Method for producing positive electrode active material

Abstract

The present invention relates to a method for producing a positive electrode active material that can not only reduce the amount of washing solution used, but also minimize deterioration of the surface of the positive electrode active material that occurs during a washing process and effectively control residual lithium, the method including: (A) preparing a lithium transition metal oxide; (B) mixing the lithium transition metal oxide with a first washing solution to perform a first washing on the lithium transition metal oxide, and then performing a first filtration; and (C) simultaneously performing a second washing and a second filtration on the lithium transition metal oxide that has been subjected to step (B) with a second washing solution using a filtration device capable of simultaneously washing with water and filtering, wherein the amount of the second washing solution is 10 parts by weight to 50 parts by weight with respect to 100 parts by weight of the first washing solution.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0038784 filed on March 25, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for producing a positive electrode active material. [Background technology]

[0003] The nickel-based positive electrode active material is manufactured by mixing a nickel-based positive electrode active material precursor with a lithium-containing raw material and then calcining the mixture. During this process, the unreacted lithium-containing raw material and by-products, such as LiOH and Li 2 CO 3 This causes problems such as residual lithium remaining on the surface of the positive electrode active material. In particular, in the case of nickel-based positive electrode active materials containing a high content of nickel, there is a problem of a large amount of residual lithium. These by-products can react with the electrolyte to cause problems such as a decrease in the long-term performance of the battery (e.g., a decrease in long-term life, an increase in resistance, etc.) and stability problems (e.g., gas generation, etc.). In addition, gelation can occur during the manufacturing process of the electrode slurry.

[0004] To prevent this, in the conventional manufacturing process of a positive electrode active material, a positive electrode active material precursor and a lithium-containing raw material are mixed and baked to manufacture a positive electrode active material, and then the positive electrode active material is washed with a washing solution (e.g., deionized water, distilled water, etc.) to control the residual lithium. Meanwhile, in order to effectively control the residual lithium, a method is available in which a large amount of washing solution is used in the washing process, but the use of a large amount of washing solution can cause process problems and can cause problems such as a decrease in battery performance due to deterioration of the surface of the positive electrode active material.

[0005] Therefore, there is a need for a method for producing a positive electrode active material that can effectively control the residual lithium and suppress the deterioration of the positive electrode active material. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing a positive electrode active material, which can minimize deterioration of the surface of the positive electrode active material that may occur during a water washing process during the preparation of the positive electrode active material, and effectively control residual lithium to minimize deterioration of battery performance. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a method for producing a positive electrode active material. (1) The present invention provides a method for producing a positive electrode active material, comprising: (A) a step of preparing a lithium transition metal oxide; (B) a step of mixing the lithium transition metal oxide with a first washing solution to perform a first washing on the lithium transition metal oxide, and then a first filtration; and (C) a step of simultaneously performing a second washing and a second filtration on the lithium transition metal oxide that has been subjected to step (B) with a second washing solution using a filtration device capable of simultaneously washing with water and filtering, wherein the amount of the second washing solution is 10 parts by weight to 50 parts by weight per 100 parts by weight of the first washing solution.

[0008] (2) The present invention provides the method for producing a positive electrode active material according to (1) above, wherein the lithium transition metal oxide contains nickel in an amount of 70 mol % or more of all metals other than lithium.

[0009] (3) The present invention provides a method for producing a positive electrode active material according to the above (1) or (2), wherein the lithium transition metal oxide has a composition represented by the following chemical formula 1: [Chemical formula 1] Li 1+a Ni x1 Co y1 M1 z1 M2 w1 O 2 In the above Chemical Formula 1, 0≦a≦0.3, 0.7≦x1<1.0, 0 <y1≦0.3、0<z1≦0.3、0≦w1≦0.2、x1+y1+z1+w1=1であり、 M1 is one or more selected from Mn and Al; M2 is one or more selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y.

[0010] (4) The present invention provides the method for producing a positive electrode active material according to any one of (1) to (3), wherein the amount of the first washing solution is 50 parts by weight to 100 parts by weight based on 100 parts by weight of the lithium transition metal oxide.

[0011] (5) The present invention provides the method for producing a positive electrode active material according to any one of the above (1) to (4), wherein the amount of the second washing solution is 5 parts by weight to 50 parts by weight based on 100 parts by weight of the lithium transition metal oxide.

[0012] (6) The present invention provides the method for producing a positive electrode active material according to any one of (1) to (5), wherein a sum of an amount of the first washing solution and an amount of the second washing solution is 55 parts by weight to 150 parts by weight per 100 parts by weight of the lithium transition metal oxide.

[0013] (7) The present invention provides the method for producing a positive electrode active material according to any one of the above (1) to (6), wherein the first water washing is performed for 5 minutes to 30 minutes.

[0014] (8) The present invention provides the method for producing a positive electrode active material according to any one of the above (1) to (7), wherein the first water washing is carried out at a temperature of 5°C to 30°C.

