Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: an electrode assembly comprising a positive electrode comprising a positive electrode active material, a negative electrode comprising a negative electrode active material, and a separator disposed 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 contains a first lithium nickel-based oxide having at least 50 wt% of a single particle type comprising one nodule and / or a single particle-like type that is an aggregate of 30 or less nodules based on the total weight of the positive electrode active material. And the negative electrode active material consists of a Si / C compound and a carbon 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 properties. Background Art

[0002] Recently, lithium secondary batteries have become a hot topic as an energy source for electric vehicles. With the popularization of the supply of electric vehicles, the demand for lithium secondary batteries that can provide a longer driving distance per charge and a reduced fast charging time is increasing.

[0003] Lithium secondary batteries are generally manufactured by a method including the following steps: forming an electrode assembly by disposing a separator between a positive electrode including a positive electrode active material composed of a lithium-containing transition metal oxide and a negative electrode including a negative electrode active material capable of storing lithium ions, disposing the electrode assembly in a battery case, injecting a non-aqueous electrolyte serving as a lithium ion transfer medium, and sealing. The non-aqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt. Generally, as the negative electrode active material of a lithium secondary battery, carbon-based materials such as natural graphite and artificial graphite are widely used. However, since the carbon-based negative electrode active material has a small capacity and a slow reaction rate with lithium, secondary batteries using the carbon-based negative electrode active material have limitations in achieving high capacity and fast charging performance.

[0004] Therefore, attempts are being made to develop lithium secondary batteries using silicon-based materials such as silicon oxide (SiOx, 0 < x < 2) having a relatively large theoretical capacity mixed with a carbon-based negative electrode active material. Compared with carbon-based materials, silicon-based materials have a high theoretical capacity and a fast reaction rate with lithium, and if silicon-based materials are applied, there are advantages of improving capacity performance and fast charging performance. However, since the conductivity of silicon-based materials is very low, their volume rapidly expands during the charge / discharge process, and due to deterioration, particle breakage or electrode detachment occurs, and the battery performance rapidly decreases, which becomes an obstacle to commercialization. Summary of the Invention

[0005] [Technical Problem]

[0006] The present invention aims to solve the above-mentioned defects, and provides a lithium secondary battery having excellent electrochemical performance by including 50 wt% or more of single particles / single-particle-like particles as a positive electrode active material and using a mixture of a SiC composite and a carbon-based negative electrode active material as a negative electrode active material.

[0007] [Technical Solution]

[0008] According to one embodiment, the present invention provides a lithium secondary battery comprising: an electrode assembly including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte, wherein the positive electrode active material contains a first lithium nickel-based oxide having at least one of a single particle type composed of one nodule and a pseudo-single particle type which is an aggregate of 30 or less nodules based on the total weight of the positive electrode active material, and the negative electrode active material is composed of a Si / C composite and a carbon-based negative electrode active material.

[0009] Meanwhile, the positive electrode active material may further contain a second lithium nickel-based oxide having a secondary particle type which is an aggregate of 40 or more primary particles.

[0010] The first lithium nickel-based oxide and the second lithium nickel-based oxide may each independently be represented by the following [Formula 1].

[0011] [Formula 1]

[0012] Li 1+x Ni a Co b M 1 c M 2 d O2

[0013] In Formula 1, M 1 is Mn, Al, or a combination thereof, M 2 includes one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, 0 ≤ x ≤ 0.5, 0.8 ≤ a < 1, 0 < b < 0.2, 0 < c < 0.2, and 0 ≤ d ≤ 0.05.

[0014] The D 50 of the first lithium nickel-based oxide may be 3 μm to 10 μm, the D 90 may be 10 μm or less, and the D 10 may be 4 μm or less.

[0015] The loading density of the positive electrode may be 5.35 mAh / cm 2 or more, the porosity may be 22% to 25%, and the cracking rate may be 30% or less.

[0016] Meanwhile, the negative electrode active material may be composed of a Si / C composite and a carbon-based negative electrode active material, and for example, may contain the Si / C composite and the carbon-based negative electrode active material in a weight ratio of 1:99 to 20:80.

[0017] The grain size of the Si / C composite may preferably be less than 20 nm, and D 50 It may preferably be 1 μm to 10 μm.

[0018] The load density of the negative electrode can be 5.7 mAh / cm 2 Above, and the porosity can be 24% to 30%.

[0019] 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, wherein the first negative electrode active material layer and the second negative electrode active material layer include Si / C composite and 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 are 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.

[0020] The electrode assembly may be a jelly roll type electrode assembly, and the battery case may be a cylindrical case. In this case, the shape factor ratio of the lithium secondary battery may be 0.4 or more.

[0021] [Beneficial Effects]

[0022] The lithium secondary battery of the present invention uses a mixture of Si / C composite and carbon-based negative electrode active material as a negative electrode active material and can achieve excellent resistance characteristics and higher unit volume capacity compared to the conventional case of using a mixture of SiO and carbon-based negative electrode active material.

[0023] In addition, the lithium secondary battery of the present invention contains more than 50 weight % of single particles and / or quasi-single particles as positive electrode active materials, and can minimize gas generation due to particle crushing during electrode formation and internal cracking during charging and discharging, and can achieve excellent safety in large-sized batteries with increased volume.

[0024] In addition, as described in the present invention, if a Si / C composite is used as a silicon-based negative electrode active material and single particles and / or quasi-single particles are included in the positive electrode active material, the effect of improving the life characteristics can be obtained compared to the case of using SiO or Si as the silicon-based negative electrode active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a diagram showing a stacked state of the electrode assembly of the present invention before winding.

[0026] Figure 2 is a cross-sectional view showing the structure of an electrode plate of the electrode assembly of the present invention.

[0027] Figure 3 This is a cross-sectional view showing the structure of a lithium secondary battery according to one embodiment of the present invention.

[0028] Figure 4 This is a cross-sectional view showing the structure of a lithium secondary battery according to another embodiment of the present invention.

[0029] Figure 5 : is a graph showing the measurement results of the electrode layer resistance of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 2.

[0030] Figure 6 : is a graph showing the measurement results of the interface resistance of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 2.

[0031] Figure 7 : is a graph showing the measurement results of direct current resistance (DCIR) of lithium secondary batteries manufactured in Examples 3 and 4 and Comparative Examples 5 and 6.

[0032] Figure 8 : is a graph showing the measurement results of the alternating current resistance (ACIR) of the lithium secondary batteries manufactured in Examples 3 and 4 and Comparative Examples 5 and 6.

[0033] Fig. 9 is a SEM photographic image showing a crushed state of positive electrode active material particles after the positive electrode manufactured in Example 4 was roll-pressed.

[0034] Fig.10 is a SEM photographic image showing a crushed state of positive electrode active material particles after the positive electrode manufactured in Comparative Example 3 was roll-pressed.

[0035] Fig.11 is a SEM photographic image showing a crushed state of positive electrode active material particles after the positive electrode manufactured in Comparative Example 4 was roll-pressed. DETAILED DESCRIPTION

[0036] Hereinafter, the present invention will be explained in more detail.

[0037] The words or terms used in this specification should not be interpreted as the meanings defined in commonly used dictionaries. Based on the principle that the inventor can appropriately define the meanings of words or terms to best explain the present invention, the words or terms should be interpreted as having a meaning consistent with the technical idea of ​​the present invention.

[0038] In the present invention, a "single particle" is a particle consisting of a single segment. In the present invention, a "quasi-single particle" refers to a composite particle formed by agglomerating 30 or less segments.

[0039] In the present invention, "grain node" refers to the particle unit body that constitutes single particles and quasi-single particles, and if observed using a scanning electron microscope (SEM) at a field of view of 5000 to 20000 times, the grain node can be a single crystal without crystal grain boundaries, or a polycrystal without obvious grain boundaries.

[0040] In the present invention, "secondary particles" refer to particles formed by agglomerating a plurality of primary particles numbering tens to hundreds. More specifically, the secondary particles are agglomerates of 40 or more primary particles.

[0041] The expression "particle" used in the present invention may include any one or all of a single particle, a quasi-single particle, a primary particle, a particle segment, and a secondary particle.

[0042] In the present invention, “D n " refers to the particle size at the point where the volume cumulative amount is n% on the volume cumulative particle size distribution of the target powder to be measured. That is, D 10 Refers to the particle size at the point where the volume accumulation is 10%, D 50 Refers to the particle size at the point where the volume accumulation is 50%, D 90 It refers to the particle size at the point where the volume accumulation is 90%. D can be measured by using the laser diffraction method. n For example, D can be measured by dispersing the target powder to be measured (e.g., positive electrode active material powder or Si / C composite powder) in a dispersion medium, introducing the dispersion into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and using the volume cumulative particle size distribution graph to obtain the particle size at the corresponding volume accumulation. n .

