Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Abstract

The present invention relates to a cathode active material and a manufacturing method thereof. The manufacturing method of the cathode active material of the present invention includes the steps of mixing a transition metal precursor and a lithium source material, and primarily firing the mixture to manufacture a lithium nickel-based oxide in a single particle or similar single particle form, secondary firing the lithium nickel-based oxide in the single particle or similar single particle form, and mixing the secondary fired lithium nickel-based oxide with a boron source material, followed by heat treatment to form a coating layer.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0121308 filed on September 10, 2021, and all the contents disclosed in the literature of the Korean Patent Application are incorporated herein by reference as part of this specification.

[0002] The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery, and more particularly, to a positive electrode active material in the form of single particles and / or quasi-single particles, a positive electrode including the same, and a lithium secondary battery.

Background Art

[0003] A lithium secondary battery generally includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode include active materials capable of intercalation and deintercalation of lithium ions.

[0004] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMnO4), lithium iron phosphate compound (LiFePO4), etc. have been used. Among these, lithium cobalt oxide has the advantages of a high operating voltage and excellent capacity characteristics, but the price of cobalt as a raw material is high, the supply is unstable, and it is difficult to apply commercially to large-capacity batteries. Lithium nickel oxide has poor structural stability and it is difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide is excellent in stability but has a problem of inferior capacity characteristics. Therefore, in order to complement the problems of lithium transition metal oxides containing Ni, Co, or Mn alone, lithium composite transition metal oxides containing two or more transition metals have been developed. Among them, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the battery field of electric vehicles.

[0005] Conventional lithium nickel cobalt manganese oxide typically consists of spherical secondary particles formed by the aggregation of tens to hundreds of primary particles. However, in the case of lithium nickel cobalt manganese oxide with such a secondary particle form, particle cracking occurs during the rolling process in the manufacturing of the positive electrode, causing primary particles to detach, and cracks to develop inside the particles during the charge-discharge process. When particle cracking or cracking occurs in the positive electrode active material, the contact area with the electrolyte increases, leading to increased gas generation due to side reactions with the electrolyte and increased degradation of the active material, resulting in a decrease in lifespan characteristics.

[0006] Furthermore, recently, there has been an increasing demand for high-power, high-capacity batteries, such as those for electric vehicles, and consequently, the nickel content in the positive electrode active material tends to increase. When the nickel content in the positive electrode active material increases, the initial capacity characteristics improve, but with repeated charging and discharging, the highly reactive nickel... +4 A large amount of ions are generated, causing structural breakdown of the positive electrode active material. This increases the degradation rate of the positive electrode active material, reducing its lifespan and thus compromising battery safety.

[0007] To address the above issues, a technique has been proposed to produce cathode active material in single-particle form rather than secondary particle form by increasing the calcination temperature during the manufacturing of lithium nickel cobalt manganese oxide. In the case of single-particle cathode active material, the contact area with the electrolyte is smaller compared to conventional secondary-particle cathode active material, resulting in fewer side reactions with the electrolyte, superior particle strength, and less particle cracking during electrode manufacturing. Therefore, applying single-particle cathode active material has the advantage of less gas generation and superior lifespan characteristics.

[0008] However, conventional single-particle positive electrode active materials have problems with high initial resistance due to poor lithium mobility because there are few interfaces between primary particles that serve as pathways for lithium ion movement within the particle, and a large amount of lithium by-products due to the relatively high firing temperature during manufacturing. To improve this, a method has been proposed in which a boron coating is formed on the surface of the positive electrode active material to remove lithium by-products and prevent contact with the electrolyte. However, when a boron coating layer is formed on a single-particle positive electrode active material, there is a problem that the initial resistance, in particular the discharge end resistance, increases significantly. [Overview of the project] [Problems that the invention aims to solve]

[0009] The present invention aims to solve the above-mentioned problems and to provide a method for producing a single-particle or quasi-single-particle positive electrode active material that can suppress the increase in initial resistance, effectively remove lithium by-products, and have excellent initial capacity and high-temperature lifetime characteristics, as well as a positive electrode active material produced thereby. [Means for solving the problem]

[0010] According to one example, the present invention provides a method for producing a positive electrode active material, comprising the steps of: mixing a transition metal precursor and a lithium raw material, and performing primary calcination at a temperature of 800°C to 1000°C to produce a lithium nickel-based oxide having at least one form among single particles and quasi-single particles; performing secondary calcination of the lithium nickel-based oxide at a temperature of 600°C to 800°C; and mixing the secondary calcined lithium nickel-based oxide with a boron raw material, followed by heat treatment to form a coating layer.

[0011] According to other examples, the present invention is A lithium nickel-based oxide having a composition represented by the following Chemical Formula 1 and having at least one of a single particle form and a quasi-single particle form, and a coating layer containing boron (B) formed on the surface of the lithium nickel-based oxide are provided, and a positive electrode active material containing a spinel-like phase on the surface of the lithium nickel-based oxide. [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O2 In Chemical Formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 is Zr, W, Ti, Mg, Ca, Sr, and Ba, and 0.8 ≦ a ≦ 1.2, 0.83 ≦ b < 1, 0 < c < 0.17, 0 < d < 0.17, 0 ≦ e ≦ 0.1.

[0012] According to still another embodiment, the present invention provides a positive electrode including a positive electrode active material layer including the positive electrode active material according to the present invention and a lithium secondary battery including the same.

Advantages of the Invention

[0013] The method for manufacturing a positive electrode active material according to the present invention is characterized in that after manufacturing a lithium nickel-based oxide having a single particle and / or quasi-single particle form, it is fired at a high temperature and then a boron coating layer is formed. When, as in the present invention, high-temperature firing is performed to form a boron coating layer, the surface structure of the lithium nickel-based oxide is improved by the high-temperature firing, and an increase in resistance after the formation of the coating layer can be suppressed, and residual lithium on the surface of the lithium nickel-based oxide is removed while reacting with boron during the formation of the coating layer, and the residual lithium can be effectively removed.

