Positive electrode active material for rechargeable lithium battery, and rechargeable lithium battery comprising same

Abstract

A positive electrode active material for a rechargeable lithium battery, according to embodiments of the present disclosure, comprises composite particles comprising lithium metal phosphate particles and a carbon coating formed on the lithium metal phosphate particles, wherein the C / Fe ratio of the composite particles measured through X-ray photoelectron spectroscopy (XPS) analysis is 5 to 80.

Description

Cathode active material for lithium secondary batteries and lithium secondary batteries containing the same

[0001] The disclosure of the present application relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery including the same.

[0002]

[0003] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as hybrid vehicles.

[0004] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries are actively being researched and developed due to their high operating voltage and energy density per unit weight, as well as their advantages in charging speed and weight reduction.

[0005] Lithium metal phosphate can be used as a positive electrode active material in a lithium secondary battery.

[0006] As the application scope of lithium secondary batteries expands, longer lifespans, higher capacities, and higher energy densities are required. However, the low ionic conductivity of lithium metal phosphate can degrade the output characteristics of lithium secondary batteries.

[0007]

[0008] According to one aspect of the present disclosure, a positive electrode active material for a lithium secondary battery having improved output characteristics and low-temperature performance can be provided.

[0009] According to one aspect of the present disclosure, a lithium secondary battery having improved output characteristics and low-temperature performance can be provided.

[0010]

[0011] A cathode active material for a lithium secondary battery according to exemplary embodiments of the present disclosure comprises composite particles comprising lithium metal phosphate particles and a carbon coating formed on the lithium metal phosphate particles, wherein the C / Fe ratio of the composite particles is 5 to 80, as defined by the following Equation 1.

[0012] [Formula 1]

[0013] C / Fe ratio = A C / A Fe

[0014] In equation 1, A C is the ratio of the number of carbon atoms on the surface to the total number of atoms on the surface of the composite particle as measured through X-ray photoelectron spectroscopy (XPS) analysis. A Fe is the ratio of the number of iron atoms in the surface to the total number of atoms in the surface as measured through XPS analysis.

[0015] In some embodiments, the XPS analysis may be performed on a square area measuring 0.9 mm in width and 0.9 mm in length at a depth of 10 nm from the surface of the composite particle toward the center.

[0016] In some embodiments, the composite particle includes a plurality of composite particles, the square region includes a plurality of square regions each including two or more of the composite particles, and the standard deviation of the C / Fe ratios measured by performing the XPS analysis on five different square regions among the plurality of square regions may be 20 or less.

[0017] In some embodiments, the C / Fe ratio may be 21 to 70.

[0018] In some embodiments, the content of the carbon coating relative to the total weight of the composite particles may be 1.0 wt% to 1.5 wt%.

[0019] In some embodiments, the lithium metal phosphate particles may be represented by the following chemical formula 1.

[0020] [Chemical Formula 1]

[0021] Li a M- x P y O 4+z

[0022] In chemical formula 1, 0.9≤a≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, -0.1≤z≤0.1, and M includes at least one selected from the group consisting of Fe, Co, Ni, and Mn.

[0023] In some embodiments, the lithium metal phosphate particles further comprise a doping element or a coating element, wherein the doping element or the coating element may each comprise at least one selected from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr.

[0024] A lithium secondary battery according to exemplary embodiments of the present disclosure includes a positive electrode including the positive electrode active material described above, and a negative electrode opposing the positive electrode.

[0025] A method for manufacturing a positive electrode active material for a lithium secondary battery according to exemplary embodiments of the present disclosure includes forming a mixed solution by mixing a lithium source, a metal phosphate, a first carbon source, and a second carbon source. The mixed solution is dried to form a mixture, and the mixture is calcined to form a positive electrode active material for a lithium secondary battery, the positive electrode active material including composite particles including lithium metal phosphate particles and a carbon coating formed on the lithium metal phosphate particles. The composite particles have a C / Fe ratio defined by the following Equation 1 of 5 to 80.

[0026] [Formula 1]

[0027] C / Fe ratio = A C / A Fe

[0028] In equation 1, A C is the ratio of the number of carbon atoms on the surface to the total number of atoms on the surface of the composite particle measured through XPS analysis. A Fe is the ratio of the number of iron atoms in the surface to the total number of atoms in the surface as measured through XPS analysis.

[0029] In some embodiments, the first carbon source may be a high molecular weight carbon source and the second carbon source may be a low molecular weight carbon source.

[0030] In some embodiments, the first carbon source may include at least one selected from the group consisting of polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenol resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt.

[0031] In some embodiments, the second carbon source may comprise at least one selected from the group consisting of glucose, fructose, galactose, lactose, sucrose and maltose.

[0032] In some embodiments, the content of the first carbon source may be from 0.5 wt% to 50 wt% relative to the weight of the second carbon source.

[0033] In some embodiments, the content of the first carbon source may be 10 wt% to 30 wt% relative to the weight of the second carbon source.

[0034] In some embodiments, the firing may be performed at 500°C to 900°C.

[0035]

[0036] According to one embodiment of the present disclosure, the energy density can be maintained or improved while the electrical conductivity and life characteristics of the positive electrode active material are improved.

[0037] According to one embodiment of the present disclosure, electrical conductivity can be improved and output characteristics and life characteristics can be improved throughout the entire region of the composite particles.