[0043] In the present invention, the "specific surface area" is measured by the BET method, and can be specifically calculated from the nitrogen absorption amount at liquid nitrogen temperature (77K) using BELSORP-minoII of BEL Japan Co.

[0044] In the present invention, the "grain size" is measured by analyzing the XRD data obtained by X-ray diffraction of the target powder to be measured (i.e., Si / C composite powder) by the Rietveld refinement method. In this case, the X-ray diffraction analysis is performed as follows: using a LynxEye XE-T position sensitive detector (light source: Cu-Kα, ) was used, the sample was placed in the groove of a holder for ordinary powders, a glass slide was used to make the surface of the sample uniform, the sample was loaded so that the height of the sample was equal to the edge of the holder, and relative to FDS0.5° and 2θ=10°-90° range, the step length was =0.016, the total scan time was =about 1 / 20 minutes. In particular, during the particle size analysis, instrument broadening realized by the fundamental parameter method (FPA) through the Bruker TOPAS program was used, and all peaks in the measurement range in the fitting process were used. Among the peak types used in TOPAS, only the Lorentz contribution was used as the first principle (FP) for peak shape fitting.

[0045] In the present invention, "loading amount (R, unit: g / 25cm 2 )" is obtained by measuring the weight W1 of the electrode punched into a size of 5 cm×5 cm and the weight W2 of the electrode current collector and substituting them into the following [Equation 1].

[0046] [Equation 1] Electrode loading (g / 25cm 2 )=(W1-W2) / 2

[0047] In the present invention, “load density (unit: mAh / cm 2 )" The total thickness T of the electrode was measured by using a thickness measuring device from Tesa Co., total (Unit: μm) and the thickness of the electrode current collector T c (unit: μm), and the electrode loading R (unit: g / 25cm 2 ), the total thickness of the electrode T total and the thickness of the electrode current collector T c Substituting into the following [Equation 2] yields:

[0048] [Equation 2] Loading density (mAh / cm 2 ) = [(R / 25) × capacity of active material per unit area] / {(T total -T c )×0.00005}

[0049] In the present invention, the “porosity (%)” is determined by vacuum drying an electrode punched into a size of 5 cm×5 cm and measuring the total thickness T′ of the electrode after vacuum drying. total The total thickness of the electrode T'c (unit: μm) and the thickness of the electrode current collector T'c (unit: μm) were measured using a thickness measuring device from Tesa Co., total , the thickness of the electrode current collector T'c (unit: μm), the electrode loading R (unit: g / 25cm 2) and electrode density D (unit: g / cc) are substituted into the following [Equation 3] to obtain.

[0050] [Equation 3] Porosity (%) = (DR / 25) / [D×{(T total -T c )×0.00005}]

[0051] Hereinafter, the present invention will be explained in more detail.

[0052] The inventors of the present invention have conducted repeated research to develop a battery with high energy density as well as excellent safety and electrochemical properties. As a result, they found that a lithium secondary battery with high energy density and excellent resistance properties can be achieved by containing more than 50 weight % of single particles and / or quasi-single particles as positive electrode active materials and by using a mixture of Si / C composites and carbon-based negative electrode active materials as negative electrode active materials, and completed the present invention.

[0053] In particular, the lithium secondary battery of the present invention comprises: an electrode assembly, which includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a separator arranged between the positive electrode and the negative electrode; an electrolyte; and a battery shell for accommodating the electrode assembly and the electrolyte, wherein the positive electrode active material comprises a first lithium nickel-based oxide, which has at least one of a single particle type consisting of one particle segment and a quasi-single particle type that is an agglomerate of 30 or less particle segments, which accounts for 50 weight % or more of the total weight of the positive electrode active material, and the negative electrode active material is a mixture of a Si / C composite and a carbon-based negative electrode active material.

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

[0055] Electrode assembly

[0056] The electrode assembly of the present invention includes a positive electrode, a separator and a negative electrode. The shape of the electrode assembly is not particularly limited, and may be various electrode assemblies, for example, a jelly roll type, a stack type, a stack-laminated type, or a stack-folded type electrode assembly.

[0057] Preferably, the electrode assembly may be a jelly-roll type electrode assembly in which a sheet-type positive electrode, a sheet-type negative electrode, and a separator disposed between the positive electrode and the negative electrode are wound in one direction.

[0058] Figure 1 FIG. 2 shows a stacked structure of an electrode assembly before winding according to an embodiment of the present invention. Figure 2 The cross-sectional structure of an electrode (positive electrode or negative electrode) according to one embodiment of the present invention is shown.

[0059] Reference Figure 1 and Figure 2The electrode assembly of the present invention can be manufactured by sequentially stacking the separator 12, the positive electrode 10, the separator 12, and the negative electrode 11 at least once and winding the stack in one direction (X).

[0060] In this case, if Figure 2 As shown, the positive electrode 10 and the negative electrode 11 may have a structure in which the active material layer 21 is formed on the sheet-shaped current collector 20 , and may include a non-coating portion 22 in which the active material layer 21 is not formed on a partial region of the current collector 20 .

[0061] If the positive electrode 10 and the negative electrode 11 include a non-coating portion 22, at least a portion of the non-coating portion of the positive electrode 10 or the negative electrode 11 can be used as an electrode tab without providing a separate electrode tab. For example, the non-coating portion 22 can be formed longer along the winding direction (X) at the end of one side of the current collector 20, and by joining the current collector plate with the positive electrode non-coating portion and the negative electrode non-coating portion, and connecting the current collector plate to the electrode terminal, a battery (for convenience, referred to as a non-tab battery) in which the electrode non-coating portion defines the electrode tab can be realized. Conventional can-type batteries have the following structure: a portion of the positive electrode collector and the negative electrode collector is cut and processed to form a positive electrode tab and a negative electrode tab in a strip shape with a narrow width, and the positive electrode tab and the negative electrode tab are electrically connected to the cover plate and the battery cover. However, in the case of a conventional can-type battery having this structure, there is the following problem: the current is concentrated on the strip electrode tab, resulting in high resistance, large heat generation and poor current collection efficiency. In particular, during fast charging, the phenomenon worsens, and there is a risk of fire or explosion of the battery. On the contrary, in the case of a tab-free battery using the non-coated portions of the positive and negative plates as tabs as described above, the area through which current passes increases and the current concentration decreases, thereby effectively reducing heat generation in the battery, thereby achieving the effect of further improving the thermal safety of the battery.

[0062] Then, the positive electrode, the negative electrode, and the separator constituting the electrode assembly of the present invention will be explained in more detail.

[0063] positive electrode

[0064] The positive electrode may have a structure in which a positive electrode active material layer is formed on one side or both sides of a sheet-shaped positive electrode collector, and the positive electrode active material layer may include a positive electrode active material and selectively further include a conductive material and a binder.

[0065] For example, the positive electrode can be manufactured by dispersing a positive electrode active material, a conductive material and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone and water to prepare a positive electrode slurry, coating the positive electrode slurry on one side or both sides of a sheet-shaped positive electrode collector, removing the solvent of the positive electrode slurry through a drying process, and rolling. Meanwhile, the positive electrode including the non-coating portion can be manufactured by not coating the positive electrode slurry on a partial area of ​​the positive electrode collector (e.g., one end of the positive electrode collector) during the coating of the positive electrode slurry.

[0066] As the positive electrode current collector, various positive electrode current collectors used in the art can be used. For example, as the positive electrode current collector, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The thickness of the positive electrode current collector can generally be 3 μm to 500 μm, and fine concavo-convex objects can be formed on the surface of the positive electrode current collector to improve the adhesion strength of the positive electrode active material. The positive electrode current collector can be used in various types, such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0067] In the present invention, the positive electrode active material may include the first lithium nickel based oxide having a single particle type formed of one segment and / or a single particle-like type which is an aggregate of segments.

[0068] Conventional lithium nickel oxides are usually in the form of spherical secondary particles formed by the agglomeration of tens to hundreds of primary particles. However, in the case of lithium nickel oxides of secondary particle type formed by the agglomeration of multiple primary particles, there are the following problems: particle crushing is likely to occur during the rolling process for manufacturing the positive electrode, thereby separating the primary particles, and cracking occurs in the particles during charging and discharging. If the positive electrode active material undergoes particle crushing or cracking in the particles, the contact area with the electrolyte may increase, and there is a problem of increased gas production due to side reactions with the electrolyte. If the gas production in the battery increases, the internal pressure of the battery increases, and there is a risk of causing the battery to explode. In particular, if the volume of the battery increases, the amount of active material in the battery increases with the increase in volume, and as a result, the gas production increases significantly, and the risk of battery fire and / or explosion may further increase.

