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

Abstract

The present invention relates to a positive electrode active material capable of improving the performance of a lithium secondary battery, and more particularly, to a positive electrode active material comprising a lithium iron phosphate-based compound in the form of primary particles or secondary particles, the value (X) according to formula 1 of the present specification being 19.000 nm×Ω or greater and 60.000 nm×Ω or less, and to a positive electrode and a lithium secondary battery comprising the positive electrode active material.

Description

Anode active material, and anode and lithium secondary battery including the same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2025-0000870 filed on January 3, 2025, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.

[0003] Technology field

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

[0005]

[0006] With the recent increase in technological development and demand for mobile devices and electric vehicles, the demand for rechargeable batteries as an energy source is rapidly rising. Among these rechargeable batteries, lithium-ion batteries, which possess high energy density and voltage, long cycle life, and low self-discharge rates, have been commercialized and are widely used.

[0007] Lithium secondary batteries consist of four major components: a positive electrode, a negative electrode, a separator, and an electrolyte. Among these, the positive electrode active material included in the positive electrode plays a significant role in determining the battery's capacity, output, and lifespan. Improving the performance of the positive electrode active material is essential for lithium secondary batteries to achieve high energy density, output, and lifespan; consequently, much research has recently been conducted to develop high-performance positive electrode active materials.

[0008] Lithium transition metal oxides, 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 as cathode active materials for lithium secondary batteries, and recently, Li[Ni a Co b Mn c ]O2, Li[Nia Co b Al c ]O2, Li[Ni a Co b Mn c Al d Lithium composite transition metal oxides containing two or more transition metals, such as O2, have been developed and are widely used.

[0009] Meanwhile, lithium iron phosphate compounds having an olivine structure are promising active materials that have excellent lifespan characteristics and superior safety features, including overcharging and over-discharging, because they have the best structural stability.

[0010] In particular, LiFePO4 exhibits excellent high-temperature stability due to the strong bonding strength of PO4. Furthermore, because it contains iron, which is resource-abundant and inexpensive, it is cheaper than the aforementioned LiCoO2, LiNiO2, or LiMn2O4, and has low toxicity, resulting in minimal environmental impact. However, since LiFePO4 has low electrical conductivity, using it as a cathode active material leads to an increase in the battery's internal resistance. Consequently, the battery capacity decreases as the polarization potential increases during circuit closure. Additionally, LiFePO4 has a low average operating voltage, resulting in low energy density.

[0011] To address this, there is a need for development to improve the performance of cathode active materials, including lithium iron phosphate-based compounds.

[0012]

[0013] The objective of the present invention is to provide a positive electrode active material capable of improving the efficiency characteristics and rate characteristics of a lithium secondary battery.

[0014] In addition, the objective of the present invention is to provide a positive electrode and a lithium secondary battery comprising the above-mentioned positive electrode active material.

[0015]

[0016] However, the problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0017]

[0018] (1) The present invention provides a positive electrode active material comprising a lithium iron phosphate compound in the form of primary or secondary particles, wherein the value (X) according to Formula 1 below is 19.000 nm × Ω or more and 60.000 nm × Ω or less.

[0019] [Equation 1]

[0020] X = (a×c / d)×(b / e)

[0021] In Equation 1 above, a is the average particle diameter of the primary particles obtained from the SEM image [μm], b is the average size of the crystallites obtained from the XRD spectrum [nm], c is the charge transfer resistance [Ω] analyzed by Electrochemical Impedance Spectroscopy (EIS) at SOC 50 when a lithium secondary battery comprising a cathode containing a cathode active material layer containing the cathode active material in an amount of 80 wt% or more and 98 wt% or less relative to the total weight of the cathode active material layer is charged to 3.7 V at 25°C using the CC (0.1C)-CV (Cut-off current: 0.05C) method, rested for 30 minutes, and then discharged to 2.5 V at 0.1C, and d is the average particle diameter (D) measured by a Particle Size Analyzer (PSA). 50 )[㎛], where e is the ratio of the intensity of the (020) plane peak to the intensity of the (200) plane peak in the XRD spectrum.

[0022] (2) The present invention provides a positive electrode active material in which, in (1) above, the lithium iron phosphate compound has a composition represented by the following chemical formula 1.

[0023] [Chemical Formula 1]

[0024] Li 1+y1 Fe 1-p1 M p1 PO4

[0025] In the above chemical formula 1, M is one or more selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, and -0.1≤y1≤0.1, 0.00≤p1<1.00.

[0026] (3) The present invention provides a positive electrode active material in which, in (1) or (2), the lithium iron phosphate compound has a molar ratio of lithium to iron of 0.90 or more and 1.05 or less.

[0027] (4) The present invention provides a positive electrode active material in any one of (1) to (3), wherein the lithium iron phosphate compound has a molar ratio of the doping element to iron of 0.00 or more and 0.02 or less, and the doping element is one or more selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y.

[0028] (5) The present invention provides a positive electrode active material in any one of (1) to (4), wherein a is 0.3000 μm or more and 0.5000 μm or less.

[0029] (6) The present invention provides a positive electrode active material in any one of (1) to (5), wherein b is 90.000 nm or more and 150.000 nm or less.

[0030] (7) The present invention provides a positive electrode active material in any one of (1) to (6), wherein c is 3.000 Ω or more and 4.000 Ω or less.

[0031] (8) The present invention provides a positive electrode active material in any one of (1) to (7), wherein d is 1.00 μm or more and 3.00 μm or less.

[0032] (9) The present invention provides a positive electrode active material in any one of (1) to (8), wherein e is 2.000 or more and 2.500 or less.

[0033] (10) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (9).

[0034] (11) The present invention provides a lithium secondary battery comprising a positive electrode according to (10) above.

[0035]

[0036] The positive electrode active material according to the present invention comprises a lithium iron phosphate-based compound in the form of primary or secondary particles, and by satisfying the value (X) according to Formula 1 described in this specification within a specific numerical range, the electron conductivity and lithium ion conductivity of the positive electrode active material are improved. Accordingly, the efficiency characteristics and rate characteristics of a battery including the positive electrode active material according to the present invention are improved.

