Negative electrode, lithium secondary battery, battery module and battery pack

Abstract

The present invention relates to a cathode having low manufacturing costs and excellent high-rate charge / discharge characteristics. The cathode according to the present invention comprises: a cathode current collector; a first cathode composite layer disposed on the cathode current collector and comprising a first cathode active material; and a second cathode composite layer disposed on the first cathode composite layer and comprising a second cathode active material; wherein the second cathode active material is composed of primary particulate artificial graphite, and the first cathode active material comprises primary particulate artificial graphite and natural graphite.

Description

Technology Field

[0001] The present invention relates to a negative electrode, a lithium secondary battery, a battery module, and a battery pack, and more specifically, to a negative electrode having excellent high-rate charge / discharge performance, a lithium secondary battery including said negative electrode, and a battery module and a battery pack including said lithium secondary battery as a unit cell. Background Technology

[0002] With the advancement of technologies such as electric vehicles, energy storage systems (ESS), and portable electronic devices, the demand for lithium secondary batteries as an energy source is rapidly increasing.

[0003] Recently, in the field of electric vehicles, there is a demand for cells with high energy density to extend the driving range on a single charge. Accordingly, lithium secondary batteries have been developed using high-nickel (High-Ni) cathode active materials or Si-based anode active materials with excellent capacity characteristics. However, because high-nickel (High-Ni) cathode active materials and Si-based anode active materials have high unit costs, their application increases the production costs of secondary batteries and electric vehicles, which is hindering the widespread adoption of electric vehicles.

[0004] Since the manufacturing cost of lithium secondary batteries is influenced by the price of raw materials that make up the lithium secondary battery, particularly the positive and negative active materials, attempts are being made to use low-cost raw materials for the positive and negative active materials. For example, a plan is being considered to apply a positive active material with a relatively low Ni content compared to high-nickel (High-Ni) positive active materials as the positive active material, and to apply a relatively low-cost primary particle form of artificial graphite instead of the expensive secondary particle form of artificial graphite as the negative active material.

[0005] However, when using low-cost raw materials, the battery performance is degraded compared to lithium secondary batteries using high-cost raw materials, making it difficult to meet market demands. Specifically, when using a cathode active material with low Ni content, the energy density decreases, and when using artificial graphite in the form of primary particles, high-rate charge / discharge performance decreases, leading to a problem of reduced rapid charging performance.

[0006] Therefore, there is a need to develop lithium secondary batteries with excellent electrochemical performance while using low-cost active material raw materials. The problem to be solved

[0007] The present invention aims to solve the above-mentioned problems by controlling the composition of the negative active material of the upper and lower layers of a multilayer negative electrode comprising two or more negative composite layers, thereby providing a negative electrode with excellent high-rate charge / discharge characteristics while using inexpensive primary particle-type artificial graphite, and a lithium secondary battery including the same. means of solving the problem

[0008] [1] The present invention provides a cathode comprising: a cathode current collector; a first cathode composite layer disposed on the cathode current collector and comprising a first cathode active material; and a second cathode composite layer disposed on the first cathode composite layer and comprising a second cathode active material, wherein the second cathode active material is made of primary particulate artificial graphite and the first cathode active material comprises primary particulate artificial graphite and natural graphite.

[0009] [2] The present invention provides a cathode in which, in [1] the first cathode active material comprises primary particulate artificial graphite : natural graphite in a weight ratio of 40 : 60 to 80 : 20.

[0010] [3] The present invention, in [1] or [2], wherein the average particle size D of the primary particle-type artificial graphite 50 This provides a cathode with a size of 9㎛ to 15㎛.

[0011] [4] The present invention provides a cathode in which the difference in average particle size between the artificial graphite and the natural graphite is 5 μm or more, in at least one of [1] to [3].

[0012] [5] The present invention provides a cathode in which, in at least one of [1] to [4], the first cathode composite layer further comprises a first cathode binder, and the first cathode binder is included in an amount of 0.1% to 4% by weight based on the total weight of the first cathode composite layer.

[0013] [6] The present invention provides a cathode in which, in at least one of [1] to [5], the second cathode composite layer further comprises a second cathode binder, and the second cathode binder is included in an amount of 0.1% to 1.5% by weight based on the total weight of the second cathode composite layer.

[0014] [7] The present invention provides a cathode having a porosity of 30% or more in at least one of [1] to [6].

[0015] [8] The present invention provides a lithium secondary battery comprising at least one of [1] to [7] a cathode, a positive electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode composite layer comprising a positive electrode active material, and the positive electrode active material comprises a single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 75 mol% among the total transition metals.

[0016] [9] The present invention provides a lithium secondary battery in which, in [8] the single-particle lithium nickel-based oxide comprises 30 or fewer nodules.

[0017]

[10] The present invention provides a lithium secondary battery in which, in [8] or [9], the single-particle lithium nickel-based oxide is represented by the following [Chemical Formula 1].

[0018] [Chemical Formula 1]

[0019] Li 1+x [Nia Co b Mn c M 1 d ]O2

[0020] In the above [Chemical Formula 1], M 1 It contains one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and -0.1≤x≤0.1, 0.5≤a≤0.75, 0 <b<0.5, 0<c<0.5, 0≤d≤0.2임.

[0021]

[11] The present invention provides a lithium secondary battery in which, in at least one of [8] to

[10] , the positive active material further comprises a coating layer comprising one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo on the surface of the single-particle lithium nickel-based oxide.

[0022]

[12] The present invention provides a lithium secondary battery having a nominal voltage of 3.68V or higher in at least one of [8] to

[11] .

[0023]

[13] The present invention provides a lithium secondary battery having a charge cut-off voltage of 4.35V or higher in at least one of [8] to

[12] .

