Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: a positive electrode including a positive electrode mixture layer containing a positive electrode active material, a negative electrode including a negative electrode mixture layer containing a negative electrode active material; and an electrolyte, wherein X defined by Equation (1) is 2 or more. Equation (1): X = 1000 / (A×B×C) In Equation (1), A is a value obtained by measuring, in seconds (sec), the time it takes for propylene carbonate to be completely impregnated in the positive electrode when 1 mL of propylene carbonate is dropped on the surface of the positive electrode, B is the sheet resistance of the positive electrode measured in Ω·cm, and C is the curvature of the positive electrode.

Description

lithium secondary battery

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0194808 filed on December 23, 2024, and all contents disclosed in said Korean Patent Application are incorporated herein as part of this specification.

[0002] The present invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery with excellent rapid charging performance.

[0003] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive and negative electrodes include an active material capable of lithium ion intercalation and deintercalation.

[0004] The electrode of a lithium secondary battery is manufactured by applying an electrode slurry containing an electrode active material, a conductive material, and a binder onto an electrode current collector, drying it, rolling the electrode until it reaches a desired thickness, and vacuum drying it.

[0005] With the recent increase in demand for electric vehicles and the like, there is a growing need for batteries with high energy density and excellent fast-charging performance. However, the fast-charging performance of lithium-ion batteries is difficult to predict because it is determined by the complex interplay of cathode, anode, and electrolyte designs. Furthermore, as various fast-charging protocols are being developed, it is difficult to determine whether a specific design offers superior or inferior fast-charging performance. Consequently, developing lithium-ion batteries with excellent fast-charging capabilities requires significant cost and time.

[0006] The present invention aims to solve the above-mentioned problems by providing a lithium secondary battery with improved rapid charging performance by designing the positive electrode to satisfy specific conditions.

[0007] [1] The present invention provides a lithium secondary battery comprising a positive electrode including a positive electrode composite layer including a positive electrode active material, a negative electrode including a negative electrode composite layer including a negative electrode active material, and an electrolyte, wherein X defined by the formula (1) is 2 or more.

[0008] Equation (1): X = 1000 / (A×B×C)

[0009] In the above equation (1), A is the time measured in seconds (sec) until the propylene carbonate is completely impregnated into the anode when 1 mL of propylene carbonate is dropped onto the anode surface, B is the sheet resistance of the anode measured in Ω·cm, and C is the curvature of the anode.

[0010] [2] The present invention provides a lithium secondary battery according to [1], wherein the time taken for 1 mL of propylene carbonate to free fall onto the surface of the anode and for the propylene carbonate to be completely impregnated into the anode is 100 seconds to 250 seconds.

[0011] [3] The present invention provides a lithium secondary battery in which the sheet resistance of the anode is 3 Ω·cm to 5 Ω·cm, in accordance with [1] or [2].

[0012] [4] The present invention provides a lithium secondary battery in which the curvature of the positive electrode is 0.3 to 0.8 in at least one of [1] to [3].

[0013] [5] The present invention provides a lithium secondary battery in which, in at least one of [1] to [4], the positive active material comprises a lithium nickel-based oxide represented by the following [Chemical Formula 1].

[0014] [Chemical Formula 1]

[0015] Li x Ni a Co b M 1 c M2 d O2

[0016] In the above [Chemical Formula 1], M 1 is one or more selected from Mn and Al, and M 2 is one or more selected from the group consisting of Zr, Y, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.90≤x≤1.1, 0.50≤a<1.0, 0 <b<0.5, 0<c<0.5, 0≤d≤0.1이다.

[0017] [6] The present invention provides a lithium secondary battery in which, in at least one of [1] to [5], the positive active material comprises a single-particle type positive active material, a secondary-particle type positive active material, or a combination thereof.

[0018] [7] The present invention provides a lithium secondary battery in which, in at least one of [1] to [6], the positive active material comprises large particles having an average particle size of 8 μm to 20 μm and small particles having an average particle size of 3 μm or more and less than 8 μm.

[0019] [8] The present invention provides a lithium secondary battery in which, in [7] the opposite is a secondary particle-type positive active material and the elementary particle is a single particle-type positive active material.

[0020] [9] The present invention provides a lithium secondary battery in which, in [7] or [8], the alleles and subatomic particles are included in a weight ratio of 5:95 to 95:5.

[0021]

[0010] The present invention provides a lithium secondary battery in which, in at least one of [1] to [9], the negative electrode active material comprises a silicon-based negative electrode active material and a graphite-based negative electrode active material.

[0022]

[0011] The present invention provides a lithium secondary battery in which the silicon-based negative electrode active material is a Si-C composite, in the

[0010] above.

[0023]

[0012] The present invention provides a lithium secondary battery in which, in at least one of

[0010] or

[0011] , the graphite-based negative electrode active material comprises artificial graphite and natural graphite.

[0024]

[0013] The present invention provides a lithium secondary battery in which, in at least one of

[0010] to

[0012] , the Si-C composite and the graphite-based negative electrode active material are included in a weight ratio of 5:95 to 20:80.

[0025]

[0014] The present invention provides a lithium secondary battery having an energy retention rate of 90% or more measured after 100 cycles of charging and discharging under 1C charging and 0.33C discharging conditions, in at least one of [1] to

[0013] .

[0026] The lithium secondary battery according to the present invention includes a positive electrode designed such that PC impregnation time (C), sheet resistance (B), and curvature (C) satisfy specific conditions. Since the positive electrode designed to satisfy the conditions of the present invention has high electrical conductivity and low lithium ion mobility resistance, it exhibits excellent high-rate charging performance, thereby enabling excellent rapid charging performance.

