Negative electrode slurry manufacturing method and apparatus, negative electrode slurry, negative electrode, and lithium secondary battery

Abstract

This application relates to a method for producing a negative electrode slurry, which includes the steps of: mixing a negative electrode active material, a conductive material, a (meth)acrylic binder, and a first solvent to obtain a mixture; measuring the initial pH of the mixture; if the initial pH of the mixture is outside the target pH range, adjusting the content of a second solvent containing a pH adjuster so that the initial pH falls within the target pH range; and obtaining a mixture within the target pH range. This prevents hydrogen gas generation and reduces the risk of explosion without damaging the components of the negative electrode slurry.

Description

[Technical Field]

[0001] The present application relates to a method and apparatus for producing a negative electrode slurry, a negative electrode slurry, a negative electrode, and a lithium secondary battery. CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0118844, filed with the Korean Intellectual Property Office on September 7, 2023, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields in this area is power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] With technological development and increasing demand for mobile devices, demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, research into methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries is actively underway.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. The negative electrode active material may be silicon-based particles with a high discharge capacity.

[0007] In particular, with the recent demand for high-density energy batteries, active research has been conducted into methods for increasing capacity by using silicon-based compounds such as Si / C and SiOx, which have a capacity 10 times greater than that of graphite-based materials, as negative electrode active materials. While silicon-based compounds, which are high-capacity materials, have the advantage of having a larger capacity than conventionally used graphite, they can generate hydrogen gas due to surface oxidation reactions during the production and storage of electrode compositions or slurries containing silicon-based compounds, which can lead to problems such as the risk of explosion and reduced phase stability.

[0008] Therefore, research is needed into the production of anodes containing silicon-based compounds while maintaining the physical properties expected of the battery components, so that the above-mentioned problems can be improved. Summary of the Invention [Problem to be solved by the invention]

[0009] In order to solve the above-mentioned problems, the present application aims to provide a method and apparatus for producing an anode slurry in which the contents of the components of the anode slurry (particularly, a second solvent containing a pH adjuster) are adjusted so that the hydrogen ion concentration (pH) is controlled, as well as an anode slurry, an anode, and a lithium secondary battery. [Means for solving the problem]

[0010] One embodiment of the present specification provides a method for producing a negative electrode slurry, including: mixing a negative electrode active material, a conductive material, a (meth)acrylic binder, and a first solvent to obtain a mixture; measuring an initial pH of the mixture; if the measured initial pH of the mixture is outside a target pH range of pH 5 to pH 7.5, adjusting the content of a second solvent containing a pH adjuster so that the initial pH falls within the target pH range, and mixing the mixture; and obtaining a negative electrode slurry that falls within the target pH range.

[0011] Another embodiment provides an apparatus for producing a negative electrode slurry, including: a supply member that supplies a negative electrode active material, a conductive material, a (meth)acrylic binder, and a first solvent; a mixing member that mixes the negative electrode active material, the conductive material, the (meth)acrylic binder, and the first solvent to obtain a mixture; a measuring member that measures the initial pH of the mixture; a calculating member that determines whether the initial pH falls within a target pH range of pH 5 or more and pH 7.5 or less; a control member that, if the initial pH does not fall within the target pH range, adjusts the content of a second solvent containing a pH adjuster and mixes the second solvent so that the initial pH falls within the target pH range; and a discharge member that discharges the negative electrode slurry that falls within the target pH range.

[0012] In another embodiment, there is provided an anode slurry produced according to the above-described method for producing an anode slurry.

[0013] In another embodiment, a negative electrode includes a negative electrode current collector layer; and a negative electrode active material layer formed by applying the negative electrode slurry to one or both surfaces of the negative electrode current collector layer.

[0014] Finally, there is provided a lithium secondary battery comprising: a first electrode; a second electrode; a separator disposed between the first electrode and the second electrode; and an electrolyte, wherein either the first electrode or the second electrode is the negative electrode. [Effects of the Invention]

[0015] According to one embodiment of the present invention, a method and apparatus for producing an anode slurry, an anode slurry, an anode, and a lithium secondary battery are characterized in that the content of components of the anode slurry (particularly, a solvent containing a pH adjuster) is controlled to fall within a target pH range, and this not only prevents the generation of hydrogen gas due to a surface oxidation reaction during production or storage of the anode slurry, but also effectively maintains the physical properties expected of the components of the anode slurry.

