Negative electrode for lithium-free secondary battery, method for preparing same, 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 and achieve uniform electrodeposition of lithium metal while being made lightweight and thin, and a method for manufacturing the same, in which 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, in which the porous metal layer includes a metal mesh layer in which a fibrous metal having a micron-sized diameter forms a mesh structure, and a metal nanostructure formed on the fibrous metal, and at least a portion of the metal nanostructures are connected to each other to define a plurality of pores on the porous metal layer.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. KR10-2023-0168063, filed on November 28, 2023, and Korean Patent Application No. KR10-2024-0165866, filed on November 20, 2024, the entire contents of which are incorporated herein by reference.

[0003] This disclosure relates to a negative electrode for a lithium-free secondary battery, a method for preparing the same, and a lithium-free secondary battery containing the same. The negative electrode can reduce weight and thickness while also reducing side reactions on the negative electrode and improving the electrochemical and lifetime characteristics of the lithium-free secondary battery. Background Technology

[0004] Lithium metal batteries are batteries that use lithium metal (Li-metal) as the negative electrode active material. Compared to batteries using graphite-based negative electrodes according to existing technologies, they theoretically have a much higher energy density and capacity. Therefore, research and development are underway to apply this type of lithium metal battery to batteries requiring high energy density.

[0005] However, lithium metal batteries still suffer from unresolved problems such as high levels of side reactions and low reversibility. Therefore, to compensate for the low reversibility of lithium metal batteries, attempts have been made to pre-store excess lithium in the negative electrode and operate the battery. However, these attempts have encountered limitations as the N / P ratio of the secondary battery increases, potentially leading to a significant decrease in the energy density of lithium metal batteries, and issues related to cost and safety arise due to excess lithium.

[0006] Recently, there has been a growing interest in anode-free secondary batteries (also known as lithium-free or anode-free secondary batteries). These lithium-free batteries are those in which a separate lithium metal layer is not formed on the negative electrode current collector during the manufacturing process; instead, the negative electrode current collector itself serves as the negative electrode. Since lithium metal is electrodeposited onto the negative electrode current collector during charging, a lithium-free secondary battery can be defined as a battery that utilizes lithium metal as the negative electrode active material. Lithium-free secondary batteries maximize the use of lithium metal's high energy density while reducing safety issues caused by excess lithium storage.

[0007] However, in the case of a negative electrode 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, including galvanic corrosion and rapid capacity loss, may occur in the negative electrode. Additionally, the negative electrode may exhibit problems such as uneven deposition and growth of lithium metal on the negative electrode current collector, leading to lithium dendrite formation.

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

[0009] However, most existing lithium-free rechargeable battery anodes inevitably have large thickness and weight due to the need to form a three-dimensional porous microstructure on the metal current collector. Therefore, when used as a negative electrode for such lithium-free rechargeable batteries, there is a significant drawback: the energy density per unit volume of the battery is greatly reduced.

[0010] In addition, the following drawbacks still exist: due to the large surface area of ​​the negative electrode, the side reactions between the current collector and the lithium metal and electrolyte deposited during charging may be further increased, which may significantly reduce the initial capacity of the secondary battery and accelerate galvanic corrosion, thereby reducing the life characteristics of the secondary battery. Summary of the Invention

[0011] [Technical Issues]

[0012] Therefore, one object of this disclosure is to provide a lithium-free secondary battery anode and its preparation method that can reduce weight and thickness, reduce galvanic corrosion and side reactions on the anode, and achieve uniform electrodeposition of lithium metal.

[0013] Another object of this disclosure is to provide a lithium-free secondary battery that includes the negative electrode and thus exhibits improved safety, electrochemical performance and lifespan characteristics.

[0014] [Technical Solution]

[0015] According to certain aspects of this disclosure, a negative electrode for a lithium-free secondary battery is provided, comprising: a porous metal layer having a three-dimensional microstructure; and a conductive carbon nanostructure formed on said porous metal layer. The porous metal layer comprises a metal mesh layer in which fibrous metal with a diameter on the order of micrometers (μm) forms a mesh structure, and metal nanostructures formed on the fibrous metal. At least a portion of the metal nanostructures are connected to each other to define a plurality of pores on the porous metal layer.

[0016] In the aforementioned negative electrode, the metal nanostructure may include metal nanofibers or metal nanofibers, and the conductive carbon nanostructure may include carbon nanotubes.

[0017] According to some embodiments, the thickness of the porous metal layer can be 10 to 30 μm, and the mass per unit area can be 4.0 to 10.0 mg / cm². Furthermore, the porosity of the porous metal layer can be 55% to 70%.

[0018] According to certain aspects of this disclosure, a method for preparing a negative electrode for a lithium-free secondary battery according to certain embodiments is provided, the method comprising the steps of: electrochemically etching a metal mesh containing a conductive metal; redepositing the conductive metal on the electrochemically etched metal mesh to form a porous metal layer in which a metal nanostructure is formed on a fibrous metal having a mesh structure; and forming a carbon nanostructure in the presence of a metal catalyst while supplying a gaseous carbon source containing an aliphatic hydrocarbon and a reducing gas.

[0019] In some embodiments of the preparation method, the electrochemical etching step and the redeposition step of the conductive metal can be carried out sequentially in situ in the same electrolytic cell, which includes: a working electrode containing a metal mesh, a counter electrode containing the same conductive metal as the metal mesh, and an electrolyte containing ions of the conductive metal and an acid.

[0020] In addition, the preparation method of some embodiments may also include a step of heat-treating the metal mesh or porous metal layer in the presence of hydrogen before the electrochemical etching step or after the redeposition step of the conductive metal.

[0021] According to another aspect of this disclosure, a lithium-free secondary battery is provided, comprising: a positive electrode containing a positive electrode active material; a negative electrode as described in some embodiments; and a separator or electrolyte layer inserted between the positive electrode and the negative electrode.

[0022] According to some embodiments, such a lithium-free secondary battery is a battery in which a lithium metal layer is electrodeposited on the porous metal layer of the negative electrode during the charging process, thereby serving as the negative electrode active material.

