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

Abstract

A positive active material for a rechargeable lithium battery according to embodiments of the present disclosure comprises lithium metal phosphate particles containing manganese and iron, the proportion of manganese being in a predetermined range.

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] 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 electric and hybrid vehicles.

[0003] 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.

[0004] A lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include an outer packaging material, for example, in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

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

[0006] As the application scope of lithium secondary batteries expands, longer lifespan, higher capacity, and higher energy density are required. However, the low ionic conductivity and energy density of lithium metal phosphate can deteriorate the output characteristics, low-temperature performance, and electrode density of lithium secondary batteries.

[0007] According to one aspect of the present disclosure, a positive electrode active material for a lithium secondary battery having improved output characteristics and lifespan characteristics can be provided.

[0008] According to one aspect of the present disclosure, a lithium secondary battery having improved output characteristics and lifespan characteristics can be provided.

[0009] A cathode active material for a lithium secondary battery according to exemplary embodiments includes lithium metal phosphate particles containing manganese and iron and satisfying the following equation 1.

[0010] [Formula 1]

[0011] (M Mn / (M Mn +M Fe ))*100-1≤Manganese capacity expression rate (%)≤(M Mn / (M Mn +M Fe ))*100+1

[0012] In equation 1, M Mn is the molar ratio of manganese among the metals excluding lithium contained in the lithium metal phosphate particles, and M Fe is the molar ratio of iron among the metals excluding lithium contained in the lithium metal phosphate particles. The manganese capacity development rate (%) is the value obtained by subtracting the SOC of the maximum height peak obtained from a charge graph in which the horizontal axis is the State of Charge (SOC) (%) and the vertical axis is the value obtained by differentiating the voltage (V) by the charge capacity (mAh / g) (dV / dQ).

[0013] In some embodiments, M Mn / (M Mn +M Fe ) can be 0.5 to 0.7.

[0014] In some embodiments, M Fe / (M Mn +M Fe ) can be 0.3 to 0.5.

[0015] In some embodiments, the lithium metal phosphate particles may satisfy Equation 2 below.

[0016] [Formula 2]

[0017] (M Mn / (M Mn +M Fe ))*100-0.5≤Manganese capacity expression rate (%)≤(M Mn / (M Mn +M Fe ))*100+0.5

[0018] In equation 2, M Mn is the molar ratio of manganese among the metals excluding lithium contained in the lithium metal phosphate particles, and M Fe is the molar ratio of iron among the metals excluding lithium contained in the lithium metal phosphate particles. The manganese capacity development rate (%) is the value obtained by subtracting the SOC of the maximum height peak obtained from a charge graph in which the horizontal axis is SOC (%) and the vertical axis is the value obtained by differentiating voltage (V) by charge capacity (mAh / g) (dV / dQ).

[0019] In some embodiments, the lithium metal phosphate particles may comprise a chemical structure or crystal structure represented by the following chemical formula 1.

[0020] [Chemical Formula 1]

[0021] Li a Mn b Fe c P d O 4+e

[0022] In chemical formula 1, 0.9≤a≤1.2, 0.5≤b≤0.7, 0.3≤c≤0.5, 0.9≤d≤1.2, -0.1≤e≤0.1.

[0023] In some embodiments, the lithium metal phosphate particles may further include a doping element or a coating element.

[0024] In some embodiments, the doping element or the coating element may include at least one selected from the group consisting of Ti, V, Na, Mg, Ca, Y, Hf, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr.

[0025] In some embodiments, the content of the doping element or coating element relative to the weight of the lithium metal phosphate particles may be 0.1 wt% to 1 wt%.

[0026] In some embodiments, the lithium metal phosphate particles may include a carbon coating formed on a surface portion.

[0027] In some embodiments, the crystal grain size in the (020) plane direction as measured through X-ray diffraction (XRD) analysis of the lithium metal phosphate particles may be from 175 nm to 600 nm.

[0028] In some embodiments, the crystal grain size can be measured via Equation 3 below.

[0029] [Formula 3]

[0030]

[0031] In Equation 3, L is the crystal grain size (nm), λ is the X-ray wavelength (nm), β is the half width (rad) of the peak of the (020) plane of the lithium metal phosphate particle, and θ is the diffraction angle (rad).

[0032] In some embodiments, the crystal grain size may be from 200 nm to 400 nm.

[0033] A lithium secondary battery according to exemplary embodiments includes a positive electrode including the positive electrode active material for a lithium secondary battery described above, and a negative electrode opposing the positive electrode.

[0034] According to one embodiment of the present disclosure, the energy density of the positive electrode active material can be improved.

[0035] According to one embodiment of the present disclosure, the output characteristics, low-temperature / high-temperature characteristics, initial efficiency, rate characteristics, and life characteristics of a lithium secondary battery can be improved.

[0036] 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-using 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.

[0037] FIG. 1 and FIG. 2 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0038] Figure 3 is a graph showing the voltage according to the state of charge (SOC) of the embodiments and comparative examples.

