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 which comprise the cathode active material. The cathode active material comprises: a lithium iron phosphate-based compound having an olivine structure; and a coating portion formed on the lithium iron phosphate-based compound and containing carbon and nitrogen, wherein the value of X1 according to equation 1 described in the present specification is 0.550-0.850, and the value of X2 according to equation 2 described in the present specification is 0.0030-0.0065.

Description

Cathode active material, and cathode and lithium secondary battery containing the same

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0122433, filed September 9, 2024, the entire contents of which are incorporated herein by reference.

[0003] Technology field

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

[0005]

[0006] With the recent technological development and increasing demand for mobile devices and electric vehicles, 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. For lithium secondary batteries to achieve high energy density, output, and lifespan, improving the performance of the cathode active material is essential. Consequently, extensive research has been conducted recently to develop high-performance cathode active materials.

[0008] Lithium transition metal oxides such as lithium cobalt oxides such as LiCoO2, lithium nickel oxides such as LiNiO2, lithium manganese oxides such as LiMnO2 or LiMn2O4, and lithium iron phosphate compounds such as LiFePO4 have been developed as positive electrode active materials for lithium secondary batteries, and recently, Li[Ni a Co b Mn c ]O2, Li[Nia Co b Al c ]O2, Li[Ni a Co b Mn c Al d ] Lithium composite transition metal oxides containing two or more transition metals, such as O2, have been developed and are widely used.

[0009] Meanwhile, lithium iron phosphate compounds with an olivine structure are promising active materials because they have excellent structural stability, excellent life characteristics, and superior safety in all aspects, including overcharge and overdischarge.

[0010] In particular, LiFePO4 has excellent high-temperature stability due to the strong bonding force of PO4, and because it contains iron, which is abundant and inexpensive, it is cheaper than the aforementioned LiCoO2, LiNiO2, or LiMn2O4, and has low toxicity, so it has a small impact on the environment. However, since LiFePO4 has low electrical conductivity, there is a problem that the internal resistance of the battery increases when LiFePO4 is used as a positive electrode active material. This causes the polarization potential to increase when the battery circuit is closed, which reduces the battery capacity. In addition, LiFePO4 has a low average operating voltage, which results in a low energy density.

[0011] To solve this problem, development is needed to improve the performance of cathode active materials including lithium iron phosphate compounds.

[0012]

[0013] The purpose of the present invention is to provide a positive electrode active material capable of improving the resistance characteristics and energy density of a lithium secondary battery by controlling the rolling density and powder resistance.

[0014] 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.

[0015]

[0016] 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.

[0017]

[0018] (1) The present invention provides a positive electrode active material comprising a lithium iron phosphate compound having an olivine structure; and a coating portion including carbon and nitrogen formed on the lithium iron phosphate compound; wherein a value (X1) according to the following formula 1 is 0.550 or more and 0.850 or less, and a value (X2) according to the following formula 2 is 0.0030 or more and 0.0065 or less.

[0019] [Formula 1]

[0020] X1 = mole fraction of oxygen / mole fraction of carbon

[0021] [Formula 2]

[0022] X2 = mole fraction of nitrogen / (mole fraction of nitrogen + mole fraction of carbon + mole fraction of oxygen)

[0023] In the above equations 1 and 2, the mole fraction is the ratio of the number of moles of each element to the number of moles of all elements present on the particle surface, as measured using an X-ray photoelectron spectroscopy (XPS).

[0024] (2) The present invention provides a positive electrode active material in the above (1), wherein the lithium iron phosphate compound has a composition represented by the following chemical formula 1.

[0025] [Chemical Formula 1]

[0026] Li 1+x Fe 1-a M a PO4

[0027] In the above chemical formula 1, M is at least one selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and -0.1≤x≤0.1, 0≤a<1.

[0028] (3) The present invention provides a positive electrode active material in (1) or (2) above, wherein the content of carbon included in the coating portion is 0.50 wt% or more and 3.00 wt% or less with respect to the total weight of the positive electrode active material.

[0029] (4) The present invention provides a positive electrode active material in any one of the above (1) to (3), wherein the molar fraction of carbon is 0.400 or more and 0.600 or less.

[0030] (5) The present invention provides a positive electrode active material in any one of the above (1) to (4), wherein the molar fraction of oxygen is 0.200 or more and 0.400 or less.

[0031] (6) The present invention provides a positive electrode active material in any one of the above (1) to (5), wherein the molar fraction of nitrogen is 0.003 or more and 0.005 or less.

[0032] (7) The present invention provides a positive electrode active material having a crystal size of 100.00 nm or more and 200.00 nm or less in any one of the above (1) to (6).

[0033] (8) The present invention is any one of the above (1) to (7), 4.0Х10 7 N / m 2 Ideal 6.0Х10 7 N / m 2 When the pressure below is applied, the pellet density is 2.000 g / cm 3 More than 2.500 g / cm 3 The following positive electrode active material is provided.

[0034] (9) The present invention is any one of the above (1) to (8), 4.0Х10 7 N / m 2 Ideal 6.0Х10 7 N / m 2 When the pressure below is applied, a positive electrode active material having a powder resistance of 25.00ΩХcm or more and 50.00ΩХcm or less is provided.

[0035] (10) The present invention provides a positive electrode comprising a positive electrode active material according to any one of (1) to (9).

[0036] (11) The present invention provides a lithium secondary battery including a positive electrode according to (9).

[0037]

[0038] The positive electrode active material according to the present invention comprises a lithium iron phosphate compound having an olivine structure; and a coating portion including carbon and nitrogen formed on the lithium iron phosphate compound; and by satisfying a value (X1) according to Equation 1 described herein and a value (X2) according to Equation 2 described herein within a specific numerical range, the positive electrode active material has the effect of having a high rolling density and a low powder resistance. Accordingly, there is the effect of improving the resistance characteristics and energy density of a battery including the positive electrode active material according to the present invention.