[0023] [Beneficial Effects]

[0024] The negative electrode for lithium-free secondary batteries in some embodiments comprises a porous metal layer formed by electrochemical etching and redeposition of conductive metal on a metal mesh containing conductive metal, and a carbon nanostructure on the porous metal layer.

[0025] As a result of various experiments conducted by the inventors, it was found that even if the porous metal layer of the negative electrode is relatively thin and has a small mass per unit area, it can still have a well-developed three-dimensional porous microstructure and a relatively large porosity suitable for uniform electrodeposition of lithium.

[0026] Furthermore, in some embodiments of the negative electrode, carbon nanostructures, such as carbon nanotubes, can be formed on the porous metal layer. These carbon nanostructures exhibit low reactivity and lithium-repellency. Due to the formation of these carbon nanostructures, lithium metal can be electrodeposited more uniformly within the porous metal layer, and the uneven growth of lithium metal on the exterior of the porous metal layer, preventing the formation of lithium dendrites, can be suppressed.

[0027] Therefore, by applying the negative electrode described in certain embodiments 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. Furthermore, uniform lithium deposition can be induced on the negative electrode, and the growth of lithium dendrites and the like can be suppressed, thereby contributing to providing a lithium-free secondary battery exhibiting high energy density and improved electrochemical performance and lifetime characteristics. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the configuration of a negative electrode for a lithium-free secondary battery according to certain embodiments of the present disclosure.

[0029] Figure 2 This is a schematic diagram showing the cross-sectional shape of a negative electrode for a lithium-free secondary battery according to certain embodiments of the present disclosure.

[0030] Figure 3a This is a schematic diagram illustrating the steps of a method for preparing a negative electrode for a lithium-free secondary battery according to some other embodiments of the present disclosure.

[0031] Figure 3b It is shown Figure 3a A schematic diagram showing the changes in the object before and after each preparation step, and an electron microscope photograph of an example of the object.

[0032] Figure 4 These are electron microscope images of the porous copper layer formed in the negative electrode preparation process described in Examples 1 to 6.

[0033] Figure 5 These are electron microscope images of the porous copper layer formed in the negative electrode preparation process described in Examples 7 to 9.

[0034] Figure 6 The results of XRD analysis of the porous copper layers described in Examples 1, 4, 7 to 9 are shown.

[0035] Figure 7 The results show the evaluation of the change of current density over time by performing constant current charge-discharge tests on half-cells manufactured using the negative electrodes described in Comparative Example 1, Comparative Example 2, and Example 4.

[0036] Figure 8 The results show the way in which the discharge capacity changes over time by conducting charge-discharge tests on batteries manufactured using the negative electrodes described in Comparative Examples 1, 4, and 8. Detailed Implementation

[0037] Throughout this specification, when a part “contains” a constituent element, it does not mean that the part excludes other constituent elements, but rather that the part may contain other constituent elements, unless otherwise specified.

[0038] Throughout this specification, the terms “approximately” or “substantially” are intended to mean close to a numerical value or range specified with permissible error, and are intended to prevent any unethical third party from unlawfully or improperly using the precise or absolute numerical values ​​disclosed for the purpose of understanding this disclosure. For example, when the porous metal layer of the negative electrode described in some embodiments is “substantially” free of oxides of conductive metals, this means that, taking into account the detectability limits of analytical instruments such as XRD, when the composition of the porous metal layer is analyzed using such an analytical instrument, the oxides of the conductive metal are not detectable above the noise level of the analytical results, and can be interpreted to include cases where the oxides are detected at the noise level of the analytical results.

[0039] Throughout this specification, the term "steps for..." as used herein does not mean "steps for...".

[0040] Throughout this specification, terms such as “diameter” or “thickness” used to describe a constituent element can be interpreted as the “maximum diameter” or “maximum thickness” of the corresponding constituent element. For example, the range of “diameter” of the metal nanostructures (e.g., metal fibers, metal nanorods, or metal nanofibers) contained in the porous metal layer of the negative electrode in some embodiments can be defined as the range of the “maximum diameter” of the thickest portion of a single strand of the nanorod or (nano)fiber.

[0041] Furthermore, it should be understood that when an element (e.g., a layer, film, region, or plate) is referred to as being "on" or "above" another element, it can be located directly above the other element, or there may be intermediate elements present. Additionally, an element (e.g., a film, region, plate, etc.) disposed "on" another element can exist in such a manner that a portion of its region overlaps with a portion of the other element in the thickness direction.

[0042] Throughout this specification, the term "lithium-free secondary battery" can refer to a secondary battery in which, in a state prior to charging or discharging (e.g., immediately after fabrication), there is no separate negative electrode active material layer, such as a single lithium metal layer or lithium alloy layer, on the negative electrode or negative electrode current collector (e.g., in some embodiments, a negative electrode comprising a conductive metal layer such as copper, a porous metal layer, or a carbon nanostructure). Therefore, the term "lithium-free secondary battery" can be defined as a secondary battery that, in a state prior to charging or discharging, does not contain a separate negative electrode active material layer (e.g., a lithium metal layer, etc.) on the negative electrode or negative electrode current collector. However, it is clear that the addition of separate insulating or functional layers, in addition to the negative electrode active material layer, is not limited. Furthermore, the term "lithium-free secondary battery" should not be construed as limiting the presence of lithium-containing positive electrode active materials, nor should it be construed as limiting the presence of a lithium metal layer or lithium-containing compound electrodeposited on the negative electrode according to charging and discharging.

[0043] Based on the above definitions, certain embodiments of this disclosure will be described in detail below with reference to the accompanying drawings. However, these embodiments are given for illustrative purposes only, and the scope of this disclosure is not limited thereto, and is defined only by the scope of the claims described below.

[0044] Figure 1 This is a schematic diagram illustrating the configuration of a negative electrode for a lithium-free secondary battery according to certain embodiments of the present disclosure. Figure 2 This is a schematic diagram showing the cross-sectional shape of a negative electrode for a lithium-free secondary battery according to certain embodiments of the present disclosure.

[0045] like Figure 1 and 2 As shown, the negative electrode for a lithium-free secondary battery according to certain embodiments of this disclosure comprises: a porous metal layer having a three-dimensional microstructure; and a conductive carbon nanostructure formed on said porous metal layer. The porous metal layer comprises a metal mesh layer in which fibrous metal with a diameter on the order of micrometers (μm) forms a mesh structure, and metal nanostructures formed on the fibrous metal, wherein at least a portion of the metal nanostructures are connected to each other to define a plurality of pores on the porous metal layer.

