Positive electrode and lithium secondary battery comprising same

Abstract

The present invention provides a positive electrode including a positive electrode composite layer including a single particle-type positive electrode active material in which a volume cumulative particle size distribution satisfies Equation 1 below, wherein the single particle-type positive electrode active material has an average particle diameter of 4 ㎛ to 10 ㎛. [Equation 1] 0.6 ≤ SL / (SR+SL)≤0.8 In Equation 1, SR is an area obtained by integrating the right region of a particle size having the maximum peak in a log-scale volume cumulative particle size distribution graph of the single particle-type positive electrode active material included in the positive electrode, and SL is an area obtained by integrating the left region of the particle size having the maximum peak in the log-scale volume cumulative particle size distribution graph of the single particle-type positive electrode active material included in the positive electrode.

Description

Anode and lithium secondary battery containing the same

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0085822, filed June 28, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a positive electrode and a lithium secondary battery including the same. More specifically, the present invention relates to a positive electrode having improved electrode density and resistance characteristics by controlling the particle distribution of a positive electrode active material within the positive electrode, and to a lithium secondary battery including the same.

[0003] A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode include an active material capable of intercalating and deintercalating lithium ions.

[0004] The electric vehicle market has recently been rapidly growing, and demand is particularly high for electric vehicles with long driving ranges on a single charge. Accordingly, research is actively underway to increase the energy density of secondary batteries by using high-nickel (High-Ni) cathode active materials with superior capacity characteristics. While High-Ni cathode active materials are attracting attention as materials for developing high-energy-density cells due to their high capacity, they also suffer from issues such as reduced thermal stability as the nickel content increases, increased side reactions during electrochemical reactions, deteriorated cycle life, and increased gas generation.

[0005] To address these issues, technologies are being developed to manufacture cathode active materials, previously manufactured in the form of secondary particles, into single particles through undersintering, thereby minimizing the interfaces within the cathode active material particles, thereby minimizing side reactions with the electrolyte, and improving thermal stability. However, single-particle cathode active materials commercialized to date have problems with their independent application, as the lithium ion diffusion path is longer than that of secondary particle cathode active materials, and undersintering causes the formation of a rock-salt structure on the surface, which reduces output performance.

[0006] In addition, in the case of commercialized single particle type positive electrode active materials, the average particle diameter D 50 Because it is small, less than 5㎛, the BET is large, the rolling density and tap density are poor, and there is a problem that clumping occurs in the slurry process, resulting in poor processability.

[0007] Therefore, it has been common to use a mixture of small-diameter single particles and large-diameter secondary particles in the past. However, in the case of mixed cathode materials of small-diameter single particles and large-diameter secondary particles, the occurrence of microcracks in the large-diameter secondary particles becomes more severe as the cycle progresses, limiting the improvement of long-term life characteristics, and the gas generation suppression effect is also insufficient.

[0008] The present invention is intended to solve the above-mentioned problems, and provides a positive electrode having excellent electrode density and resistance characteristics despite including a single-particle positive electrode active material by controlling the particle size of the positive electrode to be within a specific range, and a lithium secondary battery including the same.

[0009] [1] The present invention provides a positive electrode including a positive electrode composite layer including a single-particle type positive electrode active material having a volume cumulative particle size distribution satisfying the following Equation 1, and wherein the average particle diameter of the single-particle type positive electrode active material is 4 µm to 10 µm.

[0010] [Formula 1] 0.6 ≤ S L / (S R +S L )≤0.8

[0011] In the above equation 1, the S R is the integrated area of ​​the right region of the particle size having the maximum peak in the log scale volume cumulative particle size distribution graph of the single particle type positive electrode active material contained in the positive electrode, and S L is the integrated area of ​​the left region of the particle size having the maximum peak in the log scale volume cumulative particle size distribution graph of the single particle type positive electrode active material contained in the above positive electrode.

[0012] [2] In the above [1], the single particle type positive electrode active material may include 1 to 40 nodules.

[0013] [3] In the above [2], the nodule may have an average particle diameter of 1 µm to 10 µm.

[0014] [4] In at least one of the above [1] to [3], the single particle type positive electrode active material has an average particle diameter D 50 This can be 4㎛ to 8㎛.

[0015] [5] In at least one of the above [1] to [4], the single-particle positive electrode active material in the positive electrode may have a unimodal particle size distribution.

[0016] [6] In at least one of the above [1] to [5], the single-particle type positive electrode active material may include a lithium nickel-based oxide having a nickel content of 60 mol% or more among the total metals excluding lithium.

[0017] [7] In at least one of the above [1] to [6], the single particle type positive electrode active material may include a lithium nickel-based oxide represented by the following [chemical formula 1].

