Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery including an electrode assembly including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte. The positive electrode active material includes a first lithium nickel-based oxide in the form of at least one of a single particle consisting of one nodule and a quasi-single particle which is a complex of 30 or less nodules, in an amount of 50 wt % or more based on the total weight of the positive electrode active material. The negative electrode active material includes a Si / C composite and a carbon-based negative electrode active material.

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having excellent safety and electrochemical characteristics.

Background Art

[0002] Recently, lithium secondary batteries have been in the spotlight as an energy source for electric vehicles. As the spread of electric vehicles expands, the need for lithium secondary batteries that can travel a longer distance and shorten the rapid charging time during a single charge is increasing.

[0003] A lithium secondary battery is generally manufactured by forming an electrode assembly with a separator interposed between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including a negative electrode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte serving as a medium for transmitting lithium ions, and then sealing. The non-aqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt. Conventionally, carbon-based materials such as natural graphite and artificial graphite have been mainly used as the negative electrode active material of lithium secondary batteries. However, since such carbon-based negative electrode active materials have a small capacity and a slow reaction rate with lithium, there is a limit to achieving high capacity and rapid charging performance in secondary batteries applying them.

[0004] [[ID=1,9]] Therefore, the development of a lithium secondary battery applying a silicon-based material such as silicon oxide (SiO x , 0 < x < 2) mixed with a carbon-based negative electrode active material has been attempted. Since the silicon-based material has a higher theoretical capacity and a faster reaction rate with lithium than the carbon-based material, there is an advantage that the capacity characteristics and rapid charging performance can be improved when applying it. However, the silicon-based material has a very low electric conductivity, rapidly expands in volume during the charge / discharge process, and the particles are broken or the electrode is peeled off due to deterioration, resulting in a rapid decrease in the battery performance, which has become an obstacle to commercialization. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is intended to solve the above-mentioned problems, and provides a lithium secondary battery with excellent electrochemical performance by using a positive electrode active material containing 50% by weight or more of single particles / quasi-single particles and a negative electrode active material that is a mixture of an Si / C composite and a carbon-based negative electrode active material. [Means for solving the problem]

[0006] According to one embodiment, the present invention provides a lithium secondary battery including an electrode assembly including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte. The positive electrode active material includes a first lithium nickel-based oxide in the form of at least one of a single particle consisting of one nodule and a quasi-single particle, which is a composite of 30 or less nodules, in an amount of 50 wt % or more of the weight of the total positive electrode active material. The negative electrode active material includes a Si / C composite and a carbon-based negative electrode active material.

[0007] Meanwhile, the positive electrode active material may further include a second lithium nickel-based oxide in the form of secondary particles formed by agglomeration of 40 or more primary particles.

[0008] The first lithium nickel-based oxide and the second lithium nickel-based oxide may each be independently represented by the following [Chemical Formula 1]. [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O2 In the above Chemical Formula 1, M 1 is Mn, Al or a combination thereof, and M 2contains one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta and Nb, and 0≦x≦0.5, 0.8≦a<1, 0 <b<0.2、0<c<0.2、および0≦d≦0.05である。

[0009] The first lithium nickel-based oxide is D 50 is 3μm~10μm, D 90 is 10 μm or less, D 10 can be 4 μm or less.

[0010] The loading density of the positive electrode is 5.35 mAh / cm 2 or more, the porosity may be 22% to 25%, and the crack rate may be 30% or less.

[0011] Meanwhile, the negative electrode active material may be composed of a Si / C composite and a carbon-based negative electrode active material, and may contain, for example, the Si / C composite:carbon-based negative electrode active material in a weight ratio of 1:99 to 20:80.

[0012] The Si / C composite preferably has a grain size of 20 nm or less, and D 50 It is preferable that the thickness is about 1 μm to 10 μm.

[0013] The negative electrode has a loading density of 5.7 mAh / cm 2 or more, and the porosity may be 24% to 30%.

[0014] Meanwhile, the negative electrode may include a current collector, a first negative electrode active material layer formed on the current collector, and a second negative electrode active material layer formed on the first negative electrode active material layer, the first negative electrode active material layer and the second negative electrode active material layer containing a Si / C composite and a carbon-based negative electrode active material as negative electrode active materials, and the carbon-based negative electrode active materials contained in the first negative electrode active material layer and the second negative electrode active material layer may be different from each other. For example, the carbon-based negative electrode active material contained in the first negative electrode active material layer may be natural graphite, and the carbon-based negative electrode active material contained in the second negative electrode active material layer may be artificial graphite.

[0015] The electrode assembly may be a jelly-roll type electrode assembly, and the battery case may be a cylindrical battery having a cylindrical case, where the lithium secondary battery may have a form factor ratio of 0.4 or more. [Effects of the Invention]

[0016] The lithium secondary battery according to the present invention uses a mixture of an Si / C composite and a carbon-based negative electrode active material as the negative electrode active material, and thus has superior resistance characteristics and can achieve a higher capacity per unit volume compared to a battery using a mixture of an existing SiO and a carbon-based negative electrode active material.

[0017] In addition, the lithium secondary battery according to the present invention contains 50 wt % or more of monoparticles and / or quasi-monoparticles as a positive electrode active material, which can minimize gas generation due to particle cracking during electrode manufacturing and internal cracking during charge and discharge, thereby achieving excellent safety even in large-volume batteries.

[0018] Furthermore, when an Si / C composite is used as the silicon-based negative electrode active material and single particles and / or pseudo-single particles are contained in the positive electrode active material as in the present invention, the effect of improving the life characteristics can be obtained compared to when SiO or Si is used as the silicon-based negative electrode active material. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a diagram showing a stacked state of an electrode assembly according to the present invention before being wound up; [Figure 2] 1 is a cross-sectional view showing a structure of an electrode plate of an electrode assembly according to an embodiment of the present invention; [Figure 3] 1 is a cross-sectional view showing the structure of a lithium secondary battery according to an embodiment of the present invention. [Figure 4] FIG. 2 is a cross-sectional view showing the structure of a lithium secondary battery according to another embodiment of the present invention. [Figure 5]1 is a diagram illustrating the measurement results of the electrode layer resistance of each of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2. FIG. [Figure 6] 1 is a diagram showing the measurement results of the interface resistance of each of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2. FIG. [Figure 7] 1 is a diagram showing the measurement results of direct current resistance (DCIR) of the lithium secondary batteries manufactured in Examples 3 and 4 and Comparative Examples 5 and 6. FIG. [Figure 8] 1 is a diagram showing the measurement results of AC resistance (ACIR) of the lithium secondary batteries manufactured in Examples 3 and 4 and Comparative Examples 5 and 6. FIG. [Figure 9] 10 is a SEM photograph showing the state of cracks in the positive electrode active material particles after rolling the positive electrode produced in Example 4. [Figure 10] 10 is an SEM photograph showing the state of cracks in the positive electrode active material particles after the positive electrode produced in Comparative Example 3 was rolled. [Figure 11] 10 is an SEM photograph showing the state of cracks in the positive electrode active material particles after rolling the positive electrode produced in Comparative Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will now be described in further detail.

[0021] The 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 as having meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0022] In the present invention, a "single particle" refers to a particle consisting of one single nodule. In the present invention, a "quasi-single particle" refers to a particle that is a complex formed by an aggregation of 30 or fewer nodules.

[0023] In the present invention, the term "nodule" refers to a particle unit body constituting a single particle or a quasi-single particle, and the nodule may be a single crystal lacking a crystalline grain boundary, or a polycrystal that does not appear to have a grain boundary when observed at a magnification of 5,000 to 20,000 using a scanning electron microscope (SEM).

[0024] In the present invention, the term "secondary particles" refers to particles formed by agglomeration of several tens to several hundreds of primary particles. More specifically, secondary particles are agglomerations of 40 or more primary particles.

[0025] The term "particle" as used in the present invention may include any one or all of single particles, quasi-single particles, primary particles, nodules, and secondary particles.