[0015] (9) The present invention provides the method for producing a positive electrode active material according to any one of the above (1) to (8), wherein the second water washing is performed for 5 minutes to 30 minutes.

[0016] (10) The present invention provides the method for producing a positive electrode active material according to any one of the above (1) to (9), wherein the second water washing is carried out at a temperature of 5°C to 30°C.

[0017] (11) The present invention provides a method for producing a positive electrode active material according to any one of (1) to (10), further comprising the steps of drying the lithium transition metal oxide that has been subjected to steps (D) and (C), mixing the dried lithium transition metal oxide with a coating element-containing raw material, and heat-treating the mixture to form a coating layer. Effect of the Invention

[0018] By including steps (B) and (C), the present invention can reduce the amount of washing solution used, minimize surface deterioration of the positive electrode active material that occurs during the washing process, and effectively control residual lithium. Therefore, a battery using the positive electrode active material manufactured by the method according to the present invention can have excellent performance, particularly excellent electrochemical performance and thermal stability. [Brief description of the drawings]

[0019] [Figure 1] 1 is a graph showing the rate of change in volume at high temperatures of mono-cells produced using the positive electrode active materials produced in the Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The terms and words used in this specification and the claims should not be interpreted in a limited manner to their ordinary or dictionary meanings, but should be interpreted in a manner that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0021] In this specification, the terms "including," "comprising," or "having" are intended to indicate the presence of implemented features, numerals, steps, components, or combinations thereof, and should be understood as not precluding the presence or additional possibility of one or more other features, numerals, steps, components, or combinations thereof.

[0022] The present invention will now be described in more detail.

[0023] Method for producing positive electrode active material The present inventors have discovered that it is possible to reduce the amount of washing solution used in a washing process during the preparation of a positive electrode active material, minimize deterioration of the surface of the positive electrode active material that occurs during the washing process, and effectively remove residual lithium, thereby completing the present invention.

[0024] The method for producing a positive electrode active material according to the present invention includes the steps of (A) preparing a lithium transition metal oxide, (B) mixing the lithium transition metal oxide with a first washing solution to perform a first washing on the lithium transition metal oxide, and then performing a first filtration, and (C) simultaneously performing a second washing and a second filtration on the lithium transition metal oxide that has been subjected to step (B) with a second washing solution using a filtration device capable of simultaneously washing with water and filtering, wherein the amount of the second washing solution is 10 parts by weight to 50 parts by weight with respect to 100 parts by weight of the first washing solution.

[0025] The method for preparing a positive electrode active material according to the present invention may further include (D) a step of drying the lithium transition metal oxide obtained by step (C), and then mixing the dried lithium transition metal oxide with a coating element-containing raw material and heat-treating the mixture to form a coating layer.

[0026] Each step of the method for producing a positive electrode active material will be specifically described below.

[0027] (A) Step A method for producing a positive electrode active material according to the present invention includes the step of providing a lithium transition metal oxide.

[0028] The step of preparing the lithium transition metal oxide may include mixing a positive electrode active material precursor with a lithium-containing raw material, and calcining the mixture to produce the lithium transition metal oxide.

[0029] The positive electrode active material precursor may have a composition represented by, for example, chemical formula A or chemical formula B below.

[0030] [Chemical formula A] [Ni x Co y M1 z M2 w ](OH) 2

[0031] [Chemical formula B] [Ni x Co y M1 z M2 w ]O·OH

[0032] In Chemical Formula A and Chemical Formula B, M1 can be one or more selected from Mn and Al, and M2 can be one or more selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y.

[0033] The x means the atomic fraction of nickel among the metal elements in the precursor, and may be 0.7≦x<1, 0.7≦x≦0.98, or 0.7≦x≦0.95.

[0034] The y represents the atomic fraction of cobalt among the metal elements in the precursor, and is 0 <y≦0.3または0.01≦y≦0.3であることができる。

[0035] The z represents the element fraction of the M1 element among the metal elements in the precursor, and is 0 <z≦0.3または0.01≦z≦0.3であることができる。

[0036] The w means the element fraction of the M2 element among the metal elements in the precursor, and may be 0≦w≦0.2, 0≦w≦0.1, 0≦w≦0.05, or 0≦w≦0.02.

[0037] The lithium-containing raw material is, for example, lithium carbonate (Li 2 CO 3 ), lithium hydroxide (LiOH), LiNO 3 , C.H. 3 COOLi and Li 2 (COO) 2 At least one selected from the group consisting of, preferably, lithium carbonate (Li 2 CO 3 ), lithium hydroxide (LiOH), or a combination thereof.

[0038] When preparing the positive electrode active material, the positive electrode active material precursor and the lithium-containing raw material may be mixed in a molar ratio of 1:1 to 1:1.625 or 1:1 to 1:1.15. If the lithium-containing raw material is mixed in an amount less than this range, the capacity of the positive electrode active material may decrease, and if the lithium-containing raw material is mixed in an amount exceeding this range, unreacted Li may remain as a by-product, resulting in a decrease in capacity and separation of the positive electrode active material particles after firing (induction of an agglomeration phenomenon of the positive electrode active material).

