Positive electrode material for lithium secondary battery, method for preparing same and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode active material comprising at least one secondary particle comprising an aggregate of primary macro particles, a method for manufacturing the same, and a lithium secondary battery comprising the same. According to one embodiment of the present invention, the electrical conductivity of the surface of the positive active material can be improved by coating a conductive carbon material on the surface of the secondary particle. Accordingly, it is possible to provide a nickel-based cathode active material with improved lifespan performance by minimizing challenge network loss after cycling.

Description

Technology Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery comprising primary large particles and a method for manufacturing the same. Background Technology

[0002] Recently, accompanied by the rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity rechargeable batteries is rapidly increasing. In particular, lithium-ion batteries are gaining attention as power sources for portable devices due to their lightweight nature and high energy density. Accordingly, active research and development efforts are underway to improve the performance of lithium-ion batteries.

[0003] In a lithium secondary battery, electrical energy is produced by oxidation and reduction reactions when lithium ions are inserted into or removed from the positive and negative electrodes, which are composed of active materials capable of lithium ion intercalation and deintercalation, with an organic or polymer electrolyte charged between them.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMn2O4, etc.), and lithium iron phosphate compounds (LiFePO4) are used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide (LiCoO2) is widely used and applied as a cathode active material for high voltage applications due to its advantages of high operating voltage and excellent capacity characteristics. However, due to the rising price and supply instability of cobalt (Co), there are limitations to its mass use as a power source in fields such as electric vehicles, leading to the emergence of a need to develop cathode active materials that can replace it. Accordingly, nickel-cobalt-manganese-based lithium composite transition metal oxides (hereinafter simply referred to as 'NCM-based lithium composite transition metal oxides') have been developed in which a portion of the cobalt (Co) is substituted with nickel (Ni) and manganese (Mn).

[0005] Meanwhile, conventionally developed NCM-based lithium composite transition metal oxides are in the form of secondary particles formed by the aggregation of primary microparticles, resulting in a large specific surface area and low particle strength. Furthermore, when an electrode is manufactured using a cathode active material containing these secondary particles aggregated from primary microparticles and then rolled, severe particle breakage occurs, leading to high gas generation and reduced stability during cell operation. In particular, high-nickel (High-Ni) NCM-based lithium composite transition metal oxides, in which the nickel (Ni) content is increased to secure high capacity, are gaining attention as high-energy density cells due to their high capacity performance. However, as the nickel content increases, thermal stability decreases, and side reactions increase during electrochemical reactions, leading to problems such as increased resistance and gas generation.

[0006] To solve these problems, monoliths have been developed. Monoliths refer to particles that exist independently of the aforementioned secondary particles and do not have grain boundaries on the surface. These monoliths improve the aforementioned thermal stability and gas generation by minimizing unstable interfaces on the surface of the cathode active material.

[0007] However, these single particles have the characteristic of having a small surface area that can participate in charging and discharging compared to the aforementioned secondary particles. Therefore, when the same charging and discharging is performed, the aforementioned single particles have a large amount of current flowing per area, which increases side reactions and causes a problem of a resistive layer forming on the particle surface. In addition, when these single particles are subjected to a certain pressure during rolling, the particles break and generate fine particles; these fine particles increase unstable interfaces that cause side reactions with the electrolyte, thereby degrading the performance of the battery. The problem to be solved

[0008] The problem that the present invention aims to solve is to provide a positive active material containing a new concept of secondary particles to solve the above problem.

[0009] The problem that the present invention aims to solve is to improve electrochemical properties by forming a coating layer containing a carbon material on the surface of the secondary particles.

[0010] Specifically, cycle characteristics can be improved by minimizing conductive network losses after charging and discharging. means of solving the problem

[0011] One aspect of the present invention provides a positive electrode active material according to the following embodiments.

[0012] Specifically,

[0013] A positive electrode active material for a lithium secondary battery comprising: at least one secondary particle comprising an aggregate of primary macro particles; and a coating layer located on the surface of the secondary particle and comprising a carbon material;

[0014] The average particle size (D50) of the above primary large particles is 1.5 μm or more, and

[0015] The average particle size (D50) of the above secondary particles is 3 to 10 μm, and

[0016] The above-described positive active material provides a positive active material for a lithium secondary battery characterized by comprising a nickel-based lithium transition metal oxide.

[0017] The content of the carbon material included in the coating layer may be 0.3 to 5 parts by weight based on 100 parts by weight of the secondary particles.

[0018] The thickness of the coating layer may be 10 nm to 50 nm.

[0019] The above carbon material may include one or more selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon.

[0020] The above nickel-based lithium transition metal oxide is Li a [Ni x Coy Mn 1-x-y ]O 2+b (0.9≤a≤1.5, -0.1≤b≤1.0, 0.5≤x≤0.95, 0 <y≤0.5, M은 Mn, Mg, Al, Ti, V, Y, Zr 로 이루어진 군에서 선택된 1종 이상의 원소) 일 수 있다.

[0021] The ratio of the average particle size (D50) of the primary large particle to the average crystal size of the primary large particle may be 2 or more.

[0022] The average crystal size of the above primary macroparticles may be 130 nm or larger.

[0023] The ratio of the average particle size (D50) of the secondary particle to the average particle size (D50) of the primary large particle may be 2 to 5 times.

[0024] When the above positive active material is rolled, the primary large particle detaches from the secondary particle, and the primary large particle itself may not break.

[0025] The above rolling may be performed under 1 ton conditions.

[0026] When the above positive active material is rolled under 9 ton conditions, the proportion of fine particles smaller than 1 μm may be 1% or less.

[0027] One aspect of the present invention provides a positive electrode for a lithium secondary battery comprising the aforementioned positive electrode active material.

[0028] One aspect of the present invention provides a lithium secondary battery comprising the aforementioned positive electrode active material.

