Positive electrode slurry composition, positive electrode and lithium secondary battery produced using the same

Abstract

The positive electrode slurry composition according to the present invention includes a positive electrode active material, a conductive material, a binder, a dispersant, and a solvent. The positive electrode active material includes lithium iron phosphate. The lithium iron phosphate has an average particle diameter D 50 The dispersant is contained in an amount of 0.2 parts by weight to 0.9 parts by weight with respect to 100 parts by weight of the solid content in the positive electrode slurry composition.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0187190 dated December 24, 2021 and Korean Patent Application No. 10-2022-0178086 dated December 19, 2022.

[0002] The present invention relates to a positive electrode slurry composition, a positive electrode and a lithium secondary battery manufactured using the same, and more particularly to a positive electrode slurry composition for forming a positive electrode having excellent positive electrode adhesion, and a positive electrode and a lithium secondary battery manufactured using the same. [Background technology]

[0003] As technological development and demand for electric vehicles and energy storage systems (ESS) increases, the demand for batteries as energy sources is rapidly increasing, and various researches are being conducted on batteries that can meet various requirements. In particular, researches on lithium secondary batteries, which have high energy density and excellent life and cycle characteristics as a power source for such devices, are being actively conducted.

[0004] Lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (LNCMO), lithium iron phosphate (LFP), etc. are used as positive electrode active materials for lithium secondary batteries.

[0005] Lithium iron phosphate is inexpensive because it contains iron, a resource-rich and low-cost material. Furthermore, its low toxicity can reduce environmental pollution when used. Furthermore, because lithium iron phosphate has an olivine structure, its active material structure can be stably maintained at high temperatures compared to lithium transition metal oxides with a layered structure. This can improve high-temperature stability and high-temperature life characteristics.

[0006] However, lithium iron phosphate has a drawback in that it has low lithium mobility and low electrical conductivity compared to lithium transition metal oxides such as lithium nickel cobalt manganese oxide. Therefore, conventional methods have improved the electrical conductivity of lithium iron phosphate by coating the surface of the material with carbon and shortening the average particle size of the lithium iron phosphate to improve the mobility of lithium ions. However, as the size of the lithium iron phosphate particles decreases, the specific surface area increases, which leads to significant particle aggregation, reducing the stability of the positive electrode slurry and the coating processability. Furthermore, aggregation in the positive electrode slurry reduces the adhesion between the current collector and the positive electrode active material layer (hereinafter referred to as "positive electrode adhesion") in the manufactured positive electrode because the lithium iron phosphate and the binder are not mixed effectively.

[0007] A dispersant can be used to suppress the aggregation of the slurry, but as the content of the dispersant increases, the electrode resistance increases, and the distribution area of ​​the dispersant on the surface of the active material expands, reducing the contact area between the active material and the binder, which in turn reduces the electrode adhesion.

[0008] If the adhesive strength of the positive electrode is reduced, the positive electrode active material layer may be detached during electrode manufacturing or during charge and discharge, resulting in an increase in battery resistance and a decrease in the capacity of the secondary battery.

[0009] Conventionally, to solve these problems, techniques have been known to improve the positive electrode adhesion by increasing the overall binder content in the positive electrode active material layer, by interposing an adhesive layer such as a primer coating layer with a high binder content between the current collector and the positive electrode active material layer, or by mitigating binder migration by extending the drying time during electrode coating, thereby increasing the binder content at the interface between the current collector and the active material layer.

[0010] However, a high binder content in the active material layer has drawbacks such as a decrease in the resistance characteristics and the energy density per volume of the electrode, and a longer drying time leads to a limit in that the production costs of the electrode and secondary battery increase. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide a positive electrode slurry composition for forming a positive electrode having excellent positive electrode adhesive strength.

[0012] Another object of the present invention is to provide a positive electrode having excellent positive electrode adhesion, and a lithium secondary battery including the positive electrode, in which deterioration of resistance characteristics is minimized.

[0013] The objects of the present invention are not limited to those mentioned above, and other objects not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0014] According to one embodiment of the present invention, there is provided a positive electrode slurry composition including a positive electrode active material, a conductive material, a binder, a dispersant, and a solvent, wherein the positive electrode active material includes lithium iron phosphate, and the lithium iron phosphate has an average particle diameter D 50 The positive electrode slurry composition has a particle size of 1.5 μm or more, and the dispersant is contained in an amount of 0.2 to 0.9 parts by weight relative to 100 parts by weight of the solid content in the positive electrode slurry composition.

[0015] According to another embodiment of the present invention, there is provided a current collector and a positive electrode active material layer disposed on the current collector, the positive electrode active material layer including a positive electrode active material, a conductive material, a binder, and a dispersant, the positive electrode active material including lithium iron phosphate, and an average particle diameter D 50 The positive electrode is provided such that the particle size is 1.5 μm or more, and the dispersant is contained in the positive electrode active material layer in an amount of 0.2 wt % to 0.9 wt %.

[0016] According to another embodiment of the present invention, a positive electrode, a negative electrode, a separator, and an electrolyte are provided. The positive electrode includes a positive electrode active material, a conductive material, a binder, and a dispersant in a positive electrode active material layer. The positive electrode active material includes lithium iron phosphate. The lithium iron phosphate has an average particle diameter D 50 The positive electrode active material layer contains the dispersant in an amount of 0.2 wt % to 0.9 wt %. [Effects of the Invention]

[0017] The positive electrode slurry composition according to the present invention has an average particle size D 50 The lithium iron phosphate particles have a particle size of 1.5 μm or more, and thus can effectively prevent particle aggregation even with a relatively small amount of dispersant. As a result, the lithium iron phosphate and binder can be present in a uniformly mixed state in the positive electrode active material layer, thereby improving the positive electrode adhesion.