[0038] The cathode active material for a lithium secondary battery of the present disclosure and the lithium secondary battery comprising the same can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar and wind power generation. The cathode active material for a lithium secondary battery of the present disclosure and the lithium secondary battery comprising the same can be used in eco-friendly electric vehicles, hybrid vehicles, etc. to prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0039]

[0040] FIG. 1 and FIG. 2 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0041] Figure 3 is an X-ray photoelectron spectroscopy (XPS) analysis graph of the composite particles of Example 3 and Comparative Example 2.

[0042]

[0043] Embodiments according to the disclosure of the present application provide a positive electrode active material for a lithium secondary battery (hereinafter, abbreviated as "positive electrode active material"). In addition, a method for producing the positive electrode active material and a lithium secondary battery (hereinafter, abbreviated as "secondary battery") comprising the positive electrode active material are provided.

[0044] Hereinafter, embodiments of the present disclosure will be described in detail. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0045] In exemplary embodiments, the positive electrode active material may include composite particles comprising lithium metal phosphate particles. The positive electrode active material may include a plurality of composite particles.

[0046] The above lithium metal phosphate particles have an olivine structure and may include a crystal structure represented by the following chemical formula 1.

[0047] [Chemical Formula 1]

[0048] Li a M- x P y O 4+z

[0049] In chemical formula 1, 0.9≤a≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, -0.1≤z≤0.1, and M may include at least one selected from the group consisting of Fe, Co, Ni, and Mn.

[0050] The chemical structure represented by Chemical Formula 1 represents the bonding relationship included in the crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M includes Fe, Co, Ni and / or Mn, and Fe, Co, Ni and / or Mn can serve as the main active element of the positive electrode active material. Chemical Formula 1 is provided to express the bonding relationship of the main active elements and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0051] In one embodiment, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the positive electrode active material or the crystal structure. The auxiliary elements may be incorporated into the crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0052] The auxiliary element may include at least one selected from the group consisting of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may also function as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Fe, Co, Ni, or Mn, for example, Al.

[0053] For example, the positive electrode active material or the lithium metal phosphate particles may include a crystal structure represented by the following chemical formula 1-1.

[0054] [Chemical Formula 1-1]

[0055] Li a M-1 x M2 y P z O 4+b

[0056] In Chemical Formula 1-1, 0.98≤a≤1.56, 0.99≤x≤1.01, 0≤y≤0.05, 0.86≤z≤1.2, -0.1≤b≤0.1 may be satisfied. In Chemical Formula 1-1, M1 may include at least one selected from the group consisting of Fe, Co, Ni, and Mn. In Chemical Formula 1-1, M2 may include at least one selected from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr.

[0057] The above-described positive electrode active material or the lithium metal phosphate particles may further include a coating element or doping element. For example, elements substantially identical to or similar to the above-described auxiliary elements may be used as the coating element or doping element. For example, the above-described elements may be used singly or in combination of two or more.

[0058] For example, M2 in Chemical Formula 1-1 can be provided as a coating element or a doping element.

[0059] The above coating element or doping element may be present on the surface of the lithium metal phosphate particle, or may penetrate through the surface of the lithium metal phosphate particle and be included in the bonding structure represented by the above chemical formula 1 or chemical formula 1-1.

[0060] In one embodiment, the lithium metal phosphate particles may comprise LiFePO4.

[0061] For example, lithium metal phosphate particles may have improved stability and economic efficiency compared to other cathode active material particles.

[0062] In exemplary embodiments, the composite particles may include a carbon coating formed on the lithium metal phosphate particles. The carbon coating may enhance the electrical conductivity of the positive electrode active material, thereby improving the output characteristics of the lithium secondary battery.

[0063] For example, the carbon coating may be formed on at least a portion of the surface of the lithium metal phosphate particles.

[0064] According to some embodiments, the content of the carbon coating relative to the total weight of the composite particles may be 1.0 wt% to 1.5 wt%, and in one embodiment, 1.29 wt% to 1.37 wt%. Within this range, the electrical conductivity of the composite particles may be improved while preventing a decrease in capacity characteristics.

[0065] According to some embodiments, the thickness of the carbon coating may be about 5 nm to 30 nm. Within this range, the electrical conductivity of the composite particles may be improved while preventing a decrease in capacity characteristics.

[0066] In exemplary embodiments, the C / Fe ratio defined by Equation 1 below of the composite particles may be 5 to 80, and in some embodiments, 21 to 70.

[0067] [Formula 1]

[0068] C / Fe ratio = A C / A Fe

[0069] In equation 1, A C is the ratio of the number of carbon atoms on the surface to the total number of atoms on the surface of the composite particle measured through X-ray photoelectron spectroscopy (XPS) analysis, and A Fe is the ratio of the number of iron atoms in the surface to the total number of atoms in the surface as measured through XPS analysis.

[0070] The above XPS analysis can be performed on a square area measuring 0.9 mm in width and 0.9 mm in length at a depth of about 10 nm from the surface of the composite particle toward the center. Accordingly, the reliability of the XPS analysis can be improved and uniform measurement results can be obtained.

[0071] For example, the surface portion of the composite particle may represent the square area.

