Positive electrode and lithium secondary battery comprising same

Abstract

The present invention relates to a positive electrode and a lithium secondary battery including same, the positive electrode including a current collector and a positive electrode active material layer disposed on the current collector, wherein the positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder. The positive electrode active material includes a lithium iron phosphate-based compound, the conductive material includes carbon black, the conductive material has a BET specific surface area of 200m2 / g to 400m2 / g, and a value of R1 represented by the following Equation 1 is in a range of 180 to 500. [Equation 1] R1= {[ average particle diameter (D50) of the positive electrode active material] × [BET specific surface area of the conductive material]} / [average particle diameter (D50) of the conductive material]2. In equation 1, each of the average particle diameter (D50) value (㎛) of the positive electrode active material, the BET specific surface area value (m2 / g) of the conductive material, and the average particle diameter (D50) value (㎛) of the conductive material (µm) is a dimensionless value with units omitted.

Description

Anode and lithium secondary battery including the same

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0131920 filed on September 27, 2024, and all contents disclosed in said Korean Patent Application are incorporated herein as part of this specification.

[0002] The present invention relates to a positive electrode and a lithium secondary battery including the same.

[0003] A lithium secondary battery is generally manufactured by forming an electrode assembly by interposing a separator between a positive electrode containing a positive active material containing lithium and a negative electrode containing a negative active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that serves as a medium for transmitting lithium ions, and then sealing it.

[0004] These lithium secondary batteries are used in portable electronic devices such as mobile phones and laptops, as well as in electric vehicles, and demand is surging with the recent expansion of electric vehicle adoption. In particular, lithium secondary batteries used in electric vehicles require high energy density and excellent charging rate characteristics.

[0005] Meanwhile, lithium cobalt-based oxides, lithium nickel-based oxides, lithium manganese-based oxides, lithium nickel-cobalt-manganese-based oxides, lithium manganese phosphate compounds, and lithium iron phosphate compounds are used as positive electrode active materials for lithium secondary batteries.

[0006] Among these, lithium iron phosphate compounds are widely used as cathode active materials for lithium secondary batteries due to their excellent thermal stability, superior lifespan characteristics, safety, and low cost; however, compared to ternary cathode active materials, their relatively smaller particle size makes it difficult to form a conductive network, resulting in reduced conductivity.

[0007] Accordingly, there is a need to develop lithium secondary batteries containing lithium iron phosphate compounds that exhibit excellent thermal stability and superior lifespan characteristics despite the use of small-sized lithium iron phosphate compounds.

[0008] The present invention relates to an average particle size (D) of a positive electrode active material comprising a lithium iron phosphate-based compound. 50 ), average particle size of conductive material including carbon black (D 50 We aim to provide a cathode with improved lifespan characteristics and a lithium secondary battery containing the same by ensuring that the ) and BET specific surface area satisfy a specific equation.

[0009] [1] The present invention comprises a current collector and a positive active material layer disposed on the current collector, wherein the positive active material layer comprises a positive active material, a conductive material, and a binder, wherein the positive active material comprises a lithium iron phosphate-based compound, the conductive material comprises carbon black, and the BET specific surface area of ​​the conductive material is 200 m² 2 / g to 400m 2 A positive electrode is provided having a value of R1 of 180 to 500, expressed by the following formula 1, and is / g.

[0010] [Equation 1]

[0011] R1= {[average particle size of the positive active material (D 50 ) value] × [BET specific surface area value of conductive material]} / [average particle size of conductive material (D 50 ) value] 2

[0012] In the above Equation 1, the average particle size (D) of the positive active material 50 ) value (㎛), BET specific surface area value of the conductive material (m 2 / g) and average particle size of conductive material (D 50 Each of the ) values ​​(㎛) is a unitless number with the unit omitted.

[0013] [2] The present invention provides an anode in which the value of R2, represented by the following formula 2, is 0.9 to 1.1, in accordance with [1].

[0014] [Equation 2]

[0015] R2 = [average particle size of positive active material (D 50 ) value] / [Average particle size of conductive material (D 50 ) value]

[0016] [3] The present invention provides an anode in which the value of R3, represented by the following formula 3, is 200 to 450, in [1] or [2].

[0017] [Equation 3]

[0018] R3 = [BET specific surface area of ​​the conductive material] / [average particle size of the conductive material (D 50 ) value]

[0019] In Equation 3 above, the BET specific surface area value (m) of the conductive material 2 / g) and average particle size of conductive material (D 50 Each of the ) values ​​(㎛) is a unitless number with the unit omitted.

