Positive electrode active material, and positive electrode and lithium secondary battery comprising same

Abstract

The positive electrode active material according to the present invention comprises: a lithium composite transition metal oxide particle, which has a nickel content of 50 mol% to 80 mol% of the total metals excluding lithium and is in the form of a single particle consisting of one nodule or a quasi-single particle which is a composite of 30 or less nodules; and a coating layer formed on the surface of the lithium composite transition metal oxide particle, wherein the positive electrode active material satisfies Equation 1 below. [Equation 1] 1.0 ≤ P2 / P1 ≤ 4.0 In Equation 1, P1 represents the total pore volume of pores with a diameter exceeding 40 Å in the positive electrode active material, and P2 represents the total pore volume of pores with a diameter of 40 Å or less in the positive electrode active material.

Description

Cathode active material, cathode containing same, and lithium secondary battery

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0092287, filed July 17, 2023, Korean Patent Application No. 10-2023-0098548, filed July 27, 2023, Korean Patent Application No. 10-2024-0094050, filed July 16, 2024, and Korean Patent Application No. 10-2024-0094051, filed July 16, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery.

[0005]

[0006] A lithium secondary battery is generally composed of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode include an active material capable of intercalating and deintercalating lithium ions.

[0007] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compound (LiFePO4) have been used as cathode active materials for lithium secondary batteries. Among these, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but the high price of cobalt, which is the raw material, and its supply are unstable, making it difficult to commercially apply it to large-capacity batteries. Lithium nickel oxide has poor structural stability, making it difficult to achieve sufficient cycle life characteristics. Meanwhile, lithium manganese oxide has excellent stability but has the problem of poor 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 only Ni, Co, or Mn. Among these, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the field of electric vehicle batteries.

[0008] Single-particle cathode active materials have a smaller contact area with the electrolyte than conventional secondary particle cathode active materials, resulting in fewer side reactions with the electrolyte. Furthermore, their superior particle strength reduces particle breakage during electrode manufacturing. Therefore, the application of single-particle cathode active materials offers the advantages of superior gas generation and cycle life.

[0009] However, conventional lithium composite transition metal oxide particles in the form of single particles have relatively large primary particles compared to conventional lithium composite transition metal oxide particles in the form of secondary particles, and the interfaces between the primary particles, which serve as diffusion paths for lithium ions, are small, resulting in poor lithium mobility, low battery capacity, and poor output characteristics. Therefore, high-voltage operation is required to realize high-capacity batteries.

[0010] However, it is known that although NCM-based lithium composite transition metal oxides can achieve relatively stable performance at operating voltages of 4.3 V or less, when the operating voltage exceeds 4.35 V, side reactions with the electrolyte become severe, transition metal ions are eluted, and battery performance deteriorates rapidly. This performance deterioration is further aggravated when the temperature rises.

[0011] Accordingly, there is a need to develop a cathode active material of a lithium composite transition metal oxide in the form of single particles and / or pseudo-single particles of NCM having excellent initial efficiency and rate characteristics at high voltages of 4.35 V or higher.

[0012]

[0013] The present invention seeks to provide a cathode active material in the form of single particles and / or pseudo-single particles, which has excellent initial efficiency and rate characteristics at a high voltage of 4.35 V or higher and has the effect of improving the amount of gas generated during high-temperature storage.

[0014]

[0015] In one aspect, the present invention provides a positive electrode active material comprising a lithium composite transition metal oxide particle having a nickel content of 50 mol% to 80 mol% among all metals excluding lithium, and having a single particle shape consisting of one nodule or a pseudo-single particle shape consisting of a complex of 30 or fewer nodules; and a coating layer formed on the surface of the lithium composite transition metal oxide particle; wherein the positive electrode active material satisfies the following formula 1.

[0016] [Formula 1]

[0017] 1.0 ≤ P2 / P1 ≤ 4.0

[0018] In the above equation 1, P1 is the sum of the volumes of pores having a pore diameter exceeding 40 Å in the positive electrode active material, and P2 is the sum of the volumes of pores having a pore diameter of 40 Å or less in the positive electrode active material.

[0019] The maximum pore diameter of the above positive electrode active material may be 200Å to 300Å.

