Positive electrode active material for lithium secondary battery and lithium secondary battery comprising same

Abstract

An embodiment of the present invention provides a positive electrode active material for a lithium secondary battery. The positive electrode active material for a lithium secondary battery includes: first lithium metal phosphorus oxide particles having a single particle form; and second lithium metal phosphorus oxide particles containing iron and manganese and having a secondary particle form in which primary particles are aggregated.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery containing the positive electrode active material. Background Art

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged. With the development of the information communication and display industries, secondary batteries are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and notebook computers. In addition, in recent years, battery packs including secondary batteries are being developed and used as power sources for environmentally friendly vehicles such as electric vehicles and hybrid vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and light weight, and therefore are actively being researched and developed.

[0004] As the positive electrode active material for lithium secondary batteries, lithium metal phosphorus oxide can be used.

[0005] As the application range of lithium secondary batteries expands, longer life, high capacity and high energy density are required. For example, due to the low ionic conductivity and energy density of the lithium metal phosphorus oxide, the power characteristics, low temperature performance and electrode density of the lithium secondary battery may be reduced. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] According to one aspect of the present invention, a positive electrode active material for a lithium secondary battery having improved power characteristics and low-temperature performance can be provided.

[0008] According to one aspect of the present invention, a lithium secondary battery having improved power characteristics and low temperature performance can be provided.

[0009] (II) Technical solution

[0010] A positive active material for a lithium secondary battery according to an exemplary embodiment includes: first lithium metal phosphorus oxide particles, the first lithium metal phosphorus oxide particles having a single particle form; and second lithium metal phosphorus oxide particles, the second lithium metal phosphorus oxide particles containing iron and manganese and having a secondary particle form formed by aggregation of primary particles.

[0011] In some embodiments, the ratio of the weight of the first lithium metal phosphorus oxide particles to the total weight of the positive electrode active material for a lithium secondary battery may be 0.01 to 0.5.

[0012] In some embodiments, the average particle size (D50) of the first lithium metal phosphorus oxide particles may be smaller than the average particle size (D50) of the second lithium metal phosphorus oxide particles.

[0013] In some embodiments, the average particle size (D50) of the first lithium metal phosphorus oxide particles may be 1-10 μm.

[0014] In some embodiments, the average particle size (D50) of the primary particles forming the second lithium metal phosphorus oxide particles may be 10-100 nm, and the average particle size (D50) of the second lithium metal phosphorus oxide particles may be 1-10 μm.

[0015] In some embodiments, the first lithium metal phosphorus oxide particle may be represented by the following Chemical Formula 1.

[0016] [Chemical formula 1]

[0017] Li a M x P y O 4+z

[0018] In Chemical Formula 1, 0.9≤a≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, and −0.1≤z≤0.1 may be satisfied, and M may include at least one selected from Fe, Co, and Ni.

[0019] In some embodiments, the second lithium metal phosphorus oxide particles may be represented by the following Chemical Formula 2.

[0020] [Chemical formula 2]

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

[0022] In Chemical Formula 2, 0.9≤b≤1.2, 0.4≤c≤0.8, 0.2≤d≤0.6, 0.9≤e≤1.2, and -0.1≤f≤0.1 may be satisfied.

[0023] In some embodiments, at least one of the first lithium metal phosphorus oxide particles and the second lithium metal phosphorus oxide particles may further include a doping element or a coating element, and the doping element or the coating element 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.

[0024] In some embodiments, at least one of the first lithium metal phosphorus oxide particle and the second lithium metal phosphorus oxide particle may include a carbon coating layer formed on a surface portion.

[0025] In some embodiments, the carbon coating may contain 0.5-3.0 wt % relative to the total weight of the first lithium metal phosphorus oxide particle, or the carbon coating may contain 0.5-3.0 wt % relative to the total weight of the second lithium metal phosphorus oxide particle.

[0026] In some embodiments, the positive active material for a lithium secondary battery may further include a third lithium metal phosphorus oxide particle, the third lithium metal phosphorus oxide particle including iron and manganese and having a single particle form.

[0027] In some embodiments, a ratio of a weight of the third lithium metal phosphorus oxide particles to a total weight of the second lithium metal phosphorus oxide particles and the third lithium metal phosphorus oxide particles may be 0.01 to 0.5.

[0028] A lithium secondary battery according to an exemplary embodiment includes: a positive electrode including the positive electrode active material for a lithium secondary battery; and a negative electrode disposed opposite to the positive electrode.

[0029] (III) Beneficial effects

[0030] According to one embodiment of the present invention, lifespan characteristics of a lithium secondary battery can be improved.

[0031] According to one embodiment of the present invention, the energy density of a lithium secondary battery can be improved.

[0032] According to one embodiment of the present invention, the power characteristics of a lithium secondary battery can be improved.

[0033] According to one embodiment of the present invention, the mechanical stability of the positive electrode active material can be improved.