[0018] [Chemical Formula 1] Li 1+x [Nia Co b M 1 c M 2 d ]O2

[0019] In the above [chemical formula 1], M 1 is at least one selected from Mn and Al, and M 2 It contains at least one selected from the group consisting of Zr, Y, B, V, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and -0.2≤x≤0.2, 0.60≤a<1, 0 <b<0.40, 0<c<0.40, 0≤d≤0.2임.

[0020] [8] In at least one of the above [1] to [7], the single particle type positive electrode active material may further include a coating layer including one or more elements selected from the group consisting of Co, Al, W, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, P, B and Mo on the surface of the lithium nickel compound.

[0021] [9] In at least one of the above [1] to [8], the positive electrode has an electrode density of 3.55 g / cm 3 Ideally, 3.55 g / cm 3 3.80g / cm 3 , more preferably 3.60 g / cm 3 3.75g / cm 3 It could be.

[0022]

[0010] The present invention, the average particle diameter D 50 A method for manufacturing a positive electrode according to [1] is provided, comprising: a step of manufacturing a positive electrode slurry including a single particle type positive electrode active material having a diameter of 6 µm to 12 µm and a degree of single crystallinity of 0.3 to 0.5; a step of applying the positive electrode slurry onto a positive electrode current collector to form a positive electrode composite layer; and a step of rolling and drying the positive electrode composite layer.

[0023]

[0011] In the above

[0010] , the single particle type positive electrode active material may have a unimodal particle size distribution.

[0024]

[0012] In the above

[0010] or

[0011] , the rolling may be performed at a linear pressure of 2 ton / cm to 8 ton / cm.

[0025]

[0013] The present invention provides a lithium secondary battery comprising a positive electrode; a negative electrode; and an electrolyte of any one of the above [1] to [9].

[0026] The positive electrode according to the present invention comprises a single-particle positive electrode active material having a particle size distribution with a specific range of negative skewness, thereby exhibiting high electrode density and low resistance characteristics while also producing minimal gas during charge and discharge. Therefore, when the positive electrode according to the present invention is applied, a lithium secondary battery with excellent output and lifespan characteristics can be realized.

[0027] In addition, the positive electrode according to the present invention uses a single-particle positive electrode active material having a relatively large average particle diameter compared to conventional positive electrodes during the manufacture of the positive electrode, thereby optimizing particle breakage during electrode rolling, thereby enabling implementation of a desired particle size distribution, and even though a unimodal positive electrode active material is used, it enables implementation of an electrode density equivalent to that of a case where a bimodal positive electrode active material is used.

[0028] Figure 1 is a drawing for explaining Equation 1 according to the present invention.

[0029] Figure 2 is a drawing showing the particle size distribution of the positive electrode active material in the positive electrode composite layer of the examples and comparative examples of the present invention.

[0030] Terms or words used in this specification and the scope of the claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0031] In the present invention, "single particle type" means a particle composed of 40 or fewer nodules, and is a concept including single particles composed of one nodule and pseudo-single particles which are composites of 2 to 50 nodules. The "nodule" is a lower particle unit constituting a single particle and pseudo-single particle, and may be a single crystal without a crystalline grain boundary, or a polycrystal in which no grain boundary exists in appearance when observed under a field of view of 5,000 to 20,000 times using a scanning electron microscope.

[0032] In the present invention, "secondary particle" refers to a particle formed by agglomeration of a plurality of primary particles, for example, tens to hundreds of primary particles. Specifically, the secondary particle may be an aggregate of more than 40 primary particles.

[0033] In the present invention, “particle” is a concept including any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0034] In the present invention, the average particle diameter (D) of the nodules or primary particles mean ) means the arithmetic mean value calculated after measuring the particle size of nodules or primary particles observed in scanning electron microscope images.

[0035] In the present invention, the particle size distribution and average particle diameter (D) of the single-particle type positive electrode active material in the positive electrode composite layer 50 ) was measured using the following method.

[0036] First, the positive electrode composite layer was scraped from the positive electrode current collector to obtain positive electrode composite powder. Then, the obtained positive electrode composite powder was heat-treated at 600°C for 10 hours to remove the binder and conductive agent, and positive electrode active material powder was obtained. Then, the particle size distribution and average particle diameter (D) of the positive electrode active material powder were measured using a laser diffraction device. 50 ) was measured. Specifically, it was introduced into a laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasonic waves of about 28 kHz with an output of 60 W, and then a volume cumulative particle size distribution graph was obtained to obtain the particle size distribution and D 50 was measured. Here, “average particle diameter D50” means the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder.

[0037] In the present invention, “single crystallinity” refers to the average particle diameter (D) of the positive electrode active material powder. 50 ) for the average particle diameter (D) of nodules or primary particles mean ) of the ratio (D) mean / D 50 ) means.

[0038]

[0039] Hereinafter, the present invention will be described in more detail.

