Positive electrode slurry for lithium secondary battery and method for manufacturing positive electrode for lithium secondary battery using the same

Abstract

The present invention relates to a positive electrode slurry for a lithium secondary battery, which includes a positive electrode active material including a lithium nickel-based oxide having a composition in which the nickel content of all metals other than lithium is 50 mol % or more and which is in the form of at least one of single particles or pseudo-single particles, which are secondary particles formed by agglomeration of 30 or less primary particles; a lithium borate-based compound; a binder; a conductive material; and a solvent; a positive electrode for a lithium secondary battery, which includes a positive electrode active material layer formed by coating at least one surface of a positive electrode current collector with the positive electrode slurry; a method for manufacturing the positive electrode; and a lithium secondary battery including the positive electrode.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0009079, filed January 20, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a positive electrode slurry for a lithium secondary battery, which uses a positive electrode active material in a single particle or pseudo-single particle form that has not undergone a water washing process or a boron coating process during synthesis, and which can help improve performance in high-temperature and high-voltage operating environments; a method for manufacturing a positive electrode for a lithium secondary battery using the same; a positive electrode for a lithium secondary battery manufactured by the same; and a lithium secondary battery including the positive electrode. [Background technology]

[0003] A lithium secondary battery generally comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode contain active materials capable of intercalating and deintercalating lithium ions.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the high cost and unstable supply of cobalt, the raw material, make its commercial application in large-capacity batteries difficult. Lithium nickel oxide has poor structural stability and is difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide has excellent stability but poor capacity characteristics. Therefore, to address the issues of lithium transition metal oxides containing only Ni, Co, or Mn, lithium composite transition metal oxides containing two or more transition metals have been developed. Among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0005] Conventional lithium nickel cobalt manganese oxides are generally in the form of spherical secondary particles formed by agglomeration of tens to hundreds of primary particles. However, lithium nickel cobalt manganese oxides in the form of secondary particles formed by agglomeration of many primary particles are prone to particle cracking, where primary particles break off during the rolling process during positive electrode manufacturing, and internal cracks occur during charge and discharge. When particles of the positive electrode active material break or crack, the contact area with the electrolyte increases, which increases gas generation and degradation of the active material due to side reactions with the electrolyte, resulting in reduced lifespan.

[0006] In addition, with the recent growing demand for high-power, high-capacity batteries, such as those for electric vehicles, the nickel content in the positive electrode active material has been gradually increasing. Although increasing the nickel content in the positive electrode active material improves the initial capacity characteristics, repeated charge and discharge can cause the structure of the positive electrode active material to collapse, which increases the rate of deterioration of the positive electrode active material, resulting in poor life characteristics and reduced battery safety.

[0007] To address these issues, a technique has been proposed for producing a single-particle cathode active material rather than a secondary particle by increasing the calcination temperature during the production of lithium nickel cobalt manganese oxide. Single-particle cathode active materials have a smaller contact area with the electrolyte than conventional secondary-particle cathode active materials, resulting in fewer side reactions with the electrolyte, superior particle strength, and less particle cracking during electrode fabrication. Therefore, the use of single-particle cathode active materials offers the advantages of superior gas generation and lifespan characteristics.

[0008] However, conventional single-particle cathode active materials have poor lithium mobility due to the limited number of interfaces between primary particles that serve as paths for lithium ions to travel within the particles, and are produced at relatively high sintering temperatures, resulting in the presence of excessive amounts of lithium by-products on the surface. When excessive amounts of lithium by-products are present on the surface of the cathode active material, the amount of gas generated increases due to side reactions between the lithium by-products and the electrolyte during high-temperature storage. While the amount of gas generated can be reduced by removing the lithium by-products through water washing, the surface structure of the cathode active material is damaged during water washing, resulting in increased resistance. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to provide a positive electrode slurry that can help improve cycle characteristics under high temperature and high voltage driving conditions, a positive electrode using the same, a method for manufacturing the positive electrode, and a lithium secondary battery including the positive electrode. [Means for solving the problem]

[0010] According to one embodiment, the present invention provides a positive electrode slurry for a lithium secondary battery, the positive electrode active material including a lithium nickel-based oxide having a composition in which nickel is present in an amount of 50 mol % or more among all metals other than lithium, and in the form of at least one of single particles or quasi-single particles, which are secondary particles formed by agglomeration of 30 or less primary particles; a lithium borate-based compound; a binder; a conductive material; and a solvent.

[0011] According to another embodiment, the present invention provides a positive electrode for a lithium secondary battery, comprising a positive electrode active material layer formed by coating at least one surface of a positive electrode current collector with the positive electrode slurry.