[0046] As described in more detail below, the negative electrode in some embodiments includes, for example, a porous metal layer formed by electrochemical etching of a metal mesh containing a conductive metal and redeposition of the conductive metal, and a carbon nanostructure on the porous metal layer.

[0047] In the electrochemical etching and redeposition process, the conductive metal contained in the metal mesh layer is etched, thereby reducing the diameter of the fibrous metal. Conversely, as the conductive metal is redeposited on the fibrous metal, metal nanostructures with shapes such as metal nanorods or metal nanofibers with nanoscale diameters are formed and grown on the metal mesh layer. At least a portion of these metal nanostructures are interconnected and define micropores in the porous metal layer. Specifically, as confirmed in the following embodiments, through this fabrication process, the porous metal layer can have a thinner thickness and smaller mass per unit area than previously known lithium-free secondary battery anodes (or anode current collectors), while possessing a three-dimensional microstructure comprising multiple pores defined by the metal nanostructures.

[0048] Therefore, the negative electrode described in some embodiments can be manufactured to be thinner and lighter than existing negative electrodes for lithium-free secondary batteries, and lithium metal can be uniformly electrodeposited within the three-dimensional porous microstructure during battery charging. The negative electrode can suppress the formation of lithium dendrites due to uneven growth of lithium metal on the outside of the negative electrode, or can suppress side reactions between the negative electrode and the electrolyte, or can suppress galvanic corrosion of the negative electrode.

[0049] Furthermore, in some embodiments of the negative electrode, carbon nanostructures, such as carbon nanotubes, can be formed on the porous metal layer. These carbon nanostructures exhibit low reactivity and lithium-repellency. Due to the formation of these carbon nanostructures, lithium metal can be electrodeposited more uniformly within the porous metal layer, and the degree of lithium metal agglomeration can be controlled to a suitable size. Therefore, uneven growth of lithium metal outside the porous metal layer, leading to the formation of lithium dendrites, can be suppressed, and volume changes in the negative electrode during battery operation can be inhibited.

[0050] On the other hand, the negative electrode for a lithium-free secondary battery according to certain embodiments may include the porous metal layer as a substrate, and optionally, may also include a conductive metal layer supporting the porous metal layer. In this case, the porous metal layer and the optional conductive metal layer supporting it may be formed using any conductive metal that does not cause chemical changes in the lithium-free secondary battery and has high conductivity while exhibiting relatively low reactivity, and may be formed using any previously known conductive metal that can be used as a negative electrode current collector.

[0051] Specific examples include metals such as stainless steel, aluminum, nickel, titanium, or copper, or copper, aluminum, or stainless steel whose surfaces have been treated with carbon, nickel, titanium, silver, etc. However, considering the excellent conductivity and lightweight of the negative electrode described in some embodiments, and the ease of manufacturing the porous metal layer, the porous metal layer may contain copper.

[0052] On the other hand, the thickness of the porous metal layer can be 10 to 30 μm, or 12 to 25 μm, or 14 to 20 μm, and the mass per unit area can be 4.0 to 10.0 mg / cm³. 2 Or 4.5 to 9.0 mg / cm³ 2 Or 5.0 to 8.0 mg / cm³ 2 As described above, the porous metal layer contained in the negative electrode of certain embodiments is able to possess a well-developed porous three-dimensional microstructure through the metal fibers contained in the porous metal layer and the metal nanostructures grown therefrom, while having such a thin thickness and small mass per unit area. In this way, since lithium metal can be uniformly electrodeposited within the pores of the thin and lightweight three-dimensional microstructure, thereby suppressing the formation of lithium dendrites, etc., a lithium-free secondary battery with higher energy density and capacity can be provided.

[0053] In this porous metal layer, the fibrous metal, based on single strands of fibers, can have diameters on the micrometer (μm) scale, for example, 5 to 15 μm, 7 to 13 μm, or 8 to 12 μm. These fibers can be formed into a mesh structure with a distance of 30 to 80 μm, 40 to 75 μm, or 50 to 70 μm between the opposing fibrous metal fibers, thus forming a metal mesh layer. Furthermore, the diameters of the metal nanorods or metal nanofibers formed on the fibrous metal can be 100 to 700 nm, 150 to 650 nm, or 200 to 550 nm, respectively.

[0054] The metal nanostructures grown on the fibrous metal can be interconnected or entangled, thereby defining multiple open pores in the porous metal layer, into which lithium metal can be uniformly electrodeposited during lithium-free secondary battery charging. The porosity of the porous metal layer can be, for example, 55% to 70%, 56% to 67%, or 57% to 63%. If the porosity is higher than this value, lithium deposition may become uneven, or lithium may agglomerate unevenly inside the negative electrode, potentially increasing the risk of lithium metal desorption, lithium dendrite formation, or side reactions. Conversely, if the porosity is too low, lithium deposition may not proceed properly, causing lithium to grow unevenly outside the negative electrode, resulting in an increased volume of the negative electrode, which may degrade the characteristics of the secondary battery.

[0055] On the other hand, in the negative electrode described in some embodiments, the porous metal layer can be made of a conductive metal (e.g., copper), and more specifically, it can be made of a reduced form of a conductive metal. Here, being made of a reduced form of a conductive metal can mean that the porous metal layer is substantially free of oxides of conductive metals, such as copper oxide (Cu). xMore specifically, when the porous metal layer is analyzed by XRD, peaks from the copper oxide may not be detectable at an intensity above noise (e.g., peaks detected at 2θ at 60°–63°).

[0056] As will be described in more detail below, in the anode fabrication process of some embodiments, the porous metal layer or the metal mesh as its raw material can be heat-treated in a reducing atmosphere (hydrogen atmosphere) at high temperatures, for example, above 300°C or 500°C. The porous metal layer after this heat treatment is substantially free of oxides of conductive metals such as copper oxides, and can be formed from a reduced form of conductive metal (e.g., reduced copper itself). Furthermore, during the heat treatment process, a portion of the metal nanostructures can agglomerate to adjust their diameter, and the size of the pores defined between the metal nanostructures can also be adjusted. As a result, lithium metal can be electrodeposited more uniformly on the anode in some embodiments, and the conductivity of the anode can also be improved. Moreover, since the porous metal layer is substantially free of oxides of conductive metals, galvanic corrosion or side reactions of the anode can be suppressed.

