Negative electrode for lithium-free secondary battery and lithium-free secondary battery comprising same

Abstract

The present disclosure relates to a negative electrode for a lithium-free secondary battery capable of improving electrochemical characteristics and lifespan characteristics of a lithium-free secondary battery, a method for manufacturing the same, and a lithium-free secondary battery. The negative electrode may include a conductive metal layer; and a lithium electrodeposition inducing layer formed on the conductive metal layer and containing an intermetallic compound in which copper and zinc are bonded.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2023-0059728, filed with the Korean Intellectual Property Office on May 9, 2023, and Korean Patent Application No. 10-2024-0053381, filed with the Korean Intellectual Property Office on April 22, 2024, the disclosures of which are incorporated herein by reference in their entirety.

[0003] This disclosure relates to a negative electrode for a lithium-free secondary battery that can improve the electrochemical and lifetime characteristics of a lithium-free secondary battery, a method for manufacturing the same, and a 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 with conventional batteries that use graphite-based or lithium alloy-based negative electrodes, they theoretically have a much higher energy density and capacity. Therefore, research and development of such lithium metal batteries continues in order to apply them to batteries requiring high energy density.

[0005] However, lithium metal batteries have the following drawbacks: during charging and discharging, the negative electrode undergoes large volume changes, needle-like lithium metal layers (such as lithium dendrites) grow, and due to the highly reactive nature of lithium metal, side reactions occur between the lithium metal layer and the electrolyte, resulting in large irreversible capacity. As a result, lithium metal batteries have not yet been properly commercialized due to the high possibility of electrode short circuits and insufficient stability and lifespan characteristics.

[0006] Recently, research and interest in lithium-free secondary batteries (or anode-free secondary batteries) have been rising as an alternative to lithium metal batteries. Lithium-free secondary batteries do not form a separate lithium metal layer or other negative electrode active material layer on the negative electrode current collector; instead, the negative electrode is formed by the negative electrode current collector itself. Since lithium is electrodeposited on the negative electrode current collector during charging, such lithium-free secondary batteries can be defined as batteries that utilize lithium metal as the negative electrode active material.

[0007] However, since conventional lithium-free secondary batteries also use lithium metal as the negative electrode active material, problems such as lithium dendrite growth may still occur due to uneven lithium metal growth.

[0008] To overcome such technical limitations, techniques have been reported, such as using lithiophilic materials to fabricate current collectors or increasing the surface area of ​​current collectors to induce uniform electrodeposition of lithium.

[0009] However, most processes used in manufacturing current collectors containing such lithium-philic materials or three-dimensional current collectors with high surface areas suffer from drawbacks such as long processing times or high costs, leading to poor mass production capabilities. Furthermore, such methods present other problems, such as the difficulty in manufacturing thin current collectors and the challenge in fully utilizing the high energy density of lithium-free secondary batteries. Summary of the Invention

[0010] Technical issues

[0011] Therefore, the purpose of this disclosure is to provide a negative electrode for a lithium-free secondary battery that can improve the electrochemical and lifetime characteristics of the lithium-free secondary battery by suppressing the growth of lithium dendrites, etc., and can be manufactured in thin thickness through a simplified process, and a method thereof.

[0012] Another objective of this disclosure is to provide a lithium-free secondary battery that includes the negative electrode and thus exhibits improved electrochemical and lifetime characteristics.

[0013] Technical solution

[0014] According to one embodiment of this disclosure, a negative electrode for a lithium-free secondary battery is provided, comprising: a conductive metal layer; and a lithium deposition induction layer formed on the conductive metal layer and containing an intermetallic compound in which copper and zinc are bonded.

[0015] In such a negative electrode, the lithium-ion deposition inducing layer may comprise an intermetallic compound in which copper and zinc are bonded in a weight ratio of 2:8 to 9.5:0.5. In a further embodiment, the lithium-ion deposition inducing layer may comprise an intermetallic compound in which copper and zinc are bonded in a weight ratio of 3:7 to 9:1 and contains 0.01 to 5% by weight oxygen based on the total weight of the intermetallic compound.

[0016] Furthermore, in the negative electrode, the thickness of the lithium-ion deposition induced layer can be from 0.05 to 2 μm.

[0017] On the other hand, according to another embodiment of the present disclosure, a method for manufacturing a negative electrode is provided, the method comprising electrodepositing copper and zinc on a conductive metal layer using an electrolyte containing a copper precursor, a zinc precursor, and a pyrophosphate / ester.