[0026] In the present invention, "D n " means the particle size at the point where the volume cumulative amount is n% in the volume cumulative particle size distribution of the powder to be measured. That is, D 10 is the particle size at the point where the volume accumulation is 10%, D 50 is the particle size at the point where the cumulative volume is 50%, D 90 means the particle size at the point where the cumulative volume is 90%. n can be measured using a laser diffraction method. For example, a powder to be measured (e.g., a positive electrode active material powder or a Si / C composite powder) is dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., a Microtrac MT 3000), and irradiated with ultrasonic waves of about 28 kHz at an output of 60 W to obtain a volume cumulative particle size distribution graph. The particle size at that volume cumulative amount can then be measured using the volume cumulative particle size distribution graph.

[0027] In the present invention, the "specific surface area" is measured by the BET method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan.

[0028] In the present invention, "grain size" was measured by analyzing the XRD data obtained by X-ray diffraction analysis of the powder to be measured (i.e., Si / C composite powder) using Rietveld refinement. Here, the X-ray diffraction analysis was performed using a Bruker D8 Endeavor (light source: Cu-Kα, λ=1.54Å) equipped with a LynxEye XE-T-position sensitive detector. The sample was placed in the groove of a general powder holder, and a slide glass was used to even out the sample surface and fill the holder so that the sample height was aligned with the edge of the holder. The X-ray diffraction analysis was performed under the following conditions: FDS 0.5°, 2θ = 10° to 90°, step size = 0.016°, total scan time = approximately 1 / 20 min. Specifically, for grain size analysis, instrumental broadening was performed using the Fundamental Parameter Approach (FPA) implemented in the Bruker TOPAS program, and the entire peak range was used for fitting. Peak shape was fitted using only the Lorenzian contribution as the First Principle (FP) of the peak types available in TOPAS.

[0029] In the present invention, the "loading amount R (unit: g / 25 cm 2 ) was measured by measuring the weight W1 of the electrode punched to a size of 5 cm x 5 cm and the weight W2 of the electrode current collector, and then substituting these values ​​into the following [Equation 1].

[0030] [Equation 1] Electrode loading R (g / 25cm 2 )=(W1-W2) / 2

[0031] In the present invention, the term "loading density (unit: mAh / cm 2 ) is the total thickness of the electrode measured using a Tesa thickness measuring device. total After measuring the electrode current collector thickness Tc (unit: μm), the electrode loading R (unit: g / 25 cm 2 ) and the total thickness of the electrode T total and the thickness of the electrode current collector T c was substituted into the following formula 2 for calculation.

[0032] [Equation 2] Loading density (mAh / cm 2 ) = {(R / 25) × capacity per unit area of ​​active material} / {(T total -T c )×0.00005}

[0033] In the present invention, the "porosity (%)" is a value obtained by measuring the total thickness T' of an electrode after vacuum drying using a thickness measuring device manufactured by Tesa after the electrode is punched into a size of 5 cm x 5 cm and vacuum drying. total (unit: μm) and the thickness T' of the electrode current collector c (unit: μm) and measure the total thickness T' of the electrode after vacuum drying. total and the thickness T' of the electrode current collector c , electrode loading amount R (unit: g / 25 cm 2 ) and electrode density D (unit: g / cc) were substituted into the following [Equation 3] to measure.

[0034] [Formula 3] Porosity (%)=(DR / 25) / [D×{(T total -T c )×0.00005}]

[0035] The present invention will be described in more detail below.

[0036] As a result of extensive research into the development of a battery with high energy density and excellent safety and electrochemical properties, the inventors have discovered that a lithium secondary battery with high energy density and excellent resistance properties can be achieved by using a positive electrode active material containing 50% by weight or more of single particles and / or pseudo-single particles and a negative electrode active material that is a mixture of an Si / C composite and a carbon-based negative electrode active material, and have completed the present invention.

[0037] Specifically, the lithium secondary battery according to the present invention includes an electrode assembly including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte. The positive electrode active material includes a first lithium nickel-based oxide in the form of at least one of a single particle consisting of one nodule and a quasi-single particle, which is a complex of 30 or less nodules, in an amount of 50 wt % or more of the weight of the entire positive electrode active material. The negative electrode active material is a mixture of a Si / C composite and a carbon-based negative electrode active material.

[0038] Each component of the lithium secondary battery according to the present invention will be described in more detail below.

[0039] <Electrode assembly> The electrode assembly according to the present invention includes the above-described positive electrode, separator, and negative electrode. The shape of the electrode assembly is not particularly limited, and may be any of various electrode assemblies known in the art, such as a jelly roll type, a stack type, a stack and lamination type, or a stack and folding type electrode assembly.

[0040] Preferably, the electrode assembly may be a jelly roll type electrode assembly in which a sheet-shaped positive electrode, a sheet-shaped negative electrode, and a separator interposed between the positive electrode and the negative electrode are wound in one direction.

[0041] FIG. 1 illustrates the laminated structure of an electrode assembly according to one embodiment of the present invention before being wound, and FIG. 2 illustrates the cross-sectional structure of an electrode (positive electrode or negative electrode) according to one embodiment of the present invention.

[0042] Referring to FIGS. 1 and 2, the electrode assembly of the present invention may be manufactured by winding a laminate formed by sequentially stacking a separator 12, a positive electrode 10, a separator 12, and a negative electrode 11 at least once in one direction X.

[0043] Here, as shown in FIG. 2, the positive electrode 10 and the negative electrode 11 have a structure in which an active material layer 21 is formed on a sheet-shaped current collector 20, and may include a plain portion 22 in which the active material layer 21 is not formed in a part of the current collector 20.

[0044] When the positive electrode 10 and the negative electrode 11 include the uncoated portion 22 as described above, at least a portion of the uncoated portion of the positive electrode 10 and the negative electrode 11 can be used as an electrode tab instead of providing a separate electrode tab. For example, the uncoated portion 22 can be formed elongated along the winding direction X at one end of the current collector 20. By bonding current collecting plates to the positive and negative uncoated portions, respectively, and connecting the current collecting plates to electrode terminals, a battery in which the uncoated portions define the electrode tabs (for convenience, referred to as a tab-less battery) can be realized. Conventional can-type batteries have a structure in which portions of the positive and negative current collectors are cut to form narrow strip-shaped positive and negative tabs, which are then electrically connected to a cap plate and a battery cap. However, conventional can-type batteries with this structure have problems with current concentration in the strip-shaped electrode tabs, resulting in high resistance, excessive heat generation, and poor current collection efficiency. This phenomenon becomes particularly severe during fast charging, posing a risk of battery fire or explosion.In contrast, in the case of a tabless battery that uses the uncoated portions of the positive and negative electrode plates as electrode tabs, the area through which current passes increases and current concentration decreases, effectively reducing heat generation within the battery, thereby further improving the thermal stability of the battery.

[0045] Next, the positive electrode, negative electrode, and separator that constitute the electrode assembly of the present invention will be described in more detail.

[0046] <Positive electrode> The positive electrode may have a structure in which a positive electrode active material layer is formed on one or both sides of a sheet-shaped positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material and may optionally further include a conductive material and a binder.

[0047] For example, the positive electrode may be manufactured by dispersing a positive electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water to prepare a positive electrode slurry, applying the positive electrode slurry to one or both sides of a sheet-shaped positive electrode current collector, removing the solvent from the positive electrode slurry through a drying process, and then rolling the sheet. Meanwhile, a positive electrode including a non-coating portion may be manufactured by not applying the positive electrode slurry to a portion of the positive electrode current collector, for example, one end of the positive electrode current collector, during application of the positive electrode slurry.

[0048] The positive electrode current collector may be any of various positive electrode current collectors used in the art. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0049] In the present invention, the positive electrode active material includes a first lithium nickel-based oxide having a quasi-single particle form, which is a single particle consisting of one nodule and / or an aggregate of 30 or less nodules.

[0050] Conventional lithium nickel-based oxides generally have a spherical secondary particle form, consisting of an agglomeration of tens to hundreds of primary particles. However, lithium nickel-based oxides in this secondary particle form, consisting of an agglomeration of many primary particles, are prone to particle cracking, where primary particles break off during the rolling process during positive electrode production, and internal cracks occur during charge and discharge. When particles of the positive electrode active material crack or internal cracks occur, the contact area with the electrolyte increases, resulting in increased gas generation due to side reactions with the electrolyte. Increased gas generation within the battery increases the internal pressure of the battery, potentially leading to battery explosion. In particular, increasing the volume of the battery increases the amount of active material within the battery, which significantly increases the amount of gas generation, further increasing the risk of battery fire and / or explosion.

