Positive electrode active material, preparation method therefor, and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode active material comprising small-particle lithium iron manganese phosphate-based oxide and large-particle lithium iron phosphate-based oxide, wherein the small-particle lithium iron manganese phosphate-based oxide has an average particle diameter (D50) of 1 ㎛ or less and the large-particle lithium iron phosphate-based oxide has an average particle diameter (D50) of 4 ㎛ to 10 ㎛, with the weight ratio of the small-particle lithium iron manganese phosphate-based oxide to the large-particle lithium iron phosphate-based oxide ranging from 75: 25 to 98: 2.

Description

A positive electrode active material, a method for manufacturing the same, and a lithium secondary battery including the same

[0001] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0123561 filed on September 10, 2024 and Korean Patent Application No. 10-2025-0128654 filed on September 9, 2025, and all contents disclosed in said Korean patent application documents are incorporated herein as part of the specification.

[0002] The present invention relates to a positive electrode active material, a method for manufacturing the same, and a lithium secondary battery comprising the same. More specifically, it relates to a positive electrode active material having a bimodal particle size distribution with excellent rolling density, and a positive electrode and a lithium secondary battery comprising the same.

[0003]

[0004] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive and negative electrodes include an active material capable of lithium ion intercalation and deintercalation.

[0005] Among these, the cathode active material included in the aforementioned cathode plays a major role in determining the battery's capacity, output, and lifespan. Improving the performance of the cathode active material is essential for lithium-ion batteries to possess high energy density, output, and lifespan; consequently, extensive research is currently being conducted to develop high-performance cathode active materials.

[0006] Lithium transition metal oxides, such as lithium cobalt-based oxides like LiCoO2, lithium nickel-based oxides like LiNiO2, lithium manganese-based oxides like LiMnO2 or LiMn2O4, and lithium iron phosphate compounds like LiFePO4, have been developed as cathode active materials for lithium secondary batteries, and recently, Li[Ni a Co b Mn c ]O2, Li[Ni a Co b Alc ]O2, Li[Ni a Co b Mn c Al d Lithium composite transition metal oxides containing two or more transition metals, such as O2, have been developed and are widely used.

[0007] Meanwhile, lithium iron phosphate compounds having an olivine structure are promising active materials that have excellent lifespan characteristics and superior safety features, including overcharging and over-discharging, because they have the best structural stability.

[0008] In particular, LiFePO4 has excellent high-temperature stability due to the strong bonding strength of PO4, and because it contains iron, which is resource-abundant and inexpensive, it is cheaper than the aforementioned LiCoO2, LiNiO2, or LiMn2O4, and because it has low toxicity, it has less impact on the environment. However, since LiFePO4 has low electrical conductivity, there is a problem that the internal resistance of the battery increases when LiFePO4 is used as a positive electrode active material. In addition, since LiFePO4 has a lower density than conventional positive electrode active materials, there is a limitation that the energy density of the battery cannot be sufficiently increased, and since it typically takes the form of secondary particles assembled from primary particles, there is a problem of low output characteristics due to high interfacial resistance between primary particles.

[0009] To address this, there have been attempts to use LiFePO4 doped with manganese. However, when applying manganese-doped LiFePO4—that is, lithium iron manganese-based compounds—to batteries, there was a problem in that although the average operating voltage increased, the capacity remained low, resulting in a decrease in the actual increase in energy density.

[0010]

[0011] The present invention aims to solve the above-mentioned problems by using a small amount of a lithium iron phosphate-based compound in the form of a secondary particle with a large particle size mixed with a lithium iron phosphate-based compound with a small particle size, thereby providing a positive electrode active material with excellent rolling density and bimodal particle size characteristics.

[0012] In addition, the present invention aims to provide a positive electrode and a secondary battery having excellent energy density by including the positive electrode active material as described above.

[0013]

[0014] [1] The present invention comprises a small-sized lithium iron phosphate manganese-based oxide and a large-sized lithium iron phosphate-based oxide, wherein the small-sized lithium iron phosphate manganese-based oxide has an average particle size (D 50 ) is 1 μm or less, and the above large-diameter lithium iron phosphate-based oxide has an average particle size (D 50 The present invention provides a positive electrode active material having a particle size of 4 μm to 10 μm, wherein the small particle size lithium iron phosphate manganese-based oxide and the large particle size lithium iron phosphate-based oxide are included in a weight ratio of 75:25 to 98:2.

[0015] [2] In the present invention, the small particle size lithium iron phosphate manganese-based oxide according to [1] has an average particle size (D 50 Provides a positive electrode active material having a thickness of 0.5 μm or less.

[0016] [3] The present invention provides a positive electrode active material in which, in [1] or [2], the small particle size lithium iron phosphate manganese-based oxide and the large particle size lithium iron phosphate-based oxide are included in a weight ratio of 90:10 to 95:5.

[0017] [4] The present invention provides a positive electrode active material in which, in at least one of [1] to [3], the small-sized lithium iron phosphate manganese-based oxide has the composition of the following chemical formula 1.

[0018] [Chemical Formula 1]

[0019] Li 1+x Fe1-p-q Mn p M q (PO4)

[0020] In the above chemical formula 1, M is one or more selected from the group consisting of Ni, Co, Al, Zr, Sr, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, B, Ba, Ce, Sn, Y, V, and Zn, and -0.1≤x≤0.1, 0.4≤p≤0.8, 0≤q≤0.1.

[0021] [5] The present invention provides a positive electrode active material, wherein, in [1] or [4], the large-diameter lithium iron phosphate-based oxide is in the form of a secondary particle that is an aggregate of primary particles.

[0022] [6] The present invention provides a positive electrode active material, wherein, in at least one of [1] to [5], the large-diameter lithium iron phosphate-based oxide has the composition of the following chemical formula 2.

