KR20240139683A - Slurry for forming protective film of electrode and manufacturing method thereof, protective film of electrode and manufacturing method thereof, negative electrode for secondary battery and manufacturing method thereof and secondary battery - Google Patents

Abstract

A slurry for forming an electrode protective film is provided, which physically suppresses the formation of lithium dendrites and prevents direct reaction between an electrolyte and an anode to form a stable SEI film. One embodiment of the present invention provides a slurry for forming an electrode protective film, which includes a conductive material; a metal-based material; and a pore former.

Description

Slurry for forming a protective film of an electrode and a method for manufacturing the same, an electrode protective film and a method for manufacturing the same, a negative electrode for a secondary battery and a method for manufacturing the same, and a secondary battery {SLURRY FOR FORMING PROTECTIVE FILM OF ELECTRODE AND MANUFACTURING METHOD THEREOF, PROTECTIVE FILM OF ELECTRODE AND MANUFACTURING METHOD THEREOF, NEGATIVE ELECTRODE FOR SECONDARY BATTERY AND MANUFACTURING METHOD THEREOF AND SECONDARY BATTERY}

The present invention relates to a slurry for forming an electrode protective film and a method for producing the same, and more specifically, to a slurry for forming an electrode protective film and a method for producing the same, an electrode protective film and a method for producing the same, an anode for a secondary battery and a method for producing the same, and a secondary battery.

With the rapid development of the electrical, electronic, communications, and computer industries, the demand for secondary batteries with high energy density is rapidly increasing. In response to this demand, lithium metal batteries are attracting attention as batteries with high energy density.

A lithium metal battery is a secondary battery that uses lithium metal (Li metal) as an anode. Lithium metal has a very low standard reduction potential of -3.045 V (based on SHE: standard hydrogen electrode), and the density of the metal itself is low, so it is receiving the most attention as an anode material for high-energy density batteries.

However, when lithium metal is used as the cathode, lithium dendrites are generated during repeated charging and discharging processes, which can cause a short circuit in the battery, which causes safety issues and makes commercialization difficult.

In addition, lithium metal is a material that has high (electro)chemical reactivity with electrolytes, especially those containing carbonate-based organic solvents. As a result, as the driving cycle of a lithium metal battery progresses, a resistance layer is formed on the surface of the negative electrode due to a side reaction with the electrolyte, and the deposition/deposition of lithium ions on the surface of the negative electrode where such a resistance layer is formed is uneven, and there is a problem that the battery capacity gradually decreases.

In this regard, various materials and methods for forming a protective film on the surface of lithium metal have been proposed, but the materials and methods proposed so far have limitations in stabilizing the interface between the negative electrode and the electrolyte while maintaining uniform deposition/desorption of lithium ions on the negative electrode surface and increasing mechanical stability.

The purpose of the present invention is to provide a slurry for forming an electrode protective film that physically suppresses the formation of lithium dendrites and prevents direct reaction between an electrolyte and an anode to form a stable SEI film.

Another object of the present invention is to provide a slurry for forming an electrode protective film that can improve the cycle performance of a secondary battery by helping the movement of lithium ions smoothly.

Another object of the present invention is to provide a method for producing a slurry for forming the electrode protective film.

Another object of the present invention is to provide a method for manufacturing the electrode protective film.

Another object of the present invention is to provide a negative electrode for a secondary battery including the above electrode protective film.

Another object of the present invention is to provide a method for manufacturing the negative electrode for the secondary battery.

Another object of the present invention is to provide a secondary battery including the negative electrode for the secondary battery.

The purposes of the present invention are not limited to the purposes mentioned above, and other purposes and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. In addition, it will be easily understood that the purposes and advantages of the present invention can be realized by the means and combinations thereof indicated in the claims.

One embodiment of the present invention for achieving the above object provides a slurry for forming an electrode protective film, comprising a conductive additive; a metal material; and a pore former.

According to one specific example, the challenge material may be any one selected from the group consisting of graphene, carbon nanotubes, and combinations thereof.

According to one specific example, the carbon nanotube may be any one selected from the group consisting of single-walled carbon nanotubes, multi-walled carbon nanotubes, and combinations thereof.

According to one specific example, the electrical conductivity of the metal material may be 4.1 X 10 ⁷ S/m or more at 20°C.

According to one specific example, the electrical conductivity of the metal material may be 5.00 X 10 ⁷ S/m or more at 20°C.

According to one specific example, the metal material may be any one selected from the group consisting of copper (Cu), silver (Ag), gold (Au), and combinations thereof.

According to one specific example, the pore former may be any one selected from the group consisting of ZnO _, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, MnO ₂ , FeO, Co ₃ O ₄ , TiO ₂ and combinations thereof.

According to another embodiment of the present invention, the slurry for forming the electrode protective film may further include a binder.

Another embodiment of the present invention can provide a method for producing a slurry for forming an electrode protective film, including: (S1) a step of mixing a conductive material; a precursor including a metal-based material; and a pore former to produce a composite; and (S2) a step of mixing the composite and a binder to produce a slurry for forming an electrode protective film.

According to one specific example, the weight ratio of the conductive material and the precursor including the metal-based material (conductive material: precursor including the metal-based material) may be 1:15 to 1:20.

According to one specific example, the weight ratio of the complex and the binder (composite:binder) can be 6:4 to 9:1.

According to one specific example, the content of the pore former may be 1 to 5 wt% based on the total weight of the complex.

Another embodiment of the present invention for achieving the above object can provide an electrode protective film, in which a slurry for forming an electrode protective film is dried.

Another embodiment of the present invention for achieving the above object can provide an anode for a secondary battery, including: an anode substrate; and an electrode protective film according to various embodiments of the present invention described above, disposed on at least one surface of the anode substrate.

According to one specific example, the negative electrode substrate may include lithium metal (Li metal).

According to one specific example, the thickness of the electrode protective film may be 5 to 20 μm.

Another embodiment of the present invention for achieving the above object can provide a method for manufacturing an anode for a secondary battery, including the step of coating a slurry for forming an electrode protective film on at least one surface of a cathode substrate and then drying it.