[0029] One aspect of the present invention provides the following manufacturing method. Specifically,

[0030] (S1) A step of preparing a porous nickel-based lithium transition metal hydroxide precursor by mixing a precursor containing nickel, cobalt, and manganese with a hydroxide;

[0031] (S2) A step of preparing secondary particles by mixing and heat-treating the porous nickel-based lithium transition metal hydroxide precursor and lithium raw material; and

[0032] (S3) A step of mixing the secondary particles and the carbon material to form a coating layer containing the carbon material on the surface of the secondary particles; comprising a method for manufacturing a positive electrode active material for a lithium secondary battery,

[0033] The above-described positive active material comprises: at least one secondary particle comprising an aggregate of primary macro particles; and a coating layer located on the surface of the secondary particle and comprising a carbon material; and

[0034] The average particle size (D50) of the above primary large particles is 1.5 μm or more, and

[0035] The average particle size (D50) of the above secondary particles is 3 to 10 μm, and

[0036] The above-mentioned positive active material is a method for manufacturing a positive active material for a lithium secondary battery, characterized in that it comprises a nickel-based lithium transition metal oxide.

[0037] The above (S1) step is performed at 35 to 80 ℃, and

[0038] The above (S2) step can be performed at 700 to 1000 ℃.

[0039] The above step (S3) can be performed at room temperature.

[0040] The above (S1) step can be performed under pH 8 to 12 conditions.

[0041] A separate washing process between the above steps (S2) and (S3) may not be included.

[0042] The tap density of the porous nickel-based lithium transition metal hydroxide precursor in step (S2) above may be 2.0 g / cc or less. Effects of the invention

[0043] According to one embodiment of the present invention, a positive electrode active material comprising secondary particles including primary large particles with an increased average particle size (D50) can be provided. By using such secondary particles, a positive electrode active material with reduced resistance and increased thermal stability compared to conventional secondary particles can be provided.

[0044] According to one embodiment of the present invention, a coating layer containing a carbon material is included on the surface of a secondary particle. Accordingly, the electrical conductivity of the surface of the positive electrode active material can be improved. In addition, the surface of the secondary particle with high surface roughness can be smoothed by the carbon material coating, thereby increasing the rolling density and reducing the generation of fine particles during rolling.

[0045] In addition, by using a conductive carbon material, it is possible to avoid adding a separate conductive agent when manufacturing an electrode containing a positive active material. Accordingly, the amount of positive active material included in the electrode can be increased, thereby increasing energy density. Brief explanation of the drawing

[0046] The drawings attached to this specification illustrate preferred embodiments of the present invention and serve to help to better understand the technical concept of the present invention together with the description of the invention above; therefore, the present invention is not to be interpreted as being limited only to the matters described in such drawings. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in this specification may be exaggerated to emphasize a clearer explanation. Figure 1 shows an SEM image of a positive electrode active material according to one embodiment of the present invention. Figure 2 shows an SEM image of a positive electrode active material according to Comparative Example 1 of the present invention. Figure 3 shows an SEM image of a positive electrode active material according to Comparative Example 2 of the present invention. Figure 4 shows an SEM image of the positive electrode active material according to Comparative Example 3 of the present invention. Specific details for implementing the invention

[0047] Embodiments of the present invention will be described in detail below. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms to best describe their invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, the configurations described in the embodiments of this specification are merely one preferred embodiment of the present invention and do not represent all aspects of the technical spirit of the present invention. It should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0049] Throughout this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0051] In the present specification and claims, "comprising a plurality of crystal grains" means a crystal formed by the aggregation of two or more crystal particles having an average crystal size within a specific range. In this case, the crystal size of the crystal grains can be quantitatively analyzed using X-ray diffraction analysis (XRD) by Cu Kα X-rays (Xrα). Specifically, the average crystal size of the crystal grains can be quantitatively analyzed by placing the manufactured particles in a holder, irradiating the particles with X-rays, and analyzing the resulting diffraction grating.

[0053] In the specification and claims, D50 may be defined as the particle size at the 50% reference of the particle size distribution and may be measured using a laser diffraction method. For example, a method for measuring the average particle size (D50) of the positive active material may be to disperse the particles of the positive active material in a dispersion medium, introduce them into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiate them with ultrasound of about 28 kHz at an output of 60 W, and then calculate the average particle size (D50) corresponding to 50% of the volume accumulated in the measuring device.

[0055] In the present invention, 'primary particle' refers to a particle that does not have visible grain boundaries when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope. In the present invention, primary particles can be classified into primary micro particles and primary macro particles depending on the average particle size (D50).

[0056] In the present invention, 'secondary particle' refers to a particle formed by the aggregation of the primary particle.

[0057] In the present invention, 'single particle' refers to a particle that exists independently of the secondary particle and does not have grain boundaries on the surface, for example, a particle with a diameter of 0.5 μm or more.

[0058] In the present invention, when the term 'particle' is used, it may mean that any one or all of a single particle, a secondary particle, or a primary particle are included.

[0060] positive electrode active material

[0062] In one aspect of the present invention, a positive electrode active material in the form of secondary particles different from existing materials is provided.

[0064] Specifically,

[0065] 1) A positive electrode active material for a lithium secondary battery comprising at least one secondary particle including an aggregate of primary macro particles, wherein

[0066] 2) The average particle size (D50) of the above primary large particles is 1.5 μm or more, and

[0067] 3) A coating layer located on the surface of the secondary particle and comprising a carbon material; comprising,

[0068] 4) The average particle size (D50) of the above secondary particles is 3 to 10 μm, and

[0069] 5) The above positive active material provides a positive active material for a lithium secondary battery characterized by including a nickel-based lithium transition metal oxide.