[0018] In such a manufacturing method, the electrodeposition step can be performed by applying a voltage to an electrodeposition system comprising: a working electrode containing the conductive metal layer; a counter electrode containing an alloy of copper and zinc; and an electrolyte.

[0019] Furthermore, the manufacturing method may include, after the electrodeposition step, a heat treatment step of subjecting the electrodeposited material to heat treatment at a temperature above 200°C under a vacuum or inert gas atmosphere. By performing this heat treatment step, the chemical composition of the lithium-ion electrodeposition induced layer changes, and the electrochemical characteristics of the negative electrode can be further improved.

[0020] On the other hand, according to another embodiment of the present disclosure, a lithium-free secondary battery is provided, comprising: a positive electrode containing a positive electrode active material; a negative electrode according to one embodiment; and a separator or electrolyte layer inserted between the positive electrode and the negative electrode.

[0021] In such a lithium-free secondary battery, during the charging process, a lithium metal layer is electrodeposited on the lithium deposition induction layer of the negative electrode, thereby serving as the negative electrode active material.

[0022] Beneficial effects

[0023] According to one embodiment of the present disclosure, the negative electrode can be manufactured by a simple process of electrodepositing an intermetallic compound in which copper and zinc are combined on a conductive metal layer.

[0024] It was confirmed that by forming a lithium deposition-inducing layer containing such an intermetallic compound, the interfacial resistance and overvoltage of the negative electrode can be significantly reduced during the electrodeposition of the lithium metal layer when the battery is charged. With the reduction in resistance and overvoltage during the electrodeposition of this lithium metal layer, lithium dendrite growth and side reactions in the negative electrode of the lithium-free secondary battery can be suppressed, and the lifetime characteristics of the lithium-free secondary battery can be improved. Furthermore, the electrochemical characteristics of the lithium-free secondary battery can be improved due to the reduction in resistance, etc.

[0025] Therefore, according to this disclosure, not only can the negative electrode of a lithium-free secondary battery be manufactured in a thin form through a simplified process, but the electrochemical and life characteristics of the lithium-free secondary battery can also be improved. Attached Figure Description

[0026] Figure 1 A diagram illustrating an example of an electrodeposition system for manufacturing a negative electrode according to an embodiment of the present disclosure;

[0027] Figures 2a to 2c In Comparative Example 2 ( Figure 2a Example 1 Figure 2b ), and Example 2 ( Figure 2c Electron microscope image of the negative electrode surface formed in the process;

[0028] Figure 3 Electron micrographs showing the changes in the film quality of the lithium-ion battery deposition-induced layer before and after heat treatment during the fabrication of the negative electrode in Example 5;

[0029] Figure 4 A graph showing the results of overvoltage evaluation during lithium deposition for half-cells containing negative electrodes of Comparative Example 1 and Example 2; and

[0030] Figure 5 A graph showing the lifetime characteristics evaluation results of half-cells containing the negative electrodes of Comparative Examples 1 and 2, and Examples 1 and 2. Detailed Implementation

[0031] In this disclosure, when a part is referred to as "comprising" or "containing" a constituent element, unless otherwise stated, it means that the part may also contain other constituent elements, without excluding other constituent elements.

[0032] In this disclosure, the terms "about" or "approximately" or "substantially" are intended to mean close to a numerical value or range specified with permissible error, and are intended to prevent the accurate or absolute numerical values ​​disclosed for understanding the invention from being used unlawfully or unfairly by any unreasonable third party. In this disclosure, the term "step of..." does not mean "step for...".

[0033] In this disclosure, the term "combination of..." used in the Markush-type description refers to a mixture or combination of more than one constituent element described in the Markush type, and therefore means that this disclosure includes more than one of the constituent elements.

[0034] Furthermore, in this disclosure, the term "lithium-free secondary battery" can refer to a secondary battery in which, in its pre-charge / discharge state, such as immediately after manufacturing, the negative electrode current collector (e.g., a negative electrode current collector containing a conductive metal layer (e.g., copper), and a negative electrode current collector containing a lithium deposition induction layer) does not have a separate negative electrode active material layer, such as a lithium metal layer, a lithium alloy layer, or other carbon- or silicon-containing layers. Therefore, a "lithium-free secondary battery" can be defined as a battery in its pre-charge / discharge state where the negative electrode current collector does not contain a separate negative electrode active material layer (e.g., a lithium metal layer, etc.). However, it is self-evident that, in addition to the negative electrode active material layer, a separate insulating layer or other functional layers may be included without limitation.