[0039]

[0040] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0041] 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 spirit 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 possible manner.

[0042] In this specification, it should be understood that terms such as “include,” “have,” or “have” 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.

[0043] In this specification, mole fraction means the ratio of the number of moles of each element to the number of moles of all elements present on the particle surface, as measured using X-ray photoelectron spectroscopy (XPS).

[0044] In this specification, 'crystal size' can be quantitatively analyzed using X-ray diffraction analysis (XRD) using Cu Kα X-rays. Specifically, the average size of the crystal grains can be quantitatively analyzed by putting the particles to be measured into a holder, irradiating the particles with X-rays, and analyzing the diffraction grating that is generated. Sampling was prepared by putting the powder sample of the particles to be measured into the groove in the center of a general powder holder, smoothing the surface using a slide glass, and ensuring that the sample height is the same as the edge of the holder. Then, X-ray diffraction analysis was performed using a Bruker D8 Endeavor (light source: Cu-Kα rays, wavelength: 1.54 Å) equipped with a LynxEye XE-T position sensitive detector, under the conditions of a step size of 0.05 degrees in the range of FDS 0.5°, 2θ=10° to 100°. For the measured data, Rietveld refinement was performed considering the charge (+2 for Fe, +1 for Li, and +4 for Ti) and cation mixing at each site. During the size analysis, instrumental brodadening was considered using the Fundamental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and the entire peaks of the measurement range were used for fitting. The peak shape was fitted using only the Lorenzian contribution as the First Principle (FP) among the peak types available in TOPAS, and strain was not considered at this time.

[0045] In this specification, the pellet density is a value calculated by Equation 4 below when a force equivalent to 2,000 kgf is applied to form a pellet using an automatic pellet press. Specifically, the pellet density is a value obtained according to (1) to (3) below.

[0046] (1) Using a universal testing machine (UTM: Universal Testing Machine, Instron, Model 5966), adjust the zero point for thickness using a cylindrical mold for a circular pellet holder.

[0047] (2) Place the positive electrode active material in the above circular pellet holder, apply force until a force equivalent to 2,000 kgf is reached, and measure the thickness of the formed pellet.

[0048] (3) Calculate the pellet volume using the following equation 3, and calculate the pellet density using the following equation 4.

[0049] [Formula 3]

[0050] Pellet volume (cm) 3 ) = π(radius of the circular pellet holder (cm)) 2 Х Pellets thickness (cm)

[0051] [Formula 4]

[0052] Pellet density (g / cm) 3 ) = Positive active material weight (g) / Pellet volume (cm 3 )

[0053] In this specification, the powder resistance is a value calculated by placing 5 g of positive electrode active material powder into a cylindrical mold with an inner diameter of 2.2 cm, applying force until a force equivalent to 2,000 kgf is achieved with a cylinder with an outer diameter of 2.05 cm to form a pellet, measuring the surface resistance of the formed pellet using a 4-point probe method, and converting this into volume resistance.

[0054]

[0055] positive electrode active material

[0056] Hereinafter, the positive electrode active material according to the present invention will be described.

[0057]

[0058] The cathode active material according to the present invention includes a lithium iron phosphate compound having an olivine structure; and a coating portion including carbon and nitrogen formed on the lithium iron phosphate compound; wherein a value (X1) according to the following formula 1 is 0.550 or more and 0.850 or less, and a value (X2) according to the following formula 2 is 0.0030 or more and 0.0065 or less.

[0059] [Formula 1]

[0060] X1 = mole fraction of oxygen / mole fraction of carbon

[0061] [Formula 2]

[0062] X2 = mole fraction of nitrogen / (mole fraction of nitrogen + mole fraction of carbon + mole fraction of oxygen)

[0063] In the above equations 1 and 2, the mole fraction is the ratio of the number of moles of each element to the number of moles of all elements present on the particle surface, as measured using an X-ray photoelectron spectroscopy (XPS).

[0064]

[0065] The positive electrode active material according to the present invention, that is, the positive electrode active material comprises a lithium iron phosphate-based compound having an olivine structure; and a coating portion including carbon and nitrogen formed on the lithium iron phosphate-based compound; and when the value (X1) according to the above formula 1 is 0.550 or more and 0.850 or less, and the value (X2) according to the above formula 2 is 0.0030 or more and 0.0065 or less, the positive electrode active material has the advantage of having a large rolling density and a small powder resistance. Accordingly, a battery including the positive electrode active material according to the present invention has the effect of improving resistance characteristics and energy density characteristics.

[0066]

[0067] The above-described positive electrode active material comprises a lithium iron phosphate-based compound having an olivine structure; and a coating formed on the lithium iron phosphate-based compound, which comprises carbon and nitrogen. When the coating comprises carbon and nitrogen, the electrical conductivity is improved, resulting in a reduced powder resistance and a reduced crystal size, which results in a higher rolling density. When the positive electrode active material does not comprise the coating, there is a problem of poor electrical conductivity of the positive electrode active material, and when the coating does not comprise nitrogen, there is a problem of poor energy density of the battery due to a low rolling density.

[0068] Meanwhile, the positive electrode active material has a value (X1) according to formula 1 described herein of 0.550 or more and 0.850 or less, and a value (X2) according to formula 2 described herein of 0.0030 or more and 0.0065 or less.