[0037]

[0038] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0039] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0040] In this specification, terms such as 'comprising,' 'having,' or 'having' are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0041] In this specification, 'determinant' means a particle unit having substantially the same crystal orientation.

[0042] In this specification, the 'average size of crystallites' can be quantitatively analyzed using X-ray diffraction analysis (XRD) by Cu Kα X-rays. Specifically, the average size of crystallites can be quantitatively analyzed by placing the particle to be measured into a holder, irradiating the particle with X-rays, and analyzing the resulting diffraction grating. Sampling was prepared by placing a powder sample of the particle to be measured into a recessed groove in the center of a general powder holder, smoothing the surface using a slide glass, and ensuring the sample height was equal to the edge of the holder. Then, X-ray diffraction analysis was performed using a Bruker D8 Endeavor (light source: Cu-Kα rays, wavelength: 1.54 Å) equipped with a LynxEye XE-T position-sensitive detector, under conditions of a step size of 0.1° for the FDS 0.5° and 2θ = 10° to 100° range. For the measured data, Rietveld refinement was performed considering the charge (Fe is +2, Li is +1, Ti is +4) and cation mixing at each site. For size analysis, instrumental broadening was considered using the Fundamental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and all peaks within the measurement range were used for fitting. Peak shape was fitted using only the Lorenzian contribution as the First Principle (FP) among the peak types available in TOPAS, without considering strain.

[0043] In this specification, 'primary particle' refers to the smallest unit of particle recognized when the positive electrode active material is observed through a scanning electron microscope.

[0044] In this specification, the 'average particle size of primary particles' can be obtained from the particle size corresponding to each of the n primary particles present in the SEM image. The particle size corresponding to each of the primary particles can be verified by processing the scanning electron microscope (SEM) image using an image processing program (LG Chem, DX program). Specifically, it can be measured from a two-dimensional segmentation image divided by primary particle units obtained by image processing using an artificial intelligence model. The segmentation image can be obtained by acquiring a scanning electron microscope (SEM) image (10K magnification) of the cathode active material powder to be measured, inputting the acquired scanning electron microscope image into a U-NET structure or the like to generate a boundary image, removing the boundaries from the scanning electron microscope (SEM) image based on the boundary image to generate a boundary removal image, identifying multiple objects included in the boundary removal image, and then segmenting the SEM image into primary particle units based on the multiple objects. The particle size of the primary particles may be calculated by calculating the area of ​​each primary particle through the number of pixels corresponding to each of the n primary particles present in the segmentation image, and by using the radius of a circle having the same area as the area of ​​each primary particle to calculate the particle size of each primary particle present in the segmentation image. The average particle size of the primary particles can be calculated from the arithmetic mean of the particle sizes of the primary particles.

[0045] D in this specification min It is the minimum particle size of the silver particle, and D max is the maximum particle size, and 'D n' can be defined as the particle size corresponding to n% of the cumulative volume distribution in the particle size distribution curve (graph curve of the particle size distribution). Specifically, D 10 is the particle size corresponding to 10% of the cumulative volume distribution, and D 50 is the particle size corresponding to 50% of the volumetric cumulative distribution, and D 90 is the particle size corresponding to 90% of the cumulative volume distribution. The above average particle size is determined by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500), measuring the difference in diffraction patterns according to particle size as the particles pass through a laser beam to calculate the particle size distribution, and calculating the particle diameter at the point where the cumulative volume distribution according to particle size in the measuring device is n%, thereby D n It can measure.

[0046]

[0047] positive electrode active material

[0048] Hereinafter, the positive active material according to the present invention will be described.

[0049]

[0050] The positive electrode active material according to the present invention comprises a lithium iron phosphate-based compound in the form of primary particles or secondary particles, and the value (X) according to Formula 1 below is 19.000 nm × Ω or more and 60.000 nm × Ω or less.

[0051] [Equation 1]

[0052] X = (a×c / d)×(b / e)

[0053] In the above Equation 1,

[0054] a is the average particle size [μm] of the primary particles obtained from the SEM image, and

[0055] b is the average size of the crystallites obtained from the XRD spectrum [nm], and

[0056] c is the charge transfer resistance [Ω] analyzed by Electrochemical Impedance Spectroscopy (EIS) at SOC 50 when a lithium secondary battery comprising a cathode containing a cathode active material layer containing a cathode active material in an amount of 80 wt% or more and 98 wt% or less with respect to the total weight of the cathode active material layer is charged to 3.7 V at 25°C using the CC (0.1C)-CV (Cut-off current: 0.05C) method, rested for 30 minutes, and then discharged to 2.5 V at 0.1C.

[0057] d is the average particle size (D) measured by a Particle Size Analyzer (PSA). 50 )[㎛] and,

[0058] e is the ratio of the intensity of the (020) plane peak to the intensity of the (200) plane peak in the XRD spectrum.

[0059]

[0060] In this specification, a is an indicator related to the size of primary particles in the positive active material, b and e are indicators related to the crystal structure of the positive active material, c is an indicator related to conductivity, and d is an indicator related to the particle size of the positive active material.

[0061]

[0062] In the present invention, Equation 1, which represents the relationship between the primary particle shape, crystal structure, charge transfer resistance, and particle size of the positive active material, was used to represent the structure and conductivity of the positive active material.

[0063] In Equation 1 above, b / e is the average size of the crystallites (b) obtained from the XRD spectrum relative to the ratio (e) of the intensity of the (020) plane peak to the intensity of the (200) plane peak in the XRD spectrum, and is a conductivity-related indicator. Specifically, the smaller the average size of the crystallites, the shorter the diffusion distance of lithium ions, so the conductivity tends to be excellent. The larger the ratio of the intensity of the (020) plane peak to the intensity of the (200) plane peak, the wider the relative area of ​​the (020) plane, which is the transmission plane that serves as the path for lithium ions to move, so the conductivity tends to be excellent. If the average size of the crystallites (b) obtained from the XRD spectrum is too small, there may be a possibility that the electrochemical stability will be reduced due to an increase in defects.

