Anode slurry preparation method and apparatus, anode slurry, anode and lithium secondary battery

Abstract

The present application relates to an anode slurry preparation method comprising the steps of: mixing an anode active material, a conductive material, a (meth)acrylic binder and a first solvent, thereby obtaining a mixture; measuring the initial pH of the mixture; if the initial pH of the mixture deviates from a target pH range, adjusting the amount of a second solvent containing a pH adjuster and mixing same so that the pH comes within the target pH range; and obtaining the mixture with the pH in the target pH range. Therefore, hydrogen gas generation is prevented to reduce the risk of explosion without harming the components of the anode slurry.

Description

Method and device for manufacturing cathode slurry, cathode slurry, cathode and lithium secondary battery

[0001] The present application relates to a method and device for manufacturing a cathode slurry, a cathode slurry, a cathode, and a lithium secondary battery.

[0002] <Cross-reference to related applications>

[0003] This application claims the benefit 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.

[0004] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the most actively researched field is power generation and storage using electrochemical reactions.

[0005] A representative example of an electrochemical device that currently utilizes this electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0006] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used. Furthermore, active research is being conducted on methods for manufacturing high-density electrodes with even higher energy density per unit volume as electrodes for these high-capacity lithium secondary batteries.

[0007] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and deintercalates lithium ions from the positive electrode. Silicon particles with a high discharge capacity can be used as the negative electrode active material.

[0008] In particular, with the recent demand for high-density energy batteries, active research is being conducted on methods to increase capacity by using silicon-based compounds, such as Si / C or SiOx, as anode active materials, which have a capacity more than 10 times greater than graphite-based materials. In the case of silicon-based compounds, which are high-capacity materials, they offer the advantage of greater capacity compared to conventional graphite. However, during the manufacture and storage of electrode compositions or slurries containing silicon-based compounds, hydrogen gas may be generated due to surface oxidation, which poses problems such as the risk of explosion and decreased phase stability.

[0009] Therefore, in order to improve the above-described problems, research is needed on manufacturing a negative electrode including a silicon-based compound while maintaining the expected properties of the battery components.

[0010] The present application, in order to solve the above problem, provides a method and device for manufacturing a negative electrode slurry in which the content of a component of the negative electrode slurry (particularly, a second solvent including a pH regulator) is controlled so that the hydrogen ion concentration (pH) is controlled, a negative electrode slurry, a negative electrode, and a lithium secondary battery.

[0011] One embodiment of the present specification provides a method for producing a negative electrode slurry, comprising 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 an initial pH of the mixture; adjusting the content of a second solvent including a pH adjuster to mix the mixture so that the pH falls within the target pH range when the measured initial pH of the mixture is outside the target pH range of pH 5 or more and pH 7.5 or less; and obtaining a negative electrode slurry within the target pH range.

[0012] Another embodiment provides a device for manufacturing a negative electrode slurry, comprising: a supply member for supplying a negative electrode active material, a conductive material, a (meth)acrylic binder, and a 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 member for measuring an initial pH of the mixture; a calculating member for determining whether the initial pH falls 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 including a pH regulator so that the initial pH falls within the target pH range when the initial pH does not fall within the target pH range; and a discharge member for discharging a negative electrode slurry falling within the target pH range.

[0013] In another embodiment, a cathode slurry manufactured according to the above method for manufacturing a cathode slurry is provided.

[0014] In another embodiment, a negative electrode is provided, which includes a negative electrode current collector layer; and a negative electrode active material layer on which the negative electrode slurry is applied on one or both surfaces of the negative electrode current collector layer.

[0015] Finally, a lithium secondary battery is provided, comprising a first electrode; a second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, wherein either the first electrode or the second electrode is the negative electrode.

[0016] A method and device for manufacturing a negative electrode slurry according to one embodiment of the present invention, a negative electrode slurry, a negative electrode, and a lithium secondary battery are characterized in that the content of a component of the negative electrode slurry (particularly, a solvent including a pH regulator) is controlled to fall within a target pH range, thereby having the effect of preventing the generation of hydrogen gas due to a surface oxidation reaction during the manufacturing or storage of the negative electrode slurry, and also having the effect of effectively maintaining the expected physical properties of the component of the negative electrode slurry.

