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 comprising a lithium iron phosphate-based compound, and a cathode and a lithium secondary battery comprising the lithium iron phosphate-based cathode active material. The lithium iron phosphate-based cathode active material has a bimodal particle size distribution which satisfies Expression 1. [Expression 1] 1.00 < (Y(DR)-Y(DL)) / span ≤ 1.75, where, in a particle size distribution curve in which the x-axis is a log-scale of particle diameter (unit: ㎛) and the y-axis is volume percentage (unit: %), DR is the particle diameter when the volume percentage of the right-side peak is greatest, Y(DR) is the volume percentage (unit: %) at DR, DL is the particle diameter when the volume percentage of the left-side peak is greatest, Y(DL) is the volume percentage (unit: %) at DL, and span is ((D90-D10) / D50) (unit: ㎛).

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. 10-2024-0080828, 10-2024-0080825, 10-2024-0080829 and 10-2024-0080832, 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 positive electrode active material, a positive electrode 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 energy density and resistance 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 can be clearly understood by those skilled in the art from the description below.

[0015]

[0016] (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 satisfies the following formula 1.

[0017] [Formula 1]

[0018] 1.00 < (Y(D R )-Y(D L )) / span ≤ 1.75

[0019] In the above equation 1, 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: %), 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 , and 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 , and the span is ((D 90 -D 10 ) / D 50 )am.

[0020] (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 2.

[0021] [Formula 2]

[0022] 5.50 ≤ (Y(D R ) / span)×|R.tan|

[0023] In the above equation 2, 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: %), D R is the particle size when the volume percentage of the right peak is maximum, and Y(D R ) is D Ris the volume percentage (unit: %) value in , and the 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.

[0024] (3) The present invention provides a lithium iron phosphate-based positive electrode active material in the above (2), wherein the lithium iron phosphate-based positive electrode active material satisfies the following formula 3.

[0025] [Formula 3]

[0026] 3.40 ≤ Y(D R ) / span.

[0027] (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 4 in any one of the above (1) to (3).

[0028] [Formula 4]

[0029] -2.30 ≤ L.tan+R.tan ≤ 3.60

[0030] In the above equation 4, 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: %), D L is the particle size when the volume percentage of the left peak is maximum, and L.tan is D 10 From D L 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, and R.tan is D R From D 90It 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.

[0031] (5) 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 5 in any one of the above (1) to (4).

[0032] [Formula 5]

[0033] -6.10 ≤ R.tan / L.tan ≤ -0.40

[0034] In the above equation 5, 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: %), L.tan is D 10 From D L is the slope of the function representing the trend up to , and R.tan is D R From D 90 is the slope of the function representing the trend up to D L is the particle size when the volume percentage of the left peak is maximum, and D R is the particle diameter when the volume percentage of the right peak is maximum, and 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.

[0035] (6) 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 (5).

[0036] [Chemical Formula 1]

[0037] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4

[0038] 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, and -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1.

[0039] (7) 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 (6).

[0040] [Chemical Formula 2]

[0041] Li 1+x2 [Fe 1-a2-b2 Mn a2 M 2 b2 ]PO4

[0042] In the above chemical formula 2, M 2 is Ti, Mg or a combination thereof, -0.1≤x2≤0.1, 0≤a2≤0.9, 0 <b2≤0.1이다.

[0043] (8) In any one of the above (1) to (5), 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 2.00㎛ or less is provided.

[0044] (9) In any one of the above (1) to (5), the 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 8.00% or less.

[0045] (10) In any one of the above (1), (4) and (5), the lithium iron phosphate cathode active material is D L A lithium iron phosphate cathode active material having a particle size of 0.40㎛ or more and 0.80㎛ or less is provided.

[0046] (11) In the present invention, in the above (1), 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 4.00% or more and 8.00% or less.

[0047] (12) The present invention provides a lithium iron phosphate-based positive electrode active material having a span of 1.80 or more and 2.30 or less in any one of the above (1) to (3).

[0048] (13) In any one of the above (1) to (3), 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 2.00㎛ or less is provided.

[0049] (14) In any one of the above (1) to (5), the lithium iron phosphate cathode active material is D 10 A lithium iron phosphate cathode active material having a particle size of 0.20㎛ or more and 0.50㎛ or less is provided.

[0050] (15) In any one of the above (1) to (5), 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 5.00㎛ or less is provided.

[0051] (16) The present invention provides a lithium iron phosphate-based positive electrode active material having an R.tan of -3.00 or more and -1.00 or less in any one of the above (2), (4) and (5).

[0052] (17) The present invention provides a lithium iron phosphate-based positive electrode active material in (4) or (5) above, wherein the lithium iron phosphate-based positive electrode active material has an L.tan of 0.00 or more and 7.00 or less.

[0053] (18) 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 (17).

[0054] (19) 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 (18) is 0.5 wt% to 3.0 wt% based on the total weight of the lithium iron phosphate-based positive electrode active material.

[0055] (20) The present invention provides a positive electrode comprising a lithium iron phosphate-based positive electrode active material according to any one of (1) to (19).

[0056] (21) The present invention provides a lithium secondary battery including a positive electrode according to (20).

[0057]

[0058] The lithium iron phosphate cathode active material according to the present invention has a bimodal particle size distribution and at the same time satisfies Equation 1 described herein, thereby having a high rolling density and low resistance, thereby significantly improving the resistance characteristics and energy density of a lithium secondary battery including the same.

[0059]

[0060] Figure 1 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 , Y(D R ), D L , Y(D L ) is a drawing showing the same.

[0061] Figure 2 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Example 1.

[0062] Figure 3 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Example 2.

[0063] Figure 4 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Example 3.

[0064] Figure 5 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Example 4.