[0035] Furthermore, the term "lithium-free secondary battery" should not be construed as restricting the presence of lithium-containing positive electrode active materials, nor should it be construed as restricting the presence of lithium metal layers or lithium-containing compounds electrodeposited on the negative electrode during charging and discharging.

[0036] Below, based on the above definitions, embodiments of this disclosure will be described in detail. These embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. This disclosure is defined only by the claims.

[0037] According to one embodiment of this disclosure, a negative electrode for a lithium-free secondary battery is provided, comprising: a conductive metal layer; and a lithium deposition induction layer formed on the conductive metal layer and containing an intermetallic compound in which copper and zinc are bonded.

[0038] It has been confirmed that the intermetallic compound in which copper and zinc are chemically bonded can reduce the interfacial resistance and overvoltage of the negative electrode. This is likely due to the zinc component contained in the intermetallic compound. The reduction in interfacial resistance and overvoltage not only improves the electrochemical characteristics of the lithium-free secondary battery but also induces uniform electrodeposition of lithium metal, thereby suppressing the growth of lithium dendrites, which can lead to improved battery life characteristics.

[0039] Furthermore, the negative electrode forms an intermetallic compound of copper and zinc through electrodeposition, rather than simply forming a lithium-loving metal such as zinc on the conductive metal layer. During battery operation, lithium-loving metals such as zinc may cause volume expansion when they alloy with lithium, and such volume expansion can be a factor contributing to the insufficient lifespan of lithium-free rechargeable batteries. In contrast, the intermetallic compound can mitigate the volume expansion caused by the alloying reaction with lithium, thereby further improving the lifespan of lithium-free rechargeable batteries.

[0040] Furthermore, the negative electrode of one embodiment can not only be manufactured through a simplified electrodeposition process, but can also be formed with a thin thickness that does not include three-dimensional structures. As a result, the high energy density of lithium-free secondary batteries can be fully utilized using the negative electrode.

[0041] On the other hand, in a lithium-free secondary battery negative electrode according to one embodiment, the thickness of the conductive metal layer can be comparable to the thickness of a typical negative electrode current collector, for example, 3 to 500 μm, or 5 to 100 μm, or 7 to 30 μm.

[0042] Furthermore, the conductive metal layer is a metal with relatively low reactivity and high conductivity that does not cause any chemical changes in the battery, and can be formed by using any metal previously known to be usable as a negative electrode current collector.

[0043] Specific examples include metals such as stainless steel, aluminum, nickel, titanium, or copper, or copper, aluminum, or stainless steel that have been surface-treated with carbon, nickel, titanium, silver, etc. The conductive metal layer can be formed in various forms, such as films, sheets, foils, meshes, porous bodies, foams, or nonwoven structures. However, considering the excellent conductivity and lightweight nature of the negative current collector and the negative electrode, the conductive metal layer may comprise copper, and more specifically, the conductive metal layer may be a copper foil.

[0044] In one embodiment of the negative electrode, a lithium-ion deposition induction layer is formed on a conductive metal layer. This lithium-ion deposition induction layer may comprise, for example, an intermetallic compound in which copper and zinc are bonded, formed by electrodeposition on the conductive metal layer.

[0045] More specifically, the intermetallic compound may be a compound in which copper and zinc are chemically bonded in a weight ratio of 2:8 to 9.5:0.5, or 3:7 to 9:1, or 3:7 to 6:4. In one embodiment, the intermetallic compound does not contain any other metallic element and may be a substantially oxygen-free intermetallic compound.

[0046] If the copper content in the intermetallic compound is too high, the interfacial resistance and overvoltage of the negative electrode will increase, thereby inducing lithium dendrite growth, which may degrade the electrochemical and lifespan characteristics of the lithium-free secondary battery. Conversely, if the zinc content is too high, the side reactions between the negative electrode and the electrolyte, as well as the volume expansion of the negative electrode, will increase, which may reduce the lifespan characteristics of the lithium-free secondary battery.