[0017] In addition, since the cathode slurry according to one embodiment of the present invention prevents the generation of hydrogen gas, process stability, safety, etc. can be further secured in the future.

[0018] The left side (a) of Fig. 1 is a photograph taken under conditions in which a cathode slurry (Example 1) manufactured according to an embodiment of the present invention was left in a constant temperature chamber at 60°C for 24 hours, and the right side (b) is a photograph taken under the same conditions for a contrasting cathode slurry (Comparative Example 1).

[0019] Figure 2 is a schematic diagram of a device for manufacturing a cathode slurry according to one embodiment of the present invention.

[0020] 1: Apparatus for manufacturing cathode slurry

[0021] 100: Absence of supply

[0022] 101: Negative active material supply device

[0023] 102: Lack of supply of challenge materials

[0024] 103: (Meth)acrylic binder supply member

[0025] 104: First solvent supply unit

[0026] 105: Mixed elements

[0027] 106: Measuring member

[0028] 107: Absence of operation

[0029] 108: Control Absence

[0030] 109: Absence of exhaust

[0031] Before explaining the present invention, some terms are first defined.

[0032] When a part of this specification is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0033] In this specification, 'p to q' means a range of 'p or more and q or less' including p and q.

[0034] As used herein, the term "a polymer comprises a monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. As used herein, "a polymer comprises a monomer" is interpreted to mean that the polymer comprises the monomer as a monomer unit.

[0035] In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers unless 'homopolymer' is specified.

[0036] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-converted molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard materials. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0037] Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice it. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0038] <Method for manufacturing cathode slurry>

[0039] A method for manufacturing 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.

[0040] The method for manufacturing a negative electrode slurry according to the above embodiment can provide the effect of reducing the amount of hydrogen gas generated by a surface oxidation reaction during the manufacturing and storage of the negative electrode slurry without damaging the expected properties of the negative electrode active material, the conductive material, the (meth)acrylic binder, and the first solvent itself by controlling the content of the solvent including the pH adjuster, and ultimately can ensure battery stability.

[0041] The above target pH range may refer to a threshold that minimizes the amount of hydrogen gas generated by surface oxidation reaction during the manufacturing process of the cathode slurry and / or during storage for approximately 2 to 3 days immediately after manufacturing, so that the hydrogen gas does not directly or indirectly affect an explosion. In some cases, the pH range may vary depending on the type and content of the solvent and pH regulator included in the cathode slurry, but the upper and lower limits thereof are within the above-described target pH range.

[0042] In one embodiment of the present specification, the negative active material may include a silicon-based active material.

[0043] In this specification, the silicon-based active material has a capacity that is 10 times higher than that of the carbon-based active material, and accordingly, when the silicon-based active material is applied to an electrode, particularly an anode, an electrode having a high level of energy density can be implemented even with a thinner thickness than when the carbon-based active material is included alone.

[0044] In one embodiment of the present specification, the negative electrode active material may additionally include a carbon-based active material in addition to a silicon-based active material.

[0045] According to the above embodiment, the negative active material is composed of a mixture of a silicon-based active material and a carbon-based active material, so that the degree of volume expansion of the active material can be additionally controlled.

[0046] In one embodiment of the present specification, when the negative electrode active material is composed 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.

[0047] According to the above embodiment, since the negative electrode active material is mainly composed of a carbon-based active material compared to a silicon-based active material, the volume expansion of the active material during charge and discharge is small, so swelling is small, and the effect of excellent conductive connectivity of the electrode can be additionally provided.

[0048] 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 of the sum of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

[0049] In another embodiment, the content of the negative electrode active material may be 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 of the sum of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

[0050] When the above range of negative electrode active materials is satisfied, the performance of the negative electrode will not be degraded during the future charge and discharge process, and excellent output characteristics can be guaranteed during charge and discharge.

[0051] In one embodiment of the present specification, the silicon-based active material is SiOx (x=0), SiOx (0 <x<2) 및 Si / C 복합재로 이루어진 군에서 선택되는 1 이상을 포함할 수 있다.

