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

Abstract

The positive electrode active material according to the present invention comprises lithium composite transition metal oxide particles in a single particle form consisting of one nodule or a quasi-single particle form consisting of 30 or fewer nodules, wherein the nickel content in the total metal excluding lithium is 50 mol% to 80 mol%, and a coating layer formed on the surface of the lithium composite transition metal oxide particles; and the positive electrode active material satisfies the following formula 1: [Formula 1] 1.0 ≤ P2 / P1 ≤ 4.0 In formula 1, P1 is the sum of pore volumes in the positive electrode active material where the pore diameter exceeds 40 Å, and P2 is the sum of pore volumes in the positive electrode active material where the pore diameter is 40 Å or less.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0092287 filed on July 17, 2023, Korean Patent Application No. 10 - 2023 - 0098548 filed on July 27, 2023, Korean Patent Application No. 10 - 2024 - 0094050 filed on July 16, 2024, and Korean Patent Application No. 10 - 2024 - 0094051 filed on July 16, 2024, and all of their contents are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material, a positive electrode containing the same, and a lithium secondary battery.

Background Art

[0003] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode contain 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 has excellent stability but has the problem of inferior capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to complement the problems of lithium transition metal oxides containing Ni, Co, or Mn alone. Among them, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the battery field of electric vehicles.

[0005] In the case of the positive electrode active material in single particle form, since the contact area with the electrolyte is smaller than that of the conventional secondary particle form positive electrode active material, there are fewer side reactions with the electrolyte, excellent particle strength, and less particle cracking during electrode manufacturing. Therefore, when applying the positive electrode active material in single particle form, there are advantages such as reduced gas generation and excellent life characteristics.

[0006] However, conventional single particle form lithium composite transition metal oxide particles have a relatively larger primary particle size compared to conventional secondary particle form lithium composite transition metal oxide particles, and there are fewer interfaces between primary particles that serve as diffusion paths for lithium ions. Therefore, there are problems such as inferior lithium mobility, low battery capacity, and inferior output characteristics. Thus, driving at a high voltage is necessary to realize a high-capacity battery.

[0007] However, NCM-based lithium composite transition metal oxides can achieve relatively stable performance at driving voltages of 4.3 V or less. However, when the driving voltage exceeds 4.35 V, side reactions with the electrolyte increase, transition metal ions elute, and battery performance rapidly deteriorates. It is known that such performance degradation further worsens at higher temperatures.

[0008] Therefore, there is a need to develop a positive electrode active material of NCM-based lithium composite transition metal oxide in single particle and / or quasi-single particle form that has excellent initial efficiency and rate characteristics at high voltages of 4.35 V or more. Summary of the Invention Problems to be Solved by the Invention

[0009] The present invention provides a positive electrode active material in single particle and / or quasi-single particle form that has excellent initial efficiency and rate characteristics at high voltages of 4.35 V or more and has the effect of improving the amount of gas generation during high-temperature storage. Means for Solving the Problems

[0010] On one side, the present invention provides a positive electrode active material comprising lithium composite transition metal oxide particles in a quasi-single particle form, which is a single particle composed of one nodule or a composite of 30 nodules or less, and the content of nickel in the total metal excluding lithium is 50 mol% to 80 mol%; and a coating layer formed on the particle surface of the lithium composite transition metal oxide; and the positive electrode active material satisfies the following formula 1.

[0011] [Formula 1] 1.0 ≦ P2 / P1 ≦ 4.0 In the above formula 1, P1 is the sum of the volumes of pores in the positive electrode active material with a pore diameter exceeding 40 Å, and P2 is the sum of the volumes of pores in the positive electrode active material with a pore diameter of 40 Å or less.

[0012] The maximum pore diameter of the positive electrode active material may be 200 Å to 300 Å.

[0013] The positive electrode active material may have a total pore volume of 1.6×10 -4 cm 3 / g or less.

[0014] The lithium composite transition metal oxide particles may have a composition represented by the following chemical formula 1.

[0015] [Chemical Formula 1] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 1, M 1 is one or more selected from the group consisting of Mn and Al, M 2 includes one or more selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Zr, Sr, W, Ta, Nb, and Mo, and 1.0 ≦ a ≦ 1.5, 0.5 ≦ b ≦ 0.8, 0 < c ≦ 0.3, 0 < d ≦ 0.4, 0 ≦ e ≦ 0.2.

[0016] The coating layer may contain one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. Preferably, the coating layer may contain Al and W.

