Cathode materials and cathodes and lithium secondary batteries containing them

Abstract

This invention relates to a cathode material that can improve the performance of lithium secondary batteries, and a cathode and a lithium secondary battery comprising the cathode material. The cathode material includes a first cathode active material having an olivine structure and a second cathode active material having a layered structure, and the voltage drop (χ) of the first cathode active material according to Equation 1 described in this specification satisfies a specific range.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0009718, filed on January 22, 2024, the disclosure of which is incorporated herein by reference. Technical Field

[0003] This invention relates to cathode materials, and cathodes and lithium secondary batteries containing the cathode materials. Background Technology

[0004] Recently, with the technological development and increasing demand for mobile devices and electric vehicles, the demand for secondary batteries as energy sources has increased significantly. Among these secondary batteries, lithium secondary batteries, which have high energy density, voltage, long lifespan, and low self-discharge rate, have been commercialized and are widely used.

[0005] Lithium-ion batteries consist of four components: a positive electrode, a negative electrode, a separator, and an electrolyte. Among these components, the positive electrode active material, contained in the positive electrode, plays a significant role in determining the battery's capacity, output, and lifespan. For lithium-ion batteries with high energy density, output, and lifespan, improvements in the performance of the positive electrode active material are necessary; therefore, extensive research has been conducted in recent years to develop high-performance positive electrode active materials.

[0006] As positive electrode active materials for the aforementioned lithium secondary batteries, lithium transition metal oxides have been developed, such as: lithium cobalt-based oxides like LiCoO2; lithium nickel-based oxides like LiNiO2; lithium manganese-based oxides like LiMnO2 or LiMn2O4; and lithium iron phosphate compounds like LiFePO4 have been developed. Furthermore, lithium composite transition metal oxides containing two or more transition metals, such as Li[Ni], have recently been developed and are widely used. a Co b Mn c O2, Li[Ni a Co b Al c ]O2 and Li[Ni a Co b Mn c Al d O2.

[0007] Meanwhile, lithium iron phosphate compounds with olivine structures are promising active materials with excellent lifetime characteristics and superior advantages in all aspects of safety, including overcharge and over-discharge protection, due to their excellent structural stability.

[0008] In particular, LiFePO4 exhibits excellent high-temperature stability due to the strong bonding of PO4, and is cheaper than the aforementioned LiCoO2, LiNiO2, or LiMn2O4 because it contains abundant and low-cost iron. Furthermore, LiFePO4 has low toxicity, thus having a smaller environmental impact. However, when using LiFePO4 as a positive electrode active material, a problem arises: its low conductivity increases the battery's internal resistance. Therefore, in a closed battery circuit, the polarization potential increases, leading to a decrease in battery capacity. Additionally, because the density of LiFePO4 is lower than that of conventional positive electrode active materials, there is a limitation that the battery's energy density cannot be sufficiently increased. Moreover, LiFePO4 typically exists in the form of secondary particles where primary particles aggregate, resulting in a large interfacial resistance between the primary particles, which leads to poor output characteristics.

[0009] To address this issue, attempts have been made to use mixtures of lithium complex transition metal oxides and lithium iron phosphate compounds. However, lithium iron phosphate compounds have a lower operating voltage than lithium complex transition metal oxides, thus only the lithium complex transition metal oxides operate independently in the high-voltage range. This problem becomes problematic when applied to fields where lifespan characteristics and output performance are particularly critical.

[0010] [Existing Technical Documents]

[0011] [Patent Literature]

[0012] Japanese Patent Application Publication No. 2002-075368 Summary of the Invention

[0013] Technical issues

[0014] To address the aforementioned problems, this invention provides a positive electrode active material capable of improving battery life characteristics.

[0015] In addition, the present invention provides a positive electrode and a secondary battery that have excellent lifespan characteristics by including the above-mentioned positive electrode material.

[0016] Technical solution

[0017] (1) The present invention provides a positive electrode material comprising: a first positive electrode active material having an olivine structure; and a second positive electrode active material having a layered structure, wherein, according to Equation 1 below, the voltage drop (χ) of the first positive electrode active material is less than 0.50 V.

[0018] [Equation 1]

[0019] Voltage drop (χ) [V] = (4.25 - Open-circuit voltage (α) measured after a 20-minute rest period) [V]

[0020] In Equation 1 above, α is the open-circuit voltage measured immediately after charging a lithium secondary battery including a positive electrode to 4.25 V at 25°C using the CC (0.1C)-CV (cutoff current: 0.05C) method and after a 20-minute rest period. The positive electrode includes a positive electrode active material layer containing positive electrode active material in an amount of 80% to 98% by weight based on the total weight of the positive electrode active material layer.

[0021] (2) The positive electrode material of (1) above, wherein the first positive electrode active material comprises a lithium iron phosphate-based compound having a composition represented by Formula 1 below.

[0022] [Formula 1]

[0023] Li 1+x Fe 1-a M 1 a PO4

[0024] In Equation 1 above, M 1 It is selected from one or more of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y, and -0.1≤x≤0.1, and 0.0≤a≤0.8.

[0025] (3) The cathode material of (2) above, wherein the first cathode material further includes a carbon (C) coating formed on the lithium iron phosphate compound.

[0026] (4) The positive electrode material of (3) above, wherein, based on the total weight of the first positive electrode active material, the carbon (C) content contained in the coating is from 1.50% by weight to 5.00% by weight.

[0027] (5) The cathode material as described in any one of (1) to (4) above, wherein the average crystallite size of the first cathode active material is from 80.00 nm to 150.00 nm.

[0028] (6) The positive electrode material as described in any one of (1) to (5) above, wherein the first positive electrode active material has an average particle size (D) of 0.30 μm to 8.00 μm. 50 ).

[0029] (7) The positive electrode material as described in any one of (1) to (6) above, wherein the weight ratio of the first positive electrode active material to the second positive electrode active material is 10:90 to 90:10.

[0030] (8) The positive electrode material according to any one of (1) to (7) above, wherein the weight ratio of the first positive electrode active material to the second positive electrode active material is 10:90 to 80:10.

[0031] (9) The positive electrode material according to any one of (1) to (8) above, wherein the second positive electrode active material has a composition represented by the following formula 2.

[0032] [Formula 2]

[0033] Li 1+y1 Ni p1 Mn q1 Co r1 M 2 s1 O2

[0034] In the above formula 2, M 2 is one or more selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0.00≤y1≤0.50, 0.00<p1<1.00, 0.00<q1<0.50, 0.00<r1<0.50, and 0.000≤s1≤0.010.

[0035] (10) The positive electrode material according to any one of (1) to (10) above, wherein the average particle diameter (D 50 ) of the second positive electrode active material is 4 μm to 13 μm.

[0036] (11) The present invention provides a positive electrode comprising the positive electrode material according to any one of (1) to (10) above.

[0037] (12) The present invention provides a lithium secondary battery comprising the positive electrode of (11) above.