[0069] In contrast, compared to conventional lithium nickel oxides of secondary particle type formed by agglomeration of tens to hundreds of primary particles, lithium nickel oxides of single particle type consisting of one segment and / or single particle-like aggregates of 2-30 segments have higher particle strength, and particle breakage rarely occurs during rolling. In addition, in the case of single particle and / or single particle-like lithium nickel oxides, the number of segments as low-order particle units constituting the particles is small, and the change in volume expansion and contraction during charging and discharging is small, so the occurrence of cracking in the particles can be significantly reduced. Therefore, if single particle and / or single particle-like lithium nickel oxides are included as positive electrode active materials, the gas generation and metal dissolution caused by particle breakage and internal cracking can be significantly reduced, and therefore, excellent safety can be achieved in large batteries.

[0070] Meanwhile, the content of the first lithium nickel-based oxide may be 50 wt % or more, preferably 50 wt % to 100 wt % based on the total weight of the positive electrode active material. If the content of the first lithium nickel-based oxide is less than 50 wt % in the total amount of the positive electrode active material, the effect of suppressing particle breakage during rolling may not be significant, and the effect of suppressing gas generation and transition metal dissolution may not be achieved.

[0071] At the same time, the average particle size of the first lithium nickel oxide can be 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. If the average particle size of the particle meets the above range, a single particle and / or a single particle-like positive electrode active material with excellent electrochemical properties can be formed. If the average particle size of the particle is too small, the effect of suppressing the occurrence of particle breakage during rolling may be deteriorated, and if the average particle size of the particle is too large, the diffusion path of lithium in the particle may become longer, the resistance may increase, and the output characteristics may deteriorate.

[0072] Meanwhile, in the present invention, the D of the first lithium nickel-based oxide 50 It may be 3 μm to 10 μm, preferably 3 μm to 8 μm. 50 If D is too large, the lithium mobility in the positive electrode active material particles may deteriorate and the capacity and output properties may be adversely affected. 50 If it is too small, the phase stability of the positive electrode slurry may be deteriorated, and the coating processability may be deteriorated.

[0073] In addition, the D of the first lithium nickel-based oxide 90 The thickness of the first lithium nickel-based oxide may be less than 10 μm, preferably 5 μm to 10 μm. 90 If it is too large, the capacity and output properties may deteriorate.

[0074] In addition, the D of the first lithium nickel-based oxide 10 It may be less than 4 μm, preferably 1 μm to 4 μm. 10 When the content falls within this range, thermal stability and electrochemical properties may be more excellent.

[0075] At the same time, as required, in addition to the first lithium nickel oxide of single particle and / or quasi-single particle type, the positive electrode active material may also include a second lithium nickel oxide of secondary particle type formed by agglomeration of 40 or more primary particles. If the positive electrode active material of secondary particle type is additionally included, the effect of improving electrolyte impregnation and rollability can be obtained.

[0076] If a secondary particle type positive electrode active material is additionally included, the content of the secondary particle type positive electrode active material may be 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 contained in the positive electrode active material layer. If the content of the secondary particle type positive electrode active material is too large, the gas generation may increase, and the effect of improving safety may be deteriorated.

[0077] Meanwhile, in the present invention, the D of the second lithium nickel-based oxide 50 It may be 8 μm to 20 μm, preferably 10 μm to 20 μm. 50 When this range is satisfied, the stacking density of the positive electrode can be increased, and the energy density can be further improved.

[0078] In addition, the D of the second lithium nickel-based oxide 90 It may be less than 25 μm, preferably 10 μm to 20 μm. 90 If it is too large, the rollability may be deteriorated during the electrode manufacturing process.

[0079] In addition, the D of the second lithium nickel-based oxide 10 It may be 7 μm or less, preferably 2 μm to 6 μm. 10 When the content falls within this range, thermal stability and electrochemical properties may be more excellent.

[0080] Meanwhile, the compositions of the first lithium nickel based oxide and the second lithium nickel based oxide may be the same or different.

[0081] Specifically, the first lithium nickel-based oxide and the second lithium nickel-based oxide may each independently contain Ni in an amount of 80 mol% or more, for example, 80 mol% to less than 100 mol%, 83 mol% to less than 100 mol%, 85 mol% to less than 100 mol%, or 90 mol% to 98 mol%, based on the total number of moles of transition metals. If a lithium nickel-based oxide having a high Ni content is used, a high capacity can be achieved.

[0082] 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 [Formula 1].

[0083] [Formula 1]

[0084] Li 1+x Ni a Co b M 1 c M 2 d O2

[0085] In Formula 1, M 1 is Mn, Al, or a combination thereof, preferably Mn or Mn and Al.

[0086] M 2 may be one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from Zr, Y, Mg, and Ti, more preferably Zr, Y, or a combination thereof. The element M 2 is not necessarily included, but if included in an appropriate amount, it can play a role in promoting grain growth or improving the stability of the crystal structure during the calcination process.

[0087] 1 + x represents the lithium molar ratio in the lithium nickel-based oxide and may satisfy 0 ≤ x ≤ 0.5, 0 ≤ x ≤ 0.3, or 0 ≤ x ≤ 0.2. If the lithium molar ratio satisfies this range, the crystal structure of the lithium nickel-based oxide can be formed stably.

[0088] a represents the molar ratio of Ni in the total amount of metals other than lithium in the lithium nickel-based oxide and may satisfy 0.8 ≤ a < 1, 0.83 ≤ a < 1, 0.85 ≤ a < 1, or 0.90 ≤ a ≤ 0.98. If the nickel molar ratio satisfies this range, a high energy density can be exhibited and a high capacity can be achieved.

[0089] b represents the molar ratio of Co in the total amount of metals other than lithium in the lithium nickel-based oxide and may satisfy 0 < b < 0.2, 0 < b < 0.17, 0.01 ≤ b ≤ 0.15, or 0.01 ≤ b ≤ 0.10. If the cobalt molar ratio satisfies this range, excellent resistance properties and output properties can be achieved.

[0090] c represents the molar ratio of the M element in the total amount of metals other than lithium in the lithium nickel-based oxide, and can satisfy 0 < c < 0.2, 0 < c < 0.17, 0.01 ≤ c ≤ 0.15, or 0.01 ≤ c ≤ 0.10. If the molar ratio of the M element satisfies this range, the structural stability of the positive electrode active material is excellent. 1 c represents the molar ratio of the M element in the total amount of metals other than lithium in the lithium nickel-based oxide, and can satisfy 0 < c < 0.2, 0 < c < 0.17, 0.01 ≤ c ≤ 0.15, or 0.01 ≤ c ≤ 0.10. If the molar ratio of the M element satisfies this range, the structural stability of the positive electrode active material is excellent. 1 If the molar ratio of the M element satisfies this range, the structural stability of the positive electrode active material is excellent.

[0091] d represents the molar ratio of the M element in the total amount of metals other than lithium in the lithium nickel-based oxide, and can satisfy 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.03, or 0 ≤ d ≤ 0.02. 2 d represents the molar ratio of the M element in the total amount of metals other than lithium in the lithium nickel-based oxide, and can satisfy 0 ≤ d ≤ 0.05, 0 ≤ d ≤ 0.03, or 0 ≤ d ≤ 0.02.

[0092] Meanwhile, as needed, the first lithium nickel-based oxide and the second lithium nickel-based oxide may also include a 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 on the particle surface. Preferably, the coating element may be Al, B, Co, or a combination thereof. If the coating layer is present on the surface of the lithium nickel-based oxide particles, the contact between the electrolyte and the lithium composite transition metal oxide can be blocked by the coating layer, and due to this, the effect of reducing the dissolution of transition metals or reducing gas generation due to side reactions with the electrolyte can be obtained.

[0093] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material may be 80% by weight to 99% by weight, preferably 85% by weight to 99% by weight, and more preferably 90% by weight to 99% by weight.

[0094] Meanwhile, in addition to the positive electrode active material, the positive electrode may further include a conductive material and / or a binder.

[0095] The conductive material is used to improve the conductivity of the electrode and is not particularly limited as long as it does not cause chemical changes in the composed battery and has electronic conductivity. Specific examples may 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 cracking carbon black, carbon fiber, and carbon nanotube; metal powder or metal fiber, such as copper, nickel, aluminum, silver, etc.; conductive whiskers, such as zinc oxide, potassium titanate, etc.; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and a mixture of one or more of them may be used as the conductive material.

[0096] Preferably, the conductive material may include carbon nanotubes. In particular, the conductive material may include single-walled carbon nanotubes, multi-walled carbon nanotubes or a mixture thereof, more preferably single-walled carbon nanotubes. Single-walled carbon nanotubes are longer than other conductive materials and have a wide coverage. Therefore, if single-walled carbon nanotubes are included as conductive materials, the amount of conductive material can be reduced, the content of positive electrode active material can be increased, and the capacity can be effectively improved.