[0064] a×c / d is the product of the average particle size (a) of the primary particle obtained from an SEM image of the average particle size (D50)(d) measured by a particle size analyzer (PSA), and the charge transfer resistance (c) analyzed by electrochemical impedance spectroscopy (EIS) at SOC 50 when the lithium secondary battery containing a positive electrode containing a positive electrode active material layer containing a positive electrode active material in an amount of 80% by weight or more and 98% by weight or less relative to the total weight of the positive electrode active material layer is charged to 3.7 V at 25°C using the CC (0.1C)-CV (Cut off current: 0.05C) method, rested for 30 minutes, and then discharged to 2.5 V at 0.1C. This is a structural indicator. Specifically, the average particle size (D50) (d) measured by a particle size analyzer (PSA) and the average particle size of primary particles (a) obtained from an SEM image are indicators of the degree of particle aggregation and the number of interfaces. Charge transfer resistance is affected by the interfaces and particle size of the particles. When the average particle size of the positive active material is small and the average particle size of the primary particles is large, there are fewer interfaces of the primary particles and thus the charge transfer resistance is low; and when the size of the primary particles and the positive active material is large, the charge transfer resistance tends to be low.

[0065]

[0066] Average particle size of primary particles obtained from SEM images (a), average size of crystallites obtained from XRD spectra (b), charge transfer resistance analyzed by Electrochemical Impedance Spectroscopy (EIS) at SOC 50 when a lithium secondary battery comprising a cathode containing a cathode active material layer containing a cathode active material in an amount of 80 wt% or more and 98 wt% or less relative to the total weight of the cathode active material layer is charged to 3.7 V at 25°C using the CC (0.1C)-CV (Cut-off current: 0.05C) method, rested for 30 minutes, and then discharged to 2.5 V at 0.1C (c), and average particle size measured by a Particle Size Analyzer (PSA) (D 50 In addition to the ratio of the intensity of the (020) plane peak to the intensity of the (200) plane peak in the XRD spectrum (d) and X reflecting the relationship between a, b, c, d and e must be within a specific range so that ion and electron transfer within the positive electrode active material is efficiently carried out, thereby minimizing polarization phenomena and improving the rate characteristics and efficiency characteristics of the battery.

[0067]

[0068] The positive electrode active material according to the present invention comprises a lithium iron phosphate-based compound in the form of primary particles or secondary particles, and the value (X) according to Formula 1 is 19.000 nm × Ω or more and 60.000 nm × Ω or less. Specifically, the value (X) according to the above Equation 1 may be 19.000 nm×Ω or more, 20.000 nm×Ω or more, 21.000 nm×Ω or more, 22.000 nm×Ω or more, 23.000 nm×Ω or more, 24.000 nm×Ω or more, 25.000 nm×Ω or more, 26.000 nm×Ω or more, 27.000 nm×Ω or more, 28.000 nm×Ω or more, 29.000 nm×Ω or more, 30.000 nm×Ω or more, 31.000 nm×Ω or more, 32.000 nm×Ω or more, 33.000 nm×Ω or more, 34.000 nm×Ω or more, or 35.000 nm×Ω or more, and 58.000 nm×Ω or less, 59.000 nm×Ω or less, or It may be 60.000 nm × Ω or less. When the value (X) according to Equation 1 above is within the above range, the ionic conductivity and electrical conductivity of the positive electrode active material are improved, and accordingly, the battery containing the positive electrode active material has the effect of improving electrochemical efficiency characteristics and rate characteristics. When the value (X) according to Equation 1 above is less than 19.000 nm × Ω or greater than 60.000 nm × Ω, the electronic conductivity and lithium ion conductivity of the positive electrode active material are low, resulting in problems such as inferior capacity characteristics, efficiency characteristics, and rate characteristics, and low energy density. In particular, when the value (X) according to Equation 1 above is 35.000 nm × Ω or more and 58.000 nm × Ω or less, the size of the positive electrode active material, the size of the primary particles, and the size and number of crystallites constituting the primary particles are appropriate, thereby providing an efficient ion transport path and improving specific capacity and energy density.

[0069]

[0070] The above 'a' is the average particle size [μm] of primary particles obtained from an SEM image, that is, the average particle size value of primary particles obtained from an SEM image when the unit unit is μm. The size of primary particles in the cathode active material can be confirmed using the above 'a'. According to one embodiment of the present invention, the above 'a' may be 0.3000 μm or more and 0.5000 μm or less. Specifically, the above 'a' may be 0.3000 μm or more, 0.3100 μm or more, or 0.3200 μm or more, and may be 0.4700 μm or less, 0.4800 μm or less, 0.4900 μm or less, or 0.5000 μm or less. When the above 'a' is within the above range, the size of the primary particles can be adjusted to an appropriate degree to improve the electron conductivity and lithium-ion conductivity of the cathode active material, and the efficiency characteristics and rate characteristics of the battery manufactured using this can be improved.

[0071]

[0072] The above b is the average size of crystallites [nm] obtained from the XRD spectrum, that is, the average size value of crystallites obtained from the XRD spectrum when the unit is nm. The size of crystallites within the cathode active material can be confirmed using the above b. According to one embodiment of the present invention, the above b may be 90.000 nm or more and 150.000 nm or less. Specifically, the above b may be 90.000 nm or more, 91.000 nm or more, 92.000 nm or more, or 93.000 nm or more, and may be 144.000 nm or less, 145.000 nm or less, 146.000 nm or less, 147.000 nm or less, 148.000 nm or less, 149.000 nm or less, or 150.000 nm or less. When b is within the above range, the average size of the crystallites can be adjusted to an appropriate degree to improve the electron conductivity and lithium-ion conductivity of the positive electrode active material, and the efficiency characteristics and rate characteristics of the battery manufactured using this can be improved.