[0065] Figure 6 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Example 5.

[0066] Figure 7 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Comparative Example 1.

[0067] Figure 8 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Comparative Example 2.

[0068] Figure 9 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Comparative Example 3.

[0069] Figure 10 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Comparative Example 4.

[0070] Figure 11 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Comparative Example 5.

[0071] Figure 12 is a graph of the particle size distribution of the lithium iron phosphate-based positive electrode active material manufactured in Comparative Example 6.

[0072] Figure 13 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Comparative Example 7.

[0073] Figure 14 is a graph of the particle size distribution of the lithium iron phosphate cathode active material manufactured in Comparative Example 8.

[0074]

[0075] Hereinafter, the present invention will be described in more detail.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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) D 90 , v) D maxThe 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.

[0080]

[0081] positive electrode active material

[0082] 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 by satisfying the following equation 1.

[0083] [Formula 1]

[0084] 1.00 < (Y(D R )-Y(D L )) / span ≤ 1.75

[0085] In the above equation 1,

[0086] 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: %),

[0087] 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 ,

[0088] 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

[0089] Span is ((D 90 -D 10 ) / D 50 )(unit: ㎛).

[0090]

[0091] The present inventors have found that when a lithium iron phosphate-based positive electrode active material has a bimodal particle size distribution and satisfies the above equation 1, small particles are located in the empty spaces between large particles, so that more particles can be arranged in the same volume, thereby increasing the rolling density of the positive electrode active material, and reducing the resistance through the large surface area of ​​the small particles, thereby improving the resistance characteristics of a lithium secondary battery including the same, and have completed the present invention. Specifically, the rolling density of a positive electrode active material having a bimodal particle size distribution is affected by the volume ratio of small particles and large particles and the particle size. With respect to the above equation 1, (Y(D R )-Y(D L )) is a parameter related to the volume ratio of small particles and large particles. Among the particles having the maximum volume percentage in the positive active material on the particle size distribution curve, relatively small particles are defined as small particles, and among the particles having the maximum volume percentage in the positive active material on the particle size distribution curve, relatively large particles are defined as large particles. By calculating the difference between the volume percentage of large particles and the volume percentage of small particles, the volume of large particles compared to the volume of small particles in the positive active material is quantitatively expressed. In addition, span is a parameter related to the particle size of particles. By calculating the particle size distribution of particles in the positive active material, the ratio of the particle size to the particle size in the positive active material is indirectly expressed.

[0092] Above (Y(D R )-Y(D L )) / Span can be greater than 1.00, or less than or equal to 1.05, less than or equal to 1.25, less than or equal to 1.30, less than or equal to 1.35, less than or equal to 1.40, less than or equal to 1.45, less than or equal to 1.50, less than or equal to 1.55, less than or equal to 1.60, less than or equal to 1.65, less than or equal to 1.70, or less than or equal to 1.75.

[0093] Meanwhile, if the lithium iron phosphate cathode active material does not have a bimodal particle size distribution, the empty space between the particles cannot be efficiently filled, so the tap density or rolling density of the cathode active material is low, which causes a problem of poor energy density of the battery. In addition, if the above equation 1 is not satisfied, there are too many small particles (small particles) and too few large particles (large particles), or there are too few small particles (small particles) and too many large particles (large particles), which causes a problem of low rolling density of the cathode active material and / or high resistance. Specifically, (Y(D R )-Y(D L )) / If the span is less than 1.00, there is a problem of poor rolling density because the volume of small particles is large compared to large particles, or there are many particles with different particle sizes in the positive electrode active material, and (Y(D R )-Y(D L )) / When the span exceeds 1.75, there is a problem that small particles cannot efficiently fill the empty space between particles due to the presence of large particles with too large a volume.

[0094] According to the present invention, the lithium iron phosphate-based positive electrode active material may satisfy the following equation 2.

[0095] [Formula 2]

[0096] 5.50 ≤ (Y(D R ) / span)×|R.tan|

[0097] In the above equation 2,

[0098] 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: %),

[0099] 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 value (unit: %) in ,

[0100] Span is ((D 90 -D 10 ) / D 50 ) and,

[0101] 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.

[0102] According to the present invention, (Y(D R ) / span)×|R.tan| can be specifically greater than or equal to 5.50, greater than or equal to 5.60, or greater than or equal to 5.70, and less than or equal to 11.00.

[0103] Above (Y(D R ) / span)×|R.tan| is within the above range, small particles are located in the empty space between large particles, so that more particles can be placed in the same volume, thereby increasing the rolling density of the positive electrode active material, and reducing the resistance through the large surface area of ​​the small particles, thereby improving the energy density and resistance characteristics of the lithium secondary battery including it. In relation to the above equation 2, (Y(D R ) / span) is a parameter related to the volume ratio of large particles and particle size, which means the volume ratio and particle size uniformity of large particles in the positive electrode active material. (Y(D R ) / span) is larger, it means that there are many large particles with uniform particle size in the positive electrode active material. And, |R.tan| is a parameter indicating the volume ratio of large particles with appropriate particle size, and the smaller |R.tan| is, the higher the D R and D 90 The difference is large, or Y(D R ) and Y(D 90) means that the difference is small. In this case, in the particle size distribution curve where the x-axis is a log scale of particle size (unit: ㎛) and the y-axis is a volume percentage (unit: %), the particle sizes of the particles corresponding to the right peak may be distributed in a dispersed manner, or the volume of small particles may be larger than that of large particles, resulting in a problem of poor rolling density, or the presence of a large number of large particles with excessively large volumes may result in a problem of small particles not being able to efficiently fill the empty spaces between particles. A large |R.tan| means that a large number of large particles with uniform particle size exist.

