Lithium secondary battery, and battery module and battery pack including same

Abstract

The present invention relates to a lithium secondary battery, and a battery module and a battery pack including same, the lithium secondary battery including: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the positive electrode active material includes a lithium nickel-based oxide having a Ni content of 50 mol% to 75 mol% among all metals excluding lithium, the negative electrode active material includes 50 wt% to 100 wt% of artificial graphite, and the negative electrode has a negative electrode density 1.52g / cm3 or less as defined by the following equation (1). Equation (1): negative electrode density = (25 × La) / Ta In equation (1), La represents the cross-sectional loading amount of the negative electrode (unit: g / 25cm2), and Ta represents a value obtained by subtracting the thickness of the negative electrode current collector from the total thickness of the negative electrode (unit: cm).

Description

Lithium secondary battery, battery module including the same, and battery pack

[0001] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery with improved lifespan characteristics and swelling characteristics, and to a battery module and a battery pack including the same.

[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, which improve capacity by increasing the Ni content of the cathode active material. 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] In addition, high-nickel (High-Ni) cathode active materials have high reactivity when charge and discharge are repeated. +4 There is a problem in that the generation of a large amount of ions causes structural collapse of the positive electrode active material, which increases the degradation rate of the positive electrode active material and reduces lifespan characteristics, and Si-based negative electrode active materials have a problem in that the large volume change during charging and discharging accelerates negative electrode degradation, which in turn reduces lifespan characteristics.

[0005] To reduce the manufacturing costs of electric vehicles, technologies are being developed to secure energy density by applying cathode active materials with a relatively lower nickel content compared to high-nickel (High-Ni) materials and operating at higher voltages than conventional methods. However, when lithium-ion batteries are operated at high voltages, side reactions with the electrolyte increase, leading to increased gas generation, which in turn causes cell thickness expansion and capacity degradation.

[0006] To address these issues, various additives capable of suppressing gas generation in the electrolyte are being attempted; however, there are problems such as increased costs due to the addition of additives, and insufficient improvement as the additives are consumed over time, leading to a decline in the gas generation suppression effect.

[0007] Therefore, there is a need to develop lithium secondary batteries that are inexpensive to manufacture while also possessing excellent lifespan and swelling characteristics even under high-voltage operation.

[0008] The present invention aims to solve the above-mentioned problems by applying a single-particle lithium nickel-based oxide with a Ni content of 50 mol% to 70 mol% as the positive active material, and by controlling the artificial graphite content and negative electrode density in the negative electrode, thereby providing a lithium secondary battery with low manufacturing costs and excellent lifespan and swelling characteristics.

[0009] [1] The present invention comprises a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the positive electrode active material comprises a lithium nickel-based oxide having a Ni content of 50 mol% to 75 mol% among all metals excluding lithium, and the negative electrode active material comprises 50 weight% to 100 weight% of artificial graphite, and the negative electrode has a negative electrode density of 1.52 g / cm³ as defined by the following formula (1). 3 Provides a lithium secondary battery with less than [amount].

[0010] Equation (1): Cathode density = (25 × L)a ) / T a

[0011] In the above equation (1),

[0012] L a is the cross-sectional loading amount of the cathode (unit: g / 25cm²) 2 ) and,

[0013] T a is the value obtained by subtracting the thickness of the cathode current collector from the total thickness of the cathode (unit: cm).

[0014] [2] The present invention provides a lithium secondary battery according to [1], wherein the degree of swelling measured after performing 300 cycles of charging and discharging at 45°C and 0.33°C in a voltage range of 2.5V to 4.35V is 4.6% or less.

[0015] [3] The present invention, in [1] or [2], wherein the cross-sectional loading amount of the cathode is 0.30 to 0.36 g / 25 cm 2 It provides a lithium secondary battery.

[0016] [4] The present invention provides a lithium secondary battery in which, in at least one of [1] to [3], the ratio of the discharge capacity per unit area of ​​the cathode to the discharge capacity per unit area of ​​the anode (N / P) is 1.07 to 1.15.

[0017] [5] The present invention provides a lithium secondary battery in which, in at least one of [1] to [4], the lithium nickel-based oxide is a single-particle lithium nickel-based oxide comprising 30 or fewer nodules.