[0072] In some embodiments, the composite particle may include a plurality of composite particles. For example, two or more composite particles among the plurality of composite particles may be included within the rectangular region. In this case, A of Equation 1 C may be the ratio of the sum of the number of carbon atoms to the sum of the total number of atoms on the surface of the composite particles included in the above square area, and A in Equation 1 Fe It may be the ratio of the sum of the number of iron atoms to the sum of the total number of atoms on the surface of the composite particles contained within the commercial square area.

[0073] Within the above C / Fe ratio range, a carbon coating is sufficiently formed, thereby improving the electrical conductivity and lifespan characteristics of the positive electrode active material, and thus maintaining or improving the energy density.

[0074] When the above C / Fe ratio is less than 5, the portion of the surface of the lithium metal phosphate particles exposed to the outside increases, which may result in deterioration of the output characteristics and life characteristics.

[0075] If the above C / Fe ratio exceeds 80, the thickness of the carbon coating may increase excessively, which may lower the energy density of the secondary battery.

[0076] As described above, the positive electrode active material may include a plurality of composite particles. The square region may include a plurality of square regions, each of which includes two or more of the composite particles.

[0077] In some embodiments, the standard deviation of the C / Fe ratios measured for five different rectangular regions among the plurality of rectangular regions may be 20 or less, and in one embodiment, 15 or less. Within this range, the carbon coating may be uniformly formed in different regions of the composite particle. Accordingly, the electrical conductivity may be enhanced throughout the entire region of the composite particle, and the output characteristics and lifespan characteristics may be improved.

[0078] For example, the positive electrode active material that is the target of the above-described measurement method may be a positive electrode active material manufactured by the manufacturing method described below.

[0079] For example, the positive electrode active material that is the target of the above-described measurement method may be a positive electrode active material recovered from a lithium secondary battery or a positive electrode.

[0080] For example, a lithium secondary battery can be disassembled to obtain a positive electrode. The positive electrode can be placed in an organic solvent (e.g., N-methyl-2-pyrrolidone (NMP)) and maintained for about 5 minutes to dissolve the binder, the positive electrode current collector can be removed, and the organic solvent can be dried to remove the positive electrode.

[0081] After the drying, the remaining positive electrode active material and conductive material can be placed in a container with distilled water, stirred for about 1 hour, and left for about 10 minutes to separate the conductive material and positive electrode active material.

[0082] The separated conductive material in the upper layer of the distilled water can be removed, and the positive electrode active material settled at the bottom of the container can be obtained. The positive electrode active material can be dried in a chamber at about 100°C for about 2 hours and used as a positive electrode active material to be measured for the C / Fe ratio.

[0083] Hereinafter, a method for manufacturing a positive electrode active material including the above-described composite particles is provided.

[0084] A lithium source, a metal phosphate, a first carbon source, and a second carbon source can be dispersed and mixed in distilled water to form a mixed solution. During the mixing process, particles can be pulverized to a target size using a ball mill.

[0085] According to one embodiment, a source of the doping element and / or a source of the coating element described above may be further added to the mixed solution.

[0086] In some embodiments, the lithium source may include lithium carbonate and / or lithium hydroxide.

[0087] In some embodiments, the first carbon source may be a high-molecular weight carbon source, and the second carbon source may be a low-molecular weight carbon source. For example, the molecular weight of the first carbon source may be greater than that of the second carbon source. Accordingly, the carbon coating may be formed more uniformly.

[0088] In some embodiments, the first carbon source may include at least one selected from the group consisting of polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenolic resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene difluoride, polyacrylonitrile, polyvinyl chloride, and asphalt.

[0089] In some embodiments, the second carbon source may include at least one selected from the group consisting of glucose, fructose, galactose, lactose, sucrose, and maltose.

[0090] By introducing the first carbon source and the second carbon source having different molecular weights together at a predetermined mixing ratio, a carbon coating can be uniformly formed on the lithium metal phosphate particles.

[0091] In some embodiments, the content of the first carbon source may be 0.5 wt% to 50 wt% relative to the weight of the second carbon source, and in one embodiment, 10 wt% to 30 wt%. Within this range, a sufficient carbon coating may be uniformly formed while preventing capacity degradation.

[0092] The above mixed solution is dried (e.g., spray dried) to evaporate the distilled water and form a mixture.

[0093] The mixture that has gone through the above drying step is calcined at about 500°C to 900°C for about 5 to 12 hours under a nitrogen atmosphere, and then a classification and de-ironization process is performed to form composite particles including lithium metal phosphate and carbon coating.

[0094] The above firing can be performed, for example, at a temperature of about 600 to 750°C.

[0095] The above composite particles may have a C / Fe ratio of 5 to 80 or 21 to 70.

[0096] FIG. 1 and FIG. 2 are schematic plan views and cross-sectional views, respectively, illustrating a lithium secondary battery according to exemplary embodiments. For example, FIG. 2 is a cross-sectional view taken along line I-I' of FIG. 1 in the thickness direction.

[0097] A lithium secondary battery may include a positive electrode (100) including the positive electrode active material described above and a negative electrode (130) opposite to the positive electrode (100).

[0098] The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) formed on at least one surface of the positive electrode current collector (105).

[0099] The positive electrode current collector (105) may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector (105) may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector (105) may be 10 μm to 50 μm.

[0100] The positive electrode active material layer (110) may include the positive electrode active material described above. The positive electrode active material may include the composite particles described above. For example, the positive electrode active material may include a plurality of composite particles.