[0051] In contrast, lithium nickel-based oxides in the form of single particles consisting of one nodule and / or quasi-single particles consisting of an aggregate of 2 to 30 nodules have higher particle strength than existing lithium nickel-based oxides in the form of secondary particles, which are composed of tens to hundreds of primary particles agglomerated together. Because of this, particle cracking during rolling is virtually eliminated. Furthermore, lithium nickel-based oxides in the form of single particles and / or quasi-single particles have fewer nodules, which are the sub-particle units that make up the particles. This minimizes volumetric expansion and contraction during charge and discharge, significantly reducing the occurrence of internal cracking. Therefore, when lithium nickel-based oxides in the form of single particles and / or quasi-single particles are used as cathode active materials, gas generation and metal elution due to particle cracking and internal cracking can be significantly reduced, thereby achieving excellent safety even in large batteries.

[0052] Meanwhile, the first lithium nickel-based oxide may be contained in an amount of 50 wt % or more, preferably 50 wt % to 100 wt %, based on the total weight of the positive electrode active material. If the first lithium nickel-based oxide is contained in an amount less than 50 wt % of the total positive electrode active material, the effect of suppressing particle cracking during rolling is not sufficient, and therefore, sufficient effects of suppressing gas generation and transition metal elution cannot be obtained.

[0053] Meanwhile, the first lithium nickel-based oxide may have an average nodule particle size of 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less, for example, 0.5 μm to 5 μm, preferably 1 μm to 5 μm, and more preferably 2 μm to 5 μm. When the average nodule particle size satisfies this range, a single-particle and / or quasi-single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average nodule particle size is too small, the effect of suppressing particle cracking during rolling may be reduced. If the average nodule particle size is too large, the lithium diffusion path within the particle may be long, increasing resistance and reducing output characteristics.

[0054] On the other hand, in the present invention, the first lithium nickel-based oxide is D 50 The D of the first lithium nickel-based oxide can be 3 μm to 10 μm, preferably 3 μm to 8 μm. 50 If is too large, lithium mobility inside the positive electrode active material particles may decrease, adversely affecting capacity and output characteristics, and if is too small, the phase stability of the positive electrode slurry may decrease, resulting in poor coating processability.

[0055] The first lithium nickel-based oxide is D 90 The D of the first lithium nickel-based oxide can be 10 μm or less, preferably 5 μm to 10 μm. 90 If is too large, the capacity and output characteristics may be reduced.

[0056] The first lithium nickel-based oxide is D 10The D of the first lithium nickel-based oxide can be 4 μm or less, preferably 1 μm to 4 μm. 10 When the content of the polymer satisfies the above range, the thermal stability and electrochemical properties are more excellent.

[0057] Meanwhile, the positive electrode active material may optionally further include a second lithium-nickel-based oxide in the form of secondary particles formed by agglomeration of 40 or more primary particles in addition to the first lithium-nickel-based oxide in the form of single particles and / or quasi-single particles. When the positive electrode active material in the form of secondary particles is further included, the electrolyte impregnation property and rollability can be improved.

[0058] When a positive electrode active material in the form of secondary particles is further included, the positive electrode active material in the form of secondary particles may be included in an amount of 50 wt % or less, preferably 10 to 50 wt %, and more preferably 20 to 50 wt %, based on the total weight of the positive electrode active material included in the positive electrode active material layer. If the content of the positive electrode active material in the form of secondary particles is too high, gas generation may increase, and the effect of improving stability may be reduced.

[0059] On the other hand, in the present invention, the second lithium nickel-based oxide is D 50 The D of the second lithium nickel-based oxide can be 8 μm to 20 μm, preferably 10 μm to 20 μm. 50 When the above range is satisfied, the packing density of the positive electrode is increased, and the energy density can be further improved.

[0060] The second lithium nickel-based oxide is D 90 The D of the second lithium nickel-based oxide can be 25 μm or less, preferably 10 μm to 20 μm. 90 If the value is too large, a problem of reduced rollability may occur during electrode production.

[0061] The second lithium nickel-based oxide is D 10 The D of the second lithium nickel-based oxide can be 7 μm or less, preferably 2 μm to 6 μm. 10When the content of the polymer satisfies the above range, the thermal stability and electrochemical properties are more excellent.

[0062] Meanwhile, the first lithium nickel-based oxide and the second lithium nickel-based oxide may have the same or different compositions.

[0063] Specifically, the first lithium-nickel-based oxide and the second lithium-nickel-based oxide can each independently contain 80 mol% or more of Ni relative to the total moles of transition metals, for example, 80 mol% or more but less than 100 mol%, 83 mol% or more but less than 100 mol%, 85 mol% or more but less than 100 mol%, or 90 mol% to 98 mol% of Ni. As described above, when a lithium-nickel-based oxide with a high Ni content is used, a high capacity can be achieved.

[0064] More specifically, the first lithium nickel-based oxide and the second lithium nickel-based oxide may each independently have a composition represented by the following [Chemical Formula 1].

[0065] [Chemical formula 1] Li 1+x Ni a Co b M 1 c M 2 d O2

[0066] In the above Chemical Formula 1, M 1 can be Mn, Al or a combination thereof, preferably Mn or Mn and Al.

[0067] Said M 2 is at least one element selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta and Nb, preferably at least one element selected from the group consisting of Zr, Y, Mg and Ti, more preferably Zr, Y or a combination thereof. 2The element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0068] The 1 + x represents the lithium molar ratio in the lithium nickel-based oxide, and can be 0 ≦ x ≦ 0.5, 0 ≦ x ≦ 0.3, or 0 ≦ x ≦ 0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0069] The a represents the molar ratio of nickel among all the metals other than lithium in the lithium nickel-based oxide, and can be 0.8 ≦ a < 1, 0.83 ≦ a < 1, 0.85 ≦ a < 1 or 0.90 ≦ a ≦ 0.98. When the molar ratio of nickel satisfies the above range, it shows a high energy density and high capacity can be realized.

[0070] The b represents the molar ratio of cobalt among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < b < 0.2, 0 < b < 0.17, 0.01 ≦ b ≦ 0.15, or 0.01 ≦ b ≦ 0.10. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0071] The c represents the molar ratio of the M 1 element among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 < c < 0.2, 0 < c < 0.17, 0.01 ≦ c ≦ 0.15 or 0.01 ≦ c ≦ 0.10. When the molar ratio of the M 1 element satisfies the above range, the structure stability of the positive electrode active material is excellent.

[0072] The d represents the molar ratio of the M 2 element among all the metals other than lithium in the lithium nickel-based oxide, and can be 0 ≦ d ≦ 0.05, 0 ≦ d ≦ 0.03, or 0 ≦ d ≦ 0.02.

[0073] Meanwhile, the first lithium-nickel-based oxide and the second lithium-nickel-based oxide may, if necessary, further include a coating layer on the particle surface, the coating layer containing one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. Preferably, the coating element is Al, B, Co, or a combination thereof. When a coating layer is present on the surface of the lithium-nickel-based oxide particles, the coating layer inhibits contact between the electrolyte and the lithium composite transition metal oxide, thereby reducing the elution of the transition metal and the generation of gas due to side reactions with the electrolyte.

[0074] The positive electrode active material can be contained in an amount of 80 to 99% by weight, preferably 85 to 99% by weight, and more preferably 90 to 99% by weight, based on the total weight of the positive electrode active material layer.

[0075] Meanwhile, the positive electrode may further include a conductive material and / or a binder in addition to the positive electrode active material.

[0076] The conductive material is used to improve the conductivity of the electrode, and can be any material that does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials can be used alone or in combination.

[0077] Preferably, the conductive material may include carbon nanotubes. Specifically, the conductive material may include single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture thereof, with single-walled carbon nanotubes being particularly preferred. Single-walled carbon nanotubes are longer and have wider coverage than other conductive materials. Therefore, when single-walled carbon nanotubes are used as the conductive material, the amount of conductive material used can be reduced and the content of the positive electrode active material can be increased, which is effective in improving capacity.