[0034] According to one embodiment of the present invention, high conductivity of primary particles and high rolling density of secondary particles can be simultaneously achieved.

[0035] The positive electrode active material for lithium secondary batteries of the present invention and the lithium secondary batteries containing the positive electrode active material can be widely used in electric vehicles, battery charging stations, other green technology fields such as solar power generation and wind power generation using batteries. The positive electrode active material for lithium secondary batteries of the present invention and the lithium secondary batteries containing the positive electrode active material can be used in eco-friendly electric vehicles and hybrid vehicles, etc., to prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic cross-sectional view showing a positive electrode active material layer according to an exemplary embodiment.

[0037] Figure 2 is a schematic cross-sectional view showing a positive electrode active material layer according to an exemplary embodiment.

[0038] Figure 3 and Figure 4 1 and 2 are a schematic plan view and a schematic cross-sectional view, respectively, showing a lithium secondary battery according to an exemplary embodiment.

[0039] Description of reference numerals:

[0040] 100: positive electrode 105: positive electrode current collector

[0041] 107: positive electrode lead 110: positive electrode active material layer

[0042] 120: negative electrode active material layer 125: negative electrode current collector

[0043] 127: Negative lead 130: Negative electrode

[0044] 140: diaphragm 150: electrode assembly

[0045] 160: Shell DETAILED DESCRIPTION

[0046] The embodiment of the present invention provides a positive electrode active material for a lithium secondary battery (hereinafter, may be simply referred to as "positive electrode active material") containing lithium metal phosphorus oxide particles. In addition, a lithium secondary battery (hereinafter, may be simply referred to as "secondary battery") containing the positive electrode active material for a lithium secondary battery is provided.

[0047] Hereinafter, embodiments of the present invention will be described in detail, however, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described exemplarily.

[0048] Figure 1is a schematic cross-sectional view showing a positive electrode active material layer according to an exemplary embodiment.

[0049] See also Figure 1 A positive electrode active material layer 110 including the positive electrode active material may be formed on at least one side of the positive electrode current collector 105 .

[0050] The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof. The positive electrode current collector 105 may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, copper, or silver. For example, the thickness of the positive electrode current collector 105 may be 10-50 μm.

[0051] The positive active material includes first lithium metal phosphorus oxide particles 10 in the form of single particles and second lithium metal phosphorus oxide particles 20 in the form of secondary particles formed by aggregation of primary particles. The second lithium metal phosphorus oxide particles 20 include iron and manganese.

[0052] For example, the "primary particles" may be based on the existence of secondary particles formed by aggregation of primary particles. For example, the primary particles may be provided as one component of the secondary particles.

[0053] The term "single particle form" used in the present invention is used as a meaning to exclude secondary particles formed by agglomeration of multiple primary particles. For example, in the first lithium metal phosphorus oxide particle 10, a secondary particle structure formed by assembling or agglomerating primary particles (e.g., more than 10, more than 20, more than 30, more than 40, more than 50, etc.) may be excluded.

[0054] The term "single particle form" used in the present invention does not exclude a form having, for example, 2 to 10 single particles simply adjacent to or in contact with each other.

[0055] In some embodiments, the first lithium metal phosphorus oxide particle 10 may include a structure in which a plurality of single particles are integrated and substantially transformed into one single particle rather than an aggregate of a plurality of particles.

[0056] For example, the first lithium metal phosphorus oxide particle 10 may have a granular or spherical single particle form.

[0057] By using the first lithium metal phosphorus oxide particles 10 and the second lithium metal phosphorus oxide particles 20 together, the lifespan characteristics and the electrode density of the lithium secondary battery may be improved, and the power characteristics may be enhanced.

[0058] For example, by having the first lithium metal phosphorus oxide particles 10 in the form of a single particle, the lifespan characteristics and mechanical stability of the positive electrode active material may be improved.

[0059] For example, the second lithium metal phosphorus oxide particles 20 have a secondary particle form formed by agglomerating primary particles, so that high conductivity of the primary particles and high electrode density of the secondary particles can be achieved simultaneously. In addition, the electrolyte is impregnated through the space between the primary particles, so that power characteristics can be improved.

[0060] In some embodiments, the ratio of the weight of the first lithium metal phosphorus oxide particles 10 to the total weight of the positive electrode active material may be 0.01 to 0.5, for example, 0.15 to 0.5 or 0.3 to 0.45. Within the above range, the electrode density can be sufficiently increased, and the life characteristics and mechanical stability can be improved.

[0061] In some embodiments, the average particle size (D50) of the first lithium metal phosphorus oxide particles 10 may be smaller than the average particle size (D50) of the second lithium metal phosphorus oxide particles 20. Therefore, the first lithium metal phosphorus oxide particles 10 are present in the gaps between the second lithium metal phosphorus oxide particles 20 in the form of secondary particles, and thus the solid content of the slurry may be increased, and the electrode density and power characteristics may be improved.