[0038] Advantageous Effects

[0039] The positive electrode material according to the present invention comprises: a first positive electrode active material having an olivine structure; and a second positive electrode active material having a layered structure, wherein when the first positive electrode active material satisfies a specific condition (the voltage drop (χ) according to Equation 1 described in the present specification is 0.50 V or less), a battery comprising the positive electrode material according to the present invention can have improved high-voltage life characteristics and the like. Description of the Drawings

[0040] Figure 1 is the XRD data of the first positive electrode active material manufactured in Preparation Example 2. Detailed Description

[0041] The invention will be described in more detail below to aid in understanding it.

[0042] It should be understood that the terms or words used in the specification and claims should not be interpreted as having the meanings defined in commonly used dictionaries, and it should also be understood that, based on the principle that the inventors may appropriately define the meanings of terms or words to best interpret the invention, these terms or words should be interpreted as having meanings and concepts consistent with their meanings in the context of the relevant technology and technical ideas of the invention.

[0043] In this specification, it should also be understood that the terms “comprising,” “providing,” “having,” etc., specify the presence of the features, wholes, steps, elements, or combinations thereof, but do not preclude the presence or addition of one or more other features, wholes, steps, elements, or combinations thereof.

[0044] In this specification, “crystallite” refers to a particle unit having substantially the same crystal orientation.

[0045] In this specification, the "average size of the crystallites" can be quantitatively analyzed using X-ray diffraction (XRD) analysis via Cu Kα radiation. Specifically, XRD data of the synthesized cathode active material were obtained using a Bruker D8 XRD system (Cu-target, voltage: 45 kV, current: 40 mA, 2θ: 10° to 80°). Structural analysis of the obtained data was performed using the general structural analysis method refined by Rietveld in Highscore software manufactured by Malvern Panalytical.

[0046] The Rietveld refinement method involves calculating a diffraction pattern from an initial structural model that the material's crystal structure might possess and comparing the calculated pattern with the measured diffraction pattern of the actual synthesized material. This method introduces various structure-related factors and iteratively adjusts their values ​​until the two patterns match well.

[0047] This method involves evaluating its effectiveness by the difference between the calculated and measured diffraction patterns, and iteratively minimizing the difference between the two patterns. The crystallite size in the structure-related factors that can be applied during this method can be obtained using the full width at half maximum (FWHM) of the peaks on each crystal plane in the measured diffraction pattern.

[0048] In this specification, the average particle size (D) 50The particle size distribution (D) can be defined as the particle size at 50% of the cumulative volume distribution on the particle size distribution curve (particle size distribution curve) for each particle. For average particles, the target powder to be measured is dispersed in a dispersant and introduced into a commercially available laser diffraction particle size analyzer (e.g., the Mastersizer 3000 manufactured by Malvern). As the particles pass through the laser beam, the difference in the diffraction pattern based on the particle size is calculated, and the particle diameter at the point where the cumulative volume distribution reaches 50% of the particle diameter is calculated. This allows the measurement of D. 50 .

[0049] In this specification, the content ratio of each element in lithium iron phosphate compounds can be measured by inductively coupled plasma (ICP) analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES; Agilent 5110, Agilent Technologies).

[0050] cathode materials

[0051] The cathode material according to the present invention will be described below.

[0052] The cathode material according to the present invention comprises: a first cathode active material having an olivine structure; and a second cathode active material having a layered structure, wherein the voltage drop (χ) of the first cathode active material according to the following Equation 1 is less than 0.50V.

[0053] [Equation 1]

[0054] Voltage drop (χ) [V] = (4.25 - Open circuit voltage (α) measured after a 20-minute rest period) [V]

[0055] In Equation 1 above, α is the open-circuit voltage measured immediately after charging a lithium secondary battery including a positive electrode to 4.25 V at 25°C using the CC (0.1C)-CV (cutoff current: 0.05C) method and after a 20-minute rest period, wherein the positive electrode includes a positive electrode active material layer containing a positive electrode active material in an amount of 80% to 98% by weight based on the total weight of the positive electrode active material layer.

[0056] The inventors of this invention discovered that, in the case of a positive electrode material comprising a first positive electrode active material having an olivine structure and a second positive electrode active material having a layered structure, and a voltage drop (χ) of less than 0.50V according to Formula 1 as described in this specification, the voltage drop of the first positive electrode active material is reduced at the operating voltage of the positive electrode material, thereby improving output characteristics, resistance characteristics, and lifetime characteristics. At the same time, the first and second positive electrode active materials operate uniformly during charging and discharging, thus completing this invention.

[0057] The voltage drop in Equation 1 described in this invention is determined by the combined effect of various factors such as the composition of the cathode material, particle size, carbon (C) content in the cathode active material, and average crystallite size.

[0058] Regarding Equation 1 described in this specification, the voltage drop (χ) is calculated as the difference between 4.25 V (which is the operating voltage of the positive electrode material) and α. α is the open-circuit voltage measured immediately after charging a lithium secondary battery containing a positive electrode to 4.25 V at 25°C using the CC (0.1C)-CV (cutoff current: 0.05C) method and immediately after a 20-minute rest period, wherein the positive electrode comprises a positive electrode active material layer containing a positive electrode active material in an amount of 80% to 98% by weight based on the total weight of the positive electrode active material layer. Specifically, the voltage drop of the first positive electrode active material can be calculated as the difference between 4.25 V and α, where α is the open-circuit voltage measured immediately after the lithium secondary battery, including the positive electrode, is charged to 4.25 V at 25°C using the CC (0.1C)-CV (cutoff current: 0.05C) method and after a 20-minute rest period. The positive electrode comprises a positive electrode active material layer containing a first positive electrode active material comprising 90% by weight of the total weight of the positive electrode active material layer. A smaller α value indicates a larger voltage drop from 4.25 V. When the voltage drop (χ) is 0V, i.e., α is 4.25V, this means that no voltage drop occurs when the open-circuit voltage is measured immediately after charging a lithium secondary battery including the positive electrode to 4.25V at 25°C using the CC (0.1C)-CV (cut-off current: 0.05C) method and after a 20-minute rest period, wherein the positive electrode includes a positive electrode active material layer containing positive electrode active material in an amount of 80% to 98% by weight based on the total weight of the positive electrode active material layer.

[0059] Meanwhile, the first positive electrode active material exhibits excellent stability, but its resistance and output characteristics deteriorate in the high-voltage range. The second positive electrode active material has high output, but its use is limited by its low stability, and it is not economically viable. Furthermore, when both the first and second positive electrode active materials are included, but the voltage drop (χ) of the first positive electrode active material from the operating voltage of the positive electrode material according to Equation 1 described in this specification is greater than 0.50V, the voltage drop of the first positive electrode active material is large, thus acting as a resistor, resulting in poor high-voltage lifespan characteristics of the secondary battery containing the positive electrode material.