[0027] Figure 1 is a graph showing the cycle characteristics of lithium secondary batteries manufactured by the examples and comparative examples during low-rate charging (0.33C).

[0028] Figure 2 is a graph showing the cycle characteristics of lithium secondary batteries manufactured by the example and comparative example during high rate (1C) charging.

[0029] The present invention will be described in more detail below.

[0030] In the present invention, the “anode surface resistance” can be measured by preparing a sample by punching out an anode to be measured in a size of 5 cm × 5 cm, inserting a probe of a multi-probe resistor into the surface of the sample, applying a current (I) of 1 μA to 10 mA from the surface of the sample toward the current collector to measure the voltage (V), and then dividing the measured voltage (V) by the applied current (I). At this time, the anode may be an anode obtained by disassembling an electrode assembly. In the present invention, a multi-probe resistor with 46 probes was used, and the resistance was measured by applying a current of 10 μA.

[0031] In the present invention, "anode curvature (C)" is an indicator representing the degree to which the internal flow path of the anode composite layer is bent, and is a value defined by the following formula (A).

[0032] Equation (A): Anodic curvature (C) = L e / L0

[0033] In the above equation (A), L0 is the theoretical resistance to lithium migration within the anode composite layer, which can be calculated through the loading amount of the anode composite layer, the thickness of the anode composite layer, and the conductivity of the electrolyte. e is the actual distance that lithium ions move within the anode composite layer, and is a value calculated by measuring the electrode pore resistance through AC impedance measurement after manufacturing a cell with an anode / separator / anode structure (symmetric cell).

[0034] As a result of repeated research to develop a lithium secondary battery with excellent rapid charging performance, the inventors discovered that when the impregnation, flexibility, and sheet resistance of the positive electrode satisfy specific conditions, the lithium ionicity and electrical conductivity are maintained excellently, and positive electrode degradation is suppressed during high-rate charging, thereby enabling excellent lifespan performance even during rapid charging, and thus completed the present invention.

[0035] In the present invention, "single particle type" refers to a particle structure comprising 30 or fewer sub-particles. Here, to distinguish between the sub-particles of the single particle type and the sub-particles of the secondary particle to be described later, the sub-particles of the single particle type are referred to as nodules. The concept of a single particle type includes a single particle consisting of one nodule and a pseudo-single particle which is a complex of 2 to 30 nodules.

[0036] 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.

[0037] In the present invention, "secondary particle" refers to a particle structure comprising 31 or more sub-particles. The sub-particles of the secondary particles are called primary particles.

[0038] 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.

[0039] 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 or backscatter electron diffraction (EBSD) images. For example, the particle size of the nodules or primary particles can be measured by manufacturing an electrode using the positive electrode active material powder to be measured, then cutting the electrode before rolling using ion milling (HITACHI IM-500, acceleration voltage 6kV) to obtain a cross-section, and then measuring the number of primary particles on a scale of approximately 400±10 using an FE-SEM (JEOL JSM7900F) device under conditions of acceleration voltage 15kV and WD 15 mm.

[0040] 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.

[0041]

[0042] Specifically, the lithium secondary battery according to the present invention comprises a positive electrode including a positive electrode composite layer including a positive electrode active material, a negative electrode including a negative electrode composite layer including a negative electrode active material, and an electrolyte, wherein X defined by the formula (1) is 2 or more, preferably 2 to 5, more preferably 2 to 4.

[0043] Equation (1): X = 1000 / (A×B×C)

[0044] In the above equation (1), A is a unitless number, which is the time in seconds (sec) taken for the propylene carbonate to be completely impregnated into the anode when 1 mL of propylene carbonate is dropped onto the anode surface. Whether the propylene carbonate is completely impregnated can be determined by dropping a 1 mL drop of propylene carbonate onto the surface of the anode composite layer using a pipette or dropper and observing the presence or absence of the propylene carbonate drop on the surface of the anode composite layer. That is, if no propylene carbonate drop is observed on the anode surface, it is determined that the propylene carbonate is completely impregnated into the anode. The impregnation time of the propylene carbonate (PC) is an indicator representing the electrolyte wetting ability, and it can be determined that the shorter the PC impregnation time, the better the electrolyte wetting ability.

[0045] In the present invention, after free-falling 1 mL of propylene carbonate onto the surface of the anode, the time required until the propylene carbonate is completely impregnated into the anode may be 100 seconds to 250 seconds, preferably 150 seconds to 250 seconds, and more preferably 150 seconds to 200 seconds. If the impregnation time of the propylene carbonate is too long, the electrolyte impregnation ability decreases, reducing lithium ion mobility and potentially degrading rapid charging performance; if it is too short, the balance with the cathode is not maintained, which may lead to lithium precipitation. When the anode porosity is high, the impregnation time of the propylene carbonate may be shortened; in this case, the pores of the anode may act as resistance, potentially worsening electrical conductivity.

[0046] Since the impregnation time of propylene carbonate is determined by factors such as the porosity of the anode and the thickness of the anode composite layer, the impregnation time of propylene carbonate can be controlled by appropriately adjusting these factors.

[0047] The above B is a unitless number representing the value of the sheet resistance of the anode measured in units of Ω·cm. In the present invention, the sheet resistance of the anode may be 3 Ω·cm to 5 Ω·cm, preferably 3 Ω·cm to 4.5 Ω·cm, and more preferably 3.5 Ω·cm to 5 Ω·cm. If the sheet resistance of the anode is too high, electrical conductivity may decrease, which may degrade high-rate charging performance; if it is too low, it may not be balanced with the anode, which may cause lithium deposition.