[0097] The content of the conductive material may be 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.

[0098] Secondly, the binder can play a role in improving the adhesion between the positive active material particles and the adhesion strength between the positive active material and the positive current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof, and a mixture of one or more thereof can be used. Based on the gross weight of the positive active material layer, the content of the binder may be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight.

[0099] At the same time, the positive electrode load density can be 5.35mAh / cm 2 Above, preferably 5.35 mAh / cm 2 Up to 6.0mAh / cm 2 , more preferably 5.35 mAh / cm 2 Up to 5.80mAh / cm 2 If the loading density of the positive electrode satisfies this range, a high energy density can be achieved, and a capacity balance with a high-capacity negative electrode including a Si / C composite can be achieved.

[0100] In addition, the porosity of the positive electrode may be 22% to 25%, preferably 22.5% to 25%, and more preferably 22.8% to 24.2%. If the porosity of the positive electrode satisfies this range, excellent capacity and output properties may be exhibited.

[0101] In addition, the cracking rate of the positive electrode may be 30% or less, preferably 1 to 30%, and more preferably 1 to 20%. If the cracking rate of the positive electrode satisfies this range, gas generation and metal dissolution can be effectively suppressed.

[0102] negative electrode

[0103] The negative electrode may have a structure in which a negative electrode active material layer is formed on one side or both sides of a sheet-shaped negative electrode collector, and the negative electrode active material layer may include a negative electrode active material, a conductive material, and a binder.

[0104] In particular, the negative electrode can be prepared by dispersing a negative electrode active material, a conductive material, and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, and water to prepare a negative electrode slurry, coating the negative electrode slurry on one or both sides of a sheet-shaped negative electrode collector, removing the solvent of the negative electrode slurry through a drying process, and rolling. Meanwhile, the negative electrode including the non-coating portion can be manufactured by not coating the negative electrode slurry on a partial area of ​​the negative electrode collector (e.g., one end of the negative electrode collector) during coating the negative electrode slurry.

[0105] In the present invention, the negative electrode active material includes a Si / C composite and a carbon-based negative electrode active material.

[0106] In order to increase the capacity of secondary batteries, lithium secondary batteries using silicon-based negative electrode active materials with higher theoretical capacity have been actively studied and developed, and in particular, technology using silicon oxide as a silicon-based negative electrode active material is being studied. However, in the case of silicon oxide, the irreversible capacity is large and the initial efficiency is less than 85%, so there is a limit to increasing the capacity. At the same time, Si / C composite is a composite material of carbon and silicon, which has a higher capacity and initial efficiency than SiOx. Therefore, in the present invention, by applying a Si / C composite with a theoretical discharge capacity of more than 1600mAh / g (higher than the discharge capacity of silicon oxide) and an initial efficiency of more than 85%, a lithium secondary battery with excellent energy density compared to conventional batteries can be achieved.

[0107] In addition, according to the research of the inventors, if Si / C composite is applied as described in the present invention, the electrode and cell resistance can be reduced compared with the case of applying silicon oxide, and excellent output properties can be achieved. Lithium secondary batteries using single-particle / single-particle positive active materials have the advantages of excellent safety and life characteristics, but have the problem of deterioration of output properties due to high resistance. However, as described in the present invention, if Si / C composite is included as a negative electrode active material, the electrode and cell resistance can be reduced, and excellent output properties can be achieved.

[0108] The grain size of the Si / C composite may be 20 nm or less, preferably 1 nm to 20 nm, and more preferably 1 nm to 18 nm. If the grain size of the Si / C composite satisfies this range, it can have excellent effects of improving the resistance properties and life characteristics of the battery cell.

[0109] In addition, the D of Si / C composite50 It can be 1 μm to 15 μm, preferably 2 μm to 10 μm, and more preferably 3 μm to 10 μm. 10 It can be 5 μm or less, preferably 1 μm to 5 μm, and D 90 It may be 6 μm to 20 μm, preferably 6 μm to 15 μm. If the particle size distribution of the Si / C composite satisfies this range, the negative electrode density can be increased to achieve high energy density.

[0110] 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., preferably artificial graphite, natural graphite and a combination thereof.

[0111] Meanwhile, preferably, the negative electrode active material of the present invention does not contain a silicon-based negative electrode active material (e.g., silicon oxide and silicon) other than the Si / C composite. If a silicon-based negative electrode active material other than the Si / C composite is included, the capacity improvement effect may become less obvious, and the life characteristics may deteriorate. More preferably, the negative electrode active material of the present invention may be formed of a Si / C composite and a carbon-based negative electrode active material.

[0112] In the present invention, the negative electrode active material may include 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. If the mixing ratio of the Si / C composite and the carbon-based negative electrode active material satisfies this range, it may have excellent capacity characteristics and life characteristics.

[0113] The content of the negative electrode active material may be 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.

[0114] Meanwhile, as the negative electrode current collector, a negative electrode current collector commonly used in the art may be used, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. The thickness of the negative electrode current collector may generally be 3 μm to 500 μm, and similar to the positive electrode current collector, the adhesion strength of the negative electrode active material may be enhanced by forming fine concavo-convex objects at the surface of the current collector. For example, various types including films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc. may be used.

[0115] The conductive material is used to provide conductivity to the negative electrode, and there is no specific limitation as long as it does not cause chemical changes in the composed battery and has electronic conductivity. Specific examples may include: graphite, such as natural graphite and artificial graphite; carbon 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, silver, etc.; conductive whiskers, such as zinc oxide, potassium titanate, etc.; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and a mixture of one or more thereof can be used. Based on the total weight of the negative electrode active material layer, the content of the conductive material can be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight.

[0116] The binder can play a role in improving the adhesion between the negative electrode active material particles and the adhesion strength between the negative electrode active material and the negative electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene rubber (EPDM rubber), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and various copolymers thereof, and a mixture of one or more thereof can be used. Based on the total weight of the negative electrode active material layer, the content of the binder can be 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight.

[0117] Meanwhile, in the negative electrode, the negative electrode active material layer may have a single layer structure or a multilayer structure consisting of two or more layers. For example, the negative electrode may include a first negative electrode active material layer formed on the negative electrode current collector and a second negative electrode active material layer formed on the first negative electrode active material.

[0118] If the negative electrode active material layer has a multilayer structure consisting of two or more layers, each layer may have a different type of negative electrode active material, and a different type and / or content of a binder and / or a conductive material.

[0119] For example, the first negative electrode active material layer (lower layer) and the second negative electrode active material layer (upper layer) may contain Si / C composites and carbon-based negative electrode active materials as negative electrode active materials, wherein 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. In particular, 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. If natural graphite is used as the carbon-based negative electrode active material of the lower layer, the effect of improving the adhesion strength with the current collector can be obtained, and if artificial graphite is used as the carbon-based negative electrode active material of the upper layer, the reaction rate with lithium can be increased, and the effect of improving the output properties can be obtained.

[0120] In addition, in the total amount of negative electrode active materials, the content of carbon-based negative electrode active materials in the first negative electrode active material layer (lower layer) can be higher than that in the second negative electrode active material layer (upper layer), and in the total amount of negative electrode active materials, the content of Si / C composite in the second negative electrode active material layer can be higher than that in the first negative electrode active material layer, or the content of conductive material in the second negative electrode active material layer (upper layer) can be higher than that in the first negative electrode active material layer (lower layer). Thus, by forming a multilayer structure of negative electrode active material layers and changing the composition of each layer, the performance characteristics of the battery can be improved. For example, if the content of conductive material or Si / C composite in the upper layer is higher than that in the lower layer, the effect of improving fast charging performance can be obtained.

[0121] At the same time, the negative electrode loading density can be 5.70 mAh / cm 2 Above, preferably 5.70 mAh / cm 2 Up to 6.50mAh / cm 2 , more preferably 5.70 mAh / cm 2 Up to 6.20mAh / cm 2 If the negative electrode loading density satisfies this range, high energy density can be achieved, and the capacity balance (N / P ratio) relative to the positive electrode can be adjusted.

[0122] In addition, the porosity of the negative electrode may be 24% to 30%, preferably 24% to 28%, and more preferably 24.8% to 26.2%. If the porosity of the negative electrode satisfies this range, excellent capacity and output properties may be exhibited.

[0123] Diaphragm

[0124] The separator is used to separate the negative electrode from the positive electrode and provide a migration path for lithium ions, and any separator used in a conventional lithium secondary battery is used without specific restrictions. In particular, as a separator, a porous polymer film can be used, such as a porous polymer film formed by a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), or a stacked structure of two or more thereof can be used. In addition, conventional non-woven fabrics can be used, such as non-woven fabrics formed by high melting point glass fibers, polyethylene terephthalate fibers, etc. In addition, a coated separator comprising a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength.