[0060] Specifically, the voltage drop (χ) according to Equation 1 described in this specification can be 0.00V or higher, 0.10V or higher, 0.20V or higher, or 0.25V or higher, and can be 0.50V or lower, 0.49V or lower, 0.48V or lower, 0.47V or lower, 0.46V or lower, 0.45V or lower, 0.44V or lower, 0.42V or lower, 0.41V or lower, 0.40V or lower, 0.39V or lower, 0.38V or lower, 0.37V or lower, 0.36V or lower, 0.35V or lower, or 0.34V or lower. When the voltage drop (χ) falls within the above range, the voltage drop of the first positive electrode active material decreases from the operating voltage of the positive electrode material including the first positive electrode active material and the second positive electrode active material, the first positive electrode active material and the second positive electrode active material operate uniformly during charging and discharging, and the lifetime characteristics are improved.

[0061] According to an embodiment of the present invention, the first positive electrode active material may include a lithium iron phosphate compound having a composition represented by the following chemical formula 1.

[0062] [Formula 1]

[0063] Li 1+x Fe 1-a M 1 a PO4

[0064] In Equation 1 above, M 1 It is selected from one or more of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B, and Y, and -0.1≤x≤0.1, and 0.0≤a≤0.8.

[0065] M 1 It is a dopant element, specifically, M 1 It is selected from one or more of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B, and Y. The M mentioned above... 1 It is not mandatory to include it, but when included in an appropriate amount, it improves the stability of the particle shape and crystal structure of the positive electrode active material, which can improve the rate characteristics of the secondary battery in which it is applied.

[0066] Meanwhile, x can be above -0.1 or above 0.0, and below 0.05 or below 0.1. When x falls within the above range, structural stability can be improved.

[0067] a can be greater than or equal to 0.0, 0.1, or 0.2, and can be less than or equal to 0.3, 0.4, or 0.8. When a falls within the above ranges, it exhibits high energy density, which achieves high capacity characteristics.

[0068] According to an embodiment of the present invention, the first positive electrode active material may further include a carbon (C) coating formed on a lithium iron phosphate compound. The inclusion of a carbon (C) coating improves the electronic conductivity of the positive electrode active material.

[0069] Meanwhile, based on the total weight of the first positive electrode active material, the carbon (C) content contained in the coating can be from 1.50 wt% to 5.00 wt%. Specifically, the amount of carbon (C) contained in the coating can be 1.50 wt% or more or 2.00 wt% or more. Furthermore, the amount of carbon (C) contained in the coating can be 3.00 wt% or less, 3.50 wt% or less, 4.00 wt% or less, or 5.00 wt% or less. Specifically, the carbon (C) content contained in the coating can be 1.50 wt% or more or 2.00 wt% or more, and can be 3.00 wt% or less, 3.50 wt% or less, 4.00 wt% or less, or 5.00 wt% or less.

[0070] According to embodiments of the present invention, the average crystallite size of the first positive electrode active material can be from about 80.00 nm to about 150.00 nm. Specifically, the average crystallite size of the first positive electrode active material can be 80.00 nm or more, 90.00 nm or more, or 94.00 nm or more, and the average crystallite size can be 97.00 nm or less, 100.00 nm or less, 120.00 nm or less, or 150.00 nm or less. When the average crystallite size falls within the above range, the capacity characteristics and rate performance of the positive electrode active material can be improved.

[0071] According to an embodiment of the present invention, the average particle size (D) of the first positive electrode active material 50 The particle size can range from 0.30 μm to 8.0 μm. The average particle size (D) of the first positive electrode active material... 50 The particle size can be greater than or equal to 0.30 μm or greater than 1.00 μm, and can be less than or equal to 6.50 μm, 7.00 μm, 7.50 μm, or 8.00 μm. When the average particle size (D) of the first positive electrode active material... 50 When the values ​​fall within the above range, the electrode density may increase.

[0072] According to an embodiment of the present invention, the weight ratio of the first positive electrode active material to the second positive electrode active material may be from 10:90 to 90:10. Specifically, the weight ratio may be 10:90 to 90:10, 10:90 to 80:20, 20:80 to 90:10, 20:80 to 80:20, 30:70 to 90:10, 30:70 to 80:20, 40:60 to 90:10, or 40:60 to 80:20. When the weight ratio is within the above range, while improving stability, the resistance and output characteristics at high voltages may be excellent. The operating voltages of the first positive electrode active material and the second positive electrode active material are different. Particularly, when the weight ratio of the first positive electrode active material to the second positive electrode active material is from 10:90 to 80:20, since the voltage drop of the first positive electrode active material from the operating voltage of the positive electrode material decreases, and the first positive electrode active material and the second positive electrode active material operate uniformly during charging and discharging of the battery, the life characteristics and the like can be improved.

[0073] According to an embodiment of the present invention, the second positive electrode active material may have a composition represented by the following Formula 2.

[0074] [Formula 2]

[0075] Li 1+y1 Ni p1 Mn q1 Co r1 M 2 s1 O2

[0076] In the above Formula 2, M 2 is one or more selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0.00 ≤ y1 ≤ 0.50, 0.00 < p1 < 1.00, 0.00 < q1 < 0.50, 0.00 < r1 < 0.50, and 0.000 ≤ s1 ≤ 0.010.

[0077] The above M 2 is a doping element. Specifically, the above M 2 is one or more selected from Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt. The above M 2 is not necessarily included, but when included in an appropriate amount, it can improve the particle shape of the positive electrode active material and the stability of the crystal structure.

[0078] Meanwhile, y1 can be greater than 0.00, greater than 0.10, or greater than 0.20, and can be less than 0.30, less than 0.40, or less than 0.50. When y1 falls within the above range, high capacity characteristics and high energy density per unit volume can be achieved.

[0079] p1 is the molar ratio of nickel (Ni) to the total metals excluding lithium, which can be greater than 0.00, greater than 0.20, greater than 0.40, greater than 0.50, greater than 0.60, greater than 0.70, or greater than 0.80, and can be less than 0.90 or less than 1.00. When p1 falls within the above range, it exhibits high energy density, which enables high capacity characteristics.

[0080] q1 is the molar ratio of manganese (Mn) to the total metals excluding lithium, which can be greater than 0.00 and can be less than 0.20, 0.30, 0.40, or less than 0.50. When q1 falls within the above range, high capacity characteristics can be achieved. In addition, high-temperature stability may increase, and the decomposition reaction of the electrolyte solution may be relatively reduced.

[0081] r1 is the molar ratio of cobalt (Co) to the total metals other than lithium in a lithium-based composite transition metal oxide. It can be greater than 0.00, and can be less than 0.10, 0.20, 0.30, 0.40, or less than 0.50. When r1 falls within the above range, the structural stability can be improved.

[0082] s1 is M 2 The molar ratio of s1 to the total metals other than lithium in the lithium-based transition metal oxide can be 0.002 or higher, 0.002 or higher, or 0.004 or higher, and can be 0.006 or lower, 0.008 or lower, or 0.010 or lower. When s1 falls within the above range, it can improve the particle shape and the stability of the crystal structure.

[0083] p1, q1, r1, and s1 can satisfy p1+q1+r1+s1=1.

