Negative electrode for lithium-free secondary batteries and lithium-free secondary batteries containing the same

Abstract

The present invention relates to a negative electrode for a lithium-free secondary battery, a method for manufacturing the same, and a lithium-free secondary battery, which can improve the electrochemical properties and life characteristics of the lithium-free secondary battery. The negative electrode may include a conductive metal layer and a lithium electrodeposition induction layer formed on the conductive metal layer and containing an intermetallic compound to which copper and zinc are bonded.

Description

Technical Field

[0001] [Cross - reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0059728 filed on May 9, 2023 and Korean Patent Application No. 10 - 2024 - 0053381 filed on April 22, 2024, and all the contents disclosed in the documents of the Korean patent applications are included as part of this specification.

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

Background Art

[0003] A lithium - metal battery is a battery that applies a negative electrode active material made of a lithium - metal (Li - metal) material. Compared with a battery that applies a conventional graphite - based or lithium - alloy - based negative electrode, it has the advantages of theoretically very high energy density and capacity. Therefore, such lithium - metal batteries are being continuously studied and developed for application to batteries that require high energy density.

[0004] However, lithium - metal batteries have disadvantages such as large volume changes in the negative electrode during the charge - discharge process, growth of needle - shaped lithium - metal layers (such as lithium dendrites), side reactions between the lithium - metal layer and the electrolyte due to the characteristics of highly reactive lithium metal, and large irreversible capacity. As a result, lithium - metal batteries have a high possibility of short - circuiting of the electrodes and insufficient stability and life characteristics, and thus have not been commercialized yet.

[0005] Recently, there has been growing research and interest in lithium-free secondary batteries (anode-free secondary batteries) as an alternative to the aforementioned lithium metal batteries. These batteries form the negative electrode using the negative electrode current collector itself, without forming a separate lithium metal layer or other negative electrode active material layer on the negative electrode current collector. Such lithium-free secondary batteries can be defined as batteries that utilize lithium metal as the negative electrode active material by electrodepositing lithium onto the negative electrode current collector during charging.

[0006] However, existing lithium-free secondary batteries, or those utilizing lithium metal as the negative electrode active material, may still present problems such as the growth of lithium dendrites due to the uneven growth of lithium metal.

[0007] To overcome these technical limitations, techniques have been reported such as manufacturing current collectors with lithium-hydrophilic materials and increasing the surface area of ​​the current collector to induce uniform electrodeposition of lithium.

[0008] However, the processes applied to the fabrication of current collectors with lithium-friendly materials or three-dimensional current collectors with high surface area almost always have disadvantages such as long process times, very high costs, and low mass production capabilities. Furthermore, these methods present additional problems such as difficulty in fabricating thin current collectors and difficulty in fully utilizing the high energy density of lithium-free secondary batteries. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to provide a negative electrode for lithium-free secondary batteries and a method for manufacturing the same, which can suppress the growth of lithium dendrites and improve the electrochemical properties and lifespan characteristics of lithium-free secondary batteries, and which can be manufactured using a simplified process and in a thin thickness.

[0010] Furthermore, the present invention aims to provide a lithium-free secondary battery that includes the aforementioned negative electrode and exhibits improved electrochemical properties and lifespan characteristics. [Means for solving the problem]

[0011] According to one embodiment of the present invention, a negative electrode for a lithium-free secondary battery is provided, comprising a conductive metal layer and a lithium electrodeposition induction layer formed on the conductive metal layer and containing an intermetallic compound in which copper and zinc are bonded.

[0012] In such a negative electrode, the lithium electrodeposition induction layer may contain an intermetallic compound in which copper:zinc is bonded in a weight ratio of 2:8 to 9.5:0.5. In a further embodiment, the lithium electrodeposition induction layer may contain an intermetallic compound in which copper:zinc is bonded in a weight ratio of 3:7 to 9:1, and which contains 0.01 to 5% by weight of oxygen based on the weight of the total intermetallic compound.

[0013] Furthermore, in the negative electrode, the lithium electrodeposition induction layer can have a thickness of 0.05 to 2 μm.

[0014] On the other hand, according to another embodiment of the present invention, a method for manufacturing a negative electrode of one embodiment is provided, which includes the step of electrically depositing copper and zinc onto a conductive metal layer using an electrolyte containing a copper precursor, a zinc precursor, and pyrophosphate.

[0015] In this manufacturing method, the electrodeposition step can be carried out by applying a voltage to an electrodeposition system comprising a working electrode containing the conductive metal layer; a relative electrode containing a copper-zinc alloy; and the electrolyte.