[0018] In addition, the content of the dispersant, which does not contribute to positive electrode adhesion, may be low, minimizing the decrease in positive electrode adhesion, thereby preventing detachment of the positive electrode active material layer, reducing an increase in battery resistance, and improving battery life characteristics.

[0019] Furthermore, when the average particle size of the lithium iron phosphate particles satisfies the above range, the adhesion to the current collector during rolling is improved, and detachment of the electrode after rolling can be prevented.

[0020] Furthermore, when lithium iron phosphate having a relatively large particle size is used and the content of the dispersant is reduced as in the present invention, the area where the dispersant is distributed on the surface of the lithium iron phosphate is reduced, thereby increasing the contact area between the binder and the lithium iron phosphate, thereby maximizing the improvement effect of the positive electrode adhesion.

[0021] Furthermore, if the content of the dispersant is increased, the exposed surface area of ​​the lithium iron phosphate particles is reduced by the dispersant, which can cause a problem of degraded electrochemical properties. However, in the present invention, the content of the dispersant is relatively low, so that an increase in the electrochemical properties, particularly the battery resistance, can be suppressed. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a SEM photograph of lithium iron phosphate having an average particle size D50 of 0.8 μm used in the positive electrodes prepared in Examples and Comparative Examples. [Figure 2] 1 is a SEM photograph of lithium iron phosphate having an average particle size D50 of 1.0 μm used in the positive electrodes prepared in Examples and Comparative Examples. [Figure 3] 1 is a SEM photograph of lithium iron phosphate having an average particle size D50 of 1.2 μm used in the positive electrodes prepared in Examples and Comparative Examples. [Figure 4] 1 is a SEM photograph of lithium iron phosphate having an average particle size D50 of 2.0 μm used in the positive electrodes prepared in Examples and Comparative Examples. [Figure 5] 10 is a photograph showing a state in which a positive electrode formed using the positive electrode slurry composition of Comparative Example 4 is partially detached after rolling. [Figure 6] 1 is an SEM photograph of a cross section of a positive electrode of Example 2. [Figure 7] 1 is an SEM photograph of a cross section of a positive electrode of Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0023] The advantages and features of the present invention, as well as methods for achieving them, will become more apparent from the following detailed description of the embodiments accompanied by the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in various different forms. The present embodiments are provided so that this disclosure will be complete and will fully convey the scope of the invention to those skilled in the art. The present invention is defined only by the scope of the claims. The same reference symbols refer to the same elements throughout the specification.

[0024] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense that they can be commonly understood by a person of ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless they are clearly and specifically defined.

[0025] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless otherwise specified in the phrase. As used in this specification, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other elements other than the elements mentioned.

[0026] In this specification, when a part is said to include a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless otherwise specified to the contrary.

[0027] In this specification, the expression "A and / or B" means A or B, or A and B.

[0028] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0029] In this specification, D 50D means the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 can be measured using, for example, the laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0030] In this specification, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan.

[0031] As used herein, the term "weight average molecular weight (Mw)" refers to a value measured by gel permeation chromatography (GPC) and converted to standard polystyrene. Specifically, the weight average molecular weight is a value measured by GPC under the following conditions and converted. Standard polystyrene from an Agilent system was used to prepare the calibration curve.

[0032] <Measurement conditions> Measuring instrument: Agilent GPC (Agulent 1200 series, USA) Column: PL Mixed B 2 columns connected Column temperature: 40℃ Eluent: tetrahydrofuran Flow rate: 1.0mL / min Concentration: ~1mg / mL (100μL injection)

[0033] The positive electrode adhesive strength in this specification can be measured as follows. A positive electrode cut to a length of 150 mm and a width of 20 mm was prepared. The positive electrode active material layer was placed facing a 75 mm long and 25 mm wide glass slide, and the positive electrode was attached to the glass slide in the longitudinal direction using double-sided tape. That is, the glass slide was attached to an area corresponding to half of the positive electrode in the longitudinal direction. Then, a test sample was prepared by rolling the test sample with a roller 10 times to ensure uniform adhesion of the double-sided tape. Next, the glass slide portion of the test sample was fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the half of the positive electrode not attached to the glass slide was connected to the load cell of the UTM. The load cell was moved 50 mm at a speed of 100 mm / min, applying a 90° force, and the load applied to the load cell was measured. The minimum load measured in the 20 mm to 40 mm section of the running section was determined. This is repeated a total of five times, and the average value is evaluated as the positive electrode adhesive strength (gf / 20 mm) of each sample.

[0034] The positive electrode resistance in this specification can be measured as follows. A positive electrode having a 98 μm-thick positive electrode active material layer is cut into a specimen measuring 50 mm × 50 mm in length and width. The resistance per unit area (10 mm × 10 mm) of the specimen is measured in the thickness direction of the positive electrode active material layer using a positive electrode resistance measuring device (MP tester, HIOKI Corporation), and the measurement conditions are as follows. After measuring the positive electrode three times using the above method, the average value of the three measurements, with a standard deviation of within 10%, is taken as the positive electrode resistance.

[0035] - Current: 100μA - Speed: Slow - Voltage range: 0.5V - Resistivity of the positive electrode current collector: 2.82E for the aluminum used above -0.6 Ω cm

[0036] <Positive electrode slurry composition> A positive electrode slurry composition according to one embodiment of the present invention is for forming a positive electrode active material layer, and includes a positive electrode active material, a conductive material, a binder, a dispersant, and a solvent. The positive electrode active material includes lithium iron phosphate, and the lithium iron phosphate has an average particle diameter D 50 The dispersant is contained in an amount of 0.2 to 0.9 parts by weight relative to 100 parts by weight of the solid content in the positive electrode slurry composition.

[0037] In the case of conventional cathodes using lithium iron phosphate, aggregation of the lithium iron phosphate occurs during the preparation of the cathode slurry, resulting in a deterioration in the coating properties and electrochemical properties of the cathode slurry. To prevent this aggregation, the amount of dispersant used is increased, but as the distribution area of ​​the dispersant on the surface of the lithium iron phosphate increases, the contact area between the lithium iron phosphate and the binder decreases, resulting in a problem of a decrease in electrode adhesion.