[0084] According to one embodiment of the present invention, the average particle size (D) of the second positive electrode active material 50 The average particle size (D) of the second positive electrode active material can range from 4 μm to 13 μm. Specifically, the average particle size (D) of the second positive electrode active material... 50 The particle size can be 4μm or larger, 5μm or larger, 6μm or larger, 7μm or larger, 8μm or larger, or 9μm or larger, and can be less than 10μm, less than 11μm, less than 12μm, or less than 13μm. When the second positive electrode active material has an average particle size (D) within the above range... 50 When this is done, the average particle size (D) of the first positive electrode active material can be adjusted. 50The average particle size (D) of the second positive electrode active material 50 This is used to increase electrode density.

[0085] The first positive electrode active material of the present invention can be manufactured according to methods known in the relevant art. For example, the first positive electrode active material can be manufactured by sintering a precursor and a lithium raw material.

[0086] Specifically, the first positive electrode active material according to the present invention can be manufactured by a method for manufacturing a first positive electrode active material comprising a lithium iron phosphate compound, the method comprising (a) mixing a lithium-containing raw material and iron phosphate (FePO4) to prepare a mixture; and (b) sintering the mixture.

[0087] Lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, and hydroxyoxides can be used as lithium-containing raw materials, and there are no particular restrictions on the lithium-containing raw materials, as long as they can dissolve in water. Specifically, lithium-containing raw materials can be Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, Li₃C₆H₅O₇, etc., and any one or a mixture of two or more of them can be used.

[0088] In the process of preparing the mixture in step (a), raw materials containing doped elements, such as manganese-containing raw materials, can be further mixed.

[0089] According to the present invention, the lithium-containing raw material and iron phosphate (FePO4) used in step (a) can be mixed in amounts to obtain a compound having the composition represented by Formula 1 as described in this specification.

[0090] Following step (a) above, additional mixing of carbon-containing coating materials may also be included.

[0091] The carbon-containing raw material used for coating can be one or more selected from sucrose, glucose, polyethylene glycol, polyvinyl alcohol, and polyvinyl acetate.

[0092] The carbon-coated raw material may be included in an amount of 1.5% to 5% by weight relative to the total weight of the first positive electrode active material.

[0093] In step (b), the mixture can be sintered at 500°C to 1000°C to produce lithium iron phosphate compounds.

[0094] The first positive electrode active material manufactured according to the method for manufacturing the first positive electrode active material may have a composition represented by Equation 1 as described in this specification.

[0095] The first positive electrode active material manufactured by the method for manufacturing the first positive electrode active material may include a carbon (C) coating formed on a lithium iron phosphate compound.

[0096] The second positive electrode active material of the present invention can be manufactured according to methods known in the relevant art. For example, the second positive electrode active material can be manufactured by sintering a positive electrode active material precursor and a lithium-containing raw material.

[0097] Specifically, the second positive electrode active material can be manufactured by a method for manufacturing a second positive electrode active material, the method comprising: (A) mixing a positive electrode active material precursor (which is a composite transition metal hydroxide, a composite transition metal hydroxyl oxide, or a combination thereof) with a lithium-containing raw material to manufacture a mixture; and (B) sintering the mixture to manufacture a lithium composite transition metal oxide.

[0098] Lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, and hydroxyoxides can be used as lithium-containing raw materials, and there are no particular restrictions on the lithium-containing raw materials, as long as they can dissolve in water. Specifically, as lithium-containing raw materials, Li₂CO₃, LiNO₃, LiNO₂, LiOH, LiOH·H₂O, LiH, LiF, LiCl, LiBr, LiI, CH₃COOLi, Li₂O, Li₂SO₄, CH₃COOLi, Li₃C₆H₅O₇, and any one or a mixture of two or more of them can be used.

[0099] The composite transition metal hydroxide, composite transition metal hydroxyl oxide, or combination thereof can be mixed with a lithium-containing raw material such that the ratio (Li / M'') of the number of moles of lithium (Li) in the lithium-containing raw material to the total number of moles of transition metal (M'') in the composite transition metal hydroxide, composite transition metal hydroxyl oxide, or combination thereof is 1.00 or more, 1.01 or more, 1.02 or more, 1.03 or more, 1.04 or more, or 1.05 or more, and may be 1.06 or less, 1.07 or less, 1.08 or less, 1.09 or less, or 1.10 or less.

[0100] In the process of manufacturing the mixture in step (A) above, raw materials containing doped elements may be further included, such as aluminum-containing raw materials, zirconium-containing raw materials or yttrium-containing raw materials.

[0101] According to an embodiment of the present invention, in step (A) above, a composite transition metal hydroxide containing cobalt, nickel and manganese, a raw material containing lithium (Li) and a raw material containing doped elements can be mixed in amounts having the composition represented by Formula 2 as described in the present invention.

[0102] In step (B), the mixture can be sintered at 700°C to 1000°C to produce lithium composite transition metal oxide.

[0103] Sintering can be carried out in an oxygen atmosphere.

[0104] The second positive electrode active material manufactured according to the method for manufacturing the second positive electrode active material may have a composition represented by Formula 2 as described in this specification.

[0105] The cathode material of the present invention can be manufactured according to methods known in the relevant art. Specifically, the cathode material can be manufactured by mixing a first cathode active material and a second cathode active material.

[0106] cathode materials

[0107] The positive electrode according to the present invention will be described below.

[0108] The positive electrode according to the present invention comprises a positive electrode active material layer comprising the positive electrode material according to the present invention. Specifically, the positive electrode comprises: a positive electrode current collector; and a positive electrode active material layer formed on the positive electrode current collector and comprising the positive electrode material. Since the positive electrode material has been described in detail, a specific explanation will be omitted, and in the following, only the remaining components will be described in detail.

[0109] There are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. Materials used include, for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Furthermore, the positive electrode current collector can have a thickness from 3 μm to 500 μm, allowing for the formation of fine irregularities on its surface, thus increasing the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0110] In addition to the cathode material, the cathode active material may also include conductive materials and binders. In this case, based on the total weight of the cathode active material layer, the content of the cathode active material can be from 80% to 99% by weight, and more specifically from 85% to 98.5% by weight, and when the amount of cathode active material falls within the above range, it can exhibit excellent capacity characteristics.

[0111] Conductive materials are used to impart conductivity to the electrodes, and any conductive material can be used without particular limitation, as long as it has electronic conductivity without causing chemical changes in the battery. Specific examples can be graphite, such as natural or artificial graphite; carbon-based materials, including carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, carbon fibers, carbon nanotubes, etc.; powders or fibers of metals including copper, nickel, aluminum, silver, etc.; conductive whiskers including zinc oxide, potassium titanate, etc.; conductive metal oxides, including titanium oxide, etc.; or conductive polymers including polyphenylene derivatives, etc., and any one of them can be used alone or in mixtures of two or more. Based on the total weight of the positive electrode active material layer, the content of conductive material can be from 0.1% by weight to 15% by weight.

[0112] Adhesives can be used to improve the adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), PVDF-co-HFP copolymer, polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them may be used alone or in mixtures of two or more thereof. The adhesive content may range from 0.1% by weight to 15% by weight, based on the total weight of the positive electrode active material layer.

