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

Abstract

The present specification relates to a positive electrode active material, a method for preparing same, and a positive electrode and a lithium secondary battery comprising same, the positive electrode active material comprising: a lithium iron phosphate-based compound; and a carbon coating layer provided on a part or all of the surface of the lithium iron phosphate-based compound, wherein the content of free carbon is 800 ppm or less relative to the total weight of the positive electrode active material.

Description

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

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

[0002] This specification claims the benefit of the filing date of Patent No. 10-2024-0132844 filed with the Korean Intellectual Property Office on September 30, 2024, the contents of which are incorporated herein.

[0003] This specification relates to a positive electrode active material, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery.

[0004] Due to the recent rapid advancements in electric vehicles and various electronic products, the need for miniaturization and weight reduction of lithium-ion batteries is being further emphasized, while simultaneously, the demand for lithium-ion batteries equipped with safety and high energy density is increasing. To enhance the performance of secondary batteries, lithium iron phosphate (LiFePO4)-based cathode active materials are widely used, and carbon coating is generally applied to the surface of these materials to ensure excellent electrical conductivity. In particular, the uniform quality of the carbon coating is a critical factor, as it is closely linked to the performance of the cathode active material.

[0005] Generally, increasing the carbon content is used to improve the quality of the carbon coating layer; however, if the carbon content is increased excessively, a problem may arise where unreacted free carbon remains. An increase in free carbon lowers the press density of the cathode active material, which can consequently lead to processability issues such as reduced electrode loading and lower energy density.

[0006] In addition, lithium carbonate (Li2CO3) used in the manufacturing process of cathode active materials plays an important role as a lithium precursor; however, the lithium carbonate remaining as a residue after synthesis not only reduces the electrical conductivity of the electrode but can also act as a factor that interferes with electrochemical reactions.

[0007] The present specification relates to a positive electrode active material with improved rolling density or electrochemical performance, a method for manufacturing the same, a positive electrode including the same, and a lithium secondary battery.

[0008] The present invention relates to a lithium iron phosphate-based compound; and

[0009] It includes a carbon coating layer provided on part or all of the surface of the above-mentioned lithium iron phosphate-based compound, and

[0010] A cathode active material having a free carbon content of 800 ppm or less based on the total weight of the cathode active material is provided.

[0011] In addition, the present invention relates to a lithium-containing raw material, an iron-containing raw material, a phosphoric acid-containing raw material, and a doping element (M 1 A step of preparing a mixture containing a ) containing raw material and a carbon source; and

[0012] The method includes the step of calcining the above mixture,

[0013] The above doping element (M 1 A method for manufacturing the above-described positive electrode active material is provided, wherein the content of ) is 0.1 mol% or more and 1.9 mol% or less based on the total molar amount of the above-described phosphoric acid.

[0014] In addition, the present invention provides a positive electrode comprising the positive electrode active material described above.

[0015] In addition, the present invention provides a lithium secondary battery comprising the anode described above.

[0016] The positive active material of the present invention has the effect of improved rolling density.

[0017] The positive active material of the present invention has the effect of improving electrochemical performance when applied to a lithium secondary battery.

[0018] Figure 1 shows the experimental results according to Experimental Example 1.

[0019] The present specification will be described in detail below.

[0020] Unless otherwise defined in this specification, all technical and scientific terms are used merely to describe exemplary embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the presence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0021] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0022] The technical terms used in this specification are intended merely to refer to specific embodiments and are not intended to limit the invention. Furthermore, the singular forms used herein include plural forms unless the phrases clearly indicate otherwise.

[0023] In this specification, 'free carbon' refers to carbon that remains unreacted during the process of forming a carbon coating layer. That is, it can be understood as carbon that is not bonded to the carbon coating layer. It can be understood as 'non-bonded carbon' or 'residual carbon' and may be irregularly distributed on the surface of a lithium iron phosphate-based compound.

[0024] In this specification, 'organic carbon' refers to carbon that reacts during the process of forming a carbon coating layer and is coated on the surface of a lithium iron phosphate-based compound. It may be understood as 'bonded carbon'.

[0025] In this specification, 'inorganic carbon' refers to carbon bonded to an inorganic compound and may be formed during the synthesis of the cathode active material when lithium raw materials are used excessively or when incomplete reactions occur. Alternatively, it may be attributed to lithium carbonate used as a lithium raw material or derived from a material used as a carbon source. That is, the inorganic carbon can be understood as an impurity of the cathode active material and can be used as a means to confirm the presence and content of residual lithium.

[0026] In this specification, the presence and content of the aforementioned 'free carbon', 'organic carbon', and 'inorganic carbon' can be analyzed using a known carbon analyzer. By using a carbon analyzer, carbon dioxide (CO2) generated by calcining a sample at high temperature is detected using an infrared detector, and the presence and content of each substance can be calculated by performing stoichiometric ratio calculations. In this case, the carbon analyzer may be the Primacs series from SKALAR, specifically the Primacs SNC-100.

[0027] In this specification, the content of the aforementioned 'free carbon', 'organic carbon', and 'inorganic carbon' can be calculated using the following formula 1. The absolute weight of carbon required to calculate formula 1 can be calculated from the absolute weight of carbon dioxide generated when a sample is calcined at a high temperature using a carbon analyzer (formula 2). The absolute weight of carbon dioxide can be converted by multiplying the area of ​​the carbon dioxide peak analyzed using a carbon analyzer by a correction factor k (formula 3), and the correction factor k can be calculated using a standard sample whose carbon content is known in advance. The correction factor k is a correction factor that converts the peak area derived using a program linked to a measuring instrument into the absolute weight of carbon dioxide, and the unit of the value calculated as (k * area of ​​the carbon dioxide generation peak) may be weight (mg).

[0028] [Formula 1]

[0029] Carbon content (ppm) = Absolute weight of carbon (mg) / Weight of sample (kg)

[0030] [Formula 2]

[0031] Absolute weight of carbon (mg) = Absolute weight of carbon dioxide (mg) * (Atomic weight of carbon) / (Molecular weight of carbon dioxide)

[0032] [Formula 3]

[0033] Absolute weight of carbon dioxide (mg) = k * (Area of ​​the carbon dioxide emission peak)

[0034] [Calculation of Correction Factor k]

[0035] A standard sample with a known carbon content can be taken, and the absolute weight of carbon dioxide generated during calcination can be measured. Then, the correction factor k value can be derived using the above calculation formulas 1 to 3. The average value of the correction factors derived by repeating the process 1 to 5 times while changing the weight of the standard sample can be taken and used as the final correction factor k value.

[0036] The following describes a method for calculating the absolute weight of carbon dioxide using a carbon analyzer. First, calcination is performed while increasing the calcination temperature and calcination time. The analysis results can be obtained as a graph consisting of an x-axis and a y-axis. The x-axis represents the calcination time (unit: seconds), the y-axis represents the temperature (unit: °C) for each calcination time, and the area under the curve represents the amount of carbon dioxide generated detected using an infrared detector (see Fig. 1).