[0073]

[0074] The above c is the charge transfer resistance [Ω] analyzed by Electrochemical Impedance Spectroscopy (EIS) at an SOC of 50 when discharging to 2.5 V at 0.1C, wherein the lithium secondary battery comprising a cathode including a cathode including a cathode active material layer containing a cathode active material in an amount of 80 wt% or more and 98 wt% or less based on the total weight of the cathode active material layer is charged to 3.7 V at 25°C using the CC (0.1C)-CV (Cut-off current: 0.05C) method, rested for 30 minutes, and then discharged to 2.5 V at 0.1C; that is, when the unit is Ω, the lithium secondary battery comprising a cathode including It is the charge transfer resistance value analyzed by Electrochemical Impedance Spectroscopy (EIS) at an SOC of 50 when discharged to 2.5V at 0.1C. The above c represents conductivity. Specifically, it means that the smaller the charge transfer resistance, the greater the conductivity. Since contact with the electrolyte is easier when the surface area of ​​the positive electrode active material is larger, the charge transfer resistance tends to be smaller. According to one embodiment of the present invention, the above c may be 3.000 Ω or more and 4.000 Ω or less. Specifically, the above c may be 3.000 Ω or more, 3.100 Ω or more, or 3.200 Ω or more, and may be 4.000 Ω or less. When the above c is within the above range, the efficiency characteristics and rate characteristics of the manufactured battery can be improved by adjusting the conductivity of the positive electrode active material to an appropriate degree.

[0075]

[0076] The above d is the average particle size (D) measured by a Particle Size Analyzer (PSA). 50 )[㎛], where the unit is ㎛, the average particle size (D) measured by a Particle Size Analyzer (PSA). 50 ) is a value. The above d may be 1.00 μm or more and 3.00 μm or less. Specifically, the above d may be 1.00 μm or more, 1.10 μm or more, 1.20 μm or more, 1.30 μm or more, 1.40 μm or more, or 1.50 μm or more, and may be 2.20 μm or less, 2.30 μm or less, 2.40 μm or less, 2.50 μm or less, 2.60 μm or less, 2.70 μm or less, 2.80 μm or less, 2.90 μm or less, or 3.00 μm or less. When the above d is within the above range, the electron conductivity and lithium ion conductivity of the cathode active material can be improved by adjusting the density of the cathode active material to an appropriate degree, and the efficiency characteristics and rate characteristics of the battery manufactured using this can be improved.

[0077]

[0078] The above e is the ratio of the intensity of the (020) plane peak to the intensity of the (200) plane peak in the XRD spectrum, representing the degree of growth in the direction that serves as the movement path for lithium ions within the cathode active material. Specifically, the (200) plane is a plane with almost no permeability to lithium ions, and the (020) plane is the main permeable plane for lithium ions. Accordingly, the degree of growth in the direction that serves as the movement path for lithium ions can be confirmed by the ratio of the intensity of the (020) plane peak to the intensity of the (200) plane peak. It can be seen that the larger the above ratio, the larger the relative area of ​​the (020) plane, which is the permeable plane serving as the movement path for lithium ions. The larger the above ratio, the more effective it is in minimizing polarization phenomena and improving efficiency characteristics and rate characteristics. According to one embodiment of the present invention, the above e may be 2.000 or more and 2.500 or less. Specifically, the above e may be 2.000 or higher, 2.300 or lower, 2.400 or lower, or 2.500 or lower. When the above e is within the above range, the growth orientation of the positive electrode active material can be adjusted to an appropriate degree to improve the electron conductivity and lithium ion conductivity of the positive electrode active material, and the efficiency characteristics and rate characteristics of the battery manufactured using this can be improved.

[0079]

[0080] According to one embodiment of the present invention, the lithium iron phosphate-based compound may have a composition represented by the following chemical formula 1.

[0081] [Chemical Formula 1]

[0082] Li 1+y1 Fe 1-p1 M p1 PO4

[0083] In the above chemical formula 1, M is one or more selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn and Y, and -0.1≤y1≤0.1, 0.00≤p1<1.00.

[0084] The above M is a doping element, specifically, M may be one or more selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y.

[0085] Meanwhile, the above y1 may be -0.1 or greater, or 0 or greater and 0.1 or less. When y1 satisfies the above range, the synthesis of impurities can be suppressed and structural stability can be improved.

[0086] p1 is the mole fraction of M among all metals excluding lithium in the lithium iron phosphate compound, and may be 0 or greater, or 0.01 or greater, or 0.05 or less, 0.10 or less, 0.50 or less, or less than 1.00. When p1 satisfies the above range, lifespan characteristics can be improved by controlling the length and strength of the bond between lithium and oxygen while maintaining energy density.

[0087]

[0088] According to one embodiment of the present invention, the lithium iron phosphate-based compound may have a molar ratio of lithium to iron of 0.90 or higher and 1.05 or lower. Specifically, the lithium iron phosphate-based compound may have a molar ratio of lithium to iron of 0.90 or higher or 0.95 or higher, and may be 1.00 or lower, 1.01 or lower, 1.02 or lower, 1.03 or lower, 1.04 or lower, or 1.05 or lower. When the molar ratio of lithium to iron is within the above range, the structural stability of the cathode active material can be improved while ensuring that no residual lithium exists.

[0089]

[0090] According to one embodiment of the present invention, the lithium iron phosphate-based compound has a molar ratio of a doping element to iron of 0.00 or higher and 0.02 or lower, and the doping element may be one or more selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. Specifically, the lithium iron phosphate-based compound may have a molar ratio of a doping element to iron of 0.00 or higher, 0.01 or lower, or 0.02 or lower. When the molar ratio of a doping element to iron is within the above range, the impurity content can be lowered when forming an olivine structure, and the crystal lattice constant in the b-axis direction can be reduced to improve capacitance characteristics, resistance characteristics, and rate characteristics.

[0091]

[0092] The positive electrode active material according to the present invention may be manufactured by a manufacturing method comprising: (A) mixing a lithium raw material, a phosphate raw material, an iron raw material, and a carbon coating raw material, and optionally further mixing a doping (e.g., titanium, magnesium, etc.) element raw material to prepare a mixture; and (B) calcining the mixture to produce a calcined product, but is not limited thereto.

[0093]

[0094] The physical properties of the positive electrode active material according to the present invention can be achieved by appropriately adjusting the presence or absence and amount of doping element raw material, the amount of carbon coating raw material used, the calcination temperature, and the grinding conditions during the manufacture of the positive electrode active material, but are not limited thereto.