[0040]

[0041] anode

[0042] First, the anode according to the present invention will be described.

[0043] The positive electrode according to the present invention includes a positive electrode composite layer including a single-particle positive electrode active material having a particle size distribution satisfying the following equation (1).

[0044] Equation (1): 0.6 ≤ S L / (S R +S L )≤0.8

[0045] In the above equation 1, the S Ris the integrated area of ​​the right region of the particle size having the maximum peak in the volume cumulative particle size distribution graph of the single particle type positive electrode active material contained in the positive electrode, and the S L is the integrated area of ​​the left region of the particle size having the maximum peak in the volume cumulative particle size distribution graph of the single-particle type positive electrode active material contained in the above positive electrode.

[0046] To explain equation (1), an example of a cumulative particle size distribution graph of positive electrode active material particles is shown in Fig. 1. The area of ​​the region indicated by ① in Fig. 1 is S L , and the area of ​​the region marked ② is S R am.

[0047] When the particle size distribution of the single-particle type positive electrode active material in the positive electrode according to the present invention satisfies the range of the above formula (1), the electrode density, resistance, and life characteristics are excellent. Specifically, when the particle size distribution of the single-particle type positive electrode active material is less than 0.6, particle breakage hardly occurs during the electrode rolling process, and the effect of improving the electrode density and resistance of the positive electrode is minimal. On the other hand, when it exceeds 0.8, excessive particle breakage occurs, and there is a problem that side reactions with the electrolyte increase, gas generation increases, and life performance deteriorates.

[0048]

[0049] Meanwhile, the average particle diameter D of the single-particle positive electrode active material used in the manufacture of the positive electrode composite layer 50 By appropriately controlling the degree of crystallinity, particle size distribution, rolling conditions, etc., a positive electrode composite layer including a single particle type positive electrode active material satisfying the above formula (1) can be formed. For example, the present invention can form a positive electrode composite layer having an average particle diameter D when manufacturing the positive electrode composite layer. 50A single particle type positive electrode active material having a particle size of 6 ㎛ to 12 ㎛, preferably 6 ㎛ to 10 ㎛, more preferably 6 ㎛ to 8 ㎛, and a single crystallinity of 0.3 to 0.5, preferably 0.3 to 0.45, more preferably 0.3 to 0.4 can be used. At this time, the single crystallinity is the average particle diameter (D) of the positive electrode active material powder. 50 ) for the average particle diameter (D) of nodules or primary particles mean ) of the ratio (D) mean / D 50 ) means. When the average particle diameter and single crystallinity of the single-particle type positive electrode active material used in the manufacture of the positive electrode composite layer satisfy the above range, particle breakage occurs appropriately during rolling, making it easy to ensure that the particle size distribution of the single-particle type positive electrode active material satisfies Equation (1) after the manufacture of the positive electrode.

[0050] In addition, the above rolling can be performed at a line pressure of 2 ton / cm to 8 ton / cm, preferably 3 ton / cm to 5 ton / cm. When the line pressure satisfies the above range during rolling, particle breakage occurs appropriately during rolling, making it easy to ensure that the particle size distribution of the single-particle type positive electrode active material satisfies Equation (1) after the positive electrode is manufactured.

[0051]

[0052] Meanwhile, the single-particle type positive electrode active material may include 1 to 40 nodules, preferably 1 to 30 nodules, more preferably 1 to 25 nodules, and even more preferably 1 to 15 nodules. The single-particle type positive electrode active material has a small number of nodules constituting the particle, and thus the intra-particle interface is small, and thus the contact area with the electrolyte is small. Therefore, compared to the secondary particle type positive electrode active material in which 40 to several hundred primary particles are aggregated, which was generally used in the past, the side reaction with the electrolyte is small, and accordingly, the amount of gas generated is also significantly less. Therefore, when the single-particle type positive electrode active material is applied, excellent life characteristics can be obtained.

[0053] Meanwhile, the average particle diameter of the nodule may be 1 µm to 10 µm, preferably 1 µm to 8 µm, and more preferably 1 µm to 5 µm. When the average particle diameter of the nodule satisfies the above range, an increase in resistance can be more effectively suppressed.

[0054]

[0055] Meanwhile, in the present invention, the single particle type positive electrode active material has an average particle diameter D 50 This is 4㎛ to 10㎛, preferably 4㎛ to 8㎛, more preferably 4㎛ to 6㎛. At this time, the average particle diameter D of the single particle type positive electrode active material 50 is the average particle size of the single-particle type positive electrode active material after the positive electrode is manufactured, that is, after rolling. Since the particles of the single-particle type positive electrode active material are broken by rolling during the positive electrode manufacturing process, the average particle size of the single-particle type positive electrode active material measured after the positive electrode is manufactured is smaller than the average particle size of the single-particle type positive electrode active material introduced into the positive electrode slurry before rolling. When the average particle size of the single-particle type positive electrode active material in the positive electrode satisfies the above range, the rolling density is excellent, and thus excellent effects in terms of high-temperature life, gas generation suppression, and resistance can be obtained. Specifically, when the average particle size of the single-particle type positive electrode active material is less than 4㎛, the gas generation suppression effect is minimal, and when it exceeds 10㎛, there is a problem that the resistance of the positive electrode active material increases, resulting in a deterioration in output characteristics.