[0052] 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.

[0053] In this specification, the case of SiO2 in which x is 2 in the above SiOx is not included, and this SiO2 does not react with lithium ions and thus cannot store lithium. Therefore, it is preferable that x is within the range of the above embodiment.

[0054] In this specification, the silicon-based active material may be Si / C or Si composed of a complex of Si and C.

[0055] In this specification, two or more types of the above silicon-based active materials can be mixed and used.

[0056] In one embodiment of the present specification, the carbon-based active material may include at least one selected from the group consisting of artificial graphite, natural graphite, hard carbon, and soft carbon.

[0057] In this specification, the conductive material may be referred to as a cathode conductive material.

[0058] In this specification, the negative electrode conductive material is applied to the negative electrode and has a completely separate composition from the positive electrode conductive material applied to the positive electrode. That is, while the negative electrode conductive material serves to secure the contact between silicon-based active materials, which undergo significant volume expansion of the electrode due to charging and discharging, the positive electrode conductive material serves as a buffer when rolled and provides some conductivity, so the negative electrode conductive material and the positive electrode conductive material have different compositions and roles.

[0059] 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 of the sum of the negative active material, the conductive material, and the (meth)acrylic binder.

[0060] 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, more preferably 0.5 parts by weight or more, or 40 parts by weight or less, preferably 30 parts by weight or less, more preferably 25 parts by weight or less, based on 100 parts by weight of the sum of the negative active material, the conductive material, and the (meth)acrylic binder.

[0061] In one embodiment of the present specification, the conductive material may include at least one selected from the group consisting of a dot-shaped conductive material; a planar conductive material; and a linear conductive material.

[0062] In one embodiment of the present specification, the conductive material may include a dot-shaped conductive material and a linear conductive material.

[0063] In the present specification, the dot-shaped conductive material may be used to improve conductivity of the negative electrode, and refers to a dot-shaped or spherical conductive material that has conductivity without causing chemical change. Specifically, the dot-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black and / or artificial graphite in terms of implementing high conductivity and excellent dispersibility.

[0064] In the present specification, the planar conductive material can improve conductivity by increasing planar contact between silicon particles within the cathode, and at the same time, suppress the disconnection of the conductive path due to volume expansion. The planar conductive material can be expressed as a plate-shaped conductive material or a bulk conductive material. Examples of the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-shaped graphite.

[0065] In the present 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, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a substantially identical orientation in a longitudinal direction of the carbon nanotube units or are entangled. The carbon nanotube unit has a graphite sheet in the form of a cylinder with a nano-sized diameter, and sp 2 It has a bonding structure. At this time, depending on the angle and structure at which the graphite plane is rolled, it can exhibit the characteristics of a conductor or semiconductor. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed during the manufacture of the cathode, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0066] In this specification, the (meth)acrylic binder may mean an aqueous binder.

[0067] 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 of the sum of the negative active material, conductive material, and (meth)acrylic binder.

[0068] In this specification, the negative electrode active material, conductive material, and (meth)acrylic binder may be referred to as a negative electrode composition.

[0069] 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, more preferably 20 parts by weight or less, based on 100 parts by weight of the sum of the negative active material, the conductive material, and the (meth)acrylic binder, or 2 parts by weight or more, preferably 5 parts by weight or more, more preferably 10 parts by weight or more.

[0070] 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.

[0071] When the weight average molecular weight of the (meth)acrylic binder satisfies the above range, the electrode exhibits excellent mechanical strength and high intermolecular interaction, resulting in excellent electrode bonding properties. Furthermore, when the above range is satisfied, the viscosity of the (meth)acrylic binder can be appropriately selected, thereby further improving the coating properties of the electrode when used to manufacture a negative electrode.

[0072] In one embodiment of the present specification, the (meth)acrylic binder may be a polymer comprising one or more monomers selected from the group consisting of poly(meth)acrylic acid, poly(meth)acrylonitrile, and poly(meth)acrylamide.