[0017] The positive electrode active material may contain Al in an amount of 500 ppm to 3000 ppm based on the total weight of the positive electrode active material, and may contain W in an amount of 2000 ppm to 4000 ppm based on the total weight of the positive electrode active material.

[0018] The positive electrode active material has a BET specific surface area of ​​0.70 cm². 2 / g to 1.00cm 2 It may be / g.

[0019] The D of the positive electrode active material 50 The particle size may be between 3.0 μm and 5.0 μm.

[0020] In other respects, the present invention provides a positive electrode containing the positive electrode active material described above, and a lithium secondary battery containing the positive electrode. [Effects of the Invention]

[0021] The positive electrode active material according to the present invention contains a lithium composite transition metal oxide in single-particle or quasi-single-particle form with excellent particle strength, resulting in less particle cracking during electrode manufacturing and charging / discharging, reduced contact area with the electrolyte and suppression of side reactions with the electrolyte, reduced gas generation when applied to secondary batteries, and less degradation of the positive electrode active material, enabling the realization of excellent high-temperature life characteristics.

[0022] The present invention provides a positive electrode active material that satisfies the following formula 1.

[0023] [Formula 1] 1.0 ≤ P2 / P1 ≤ 4.0 In formula 1, P1 is the sum of the volumes of pores in the positive electrode active material whose pore diameter exceeds 40 Å, and P2 is the sum of the volumes of pores in the positive electrode active material whose pore diameter is 40 Å or less.

[0024] Here, P2 mainly represents the porosity of the aggregate, which is the aggregated state of the coating material, and P1 mainly represents the remaining porosity of the positive electrode active material. When P2 / P1 satisfies a specific range, it means that the coating layer is uniformly distributed on the surface of the positive electrode active material, the content of the coating material is appropriate, and surface reactions are easily suppressed. Therefore, battery performance can be improved through the reaction between residual lithium and the coating material on the surface of the positive electrode active material, and durability can be improved by suppressing the reaction between the electrolyte and the positive electrode active material during battery operation. [Brief explanation of the drawing]

[0025] [Figure 1] This is an SEM image of the surface of the positive electrode active material produced in Example 1 of the present invention. [Figure 2] This is an SEM image of the surface of the positive electrode active material produced in Comparative Example 1 of the present invention. [Figure 3] These are the results of analyzing the positive electrodes produced in the examples and comparative examples of the present invention using the BJH (Barrett-Joyner-Halenda) method. [Figure 4] This graph shows the amount of gas generated by electrodes manufactured in the examples and comparative examples of the present invention, under different storage cycles at high temperatures. [Modes for carrying out the invention]

[0026] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or lexicographical 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.

[0027] In this invention, a "single particle" is a particle consisting of one nodule. In this invention, a "quasi-single particle" means a composite particle formed of 30 or fewer nodules.

[0028] In the present invention, "nodule" means a particle unit body that constitutes a single particle or a quasi-single particle, and the nodule may be a single crystal lacking crystalline grain boundaries, or a polycrystalline material that does not have visible grain boundaries when observed with a scanning electron microscope (SEM) at a field of view of 5,000 to 20,000 times. The average particle size of the nodule may be measured by the arithmetic mean of the particle sizes of each nodule measured with a scanning electron microscope (SEM).

[0029] In this invention, "secondary particle" refers to a particle formed by the aggregation of several tens to several hundred primary particles. More specifically, a secondary particle is an aggregate of 40 or more primary particles.

[0030] The term "particle" as used in this invention may include any one or all of the following: single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0031] In the present invention, "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. 50 This can be measured using the laser diffraction method. For example, the positive electrode active material powder may be dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000), irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and after obtaining a volume-cumulative particle size distribution graph, the size of the particle corresponding to 50% of the volume-cumulative amount may be determined.

[0032] In the present invention, the term "driving voltage" refers to the voltage at which lithium ions are desorbed when a voltage is applied, and preferably refers to the voltage at which the desorbed lithium ions move to the negative electrode.

[0033] In this invention, the "BET specific surface area" is calculated from nitrogen adsorption isotherms at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan, and in the case of specific surface area, it can be calculated via the BET (Brunauer-Emmett-Teller) multipoint method.

[0034] In this invention, the "pore volume" may be measured by a formula using the BJH (Barrett-Joyner-Halenda) method via nitrogen adsorption. The pore volume is calculated using a BJH (Barrett-Joyner-Halenda) plot for pores with diameters ranging from 8.7 Å to 250 Å (i.e., from 0.87 nm to 25 nm).

