Cathode active material composite and method for producing the same

Abstract

The present invention relates to a novel positive electrode active material composite in which a conductive material is uniformly coated on the surface of a positive electrode active material. The positive electrode active material composite of the present invention has low powder resistance, excellent electrical properties, and the conductive material is uniformly dispersed on the surface of the positive electrode active material, making it particularly suitable for use in the manufacture of dry electrodes.

Description

[Technical Field]

[0001] This application claims priority rights under Korean Patent Applications No. 10-2023-0078417, No. 10-2023-0078418, No. 10-2023-0078419 and No. 10-2023-0078420 dated 19 June 2023, and all content disclosed in the documents of said Korean Patent Applications is incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material composite comprising a conductive material and a positive electrode active material, and a method for producing the same. [Background technology]

[0003] Electrical energy is easy to convert, transmit, and store, and offers the advantage of being usable in a variety of situations regardless of time or place. As a result, it is used in many areas of modern society. In particular, products that store and use electrical energy, such as portable devices and electric vehicles, have become widely used recently, and consequently, research on rechargeable batteries capable of storing electrical energy is also actively being conducted.

[0004] Various types of rechargeable batteries have been developed that can be used again after all their electrical energy has been discharged, but lithium-ion batteries, which have the best energy density, are used and researched very frequently.

[0005] A lithium secondary battery generally consists of four major components: a positive electrode, a negative electrode, an electrolyte, and a separator. Most lithium secondary batteries are manufactured by producing the positive and negative electrodes separately, assembling them with the separator to form an electrode assembly, and then injecting the electrolyte into the assembly. On the other hand, when manufacturing the positive and negative electrodes, the most widely used method is the wet process. The wet process involves mixing an active material with a conductive material, a binder, and an organic solvent to produce a slurry, and then coating the slurry onto a current collector. In the case of the wet process, there is an advantage that a relatively uniform coating can be achieved. However, during the process of removing the solvent, defects may occur in the electrode, and there is a limit in that it is difficult to increase the thickness of a single electrode beyond a certain level due to the fluidity of the slurry itself. Also, as the organic solvent used generally has a high boiling point, a large amount of energy is consumed during the process of removing the solvent, and there is also a problem that environmental pollution may be caused depending on the use of the solvent.

[0006] Therefore, as a method for solving the problems of such a conventional wet process, recently, a dry process has been studied. The dry process is a method of manufacturing an electrode by dry-mixing an active material, a conductive material, and a binder without using an organic solvent and micro-fibrillating the binder. However, such a normal dry process also has disadvantages in the dispersion of the conductive material itself.

[0007] Therefore, there is a need for research on a novel method for manufacturing an electrode that can uniformly disperse the conductive material and also solve the problems in the conventional wet process.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] The object of the present invention relates to a novel cathode active material composite and a method for manufacturing the same, which can be used in the dry manufacturing process of a cathode. Since the cathode active material composite of the present invention has a form in which a conductive material is uniformly coated on the surface of the cathode active material, the dispersibility of the conductive material in the electrode state can be improved.

[0010] Further, the cathode active material composite of the present invention can be manufactured in the form of an electrode without using a solvent hereinafter, and does not have the limitations occurring in the conventional wet manufacturing process of a cathode.

Means for Solving the Problems

[0011] In order to solve the above problems, the present invention provides a cathode active material composite and a method for manufacturing the same.

[0012] Specifically, (1) the present invention provides a cathode active material composite including a cathode active material and a coating layer formed on the surface of the cathode active material, wherein the coating layer contains a conductive material and the content of residual solvent is 0.18 to 1.0% by weight.

[0013] (2) The present invention provides a cathode active material composite according to (1) above, wherein the content of the residual solvent is 0.2 to 0.5% by weight.

[0014] (3) The present invention provides a cathode active material composite according to (1) or (2) above, wherein the cathode active material is LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mn c )O2 (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + C = 1), LiNi 1-y Co y O2 (O < y < 1), LiCo 1-y Mn y O2 (O < y < 1), LiNi 1-y Mn y O2 (O ≦ y < 1), Li(Ni a Co b Mn c )O4 (0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + C = 2), LiMn 2-z ​z O4(0 < z < 2), LiMn 2-z Co z To provide a positive electrode active material composite that is one or more selected from the group consisting of O4(0 < z < 2), LiCoPO4, and LiFePO4.

[0015] (4) In any one of (1) to (3) above, the present invention provides a positive electrode active material composite in which the conductive material is one or more selected from the group consisting of single-walled carbon nanofibers, multi-walled carbon nanofibers, carbon black, and ketjen black.

[0016] (5) In any one of (1) to (4) above, the present invention provides a positive electrode active material composite in which the average diameter of the single-walled carbon nanotube is 0.5 to 2 nm.

[0017] (6) In any one of (1) to (5) above, the present invention provides a positive electrode active material composite in which the average diameter of the multi-walled carbon nanotube is 100 nm or less.

[0018] (7) In any one of (1) to (6) above, the present invention provides a positive electrode active material composite in which the D50 of the carbon black is 1 to 50 μm.

[0019] (8) In any one of (1) to (7) above, the present invention provides a positive electrode active material composite in which the pore volume of the ketjen black is 200 to 600 cm 3 / 100 g.

[0020] (9) In any one of (1) to (8) above, the present invention provides a positive electrode active material composite in which the content of the conductive material with respect to the total weight of the positive electrode active material composite is 0.01 to 10% by weight.

