Negative electrode for lithium-free secondary battery, manufacturing method therefor, and lithium-free secondary battery comprising same

Abstract

The present invention relates to a negative electrode for a lithium-free secondary battery, which can reduce galvanic corrosion and side reactions on the negative electrode while being lightweight and thin and enables uniform electrodeposition of lithium metal, and a manufacturing method therefor, wherein the negative electrode for a lithium-free secondary battery is characterized by comprising: a porous metal layer having a three-dimensional microstructure; and a conductive carbon nanostructure formed on the porous metal layer, wherein the porous metal layer comprises a metal mesh layer in which a fibrous metal having a micron-scale diameter forms a network structure, and a metal nanostructure formed on the fibrous metal, and at least some parts of the metal nanostructure are connected to each other to define a plurality of pores on the porous metal layer.

Description

Anode for lithium-free secondary battery, method for manufacturing same, and lithium-free secondary battery comprising same

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0168063, filed November 28, 2023, and Korean Patent Application No. 10-2024-0165866, filed November 20, 2024, the entire contents of which are incorporated herein by reference.

[0003] 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 lightweight and thin while reducing side reactions on the negative electrode and improving the electrochemical characteristics and lifespan characteristics of the lithium-free secondary battery.

[0004] Lithium metal batteries utilize lithium metal (Li-metal) as the anode active material. Compared to conventional graphite-based anodes, lithium metal batteries theoretically offer higher energy density and capacity. Therefore, research and development are ongoing to apply these lithium metal batteries to batteries requiring high energy densities.

[0005] However, lithium metal batteries still suffer from unresolved issues, such as large side reactions and low reversibility. To compensate for this low reversibility, attempts have been made to pre-store excess lithium in the cathode and operate the lithium metal battery. However, as the N / P ratio of secondary batteries increases, the energy density of the lithium metal battery can significantly decrease, and the excess lithium can also cause cost and safety issues, thus limiting these attempts.

[0006] Recently, interest in non-anode secondary batteries, also known as lithium-free secondary batteries or anode-free secondary batteries, has been increasing. Such lithium-free secondary batteries refer to secondary batteries that include the anode current collector itself as the anode, without forming a separate lithium metal layer on the anode current collector during the manufacturing process. Such lithium-free secondary batteries can be defined as batteries that utilize lithium metal as an anode active material, as lithium metal is electrodeposited on the anode current collector during charging. The lithium-free secondary batteries can maximize the high energy density of lithium metal while reducing safety issues such as those caused by excessive lithium storage.

[0007] However, in the case of these negative electrodes for lithium-free secondary batteries, since 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, many side reactions and rapid capacity loss, including galvanic corrosion, may occur in the negative electrode. In addition, the problem of lithium dendrites occurring due to uneven deposition and growth of lithium metal on the negative electrode current collector may also occur.

[0008] Previously, a method of increasing the surface area of ​​the negative electrode by forming a three-dimensional porous microstructure on the negative electrode collector to induce uniform growth of lithium on the negative electrode collector and suppress the formation of lithium dendrites has been studied.

[0009] However, existing lithium-free secondary battery anodes are often inevitably large in thickness and weight due to the need to form a three-dimensional porous microstructure on the metal current collector. Therefore, when applied to these lithium-free secondary battery anodes, the volumetric energy density of the battery is significantly reduced.

[0010] In addition, due to the large surface area of ​​the negative electrode, side reactions between the current collector and the lithium metal and electrolyte deposited during charging may further increase, which may significantly reduce the initial capacity of the secondary battery, and galvanic corrosion may be accelerated, which may lower the life characteristics of the secondary battery, etc., still present disadvantages.

[0011] Accordingly, the present invention provides a negative electrode for a lithium-free secondary battery and a method for manufacturing the same, which can reduce galvanic corrosion and side reactions on the negative electrode while enabling lightweight and thin-walled construction and enables uniform deposition of lithium metal.

[0012] The present invention also provides a lithium-free secondary battery exhibiting improved safety, electrochemical characteristics, and lifespan characteristics, including the negative electrode.

[0013] According to one embodiment of the invention, there is provided a porous metal layer having a three-dimensional microstructure; and a conductive carbon nanostructure formed on the porous metal layer.

[0014] The porous metal layer includes a metal mesh layer in which fibrous metal having a diameter on the micron (㎛) scale forms a network structure, and a metal nanostructure formed on the fibrous metal.

[0015] A negative electrode for a lithium-free secondary battery is provided in which at least some of the above metal nanostructures are interconnected to define a plurality of pores on the porous metal layer.

[0016] In such a cathode, the metal nanostructure may include a metal nanorod or a metal nanofiber, and the conductive carbon nanostructure may include a carbon nanotube.

[0017] Additionally, the porous metal layer may have a thickness of 10 to 30 μm and a density of 4.0 to 10.0 mg / cm 2It can have a mass per unit area of ​​. In addition, the porous metal layer can have a porosity of 55 to 70%.

[0018] According to another embodiment of the invention, a method for manufacturing an anode for a lithium-free secondary battery of the above embodiment is provided, comprising: performing electrochemical etching on a metal mesh including a conductive metal; redepositing the conductive metal on the metal mesh on which the electrochemical etching has been performed to form a porous metal layer in which a metal nanostructure is formed on a fibrous metal having a network structure; and supplying a gaseous carbon source including an aliphatic hydrocarbon and a reducing gas to the porous metal layer in the presence of a metal catalyst, thereby forming a carbon nanostructure.

[0019] In this manufacturing method, the electrochemical etching step and the re-deposition step of the conductive metal may be sequentially performed in-situ within the same electrolytic cell comprising a working electrode including the metal mesh, a counter electrode including the same conductive metal as the metal mesh, and an electrolyte including ions of the conductive metal and an acid.

[0020] In addition, in the manufacturing method of the other embodiment, a step of heat treating the metal mesh or porous metal layer in the presence of hydrogen gas may be further included before the electrochemical etching step or after the re-deposition step of the conductive metal.

[0021] Meanwhile, according to a further embodiment of the invention, a lithium-free secondary battery is provided, comprising: a positive electrode including a positive active material; a negative electrode according to one embodiment; and a separator or electrolyte layer interposed between the positive electrode and the negative electrode.