[0056] Meanwhile, the single-particle type positive electrode active material may have a unimodal particle size distribution. This is because, when the condition of the above formula (1) is satisfied, even when the material has a unimodal particle size distribution, excellent electrode density can be achieved.

[0057]

[0058] The above single particle type positive electrode active material may include a lithium nickel-based oxide having a nickel content of 60 mol% or more among all metals excluding lithium, and may include, for example, a lithium nickel-based oxide represented by the following [chemical formula 1].

[0059] [Chemical Formula 1] Li 1+x [Ni a Co b M 1 c M 2 d ]O2

[0060] In the above [chemical formula 1], M 1 is Mn, Al or a combination thereof, and preferably may be Mn or a combination of Mn and Al.

[0061] Above M 2 It may include at least one selected from the group consisting of Zr, Y, B, V, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S. M 2 When elements are included, the structural stability of lithium nickel oxide particles is improved, enabling better performance of life characteristics.

[0062] The above 1+x represents the lithium molar ratio in the lithium nickel-based oxide, and may be -0.2≤x≤0.2, -0.1≤x≤0.1, or 0≤x≤0.1. When x satisfies the above range, a stable layered crystal structure can be formed.

[0063] The above a represents the molar ratio of nickel among all metals excluding lithium in the lithium nickel-based oxide, and may be 0.60≤a<1.0, 0.60≤a≤0.99, or 0.80≤a≤0.97. When a satisfies the above range, high capacity can be achieved.

[0064] The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel oxide, and is 0. <b<0.40, 0.01≤b≤0.35 또는 0.01≤b≤0.20일 수 있다.

[0065] The above c represents the molar ratio of the M1 element among all metals excluding lithium in the lithium nickel oxide, and is 0. <c<0.40, 0.01≤c≤0.35 또는 0.01≤c≤0.20일 수 있다.

[0066] The above d is M of all metals except lithium in lithium nickel oxide. 2 It represents the molar ratio of elements, and can be 0≤d≤0.20, or 0≤d≤0.10. M 2 When the molar ratio of the elements satisfies the above range, the structural stability, capacity characteristics, and resistance characteristics of the positive electrode active material can be excellent.

[0067]

[0068] Meanwhile, the single-particle type positive electrode active material may further include a coating layer on the surface of the lithium nickel-based oxide. The coating layer may include one or more elements selected from the group consisting of Co, Al, W, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, P, B, and Mo. When the coating layer is formed on the surface of the lithium nickel-based oxide, effects such as improvement of surface resistance characteristics, prevention of agglomeration during preparation of positive electrode slurry, and reduction of gas generation through reduction of contact area with the electrolyte may be obtained. Preferably, the coating layer may include Co, Al, Nb, Ti, B, or a combination thereof.

[0069]

[0070] The single-particle type positive electrode active material can be manufactured by purchasing and using a commercially available material or by calcining a mixture of a transition metal precursor and a lithium raw material. Specifically, a single-particle type positive electrode active material can be manufactured by mixing and calcining a transition metal precursor and a lithium raw material to manufacture a single-particle type lithium nickel-based oxide, and, if necessary, performing a step of coating the single-particle type lithium nickel-based oxide.

[0071] At this time, the transition metal precursors include nickel and cobalt, and optionally M 1 and M 2A hydroxide containing the element can be used. The transition metal precursor can be purchased and used as a commercially available precursor, or can be manufactured using a precursor manufacturing method known in the art, such as a coprecipitation method.

[0072] As the above lithium raw material, lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide may be used, and for example, Li2CO3, LiNO3, LiNO2, LiOH, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or a mixture thereof may be used.

[0073] Meanwhile, the lithium raw material and the positive electrode active material precursor may be mixed so that the molar ratio of Li: total metal in the precursor is 1:1 to 1.1:1, preferably 1:1 to 1.05:1, more preferably 1.01:1 to 1.03:1. When the mixing ratio of the lithium raw material and the metal in the positive electrode active material precursor satisfies the above range, the layered crystal structure of the positive electrode active material is well developed, so that a positive electrode active material with excellent capacity characteristics and structural stability can be manufactured.

