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

Abstract

The present invention relates to: a lithium iron phosphate-based cathode active material; and a cathode and a lithium secondary battery which comprise same, the lithium iron phosphate-based cathode active material comprising a lithium iron phosphate-based compound and having a bimodal particle size distribution in which, in a particle size distribution curve in which the x-axis represents particle diameter (unit: μm) on a log scale and the y-axis represents volume percentage (unit: %), the slope of a straight line passing through an inflection point and a point at which the volume percentage of a right peak is at a maximum is 5-7.

Description

Cathode active material, cathode and lithium secondary battery containing same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority to Korean Patent Application Nos. 10-2024-0080826, 10-2024-0080827, 10-2024-0080830 and 10-2024-0080831, filed June 21, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a lithium iron phosphate-based cathode active material, a cathode including the same, and a lithium secondary battery.

[0005]

[0006] As technological development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used.

[0007] Lithium secondary batteries are composed of four major components: a cathode, an anode, a separator, and an electrolyte. Among these, the cathode active material contained in the cathode plays a significant role in determining the battery's capacity, output, and lifespan. Currently used cathode active materials include NCM-based cathode active materials containing nickel, cobalt, manganese, and / or aluminum, and LFP (lithium iron phosphate)-based cathode active materials. Meanwhile, improving the performance of cathode active materials is essential for lithium secondary batteries to achieve high energy density, output, and lifespan. Consequently, extensive research has been conducted recently to develop high-performance cathode active materials.

[0008] Recently, with the increasing use of lithium secondary batteries, active development of NCM-based cathode active materials with increased nickel content is being actively conducted to increase the energy density of the batteries, especially the capacity. However, NCM-based cathode active materials with increased nickel content have the problem of reduced thermal stability due to structural instability caused by the high nickel content. On the other hand, LFP-based cathode active materials, which are olivine-structured cathode active materials, have the advantage of excellent thermal stability and price competitiveness, although they have lower capacity than NCM-based cathode active materials. However, batteries containing LFP-based cathode active materials have lower operating voltage and specific capacity than batteries containing NCM-based cathode active materials, resulting in lower energy density. In addition, LFP-based cathode active materials have low electronic conductivity and phase differences during charge and discharge, which reduces electrochemical efficiency.

[0009] Accordingly, development is needed to improve the performance of LFP-based cathode active materials.

[0010]

[0011] The purpose of the present invention is to provide a lithium iron phosphate-based positive electrode active material capable of improving the efficiency and output characteristics of a lithium secondary battery.

[0012] In addition, an object of the present invention is to provide a positive electrode and a lithium secondary battery including the positive electrode active material.

[0013]

[0014] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0015]

[0016] To solve the above problem, the present invention provides a lithium iron phosphate-based positive electrode active material, a positive electrode including the same, and a lithium secondary battery.

[0017]

[0018] (1) The present invention provides a lithium iron phosphate cathode active material comprising a lithium iron phosphate compound, wherein the lithium iron phosphate cathode active material has a bimodal particle size distribution, and a slope of a straight line passing through an inflection point and a point where the volume percentage of the right peak is maximum in a particle size distribution curve in which the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %) is 5 or more and 7 or less.

[0019] (2) The present invention provides a lithium iron phosphate-based positive electrode active material in the above (1), wherein the lithium iron phosphate-based positive electrode active material satisfies the following formula 1.

[0020] [Formula 1]

[0021] -2.10 < R.tan < -1.00

[0022] In the above equation 1,

[0023] R.tan is a particle size distribution curve in which the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %). R From D 90 is the slope of the function representing the trend up to ,

[0024] D R is the particle size when the volume percentage of the right peak is maximum,

[0025] The function representing the above trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

[0026] (3) The present invention provides a lithium iron phosphate-based positive electrode active material according to (1) or (2), wherein the lithium iron phosphate-based positive electrode active material satisfies the following formula 2.

[0027] [Formula 2]

[0028]

[0029] In the above equation 2,

[0030] In a particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %),

[0031] D R is the particle size when the volume percentage of the right peak is maximum, and Y(D R ) is D R is the volume percentage (unit: %) in

[0032] Span is ((D 90 -D 10 ) / D 50 ) and,

[0033] R.tan is D R From D 90 It is the slope of the function representing the trend up to , and the function representing the trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

[0034] (4) The present invention provides a lithium iron phosphate-based positive electrode active material, wherein the lithium iron phosphate-based positive electrode active material satisfies the following formula 3 in any one of the above (1) to (3).

[0035] [Formula 3]

[0036]

[0037] In the above equation 3,

[0038] In a particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %),

[0039] D R is the particle size when the volume percentage of the right peak is maximum, and Y(D R ) is D R is the volume percentage (unit: %) in ,

[0040] D L is the particle diameter when the volume percentage of the left peak is maximum, and Y(DL ) is D L is the volume percentage (unit: %) in

[0041] Span is ((D 90 -D 10 ) / D 50 ) and,

[0042] R.tan is D R From D 90 It is the slope of the function representing the trend up to , and the function representing the trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

[0043] (5) In the present invention, in the above (3) or (4), the lithium iron phosphate cathode active material is D R A lithium iron phosphate cathode active material having a particle size of 1.00㎛ or more and 5.00㎛ or less is provided.

[0044] (6) In the present invention, in the above (3) or (4), the lithium iron phosphate cathode active material is D R Volume percentage in (Y(D) R )) provides a lithium iron phosphate cathode active material having a content of 4.00% or more and 10.00% or less.

[0045] (7) The present invention provides a lithium iron phosphate-based positive electrode active material in the above (3) having an R.tan of -2.10 or more and -1.00 or less.

[0046] (8) In the present invention, in the above (4), the lithium iron phosphate cathode active material is D L A lithium iron phosphate cathode active material having a particle size of 0.30㎛ or more and 0.80㎛ or less is provided.

[0047] (9) In the present invention, in the above (4), the lithium iron phosphate cathode active material is D L Volume percentage in (Y(D) L )) provides a lithium iron phosphate cathode active material having a content of 1.00% or more and 8.00% or less.

[0048] (10) In any one of the above (1) to (9), the lithium iron phosphate cathode active material has a span ((D) 90 -D 10 ) / D 50 ) provides a lithium iron phosphate cathode active material having a value of 1.50 or more and 2.50 or less.

[0049] (11) In any one of the above (1) to (10), the lithium iron phosphate cathode active material is D 50 A lithium iron phosphate cathode active material having a particle size of 0.80㎛ or more and 3.00㎛ or less is provided.

[0050] (12) In any one of the above (1) to (11), the lithium iron phosphate cathode active material is D 10 A lithium iron phosphate cathode active material having a particle size of 0.35㎛ or more and 0.80㎛ or less is provided.