[0039] The calcination can be carried out at a temperature of 700°C to 1000°C. If the calcination temperature is less than 700°C, the raw materials may remain in the particles due to insufficient reaction, which may reduce the high temperature stability of the battery, and the volume density and crystallinity may decrease, resulting in reduced structural stability. On the other hand, if the calcination temperature exceeds 1000°C, uneven growth of the particles may occur, and the particles may be difficult to disintegrate, resulting in reduced capacity. On the other hand, in consideration of the control of the particle size, capacity, stability, and reduction of lithium-containing by-products of the positive electrode active material to be produced, the calcination temperature may more preferably be 700°C to 980°C.

[0040] The firing can be carried out for 5 hours to 35 hours. When the firing time is less than 5 hours, the reaction time may be excessively short and it may be difficult to obtain a highly crystalline positive electrode active material. When it exceeds 35 hours, the particle size may become excessively large and the production efficiency may decrease.

[0041] According to the present invention, the lithium transition metal oxide can contain 70 mol% or more of nickel among the total metals other than lithium. Specifically, the lithium transition metal oxide can have a composition represented by the following Chemical Formula 1.

[0042] [Chemical Formula 1] Li 1+a Ni x1 Co y1 M1 z1 M2 w1 O 2

[0043] In Chemical Formula 1, 0 ≦ a ≦ 0.3, 0.7 ≦ x1 < 1.0, 0 < y1 ≦ 0.3, 0 < z1 ≦ 0.3, 0 ≦ w1 ≦ 0.2, x1 + y1 + z1 + w1 = 1, M1 is one or more selected from Mn and Al, and M2 can be one or more selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y.

[0044] The x1 means the atomic fraction of nickel among the metal elements other than lithium in the lithium transition metal oxide, and can be 0.7 ≦ x1 < 1, 0.7 ≦ x1 ≦ 0.98, or 0.7 ≦ x1 ≦ 0.95.

[0045] The y1 means the atomic fraction of cobalt among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < y1 ≦ 0.3 or 0.01 ≦ y1 ≦ 0.3.

[0046] The z1 means the elemental fraction of the M1 element among the metal elements other than lithium in the lithium transition metal oxide, and can be 0 < z1 ≦ 0.3 or 0.01 ≦ z1 ≦ 0.3.

[0047] The w1 means the element fraction of the M2 element among metal elements other than lithium in the lithium transition metal oxide, and may be 0≦w1≦0.2, 0≦w1≦0.1, 0≦w1≦0.05, or 0≦w1≦0.02.

[0048] (B) Step and (C) Step The method for producing a positive electrode active material according to the present invention includes a step (B) of mixing the lithium transition metal oxide with a first washing solution to perform a first washing on the lithium transition metal oxide, and then performing a first filtration, and a step (C) of simultaneously performing a second washing and a second filtration on the lithium transition metal oxide that has been subjected to step (B) with a second washing solution using a filtration device capable of simultaneously washing with water and filtering.

[0049] When the lithium transition metal oxide that has been subjected to step (B) is subjected to a second washing and a second filtration simultaneously with a second washing solution using a filtration device capable of simultaneous washing and filtration, ions remaining on the surface of the positive electrode active material are easily removed, which is advantageous in terms of preventing surface deterioration of the positive electrode active material and reducing residual lithium, compared to mixing the lithium transition metal oxide with the washing solution, washing with water, and then filtering as in step (B).

[0050] In addition, when steps (B) and (C) are performed in this order, unnecessary ions on the surface of the positive electrode active material can be removed more quickly than when step (C) is performed first and then step (B).

[0051] The filtering device capable of simultaneously performing washing and filtering may be, but is not limited to, a funnel filter, a filter press, or the like.

[0052] Here, the amount of the second washing solution is 10 to 50 parts by weight with respect to 100 parts by weight of the first washing solution. On the other hand, when the lithium transition metal oxide that has undergone step (B) is collected and step (C) is performed, the amount of the second washing solution is determined based on the total amount of the first washing solution used in step (B). That is, when the lithium transition metal oxide that has undergone step (B) is collected and step (C) is performed, the amount of the second washing solution is 10 to 50 parts by weight with respect to 100 parts by weight of the total amount of the first washing solution used in step (B).

[0053] When the amount of the second washing solution satisfies the above range, deterioration of the surface of the positive electrode active material occurring during the washing process can be minimized and residual ions on the surface of the positive electrode active material can be effectively controlled. As a result, a battery using the positive electrode active material manufactured by the method according to the present invention can have excellent performance, particularly excellent electrochemical performance and thermal stability. Meanwhile, when the amount of the second washing solution is less than 10 parts by weight with respect to 100 parts by weight of the first washing solution, ions on the surface of the positive electrode active material may not be sufficiently removed, and when it exceeds 50 parts by weight, ions on the surface and inside of the positive electrode active material may be removed.