[0014] Conventionally, coating layers were typically manufactured by adding a boron source to single-particle lithium nickel oxide and then heat-treating it. While this conventional method removes residual lithium during the production of the boron coating layer, it has the problem of increasing resistance due to the formation of an electrically inert rock-salt phase on the surface of the single particles during the heat treatment process for coating layer formation. In the case of single-particle lithium nickel oxide, the resistance characteristics are inferior to those of secondary-particle lithium nickel oxide, so if further resistance increases occur during coating layer formation, the output characteristics deteriorate significantly, making it difficult to use. In particular, when forming the coating layer using the conventional method, the resistance increases sharply in the low SOC region, making it difficult to apply to electric vehicle batteries that require high output in the low SOC region.

[0015] However, as in the present invention, when high-temperature firing is performed before the formation of the coating layer, a spinel-like structure is formed on the surface of the single particles and / or similar single particles, and this spinel-like structure is maintained even after the formation of the coating layer, preventing the formation of a rock salt phase. Therefore, the increase in resistance (hereinafter referred to as discharge end resistance) in the low SOC region (for example, the region with an SOC of 10% or less) can be minimized.

[0016] Furthermore, according to the manufacturing method of the present invention, residual lithium can be effectively removed without performing a water washing step. In the case of high-nickel cathode materials with a high nickel content of 80 mol% or more, an excess amount of lithium by-products is generated during the manufacturing process, and when such lithium by-products are present, there is a problem that the electrolyte and lithium by-products react and generate gas. Therefore, conventionally, it has been common to remove the lithium by-products of high-nickel cathode materials by performing a water washing step before use. However, in the case of lithium nickel-based oxides in single-particle or quasi-single-particle form, unlike lithium nickel-based oxides in secondary-particle form, performing a water washing step causes a significant increase in initial resistance and a decrease in output characteristics. However, as in the present invention, by forming a boron coating layer after high-temperature firing, it is possible to manufacture cathode active materials with a low amount of residual lithium without performing a water washing step that causes an increase in resistance.

[0017] Furthermore, the positive electrode active material according to the present invention contains lithium nickel-based oxide in single-particle and / or quasi-single-particle form with high particle strength. As a result, during electrode manufacturing and charging / discharging, particle cracking is reduced, the amount of residual lithium is reduced, and the occurrence of side reactions with the electrolyte is suppressed. Therefore, when applied to secondary batteries, the amount of gas generated is reduced, and high-temperature life characteristics are excellent.

[0018] Furthermore, the positive electrode active material according to the present invention, even after the formation of the coating layer, contains a spinel-like structure on the surface of the lithium nickel-based oxide, resulting in minimal resistance increase even at low SOC and high-temperature charge / discharge conditions, and enabling the realization of excellent output characteristics.

[0019] Furthermore, as in the present invention, when a boron coating layer is formed on a lithium nickel-based oxide in single-particle and / or quasi-single-particle form, superior initial capacity characteristics can be achieved compared to a positive electrode active material without a coating layer. [Brief explanation of the drawing]

[0020] [Figure 1] This is a photograph showing the TEM analysis results of the surface and interior of the positive electrode active material produced by the example. [Figure 2] This is a photograph showing the TEM analysis results of the surface and interior of the positive electrode active material produced by Comparative Example 1. [Figure 3] This is a photograph showing the TEM analysis results of the surface and interior of the positive electrode active material produced by Comparative Example 2. [Figure 4] This is a photograph showing the TEM analysis results of the surface and interior of the positive electrode active material produced by Comparative Example 3. [Figure 5] This graph shows the resistance characteristics of secondary batteries using the positive electrode active materials produced by Example and Comparative Example 2, as they vary in their State of Charge (SOC). [Figure 6] This graph shows the high-temperature life characteristics of secondary batteries using the positive electrode active materials produced according to Examples and Comparative Examples 1-3. [Modes for carrying out the invention]

[0021] The present invention will be described in more detail below.

[0022] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0023] In this invention, "single particle" refers to a particle consisting of a single nodule. In this invention, "nodule" refers to a particle unit that constitutes a single particle or a quasi-single particle, and the nodule can be a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which no grain boundaries are visible when observed with a scanning electron microscope (SEM) at a field of view of 5000x to 20000x. In this invention, "quasi-single particle" refers to a particle that is a composite formed of 30 or fewer nodules.

[0024] In this invention, "secondary particle" refers to a particle formed by the aggregation of several tens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of 50 or more primary particles.

[0025] As used in this invention, the term "particle" may include one or all of the following: single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0026] In this invention, "average particle size D 50 " refers to the particle size at the 50% reference level of the volume-cumulative particle size distribution of the positive electrode active material powder. When the lithium nickel oxide is a secondary particle, the average particle size refers to the average particle size of the secondary particles, and when the lithium nickel oxide is a mixture of single particles and quasi-single particles, the average particle size refers to the average particle size of the particles in these combinations. The average particle size D 50 This can be measured using the laser diffraction method. For example, after dispersing the coating precursor or cathode active material powder in a dispersion medium, the material is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves at approximately 28 kHz are irradiated at an output of 60 W. After obtaining a volume-cumulative particle size distribution graph, the particle size corresponding to 50% of the volume-cumulative amount is determined.

[0027] Method for manufacturing positive electrode active material First, the method for producing the positive electrode active material according to the present invention will be described.

[0028] The method for producing a positive electrode active material according to the present invention includes the steps of: (1) mixing a transition metal precursor and a lithium raw material and performing primary calcination at a temperature of 800°C to 1000°C to produce a lithium nickel-based oxide having at least one form of single particles and quasi-single particles; (2) performing secondary calcination of the lithium nickel-based oxide at a temperature of 600°C to 800°C; and (3) mixing the secondary calcined lithium nickel-based oxide with a boron raw material and then heat-treating it to form a coating layer.

[0029] (1) Manufacturing steps for lithium nickel oxide First, a transition metal precursor and a lithium raw material are mixed and subjected to primary calcination to produce lithium nickel-based oxide in single-particle and / or similar single-particle form.

[0030] Here, the transition metal precursor may be purchased and used from a commercially available nickel-cobalt-manganese hydroxide or other precursor, or it may be produced by a precursor manufacturing method well known in the art.

[0031] Preferably, the transition metal precursor used in the present invention may be a transition metal hydroxide containing nickel and cobalt, with a Ni content of 80 mol% or more of the total transition metal, and more preferably, a nickel-cobalt-manganese hydroxide with a Ni content of 80 mol% or more. When the nickel content in the transition metal precursor satisfies the above range, high capacity characteristics can be achieved.