[0016] Furthermore, the negative electrode slurry according to an embodiment of the present invention prevents the generation of hydrogen gas, thereby further ensuring the stability and safety of future processes. [Brief explanation of the drawings]

[0017] [Figure 1] (a) on the left is a photograph of the negative electrode slurry prepared according to an embodiment of the present invention (Example 1) after being left in a constant temperature chamber at 60°C for 24 hours, and (b) on the right is a photograph of the negative electrode slurry (Comparative Example 1) taken under the same conditions. [Figure 2] 1 is a schematic diagram of an apparatus for producing a negative electrode slurry according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Before describing the present invention, some terms will first be defined.

[0019] In this specification, when a part is said to "comprise" a certain component, this does not mean that it may further include other components, unless specifically stated to the contrary, but rather that it does not exclude other components.

[0020] In this specification, "p to q" means the range "not less than p and not more than q", including p and q.

[0021] As used herein, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. As used herein, when a polymer contains a monomer, this is interpreted as the same as saying that the polymer contains the monomer as a monomer unit.

[0022] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless specifically referred to as a "homopolymer."

[0023] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) of various degrees of polymerization as standard substances for molecular weight measurement. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0024] Although the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the disclosed embodiments, and that the invention may be embodied in various different forms, as defined by the appended claims.

[0025] <Method for producing negative electrode slurry> A method for producing a negative electrode slurry according to one embodiment of the present specification is characterized in that, when the initial pH of a mixture of a negative electrode active material, a conductive material, a (meth)acrylic binder, and a first solvent (not including a pH adjuster) does not fall within a target pH range, a second solvent is added and mixed to adjust the content, thereby achieving the target pH.

[0026] The method for producing a negative electrode slurry according to the above embodiment can reduce the amount of hydrogen gas generated by a surface oxidation reaction during the production and storage of the negative electrode slurry, without impairing the physical properties expected from the negative electrode active material, the conductive material, the (meth)acrylic binder, and the first solvent itself, by adjusting the content of the solvent including the pH adjuster, thereby ultimately ensuring the stability of the battery.

[0027] The target pH range may refer to a threshold for minimizing hydrogen gas generation so that hydrogen gas generated during the surface oxidation reaction does not directly or indirectly affect explosion during the manufacturing process of the negative electrode slurry and / or during storage for about 2 to 3 days immediately after manufacturing. Although this may vary depending on the type and content of the solvent and pH adjuster contained in the negative electrode slurry, the upper and lower limits are within the target pH range.

[0028] In one embodiment of the present specification, the negative electrode active material may include a silicon-based active material.

[0029] In this specification, the silicon-based active material has a capacity 10 times or more higher than that of the carbon-based active material. Therefore, when the silicon-based active material is applied to an electrode, particularly an anode, it is possible to realize an electrode having a higher level of energy density even with a thinner thickness than when the electrode contains only a carbon-based active material.

[0030] In one embodiment of the present specification, the negative electrode active material may further include a carbon-based active material in addition to a silicon-based active material.

[0031] According to the embodiment, the negative electrode active material is made of a mixture of a silicon-based active material and a carbon-based active material, and the degree of volume expansion of the active material can be further controlled.

[0032] In one embodiment of the present specification, when the negative electrode active material is made of a silicon-based active material and a carbon-based active material, the composition ratio between the silicon-based active material and the carbon-based active material may be within a range of 2:98 to 30:70.

[0033] According to the above embodiment, since the negative electrode active material is mainly composed of a carbon-based active material rather than a silicon-based active material, the volume expansion of the active material during charging and discharging is small, which can further provide the effect of reducing swelling and improving the conductive connectivity of the electrode.

[0034] In one embodiment of the present specification, the content of the negative electrode active material may be 60 parts by weight or more and 96 parts by weight or less, based on 100 parts by weight in total of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

[0035] In another embodiment, the content of the negative electrode active material is 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, or 96 parts by weight or less, preferably 90 parts by weight or less, based on 100 parts by weight in total of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

[0036] When the range of the negative electrode active material is satisfied, excellent output characteristics in charging and discharging can be guaranteed without degrading the performance of the negative electrode in the subsequent charge-discharge process.

[0037] In one embodiment of the present specification, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), and Si / C composite materials.