[0051] (13) In any one of the above (1) to (12), the lithium iron phosphate cathode active material is D 90 A lithium iron phosphate cathode active material having a particle size of 2.00㎛ or more and 4.00㎛ or less is provided.

[0052] (14) The present invention provides a lithium iron phosphate cathode active material, wherein the lithium iron phosphate compound has a composition represented by the following chemical formula 1, in any one of the above (1) to (13).

[0053] [Chemical Formula 1]

[0054] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4

[0055] In the above chemical formula 1,

[0056] M 1is at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Mo, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y,

[0057] -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1.

[0058] (15) The present invention provides a lithium iron phosphate cathode active material, wherein the lithium iron phosphate compound has a composition represented by the following chemical formula 2, in any one of the above (1) to (14).

[0059] [Chemical Formula 2]

[0060] Li 1+x2 [Fe 1-a2-b2 Mn a2 Ti b2 ]PO4

[0061] In the above chemical formula 2,

[0062] -0.1≤x2≤0.1, 0≤a2≤0.9, 0 <b2≤0.1이다.

[0063] (16) The present invention provides a lithium iron phosphate-based positive electrode active material, wherein the lithium iron phosphate-based positive electrode active material further includes a coating portion including carbon (C) formed on the lithium iron phosphate-based compound in any one of the above (1) to (15).

[0064] (17) The present invention provides a lithium iron phosphate-based positive electrode active material in which the content of carbon (C) included in the coating portion in the above (16) is 0.5 wt% to 3.0 wt% based on the total weight of the lithium iron phosphate-based positive electrode active material.

[0065] (18) The present invention provides a positive electrode comprising a lithium iron phosphate-based positive electrode active material according to any one of (1) to (17).

[0066] (19) The present invention provides a lithium secondary battery including a positive electrode according to (18).

[0067]

[0068] The lithium iron phosphate cathode active material according to the present invention has a bimodal particle size distribution, and at the same time, the slope of a straight line passing through an inflection point and a point where the volume percentage of the right peak is maximum in the particle size distribution curve satisfies a value of 5 or more and 7 or less, thereby significantly improving the efficiency and output characteristics of a lithium secondary battery including the same.

[0069]

[0070] Figure 1 is a drawing showing a particle size distribution curve in which the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %), and a straight line passing through an inflection point (A) and a point (B) where the volume percentage of the right peak is maximum.

[0071] Figure 2 is a graph of the particle size distribution of the positive electrode active material of Example 1.

[0072] Figure 3 is a graph of the particle size distribution of the positive electrode active material of Example 2.

[0073] Figure 4 is a graph of the particle size distribution of the positive electrode active material of Example 3.

[0074] Figure 5 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 1.

[0075] Figure 6 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 2.

[0076] Figure 7 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 3.

[0077] Figure 8 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 4.

[0078] Figure 9 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 5.

[0079] Figure 10 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 6.

[0080] Figure 11 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 7.

[0081] Figure 12 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 8.

[0082] Figure 13 is a graph of the particle size distribution of the positive electrode active material of Comparative Example 9.

[0083]

[0084] Hereinafter, the present invention will be described in more detail.

[0085] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0086] It should be understood that the terms “include,” “comprising,” or “having” used in this specification are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0087] The term "on" in this specification means not only when a configuration is formed directly on top of another configuration, but also when a third configuration is interposed between these configurations.

[0088] In this specification i) D min , ii) D 10 , iii) D 50 , iv) D 90 , v) D max In the particle size distribution curve of the positive electrode active material, each can be defined as i) minimum particle size, ii) particle size corresponding to 10% of the volume cumulative distribution, iii) particle size corresponding to 50% of the volume cumulative distribution, iv) particle size corresponding to 90% of the volume cumulative distribution, and v) maximum particle size. The above i) D min , ii) D 10 , iii) D 50 , iv) D90 , v) D max The particle size distribution can be obtained by dispersing the target powder in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Mastersizer 3000, Malvern Panalytical), and measuring the difference in diffraction pattern according to particle size when the particles pass through the laser beam.

[0089]

[0090] positive electrode active material

[0091] The cathode active material according to the present invention is a lithium iron phosphate cathode active material including a lithium iron phosphate compound, wherein the lithium iron phosphate cathode active material has a bimodal particle size distribution, and is characterized in that the slope of a straight line passing through an inflection point and a point where the volume percentage of the right peak is maximum in a particle size distribution curve in which the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %) is 5 or more and 7 or less.

[0092] Figure 1 is a drawing showing a particle size distribution curve in which the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %), and a straight line passing through an inflection point (A) and a point (B) where the volume percentage of the right peak is maximum.

[0093] The present inventors have found that when a lithium iron phosphate-based positive electrode active material has a bimodal particle size distribution and at the same time, the slope of a straight line passing through an inflection point and a point where the volume percentage of the right peak is maximum in the particle size distribution curve satisfies a range of 5 to 7, the tap density of the positive electrode active material is high, so that the energy density of a battery including the positive electrode active material can be improved, and a uniform electrode slurry can be prepared to improve battery efficiency and output characteristics, thereby completing the present invention.

[0094] Meanwhile, if the lithium iron phosphate-based cathode active material does not have a bimodal particle size distribution, the tap density of the cathode active material is low, which causes the energy density of the battery to be poor. In addition, if the slope of the straight line passing through the inflection point and the point where the volume percentage of the right peak is maximum on the particle size distribution curve, where the x-axis is a logarithmic scale of particle size (unit: ㎛) and the y-axis is a volume percentage (unit: %), is less than 5, there are many small particles, which causes the electrode slurry to be manufactured unevenly, which causes the efficiency of the battery to decrease, and if the slope exceeds 7, there are many large particles, which causes the distance that lithium ions must travel to increase, which causes the efficiency of the battery to decrease. Specifically, if the slope is less than 5, it means that the peak of the large particles (the value with the maximum Volume% measured at the right peak) is on the right (in the direction of increasing particle size), which means that the overall amount of large particles is large, which causes the diffusion path of Li ions to become longer, and Li ions are not sufficiently inserted, which causes the electrochemical efficiency to be low. In addition, when the slope exceeds 7, it means that the span of the opposing particles is small, and since there are many opposing particles of similar size, the contact area between particles becomes small, and the empty space between particles makes it difficult for Li ions to move, which may lower the electrochemical efficiency.

[0095]

[0096] According to the present invention, the slope of a straight line passing through an inflection point and a point where the volume percentage of the right peak is maximum in the particle size distribution curve may be specifically 5.00 or more, 5.10 or more, 5.20 or more, 5.30 or more, 5.40 or more, 5.50 or more, 5.60 or more, 5.70 or more, 5.80 or more, 5.90 or more, or 6.00 or more, or 6.70 or less, 6.80 or less, 6.90 or less, or 7.00 or less.