[0057] On the other hand, in the negative electrode described in some embodiments, a conductive carbon nanostructure made of carbon nanotubes or carbon nanofibers can be formed on the porous metal layer (e.g., a metal mesh layer containing the fibrous metal). As described above, due to the lithium-repellency of the carbon nanostructure, lithium metal can be electrodeposited more uniformly within the porous metal layer, and the growth of this lithium metal on the exterior of the negative electrode and the growth of lithium dendrites can be suppressed. Furthermore, due to the low reactivity of carbon nanotubes, etc., side reactions between the negative electrode, the electrodeposited lithium metal layer, and the electrolyte described in some embodiments can be further reduced, and the negative electrode can exhibit even more improved electrochemical characteristics.

[0058] Conductive carbon nanostructures, such as carbon nanotubes, can be directly synthesized and grown on the porous metal layer during the anode fabrication process. To this end, a metal catalyst (such as alumina and iron) for synthesizing carbon nanotubes is applied to the porous metal layer in a thin layer, and a gaseous carbon source is applied to the metal catalyst layer to synthesize carbon nanotubes, etc.

[0059] In some embodiments of the negative electrode, for example, a catalyst layer containing aluminum, iron, or ions derived from a metal catalyst is also formed on the porous metal layer, and a conductive carbon nanostructure, such as carbon nanotubes, can be formed on the catalyst layer. In this case, the thickness of the catalyst layer can be, for example, 10 to 50 nm or 15 to 30 nm. Due to this configuration, the conductive carbon nanostructure can be uniformly formed with a thin thickness near the surface of the porous metal layer. Thus, a lithium metal layer can be more uniformly electrodeposited to a suitable size on the negative electrode.

[0060] On the other hand, according to certain embodiments of this disclosure, a method for preparing the negative electrode described in some of the above embodiments is provided. The method for preparing the negative electrode may include, for example, the steps of: electrochemically etching a metal mesh containing a conductive metal; re-depositing the conductive metal on the electrochemically etched metal mesh to form a porous metal layer in which a metal nanostructure is formed on a fibrous metal having a mesh structure; and the step of forming a carbon nanostructure in the presence of a metal catalyst while simultaneously supplying a gaseous carbon source containing an aliphatic hydrocarbon and a reducing gas.

[0061] Figure 3a This is a schematic diagram illustrating the steps of a method for preparing a negative electrode for a lithium-free secondary battery according to certain embodiments of the present disclosure. Figure 3b This is a schematic diagram showing the changes in the object before and after each preparation step, and below it is an example of an electron microscope photograph showing the changes in the object.

[0062] Reference Figure 3a and 3b In the preparation method, for example, an electrochemical etching and redeposition of the conductive metal are performed using a metal mesh containing a conductive metal such as copper. Therefore, as the conductive metal is etched and then deposited onto the fibrous metal of the metal mesh, multiple metal nanostructures, such as bundles of metal nanorods or metal nanofibers, can be grown and formed on the fibrous metal. These metal nanostructures can be at least partially connected to define multiple pores, forming the porous metal layer of the negative electrode as described in some embodiments.

[0063] Subsequently, a metal catalyst containing alumina and iron is added to the porous metal layer, and heat treatment is performed simultaneously with the supply of a gaseous carbon source containing aliphatic hydrocarbons and a reducing gas to the metal catalyst, enabling the synthesis and growth of carbon nanostructures such as carbon nanotubes. Thus, it is possible to prepare anodes in certain embodiments that incorporate well-developed three-dimensional porous microstructures and carbon nanostructures while achieving reductions in thickness and weight.

[0064] On the other hand, in this preparation method, considering the porosity, thickness, etc., of the porous metal layer to be prepared, the metal mesh used as raw material can be a commercially available conductive metal mesh with suitable mesh size and dimensions. In a specific embodiment, the metal mesh may comprise metal wires (or fibrous metal) with diameters of 20 to 40 μm, 22 to 35 μm, or 23 to 30 μm, and the metal wires may form a mesh structure with a mesh size of 200 to 500 meshes or 300 to 400 meshes. Thus, a negative electrode with suitable porosity and a porous three-dimensional microstructure, as described in some embodiments, can be formed.

[0065] In addition, such as Figure 3a As shown in the first figure, the electrochemical etching step and the redeposition step of the conductive metal can be performed sequentially in the same electrolytic cell. In a more specific embodiment, the electrochemical etching step and the redeposition step of the conductive metal can be performed in the same electrolytic cell comprising a working electrode containing the metal mesh, a counter electrode containing the same conductive metal as the metal mesh (e.g., a conductive metal sheet such as copper foil), and an electrolyte containing ions of the conductive metal and an acid.

[0066] In this case, the electrolyte may contain, for example, copper ions and sulfuric acid. According to a more specific embodiment, the electrolyte may be an aqueous electrolyte containing copper sulfate (CuSO4) and sulfuric acid. According to some embodiments, the electrolyte may be an aqueous electrolyte containing 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 sulfuric acid, etc., is too low, the redeposition of conductive metals such as copper may not proceed uniformly.

[0067] Furthermore, in some embodiments of the preparation method, the electrochemical etching step can be performed with an applied current density of 30 to 60 mA / cm². 2 Or 35 to 55 mA / cm 2 Constant current etching is performed under constant current conditions. If the current density is too low, the conductive metal may not be properly etched from the metal mesh; 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 final negative electrode to potentially disintegrate.

[0068] On the other hand, in the electrochemical etching step, the etched conductive metal ions (e.g., copper ions) migrate to the counter electrode, where they act as a conductive metal source in the redeposition step. In this redeposition step, the conductive metal ions migrate 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.

[0069] This redeposition step can be performed with an applied voltage of 2.2V to 2.7V, or 2.3V to 2.5V. In this case, if the applied voltage is too low, it may be difficult to uniformly deposit the conductive metal on a large area of ​​metal mesh.