[0113] Besides using the aforementioned positive electrode, the positive electrode can be manufactured by known methods for manufacturing positive electrodes. Specifically, the positive electrode can be manufactured by applying a composition for forming the positive electrode active material layer onto a positive electrode current collector, followed by drying and rolling, wherein the composition is manufactured by dissolving or dispersing the positive electrode material, along with selective binders and conductive materials, in a solvent. The type and amount of the positive electrode, binder, and conductive materials are the same as described above. Alternatively, in another manner, the positive electrode can be manufactured by casting the composition for forming the positive electrode active material layer onto a separate carrier, and then pressing the film layer, separated from the carrier, onto the positive electrode current collector.

[0114] The solvent can be any solvent commonly used in the technical field to which this invention pertains, and can be dimethyl sulfoxide (DMSO), isopropanol, N-methyl-2-pyrrolidone (NMP), acetone, water, etc., and can be any one of them alone or a mixture of two or more thereof. The amount of solvent used is sufficient to have a viscosity that can dissolve or disperse the positive electrode active material, conductive material, and binder, and exhibits excellent consistency uniformity during the application in the manufacture of the positive electrode.

[0115] Lithium secondary batteries

[0116] The lithium secondary battery according to the present invention will be described below.

[0117] This invention can manufacture an electrochemical device including a positive electrode. Specifically, the electrochemical device can be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0118] Specifically, a lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, and a separator and electrolyte disposed between the positive and negative electrodes. The positive electrode is the same as described above, so a detailed description is omitted. In the following text, only the other components will be described in detail.

[0119] Furthermore, the lithium secondary battery may further include a battery case housing an electrode assembly that houses the positive electrode, negative electrode, and separator, as well as a sealing member that selectively seals the electrode case.

[0120] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material on the negative electrode current collector.

[0121] There are no particular restrictions on the negative electrode current collector, as long as it is conductive and does not cause chemical changes in the battery. Materials such as copper, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. Furthermore, the negative electrode current collector can typically have a thickness from 3 μm to 500 μm, allowing for the formation of fine irregularities on its surface, thus increasing the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes, such as films, foils, meshes, porous materials, foams, or nonwoven materials.

[0122] In addition to the negative electrode active material, the negative electrode active material layer may also selectively include adhesives and conductive materials.

[0123] Compounds capable of reversibly inserting and deintercalating lithium can be used as anode active materials. Specific examples of anode active materials can include: carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fibers, and amorphous carbon; metallic materials capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides that can be doped and dedoped with lithium, such as vanadium oxides and lithium vanadium oxides; composite materials comprising metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites; and so on, any one of them or a mixture of two or more of them can be used. Furthermore, thin films of metallic lithium can be used as anode active materials. Additionally, low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Typical examples of low-crystallinity carbon can be soft carbon and hard carbon, while typical examples of high-crystallinity carbon can be irregular, planar, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, carbon fibers based on mesophase pitch, mesophase carbon microspheres, mesophase pitch, and high-temperature sintered carbon such as coke derived from petroleum or coal tar pitch.

[0124] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be from 80% to 99% by weight.

[0125] Adhesives are components that facilitate bonding between conductive materials, active materials, and current collectors, and their content is typically from 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0126] Conductive materials are components used to further improve the conductivity of the negative electrode active material, and can be added in an amount of less than 10% by weight, specifically less than 5% by weight, based on the total weight of the negative electrode active material layer. Conductive materials are not particularly limited, as long as they are conductive without causing chemical changes in the battery. Examples of conductive materials that can be used include: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers, such as carbon fibers or metal fibers; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0127] The negative electrode active material layer can be manufactured by applying a composition for forming the negative electrode active material layer onto a negative electrode current collector and then drying it, or by casting the composition for forming the negative electrode active material layer onto a separate carrier and then pressing the film layer obtained by peeling it off from the carrier onto the negative electrode current collector, wherein the composition for forming the negative electrode active material layer is manufactured by dissolving or dispersing the negative electrode active material in a solvent and selectively dissolving or dispersing the binder and conductive material.

[0128] Meanwhile, for lithium secondary batteries, the separator separates the negative and positive electrodes and provides a path for lithium ion movement. Any separator can be used without particular limitation, as long as it is commonly used in lithium secondary batteries. In particular, separators with high electrolyte solution retention capacity and low resistance to electrolyte ion movement are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or laminated structures having two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Additionally, separators coated with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and separators with single-layer or multi-layer structures can optionally be used.

[0129] Furthermore, the electrolyte used in this invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which can be used to manufacture lithium secondary batteries, but this invention is not limited thereto.

[0130] Specifically, electrolytes may include organic solvents and lithium salts.

[0131] Any organic solvent can be used without particular limitation, as long as it serves as a medium allowing the movement of ions involved in the electrochemical reactions of the battery. Specifically, as organic solvents, the following can be used: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone-based solvents, such as cyclohexanone; aromatic solvents, such as benzene or fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), or propylene carbonate (PC); alcohol solvents, such as ethanol or isopropanol; nitriles, such as R-CN (R is a C2 to C20 hydrocarbon group having a straight-chain, branched, or cyclic structure, and may include double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; sulfolane, etc. Among these, carbonate solvents are preferred as organic solvents. Furthermore, a mixture of cyclic carbonate compounds and linear carbonate compounds is more preferably used as an organic solvent. Cyclic carbonate compounds (e.g., ethylene carbonate, propylene carbonate, etc.) have high viscosity and high dielectric constant, which can increase the charge and discharge capacity of the battery, while linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) have low viscosity. In this case, when cyclic carbonates and linear carbonates are mixed in a volume ratio of approximately 1:9, the electrolyte solution can exhibit excellent performance.

[0132] Any lithium salt can be used without particular restriction, as long as it provides the lithium ions used in lithium secondary batteries. Specifically, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2 can be used as lithium salts. Lithium salts can be used in concentration ranges from 0.1 to 5.0 M, and specifically from 0.1 to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has suitable conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can move efficiently.

[0133] In addition to the electrolyte, to improve battery life characteristics, prevent battery capacity reduction, and increase battery discharge capacity, the electrolyte may also include one or more additives, such as halogenated alkylene carbonates like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, triammonium hexaphosphate, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, based on the total weight of the electrolyte, the content of the additives can be from 0.1% by weight to 10% by weight, and specifically from 0.1% by weight to 5% by weight.

[0134] As described above, lithium secondary batteries containing the cathode material according to the present invention exhibit excellent resistivity characteristics and are therefore suitable for use in portable devices such as mobile phones, laptops, computers and digital cameras; and electric vehicles such as hybrid electric vehicles (HEVs); and so on.

[0135] Therefore, according to another embodiment of the present invention, a battery module including a lithium secondary battery as a unit cell is provided, and a battery pack including the battery module is provided.

[0136] Battery modules or battery packs can be used as a power source for any one or more of the following medium or large devices: power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or energy storage systems.

[0137] The appearance of the lithium secondary battery according to the present invention is not particularly limited, but it can be cylindrical, prismatic, pouch-shaped or coin-shaped using a can.

[0138] The lithium secondary battery according to the present invention can be used not only in battery cells for powering small devices, but also preferably as a unit cell in medium and large battery modules comprising multiple battery cells.