[0023] [Chemical Formula 2]

[0024] LiFe 1-y M' y PO4

[0025] In the above chemical formula 2, M' is one or more selected from the group consisting of Ni, Co, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir and V, and 0≤y<1.

[0026] [7] The present invention provides a positive active material having a bimodal particle size distribution, wherein at least one of [1] to [6] above, the positive active material has a bimodal particle size distribution.

[0027] [8] In the present invention, in at least one of [1] to [7], the positive active material is D 10 The present invention provides a positive electrode active material having a thickness of 0.25 μm to 0.90 μm.

[0028] [9] In the present invention, in at least one of [1] to [8], the positive active material is D 50 The present invention provides a positive electrode active material having a thickness of 0.4 μm to 1.0 μm.

[0029]

[0010] The present invention, in at least one of [1] to [9], D 90 The present invention provides a positive electrode active material having a thickness of 3.1 μm to 10.0 μm.

[0030]

[0011] The present invention provides a positive active material, wherein, in at least one of [1] to

[0010] , the positive active material has a rolled density of 2.58 g / cc or more measured after being pressed to 9 ton.

[0031]

[0012] The present invention provides a positive electrode for a lithium secondary battery comprising a positive electrode active material according to at least one of [1] to

[0011] .

[0032]

[0013] The present invention provides a positive electrode for a lithium secondary battery, wherein, in

[0012] the positive electrode has a charge volume energy density of 1533 Wh / L or more.

[0033]

[0014] The present invention provides a lithium secondary battery comprising a positive electrode for a lithium secondary battery of

[0012] or

[0013] .

[0034]

[0035] The positive electrode active material according to the present invention can improve the rolling density by mixing a small-sized lithium iron phosphate manganese-based oxide with a large-sized lithium iron phosphate-based oxide in a weight ratio of 75:25 to 98:2, thereby allowing the small-sized positive electrode active material to be filled between the large-sized positive electrode active materials, and thus improving the energy density of the electrode when applied to a positive electrode for a secondary battery.

[0036] Accordingly, it is possible to realize a secondary battery with excellent high-temperature life characteristics, output characteristics, and capacity characteristics.

[0037]

[0038] Terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0039] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0040] In this specification, terms such as “comprising,” “having,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof. Furthermore, in this specification, when a part such as a layer, film, region, or plate is described as being formed on another part, the direction in which it is formed is not limited to the upward direction but includes being formed in the lateral or downward direction.

[0041]

[0042] In the present invention, "primary particle" refers to a particle unit in which no grain boundaries appear when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope.

[0043] In the present invention, "secondary particle" refers to a particle formed by the aggregation of tens to hundreds of multiple primary particles. More specifically, the secondary particle is an aggregate of 30 or more primary particles.

[0044] The expression "particle" used in the present invention may include either a primary particle and a secondary particle, or both of them.

[0045] In the present invention, "D x " refers to the particle size at the x% standard of the volume cumulative particle size distribution of the positive active material. The above D x It can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Malvern Mastersizer 3000), irradiated with ultrasound of about 28 kHz at an output of 60 W, obtained a volume cumulative particle size distribution graph, and then measured by determining the particle size corresponding to x% of the volume cumulative amount.

[0046] In the present invention, “rate capability” refers to a characteristic regarding the capacity that is expressed according to the charge and discharge rate of a lithium secondary battery, and a positive electrode with high rate capability means that it expresses high capacity even at high charge and discharge rates. For example, after charging the lithium secondary battery under the same conditions, it can be evaluated as a capacity expression rate (%) calculated through the ratio of the discharge capacity measured at a discharge rate of 0.1 C-rate and at a discharge rate of 1 C-rate or higher, respectively, at the same voltage and temperature.

[0047]

[0048] The present invention will be described in more detail below.

[0049] The inventors have discovered that in order to improve the energy density and rate characteristics of a lithium secondary battery, a lithium secondary battery with excellent energy density and rate characteristics can be realized by controlling the particle size and mixing ratio of a lithium iron phosphate manganese-based oxide with excellent rate characteristics and high average voltage and a lithium iron phosphate-based oxide with relatively excellent capacity characteristics, and have completed the present invention.

[0050] The above-mentioned lithium iron phosphate manganese oxide and lithium iron phosphate oxide having an olivine structure have a one-dimensional diffusion path for lithium ions within the crystal structure, and thus have the problem of low lithium ion conductivity during charging and discharging.

[0051] Among these, lithium iron phosphate manganese-based oxide is a cathode active material in which some of the Fe in Fe-based olivine structure lithium oxide is substituted with Mn to increase the operating voltage, and although it has excellent rate characteristics, it is difficult to realize a high-density electrode in terms of limiting the increase in solid content in the slurry due to the small particle size and unfavorable rolling.

[0052] In contrast, lithium iron phosphate-based compounds have higher electronic and lithium ion conductivity compared to lithium iron manganese phosphate-based compounds, resulting in superior charge output and minimal impact on battery performance even when the average particle size is significantly controlled; however, they have the problem of low energy density due to the low operating voltage.

[0053] Meanwhile, average particle size (D 50 When different large and small particle sizes are mixed and used, the small particle sizes fill the voids between the large particle sizes, so electrode coating can be done with a relatively high rolling density compared to when using particles with one type of average particle size, and as a result, the energy density of the electrode can be increased.

[0054] Accordingly, we intend to apply the appropriate particle size and mixing ratio of each oxide to a lithium secondary battery by mixing a large-sized lithium iron phosphate-based oxide with a small-sized lithium iron phosphate-based oxide with a controlled particle size to improve rolling density through bimodalization of particle size distribution and to increase the solid content in the slurry to secure high energy density.