[0020] [4] The present invention, in at least one of [1] to [3], wherein the average particle size (D) of the conductive material is 50 ) provides an anode having a diameter of 0.7㎛ to 1.3㎛.

[0021] [5] The present invention, in at least one of [1] to [4], wherein the average particle size (D) of the positive electrode active material is 50 ) provides an anode having a diameter of 0.6㎛ to 1.6㎛.

[0022] [6] The present invention provides an anode represented by the following chemical formula 1, wherein at least one of [1] to [5] above is a lithium iron phosphate compound.

[0023] [Chemical Formula 1]

[0024] Li 1+x [Fe 1-y M y ]PO4

[0025] In the above chemical formula 1, M comprises one or more selected from the group consisting of Ni, Co, Mn, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir, and V, and -0.5≤x≤0.5, 0≤y<1.

[0026] [7] The present invention provides an anode in which, in at least one of [1] to [6], the conductive material is included in an amount of 0.5% to 5.0% by weight based on the total weight of the anode active material layer.

[0027] [8] The present invention provides a positive electrode in which, in at least one of [1] to [7], the positive electrode active material further comprises a conductive coating layer.

[0028] [9] The present invention provides a positive electrode in which, in at least one of [1] to [8], the weight ratio of the positive electrode active material and the conductive material is 90:10 to 99:1.

[0029]

[0010] The present invention provides an anode comprising at least one of [1] to [9], wherein the binder comprises one or more selected from the group consisting of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC).

[0030]

[0011] The present invention provides an anode having a porosity of 15% to 40% in at least one of [1] to

[0010] .

[0031]

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

[0011] .

[0032] The anode according to the present invention controls the BET specific surface area of ​​a conductive material including carbon black, and the average particle size (D) of the conductive material 50 The average particle size (D) of the positive electrode active material containing the lithium iron phosphate-based compound 50It is adjusted to a level similar to that of ), and as a result, the formation of a conductive network within the electrode is facilitated, so consequently, excellent lifespan characteristics of the cathode and lithium secondary battery containing it can be achieved.

[0033] The present invention will be described in more detail below.

[0034] 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.

[0035] In the present invention, 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 excluding in advance the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0036] In the present invention, the “BET specific surface area” is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BEL Japan’s BELSORP-mino II.

[0037] In the present invention, "average particle size (D 50 )" refers to the particle size at the 50% reference of the volumetric cumulative particle size distribution. The above average particle size (D 50 ) can be measured using the laser diffraction method. The laser diffraction method generally enables the measurement of particle sizes ranging from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0038] 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 50 or more primary particles.

[0039]

[0040] The present invention will be described in detail below.

[0041] The positive electrode and lithium secondary battery according to the present invention include at least one of the configurations disclosed below, and may include any combination of technically feasible configurations among the configurations below.

[0042]

[0043] <Polar>

[0044] Hereinafter, the anode according to the present invention will be described.

[0045] The positive electrode according to the present invention comprises a current collector and a positive electrode active material layer disposed on the current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a conductive material, and a binder, wherein the positive electrode active material comprises a lithium iron phosphate-based compound, the conductive material comprises carbon black, and the BET specific surface area of ​​the conductive material is 200 m² 2 / g to 400m 2 / g, and the value of R1 represented by the following Equation 1 is 180 to 500.

[0046] [Equation 1]

[0047] R1= {[average particle size of the positive active material (D 50 ) value] × [BET specific surface area value of conductive material]} / [average particle size of conductive material (D 50 ) value] 2

[0048] In the above Equation 1, the average particle size (D) of the positive active material 50 ) value (㎛), BET specific surface area value of the conductive material (m 2 / g) and average particle size of conductive material (D 50 Each of the ) values ​​(㎛) is a unitless number with the unit omitted.

[0049]

[0050] In the case of a positive electrode active material containing a lithium iron phosphate compound, the relative average particle size (D) compared to a nickel-cobalt-manganese ternary positive electrode active material 50 Because ) is small, in order to form a conductive network within the electrode, it must be uniformly dispersed, and the average particle size (D 50 A conductive material with a small ) is required. However, in the case of carbon nanotubes, which are widely used as conventional conductive materials, their length reaches several micrometers (㎛) but their diameter is only tens of nanometers (nm), so agglomeration occurs between particles; therefore, the average particle size (D 50 When this is mixed with a small positive electrode active material, it is difficult to achieve uniform dispersion, which has the disadvantage of potentially leading to a lack of electrical conduction pathways.

[0051] However, in the case of carbon black, it consists of very fine particles that are close to spherical, and due to the small particle size, it has the advantage of being easily mixed with the cathode active material containing lithium iron phosphate compounds and uniformly dispersed to form a consistent conduction path within the electrode, thereby forming a conductive network.