[0070] The above secondary particles have the characteristics of 1) to 5), thereby providing a nickel-based cathode active material with improved stability at high temperature and high voltage.

[0071] Below, the characteristics 1) to 5) of the secondary particle are explained in detail.

[0073] Particle forms and primary macroparticles

[0075] Generally, nickel-based lithium transition metal oxides are secondary particles. These secondary particles may be in the form of aggregated primary particles.

[0076] Specifically, dense nickel-based lithium transition metal hydroxide secondary particles produced by the coprecipitation method are used as a precursor, and when this precursor is mixed with a lithium precursor and calcined at a temperature below 960°C, lithium transition metal oxide secondary particles containing primary fine particles can be obtained. However, when a positive electrode active material containing such conventional secondary particles is coated onto a current collector and then rolled, the particles themselves break, causing the specific surface area to increase. When the specific surface area increases, rock salt is formed on the surface, which causes a problem of reduced resistance.

[0077] To address these issues, single-particle cathode active materials have been additionally developed. Specifically, unlike the conventional method using the aforementioned dense nickel-based lithium transition metal hydroxide secondary particles as a precursor, a porous precursor is used relative to the conventional precursor, and by increasing the calcination temperature relative to the same nickel content, a nickel-based lithium transition metal oxide that no longer has the form of secondary particles can be obtained as a single particle. However, these single particles have a problem in that the crystal structure of the particle surface changes from a layered structure to a rock-salt structure during single-particle synthesis. The surface of the rock-salt structure, which is an insulator, hinders the movement of lithium ions during charging and discharging, thereby reducing the battery's lifespan.

[0079] One aspect of the present invention is to solve these problems.

[0080] When firing with a high-density precursor identical to the existing one, only the firing temperature is increased, the average diameter of the primary particles (D50) and the average diameter of the secondary particles (D50) inevitably increase.

[0081] On the other hand, the secondary particle according to one aspect of the present invention differs from the conventional single particle obtaining method in the following respects.

[0082] As previously mentioned, conventional single particles are formed by using the existing precursor for secondary particles as is and only increasing the primary calcination temperature. On the other hand, the secondary particles according to one aspect of the present invention use a precursor with high porosity separately. Accordingly, primary large particles with a large particle size can be grown without raising the calcination temperature, while secondary particles can grow relatively less compared to conventional ones.

[0083] Accordingly, the secondary particle according to one aspect of the present invention has an average particle size (D50) that is the same or similar as that of the prior art, while having a larger average diameter (D50) of the primary particle. That is, unlike the general form of the prior art cathode active material, which is a form in which primary particles with small average particle sizes gather to form a secondary particle, the invention provides a secondary particle form in which primary large particles with increased primary particle size are aggregated.

[0085] In the present invention, 'primary large particles' are those with an average diameter (D50) of 1.5 μm or more.

[0086] In a specific embodiment of the present invention, the average particle size of the primary large particles may be 1.5 μm or more, 2 μm or more, 2.5 μm or more, 3 μm or more, or 3.5 μm or more, and may be 5 μm or less, 4.5 μm or less, or 4 μm or less. If the average particle size of the primary large particles is less than 1.5 μm, it corresponds to conventional secondary small particles, and there may be a problem of particle breakage occurring during rolling.

[0088] In the present invention, it is preferable that the ratio of the average particle size (D50) to the average crystal size of the 'primary large particle' is 2 or greater. That is, when compared to the primary micro particles constituting the conventional secondary particles, the average particle size and average crystal size of the primary large particle can grow simultaneously.

[0089] From the perspective of cracking, it is advantageous to have a large average particle size without visible grain boundaries, as with conventional single particles. Accordingly, the inventors focused on increasing the average particle size (D50) of the primary particles. However, they discovered that when only the average particle size (D50) of the primary particles is increased due to factors such as under-firing, rock salt forms on the surface of the primary particles and the resistance increases. To solve this problem, the inventors confirmed that the resistance decreases when the crystal size of the primary large particles is increased simultaneously.

[0090] That is, the primary large particles in the present invention are preferably particles that have not only a large average particle size but also an average crystal size, and do not have external grain boundaries.

[0091] In this way, when the average particle size and average crystal size of the primary particles grow simultaneously, the resistance is lowered compared to conventional single particles, which have a large increase in resistance due to rock salt forming on the surface from firing at high temperatures, and it is also advantageous in terms of long lifespan.

[0092] As such, compared to conventional single particles, the "secondary particle composed of aggregates of secondary large particles" used in one aspect of the present invention is advantageous in that the resistance is lowered due to the increase in the size of the primary particle itself and the reduction in the formation of rock salt.

[0094] At this time, the average crystal size of the primary large particle can be quantitatively analyzed using X-ray diffraction analysis (XRD) by Cu Kα X-rays. Specifically, the average crystal size of the primary large particle can be quantitatively analyzed by placing the manufactured particle in a holder and irradiating the particle with X-rays, and analyzing the resulting diffraction grating.

[0095] In a specific embodiment of the present invention, the ratio of the average particle size (D50) to the average crystal size may be 2 or more, 2.5 or more, 3 or more, and 50 or less, 40 or less, 35 or less.

[0096] In addition, the average crystal size of the primary macroparticle may be 130 nm or more, 150 nm or more, 170 nm or more, or 200 nm or more, and may be 300 nm or less, 270 nm or less, or 250 nm or less.

[0098] secondary particles

[0100] According to one aspect of the present invention, the secondary particle has an average particle size (D50) that is the same or similar as that of the prior art, while having a larger average diameter (D50) of the primary particle. That is, unlike the general form of the prior art cathode active material, which is a form in which primary particles with small average particle sizes are gathered to form a secondary particle, the invention provides a secondary particle form in which primary large particles with increased primary particle size are aggregated.

