9 μm, and an aqueous electrolyte containing 50 mM copper sulfate and 200 mM sulfuric acid.

[0101] In the aforementioned electrolytic cell, 40 mA / cm² 2 A constant current was applied at the specified current density to perform electrochemical etching from the copper mesh. This etching was carried out for 9 minutes to remove copper ions from the copper mesh. Subsequently, under an applied voltage of 2.4V, copper was re-deposited from the copper foil onto the copper mesh for 2 minutes.

[0102] Subsequently, the sample of the porous copper layer after the re-deposition was placed in a quartz boat connected to a magnetic transporter. The sample was then placed in the center of a tube furnace chamber heated to 775°C with 80% hydrogen (helium atmosphere) gas flowing through it, and then removed for heat treatment. At this time, the heat treatment conditions were varied for each example, based on the heat treatment time from when the sample was placed in to when it was removed, as follows: no heat treatment (Example 1), 3 minutes of heat treatment (Example 2), 6 minutes of heat treatment (Example 3), 12 minutes of heat treatment (Example 4), 24 minutes of heat treatment (Example 5), and 60 minutes of heat treatment (Example 6).

[0103] Electron microscope images of the porous copper layers formed by the heat treatment described above are shown in Figures 4a to 4f, respectively. This confirms that numerous nanorod or nanofiber-shaped copper nanostructures are formed on the porous copper layers of Examples 1 to 6, and that these nanostructures define the nanopores. Furthermore, among Examples 1 to 6, it was confirmed that Examples 2 to 4 formed a suitable porous structure for uniform electrodeposition of lithium metal, and that when the heat treatment time is longer, the pores tend to narrow due to aggregation between the copper nanostructures.

[0104] Meanwhile, after the heat treatment had proceeded, an E-beam was irradiated to deposit 20 nm of Al2O3 and 2 nm of Fe onto one surface of the porous copper layer to form a metal catalyst layer. Subsequently, carbon nanotubes were synthesized on the metal catalyst layer for 12 to 20 minutes in a tube furnace heated to 775°C, where the heat treatment had been performed, under the supply of 410 sccm of He, 100 sccm of ethylene gas, and 100 sccm of hydrogen gas.

[0105] This allowed us to manufacture the negative electrodes for lithium-free secondary batteries of Examples 1 to 6.

[0106] Examples 7-9: Manufacturing of negative electrodes for lithium-free secondary batteries A porous copper layer was manufactured by electrochemical etching and copper re-deposition using the same method as in Examples 1 to 6 described above.

[0107] Subsequently, the porous copper layer sample, after the re-deposition process was completed, was placed in a chamber of a tube furnace connected to a vacuum pump. While flowing 3.9% hydrogen gas (Ar-based) through the chamber, the sample was heated at a rate of 10°C / min to reach 400°C to 600°C, and then maintained at that temperature for 1 hour. During this time, the heat treatment temperature was varied for each example, using the heated sample temperature as a reference, as shown in the examples: 400°C (Example 7), 500°C (Example 8), and 600°C (Example 7).

[0108] Figure 5 shows electron microscope images of the porous copper layers formed by the heat treatment described above, categorized by heat treatment temperature. This confirms that numerous nanorod or nanofiber-shaped copper nanostructures are formed on the porous copper layers of Examples 7-9, and that these nanostructures define the nanopores. Furthermore, among Examples 7-9, it was confirmed that Example 8 formed a suitable porous structure for uniform electrodeposition of lithium metal, while at lower heat treatment temperatures (Example 7), the connection of the nanostructures was insufficient, resulting in insufficient formation of a porous structure. Conversely, in Example 9, where the heat treatment temperature was higher, it was confirmed that the pores tended to narrow due to aggregation between the copper nanostructures.

[0109] Furthermore, the porous copper layers of Examples 1, 4, and 7-9 were analyzed by XRD, and the analysis results are shown in Figure 6. Referring to Figure 6, it was confirmed that in Example 1, which was not heat-treated, a peak originating from copper oxide was detected at 2θ between 60° and 63°, but this peak was not detected in Examples 4, 7-9, which were heat-treated.

[0110] On the other hand, after the heat treatment was completed, carbon nanotubes were synthesized on the porous copper layers of Examples 7 to 9 in the same manner as in Examples 1 to 6, and the negative electrodes for lithium-free secondary batteries of Examples 7 to 9 were manufactured.