[0101] The content of the composite particles in the total weight of the positive electrode active material may be 50 wt% or more. In some embodiments, the content of the composite particles in the total weight of the positive electrode active material may be 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0102] In one embodiment, the positive electrode active material may be substantially composed of the composite particles.

[0103] The above-described positive electrode active material can be mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry can be coated on at least one surface of a positive electrode current collector (105), and then dried and rolled to prepare a positive electrode active material layer (110). The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. The positive electrode active material layer (110) can further include a binder and optionally can further include a conductive agent, a thickener, etc.

[0104] As the above solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used.

[0105] The above binder may include polyvinylidenefluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0106] In one embodiment, a PVDF-based binder may be used as the positive electrode binder. In this case, the amount of binder used to form the positive electrode active material layer (110) may be reduced, while the amount of positive electrode active material may be relatively increased. Accordingly, the output characteristics and capacity characteristics of the secondary battery may be improved.

[0107] The conductive material may be added to enhance the conductivity and / or mobility of lithium ions or electrons of the positive electrode active material layer (110). For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black (e.g., Denka Black), acetylene black, Ketjen Black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3. These may be used alone or in combination of two or more.

[0108] The positive electrode slurry may further include a thickener and / or a dispersant. In one embodiment, the positive electrode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0109] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed on at least one surface of the negative electrode current collector (125).

[0110] For example, the negative electrode current collector (125) may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, etc. These may be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector (125) may be 10 μm to 50 μm.

[0111] The negative electrode active material layer (120) may include a negative electrode active material. A material capable of adsorbing and desorbing lithium ions may be used as the negative electrode active material. For example, the negative electrode active material may be a carbon-based material such as crystalline carbon, amorphous carbon, a carbon composite, or carbon fiber; lithium metal; a lithium alloy; a silicon (Si)-containing material, or a tin (Sn)-containing material. These may be used alone or in combination of two or more.

[0112] The above amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc.

[0113] The above crystalline carbon may include graphitic carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0114] The above lithium metal may include pure lithium metal and / or lithium metal having a protective layer formed thereon for suppressing dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on a negative electrode current collector (125) may be used as the negative electrode active material layer (120). In one embodiment, a lithium thin film layer may also be used as the negative electrode active material layer (120).

[0115] Elements included in the above lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. These may be used alone or in combination of two or more.

[0116] The above silicon-containing material can provide increased capacity characteristics. The above silicon-containing material is Si, SiO x (0 <x<2), 금속 도핑된 SiO x (0 <x<2), 실리콘-탄소 복합체 등을 포함할 수 있다.

[0117] The above metal may include lithium and / or magnesium, and the metal-doped SiO x (0 <x<2)는 금속 실리케이트를 포함할 수 있다.

[0118] The above negative electrode active material can be mixed in a solvent to prepare a negative electrode slurry. After coating / depositing the negative electrode slurry on a negative electrode current collector (125), drying and rolling can be performed to prepare a negative electrode active material layer (120). The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. The negative electrode active material layer (120) can further include a binder and optionally can further include a conductive agent, a thickener, etc.

[0119] The solvent included in the cathode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc. These may be used alone or in combination of two or more.

[0120] The above-described materials that can be used in manufacturing the positive electrode (100) as the binder, conductive agent and thickener can be used.

[0121] In some embodiments, a styrene-butadiene rubber (SBR)-based binder, a carboxymethyl cellulose (CMC)-based binder, a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene, PEDOT)-based binder, or the like may be used as the negative electrode binder. These may be used alone or in combination of two or more.

[0122] In exemplary embodiments, a separator (140) may be interposed between the anode (100) and the cathode (130). The separator (140) may be configured to prevent electrical short-circuiting between the anode (100) and the cathode (130) and to allow ion flow. For example, the thickness of the separator may be 10 μm to 20 μm.

[0123] For example, the separator (140) may include a porous polymer film or a porous nonwoven fabric.

[0124] The above porous polymer film may include a polyolefin polymer such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. These may be used alone or in combination of two or more.

[0125] The above porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0126] The separator (140) may include a ceramic material. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0127] The separator (140) may have a single-layer or multi-layer structure including the above-described polymer film and / or non-woven fabric.

[0128] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of electrode cells may be stacked to form an electrode assembly (150) in the form of, for example, a jelly roll. For example, the electrode assembly (150) may be formed through winding, stacking, z-folding, stack-folding, etc. of the separator (140).

[0129] An electrode assembly (150) may be housed together with an electrolyte within a case (160) to define a lithium secondary battery. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0130] The non-aqueous electrolyte may include a lithium salt as an electrolyte and an organic solvent. For example, the lithium salt may be Li + X - can be expressed as. For example, the anion (X) of the lithium salt - ) as F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (CF3)3PF3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (CF3)4PF2<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (CF3)5PF<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (CF3)6P<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , CF3SO3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , CF3CF2SO3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (CF3SO2)2N<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (FSO2)2N<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , CF3CF2(CF3)2CO<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (CF3SO2)2CH<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (SF5)3C<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (CF3SO2)3C<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , CF3(CF2)7SO3<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , CF3CO2<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , CH3CO2<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , SCN<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> , (CF3CF2SO2)2N<h2 style=";text-align:left;direction:ltr"> - <h2 style=";text-align:left;direction:ltr"> 등을 예시할 수 있다.<h2 style=";text-align:left;direction:ltr"> <h2 style=";text-align:left;direction:ltr">

[0131] Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methylacetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, Tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, propylene sulfite, etc. can be used. These can be used alone or in combination of two or more.