[0055]

[0056] The configuration of the present invention will be described in more detail below.

[0057] The positive electrode active material according to the present invention, the positive electrode including the same, and the lithium secondary battery comprise at least one of the configurations disclosed below, and may comprise any combination of technically feasible configurations among the configurations below.

[0058]

[0059] positive electrode active material

[0060]

[0061] The positive electrode active material according to the present invention comprises a small-sized lithium iron phosphate manganese-based oxide and a large-sized lithium iron phosphate-based oxide, wherein the small-sized lithium iron phosphate manganese-based oxide has an average particle size (D 50 ) is 1 μm or less, and the above large-diameter lithium iron phosphate-based oxide has an average particle size (D 50 The particle size is 4 μm to 10 μm, and the above and small particle size lithium iron phosphate manganese-based oxide and large particle size lithium iron phosphate-based oxide are included in a weight ratio of 75:25 to 98:2.

[0062]

[0063] Meanwhile, the above-mentioned small-sized lithium iron phosphate manganese-based oxide has an average particle size (D 50 The average particle size of the lithium iron phosphate manganese oxide may be 1 μm or less, specifically 0.9 μm or less, more specifically 0.8 μm or less, even more specifically 0.7 μm or 0.6 μm or less, and most specifically 0.5 μm or less. When the average particle size of the lithium iron phosphate manganese oxide satisfies the above-described range, the rate characteristics may be excellent, and small lithium iron phosphate manganese oxide particles of 1 μm or less can more densely fill the voids between large-sized lithium iron phosphate oxide particles, thereby improving energy density. In addition, the ion transport path is shortened, reducing resistance within the electrode and relieving stress, thereby enabling low resistance characteristics and excellent lifespan characteristics, and consequently, the overall performance of the battery may be improved.

[0064] The above-mentioned small-sized lithium iron phosphate manganese-based oxide may be in the form of primary particles, which are a primary structure of a single particle.

[0065] The above-mentioned small-sized lithium iron phosphate manganese-based oxide may have the composition of the following chemical formula 1.

[0066] [Chemical Formula 1]

[0067] Li 1+x Fe 1-p-q Mn p M q (PO4)

[0068] In the above chemical formula 1, M may include one or more selected from the group consisting of Ni, Co, Al, Zr, Sr, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, B, Ba, Ce, Sn, Y, V, and Zn. Although M is not necessarily included, if included in an appropriate amount, the particle shape of the cathode active material may be improved and the stability of the crystal structure may be enhanced.

[0069] In the above chemical formula 1, x is -0.1 ≤ x ≤ 0.1. If the above range is satisfied, high capacity characteristics and high energy density per unit volume can be realized.

[0070] In the above chemical formula 1, p represents the mole fraction of manganese among the total metals excluding lithium in the lithium iron phosphate manganese-based oxide, which may be 0.4 or more or 0.5 or more, and 0.8 or less or 0.7 or less. When satisfying the above ranges, high energy density can be exhibited.

[0071] In the above chemical formula 1, q is the mole fraction of M among all metals excluding lithium in the lithium iron phosphate manganese-based oxide, and may be 0 or more, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.1 or more, and may be 0.2 or less, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, or 0.11 or less. When q satisfies the above range, the structural stability of the lithium iron phosphate manganese-based oxide can be improved.

[0072]

[0073] Meanwhile, the above-mentioned large-diameter lithium iron phosphate-based oxide has an average particle size (D 50 The size may be 4 μm or more, specifically 4.5 μm or more, more specifically 5 μm or more or 5.5 μm or more, and more specifically 6 μm or more, and 10 μm or less, specifically 9.5 μm or less, more specifically 9 μm or 8.5 μm or less, and more specifically 8 μm or less. When the above range is satisfied, the slurry processability of the cathode active material is excellent, and by having a wide bimodal particle size distribution, it is advantageous in terms of space utilization, which improves rolling density and increases the energy density of the electrode, and can improve efficiency and rate characteristics.

[0074] The above-mentioned large-diameter lithium iron phosphate-based oxide may be in the form of secondary particles, which are aggregates of primary particles. When the lithium iron phosphate-based oxide is in the form of secondary particles, the average particle size can be increased, the decrease in dispersibility due to particle aggregation during cathode manufacturing can be suppressed, and high energy density can be secured.

[0075] The above-mentioned large-diameter lithium iron phosphate-based oxide may have the composition of Chemical Formula 2 below.

[0076] [Chemical Formula 2]

[0077] LiFe 1-y M' y PO4

[0078] In the above chemical formula 2, M' may include one or more selected from the group consisting of Ni, Co, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir, and V. Although M' is not necessarily included, if included in an appropriate amount, conductivity and capacitance characteristics may be improved.

[0079] In the above chemical formula 2, y is the mole fraction of M' among the total metals excluding lithium in the lithium iron phosphate-based oxide, and 0≤y<1.

[0080]

[0081] Meanwhile, the above-mentioned positive active material may have a bimodal particle size distribution. When the positive active material has a bimodal particle size distribution, small-diameter particles fill the voids between large-diameter particles, thereby improving rolling density and dispersing stress during rolling, which can prevent particle breakage.

[0082] The above positive active material is D 10 This may be 0.25 μm to 0.90 μm, specifically 0.25 μm to 0.80 μm, more specifically 0.25 μm to 0.70 μm or 0.25 μm to 0.60 μm, even more specifically 0.25 μm to 0.50 μm or 0.25 μm to 0.40 μm, most specifically 0.25 μm to 0.30 μm. When the above range is satisfied, a distinct bimodal particle size distribution can be achieved.