[0095]

[0096] The above lithium raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide. Specifically, the above lithium raw material may be Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, etc.

[0097] The above lithium raw material may be introduced such that the molar ratio of lithium to iron is 0.9 or higher and 1.05 or lower.

[0098] The above phosphoric acid raw material may be FePO4, H3PO4, NH4H2PO4, (NH4)2HPO4, P2O5, etc.

[0099]

[0100] The above iron raw material may be an iron-containing phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide, or oxyhydroxide. Specifically, the above iron raw material may be FePO4, FeSO4, FeC2O4·2H2O, FeCl2, etc.

[0101] The above-mentioned phosphoric acid raw material and iron raw material may be the same. For example, it may be iron phosphate (FePO4).

[0102]

[0103] The above carbon coating raw material can provide a coating portion containing carbon by calcination, and accordingly, the electrical conductivity of the positive electrode active material can be improved. The above carbon coating raw material may be sucrose, glucose, lactose, starch, oligosaccharide, polyoligosaccharide, fructose, cellulose, vinyl resin, cellulose-based resin, phenolic resin, pitch-based resin, tar-based resin, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, citric acid, ammonium citrate, etc. Specifically, the above carbon coating raw material may be glucose.

[0104] The carbon coating raw material may be introduced in an amount of 5% to 15% by weight relative to the total weight of the lithium raw material, phosphoric acid raw material, and iron raw material. Specifically, the carbon coating raw material may be introduced in an amount of 7% to 12% by weight relative to the total weight of the lithium raw material, phosphoric acid raw material, and iron raw material. In this case, the carbon coating raw material is utilized as a material for the oxidation-reduction reaction that proceeds during the process of forming lithium iron phosphate crystals, and an appropriate amount of carbon is coated to improve conductivity.

[0105]

[0106] The above doping element raw material may be a phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, oxide, hydroxide, or oxyhydroxide containing the above doping element, and in this case, the above doping element may be one or more selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. Specifically, if the above doping element is titanium, it may be titanium dioxide, titanium nitrate, titanium sulfate, etc., and if it is magnesium, it may be magnesium dioxide, magnesium nitrate, magnesium sulfate, etc. The above doping element raw material may be introduced such that the molar ratio of the doping element to iron is 0 or greater and 0.02 or less.

[0107]

[0108] The above lithium raw material, phosphate raw material, iron raw material, and doping element raw material can be mixed in an amount such that the lithium iron phosphate-based compound included in the resulting cathode active material has a composition represented by Chemical Formula 1.

[0109]

[0110] The mixing of the above raw materials may be wet mixing or dry mixing.

[0111] In the case where the above mixing is a wet mixing, water may be used as a solvent, and the raw materials may be simply mixed in water, and then the mixed solution may be wet-ground using a bead mill, but is not limited thereto. The above wet grinding may be performed for 30 minutes or more and 120 minutes or less. If the above wet grinding is performed for less than 30 minutes, there is a problem that grinding and disintegration are not sufficiently achieved, and if it is performed for more than 120 minutes, there is a problem such as the size of the crystallites of the cathode active material synthesized during calcination becoming smaller.

[0112]

[0113] Meanwhile, in the case of wet mixing, a dried powder (mixture) can be obtained by finally spray drying.

[0114] Specifically, the above spray drying may be performed using a nozzle-type spray dryer, and the spray drying may be performed at an inlet temperature of 180°C to 230°C and an outlet temperature of 80°C to 95°C. In this case, a dried product with uniformly coated carbon can be obtained. If the outlet temperature exceeds 95°C, there is a problem that the size of the primary particles and crystallites becomes excessively large.

[0115]

[0116] The above calcination can be performed for 8 to 12 hours at a temperature of 750°C to 850°C. In this case, through the optimized calcination temperature, appropriate primary particles are formed and no impurities are formed, so an anode active material with high rolling density and low resistance can be manufactured. If the above calcination is performed at a temperature of 700°C or lower, it is difficult to form a single phase of LiFePO4, and there is a problem that impurities such as Li3PO4 or Fe2P2O7 appear.

[0117] The above calcination may be performed under an inert atmosphere. Specifically, the above calcination may be performed under a nitrogen atmosphere.

[0118]

[0119] Formula 1 described in this specification is determined by a combination of factors, such as the mixing amount of carbon coating raw materials, wet grinding time, spray drying outlet temperature, and calcination temperature. As the mixing amount of carbon coating raw materials increases, the carbon coating part hinders particle growth, so a, b, and d in Formula 1 described in this specification tend to be small, and c tends to be small because conductivity increases due to the carbon coating. As the wet grinding time increases, the materials are ground finer and the specific surface area increases, resulting in excellent reactivity between raw materials; therefore, b and d in Formula 1 described in this specification tend to be small and e tends to be large. As the spray drying outlet temperature increases, a, b, and d tend to be large due to particle aggregation and recrystallization; and as the calcination temperature increases, d in Formula 1 described in this specification tends to be large due to excellent reactivity between raw materials. Since the above factors do not have a linear relationship, they must be appropriately adjusted to improve efficiency and rate characteristics.

[0120]

[0121] Specifically, when the carbon coating raw material is added at 7% by weight relative to the total weight of the lithium raw material, phosphoric acid raw material, and iron raw material, the wet grinding time may be 50 minutes or less, the spray drying outlet temperature may be 80°C or less, and the calcination temperature may be 780°C or more and 800°C or less; and when the carbon coating raw material is added at 12% by weight relative to the total weight of the lithium raw material, phosphoric acid raw material, and iron raw material, the wet grinding time may be 30 minutes or more and 120 minutes or less, the spray drying outlet temperature may be 85°C or more and 90°C or less, and the calcination temperature may be 780°C or less.

[0122]

[0123] The positive active material manufactured according to the above method may have a value (X) according to Formula 1 described in this specification of 19.000 nm × Ω or more and 60.000 nm × Ω or less.

[0124]

[0125] anode

[0126] Next, the anode according to the present invention will be described.