[0062] The term “average particle size”, “D50” or “average particle size (D50)” used in the present invention may refer to a particle size corresponding to a volume cumulative percentage of 50% in a particle size distribution obtained from the volume of particles.

[0063] According to some embodiments, the average particle size (D50) of the first lithium metal phosphorus oxide particles 10 may be 1-10 μm, for example, 1-5 μm or 3-5 μm. Within the above range, the driving voltage and energy density of the lithium secondary battery may be increased, and the power characteristics may be improved.

[0064] According to some embodiments, the average particle size (D50) of the primary particles forming the second lithium metal phosphorus oxide particles 20 may be 10-100 nm, for example, 30-70 nm. Within the above range, the average particle size (D50) of the second lithium metal phosphorus oxide particles 20 in the form of secondary particles may be adjusted to an appropriate range.

[0065] In some embodiments, the average particle size (D50) of the second lithium metal phosphorus oxide particles 20 may be 1-10 μm, for example, 4-9 μm or 5-7 μm. Within the above range, the electrode density may be increased, and the power characteristics may be improved.

[0066] In some embodiments, the first lithium metal phosphorus oxide particle 10 may have an olivine structure, and may include a crystal structure represented by the following Chemical Formula 1.

[0067] [Chemical formula 1]

[0068] Li a M x P y O 4+z

[0069] In Chemical Formula 1, 0.9≤a≤1.2, 0.99≤x≤1.01, 0.9≤y≤1.2, and −0.1≤z≤0.1 may be satisfied, and M may include at least one selected from Fe, Co, and Ni.

[0070] In some embodiments, the second lithium metal phosphorus oxide particle 20 may have an olivine structure, and may include a crystal structure represented by Chemical Formula 2 below.

[0071] [Chemical formula 2]

[0072] Li b Mn c Fe d P e O 4+f

[0073] In Chemical Formula 2, 0.9≤b≤1.2, 0.4≤c≤0.8, 0.2≤d≤0.6, 0.9≤e≤1.2, and -0.1≤f≤0.1 may be satisfied.

[0074] The chemical structures represented by Chemical Formula 1 and Chemical Formula 2 respectively represent the bonding relationship contained in the crystal structure of the first lithium metal phosphorus oxide particle 10 and the second lithium metal phosphorus oxide particle 20, and do not exclude other additional elements. For example, in Chemical Formula 1, M may include Fe, Co and / or Ni, and Fe, Co and / or Ni may be provided as the main active element of the positive electrode active material. Chemical Formula 1 and Chemical Formula 2 are provided to represent the bonding relationship of the main active elements, and should be understood as formulas including the introduction and substitution of additional elements.

[0075] In one embodiment, in addition to the main active element, at least one of the first lithium metal phosphorus oxide particle 10 and the second lithium metal phosphorus oxide particle 20 may further include an auxiliary element for enhancing the chemical stability of the positive electrode active material or the crystal structure. The auxiliary element may be mixed together into the crystal structure and form a bond, and it should be understood that this case is also included in the chemical structure represented by Chemical Formula 1 or Chemical Formula 2.

[0076] The auxiliary element may include, for example, at least one selected from 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 function as an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Fe, Co, Ni, or Mn, such as Al.

[0077] According to some embodiments, at least one of the first lithium metal phosphorus oxide particles 10 and the second lithium metal phosphorus oxide particles 20 may further include a coating element or a doping element. For example, an element substantially the same as or similar to the above-mentioned auxiliary element may be used as the coating element or the doping element. For example, one or a combination of two or more of the above-mentioned elements may be used as the coating element or the doping element.

[0078] The coating element or the doping element may be present on the surface of at least one of the first lithium metal phosphorus oxide particle 10 and the second lithium metal phosphorus oxide particle, or may be infiltrated through the surface of at least one of the first lithium metal phosphorus oxide particle 10 and the second lithium metal phosphorus oxide particle and included in the bonding structure represented by the Chemical Formula 1 or the Chemical Formula 2.

[0079] In one embodiment, the first lithium metal phosphorus oxide particles 10 may include LiFePO 4 .

[0080] For example, the first lithium metal phosphorus oxide particles 10 and the second lithium metal phosphorus oxide particles 20 may have improved structural stability and economy compared to other kinds of positive active material particles.

[0081] In some embodiments, at least one of the first lithium metal phosphorus oxide particle 10 and the second lithium metal phosphorus oxide particle 20 may include a carbon coating layer formed on the surface portion. Therefore, the conductivity of the positive electrode active material may be improved, thereby improving power characteristics.

[0082] For example, the content of the carbon coating layer may be 0.5-3.0 wt % in the total weight of the particles including the carbon coating layer.

[0083] For example, the carbon coating may contain 0.5-3.0 wt % of the total weight of the first lithium metal phosphorus oxide particle 10. For example, the carbon coating may contain 0.5-3.0 wt % of the total weight of the second lithium metal phosphorus oxide particle 20. Within the above range, the power characteristics can be sufficiently improved, and the low temperature characteristics of the positive electrode active material can be suppressed from being reduced.