[0022] In these lithium-free secondary batteries, a lithium metal layer is deposited on the porous metal layer of the negative electrode during the charging process, thereby acting as a negative electrode active material.

[0023] An example of a lithium-free secondary battery negative electrode comprises a porous metal layer formed through electrochemical etching and re-deposition of a conductive metal on a metal mesh including a conductive metal, and a carbon nanostructure on the porous metal layer.

[0024] The inventors' experimental results confirmed that the porous metal layer of the negative electrode can have a developed three-dimensional porous microstructure and a relatively large porosity suitable for uniform electrodeposition of lithium while having a relatively thin thickness and a small mass per unit area.

[0025] Additionally, in the negative electrode of one embodiment, carbon nanostructures such as carbon nanotubes may be formed on the porous metal layer. Such carbon nanostructures may exhibit low reactivity and non-affinity (lithiophobicity) toward lithium metal. By forming such carbon nanostructures, lithium metal can be more uniformly deposited within the porous metal layer, and lithium metal can be suppressed from growing unevenly outside the porous metal layer, thereby forming lithium dendrites, etc.

[0026] Accordingly, by applying the negative electrode of the above embodiment to a lithium-free secondary battery, the negative electrode can be made lighter and thinner, while significantly reducing galvanic corrosion and side reactions on the negative electrode. Furthermore, by inducing uniform lithium deposition on the negative electrode, the growth of lithium dendrites and the like can be suppressed, contributing to the provision of a lithium-free secondary battery exhibiting high energy density, improved electrochemical characteristics, and lifespan characteristics.

[0027] FIG. 1 is a schematic diagram schematically showing the configuration of a negative electrode for a lithium-free secondary battery according to one embodiment of the invention.

[0028] Figure 2 is a schematic diagram schematically showing the cross-sectional shape of a negative electrode for a lithium-free secondary battery according to one embodiment of the invention.

[0029] Figure 3a is a schematic diagram schematically showing each step of a method for manufacturing a negative electrode for a lithium-free secondary battery according to another embodiment of the invention.

[0030] Figure 3b is a schematic diagram schematically showing the change in the object before and after each manufacturing step of Figure 3a is performed, and an electron microscope photograph of an example of the object.

[0031] Figure 4 is an electron microscope photograph of a porous copper layer formed during the cathode manufacturing process of Examples 1 to 6.

[0032] Figure 5 is an electron microscope photograph of a porous copper layer formed during the cathode manufacturing process of Examples 7 to 9.

[0033] Figure 6 shows the results of XRD analysis of the porous copper layers of Examples 1, 4, 7 to 9.

[0034] Figure 7 shows the results of evaluating the change in current density over time by conducting galvanic charging and discharging on half cells manufactured using the cathodes of Comparative Example 1, Comparative Example 2, and Example 4.

[0035] Figure 7 shows the results of evaluating the change in current density over time by conducting galvanic charging and discharging on half cells manufactured using the cathodes of Comparative Example 1, Comparative Example 2, and Example 4.

[0036] Figure 8 shows the results of evaluating the change in discharge capacity per cycle by conducting a charge / discharge test on batteries manufactured using the negative electrodes of Comparative Example 1, Examples 4 and 8.

[0037] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless specifically stated otherwise.

[0038] As used throughout this specification, the terms "about," "substantially," and the like are used in a sense of degree or close to that degree when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly using the disclosure in which exact or absolute figures are mentioned to aid the understanding of the present invention. For example, when it is said that the porous metal layer of the cathode of one embodiment "substantially" does not include an oxide of the conductive metal, this means that when the components of the porous metal layer are analyzed with an analytical device such as XRD, taking into account the detectable limit of the analytical device, the oxide of the conductive metal is not detected above the noise of the analysis result, and can be interpreted to encompass a case in which the oxide is detected at the noise level of the analysis result.

[0039] The terms “step of” or “step of” as used throughout this specification do not mean “step for”.

[0040] Throughout this specification, terms indicating the scale of a component, such as “diameter” or “thickness,” may be interpreted to mean “maximum diameter” or “maximum thickness” of the component. For example, the “diameter” range of a metal nanostructure, such as a metal fiber, metal nanorod, or metal nanofiber, included in the porous metal layer of the cathode of one embodiment may be defined as the range for the “maximum diameter” of the thickest part of a single strand of nanorod or (nano)fiber.

[0041] Furthermore, when a part such as a layer, film, region, or plate is said to be “on” another part, this includes not only cases where it is “directly on” the other part, but also cases where there is another part in between. Additionally, a part such as a film, region, or plate that is “on” the other part may have a portion thereof overlap with a portion of the other part in the thickness direction.

[0042] In addition, throughout this specification, the term “lithium-free secondary battery” may refer to a secondary battery in which, before charging and discharging, for example, immediately after manufacturing, 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 the negative electrode current collector (for example, an negative electrode in one embodiment including a conductive metal layer such as copper, a porous metal layer, and a carbon nanostructure). Accordingly, the “lithium-free secondary battery” may be defined as not including, before charging and discharging, a separate negative electrode active material layer (for example, a lithium metal layer, etc.) on the negative electrode or the negative electrode current collector. However, it should be understood that addition of a separate insulating layer or functional layer other than the negative electrode active material layer is not limited. In addition, the term “lithium-free secondary battery” cannot be interpreted as limiting the presence of a lithium-containing positive electrode active material, or limiting the presence of a lithium metal layer or a lithium-containing compound deposited on the negative electrode as a result of charging and discharging.

[0043]

[0044] Hereinafter, based on the above definitions, embodiments of the invention will be described in detail with reference to the attached drawings. However, these are presented as examples and are not intended to limit the invention. The invention is defined solely by the scope of the claims set forth below.

[0045] FIG. 1 is a schematic diagram schematically showing the configuration of a negative electrode for a lithium-free secondary battery according to one embodiment of the invention, and FIG. 2 is a schematic diagram schematically showing the cross-sectional shape of a negative electrode for a lithium-free secondary battery according to one embodiment of the invention.

[0046] As illustrated in FIGS. 1 and 2, a negative electrode for a lithium-free secondary battery according to one embodiment of the invention includes a porous metal layer having a three-dimensional microstructure; and a conductive carbon nanostructure formed on the porous metal layer.

[0047] The porous metal layer includes a metal mesh layer in which fibrous metal having a diameter on the micron (㎛) scale forms a network structure, and metal nanostructures formed on the fibrous metal, and at least some of the metal nanostructures are connected to each other to define a plurality of pores on the porous metal layer.