[0101] In a specific embodiment of the present invention, the secondary particles may be aggregated from one to ten primary large particles. More specifically, the secondary particles may be aggregated from one or more, two or more, three or more, or four or more primary large particles within the numerical range, or may be aggregated from ten or fewer, nine or fewer, eight or fewer, or seven or fewer primary large particles within the numerical range.

[0102] According to one aspect of the present invention, the secondary particle has an average diameter (D50) of 3 μm to 10 μm. More specifically, it is 3 μm or more, 3.5 μm or more, 4 μm or more, or 4.5 μm or more, and 10 μm or less, 8 μm or less, or 7 μm or less.

[0104] Generally, regardless of particle shape, when the composition is the same, as the calcination temperature increases, the particle size and the average crystal size within the particle increase. On the other hand, according to one aspect of the present invention, by using a porous precursor, primary large particles with a large particle size can be grown without raising the calcination temperature higher than in the conventional method, while secondary particles can grow relatively less compared to the conventional method.

[0105] Accordingly, according to one aspect of the present invention, the secondary particle is composed of a primary large particle having an average diameter (D50) that is the same or similar to that of a conventional secondary particle, and having a larger average diameter and average crystal size compared to a conventional primary fine particle.

[0106] In a specific embodiment of the present invention, the ratio of the average particle size (D50) of the secondary particle to the average particle size (D50) of the primary large particle may be 2 to 5 times.

[0107] At this time, when rolling the secondary particles, the primary large particles may fall off, and the primary large particles themselves may not break. At this time, the rolling condition may be 1 ton to 9 ton. Specifically, it may be 1 ton.

[0109] The above secondary particles include nickel-based lithium transition metal oxides.

[0110] Specifically, the nickel-based lithium transition metal oxide is Li a [Ni x Co y Mn 1-x-y ]O 2+b (0.9≤a≤1.5, -0.1≤b≤1.0, 0.5≤x≤0.95, 0 <y≤0.5, M은 Mn, Mg, Al, Ti, V, Y, Zr 로 이루어진 군에서 선택된 1종 이상의 원소)을 포함하는 것이다.

[0111] For example, the nickel-based lithium transition metal oxide mentioned above is LiNi 0.8 Co0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2 and LiNi 0.5 Co 0.3 Mn 0.2 It can be selected from a group consisting of O2.

[0112] Nickel (Ni) is an element that contributes to the high potential and high capacity of secondary batteries, and the amount corresponding to x is 0 <x<1의 양으로 포함될 수 있다. x값이 0인 경우 충방전 용량 특성이 저하될 우려가 있고, x값이 1 초과인 경우 활물질의 구조 및 열 안정성 저하, 이에 따른 수명 특성 저하의 우려가 있다. 니켈 함량의 제어에 따른 고전위화 및 고용량화 효과를 고려할 때 상기 니켈은 보다 구체적으로 0.5≤x<1, 보다 더 구체적으로는 0.5≤x≤0.8의 양으로 포함될 수 있다.

[0113] Cobalt (Co) is an element that contributes to improving the charge-discharge cycle characteristics of active materials, and the amount corresponding to y is 0 <y≤0.35의 양으로 포함될 수 있다. y=0인 경우 구조 안정성 저하 및 리튬이온 전도도 저하로 인한 충방전 용량 저하의 우려가 있고, y가 0.35 초과하는 경우 양극 활물질의 구동 전압이 높아져 주어진 상한 전압 하에서 충방전 용량 저하의 우려가 있다. 코발트 함량의 제어에 따른 활물질의 사이클 특성 향상 효과를 고려할 때, 상기 코발트는 보다 구체적으로 0.1혏<0.35, 보다 더 구체적으로는 0.1≤y≤0.3의 양으로 포함될 수 있다.

[0115] Meanwhile, in the present invention, the secondary particle comprises a coating layer in which a portion of the surface of the particle includes a carbon material.

[0116] The content of the carbon material included in the coating layer may be 0.3 to 5 parts by weight based on 100 parts by weight of the secondary particles.

[0117] The thickness of the coating layer may be 10 nm to 50 nm.

[0118] The above carbon material may include one or more selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon.

[0119] In this way, by including a carbon material coating layer, the electrical conductivity of the surface of the positive electrode active material can be improved. In addition, the surface of secondary particles with high surface roughness can be smoothed by the carbon material coating, thereby increasing rolling density and reducing the generation of fine particles during rolling. Specifically, when the positive electrode active material is rolled under 9 ton conditions, the proportion of fine particles smaller than 1 μm may be 1% or less, more specifically 0.6% or less.

[0120] In addition, by using a conductive carbon material, it is possible to avoid adding a separate conductive agent when manufacturing an electrode containing a positive active material. Accordingly, the amount of positive active material included in the electrode can be increased, thereby increasing energy density.

[0122] Method for manufacturing positive electrode active material

[0124] A positive electrode active material according to one aspect of the present invention may be manufactured in the following manner. However, it is not limited thereto.

[0126] Specifically, (S1) a step of preparing a porous nickel-based lithium transition metal hydroxide precursor by mixing a precursor containing nickel, cobalt, and manganese with a hydroxide;

[0127] (S2) A step of preparing secondary particles by mixing and heat-treating the porous nickel-based lithium transition metal hydroxide precursor and lithium raw material; and

[0128] (S3) Includes the step of mixing and milling the secondary particles and carbon material compound,

[0129] The above-described positive active material comprises at least one secondary particle comprising an aggregate of primary macro particles; and a coating layer located on the surface of the secondary particle and comprising a carbon material; as a positive active material for a lithium secondary battery,

[0130] The average particle size (D50) of the above primary large particles is 1.5㎛ or larger, and

[0131] The average particle size (D50) of the above secondary particles is 3 to 10 μm, and

[0132] The above-mentioned positive electrode active material relates to a method for manufacturing a positive electrode active material for a lithium secondary battery comprising a nickel-based lithium transition metal oxide.