[0125] Electrolytes

[0126] As the electrolyte used in the present invention, various electrolytes used in lithium secondary batteries, such as organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc. can be used, and their types are not particularly limited.

[0127] In particular, the electrolyte may include an organic solvent and a lithium salt.

[0128] The organic solvent may use any organic solvent that can act as a migration medium for ions participating in the electrochemical reaction of the battery without specific restrictions. In particular, as the organic solvent, 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; carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitrile such as R-CN (R is a hydrocarbon group having a linear, branched or cyclic structure of 2 to 20 carbon atoms, and may contain a double bond, an aromatic ring or an ether bond); amide such as dimethylformamide; dioxolane such as 1,3-dioxolane; or cyclopentane sulfone. Among them, carbonate solvents are preferred, and a mixture of a cyclic carbonate having high ionic conductivity and high dielectric properties (such as ethylene carbonate or propylene carbonate) and a low-viscosity straight-chain carbonate compound (such as ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) which can improve the charge and discharge performance of the battery is more preferred.

[0129] The lithium salt can use any compound that can provide the lithium ions used in the lithium secondary battery without specific restrictions. In particular, the lithium salt can use LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The concentration of the lithium salt can be 0.1 to 5.0M, preferably 0.1 to 3.0M. If the concentration of the lithium salt is within this range, the electrolyte can have appropriate conductivity and viscosity, so that excellent electrolyte performance can be exhibited, and lithium ions can be effectively migrated.

[0130] At the same time, in order to improve the life characteristics of the battery, suppress the reduction of the battery capacity and improve the discharge capacity of the battery, the electrolyte may also contain additives other than these components. For example, the electrolyte may contain at least one or more additives selected from the group consisting of cyclic carbonate compounds, halogenated carbonate compounds, sultone compounds, sulfate compounds, phosphate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds and lithium salt compounds.

[0131] Examples of the cyclic carbonate-based compound may include vinylene carbonate (VC) or vinyl ethylene carbonate.

[0132] Examples of the halogenated carbonate-based compounds may include fluoroethylene carbonate.

[0133] Examples of the sultone compound may include at least one compound selected from the group consisting of 1,3-propane sultone (PS), 1,4-butane sultone, ethylene sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, and 1-methyl-1,3-propene sultone.

[0134] Examples of the sulfate compound may include ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

[0135] Examples of the phosphate compound may include one or more compounds selected from the group consisting of lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, tetramethyltrimethylsilylphosphate, trimethylsilylphosphite, tris(2,2,2-trifluoroethyl)phosphate and tris(trifluoroethyl)phosphite.

[0136] Examples of borate compounds may include tetraphenylborate, lithium difluorooxalatoborate (LiODFB), and lithium bisoxalatoborate (LiB(C2O4)2, LiBOB).

[0137] Examples of the nitrile compound may include at least one compound selected from the group consisting of succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, octanonitrile, heptanenitrile, cyclopentanenitrile, cyclohexanenitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, benzyl cyanide, 2-fluorophenyl cyanide and 4-fluorophenyl cyanide.

[0138] Examples of the benzene-based compound may include fluorobenzene, examples of the amine-based compound may include triethanolamine or ethylenediamine, and examples of the silane-based compound may include tetravinylsilane.

[0139] The lithium salt-based compound is a compound different from the lithium salt contained in the non-aqueous electrolyte, and may include lithium difluorophosphate (LiDFP), LiPO 2 F 2 , or LiBF 4 .

[0140] The additive may be included in an amount of 0.1 to 10 wt %, preferably 0.1 to 5 wt %, based on the total weight of the electrolyte.

[0141] Lithium secondary battery

[0142] Next, the lithium secondary battery of the present invention will be explained.

[0143] The lithium secondary battery of the present invention comprises: an electrode assembly including a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode; an electrolyte; and a battery case accommodating the electrode assembly and the electrolyte. The constituent components of the electrode assembly and the electrolyte are the same as described above, and specific description thereof will be omitted.

[0144] Meanwhile, the battery case may be a prismatic case, a cylindrical case, a pouch case, etc. used in the related art, and may preferably be a cylindrical case. In particular, the battery case may be a can-type battery case including a battery can containing an electrode assembly and an electrolyte and a sealing body sealing an open end of the battery can.

[0145] Preferably, the lithium secondary battery of the present invention may be a cylindrical battery including a cylindrical battery shell, more preferably a large-sized cylindrical battery having a shape factor ratio (defined as a value obtained by dividing the diameter of a cylindrical battery by its height, i.e., a ratio of diameter (Ф) to height (H)) of 0.4 or more. Here, the shape factor refers to a value representing the diameter and height of a cylindrical battery.

[0146] The cylindrical battery of the present invention can be, for example, a 46110 battery cell (diameter 46 mm, height 110 mm, shape factor ratio of 0.418), a 4875 battery cell (diameter 48 mm, height 75 mm, shape factor ratio of 0.640), a 48110 battery cell (diameter 48 mm, height 110 mm, shape factor ratio of 0.436), a 4880 battery cell (diameter 48 mm, height 80 mm, shape factor ratio of 0.600) or a 4680 battery cell (diameter 46 mm, height 80 mm, shape factor ratio of 0.575). In the numerical value representing the shape factor, the first two digits represent the diameter of the battery cell, and the last two or three digits represent the height of the battery cell.

[0147] Since the lithium secondary battery of the present invention includes a single particle and / or a single particle-like positive electrode active material, the amount of gas generation can be small, and excellent thermal safety can be achieved even in the case where the shape factor ratio is 0.4 or more.

[0148] exist Figure 3 and Figure 4 In the embodiment of the lithium secondary battery of the present invention, reference will be made to Figure 3 and Figure 4 The lithium secondary battery of the present invention is described. However, Figure 3 and Figure 4 Only embodiments of the present invention are shown, and the structure of the battery of the present invention is not limited to Figure 3 or Figure 4 range shown.

[0149] First, refer to Figure 3 A battery 140 according to one embodiment of the present invention includes an electrode assembly 141 , a battery can 142 accommodating the electrode assembly 141 and an electrolyte, and a sealing body 143 sealing an open end of the battery can 142 .

[0150] The battery can 142 is a container having an opening formed at the top, and is formed of a conductive metal material such as aluminum or steel. The battery can accommodates the electrode assembly 141 in an internal space through the opening at the top, and also accommodates an electrolyte.

[0151] The battery can 142 is electrically connected to the non-coating portion 146 a of the negative electrode plate, and plays a role of contacting an external power source and transmitting a current applied from the external power source to the negative terminal of the negative electrode plate.

[0152] If necessary, a bead portion 147 and a crimping portion 148 may be provided at the top of the battery can 142. The bead portion 147 may be formed by pressing the outer peripheral surface of the battery can 142 to a distance D1. The bead portion 147 prevents the electrode assembly 141 contained in the battery can 142 from moving out through the top opening portion of the battery can 142, and may function as a support member for placing the sealing body 143.

[0153] The crimping portion 148 may be formed on the bead portion 147 and have an extended and curved shape to surround the outer circumferential surface of the cover plate 143 a disposed on the bead portion 147 and a portion of the upper surface of the cover plate 143 a .

[0154] Next, the sealing body 143 is used to seal the open end of the battery can 142, and includes a cover plate 143a and a first gasket (143b) that provides airtightness and insulation between the cover plate 143a and the battery can 142, and may also include a connecting plate 143c that is electrically and mechanically connected to the cover plate 143a as needed. The cover plate 143a may be pressed onto a round edge portion 147 formed on the battery can 142, and may be fixed by a crimping portion 148.

[0155] The cover plate 143a is a component formed of a metal material having conductivity and covering the top opening portion of the battery can 142. The cover plate 143a is electrically connected to the positive plate of the electrode assembly 141 and is electrically insulated from the battery can 142 by the first gasket 143b. Therefore, the cover plate 143a can play the role of a positive terminal of the secondary battery. The cover plate 143a may be provided with a protrusion 143d protruding upward from the winding center C thereof, and the protrusion 143d may be in contact with an external power source to allow current to be applied from the external power source.

[0156] A first gasket 143 b may be provided between the cap plate 143 a 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 143 a .

[0157] Meanwhile, the battery 140 of the present invention may further include current collecting plates 144 and 145 as required. The current collecting plates are bonded to the non-coating portion 146a of the positive electrode plate and the non-coating portion 146b of the negative electrode plate, and are connected to the electrode terminals (ie, the positive terminal and the negative terminal).

[0158] In particular, the battery 140 of the present invention may include a first current collecting plate 144 coupled to the top of the electrode assembly 141 and a second current collecting plate 145 coupled to the bottom of the electrode assembly 141 .

[0159] A first current collecting plate 144 and / or a second current collecting plate 145 may also be included.