[0048] The cathode of the above embodiment comprises, for example, a porous metal layer formed through electrochemical etching and re-deposition of a conductive metal on a metal mesh layer including a conductive metal, and carbon nanostructures on the porous metal layer, as described in more detail below.

[0049] In the process of the electrochemical etching and redeposition, the conductive metal included in the metal mesh layer is etched to reduce the diameter of the fibrous metal, and while the conductive metal is redeposited on the fibrous metal, metal nanostructures having the shape of, for example, metal nanorods or metal nanofibers having a nano-scale diameter are formed and grown on the metal mesh layer. At least some of these metal nanostructures are connected to each other, thereby defining fine pores on the porous metal layer. In particular, as confirmed in the following examples and the like, through the manufacturing process, the porous metal layer can have a three-dimensional microstructure including a plurality of pores defined by the metal nanostructures while having a thinner thickness and a smaller mass per unit area than previously known negative electrodes (or negative electrode current collectors) for lithium-free secondary batteries.

[0050] Accordingly, the negative electrode of one embodiment can be made thinner and lighter than a conventional negative electrode for a lithium-free secondary battery, and at the same time, lithium metal can be uniformly deposited within the three-dimensional porous microstructure when the battery is charged, and lithium metal can be prevented from growing unevenly outside the negative electrode to form lithium dendrites, or side reactions between the negative electrode and the electrolyte, or galvanic corrosion of the negative electrode.

[0051] In addition, in the negative electrode of one embodiment, carbon nanostructures such as carbon nanotubes may be formed on the porous metal layer. Such carbon nanostructures may exhibit low reactivity and non-affinity (lithiophobicity) toward lithium metal. By forming such carbon nanostructures, lithium metal may be more uniformly deposited within the porous metal layer, and the degree of aggregation of the lithium metal may be controlled to an appropriate size. Accordingly, it is possible to suppress the formation of lithium dendrites and the like due to uneven growth of lithium metal outside the porous metal layer, and to suppress volume changes of the negative electrode during the operation of the battery.

[0052] Meanwhile, the negative electrode for a lithium-free secondary battery according to the above embodiment may include the porous metal layer as its substrate, and in some cases, may further include a conductive metal layer supporting the porous metal layer. In this case, the porous metal layer and optionally the conductive metal layer supporting the porous metal layer may be formed using any conductive metal that has been previously known to be usable as an anode current collector, as a metal that does not cause chemical changes in the lithium-free secondary battery, has relatively low reactivity, and high conductivity.

[0053] Specific examples thereof include metals such as stainless steel, aluminum, nickel, titanium, or copper, or metals surface-treated with carbon, nickel, titanium, silver, or the like on the surface of copper, aluminum, or stainless steel. However, considering the excellent conductivity and light weight of the cathode of one embodiment, and the ease of manufacturing the porous metal layer, the porous metal layer may include copper.

[0054] Meanwhile, the porous metal layer may have a thickness of 10 to 30 μm, or 12 to 25 μm, or 14 to 20 μm, and a mass per unit area of ​​4.0 to 10.0 mg / cm 2, or 4.5 to 9.0 mg / cm 2 , or 5.0 to 8.0 mg / cm 2 As described above, the porous metal layer included in the negative electrode of one embodiment may have a thin thickness and a small mass per unit area, while having a porous three-dimensional microstructure developed by the metal fibers included in the porous metal layer and the metal nanostructures grown therefrom. In this way, lithium metal is uniformly deposited within the pores of the thinned and lightweight three-dimensional microstructure, thereby suppressing the formation of lithium dendrites and the like, thereby enabling the provision of a lithium-free secondary battery having a higher energy density and capacity.

[0055] In such a porous metal layer, the fibrous metal may have a diameter in the micron (㎛) scale, for example, 5 to 15 ㎛, or 7 to 13 ㎛, or 8 to 12 ㎛, based on a single strand of fiber, and may form a metal mesh layer by forming a network structure such that the distance between the fibrous metals facing each other is 30 to 80 ㎛, or 40 to 75 ㎛, or 50 to 70 ㎛. In addition, the metal nanostructures in the shape of metal nanorods or metal nanofibers formed on the fibrous metal may have a diameter of 100 to 700 nm, or 150 to 650 nm, or 200 to 550 nm, respectively.

[0056] The metal nanostructures grown on the fibrous metal can be interconnected or entangled to define a plurality of open pores within the porous metal layer, and lithium metal can be uniformly deposited within these pores when charging a 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%. If the porosity is higher than this, lithium deposition may be uneven or lithium may be unevenly aggregated within the negative electrode, which may increase lithium metal desorption, lithium dendrite formation, or side reactions. Conversely, if the porosity is excessively low, lithium deposition may not be properly performed, lithium may grow unevenly outside the negative electrode, and an increase in the volume of the negative electrode may occur, which may deteriorate the characteristics of the secondary battery.

[0057] Meanwhile, in the cathode of the above-described embodiment, the porous metal layer may be made of a conductive metal such as copper, and more specifically, may be made of a conductive metal in a reduced form. In this case, being made of a conductive metal in a reduced form means that the porous metal layer is, for example, copper oxide (Cu x O) may mean that the porous metal layer does not substantially contain an oxide of a conductive metal such as copper oxide. More specifically, when the porous metal layer is analyzed by XRD, a peak derived from copper oxide, for example, a peak detected at 2θ of 60° to 63°, may not be detected with an intensity higher than noise.

[0058] As will be described in more detail below, during the negative electrode manufacturing process of one embodiment, the porous metal layer or the metal mesh used as the raw material thereof may be heat-treated under a reducing atmosphere (hydrogen atmosphere), for example, at a high temperature of 300°C or higher or 500°C or higher. The porous metal layer that has undergone such heat treatment may substantially not contain an oxide of a conductive metal such as copper oxide, and the porous metal layer may be formed of a reduced form of the conductive metal (for example, reduced copper itself). In addition, during the heat treatment process, some of the metal nanostructures may aggregate, so that their diameters may be controlled, and the sizes of the pores defined between the metal nanostructures may also be controlled together. As a result, lithium metal may be more uniformly deposited on the negative electrode of one embodiment, and the conductivity of the negative electrode may also be further improved. In addition, since the porous metal layer does not substantially contain an oxide of a conductive metal, galvanic corrosion or side reactions of the negative electrode may be suppressed.

