Secondary batteries

Abstract

The present invention provides a battery comprising a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material, and the positive electrode active material includes 15 wt % or more of a first positive electrode active material in a single particle form, and the negative electrode includes a carbon-based active material and a silicone-based active material, and a weight E of the electrolyte impregnated in the positive electrode is 15 wt % or more of the first positive electrode active material in a single particle form. P Weight E of the electrolyte impregnated in the negative electrode N Percentage of E N / E P is 0.9 or more.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183720, filed December 23, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a secondary battery, and more particularly to a lithium secondary battery. [Background technology]

[0003] In recent years, with the rapid spread of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity lithium secondary batteries has been rapidly increasing. In particular, with the rapid development of portable electronic devices, there is a demand for the development of lithium secondary batteries that can be used at high voltages and have high energy density.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, etc. The positive electrode and the negative electrode may have an active material layer containing a positive electrode active material or a negative electrode active material formed on a current collector. The positive electrode typically uses a lithium-containing metal oxide such as lithium cobalt oxide (LiCoO), lithium manganese oxide (LiMnO), or lithium nickel cobalt manganese oxide as the positive electrode active material, while the negative electrode typically uses a lithium-free carbon-based active material or a silicone-based active material as the negative electrode active material.

[0005] Recently, the use of lithium transition metal oxides containing a high content of nickel has been considered to increase the capacity of positive electrodes, and in particular, these materials are used in the form of secondary particles to improve the diffusion rate of lithium ions. However, such lithium transition metal oxides in the form of secondary particles have a problem in that they degrade rapidly during charge and discharge. To address this problem, the use of lithium transition metal oxides in the form of single particles as positive electrode active materials has also been considered.

[0006] On the other hand, carbon-based active materials (such as graphite) are mainly used for the negative electrode because they have excellent lifespan and stability, but the use of silicone-based active materials is also being considered to achieve high energy density and improve capacity. However, silicone-based active materials undergo significant volume expansion during charging and discharging, which causes problems such as reduced lifespan and increased resistance, preventing their widespread use. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a secondary battery having high energy density and improved life performance. [Means for solving the problem]

[0008] The present invention provides a battery comprising a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material, and the positive electrode active material includes 15 wt % or more of a first positive electrode active material in a single particle form, and the negative electrode includes a carbon-based active material and a silicone-based active material, and a weight E of the electrolyte impregnated in the positive electrode is 15 wt % or more of the first positive electrode active material in a single particle form. P Weight E of the electrolyte impregnated in the negative electrode N Percentage of E N / E P The secondary battery has a resistance of 0.9 or more. [Effects of the Invention]

[0009] The secondary battery of the present invention includes a positive electrode including a positive electrode active material, the positive electrode active material including a specific content of a first positive electrode active material in a single particle form, and a negative electrode including a carbon-based active material and a silicone-based active material, and the weight E of an electrolyte impregnated in the positive electrode is P Weight E of the electrolyte impregnated in the negative electrode N Percentage of E N / E Pis in a specific range. By virtue of the above-mentioned characteristics, the secondary battery according to the present invention can achieve a high energy density and have an excellent life performance. DETAILED DESCRIPTION OF THE INVENTION

[0010] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0011] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0012] As used herein, terms such as "comprises," "comprises," or "having" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the presence or possible addition of one or more other features, numbers, steps, components, or combinations thereof.

[0013] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 50 ) can be measured, for example, by the laser diffraction method. The laser diffraction method is generally capable of measuring particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0014] The present invention will be specifically described below.

[0015] <Secondary battery> The present invention relates to a secondary battery, and more particularly to a lithium secondary battery.

[0016] Specifically, the secondary battery according to the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode includes a positive electrode active material, and the positive electrode active material includes 15 wt % or more of a first positive electrode active material in a single particle form, and the negative electrode includes a carbon-based active material and a silicone-based active material, and the weight E of the electrolyte impregnated in the positive electrode is P Weight E of the electrolyte impregnated in the negative electrode N Percentage of E N / E P is 0.9 or more.

[0017] The secondary battery of the present invention includes a positive electrode including a positive electrode active material, the positive electrode active material including a specific content of a first positive electrode active material in a single particle form, and a negative electrode including a carbon-based active material and a silicone-based active material, and a weight E of an electrolyte impregnated in the positive electrode. P Weight E of the electrolyte impregnated in the negative electrode N Percentage of E N / E P The positive electrode is characterized by being in a specific range. By including a first positive electrode active material in the positive electrode, the life performance of the positive electrode and the energy density can be improved. However, the use of a first positive electrode active material in a single particle form increases the amount of electrolyte impregnated in the positive electrode, while the amount of electrolyte impregnated in the negative electrode relatively decreases. Such a decrease in the amount of electrolyte impregnated in the negative electrode causes rapid deterioration of the life of a negative electrode containing a carbon-based active material and a silicone-based active material. In order to prevent such a problem, the present invention provides a method for manufacturing a negative electrode using the first positive electrode active material. N / E P is adjusted to a specific range, which allows sufficient electrolyte impregnation into the positive and negative electrodes, thereby achieving a high energy density and realizing a secondary battery with excellent life performance.

[0018] (1) Positive electrode The positive electrode includes a positive electrode active material.

[0019] The positive electrode active material includes a first positive electrode active material in the form of a single particle, and the positive electrode active material includes the first positive electrode active material in an amount of 15 wt % or more.