[0038] To solve the above problems, researchers have conducted extensive research and have found that the average particle size D 50 It has been found that when the particle size is 1.5 μm or more and the dispersant is contained in an amount of 0.2 to 0.9 parts by weight per 100 parts by weight of the solid content in the positive electrode slurry composition, the area where the dispersant is distributed on the surface of the lithium iron phosphate is reduced, and the contact area between the binder and the lithium iron phosphate is increased, thereby significantly improving the positive electrode adhesive strength. This will be described in detail in this specification.

[0039] (1) Positive electrode active material The positive electrode active material may include lithium iron phosphate. When the positive electrode active material includes lithium iron phosphate, the stability of the positive electrode including the positive electrode active material is significantly improved, thereby significantly reducing the risk of fire in a lithium secondary battery including the positive electrode.

[0040] The lithium iron phosphate may be a compound represented by the following formula 1:

[0041] [Chemical formula 1] Li1+a Fe 1-x M x (PO 4-b )X b

[0042] (In the above chemical formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, and x are −0.5≦a≦0.5, 0≦b≦0.1, and 0≦x≦0.5, respectively.)

[0043] For example, the lithium iron phosphate may be LiFePO4.

[0044] The average particle size D of the lithium iron phosphate 50 The average particle size of the lithium iron phosphate may be 1.5 μm or more. If the average particle size of the lithium iron phosphate is less than 1.5 μm, the lithium iron phosphate may be excessively agglomerated in the positive electrode slurry composition. As a result, the lithium iron phosphate and the binder may not be effectively mixed, resulting in a decrease in the adhesive strength of the positive electrode. Furthermore, if the content of the dispersant is increased to suppress the agglomeration, the distribution area of ​​the dispersant on the surface of the lithium iron phosphate may increase, thereby reducing the contact area between the lithium iron phosphate and the binder and decreasing the adhesive strength of the positive electrode. If the adhesive strength of the positive electrode is decreased, the resistance increases during the charge and discharge process of the battery, resulting in a decrease in the life characteristics of the battery.

[0045] The average particle size D of the lithium iron phosphate 50 When the particle size is 1.5 μm or more, aggregation of the lithium iron phosphate can be suppressed even when a small amount of dispersant is used, and the area where the dispersant is distributed on the surface of the lithium iron phosphate is reduced, thereby increasing the contact area between the binder and the lithium iron phosphate and improving the positive electrode adhesive strength. Furthermore, detachment of the positive electrode active material layer during battery operation is prevented, thereby suppressing an increase in battery resistance and improving the battery life characteristics.

[0046] Specifically, the average particle diameter D of the lithium iron phosphate 50 The average particle diameter D of the lithium iron phosphate may be 1.5 μm to 4.5 μm, more specifically 1.7 μm to 3.0 μm. 50 When satisfies the above range, the positive electrode adhesive strength is improved for the above-mentioned reasons, and detachment of the positive electrode active material layer is prevented, thereby suppressing an increase in battery resistance, while preventing an increase in battery resistance caused by lithium iron phosphate with large particle diameters.

[0047] The lithium iron phosphate may be in the form of secondary particles. The secondary particle form refers to a form in which a plurality of primary particles of lithium iron phosphate in the form of single particles are bonded to each other to form a larger particle. Here, "bonded" does not simply mean agglomerated by van der Waals bonds, but may also mean chemically bonded. When the lithium iron phosphate is in the form of secondary particles, the average particle diameter D of the lithium iron phosphate described above can be 50 is the average particle size of the secondary particles D 50 This applies to:

[0048] The average particle size D of the primary particles of the lithium iron phosphate 50 The thickness may be 50 nm to 400 nm, specifically 70 nm to 300 nm, and more specifically 100 nm to 200 nm. When the thickness satisfies the above range, the migration path of lithium ions is short and the content of defects in the crystal structure is kept low, thereby improving the resistance performance.

[0049] The BET specific surface area of ​​the lithium iron phosphate is 5m 2 / g~20m 2 / g, specifically 7m 2 / g~18m 2 / g, more specifically 9m 2 / g~16m 2 / g. This range corresponds to a lower value compared to typical lithium iron phosphate. When this range is satisfied, aggregation of the lithium iron phosphate can be effectively suppressed even in a positive electrode slurry composition with a relatively low dispersant content.

[0050] The lithium iron phosphate may be included in an amount of 94.8 to 98.0 parts by weight, specifically 95.0 to 98.0 parts by weight, more specifically 95.1 to 98.0 parts by weight, relative to 100 parts by weight of the solid content in the positive electrode slurry composition. When the content of the lithium iron phosphate satisfies the above range, the energy density per weight / volume of the positive electrode can be increased.

[0051] The lithium iron phosphate may further include a carbon coating layer formed on the surface of the lithium iron phosphate, which may improve the electrical conductivity of the lithium iron phosphate and reduce the resistance of the positive electrode.

[0052] The carbon coating layer may be formed using at least one raw material selected from the group consisting of glucose, sucrose, lactose, starch, oligosaccharides, polyoligosaccharides, fructose, cellulose, furfuryl alcohol polymers, ethylene-ethylene oxide block copolymers, vinyl resins, cellulose resins, phenolic resins, pitch resins, and tar resins. Specifically, the carbon coating layer may be formed by disposing the raw material on the surface of the lithium iron phosphate and then firing the resulting material.

[0053] (2) Dispersant The dispersant prevents the lithium iron phosphate from excessively agglomerating in the positive electrode slurry composition, allowing the lithium iron phosphate to be effectively dispersed and present in the prepared positive electrode active material layer.

[0054] The dispersant may include a hydrogenated nitrile copolymer, and specifically, the dispersant may be a hydrogenated nitrile copolymer.