[0059] Meanwhile, in the negative electrode of the above-described embodiment, a conductive carbon nanostructure made of carbon nanotubes or carbon nanofibers may be formed on the porous metal layer, for example, a metal mesh layer including the fibrous metal. As described above, due to the lithium non-affinity of the carbon nanostructure, lithium metal may be more uniformly deposited within the porous metal layer, and the growth of lithium dendrites due to the lithium metal growing outside the negative electrode may be suppressed. In addition, due to the low reactivity of the carbon nanotubes and the like, side reactions between the negative electrode of the above-described embodiment, the deposited lithium metal layer, and the electrolyte may be further reduced, and the negative electrode may exhibit more improved electrochemical characteristics.

[0060] Conductive carbon nanostructures such as carbon nanotubes can be directly synthesized and grown on the porous metal layer during the manufacturing process of the cathode. To this end, a metal catalyst for synthesizing carbon nanotubes, such as aluminum oxide and iron, is thinly coated on the porous metal layer, and a gaseous carbon source is applied onto the metal catalyst layer to synthesize the carbon nanotubes, etc.

[0061] In this embodiment, in the negative electrode, for example, a catalyst layer containing aluminum, iron or ions thereof derived from the metal catalyst may be further formed on the porous metal layer, and conductive carbon nanostructures such as carbon nanotubes may be formed on the catalyst layer. At this time, the catalyst layer may have a thickness of, for example, 10 to 50 nm or 15 to 30 nm. Due to this form, the conductive carbon nanostructures can be uniformly formed with a thin thickness near the surface of the porous metal layer. As a result, a lithium metal layer can be deposited and formed on the negative electrode more uniformly and in an appropriate size.

[0062] Meanwhile, according to another embodiment of the invention, a method for manufacturing the cathode of the above-described embodiment is provided. The method for manufacturing the cathode may include, for example, a step of performing electrochemical etching on a metal mesh including a conductive metal; a step of redepositing the conductive metal on the metal mesh on which the electrochemical etching has been performed, thereby forming a porous metal layer in which a metal nanostructure is formed on a fibrous metal having a network structure; and a step of forming a carbon nanostructure by supplying a gaseous carbon source including an aliphatic hydrocarbon and a reducing gas to the porous metal layer in the presence of a metal catalyst.

[0063] FIG. 3a schematically illustrates each step of a method for manufacturing a negative electrode for a lithium-free secondary battery according to another embodiment of the invention, and FIG. 3b schematically illustrates the change in an object before and after each manufacturing step is performed, while the lower part of FIG. 3b illustrates an example of an electron microscope dictionary showing the change in an object.

[0064] Referring to FIGS. 3A and 3B , in the manufacturing method, electrochemical etching and re-deposition of the conductive metal are performed using a metal mesh including a conductive metal such as copper, for example. As a result, as the conductive metal is etched and re-deposited on the fibrous metal of the metal mesh, a plurality of metal nanostructures, for example, bundles of metal nanorods or metal nanofibers, can grow and form on the fibrous metal. At least some of these metal nanostructures can be connected to define a plurality of pores, and can form a porous metal layer of the cathode of one embodiment.

[0065] Thereafter, a metal catalyst including, for example, aluminum oxide and iron is added onto the porous metal layer, and a gaseous carbon source including an aliphatic hydrocarbon and a reducing gas are supplied onto the metal catalyst while heat treatment is performed, thereby allowing the synthesis and growth of carbon nanostructures such as carbon nanotubes to proceed. In this way, an example of a cathode having a thin and lightweight structure and including an advanced three-dimensional porous microstructure and carbon nanostructure can be manufactured.

[0066] Meanwhile, in this manufacturing method, the metal mesh used as the raw material may be a commercially available conductive metal mesh having an appropriate aperture size and scale, taking into consideration the porosity and thickness of the porous metal layer to be finally manufactured. In a specific example, the metal mesh may include a metal wire (or fibrous metal) having a diameter of 20 to 40 μm, or 22 to 35 μm, or 23 to 30 μm, and the metal wires may form a mesh structure so as to have an aperture size of 200 to 500 mesh, or 300 to 400 mesh. In this way, an embodiment of a negative electrode having an appropriate porosity and a porous three-dimensional microstructure can be formed.

[0067] Additionally, as illustrated in the first drawing of FIG. 3A, the electrochemical etching step and the re-deposition step of the conductive metal may be sequentially performed within the same electrolytic cell. In a more specific example, the electrolytic cell may be performed within the same electrolytic cell, which includes a working electrode including the metal mesh, a counter electrode including a conductive metal identical to the metal mesh, for example, a conductive metal sheet such as copper foil, and an electrolyte including ions of the conductive metal and an acid.

[0068] At this time, the electrolyte may include, for example, copper ions and sulfuric acid, and according to a more specific example, it may be an aqueous electrolyte including copper sulfate (CuSO4) and sulfuric acid. According to one embodiment, the electrolyte may be an aqueous electrolyte including copper sulfate (CuSO4) at a concentration of 20 to 100 mM, or 30 to 80 mM, and sulfuric acid at a concentration of 100 to 300 mM, or 150 to 250 mM. If the concentration of the sulfuric acid, etc. is excessively low, the redeposition of the conductive metal such as copper may not occur uniformly.

[0069] In addition, in the manufacturing method of the other embodiment, the electrochemical etching step is 30 to 60 mA / cm 2 , or 35 to 55 mA / cm 2 Constant current etching can be performed under constant current application at a current density of . If the current density is too low, the conductive metal may not be properly etched from the metal mesh, and if the current density is too high, the conductive metal may be etched unevenly, causing the three-dimensional microstructure of the porous metal layer in the finally formed cathode to collapse.

[0070] Meanwhile, in the electrochemical etching step, the etched conductive metal ions, for example, copper ions, move to the counter electrode, which serves as a source of conductive metal in the redeposition step of the conductive metal. In this redeposition step, the ions of the conductive metal move from the counter electrode to the working electrode, and are deposited on the metal wires (fibrous metal) of the metal mesh, thereby forming a metal nanostructure of metal nanorods or metal nanofibers.