[0016] Furthermore, the manufacturing method may further include a step of heat-treating the electrodeposited material at a temperature of 200°C or higher under a vacuum or inert gas atmosphere after the electrodeposit step, and as such a heat treatment step progresses, the chemical composition of the lithium electrodeposited induction layer changes, and the electrochemical properties of the negative electrode can be further improved.

[0017] On the other hand, according to a further embodiment of the present invention, a lithium-free secondary battery is provided comprising a positive electrode containing a positive electrode active material; a negative electrode of the above embodiment; and a separation membrane or electrolyte layer interposed between the positive electrode and the negative electrode.

[0018] In such lithium-free secondary batteries, a lithium metal layer is electrodeposited onto the lithium electrodeposition induction layer of the negative electrode during the charging process, and acts as the negative electrode active material. [Effects of the Invention]

[0019] A negative electrode according to one embodiment of the present invention can be manufactured by a simple process of electrically depositing an intermetallic compound in which copper and zinc are bonded onto a conductive metal layer.

[0020] It has been confirmed that the formation of a lithium electrodeposition induction layer containing such intermetallic compounds significantly reduces the interfacial resistance and overvoltage of the negative electrode during the electrodeposition process of the lithium metal layer during battery charging. This reduction in resistance and overvoltage during the electrodeposition of the lithium metal layer suppresses the growth of lithium dendrites and side reactions at the negative electrode of lithium-free secondary batteries, potentially improving the lifespan characteristics of lithium-free secondary batteries. Furthermore, the electrochemical properties of lithium-free secondary batteries can be improved due to the reduction in resistance.

[0021] According to the present invention, not only can the negative electrode of a lithium-free secondary battery be manufactured in a thin form using a simplified process, but the electrochemical properties and lifespan characteristics of the lithium-free secondary battery can also be improved. [Brief explanation of the drawing]

[0022] [Figure 1] This diagram schematically shows an example of an electro-deposition system used for manufacturing a negative electrode according to an embodiment of the present invention. [Figure 2a]Figures 2a and 2c are photographs of the negative electrode surfaces formed in Comparative Example 2 (Figure 2a), Example 1 (Figure 2b), and Example 2 (Figure 2c), respectively, analyzed using an electron microscope. [Figure 2b] Figures 2a and 2c are photographs of the negative electrode surfaces formed in Comparative Example 2 (Figure 2a), Example 1 (Figure 2b), and Example 2 (Figure 2c), respectively, analyzed using an electron microscope. [Figure 2c] Figures 2a and 2c are photographs of the negative electrode surfaces formed in Comparative Example 2 (Figure 2a), Example 1 (Figure 2b), and Example 2 (Figure 2c), respectively, analyzed using an electron microscope. [Figure 3] This photograph shows the changes in the film quality of the lithium electrodeposition induction layer before and after heat treatment during the manufacturing process of the negative electrode in Example 5, as analyzed by electron microscope. [Figure 4] This graph shows the overvoltage evaluation results during lithium electrodeposition for half-cells including the negative electrodes of Comparative Example 1 and Example 2. [Figure 5] This graph shows the results of evaluating the life characteristics of half-cells including the negative electrodes of Comparative Examples 1 and 2, and Examples 1 and 2. [Modes for carrying out the invention]

[0023] In this specification, when a part "includes" a component, unless otherwise stated, it means that it may include other components rather than excluding them.

[0024] Terms of degree used throughout this specification, such as “about,” “substantially,” etc., are used in the numerical sense or in the sense close to the numerical sense in which the manufacturing and material tolerances inherent to the meaning referred to are presented, and are used to aid in understanding this application and to prevent malicious infringers from unfairly exploiting disclosures that refer to exact or absolute numerical values. Terms of degree used throughout this specification, such as “steps to,” or “steps of,” do not mean “steps for.”

[0025] In this specification, the term “these combinations” in a maxi expression means one or more mixtures or combinations selected from the group of components described in the maxi expression, and means including one or more selected from the group of components.

[0026] Furthermore, in this specification, "lithium-free secondary battery" can refer to a secondary battery in its pre-charge / discharge state, for example, immediately after manufacture, in which no additional negative electrode active material layer, such as a lithium metal layer, lithium alloy layer, or other carbon or silicon-containing layer, exists on the negative electrode current collector (for example, a negative electrode current collector containing a conductive metal layer such as copper and a lithium electrodeposition induction layer). Therefore, the "lithium-free secondary battery" can be defined as one that, in its pre-charge / discharge state, does not contain any additional negative electrode active material layer (for example, a lithium metal layer) on the negative electrode current collector. However, it goes without saying that the addition of additional insulating or functional layers other than the negative electrode active material layer is not restricted.