[0073] The above polymer may be a homopolymer composed of one type of monomer as a repeating unit, or a copolymer containing two or more different types of monomers as repeating units.

[0074] In the present specification, a polymerization initiator is used for the production of the (meth)acrylic binder, and ammonium persulfate can be used as an example of the polymerization initiator, but is not limited thereto.

[0075] In the present specification, the (meth)acrylic binder including a plurality of compounds having a specific ratio (expressed as parts by weight or weight ratio) may mean that each compound (e.g., (meth)acrylamide, (meth)acrylic acid, (meth)acrylonitrile) is included as a monomer of the (meth)acrylic binder polymer.

[0076] In this specification, the (meth)acrylic binder may include multiple compounds as monomers, and the monomer with the largest content may be considered as a representative, and may be named a 'monomer' compound.

[0077] In this specification, '(meth)acryl...' may mean methacryl and / or (meth)acryl.

[0078] In the present specification, when the (meth)acrylic binder is a copolymer containing two or more monomers as repeating units, the ratio of each monomer is not particularly limited as long as it belongs to the (meth)acrylic binder.

[0079] In this specification, the copolymer may be a random copolymer, a graft copolymer, a block copolymer, etc., but is not particularly limited.

[0080] In some cases, by appropriately adjusting the average particle diameter (D50) of the silicon-based active material or appropriately adjusting the specific surface area of ​​the particles, thereby controlling the viscosity of the electrode slurry within an appropriate range, the dispersion of the negative electrode slurry components (e.g., conductive agent, (meth)acrylic binder, silicon-based active material, carbon-based active material, etc.) can be improved. Accordingly, the contact area between the components is improved, so that the conductive network can be sustained, the capacity retention rate can be increased, and the phenomenon of current density unevenness during charge / discharge can also be prevented.

[0081] In some cases, the viscosity of the cathode slurry can be adjusted to be 2,000 cPs or more and 50,000 cPs or less.

[0082] When the negative electrode slurry satisfies the above viscosity range, the storage properties are excellent, and the coating properties can be further improved when the negative electrode slurry is coated on one or both sides of the negative electrode current collector layer in the future.

[0083] <Cathode slurry manufacturing device>

[0084] According to one embodiment of the present specification, a device (1) for manufacturing a cathode slurry includes, according to FIG. 3, a supply member (100), a mixing member (105), a measuring member (106), a calculation member (107), a control member (108), and a discharge member (109), and is characterized in that the calculation member determines whether the pH falls within a target pH range (pH 5 or more and pH 7.5 or less), and when the initial pH does not fall within the target pH range, the control member adjusts the content of a second solvent (including a pH regulator).

[0085] One embodiment of the present specification may further include a monitoring member capable of checking in real time whether the pH falls within the target pH range.

[0086] One embodiment of the present specification may further include a component that stores the difference between the initial pH and the target pH region measured according to the type and content of each of the solvent and pH, and subsequently stores the result of addition and mixing through the control component, so that when applied to a future process, the component performs machine learning in the direction of eliminating the difference between the initial pH and the target pH region from the supply component or reducing the difference.

[0087] In this specification, the supply member means a supply member known in the art, and is not particularly limited, as long as the supply target (e.g., negative active material (101), conductive material (102), (meth)acrylic binder (103), and first solvent (104)) is supplied to a desired location in a desired amount without loss.

[0088] In this specification, the above-mentioned mixing member means a mixing member known in the art as long as the mixing objects (negative active material, conductive material, (meth)acrylic binder, and first solvent) are uniformly mixed, and is not particularly limited.

[0089] In this specification, the measuring member means a measuring member known in the art as long as 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) is accurately measured, and is not particularly limited.

[0090] In this specification, the above calculation member means a calculation member known in the art as long as the calculation target (the difference between the initial pH of the mixture and the target pH range) can be calculated, and is not particularly limited.

[0091] In this specification, the control member refers to a control member known in the art as long as the control object (second solvent) can be precisely controlled, and is not particularly limited.

[0092] In this specification, the discharge member refers to a discharge member known in the art as long as it can discharge the discharge target (mixture or cathode slurry belonging to the target pH range), and is not particularly limited.