[0139] Embodiments of the present invention will be described in detail below to enable those skilled in the art to readily implement the invention. However, the present invention can be implemented in various forms and is not limited to the embodiments described herein.

[0140] Methods of implementing the present invention

[0141] Preparation Example

[0142] Preparation Example 1

[0143] Li₂CO₃ and FePO₄ were mixed to achieve a Li:Fe molar ratio of 1.05:1, and then mixed with water to achieve a solid powder concentration of 20% by weight. The mixture was then wet-milled using a bead mill to prepare a slurry (D). 50 (200 nm). The slurry was then mixed with sucrose to prepare a mixture. In this case, sucrose was mixed at 12% by weight, based on the total weight of Li₂CO₃ and FePO₄.

[0144] The mixture was spray-dried (inlet temperature 230°C, outlet temperature 95°C) and then sintered at 700°C for 10 hours under a nitrogen atmosphere to produce a first positive electrode active material, on which a carbon (C) coating was formed on a lithium iron phosphate compound having a composition represented by LiFePO4.

[0145] Preparation Example 2

[0146] Except that the mixture was pulverized using a jet mill after spray drying (inlet temperature 230°C, outlet temperature 95°C) and then sintered at 700°C under a nitrogen atmosphere for 10 hours, a first positive electrode active material was prepared in the same manner as in Preparation Example 1, on which a carbon-containing (C) coating was formed on a lithium iron phosphate compound having a composition represented by LiFePO4.

[0147] Preparation Example 3

[0148] Except for mixing sucrose in an amount of 10% by weight based on the total weight of Li2CO3 and FePO4, then spray-drying the mixture (inlet temperature 230°C, outlet temperature 95°C) and then sintering it at 700°C for 10 hours under a nitrogen atmosphere, a first positive electrode active material was prepared in the same manner as in Preparation Example 1, on which a carbon (C) coating was formed on a lithium iron phosphate compound having a composition represented by LiFePO4.

[0149] Preparation Example 4

[0150] Except that the mixture was pulverized using a jet mill after spray drying (inlet temperature 230°C, outlet temperature 95°C) and then sintered at 700°C under a nitrogen atmosphere for 10 hours, the first positive electrode active material was manufactured in the same manner as in Preparation Example 3, on which a carbon (C) coating was formed on a lithium iron phosphate compound having a composition represented by LiFePO4.

[0151] Preparation Example 5

[0152] Except for mixing sucrose in an amount of 6% by weight based on the total weight of Li2CO3 and FePO4, then spray-drying the mixture (inlet temperature 230°C, outlet temperature 95°C) and then sintering it at 750°C for 10 hours under a nitrogen atmosphere, a first positive electrode active material was prepared in the same manner as in Preparation Example 1, on which a carbon (C) coating was formed on a lithium iron phosphate compound having a composition represented by LiFePO4.

[0153] Preparation Example 6

[0154] Except that the mixture was pulverized using a jet mill after spray drying (inlet temperature 230°C, outlet temperature 95°C) and then sintered at 750°C under a nitrogen atmosphere for 10 hours, the first positive electrode active material was manufactured in the same manner as in Preparation Example 5, on which a carbon-containing (C) coating was formed on a lithium iron phosphate compound having a composition represented by LiFePO4.

[0155] Examples and Comparative Examples

[0156] Example 1

[0157] Prepare with Li 1.03 Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 O2 represents the composition of the second positive electrode active material (manufacturer: LG Chem Co., Ltd., D 50 (10μm, secondary particle form).

[0158] The first positive electrode active material and the second positive electrode active material manufactured in Preparation Example 1 are mixed such that the weight ratio is 40:60 to manufacture the positive electrode material.

[0159] Example 2

[0160] Except for mixing the first positive electrode active material and the second positive electrode active material in a weight ratio of 80:20 to manufacture the positive electrode material, the positive electrode material is manufactured in the same manner as in Example 1.

[0161] Example 3

[0162] Prepare with Li 1.03 Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 O2 represents the composition of the second positive electrode active material (manufacturer: LG Chem Co., Ltd., D 50 (10μm, secondary particle form).

[0163] The first positive electrode active material and the second positive electrode active material manufactured in Preparation Example 2 are mixed such that the weight ratio is 40:60 to manufacture the positive electrode material.

[0164] Example 4

[0165] Except for mixing the first positive electrode active material and the second positive electrode active material in a weight ratio of 80:20 to manufacture the positive electrode material, the positive electrode material is manufactured in the same manner as in Example 3.

[0166] Example 5

[0167] Prepare with Li 1.03 Ni 0.81 Mn 0.12 Co 0.05 Al 0.02 O2 represents the composition of the second positive electrode active material (manufacturer: LG Chem Co., Ltd., D 50 (4μm, secondary particle form).

[0168] The first positive electrode active material and the second positive electrode active material manufactured in Preparation Example 2 are mixed such that the weight ratio is 40:60 to manufacture the positive electrode material.

[0169] Example 6

[0170] Except for mixing the first positive electrode active material and the second positive electrode active material in a weight ratio of 80:20 to manufacture the positive electrode material, the positive electrode material is manufactured in the same manner as in Example 5.

[0171] Example 7

[0172] Prepare with Li 1.03 Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 O2 represents the composition of the second positive electrode active material (manufacturer: LG Chem Co., Ltd., D 50 (10μm, secondary particle form).

[0173] The first positive electrode active material prepared in Preparation Example 3 and the second positive electrode active material are mixed to a weight ratio of 40:60 to prepare the positive electrode material.

[0174] Example 8

[0175] Prepare with Li 1.03 Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 O2 represents the composition of the second positive electrode active material (manufacturer: LG Chem Co., Ltd., D50 (10μm, secondary particle form).

[0176] The first positive electrode active material prepared in Preparation Example 4 and the second positive electrode active material are mixed to a weight ratio of 40:60 to prepare the positive electrode material.

[0177] Example 9

[0178] Except for mixing the first positive electrode active material and the second positive electrode active material in a weight ratio of 90:10 to manufacture the positive electrode material, the positive electrode material is manufactured in the same manner as in Preparation Example 3.

[0179] Comparative Example 1

[0180] Prepare with Li 1.03 Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 O2 represents the composition of the second positive electrode active material (manufacturer: LG Chem Co., Ltd., D 50 (10μm, secondary particle form).

[0181] The first positive electrode active material and the second positive electrode active material prepared in Preparation Example 5 are mixed such that the weight ratio is 40:60 to prepare the positive electrode material.

[0182] Comparative Example 2

[0183] Except that the first positive electrode active material and the second positive electrode active material are mixed in a weight ratio of 80:20, the positive electrode material is manufactured in the same manner as in Comparative Example 1.

[0184] Comparative Example 3

[0185] Prepare with Li 1.03 Ni 0.86 Mn 0.07 Co 0.05 Al 0.02 O2 represents the composition of the second positive electrode active material (manufacturer: LG Chem Co., Ltd., D 50 (10μm, secondary particle form).

[0186] The first positive electrode active material and the second positive electrode active material prepared in Preparation Example 6 are mixed such that the weight ratio is 40:60 to prepare the positive electrode material.

