Positive electrode active material and method for producing same

Abstract

The present invention relates to a positive electrode active material which can be easily applied to a lithium secondary battery by suppressing a gelling phenomenon while having a high nickel content, and a method for manufacturing the same. Specifically, the present invention relates to a positive electrode active material and a method for manufacturing the same, the positive electrode active material comprising: a lithium transition metal oxide; and a coating layer on a surface of the lithium transition metal oxide and including a Li-B-O solid solution, in which the positive electrode active material has a residual lithium by-product content of 0.3 to 1.0 wt%, a molar ratio of LiB2O3 to LiBO3 (LiB2O3 / LiBO3) in the coating layer is 1.6 or more, and B3O5 in the coating layer is 19 mol% or less with respect to the total ionic material.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0136136, filed on October 12, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to positive electrode active materials and their manufacturing methods. Background Technology

[0004] With the technological advancements and increasing demands of mobile devices, the need for secondary batteries as an energy source is rapidly growing. Among secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0005] Lithium transition metal composite oxides are used as positive electrode active materials in lithium secondary batteries, with lithium cobalt composite metal oxide (LiCoO2) being the primary choice due to its high operating voltage and excellent capacity characteristics. However, LiCoO2 suffers from very poor thermal properties due to the instability of its crystal structure caused by delithiation, and is also expensive, thus limiting its large-scale use as a power source in fields such as electric vehicles.

[0006] As alternatives to LiCoO2, lithium manganese composite metal oxides (LiMnO2 or LiMn2O4, etc.), lithium iron phosphate compounds (LiFePO4, etc.), or lithium nickel composite metal oxides (LiNiO2, etc.) have been developed. Among these, research and development of lithium nickel composite metal oxides, which have a high reversible capacity of approximately 200 mAh / g and are easy to implement in large-capacity batteries, is being carried out more actively. However, compared with LiCoO2, LiNiO2 has poorer thermal stability and suffers from the following problem: when an internal short circuit occurs during charging due to external pressure, the positive electrode active material itself decomposes, leading to battery rupture and combustion.

[0007] Therefore, as a method to improve low thermal stability while maintaining the excellent reversible capacity of LiNiO2, nickel-cobalt-manganese-based lithium composite transition metal oxides in which some Ni is replaced by Mn and Co, and nickel-cobalt-aluminum-based lithium composite transition metal oxides in which some Ni is replaced by Mn and Al have been developed.

[0008] Unreacted lithium byproducts (such as LiOH and Li₂CO₃) exist on the surface of lithium complex transition metal oxides during manufacturing. To minimize these lithium byproducts, it is customary to wash the calcined products obtained by calcining the cathode active material precursor and lithium-containing raw materials, followed by washing with inorganic oxides (such as Al₂O₃). 3)The coating method is an option. However, this involves a two-step process of washing and coating, which presents a cost burden. Furthermore, due to the use of inorganic oxide powders, the coating uniformity is low, resulting in a thick coating primarily forming only on the surface of secondary particles. Consequently, it is difficult to achieve excellent lithium-ion conductivity and conductivity, and side reactions with the electrolyte may occur, leading to reduced battery capacity, output, and lifespan.

[0009] Therefore, there is a need for a method for manufacturing positive electrode active materials that suppresses side reactions with the electrolyte by minimizing residual lithium that may remain on the surface of the positive electrode active material while achieving a uniform and thin coating on the surface of the primary particles of the positive electrode active material, and thus has excellent capacity and lifetime characteristics.

[0010] In particular, when the positive electrode active material has a nickel content of 80% or more, the alkalinity of the slurry used for the positive electrode in lithium secondary batteries increases due to the influence of impurities (such as LiOH and Li2CO3). This hinders the uniform dispersion of the slurry and causes the positive electrode active material and conductive material to agglomerate and gel. This gelation phenomenon reduces the fluidity of the slurry, thereby hindering the coating process on the electrode and significantly reducing the efficiency of the lithium secondary battery manufacturing process.

[0011] [Existing Technical Documents]

[0012] [Patent Literature]

[0013] (Patent Document 1) JP WO2015-186321 A1 Summary of the Invention

[0014] Technical issues

[0015] The purpose of this invention is to provide a positive electrode active material that can be easily applied to lithium secondary batteries while having a high nickel content and suppressing gelation.

[0016] Technical solution

[0017] To achieve the above objectives, the present invention provides a positive electrode active material, a method for manufacturing the positive electrode active material, a positive electrode, and a lithium secondary battery.

[0018] (1) The present invention provides a positive electrode active material comprising: a lithium transition metal oxide; and a coating on the surface of the lithium transition metal oxide and comprising a Li-BO solid solution, wherein the positive electrode active material has a residual lithium by-product content of 0.3 to 1.0% by weight, the molar ratio of LiB2O3 to LiBO3 in the coating (LiB2O3 / LiBO3) is 1.6 or more, and the B3O5 in the coating is 19 mol% or less relative to all ionic materials.

[0019] (2) The present invention provides a positive electrode active material according to (1) above, wherein the lithium transition metal oxide is a compound represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x [Ni a Co b Mn c M d O 2-y in: -0.1 <x<0.2,0.5<a<1,0<b<0.4,0<c<0.3,0<d<0.05,a+b+c+d=1,0≤y≤0.1, M is at least one element selected from the group consisting of Al, Mg, V, Ti, and Zr.