[0074] Meanwhile, the sintering is performed at a temperature capable of forming a single-particle lithium nickel-based oxide. In order to form a single-particle lithium nickel-based oxide, the sintering should be performed at a higher temperature than that used in the conventional secondary particle lithium nickel-based oxide production. For example, when the precursor composition is the same, the sintering should be performed at a temperature that is about 30°C to 100°C higher than that used in the conventional secondary particle lithium nickel-based oxide production. The sintering temperature for producing a single-particle lithium nickel-based oxide may vary depending on the metal composition in the precursor. For example, when a high-nickel (High-Ni) single-particle lithium nickel-based oxide having a nickel (Ni) content of 80 mol% or more is to be produced, the sintering temperature may be about 700°C to 1000°C, preferably about 750°C to 950°C, and more preferably about 800°C to 950°C. When the sintering temperature satisfies the above range, a single-particle lithium nickel-based oxide having excellent electrochemical properties can be produced. When the sintering temperature is less than 700℃, a cathode active material in the form of secondary particles is produced, and when it exceeds 1000℃, excessive sintering occurs and a layered crystal structure is not properly formed, resulting in a deterioration in electrochemical properties.

[0075] In addition, the above-mentioned calcination can be performed for 6 to 35 hours, preferably 6 to 20 hours, and more preferably 6 to 15 hours under an oxygen atmosphere. When the calcination time satisfies the above range, a single-particle lithium nickel-based oxide can be formed. If the primary calcination time is too short, particle growth is insufficient, and a secondary particle lithium nickel-based oxide is formed, and if it is too long, a rock salt phase may occur, which may deteriorate the electrochemical characteristics of the active material. In the present specification, an oxygen atmosphere means an atmosphere containing oxygen sufficient for calcination, including an air atmosphere. In particular, it is preferable to perform the calcination in an atmosphere having a higher oxygen partial pressure than an air atmosphere.

[0076] Meanwhile, M may be added as needed during the above firing. 1 Containing raw materials and / or M 2 The raw materials contained can be mixed and fired together, the above M 1 Contains raw materials and M 2 Contains raw materials M 1 Metal or M 2 It may be an acetate, carbonate, nitrate, sulfate, halide, sulfide or oxide of the metal.

[0077] Meanwhile, if necessary, the single particle lithium nickel oxide manufactured as described above and the coating raw material are mixed and heat-treated to form a coating layer.

[0078] The above coating raw material may be, for example, an oxide, hydroxide, acetate, carbonate, nitrate, sulfate, halide, or sulfide containing one or more elements selected from the group consisting of Co, Al, W, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, P, B, and Mo.

[0079] Meanwhile, the heat treatment temperature can be appropriately controlled depending on the coating raw material, and preferably, it can be 200°C to 800°C, or 300°C to 700°C.

[0080]

[0081] The above-described positive electrode composite layer may contain the positive electrode active material in an amount of 93 wt% to 99 wt%, preferably 95 wt% to 98 wt%, and more preferably 95 wt% to 97 wt%, based on the total weight of the positive electrode composite layer. When the content of the positive electrode active material satisfies the above range, a high energy density can be realized. Preferably, the positive electrode active material may be formed of a single-particle type positive electrode active material, but is not limited thereto.

[0082]

[0083] Meanwhile, the positive electrode composite layer may further include a conductive material and a binder in addition to the positive electrode active material described above.

[0084] The above-mentioned positive electrode conductive material is used to provide conductivity to the positive electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, carbon fiber, and carbon nanotube; 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; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0085] The above-mentioned positive electrode conductive material may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 8 wt%, and more preferably 1 to 5 wt%, based on the total weight of the positive electrode composite layer.

[0086] Next, the positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used.

[0087] The above positive electrode binder may be included in an amount of 0.5 wt% to 5 wt%, preferably 1 wt% to 4 wt%, and more preferably 1 wt% to 3 wt% based on the total weight of the positive electrode composite layer.

[0088]

[0089] The positive electrode of the present invention can be manufactured, for example, through a step of manufacturing a positive electrode slurry containing a positive electrode active material, a step of applying the positive electrode slurry onto a positive electrode current collector to form a positive electrode composite layer, and a step of rolling and drying the positive electrode composite layer.

[0090] More specifically, the positive electrode of the present invention can be manufactured by a method of preparing a positive electrode slurry by mixing a positive electrode active material, a positive electrode binder, and / or a positive electrode conductive material in a solvent, applying the prepared positive electrode slurry onto a positive electrode current collector to form a positive electrode composite layer, and then rolling and forming the mixture.