[0021] (10) The present invention provides a positive electrode active material composite in which, in any one of (1) to (9) above, the residual solvent is one or more selected from the group consisting of amide polar organic solvents, alcohol solvents, glycol solvents, glycol ether solvents, ketone solvents and ester solvents, and the boiling point of the residual solvent is 120°C or lower.

[0022] (11) The present invention provides a method for producing a positive electrode active material composite, comprising the steps of: (S1) mixing the conductive material, dispersant and solvent to produce a predispersion; (S2) mixing the predispersion with a positive electrode active material to produce a positive electrode active material mixture; and (S3) drying the positive electrode active material mixture to produce a positive electrode active material composite, wherein the solvent is one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents and ester-based solvents, and the boiling point of the solvent is 120°C or lower.

[0023] (12) The present invention provides a method for producing a cathode active material composite in which step S3 is carried out under temperature conditions of 60 to 200°C as described in (11).

[0024] (13) The present invention provides a method for producing a cathode active material composite in which step S3 is carried out for 0.5 to 8 hours, in accordance with (11) or (12).

[0025] (14) The present invention provides a method for producing a positive electrode active material composite in which, in any one of (11) to (13), the initial viscosity of the pre-dispersion produced in step S1 is 40,000 cP or less. [Effects of the Invention]

[0026] The positive electrode active material composite of the present invention has technical advantages in that it has low powder resistance, excellent electrical properties, and can be manufactured into electrode form without the use of solvents, thus avoiding the problems associated with conventional wet processes. [Modes for carrying out the invention]

[0027] The present invention will be described in more detail below.

[0028] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0029] Cathode active material composite The present invention provides a positive electrode active material composite comprising a positive electrode active material and a coating layer formed on the surface of the positive electrode active material, wherein the coating layer contains a conductive material and has a residual solvent content of 0.18 to 1.0% by weight.

[0030] Conventional dry electrode manufacturing processes have the problem that the conductive material cannot be sufficiently dispersed in the mixture because the active material, conductive material, and binder are mixed in a single step. In the present invention, the conductive material is pre-coated onto the surface of the active material to ensure the dispersibility of the conductive material and solve the aforementioned problem.

[0031] Specifically, the positive electrode active material composite of the present invention can be manufactured by mixing a positive electrode active material and a conductive material with a specific solvent and then drying it under specific conditions, thereby allowing the solvent content remaining in the positive electrode active material composite to be 0.18 to 1.0% by weight. More specifically, the solvent content remaining in the positive electrode active material composite can be 0.18% by weight or more, 0.19% by weight or more, 0.2% by weight or more, 0.21% by weight or more, 0.22% by weight or more, 0.23% by weight or more, 0.24% by weight or more, 0.25% by weight or more, 0.26% by weight or more, 0.27% by weight or more, or 0.28% by weight or more, and can be 1.0% by weight or less, 0.95% by weight or less, 0.9% by weight or less, 0.85% by weight or less, 0.8% by weight or less, 0.75% by weight or less, 0.7% by weight or less, 0.65% by weight or less, 0.6% by weight or less, 0.55% by weight or less, 0.5% by weight or less, or 0.45% by weight or less. The positive electrode active material composite of the present invention has a residual solvent content within the range described above. Unlike a positive electrode active material manufactured by simply dry-mixing a conductive material and a positive electrode active material, where a conductive material is applied to a portion of the surface of the positive electrode active material, the residual solvent content can be kept low within the range described above by optimizing the solvent and drying conditions during the manufacturing process. If the residual solvent content is too high, the solvent remaining in the positive electrode active material composite may act as an impurity thereafter, causing undesirable problems during the electrode manufacturing process, and additional steps that are unnecessary in the dry electrode manufacturing process may be required to remove the impurities. On the other hand, if the residual solvent content is too low, it means that the drying conditions during the manufacturing process of the positive electrode active material composite were very harsh, which may cause the positive electrode active material to disintegrate or disappear during the drying process, leading to problems with the durability of the positive electrode active material composite, and as a result, the resistance of the positive electrode active material composite may increase or the conductivity may decrease.

[0032] On the other hand, the residual solvent content may be determined by measuring and calculating the remaining solvent content after partially removing the positive electrode active material composite and heating it at 200°C for 15 minutes. The residual solvent content can be measured and calculated using conventional moisture content measuring equipment, for example, a heating-type moisture meter can be used, more specifically, a heating-type moisture meter such as the AMD MX-50 product can be used. On the other hand, the heating method in the moisture meter can be a straight-tube halogen lamp.

[0033] The positive electrode active material composite of the present invention can be used in the manufacture of dry electrodes. Since the positive electrode active material composite of the present invention has a form in which a conductive material is already dispersed on the surface of the active material, a dry electrode can be manufactured by mixing the positive electrode active material composite with a binder and then microfiberizing it, without using another solvent for dispersing the conductive material. The form of the dry electrode is not particularly limited, and conventional manufacturing methods used for manufacturing dry electrodes can be applied to the positive electrode active material composite of the present invention.

[0034] The following describes in more detail each component included in the positive electrode active material composite of the present invention.