[0020] (3) The present invention provides a positive electrode active material according to (1) or (2) above, wherein the LiBO3 in the coating is 3 to 10 mol relative to all ionic materials.

[0021] (4) The present invention provides a positive electrode active material according to any one of (1) to (3) above, wherein the LiBO3 in the coating is 3 to 25 mol relative to the total ionic material.

[0022] (5) The present invention provides a positive electrode active material according to any one of (1) to (4) above, wherein the coating comprising the Li-BO solid solution has a thickness of 5 to 10 nm.

[0023] (6) The present invention provides a method for manufacturing a positive electrode active material, the method comprising the following steps: 1) mixing and calcining a positive electrode active material precursor comprising a transition metal hydroxide and a lithium-containing raw material to produce a calcined product comprising a lithium transition metal oxide; 2) washing the calcined product to produce a washed product having a residual lithium content of 0.3 to 0.9% by weight on the surface of the lithium transition metal oxide; 3) mixing the washed product and a boron-containing raw material; and 4) heat-treating the mixture in step 3) at 200°C to 290°C to form a coating comprising a Li-BO solid solution on the surface of the lithium transition metal oxide, wherein the amount of the boron-containing raw material is 700 ppm to 1200 ppm by weight based on the weight of the washed product.

[0024] (7) The present invention provides a method for manufacturing a positive electrode active material according to (6) above, wherein the washing is performed by adding 30 to 150 parts by weight of a washing solution based on 100 parts by weight of the calcined product.

[0025] (8) The present invention provides a method for manufacturing a positive electrode active material according to (6) or (7) above, wherein the residual lithium is at least one selected from the group consisting of LiOH and Li2CO3.

[0026] (9) The present invention provides a method for manufacturing a positive electrode active material according to any one of (6) to (8) above, wherein the residual lithium participates as a reactant in the formation of the Li-BO solid solution in step 4).

[0027] (10) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (5) above.

[0028] (11) The present invention provides a lithium secondary battery comprising: a positive electrode as described in (10) above; a negative electrode; and a separator and an electrolyte disposed between the positive electrode and the negative electrode.

[0029] Beneficial effects

[0030] The positive electrode active material of the present invention can be used to manufacture lithium secondary batteries with improved lifespan characteristics and electrochemical properties. Attached Figure Description

[0031] Figure 1 The variation of the LiB2O3 / LiBO3 molar ratio with boron coating content is shown.

[0032] Figure 2 The variation of the LiB2O3 / LiBO3 molar ratio with boron coating temperature is shown. Detailed Implementation

[0033] In the following, the present invention will be described in more detail to facilitate understanding of the present invention.

[0034] The terms or words used in the description and claims of the present invention should not be construed as limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts consistent with the technical spirit of the present invention based on the concept that the inventor can fully define the terms to best describe the principles of his invention.

[0035] In the following, the present invention will be described in detail. ​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0042] c represents the atomic fraction of manganese in the lithium composite transition metal oxide, and can be 0 < c < 0.3, 0 < c ≤ 0.25, more preferably 0.1 ≤ c ≤ 0.25.

[0043] d represents the atomic fraction of the doping element M in the lithium composite transition metal oxide, and can be 0 < d < 0.05, more preferably 0.01 ≤ d ≤ 0.04.

[0044] As described above, the lithium transition metal oxide of the present invention can have excellent capacity characteristics by containing a high concentration of nickel of more than 50% by weight in all transition metals. However, despite the above advantages, the problem with conventional lithium transition metal oxides having a high nickel content is that due to thermodynamic instability, the change over time when exposed to the atmosphere becomes serious, and the positive electrode slurry experiences an increase in viscosity and gelation over time.

[0045] As described below, the positive electrode active material according to the present invention includes an Li - B - O coating with an appropriate content and composition, thereby obtaining the above advantages while suppressing problems caused by changes over time and preventing gelation, and thus improving stability and battery performance when applied to a lithium secondary battery.

[0046] In the present invention, the positive electrode active material includes a coating located on the surface of the lithium transition metal oxide and containing an Li - B - O solid solution.

[0047] Specifically, the Li - B - O solid solution can include at least one selected from the group consisting of LiBO3, LiB2O3, LiB2O4, B3O5, and LiB3O6, and the lithium ion conductivity and electrical conductivity of the coating containing the Li - B - O solid solution are excellent, enabling the realization of a lithium secondary battery with a small internal resistance.

[0048] In the present invention, the lithium transition metal oxide contained in the positive electrode active material is obtained by reacting a transition metal composite material (or high - nickel - based precursor) containing a transition metal (such as nickel, cobalt, or manganese) with a lithium compound (such as LiOH or Li2CO3), and can be prepared from a washing product that has been calcined (heat - treated) at a high temperature and has undergone a washing process to control the residual lithium on the surface.

[0049] In addition, as described below, the positive electrode active material of the present invention can be manufactured using a washing product having a residual lithium amount of 0.3 to 0.9% by weight, particularly 0.3 to 0.8% by weight or 0.3 to 0.7% by weight, on the surface of the lithium transition metal oxide.

[0050] As described above, the positive electrode active material of the present invention can ultimately comprise a Li-BO solid solution, while having a residual lithium byproduct content of 0.3 to 1.0 wt%, 0.4 to 0.8 wt%, or 0.5 to 0.7 wt%.

