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

Abstract

The present invention relates to a cathode active material, and a cathode and a lithium secondary battery that include same, the cathode active material comprising a lithium manganese iron phosphate-based compound and having a value of 5 or less as calculated by mathematical expression 1. When the cathode active material is applied to the lithium secondary battery, charge / discharge rate characteristics are excellent. [Mathematical expression 1] │0.5∗LB-LD│∗103 In mathematical expression 1, LB is a b-axis length (unit: Å) of a crystal structure of the lithium manganese iron phosphate-based compound, and LD is a (020) d-spacing (unit: Å) between crystal structures of the lithium manganese iron phosphate-based compound.

Description

Cathode active material, cathode and lithium secondary battery containing same

[0001] Cross-citation with related application(s)

[0002] This specification claims the benefit of priority to Korean Patent Application No. 10-2024-0117463, filed August 30, 2024, and all contents of the literature contained in that Korean patent application are incorporated herein by reference.

[0003] The present specification relates to a cathode active material, a cathode including the same, and a lithium secondary battery.

[0004] Recently, there have been attempts to apply lithium manganese iron phosphate (LMFP) to electric vehicles (EVs), energy storage systems (ESS), and portable electronic devices.

[0005] Lithium iron manganese phosphate compounds are compounds doped with manganese, which are conventional lithium iron phosphate compounds. Compared to conventional lithium iron phosphate compounds, they possess higher energy density and higher output. Furthermore, lithium iron manganese phosphate compounds have a low risk of explosion, making them suitable for applications requiring high safety and boasting a long life cycle.

[0006] Despite the above-mentioned advantages, lithium iron phosphate compounds have inherently low electrical conductivity and lower energy density than nickel cobalt manganese compounds (NCM) or lithium cobalt oxide (LCO).

[0007] To address the above issues, attempts have been made to improve the properties of lithium iron manganese phosphate compounds, such as by coating them with carbon (C). However, these attempts have not fundamentally resolved the problem. To address the fundamental issues of lithium iron manganese phosphate compounds, further research and improvement of their crystal structure and properties are expected to be necessary.

[0008] The present invention provides a cathode active material having excellent charge / discharge capacity and rate characteristics when applied to a lithium secondary battery, a cathode active material including the same, and a lithium secondary battery.

[0009] The present invention comprises a lithium phosphate iron manganese compound,

[0010] A positive electrode active material is provided, the value of which calculated by the following mathematical formula 1 is 5 or less.

[0011] [Mathematical Formula 1]

[0012] |0.5*L B -L D |*10 3

[0013] In mathematical formula 1,

[0014] L B is the b-axis length (unit: Å) of the crystal structure of the lithium phosphate iron manganese compound,

[0015] L D is the (020) interplanar distance (d-spacing, unit: Å) between the crystal structures of the above lithium phosphate iron manganese compound.

[0016] In addition, the present invention provides a positive electrode comprising the positive electrode active material described above.

[0017] In addition, the present invention provides a lithium secondary battery including the above-described positive electrode.

[0018] When the positive electrode active material of the present invention is applied to a lithium secondary battery, it has an excellent charge / discharge capacity effect.

[0019] When the positive electrode active material of the present invention is applied to a lithium secondary battery, it has the effect of excellent rate characteristics.

[0020] Hereinafter, the specification will be described in detail.

[0021] Unless otherwise defined herein, all technical and scientific terms used herein are used merely to describe exemplary embodiments and are not intended to be limiting of the present invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, it should be understood that the terms "comprises," "includes," or "has" indicate the presence of a feature, number, step, component, or combination thereof, but do not preclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0022] The present invention is susceptible to various modifications and takes various forms. Specific embodiments are illustrated and described in detail below. However, this is not intended to limit the present invention to specific disclosed forms, but rather to encompass all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

[0023] The technical terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. Furthermore, the singular forms "singular" and "in" also include plural forms, unless the context clearly dictates otherwise.

[0024] In this specification, the term 'b-axis' refers to one of the three axes of the crystal lattice in the crystal structure of a lithium phosphate iron manganese compound, and refers to the direction extending along the (010) plane of the crystal lattice. The b-axis is the main path along which lithium ions diffuse within the crystal. Here, the b-axis length refers to the lattice spacing or lattice constant in the b-axis direction within the crystal lattice.

[0025] In this specification, 'd-spacing' refers to the spacing between atomic planes within a crystal structure. For example, '(020) d-spacing' refers to the distance between (020) planes of a crystal of a lithium phosphate iron manganese compound. The (020) plane refers to a plane that satisfies the Miller index (h=0, k=2, l=0), and is a plane that affects the mobility and storage capacity of lithium ions.

[0026] In this specification, the term "average grain size" refers to the size of a region within a single crystal having a well-ordered atomic arrangement. This region is referred to as a grain and may form a boundary with other grains.

[0027] In the present specification, lattice constants or lattice properties such as 'a-axis', 'b-axis', 'c-axis', 'd-spacing', and 'average grain size' can be measured using Rietveld refinement. Rietveld refinement is a method of obtaining a calculated diffraction pattern from an initial structural model that a crystal structure may have, comparing it with a measured diffraction pattern of an actual synthetic material, and gradually and repeatedly adjusting the values ​​by introducing various structural factors until the two patterns match well. This method determines whether the calculated pattern is valid based on the difference between the calculated pattern and the measured pattern, and repeats the process until the difference between the two patterns becomes minimal.

[0028] At this time, the analysis method can use Highscore software from Malvern Panalytical, etc. For example, after deriving the X-ray diffraction pattern of the lithium iron manganese phosphate compound, the initial structural model and the diffraction pattern model of the lithium iron manganese phosphate compound manufactured in the present invention are input into the Rietveld program (such as TOPAS), and the position and shape of each diffraction peak are optimized. Afterwards, the corresponding values ​​can be derived through correction and iterative calculation until the difference between the two diffraction pattern models is minimized. Meanwhile, analysis can be performed based on Bragg's Law, but this is no longer limited.

[0029] In the present specification, the average particle diameter (D) of the lithium phosphate iron manganese compound 50 ) refers to the overall size of individual particles of lithium phosphate iron manganese compound, which may include one or more crystal grains. The average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume-based cumulative distribution in the particle size distribution curve (graph curve of particle size distribution) of each particle. The above average particle size is calculated by dispersing the powder to be measured in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Mastersizer 3000, Malvern) and measuring the difference in diffraction pattern according to particle size when the particles pass through the laser beam, and calculating the particle size at the point where it becomes 50% of the volume-based cumulative distribution according to particle size in the measuring device, thereby obtaining the average particle diameter (D 50 ) can be measured.

[0030] The present invention provides a positive electrode active material comprising a lithium phosphate iron manganese compound and having a value calculated by the following mathematical formula 1 of 5 or less.

[0031] [Mathematical Formula 1]

[0032] |0.5*L B -L D |*10 3

[0033] In mathematical formula 1,

[0034] L B is the b-axis length (unit: Å) of the crystal structure of the lithium phosphate iron manganese compound,

[0035] L D is the (020) interplanar distance (d-spacing, unit: Å) between the crystal structures of the above lithium phosphate iron manganese compound.

[0036] The cathode active material of the present invention has the effect of improving lithium ion mobility by adjusting the value calculated by the above mathematical formula 1 to 5 or less. In addition, it has the characteristic of maintaining excellent structural stability of the crystal structure. When the cathode active material having the above characteristics is applied to a lithium secondary battery, it has the effect of improving the charge / discharge speed or charge / discharge capacity.