[0160] The first current collecting plate 144 is joined to the top of the electrode assembly 141. The first current collecting plate 144 is composed of a conductive metal material such as aluminum, copper and nickel, and is electrically connected to the non-coating portion 146a of the positive electrode plate. The lead 149 may be connected to the first current collecting plate 144. The lead 149 may extend above the electrode assembly 141 and join to the connecting plate 143c, or directly join to the bottom of the cap plate 143a. The joining between the lead 149 and other components may be achieved by welding. Preferably, the first current collecting plate 144 may be formed integrally 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.

[0161] Meanwhile, the first current collecting plate 144 may be joined to the end of the non-coating portion 146 a of the positive electrode plate, and the joining may be achieved by a method such as laser welding, resistance welding, ultrasonic welding, or soldering.

[0162] The second current collecting plate 145 is joined to the bottom of the electrode assembly 141. The second current collecting plate 145 is formed of a conductive metal material such as aluminum, copper, and nickel, and is electrically connected to the non-coating portion 146b of the negative electrode plate. One side of the second current collecting plate 145 may be joined to the non-coating portion 146b of the negative electrode plate, and the opposite side may be joined to the inner bottom surface of the battery can 142. In this case, the joining may be achieved by methods such as laser welding, resistance welding, ultrasonic welding, and soldering.

[0163] Meanwhile, the battery 140 of the present invention may further include an insulator 146 as needed. The insulator 146 may be provided to cover the top of the first current collecting plate 144. Since the insulator 146 covers the first current collecting plate 144, direct contact between the first current collecting plate 144 and the inner circumference of the battery can 142 may be blocked.

[0164] The insulator 146 is provided with a lead hole 151 through which the lead 149 extending upward from the first current collecting plate 144 can be led out. The lead 149 can be led out upward through the lead hole 151 and coupled with the bottom of the connection plate 143c or the bottom of the cap plate 143a.

[0165] The insulator 146 may be formed of a polymer resin, for example, a polymer resin material such as polyethylene, polypropylene, polyimide, and polybutylene terephthalate.

[0166] Meanwhile, the battery 140 of the present invention may further include a vent 152 formed at the bottom of the battery can 142 as required. The vent 152 corresponds to an area in the bottom of the battery can 142 that is thinner than the surrounding area. Since the vent 152 is thin, it is structurally weaker than the surrounding area. Therefore, if the internal pressure of the battery 140 increases to a certain level or more, the vent 152 ruptures and the gas in the battery can 142 is discharged to the outside, thereby preventing the battery from exploding.

[0167] Then, refer to Figure 4 A lithium secondary battery according to another embodiment of the present invention will be described.

[0168] Reference Figure 4 ,and Figure 3 Compared to the battery 140 shown in FIG. 1 , a battery 170 according to another embodiment of the present invention has a different battery can and sealing body structure, and the configurations of the electrode assembly and the electrolyte are substantially the same.

[0169] In particular, the battery 170 includes a battery can 171 through which a riveted terminal 172 is installed. The riveted terminal 172 is installed on a partially closed closed surface (top in the figure) of one end of the battery can 171. The riveted terminal 172 is riveted to a through hole (first opening of the first end) of the battery can 171, and an insulating second gasket 173 is provided therebetween. The riveted terminal 172 is exposed to the outside in a direction opposite to the direction of gravity.

[0170] The riveted terminal 172 includes a terminal exposure portion 172a and a terminal insertion portion 172b. The terminal exposure portion 172a is exposed outside the closed surface of the battery can 171. The terminal exposure portion 172a may be positioned near the center of the partially closed surface of the battery can 171. The maximum diameter of the terminal exposure portion 172a may be formed to be larger than the maximum diameter of the through hole formed in the battery can 171. The terminal insertion portion 172b may pass through the vicinity of the center of the partially closed closed surface of the battery can 171 and be electrically connected to the non-coating portion 146a of the positive plate. The terminal insertion portion 172b may be riveted on the inner surface of the battery can 171. That is, the end of the terminal insertion portion 172b may have a shape bent 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.

[0171] The bottom of the terminal insertion portion 172b can be welded to the first current collecting plate 144 connected to the non-coating portion 146a of the positive plate. Between the first current collecting plate 144 and the inner surface of the battery can 171, an insulating cover 174 formed of an insulating material can be provided. The insulating cover 174 covers the top of the first current collecting plate 144 and the top edge portion of the electrode assembly 141. Therefore, it can prevent a short circuit caused by the contact between the outer non-coating portion B3 of the electrode assembly 141 and the inner surface of the battery can 171 having different polarities. The terminal insertion portion 172b of the riveted terminal 172 can penetrate the insulating cover 174 and be welded to the first current collecting plate 144.

[0172] The second gasket 173 is disposed between the battery can 171 and the rivet terminal 172 to block electrical contact between the battery can 171 and the rivet terminal 172 having opposite polarities. Therefore, the top of the battery can 171 having a substantially flat shape may function as a positive terminal of the battery 170.

[0173] The second gasket 173 includes a gasket exposure portion 173a and a gasket insertion portion 173b. The gasket exposure portion 173a is disposed between the terminal exposure portion 172a of the riveted terminal 172 and the battery can 171. The gasket insertion portion 173b is disposed between the terminal insertion portion 172b of the riveted terminal 172 and the battery can 171. The gasket insertion portion 173b can be deformed together during the riveting process of the terminal insertion portion 172b and is in close contact with the inner surface of the battery can 171. The second gasket 173 may be formed of, for example, an insulating polymer resin.

[0174] The gasket exposed portion 173a of the second gasket 173 may have an extended shape to cover the periphery of the terminal exposed portion 172a of the riveted terminal 172. If the second gasket 173 covers the periphery of the riveted terminal 172, a short circuit may be prevented from occurring during the process of connecting an electrical connection component such as a bus bar to the top of the battery can 171 and / or the riveted terminal 172. Although not shown, the gasket exposed portion 173a may have an extended shape to cover the top and a portion of the periphery of the terminal exposed portion 172a.

[0175] In the case where the second gasket 173 is formed of a polymer resin, the second gasket 173 may be joined to the battery can 171 and the riveted terminal 172 by heat fusion. In this case, the airtightness at the joining interface between the second gasket 173 and the riveted terminal 172 and at the joining interface between the second gasket 173 and the battery can 171 may be enhanced. Meanwhile, if the gasket exposed portion 173a of the second gasket 173 has a shape extending to the top of the terminal exposed portion 172a, the riveted terminal 172 may be integrally joined to the second gasket (173) by insert injection.

[0176] The remaining area 175 of the top of the battery can 171 excluding 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 .

[0177] The second current collecting plate 176 is coupled to the bottom of the electrode assembly 141. The second current collecting plate 176 is formed of a metal material having conductivity, such as aluminum, steel, copper, and nickel, and is electrically connected to the non-coating portion 146b of the negative electrode plate.

[0178] Preferably, the second current collecting plate 176 is electrically connected to the battery can 171. To this end, at least a portion of the edge portion of the second current collecting plate 176 may be disposed between the inner surface of the battery can 171 and the first gasket 178b and fixed. In one embodiment, at least a portion of the edge portion of the second current collecting plate 176 may be formed on the bottom of the battery can 171 by welding in a supporting state on the bottom surface of the bead portion 180 and fixed at the bead portion 180. In a modified embodiment, at least a portion of the edge portion of the second current collecting plate 176 may be directly welded to the inner surface of the battery can 171.

[0179] The second current collecting plate 176 may be provided with a plurality of irregularities radially formed on a surface facing the non-coating portion 146b. In the case where the irregularities are formed, the second current collecting plate 176 may be pressed to dispose the irregularities in the non-coating portion 146b.

[0180] Preferably, the second current collecting plate 176 and the end portion of the non-coating portion 146 b may be joined by, for example, laser welding.

[0181] The sealing body 178 that seals the bottom open end of the battery can 171 includes a cover plate 178a and a first gasket 178b. The first gasket 178b electrically isolates the cover plate 178a from the battery can 171. The crimping portion 181 fixes the edge of the cover plate 178a and the first gasket 178b together. The cover plate 178a is provided with a vent 179. The configuration of the vent 179 is substantially the same as that of the above-mentioned embodiment.

[0182] Preferably, the cover plate 178a is formed of a metal material having electrical conductivity. However, since the first gasket 178b is disposed between the cover plate 178a and the battery can 171, the cover plate 178a does not have electrical polarity. The seal 178 serves to seal the open end of the bottom of the battery can 171 and to discharge gas if the internal pressure of the battery cell 170 increases above a critical value.