[0027] Furthermore, the term "lithium-free secondary battery" cannot be interpreted as restricting the presence of lithium-containing positive electrode active material or the presence of a lithium metal layer or lithium-containing compound that is electrodeposited on the negative electrode during charging and discharging.

[0028] The following describes in detail examples of the implementation of the present invention based on the definitions described above. However, these are presented as examples only and do not limit the invention; the present invention is defined only by the scope of the claims described later.

[0029] An embodiment of the present invention provides a negative electrode for a lithium-free secondary battery which may include a conductive metal layer and a lithium electrodeposition induction layer formed on the conductive metal layer and comprising an intermetallic compound to which copper and zinc are bonded.

[0030] It was confirmed that the formation of an intermetallic compound in which copper and zinc are chemically bonded reduces the interfacial resistance and overpotential of the negative electrode. This is thought to be due to the zinc component contained in the intermetallic compound. This reduction in interfacial resistance and overpotential not only improves the electrochemical properties of lithium-free secondary batteries, but also induces uniform electrodeposition of lithium metal, suppressing the growth of lithium dendrites, which may lead to an improvement in the lifespan characteristics of lithium-free secondary batteries.

[0031] Furthermore, instead of simply forming a lithium-hydrophilic metal such as zinc on a conductive metal layer, the negative electrode forms an intermetallic compound of copper and zinc by electrodeposition. During the battery operation process, the lithium-hydrophilic metal such as zinc may undergo an alloying reaction with lithium, causing volume expansion. Such volume expansion can be a factor that prevents lithium-free secondary batteries from fully exhibiting their lifespan characteristics. In contrast, the intermetallic compound can mitigate the volume expansion caused by the alloying reaction with lithium, further improving the lifespan characteristics of lithium-free secondary batteries.

[0032] Furthermore, the negative electrode of the above embodiment can be manufactured not only by a simplified electro-deposition process, but also by being formed to a thin thickness without a three-dimensional structure. As a result, the high energy density of lithium-free secondary batteries can be fully utilized by using the negative electrode.

[0033] On the other hand, in the negative electrode for a lithium-free secondary battery according to the above embodiment, the conductive metal layer can have a thickness equivalent to that of a general negative electrode current collector, for example, 3 to 500 μm, or 5 to 100 μm, or 7 to 50 μm.

[0034] Furthermore, the conductive metal layer can be formed using any metal that does not cause chemical changes in the battery, has relatively low reactivity, and possesses high conductivity, and which has been known to be usable as a negative electrode current collector.

[0035] Specific examples include metals such as stainless steel, aluminum, nickel, titanium, or copper, or copper, aluminum, or stainless steel surfaces that have been surface-treated with carbon, nickel, titanium, silver, etc. Such conductive metal layers can be formed in various forms such as films, sheets, foils, nets, porous materials, foams, or nonwoven fabrics. However, considering the excellent conductivity and light weight of the negative electrode current collector and negative electrode, and the appropriate formation of the lithium electrodeposition induction layer, the conductive metal layer may contain copper, and more specifically, the conductive metal layer may be copper foil.

[0036] In the negative electrode of the above embodiment, a lithium electrodeposition induction layer is formed on the conductive metal layer. Such a lithium electrodeposition induction layer may include, for example, an intermetallic compound in which copper and zinc are bonded, formed by electrodeposition on the conductive metal layer.

[0037] 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 specific example, the intermetallic compound may be an intermetallic compound that does not contain any further metal elements and is substantially oxygen-free.

[0038] If the copper content in the intermetallic compound becomes excessively high, the interfacial resistance and overpotential of the negative electrode will increase, potentially inducing lithium dendrite growth and degrading the electrochemical properties and lifespan of the lithium-free secondary battery. Conversely, if the zinc content becomes excessively high, side reactions between the negative electrode and electrolyte, as well as volume expansion of the negative electrode, will increase, potentially degrading the lifespan of the lithium-free secondary battery.

[0039] As will be explained in more detail below, the lithium electrodeposited layer containing the intermetallic compound can be further heat-treated after being formed by electrodeposition. This is thought to be because such heat treatment causes some of the zinc component to diffuse from the lithium electrodeposited layer into the surrounding conductive metal layer, and a small amount of zinc component to volatilize. As a result, the chemical composition of the lithium electrodeposited layer changes, while micro-defects are removed, making the lithium electrodeposited layer more uniform and denser.