[0093] In one embodiment of the present invention, the target pH range may be pH 5 or higher and pH 7.5 or lower.

[0094] In this specification, the contents of the negative electrode slurry, negative electrode active material, conductive agent, (meth)acrylic binder, solvent, and target pH range may be applied to the above-mentioned contents.

[0095] <Cathode slurry>

[0096] Another embodiment of the present invention provides a cathode slurry manufactured according to the method for manufacturing the cathode slurry.

[0097] Since the cathode slurry according to the present invention is directly applied to the above-described cathode slurry manufacturing method, the contents of the cathode slurry manufacturing method can be directly applied to the cathode slurry obtained thereby.

[0098] <Cathode>

[0099] Another embodiment of the present invention provides a negative electrode including a negative electrode current collector layer; and a negative electrode active material layer having the above-described negative electrode slurry applied to one or both surfaces of the negative electrode current collector layer.

[0100] Since the cathode according to the above implementation state uses the cathode slurry described above as is, the contents regarding the cathode slurry described above can be applied as is.

[0101] In the present specification, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. The negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0102] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, 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.

[0103] However, the thickness can be varied depending on the type and purpose of the cathode used and is not limited thereto.

[0104] Lithium secondary battery

[0105] In one embodiment of the present invention, a lithium secondary battery is provided, which comprises a first electrode; a second electrode; a separator provided between the first electrode and the second electrode; and an electrolyte, wherein either the first electrode or the second electrode is the negative electrode described above.

[0106] Since the lithium secondary battery according to the above embodiment includes the negative electrode as is, the contents regarding the negative electrode can be applied as is.

[0107] In this specification, the first electrode may be a cathode and the second electrode may be an anode.

[0108] In this specification, the first electrode may be an anode, and the second electrode may be a cathode.

[0109] Specifically, the secondary battery may include a cathode, a cathode, a separator interposed between the cathode and the anode, and an electrolyte, wherein the cathode is the same as the cathode described above. Since the cathode has been described above, a detailed description thereof will be omitted.

[0110] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and including the positive electrode active material.

[0111] In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 µm to 500 µm, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0112] The above positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2Ni-site type lithium nickel oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxide represented by O2 (wherein, 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 (wherein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

[0113] The above-described positive electrode active material layer may include a positive electrode conductive material and a positive electrode (meth)acrylic binder together with the positive electrode active material described above.

[0114] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, it can be used without special restrictions as long as it does not cause a chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0115] In addition, the positive electrode (meth)acrylic binder plays a role in improving the adhesion between positive electrode active material particles and the adhesiveness 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), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0116] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0117] Examples of the above electrolyte include, but are not limited to, 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 the manufacture of lithium secondary batteries.

[0118] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0119] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone (NMP), propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used. there is.

[0120] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0121] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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 can be used.

[0122] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0123] 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 battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus 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.

[0124] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0125] Manufacturing example. Manufacturing of (meth)acrylic binder

[0126] <Manufacturing Example 1>

[0127] In a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet pipe, monomers (meth)acrylamide (acryl amide, 50% aqueous solution) and AA (acrylic acid, 80% aqueous solution) were mixed at a molar ratio of 6:4, and a polymerization initiator (ammonium persulfate) was added at 0.1 part by weight per 100 parts by weight of the total monomers, and the mixture was reacted at 80°C for 6 hours to produce a polymer in an aqueous solution state.

[0128] Next, a 0.1 molar concentration NaOH aqueous solution was added dropwise to the polymer in the aqueous solution state for neutralization, thereby producing a (meth)acrylic binder with a pH of 7.9.

[0129] <Manufacturing Example 2>

[0130] A (meth)acrylic binder was manufactured in the same manner as in Manufacturing Example 1, except that a 0.1 molar concentration NaOH aqueous solution was added dropwise in the neutralization step to manufacture a (meth)acrylic binder having a pH of 6.6.

[0131] <Manufacturing Example 3>

[0132] A polymer was prepared using AA (80% acrylic acid aqueous solution) alone as a monomer, and a (meth)acrylic binder having a pH of 2.1 was prepared.