[0078] The conductive material may be contained in an amount of 2 wt % or less, 0.01 wt % to 2 wt %, or 0.01 wt % to 1 wt % based on the total weight of the positive electrode active material layer.

[0079] The binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the positive electrode active material layer.

[0080] On the other hand, the positive electrode has a loading density of 5.35 mAh / cm 2 More than 5.35mAh / cm 2 ~6.0mAh / cm2 , more preferably 5.35 mAh / cm 2 ~5.80cm 2 When the positive electrode loading density satisfies the above range, a high energy density can be achieved, and a capacity balance can be achieved with a high-capacity negative electrode containing a Si / C composite.

[0081] The positive electrode may have a porosity of 22% to 25%, preferably 22.5% to 25%, and more preferably 22.8% to 24.2%. When the positive electrode porosity satisfies the above range, the capacity and output characteristics are excellent.

[0082] The positive electrode may have a crack rate of 30% or less, preferably 1 to 30%, and more preferably 1 to 20%. When the crack rate of the positive electrode satisfies the above range, gas generation and metal elution can be effectively suppressed.

[0083] <Negative electrode> The negative electrode may have a structure in which a negative electrode active material layer is formed on one or both sides of a sheet-shaped negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder.

[0084] Specifically, the negative electrode may be manufactured by coating one or both surfaces of a sheet-shaped negative electrode current collector with a negative electrode slurry prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and then drying the coated negative electrode current collector to remove the solvent. Meanwhile, a negative electrode plate including a non-coated portion may be manufactured by not coating a portion of the negative electrode current collector, for example, one end of the negative electrode current collector, with the negative electrode slurry during coating.

[0085] In the present invention, the negative electrode active material includes a Si / C composite and a carbon-based negative electrode active material.

[0086] To increase the capacity of secondary batteries, active research and development has been conducted on lithium secondary batteries that use silicon-based anode active materials with high theoretical capacity. In particular, many technologies have been developed using silicon oxide as a silicon-based anode active material. However, silicon oxide has a high irreversible capacity and a low initial efficiency of 85% or less, limiting the increase in capacity. On the other hand, the Si / C composite is a composite material of carbon and silicon, and has higher capacity and initial efficiency than SiOx. Therefore, the present invention utilizes an excellent Si / C composite with a theoretical discharge capacity of 1600 mAh / g or more, a higher discharge capacity than silicon oxide, and an initial efficiency of 85% or more, thereby achieving a lithium secondary battery with superior energy density compared to conventional batteries.

[0087] Furthermore, according to the research of the present inventors, when a Si / C composite is used as in the present invention, electrode and cell resistances are lower than when silicon oxide is used, and excellent output characteristics can be achieved. Lithium secondary batteries using single-particle / quasi-single-particle positive electrode active materials have the advantage of excellent safety and life characteristics, but have the problem of high resistance and reduced output characteristics. However, when a Si / C composite is used as the negative electrode active material as in the present invention, electrode and cell resistances are lower, and excellent output characteristics can be achieved.

[0088] The Si / C composite may have a 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 improvements in cell resistance characteristics and life characteristics are achieved.

[0089] In addition, the Si / C composite is D 50 The Si / C composite may have a diameter of 1 μm to 15 μm, preferably 2 μm to 10 μm, and more preferably 3 μm to 10 μm. 10 can be 5 μm or less, preferably 1 to 5 μm, and D 90When the particle size distribution of the Si / C composite satisfies the above range, the negative electrode density becomes high and a high energy density can be achieved.

[0090] Meanwhile, the carbon-based negative electrode active material may be, for example, artificial graphite, natural graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, etc., and preferably, artificial graphite, natural graphite, or a combination thereof.

[0091] On the other hand, the negative electrode active material of the present invention preferably does not contain any silicon-based negative electrode active material (e.g., silicon oxide, silicon) other than the Si / C composite. If a silicon-based negative electrode active material other than the Si / C composite is contained, the capacity improvement effect may be minimal and the life characteristics may be reduced. More preferably, the negative electrode active material of the present invention may consist of an Si / C composite and a carbon-based negative electrode active material.

[0092] In the present invention, the negative electrode active material may contain a Si / C composite and a carbon-based negative electrode active material in a weight ratio of 1:99 to 20:80, preferably 1:99 to 15:85, and more preferably 4:96 to 10:90. When the mixing ratio of the Si / C composite and the carbon-based negative electrode active material satisfies the above range, both the capacity characteristic and the life characteristic are excellent.

[0093] The negative electrode active material may be contained in an amount of 80 to 99 wt %, preferably 85 to 99 wt %, and more preferably 90 to 99 wt %, based on the total weight of the negative electrode active material layer.

[0094] Meanwhile, the negative electrode current collector may be a negative electrode current collector commonly used in the art, such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or aluminum-cadmium alloy. The negative electrode current collector typically has a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, the surface of the current collector may be formed with fine irregularities to enhance the binding strength of the negative electrode active material. The negative electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0095] The conductive material is used to impart conductivity to the negative electrode. Any conductive material can be used without particular limitations, as long as it does not cause chemical changes in the battery and has electronic conductivity. 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, and carbon nanotubes; metal powder or fiber, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. These materials can be used alone or in combination. The conductive material is typically present in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0096] The binder functions to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination. The binder may be included in an amount of 1 to 30 wt %, preferably 1 to 20 wt %, and more preferably 1 to 10 wt %, based on the total weight of the negative electrode active material layer.

[0097] Meanwhile, the negative electrode may have a single-layer or multi-layer structure in which the negative electrode active material layer is composed of two or more layers. For example, the negative electrode may include a first negative electrode active material layer formed on a negative electrode current collector and a second negative electrode active material layer formed on the first negative electrode active material layer.

[0098] When the negative electrode active material layer has a multi-layer structure composed of two or more layers, the layers may differ from one another in the type of negative electrode active material, the type and / or content of binder and / or conductive material.

[0099] For example, the first negative electrode active material layer (lower layer) and the second negative electrode active material layer (upper layer) may contain a Si / C composite and a carbon-based negative electrode active material as negative electrode active materials, and the types of carbon-based negative electrode active materials contained in the first negative electrode active material layer and the second negative electrode active material layer may be different. Specifically, the carbon-based negative electrode active material contained in the first negative electrode active material layer may be natural graphite, and the carbon-based negative electrode active material contained in the second negative electrode active material layer may be artificial graphite. When natural graphite is used as the carbon-based negative electrode active material in the lower layer, the adhesion to the current collector may be improved, and when artificial graphite is used as the carbon-based negative electrode active material in the upper layer, the reaction rate with lithium may be increased, resulting in improved output characteristics.

[0100] Alternatively, the first negative electrode active material layer (lower layer) may be formed to have a higher carbon-based negative electrode active material content than the second negative electrode active material layer (upper layer), and the second negative electrode active material layer may be formed to have a higher Si / C composite content than the first negative electrode active material layer, or the second negative electrode active material layer (lower layer) may be formed to have a higher conductive material content than the first negative electrode active material layer (upper layer). In this way, by forming the negative electrode active material layer in a multilayer structure and differentiating the compositions of each layer, the performance characteristics of the battery can be improved. For example, by forming the upper layer to have a higher conductive material or Si / C composite content than the lower layer, the effect of improving rapid charging performance can be obtained.

[0101] On the other hand, the negative electrode has a loading density of 5.70 mAh / cm 2 More than 5.70mAh / cm 2 ~6.50mAh / cm 2 , more preferably 5.70 mAh / cm 2 ~6.20 mAh / cm 2 When the negative electrode loading density satisfies the above range, a high energy density can be achieved, and a capacity balance (N / P ratio) with the positive electrode can be achieved.

[0102] The negative electrode may have a porosity of 24% to 30%, preferably 24% to 28%, and more preferably 24.8% to 26.2%. When the negative electrode porosity satisfies this range, the capacity and output characteristics are excellent.

[0103] <Separator> The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. Specifically, the separator may be a porous polymer film, such as 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, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may also be used.

[0104] <Electrolytes> The electrolyte used in the present invention is not particularly limited to any particular type, and may be any of various electrolytes that can be used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes.