[0032] Specifically, the transition metal precursor may have a composition represented by the following [Chemical Formula 2].

[0033] [Chemical formula 2] Ni x Co y M 1 z M 2 w (OH)2

[0034] In the above chemical formula 2, M 1is Mn, Al, or a combination thereof, preferably Mn or a combination of Mn and Al.

[0035] Said M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof.

[0036] Said x represents the molar ratio of nickel among all the metals in the precursor, and can be 0.8 ≤ x < 1, 0.82 ≤ x < 1, or 0.83 ≤ x < 1. When the molar ratio of nickel satisfies the above range, it exhibits a high energy density and enables the realization of a high capacity.

[0037] Said y represents the cobalt molar ratio among all the metals in the precursor, and can be 0 < y < 0.2, 0 < y < 0.18, or 0.01 ≤ y ≤ 0.17. When the cobalt molar ratio satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0038] Said z represents the molar ratio of the M 1 element among all the metals in the precursor, and can be 0 < z < 0.2, 0 < z < 0.18, or 0.01 ≤ z ≤ 0.17. When the molar ratio of the M 1 element satisfies the above range, the cathode active material exhibits excellent structural stability.

[0039] Said w represents the molar ratio of the M 2 element among all the metals in the precursor, and can be 0 ≤ w ≤ 0.1 or 0 ≤ w ≤ 0.05.

[0040] For example, the transition metal precursor can be produced by introducing a transition metal aqueous solution, forming an ammonium cation complex, and reacting a basic compound into a reactor and performing a coprecipitation reaction while stirring.

[0041] The transition metal aqueous solution can be produced by dissolving a transition metal-containing raw material in a solvent such as water. For example, it can be produced by dissolving a nickel-containing raw material or a cobalt-containing raw material in water. Furthermore, if necessary, the transition metal aqueous solution can be M 1 Raw materials and / or M 2 It may further contain metal-containing raw materials.

[0042] On the other hand, the transition metal-containing raw material can be an acetate, carbonate, nitrate, sulfate, halide, sulfide, or oxide of the transition metal.

[0043] Specifically, the nickel-containing raw material can be, for example, NiO, NiCO3·2Ni(OH)2·4H2O, NiC2O2·2H2O, Ni(NO3)2·6H2O, NiSO4, NiSO4·6H2O, nickel halides, or combinations thereof.

[0044] The cobalt-containing raw material can be, for example, CoSO4, Co(OCOCH3)2·4H2O, Co(NO3)2·6H2O, CoSO4·7H2O, or a combination thereof.

[0045] Said M 1 The included raw materials may be manganese-containing raw materials and / or aluminum-containing raw materials. The manganese-containing raw materials may be, for example, Mn2O3, MnO2, Mn3O4, MnCO3, Mn(NO3)2, MnSO4·H2O, manganese acetate, manganese halides, or combinations thereof, and the aluminum-containing raw materials may be, for example, Al2O3, Al(OH)3, Al(NO3)3, Al2(SO4)3, (HO)2AlCH3CO2, HOAl(CH3CO2)2, Al(CH3CO2)3, aluminum halides, or combinations thereof. However, in the case of Al, it may not be added to the transition metal aqueous solution but may be added together with the lithium raw material in the calcination step described later.

[0046] M 2The raw materials contained are M 2 These can be metal acetates, carbonates, nitrates, sulfates, halides, sulfides, or oxides.

[0047] The amount of each transition metal-containing raw material to be added can be determined by considering the molar ratio of the transition metal in the cathode active material that is ultimately to be produced.

[0048] On the other hand, the ammonium cation complex-forming agent may contain at least one compound selected from the group consisting of NH4OH, (NH4)2SO4, NH4NO3, NH4Cl, CH3COONH4, and (NH4)2CO3, and the compound may be introduced into the reactor in the form of a solution in which it is dissolved in a solvent. Here, the solvent may be water, or a mixture of water and an organic solvent that can be homogeneously mixed with water (specifically, an alcohol, etc.).

[0049] The basic compound can be at least one compound selected from the group consisting of NaOH, KOH, and Ca(OH)2, and the compound can be introduced into the reactor in the form of a solution in which it is dissolved in a solvent. Here, the solvent can be water, or a mixture of water and an organic solvent that is homogeneously miscible with water (specifically, an alcohol, etc.).

[0050] As described above, when an aqueous transition metal solution, an ammonium cation complex-forming agent, and a basic compound are added to the reactor and stirred, the transition metal in the aqueous transition metal solution coprecipitates, generating precursor particles in the form of transition metal hydroxides.

[0051] Here, the transition metal aqueous solution, ammonium cation complex-forming agent, and basic compound are added in amounts such that the pH of the reaction solution falls within the desired range.

[0052] Once the precursor particles are formed by the method described above, the particles are separated from the reaction solution to obtain the transition metal precursor. For example, the reaction solution can be filtered to separate the transition metal precursor, and then the separated transition metal precursor can be washed with water and dried to obtain the transition metal precursor. Here, if necessary, steps such as grinding and / or classification can also be performed.

[0053] Next, the transition metal precursor and the lithium raw material are mixed and then subjected to primary calcination to produce lithium nickel-based oxide in the form of single particles and / or similar single particles. Here, if necessary, M 1 Contains raw materials and / or M 2 The raw materials can be mixed together and fired, M 1 Contains raw materials and / or M 2 Specific examples of the raw materials contained are as described above.

[0054] As the lithium raw material, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides can be used, for example, LI2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof can be used.

[0055] On the other hand, the lithium raw material and the positive electrode active material precursor can be mixed such that the molar ratio of Li to the total metal in the precursor is 1:1 to 1.1:1, preferably 1.02:1 to 1.05:1. When the mixing ratio of the lithium raw material and the metal in the positive electrode active material precursor satisfies the above range, the layered crystal structure of the positive electrode active material develops well, and a positive electrode active material with excellent capacity characteristics and structural stability can be produced.