[0070] On the other hand, the preparation method described in some embodiments above may further include the step of heat-treating the metal mesh or the porous metal layer at a temperature above 300°C in a reducing gas atmosphere (e.g., in the presence of hydrogen) before the electrochemical etching step or after the redeposition step of the conductive metal. In a specific embodiment, the heat treatment may be performed on the porous metal layer after the redeposition step.

[0071] The result of this heat treatment is the ability to reduce the oxides of the conductive metal remaining on the porous metal layer, and to form the porous metal layer from the reduced conductive metal, which may be substantially free of oxides of the conductive metal. Therefore, the porous metal layer and the negative electrode containing it can exhibit improved conductivity and low resistance.

[0072] Furthermore, since the heat treatment is performed at appropriate temperature and time, a portion of the metal nanostructures formed on the porous metal layer may aggregate, and the distribution and size of the pores defined between them can be adjusted. Therefore, lithium metal can be deposited more uniformly on the negative electrode as described in some embodiments, and the formation of lithium dendrites can be suppressed.

[0073] To reduce the oxide of the conductive metal, the heat treatment step can be performed at a temperature above 300°C for at least 5 minutes. More preferably, the heat treatment step can be performed at a temperature above 500°C to optimize the pore distribution and size for proper agglomeration of the metal nanostructure and for uniform electrodeposition of lithium metal. Furthermore, if the heat treatment temperature is too high or the heat treatment time is too long, the metal nanostructure may excessively agglomerate, and the pore size may excessively decrease. Therefore, the heat treatment step can be performed at a temperature of 300 to 800°C or 500 to 800°C for 5 minutes to 1.5 hours.

[0074] On the other hand, the heat treatment step can be carried out continuously in the same reactor as the subsequent carbon nanostructure formation step. For this continuous process, the heat treatment can be carried out at a temperature of 600 to 800°C for 5 to 20 minutes, and then the subsequent carbon nanostructure synthesis step can also be carried out continuously in the same reactor.

[0075] On the other hand, after the redeposition step or selective heat treatment step of the conductive metal, for example, a metal catalyst containing alumina and iron is added to the porous metal layer. Meanwhile, heat treatment is performed simultaneously with a gaseous carbon source containing aliphatic hydrocarbons and a reducing gas in the presence of this metal catalyst, thereby synthesizing carbon nanostructures such as carbon nanotubes. Thus, the carbon nanostructures can be grown on the porous metal layer (more specifically, on the metal mesh layer and the metal nanoprecursor), thereby preparing anodes in certain embodiments.

[0076] In this configuration, the gaseous carbon source may comprise, for example, an aliphatic hydrocarbon such as ethylene gas with 1 to 5 carbon atoms, and the reducing gas may comprise hydrogen gas. Furthermore, in the metal catalyst containing alumina and iron, alumina may be added at a thickness of 10 to 25 nm, while iron may be added at a thickness of 1 to 5 nm. If the metal catalyst is too thin, it may be contaminated by the diffusion of conductive metals such as copper, or it may not be able to adequately form carbon nanostructures such as carbon nanotubes. Additionally, the metal catalyst containing alumina and iron can be deposited on the porous metal layer under electron beam irradiation.

[0077] In addition, the heat treatment process used to synthesize the carbon nanostructure can be carried out at a temperature of 600 to 800°C for 5 to 20 minutes or 10 to 20 minutes, depending on the general synthesis conditions of carbon nanotubes, etc., so that the carbon nano precursor can grow sufficiently.

[0078] On the other hand, according to another aspect of this disclosure, a lithium-free secondary battery comprising a negative electrode as described in certain embodiments is provided. This lithium-free secondary battery may comprise, for example, the negative electrode as described in certain embodiments; 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. Furthermore, the lithium-free secondary battery may, in addition to comprising a separator, also comprise an electrolyte containing a lithium salt and a non-aqueous organic solvent.

[0079] In this 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 the lithium-free secondary battery is charged and discharged, lithium ions migrating from the positive electrode may electrodeposit on the porous metal layer of the negative electrode, thereby forming a lithium metal layer or a lithium alloy layer, and the lithium metal layer can serve as the negative electrode active material.

[0080] On the other hand, in the lithium-free secondary battery of a further embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

[0081] The positive electrode may be prepared by mixing an active material, a binder, and optionally a conductive material, a filler, etc. in a solvent to prepare a positive electrode paste composition, and coating the composition onto the positive electrode current collector.

[0082] The thickness of the positive electrode current collector is generally 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause any chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel whose surface is treated with carbon, nickel, titanium, silver, etc. can be used. The current collector may have fine concavities and convexities formed on its surface to enhance the adhesion of the positive electrode active material. For example, the current collector can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric structure.

[0083] In addition, the positive electrode active material is a compound capable of reversibly inserting and extracting lithium. Specifically, it may include a lithium metal oxide containing lithium and at least one metal (such as iron, cobalt, manganese, nickel, or aluminum).

[0084] More specifically, the lithium metal oxide may include lithium manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium cobalt-based oxides (such as LiCoO2, etc.), lithium nickel-based oxides (such as LiNiO2, etc.), lithium nickel manganese-based oxides (such as LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium nickel cobalt-based oxides (such as LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1), etc.), lithium manganese cobalt-based oxides (such as LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium nickel manganese cobalt-based oxides (such as 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, and p1 + q1 + r1 = 2), etc.), or a lithium nickel cobalt transition metal (M) oxide (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 the respective elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is at least one selected from Al, Mg, and Ti, X is at least one selected from F, S, and N, and -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1)), and can include any one of them or a mixture of two or more thereof.

[0085] Among them, the positive electrode active material includes a lithium metal oxide containing lithium and two or more transition metals selected from the group consisting of nickel, manganese, cobalt, and aluminum. Among them, based on the total transition metal content excluding lithium, the nickel content of the lithium metal oxide can be 50 mol% or more, or 60 to 99 mol%, or 70 to 95 mol%. For example, such a lithium metal oxide can be represented by the following formula 1: [Formula 1] Li x Ni a Co b M 1 c M 2 d O2 Where in Formula 1, M 1 can be one or more selected from Mn and Al, M 2 can 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, where 0.90 ≤ x ≤ 1.1, or 0.95 ≤ x ≤ 1.08, or 1.0 ≤ x ≤ 1.08, and 0.50 ≤ a < 1.0, or 0.60 ≤ a ≤ 0.99, or 0.70 ≤ a ≤ 0.95. In addition, 0 < b ≤ 0.3, 0 < c ≤ 0.3, and 0 ≤ d ≤ 0.1.