[0187] Comparative Example 4

[0188] Except that the first positive electrode active material and the second positive electrode active material are mixed at a weight ratio of 80:20, the positive electrode material is manufactured in the same manner as in Comparative Example 3.

[0189] Comparative Example 5

[0190] The first positive electrode active material in Preparation Example 2 was used as the positive electrode material in Comparative Example 6.

[0191] Experimental Example

[0192] Experimental Example 1: XRD Analysis

[0193] XRD analysis was performed on each first positive electrode active material used in all embodiments. The XRD data of the first positive electrode active material manufactured according to Preparation Example 2 are shown in Figure 2, and the average crystallite size (nm) of the first positive electrode active materials used in all embodiments is listed in Table 3 below.

[0194] In this case, 2g to 3g of positive electrode active material particles were taken from the positive electrode active material powder and XRD measurements were performed in the 2θ range of 10° to 80° using a Bruker-manufactured D8 XRD under Cu-Kα radiation (wavelength), an accelerating voltage of 45kV and a current of 40mA, at a scan rate of 0.2° / sec.

[0195] Figure 1 The data are XRD data of the first positive electrode active material prepared according to Preparation Example 2.

[0196] refer to Figure 1 This confirms that the first positive electrode active material manufactured in Preparation Example 2 includes an olivine structure.

[0197] Experimental Example 2: Battery Characteristic Evaluation 1

[0198] Manufacturing of coin-type half-cells

[0199] 90% by weight of the first positive electrode active material used in all embodiments, 5.0% by weight of carbon black as a conductive material, and 5.0% by weight of polyvinylidene fluoride (PVDF) as a binder were mixed in N-methyl-2-pyrrolidone (NMP) solvent to prepare a positive electrode slurry. The prepared positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to produce a positive electrode.

[0200] A lithium metal electrode is used as the negative electrode, and a porous polyethylene membrane is provided between the positive and negative electrodes to manufacture an electrode assembly. The electrode assembly is placed in a battery case, and an electrolyte solution is injected to manufacture a coin-shaped half-cell. The electrolyte solution contains 1.0 M LiPF6 dissolved in an organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) are mixed in a volume ratio of 3:4:3.

[0201] Battery performance evaluation 1

[0202] At 25°C, the voltage was charged to 3.65V using the CC (0.1C)-CV (cutoff current: 0.05C) method, followed by a 20-minute rest period, and then discharged to 2.5V using the CC (0.1C) method. The open-circuit voltage (OCV) was measured during this initial charging and discharging process. The open-circuit voltages measured at 3.65V are listed in Table 1 below.

[0203] As described above, at 25°C, after the initial charge and discharge process, the voltage was charged to 4.25 V using the CC (0.1C)-CV (cutoff current: 0.05C) method, followed by a 20-minute rest period, and then discharged to 2.5 V using the CC (0.1C) method. The open-circuit voltage (OCV) measured at 4.25 V is listed in Table 2 below.

[0204] [Table 1]

[0205] [Table 2]

[0206] Referring to Tables 1 and 2, it was confirmed that the open-circuit voltage drop of the first positive electrode active material manufactured in the preparation example, measured by the method described in this specification, ranged from approximately 0.099 V to 0.215 V from 3.65 V, and the open-circuit voltage drop from 4.25 V, measured by the method described in this specification, ranged from approximately 0.28 V to 0.53 V. Therefore, it was confirmed that the open-circuit voltage drop from 4.25 V was greater than that from 3.65 V. Furthermore, when the open-circuit voltage drop of the first positive electrode active material manufactured in the preparation example, measured by the method described in this specification, was below 0.5 V from 4.25 V, the voltage drop of the first positive electrode active material at the operating voltage (4.25 V) of the positive electrode material was relatively small. This allows for improved lifetime characteristics while ensuring uniform operation of both the first and second positive electrode active materials during charge and discharge cycles.

[0207] Referring to Table 2 above, it is confirmed that the open-circuit voltage drop from 4.25 V of the first positive electrode active material manufactured in Preparation Examples 5 and 6, measured by the method described in this specification, is the largest, followed by the open-circuit voltage drop of the first positive electrode active material manufactured in Preparation Examples 3 and 4, and the smallest open-circuit voltage drop of the first positive electrode active material manufactured in Preparation Examples 1 and 2. Referring to Table 1 above, regarding the open-circuit voltage drop from 3.65 V measured by the method described in this specification, the value of the first positive electrode active material manufactured in Preparation Examples 5 and 6 is the largest, followed by the value of the first positive electrode active material manufactured in Preparation Examples 1 and 2, and the smallest value of the first positive electrode active material manufactured in Preparation Examples 3 and 4. Therefore, it can be seen that the open-circuit voltage drop from 4.25 V measured by the method described in this specification has a different trend than the open-circuit voltage drop from 3.65 V measured by the method described in this specification.

[0208] Therefore, it can be confirmed that the cathode material according to the present invention has its technical features in terms of open-circuit voltage drop according to Equation 1 of this specification, which is caused by the combined effect of composition, particle size, carbon (C) content in the cathode active material, average crystallite size, etc.

[0209] Experiment Example 3: Measurement of Carbon (C) Content

[0210] The carbon (C) content in each of the first positive electrode active materials was measured, and the carbon (C) content based on the total weight of the first positive electrode active materials (the carbon (C) content (weight%) of the first positive electrode active materials is listed in Table 3 below.

[0211] Carbon content was measured using a carbon-sulfur analyzer (CS844, LECO). Specifically, 1g of the positive electrode active material powder sample was taken and placed in a crucible, which was then installed in a high-frequency induction furnace for automated analysis. In the high-frequency induction furnace, the carbon gas in the sample combined with O2 to produce CO and CO2. Since C is measured via a CO2 infrared detector, CuO was used to completely convert the CO gas into CO2, and then a CO2 infrared absorption detector was used to measure the C content as CO2 gas.

[0212] Experiment Example 4: Average Particle Size Measurement

[0213] To measure the average particle size of each first and second positive electrode active material used in all embodiments, the particle size was measured using a PSA (Malvern Panalytical Ltd., Mastersizer 3000), and the measurement results are listed in Table 3 below.

[0214] [Table 3]

[0215] Referring to Table 3, it is confirmed that the carbon (C) content in the first positive electrode active material used in the examples is from 1.50% to 5.00% by weight based on the total weight of the first positive electrode active material, and the average crystallite size of the first positive electrode active material used in the examples is from 80 nm to 150 nm. Furthermore, it is confirmed that the average particle size (D) of the first positive electrode active material is... 50 The particle size ranges from 0.3 μm to 8.0 μm, and the average particle size (D) of the second positive electrode active material is... 50 The thickness ranges from 4μm to 13μm.

[0216] Experimental Example 5: Battery Characteristic Evaluation 2

[0217] Manufacturing of coin-type half-cells

[0218] 90% by weight of a first positive electrode material manufactured according to the examples and comparative examples, 5.0% by weight of carbon black as a conductive material, and 5.0% by weight of polyvinylidene fluoride (PVDF) as a binder were mixed in N-methyl-2-pyrrolidone (NMP) solvent to prepare a positive electrode slurry. The prepared positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to manufacture a positive electrode.