[0056] On the other hand, the firing is carried out at a temperature capable of forming single particles and / or quasi-single particles. In order to form single particles and / or quasi-single particles, firing must be carried out at a higher temperature than that used when conventional secondary particle form lithium nickel oxides are manufactured. For example, if the precursor composition is the same, firing must be carried out at a temperature approximately 30°C to 100°C higher than that used when conventional secondary particle form lithium nickel oxides are manufactured. The firing temperature for forming single particles and / or quasi-single particles can be varied depending on the metal composition in the precursor. For example, when attempting to form high-nickel (High-Ni) lithium nickel oxide, which has a nickel (Ni) content of 80 mol% or more, as single particles or quasi-single particles, the primary firing temperature can be approximately 800°C to 1000°C, preferably 800°C to 950°C, and more preferably 850°C to 950°C. When the primary firing temperature satisfies the above range, lithium nickel oxides in single particle and / or quasi-single particle form with excellent electrochemical properties can be manufactured. If the primary firing temperature is below 800°C, a positive electrode active material in the form of secondary particles is produced. If it exceeds 1000°C, excessive firing occurs, preventing sufficient formation of a layered crystalline structure and resulting in reduced electrochemical properties.

[0057] Furthermore, the primary calcination can be carried out in an oxygen atmosphere for 6 to 35 hours, preferably 6 to 20 hours, and more preferably 6 to 12 hours. In this specification, an oxygen atmosphere means an atmosphere containing an amount of oxygen sufficient for calcination, including an atmospheric atmosphere. In particular, it is preferable to carry out the calcination in an atmosphere where the partial pressure of oxygen is higher than that of an atmospheric atmosphere. When the primary calcination time satisfies the above range, lithium nickel oxide in the form of single particles and / or quasi-single particles can be formed. If the primary calcination time is excessively short, particle growth is insufficient and lithium nickel oxide in the form of secondary particles is formed, and if it is excessively long, a rock salt phase may occur and the electrochemical properties of the active material may deteriorate.

[0058] The lithium nickel oxide produced by the primary calcination described above may have the following forms: single particles consisting of one nodule, quasi-single particles which are composites of 30 or fewer nodules, preferably 2 to 20, more preferably 2 to 10, or mixtures thereof.

[0059] Furthermore, the lithium nickel oxide may have a composition in which the nickel content of the total metals other than lithium is 80 mol% or more, preferably 82 mol% or more, and more preferably 83 mol% or more. Specifically, it may be a lithium nickel cobalt manganese oxide in which the nickel content of the total metals other than lithium is 80 mol% or more, preferably 82 mol% or more, and more preferably 83 mol% or more. When the nickel content in the lithium nickel oxide satisfies the above range, a high energy density can be achieved.

[0060] More specifically, the lithium nickel oxide may have a composition represented by the following [Chemical Formula 1].

[0061] [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2

[0062] In the above chemical formula 1, M 1 This can be Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

[0063] Said M 2 This is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2The element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0064] The a represents the molar ratio of lithium in the lithium nickel-based oxide, and can be 0.8 ≦ a ≦ 1.2, 0.85 ≦ a ≦ 1.15, or 0.9 ≦ a ≦ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0065] The b represents the molar ratio of nickel among all the metals other than lithium in the lithium nickel-based oxide, and can be 0.8 ≦ b < 1, 0.82 ≦ b < 1, or 0.83 ≦ b < 1. When the molar ratio of nickel satisfies the above range, it shows a high energy density and high capacity can be realized.

[0066] The c represents the molar ratio of cobalt among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < c < 0.2, 0 < c < 0.18, or 0.01 ≦ c ≦ 0.17. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0067] The d represents the molar ratio of the M 1 element among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < d < 0.2, 0 < d < 0.18, or 0.01 ≦ d ≦ 0.17. When the molar ratio of the M 1 element satisfies the above range, the positive electrode active material shows excellent structural stability.

[0068] The e represents the molar ratio of the M 2 element among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 ≦ e ≦ 0.1, or 0 ≦ e ≦ 0.05.

[0069] On the other hand, it is preferable to perform a milling step after the primary firing step in order to remove large particles caused by entanglement and aggregation between particles and to obtain the desired average particle size.

[0070] The milling can be carried out by a common milling method well known in the art, such as a jet-mill. The milling can be carried out, for example, under conditions of a grinding pressure of 1 to 2 bar, a classifier speed of 500 to 3000 rpm, and a feed rate of 2000 to 6000 g / hr.

[0071] On the other hand, the milling is preferably carried out in an atmosphere with low moisture content, such as a dry air atmosphere. This is because exposure of lithium nickel oxide to moisture can increase the generation of lithium by-products and degrade the surface properties of the active material.

[0072] (2) Secondary firing step Next, the lithium nickel oxide in single-particle and / or quasi-single-particle form produced by the method described above is subjected to secondary calcination.

[0073] Here, the secondary firing temperature can be 600°C to 800°C, preferably around 650°C to 750°C. When the secondary firing temperature is within this range, the surface structure of the lithium nickel oxide deforms into a spinel-like structure, which can suppress the increase in resistance after the formation of the coating layer and reduce the amount of residual lithium. If the secondary firing temperature is too low, no change in the surface structure of the lithium nickel oxide occurs, and a rock salt phase may form during the formation of the coating layer. If the temperature is too high, a change in the crystal structure occurs even inside the lithium nickel oxide, and the electrochemical properties deteriorate.

[0074] Furthermore, the secondary calcination can be carried out in an oxygen atmosphere for 2 to 10 hours, preferably 4 to 6 hours. If the secondary calcination time is too short, the effect of removing lithium by-products is not sufficient, and if it is too long, excessive recrystallization may occur, potentially degrading the electrochemical properties of the positive electrode active material.

[0075] (3) Step of forming a boron coating layer Next, the lithium nickel oxide that has been secondarily calcined is mixed with the boron (B) raw material, and then heat-treated to form a coating layer.

[0076] The boron(B) raw material mentioned above may be, but is not limited to, boric acid or boron oxide.

[0077] On the other hand, the lithium nickel oxide and the boron (B) raw material can be mixed in solid phase or liquid phase. However, in the case of liquid phase mixing, the process is complex and the lithium nickel oxide may be damaged by the solvent during the coating process. Therefore, mixing by solid phase is more preferable.