[0039] Figure 4 is a graph in which the state of charge (SOC) is on the horizontal axis and the voltage is differentiated by the charge capacity (dV / dQ) on the vertical axis in the embodiments and comparative examples.

[0040] Embodiments of the present disclosure provide a positive electrode active material for a lithium secondary battery (hereinafter, abbreviated as “positive electrode active material”) comprising lithium metal phosphate particles. In addition, a lithium secondary battery (hereinafter, abbreviated as “secondary battery”) comprising the positive electrode active material for a lithium secondary battery is provided.

[0041] 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.

[0042] In exemplary embodiments, the cathode active material comprises lithium metal phosphate particles containing manganese (Mn) and iron (Fe). Accordingly, the structural and chemical stability of the cathode active material can be improved, while the energy density can be enhanced through the manganese.

[0043] In some embodiments, the lithium metal phosphate particles have an olivine structure and may include a chemical structure or crystal structure represented by the following chemical formula 1.

[0044] [Chemical Formula 1]

[0045] Li a Mn b Fe c P d O 4+e

[0046] In chemical formula 1, 0.9≤a≤1.2, 0.5≤b≤0.7, 0.3≤c≤0.5, 0.9≤d≤1.2, -0.1≤e≤0.1.

[0047] The chemical structure or crystal structure represented by Chemical Formula 1 represents the bonding relationship included in the chemical structure or crystal structure of the lithium metal phosphate particle and does not exclude other additional elements. For example, in Chemical Formula 1, Mn and / or Fe may 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 element and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0048] In one embodiment, the lithium metal phosphate particles may further include auxiliary elements to enhance the chemical stability of the cathode active material or the crystal structure in addition to the main active element. The auxiliary elements may be incorporated into the chemical structure or 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.

[0049] The auxiliary element may include at least one selected from the group consisting of, for example, Ti, V, Na, Mg, Ca, Y, Hf, 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 act as an auxiliary active element contributing to the capacity / output activity of the positive electrode active material, for example, together with Mn and / or Fe.

[0050] According to some embodiments, the lithium metal phosphate particles may further include a coating element or doping element. For example, elements substantially identical to or similar to the auxiliary elements described above 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.

[0051] 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.

[0052] In some embodiments, the content of the doping element or coating element relative to the weight of the lithium metal phosphate particles may be 0.1 wt% to 1 wt%. Within this range, the ionic conductivity of the lithium metal phosphate particles may be improved, manganese dissolution, etc. may be suppressed, and structural stability may be improved.

[0053] In exemplary embodiments, the lithium metal phosphate particles satisfy the following equation 1.

[0054] [Formula 1]

[0055] (M Mn / (M Mn +M Fe ))*100-1≤Manganese capacity expression rate (%)≤(M Mn / (M Mn +M Fe ))*100+1

[0056] In equation 1, M Mn is the molar ratio of manganese among the metals excluding lithium contained in the lithium metal phosphate particles, and M Fe is the molar ratio of iron among the metals excluding lithium contained in the above lithium metal phosphate particles.

[0057] In Equation 1, the manganese capacity development rate (%) is the SOC of the highest peak (e.g., the peak with the highest height) obtained from a charge graph with the horizontal axis representing the state of charge (SOC) (%) and the vertical axis representing the value (dV / dQ) obtained by differentiating voltage (V) by charge capacity (mAh / g). This value is obtained by subtracting the SOC of the highest peak (e.g., the peak with the highest height) from 100.

[0058] For example, the manganese capacity development rate can represent the actual capacity contribution rate of manganese and iron contained in lithium metal phosphate particles.

[0059] For example, in equation 1 (M Mn / (M Mn +M Fe ))*100 can represent the theoretical capacity contribution rate of manganese among manganese and iron contained in lithium metal phosphate particles.

[0060] According to Equation 1, the theoretical capacity contribution rate (e.g., (M in Equation 1)) of manganese and iron contained in lithium metal phosphate particles is compared to the actual capacity contribution rate (e.g., the manganese capacity development rate) of manganese. Mn / (M Mn +M Fe ))*100) may be less than 1%. Accordingly, the capacity development of manganese contained in the lithium metal phosphate particles may be sufficiently performed, thereby improving the energy density of the cathode active material. Accordingly, the output characteristics, low / high temperature characteristics, initial efficiency, rate characteristics, and life characteristics of a lithium secondary battery including the cathode active material may be improved.

[0061] The above SOC may be a normalized value of the charge capacity of a lithium secondary battery during charging on a scale of 0% to 100%.

[0062] In exemplary embodiments, after a Mars charge / discharge is performed on a lithium secondary battery, the lithium secondary battery is charged once and the voltage change according to SOC can be measured and displayed in a graph (see FIG. 3).

[0063] For example, there may be an iron-derived plateau at about 3.5 V in the graph above, and a manganese-derived plateau at about 4.1 V. Accordingly, manganese may provide a higher charge voltage than iron and may have a larger capacity contribution than iron.