[0097]

[0098] According to the present invention, the lithium iron phosphate-based positive electrode active material may satisfy the following equation 1. In this case, the efficiency of a lithium secondary battery including the same may be improved.

[0099] [Formula 1]

[0100] -2.10 < R.tan < -1.00

[0101] In the above equation 1,

[0102] R.tan is a particle size distribution curve in which the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %). R From D 90 is the slope of the function representing the trend up to ,

[0103] D R is the particle size when the volume percentage of the right peak is maximum,

[0104] The function representing the above trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

[0105] Specifically, the lithium iron phosphate-based positive electrode active material according to the present invention may have an R.tan value of -2.10 or more, or -2.05 or more, and may be -1.30 or less, -1.25 or less, -1.20 or less, -1.15 or less, -1.10 or less, -1.05 or less, or -1.00 or less.

[0106]

[0107] According to the present invention, the lithium iron phosphate-based cathode active material may satisfy the following equation 2. In this case, small particles are positioned in the empty spaces between large particles, allowing more particles to be placed in the same volume, thereby increasing the charge / discharge characteristics of the cathode active material, and producing a uniform electrode slurry, thereby improving the efficiency and output characteristics of a lithium secondary battery including the same.

[0108] [Formula 2]

[0109]

[0110] In the above equation 2,

[0111] In a particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %),

[0112] D R is the particle size when the volume percentage of the right peak is maximum, and Y(D R ) is D R is the volume percentage (unit: %) in

[0113] Span is ((D 90 -D 10 ) / D 50 ) and,

[0114] R.tan is D R From D 90 It is the slope of the function representing the trend up to , and the function representing the trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

[0115] For reference, Y(D R ) / For span, the larger the number of uniform particles, the larger the number, so a larger number means an increase in the number of particles.

[0116] Specifically, the lithium iron phosphate cathode active material according to the present invention comprises (Y(D) R ) / span)×|R.tan| can be greater than or equal to 3.00, greater than or equal to 3.10, or greater than or equal to 3.20, and less than or equal to 7.00.

[0117]

[0118] According to the present invention, the lithium iron phosphate-based cathode active material may satisfy the following equation 3. In this case, small particles are positioned in the empty spaces between large particles, allowing more particles to be placed in the same volume, thereby increasing the charge / discharge characteristics of the cathode active material, and producing a uniform electrode slurry, thereby improving the efficiency and output characteristics of a lithium secondary battery including the same.

[0119] [Formula 3]

[0120]

[0121] In the above equation 3,

[0122] In a particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %),

[0123] D R is the particle size when the volume percentage of the right peak is maximum, and Y(D R ) is D R is the volume percentage (unit: %) in ,

[0124] D L is the particle diameter when the volume percentage of the left peak is maximum, and Y(D L ) is D L is the volume percentage (unit: %) in

[0125] Span is ((D 90 -D 10 ) / D 50 ) and,

[0126] R.tan is D R From D 90 It is the slope of the function representing the trend up to , and the function representing the trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

[0127] For reference, (Y(D R )-Y(D L)) / In the case of span, if it is negative, it means there are many small particles, and if it is positive, it means there are many large particles. Also, since the denominator is span, it represents uniformity, and the smaller the span, the more uniform it is, so (Y(D R )-Y(D L )) / The larger the span value, the higher the uniformity.

[0128] Specifically, the lithium iron phosphate cathode active material according to the present invention comprises the above [(Y(D R )-Y(D L )) / span]×|R.tan| value can be greater than or equal to -0.20, or greater than or equal to -0.15, and less than or equal to 2.55, or less than or equal to 2.60.

[0129]

[0130] According to the present invention, when the lithium iron phosphate-based positive electrode active material satisfies the above formula 2 or formula 3, the lithium iron phosphate-based positive electrode active material is D R This may be 1.00㎛ or more and 5.00㎛ or less. Specifically, the above D R The size may be 1.00 ㎛ or more, 1.05 ㎛ or more, or 1.10 ㎛ or more, and may be 1.65 ㎛ or less, 1.70 ㎛ or less, 1.80 ㎛ or less, 1.90 ㎛ or less, 2.00 ㎛ or less, 3.00 ㎛ or less, 4.00 ㎛ or less, or 5.00 ㎛ or less.

[0131]

[0132] According to the present invention, when the lithium iron phosphate-based positive electrode active material satisfies the above formula 2 or formula 3, the lithium iron phosphate-based positive electrode active material is D R Volume percentage in (Y(D) R )) may be 4.00% or more and 10.00% or less. Specifically, the above D R Volume percentage in (Y(D) R)) may be 4.00% or more, 4.10% or more, 4.20% or more, 4.30% or more, 4.40% or more, 4.50% or more, 4.60% or more, 4.70% or more, 4.80% or more, 4.90% or more, 5.00% or more, 5.10% or more, 5.20% or more, 5.30% or more, or 5.40% or more, and may be 6.80% or less, 6.90% or less, 7.00% or less, 7.50% or less, 8.00% or less, 8.50% or less, 9.00% or less, 9.50% or less, or 10.00% or less.

[0133]

[0134] According to the present invention, when the lithium iron phosphate-based positive electrode active material satisfies the above formula 2, the lithium iron phosphate-based positive electrode active material may have an R.tan of -2.10 or more and -1.00 or less. In this case, in a distribution having a bimodal particle size distribution, the uniformity of a portion with a large particle size may be increased, thereby improving the efficiency and output characteristics of the battery. Specifically, the R.tan value may be -2.10 or more, or -2.05 or more, and -1.30 or less, -1.25 or less, -1.20 or less, -1.15 or less, -1.10 or less, -1.05 or less, or -1.00 or less.

[0135]

[0136] According to the present invention, when the lithium iron phosphate-based cathode active material satisfies the above formula 3, the lithium iron phosphate-based cathode active material is D L This may be 0.30㎛ or more and 0.80㎛ or less. Specifically, the above D L The silver may be 0.30㎛ or more, 0.40㎛ or more, or 0.50㎛ or more, and may be 0.60㎛ or less, 0.70㎛ or less, or 0.80㎛ or less.

[0137]

[0138] According to the present invention, when the lithium iron phosphate-based cathode active material satisfies the above formula 4, the lithium iron phosphate-based cathode active material is D LVolume percentage in (Y(D) L )) may be 1.00% or more and 8.00% or less. Specifically, the above D L Volume percentage in (Y(D) L )) may be 1.00% or more, 2.00% or more, 3.00% or more, 4.00% or more, 4.10% or more, or 4.20% or more, and may be 6.00% or less, 6.50% or less, 7.00% or less, 7.50% or less, or 8.00% or less.