[0020] The above positive electrode active material has a total pore volume of 1.6×10 -4 cm 3 / g may be less.

[0021] The above lithium composite transition metal oxide particles may have a composition represented by the following chemical formula 1.

[0022] [Chemical Formula 1]

[0023] Li a Ni b Co c M 1 d M 2 e O2

[0024] In the above chemical formula 1, M 1 is at least one selected from the group consisting of Mn and Al, and M 2 It contains at least one 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≤0.2임.

[0025] The coating layer may include 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 include Al and W.

[0026] The above 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.

[0027] The above positive electrode active material has a BET specific surface area of ​​0.70 cm 2 / g to 1.00cm 2 It could be / g.

[0028] D of the above positive electrode active material 50 It may be 3.0㎛ to 5.0㎛.

[0029]

[0030] In another aspect, a positive electrode including the above-described positive electrode active material and a lithium secondary battery including the positive electrode are provided.

[0031]

[0032] The cathode active material according to the present invention includes a lithium composite transition metal oxide in the form of a single particle or pseudo-single particle with excellent particle strength, so that there is less particle breakage during electrode manufacturing and charge / discharge, and the contact area with the electrolyte is small, so that side reactions with the electrolyte are suppressed, and when applied to a secondary battery, the amount of gas generated is small, and the cathode active material degradation is small, so that excellent high-temperature life characteristics can be realized.

[0033] The present invention provides a positive electrode active material satisfying the following formula 1.

[0034] [Formula 1]

[0035] 1.0 ≤ P2 / P1 ≤ 4.0

[0036] In the above equation 1, P1 is the sum of the volumes of pores having a pore diameter exceeding 40 Å in the positive electrode active material, and P2 is the sum of the volumes of pores having a pore diameter of 40 Å or less in the positive electrode active material.

[0037] Here, P2 mainly represents the pores of the aggregates in which the coating material is aggregated, and P1 mainly represents the remaining pores of the positive electrode active material. When the P2 / P1 satisfies a specific range, it means that the coating layer is evenly distributed on the surface of the positive electrode active material, and the content of the coating material is appropriate, making it easy to suppress the surface reaction. Therefore, the battery performance can be improved through the reaction between the residual lithium and the coating material on the surface of the positive electrode active material, and the durability can be improved by suppressing the reaction between the electrolyte and the positive electrode active material during battery operation.

[0038]

[0039] Figure 1 is a SEM image of the surface of a positive electrode active material manufactured in Example 1 of the present invention.

[0040] Figure 2 is an SEM image of the surface of the positive electrode active material manufactured in Comparative Example 1 of the present invention.

[0041] Figure 3 shows the results of analyzing the positive electrodes manufactured in the examples and comparative examples of the present invention using the BJH (Barrett-Joyner-Halenda) method.

[0042] Figure 4 is a graph showing the amount of gas generated per storage cycle at high temperatures of electrodes manufactured in examples and comparative examples of the present invention.

[0043]

[0044] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best possible manner.

[0045] In the present invention, a "single particle" is a particle composed of one nodule. In the present invention, a "quasi-single particle" means a composite particle formed of 30 or fewer nodules.

[0046] In the present invention, "nodule" means a particle unit body constituting a single particle and a pseudo-single particle, and the nodule may be a single crystal lacking a crystalline grain boundary, or a polycrystal in which no grain boundary exists in appearance when observed with a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000 times. The average particle diameter of the nodule may be measured as the arithmetic mean value of the particle diameters of each nodule measured using a scanning electron microscope (SEM).

[0047] In the present invention, "secondary particle" refers to a particle formed by the agglomeration of tens to hundreds of primary particles. More specifically, the secondary particle is an agglomerate of 40 or more primary particles.

[0048] The expression "particle" used in the present invention may include any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0049] In the present invention, "D 50 " means the particle size based on 50% of the volume cumulative particle size distribution of the positive electrode active material. The above D 50 can be measured using a laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume cumulative amount.

[0050] The "driving voltage" used in the present invention refers to a voltage at which lithium ions are desorbed when voltage is applied, and may preferably refer to a voltage at which the desorbed lithium ions move to the negative electrode.