[0051] In this invention, the molar ratio of LiB2O3 to LiBO3 in the coating (LiB2O3 / LiBO3) is 1.6 or more, and specifically it can be 1.6 to 3.0 or 1.6 to 2.6.

[0052] When the LiB2O3 / LiBO3 ratio in the coating meets the above-mentioned numerical range, it means that a boron-rich Li-BO solid solution is formed in the coating.

[0053] When the LiB2O3 / LiBO3 ratio is less than 1.6 (outside the range mentioned above), when using positive electrode active materials to manufacture electrodes, the viscosity of the positive electrode slurry increases and gelation occurs over time. This may ultimately degrade the physical stability of the lithium secondary battery and may also cause problems such as reduced processability due to blockage during the slurry coating process.

[0054] In this invention, the B3O5 in the coating can be less than 19 mol% relative to all ionic materials, particularly 8 to 17 mol%, 12 to 16 mol%, or 15 to 16 mol%.

[0055] When the B3O5 in the coating meets the above-mentioned numerical range, it means that a Li-BO solid solution is formed to prevent the slurry in the coating from gelling and to exhibit excellent electrochemical properties.

[0056] When B3O5 exceeds 19 mol% (outside the above range), the following problem may occur: when using positive electrode active materials to manufacture electrodes, the electrochemical properties are severely degraded.

[0057] In this invention, the LiBO3 in the coating can be 3 to 10 mol%, particularly 5 to 8 mol%, or 6 mol%, relative to all ionic materials.

[0058] In addition, the LiB2O3 in the coating can be 3 to 25 mol%, particularly 5 to 18 mol%, or 10 to 15 mol%, relative to all ionic materials.

[0059] When LiBO3 and LiB2O3 are within the above range, this means that a Li-BO solid solution is formed to delay gelation in the coating.

[0060] In this invention, the thickness of the coating containing the Li-BO solid solution can be 5 to 10 nm.

[0061] In this invention, the positive electrode active material can be a secondary particle with a diameter of 12 μm, or a single particle with a size of 3 to 9 μm, but is not limited thereto.

[0062] <Manufacturing Methods of Positive Electrode Active Materials>

[0063] The method for manufacturing the positive electrode active material of the present invention is characterized by comprising the following steps: 1) mixing and calcining a positive electrode active material precursor containing a transition metal hydroxide and a lithium-containing raw material to produce a calcined product containing a lithium transition metal oxide; 2) washing the calcined product to produce a washed product having a residual lithium content of 0.3 to 0.9% by weight on the surface of the lithium transition metal oxide; 3) mixing the washed product and a boron-containing raw material; and 4) heat-treating the mixture in step 3) at 200°C to 290°C to form a coating containing a Li-BO solid solution on the surface of the lithium transition metal oxide, wherein the amount of the boron-containing raw material used is 700 ppm to 1200 ppm by weight, based on the weight of the washed product.

[0064] Step 1)

[0065] This is a step of mixing and calcining a positive electrode active material precursor containing transition metal hydroxides and a lithium-containing raw material to produce a calcined product containing lithium transition metal oxides.

[0066] Transition metal hydroxides can be used by purchasing commercially available cathode active material precursors, or they can be prepared according to methods known in the art for manufacturing cathode active material precursors. For example, the precursor can be prepared by adding an ammonium cation-containing complexing agent and a basic compound to a transition metal solution containing nickel-containing, cobalt-containing, and manganese-containing raw materials and carrying out a co-precipitation reaction.

[0067] The positive electrode active material precursor may include secondary particles formed by the aggregation of primary particles, and may be represented by the following chemical formula 2: [Chemical Formula 2] Ni a’ Co b’ Mn c’ M d’ (OH)2 in: 0.5 ’ <1,0 ’ <0.4, 0 <c ’ <0.3, 0 <d ’ <0.05, a ’ +b ’ +c ’ +d ’ =1, ​​M is at least one element selected from the group consisting of Al, Mg, V, Ti, and Zr.

[0068] a' refers to the atomic fraction of nickel in the precursor and can be 0.5 < a' < 1, preferably 0.6 ≤ a' < 1, 0.7 ≤ a' < 1, more preferably 0.7 ≤ a' ≤ 0.95.

[0069] b' refers to the atomic fraction of cobalt in the precursor and can be 0 < b' < 0.4, preferably 0.1 ≤ b' < 0.4, more preferably 0.1 ≤ b' ≤ 0.35.

[0070] c' refers to the atomic fraction of manganese in the precursor and can be 0 < c' < 0.3, 0 < c' ≤ 0.25, more preferably 0.1 ≤ c' ≤ 0.25.

[0071] d' refers to the atomic fraction of the doping element M in the precursor and can be 0 < d' < 0.05, more preferably 0.01 ≤ d' ≤ 0.04.

[0072] The lithium-containing raw material may include at least one selected from the group consisting of lithium hydroxide hydrate, lithium carbonate, and lithium hydroxide. The lithium-containing raw material may particularly be lithium hydroxide hydrate, more particularly LiOH·H2O. In this case, the reactivity between the precursor having a high nickel atomic fraction among the metal elements in the precursor and the lithium-containing raw material can be improved.