[0038] In the present specification, the silicon-based active material may exist in, for example, a crystalline or amorphous form. Specifically, the silicon particles of the silicon-based active material may preferably be spherical particles, but are not limited thereto.

[0039] In the present specification, in the case of SiOx, SiO2 where x is 2 is not included. Since this SiO2 does not react with lithium ions, it cannot store lithium. Therefore, x is preferably within the range of the above embodiment.

[0040] In the present specification, the silicon-based active material may be Si / C or Si composed of a composite of Si and C.

[0041] In the present specification, two or more kinds of the silicon-based active material may be mixed and used.

[0042] In one embodiment of the present specification, the carbon-based active material may include one or more selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0043] In this specification, the conductive material may be referred to as a negative electrode conductive material.

[0044] In this specification, the negative electrode conductive material is applied to the negative electrode and has a completely different structure from the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material serves to secure the contact point between the silicon-based active materials, which undergo a large volume expansion of the electrode upon charging and discharging, whereas the positive electrode conductive material serves to provide a buffer during rolling and also to impart some conductivity. Thus, the negative electrode conductive material and the positive electrode conductive material have different structures and roles.

[0045] In one embodiment of the present specification, the content of the conductive material may be 0.01 parts by weight or more and 40 parts by weight or less, based on 100 parts by weight in total of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

[0046] In another embodiment, the content of the conductive material may be 0.01 parts by weight or more, preferably 0.03 parts by weight or more, and more preferably 0.5 parts by weight or more, or 40 parts by weight or less, preferably 30 parts by weight or less, and more preferably 25 parts by weight or less, based on 100 parts by weight in total of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

[0047] In one embodiment of the present specification, the conductive material may include one or more selected from the group consisting of a dot-like conductive material, a planar conductive material, and a linear conductive material.

[0048] In one embodiment of the present specification, the conductive material may include dot-shaped conductive material and linear conductive material.

[0049] In this specification, the dot-like conductive material refers to a dot-like or spherical conductive material that can be used to improve the conductivity of a negative electrode and has conductivity without undergoing chemical changes. Specifically, the dot-like conductive material is at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives. Preferably, the dot-like conductive material may include carbon black and / or artificial graphite, which can achieve high conductivity and have excellent dispersibility.

[0050] In this specification, the planar conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode, and at the same time, can prevent the conductive path from being broken due to volume expansion. The planar conductive material may be referred to as a plate-type conductive material or a bulk-type conductive material. Examples of the planar conductive material may include at least one selected from the group consisting of plate-type graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-type graphite.

[0051] In this specification, the linear conductive material may be a carbon nanotube. The carbon nanotube may be a bundle-type carbon nanotube. The bundle-type carbon nanotube may include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a bundle- or rope-like secondary shape in which a plurality of carbon nanotube monomers are arranged side by side or entangled with the longitudinal axes of the carbon nanotube monomers in substantially the same orientation. The carbon nanotube units have graphite sheets in the form of cylinders with nano-sized diameters, and sp 2The bundled carbon nanotubes have a bonding structure. Depending on the angle and structure of the graphite plane wrapping, they can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be dispersed more uniformly during the manufacture of the anode, smoothly forming a conductive network within the anode, thereby improving the conductivity of the anode.

[0052] In this specification, the (meth)acrylic binder may refer to a water-based binder.

[0053] In one embodiment of the present specification, the content of the (meth)acrylic binder may be 2 parts by weight or more and 30 parts by weight or less, based on 100 parts by weight in total of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

[0054] In this specification, the negative electrode active material, the conductive material, and the (meth)acrylic binder can be referred to as a negative electrode composition.

[0055] In another embodiment, the content of the (meth)acrylic binder may be 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, or 2 parts by weight or more, preferably 5 parts by weight or more, and more preferably 10 parts by weight or more, based on 100 parts by weight in total of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

[0056] In one embodiment of the present specification, the weight average molecular weight of the (meth)acrylic binder may be 100,000 g / mol or more and 1,500,000 g / mol or less.

[0057] When the weight-average molecular weight of the (meth)acrylic binder satisfies the above range, the binder exhibits excellent mechanical strength, high intermolecular interaction, and excellent electrode binding strength. Furthermore, when the weight-average molecular weight satisfies the above range, the viscosity of the (meth)acrylic binder can be selected within an appropriate range, and when a negative electrode is manufactured using the binder, the coating properties of the electrode can be further improved.