For example, the step of coating the slurry for forming the electrode protective film may be a step using at least one method selected from the group consisting of doctor blade coating, dip coating, gravure coating, slit die coating, spin coating, comma coating, bar coating, reverse roll coating, screen coating, and cap coating.

According to one specific example, the slurry for forming the coated electrode protective film can be dried at 40 to 80° C. for 10 to 40 hours.

Another embodiment of the present invention for achieving the above object can provide a secondary battery including: a negative electrode for the secondary battery; a positive electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

The above-mentioned solution to the problem does not enumerate all the features of the present invention. The various features of the present invention and the advantages and effects thereof can be understood in more detail by referring to the specific examples below.

According to one aspect of the present invention, even if charging and discharging of a battery is repeated, the formation of lithium dendrites can be suppressed, thereby preventing damage to a separator.

According to another aspect of the present invention, a stable SEI film can be formed by physically suppressing the formation of lithium dendrites and preventing direct reaction between the electrolyte and the negative electrode.

According to another aspect of the present invention, the cycle performance of a secondary battery can be improved by helping the movement of lithium ions to proceed smoothly.

In addition to the effects described above, the specific effects of the present invention are described below together with the specific contents for carrying out the invention.

Figure 1 is a flow chart of a method for manufacturing a slurry for forming an electrode protective film according to one embodiment of the present invention.
Figure 2 is a schematic diagram of a method for manufacturing a slurry for forming an electrode protective film according to one embodiment of the present invention.
Fig. 3a is an SEM image of a cathode according to Example 1. Fig. 3b is an SEM image of a cathode according to Comparative Example 2. Fig. 3c is an SEM image of a cathode according to Comparative Example 3.
Fig. 4a is an SEM photograph of a vertical cross-section of a cathode according to Example 1. Fig. 4b is an SEM photograph of a vertical cross-section of a cathode according to Comparative Example 2. Fig. 4c is an SEM photograph of a vertical cross-section of a cathode according to Comparative Example 3.
Figure 5 is a graph of voltage over time of batteries according to Example 1 and Comparative Examples 1 to 3.
Figure 6 is a graph of voltage over time of the batteries according to Example 1 and Comparative Examples 1 to 3.
Figure 7 is a graph evaluating the life characteristics of batteries according to Example 1, Comparative Examples 1 and 3.
Figure 8 is a graph showing the electrochemical impedance measured by electrochemical impedance spectroscopy for the lithium symmetric batteries of Example 1 and Comparative Examples 1 to 3.
Fig. 9a is an SEM image of the electrode according to Example 1 after the cycle test of Experimental Example 4. Fig. 9b is an SEM image of the electrode according to Comparative Example 1 after the cycle test of Experimental Example 4. Fig. 9c is an SEM image of the electrode according to Comparative Example 2 after the cycle test of Experimental Example 4. Fig. 9d is an SEM image of the electrode according to Comparative Example 3 after the cycle test of Experimental Example 4.
Fig. 10a is an SEM image taken vertically through the electrode of Fig. 9a. Fig. 10b is an SEM image taken vertically through the electrode of Fig. 9b. Fig. 10c is an SEM image taken vertically through the electrode of Fig. 9c. Fig. 10d is an SEM image taken vertically through the electrode of Fig. 9d.

Hereinafter, the principles of preferred embodiments of the present invention will be described in detail with reference to the attached drawings and descriptions. However, the drawings and the descriptions given below are for preferred implementation methods among various methods for effectively explaining the features of the present invention, and the present invention is not limited to the drawings and descriptions below.

While terms such as first or second may be used to describe various components, these terms should be construed only for the purpose of distinguishing one component from another. For example, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component.

Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, the terms "comprises" or "has" and the like are intended to specify the presence of a described feature, number, step, operation, component, part, or combination thereof, but should be understood to not preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

When describing the present invention, the numerical range indicated by the term 'to' indicates a numerical range that includes the values described before and after the term as the lower limit and the upper limit, respectively. When multiple numerical values are disclosed as the upper and lower limits of an arbitrary numerical range, the numerical range disclosed in this specification can be understood as an arbitrary numerical range that uses any one of the multiple lower limit values and any one of the multiple upper limit values as the lower limit and the upper limit, respectively.

The present invention provides a slurry for forming an electrode protective film, which includes a conductive material; a metal-based material; and a pore former.

Previously, when lithium metal was used as a cathode, there was a problem in that lithium dendrites were generated during repeated charging and discharging processes, causing a short circuit in the battery, which lowered the safety of the battery.

In addition, lithium metal is a material that has high (electro)chemical reactivity with electrolytes, especially those containing carbonate-based organic solvents. As a result, as the driving cycle of a lithium metal battery progresses, a resistance layer is formed on the surface of the negative electrode due to a side reaction with the electrolyte, and the deposition/deposition of lithium ions on the surface of the negative electrode on which such a resistance layer is formed is uneven, and there is a problem that the battery capacity gradually decreases.

According to the present invention, by implementing an electrode protective film using a slurry for forming an electrode protective film including a conductive material; a metal-based material; and a pore former, the safety of the battery can be improved by suppressing the formation of lithium dendrites even when charge and discharge of the battery are repeated.

According to the present invention, by implementing an electrode protective film using a slurry for forming an electrode protective film including a conductive material; a metal-based material; and a pore former, it is possible to physically suppress the formation of lithium dendrites and prevent excessive reaction between an electrolyte and an anode, thereby generating a stable SEI film.

According to the present invention, by implementing an electrode protective film using a slurry for forming an electrode protective film including a conductive material; a metal-based material; and a pore former, the cycle performance of a secondary battery can be improved by helping the movement of lithium ions to proceed smoothly.

Below, the composition of the present invention is described in more detail.

1. Slurry for forming electrode protective film and method for manufacturing same

The slurry for forming an electrode protective film according to the present invention contains a conductive additive that helps the flow of electricity and electrons and improves the conductivity of the slurry for forming an electrode protective film.