[0083] The above positive active material is D 50This can be 0.4 μm to 1.0 μm, specifically 0.4 μm to 0.9 μm, more specifically 0.4 μm to 0.8 μm, and most specifically 0.4 μm to 0.7 μm. When the above range is satisfied, the small-particle lithium iron phosphate manganese-based oxide is appropriately distributed among the large-particle lithium iron phosphate-based oxides, so the filling rate can be excellent.

[0084] The above positive active material is D 90 This can be 3.1 μm to 10.0 μm, more specifically 3.2 μm to 9.5 μm, even more specifically 3.3 μm to 9.0 μm, and most specifically 3.4 μm to 8.5 μm. When the above range is satisfied, a distinct bimodal particle size distribution can be achieved.

[0085]

[0086] Meanwhile, the above positive active material may have a rolled density of 2.35 g / cc, specifically 2.38 g / cc or more, measured after pressurizing to 3 ton.

[0087] Meanwhile, the above positive active material may have a rolled density of 2.48 g / cc, specifically 2.50 g / cc or more, measured after pressurizing to 6 ton.

[0088] Meanwhile, the above-mentioned positive active material may have a rolled density of 2.58 g / cc, specifically 2.59 g / cc or higher, measured after pressurizing to 9 ton. If the positive active material satisfies the above range, high energy density can be achieved.

[0089]

[0090] Meanwhile, a large-sized lithium iron phosphate-based oxide may be included in a small-sized lithium iron phosphate-based oxide in a weight ratio of 75:25 to 98:2, specifically in a weight ratio of 80:20 to 98:2, more specifically in a weight ratio of 83:17 to 97:3, even more specifically in a weight ratio of 85:15 to 96:4, and most specifically in a weight ratio of 90:10 to 95:5. When the above range is satisfied, the energy density improvement effect due to the bimodalization of the particle size distribution can be maximized while maintaining the rate characteristics of the lithium iron phosphate manganese-based oxide. When large-sized lithium iron phosphate-based oxide is included in a weight ratio of 90:10 to 95:5 with small-sized lithium iron phosphate manganese-based oxide, the tap density and rolling density can be improved, and the best energy density can be achieved by minimizing the loss of the average operating voltage due to the addition of lithium iron phosphate-based oxide.

[0091]

[0092] anode

[0093] The present invention provides a positive electrode comprising the above positive electrode active material.

[0094] The anode according to the present invention comprises an anode active material layer comprising an anode active material according to the present invention. Specifically, the anode comprises an anode current collector and an anode active material layer formed on the anode current collector and comprising the anode active material. Since the anode active material has been described above, a detailed explanation is omitted, and only the remaining components are described in detail below.

[0095] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0096] The above positive active material layer may include a positive conductive material and a positive binder together with the positive active material. In this case, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 85% to 98.5% by weight, based on the total weight of the positive active material layer, and may exhibit excellent capacity characteristics within this range.

[0097] The above-mentioned positive electrode conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fibers; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above-mentioned positive electrode conductive material may be included in an amount of 0.1% to 15% by weight relative to the total weight of the positive electrode active material layer.

[0098] The anode binder described above serves to improve adhesion between anode active material particles and adhesion between the anode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The anode binder may be included in an amount of 0.1% to 15% by weight relative to the total weight of the anode active material layer.

[0099] The above-described anode may be manufactured according to a conventional anode manufacturing method, except for using the above-described anode active material. Specifically, it may be manufactured by applying a composition for forming an anode active material layer, prepared by dissolving or dispersing the above-described anode active material and, optionally, a binder and a conductive material in a solvent, onto an anode current collector, followed by drying and rolling. At this time, the types and contents of the anode active material, binder, and conductive material are as described above. Alternatively, the above-described anode may be manufactured by casting the composition for forming an anode active material layer onto a separate support, and then laminating the film obtained by peeling from the support onto an anode current collector.

[0100] The above solvent may be a solvent commonly used in the relevant technical field, and may include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of the above solvent used is sufficient if it has a viscosity that dissolves or disperses the anode active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and subsequently provides excellent thickness uniformity when coated for anode manufacturing.

[0101]

[0102] When the anode according to the present invention is charged and discharged at a 0.1 C-rate, the initial charge / discharge capacity efficiency may be 96.4% or higher, specifically 96.5% or higher, and more specifically 96.6% or higher.

[0103] The anode according to the present invention may have a charge volume energy density of 1533 Wh / L or more, specifically 1534 Wh / L or more, more specifically 1535 Wh / L or more, and even more specifically 1536 Wh / L or more.

[0104]

[0105] lithium secondary battery

[0106] Next, a lithium secondary battery according to the present invention will be described.

[0107] A lithium secondary battery according to the present invention comprises a positive electrode for a lithium secondary battery according to the present invention. Specifically, it comprises a negative electrode disposed opposite to the positive electrode and an electrolyte. Optionally, the lithium secondary battery according to the present invention may further comprise a separator interposed between the positive electrode and the negative electrode.

[0108] Since the anode above is the same as described above, the remaining components excluding the anode will be described below.

[0109]

[0110] (1) Cathode

[0111] In a lithium secondary battery according to the present invention, the negative electrode comprises a negative electrode active material layer including a negative electrode active material, and specifically, may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0112] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0113] The above negative electrode active material layer may be located on the negative electrode current collector, and specifically, may be located on one or both sides of the negative electrode current collector. The above negative electrode active material layer may have a single-layer structure or a multi-layer structure of two or more layers.

[0114] When the negative electrode active material layer is a multilayer structure composed of two or more layers, the types and / or contents of the negative electrode active material, negative electrode binder, and / or negative electrode conductive material in each layer may differ from one another. By forming the negative electrode active material layer into a multilayer structure and varying the composition of each layer, the performance characteristics of the battery, such as rapid charging performance and output characteristics, can be appropriately controlled.