[0064] For example, iron may be oxidized before manganese. Accordingly, iron-derived plateaus may appear at relatively low SOCs, and manganese-derived plateaus may appear at relatively high SOCs. For example, an inflection point may exist between the iron-derived plateaus and the manganese-derived plateaus.

[0065] For example, a differential graph can be obtained by using the voltage of the graph as a value differentiated by the charge capacity or SOC along the vertical axis and using SOC along the horizontal axis. The SOC of the maximum height peak can represent the SOC at the point with the maximum height of the differential graph.

[0066] For example, the SOC of the maximum height peak of the above differential graph may be the SOC at the inflection point of the graph. For example, the SOC of the maximum height peak may indicate the point at which oxidation of manganese begins after oxidation of iron.

[0067] In some embodiments, M of Equation 1 Mn / (M Mn +M Fe) may be 0.5 to 0.7. In the above range, the energy density of the positive electrode active material can be sufficiently improved while the structural / chemical stability can be improved.

[0068] In some embodiments, M Fe / (M Mn +M Fe ) can be 0.3 to 0.5. In the above range, the energy density can be improved while the structural / chemical stability of the positive electrode active material is improved. For example, M Mn and M Fe may have the same meaning as the above formula 1.

[0069] In some embodiments, the lithium metal phosphate particles may satisfy Equation 2 below.

[0070] [Formula 2]

[0071] (M Mn / (M Mn +M Fe ))*100-0.5≤Manganese capacity expression rate (%)≤(M Mn / (M Mn +M Fe ))*100+0.5

[0072] In equation 2, M Mn , M Fe And the manganese capacity expression rate may have the same meaning as the above formula 1.

[0073] According to Equation 2, the theoretical capacity contribution rate (e.g., (M in Equation 1)) of manganese and iron contained in lithium metal phosphate particles is compared to the actual capacity contribution rate (e.g., the manganese capacity development rate) of manganese. Mn / (M Mn +M Fe ))*100) may be less than 0.5%. Accordingly, the energy density of the positive electrode active material may be further improved, and the output characteristics, low-temperature / high-temperature characteristics, initial efficiency, rate characteristics, and life characteristics of the lithium secondary battery may be further improved.

[0074] In some embodiments, the lithium metal phosphate particles may include a carbon coating formed on their surface. Accordingly, the electrical conductivity of the positive electrode active material may be improved, thereby enhancing output characteristics.

[0075] For example, the content of the carbon coating may be 0.5 wt% to 3.0 wt% relative to the total weight of the lithium metal phosphate particles. Within this range, the output characteristics may be sufficiently improved while the deterioration of the low-temperature characteristics of the positive electrode active material may be suppressed.

[0076] In some embodiments, the crystal grain size in the (020) plane direction as measured through X-ray diffraction (XRD) analysis of the lithium metal phosphate particles may be 175 nm to 600 nm, and in some embodiments, 200 nm to 400 nm. In this range, the structural stability of the positive electrode active material may be improved while the manganese capacity development rate is improved.

[0077] In some embodiments, the grain size of the lithium metal phosphate particles in the (020) plane direction can be measured through the Scherrer equation represented by Equation 3 below.

[0078] [Formula 3]

[0079]

[0080] In Equation 3, L represents the crystal grain size (nm), λ represents the X-ray wavelength (nm), β represents the half width (rad) of the (020) plane peak of the lithium metal phosphate particle, and θ represents the diffraction angle (rad).

[0081] In some embodiments, β in Equation 3 above can be a half-width corrected for the equipment-derived value. In one embodiment, Si can be used as a standard material to reflect the equipment-derived value. In this case, the half-width profile of Si over the entire 2θ range can be fitted to express the equipment-derived half-width as a function of 2θ. Then, the value obtained by subtracting the equipment-derived half-width value at the corresponding 2θ from the function can be used as β.

[0082] In exemplary embodiments, the manganese capacity development rate of Equation 1 can be controlled by comprehensively controlling the physical properties such as the molar ratio of manganese to iron contained in the lithium metal phosphate particles, the addition of doping elements or coating elements, carbon coating, and grain size in the (020) plane direction. In addition, the manganese capacity development rate of Equation 1 can be controlled by controlling the process conditions such as the mixing method of the manganese source and the iron source (liquid mixing or dry mixing), whether or not to perform high-temperature heat treatment before chemical charge / discharge, and the sintering temperature and time together with the above physical properties.

[0083] The manganese capacity development rate of Equation 1 does not entirely depend on any of the above-described physical properties and process conditions, and lithium metal phosphate particles satisfying Equation 1 can be formed by appropriately controlling each of the above-described physical properties and process conditions based on the disclosure of the present application.

[0084] 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.

[0085] The structures illustrated in FIGS. 1 and 2 are examples for convenience of explanation, and the structure of the lithium secondary battery according to embodiments of the present disclosure is not limited thereto.