[0069] In relation to this, the value (X1) according to Equation 1 described herein is a parameter related to the degree of generation of disorder or defects in carbon crystals and the particle size. The larger X1 is, the more carbon crystals with disorder or defects are present. The degree of generation of disorder or defects in carbon crystals is related to the generation of particles of the positive electrode active material. Specifically, particle generation consists of crystal growth and crystal aggregation of particles. Since crystal growth and crystal aggregation are controlled depending on the amount of carbon crystals with disorder or defects in the coating portion, the crystal size of the particles changes, which affects the rolling density and powder resistance of the positive electrode active material. For example, in the case of the same manufacturing process, when the coating portion contains carbon and nitrogen, the content of disordered carbon crystals or carbon crystals with defects in the coating portion increases compared to when the coating portion contains only carbon. If the amount of disordered or defective carbon crystals in the coating part containing carbon is small, the thickness of the coating part containing carbon may be thick, and thus, there is a problem that the carbon interferes with the crystal growth of the positive electrode active material. If the amount of disordered or defective carbon crystals in the coating part containing carbon is excessive, there is a problem that the coating part interferes with the coagulation between crystals. The present invention controls the amount of disordered or defective carbon crystals in the coating part by controlling X1 of the coating part containing carbon and nitrogen, that is, the mole fraction of oxygen to the mole fraction of carbon, to be 0.550 or more and 0.850 or less, and optimizes the rolling density and powder resistance by controlling the crystal size of the positive electrode active material.

[0070] In addition, the value (X2) according to Equation 2 described herein is a parameter related to the degree of disorder or defect generation in carbon crystals and the amount of free electrons in the carbon layer. The larger the X2, the more carbon crystals with disorder or defects there are. The degree of disorder or defect generation in carbon crystals is related to the amount of free electrons in the carbon layer. Specifically, the free electrons in the carbon layer mean the number of electrons that can be inserted or deintercalated. If the amount of carbon crystals with disorder or defects in the coating portion containing carbon is small, the number of electrons that can be inserted or deintercalated is small, which affects the conductivity of the positive electrode active material. For example, in the case of the same manufacturing process, when the coating portion contains carbon and nitrogen, the content of disordered carbon crystals or carbon crystals with defects in the coating portion increases compared to when the coating portion contains only carbon, thereby increasing the free electrons in the carbon layer. If the number of free electrons in the carbon layer is small, there is a problem of poor conductivity, and if the number of free electrons in the carbon layer is excessive, there is a problem of poor life characteristics. The present invention controls the amount of carbon crystals with disorder or defects in the coating part by controlling X2 of the coating part including carbon and nitrogen, that is, the mole fraction of nitrogen with respect to the sum of the mole fraction of nitrogen, the mole fraction of carbon, and the mole fraction of oxygen, to 0.0030 or more and 0.0065 or less, and optimizes the rolling density and powder resistance by controlling the content of free electrons in the carbon layer.

[0071] Specifically, the value (X1) according to the formula 1 described herein may be 0.550 or more, or 0.555 or more, and may be 0.820 or less, 0.830 or less, 0.840 or less, or 0.850 or less, and the value (X2) according to the formula 2 described herein may be 0.0030 or more, 0.0031 or more, 0.0032 or more, 0.0033 or more, 0.0034 or more, or 0.0035 or more, and may be 0.0063 or less, 0.0064 or less, or 0.0065 or less. The above X1 and When X2 is within the above range, there is an advantage in that the rolling density of the positive electrode active material is high while the powder resistance is low. Accordingly, the battery including the positive electrode active material according to the present invention has the effect of improving resistance characteristics and energy density, etc. When X1 exceeds 0.850 or is less than 0.550, there is a problem in that the rolling density is low or the powder resistance is high, and when X2 is less than 0.0030 or is more than 0.0065, there is a problem in that the rolling density is low or the powder resistance is high.

[0072]

[0073] According to one embodiment of the present invention, the lithium iron phosphate compound may have a composition represented by the following chemical formula 1.

[0074] [Chemical Formula 1]

[0075] Li 1+x Fe 1-a M a PO4

[0076] In the above chemical formula 1, M is at least one selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and -0.1≤x≤0.1, 0≤a<1.

[0077] The above M is a doping element, and specifically, M may be at least one selected from the group consisting of Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y.

[0078] Meanwhile, the above x may be -0.1 or more, or 0 or more and 0.1 or less. When x satisfies the above range, the synthesis of impurities can be suppressed and structural stability can be improved.

[0079] a is the molar fraction of M among all metals excluding lithium in the lithium iron phosphate compound, and may be 0 or more, or 0.01 or more, and may be 0.05 or less, 0.1 or less, 0.5 or less, or less than 1. When a satisfies the above range, the life characteristics can be improved by controlling the length and strength of the bond between lithium and oxygen while maintaining the energy density.

[0080]

[0081] According to one embodiment of the present invention, the content of carbon included in the coating portion may be 0.50 wt% or more and 3.00 wt% or less based on the total weight of the positive electrode active material. Specifically, the content of carbon included in the coating portion may be 0.50 wt% or more, 1.50 wt% or less, 2.00 wt% or less, 2.50 wt% or less, or 3.00 wt% or less. When the content of carbon included in the coating portion is within the above range, the electronic conductivity of the positive electrode active material may be improved without acting as a resistor.

[0082]

[0083] According to one embodiment of the present invention, the mole fraction of the carbon may be 0.400 or more and 0.600 or less. Specifically, the mole fraction of the carbon may be 0.400 or more, 0.410 or more, 0.420 or more, 0.430 or more, 0.440 or more, or 0.450 or more, and 0.550 or less, 0.560 or less, 0.570 or less, 0.580 or less, 0.590 or less, or 0.600 or less. When the mole fraction of the carbon is within the above range, the electronic conductivity of the positive electrode active material may be improved without acting as a resistor.

[0084]

[0085] According to one embodiment of the present invention, the mole fraction of oxygen may be 0.200 or more and 0.400 or less. Specifically, the mole fraction of oxygen may be 0.200 or more, 0.210 or more, 0.220 or more, 0.230 or more, 0.240 or more, 0.250 or more, 0.260 or more, 0.270 or more, or 0.280 or more, and may be 0.350 or less, 0.360 or less, 0.370 or less, 0.380 or less, 0.390 or less, or 0.400 or less. When the mole fraction of oxygen is within the above range, the crystal size of the positive electrode active material can be controlled.