[0037] First, when the temperature is raised from a constant first starting temperature to a first ending temperature under an oxygen gas (O2) environment and the amount of carbon dioxide generated over time is plotted as a curve, it can be confirmed that two first and second peaks appear sequentially. At this time, the first peak appearing at a low firing temperature may be a carbon dioxide peak derived from organic carbon, and the second peak appearing at a high firing temperature may be a carbon dioxide peak derived from free carbon. At this time, by adjusting the range of the first starting temperature and the first ending temperature, it is possible to prevent organic carbon and free carbon from being omitted from the analysis and save the time required for the analysis.

[0038] In addition, when the temperature is raised from a second starting temperature to a second ending temperature under an inert gas environment and the amount of carbon dioxide generated over calcination time is plotted as a curve, it can be confirmed that a third peak appears. The third peak may be a carbon dioxide peak originating from inorganic carbon. At this time, by adjusting the range of the second starting temperature and the second ending temperature, the inorganic carbon is prevented from being omitted from the analysis, and the time required for the analysis can be saved. In this case, the inert gas may be helium. Furthermore, the third peak may be the largest peak appearing during the analysis process.

[0039] The first starting temperature may be 500°C or lower. Specifically, it may be 480°C or lower, 460°C or lower, 440°C or lower, or 420°C or lower. Additionally, it may be 100°C or higher, 200°C or higher, 300°C or higher, or 350°C or higher. If the temperature is lower than the above numerical range, the processability is reduced due to the low initial firing temperature, and if the temperature is higher than the above numerical range, organic carbon or free carbon to be detected may be omitted.

[0040] The above first terminal temperature may be 550°C or higher and 700°C or lower. If it is lower than the above numerical range, organic carbon or free carbon to be detected may be omitted, and if it is higher than the above numerical range, the energy required for heating may be excessive.

[0041] The second starting temperature above may be 550°C or higher. Specifically, it may be 560°C or higher, 570°C or higher, 580°C or higher, 590°C or higher, or 600°C or higher. Additionally, it may be 700°C or lower, 670°C or lower, 650°C or lower, 620°C or lower, or 610°C or lower.

[0042] The above second terminal temperature may be 1,000°C or higher. Specifically, it may be 1,020°C or higher, 1,040°C or higher, 1,060°C or higher, 1,080°C or higher, or 1,090°C or higher. Additionally, it may be 1,300°C or lower, 1,250°C or lower, 1,200°C or lower, 1,150°C or lower, or 1,120°C or lower. If the value is lower than the above numerical range, the inorganic carbon to be detected may be omitted, and if the value is higher than the above numerical range, the energy required for heating may be excessive.

[0043] In this specification, 'average grain size' refers to the size of a region within a single crystal that has a well-ordered atomic arrangement. This region is named as a single grain and forms a boundary with other grains. The average grain size can be quantitatively analyzed using X-ray diffraction analysis (XRD) by Cu Kα X-rays. Specifically, XRD data of the synthesized cathode active material can be obtained using a Bruker D8 XRD instrument (Cu-target, voltage: 45kV, current: 40mA, 2θ: 10 to 100 degrees), and structural analysis of the obtained data can be performed using the Rietveld refining method, a general structural analysis method, using Malvern Panalytical's Highscore software.

[0044] The aforementioned Rietveld refining method is a technique that obtains a diffraction pattern calculated from an initial structural model of the crystal structure of the materials and compares it with the measured diffraction pattern of the actual synthesized material. It involves introducing various structure-related factors and iteratively adjusting their values ​​until the two patterns match well. This method assesses validity based on the difference between the calculated and measured patterns and repeats the process until the difference between the two patterns is minimized. Among the structure-related factors that can be introduced in this process, crystal size can be derived using the full width at half maximum (FWHM) of the peaks of each crystal plane appearing in the measured diffraction pattern.

[0045] The present invention provides a positive electrode active material comprising a lithium iron phosphate-based compound; and a carbon coating layer provided on part or all of the surface of the lithium iron phosphate-based compound, wherein the free carbon content is 800 ppm or less based on the total weight of the positive electrode active material.

[0046] Generally, lithium iron phosphate-based compounds provide a pathway for lithium ions to move, enabling a stable supply of energy during the charging and discharging process of a battery. While they possess excellent heat resistance and chemical resistance, they have a limitation in that they have relatively low electrical conductivity. The carbon coating layer can compensate for the low electrical conductivity of the lithium iron phosphate-based compound. The carbon coating layer is formed on the surface of the lithium iron phosphate-based compound by carbonizing a carbon source such as sucrose; however, free carbon may be generated that remains after the carbon coating layer is formed. If an excess of this free carbon is present, the rolling density of the cathode active material decreases, which may lead to a reduction in energy density when applied to a secondary battery. Furthermore, since free carbon can interfere with electrochemical reactions, reduce coating performance during electrode coating, and lower battery capacity, it is necessary to maintain a low content of free carbon.

[0047] The cathode active material of the present invention is characterized by having a free carbon content of 800 ppm or less based on the total weight of the cathode active material. Specifically, it may be 700 ppm or less, 600 ppm or less, 500 ppm or less, 450 ppm or less, 350 ppm or less, 300 ppm or less, 250 ppm or less, 200 ppm or less, or 150 ppm or less. Within the above numerical ranges, the electrochemical reaction is maintained excellently, and the rolling density of the cathode active material is maintained excellently, thereby improving energy density. When the above cathode active material is applied to a secondary battery, the charge / discharge speed or charge / discharge capacity can be improved. Considering the effects intended by the present invention, a lower free carbon content is preferable, so the lower limit is not specifically limited. However, a small amount may be included within a range where negative effects caused by free carbon do not manifest, and the lower limit may be 1 ppm or more, 10 ppm or more, or 20 ppm or more.

[0048] In the present invention, the free carbon content can be achieved by changing the type or content of the carbon source used in the manufacture of the cathode active material, changing the type or content of the doping element, or adjusting the calcination temperature.

[0049] In the present invention, the value of the positive active material calculated by the following mathematical formula 1 may be 7% or less.

[0050] [Mathematical Formula 1]

[0051] C f / (C f +C o )*100(%)

[0052] In mathematical formula 1,

[0053] The above C f is the free carbon content based on the total weight of the cathode active material, and

[0054] The above C o is the organic carbon content based on the total weight of the positive electrode active material.

[0055] In the present invention, the value of the positive electrode active material calculated by the above mathematical formula 1 may be 6.5% or less, 6% or less, 5.5% or less, 5% or less, 4.5% or less, 4% or less, or 3.8% or less. The value calculated by the above mathematical formula 1 refers to the ratio of the content of free carbon to the sum of free carbon and organic carbon, and may refer to the ratio of the content of carbon elements that exist as free carbon among carbon sources and are not formed into a carbon coating layer. By maintaining a low free carbon content within the above numerical range, the rolling density of the positive electrode active material is improved, the electrochemical reaction is not hindered, and the energy density can be improved.