[0052] Accordingly, the inventors of the present invention have an average particle size (D) such as a positive electrode active material containing a lithium iron phosphate-based compound. 50 Carbon black was used as a conductive material that maintains dispersibility even when mixed with a small cathode active material, and to optimize dispersibility, the BET specific surface area of ​​the carbon black conductive material was increased so that the average particle size (D) of the carbon black conductive material 50 ) average particle size (D) of a positive electrode active material containing a lithium iron phosphate-based compound 50 The positive electrode active materials were adjusted to be small enough to be similar to ), and accordingly, excellent electrical conductivity was achieved by connecting the positive electrode active materials with a conductive material to form a conductive network, and a lithium secondary battery exhibiting excellent lifespan characteristics was developed by including such a positive electrode.

[0053] Hereinafter, the anode according to the present invention will be described in more detail.

[0054]

[0055] The anode according to the present invention has a value of R1 represented by the following formula 1 of 180 to 500.

[0056] [Equation 1]

[0057] R1= {[average particle size of the positive active material (D 50 ) value] × [BET specific surface area value of conductive material]} / [average particle size of conductive material (D 50 ) value] 2

[0058] In the above Equation 1, the average particle size (D) of the positive active material 50 ) value (㎛), BET specific surface area value of the conductive material (m 2 / g) and average particle size of conductive material (D 50 Each of the ) values ​​(㎛) is a unitless number with the unit omitted.

[0059] If the value of R1 above is less than 180, the BET specific surface area of ​​the conductive material is excessively small, or the average particle size (D) of the conductive material 50 This corresponds to the case where ) is excessively large, where the conductive material is not uniformly distributed with the positive active material, so the conductive network is not properly formed, and the average particle size (D 50 There is a problem in that the electrical conductivity of the electrode decreases and the battery life characteristics deteriorate due to insufficient contact area with the cathode active material containing a small lithium iron phosphate-based compound. In addition, there is also a problem in that the electrode reaction proceeds inefficiently as the contact area between the conductive material and the electrolyte is reduced, leading to decreased electrode activation and deterioration of the battery life characteristics. If the value of R1 exceeds 500, the BET specific surface area of ​​the conductive material is excessively large, or the average particle size (D) of the conductive material 50This corresponds to the case where ) is excessively small, where excessive reaction with the electrolyte leads to the excessive formation of the SEI (Solid Electrolyte Interphase) layer, which increases resistance and degrades lifespan characteristics, and the average particle size (D) of the conductive material 50 There is a problem where the conductive material is not uniformly distributed because the aggregation phenomenon occurs due to the excessively small size.

[0060] Specifically, the value of R1 may be 200 or more, 215 or more, or 250 or more, more specifically 280 or more, and specifically 480 or less, 430 or less, or 380 or less, more specifically 330 or less. When the above range is satisfied, a balanced interaction between the conductive material and the positive electrode active material is achieved, which can increase the electrical conductivity of the electrode, and an appropriate distribution of the conductive material and a stable conductive network are formed, which reduces resistance and maximizes the lifespan characteristics.

[0061]

[0062] In addition, the value of R2 represented by the following Equation 2 may be 0.9 to 1.2, specifically 0.9 to 1.18, and more specifically 0.95 to 1.15.

[0063] [Equation 2]

[0064] R2 = [average particle size of positive active material (D 50 ) value] / [Average particle size of conductive material (D 50 ) value]

[0065] If the value of R2 satisfies the above range, the average particle size (D) of the positive active material and the conductive material 50 Since it is similar and uniformly dispersed within the electrode, it has the effect of forming a stable conductive network, and by widening the contact area between the positive active material and the conductive material, it allows the electrochemical reaction to proceed more efficiently, thereby improving lifespan characteristics.

[0066]

[0067] In addition, the value of R3 represented by the following Equation 3 may be 200 to 550, specifically 210 to 520, more specifically 210 to 300.

[0068] [Equation 3]

[0069] R3 = [BET specific surface area of ​​the conductive material] / [average particle size of the conductive material (D 50 ) value]

[0070] In Equation 3 above, the BET specific surface area value (m) of the conductive material 2 / g) and average particle size of conductive material (D 50 Each of the values ​​(㎛) is a unitless number with the unit omitted.