[0086]

[0087] According to one embodiment of the present invention, the mole fraction of nitrogen may be 0.003 or more and 0.005 or less. When the mole fraction of nitrogen is within the above range, the crystal size of the positive electrode active material can be controlled, the rolling density of the positive electrode active material can be increased, and the powder resistance can be reduced.

[0088]

[0089] According to one embodiment of the present invention, the positive electrode active material may have a crystal size of 100.00 nm or more and 200.00 nm or less. Specifically, the positive electrode active material may have a crystal size of 100.00 nm or more, 110.00 nm or more, 120.00 nm or more, 130.00 nm or more, or 140.00 nm or more, 190.00 nm or more, or 200.00 nm or more. When the crystal size of the positive electrode active material is within the above range, the electrode density can be improved, and the capacity characteristics of the battery can be improved, etc.

[0090]

[0091] According to one embodiment of the present invention, the positive electrode active material is 4.0Х10 7 N / m 2 Ideal 6.0Х10 7 N / m 2 When the pressure below is applied, the pellet density is 2.000 g / cm 3 More than 2.500 g / cm 3 It may be as follows. Specifically, the positive electrode active material is 4.0Х10 7 N / m 2 Ideal 6.0Х10 7 N / m 2 When the pressure below is applied, the pellet density is 2.000 g / cm 3 or 2.050 g / cm 3 It may be more than 2.200 g / cm 3 Below, 2.300 g / cm 3 Below, 2.400 g / cm 3 or less, or 2.500 g / cm 3 It may be as follows. When the pellet density of the positive electrode active material is within the above range, the electrode density can be improved and the life characteristics of the battery can be improved.

[0092]

[0093] According to one embodiment of the present invention, the positive electrode active material is 4.0Х10 7 N / m2 Ideal 6.0Х10 7 N / m 2 When the pressure below is applied, the powder resistance may be 25.00ΩХcm or more and 50.00ΩХcm or less. Specifically, the positive electrode active material may have a resistance of 4.0Х10 7 N / m 2 Ideal 6.0Х10 7 N / m 2 When the pressure below is applied, the powder resistance may be 25.00ΩХcm or more, or 30.00ΩХcm or more, and 49.00ΩХcm or less, or 50.00ΩХcm or less. When the powder resistance of the positive electrode active material is within the above range, the positive electrode active material has low resistance, excellent conductivity, and improved electrochemical properties.

[0094]

[0095] The 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, a carbon coating raw material, and a nitrogen coating raw material, and optionally further mixing a doping element raw material (e.g., titanium, magnesium, etc.) to manufacture a mixture; (B) a step of firing the mixture to manufacture a sintered product; and (C) a step of pulverizing the sintered product.

[0096]

[0097] The properties of the positive electrode active material according to the present invention can be implemented by appropriately controlling the presence or absence and amount of doping element raw material added during the manufacture of the positive electrode active material, the amount of carbon coating raw material used, the firing temperature, the grinding conditions, etc., but are not limited thereto.

[0098]

[0099] 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.

[0100] The above phosphoric acid raw material may be FePO4, H3PO4, NH4H2PO4, (NH4)2HPO4, P2O5, etc.

[0101] 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.

[0102] The above phosphate raw material and iron raw material may be the same. For example, it may be iron phosphate (FePO4).

[0103]

[0104] The above carbon coating raw material can provide a coating portion including carbon by firing, and thus the electrical conductivity of the 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.

[0105] The carbon coating raw material may be added in an amount of 5 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. Specifically, the carbon coating raw material may be added in an amount of 8 wt% to 10 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 an oxidation-reduction reaction that occurs during the process of forming lithium iron phosphate crystals, and an appropriate amount of carbon may be coated to improve conductivity.

[0106]

[0107] The above nitrogen coating raw material can provide a coating portion containing nitrogen by firing, thereby improving the electrical conductivity of the positive electrode active material, controlling the crystal size, increasing the rolling density, and improving the powder resistance. The above nitrogen coating raw material can be a nitrogen-containing organic material, for example, C6H 14 N2O7, dopamine, melanin, ammonia gas, NTA (Nitrilotriacetic acid), acetonitrile, polyacrylonitrile, etc. Specifically, the nitrogen coating raw material may be C6H 14 It could be N2O7.

[0108] The above nitrogen coating raw material may be added in an amount of 0.5 wt% or less relative to the total weight of the lithium raw material, phosphate raw material, iron raw material, and doping element raw material. In this case, the nitrogen coating raw material is utilized as a material for the oxidation-reduction reaction that occurs during the formation of lithium iron phosphate crystals, and an appropriate amount of nitrogen may be coated to improve conductivity, etc.

[0109]

[0110] 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 Mn, Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn 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.

[0111]

[0112] The above lithium raw material, phosphate raw material, iron raw material, and doping element raw material may be mixed in an amount such that the lithium iron phosphate compound included in the resulting positive electrode active material has a composition represented by the above chemical formula 1. At this time, a step of additionally mixing a dispersant may be included. Specifically, the dispersant may be polyethylene glycol (PEG). The dispersant may be added in an amount of 4 wt% or less relative to the total weight of the lithium raw material, phosphate raw material, iron raw material, and doping element raw material.

[0113]

[0114] The mixing of the above raw materials may be wet mixing or dry mixing.

[0115] 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 μm in size) and mixed, but is not limited thereto.

[0116]

[0117] Meanwhile, in the case of wet mixing, a powder (mixture) that has been completely dried can be obtained through spray drying.

[0118]

[0119] The above firing can be performed at a temperature of 700°C to 850°C. In this case, the optimized firing temperature allows for the formation of appropriate primary particles and the absence of impurities, thereby producing a positive electrode active material with high rolling density and low resistance. If the firing temperature is below 700°C, there is a problem of insufficient thermal energy required for crystal growth.