Specifically, the challenge material may be any one selected from the group consisting of graphene, carbon nanotubes, and combinations thereof.

In one embodiment of the present invention, the length of the multi-walled carbon nanotube may be 20 nm to 2 μm, and the average diameter may be 20 nm to 30 nm.

In one embodiment of the present invention, the content of the conductive material may be 10 to 15 wt%, and specifically 15 to 15.4 wt%, based on the weight of the total solid content of the slurry for forming the electrode protective film.

When the content of the above-mentioned conductive agent satisfies the above-mentioned numerical range, the conductivity of the slurry for forming an electrode protective film can be sufficiently improved, and since the conductive agent does not form aggregates, coating of the slurry for forming an electrode protective film can be easily achieved.

The slurry for forming an electrode protective film according to the present invention includes a metal material that, when combined with the conductive material, improves the conductivity of the slurry for forming an electrode protective film and increases the tensile strength of the electrode protective film, thereby minimizing volume expansion of the electrode protective film during the charge/discharge process of a battery. If the slurry for forming an electrode protective film includes a conductive material but does not include a metal material, or includes a metal material but does not include a conductive material, a problem may occur in which the tensile strength of the electrode protective film cannot be sufficiently increased. Accordingly, volume expansion of the electrode protective film may occur during the charge/discharge process of the battery, which may deteriorate the structural stability of the electrode protective film.

According to one embodiment of the present invention, the electrical conductivity of the metal material may be 4.1 X 10 ⁷ S/m or more at 20°C, specifically, 5.00 X 10 ⁷ S/m or more. When the electrical conductivity of the metal material satisfies the above numerical range, the conductivity of the slurry for forming an electrode protective film can be sufficiently improved, and the tensile strength of the electrode protective film can be increased, thereby minimizing volume expansion of the electrode during the charge and discharge process of the battery. For example, the electrical conductivity of the metal material can be measured using a metal conductivity meter commercially available in the relevant technical field.

For example, the metal material may be any one selected from the group consisting of copper (Cu), silver (Ag), gold (Au), and combinations thereof, and specifically may be copper (Cu).

In one embodiment of the present invention, the content of the metal-based material may be 85 to 95 wt%, specifically 90 to 92 wt%, based on the weight of the total solid content of the slurry for forming the electrode protective film. When the content of the metal-based material satisfies the numerical range, the conductivity of the slurry for forming the electrode protective film can be sufficiently improved, and the tensile strength of the electrode protective film can be increased, thereby minimizing volume expansion of the electrode during the charge and discharge process of the battery.

The slurry for forming an electrode protective film according to the present invention has lithium-friendly properties and includes a pore former to induce the formation of pores in the electrode protective film and help smooth movement of lithium ions.

Specifically, the pore former may be any one selected from the group consisting of ZnO _, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, MnO ₂ , FeO, Co ₃ O ₄ , TiO ₂ and combinations thereof, and more specifically, may be ZnO due to its lithiophilic properties.

Specifically, the particle size (D ₅₀ ) of the pore-forming agent may be 50 to 250 nm, and more specifically, 20 to 200 nm. When the particle size of the pore-forming agent satisfies the numerical range, the viscosity of the slurry for forming an electrode protective film is implemented at an appropriate level, so that coating of the slurry for forming an electrode protective film can be easily achieved.

In one embodiment of the present invention, the content of the pore-forming agent may be 1 to 3 wt%, specifically 2 to 2.5 wt%, based on the weight of the total solid content of the slurry for forming the electrode protective film. When the content of the pore-forming agent satisfies the numerical range, it can effectively induce the formation of pores in the electrode protective film, thereby helping smooth movement of lithium ions.

The slurry for forming an electrode protective film according to the present invention may further include a binder to induce bonding between the conductive material, the metal-based material, and the pore-forming agent.

For example, a polymer commonly used in electrodes in the relevant technical field can be used as the binder. These binders include, but are not limited to, poly(vinylidene fluoride), poly(vinylidene fluoride co -hexafluoropropylene), poly(vinylidene fluoride- co -trichloroethylene), poly(methylmethacrylate), poly(ethylhexylacrylate), poly(butylacrylate), poly(acrylonitrile), poly(vinylpyrrolidone), poly(vinyl acetate), poly(ethylene-co-vinyl acetate), poly(ethylene oxide), It may be at least one selected from, but is not limited to, polyacrylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyano ethyl pullulan, cyano ethyl poly(vinylalcohol), cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

In one embodiment of the present invention, the content of the binder may be 5 to 20 wt%, specifically 8 to 15 wt%, and more specifically 9 to 12 wt%, based on the weight of the total solid content of the slurry for forming the electrode protective film. When the content of the binder satisfies the numerical range, the bonding between the conductive material, the metal-based material, and the pore-forming agent can be effectively induced, and the viscosity of the slurry for forming the electrode protective film can be maintained at an appropriate level.

Another embodiment of the present invention can provide a method for producing a slurry for forming an electrode protective film, including the steps of (S1) mixing a conductive material; a precursor including a metal-based material; and a pore former to produce a composite; and (S2) mixing the composite and a binder to produce a slurry for forming an electrode protective film.

Figure 1 is a flow chart of a method for manufacturing a slurry for forming an electrode protective film according to one embodiment of the present invention.

Figure 2 is a schematic diagram of a method for manufacturing a slurry for forming an electrode protective film according to one embodiment of the present invention.

The previously mentioned parts and repeated explanations are briefly explained or omitted.

Referring to FIGS. 1 and 2, the method for manufacturing a slurry for forming an electrode protective film according to the present invention may include a step of manufacturing a composite by first mixing (S1) a conductive material; a precursor including a metal-based material; and a pore former.

In the above step (S1), the precursor including the metal-based material may be a salt compound including a metal ion, and specifically, may be CuCl _2· 2H ₂ O(aq).

The above step (S1) can be performed using a commercially available stirrer in the relevant technical field, and specifically, can be a step performed at 500 to 2000 rpm for 10 to 40 hours using a stirrer.