[0139]

[0140] According to the present invention, the lithium iron phosphate cathode active material has a span ((D 90 -D 10 ) / D 50 ) may be 1.50 or more and 2.50 or less. Specifically, the span value may be 1.50 or more, 1.60 or more, 1.70 or more, 1.80 or more, or 1.90 or more, and may be 2.30 or less, 2.35 or less, 2.40 or less, 2.45 or less, or 2.50 or less. In this case, the particle size distribution dispersion of all particles is appropriate, so that the rolling density can be improved.

[0141]

[0142] According to the present invention, the lithium iron phosphate cathode active material is D 50 This may be 0.80㎛ or more and 3.00㎛ or less. Specifically, the above D 50 The particle size may be 0.80㎛ or more, 0.90㎛ or more, 1.00㎛ or more, 1.10㎛ or more, 1.20㎛ or more, 1.30㎛ or more, or 1.35㎛ or more, and may be 1.50㎛ or less, 1.60㎛ or less, 1.70㎛ or less, 1.80㎛ or less, 1.90㎛ or less, 2.00㎛ or less, 2.50㎛ or less, or 3.00㎛ or less. In this case, the particle size and the particle size distribution dispersion of all particles are appropriately secured, so that the rolling density can be improved.

[0143] According to the present invention, the lithium iron phosphate cathode active material is D10 This may be 0.35㎛ or more and 0.80㎛ or less. Specifically, the above D 10 The particle size may be 0.35㎛ or more, 0.40㎛ or more, or 0.45㎛ or more, and may be 0.50㎛ or less, 0.60㎛ or less, 0.70㎛ or less, or 0.80㎛ or less. In this case, the particle size and particle size distribution of the small particles are appropriate, so that the rolling density can be improved.

[0144] According to the present invention, the lithium iron phosphate cathode active material is D 90 This may be 2.00㎛ or more and 4.00㎛ or less. Specifically, the above D 90 The size of the large particles may be 2.00 ㎛ or more, 2.10 ㎛ or more, 2.20 ㎛ or more, 2.30 ㎛ or more, 2.40 ㎛ or more, 2.50 ㎛ or more, 2.60 ㎛ or more, 2.70 ㎛ or more, 2.80 ㎛ or more, 2.90 ㎛ or more, 3.00 ㎛ or more, 3.10 ㎛ or more, or 3.20 ㎛ or more, or 3.80 ㎛ or less, 3.90 ㎛ or less, or 4.00 ㎛ or less. In this case, the particle size and particle size distribution of the large particles are appropriate, so that the rolling density can be improved.

[0145]

[0146] According to the present invention, the lithium iron phosphate compound may have a composition represented by the following chemical formula 1.

[0147] [Chemical Formula 1]

[0148] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4

[0149] In the above chemical formula 1,

[0150] M 1 is at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Mo, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y,

[0151] -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1.

[0152] The above x can be from -0.1 to 0.1. When x satisfies the above range, high capacity characteristics and high energy density per unit volume can be realized.

[0153] The above a is the mole fraction of manganese (Mn) among all metals excluding lithium in the lithium iron phosphate compound, and may be 0 or more and 0.9 or less. Specifically, the above a may be 0 or more, and 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, 0.5 or less, 0.6 or less, 0.7 or less, 0.8 or less, or 0.9 or less. When a is within the above range, the charge / discharge voltage range may be widened, thereby increasing the energy density.

[0154] The above b is M among all metals except lithium in the lithium complex transition metal oxide. 1 The mole fraction of b may be 0 or more and 0.1 or less. Specifically, b may be 0 or more, more than 0, 0.001 or more, 0.002 or more, 0.003 or more, 0.004 or more, 0.005 or more, 0.006 or more, 0.007 or more, 0.008 or more, or 0.009 or more, and may be 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, or 0.1 or less. When b is within the above range, ionic conductivity and electrical conductivity may be improved.

[0155] The above 1-ab may be greater than 0 and less than or equal to 1.0, or greater than or equal to 0.1 and less than 1.0.

[0156]

[0157] According to the present invention, the lithium iron phosphate compound may have a composition represented by the following chemical formula 2. In this case, the crystal size is reduced, thereby reducing the diffusion distance of lithium ions within the crystal, thereby providing the advantage of improved conductivity.

[0158] [Chemical Formula 2]

[0159] Li 1+x2 [Fe 1-a2-b2 Mn a2 Ti b2 ]PO4

[0160] In the above chemical formula 2,

[0161] -0.1≤x2≤0.1, 0≤a2≤0.9, 0 <b2≤0.1이다.

[0162] The above x2 can be from -0.1 to 0.1. When x2 satisfies the above range, high capacity characteristics and high energy density per unit volume can be realized.

[0163] The above a2 is the mole fraction of manganese (Mn) among all metals excluding lithium in the lithium iron phosphate compound, and may be 0 or more and 0.9 or less. Specifically, the above a2 may be 0 or more, and 0.1 or less, 0.2 or less, 0.3 or less, 0.4 or less, 0.5 or less, 0.6 or less, 0.7 or less, 0.8 or less, or 0.9 or less. When a2 is within the above range, the charge / discharge voltage range may be widened, thereby increasing the energy density.

[0164] The above b2 is the mole fraction of titanium (Ti) among the total metals excluding lithium in the lithium composite transition metal oxide, and may be greater than 0 and less than or equal to 0.1. Specifically, the above b2 may be greater than 0, 0.001 or more, 0.002 or more, 0.003 or more, 0.004 or more, 0.005 or more, 0.006 or more, 0.007 or more, 0.008 or more, or 0.009 or more, and may be 0.01 or less, 0.02 or less, 0.03 or less, 0.04 or less, 0.05 or less, 0.06 or less, 0.07 or less, 0.08 or less, 0.09 or less, or 0.1 or less. When b2 is within the above range, ionic conductivity and electrical conductivity may be improved.

[0165] The above 1-a2-b2 may be 0.1 or more and less than 1.0.

[0166]

[0167] According to the present invention, the lithium iron phosphate-based positive electrode active material may further include a coating portion including carbon (C) formed on the lithium iron phosphate-based compound to improve electronic conductivity.

[0168]

[0169] According to the present invention, the content of carbon (C) included in the coating portion may be 0.5 wt% to 3.0 wt% based on the total weight of the lithium iron phosphate-based positive electrode active material. When the content of carbon (C) included in the coating portion is within the above range, the electronic conductivity of the positive electrode active material may be improved without acting as a resistor.