[0024]

[14] The present invention provides a battery module comprising at least one of the lithium secondary batteries [8] to

[13] as a unit cell.

[0025]

[15] The present invention provides a battery module comprising 10 to 50 unit cells, wherein the battery module in

[14] comprises 10 to 50 unit cells.

[0026]

[16] The present invention provides a battery pack comprising at least one of the lithium secondary batteries [8] to

[13] as a unit cell.

[0027]

[17] The present invention provides a battery pack comprising 10 to 1,000 unit cells, wherein the battery pack according to

[16] comprises 10 to 1,000 unit cells.

[0028]

[18] The present invention provides a battery pack comprising the secondary battery module of

[14] . Effects of the invention

[0029] The cathode according to the present invention uses primary particulate artificial graphite, which is relatively inexpensive, as the cathode active material, so the manufacturing cost is low.

[0030] In addition, the cathode according to the present invention uses 100% primary particle-type artificial graphite as the cathode active material in the upper layer and uses a mixture of primary particle-type artificial graphite and natural graphite in the lower layer, thereby having low pore resistance and flexibility of the cathode and excellent high-rate charge / discharge performance.

[0031] The lithium secondary battery according to the present invention uses primary particulate artificial graphite as the negative electrode active material and a positive electrode active material with a relatively low Ni content as the positive electrode active material, so the manufacturing cost is low and it has excellent price competitiveness.

[0032] The lithium secondary battery according to the present invention uses a single-particle lithium nickel-based oxide having a nickel content of 50 mol% to 75 mol% as the positive active material, thereby preventing the positive active material from rapidly degrading at a high voltage of 4.35 V or higher. Accordingly, since the lithium secondary battery according to the present invention can operate at a higher voltage than conventional batteries, it can achieve a relatively high energy density despite having a low Ni content in the positive active material. Brief explanation of the drawing

[0033] Figure 1 is a scanning electron microscope image of a single-particle positive electrode active material. Figure 2 is a scanning electron microscope image of a pseudo-single particle cathode active material. Figure 3 is a scanning electron microscope image of a secondary particle positive electrode active material. Specific details for implementing the invention

[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, "average particle size D50" refers to a particle size corresponding to 50% of the volume cumulative amount of the volume cumulative particle size distribution of the powder to be measured, and can be measured using a laser diffraction method. For example, the powder to be measured can be measured by dispersing it in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasound of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then determining the particle size corresponding to 50% of the volume cumulative amount.

[0036] In the present invention, "porosity (P)" is a percentage of the volume of pores relative to the total volume of the electrode composite layer, and is a value calculated by measuring the actual density of the electrode, dividing it by the theoretical electrode density, and then multiplying by 100.

[0037] In the present invention, "single particle type" refers to an aggregate composed of 30 or fewer sub-particles, and each sub-particle unit forming the single particle type is called a "nodule." The "single particle type" is a concept that includes a single particle composed of one nodule and a pseudo-single particle which is a composite of 2 to 30 nodules. Fig. 1 shows a scanning electron microscope image of a positive electrode active material in a single particle form, and Fig. 2 shows a scanning electron microscope image of a positive electrode active material in a pseudo-single particle form.

[0038] The above “nodule” is a sub-grain unit constituting a single particle and a pseudo-single particle, and may be a single crystal that does not have crystalline grain boundaries, or a polycrystalline one in which no grain boundaries appear to exist when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope.

[0039] In the present invention, "secondary particle" refers to an aggregate composed of more than 30 sub-particles, and each sub-particle unit forming the secondary particle is called a "primary particle." Figure 3 shows a scanning electron microscope (SEM) image of a positive electrode active material in the form of a secondary particle.

[0040] In the present invention, the term “particle” is a concept that includes any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0041] In the present invention, the average particle size (D) of the nodule or primary particle mean ) refers to the arithmetic mean value calculated after measuring the particle sizes of nodules or primary particles observed in scanning electron microscope images.

[0042] 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 a liquid nitrogen temperature (77K) using BEL Japan’s BELSORP-mini II.

[0044] As a result of repeated research to develop a lithium secondary battery with low manufacturing costs and excellent electrochemical performance, the inventors discovered that by applying 100% primary particle-type artificial graphite as the negative active material of the upper layer of a multilayer negative electrode comprising two or more negative composite layers, and applying a mixture of primary particle-type artificial graphite and natural graphite as the negative active material of the lower layer, it is possible to achieve high-rate charge / discharge performance equivalent to or greater than that of using secondary particle-type artificial graphite while keeping manufacturing costs low, and thus completed the present invention.

[0046] The present invention will be described in more detail below.

[0048] cathode

[0049] First, the cathode according to the present invention will be described.

[0050] The cathode according to the present invention comprises: a cathode current collector; a first cathode composite layer disposed on the cathode current collector and comprising a first cathode active material; and a second cathode composite layer disposed on the first cathode composite layer and comprising a second cathode active material; wherein the second cathode active material is composed of primary particulate artificial graphite, and the first cathode active material comprises primary particulate artificial graphite and natural graphite.

[0052] 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 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.

[0054] The first cathode composite layer is disposed on a cathode current collector and includes a first cathode active material. If necessary, the first cathode composite layer may further include a first cathode conductive material and / or a first cathode binder.

[0055] The first cathode active material may be a graphite-based cathode active material, for example, artificial graphite, natural graphite, or a combination thereof.

[0056] Preferably, the first cathode active material may include artificial graphite and natural graphite. The first cathode active material may include artificial graphite and natural graphite in a weight ratio of 40:60 to 80:20, 40:60 to 70:30, or 50:50 to 70:30. When the weight ratio of artificial graphite and natural graphite in the first cathode composite layer disposed close to the cathode current collector satisfies the above range, excellent cathode capacitance and adhesion to the cathode current collector are exhibited.