[0091] At this time, the positive electrode active material included in the positive electrode slurry has, for example, an average particle diameter D 50 It may be a single particle type positive electrode active material having an average particle size of 6 ㎛ to 12 ㎛, preferably 6 ㎛ to 10 ㎛, more preferably 6 ㎛ to 8 ㎛, and a single crystallinity of 0.3 to 0.5, preferably 0.3 to 0.45, more preferably 0.3 to 0.4. The average particle size D as described above 50 When manufacturing a positive electrode using a single particle type positive electrode active material that satisfies single crystallinity, the particle size distribution of the positive electrode active material in the positive electrode composite layer after rolling can satisfy equation (1).

[0092]

[0093] Meanwhile, solvents commonly used in the art may be used as the solvent for the positive electrode slurry, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water, which may be used alone or in combination of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0094] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change 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 positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0095]

[0096] Meanwhile, the rolling may be performed at a linear pressure of, for example, 2 ton / cm to 8 ton / cm, preferably 3 ton / cm to 5 ton / cm, but is not limited thereto. If the linear pressure is too high during rolling, excessive particle breakage may occur, which may increase side reactions with the electrolyte, thereby increasing gas generation and deteriorating life characteristics. If the linear pressure is too low, particle breakage may be too little, making it difficult for the particle size distribution of the single-particle type positive electrode active material to satisfy Equation (1) after positive electrode manufacturing, and the electrode density may decrease, resulting in a decrease in energy density.

[0097]

[0098] The positive electrode according to the present invention has an electrode density of 3.55 g / cm 3 Ideally, 3.55 g / cm 3 3.80g / cm 3 , more preferably 3.60 g / cm 3 3.75g / cm 3 It can be done. If the electrode density satisfies the above range, high energy density can be achieved.

[0099]

[0100] lithium secondary battery

[0101] Next, a lithium secondary battery according to the present invention will be described.

[0102] The lithium secondary battery of the present invention comprises the positive electrode according to the present invention. Specifically, the lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite 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.

[0103]

[0104] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0105] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode composite layer positioned on the negative electrode current collector.

[0106] The negative electrode 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., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0107]

[0108] The above negative electrode composite layer optionally includes a negative electrode binder and a negative electrode conductive material together with a negative electrode active material.

[0109] As the 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 alloy, Sn alloy, or Al alloy; SiO β (0 <β< 2), metal oxides capable of doping and dedoping lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used.

[0110] In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch derived cokes.

[0111] The above-described negative electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. 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, carbon fiber, and carbon nanotube; 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 the like. One of these may be used alone or a mixture of two or more may be used. The negative electrode conductive material may typically be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode composite layer.

[0112] The above negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above negative electrode binder may be included in an amount of 1 to 30 wt%, preferably 1 to 20 wt%, and more preferably 1 to 10 wt%, based on the total weight of the negative electrode composite layer.

[0113] The above-described negative electrode composite layer may be manufactured by, for example, applying a negative electrode slurry containing a negative electrode active material, and optionally a negative electrode binder and a negative electrode conductive material, and drying the same on a negative electrode current collector, or by casting the negative electrode slurry on a separate support and then laminating the resulting film on a negative electrode current collector by peeling the film off from the support.

[0114] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0115] In addition, examples of the electrolyte used in the present invention include, but are not limited to, 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 manufacture of lithium secondary batteries.

[0116] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0117] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0118] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, 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 within the range of 0.1 to 5.0 M, and preferably 0.1 to 3.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0119] In addition to the electrolyte components, the electrolyte may further include additives for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. For example, the additives may include haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, either singly or in mixtures, but are not limited thereto. The additives may be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte.

[0120] As described above, a lithium secondary battery including a positive electrode according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0121] According to another embodiment of the present invention, a battery module or battery pack including the lithium secondary battery as a unit cell is provided.

[0122]

[0123] The above battery module or battery pack can 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.

[0124]

[0125] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0126]

[0127] Example 1

[0128] The average particle size is 6.5 ㎛, the degree of single crystallinity is 0.33, and S is measured by a log scale volume cumulative particle size distribution graph. L / (S R +S L ) single particle type positive electrode active material powder (LiNi) with a value of 0.5 0.8 Co 0.1 Mn 0.1O2) was prepared. The positive electrode active material powder, conductive agent (Super P), and PVdF binder were mixed in a weight ratio of 96:2:2 in N-methylpyrrolidone to prepare a positive electrode slurry. The positive electrode slurry was applied onto an aluminum current collector, dried, and then rolled at a linear pressure of 3.5 ton / cm to form a positive electrode composite layer, thereby preparing a positive electrode.

[0129]

[0130] Example 2

[0131] The positive electrode active material powder has an average particle size of 7.2 ㎛, a single crystallinity of 0.36, and S measured by a log scale volume cumulative particle size distribution graph. L / (S R +S L ) single particle type positive electrode active material powder (LiNi) with a value of 0.5 0.8 Co 0.1 Mn 0.1 The anode was manufactured in the same manner as in Example 1, except that O2 was used.