[0058] In one embodiment of the present specification, the (meth)acrylic binder may be a polymer containing one or more monomers selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylonitrile, and poly(meth)acrylamide.

[0059] The polymer may be a homopolymer consisting of one type of monomer as a repeating unit, or a copolymer consisting of two or more different types of monomers as a repeating unit.

[0060] In the present specification, a polymerization initiator is used to prepare the (meth)acrylic binder, and an example of the polymerization initiator may be ammonium persulfate, but is not limited thereto.

[0061] In this specification, the (meth)acrylic binder containing a plurality of compounds having a specific ratio (expressed in parts by weight or weight ratio) may mean that each compound (e.g., (meth)acrylamide, (meth)acrylic acid, (meth)acrylonitrile) is contained as a monomer of the (meth)acrylic binder polymer.

[0062] In this specification, the (meth)acrylic binder contains a plurality of compounds as monomers, and the monomer with the highest content is regarded as the representative and can be named a "monomer" compound.

[0063] As used herein, "(meth)acrylic..." can mean methacryl and / or (meth)acrylic.

[0064] In this specification, when the (meth)acrylic binder is a copolymer containing two or more types of monomers as repeating units, the ratio of each monomer is not particularly limited as long as it belongs to the (meth)acrylic binder.

[0065] In this specification, the copolymer may be a random copolymer, a graft copolymer, a block copolymer, or the like, but is not particularly limited.

[0066] In some cases, controlling the viscosity of the electrode slurry within an appropriate range by appropriately adjusting the average particle size (D50) of the silicon-based active material or the specific surface area of ​​the particles can improve the dispersion of the components of the negative electrode slurry (e.g., conductive material, (meth)acrylic binder, silicon-based active material, carbon-based active material, etc.), thereby improving the contact area between the components, maintaining the conductive network, increasing capacity retention, and preventing non-uniform current density during charging and discharging.

[0067] In some cases, the viscosity of the negative electrode slurry may be adjusted to be 2,000 cPs or more and 50,000 cPs or less.

[0068] When the negative electrode slurry satisfies the above viscosity range, it has excellent storage stability, and when the negative electrode slurry is subsequently coated on one or both sides of a negative electrode current collector layer, the coating properties can be further improved.

[0069] <Negative electrode slurry manufacturing equipment> According to FIG. 2 , the negative electrode slurry manufacturing apparatus 1 according to one embodiment of the present specification includes the supply member 100, the mixing member 105, the measuring member 106, the calculating member 107, the control member 108, and the discharge member 109, and is characterized in that the calculating member determines whether the initial pH is within a target pH range (pH 5 or more and pH 7.5 or less), and if the initial pH does not fall within the target pH range, the control member adjusts the content of the second solvent (including a pH adjuster).

[0070] One embodiment of the present specification may further include a monitoring member that can confirm in real time whether or not the pH falls within the target pH range.

[0071] One embodiment of the present specification may further include a component that stores the difference between the initial pH measured according to the type and content of the solvent and pH and the target pH range, stores the results of subsequent addition and mixing via the control component accordingly, and, when applied to a subsequent step, performs machine learning to eliminate or reduce the difference between the initial pH and the target pH range from the supply component.

[0072] In this specification, the supply member refers to a supply member known in the art, and is not particularly limited, as long as it supplies the objects to be supplied (e.g., negative electrode active material 101, conductive material 102, (meth)acrylic binder 103, and first solvent 104) to the desired locations with the desired contents without loss.

[0073] In this specification, the mixing material refers to any mixing material known in the art, as long as the materials to be mixed (negative electrode active material, conductive material, (meth)acrylic binder, and first solvent) are mixed uniformly, and is not particularly limited.

[0074] In this specification, the measuring member refers to any measuring member known in the art, and is not particularly limited, as long as it can accurately measure the pH of the measurement target (a (homogeneous) mixture of a negative electrode active material, a conductive material, a (meth)acrylic binder, and a first solvent).

[0075] In this specification, the calculation element refers to any calculation element known in the art, as long as it can calculate the object of calculation (the difference between the initial pH of the mixture and the target pH region), and is not particularly limited.

[0076] In this specification, the control element refers to any control element known in the art, as long as it precisely controls the controlled object (second solvent), and is not particularly limited.