[0084] Figure 2 is a schematic cross-sectional view showing a positive electrode active material layer according to an exemplary embodiment.

[0085] See also Figure 2 The positive active material may further include third lithium metal phosphorus oxide particles 30 , which include iron and manganese and have a single particle form.

[0086] For example, the third lithium metal phosphorus oxide particles 30 may have substantially the same composition and size as the primary particles forming the second lithium metal phosphorus oxide particles 20 .

[0087] For example, the third lithium metal phosphorus oxide particles 30 may be represented by Chemical Formula 2, and may have an average particle size (D50) ranging from 10 to 100 nm.

[0088] For example, the third lithium metal phosphorus oxide particles 30 may be included in the positive active material as individual particles distinguished and separated from the first lithium metal phosphorus oxide particles 10 and the second lithium metal phosphorus oxide particles 20 .

[0089] By having the third lithium metal phosphorus oxide particles 30 having an average particle size (D50) smaller than the first lithium metal phosphorus oxide particles 10 and the second lithium metal phosphorus oxide particles 20, the solid content of the slurry may be increased, and the electrode density and low temperature power characteristics may be further improved.

[0090] According to some embodiments, the weight ratio of the third lithium metal phosphorus oxide particles 30 to the total weight of the second lithium metal phosphorus oxide particles 20 and the third lithium metal phosphorus oxide particles 30 may be 0.01 to 0.5, for example, 0.2 to 0.4. Within the above range, the electrode density can be sufficiently increased, and the low temperature power characteristics can be improved.

[0091] Figure 3 and Figure 4 1 and 2 are schematic plan views and schematic cross-sectional views respectively showing a lithium secondary battery according to an exemplary embodiment. Figure 4 It is along Figure 3 A cross-sectional view taken along the thickness direction along the line II'.

[0092] Figure 3 and Figure 4 The structure shown in FIG. 1 is an example for convenience of explanation, and the structure of the lithium secondary battery according to the embodiment of the present invention is not limited thereto.

[0093] See also Figure 3 and Figure 4 The lithium secondary battery may include a positive electrode 100 and a negative electrode 130 , wherein the positive electrode 100 includes the positive electrode active material, and the negative electrode 130 is disposed opposite to the positive electrode 100 .

[0094] The positive electrode 100 may include a positive electrode active material layer 110 formed by coating a positive electrode active material on at least one side of a positive electrode collector 105 .

[0095] The positive electrode active material may include a plurality of first lithium metal phosphorus oxide particles 10 and second lithium metal phosphorus oxide particles 20. For example, the total amount of the lithium metal phosphorus oxide particles (10, 20, 30) may be 50% by weight or more of the total weight of the positive electrode active material. In some embodiments, the total amount of the lithium metal phosphorus oxide particles (10, 20, 30) may be 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more of the total weight of the positive electrode active material.

[0096] In one embodiment, the positive electrode active material may consist essentially of lithium metal phosphorus oxide particles (10, 20, 30).

[0097] For example, the positive electrode active material may be mixed and stirred with a binder, a conductive material and / or a dispersing material in a solvent to prepare a positive electrode slurry. The positive electrode slurry may be coated on at least one side of the positive electrode collector 105 and then dried and rolled to manufacture the positive electrode 100.

[0098] The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or alloys thereof. The positive electrode current collector 105 may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, copper, or silver.

[0099] The binder may include an organic binder such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, or a water-based binder such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0100] For example, as a binder for forming the positive electrode, a PVDF-based binder can be used. In this case, the amount of the binder used to form the positive active material layer 110 can be reduced, and the amount of the positive active material can be relatively increased, so the power and capacity of the secondary battery can be improved.

[0101] The conductive material may be included to promote electron migration between active material particles. For example, the conductive material may include carbon-based conductive materials such as graphite, carbon black, graphene, and carbon nanotubes and / or metal-based conductive materials such as perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, and LaSrMnO3.

[0102] The negative electrode 130 may include a negative electrode collector 125 and a negative electrode active material layer 120 formed by coating a negative electrode active material on at least one side of the negative electrode collector 125 .

[0103] The negative electrode active material may contain a substance that can embed and deintercalate lithium ions. For example, carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, carbon fibers, lithium alloys, silicon or tin, etc. can be used. Examples of amorphous carbon include hard carbon, coke, mesocarbon microbeads (MCMB) calcined below 1500°C, mesophase pitch-based carbon fibers (MPCF), etc. Examples of crystalline carbon include natural graphite, graphitized coke, graphitized MCMB, graphitized MPCF, and other graphite-based carbons. Elements contained in the lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc.

[0104] For example, the negative electrode current collector 125 may include copper foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper, 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 10-50 μm.