[0086] 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).

[0087] 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).

[0088] 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.

[0089] The positive electrode active material layer (110) may include the positive electrode active material described above.

[0090] The positive electrode active material may include a plurality of the above-described lithium metal phosphate particles. The content of the lithium metal phosphate particles in the total weight of the positive electrode active material may be 50 wt% or more. In some embodiments, the content of the lithium metal phosphate 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.

[0091] In one embodiment, the positive electrode active material may consist essentially of lithium metal phosphate particles.

[0092] 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.

[0093] As the above solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used.

[0094] 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.

[0095] 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.

[0096] 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, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, etc., and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc. These may be used alone or in combination of two or more.

[0097] 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).

[0098] 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).

[0099] 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.

[0100] 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.

[0101] The above amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbead (MCMB), mesophase pitch-based carbon fiber (MPCF), etc.

[0102] The above crystalline carbon may include graphitic carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0103] 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).

[0104] 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.

[0105] 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.

[0106] The above metal may include lithium and / or magnesium, and the metal-doped SiO x (0 <x<2)는 금속 실리케이트를 포함할 수 있다.

[0107] 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.

[0108] 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.

[0109] The above-described materials that can be used in manufacturing the positive electrode (100) as the binder, conductive agent and thickener can be used.

[0110] 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.

[0111] 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.

[0112] For example, the separator (140) may include a porous polymer film or a porous nonwoven fabric.

[0113] 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, and an ethylene / methacrylate copolymer. These may be used alone or in combination of two or more.

[0114] The above porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0115] 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.

[0116] The separator (140) may have a single-layer or multi-layer structure including the above-described polymer film and / or non-woven fabric.

[0117] 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).

[0118] 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.

[0119] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - is expressed as and the anion of the lithium salt (X - ) as F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 -, CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples include:

[0120] 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, and propylene sulfite can be used. These can be used alone or in combination of two or more.

[0121] 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.

[0122] The above cyclic carbonate compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0123] The above fluorine-substituted cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0124] The above sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0125] The above cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0126] The above cyclic sulfite compound may include ethylene sulfite, butylene sulfite, etc.

[0127] The above phosphate compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0128] The above borate compound may include lithium bis(oxalate) borate, etc.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] As illustrated in FIG. 3, 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).

[0133] The above lithium secondary battery can be manufactured in a cylindrical, square, pouch or coin shape using, for example, a can.

[0134] 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.

[0135] Example 1

[0136] Preparation of lithium metal phosphate particles

[0137] MnPO4 powder, FePO4 powder, Li2CO 3-- Powder, TiO -2Powder and glucose were added to distilled water, and zirconia balls were added, mixed and ground using a ball mill. The total content of powder was 50 wt% based on the total weight of the mixture. The input amounts of MnPO4 powder and FePO4 powder were adjusted so that the molar ratio of Mn and Fe was 6:4. The input amount of TiO2 powder was adjusted so that the Ti content was 0.5 wt% based on the total weight of lithium metal phosphate particles. The content of glucose based on the total weight of lithium metal phosphate particles was 10 wt%.

[0138] The above mixing and grinding were performed at 200 rpm for 60 minutes to prepare a slurry. The zirconia balls were removed, and the slurry was spray-dried to obtain a mixture powder.

[0139] The above mixture powder is put into a firing chamber, nitrogen (N2) gas is injected into the firing chamber, and fired at 650°C for 4 hours to produce a Ti-doped and carbon-coated preliminary lithium metal phosphate (LiMn 0.6 Fe 0.4 PO4) particles were obtained.

[0140] The above-mentioned lithium metal phosphate particles were ground and classified using a jet mill to produce lithium metal phosphate particles having a particle size of 1.5 μm.

[0141] Manufacturing of lithium secondary batteries

[0142] The above lithium metal phosphate particles were used as a cathode active material.

[0143] The positive electrode slurry was prepared by mixing the positive electrode active material, Denka Black as a conductive agent, and PVDF as a binder in a mass ratio of 93:5:2. The positive electrode slurry was coated on an aluminum current collector (15 μm thick), dried, and rolled to prepare a positive electrode including a positive electrode active material layer.

[0144] Lithium metal (Li metal) was used as the negative active material.

[0145] The manufactured positive and negative electrodes 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) can represent a circle with a diameter of N mm.

[0146] 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 (CR2016) and injecting electrolyte, and aging was performed for more than 12 hours so that the electrolyte could be impregnated into the inside of the electrode.

[0147] A 1M LiPF6 solution prepared using a mixed solvent of EC / EMC (30 / 70; volume ratio) was used as the electrolyte.

[0148] The lithium secondary battery manufactured as described above was subjected to charge and discharge (charge condition CC-CV 0.1C 3.8V 0.05C CUT-OFF, discharge condition CC 0.1C 2.5V CUT-OFF).