[0077] In this specification, the discharge member refers to any discharge member known in the art as long as it can discharge the object to be discharged (a mixture or negative electrode slurry falling within a target pH range), and is not particularly limited.

[0078] In one embodiment of the present invention, the target pH range may be pH 5 or higher and pH 7.5 or lower.

[0079] In this specification, the above-mentioned contents can be applied to the negative electrode slurry, the negative electrode active material, the conductive material, the (meth)acrylic binder, the solvent, and the target pH range.

[0080] <Negative electrode slurry> Another embodiment of the present invention provides an anode slurry prepared according to the above method for preparing an anode slurry.

[0081] The negative electrode slurry according to the present invention can be produced by the above-described method for producing a negative electrode slurry. Therefore, the negative electrode slurry obtained by the method can be directly applied to the negative electrode slurry.

[0082] <Negative electrode> Another embodiment of the present invention provides a negative electrode including a negative electrode current collector layer; and a negative electrode active material layer formed by coating one or both surfaces of the negative electrode current collector layer with the above-described negative electrode slurry.

[0083] The negative electrode according to this embodiment uses the above-described negative electrode slurry as is, and therefore, the above-described content regarding the negative electrode slurry can be applied as is.

[0084] In this specification, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc., can be used. Furthermore, the surface can be provided with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0085] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

[0086] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0087] <Lithium secondary battery> In one embodiment of the present invention, there is provided a lithium secondary battery including: a first electrode; a second electrode; a separator disposed between the first electrode and the second electrode; and an electrolyte, wherein either the first electrode or the second electrode is the aforementioned negative electrode.

[0088] The lithium secondary battery according to the above embodiment includes the negative electrode as is, and therefore, the content regarding the negative electrode can be applied as is.

[0089] In this specification, the first electrode may be a negative electrode and the second electrode may be a positive electrode.

[0090] In this specification, the first electrode may be a positive electrode and the second electrode may be a negative electrode.

[0091] Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0092] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0093] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. It can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0094] The positive electrode active material may be a commonly used positive electrode active material, such as a layered compound or a compound substituted with one or more transition metals, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2); a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3Examples of the lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0095] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode (meth)acrylic binder in addition to the above-mentioned positive electrode active material.

[0096] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the constructed battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0097] The positive electrode (meth)acrylic binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, poly(meth)acrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0098] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without limitation. A separator with low resistance to electrolyte ion movement and excellent electrolyte humidification is particularly preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminates of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may be used, and may be used in a single-layer or multi-layer structure.

[0099] Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries, but are not limited to these.

[0100] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0101] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone (NMP), propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0102] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferably used because they are high-viscosity organic solvents with high dielectric constants and can effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore, such a mixture is more preferably used.

[0103] The metal salt can be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt can be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 -, (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0104] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0105] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Example]

[0106] Below, preferred examples are shown to help understand the present invention, but these examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0107] Manufacturing example: Manufacturing of (meth)acrylic binder <Production Example 1> In a reactor equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, (meth)acrylamide (50% aqueous solution) and AA (80% aqueous solution) were mixed as monomers in a molar ratio of 6:4, and a polymerization initiator (ammonium persulfate) was added in an amount of 0.1 parts by weight per 100 parts by weight of the total monomers. The mixture was reacted at 80°C for 6 hours to produce a polymer in an aqueous solution state.

[0108] Next, for neutralization, a 0.1 molar NaOH aqueous solution was added dropwise to the polymer in the aqueous solution state to produce a (meth)acrylic binder with a pH of 7.9.

[0109] <Production Example 2> A (meth)acrylic binder was prepared in the same manner as in Preparation Example 1, except that a 0.1 molar NaOH aqueous solution was added dropwise in the neutralization step to prepare a (meth)acrylic binder with a pH of 6.6.

[0110] <Production Example 3> A polymer was produced using AA (80% aqueous solution of acrylic acid) alone as a monomer, and a (meth)acrylic binder with a pH of 2.1 was produced.

[0111] Example: Preparation of negative electrode slurry Example 1 As the negative electrode active material, artificial graphite with D50 = 10 μm and Si with D50 = 6 μm were used. As the conductive materials, two types, carbon black (product name: SuperC45, Timca) and SWCNT (product name: Tuball OCSiAl), were used. Using the (meth)acrylic binder of Production Example 1 as the (meth)acrylic binder, graphite:Si:C45:SWCNT:(meth)acrylic binder = 81:12:1.8:0.2:5 was mixed to produce Mixture 1.