[0105] In some embodiments, the negative electrode active material may be mixed and stirred with a binder, a conductive material and / or a dispersing material in a solvent to prepare a slurry. The slurry may be coated on the negative electrode current collector, dried and rolled to manufacture the negative electrode 130 .

[0106] The binder and the conductive material may use materials substantially the same as or similar to the above-mentioned materials. In some embodiments, for compatibility with the carbon-based active material, the binder used to form the negative electrode may include a water-based binder such as styrene-butadiene rubber (SBR), and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0107] In some embodiments, a separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. The separator 140 may also include a non-woven fabric formed of a high melting point glass fiber, a polyethylene terephthalate fiber, etc.

[0108] According to an exemplary embodiment, a battery cell is defined by a positive electrode 100, a negative electrode 130, and a separator 140, and a plurality of the battery cells may be stacked to form, for example, an electrode assembly 150 in the form of a jelly roll. For example, the electrode assembly 150 may be formed by winding, stacking, z-folding, stack-folding, etc., of the separator 140.

[0109] The electrode assembly is housed in the case 160 together with an electrolyte, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0110] The non-aqueous electrolyte may include a lithium salt as an electrolyte and an organic solvent. The lithium salt may be, for example, Li + X - Indicates that, as the anion of the lithium salt (X - ), we can exemplify 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 - 、(CF3CF2SO2)2N - The organic solvent may be propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (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 ( ... ether, DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, cyclopentane, γ-butyrolactone and propylene sulfite, etc. These can be used alone or in combination of two or more.

[0111] The non-aqueous electrolyte may further include additives. The additives may include, for example, cyclic carbonate-based compounds, fluorine-substituted carbonate-based compounds, sultone-based compounds, cyclic sulfate-based compounds, cyclic sulfite-based compounds, phosphate-based compounds, borate-based compounds, etc. These may be used alone or in combination of two or more.

[0112] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and the like.

[0113] The fluorine-substituted carbonate-based compound may include fluoroethylene carbonate (FEC) and the like.

[0114] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, and the like.

[0115] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, and the like.

[0116] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, and the like.

[0117] The phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, and the like.

[0118] The borate-based compound may include lithium bis(oxalate) borate and the like.

[0119] In some embodiments, a solid electrolyte may be used instead of the non-aqueous electrolyte. In this case, the lithium secondary battery may be made into an all-solid-state battery. In addition, a solid electrolyte layer may be provided between the positive electrode 100 and the negative electrode 130 instead of the separator 140.

[0120] The solid electrolyte may include a sulfide-based electrolyte. As non-limiting examples, 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 and n are positive numbers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p and 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.

[0121] In one embodiment, the solid electrolyte may also include an oxide-based amorphous solid electrolyte such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0122] like Figure 3 and Figure 4 As shown, the tabs (positive tabs and negative tabs) may protrude from the positive current collector 105 and the negative current collector 125 belonging to each battery cell and extend to one side of the shell 160. The tabs may be fused with the one side of the shell 160 and form electrode leads (positive lead 107 and negative lead 127) extending to the outside of the shell 160 or exposed to the outside of the shell 160.

[0123] The lithium secondary battery may be manufactured in, for example, a cylindrical shape using a can, a prismatic shape, a pouch type, a coin shape, or the like.

[0124] The embodiments of the present invention are further described below with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are only used to illustrate the present invention and are not used to limit the claims. Various variations and modifications can be made to the examples within the scope of the scope and technical concept of the present invention, which is obvious to those skilled in the art, and it is natural that such variations and modifications belong to the scope of the claims.

[0125] Preparation Example 1 - First Lithium Metal Phosphorus Oxide Particle (LFP (Single Particle))

[0126] Lithium carbonate and iron phosphate as lithium sources and sodium hexametaphosphate as a dispersant are added to distilled water, and the particles are mixed and crushed by a ball mill to form a mixed solution containing LiFePO4.

[0127] The formed mixed solution containing LiFePO4 was dried using a spray dryer provided with a micro nozzle form.

[0128] The dried powder was calcined at about 600-750° C. for about 5-12 hours under a nitrogen atmosphere and then subjected to an iron removal process to obtain LiFePO 4 particles.

[0129] The LiFePO 4 particles were pulverized and classified using a ball mill to prepare first lithium metal phosphorus oxide particles (LFP) having an average particle size (D50) as shown in Table 1.

[0130] Preparation Example 2 - Second lithium metal phosphorus oxide particles (LMFP (secondary particles)) and third lithium metal phosphorus oxide particles (LMFP (primary particles))

[0131] MnO, H3PO4, Fe3O4 and Li2CO3 were mixed using a ball mill. The mixture was calcined at 450°C for 4 hours and at 600°C for 6 hours in an argon (Ar) atmosphere to obtain LiMn in the form of single particles. 0.6 Fe 0.4 PO4 particles.

[0132] The LiMn 0.6 Fe 0.4 The PO4 single particles were pulverized and classified to obtain third lithium metal phosphorus oxide particles (LMFP (primary particles)) having an average particle size (D50) as shown in Table 1.