[0149] Examples 2 to 5 and 7 to 10

[0150] A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the input amounts of MnPO4 powder and FePO4 powder were adjusted so that the molar ratio of Mn and Fe was as described in Table 2 below, and the input amount of TiO2 was adjusted so that the content of Ti relative to the total weight of lithium metal phosphate particles was as described in Table 2 below.

[0151] Chemical formula of the preliminary lithium metal phosphate particles (LiMn in Example 1) 0.6 Fe 0.4 PO4) was changed according to the molar ratio of Mn and Fe.

[0152] Example 6

[0153] A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the amounts of MnPO4 powder and FePO4 powder were adjusted so that the molar ratio of Mn and Fe was as described in Table 2 below, and that the same amount of V was added instead of Ti.

[0154] Chemical formula of the preliminary lithium metal phosphate particles (LiMn in Example 1) 0.6 Fe 0.4 PO4) was changed according to the molar ratio of Mn and Fe.

[0155] Example 11

[0156] Manufactured LiMn 0.6 Fe 0.4 A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that PO4 particles and citric acid were mixed and calcined at 400°C for 6 hours to form a carbon coating.

[0157] The amount of citric acid added was adjusted so that the content of the carbon coating was 2.5 wt% relative to the total weight of the lithium metal phosphate particles.

[0158] Example 12

[0159] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above-mentioned calcination was performed at 500°C for 4 hours.

[0160] Example 13

[0161] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above-mentioned calcination was performed at 500°C for 6 hours.

[0162] Example 14

[0163] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above-mentioned calcination was performed at 650°C for 6 hours.

[0164] Example 15

[0165] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above-mentioned calcination was performed at 700°C for 4 hours.

[0166] Example 16

[0167] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above-mentioned calcination was performed at 480°C for 4 hours.

[0168] Example 17

[0169] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above-mentioned calcination was performed at 700°C for 5 hours.

[0170] Example 18

[0171] A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the input amounts of MnPO4 powder and FePO4 powder were adjusted so that the molar ratio of Mn and Fe was as described in Table 2 below, the input amount of TiO2 was adjusted so that the content of Ti relative to the total weight of lithium metal phosphate particles was as described in Table 2 below, and the calcination was performed at 700°C for 6 hours.

[0172] Chemical formula of the preliminary lithium metal phosphate particles (LiMn in Example 1) 0.6 Fe 0.4 PO4) was changed according to the molar ratio of Mn and Fe.

[0173] For the manufactured lithium secondary battery, ignition charging was performed at 45°C, and after lowering the chamber temperature to room temperature, ignition discharging was performed approximately 12 hours later.

[0174] Example 19

[0175] As raw materials, Mn(NO3)2·4H2O powder and Fe(NO3)3·9H2O powder were added to pure water and mixed to form an aqueous solution, and NH4H2PO4 powder and Li2CO were added. 3--Powder, glucose powder and TiO -2 The powders were introduced and mixed. The input amounts of Mn(NO3)2·4H2O powder and Fe(NO3)3·9H2O powder were adjusted so that the molar ratio of Mn and Fe was 6:4. The input amount of TiO2 powder was adjusted so that the Ti content was 0.5 wt% relative to the total weight of lithium metal phosphate particles. The glucose content relative to the total weight of lithium metal phosphate particles was 10 wt%.

[0176] The above mixing was performed in a stirring reactor at 1000 rpm for 5 hours. The solid precipitated after the mixing was dried and then placed in a calcination chamber. Nitrogen (N2) gas was introduced into the calcination chamber and calcined at 700°C for 4 hours to produce a Ti-doped and carbon-coated preliminary lithium metal phosphate (LiMn 0.6 Fe 0.4 PO4) particles were obtained.

[0177] The above-mentioned lithium metal phosphate particles were ground and classified using a jet mill to produce lithium metal phosphate particles having a particle size of 1.5 μm.

[0178] Except for the above, a lithium secondary battery was manufactured in the same manner as in Example 1.

[0179] Example 20

[0180] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 19, except that TiO2 powder was not added as a raw material.

[0181] For the manufactured lithium secondary battery, ignition charging was performed at 45°C, and after lowering the chamber temperature to room temperature, ignition discharging was performed approximately 12 hours later.

[0182] Comparative Example 1

[0183] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that TiO2 was not added as a raw material and the calcination was performed at 680°C for 4 hours.

[0184] Comparative Example 2

[0185] A positive electrode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that TiO2 was not added as a raw material and the calcination was performed at 680°C for 4 hours.

[0186] Comparative Example 3

[0187] A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the sintering was performed at 650°C for 6 hours and the amount of TiO2 powder added was adjusted so that the Ti content was 0.05 wt% relative to the total weight of lithium metal phosphate particles.

[0188] Comparative Example 4

[0189] A cathode active material and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the sintering was performed at 650°C for 15 hours and the amount of TiO2 powder added was adjusted so that the Ti content was 0.2 wt% relative to the total weight of lithium metal phosphate particles.