[0035] positive electrode active material The positive electrode active material according to the present invention will be described below.

[0036] The positive electrode active material according to the present invention comprises (1) lithium composite transition metal oxide particles in single-particle or quasi-single-particle form, and (2) a coating layer formed on the surface of the lithium composite transition metal oxide particles.

[0037] Specifically, the positive electrode active material satisfies the following formula 1.

[0038] [Formula 1] 1.0 ≤ P2 / P1 ≤ 4.0 P1 is the sum of the volumes of pores in the positive electrode active material whose pore diameter exceeds 40 Å, and P2 is the sum of the volumes of pores in the positive electrode active material whose pore diameter is 40 Å or less.

[0039] (1) Lithium composite transition metal oxide particles The lithium composite transition metal oxide particles are in the form of single particles consisting of one nodule or quasi-single particles, which are composites of 30 or fewer nodules, preferably 2 to 20, and more preferably 2 to 10. Such single-particle and / or quasi-single-particle lithium composite transition metal oxides have higher particle strength than existing secondary-particle lithium composite transition metal oxides in which tens to hundreds of primary particles are aggregated, resulting in less particle cracking during rolling.

[0040] Furthermore, in the case of lithium composite transition metal oxides in single-particle or quasi-single-particle form according to the present invention, the number of lower-component elements (i.e., nodules) that make up the particles is small, so there is little change due to volume expansion and contraction of the primary particles during charging and discharging, and as a result the occurrence of cracks inside the particles is significantly reduced.

[0041] On the other hand, the lithium composite transition metal oxide particles may have a composition in which the nickel content in the total metal excluding lithium is 50 mol% to 80 mol%, preferably 50 mol% to 75 mol%, more preferably 55 mol% to 75 mol%, or 55 mol% to 70 mol%.

[0042] More specifically, the lithium composite transition metal oxide particles may have a composition represented by the following [Chemical Formula 1].

[0043] [Chemical formula 1] Li a Ni b Co c M 1 d M 2 e O2 In the above chemical formula 1, M 1 is one or more selected from the group consisting of Mn and Al, preferably Mn or a combination of Mn and Al, M 2 This may include one or more elements selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Zr, Sr, W, Ta, Nb, and Mo. 2The element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting the growth of particles during firing or improving the crystal structure stability.

[0044] Said a represents the molar ratio of lithium in the lithium composite transition metal oxide, and may be 1.0 ≤ a ≤ 1.5, 1.0 ≤ a < 1.5, or 1.0 ≤ a ≤ 1.2. When the molar ratio of lithium satisfies the above range, a stable layered crystal structure may be formed.

[0045] When the above range is satisfied, a stable layered crystal structure may be formed.

[0046] Said b represents the molar ratio of nickel in the total metal excluding lithium in the lithium composite transition metal oxide particles, and may be 0.5 ≤ b ≤ 0.8, 0.50 ≤ b ≤ 0.75, 0.55 ≤ b ≤ 0.70 or 0.55 ≤ b ≤ 0.65. Since the higher the content of nickel among the transition metals, the higher the capacity that can be realized, it is more advantageous for realizing high capacity that the nickel content is 0.5 or more.

[0047] Said c represents the molar ratio of cobalt in the total metal excluding lithium in the lithium nickel-based oxide, and may be 0 < c ≤ 0.3, 0 < c ≤ 0.25, 0 < c ≤ 0.2, 0 < c ≤ 0.15 or 0 < c ≤ 0.1. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0048] Said d represents the molar ratio of M in the total metal excluding lithium in the lithium nickel-based oxide 1 and may be 0 < d ≤ 0.4, 0.1 ≤ d ≤ 0.4, 0.15 ≤ d ≤ 0.4 or 0.2 < d ≤ 0.4. When the molar ratio of M 1 satisfies the above range, the structural stability of the positive electrode active material can be excellently shown.

[0049] Said e represents the molar ratio of M in the total metal excluding lithium in the lithium composite transition metal oxide 2This represents the molar ratio of elements, and may be 0 ≤ e ≤ 0.2, 0 ≤ e ≤ 0.15, or 0 ≤ e ≤ 0.1. 2 When present in appropriate amounts, it can play a role in promoting grain growth during firing and improving crystalline structure stability.