[0051] In the present invention, the "BET specific surface area" is calculated from a nitrogen adsorption isotherm at liquid nitrogen temperature (77 K) using BELSORP-mino II of BEL Japan, and the specific surface area can be calculated using the BET (Brunauer-Emmett-Teller) multi-point method.

[0052] In the present invention, the "pore volume" can be measured by a calculation formula according to the Barrett-Joyer-Halenda (BJH) method using a nitrogen adsorption method. The pore volume is calculated using a Barrett-Joyner-Halenda (BJH) plot for pores with diameters of 8.7 Å to 250 Å (i.e., 0.87 nm to 25 nm).

[0053]

[0054] positive electrode active material

[0055] Hereinafter, the positive electrode active material according to the present invention will be described.

[0056] The cathode active material according to the present invention comprises (1) lithium composite transition metal oxide particles in the form of single particles or pseudo-single particles, and (2) a coating layer formed on the surface of the lithium composite transition metal oxide particles.

[0057] Specifically, the positive electrode active material satisfies the following equation 1.

[0058] [Formula 1]

[0059] 1.0 ≤ P2 / P1 ≤ 4.0

[0060] P1 is the sum of the volumes of pores having a pore diameter exceeding 40 Å in the positive electrode active material, and P2 is the sum of the volumes of pores having a pore diameter of 40 Å or less in the positive electrode active material.

[0061]

[0062] (1) Lithium composite transition metal oxide particles

[0063] The lithium composite transition metal oxide particles are in the form of single particles consisting of one nodule or pseudo-single particles consisting of a composite of 30 or fewer, preferably 2 to 20, and more preferably 2 to 10 nodules. Such lithium composite transition metal oxides in the form of single particles and / or pseudo-single particles have higher particle strength than conventional secondary particle-type lithium composite transition metal oxides in which tens to hundreds of primary particles are aggregated, and thus particle breakage is less likely to occur during rolling.

[0064] In addition, in the case of the lithium composite transition metal oxide in the form of a single particle or pseudo-single particle according to the present invention, since the number of sub-components (i.e., nodules) constituting the particle is small, the change due to volume expansion and contraction of the primary particles during charge and discharge is small, and accordingly, the occurrence of cracks inside the particle is also significantly reduced.

[0065]

[0066] Meanwhile, the lithium composite transition metal oxide particles may have a composition in which the nickel content among the total metals 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%.

[0067] More specifically, the lithium composite transition metal oxide particles may have a composition represented by the following [chemical formula 1].

[0068] [Chemical Formula 1]

[0069] Li a Ni b Co c M 1 d M 2 e O2

[0070] In the above chemical formula 1, M 1 is at least one selected from the group consisting of Mn and Al, preferably Mn or a combination of Mn and Al, and M 2 It may include at least one selected from the group consisting of Ti, Mg, Zr, Y, Ba, Ca, Zr, Sr, W, Ta, Nb, and Mo. M 2 Although elements are not essential, when included in appropriate amounts, they can promote grain growth during firing or play a role in improving crystal structure stability.

[0071] The above 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 can be formed.

[0072] When the range is satisfied, a stable layered crystal structure can be formed.

[0073] The above b represents the molar ratio of nickel among the total metals 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 a higher content of nickel among the transition metals enables a higher capacity to be realized, a nickel content of 0.5 or more is more advantageous for realizing high capacity.

[0074] The above c represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel oxide, and is 0. <c≤0.3, 0<c≤0.25, 0<c≤0.2, 0<c≤0.15 또는 0<c≤0.1일 수 있다. 코발트의 몰비가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0075] The above d represents the molar ratio of manganese among all metals excluding lithium in the lithium nickel oxide, and is 0. <d≤0.4, 0.1≤d≤0.4, 0.15≤d≤0.4 또는 0.2<d≤0.4일 수 있다. 망간의 몰비가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타날 수 있다.

[0076] The above e is M of all metals except lithium in the lithium complex transition metal oxide. 2 It represents the molar ratio of elements, and can be 0≤e≤0.2, 0≤e≤0.15, or 0≤e≤0.1. M 1 When included in an appropriate amount, it can play a role in promoting grain growth during firing or improving crystal structure stability.