[0115] Meanwhile, as the above-mentioned cathode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides capable of doping and dedoping lithium such as SiOβ (0 < β < 2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the above-mentioned metallic compounds and carbonaceous materials such as Si-C composites or Sn-C composites, and any one or more of these may be used.

[0116] Meanwhile, both low-crystallinity carbon and high-crystallinity carbon can be used as the aforementioned carbonaceous materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0117] Specifically, the cathode active material may be a carbon-based cathode active material, wherein the carbon-based cathode active material may include, for example, natural graphite, artificial graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, or a combination thereof. More preferably, the carbon-based cathode active material may include natural graphite and artificial graphite.

[0118] The above carbon-based negative electrode active material has an average particle size D 50 This can be 0.1 μm to 30 μm, preferably 0.5 μm to 30 μm.

[0119] The above-mentioned negative electrode active material may be included in an amount of 80% to 98% by weight, preferably 90% to 98% by weight, and more preferably 93% to 98% by weight, based on the total weight of the negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, excellent energy density can be achieved.

[0120] Meanwhile, the above-mentioned cathode active material layer may further include a cathode conductive material and / or a cathode binder together with the cathode active material.

[0121] The cathode conductive material is used to impart conductivity to the cathode, and in the battery being constructed, it can be used without special restrictions as long as it has electronic conductivity without causing chemical changes. Specific examples include carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more of them may be used.

[0122] The above-mentioned cathode conductive material may typically be included in an amount of 0.1% to 10% by weight, specifically 0.1% to 8% by weight, more specifically 0.1% to 5% by weight, based on the total weight of the cathode active material layer.

[0123] The above-mentioned cathode binder serves to improve adhesion between cathode active material particles and adhesion between the cathode active material and the cathode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0124] The above-mentioned cathode binder may be included in an amount of 0.1% to 10% by weight, preferably 0.5% to 10% by weight, and more preferably 1% to 8% by weight, based on the total weight of the cathode active material layer.

[0125] The above cathode may be manufactured by methods known in the art. For example, the cathode may be manufactured by mixing a cathode active material, a cathode binder, and / or a cathode conductive material in a solvent to prepare a cathode slurry, applying the cathode slurry onto a cathode current collector, and then drying and rolling, or by casting the cathode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0126] Meanwhile, solvents commonly used in the relevant technical field may be used as the solvent for the cathode slurry, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, or mixtures thereof, but are not limited thereto. The solvent may be used in an amount that dissolves or disperses the cathode active material, cathode conductive material, and cathode binder, and has a viscosity such that the cathode slurry can be uniformly coated.

[0127]

[0128] (2) Electrolyte

[0129] The electrolyte according to the present invention may include a lithium salt and an organic solvent.

[0130]

[0131] The above lithium salt can be used without special limitations as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 M to 5.0 M, more preferably 0.1 M to 3.0 M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and allow lithium ions to move effectively.

[0132]

[0133] The above organic solvent may include at least one of a cyclic carbonate-based organic solvent, a linear carbonate-based organic solvent, a linear ester-based organic solvent, and a cyclic ester-based organic solvent.

[0134] The above-mentioned cyclic carbonate-based organic solvent is a high-viscosity organic solvent and may include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

[0135] In addition, the above-mentioned linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and as a representative example, at least one organic solvent selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate may be used, and specifically, it may include ethylmethyl carbonate (EMC).

[0136] Specific examples of the above linear ester-based organic solvent may include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0137] The above-mentioned cyclic ester-based organic solvent may include at least one organic solvent selected from the group consisting of butyrolactone, valerolactone, and caprolactone.

[0138] Preferably, the electrolyte according to the present invention may include ethylene carbonate and dimethyl carbonate as organic solvents.

[0139]

[0140] Meanwhile, in addition to the electrolyte components, the above electrolyte may additionally include other additives for the purpose of improving the lifespan characteristics of the battery, suppressing the reduction of battery capacity, and improving the discharge capacity of the battery.

[0141] These other additives may include at least one other additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds different from the lithium salt contained in the electrolyte, as representative examples.

[0142] Specifically, the above other additives are vinylene carbonate (VC), vinylethylene carbonate, fluoroethylene carbonate (FEC), 1,3-propane sulfone (PS), 1,4-butane sulfone, ethene sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, 1-methyl-1,3-propene sulfone, ethylene sulfate (ESA), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), tetraphenyl borate, lithium oxalyl difluoroborate, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, Examples include one or more compounds selected from the group consisting of 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, LiN(SO2F)2 (Lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI), LiPO2F2, LiODFB, LiBOB (lithium bis-oxalate toborate (LiB(C2O4)2)) and LiBF4.

[0143] The above other additives may be included in an amount of 0.01% to 20% by weight based on the total weight of the electrolyte, and preferably in an amount of 0.05% to 5.0% by weight. If the content of the above other additives is less than 0.01% by weight, the effect of improving low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery is negligible, and if the content of the above other additives exceeds 20% by weight, there is a possibility that excessive side reactions may occur within the electrolyte during charging and discharging of the battery. In particular, when the above SEI film-forming additives are added in excess, they may not decompose sufficiently at high temperatures and may remain as unreacted substances or precipitated within the electrolyte at room temperature. Accordingly, side reactions that degrade the lifespan or resistance characteristics of the secondary battery may occur.

[0144]

[0145] (3) Separator

[0146] The above separator physically separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions; any separator typically used in lithium secondary batteries can be used without any special restrictions. In this case, the separator may be interposed between the positive electrode and the negative electrode.