[0134] The method for manufacturing the above positive active material is further explained step by step.

[0135] First, a positive electrode active material precursor containing nickel (Ni), cobalt (Co), and manganese (Mn) is prepared.

[0136] At this time, the precursor for manufacturing the positive electrode active material may be purchased and used as a commercially available positive electrode active material precursor, or may be manufactured according to a method for manufacturing a positive electrode active material precursor well known in the relevant technical field.

[0137] For example, the above precursor may be prepared by co-precipitating a transition metal solution containing a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material by adding an ammonium cation-containing complex-forming agent and a basic compound.

[0138] The above nickel-containing raw material may be, for example, nickel-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically, may be Ni(OH)2, NiO, NiOOH, NiCO3ㆍ2Ni(OH)2ㆍ4H2O, NiC2O2ㆍ2H2O, Ni(NO3)2ㆍ6H2O, NiSO4, NiSO4ㆍ6H2O, nickel fatty acid salts, nickel halides, or combinations thereof, but are not limited thereto.

[0139] The above cobalt-containing raw material may be a cobalt-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, or oxyhydroxide, and specifically may be Co(OH)2, CoOOH, Co(OCOCH3)2ㆍ4H2O, Co(NO3)2ㆍ6H2O, CoSO4, Co(SO4)2ㆍ7H2O or a combination thereof, but is not limited thereto.

[0140] The above manganese-containing raw material may be, for example, a manganese-containing acetate, nitrate, sulfate, halide, sulfide, hydroxide, oxide, oxyhydroxide, or a combination thereof, and specifically, manganese oxides such as Mn2O3, MnO2, Mn3O4, etc.; manganese salts such as MnCO3, Mn(NO3)2, MnSO4, manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acid, manganese fatty acid; manganese oxyhydroxide, manganese chloride, or a combination thereof, but is not limited thereto.

[0141] The above transition metal solution may be prepared by adding a nickel-containing raw material, a cobalt-containing raw material, and a manganese-containing raw material to a solvent, specifically water, or a mixed solvent of an organic solvent that can be uniformly mixed with water (e.g., alcohol, etc.), or by mixing an aqueous solution of a nickel-containing raw material, an aqueous solution of a cobalt-containing raw material, and a manganese-containing raw material.

[0142] The above ammonium cation-containing complex-forming agent may be, for example, NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, NH4CO3, or a combination thereof, but is not limited thereto. Meanwhile, the above ammonium cation-containing complex-forming agent may be used in the form of an aqueous solution, and in this case, water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) may be used as the solvent.

[0143] The above basic compound may be a hydroxide of an alkali metal or alkaline earth metal, such as NaOH, KOH, or Ca(OH)2, a hydrate thereof, or a combination thereof. The above basic compound may also be used in the form of an aqueous solution, in which case water or a mixture of water and an organic solvent that is uniformly miscible with water (specifically, alcohol, etc.) may be used as the solvent.

[0144] The above basic compound is added to adjust the pH of the reaction solution, and can be added in an amount such that the pH of the metal solution becomes 8 to 12.

[0145] Afterwards, a porous nickel-based lithium transition metal hydroxide precursor can be prepared by mixing a precursor containing nickel, cobalt, and manganese with a hydroxide.

[0146] At this time, the co-precipitation reaction can be carried out at a temperature of 35°C to 80°C under an inert atmosphere such as nitrogen or argon.

[0147] Accordingly, a porous nickel-based lithium transition metal hydroxide precursor can be prepared by mixing a precursor containing nickel, cobalt and manganese with a hydroxide (S1).

[0148] By the process described above, nickel-cobalt-manganese hydroxide particles are generated and precipitated in the reaction solution. By controlling the concentrations of the nickel-containing raw material, the cobalt-containing raw material, and the manganese-containing raw material, a precursor can be prepared in which the nickel (Ni) content is 60 mol% or more of the total metal content. The precipitated nickel-cobalt-manganese hydroxide particles can be separated by a conventional method and dried to obtain a nickel-cobalt-manganese precursor. The precursor may be a secondary particle formed by the aggregation of primary particles.

[0150] Afterwards, the aforementioned precursor and lithium raw material are mixed and heat-treated (first calcination) (S2).

[0151] The above lithium raw material may include lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides, and is not particularly limited as long as it is soluble in water. Specifically, the above lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, or Li3C6H5O7, and any one or more of these may be used.

[0152] In the case of a high-Ni NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 60 mol% or more, the above first calcination can be performed at 700 to 1,000 ℃, more preferably at 780 to 980 ℃, and even more preferably at 780 to 900 ℃. The above first calcination can be performed under an air or oxygen atmosphere and can be carried out for 15 to 35 hours.

[0153] Next, after the first firing, the second particles and the carbon material compound are mixed and then milled (S3).

[0154] In one aspect of the present invention, unlike conventional methods, the carbon material compound coating is applied by a physical method. For example, the carbon material compound can be coated on the surface of secondary particles by mixing or milling.

[0155] That is, the above step (S3) can be performed at room temperature.

[0156] In other words, the above step (S3) does not undergo a separate heat treatment process. As such, by not undergoing a heat treatment process, the positive electrode active material according to one aspect of the present invention can be manufactured with only a simple process. Furthermore, by not undergoing a separate heat treatment process, the oxidation state or structure of the transition metal compound can be avoided. Accordingly, a positive electrode active material with minimal side reactions can be manufactured.