For example, in the step (S1), the pore former may be a micronized pore former.

In one embodiment of the present invention, the weight ratio of the conductive material and the precursor including the metal-based material (conductive material: precursor including the metal-based material) may be 1:15 to 1:25, and specifically, 1:15 to 1:20.

In this case, the precursor including the metal-based material may be a salt compound, and the precursor including the metal-based material may be dissolved in distilled water to manufacture the complex in an aqueous solution state including metal ions. When the weight ratio of the conductive material and the precursor including the metal-based material satisfies the numerical range, the conductivity of the slurry for forming an electrode protective film can be further improved and the tensile strength of the electrode protective film can be increased, thereby further minimizing volume expansion of the electrode protective film during the charge/discharge process of the battery. If the slurry for forming an electrode protective film includes a conductive material but does not include a precursor including a metal-based material, or includes a precursor including a metal-based material but does not include a conductive material, a problem may occur in which the tensile strength of the electrode protective film cannot be sufficiently increased. Accordingly, volume expansion may occur during the charge/discharge process of the battery, which may deteriorate the structural stability of the electrode.

According to another embodiment of the present invention, the content of the pore former may be 1 to 5 wt% based on the total weight of the composite, and specifically 1 to 2 wt%. When the content of the pore former satisfies the numerical range based on the total weight of the composite, the formation of pores in the electrode protective film may be induced to help smooth movement of lithium ions.

The method for producing a slurry for forming an electrode protective film according to the present invention may include a step of producing a slurry for forming an electrode protective film by mixing the complex and a binder (S2) to induce binding between solid components.

According to one embodiment of the present invention, the weight ratio of the complex to the binder (composite:binder) may be 6:4 to 9:1, specifically 7:3 to 9:1, and more specifically 8:2 to 9:1. When the weight ratio of the complex to the binder satisfies the numerical range, binding can be effectively achieved between solid components included in the slurry for forming an electrode protective film, and the viscosity of the slurry for forming an electrode protective film can be maintained at an appropriate level, thereby ensuring ease of coating.

2. Electrode protection film

Another embodiment of the present invention can provide a dried electrode protective film formed by the slurry for forming an electrode protective film according to various embodiments of the present invention described above.

According to one embodiment of the present invention, the average size of the pores formed in the electrode protective film may be 10 to 20 nm. The pores formed in the electrode protective film can be analyzed through a SEM image of a cross-section obtained by cutting the electrode protective film vertically.

3. Negative electrode for secondary battery and its manufacturing method

A negative electrode for a secondary battery according to the present invention may include a negative electrode substrate; and an electrode protective film disposed on at least one surface of the negative electrode substrate.

Specifically, the negative electrode substrate may include lithium metal having a thickness of 5 to 300 μm. In the past, when lithium metal was used as the negative electrode, lithium dendrites were generated during repeated charge and discharge processes, which could cause a short circuit in the battery and there were safety issues.

In addition, lithium metal is a material that has high (electro)chemical reactivity with electrolytes, especially those containing carbonate-based organic solvents. As a result, as the driving cycle of a lithium metal battery progresses, a resistance layer is formed on the surface of the negative electrode due to a side reaction with the electrolyte, and the deposition/deposition of lithium ions on the surface of the negative electrode where such a resistance layer is formed is uneven, and there is a problem that the battery capacity gradually decreases.

According to one embodiment of the present invention, by forming an electrode protective film on at least one surface of lithium metal, the formation of lithium dendrites can be suppressed even when charging and discharging of the battery is repeated, thereby improving the safety of the battery.

According to one embodiment of the present invention, by forming an electrode protective film on at least one surface of lithium metal, the formation of lithium dendrites can be physically suppressed and direct reaction between the electrolyte and the negative electrode can be prevented, thereby generating a stable SEI film.

According to another embodiment of the present invention, by forming an electrode protective film on at least one surface of lithium metal, the movement of lithium ions can be facilitated, thereby improving the cycle performance of a secondary battery.

In one embodiment of the present invention, the thickness of the electrode protective film may be 5 to 20 μm. However, the technical idea of the present invention is not limited thereto and may be appropriately modified.

Another embodiment of the present invention can provide a method for manufacturing an anode for a secondary battery, including the step of coating a slurry for forming an electrode protective film according to the embodiment of the present invention described above on at least one surface of a cathode substrate and then drying it.

For example, the step of coating the slurry for forming the electrode protective film may be a step using at least one method selected from the group consisting of doctor blade coating, dip coating, gravure coating, slit die coating, spin coating, comma coating, bar coating, reverse roll coating, screen coating, and cap coating.

For example, the slurry for forming the coated electrode protective film can be dried at 40 to 80° C. for 10 to 40 hours. A vacuum oven commercially available in the art can be used to dry the slurry for forming the coated electrode protective film.

4. Secondary battery

Another embodiment of the present invention can provide a secondary battery including a negative electrode, a positive electrode for a secondary battery according to various embodiments of the present invention described above; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

anode

The positive electrode according to the present invention may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, a conductive material, and a positive electrode binder.

For example, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like. The positive electrode current collector may typically have a thickness of 6 to 20 μm.

For example, the positive electrode active material may include a lithium transition metal oxide. The above lithium transition metal oxides include, for example, Li _x1 CoO ₂ (0.5<x1<1.3), Li _x2 NiO ₂ (0.5<x2<1.3), Li _x3 MnO ₂ (0.5<x3<1.3), Li _x4 Mn ₂ O ₄ (0.5<x4<1.3), Li _x5 (Ni _a1 Co _b1 Mn _c1 )O ₂ (0.5<x5<1.3, 0<a1<1, 0<b1<1, 0<c1<1, a1+b1+c1=1), Li _x6 Ni _1-y1 Co _y1 O ₂ (0.5<x6<1.3, 0<y1<1), Li _x7 Co _1-y2 Mn _y2 O ₂ (0.5<x7<1.3, 0≤2<1), Li _x8 Ni _1-y3 Mn _y3 O ₂ (0.5<x8<1.3, O≤3<1), Li _x9 (Ni _a2 Co _b2 Mn _c2 )O ₄ (0.5<x9<1.3, 0<a2<2, 0<b2<2, 0<c2<2, a2+b2+c2=2), Li _x10 Mn _2-z1 Ni _z1 O ₄ (0.5<x10<1.3, 0<z1<2), Li _x11 Mn _2-z2 Co _z2 O ₄ (0.5<x11<1.3, 0<z2<2), Li _x12 CoPO ₄ (0.5<x12<1.3), and Li _x13 FePO ₄ (0.5<x13<1.3).