[0048] Since the sheet resistance of the anode is determined by the influence of the type of anode conductive material used, the content of the anode conductive material, the type of anode active material, and the type and content of the binder, the sheet resistance of the anode can be controlled by appropriately adjusting these factors during anode manufacturing.

[0049] The above C is a bending value of the anode, which is a unitless number and is an indicator representing the degree to which the internal flow path of the anode composite layer is bent. In the present invention, the bending value of the anode may be 0.3 to 0.8, preferably 0.4 to 0.8, and more preferably 0.4 to 0.7. When the anode bending value satisfies the above range, lithium ions move smoothly within the anode composite layer, and excellent high-rate charging performance may be exhibited.

[0050] Since anode bending is determined by a complex interplay of factors such as the type of anode active material, particle size distribution, particle diameter, degree of rolling, porosity, and pore size distribution, anode bending can be controlled by appropriately adjusting these factors during anode manufacturing.

[0051] During high-rate charging, the current is charged at a rapid speed, so the movement of electrons and lithium ions within the anode must occur quickly. If the movement of electrons and lithium ions within the anode is delayed, lithium precipitation may occur. This is because the surface resistance of the anode active material increases, leading to heat generation and side reactions, which can accelerate the increase in anode resistance and consequently cause cell degradation. Accordingly, the inventors have conducted continuous research to develop a battery capable of suppressing cell degradation during high-rate charging. As a result, they discovered that cell degradation during high-rate charging can be effectively suppressed when the anode is manufactured such that X, defined by the relationship between the electrolyte impregnation, sheet resistance, and curvature of the anode, is 2 or greater. When X is less than 2, the electrolyte impregnation of the anode decreases, resulting in a longer impregnation time. When the anode sheet resistance and curvature are high, the electrical conductivity and lithium mobility in the anode decrease, causing a rapid increase in anode resistance and a degradation of lifespan characteristics. When charging at a low rate, the increase in resistance due to the above factors is relatively small and thus less affected, but when charging at a high rate, the anode resistance increases rapidly, causing the balance of electrical conductivity, lithium mobility resistance, and ion conductivity between the cathode and the anode to rapidly collapse, thereby accelerating cell degradation.

[0052] On the other hand, if X is too large, the electrochemical reactivity at the anode becomes excessively high compared to the cathode, which can cause a load on the lithium ion intercalation reaction at the cathode and lead to lithium precipitation. Therefore, it is more preferable that X be 5 or less, or 4 or less.

[0053]

[0054] Hereinafter, each component of the lithium secondary battery of the present invention will be described in more detail.

[0055]

[0056] anode

[0057] 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 disposed on at least one surface of the anode current collector and comprising an anode active material. The anode composite layer may further comprise an anode conductive material and an anode binder in addition to the anode active material.

[0058] The above-mentioned cathode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may include a lithium metal oxide containing lithium and one or more metals such as cobalt, manganese, nickel, or aluminum. More specifically, the lithium metal oxide is a lithium-manganese-based oxide (e.g., LiMnO2, LiMn2O4, etc.), a lithium-cobalt-based oxide (e.g., LiCoO2, etc.), a lithium-nickel-based oxide (e.g., LiNiO2, etc.), or a lithium-nickel-manganese-based oxide (e.g., LiNi 1-Y Mn Y O2(here, 0 <Y<1), LiMn 2-Z Ni Z O4 (where 0 < Z < 2), etc.), lithium-nickel-cobalt oxides (e.g., LiNi 1-Y1 Co Y1 O2(here, 0 <Y1<1) 등), 리튬-망간-코발트계 산화물(예를 들면, LiCo 1-Y2 Mn Y2 O2(here, 0 <Y2<1), LiMn 2-Z1 Co Z1 O4 (where 0 < Z1 < 2), etc.), lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni p Co q Mn r )O2(where, 0<p<1, 0<q<1, 0<r<1, p+q+r=1) or Li(Ni p1 Co q1 Mn r1 )O4 (where 0<p1<2, 0<q1<2, 0<r1<2, p1+q1+r1=2), etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Nip2 Co q2 Mn r2 M s2 Examples include )O2(wherein M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, and p2, q2, r2 and s2 are each atomic fractions of independent elements, such that 0<p2<1, 0<q2<1, 0<r2<1, 0<s2<1, p2+q2+r2+s2=1), etc., and any one or more of these compounds may be included.

[0059] Preferably, the positive electrode active material may include a lithium nickel-based oxide represented by the following [Chemical Formula 1].

[0060] [Chemical Formula 1]

[0061] Li x Ni a Co b M 1 c M 2 d O2

[0062] In the above chemical formula 1, the M 1 It is one or more selected from Mn and Al, and preferably, for durability, it may be Mn or a combination of Mn and Al.

[0063] M 2 It may be one or more selected from the group consisting of Zr, Y, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S.

[0064] The above x represents the atomic fraction of lithium in the lithium transition metal oxide, and may be 0.90≤x≤1.1, preferably 0.95≤x≤1.08, and more preferably 1.0≤x≤1.08.

[0065] The above a represents the atomic fraction of nickel among metal elements excluding lithium in the lithium transition metal oxide, and may be 0.50≤a<1.0, 0.60≤a≤0.99, 0.65≤a≤0.98, or 0.80≤a≤0.98. When the nickel content satisfies the above range, high capacity characteristics can be achieved.

[0066] The above b represents the atomic fraction of cobalt among the metal elements excluding lithium in the lithium transition metal oxide, where 0 <b<0.5, 0<b<0.4, 0<b<0.35 또는 0.01≤b<0.2일 수 있다.