[0056] In the present invention, the value of the positive active material calculated by the following mathematical formula 2 may be 13% or less.

[0057] [Mathematical Formula 2]

[0058] C i / (C f+C o +Ci)*100(%)

[0059] In mathematical formula 2,

[0060] The above C f is the free carbon content based on the total weight of the cathode active material, and

[0061] The above C o is the organic carbon content based on the total weight of the cathode active material, and

[0062] The above C i is the content of inorganic carbon based on the total weight of the positive electrode active material.

[0063] In the present invention, the value of the positive active material calculated by the following mathematical formula 2 may be 12% or less, 10% or less, or 8% or less. Additionally, it may be 1% or more, 2% or more, or 3% or more. Within the above numerical range, the charge / discharge speed or charge / discharge capacity can be improved, and battery operation stability can be ensured.

[0064] In the present invention, the value of the positive active material calculated by the following mathematical formula 3 may be 1.1% or more.

[0065] [Mathematical Formula 3]

[0066] Sc / (C f +C o +C i )*100(%)

[0067] In mathematical formula 3,

[0068] The above Sc is the average grain size (unit: nm) of a lithium iron phosphate-based compound, and

[0069] The above C f is the free carbon content (unit: ppm) based on the total weight of the cathode active material, and

[0070] The above C o is the organic carbon content based on the total weight of the cathode active material, and

[0071] The above C iis the content of inorganic carbon based on the total weight of the positive electrode active material.

[0072] In the present invention, the value of the positive electrode active material calculated by the following mathematical formula 3 may be 1.15% or more, 1.2% or more, 1.25% or more, 1.3% or more, or 1.35% or more. Additionally, it may be 5% or less, 4% or less, or 3% or less. Within the above numerical range, by preventing the average crystal grain size from becoming excessively large, it is possible to form a thin and uniform carbon coating layer, thereby maintaining a low content of free carbon.

[0073] In the present invention, the content of the inorganic carbon may be 1,500 ppm or less based on the total weight of the cathode active material. Specifically, it may be 1,000 ppm or less, 900 ppm or less, 800 ppm or less, 750 ppm or less, or 700 ppm or less. The inorganic carbon may be derived from residual lithium such as lithium carbonate (Li2CO3). The residual lithium may dissolve in N-methylpyrrolidone (NMP) solvent during electrode fabrication and alkalize the solvent, and the alkalize solvent may cause problems in electrode fabrication by mixing with polyvinylpyrrolidone fluoride binder (Polyvinylidene fluoride: PVdF) and gelatinizing the slurry. Meanwhile, lithium carbonate is produced by the reaction of LiOH and CO2. Since the water molecules generated at this time react with the electrolyte to produce gases such as lithium fluoride (LiF) and hydrogen fluoride (HF) and can degrade the electrochemical performance of the active material, it is important to maintain a low residual lithium content. Within the above numerical range, the charge / discharge speed or charge / discharge capacity can be improved, and battery stability can be ensured. Considering the effects intended by the present invention, it is preferable for the content of inorganic carbon to be lower, so the lower limit is not specifically limited. However, a small amount may be included within a range where negative effects caused by inorganic carbon do not manifest, and the lower limit may be 10 ppm or more or 20 ppm or more.

[0074] In the present invention, the total content of free carbon, organic carbon, and inorganic carbon may be 7,000 ppm or more and 20,000 ppm or less based on the total weight of the cathode active material. Preferably, it may be 7,500 ppm or more, 8,000 ppm or more, 8,500 ppm or more, or 9,000 ppm or more. Additionally, it may be 15,000 ppm or less, 14,000 ppm or less, 13,000 ppm or less, or 12,000 ppm or less. Within the above numerical range, the carbon coating layer is uniformly formed, and electrical conductivity can be improved.

[0075] 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 content of free carbon can be reduced, and the carbon coating layer can be uniformly formed so that electrical conductivity can be improved.

[0076] In the present invention, the average grain size of the lithium iron phosphate-based compound may be 120 nm or more and 500 nm or less. Preferably, it may be 130 nm or more, 140 nm or more, 150 nm or more, 160 nm or more, or 170 nm or more. Additionally, it may be 300 nm or less, 280 nm or less, 250 nm or less, 220 nm or less, or 200 nm or less. Within the above numerical range, by preventing the average grain size from becoming excessively large, it is possible to form a thin and uniform carbon coating layer, thereby maintaining a low free carbon content. Furthermore, by securing a sufficient average grain size, the mechanical strength of the material is improved, and the stability of the electrode structure can be maintained even during repeated charge and discharge processes.

[0077] The positive electrode active material of the present invention includes a carbon coating layer provided on part or all of the surface of the lithium iron phosphate-based compound. At this time, the carbon coating layer may be provided on an area of ​​10% or more and 100% or less based on the total surface area of ​​the lithium iron phosphate-based compound. Within the above numerical range, uniform formation of the carbon coating layer is possible, so the content of the free carbon described above can be maintained low.

[0078] In the present invention, the lithium iron phosphate-based compound comprises one or more doping elements (M) selected from the group consisting of 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, and La. 1 It may include ). As the lithium iron phosphate-based compound contains a doping element, the interfacial reactivity between carbon or a carbon source and the lithium iron phosphate-based compound can be increased, thereby reducing the content of free carbon. In addition, the carbon coating layer is formed uniformly, which can reduce surface defects and improve the adhesion between the carbon coating layer and the lithium iron phosphate-based compound.

[0079] In the present invention, the doping element (M 1 ) can be Ti. In this case, the crystal structure of the lithium iron phosphate-based compound is not distorted, so a lithium ion pathway can be secured and the quality of the carbon coating layer can be improved. Specifically, it can prevent the excessive generation of free carbon.

[0080] In the present invention, the doping element (M 1The content of ) may be 500 ppm or more and 6,000 ppm or less based on the total weight of the cathode active material. Preferably, it may be 800 ppm or more, 1,000 ppm or more, 1,200 ppm or more, or 1,500 ppm or more. Additionally, it may be 5,000 ppm or less, 4,000 ppm or less, or 3,000 ppm or less. Within the above numerical range, electrical conductivity, surface reactivity, and mechanical strength due to the doping element may be improved. Furthermore, the adhesion or reactivity between the carbon coating layer and the lithium iron phosphate-based compound is improved, enabling the formation of a uniform carbon coating layer, thereby allowing for a reduction in the free carbon content. On the other hand, if the doping element content falls below the above numerical range, the effect of improving physical properties due to elemental doping may be negligible. Conversely, if the doping element content exceeds the above numerical range, the doping element itself may form an inactive region.