[0219] A lithium metal electrode is used as the negative electrode, and a porous polyethylene membrane is provided between the positive and negative electrodes to manufacture an electrode assembly. The electrode assembly is placed in a battery case, and an electrolyte solution is injected to manufacture a coin-shaped half-cell. The electrolyte solution contains 1.0 M LiPF6 dissolved in an organic solvent in which ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) are mixed in a volume ratio of 3:4:3.

[0220] Battery performance evaluation 2

[0221] The coin-type half-cell was charged to 4.25V at 25°C using the CC (0.1C)-CV (cutoff current: 0.05C) method and discharged to 2.5V using the CC (0.1C) method. Then, the battery was charged at 45°C using the CC (0.33C)-CV (cutoff current: 0.05C) method and discharged to 2.5V using the CC (0.33C) method. This process was repeated for a total of 30 cycles, and the resistance was measured by the voltage change over 60 seconds during the 1st and 30th cycles. The percentage increase in resistance (%) between the resistance (Ω) at the 30th cycle and the measured resistance (Ω) at the 1st cycle is listed in Table 4.

[0222] [Table 4]

[0223] Referring to Table 4, in the case of a lithium secondary battery including the positive electrode material manufactured in Examples 1 to 9, that is, the positive electrode material included in the lithium secondary battery includes: a first positive electrode active material that meets the specific conditions described in this specification (the lithium secondary battery includes a positive electrode, which includes a positive electrode active material layer, the positive electrode active material layer containing a first positive electrode active material in an amount of 80% to 98% by weight based on the total weight of the positive electrode active material layer, and the voltage drop (χ) according to Equation 1 is 0.5V or less); and a second positive electrode active material, which has been shown to have a resistance increase rate (%) lower than the resistance increase rate of the secondary battery described below, which includes: the positive electrode material manufactured according to Comparative Examples 1 to 4, that is, the positive electrode material includes a first positive electrode active material that does not meet the specific conditions described in this specification; and a second positive electrode active material. Specifically, when a first positive electrode active material and a second positive electrode active material that do not meet the specific conditions of this specification are included, during charging and discharging, due to the large voltage drop of the first positive electrode active material from the operating voltage (4.25 V) of the positive electrode material, the first and second positive electrode active materials operate unevenly, thus the positive electrode material deteriorates during charging and discharging, resulting in an increased resistance increase rate. Furthermore, it has been confirmed that batteries including the positive electrode material manufactured in Example 9 (with a weight ratio of 90:10 for the first and second positive electrode active materials) have a higher resistance increase rate than batteries including the positive electrode materials manufactured in Examples 1 to 8 (with a weight ratio of 10:90 to 80:20 for the first and second positive electrode active materials).

[0224] Furthermore, it can be confirmed that in the case of secondary batteries containing the positive electrode materials manufactured in Examples 1 to 9 (i.e., the positive electrode material comprises: a first positive electrode active material having an olivine structure; and a second positive electrode active material having a layered structure), the resistance increase rate (%) is lower compared to secondary batteries containing the positive electrode material prepared in Comparative Example 5 (i.e., the positive electrode material does not contain the second positive electrode active material having a layered structure). Specifically, when the positive electrode material manufactured according to Comparative Example 5 is included, that is, when a positive electrode material is included but not the second positive electrode active material having a layered structure, and only the first positive electrode active material having an olivine structure is included, it has been confirmed that secondary batteries containing this positive electrode material tend to have a high resistance increase rate because the positive electrode material deteriorates rapidly in a voltage range exceeding the operating voltage (4.25 V) of the first positive electrode active material.

[0225] In summary, when considering a positive electrode material comprising a first positive electrode active material having an olivine structure and satisfying the specific conditions described in this invention, and a second positive electrode active material having a layered structure, it can be seen that the lithium secondary battery containing the positive electrode material is relatively stable even during charge and discharge cycles at the operating voltage of the positive electrode material.

Claims

1. A positive electrode material, comprising: a first positive electrode active material having an olivine structure; and a second positive electrode active material having a layered structure, in, According to Equation 1 below, the voltage drop (χ) of the first positive electrode active material is 0.50 V or less: [Equation 1] Voltage drop (χ) [V] = (4.25 - open circuit voltage (α) measured after a 20-minute rest period) [V] Wherein, in Equation 1 above, α is the open circuit voltage measured immediately after a 20-minute rest period when a lithium secondary battery including the positive electrode is charged to 4.25 V at 25°C using the CC (0.1C)-CV (cut-off current: 0.05C) method. The positive electrode includes a positive electrode active material layer, and the positive electrode active material layer contains the positive electrode active material in an amount of 80% to 98% by weight based on the total weight of the positive electrode active material layer.

2. The cathode material according to claim 1, wherein, The first positive electrode active material includes a lithium iron phosphate compound having a composition represented by Formula 1 below: [Formula 1] Li 1+x Fe 1-a M 1 a PO4 Wherein, in Formula 1 above, M 1 It is selected from one or more of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B, and Y, and -0.1 ≤ x ≤ 0.1, and 0.0 ≤ a ≤ 0.

8.

3. The cathode material according to claim 2, wherein, The first positive electrode material further includes a carbon (C) coating formed on the lithium iron phosphate compound.

4. The cathode material according to claim 3, wherein, Based on the total weight of the first positive electrode active material, the carbon (C) content contained in the coating is 1.50% to 5.00% by weight.

5. The cathode material according to claim 1, wherein, The average crystallite size of the first positive electrode active material is 80.00 nm to 150.00 nm.

6. The cathode material according to claim 1, wherein, The average particle size (D) of the first positive electrode active material 50 The range is from 0.30 μm to 8.00 μm.

7. The cathode material according to claim 1, wherein, The weight ratio of the first positive electrode active material to the second positive electrode active material is 10:90 to 90:

10.

8. The cathode material according to claim 1, wherein, The weight ratio of the first positive electrode active material to the second positive electrode active material is 10:90 to 80:

20.

9. The cathode material according to claim 1, wherein, The second positive electrode active material has a composition represented by Formula 2 below: [Formula 2] Li 1+y1 Ni p1 Mr q1 Co r1 M 2 s1 O2 Wherein, in Formula 2 above, M 2 It is selected from one or more of Zr, Al, Re, V, Cr, Fe, Ga, Si, B, Ru, Ti, Nb, Mo, Mg, W, Na, and Pt, and 0.00 ≤ y1 ≤ 0.50, 0.00 < p,1 < 1.00, 0.00 < q1 < 0.50, 0.00 < r1 < 0.50, and 0.000 ≤ s1 ≤ 0.

010.

10. The cathode material according to claim 1, wherein, The average particle size (D) of the second positive electrode active material 50 The thickness ranges from 4 μm to 13 μm.

11. A positive electrode, comprising the positive electrode material according to any one of Claims 1 to 10.

12. A lithium secondary battery, comprising the positive electrode according to Claim 11.

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