[0057] The above natural graphite may be any natural graphite commonly used in the relevant technical field, and its type is not particularly limited.

[0058] The above natural graphite has an average particle size D 50 This can be 2㎛ to 30㎛, preferably 5㎛ to 30㎛, more preferably 15㎛ to 25㎛. Average particle size D of natural graphite 50 When the above range is satisfied, the adhesion to the cathode current collector and the cathode density are excellent.

[0059] It is preferable that the above artificial graphite is primary particle-type artificial graphite.

[0060] Artificial graphite is manufactured by crushing carbon materials such as petroleum coke and / or coal coke, molding them into a desired shape, carbonizing them through heat treatment, and then graphitizing them through ultra-high temperature heat treatment at 2700°C to 3000°C. The artificial graphite produced through the graphitization process has a single particle (primary particle) form. Since the lithium ion diffusion path of the single-particle artificial graphite is long and the crystal orientation is non-uniform, using it directly as an active material for secondary batteries does not result in sufficient high-rate charge / discharge characteristics. Therefore, to date, secondary particle artificial graphite, which is formed by mixing the primary particle artificial graphite with a binder and then heat-treating it, has been mainly used as a negative electrode active material for secondary batteries. Secondary particle-type artificial graphite has the advantage of superior high-rate charge / discharge characteristics compared to primary particle-type artificial graphite because crystal orientation, structural stability, and lithium ion mobility are increased as the particle arrangement is adjusted and densified during the assembly process. However, there is a problem in that the unit cost is high because an additional assembly process is required to manufacture secondary particle-type artificial graphite. Therefore, using primary particle-type artificial graphite as the artificial graphite can lower the manufacturing cost of the anode and lithium secondary battery.

[0061] However, there is a problem that high-rate charge / discharge characteristics are reduced when primary particle-type artificial graphite is used or when secondary particle-type artificial graphite is used. However, as described below, in the present invention, the negative active material of the second negative composite layer (upper layer) disposed on the surface of the negative electrode is composed of 100% primary particle-type artificial graphite, and a mixture of primary particle-type artificial graphite and natural graphite is applied as the negative active material of the first negative composite layer (lower layer), thereby reducing the curvature of the negative composite layer and improving the mobility of lithium ions within the negative electrode, so that high-rate charge / discharge characteristics equivalent to or better than those when secondary particle-type artificial graphite is used can be achieved despite the use of primary particle-type artificial graphite.

[0062] Meanwhile, the natural graphite and artificial graphite included in the first cathode composite layer have an average particle size D 50 The difference may be 5㎛ or more, preferably 5㎛ to 15㎛, and more preferably 5㎛ to 10㎛. When the difference in average particle size between natural graphite and artificial graphite satisfies the above range, the electrode density of the first cathode composite layer increases, thereby enabling high capacity.

[0063] Preferably, the average particle size D50 of the artificial graphite included in the first cathode composite layer may be 9㎛ to 15㎛, preferably 10㎛ to 15㎛, and more preferably 10㎛ to 13㎛. Average particle size D 50 When the above range is satisfied, the tap density increases due to the difference in particle size with natural graphite, and as the tap density increases, the stress generated during rolling is relieved, thereby mitigating the negative electrode expansion that occurs during battery charging and discharging, and thus the effect of reducing the increase in thickness can be obtained.

[0065] The first cathode active material may be included in an amount of 94% to 99% by weight, preferably 95% to 99% by weight, and more preferably 95% to 98% by weight, based on the total weight of the first cathode composite layer. When the content of the first cathode active material satisfies the above range, excellent capacity characteristics and rapid charging performance are exhibited.

[0067] Next, the first cathode conductive material is used to impart conductivity to the cathode, and in the battery being constructed, any material that has electronic conductivity without causing chemical changes can be used without special limitations. 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, carbon fiber, carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or 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.

[0068] The first cathode conductive material may be included in an amount of 0.1% to 5% by weight, 0.1% to 4% by weight, or 0.2% to 3% by weight based on the total weight of the first cathode composite layer. When the content of the first cathode conductive material satisfies the above range, the battery conductivity within the cathode can be improved while minimizing the degradation of capacity and rapid charging performance.

[0070] Next, the first 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.

[0071] The first cathode binder may be included in an amount of 4% by weight or less, preferably 0.1% to 4% by weight, more preferably 0.5% to 3.6% by weight, and even more preferably 1.0% to 2.8% by weight, based on the total weight of the first cathode composite layer. When the content of the first cathode binder satisfies the above range, excellent high-rate charge / discharge characteristics can be achieved. If the content of the first cathode binder is too high, the resistance within the cathode increases and lithium mobility decreases, resulting in reduced rapid charging performance. On the other hand, if the content of the first cathode binder is too low, the adhesion between the cathode current collector and the first cathode composite layer decreases, which may lead to a decrease in lifespan characteristics; therefore, it is more preferable that the content of the first cathode binder be 0.1% by weight or more, 0.5% by weight or more, or 1% by weight or more.

[0073] The second cathode composite layer is disposed on the first cathode composite layer and includes a second cathode active material. If necessary, the second cathode composite layer may further include a second cathode conductive material and / or a second cathode binder.

[0074] The above second cathode active material is composed of primary particulate artificial graphite.

[0075] In the case of primary particle-type artificial graphite, since the degree of sphericity is better than that of aggregated secondary particle-type artificial graphite, if the cathode active material of the second cathode composite layer is composed solely of primary particle-type artificial graphite, the cathode curvature is reduced and the lithium ion mobility within the cathode is increased, thereby enabling high-rate charge / discharge characteristics equivalent to or better than those achieved when secondary particle-type artificial graphite is used.