[0190] For the manufactured lithium secondary battery, ignition charging was performed at 45°C, and after lowering the chamber temperature to room temperature, ignition discharging was performed approximately 12 hours later.

[0191]

[0192] Experimental example

[0193] (1) Measurement of crystal grain size

[0194] The crystal grain size of lithium metal phosphate particles manufactured according to the above-described examples and comparative examples was calculated using XRD analysis and Equation 3.

[0195] Specific XRD analysis equipment / conditions are as listed in Table 1 below.

[0196] XRD (X-Ray Diffractometer) EmpyreanmakerPanalyticalanode MaterialCuk-Alpha1 Wavelength1.540598 åGenerator VOLTAGE45 Kvtube Current40 MASCAN Range10 ~ 120 o Scan Step Size 0.0065 o Divergence slit1 / 4 o Antiscatter slit1 / 2 o

[0197] (2) Measurement of manganese capacity development rate

[0198] A graph was obtained by measuring the voltage change according to SOC while charging the lithium secondary battery manufactured according to the above-described examples and comparative examples once.

[0199] A differential graph was obtained using the voltage of the graph differentiated by the charge capacity (dV / dQ) as the vertical axis and the SOC (%) as the horizontal axis. The SOC at the point with the maximum height of the differential graph was defined as the SOC of the maximum height peak. The manganese capacity development rate was measured by subtracting the SOC of the maximum height peak from 100.

[0200] The voltage change according to SOC was measured using Toyo System's TOSCAT-3100 (specification: 5V / 100mA), and the capacity data by voltage was obtained using the TOSCAT Graph program.

[0201] Figure 3 is a graph showing the voltage according to the state of charge (SOC) of Example 1 and Comparative Examples 1 to 3.

[0202] Figure 4 is a graph in which the state of charge (SOC) is plotted on the horizontal axis and the voltage is differentiated by the charge capacity (dV / dQ) on the vertical axis in Example 1 and Comparative Examples 1 to 3.

[0203] (3) Measurement of initial charge / discharge capacity and evaluation of initial capacity efficiency

[0204] The lithium secondary batteries manufactured according to the above-described examples and comparative examples were charged (CC-CV 0.1C 4.3V 0.05C CUT-OFF) in a 25°C chamber, and then the battery capacity (initial charge capacity) was measured. Then, the batteries were discharged again (CC 0.1C 2.5V CUT-OFF), and then the battery capacity (initial discharge capacity) was measured.

[0205] The initial capacity efficiency was evaluated by converting the value obtained by dividing the measured initial discharge capacity by the measured initial charge capacity into a percentage (%).

[0206] (4) Rate characteristic evaluation

[0207] For the lithium secondary batteries manufactured according to the above-described examples and comparative examples, charging (CC-CV 0.5C 4.3V 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.

[0208] For the lithium secondary batteries manufactured according to the above-described examples and comparative examples, charging (CC-CV 0.5C 4.3V 0.05C CUT-OFF) and discharging (CC 0.33C 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 0.33C discharge capacity.

[0209] For lithium secondary batteries manufactured according to the above-described examples and comparative examples, charging (CC-CV 0.5C 4.3V 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.

[0210] The lithium secondary batteries manufactured according to the above-described examples and comparative examples were charged (CC-CV 0.5C 4.3V 0.05C CUT-OFF) and discharged (CC 2C 2.5V CUT-OFF) at room temperature (25°C), and the discharge capacity was measured. The measured discharge capacity was evaluated as the 2C discharge capacity.

[0211] The ratio of 0.33C discharge capacity to 0.1C discharge capacity (0.33C / 0.1C)(%) was calculated by dividing the 0.33C discharge capacity by the 0.1C discharge capacity.

[0212] The ratio of 1C discharge capacity to 0.1C discharge capacity (1C / 0.1C)(%) was calculated as a percentage by dividing the 1C discharge capacity by the 0.1C discharge capacity.

[0213] The ratio of 2C discharge capacity to 0.1C discharge capacity (2C / 0.1C)(%) was calculated as a percentage by dividing the 2C discharge capacity by the 0.1C discharge capacity.

[0214] (5) Evaluation of low-temperature output characteristics

[0215] For the lithium secondary batteries manufactured according to the above-described examples and comparative examples, charging (CC-CV 0.5C 4.3V 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 room temperature discharge capacity.

[0216] For lithium secondary batteries manufactured according to the above-described examples and comparative examples, charging (CC-CV 0.5C 4.3V 0.05C CUT-OFF) and discharging (CC 0.1C 2.5V CUT-OFF) were performed at low temperature (-7°C), and the discharge capacity was measured. The measured discharge capacity was evaluated as the low-temperature discharge capacity.

[0217] The low-temperature output characteristics (%) were calculated as a percentage by dividing the low-temperature discharge capacity by the room-temperature discharge capacity.