[0071] This redeposition step can be performed under an applied voltage of 2.2 V to 2.7 V, or 2.3 V to 2.5 V. However, if the applied voltage is too low, uniform deposition of the conductive metal on a large-area metal mesh layer may be difficult.

[0072] Meanwhile, in the manufacturing method of the other embodiment described above, a step of heat treating the metal mesh or porous metal layer at 300°C or higher under a reducing gas atmosphere (e.g., in the presence of hydrogen gas) may be further performed before the electrochemical etching step or after the re-deposition step of the conductive metal. In a specific example, the heat treatment may be performed on the porous metal layer after the re-deposition step.

[0073] As a result of this heat treatment, the oxide of the conductive metal remaining on the porous metal layer can be reduced, and the porous metal layer can be formed of the conductive metal in a reduced form without substantially including the oxide of the conductive metal. As a result, the porous metal layer and the cathode including the porous metal layer can exhibit improved conductivity and low resistance.

[0074] Furthermore, as heat treatment is performed at an appropriate temperature and time, some of the metal nanostructures formed on the porous metal layer may aggregate, thereby controlling the distribution and size of the pores defined therebetween. This allows lithium metal to be more uniformly deposited on the negative electrode of one embodiment, and the formation of lithium dendrites can be suppressed.

[0075] The above heat treatment step may be performed at a temperature of 300°C or higher for 5 minutes or longer to reduce the oxide of the conductive metal, and more preferably, it may be performed 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 lithium metal. In addition, if the heat treatment temperature is excessively high or the heat treatment time is excessively long, the metal nanostructure may be excessively aggregated, and the pore size, etc. may be excessively reduced. Therefore, the heat treatment step may be performed at a temperature of 300 to 800°C, or 500 to 800°C, for 5 minutes to 1.5 hours.

[0076] Meanwhile, the heat treatment step may be performed continuously within the same reactor as the subsequent carbon nanostructure formation step. For this continuous process, the heat treatment may be performed at a temperature of 600 to 800°C for 5 to 20 minutes, followed by the subsequent carbon nanostructure synthesis process in the same reactor.

[0077] Meanwhile, after the step of re-depositing the conductive metal or the step of selective heat treatment, for example, a metal catalyst including aluminum oxide and iron is added onto the porous metal layer, and in the presence of this metal catalyst, a gaseous carbon source including an aliphatic hydrocarbon and a reducing gas are supplied while heat treatment is performed, thereby synthesizing carbon nanostructures such as carbon nanotubes. As a result, the carbon nanostructures can grow on the porous metal layer, more specifically, on the metal mesh layer and the metal nano precursor, thereby manufacturing an anode according to one embodiment.

[0078] At this time, the gaseous carbon source may include, for example, an aliphatic hydrocarbon having 1 to 5 carbon atoms, for example, ethylene gas, and the reducing gas may include hydrogen gas. In addition, the metal catalyst including aluminum oxide and iron may be added such that the aluminum oxide is added to a thickness of 10 to 25 nm, while the iron is added to a thickness of 1 to 5 nm. If the added thickness of the metal catalyst is too thin, the metal catalyst may be contaminated by diffusion of a conductive metal such as copper, or sufficient carbon nanostructures such as carbon nanotubes may not be formed. In addition, the metal catalyst including aluminum oxide and iron may be deposited on the porous metal layer under irradiation with an E-beam.

[0079] In addition, the heat treatment process for synthesizing the carbon nanostructure can be performed at a temperature of 600 to 800°C for 5 to 20 minutes, or 10 to 20 minutes, depending on the synthesis conditions of general carbon nanotubes, etc., thereby allowing the carbon nano precursor to sufficiently grow.

[0080] Meanwhile, according to a further embodiment of the invention, a lithium-free secondary battery comprising the negative electrode of the above-described embodiment is provided. Such a lithium-free secondary battery may include, for example, the negative electrode of the above-described embodiment; a positive electrode facing the negative electrode and comprising a positive electrode active material; and a separator or electrolyte layer interposed between the positive electrode and the negative electrode. In addition, the lithium-free secondary battery may further comprise, together with the separator, an electrolyte comprising a lithium salt and a non-aqueous organic solvent.

[0081] In such lithium-free secondary batteries, the negative electrode does not include a separate negative electrode active material layer, such as a lithium metal layer, before charging or discharging. However, as the lithium-free secondary battery is charged or discharged, lithium ions moved from the positive electrode may be deposited on the porous metal layer of the negative electrode, thereby forming a lithium metal layer or a lithium alloy layer, and such a lithium metal layer or the like may function as a negative electrode active material.

[0082] Meanwhile, in the lithium-free secondary battery of the above additional embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer positioned on the positive electrode current collector.

[0083] These positive electrodes can be manufactured by mixing an active material and a binder, and in some cases, a conductive material, a filler, etc. in a solvent to prepare a positive electrode slurry composition, and applying the composition to a positive electrode current collector.

[0084] The above-described positive electrode current collector may generally have a thickness of 3 to 500 μm. In addition, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may also form fine unevenness on its surface to increase the adhesive strength of the positive electrode active material, and various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric are possible.

[0085] And, in the case of the above positive electrode active material, it may include a compound capable of reversible intercalation and deintercalation of lithium, specifically a lithium metal oxide containing one or more metals such as iron, cobalt, manganese, nickel, or aluminum and lithium.

[0086] Specifically, the lithium metal oxide is a lithium-manganese oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt oxide (e.g., LiCoO2, etc.), a lithium-nickel oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese oxide (e.g., LiNi 1-Y Mn Y O2 (here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0<Z<2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2 (here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2 (here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (wherein, 0<Z1<2) etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mnr )O2(wherein, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (wherein, 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2) etc.), lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni p2 Co q2 Mn r2 M s2 )O2 (wherein, M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are 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 (Here, M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, -0.5≤a≤+0.5, 0≤x≤0.5, 0≤b≤0.1), and any one or two or more compounds thereof may be included.

[0087] Among these, the positive electrode active material includes a lithium metal oxide including lithium and two or more metals selected from the group consisting of nickel, manganese, cobalt, and aluminum, and the lithium metal oxide may include nickel in an amount of 50 mol% or more, or 60 to 99 mol%, or 70 to 95 mol%, based on the total metal content excluding lithium. Such a lithium metal oxide may be represented by, for example, the following chemical formula 1:

[0088] [Chemical Formula 1]

[0089] Li x Ni a Co b M1 c M 2 d O2

[0090] In the above chemical formula 1, the M 1 Mn and Al may be one or more selected from or a combination thereof, and M 2 may be at least one 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. In addition, 0 <b≤0.3이고, 0<c≤0.3이고, 0≤d≤0.1일 수 있다.