[0112] To the said Mixture 1 (initial pH = 8.4), a 0.03 M phosphoric acid aqueous solution (pH = 1.93) was added and stirred until the target pH of 6.7 was reached to produce a negative electrode slurry.

[0113] <Example 2 As the negative electrode active material, artificial graphite with D50 = 10 μm and Si / C with D50 = 6 μm were used. As the conductive materials, two types, carbon black (product name: SuperC45, Timca) and SWCNT (product name: Tuball OCSiAl), were used. Using the (meth)acrylic binder of Production Example 2 as the (meth)acrylic binder, graphite:Si / C:C45:SWCNT:(meth)acrylic binder = 79:12:1.9:0.1:7 was mixed to produce Mixture 2.

[0114] To the said Mixture 2 (initial pH = 7.8), a 0.03 M phosphoric acid aqueous solution (pH = 1.93) was added and stirred until the target pH of 5.4 was reached to produce a negative electrode slurry.

[0115] <Example 3 As the negative electrode active material, artificial graphite with D50 = 10 μm and SiOx (0 < x < 2) with D50 = 6 μm were used. As the conductive materials, two types, carbon black (product name: SuperC45, Timca) and SWCNT (product name: Tuball OCSiAl), were used. Using the (meth)acrylic binder of Production Example 3 as the (meth)acrylic binder, graphite:SiOx:C45:SWCNT:(meth)acrylic binder = 81:10:1.9:0.1:7 was mixed to produce Mixture 3.

[0116] A 0.1 M aqueous sulfuric acid solution (pH=0.7) was added to the mixture 3 (initial pH=9.3) and stirred until the target pH reached 7.1, thereby preparing a negative electrode slurry.

[0117] <Comparative Example 1> A negative electrode slurry was prepared in the same manner as in Example 1, except that Mixture 1 (not subjected to the step of adjusting to the target pH, ie, initial pH=8.4) was used.

[0118] <Comparative Example 2> A negative electrode slurry was prepared in the same manner as in Example 2, except that Mixture 2 (not subjected to the step of adjusting to the target pH, ie, initial pH=7.8) was used.

[0119] <Comparative Example 3> A negative electrode slurry was prepared in the same manner as in Example 3, except that Mixture 3 (not subjected to the step of adjusting to the target pH, ie, initial pH=9.3) was used.

[0120] Experimental example. <Experimental Example 1: Measurement of H2 gas generation amount from negative electrode slurry> 5 g of each of the negative electrode slurries of Examples 1 to 3 and Comparative Examples 1 to 3 was placed in a 9 cm x 9 cm pouch and sealed.

[0121] Next, the sealed pouches were left in a thermostatic chamber at 60° C. for 24 hours. After being left under these conditions, the pouch (a) containing the negative electrode slurry of Example 1 and the pouch (b) containing the negative electrode slurry of Comparative Example 1 were as shown in the photographs in FIG.

[0122] The gas generated in the pouch was then collected and the amount of H2 gas generated was quantitatively analyzed using GC / MS. The measurement results are shown in Table 1 below.

[0123] <Experimental Example 2: Battery manufacturing and battery characteristic evaluation (initial efficiency and capacity retention rate)> The negative electrode slurry was coated onto 18 μm-thick copper foil and dried. A 50 μm-thick negative electrode active material layer was formed on one side of the copper foil, and a circular 14 mm diameter was punched out to prepare a test electrode (negative electrode). A 0.3 mm-thick metallic lithium foil was used as the positive electrode. A 0.1 mm-thick porous polyethylene sheet was used as the separator. The electrolyte used was a 1:1 volumetric mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in which LiPF6 was dissolved as a lithium salt at a concentration of approximately 1 mol / L.

[0124] The negative electrode, positive electrode, separator, and electrolyte were sealed in a stainless steel container to prepare a coin cell for evaluation, 2 mm thick and 32 mm in diameter. The coin cell was charged at a constant current of 0.05 C until the voltage reached 0.01 V, and then discharged at a constant current of 0.05 C until the voltage reached 1.5 V to determine the discharge capacity and initial efficiency. The cycle characteristics were then measured at a constant current of 0.2 C within the same voltage range as above, and a capacity retention test was conducted. The results are shown in Table 1 below.