[0055] Specifically, the hydrogenated nitrile copolymer may be a copolymer containing structural units derived from an α,β-unsaturated nitrile and structural units derived from a hydrogenated conjugated diene, or a copolymer containing structural units derived from an α,β-unsaturated nitrile, structural units derived from a conjugated diene, and structural units derived from a hydrogenated conjugated diene. Examples of the α,β-unsaturated nitrile monomer include acrylonitrile and methacrylonitrile, and these may be used alone or in combination. Examples of the conjugated diene monomer include conjugated diene monomers having 4 to 6 carbon atoms, such as 1,3-butadiene, isoprene, and 2,3-methylbutadiene, and these may be used alone or in combination.

[0056] More specifically, the hydrogenated nitrile copolymer may be hydrogenated nitrile butadiene rubber (H-NBR).

[0057] The weight average molecular weight of the hydrogenated nitrile butadiene rubber may be 10,000 to 400,000, specifically 20,000 to 350,000, and more specifically 30,000 to 260,000. Since the average particle size of the lithium iron phosphate described above is larger than that of conventionally used lithium iron phosphate, it is preferable that the weight average molecular weight of the hydrogenated nitrile butadiene rubber satisfies the above range from the viewpoint of preventing aggregation of the lithium iron phosphate and effectively dispersing it.

[0058] The dispersant may be contained in an amount of 0.2 to 0.9 parts by weight, specifically 0.2 to 0.7 parts by weight, and more specifically 0.2 to 0.5 parts by weight, relative to 100 parts by weight of the solid content in the positive electrode slurry composition. 50When the particle size is 1.5 μm or more, aggregation of the lithium iron phosphate can be effectively suppressed even when the dispersant content is relatively low. Furthermore, since the content of the dispersant in the positive electrode active material layer is low, the bonding area between the lithium iron phosphate and the binder can be increased, thereby further improving the positive electrode adhesion. As a result, the positive electrode resistance and battery life characteristics can be improved.

[0059] In particular, when the dispersant is contained in an amount of 0.2 to 0.7 parts by weight relative to 100 parts by weight of the solid content in the positive electrode slurry composition, the content of the dispersant, which does not contribute to the adhesive strength, is reduced compared to the content of the binder, which directly affects the adhesive strength, and the positive electrode adhesive strength can be more significantly improved.

[0060] If the content of the dispersant exceeds 0.9 parts by weight based on 100 parts by weight of the solid content in the positive electrode slurry composition, the bonding area between the lithium iron phosphate and the binder may decrease due to the excessive content of the dispersant, which may result in a decrease in positive electrode adhesive strength. Conversely, if the content of the dispersant is less than 0.2 parts by weight based on 100 parts by weight of the solid content in the positive electrode slurry composition, excessive aggregation between the lithium iron phosphate particles may prevent the lithium iron phosphate and the binder from being effectively mixed, which may result in a decrease in positive electrode adhesive strength.

[0061] (3) Binder The binder functions to bind the positive electrode active material and conductive material, etc., and to aid in binding to the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers thereof, and these may be used alone or in combination.

[0062] The binder may be contained in an amount of 1 to 4 parts by weight, specifically 1.5 to 4 parts by weight, more specifically 2 to 3.5 parts by weight, relative to 100 parts by weight of the solid content in the positive electrode slurry composition. When the binder content satisfies the above range, the contact area between the binder and lithium iron phosphate is increased, thereby ensuring excellent positive electrode adhesive strength.

[0063] (4) Conductive material The conductive material is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. Examples include graphite; carbon black, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers, such as carbon fiber and metal fiber; metal powders, such as carbon fluoride, aluminum, and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives. Specific examples of commercially available conductive materials include acetylene black products from Chevron Chemical Company, Denka Singapore Private Limited, and Gulf Oil Company; Ketjenblack, EC series (products of Armak Company), Vulcan XC-72 (products of Cabot Company), and Super P (products of Timcal). Preferably, the conductive material is carbon nanotubes. The conductive network of carbon nanotubes is particularly preferable as a conductive material contained in the positive electrode slurry composition of the present invention because it can alleviate the migration phenomenon of the binder during the drying process of the positive electrode slurry composition.

[0064] The conductive material may be contained in an amount of 0.1 to 3.0 parts by weight, specifically 0.2 to 2.0 parts by weight, more specifically 0.6 to 1.2 parts by weight, per 100 parts by weight of the solid content in the positive electrode slurry composition. When the amount is within this range, a positive electrode conductive network is ensured, thereby improving the electrical conductivity of the positive electrode.

[0065] (5) Solvent The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, or water, and one or more of these may be used alone or in combination.

[0066] The positive electrode slurry composition may include a solid content and the solvent. In this case, the solid content may include at least one of a positive electrode active material, a conductive material, a binder, and a dispersant.

[0067] According to one embodiment of the present invention, the solid content of the composition may be 40% by weight to 75% by weight, specifically 50% by weight to 70% by weight, and more specifically 55% by weight to 65% by weight. When the solid content satisfies the above range, the composition may have a slurry viscosity suitable for a slurry coating process such as slot-die coating.

[0068] In this case, the composition may contain, relative to 100 parts by weight of the solid content in the positive electrode slurry composition, 0.1 to 3.0 parts by weight of the conductive material, 1 to 4 parts by weight of the binder, and 0.2 to 0.9 parts by weight of the dispersant. When the contents of the conductive material, binder, and dispersant satisfy the above ranges, aggregation of lithium iron phosphate can be suppressed, thereby significantly improving the positive electrode adhesive strength.

[0069] <Positive electrode> Next, the positive electrode according to the present invention will be described.