[0133] In an argon (Ar) atmosphere, the graded LiMn 0.6 Fe 0.4PO4 single particles were calcined for 6 hours to obtain LiMn in the form of secondary particles formed by aggregation of primary particles. 0.6 Fe 0.4 PO4 particles.

[0134] The LiMn 0.6 Fe 0.4 The PO 4 secondary particles were pulverized and classified to prepare second lithium metal phosphorus oxide particles (LMFP (secondary particles)) having an average particle size (D50) as shown in Table 1.

[0135] Example 1 to Example 17

[0136] According to Preparation Example 1 and Preparation Example 2, first lithium metal phosphorus oxide particles and second lithium metal phosphorus oxide particles having an average particle size (D50) as described in Table 1 were prepared, mixed to have a weight ratio as described in Table 1, and used as positive electrode active materials.

[0137] The positive electrode active material, acetylene black (Denka Black) as a conductive material, and PVDF as a binder are mixed in a mass ratio of 93:5:2 to prepare a positive electrode slurry. A positive electrode including a positive electrode active material layer is manufactured, wherein the positive electrode active material layer is formed by coating the positive electrode slurry on an aluminum current collector and drying and rolling. The solid content of the positive electrode slurry and the mass to volume ratio (electrode density) of the positive electrode active material layer after rolling are recorded in Table 4.

[0138] Lithium metal is used as the negative electrode active material.

[0139] The positive electrode and negative electrode manufactured as described above were notched into circular shapes with diameters of Φ14 and Φ16, respectively, and stacked, and a separator (polyethylene, 13 μm thick) cut into Φ19 was set between the positive electrode and the negative electrode to form a battery cell. The battery cell was assembled by placing the battery cell in an outer packaging material of a coin battery cell with a diameter of 20 mm and a height of 1.6 mm and injecting an electrolyte, and aged for more than 12 hours so that the electrolyte was impregnated into the inside of the electrode.

[0140] As the electrolyte, a 1 M LiPF6 solution prepared using a mixed solvent of EC / EMC (30 / 70; volume ratio) was used.

[0141] The secondary battery manufactured as described above was subjected to formation charge and discharge (the charging condition was CC-CV 0.1C 3.8V 0.05C CUT-OFF, and the discharging condition was CC 0.1C 2.5V CUT-OFF).

[0142] Example 18 to Example 22

[0143] The positive electrode active material and the lithium secondary battery were manufactured by the same method as in Example 3, except that in Preparation Example 1, citric acid was further added as a raw material so that the content of the carbon coating relative to the total weight of the first lithium metal phosphorus oxide particles was as shown in Table 1.

[0144] Embodiment 23

[0145] A positive electrode active material and a lithium secondary battery were manufactured by the same method as in Example 3, except that in Preparation Example 2, citric acid was further added as a raw material so that the content of the carbon coating relative to the total weight of the second lithium metal phosphorus oxide particles was as shown in Table 1.

[0146] Example 24 to Example 28

[0147] According to Preparation Example 2, third lithium metal phosphorus oxide particles having an average particle size (D50) of 50 nm were prepared.

[0148] The prepared third lithium metal phosphorus oxide particles were mixed with the first lithium metal phosphorus oxide particles and the second lithium metal phosphorus oxide particles to have a weight ratio as described in Table 2 and used as a positive electrode active material.

[0149] The first lithium metal phosphorus oxide particles and the second lithium metal phosphorus oxide particles used are the same particles as the first lithium metal phosphorus oxide particles and the second lithium metal phosphorus oxide particles of Example 3, respectively.

[0150] A lithium secondary battery was manufactured by the same method as in Example 3, except that the above-mentioned positive electrode active material was used.

[0151] Comparative Example 1

[0152] A lithium secondary battery was manufactured by the same method as in Example 3, except that only the first lithium metal phosphorus oxide particles as in Example 3 were used as the positive electrode active material.

[0153] Comparative Example 2

[0154] A lithium secondary battery was manufactured by the same method as in Example 3, except that only the second lithium metal phosphorus oxide particles as in Example 3 were used as the positive electrode active material.

[0155] Comparative Example 3

[0156] The first lithium metal phosphorus oxide particles and the third lithium metal phosphorus oxide particles having the average particle diameter (D50) as described in Table 1 were prepared according to Preparation Example 1 and Preparation Example 2, respectively, and then mixed to have the weight ratio described in Table 3 and used as positive electrode active materials.

[0157] A lithium secondary battery was manufactured by the same method as in Example 3, except that the above-mentioned positive electrode active material was used.

[0158] Comparative Example 4

[0159] The single-particle LiFePO4 particles prepared according to Preparation Example 1 were calcined at 650-700° C. for 6 hours under an argon (Ar) atmosphere to prepare LiFePO4 particles in the form of secondary particles formed by aggregation of primary particles. The prepared LiFePO4 particles were classified to prepare first lithium metal phosphorus oxide particles (LFP (secondary particles)) having an average particle size (D50) of 10 μm.