[0077]

[0078] However, it is known that NCM-based lithium composite transition metal oxides can achieve relatively stable performance at operating voltages of 4.3 V or less, but when the operating voltage exceeds 4.35 V, side reactions with the electrolyte become severe, transition metal ions are eluted, and battery performance deteriorates rapidly. This performance deterioration is further aggravated when the temperature rises.

[0079] Accordingly, the inventors of the present invention have designed a new parameter to select a positive electrode active material capable of stable operation at a high voltage of 4.35 V or higher, and specifically, confirmed that when the positive electrode active material satisfies the following Equation 1, it can contribute to improving the performance of the battery by including positive electrode active material particles in an optimal state.

[0080] [Formula 1]

[0081] 1.0 ≤ P2 / P1 ≤ 4.0

[0082] In the above equation 1, P1 is the sum of the volumes of pores having a pore diameter exceeding 40 Å in the positive electrode active material, and P2 is the sum of the volumes of pores having a pore diameter of 40 Å or less in the positive electrode active material. Preferably, the P2 / P1 value of the positive electrode active material may be 1.0 to 3.5, more preferably 1.0 to 3.2.

[0083] When the above P2 / P1 value exceeds 4.0, it indicates a state in which the pores of the aggregates of the coating layer are high compared to the pores of the positive electrode active material itself, which means that the coating layer is not evenly distributed on the surface of the positive electrode active material and the coating material is formed as a large amount of aggregates, and this means a state in which the sum of the volumes of pores with small pore diameters is high compared to the pores of the positive electrode active material itself. When the coating material is not evenly distributed on the surface of the positive electrode active material, 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 there is a problem in that the durability may be reduced because the surface side reaction of the electrolyte and the positive electrode active material is not suppressed, resulting in a large amount of gas generation.

[0084] In addition, when the P2 / P1 value is less than 1.0, the pores of the coating layer aggregates are low compared to the pores of the positive electrode active material itself, or the content of the coating material is excessively low, so that the ability of the coating layer to evenly cover the surface of the positive electrode active material is reduced. This means that the sum of the volumes of pores with small pore diameters is low compared to the pores of the positive electrode active material itself. In the above case, it is difficult to suppress the surface reaction of the positive electrode active material, so there is a problem that the amount of gas generated may increase and the durability may be reduced. That is, when the above range is satisfied, the coating layer is evenly distributed on the surface of the positive electrode active material, and it is easy to suppress the surface reaction of the positive electrode active material, so the initial efficiency, rate characteristics, and high-temperature storage characteristics of the battery may be excellent.

[0085]

[0086] Meanwhile, in the case of Equation 1, which divides the pore diameter in the positive electrode active material into those exceeding and below 40Å and uses the sum of the volumes of each pore as a factor, the reference value of 40Å may be a unique value that can clearly represent the uniformity of the coating. For example, since lithium composite transition metal oxide particles in the form of single particles or pseudo-single particles are usually larger than the coating material, the pore diameter in the form of single particles or the pore diameter formed while forming pseudo-single particles is relatively larger than the pore diameter formed in the coating material, and the pore diameter is mainly larger than 40Å. By the same principle, the coating material is usually small in particle size, so the pore diameter in the form of the coating material alone or the pore diameter formed when the coating material forms aggregates is smaller than the pore diameter formed while forming pseudo-single particles, and the pore diameter is mainly 40Å or less. That is, in the case of formula 1 of the present invention, it has a characteristic in that the uniformity of the coating can be more clearly indicated by dividing the pore diameter generated in the coating material or the coating material aggregate and the pore diameter generated when the lithium complex transition metal oxide forms a single particle or pseudo-single particle form by 40 Å.

[0087]

[0088] Meanwhile, the sum (P1) of pore volumes having a pore diameter exceeding 40Å in the positive electrode active material satisfying the aforementioned P2 / P1 range and the sum (P2) of pore volumes having a pore diameter of 40Å or less in the positive electrode active material can be controlled by various methods, but preferably, it can be implemented by controlling the content of Ni included in the lithium nickel-based oxide particles, the composition of the lithium nickel-based oxide particles, the temperature and / or time conditions during firing of the precursor for the positive electrode active material and the lithium source, the firing temperature and / or firing time during formation of the coating layer formed on the oxide particles, the content and / or composition of the coating element, and the grinding conditions of the positive electrode active material powder.