[0070] The positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. In this case, the positive electrode active material layer includes a positive electrode active material, a conductive material, a binder, and a dispersant. The positive electrode active material includes lithium iron phosphate, and the lithium iron phosphate has an average particle diameter D 50 The positive electrode active material layer has a particle size of 1.5 μm or more, and the dispersant is contained in the positive electrode active material layer at 0.2 wt % to 0.9 wt %. The positive electrode can be formed using the positive electrode slurry composition of the above-described embodiment. The positive electrode active material, dispersant, binder, and conductive material are as described above.

[0071] The positive electrode according to the present invention has an average particle diameter D of lithium iron phosphate. 50 The thickness of the positive electrode active material layer is 1.5 μm or more, and the dispersant is contained in the positive electrode active material layer in an amount of 0.2 wt % to 0.9 wt %, thereby improving adhesion. As a result, even if a separate layer for improving adhesion, such as a primer coating layer or binder layer having a high binder component content, is provided between the positive electrode current collector and the positive electrode active material layer, the positive electrode active material layer can have adhesion at a level equal to or greater than that of a positive electrode having such a layer.

[0072] The positive electrode current collector is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like.

[0073] The positive electrode current collector may have a thickness of 3 μm to 500 μm, and may have fine irregularities on its surface to enhance adhesion to the positive electrode active material layer. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0074] The positive electrode active material layer is located on at least one surface of the positive electrode current collector and may be formed from the above-described positive electrode slurry composition.

[0075] The positive electrode may be prepared according to a typical positive electrode preparation method, except for using the positive electrode slurry composition described above, specifically, by stirring and mixing the positive electrode slurry composition, applying the positive electrode slurry composition onto a positive electrode current collector, and then drying and rolling the applied positive electrode slurry composition.

[0076] Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry composition on a separate support, peeling the resulting film from the support, and laminating the resulting film on a positive electrode current collector.

[0077] The positive electrode according to an embodiment of the present invention may have excellent positive electrode adhesion. Specifically, in the positive electrode, the positive electrode active material layer may have improved adhesion to the positive electrode current collector. As a result, detachment of the positive electrode is prevented, thereby reducing the cell resistance of the secondary battery, improving the capacity and output characteristics of the battery, and reducing defects occurring during the manufacturing process.

[0078] When measured by a 90° peel test, the positive electrode adhesive strength may be 32 gf / 20 mm or more, specifically 35 gf / 20 mm or more, more specifically 40 gf / 20 mm to 200 gf / 20 mm. This range corresponds to a higher level of positive electrode adhesive strength than that of a conventional positive electrode using lithium iron phosphate. This is due to the average particle diameter D of the lithium iron phosphate. 50 This can be achieved because the dispersant is contained in the positive electrode active material layer in an amount of 0.2 wt % to 0.9 wt %.

[0079] In addition, the positive electrode according to one embodiment of the present invention may have a structure in which the positive electrode active material layer directly faces the positive electrode current collector, and may not include a separate layer for improving adhesion between the positive electrode active material layer and the positive electrode current collector. Even if a separate layer such as a binder layer, adhesive layer, bonding layer, or primer coating layer that may be interposed between the positive electrode current collector and the positive electrode active material layer for improving adhesion is not included, the positive electrode according to the present invention may exhibit excellent adhesion, such that the interfacial adhesion between the positive electrode current collector and the positive electrode active material layer falls within the above numerical range.

[0080] On the other hand, the resistance per unit area of ​​the positive electrode is 9 Ω / cm 2 Specifically, 8Ω / cm 2 More specifically, 7Ω / cm 2 Below, for example, 1Ω / cm 2 ~9Ω / cm 2 The resistance can be achieved by minimizing the aggregation of the lithium iron phosphate and by using a low amount of the dispersant.

[0081] <Lithium secondary battery> Next, the lithium secondary battery according to the present invention will be described.

[0082] The lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0083] In the lithium secondary battery, the positive electrode is as described above. For example, the positive electrode includes a positive electrode active material, a conductive material, a binder, and a dispersant in a positive electrode active material layer, the positive electrode active material includes lithium iron phosphate, and the lithium iron phosphate has an average particle diameter D 50 The particle size is 1.5 μm or more, and the dispersant is contained in the positive electrode active material layer in an amount of 0.2 wt % to 0.9 wt %.

[0084] The negative electrode can be manufactured, for example, by preparing a negative electrode-forming composition containing a negative electrode active material, a negative electrode binder, and a negative electrode conductive material on a negative electrode current collector, and then coating the composition on the negative electrode current collector.

[0085] The negative electrode active material is not particularly limited, and may generally be a compound capable of reversible lithium intercalation and deintercalation. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, and highly crystalline carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and composites containing metallic compounds and carbonaceous materials. Low-crystalline carbon includes soft carbon and hard carbon, while highly crystalline carbon includes natural graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-calcined carbon such as petroleum or coal tar pitch-derived cokes. These materials may be used alone or in combination. A thin film of metallic lithium may also be used as the negative electrode active material.

[0086] The negative electrode conductive material is used to impart conductivity to the electrode and can be any material that is electronically conductive without causing chemical changes in the resulting battery. Specific examples include graphite (e.g., natural graphite or artificial graphite); carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black; carbon-based materials (e.g., carbon fiber and carbon nanotubes); metal powder or fiber (e.g., copper, nickel, aluminum, silver); conductive whiskers (e.g., zinc oxide or potassium titanate); conductive metal oxides (e.g., titanium oxide); and conductive polymers (e.g., polyphenylene derivatives). These materials may be used alone or in combination. The negative electrode conductive material is typically present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0087] The negative electrode binder serves to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or more of these may be used alone or in combination. The negative electrode binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt% of the total weight of the negative electrode active material layer.

[0088] Meanwhile, the negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce 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. may be used.

[0089] The negative electrode current collector may typically have a thickness of 3 to 500 μm, and like the positive electrode current collector, the negative electrode current collector may have fine irregularities on its surface to enhance the binding force of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0090] Meanwhile, in the lithium secondary battery, the separator can be any material commonly used as a separator in lithium secondary batteries. In particular, a material that exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as 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, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. The separator can be a porous thin film having a pore diameter of 0.01 μm to 10 μm and a thickness of 5 μm to 300 μm.