[0104]

[0105] According to the present invention, the lithium iron phosphate-based positive electrode active material may satisfy the following equation 3.

[0106] [Formula 3]

[0107] 3.40 ≤ Y(D R ) / span.

[0108] Specifically, the above Y(D R ) / span can be 3.40 or more and 3.80 or less. The above Y(D R ) / span is within the above range, the number of particles increases, so that the rolling density and resistance can be improved. With respect to the above equation 3, (Y(D R ) / span) is a parameter related to the volume ratio of large particles and particle size, which means the volume ratio and particle size uniformity of large particles in the positive electrode active material. (Y(D R ) / span) is larger, it means that there are many large particles with a uniform particle size in the positive electrode active material.

[0109]

[0110] According to the present invention, the lithium iron phosphate-based positive electrode active material may satisfy the following equation 4.

[0111] [Formula 4]

[0112] -2.30 ≤ L.tan+R.tan ≤ 3.60

[0113] In the above equation 4,

[0114] 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: %),

[0115] D L is the particle size when the volume percentage of the left peak is maximum, and L.tan is D 10 From D L is the slope of the function representing the trend up to

[0116] D R is the particle size when the volume percentage of the right peak is maximum, and R.tan is D R From D 90 is the slope of the function representing the trend up to

[0117] 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.

[0118] Specifically, the above L.tan+R.tan may be -2.30 or more, or -2.25 or more, and may be 3.58 or less, or 3.60 or less.

[0119] When the above L.tan+R.tan is within the above range, small particles are located in the empty space between large particles, so that more particles can be placed in the same volume, thereby increasing the rolling density of the positive electrode active material, and reducing the resistance through the large surface area of ​​the small particles, thereby improving the energy density and resistance characteristics of the lithium secondary battery including it. In relation to Equation 4, L.tan is a parameter indicating the volume ratio of small particles with an appropriate particle size, and a small L.tan is D L This is shifted to the left, or Y(D L) means that it is small. In this case, there is a problem that the rolling density is poor because the volume of large particles is large compared to small particles, or there is a problem that the resistance characteristics are poor because small particles with too small volume exist. A large L.tan means that there are many small particles with uniform particle size. R.tan is a parameter that indicates the volume ratio of large particles with appropriate particle size, and |R.tan| is small when D R and D 90 The difference is large, or Y(D R ) and Y(D 90 ) means that the difference is small. In this case, 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 particle diameters of the particles corresponding to the right peak may be distributed in a dispersed manner, or the volume of small particles may be large compared to large particles, resulting in a problem of poor rolling density, and the presence of large particles with too large a volume may cause a problem in that small particles cannot efficiently fill the empty space between particles. A large |R.tan| means that there are many large particles with uniform particle diameters. For reference, the above D 10, D L, D R and D 90 satisfies the following relation 1, and Y(D 10 ) and Y(D L ) satisfies the following relation 2, and Y(D R ) and Y(D 90 ) is preferably satisfied by the following relationship 3.

[0120] [Relationship 1] D 10 < D L < D R < D 90

[0121] [Relationship 2] Y(D 10 ) < Y(D L )

[0122] [Relationship 3] Y(D 90) < Y(D R )

[0123]

[0124] According to the present invention, the lithium iron phosphate-based positive electrode active material may satisfy the following equation 5.

[0125] [Formula 5]

[0126] -6.10 ≤ R.tan / L.tan ≤ -0.40

[0127] In the above equation 5,

[0128] 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: %),

[0129] L.tan is D 10 From D L is the slope of the function representing the trend up to ,

[0130] R.tan is D R From D 90 is the slope of the function representing the trend up to

[0131] D L is the particle size when the volume percentage of the left peak is maximum,

[0132] D R is the particle size when the volume percentage of the right peak is maximum,

[0133] 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.

[0134] Specifically, the R.tan / L.tan may be -6.10 or more, or -6.05 or more, and -0.40 or less, -0.41 or less, -0.42 or less, or -0.43 or less. When the R.tan / L.tan is within the above range, small particles are located in the empty space between large particles, so that more particles can be arranged in the same volume, thereby increasing the rolling density of the positive electrode active material, and reducing the resistance through the large surface area of ​​the small particles, thereby improving the energy density and resistance characteristics of a lithium secondary battery including the same. In relation to Equation 5, L.tan is a parameter representing the volume ratio of small particles of an appropriate particle size, and a smaller L.tan is D L This is shifted to the left, or Y(D L ) means that it is small. In this case, there is a problem that the rolling density is poor because the volume of large particles is large compared to small particles, or there is a problem that the resistance characteristics are poor because small particles with too small volume exist. A large L.tan means that there are many small particles with uniform particle size. R.tan is a parameter that indicates the volume ratio of large particles with appropriate particle size, and |R.tan| is small when D R and D 90 The difference is large, or Y(D R ) and Y(D 90 ) means that the difference is small. In this case, 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 particle diameters of the particles corresponding to the right peak may be distributed in a dispersed manner, or the volume of small particles may be large compared to large particles, resulting in a problem of poor rolling density, and the presence of large particles with too large a volume may cause a problem in that small particles cannot efficiently fill the empty space between particles. A large |R.tan| means that there are many large particles with uniform particle diameters. For reference, the above D 10, D L, D R and D 90satisfies the following relation 1, and Y(D 10 ) and Y(D L ) satisfies the following relation 2, and Y(D R ) and Y(D 90 ) is preferably satisfied by the following relationship 3.

[0135] [Relationship 1] D 10 < D L < D R < D 90

[0136] [Relationship 2] Y(D 10 ) < Y(D L )

[0137] [Relationship 3] Y(D 90 ) < Y(D R )

[0138]

[0139] According to the present invention, the lithium iron phosphate compound may have a composition represented by the following chemical formula 1.