[0170]

[0171] According to the present invention, the lithium iron phosphate-based positive electrode active material may exist in a mixed form of a non-agglomerated primary particle (single particle) and a secondary particle form in which the primary particles are aggregated.

[0172]

[0173] The lithium iron phosphate cathode active material according to the present invention can be manufactured by a manufacturing method including, but not limited to, (A) a step of 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 element raw material (e.g., titanium, magnesium, etc.) to manufacture a mixture; (B) a step of firing the mixture to manufacture a sintered product; and (C) a step of pulverizing the sintered product.

[0174]

[0175] The properties of the lithium iron phosphate cathode active material according to the present invention can be implemented by appropriately controlling the presence and amount of doping element raw material added during the manufacture of the cathode active material, the amount of carbon coating raw material used, the sintering temperature, the grinding conditions, etc., but are not limited thereto.

[0176] For reference, if the input amount of doping element raw material (e.g., input amount of Ti raw material) is low, the ratio of large particles to small particles increases, and the intensity of the peak of large particles increases, so that in the particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %), the slope of the straight line passing through the inflection point and the point where the volume percentage of the right peak is maximum increases.

[0177] In addition, the carbon coating raw material is one of the factors that suppresses interparticle growth, and if the amount used is low, interparticle growth occurs actively, increasing the ratio of large particles to small particles. Accordingly, in the particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %), the slope of the straight line passing through the inflection point and the point where the volume percentage of the right peak is maximum increases.

[0178] And, when grinding a sintered product, if the grinding pressure increases, the ratio of small particles to large particles increases, and the slope of the straight line passing through the inflection point and the point where the volume percentage of the right peak is maximum in the particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %) decreases.

[0179]

[0180] 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, LiOHㆍH2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or the like.

[0181] The above phosphoric acid raw material may be FePO4, H3PO4, NH4H2PO4, (NH4)2HPO4, P2O5, etc.

[0182] The above iron raw material may be an iron-containing phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide, etc. Specifically, the above iron raw material may be FePO4, FeSO4, FeC2O4·2H2O, FeCl2, etc.

[0183] The above phosphate raw material and iron raw material may be the same. For example, it may be iron phosphate (FePO4).

[0184]

[0185] The above carbon coating raw material can provide a carbon coating layer by calcination, and thus the electrical conductivity of the lithium iron phosphate cathode active material can be improved. The carbon coating raw material can be sucrose, glucose, lactose, starch, oligosaccharide, polyoligosaccharide, fructose, cellulose, vinyl resin, cellulose resin, phenol resin, pitch resin, tar resin, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, citric acid, ammonium citrate, etc. Specifically, the carbon coating raw material can be sucrose.

[0186] The carbon coating raw material may be added in an amount of 5 to 15 wt%, specifically 10 to 15 wt%, relative to the total weight of the lithium raw material, phosphate raw material, iron raw material, and doping element raw material. In this case, an appropriate amount of carbon may be coated, thereby improving conductivity.

[0187]

[0188] The above doping element raw material may be a phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, oxide, hydroxide or oxyhydroxide containing the doping element, and at this time, the doping element may be at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Mo, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y. Specifically, when the doping element is titanium, it may be titanium dioxide, titanium nitrate, titanium sulfate, etc., and when it is magnesium, it may be magnesium dioxide, magnesium nitrate, magnesium sulfate, etc.

[0189]

[0190] When preparing the mixture in step (A) above, the mixture can be prepared by further mixing in a manganese raw material.

[0191] The above manganese raw material may be a manganese-containing phosphate, iron phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide.

[0192]

[0193] The above lithium raw material, phosphate raw material, iron raw material, doping element raw material and / or manganese raw material can be mixed in an amount such that the lithium iron phosphate compound included in the resulting lithium iron phosphate positive electrode active material has a composition represented by the above chemical formula 1 or 2.

[0194]

[0195] The mixing of the above raw materials may be wet mixing or dry mixing.

[0196] If the above mixing is 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 with a bead mill (conditions: 20 to 50 Hz, using beads of 0.3 to 1 μm in size) and mixed, but is not limited thereto.

[0197]

[0198] Meanwhile, in the case of wet mixing, a powder (mixture) that has been completely dried can be obtained through spray drying.

[0199]

[0200] The above-described sintering can be performed at a temperature of 700°C to 800°C. In this case, a positive electrode active material having an appropriate size can be obtained. Specifically, the above-described sintering can be performed at a temperature of 700°C or higher, 710°C or higher, 720°C or higher, 730°C or higher, 740°C or higher, or 750°C or higher, and 780°C or lower, 790°C or lower, or 800°C or lower. In this case, a positive electrode active material having a single phase can be synthesized, thereby realizing desired electrochemical performance.

[0201] The above calcination may be performed under an inert atmosphere. Specifically, the above calcination may be performed under a nitrogen atmosphere.

[0202]

[0203] The crushing of the above-mentioned product may be performed using a jet mill under conditions of a feeding pressure of 5 to 10 bar and a grinding pressure of 0.5 to 5.0 bar. Specifically, the crushing may be performed using a jet mill under conditions of a feeding pressure of 6 bar and a grinding pressure of 1 bar.

[0204]

[0205] As a specific example, the lithium iron phosphate cathode active material according to the present invention can be manufactured by the following method.

[0206] First, Li2CO3, FePO4, and TiO2 are mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) is (1.01 to 1.05):(1):(0.005 to 0.5), and sucrose is added in an amount of 10 to 15 wt% based on the total weight of Li2CO3, FePO4, and TiO2 to prepare a mixed solution. Thereafter, in order to mix and grind the raw materials, the mixed solution is wet-ground with a beads mill to obtain a slurry. The slurry is dried through spray drying. Thereafter, the dried powder is fired at 750 to 800°C under a nitrogen atmosphere to produce a fired product. The fired product is pulverized with a jet mill (feeding pressure: 6 bar, grinding pressure: 1 bar) to produce a cathode active material.

[0207]

[0208] anode

[0209] In addition, the present invention provides a positive electrode comprising the positive electrode active material described above. The positive electrode may be a positive electrode for a lithium secondary battery.

[0210] Specifically, the positive electrode includes a positive electrode current collector, and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector and including the positive electrode active material described above.

[0211] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change 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 positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0212]

[0213] The above positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material.

[0214] At this time, the positive electrode active material may be included in an amount of 80 to 99 wt%, more specifically 85 to 98 wt%, based on the total weight of the positive electrode active material layer. When included in the above content range, excellent capacity characteristics can be exhibited.