[0183] Preferably, the riveted terminal 172 electrically connected to the non-coating portion 146a of the positive plate is used as the positive terminal. In addition, a portion 175 of the upper surface of the battery can 171 other than the riveted terminal 172 is electrically connected to the non-coating portion 146b of the negative plate through the second current collector 176, and is used as a negative terminal. Thus, if the two electrode terminals are positioned at the top of the battery, electrical connection components such as bus bars can be provided only on one side of the battery 170. This can simplify the battery packaging structure and improve energy density. In addition, since the portion 175 used as the negative terminal has a substantially flat shape, a sufficient bonding area can be ensured to bond electrical connection portions such as bus bars. Therefore, the battery 170 can reduce the resistance at the bonding portion of the electrical connection components to a desired level.

[0184] 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 lithium secondary batteries of the present invention electrically connected and a battery pack housing for accommodating the assembly, and the battery pack housing may include a bus bar, a cooling unit, an external terminal, etc. for electrically connecting the lithium secondary batteries. The battery pack can be installed on a vehicle. For example, the vehicle can be an electric vehicle, a hybrid vehicle, or a plug-in hybrid vehicle. The vehicle includes a four-wheeled vehicle or a two-wheeled vehicle.

[0185] Example

[0186] Hereinafter, the present invention will be explained in more detail with reference to specific embodiments.

[0187] Example 1

[0188] <Manufacturing of positive electrode>

[0189] The positive electrode active material: porous carbon: carbon nanotube: PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 97.09:0.6:0.02 to prepare a positive electrode slurry. In this case, as the positive electrode active material, Li[Ni 0.93 Co 0.05 Mn 0.016 Al 0.004 ]A mixture of single particles and quasi-single particles of O2.

[0190] The positive electrode slurry was applied to one side of the aluminum current collector, dried at 130°C and roll-pressed to produce a positive electrode. In this case, the loading density of the positive electrode was 650 mg / 25 cm 2 (5.40mAh / cm 2 ), the porosity of the positive electrode was 23.5%, and the thickness of the positive electrode was 163 μm.

[0191] <Manufacturing of negative electrode>

[0192] The first negative electrode active material: conductive material: binder: carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 98.04:0.06:1:0.9 to prepare the first negative electrode slurry. In this case, a mixture of natural graphite: Si / C composite at a weight ratio of 85:15 was used as the first negative electrode active material, single-walled CNT was used as the conductive material, and styrene butadiene rubber (SBR) was used as the binder.

[0193] Then, the second negative electrode active material: conductive material: binder: CMC were mixed in water at a weight ratio of 98.04:0.06:1:0.9 to prepare a second negative electrode slurry. In this case, a mixture of artificial graphite: Si / C composite at a weight ratio of 85:15 was used as the second negative electrode active material, single-walled CNT was used as the conductive material, and SBR was used as the binder.

[0194] The first negative electrode slurry and the second negative electrode slurry were sequentially coated on the surface of the copper current collector sheet, dried at 150°C and roll-pressed to produce the negative electrode. The loading density of the negative electrode was 283 mg / 25 cm 2 (5.94mAh / cm 2 ), the porosity of the negative electrode was 25.1%, and the thickness of the negative electrode was 143 μm.

[0195] <Manufacturing of lithium secondary batteries>

[0196] The electrode assembly is manufactured by placing the separator between the positive electrode and the negative electrode thus manufactured, stacking and winding the separator / positive electrode / separator / negative electrode in the order of separator / positive electrode / separator. The electrode assembly thus manufactured is placed in a cylindrical battery can, injected with electrolyte, and sealed to manufacture a 4680 battery cell.

[0197] Example 2

[0198] The positive electrode, the negative electrode and the lithium secondary battery were manufactured by the same method as in Example 1, except that a mixture of natural graphite:Si / C composite in a weight ratio of 91.5:8.5 was used as the first negative electrode active material, and a mixture of artificial graphite:Si / C composite in a weight ratio of 91.5:8.5 was used as the second negative electrode active material.

[0199] Example 3

[0200] The positive electrode, the negative electrode and the lithium secondary battery were manufactured by the same method as in Example 1, except that a mixture of natural graphite:Si / C composite in a weight ratio of 88.5:11.5 was used as the first negative electrode active material, and a mixture of artificial graphite:Si / C composite in a weight ratio of 88.5:11.5 was used as the second negative electrode active material.

[0201] Example 4

[0202] The positive electrode, the negative electrode and the lithium secondary battery were manufactured by the same method as in Example 3, except that the Li[Ni] 0.93 Co 0.05 Mn 0.016 Al 0.004 ]O2 and Li[Ni 0.89 Co 0.066 Mn 0.043 Al 0.001 ]O2 in a weight ratio of 50:50 was used as a positive electrode active material.

[0203] Comparative Example 1

[0204] The positive electrode active material: porous carbon: carbon nanotube: PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 96.45:0.6:0.02 to prepare a positive electrode slurry. In this case, as the positive electrode active material, a mixture of single particles and quasi-single particles of Li[Ni] coated with boron (B) was used. 0.93 Co 0.05 Mn 0.016 Al 0.004 ]O2.

[0205] The positive electrode slurry was coated on one side of the aluminum current collector, dried at 130°C and roll-pressed to produce the positive electrode. The loading density of the positive electrode was 640 mg / 25 cm 2 (5.29mAh / cm 2 ), the porosity of the positive electrode was 23.0%, and the thickness of the positive electrode was 162 μm.

[0206] <Manufacturing of negative electrode>

[0207] The first negative electrode active material: conductive material: binder: CMC were mixed in water at a weight ratio of 98.04:0.06:1:0.9 to prepare a first negative electrode slurry. In this case, a mixture of natural graphite: SiO2 at a weight ratio of 85:15 was used as the first negative electrode active material, single-walled CNTs were used as the conductive material, and styrene butadiene rubber (SBR) was used as the binder.

[0208] Then, the second negative electrode active material: conductive material: binder: CMC were mixed in water at a weight ratio of 98.04:0.06:1:0.9 to prepare a second negative electrode slurry. In this case, a mixture of artificial graphite: SiO2 at a weight ratio of 85:15 was used as the second negative electrode active material, single-walled CNT was used as the conductive material, and SBR was used as the binder.

[0209] The first negative electrode slurry and the second negative electrode slurry were sequentially coated on the surface of the copper current collector sheet, dried at 150°C and roll-pressed to produce the negative electrode. The loading density of the negative electrode was 356 mg / 25 cm 2 (5.69mAh / cm 2 ), the porosity of the negative electrode was 25.0%, and the thickness of the negative electrode was 179 μm.

[0210] <Manufacturing of lithium secondary batteries>

[0211] The electrode assembly is manufactured by placing the separator between the positive electrode and the negative electrode thus manufactured, stacking and winding the separator / positive electrode / separator / negative electrode in the order of separator / positive electrode / separator. The electrode assembly thus manufactured is placed in a cylindrical battery can, injected with electrolyte, and sealed to manufacture a 4680 battery cell.

[0212] Comparative Example 2

[0213] The positive electrode, the negative electrode and the lithium secondary battery were manufactured by the same method as in Comparative Example 1, except that the positive electrode active material: porous carbon: carbon nanotube: PVDF binder were mixed in N-methylpyrrolidone at a weight ratio of 97.12:0.6:0.02 to prepare a positive electrode slurry, and a positive electrode exhibiting a conductivity of 632 mg / 25 cm 2 (5.3mAh / cm 2 ) of the positive electrode loading density, 23.7% of the positive electrode porosity and 160 μm of the positive electrode thickness, and the production showed 396 mg / 25 cm 2 (5.94mAh / cm 2 ) of negative electrode loading density, negative electrode porosity of 25.0% and negative electrode thickness of 189 μm.

[0214] Comparative Example 3

[0215] The positive electrode, the negative electrode and the lithium secondary battery were manufactured by the same method as in Example 3, except that the positive electrode slurry was prepared by mixing the positive electrode active material: porous carbon: carbon nanotube: PVDF binder in a weight ratio of 97.09:0.4:0.02 in N-methylpyrrolidone, and the secondary particle type of Li[Ni 0.89 Co 0.066 Mn 0.043 Al 0.001 ]O2 is used as the positive electrode active material.

[0216] Comparative Example 4

[0217] The positive electrode, the negative electrode and the lithium secondary battery were manufactured by the same method as in Example 3, except that the Li[Ni] 0.93 Co0.05 Mn 0.016 Al 0.004 ]O2 and secondary particle type boron (B) coated Li[Ni 0.89 Co 0.066 Mn 0.043 Al 0.001 ]O2 in a weight ratio of 30:70 was used as a positive electrode active material.

[0218] Comparative Example 5

[0219] A positive electrode, a negative electrode, and a lithium secondary battery were manufactured by the same method as in Example 1, except that a mixture of natural graphite:SiO with a weight ratio of 88.5:11.5 was used as the first negative electrode active material, and a mixture of artificial graphite:SiO with a weight ratio of 88.5:11.5 was used as the second negative electrode active material.