[0040] In a specific example, the lithium electrodeposited induction layer after heat treatment is chemically bonded with copper and zinc in a weight ratio of 3:7 to 9:1, 5:5 to 9:1, or 7:3 to 9:1, and may contain an intermetallic compound containing oxygen in an amount of 5% or less 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.

[0041] In one embodiment, the negative electrode includes a lithium electrodeposition induction layer that has been homogenized and densified by the heat treatment. As a result, the interfacial resistance of the negative electrode is further reduced, and the electrochemical properties or lifespan characteristics of the lithium-free secondary battery can be improved. This is thought to be because the lithium electrodeposition induction layer after heat treatment induces more uniform lithium electrodeposition, further suppressing the formation of lithium dendrites and the like.

[0042] The lithium electrodeposited induction layer described above 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, it is possible to effectively reduce the resistance and overvoltage of the lithium-free secondary battery while reducing the decrease in energy density of the battery due to the increase in the thickness of the negative electrode.

[0043] On the other hand, according to another embodiment of the present invention, a method for manufacturing a negative electrode for a lithium-free secondary battery of the above-described embodiment is provided. Such a method for manufacturing a negative electrode may include using an electrolyte comprising a copper precursor, a zinc precursor, and pyrophosphate, and electrodepositing copper and zinc onto a conductive metal layer.

[0044] In this manufacturing method, the electrodeposition step can be carried out by applying a voltage to an electrodeposition system comprising a working electrode containing the conductive metal layer; a relative electrode containing a copper-zinc alloy; and the electrolyte. Figure 1 shows an example of such an electrodeposition system, in which copper foil is used as the working electrode and brass mesh (an alloy containing copper and zinc in a weight ratio of 65:35) is used as the relative electrode.

[0045] By applying a voltage of, for example, 1.5V or higher, or 1.5V to 3.0V, to such an electrodeposition system and performing electrodeposition for 1 to 30 minutes, 5 to 20 minutes, or 7 to 15 minutes, copper and zinc ions move from the relative electrode to the working electrode, and an intermetallic compound in which copper and zinc are bonded is deposited on the conductive metal layer, thereby forming the lithium electrodeposition induction layer. In particular, by controlling the electrodeposition time, the life characteristics of the secondary battery can be further improved.

[0046] In this case, the electrolyte may contain a copper precursor, a zinc precursor, and a pyrophosphate. For the copper precursor and zinc precursor, copper salts and sulfates such as copper sulfate or zinc sulfate can be used. Furthermore, as an additive to induce electrodeposition, metal pyrophosphates, such as K2P2O7, which is an alkali (earth) metal pyrophosphate, can be used as the pyrophosphate.

[0047] Furthermore, as a specific example, the electrolyte can be an aqueous solution containing a metal pyrophosphate at a concentration of 70-800 mM, 80-300 mM, or 90-200 mM, a copper precursor at a concentration of 10-50 mM, or 20-40 mM, and a zinc precursor at a concentration of 10-50 mM, or 20-40 mM. By adjusting the concentrations of the copper precursor and / or zinc precursor in such an electrolyte, the chemical composition of the intermetallic compounds of copper and zinc contained in the lithium electrodeposition induction layer, for example, the bonding ratio of copper and zinc, can be adjusted.

[0048] Furthermore, the morphology of the lithium electrodeposition induction layer can be adjusted by adjusting the concentration of the metal pyrophosphate in the electrolyte. For example, by adjusting the concentration of the metal pyrophosphate to 80-300 mM, the lithium electrodeposition induction layer can be formed into a thin film, allowing the negative electrode of the lithium-free secondary battery to be thinner and have electrochemical properties such as higher energy density. Conversely, if the concentration of the metal pyrophosphate becomes excessively high or the applied voltage in the electrodeposition step becomes excessively high, the intermetallic compounds contained in the lithium electrodeposition induction layer may form a branched microstructure, which may be undesirable in terms of the lifespan characteristics of the lithium-free secondary battery and the uniform electrodeposition of the lithium metal layer during charging and discharging.

[0049] On the other hand, the manufacturing method of the other realization example described above may further involve a step of surface-treating the conductive metal layer with a sulfuric acid solution or the like before the electrical deposition step to remove oxides from the surface of the conductive metal layer. This allows for better formation of the lithium electrodeposition induction layer and further reduces the resistance of the negative electrode in one embodiment.