[0132] The above non-aqueous electrolyte may further include additives. The additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc. These may be used alone or in combination of two or more.

[0133] The above cyclic carbonate compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0134] The above fluorine-substituted cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0135] The above sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0136] The above cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0137] The above cyclic sulfite compound may include ethylene sulfite, butylene sulfite, etc.

[0138] The above phosphate compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0139] The above borate compound may include lithium bis(oxalate) borate, etc.

[0140] In some embodiments, a solid electrolyte may be used instead of the non-aqueous electrolyte described above. In this case, the lithium secondary battery may be manufactured in the form of an all-solid-state battery. Furthermore, a solid electrolyte layer may be placed between the positive electrode (100) and negative electrode (130) instead of the separator (140) described above.

[0141] The solid electrolyte may include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte may include Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are positive numbers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , (p, q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li7-xPS6-xCl x (0≤x≤2), Li7-xPS6-xBr x (0≤x≤2), Li7-xPS6-xI x (0≤x≤2) etc. These can be used alone or in combination of two or more.

[0142] In one embodiment, the solid electrolyte may include an oxide-based amorphous solid electrolyte, such as, for example, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0143] As illustrated in FIG. 2, electrode tabs (positive electrode tab and negative electrode tab) may protrude from the positive electrode collector (105) and negative electrode collector (125) belonging to each electrode cell and extend to one side of the case (160). The electrode tabs may be fused together with the one side of the case (160) to form electrode leads (positive electrode lead (107) and negative electrode lead (127)) that extend or are exposed to the outside of the case (160).

[0144] The above lithium secondary battery can be manufactured in a cylindrical, square, pouch or coin shape using, for example, a can.

[0145] The embodiments of the present disclosure described above include the following aspects and can be implemented through at least one of the following aspects.

[0146] A cathode active material for a lithium secondary battery according to a first aspect of the present disclosure comprises composite particles comprising lithium metal phosphate particles and a carbon coating formed on the lithium metal phosphate particles, wherein the C / Fe ratio of the composite particles is 5 to 80 as defined by the following formula 1.

[0147] [Formula 1]

[0148] C / Fe ratio = A C / A Fe

[0149] In equation 1, A C is the ratio of the number of carbon atoms on the surface to the total number of atoms on the surface of the composite particle as measured through X-ray photoelectron spectroscopy (XPS) analysis. A Feis the ratio of the number of iron atoms in the surface to the total number of atoms in the surface as measured through XPS analysis.

[0150] In the first aspect, according to the second aspect, the XPS analysis can be performed on a square area of ​​0.9 mm in width and 0.9 mm in length at a depth of 10 nm from the surface of the composite particle toward the center.

[0151] In the second aspect, according to the third aspect, the composite particle includes a plurality of composite particles, the square region includes a plurality of square regions each including two or more of the composite particles, and the standard deviation of the C / Fe ratios measured by performing the XPS analysis on five different square regions among the plurality of square regions may be 20 or less.

[0152] In any one of the first to third aspects, according to the fourth aspect, the C / Fe ratio may be 21 to 70.

[0153] In any one of the first to fourth aspects, according to the fifth aspect, the content of the carbon coating relative to the total weight of the composite particles may be 1.0 wt% to 1.5 wt%.

[0154] In any one of the first to fifth aspects, according to the sixth aspect, the lithium metal phosphate particles may be represented by the following chemical formula 1.

[0155] [Chemical Formula 1]

[0156] Li a M- x P y O 4+z

[0157] In chemical formula 1, 0.9≤a≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, -0.1≤z≤0.1, and M includes at least one selected from the group consisting of Fe, Co, Ni, and Mn.

[0158] In any one of the first to sixth aspects, according to the seventh aspect, the lithium metal phosphate particles further include a doping element or a coating element, and the doping element or the coating element may each include at least one selected from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr.

[0159] A lithium secondary battery according to an eighth aspect of the present disclosure comprises a positive electrode including a positive electrode active material according to any one of the first to seventh aspects, and a negative electrode opposite to the positive electrode.

[0160] According to a ninth aspect of the present disclosure, a method for producing a positive electrode active material for a lithium secondary battery comprises mixing a lithium source, a metal phosphate, a first carbon source, and a second carbon source to form a mixed solution. The mixed solution is dried to form a mixture, and the mixture is calcined to form a positive electrode active material for a lithium secondary battery comprising composite particles comprising lithium metal phosphate particles and a carbon coating formed on the lithium metal phosphate particles. The C / Fe ratio of the composite particles, defined by the following Equation 1, is 5 to 80.

[0161] [Formula 1]

[0162] C / Fe ratio = A C / A Fe

[0163] In equation 1, A Cis the ratio of the number of carbon atoms on the surface to the total number of atoms on the surface of the composite particle measured through XPS analysis. A Fe is the ratio of the number of iron atoms in the surface to the total number of atoms in the surface as measured through XPS analysis.