[0050] However, while NCM-based lithium composite transition metal oxides can achieve relatively stable performance at drive voltages of 4.3V or less, it is known that when the drive voltage exceeds 4.35V, side reactions with the electrolyte increase, transition metal ions dissolve, and battery performance deteriorates rapidly. This performance deterioration worsens further at higher temperatures.

[0051] Therefore, the inventors devised novel parameters to select positive electrode active materials that can be stably driven at high voltages of 4.35V or higher. Specifically, they confirmed that when the positive electrode active material satisfies the following formula 1, it can contribute to improving the performance of the battery, including positive electrode active material particles in an optimal state.

[0052] [Formula 1] 1.0 ≤ P2 / P1 ≤ 4.0 In formula 1, P1 is the sum of the volumes of pores in the positive electrode active material whose pore diameter exceeds 40 Å, and P2 is the sum of the volumes of pores in the positive electrode active material whose pore diameter is 40 Å or less. Preferably, the P2 / P1 value of the positive electrode active material is 1.0 to 3.5, more preferably 1.0 to 3.2.

[0053] When the P2 / P1 value exceeds 4.0, it indicates that the porosity of the coating layer aggregates is higher than that of the positive electrode active material itself. This means that the coating layer cannot be uniformly distributed on the surface of the positive electrode active material and is formed as aggregates of a large amount of solidified coating material. Consequently, the sum of the volumes of pores with small pore diameters is higher than that of the positive electrode active material itself. If the coating material cannot be uniformly distributed on the surface of the positive electrode active material, there is no performance improvement effect through the reaction between residual lithium on the surface of the positive electrode active material and the coating material. This prevents suppression of surface side reactions between the electrolyte and the positive electrode active material, leading to increased gas generation and reduced durability.

[0054] Furthermore, if the P2 / P1 value is less than 1.0, it means that the porosity of the coating layer aggregate is lower than that of the positive electrode active material itself, or that the content of the coating material is excessively low, reducing the ability of the coating layer to uniformly cover the surface of the positive electrode active material. This means that the sum of the volumes of pores with small pore diameters is lower than that of the positive electrode active material itself. In such cases, it is difficult to suppress the surface reaction of the positive electrode active material, which leads to increased gas generation and reduced durability. On the other hand, when the above range is met, the coating layer is uniformly distributed on the surface of the positive electrode active material, making it easy to suppress the surface reaction of the positive electrode active material, and the battery may have excellent initial efficiency, rate characteristics, and high-temperature storage characteristics.

[0055] On the other hand, in the case of Equation 1, which divides the pore diameter in the positive electrode active material into those exceeding and excluding 40 Å and uses the sum of the volumes of each pore as a factor, the aforementioned reference value of 40 Å may be a unique numerical value that can clearly demonstrate the uniformity of the coating. For example, lithium composite transition metal oxide particles, which are in single-particle or quasi-single-particle form compared to the coating material, are usually larger in size, so the pore diameter in single-particle form or the pore diameter that arises when forming a quasi-single-particle form is relatively larger than the pore diameter that arises in the coating material, and the pore diameter is mainly exceeding 40 Å. By the same principle, the coating material is usually smaller in size, and the pore diameter of the coating material alone or the pore diameter that arises when the coating material forms aggregates is smaller than the pore diameter that arises when forming single-particle or quasi-single-particle form, and the pore diameter is mainly 40 Å or less. In other words, in the case of Formula 1 of the present invention, one characteristic is that by separating the pore diameters generated in the coating material or aggregate of the coating material from the pore diameters generated when the lithium composite transition metal oxide forms single or quasi-single particle forms, based on a 40 Å reference, the uniformity of the coating can be shown more clearly.

[0056] On the other hand, the sum of pore volumes (P1) in the positive electrode active material where the pore diameter exceeds 40 Å and satisfying the aforementioned P2 / P1 range, and the sum of pore volumes (P2) in the positive electrode active material where the pore diameter is 40 Å or less, can be controlled by various methods, but preferably by controlling the Ni content contained in the lithium nickel oxide particles, the composition of the lithium nickel oxide particles, the temperature and / or time conditions during firing of the positive electrode active material precursor and lithium source, the firing temperature and / or firing time during the formation of the coating layer formed on the oxide particles, the content and / or composition of the coating elements, and the grinding conditions of the positive electrode active material powder.

[0057] The maximum pore diameter of the positive electrode active material according to the present invention may be 200 Å to 300 Å. Preferably, it may be 210 Å to 290 Å, and more preferably 220 Å to 280 Å. When the above range is satisfied, it is preferable in that the degree of particle cracking of the active material inside the electrode is small, and the phenomenon of deterioration of gas generation inside the cell can be prevented.