[0220] Comparative Example 6

[0221] The positive electrode, the negative electrode and the lithium secondary battery were manufactured by the same method as in Example 1, except that a mixture of natural graphite:SiO:Si / C composite in a weight ratio of 88.5:9.2:2.3 was used as the first negative electrode active material, and a mixture of artificial graphite:SiO:Si / C composite in a weight ratio of 88.5:9.2:2.3 was used as the second negative electrode active material.

[0222] Experimental Example 1-Evaluation of Negative Electrode Resistance

[0223] 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 total sheet resistance of each of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 2 were measured using an MP resistor.

[0224] The measurement results are shown in Table 1 and Figure 5 and Figure 6 Shown in. Figure 5 is a graph showing the electrode layer resistance of lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 2, Figure 6 : is a graph showing the interface resistance of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 2.

[0225] [Table 1]

[0226] <![CDATA[Electrode layer resistance (Ω·cm 2 )]]> <![CDATA[Interface resistance (Ω·cm 2 )]]> <![CDATA[Total sheet resistance (Ω·cm 2 )]]> Example 1 0.0019 0.0044 0.00063 Example 2 0.00016 0.0039 0.0054 Example 3 0.00015 0.0051 0.0066 Comparative Example 1 0.00032 0.0143 0.0175 Comparative Example 2 0.00030 0.0107 0.0137

[0227] Through Table 1 and Figure 5 to Figure 6It can be confirmed that the lithium secondary batteries of Examples 1 to 3 using a mixture of Si / C composite and graphite as the negative electrode active material exhibit lower resistance properties than the lithium secondary batteries of Comparative Examples 1 to 2 using a mixture of SiO and graphite as the negative electrode active material.

[0228] Experimental Example 2

[0229] The direct current resistance (DC-IR) and alternating current resistance (AC-IR) of each lithium secondary battery manufactured in Examples 3 to 4 and Comparative Examples 5 to 6 were measured. Figure 7 and Figure 8 Shown in.

[0230] pass Figure 7 and Figure 8 It can be confirmed that the resistance properties of the lithium secondary batteries of Examples 3 and 4 using a mixture of Si / C composite and graphite as the negative electrode active material are lower than those of Comparative Example 5 using a mixture of SiO and graphite as the negative electrode active material and Comparative Example 6 using a mixture of SiO, Si / C composite and graphite as the negative electrode active material.

[0231] Experimental Example 3

[0232] The porosity (%), rolling rate (%) and cracking rate (%) of the positive electrodes manufactured in Examples 3 to 4 and Comparative Examples 3 to 4 were measured and shown in the following [Table 2]. In this case, the cracking rate (%) was calculated as the ratio of the area occupied by cracked particles to the total area of ​​the image measured by the SEM image after measuring the cross-sectional SEM image of the positive electrode.

[0233] In addition, Figures 9 to 11 , SEM photographic images showing the state after roll-pressing the positive electrodes manufactured in Example 4, Comparative Example 3, and Comparative Example 4 are shown.

[0234] [Table 2]

[0235]

[0236] By [Table 2] and Figures 9 to 11 It can be confirmed that when the weight ratio of the single particles in the total amount of the positive electrode active material is 50% or more (Examples 3 and 4), the particle cracking rate is significantly reduced.

[0237] Experimental Example 4-Gas Production

[0238] The lithium secondary batteries manufactured in Examples 3 to 4 and Comparative Example 4 were stored at 72° C. for 3 days, and then the gas generation amounts were measured using gas chromatography. The measurement results are shown in Table 3 below.

[0239] [Table 3]

[0240] Example 3 Example 4 Comparative Example 4 <![CDATA[H2]]> 0.5 0.8 0.7 CO 3.4 5.1 8.1 <![CDATA[CO2]]> 1.3 4.4 9.0 <![CDATA[CH4]]> 18.0 14.0 15.0 <![CDATA[C2H2]]> <0.1 <0.1 <0.1 <![CDATA[C2H4]]> 0.1 0.1 0.1 <![CDATA[C2H6]]> 0.3 0.3 0.3 <![CDATA[C3H6]]> <0.1 <0.1 <0.1 <![CDATA[C3H8]]> <0.1 <0.1 <0.1 Total volume (ml) 23.7 23.8 32.4

[0241] From [Table 3], it can be confirmed that as the content of single particles / quasi-single particles in the positive electrode active material increases, the amount of gas generation decreases.

[0242] Experimental Example 5-Metal Dissolution

[0243] The lithium secondary batteries manufactured in Examples 3 to 4 and Comparative Example 4 were charged to 4.2V at 0.2C at 72°C, and activated by discharging to 2.5V at 0.2C, and then stored at 80°C for 1 day. Immediately after activation and after storage at 80°C, the lithium secondary batteries were decomposed, the negative electrodes were recollected, and the amount of metal dissolution attached to the negative electrode surface was measured using an ICP-OES (Avio550MAX, Perkinelme) device. The measurement results are shown in [Table 4] below.

[0244] [Table 4]

[0245]

[0246] As shown in Table 4, in the case of Examples 3 and 4 in which the content of the single particle in the positive electrode active material was 50% by weight or more, the increase rate of the metal dissolution amount after high-temperature storage relative to the metal dissolution amount after activation was at a level of 100% to 105%. On the contrary, in the case of Comparative Example 4 in which the content of the single particle in the positive electrode active material was 30% by weight, the metal dissolution amount after high-temperature storage increased by 358% relative to the metal dissolution amount after activation, which was very high compared with Examples 3 and 4.

[0247] Experimental Example 6-Life Evaluation

[0248] The lithium secondary batteries manufactured in Example 3, Comparative Example 5 and Comparative Example 6 were charged to 4.25V at 0.2C and discharged to 2.5V at 0.2C, and the above was regarded as one cycle, and the charging and discharging were repeated, and the capacity retention rate (%) and the resistance increase rate (%) were measured after 100 cycles, 200 cycles and 300 cycles. The measurement results are shown in [Table 5] below.

[0249] [Table 5]

[0250]

[0251] From [Table 5], it can be confirmed that the lithium secondary battery of Example 3 has excellent life characteristics compared with the lithium secondary batteries of Comparative Examples 5 and 6.

Claims

1. A lithium secondary battery comprising: An electrode assembly, the electrode assembly comprising: A positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode; Electrolytes; and a battery case accommodating the electrode assembly and the electrolyte, wherein the positive electrode active material comprises a first lithium nickel-based oxide having at least one of a single particle type consisting of one segment and a quasi-single particle type being an agglomerate of 30 or less segments, based on 50 wt % or more of the total weight of the positive electrode active material; and The negative electrode active material consists of a Si / C composite and a carbon-based negative electrode active material.

2. The lithium secondary battery according to claim 1, wherein The positive electrode active material further includes a second lithium nickel-based oxide having a secondary particle type that is an aggregate of 40 or more primary particles.

3. The lithium secondary battery according to claim 1 or 2, wherein: The first lithium nickel-based oxide and the second lithium nickel-based oxide are each independently represented by the following [Formula 1]: [Formula 1] Li 1+x Ni a Co b M 1 c M 2 d O2 In Formula 1, M 1 is Mn, Al, or a combination thereof, and M 2 includes one or more selected from the group consisting of W, Zr, Y, Ba, Ca, Ti, Mg, Ta, and Nb, 0 ≤ x ≤ 0.5, 0.8 ≤ a < 1, 0 < b < 0.2, 0 < c < 0.2, and 0 ≤ d ≤ 0.

05.

4. The lithium secondary battery according to claim 1, wherein The first lithium nickel oxide has a D 50 3μm to 10μm.

5. The lithium secondary battery according to claim 1, wherein The first lithium nickel oxide has a D 90 is less than 10 μm, and D 10 Less than 4μm.

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

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

8. The lithium secondary battery according to claim 1, wherein The cracking rate of the positive electrode is less than 30%.

9. The lithium secondary battery according to claim 1, wherein: The negative electrode active material includes a Si / C composite and a 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 grain size of the Si / C composite is less than 20 nm.

11. The lithium secondary battery according to claim 1, wherein The Si / C composite has a D 50 1μm to 10μm.

12. The lithium secondary battery according to claim 1, wherein The load density of the negative electrode is 5.7 mAh / cm 2 above.

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

14. The lithium secondary battery according to claim 1, wherein 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. The first negative electrode active material layer and the second negative electrode active material layer contain Si / C composite and 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 are different from each other.

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

16. The lithium secondary battery according to claim 1, wherein: The electrode assembly is a jelly-roll type electrode assembly.

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

18. The lithium secondary battery according to claim 17, wherein: The lithium secondary battery has a shape factor ratio of 0.4 or more.

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