[0215] At this time, the conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. 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, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and 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 the like, and one type alone or a mixture of two or more types thereof may be used. The conductive material may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0216]

[0217] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0218]

[0219] The above-mentioned positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above-mentioned positive electrode active material is used. Specifically, the positive electrode slurry, prepared by dissolving or dispersing the above-mentioned positive electrode active material and optionally a binder and a conductive agent in a solvent, is applied onto a positive electrode current collector, and then dried and rolled. At this time, the types and contents of the positive electrode active material, binder, and conductive agent are as described above.

[0220]

[0221] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the positive electrode slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for positive electrode manufacturing.

[0222]

[0223] Alternatively, the positive electrode may be manufactured by casting the positive electrode slurry onto a separate support, then peeling the film from the support and laminating the resulting film onto a positive electrode current collector.

[0224]

[0225] lithium secondary battery

[0226] In addition, the present invention can manufacture an electrochemical device including the positive electrode. The electrochemical device may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0227] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is the same as described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0228] In addition, the lithium secondary battery may optionally further include a battery container that houses the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0229]

[0230] In the above lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector.

[0231] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0232]

[0233] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0234] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β(0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fiber-like forms, 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.

[0235] The above negative electrode active material may be included in an amount of 80 wt% to 99 wt% based on the total weight of the negative electrode active material layer.

[0236]

[0237] The above binder is a component that assists in bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1 wt% to 10 wt% based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0238] The conductive agent is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10 wt% or less, preferably 5 wt% or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0239]

[0240] The above negative electrode active material layer can be manufactured by applying and drying a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material, in a solvent on a negative electrode current collector, or by casting the negative electrode slurry on a separate support and then laminating the obtained film by peeling it off from the support on a negative electrode current collector.

[0241]

[0242] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0243]

[0244] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0245] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0246] As the organic solvent, any solvent that can serve as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent includes ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); Alcohol solvents such as ethyl alcohol, isopropyl alcohol, etc.; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc. can be used. Among these, carbonate solvents are preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of a battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable.

[0247] The above lithium salt can be used without any special limitation as long as it is a compound that can provide lithium ions used in a lithium secondary battery. Specifically, the above lithium salt is LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2 can be used. The concentration of the lithium salt is preferably within the range of 0.1 to 4.0 M, and preferably, 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0248]

[0249] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the total weight of the electrolyte.

[0250]

[0251] As described above, a lithium secondary battery including a cathode active material according to the present invention exhibits excellent efficiency and output characteristics, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0252] Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0253] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0254] There is no particular limitation on the external shape of the lithium secondary battery of the present invention, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0255] 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 be preferably used as a unit battery in a medium- to large-sized battery module including a plurality of battery cells.

[0256]

[0257] Hereinafter, the present invention will be described in detail with reference to examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention should not be construed as being limited to the examples described below. These examples are provided to more fully explain the present invention to those of ordinary skill in the art.

[0258]

[0259] Examples and Comparative Examples

[0260] Example 1

[0261] Li2CO3, FePO4, 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 sucrose was added in an amount of 14 wt% based on the total weight of Li2CO3, FePO4, and TiO2 to prepare a mixed solution. For mixing and grinding of the raw materials, the mixed solution was wet-ground for 1 hour at 30 Hz with a beads mill to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0262] Afterwards, the dried powder (hereinafter, the mixture) was fired at 780°C for 10 hours under a nitrogen atmosphere to produce a fired product. The fired product was pulverized with a jet mill (feeding pressure: 6 bar, grinding pressure: 1 bar) to form a LiFe coating layer containing carbon. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0263]

[0264] Example 2

[0265] A positive electrode active material was manufactured in the same manner as in Example 1, except that the sintering was performed at 750°C instead of 780°C.

[0266]

[0267] Example 3

[0268] A positive electrode active material was manufactured in the same manner as in Example 1, except that sucrose was added at 10 wt% instead of 14 wt% based on the total weight of Li2CO3, FePO4, and TiO2, and that calcination was performed at 800°C instead of 780°C.

[0269]

[0270] Comparative Example 1

[0271] Li2CO3 and FePO4 were mixed with water in an amount such that the molar ratio of lithium to iron (Li:Fe) was 1.03:1, and sucrose was added in an amount of 8 wt% based on the total weight of Li2CO3 and FePO4 to prepare a mixed solution. For mixing and grinding of the raw materials, the mixed solution was wet-ground for 1 hour at 30 Hz in a beads mill to obtain a slurry. The slurry was dried through spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0272] Afterwards, the dried powder (hereinafter, the mixture) was fired at 750°C for 10 hours under a nitrogen atmosphere to produce a fired product. The fired product was pulverized using a jet mill (feeding pressure: 6 bar, grinding pressure: 1 bar) to produce a LiFePO4 positive electrode active material having a carbon-containing coating layer formed thereon.

[0273]

[0274] Comparative Example 2

[0275] Li2CO3, FePO4, and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.005, and sucrose was added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4, and TiO2 to prepare a mixed solution. For mixing and grinding of the raw materials, the mixed solution was wet-ground for 1 hour at 30 Hz with a beads mill to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0276] Afterwards, the dried powder (hereinafter, the mixture) was fired at 750°C for 10 hours under a nitrogen atmosphere to produce a fired product. The fired product was pulverized with a jet mill (feeding pressure: 6 bar, grinding pressure: 1 bar) to form a LiFe coating layer containing carbon. 0.995 Ti 0.005 PO4 positive electrode active material was manufactured.

[0277]

[0278] Comparative Example 3

[0279] A positive electrode active material was manufactured in the same manner as in Comparative Example 2, except that the sintering was performed at 780°C instead of 750°C.

[0280]

[0281] Comparative Example 4

[0282] A cathode active material was manufactured in the same manner as in Example 1, except that sucrose was added at 8 wt% instead of 14 wt% based on the total weight of Li2CO3, FePO4, and TiO2.

[0283]

[0284] Comparative Example 5

[0285] Li2CO3, FePO4, and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.03:1:0.008, and sucrose was added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4, and TiO2 to prepare a mixed solution. For mixing and grinding of the raw materials, the mixed solution was wet-ground for 1 hour at 30 Hz in a beads mill to obtain a slurry. The slurry was dried through spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0286] Afterwards, the dried powder (hereinafter, the mixture) was fired at 780°C for 10 hours under a nitrogen atmosphere to produce a fired product. The fired product was pulverized with a jet mill (feeding pressure: 6 bar, grinding pressure: 1 bar) to form a LiFe coating layer containing carbon. 0.992 Ti 0.008 PO4 positive electrode active material was manufactured.

[0287]

[0288] Comparative Example 6

[0289] A positive electrode active material was manufactured in the same manner as in Example 1, except that sucrose was added at 9.65 wt% instead of 14 wt% based on the total weight of Li2CO3, FePO4, and TiO2, calcination was performed at 800°C instead of 780°C, and grinding was performed under a feeding pressure of 6 bar and a grinding pressure of 2 bar.