[0140] [Chemical Formula 1]

[0141] Li 1+x [Fe 1-a-b Mn a M 1 b ]PO4

[0142] In the above chemical formula 1,

[0143] M 1 is at least one selected from the group consisting of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, Na, Si, Ca, B and Y,

[0144] -0.1≤x≤0.1, 0≤a≤0.9, 0≤b≤0.1.

[0145] The above x can be from -0.1 to 0.1. When x satisfies the above range, high-capacity characteristics can be implemented, and byproducts can be minimized during manufacturing.

[0146] 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.

[0147] 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, or 0.003 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.

[0148] The above 1-ab may be greater than 0 and less than or equal to 1.0.

[0149]

[0150] According to the present invention, the lithium iron phosphate compound may have a composition represented by the following chemical formula 2. When Ti and / or Mg are doped at the Fe site, particle growth is controlled to increase particle size uniformity, thereby improving span, etc., and thus improving rolling density.

[0151] [Chemical Formula 2]

[0152] Li 1+x2 [Fe 1-a2-b2 Mn a2 M 2 b2 ]PO4

[0153] In the above chemical formula 2,

[0154] M 2is Ti, Mg or a combination thereof,

[0155] -0.1≤x2≤0.1, 0≤a2≤0.9, 0 <b2≤0.1이다.

[0156]

[0157] According to the present invention, the lithium iron phosphate cathode active material is D R This may be 1.00㎛ or more and 2.00㎛ or less. Specifically, the above D R The size may be 1.00㎛ or more, 1.10㎛ or more, 1.20㎛ or more, 1.30㎛ or more, or 1.40㎛ or more, and may be 1.90㎛ or less, or 2.00㎛ or less. In this case, since large particles of an appropriate particle size exist, the rolling density and resistance can be improved.

[0158]

[0159] According to the present invention, the lithium iron phosphate cathode active material is D R Volume percentage in (Y(D) R )) may be 4.00% or more and 8.00% or less. Specifically, the Y(D R ) may be 4.00% or more, 4.50% or more, 5.00% or more, 5.50% or more, 6.00% or more, or 6.50% or more, and 7.50% or less, or 8.00% or less. In this case, the number of large particles is present to an appropriate degree, so that the rolling density and resistance can be improved.

[0160]

[0161] According to the present invention, the lithium iron phosphate cathode active material is D L This may be 0.40㎛ or more and 0.80㎛ or less. Specifically, the above D L The size may be 0.40㎛ or more, or 0.45㎛ or more, or 0.60㎛ or less, 0.65㎛ or less, 0.70㎛ or less, 0.75㎛ or less, or 0.80㎛ or less. In this case, small particles of an appropriate particle size are present, so that the rolling density and resistance can be improved.

[0162]

[0163] According to the present invention, the lithium iron phosphate cathode active material is D L Volume percentage in (Y(D) L )) may be 4.00% or more and 8.00% or less. Specifically, the Y(D R ) may be 4.00% or more, 5.50% or less, 6.00% or less, 6.50% or less, 7.00% or less, 7.50% or less, or 8.00% or less. In this case, the number of small particles is present in an appropriate degree, so that the rolling density and resistance can be improved.

[0164]

[0165] According to the present invention, the lithium iron phosphate-based positive electrode active material may have a span of 1.80 or more and 2.30 or less. Specifically, the span may be 1.80 or more, or 1.85 or more, and 2.00 or less, 2.05 or less, 2.10 or less, 2.15 or less, 2.20 or less, 2.25 or less, or 2.30 or less. In this case, the uniformity of the particles may be increased, thereby improving the rolling density.

[0166]

[0167] According to the present invention, the lithium iron phosphate cathode active material is D 50 This may be 0.80㎛ or more and 2.00㎛ or less. Specifically, the above D 50 The particle size may be 0.80㎛ or more, 0.85㎛ or more, 0.90㎛ or more, 0.95㎛ or more, or 1.00㎛ or more, or 1.50㎛ or less, 1.55㎛ or less, 1.60㎛ or less, 1.65㎛ or less, 1.70㎛ or less, 1.75㎛ or less, 1.80㎛ or less, 1.85㎛ or less, 1.90㎛ or less, 1.95㎛ or less, or 2.00㎛ 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.

[0168]

[0169] According to the present invention, the lithium iron phosphate cathode active material is D 10 This may be 0.20㎛ or more and 0.50㎛ or less. Specifically, the above D 10 The particle size may be 0.20㎛ or more, 0.25㎛ or more, 0.30㎛ or more, 0.35㎛ or more, or 0.40㎛ or more, and may be 0.50㎛ 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.

[0170]

[0171] According to the present invention, the lithium iron phosphate cathode active material is D 90 This may be 2.00㎛ or more and 5.00㎛ or less. Specifically, the above D 90 The size may be 2.00㎛ or more, 2.50㎛ or more, or 3.00㎛ or more, or 3.50㎛ or less, 4.00㎛ or less, 4.50㎛ or less, or 5.00㎛ 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.

[0172]

[0173] According to the present invention, the lithium iron phosphate-based positive electrode active material may have an R.tan of -3.00 or more and -1.00 or less. Specifically, the R.tan may be -3.00 or more, -2.90 or more, -2.80 or more, or -2.70 or more, and -1.60 or less, -1.50 or less, -1.40 or less, -1.30 or less, -1.20 or less, -1.10 or less, or -1.00 or less. In this case, in a distribution having a bimodal particle size distribution, the uniformity of particles with large particle sizes is increased, so that the rolling density can be improved.