[0067] The above c is M among the metal elements excluding lithium in the lithium transition metal oxide. 1 Representing the atomic fraction of, 0 <c<0.5, 0<c<0.4, 0<c<0.35 또는 0.01≤c<0.2일 수 있다.

[0068] The above d is M among the metal elements excluding lithium in the lithium transition metal oxide. 2 It represents the atomic fraction of , which can be 0≤d≤0.1 or 0≤d≤0.05.

[0069]

[0070] The above-mentioned positive active material may include two or more types of particles with different average particle sizes. For example, the above-mentioned positive active material may include large particles with an average particle size of 8 μm to 20 μm, preferably 10 μm to 18 μm, more preferably 10 μm to 15 μm, and small particles with an average particle size of 3 μm or more and less than 8 μm, preferably 3 μm to 7.5 μm, more preferably 3 μm to 7 μm. When including large and small particles with different average particle sizes, the positive density can be increased to improve energy density.

[0071] The above alleles and subatomic particles may be included in a weight ratio of 5:95 to 95:5, 30:70 to 95:5, 50:50 to 95:5, or 50:50 to 90:10.

[0072]

[0073] The above-mentioned positive electrode active material may include a single-particle type positive electrode active material, a secondary-particle type positive electrode active material, or a combination thereof. Preferably, the above-mentioned positive electrode active material may include a single-particle type positive electrode active material and a secondary-particle type positive electrode active material. Although the single-particle type positive electrode active material exhibits superior high-temperature storage characteristics and high-temperature life characteristics compared to the secondary-particle type positive electrode active material, its output characteristics are inferior due to its higher resistance compared to the secondary-particle type positive electrode active material. When a mixture of the single-particle type positive electrode active material and the secondary-particle type positive electrode active material is used, high-temperature characteristics can be improved while minimizing resistance and / or output degradation.

[0074] The above single-particle type cathode active material is a cathode active material comprising particles composed of 30 or fewer, preferably 1 to 25, more preferably 1 to 15 nodules, and includes a single particle composed of 1 nodule and a pseudo-single particle which is a composite of 2 to 30 nodules.

[0075] 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, small particle breakage is minimized during electrode manufacturing, and excessive resistance can be prevented.

[0076] The above single-particle type positive electrode active material has an average particle size (D 50 ) may be 3.0㎛ to 8.0㎛, preferably 3.0㎛ to 7.5㎛, more preferably 3.0㎛ to 7.0㎛. The average particle size (D) of the single-particle type cathode active material. 50 When ) satisfies the above range, appropriate tap density and anode resistance can be realized, and an anode with high electrode density can be manufactured. Average particle size (D) of the single-particle anode active material 50If ) is too small, the electrolyte impregnation is reduced, and if it is too large, problems such as reduced tap density and increased resistance may occur.

[0077] The secondary particle type cathode active material is a cathode active material comprising aggregates of 31 or more, preferably 40 or more, and more preferably 50 or more primary particles.

[0078] The above secondary particle-type cathode active material has an average particle size (D 50 ) may be 8㎛ to 20㎛, preferably 10㎛ to 18㎛, more preferably 10㎛ to 15㎛. The average particle size (D) of the secondary particle-type cathode active material. 50 When the above range is satisfied, an appropriate tap density can be achieved, and an anode with high electrode density can be manufactured.

[0079] The above single-particle type positive electrode active material and secondary-particle type positive electrode active material may each independently include a lithium nickel-based oxide.

[0080] For example, the single-particle type cathode active material and the secondary-particle type cathode active material may each independently comprise a lithium nickel-based transition metal oxide having a Ni content of 80 mol% or more, 83 mol% or more, 86 mol% or more, 90 mol% or more, or 90 mol% to 96 mol% among the total metals excluding lithium. When the Ni content of the single-particle type cathode active material and the secondary-particle type cathode active material satisfies the above range, high capacity characteristics can be achieved.

[0081] More specifically, the single-particle type positive electrode active material and the secondary-particle type positive electrode active material may each independently include a lithium nickel-based oxide represented by the following [Chemical Formula 2].

[0082] [Chemical Formula 2]

[0083] Li 1+x1 [Ni a1 Co b1 M a c1 M b d1]O2

[0084] In the above [Chemical Formula 2], M a It may be Mn, Al, or a combination thereof, and preferably may be Mn or a combination of Mn and Al.

[0085] The above M b It may include one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo. b When the element is included, the structural stability of the lithium nickel-based oxide particles is improved, enabling excellent lifespan characteristics during high-voltage operation. Preferably, the above M b 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.

[0086] The above 1+x1 represents the lithium molar ratio in the lithium nickel-based oxide, and may be -0.1≤x1≤0.1, 0≤x1≤0.1, or 0≤x1≤0.07. When 1+x1 satisfies the above range, a stable layered crystal structure can be formed.

[0087] The above a1 represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.80≤a1≤0.99, 0.83≤a1≤0.99, 0.86≤a1≤0.98, or 0.90≤a1≤0.96.

[0088] The above b1 represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b1<0.20, 0<b1<0.17 0.01≤b1<0.14 또는 0.01≤b1≤0.10일 수 있다.

[0089] The above c1 is M among the total metals excluding lithium in the lithium nickel-based oxide. 1Representing the molar ratio of elements, 0 <c1<0.20, 0<c1<0.17, 0.01≤c1<0.14 또는 0.01≤c1≤0.10일 수 있다.

[0090] The above d1 is M among the total metals excluding lithium in the lithium nickel-based oxide. 2 Representing the molar ratio of elements, 0≤d1≤0.2, 0≤d1≤0.1, or 0 <d1≤0.1일 수 있다. M 2 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.