According to another embodiment of the present invention, the positive electrode may be lithium metal. When the positive electrode is lithium metal, a lithium symmetric cell may be implemented.

The conductive material used in the above positive electrode can improve conductivity between active material particles or with a metal current collector and prevent the binder from acting as an insulator. The conductive material may be, for example, a mixture of one or two or more conductive materials selected from the group consisting of graphite, carbon black, carbon fibers, metal fibers, metal powders, conductive whiskers, conductive metal oxides, activated carbon, and polyphenylene derivatives, and more specifically, may be a mixture of one or more conductive materials selected from the group consisting of natural graphite, artificial graphite, Super-p, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium oxide.

The above positive electrode binder is, for example, polyvinylidene fluoride , polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride- co -trichloroethylene, polymethylmethacrylate, polyethylhexylacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, It may be at least one selected from, but is not limited to, polyacrylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyano ethyl pullulan, cyano ethyl poly(vinylalcohol), cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose.

Membrane

The separation membrane according to the present invention may be a porous substrate or may include a coating layer on at least one surface of the porous substrate.

The porous substrate according to the present invention can be a porous structure having high resistance to electrolyte and fine pore diameters, capable of providing a path for lithium ions to move while electrically insulating the negative electrode and the positive electrode to prevent short circuits.

As a constituent material of the porous substrate, any organic or inorganic material having electrical insulation can be used without particular limitation. The porous substrate may include, for example, at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyvinyl terephthalate, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylene naphthalene, and may specifically include polyolefin. Polyolefin not only has excellent coatability, but also can increase the ratio of the electrode active material layer in the battery by making the separator thin, thereby increasing the capacity per volume. Specifically, the weight average molecular weight (M _w ) of the polyolefin can be 100,000 to 500,000 g/mol. If the weight average molecular weight of the polyolefin is less than the above numerical range, it may be difficult to secure sufficient mechanical properties, and if it exceeds the above numerical range, the shutdown function may not be implemented or molding may become difficult. The shutdown function refers to the function of blocking the movement of ions and preventing thermal runaway of the battery by melting the thermoplastic resin and closing the pores of the porous substrate when the temperature of the secondary battery increases.

The thickness of the porous substrate may be, for example, 3 to 50 μm or 4 to 15 μm. If the thickness of the porous substrate is less than the numerical range, the function of the conductive barrier may not be sufficient, and if it exceeds the numerical range, the resistance of the separator may excessively increase.

The average diameter of the pores included in the porous substrate may be, for example, 10 to 100 nm. The pores included in the porous substrate have a structure in which they are interconnected with each other, so that gas or liquid can pass from one side of the porous substrate to the other side.

The coating layer according to the present invention can improve the mechanical strength and heat resistance of a separator for a secondary battery, and increase the ion conductivity within the secondary battery.

The coating layer according to the present invention is disposed on one side of the porous substrate. Specifically, since the coating layer is disposed only on one side of the porous substrate, the amount of electrode active material can be increased by the thickness reduced compared to both sides, which can be advantageous for the energy density of the battery.

The packing density of the coating layer may be 0.1 to 20 g/cm ³ , specifically 0.5 to 12 g/cm ³ , and more specifically 1 to 3 g/cm ³ . When the packing density of the coating layer satisfies the numerical range, the permeability of lithium ions may be advantageous, and the heat resistance of the separator may be maintained at an appropriate level. Meanwhile, the packing density is the density of the coating layer loaded at a height of 1 μm per unit area (m ² ) of the porous substrate.

The thickness of the coating layer may be 0.1 to 10 μm, specifically 1 to 3 μm, and more specifically 1.4 to 1.6 μm. When the thickness of the coating layer satisfies the numerical range, the insulation and thermal stability of the separator can be increased, while improving the energy density of the battery.

The coating layer according to the present invention may include a binder polymer and inorganic particles.

The binder polymer according to the present invention can connect inorganic particles and stably fix them. The above binder polymers include, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, poly(ethylene-co-vinyl acetate), polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, One or more selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene butadiene copolymer, polyimide, and styrene-butadiene rubber may be used in combination.

According to another embodiment of the present invention, the weight ratio of the inorganic particles and the binder polymer (inorganic particles: binder polymer) may be 50:50 to 99:1, and specifically, 70:30 to 95:5. When the content ratio of the inorganic particles to the binder polymer is less than the above numerical range, the content of the binder polymer increases, which may deteriorate the thermal safety improvement performance of the separator, and the pore size and porosity may decrease due to a decrease in the empty space formed between the inorganic particles, which may cause a deterioration in the performance of the final battery, and when the numerical range is exceeded, the content of the binder polymer is too small, which may weaken the peeling resistance of the coating layer.

The inorganic particles according to the present invention can contribute to improving the mechanical strength and heat resistance of a separator for a secondary battery. Specifically, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and/or reduction reactions in the operating voltage range of the applied secondary battery (e.g., 0 to 5 V based on Li/Li ⁺ ).

For example, when using inorganic particles having a high dielectric constant as inorganic particles, it can contribute to increasing the degree of dissociation of electrolyte salt, such as lithium salt, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte. For the reasons described above, the inorganic particles may be inorganic particles having a dielectric constant of 5 or higher, inorganic particles having lithium ion transfer capability, or a mixture thereof.