[0071] If the value of R3 satisfies the above range, the BET specific surface area value of the conductive material is appropriately large and the average particle size (D) of the conductive material 50 Since the value is small to an appropriate level, this balance allows the conductive material to form a uniform electron transfer path within the electrode, so the electrode operates stably during the charging and discharging process of the battery, and accordingly, a high capacity retention rate can be formed. Furthermore, by controlling the BET specific surface area of ​​the conductive material so that it is not excessively large, the formation of the SEI (Solid Electrolyte Interphase) layer can also be controlled so that the increase in internal resistance of the battery is minimized, thereby reducing the rate of increase in resistance.

[0072]

[0073] Meanwhile, the current collector according to the present invention 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.

[0074] In addition, the current collector may typically have a thickness of 3 μm to 500 μm, and specifically, may have a thickness of 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. 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.

[0075] The positive active material layer is disposed on the current collector. The positive active material layer may be disposed on at least one surface of the current collector. Specifically, the positive active material layer may be disposed on one or both surfaces of the current collector.

[0076]

[0077] The above positive active material layer comprises a positive active material, a conductive material, and a binder.

[0078]

[0079] First, the conductive material of the present invention will be described.

[0080] The conductive material of the present invention includes carbon black. Carbon black has high electrical conductivity, which can significantly improve electrical conductivity when mixed with a positive electrode active material. It is composed of fine particles, which provides a large specific surface area, thereby increasing the contact area with the positive electrode active material and making the conduction path denser, thus improving the conductive network. Furthermore, since it can be evenly dispersed, it can maintain uniform performance of the entire electrode by uniformly distributing the conductive material even when applied to a positive electrode active material containing a lithium iron phosphate-based compound with small particle size. Additionally, since particle size control according to the size of the positive electrode active material is easy, it has the advantage of being effective even when used with small particles, such as a positive electrode active material containing a lithium iron phosphate-based compound.

[0081] The carbon black above may include secondary particles formed by the aggregation of primary carbon black particles, and specifically, may be secondary particles. The BET specific surface area of ​​the carbon black can be controlled by controlling the particle size of the primary particles. The BET specific surface area of ​​the conductive material is 200 m² 2 / g to 400m 2 / g. The BET specific surface area of ​​the above conductive material is 200m² 2 If less than / g, the average particle size of the conductive material (D 50 The average particle size (D) of the positive electrode active material containing the lithium iron phosphate-based compound 50 Since it becomes excessively large compared to ), there is a problem in that the contact area between the conductive material and the cathode active material containing a lithium iron phosphate compound decreases, weakening the conductive network and reducing energy density, and the BET specific surface area of ​​the conductive material is 400m 2 If exceeding / g, the average particle size of the conductive material (D 50 Because the particles become excessively small and aggregate with each other, there is a problem that the viscosity is high and the particles are not uniformly dispersed when manufacturing the anode slurry later.

[0082] Specifically, the BET specific surface area of ​​the conductive material is 220 m² 2 / g or more, more specifically 230m 2 It can be more than / g, specifically 350m 2 / g or less or 320m 2 / g or less, more specifically 290 m 2 It may be less than / g. If included in the above range, the average particle size (D) of the conductive material is similar to that of the cathode active material containing a lithium iron phosphate-based compound. 50 Since it can have ), the contact area between the positive active material and the conductive material is optimized, and accordingly, an electron transport path is effectively formed, which improves the energy density and charge / discharge efficiency of the battery, and subsequently, the conductive material can be uniformly dispersed within the positive slurry.

[0083] Average particle size (D) of the above conductive material50 ) may be 0.7㎛ to 1.3㎛, specifically 0.8㎛ to 1.2㎛, and more specifically 0.85㎛ to 1.15㎛. When the above range is satisfied, the average particle size (D) with respect to the cathode active material containing a lithium iron phosphate-based compound is 50 Since the positive electrode active material and the conductive material are similar, the positive electrode active material and the conductive material can be evenly mixed to form an efficient conductive network within the electrode, and the conductive material can be uniformly mixed within the positive electrode slurry later on because it is easy to disperse.

[0084] The conductive material may be included in an amount of 0.5% to 5.0% by weight, specifically 0.8% to 4.0% by weight, and more specifically 1.0% to 2.0% by weight, based on the total weight of the positive electrode active material layer. When included within the above range, the electrode capacity is excellent, and the effect of forming a conductive path can be maximized by optimizing dispersibility.

[0085]

[0086] Next, the positive active material of the present invention will be described.

[0087] The positive electrode active material of the present invention comprises a lithium iron phosphate-based compound. The lithium iron phosphate-based compound has excellent thermal stability, which has the advantage of providing excellent lifespan characteristics and stability for lithium secondary batteries.

[0088] The above lithium iron phosphate-based compound may be represented by the following chemical formula 1.