[0054] The present invention includes steps (B) and (C) as a water washing process, which not only reduces the amount of water used for washing, but also minimizes surface deterioration of the positive electrode active material that occurs during the water washing process and effectively controls residual lithium, so that a battery using the positive electrode active material manufactured by the method of the present invention can have excellent performance.

[0055] According to the present invention, even when using a lithium transition metal oxide containing a high content of nickel as represented by Chemical Formula 1, by performing a water washing process as in the present invention, it is possible to minimize deterioration of the surface of the positive active material caused by the water washing process and effectively control residual lithium, thereby providing a positive active material with excellent performance.

[0056] According to the present invention, the amount of the first washing solution may be 50 parts by weight to 100 parts by weight based on 100 parts by weight of the lithium transition metal oxide. If the amount of the first washing solution is less than 50 parts by weight based on 100 parts by weight of the lithium transition metal oxide, unnecessary ions on the surface of the positive electrode active material may not be sufficiently removed, and if it exceeds 100 parts by weight, lithium inside the positive electrode active material may leak due to an excess of washing solution.

[0057] According to the present invention, the amount of the second washing solution may be 5 parts by weight to 50 parts by weight, specifically 10 parts by weight to 30 parts by weight, based on 100 parts by weight of the lithium transition metal oxide. The sum of the amount of the first washing solution and the amount of the second washing solution may be 55 parts by weight to 150 parts by weight, specifically 60 parts by weight to 130 parts by weight, and more specifically 60 parts by weight to 125 parts by weight, based on 100 parts by weight of the lithium transition metal oxide. In this case, residual ions on the surface of the positive electrode active material can be effectively removed, and deterioration of the surface of the positive electrode active material that occurs during the water washing process can be minimized.

[0058] According to the present invention, the solvents of the first washing solution and the second washing solution may each independently be one or more selected from deionized water, distilled water, ethanol, and industrial water. Specifically, the solvents of the first washing solution and the second washing solution may be deionized water and / or distilled water. In this case, lithium is easily dissolved, which may help to remove residual lithium present on the surface.

[0059] According to the present invention, the first water washing may be performed for 5 to 30 minutes, specifically 5 to 20 minutes, and more specifically 5 to 15 minutes. When the first water washing time is within the above range, only the remaining lithium on the surface can be removed, and dissolution of the lithium inserted inside can be suppressed to the maximum.

[0060] According to the present invention, the first water washing can be performed at a temperature of 5° C. to 30° C., specifically, 5° C. to 25° C. When the first water washing is performed at a temperature within the above range, there is an advantage that it is useful for controlling lithium carbonate which is easily dissolved in a washing solution at a low temperature.

[0061] According to the present invention, the second water washing may be performed for 5 to 30 minutes, specifically 5 to 20 minutes, and more specifically 5 to 15 minutes. Also, the second water washing may be performed at a temperature of 5° C. to 30° C., specifically 5° C. to 25° C. When the time and temperature of the second water washing process are within the above ranges, there is an advantage in that it is useful for controlling ions present on the surface of the positive electrode active material.

[0062] (D) Step The method for preparing a positive electrode active material according to the present invention may further include a step of drying the lithium transition metal oxide after step (C), mixing a coating element-containing raw material with the dried lithium transition metal oxide, and heat-treating the mixture to form a coating layer, thereby preparing a positive electrode active material having a coating layer formed on a surface of the lithium transition metal oxide.

[0063] The drying step is a step for removing moisture from the positive electrode active material that contains moisture after the water washing step, and can be performed under a temperature condition of 100° C. to 150° C. for 12 hours or more.

[0064] The metal element contained in the coating element-containing raw material may be Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S, and Y. The coating element-containing raw material may be acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide containing the metal element. For example, when the metal element is B, boric acid (H 3 BO 3 ) etc. can be used.

[0065] The coating element-containing raw material may be included in the dried lithium transition metal oxide in an amount of 200 ppm to 2000 ppm by weight. When the amount of the coating element-containing raw material is within the above range, the capacity of the battery may be improved, and the resulting coating layer may suppress a direct reaction between the electrolyte and the lithium transition metal oxide, thereby improving the long-term performance characteristics of the battery.

[0066] The heat treatment can be performed at a temperature of 200°C to 400°C. When the heat treatment temperature is within the above range, a coating layer can be formed while maintaining the structural stability of the transition metal oxide. The heat treatment can be performed for 1 hour to 10 hours. When the heat treatment time is within the above range, an appropriate coating layer can be formed and production efficiency can be improved.

[0067] positive electrode The present invention can also provide a positive electrode for a lithium secondary battery, which contains the positive electrode active material produced by the above-mentioned method.

[0068] Specifically, 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 and including the above-mentioned positive electrode active material.