[0120] The above calcination may be performed under an inert atmosphere. Specifically, the above calcination may be performed under a nitrogen atmosphere.

[0121]

[0122] 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.

[0123]

[0124] According to one embodiment of the present invention, when manufactured to satisfy the following formula 5, the value (X1) according to formula 1 described in the present invention may be 0.55 or more and 0.85 or less, and the value (X2) according to formula 2 described in the present invention may be 0.003 or more and 0.0065 or less.

[0125] [Formula 5]

[0126] 2,400 (℃ × weight%) ≤ sintering temperature (℃) × (mixing amount of dispersant (weight%) + 10 × mixing amount of nitrogen coating raw material (weight%)) ≤ 4,500 (℃ × weight%)

[0127] Specifically, in order to satisfy the value (X1) according to formula 1 described in the present invention and the value (X2) according to formula 2 described in the present invention, the value according to formula 5 may be 2,400°C×wt% or more during manufacturing, and may be manufactured to be 4,000°C×wt% or less, 4,100°C×wt% or less, 4,200°C×wt% or less, 4,300°C×wt% or less, 4,400°C×wt% or less, or 4,500°C×wt% or less.

[0128] According to one embodiment of the present invention, the smaller the value according to the above formula 5, the smaller the value (X2) according to the formula 2 described in the present invention.

[0129]

[0130] anode

[0131] Next, the anode according to the present invention will be described.

[0132] The positive electrode according to the present invention comprises a positive electrode active material layer comprising the positive electrode active material according to the present invention. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, and comprising the positive electrode 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.

[0133]

[0134] 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 µm 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.

[0135]

[0136] The above-mentioned positive electrode active material layer may include a conductive material and a binder together with the positive electrode active material. At this time, the positive electrode active material may be included in an amount of 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.

[0137]

[0138] 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. One type alone or a mixture of two or more types of these may be used. The conductive material may be included in an amount of 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0139]

[0140] 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, tetrafluoroethylene, 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 0.1 wt% to 15 wt% based on the total weight of the positive electrode active material layer.

[0141]

[0142] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the positive electrode active material described above is used. 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. Alternatively, 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.

[0143]

[0144] 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 slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0145]

[0146] lithium secondary battery

[0147] Next, a lithium secondary battery according to the present invention will be described.

[0148] The present invention can manufacture an electrochemical device including the above-described positive electrode. The electrochemical device may be, specifically, a battery, a capacitor, or the like, and more specifically, a lithium secondary battery.

[0149]

[0150] 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.

[0151]

[0152] 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.

[0153]

[0154] 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.

[0155] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. 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]

[0157] The above negative electrode active material layer optionally includes a binder and a conductive material together with the negative electrode active material.

[0158]

[0159] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β(0<β<2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbonaceous material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and representative examples of high-crystalline carbon include natural graphite or artificial graphite in the form of amorphous, plate-like, flaky, spherical, or fibers, 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.

[0160] 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.

[0161]

[0162] 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, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0163]

[0164] 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 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; 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.

[0165]

[0166] The negative electrode active material layer may be manufactured by applying and drying a composition for forming a negative electrode active material layer prepared by dissolving or dispersing a negative electrode active material, and optionally a binder and a conductive material in a solvent, 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.

[0167]

[0168] 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.

[0169]

[0170] 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.

[0171] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0172] 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.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.

[0173]

[0174] 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.

[0175]

[0176] 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 additive 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.

[0177]

[0178] As described above, a lithium secondary battery including a cathode active material according to the present invention exhibits excellent resistance characteristics and energy density, 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).

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183]

[0184] 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.

[0185]

[0186]

[0187] Examples and Comparative Examples

[0188] Example 1

[0189] Li2CO3, FePO4(D 50 : 5.49㎛) 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 8 wt% based on the total weight of Li2CO3, FePO4, and TiO2, and C6H 14 A mixed solution was prepared by adding N2O7 in an amount of 0.5 wt% relative to the total weight of Li2CO3, FePO4, and TiO2. To mix and grind the raw materials, the mixed solution was wet-milled in a beads mill at 30 Hz for 1 hour to obtain a slurry. The slurry was dried by spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0190] 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: 2 bar) with a jet mill to have a particle size distribution as shown in Fig. 1, thereby forming a LiFe coating containing carbon and nitrogen. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0191]

[0192] Example 2

[0193] Sucrose is added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and polyethylene glycol (PEG) is added in an amount of 1 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and C6H 14LiFe having a coating portion containing carbon and nitrogen formed in the same manner as in Example 1, except that N2O7 was added in an amount of 0.25 wt% instead of 0.5 wt% based on the total weight of Li2CO3, FePO4 and TiO2. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0194]

[0195] Example 3

[0196] Sucrose is added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and polyethylene glycol (PEG) is added in an amount of 2 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and C6H 14 LiFe having a coating portion containing carbon and nitrogen formed in the same manner as in Example 1, except that N2O7 was added in an amount of 0.1 wt% instead of 0.5 wt% based on the total weight of Li2CO3, FePO4 and TiO2. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0197]

[0198] Example 4

[0199] Sucrose is added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and polyethylene glycol (PEG) is added in an amount of 2 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and C6H 14 LiFe having a coating portion containing carbon and nitrogen formed in the same manner as in Example 1, except that N2O7 was added in an amount of 0.25 wt% instead of 0.5 wt% based on the total weight of Li2CO3, FePO4 and TiO2. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0200]

[0201] Comparative Example 1

[0202] C6H 14 LiFe having a coating portion containing carbon and nitrogen formed in the same manner as in Example 1, except that N2O7 was added in an amount of 1 wt% instead of 0.5 wt% based on the total weight of Li2CO3, FePO4 and TiO2. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0203]

[0204] Comparative Example 2

[0205] LiFe having a coating portion including carbon and nitrogen formed in the same manner as in Example 1, except that sucrose was added in an amount of 8 wt% relative to the total weight of Li2CO3, FePO4 and TiO2, and polyethylene glycol (PEG) was added in an amount of 1 wt% relative to the total weight of Li2CO3, FePO4 and TiO2. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0206]

[0207] Comparative Example 3

[0208] C6H 14 LiFe, a carbon-containing coating was formed in the same manner as in Example 1, except that N2O7 was not added. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0209]

[0210] Comparative Example 4

[0211] Sucrose is added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and polyethylene glycol (PEG) is added in an amount of 1 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and C6H 14 LiFe, a carbon-containing coating was formed in the same manner as in Example 1, except that N2O7 was not added. 0.99 Ti 0.01PO4 positive electrode active material was manufactured.