[0047] As will be described in more detail below, the lithium-ion deposition-induced layer containing the intermetallic compound can be formed by electrodeposition followed by further heat treatment. This is likely because, due to such heat treatment, some zinc components diffuse from the lithium-ion deposition-induced layer to the surrounding area of ​​the conductive metal layer, etc., and trace amounts of zinc components volatilize. As a result, the chemical composition of the lithium-ion deposition-induced layer changes, while minor defects are eliminated, thereby making the lithium-ion deposition-induced layer more uniform and dense.

[0048] In one specific example, the heat-treated lithium-ion deposition-induced layer may comprise an intermetallic compound in which copper and zinc are chemically bonded in a weight ratio of 3:7 to 9:1, or 5:5 to 9:1, or 7:3 to 9:1, and the oxygen content is less than 5% by weight, or 0.01 to 5% by weight, or 0.1 to 3% by weight, based on the total weight of the intermetallic compound.

[0049] One embodiment of the negative electrode, by comprising a lithium deposition-inducing layer that becomes uniform and dense through heat treatment, can further reduce the interfacial resistance of the negative electrode and also improve the electrochemical or lifetime characteristics of the lithium-free secondary battery. This is presumably because the heat-treated lithium deposition-inducing layer induces more uniform lithium deposition and can further suppress the formation of lithium dendrites.

[0050] The aforementioned lithium-ion deposition induction layer can be formed on the conductive metal layer with a thickness of 0.05 to 2 μm, 0.1 to 1 μm, or 0.1 to 0.5 μm. By forming such a thickness, the resistance and overvoltage of the lithium-free secondary battery can be effectively reduced, while the decrease in battery energy density caused by the increase in the thickness of the negative electrode can be reduced.

[0051] On the other hand, according to another embodiment of this disclosure, a method for manufacturing a negative electrode for a lithium-free secondary battery according to one embodiment described above is provided. Such a method for manufacturing a negative electrode may include the step of electrodepositing copper and zinc on a conductive metal layer using an electrolyte containing a copper precursor, a zinc precursor, and a pyrophosphate / ester.

[0052] In such a manufacturing method, the electrodeposition step can be performed by applying a voltage to an electrodeposition system comprising a working electrode containing a conductive metal layer; a counter electrode containing an alloy of copper and zinc; and an electrolyte. Figure 1 An example of such an electrodeposition system is shown, in which copper foil is used as the working electrode and brass mesh (an alloy of copper and zinc in a 65:35 weight ratio) is used as the counter electrode.

[0053] For example, if a voltage of 1.5V or higher, or 1.5V to 3.0V, is applied to the electrodeposition system, and electrodeposition is performed for 1 to 30 minutes, 5 to 20 minutes, or 7 to 15 minutes, copper and zinc ions migrate from the counter electrode to the working electrode, and an intermetallic compound in which copper and zinc are combined is deposited on the conductive metal layer, thereby forming the lithium-ion electrodeposition-induced layer. In particular, by controlling the above-mentioned electrodeposition time, the lifespan characteristics of the secondary battery can be further improved.

[0054] In this case, the electrolyte may contain a copper precursor, a zinc precursor, and a pyrophosphate / ester. As the copper and zinc precursors, for example, copper salts and sulfates, such as copper sulfate or zinc sulfate, may be used. Additionally, the pyrophosphate / ester is an additive that induces electrodeposition and may contain a metal pyrophosphate, such as an alkali (earth) metal pyrophosphate, K₂P₂O₇, etc.

[0055] Furthermore, in one specific example, the electrolyte may be an aqueous solution containing a metal pyrophosphate at a concentration of 70 to 800 mM, or 80 to 300 mM, or 90 to 200 mM, a copper precursor at a concentration of 10 to 50 mM, or 20 to 40 mM, and a zinc precursor at a concentration of 10 to 50 mM, or 20 to 40 mM. In this electrolyte, adjusting the concentrations of the copper precursor and / or the zinc precursor allows for adjustment of the chemical composition of the intermetallic compound of copper and zinc contained in the lithium-ion deposition induction layer, such as the copper-zinc binding ratio.

[0056] Furthermore, the shape of the lithium-ion deposition-induced layer can be adjusted by regulating the concentration of the metal pyrophosphate in the electrolyte. For example, by adjusting the concentration of the metal pyrophosphate to 80 to 300 mM, the lithium-ion deposition-induced layer is formed as a thin film, thereby allowing the negative electrode of the lithium-free secondary battery to be formed thinner and possessing, for example, high energy density electrochemical characteristics. Conversely, if the concentration of the metal pyrophosphate is too high or the voltage applied during the electrodeposition step is too high, the intermetallic compounds contained in the lithium-ion deposition-induced layer will form dendritic microstructures, which may be undesirable for the lifetime characteristics of the lithium-free secondary battery or for the uniform electrodeposition of the lithium metal layer during charge and discharge.

