Positive electrode slurry composition, positive electrode manufactured using same, and battery comprising same

Abstract

The present invention relates to a positive electrode slurry composition for reducing a curl phenomenon in an electrode, a positive electrode manufactured using the positive electrode slurry composition, and a battery comprising the positive electrode. In the positive electrode paste composition, based on the total weight of the composition, the composition comprises 10 wt% to 78 wt% of a positive electrode active material, 0.1 wt% to 10 wt% of a conductive material, 1 wt% to 50 wt% of a binder, 0.1 wt% to 10 wt% of an alcohol, and the balance of water, where the composition comprises 0.1 wt% to 15 wt% of an alcohol and 85 wt% to 99.9 wt% of water based on the total weight of the alcohol and water, wherein the positive electrode active material is a sulfur-carbon compound, the binder is a 3% aqueous solution which is obtained by mixing two polyacrylic acids according to a weight ratio of 5: 2 and is completely neutralized by lithium hydroxide, and the alcohol is propanol or ethanol. The positive electrode slurry composition can greatly improve the dispersibility of the positive electrode active material and the conductive material, and significantly reduce the curl phenomenon in the electrode.

Description

[0001] This invention patent application is a divisional application based on the Chinese invention patent application with application date of January 11, 2019, application number 201980006826.X, and invention name “Positive electrode slurry composition, positive electrode manufactured using the positive electrode slurry composition, and battery containing the positive electrode”. Technical Field

[0002] This application claims priority from Korean Patent Application No. 10-2018-0003656 filed on January 11, 2018, with the Korean Intellectual Property Office (KIPO), and Korean Patent Application No. 10-2019-0003703 filed on January 11, 2019, with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a positive electrode slurry composition, a positive electrode manufactured using the positive electrode slurry composition, and a battery including the positive electrode. Background Art

[0004] As the application fields of energy storage technology expand not only to mobile phones, tablets and laptop computers, and camcorders, but also to electric vehicles (EVs) and hybrid electric vehicles (HEVs), the demand for research and development of electrochemical devices for energy storage continues to increase.

[0005] In particular, attention has been paid to the development of secondary batteries such as rechargeable / dischargeable lithium-sulfur batteries, etc. In recent years, research and development into designing new electrodes and batteries has been actively conducted to improve the capacity density and specific energy of secondary batteries.

[0006] Lithium-sulfur (Li-S) batteries have attracted considerable attention as next-generation secondary batteries that can replace lithium-ion batteries due to their high energy density. Generally speaking, a lithium-sulfur battery has a structure in which a lithium electrolyte is impregnated into an electrode assembly, which includes a positive electrode containing a sulfur-carbon composite as an electrode active material, a negative electrode containing lithium metal or a lithium alloy, and a separator.

[0007] The positive electrode of such a lithium-sulfur battery is generally manufactured by coating a positive electrode slurry on a metal foil. In this case, the positive electrode slurry is prepared by mixing an electrode mixture containing a positive electrode active material for storing energy, a conductive material for imparting conductivity, and a binder (PVdF) for adhering them to the electrode foil in a solvent such as water and N-methylpyrrolidone (NMP).

[0008] In the above-mentioned positive electrode slurry, the dispersion of the positive electrode active material and / or the conductive material has a significant impact on the processability during electrode manufacturing and the characteristics of the resulting electrode. Therefore, various methods have been studied to improve the dispersion of the positive electrode active material and / or the conductive material in the positive electrode slurry.

[0009] For example, Korean Patent Publication No. 10-2015-0025665 discloses a "positive electrode slurry for a secondary battery, characterized by comprising a positive electrode active material, a conductive material, a binder, a dispersant, and an aqueous solvent, wherein the dispersant is a copolymer comprising a main chain having ionic characteristics and a side chain having nonionic surfactant characteristics."

[0010] However, as disclosed in this patent document, when an additional dispersant is used, the manufacturing process of the electrode becomes complicated and results in an increase in the manufacturing cost of the electrode, which is economically undesirable.

[0011] Therefore, there is a need to develop a method capable of improving the dispersibility of a positive electrode active material and / or a conductive material without using any additional dispersant.