[0037] The value calculated by the above mathematical formula 1 represents the difference between the b-axis length and the (020) interplanar spacing (d-spacing), and can be understood as an indicator of the balance of the lithium phosphate iron manganese compound crystal structure. If the b-axis length becomes excessively long or short, the (020) interplanar spacing also changes, which can induce serious strain within the crystal structure. This strain can increase the possibility of occurrence of anti-site defects between lithium ions and transition metals.

[0038] When the value calculated by the above mathematical formula 1 is adjusted to 5 or less, the crystal structure of the lithium iron manganese phosphate compound is stably maintained, thereby maintaining a path for lithium ions to move from the correct location, and preventing the occurrence of anti-site defects between lithium ions and transition metals. This can improve the charge / discharge capacity and rate characteristics when applied to lithium secondary batteries.

[0039] In the present invention, the value calculated by the above mathematical formula 1 may be 5 or less. Preferably, it may be 4.8 or less, 4.5 or less, 4.3 or less, 4 or less, 3.8 or less, 3 or less, 2 or less, 1.5 or less, 1.4 or less, 1.2 or less, 1.1 or less, or 1 or less. In addition, it may be 0.001 or more, 0.005 or more, 0.01 or more, 0.05 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. In the above numerical range, the diffusion speed of lithium ions is excellently maintained, and the occurrence of position exchange defects between lithium ions and transition metals is prevented, thereby maintaining the stability of the crystal structure, thereby improving the charge / discharge speed and rate characteristics.

[0040] The value calculated by the above mathematical formula 1 can be achieved by changing the physical or chemical properties of the lithium iron manganese phosphate compound. Specifically, it can be achieved by changing the type and content of the carbon source, adjusting the average particle size, adjusting the crystal structure to an olivine structure, or changing the Fe / Mn composition ratio of the lithium iron manganese phosphate compound. Alternatively, it can be achieved by doping with an element other than lithium, phosphate, iron, and manganese, or by changing the sintering temperature or time.

[0041] L in the above mathematical formula 1 B and L D Each is a dimensionless number excluding the unit (Å). For example, if the b-axis length of the crystal structure of the lithium phosphate iron manganese compound is 6.03538Å, when substituting in mathematical equation 1, L B It becomes 6.03538.

[0042] In the present invention, the value calculated by the following mathematical formula 2 may be 2.1 or more and 4.1 or less.

[0043] [Equation 2]

[0044] L C / (|(L B -6)|*103 )

[0045] In mathematical expression 2,

[0046] L B is the b-axis length (unit: Å) of the crystal structure of the lithium phosphate iron manganese compound,

[0047] L C is the average crystal grain size (unit: nm) of the above lithium phosphate iron manganese compound.

[0048] In the present invention, the value calculated by the above mathematical formula 2 may be 2.2 or more, 2.3 or more, 2.5 or more, 2.7 or more, 2.9 or more, 3 or more, 3.05 or more, or 3.1 or more. In addition, it may be 4 or less, 3.9 or less, 3.8 or less, or 3.75 or less. In the above numerical range, the average crystal grain size of the lithium iron manganese phosphate compound and the b-axis length of the crystal structure can be simultaneously controlled, thereby facilitating lithium diffusion and improving the structural stability of the microstructure. In this case, there is an effect of improving charge / discharge performance.

[0049] In the present invention, the average crystal grain size of the lithium iron manganese phosphate compound may be 50 nm or more and 135 nm or less. Specifically, it may be 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, or 100 nm or more. In addition, it may be 132 nm or less, 130 nm or less, 128 nm or less, 125 nm or less, or 120 nm or less. In the above numerical range, by maintaining the stress within the lithium iron manganese phosphate compound crystal at a certain level, the value of the b-axis length is prevented from becoming excessively large, and the interplanar distance secured due to the (020) interplanar distance (d-spacing) can be stably maintained. In addition, by improving the mechanical strength of the material, the stability of the electrode structure can be maintained even during repeated charge and discharge processes.

[0050] In the present invention, the (020) interplanar distance (d-spacing) of the lithium phosphate iron manganese compound may be 3Å or more and 3.5Å or less. Preferably, it may be 3.01Å or more, 3.012Å or more, 3.013Å or more, 3.014Å or more, or 3.015Å or more. In addition, it may be 3.4Å or less, 3.3Å or less, 3.2Å or less, 3.15Å or less, 3.1Å or less, 3.05Å or less, 3.04Å or less, 3.035Å or less, 3.03Å or less, 3.028Å or less, 3.026Å or less, 3.025Å or less, 3.024Å or less, or 3.022Å or less. In the above numerical range, the insertion / de-insertion of lithium ions can be facilitated, thereby improving the rate characteristics. In addition, by reducing the occurrence of anti-site defects between lithium ions and transition metals, the charge / discharge capacity can be improved, and stability that allows crystals to be maintained during the charge / discharge process can be secured.

[0051] In the present invention, the a-axis length of the crystal structure of the lithium iron manganese phosphate compound may be 10 Å or more and 11 Å or less. Preferably, it may be 10.1 Å or more, 10.2 Å or more, 10.3 Å or more, or 10.36 Å or more. In addition, it may be 10.8 Å or less, 10.6 Å or less, 10.4 Å or less, or 10.37 Å or less. The a-axis length is a variable that affects the crystal size, and as the crystal size increases, the b-axis length becomes longer, which may make the diffusion of lithium ions difficult. When the above numerical range is satisfied, excellent lithium ion diffusion performance can be secured even with a small crystal size.

[0052] In the present invention, the c-axis length of the crystal structure of the lithium iron manganese phosphate compound may be 4 Å or more and 5 Å or less. Preferably, it may be 4.1 Å or more, 4.2 Å or more, 4.6 Å or more, or 4.7 Å or more. In addition, it may be 4.9 Å or less, 4.85 Å or less, 4.8 Å or less, or 4.75 Å or less. The c-axis length is a variable that affects the crystal size, and as the crystal size increases, the b-axis length becomes longer, which may make the diffusion of lithium ions difficult. When the above numerical range is satisfied, excellent lithium ion diffusion performance can be secured even with a small crystal size.

[0053] In the present invention, the average particle diameter (D) of the lithium phosphate iron manganese compound 50 ) may be 0.2㎛ or more and 1㎛ or less. Preferably, it may be 0.25㎛ or more, 0.3㎛ or more, 0.35㎛ or more, 0.4㎛ or more, or 0.45㎛ or more. In addition, it may be 0.95㎛ or less, 0.9㎛ or less, or 0.85㎛ or less. In the above numerical range, by maintaining the stress within the lithium phosphate iron manganese compound crystal at a certain level, the value of the b-axis length is prevented from becoming excessively large, and the interplanar distance secured due to the (020) interplanar distance (d-spacing) can be stably maintained. In addition, the rolling density is improved, which has the effect of improving the electrode processability, and the surface area per unit mass is increased, which is advantageous for the insertion / de-insertion reaction of lithium ions, so that the charge / discharge speed can be improved.

[0054] In the present invention, the average crystal grain size of the lithium phosphate iron manganese compound is the average particle diameter (D) of the lithium phosphate iron manganese compound. 50) may be 10% or more and 35% or less based on 100%. Preferably, it may be 11% or more, 12% or more, 13% or more, or 14% or more. In addition, it may be 33% or less, 30% or less, 28% or less, 26% or less, or 25% or less. In the above numerical range, the diffusion of lithium ions is smooth, and internal stress and strain can be alleviated to improve structural stability. In this case, the cycle performance can be improved when applied to a battery. If it is less than the above numerical range, the crystal grains may be too fine, which may increase the surface reaction and deteriorate the structural stability. In addition, if it exceeds the above numerical range, the lithium ion diffusion path may be long, which may cause internal resistance. On the other hand, if it is adjusted to the above numerical range, there is an effect of minimizing the lattice deformation that may occur in the b-axis direction.