[0147] Specifically, 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, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing a ceramic component or a polymer material may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0148]

[0149] The lithium secondary battery according to the present invention as described above can be usefully applied to portable devices such as mobile phones, laptop computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs). Since the lithium secondary battery according to the present invention can achieve excellent output characteristics even under low temperature conditions, it can be particularly usefully applied in the field of electric vehicles.

[0150]

[0151] According to another embodiment of the present invention, a battery module comprising a lithium secondary battery according to the present invention as a unit cell and a battery pack comprising the same are provided.

[0152]

[0153] The above battery module or battery pack can be used as a power source for one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0154]

[0155] The present invention will be explained more specifically through the following specific embodiments.

[0156]

[0157] Preparation Example. Preparation of Examples and Comparative Examples

[0158] Small-sized lithium iron phosphate manganese oxide

[0159] It is a small-particle lithium iron phosphate manganese-based oxide with a molar ratio of Li:Mn:Fe:PO4 of 1.06:0.60:0.40:1.02 and an average particle size D 50 A lithium iron phosphate manganese-based oxide with a thickness of 0.4 μm was prepared.

[0160]

[0161] Large-diameter lithium iron phosphate oxide

[0162] It is a large-diameter lithium iron phosphate-based oxide with a molar ratio of Li:Fe:PO4 of 1.08:1.00:1.03, and as a secondary particle powder consisting of aggregates of primary particles, with an average particle size D 50 A lithium iron phosphate-based oxide with a thickness of 7.2 μm was prepared.

[0163]

[0164] small-particle lithium iron phosphate-based oxide

[0165] It is a small-sized lithium iron phosphate-based oxide with a molar ratio of Li:Fe:PO4 of 1.07:1.00:1.06 and an average particle size D 50 A lithium iron phosphate-based oxide with a thickness of 1.02 μm was prepared.

[0166]

[0167] The lithium iron phosphate manganese-based oxide and lithium iron phosphate-based oxide prepared as above were mixed in the weight ratios listed in Table 1 below to prepare the cathode active materials of Examples 1 to 2 and Comparative Examples 1 to 9.

[0168] Small particle size lithium iron phosphate manganese-based oxide (0.4 μm) Large particle size lithium iron phosphate-based oxide (7.2 μm) Small particle size lithium iron phosphate-based oxide (1.02 μm) Example 19550 Example 290100 Comparative Example 110000 Comparative Example 240600 Comparative Example 330700 Comparative Example 420800 Comparative Example 510900 Comparative Example 601000 Comparative Example 79505 Comparative Example 890010 Comparative Example 900100

[0169] Experimental Example 1. Particle Size Distribution Analysis

[0170] To compare the particle size distributions of the above examples and comparative examples, volume cumulative particle size distribution graphs of Examples and Comparative Examples 1, 6 to 9 were obtained using the laser diffraction method, and then D0, D 10 , D 50 , D 90 and D 100This is shown in Table 2 below.

[0171] [㎛]D0D 10 D 50 D 90 D 100 Example 10.1890.290.463.7340.0 Example 20.1890.290.488.2740.1 Comparative Example 10.1890.270.400.620.87 Comparative Example 60.3601.887.2017.340.1 Comparative Example 70.1890.280.450.825.90 Comparative Example 80.1890.290.460.975.89 Comparative Example 90.2440.451.023.075.89

[0172] Referring to the results in Table 2 above, the average particle size D 50 Average particle size D in this 0.4 μm lithium iron phosphate manganese-based oxide 50 Compared to Comparative Examples 7 to 8, which mixed a lithium iron phosphate-based oxide of 1.02 μm, D 50 'D' of Examples 1 and 2 mixed with this 7.2 μm lithium iron phosphate-based oxide 100 -D0' and 'D 90 -D 10 It can be confirmed that the value is large, which means it has a much wider and more distinct bimodal particle size distribution.

[0173] Experimental Example 2. Evaluation of Rolled Density

[0174] The rolling density of each of the positive electrode active materials of the example and comparative example prepared in the above manufacturing example was measured using a density meter (Caver Pellet Press). Specifically, 1 g of the positive electrode active material prepared in each of the above example and comparative example was divided and filled without gaps into a cylindrical holder with a diameter of 13 mm, and then the rolling density of each was measured by applying pressures of 3 ton, 6 ton, and 9 ton.

[0175] The results of the above rolling density measurement are as shown in Table 3 below.

[0176] Rolled Density [g / cc] Pressure 3 ton 6 ton 9 ton Example 1 2.38 8 2.5 1 8 2.5 91 Example 2 2.40 8 2.5 3 7 2.6 14 Comparative Example 1 2.37 0 2.5 0 2 2.5 70 Comparative Example 2 2.30 8 2.46 2 2.5 41 Comparative Example 3 2.30 1 2.46 0 2.5 40 Comparative Example 4 2.29 5 2.45 7 2.5 40 Comparative Example 5 2.28 9 2.45 4 2.5 39 Comparative Example 6 2.28 2 2.45 2 2.5 39 Comparative Example 7 2.38 1 2.5 10 2.5 77 Comparative Example 8 2.5 10 2.5 2 7 2.5 92 Comparative Example 9 2.5 7 7 2.5 9 2 2.6 76

[0177] In Table 3 above, when comparing the results of Comparative Example 6, composed solely of large-particle lithium iron phosphate-based oxide; Comparative Example 9, composed solely of small-particle lithium iron phosphate-based oxide; and Comparative Example 1, composed solely of small-particle lithium iron phosphate-manganese-based oxide, it can be seen that the rolling density of the large-particle lithium iron phosphate-based oxide is lower than that of not only the small-particle lithium iron phosphate-based oxide but also the small-particle lithium iron phosphate-manganese-based oxide. Nevertheless, the results of Examples 1 and 2 confirm that when mixed in a small amount with the small-particle lithium iron phosphate-manganese-based oxide, the rolling density can be improved compared to Comparative Example 1, which is a cathode active material composed solely of lithium iron phosphate-manganese-based oxide. In particular, when comparing the results of Examples 1 and 2 with Comparative Examples 1 to 5, in the case of Comparative Examples 2 to 5, where the large-particle lithium iron phosphate-based oxide is mixed in excess, the rolling density is lower than that of Comparative Example 1, whereas when the large-particle lithium iron phosphate-based oxide is mixed in a small amount It can be confirmed that Examples 1 and 2, which are mixed and have a weight ratio of 75:25 to 2:98, have an increased rolling density compared to Comparative Example 1.