[0018] [6] The present invention provides a lithium secondary battery in which, in at least one of [1] to [5], the lithium nickel-based oxide is represented by the following [Chemical Formula 1].

[0019] [Chemical Formula 1]

[0020] Li 1+x [Ni a Co b Mn c M1 d ]O2

[0021] 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.

[0022] [7] The present invention provides a lithium secondary battery in which, in at least one of [1] to [6], 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 lithium nickel-based oxide.

[0023] [8] The present invention provides a lithium secondary battery having a nominal voltage of 3.68V or higher in at least one of [1] to [7].

[0024] [9] The present invention provides a lithium secondary battery having a charge cut-off voltage of 4.35V or higher in at least one of [1] to [8].

[0025]

[0010] The present invention provides a battery module comprising at least one of the lithium secondary batteries [1] to [9] as a unit cell.

[0026]

[0011] The present invention provides a battery module comprising 10 to 50 unit cells, wherein the battery module in

[0010] comprises 10 to 50 unit cells.

[0027]

[0012] The present invention provides a battery pack comprising at least one of the lithium secondary batteries [1] to [9] as a unit cell.

[0028]

[0013] The present invention provides a battery pack according to

[0012] , wherein the battery pack comprises 10 to 1,000 unit cells.

[0029]

[0014] The present invention provides a battery pack comprising the battery module of

[0010] or

[0011] .

[0030] 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, and thus can achieve excellent lifespan characteristics.

[0031] The lithium secondary battery according to the present invention controls the content of artificial graphite among the negative electrode active material and the electrode density of the negative electrode to a specific range, and uses a single-particle lithium nickel-based oxide with a nickel content of 50 mol% to 75 mol% as the positive electrode active material, thereby suppressing gas generation and enabling excellent swelling characteristics.

[0032] Figure 1 is a scanning electron microscope image of a single-particle positive electrode active material.

[0033] Figure 2 is a scanning electron microscope image of a pseudo-single particle cathode active material.

[0034] Figure 3 is a scanning electron microscope image of a secondary particle positive electrode active material.

[0035] 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.

[0036] In the present invention, "single particle type" refers to a particle composed of 30 or fewer nodules, and 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.

[0037] 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.

[0038] In the present invention, "secondary particle" refers to a particle formed by the aggregation of a plurality of primary particles, for example, tens to hundreds of primary particles. Specifically, the secondary particle may be an aggregate of more than 30 primary particles. FIG. 3 shows a scanning electron microscope (SEM) image of a positive electrode active material in the form of a secondary particle.

[0039] 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.

[0040] In the present invention, the average particle size (Dmean) of nodules or primary particles refers to the arithmetic mean value calculated after measuring the particle sizes of nodules or primary particles observed in scanning electron microscope images.

[0041] 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.

[0042] In the present invention, “cross-sectional loading amount of the cathode (unit: g / 25cm²) 2 )” can be measured in the following ways.

[0043] First, a cathode sample is prepared by stamping a cathode into a size of 5 cm × 5 cm. Then, the weight W of the cathode sample is measured using an electronic balance or the like. Then, the cathode sample is washed to remove the cathode composite layer, and the weight W1 of the cathode current collector is measured. If the cathode sample is a double-sided coated cathode, the cathode cross-sectional loading amount L can be calculated as L = (W - W1) / 2, and if the cathode sample is a single-sided coated cathode, the cathode cross-sectional loading amount L can be calculated as L = W - W1.

[0044] In the present invention, "N / P" is the discharge capacity per unit area of ​​the anode (unit: mAh / cm² 2 Discharge capacity per unit area of ​​the cathode for ) (Unit: mAh / cm² 2It refers to the ratio of ) and can be measured by the following method. An anode sample and a cathode sample are prepared by stamping the anode and cathode into a fixed area, respectively. Then, the weight W of the sample is measured using an electronic balance or the like, and after washing the sample to remove the composite layer, the weight W1 of the current collector is measured and used to determine the cross-sectional loading amount. If the sample is a double-sided coated electrode, the cross-sectional loading amount L can be calculated as (W - W1) / (2 × sample area); if the sample is a single-sided coated electrode, the cross-sectional loading amount L can be calculated as (W - W1) / sample area. The discharge capacity per unit area of ​​the anode is obtained by multiplying the anode cross-sectional loading amount L by the theoretical capacity of the anode active material and the weight ratio of the anode active material, and the discharge capacity per unit area of ​​the cathode is obtained by multiplying the cathode cross-sectional loading amount by the theoretical capacity of the cathode active material and the weight ratio of the cathode active material. Then, N / P can be calculated by dividing the discharge capacity per unit area of ​​the cathode by the discharge capacity per unit area of ​​the anode.