[0055] In the present invention, the lithium iron manganese phosphate compound may include an olivine structure. In this case, since it has a strong PO bond, it can prevent the crystal structure from collapsing during the charge / discharge process, so there is an effect of improving high-temperature stability. In addition, since lithium ions mainly move along the b-axis within the olivine structure, the effect of the value calculated by the above-described mathematical formula 1 may be more prominent in the olivine structure. The olivine structure can be confirmed using X-ray diffraction (XRD) analysis.

[0056] In the present invention, the lithium phosphate iron manganese compound can be represented by the following chemical formula 1.

[0057] [Chemical Formula 1]

[0058] Li 1+y1 Fe a Mn b M 1 c (PO4)

[0059] In the above chemical formula 1,

[0060] Above M1 is Mg, Al, Si, Ca, Sc, Ti, V, Cr, K, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, La or a combination thereof,

[0061] -0.2≤y1<1, 0<a<1, 0<b<1, 0≤c<1, a+b+c=1.

[0062] In the present invention, a, b, and c of chemical formula 1 may mean the molar content of each component. Specifically, they may mean the molar content of the remaining elements excluding lithium (Li) and phosphoric acid (PO4) among the positive electrode active material represented by the chemical formula. For example, when a and b are 0.5 and c is 0, the remaining elements (Fe, Mn, M) excluding lithium (Li) and phosphoric acid (PO4) among the positive electrode active material represented by chemical formula 1 1 ) based on the total moles of Fe and Mn, the molar content of each is 50 mol%, and M 1 The molar content of M may be 0 mol%. Meanwhile, M 1 In the case of two or more elements, c may be the molar content calculated based on the total number of moles of the two or more elements.

[0063] In the present invention, y may be 0, 0.1 or more, 0.2 or more, or 0.3 or more. Additionally, it may be 0.9 or less, 0.8 or less, or 0.7 or less. Within the above numerical range, the capacity may increase while maintaining the charge / discharge characteristics.

[0064] In the present invention, the value calculated as b / (a+b) may be 0.01 or more and 0.5 or less. Preferably, it may be 0.02 or more, 0.05 or more, 0.1 or more, 0.15 or more, or 0.2 or more. In addition, it may be 0.45 or less, 0.4 or less, 0.38 or less, 0.36 or less, or 0.34 or less. In the above numerical range, the energy density and charge / discharge speed may be improved, and the cycle life stability may be improved. In addition, the lifespan may be prevented from being reduced due to manganese dissolution.

[0065] In the present invention, the value calculated as b / (a+b) may be 0.55 or more and 0.9 or less. Preferably, it may be 0.52 or more, 0.55 or more, 0.6 or more, or 0.65 or more. In addition, it may be 0.8 or less, or 0.75 or less. In the lithium iron manganese phosphate compound, when the value calculated as b / (a+b) is 0.55 or more and 0.9 or less, the manganese content is high, so the effect of structural change by manganese ions is more pronounced. Specifically, as the content of iron ions decreases, electrical conductivity may decrease, but the b-axis length and the interplanar distance (d-spacing) increase, thereby providing an effect of increasing the stability of the crystal structure.

[0066] In the present invention, c may be 0 or more and 0.1 or less. Preferably, it may be 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, or 0.02 or less. In addition, it may be 0.001 or more, 0.002 or more, or 0.003 or more. In the above numerical range, the effect by element doping is excellently maintained, and the lattice stability or electrical conductivity can be prevented from being deteriorated by excessive doping.

[0067] In the present invention, M 1refers to an element doped into a lithium phosphate iron manganese compound to obtain effects such as electrical conductivity and structural stability. More specifically, M 1 It can be Mg, Al, Ti, V, Co, Zr, W or a combination thereof.

[0068] In the present invention, the M 1 It may include at least one selected from the group consisting of V; and Mg, Al, Ti, and Zr. Specifically, it may be V and Mg; V and Al; V and Ti; or V and Zr. That is, when V is used together with another element, the effect of improving electrical conductivity by V and the effect of the other element are complementary, so that both electrochemical properties and stability properties can be improved. The effects of each of these elements will be described later.

[0069] Above M 1 When Mg is used, the lithium ion mobility characteristics can be improved, thereby improving the charge / discharge efficiency, and the lithium phosphate iron manganese compound particle growth can be easily controlled, thereby improving stability.

[0070] Above M 1 When Al is used, lithium ion conductivity can be improved, electrochemical reactivity can be improved, and output characteristics can be improved.

[0071] Above M 1 When using Ti, the thermal stability can be improved by improving the structural stability.

[0072] Above M 1 When V is used, the electrical conductivity can be improved, which can improve the power density when applied to lithium secondary batteries.

[0073] Above M 1 When using Zr, the structural strength can be increased to improve durability, and the compatibility with the electrolyte can be excellent to improve stability.

[0074] In the present invention, the manganese content of the lithium iron manganese phosphate compound may be 10 mol% or more and 50 mol% or less based on the total mole number of transition metals. Preferably, it may be 12 mol% or more, 15 mol% or more, 20 mol% or more, 25 mol% or more, or 28 mol% or more. In addition, it may be 45 mol% or less, 40 mol% or less, 35 mol% or less, or 30 mol% or less. Within the above numerical range, the energy density and charge / discharge speed may be improved, and the cycle life stability may be improved. In addition, the lifespan may be prevented from being reduced due to manganese dissolution.

[0075] In the present invention, the positive electrode active material may further include at least one selected from the group consisting of lithium iron phosphate (LFP), lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese aluminum oxide (NCMA), lithium manganese oxide (LMO), and overlithiated oxide (OLO). These materials may be referred to as second compounds and may have a different composition from the lithium iron manganese phosphate compound described above.

[0076] In the present invention, the weight ratio of the lithium phosphate iron manganese compound and the second compound may be 1:9 to 9:1. Preferably, it may be 2:8 to 8:2 or 3:7 to 7:3.

[0077] In the present invention, the lithium phosphate iron manganese compound may include a carbon coating layer on part or all of its surface. By including the carbon coating layer, the electrical conductivity of the positive electrode active material can be improved.

[0078] In the present invention, the carbon coating layer may be derived from hard carbon. An example of the hard carbon is sucrose. In this case, a carbon coating layer with a fine structure can be formed, and the carbon coating layer is stably formed around the crystal lattice of the lithium iron manganese phosphate compound, thereby preventing internal stress and volume change, thereby enabling the manufactured lithium iron manganese phosphate compound to satisfy the above-described mathematical formula 1.

[0079] In the present invention, the content of carbon included in the carbon coating layer may be 1 wt% or more and 3 wt% or less based on the total weight of the positive electrode active material. Preferably, it may be 1 wt% or more, 1.1 wt% or more, 1.2 wt% or more, 1.3 wt% or more, 1.4 wt% or more, 1.5 wt% or more, 1.6 wt% or more, 1.7 wt% or more, 1.8 wt% or more, 1.9 wt% or more, or 2 wt% or more, and 2.1 wt% or less, 2.2 wt% or less, 2.3 wt% or less, 2.4 wt% or less, 2.5 wt% or less, 2.6 wt% or less, 2.7 wt% or less, 2.8 wt% or less, 2.9 wt% or less, or 3 wt% or less. Within the above numerical range, the carbon coating layer may not act as a resistor while improving the electronic conductivity of the positive electrode active material.

[0080] In the present invention, the thickness of the carbon coating layer may be 10 nm or more and 50 nm or less. Preferably, it may be 10 nm or more and 40 nm or less, or 10 nm or more and 30 nm or less. Within the above numerical range, the carbon coating layer may improve the electronic conductivity of the positive electrode active material without acting as a resistor.