[0057] On the other hand, in the manufacturing methods of the other embodiments described above, before the electrodeposition step, a step of surface treatment with sulfuric acid solution or the like may be performed to remove oxides from the surface of the conductive metal layer. This allows for the formation of a lithium electrode deposition induction layer and further reduces the resistance of the negative electrode in one embodiment.

[0058] Furthermore, the method for manufacturing the negative electrode in other embodiments may further include, after the electrodeposition step, a heat treatment step of the electrodeposition material at a temperature above 200°C, or 200 to 600°C, or 200 to 400°C under a vacuum and / or inert gas atmosphere. By performing such heat treatment, the chemical composition of the lithium-ion deposition inducing layer changes, while eliminating minor defects, thereby making the lithium-ion deposition inducing layer more uniform and dense, and enabling the formation of a better lithium-ion deposition inducing layer.

[0059] On the other hand, according to another embodiment of this disclosure, a lithium-free secondary battery comprising the negative electrode of one of the above embodiments is provided. Such a lithium-free secondary battery may comprise, for example, the negative electrode of one of the above embodiments; a positive electrode facing the negative electrode and containing 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 also include an electrolyte containing a lithium salt and a non-aqueous organic solvent together with the separator.

[0060] In such a lithium-free secondary battery, the negative electrode does not contain a separate negative electrode active material layer before charging and discharging. However, as the lithium-free secondary battery is charged and discharged, lithium ions migrating from the positive electrode can be electrodeposited on the lithium electrodeposition induction layer of the negative electrode, such as a thin film of an intermetallic compound in which copper and zinc are combined, thereby forming a lithium metal layer or a lithium alloy layer. This lithium metal layer or lithium alloy layer can serve as the negative electrode active material.

[0061] In addition, during the initial charge and discharge, a solid electrolyte interface can be formed on the lithium deposition induction layer of the negative electrode through the reaction of lithium ions and the electrolyte. The solid electrolyte interface can contain, for example, lithium fluoride and can inhibit further side reactions with the electrolyte.

[0062] On the other hand, in a lithium-free secondary battery according to another 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.

[0063] Such a positive electrode can be manufactured by mixing an active material, a binder, and optionally a conductive material, a filler, etc. in a solvent to prepare a positive electrode paste composition and coating the paste composition onto the positive electrode current collector.

[0064] 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, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel treated with carbon, nickel, titanium, silver, etc. on the surface can be used. In addition, the current collector may have fine irregularities 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, sheet, foil, net, porous body, foam, and non-woven fabric structure.

[0065] 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).

[0066] 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 2-Z1 , 1-Y2 , Y2 , 1-Y1 , Y1 , q , r , Z1 , p 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[[ID=)O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, and 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 lithium nickel cobalt transition metal (M) oxide (such as 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 atomic fractions of respective independent elements, where 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, and p2 + q2 + r2 + s2 = 1), etc.), lithium iron phosphate (such as 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, -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1)), etc., and any one of them or a mixture of two or more of them can be used.

[0067] Among them, the positive electrode active material contains a lithium metal oxide containing lithium and two or more transition metals selected from the group consisting of nickel, manganese, cobalt, and aluminum. Based on the content of the total transition metals other than lithium, the content of nickel in the lithium metal oxide can be 50 mol% or more, or 60 to 99 mol%, or 70 to 95 mol%. Such a lithium metal oxide can be represented, for example, by the following Chemical Formula 1:

[0068] [Chemical Formula 1]

[0069] Li x Ni a Co b M 1 c M 2 d O2

[0070] Among them, in Formula 1, M 1 can be one or more selected from Mn and Al or a combination thereof, M 2It may be selected from one or more of the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, 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 ≤ 0.9. In addition, 0 < b ≤ 0.3, 0 < c ≤ 0.3, and 0 ≤ d ≤ 0.1.

[0071] The lithium metal oxide containing such a high content of nickel is used as a positive electrode active material and is combined with the negative electrode of one embodiment, thereby being able to further improve the output characteristics, capacity characteristics, life characteristics, etc. of the lithium-free secondary battery.