[0133] Example. Preparation of cathode slurry

[0134] <Example 1>

[0135] D50=10 ㎛ artificial graphite and D50=6 ㎛ Si were used as negative active materials, carbon black (product name: Super C45, Timca) and two types of SWCNT (product name: Tuball OCSiAl) were used as conductive materials, and the (meth)acrylic binder of Manufacturing Example 1 was used as a (meth)acrylic binder, and the mixture 1 was prepared by mixing Graphite:Si:C45:SWCNT:(meth)acrylic binder = 81:12:1.8:0.2:5.

[0136] A 0.03 M phosphoric acid aqueous solution (pH = 1.93) was added and stirred to the above mixture 1 (initial pH = 8.4) until the target pH became 6.7, thereby preparing a cathode slurry.

[0137] <Example 2>

[0138] D50=10 ㎛ artificial graphite and D50=6 ㎛ Si / C were used as negative active materials, carbon black (product name: Super C45, Timca) and two types of SWCNT (product name: Tuball OCSiAl) were used as conductive materials, and the (meth)acrylic binder of Manufacturing Example 2 was used as a (meth)acrylic binder, and Graphite:Si / C:C45:SWCNT:(meth)acrylic binder = 79:12:1.9:0.1:7 was mixed to prepare Mixture 2.

[0139] A 0.03 M phosphoric acid aqueous solution (pH = 1.93) was added and stirred to the above mixture 2 (initial pH = 7.8) until the target pH became 5.4, thereby preparing a cathode slurry.

[0140] <Example 3>

[0141] As negative active materials, D50=10 ㎛ artificial graphite and D50=6 ㎛ SiOx(0 <x<2)를 사용하고, 도전재로 카본 블랙(제품명:Super C45, Timca사) 및 SWCNT(제품명:Tuball OCSiAl사) 2종을 사용하고, (메트)아크릴계 바인더로서 제조예 3의 (메트)아크릴계 바인더를 사용하여 Graphite:SiOx:C45:SWCNT:(메트)아크릴계 바인더=81:10:1.9:0.1:7로 혼합하여 혼합물 3을 제조하였다.

[0142] A 0.1 M sulfuric acid aqueous solution (pH = 0.7) was added and stirred to the above mixture 3 (initial pH = 9.3) until the target pH became 7.1, thereby preparing a cathode slurry.

[0143] <Comparative Example 1>

[0144] A cathode slurry was prepared in the same manner as in Example 1, except that the above mixture 1 (without going through the step of adjusting to the target pH, i.e., initial pH = 8.4) was used.

[0145] Comparative Example 2

[0146] A cathode slurry was prepared in the same manner as in Example 2, except that the above mixture 2 (without going through the step of adjusting to the target pH, i.e., initial pH = 7.8) was used.

[0147] <Comparative Example 3>

[0148] A cathode slurry was prepared in the same manner as in Example 3, except that the above mixture 3 (without going through the step of adjusting to the target pH, i.e., initial pH = 9.3) was used.

[0149] Experimental example.

[0150] <Experimental Example 1: Measurement of H2 gas production from cathode slurry>

[0151] 5 g of the cathode slurry of Examples 1 to 3 and Comparative Examples 1 to 3 was each placed in a pouch measuring 9 cm X 9 cm and sealed.

[0152] Then, the sealed pouch was left in a constant temperature chamber at 60°C for 24 h. After leaving under the above 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 are as shown in the photograph of Fig. 1.

[0153] Then, the gas generated in the pouch was captured, and the amount of H2 gas generated was quantitatively analyzed using GC / MS. The measurement results are shown in Table 1 below.

[0154] <Experimental Example 2: Battery Manufacturing and Battery Characteristic Evaluation (Initial Efficiency and Capacity Retention Rate)>

[0155] The above-mentioned negative electrode slurry was coated on a copper foil having a thickness of 18 μm and dried, and a negative electrode active material layer having a thickness of 50 μm was formed on one side of the copper foil, which was then punched into a circle having a diameter of 14 Φ (mm) to manufacture a test electrode (negative electrode). A metallic lithium foil having a thickness of 0.3 mm was used as the positive electrode. A porous polyethylene sheet having a thickness of 0.1 mm was used as the separator. In addition, as the electrolyte, LiPF6 was dissolved as a lithium salt at a concentration of about 1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1:1.