[0081] In the present invention, the value calculated by the following mathematical formula 3 of the positive electrode active material may be 80% or more. Preferably, it may be 81% or more, 82% or more, 83% or more, 84% or more, 85% or more, or 86% or more.

[0082] [Equation 3]

[0083] 4C discharge rate characteristics = 4C discharge capacity / discharge rated capacity * 100(%)

[0084] In mathematical formula 3,

[0085] 4C discharge capacity is the discharge capacity when charging to 4.25V at 0.1C in CCCV mode at 25℃ and discharging to 2.5V at a constant current of 4.0C.

[0086] The discharge rating capacity is the capacity measured at a measurement temperature of 25℃, a discharge current at 0.1C, and a terminal voltage of 2.5V.

[0087] In the present invention, the value calculated by the following mathematical formula 4 of the positive electrode active material may be 84% or more. Preferably, it may be 86% or more or 88% or more.

[0088] [Equation 4]

[0089] 1C charge rate characteristics = 1C charge capacity / charge rated capacity * 100(%)

[0090] In the present invention, the value of the positive electrode active material calculated by the following mathematical formula 5 may be 81% or more. Preferably, it may be 82% or more or 83% or more.

[0091] [Equation 5]

[0092] 2C charge rate characteristics = 2C charge capacity / charge rated capacity * 100(%)

[0093] In mathematical expressions 4 and 5,

[0094] 1C charge capacity is the charge capacity when charging at 0.1C, discharging, and then charging at 1C until the voltage reaches 4.25V.

[0095] 2C charge capacity is the charge capacity when charging at 0.1C, discharging, and then charging at 2C until the voltage reaches 4.25V.

[0096] The above rated charging capacity is the capacity measured at a measurement temperature of 25°C, a charging current of 0.1C, and a terminal voltage of 4.25V.

[0097] The values ​​calculated by the above mathematical expressions 3, 4 and 5 may be values ​​measured and calculated when the positive electrode active material is applied to a half-cell.

[0098] The above half-cell is an electrochemical cell used to evaluate the electrochemical performance of electrode materials.

[0099] The above half-cell may include an electrode; a reference electrode; an electrolyte; and a separator.

[0100] The electrode of the above half-cell may be an anode or a cathode. The electrode is determined by the type of material to be evaluated according to the purpose of the half-cell, and in the present invention, it may be an anode.

[0101] The reference electrode of the above half-cell may include lithium metal. The lithium metal acts as a source of lithium ions.

[0102] One embodiment of the present invention provides a method for manufacturing the above-described positive electrode active material.

[0103] The method for producing the above positive electrode active material includes a step of producing a mixture; and a step of calcining the mixture.

[0104] In the present invention, the method for producing the positive electrode active material includes a step of pulverizing the mixture; a step of drying the mixture, or a combination thereof.

[0105] In the present invention, the step of preparing the mixture may include a step of mixing positive electrode active material raw materials.

[0106] In the present invention, the positive electrode active material raw material may include a lithium-containing raw material, a manganese-containing raw material, an iron-containing raw material, and a phosphoric acid-containing raw material.

[0107] In the present invention, the lithium-containing raw material may be a lithium-containing sulfate, nitrate, acetate, carbonate, oxalate, citrate, halide, hydroxide or oxyhydroxide, and is not particularly limited as long as it can be dissolved in water. Specifically, lithium carbonate (Li2CO3), lithium hydroxide (LiOH), lithium nitrate (LiNO3) , It may be lithium acetate (CH3COOLi) and Li2(COO)2 or a combination thereof. Specifically, it may be lithium carbonate (Li2CO3), lithium hydroxide (LiOH) or a combination thereof.

[0108] In the present invention, the manganese-containing raw material is MnSO4, MnPO 3, It may be at least one selected from the group consisting of MnPO4, MnCO3, MnFeO, Mn2O3, MnO2, Mn3O4, Mn(NO3)2, manganese acetate, manganese dicarboxylate, manganese citrate, manganese salts of fatty acid manganese, oxyhydroxides and halides of manganese chloride, and a mixture of one or two or more of these may be used.

[0109] In the present invention, the iron-containing raw material may be iron sulfate (FeSO4), iron oxide (FeO), iron oxalate (FeC2O4), iron phosphate (FePO4), iron diphosphate {Fe3(PO4)2}, or a combination thereof. Preferably, iron phosphate may be used. In this case, it has high chemical stability and contains phosphoric acid in the compound itself, so that the use of additional phosphate can be reduced.

[0110] In the present invention, the phosphoric acid-containing raw material may include lithium phosphate (Li3PO4), lithium dihydrogen phosphate (LiH2PO4), ammonium dihydrogen phosphate {(NH4)2HPO4}, ammonium hydrogen phosphate (NH4H2PO4), phosphoric acid (H3PO4), etc., and these may be used alone or in combination of two or more. Preferably, ammonium dihydrogen phosphate or ammonium hydrogen phosphate may be used. In this case, by-products of the chemical reaction can be reduced and the pH of the reaction system can be stabilized.

[0111] In the present invention, the mixture may include a raw material containing a doping element.

[0112] In the present invention, the doping element-containing raw material is a doping element (M) including Mg, Al, Si, Ca, Sc, Ti, V, Cr, K, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, La or a combination thereof. 1 ) may be included. Meanwhile, in addition to the elements described above, other elements may be included to improve chemical performance or physical performance, and non-metallic elements such as F, S, and N may also be included to improve electrochemical performance.

[0113] In the present invention, the doping element-containing raw material may be an oxide, chloride, nitrate, sulfate compound, oxalate compound, or a combination thereof of the doping element.

[0114] In the present invention, when the doping element is aluminum (Al), the doping element-containing raw material may be aluminum oxide (Al2O3), aluminum hydroxide (Al(OH)3), aluminum nitrate {Al(NO3)3}, aluminum sulfate {Al2(SO4)3}, aluminum dihydrogen acetate {(HO)2AlCH3CO2}, aluminum monohydrogen acetate {HOAl(CH3CO2)2}, aluminum acetate {Al(CH3CO2)3}, aluminum halide, or a combination thereof. Preferably, aluminum hydroxide can be used. In this case, the doping process does not require excessive temperature, is environmentally friendly because no components other than water are detected as byproducts, and has the effect of enabling uniform doping.

[0115] In the present invention, when the doping element is vanadium (V), the doping element-containing raw material may be vanadium oxide. The vanadium oxide may be VO2, V2O3, V2O5, or a combination thereof. Preferably, it may be V2O5. V2O5 has high reactivity, which can improve doping efficiency, and has excellent heat resistance, which has the effect of stably maintaining the crystal structure of the lithium phosphate iron manganese compound during the sintering process.

[0116] In the present invention, when the doping element is magnesium (Mg), the doping element-containing raw material may be magnesium oxide (MgO), magnesium hydroxide {Mg(OH)2}, magnesium chloride (MgCl2), or a combination thereof. Preferably, magnesium oxide may be used. Magnesium oxide has excellent thermal stability and thus does not decompose and is maintained even during high-temperature heat treatment, and has excellent dispersibility of magnesium oxide, resulting in excellent doping efficiency.

[0117] In the present invention, when the doping element is zirconium (Zr), the doping element-containing raw material may be zirconium oxide (ZrO2), zirconium chloride (ZrCl4), or a combination thereof. Preferably, zirconium oxide may be used. Zirconium oxide has excellent thermal stability and thus does not decompose even during high-temperature heat treatment, and has excellent reactivity and excellent doping efficiency.

[0118] In the present invention, when the doping element is titanium (Ti), the doping element-containing raw material may be titanium oxide (TiO2). Titanium oxide has excellent thermal stability, so it is maintained without decomposition even during high-temperature heat treatment, and has excellent reactivity.