[0035] positive electrode active material The positive electrode active material included in the positive electrode active material composite of the present invention can be used without particular limitations as long as it is suitable for use as a positive electrode active material in a lithium secondary battery. More specifically, the positive electrode active material can be one or more selected from the group consisting of lithium-manganese oxide, lithium-cobalt oxide, lithium-nickel oxide, lithium-nickel-manganese oxide, lithium-nickel-cobalt oxide, lithium-manganese-cobalt oxide, lithium-nickel-manganese-cobalt oxide, lithium-nickel-cobalt-transition metal oxide, lithium cobalt phosphate, and lithium iron phosphate. More specifically, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mn c)O2(0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + C = 1), LiNi 1-y Co y O2(0 < y < 1), LiCo 1-y Mn y O2(0 < y < 1), LiNi 1-y Mn y O2(0 ≤ y < 1), Li(Ni a Co b Mn c )O4(0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + C = 2), LiMn 2-z Ni z O4(0 < z < 2), LiMn 2-z Co z O4(0 < z < 2), any one selected from the group consisting of LiCoPO4 and LiFePO4 or a mixture of two or more of these can be used conductive material The conductive material contained in the positive electrode active material composite of the present invention can be one or more selected from the group consisting of single - wall carbon nanotubes, multi - wall carbon nanotubes, carbon black, and Ketjen black.

[0036] Since the characteristics of the conductive material are partially different depending on its type, an appropriate conductive material can be selected and used from the above - mentioned ones according to the intended effect.

[0037] <00​​

[0038] The average diameter of the single-wall carbon nanotubes used in this invention can be 0.5 to 2 nm, preferably 0.5 to 1.5 nm. Furthermore, the BET specific surface area of ​​the single-wall carbon nanotubes used in this invention is 800 to 1600 m². 2 It can be / g, preferably 1000~1500m 2 The density can be / g. Furthermore, the length of the single-wall carbon nanotubes used in this invention can be 1 μm or more, preferably 3 μm or more. When the physical properties of the single-wall carbon nanotubes satisfy the above conditions, their function as a conductive material can be particularly excellent.

[0039] The average diameter of the single-walled carbon nanotubes can be measured after observing them with a transmission electron microscope (TEM). The BET specific surface area of ​​the single-walled carbon nanotubes can be calculated from the amount of gas adsorbed using BET measurement equipment. The length of the single-walled carbon nanotubes can be measured using an atomic force microscope (AFM). Furthermore, the D50 of the single-walled carbon nanotubes can be measured using a laser particle size analyzer.

[0040] Furthermore, Raman analysis of the single-walled carbon nanotubes revealed G / I D The value can be 30 or more, preferably 50 or more. G / I D The value represents the crystallinity of the carbon nanotube, as described above. G / I D The higher the value, the better the crystallinity of the carbon nanotubes, and the better the electrical conductivity can be achieved even with a small amount of content. G / I DThe value can be calculated as the ratio of the G-band peak intensity to the D-band peak intensity of the Raman spectrum obtained for single-wall carbon nanotubes. The G-band peak is obtained during Raman spectral analysis at a wavelength of approximately 1550-1600 cm. -1 The peak is shown in the range of 1300-1400 cm⁻¹, and the D-band peak is shown in Raman spectral analysis at 1300-1400 cm⁻¹. -1 This refers to the peak shown within a certain range.

[0041] On the other hand, the multi-walled carbon nanotube has the advantage of being able to secure high electrical conductivity due to its one-dimensional structure, which in turn provides a technical advantage in terms of energy density.

[0042] The average diameter of the multi-walled carbon nanotubes used in this invention can be 100 nm or less, preferably 5 to 20 nm. Furthermore, the BET specific surface area of ​​the multi-walled carbon nanotubes used in this invention is 300 m². 2 It can be less than or equal to / g, preferably 150-250m 2 It can be / g. When the physical properties of multi-walled carbon nanotubes satisfy the above conditions, their function as a conductive material can be particularly excellent.

[0043] The average diameter of the multi-walled carbon nanotubes can be measured after observing them with a transmission electron microscope (TEM). Furthermore, the BET specific surface area of ​​the multi-walled carbon nanotubes can be calculated from the amount of gas adsorbed using BET measurement equipment.

[0044] On the other hand, carbon black exhibits excellent conductivity and is the most widely used component as a conductive material.

[0045] The BET specific surface area of ​​the carbon black used in this invention is 5 to 1000 m². 2 It can be / g, preferably 20-300m 2The density can be / g. Furthermore, the D50 of the carbon black used in this invention can be 1 to 50 μm, preferably 1 to 20 μm. In addition, the primary particle size of the carbon black used in this invention can be 500 nm or less, preferably 100 nm or less. When the physical properties of the carbon black satisfy the above conditions, its function as a conductive material can be particularly excellent.

[0046] The BET specific surface area of ​​the carbon black can be calculated from the amount of gas adsorbed using BET measuring equipment. Furthermore, the D50 of the carbon black can be measured using a dry method with a laser particle size analyzer (Mastersizer 3000, Malvern).

[0047] On the other hand, Ketjenblack is a type of carbon black and is known as a highly conductive material that can achieve high performance even with the same carbon black content. While carbon black requires a large amount to achieve a certain level of performance, Ketjenblack has the advantage of being able to achieve a similar level of performance with a relatively small amount.

[0048] The BET specific surface area of ​​the Ketjenblack used in this invention is 500 to 2000 m². 2 It can be / g, preferably 600-1600m 2 It can be / g. Also, the pore volume of Ketjenbrak used in this invention is 200-600 cm³. 3 It can be / 100g, preferably 300-500cm 3 It can be / 100g. Furthermore, the D50 of the Ketjenblack used in this invention can be 5 to 30 mm, preferably 8 to 20 mm. When the physical properties of the Ketjenblack satisfy the above conditions, its function as a conductive material can be particularly excellent.

[0049] The BET specific surface area of ​​Ketjenblack can be calculated from the gas adsorption amount using BET measuring equipment. The pore volume of Ketjenblack can be measured using an oil absorption measuring device in accordance with ASTM D2414-21. Furthermore, the D50 of Ketjenblack can be measured using a dry method with a laser particle size analyzer (Mastersizer 3000, Malvern).