The inorganic particles having a dielectric constant of 5 or higher are selected from the group consisting of Al ₂ O ₃ , SiO ₂ , ZrO ₂ , AlO(OH), Al(OH) ₃ , Mg(OH) ₂ , BaSO ₄ , TiO ₂ , BaTiO ₃ , Pb(Zr _x Ti _1-x )O ₃ (PZT, where 0 <x<1), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT, where 0 < x <1 and 0 < y <1), (1-x)Pb(Mg _1/3 Nb _2/3 )O _3-x PbTiO ₃ (PMN-PT, where 0 < x <1), HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO and SiC. It can be a selected type or a mixture of two or more types.

The inorganic particles having the lithium ion transport capability are lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li _x Al _y Ti _z (PO ₄ ) ₃ , 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) _x O _y series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li _x La _y TiO ₃ , 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , 0 < x < 4, 0 < y < 1, 0 < w < 5), and lithium nitride (Li _x The glass may be one or a mixture of two or more selected from the group consisting of N _y , 0 < x <4, 0 < y < 2), SiS ₂ series glass (Li _x Si _y S _z , 0 < x < 3, 0 < y < 2, 0 < z < 4), and P ₂ S ₅ series glass (Li _x P _y S _z , 0 < x < 3, 0 < y < 3, 0 < z < 7).

For example, the average particle diameter ( _D50 ) of the above-mentioned inorganic particles may be 1 nm to 10 μm, specifically 10 nm to 2 μm, and more specifically 50 nm to 1 μm, for forming a coating layer of uniform thickness and an appropriate porosity. The "average particle diameter (D50)" refers to the particle diameter at the 50% point of the cumulative distribution of the number of particles according to particle diameter. The average particle diameter can be measured using a laser diffraction method. Specifically, after the target powder is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction pattern according to particle size is measured when the particles pass through a laser beam, thereby calculating the particle size distribution.

Electrolyte

The electrolyte according to the present invention may include a solvent and a lithium salt.

The solvent according to the present invention may be, for example, one or a mixture of two or more selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dioxolane (DOL), dimethoxyethane (DME), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate, and butyl propionate.

The lithium salt according to the present invention may include anions such as, for example, NO ^3- , F ^- , Cl ^- , Br ^- , I ^- , PF ₆ ^{- ,} and specifically, may include LiTFSI (lithium bis-trifluoromethanesulfonimide) and LiNO _3, LiPF ₆ , and the like.

The secondary battery according to the present invention may be a cylindrical, square, or pouch-shaped secondary battery, but is not particularly limited as long as it corresponds to a charging/discharging device.

Another embodiment of the present invention can provide a battery module including the secondary battery as a unit cell and a battery pack including the same. The battery pack can be used as a power source for one or more medium- to large-sized devices selected from the group consisting of, for example, a power tool; an electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

Hereinafter, embodiments of the present invention will be described in detail so that a person having ordinary skill in the art to which the present invention pertains can easily implement the present invention, but this is only an example, and the scope of the rights of the present invention is not limited by the following contents.

[Manufacturing Example 1: Manufacturing of slurry for forming electrode protective film]

<Preparation Example 1: Preparation of MWCNT-Cu-ZnO slurry>

Steps for manufacturing a complex

0.2 g of multi-walled carbon nanotubes having an average diameter of 20 nm and an average length of 2 μm and 3 g of CuCl _2· 2H ₂ O(aq) dissolved in 300 mL of distilled water were mixed and stirred for 24 hours. The stirred resultant was then finely divided into particles (D ₅₀ ) of 1 μm, resulting in ZnO. After adding 0.064 g, mixing was performed to prepare 0.09 g of the complex (CCZ).

Steps for preparing slurry

A slurry according to Preparation Example 1 was prepared by adding a mixture of 0.09 g of the above-mentioned manufactured complex and poly(vinylidene fluoride -co-hexafluoropropylene; PVDF-HFP) in a weight ratio of 9:1 to 0.49 g of dimethyl formamide (DMF).

<Comparative Preparation Example 1: Preparation of MWCNT slurry> A slurry was prepared in the same manner as in Implementation Preparation Example 1, except that a solution containing 3 g of CuCl ₂ 2H ₂ O (aq) dissolved in 300 mL of distilled water was used and micronized ZnO was not used.

<Comparative Preparation Example 2: Preparation of MWCNT-Cu Slurry>

A slurry was prepared in the same manner as in Preparation Example 1, except that micronized ZnO was not used.

Unit (g) MWCNT MWCNT-Cu Composite MWCNT-Cu-Zinc Oxide Composite PVDF-HFP DMF Implementation Preparation Example 1 - - 0.09 0.01 0.49 Comparison Preparation Example 1 0.09 - - 0.01 1.09 Comparison Preparation Example 2 - 0.09 - 0.01 0.39

[Manufacturing Example 2: Manufacturing of a negative electrode for a secondary battery]

<Example 1: Cathode prepared from MWCNT-Cu-ZnO slurry>

The slurry for forming an electrode protective film of the above Preparation Example 1 was applied onto lithium metal having a thickness of 5 μm using a doctor blade, and then dried in a vacuum oven at 45°C for 24 hours to manufacture a negative electrode. The above process was all performed in a dry room.

<Comparative Example 1: Negative electrode made of lithium metal (Li metal)>

Lithium metal (Li metal) with a thickness of 5 μm and without an electrode protective film was prepared.

<Comparative Example 2: Cathode manufactured with MWCNT slurry>

A negative electrode was manufactured in the same manner as in Example 1, but the slurry for forming an electrode protective film of Comparative Preparation Example 1 was used instead of the slurry for forming an electrode protective film of Preparation Example 1.

<Comparative Example 3: Cathode manufactured with MWCNT-Cu slurry>

A cathode was manufactured in the same manner as in Example 1, but instead of the slurry for forming an electrode protective film of Preparation Example 1, the slurry for forming an electrode protective film of Comparative Preparation Example 2 was used.

[Experimental Example 1: SEM image of the cathode]

Fig. 3a is an SEM image of a cathode according to Example 1. Fig. 3b is an SEM image of a cathode according to Comparative Example 2. Fig. 3c is an SEM image of a cathode according to Comparative Example 3.