[0020] The first positive electrode active material has the advantage of being in the form of single particles, which reduces cracking compared to other active materials in the form of secondary particles, resulting in excellent durability. However, the first positive electrode active material has a problem of high electrolyte impregnation due to permeation, which may lead to imbalances in the electrolyte impregnation amounts of the positive and negative electrodes. In response to this problem, the present invention can ensure sufficient electrolyte impregnation in both the negative and positive electrodes by adjusting the ratio of the electrolyte impregnation amounts of the negative and positive electrodes, as described below.

[0021] In this specification, the term "single particle" refers to a primary structure of a single particle, consisting of primary particles rather than secondary particles. On the other hand, in this specification, the term "secondary particle" refers to an aggregate, i.e., a secondary structure, in which primary particles are aggregated together due to physical or chemical bonding between the primary particles without any intentional aggregation or granulation process of the primary particles that make up the secondary particle.

[0022] The average particle size (D 50 ) may be 0.1 μm to 5 μm, specifically 0.5 μm to 4.5 μm, and more specifically 1.5 μm to 4.5 μm.

[0023] The first positive electrode active material may include a lithium composite transition metal oxide represented by the following Chemical Formula 1:

[0024] [Chemical formula 1] Li a1 Ni b1 Co c1 M 1 d1 M 2 e1 O2

[0025] In the above Chemical Formula 1, M 1It may be Mn, Al, or a combination thereof, preferably Mn, or Mn and Al.

[0026] Said M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. The M 2 element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0027] Said a1 represents the molar ratio of lithium in the lithium transition metal oxide, and may be 0.8 ≦ a1 ≦ 1.3, 0.9 ≦ a1 ≦ 1.3, or 1.0 ≦ a1 ≦ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium transition metal oxide can be stably formed.

[0028] Said b1 represents the molar ratio of nickel among all the metals excluding lithium in the lithium transition metal oxide, and may be 0.8 ≦ b1 < 1, 0.82 ≦ b1 < 1, 0.83 ≦ b1 < 1, or 0.85 ≦ b1 < 1. When the molar ratio of nickel satisfies the above range, it shows a high energy density and high capacity can be realized.

[0029] Said c1 represents the molar ratio of cobalt among all the metals excluding lithium in the lithium transition metal oxide, and may be 0 < c1 < 0.2, 0 < c1 < 0.18, or 0.01 ≦ c1 ≦ 0.17. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0030] Said d1 represents the molar ratio of the M 1 element among all the metals excluding lithium in the lithium transition metal oxide, and may be 0 < d1 < 0.2, 0 < d1 < 0.18, or 0.01 ≦ d1 ≦ 0.17. The M 1When the molar ratio of the elements satisfies the above range, the positive electrode active material has excellent structural stability.

[0031] The e1 is M among all metals except for lithium in the lithium transition metal oxide. 2 It represents the molar ratio of the elements and may be 0≦e1≦0.1, or 0≦e1≦0.05.

[0032] The positive electrode active material includes a first positive electrode active material in an amount of 15 wt% or more. If the first positive electrode active material is included in an amount less than 15 wt%, lithium mobility is significantly reduced, and the intended improvement in life performance is not achieved. The positive electrode active material may include the first positive electrode active material in an amount of 100 wt% or less, and more specifically, the positive electrode active material may consist of the first positive electrode active material.

[0033] The positive electrode active material may further include a second positive electrode active material in the form of secondary particles together with the first positive electrode active material. Specifically, the positive electrode active material may consist of the first positive electrode active material or may be a mixture of the first positive electrode active material and the second positive electrode active material.

[0034] When the second positive electrode active material in the form of secondary particles is used together with the first positive electrode active material in the form of single particles, it is preferable because the lithium mobility of the positive electrode can be further improved.

[0035] The second positive electrode active material may include a lithium composite transition metal oxide represented by the following Chemical Formula 2:

[0036] [Chemical formula 2] Li a2 Ni b2 Co c2 M 3 d2 M 4 e2 O2

[0037] In the above chemical formula 2, M 3 may be Mn, Al, or a combination thereof, preferably Mn, or Mn and Al.

[0038] The above-mentioned M 4 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. M 2 The element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0039] The above-mentioned a2 represents the molar ratio of lithium in the lithium transition metal oxide, and may be 0.8 ≦ a2 ≦ 1.3, 0.9 ≦ a2 ≦ 1.3, or 1.0 ≦ a2 ≦ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium transition metal oxide can be stably formed.

[0040] The above-mentioned b2 represents the molar ratio of nickel among all the metals excluding lithium in the lithium transition metal oxide, and may be 0.8 ≦ b2 < 1, 0.82 ≦ b2 < 1, 0.83 ≦ b2 < 1, or 0.85 ≦ b2 < 1. When the molar ratio of nickel satisfies the above range, it exhibits a high energy density and high capacity can be realized.

[0041] The above-mentioned c2 represents the molar ratio of cobalt among all the metals excluding lithium in the lithium transition metal oxide, and may be 0 < c2 < 0.2, 0 < c2 < 0.18, or 0.01 ≦ c2 ≦ 0.17. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0042] The above-mentioned d2 represents the molar ratio of the M 3 element among all the metals excluding lithium in the lithium transition metal oxide, and may be 0 < d2 < 0.2, 0 < d2 < 0.18, or 0.01 ≦ d2 ≦ 0.17. M 3 When the molar ratio of the element satisfies the above range, it has excellent structural stability of the positive electrode active material.

[0043] The e2 is M among all metals except for lithium in the lithium transition metal oxide. 4 represents the molar ratio of the elements, and may be 0≦e2≦0.1, or 0≦e2≦0.05.