[0091]

[0092] The above single-particle type positive active material and the above secondary-particle type positive active material have different average particle sizes (D 50 Can have ).

[0093] Preferably, the average particle size (D) of the above-mentioned single-particle type positive electrode active material 50 The average particle size (D) of the secondary particulate cathode active material 50 It can be smaller than ). That is, the single-particle type cathode active material can be a small particle, and the secondary-particle type cathode active material can be an allotrope. Conventionally, it was common to use a mixture of large particles in the form of secondary particles and small particles in the form of secondary particles as bimodal cathode materials; however, in this case, there was a problem in that fine particles were generated as small particles broke during the cathode rolling process, which increased side reactions with the electrolyte and degraded lifespan characteristics. However, since the single-particle type cathode active material undergoes under-scaling during the manufacturing process, the particle strength is higher than that of the secondary-particle type cathode active material. Therefore, when the single-particle type cathode active material is used as a small particle as in the present invention, the breaking of small particles during the rolling process can be minimized, and accordingly, side reactions with the electrolyte are reduced, thereby achieving the effect of improving lifespan characteristics.

[0094] The above single-particle type positive active material and secondary-particle type positive active material may be included in a weight ratio of 30:70 to 70:30, preferably 40:60 to 60:40, more preferably 45:55 to 55:45.

[0095]

[0096] The above positive active material is, if necessary, a coating element M on a lithium nickel-based oxide. c It may further include a coating layer comprising Li-M c It may include a solid solution of -O. The coating element M c It may include one or more selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, B, Ca, Sr, W, Ta, Nb, and Mo. Preferably, the coating element M c It may include two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, and W. When a coating layer is formed on a lithium nickel-based oxide, the surface structure of the positive electrode active material is stabilized, and side reactions with the electrolyte can be effectively suppressed.

[0097]

[0098] The above positive active material may be included in an amount of 60 to 99 weight%, preferably 70 to 99 weight%, and more preferably 80 to 98 weight% based on the total weight of the positive composite layer.

[0099] The above-mentioned anode binder is a component that assists in the bonding of the anode active material and the anode conductive material, as well as in the bonding to the current collector.

[0100] Examples of such anode binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene (PE), polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers.

[0101] Typically, the anode binder may be included in an amount of 1 to 20 weight%, preferably 1 to 15 weight%, and more preferably 1 to 10 weight% based on the total weight of the anode composite layer.

[0102] The above-mentioned positive electrode conductive material is a component intended to further enhance the conductivity of the positive electrode active material, and is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, carbon powders such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powders such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers such as carbon fibers or metal fibers; fluorocarbon powder; conductive powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives may be used.

[0103] Typically, the anode conductive material may be included in an amount of 1 to 20 weight%, preferably 1 to 15 weight%, and more preferably 1 to 10 weight% based on the total weight of the anode composite layer.

[0104]

[0105] The above anode may be manufactured according to a conventional anode manufacturing method. Specifically, the above anode may be manufactured by coating an anode slurry containing an anode active material, an anode binder, an anode conductive material, and a solvent onto an anode current collector and then rolling to form an anode composite layer, or by casting the anode slurry onto a separate support and then laminating a film obtained by peeling from the support onto an anode current collector.

[0106] The anode current collector mentioned above may be any anode current collector commonly used in the relevant technical field, for example, aluminum, stainless steel, nickel, titanium, calcined carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. The anode current collector may typically have a thickness of 3 μm to 500 μm. If necessary, fine irregularities may be formed on the surface of the anode current collector to strengthen the bonding strength of the negative electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0107] The solvent for the anode slurry may include organic solvents such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), and acetone, and may be used in an amount that results in a desirable viscosity when including the anode active material, anode binder, and anode conductive material. For example, the concentration of the solid component, which includes the anode active material and optionally the anode binder and anode conductive material, may be 50 to 95 weight%, preferably 70 to 95 weight%, and more preferably 70 to 90 weight%.

[0108]

[0109] cathode

[0110] The cathode according to the present invention comprises a cathode composite layer comprising a cathode active material. Specifically, the cathode comprises a cathode current collector; and a cathode composite layer disposed on at least one surface of the cathode current collector and comprising a cathode active material. The cathode composite layer may further comprise a cathode conductive material and a cathode binder in addition to the cathode active material.

[0111] The above-mentioned cathode active material may be cathode active materials commonly used in the relevant technical field, such as graphite-based cathode active materials like artificial graphite and natural graphite, silicon-based cathode active materials like silicon, silicon oxide, and Si-C composites, and combinations thereof.

[0112] Preferably, the negative electrode active material may include a silicon-based negative electrode active material and a graphite-based negative electrode active material. More preferably, the negative electrode active material may include a Si-C composite and a graphite-based negative electrode active material.

[0113] The above Si-C composite is a material having a structure in which silicon and carbon are composited by depositing or embedding Si within a carbon matrix. Compared to silicon oxide (SiO), which was conventionally used as a Si-based negative electrode active material, it has lower irreversible capacity and superior conductivity. Therefore, when using a Si-C composite, higher energy density can be achieved compared to when using silicon oxide, and rapid charging performance can be further improved.

[0114] Preferably, the Si-C composite may have a Si grain size of 20 nm or less, preferably 1 nm to 20 nm, and more preferably 1 nm to 18 nm. When the grain size of the Si-C composite satisfies the above range, excellent improvement effects on cell resistance characteristics and lifespan characteristics are observed.