[0069] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0070] The positive electrode active material layer may contain a conductive material and a binder in addition to the positive electrode active material.

[0071] Here, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, more specifically, 85 wt% to 98 wt%, based on the total weight of the positive electrode active material layer. When included in the above content range, excellent capacity characteristics can be exhibited.

[0072] Here, the conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause a chemical change in the battery to be constructed and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives, and one or more of these can be used alone or in combination. The conductive material can be contained in an amount of 1% by weight to 30% by weight based on the total weight of the positive electrode active material layer.

[0073] The binder serves to improve the adhesion between the positive electrode active material particles and the adhesive strength between the positive electrode active material and the 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 polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and one or more of these may be used alone or in combination. The binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0074] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material. Specifically, the positive electrode can be manufactured by applying a positive electrode mixture prepared by dissolving or dispersing the positive electrode active material and, optionally, a binder and a conductive material in a solvent onto a positive electrode current collector, followed by drying and rolling. Here, the types and contents of the positive electrode active material, binder, and conductive material are as described above. In addition, as another method, the positive electrode can be manufactured by casting the positive electrode mixture onto another support, peeling it off from the support, and laminating the resulting film onto the positive electrode current collector.

[0075] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination of two or more of these. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for the manufacture of a positive electrode, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0076] Lithium secondary battery In addition, the present invention can provide an electrochemical device including the positive electrode. The electrochemical device can be, for example, a battery or a capacitor, and more specifically, a lithium secondary battery.

[0077] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is as described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0078] Also, the lithium secondary battery may optionally further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0079] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0080] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity, and may be, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector may have a thickness of usually 3 μm to 500 μm, and like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to strengthen the binding force of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0081] The negative electrode active material layer includes a negative electrode active material, and optionally a binder and a conductive material.

[0082] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous 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; SiO β (0<β<2), SnO 2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the metallic compounds and carbonaceous materials, such as Si-C composites and Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a thin film of metallic lithium may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low crystalline carbon include soft carbon and hard carbon, and representative examples of high crystalline carbon include amorphous, plate-like, flake-like, spherical or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature fired carbon such as petroleum or coal tar pitch derived cokes.

[0083] The negative electrode active material may be included in an amount of 80% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0084] The binder is a component that facilitates bonding between the conductive material, the active material, and the current collector, and can be added in an amount of 0.1% by weight to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0085] The conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, specifically 5% by weight or less, based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and examples of such conductive materials include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; 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.

[0086] The negative electrode active material layer can be produced by applying a negative electrode mixture, which is prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent, onto a negative electrode current collector and drying the applied mixture. Alternatively, the negative electrode mixture can be cast onto a separate support, and then peeled off from the support to obtain a film, which can be laminated onto the negative electrode current collector.

[0087] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator that is generally used as a separator in a lithium secondary battery can be used without any particular limitation. In particular, a separator that has low resistance to ion movement of the electrolyte and has excellent humidification ability of the electrolyte solution is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high-melting point glass fiber, a polyethylene terephthalate fiber, etc., can be used. In addition, a coated separator containing a ceramic component or a polymeric material can be used to ensure heat resistance or mechanical strength, and can be selectively used as a single layer or a multilayer structure.

[0088] In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0089] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0090] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent such as dibutyl ether or tetrahydrofuran; a ketone solvent such as cyclohexanone; an aromatic hydrocarbon solvent such as benzene or fluorobenzene; dimethylcarbonate (DMC) or diethylcarbonate (DEC). ,workman Examples of the solvents that can be used include carbonate-based solvents such as ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. 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 high dielectric constant that can enhance the charge / discharge performance of a battery and a low-viscosity straight-chain carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, the cyclic carbonate and the linear carbonate are mixed in a volume ratio of about 1:1 to about 1:9, so that the electrolyte exhibits excellent performance.

[0091] The lithium salt can be used without any particular limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAlO 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC 4 F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 , LiCl, LiI, or LiB(C 2 O 4 ) 2 The lithium salt may be used at a concentration within the range of 0.1 M to 2.0 M. When the lithium salt concentration is within the above range, the electrolyte has appropriate conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, allowing lithium ions to migrate effectively.

[0092] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, 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, in order to improve the life characteristics of the battery, suppress the decrease in the capacity of the battery, and improve the discharge capacity of the battery. In this case, the additives may be contained in an amount of 0.1% by weight to 5% by weight based on the total weight of the electrolyte.

[0093] As described above, the lithium secondary battery including the positive electrode active material according to the present invention stably exhibits excellent discharge capacity, output characteristics and life characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0094] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0095] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0096] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0097] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also preferably as a unit battery in a medium- to large-sized battery module including a large number of battery cells.

[0098] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein.