[0012] According to another embodiment, the present invention provides a positive electrode for a lithium secondary battery, comprising a positive electrode active material including a lithium nickel-based oxide having a composition in which the nickel content of all metals other than lithium is 50 mol % or more and in the form of at least one of single particles or quasi-single particles, which are secondary particles formed by agglomeration of 30 or less primary particles, and further comprising a lithium borate-based compound.

[0013] In another embodiment, the present invention provides a method for manufacturing a positive electrode for a lithium secondary battery, the method including: mixing a positive electrode active material including a lithium nickel-based oxide having a composition in which nickel is present in an amount of 50 mol % or more among all metals other than lithium, and in the form of at least one of single particles or quasi-single particles, which are secondary particles formed by agglomeration of 30 or fewer primary particles, with a lithium borate-based compound, a binder, a conductive material, and a solvent to prepare a positive electrode slurry; and coating the positive electrode slurry on at least one surface of a positive electrode current collector to form a positive electrode active material layer.

[0014] According to another embodiment, the present invention provides a lithium secondary battery including the positive electrode, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0015] When a positive electrode is manufactured using the positive electrode slurry according to the present invention, the particle surface can be stabilized and the capacity expression rate can be increased without performing boron coating and water washing processes in the synthesis process of lithium nickel-based oxide, and ultimately, the performance of a lithium secondary battery at high temperature and high voltage can be improved.

[0016] In a conventional manufacturing process for a cathode active material, residual lithium present on the surface of lithium transition metal oxide particles is removed by a water washing process after calcination. However, during this process, the particle surface may react with water, causing the layered structure to collapse or be damaged. This may lead to a decrease in the capacity and rate-limiting characteristics of the battery, an increase in resistance at high temperatures, etc.

[0017] To prevent damage during the water washing process, a method of forming a boron coating layer on the surface of the particles has been commonly used. However, this method requires a high-temperature sintering process, and as the boron grows into a plate-like shape, the particles become harder, potentially making subsequent rolling more difficult. Furthermore, the boron coating layer, due to its amorphous nature, can cause further problems by increasing the surface resistance of the particles. In particular, positive electrode active materials in the form of single particles not only have relatively lower lithium mobility and higher initial resistance than those in the form of secondary particles, but also tend to convert to a rock salt phase, an electrochemically inactive phase, more easily when the sintering temperature is increased to form single particles, further increasing the surface resistance.

[0018] Therefore, in the present invention, it was confirmed that by incorporating a lithium borate compound into the positive electrode slurry, the effects of boron coating can be achieved without the need for a boron coating process or a water washing process in the manufacturing process of the positive electrode active material. That is, it is possible to achieve effects such as stabilizing the particle surface, suppressing side reactions, and improving capacity without causing the problems of increased surface resistance due to boron coating and surface damage due to the water washing process.

[0019] In addition, the lithium borate-based compound dispersed in the positive electrode dissolves in the electrolyte and leaks out during the electrolyte injection and battery activation process, forming pores inside the positive electrode. The electrolyte then permeates these pores, increasing the remaining amount of electrolyte. The lithium borate-based compound dissolved in the electrolyte also secures additional lithium ions, which are used in place of LiPF6 salt. This also helps to improve the battery life by suppressing decomposition of the electrolyte. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a graph showing the results of evaluation of the room temperature life of batteries to which positive electrodes of Examples and Comparative Examples are applied. [Figure 2] 1 is a graph showing the evaluation results of high-temperature life of batteries to which positive electrodes of Examples and Comparative Examples are applied. DETAILED DESCRIPTION OF THE INVENTION

[0021] Each of the components of the present invention will be described in more detail below.

[0022] In the present invention, the term "primary particle" refers to a particle unit that does not appear to have grain boundaries when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope, and the term "secondary particle" refers to a particle formed by aggregation of multiple primary particles.

[0023] In the present invention, the "average particle size of primary particles" refers to the arithmetic mean value calculated after measuring the particle sizes of at least 20 primary particles observed in a scanning electron microscope image. Here, the particle size refers to the diameter of the longest axis of the primary particles.

[0024] In the present invention, "secondary particles" are particles formed by agglomeration of a plurality of primary particles. In the present invention, secondary particles formed by agglomeration of 30 or less primary particles are called pseudo-single particles to distinguish them from conventional secondary particles formed by agglomeration of tens to hundreds of primary particles.

[0025] In the present invention, "D50" refers to the particle size corresponding to 50% cumulative volume in the volume cumulative particle size distribution of the particle powder, and can be measured using a laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., S-3500 manufactured by Microtrac), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W. A volume cumulative particle size distribution graph is then obtained, and the particle size at the point where the volume cumulative amount is 50% on the obtained volume cumulative particle size distribution graph is determined.