[0089] [Chemical Formula 1]

[0090] Li 1+x [Fe 1-y M y ]PO4

[0091] In the above chemical formula 1, M may include one or more selected from the group consisting of Ni, Co, Mn, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir, and V. The above lithium iron phosphate-based compound may be doped with M. In this case, the diffusivity of lithium ions is increased, and consequently, the electrochemical properties of a lithium secondary battery containing a positive electrode active material may be improved.

[0092] In addition, the above x may be -0.5 ≤ x ≤ 0.5, specifically -0.2 ≤ x ≤ 0.2, and more specifically -0.1 ≤ x ≤ 0.1.

[0093] In addition, the above y may be 0≤y<1, specifically 0≤y<0.3, more specifically 0≤y<0.05.

[0094] The above lithium iron phosphate compound may be, for example, LiFePO4, Li(Fe, Mn)PO4, Li(Fe, Co)PO4, Li(Fe, Ni)PO4, or a mixture thereof, and specifically may be LiFePO4.

[0095] The above lithium iron phosphate-based compound may further include a conductive coating layer on its surface. The conductive coating layer is intended to improve the conductivity of the lithium iron phosphate-based compound and may include one or more mixtures selected from the group consisting of carbon-based materials, metals, and conductive polymers. Among these, when a conductive coating layer of a carbon-based material is included, the conductivity can be effectively improved without significantly increasing the weight of the lithium iron phosphate-based compound.

[0096] The conductive coating layer can be formed according to a conventional method for forming a coating layer and may be included in an amount of 1% to 7% by weight, specifically 1% to 5% by weight, based on the total weight of the lithium iron phosphate-based compound. When included within the above range, the problem of degrading battery characteristics due to a relative decrease in LFP content can be prevented, and the conductivity is improved due to the formation of the conductive layer.

[0097] Average particle size (D of the above positive active material) 50 The particle size may be 0.6㎛ to 1.6㎛, specifically 0.8㎛ to 1.4㎛, and more specifically 0.85㎛ to 1.2㎛. When the above range is satisfied, the distance of lithium ions entering and exiting the positive electrode active material is shortened due to the small particle size, which is advantageous in terms of capacity and output.

[0098] The above positive active material may be included in an amount of 80% to 99% by weight, specifically 90% to 98% by weight, and more specifically 95% to 98% by weight, based on the total weight of the positive active material layer. When included within the above range, it is excellent in terms of the capacity and energy density of the electrode, and can exhibit excellent effects in terms of both the functional optimization of the conductive material and the binder.

[0099] The weight ratio of the positive active material and the conductive material may be 90:10 to 99:1, specifically 95:5 to 99:1, and more specifically 96:4 to 99:1. When the above range is satisfied, a balance is achieved between the positive active material and the conductive material, providing a sufficient electron transport path within the electrode, so that the electrode operates stably even during the charging and discharging process, thereby minimizing the decrease in capacity of the lithium secondary battery and suppressing the increase in resistance.

[0100]

[0101] Next, the binder of the present invention will be described.

[0102] The binder of the present invention serves to improve adhesion between positive active material particles and adhesion between the positive active material and the current collector. Preferably, the binder may include one or more selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

[0103] The binder may be included in an amount of 0.1% to 10.0% by weight, specifically 1.0% to 5.0% by weight, and more specifically 2.0% to 4.0% by weight, based on the total weight of the positive electrode active material layer. When the content of the binder is included in the above range, it has the effect of increasing the energy density per volume while lowering the resistance of the electrode and maintaining the adhesion of the electrode.

[0104]

[0105] The above anode may have a porosity of 15% to 40%, specifically 20% to 35%, and more specifically 25% to 30%. When the above range is satisfied, the electrolyte impregnation is improved, and superior capacity characteristics can be achieved.

[0106]

[0107] The anode may be manufactured by methods known in the art. For example, the anode may be manufactured by mixing an anode active material, a binder, and a conductive material in a solvent to prepare an anode slurry, applying the anode slurry onto a current collector, and then drying and rolling, or by casting the anode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto a current collector. In this case, the solvent for the anode slurry may be any anode slurry solvents generally used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, or a mixture thereof, but is not limited thereto. The solvent may be used in an amount that dissolves or disperses the anode active material, the conductive material, and the binder, and has a viscosity such that the cathode slurry can be uniformly coated.

[0108]

[0109] Lithium secondary battery

[0110] Hereinafter, a lithium secondary battery according to the present invention will be described.

[0111] A lithium secondary battery according to the present invention comprises a positive electrode according to the present invention; 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.