[0105] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0106] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0107] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO), LiCl, LiI, and LiB(C, O) . The lithium salt concentration is preferably within a range of 0.1 to 5.0 M, and more preferably 0.1 to 3.0 M. When the lithium salt concentration is within this range, the electrolyte exhibits appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0108] Meanwhile, in addition to the above components, the electrolyte may further include additives for the purposes of improving the life characteristics of the battery, suppressing a decrease in the battery capacity, improving the discharge capacity of the battery, etc. For example, the electrolyte may include at least one additive selected from the group consisting of a cyclic carbonate-based compound, a halogen-substituted carbonate-based compound, a sultone-based compound, a sulfate-based compound, a phosphate-based compound, a borate-based compound, a nitrile-based compound, a benzene-based compound, an amine-based compound, a silane-based compound, and a lithium salt-based compound.

[0109] Examples of the cyclic carbonate compound include vinylene carbonate (VC) or vinylethylene carbonate.

[0110] An example of the halogen-substituted carbonate compound is fluoroethylene carbonate (FEC).

[0111] Examples of the sultone-based compound include at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0112] Examples of the sulfate-based compound include ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0113] Examples of the phosphate-based compound include one or more compounds selected from the group consisting of lithium difluoro(bisoxalate)phosphate, lithium difluorophosphate, tetramethyltrimethylsilylphosphate, trimethylsilylphosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0114] Examples of the borate-based compounds include tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), and lithium bisoxalateborate (LiB(C2O4)2, LiBOB).

[0115] Examples of the nitrile compound include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0116] An example of the benzene-based compound is fluorobenzene, an example of the amine-based compound is triethanolamine or ethylenediamine, and an example of the silane-based compound is tetravinylsilane.

[0117] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and examples thereof include lithium difluorophosphate (LiDFP), LiPO2F2, and LiBF4.

[0118] The additive may be contained in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the electrolyte.

[0119] <Lithium secondary battery> Next, the lithium secondary battery according to the present invention will be described.

[0120] The lithium secondary battery according to the present invention includes an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, an electrolyte, and a battery case containing the electrode assembly and the electrolyte. The components of the electrode assembly and the electrolyte are as described above, and detailed description thereof will be omitted.

[0121] Meanwhile, the battery case may be a prismatic case, a cylindrical case, a pouch-type case, or the like commonly used in the art, and preferably a cylindrical case. Specifically, the battery case may be a can-type battery case including a battery can in which the electrode assembly and the electrolyte are housed, and a sealing body that seals the open end of the battery can.

[0122] Preferably, the lithium secondary battery according to the present invention is a cylindrical battery including a cylindrical battery case, and more preferably a large cylindrical battery having a form factor ratio (defined as the ratio of the diameter (Φ) to the height (H) of a cylindrical battery divided by the diameter of the cylindrical battery) of 0.4 or more. Here, the form factor refers to values ​​indicating the diameter and height of a cylindrical battery.

[0123] Cylindrical batteries according to the present invention can be, for example, a 46110 cell (diameter 46 mm, height 110 mm, form factor ratio 0.418), a 4875 cell (diameter 48 mm, height 75 mm, form factor ratio 0.640), a 48110 cell (diameter 48 mm, height 110 mm, form factor ratio 0.436), a 4880 cell (diameter 48 mm, height 80 mm, form factor ratio 0.600), or a 4680 cell (diameter 46 mm, height 80 mm, form factor ratio 0.575). In the form factor number, the first two digits indicate the cell diameter, and the next two or three digits indicate the cell height.

[0124] Since the lithium secondary battery according to the present invention includes a positive electrode active material in the form of a single particle and / or a quasi-single particle, it generates less gas than conventional batteries and can achieve excellent thermal stability even when the form factor ratio is 0.4 or more.

[0125] Figures 3 and 4 illustrate an embodiment of a lithium secondary battery according to the present invention. Hereinafter, the lithium secondary battery according to the present invention will be described with reference to Figures 3 and 4. However, Figures 3 and 4 illustrate one embodiment of the present invention, and the structure of the battery according to the present invention is not limited to the scope disclosed in Figures 3 or 4.

[0126] First, referring to FIG. 3, a battery 140 according to one embodiment of the present invention includes a jelly-roll type electrode assembly 141, a battery can 142 in which the electrode assembly 141 and an electrolyte are housed, and a seal 143 that seals the open end of the battery can 142.

[0127] The battery can 142 is a container with an opening at the top and is made of a conductive metal material such as aluminum or steel. The battery can accommodates the electrode assembly 141 in the inner space through the opening at the top, along with the electrolyte.

[0128] The battery can 142 is electrically connected to the uncoated portion 146b of the negative electrode plate and functions as a negative electrode terminal that contacts an external power source and transfers current applied from the external power source to the negative electrode plate.

[0129] If necessary, a beading portion 147 and a crimping portion 148 may be provided on the upper end of the battery can 142. The beading portion 147 may be formed by pressing the outer circumferential surface of the battery can 142 to a distance D1. The beading portion 147 prevents the electrode assembly 141 housed inside the battery can 142 from being removed through the upper opening of the battery can 142, and may function as a support on which the sealing body 143 is placed.

[0130] The crimping portion 148 may be formed on the beading portion 147, and has an extended and bent shape to enclose the outer circumferential surface of the cap plate 143a disposed on the beading portion 147 and a part of the upper surface of the cap plate 143a.

[0131] Next, the sealing body 143 is for sealing the open end of the battery can 142, and includes a cap plate 143a, a first gasket 143b having insulating properties and providing airtightness between the cap plate 143a and the battery can 142, and may further include a connection plate 143c electrically and mechanically coupled to the cap plate 143a, if necessary. The cap plate 143a may be crimped onto a beading portion 147 formed on the battery can 142 and fixed by a crimping portion 148.

[0132] The cap plate 143a is a component made of a conductive metal material and covers the upper opening of the battery can 142. The cap plate 143a is electrically connected to the positive electrode plate of the electrode assembly 141 and is electrically insulated from the battery can 142 via a first gasket 143b. Therefore, the cap plate 143a can function as a positive electrode terminal of the secondary battery. The cap plate 143a may have a protrusion 143d that protrudes upward from the winding center C, and the protrusion 143d may come into contact with an external power source so that current can be applied from the external power source.

[0133] A first gasket 143b may be interposed between the cap plate 143a and the crimping portion 148 to ensure airtightness of the battery can 142 and to electrically insulate the battery can 142 from the cap plate 143a.

[0134] Meanwhile, the battery 140 according to the present invention may further include current collecting plates 144 and 145, if necessary. The current collecting plates are bonded to the uncoated portion 146a of the positive electrode plate and the uncoated portion 146b of the negative electrode plate, and are connected to the electrode terminals (i.e., the positive electrode terminal and the negative electrode terminal).

[0135] Specifically, the battery 140 according to the present invention may include a first current collecting plate 144 coupled to the upper part of the electrode assembly 141 and a second current collecting plate 145 coupled to the lower part of the electrode assembly 141 .

[0136] A first current collecting plate 144 and / or a second current collecting plate 145 may further be included.

[0137] The first current collecting plate 144 is coupled to the upper part of the electrode assembly 141. The first current collecting plate 144 is made of a conductive metal material such as aluminum, copper, or nickel, and is electrically connected to the uncoated portion 146a of the positive electrode plate. A lead 149 may be coupled to the first current collecting plate 144. The lead 149 may extend upwardly of the electrode assembly 141 and be coupled to the connecting plate 143c, or may be directly coupled to the lower surface of the cap plate 143a. The lead 149 may be coupled to other components by welding. Preferably, the first current collecting plate 144 may be integrally formed with the lead 149. In this case, the lead 149 may have a long plate shape extending outward from the center of the first current collecting plate 144.

[0138] Meanwhile, the first current collecting plate 144 is coupled to the end of the uncoated portion 146a of the positive electrode plate, and the coupling may be performed by, for example, laser welding, resistance welding, ultrasonic welding, soldering, or the like.

[0139] The second current collecting plate 145 is coupled to the lower part of the electrode assembly 141. The second current collecting plate 145 is made of a conductive metal material such as aluminum, copper, or nickel, and is electrically connected to the uncoated portion 146b of the negative electrode plate. One side of the second current collecting plate 145 may be coupled to the uncoated portion 146b of the negative electrode plate, and the opposite side may be coupled to the inner bottom surface of the battery can 142. Here, the coupling may be performed by a method such as laser welding, resistance welding, ultrasonic welding, or soldering.