[0099] Manufacturing Example Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 (OH) 2 The precursor having the composition represented by the formula (I) was mixed with LiOH in a molar ratio of 1:1.05, and then calcined at 780°C for 10 hours in an oxygen atmosphere to obtain Li[Ni 0.86 Co 0.05 Mn 0.07 Al 0.02 ]O 2 A lithium transition metal oxide having the composition represented by the following formula was produced.

[0100] Examples and Comparative Examples Example 1 100 parts by weight of the lithium transition metal oxide produced in the Production Example was mixed with 50 parts by weight of deionized water (first washing solution), and the mixture was washed with first water at 25° C. for 10 minutes, and then filtered with a filter press for 5 minutes. Then, 10 parts by weight of deionized water (second washing solution) was passed through 100 parts by weight of the lithium transition metal oxide at 25° C. for 5 minutes using a filter press, and the mixture was washed with second water and filtered. The mixture was then dried in a vacuum oven at 130° C. for 12 hours or more to produce a positive electrode active material.

[0101] Examples 2 to 4 A positive electrode active material was prepared in the same manner as in Example 1, except that the amounts of the first washing solution and the second washing solution were adjusted as shown in Table 1 below.

[0102] Examples 5 and 6 In Example 1, the amounts of the first and second washing solutions were adjusted as shown in Table 1 below, and the lithium transition metal oxide was dried in a vacuum oven at 130° C. for 12 hours or more. 3 BO 3 The powder was mixed with dried lithium transition metal oxide in a weight amount of 1000 ppm, and heat-treated at 300° C. for 5 hours to produce a positive electrode active material in which a coating layer was formed on the surface of the lithium transition metal oxide. A positive electrode active material was produced in the same manner as in Example 1.

[0103] Comparative Example 1 100 parts by weight of the lithium transition metal oxide prepared in Preparation Example was mixed with 60 parts by weight of deionized water, washed with water at 25°C for 5 minutes, filtered using a filter press for 5 minutes, and dried in a vacuum oven at 130°C for 12 hours or more to prepare a positive electrode active material.

[0104] Comparative Example 2 100 parts by weight of the lithium transition metal oxide prepared in Preparation Example was mixed with 50 parts by weight of deionized water, washed for 10 minutes at 25° C., and filtered for 5 minutes using a filter press. Then, 50 parts by weight of the lithium transition metal oxide was mixed with 100 parts by weight of the lithium transition metal oxide, washed for 10 minutes at 25° C., filtered for 10 minutes using a filter press, and dried in a vacuum oven at 130° C. for 12 hours or more to prepare a positive electrode active material.

[0105] Comparative Examples 3 to 5 Positive active materials were prepared in the same manner as in Comparative Example 1, except that the amounts of deionized water were adjusted to 75 parts by weight, 110 parts by weight, and 125 parts by weight, respectively.

[0106] Comparative Example 6 100 parts by weight of the lithium transition metal oxide produced in the production example was mixed with 110 parts by weight of deionized water, washed with water at 25°C for 5 minutes, filtered using a filter press for 5 minutes, and dried in a vacuum oven at 130°C for 12 hours or more. 3 BO3 The powder was mixed with dried lithium transition metal oxide in a weight amount of 1000 ppm, and heat-treated at 300° C. for 5 hours to produce a positive electrode active material in which a coating layer was formed on the surface of the lithium transition metal oxide.

[0107] Comparative Example 7 In Comparative Example 6, a positive electrode active material was prepared in the same manner as in Comparative Example 1, except that the amount of deionized water was adjusted to 125 parts by weight.

[0108] Comparative Examples 8 and 9 A positive electrode active material was prepared in the same manner as in Example 1, except that the amounts of the first washing solution and the second washing solution were adjusted as shown in Table 1 below.

[0109] [Table 1]

[0110] Experimental Example Experimental Example 1: Evaluation of residual lithium and BET specific surface area 5 g of each of the positive electrode active materials prepared in the Examples and Comparative Examples was added to 100 ml of deionized water and stirred for 5 minutes. The solution was then filtered and 0.1 M HCl was added until the pH of the solution reached 4. The amount of residual lithium (LiOH, Li 2 CO 3 ) was calculated and is shown in Table 2 below.

[0111] In addition, 3 g of each of the positive electrode active materials prepared in the Examples and Comparative Examples was placed in a sample tube and pretreated at 150° C. for 2 hours. The sample tube was then connected to a port of a BET measurement device (Micromeritiecs Tristar2 3000). The amount of nitrogen gas adsorbed on the surface of the sample was measured in a relative pressure range of 0.01 to 0.2, and the surface area per unit weight of the sample was calculated and shown in Table 2 below.

[0112] [Table 2]

[0113] Referring to Table 2, when comparing Example 1 and Comparative Example 1, Example 2 and Comparative Example 3, Example 3 and Comparative Example 4, Example 4 and Comparative Example 5, Example 5 and Comparative Example 6, and Example 6 and Comparative Example 7, which use the same total amount of washing solution, it can be seen that when steps (B) and (C) are included as in the present invention, residual lithium can be more effectively controlled.