[0044] The average particle size (D 50 ) is the average particle size (D 50 ) In this case, the positive electrode active material according to the present invention has a bimodal structure including a second positive electrode active material in the form of secondary particles and having a relatively large particle size, and a first positive electrode active material in the form of single particles and having a relatively small particle size. This improves the energy density of the positive electrode, minimizes particle cracking of the second positive electrode active material, and improves the life performance by introducing the first positive electrode active material (single particles). Furthermore, the use of relatively small particle size particles as the first positive electrode active material minimizes the decrease in lithium mobility.

[0045] The average particle size (D 50 ) may be 6 μm to 30 μm, specifically 8 μm to 20 μm.

[0046] In the present invention, the average particle size (D 50 ) relative to the average particle size (D 50 ) may be 1.1 or more, specifically 2 or more, and more specifically 3 or more. 50 When the average particle size (D) of the first positive electrode active material satisfies the above range, the press density of the positive electrode active material increases, thereby improving the electrode density during electrode manufacturing, and achieving excellent energy density. 50 It is also preferable to adjust the average particle diameter (D) of the first positive electrode active material to the above range in order to minimize the decrease in lithium mobility due to the use of single particles. 50 ) relative to the average particle size (D 50 The upper limit of the ratio of the average particle diameter (D 50) relative to the average particle size (D 50 ) may be 10 or less, 8 or less, 6 or less, or 4 or less.

[0047] When the positive electrode active material further includes a second positive electrode active material, the weight ratio of the first positive electrode active material to the second positive electrode active material may be 15:85 to 99:1, specifically 20:80 to 80:20, more specifically 25:75 to 60:40, and even more specifically 28:72 to 45:55. When the weight ratio is within the above range, the electrode density of the positive electrode can be further increased, and life performance and lithium mobility can be improved in a balanced manner, which is preferable.

[0048] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0049] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the positive electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and may specifically include aluminum.

[0050] The positive electrode current collector usually has a thickness of 3 to 500 μm.

[0051] The positive electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0052] The positive electrode active material layer may be disposed on the positive electrode current collector, specifically, on one or both sides of the positive electrode current collector.

[0053] The positive electrode active material layer may contain the positive electrode active material described above.

[0054] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight, preferably 92% by weight to 98% by weight, in consideration of sufficient capacity of the positive electrode active material.

[0055] The positive electrode active material layer may further include a positive electrode binder and a positive electrode conductive material in addition to the positive electrode active material.

[0056] The positive electrode binder is a component that assists in binding the active material and conductive material, etc., and in binding to the current collector, and specifically may contain at least one selected from the group consisting of polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, and fluororubber, and preferably polyvinylidene fluoride.

[0057] The positive electrode binder may be contained in the positive electrode active material layer in an amount of 0.1 wt % to 10 wt %, preferably 0.1 wt % to 3 wt %, more specifically 0.5 wt % to 2.5 wt %, in order to ensure sufficient binding strength between components such as the positive electrode active material.

[0058] The positive electrode conductive material is used to assist and improve the conductivity of the secondary battery, and is not particularly limited as long as it does not cause chemical changes and is conductive. Specifically, the conductive material may include at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon nanotubes such as single-walled carbon nanotubes and multi-walled carbon nanotubes; fluorocarbons; metal powders such as aluminum and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives. Specifically, in order to improve conductivity, the conductive material may include carbon black and carbon nanotubes, more specifically, carbon black and multi-walled carbon nanotubes.

[0059] In order to ensure sufficient electrical conductivity, the positive electrode conductive material may be contained in the positive electrode active material layer in an amount of 0.1 wt % to 10 wt %, specifically 0.1 wt % to 3.0 wt %, and more specifically 0.5 wt % to 2.5 wt %.

[0060] The thickness of the positive electrode active material layer may be 30 μm to 400 μm, preferably 60 μm to 200 μm.

[0061] The loading of the positive electrode is 2 mAh / cm 2 ~6mAh / cm 2 , specifically 2.5mAh / cm 2 ~4.5mAh / cm 2 It may be.

[0062] The porosity of the positive electrode may be 18% to 32%, specifically 20% to 30%, more specifically 20% to 25%, and even more specifically 21% to 23%.

[0063] The porosity of the positive electrode can be calculated by the following mathematical formula A.

[0064] [Mathematical formula A] Porosity of positive electrode (%) = {1 - (electrode density of positive electrode / true density of positive electrode)} x 100

[0065] In Equation A, the true density of the positive electrode is the density of the positive electrode active material layer measured when a positive electrode of a certain size is taken and pressed using a press until the thickness of the positive electrode remains unchanged, and the electrode density of the positive electrode is the density of the positive electrode active material layer measured when a positive electrode of a certain size is taken.

[0066] The positive electrode may be manufactured by coating a positive electrode slurry containing a positive electrode active material, and optionally a positive electrode binder, a positive electrode conductive material, and a solvent for forming the positive electrode slurry, on the positive electrode current collector, followed by drying and rolling.

[0067] The solvent for forming the positive electrode slurry may include an organic solvent such as NMP (N-methyl-2-pyrrolidone) and may be used in an amount that provides a suitable viscosity when containing the positive electrode active material, and optionally a positive electrode binder and a positive electrode conductive material, etc. For example, the solvent for forming the positive electrode slurry may be included in the positive electrode slurry so that the concentration of solids including the positive electrode active material, and optionally a positive electrode binder and a positive electrode conductive material is 50 wt % to 95 wt %, preferably 70 wt % to 90 wt %.

[0068] (2) Negative electrode The negative electrode may be disposed opposite the positive electrode.

[0069] The negative electrode includes a negative electrode active material.

[0070] The negative electrode active material is characterized by including a carbon-based active material and a silicone-based active material.