[0156] The above-mentioned cathode, anode, separator, and electrolyte were sealed in a stainless steel container to manufacture a coin cell for evaluation with a thickness of 2 mm and a diameter of 32 mm. The coin cell was charged at a constant current of 0.05 C until the voltage became 0.01 V, and discharged at a constant current of 0.05 C until the voltage became 1.5 V to obtain the discharge capacity and initial efficiency. Afterwards, the cycle characteristics were performed at a constant current of 0.2 C in the same voltage range as above to conduct a capacity retention test, and the results are shown in Table 1 below.

[0157]

[0158] 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 in the slurry manufacturing step, and the lithium secondary batteries using the same, had low hydrogen gas generation and excellent initial efficiency and cycle capacity retention.

[0159] In contrast, the negative electrode slurries of Comparative Examples 1 to 3 and the lithium secondary batteries using the same, which were not controlled within the target pH range, may be judged to have a high risk of explosion, as the amount of hydrogen gas generated is at least 150 times different from that of the examples, even though they have appropriate initial efficiency and capacity retention rate.

Claims

1. A step of obtaining a mixture by mixing a negative active material, a conductive material, a (meth)acrylic binder, and a first solvent; A step of measuring the initial pH of the above mixture; When the initial pH of the measured mixture is outside the target pH range of pH 5 or more and pH 7.5 or less, a step of mixing by adjusting the content of the second solvent including a pH adjuster so that it falls within the target pH range; and A method for producing a cathode slurry, comprising the step of obtaining a cathode slurry falling within the above target pH range.

2. In claim 1, A method for manufacturing a negative electrode slurry, wherein the 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 of the sum of the negative electrode active material, the conductive material, and the (meth)acrylic binder.

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

4. In claim 3, The above silicon-based active material is SiOx (x=0), SiOx (0 <x<2) 및 Si / C 복합재로 이루어진 군에서 선택되는 1 이상을 포함하는 것인 음극 슬러리의 제조 방법.

5. In claim 3, A method for producing a negative electrode slurry, wherein the negative electrode active material further includes a carbon-based active material.

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

7. In claim 1, A method for manufacturing a negative electrode slurry, wherein the content of the conductive agent is 0.01 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the sum of the negative electrode active material, the conductive agent, and the (meth)acrylic binder.

8. In claim 1, A method for producing a cathode slurry, wherein the conductive material comprises at least one selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

9. In claim 1, A method for manufacturing a negative electrode slurry, wherein the content of the above (meth)acrylic binder is 2 parts by weight or more and 30 parts by weight or less based on 100 parts by weight of the sum of the above negative electrode active material, conductive material, and (meth)acrylic binder.

10. In claim 1, A method for producing a cathode slurry, wherein the weight average molecular weight of the above (meth)acrylic binder is 100,000 g / mol or more and 1,500,000 g / mol or less.

11. In claim 1, A method for producing a negative electrode slurry, wherein the above (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 supply member for supplying a negative electrode active material, a conductive material, a (meth)acrylic binder, and a first solvent; A mixing member that obtains a mixture by mixing the above negative active material, conductive material, (meth)acrylic binder, and first solvent; A measuring member for measuring the initial pH of the above mixture; A calculation unit for determining whether the initial pH falls within a target pH range of pH 5 or higher and pH 7.5 or lower; A control member for mixing by adjusting the content of a second solvent including a pH regulator so that the initial pH falls within the target pH range when the initial pH does not fall within the target pH range; and A discharge member for discharging cathode slurry within the above target pH range. A device for manufacturing a cathode slurry comprising:

13. A cathode slurry manufactured according to the method for manufacturing a cathode slurry of any one of claims 1 to 11.

14. A negative electrode comprising a negative electrode current collector layer; and a negative electrode active material layer having a negative electrode slurry according to claim 13 applied to one or both surfaces of the negative electrode current collector layer.

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

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