[0114] Experimental Example 2: Evaluation of half-cell characteristics Lithium secondary batteries were produced using the positive electrode active materials produced in the Examples and Comparative Examples, and the charge / discharge capacity, capacity retention rate at high temperature, and resistance increase rate of each lithium secondary battery were evaluated.

[0115] Specifically, the positive electrode active materials prepared in the examples and comparative examples were mixed with carbon black conductive material and PVdF binder in a weight ratio of 97.5:1.0:1.5 in NMP solvent to prepare positive electrode slurry. The positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare a positive electrode. Meanwhile, a Li metal disk was used as the negative electrode active material. An electrode assembly was prepared by interposing a separator between the positive and negative electrodes prepared as above, and the assembly was placed inside a battery case, and an electrolyte was injected into the case to prepare a lithium secondary battery. In this case, the electrolyte was 1M LiPF in an organic solvent of EC / EMC / DMC (3 / 3 / 4, vol%). 6 An electrolyte solution containing the above dissolved therein was injected into the battery to prepare a lithium secondary battery.

[0116] The lithium secondary battery prepared as above was charged at a constant current of 0.1 C at 25° C. until the voltage reached 4.3 V, and then discharged at a constant current of 0.1 C until the voltage reached 3.0 V. The charge capacity, discharge capacity, charge / discharge efficiency, and DCIR are shown in Table 3.

[0117] The capacity of the lithium secondary battery was measured by repeating 30 charge-discharge cycles, in which the battery was charged at a constant current of 0.33 C at 45° C. in the range of 3.0 to 4.3 V until the voltage reached 4.3 V, and then discharged at a constant current of 0.33 C until the voltage reached 3.0 V. In particular, the ratio of the 30th cycle capacity to the 1st cycle capacity was taken as the capacity retention rate, which is shown in Table 1 below. In addition, the voltage drop for 60 seconds after the start of discharge in each cycle was measured, and this was divided by the applied current value to measure the resistance at high temperature. In particular, the increase rate of the 30th cycle resistance value to the 1st cycle resistance value is shown in Table 3.

[0118] [Table 3]

[0119] Referring to Table 3, comparing Example 1 and Comparative Example 1, Example 2 and Comparative Example 3, Example 3 and Comparative Example 4, Example 4 and Comparative Example 5, Example 5 and Comparative Example 6, and Example 6 and Comparative Example 7, in which the total amount of washing solution used is the same, it can be seen that when step (B) and step (C) are included as in the present invention, the residual lithium can be more effectively controlled, the charge / discharge efficiency is better, the DCIR value is smaller, and the cycle characteristics are particularly excellent.

[0120] In addition, by comparing Examples 3 and 4, which are different only in the amount of the second washing solution, with Comparative Examples 8 and 9, it can be confirmed that, as in the present invention, when the amount of the second washing solution is 10 parts by weight to 50 parts by weight relative to 100 parts by weight of the first washing solution, the charge / discharge efficiency is better and the cycle characteristics are particularly excellent. On the other hand, in the case of Comparative Example 8, in which the amount of the second washing solution is less than 10 parts by weight relative to 100 parts by weight of the first washing solution, it can be confirmed that the ions on the surface of the positive electrode active material are not sufficiently removed, the charge / discharge efficiency is low, the DCIR value is high, and the cycle characteristics are not good. And, in the case of Comparative Example 9, in which the amount of the second washing solution is more than 50 parts by weight relative to 100 parts by weight of the first washing solution, it can be confirmed that not only the ions on the surface of the positive electrode active material but also the lithium ions present inside are removed, resulting in low charge / discharge efficiency and poor cycle characteristics.

[0121] In addition, in the case of Comparative Example 2 in which step (B) was repeated twice without including step (C), it was confirmed that the charge / discharge efficiency was low, the DCIR value was high, and the cycle characteristics were not good.

[0122] Experimental Example 3: Evaluation of volume change of monocell Monocells were manufactured using the positive electrode active materials manufactured in the examples and comparative examples, and the volume change rate at high temperatures was measured for each monocell.

[0123] Specifically, the positive electrode active materials prepared in the examples and comparative examples were mixed with carbon black conductive material and PVdF binder in a weight ratio of 97.5:1.0:1.5 in NMP solvent to prepare positive electrode slurry. The positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and rolled to prepare a positive electrode. A negative electrode active material, which was a mixture of natural graphite and artificial graphite in a ratio of 9:1, conductive material, additives, and binders in a weight ratio of 95.6:1.0:2.3:1.1, was mixed in NMP solvent to prepare a negative electrode slurry, which was applied to one side of a copper current collector, dried, and rolled to prepare a negative electrode. An electrode assembly was prepared by interposing a separator between the positive and negative electrodes prepared as above, and the electrodes were laminated at 80°C to properly bond them, and aluminum and nickel tabs were welded, and the mixture was placed in an aluminum pouch and an electrolyte was injected to prepare a mono cell. The electrolyte used was 0.7M LiPF in an organic solvent (EC / EMC (3 / 7, vol%)). 6 The electrolyte used was a solution of