[0071] The negative electrode according to the present invention can have a high energy density and a thin thickness by using a silicone-based active material having high capacity characteristics together with a carbon-based active material. In particular, when the negative electrode according to the present invention is used together with the above-described positive electrode, it is preferable because the secondary battery can achieve a high level of energy density as a whole. When only a carbon-based active material is used as the negative electrode active material, it is difficult to ensure a high capacity per unit volume compared to the case where a carbon-based active material and a silicone-based active material are used in combination. In order to achieve a high capacity, the thickness of the negative electrode has to be increased. However, as the thickness of the negative electrode increases, the intercalation rate of lithium from the positive electrode becomes slower, so the rapid charging performance cannot be improved.

[0072] The carbon-based active material may include at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon, and specifically, it may be graphite. The graphite may include at least one selected from the group consisting of artificial graphite and natural graphite, for example.

[0073] The average particle diameter (D 50 ) of the carbon-based active material may be 5 μm to 35 μm, preferably 10 μm to 20 μm, from the viewpoint of achieving structural stability during charge and discharge and reducing side reactions with the electrolyte.

[0074] The silicone-based active material may include a silicone-based compound represented by SiO x (0 ≦ x < 2). The silicone-based compound may be represented by the chemical formula of SiO x (0 ≦ x < 2), and specifically, it may be represented by the chemical formula of SiO x (0 < x < 2). On the other hand, in the case of SiO2 (when x = 2), it does not react with lithium ions, so lithium cannot be stored. Therefore, it is preferable that x is within the above range. Specifically, the silicone-based compound may be represented by the chemical formula of SiO x (0.5 ≦ x ≦ 1.5).

[0075] More specifically, the silicone-based active material is SiO x The battery may include a silicone-based compound represented by the formula (0≦x<2) and a metal doped into the silicone-based compound. Silicon-based active materials generally suffer from the problem of irreversible sites in the silicone-based active material, which can cause an irreversible reaction in which some of the lithium that migrates to the negative electrode during initial charging does not return to the positive electrode during discharge. To prevent this problem, the metal is introduced by doping the silicone-based compound to reduce the irreversible phase of the silicone-based compound and improve efficiency.

[0076] The metal is doped into the silicone-based compound. Specifically, the metal may be located inside, on the surface, or both inside and on the surface of the silicone-based compound. The metal may be doped into the silicone-based compound and form a metal silicate with a silicone oxide contained in the first silicone-based compound.

[0077] The metal may include at least one metal selected from the group consisting of Li, Mg, Ca, and Al. Specifically, at least one metal selected from the group consisting of Li and Mg, more specifically Mg, may be included, since this allows for excellent control of volume expansion of the silicone-based oxide particles, prevention of damage, and improvement of initial efficiency.

[0078] The weight of the metal may be 1 wt% to 30 wt%, specifically 5 wt% to 20 wt%, based on the total weight of the silicone-based compound and the metal. When the weight is within this range, the irreversible capacity of the first silicone-based active material can be sufficiently eliminated and a decrease in capacity due to excessive metal doping can be prevented. The metal content can be measured by ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0079] The silicone-based active material may further include a carbon coating layer disposed on the surface thereof, which may function as a protective layer to suppress volume expansion of the silicone-based active material and prevent side reactions with the electrolyte.

[0080] The carbon coating layer may be contained in the silicone-based active material in an amount of 0.1 wt % to 10 wt %, preferably 3 wt % to 7 wt %, in the above range, which is preferable because the carbon coating layer can effectively control the volume expansion of the silicone-based active material and prevent side reactions with the electrolyte.

[0081] The carbon coating layer may be an amorphous carbon coating layer, and may be formed by chemical vapor deposition (CVD) using at least one hydrocarbon gas selected from the group consisting of methane, ethane, and acetylene.

[0082] The average particle size (D 50 ) may be 1 μm to 15 μm, more preferably 2 μm to 10 μm, in order to ensure structural stability of the active material during charge and discharge, to prevent the problem of excessive volume expansion / contraction due to excessively large particle size, and to prevent the problem of reduced initial efficiency due to excessively small particle size.

[0083] The weight ratio of the carbon-based active material to the silicone-based active material may be 60:40 to 99:1, specifically 83:17 to 99:1, and more specifically 88:12 to 98:2. When the weight ratio is within the above range, the effect of the silicone-based active material on volume expansion is reduced, and sufficient capacity of the negative electrode can be ensured, making it possible to realize a high-loading negative electrode.

[0084] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0085] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the negative electrode current collector may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy, and may specifically include copper.

[0086] The negative electrode current collector usually has a thickness of 3 to 500 μm.

[0087] The negative electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0088] The negative electrode active material layer may be formed on at least one surface of the negative electrode current collector. Specifically, the negative electrode active material layer may be formed on one or both surfaces of the negative electrode current collector.

[0089] The negative electrode active material layer contains the above-described negative electrode active material.

[0090] The negative electrode active material may be contained in the negative electrode active material layer in an amount of 65% by weight to 98% by weight, specifically 80% by weight to 95% by weight.

[0091] The negative electrode active material layer may further include a negative electrode binder and a negative electrode conductive material in addition to the negative electrode active material.

[0092] The negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber, acrylic rubber, butyl rubber, fluororubber, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl alcohol (PVA), polyacrylic acid (PAA), polyethylene glycol (PEG), polyacrylonitrile (PAN), and polyacrylamide (PAM), in order to further improve electrode adhesive strength and provide sufficient resistance to volume expansion / contraction of the active material. Specifically, the negative electrode binder may include styrene butadiene rubber (SBR).

[0093] The negative electrode binder may be included in the negative electrode active material layer in an amount of 0.1 wt % to 10 wt %, specifically 2 wt % to 8 wt %. When the amount is within the above range, it is possible to realize a negative electrode having excellent capacity in addition to improving adhesive strength and controlling thickness expansion of the negative electrode, which is preferable.