[0050] The content of the conductive material relative to the total weight of the positive electrode active material composite can be 0.01 to 10% by weight. More specifically, the content of the conductive material relative to the total weight of the positive electrode active material composite can vary in part depending on the type of conductive material. If the conductive material is carbon nanotube-based, the content can be 0.01% by weight or more, 0.05% by weight or more, or 0.1% by weight or more, and 10% by weight or less, 5% by weight or less, 1% by weight or less, or 0.5% by weight or less. On the other hand, if the conductive material is carbon black-based, the content can be 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more, and 10% by weight or less, 5% by weight or less, 3% by weight or less, or 1.5% by weight or less. If the content of the conductive material is less than this, the electrical conductivity of the positive electrode active material composite may not be sufficient, and if the content of the conductive material is higher than that described above, the processability of the positive electrode active material composite may decrease.

[0051] Residual solvent As described above, the positive electrode active material composite of the present invention is manufactured by mixing the positive electrode active material and the conductive material in the presence of a solvent and then drying it; therefore, a portion of the solvent may remain within the positive electrode active material composite.

[0052] More specifically, the residual solvent may have a boiling point of 120°C or less, more specifically, a boiling point of 100°C or less, and particularly preferably, a boiling point of 60 to 100°C. Specific examples of the residual solvent include amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, or ester-based solvents that satisfy the boiling point conditions, and particularly preferably, alcohols with 4 or fewer carbon atoms can be used. More specifically, the residual solvent may be one or more selected from the group consisting of isopropyl alcohol, ethanol, 1-propyl alcohol, and 1-butyl alcohol. When the solvents listed above are used in the manufacturing process of the positive electrode active material complex, most of the solvent can be removed even under relatively mild drying conditions, and problems such as damage to the positive electrode active material during the solvent removal process do not occur, which is preferable.

[0053] Electrical characteristics The positive electrode active material composite provided by the present invention can be easily used in the manufacture of dry electrodes, and in particular, dry electrodes manufactured using the positive electrode active material composite of the present invention have the characteristics of low sheet resistance and excellent conductivity.

[0054] The sheet resistance value measured for a dry electrode obtained by mixing the positive electrode active material composite provided by the present invention with a binder capable of microfibrillation can be 42.5 Ω / sq or less, preferably 42.5 Ω / sq or less, 42.0 Ω / sq or less, 41.5 Ω / sq or less, 41 Ω / sq or less, 40.5 Ω / sq or less, 40 Ω / sq or less, 39.5 Ω / sq or less, or 39 Ω / sq or less, and can be 20 Ω / sq or more, 21 Ω / sq or more, 22 Ω / sq or more, 23 Ω / sq or more, 24 Ω / sq or more, 25 Ω / sq or more, 26 Ω / sq or more, or 26.5 Ω / sq or more.

[0055] Furthermore, the conductivity value measured for the dry electrode can be 0.085 S / cm or higher, preferably 0.085 S / cm or higher, 0.09 S / cm or higher, 0.095 S / cm or higher, or 0.1 S / cm or higher, and can be 0.2 S / cm or lower, 0.19 S / cm or lower, 0.18 S / cm or lower, 0.17 S / cm or lower, 0.16 S / cm or lower, 0.15 S / cm or lower, 0.14 S / cm or lower, or 0.135 S / cm or lower.

[0056] On the other hand, in the dry electrode, the weight ratio of the positive electrode active material composite to the binder that can be microfibrillated can be 95:5 to 99.9:0.1, and preferably 97:3 to 99.5:0.5.

[0057] The aforementioned sheet resistance and conductivity can be measured using resistance measuring equipment, for example, using resistance measuring equipment such as HPRM-FA2 (manufactured by HANTECH Corporation).

[0058] Method for manufacturing a cathode active material composite The present invention provides a method for producing the above-described positive electrode active material composite. More specifically, the present invention provides a method for producing a positive electrode active material composite comprising the steps of: (S1) mixing a conductive material, a dispersant and a solvent to produce a predispersion; (S2) mixing the predispersion and a positive electrode active material to produce a positive electrode active material mixture; and (S3) drying the positive electrode active material mixture to produce a positive electrode active material composite, wherein the solvent is one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents and ester-based solvents, and the boiling point of the solvent is 120°C or lower.

[0059] S1 Step In step S1, a pre-dispersion is first prepared for coating the surface of the positive electrode active material with the conductive material. When the conductive material is pre-dispersed and mixed with the positive electrode active material, the conductive material can be uniformly coated onto the surface of the positive electrode active material. On the other hand, the dispersant used in this step is not particularly limited as long as it is known to be usable for dispersing conductive materials, and for example, one or more selected from the group consisting of polyvinylpyrrolidone, polyacrylate hydrazide, poly-N-vinyl-5-methoxazolidone, N-alkylpolyimine, N-acetylpolyimine, polyacrylamide, poly-L-lysine hydrobromide, benzyl-dodecyl-dimethylammonium chloride, and polyethyleneimine can be used. The weight ratio of conductive material to dispersant in the pre-dispersion can be 100:20 to 100:500, preferably 100:30 to 100:200. When the content of the dispersant is within the above-mentioned range, the conductive material can be properly dispersed.

[0060] Furthermore, the solvent is the same as the residual solvent described above, and a portion of the solvent used in this step remains and can be included in the positive electrode active material complex as a residual solvent. Therefore, the solvent, like the residual solvent described above, is one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, and ester-based solvents, and its boiling point may be 120°C or lower.