[0089]

[0090] 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 may be preferable in that the degree of breakage of the active material particles inside the electrode is reduced, thereby preventing the phenomenon of gas generation becoming more severe inside the cell.

[0091]

[0092] The positive electrode active material according to the present invention has a total pore volume of 1.6×10 -4 cm 3 / g or less. 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 / g. If the above range is satisfied, it may be desirable in that the degree of breakage of active material particles inside the electrode is small, thereby preventing the phenomenon of gas generation becoming more severe inside the cell.

[0093]

[0094] (2) Coating layer

[0095] The cathode active material according to the present invention includes a coating layer formed on the surface of a lithium composite transition metal oxide particle in the form of a single particle or a pseudo-single particle.

[0096]

[0097] Ni-based cathode active materials have a high capacity because the content of nickel among the transition metals that make up the cathode active material is higher than that of other transition metals, but there is unstable Ni present on the surface of the cathode active material. 3+ , Ni 4+There is a limitation of structural instability due to ions. To address this structural instability, various technologies are being studied to modify the surface of the positive electrode active material.

[0098]

[0099] The cathode active material according to the present invention may include a coating layer including at least one 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.

[0100] Preferably, the coating layer may include Al and W as coating elements. When the coating layer includes Al and W, it can exhibit superior high-temperature life characteristics compared to a case where it includes only each coating element.

[0101] 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. The Al may preferably be contained in an amount of 1000 ppm to 2500 ppm, more preferably 1000 ppm to 2000 ppm based on the total weight of the positive electrode active material.

[0102] The positive electrode active material according to the present invention may contain W in an amount of 2000 ppm to 4000 ppm based on the total weight of the positive electrode active material. The W may preferably be contained in an amount of 2000 ppm to 3500 ppm, more preferably 2000 ppm to 3000 ppm based on the total weight of the positive electrode active material.

[0103] When the weight of the above Al or W satisfies the above numerical range, the surface side reaction of the positive electrode active material and the electrolyte for battery operation at high voltage can be suppressed.

[0104]

[0105] Meanwhile, the positive electrode active material according to the present invention has a BET specific surface area of ​​0.70 m 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 / g. If the surface coating of the positive electrode active material is uniform, the BET specific surface area may decrease compared to before coating. The BET specific surface area is 1.00 m 2 / g or more of the positive active material means that the porosity of the aggregates of the coating layer is high compared to the porosity of the positive active material itself, and the coating layer is not evenly distributed on the surface of the positive active material, but is formed as a large number of aggregates. In this case, when the coating material is not evenly distributed on the surface of the positive active material, there is no performance improvement effect through the reaction of the residual lithium on the surface of the positive active material with the coating material, and there is a problem in that the durability is low because the surface side reaction between the positive active material and the electrolyte is not suppressed.

[0106]

[0107] Meanwhile, the positive electrode active material according to the present invention is D 50 The D of the positive electrode active material may be 3.0 ㎛ to 5.0 ㎛, preferably 3.2 ㎛ to 5.0 ㎛, and more preferably 3.5 ㎛ to 4.8 ㎛. 50 If it is less than 3.0㎛, it is difficult to form an active material layer during electrode manufacturing, the electrolyte impregnation property is poor, and the electrochemical properties are deteriorated. 50 If it exceeds 5.0㎛, there is a problem that lithium mobility decreases, resistance increases, and output characteristics deteriorate.

[0108]

[0109] anode

[0110] The positive electrode according to the present invention comprises the positive electrode active material of the present invention described above. Specifically, the positive electrode comprises a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode active material of the present invention. Since the positive electrode active material has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0111]

[0112] The positive electrode current collector may include a highly conductive metal, and is not particularly limited as long as it is a metal to which the positive electrode active material layer can be easily adhered, but is not reactive in the voltage range of the battery. The positive electrode current collector may be made of, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. In addition, the positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0113]

[0114] The above positive electrode active material layer may optionally include a conductive material and a binder, together with the positive electrode active material, as needed.

[0115] At this time, the positive electrode active material may be included in an amount of 80% to 99% by weight, more specifically 90% to 98% by weight, based on the total weight of the positive electrode active material layer.