[0081] In the present invention, the doping element (M 1 The content of the doping element may be 0.1 mol% or more and 1.9 mol% or less based on the total molar amount of phosphoric acid (PO4) in the lithium iron phosphate-based compound. Preferably, it may be 0.2 mol% or more, 0.3 mol% or more, 0.4 mol% or more, or 0.5 mol% or more. Additionally, it may be 1.8 mol% or less, 1.6 mol% or less, 1.4 mol% or less, or 1 mol% or less. Within the above numerical range, electrical conductivity, surface reactivity, and mechanical strength may be improved by the doping element. Furthermore, the adhesion or reactivity between the carbon coating layer and the lithium iron phosphate-based compound is improved, enabling the formation of a uniform carbon coating layer, thereby allowing for a reduction in the free carbon content. On the other hand, if the doping element content falls below the above numerical range, the effect of improving physical properties by elemental doping may be negligible. Conversely, if the doping element content exceeds the above numerical range, the doping element itself may form an inactive region.

[0082] In the present invention, the lithium iron phosphate-based compound can be represented by the following chemical formula 1.

[0083] [Chemical Formula 1]

[0084] Li 1+y1 Fe a Mn b M 1 c (PO4)

[0085] In the above chemical formula 1,

[0086] The 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, and

[0087] -0.2≤y1<1, 0<a<1, 0≤b<1, 0≤c<1, a+b+c=1.

[0088] In the present invention, y1 may be -0.2 or greater, -0.1 or greater, or 0 or greater, and may be 0.8 or less, 0.6 or less, 0.4 or less, 0.2 or less, or 0.1 or less. When y1 satisfies the above range, structural stability may be improved.

[0089] In the present invention, the value calculated as a / (a+b) may be 0.5 or more and 1 or less. Additionally, it may be 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 0.95 or more, 0.99 or more, or 1.

[0090] In the present invention, b may be 0. In this case, it may be a lithium iron phosphate-based compound in which manganese is not present in the compound.

[0091] In the present invention, c may be 0 or more and 0.1 or less. Additionally, it may be 0.001 or more, 0.002 or more, 0.003 or more, or 0.005 or more. Additionally, it may be 0.019 or less, 0.018 or less, 0.016 or less, 0.014 or less, or 0.01 or less. The effect of the above numerical range is due to the above-described doping element (M 1 It is identical to the effects and technical significance caused by ).

[0092] In the present invention, the above M 1 It refers to an element that is doped into lithium iron phosphate compounds and can be used to obtain effects such as electrical conductivity and structural stability.

[0093] In the present invention, the above M 1 It may be 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. Meanwhile, to improve chemical or physical performance, other elements may be included in addition to the elements described above, and non-metallic elements such as F, S, and N may also be included to improve electrochemical performance.

[0094] In the present invention, the above M 1 It may be Mg, Al, Ti, V, Co, Ni, Zr, or a combination thereof.

[0095] In the present invention, the above M 1 It may be Mg, Al, Ti, V, Zr, or a combination thereof. The above elements are highly effective for improving lithium ion mobility characteristics or ensuring structural stability, and their effects can be further enhanced depending on the combination used. Specifically, the above M 1It may be one or more types selected from the group consisting of Mg, Al, Ti, V, and Zr.

[0096] In the present invention, the above M 1 When using Mg, the charge and discharge efficiency can be improved by improving the mobility characteristics of lithium ions, and stability can be improved by facilitating the control of lithium iron phosphate-based compound particle growth.

[0097] In the present invention, the above M 1 When using Al, the output characteristics can be improved by enhancing lithium-ion conductivity and improving electrochemical reactivity.

[0098] In the present invention, the above M 1 When using Ti, the free carbon content can be controlled within the aforementioned range. Specifically, when Ti is doped, surface activation of the lithium iron phosphate-based compound is promoted, thereby improving adhesion between the carbon coating layer and the lithium iron phosphate-based compound. Additionally, by controlling the crystal structure of the lithium iron phosphate-based compound, the carbon coating layer can be formed uniformly. In other words, by coating with Ti, the surface characteristics of the lithium iron phosphate-based compound are improved, allowing the free carbon content to be maintained at a low level.

[0099] In the present invention, the above M 1 When using V, electrical conductivity is improved, which can improve power density when applied to lithium secondary batteries.

[0100] In the present invention, the above M 1 When Zr is used, structural strength can be increased to improve durability, and excellent compatibility with the electrolyte can be improved to enhance stability.

[0101] In the present invention, the rolled density of the positive electrode active material under a pressure of 2,000 kgf may be 1.9 g / cc or higher. Preferably, it may be 2 g / cc or higher, 2.05 g / cc or higher, 2.08 g / cc or higher, 2.1 g / cc or higher, or 2.12 g / cc or higher. Within the above numerical range, the energy density is high, which can improve battery capacity when applied to a secondary battery. The above numerical range of rolled density can be achieved by controlling the free carbon content described above to be low. Specifically, by controlling the free carbon content to be low, the space between adjacent positive electrode active materials can be reduced to achieve the numerical range of rolled density. Considering the effects intended by the present invention, a higher rolled density is preferable, so an upper limit is not specifically limited. However, the upper limit may be 10 g / cc or lower or 5 g / cc or lower. The above rolled density can be measured using HPRM-1000. Specifically, 5g of positive active material is placed into a cylindrical mold with a cross-sectional diameter of 1.2cm, and then the mold containing the positive active material is pressed with a force of 2,000kgf, and the height of the mold is then measured with a vernier caliper to obtain the rolling density.

[0102] In the present invention, the resistivity of the positive electrode active material may be 400 Ω·cm or less. Preferably, it may be 300 Ω·cm or less, 250 Ω·cm or less, 200 Ω·cm or less, 180 Ω·cm or less, 170 Ω·cm or less, 160 Ω·cm or less, or 150 Ω·cm or less. Within the above numerical range, electrical conductivity can be improved, thereby enhancing battery performance when applied to a secondary battery. The above numerical range of resistivity can be achieved by controlling the free carbon content described above to a low level. Specifically, by controlling the free carbon content to a low level, the contact between particles within the positive electrode active material can be made uniform, thereby achieving the above numerical range of resistivity. At this time, the measurement temperature of the resistivity may be 25℃.

[0103] In the present invention, the positive electrode active material may further include one or more selected from the group consisting of 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). At this time, these materials may be different from the lithium iron phosphate-based compounds described above and may be named as the second compound.

[0104] In the present invention, the weight ratio of the lithium iron phosphate-based 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.

[0105] The present invention relates to a lithium-containing raw material, an iron-containing raw material, a phosphoric acid-containing raw material, and a doping element (M 1 The method comprises the steps of: preparing a mixture containing a raw material containing ) and a carbon source; and calcining the mixture, wherein the doping element (M 1 A method for manufacturing the above-described positive electrode active material is provided, wherein the content of ) is 0.1 mol% or more and 1.9 mol% or less based on the total molar amount of the above-described phosphoric acid.