[0058] The positive electrode active material according to the present invention has a total pore volume of 1.6 × 10⁻⁶ -4 cm 3 It may be less than or equal to / g. Preferably 0.1 × 10 -4 cm 3 / g to 1.6 × 10 -4 cm 3 / g, more preferably 0.5 × 10 -4 cm 3 / g to 1.4 × 10 -4 cm 3 It may be / g. When the above range is satisfied, it is preferable in that the degree of particle fracture of the active material inside the electrode is small, and the phenomenon of deterioration of gas generation inside the cell can be prevented.

[0059] (2) Coating layer The positive electrode active material according to the present invention includes a coating layer formed on the particle surface of a lithium composite transition metal oxide in single-particle or quasi-single-particle form.

[0060] Ni-based positive electrode active materials have high capacity because the nickel content among the transition metals constituting the positive electrode active material is higher than that of other transition metals, but unstable nickel is present on the surface of the positive electrode active material. 3+ Ni 4+ A limitation exists in that the material exhibits structural instability due to ions. To overcome this structural instability, various techniques for modifying the surface of the positive electrode active material are being researched.

[0061] The positive electrode active material according to the present invention may include a coating layer containing one or more elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S as a coating element.

[0062] Preferably, the coating layer may contain Al and W as coating elements. When the coating layer contains Al and W, superior high-temperature lifetime characteristics can be achieved compared to when it contains only each coating element.

[0063] In this case, the positive electrode active material according to the present invention may contain Al in an amount of 500 ppm to 3000 ppm based on the total weight of the positive electrode active material. Preferably, the amount of Al is 1000 ppm to 2500 ppm, more preferably 1000 ppm to 2000 ppm based on the total weight of the positive electrode active material.

[0064] The positive electrode active material according to the present invention may contain W in an amount of 2,000 ppm to 4,000 ppm based on the total weight of the positive electrode active material. Preferably, W may be contained in an amount of 2,000 ppm to 3,500 ppm, more preferably 2,000 ppm to 3,000 ppm, based on the total weight of the positive electrode active material.

[0065] When the weight of Al or W satisfies the aforementioned numerical range, surface side reactions between the positive electrode active material and the electrolyte for high-voltage battery operation can be suppressed.

[0066] On the other hand, the positive electrode active material according to the present invention has a BET specific surface area of ​​0.70 m². 2 / g to 1.00m 2 / g, preferably 0.75m 2 / g to 1.00m 2 / g, more preferably 0.80m 2 / g to 0.95m 2 It may be / g. When the surface coating of the positive electrode active material is uniform, the BET specific surface area decreases compared to before coating. The BET specific surface area is 1.00 m². 2 A positive electrode active material with a void ratio exceeding / g indicates that the void ratio of the coating layer aggregates is higher than that of the positive electrode active material itself. This means that the coating layer cannot be uniformly distributed on the surface of the positive electrode active material and is instead formed by a large amount of aggregates. When the coating material cannot be uniformly distributed on the surface of the positive electrode active material in this way, there is no performance improvement effect through the reaction between the residual lithium on the surface of the positive electrode active material and the coating material, and surface side reactions between the positive electrode active material and the electrolyte cannot be suppressed, resulting in poor durability.

[0067] On the other hand, the positive electrode active material according to the present invention is D 50 The diameter may be 3.0 μm to 5.0 μm, preferably 3.2 μm to 5.0 μm, and more preferably 3.5 μm to 4.8 μm. D of the positive electrode active material 50 If the thickness is less than 3.0 μm, it becomes difficult to form the active material layer during electrode manufacturing, the impregnation of the electrolyte is poor, and the electrochemical properties deteriorate. 50 If the particle size exceeds 5.0 μm, there are problems such as reduced lithium mobility, increased resistance, and decreased output characteristics.

[0068] positive electrode The positive electrode according to the present invention includes the positive electrode active material of the present invention as described above. 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 the positive electrode active material layer includes the positive electrode active material according to the present invention. Since the positive electrode active material has been described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0069] The positive electrode current collector may contain a highly conductive metal, allowing the positive electrode active material layer to adhere easily, but it is not particularly limited as long as it is unreactive within the battery voltage range. The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc. The positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in a variety of forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0070] The positive electrode active material layer may optionally contain a conductive material and a binder together with the positive electrode active material.