[0072] Based on the total weight of the positive electrode active material layer, the content of the above positive electrode active material may be 60 to 99% by weight, or 70 to 99% by weight, or 80 to 98% by weight.

[0073] On the other hand, the conductive material contained in the positive electrode active material layer is a component for further improving the conductivity of the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity and does not cause any chemical changes in the battery. For example, conductive materials that can be used include: carbon powders, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal crack carbon black; graphite powders, such as natural graphite, artificial graphite, or graphite with a well-developed crystal structure; conductive nanomaterials, such as carbon nanofibers or carbon nanotubes; fluorinated carbon 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 them, the conductive material contains conductive nanomaterials, such as carbon nanotubes or carbon nanofibers, which can further reduce the resistance of the lithium-free secondary battery and further enhance the output characteristics.

[0074] Generally, based on the total weight of the positive electrode active material layer, the content of the conductive material may be 1 to 20% by weight, or 1 to 15% by weight, or 1 to 10% by weight.

[0075] The binder selectively contained in the positive electrode active material layer is a component that aids in the binding between the positive electrode active material and the conductive material and the binding 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 rubber, sulfonated ethylene propylene diene monomer rubber, nitrile rubber, styrene-butadiene rubber, fluororubber, etc. Mixtures or copolymers of two or more selected from these may also be used.

[0076] 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.

[0077] Alternatively, fillers may be added to the positive electrode as a component to suppress its expansion. There are no particular limitations on such fillers, as long as they suppress electrode expansion and do not cause any chemical changes in the battery; examples may include olefin polymers (e.g., polyethylene and polypropylene) and fibrous materials (e.g., glass fibers and carbon fibers).

[0078] The aforementioned positive electrode can be prepared, for example, by dispersing and mixing the positive electrode active material, the binder, and the conductive material 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.

[0079] On the other hand, the lithium-free secondary battery of the other embodiments may also include an electrolyte containing a non-aqueous organic solvent and a lithium salt.

[0080] The lithium salt contained in the electrolyte serves as a medium for transporting ions within the secondary battery. For example, the lithium salt may contain Li. + It can be a cation and may also contain 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 - The anions in the group.

[0081] Specifically, the lithium salt may include lithium selected from LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB. 10 Cl 10 At least one 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).

[0082] The concentration of the lithium salt can be appropriately varied within a normally usable range, and can be contained in the electrolyte at a concentration of 0.4M to 6M, or at a concentration of 0.5M to 5M.

[0083] In a more specific example, the electrolyte may contain a relatively low concentration of lithium salt, between 0.4 M and less than 2 M, or between 0.5 M and 1.5 M, but may contain a high concentration of lithium salt, between 2 M and 6 M, or between 2.5 M and 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.

[0084] 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 organic solvent known to be applicable to lithium-ion battery electrolytes may be used. Examples of such organic solvents include at least one selected from the group consisting of carbonate solvents, ether solvents, nitrile solvents, phosphate ester solvents, and sulfone solvents. However, considering the stability of the lithium metal layer electrodeposited on the lithium electrodeposition induction layer, the non-aqueous organic solvent preferably includes a carbonate solvent or an ether solvent.

[0085] More specifically, the carbonate solvent may include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butyl carbonate, fluoroethylene carbonate, methyl propyl carbonate, methyl ethyl carbonate, ethyl propyl carbonate, ethyl 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.

[0086] Furthermore, the ether solvent may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, or tetrahydrofuran derivatives (e.g., 2-methyltetrahydrofuran), and the nitrile solvent may include succinic anhydride, adiponitrile, sebacate, acetonitrile, propionitrile, etc. Additionally, the sulfone solvent may include dimethyl sulfone, ethylmethyl sulfone, sulfolane, etc.

[0087] 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.

[0088] Such porous membranes can be manufactured from olefin polymers (e.g., 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 to these. However, porous polyethylene or porous glass fiber nonwoven fabric (glass filter) is preferred as the membrane, and porous glass filter (glass fiber nonwoven fabric) is more preferred. The membrane can be an insulating film with high ion permeability and mechanical strength. The pore size of the membrane is generally in the range of 0.01 to 10 μm, and the thickness is generally in the range of 5 to 300 μm, but is not limited to these.