[0106] In the present invention, the doping element (M 1The content of ) may be 0.1 mol% or more and 1.9 mol% or less based on the total moles of phosphoric acid (PO4). Preferably, it may be 0.2 mol% or more, 0.3 mol% or more, 0.4 mol% or more, or 0.5 mol% or more. Additionally, it may be 1.8 mol% or less, 1.6 mol% or less, 1.4 mol% or less, or 1 mol% or less. Within the above numerical range, electrical conductivity, surface reactivity, and mechanical strength may be improved by the doping element. Furthermore, the adhesion or reactivity between the carbon coating layer and the lithium iron phosphate-based compound is improved, enabling the formation of a uniform carbon coating layer, thereby allowing for a reduction in the free carbon content. On the other hand, if the doping element content falls below the above numerical range, the effect of improving physical properties by elemental doping may be negligible. Conversely, if the doping element content exceeds the above numerical range, the doping element itself may form an inactive region.

[0107] In the present invention, the calcination temperature of the step of calcining the mixture may be 770°C or higher and 1,000°C or lower. The calcination temperature may be 770°C or higher and 1,000°C or lower. Preferably, it may be 780°C or higher and 980°C or lower, 790°C or higher and 950°C or lower, 800°C or higher and 930°C or lower, or 810°C or higher and 900°C or lower. Within the above numerical range, the reaction between the carbon coating layer and the surface of the lithium iron phosphate-based compound is activated, allowing carbon to be evenly bonded to the surface of the lithium iron phosphate-based compound. If the calcination temperature is lower than the above, carbon may not be sufficiently bonded to the surface of the lithium iron phosphate-based compound and may exist as free carbon, and if the calcination temperature is exceeded, deformation may occur in the crystal structure of the lithium iron phosphate.

[0108] In the present invention, the calcination time of the step of calcining the mixture may be 1 hour to 50 hours. Preferably, it may be 2 hours to 20 hours or 5 hours to 15 hours. Within the above numerical range, the generation of free carbon can be reduced as time is secured for carbon to diffuse evenly onto the surface of the lithium iron phosphate-based compound and for carbon to bond to the lithium iron phosphate-based compound. If the calcination time is insufficient, the carbon coating layer is formed incompletely, and if the calcination time is exceeded, deformation may occur in the crystal structure of the lithium iron phosphate.

[0109] 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 to secure electrochemical properties due to the iron ions.

[0110] 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 remainder of the gas may be hydrogen (H2).

[0111] In the present invention, the step of calcining the mixture can be performed in a furnace.

[0112] 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 is soluble in water. Specifically, lithium carbonate (Li2CO3), lithium hydroxide (LiOH), and 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.

[0113] 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, chemical stability is high, and since the compound itself contains phosphoric acid, the use of additional phosphates can be reduced.

[0114] 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 monohydrogen phosphate (NH4H2PO4), phosphoric acid (H3PO4), etc., and may be used alone or in a mixture of two or more. Preferably, ammonium dihydrogen phosphate or ammonium monohydrogen phosphate may be used. In this case, chemical reaction by-products can be reduced and the pH of the reaction system can be stabilized.

[0115] In the present invention, the doping element (M 1 The raw material containing ) is a doping element (M) comprising 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 It may include ).

[0116] In the present invention, the raw material containing the doping element may be an oxide, chloride, nitrate, sulfate compound, oxalate compound, or a combination thereof of the doping element.

[0117] In the present invention, when the doping element is titanium (Ti), the raw material containing the doping element may be titanium oxide (TiO2). Titanium oxide has excellent thermal stability, so it is maintained without decomposing even during high-temperature heat treatment, and has the effect of excellent reactivity.

[0118] In the present invention, when the doping element is aluminum (Al), the raw material containing the doping element 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 halides, or a combination thereof. Preferably, aluminum hydroxide may be used. In this case, excessive temperature is not required during the doping process, and since no components other than water are detected as byproducts, it is environmentally friendly and has the effect of enabling uniform doping.

[0119] In the present invention, when the doping element is vanadium (V), the raw material containing the doping element 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 since it has excellent heat resistance, it has the effect of stably maintaining the crystal structure of the lithium iron phosphate-based compound during the calcination process.

[0120] In the present invention, when the doping element is magnesium (Mg), the raw material containing the doping element 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 remains intact without decomposing even during high-temperature heat treatment, and has excellent dispersibility, which has the effect of excellent doping efficiency.

[0121] In the present invention, when the doping element is zirconium (Zr), the raw material containing the doping element may be zirconium oxide (ZrO2), zirconium chloride (ZrCl4), or a combination thereof. Preferably, zirconium oxide may be used. Zirconium oxide has excellent thermal stability, so it is maintained without decomposing even during high-temperature heat treatment, and has excellent reactivity and doping efficiency.

[0122] In the present invention, the carbon source is a material that serves as a raw material for a carbon coating layer and may be sucrose, glucose, polyethylene glycol, polyvinyl alcohol, polyvinyl acetate, or a combination thereof. Preferably, it may be sucrose or glucose. In this case, it has the effect of easily thermally decomposing even at low temperatures, thereby facilitating the formation of a carbon coating layer. Furthermore, since sucrose is uniformly carbonized upon heat treatment and glucose is well soluble in water and easily adsorbed onto a lithium iron phosphate-based compound, the carbon coating is uniformly formed and the microstructure is easy to control.

[0123] In the present invention, the solid content of the mixture may be 10 wt% to 40 wt%. Preferably, it may be 15 wt% to 35 wt% or 25 wt% to 35 wt%. 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 solid content of the mixture can be achieved by adding a solvent such as water (H2O).

[0124] In the present invention, the method for manufacturing the positive electrode active material comprises the step of grinding the mixture; the step of drying the mixture or a combination thereof.

[0125] In the present invention, the step of grinding the mixture is a step of breaking the necking between particles and controlling the particle size. In addition, it is possible to maintain a uniform particle size distribution and prevent particles from aggregating with each other.

[0126] In the present invention, the step of grinding the mixture may use bead milling, ball milling, jet milling, ultrasonic milling, or vibratory milling, or a combination thereof.

[0127] 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 is increased, thereby enabling the stable formation and growth of the crystal structure.

[0128] In the present invention, in the step of grinding the mixture, the average particle size (D) of the ground particles 50 :nm) may be 300nm or more and 3,000nm or less. Preferably, it may be 400nm to 2,500nm or 500nm to 2,000nm. Within the above numerical range, the reaction rate increases during the calcination step, and the formation and growth of the crystal structure can be performed stably.

[0129] In the present invention, a step of secondary grinding of the mixture can be performed after the step of calcining the mixture. At this time, the particle size of the final product can be finely controlled.

[0130] 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 calcination process.

[0131] In the present invention, the step of drying the mixture may be performed before the step of grinding the mixture; after the step of grinding the mixture; before the step of calcining the mixture; or in a combination thereof.

[0132] In the present invention, if the step of drying the mixture is performed before the step of grinding the mixture, the mixture is easily broken, and the grinding efficiency is improved.

[0133] In the present invention, if the step of drying the mixture is performed after the step of grinding the mixture, moisture introduced during the grinding step can be removed.