[0071] In this case, the positive electrode active material may be present in an amount of 80% to 99% by weight, more specifically 90% to 98% by weight, relative to the total weight of the positive electrode active material layer.

[0072] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it has electronic conductivity in the battery without causing a chemical change. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; 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 may be used alone or in mixtures of two or more. The conductive material may be included in an amount of 0.01% to 10% by weight, preferably 0.1% to 9% by weight, and more preferably 0.1% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0073] The binder plays a role in improving the adhesion between particles of the positive electrode active material and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which the hydrogen atoms of these materials are substituted with Li, Na, or Ca, or various copolymers thereof. One of these materials alone or a mixture of two or more may 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.

[0074] The positive electrode may be manufactured by a conventional positive electrode manufacturing method, except that the positive electrode active material is used. Specifically, it can be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode active material and, if necessary, a binder, a conductive material, and a dispersant in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0075] The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one or more of these may be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for positive electrode manufacturing.

[0076] Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0077] Lithium-ion rechargeable battery Next, we will describe the lithium secondary battery according to the present invention.

[0078] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator membrane and electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as described earlier, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0079] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, the negative electrode, and the separator membrane, and a sealing member for sealing the battery container.

[0080] In the lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0081] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel with surface treatment of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector can usually have a thickness of 3 μm 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 may be used in a variety of forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0082] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0083] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. βExamples include lithium-doped and dedoped metal oxides such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the aforementioned metal compound and a carbonaceous material, such as Si-C composites or Sn-C composites. One or more of these mixtures may be used. A metallic lithium thin film may also be used as the negative electrode active material. Furthermore, low-crystallinity carbon and high-crystallinity carbon may all be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon micro beads, mesophase pitches, and high-temperature heat-treated carbon such as petroleum or coal tar pitch-derived cokes.

[0084] The negative electrode active material may be present in an amount of 80% to 99% by weight, 82% to 99% by weight, or 84% to 99% by weight, based on the total weight of the negative electrode active material layer.

[0085] The binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is usually added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0086] The conductive material is a component for further improving the conductivity of the negative electrode active material and may be included in an amount of 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight relative to the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and may be used, for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers such as carbon fibers or metal fibers; carbon fluoride; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0087] The negative electrode active material layer may be manufactured by coating and drying a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector, or by casting the negative electrode slurry composition onto a separate support, peeling it off the support, and laminating the resulting film onto the negative electrode current collector.

[0088] On the other hand, in the lithium secondary battery, the separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is the type of separation membrane that is normally used in lithium secondary batteries, and it is especially preferable that it has low resistance to ion movement of the electrolyte while having excellent moisture absorption performance for the electrolyte. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexane copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof may 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, a coated separation membrane containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and it may be used selectively in a single-layer or multi-layer structure.

[0089] Furthermore, examples of 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.

[0090] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0091] The organic solvent can be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move, without any particular limitations. 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), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethanol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Of 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.

[0092] The lithium salt can be any compound that can provide lithium ions for use in lithium secondary batteries, without any particular limitations. Specifically, the anion of the lithium salt may be F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - The lithium salt may be one or more selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, and more preferably 1.0 M to 2.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0093] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexalic acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be present in an amount of 0.1% to 10.0% by weight relative to the total weight of the electrolyte.

[0094] As described above, the lithium secondary battery according to the present invention has excellent stability and electrochemical performance even at high voltages, so the charge termination voltage during operation is 4.35V or higher, and when operated at such a high voltage, it can achieve superior high-capacity characteristics compared to conventional lithium secondary batteries. The operating voltage of the lithium secondary battery according to the present invention may be 2.5V to 4.5V, preferably 2.5V to 4.4V.

[0095] On the other hand, the lithium secondary battery may have a nominal voltage of 3.68V or higher, preferably 3.68V to 3.80V, and more preferably 3.69V to 3.75V. In this case, the nominal voltage refers to the average voltage value during discharge of the lithium secondary battery. Since the energy density of a lithium secondary battery is calculated as the product of the average voltage and average current during discharge, a higher nominal voltage results in increased energy density. Conventional lithium secondary batteries using lithium nickel cobalt manganese oxide as the positive electrode active material generally have a charge cut-off voltage of 4.25V, in which case the nominal voltage was 3.6V. Conversely, raising the charge termination voltage to 4.35V or higher to achieve a nominal voltage of 3.68V or higher is preferable in that it can realize a high energy density.