[0089] In other embodiments of the lithium-free secondary battery, the separator may be integrated with the electrolyte and inserted between the positive and negative electrodes in the form of an electrolyte layer or electrolyte membrane. In one example, the electrolyte layer or electrolyte membrane may be in the form of a polymer matrix containing the aforementioned lithium salt and non-aqueous organic solvent, or it may be in the form of a solid electrolyte. Furthermore, known polymer-based solid electrolytes or the like may be used as the polymer matrix.

[0090] The lithium-free secondary battery described above can be a semi-solid battery using a combination of liquid electrolyte and solid electrolyte, or a fully solid battery having a solid electrolyte layer, depending on the presence or absence of the electrolyte layer and its shape.

[0091] On the other hand, the lithium-free secondary battery of the other embodiments can be manufactured according to conventional methods in the art. For example, the lithium-free secondary battery can be prepared by: housing an electrode assembly including a positive electrode, a negative electrode and a separator in a housing, and injecting and impregnating the aforementioned electrolyte into the housing; or housing an electrode assembly including a positive electrode, a negative electrode and an electrolyte layer in a housing.

[0092] Such lithium-free secondary batteries can be used not only as battery cells for powering small devices, but are also particularly suitable as unit batteries in battery modules for powering medium to large devices.

[0093] The preferred embodiments, comparative examples, and experimental examples used to evaluate them of the present invention will now be described. However, the following embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention.

[0094] Comparative Examples 1 and 2 and Examples 1 and 2: Manufacturing of negative electrode materials for lithium-free secondary batteries

[0095] First, copper foil itself was used as the negative electrode for Comparative Example 1. Furthermore, the negative electrodes for Comparative Example 2 and Examples 1 and 2 were manufactured using the following method: Pyrophosphate (K₂P₂O₇), copper sulfate, and zinc sulfate were dissolved in deionized water at the concentrations (mM) shown in Table 1 below to prepare an electrolyte for electrodeposition.

[0096] On the other hand, preparations such as Figure 1 The electrodeposition system shown contains a copper foil working electrode and a brass mesh (an alloy mesh with a weight ratio of Cu:Zn = 65:35) as a counter electrode. Each electrode is pre-soaked in a 1M sulfuric acid aqueous solution for about 30 minutes before use to remove surface oxides.

[0097] An acid-treated copper foil working electrode and a brass mesh counter electrode are attached to an electrodeposition fixture, and then connected to the negative and positive terminals of a power supply, respectively. The electrodeposition fixture, with both the working and counter electrodes connected, is placed vertically in a water bath containing an electrolyte for electrodeposition. An electrodeposition process is then performed for 10 minutes under constant voltage (2.0V) to form a lithium-ion deposition-inducing layer on the copper foil. This lithium-ion deposition-inducing layer contains an intermetallic compound in which copper and zinc are bonded.

[0098] After the electrodeposition process, the copper foil on which the lithium electrodeposition induction layer is formed is separated from the electrodeposition fixture and then washed in deionized water to remove all electrolyte residues used in the electrodeposition process. Through the above process, negative electrodes for lithium-free secondary batteries of Comparative Example 2 and Examples 1 and 2 were manufactured, respectively.

[0099]

[0100] The negative electrode surfaces formed in Comparative Example 2 and Examples 1 and 2 were analyzed using an electron microscope, as shown below. Figures 2a to 2c As shown. This confirms that in Examples 1 and 2, a lithium-ion electrodeposition-induced layer containing intermetallic compounds was successfully formed.

[0101] Examples 3 to 5 Manufacturing of negative electrodes for lithium-free secondary batteries

[0102] The negative electrode sample prepared in Example 2 was placed in a vacuum furnace (-0.1 MPa) and then heat-treated at each temperature listed in Table 2 below under an argon atmosphere with a flow rate of 5 SLPM. The heat treatment process time was set as TS (time required to reach the target temperature shown in Table 2 below) = 1 hour and Tm (time required to maintain the target temperature shown in Table 2 below) = 2 hours.

[0103] The negative electrodes of Examples 3 to 5 were manufactured through this additional heat treatment. The compositional changes of the intermetallic compounds contained in the lithium-ion deposition-induced layer in the negative electrodes of Examples 3 to 5 were confirmed and summarized in Table 2 below. Electron microscopy was used to analyze the film quality changes of the lithium-ion deposition-induced layer before and after the treatment in Example 5, such as... Figure 3 As shown.