[0132]

[0133] Comparative Example 1

[0134] The positive electrode active material powder has an average particle size of 4.0 ㎛, a single crystallinity of 0.50, and S measured by a log scale volume cumulative particle size distribution graph. L / (S R +S L ) single particle type positive electrode active material powder (LiNi) with a value of 0.5 0.8 Co 0.1 Mn 0.1 The anode was manufactured in the same manner as in Example 1, except that O2 was used.

[0135]

[0136] Comparative Example 2

[0137] The positive electrode active material powder has an average particle size of 7.0 ㎛, a single crystallinity of 0.61, and S measured by a log scale volume cumulative particle size distribution graph. L / (S R +S L) single particle type positive electrode active material powder (LiNi) with a value of 0.50 0.8 Co 0.1 Mn 0.1 The anode was manufactured in the same manner as in Example 1, except that O2 was used.

[0138]

[0139] Comparative Example 3

[0140] The positive electrode active material powder has an average particle size of 9 ㎛, a single crystallinity of 0.04, and S measured by a log scale volume cumulative particle size distribution graph. L / (S R +S L ) secondary particle type positive electrode active material powder (LiNi) with a value of 0.5 0.8 Co 0.1 Mn 0.1 The anode was manufactured in the same manner as in Example 1, except that O2 was used.

[0141]

[0142] Comparative Example 4

[0143] The average particle size of the positive electrode active material powder is 4㎛, the degree of single crystallinity is 0.38, and S measured by a log scale volume cumulative particle size distribution graph L / (S R +S L ) single particle type positive electrode active material powder (LiNi) with a value of 0.5 0.8 Co 0.1 Mn 0.1 The anode was manufactured in the same manner as in Example 1, except that O2 was used.

[0144]

[0145] Experimental Example 1

[0146] The volume cumulative particle size distribution and rolling density of the positive electrode active materials manufactured by Examples 1 to 2 and Comparative Examples 1 to 4 were measured by the following method. Using the measured cumulative particle size distribution graph (log scale), S L / (S R +S L ) values ​​were calculated.

[0147] The measurement results are shown in Table 1 and Fig. 2 below.

[0148]

[0149] (1) Method for measuring particle size distribution

[0150] The positive electrode composite layer was scraped off on the positive electrode current collector of the positive electrode manufactured by the examples and comparative examples to obtain positive electrode composite powder. Then, the obtained positive electrode composite powder was heat-treated at 600°C for 10 hours to remove the binder and the conductive agent, and positive electrode active material powder was obtained. Then, the positive electrode active material powder was introduced into a laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W to obtain a logarithmic scale volume cumulative particle size distribution graph. Then, using the measured cumulative particle size distribution graph (log scale), the D of the positive electrode active material 50 and S L / (S R +S L ) values ​​were measured.

[0151]

[0152] (2) Electrode density (g / cm) 3 )

[0153] The anode manufactured in the examples and comparative examples was punched into a 14-pie circle, and the weight of the punched anode, W t and thickness T t Then, the weight Wc and thickness T of the positive electrode collector were measured from the above-mentioned positive electrode. c After measuring, W t at Calculate the weight of the anode composite layer W by subtracting Wc, and T t In T c The thickness T of the bipolar composite layer was calculated by subtracting . Then, the electrode density was calculated using the above weight W and thickness T.

[0154]

[0155] S of the cathode active material after single crystallinity cathode manufacturingL / (S R +S L ) After manufacturing the positive electrode, the positive electrode active material D 50 (㎛) Electrode density (g / cm) 3 ) Example 10.330.664.8053.60 Example 20.360.704.8353.69 Comparative Example 10.500.562.93.40 Comparative Example 20.610.584.183.51 Comparative Example 30.040.816.163.45 Comparative Example 40.380.613.853.43

[0156] Experimental Example 2

[0157] An electrode assembly was manufactured by interposing a polyethylene separator between each of the positive electrodes and the lithium metal electrode manufactured in Examples 1 to 2 and Comparative Examples 1 to 4, and then the electrode assembly was placed in a battery case and an electrolyte was injected to manufacture a half cell. At this time, the electrolyte was manufactured by dissolving 1 M LiPF6 in a mixed organic solvent containing ethylene carbonate: dimethyl carbonate: diethyl carbonate in a volume ratio of 3:4:3.

[0158]

[0159] The initial resistance and gas generation of the lithium secondary battery described above were measured using the following methods. The measurement results are shown in [Table 2] below.

[0160] (1) Initial resistance (Ω): After performing the activation process (formation) for each half-cell manufactured as described above, the PNE-0506 charger / discharger (manufacturer: PNE Solution Co., Ltd.) was used to charge the cell at 0.33C at 25℃ to 4.3V under constant current-constant voltage conditions, discharge it at 0.33C to 50% SOC, and then measure the voltage drop that appears when a discharge pulse is applied for 10 seconds at a constant current of 1.0C to obtain the initial resistance value.