[0112] Since the anode above is the same as described above, the remaining components excluding the anode will be described below.

[0113]

[0114] (1) Cathode

[0115] In a lithium secondary battery according to the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material, a binder, and a conductive material.

[0116] 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, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used.

[0117] The above-mentioned negative current collector can typically have a thickness of 3 μm to 500 μm, and specifically, can have a thickness of 300 μm or less, 200 μm or less, 100 μm or less, or 80 μm or less. Fine irregularities may be formed on the surface of the current collector to strengthen the bonding force with the negative active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0118] The above negative active material layer may be disposed on the negative current collector. The above negative active material layer may be disposed on at least one surface of the negative current collector. Specifically, the above negative active material layer may be disposed on one or both surfaces of the negative current collector.

[0119] The above-mentioned negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium, for example, carbon materials such as artificial graphite, natural graphite, Kish graphite, pyrolytic carbon, meso-carbon microbeads, mesophase pitches, petroleum or coal tar pitch-derived cokes, mesophase pitch-based carbon fiber, graphitized carbon fiber, amorphous carbon, softened carbon, or hardened carbon; (semi)metallic materials capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; SiO b (0 <b≤2), SnO2, 바나듐 산화물, 리튬 바나듐 산화물과 같이 리튬을 도프 및 탈도프할 수 있는 (준)금속 산화물 재료; Si-C 복합체 또는 Sn-C 복합체과 같은 이종 복합 재료; 또는 금속 리튬 박막 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다.

[0120] Specifically, the cathode active material may comprise one or more selected from the group consisting of silicon-based active materials, carbon-based active materials, and silicon-carbon composite active materials; more specifically, the carbon-based active material may comprise one or more selected from the group consisting of artificial graphite, natural graphite, softened carbon, and hardened carbon, and the silicon-based active material may comprise pure Si particles and / or SiO₂ b (0 <b≤2)를 포함할 수 있으며, 상기 실리콘-탄소 복합계 활물질은 Si-C 복합체를 포함할 수 있다. 또한, 상기 음극 활물질은 상기한 물질들 중에서 2 이상이 혼합된 혼합 활물질이 적용될 수도 있다.

[0121] The above-mentioned negative electrode active material may be included in an amount of 60% to 99% by weight based on the total weight of the negative electrode active material layer, specifically in an amount of 70% or more, 80% or more, 85% or more, or 90% or more by weight, and may also be included in an amount of 98% or less, 97% or less by weight, or 95% or less by weight.

[0122] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1% to 10% by weight based on the total weight of the negative active material layer, and can be included in an amount of 0.2% or more, 0.3% or more, or 0.5% or more by weight, and can also be included in an amount of 8% or less, or 5% or less by weight. Examples of such binders may include one or more selected from the group consisting of styrene-butadiene copolymer, acrylate styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, and polyvinyl alcohol. Among these, it may include one or more selected from the group consisting of styrene-butadiene copolymer, acrylate styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, carboxymethyl cellulose, hydroxypropylmethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, cellulose acetate butylate, cellulose acetate propionate, cyanoethylfluran, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose. Specifically, it is preferable to use carboxymethyl cellulose, hydroxypropylmethyl cellulose, hydroxypropyl cellulose, or a mixture thereof.

[0123] The above conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, specifically 5% by weight or less, 3% by weight or less, 2% by weight or less, or 1% by weight or less based on the total weight of the negative electrode active material layer, and may also be included in an amount of 0.01% by weight or more, 0.05% by weight or more, 0.08% by weight or more, 0.1% by weight or more, or 0.3% by weight or more. Such conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powder such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives, etc. may be used.

[0124] The above-mentioned cathode active material layer may be manufactured by applying a cathode slurry composition, prepared by dissolving or dispersing a cathode active material and optionally a binder and a conductive material in a solvent, onto a cathode current collector and drying it, or by casting the cathode slurry composition onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0125]

[0126] (2) Electrolyte

[0127] Examples of the above electrolytes that can be used in the manufacture of lithium secondary batteries include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these.

[0128] The above electrolyte may include a lithium salt and an organic solvent.

[0129] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. It is preferable to use the lithium salt within the range of 0.1 to 2.0 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 lithium ions can move effectively.

[0130] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0131] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the above additives may be included in an amount of 0.1 to 5 weight% based on the total weight of the electrolyte.

[0132]

[0133] (3) Separator

[0134] 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.

[0135] 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.

[0136]

[0137] 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.

[0138] 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.

[0139] 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.