[0026] Positive electrode slurry The positive electrode slurry according to the present invention includes a positive electrode active material, a lithium borate-based compound, a binder, a conductive material, and a solvent. The positive electrode active material is a lithium nickel-based oxide having a composition in which nickel is present in an amount of 50 mol% or more among all metals other than lithium, and is in the form of at least one of single particles or quasi-single particles. The quasi-single particles are secondary particles formed by agglomeration of 30 or less primary particles.

[0027] In one embodiment of the present invention, the lithium borate-based compound may be lithium tetraborate (Li2B4O7). Lithium tetraborate has lower reactivity with moisture than other lithium salt compounds such as LiPF6, LiBF4, LiN(SO2CF2CF3)2, LiNO3, and LiB(C2O4)2, and is therefore advantageous in preventing side reactions with moisture, such as elution of positive electrode transition metals, corrosion of the current collector, and decomposition of the electrolyte.

[0028] Meanwhile, the lithium borate-based compound may be included in an amount of 0.005 to 0.5 parts by weight, preferably 0.005 to 0.1 parts by weight, and more preferably 0.007 to 0.05 parts by weight, relative to 100 parts by weight of the lithium nickel-based oxide. When the lithium borate-based compound is included in an amount of 0.005 parts by weight or more relative to 100 parts by weight of the lithium nickel-based oxide, the effect of adding the lithium borate-based compound can be fully realized, but an amount of 0.5 parts by weight or less is preferred in terms of preventing the hardness from increasing due to boron, making rolling difficult.

[0029] The lithium nickel-based oxide may have a nickel content of 55 mol % or more, preferably 60 mol % or more, of all metals other than lithium.

[0030] Specifically, the lithium nickel-based oxide may have a composition represented by the following Chemical Formula 1:

[0031] [Chemical formula 1] Li 1+x (Ni a Co b M 1 c M 2 d )O2

[0032] In the above Chemical Formula 1, M 1 is Mn, Al or a combination thereof, M 2 is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, 1 + x, a, b, c, and d are the atomic fractions of each individual element, -0.2≦x≦0.2, 0.50≦a<1, 0 <b<0.50、0<c<0.50、0≦d≦0.10、a+b+c+d=1である。

[0033] The 1 + x represents the lithium molar ratio in the lithium nickel-based oxide, and it can be -0.1 ≦ x ≦ 0.2, or 0 ≦ x ≦ 0.2. When the lithium molar ratio satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0034] The a represents the nickel molar ratio among all the metals other than lithium in the lithium nickel-based oxide, and it can be 0.50 < a < 1, 0.55 ≦ a < 1, or 0.60 ≦ a < 1. When the nickel molar ratio satisfies the above range, it shows a high energy density and high capacity can be realized, and it can be stably driven at a high voltage.

[0035] The b represents the cobalt molar ratio among all the metals other than lithium in the lithium nickel-based oxide, and it can be 0 < b ≦ 0.40, 0 < b ≦ 0.25, or 0 < b ≦ 0.15. When the cobalt molar ratio satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0036] The c represents the molar ratio of M among all the metals other than lithium in the lithium nickel-based oxide 1 and it can be 0 < c ≦ 0.40, 0 < c ≦ 0.35, or 0 < c ≦ 0.30. For example, when M 1 is Mn, when the molar ratio of Mn satisfies the above range, the structure stability of the positive electrode active material is excellent.

[0037] The d represents the molar ratio of the M element among all the metals other than lithium in the lithium nickel-based oxide, and the d can be 0 ≦ d ≦ 0.08, 0 ≦ d ≦ 0.05, or 0 ≦ d ≦ 0.03. 2

[0038] Preferably, M 1 in Chemical Formula 1 can be Mn. That is, the lithium nickel-based oxide can be a lithium nickel cobalt manganese-based oxide.

[0039] Meanwhile, the lithium nickel-based oxide may include a coating layer containing one or more elements of Al and W on the surface of the particles, preferably Al and W. In this case, the coating layer reacts with the lithium by-products remaining on the surface to form LiAlO2, LiWO3, etc., thereby reducing the amount of residual lithium by-products and the amount of gas generated. The coating element may exist in the form of an oxide in the coating layer and may be formed by methods such as dry coating, wet coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). Among these, atomic layer deposition is preferred because it allows for the formation of a large coating layer.

[0040] The area where the coating layer is formed can be 10% to 100%, preferably 30% to 100%, and more preferably 50% to 100% of the total surface area of ​​the lithium nickel-based oxide particles. When the area where the coating layer is formed satisfies the above range, the amount of gas generation can be reduced and the life characteristics can be improved.