[0111] Test Example 1: Evaluation of the physical properties of the negative electrode The thicknesses of the negative electrodes of Comparative Examples 1 and 2 and Example 4 were measured using cross-sectional observation with an electron scanning microscope (Hitachi, SU5000) and a thickness measuring instrument (Mitutoyo, 547-401A). The mass per unit area was measured using an ultra-precision balance (RADWAG, XA52.4Y) after cutting the negative electrode into a 19-mm diameter circle using a disk puncher (Wellcos, WC-H125). The evaluation results were compared and shown in Table 1 below. Also, the mass and thickness per unit area, and the true density value of copper (8.95 g / cm 3 ) were used to calculate the porosity of each negative electrode.

[0112]

Table 1

[0113] Referring to Table 1 above, the negative electrode of Example 4 has a developed porous three-dimensional fine structure, showing a high porosity suitable for uniform lithium electrodeposition, while having a very thin thickness and a low mass per unit area compared to the negative electrode of Comparative Example 2. It was thus confirmed that it is possible to provide a lithium-free secondary battery with a higher energy density by utilizing the negative electrode of Example 4.

[0114] Test Example 2: Evaluation of the Resistance and Galvanic Corrosion Resistance of the Negative Electrode Half-cells were fabricated using the negative electrodes of Comparative Example 1, Example 1, and Example 4. Such half-cells included a lithium foil as the negative electrode and the counter electrode, and contained 75 μl of an electrolyte of 0.6 M LiBF4 + 0.6 M LiBF2(C2O4) in FEC / DEC (volume ratio of 1:2). For such half-cells, under the conditions of 10 -3 ~10 6 Hz and 50 mV, the charge transfer resistance and Ohmic resistance of each negative electrode were evaluated by EIS (Electrochemical Impedance Spectroscopy) analysis, and the evaluation results were compared and shown in Table 2 below.

[0115] [Table 2]

[0116] Referring to Table 2 above, it was confirmed that the negative electrodes of Examples 1 and 4 exhibited lower resistance compared to Comparative Example 1 due to the formation of a porous three-dimensional microstructure. Furthermore, it was confirmed that the negative electrode of Example 4 exhibited higher charge transfer resistance and lower ohmic resistance compared to Example 1. This is because the lithium-affinity copper oxide in Example 4 was reduced and removed during heat treatment, and it was confirmed that the negative electrode of Example 4 exhibited even greater conductivity than that of Example 1.

[0117] Furthermore, using the negative electrodes of Comparative Example 1, Comparative Example 2, and Example 4, the same half-cells as described above were manufactured, and galvanic charging and discharging was performed using these half-cells to evaluate the current density over time. The evaluation results are shown in Figure 7.

[0118] As shown in Figure 7, which illustrates the change in current density over time, it was confirmed that the negative electrode of Example 4 exhibits approximately 75% less galvanic corrosion compared to the negative electrode of Comparative Example 2, which corresponds to a conventional negative electrode with a three-dimensional porous microstructure.

[0119] Test Example 3: Evaluation of Capacity Characteristics by Cycle A battery was manufactured using the negative electrodes of Comparative Example 1, Example 4, and Example 8. Such a battery uses the aforementioned negative electrode and NCM811(LiNi 0.8 Co 0.1 Mn 0.1 The device contained a positive electrode with O2 as the positive electrode active material, a polyethylene separation membrane, and 75 μl of an electrolyte consisting of 0.6 M LiBF4 + 0.6 M LiBF2 (C2O4) in FEC / DEC (1:2 volume ratio).

[0120] For such a battery, 4mAh·cm -2The change in discharge capacity for each cycle was evaluated while charging and discharging under the conditions of (0.5C, cutoff voltage: 4.5V), and the evaluation results are shown in Figure 8.

[0121] Referring to Figure 8, it was confirmed that the lithium-free secondary battery containing the negative electrode of the example showed superior capacity in each cycle compared to the battery containing the negative electrode of the comparative example.