[0134] In the present invention, if the step of drying the mixture is performed prior to the step of calcining the mixture, moisture or impurities within the material are removed, thereby improving reactivity during the calcination process and enhancing crystallinity. If moisture or impurities are not sufficiently removed before calcination, pores formed by them may occur, resulting in defects in the crystal structure.

[0135] In the present invention, the step of drying the mixture may be performed in a temperature range of 50°C to 300°C. Preferably, it may be performed in a temperature range of 80°C to 250°C or 100°C to 200°C. Within these numerical ranges, moisture can be sufficiently removed and thermal deformation of the material can be prevented. The temperature may be the average temperature of the inlet and outlet temperatures when using spray drying.

[0136] In the present invention, the step of drying the mixture may be performed for 10 minutes to 10 hours. Preferably, it may be performed for 30 minutes to 5 hours or 40 minutes to 3 hours. Within these numerical ranges, moisture is sufficiently removed, and thermal deformation of the material can be prevented.

[0137] In the present invention, the step of drying the mixture may be oven drying, vacuum drying, spray drying, or a combination thereof. Preferably, simple mass production can be achieved by using spray drying or oven drying.

[0138] In the present invention, the step of drying the mixture may 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 may be performed at an inlet temperature of 180°C to 270°C and an outlet temperature of 70°C to 110°C, or at 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 thermal denaturation can be prevented. In addition, in the above outlet temperature range, moisture remaining in the powder can be sufficiently removed and thermal denaturation can be prevented.

[0139] The present invention provides a positive electrode comprising the positive electrode active material described above.

[0140] In the present invention, the anode comprises an anode active material layer comprising the anode active material described above. Specifically, the anode comprises an anode current collector and an anode active material layer formed on the anode current collector and comprising the anode active material. Since the anode active material has been described above, a detailed description is omitted, and only the remaining components are described in detail below.

[0141] In the present invention, the positive current collector is not particularly limited as long as it is conductive without causing 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 current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0142] In the present invention, the positive active material layer may include a conductive material and a binder together with the positive active material. At this time, the content of the positive active material may be 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and excellent capacity characteristics may be exhibited within this range.

[0143] In the present invention, the conductive material is used to impart conductivity to the electrode, and can be used without special limitations as long as it has electronic conductivity without causing chemical changes in the battery being constructed. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The content of the conductive material may be 0.1% to 15% by weight with respect to the total weight of the positive electrode active material layer.

[0144] In the present invention, the binder serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The content of the binder may be 0.1% to 15% by weight based on the total weight of the positive active material layer.

[0145] In the present invention, the anode may be manufactured according to a conventional anode manufacturing method, except for using the anode active material. Specifically, it may be manufactured by applying a composition for forming an anode active material layer, prepared by dissolving or dispersing the anode active material and, optionally, a binder and a conductive material in a solvent, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above. Alternatively, the anode may be manufactured by casting the composition for forming an anode active material layer onto a separate support, and then laminating the film obtained by peeling from the support onto an anode current collector.

[0146] 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 alone or a mixture of two or more may be used. The amount of solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0147] The present invention provides an electrochemical device comprising the anode described above. Specifically, the electrochemical device may be a battery, a capacitor, etc., and more specifically, may be a lithium secondary battery.

[0148] The present invention provides a lithium secondary battery comprising the anode described above.

[0149] In the present invention, the lithium secondary battery specifically comprises a positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode. Since the positive electrode is identical to the one described above, a detailed description is omitted, and only the remaining components are described in detail below.

[0150] In the present invention, the lithium secondary battery may optionally further include a battery container that accommodates the electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0151] In the present invention, the cathode comprises a cathode current collector and a cathode active material layer located on the cathode current collector.

[0152] 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., and aluminum-cadmium alloy may be used. In addition, the negative electrode current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0153] The above-mentioned cathode active material layer optionally includes a binder and a conductive material together with the cathode active material.

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

[0155] 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.

[0156] In the present invention, the binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0157] In the present invention, the conductive material may be added as a component to further improve the conductivity of the negative electrode active material in an amount of 10% by weight or less, specifically 5% by weight or less, based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0158] In the present invention, 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 onto a separate support and then laminating the film obtained by peeling from the support onto a negative electrode current collector.

[0159] In the present invention, the separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used in lithium secondary batteries may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0160] In the present invention, the electrolyte may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, etc., which are usable in the manufacture of a lithium secondary battery. Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0161] In the present invention, the organic solvent may be used without special limitations 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 may be an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; or an aromatic hydrocarbon-based solvent such as benzene or fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.In this case, using a mixture of cyclic carbonate and chain carbonate in a volume ratio of about 1:1 to about 1:9 can result in excellent performance of the electrolyte.

[0162] In the present invention, the lithium salt can be used without special limitations 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, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, specifically 0.1 to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0163] In the present invention, in addition to the electrolyte components, the electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10 weight%, specifically 0.1 to 5 weight%, based on the total weight of the electrolyte.

[0164] Since the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent lifespan and capacity characteristics, it is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0165] In the present invention, a battery module comprising the lithium secondary battery as a unit cell and a battery pack comprising the same are provided.

[0166] In the present invention, the battery module or battery pack may be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0167] In the present invention, the external shape of the lithium secondary battery is not particularly limited, but can be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0168] In the present invention, the lithium secondary battery can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells.

[0169] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0170] <Examples and Comparative Examples>

[0171] <Example 1>

[0172] A mixture was prepared by mixing Li2CO3, FePO4, NH4H2PO4, sucrose, and TiO2. At this time, the sucrose content was 8 parts by weight based on 100 parts by weight of the total of Li2CO3, FePO4, and NH4H2PO4.

[0173] The above mixture is wet-milled using a bead mill to obtain a slurry (average particle size D 50 : 100nm) was manufactured.

[0174] The moisture was removed from the above slurry using a spray dryer, the dried slurry was placed in a heat-resistant graphite container (graphite saggar), and calcined in a furnace under a nitrogen atmosphere at a calcination temperature of 800°C for 10 hours, thereby producing a LiFe that is Ti-doped and has a carbon coating layer formed on a portion of its surface. 0.995 Ti 0.005 A lithium iron phosphate-based compound having a composition represented by PO4 was prepared.

[0175] At this time, the Ti content was 0.5 mol% based on the total moles of PO4 and 1,542 ppm based on the total weight of the lithium iron phosphate-based compound.

[0176] <Examples 2 to 14 and Comparative Examples 1 to 3>

[0177] A lithium iron phosphate-based compound was prepared in the same manner as in Example 1, except that the Ti content and calcination temperature were changed to the conditions of Tables 1 and 2 below. At this time, the Ti content (mol%) was based on the total moles of PO4, and the Ti content (ppm) was based on the total weight of the lithium iron phosphate-based compound.

[0178] <Experimental Example>

[0179] <Experimental Example 1: Carbon Content Analysis>

[0180] A sample of 100 mg containing a positive electrode active material containing a lithium iron phosphate-based compound prepared in each of the examples and comparative examples was prepared and placed in a ceramic container.