[0127] The anode according to the present invention comprises an anode active material layer comprising an anode active material according to the present invention. Specifically, the anode comprises an anode current collector and an anode active material layer formed on the anode current collector and comprising the anode active material. Since the anode active material has been described above, a detailed explanation is omitted, and only the remaining components are described in detail below.

[0128]

[0129] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0130]

[0131] The above positive active material layer may include a conductive material and a binder together with the positive active material. In this case, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and may exhibit excellent capacity characteristics within this range.

[0132]

[0133] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. 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 powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0134]

[0135] The above binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 0.1% to 15% by weight based on the total weight of the positive active material layer.

[0136]

[0137] The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it may be manufactured by applying a composition for forming an anode active material layer, prepared by dissolving or dispersing the above-described anode active material and, optionally, a binder and a conductive material in a solvent, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above. Alternatively, the above-described anode may be manufactured by casting the composition for forming an anode active material layer onto a separate support, and then laminating the film obtained by peeling from the support onto an anode current collector.

[0138]

[0139] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0140]

[0141] lithium secondary battery

[0142] Next, a lithium secondary battery according to the present invention will be described.

[0143] The present invention can manufacture an electrochemical device comprising the anode. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, a lithium secondary battery.

[0144]

[0145] Specifically, the above lithium secondary battery comprises a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is identical to the one described above, a detailed description is omitted, and only the remaining components are described in detail below.

[0146]

[0147] In addition, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, negative electrode, and separator, and a sealing member that seals the battery container.

[0148]

[0149] In the above lithium secondary battery, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0150] The above-mentioned negative 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, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0151]

[0152] The above-mentioned cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

[0153]

[0154] As the above-mentioned negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO₂ β Examples include metal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used. Additionally, a metallic lithium thin film may be used as the negative electrode active material. Furthermore, the carbon material may include low-crystallinity carbon and high-crystallinity carbon. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0155] The above-mentioned negative electrode active material may be included in an amount of 80% to 99% by weight relative to the total weight of the negative electrode active material layer.

[0156]

[0157] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0158]

[0159] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, specifically 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; metal powder such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0160]

[0161] The above-mentioned negative electrode active material layer may be manufactured by applying and drying a composition for forming a negative electrode active material layer, prepared by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive material in a solvent, or by casting the composition for forming a negative electrode active material layer onto a separate support and then laminating the film obtained by peeling from the support onto a negative electrode current collector.

[0162]

[0163] Meanwhile, in the above-mentioned lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0164]

[0165] In addition, the electrolytes used in the present invention may include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., which are usable when manufacturing lithium secondary batteries, but are not limited to these.

[0166] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0167] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; and carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). Alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond-directing ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, carbonate-based solvents are preferred, 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 low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0168]

[0169] The above lithium salt can be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, specifically 0.1 to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0170]

[0171] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10 weight%, specifically 0.1 to 5 weight%, based on the total weight of the electrolyte.

[0172]

[0173] As described above, since the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent electrochemical efficiency and rate characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, and in electric vehicle fields such as hybrid electric vehicles (HEV).

[0174] Accordingly, according to another embodiment of the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0175] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0176] The external shape of the lithium secondary battery of the present invention is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0177] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0178]

[0179] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0180]

[0181] Examples and Comparative Examples

[0182] Example 1

[0183] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 7% by weight relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 50 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 80 ℃).

[0184] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 800°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 1.5 weight% with respect to the total weight of the positive electrode active material.

[0185]

[0186] Example 2

[0187] Li2CO3, FePO4(D 50Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 12 wt% relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 120 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 85 ℃).

[0188] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 780°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 2.5 weight% with respect to the total weight of the positive electrode active material.

[0189]

[0190] Example 3

[0191] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 12 wt% relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 30 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 90 ℃).

[0192] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 780°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 2.4 weight% with respect to the total weight of the positive electrode active material.

[0193]

[0194] Comparative Example 1

[0195] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 7 wt% relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 50 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 85 ℃).

[0196] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 700°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 1.3 weight% with respect to the total weight of the positive electrode active material.

[0197]

[0198] Comparative Example 2

[0199] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 7 wt% relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 60 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 100 ℃).

[0200] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 800°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 1.4 weight% with respect to the total weight of the positive electrode active material.

[0201]

[0202] Comparative Example 3

[0203] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 10 wt% relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 90 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 95 ℃).

[0204] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 780°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 includes a coating portion containing carbon, and the carbon content included in the coating portion is about 2.0 weight% with respect to the total weight of the positive electrode active material.

[0205]

[0206] Comparative Example 4

[0207] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 7% by weight relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 50 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 90 ℃).

[0208] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 780°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 1.3 weight% with respect to the total weight of the positive electrode active material.

[0209]

[0210] Comparative Example 5

[0211] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 8% by weight relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 50 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 90 ℃).

[0212] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 800°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 1.6 weight% with respect to the total weight of the positive electrode active material.

[0213]

[0214] Comparative Example 6

[0215] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 7% by weight relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 50 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 80 ℃).

[0216] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 780°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 1.3 weight% with respect to the total weight of the positive electrode active material.

[0217]

[0218] Comparative Example 7

[0219] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 7% by weight relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 30 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 85 ℃).

[0220] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 800°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 1.4 weight% with respect to the total weight of the positive electrode active material.

[0221]

[0222] Comparative Example 8

[0223] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 7% by weight relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 30 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 90 ℃).

[0224] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 770°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 comprises a coating portion containing carbon, wherein the carbon content in the coating portion is about 1.5 weight% with respect to the total weight of the positive electrode active material.

[0225]

[0226] Comparative Example 9

[0227] Li2CO3, FePO4(D 50 Li2CO3 (3.5±1.5㎛) and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.01, and glucose was added in an amount of 12 wt% relative to the total weight of Li2CO3 and FePO4 to prepare a mixed solution. To mix and grind the raw materials, the mixed solution was wet-ground in a beads mill for 90 minutes to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 200 ℃, outlet temperature: 100 ℃).