[0041] On the other hand, when the coating layer contains Al, the content of Al in the coating layer can be 5 wt % or less, preferably 0.1 to 5 wt %, and more preferably 0.5 to 1 wt %, based on the total weight of the lithium nickel-based oxide.When the coating layer contains W, the content of W in the coating layer can be 5 wt % or less, preferably 0.1 to 5 wt %, and more preferably 0.5 to 1 wt %, based on the total weight of the lithium nickel-based oxide.

[0042] In the lithium nickel-based oxide, when measuring the weight of the lithium compound remaining on the particle surface, the amount of Li2CO3 may be greater than that of LiOH. Considering that Li2CO3 is more easily removed than LiOH by washing the surface with water, having a greater amount of Li2CO3 than LiOH means that a water washing process is not required, which has the effect of reducing the initial resistance.

[0043] Specifically, the content of Li2CO3 may be 0.1 wt% to 0.5 wt% based on the total weight of the lithium nickel-based oxide, and the content of LiOH may be 0.01 wt% to 0.05 wt% based on the total weight of the lithium nickel-based oxide. The contents of LiOH and Li2CO3 can be confirmed by pH titration of the lithium nickel-based oxide.

[0044] On the other hand, the D of the lithium nickel oxide 50 The thickness can be 2 μm to 8 μm, preferably 2 μm to 5 μm, and more preferably 3 μm to 4 μm.

[0045] Meanwhile, the positive electrode active material may be included in an amount of 80 wt% to 99 wt%, specifically 90 wt% to 99 wt%, based on the total weight of the solid content of the positive electrode slurry. If the content of the positive electrode active material is less than 80 wt%, the energy density may be reduced, resulting in a decrease in capacity.

[0046] Meanwhile, the binder may be at least one selected from the group consisting of polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof, and is preferably polyvinylidene fluoride (PVDF).

[0047] The binder may be contained in an amount of 0.5 wt % to 2.5 wt %, preferably 0.5 wt % to 2 wt %, and more preferably 1 wt % to 2 wt %, based on the total weight of the solid content of the positive electrode slurry. When the binder content is within this range, sufficient adhesion to the current collector and bonding between particles can be ensured, improving the durability of the positive electrode and maintaining low initial resistance.

[0048] The conductive material may be at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; carbon-based materials such as carbon fibers and carbon nanotubes; 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; and conductive polymers such as polyphenylene derivatives, and preferably carbon black.

[0049] The conductive material may be contained in an amount of 0.5 wt % to 2.5 wt %, preferably 0.5 wt % to 2 wt %, and more preferably 1 wt % to 2 wt %, based on the total weight of the solid content of the positive electrode slurry. When the content of the conductive material is within this range, it is preferable in that the conductivity between the active materials can be maintained and the dead volume can be reduced.

[0050] The solvent for the positive electrode slurry may be an organic solvent such as N-methyl-2-pyrrolidone (NMP), and may be used in an amount sufficient to achieve a desired viscosity. For example, the solid content of the positive electrode slurry may be 40 wt % to 90 wt %, preferably 50 wt % to 85 wt %, and more preferably 60 wt % to 70 wt %, based on the total weight of the positive electrode slurry.

[0051] Positive electrode and method for manufacturing the same The positive electrode according to the present invention includes a positive electrode active material layer formed by coating at least one surface of a positive electrode current collector with a positive electrode slurry.

[0052] The positive electrode current collector may be any material that does not cause chemical changes in the battery and is conductive. 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. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and the positive electrode current collector may have a fine irregularity on its surface to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0053] The porosity of the positive electrode active material layer may be 19% to 25%, preferably 20% to 24%, and more preferably 21% to 23%. As described above, such porosity can be exhibited by the lithium borate-based compound flowing into the electrolyte. Here, the porosity refers to a value calculated by the following [Equation 1]:

[0054] [Formula 1] Porosity of the positive electrode active material layer (%) = ((true density of the positive electrode active material - density of the positive electrode) / true density of the positive electrode active material) × 100

[0055] In the above formula 1, the density of the positive electrode is a value calculated by the following formula 2.

[0056] [Formula 2] Positive electrode density = (weight of positive electrode - weight of positive electrode current collector) / (a ​​× b)

[0057] In the above formula 2, a is the area of ​​the positive electrode, and b is the value obtained by subtracting the thickness of the positive electrode current collector from the thickness of the positive electrode.

[0058] On the other hand, the method for producing a positive electrode according to the present invention comprises the steps of: A positive electrode active material including a lithium nickel-based oxide having a composition in which nickel content among all metals other than lithium is 50 mol % or more and in the form of at least one of single particles or quasi-single particles which are secondary particles formed by agglomeration of 30 or less primary particles, a lithium borate-based compound, a binder, a conductive material, and a solvent is mixed to prepare a positive electrode slurry; and coating at least one surface of a positive electrode current collector with the positive electrode slurry to form a positive electrode active material layer.