[0078] Furthermore, the lithium nickel oxide and the boron (B) raw material can be mixed in a weight ratio of 100:0.05 to 100:0.3, preferably 100:0.05 to 100:0.2, and more preferably 100:0.1 to 100:0.2. When the mixing ratio of the lithium nickel oxide and the boron raw material satisfies the above range, a positive electrode active material with excellent capacitance characteristics and resistance characteristics can be produced.

[0079] On the other hand, the heat treatment is preferably carried out in a temperature range of 200°C to 500°C, more preferably 200°C to 400°C. When the heat treatment temperature during the formation of the coating layer meets the above range, the coating layer is uniformly formed on the surface of the lithium nickel oxide, and deformation of the lithium nickel oxide due to the heat treatment can be minimized.

[0080] On the other hand, it is preferable that the method for producing the positive electrode active material according to the present invention does not include a water washing step. Conventionally, when producing high-nickel (High-Ni) NCM-based lithium nickel oxides having a nickel (Ni) content of 80 mol% or more, it was common to perform a water washing step after firing in order to reduce the content of lithium by-products. However, according to the inventors' research, when a water washing step is performed when producing positive electrode active materials in single-particle or quasi-single-particle form, the surface properties of the lithium nickel oxide deteriorate during the water washing process, and the resistance increases. Therefore, in the production of the positive electrode active material according to the present invention, water washing is omitted, and the residual lithium on the surface of the lithium nickel oxide is consumed during the secondary firing and coating layer formation process, thereby improving the resistance characteristics.

[0081] positive electrode active material Next, the positive electrode active material according to the present invention will be described.

[0082] The positive electrode active material according to the present invention comprises (1) a lithium nickel-based oxide having at least one form among single particles and quasi-single particles, and (2) a coating layer formed on the surface of the lithium nickel-based oxide and containing boron (B). The positive electrode active material according to the present invention can be manufactured by the manufacturing method of the present invention described above.

[0083] (1) Lithium nickel oxide particles The lithium nickel oxide particles are single particles consisting of one nodule or quasi-single particles which are composites of 30 or fewer nodules, preferably 2 to 20, more preferably 2 to 10.

[0084] These single-particle and / or quasi-single-particle lithium nickel oxide particles have higher particle strength compared to existing secondary-particle lithium nickel oxides in which tens to hundreds of primary particles are aggregated, resulting in less particle cracking during rolling.

[0085] Furthermore, in the case of lithium nickel-based oxides in single-particle and / or quasi-single-particle form according to the present invention, the number of nodules constituting the particles is small, so there is less change due to volume expansion and contraction of the nodules during charging and discharging, which significantly reduces the occurrence of cracks inside the particles.

[0086] On the other hand, the lithium nickel oxide particles may have a composition in which the nickel content of the total metals other than lithium is 80 mol% or more, preferably 82 mol% or more, and more preferably 83 mol% or more. Specifically, they may be lithium nickel cobalt manganese oxides in which the nickel content of the total metals other than lithium is 80 mol% or more, preferably 82 mol% or more, and more preferably 83 mol% or more. When the nickel content in the lithium nickel oxide particles satisfies the above range, a high energy density can be achieved.

[0087] More specifically, the lithium nickel oxide particles may have a composition represented by the following [Chemical Formula 1].

[0088] [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2

[0089] In the above chemical formula 1, M 1 This can be Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

[0090] Said M 2 This is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2The element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0091] The above-mentioned a represents the molar ratio of lithium in the lithium nickel-based oxide, and can be 0.8 ≦ a ≦ 1.2, 0.85 ≦ a ≦ 1.15, or 0.9 ≦ a ≦ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0092] The above-mentioned b represents the molar ratio of nickel among all the metals other than lithium in the lithium nickel-based oxide, and can be 0.8 ≦ b < 1, 0.82 ≦ b < 1, or 0.83 ≦ b < 1. When the molar ratio of nickel satisfies the above range, it shows a high energy density and high capacity can be realized.

[0093] The above-mentioned c represents the cobalt molar ratio among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < c < 0.2, 0 < c < 0.18, or 0.01 ≦ c ≦ 0.17. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0094] The above-mentioned d represents the molar ratio of the M 1 element among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < d < 0.2, 0 < d < 0.18, or 0.01 ≦ d ≦ 0.17. When the molar ratio of the M 1 element satisfies the above range, the positive electrode active material shows excellent structural stability.

[0095] The above-mentioned e represents the molar ratio of the M 2 element among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 ≦ e ≦ 0.1, or 0 ≦ e ≦ 0.05.

[0096] (2) Coating layer The positive electrode active material according to the present invention comprises a boron coating layer on the surface of lithium nickel-based oxide particles in the single-particle and / or quasi-single-particle form described above.

[0097] When a boron coating layer is formed on the surface of lithium nickel oxide particles in single-particle and / or quasi-single-particle form, the boron coating layer facilitates lithium migration on the surface of the lithium nickel oxide particles, resulting in an improved initial capacity compared to cases where no coating layer is formed.

[0098] On the other hand, the boron (B) can be present in an amount of 100 ppm to 2000 ppm, preferably 300 ppm to 1500 ppm, and more preferably 500 ppm to 1000 ppm, relative to the total weight of the positive electrode active material. When the boron content satisfies the above range, an excellent capacity-increasing effect is observed.

[0099] Furthermore, the coating layer can have an average thickness of 10 nm to 300 nm, preferably 20 nm to 200 nm, and more preferably 50 nm to 100 nm. If the coating layer is excessively thick, the initial resistance may increase, and if it is excessively thin, the effect of reducing residual lithium and increasing capacity will be minimal.

[0100] On the other hand, the positive electrode active material according to the present invention contains a spinel-like phase on the surface of the lithium nickel oxide. As described above, if a high-temperature secondary firing is performed before the formation of the coating layer, the spinel-like phase is formed on the surface of the lithium nickel oxide by the secondary firing. When a spinel-like phase is formed on the surface of the lithium nickel oxide as in the present invention, the formation of a rock salt phase that causes an increase in resistance is suppressed during the formation of the coating layer, thereby minimizing the increase in resistance.