[0091] By using a lithium metal oxide containing such a high nickel content as a positive electrode active material and combining it with an anode of one embodiment, the output and capacity characteristics, as well as the life characteristics, of a lithium-free secondary battery can be further improved.

[0092] The above-described positive electrode active material may be included in an amount of 60 to 99 wt%, or 70 to 99 wt%, or 80 to 98 wt% based on the total weight of the positive electrode active material layer.

[0093] Meanwhile, the conductive material included in the positive electrode active material layer is a component for further improving the conductivity of the positive electrode active material. The conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery. For example, 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 crystal structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powder such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. can be used. Among these, the conductive material can further lower the resistance of a lithium-free secondary battery and improve output characteristics, etc. by including a conductive nanomaterial such as carbon nanotubes or carbon nanofibers.

[0094] Typically, the conductive material may be included in an amount of 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt% based on the total weight of the positive electrode active material layer.

[0095] The binder optionally included in the above-described positive electrode active material layer is a component that assists in the bonding of the positive electrode active material and the conductive material, and in the bonding to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber, and a mixture or copolymer of two or more selected from these may also be used.

[0096] Typically, the binder may be included in an amount of 1 to 20 wt%, or 1 to 15 wt%, or 1 to 10 wt% based on the total weight of the positive electrode active material layer.

[0097] Additionally, a filler may be optionally added to the positive electrode as a component that suppresses its expansion. Such filler is not particularly limited as long as it can suppress the expansion of the electrode without causing chemical changes in the battery. Examples of fillers that can be used include olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber; and the like.

[0098] The above-described positive electrode can be manufactured by dispersing and mixing the positive electrode active material, binder, and conductive agent in a dispersion medium (solvent) to make a slurry, applying the slurry on a metal current collector, and then drying and rolling. At this time, the dispersion medium may be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto.

[0099] Meanwhile, the lithium-free secondary battery of the other embodiment may further include an electrolyte including a non-aqueous organic solvent and a lithium salt.

[0100] The lithium salt included in the above electrolyte is used as a medium for transferring ions within a secondary battery. Lithium salt is, for example, Li as a cation. + Including, 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 may include an anion selected from the group consisting of .

[0101] Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF4, LiClO4, LiB 10 Cl 10, 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).

[0102] The concentration of the above lithium salt can be appropriately changed within a commonly usable range, and can be included in the electrolyte at a concentration of 0.4 M to 6 M, or a concentration of 0.5 M to 5 M.

[0103] In a more specific embodiment, the electrolyte may contain a lithium salt at a relatively low concentration of 0.4 M or more and less than 2 M, or 0.5 M to 1.5 M, but may also contain the 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.

[0104] Meanwhile, the type of non-aqueous organic solvent that can be included in the electrolyte is not particularly limited, and any organic solvent that has been previously known to be applicable to electrolytes of lithium ion batteries, etc., can be used. Examples of such organic solvents include at least one selected from the group consisting of carbonate solvents, ether solvents, nitrile solvents, phosphate solvents, and sulfone solvents. However, considering the stability of the lithium metal layer electrodeposited on the lithium electrodeposition induction layer, etc., it is preferable that the non-aqueous organic solvent include a carbonate solvent or an ether solvent.

[0105] More specifically, as the carbonate solvent, 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 can be used, and as the phosphate solvent, trimethyl phosphate, triethyl phosphate or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide can be used.

[0106] In addition, as the ether solvent, dibutyl ether, tetraglyme, diglyme, dimethoxy ethane, or tetrahydrofuran derivatives such as 2-methyl tetrahydrofuran can be used, and as the nitrile solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. In addition, as the sulfone solvent, dimethyl sulfone, ethylmethyl sulfone, or sulforane can be used.

[0107] Meanwhile, the lithium-free secondary battery described above may further include a porous separator interposed between the positive electrode and the negative electrode.

[0108] These porous membranes can be made of olefin polymers such as polyethylene and polypropylene, glass fibers, etc. in the form of sheets, multi-membranes, microporous films, woven fabrics, and non-woven fabrics, but are not necessarily limited thereto. However, it may be preferable to use porous polyethylene or porous glass fiber non-woven fabric (glass filter) as the membrane, and it may be more preferable to use porous glass filter (glass fiber non-woven fabric) as the membrane. The membrane may be an insulating thin film having high ion permeability and mechanical strength, and the pore diameter of the membrane may generally be in the range of 0.01 to 10 ㎛, and the thickness may generally be in the range of 5 to 300 ㎛, but is not limited thereto.

[0109] In addition, in another example of the lithium-free secondary battery, the separator may be integrated with the electrolyte and interposed between the positive and negative electrodes in the form of an electrolyte layer or electrolyte film. In one example, the electrolyte layer or electrolyte film may be in the form of a polymer matrix containing the lithium salt and a non-aqueous organic solvent described above, or in the form of a solid electrolyte. In addition, a well-known polymer-based solid electrolyte, etc. may be used as the polymer matrix.

[0110] 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 an all-solid battery having a solid electrolyte layer, depending on whether the electrolyte layer is included and its shape, etc.

[0111] Meanwhile, the lithium-free secondary battery of the above-described other embodiment can be manufactured according to a conventional method in the art. For example, the electrode assembly including the positive electrode, negative electrode, and separator can be housed in a case, and manufactured by a method of injecting and impregnating the electrolyte described above, or the electrode assembly including the positive electrode, negative electrode, and electrolyte layer can be housed in a case, and manufactured.

[0112] These lithium-free secondary batteries can be applied to battery cells used as power sources for small devices, and are particularly suitable for use as unit cells in battery modules that serve as power sources for medium- to large-sized devices.

[0113]

[0114] Below, preferred embodiments of the invention, comparative examples to compare with them, and experimental examples for evaluating them are described. However, the following examples are merely preferred embodiments of the invention, and the present invention is not limited to the following examples.