[0164] In the ninth aspect, according to the tenth aspect, the first carbon source may be a high molecular carbon source and the second carbon source may be a low molecular carbon source.

[0165] In the ninth aspect or the tenth aspect, according to the eleventh aspect, the first carbon source may include at least one selected from the group consisting of polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenol resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt.

[0166] In the ninth aspect or the eleventh aspect, according to the twelfth aspect, the second carbon source may include at least one selected from the group consisting of glucose, fructose, galactose, lactose, sucrose and maltose.

[0167] In the ninth aspect or the twelfth aspect, according to the thirteenth aspect, the content of the first carbon source may be 0.5 wt% to 50 wt% relative to the weight of the second carbon source.

[0168] In the ninth aspect or the thirteenth aspect, according to the fourteenth aspect, the content of the first carbon source may be 10 wt% to 30 wt% relative to the weight of the second carbon source.

[0169] In the ninth aspect or the fourteenth aspect, according to the fifteenth aspect, the firing can be performed at 500°C to 900°C.

[0170] Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope and technical idea of ​​the present disclosure, and it is also natural that such changes and modifications fall within the scope of the appended claims.

[0171] Examples 1, 5, 6, 8 and 9, and Comparative Examples 1 to 4

[0172] Manufacturing of composite particles

[0173] Lithium carbonate as a lithium source, iron phosphate as a metal phosphate, polyethylene as a first carbon source, and glucose as a second carbon source were added to distilled water, and the particles were mixed and pulverized through a ball mill to form a mixed solution containing LiFePO4.

[0174] The content of the first carbon source relative to the weight of the second carbon source was adjusted as shown in Table 1.

[0175] The mixed solution containing the formed LiFePO4 was dried using a spray dryer equipped with a micro-nozzle shape.

[0176] The dried powder was calcined at about 600°C to 750°C for about 5 to 12 hours under a nitrogen atmosphere, and then subjected to a classification and de-ironization process to produce composite particles having a carbon coating formed on lithium metal phosphate particles.

[0177] Manufacturing of lithium secondary batteries

[0178] A lithium secondary battery was manufactured using the above composite particles as a positive electrode active material.

[0179] Specifically, a positive electrode slurry was prepared by mixing the positive electrode active material, the conductive material Denka Black, and the binder PVDF in a mass ratio of 93:5:2, respectively. The positive electrode slurry was coated on an aluminum current collector, followed by drying and rolling to produce a positive electrode including a positive electrode active material layer. After rolling, the target electrode density of the positive electrode was adjusted to 2.45 g / cc.

[0180] Lithium metal was used as the negative active material.

[0181] The positive and negative electrodes manufactured as described above were notched into circular shapes with diameters of Φ14 and Φ16, respectively, and laminated, and a separator (polyethylene, thickness 13 ㎛) notched into Φ19 was interposed between the positive and negative electrodes to form an electrode cell. ΦN (N is a positive number) represents a circle with a diameter of N mm.

[0182] The above electrode cell was assembled by placing it in a coin cell outer case having a diameter of 20 mm and a height of 1.6 mm, injecting electrolyte, and aging for more than 12 hours so that the electrolyte could be impregnated into the inside of the electrode.

[0183] The electrolyte used was a 1M LiPF6 solution formed using a mixed solvent of EC / EMC (30 / 70; volume ratio).

[0184] The secondary battery manufactured as described above was subjected to charge and discharge (charge conditions: CC-CV 0.1C 3.8V0.05C CUT-OFF, discharge conditions: CC 0.1C 2.5V CUT-OFF).

[0185] Example 2

[0186] Composite particles and a lithium secondary battery were manufactured in the same manner as in Example 1, except that polyvinyl alcohol was used instead of polyethylene as the first carbon source, fructose was used instead of glucose as the second carbon source, and the content of the first carbon source relative to the weight of the second carbon source was adjusted as shown in Table 1.

[0187] Example 3

[0188] Composite particles and a lithium secondary battery were manufactured in the same manner as in Example 1, except that polyethylene glycol was used instead of polyethylene as the first carbon source, galactose was used instead of glucose as the second carbon source, and the content of the first carbon source relative to the weight of the second carbon source was adjusted as shown in Table 1.

[0189] Example 4

[0190] Composite particles and a lithium secondary battery were manufactured in the same manner as in Example 1, except that polyaniline was used instead of polyethylene as the first carbon source, lactose was used instead of glucose as the second carbon source, and the content of the first carbon source relative to the weight of the second carbon source was adjusted as shown in Table 1.

[0191] Example 7

[0192] Composite particles and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the composite particles were fired at about 550°C for about 12 hours under a nitrogen atmosphere and the content of the first carbon source relative to the weight of the second carbon source was adjusted as shown in Table 1.

[0193]

[0194] Experimental example

[0195] (1) XPS analysis - C / Fe ratio measurement

[0196] After the composite particles manufactured according to the above-described examples and comparative examples were applied onto a substrate, XPS analysis was performed under the following conditions. The XPS analysis was performed using an ESCALAB 250Xi device from Thermo Fisher Scientific.