[0119] In the present invention, the mixture may include a carbon source. The carbon source may be carbonized during the step of calcining the mixture, thereby forming a carbon coating layer.

[0120] In the present invention, the carbon source may be sucrose, glucose, polyethylene glycol, polyvinyl alcohol, polyvinyl acetate, or a combination thereof. Preferably, it may be sucrose or glucose, and more preferably, it may be sucrose. When sucrose is used, it is possible to form a carbon coating layer having a uniform and thin thickness, and the carbon coating layer is stably formed around the crystal lattice of the lithium iron manganese phosphate compound, thereby preventing internal stress and volume change from occurring, so that the manufactured lithium iron manganese phosphate compound can satisfy the above-described mathematical formula 1.

[0121] In the present invention, the content of the carbon source may be 3 parts by weight or more and 15 parts by weight or less based on the total weight of the positive electrode active material raw material. Preferably, it may be 5 parts by weight or more, 7 parts by weight or more, or 9 parts by weight or more. In addition, it may be 13 parts by weight or less or 11 parts by weight or less. Within the above numerical range, uniform carbon coating is possible, and the energy density of the positive electrode material may be improved. In this case, the total weight of the positive electrode active material raw material refers to the total weight of the lithium-containing raw material, the manganese-containing raw material, the iron-containing raw material, and the phosphoric acid-containing raw material.

[0122] In the present invention, the solids content of the mixture may be 10 wt% or more and 40 wt% or less. Preferably, it may be 15 wt% or more, 20 wt% or more, or 25 wt% or more. In addition, it may be 38 wt% or less, 35 wt% or less, or 31 wt% or less. Within the above numerical range, the processability can be improved by preventing an increase in viscosity, and a uniform carbon coating can be achieved. The solids content of the mixture can be achieved by adding a solvent such as water (H2O).

[0123] In the present invention, the firing temperature in the step of firing the mixture may be 500°C or higher and 900°C or lower. Preferably, it may be 600°C or higher, 650°C or higher, 670°C or higher, or 680°C or higher. In addition, it may be 850°C or lower, 820°C or lower, or 800°C or lower. Within the above numerical range, the raw materials can sufficiently react to form a stable crystal structure, and excessive particle growth or a reduction in the b-axis length can be prevented. In other words, the electrochemical characteristics and crystallinity of the positive electrode active material can be improved under the above temperature conditions.

[0124] In the present invention, the firing time of the step of firing the mixture may be 1 hour or more and 50 hours or less. Preferably, it may be 2 hours or more, 5 hours or more, or 8 hours or more. Additionally, it may be 20 hours or less or 15 hours or less. Within the above numerical range, the effects of controlling the firing temperature described above can be secured without setting the firing temperature excessively.

[0125] In the present invention, the step of calcining the mixture may be performed in a reducing atmosphere. In this case, the oxidation state of the iron ions can be easily controlled, thereby ensuring electrochemical properties due to the iron ions.

[0126] In the present invention, the step of calcining the mixture may be performed under inert gas conditions. The inert gas may be argon (Ar), nitrogen (N2), or a combination thereof. The inert gas conditions may mean that the molar content of the inert gas in the space where the mixture is calcined is 70 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more. The remaining gas may be hydrogen (H2).

[0127] In the present invention, the step of calcining the mixture can be performed in a furnace.

[0128] In the present invention, the step of crushing the mixture is a step for breaking up necking between particles and controlling particle size. Furthermore, it can maintain a uniform particle size distribution and prevent particles from agglomerating with each other.

[0129] In the present invention, the step of grinding the mixture may use bead milling, ball milling, jet milling, ultrasonic milling, vibratory milling, or a combination thereof.

[0130] In the present invention, the step of grinding the mixture may be performed prior to the step of calcining the mixture. By controlling the particle size through grinding prior to calcination, the reaction rate for calcination increases, thereby enabling the formation and growth of a crystal structure to be performed stably.

[0131] In the present invention, in the step of crushing the mixture, the average particle diameter (D) of the crushed particles 50 ) may be 300 nm or more and 3,000 nm or less. Preferably, it may be 400 nm or more or 500 nm or more. In addition, it may be 2,500 nm or less, 2,000 nm or less or 1,000 nm or less. In the above numerical range, the reaction rate increases in the sintering step, and the formation and growth of the crystal structure can be stably performed.

[0132] In the present invention, a step of secondary crushing of the mixture may be performed after the step of calcining the mixture. At this time, the particle size of the final product can be finely controlled.

[0133] In the present invention, the step of drying the mixture is a step of removing moisture present in the mixture to ensure excellent quality in subsequent processes such as a grinding process or a firing process.

[0134] In the present invention, the step of drying the mixture may be performed before the step of pulverizing the mixture; after the step of pulverizing the mixture; before the step of calcining the mixture; or a combination thereof.

[0135] In the present invention, when the step of drying the mixture is performed before the step of crushing the mixture, there is an effect of improving the crushing efficiency by making the mixture easily crushed.

[0136] In the present invention, when the step of drying the mixture is performed after the step of crushing the mixture, moisture introduced in the crushing step can be removed.

[0137] In the present invention, if the step of drying the mixture is performed before the step of firing the mixture, moisture or impurities within the material are removed, thereby enhancing reactivity during the firing process, thereby improving crystallinity. If moisture or impurities are not sufficiently removed before firing, pores may form due to these impurities, resulting in defects in the crystal structure.

[0138] In the present invention, the drying temperature in the step of drying the mixture may be 50°C or higher and 300°C or lower. Preferably, it may be 80°C or higher or 100°C or higher. Additionally, it may be performed at a temperature range of 250°C or lower or 200°C or lower. Within the above numerical range, moisture can be sufficiently removed and the material can be prevented from thermal deformation. The above temperature may be the average temperature of the inlet temperature and the outlet temperature when spray drying is used.

[0139] In the present invention, the drying time of the step of drying the mixture may be 10 minutes or more and 10 hours or less. Preferably, it may be 30 minutes or more or 40 minutes or more. Additionally, it may be 5 hours or less or 3 hours or less. Within the above numerical range, moisture is sufficiently removed and thermal deformation of the material can be prevented.

[0140] In the present invention, the step of drying the mixture may be oven drying, vacuum drying, spray drying, or a combination thereof. Preferably, spray drying or oven drying can be used for simple and mass production.

[0141] In the present invention, the step of drying the mixture can be performed using spray drying at an inlet temperature of 150°C to 300°C and an outlet temperature of 60°C to 120°C. Preferably, it can be performed at an inlet temperature of 180°C to 270°C and an outlet temperature of 70°C to 110°C, or an inlet temperature of 200°C to 250°C and an outlet temperature of 80°C to 100°C. In the above inlet temperature range, the drying speed is improved and heat-induced denaturation can be prevented. In addition, in the above outlet temperature range, moisture remaining in the powder can be sufficiently removed and heat-induced denaturation can be prevented.

[0142] The present invention provides a positive electrode comprising the positive electrode active material described above.

[0143] In the present invention, the positive electrode comprises a positive electrode active material layer comprising the positive electrode active material described above. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and comprising the positive electrode active material. Since the positive electrode active material has been described above, a detailed description thereof will be omitted, and only the remaining components will be described in detail below.

[0144] In the present invention, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause chemical changes in the battery. 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 µm to 500 µm, and fine unevenness may be formed on the surface of the 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.

[0145] In the present invention, the positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material. At this time, the content of the positive electrode active material may be 80 wt% to 99 wt%, more specifically 85 wt% to 98.5 wt%, based on the total weight of the positive electrode active material layer, and excellent capacity characteristics may be exhibited within this range.