[0115] In addition, the above Si-C composite is D 50This can be 1㎛ to 15㎛, preferably 2㎛ to 10㎛, more preferably 3㎛ to 10㎛. In addition, the Si-C composite is D 10 This can be 5㎛ or less, preferably 1 to 5㎛, and D 90 This can be 6㎛ to 20㎛, preferably 6㎛ to 15㎛. When the particle size distribution of the Si-C composite satisfies the above range, the cathode electrode density is increased, and high energy density can be achieved.

[0116] Meanwhile, while using a Si-C composite as a negative electrode active material can improve capacity and rapid charging performance, there is a problem where lifespan characteristics deteriorate due to volume changes in the Si-C composite during charging and discharging. However, if a Si-C composite is used together with a graphite-based negative electrode active material, the volume change of the Si-C composite during charging and discharging is suppressed by the graphite-based negative electrode active material, thereby improving lifespan characteristics.

[0117] The graphite-based negative electrode active material comprises artificial graphite. Preferably, the graphite-based negative electrode active material may be a mixture of artificial graphite and natural graphite.

[0118] The above artificial graphite may be included in an amount of 40% to 60% by weight, preferably 45% to 55% by weight, and more preferably 47% to 53% by weight, based on the total weight of the graphite-based negative electrode active material. When the content of artificial graphite in the graphite-based negative electrode active material satisfies the above range, the rate characteristics and processability of the negative electrode are excellent, and the volume expansion of the Si-C composite during charging and discharging is suppressed, thereby further improving the lifespan characteristics.

[0119] When the graphite-based cathode active material is a mixture of artificial graphite and natural graphite, the weight ratio of artificial graphite to natural graphite may be 40:60 to 60:40, preferably 45:55 to 55:45, and more preferably 47:53 to 53:47. When the mixing ratio of artificial graphite and natural graphite satisfies the above range, the rate characteristics and processability of the cathode are exhibited to be even better, and the volume change of the Si-C composite during charging and discharging can be effectively suppressed.

[0120] Meanwhile, in the present invention, the Si-C composite and the graphite-based negative electrode active material may be included in a weight ratio of 5:95 to 20:80, preferably 5:95 to 15:85, and more preferably 5:95 to 10:90. When the mixing ratio of the Si-C composite and the graphite-based negative electrode active material satisfies the above range, both rapid charging performance and lifespan characteristics are excellent.

[0121] The total content of the total negative electrode active material, which is the sum of the graphite-based negative electrode active material and the Si-C composite, may be 80 to 99 weight%, preferably 85 to 99 weight%, and more preferably 90 to 99 weight% with respect to the total weight of the negative electrode composite layer.

[0122] Meanwhile, the above-mentioned cathode conductive material is used to impart conductivity to the cathode, and can be used without special restrictions as long as it is used as a conductive material for a lithium secondary battery. Specific examples of the above-mentioned cathode conductive material include carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube; metal 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. Preferably, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube, or a combination thereof may be used as the above-mentioned cathode conductive material, and it is more preferable to use point-type conductive materials and linear-type conductive materials together in terms of improving conductivity. At this time, the point-shaped conductive material is a material having a particle shape in which the contact form with the negative electrode active material is in the form of a point, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc., and the linear conductive material is a material in which the contact form with the negative electrode active material is in the form of a line, such as carbon fiber, carbon nanotube, etc.

[0123] The above cathode conductive material may typically be included in an amount of 1 to 30 weight%, preferably 1 to 20 weight%, and more preferably 1 to 10 weight% based on the total weight of the cathode composite layer.

[0124] Next, the above-mentioned negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector, and any material used as a negative electrode binder for a lithium secondary battery can be used without special restrictions. Specific examples of negative electrode binders 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.

[0125] The above cathode binder may be included in an amount of 1 to 30 weight%, preferably 1 to 20 weight%, more preferably 1 to 10 weight% based on the total weight of the cathode composite layer.

[0126] Meanwhile, the above-mentioned cathode composite layer may be formed as a single-layer structure or a multi-layer structure. When the cathode composite layer is a multi-layer structure composed of two or more layers, the types and / or contents of the cathode active material, cathode binder, and / or cathode conductive material in each layer may differ from one another. By forming the cathode active material layer as a multi-layer structure and varying the composition of each layer, the performance characteristics of the battery, such as rapid charging performance and output characteristics, can be appropriately controlled.

[0127] The above-mentioned cathode can be manufactured according to a conventional cathode manufacturing method. Specifically, the cathode according to the present invention may be manufactured by dissolving or dispersing a cathode active material, a cathode binder, a cathode conductive material, and / or a dispersant in a solvent to prepare a cathode slurry composition, then applying the cathode slurry onto a cathode current collector and then drying and rolling, or by casting the cathode slurry composition onto a separate support and then laminating a film obtained by peeling off from the support onto a cathode current collector.

[0128] As the above-mentioned negative current collector, negative current collectors generally used in the relevant technical field may be used, for example, copper, stainless steel, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm. If necessary, fine irregularities may be formed on the surface of the above-mentioned negative 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.

[0129] As the solvent for the above-mentioned cathode slurry, common solvents used in the art for manufacturing cathode slurries, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethyl formamide (DMF), acetone, water, or mixtures thereof may be used. The amount of the solvent used is sufficient if it is sufficient to dissolve or disperse the cathode active material, conductive material, binder, and dispersant, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when coated for cathode manufacturing thereafter.

[0130]

[0131] electrolytes

[0132] In the present invention, the electrolyte may include an organic solvent and a lithium salt.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] Examples of the above-mentioned cyclic carbonate compounds include vinylene carbonate (VC) or vinylethylene carbonate.

[0137] Examples of the above-mentioned halogen-substituted carbonate compounds include fluoroethylene carbonate (FEC).

[0138] 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.