[0197] [XPS Analysis Conditions]

[0198] i) X-ray type: Al k alpha, 1486.68 eV, 900 ㎛ Beam size

[0199] ii) Analyzer: CAE (constant analyzer energy) Mode

[0200] iii) Number of scans: 2(survey scan), 50(narrow scan)

[0201] iv) Pass energy: 150 eV (survey scan), 20 eV (narrow scan)

[0202] Specifically, XPS analysis was performed on a square area measuring 0.9 mm in width and 0.9 mm in length at a depth of about 10 nm from the surface of the composite particles toward the center. The square area contained multiple composite particles.

[0203] A measured through XPS analysis C and A Fe The C / Fe ratio was calculated by substituting it into Equation 1.

[0204] Figure 3 is an XPS analysis graph of the composite particles of Example 3 and Comparative Example 2.

[0205] Referring to Fig. 3, C1s peak and Fe2p peak can be obtained through XPS analysis, and A of Equation 1 can be obtained through the C1s peak and Fe2p. C and A Fe can be measured respectively.

[0206] The C / Fe ratios were measured by performing the XPS analysis described above for the five different square areas, and the standard deviation of the C / Fe ratios was calculated.

[0207] (2) Carbon content measurement

[0208] The carbon content relative to the total weight of the composite particles manufactured according to the above-described examples and comparative examples was measured using a C / S analyzer (carbon / sulfur analyzer, CS844, LECO).

[0209] Specifically, the carbon content in the sample was quantitatively analyzed by detecting CO-2 generated by burning 1 g of a positive electrode active material sample.

[0210] (3) Electrical conductivity measurement

[0211] The electrical conductivity of the composite particles manufactured according to the above-described examples and comparative examples was measured using a powder resistance measuring device (MCP-PD51, Nittoseiko analytech).

[0212] Specifically, 2 g of a positive electrode active material sample was pressurized to a density of approximately 2.0 g / cc, and then the resistance and electrical conductivity of the sample were measured.

[0213] The analysis conditions are as follows.

[0214] Start lane: 1 Ohm

[0215] Voltage limiter: 10 V

[0216] Probe: 4-pin probe (electrode distance 3.0 mm / electrode radius 0.7 mm / sample radius: 10.0 mm)

[0217] (4) Energy density measurement

[0218] The energy density was measured using a program within the battery charging / discharging device based on the capacity measured during a Mars charge (CC-CV 0.1C 3.8V 0.05C CUT-OFF) of a lithium secondary battery manufactured according to the above-described examples and comparative examples.

[0219] The calculation method within the program is as follows.

[0220] Energy density (mWh / g) = Mars charging capacity (mAh / g) x average voltage (V)

[0221] (5) Measurement of the ratio of 1C discharge capacity to 0.1C discharge capacity

[0222] For the lithium secondary batteries manufactured according to the above-described examples and comparative examples, charging (CC-CV 0.5C 3.8V 0.05C CUT-OFF) and discharging (CC 0.1C 2.5V CUT-OFF) were performed at room temperature (25°C), and the discharge capacity was measured. The measured discharge capacity was evaluated as the 0.1C discharge capacity.

[0223] For the lithium secondary batteries manufactured according to the above-described examples and comparative examples, charging (CC-CV 0.5C 3.8V 0.05C CUT-OFF) and discharging (CC 1C 2.5V CUT-OFF) were performed at room temperature (25°C), and the discharge capacity was measured. The measured discharge capacity was evaluated as the 1C discharge capacity.

[0224] The ratio (%) of 1C discharge capacity to 0.1C discharge capacity was calculated by dividing 1C discharge capacity by 0.1C discharge capacity and multiplying by 100.

[0225] (6) Capacity maintenance rate evaluation (500 cycles)

[0226] For the lithium secondary batteries of the above-described examples and comparative examples, charging (CC-CV 0.5C 3.8V 0.05C CUT-OFF) and discharging (CC 0.5C 2.5V CUT-OFF) were repeated 500 times at room temperature (25°C), and the capacity retention rate was evaluated by dividing the discharge capacity at 500 times by the discharge capacity at 1 time and multiplying by 100.

[0227] The content of the first carbon source relative to the weight of the second carbon source in the examples and comparative examples, the measurement results, and the evaluation results are shown in Tables 1 and 2 below.

[0228] First carbon source content (wt%)Carbon content (wt%)C / Fe ratioStandard deviation of C / Fe ratioExample 1301.377010.1Example 2501.34638.5Example 3101.38395.6Example 451.292111.5Example 5300.97817.9Example 6301.527519.1Example 7401.354622.3Example 80.41.03510.5Example 9511.488015.4Comparative example 11001.628825.1Comparative example 201.558218.2Comparative example 3651.32430.5Comparative example 4701.02218.6

[0229] Electrical Conductivity (S / cm) Energy Density (mWh / g) Ratio of 1C discharge capacity to 0.1C discharge capacity (%) Capacity Retention Rate (%, 500cyc) Example 10.9573.190.895 Example 20.8576.990.695 Example 30.6578.790.896 Example 40.4577.391.098 Example 50.5580.190.193 Example 60.7568.591.198 Example 70.5575.290.993 Example 80.5579.190.392 Example 90.7569.491.097 Comparative Example 10.3521.888.787 Comparative Example 20.2543.588.588Comparative example 30.06565.482.482Comparative example 40.01559.178.284

[0230] Referring to Tables 1 and 2, in examples where the C / Fe ratio is 5 to 80, the electrical conductivity, energy density, output characteristics, and capacity retention rate were improved compared to the comparative examples.