[0228] Subsequently, the dried powder (hereinafter referred to as the mixture) was calcined at 800°C for 10 hours under a nitrogen atmosphere to produce a calcined product. The calcined product was ground using a jet mill to produce an anode active material. At this time, the anode active material was LiFe 0.99 Ti 0.01 The lithium iron phosphate-based compound having a composition represented by PO4 includes a carbon-containing coating portion, and the carbon content included in the coating portion is about 2.1 weight% with respect to the total weight of the positive electrode active material.

[0229]

[0230] Glucose Mixture Amount (Wet%) Wet Grinding Time (Min) Spray Drying Outlet Temperature (°C) Calcination Temperature (°C) Example 1 750 80 800 Example 2 12 12 0 85 780 Example 3 12 30 90 780 Comparative Example 1 750 85 700 Comparative Example 2 760 10 800 Comparative Example 3 10 90 95 780 Comparative Example 4 750 90 780 Comparative Example 5 850 90 800 Comparative Example 6 750 80 780 Comparative Example 7 730 85 800 Comparative Example 8 730 90 770 Comparative Example 9 12 90 10 800

[0231] Experimental Example

[0232] Experimental Example 1: XRD Spectrum Analysis 1

[0233] For each cathode active material prepared in the above examples and comparative examples, the average size of the crystallites (b) [nm] was determined after XRD analysis, and the results are shown in Table 2 below.

[0234] At this time, the XRD measurement was performed using a Bruker D8 Endeavor, and 0.5g to 1.5g of positive active material particles were taken from each positive active material powder and measured at a scan rate of 6° / min from 2θ 10° to 100° under conditions of Cu-Kα line (wavelength 1.54 Å), acceleration voltage 40 kV, and current 40 mA.

[0235]

[0236] Experimental Example 2: XRD Spectrum Analysis 2

[0237] For each cathode active material prepared in the above examples and comparative examples, after XRD analysis, the intensity of the (200) plane peak and the intensity of the (020) plane peak were confirmed, the ratio (e) of the intensity of the (020) plane peak to the intensity of the (200) plane peak was calculated, and the results are shown in Table 2 below.

[0238] For reference, the above (200) plane peak is a peak that appears at a point where 2θ of the XRD spectrum is about 17 to 17.5, and the above (020) plane peak is a peak that appears at a point where 2θ of the XRD spectrum is about 30 to 30.1.

[0239]

[0240] Experimental Example 3: SEM Image Analysis

[0241] SEM images of the cathode active materials prepared in the above examples and comparative examples were obtained using an SEM (JEOL, JSM7610F-plus), and the average particle size (a) [nm] of the primary particles of the cathode active materials prepared in the examples and comparative examples was obtained using an image processing program (LG Chem, DX program), and the results are shown in Table 2 below.

[0242] Specifically, SEM images (approx. 10K magnification) of the cathode active materials prepared in the examples and comparative examples were obtained using an SEM (JEOL, JSM7610F-plus), and a two-dimensional segmentation image was obtained by dividing the boundaries of the primary particles present in the SEM image and displaying them in random colors using an image processing program (LG Chem, DX program). The average particle size (a) of the primary particles was determined from the segmentation image.

[0243]

[0244] Experimental Example 4: PSA Analysis

[0245] The average particle size (D) of each cathode active material prepared in the examples and comparative examples using a PSA (Mastersizer 3000, Malvern) 50 )(d)[㎛] was measured and shown in Table 2 below.

[0246]

[0247] Experimental Example 5: Evaluation of Battery Characteristics

[0248] - Manufacturing of coin-type half-batteries

[0249] An anode slurry was prepared by mixing 95 wt% of each anode active material prepared in the above examples and comparative examples, 2 wt% of carbon black as a conductive material, and 3 wt% of polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent. The anode slurry prepared above was coated on one side of an aluminum current collector, dried at 130°C, and then rolled to produce an anode.

[0250] An electrode assembly was prepared using a lithium metal electrode as the negative electrode and a porous polyethylene separator interposed between the positive and negative electrodes. This was placed inside a battery case, and a coin-type half-cell was fabricated by injecting an electrolyte solution in which 1M LiPF6 was dissolved in an organic solvent mixed with ethylene carbonate (EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) in a volume ratio of 3:3:4. Subsequently, a rest period of 24 hours was observed.

[0251]

[0252] The above coin-type half-cell was charged to 3.7V in CC (0.1C)-CV (Cut-off current: 0.05C) mode at 25℃, rested for 30 minutes, and then discharged to 2.5V at 0.1C to perform an initial charge-discharge cycle and measure the initial charge-discharge capacity (mAh / g). The percentage of discharge capacity relative to the charge capacity (efficiency (%)) was calculated and is shown in Table 3 below.

[0253] After performing the initial charge / discharge cycle, charge to 3.7V at 25℃ in CC (0.33C) - CV (Cut-off current: 0.05C) mode, then rest for 30 minutes, and then discharge to 2.5V at 0.1C to check the discharge capacity; then charge to 3.7V at 25℃ in CC (0.2C) - CV (Cut-off current: 0.05C) mode, then rest for 30 minutes, and then discharge to 2.5V at 0.1C to check the discharge capacity (discharge capacity of 0.2C); then charge to 3.7V at 25℃ in CC (1.0C) - CV (Cut-off current: 0.05C) mode, then rest for 30 minutes, and then discharge to 2.5V at 0.1C to check the discharge capacity; and then at 25℃ in CC (2.0C) - CV (Cut-off After charging to 3.7V in the current: 0.05C mode, and after a 30-minute rest period, the discharge capacity (discharge capacity of 2.0C) was checked by discharging to 2.5V at 0.1C. The percentage of the discharge capacity of 2.0C relative to the discharge capacity of 0.2C (2.0C / 0.2C(%)) was calculated, and the results are shown in Table 3 below.

[0254] In addition, the charge transfer resistance (c) [Ω] was analyzed and is shown in Table 2 below. The charge transfer resistance is a value analyzed by electrochemical impedance spectroscopy (EIS) with an amplitude of 100 mV and a frequency range of 100 mHz to 1 MHz when the SOC is 50 in the initial charge-discharge cycle.