[0181] Under an oxygen gas (O2) environment, the firing temperature was raised for 800 seconds starting at a first starting temperature (T0) of 400°C to a first ending temperature (T1) of 600°C, and the first ending temperature was maintained for 500 seconds. At this time, the amount of carbon dioxide generated at each firing time was recorded and plotted as a curve, and it was confirmed that two peaks (sequentially, the first peak and the second peak) with maximum carbon dioxide generation values ​​appeared at firing temperatures of 460°C and 550°C, respectively. The area of ​​the first peak was calculated and recorded as the area of ​​the carbon dioxide peak derived from organic carbon, and the area of ​​the second peak was calculated and recorded as the area of ​​the carbon dioxide peak derived from free carbon.

[0182] Under a helium gas (He) environment, the temperature was raised from a second starting temperature of 600°C to a second terminal temperature of 1,100°C over 300 seconds and maintained at the second terminal temperature. At this time, it was confirmed that a third peak appeared at 900°C, where the amount of carbon dioxide generated had a maximum value. The area of ​​the third peak was calculated and recorded as the area of ​​the carbon dioxide peak originating from inorganic carbon.

[0183] In the above calcination process, the experimental results for the cathode active material sample of Example 1 are shown in Fig. 1. Line (a) in Fig. 1 represents the calcination temperature (°C) for each process, and line (b) represents the peaks of carbon dioxide generated in each process. It was confirmed that during the calcination process, the first peak appeared at approximately 460°C, the second peak appeared at approximately 550°C, and the third peak appeared at approximately 900°C.

[0184] Using the following formulas 1 to 3, the absolute weight (mg) of carbon dioxide was calculated by multiplying the area of ​​each carbon dioxide peak by the correction factor k, and the carbon content (ppm) was calculated from this. To calculate the correction factor k, 10 mg of the standard sample below was taken and calcined under the same conditions as described above, and the correction factor k was derived using formulas 1 to 3. The average of the correction factor k values ​​derived by changing the weight of the standard sample to 20 mg, 50 mg, 100 mg, 200 mg, and 500 mg was taken and used as the final correction factor k.

[0185] [Formula 1]

[0186] Carbon content (ppm) = Absolute weight of carbon (mg) / Weight of sample (kg)

[0187] [Formula 2]

[0188] Absolute weight of carbon (mg) = Absolute weight of carbon dioxide (mg) * (Atomic weight of carbon) / (Molecular weight of carbon dioxide)

[0189] [Formula 3]

[0190] Absolute weight of carbon dioxide (mg) = k * (Area of ​​the carbon dioxide emission peak)

[0191] <Sample Information>

[0192] Manufacturer: Thermo Fisher Scientific

[0193] Product Name: BBOT STD

[0194] Product Number (PN): 338 35210

[0195] Molecular formula: C 26 H 26 N2SO2

[0196] Composition: Carbon (72.52 wt%), Hydrogen (6.1 wt%), Nitrogen (6.48 wt%), Sulfur (7.42 wt%), Oxygen (7.39 wt%)

[0197] Meanwhile, the values ​​calculated using the following mathematical formulas 1 to 3 were calculated and recorded in Table 1 and Table 2.

[0198] [Mathematical Formula 1]

[0199] C f / (C f +C o )*100(%)

[0200] [Mathematical Formula 2]

[0201] C i / (C f +C o +C i )*100(%)

[0202] [Mathematical Formula 3]

[0203] Sc / (C f +C o +C i )*100(%)

[0204] In mathematical formulas 1 to 3,

[0205] The above Sc is the average grain size (unit: nm) of the lithium iron phosphate-based compound, a value calculated using Experimental Example 2 described below, and

[0206] The above C f is the free carbon content (unit: ppm) based on the total weight of the cathode active material, and

[0207] The above C o is the organic carbon content (unit: ppm) based on the total weight of the cathode active material, and

[0208] The above C i is the content of inorganic carbon (unit: ppm) based on the total weight of the positive electrode active material.

[0209] <Experimental Example 2: Measurement of Average Grain Size>

[0210] XRD data of the lithium iron phosphate-based compounds prepared in the examples and comparative examples were obtained using a Bruker D8 XRD instrument (Cu-target, voltage: 45kV, current: 40mA, 2θ: 10 to 100 degrees), and the obtained data was measured by proceeding with the Rietveld refining method using Malvern Panalytical's Highscore software and recorded in Tables 1 and 2.

[0211] <Experimental Example 3: Measurement of Rolled Density>

[0212] 5g of the lithium iron phosphate-based compounds prepared in the examples and comparative examples were placed into a cylindrical mold with a cross-sectional diameter of 1.2cm inside a powder physical property measuring device (Manufacturer: Hantech, Product Name: HPRM-1000), and then the mold was pressed with a force of 2,000kgf. Afterward, the height of the mold was measured with a vernier caliper, and the rolling density was calculated and recorded in Tables 1 and 2.

[0213] <Experimental Example 4: Resistivity Measurement>

[0214] Samples were prepared by molding the lithium iron phosphate-based compounds prepared in the examples and comparative examples into cylindrical plates. Electrodes were attached to both sides of the prepared samples, and current was passed through them, after which the voltage drop between the two electrodes was measured. Through this, the resistance value was determined, and the resistivity was calculated by multiplying the cross-sectional area of ​​the sample by the length and dividing by the length, and recorded in Tables 1 and 2.

[0215] <Experimental Example 5: Evaluation of Battery Characteristics>

[0216] Manufacturing of lithium secondary battery half cells

[0217] A positive electrode active material containing a lithium iron phosphate-based compound prepared in each of the examples and comparative examples, a carbon black conductive material, and a polyvinylidene fluoride (PVdF) binder were mixed in an N-methylpyrrolidone solvent in a weight ratio of 90:5:5 to prepare a positive electrode composite, which was then coated on one side of an aluminum current collector, dried at 130°C, and rolled to produce a positive electrode.

[0218] Lithium metal was prepared as the cathode.

[0219] 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, after which an electrolyte was injected into the case to manufacture a lithium secondary battery. At this time, the electrolyte was prepared by dissolving 1M concentration 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).

[0220] Evaluation of charge and discharge characteristics

[0221] For each manufactured lithium secondary battery half cell, the charging capacity and discharging capacity were checked and recorded in Tables 1 and 2 by charging at 25°C in CCCV mode (Constant Current, Constant Voltage) until the voltage reached 4.25V at 0.1C, and after resting for 20 minutes, discharging at a constant current of 0.1C until the voltage reached 2.5V.