[0086] 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, enables further improvement in the output, capacity characteristics, lifespan characteristics, etc. of the lithium-free secondary battery.

[0087] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be 60 to 99% by weight, or 70 to 99% by weight, or 80 to 98% by weight.

[0088] On the other hand, the conductive material contained in the positive electrode active material layer is a component used to further improve the conductivity of the positive electrode active material. There are no particular limitations on this conductive material, as long as it is conductive and does not cause any chemical changes in the battery. For example, conductive materials that can be used include: carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon 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; fluorocarbon powders; conductive powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxides; or conductive materials, such as polyphenylene derivatives. Among these, the conductive material includes conductive nanomaterials such as carbon nanotubes or carbon nanofibers, which can further reduce the resistance of the lithium-free secondary battery and further enhance its output characteristics.

[0089] Typically, based on the total weight of the positive electrode active material layer, the content of the conductive material can be 1 to 20% by weight, or 1 to 15% by weight, or 1 to 10% by weight.

[0090] The binder selectively included in the positive electrode active material layer is a component that facilitates bonding between the positive electrode active material and the conductive material, as well as bonding to the current collector. Examples of the binder may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, nitrile rubber, styrene-butadiene rubber, fluororubber, etc. Mixtures or copolymers selected from these materials may also be used.

[0091] Typically, based on the total weight of the positive electrode active material layer, the content of the binder can be 1 to 20% by weight, or 1 to 15% by weight, or 1 to 10% by weight.

[0092] Alternatively, filler may be added to the positive electrode as a component to suppress its expansion. There are no particular limitations on such filler, as long as it can suppress the expansion of the electrode without causing any chemical changes in the battery; examples may include olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.

[0093] The aforementioned positive electrode can be prepared by, for example, dispersing and mixing the positive electrode active material, the binder, the conductive material, etc., in a dispersion medium (solvent) to form a slurry, coating the slurry onto a metal current collector, and then drying and calendering it. In this case, the dispersion medium can be NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof, but is not necessarily limited to these.

[0094] On the other hand, some other embodiments of the lithium-free secondary battery also include an electrolyte containing a non-aqueous organic solvent and a lithium salt.

[0095] The lithium salt contained in the electrolyte serves as a medium for ion transport within the secondary battery. For example, the lithium salt may contain Li. + As a cation, and may contain F selected together. - 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 - The anions in the group.

[0096] Specifically, the lithium salt may include, selected from, LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 One or more of the following groups: 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).

[0097] The concentration of the lithium salt can be appropriately varied within a normally usable range, and can be included in the electrolyte at a concentration of 0.4 to 6 M or 0.5 M to 5 M.

[0098] In a more specific embodiment, the electrolyte may contain the lithium salt at a relatively low concentration of 0.4 M or more but less than 2 M, or from 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 from 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.

[0099] On the other hand, there are no particular limitations on the types of non-aqueous organic solvents that may be included in the electrolyte; any known organic solvent suitable for lithium-ion battery electrolytes may 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, the non-aqueous organic solvent preferably comprises a carbonate-based solvent or an ether-based solvent.

[0100] More specifically, the carbonate solvent may include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butyl carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, methyl (2,2,2-trifluoroethyl) carbonate, etc., and the phosphate solvent may include trimethyl phosphate, triethyl phosphate, 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphine 2-oxide, etc.

[0101] Furthermore, the ether solvent may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, or tetrahydrofuran derivatives (e.g., 2-methyltetrahydrofuran); the nitrile solvent may include succinic anhydride, adiponitrile, sebacate, acetonitrile, propionitrile, etc. Additionally, the sulfone solvent may include dimethyl sulfone, ethyl methyl sulfone, sulfolane, etc.

[0102] On the other hand, the aforementioned lithium-free secondary battery may also include a porous separator inserted between the positive electrode and the negative electrode.

[0103] Such porous membranes can be manufactured from olefin polymers such as polyethylene and polypropylene, glass fibers, etc., in the form of sheets, multilayer membranes, microporous membranes, woven fabrics, and nonwoven fabrics, but are not necessarily limited thereto. However, porous polyethylene or porous glass fiber nonwoven fabric (glass filter) is preferably used as the membrane, and porous glass filter (glass fiber nonwoven fabric) is more preferably used as the membrane. The membrane can be an insulating film with high ion permeability and mechanical strength, and the pore size of the membrane is typically in the range of 0.01 to 10 μm, and the thickness is typically in the range of 5 to 300 μm, but is not limited thereto.

[0104] In some other embodiments of the lithium-free secondary battery, the separator may be integrated with the electrolyte and inserted between the positive and negative electrodes as an electrolyte layer or electrolyte membrane. In one embodiment, the electrolyte layer or electrolyte membrane may be in the form of a polymer matrix containing the lithium salt and the non-aqueous organic solvent, or in the form of a solid electrolyte. Known polymer-based solid electrolytes, etc., can be used as the polymer matrix.

[0105] Depending on the presence or absence of the electrolyte layer, its shape, etc., the lithium-free secondary battery described in some embodiments as above may be a semi-solid battery using a combination of liquid electrolyte and solid electrolyte, or an all-solid battery having a solid electrolyte layer.

[0106] On the other hand, the lithium-free secondary battery described in certain other embodiments can be prepared according to conventional methods in the art. For example, the lithium-free secondary battery can be prepared by: assembling an electrode assembly comprising a positive electrode, a negative electrode, and a separator into a housing, and injecting and impregnating the aforementioned electrolyte into the housing; or assembling an electrode assembly comprising a positive electrode, a negative electrode, and an electrolyte layer into a housing.

[0107] This type of lithium secondary battery can be used not only as a battery cell for powering small devices, but is also particularly suitable as a unit battery in a battery module for powering medium to large devices.