[0218] (6) Evaluation of high-temperature storage characteristics (high-temperature capacity retention rate) - 60 ℃

[0219] After the lithium secondary batteries according to the above-described examples and comparative examples were left in a 60°C chamber for 8 weeks, they were charged (CC-CV 0.1C 4.3V 0.05C CUT-OFF) and discharged (CC 0.1C 2.5V CUT-OFF) and the discharge capacity was measured.

[0220] The above discharge capacity was divided by the initial discharge capacity measured in Experimental Example (3) and calculated as a percentage.

[0221] (7) Evaluation of room temperature capacity retention rate - 25 ℃

[0222] For lithium secondary batteries according to examples and comparative examples, charging (CC-CV 0.5C 4.3V 0.01C CUT-OFF) and discharging (CC 0.1C 2.5V CUT-OFF) were repeated 50 times, and the capacity retention rate was evaluated as a percentage of the discharge capacity at 50 times divided by the discharge capacity at 1 time.

[0223] The molar ratio of Mn and Fe, the content of doping element (Ti or V) relative to the total weight of lithium metal phosphate particles, and the crystal grain size in the (020) plane direction of the above-described examples and comparative examples are shown in Table 2 below.

[0224] Among the measurement and evaluation results described above, the crystal grain size is shown in Table 2 below, and the remaining measurement and evaluation results are shown in Tables 3 and 4 below.

[0225] Manganese capacity development rate and 100*M of Equation 1 Mn / (M Mn +M Fe ) The absolute value of the difference (difference in manganese capacity expression rate) is shown in Table 3.

[0226] Mn:Fe Molar undoped element (Ti or V) content (wt%) (020) Grain size (nm) in the direction of the plane Example 16:40.5215 Example 25:50.5212 Example 37:30.5230 Example 44.5:5.50.5210 Example 57.5:2.50.5254 Example 66:40.5245 Example 76:40.4208 Example 86:41.0210 Example 96:40.08264 Example 106:41.1218 Example 116:40.5217 Example 126:40.5175 Example 136:40.5197 Example 146:40.5376 Example 156:40.5600 Example 166:40.5173 Example 176:40.5604 Example 187.5:2.51.1216 Example 196:40.5406 Example 206:40.289 Comparative Example 16:40.5255 Comparative Example 26.5:3.50513 Comparative Example 37:30475 Comparative Example 46:40.05225

[0227] Manganese capacity development rate (%) 100*M Mn / (M Mn +M Fe)(%)Manganese capacity development rate difference(%)Initial charge capacity(mAh / g)Initial discharge capacity(mAh / g)Initial efficiency(%)Example 160.2600.2155.5152.297.9Example 249.7500.3155.4152.097.8Example 369.6700.4155.5152.397.9Example 444.3450.7153.2149.297.4Example 574.4750.6153.3149.597.5Example 660.1600.1154.8151.297.7Example 759.8600.2154.9151.597.8Example 860.2600.2155.3151.797.7 Example 959.0601.0155.1151.597.7 Example 1059.2600.8155.0151.497.7 Example 1159.5600.5155.6152.698.1 Example 1259.6600.4155.4152.197.9 Example 1359.6600.4153.6150.197.7 Example 1459.4600.6153.4150.097.8 Example 1559.3600.7152.9148.997.4 Example 1659.0601.0151.9147.397.0Example 1759.1600.9152.1147.797.1Example 1874.2750.8153.0148.997.3Example 1959.1600.9154.2150.397.5Example 2059.2600.8154.8151.197.6Comparative Example 158602151.3145.696.2Comparative Example 261654150.8144.996.1Comparative Example 363.5706.5148.6142.495.8Comparative Example 458.8601.2149.3143.095.8

[0228] Rate characteristics (%) Low temperature (-7 ℃) Output characteristics (%) High temperature (60 ℃) Storage characteristics (%) Capacity retention rate (%, 50cyc) 0.33C / 0.1C 1C / 0.1C 2C / 0.1C Example 198.294.99 2.28 8.7 96.99 7.5 Example 298.195.09 2.38 8.99 6.89 7.5 Example 398.294.89 2.08 8.89 6.89 7.4 Example 497.594.49 1.38 6.99 5.296.7 Example 597.694.39 1.58 7.195.497.0 Example 698.195.09 2.18 8.596.697.2 Example 797.994.891.988.696.497.3 Example 897.894.591.688.396.497.1 Example 997.494.290.987.295.897.5 Example 1097.594.391.085.694.997.3 Example 1198.194.992.288.797.197.3 Example 1297.794.592.088.596.597.1 Example 1397.894.891.988.696.496.5 Example 1497.794.691.888.395.896.4 Example 1597.594.191.387.995.696.2 Example 1697.393.790.786.095.095.9 Example 1797.393.590.885.994.995.9 Example 1897.794.891.987.096.596.5 Example 1997.594.591.786.996.797.0 Example 2097.694.491.884.596.897.3 Comparative Example 197.092.789.281.293.595.4 Comparative Example 296.692.989.879.790.792.9 Comparative Example 395.790.485.369.581.584.1Comparative example 495.891.388.570.382.185.0

[0229] Referring to Tables 3 and 4, in the examples satisfying Equation 1, the initial capacity, initial efficiency, rate characteristics, low-temperature output characteristics, high-temperature storage characteristics, and capacity retention rate were improved compared to the comparative examples.