[0094] The negative electrode conductive material is used to improve the conductivity of the negative electrode active material layer and is preferably conductive without causing chemical changes. Specifically, the negative electrode conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives.

[0095] The conductive material may be contained in the negative electrode active material layer in an amount of 0.1% by weight to 10% by weight. When the conductive material is contained in the above range, it is possible to control volume expansion due to charge and discharge, and it is preferable from the viewpoint of preventing discontinuity of the conductive network due to volume expansion of the negative electrode active material.

[0096] The negative electrode active material layer may further include a thickener, and the thickener may include carboxymethyl cellulose (CMC).

[0097] The thickener may be contained in the negative electrode active material layer in an amount of 0.5 wt % to 5 wt %, but is not limited thereto.

[0098] The loading amount of the negative electrode active material layer is 2 mAh / cm 2 ~6mAh / cm 2 , specifically 3mAh / cm 2 ~5mAh / cm 2 It may be.

[0099] The thickness of the negative electrode active material layer may be 20 μm to 200 μm, specifically 50 μm to 130 μm. By using a carbon-based active material and a silicone-based active material, the negative electrode according to the present invention can achieve a thin negative electrode with a high energy density, and the intercalation of lithium ions from the positive electrode can be smooth, thereby improving rapid charging performance.

[0100] The negative electrode active material layer may be manufactured by adding the carbon-based active material and the silicone-based active material, and optionally a negative electrode binder, a negative electrode conductive material, and / or a thickener to a solvent (e.g., water) to prepare a negative electrode slurry, and then coating, rolling, and drying the negative electrode slurry on the negative electrode current collector.

[0101] The porosity of the negative electrode may be 20% to 40%, specifically 23% to 32%.

[0102] The porosity of the negative electrode can be calculated by the following mathematical formula B.

[0103] [Mathematical formula B] Porosity of negative electrode (%) = {1 - (electrode density of negative electrode / true density of negative electrode)} × 100

[0104] In Equation B, the true density of the negative electrode is the density of the negative electrode active material layer measured when a negative electrode of a certain size is taken and pressed using a press until the thickness of the negative electrode remains unchanged, and the electrode density of the negative electrode is the density of the negative electrode active material layer measured when a negative electrode of a certain size is taken.

[0105] The negative electrode active material layer may have a double layer structure, specifically, the negative electrode active material layer may include a first negative electrode active material layer disposed on the negative electrode current collector and a second negative electrode active material layer disposed on the first negative electrode active material layer.

[0106] Specifically, the negative electrode active material may include a first negative electrode active material and a second negative electrode active material. The first negative electrode active material may include a first carbon-based active material and a first silicone-based active material. The second negative electrode active material may include a second carbon-based active material and a second silicone-based active material. Furthermore, the first negative electrode active material layer may include the first carbon-based active material and the first silicone-based active material, and the second negative electrode active material layer may include the second carbon-based active material and the second silicone-based active material.

[0107] In this specification, the terms "first negative electrode active material and second negative electrode active material", "first carbon-based active material" and "second carbon-based active material", and "first silicone-based active material" and "second silicone-based active material" are terms used to describe the locations where the carbon-based active material and silicone-based active material are contained, respectively, and the above descriptions of the carbon-based active material and silicone-based active material can be similarly applied.

[0108] The first negative electrode active material layer may contain the first carbon-based active material and the first silicone-based active material in a weight ratio of 60:40 to 99:1, specifically 83:17 to 99:1, more specifically 88:12 to 98:2. The second negative electrode active material layer may contain the second carbon-based active material and the second silicone-based active material in a weight ratio of 60:40 to 99:1, specifically 83:17 to 99:1, more specifically 88:12 to 98:2. When the ratios are within the above ranges, the effect of volume expansion of the silicone-based active material is reduced, sufficient capacity of the negative electrode can be secured, and a high-loading negative electrode can be realized.

[0109] When the negative electrode active material layer includes a first negative electrode active material layer and a second negative electrode active material layer, and the negative electrode active material layer includes the above-mentioned negative electrode binder, negative electrode conductive material, and / or thickener, the negative electrode binder may include a first negative electrode binder and a second negative electrode binder, the negative electrode conductive material may include a first negative electrode conductive material and a second negative electrode conductive material, and the thickener may include a first thickener and a second thickener. In this case, the first negative electrode active material layer may further include the first negative electrode binder, the first negative electrode conductive material, and / or the first thickener in addition to the first carbon-based active material and the first silicone-based active material. The second negative electrode active material layer may include the second negative electrode binder, the second negative electrode conductive material, and / or the second thickener in addition to the second carbon-based active material and the second silicone-based active material.

[0110] In this specification, the terms "first negative electrode binder" and "second negative electrode binder", "first negative electrode conductive material" and "second negative electrode conductive material", and "first thickener" and "second thickener" are terms used to describe locations where the negative electrode binder, negative electrode conductive material, and thickener are contained, and the above descriptions of the negative electrode binder, negative electrode conductive material, and thickener can be similarly applied.

[0111] The first negative electrode binder may be contained in the first negative electrode active material layer at a content of 0.1% by weight to 10% by weight, specifically 2% by weight to 8% by weight, and the second negative electrode binder may be contained in the second negative electrode active material layer at a content of 0.1% by weight to 10% by weight, specifically 2% by weight to 8% by weight.

[0112] The first conductive material may be contained in the first negative electrode active material layer in an amount of 0.1 wt % to 10 wt %, and the second conductive material may be contained in the second negative electrode active material layer in an amount of 0.1 wt % to 10 wt %.