[0146] In the present invention, the conductive material is used to provide conductivity to the electrode, and can be used without special limitation as long as it does not cause chemical change and has electronic conductivity. 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. One of these may be used alone or a mixture of two or more may be used. The content of the conductive material may be 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0147] In the present invention, the 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 thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The content of the binder may be 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0148] In the present invention, the positive electrode can be manufactured according to a conventional positive electrode manufacturing method. Specifically, the positive electrode can be manufactured by coating a composition for forming a positive electrode active material layer, which is manufactured by dissolving or dispersing the positive electrode active material and optionally a binder and a conductive material in a solvent, on a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, binder, and conductive material are as described above. In addition, as another method, the positive electrode can be manufactured by casting the composition for forming a positive electrode active material layer on a separate support, and then laminating the film obtained by peeling it from the support on a positive electrode current collector.

[0149] In the present invention, the solvent may be a solvent generally used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these may be used alone or as a mixture of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0150] The present invention provides an electrochemical device comprising the above-described positive electrode. Specifically, the electrochemical device may be a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0151] The present invention provides a lithium secondary battery including the above-described positive electrode.

[0152] In the present invention, the lithium secondary battery includes a positive electrode, a negative electrode, and a separator and electrolyte provided between the positive electrode and the negative electrode.

[0153] 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.

[0154] In the present invention, the negative electrode includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0155] In the present invention, 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.

[0156] In the present invention, the negative electrode active material layer further includes a binder, a conductive material, and a combination thereof in addition to the negative electrode active material.

[0157] In the present invention, a compound capable of reversible intercalation and deintercalation of lithium may be used as the negative electrode active material. 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.

[0158] In the present invention, the content of the negative electrode active material may be 80% to 99% by weight based on the total weight of the negative electrode active material layer.

[0159] In the present invention, the 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0160] In the present invention, 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, specifically, 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 without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, and 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.

[0161] In the present invention, the negative electrode active material layer can be manufactured by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, on a negative electrode current collector, or by casting the composition for forming a negative electrode active material layer on a separate support, and then laminating the film obtained by peeling it off from the support on a negative electrode current collector.

[0162] In the present invention, 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 particular limitation, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also 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.

[0163] In the present invention, the electrolyte may include, but is 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. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0164] In the present invention, the organic solvent may be used without particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent 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 and isopropyl alcohol; nitriles such as R-CN (where 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 can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0165] In the present invention, the lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, specifically, 0.1 to 3.0 M. When the concentration of the lithium salt 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.

[0166] In the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 10 wt%, specifically, 0.1 to 5 wt%, based on the total weight of the electrolyte.

[0167] As described above, a lithium secondary battery including a cathode active material according to the present invention exhibits excellent life characteristics and capacity 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).

[0168] 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.

[0169] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0170] There is no particular limitation on the external shape of the above lithium secondary battery, but it may be a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0171] The above lithium secondary battery 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.

[0172] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0173] <Examples and Comparative Examples>

[0174] <Example 1>

[0175] Lithium-containing raw material (Li2CO3), iron-containing raw material (FePO4), manganese-containing raw material (MnPO3), and phosphoric acid-containing raw material (NH4H2PO4) were mixed so that the molar ratio of Li:Fe:Mn:PO4 was 1:0.7:0.3:1. After that, Li2CO3, FePO 4, For 100 parts by weight of the total weight of MnPO4 and NH4H2PO4, 10 parts by weight of sucrose was mixed as a carbon source. Water was mixed so that the solid content became 30 wt% to prepare a mixture.

[0176] The above mixture was wet ground with a bead mill to form a slurry (average particle size D 50 : 700 nm) was manufactured.

[0177] The above mixture was spray dried (inlet temperature 235°C, outlet temperature 90°C, for 1 hour) to remove moisture.

[0178] LiFe was calcined for 10 hours under a nitrogen atmosphere and a calcination temperature of 750℃. 0.7 Mn 0.3 A lithium iron phosphate compound having a composition represented by PO4 was prepared.

[0179] <Example 2>

[0180] Li2CO3, FePO4, MnCO3, NH4H2PO4, V2O5, and MgO were mixed so that the molar ratio of Li:Fe:Mn:V:Mg:PO4 was 1:0.693:0.297:0.005:0.005:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0181] <Example 3>

[0182] Li2CO3, FePO4, MnCO3, NH4H2PO4, and TiO2 were mixed so that the molar ratio of Li:Fe:Mn:Ti:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0183] <Example 4>

[0184] Li2CO3, FePO4, MnCO3, NH4H2PO4, Al(OH)3, and V2O5 were mixed so that the molar ratio of Li:Fe:Mn:Al:V:PO4 was 1:0.693:0.297:0.005:0.005:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0185] <Example 5>

[0186] Li2CO3, FePO4, MnCO3, NH4H2PO4, and V2O5 were mixed so that the molar ratio of Li:Fe:Mn:V:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0187] <Example 6>

[0188] Li2CO3, FePO4, MnCO3, NH4H2PO4, and V2O5 were mixed so that the molar ratio of Li:Fe:Mn:V:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0189] <Example 7>

[0190] Li2CO3, FePO4, MnCO3, NH4H2PO4, V2O5, and MgO were mixed so that the molar ratio of Li:Fe:Mn:V:Mg:PO4 was 1:0.693:0.297:0.005:0.005:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0191] <Example 8>

[0192] Li2CO3, FePO4, MnCO3, NH4H2PO4, and V2O5 were mixed so that the molar ratio of Li:Fe:Mn:V:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0193] <Example 9>

[0194] Li2CO3, FePO4, MnCO3, NH4H2PO4, V2O5, and TiO2 were mixed so that the molar ratio of Li:Fe:Mn:V:Ti:PO4 was 1:0.693:0.297:0.005:0.005:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0195] <Example 10>

[0196] Li2CO3, MnCO3, FePO4, NH4H2PO4, V2O5, and ZrO2 were mixed so that the molar ratio of Li:Fe:Mn:V:Zr:PO4 was 1:0.693:0.297:0.005:0.005:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0197] <Example 11>

[0198] Li2CO3, FePO4, MnCO3, NH4H2PO4, and TiO2 were mixed so that the molar ratio of Li:Fe:Mn:Ti:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0199] <Example 12>

[0200] Li2CO3, FePO4, MnCO3, LiH2PO4, and V2O5 were mixed so that the molar ratio of Li:Fe:Mn:V:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0201] <Example 13>

[0202] Li2CO3, FePO4, MnCO3, NH4H2PO4, and V2O5 were mixed so that the molar ratio of Li:Fe:Mn:V:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0203] <Example 14>

[0204] Li2CO3, FePO4, MnCO3, LiH2PO4, V2O 5, MgO and TiO2 were mixed so that the molar ratio of Li:Fe:Mn:V:Mg:Ti:PO4 was 1:0.6895:0.2955:0.0025:0.005:0.0075:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0205] <Comparative Example 1>

[0206] Li2CO3, FePO4, MnCO3, LiH2PO4, V2O 5, MgO and TiO2 were mixed so that the molar ratio of Li:Fe:Mn:V:Mg:Ti:PO4 was 1:0.6895:0.2955:0.0025:0.005:0.0075:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0207] <Comparative Example 2>

[0208] Li2CO3, FePO4, MnPO4, and NH4H2PO4 were mixed so that the molar ratio of Li:Fe:Mn:PO4 was 1:0.7:0.3:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0209] <Comparative Example 3>

[0210] Li2CO3, FePO4, MnCO3, LiH2PO4, V2O5, and MgO were mixed so that the molar ratio of Li:Fe:Mn:V:Mg:PO4 was 1:0.693:0.297:0.005:0.005:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0211] <Comparative Example 4>

[0212] Li2CO3, FePO4, MnCO3, LiH2PO4, V2O 5, MgO and TiO2 were mixed so that the molar ratio of Li:Fe:Mn:V:Mg:Ti:PO4 was 1:0.693:0.297:0.0025:0.005:0.0025:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0213] Comparative Example 5

[0214] Li2CO3, FePO4, MnCO3, NH4H2PO4, and V2O5 were mixed so that the molar ratio of Li:Fe:Mn:V:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0215] <Comparative Example 6>

[0216] Li2CO3, FePO4, MnPO4, NH4H2PO4, and V2O5 were mixed so that the molar ratio of Li:Fe:Mn:V:PO4 was 1:0.693:0.297:0.01:1. The remaining process conditions were changed to those in Table 1 below to manufacture a lithium iron manganese phosphate compound.