[0096] Furthermore, the lithium secondary battery according to the present invention exhibits excellent discharge capacity, output characteristics, and capacity retention rate stably, making it useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the electric vehicle sector, including hybrid electric vehicles (HEVs).

[0097] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary as a unit cell and a battery pack including the same are provided.

[0098] The aforementioned battery module or battery pack may be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0099] 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 may be realized in a variety of different forms and is not limited to the embodiments described herein.

[0100] Examples and Comparative Examples Example 1 A lithium composite transition metal hydroxide precursor with a Ni:Co:Mn molar ratio of 0.6:0.1:0.3 and a lithium raw material (LiOH) are mixed so that the transition metal (Ni+Co+Mn):Li molar ratio is 1:1.05, and then calcined at 940°C for 20 hours to produce Li[Ni 0.6 Co 0.1 Mn 0.3 A positive electrode active material powder with the composition of ]O2 was prepared. Subsequently, the positive electrode active material powder was coarsely ground using a jaw crusher, and then dry-ground to a level of 4 μm using a jet mill.

[0101] Subsequently, the positive electrode active material powder, Al2O3, and WO3 were mixed three times using an ACM apparatus so that the molar ratio of positive electrode active material powder:Al:W was 100:0.3:0.1. After mixing, the mixture was fired at 450°C for 5 hours to produce positive electrode active material powder with Al and W coating layers formed.

[0102] Comparative Example 1 The positive electrode active material powder was produced in the same manner as in Example 1, except that the positive electrode active material powder, Al2O3, and WO3 were mixed once using an ACM apparatus.

[0103] Experimental Example 1: Observation of the surface of the positive electrode active material Using a scanning electron microscope, SEM images of the positive electrode active material powders produced in Example 1 and Comparative Example 1 were obtained.

[0104] Figure 1 is an SEM image of the surface of the positive electrode active material produced in Example 1 of the present invention, and Figure 2 is an SEM image of the surface of the positive electrode active material produced in Comparative Example 1 of the present invention.

[0105] Figures 1 and 2 show that a coating layer was uniformly formed on the surface of the positive electrode active material in Example 1, but the coating layer was not uniformly formed on the surface of the positive electrode active material in Comparative Example 1, but rather concentrated in specific areas.

[0106] Experimental Example 2: Measurement of BET specific surface area and pore volume The BET specific surface area, coating element (Al, W) weight, and pore volume of the positive electrode active materials produced in Example 1 and Comparative Example 1 were measured and calculated. The measured and calculated values ​​are shown in Tables 1 and 2 and Figure 3 below.

[0107] Specifically, the BET specific surface area of ​​the positive electrode active material was calculated from nitrogen adsorption isotherms at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan, and in the case of specific surface area, it was calculated via the BET (Brunauer-Emmett-Teller) multipoint method.

[0108] On the other hand, the Al and W weights of the positive electrode active material were measured by ICP using an ICP-OES (PerkinElmer, Optima7300DV) instrument after taking a sample of 4g of positive electrode active material powder.

[0109] On the other hand, the pore volume of the positive electrode active material may be measured using the BJH (Barrett-Joyner-Halenda) method via nitrogen adsorption using BELSORP-minoII from BEL Japan. The pore volume is calculated using a BJH (Barrett-Joyner-Halenda) plot for pores with diameters from 8.7 Å to 250 Å (i.e., from 0.87 nm to 25 nm). In this case, P1 is defined as the sum of the volumes of pores with a diameter greater than 40 Å, and P2 is defined as the sum of the volumes of pores with a diameter of 40 Å or less.

[0110] [Table 1]

[0111] [Table 2]

[0112] Experimental Example 3: Evaluation of Initial Efficiency The initial efficiency of lithium secondary battery half-cells manufactured using the positive electrode active materials produced in Example 1 and Comparative Example 1, respectively, was evaluated as described below.

[0113] <Manufacturing of lithium-ion secondary batteries> The positive electrode active material, conductive material (CarbonBlack), and PVDF binder prepared in Example 1 and Comparative Example 1, respectively, were mixed in N-methylpyrrolidone in a weight ratio of 95:2:3 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 60°C, and then rolled to produce a positive electrode.

[0114] The negative electrode was manufactured using lithium metal, with a separation membrane interposed between the positive electrode and the negative electrode manufactured by the method described above to produce an electrode assembly. This assembly was then placed inside the battery case, and an electrolyte was injected into the case to produce a battery cell. The electrolyte was prepared by dissolving 0.6 M LiPF6 in a mixed organic solvent of ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC) in a volume ratio of 1:2:1, and adding 2% by weight of vinylene carbonate (VC).