[0222] Classification Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Manufacturing Conditions Ti Content (mol%) 0.5 0.5 0.5 1 1 1 1 0.8 0.8 Ti Content (ppm) 1,542 1,542 1,542 3,084 3,084 3,084 3,084 2,467 2,467 Calcination Temperature (°C) 800 780 750 820 800 780 750 820 800 Experimental Example 1 Free Carbon (ppm) 310 415 330 145 195 255 290 80 400 Organic Carbon (ppm) 9,410 10,805 10,5809,6509,3709,905 10,2808,98010,670 Inorganic Carbon (ppm) 565 755 795 4755 70655 800360 730 Formula 1 (%) 3.19 3.70 3.02 1.48 2.042.51 2.740.88 3.61 Formula 2 (%) 5.49 6.36.79 4.63 5.62 6.067.043.82 6.19 Formula 3 (%) 1.82 1.38 1.58 1.93 1.88 1.87 1.59 1.89 1.54 Total Carbon Content (ppm) 10,285 11,975 11,705 10,270 10,135 10,815 11,370 9,420 11,800 Experimental Example 2 Average grain size (nm) 186.68 165.08 184.62 197.94 190.56 201.89 181.17 178.22 181.59 Experimental Example 3 Rolled density (g / cc) 2.14 52.09 82.08 62.13 22.07 12.08 92.09 92.13 52.118 Experimental Example 4 Resistivity (Ω·cm) 46.86 61.45 139.88 3.71 105.21 07.31 66 75.47 43.05 Experimental Example 5 Charge capacity (mAh / g)161.4 164.5 163.4 163.6 165.3 164 164.1 160 162.1 Discharge Capacity (mAh / g)149.1 156.2 156.7 153.9 159.2 157.5 160.1 147.5 155.1

[0223] Classification Example 10 Example 11 Example 12 Example 13 Example 14 Comparative Example 1 Comparative Example 2 Comparative Example 3 Manufacturing Conditions Ti Content (mol%) 0.8 0.7 0.7 0.9 0.9 2 2 2 Ti Content (ppm) 2.46 7 2.15 9 ​​2.15 9 ​​2.77 5 2.77 5 6.16 8 6.16 8 6.16 8 Calcination Temperature (°C) 780 820 800 820 800 800 780 75 0 Experimental Example 1 Free Carbon (ppm) 200 120 110 130 140 980 820 80 5 Organic Carbon (ppm) 10.4 10 10.3 5 10.3 25 9.8 25 9.77 0 9.0 20 8.8 25 9.26 5 Inorganic Carbon (ppm) 600 465 435 455 440 1,565 1,535 1,585 Formula 1 (%) 1.89 1.15 1.05 1.31 1.41 9.80 8.50 7.99 Formula 2 (%) 5.35 4.27 44.37 4.25 13.53 13.73 13.6 Formula 3 (%) 1.65 1.79 1.86 1.89 21 1.06 1.02 Total Carbon Content (ppm) 11,210 10,890 10,870 10,410 10,350 11,565 11,180 11,655 Experimental Example 2 Average Grain Size (nm) 185.05 194.76 202.7196.67 206.81 15.92 118.84 118.67 Experimental Example 3 Rolled Density (g / cc) 2.06 42.10 92.10 52.11 42.10 81.81 21.80 11.817 Experimental Example 4 Resistivity (Ω·cm) 93.15 48.52 70.63 53.92 99.87 421.17 63.39 84.6 Experimental Example 5 Charge Capacity (mAh / g) 163 160.31 61.41 62.81 62.21 62.41 62.310 8.4 Discharge Capacity (mAh / g)156.3149.5150.1152.9152.3161.4161.495.5

[0224] From the above results, it was confirmed that a cathode active material in which the free carbon content is controlled to 800 ppm or less based on the total weight of the cathode active material has a high rolling density, low resistivity, and improved battery capacity (Examples 1 to 14).

[0225] On the other hand, when the free carbon content exceeds 800 ppm based on the total weight of the cathode active material, it was confirmed that the rolling density is low or the resistivity is high (Comparative Examples 1 to 3).

Claims

Lithium iron phosphate-based compounds; and It includes a carbon coating layer provided on part or all of the surface of the above-mentioned lithium iron phosphate-based compound, and A positive electrode active material having a free carbon content of 800 ppm or less based on the total weight of the positive electrode active material. In claim 1, A positive active material having a value of 7% or less calculated by the following mathematical formula 1: [Mathematical Formula 1] C f / (C f +C o )*100(%) In mathematical formula 1, The above C f is the free carbon content (unit: ppm) based on the total weight of the cathode active material, and The above C o is the organic carbon content (unit: ppm) based on the total weight of the positive electrode active material. In claim 1, Anode active material with a value of 13% or less calculated by the following mathematical formula 2: [Mathematical Formula 2] C i / (C f +C o +C i )*100(%) In mathematical formula 2, The above C f is the free carbon content (unit: ppm) based on the total weight of the cathode active material, and The above C o is the organic carbon content based on the total weight of the cathode active material, and The above C i is the content of inorganic carbon based on the total weight of the positive electrode active material. In claim 1, Anode active material with a value of 1.1% or more calculated by the following mathematical formula 3: [Mathematical Formula 3] Sc / (C f +C o +C i )*100(%) In mathematical formula 3, The above Sc is the average grain size (unit: nm) of a lithium iron phosphate-based compound, and The above C f is the free carbon content (unit: ppm) based on the total weight of the cathode active material, and The above C o is the organic carbon content based on the total weight of the cathode active material, and The above C i is the content of inorganic carbon based on the total weight of the positive electrode active material. In claim 1, A cathode active material having a total content of free carbon, organic carbon, and inorganic carbon of 7,000 ppm or more and 20,000 ppm or less based on the total weight of the cathode active material. In claim 1, A positive active material having a carbon coating layer thickness of 10 nm or more and 50 nm or less. In claim 1, The above lithium iron phosphate-based compound comprises one or more doping elements (M) selected from the group consisting of 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, and La. 1 A positive electrode active material containing ). In claim 7, The above doping element (M 1 A positive electrode active material having a content of ) of 500 ppm or more and 6,000 ppm or less based on the total weight of the positive electrode active material. In claim 1, The above lithium iron phosphate-based compound is a positive 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, The 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, and -0.2≤y1<1, 0<a<1, 0≤b<1, 0≤c<1, a+b+c=1. In claim 1, A positive active material having a rolled density of 1.9 g / cc or more under a pressure of 2,000 kgf. In claim 1, A positive active material having a resistivity of 400 Ω·cm or less. In claim 1, A positive electrode active material further comprising one or more selected from the group consisting of 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). Lithium-containing raw materials, iron-containing raw materials, phosphoric acid-containing raw materials and doping elements (M 1 A step of preparing a mixture containing a ) containing raw material and a carbon source; and The method includes the step of calcining the above mixture, The above doping element (M 1 A method for manufacturing an anode active material according to any one of claims 1 to 12, wherein the content of ) is 0.1 mol% or more and 1.9 mol% or less based on the total molar amount of the phosphoric acid. A positive electrode comprising a positive electrode active material according to any one of claims 1 to 12. A lithium secondary battery comprising a positive electrode according to claim 14.

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