[0091] Meanwhile, in the lithium secondary battery, the electrolyte may include an organic solvent and a lithium salt that are commonly used in electrolytes, and is not particularly limited.

[0092] The organic solvent may be any solvent capable of serving as a medium through which ions involved in the electrochemical reaction of the battery can migrate. Specific examples of the organic solvent include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether and tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylenecarbonate (PC).

[0093] Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0094] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, examples of the lithium salt include LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, and LiB(C, O) . The lithium salt is preferably contained in the electrolyte at a concentration of about 0.6 mol% to 2 mol%.

[0095] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine 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 battery's life characteristics, suppressing battery capacity reduction, improving the battery's discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0096] The lithium secondary battery of the present invention may be manufactured by forming an electrode assembly by disposing a separator between a positive electrode and a negative electrode, and then placing the electrode assembly in a cylindrical or prismatic battery case and injecting an electrolyte thereinto, or by stacking the electrode assemblies, impregnating them with an electrolyte, and then placing the resulting assembly in a battery case and sealing it.

[0097] When fabricating the lithium secondary battery of the present invention, the electrode assembly may be dried to remove one or more organic solvents used in fabricating the positive electrode, such as N-methyl-2-pyrrolidone (NMP), acetone, ethanol, propylene carbonate, ethyl methyl carbonate, ethylene carbonate, and dimethyl carbonate. If an electrolyte having the same organic solvent as that used in fabricating the positive electrode is used, the step of drying the electrode assembly may be omitted.

[0098] The battery case may be one commonly used in the art, and the shape of the battery case is not limited depending on the intended use of the battery. For example, the battery case may be a cylindrical case using a can, a square case, a pouch case, or a coin case.

[0099] The lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, laptops, and digital cameras, energy storage systems (ESS), and electric vehicles such as hybrid electric vehicles (HEV), etc.

[0100] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0101] (Example 1: Production of positive electrode) (1) Preparation of Positive Electrode Slurry Composition Average particle size D as positive electrode active material 50 is 2 μm, and the BET specific surface area is 11 m 2A positive electrode slurry composition was prepared by adding 0.01g of LiFePO4, carbon nanotubes (CNTs) as a conductive material, polyvinylidene difluoride (PVDF) as a binder, and hydrogenated nitrile butadiene rubber (H-NBR) as a dispersant to an N-methylpyrrolidone solvent and stirring. The positive electrode active material, conductive material, binder, and dispersant were present in a weight ratio of 95.7:1.0:3.0:0.3, and the solids content of the positive electrode slurry composition was 60 wt%.

[0102] (2) Manufacturing of the positive electrode The positive electrode slurry composition was applied to a 15 μm-thick aluminum thin film and then vacuum-dried at 130° C. for 10 hours. The positive electrode was then rolled to prepare a positive electrode active material layer with a porosity of 29%. The positive electrode active material layer had a thickness of 98 μm and a loading capacity of 3.6 mAh / cm. 2 It was.

[0103] (Example 2: Production of positive electrode) A positive electrode was prepared in the same manner as in Example 1, except that the positive electrode active material and the dispersant were mixed in a weight ratio of 95.2:0.8.

[0104] (Comparative Example 1: Production of Positive Electrode) A positive electrode was prepared in the same manner as in Example 1, except that the positive electrode active material and the dispersant were mixed in a weight ratio of 94.65:1.35.

[0105] (Comparative Example 2: Production of Positive Electrode) Average particle size D 50 A positive electrode was manufactured in the same manner as in Comparative Example 1, except that a positive electrode active material with a particle size of 0.8 μm was used.

[0106] (Comparative Example 3: Production of Positive Electrode) Average particle size D 50 A positive electrode was prepared in the same manner as in Comparative Example 1, except that a positive electrode active material having a particle size of 1.0 μm was used and the positive electrode active material and the dispersant were mixed in a weight ratio of 95.2:0.8.

[0107] (Comparative Example 4: Production of Positive Electrode) Average particle size D 50 A positive electrode was manufactured in the same manner as in Comparative Example 1, except that a positive electrode active material with a particle size of 1.2 μm was used.

[0108] [Table 1]

[0109] On the other hand, Figs. 1 to 4 show the average particle diameter D 50 are SEM photographs of lithium iron phosphate with particle sizes of 0.8 μm, 1.0 μm, 1.2 μm, and 2.0 μm, respectively. Specifically, Fig. 1 is an SEM photograph of Comparative Example 2, Fig. 2 is an SEM photograph of Comparative Example 3, Fig. 3 is an SEM photograph of Comparative Example 4, and Fig. 4 is an SEM photograph of lithium iron phosphate contained in the positive electrodes prepared in Examples 1 and 2 and Comparative Example 1, where the lithium iron phosphate is formed in the form of primary particles and / or secondary particles in the positive electrodes.

[0110] FIG. 6 is an SEM photograph of a cross section of a positive electrode of Example 2, and FIG. 7 is an SEM photograph of a cross section of a positive electrode of Comparative Example 3. In these figures, bright contrast indicates lithium iron phosphate, and dark contrast indicates clumps of the conductive material and binder. The more uniformly dispersed the conductive material agglomeration regions are, and the smaller the area of ​​each conductive material agglomeration region, the better the dispersion between the positive electrode active material, conductive material, and binder. Furthermore, the more spherical the shape of the conductive material agglomeration regions, the more minimized the surface area of ​​the agglomerated conductive material. As a result, the surface area of ​​the positive electrode active material adjacent to the conductive material that cannot participate in lithium intercalation / deintercalation reactions is minimized, thereby reducing the discharge resistance of the lithium secondary battery.