[0124] The mono cell prepared as above was charged at 25°C for 3 hours at a current of 0.1C, and then one side of the pouch was opened, vacuum degassed, and resealed. Then, charge and discharge were repeated three times at a current of 0.33C, and then charging was performed at a current of 0.33C. The charged mono cell was opened and the negative electrode was separated, and then the positive electrodes and separators were alternately stacked in groups of three, placed in an aluminum pouch, and electrolyte was injected to prepare a cell for volume measurement. The electrolyte was 0.7M LiPF in an organic solvent of EC / EMC (3 / 7, vol%). 6 The electrolyte used was a solution of the above. The cells were stored in an oven at 60℃, and then taken out every week to measure the volume change rate at room temperature for 12 weeks. The volume change rate of each cell compared to the initial volume is shown in Figure 1.

[0125] Referring to FIG. 1, when comparing Example 1 and Comparative Example 1, Example 2 and Comparative Example 3, Example 3 and Comparative Example 4, Example 4 and Comparative Example 5, Example 5 and Comparative Example 6, and Example 6 and Comparative Example 7, which use the same total amount of washing solution, it can be seen that when steps (B) and (C) are included as in the present invention, residual lithium can be more effectively controlled and the volume change rate of the cell at high temperatures is smaller.

[0126] On the other hand, in the case of Comparative Example 8, in which the amount of the second washing solution was less than 10 parts by weight relative to 100 parts by weight of the first washing solution, it was confirmed that the ions on the surface of the positive electrode active material were not sufficiently removed, and the volume change rate of the cell was large at high temperatures.And in the case of Comparative Example 9, in which the amount of the second washing solution was more than 50 parts by weight relative to 100 parts by weight of the first washing solution, it was confirmed that not only the ions on the surface of the positive electrode active material but also the lithium ions present inside were removed, and the volume change rate of the cell was large at high temperatures.

[0127] Also, in the case of Comparative Example 2 in which step (B) was repeated twice without step (C), it was confirmed that there was a problem in that the cell volume change rate was the largest at high temperatures.

Claims

1. (A) providing a lithium transition metal oxide; (B) mixing the lithium transition metal oxide with a first washing solution to perform a first water wash on the lithium transition metal oxide, and then performing a first filtration; (C) performing a second washing and a second filtration simultaneously on the lithium transition metal oxide that has been subjected to step (B) with a second washing solution using a filtration device capable of simultaneously performing washing and filtration; the amount of the first washing solution is 50 parts by weight to 100 parts by weight based on 100 parts by weight of the lithium transition metal oxide; The amount of the second washing solution is 10 parts by weight to 50 parts by weight based on 100 parts by weight of the first washing solution.

2. The method for producing a positive electrode active material according to claim 1 , wherein the lithium transition metal oxide contains nickel in an amount of 70 mol % or more of all metals other than lithium.

3. The method for producing a positive electrode active material according to claim 1 or 2, wherein the lithium transition metal oxide has a composition represented by the following Chemical Formula 1: [Chemical formula 1] Li １＋ａ Ni ｘ１ Co ｙ１ M1 ｚ１ M2 ｗ１ O ２ In the above Chemical Formula 1, 0≦a≦0.3, 0.7≦x1<1.0, 0<y1≦0.3, 0<z1≦0.3, 0≦w1≦0.2, and x1+y1+z1+w1=1; M1 is one or more selected from Mn and Al; M2 is one or more selected from Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, F, P, S and Y.

4. 4. The method for producing a positive electrode active material according to claim 1, wherein an amount of the second washing solution is 5 parts by weight to 50 parts by weight based on 100 parts by weight of the lithium transition metal oxide.

5. 5. The method for producing a positive electrode active material according to claim 1, wherein a sum of an amount of the first washing solution and an amount of the second washing solution is 55 parts by weight to 150 parts by weight per 100 parts by weight of the lithium transition metal oxide.

6. The method for producing a positive electrode active material according to any one of claims 1 to 5, wherein the first water washing is performed for 5 minutes to 30 minutes.

7. The method for producing a positive electrode active material according to any one of claims 1 to 6, wherein the first water washing is carried out at a temperature of 5°C to 30°C.

8. The method for producing a positive electrode active material according to any one of claims 1 to 7, wherein the second water washing is performed for 5 minutes to 30 minutes.

9. The method for producing a positive electrode active material according to any one of claims 1 to 8, wherein the second water washing is carried out at a temperature of 5°C to 30°C.

10. 10. The method for producing a positive electrode active material according to claim 1, further comprising the steps of: (D) drying the lithium transition metal oxide obtained by step (C), and then mixing the dried lithium transition metal oxide with a coating element-containing raw material and heat-treating the mixture to form a coating layer.

Images