[0012] [Prior art literature]

[0013] [Patent Document]

[0014] Korean Patent Publication No. 10-2015-0025665 Summary of the Invention

[0015]

Technical Issues

[0016] The present invention is proposed to solve the problems of the prior art. One object of the present invention is to provide a slurry composition for manufacturing a positive electrode, which can greatly improve the dispersibility of the positive electrode active material and the conductive material, reduce the surface roughness of the electrode, and significantly reduce the curling phenomenon in the electrode.

[0017] Another object of the present invention is to provide a slurry composition for manufacturing a positive electrode, which shows excellent dispersibility without using any additional dispersant, suppresses the curling phenomenon in the electrode, and has advantages in the manufacturing process of the battery.

[0018] Another object of the present invention is to provide a positive electrode for a battery manufactured using the slurry composition for manufacturing a positive electrode and a battery comprising the positive electrode.

[0019]

Technical solution

[0020] In order to solve the above problems, according to one aspect of the present invention, a positive electrode slurry composition is provided, which includes a positive electrode active material, a binder, alcohol and water, wherein the content of the alcohol is in the range of 0.1 wt % to 10 wt % based on the total weight of the composition.

[0021] According to another aspect of the present invention, a positive electrode is provided. The positive electrode is manufactured by coating the positive electrode slurry composition of the present invention on a current collector.

[0022] According to yet another aspect of the present invention, there is provided a battery, comprising:

[0023] The positive electrode of the present invention;

[0024] a negative electrode comprising lithium metal or a lithium alloy as the negative electrode active material;

[0025] A separator provided between the positive electrode and the negative electrode; and

[0026] electrolytes.

[0027] Beneficial effects

[0028] The slurry composition for manufacturing a positive electrode according to the present invention has the effects of significantly improving the dispersibility of the positive electrode active material and the conductive material, reducing the surface roughness of the electrode, and significantly reducing the curling phenomenon in the electrode. In addition, the slurry composition of the present invention has the economic advantage of not using a dispersant or significantly reducing the amount of dispersant used.

[0029] A battery including a positive electrode manufactured using the slurry composition for manufacturing a positive electrode has the effects of greatly improving capacity, life characteristics, and economic feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 These are photographs obtained by photographing the curled states of the electrodes manufactured in Examples 5 to 8 and Comparative Examples 4 and 5, observed in Experimental Example 1. DETAILED DESCRIPTION

[0031] Hereinafter, the present invention will be described in more detail.

[0032] The present invention relates to a positive electrode slurry composition, which comprises a positive electrode active material, a binder, alcohol and water, characterized in that the content of the alcohol is in the range of 0.1 wt % to 10 wt % based on the total weight of the composition.

[0033] The inventors have noticed that the positive electrode active material and conductive material of the battery are not easily mixed with a strong polar binder or water in an aqueous slurry. In other words, since very weak polar materials are used as the positive electrode active material and conductive material, these very weak polar materials are not easily mixed with a strong polar binder or water in an aqueous slurry. Therefore, the present invention is characterized in that a solution to the above-mentioned problem is provided. In other words, the present invention has the following technical features, namely, adding an amphiphilic alcohol solvent to improve the dispersibility of carbon and sulfur particles that exhibit weak polarity. Since the above-mentioned alcohol solvent evaporates during the drying process so that it does not remain in the electrode, the weight of the electrode does not increase. In addition, since the alcohol solvent does not increase the resistance, the energy density of the electrode does not decrease.

[0034] A C1 to C5 lower alcohol aqueous solution can be used as the alcohol aqueous solution. Alcohols with very high vapor pressures have the disadvantage that the solid content in the slurry may decrease during slurry preparation due to their high evaporation rate. In addition, alcohols with very low vapor pressures have the disadvantage that the drying temperature needs to be increased or the drying time needs to be extended due to their low drying rate. Among the C1 to C5 lower alcohol aqueous solutions, a propanol aqueous solution can be more preferably used. This is because a propanol aqueous solution has a vapor pressure similar to that of water within the temperature range of 20°C to 80°C for slurry preparation and electrode drying. Therefore, it has a low probability of reducing the dispersion effect and causing changes in the solid content in the slurry due to evaporation of the alcohol during slurry preparation, and is suitable for conventional electrode drying procedures without requiring major changes. The propanol aqueous solution includes a 1-propanol aqueous solution.