[0045]

[0046] The inventors of the present invention have completed the present invention by conducting repeated research to develop a lithium secondary battery with relatively low manufacturing costs and excellent lifespan and swelling characteristics, and 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 and controlling the content of artificial graphite and the negative electrode density among the negative electrode active materials to a specific range, thereby improving lifespan and swelling characteristics.

[0047]

[0048] A lithium secondary battery according to the present invention comprises a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and an electrolyte.

[0049] The lithium secondary battery according to the present invention comprises a lithium nickel-based oxide as a positive electrode active material, wherein the Ni content among the total metals excluding lithium is 50 mol% to 75 mol%.

[0050] Single-particle lithium nickel-based oxides with a nickel content of 50 mol% to 75 mol% have superior structural stability compared to high-nickel (High-Ni) lithium transition metal oxides with a nickel content of 80 mol% or more, so they can prevent rapid degradation of the cathode active material even when operated at high voltages of 4.35 V or higher, and because the contact interface with the electrolyte is small, the amount of gas generated during charging and discharging is low.

[0051] The lithium secondary battery according to the present invention includes artificial graphite in an amount of 50% to 100% by weight among the negative electrode active materials. When the negative electrode active material includes artificial graphite in an amount of 50% by weight or more, excellent lifespan characteristics and swelling characteristics can be achieved. If the content of natural graphite in the negative electrode active material exceeds 50% by weight, gas generation increases during high-voltage operation, and cell swelling increases.

[0052] Meanwhile, graphite-based anode active materials, such as natural and synthetic graphite, exhibit less volume change during charging and discharging and have lower unit costs compared to silicon-based anode active materials. Therefore, using graphite-based anode active materials can reduce secondary battery manufacturing costs and enable excellent lifespan characteristics.

[0053] Meanwhile, the above cathode has a cathode density of 1.52 g / cm³ defined by the following formula (1). 3 Below, preferably 1.45 g / cm³ 3 Up to 1.52 g / cm² 3 , more preferably 1.48 g / cm³ 3 Up to 1.52 g / cm² 3 am.

[0054] Equation (1): Cathode density [Unit: g / cm³ 3 ] = (25 × L a ) / T a

[0055] In the above equation (1), L a is the cross-sectional loading amount of the cathode (unit: g / 25cm²) 2 ) and, Ta is the value obtained by subtracting the thickness of the cathode current collector from the total thickness of the cathode (unit: cm).

[0056] The cathode density is 1.52 g / cm³ 3 If it exceeds, particle breakage and electrode degradation are accelerated due to insufficient internal voids of the cathode, and swelling characteristics are degraded.

[0057]

[0058] The components of the lithium secondary battery according to the present invention will be described in more detail below.

[0059]

[0060] anode

[0061] A lithium secondary battery according to the present invention comprises a positive electrode comprising a positive electrode active material. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode composite layer formed on at least one surface of the positive electrode current collector, wherein the positive electrode composite layer comprises a positive electrode active material. In addition, the positive electrode composite layer may further comprise a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material.

[0062] 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.

[0063]

[0064] The above positive active material may include a 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%.

[0065] 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 positive electrode active material decreases during charging and discharging, leading to rapid degradation of the positive electrode. This phenomenon is further exacerbated during high-voltage operation. In contrast, lithium nickel-based oxides with a Ni content of 50 mol% to 75 mol% have higher structural stability at high voltage compared to lithium nickel-based oxides with a nickel content of 80 mol% or more, thus minimizing the degradation of lifespan characteristics during high-voltage operation. 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%.

[0066] 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].

[0067] [Chemical Formula 1]

[0068] Li 1+x [Ni a Co b Mn c M 1 d ]O2

[0069] 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 M1 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.

[0070] 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.

[0071] 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.