[0108] Preferred embodiments, comparative examples, and experimental examples for evaluating the present invention will be described below. However, the following examples are merely preferred embodiments of the present invention and are not intended to limit the scope of the invention.

[0109] 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.

[0110] Comparative Example 2: Preparation of negative electrode for lithium-free secondary batteries

[0111] A copper mesh with a wire diameter of 25 μm and a mesh size of 300–400 mesh is used. Additionally, an electrolytic cell is used, comprising a working electrode containing the copper mesh, a counter electrode made of copper foil with a thickness of 9 μm, and an aqueous electrolyte containing copper sulfate at a concentration of 50 mM and sulfuric acid at a concentration of 200 mM.

[0112] In the electrolytic cell, copper is deposited from the copper foil onto the copper mesh by applying a constant voltage of 2.4V for 720 seconds. This deposition forms a copper nanostructure in the form of nanoprotrusions on the copper mesh, which is used as the negative electrode for the lithium-free secondary battery of Comparative Example 2.

[0113] Examples 1 to 6: Preparation of negative electrodes for lithium-free secondary batteries

[0114] A copper mesh with a wire diameter of 25 μm and a mesh size of 300–400 mesh is used. Additionally, an electrolytic cell is used comprising a working electrode containing the copper mesh, a counter electrode containing a copper foil with a thickness of 9 μm, and an aqueous electrolyte containing copper sulfate at a concentration of 50 mM and sulfuric acid at a concentration of 200 mM.

[0115] In the electrolytic cell, through a flow rate of 40 mA / cm 2 A constant current was applied to electrochemically etch the copper mesh at a current density of 9 minutes, during which copper ions were removed from the copper mesh. Then, copper was redeposited from the copper foil onto the copper mesh for 2 minutes at an applied voltage of 2.4V.

[0116] Subsequently, the sample with the redeposited porous copper layer was placed on a quartz boat connected to a magnetic conveyor. The resulting sample was then placed in the center of a chamber in a tube furnace heated to 775°C and purged with 80% hydrogen (helium) gas. It was then removed and subjected to heat treatment. Based on the heat treatment time for placing and removing the sample, the heat treatment conditions were varied for each embodiment, for example, no heat treatment (Example 1), heat treatment for 3 minutes (Example 2), heat treatment for 6 minutes (Example 3), heat treatment for 12 minutes (Example 4), heat treatment for 24 minutes (Example 5), and heat treatment for 60 minutes (Example 6).

[0117] Figure 4 Electron micrographs of the porous copper layers formed by the heat treatment are shown in Figures a through 4f. The photographs confirm that a large number of copper nanostructures in the shape of nanorods or nanofibers are formed on the porous copper layers of Examples 1 through 6, and these nanostructures define the nanopores. Furthermore, it is confirmed that porous structures suitable for uniform lithium metal electrodeposition are formed in Examples 1 through 6, and in Examples 2 through 4. When the heat treatment time is longer than that, the pores tend to narrow due to the aggregation of the copper nanostructures.

[0118] On the other hand, after the heat treatment, 20 nm of Al₂O₃ and 2 nm of Fe are deposited on one surface of the porous copper layer by electron beam irradiation, thereby forming a metal catalyst layer. Then, while supplying 410 sccm of He, 100 sccm of ethylene gas and 100 sccm of hydrogen gas to the metal catalyst layer, carbon nanotubes are synthesized in a tube furnace heated to 775°C for 12 to 20 minutes.

[0119] Therefore, negative electrodes for lithium-free secondary batteries in Examples 1 to 6 were prepared respectively.

[0120] Examples 7 to 9: Preparation of negative electrodes for lithium-free secondary batteries

[0121] Porous copper layers were fabricated by electrochemical etching and copper redeposition, in the same manner as in Examples 1 to 6.

[0122] Subsequently, the sample with the re-deposited porous copper layer was placed in the chamber of a tube furnace connected to a vacuum pump. While introducing 3.9% hydrogen gas (Ar substrate), the chamber was heated at a rate of 10°C / min to reach 400–600°C, and then held at this temperature for 1 hour. During this time, the heat treatment temperature for each embodiment was varied based on the sample's initial heat treatment temperature, for example, 400°C (Example 7), 500°C (Example 8), and 600°C (Example 9).

[0123] Electron micrographs of the porous copper layer formed by the heat treatment at each heat treatment temperature are shown below. Figure 5 The photographs 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 these nanostructures defined the nanopores. Furthermore, it was confirmed that in Examples 7 to 9, and in Example 8, a porous structure suitable for uniform lithium metal deposition was formed. However, when the heat treatment temperature was lower than that (Example 7), the nanostructures were not sufficiently connected, and the porous structure was not fully formed. Conversely, in Example 9, with its higher heat treatment temperature, it was confirmed that the pores tended to narrow due to the aggregation of the copper nanostructures.

[0124] In addition, the porous copper layers of Examples 1, 4, and 7 to 9 were analyzed by XRD, and the results are shown in... Figure 6 (See also) Figure 6 It was confirmed that a peak from copper oxide was detected at 2θ of 60° to 63° in Example 1 without heat treatment, but this peak was not detected in Examples 4, 7 to 9 with heat treatment.

[0125] On the other hand, after heat treatment, carbon nanotubes were synthesized on the porous copper layer of Examples 7 to 9 in the same manner as in Examples 1 to 6, thereby preparing the negative electrodes for lithium-free secondary batteries of Examples 7 to 9 respectively.

[0126] Experimental Example 1: Evaluation of the Physical Properties of the Negative Electrode

[0127] The thickness of the negative electrodes of Comparative Examples 1, 2, and Example 4 was measured by cross-sectional observation using a scanning electron microscope (Hitachi SU5000) and by using a thickness measuring device (Mitutoyo 547-401A). The negative electrodes were cut into circles with a diameter of 19 mm using a disc punch (Wellcos WC-H125), and the mass per unit area was measured using a high-precision balance (Redway XA52.4Y). The evaluation results are shown in Table 1 below. Furthermore, the mass per unit area, thickness, and true density of copper (8.95 g / cm³) were used as indicators. 3 Calculate the porosity of each negative electrode.