[0139] Examples of the above sulfate compounds include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0140] 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.

[0141] Examples of the above borate compounds include tetraphenylborate, lithium oxalyl difluoroborate (LiODFB), and lithium bisoxalate toborate (LiB(C2O4)2, LiBOB).

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146]

[0147] Separator

[0148] 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.

[0149]

[0150] The lithium secondary battery according to the present invention as described above has excellent lifespan characteristics even during high-rate charging and discharging, with an energy retention rate of 90% or more, 92% or more, or 94% or more, measured after 100 cycles of charging and discharging under conditions of 1C charging and 0.33C discharging.

[0151]

[0152] A lithium secondary battery according to the present invention as described above can be used to manufacture a battery pack. The battery pack comprises an assembly of lithium secondary batteries according to the present invention electrically connected and a pack housing that accommodates the same, wherein the pack housing may include a busbar for electrically connecting the lithium secondary batteries, a cooling unit, an external terminal, etc. The battery pack may be mounted in a vehicle. The vehicle may be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle includes a four-wheeled vehicle or a two-wheeled vehicle. In particular, the lithium secondary battery according to the present invention has high energy density and excellent rapid charging performance, so it can be usefully used as a battery for an electric vehicle.

[0153]

[0154] The present invention will be explained in more detail below through specific embodiments. However, the following embodiments are intended only to aid in understanding the present invention, and the scope of the present invention is not limited to these embodiments.

[0155]

[0156] Example 1

[0157] <Anode Manufacturing>

[0158] A cathode slurry was prepared by adding cathode active material, cathode conductive material, and cathode binder to N-methylpyrrolidone in a weight ratio of 97:1.5:1.5. As the cathode active material, single-particle LiN with an average particle size of 5 μm was used. 0.9 Co 0.05 Mn 0.05 O2 and secondary particulate LiN with an average particle size of 13 µm 0.9 Co 0.05 Mn 0.05 O2 was mixed in a weight ratio of 10:90 and used, and Super P was used as the anode conductive material. In addition, PVdF was used as the anode binder.

[0159] The above anode slurry was applied onto an aluminum current collector, and then dried and rolled to manufacture an anode.

[0160]

[0161] Cathode Manufacturing

[0162] A cathode slurry was prepared by adding cathode active material : cathode conductive material : cathode binder to distilled water in a weight ratio of 97 : 0.5 : 2.5.

[0163] As the cathode active material of the cathode slurry, a Si-C composite and a graphite-based cathode active material were mixed in a weight ratio of 5:95 and, as the graphite-based cathode active material, artificial graphite and natural graphite were mixed in a weight ratio of 50:50. Single-walled CNTs were used as the cathode conductive material. In addition, as the cathode binder, styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 1.5:1.0.

[0164] After applying the above cathode slurry onto a copper current collector, the cathode was manufactured by drying, rolling, and vacuum drying.

[0165]

[0166] Electrolytes

[0167] An electrolyte was prepared by dissolving LiPF6 in a non-aqueous organic solvent mixed with ethylene carbonate and dimethyl carbonate in a volume ratio of 30:70 to a concentration of 1.5 M, and then adding 4% by weight of vinylene carbonate.

[0168]

[0169] Lithium secondary battery manufacturing

[0170] An electrode assembly was manufactured by interposing a separator between the anode and cathode manufactured as described above, laminating them, and then winding the resulting structure; the electrode assembly was then housed in a cylindrical battery case, and the electrolyte was injected to manufacture a lithium secondary battery.

[0171]

[0172] Example 2:

[0173] Single-particle LiN with an average particle size of 5㎛ is used as the cathode active material during cathode manufacturing 0.9 Co 0.05 Mn 0.05 O2 and secondary particulate LiN with an average particle size of 13 µm 0.9 Co 0.05 Mn 0.05 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that O2 was mixed and used in a weight ratio of 20:80.

[0174]

[0175] Example 3:

[0176] Single-particle LiN with an average particle size of 4㎛ is used as the cathode active material during cathode manufacturing 0.9 Co 0.05 Mn 0.05 O2 and secondary particulate LiN with an average particle size of 13 µm 0.9 Co 0.05 Mn 0.05 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that O2 was mixed and used in a weight ratio of 10:90.

[0177]

[0178] Comparative Example 1

[0179] Single-particle LiN with an average particle size of 5㎛ is used as the cathode active material during cathode manufacturing 0.9 Co 0.05 Mn 0.05 O2 and secondary particulate LiN with an average particle size of 13 µm 0.9 Co 0.05 Mn 0.05 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that O2 was mixed and used in a weight ratio of 60:40.

[0180]

[0181] Comparative Example 2

[0182] Single-particle LiN with an average particle size of 6.5㎛ is used as the cathode active material during cathode manufacturing0.9 Co 0.05 Mn 0.05 O2 and secondary particulate LiN with an average particle size of 13 µm 0.9 Co 0.05 Mn 0.05 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that O2 was mixed and used in a weight ratio of 10:90.

[0183]

[0184] Experimental Example 1: Measurement of Anode Properties

[0185] For the anodes prepared in the examples and comparative examples, the PC (propylene carbonate) impregnation time (A), sheet resistance (B), and flexibility (C) were measured in the following manner. The measurement results are shown in Table 1 below.

[0186] (1) PC impregnation time (unit: sec): After dropping 1 mL of propylene carbonate droplets onto the surface of the anode composite layer using a pipette, the time taken for the propylene carbonate droplets to disappear was measured.