[0061] In this step, the content of the conductive material in the pre-dispersion can be 0.05 to 10% by weight. More specifically, the content of the conductive material in the pre-dispersion can vary in part depending on the type of conductive material. If the conductive material is a single-wall carbon nanotube, the content of the conductive material in the pre-dispersion can be 0.05 to 5% by weight, preferably 0.1 to 1% by weight. On the other hand, if the conductive material is a multi-wall carbon nanotube, the content of the multi-wall conductive material in the pre-dispersion can be 0.05 to 10% by weight, preferably 1 to 5% by weight. On the other hand, if the conductive material is a carbon black-based conductive material, the content of the conductive material in the pre-dispersion can be 0.1 to 10% by weight, preferably 0.5 to 5% by weight. If the content of the conductive material in the pre-dispersion is too low, the amount of conductive material coated on the positive electrode active material may be too small. If the content of the conductive material in the pre-dispersion is too high, the pre-dispersion of the conductive material itself may not be easy.

[0062] On the other hand, if the conductive material is a single-wall carbon nanotube, the D50 of the single-wall carbon nanotubes in the pre-dispersion produced in this step can be 30 μm or less, and preferably 5 to 20 μm.

[0063] On the other hand, if the conductive material is a multi-walled carbon nanotube, the D50 of the multi-walled carbon nanotubes in the pre-dispersion produced in this step can be 20 μm or less, and preferably 3 to 15 μm.

[0064] On the other hand, if the conductive material is carbon black, the D50 of the carbon black in the pre-dispersion produced in this step can be 20 μm or less, preferably 3 to 15 μm. Also, the initial viscosity of the pre-dispersion can be 40,000 cP or less, preferably 1,000 to 20,000 cP. If the initial viscosity of the pre-dispersion is too high, the processability will decrease, and mixing of the pre-dispersion and the positive electrode active material may not be smooth. On the other hand, the initial viscosity can be the value obtained after stabilization for 5 minutes using a Tokki viscometer with a reading of 2.5 / s.

[0065] The initial viscosity of the pre-dispersion can be 40,000 cP or less, preferably 1,000 cP or more, 3,000 cP or more, or 5,000 cP or more, and can be 40,000 cP or less, 30,000 cP or less, 20,000 cP or less, or 15,000 cP or less. If the initial viscosity of the pre-dispersion is too high, processability may decrease, and mixing of the pre-dispersion and the positive electrode active material may not be smooth. On the other hand, the initial viscosity can be the value obtained after stabilization for 5 minutes using a Tokki viscometer with a reading of 2.5 / s.

[0066] S2 Step A subsequent step may be performed in which the previously manufactured pre-dispersion is mixed with the positive electrode active material. The amount of positive electrode active material mixed in this step can be 5 to 500 parts by weight, preferably 20 to 100 parts by weight, per 100 parts by weight of the pre-dispersion. Within the above range, the content ratio of positive electrode active material to conductive material can be appropriate.

[0067] S3 Step After mixing the pre-dispersion and the positive electrode active material, the solvent can be removed by drying, and a positive electrode active material composite can be obtained in which a conductive material is coated on the surface of the positive electrode active material.

[0068] In this step, considering the properties of the solvent described above, drying can be performed at a relatively low temperature, more specifically, at a temperature of 60 to 200°C, and particularly preferably at a temperature of 80 to 150°C. Within the above temperature range, the solvent can be removed without degradation of the positive electrode active material, and in particular, the residual solvent content can be controlled within the aforementioned range. Furthermore, drying in this step can be carried out for 0.5 to 8 hours, preferably 0.5 to 2 hours. If the drying time is too long, the amount of energy consumed in the manufacturing process may become excessive, and if the drying time is too short, the solvent may not be sufficiently removed.

[0069] The present invention will be described in more detail below with reference to examples and experimental examples, but the present invention is not limited to these examples and experimental examples. The examples of the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0070] material As the positive electrode active material, Li(Ni 0.8 Co 0.1 Mn 0.1 A lithium-nickel-manganese-cobalt oxide represented by )O2 was prepared, and the following four types of conductive materials were prepared. In addition, polyvinylpyrrolidone was prepared as a dispersant, and isopropyl alcohol and N-methyl-2-pyrrolidone (NMP) were prepared as solvents.

[0071] 1) Single-walled carbon nanotubes: As single-walled carbon nanotubes, they have an average diameter of 1.5 nm and a BET specific surface area of ​​1200 m². 2 / g is I G / I D We prepared items with a value of 70 or higher.

[0072] 2) Multiwalled carbon nanotubes: These multiwalled carbon nanotubes have an average diameter of 10 nm and a BET specific surface area of ​​183 m². 2 We prepared items that are / g.

[0073] 3) Carbon Black: As carbon black, the BET specific surface area is 63.2 m². 2 We prepared samples with a density of / g and a primary particle size of 50 nm or less.

[0074] 4) Ketjenblack: Ketjenblack has a BET specific surface area of ​​1,270 m². 2 The stomata volume is 495 cm³ / g. 3 I prepared a D50 that weighs 100g and has a 12.5mm lens.

[0075] Example 1-1 498.5 g of isopropyl alcohol was mixed with 1.0 g of the dispersant and 0.5 g of the single-wall carbon nanotubes of the material. A pre-dispersion was prepared by pre-dispersing the mixture using a high-pressure homogenizer, and 99.5 g of the cathode active material was added to the pre-dispersion. The mixture was then uniformly mixed using a circular mixer and dried at 130°C for 30 minutes to produce a cathode active material composite.