[0059] A method for manufacturing a positive electrode according to an embodiment of the present invention further includes a step of preparing a lithium nickel-based oxide by calcining a mixture of a nickel transition metal precursor having a nickel content of 50 mol % or more and a lithium source material, and the step of preparing the lithium nickel-based oxide does not necessarily include a water washing step after the calcination. As described above, the water washing process can deteriorate the surface properties of the lithium nickel-based oxide and increase its resistance, so it is preferable to avoid the water washing step by introducing the positive electrode slurry according to the present invention.

[0060] Here, the nickel transition metal precursor may be a commercially available precursor or may be prepared by a precursor preparation method well known in the art.

[0061] Preferably, the nickel transition metal precursor is a nickel transition metal hydroxide having a nickel content of 50 mol% or more of the total transition metals, and more preferably, a nickel transition metal hydroxide having a nickel content of 55 mol% or more, or 60 mol% or more. When the nickel content in the nickel transition metal precursor satisfies this range, high capacity characteristics can be achieved.

[0062] For example, the precursor may be prepared by co-precipitation of an aqueous transition metal solution, an ammonium cation complex, and a basic compound in a reactor while stirring.

[0063] The transition metal aqueous solution can be prepared by dissolving a transition metal-containing raw material in a solvent such as water. For example, a nickel-containing raw material, a cobalt-containing raw material, and a M 1 It can be produced by dissolving the raw materials in water.

[0064] Meanwhile, the transition metal-containing raw material may be acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of the transition metal.

[0065] Specifically, the nickel-containing source material may be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0066] The cobalt-containing source material can be, for example, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0067] Said M 1 The raw materials contained are M 1 When is manganese, it can be, for example, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halide, or a combination thereof.

[0068] Here, the amount of each transition metal-containing raw material to be added may be determined in consideration of the molar ratio of the transition metal in the final cathode active material to be produced.

[0069] The ammonium cation complexing agent may include at least one compound selected from the group consisting of NHOH, (NH)SO, NHNO, NHCl, CHCOONH, and (NH)CO, and may be added to the reactor in the form of a solution in which the compound is dissolved in a solvent, which may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0070] The basic compound may be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and may be added to the reactor in the form of a solution in which the compound is dissolved in a solvent, which may be water or a mixture of water and an organic solvent (e.g., alcohol) that is uniformly miscible with water.

[0071] As described above, when the aqueous transition metal solution, the ammonium cation complexing agent, and the basic compound are charged into a reactor and stirred, the transition metal in the aqueous transition metal solution is coprecipitated to produce precursor particles in the form of transition metal hydroxide.

[0072] Here, the aqueous transition metal solution, the ammonium cation complex-forming agent, and the basic compound are added in amounts such that the pH of the reaction solution falls within a desired range.

[0073] Once the precursor particles are formed by the above method, they are separated from the reaction solution to obtain the precursor. For example, the reaction solution can be filtered to separate the precursor from the reaction solution, and the separated precursor can then be washed with water and dried to obtain the precursor. Here, steps such as pulverization and / or classification can be performed as necessary.

[0074] The nickel transition metal precursor thus prepared is mixed with a lithium source material and then calcined to prepare a lithium nickel-based oxide. 2 The metal-containing raw materials can be mixed together and fired.

[0075] The lithium source material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide, such as Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, Li3C6H5O7, or a mixture thereof.

[0076] Meanwhile, the lithium source material and the nickel transition metal precursor may be mixed so that the molar ratio of Li:total metals in the precursor is 1:1 to 1.2:1, preferably 1:1 to 1.1:1. When the mixing ratio of the lithium source material to the metals in the precursor satisfies this range, the layered crystal structure of the lithium nickel-based oxide is well developed, and a positive electrode active material with excellent capacity characteristics and structural stability can be produced.

[0077] Meanwhile, the calcination is carried out at a temperature at which single particles or quasi-single particles can be formed. To form single particles or quasi-single particles, the calcination must be carried out at a temperature higher than that used in the preparation of conventional lithium composite transition metal oxides in the form of secondary particles. For example, when the precursor composition is the same, the calcination must be carried out at a temperature about 30°C to 100°C higher than that used in the preparation of conventional lithium composite transition metal oxides in the form of secondary particles.

[0078] In one embodiment of the present invention, the calcination in the step of preparing the lithium nickel-based oxide can be carried out at 700°C to 1,050°C, preferably 750°C to 1,000°C, and more preferably 800°C to 900°C.