[0140]

[0141] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are intended only to enable a person skilled in the art to fully understand and easily implement the present invention, and the scope of the present invention is not limited to the following embodiments.

[0142]

[0143] Examples 1 to 5 and Comparative Examples 1 to 4

[0144] Examples 1 to 5 and Comparative Examples 1 to 4 were prepared by applying a lithium iron phosphate-based compound having the same composition as LiFePO4 as the positive electrode active material having particle size characteristics as described in Table 1 below, and applying carbon black having the same particle size characteristics and specific surface area as described in Table 1 below as the conductive material.

[0145] Specifically, the above-mentioned positive active material, conductive material, and PVDF binder were mixed in a weight ratio of 96:1.2:2.8, N-methylpyrrolidone solvent was added to obtain a solid content of 60%, and the mixture was mixed using a homogenizer at 2,500 rpm for 1 hour to prepare a positive slurry.

[0146] Afterwards, the anode slurry was applied to one side of an aluminum current collector, dried at 130°C, and then rolled twice using a roll-to-roll rolling machine at a linear pressure of 1 ton / cm to manufacture the anode.

[0147] In addition, the values ​​of R1, R2, and R3, represented by the following Equations 1 to 3 of the anode, were calculated and shown in Table 1.

[0148] [Equation 1]

[0149] R1= {[average particle size of the positive active material (D 50 ) value] × [BET specific surface area value of conductive material]} / [average particle size of conductive material (D 50 ) value] 2

[0150]

[0151] [Equation 2]

[0152] R2 = [average particle size of positive active material (D 50 ) value] / [Average particle size of conductive material (D 50 ) value]

[0153]

[0154] [Equation 3]

[0155] R3 = [BET specific surface area of ​​the conductive material] / [average particle size of the conductive material (D50 ) value]

[0156]

[0157] In the above Equations 1 to 3, the average particle size (D) of the positive active material 50 ) value (㎛), BET specific surface area value of the conductive material (m 2 / g) and average particle size of conductive material (D 50 Each of the ) values ​​(㎛) is a unitless number with the unit omitted.

[0158]

[0159] Average particle size of the positive active material (D 50 )[㎛] Average particle size of conductive material (D 50 )[㎛] BET specific surface area of ​​conductive material[m 2 / g]R1 value R2 value R3 value Example 11.11.0 273300.3 1.1273.0 Example 21.11.1240218.21.0218.2 Example 31.05 1.0270283.5 1.1270.0 Example 41.05 0.85301437.4 1.2354.1 Example 50.6 0.65334474.30.9513.8 Comparative Example 10.6 0.7 185226.5 0.9264.3 Comparative Example 21.10.65170442.6 1.7261.5 Comparative Example 30.6 1.220585.40.5170.8 Comparative Example 41.10.7317711.61.6452.9

[0160] 1) Average particle size (D 50 The specific surface area was measured by dispersing the positive active material powder and the conductive material powder, respectively, in a dispersion medium, introducing them into a laser diffraction particle size measuring device (Microtrac MT 3000), irradiating them with ultrasound of approximately 28 kHz at an output of 60 W, obtaining a volume-cumulative particle size distribution graph, and determining the particle size corresponding to 50% of the volume-cumulative amount.2) The specific surface area was measured by the BET method and was calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using BEL Japan's BELSORP-mino II.

[0161]

[0162] Experimental Example 1: Evaluation of Dose Retention Rate

[0163] Manufacture of Lithium Secondary Batteries

[0164] Artificial graphite was used as the negative electrode active material. A negative electrode was prepared comprising a negative electrode active material layer containing the above negative electrode active material, negative electrode binders CMC and SBR, and negative electrode conductive material carbon black in a weight ratio of 96 : 1.0 : 2.5 : 0.5. Copper foil was used as the negative electrode current collector.

[0165] An electrode assembly was prepared by interposing a separator between the anode prepared in Examples 1 to 4 and Comparative Examples 1 to 4 and the cathode, and then the assembly was placed inside a battery case, and an electrolyte was injected into the case to manufacture a lithium secondary battery. The electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1.2 M in a solvent mixed with ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3.

[0166]

[0167] <Position Retention Rate Evaluation>

[0168] Each of the lithium secondary batteries manufactured above was charged to 3.8V at 45℃ under CC / CV and 0.5C conditions using an electrochemical charge / discharger, and then discharged to 2.5V under CC and 1.0C conditions as one cycle, and the capacity retention rate was measured.

[0169] The capacity retention rate was calculated using the formula below, and the capacity retention rate at 100 cycles is shown in Table 2 below.