[0076] Examples 1-2 The cathode active material composite was manufactured in the same manner as in Example 1-1, except that it was dried at 200°C for 30 minutes.

[0077] Examples 1-3 A cathode active material composite was produced in the same manner as in Example 1-1, except that 497 g of isopropyl alcohol was used, 2.0 g of a dispersant and 1.0 g of the single-wall carbon nanotubes of the aforementioned material were used so that the carbon nanotube content in the pre-dispersion was 0.2% by weight, and 199 g of the cathode active material to be mixed was used.

[0078] Comparative Example 1-1 The cathode active material complex was produced in the same manner as in Example 1-1, except that 498.5 g of N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol.

[0079] Comparative Example 1-2 The cathode active material composite was produced in the same manner as in Example 1-1, except that 498.5 g of N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol and dried at 200°C for 4 hours.

[0080] Comparative Examples 1-3 The cathode active material composite was produced in the same manner as in Example 1-1, except that 498.5 g of N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol and dried at 200°C for 24 hours.

[0081] Comparative Example 1-4 The cathode active material composite was produced in the same manner as in Examples 1-3, except that 83 g of water and 415.5 g of ethanol were used as solvents instead of isopropyl alcohol.

[0082] Comparative Examples 1-5 The cathode active material composite was produced in the same manner as in Example 1-1, except that 83 g of water and 415.5 g of ethanol were used as solvents instead of isopropyl alcohol, and the drying time was extended to 24 hours.

[0083] Comparative Examples 1-6 A cathode active material composite was produced in the same manner as in Example 1-1, except that the drying time was changed to 16 hours.

[0084] Table 1 below summarizes the content (by weight) of each component in the pre-dispersion, drying temperature (°C), and time (minutes) during the manufacturing process of Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-6, in which a cathode active material composite was manufactured using single-wall carbon nanotubes as a conductive material.

[0085] [Table 1]

[0086] Example 2-1 493.5 g of isopropyl alcohol was mixed with 1.5 g of a dispersant and 5 g of the multi-walled carbon nanotubes of the material. A pre-dispersion was prepared by pre-dispersing the mixture using a high-pressure homogenizer, and 242.5 g of the cathode active material was added to the pre-dispersion. The mixture was then uniformly mixed using a circular mixer, and dried at 130°C for 30 minutes to produce a cathode active material composite.

[0087] Example 2-2 487 g of isopropyl alcohol was mixed with 3 g of a dispersant and 10 g of the multi-walled carbon nanotubes of the material. A pre-dispersion was prepared by pre-dispersing the mixture using a high-pressure homogenizer, and 485 g of the cathode active material was added to the pre-dispersion. The mixture was then uniformly mixed using a circular mixer, and dried at 130°C for 30 minutes to produce a cathode active material composite.

[0088] Examples 2-3 The cathode active material composite was produced in the same manner as in Example 2-1, except that it was dried at 200°C for 30 minutes.

[0089] Comparative Example 2-1 The cathode active material complex was produced in the same manner as in Example 2-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol.

[0090] Comparative Example 2-2 The cathode active material composite was produced in the same manner as in Example 2-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol and dried at 200°C for 8 hours.

[0091] Comparative Example 2-3 The cathode active material composite was produced in the same manner as in Example 2-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol and dried at 200°C for 24 hours.

[0092] Comparative Example 2-4 A cathode active material composite was produced in the same manner as in Example 2-1, except that 82.5 g of water and 411 g of ethanol were used as solvents.

[0093] Comparative Example 2-5 A cathode active material composite was produced in the same manner as in Example 2-1, except that the drying time was changed to 16 hours.

[0094] Comparative Example 2-6 The cathode active material composite was produced in the same manner as in Comparative Example 2-4, except that the drying time was changed to 24 hours.

[0095] Table 2 below summarizes the content (by weight) of each component in the pre-dispersion during the manufacturing process of Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-6, in which a cathode active material composite was manufactured using multi-walled carbon nanotubes as a conductive material, as well as the drying temperature (°C) and time (minutes).

[0096] [Table 2]

[0097] Example 3-1 493.5 g of isopropyl alcohol was mixed with 1.5 g of a dispersant and 5 g of carbon black from the material. A pre-dispersion was prepared by pre-dispersing the mixture using a high-pressure homogenizer, and 242.5 g of the positive electrode active material was added to the pre-dispersion. The mixture was then uniformly mixed using a circular mixer, and dried at 130°C for 30 minutes to produce a positive electrode active material composite.

[0098] Example 3-2 487 g of isopropyl alcohol was mixed with 3 g of a dispersant and 10 g of carbon black from the material. A pre-dispersion was prepared by pre-dispersing the mixture using a high-pressure homogenizer, and 485 g of the cathode active material was added to the pre-dispersion. The mixture was then uniformly mixed using a circular mixer, and dried at 130°C for 30 minutes to produce a cathode active material composite.

[0099] Example 3-3 The cathode active material composite was manufactured in the same manner as in Example 3-1, except that it was dried at 200°C for 30 minutes.

[0100] Comparative Example 3-1 The cathode active material complex was produced in the same manner as in Example 3-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol.

[0101] Comparative Example 3-2 The cathode active material composite was produced in the same manner as in Example 3-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol and dried at 200°C for 8 hours.

[0102] Comparative Example 3-3 The cathode active material composite was produced in the same manner as in Example 3-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol and dried at 200°C for 24 hours.

[0103] Comparative Example 3-4 The cathode active material composite was produced in the same manner as in Example 3-1, except that 82.5 g of water and 411 g of ethanol were used as solvents.