[0111] In the positive electrode of Example 2, the conductive material agglomeration regions were uniformly dispersed overall, and the deviation in the area of ​​the conductive material agglomeration regions was small, confirming that the conductive material agglomeration regions were nearly spherical, compared to the positive electrode of Comparative Example 3. In the positive electrode of Comparative Example 3, the deviation in the area of ​​the conductive material agglomeration regions was large, with several conductive material agglomeration regions being as large as 10 μm in length in the major axis direction.

[0112] The positive electrode of Example 2 has the same content of dispersant as the positive electrode of Comparative Example 3, but the average particle diameter D of lithium iron phosphate is 50 It can be confirmed that the dispersion of the positive electrode active material, conductive material, and binder is good from the difference in the positive electrode active material, conductive material, and binder. Furthermore, the positive electrode of Example 2 is expected to have better discharge resistance in a lithium secondary battery than the positive electrode of Comparative Example 3 because the conductive material is spherically aggregated.

[0113] (Experimental Example 1 - Evaluation of Positive Electrode Adhesion Strength) The adhesive strength between the positive electrode active material layer and the positive electrode current collector in each of the positive electrodes produced in Examples 1 and 2 and Comparative Examples 1 to 4 was compared.

[0114] Specifically, each of the positive electrodes produced in Examples 1 and 2 and Comparative Examples 1 to 4 was cut to a length of 150 mm and a width of 20 mm, and the positive electrode surface was attached longitudinally to a 75 mm long and 25 mm wide glass slide using double-sided tape. That is, the glass slide was attached to an area corresponding to half of the positive electrode in the longitudinal direction. Then, a roller was rolled 10 times to ensure uniform adhesion of the double-sided tape, producing an evaluation sample.

[0115] Next, the glass slide portion of the evaluation sample was fixed to the sample stage of a Universal Testing Machine (UTM) (LS5, AMETEK), and the half of the positive electrode without the glass slide was connected to the load cell of the UTM. The load cell was moved 50 mm at a speed of 100 mm / min, applying a 90° force, and the load applied to the load cell was measured. The minimum load measured in the 20 mm to 40 mm section of the moving section was recorded as the positive electrode adhesive strength (gf / 20 mm) of each sample. A total of five measurements were made for each positive electrode, and the average values ​​are shown in Table 2 below.

[0116] (Experimental Example 2 - Measurement of Positive Electrode Resistance) The resistance values ​​of the positive electrodes produced in Examples 1 and 2 and Comparative Examples 1 to 4 were measured and compared.

[0117] Specifically, the positive electrodes containing 98 μm-thick positive electrode active material layers produced in Examples 1 and 2 and Comparative Examples 1 to 4 were cut into pieces measuring 50 mm x 50 mm. Using a positive electrode resistance meter (MP tester, HIOKI Corporation), the resistance per unit area (10 mm x 10 mm) was measured in the thickness direction of the positive electrode active material layer under the following measurement conditions. Each positive electrode was measured three times, and the average of the three measurements, with a standard deviation of 10% or less, is shown in Table 2 below.

[0118] - Current: 100μA - Speed: Slow - Voltage range: 0.5V - Resistivity of the positive electrode current collector: 2.82E for the aluminum used above -0.6 Ω cm

[0119] (Experimental Example 3 - Measurement of Cell Resistance) (1) Manufacture of lithium secondary batteries Anode slurry was prepared by mixing artificial graphite as the anode active material, super C as the conductive material, and SBR / CMC as the binder in a weight ratio of 96:1:3. The anode was then coated on one side of a copper current collector, dried at 130°C, and rolled to prepare anode. The loading capacity of the anode active material layer of the prepared anode was 3.6 mAh / cm. 2 The porosity was 29%.

[0120] Next, an 18 μm-thick polypropylene separator was interposed between the fabricated positive and negative electrodes to fabricate an electrode assembly. The electrode assembly was placed in an aluminum pouch-type battery case, and 500 μL of an electrolyte solution consisting of 1.0 M LiPF6 and 2 wt% vinylene carbonate (VC) dissolved in an organic solvent (EC / EMC / DMC = 3:3:4 volume ratio) was poured into it, followed by vacuum sealing. The electrolyte was aged for one day, activated for three hours at 7.9 mAh, and then aged for three more days. Finally, a degassing process was performed to fabricate a lithium secondary battery.

[0121] (2) Cell resistance measurement The cell resistance values ​​of the lithium secondary batteries manufactured using the positive electrodes of Examples 1 and 2 and Comparative Examples 1 to 4 were measured and compared.

[0122] Specifically, for each of the lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 4, the cell resistance (discharge resistance at SOC50) was measured as a value obtained by dividing the voltage drop that occurred when a discharge pulse of 197.5 mAh was applied for 10 seconds at a SOC (State of charge) of 50% by the current value.

[0123] In this case, the initial cell resistance refers to the resistance value measured after the lithium secondary battery is manufactured, and the cell resistance after 100 cycles refers to the resistance value measured after 100 charge / discharge cycles at 26.3 mAh, in the range of 2.5 V to 3.6 V, and in an environment of 45° C. The measurement results are shown in Table 2 below.

[0124] [Table 2]

[0125] From Table 2 above, it can be seen that the positive electrode of Comparative Example 1, in which the dispersant content in the positive electrode active material layer exceeds 0.9 wt %, has significantly lower positive electrode adhesion than the positive electrodes of Examples 1 and 2, and that the positive electrode of Comparative Example 1 has higher positive electrode resistance than the positive electrodes of Examples 1 and 2. It can also be seen that the initial cell resistance of the lithium secondary battery using the positive electrode of Comparative Example 1 is higher than that of Example 1, and that the cell resistance after 100 cycles increases significantly compared to the initial cell resistance.