[0035] In the present invention, the alcohol may be included in an amount of 0.1 to 10 wt %, more preferably 1 to 7 wt %, based on the total weight of the composition.

[0036] When the alcohol aqueous solution contained in the positive electrode slurry composition is contained within the above-mentioned content range, the dispersibility of the positive electrode active material and / or the conductive material is greatly improved, the surface roughness of the electrode is reduced, and the curling phenomenon in the electrode is significantly reduced. In particular, when the electrode curls during electrode manufacturing, cracks may appear on the electrode when the electrode is flattened during the manufacturing process of the battery, or the electrode may be separated from the current collector, which will lead to increased processing difficulty and cost. Therefore, the improvement of these problems provides great advantages in manufacturing electrodes.

[0037] When the alcohol is included in an amount less than 0.1 wt %, it may be difficult to expect the desired effects as described above. On the other hand, when the alcohol content is greater than 10 wt %, the solubility of the binder in the alcohol may decrease, making it difficult to prepare the slurry.

[0038] The positive electrode slurry composition may include 10 to 78 wt % of the positive active material, 1 to 50 wt % of the binder, 0.1 to 10 wt % of the alcohol, and the balance water, based on the total weight of the composition, but the present invention is not limited thereto.

[0039] In addition, the composition may further include 0.1 to 10 wt % of a conductive material.

[0040] The positive electrode slurry composition of the present invention may include 2 to 45 parts by weight, more preferably 5 to 30 parts by weight, of the alcohol, based on 100 parts by weight in total of the positive active material and the conductive material.

[0041] In addition, based on the total weight of the alcohol and the water, the positive electrode slurry composition of the present invention may include 0.1 wt % to 15 wt % of the alcohol and 85 wt % to 99.9 wt % of water, more preferably 0.5 wt % to 10 wt % of the alcohol and 90 wt % to 99.5 wt % of water, and further preferably 1 wt % to 7 wt % of the alcohol and 93 wt % to 99 wt % of water.

[0042] When the content ratio of the alcohol contained in the positive electrode slurry composition satisfies this content range, the dispersibility of the positive electrode active material and / or the conductive material can be greatly improved, the surface roughness of the electrode can be reduced, and the curling phenomenon of the electrode can be significantly reduced. In particular, when the electrode curls during electrode manufacturing, cracks may appear on the electrode when the electrode is flattened during the manufacturing process of the battery, or the electrode may be detached from the current collector, which will lead to increased processing difficulty and cost. Therefore, the improvement of these problems provides great advantages in manufacturing electrodes.

[0043] The positive electrode slurry composition of the present invention has a very excellent characteristic of greatly improving the dispersibility of the positive electrode active material and / or the conductive material without using any dispersant.

[0044] The positive electrode slurry composition of the present invention can be preferably used to manufacture a positive electrode for a lithium-sulfur battery. In this case, a sulfur-carbon composite can be preferably used as the positive electrode active material.

[0045] Furthermore, the present invention relates to a positive electrode manufactured by coating the positive electrode slurry composition of the present invention on a current collector.

[0046] A current collector known in the related art may be used as the current collector, and the manufacturing method of the positive electrode may also be performed according to a method known in the art.

[0047] The positive electrode of the present invention provides a very excellent effect on the energy density of the electrode.

[0048] Furthermore, the present invention relates to a battery comprising:

[0049] The positive electrode of the present invention;

[0050] a negative electrode comprising lithium metal or a lithium alloy as the negative electrode active material;

[0051] A separator provided between the positive electrode and the negative electrode; and

[0052] electrolytes.

[0053] The battery may be a lithium-sulfur battery.

[0054] Regarding the positive electrode, the above contents can be applied as they are.

[0055] The negative electrode of the battery according to the present invention may be a negative electrode containing lithium metal or lithium alloy as a negative electrode active material. In this case, a negative electrode known in the related art can be used as the negative electrode without any limitation.

[0056] As the lithium alloy used as the negative electrode active material, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn can be used.