[0072] When a satisfies the above range, it can be stably driven at high voltage to realize high capacity and long lifespan characteristics.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078]

[0079] The above lithium nickel-based oxide may be a single-particle lithium nickel-based oxide containing 30 or fewer nodules.

[0080] 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, leading to swelling and rapid degradation of the performance of the lithium secondary battery. In contrast, single-particle lithium nickel-based oxides have a smaller 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 occurrence of swelling and degradation of life characteristics under high temperature and / or high voltage conditions can be minimized.

[0081] 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.

[0082] 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.

[0083] The above lithium nickel-based oxide is D50 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.

[0084]

[0085] 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.

[0086]

[0087] 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.

[0088] 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.

[0089]

[0090] 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.

[0091] 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.

[0092]

[0093] 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.

[0094] 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.

[0095]

[0096] 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.

[0097] 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 is sufficient to dissolve or disperse the anode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that exhibits excellent thickness uniformity when coated for anode manufacturing thereafter.

[0098]

[0099] cathode

[0100] A lithium secondary battery according to the present invention comprises a negative electrode comprising a negative electrode active material. Specifically, the negative electrode comprises a negative electrode current collector and a negative electrode composite layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode composite layer comprises a negative electrode active material. In addition, the negative electrode composite layer may further comprise a negative electrode conductive material and a negative electrode binder in addition to the negative electrode active material.

[0101] 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.

[0102]

[0103] The above-mentioned cathode active material may be composed of a graphite-based cathode active material, and preferably may be artificial graphite or a mixture of artificial graphite and natural graphite.

[0104] The above-mentioned cathode active material includes artificial graphite. The artificial graphite may be included in an amount of 50% to 100% by weight, 60% to 100% by weight, or 70% to 100% by weight based on the total weight of the cathode active material.

[0105] When the cathode active material contains artificial graphite in an amount of 50 wt% or more, excellent lifespan characteristics and swelling characteristics can be achieved. When the content of artificial graphite in the cathode active material is less than 50 wt%, gas generation increases during high-voltage operation, and cell swelling increases.

[0106] The above-mentioned cathode active material may further include natural graphite, and the natural graphite may be included in an amount of 0 to 50 weight%, 10 to 50 weight%, or 10 to 30 weight% based on the total weight of the cathode active material. If the content of natural graphite exceeds 50 weight%, gas generation increases during high-voltage operation, which may increase cell swelling.

[0107]

[0108] The above-mentioned cathode 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 cathode composite layer. When the content of the cathode active material satisfies the above range, excellent energy density can be achieved.

[0109] Next, the above-mentioned cathode conductive material is used to impart conductivity to the cathode, and in the battery being constructed, it may be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, 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.

[0110] The above cathode conductive material may typically be included in an amount of 0.1 to 10 weight%, preferably 0.25 to 8 weight%, and more preferably 0.25 to 5 weight% based on the total weight of the cathode composite layer.

[0111] The above-mentioned cathode binder serves to improve adhesion between cathode active material particles and adhesion between the cathode active material and the cathode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0112] The above cathode 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.

[0113]

[0114] Meanwhile, in the lithium secondary battery according to the present invention, the negative electrode composite layer may have a single-layer structure or a multi-layer structure of two or more layers. For example, the negative electrode may include a first negative electrode composite layer formed on at least one surface of a negative electrode current collector and comprising a first negative electrode active material; and a second negative electrode composite layer formed on the first negative electrode composite layer and comprising a second negative electrode active material. In this case, the first negative electrode active material and the second negative electrode active material may be composed of carbon-based negative electrode active materials, for example, natural graphite, artificial graphite, or a combination thereof.

[0115] The above cathode may be manufactured according to a conventional cathode manufacturing method. For example, the above cathode may be manufactured by mixing a cathode active material, a cathode binder, and / or a cathode conductive material in a solvent to prepare a cathode slurry, applying the cathode slurry onto a cathode current collector, and then drying and rolling, or by casting the cathode slurry onto a separate support and then laminating a film obtained by peeling off from the support onto a cathode current collector.

[0116] As solvents for the 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 is sufficient to dissolve or disperse the cathode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that provides excellent thickness uniformity when coated for subsequent anode manufacturing.