[0140] Meanwhile, the battery 140 according to the present invention may further include an insulator 146, if necessary. The insulator 146 may be disposed to cover the upper surface of the first current collecting plate 144. By covering the first current collecting plate 144 with the insulator 146, direct contact between the first current collecting plate 144 and the inner peripheral surface of the battery can 142 can be prevented.

[0141] The insulator 146 has lead holes 151 through which the leads 149 extending upward from the first current collecting plate 144 are drawn out. The leads 149 are drawn out upward through the lead holes 151 and coupled to the lower surface of the connecting plate 143c or the lower surface of the cap plate 143a.

[0142] The insulator 146 may be made of insulating polymer resin, such as polyethylene, polypropylene, polyimide, or polybutylene terephthalate.

[0143] Meanwhile, the battery 140 according to the present invention may further include a vent 152 formed on the bottom surface of the battery can 142, if necessary. The vent 152 corresponds to a region of the bottom surface of the battery can 142 that is thinner than the surrounding region. Because the vent 152 is thinner, it is structurally more fragile than the surrounding region. Therefore, when the pressure inside the battery 140 increases above a predetermined level, the vent 152 ruptures, releasing gas inside the battery can 142 to the outside and preventing the battery from exploding.

[0144] Next, with reference to FIG. 4, a lithium secondary battery according to another embodiment of the present invention will be described.

[0145] Referring to FIG. 4, a battery 170 according to another embodiment of the present invention has a different structure of the battery can and the sealed body compared to the battery 140 shown in FIG. 3, but the configuration of the electrode assembly and electrolyte is substantially the same.

[0146] Specifically, the battery 170 includes a battery can 171 through which a rivet terminal 172 is installed. The rivet terminal 172 is installed on a partially closed surface (top surface in the drawing) at one end of the battery can 171. The rivet terminal 172 is riveted into a through-hole (first opening at a first end) of the battery can 171 with an insulating second gasket 173 interposed therebetween. The rivet terminal 172 is exposed to the outside in the direction opposite to the direction of gravity.

[0147] The rivet terminal 172 includes a terminal exposure portion 172a and a terminal insertion portion 172b. The terminal exposure portion 172a is exposed to the outside of the closed surface of the battery can 171. The terminal exposure portion 172a may be located approximately at the center of the partially closed surface of the battery can 171. The maximum diameter of the terminal exposure portion 172a may be larger than the maximum diameter of the through hole formed in the battery can 171. The terminal insertion portion 172b may penetrate approximately the center of the partially closed surface of the battery can 171 and be electrically connected to the uncoated portion 146a of the positive electrode plate. The terminal insertion portion 172b may be rivet-connected to the inner surface of the battery can 171. That is, an end of the terminal insertion portion 172b may be curved toward the inner surface of the battery can 171. The maximum diameter of the end of the terminal insertion portion 172b may be larger than the maximum diameter of the through hole of the battery can 171.

[0148] The lower end surface of the terminal insertion portion 172b may be welded to the first current collecting plate 144 connected to the uncoated portion 146a of the positive electrode plate. An insulating cap 174 made of an insulating material may be interposed between the first current collecting plate 144 and the inner surface of the battery can 171. The insulating cap 174 covers the upper portion of the first current collecting plate 144 and the upper edge of the electrode assembly 141. This prevents the uncoated portion B3 on the outer periphery of the electrode assembly 141 from coming into contact with the inner surface of the battery can 171 having the opposite polarity, causing a short circuit. The terminal insertion portion 172b of the rivet terminal 172 may penetrate the insulating cap 174 and be welded to the first current collecting plate 144.

[0149] The second gasket 173 is interposed between the battery can 171 and the rivet terminal 172 to prevent electrical contact between the battery can 171 and the rivet terminal 172, which have opposite polarities. As a result, the upper surface of the battery can 171, which has a substantially flat shape, can function as the positive terminal of the battery 170.

[0150] The second gasket 173 includes a gasket exposing portion 173a and a gasket inserting portion 173b. The gasket exposing portion 173a is interposed between the terminal exposing portion 172a of the rivet terminal 172 and the battery can 171. The gasket inserting portion 173b is interposed between the terminal inserting portion 172b of the rivet terminal 172 and the battery can 171. The gasket inserting portion 173b is deformed when the terminal inserting portion 172b is riveted, and can be tightly attached to the inner surface of the battery can 171. The second gasket 173 may be made of, for example, an insulating polymer resin.

[0151] The gasket exposing portion 173a of the second gasket 173 may extend to cover the outer circumferential surface of the terminal exposing portion 172a of the rivet terminal 172. When the second gasket 173 covers the outer circumferential surface of the rivet terminal 172, it is possible to prevent a short circuit from occurring during the process of connecting an electrical connecting component, such as a bus bar, to the upper surface of the battery can 171 and / or the rivet terminal 172. Although not shown in the drawings, the gasket exposing portion 173a may extend to cover not only the outer circumferential surface of the terminal exposing portion 172a but also a portion of the upper surface.

[0152] When the second gasket 173 is made of a polymer resin, the second gasket 173 can be joined to the battery can 171 and the rivet terminal 172 by heat sealing. In this case, it is possible to strengthen the airtightness at the joining interface between the second gasket 173 and the rivet terminal 172 and at the joining interface between the second gasket 173 and the battery can 171. Meanwhile, when the gasket exposed portion 173a of the second gasket 173 has a shape that extends to the upper surface of the terminal exposed portion 172a, the rivet terminal 172 can be joined integrally with the second gasket 173 by insert injection.

[0153] The remaining area 175 of the top surface of the battery can 171 other than the area occupied by the rivet terminal 172 and the second gasket 173 corresponds to a negative terminal having a polarity opposite to that of the rivet terminal 172 .

[0154] The second current collecting plate 176 is coupled to the lower part of the electrode assembly 141. The second current collecting plate 176 is made of a conductive metal material such as aluminum, steel, copper, or nickel, and is electrically connected to the uncoated portion 146b of the negative electrode plate.

[0155] Preferably, the second current collecting plate 176 is electrically connected to the battery can 171. To this end, the second current collecting plate 176 may be fixed with at least a portion of its edge interposed between the inner surface of the battery can 171 and the first gasket 178b. As an example, at least a portion of the edge of the second current collecting plate 176 may be supported by a lower end surface of a beading portion 180 formed at the lower end of the battery can 171 and fixed to the beading portion 180 by welding. In a modified example, at least a portion of the edge of the second current collecting plate 176 may be directly welded to the inner wall surface of the battery can 171.

[0156] The second current collecting plate 176 may have a plurality of projections and recesses formed radially on the surface facing the non-coating portion 146b. When the projections and recesses are formed, the second current collecting plate 176 may be pressed to press the projections and recesses into the non-coating portion 146b.

[0157] Preferably, the end of the second current collecting plate 176 and the uncoated portion 146b can be joined by welding, for example, laser welding.

[0158] The sealing body 178 that seals the lower open end of the battery can 171 includes a cap plate 178a and a first gasket 178b. The first gasket 178b electrically isolates the cap plate 178a from the battery can 171. A crimping portion 181 secures the edge of the cap plate 178a and the first gasket 178b together. The cap plate 178a is provided with a vent portion 179. The configuration of the vent portion 179 is substantially the same as in the above-described embodiment.

[0159] Preferably, the cap plate 178a is made of a conductive metal material. However, the cap plate 178a does not have electrical polarity because a first gasket 178b is interposed between the cap plate 178a and the battery can 171. The seal 178 seals the open end of the lower part of the battery can 171 and functions to discharge gas when the internal pressure of the battery cell 170 exceeds a critical value.

[0160] Preferably, the rivet terminal 172 electrically connected to the uncoated portion 146a of the positive electrode plate is used as the positive electrode terminal. Furthermore, the portion 175 of the upper surface of the battery can 171, other than the rivet terminal 172, electrically connected to the uncoated portion 146b of the negative electrode plate via the second current collecting plate 176 is used as the negative electrode terminal. When two electrode terminals are located on the upper portion of the battery, electrical connection components such as bus bars can be disposed on only one side of the battery 170. This can simplify the battery pack structure and improve energy density. Furthermore, the portion 175 used as the negative electrode terminal has a substantially flat shape, ensuring a sufficient bonding area when bonding electrical connection components such as bus bars. This allows the battery 170 to reduce resistance at the bonding points of the electrical connection components to a desirable level.