[0174]

[0175] According to the present invention, the lithium iron phosphate-based positive electrode active material may have an L.tan of 0.00 or more and 7.00 or less. Specifically, the L.tan may be 0.00 or more, 0.10 or more, 0.20 or more, 0.30 or more, or 0.40 or more, and 6.30 or less, 6.40 or less, 6.50 or less, 6.60 or less, 6.70 or less, 6.80 or less, 6.90 or less, or 7.00 or less. In this case, in a distribution having a bimodal particle size distribution, the uniformity of particles with small particle sizes is increased, so that the rolling density can be improved.

[0176]

[0177] 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.

[0178]

[0179] 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 while also improving the rolling density.

[0180]

[0181] According to the present invention, the lithium iron phosphate-based positive electrode active material may be in the form of secondary particles in which primary particles are aggregated, and may be in the form in which several to several hundred or more primary particles are aggregated.

[0182]

[0183] 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 fired product; and (C) a step of pulverizing the fired product.

[0184]

[0185] 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.

[0186]

[0187] 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.

[0188] The above phosphoric acid raw material may be FePO4, H3PO4, NH4H2PO4, (NH4)2HPO4, P2O5, etc.

[0189] 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.

[0190] The above phosphate raw material and iron raw material may be the same. For example, it may be iron phosphate (FePO4).

[0191]

[0192] The above carbon coating raw material can provide a carbon coating portion by sintering, and thus the electrical conductivity of the lithium iron phosphate-based positive electrode 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.

[0193] The carbon coating raw material may be added in an amount of 5 wt% to 20 wt%, specifically 10 wt% to 15 wt%, based on the total weight of the lithium raw material, the phosphate raw material, the iron raw material, and the doping element raw material. In this case, the carbon coating raw material is utilized as a material for the oxidation-reduction reaction that occurs in the process of forming lithium iron phosphate crystals, and an appropriate amount of carbon may be coated to improve conductivity. Specifically, as the proportion of carbon in the mixture increases, particle growth is suppressed, and the number of small particles tends to increase or the number of large particles tends to decrease.

[0194] In addition, if the reactants of the reduction reaction are excessive, the reaction occurs excessively and impurities are generated. If the ratio of carbon in the mixture is not appropriate, there is a problem that the oxidation-reduction reaction does not occur sufficiently and impurities are generated. When the carbon coating raw material is sucrose, if it is 8 to 11 wt% based on the total weight of the lithium raw material, the phosphate raw material, the iron raw material, and the doping element raw material, a lithium iron phosphate-based positive electrode active material having a bimodal particle size distribution and satisfying Equation 1 described in the present specification can be manufactured.

[0195]

[0196] 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, 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.

[0197]

[0198] When preparing the mixture in step (A) above, the mixture can be prepared by further mixing in a manganese raw material.

[0199] The above manganese raw material may be a manganese-containing phosphate, iron phosphate, sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide.

[0200] The above manganese raw material, phosphate raw material and iron raw material may be the same. For example, Mn α Fe (1-α)PO4 (where 0<α<1.0) may be present.

[0201]

[0202] 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.

[0203] The above lithium raw material and iron raw material can be mixed in a ratio such that the resulting lithium iron phosphate-based positive electrode active material has a bimodal particle size distribution and satisfies Equation 1 described herein. Specifically, the particle size distribution of the lithium iron phosphate-based compound is different depending on the ratio of lithium and iron included in the mixture. When the ratio of lithium to iron included in the mixture increases, the ratio of lithium to iron in the lithium iron phosphate-based positive electrode active material included in the manufactured lithium iron phosphate-based compound increases, and in this case, the ratio of small particles tends to increase or the ratio of large particles tends to decrease. The particle size distribution changes organically, and when the Li:Fe included in the mixture is 1.02 to 1.04:1, a lithium iron phosphate-based positive electrode active material satisfying Equation 1 described herein can be manufactured.

[0204]

[0205] The mixing of the above raw materials may be wet mixing or dry mixing.

[0206] 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 40 Hz, using beads of 0.3 to 1 ㎛ size), but is not limited thereto.

[0207]

[0208] Meanwhile, in the case of wet mixing, a powder (mixture) that has been completely dried can be obtained through spray drying.

[0209]

[0210] The above sintering can be performed at a temperature of 750°C to 830°C. In this case, through the optimized sintering temperature, appropriate primary particles are formed and impurities are not formed, so that a positive electrode active material with a high rolling density and low resistance can be manufactured. Specifically, when the mixture does not contain a doping element-containing raw material, the sintering can be performed at a temperature of 750°C or more and less than 800°C, and when the mixture contains a doping element-containing raw material, the sintering can be performed at a temperature of 800°C or more and 830°C or less. When the mixture contains a doping element-containing raw material, the reaction temperature of the mixture increases, and the doping element hinders the growth of particles. Therefore, sintering must be performed at a higher temperature than when the mixture does not contain a doping element-containing raw material, so that a lithium iron phosphate-based positive electrode active material having a bimodal particle size distribution and satisfying Equation 1 described herein can be manufactured.

[0211] Meanwhile, when sintering is performed at a temperature lower than 750°C, the proportion of small particles increases, the coating is not properly formed, and the manufactured lithium iron phosphate cathode active material has a low density and high resistance.

[0212]

[0213] The above calcination may be performed under an inert atmosphere. Specifically, the above calcination may be performed under a nitrogen atmosphere.

[0214]

[0215] The crushing of the above-mentioned sintered product may be performed to have a particle size distribution modification according to the present invention, and may be performed, for example, 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.

[0216]

[0217] anode

[0218] 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.

[0219] 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.

[0220] 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.

[0221]

[0222] The above positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material.

[0223] 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.

[0224] 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.

[0225]

[0226] 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.