[0050] Furthermore, the negative electrode manufacturing method of the other embodiment described above may further include a step of heat-treating the electrodeposited material in a vacuum and / or inert gas atmosphere at a temperature of 200°C or higher, or 200-600°C, or 200-400°C, after the electrodeposited step. As such heat treatment progresses, the chemical composition of the lithium electrodeposited induction layer changes, while fine defects are removed, the lithium electrodeposited induction layer becomes more uniform and denser, and a better lithium electrodeposited induction layer can be formed.

[0051] On the other hand, a further embodiment of the present invention provides a lithium-free secondary battery comprising the negative electrode of one embodiment described above. Such a lithium-free secondary battery may include, for example, the negative electrode of one embodiment described above; a positive electrode containing a positive electrode active material facing the negative electrode; and a separation membrane or electrolyte layer interposed between the positive and negative electrodes. Furthermore, the lithium-free secondary battery may further include an electrolyte comprising a lithium salt and a non-aqueous organic solvent together with the separation membrane.

[0052] 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 charging and discharging of the lithium-free secondary battery progresses, lithium ions that have moved from the positive electrode are electrodeposited onto the lithium electrodeposition induction layer of the negative electrode, for example, a thin film of an intermetallic compound in which copper and zinc are bonded, forming a lithium metal layer or lithium alloy layer, and such a lithium metal layer or lithium alloy layer can act as a negative electrode active material.

[0053] Furthermore, a solid electrolyte interface film can be further formed on the lithium electrodeposition induction layer of the negative electrode by the reaction of lithium ions with the electrolyte during initial charging and discharging. Such a solid electrolyte interface film may contain, for example, lithium fluoride, and can suppress further side reactions with the electrolyte.

[0054] On the other hand, in the lithium-free secondary battery of the additional implementation example, the positive electrode may include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

[0055] Such a positive electrode can be manufactured by mixing an active material, a binder, and possibly a conductive material, a filler, etc., in a solvent to produce a positive electrode slurry composition, which is then applied to a positive electrode current collector.

[0056] The positive electrode current collector can generally have a thickness of 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. can be used. The current collector can also form fine irregularities on its surface to increase the adhesive force of the positive electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven bodies, etc. are possible.

[0057] In the case of the positive electrode active material, it is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it can include lithium metal oxides containing one or more metals such as iron, cobalt, manganese, nickel, or aluminum and lithium.

[0058] Specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2 (where 0 < Y < 1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2, etc.), a lithium-nickel-cobalt-based oxide (e.g., LiNi 1-Y1 Co Y1 O2 (where 0 < Y1 < 1, etc.), a lithium-manganese-cobalt-based oxide (e.g., LiCo 1-Y2 Mn Y2 O2 (where 0 < Y2 < 1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), a lithium-nickel-manganese-cobalt-based oxide (e.g., Li(Ni p Co q Mn r)O2 (where 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2), etc.), 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 independent elements, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1), etc.), or lithium iron phosphate (e.g., Li 1+a Fe 1-x M x (PO 4-b )X b (where M is one or more selected from Al, Mg, and Ti, X is one or more selected from F, S, and N, -0.5 ≤ a ≤ +0.5, 0 ≤ x ≤ 0.5, 0 ≤ b ≤ 0.1), etc., and any one or two or more of these compounds can be included.

[0059] Among these, the positive electrode active material includes lithium; and a lithium metal oxide containing two or more metals selected from the group consisting of nickel, manganese, cobalt, and aluminum, and the lithium metal oxide can contain 50 mol% or more, or 60 to 99 mol%, or 70 to 95 mol% of nickel based on the total metal content excluding lithium. Such a lithium metal oxide can be represented, for example, by the following Chemical Formula 1: [Chemical Formula 1] Li x Ni a Co b M 1 cM 2 d O2 In the Chemical Formula 1, the M 1M may be one or more selected from Mn and Al, or a combination thereof. 2 x may be one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and may be 0.90≦x≦1.1, or 0.95≦x≦1.08, or 1.0≦x≦1.08, and may be 0.50≦a<1.0, or 0.60≦a≦0.99, or 0.70≦a≦0.95. Also, 0 <b≦0.3であり、0<c≦0.3であり、0≦d≦0.1であってもよい。

[0060] By using a lithium metal oxide with such a high nickel content as the positive electrode active material and combining it with the negative electrode of one embodiment, the output, capacity characteristics, and lifespan characteristics of a lithium-free secondary battery can be further improved.