[0161] The lithium secondary battery of the present invention as described above can be used to manufacture a battery pack. The battery pack includes an assembly of electrically connected lithium secondary batteries according to the present invention and a pack housing that accommodates the assembly, and the pack housing can include a bus bar for electrically connecting the lithium secondary batteries, a cooling unit, external terminals, etc. The battery pack can be installed in a vehicle. The vehicle can be, for example, an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle can be a four-wheeled vehicle or a two-wheeled vehicle.

[0162] The present invention will now be described in more detail with reference to specific examples.

[0163] [Example 1] <Production of positive electrodes> The positive electrode active material, porous carbon, carbon nanotubes, and PVDF binder were mixed in a weight ratio of 97.09:0.6:0.02 in N-methylpyrrolidone to prepare a positive electrode slurry. Here, the positive electrode active material was a mixture of single particles and pseudo-single particles of boron (B)-coated Li[Ni 0.93 Co 0.05 Mn 0.016 Al 0.004 ]O2 was used.

[0164] The positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to prepare a positive electrode. Here, the loading density of the positive electrode was 650 mg / 25 cm. 2 (5.40mAh / cm 2 ), the positive electrode porosity was 23.5%, and the positive electrode thickness was 163 μm.

[0165] <Production of negative electrodes> A first negative electrode slurry was prepared by mixing the first negative electrode active material, conductive material, binder, and carboxymethyl cellulose (CMC) in water at a weight ratio of 98.04:0.06:1:0.9. Here, the first negative electrode active material was a mixture of natural graphite and Si / C composite at a weight ratio of 85:15, and the conductive material was single-walled CNT, and the binder was styrene-butadiene rubber (SBR).

[0166] Next, a second negative electrode slurry was prepared by mixing the second negative electrode active material, conductive material, binder, and CMC in a weight ratio of 98.04:0.06:1:0.9 in water. Here, the second negative electrode active material was a mixture of artificial graphite and Si / C composite in a weight ratio of 85:15, and the conductive material was single-walled CNT and the binder was SBR.

[0167] The first and second negative electrode slurries were applied in sequence to the surface of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. The loading density of the negative electrode was 283 mg / 25 cm. 2 (5.94mAh / cm 2), the negative electrode porosity was 25.1%, and the negative electrode thickness was 143 μm.

[0168] <Manufacturing lithium secondary batteries> The cathode and anode were stacked in the order of separator / cathode / separator / anode with a separator interposed between them to prepare a wound electrode assembly. The electrode assembly was inserted into a cylindrical battery can, and an electrolyte was injected and sealed to prepare a 4680 cell.

[0169] [Example 2] A positive electrode, a negative electrode, and a lithium secondary battery were fabricated in the same manner as in Example 1, except that a first negative electrode active material was a mixture of natural graphite and Si / C composites in a weight ratio of 91.5:8.5, and a second negative electrode active material was a mixture of artificial graphite and Si / C composites in a weight ratio of 91.5:8.5.

[0170] [Example 3] A positive electrode, a negative electrode, and a lithium secondary battery were fabricated in the same manner as in Example 1, except that a first negative electrode active material was a mixture of natural graphite and Si / C composites in a weight ratio of 88.5:11.5, and a second negative electrode active material was a mixture of artificial graphite and Si / C composites in a weight ratio of 88.5:11.5.

[0171] [Example 4] As a positive electrode active material, boron (B)-coated Li[Ni 0.93 Co 0.05 Mn 0.016 Al 0.004 ]O2 and secondary particle form boron (B) coated Li[Ni 0.89 Co 0.066 Mn 0.043 Al 0.001 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 3, except that a mixture of 1,000 sulphite and 1,000 sulphite was used in a weight ratio of 50:50.

[0172] [Comparative Example 1] The positive electrode active material, porous carbon, carbon nanotubes, and PVDF binder were mixed in a weight ratio of 96.45:0.6:0.02 in N-methylpyrrolidone to prepare a positive electrode slurry. Here, the positive electrode active material was a mixture of single particles and pseudo-single particles of boron (B)-coated Li[Ni 0.93 Co 0.05 Mn 0.016 Al 0.004 ]O2 was used.

[0173] The positive electrode slurry was applied to one side of an aluminum current collector, dried at 130°C, and then rolled to prepare a positive electrode. The loading density of the positive electrode was 640 mg / 25 cm. 2 (5.29mAh / cm 2 ), the positive electrode porosity was 23.0%, and the positive electrode thickness was 162 μm.

[0174] <Production of negative electrodes> A first negative electrode slurry was prepared by mixing the first negative electrode active material, conductive material, binder, and CMC in a weight ratio of 98.04:0.06:1:0.9 in water. Here, the first negative electrode active material was a mixture of natural graphite and SiO in a weight ratio of 85:15, and the conductive material was single-walled CNT, and the binder was styrene-butadiene rubber (SBR).

[0175] Next, a second negative electrode slurry was prepared by mixing the second negative electrode active material, conductive material, binder, and CMC in a weight ratio of 98.04:0.06:1:0.9 in water. Here, the second negative electrode active material was a mixture of artificial graphite and SiO in a weight ratio of 85:15, and single-walled CNTs were used as the conductive material and styrene-butadiene rubber (SBR) as the binder.

[0176] The first and second negative electrode slurries were applied in sequence to the surface of a copper current collector sheet, dried at 150°C, and then rolled to prepare a negative electrode. The loading density of the negative electrode was 356 mg / 25 cm. 2 (5.69mAh / cm 2 ), the negative electrode porosity was 25.0%, and the negative electrode thickness was 179 μm.

[0177] <Manufacturing lithium secondary batteries> The cathode and anode were stacked in the order of separator / cathode / separator / anode with a separator interposed between them to prepare a wound electrode assembly. The electrode assembly was inserted into a cylindrical battery can, and an electrolyte was injected and sealed to prepare a 4680 cell.

[0178] Comparative Example 2 Positive electrode active material: porous carbon: carbon nanotubes: PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 97.12:0.6:0.02 to prepare a positive electrode slurry, and the loading density of the positive electrode was 632 mg / 25 cm. 2 (5.33mAh / cm 2 ), the positive electrode was manufactured so that the positive electrode porosity was 23.7%, the positive electrode thickness was 160 μm, and the negative electrode loading density was 396 mg / 25 cm 2 (5.94mAh / cm 2 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Comparative Example 1, except that the negative electrode was manufactured so that the porosity of the negative electrode was 25.0% and the thickness of the negative electrode was 189 μm.

[0179] Comparative Example 3 Positive electrode active material: Porous carbon: Carbon nanotubes: PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 97.09:0.4:0.02 to prepare a positive electrode slurry. The positive electrode active material was boron (B)-coated Li[Ni] in the form of secondary particles. 0.89 Co 0.066 Mn 0.043 Al 0.001 A positive electrode, a negative electrode, and a lithium secondary battery were produced in the same manner as in Example 3, except that ]O2 was used.

[0180] Comparative Example 4 The positive electrode active material is a mixture of single particles and pseudo-single particles, and is a boron (B)-coated Li[Ni 0.93 Co 0.05 Mn 0.016 Al 0.004]O2 and secondary particle form boron (B) coated Li[Ni 0.89 Co 0.066 Mn 0.043 Al 0.001 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 3, except that a mixture of 1,024,036,048,052, and 1,024,052 was used in a weight ratio of 30:70.

[0181] Comparative Example 5 A positive electrode, a negative electrode, and a lithium secondary battery were fabricated in the same manner as in Example 1, except that the first negative electrode active material was a mixture of natural graphite and SiO in a weight ratio of 88.5:11.5, and the second negative electrode active material was a mixture of artificial graphite and SiO in a weight ratio of 88.5:11.5.