[0104] Comparative Example 3-5 The cathode active material composite was manufactured in the same manner as in Example 3-1, except that the drying time was changed to 16 hours.

[0105] Comparative Example 3-6 The cathode active material composite was produced in the same manner as in Comparative Examples 3-4, except that the drying time was 24 hours.

[0106] Table 3 below summarizes the content (by weight) of each component in the pre-dispersion during the manufacturing process of Examples 3-1 to 3-3 and Comparative Examples 3-1 to 3-6, in which carbon black was used as a conductive material to produce a cathode active material composite, as well as the drying temperature (°C) and time (minutes).

[0107] [Table 3]

[0108] Example 4-1 487 g of isopropyl alcohol was mixed with 3 g of a dispersant and 10 g of the Ketjenblack material. A pre-dispersion was prepared by pre-dispersing the mixture using a high-pressure homogenizer, and 485 g of the cathode active material was added to the pre-dispersion. The mixture was then uniformly mixed using a circular mixer, and dried at 130°C for 30 minutes to produce a cathode active material composite.

[0109] Example 4-2 The cathode active material composite was produced in the same manner as in Example 4-1, except that it was dried at 200°C for 30 minutes.

[0110] Example 4-3 474 g of isopropyl alcohol was mixed with 6 g of a dispersant and 20 g of the Ketjenblack material. A pre-dispersion was prepared by pre-dispersing the mixture using a high-pressure homogenizer, and 970 g of the cathode active material was added to the pre-dispersion. The mixture was then uniformly mixed using a circular mixer, and dried at 130°C for 30 minutes to produce a cathode active material composite.

[0111] Comparative Example 4-1 The cathode active material complex was produced in the same manner as in Example 4-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol.

[0112] Comparative Example 4-2 The cathode active material composite was produced in the same manner as in Example 4-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol and dried at 200°C for 8 hours.

[0113] Comparative Example 4-3 The cathode active material composite was produced in the same manner as in Example 4-1, except that N-methyl-2-pyrrolidone was used as the solvent instead of isopropyl alcohol and dried at 200°C for 24 hours.

[0114] Comparative Example 4-4 The cathode active material composite was produced in the same manner as in Example 4-1, except that 81 g of water and 406 g of ethanol were used as solvents.

[0115] Comparative Example 4-5 A cathode active material composite was produced in the same manner as in Example 4-1, except that the drying time was changed to 16 hours.

[0116] Comparative Example 4-6 The cathode active material composite was produced in the same manner as in Comparative Example 4-4, except that the drying time was changed to 24 hours.

[0117] Table 4 below summarizes the content (by weight) of each component in the pre-dispersion during the manufacturing process of Examples 4-1 to 4-3 and Comparative Examples 4-1 to 4-6, in which Ketjenblack was used as a conductive material to produce a cathode active material composite, as well as the drying temperature (°C) and time (minutes).

[0118] [Table 4]

[0119] Experimental Example 1. Measurement of residual solvent content in the positive electrode active material composite. Two g of the cathode active material composites produced in the above examples and comparative examples were pretreated by heating at 200°C for 15 minutes. The pretreated samples were placed in a heating-type moisture meter (AMD MX-50) and the residual solvent content (by weight) in the samples was measured. The results are summarized in Table 5 below.

[0120] [Table 5]

[0121] As can be seen from Table 5 above, in the case of Comparative Examples 1-1 to 1-3, Comparative Examples 2-1 to 2-3, Comparative Examples 3-1 to 3-3, and Comparative Examples 4-1 to 4-3, which used NMP, a solvent commonly used in the past, when dried under the same conditions as the examples of the present invention, the residual solvent content was found to be so high that it could not be measured. Furthermore, even when dried at a much higher temperature and for a longer time than the examples of the present invention, the residual solvent content was found to exceed 2% by weight.

[0122] Furthermore, in Comparative Examples 1-4 to 1-5, 2-4 to 2-5, 3-4 to 3-5, and 4-4 to 4-5, which used a mixture of water and ethanol as the solvent, it was confirmed that when drying was performed under the same conditions as the present invention, the residual solvent content exceeded 1% by weight, and when the drying time was extended significantly, the residual solvent content decreased to less than 0.2% by weight. Also, in Comparative Examples 1-6, 2-6, 3-6, and 4-6, which used isopropyl alcohol as the solvent, similar to the examples of the present invention, but with an extended drying time, it was confirmed that the residual solvent content decreased to less than 0.2% by weight.

[0123] On the other hand, in Examples 2-2, 3-2, and 4-3, which used a pre-dispersion of a higher concentration, the residual solvent content was not measured separately. However, considering that the residual solvent content of Example 1-3 is the same as that of Example 1-1, it is expected that the residual solvent content of Examples 2-3, 3-2, and 4-3 will also be the same as that of Examples 2-1, 3-1, and 4-1, respectively.

[0124] On the other hand, in the case of Comparative Example 1, NMP was used as the solvent and the drying time was shortened, resulting in an excessive amount of residual solvent, and it was confirmed that the amount of residual solvent itself could not be measured.

[0125] Experimental Example 2. Confirmation of the electrical conductivity of the positive electrode active material composite. The cathode active material composites prepared in the above examples and comparative examples were mixed with polytetrafluoroethylene (PTFE) as a binder in a weight ratio of 99:1. The mixture was then kneaded on a bench kneader for 90 seconds, followed by grinding for 10 seconds to produce flake-shaped samples for measuring electrical conductivity. All samples were made to a thickness of 2.8 mm.