[0061] The positive electrode active material described above may be present in an amount of 60-99% by weight, 70-99% by weight, or 80-98% by weight, based on the total weight of the positive electrode active material layer.

[0062] On the other hand, the conductive material contained in the positive electrode active material layer is a component for further improving the conductivity of the positive electrode active material. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive nanomaterials such as carbon nanofibers or carbon nanotubes; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used. Among these, the conductive material may include conductive nanomaterials such as carbon nanotubes or carbon nanofibers, which can further reduce the resistance of the lithium-free secondary battery and further improve its output characteristics.

[0063] Typically, the conductive material can be present in an amount of 1 to 20% by weight, 1 to 15% by weight, or 1 to 10% by weight, based on the total weight of the positive electrode active material layer.

[0064] The binder selectively included in the positive electrode active material layer is a component that assists in the bonding of the positive electrode active material to conductive materials and to the current collector. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, nitrile rubber, styrene-butadiene rubber, or fluororubber. A mixture or copolymer of two or more of these can also be used.

[0065] Typically, the binder may be present in an amount of 1-20% by weight, 1-15% by weight, or 1-10% by weight, based on the total weight of the positive electrode active material layer.

[0066] Furthermore, a filler can be selectively added to the positive electrode as a component to suppress its expansion. Such a filler is not particularly limited as long as it can suppress the expansion of the electrode without causing a chemical change in the battery, and for example, orifine polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. can be used.

[0067] The positive electrode described above can be manufactured by dispersing and mixing the positive electrode active material, binder, and conductive material in a dispersion medium (solvent) to create a slurry, applying this slurry to a metal current collector, and then drying and rolling it. In this case, the dispersion medium can be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof, but is not necessarily limited to these.

[0068] On the other hand, the lithium-free secondary battery of the other realization example may further include an electrolyte containing a non-aqueous organic solvent and a lithium salt.

[0069] The lithium salt contained in the electrolyte is used as a medium for transferring ions in the secondary battery. The lithium salt is, for example, Li as a cation. + Includes F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - , (CF3CF2SO2)2N - (CF3SO2)2N - , (F S O2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 -(CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - , C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CF3(CF2)7SO3 - and SCN - It can also include anions selected from the group consisting of the following.

[0070] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10 It may contain one or more selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBF2 (C2O4), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2, and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2).

[0071] The concentration of the lithium salt can be appropriately changed within a range that is normally usable, and can be included in the electrolyte at a concentration of 0.4 M to 6 M, or 0.5 M to 5 M.

[0072] In a more specific embodiment, the electrolyte may contain lithium salt at a relatively low concentration of 0.4 M to less than 2 M, or 0.5 M to 1.5 M, but it may also contain lithium salt at a high concentration of 2 M to 6 M, or 2.5 M to 5.5 M. By using an electrolyte containing such a high concentration of lithium salt, the output characteristics of the secondary battery can be further improved.

[0073] On the other hand, the type of non-aqueous organic solvent that can be included in the electrolyte is not particularly limited, and any organic solvent that has been known to be applicable to lithium-ion batteries and the like can be used. Examples of such organic solvents include one or more selected from the group consisting of carbonate-based solvents, ether-based solvents, nitrile-based solvents, phosphate-based solvents, and sulfone-based solvents. However, considering the stability of the lithium metal layer electrodeposited on the lithium electrodeposition induction layer, it is preferable that the non-aqueous organic solvent includes a carbonate-based solvent or an ether-based solvent.

[0074] More specifically, as the carbonate-based solvent, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, methyl propyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, or methyl (2,2,2-trifluoroethyl) carbonate can be used, and as the phosphate-based solvent, trimethyl phosphate, triethyl phosphate, or 2-(2,2,2-trifluoroethoxy)-1,3,2-dioxaphosphorane 2-oxide can be used.

[0075] Furthermore, as the ether-based solvent, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, or tetrahydrofuran derivatives such as 2-methyltetrahydrofuran can be used, and as the nitrile-based solvent, succinonitrile, adiponitrile, sebaconitrile, acetonitrile, or propionitrile can be used. Furthermore, as the sulfone-based solvent, dimethyl sulfone, ethyl methyl sulfone, or sulforane can be used.

[0076] On the other hand, the lithium-free secondary battery described above may further include a porous separator membrane interposed between the positive electrode and the negative electrode.