[0079] When the calcination temperature satisfies the above range, a positive electrode active material in the form of a single particle or quasi-single particle with excellent electrochemical properties can be produced. Specifically, the calcination temperature is preferably 700°C or higher to prevent the formation of secondary particles, but is preferably 1,050°C or lower because excessive calcination may prevent the proper formation of a layered crystal structure and result in reduced electrochemical properties.

[0080] The firing may be carried out in an oxygen atmosphere for 5 to 35 hours. In this specification, the term "oxygen atmosphere" refers to an atmosphere containing sufficient oxygen for firing, including the air atmosphere. In particular, firing is preferably carried out in an atmosphere having a higher oxygen partial pressure than the air atmosphere.

[0081] In addition, the method for manufacturing a cathode according to an embodiment of the present invention may not include a step of forming a boron coating on the lithium nickel-based oxide between the steps of preparing the lithium nickel-based oxide and preparing the cathode slurry. As described above, since the boron coating layer increases surface resistance, it is preferable to not include a separate boron coating layer formation process by introducing the cathode slurry according to the present invention.

[0082] In the step of forming the positive electrode active material layer, the loading amount of the positive electrode slurry is 14 mg / cm 2 ~24mg / cm 2 , preferably 16 mg / cm 2 ~22mg / cm 2 , and more preferably 18 mg / cm 2 ~20mg / cm 2 It can be.

[0083] The method for manufacturing a positive electrode for a lithium secondary battery according to an embodiment of the present invention may further include rolling the stack of the positive electrode current collector and the positive electrode active material layer. The rolling may be performed by cutting the stack, placing it between two rolls, and compressing it by adjusting the gap between the rolls.

[0084] The above description of the components of the positive electrode slurry can be applied to the components of the method for producing a positive electrode for a lithium secondary battery according to an embodiment of the present invention.

[0085] Lithium secondary battery Next, the lithium secondary battery according to the present invention will be described.

[0086] The lithium secondary battery of the present invention includes the above-mentioned positive electrode for lithium secondary batteries, a negative electrode containing a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

[0087] In one embodiment of the present invention, the lithium secondary battery can have a driving voltage of 4.3 V or higher, specifically 4.3 V to 4.5 V, and more specifically 4.35 V to 4.45 V. The positive electrode according to the present invention includes a B coating, which reduces contact with the electrolyte and suppresses side reactions such as metal elution, thereby exhibiting excellent characteristics at high voltages, and thus a lithium secondary battery including the same can be driven at high voltages.

[0088] The lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0089] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0090] The negative electrode current collector may be any material that does not cause chemical changes in the battery and has high conductivity, and examples of such materials include copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the current collector may have fine irregularities on its surface to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0091] The negative electrode active material layer may optionally contain a binder and a conductive material in addition to the negative electrode active material.

[0092] The negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples thereof include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, and Al alloys; and SiO. β (0<β<2), metal oxides that can be doped and dedoped with lithium, such as SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the above metallic 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.

[0093] In addition, a metallic lithium thin film can be used as the negative electrode active material. The carbon material can be either low-crystalline or high-crystalline carbon. Typical low-crystalline carbons include soft carbon and hard carbon, while typical high-crystalline carbons include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbeads, mesophase pitches, and high-temperature-fired carbons such as petroleum or coal tar pitch-derived cokes.

[0094] The conductive material in the negative electrode active material layer is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations, as long as it does not cause chemical changes in the resulting battery and has electronic conductivity. 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 nanotubes; metal powder or fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material is typically present in an amount of 1 wt % to 30 wt %, preferably 1 wt % to 20 wt %, and more preferably 1 wt % to 10 wt %, based on the total weight of the negative electrode active material layer.

[0095] The binder in the negative electrode active material layer serves to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination. The binder may be present in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt% based on the total weight of the negative electrode active material layer.

[0096] For example, the negative electrode active material layer may be manufactured by applying a negative electrode slurry containing a negative electrode active material, and optionally a binder and a conductive material, onto a negative electrode current collector and drying the applied slurry, or by casting the negative electrode slurry onto a separate support, peeling the resulting film from the support, and laminating the resulting film onto the negative electrode current collector.

[0097] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material can also be used, and can be selectively used in a single-layer or multi-layer structure.

[0098] In addition, the electrolyte contained in the lithium secondary battery according to the present invention may be, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte.

[0099] In one embodiment of the present invention, the electrolyte may be an organic liquid electrolyte containing an organic solvent and a lithium salt.