[0057] The separator provided between the positive electrode and the negative electrode is used to isolate or insulate the positive electrode and the negative electrode from each other and to enable lithium ions to transfer between the positive electrode and the negative electrode, and can be composed of a porous non-conductive material or an insulating material, but the present invention is not limited thereto. For example, a separator known in the related art can be used here.

[0058] The separator may be a separate component such as a membrane, or may be a coating added to the positive electrode and / or negative electrode. For example, materials constituting the separator include polyolefins such as polyethylene and polypropylene; glass fiber filter paper; and ceramics, but the present invention is not limited thereto. In this case, the separator may have a thickness of about 5 μm to about 50 μm, particularly about 5 μm to about 25 μm.

[0059] As the electrolyte, an electrolyte known in the related art can be used. For example, an electrolyte containing a lithium salt and an organic solvent can be used. The electrolyte can be configured so that the electrolyte is impregnated into the negative electrode, the positive electrode, and the separator.

[0060] For example, a single solvent or a mixture of two or more organic solvents can be used as the organic solvent contained in the electrolyte. When a mixture of two or more organic solvents is used, one or more solvents can be selected from two or more groups of the weak polar solvent group, the strong polar solvent group and the lithium metal protection solvent group, and then used. The weak polar solvent is defined as a solvent with a dielectric constant of less than 15 that can dissolve sulfur element in an aromatic compound, a bicyclic ether or a non-cyclic carbonate, and the strong polar solvent is defined as a solvent with a dielectric constant greater than 15 that can dissolve lithium polysulfide in a cyclic carbonate, a sulfoxide compound, a lactone compound, a ketone compound, an ester compound, a sulfate compound or a sulfite compound, and the lithium metal protection solvent is defined as a solvent with a charge / discharge cycle efficiency of more than 50% that forms a stable solid electrolyte interface (SEI) on lithium metal, such as a saturated ether compound, an unsaturated ether compound, a heterocyclic compound containing N, O, S or a combination thereof.

[0061] Specific examples of the weak polar solvent include xylene, dimethoxyethane, 2-methyltetrahydrofuran, diethyl carbonate, dimethyl carbonate, toluene, dimethyl ether, ethyl ether, diglyme, tetraglyme, and the like, but the present invention is not limited thereto.

[0062] Specific examples of the strongly polar solvent include hexamethylphosphoric triamide, γ-butyrolactone, acetonitrile, ethylene carbonate, propylene carbonate, N-methylpyrrolidone, 3-methyl-2- Oxazolidinone, dimethylformamide, sulfolane, dimethylacetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, ethylene glycol sulfite, etc., but the present invention is not limited thereto.

[0063] Specific examples of lithium metal protective solvents include tetrahydrofuran, ethylene oxide, dioxolane, 3,5-dimethylisothiazolinone, oxazole, furan, 2-methylfuran, 1,4-dioxane, 4-methyldioxolane, etc., but the present invention is not limited thereto.

[0064] In addition to the features of the present invention as described above, the battery may be constructed by applying techniques known in the relevant art.

[0065] [Embodiments of the present invention]

[0066] Hereinafter, preferred embodiments of the present invention are provided to help understand the present invention. However, it should be understood by those skilled in the art that the detailed description disclosed herein is given only by way of illustration of the present invention and that various changes and modifications may be made without departing from the spirit and scope of the present invention. In addition, it will be apparent that such changes and modifications fall within the scope of the appended claims.

[0067] Example 1: Preparation of a slurry composition for manufacturing a positive electrode

[0068] Sulfur (available from Sigma-Aldrich) and carbon nanotubes (CNTs) were mixed and heat-treated at 155°C to prepare a sulfur-carbon composite. Vapor-grown carbon fibers (VGCFs) were used as the conductive material. A 3% aqueous solution in which two polyacrylic acids (available from Sigma-Aldrich; molecular weights: 450,000 and 1,250,000; and mixed in a weight ratio of 5:2) were completely neutralized by lithium hydroxide (available from Sigma-Aldrich) was used as a binder. The sulfur-carbon composite, conductive material, and binder solution as described above were mixed with a 1-propanol aqueous solution to prepare a slurry composition for manufacturing a positive electrode. In the slurry, the sulfur-carbon composite, conductive material, and binder were present in a weight ratio of 88:5:7, and the solid component and solvent (1-propanol and water) were present in a weight ratio of 23:77. In addition, the content of 1-propanol in the slurry was set to 0.77% by weight.