[0126] Average particle size D of lithium iron phosphate 50It can be seen that the positive electrode of Comparative Example 3, in which the particle size is less than 1.5 μm, has lower positive electrode adhesion strength than the positive electrodes of Examples 1 and 2, and that the positive electrode of Comparative Example 3 has significantly higher positive electrode resistance than the positive electrodes of Examples 1 and 2. In addition, it can be seen that the initial cell resistance of a lithium secondary battery using the positive electrode of Comparative Example 3 is higher than that of Example 1, and that the cell resistance after 100 cycles increases compared to the initial cell resistance. However, it can be seen that the positive electrode of Comparative Example 3 has a larger particle size of the positive electrode active material than Comparative Example 2 and a lower content of dispersant than Comparative Example 4, and therefore, no detachment of the positive electrode active material layer occurs.

[0127] Average particle size D of lithium iron phosphate 50 The positive electrodes of Comparative Examples 2 and 4, in which the thickness was less than 1.5 μm but the dispersant content in the positive electrode active material layer exceeded 0.9 wt %, exhibited significantly reduced positive electrode adhesion. During the rolling process, the positive electrode active material layer of Comparative Example 2 was completely detached from the current collector, while the positive electrode active material layer of Comparative Example 4 was partially detached from the current collector. For example, FIG. 5 is a photograph showing a state in which a positive electrode formed using the positive electrode slurry composition of Comparative Example 4 was partially detached after rolling, and the positive electrode active material layer of Comparative Example 4 was partially detached from the current collector as shown. Therefore, it was impossible to measure the positive electrode adhesion, positive electrode resistance, initial cell resistance, and cell resistance after 100 cycles for the positive electrodes and lithium secondary batteries of Comparative Examples 2 and 4.

[0128] Meanwhile, it can be seen that the positive electrode of Example 1 has higher positive electrode adhesion and lower resistance than the positive electrode of Example 2. It can also be seen that the lithium secondary battery using the positive electrode of Example 1 has lower initial cell resistance and cell resistance after 100 cycles than the lithium secondary battery using the positive electrode of Example 2.

Claims

1. A positive electrode slurry composition comprising a positive electrode active material, a conductive material, a binder, a dispersant, and a solvent, the positive electrode active material contains lithium iron phosphate, The average particle diameter D of the lithium iron phosphate ５０ is 1.5 μm or more and 4.5 μm or less, the dispersant is a hydrogenated nitrile-butadiene rubber, the dispersant is included in an amount of 0.2 parts by weight to 0.9 parts by weight based on 100 parts by weight of the solid content in the positive electrode slurry composition; the conductive material is a carbon nanotube; The positive electrode slurry composition includes the conductive material in an amount of 0.1 to 3.0 parts by weight per 100 parts by weight of a solid content in the positive electrode slurry composition.

2. The positive electrode slurry composition of claim 1 , wherein the lithium iron phosphate is in the form of secondary particles formed by bonding a plurality of primary particles of lithium iron phosphate to each other.

3. 2. The positive electrode slurry composition of claim 1, wherein the lithium iron phosphate is a compound represented by the following formula 1: [Chemical formula 1] Li １＋ａ Fe １－ｘ M ｘ (PO ４－ｂ )X ｂ (In the above Chemical Formula 1, M includes one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; X includes one or more elements selected from the group consisting of F, S, and N; and a, b, and x are −0.5≦a≦0.5, 0≦b≦0.1, and 0≦x≦0.5, respectively.)

4. The positive electrode slurry composition of claim 1, wherein the lithium iron phosphate is contained in an amount of 94.8 to 98.0 parts by weight based on 100 parts by weight of a solid content in the positive electrode slurry composition.

5. The positive electrode slurry composition according to claim 1, wherein the dispersant is contained in an amount of 0.2 to 0.7 parts by weight based on 100 parts by weight of a solid content in the positive electrode slurry composition.

6. The positive electrode slurry composition according to claim 1, wherein the binder is contained in an amount of 1 to 4 parts by weight based on 100 parts by weight of a solid content in the positive electrode slurry composition.

7. 7. The positive electrode slurry composition according to claim 1, wherein the positive electrode slurry composition has a solid content of 40% by weight to 75% by weight.

8. a positive electrode current collector; and a positive electrode active material layer located on at least one surface of the positive electrode current collector, The positive electrode active material layer is The positive electrode active material includes a conductive material, a binder, and a dispersant. the positive electrode active material contains lithium iron phosphate, The average particle diameter D of the lithium iron phosphate ５０ is 1.5 μm or more and 4.5 μm or less, the dispersant is a hydrogenated nitrile-butadiene rubber, the dispersant is contained in the positive electrode active material layer in an amount of 0.2 wt % to 0.9 wt %; the conductive material is a carbon nanotube; The conductive material is contained in the positive electrode active material layer in an amount of 0.1% by weight to 3.0% by weight.

9. 9. The positive electrode according to claim 8, wherein the positive electrode adhesive strength measured by a 90° peel test is 32 gf / 20 mm or more.

10. The resistance per unit area in the thickness direction of the positive electrode is 9 Ω / cm ２ 9. The positive electrode of claim 8, wherein:

11. The positive electrode according to claim 8 , wherein the positive electrode active material layer directly faces the positive electrode current collector.

12. The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. the positive electrode includes a positive electrode active material, a conductive material, a binder, and a dispersant in a positive electrode active material layer; the positive electrode active material contains lithium iron phosphate, The average particle diameter D of the lithium iron phosphate ５０ is 1.5 μm or more and 4.5 μm or less, the dispersant is a hydrogenated nitrile-butadiene rubber, the dispersant is contained in the positive electrode active material layer in an amount of 0.2 wt % to 0.9 wt %; the conductive material is a carbon nanotube; The conductive material is contained in the positive electrode active material layer in an amount of 0.1% by weight to 3.0% by weight.

13. agitating and mixing the cathode slurry composition of claim 1; and applying the positive electrode slurry composition onto a positive electrode current collector, followed by drying and rolling.

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