[0101] Furthermore, the positive electrode active material according to the present invention has a low amount of residual lithium because residual lithium present on the surface of the lithium nickel-based oxide is removed during the secondary firing and coating layer formation process. Specifically, the positive electrode active material according to the present invention can have a residual lithium content of 0.5% by weight or less, preferably 0.01 to 0.5% by weight, and more preferably 0.01 to 0.4% by weight. Because the residual lithium content is so low, the phenomenon of gas generation due to the reaction of residual lithium with the electrolyte during charging and discharging and / or at high temperatures can be minimized, thereby achieving excellent lifespan characteristics.

[0102] On the other hand, the positive electrode active material according to the present invention may have an average particle size of nodules of 0.5 μm to 3 μm, preferably 0.8 μm to 2.5 μm, and more preferably 0.8 μm to 1.5 μm. When the average particle size of the nodules satisfies the above range, a positive electrode active material in the form of single particles and / or quasi-single particles with excellent electrochemical properties can be formed. If the average particle size of the nodules is excessively small, the number of aggregated nodules forming lithium nickel oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size of the nodules is excessively large, the lithium diffusion path inside the nodule becomes longer, increasing resistance and potentially degrading the output characteristics.

[0103] Furthermore, the positive electrode active material has an average particle size D 50 However, it can be 2 μm to 6 μm, preferably 2 μm to 5 μm, and more preferably 3 μm to 5 μm. D of the positive electrode active material 50 If it is excessively small, it becomes difficult to form the active material layer during electrode manufacturing, the impregnation of the electrolyte decreases, and the electrochemical properties deteriorate. 50 If this value is excessively large, the resistance increases, leading to a problem of degraded output characteristics.

[0104] Furthermore, the positive electrode active material can have an average crystallite size of 150 nm to 300 nm, 200 nm to 280 nm, or 200 nm to 250 nm. When the average crystallite size satisfies the above range, the formation of the rock salt phase is reduced during the production of lithium nickel oxide, making it possible to produce a positive electrode active material in single-particle or quasi-single-particle form with excellent resistance characteristics. Generally, positive electrode active materials in single-particle or quasi-single-particle form are produced by increasing the firing temperature to increase the size of the nodule. However, if only the size of the nodule is increased while the crystallite size remains small, there is a problem in that the rock salt phase is formed on the surface of the nodule, increasing the resistance. However, when both the average crystallite size and the average grain size of the nodule are increased, the formation of the rock salt phase is minimized, and the increase in resistance is suppressed.

[0105] As described above, when the positive electrode active material of the present invention, which includes a boron coating layer on the surface of lithium nickel oxide particles in single-particle or quasi-single-particle form and has a spinel-like phase formed on the surface of the lithium nickel oxide, is applied, a secondary battery with low discharge end resistance, high initial capacity, and excellent high-temperature cycle characteristics can be realized. In particular, when the positive electrode active material of the present invention is applied, both discharge end resistance and high-temperature cycle resistance characteristics can be improved simultaneously.

[0106] Specifically, when a coin half-cell is manufactured using the positive electrode active material according to the present invention, the resistance of the coin half-cell at SOC90 (R 90 ) Resistance at SOC10 (R 10 ) ratio R 10 / R 90 The coefficient of resistance is 3 or less, preferably 1 to 3, more preferably 1.5 to 3, and the coin half cell can have a resistance increase rate of 100% or less, preferably 50 to 100%, after 50 cycles at 45°C.

[0107] Here, the coin half-cell contains a positive electrode active material:conductive material:binder in a weight ratio of 96:2:2 within the positive electrode active material layer, and uses a lithium metal electrode as the negative electrode. The electrolyte used is prepared by dissolving 1M LiPF6 in a mixed organic solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate in a volume ratio of 1:2:1, and adding 2% by weight of vinylene carbonate (VC).

[0108] Furthermore, the R 10 and R 90 The voltage was measured by applying a current of 2.5C for 10 seconds using SOC90 and SOC10 while discharging a coin half-cell once at 2.5~4.25V under 0.1C / 0.1C conditions, then charging it again to 4.25V, and discharging it 10% at a time until the cell discharge capacity was reduced to 10%, and measuring the voltage change.

[0109] Furthermore, the resistance increase rate after 50 cycles is the percentage of the resistance after 50 cycles relative to the resistance after 1 cycle, when one cycle is defined as charging and discharging the coin half-cell at 45°C with a voltage of 2.5V to 4.25V and a current of 0.1C / 0.1C.

[0110] positive electrode Next, the positive electrode according to the present invention will be described.

[0111] The positive electrode according to the present invention includes a positive electrode active material layer containing the positive electrode active material according to the present invention. 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 the positive electrode active material.

[0112] In the positive electrode, the positive electrode current collector is not particularly limited as long as it 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 with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to increase the adhesion strength of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0113] Furthermore, the positive electrode active material layer may include a conductive material and a binder in addition to the positive electrode active material described above.

[0114] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used. The conductive material can usually be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0115] The binder plays a role in improving 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 include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used. The binder may be present in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the positive electrode active material layer.

[0116] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode. For example, the positive electrode can be manufactured by mixing a positive electrode active material, a binder, and / or a conductive material in a solvent to produce a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling it.

[0117] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more can be used. The amount of solvent used should be such that it dissolves or disperses the positive electrode active material, conductive material, and binder, and has a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0118] Alternatively, the positive electrode can be manufactured by casting the positive electrode slurry onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0119] Lithium-ion battery Next, the lithium secondary battery according to the present invention will be described.

[0120] The lithium secondary battery of the present invention includes the positive electrode according to the present invention. Specifically, the lithium secondary battery includes a positive electrode, a negative electrode positioned opposite the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is as described above. The lithium secondary battery may further optionally include a battery container for housing the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0121] In the lithium secondary battery described above, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0122] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can usually have a thickness of 3 to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0123] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0124] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. β Examples include (0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides that can be doped and dedoped with lithium; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and one or more mixtures of these can be used.

[0125] Furthermore, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Typical low-crystallinity carbons include soft carbon and hard carbon, while typical high-crystallinity carbons include amorphous, plate-like, flaky, spherical or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0126] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these alone or a mixture of two or more can be used. The conductive material can usually be contained in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0127] The binder plays a role in improving adhesion between negative electrode active material particles and adhesion 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, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more can be used. The binder may be present in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, relative to the total weight of the negative electrode active material layer.