[0113] The first thickener may be contained in the first negative electrode active material layer in an amount of 0.5% by weight to 5% by weight, and the second thickener may be contained in the second negative electrode active material layer in an amount of 0.5% by weight to 5% by weight.

[0114] When the negative electrode active material layer includes the first negative electrode active material layer and the second negative electrode active material layer, the method for producing the negative electrode is not particularly limited as long as the first negative electrode active material layer and the second negative electrode active material layer having the above-mentioned characteristics can be realized. For example, the negative electrode according to the present invention can be produced by dispersing a first negative electrode active material (a first carbon-based active material, a first silicone-based active material), a first binder, a first conductive material, and / or a thickener in a solvent (e.g., water) to produce a slurry for the first negative electrode active material layer, dispersing the second negative electrode active material (a second carbon-based active material, a second silicone-based active material), a second binder, and / or a second conductive material in a solvent (e.g., water) to produce a slurry for the second negative electrode active material layer, and then applying the resulting slurry to a negative electrode current collector. More specifically, the negative electrode according to the present invention can be manufactured by applying the slurry for the first negative electrode active material layer prepared above to a negative electrode current collector, rolling and drying the slurry, and then applying the slurry for the second negative electrode active material layer prepared above onto the first negative electrode active material layer, rolling and drying the slurry. Alternatively, the negative electrode according to the present invention can be manufactured by applying the slurry for the first negative electrode active material layer to a negative electrode current collector, and substantially simultaneously applying the slurry for the second negative electrode active material layer onto the applied slurry for the first negative electrode active material layer, and then rolling and drying the slurry.

[0115] (3) Separator The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte humidification are preferred. Specifically, porous polymer films, such as those made of polyolefin-based polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, can be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, coated separators containing ceramic components or polymeric materials can also be used, and they can be selectively used in single-layer or multi-layer structures.

[0116] (4) Electrolyte The electrolyte is contained in the secondary battery and is impregnated into the positive electrode and the negative electrode.

[0117] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of secondary batteries, but are not limited to these.

[0118] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0119] The lithium salt can be any compound capable of providing lithium ions used in lithium secondary batteries. Specifically, examples of the lithium salt include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, and LiB(C2O4)2. The lithium salt concentration is preferably within the range of 0.1M to 2.0M. When the lithium salt concentration falls within this range, the electrolyte has appropriate conductivity and viscosity, resulting in excellent electrolyte performance and efficient lithium ion migration.

[0120] The organic solvent may include at least one selected from linear carbonates, cyclic carbonates, linear esters, cyclic esters, ethers, glymes, and nitriles.

[0121] The linear carbonate may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate.

[0122] The cyclic carbonate may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate.

[0123] Specific examples of the linear ester include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0124] Specific examples of the cyclic ester include, but are not limited to, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0125] Specific examples of the ether include, but are not limited to, dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL).

[0126] Specific examples of the glyme include, but are not limited to, dimethoxyethane (glyme, DME), diethoxyethane, diglyme, triglyme, and tetraglyme (TEGDME).

[0127] Specific examples of the nitrile include, but are not limited to, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0128] More specifically, the organic solvent may include a cyclic carbonate, a linear ester, and a halogen-containing cyclic carbonate. In this case, the cyclic carbonate can enhance the high dielectric constant and ionic conductivity, while the linear ester can achieve a suitable viscosity, improve electrolyte impregnation, and reduce the degree of reductive decomposition at high voltage. This is preferable from the viewpoint of improving stability and life performance at high voltage. In particular, the halogen-containing cyclic carbonate is preferable because it can form a stable solid electrolyte interface layer (SEI layer) in the negative electrode of the present invention using a silicone-based active material.

[0129] When the organic solvent contains a cyclic carbonate, a linear ester, and a halogen-containing cyclic carbonate, the cyclic carbonate may be a halogen-free cyclic carbonate and may include at least one selected from ethylene carbonate and propylene carbonate, the linear ester may include at least one selected from ethyl propionate and propyl propionate, and the halogen-containing cyclic carbonate may include at least one selected from fluoroethylene carbonate and difluoroethylene carbonate.

[0130] When the organic solvent contains a cyclic carbonate, a linear ester, and a halogen-containing cyclic carbonate, the cyclic carbonate may be contained in the organic solvent at 10% by weight to 50% by weight, specifically 15% by weight to 30% by weight, the linear ester may be contained in the organic solvent at 30% by weight to 80% by weight, specifically 40% by weight to 70% by weight, and the halogen-containing cyclic carbonate may be contained in the organic solvent at 5% by weight to 30% by weight, specifically 10% by weight to 25% by weight.

[0131] The electrolyte may further contain an additive in addition to the lithium salt and the organic solvent.

[0132] The additive may include at least one selected from the group consisting of vinyl ethylene carbonate, propane sultone, LiBF (lithium tetrafluoroborate), LiODFB (lithium difluoro(oxalato)borate), 1,3,6-HTCN (hexane tri-cyanide), and NaO (sodium superoxide), specifically, fluoroethylene carbonate, difluoroethylene carbonate, vinyl ethylene carbonate, propane sultone, LiBF (lithium tetrafluoroborate), LiODFB (lithium difluoro(oxalato)borate), 1,3,6-HTCN (hexane tri-cyanide), succinonitrile, 1,4-dicyano-2-butyne, adiponitrile, lithium difluorophosphate (LiPOF), and NaO (sodium superoxide).

[0133] The other additives may be contained in the electrolyte in an amount of 0.1 wt % to 20 wt %, specifically 1 wt % to 10 wt %, but are not limited thereto.