[0161] (2) Gas generation amount (μl): Two half-cells manufactured as described above were each charged to 4.3 V at 0.1 C in constant current-constant voltage mode (charge cutoff condition: 1 / 20 C). Then, the charged cells were disassembled to obtain two anodes and two separators, and the anodes and separators were alternately laminated on the lower plate of the coin cell, and the electrolyte was injected, and the coin cell was reassembled. After storage at 70°C for 4 weeks, the amount of gas generated was measured using GC-MS (Gas Chromatograph-Mass Spectrometer).

[0162] Initial resistance (Ω) Gas generation amount (μl) Example 11.4852 Example 21.5148 Comparative example 11.4879 Comparative example 21.7249 Comparative example 31.45126 Comparative example 41.4391

[0163] As shown in Table 2 above, the batteries using the positive electrodes of Examples 1 and 2 showed excellent initial resistance and gas evolution characteristics. In comparison, the S of the positive electrode active material after manufacturing the positive electrode L / (S R +S L ) In the case of Comparative Examples 1 to 3, where the values ​​are outside the scope of the present invention, it can be confirmed that one of the initial resistance and gas generation characteristics is inferior. In addition, after manufacturing the positive electrode, the S of the positive electrode active material L / (S R +S L ) Even if the value satisfies the range of the present invention, in the case of Comparative Example 4 where the average particle diameter of the positive electrode active material is outside the range of the present invention, it can be confirmed that the resistance characteristics are excellent but the gas generation characteristics are inferior.

Claims

1. A positive electrode composite layer including a single-particle type positive electrode active material having a volume cumulative particle size distribution satisfying the following equation 1, A positive electrode having an average particle diameter of the above single-particle positive electrode active material of 4 ㎛ to 10 ㎛. [Formula 1] 0.6 ≤ S L / (S R +S L )≤0.8 In the above equation 1, the S R is the integrated area of ​​the right region of the particle size having the maximum peak in the log-scale volume cumulative particle size distribution graph of the single-particle type positive electrode active material contained in the positive electrode, and S L is the integrated area of ​​the left region of the particle size having the maximum peak in the log-scale volume cumulative particle size distribution graph of the single-particle type positive electrode active material contained in the above positive electrode.

2. In paragraph 1, A cathode in which the single particle type cathode active material comprises 1 to 40 nodules.

3. In paragraph 2, The above nodule is an anode having an average particle diameter of 1 ㎛ to 10 ㎛.

4. In paragraph 1, The above single particle type positive electrode active material is a positive electrode having an average particle diameter of 4㎛ to 8㎛.

5. In paragraph 1, A positive electrode having the above single particle type positive electrode active material having a unimodal particle size distribution.

6. In paragraph 1, The above single particle type positive electrode active material is a positive electrode including a lithium nickel oxide having a nickel content of 60 mol% or more among all metals excluding lithium.

7. In paragraph 1, The above single particle type positive electrode active material is a positive electrode including a lithium nickel-based oxide represented by the following [chemical formula 1]. [Chemical Formula 1] Li 1+x [Ni a Co b M 1 c M 2 d ]O2 In the above [chemical formula 1], M 1 is at least one selected from Mn and Al, and M 2 It contains at least one selected from the group consisting of Zr, Y, B, V, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P and S, and -0.2≤x≤0.2, 0.60≤a<1, 0 <b<0.40, 0<c<0.40, 0≤d≤0.2임.

8. In paragraph 7, A cathode in which the single particle type cathode active material further includes a coating layer comprising at least one element selected from the group consisting of Co, Al, W, Ti, Mg, Zr, Y, Ba, Ca, Sr, Ta, Nb, P, B and Mo on the surface of the lithium nickel compound.

9. In paragraph 1, The above anode has an electrode density of 3.55 g / cm 3 Ideal bipolar.

10. A method for manufacturing an anode according to claim 1, Average particle diameter D 50 A step of preparing a cathode slurry comprising a single particle type cathode active material having a diameter of 6 ㎛ to 12 ㎛ and a degree of single crystallinity of 0.3 to 0.5; A step of forming a positive electrode composite layer by applying the positive electrode slurry onto a positive electrode current collector; and A method for manufacturing an anode, comprising the steps of rolling and drying the anode composite layer.

11. In paragraph 10, A method for manufacturing a positive electrode, wherein the single-particle positive electrode active material has a unimodal particle size distribution.

12. In paragraph 10, A method for manufacturing an anode, wherein the above rolling is performed at a pressure of 2 ton / cm to 8 ton / cm.

13. The positive electrode of any one of claims 1 to 9; cathode; and A lithium secondary battery containing an electrolyte.

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