[0178] In addition, referring to the results of Comparative Examples 7 and 8, it can be seen that in the case of small-particle lithium iron phosphate-based oxide, even when mixed with lithium iron phosphate manganese-based oxide of different particle sizes, the effect of improving rolling density is negligible compared to the case where large-particle lithium iron phosphate-based oxide, which has relatively inferior rolling density, is mixed at the same mixing ratio. This is interpreted as being advantageous in terms of space utilization because Examples 1 and 2 have a wide bimodal particle size distribution, as shown in the result of Experimental Example 1 above.

[0179]

[0180] Experimental Example 3. Battery Performance Evaluation

[0181] Manufacture of Lithium Secondary Battery Half Cells

[0182] A positive electrode active material, carbon black conductive material, and PVDF binder of each of the above Examples 1 to 2 and Comparative Examples 1, 6 to 9 were mixed in an N-methylpyrrolidone solvent in a weight ratio of 90:5:5 to prepare a positive electrode slurry, which was then coated on one side of an aluminum current collector, dried at 130°C, and rolled to produce a positive electrode.

[0183] An electrode assembly was manufactured by interposing a porous polyethylene separator between the anode manufactured as described above and a cathode made of lithium metal, and a lithium secondary battery half cell was manufactured by placing the electrode assembly inside a case and injecting an electrolyte into the case. As the electrolyte, LiPF6 was dissolved to a concentration of 1M in a solvent in which ethylene carbonate (EC), diethylene carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:2:1 and vinylene carbonate (VC) was added at 2wt%.

[0184]

[0185] 3-1. Evaluation of Capacity Characteristics

[0186] After leaving the above-manufactured half cells for 24 hours, they were each charged to 4.25 V at 25 ℃ at a rate of 0.1 C-rate, left for 30 minutes, and discharged to 2.5 V at a rate of 0.1 C-rate to measure the initial charge / discharge capacity. The efficiency (%) was expressed as the percentage of the initial discharge capacity relative to the initial charge capacity, and this was shown in Table 4 below along with the initial charge / discharge capacity.

[0187] [mAh / g][%] Initial Charge Capacity Initial Discharge Capacity Efficiency Example 1 154.0 148.9 96.7 Example 2 154.9 151.0 97.5 Comparative Example 1 153.3 147.4 96.2 Comparative Example 6 162.6 159.6 98.2 Comparative Example 7 153.8 148.0 96.2 Comparative Example 8 154.6 148.9 96.3 Comparative Example 9 162.4 158.0 97.3

[0188] Referring to the results in Table 4 above, it can be seen that Comparative Examples 6 and 9, composed of lithium iron phosphate-based oxide, have excellent initial charge / discharge capacity and efficiency. However, when comparing the results of Comparative Examples 1 and 7 to 8, it can be seen that even when small-particle lithium iron phosphate-based oxide, which has excellent initial charge / discharge capacity and efficiency, is mixed with lithium iron phosphate manganese-based oxide, the effect of improving efficiency is minimal. On the other hand, when comparing the results of Comparative Example 1 and Examples 1 to 2, it can be seen that when large-particle lithium iron phosphate-based oxide is mixed, the efficiency of the battery is improved relatively significantly.

[0189]

[0190] 3-2. Evaluation of Rate Characteristics

[0191] After charging the above-manufactured half cell to 4.25 V at 25 ℃ with a 0.1 C-rate, leaving it for 30 minutes, and discharging it to 2.5 V at a specific C-rate (1.0 C, 4.0 C), the discharge capacity according to each rate limit condition was measured, and the percentage of the discharge capacity under each rate limit condition relative to the initial discharge capacity shown in Table 4 above was defined as the capacity development rate (%) and is shown together in Table 5 below.

[0192] Discharge Capacity [mAh / g] Capacity Development Rate [%] 1.0 C 4.0 C 1.0 C 4.0 C Example 1 137.7 128.4 92.5 86.2 Example 2 139.3 129.2 92.3 85.6 Comparative Example 1 136.3 127.7 92.5 86.6 Comparative Example 6 143.8 132.9 90.1 83.3 Comparative Example 7 135.8 126.3 91.8 85.3 Comparative Example 8 135.4 125.6 90.9 84.4 Comparative Example 9 134.1 117.6 84.9 74.4

[0193] Referring to the results in Table 5 above, it can be confirmed through the results of Comparative Examples 1, 6, and 9 that the lithium iron phosphate manganese-based oxide has superior rate characteristics compared to the lithium iron phosphate-based oxide. Furthermore, by comparing the results of Examples 1 and 2 with Comparative Example 1, it can be confirmed that when a small amount of lithium iron phosphate-based oxide is mixed with the lithium iron phosphate manganese-based oxide, even if the lithium iron phosphate-based oxide with inferior rate characteristics is mixed, rate characteristics similar to those of the cathode active material composed solely of lithium iron phosphate manganese-based oxide can be achieved.

[0194] 3-3. Average Voltage Measurement

[0195] The average charging voltage was measured during the charging and discharging process in which the above-manufactured half cell was charged to 4.25 V at 25 ℃ at a 0.1 C-rate, left for 30 minutes, and then discharged to 2.5 V at a 0.1 C-rate, and is shown in Table 6 below.