[0126] The sheet resistance and conductivity of the manufactured samples were measured, and each characteristic was measured using the following method.

[0127] 1) Sheet resistance (Ω / sq): Measured using a resistance measuring device (HPRM-FA2, manufactured by HANTECH Co., Ltd.). Specifically, after loading a flake-shaped sample into the resistance measuring device, a weight of up to 2 tons was applied to minimize the air gap, and the resistance was measured.

[0128] 2) Conductivity (S / cm): This was automatically calculated within the resistance measuring equipment using the thickness and resistance values ​​of the sample measured by the resistance measuring equipment.

[0129] The measurement results are summarized in Tables 6-9 below.

[0130] [Table 6]

[0131] [Table 7]

[0132] [Table 8]

[0133] [Table 9]

[0134] As summarized in Tables 6-9 above, the samples prepared by mixing the positive electrode active material composite and binder of the present invention exhibited significantly lower sheet resistance, higher conductivity, and superior electrical properties compared to samples prepared using positive electrode active material composites with a residual solvent content of less than 0.18% by weight or more than 1.0% by weight. On the other hand, in the cases of Comparative Examples 1-1, 2-1, 3-1, and 4-1, the excessive residual solvent content in the positive electrode active material composite made the microfibrillation of the binder itself difficult, and thus the preparation of the samples was not easy.

[0135] In particular, in the case of comparative examples where the residual solvent content of the positive electrode active material composite was higher than that of the examples, the sheet resistance and conductivity were significantly inferior to those of the examples. This is thought to be because the excess residual solvent remaining in the composite acted as an impurity, degrading the electrical properties of the active material composite. On the other hand, in the case of comparative examples where the residual solvent content was too low, the electrical properties were also inferior to those of the examples. This is expected to be due to a phenomenon in which the durability of the composite deteriorated during the process of removing excess residual solvent during drying.

[0136] From the above results, it was confirmed that by appropriately controlling the solvent used in the process of coating the surface of the positive electrode active material with a conductive material, and the temperature and time during the drying process, a positive electrode active material composite with an optimal residual solvent content can be manufactured. In particular, by appropriately controlling the residual solvent content within the positive electrode active material composite, it is possible to manufacture a positive electrode active material composite that is easy to produce and has excellent electrical properties.

Claims

1. Positive electrode active material and, The coating layer formed on the surface of the positive electrode active material is included. The coating layer includes a conductive material, A cathode active material composite having a residual solvent content of 0.18% by weight or more and 1.0% by weight or less.

2. The positive electrode active material composite according to claim 1, wherein the content of the residual solvent is 0.2% by weight or more and 0.5% by weight or less.

3. The positive electrode active material is LiCoO ２ , LiNiO ２ , LiMnO ２ , LiMn ２ O ４ , Li(Ni ａ Co ｂ Mn ｃ )O ２ (0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + C = 1), LiNi １－ｙ Co ｙ O ２ (0 < y < 1), LiCo １－ｙ Mn ｙ O ２ (0 < y < 1), LiNi １－ｙ Mn ｙ O ２ (0 ≤ y < 1), Li(Ni ａ Co ｂ Mn ｃ )O ４ (0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + C = 2), LiMn ２－ｚ Ni ｚ O ４ (0 < z < 2), LiMn ２－ｚ Co ｚ O ４ (0 < z < 2), LiCoPO ４ and LiFePO ４ The positive electrode active material composite according to claim 1, which is one or more selected from the group consisting of.

4. The cathode active material composite according to claim 1, wherein the conductive material is one or more selected from the group consisting of single-wall carbon nanotubes, multi-wall carbon nanotubes, carbon black, and Ketjenblack.

5. The cathode active material composite according to claim 4, wherein the average diameter of the single-wall carbon nanotubes is 0.5 nm or more and 2 nm or less.

6. The cathode active material composite according to claim 4, wherein the average diameter of the multi-walled carbon nanotubes is 100 nm or less.

7. The cathode active material composite according to claim 4, wherein the D50 of the carbon black is 1 μm or more and 50 μm or less.

8. The pore volume of the aforementioned Ketjenbrak is 200 cm³. ３ / 100g or more, 600cm ３ The positive electrode active material composite according to claim 4, wherein the amount is 100g or less.

9. The positive electrode active material composite according to claim 1, wherein the content of the conductive material relative to the total weight of the positive electrode active material composite is 0.01% by weight or more and 10% by weight or less.

10. The positive electrode active material composite according to any one of claims 1 to 9, wherein the residual solvent is one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, and ester-based solvents, and the boiling point of the residual solvent is 120°C or lower.

11. Step (S1) involves mixing a conductive material, a dispersant, and a solvent to produce a pre-dispersion, Step (S2) involves mixing the pre-dispersion with the positive electrode active material to produce a positive electrode active material mixture, The step (S3) involves drying the positive electrode active material mixture to produce a positive electrode active material composite, The solvent is one or more selected from the group consisting of amide-based polar organic solvents, alcohol-based solvents, glycol-based solvents, glycol ether-based solvents, ketone-based solvents, and ester-based solvents. A method for producing a positive electrode active material composite, characterized in that the boiling point of the solvent is 120°C or lower.

12. The method for producing a cathode active material composite according to claim 11, wherein step S3 is performed under temperature conditions of 60°C or higher and 200°C or lower.

13. The method for producing a cathode active material composite according to claim 11, wherein step S3 is performed for 0.5 hours or more and 8 hours or less.

14. The method for producing a positive electrode active material composite according to any one of claims 11 to 13, wherein the initial viscosity of the pre-dispersion produced in step S1 is 40,000 cP or less.

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