[0076] The above primary particulate artificial graphite has an average particle size D 50 This can be 9㎛ to 15㎛, preferably 10㎛ to 15㎛, more preferably 10㎛ to 13㎛. Average particle size D of primary particulate artificial graphite 50When the above range is satisfied, the effect of suppressing side reactions with the electrolyte and improving lithium mobility can be obtained. If the average particle size of the primary particle-type artificial graphite is too large, lithium ion mobility may be reduced, and if it is too small, a problem may arise in which gas generation due to side reactions with the electrolyte increases.

[0077] The above primary particulate artificial graphite may have an orientation index (OI) of 12 to 36, preferably 12 to 30, and more preferably 15 to 25. When the orientation index (OI) satisfies the above range, cost reduction, improved rapid charging performance, and cathode expansion suppression effects can be obtained. If the orientation index is too small, the manufacturing cost of the artificial graphite increases, resulting in a small cost reduction effect; if it is too large, rapid charging performance deteriorates, and it is difficult to suppress the increase in thickness caused by cathode expansion during charging and discharging.

[0078] The above primary particulate artificial graphite has a BET specific surface area of ​​0.3 m² 2 / g to 1.7m 2 / g, preferably 0.5m 2 / g to 1.5m 2 / g, more preferably 0.7m 2 / g to 1.3m 2 It may be / g. When the BET specific surface area satisfies the above range, cathode activation can be stably performed by reacting appropriately with the electrolyte. If the BET specific surface area is too small, a problem may arise where the reactivity between the cathode and the electrolyte is reduced, and if it is too large, a problem may arise where the reactivity with the electrolyte is excessive, leading to electrolyte consumption and gas generation.

[0079] The above primary particulate artificial graphite may have a tap density of 0.8 g / cc to 2.0 g / cc, preferably 0.8 g / cc to 1.8 g / cc, and more preferably 0.9 g / cc to 1.6 g / cc. When the tap density satisfies the above range, it is advantageous to secure electrode processability and rapid charging performance. If the tap density is too small, the curvature within the cathode increases, which may degrade rapid charging performance, and if it is too large, stress may occur during cathode manufacturing, which may cause a problem of increased thickness during cathode activation.

[0080] The second cathode active material may be included in an amount of 97% to 99% by weight, preferably 97% to 99% by weight, and more preferably 97.5% to 99% by weight, based on the total weight of the second cathode composite layer. When the content of the second cathode active material satisfies the above range, excellent capacity characteristics and rapid charging performance are exhibited.

[0082] Next, the second cathode conductive material is used to impart conductivity to the cathode, and in the battery being constructed, any material that has electronic conductivity without causing chemical changes can be used without special limitations. 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, carbon fiber, carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or 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.

[0083] The second cathode conductive material may be included in an amount of 0.1% to 3% by weight, 0.1% to 2% by weight, or 0.2% to 2% by weight based on the total weight of the second cathode composite layer. When the content of the second cathode conductive material satisfies the above range, the battery conductivity within the cathode can be improved while minimizing the degradation of capacity and rapid charging performance.

[0085] Next, the second 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.

[0086] The second cathode binder may be included in an amount of 1.5% by weight or less, preferably 0.1% to 1.5% by weight, more preferably 0.2% to 1% by weight, and even more preferably 0.2% to 1% by weight, based on the total weight of the second cathode composite layer. When the content of the second cathode binder satisfies the above range, the resistance of the second cathode composite layer is reduced, and the effect of improving high-rate charge / discharge performance is more excellent.

[0088] Meanwhile, the thickness ratio of the first cathode composite layer and the second cathode composite layer may be approximately 3:7 to 7:3, or 4:6 to 6:4. When the thickness ratio of the first cathode composite layer and the second cathode composite layer satisfies the above range, excellent electrode processability and cell performance are exhibited. If there is a large difference in thickness between the first cathode composite layer or the second cathode composite layer, it is difficult to ensure processability during the coating of the composite layer, and cell performance may be degraded due to the difference in electrochemical reactivity between the upper layer and the lower layer during charging and discharging.

[0090] The above-mentioned cathode may have a porosity of 30% or more, more than 30%, 31% to 50%, 31% to 40%, or 32% to 40%. When the porosity of the cathode satisfies the above range, excellent rapid charging performance can be achieved. If the cathode porosity is too small, the curvature within the cathode increases, and as a result, high-rate charge / discharge characteristics may deteriorate.

[0092] The above cathode may be manufactured according to a conventional cathode manufacturing method. For example, the above cathode may be manufactured by mixing a first cathode active material, a first cathode binder, and / or a first cathode conductive material in a solvent to prepare a first cathode slurry, mixing a second cathode active material, a second cathode binder, and / or a second cathode conductive material in a solvent to prepare a second cathode slurry, then applying the first cathode slurry and the second cathode slurry sequentially or simultaneously onto a cathode current collector, and then drying and rolling.

[0093] As solvents for the first cathode slurry and / or the second cathode slurry, solvents commonly used in the relevant technical field may be used; for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc., may be used individually or as a mixture of two or more. The amount of the solvent used is sufficient if it has a viscosity that dissolves or disperses the cathode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and provides excellent thickness uniformity when coated for subsequent anode manufacturing.

[0095] lithium secondary battery

[0096] Next, a lithium secondary battery according to the present invention will be described.

[0097] The lithium secondary battery according to the present invention comprises the negative electrode, positive electrode, and electrolyte according to the present invention as described above. Since the negative electrode has been described above, components other than the negative electrode will be described below.