[0128] [Table 1]

[0129] Referring to Table 1, it was confirmed that the negative electrode of Example 4 not only possesses a well-developed porous three-dimensional microstructure, thereby exhibiting high porosity suitable for uniform lithium deposition, but also has a very thin thickness and low mass per unit area compared to the negative electrode of Comparative Example 2. In summary, it was confirmed that a lithium-free secondary battery with higher energy density can be provided by utilizing the negative electrode of Example 4.

[0130] Experimental Example 2: Evaluation of Resistance and Galvanic Corrosion of the Negative Electrode

[0131] Half-cells were fabricated using the negative electrodes of Comparative Example 1, Example 1, and Example 4. The half-cells were formed comprising the aforementioned negative electrode, a lithium foil as a counter electrode, and 75 μl of electrolyte (0.6 M LiBF4 + 0.6 M LiBF2(C2O4) in FEC / DEC (volume ratio 1:2). For these half-cells, at 10... -3 Up to 10 6 The charge transfer resistance and ohmic resistance of each negative electrode were evaluated by EIS (electrochemical impedance spectroscopy) under the conditions of Hz and 50mV. The evaluation results are compared and shown in Table 2 below.

[0132] [Table 2]

[0133] Referring to Table 2, it was confirmed that the negative electrodes of Examples 1 and 4 exhibited lower resistance than Comparative Example 1 due to the formation of porous three-dimensional microstructures. Furthermore, it was confirmed that the negative electrode of Example 4 exhibited higher charge transfer resistance and lower ohmic resistance compared to the negative electrode of 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 improved conductivity compared to the negative electrode of Example 1.

[0134] In addition, using the negative electrodes of Comparative Example 1, Comparative Example 2, and Example 4, the same half-cells as described above were manufactured, and the change in current density over time was evaluated while performing thermocouple charge-discharge on these half-cells. The evaluation results are shown below. Figure 7 middle.

[0135] pass Figure 7 The way the current density changes over time, as shown in the figure, confirms that the galvanic corrosion of the negative electrode of Example 4 is reduced by about 75% compared to the negative electrode of Comparative Example 2, which corresponds to the existing negative electrode with an introduced three-dimensional porous microstructure.

[0136] Experimental Example 3: Evaluation of Capacity Characteristics in Each Cycle

[0137] A battery was manufactured using the negative electrodes of Comparative Example 1, Example 4, and Example 8. This battery was formed to include the aforementioned negative electrode and a component containing NCM811 (LiNi). 0.8 Co 0.1 Mn 0.1 The positive electrode is composed of O2 as the positive electrode active material, a polyethylene separator, and 75 μl of electrolyte (0.6 M LiBF4 + 0.6 M LiBF2 (C2O4) in FEC / DEC (volume ratio 1:2).

[0138] For these batteries, at 4mAh·cm -2The discharge capacity change in each cycle was evaluated under charge and discharge conditions (0.5C, cutoff voltage: 4.5V). The evaluation results are shown in... Figure 8 middle.

[0139] Reference Figure 8 It has been confirmed that, compared with the battery containing the negative electrode of the comparative example, the lithium-free secondary battery containing the negative electrode of the embodiment exhibits superior capacity per cycle.

Claims

1. A negative electrode for a lithium-free secondary battery, comprising: Porous metal layers with three-dimensional microstructures; and The conductive carbon nanostructure formed on the porous metal layer, The porous metal layer comprises a metal mesh layer in which fibrous metal with a diameter on the order of micrometers (μm) forms a mesh structure, and metal nanostructures formed on the fibrous metal. At least a portion of the metal nanostructures are connected to each other to define a plurality of pores on the porous metal layer.

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

3. The negative electrode for a lithium-free secondary battery according to claim 1, wherein the porous metal layer comprises copper.

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

5. The negative electrode for a lithium-free secondary battery according to claim 1, wherein the conductive carbon nanostructure comprises carbon nanotubes.

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

7. The negative electrode for a lithium-free secondary battery according to claim 1, wherein the surface area mass of the porous metal layer is 4.0 to 10.0 mg / cm³. 2 .

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

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

10. The negative electrode for a lithium-free secondary battery according to claim 1, wherein the porous metal layer is made of a conductive metal in a reduced form and is substantially free of oxides of the conductive metal.

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

12. A method for preparing a negative electrode for a lithium-free secondary battery according to claim 1, the method comprising the following steps: Electrochemical etching of a metal mesh containing conductive metal; The conductive metal is then redeposited on the metal mesh that has undergone the electrochemical etching, thereby forming a porous metal layer in which a metal nanostructure is formed on the fibrous metal having a mesh structure; and In the presence of a metal catalyst, carbon nanostructures are formed while supplying a gaseous carbon source containing aliphatic hydrocarbons and a reducing gas.

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

14. The method for preparing a negative electrode for a lithium-free secondary battery according to claim 12, wherein the electrochemical etching and the redeposition of the conductive metal are performed sequentially in the same electrolytic cell, the electrolytic cell comprising: Working electrode containing the metal mesh, The counter electrode contains the same conductive metal as the metal mesh, and An electrolyte containing ions of the conductive metal and an acid.

15. The method for preparing a negative electrode for a lithium-free secondary battery according to claim 12, wherein the electrochemical etching is performed under an application of 30 to 60 mA / cm 2 It is performed under constant current conditions.

16. The method for preparing a negative electrode for a lithium-free secondary battery according to claim 12, wherein the redeposition of the conductive metal is performed under a voltage of 2.2V to 2.7V.

17. The method for preparing a negative electrode for a lithium-free secondary battery according to claim 12 further includes heat-treating the metal mesh or porous metal layer in the presence of hydrogen before the electrochemical etching or after the redeposition of the conductive metal.

18. The method for preparing a negative electrode for a lithium-free secondary battery according to claim 17, wherein the heat treatment is performed after the redeposition of the conductive metal, and the formation of the carbon nanostructure is carried out continuously in the same reactor in which the heat treatment has been performed.

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

20. The method for preparing 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 preparing 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. A lithium-free secondary battery, comprising: A cathode containing positive electrode active material; The negative electrode according to claim 1; and A diaphragm or electrolyte layer inserted between the positive electrode and the negative electrode.

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

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