[0115]

[0116] Comparative Example 1:

[0117] Copper foil having a thickness of 9㎛ was used as the negative electrode for the lithium-free secondary battery of Comparative Example 1.

[0118]

[0119] Comparative Example 2: Manufacturing of a negative electrode for a lithium-free secondary battery

[0120] A copper mesh with a wire diameter of 25 μm and an aperture size of 300 to 400 mesh was used. In addition, an electrolytic cell containing a working electrode including this copper mesh, a counter electrode composed of a copper foil with a thickness of 9 μm, and an aqueous electrolyte containing 50 mM copper sulfate and 200 mM sulfuric acid was used.

[0121] Within the electrolytic cell, a constant voltage of 2.4 V was applied for 720 seconds to deposit copper from the copper foil onto the copper mesh. Through this deposition, a copper nanostructure in the form of nanoprotrusions was formed on the copper mesh, which was used as the negative electrode for the lithium-free secondary battery of Comparative Example 2.

[0122]

[0123] Examples 1 to 6: Preparation of negative electrode for lithium-free secondary battery

[0124] A copper mesh with a wire diameter of 25 μm and an aperture size of 300 to 400 mesh was used. In addition, an electrolytic cell containing a working electrode including the copper mesh, a counter electrode including a copper foil having a thickness of 9 μm, and an aqueous electrolyte including 50 mM copper sulfate and 200 mM sulfuric acid was used.

[0125] In the above electrolytic cell, 40 mA / cm 2 Electrochemical etching was performed from the copper mesh by applying a constant current at a current density of . The etching was performed for 9 minutes, thereby desorbing copper ions from the copper mesh. Subsequently, under an application of a voltage of 2.4 V, copper was redeposited from the copper foil onto the copper mesh for 2 minutes.

[0126] Afterwards, the sample of the porous copper layer on which the redeposition was completed was placed on a quartz boat connected to a magnetic transporter, and the sample was placed in the center of the chamber of a tube furnace heated to 775°C with 80% hydrogen (helium atmosphere) gas flowing, and then taken out to perform heat treatment. At this time, based on the heat treatment time of putting in and taking out the sample, the heat treatment conditions were different for each example, such as 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).

[0127] Electron micrographs of the porous copper layers formed by the above heat treatment are shown in Figs. 4a to 4f, respectively. Through this, it was confirmed that a large number of copper nanostructures in the shape of nanorods or nanofibers were formed on the porous copper layers of Examples 1 to 6, and that nanopores were defined by these nanostructures. In addition, among Examples 1 to 6, it was confirmed that an appropriate porous structure for uniform electrodeposition of lithium metal was formed in Examples 2 to 4, and that when the heat treatment time was longer than this, the pores tended to narrow due to agglomeration between copper nanostructures.

[0128] Meanwhile, after the heat treatment, 20 nm of Al2O3 and 2 nm of Fe were deposited on one surface of the porous copper layer by irradiating with E-beam to form a metal catalyst layer. Subsequently, carbon nanotube synthesis was performed for 12 to 20 minutes in a tube furnace heated to 775°C, where the heat treatment was performed, under the supply of 410 sccm of He, 100 sccm of ethylene gas, and 100 sccm of hydrogen gas on the metal catalyst layer.

[0129] Thus, negative electrodes for lithium-free secondary batteries of Examples 1 to 6 were each manufactured.

[0130]

[0131] Examples 7 to 9: Preparation of negative electrode for lithium-free secondary battery

[0132] A porous copper layer was manufactured by performing electrochemical etching and copper redeposition in the same manner as in Examples 1 to 6 above.

[0133] Thereafter, the sample of the porous copper layer on which the redeposition was completed was placed in the chamber of a tube furnace connected to a vacuum pump. While flowing 3.9% hydrogen gas (Ar base) into the chamber, it was heated at a heating rate of 10°C / min to reach 400 to 600°C and then maintained at that temperature for 1 hour. At this time, based on the elevated heat treatment temperature of the sample, each heat treatment temperature was different for each example, such as 400°C (Example 7), 500°C (Example 8), and 600°C (Example 7).

[0134] The electron microscope images of the porous copper layers formed by the above heat treatment are shown in Fig. 5 according to the heat treatment temperature. Through this, it was confirmed that a large number of copper nanostructures in the shape of nanorods or nanofibers were formed on the porous copper layers of Examples 7 to 9, and that nanopores were defined by these nanostructures. In addition, among Examples 7 to 9, it was confirmed that an appropriate porous structure for uniform electrodeposition of lithium metal was formed in Example 8, and when the heat treatment temperature was lower than this (Example 7), the connection between the nanostructures was insufficient, so that the porous structure was not sufficiently formed. On the contrary, in Example 9, where the heat treatment temperature was high, it was confirmed that the pores tended to narrow due to aggregation between the copper nanostructures.

[0135] Additionally, the porous copper layers of Examples 1, 4, 7 to 9 were analyzed by XRD, and the analysis results are shown in Fig. 6. Referring to Fig. 6, in Example 1, which was not subjected to heat treatment, a peak derived from copper oxide was detected at 2θ of 60° to 63°, but in Examples 4, 7 to 9, which were subjected to heat treatment, it was confirmed that the corresponding peak was not detected.

[0136] Meanwhile, after the heat treatment was performed, carbon nanotubes were synthesized on the porous copper layer of Examples 7 to 9 using the same method as Examples 1 to 6, thereby manufacturing negative electrodes for lithium-free secondary batteries of Examples 7 to 9, respectively.

[0137]

[0138] Test Example 1: Evaluation of the physical properties of the cathode

[0139] The thickness of the cathodes of Comparative Examples 1, 2 and Example 4 was measured by cross-sectional observation using a scanning electron microscope (Hitachi, SU5000) and a thickness measuring device (Mitutoyo, 547-401A). The mass per unit area was measured by cutting the cathodes into circles with a diameter of 19 mm using a disk puncher (Wellcos, WC-H125) and then using an ultra-precision balance (RADWAG, XA52.4Y). The evaluation results are shown in Table 1 below. In addition, the mass per unit area and thickness, and the true density value of copper (8.95 g / cm 3 ) was used to calculate the porosity of each cathode.