[0117]

[0118] The above cathode has a cathode density of 1.52 g / cm³, defined by the following equation (1). 3 Below, preferably 1.45 g / cm³ 3 Up to 1.52 g / cm² 3 , more preferably 1.48 g / cm³ 3 Up to 1.52 g / cm² 3 am.

[0119] Equation (1): Cathode density [Unit: g / cm³ 3 ] = (25 × L a ) / T a

[0120] In the above equation (1), L a is the cross-sectional loading amount of the cathode (unit: g / 25cm²) 2 ) and, T a is the value obtained by subtracting the thickness of the cathode current collector from the total thickness of the cathode (unit: cm).

[0121] The cathode density is 1.52 g / cm³ 3 If it exceeds, particle breakage and electrode degradation are accelerated due to insufficient internal voids of the cathode, and swelling characteristics are degraded.

[0122] In addition, the cathode has a cross-sectional loading amount of 0.30 g / cm² 2 Inner paper 0.36g / 25cm2 , 0.31g / cm 2 Inner paper 0.36g / 25cm 2 , or 0.31g / cm³ 2 Up to 0.355 g / cm² 2 It may be possible. When the cross-sectional loading amount of the cathode satisfies the above range, the internal porosity of the cathode can be appropriately formed.

[0123]

[0124] Meanwhile, in the present invention, the discharge capacity per unit area of ​​the anode (unit: mAh / cm²) 2 Discharge capacity per unit area of ​​the cathode for ) (Unit: mAh / cm² 2 The ratio N / P of ) can be 1.07 to 1.15 or 1.07 to 1.12. When N / P satisfies the above range, a margin of safety can be secured to prevent reversal of anode capacity relative to cathode capacity.

[0125]

[0126] electrolytes

[0127] 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.

[0128] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0133] Examples of the above-mentioned halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0134] 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.

[0135] Examples of the above sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0136] 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.

[0137] Examples of the above borate compounds include tetraphenylborate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate toborate (LiB(C2O4)2, LiBOB).

[0138] 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.

[0139] 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.

[0140] The above lithium salt-based compound is a compound different from the lithium salt included in the above-mentioned non-aqueous electrolyte, and examples include lithium difluorophosphate (LiDFP), LiPO2F2, or LiBF4.

[0141] 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.

[0142]

[0143] Separator

[0144] The lithium secondary battery according to the present invention may further include a separator between the positive electrode and the negative electrode as needed. The separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used as a separator in a lithium secondary battery may be used without special limitations, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity.

[0145] For example, the above separator may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof; or a porous nonwoven fabric made of a high melting point glass fiber, a polyethylene terephthalate fiber, etc. as a substrate.

[0146] In addition, a coating layer containing ceramic components and / or polymer materials may be formed on at least one surface of the above substrate to ensure heat resistance or mechanical strength.

[0147]

[0148] 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.

[0149]

[0150] 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.

[0151]

[0152] The lithium secondary battery according to the present invention controls the content of artificial graphite among the negative electrode active materials and the electrode density of the negative electrode to a specific range, and uses a single-particle lithium nickel-based oxide with a nickel content of 50 mol% to 75 mol% as the positive electrode active material, thereby suppressing gas generation and enabling excellent swelling characteristics. Specifically, the lithium secondary battery according to the present invention has a swelling degree of 4.6% or less, preferably 4.5% or less, and more preferably 4.4% or less, measured after performing 300 cycles of charge-discharge at 0.33C at 45°C in a voltage range of 2.5V to 4.35V. At this time, the swelling degree is a value defined by the following equation (2).

[0153] Equation (2): Swelling (%) = {(t - t0) / t} × 100

[0154] In equation (2), t0 is the initial thickness of the lithium secondary battery measured before performing 300 cycles of charge and discharge, and t is the thickness of the fully charged lithium secondary battery measured after 300 cycles of charge and discharge.

[0155] The above cycle is defined as charging and discharging the secondary battery at 45°C at 0.33°C in a voltage range of 2.5V to 4.35V as one cycle. Meanwhile, the above charging, discharging, and thickness measurement were carried out with the lithium secondary battery mounted on a jig applying a pressure of approximately 4000 kgf / mm.

[0156]

[0157] 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.

[0158] 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.

[0159] 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.

[0160] In addition, the present invention provides a pack cell assembly.

[0161] 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.