[0196] Average Charging Voltage [V] Example 13.85 Example 23.83 Comparative Example 13.87 Comparative Example 63.51 Comparative Example 73.84 Comparative Example 83.82 Comparative Example 93.48

[0197] Referring to the results in Table 6 above, it can be seen that the average charging voltage of lithium iron manganese oxide is superior to that of lithium iron phosphate-based oxide, and that the average charging voltage is higher as the ratio of lithium iron manganese oxide to lithium iron phosphate-based oxide in the cathode active material increases. Additionally, it can be observed that the average charging voltage decreases when lithium iron phosphate-based oxide is mixed with lithium iron manganese oxide.

[0198] 3-4. Energy Density Evaluation

[0199] Based on the rolling density, average charging voltage, and initial charging capacity values ​​measured in the above experimental example, the charging weight energy density and charging volume energy density were calculated according to Equations 1 and 2 below and are shown in Table 7 below.

[0200] [Equation 1]

[0201] Gravimetric Energy Density (Wh / kg) = Average Charging Voltage * 0.1 C Charging Capacity

[0202] [Equation 2]

[0203] Charge Volume Energy Density (Wh / L) = Average Charge Voltage * 0.1 C Charge Capacity * Rolled Density

[0204] Charged Gravimetric Energy Density [Wh / kg] Charged Volumetric Energy Density [Wh / L] Example 1 5931536 Example 2 5931551 Comparative Example 1 5931525 Comparative Example 6 5711449 Comparative Example 7 5911522 Comparative Example 8 5911531 Comparative Example 9 5651512

[0205] *211 Referring to the results of Table 7 above, it can be confirmed that the charge volume energy density of Examples 1 and 2 is the best. In particular, the fact that the final charge volume energy density is the best, despite having a lower initial charge capacity compared to Comparative Examples 6 and 9 made of lithium iron phosphate-based oxide and a lower average charge voltage compared to Comparative Example 1 made of lithium iron phosphate-based manganese oxide, is interpreted as being due to the improvement in rolling density, and means that the mixing ratio of small-particle lithium iron phosphate-based manganese oxide and large-particle lithium iron phosphate-based oxide according to the present invention has been optimized to maximize the energy density improvement effect.

[0206]

[0207] From the foregoing description, those skilled in the art to which the present invention pertains will understand that the present invention may be implemented in other specific forms without altering its technical concept or essential features. In this regard, the embodiments described above should be understood as illustrative in all respects and not restrictive. The scope of the present invention should be interpreted as including all modifications or variations derived from the meaning and scope of the claims set forth below and their equivalents, rather than from the detailed description above.

Claims

1. Includes small-sized lithium iron phosphate manganese-based oxide and large-sized lithium iron phosphate-based oxide, and The above-mentioned small-sized lithium iron phosphate manganese-based oxide has an average particle size (D 50 ) is 1 μm or less, and The above-mentioned large-diameter lithium iron phosphate-based oxide has an average particle size (D 50 ) is 4 μm to 10 μm, and A positive electrode active material comprising the above and small-sized lithium iron phosphate manganese-based oxide and large-sized lithium iron phosphate-based oxide in a weight ratio of 75:25 to 98:

2.

2. In Paragraph 1, The above-mentioned small-sized lithium iron phosphate manganese-based oxide has an average particle size (D 50 A positive electrode active material having a thickness of 0.5 μm or less.

3. In Paragraph 1, A positive electrode active material comprising the above-mentioned small-sized lithium iron phosphate manganese-based oxide and large-sized lithium iron phosphate-based oxide in a weight ratio of 90:10 to 95:

5.

4. In Paragraph 1, The above-mentioned small-sized lithium iron phosphate manganese-based oxide is a positive electrode active material having the composition of the following chemical formula 1. [Chemical Formula 1] Li 1+x Fe 1-p-q Mn p M q (PO4) In the above chemical formula 1, The above M is one or more selected from the group consisting of Ni, Co, Al, Zr, Sr, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, B, Ba, Ce, Sn, Y, V and Zn, and -0.1≤x≤0.1, 0.4≤p≤0.8, 0≤q≤0.

1.

5. In Paragraph 1, The above-mentioned large-diameter lithium iron phosphate-based oxide is a positive electrode active material in the form of secondary particles that are aggregates of primary particles.

6. In Paragraph 1, The above-mentioned large-diameter lithium iron phosphate-based oxide is a positive electrode active material having the composition of Chemical Formula 2 below. [Chemical Formula 2] LiFe 1-y M' y PO4 In the above chemical formula 2, M' is one or more selected from the group consisting of Ni, Co, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir and V, and 0≤y<1.

7. In Paragraph 1, The above positive active material is a positive active material having a bimodal particle size distribution.

8. In Paragraph 1, The above positive active material is D 10 A positive electrode active material having a thickness of 0.25 μm to 0.90 μm.

9. In Paragraph 1, The above positive active material is D 50 A positive electrode active material having a thickness of 0.4 μm to 1.0 μm.

10. In Paragraph 1, The above positive active material is D 90 A positive electrode active material having a thickness of 3.1 μm to 10.0 μm.

11. In Paragraph 1, The above positive active material is a positive active material having a rolled density of 2.58 g / cc or more measured after pressurizing to 9 ton.

12. A positive electrode for a lithium secondary battery comprising a positive electrode active material according to claim 1.

13. In Paragraph 12, The above-mentioned anode is a cathode for a lithium secondary battery having a charge volume energy density of 1533 Wh / L or higher.

14. A lithium secondary battery comprising a positive electrode for a lithium secondary battery according to claim 12.