[0125] [Table 1]

[0126] As shown in the results in Table 1 above, the negative electrode slurries of Examples 1 to 3, which were controlled to the target pH range during the slurry production stage, and the lithium secondary batteries using these slurries, generated less hydrogen gas and also had excellent initial efficiency and cycle capacity retention.

[0127] In contrast, the negative electrode slurries of Comparative Examples 1 to 3, which were not controlled to the target pH range, and the lithium secondary batteries using these slurries had appropriate initial efficiencies and capacity retention rates, but the amount of hydrogen gas generated was at least 150 times higher than in the Examples, and therefore it can be determined that there is a high risk of explosion. [Explanation of symbols]

[0128] 1. Negative electrode slurry manufacturing equipment 100 Supply member 101 Negative electrode active material supply member 102 Conductive material supply member 103 (Meth)acrylic binder supply member 104 First solvent supply member 105 Mixing element 106 Measuring member 107 Calculation member 108 Control member 109 Discharge member

Claims

1. mixing a negative electrode active material, a conductive material, a (meth)acrylic binder, and a first solvent to obtain a mixture; measuring the initial pH of the mixture; If the measured initial pH of the mixture is outside the target pH range of pH 5 to pH 7.5, adjusting the content of a second solvent containing a pH adjuster so that the initial pH of the mixture falls within the target pH range and mixing the mixture; and obtaining a negative electrode slurry having a target pH range; A method for producing a negative electrode slurry, comprising:

2. 2. The method for producing a negative electrode slurry according to claim 1, wherein a content of the negative electrode active material is 60 parts by weight or more and 96 parts by weight or less, based on 100 parts by weight in total of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

3. The method for producing a negative electrode slurry according to claim 1 , wherein the negative electrode active material includes a silicon-based active material.

4. 4. The method for producing a negative electrode slurry according to claim 3, wherein the silicon-based active material comprises one or more selected from the group consisting of SiOx (x=0), SiOx (0<x<2), and a Si / C composite material.

5. The method for producing a negative electrode slurry according to claim 3 , wherein the negative electrode active material further comprises a carbon-based active material.

6. The method for producing a negative electrode slurry according to claim 5 , wherein the carbon-based active material comprises at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

7. 2. The method for producing a negative electrode slurry according to claim 1, wherein a content of the conductive material is 0.01 parts by weight or more and 40 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

8. The method for producing a negative electrode slurry according to claim 1 , wherein the conductive material includes at least one selected from the group consisting of a dot-like conductive material, a sheet-like conductive material, and a linear conductive material.

9. 2. The method for producing a negative electrode slurry according to claim 1, wherein a content of the (meth)acrylic binder is 2 parts by weight or more and 30 parts by weight or less, based on a total of 100 parts by weight of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

10. The method for producing a negative electrode slurry according to claim 1 , wherein the (meth)acrylic binder has a weight average molecular weight of 100,000 g / mol or more and 1,500,000 g / mol or less.

11. 2. The method for producing a negative electrode slurry according to claim 1, wherein the (meth)acrylic binder is a homopolymer or copolymer selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylonitrile, and poly(meth)acrylamide.

12. a supplying member that supplies the negative electrode active material, the conductive material, the (meth)acrylic binder, and the first solvent; a mixing member for mixing the negative electrode active material, the conductive material, the (meth)acrylic binder, and the first solvent to obtain a mixture; a measuring element for measuring the initial pH of the mixture; a calculating element for determining whether the initial pH is within a target pH range of pH 5 or more and pH 7.5 or less; a control member for adjusting and mixing the content of a second solvent containing a pH adjuster so that the initial pH falls within the target pH range if the initial pH does not fall within the target pH range; and a discharge member for discharging the negative electrode slurry that falls within the target pH range; An apparatus for producing a negative electrode slurry, comprising:

13. An anode slurry produced by the method for producing an anode slurry according to any one of claims 1 to 11.

14. An anode comprising: an anode current collector layer; and an anode active material layer formed by applying the anode slurry according to claim 13 to one or both surfaces of the anode current collector layer.

15. A lithium secondary battery comprising: a first electrode; a second electrode; a separator disposed between the first electrode and the second electrode; and an electrolyte, The lithium secondary battery, wherein either the first electrode or the second electrode is the negative electrode according to claim 14 .

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