[0100] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethanol and isopropyl alcohol, nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0101] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(C, F, SO), LiN(C, F, SO), LiN(CF, SO), LiCl, LiI, or LiB(C, O) . The lithium salt concentration is preferably in the range of 0.1 M to 5.0 M, and more preferably 0.1 M to 3.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0102] In addition to the electrolyte components, the electrolyte may further contain additives for purposes such as improving battery life characteristics, suppressing battery capacity loss, and improving battery discharge capacity. Examples of additives include, but are not limited to, carbonate-based compounds, sultone-based compounds, sulfate-based compounds, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, which may be used alone or in combination. The additives may be present in an amount of 0.1 wt % to 10 wt %, preferably 0.1 wt % to 5 wt %, based on the total weight of the electrolyte.

[0103] As described above, the lithium secondary battery including the positive electrode according to the present invention has excellent initial resistance and high-temperature storage characteristics, and is therefore useful in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles.

[0104] Therefore, according to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0105] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices, such as a power tool, an electric vehicle (EV), or a power storage system.

[0106] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the preferred embodiments so that those skilled in the art can easily carry out the present invention.

[0107] [Examples and Comparative Examples: Production of Positive Electrode] Example 1 Transition metal precursor Ni 0.60 Co 0.10 Mn 0.30 (OH)2 and LiOH·H2O were mixed so that the molar ratio of transition metals (Ni+Co+Mn):Li was 1:1.05, and the mixture was heated to 850°C at a heating rate of 5°C / min, maintained at this temperature for 10 hours, and then cooled to room temperature at a cooling rate of 5°C / min to obtain Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2, and D 50 A lithium nickel cobalt manganese-based oxide with a particle size of 3.5 μm was prepared. Next, a coating layer containing Al and W was formed on the surface. The prepared lithium nickel cobalt manganese-based oxide was observed under a scanning electron microscope and was confirmed to have a single particle morphology.

[0108] The lithium nickel cobalt manganese oxide, carbon black conductive material, and PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 97.3:1.43:1.27, and 0.01 parts by weight of Li2B4O7 was added to 100 parts by weight of the lithium nickel cobalt manganese oxide to prepare a positive electrode slurry with a solid content of 74% by weight.

[0109] The prepared positive electrode slurry was applied to one side of a 10 μm thick aluminum current collector at a concentration of 20 mg / cm. 2 After coating with a loading amount of 1000 ppm, the coating was dried at 130° C. to prepare a positive electrode active material layer.

[0110] The laminate in which the positive electrode active material layer was formed on the current collector was cut and then placed between two rolling rolls and rolled at 25° C. After rolling, the porosity of the positive electrode active material layer calculated by Equation 1 was 22%.

[0111] Comparative Example 1 A positive electrode was prepared in the same manner as in Example 1, except that Li2B4O7 was not added during the preparation of the positive electrode slurry, and the lithium nickel cobalt manganese-based oxide, the carbon black conductive material, and the PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 97.3:1.43:1.27 to prepare the positive electrode slurry.

[0112] [Experimental Example 1: Evaluation of lifespan at room temperature and high temperature] (1) Battery manufacturing An electrode assembly was prepared by interposing a 15 μm thick polyethylene separator between each of the positive electrodes and lithium metal negative electrodes prepared in the Examples and Comparative Examples, and then the assembly was placed inside a battery case. An electrolyte solution was injected into the case, and the case was sealed and activated to prepare a half cell.

[0113] The electrolyte was prepared by dissolving 1M LiPF6 in a mixed organic solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7 to prepare an organic solution, and then mixing 0.2 wt% vinylene carbonate (VC) into the solution.

[0114] (2) Room temperature life evaluation Each of the prepared batteries was charged at a rate of 0.7 C under constant current / constant voltage conditions at 25°C to 4.4 V, and then discharged at a constant current of 0.5 C to 3.0 V after a 0.05 C current cutoff. The capacity retention rate was measured after 200 or more charge / discharge cycles, and the results are shown in Figure 1.

[0115] (3) High-temperature life evaluation Each of the prepared batteries was charged at a rate of 0.7 C under constant current / constant voltage conditions at 45° C. up to 4.4 V, and then discharged at a constant current of 0.5 C down to 3.0 V after a 0.05 C current cutoff. The capacity retention rate after 300 charge / discharge cycles was measured, and the results are shown in Figure 2.

[0116] 1 and 2, when the positive electrode of Example 1, in which Li2B4O7 was added during the preparation of the positive electrode slurry, was compared with the positive electrode of Comparative Example 1, in which Li2B4O7 was not added, it was confirmed that the positive electrode of Example 1 had a significantly superior effect of improving the life at high temperatures. This shows that adding Li2B4O7 during the preparation of the positive electrode slurry as described above stabilizes the particle surface, suppresses side reactions, and ultimately has the effect of improving the life of the battery.