[0162] 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.

[0163]

[0164] 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.

[0165]

[0166] Example 1

[0167] Cathode Manufacturing

[0168] A cathode slurry was prepared by mixing a cathode active material, a cathode conductive material, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in water in a weight ratio of 96.75:0.50:1.70:1.05. As the cathode active material, a mixture of artificial graphite and natural graphite in a weight ratio of 50:50 was used, and as the cathode conductive material, carbon black was used.

[0169] The above cathode slurry is loaded onto both sides of the copper current collector with a cross-sectional loading amount of 0.3108g / 25cm 2 It is coated to achieve the desired result, dried, and then rolled to obtain a cathode density of 1.512 g / cm³ 3 A phosphorus cathode was manufactured.

[0170]

[0171] <Anode Manufacturing>

[0172] A cathode slurry was prepared by mixing a cathode active material, a cathode conductive material, and a PVDF binder in a weight ratio of 97.00:1.20:1.44 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 carbon nanotubes were used as the positive electrode conductive material.

[0173] The above anode slurry was applied to both sides of an aluminum current collector so that the N / P ratio was 1.073, and after drying, the anode was manufactured by rolling.

[0174]

[0175] Lithium secondary battery manufacturing

[0176] An electrode assembly was manufactured by placing a polyethylene separator between the anode and cathode manufactured above, and after inserting the electrode assembly into a battery case, the electrolyte manufactured above was injected and sealed to manufacture a lithium secondary battery.

[0177]

[0178] Example 2

[0179] When manufacturing the cathode, a mixture of artificial graphite and natural graphite in a weight ratio of 80:20 is used as the cathode active material, and the cathode slurry is applied to both sides of the copper current collector with a cross-sectional loading amount of 0.3546g / 25cm 2 It is coated to achieve the desired density, dried, and then rolled to obtain a cathode density of 1.504 g / cm³ 3 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a negative electrode was manufactured.

[0180]

[0181] Example 3

[0182] When manufacturing the cathode, 100 wt% artificial graphite is used as the cathode active material, and the cathode slurry is applied to both sides of a copper current collector with a cross-sectional loading amount of 0.3535 g / 25 cm 2 It is coated to achieve the desired result, dried, and then rolled to obtain a cathode density of 1.482 g / cm³ 3 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a negative electrode was manufactured and a positive electrode was manufactured such that the N / P ratio was 1.11.

[0183]

[0184] Comparative Example 1

[0185] During cathode manufacturing, the cathode slurry is loaded onto both sides of the copper current collector with a cross-sectional loading amount of 0.3111g / 25cm 2 It is coated to achieve the desired result, dried, and then rolled to obtain a cathode density of 1.565 g / cm³ 3 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a negative electrode was manufactured and a positive electrode was manufactured such that the N / P ratio was 1.074.

[0186]

[0187] Comparative Example 2

[0188] When manufacturing the cathode, natural graphite is used exclusively as the cathode active material, and the cathode slurry is applied to both sides of a copper current collector with a cross-sectional loading amount of 0.3051g / 25cm 2 It is coated to achieve the desired result, dried, and then rolled to obtain a cathode density of 1.542 g / cm³ 3 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a negative electrode was manufactured and a positive electrode was manufactured such that the N / P ratio was 1.081.

[0189]

[0190] Positive electrode active material negative electrode active material negative electrode cross-sectional loading amount [g / 25cm 2 ]Cathode density[g / cm³ 3]N / P Example 1 Stage Particle NCM613 Artificial Graphite 50wt%, Natural Graphite 50wt% 0.3108 1.512 1.073 Example 2 Stage Particle NCM613 Artificial Graphite 80wt%, Natural Graphite 20wt% 0.3546 1.504 1.073 Example 3 Stage Particle NCM613 Artificial Graphite 100wt% 0.3535 1.482 1.11 Comparative Example 1 Stage Particle NCM613 Artificial Graphite 50wt%, Natural Graphite 50wt% 0.3111 1.565 1.074 Comparative Example 2 Stage Particle NCM613 Natural Graphite 100wt% 0.3051 1.542 1.081

[0191] Experimental Example 1: Evaluation of Life Characteristics

[0192] Each lithium secondary battery prepared in the above examples and comparative examples was charged and discharged for up to 300 cycles at 45°C at 0.33°C in a voltage range of 2.5V to 4.35V, and the capacity retention rate and resistance increase rate were measured. The measurement results are shown in [Table 2] below.