[0160] A lithium secondary battery was manufactured by the same method as in Example 3, except that the LFP (secondary particles) and the same second lithium metal phosphorus oxide particles as in Example 3 were mixed to have a weight ratio as described in Table 3 and used as a positive electrode active material.

[0161] Experimental Example 1

[0162] (1) Measurement of average particle size (D50)

[0163] The average particle diameters (D50) of the first to third lithium metal phosphorus oxide particles used in the above-mentioned Examples and Comparative Examples were measured by a laser particle size analyzer (S3500 bluewave, Microtrac).

[0164] Measurement conditions: circulation rate 65mL / sec

[0165] Measuring time: 10-30 seconds

[0166] (2) Measurement of carbon coating content

[0167] The carbon contents of the positive active materials prepared according to the above examples and comparative examples were measured by a carbon / sulfur analyzer (CS844, LECO).

[0168] Specifically, the carbon content in the sample is quantitatively analyzed by detecting the CO2 generated by burning 1 g of the positive electrode active material sample.

[0169] The measured carbon content is divided by the added weight of the particles comprising the carbon coating (the first lithium metal phosphorus oxide particles or the second lithium metal phosphorus oxide particles) and expressed as a percentage.

[0170] The mixed components, weight ratios, average particle sizes (D50) and carbon coating contents of the positive electrode active materials are shown in Tables 1 to 3 below. The "weight ratio of LMFP (single particle)" in Table 2 is the ratio of the weight of LMFP (single particle) to the total weight of LMFP (secondary particles) and LMFP (single particle).

[0171] [Table 1]

[0172]

[0173] [Table 2]

[0174]

[0175] [Table 3]

[0176]

[0177] Experimental Example 2

[0178] (1) Evaluation of capacity retention (100 cycles)

[0179] At room temperature (25° C.), the lithium secondary batteries manufactured according to the above embodiments and comparative examples were charged (CC-CV 0.1C 0.01V 0.01C cutoff) and discharged (CC 0.1C 1.5V cutoff) 100 times, and the 100th discharge capacity and the 1st discharge capacity were measured. Each cycle was left to stand for 10 minutes.

[0180] The 100th discharge capacity was divided by the 1st discharge capacity and the result was calculated as a percentage. The calculated value was evaluated as the capacity retention rate.

[0181] (2) Measurement of the ratio of 2C discharge capacity to 0.1C discharge capacity

[0182] At room temperature (25° C.), the lithium secondary batteries manufactured according to the above examples and comparative examples were charged (CC-CV 0.5C 3.65V 0.05C cutoff) and discharged (CC 0.1C 2.5V cutoff), and the discharge capacity was measured. The measured discharge capacity was evaluated as 0.1C discharge capacity.

[0183] At room temperature (25° C.), the lithium secondary batteries manufactured according to the above examples and comparative examples were charged (CC-CV 0.5C 3.65V 0.05C cutoff) and discharged (CC 2C 2.5V cutoff), and the discharge capacity was measured. The measured discharge capacity was evaluated as 2C discharge capacity.

[0184] The 2C discharge capacity was divided by the 0.1C discharge capacity and the ratio (%) of the 2C discharge capacity to the 0.1C discharge capacity was calculated as a percentage.

[0185] (3) Evaluation of low temperature power characteristics

[0186] At room temperature (25° C.), the lithium secondary batteries manufactured according to the above examples and comparative examples were charged (CC-CV 0.5C 3.65V 0.05C cutoff) and discharged (CC 0.1C 2.5V cutoff), and the discharge capacity was measured. The measured discharge capacity was evaluated as the room temperature discharge capacity.

[0187] The lithium secondary batteries manufactured according to the above examples and comparative examples were charged (CC-CV 0.5C 3.65V 0.05C cutoff) and discharged (CC 0.1C 2.5V cutoff) at low temperature (-7°C), and the discharge capacity was measured. The measured discharge capacity was evaluated as the low temperature discharge capacity.

[0188] The low temperature discharge capacity was divided by the normal temperature discharge capacity and the low temperature power characteristic was calculated as a percentage (%).

[0189] The evaluation results are shown in Tables 4 and 5 below.

[0190] [Table 4]

[0191]

[0192] [Table 5]

[0193]

[0194] Referring to Tables 4 and 5, in the embodiments using both the first lithium metal phosphorus oxide particles in the form of single particles and the second lithium metal phosphorus oxide particles containing iron and manganese and in the form of secondary particles formed by aggregation of primary particles, the electrode density, capacity retention, discharge capacity at different rates, and low-temperature power characteristics are improved as a whole compared to the comparative examples.

[0195] In Example 6, in which the ratio of the weight of the first lithium metal phosphorus oxide particles to the total weight of the positive electrode active material was less than 0.01, the solid content and the capacity retention rate in the slurry were relatively reduced compared with other examples.