[0187] (2) Anode sheet resistance (unit: Ω·cm): A sample was prepared by stamping an anode to a size of 5cm × 5cm, and a probe of a multi-probe resistor with 46 probes was inserted into the surface of the sample. A current of 10μA (I) was applied from the surface of the sample toward the current collector to measure the voltage (V), and then the resistance was measured by dividing the measured voltage (V) by the applied current (I).

[0188] (3) Curvature (C): An electrode assembly was manufactured by interposing a separator between two anodes, the electrode assembly was placed in a battery case, an electrolyte that does not contain lithium salt (ethylene carbonate : ethylmethyl carbonate = 3 : 7 v / v%) was injected, and the symmetric coin cell was manufactured by aging for 12 to 24 hours. Then, a current of 0.1 to 10000 Hz and 10 mV was applied to the manufactured symmetric coin cell, and the electrode pore resistance was measured using a graph measured by EIS (Electrochemical Impedance Spectroscopy) to calculate the average movement distance Le of lithium ions inside the anode composite layer, and the curvature was calculated by dividing this by the thickness L0 of the anode composite layer.

[0189]

[0190] PC Impregnation Time (A) Anode Sheet Resistance (B) Anode Curvature (C) X Example 1 190 4.198 0.5 22.4 110 Example 2 232 4.38 70.4 72.09 5 Example 3 198 4.01 10.4 92.56 97 Comparative Example 1 292 5.18 70.5 21.26 97 Comparative Example 2 213 6.49 90.4 31.68 00

[0191] Experimental Example 2:

[0192] The lithium secondary batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 2 were charged at 24°C at 0.33C in CCCV mode with a maximum charging voltage of 4.25V and a 0.05C cut-off condition, and then discharged to 2.5V in 0.33C in CC mode. The energy retention rate (%) was measured by repeating the charging and discharging cycles up to 100 cycles, with one cycle defined as discharging to 2.5V. The measurement results are shown in Figure 1.

[0193] In addition, the lithium secondary batteries prepared according to Examples 1 to 3 and Comparative Examples 1 to 2 were charged at 24°C at 1.0C in CCCV mode with a maximum charging voltage of 4.25V and a 0.05C cut-off condition, and then discharged to 2.5V in 0.33C in CC mode, with the charge-discharge cycle being repeated up to 100 cycles to measure the energy retention rate (%). The measurement results are shown in Figure 2.

[0194]

[0195] Through FIGS. 1 and 2, it can be seen that the lithium secondary batteries of Examples 1 to 3, which apply a positive electrode where X defined by Equation (1) is 2 or more, maintain a high energy retention rate during low and high rate charging and discharging, and in particular, the energy retention rate of Examples 1 to 3 is significantly superior to that of Examples 1 to 2 in comparison during high rate charging and discharging.

Claims

1. A positive electrode comprising a positive electrode composite layer comprising a positive electrode active material, a negative electrode comprising a negative electrode composite layer comprising a negative electrode active material, and an electrolyte, and A lithium secondary battery in which X, defined by the above equation (1), is 2 or more. Equation (1): X = 1000 / (A×B×C) In the above equation (1), A is the time in seconds (sec) measured until the propylene carbonate is completely impregnated into the anode when 1 mL of propylene carbonate is dropped onto the anode surface, B is the sheet resistance of the anode measured in Ω·cm, and C is the curvature of the anode.

2. In Paragraph 1, A lithium secondary battery in which, after free-falling 1 mL of propylene carbonate onto the anode surface, the time taken until the propylene carbonate is completely impregnated into the anode is 100 to 250 seconds.

3. In Paragraph 1, The above positive electrode is a lithium secondary battery having a sheet resistance of 3 Ω·cm to 5 Ω·cm.

4. In Paragraph 1, The above positive electrode is a lithium secondary battery having a curvature of 0.3 to 0.

8.

5. In Paragraph 1, A lithium secondary battery in which the above positive active material comprises a lithium nickel-based oxide represented by the following [Chemical Formula 1]. [Chemical Formula 1] Li x Ni a Co b M 1 c M 2 d O2 In the above [Chemical Formula 1], M 1 is one or more selected from Mn and Al, and M 2 is one or more selected from the group consisting of Zr, Y, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S, and 0.90≤x≤1.1, 0.50≤a<1.0, 0 <b<0.5, 0<c<0.5, 0≤d≤0.1임.

6. In Paragraph 1, A lithium secondary battery in which the above-mentioned positive active material comprises a single-particle type positive active material, a secondary-particle type positive active material, or a combination thereof.

7. In Paragraph 1, A lithium secondary battery in which the above positive active material comprises large particles having an average particle size of 8㎛ to 20㎛ and small particles having an average particle size of 3㎛ or more and less than 8㎛.

8. In Paragraph 7, A lithium secondary battery in which the above-mentioned opposite is a secondary particle-type positive active material and the above-mentioned elementary particle is a single particle-type positive active material.

9. In Paragraph 7, A lithium secondary battery in which the above alleles and subatomic particles are included in a weight ratio of 5:95 to 95:

5.

10. In Paragraph 1, A lithium secondary battery in which the above-mentioned negative electrode active material includes a silicon-based negative electrode active material and a graphite-based negative electrode active material.

11. In Paragraph 10, The above silicon-based negative electrode active material is a Si-C composite lithium secondary battery.

12. In Paragraph 10, A lithium secondary battery in which the above graphite-based negative electrode active material includes artificial graphite and natural graphite.

13. In Paragraph 10, A lithium secondary battery comprising the silicon-based composite and the graphite-based negative electrode active material in a weight ratio of 5:95 to 20:

80.

14. In Paragraph 1, A lithium secondary battery having an energy retention rate of 90% or more measured after 100 charge-discharge cycles under 1C charge and 0.33C discharge conditions.

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