[0193]

[0194] Experimental Example 2: Evaluation of Swelling Degree

[0195] Each lithium secondary battery manufactured in the above examples and comparative examples was mounted on a jig to measure the initial thickness t0, and then 300 cycles of charge-discharge were performed at 45°C at 0.33C in a voltage range of 2.5V to 4.35V. Then, after 300 cycles of charge-discharge, the thickness t of the lithium secondary battery was measured and substituted into the following equation (2) to measure the degree of swelling. The measurement results are shown in [Table 2] below.

[0196] Equation (2): Swelling (%) = {(t - t0) / t} × 100

[0197] Capacitance Retention Rate (%) Resistance Increase Rate (%) Swelling Degree (%) Example 194.5 57 25.5 334.36 Example 296.3 691 1.5 603.77 Example 392.0 41 22.9 523.96 Comparative Example 194.1 89 36.1 97 4.61 Comparative Example 291.4 1351.0 235.82

[0198] Through Table 2 above, it can be confirmed that the lithium secondary batteries of Examples 1 to 3, which use single particles as the positive active material, contain 50% to 100% by weight of artificial graphite, and have a negative electrode density of 1.52 g / cc or less, exhibit superior high-temperature life characteristics and swelling characteristics compared to Comparative Example 1, which has a negative electrode density exceeding 1.52 g / cc, and Comparative Example 2, which uses only natural graphite and has a negative electrode density exceeding 1.52 g / cc.

Claims

1. A lithium secondary battery comprising a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, and The above-mentioned positive electrode active material comprises a lithium nickel-based oxide having a Ni content of 50 mol% to 75 mol% among the total metals excluding lithium, and The above-mentioned negative electrode active material comprises 50% to 100% by weight of artificial graphite, and The above cathode has a cathode density of 1.52 g / cm³ defined by the following formula (1). 3 Lithium secondary battery with less than 100 Equation (1): Cathode density (g / cm²) 3 ) = (25 × L a ) / T a In the above equation (1), L a is the cross-sectional loading amount of the cathode (unit: g / 25cm²) 2 ) and, T a is the value obtained by subtracting the thickness of the cathode current collector from the total thickness of the cathode (unit: cm).

2. In Paragraph 1, The above lithium secondary battery is a lithium secondary battery having a swelling degree of 4.6% or less measured after performing 300 cycles of charge and discharge at 45℃ and 0.33C in a voltage range of 2.5V to 4.35V.

3. In Paragraph 1, The cross-sectional loading amount of the above cathode is 0.30 to 0.36 g / 25 cm 2 lithium secondary battery.

4. In Paragraph 1, The above lithium secondary battery is a lithium secondary battery in which the ratio of the discharge capacity per unit area of ​​the negative electrode to the discharge capacity per unit area of ​​the positive electrode (N / P) is 1.07 to 1.

15.

5. In Paragraph 1, The above lithium nickel-based oxide is a lithium secondary battery that is a single-particle lithium nickel-based oxide containing 30 or fewer nodules.

6. In Paragraph 1, A lithium secondary battery in which the above lithium nickel-based oxide is represented by the following [Chemical Formula 1]. [Chemical Formula 1] Li 1+x [Ni a Co b Mr 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.

7. In Paragraph 1, A lithium secondary battery wherein the above positive active material further comprises a coating layer on the surface of the lithium nickel-based oxide containing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

8. In Paragraph 1, The above lithium secondary battery is a lithium secondary battery with a nominal voltage of 3.68V or higher.

9. In Paragraph 1, The above lithium secondary battery is a lithium secondary battery having a charge cut-off voltage of 4.35V or higher.

10. A battery module comprising a lithium secondary battery of any one of claims 1 to 9 as a unit cell.

11. In Paragraph 10, The above battery module is a battery module comprising 10 to 50 unit cells.

12. A battery pack comprising a lithium secondary battery of any one of claims 1 to 9 as a unit cell.

13. In Paragraph 12, The above battery pack is a battery pack comprising 10 to 1,000 unit cells.

14. A battery pack comprising the secondary battery module of claim 10.

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