[0099] anode

[0100] The anode according to the present invention comprises an anode composite layer comprising an anode active material. Specifically, the anode comprises an anode current collector and an anode composite layer formed on at least one surface of the anode current collector, wherein the anode composite layer comprises an anode active material. In addition, the anode composite layer may further comprise an anode conductive material and an anode binder in addition to the anode active material.

[0101] 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 to 500 μm, and fine irregularities may be formed on the surface of the positive 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.

[0103] The above-mentioned positive active material may include, for example, a single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 75 mol%, preferably 50 mol% to 70 mol%, more preferably 55 mol% to 70 mol%.

[0104] As the nickel content in lithium nickel-based oxides increases, the reactivity of Ni increases. +4 As the number of ions increases, the structural stability of the cathode active material decreases during charging and discharging, leading to rapid cathode degradation. This phenomenon is further exacerbated during high-voltage operation. In contrast, single-particle lithium nickel-based oxides with a nickel content of 50 mol% to 75 mol% are cheaper and have superior structural stability compared to high-nickel (High-Ni) lithium transition metal oxides with a nickel content of 80 mol% or more, which can prevent rapid degradation of the cathode active material even when operated at high voltages of 4.35 V or higher. Therefore, using a single-particle lithium nickel-based oxide with a nickel content of 50 mol% to 75 mol% as the cathode active material allows the battery to be operated at higher voltages compared to conventional methods, thereby improving energy density. However, since capacity characteristics deteriorate if the Ni content is too low, it is preferable that the Ni content of the lithium nickel-based oxide be approximately 50 mol% to 75 mol%.

[0106] Specifically, the lithium nickel-based oxide may be a lithium transition metal oxide containing nickel, manganese and cobalt, and, for example, may be represented by the following [Chemical Formula 1].

[0107] [Chemical Formula 1]

[0108] Li 1+x [Ni a Co b Mn c M 1 d ]O2

[0109] In the above [Chemical Formula 1], M 1 It may contain one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo. 1 When the element is included, the structural stability of the lithium nickel-based oxide particles is improved, enabling superior lifespan characteristics during high-voltage operation. Preferably, the above M 1 The elements may include one or more selected from the group consisting of Ti, Mg, Al, Zr, and Y, and more preferably, may include two or more selected from the group consisting of Ti, Mg, Al, Zr, and Y.

[0110] The above 1+x represents the lithium molar ratio in the lithium nickel-based oxide, and may be -0.1≤x≤0.1, 0≤x≤0.1, or 0≤x≤0.07. When 1+x satisfies the above range, a stable layered crystal structure can be formed.

[0111] The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.50≤a≤0.75, 0.50≤a≤0.70, or 0.55≤a≤0.70.

[0112] When a satisfies the above range, it can be stably driven at high voltage to realize high capacity and long lifespan characteristics.

[0113] The above b represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b<0.50, 0.05≤b≤0.40 또는 0.05≤b≤0.30일 수 있다.

[0114] The above c represents the molar ratio of manganese among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <c<0.50, 0.05≤c≤0.40 또는 0.10≤c≤0.40일 수 있다.

[0115] The above d is M among the total metals excluding lithium in the lithium nickel-based oxide. 1 Representing the molar ratio of elements, 0 ≤ d ≤ 0.20, 0 ≤ d ≤ 0.10, or 0 <d≤0.10일 수 있다. M 1 When the molar ratio of the elements satisfies the above range, both the structural stability and capacity of the positive active material can be excellent.

[0116] The above lithium nickel-based oxide may further include a coating layer on its surface comprising one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

[0117] When a coating layer is present on the surface of a lithium nickel-based oxide, contact between the electrolyte and the lithium nickel-based oxide is suppressed by the coating layer. This reduces the leaching of transition metals or gas generation caused by side reactions with the electrolyte, thereby further improving stability during thermal runaway. Preferably, the coating layer may include two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and more preferably, may include two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, and W.

[0119] The above lithium nickel-based oxide may be a single-particle lithium nickel-based oxide containing 30 or fewer nodules.

[0120] In the case of lithium nickel-based oxides in the form of secondary particles aggregated from more than 30 to hundreds of primary particles, the contact area with the electrolyte is large, resulting in significant side reactions with the electrolyte and the generation of gas during these side reactions. Under high temperature and / or high voltage conditions, the amount of gas generated and the side reactions with the electrolyte increase further, causing the performance of the lithium secondary battery to degrade rapidly. In contrast, single-particle lithium nickel-based oxides have a small number of nodules constituting the particles, and consequently, fewer interfaces within the particles, resulting in a smaller contact area with the electrolyte. Consequently, compared to secondary particles, they exhibit fewer side reactions with the electrolyte and generate significantly less gas. Therefore, when single-particle lithium nickel-based oxides are applied as cathode active materials, the degradation of lifespan characteristics under high temperature and / or high voltage conditions can be minimized.

[0121] The above single-particle lithium nickel-based oxide preferably comprises 30 or fewer nodules, preferably 1 to 25, and more preferably 1 to 15 nodules. If the number of nodules constituting the lithium nickel-based oxide exceeds 30, particle breakage increases during electrode manufacturing, and the occurrence of internal cracks due to volume expansion / contraction of nodules during charging and discharging increases, which may reduce the effect of improving high-temperature life characteristics and high-temperature storage characteristics.

[0122] The above nodules may have an average particle size of 0.8㎛ to 4.0㎛, preferably 0.8㎛ to 3㎛, and more preferably 1.0㎛ to 3.0㎛. When the average particle size of the nodules satisfies the above range, particle breakage during electrode manufacturing is minimized, and the increase in resistance can be suppressed more effectively. At this time, the average particle size of the nodules refers to a value obtained by measuring the particle sizes of the nodules observed in the SEM image obtained by analyzing the positive electrode active material powder with a scanning electron microscope, and then calculating the arithmetic mean of the measured values.