[0134] (5)E N / E P According to the present invention, the weight E of the electrolyte impregnated in the positive electrode P Weight E of the electrolyte impregnated in the negative electrode N Percentage of E N / E P is 0.9 or more.

[0135] As mentioned above, when the positive electrode active material contains 15 wt % or more of the first positive electrode active material in a single particle form, there is a problem of increased electrolyte impregnation in the positive electrode due to permeation. This uneven distribution of electrolyte in the positive electrode results in a relative decrease in the electrolyte impregnation in the negative electrode. If the negative electrode is not sufficiently impregnated with electrolyte, problems such as reduced charge / discharge performance and increased resistance occur, leading to rapid performance degradation of the secondary battery. These problems are particularly severe when a silicone-based active material with low durability is used as the negative electrode active material.

[0136] In order to solve this problem, the secondary battery of the present invention uses the above-mentioned positive electrode and negative electrode, and the weight E of the electrolyte impregnated in the positive electrode P Weight E of the electrolyte impregnated in the negative electrode N Percentage of E N / E P The characteristic of this method is that the E N / E P If the ratio is less than 0.9, the amount of electrolyte impregnated into the positive electrode increases excessively, resulting in an imbalance in the electrolyte impregnation between the positive electrode and the negative electrode, which may result in a rapid deterioration in life performance.

[0137] The above E N / E P may be 0.9 or more, specifically 1 or more, more specifically 1.3 or more, and when it is in the above range, the electrolyte is impregnated into the positive electrode and the negative electrode in a balanced manner, and a secondary battery having a high energy density and a significantly improved life performance can be realized. N / E P The upper limit of E is not particularly limited. N / E P may be 1.6 or less, specifically 1.5 or less.

[0138] The above E N / E P can be adjusted by adjusting the thickness, loading amount, porosity, etc. of the positive and negative electrodes, and the impregnation of the positive and negative electrodes with the electrolyte, but is not limited thereto.

[0139] The above E N / E P The E may be measured one week or more after the electrolyte is injected into the secondary battery, or after the secondary battery has undergone an activation process, or after the secondary battery has undergone an activation process and the SOC of the secondary battery is greater than 0% and less than 30%. N / E P can be measured after the secondary battery is subjected to an activation process. N / EP The condition of the activation process is not limited as long as it is measured after the secondary battery is subjected to an activation process, and for example, it may be measured in a BOL (Beginning of Life) state or in a state in which the secondary battery is shipped after being manufactured.

[0140] The above E N / E P can be calculated in the following way:

[0141] (a1) Separating the negative electrode and the positive electrode from the secondary battery, and measuring the weight E of the negative electrode N1 and the weight E of the positive electrode P1 measuring each of the (a2) The separated negative electrode and positive electrode are washed with a solvent to remove the electrolyte, and then dried, after which the weight E of the negative electrode is N2 and the weight E of the positive electrode P2 and (a3) According to the following mathematical formula 1, E N / E P A step of calculating

[0142] [Mathematical formula 1] E N / E P =(E N1 -E N2 ) / (E P1 -E P2 )

[0143] The above E N / E P In the calculation method of (1), the separated negative electrode and positive electrode may be washed using a solvent such as dimethyl carbonate.

[0144] The drying step performed after washing the negative electrode and the positive electrode may be performed under vacuum at a temperature of 25° C. to 55° C. The drying step may be performed for 0.5 hours to 12 hours.

[0145] In the secondary battery of the present invention, the N / P ratio calculated by the following mathematical formula C may be 1.0 to 1.2, preferably 1.02 to 1.10.

[0146] [Mathematical formula C] N / P ratio={(discharge capacity per unit area of ​​the negative electrode) / (discharge capacity per unit area of ​​the positive electrode)}.

[0147] Specifically, the discharge capacity per unit area of ​​the negative electrode can be determined by the following method. First, a negative electrode sample identical to a used negative electrode is prepared. A coin-shaped half-cell is fabricated including the negative electrode sample, a lithium metal counter electrode facing the negative electrode, a separator interposed between the negative electrode and the lithium metal counter electrode, and an electrolyte, and the discharge capacity is determined. The discharge capacity per unit area of ​​the negative electrode can be determined by dividing the discharge capacity by the area of ​​the negative electrode sample.

[0148] The discharge capacity per unit area of ​​the positive electrode can be determined by the following method. First, a positive electrode sample identical to a used positive electrode is prepared. A coin-shaped half-cell is fabricated including the positive electrode sample, a lithium metal counter electrode facing the positive electrode, a separator interposed between the negative electrode and the lithium metal counter electrode, and an electrolyte, and the discharge capacity is determined. The discharge capacity per unit area of ​​the positive electrode can be determined by dividing the discharge capacity by the area of ​​the positive electrode sample.

[0149] The secondary battery may further include a battery case that accommodates the negative electrode, the positive electrode, the separator, and the electrolyte.

[0150] The secondary battery may be manufactured by preparing an electrode assembly including the positive electrode, a negative electrode facing the positive electrode, and a separator interposed between the positive electrode and the negative electrode, placing the electrode assembly in a battery case, injecting an electrolyte into the battery case, and sealing the battery case.

[0151] The present invention also provides a battery module including the secondary battery as a unit cell, and a battery pack including the same.

[0152] The battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); and power storage systems.

[0153] The external shape of the secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0154] The secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also as a unit battery in a medium- to large-sized battery module containing a large number of battery cells.

[0155] Examples of the medium to large size devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0156] Although the present invention may be embodied in various different forms, it is not intended to be limited to the embodiments set forth herein, and the present invention is not limited to the embodiments set forth herein.