[0290]

[0291] Comparative Example 7

[0292] A positive electrode active material was manufactured in the same manner as in Example 1, except that sucrose was added at 10 wt% instead of 14 wt% based on the total weight of Li2CO3, FePO4, and TiO2, calcination was performed at 800°C instead of 780°C, and grinding was performed under a feeding pressure of 6 bar and a grinding pressure of 2 bar.

[0293]

[0294] Comparative Example 8

[0295] A positive electrode active material was manufactured in the same manner as in Example 1, except that sucrose was added at 10 wt% instead of 14 wt% based on the total weight of Li2CO3, FePO4, and TiO2, and that grinding was performed under a feeding pressure of 6 bar and a grinding pressure of 2 bar.

[0296]

[0297] Comparative Example 9

[0298] A cathode active material was manufactured in the same manner as in Comparative Example 2, except that sucrose was added at 8.5 wt% instead of 14 wt% based on the total weight of Li2CO3, FePO4, and TiO2, and that calcination was performed at 780°C instead of 750°C.

[0299]

[0300] Experimental example

[0301] Experimental Example 1: Particle Size Distribution Measurement

[0302] 5 ml of deionized water and 100 μl of a dispersant (Triton X-100) were added to a conical tube. Then, 1 mg of each of the positive electrode active material powders of Examples 1 to 3 and Comparative Examples 1 to 9 was weighed and added to the conical tube. Sonication was performed for about 1 minute to disperse the positive electrode active material powders, and the solution in the conical tube was poured into an analysis beaker containing 450 ml of deionized water to prepare a sample.

[0303] The above samples were analyzed using PSA (Mastersizer 3000, Malvern) to obtain particle size distribution graphs of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 to 9, respectively, which are shown in Figs. 2 to 13. Specifically, Figs. 2 to 4 sequentially show particle size distribution graphs of the positive electrode active materials of Examples 1 to 3, respectively, and Figs. 5 to 13 sequentially show particle size distribution graphs of the positive electrode active materials of Comparative Examples 1 to 9, respectively.

[0304] And, from the particle size distribution graph, the slope of the straight line passing through the inflection point and the point where the volume percentage of the right peak is maximum is obtained, and this is shown in Table 1 below.

[0305] Also, from the particle size distribution graph, D min , D 10 , D 50 , D 90 , D max , span value, R.tan, D R , Y(D R ), D L , Y(D L ) was obtained and is shown in Table 1 or Table 2 below.

[0306] And, (Y(D R )) / span × |R.tan| and (Y(D R )- Y(D L )) / span × |R.tan| was calculated and shown in Table 2 below.

[0307] Slope D min (㎛)D 10 (㎛)D 50 (㎛)D 90 (㎛)D max (㎛) Span Example 16.000.240.491.433.7721.202.30 Example 26.580.240.491.463.597.642.12 Example 36.670.240.461.393.225.961.98 Comparative Example 17.890.210.411.142.544.581.87 Comparative Example 214.380.280.591.934.147.611.84 Comparative Example 315.660.280.632.094.256.721.73 Comparative Example 417.810.280.682.264.557.641.71 Comparative Example 512.890.280.732.956.1512.701.84Comparative example 64.740.240.531.663.265.211.65Comparative example 73.150.240.491.693.646.721.87Comparative example 81.200.210.370.842.184.032.16Comparative example 93.230.210.380.872.003.551.87

[0308] Distinction R.tanD R (㎛)Y(D R ) (%)D L (㎛)Y(D L ) (%)(Y(D R ) / span × |R.tan|(Y(D R )- Y(D L )) / span × |R.tan|Example 1-1.381.655.480.594.833.290.39Example 2-1.661.135.780.525.954.53-0.13Example 3-2.031.656.770.594.296.932.54Comparative Example 1-2.691.457.050.465.0810.142.83Comparative Example 2-2.272.137.540.593.199.305.36Comparative Example 3-1.642.427.940.683.027.554.68Comparative Example 4-2.062.648.130.592.429.816.89Comparative Example 5-0.443.557.830.592.051.881.39Comparative Example 6-2.641.888.500.523.2313.598.42Comparative Example 7-2.022.137.370.523.857.983.81Comparative Example 8-2.011.285.650.466.795.26-1.06Comparative Example 9-2.531.136.650.526.419.020.33

[0309]

[0310] Experimental Example 2: Battery Performance Evaluation

[0311] The positive electrode active materials, carbon black conductive agents, and polyvinylidene fluoride (PVdF) binders of Examples 1 to 3 and Comparative Examples 1 to 9 were mixed in a weight ratio of 95:2:3 in an N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried at 100°C, and then rolled to prepare a positive electrode.

[0312] Lithium metal was used as the cathode.

[0313] An electrode assembly was manufactured by interposing a porous polyethylene separator between the positive and negative electrodes. The electrode assembly was placed inside a battery case and an electrolyte was injected to manufacture a lithium secondary battery (half cell). At this time, the electrolyte was a solution prepared by dissolving 1.0 M LiPF6 and 2 wt% vinyl carbonate (VC) in an organic solvent mixed with ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 1:2:1.

[0314]

[0315] As described above, lithium secondary batteries (half cells) were manufactured and left for 24 hours. Each lithium secondary battery was then charged to 3.7 V in CC (0.1 C)-CV (Cut-off current: 0.05 C) mode at 25°C, left for 30 minutes, and discharged to 2.5 V at 0.1 C, and the initial charge / discharge capacity was measured. At this time, the percentage of the initial discharge capacity to the initial charge capacity was expressed as efficiency (%), and is shown together with the charge / discharge capacity in Table 3 below.

[0316]

[0317] After that, charge to 3.7 V in CC(0.33C)-CV(Cut-off current: 0.05C) mode at 25℃, leave for 30 minutes, discharge to 2.5 V at 0.33C, charge to 3.7 V in CC(0.2C)-CV(Cut-off current: 0.05C) mode at 25℃, leave for 30 minutes, discharge to 2.5 V at 0.2C, charge to 3.7 V in CC(0.2C)-CV(Cut-off current: 0.05C) mode at 25℃, leave for 30 minutes, discharge to 2.5 V at 1.0C, charge to 3.7 V in CC(0.2C)-CV(Cut-off current: 0.05C) mode at 25℃, leave for 30 minutes, The discharge capacity was measured while discharging to 2.5 V at 2.0 C. The percentage of the 2.0 C discharge capacity to the 0.1 C discharge capacity is expressed as 2 C / 0.1 C (%) and is shown in Table 3 below.