[0128] The negative electrode active material layer can also be manufactured, for example, by applying a negative electrode slurry containing a negative electrode active material and selectively a binder and conductive material onto a negative electrode current collector and drying it, or by casting the negative electrode slurry onto another support, peeling it off this support, and then laminating the resulting film onto the negative electrode current collector.

[0129] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent moisture-absorbing capacity for the electrolyte are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0130] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0131] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0132] The organic solvent can be used without particular limitations as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group, which can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0133] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, more preferably 0.1 to 3.0 M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0134] In addition to the electrolyte components, the electrolyte may further contain additives for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. For example, the additives may be, but are not limited to, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethyl alcoholamine, cyclic ether, ethylenediamine, n-glyme, hexamethyl phosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethyl alcohol, or aluminum trichloride, either alone or in combination. The additives may be present in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, relative to the total weight of the electrolyte.

[0135] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention not only has excellent initial capacity and life characteristics, but also exhibits low discharge end resistance in the low SOC range, particularly at SOC of 10% or less, making it useful in the field of electric vehicles.

[0136] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0137] Examples Transition metal precursor Ni 0.83 Co 0.11 Mn 0.06 (OH)2 and LiOH·H2O were mixed so that the weight ratio of the transition metal (Ni+Co+Mn):Li was 1:1.03, and then the mixture was pre-calcined at 900°C for 10 hours before being milled to produce a lithium nickel oxide. It was confirmed that the produced lithium nickel oxide powder contained a mixture of single particles and quasi-single particles.

[0138] The lithium nickel oxide powder produced as described above was subjected to secondary calcination at 700°C for 8 hours.

[0139] Subsequently, the secondary calcined lithium nickel oxide and boric acid were mixed in a weight ratio of 100:0.15 and heat-treated at 300°C for 5 hours to produce a positive electrode active material in which a boron coating layer was formed on the surface of the lithium nickel oxide.

[0140] Comparative Example 1 Transition metal precursor Ni 0.83 Co 0.11 Mn 0.06 (OH)2 and LiOH·H2O were mixed so that the weight ratio of the transition metal (Ni+Co+Mn):Li was 1:1.03, then calcined at 900°C for 10 hours and milled to produce lithium nickel oxide powder. It was confirmed that the lithium nickel oxide powder produced by the calcination contained a mixture of single particles and quasi-single particles. The lithium nickel oxide produced above was used as the positive electrode active material.

[0141] Comparative Example 2 Transition metal precursor Ni 0.83 Co 0.11 Mn 0.06(OH)2 and LiOH·H2O were mixed so that the weight ratio of the transition metal (Ni+Co+Mn):Li was 1:1.03, then calcined at 900°C for 10 hours and milled to produce lithium nickel oxide. It was confirmed that the lithium nickel oxide powder produced by the calcination contained a mixture of single particles and quasi-single particles.

[0142] After washing the lithium nickel oxide produced as described above with water, the lithium nickel oxide and boric acid were mixed in a weight ratio of 100:0.15, and the mixture was heat-treated at 300°C for 5 hours to produce a positive electrode active material in which a boron coating layer was formed on the surface of the lithium nickel oxide.

[0143] Comparative Example 3 Transition metal precursor Ni 0.83 Co 0.11 Mn 0.06 (OH)2 and LiOH·H2O were mixed so that the weight ratio of the transition metal (Ni+Co+Mn):Li was 1:1.03, then calcined at 900°C for 10 hours and milled to produce lithium nickel oxide. It was confirmed that the lithium nickel oxide powder produced by the calcination contained a mixture of single particles and quasi-single particles.

[0144] The lithium nickel oxide produced as described above was subjected to secondary calcination at 700°C for 8 hours to produce the positive electrode active material.

[0145] Experimental Example 1: Structural Analysis The positive electrode active material particles produced in the above examples and comparative examples 1 to 3 were analyzed using a transmission electron microscope (TEM) to confirm the surface and internal structure of the positive electrode active material particles. The measurement results are shown in Figures 1 to 4.

[0146] As shown in Figures 1 and 3, the positive electrode active material of the example and Comparative Example 3, which underwent high-temperature secondary firing, exhibits a spinel-like phase on the particle surface, whereas in Comparative Examples 1 and 2, which did not undergo high-temperature secondary firing, a rock salt phase is observed on the particle surface. Since the rock salt phase is electrically inert, its presence on the particle surface of the positive electrode active material increases resistance, thereby degrading the output characteristics.

[0147] Experimental Example 2: Measurement of Residual Lithium Content Five g of the positive electrode active material powder produced in the above examples and Comparative Examples 1-2 was dispersed in 100 mL of water, and the change in pH value was measured while titrating with 0.1 M HCl to obtain a pH titration curve. Using the pH titration curve, the amount of residual LiOH and LiCO3 in each positive electrode active material was calculated, and the sum of these values ​​was evaluated as the amount of residual lithium. The measurement results are shown in [Table 1] below.

[0148] [Table 1]

[0149] As shown in [Table 1] above, the positive electrode active material of the example produced by the method of the present invention has a significantly lower amount of residual lithium compared to the positive electrode active material of Comparative Example 1, and it can be confirmed that it has a lower level of residual lithium than Comparative Example 2, which underwent a water washing process, even though a water washing process was not performed.

[0150] <Manufacturing of secondary batteries> The positive electrode active material, conductive material (carbon black, Denka), and PVDF binder prepared in Examples and Comparative Examples 1-3 were mixed in N-methylpyrrolidone in a weight ratio of 96:2:2 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode.

[0151] A lithium metal electrode was used as the negative electrode.

[0152] After manufacturing an electrode assembly with a separator interposed between the positive and negative electrodes, the assembly was placed inside a battery case, and then an electrolyte was injected into the case to produce a coin-half cell. The electrolyte was prepared by dissolving 1M LiPF6 in a mixed organic solvent of ethylene carbonate / dimethyl carbonate / diethyl carbonate in a volume ratio of 1:2:1, and adding 2% by weight of vinylene carbonate (VC).

[0153] Experimental Example 3: Evaluation of Initial Capacity Each of the coin half-cells manufactured as described above was charged to 4.25V at 0.1C, and then discharged to 2.5V at 0.1C to measure its initial charge capacity and initial discharge capacity. The measurement results are shown in [Table 2] below.