[0140] Thickness (㎛)Porosity (%)Mass per unit area (mg / cm) 2 ) Comparative Example 1908.9 Comparative Example 27054.628.4 Example 41562.85.02

[0141] Referring to Table 1 above, it was confirmed that the negative electrode of Example 4 had a developed porous three-dimensional microstructure, thereby exhibiting a high porosity suitable for uniform lithium deposition, while having a very thin thickness and low mass per unit area compared to the negative electrode of Comparative Example 2. Through this, it was 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.

[0142]

[0143] Test Example 2: Evaluation of cathode resistance and galvanic corrosion resistance

[0144] Half cells were manufactured using the negative electrodes of Comparative Example 1, Example 1, and Example 4. These half cells included lithium foil as the negative electrode and counter electrode, and 75 μl of an electrolyte of 0.6 M LiBF4 + 0.6 M LiBF2(C2O4) in FEC / DEC (1:2 volume ratio). For these half cells, 10 -3 10 inland 6 Under the conditions of Hz, 50 mV, the charge transfer resistance and Ohmic resistance of each cathode were evaluated by EIS (Electrochemical Impedance Spectroscopy) analysis, and the evaluation results were compared and presented in Table 2 below.

[0145] Charge transfer resistance (Ω)Ohmic resistance (Ω)Comparative example 15208.25Example 1349.84Example 41368.05

[0146] Referring to Table 2 above, it was confirmed that the negative electrodes of Examples 1 and 4 exhibited lower resistance than that of Comparative Example 1 due to the formation of a porous three-dimensional microstructure. In addition, it was confirmed that the negative electrode of Example 4 exhibited greater charge transfer resistance and smaller Ohmic resistance than that of Example 1. This is because the copper oxide having lithium affinity in Example 4 was reduced and removed during heat treatment, and it was confirmed that the negative electrode of Example 4 exhibited more improved conductivity than that of Example 1.

[0147] Additionally, using the cathodes of Comparative Examples 1, 2, and 4, half-cells identical to those described above were manufactured, and the current density over time was evaluated while conducting galvanic charging and discharging using these half-cells. The results of this evaluation are shown in Fig. 7.

[0148] Through the change pattern of current density over time shown in Fig. 7, it was confirmed that the cathode of Example 4 had galvanic corrosion reduced by approximately 75% compared to the cathode of Comparative Example 2, which corresponds to the existing cathode with a three-dimensional porous microstructure introduced.

[0149]

[0150] Test Example 3: Cycle-by-cycle capacity characteristic evaluation

[0151] Batteries were manufactured using the negative electrodes of Comparative Example 1, Example 4 and Example 8. These batteries were manufactured using the negative electrode and NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 It included a cathode containing O2) as a cathode active material, a polyethylene separator, and 75 μl of an electrolyte of 0.6 M LiBF4 + 0.6 M LiBF2(C2O4) in FEC / DEC (1:2 volume ratio).

[0152] For these batteries, 4 mAh·cm -2 While charging and discharging were performed under the conditions of (0.5 C, cut-off voltage: 4.5 V), the change in discharge capacity per cycle was evaluated, and the evaluation results are shown in Fig. 8.

[0153] Referring to Fig. 8, it was confirmed that the lithium-free secondary battery including the negative electrode of the example exhibited a better capacity per cycle than the battery including the negative electrode of the comparative example.

Claims

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

2. A negative electrode for a lithium-free secondary battery further comprising a conductive metal layer supporting the porous metal layer in the first paragraph.

3. In the first paragraph, the porous metal layer is a negative electrode for a lithium-free secondary battery containing copper.

4. In the first paragraph, the metal nano structure is a negative electrode for a lithium-free secondary battery including a metal nano rod or a metal nano fiber.

5. In the first paragraph, the conductive carbon nano structure is a negative electrode for a lithium-free secondary battery including carbon nanotubes.

6. A negative electrode for a lithium-free secondary battery according to claim 1, wherein the porous metal layer has a thickness of 10 to 30 μm.

7. In the first paragraph, the porous metal layer has a density of 4.0 to 10.0 mg / cm 2 A negative electrode for a lithium-free secondary battery having a mass per unit area of ​​.

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

9. A negative electrode for a lithium-free secondary battery, wherein the porous metal layer in the first paragraph has a porosity of 55 to 70%.

10. A negative electrode for a lithium-free secondary battery in the first paragraph, wherein the porous metal layer is made of a reduced form of a conductive metal and substantially does not contain an oxide of the conductive metal.

11. A negative electrode for a lithium-free secondary battery, comprising: aluminum or iron; and further comprising a catalyst layer formed on the porous metal layer, wherein the conductive carbon nanostructure is formed on the catalyst layer.

12. A step of performing electrochemical etching on a metal mesh containing a conductive metal; A step of forming a porous metal layer in which a metal nanostructure is formed on a fibrous metal having a network structure by re-depositing the conductive metal on the metal mesh on which the electrochemical etching has been performed; and A method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 1, comprising the step of forming a carbon nanostructure while supplying a gaseous carbon source including an aliphatic hydrocarbon and a reducing gas on the porous metal layer in the presence of a metal catalyst.

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

14. In the 12th paragraph, the electrochemical etching step and the re-deposition step of the conductive metal, A working electrode including the above metal mesh, A counter electrode comprising the same conductive metal as the above metal mesh, and A method for manufacturing a negative electrode for a lithium-free secondary battery, the method comprising sequentially processing an electrolyte including ions of the conductive metal and an acid in the same electrolytic cell.

15. In the 12th paragraph, the electrochemical etching step is 30 to 60 mA / cm 2 A method for manufacturing a negative electrode for a lithium-free secondary battery, the method comprising: applying a constant current; 16. A method for manufacturing a negative electrode for a lithium-free secondary battery, wherein in the 12th paragraph, the step of re-depositing the conductive metal is performed under an application of a voltage of 2.2 V to 2.7 V.

17. A method for manufacturing a negative electrode for a lithium-free secondary battery, the method further comprising 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 in the 12th paragraph.

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

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

20. A method for producing a negative electrode for a lithium-free secondary battery, wherein the metal catalyst comprises aluminum oxide and iron in the 12th paragraph.

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

22. A cathode comprising a cathode active material; The cathode of clause 1; and A lithium-free secondary battery comprising a separator or electrolyte layer interposed between the positive and negative electrodes.

23. A lithium-free secondary battery further comprising a lithium metal layer deposited on the porous metal layer of the negative electrode by charging the lithium-free secondary battery in claim 22.

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