[0318]

[0319] ClassificationCharge capacity (mAh / g)Discharge capacity (mAh / g)Efficiency (%)2C / 0.1C (%)Example 1162.9162.699.887.9Example 2160.6158.798.887.6Example 3163.5162.399.286.2Comparative example 1163.4158.496.983.5Comparative example 2163.4156.795.974.4Comparative example 3164.3156.195.074.6Comparative example 4164.0157.596.075.2Comparative example 5163.6157.796.474.1Comparative example 6161.2155.296.376.3Comparative example 7162.0158.898.081.1Comparative example 8162.5158.697.684.4Comparative example 9164.1160.697.881.8

[0320] Referring to FIGS. 2 to 13 and Table 1 above, it can be confirmed that the positive electrode active materials of Examples 1 to 3 have a bimodal particle size distribution, and at the same time, the slope of the straight line passing through the inflection point and the point where the volume percentage of the right peak is maximum in the particle size distribution curve is 5 or more and 7 or less.

[0321] In comparison, the positive electrode active materials of Comparative Examples 1 to 9 have a bimodal particle size distribution, but it can be confirmed that the slope of the straight line passing through the inflection point and the point where the volume percentage of the right peak is maximum in the particle size distribution curve is less than 5 or greater than 7.

[0322] And, referring to Table 3 above, it can be confirmed that the lithium secondary batteries including the positive electrode active materials of Examples 1 to 3 have significantly superior efficiency and rate characteristics compared to the lithium secondary batteries including the positive electrode active materials of Comparative Examples 1 to 9.

[0323] This is because, when the lithium iron phosphate-based positive electrode active material has a bimodal particle size distribution and, at the same time, the slope of the straight line passing through the inflection point and the point where the volume percentage of the right peak is maximum in the particle size distribution curve is 5 or more and 7 or less, the tap density of the positive electrode active material is high, so that the energy density of a battery including the positive electrode active material can be improved, and a uniform electrode slurry can be manufactured, so that the battery efficiency and output characteristics can be improved.

[0324] In conclusion, it can be seen that the positive electrode active material according to the present invention can significantly improve the efficiency and output characteristics of a lithium secondary battery.

Claims

1. A lithium iron phosphate cathode active material comprising a lithium iron phosphate compound, The lithium iron phosphate-based cathode active material has a bimodal particle size distribution, and the slope of a straight line passing through an inflection point and a point where the volume percentage of the right peak is maximum in a particle size distribution curve in which the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %) is 5 or more and 7 or less.

2. In claim 1, The above lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material that satisfies the following formula 1: [Formula 1] -2.10 < R.tan < -1.00 In the above equation 1, R.tan is a particle size distribution curve in which the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %). R From D 90 is the slope of the function representing the trend up to , D R is the particle size when the volume percentage of the right peak is maximum, The function representing the above trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

3. In claim 1, The above lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material that satisfies the following formula 2: [Formula 2] In the above equation 2, In a particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %), D R is the particle size when the volume percentage of the right peak is maximum, and Y(D R ) is D R is the volume percentage (unit: %) in Span is ((D 90 -D 10 ) / D 50 ) and, R.tan is D R From D 90 It is the slope of the function representing the trend up to , and the function representing the trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

4. In claim 1, The above lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material that satisfies the following formula 3: [Formula 3] In the above equation 3, In a particle size distribution curve where the x-axis is a log scale of particle diameter (unit: ㎛) and the y-axis is a volume percentage (unit: %), D R is the particle size when the volume percentage of the right peak is maximum, and Y(D R ) is D R is the volume percentage (unit: %) in , D L is the particle diameter when the volume percentage of the left peak is maximum, and Y(D L ) is D L is the volume percentage (unit: %) in Span is ((D 90 -D 10 ) / D 50 ) and, R.tan is D R From D 90 It is the slope of the function representing the trend up to , and the function representing the trend is a linear regression function when the residual sum of squares is minimum according to the least squares method.

5. In claim 3 or 4, The above lithium iron phosphate cathode active material is D R A lithium iron phosphate-based positive electrode active material having a particle size of 1.00㎛ or more and 5.00㎛ or less.

6. In claim 3 or 4, The above lithium iron phosphate cathode active material is D R Volume percentage in (Y(D) R )) Lithium iron phosphate cathode active material having a content of 4.00% or more and 10.00% or less.

7. In claim 3, The above lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material having an R.tan of -2.10 or more and -1.00 or less.

8. In claim 4, The above lithium iron phosphate cathode active material is D L A lithium iron phosphate-based positive electrode active material having a particle size of 0.30㎛ or more and 0.80㎛ or less.

9. In claim 4, The above lithium iron phosphate cathode active material is D L Volume percentage in (Y(D) L )) Lithium iron phosphate cathode active material having a content of 1.00% or more and 8.00% or less.

10. In claim 1, The above lithium iron phosphate cathode active material has a span ((D 90 -D 10 ) / D 50 ) Lithium iron phosphate cathode active material having a value of 1.50 or more and 2.50 or less.

11. In claim 1, The above lithium iron phosphate cathode active material is D 50 A lithium iron phosphate-based positive electrode active material having a particle size of 0.80㎛ or more and 3.00㎛ or less.

12. In claim 1, The above lithium iron phosphate cathode active material is D 10 A lithium iron phosphate-based positive electrode active material having a particle size of 0.35㎛ or more and 0.80㎛ or less.

13. In claim 1, The above lithium iron phosphate cathode active material is D 90 A lithium iron phosphate-based positive electrode active material having a particle size of 2.00㎛ or more and 4.00㎛ or less.

14. In claim 1, The lithium iron phosphate compound is a lithium iron phosphate cathode active material having a composition represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4 In the above chemical formula 1, M 1 is at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Mo, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y, -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.

1.

15. In claim 1, The lithium iron phosphate compound is a lithium iron phosphate cathode active material having a composition represented by the following chemical formula 2: [Chemical Formula 2] Li 1+x2 [Fe 1-a2-b2 Mn a2 You b2 ]PO4 In the above chemical formula 2, -0.1≤x2≤0.1, 0≤a2≤0.9, 0 <b2≤0.1이다.

16. In claim 1, A lithium iron phosphate-based cathode active material further comprising a coating portion including carbon (C) formed on the lithium iron phosphate-based compound.

17. In claim 16, A lithium iron phosphate-based positive electrode active material having a carbon (C) content included in the coating portion of 0.5 wt% to 3.0 wt% based on the total weight of the lithium iron phosphate-based positive electrode active material.

18. A cathode comprising a lithium iron phosphate cathode active material according to claim 1.

19. A lithium secondary battery comprising a positive electrode according to claim 18.

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