[0227]

[0228] 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.

[0229]

[0230] 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.

[0231]

[0232] 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.

[0233]

[0234] lithium secondary battery

[0235] 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.

[0236] 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.

[0237] 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.

[0238]

[0239] 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.

[0240] 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.

[0241]

[0242] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0243] 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 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.

[0244] 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.

[0245]

[0246] 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.

[0247] 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.

[0248]

[0249] 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.

[0250]

[0251] 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, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure.

[0252]

[0253] 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.

[0254] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0255] 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.

[0256] 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.

[0257]

[0258] 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.

[0259]

[0260] As described above, a lithium secondary battery including a positive electrode active material according to the present invention has excellent energy density and resistance 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).

[0261] 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.

[0262] 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.

[0263] 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.

[0264] 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.

[0265]

[0266] 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. The examples of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0267]

[0268] Examples and Comparative Examples

[0269] Example 1

[0270] 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 10 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).

[0271] Afterwards, the dried powder (hereinafter, the mixture) was fired at 800°C for 10 hours under a nitrogen atmosphere to produce a fired product. The fired product was pulverized (feeding pressure: 6 bar, grinding pressure: 1 bar) with a jet mill to have a particle size distribution as shown in Fig. 1, thereby forming a LiFe coating portion containing carbon. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0272]

[0273] Example 2

[0274] A LiFePO4 positive electrode active material having a carbon-containing coating formed thereon was manufactured in the same manner as in Example 1, except that a mixed solution was prepared by adding sucrose in an amount of 8 wt% instead of 10 wt% based on the total weight of Li2CO3 and FePO4 without mixing TiO2, and that the mixture was fired at 750°C instead of 800°C for 10 hours in a nitrogen atmosphere to manufacture a fired product.

[0275]

[0276] Example 3

[0277] LiFe having a carbon-containing coating formed in the same manner as in Example 1, except that a mixed solution was prepared by adding sucrose in an amount of 10.25 wt% instead of 10 wt% based on the total weight of Li2CO3 and FePO4. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0278]

[0279] Example 4

[0280] LiFe having a carbon-containing coating formed in the same manner as Example 1, except that the mixed solution was prepared by adding sucrose in an amount of 8.6 wt% instead of 10 wt% based on the total weight of Li2CO3 and FePO4. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0281]

[0282] Example 5

[0283] LiFe having a carbon-containing coating formed in the same manner as Example 1, except that the mixed solution was prepared by adding sucrose in an amount of 9.0 wt% instead of 10 wt% based on the total weight of Li2CO3 and FePO4. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0284]

[0285] Comparative Example 1

[0286] LiFe having a carbon-containing coating formed in the same manner as Example 1, except that a mixed solution was prepared by adding sucrose in an amount of 14 wt% instead of 10 wt% based on the total weight of Li2CO3, FePO4, and TiO2, and that the mixture was fired at 780°C instead of 800°C for 10 hours under a nitrogen atmosphere to produce a fired product. 0.99 Ti 0.01PO4 positive electrode active material was manufactured.

[0287]

[0288] Comparative Example 2

[0289] LiFe having a carbon-containing coating formed in the same manner as Example 1, except that a mixed solution was prepared by adding sucrose in an amount of 14 wt% instead of 10 wt% based on the total weight of Li2CO3, FePO4, and TiO2, and that the mixture was fired at 780°C instead of 800°C for 10 hours under a nitrogen atmosphere to produce a fired product. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0290]

[0291] Comparative Example 3

[0292] LiFe having a carbon-containing coating formed in the same manner as Example 1, except that the mixture was fired for 10 hours at 750°C instead of 800°C in a nitrogen atmosphere to produce a sintered product. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0293]

[0294] Comparative Example 4

[0295] LiFe having a carbon-containing coating formed in the same manner as Example 1, except that the mixture was fired for 10 hours at 780°C instead of 800°C under a nitrogen atmosphere to produce a sintered product. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0296]

[0297] Comparative Example 5

[0298] A LiFePO4 positive electrode active material having a carbon-containing coating formed thereon was manufactured in the same manner as in Example 1, except that a mixed solution was prepared by adding sucrose in an amount of 12 wt% instead of 10 wt% based on the total weight of Li2CO3 and FePO4 without mixing TiO2, and that the mixture was fired at 700°C instead of 800°C for 10 hours in a nitrogen atmosphere to manufacture a fired product.

[0299]

[0300] Comparative Example 6

[0301] A LiFePO4 positive electrode active material having a carbon-containing coating formed thereon was manufactured in the same manner as in Example 1, except that TiO2 was not mixed and the mixture was fired for 10 hours at 700°C instead of 800°C in a nitrogen atmosphere to manufacture a sintered product.

[0302]

[0303] Comparative Example 7

[0304] LiFe having a carbon-containing coating formed in the same manner as in Example 1, except that Li2CO3, FePO4 and TiO2 were mixed with water in an amount such that the molar ratio of lithium:iron:titanium (Li:Fe:Ti) was 1.05:1:0.01 instead of 1.03:1:0.01, and that sucrose was added in an amount of 12 wt% instead of 10 wt% based on the total weight of Li2CO3, FePO4 and TiO2 to prepare a mixed solution, and that the mixture was fired at 780°C instead of 800°C for 10 hours under a nitrogen atmosphere to produce a fired product. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0305]

[0306] Comparative Example 8

[0307] LiFe having a carbon-containing coating formed in the same manner as in Example 1, except that 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 instead of 1.03:1:0.01, and that sucrose was added in an amount of 8 wt% instead of 10 wt% based on the total weight of Li2CO3, FePO4 and TiO2 to prepare a mixed solution, and that the mixture was fired at 780°C instead of 800°C for 10 hours under a nitrogen atmosphere to produce a fired product. 0.992 Ti 0.008 PO4 positive electrode active material was manufactured.