[0073] The precursor of the positive electrode active material and the lithium-containing raw material may be mixed at a molar ratio of 1:1.0 to 1:1.10, particularly 1:1.03 to 1:1.08, more particularly 1:1.05 to 1:1.07.

[0074] When the precursor of the positive electrode active material and the lithium-containing raw material are mixed at the above molar ratio, the capacity of the positive electrode active material may not decrease, the problem of unreacted Li remaining as a by-product may not occur, and the capacity reduction and separation phenomenon of the positive electrode active material particles after calcination can also be suppressed.

[0075] The calcination in step 1) may be carried out at 700 °C to 950 °C. The calcination temperature may particularly be 750 °C to 850 °C, more particularly 750 °C to 800 °C or 730 °C to 760 °C. When the calcination temperature is within the above range, crystals can be formed in appropriate sizes and the process cost may not be high.

[0076] The calcination in step 1) may be carried out in an oxygen atmosphere. In this case, a calcination product having a structurally stable phase can be formed.

[0077] The calcination in step 1) can be carried out for 5 to 24 hours. Calcination can be particularly carried out for 5 to 12 hours, and more particularly for 5 to 10 hours. When the calcination time is within the above range, calcination can be carried out well without depending on the deviation of the calcination position (uniformity).

[0078] Step 2)

[0079] This is a step of washing the calcined product prepared in step 1) above to produce a washed product having a residual lithium content of 0.3 to 0.9% by weight on the surface of the lithium transition metal oxide.

[0080] Washing is a process used to control residual lithium on the surface of the lithium transition metal oxide prepared in step 1) above, and by washing, the amount of residual lithium on the surface of the lithium transition metal oxide can be controlled to be 0.3 to 0.9 wt%, particularly 0.3 to 0.8 wt% or 0.3 to 0.7 wt%.

[0081] As described above, by manufacturing a washing product with a controlled residual lithium content, the present invention can ultimately produce a positive electrode active material comprising a coating, the coating comprising a Li-BO solid solution and having the characteristics of slowing gelation and having high lithium mobility.

[0082] Specifically, residual lithium is used as a reactant in the fabrication of a coating containing a Li-BO solid solution. When the residual lithium content is less than 0.4% by weight, the residual lithium content on the surface capable of forming a Li-BO solid solution is insufficient, causing lithium within the lithium transition metal oxide core to participate in the reaction for Li-BO solid solution formation. In this case, the breakdown of the layer structure consisting of the core and coating is accelerated, which may lead to an increased rate of resistance increase when used in lithium secondary batteries. Furthermore, when the residual lithium content exceeds 0.9% by weight, unreacted residual lithium remains even after the Li-BO solid solution is formed, which may reduce lithium diffusivity, resulting in reduced capacity and increased resistance when used in lithium secondary batteries.

[0083] The residual lithium may be at least one selected from the group consisting of LiOH and Li2CO3, but is not limited thereto.

[0084] In this invention, washing can be carried out by adding 30 to 150 parts by weight of washing solution based on 100 parts by weight of calcined product, and specifically, it can be carried out by adding 30 to 85 parts by weight or 30 to 80 parts by weight of washing solution based on 100 parts by weight of calcined product.

[0085] When the washing solution is used at the above concentration, residual lithium on the surface of lithium transition metal oxides can be controlled as intended in this invention, the calcined product will not gel, and excessive dissolution of lithium in the calcined product can be prevented.

[0086] In addition, washing can be carried out at temperatures ranging from 10°C to 80°C, especially at temperatures ranging from 15°C to 65°C or from 20°C to 30°C.

[0087] Washing can be done for 1 minute to 120 minutes, especially 3 minutes to 60 minutes or 5 minutes to 30 minutes.

[0088] In this invention, the solvent of the washing solution can be at least one selected from the group consisting of deionized water, distilled water, and ethanol. Specifically, the solvent of the washing solution can be deionized water and / or distilled water, but is not limited thereto.

[0089] After washing and before step 3), a drying process can be further performed. Drying is used to remove moisture from the water-containing lithium transition metal oxide by the washing process, and can be carried out at 60°C to 150°C after removing moisture using a vacuum pump. Specifically, drying can be carried out at a temperature of 60°C to 150°C for more than 12 hours.

[0090] Step 3)

[0091] This is the step of mixing the washing product prepared in step 2) above with the boron-containing raw material.

[0092] Based on the washing product, the boron-containing raw material can be 700 to 1200 ppm by weight, particularly 700 to 1000 ppm by weight, or 800 to 1000 ppm by weight.

[0093] When the boron content of the raw material is less than 700 ppm by weight, gelation can proceed rapidly, while when the boron content of the raw material is greater than 1200 ppm by weight, the electrochemical characteristics of the battery may deteriorate.

[0094] As described above, if the content of boron-containing raw materials is within the above range, a coating containing Li-BO solid solution is uniformly formed to have an appropriate thickness, and when the manufactured positive electrode active material is applied to the battery, the battery life characteristics can be improved.

[0095] The boron-containing raw material can be at least one selected from the group consisting of H3BO3, B2O3, B2H4O4, LiBO2, Li2B4O7, and AlBO3. The boron-containing raw material can be particularly H3BO3 or B2O3, and more particularly H3BO3. In this case, due to the low melting point of the boron-containing raw material, a uniform coating can be formed.