[0104]

[0105] Refer to Table 2 and Figure 3 The compositional changes of the intermetallic compounds contained in the lithium-ion deposition-induced layer caused by the heat treatment were confirmed. Furthermore, it was confirmed that minor defects in the lithium-ion deposition-induced layer were eliminated, and the film became denser.

[0106] Test Example 1: Overvoltage Evaluation

[0107] Half-cells were manufactured using the negative electrodes of Comparative Example 1 and Example 2. Such half-cells contained the aforementioned negative electrode and a lithium foil as a counter electrode, and contained 75 μL of an electrolyte comprising 0.6 M LiBF4 + 0.6 M LiBF2 (C2O4) in an FEC / DEC (volume ratio 1:2). For such half-cells, when the capacity was 0.5 mAh·cm⁻¹… -2 Lithium at 10 μA·cm-2 During electrodeposition, the lithium electrodeposition overvoltage applied to each negative electrode is evaluated, and the evaluation results are as follows: Figure 4 As shown.

[0108] Reference Figure 4 It was confirmed that a lower lithium deposition overvoltage was applied during lithium deposition using the negative electrode of Example 2. This confirms that uniform lithium electrodeposition was induced on the lithium deposition induction layer contained in the negative electrode of the example.

[0109] Experimental Example 2: Evaluation of Battery Life Characteristics

[0110] Half-cells containing the negative electrodes of Comparative Examples 1 and 2 and Examples 1 and 2 were prepared in the same manner as in Test Example 2. When at 1 mAh·cm⁻¹ -2 @0.5mA·cm -2 When such a half-cell is charged and discharged under conditions of (0.5C, cutoff voltage: 1V), the stable charge-discharge cycle performance is evaluated by a galvanic charge-discharge test. The evaluation results are compared and presented below. Figure 5 middle.

[0111] Reference Figure 5 It was confirmed that stable charge-discharge was achieved in the secondary battery containing the negative electrode of Example 2 during longer cycles. In particular, it was confirmed that stable charge-discharge was achieved in the secondary battery containing the negative electrode of Example 2 during the longest cycles.

Claims

1. A negative electrode for a lithium-free secondary battery, comprising: Conductive metal layer; and A lithium-ion battery deposition induction layer, the lithium-ion battery deposition induction layer being formed on the conductive metal layer and containing an intermetallic compound in which copper and zinc are bonded.

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

3. The negative electrode for a lithium-free secondary battery according to claim 1, wherein the lithium-ion deposition inducing layer comprises an intermetallic compound in which copper and zinc are bonded in a weight ratio of 2:8 to 9.5:0.

5.

4. The negative electrode for a lithium-free secondary battery according to claim 1, wherein the lithium-ion deposition inducing layer comprises an intermetallic compound in which copper and zinc are combined in a weight ratio of 3:7 to 9:1 and contains 0.01 to 5% by weight of oxygen based on the total weight of the intermetallic compound.

5. The negative electrode for a lithium-free secondary battery according to claim 1, wherein the thickness of the lithium-ion deposition induced layer is 0.05 to 2 μm.

6. A method for manufacturing a negative electrode for a lithium-free secondary battery as claimed in claim 1, the method comprising electrodepositing copper and zinc on a conductive metal layer using an electrolyte containing a copper precursor, a zinc precursor, and a pyrophosphate / ester.

7. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 6, wherein the electrodeposition step is performed by applying a voltage to an electrodeposition system, the electrodeposition system comprising: a working electrode containing the conductive metal layer; a counter electrode containing an alloy of copper and zinc; and an electrolyte.

8. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 6, wherein the electrolyte is an aqueous solution containing a metal pyrophosphate at a concentration of 70 to 800 mM, a copper precursor at a concentration of 10 to 50 mM, and a zinc precursor at a concentration of 10 to 50 mM.

9. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 6, wherein after the electrodeposition step, the method further comprises heat-treating the electrodeposited material at a temperature above 200°C in a vacuum or inert gas atmosphere.

10. A lithium-free secondary battery, comprising: A cathode containing positive electrode active material; The negative electrode as described in claim 1; and A diaphragm or electrolyte layer inserted between the positive electrode and the negative electrode.

11. The lithium-free secondary battery of claim 10, further comprising a lithium metal layer electrodeposited on the lithium deposition inducing layer of the negative electrode by charging the lithium-free secondary battery.

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