Claims

1. A porous metal layer having a three-dimensional microstructure; and The porous metal layer comprises a conductive carbon nanostructure formed on the porous metal layer, The porous metal layer includes a metal mesh layer in which fibrous metal having a diameter on the micron (μm) scale forms a network structure, and a metal nanostructure formed on the fibrous metal. At least a portion of the metal nanostructures are interconnected, defining a plurality of pores on the porous metal layer, for a lithium-free secondary battery negative electrode.

2. The negative electrode for a lithium-free secondary battery according to claim 1, further comprising a conductive metal layer supporting the porous metal layer.

3. The porous metal layer comprises copper, as described in claim 1, for a lithium-free secondary battery negative electrode.

4. The negative electrode for a lithium-free secondary battery according to claim 1, wherein the metal nanostructure comprises a metal nanorod or a metal nanofiber.

5. The conductive carbon nanostructure comprises carbon nanotubes, as described in claim 1, for a lithium-free secondary battery anode.

6. The porous metal layer has a thickness of 10 μm to 30 μm, as described in claim 1, for a lithium-free secondary battery negative electrode.

7. The porous metal layer is 4.0 mg / cm³ ２ ~10.0mg / cm ２ A negative electrode for a lithium-free secondary battery according to claim 1, having a mass per unit area.

8. The negative electrode for a lithium-free secondary battery according to claim 4, wherein the fibrous metal has a diameter of 5 μm to 15 μm, and the metal nanorod or metal nanofiber has a diameter of 100 nm to 700 nm.

9. The porous metal layer has a porosity of 55% to 70% as the negative electrode for a lithium-free secondary battery according to claim 1.

10. The anode for a lithium-free secondary battery according to claim 1, wherein the porous metal layer consists of a conductive metal in a reduced form and substantially does not contain oxides of the conductive metal.

11. The negative electrode for a lithium-free secondary battery according to claim 1, further comprising an aluminum or iron catalyst layer formed on the porous metal layer, wherein the conductive carbon nanostructure is formed on the catalyst layer.

12. A step of electrochemical etching on a metal mesh containing conductive metal; The steps include: re-depositing the conductive metal onto the electrochemically etched metal mesh to form a porous metal layer on which metal nanostructures are formed on the fibrous metal having a network structure; and A method for producing a negative electrode for a lithium-free secondary battery according to any one of claims 1 to 11, comprising the step of forming a carbon nanostructure on the porous metal layer while supplying a gaseous carbon source containing aliphatic hydrocarbons and a reducing gas in the presence of a metal catalyst.

13. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 12, wherein the metal mesh comprises a metal wire having a diameter of 20 μm to 40 μm and has a mesh size of 200 mesh to 500 mesh.

14. The electrochemical etching step and the re-deposition step of the conductive metal are, The working electrode including the aforementioned metal mesh, A counter electrode containing the same conductive metal as the aforementioned metal mesh, A method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 12, which is carried out sequentially in the same electrolytic cell containing the conductive metal ions and an electrolyte containing an acid.

15. The electrochemical etching step is performed at 30 mA / cm². ２ ~60 mA / cm ２ A method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 12, which is carried out under the application of a constant current.

16. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 12, wherein the step of re-depositing the conductive metal is performed under an applied voltage of 2.2V to 2.7V.

17. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 12, further comprising the step of heat-treating the metal mesh or the porous metal layer in the presence of hydrogen gas before the electrochemical etching step or after the re-deposition step of the conductive metal.

18. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 17, wherein the heat treatment step is performed after the re-deposition step of the conductive metal, and the carbon nanostructure formation step is performed continuously in the same reactor in which the heat treatment step was performed.

19. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 17, wherein the heat treatment step is performed at a temperature of 300°C to 800°C for 5 minutes to 1.5 hours.

20. The method for producing a negative electrode for a lithium-free secondary battery according to claim 12, wherein the metal catalyst comprises aluminum oxide and iron.

21. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 12, wherein the gaseous carbon source comprises ethylene gas, and the reducing gas comprises hydrogen gas.

22. Positive electrode containing positive electrode active material; The negative electrode according to any one of claims 1 to 11; and A lithium-free secondary battery comprising a separation membrane or electrolyte layer interposed between the positive electrode and the negative electrode.

23. The lithium-free secondary battery according to claim 22, further comprising a lithium metal layer that is electrodeposited onto the porous metal layer of the negative electrode by charging the lithium-free secondary battery.

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