[0116]

[0117] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, 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 or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.01 wt% to 10 wt%, preferably 0.1 wt% to 9 wt%, and more preferably 0.1 wt% to 5 wt%, based on the total weight of the positive electrode active material layer.

[0118]

[0119] The above binder serves to improve the adhesion between positive electrode active material particles 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), polyvinylalcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and polymers in which hydrogens of these are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The above binder may be included in an amount of 1 wt% to 30 wt%, preferably 1 wt% to 20 wt%, and more preferably 1 wt% to 10 wt%, based on the total weight of the positive electrode active material layer.

[0120]

[0121] The above-mentioned positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above-mentioned positive electrode active material is used. Specifically, the positive electrode slurry composition, prepared by dissolving or dispersing the above-mentioned positive electrode active material and optionally a binder, a conductive agent, and a dispersant in a solvent as needed, is applied onto a positive electrode current collector, followed by drying and rolling.

[0122] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0123]

[0124] Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry composition onto a separate support, peeling the resulting film from the support, and laminating the resulting film onto a positive electrode current collector.

[0125]

[0126] lithium secondary battery

[0127] Next, a lithium secondary battery according to the present invention will be described.

[0128]

[0129] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as described above, a detailed description thereof will be omitted, and only the remaining components will be specifically described below.

[0130] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0131]

[0132] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0133] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0134]

[0135] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0136] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β(0 < β < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fibers, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature heat-treated carbon such as petroleum or coal tar pitch derived cokes.

[0137] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt%, 82 wt% to 99 wt%, or 84 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0138]

[0139] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0140]

[0141] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be included in an amount of 1 wt% to 30 wt%, 1 wt% to 20 wt%, or 1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder 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.

[0142]

[0143] The above negative electrode active material layer can be manufactured by applying and drying a negative electrode slurry composition prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the negative electrode slurry composition on a separate support, and then laminating the obtained film by peeling it off from the support on a negative electrode current collector.

[0144]

[0145] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0146]

[0147] In addition, the electrolyte used in the present invention may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc. that can be used in the manufacture of a lithium secondary battery.

[0148] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0149] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R represents a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0150]

[0151] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the anion of the above lithium salt is 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 - It may be at least one selected from the group consisting of, and the lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. The concentration of the lithium salt is preferably within the range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0152]

[0153] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 10.0 wt% based on the total weight of the electrolyte.

[0154]

[0155] Since the lithium secondary battery according to the present invention as described above has excellent stability and electrochemical performance even at high voltages, the end-of-charge voltage during operation can be 4.35 V or higher, and when operated at such a high voltage, it can implement superior high-capacity characteristics compared to conventional lithium secondary batteries. The operating voltage of the lithium secondary battery according to the present invention can be 2.5 V to 4.5 V, preferably 2.5 V to 4.4 V.

[0156]

[0157] Meanwhile, the lithium secondary battery may have a nominal voltage of 3.68 V or higher, preferably 3.68 V to 3.80 V, and more preferably 3.69 V to 3.75 V. At this time, the nominal voltage refers to the average voltage value during discharge of the lithium secondary battery. Since the energy density of the lithium secondary battery is calculated by the product of the average voltage and the average current during discharge, the energy density increases when the nominal voltage is high. In the past, lithium secondary batteries that applied lithium nickel cobalt manganese oxide as a cathode active material generally had a charge cut-off voltage of about 4.25 V, and in this case, the nominal voltage was about 3.6 V. In contrast, it may be preferable in that a high energy density can be realized when the charge end voltage is increased to 4.35 V or higher so that the nominal voltage is 3.68 V or higher.

[0158]

[0159] In addition, since the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0160] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0161] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0162]

[0163] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0164]

[0165] Examples and Comparative Examples

[0166] Example 1

[0167] The lithium composite transition metal hydroxide precursor with a molar ratio of Ni:Co:Mn of 0.6:0.1:0.3 and the lithium raw material (LiOH) were mixed so that the molar ratio of transition metal (Ni+Co+Mn):Li was 1:1.05, and then calcined at 940°C for 20 hours to obtain Li[Ni 0.6 Co 0.1 Mn 0.3 ]O2 composition positive electrode active material powder was manufactured. Then, the positive electrode active material powder was coarsely crushed using a jaw crusher and then dry-pulverized to a size of 4 μm in a jet mill.