[0096] Step 4)

[0097] This is a step of heat-treating the mixture in step 3) at 200°C to 290°C to form a coating containing a Li-BO solid solution on the surface of a lithium transition metal oxide. The heat treatment temperature can be 220°C to 290°C, 230°C, or 290°C.

[0098] If the heat treatment temperature is less than 200°C, electrochemical properties such as charge / discharge capacity may deteriorate. If the heat treatment temperature exceeds 290°C, a large amount of Li-rich LBO layer may be formed, which allows gelation to proceed rapidly and may deteriorate electrochemical properties (discharge capacity, resistance, etc.).

[0099] Heat treatment can be performed in an oxygen atmosphere, a nitrogen atmosphere, or an atmospheric atmosphere. Specifically, heat treatment can be performed in an oxygen atmosphere.

[0100] Heat treatment can be carried out for 5 to 24 hours. If the heat treatment time is within this range, a suitable coating can be formed and production efficiency can be improved.

[0101] The residual lithium on the surface of the lithium transition metal oxide, whose content is controlled in step 2), reacts with the boron-containing raw material through heat treatment in step 4) and participates as a reactant in the formation of Li-BO solid solution.

[0102] <Positive electrode and lithium secondary battery>

[0103] It can provide a positive electrode and a lithium secondary battery including that positive electrode.

[0104] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing positive electrode active material.

[0105] In the positive electrode, there are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. It can be, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc. Furthermore, the positive electrode current collector typically has a thickness of 3 μm to 500 μm and may have fine irregularities formed on its surface to increase the adhesion of the positive electrode active material. For example, it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0106] In addition, the positive electrode active material layer may include conductive materials and adhesives together with the aforementioned positive electrode active material.

[0107] Here, the conductive material is used to impart conductivity to the electrode and can be any material without particular limitations, as long as it is conductive without causing chemical changes in the battery to be configured. Specific examples may include graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, and carbon fibers; powders or fibers of metals (e.g., copper, nickel, aluminum, silver, etc.); conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one or a mixture of two or more of them may be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can typically be from 1% to 30% by weight.

[0108] In addition, adhesives are used to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, 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, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the adhesive content can be from 1% by weight to 30% by weight.

[0109] In addition to using the aforementioned positive electrode active material, the positive electrode can be manufactured according to conventional positive electrode manufacturing methods. Specifically, it can be manufactured by applying a positive electrode active material layer forming composition to a positive electrode current collector, followed by drying and rolling, wherein the composition comprises the aforementioned positive electrode active material and optionally a binder and a conductive material. The types and amounts of the positive electrode active material, binder, and conductive material are as described above.

[0110] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, water, etc., and any one or a mixture of two or more of them can be used. Considering the application thickness and manufacturing yield of the slurry, the solvent can be used in an amount sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and it allows the slurry to have a viscosity that exhibits excellent thickness uniformity when applied for subsequent positive electrode production.

[0111] Alternatively, a positive electrode can be manufactured by casting a composition for forming a positive electrode active material layer onto a separate support, peeling the film off the support, and then pressing the film onto a positive electrode current collector.

[0112] Furthermore, the present invention can also provide an electrochemical device including a positive electrode. The electrochemical device can be, in particular, a battery, a capacitor, etc., and more particularly, a lithium secondary battery.

[0113] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode placed opposite the positive electrode, and a separator and an electrolyte disposed between the positive and negative electrodes, wherein the positive electrode is as described above. Additionally, the lithium secondary battery may optionally include a battery container for housing an electrode assembly formed by the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0114] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector.

[0115] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity without causing chemical changes in the battery. It can be, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or copper or stainless steel, aluminum-cadmium alloys, etc., surface-treated with carbon, nickel, titanium, silver, etc. Furthermore, the negative electrode current collector typically has a thickness from 3 μm to 500 μm, and like the positive electrode current collector, it can have fine irregularities formed on its surface to increase the adhesion of the negative electrode active material. For example, it can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, nonwoven fabrics, etc.

[0116] The negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material. For example, the negative electrode active material layer can be manufactured by applying a negative electrode forming composition comprising the negative electrode active material and optionally a binder and a conductive material onto a negative electrode current collector and drying it. Alternatively, the negative electrode forming composition can be cast onto a separate support, the film can be peeled off from the support, and then the film can be laminated onto the negative electrode current collector to manufacture the negative electrode active material layer.

[0117] As anode active materials, compounds capable of reversibly inserting and de-intercalating lithium can be used. Specific examples include carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic compounds that can form alloys with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of doping and de-doping lithium, such as SiO₂. β(0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composite materials including 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 them can be used. Furthermore, lithium metal films can also be used as negative electrode active materials. Additionally, as carbon materials, all types of carbon can be low-crystallinity carbon, high-crystallinity carbon, etc. Representative examples of low-crystallinity carbon can include soft carbon and hard carbon, and representative examples of high-crystallinity carbon can include amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon, such as coke derived from petroleum or coal tar pitch.

[0118] In addition, the adhesive and conductive materials can be the same as those described above in the positive electrode section.