[0212]

[0213] Comparative Example 5

[0214] Sucrose is added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and polyethylene glycol (PEG) is added in an amount of 2 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and C6H 14 LiFe, a carbon-containing coating was formed in the same manner as in Example 1, except that N2O7 was not added. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0215]

[0216] Comparative Example 6

[0217] Sucrose is added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and polyethylene glycol (PEG) is added in an amount of 2 wt% based on the total weight of Li2CO3, FePO4 and TiO2, C6H 14 LiFe having a coating portion containing carbon and nitrogen was formed in the same manner as in Example 1, except that N2O7 was added in an amount of 0.05 wt% instead of 0.5 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and that calcination was performed for 9 hours instead of 10 hours. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0218]

[0219] Comparative Example 7

[0220] Sucrose is added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and polyethylene glycol (PEG) is added in an amount of 2 wt% based on the total weight of Li2CO3, FePO4 and TiO2, and C6H 14LiFe having a coating portion containing carbon and nitrogen formed in the same manner as in Example 1, except that N2O7 was added in an amount of 1 wt% instead of 0.5 wt% based on the total weight of Li2CO3, FePO4 and TiO2. 0.99 Ti 0.01 PO4 positive electrode active material was manufactured.

[0221]

[0222] Comparative Example 8

[0223] Li2CO3 and FePO4(D 50 : 5.49㎛) was mixed with water in an amount such that the lithium:iron molar ratio (Li:Fe) was 1.03:1, sucrose was added in an amount of 8 wt% based on the total weight of Li2CO3, FePO4, and TiO2, and polyethylene glycol (PEG) was added in an amount of 2 wt% based on the total weight of Li2CO3 and FePO4 to prepare a mixed solution. For mixing and grinding of the raw materials, the mixed solution was wet-ground for 1 hour at 30 Hz with a beads mill to obtain a slurry. The slurry was dried through spray drying (inlet temperature: 235°C, outlet temperature: 93°C).

[0224] Thereafter, the dried powder (hereinafter, the mixture) was fired at 680°C for 10 hours under a nitrogen atmosphere to produce a fired product. The fired product was pulverized (feeding pressure: 6 bar, grinding pressure: 2 bar) using a jet mill to have a particle size distribution as shown in Fig. 1, thereby producing a LiFePO4 positive electrode active material having a coating portion containing carbon and nitrogen.

[0225]

[0226] Mixing amount (weight%)Calcining time (hours)SucrosePolyethylene glycolC6H 14N2O7Example 1800.510Example 2810.2510Example 3820.110Example 4820.2510Comparative Example 180110Comparative Example 2810.510Comparative Example 380010Comparative Example 481010Comparative Example 582010Comparative Example 6820.059Comparative Example 782110Comparative Example 882010

[0227] Experimental Example Experimental Example 1: XPS Analysis

[0228] The distribution of carbon, nitrogen, and oxygen on the surface of the coating portion of each positive electrode active material manufactured in the above examples and comparative examples was analyzed using ESCA (K-Alpha, Thermo Fisher Scientific Inc.).

[0229] Specifically, under depth profiling conditions, etching was performed at a rate of 0.3 nm / 10 s using an Ar ion source, and the contents of carbon, nitrogen, and oxygen contained in the 0 to 100 nm region from the surface of the positive electrode active material toward the center of the positive electrode active material particles were measured, and the ratio of the mole number of each element to the mole number of the total elements (mole fraction) was calculated and shown in Table 2 below.

[0230] And, the values ​​(X1) according to Equation 1 and (X2) according to Equation 2 described in this specification were calculated with the above molar fraction and are shown in Table 2 below.

[0231]

[0232] Mole fraction X1 X2 Carbon Oxygen Nitrogen Example 10.48 30.32 60.00 50.67 50.00 61 Example 20.5 30.29 40.00 40.55 50.00 48 Example 30.46 60.34 40.00 30.73 80.00 37 Example 40.45 40.36 90.00 30.81 30.00 36 Comparative Example 10.37 30.39 90.00 81.07 00.01 03 Comparative Example 20.37 50.35 70.00 50.95 20.00 68 Comparative Example 30.54 20.29 70.00 0.54 8- Comparative Example 40.5310.3100.0000.589-Comparative example 50.5280.3060.0000.580-Comparative example 60.3940.3380.0010.8580.0014Comparative example 70.4230.3850.0090.9100.0110Comparative example 80.3770.3120.0000.830-