[0154] [Table 2]

[0155] Table 2 above confirms that the initial discharge capacity of the cell to which the positive electrode active material of Example 1, manufactured by the method of the present invention, is applied is higher than that of the cells to which the positive electrode active materials of Comparative Examples 1 to 3 are applied. In particular, compared with Comparative Examples 1 and 3, which do not have a boron coating layer, it can be confirmed that the charging capacity and discharging capacity of Example 1 are significantly superior despite having the same composition.

[0156] Experimental Example 4: Evaluation of Resistivity using SOC Coin half-cells manufactured using the positive electrode active materials of Example and Comparative Example 2 were charged and discharged once at 2.5 to 4.25V under 0.1C / 0.1C conditions, then charged again to 4.25V, and the resistance (in Ω) by State of Charge (SOC) was measured while discharging the cells 10% at a time until the cell discharge capacity was reduced to 10%. Here, the resistance was measured by the change in voltage when a current of 2.5C was applied to each SOC for 10 seconds. The measurement results are shown in Figure 5 and Table 3 below.

[0157] [Table 3]

[0158] Referring to Table 3 and Figure 5, it can be confirmed that the cell using the positive electrode active material of Example 1, manufactured by the method of the present invention, exhibits superior resistance characteristics compared to the cell using the positive electrode active material of Comparative Example 2. In particular, in the case of the cell using the positive electrode active material of Comparative Example 2, in which a boron coating layer was formed without high-temperature firing, the resistance increased very rapidly as the SOC decreased.

[0159] Experimental Example 5: Measurement of High-Temperature Life Characteristics Each coin half-cell manufactured as described above was charged and discharged at 45°C at 2.5V to 4.25V and 0.1C / 0.1C for 50 charge-discharge cycles. After these cycles, the capacity retention rate and resistance increase rate were measured to evaluate the life characteristics. The measurement results are shown in Table 4 and Figure 6 below.

[0160] [Table 4]

[0161] As shown in Table 4 and Figure 6 above, it can be confirmed that cells using the positive electrode active materials of the examples manufactured by the method of the present invention exhibit superior high-temperature lifetime characteristics compared to cells using the positive electrode active materials of Comparative Examples 1 to 3.

[0162] In the case of cells using the positive electrode active materials of Comparative Examples 1 and 3, which do not have a boron coating layer, the capacity retention rate was low and a significant increase in resistance occurred. On the other hand, the positive electrode active material of Comparative Example 2, which has a boron coating layer, shows good high-temperature lifetime characteristics, but as shown in Table 3, it has the problem of a significant increase in discharge end resistance.

Claims

1. A step of mixing a transition metal precursor and a lithium raw material, and performing primary calcination at a temperature of 800°C to 1000°C to produce a lithium nickel-based oxide having at least one form of single particles and quasi-single particles, The steps include: second firing the lithium nickel oxide at a temperature of 600°C to 800°C; The step includes mixing the secondary calcined lithium nickel oxide with a boron raw material, and then heat-treating it to form a coating layer. A method for producing a positive electrode active material, wherein the average particle size of nodules, which are particle units constituting the single particles and quasi-single particles, is 0.5 μm to 3 μm, The lithium nickel oxide has a composition represented by the following [Chemical Formula 1], and the method for producing the positive electrode active material is as follows: [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O 2 In the above chemical formula 1, M1 is Mn, Al, or a combination thereof, and M2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, with 0.8 ≤ a ≤ 1.2, 0.8 ≤ b < 1, 0 < c < 0.2, 0 < d < 0.2, and 0 ≤ e ≤ 0.

1.

2. The method for producing a positive electrode active material according to claim 1, wherein the transition metal precursor is nickel-cobalt-manganese hydroxide having a Ni content of 80 mol% or more.

3. The method for producing a positive electrode active material according to claim 1, wherein the primary firing temperature is 800°C to 950°C.

4. The method for producing a positive electrode active material according to claim 1, wherein the primary calcination is carried out in an oxygen atmosphere for 6 to 35 hours.

5. The method for producing a positive electrode active material according to claim 1, wherein the secondary firing temperature is 650°C to 750°C.

6. The method for producing a positive electrode active material according to claim 1, wherein the secondary firing is carried out in an oxygen atmosphere for 2 to 10 hours.

7. The method for producing a positive electrode active material according to claim 1, wherein the heat treatment temperature is 200°C to 500°C.

8. A method for producing a positive electrode active material according to claim 1, which does not include a water washing step.

9. A lithium nickel-based oxide having the composition represented by the following chemical formula 1, and having at least one form among single particles and quasi-single particles, The lithium nickel oxide is formed on the surface of the lithium nickel oxide and includes a coating layer containing boron (B), The lithium nickel oxide surface contains a spinel-like phase, The positive electrode active material has an average particle size of 0.5 μm to 3 μm for nodules, which are particle units constituting the single particles and quasi-single particles: [Chemical formula 1] Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the chemical formula (1), M １ is Mn, Al or a combination thereof, and M ２ is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, and 0.8 ≦ a ≦ 1.2, 0.8 ≦ b < 1, 0 < c < 0.2, 0 < d < 0.2, 0 ≦ e ≦ 0.

1.

10. The positive electrode active material according to claim 9, wherein the single particle is a particle consisting of one nodule, and the quasi-single particle is a composite of 30 or fewer nodules.

11. The positive electrode active material according to claim 9, wherein the positive electrode active material has a residual lithium content of 0.5% by weight or less.

12. A coin half-cell is manufactured using the aforementioned positive electrode active material. The ratio R of the resistance at SOC10 to the resistance at SOC90 was measured while the coin half-cell was charged to 4.25V under the 0.1C / 0.1C conditions and then discharged to 2.5V. １０ / R ９０ is 3 or less, The positive electrode active material according to claim 9, wherein one cycle involves charging and discharging the coin half cell at 45°C at 2.5V to 4.25V and 0.1C / 0.1C, and after 50 charge-discharge cycles, the measured resistance increase rate is 100% or less.

13. A positive electrode comprising the positive electrode active material according to any one of claims 9 to 12.

14. A lithium secondary battery comprising the positive electrode described in claim 13.

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