[0119] Meanwhile, in lithium-ion secondary batteries, the separator is used to separate the negative and positive electrodes and provide a channel for lithium-ion movement. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium-ion secondary batteries. In particular, separators with excellent water retention capacity for the electrolyte and low resistance to electrolyte ion migration are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made of polyolefin-based polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or laminated structures with two or more layers. Alternatively, conventional porous nonwoven fabrics can also be used, such as nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, to ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymer materials can be used, and can optionally be used in single-layer or multi-layer structures.

[0120] Furthermore, the electrolyte used in this invention can be an organic liquid electrolyte, inorganic liquid electrolyte, solid polymer electrolyte, gel polymer electrolyte, solid inorganic electrolyte, molten inorganic electrolyte, etc., which can be used to prepare lithium secondary batteries, but is not limited to these.

[0121] Specifically, electrolytes may include organic solvents and lithium salts.

[0122] As an organic solvent, any solvent can be used without particular limitation, as long as it can serve as a medium through which ions involved in the electrochemical reactions of the battery can move. Specifically, the organic solvent can be an ester solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether solvent, such as dibutyl ether or tetrahydrofuran; a ketone solvent, such as cyclohexanone; an aromatic solvent, such as benzene or fluorobenzene; a carbonate solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); an alcohol solvent, such as ethanol or isopropanol; a nitrile, such as R-CN (where R is a straight-chain, branched, or cyclic C2-C20 hydrocarbon group, and may include double-bonded aromatic rings or ether bonds); an amide, such as dimethylformamide; a dioxolane, such as 1,3-dioxolane; or sulfolane. Carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate, propylene carbonate, etc.) with high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) are even more preferred. In this case, excellent electrolyte performance can be obtained by mixing cyclic carbonates and linear carbonates in a volume ratio of about 1:1 to about 1:9.

[0123] Lithium salts can be any compound without particular limitation, as long as they can provide lithium ions for lithium secondary batteries. Specifically, lithium salts can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. Lithium salts are preferably used at concentrations from 0.1 M to 2.0 M. When the concentration of the lithium salt is within this range, the electrolyte exhibits suitable conductivity and viscosity, thereby demonstrating excellent electrolyte performance, and lithium ions can move efficiently.

[0124] To improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, in addition to the electrolyte components mentioned above, the electrolyte may also include one or more additives, such as alkylene carbonate halogenated compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphotriamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the content of additives may be from 0.1% by weight to 5% by weight, based on the total weight of the electrolyte.

[0125] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention stably exhibit excellent discharge capacity, output characteristics and capacity retention, and therefore can be used in the fields of portable devices (e.g., mobile phones, laptops, digital cameras) and electric vehicles (e.g., hybrid electric vehicles (HEVs)).

[0126] Therefore, the present invention can provide a battery module including a lithium secondary battery as a unit battery and a battery pack including the battery module.

[0127] The battery module or battery pack can be used as a power source for any one or more of the following medium and large-sized devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0128] Example

[0129] The invention will be described in more detail below by way of examples. However, the following examples are intended to illustrate the invention, and the scope of the invention is not limited thereto.

[0130] Preparation Example

[0131] Preparation Example 1

[0132] Transition metal hydroxides (composition: Ni) 0.96 Co 0.02 Mn 0.02 (OH)2) and LiOH are mixed in a ratio of 1:1.04, and then aluminum hydroxide (Al(OH)3) is further mixed in at a concentration of 3 mol% based on transition metal hydroxide, so that the final composition of the positive electrode active material is LiNi 0.93 Co 0.02 Mn 0.02 Al 0.03 O2 was used, and the mixture was calcined at 720°C for 12 hours under an oxidizing atmosphere to prepare the calcined product. The residual lithium content in the calcined product was 1.4% by weight.

[0133] Example

[0134] Example 1

[0135] 100 g of the calcined product with 1.4 wt% residual lithium prepared in Preparation Example 1 was mixed with 40 g of distilled water and stirred for 5 minutes to prepare a washed product with 0.7 wt% residual lithium (composition: LiNi). 0.93 Co 0.02 Mn 0.02 Al 0.03 O2). The prepared washing product was mixed with 900 ppm of boron-containing raw material by weight and heat-treated at 255°C to produce a positive electrode active material with a coating containing Li-BO solid solution formed on the surface.

[0136] Example 2

[0137] 100 g of the calcined product with 1.4 wt% residual lithium prepared in Preparation Example 1 was mixed with 40 g of distilled water and stirred for 5 minutes to prepare a washed product with 0.7 wt% residual lithium (composition: LiNi). 0.93 Co 0.02 Mn 0.02 Al 0.03 O2). The prepared washing product was mixed with 900 ppm of boron-containing raw material by weight and heat-treated at 265°C to produce a positive electrode active material with a coating containing a Li-BO solid solution formed on the surface.

[0138] Example 3

[0139] 100 g of the calcined product with 1.4 wt% residual lithium prepared in Preparation Example 1 was mixed with 40 g of distilled water and stirred for 5 minutes to prepare a washed product with 0.7 wt% residual lithium (composition: LiNi). 0.93 Co 0.02 Mn 0.02 Al 0.03 O2). The prepared washing product was mixed with 900 ppm of boron-containing raw material by weight and heat-treated at 275°C to produce a positive electrode active material with a coating containing Li-BO solid solution formed on the surface.