Referring to FIGS. 3a to 3c, it can be confirmed that the cathode according to Example 1 has pores formed compared to the cathodes according to Comparative Examples 2 and 3 by including ZnO, which is a pore former.

Fig. 4a is an SEM photograph of a vertical cross-section of a cathode according to Example 1. Fig. 4b is an SEM photograph of a vertical cross-section of a cathode according to Comparative Example 2. Fig. 4c is an SEM photograph of a vertical cross-section of a cathode according to Comparative Example 3.

Referring to FIGS. 4a to 4c, it can be confirmed that the cathodes according to Example 1 and Comparative Examples 2 and 3 have an electrode protective film uniformly coated on their surfaces.

[Experimental Example 2: Evaluation of electrochemical characteristics of secondary batteries]

Each of the electrodes of Example 1 and Comparative Examples 1 to 3 manufactured above was punched into two pieces with a diameter of 16 mm, and a polyethylene separator (thickness: 20 μm) was interposed therebetween to manufacture an electrode assembly. An electrolyte solution in which 1 M LiTFSI (lithium bis-trifluoromethanesulfonimide) salt was dissolved in a mixed solvent of DOL (dioxolane) and DME (dimethoxyethane) in a 1:1 volume ratio (v/v) and 2 wt% LiNO ₃ was added was injected into the electrode assembly to manufacture a lithium symmetric cell.

The voltage according to the cycle was measured in the lithium symmetric battery according to Example 1 and Comparative Examples 1 to 3. The electrochemical evaluation conditions were that a cycle test was conducted up to a capacity of 1 mAh cm ^-2 at a current density of 0.5 mA cm ^-2 .

Figure 5 is a graph showing voltage change over time of the batteries according to Example 1 and Comparative Examples 1 to 3.

Comparing Comparative Examples 1 to 3 with Example 1 in terms of the composition of the electrode passivation film, it can be confirmed that the electrode of Example 1 including an electrode passivation film including a conductive material, a metal-based material, and a pore-forming agent exhibits stable charge/discharge even as the number of cycles increases, compared to the electrode of Comparative Example 1 in which no electrode passivation film is formed, the electrode of Comparative Example 2 including an electrode passivation film not including a metal-based material and a pore-forming agent, and the electrode of Comparative Example 3 including an electrode passivation film not including a pore-forming agent. It can be inferred that this is because the electrode passivation film according to Example 1 contributes to forming a stable SEI film and simultaneously prevents the growth of lithium dendrites.

[Experimental Example 3: Evaluation of electrochemical characteristics of secondary batteries]

Lithium symmetric cells according to Example 1 and Comparative Examples 1 to 3 were manufactured in the same manner as in Experimental Example 2, except that 1 M LiPF ₆ salt was dissolved in a mixed solvent containing EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 1:1 and an electrolyte solution containing 5 vol% FEC (fluoroethylene carbonate) was injected.

The voltage of the lithium symmetric batteries of Example 1 and Comparative Examples 1 to 3 was measured.

The electrochemical evaluation conditions were as follows: 0.1 mA/cm ² (5 cycles) → 0.5 mA/cm ² (5 cycles) → 1 mA/cm ² ( ⁵ cycles) → 3 mA/cm ² (5 cycles) → 5 mA/cm ² (5 cycles) → 0.5 mA/cm ² (5 cycles) up to a capacity of 1 mAh cm -2.

Figure 6 is a graph of voltage over time of the batteries according to Example 1 and Comparative Examples 1 to 3.

Comparing Comparative Examples 1 to 3 with Example 1 in terms of the composition of the electrode passivation film, it can be confirmed that the electrode of Example 1 including an electrode passivation film including a conductive material, a metal-based material, and a pore-forming agent has very low voltage hysteresis compared to the electrode of Comparative Example 1 in which no electrode passivation film is formed, the electrode of Comparative Example 2 including an electrode passivation film not including a metal-based material and a pore-forming agent, and the electrode of Comparative Example 3 including an electrode passivation film not including a pore-forming agent. In other words, this means that the resistance within the battery of Example 1 is relatively low.

Example 1 shows that the resistance is low even at high current densities, and thus the battery can be operated stably even at high current densities. This suggests that the insertion and de-insertion of lithium ions occur at a fast rate due to the formation of a stable SEI film and low resistance.

[Experimental Example 4: Evaluation of the life performance of secondary batteries according to cycles]

A cathode was manufactured using NCM811 (Ni:Co:Mn = 8:1:1) as a cathode active material. Specifically, a mixture of NCM811:conductive material (Super-P): PVDF in a weight ratio of 96.5:1.5:2 was added to N-methylpyrrolidone (NMP) to manufacture a cathode slurry. The cathode slurry (loading amount: 16.9 mg/cm ² ) was coated on a 12 μm thick aluminum foil, and then dried (overnight) at 110° C. to manufacture a 76 μm thick cathode. The cathode, a polyethylene separator (thickness: 20 μm), and the anode manufactured by the methods according to each of Example 1 and Comparative Example 1 were sequentially stacked and then lamination was performed to manufacture an electrode assembly. The electrode assembly was loaded into a coin cell case, and an electrolyte was injected to manufacture a coin cell. In this case, an electrolyte was used in which 1 M LiTFSI (lithium bis-trifluoromethanesulfonimide) salt was dissolved in a mixed solvent of DOL (dioxolane) and DME (dimethoxyethane) in a 1:1 volume ratio (v/v) and 0.2 M LiNO ₃ (75 ㎕) was added.

The cycleability evaluation was performed using the coin cell manufactured above. The cycleability evaluation conditions were charging/discharging at a rate of 2.0C in a voltage range of 3 V to 4.2 V, and the results are shown in Fig. 7. Unlike Example 1, it can be confirmed that the battery of Comparative Example 1 was severely deteriorated at 40 cycles.

[Experimental Example 5: Evaluation of Electrochemical Impedance Characteristics of Secondary Battery ]

A lithium symmetric cell was manufactured in the same manner as in Experimental Example 2 above.