[0115] Specifically, after the manufactured half-cells were activated (formed), they were each charged at 25°C with a constant current of 0.1C until the voltage reached 4.4V, and then discharged at a constant current of 0.1C until the voltage reached 2.5V. The initial charge capacity, initial discharge capacity, and the ratio of the initial discharge capacity to the initial charge capacity were defined as the initial efficiency and are shown in [Table 3] below.

[0116] [Table 3]

[0117] Through [Table 3] above, it can be confirmed that the initial charge / discharge capacity and efficiency of the lithium secondary battery containing the positive electrode active material of Example 1 are superior to those of Comparative Example 1.

[0118] Experimental Example 4: Evaluation of Rate Characteristics The lithium secondary battery half-cells that had been charged and discharged once from Experimental Example 3 were charged / discharged under the same conditions as in [Table 4] to evaluate their rate characteristics. The results are shown in [Table 4] below.

[0119] [Table 4]

[0120] As shown in [Table 4] above, it can be confirmed that the rate characteristics of the lithium secondary battery containing the positive electrode active material of Example 1 are superior to those of Comparative Example 1.

[0121] Experimental Example 5: Evaluation of Gas Generation During High-Temperature Storage The amount of gas generated during high-temperature storage was measured for lithium secondary battery half cells manufactured as described above using the positive electrode active materials produced in Example 1 and Comparative Example 1, respectively. Specifically, the amount of gas generated for the manufactured half cells at 60°C for 8 weeks was measured for each storage period and is shown in Figure 4.

[0122] Figure 4 shows that the amount of gas generated at different storage cycles for the lithium secondary battery containing the positive electrode active material of Example 1 at 60°C is significantly lower than that of Comparative Example 1.

Claims

1. A positive electrode active material comprising lithium composite transition metal oxide particles having a nickel content of 50 mol% to 80 mol% in the total metal excluding lithium, and being in the form of single particles consisting of one nodule or quasi-single particles consisting of 30 or fewer nodules; and a coating layer formed on the surface of the lithium composite transition metal oxide particles; The following equation 1 is satisfied, [Formula 1] 1.0 ≤ P2 / P1 ≤ 4.0 In formula 1, P1 is the sum of the volumes of pores in the positive electrode active material whose pore diameter exceeds 40 Å, and P2 is the sum of the volumes of pores in the positive electrode active material whose pore diameter is 40 Å or less.

2. The positive electrode active material according to claim 1, wherein the maximum pore diameter of the positive electrode active material is 200 Å to 300 Å.

3. The positive electrode active material has a total pore volume of 1.6 × 10⁻⁶ －４ cm ３ The positive electrode active material according to claim 1, wherein the amount is less than or equal to / g.

4. The lithium composite transition metal oxide particles have a composition represented by the following chemical formula 1, [Chemical formula 1] Li ａ Ni ｂ Co ｃ M １ ｄ M ２ ｅ O ２ In the above chemical formula 1, M １ is one or more selected from the group consisting of Mn and Al, ２ The positive electrode active material according to claim 1, wherein is one or more selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Zr, Sr, W, Ta, Nb, and Mo, and satisfies 1.0 ≤ a ≤ 1.5, 0.5 ≤ b ≤ 0.8, 0 < c ≤ 0.3, 0 < d ≤ 0.4, and 0 ≤ e ≤ 0.

2.

5. The positive electrode active material according to claim 1, wherein the coating layer contains one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S.

6. The positive electrode active material according to claim 1, wherein the coating layer contains Al and W as coating elements.

7. The positive electrode active material according to claim 6, wherein the positive electrode active material contains Al in an amount of 500 ppm to 3000 ppm based on the total weight of the positive electrode active material.

8. The positive electrode active material according to claim 6, wherein the positive electrode active material contains W in an amount of 2,000 ppm to 4,000 ppm based on the total weight of the positive electrode active material.

9. The positive electrode active material has a BET specific surface area of ​​0.70 cm². ２ / g to 1.00cm ２ The positive electrode active material according to claim 1, wherein the value is / g.

10. The D of the positive electrode active material ５０ The positive electrode active material according to claim 1, wherein the particle size is between 3.0 μm and 5.0 μm.

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

12. A lithium secondary battery comprising the positive electrode described in claim 11.

13. The lithium secondary battery according to claim 12, wherein the lithium secondary battery has a charging termination voltage of 4.35V or higher during operation.

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