[0140] Example 4

[0141] 100 g of the calcined product with 1.4 wt% residual lithium prepared in Preparation Example 1 was mixed with 40 g of distilled water and stirred for 5 minutes to prepare a washed product with 0.7 wt% residual lithium (composition: LiNi). 0.93 Co 0.02 Mn 0.02 Al0.03 O2). The prepared washing product was mixed with 900 ppm of boron-containing raw material by weight and heat-treated at 285°C to produce a positive electrode active material with a coating containing Li-BO solid solution formed on the surface.

[0142] Comparative Example 1

[0143] 100 g of the calcined product with 1.4 wt% residual lithium prepared in Preparation Example 1 was mixed with 90 g of distilled water and stirred for 5 minutes to prepare a washed product with 0.3 wt% residual lithium (composition: LiNi). 0.93 Co 0.02 Mn 0.02 Al 0.03 The prepared washing product was mixed with 900 ppm of boron-containing raw material by weight and heat-treated at 255°C to manufacture the positive electrode active material.

[0144] Comparative Example 2

[0145] 100 g of the calcined product with 1.4 wt% residual lithium prepared in Preparation Example 1 was mixed with 20 g of distilled water and stirred for 5 minutes to prepare a washed product with 1.0 wt% residual lithium (composition: LiNi). 0.93 Co 0.02 Mn 0.02 Al 0.03 O2). The prepared washing product was mixed with 900 ppm of boron-containing raw material by weight and heat-treated at 255°C to manufacture the positive electrode active material.

[0146] Comparative Example 3

[0147] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 300 ppm by weight and heat-treated at 300°C.

[0148] Comparative Example 4

[0149] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 500 ppm by weight and heat-treated at 300°C.

[0150] Comparative Example 5

[0151] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 700 ppm by weight and heat-treated at 300°C.

[0152] Comparative Example 6

[0153] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw materials were mixed at 900 ppm by weight and heat-treated at 300°C.

[0154] Comparative Example 7

[0155] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 1100 ppm by weight and heat-treated at 295°C.

[0156] Comparative Example 8

[0157] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 700 ppm by weight and heat-treated at 255°C.

[0158] Comparative Example 9

[0159] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 700 ppm by weight and heat-treated at 275°C.

[0160] Comparative Example 10

[0161] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 700 ppm by weight and heat-treated at 295°C.

[0162] Comparative Example 11

[0163] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 700 ppm by weight and heat-treated at 315°C.

[0164] Comparative Example 12

[0165] The positive electrode active material was manufactured in the same manner as in Example 1, except that the boron-containing raw material was mixed at 700 ppm by weight and heat-treated at 335°C.

[0166] [Table 1]

[0167] Experimental Example 1

[0168] Take 5 g of each of the above-described examples and comparative examples of positive electrode active material, place it in a beaker containing 100 ml of distilled water, and stir at 300 rpm for 5 minutes to dissolve the residual lithium on the surface. Then remove the positive electrode active material from the residual lithium solution by using a filter with an average pore size of 0.5 μm to 5 μm.

[0169] The amount of lithium in the solution was measured by titrating the remaining lithium solution after removing the positive electrode active material with a 1N HCl solution.

[0170] The amount of lithium in the solution was measured using an automatic titrator. The first inflection point (EP1) at which the pH changes rapidly between pH 7 and 9 and the endpoint (FP) at which the pH reaches 5 were measured, and the contents of Li₂CO₃ and LiOH were calculated using the following mathematical formula.

[0171] Li2CO3 content (%): (FP-EP1)×0.1×0.001×(Mw of Li2CO3(73.89) / 5)×100

[0172] LiOH content (%): (2×EP1-FP)×0.1×0.001×(Mw of LiOH(23.94) / 5)×100

[0173] The calculated Li2CO3 and LiOH contents were added to measure the content of lithium derivatives remaining on the final surface, and the content of lithium derivatives remaining on the surface (residual lithium) was converted into a weight based on the total weight of the positive electrode active material.

[0174] [Table 2]

[0175] As shown in Table 2 above, positive electrode active materials with a residual lithium by-product content of 0.6% by weight were manufactured in Examples 1 to 4 of the present invention, and positive electrode active materials with a residual lithium by-product content of 0.3% to 1.0% by weight were manufactured in Comparative Examples 1 and 2.

[0176] Experiment Example 2

[0177] Coin-shaped half-cells were fabricated using the positive electrode active materials of the above embodiments and comparative examples, and the initial characteristics and lifetime characteristics of each cell were evaluated.

[0178] Specifically, each positive electrode active material, carbon black conductive material, and PVDF binder are mixed in NMP solvent at a weight ratio of 97.5:1.0:1.5 to prepare a positive electrode slurry. The positive electrode slurry is applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to prepare the positive electrode. Simultaneously, a Li metal disk is used as the negative electrode active material. A separator is inserted between the prepared positive and negative electrodes to fabricate an electrode assembly located within the battery casing. Subsequently, an electrolyte is injected into the casing to fabricate a coin-shaped half-cell. In this case, an electrolyte containing 1 M LiPF6 dissolved in an organic solvent with EC / EMC / DEC (3 / 3 / 4, vol%) is injected as the electrolyte to fabricate the battery.

[0179] Each lithium secondary battery manufactured above was charged to 4.25 V at a constant current of 0.2 C and cut off at 0.05 C at room temperature. It was then discharged to 2.5 V at a constant current of 0.2 C, and the initial discharge capacity and initial resistance were calculated.