[0158] Meanwhile, a separate washing process may not be included between the above step (S2) and the above step (S3). At this time, the total amount of lithium remaining on the particle surface after the first calcination may be 0.5 to 1.5 wt% relative to the total weight of the positive electrode active material. Conventionally, a washing process was performed to remove lithium by-products present on the surface of the positive electrode active material. This is because the presence of lithium by-products caused problems such as adverse reactions with the electrolyte when applied to a battery and increased gas generation during high-temperature storage. On the other hand, in the manufacturing method according to one aspect of the present invention, a separate washing process is not performed. Accordingly, lithium by-products are present on the particle surface, and when such lithium by-products are 0.5 to 1.5 wt% relative to the total weight of the positive electrode active material, a positive electrode active material having a secondary particle aggregate including a primary large particle according to one aspect of the present invention can be manufactured.

[0160] Positive electrodes and lithium secondary batteries

[0162] According to another embodiment of the present invention, a positive electrode for a lithium secondary battery and a lithium secondary battery comprising the positive electrode active material are provided.

[0164] Specifically, the anode comprises an anode current collector and an anode active material layer formed on the anode current collector and including the anode active material.

[0165] In the above-mentioned positive electrode, the positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above-mentioned positive current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the above-mentioned positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0166] The above positive active material layer may include a conductive material and a binder along with the positive active material described above.

[0167] At this time, the conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that possesses electronic conductivity without causing chemical changes can be used without special limitations. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The conductive material may typically be included in an amount of 1 to 30 weight percent relative to the total weight of the positive electrode active material layer.

[0168] In addition, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the positive current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The binder may be included in an amount of 1 to 30 weight% based on the total weight of the positive active material layer.

[0169] The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it may be manufactured by applying a composition for forming an anode active material layer, comprising the above-described anode active material and optionally a binder and a conductive material, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above.

[0170] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0171] Alternatively, the anode may be manufactured by casting the composition for forming the anode active material layer onto a separate support, and then laminating the film obtained by peeling off from the support onto an anode current collector.

[0173] According to another embodiment of the present invention, an electrochemical device comprising the anode is provided. Specifically, the electrochemical device may be a battery or a capacitor, and more specifically, may be a lithium secondary battery.

[0174] The above lithium secondary battery specifically comprises a positive electrode, a negative electrode positioned opposite to the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. Additionally, the lithium secondary battery may optionally further include a battery container housing an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member for sealing the battery container.

[0175] In the above lithium secondary battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0176] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0177] The above-mentioned cathode active material layer includes a cathode active material and optionally a binder and a conductive material. The above-mentioned cathode active material layer may be manufactured, for example, by applying a cathode forming composition comprising a cathode active material and optionally a binder and a conductive material onto a cathode current collector and drying it, or by casting the cathode forming composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0178] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples 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, or Al alloys; metal oxides capable of doping and dedoping lithium, such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon may be used as the carbon material. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity 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 calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0179] In addition, the binder and conductive material mentioned above may be the same as those described above for the anode.

[0180] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0181] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0182] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0183] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a hydrocarbon group with a straight, branched, or cyclic structure having C2 to C20 and may include a double bond-directing ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate having a high dielectric constant (e.g., ethylene carbonate or propylene carbonate, etc.) that can improve the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred. In this case, using a mixture of the cyclic carbonate and the chain carbonate in a volume ratio of about 1:1 to about 1:9 may result in excellent performance of the electrolyte.

[0184] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0185] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0186] As described above, a lithium secondary battery containing a positive electrode active material according to the present invention is useful in portable devices such as mobile phones, laptop computers, and digital cameras, and in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0187] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0188] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0189] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0191] Comparative Example 1.

[0192] 4 liters of distilled water were added to a co-precipitation reactor (capacity 20 L) and the temperature was maintained at 50 ℃. A transition metal solution with a concentration of 3.2 mol / L, prepared by mixing NiSO4, CoSO4, and MnSO4 such that the molar ratio of nickel:cobalt:manganese was 0.8:0.1:0.1, was continuously fed into the reactor at a rate of 300 mL / hr, and a 28 wt% aqueous ammonia solution was fed at a rate of 42 mL / hr. The impeller speed was set to 400 rpm for stirring, and a 40 wt% sodium hydroxide solution was added to maintain a pH of 9. The co-precipitation reaction was carried out for 10 hours to form precursor particles. The precursor particles were separated, washed, and dried in an oven at 130 ℃ to produce the precursor.

[0193] Ni synthesized by coprecipitation reaction 0.8 Co 0.1 Mn 0.1(OH)2 precursors are mixed with Li2CO3 such that the Li / Me(Ni, Co, Mn) molar ratio is 1.05, and heat-treated at 850 °C in an oxygen atmosphere for 10 hours to produce LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode active material containing O2 nickel-based lithium transition metal oxide secondary particles was prepared.

[0194] In Comparative Example 1, the secondary particle includes a primary large particle.

[0196] Example 1.

[0197] A secondary particle prepared in Comparative Example 1 and Ketjen black were mixed in a weight ratio of 99:1, then fed into a Nobilta mixer and milled at a rotation speed of 3000 rpm for 10 minutes to prepare an anode active material coated with a Ketjen black carbon material on the surface of the secondary particle.

[0199] Example 2.

[0200] A positive electrode active material was prepared by coating the surface of a secondary particle with a Ketjen black carbon material in the same manner as in Example 1, except that the secondary particle prepared in Comparative Example 1 was mixed with Ketjen black in a weight ratio of 99.5:0.5.

[0202] Comparative Example 2.

[0203] After adding 4 liters of distilled water to a co-precipitation reactor (capacity 20 L) and maintaining the temperature at 50 °C, 100 mL of a 28 wt% aqueous ammonia solution was added. Subsequently, a 3.2 mol / L transition metal solution, mixed with NiSO4, CoSO4, and MnSO4 at a nickel:cobalt:manganese molar ratio of 0.8:0.1:0.1, and a 28 wt% aqueous ammonia solution were continuously added to the reactor at a rate of 300 mL / hr and 42 mL / hr, respectively. The impeller speed was set to 400 rpm for stirring, and a 40 wt% sodium hydroxide solution was added to maintain the pH at 11.0. The co-precipitation reaction was carried out for 24 hours to form precursor particles. The precursor particles were separated, washed, and dried in an oven at 130 °C to produce the precursor.