[0255] Then, using the above a, b, c, d, and e, the value (X) according to Equation 1 described in the present specification was calculated, and the result is shown in Table 2 below.

[0256]

[0257] a[㎛]b[nm]c[Ω]d[㎛]eX[nm×Ω] Example 10.3284113.5843.3461.662.12135.448 Example 20.394293.3683.2141.502.25335.003 Example 30.4693143.3473.9102.192.08457.633 Comparative Example 10.4926123.2014.0011.762.16463.754 Comparative Example 20.5042151.8474.3152.232.08770.984 Comparative Example 30.5167121.5333.7801.532.01177.147 Comparative Example 40.6936164.6134.2352.541.99695.375 Comparative Example 50.6423156.9744.4082.151.899108.854 Comparative Example 60.3281133.0615.3961.092.067104.566 Comparative Example 70.5562156.0444.5831.702.001116.932 Comparative Example 80.4562158.0434.1131.652.00289.788 Comparative Example 90.2984120.1063.4462.952.22318.833

[0258] Efficiency (%) 2.0C / 0.2C (%) Example 1 100.0 92.0 Example 2 99.7 90.3 Example 3 99.18 5.3 Comparative Example 1 96.4 84.6 Comparative Example 2 96.0 82.3 Comparative Example 3 95.9 82.1 Comparative Example 4 95.9 78.0 Comparative Example 5 95.7 79.9 Comparative Example 6 95.18 1.9 Comparative Example 794.9 78.8 Comparative Example 8 95.8 78.2 Comparative Example 9 95.2 75.0

[0259] Through Tables 2 and 3, it was confirmed that the positive active materials prepared in Examples 1 to 3 have a value (X) according to Formula 1 described in this specification of 19.000 nm × Ω or more and 60.000 nm × Ω or less. In addition, it was confirmed that the positive active materials prepared in Examples 1 to 3 have a of 0.3000 μm or more and 0.5000 μm or less, b of 90.000 nm or more and 150.000 nm or less, d of 1.00 μm or more and 3.00 μm or less, and e of 2.000 or more and 2.500 or less. In addition, it was confirmed that the battery containing the positive active material prepared in Examples 1 to 3 has a value of c of 3.000 Ω or more and 4.000 Ω or less. On the other hand, it was confirmed that the positive active material prepared in Comparative Examples 1 to 8 has a value (X) according to Formula 1 described in this specification greater than 60.000 nm × Ω, and the positive active material prepared in Comparative Example 9 has a value (X) according to Formula 1 described in this specification less than 19.000 nm × Ω. In addition, it was confirmed that the positive active material prepared in Comparative Examples 2 to 5 and 7 has a value of a greater than 0.5000 μm, and the positive active material prepared in Comparative Example 9 has a value of a less than 0.3000 μm. It was confirmed that the positive active materials prepared in Comparative Examples 2, 4, 5, 7, and 8 have a b value greater than 150.000 nm, the batteries containing the positive active materials prepared in Comparative Examples 1, 2, and 4 to 8 have a c value greater than 4.000 Ω, and the positive active materials prepared in Comparative Examples 4 and 5 have an e value less than 2.000.

[0260] In conclusion, it can be seen that the values ​​(X), a, b, c, d, and e according to Formula 1 described in this specification are technical features that appear when manufacturing a positive electrode active material by controlling the carbon coating raw material, wet grinding time, spray drying outlet temperature, and calcination temperature in combination.

[0261]

[0262] Through Table 3, it was confirmed that the batteries containing the positive active materials prepared in Examples 1 to 3 had superior efficiency and rate characteristics compared to the batteries containing the positive active materials prepared in Comparative Examples 1 to 9.

Claims

1. Includes a lithium iron phosphate-based compound in the form of primary or secondary particles, and A positive active material having a value (X) according to Formula 1 below of 19.000 nm × Ω or more and 60.000 nm × Ω or less: [Equation 1] X = (a×c / d)×(b / e) In the above Equation 1, a is the average particle size [μm] of the primary particles obtained from the SEM image, and b is the average size of the crystallites obtained from the XRD spectrum [nm], and c is the charge transfer resistance [Ω] analyzed by Electrochemical Impedance Spectroscopy (EIS) at SOC 50 when a lithium secondary battery comprising a cathode containing a cathode active material layer containing a cathode active material in an amount of 80 wt% or more and 98 wt% or less with respect to the total weight of the cathode active material layer is charged to 3.7 V at 25°C using the CC (0.1C)-CV (Cut-off current: 0.05C) method, rested for 30 minutes, and then discharged to 2.5 V at 0.1C. d is the average particle size (D) measured by a Particle Size Analyzer (PSA). 50 )[㎛] and, e is the ratio of the intensity of the (020) plane peak to the intensity of the (200) plane peak in the XRD spectrum.

2. In Claim 1, The above lithium iron phosphate-based compound is a positive electrode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li 1+y1 Fe 1-p1 M p1 PO4 In the above chemical formula 1, M is one or more selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and -0.1≤y1≤0.1, 0.00≤p1<1.

00.

3. In Claim 1, The above lithium iron phosphate-based compound is a positive electrode active material having a molar ratio of lithium to iron of 0.90 or more and 1.05 or less.

4. In Claim 1, The above lithium iron phosphate-based compound has a molar ratio of the doping element to iron of 0.00 or more and 0.02 or less, and The above doping element is one or more selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and is a positive active material.

5. In Claim 1, The above a is a positive active material having a thickness of 0.3000 μm or more and 0.5000 μm or less.

6. In Claim 1, The above b is a positive active material having a thickness of 90,000 nm or more and 150,000 nm or less.

7. In Claim 1, The above c is a positive active material having a resistance of 3,000 Ω or more and 4,000 Ω or less.

8. In Claim 1, The above d is a positive active material having a thickness of 1.00 μm or more and 3.00 μm or less.

9. In Claim 1, The above-mentioned positive active material, wherein e is 2.000 or more and 2.500 or less.

10. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 9.

11. A lithium secondary battery comprising a positive electrode according to claim 10.