[0182] Comparative Example 6 A positive electrode, a negative electrode, and a lithium secondary battery were fabricated in the same manner as in Example 1, except that a natural graphite:SiO:Si / C composite mixed in a weight ratio of 88.5:9.2:2:3 was used as the first negative electrode active material, and an artificial graphite:SiO:Si / C composite mixed in a weight ratio of 88.5:9.2:2:3 was used as the second negative electrode active material.

[0183] [Experimental Example 1 - Evaluation of negative electrode resistance] The electrode layer resistance of the negative electrode, the interface resistance between the negative electrode current collector and the negative electrode active material layer, and the overall sheet resistance of each of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 and 2 were measured using an MP resistor.

[0184] The measurement results are shown in Table 1 below and Figures 5 and 6. Figure 5 is a graph showing the electrode layer resistance of the lithium secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 and 2, and Figure 6 is a graph showing the interface resistance of the lithium secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 and 2.

[0185] [Table 1]

[0186] Referring to Table 1 and FIGS. 5 and 6, it can be seen that the lithium secondary batteries of Examples 1 to 3, which used a mixture of Si / C composite and graphite as the negative electrode active material, have lower resistance characteristics than the lithium secondary batteries of Comparative Examples 1 and 2, which used a mixture of SiO and graphite as the negative electrode active material.

[0187] [Experimental Example 2] The direct current resistance (DC-IR) and alternating current resistance (AC-IR) were measured for the lithium secondary batteries manufactured in Examples 3 and 4 and Comparative Examples 5 and 6. The measurement results are shown in FIGS.

[0188] 7 and 8, it can be seen that the resistance characteristics of the lithium secondary batteries of Examples 3 and 4, in which a mixture of Si / C composite and graphite was used as the negative electrode active material, were lower than those of Comparative Example 5, in which a mixture of SiO and graphite was used as the negative electrode active material, and Comparative Example 6, in which a mixture of SiO, Si / C composite and graphite was used as the negative electrode active material.

[0189] [Experimental Example 3] The porosity (%), rolling ratio (%), and crack ratio (%) of the positive electrodes prepared in Examples 3 and 4 and Comparative Examples 3 and 4 were measured and are shown in Table 2. Here, the crack ratio (%) was calculated by measuring a cross-sectional SEM image of the positive electrode and then calculating the ratio of the area occupied by cracked particles to the total area of ​​the SEM image.

[0190] 9 to 11 are SEM photographs showing the state of the positive electrodes produced in Example 4, Comparative Example 3, and Comparative Example 4 after rolling.

[0191] [Table 2]

[0192] Referring to Table 2 and FIGS. 9 to 11, it can be seen that when the weight ratio of single particles to the total positive electrode active material is 50% or more (Examples 3 and 4), the particle crack rate is significantly reduced.

[0193] [Experimental Example 4 - Amount of gas generated] The lithium secondary batteries manufactured in Examples 3 and 4 and Comparative Example 4 were stored at 72° C. for 3 days, and then the amount of gas generated was measured using gas chromatography. The measurement results are shown in Table 3 below.

[0194] [Table 3]

[0195] Referring to Table 3, it can be seen that the amount of gas generated decreases as the content of single particles / quasi-single particles in the positive electrode active material increases.

[0196] [Experimental Example 5 - Metal elution amount] The lithium secondary batteries prepared in Examples 3 and 4 and Comparative Example 4 were activated by charging at 0.2 C at 72°C to 4.2 V, discharging at 0.2 C to 2.5 V, and then storing at 80°C for 1 day. Immediately after activation and after storage at 80°C, the lithium secondary batteries were disassembled to collect the negative electrodes, and the amount of metal elution attached to the surface of the negative electrodes was measured using an ICP-OES (Avio 550MAX, Perkinelme) device. The measurement results are shown in Table 4 below.

[0197] [Table 4]

[0198] As shown in Table 4, in the case of Examples 3 and 4, in which the content of single particles in the positive electrode active material is 50 wt % or more, the increase in the amount of metal elution after high-temperature storage compared to after activation is at the level of 100% to 105%, whereas in the case of Comparative Example 4, in which the content of single particles in the positive electrode active material is 30 wt %, the increase in the amount of metal elution after high-temperature storage compared to after activation is 358%, indicating a much higher increase in the amount of metal elution compared to Examples 3 and 4.

[0199] [Experimental Example 6 - Lifespan Evaluation] The lithium secondary batteries prepared in Example 3, Comparative Example 5, and Comparative Example 6 were repeatedly charged to 4.25 V at 0.2 C and then discharged to 2.5 V at 0.2 C, counting as one cycle, and the capacity retention rate (%) and resistance increase rate (%) were measured after 100 cycles, 200 cycles, and 300 cycles. The measurement results are shown in Table 5 below.

[0200] [Table 5]

[0201] Referring to Table 5, it can be seen that the lithium secondary battery of Example 3 has superior life characteristics compared to the lithium secondary batteries of Comparative Examples 5 and 6.

Claims

1. A lithium secondary battery comprising: an electrode assembly including a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte, The positive electrode active material includes a first lithium nickel-based oxide in the form of at least one of a single particle consisting of one nodule and a quasi-single particle which is an aggregate of 30 or less nodules, in an amount of 50 wt % or more based on the total weight of the positive electrode active material, The negative electrode active material of the lithium secondary battery is made of a Si / C composite and a carbon-based negative electrode active material.

2. The lithium secondary battery of claim 1 , wherein the positive electrode active material further comprises a second lithium nickel-based oxide in the form of secondary particles formed by agglomeration of 40 or more primary particles.

3. 3. The lithium secondary battery according to claim 1, wherein the first lithium nickel-based oxide and the second lithium nickel-based oxide are each independently represented by the following Chemical Formula 1: [Chemical formula 1] Li １＋ｘ Ni ａ Co ｂ M １ ｃ M ２ ｄ O ２ In the above formula 1, M １ is Mn, Al or a combination thereof, and M ２ includes one or more elements selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, and 0≦x≦0.5, 0.8≦a<1, 0<b<0.2, 0<c<0.2, and 0≦d≦0.

05.

4. The first lithium nickel-based oxide is D ５０ 2. The lithium secondary battery according to claim 1, wherein the average particle size is 3 μm to 10 μm.

5. The first lithium nickel-based oxide is D ９０ is 10 μm or less, and D １０ 2. The lithium secondary battery according to claim 1, wherein the thickness is 4 μm or less.

6. The loading density of the positive electrode is 5.35 mAh / cm ２ The lithium secondary battery according to claim 1 .

7. 2. The lithium secondary battery according to claim 1, wherein the positive electrode has a porosity of 22% to 25%.

8. 2. The lithium secondary battery according to claim 1, wherein the positive electrode has a crack rate of 30% or less.

9. 2. The lithium secondary battery according to claim 1, wherein the negative electrode active material comprises a Si / C composite:carbon-based negative electrode active material in a weight ratio of 1:99 to 20:

80.

10. The lithium secondary battery according to claim 1 , wherein the Si / C composite has a grain size of 20 nm or less.

11. The Si / C composite is D ５０ 2. The lithium secondary battery according to claim 1, wherein the average particle diameter is 1 μm to 10 μm.

12. The negative electrode has a loading density of 5.7 mAh / cm ２ The lithium secondary battery according to claim 1 .

13. 2. The lithium secondary battery according to claim 1, wherein the negative electrode has a porosity of 24% to 30%.

14. the negative electrode includes a current collector, a first negative electrode active material layer formed on the current collector, and a second negative electrode active material layer formed on the first negative electrode active material layer; 2. The lithium secondary battery of claim 1, wherein the first and second negative electrode active material layers contain a Si / C composite and a carbon-based negative electrode active material as negative electrode active materials, and the carbon-based negative electrode active materials contained in the first and second negative electrode active material layers are different from each other.

15. the carbon-based negative electrode active material contained in the first negative electrode active material layer is natural graphite, The lithium secondary battery of claim 14 , wherein the carbon-based negative electrode active material contained in the second negative electrode active material layer is artificial graphite.

16. The lithium secondary battery of claim 1 , wherein the electrode assembly is a jelly-roll type electrode assembly.

17. 2. The lithium secondary battery according to claim 1, wherein the battery case is a cylindrical case.

18. 18. The lithium secondary battery according to claim 17, wherein the lithium secondary battery has a form factor ratio of 0.4 or greater.

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