[0217] <Experimental Example>

[0218] Experimental Example 1: Rietveld Refinement

[0219] X-ray diffraction patterns were obtained using an X-ray diffraction instrument (manufacturer: Bruker, product name: D8 Endeavor, Cu-target, voltage: 45 kV, current: 40 mA). The measurement conditions were a fixed divergence slit of 0.5 degrees, time per step of 0.5 s, and a 2θ range of 10 to 100 degrees.

[0220] For the obtained X-ray diffraction pattern, the b-axis length (L) of the crystal structure of the lithium phosphate iron manganese compound was determined by analyzing it with the Rietveld refinement method using Highscore software. B ), the average grain size (L) of lithium phosphate iron manganese compounds C ) and the (020) interplanar distance (L) of lithium phosphate iron manganese compounds D ) was calculated.

[0221] The values ​​calculated using the following mathematical formulas 1 and 2 were derived and recorded in Tables 2 and 3 below.

[0222] [Mathematical Formula 1]

[0223] |0.5*L B -L D |*10 3

[0224] [Equation 2]

[0225] L C / (|(L B -6)|*10 3 )

[0226] In mathematical expressions 1 and 2,

[0227] L B is the b-axis length (unit: Å) of the crystal structure of the lithium phosphate iron manganese compound,

[0228] L C is the average crystal grain size (unit: nm) of the lithium phosphate iron manganese compound,

[0229] L Dis the (020) interplanar distance (d-spacing, unit: Å) between the crystal structures of the above lithium phosphate iron manganese compound.

[0230] <Experimental Example 2: Measurement of average particle size>

[0231] The lithium iron manganese phosphate compound manufactured in the examples and comparative examples was mixed with 0.5 mL of a nonionic surfactant (Triton X-100), dispersed in 50 mL of deionized water, and then placed in a conical tube. The lithium iron manganese phosphate compound powders were dispersed for 5 minutes using an ultrasonic disperser to prevent them from clumping together, and then poured into an analytical beaker containing 450 mL of deionized water. The beaker was introduced into a laser diffraction particle size measuring device (Malvern's S3500), and the difference in diffraction patterns according to particle size when the particles pass through the laser beam was measured to calculate the particle size distribution, and the particle size at the point where it becomes 50% in the volume-based cumulative particle size distribution curve was calculated, thereby obtaining D 50 was measured and named as the average particle diameter.

[0232] Average particle size (D) of lithium phosphate iron manganese compound 50 ) Average grain size (L) of lithium phosphate iron manganese compound based on 100% C / D 50 ) were calculated and recorded in Tables 2 and 3 below.

[0233] <Experimental Example 3: Battery Performance Evaluation>

[0234] Manufacturing of lithium secondary battery half cells

[0235] In each of the examples and comparative examples, a cathode active material including a lithium phosphate iron manganese compound, a carbon black conductive agent, and a polyvinylidene fluoride (PVdF) binder were mixed in a weight ratio of 90:5:5 in an N-methylpyrrolidone solvent to prepare a cathode composite, which was then applied to one surface of an aluminum current collector, dried at 130°C, and rolled to prepare a cathode composite.

[0236] Lithium metal was prepared as the cathode.

[0237] An electrode assembly was manufactured by interposing a porous polyethylene separator between the manufactured positive and negative electrodes, and the electrode assembly was placed inside a case, and then an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was manufactured by dissolving 1 M lithium hexafluorophosphate (LiPF6) in an organic solvent composed of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate / (mixed volume ratio of EC / EMC / DEC = 3 / 4 / 3).

[0238] Initial charge / discharge characteristics evaluation

[0239] For each manufactured lithium secondary battery half cell, it was charged at 0.1C in CCCV mode (Constant Current, Constant Voltage) at 25℃ until it reached 4.25V, and after 20 minutes of rest, it was discharged at a constant current of 0.1C until it reached 2.5V to check the charge capacity (a) and discharge capacity (b), which were recorded in Tables 2 and 3.

[0240] C-rate evaluation

[0241] Rate characteristics refer to the charge or discharge rate set based on the rated capacity of the battery. In a discharge test, the battery was fully charged and then discharged at a specific C-rate, and the discharge capacity (the product of the discharge current and the discharge time) was calculated. In a charge test, the battery was fully discharged and then charged at a specific C-rate, and the charge capacity (the product of the charge current and the charge time) was calculated.

[0242] For each manufactured lithium secondary battery half cell, the discharge capacity was calculated when the battery was charged to 4.25 V at 0.1 C in CCCV mode at 25°C and discharged to 2.5 V at a constant current of 4.0 C (4C discharge capacity).

[0243] The charge rate characteristics were calculated by charging at 0.1C, discharging, and then charging at 1C and 2C until the voltage reached 4.25V, and calculating the charge capacity at each current state (1C charge capacity and 2C charge capacity).

[0244] At this time, the discharge rated capacity was measured at a measurement temperature of 25℃, a discharge current at 0.1C, and a terminal voltage of 2.5V. The charge rated capacity was measured at a charge current at 0.1C and a terminal voltage of 4.25V.

[0245] Based on the measured values, the values ​​calculated using the following mathematical formulas 3 to 5 were calculated and recorded in Tables 2 and 3.

[0246] [Equation 3]

[0247] 4C discharge rate characteristics = 4C discharge capacity / discharge rated capacity * 100(%)

[0248] [Equation 4]

[0249] 1C charge rate characteristics = 1C charge capacity / charge rated capacity * 100(%)

[0250] [Equation 5]

[0251] 2C charge rate characteristics = 2C charge capacity / charge rated capacity * 100(%)

[0252] Classification Lithium phosphate iron manganese compound composition Carbon source type Carbon source content (weight part) Solid content (wt%) Average particle size (D 50 : nm) Firing temperature (℃) Firing time (hr) Example 1 LiFe 0.7 Mn 0.3 PO4SC103070075010Example 2LiFe 0.693 Mn 0.297 V 0.005 Mg 0.005 PO4SC73070075010Example 3LiFe 0.693 Mn 0.297 Ti 0.01 PO4SC63070080010Example 4LiFe 0.693 Mn 0.297 Al 0.005 V0.005 PO4SC73070075010Example 5LiFe 0.693 Mn 0.297 V 0.01 PO4SC63070070010Example 6LiFe 0.693 Mn 0.297 V 0.01 PO4SC53070080010Example 7LiFe 0.693 Mn 0.297 V 0.005 Mg 0.005 PO4SC63070080010Example 8LiFe 0.693 Mn 0.297 V 0.01 PO4SC63070080010Example 9LiFe 0.693 Mn 0.297 V 0.005 Ti 0.005 PO4SC63070080010Example 10LiFe 0.693 Mn 0.297 V 0.005 Zr 0.005 PO4SC73070075010Example 11LiFe 0.693 Mn 0.297 Ti 0.01 PO4SC63070070010Example 12LiFe 0.693 Mn 0.297 V 0.01 PO4GC83090070010Example 13LiFe 0.693 Mn 0.297 V 0.01 PO4GC6%35%1,60070010Example 14LiFe 0.297 Mn 0.693 V 0.0025 Mg 0.005 Ti 0.0025 PO4GC6%30%70070010Comparative Example 1LiFe 0.6895 Mn 0.2955 V 0.0025 Mg 0.005 Ti 0.0075 PO4GC63070070010Comparative Example 2LiFe 0.7 Mn 0.3 PO4GC84070075010Comparative Example 3LiFe 0.693 Mn 0.297 V 0.005 Mg 0.005PO4GC63070070010Comparative Example 4LiFe 0.693 Mn 0.297 V 0.0025 Mg 0.005 Ti 0.0025 PO4GC63070070010Comparative Example 5LiFe 0.693 Mn 0.297 V 0.01 PO4GC63070075010Comparative Example 6LiFe 0.693 Mn 0.297 V 0.01 PO4GC84070075010*Carbon source: Used in the raw material mixing stage, where SC and GC represent sucrose and glucose, respectively.*Average particle size: The average particle size (D) of the slurry manufactured in the grinding and particle size control stages. 50 ) means