[0204] Ni synthesized by coprecipitation reaction 0.8 Co 0.1 Mn 0.1 (OH)2 precursors are mixed with Li2CO3 such that the Li / Me(Ni, Co, Mn) molar ratio is 1.05, and heat-treated at 800 °C in an oxygen atmosphere for 10 hours to produce LiNi 0.8 Co 0.1 Mn 0.1 A positive electrode active material containing O2 lithium complex transition metal oxide secondary particles was prepared.

[0205] In Comparative Example 2, the secondary particle includes the primary fine particle.

[0207] Comparative Example 3.

[0208] A secondary particle prepared in Comparative Example 2 and Ketjen black were mixed in a weight ratio of 99:1, then fed into a Nobilta mixer and milled at a rotation speed of 3000 rpm for 10 minutes to prepare an anode active material coated with a Ketjen black carbon material on the surface of the secondary particle.

[0210] [Experimental Example 1: Measurement of Electrical Conductivity]

[0211] The electrical conductivity of the positive electrode active materials according to Comparative Examples 1 to 3 and Example 1 was measured after rolling under 1 ton conditions. The results are shown in Table 1.

[0212] Electrical conductivity was measured using a powder resistance measuring device. Specifically, 5g of the positive active material of Example 1 and Comparative Examples 1 to 3 was each placed into a cylindrical 4-pin probe mold, and then the mold containing the positive active material was pressurized to 1 ton to measure the powder resistance and calculate the electrical conductivity.

[0213] Electrical conductivity (S / cm) Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 When pressurized to 1 ton 2.71*10 -4 1.43*10 -2 9.51*10 -3 3.94*10 -4 3.55*10 -3

[0214] As can be seen in Table 1, it can be confirmed that the electrical conductivity of Examples 1 and 2 increased by 53 times and 35 times, respectively, compared to Comparative Example 1. On the other hand, in Comparative Examples 2 and 3, which used secondary particles containing conventional primary fine particles rather than secondary particles containing primary large particles according to the present invention, it was confirmed that the electrical conductivity increased by 9 times after carbon material coating (Comparative Example 3) compared to before carbon material coating (Comparative Example 2). From this, it was confirmed that the effect is more pronounced when carbon material is coated on secondary particles containing primary large particles according to one aspect of the present invention. Furthermore, looking at objective figures, it can be confirmed that the electrical conductivity of Example 1 is higher than that of Comparative Example 3, and Example 2, in which the amount of carbon material coating was reduced by half, also has higher electrical conductivity than Comparative Example 3.

[0215] [Experimental Example 2: Measurement of Rolled Density]

[0216] The positive active materials prepared in Examples 1-2 and Comparative Examples 1 to 3 above were rolled under 1 ton conditions, and the rolling density was measured. The results are shown in Table 2 below.

[0217] Rolling density was measured using HPRM-1000. Specifically, 5g of the positive active material of Example 1 and Comparative Examples 1 to 3 was each placed into a cylindrical mold, and then the mold containing the positive active material was pressurized to 1 ton. Afterward, the height of the pressurized mold was measured with a vernier caliper, and the rolling density was calculated.

[0218] Rolled density (g / cc) Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 When pressurized to 1 ton 2.81 3.09 2.95 2.6 2.84

[0219] As can be seen from Table 2, it can be confirmed that the rolling density increases by about 5 to 10% when a carbon material is coated. However, the rolling density value is superior when a carbon material is coated on a secondary particle containing a primary large particle according to one aspect of the present invention compared to when a carbon material is coated on a secondary particle containing a primary fine particle. [Experimental Example 3: Presence ratio of fine particles smaller than 1 μm under 9-ton rolling conditions]

[0220] 5g of each positive electrode active material prepared in Examples 1-2 and Comparative Examples 1 to 3 was placed into a cylindrical metal mold with a diameter of 2cm, and after being rolled under 9 ton conditions by applying pressure using a metal cylinder of the same diameter and recovered, the particle size distribution of each positive electrode active material was measured using PSD (Particle Size Distribution), and the results are shown in Table 3 below.

[0221] Percentage of fine particles smaller than 1 µm (%) Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 Before rolling 0 0 0 0 0 After rolling 1.91 0.18 0.51 9.14 13.63

[0222] As can be seen in Table 3, in the case of Examples 1-2, it was confirmed that fine particle formation was improved by approximately 90.6% and 73.3%. On the other hand, in the case of Comparative Example 3, in which a carbon material was coated on secondary particles containing primary fine particles, it was confirmed that fine particle formation was not improved compared to Comparative Example 2 before the carbon material coating, and was rather 49.1% inferior.

[0223] [Experimental Example 4: Comparison of Remaining Capacity of Batteries After 100 Charge-Discharge Cycles]

[0224] A lithium secondary battery half cell was manufactured using the positive active material prepared in Examples 1-2 and Comparative Examples 1 to 3, and the capacity retention rate and resistance increase rate were measured in the following way.

[0226] Each of the positive active materials, carbon black conductive material, and PVdF binder prepared in the examples and comparative examples were mixed in a weight ratio of 96:2:2 in an N-methylpyrrolidone solvent to prepare a positive composite material, which was then coated on one side of an aluminum current collector, dried at 100°C, and rolled to produce a positive electrode.

[0227] The cathode used lithium metal.