[0123] The above lithium nickel-based oxide is D 50 This can be 2.0㎛ to 10.0㎛, preferably 2.0㎛ to 8.0㎛. More preferably, it is about 3.0㎛ to 7.0㎛. D of lithium nickel-based oxide 50 If this is too small, processability during electrode manufacturing decreases, and electrolyte impregnation decreases, which may increase electrochemical properties, and D 50 If this is too large, there is a problem in that resistance increases and output characteristics deteriorate.

[0125] The single-particle lithium nickel-based oxide having a nickel content of 50 mol% to 75 mol% may be included in the total positive electrode active material within the positive electrode composite layer in an amount of more than 50 weight%, preferably 55 weight% or more, more preferably 60 weight% or more, even more preferably 70 weight% or more, and even more preferably 100 weight%. When the proportion of the single-particle lithium nickel-based oxide having a nickel content of 50 mol% to 75 mol% in the total weight of the positive electrode active material satisfies the above range, excellent lifespan characteristics can be obtained even when operating at high voltage.

[0127] The above-mentioned positive composite layer may include a positive active material other than a single-particle lithium nickel-based oxide with a nickel content of 50 mol% to 75 mol%, that is, a lithium nickel-based oxide with a nickel content exceeding 75 mol% or a secondary-particle lithium nickel-based oxide, but if the proportion of the lithium nickel-based oxide with a nickel content exceeding 75 mol% or the secondary-particle lithium nickel-based oxide is 50 weight% or more of the total positive active material, the lifespan characteristics may be degraded during high-voltage operation.

[0128] The above-mentioned positive 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 positive composite layer. When the content of the positive active material satisfies the above range, excellent energy density can be achieved.

[0130] Next, the above-mentioned positive electrode conductive material is used to impart conductivity to the positive electrode, and in the battery being constructed, any material that possesses electronic conductivity without causing chemical changes can be used without any particular limitations. 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, carbon fiber, carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or 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 these may be used.

[0131] The above-mentioned positive conductive material may typically be included in an amount of 0.1 to 10 weight%, preferably 0.5 to 8 weight%, and more preferably 0.5 to 5 weight% based on the total weight of the positive composite layer.

[0133] Next, the anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode 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.

[0134] The above anode binder may be included in an amount of 1 to 10 weight%, preferably 1 to 8 weight%, more preferably 1 to 5 weight% based on the total weight of the anode composite layer.

[0136] The above anode may be manufactured according to a conventional anode manufacturing method. For example, the above anode may be manufactured by mixing an anode active material, an anode binder, and / or an anode conductive material in a solvent to prepare an anode slurry, applying the anode slurry onto an anode 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 an anode current collector.

[0137] Meanwhile, solvents commonly used in the relevant technical field may be used as solvents for the anode slurry; for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc., may be used individually or as a mixture of two or more. The amount of the 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 and manufacturing yield of the slurry, and provides excellent thickness uniformity when applied for anode manufacturing thereafter.

[0139] electrolytes

[0140] The electrolyte used in the present invention may be any of the various electrolytes usable in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., and the types thereof are not particularly limited.

[0141] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0142] 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 C2 to C20 structures 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.

[0143] 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, LiB(C2O4)2, or combinations thereof. The concentration of the lithium salt is preferably used within the range of 0.1 to 5.0 M, more preferably 0.1 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.

[0144] Meanwhile, in addition to the above components, the electrolyte may additionally include 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. For example, the electrolyte may include at least one additive selected from the group consisting of cyclic carbonate compounds, halogen-substituted carbonate compounds, sulfone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds.

[0145] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0146] Examples of the above-mentioned halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0147] Examples of the above sulfone-based compounds include at least one compound selected from the group consisting of 1,3-propane sulfone (PS), 1,4-butane sulfone, ethen sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, and 1-methyl-1,3-propene sulfone.

[0148] Examples of the above sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0149] Examples of the above-mentioned phosphate compounds include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyl trimethylsilyl phosphate, trimethylsilyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0150] Examples of the above borate compounds include tetraphenylborate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate toborate (LiB(C2O4)2, LiBOB).

[0151] Examples of the above nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0152] Examples of the above benzene-based compounds include fluorobenzene, examples of the above amine-based compounds include triethanolamine or ethylenediamine, and examples of the above silane-based compounds include tetravinylsilane.

[0153] The above lithium salt-based compound is a compound different from the lithium salt included in the above non-aqueous electrolyte, and examples include lithium difluorophosphate (LiDFP), LiPO2F2, or LiBF4.

[0154] The above additive may be included in an amount of 0.1 to 10 weight%, preferably 0.1 to 5 weight%, based on the total weight of the electrolyte.

[0156] Separator

[0157] The above separator 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. Specifically, the separator may be a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength.

[0159] The lithium secondary battery according to the present invention may have a nominal voltage of 3.68V or higher, preferably 3.68V to 3.80V, and more preferably 3.69V to 3.75V. In this case, the nominal voltage refers to the average voltage value during discharge of the lithium secondary battery. Since the energy density of the lithium secondary battery is calculated as the product of the average voltage and average current during discharge, the energy density increases when the nominal voltage is high. Conventional lithium secondary batteries using lithium nickel-cobalt-manganese oxide as the positive electrode active material generally had a charge cut-off voltage of 4.25V, in which case the nominal voltage was 3.6V. In contrast, the present invention enables the realization of high energy density by raising the charge cut-off voltage to 4.35V or higher so that the nominal voltage becomes 3.68V or higher. Specifically, the lithium secondary battery according to the present invention may have an energy density of 500 Wh / L or more, 500 Wh / L to 800 Wh / L, 550 Wh / L to 800 Wh / L, or 600 Wh / L to 750 Wh / L.