[0168] Afterwards, the positive electrode active material powder, Al2O3, and WO3 were mixed three times using ACM equipment so that the molar ratio of the positive electrode active material powder: Al: W was 100:0.3:0.1, and then calcined at 450°C for 5 hours to manufacture a positive electrode active material powder having an Al and W coating layer formed thereon.

[0169]

[0170] Comparative Example 1

[0171] The positive electrode active material powder was manufactured 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 device.

[0172]

[0173] Experimental Example 1: Surface observation of positive electrode active material

[0174] Using a scanning electron microscope, SEM images of the positive electrode active material powders manufactured in Example 1 and Comparative Example 1 were obtained.

[0175] Fig. 1 is an SEM image of the surface of a positive electrode active material manufactured in Example 1 of the present invention, and Fig. 2 is an SEM image of the surface of a positive electrode active material manufactured in Comparative Example 1 of the present invention.

[0176] Through Figures 1 and 2, it can be confirmed that the coating layer was formed uniformly on the surface of the positive electrode active material of Example 1, but the coating layer was not formed uniformly on the surface of the positive electrode active material of Comparative Example 1, but was formed concentrated in a specific area.

[0177]

[0178] Experimental Example 2: Measurement of BET surface area and pore volume

[0179] The BET specific surface area, coating element (Al, W) weight, and pore volume of the positive electrode active materials manufactured in Example 1 and Comparative Example 1 were measured and calculated, respectively. The measured and calculated values ​​are shown in [Table 1], [Table 2], and Fig. 3 below.

[0180] Specifically, the BET specific surface area of ​​the positive electrode active material was calculated from the nitrogen adsorption isotherm at liquid nitrogen temperature (77 K) using BELSORP-mino II of BEL Japan, and the specific surface area was calculated using the BET (Brunauer-Emmett-Teller) multi-point method.

[0181] Meanwhile, the weight of Al and W in the positive electrode active material was measured by the ICP method using an ICP-OES (PerkinElmer, Optima7300DV) device after collecting 4 g of positive electrode active material powder.

[0182] Meanwhile, the pore volume of the positive electrode active material can be measured by a calculation formula based on the Barrett-Joyer-Halenda (BJH) method through nitrogen adsorption using BELSORP-mino II of BEL Japan, and the pore volume is calculated using the Barrett-Joyner-Halenda (BJH) plot for pores with diameters of 8.7Å to 250Å (i.e., 0.87 nm to 25 nm). Here, P1 is defined as the sum of the volumes of pores with a pore diameter exceeding 40Å, and P2 is defined as the sum of the volumes of pores with a pore diameter of 40Å or less.

[0183]

[0184] Particle morphologyNi content[mol%]BET specific surface area[cm 3 / g]Coating element weight [ppm]Example 1 Single particle 600.91Al: 1400 W: 2800Comparative example 1 Single particle 601.08Al: 1400 W: 2800

[0185] P1(cm 3 / g)P2(cm 3 / g)P2 / P1 Example 13.30Ⅹ10 -5 1.05Ⅹ10 -4 3.18 Comparative Example 13.13Ⅹ10 -5 1.35Ⅹ10 -4 4.31

[0186] Experimental Example 3: Initial Efficiency Evaluation

[0187] The initial efficiency was evaluated for lithium secondary battery half cells manufactured as follows using the positive electrode active materials manufactured in Example 1 and Comparative Example 1, respectively.

[0188]

[0189] <Manufacturing of Lithium Secondary Batteries>

[0190] The positive electrode active material, conductive agent (Carbon Black), and PVDF binder manufactured in Example 1 and Comparative Example 1, respectively, were mixed in N-methylpyrrolidone at a weight ratio of 95:2:3 to manufacture 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 manufacture a positive electrode.

[0191] Lithium metal was used as the negative electrode, and a separator was interposed between the positive and negative electrodes manufactured by the above-described method to manufacture an electrode assembly, which was then placed inside a battery case, and an electrolyte was injected into the case to manufacture a battery cell. The electrolyte was manufactured by dissolving 0.6 M LiPF6 in a mixed organic solvent of ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:2:1 by volume, and adding 2 wt% of vinylene carbonate (VC).