[0253] Classification Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Experimental Example 1L B 6.035386.033856.034866.034006.033516.033936.034486.033626.034576.03424L C 125110111110125121119106109107L D 3.019153.015553.016093.017973.015863.017783.017923.017373.016733.01752Mathematical formula 11.461.37251.3420.9690.8930.8160.6780.56150.55550.9385Mathematical formula 23.533.253.183.243.733.573.453.153.153.12Experimental example 2D 50 (㎛)0.5890.5320.5190.6460.8370.520.4970.4570.4570.532L C / D 50(%)21.220.721.417.014.923.323.923.223.920.1Experimental example 3(a)154.4156.2154.9156.6158.1158.3158.2157.9158.1155.5(b)1 52.4156.2154.2156.5157.8157157.6157.3157.8155.6(c)86.688.1 86.48887.686.787.388.487.488.4(d)88.290.689.590.590.189.28 9.891.190.490.7(e)83.786.385.286.185.484.285.186.886.386.7L B: The b-axis length (unit: Å) of the crystal structure of lithium phosphate iron manganese compounds L C: Average grain size of lithium phosphate iron manganese compound (unit: nm) L D: (020) interplanar distance (d-spacing, unit: Å)D of lithium phosphate iron manganese compounds 50 : Average particle size of lithium phosphate iron manganese compound (unit: ㎛) (a): Charge capacity (mAh / g) (b): Discharge capacity (mAh / g) (c): 4C discharge rate characteristics (%) (d): 1C charge rate characteristics (%) (e): 2C charge rate characteristics (%)

[0254] Classification Example 11 Example 12 Example 13 Example 14 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Experimental Example 1L B 6.034816.034326.033136.060376.034646.035426.033826.034616.034066.03556L C 120109114131152161159154140177L D 3.019383.020923.011793.030193.012023.012233.011233.011333.023083.02474 Mathematical Formula 11.9773.76154.7750.00555.35.4785.685.9756.0496.961 Mathematical Formula 23.453.183.442.174.394.554.704.454.114.98 Experimental Example 2D 50(㎛)0.4980.5390.5040.1141.3611.371.520.8060.5L C / D 50 (%)24.120.222.6222.5111.1816.111.6110.1317.3735.4Experimental example 3(a)157.5158156.4152.2147.1140.8141.1143.2146.7149.1(b)156.3156.8156.2148.2140.4125132133.8132.5139.7(c)86.387.38 6.188.379.572.376.477.176.378.1(d)89.591.589.786.981.182.182.881.782.982.3(e)85.18784.779.777.97880.279.278.878.6L B, L C, L D, D 50, (a) to (e): As described in Table 2

[0255] From the above results, it was confirmed that when the value calculated by mathematical formula 1 of the positive electrode active material was 5 or less, the charge / discharge capacity was high and the rate characteristics were maintained at a high level. This is because the lithium ion diffusion characteristics of the positive electrode active material of the examples were excellent and the crystal structure was stabilized (Examples 1 to 14).

[0256] On the other hand, it was confirmed that the comparative positive electrode active material had low charge / discharge capacity or low rate characteristics. This is because the lithium ion diffusion characteristics of the comparative positive electrode active material were poor or its crystal structure was not stabilized. Specifically, it was confirmed that the value calculated using mathematical formula 1 exceeded 5, resulting in low charge / discharge capacity or deteriorated rate characteristics.

Claims

Contains a lithium phosphate iron manganese compound, A positive electrode active material having a value of 5 or less calculated by the following mathematical formula 1: [Mathematical Formula 1] |0.5*L B -L D |*10 3 In mathematical expression 1, L B is the b-axis length (unit: Å) of the crystal structure of the lithium phosphate iron manganese compound, L D is the (020) interplanar distance (d-spacing, unit: Å) between the crystal structures of the above lithium phosphate iron manganese compound. In claim 1, A positive electrode active material having a value calculated by the following mathematical formula 2 of 2.1 or more and 4.1 or less: [Equation 2] L C / (|(L B -6)|*10 3 ) In mathematical expression 2, L B is the b-axis length (unit: Å) of the crystal structure of the lithium phosphate iron manganese compound, L C is the average crystal grain size (unit: nm) of the above lithium phosphate iron manganese compound. In claim 1, A cathode active material having a b-axis length of the crystal structure of the lithium phosphate iron manganese compound of 6Å or more and 6.5Å or less. In claim 1, A cathode active material having a (020) interplanar distance between crystal structures of the lithium phosphate iron manganese compound of the above-mentioned type is 3Å or more and 3.5Å or less. In claim 1, A cathode active material having an average crystal grain size of the lithium phosphate iron manganese compound of 50 nm or more and 135 nm or less. In claim 1, The average particle diameter (D) of the above lithium phosphate iron manganese compound 50 ) A positive electrode active material having a particle size of 0.2㎛ or more and 1㎛ or less. In claim 1, The average crystal grain size of the above lithium phosphate iron manganese compound is the average particle diameter (D) of the above lithium phosphate iron manganese compound 50 ) Positive electrode active material with a content of 10% or more and 35% or less based on 100%. In claim 1, The above lithium phosphate iron manganese compound is a cathode active material containing an olivine structure. In claim 1, The above lithium phosphate iron manganese compound is a positive electrode active material represented by the following chemical formula 1: [Chemical Formula 1] Li 1+y1 Fe a Mn b M 1 c (PO4) In the above chemical formula 1, Above M 1 is Mg, Al, Si, Ca, Sc, Ti, V, Cr, K, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi, La or a combination thereof, -0.2≤y1<1, 0<a<1, 0<b<1, 0≤c<1, a+b+c=1. In claim 9, A positive electrode active material having a value calculated as b / (a+b) of 0.01 or more and 0.5 or less. In claim 9, A positive electrode active material having a value calculated as b / (a+b) of 0.55 or more and 0.9 or less. In claim 1, A cathode active material further comprising at least one selected from the group consisting of lithium iron phosphate (LFP), lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese aluminum oxide (NCMA), lithium manganese oxide (LMO), and overlithiated oxide (OLO). In claim 1, A positive electrode active material having a value of 80% or more calculated by the following mathematical formula 3: [Equation 3] 4C discharge rate characteristics = 4C discharge capacity / discharge rated capacity * 100(%) In mathematical formula 3, 4C discharge capacity is the discharge capacity when charging to 4.25V at 0.1C in CCCV mode at 25℃ and discharging to 2.5V at a constant current of 4.0C. The discharge rating capacity is the capacity measured at a measurement temperature of 25℃, a discharge current at 0.1C, and a terminal voltage of 2.5V. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 13. A lithium secondary battery comprising a positive electrode according to claim 14.