[0077] Such porous separation membranes can be made from olefin polymers such as polyethylene and polypropylene, glass fibers, etc., in the form of sheets, multilayer membranes, fine porous films, woven fabrics, and nonwoven fabrics, but are not necessarily limited to these forms. However, it is preferable to use porous polyethylene or porous glass fiber nonwoven fabric (glass filter) as the separation membrane, and it is more preferable to use porous glass filter (glass fiber nonwoven fabric) as the separation membrane. The separation membrane can also be a thin insulating film with high ion permeability and mechanical strength, and the pore diameter of the separation membrane can generally be in the range of 0.01 to 10 μm, and the thickness can generally be in the range of 5 to 300 μm, but are not limited to these forms.

[0078] Furthermore, in another example of the lithium-free secondary battery, the separation membrane may be integrated with the electrolyte to form an electrolyte layer or electrolyte film interposed between the positive and negative electrodes. For example, the electrolyte layer or electrolyte film may be in a form containing the above-mentioned lithium salt and non-aqueous organic solvent within a polymer matrix, or it may be in a form containing a solid electrolyte. As the polymer matrix, well-known polymer-based solid electrolytes can be used.

[0079] The lithium-free secondary batteries described above can be semi-solid batteries that use both liquid and solid electrolytes, or all-solid batteries that have a solid electrolyte layer, depending on the presence and form of the electrolyte layer.

[0080] On the other hand, the lithium-free secondary batteries of the other embodiments described above can be manufactured by conventional methods in the art. For example, they can be manufactured by a method in which an electrode assembly including a positive electrode, a negative electrode and a separator membrane is housed in a case and the electrolyte described above is injected and impregnated, or by a method in which an electrode assembly including a positive electrode, a negative electrode and an electrolyte layer is housed in a case.

[0081] Such lithium-free rechargeable batteries can be applied not only to battery cells used as power sources for small devices, but also to units of battery modules that power medium to large devices.

[0082] The following describes preferred embodiments of the invention, comparative examples, and experimental examples for evaluating them. However, the following embodiments are merely preferred embodiments of the present invention, and the present invention is not limited to these embodiments.

[0083] Comparative Examples 1 and 2, Examples 1 and 2: Manufacturing of anodes for lithium-free secondary batteries First, the copper foil itself was used as the negative electrode in Comparative Example 1. The negative electrodes for Comparative Example 2, and Examples 1 and 2 were manufactured by the following method: Pyrophosphate (K2P2O7), copper sulfate, and zinc sulfate were dissolved in DI water solvent at the concentrations (mM) shown in Table 1 below to prepare electrolytes for electrodeposition.

[0084] On the other hand, an electrodeposition system as shown in Figure 1 was prepared. This electrodeposition system included a copper foil working electrode and a brass mesh (an alloy mesh containing Cu:Zn in a weight ratio of 65:35) as a relative electrode. Each electrode was used after being pre-soaked in a 1M sulfuric acid aqueous solution for about 30 minutes to remove surface oxides.

[0085] After attaching the acid-treated copper foil working electrode and the brass mesh relative electrode to the electrodeposition jig, they were connected to the (-) and (+) terminals of the power supply, respectively. The electrodeposition jig, with all the working and relative electrodes connected, was then placed vertically in a water tank containing the electrodeposition electrolyte, and the electrodeposition process was carried out for 10 minutes under constant voltage (2.0V) conditions to form a lithium electrodeposition induction layer containing an intermetallic compound in which copper and zinc are bonded on the copper foil.

[0086] After the electrodeposition process, the copper foil on which the lithium electrodeposition induction layer was formed was separated from the electrodeposition jig and then washed with DI water to remove all electrolyte residue used in the electrodeposition process. Through the above process, the lithium-free secondary battery negative electrodes of Comparative Example 2, Examples 1 and 2 were manufactured, respectively.

[0087] [Table 1]

[0088] The negative electrode surfaces formed in Comparative Example 2, Examples 1 and 2 were analyzed using an electron microscope and are shown in Figures 2a to 2c, respectively. This confirmed that the lithium electrodeposition induction layer containing the intermetallic compound was successfully formed in Examples 1 and 2.

[0089] Examples 3-5: Manufacturing of negative electrodes for lithium-free secondary batteries The negative electrode samples produced in Example 2 were placed in a vacuum furnace at (-0.1 MPa) and then heat-treated at the temperatures listed in Table 2 below under an Ar gas atmosphere with a flow rate of 5 (SLPM). The heat treatment process time was set as follows: TS (time to reach the target temperature listed in Table 2 below) = 1 hour, Tm (maintenance time at the target temperature listed in Table 2 below) = 2 hours.