[0170] Capacity Retention Rate (%) = (Discharge Capacity after 100 Cycles / Discharge Capacity after 1 Cycle) × 100

[0171]

[0172] Experimental Example 2: Evaluation of Resistance Increase Rate

[0173] Each of the lithium secondary batteries manufactured above was charged to 3.8V at 25℃ under CC / CV, 0.5C conditions using an electrochemical charge / discharger, and then discharged to 2.5V under CC, 1.0C conditions, with this being one cycle of charge / discharge.

[0174] After one cycle of charging and discharging, the discharge capacity after one cycle was measured using an electrochemical charge / discharger, and the SOC was adjusted to 50%. Then, a pulse of 2.5C was applied for 10 seconds, and the initial resistance was calculated through the difference between the voltage before and after the pulse application.

[0175] In addition, the resistance was calculated using the same method as above after cycle charging and discharging, and the resistance growth rate was calculated using the formula below. The resistance growth rate at 100 cycles is shown in Table 2 below.

[0176] Resistance increase rate (%) = {(Resistance after 100 charge / discharge cycles - Initial resistance) / Initial resistance} × 100

[0177]

[0178] Capacitance retention rate (%, @100th cycle) Resistance increase rate (%, @100th cycle) Example 1 92.5 2.97 Example 2 92.2 3.54 Example 3 92.4 3.37 Example 4 92.15.63 Example 5 92.2 3.97 Comparative Example 187.9 13.51 Comparative Example 287.2 14.10 Comparative Example 387.9 22.18 Comparative Example 487.0 22.07

[0179] Referring to Table 2 above, the BET specific surface area of ​​the conductive material is 200 m² 2 / g to 400m 2 It can be confirmed that the lithium secondary batteries of Examples 1 to 5, which are included in the range of / g and have a value of R1 in the range of 180 to 500, exhibit a superior cycle capacity retention rate and a low resistance increase rate compared to the lithium secondary batteries of Comparative Examples 1 to 4, which are not.

Claims

1. The entire house; and A positive active material layer disposed on the above current collector; comprising, The above positive active material layer comprises a positive active material, a conductive material, and a binder, and The above positive active material includes a lithium iron phosphate-based compound, and The above conductive material includes carbon black, and The BET specific surface area of ​​the above conductive material is 200m² 2 / g to 400m 2 / g and, An anode having a value of R1 represented by the following Equation 1 of 180 to 500. [Equation 1] R1= {[average particle size of the positive active material (D 50 ) value] × [BET specific surface area value of conductive material]} / [average particle size of conductive material (D 50 ) value] 2 In the above Equation 1, the average particle size (D) of the positive active material 50 ) value (㎛), BET specific surface area value of the conductive material (m 2 / g) and average particle size of conductive material (D 50 Each of the ) values ​​(㎛) is a unitless number with the unit omitted.

2. In Claim 1, An anode having a value of R2 of 0.9 to 1.1, represented by the following Equation 2. [Equation 2] R2 = [average particle size of positive active material (D 50 ) value] / [Average particle size of conductive material (D 50 ) value] 3. In Claim 1, An anode having a value of R3 of 200 to 450, represented by the following Equation 3. [Equation 3] R3 = [BET specific surface area of ​​the conductive material] / [average particle size of the conductive material (D 50 ) value] In Equation 3 above, the BET specific surface area value (m) of the conductive material 2 / g) and average particle size of conductive material (D 50 Each of the ) values ​​(㎛) is a unitless number with the unit omitted.

4. In Claim 1, Average particle size (D) of the above conductive material 50 ) is an anode with a diameter of 0.7㎛ to 1.3㎛.

5. In Claim 1, Average particle size (D of the above positive active material) 50 ) is an anode with a diameter of 0.6㎛ to 1.6㎛.

6. In Claim 1, The above lithium iron phosphate-based compound is an anode represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x [Fe 1-y M y ]PO4 In the above chemical formula 1, M comprises one or more selected from the group consisting of Ni, Co, Mn, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir, and V, and -0.5≤x≤0.5, 0≤y<1.

7. In Claim 1, The above lithium iron phosphate-based compound is an anode further comprising a conductive coating layer.

8. In Claim 1, The above conductive material is included in an amount of 0.5% to 5.0% by weight based on the total weight of the above positive active material layer.

9. In Claim 1, A positive electrode in which the weight ratio of the positive electrode active material and the conductive material is 90:10 to 99:

1.

10. In Claim 1, The above binder comprises one or more selected from the group consisting of styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE).

11. In Claim 1, The above anode is an anode having a porosity of 15% to 40%.

12. A lithium secondary battery comprising the positive electrode of Claim 1.