[0069] Example 2: Preparation of slurry composition for manufacturing positive electrode

[0070] A slurry composition for producing a positive electrode was prepared in the same manner as in Example 1, except that the content of 1-propanol in the slurry used in Example 1 was set to 3.85 wt %.

[0071] Example 3: Preparation of slurry composition for manufacturing positive electrode

[0072] A slurry composition for producing a positive electrode was prepared in the same manner as in Example 1, except that the content of 1-propanol in the slurry used in Example 1 was set to 7.7% by weight.

[0073] Example 4: Preparation of slurry composition for manufacturing positive electrode

[0074] A slurry composition for manufacturing a positive electrode was prepared in the same manner as in Example 1, except that ethanol was used instead of 1-propanol in the slurry used in Example 1, and the content of ethanol was set to 3.85 wt %.

[0075] Comparative Example 1: Preparation of a slurry composition for manufacturing a positive electrode

[0076] A slurry composition for manufacturing a positive electrode was prepared in the same manner as in Example 1, except that water was used instead of the 1-propanol aqueous solution used as a solvent in Example 1.

[0077] Comparative Example 2: Preparation of a slurry composition for manufacturing a positive electrode

[0078] The sulfur-carbon composite, conductive material, and binder used in Comparative Example 1 were further mixed with a dispersant (PVA; polyvinyl alcohol) to a weight ratio of 87:5:7:1. A slurry composition for manufacturing a positive electrode was prepared by adjusting the weight ratio of the solid component to water to 25:75.

[0079] Comparative Example 3: Preparation of a slurry composition for manufacturing a positive electrode

[0080] A slurry composition for producing a positive electrode was prepared in the same manner as in Example 1, except that the content of 1-propanol in the slurry used in Example 1 was set to 11.55 wt %. However, since the solubility of the binder decreased, the viscosity of the slurry increased to such an extent that the components could not be mixed, and thus the slurry could not be prepared in a normal manner.

[0081] Example 5: Preparation of positive electrode

[0082] The slurry composition for manufacturing a positive electrode prepared in Example 1 was applied to an aluminum current collector until the amount of the slurry composition reached 11.4 mg / cm 2 To manufacture the positive electrode.

[0083] Example 6: Preparation of positive electrode

[0084] The slurry composition for manufacturing a positive electrode prepared in Example 2 was applied to an aluminum current collector until the amount of the slurry composition reached 11.4 mg / cm 2 To manufacture the positive electrode.

[0085] Example 7: Preparation of positive electrode

[0086] The slurry composition for manufacturing a positive electrode prepared in Example 3 was applied to an aluminum current collector until the amount of the slurry composition reached 11.4 mg / cm 2 To manufacture the positive electrode.

[0087] Example 8: Preparation of positive electrode

[0088] The slurry composition for manufacturing a positive electrode prepared in Example 4 was applied to an aluminum current collector until the amount of the slurry composition reached 11.4 mg / cm 2 To manufacture the positive electrode.

[0089] Comparative Example 4: Preparation of positive electrode

[0090] The slurry composition for manufacturing a positive electrode prepared in Comparative Example 1 was applied to an aluminum current collector until the amount of the slurry composition reached 11.4 mg / cm 2 To manufacture the positive electrode.

[0091] Comparative Example 5: Preparation of positive electrode

[0092] The slurry composition for manufacturing a positive electrode prepared in Comparative Example 2 was applied to an aluminum current collector until the amount of the slurry composition reached 11.4 mg / cm 2 To manufacture the positive electrode.

[0093] Examples 9 to 12 and Comparative Examples 6 to 7: Production of Batteries

[0094] Lithium-sulfur secondary batteries of Examples 9 to 12 and Comparative Examples 6 and 7 were manufactured using the positive electrodes manufactured in Examples 5 and 8 and Comparative Examples 4 and 5; a lithium foil having a thickness of approximately 45 μm as a negative electrode; an electrolyte obtained by adding 1M lithium bistrifluoromethanesulfonyl imide (LiTFSI) and 1% by weight of LiNO3 to an ether solvent; and a 20 μm thick polyolefin as a separator. Details are listed in Table 1 below.