[0230] M in Equation 1 Mn / (M Mn +M Fe) exceeded 0.5 to 0.7, the capacity characteristics, output characteristics, and life characteristics were relatively lowered compared to other examples.

[0231] In Examples 9 and 10, where the content of the doping element was outside of 0.1 wt% to 1 wt% relative to the weight of the lithium metal phosphate particles, the output characteristics and life characteristics were relatively lowered compared to other examples.

[0232] In Examples 16 and 17, where the crystal grain size in the (020) plane direction of the lithium metal phosphate particles was outside of 175 nm to 600 nm, the capacity characteristics, output characteristics, and life characteristics were relatively lowered compared to other examples.

Claims

1. A cathode active material for a lithium secondary battery, comprising lithium metal phosphate particles containing manganese and iron and satisfying the following formula 1: [Formula 1] (M Mn / (M Mn +M Fe ))*100-1≤Manganese capacity expression rate (%)≤(M Mn / (M Mn +M Fe ))*100+1 (In Equation 1, M Mn is the molar ratio of manganese among the metals excluding lithium contained in the lithium metal phosphate particles, and M Fe is the molar ratio of iron among the metals excluding lithium contained in the lithium metal phosphate particles, The manganese capacity development rate (%) is the SOC of the highest peak obtained from a charge graph in which the horizontal axis is the State of Charge (SOC) (%) and the vertical axis is the value obtained by differentiating voltage (V) by charge capacity (mAh / g) (dV / dQ). The SOC is the value obtained by subtracting 100 from the SOC.

2. In claim 1, M Mn / (M Mn +M Fe ) is a positive electrode active material for a lithium secondary battery, having a molecular weight of 0.5 to 0.

7.

3. In claim 1, M Fe / (M Mn +M Fe ) is a positive electrode active material for a lithium secondary battery, having a molecular weight of 0.3 to 0.

5.

4. In claim 1, the lithium metal phosphate particles are a positive electrode active material for a lithium secondary battery, satisfying the following formula 2: [Formula 2] (M Mn / (M Mn +M Fe ))*100-0.5≤Manganese capacity expression rate (%)≤(M Mn / (M Mn +M Fe ))*100+0.5 (In equation 2, M Mn is the molar ratio of manganese among the metals excluding lithium contained in the lithium metal phosphate particles, and M Fe is the molar ratio of iron among the metals excluding lithium contained in the lithium metal phosphate particles, The manganese capacity development rate (%) is the SOC of the highest peak obtained from a charge graph with SOC (%) as the horizontal axis and the value (dV / dQ) obtained by differentiating voltage (V) by charge capacity (mAh / g) as the vertical axis, which is the value obtained by subtracting 100 from the SOC.

5. In claim 1, the lithium metal phosphate particle is a positive electrode active material for a lithium secondary battery, which comprises a chemical structure or crystal structure represented by the following chemical formula 1: [Chemical Formula 1] Li a Mr b Feb c Q d O 4+e (In Chemical Formula 1, 0.9≤a≤1.2, 0.5≤b≤0.7, 0.3≤c≤0.5, 0.9≤d≤1.2, -0.1≤e≤0.1).

6. A positive electrode active material for a lithium secondary battery according to claim 1, wherein the lithium metal phosphate particles further comprise a doping element or a coating element.

7. 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 Ti, V, Na, Mg, Ca, Y, Hf, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr, in claim 6.

8. A positive electrode active material for a lithium secondary battery, wherein the content of the doping element or coating element relative to the weight of the lithium metal phosphate particles in claim 6 is 0.1 wt% to 1 wt%.

9. A positive electrode active material for a lithium secondary battery, wherein the lithium metal phosphate particles according to claim 1 include a carbon coating formed on a surface portion.

10. A cathode active material for a lithium secondary battery, wherein the crystal grain size in the (020) plane direction measured through X-ray diffraction (XRD) analysis of the lithium metal phosphate particles in claim 1 is 175 nm to 600 nm.

11. In claim 10, the crystal grain size is measured through the following equation 3, a positive electrode active material for a lithium secondary battery: [Formula 3] (In Equation 3, L is the crystal grain size (nm), λ is the X-ray wavelength (nm), β is the half width (rad) of the peak of the (020) plane of the lithium metal phosphate particle, and θ is the diffraction angle (rad).) 12. A cathode active material for a lithium secondary battery, wherein the crystal grain size of claim 1 is 200 nm to 400 nm.

13. A positive electrode comprising the positive electrode active material for a lithium secondary battery of claim 1; and A lithium secondary battery comprising a cathode opposite to the positive electrode.

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