[0233] Through Table 2, it was confirmed that the positive electrode active materials of Examples 1 to 4 include a coating portion including carbon and nitrogen formed on a lithium iron phosphate compound, and the value (X1) according to Equation 1 described herein is 0.550 or more and 0.850 or less, and the value (X2) according to Equation 2 described herein is 0.0030 or more and 0.0065 or less. In addition, it was confirmed that the positive electrode active materials of Examples 1 to 2 have a mole fraction of carbon of 0.400 or more and 0.600 or less, a mole fraction of oxygen of 0.200 or more and 0.400 or less, and a mole fraction of nitrogen of 0.003 or more and 0.005 or less. On the other hand, the positive electrode active materials of Comparative Examples 1, 2 and 7 have a value (X1) according to Formula 1 described herein of more than 0.850, a value (X2) according to Formula 2 described herein of more than 0.0065, the positive electrode active material of Comparative Example 3 has a value (X1) according to Formula 1 described herein of less than 0.550, the positive electrode active material of Comparative Example 6 has a value (X2) according to Formula 2 described herein of less than 0.0030, and it was confirmed that Comparative Examples 3 to 6 do not have a value (X2) according to Formula 2 described herein because the coating formed on the lithium iron phosphate compound does not contain nitrogen. In addition, it was confirmed that the positive electrode active materials of Comparative Examples 1, 2 and 6 have a mole fraction of carbon of less than 0.400, the positive electrode active material of Comparative Example 6 has a mole fraction of nitrogen of less than 0.003, and the positive electrode active material of Comparative Examples 1 and 7 It was confirmed that the positive electrode active material had a nitrogen mole fraction exceeding 0.005, and it was confirmed that the positive electrode active materials of Comparative Examples 3 to 6 did not contain nitrogen.

[0234]

[0235] Experimental Example 2: Measurement of Carbon (C) Content

[0236] For each positive electrode active material manufactured in the examples and comparative examples, the carbon content in the positive electrode active material was measured, and the carbon content (carbon (C) content (weight %)) relative to the total weight of the positive electrode active material is shown in Table 3 below.

[0237] The above carbon content is measured using a carbon-sulfur analyzer (CS844, LECO). Specifically, 1 g of a positive electrode active material powder sample is collected, placed in a crucible, and installed in a high-frequency induction furnace, and analysis is performed automatically. The C gas of the sample generated in the high-frequency induction furnace combines with the combustion gas O2 to produce CO and CO2. Since C is measured by a CO2 infrared detector, all CO-type gas is converted to CO2 through CuO, and then the carbon content in the CO2-type gas is measured using a CO2 infrared absorption detector.

[0238]

[0239] Carbon (C) content (wt%) Example 10.86 Example 21.22 Example 31.43 Example 41.38 Comparative Example 11.32 Comparative Example 21.47 Comparative Example 30.97 Comparative Example 41.08 Comparative Example 51.33 Comparative Example 61.37 Comparative Example 71.59 Comparative Example 81.44

[0240] Through Table 3, it was confirmed that the content of carbon included in the coating portion of the positive electrode active materials of Examples 1 to 4 was 0.50 wt% or more and 3.00 wt% or less with respect to the total weight of the positive electrode active materials.

[0241] Experimental Example 3: Crystal Size Measurement

[0242] For each positive electrode active material manufactured in the above examples and comparative examples, the crystal size (nm) after XRD measurement is shown in Table 4 below.

[0243] At this time, the XRD measurement was performed using Bruker's AXS D8 Endeavor, and 0.5 g to 1.5 g of positive electrode active material particles were collected from each positive electrode active material powder, and measured at a scan speed of 0.05 ° / sec from 2θ 10 ° to 100 ° under the conditions of Cu-Kα ray (wavelength 1.54 Å), acceleration voltage 40 kV, and current 40 mA.

[0244]

[0245] Crystal size (nm) Example 1 187.40 Example 2 182.48 Example 3 144.52 Example 4 139.39 Comparative Example 1 1116.58 Comparative Example 2 117.95 Comparative Example 3 192.09 Comparative Example 4 178.86 Comparative Example 5 147.98 Comparative Example 6 158.50 Comparative Example 7 110.40 Comparative Example 8 167.90

[0246] Through Table 4, it was confirmed that the positive electrode active materials of Examples 1 to 4 had a crystal size of 100.00 nm or more and 200.00 nm or less.

[0247] Experimental Example 4: Pellet Density Measurement

[0248] Using an automatic pellet press (Auto Pellet Press, Carver, 3887.4), a cylindrical mold was used to adjust the zero point for thickness on a circular pellet holder with a diameter of 2.2 mm. Then, 5 g of each of the positive electrode active materials manufactured in the examples and comparative examples was taken on the circular pellet holder, and a force was applied until a force equivalent to 2,000 kgf was reached, and the thickness of the formed pellets was measured. At this time, the pressure applied to the positive electrode active material was 5.2 X 10 7 N / m 2 am.

[0249] Next, the pellet volume is calculated using the following equation 3, and the pellet density (g / cm) is calculated using the following equation 4. 3 ) was calculated and shown in Table 5 below.

[0250] [Formula 3]

[0251] Pellet volume (cm) 3 ) = π(radius of the circular pellet holder (cm)) 2 Х Pellets thickness (cm)

[0252] [Formula 4]

[0253] Pellet density (g / cm) 3 ) = Positive active material weight (g) / Pellet volume (cm 3 )

[0254]

[0255] Pellet density (g / cm) 3 ) Example 12.090 Example 22.151 Example 32.200 Example 42.140 Comparative Example 11.778 Comparative Example 21.888 Comparative Example 32.071 Comparative Example 42.169 Comparative Example 52.236 Comparative Example 61.848 Comparative Example 71.970 Comparative Example 82.020

[0256] Through Table 5, the positive electrode active materials of Examples 1 to 4 have a molecular weight of 5.2Х10 7 N / m 2 When pressure was applied, the pellet density was 2.000 g / cm 3 More than 2.500 g / cm 3 It was confirmed that the following. On the other hand, the positive electrode active materials of comparative examples 1, 2, 6 and 7 were 5.2Х10 7 N / m 2 When pressure was applied, the pellet density was 2.000 g / cm 3 It was confirmed that it was less than .

[0257] Experimental Example 5: Powder Resistance Measurement

[0258] Each 5g of the positive electrode active material manufactured in the examples and comparative examples was placed in a 2.2cm diameter circular 4Point Probe (Gold Pin) mold, and a force of 2000kgf was applied. The volume resistivity was measured using a resistance measuring device from Hantech, and this was converted into powder resistivity (ΩХcm) and shown in Table 6 below. At this time, the pressure applied to the positive electrode active material was 5.2Х10 7 N / m 2 am.