Claims

1. A positive electrode slurry for a lithium secondary battery includes a positive electrode active material containing a lithium nickel-based oxide having a composition in which the content of nickel among all metals other than lithium is 50 mol % or more, and which is in the form of at least one of single particles or pseudo-single particles, which are secondary particles formed by agglomeration of 30 or less primary particles; a lithium borate-based compound; a binder; a conductive material; and a solvent.

2. The lithium borate-based compound is lithium tetraborate (Li ２ B ４ O ７ 2. The positive electrode slurry for a lithium secondary battery according to claim 1, wherein the positive electrode slurry is a sintered body.

3. 2. The positive electrode slurry for a lithium secondary battery according to claim 1, wherein the lithium borate-based compound is contained in an amount of 0.005 to 0.5 parts by weight based on 100 parts by weight of the lithium nickel-based oxide.

4. 2. The positive electrode slurry for a lithium secondary battery according to claim 1, wherein the binder is contained in an amount of 0.5 wt % to 2.5 wt % based on the total weight of the solid content of the positive electrode slurry.

5. 2. The positive electrode slurry for a lithium secondary battery according to claim 1, wherein the conductive material is contained in an amount of 0.5 wt % to 2.5 wt % based on the total weight of the solid content of the positive electrode slurry.

6. 2. The positive electrode slurry for a lithium secondary battery according to claim 1, wherein the solid content of the positive electrode slurry is 40 wt % to 90 wt % based on the total weight of the positive electrode slurry.

7. The lithium nickel-based oxide has a composition represented by the following Chemical Formula 1: [Chemical formula 1] Li １＋ｘ (N ａ Co ｂ M １ ｃ M ２ ｄ )O ２ In the above Chemical Formula 1, M １ is Mn, Al or a combination thereof; M ２ is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; 1 + x, a, b, c, and d are the atomic fractions of each independent element, 2. The positive electrode slurry for lithium secondary batteries according to claim 1, wherein −0.2≦x≦0.2, 0.50≦a<1, 0<b<0.50, 0<c<0.50, 0≦d≦0.10, and a+b+c+d=1.

8. 2. The positive electrode slurry for a lithium secondary battery according to claim 1, wherein the lithium nickel-based oxide particles have a coating layer containing at least one element selected from the group consisting of Al and W on the surface of the particles.

9. The lithium nickel oxide D ５０ The positive electrode slurry for lithium secondary batteries according to claim 1, wherein the particle size is 2 μm to 8 μm.

10. The lithium nickel-based oxide is such that when the weight of the lithium compound remaining on the surface of the particles is measured, Li ２ CO ３ The positive electrode slurry for a lithium secondary battery according to claim 1, wherein the positive electrode slurry contains more than LiOH.

11. A positive electrode for a lithium secondary battery, comprising a positive electrode active material layer coated on at least one surface of a positive electrode current collector with the positive electrode slurry according to claim 1 .

12. The positive electrode for a lithium secondary battery according to claim 11, wherein the positive electrode active material layer has a porosity of 19% to 25%.

13. The positive electrode active material includes a lithium nickel-based oxide having a composition in which the content of nickel among all metals other than lithium is 50 mol % or more, and the lithium nickel-based oxide is in the form of at least one of a single particle or a quasi-single particle, which is a secondary particle formed by agglomeration of 30 or less primary particles; A positive electrode for a lithium secondary battery, comprising a lithium borate-based compound.

14. a step of preparing a positive electrode slurry by mixing a positive electrode active material including a lithium nickel-based oxide having a composition in which the content of nickel among all metals other than lithium is 50 mol % or more and which is in the form of at least one of single particles or pseudo-single particles, which are secondary particles formed by agglomeration of 30 or less primary particles; a lithium borate-based compound; a binder; a conductive material; and a solvent; and coating at least one surface of a positive electrode current collector with the positive electrode slurry to form a positive electrode active material layer.

15. The method further includes a step of calcining a mixture of a nickel transition metal precursor having a nickel content of 50 mol% or more and a lithium source material to prepare the lithium nickel-based oxide; The method for producing a positive electrode for a lithium secondary battery according to claim 14 , wherein the step of preparing the lithium nickel-based oxide does not include a step of washing with water after the firing.

16. 16. The method for producing a positive electrode for a lithium secondary battery according to claim 15, wherein the method does not include a step of applying a boron coating to the lithium nickel-based oxide between the step of preparing the lithium nickel-based oxide and the step of producing the positive electrode slurry.

17. The positive electrode according to claim 11 or 13, a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an electrolyte.

18. 18. The lithium secondary battery according to claim 17, wherein the driving voltage is 4.3 V or more.

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