[0196] In Example 7, in which the ratio of the weight of the first lithium metal phosphorus oxide particles to the total weight of the positive electrode active material exceeded 0.5, the low-temperature power characteristics were relatively lowered compared to the other examples.

[0197] In Example 8 in which the average particle size (D50) of the first lithium metal phosphorus oxide particles was less than 1 μm, the low-temperature power characteristics were relatively reduced compared to the other examples.

[0198] In Example 12 in which the average particle size (D50) of the first lithium metal phosphorus oxide particles exceeded 10 μm, the solid content in the slurry and the positive electrode density were relatively reduced compared to the other examples.

[0199] In Example 13 where the average particle size (D50) of primary particles forming the second lithium metal phosphorus oxide particles was less than 10 nm and the average particle size of the second lithium metal phosphorus oxide particles was less than 1 μm, the low temperature power characteristics were relatively lowered compared to other examples.

[0200] In Example 17, in which the average particle size (D50) of primary particles forming the second lithium metal phosphorus oxide particles exceeded 100 nm and the average particle size of the second lithium metal phosphorus oxide particles exceeded 10 μm, the solid content in the slurry and the positive electrode density were relatively lower than those in other examples.

[0201] In Example 28 where the ratio of the weight of the third lithium metal phosphorus oxide particles to the total weight of the second lithium metal phosphorus oxide particles and the third lithium metal phosphorus oxide particles exceeded 0.5, the ratio of the 2C discharge capacity to the 0.1C discharge capacity was relatively reduced compared to Examples 24 to 27 where the above weight ratio was 0.01 to 0.5.

Claims

1. A positive electrode active material for a lithium secondary battery, comprising: a first lithium metal phosphorus oxide particle, the first lithium metal phosphorus oxide particle having a single particle form; and The second lithium metal phosphorus oxide particles contain iron and manganese and have a secondary particle form formed by aggregation of primary particles.

2. The positive electrode active material for lithium secondary battery according to claim 1, wherein The ratio of the weight of the first lithium metal phosphorus oxide particles to the total weight of the positive electrode active material for a lithium secondary battery is 0.01 to 0.

5.

3. The positive electrode active material for lithium secondary battery according to claim 1, wherein An average particle size D50 of the first lithium metal phosphorus oxide particles is smaller than an average particle size D50 of the second lithium metal phosphorus oxide particles.

4. The positive electrode active material for lithium secondary battery according to claim 1, wherein The average particle size D50 of the first lithium metal phosphorus oxide particles is 1-10 μm.

5. The positive electrode active material for lithium secondary battery according to claim 1, wherein The average particle size D50 of the primary particles forming the second lithium metal phosphorus oxide particles is 10-100 nm, and the average particle size D50 of the second lithium metal phosphorus oxide particles is 1-10 μm.

6. The positive electrode active material for lithium secondary battery according to claim 1, wherein The first lithium metal phosphorus oxide particle is 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 Fe, Co, and Ni.

7. The positive electrode active material for lithium secondary battery according to claim 1, wherein The second lithium metal phosphorus oxide particle is represented by the following Chemical Formula 2: [Chemical formula 2] Li b Mr c Feb d Q e O 4+f In Chemical Formula 2, 0.9≤b≤1.2, 0.4≤c≤0.8, 0.2≤d≤0.6, 0.9≤e≤1.2, and -0.1≤f≤0.

1.

8. The positive electrode active material for lithium secondary battery according to claim 1, wherein At least one of the first lithium metal phosphorus oxide particles and the second lithium metal phosphorus oxide particles further comprises a doping element or a coating element, The doping element or the coating element includes at least one selected from 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.

9. The positive electrode active material for lithium secondary battery according to claim 1, wherein At least one of the first lithium metal phosphorus oxide particles and the second lithium metal phosphorus oxide particles includes a carbon coating layer formed on a surface portion.

10. The positive electrode active material for lithium secondary battery according to claim 9, wherein The carbon coating has an amount of 0.5-3.0 wt % relative to the total weight of the first lithium metal phosphorus oxide particle, or has an amount of 0.5-3.0 wt % relative to the total weight of the second lithium metal phosphorus oxide particle.

11. The positive electrode active material for lithium secondary battery according to claim 1, wherein The positive electrode active material for a lithium secondary battery further includes third lithium metal phosphorus oxide particles, the third lithium metal phosphorus oxide particles include iron and manganese, and have a single particle form.

12. The positive electrode active material for lithium secondary battery according to claim 11, wherein A ratio of a weight of the third lithium metal phosphorus oxide particles to a total weight of the second lithium metal phosphorus oxide particles and the third lithium metal phosphorus oxide particles is 0.01 to 0.

5.

13. A lithium secondary battery comprising: A positive electrode, the positive electrode comprising the positive electrode active material for a lithium secondary battery according to claim 1; as well as A negative electrode is arranged opposite to the positive electrode.

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