[0308]

[0309] Experimental Example 1: Particle Size Distribution Measurement

[0310] 5 ml of deionized water and 100 μl of dispersant (Triton X-100) were added to a conical tube. Thereafter, 1 mg of each of the positive electrode active material powders of the examples and comparative examples 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.

[0311] The above samples were analyzed using PSA (Mastersizer 3000, Malvern) to obtain particle size distribution graphs for each of the positive electrode active materials of the examples and comparative examples, which are shown in Figures 2 to 14. Specifically, FIG. 2 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Example 1, FIG. 3 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Example 2, FIG. 4 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Example 3, FIG. 5 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Example 4, FIG. 6 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Example 5, FIG. 7 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Comparative Example 1, FIG. 8 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Comparative Example 2, FIG. 9 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Comparative Example 3, FIG. 10 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Comparative Example 4, and FIG. 11 is a particle size distribution graph of a lithium iron phosphate-based positive electrode active material manufactured in Comparative Example 5. This is a particle size distribution graph of the manufactured lithium iron phosphate cathode active material, FIG. 12 is a particle size distribution graph of the manufactured lithium iron phosphate cathode active material in Comparative Example 6, FIG. 13 is a particle size distribution graph of the manufactured lithium iron phosphate cathode active material in Comparative Example 7, and FIG. 14 is a particle size distribution graph of the manufactured lithium iron phosphate cathode active material in Comparative Example 8.

[0312]

[0313] And, from the particle size distribution graph, Y(D R ), Y(D L ), Y(D 10 ), Y(D 90 ) D min , D 10 , D 50 , D 90 , D max , D R , D L, R.tan and L.tan were obtained, and these are shown in Table 1 below.

[0314] Also, span((D 90 - D 10 ) / D 50 ), (Y(D R )-Y(D L )) / span, Y(D R ) / span. (Y(D R ) / span)×|R.tan|, L.tan+R.tan, and R.tan / L.tan values ​​were calculated and shown in Table 2 below.

[0315]

[0316] Classification Y(D R )(%)Y(D L )(%)Y(D 10 )(%)Y(D 90 )(%)D min (㎛)D 10 (㎛)D 50 (㎛)D 90 (㎛)D max (㎛)D R (㎛)D L(㎛)R.tanL.tanExample 16.774.294.093.590.240.461.393.225.921.650.59-2.031.52Example 27.055.084.774.120.210.411.142.544.581.450.46-2.696.27Example 36.724.324.174.050.240.461.423.246.721.650.52-1.682.34Example 46.914.614.233.760.210.441.222.735.211.450.52-2.464.58Example 57.214.034.003.250.240.461.503.376.721.880.52-2.660.44Comparative Example 12.518.586.782.460.210.340.652.145.212.130.46-4.6014.67Comparative Example 21.359.206.882.160.210.340.621.754.032.750.46-0.8118.85Comparative Example 33.326.875.762.810.210.380.842.787.642.420.52-1.427.49 Comparative example 43.716.805.353.220.210.370.842.556.722.130.52-1.179.73 Comparative example 56.315.564.613.150.210.421.072.775.211.450.59-2.395.59 Comparative example 61.359.207.692.620.210.340.601.464.032.750.46-0.9812.38 Comparative example 75.664.003.843.090.240.531.895.1612.702.420.59-0.942.35Comparative example 87.832.242.196.680.280.732.956.1512.703.550.59-0.44-0.36

[0317] Separation span (Y(D) R )-Y(D L )) / SpanY(D R ) / span(Y(D R) / span)×|R.tan|L.tan+R.tanR.tan / L.tanExample 11.991.253.416.92-0.51-1.34Example 21.871.053.7710.153.58-0.43Example 31.961.233.435.770.66-0.72Example 41.881.233.689.062.12-0.54Example 51.941.643.729.89-2.22-6.05Comparative Example 12.77-2.190.914.1710.07-0.31Comparative Example 22.27-3.450.590.4818.04-0.04Comparative Example 32.86-1.241.161.656.07-0.19Comparative Example 42.60-1.191.431.678.56-0.12Comparative Example 52.200.342.876.873.20-0.43Comparative Example 61.87-4.210.720.7111.40-0.08Comparative Example 72.450.682.312.171.41-0.40Comparative Example 81.843.044.261.88-0.801.22

[0318] Through Figs. 2 to 14, it was confirmed that the lithium iron phosphate-based positive electrode active materials manufactured in Examples 1 to 5 had a bimodal particle size distribution. Through Figs. 2 to 14 and Tables 1 and 2, it was confirmed that the lithium iron phosphate-based positive electrode active materials manufactured in Examples 1 to 5 satisfied Formulas 1 to 5 described in the present invention. In addition, the lithium iron phosphate-based positive electrode active materials manufactured in Examples 1 to 5 had a D R This is 1.00㎛ or more and 2.00㎛ or less, and D R Volume percentage in (Y(D) R )) is 4.00% or more and 8.00% or less, and D L This is 0.40㎛ or more and 0.80㎛ or less, and D L Volume percentage in (Y(D) L )) is 4.00% or more and 8.00% or less, and the span is 1.80 or more and 2.30 or less, and D 50 This is 0.80㎛ or more and 2.00㎛ or less, and D 10It was confirmed that the thickness was 0.20㎛ or more and 0.50㎛ or less, 2.00㎛ or more and 5.00㎛ or less, R.tan was -3.00 or more and -1.00 or less, and L.tan was 0.00 or more and 7.00 or less.