[0228] An electrode assembly was manufactured by interposing a porous polyethylene separator between the anode and cathode manufactured as described above, and after placing the electrode assembly inside a case, an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1.0 M concentration lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / (mixed volume ratio of EC / EMC / DEC = 3 / 4 / 3).

[0230] For the manufactured lithium secondary battery half cell, the life characteristics were evaluated by measuring the capacity retention rate during 100 charge-discharge cycles, in which the cell was charged at 0.7C in CC-CV mode at 45°C until it reached 4.2V, and discharged at a constant current of 0.5C until it reached 3.0V. The results are shown in Table 4 below.

[0231] After 100 cycles Comparative Example 1 Example 1 Example 2 Comparative Example 2 Comparative Example 3 Capacity retention rate (%) 94.0 97.2 96.5 92.9 93.0 Resistance increase rate (%) 158.5 112.4 120.3 114.4 118.6

[0232] As can be seen in Table 4, it can be confirmed that in the case of Examples 1-2, both the capacitance retention rate and the resistance increase rate are superior compared to Comparative Example 1. On the other hand, in the case of Comparative Examples 2 and 3 regarding secondary particles containing primary fine particles, it was confirmed that in the case of Comparative Example 3 coated with carbon material, the capacitance retention rate was at an equivalent level compared to Comparative Example 2 not coated with carbon material, and the resistance increase rate was actually higher.

Claims

Claim 1 A positive electrode active material for a lithium secondary battery comprising only at least one secondary particle including an aggregate of primary macro particles; and a coating layer located on the surface of the secondary particle and including a carbon material, wherein the average particle size (D50) of the primary macro particles is 1.5 to 5 μm, the average particle size (D50) of the secondary particles is 3 to 10 μm, the positive electrode active material comprises a nickel-based lithium transition metal oxide, and the ratio of the average particle size (D50) of the primary macro particles to the average crystal size of the primary macro particles is 2 or more. Claim 2 A positive electrode active material for a lithium secondary battery according to claim 1, characterized in that the content of the carbon material included in the coating layer is 0.3 to 5 parts by weight based on 100 parts by weight of the secondary particle. Claim 3 A positive electrode active material for a lithium secondary battery according to claim 1, characterized in that the thickness of the coating layer is 10 nm to 50 nm. Claim 4 A positive electrode active material for a lithium secondary battery according to claim 1, characterized in that the carbon material comprises one or more selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanoribbons, carbon nanobelts, carbon nanorods, graphene, graphene oxide, reduced graphene oxide, carbon black, activated carbon, and mesoporous carbon. Claim 5 In claim 1, the nickel-based lithium transition metal oxide is Li a [Ni x Co y Mn 1-x-y ]O 2+b (0.9≤a≤1.5, -0.1≤b≤1.0, 0.5≤x≤0.95, 0 <y≤0.5, M은 Mn, Mg, Al, Ti, V, Y, Zr 로 이루어진 군에서 선택된 1종 이상의 원소) 인 것을 특징으로 하는 리튬 이차 전지용 양극 활물질. Claim 6 delete Claim 7 A positive electrode active material for a lithium secondary battery, characterized in that, in claim 1, the average crystal size of the primary large particles is 130 nm or more. Claim 8 A positive electrode active material for a lithium secondary battery, characterized in that, in claim 1, the ratio of the average particle size (D50) of the secondary particle to the average particle size (D50) of the primary large particle is 2 to 5 times. Claim 9 A positive electrode active material for a lithium secondary battery according to claim 1, characterized in that when the positive electrode active material is rolled, the primary large particle detaches from the secondary particle, and the primary large particle itself does not break. Claim 10 A positive electrode active material for a lithium secondary battery, characterized in that, in claim 9, the above rolling is performed under 1 ton conditions. Claim 11 A positive electrode active material for a lithium secondary battery according to claim 1, characterized in that when the positive electrode active material is rolled under 9 ton conditions, the proportion of fine particles smaller than 1 μm is 1% or less. Claim 12 A positive electrode for a lithium secondary battery comprising a positive electrode active material according to claim 1. Claim 13 A lithium secondary battery comprising a positive electrode active material according to claim 1. Claim 14 (S1) a step of preparing a porous nickel-based lithium transition metal hydroxide precursor by mixing a precursor containing nickel, cobalt, and manganese with a hydroxide; (S2) a step of preparing a secondary particle by mixing and heat-treating the porous nickel-based lithium transition metal hydroxide precursor and a lithium raw material; and (S3) a step of forming a coating layer containing the carbon material on the surface of the secondary particle by mixing the secondary particle with a carbon material; wherein the positive active material comprises at least one secondary particle including an aggregate of a primary macro particle; A method for manufacturing a positive electrode active material for a lithium secondary battery, characterized in that it comprises only a coating layer containing a carbon material located on the surface of the secondary particles, wherein the average particle size (D50) of the primary large particles is 1.5 to 5.0 μm, the average particle size (D50) of the secondary particles is 3 to 10 μm, the positive electrode active material comprises a nickel-based lithium transition metal oxide, and the ratio of the average particle size (D50) of the primary large particles to the average crystal size of the primary large particles is 2 or more. Claim 15 A method for manufacturing an anode active material according to claim 14, wherein step (S1) is performed at 35 to 80 ℃ and step (S2) is performed at 700 to 1000 ℃. Claim 16 A method for manufacturing a positive electrode active material according to claim 14, wherein the above (S3) step is performed at room temperature. Claim 17 A method for manufacturing an anode active material according to claim 14, wherein the above (S1) step is performed under pH 8 to 12 conditions. Claim 18 A method for manufacturing an anode active material according to claim 14, characterized in that it does not include a separate washing process between step (S2) and step (S3). Claim 19 A method for manufacturing an anode active material according to claim 14, characterized in that the tap density of the porous nickel-based lithium transition metal hydroxide precursor in step (S2) is 2.0 g / cc or less.

Images