[0095]

Table 1

[0096]

[0097] Experimental Example 1: Evaluation of physical properties and shape of electrodes manufactured using the slurry composition for manufacturing a positive electrode

[0098] The surface roughness values ​​of the positive electrodes manufactured in Examples 5 to 8 and Comparative Examples 4 and 5 were measured, and the shapes of the electrodes after drying were observed with the naked eye. The results are listed in Tables 2 and 3 below. Figure 1 middle.

[0099]

Table 2

[0100]

[0101] As shown in Table 2 and Figure 1 As can be seen in FIG, it was confirmed that the surface roughness values ​​of the electrodes manufactured in Examples 5 to 8 of the present invention were the same as or significantly improved compared to the electrode of Comparative Example 4 in which only water was used as a solvent.

[0102] It is also shown that the electrode curling of the electrodes manufactured in Examples 5 to 8 of the present invention after drying the electrodes is significantly improved compared to the electrode of Comparative Example 4 in which only water is used as a solvent, and is the same as or significantly improved compared to the electrode of Comparative Example 5 in which a dispersant is used.

[0103] In addition, the electrode of Comparative Example 4, in which only water was used as a solvent, had the following problems: cracks appeared on the electrode when the rolled electrode was flattened, and the electrode was detached. However, in the case of the electrodes of Examples 5 to 8 of the present invention, no cracks or detachment occurred.

[0104] Experimental Example 2: Evaluation of Battery Energy Density

[0105] The energy densities of the batteries manufactured in Examples 9 to 12 and Comparative Example 7 were measured according to the following method.

[0106] <Analysis Conditions>

[0107] - Equipment: 100mA class charger / discharger

[0108] -Discharge: 0.1C, constant current mode, discharge ends when the voltage reaches 1.8V

[0109] - Temperature: 25℃

[0110] The energy density was calculated by dividing the energy of the battery measured after discharge by the weight of the positive electrode (excluding the current collector), and three identical batteries were manufactured for each condition. In this case, the results are expressed as an average value.

[0111]

Table 3

[0112]

[0113] As can be seen from Table 3, it is shown that the batteries manufactured in Examples 9 to 12 of the present invention exhibited excellent energy density even when no additional dispersant was used, compared with the battery of Comparative Example 7 in which a dispersant was used.

Claims

1. A positive electrode slurry composition for reducing curling in an electrode, wherein the composition comprises, based on the total weight of the composition, 10 to 78 weight % of a positive electrode active material, 0.1 to 10 weight % of a conductive material, 1 to 50 weight % of a binder, 0.1 to 10 weight % of an alcohol, and the balance water, wherein the composition comprises 0.1 wt % to 15 wt % of the alcohol and 85 wt % to 99.9 wt % of water based on the total weight of the alcohol and the water, The positive electrode active material is a sulfur-carbon composite. The binder is a 3% aqueous solution of two polyacrylic acids having molecular weights of 450,000 and 1,250,000, respectively, mixed in a weight ratio of 5:2 and completely neutralized with lithium hydroxide, wherein the two polyacrylic acids and the lithium hydroxide are purchased from Sigma-Aldrich. The alcohol is propanol or ethanol. 2 . The positive electrode slurry composition according to claim 1 , wherein the composition comprises 2 to 45 parts by weight of the alcohol based on a total of 100 parts by weight of the positive electrode active material and the conductive material. 3 . The positive electrode slurry composition according to claim 1 , wherein the composition is used to manufacture a positive electrode for a lithium-sulfur battery. 4 . A positive electrode manufactured by coating the positive electrode slurry composition according to claim 1 on a current collector.

5. A battery comprising: The positive electrode according to claim 4; a negative electrode comprising lithium metal or a lithium alloy as the negative electrode active material; A separator provided between the positive electrode and the negative electrode; and electrolytes.

6. The battery according to claim 5, wherein the lithium alloy is an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al, and Sn.

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