[0319] In comparison, it was confirmed that the lithium iron phosphate cathode active materials manufactured in Comparative Examples 1 to 8 did not satisfy Equations 1 to 5 described in the present invention.

[0320]

[0321] Experimental Example 2: Rolling Density Measurement

[0322] Each of the positive electrode active material powders of the examples and comparative examples was weighed at 5 g and filled into a mold for measuring the rolling density. The mold was placed in a measuring device, and the measurement weight was set to 2 tons. The rolling density was measured, and the results are shown in Table 3 below. That is, the rolling density is 2000 kgf / cm of the positive electrode active material. 2 This is the value measured after pressing with pressure.

[0323]

[0324] Experimental Example 3: Resistance (R) Measurement

[0325] Each of the positive electrode active material powders of the examples and comparative examples was weighed at 5 g and filled into a mold for resistance measurement (4-point probe mold), and 2000 kgf / cm 2 After applying pressure, the current and voltage flowing through the pressurized powder were measured using four probes (4-point probe) present in the mold for measuring the resistance, and the resistance value was derived. The results are shown in Table 3 below.

[0326] In addition, the volume resistance (VR) of the powder was derived by multiplying the resistance value by the thickness of the powder in the mold for measuring the resistance, and the results are shown in Table 3 below.

[0327]

[0328] Rolling density (g / cc) R (Ω) VR (Ω cm) Example 12.10 5 5.8 20 16.63 Example 22.08 118.39 0 32.71 Example 32.19 16.26 0 34.07 Example 42.02 49.69 0 25.00 Example 52.27 5 5.39 8 14.09 Comparative Example 11.84 6 2.01 7 6.53 Comparative Example 21.85 23 2.98 0 107.2 Comparative Example 31.87 28.47 0 26.7 Comparative Example 41.91 12.58 7 8.14 Comparative Example 52.00 65.32 215.72 Comparative Example 61.96 9 12.57 0 38.19 Comparative Example 71.91010.64033.22 Comparative example 81.95768.500198

[0329] Through Table 3, it was confirmed that the lithium iron phosphate-based positive electrode active materials manufactured in Examples 1 to 5 had a rolling density of 2.020 g / cc or more, a resistance (R) of 19Ω or less, and a volume resistivity (VR) of 35Ω·cm or less. In contrast, it was confirmed that the lithium iron phosphate-based positive electrode active materials manufactured in Comparative Examples 1 to 8 had a rolling density of less than 2.020 g / cc. In addition, it was confirmed that the lithium iron phosphate-based positive electrode active materials manufactured in Comparative Examples 2 and 8 had a resistance (R) of more than 19Ω, and it was confirmed that the lithium iron phosphate-based positive electrode active materials manufactured in Comparative Examples 2, 6, and 8 had a volume resistivity (VR) of more than 35Ω·cm.

[0330] From this, as a lithium iron phosphate cathode active material including a lithium iron phosphate compound,

[0331] The above lithium iron phosphate cathode active material has a bimodal particle size distribution, and when it satisfies Equation 1 described herein, it was confirmed that the rolling density is high and the resistance and volume resistivity are low.

Claims

A lithium iron phosphate cathode active material comprising a lithium iron phosphate compound, The above lithium iron phosphate cathode active material has a bimodal particle size distribution and satisfies the following equation 1: [Formula 1] 1.00 < (Y(D R )-Y(D L )) / span ≤ 1.75 In the above equation 1, 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 )am. 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] 5.50 ≤ (Y(D R ) / span)×|R.tan| 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 value (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. In claim 2, 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] 3.40 ≤ Y(D R ) / span. 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 4: [Formula 4] -2.30 ≤ L.tan+R.tan ≤ 3.60 In the above equation 4, 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 L is the particle size when the volume percentage of the left peak is maximum, and L.tan is D 10 From D L 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, and R.tan is D R From D 90 is the slope of the function representing the trend up to 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. 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 5: [Formula 5] -6.10 ≤ R.tan / L.tan ≤ -0.40 In the above equation 5, 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: %), L.tan is D 10 From D L is the slope of the function representing the trend up to , R.tan is D R From D 90 is the slope of the function representing the trend up to D L is the particle size when the volume percentage of the left peak is maximum, 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. 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. 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 M 2 b2 ]PO4 In the above chemical formula 2, M 2 is Ti, Mg or a combination thereof, -0.1≤x2≤0.1, 0≤a2≤0.9, 0 <b2≤0.1이다. In any one of claims 1 to 5, The above 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 2.00㎛ or less. In any one of claims 1 to 5, 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 8.00% or less. In any one of claims 1, 4 and 5, The above lithium iron phosphate cathode active material is D L This lithium iron phosphate cathode active material having a particle size of 0.40㎛ or more and 0.80㎛ or less. In claim 1, 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 4.00% or more and 8.00% or less. In any one of claims 1 to 3, The above lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material having a span of 1.80 or more and 2.30 or less. In any one of claims 1 to 3, The above lithium iron phosphate cathode active material is D 50A lithium iron phosphate-based positive electrode active material having a particle size of 0.80㎛ or more and 2.00㎛ or less. In any one of claims 1 to 5, 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 0.20㎛ or more and 0.50㎛ or less. In any one of claims 1 to 5, The above 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 5.00㎛ or less. In any one of claims 2, 4 and 5, The above lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material having an R.tan of -3.00 or more and -1.00 or less. In claim 4 or 5, The above lithium iron phosphate-based cathode active material is a lithium iron phosphate-based cathode active material having an L.tan of 0.00 or more and 7.00 or less. 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. In claim 18, 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. A positive electrode comprising a lithium iron phosphate-based positive electrode active material according to any one of claims 1 to 19. A lithium secondary battery comprising a positive electrode according to claim 20.

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