[0090] The negative electrodes of Examples 3 to 5 were manufactured after undergoing this additional heat treatment. After confirming the changes in the composition of the intermetallic compounds contained in the lithium electrodeposition induction layer of the negative electrodes of Examples 3 to 5, the results are summarized in Table 2 below. In Example 5, the changes in the film quality of the lithium electrodeposition induction layer before and after treatment were analyzed using an electron microscope and are shown in Figure 3.

[0091] [Table 2]

[0092] Referring to Table 2 and Figure 3, it was confirmed that the heat treatment resulted in a change in the composition of the intermetallic compounds contained in the lithium electrodeposition induction layer, and that the fine defects contained in the lithium electrodeposition induction layer were removed, resulting in a denser film.

[0093] Test Example 1: Overvoltage Evaluation Half-cells were manufactured using the negative electrodes of Comparative Example 1 and Example 2. These half-cells contained lithium foil as the negative electrode and relative electrode, and 75 μl of an electrolyte mixture of 0.6 M LiBF4 + 0.6 M LiBF2(C2O4) in FEC / DEC (1:2 volume ratio). For such half-cells, a capacitance of 0.5 mAh·cm was obtained. -2 Lithium capacity 10 μA·cm -2 When electrodeposited, the lithium electrodeposition overvoltage applied to each negative electrode was evaluated, and the evaluation results are shown in Figure 4.

[0094] Referring to Figure 4, it was confirmed that a lower lithium electrodeposition overvoltage was applied when lithium electrodeposition was performed using the negative electrode of Example 2. This confirmed that uniform electrodeposition of lithium was induced on the lithium electrodeposition induction layer contained in the negative electrode of the example.

[0095] Test Example 2: Evaluation of Battery Life Characteristics Similar to Test Example 2, half-cells including the negative electrodes of Comparative Examples 1 and 2, and Examples 1 and 2 were prepared.

[0096] For such a half-cell, 1 mAh·cm -2 @0.5mA·cm -2 Under the conditions of 0.5C and a cutoff voltage of 1V, the cycles in which stable charge and discharge occurred were evaluated through galvanic charge-discharge tests. The results of each evaluation are shown in comparison in Figure 5.

[0097] Referring to Figure 5, it was confirmed that the secondary batteries including the negative electrode in the examples exhibited stable charging and discharging over longer cycles, and in particular, the secondary battery including the negative electrode in Example 2 exhibited the most stable charging and discharging over the longest cycles.

Claims

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

2. The conductive metal layer comprises copper, wherein the negative electrode for a lithium-free secondary battery is as described in claim 1.

3. The lithium electrodeposition induction layer comprises an intermetallic compound in which copper and zinc are bonded in a weight ratio of 2:8 to 9.5:0.5, as described in claim 1, for a lithium-free secondary battery negative electrode.

4. The lithium electrodeposition induction layer is bonded with copper and zinc in a weight ratio of 3:7 to 9:1, and contains an intermetallic compound containing oxygen in an amount of 0.01 to 5% by weight, based on the total weight of the intermetallic compound, as described in claim 1 for a lithium-free secondary battery negative electrode.

5. The lithium electrodeposition induction layer has a thickness of 0.05 μm to 2 μm, as described in claim 1, for a lithium-free secondary battery negative electrode.

6. A method for producing a negative electrode for a lithium-free secondary battery according to any one of claims 1 to 5, comprising the step of electrically depositing copper and zinc onto a conductive metal layer using an electrolyte containing a copper precursor, a zinc precursor, and pyrophosphate.

7. The method for manufacturing a negative electrode for a lithium-free secondary battery according to claim 6, wherein the electrical deposition step is carried out by applying a voltage to an electrodeposition system comprising a working electrode including the conductive metal layer; a relative electrode including a copper-zinc alloy; and the electrolyte.

8. The method for producing 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 mM to 800 mM, a copper precursor at a concentration of 10 mM to 50 mM, and a zinc precursor at a concentration of 10 mM to 50 mM.

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

10. Positive electrode containing positive electrode active material; The negative electrode according to any one of claims 1 to 5; and A lithium-free secondary battery comprising a separation membrane or electrolyte layer interposed between the positive electrode and the negative electrode.

11. The lithium-free secondary battery according to claim 10, further comprising a lithium metal layer that is electrodeposited onto the lithium electrodeposition induction layer of the negative electrode by charging the lithium-free secondary battery.

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