[0192] Specifically, after activating (forming) the manufactured half-cells, they were each charged at a constant current of 0.1 C at 25°C until the voltage reached 4.4 V, and then discharged at a constant current of 0.1 C until the voltage reached 2.5 V. The initial charge capacity, initial discharge capacity, and the ratio of the initial discharge capacity to the initial charge capacity were calculated as the initial efficiency and are shown in [Table 3] below.

[0193] Initial charge capacity [mAh / g] Initial discharge capacity [mAh / g] Initial efficiency [%] Example 1215.2 196.0 9 1.1 Comparative example 1214.7 195.0 9 0.8

[0194] Through the above [Table 3], it can be confirmed that the initial charge / discharge capacity and efficiency of the lithium secondary battery including the positive electrode active material of Example 1 are superior to those of Comparative Example 1.

[0195]

[0196] Experimental Example 4: Rate Characteristic Evaluation

[0197] In the above Experimental Example 3, the half-cell of a lithium secondary battery charged and discharged once was charged / discharged under the conditions shown in [Table 4] to evaluate the rate characteristics. The results are shown in [Table 4] below.

[0198]

[0199] 0.33C / 0.33C1.0C / 0.1C2.0C / 0.1CExample 196.591.987.9Comparative Example 196.191.687.8

[0200] Through the above [Table 4], it can be confirmed that the rate characteristics of the lithium secondary battery including the positive electrode active material of Example 1 are better than those of Comparative Example 1.

[0201]

[0202] Experimental Example 5: Evaluation of Gas Emission During High-Temperature Storage

[0203] 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 manufactured in Example 1 and Comparative Example 1, respectively. Specifically, the amount of gas generated for each 8-week storage cycle at 60°C for the manufactured half cells was measured, and the results are shown in Fig. 4.

[0204] Through Fig. 4, it can be confirmed that the amount of gas generated per storage cycle at 60°C of the lithium secondary battery including the positive electrode active material of Example 1 is significantly lower than that of Comparative Example 1.

Claims

1. A cathode active material comprising: a lithium composite transition metal oxide particle having a nickel content of 50 mol% to 80 mol% among all metals excluding lithium, and having a single particle composed of one nodule or a pseudo-single particle form composed of 30 or fewer nodules; and a coating layer formed on the surface of the lithium composite transition metal oxide particle; The above positive electrode active material is a positive electrode active material that satisfies the following equation 1: [Formula 1] 1.0 ≤ P2 / P1 ≤ 4.0 In the above equation 1, P1 is the sum of the volumes of pores having a pore diameter exceeding 40 Å in the positive electrode active material, and P2 is the sum of the volumes of pores having a pore diameter of 40 Å or less in the positive electrode active material.

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

3. In claim 1, The above positive electrode active material has a total pore volume of 1.6×10 -4 cm 3 A positive electrode active material having a mass of / g or less.

4. In claim 1, The above lithium composite transition metal oxide particles are cathode active materials having a composition represented by the following chemical formula 1: [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 at least one selected from the group consisting of Mn and Al, and M 2 It contains at least one 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≤0.2임.

5. In claim 1, A cathode active material, wherein the coating layer comprises at least one coating element 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. In claim 1, A positive electrode active material, wherein the coating layer comprises coating elements of Al and W.

7. In claim 6, The above positive electrode active material is a positive electrode active material containing Al in an amount of 500 ppm to 3000 ppm based on the total weight of the positive electrode active material.

8. In claim 6, The positive electrode active material is a positive electrode active material containing W in an amount of 2000 ppm to 4000 ppm based on the total weight of the positive electrode active material.

9. In claim 1, The above positive electrode active material has a BET specific surface area of ​​0.70 cm 2 / g to 1.00cm 2 / g, positive electrode active material.

10. In claim 1, D of the above positive electrode active material 50 A positive electrode active material having a diameter of 3.0㎛ to 5.0㎛.

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

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

13. In claim 12, The above lithium secondary battery has a charging end voltage when operated. Lithium secondary battery with a voltage of 4.35 V or higher.

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