Figure 8 is a graph showing the electrochemical impedance measured by electrochemical impedance spectroscopy for the lithium symmetric batteries of Example 1 and Comparative Examples 1 to 3. The electrochemical evaluation conditions were as follows: one cycle was performed at a current density of 0.5 mA cm ^-2 up to a capacity of 1 mAh cm ^-2 , and then impedance measurement (Fi = 200000 Hz, Ff = 0.1 Hz) by electrochemical impedance spectroscopy was performed.

Comparing Comparative Examples 1 to 3 with Example 1 in terms of the composition of the electrode passivation film, it can be confirmed that the electrode of Example 1 including an electrode passivation film including a conductive material, a metal-based material, and a pore-forming agent has significantly lower resistance than the electrode of Comparative Example 1 in which an electrode passivation film is not formed, the electrode of Comparative Example 2 including an electrode passivation film not including a metal-based material and a pore-forming agent, and the electrode of Comparative Example 3 including an electrode passivation film not including a pore-forming agent. This confirms that the electrode passivation film of Example 1 functions as a passivation film and not a resistive layer, and it can be inferred that pores are created due to the addition of a lithium-friendly pore-forming agent (e.g., ZnO) to facilitate the movement of lithium ions.

[Experimental Example 6: SEM image of electrode after cycle test]

Fig. 9a is an SEM image of the electrode according to Example 1 after the cycle test of Experimental Example 4. Fig. 9b is an SEM image of the electrode according to Comparative Example 1 after the cycle test of Experimental Example 4. Fig. 9c is an SEM image of the electrode according to Comparative Example 2 after the cycle test of Experimental Example 4. Fig. 9d is an SEM image of the electrode according to Comparative Example 3 after the cycle test of Experimental Example 4.

Fig. 10a is an SEM image taken vertically through the electrode of Fig. 9a. Fig. 10b is an SEM image taken vertically through the electrode of Fig. 9b. Fig. 10c is an SEM image taken vertically through the electrode of Fig. 9c. Fig. 10d is an SEM image taken vertically through the electrode of Fig. 9d.

Referring to FIGS. 9A to 9D and 10A to 10D, it can be confirmed that the electrode protective film of Example 1 physically suppresses lithium ion dendrites accumulating on the surface of the lithium metal, and at the same time, the electrode protective film remains structurally stable on the surface of the lithium metal even after the cycle test.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention.

Claims (20)

Conductive additive;
Metallic materials; and
Containing a pore former;
Slurry for forming an electrode protective film.
In the first paragraph,
The above challenge is,
Any one selected from the group consisting of graphene, carbon nanotubes, and combinations thereof,
Slurry for forming an electrode protective film.
In the second paragraph,
The above carbon nanotubes
Any one selected from the group consisting of single-walled carbon nanotubes, multi-walled carbon nanotubes, and combinations thereof,
Slurry for forming an electrode protective film.
In the first paragraph,
The electrical conductivity of the above metal material is 4.1 X 10 ⁷ S/m or more at 20℃.
Slurry for forming an electrode protective film.
In paragraph 4,
The electrical conductivity of the above metal material is 5.00 X 10 ⁷ S/m or more at 20℃.
Slurry for forming an electrode protective film.
In the first paragraph,
The above metal material is,
Any one selected from the group consisting of copper (Cu), silver (Ag), gold (Au) and combinations thereof.
Slurry for forming an electrode protective film.
In the first paragraph,
The above pore forming agent is,
Any one selected from the group consisting of ZnO _{, Al2O3} , _SiO2 , _ZrO2 , _SnO2 , _CeO2 , _MgO , _NiO , CaO, _MnO2 , FeO, _Co3O4 , _TiO2 and combinations thereof,
Slurry for forming an electrode protective film.
In the first paragraph,
Binder; including more
Slurry for forming an electrode protective film.
(S1) a step of manufacturing a composite by mixing a precursor including a metal-based material; and a pore former; and
(S2) a step of preparing a slurry for forming an electrode protective film by mixing the above complex and a binder; including;
A method for producing a slurry for forming an electrode protective film.
In Article 9,
The weight ratio of the precursor including the above-mentioned conductive material and the above-mentioned metal-based material (conductive material: precursor including the metal-based material) is 1:15 to 1:20.
A method for producing a slurry for forming an electrode protective film.
In Article 9,
The weight ratio of the above complex and the above binder (composite:binder) is 6:4 to 9:1.
A method for producing a slurry for forming an electrode protective film.
In Article 9,
The content of the above pore forming agent is 1 to 5 wt% based on the total weight of the above complex.
A method for producing a slurry for forming an electrode protective film.
An electrode protective film, wherein the slurry for forming an electrode protective film according to any one of claims 1 to 8 is dried.
cathode substrate; and
An electrode protective film according to claim 13, disposed on at least one surface of the cathode substrate;
Cathode for secondary batteries.
In Article 14,
The above negative electrode material contains lithium metal (Li metal).
Cathode for secondary batteries.
In Article 14,
The thickness of the above electrode protective film is 5 to 20㎛.
Cathode for secondary batteries.
A step of coating a slurry for forming an electrode protective film according to any one of claims 1 to 8 on at least one surface of a cathode substrate and then drying it;
Method for manufacturing a negative electrode for a secondary battery.
In Article 17,
The step of coating the slurry for forming the above electrode protective film is:
A step of using at least one method selected from the group consisting of doctor blade coating, dip coating, gravure coating, slit die coating, spin coating, comma coating, bar coating, reverse roll coating, screen coating, and cap coating.
Method for manufacturing a negative electrode for a secondary battery.
In Article 17,
The slurry for forming the above-mentioned coated electrode protective film is dried at 40 to 80°C for 10 to 40 hours.
Method for manufacturing a negative electrode for a secondary battery.
A negative electrode for a secondary battery according to any one of claims 14 to 16;
anode;
A separator interposed between the cathode and the anode; and
containing electrolyte;
Secondary battery.