[0161] In the lithium secondary battery according to the present invention, it is preferable that the charge cut-off voltage (full charge voltage) be 4.35V or higher, preferably 4.35V to 5V, and more preferably 4.35V to 4.5V. When the charge cut-off voltage satisfies the above range, the capacity of the positive electrode active material increases, and the nominal voltage increases, thereby enabling the realization of high energy density. Generally, as the charge cut-off voltage increases, the capacity of the positive electrode active material increases. However, there is a problem in that if the driving voltage increases, side reactions with the electrolyte during charging and discharging increase, and structural collapse of the positive electrode active material occurs rapidly, causing the lifespan characteristics to deteriorate rapidly. Such problems are more pronounced in high-nickel lithium nickel-cobalt-manganese oxides with a high nickel content. Therefore, conventionally, when lithium nickel-cobalt-manganese oxides were used as positive electrode active materials, the charge cut-off voltage was generally around 4.25V. However, in the present invention, by applying a single-particle lithium nickel-based oxide with a Ni content of 50 mol% to 75 mol% as the positive electrode active material, excellent lifespan characteristics can be maintained even when the charge cut-off voltage is 4.35V or higher.

[0163] The lithium secondary battery according to the present invention applies primary particle-type artificial graphite, which is relatively inexpensive, and single particle-type lithium nickel-based oxide with a Ni content of 50 to 75 mol% as the positive electrode active material and negative electrode active material, so it exhibits excellent energy density and rapid charging performance despite the low manufacturing cost.

[0165] The lithium secondary battery according to the present invention 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). The lithium secondary battery according to the present invention can achieve high energy density by operating at high voltage and can be particularly useful in the electric vehicle field because it exhibits excellent safety in the event of thermal runaway.

[0166] 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 a plurality of battery modules are provided.

[0167] According to another embodiment of the present invention, a battery pack comprising a plurality of lithium secondary batteries according to the present invention as unit cells is provided. The battery pack may not include a battery module.

[0169] In addition, the present invention provides a pack cell assembly.

[0170] According to one embodiment, the battery module may include 10 to 50, preferably 16 to 36 unit cells. The battery pack may include 10 to 1,000, preferably 10 to 500 unit cells.

[0172] 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.

[0174] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0176] Example 1

[0177] Cathode Manufacturing

[0178] A first cathode slurry was prepared by mixing the first cathode active material, carbon black, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water at a weight ratio of 95.9:0.5:2.6:1.0. As the first cathode active material, a mixture of primary particulate artificial graphite and natural graphite was used at a weight ratio of 60:40, and as the primary particulate artificial graphite, D 50 This uses primary particle-type artificial graphite with a particle size of 11.6㎛, and as the natural graphite, D 50 Natural graphite with a thickness of 18㎛ was used.

[0179] Next, a second cathode slurry was prepared by mixing the second cathode active material : carbon black : styrene-butadiene rubber (SBR) : carboxymethyl cellulose (CMC) in water at a weight ratio of 97.4 : 0.5 : 1.0 : 1.1. As the second cathode active material, D 50 100% of this 11.6㎛ primary particle type artificial graphite was used.

[0180] The first cathode slurry and the second cathode slurry are sequentially applied onto a copper current collector, dried, and then rolled to obtain a porosity of 34% and a loading amount of 4.7 mAh / cm² 2 A phosphorus cathode was manufactured.

[0182] <Anode Manufacturing>

[0183] A cathode slurry was prepared by mixing a cathode active material, a cathode conductive material, and a PVDF binder in a weight ratio of 97:1.2:1.8 in N-methylpyrrolidone (NMP). At this time, the cathode active material was single-particle Li[Ni 0.6 Co 0.1 Mn 0.3 O2 was used, and a mixture of carbon nanotubes and carbon black was used as the anode conductive material.

[0184] The above anode slurry was applied onto an aluminum current collector, dried, and then rolled to manufacture an anode.

[0186] Lithium secondary battery manufacturing

[0187] An electrode assembly was manufactured by placing a polyethylene separator between the anode and cathode manufactured above, and a lithium secondary battery was manufactured by inserting the electrode assembly into a battery case, injecting an electrolyte, and sealing it.

[0189] Example 2

[0190] A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that when preparing the first negative electrode slurry, the first negative electrode active material : carbon black : styrene-butadiene rubber (SBR) : carboxymethyl cellulose (CMC) were mixed in a weight ratio of 94.9 : 0.5 : 3.6 : 1.0.

[0192] Comparative Example 1

[0193] When manufacturing the second cathode slurry, D as the second cathode active material 50 This 11.6㎛ primary particulate artificial graphite: D 50 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 18㎛ secondary particle-type artificial graphite was mixed and used in a weight ratio of 50:50.

[0195] Comparative Example 2

[0196] When manufacturing the second cathode slurry, D as the second cathode active material 50 This 11.6㎛ primary particulate artificial graphite: D 50 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that natural graphite with a thickness of 18 μm was mixed and used in a weight ratio of 50:50.

[0198] Comparative Example 3

[0199] When manufacturing the first cathode slurry, D as the first cathode active material 50A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 100% of the 18㎛ secondary particle-type artificial graphite was used.

[0201] Comparative Example 4

[0202] When manufacturing the second cathode slurry, D as the second cathode active material 50 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 100% of the 18㎛ secondary particle-type artificial graphite was used.

[0204] Comparative Example 5

[0205] When manufacturing the first cathode slurry, D as the first cathode active material 50 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 100% natural graphite with a thickness of 18 μm was used.