[0259] Powder resistance (ΩХcm) Example 148.25 Example 231.10 Example 340.00 Example 428.98 Comparative Example 191.56 Comparative Example 271.93 Comparative Example 3105.20 Comparative Example 4130.00 Comparative Example 5100.20 Comparative Example 632.20 Comparative Example 78.20 Comparative Example 821.00

[0260] Through Table 6, the positive electrode active materials of Examples 1 to 4 had a molecular weight of 5.2Х107 N / m 2 When pressure was applied, it was confirmed that the powder resistance was 25.00ΩХcm or more and 50.00ΩХcm or less. On the other hand, 5.2Х10 7 N / m 2 When pressure was applied, it was confirmed that the positive electrode active materials of Comparative Examples 1 to 5 had a powder resistance of more than 50.00ΩХcm, and the positive electrode active material of Comparative Example 7 had a powder resistance of less than 25.00ΩХcm.

[0261] Experimental Example 6: Battery Characteristics Evaluation

[0262] - Coin-type half-cell manufacturing

[0263] A positive electrode slurry was prepared by mixing 95 wt% of each of the positive electrode active materials manufactured in the above examples and comparative examples, 2 wt% of carbon black as a conductive agent, and 3 wt% of polyvinylidene fluoride (PVDF) as a binder in an N-methylpyrrolidone (NMP) solvent. The prepared positive electrode slurry was applied to one surface of an aluminum current collector, dried at 100°C, and then rolled to prepare a positive electrode.

[0264] An electrode assembly was manufactured using a lithium metal electrode as the negative electrode and a porous polyethylene separator interposed between the positive and negative electrodes. This was placed inside a battery case, and a coin-type half-cell was manufactured by injecting an electrolyte solution containing 1 M LiPF6 dissolved in an organic solvent containing ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 1:2:1 and 2 wt% vinyl carbonate (VC).

[0265]

[0266] Electrochemical Impedance Spentroscopy Evaluation

[0267] The above coin-type half-cell was charged to 3.7 V in CC (0.1 C)-CV (Cut-off current: 0.05 C) mode at 25°C, and then, after a 24-hour rest period, discharged to 2.5 V at 0.1 C, and the discharge capacity (mAh / g) was measured. The resistance (Ω) was calculated and shown in Table 7 below. The resistance is a value calculated by dividing the difference between the voltage at 60 seconds and the initial voltage while discharging at a constant current of 0.1 C in the charge / discharge cycle by the applied current.

[0268] For reference, the above resistance (Ω) is R ohm , R CEI and R ct As a sum of the above R ohm means the external electrolyte resistance, and can be confirmed by the real impedance axis intercept when analyzing the Nyquist plot, and the above R CEI refers to the charge transfer resistance in the internal electrode, especially in the SEI generated on the surface of the positive electrode particles, and can be confirmed by the diameter of the first semicircle when analyzing the Nyquist plot, and the R ct It refers to the charge transfer resistance representing the lithium ion redox reaction at the electrode material interface, and can be confirmed by the diameter of the second semicircle when analyzing the Nyquist plot.

[0269]

[0270] Resistance (Ω) Example 17.343 Example 27.465 Example 37.652 Example 46.776 Comparative Example 18.511 Comparative Example 28.885 Comparative Example 38.592 Comparative Example 49.552 Comparative Example 58.887 Comparative Example 612.778 Comparative Example 712.305 Comparative Example 834.998

[0271] Through Table 7, it was confirmed that the batteries including the positive electrode active materials of Examples 1 to 4 had lower resistance than Comparative Examples 1 to 7, specifically, the sum of the external electrolyte resistance, the charge transfer resistance in the SEI generated on the surface of the internal electrode particles, and the charge transfer resistance representing the lithium ion oxidation-reduction reaction at the electrode material interface.

Claims

1. A lithium iron phosphate compound having an olivine structure; and A coating portion including carbon and nitrogen formed on the lithium iron phosphate compound; The value (X1) according to the following formula 1 is 0.550 or more and 0.850 or less, A positive electrode active material having a value (X2) according to the following formula 2 of 0.0030 or more and 0.0065 or less: [Formula 1] X1 = mole fraction of oxygen / mole fraction of carbon [Formula 2] X2 = mole fraction of nitrogen / (mole fraction of nitrogen + mole fraction of carbon + mole fraction of oxygen) In the above equations 1 and 2, The above mole fraction is the ratio of the number of moles of each element to the number of moles of all elements present on the particle surface, as measured using an X-ray photoelectron spectroscopy (XPS).

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

3. In claim 1, A positive electrode active material having a carbon content included in the above coating portion of 0.50 wt% or more and 3.00 wt% or less based on the total weight of the positive electrode active material.

4. In claim 1, A positive electrode active material having a molar fraction of carbon of 0.400 or more and 0.600 or less.

5. In claim 1, A positive electrode active material having a mole fraction of oxygen of 0.200 or more and 0.400 or less.

6. In claim 1, A positive electrode active material having a molar fraction of nitrogen of 0.003 or more and 0.005 or less.

7. In claim 1, A cathode active material having a crystal size of 100.00 nm or more and 200.00 nm or less.

8. In claim 1, 4.0Х10 7 N / m 2 Ideal 6.0Х10 7 N / m 2 When the pressure below is applied, the pellet density is 2.000 g / cm 3 More than 2.500 g / cm 3 Below is the positive electrode active material.

9. In claim 1, 4.0Х10 7 N / m 2 Ideal 6.0Х10 7 N / m 2 A positive electrode active material having a powder resistance of 25.00ΩХcm or more and 50.00ΩХcm or less when the following pressure is applied.

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

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