[0180] Subsequently, it was charged to 4.25 V at a constant current of 0.3 C, cut off at 0.005 C at 45°C, and then discharged to 2.5 V at a constant current of 0.3 C. This cycle was repeated 30 times. In this case, the rate of increase in resistance was calculated as the percentage increase in resistance in the 30th cycle relative to the 1st cycle.

[0181] [Table 3]

[0182] As shown in Table 3 above, it can be confirmed that the characteristics of the secondary battery in the battery using the positive electrode active material of the example are improved.

[0183] On the other hand, it can be seen that in Comparative Example 1, the residual lithium was too low, resulting in a large increase in resistance, while in Comparative Example 2, the residual lithium was excessive, resulting in a small capacity and a large resistance. Furthermore, in the cases of Comparative Examples 3 to 12, it can be confirmed that there are problems such as low initial discharge capacity, high initial resistance, or low resistance increase rate.

[0184] Experimental Example 3

[0185] The LBO layer was analyzed using ToF-SIM and XPS, and the molar ratio of LiB2O3 to LiBO3 in the coating (LiB2O3 / LiBO3) and the content of B3O5 relative to all ionic materials were calculated.

[0186] The IonTOF (Germany) ToF-SIMS5 was used as the ToF-SIM device, and the analysis was performed under the following conditions: Negative mode: 1) Primary ion: Bi3+ 30keV 2) X-ray spot size: 400 μm 3) Raster size: 500×500 4) Cycle time: 100 μs 5) Scans: 10 times [Table 4]

[0187] As shown in Table 4 above, in Comparative Examples 3 to 7 and 10 to 12 where the heat treatment temperature was too high and in Comparative Examples 8 and 9 where the amount of boron-containing raw material used was too low, the positive electrode active materials manufactured did not meet the LiB2O3 / LiBO3 and B3O5 content as defined in this invention.

[0188] Experiment Example 4

[0189] The viscosity of the prepared cathode slurry was measured using a Brookfield viscometer at 25°C, SC4-25, 26 rpm, and 16 rpm. Since 30,000 cp is the measurement limit under these conditions, it was set as the measurement stop point.

[0190] [Table 5]

[0191] As shown in Table 5 above, in Example 1 where the LiB2O3 / LiBO3 value is as high as 1.6 or above, it was confirmed that the increase in slurry viscosity was reduced compared to the comparative example.

[0192] In summary, it can be seen that the positive electrode active material of the present invention has a high nickel content while suppressing gelation, and therefore can be easily applied to lithium secondary batteries, and can also improve the life characteristics and electrochemical properties of lithium secondary batteries.

Claims

1. A positive electrode active material, comprising: Lithium transition metal oxides; and A coating located on the surface of the lithium transition metal oxide and comprising a Li-BO solid solution. The positive electrode active material has a residual lithium by-product content of 0.3% to 1.0% by weight. The molar ratio of LiB2O3 to LiBO3 in the coating (LiB2O3 / LiBO3) is 1.6 or higher, and The B3O5 content in the coating is less than 19 mol% relative to the total ionic material.

2. The positive electrode active material as described in claim 1, wherein, The lithium transition metal oxide is represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x [Ni a Co b Mr c M d ]O 2-y in: -0.1 <x<0.2,0.5<a<1,0<b<0.4,0<c<0.3,0<d<0.05,a+b+c+d=1,0≤y≤0.1, M is at least one element selected from the group consisting of Al, Mg, V, Ti, and Zr.

3. The positive electrode active material as described in claim 1, wherein, The LiBO3 content in the coating is 3 mol% to 10 mol% relative to the total ionic material.

4. The positive electrode active material as described in claim 1, wherein, The LiB2O3 in the coating is 3 mol% to 25 mol% relative to all ionic materials.

5. The positive electrode active material as described in claim 1, wherein, The thickness of the coating containing the Li-BO solid solution is 5 nm to 10 nm.

6. A method for manufacturing a positive electrode active material, the method comprising the following steps: 1) Mix and calcine a positive electrode active material precursor containing transition metal hydroxide and lithium-containing raw material to produce a calcined product containing lithium transition metal oxide; 2) Wash the calcined product to produce a wash product having a residual lithium content of 0.3% to 0.9% by weight on the surface of the lithium transition metal oxide; 3) A mixture is prepared by mixing the washing product and the boron-containing raw material; and 4) The mixture in step 3) is heat-treated at 200°C to 290°C to form a coating containing a Li-BO solid solution on the surface of the lithium transition metal oxide. Based on the washing product, the amount of the boron-containing raw material used is 700 ppm to 1200 ppm by weight.

7. The method for manufacturing the positive electrode active material as described in claim 6, wherein, The washing is performed by adding 30 to 150 parts by weight of a washing solution based on 100 parts by weight of the calcined product.

8. The method for manufacturing the positive electrode active material as described in claim 6, wherein, The residual lithium is at least one selected from the group consisting of LiOH and Li2CO3.

9. The method for manufacturing the positive electrode active material as described in claim 6, wherein, The residual lithium participates as a reactant in the formation of the Li-BO solid solution in step 4).

10. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 5.

11. A lithium secondary battery, comprising: The positive electrode, the negative electrode, and the membrane and electrolyte disposed between the positive electrode and the negative electrode as claimed in claim 10.

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