[0231] In Example 5, where the carbon content was less than 1.0 wt% relative to the total weight of the composite particles, the electrical conductivity, output characteristics, and life characteristics were relatively deteriorated.

[0232] In Example 6, where the carbon content exceeded 1.5 wt% relative to the total weight of the composite particles, the energy density was relatively reduced.

[0233] In Example 7, where the standard deviation of the C / Fe ratios exceeded 20, the capacity retention rate was relatively reduced.

[0234] In Example 8, where the content of the first carbon source was less than 0.5 wt% relative to the weight of the second carbon source, the electrical conductivity, output characteristics, and life characteristics were relatively deteriorated.

[0235] In Example 9, where the content of the first carbon source exceeds 50 wt% relative to the weight of the second carbon source, the energy density was relatively reduced.

[0236] In comparative examples 1 and 2 where the C / Fe ratio exceeded 80, the energy density was reduced.

[0237] In comparative examples 3 and 4 where the C / Fe ratio was less than 5, the electrical conductivity, output characteristics, and life characteristics were deteriorated.

Claims

1. Lithium metal phosphate particles; and Comprising composite particles comprising a carbon coating formed on the lithium metal phosphate particles, A cathode active material for a lithium secondary battery, wherein the C / Fe ratio of the composite particles is 5 to 80, as defined by the following formula 1: [Formula 1] C / Fe ratio = A C / A Fe (In Equation 1, A C is the ratio of the number of carbon atoms on the surface to the total number of atoms on the surface of the composite particle as measured by X-ray photoelectron spectroscopy (XPS) analysis, and A Fe is the ratio of the number of iron atoms in the surface area to the total number of atoms in the surface area as measured by XPS analysis.

2. A cathode active material for a lithium secondary battery, wherein in claim 1, the XPS analysis is performed on a square area measuring 0.9 mm in width and 0.9 mm in length at a depth of 10 nm from the surface of the composite particle toward the center.

3. In claim 2, the composite particle includes a plurality of composite particles, and the square region includes a plurality of square regions each including two or more of the composite particles. A cathode active material for a lithium secondary battery, wherein the standard deviation of the C / Fe ratios measured by performing the XPS analysis on five different square regions among the plurality of square regions is 20 or less.

4. A cathode active material for a lithium secondary battery, wherein the C / Fe ratio in claim 1 is 21 to 70.

5. A cathode active material for a lithium secondary battery, wherein the content of the carbon coating in claim 1 is 1.0 wt% to 1.5 wt% relative to the total weight of the composite particles.

6. In claim 1, the lithium metal phosphate particle is a positive electrode active material for a lithium secondary battery, represented by the following chemical formula 1: [Chemical Formula 1] Li a M- x P y Oh 4+z (In Chemical Formula 1, 0.9≤a≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, -0.1≤z≤0.1, and M includes at least one selected from the group consisting of Fe, Co, Ni, and Mn).

7. In claim 1, the lithium metal phosphate particles further include a doping element or a coating element, A cathode active material for a lithium secondary battery, wherein the doping element or the coating element comprises at least one selected from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr.

8. A cathode comprising the cathode active material for a lithium secondary battery according to claim 1; and A lithium secondary battery comprising a cathode opposing the positive electrode.

9. A step of forming a mixed solution by mixing a lithium source, a metal phosphate, a first carbon source, and a second carbon source; A step of drying the above mixed solution to form a mixture; and A step of sintering the mixture to form a cathode active material for a lithium secondary battery comprising composite particles including lithium metal phosphate particles and a carbon coating formed on the lithium metal phosphate particles, A method for producing a cathode active material for a lithium secondary battery, wherein the C / Fe ratio of the composite particles is 5 to 80, as defined by the following formula 1: [Formula 1] C / Fe ratio = A C / A Fe (In Equation 1, A C is the ratio of the number of carbon atoms on the surface to the total number of atoms on the surface of the composite particle measured through XPS analysis, and A Fe is the ratio of the number of iron atoms in the surface area to the total number of atoms in the surface area as measured by XPS analysis.

10. A method for producing a positive electrode active material for a lithium secondary battery according to claim 9, wherein the first carbon source is a high molecular carbon source and the second carbon source is a low molecular carbon source.

11. A method for producing a cathode active material for a lithium secondary battery according to claim 9, wherein the first carbon source comprises at least one selected from the group consisting of polyethylene, polyvinyl alcohol, polyethylene glycol, polyaniline, epoxy resin, phenol resin, furfural resin, acrylic resin, polyethylene oxide, polyvinylidene fluoride, polyacrylonitrile, polyvinyl chloride, and asphalt.

12. A method for producing a positive electrode active material for a lithium secondary battery, wherein the second carbon source according to claim 9 comprises at least one selected from the group consisting of glucose, fructose, galactose, lactose, sucrose, and maltose.

13. A method for producing a positive electrode active material for a lithium secondary battery, wherein the content of the first carbon source is 0.5 wt% to 50 wt% relative to the weight of the second carbon source according to claim 9.

14. A method for producing a positive electrode active material for a lithium secondary battery, wherein the content of the first carbon source is 10 wt% to 30 wt% relative to the weight of the second carbon source according to claim 9.

15. A method for producing a positive electrode active material for a lithium secondary battery, wherein the sintering is performed at 500° C. to 900° C. according to claim 9.

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