[0207] Experimental Example 1: Measurement of Cathode Pore Resistance and Flexibility

[0208] An electrode assembly was prepared by interposing a separator between two negative electrodes prepared in Examples 1 to 2 and Comparative Examples 1 to 5, the electrode assembly was placed in a battery case, an electrolyte not containing lithium salt (ethylene carbonate : ethylmethyl carbonate = 3 : 7 v / v%) was injected, and the mixture was aged for 12 to 24 hours to prepare a symmetric coin cell.

[0209] Then, after applying a current of 0.1 to 1,000,000 Hz and 10 MV to the fabricated symmetric coin cell, the pore resistance (R) of the cathode was determined using the graph measured by EIS (Electrochemical Impedance Spectroscopy). pore The average travel distance Ls of lithium ions inside the cathode composite layer was calculated by measuring ), and the curvature (τ) was calculated by dividing this by the thickness L0 of the cathode composite layer.

[0210] The measurement results are shown in [Table 1] below.

[0211] Pore ​​resistance (R pore , Ω) Curvature (τ) Example 1 6.59 1.77 Example 2 7.11 1.91 Comparative Example 1 7.63 2.05 Comparative Example 2 7.26 1.95 Comparative Example 3 7.63 2.05 Comparative Example 4 7.82 2.10 Comparative Example 5 9.01 2.42

[0212] Through [Table 1] above, it can be confirmed that the cathodes of Examples 1 and 2, in which 100% of primary particulate artificial graphite is used in the second cathode composite layer, exhibit lower pore resistance and curvature compared to the cathodes of Comparative Examples 1 to 5. Lower pore resistance and curvature of the cathode improve lithium ion mobility within the cathode, thereby achieving the effect of improved rapid charging performance.

[0214] Experimental Example 2: Evaluation of Rapid Charging Performance

[0215] The time taken to charge each of the lithium secondary batteries prepared in Examples 1 to 2 and Comparative Examples 1 to 5 from SOC 8 to SOC 80 was measured while varying the charging current rate from 0.25 C-rate to 3.0 C-rate. The measurement results are shown in [Table 2] below.

[0216] Fast charging time (min) Example 1 26.5 Example 2 28.5 Comparative Example 1 29.4 Comparative Example 2 30.5 Comparative Example 3 31.1 Comparative Example 4 32.2 Comparative Example 5 35.5

[0217] As shown in Table 2 above, it can be confirmed that the lithium secondary batteries of Examples 1 and 2, despite using relatively inexpensive primary particle-type artificial graphite, have superior rapid charging performance compared to Comparative Examples 1, 2, and 4, which use secondary particle-type artificial graphite or natural graphite in the second negative electrode composite layer, and Comparative Examples 3 and 5, which use secondary particle-type artificial graphite or natural graphite in the first negative electrode composite layer.

Claims

Claim 1 A cathode comprising: a cathode current collector; a first cathode composite layer disposed on the cathode current collector and comprising a first cathode active material; and a second cathode composite layer disposed on the first cathode composite layer and comprising a second cathode active material; wherein the second cathode active material is composed of primary particulate artificial graphite, and the first cathode active material comprises primary particulate artificial graphite and natural graphite. Claim 2 The cathode according to claim 1, wherein the first cathode active material comprises primary particulate artificial graphite : natural graphite in a weight ratio of 40 : 60 to 80 :

20. Claim 3 In claim 1, the average particle size D of the primary particle-type artificial graphite 50 This cathode is 9㎛ to 15㎛. Claim 4 A cathode according to claim 1, wherein the difference in average particle size between the primary particulate artificial graphite and the natural graphite included in the first cathode active material is 5㎛ or more. Claim 5 The cathode according to claim 1, wherein the first cathode composite layer further comprises a first cathode binder, and the first cathode binder is included in an amount of 0.1% to 4% by weight based on the total weight of the first cathode composite layer. Claim 6 The cathode according to claim 1, wherein the second cathode composite layer further comprises a second cathode binder, and the second cathode binder is included in an amount of 0.1% to 1.5% by weight based on the total weight of the second cathode composite layer. Claim 7 In claim 1, the cathode is a cathode having a porosity of 30% or more. Claim 8 A lithium secondary battery comprising a cathode, a positive electrode, and an electrolyte according to claim 1, wherein the positive electrode comprises a positive electrode composite layer comprising a positive electrode active material, and the positive electrode active material comprises a single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 75 mol% among the total transition metals. Claim 9 A lithium secondary battery according to claim 8, wherein the single-particle lithium nickel-based oxide comprises 30 or fewer nodules. Claim 10 A lithium secondary battery according to claim 8, wherein the single-particle lithium nickel-based oxide is represented by the following [Chemical Formula 1]. [Chemical Formula 1] Li 1+x [Ni a Co b Mn c M 1 d ]O2 In the above [Chemical Formula 1], M 1 It contains one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and -0.1≤x≤0.1, 0.5≤a≤0.75, 0 <b<0.5, 0<c<0.5, 0≤d≤0.2임. Claim 11 A lithium secondary battery according to claim 8, wherein the positive electrode active material further comprises a coating layer containing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo on the surface of the single-particle lithium nickel-based oxide. Claim 12 In claim 8, the lithium secondary battery is a lithium secondary battery having a nominal voltage of 3.68V or higher. Claim 13 In claim 8, the lithium secondary battery is a lithium secondary battery having a charge cut-off voltage of 4.35V or higher. Claim 14 A battery module comprising a lithium secondary battery of any one of claims 8 to 13 as a unit cell. Claim 15 In claim 14, the battery module comprises 10 to 50 unit cells. Claim 16 A battery pack comprising a lithium secondary battery of any one of claims 8 to 13 as a unit cell. Claim 17 In claim 16, the battery pack comprises 10 to 1,000 unit cells. Claim 18 A battery pack comprising the secondary battery module of claim 14.

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