[0157] Example Example 1: Manufacturing of secondary battery 1. Manufacturing the cathode As the first positive electrode active material, Li[Ni 0.8 Co 0.1 Mn 0.1 The first positive electrode active material was in the form of single particles, and had an average particle size (D 50) was 3 μm.

[0158] As the second positive electrode active material, Li[Ni 0.8 Co 0.1 Mn 0.1 The second positive electrode active material was in the form of secondary particles with an average particle size (D 50 ) was 10 μm.

[0159] The first positive electrode active material and the second positive electrode active material were mixed in a weight ratio of 50:50 to prepare a positive electrode active material.

[0160] The positive electrode active material, carbon nanotubes as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were added in a weight ratio of 98:1:1 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry.

[0161] The positive electrode slurry was applied to an aluminum current collector (thickness: 15 μm) at 4 mAh / cm 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 110 μm), and the porosity of the positive electrode was adjusted to 21%.

[0162] 2. Manufacturing the negative electrode Graphite (average particle size (D 50 SiO (average particle size (D): 18 μm) as a silicone-based active material 50 The carbon-based active material and the silicone-based active material were mixed in a weight ratio of 95:5 to prepare a negative electrode active material.

[0163] The negative electrode active material, styrene butadiene rubber (SBR) as a negative electrode binder, carboxymethyl cellulose (CMC) as a thickener, and carbon black as a negative electrode conductive material were mixed in a weight ratio of 95.3:2.5:1.2:1.0 and added to water as a solvent to prepare a negative electrode slurry.

[0164] The negative electrode slurry prepared above was applied to a copper foil (thickness: 8 μm) as a negative electrode current collector at a rate of 4.3 mAh / cm 2 The negative electrode was fabricated by applying the coating at a loading amount of 100 μm, rolling it, and drying it in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer (thickness: μm). The porosity of the negative electrode was 25%.

[0165] 3. Secondary battery manufacturing A polyethylene separator was interposed between the negative electrode and positive electrode prepared as described above, and an electrolyte was injected to prepare a secondary battery of Example 1. The electrolyte used was an organic solvent made by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 30:70, to which LiPF6 was added as a lithium salt at a concentration of 1.0 mol / L.

[0166] The N / P ratio of the secondary battery of Example 1 was 1.08.

[0167] 4.E N / E P Measurement of The secondary battery manufactured as described above was activated to be in a BOL (Beginning of LiFe) state. The negative electrode and the positive electrode were separated from the secondary battery in the BOL state, and the weight E of the negative electrode was measured. N1 and the weight E of the positive electrode P1 were measured respectively.

[0168] The separated negative electrode and positive electrode were washed with a solvent (dimethyl carbonate) to remove the electrolyte, and then dried under vacuum at 25°C for 6 hours. After that, the weight of the negative electrode, E N2 and the weight E of the positive electrode P2 were measured respectively.

[0169] Next, E is calculated using the following mathematical formula 1. N / E P was calculated and the value was 1.21.

[0170] [Mathematical formula 1] E N / E P=(E N1 -E N2 ) / (E P1 -E P2 )

[0171] Example 2: Manufacturing of secondary battery A secondary battery was fabricated in the same manner as in Example 1, except that the first and second positive electrode active materials were mixed in a weight ratio of 30:70 to prepare a positive electrode active material. In Example 2, the loading amount of the positive electrode slurry was 4 mAh / cm. 2 The thickness of the positive electrode active material layer was 112 μm, and the porosity of the positive electrode was adjusted to 22%.

[0172] Example 2E N / E P The N / P ratio of the secondary battery of Example 2 was 1.08.

[0173] Example 3: Production of secondary battery A positive electrode and a secondary battery were fabricated in the same manner as in Example 1, except that the second positive electrode active material was not used as the positive electrode active material, and only the first positive electrode active material was used. In Example 3, the loading amount of the positive electrode slurry was 4 mAh / cm. 2 The thickness of the positive electrode active material layer was 118 μm, and the porosity of the positive electrode was adjusted to 28%.

[0174] Example 3E N / E P The N / P ratio of the secondary battery of Example 3 was 1.08.

[0175] Comparative Example 1: Manufacturing of secondary battery A positive electrode and a secondary battery were fabricated in the same manner as in Example 1, except that the second positive electrode active material was not used as the positive electrode active material, and only the first positive electrode active material was used, and the porosity of the positive electrode was adjusted to 20% by adjusting the pressure of the roll press. In Comparative Example 1, the loading amount of the positive electrode slurry was 4 mAh / cm. 2 The thickness of the positive electrode active material layer was 112 μm, and the porosity of the positive electrode was 20%.

[0176] Comparative Example 1 E N / E P The N / P ratio of the secondary battery of Comparative Example 1 was 1.08.

[0177] Comparative Example 2: Manufacturing of secondary battery A secondary battery was fabricated in the same manner as in Example 1, except that the first and second positive electrode active materials were mixed in a weight ratio of 10:90 to prepare a positive electrode active material. In Comparative Example 2, the loading amount of the positive electrode slurry was 4 mAh / cm. 2 The thickness of the positive electrode active material layer was 122 μm, and the porosity of the positive electrode was adjusted to 28%.

[0178] Comparative Example 2 E N / E P The N / P ratio of the secondary battery of Comparative Example 2 was 1.08.

[0179] Experimental Example Experimental Example 1: Evaluation of capacity retention rate The lithium secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 manufactured above were subjected to cycle charging and discharging using an electrochemical charger / discharger, where one cycle consisted of charging to 4.2 V, 1 / 40 C under conditions of 25°C, CC / CV, and 0.33 C, and then discharging to 2.5 V under conditions of CC and 0.5 C.

[0180] (1) Capacity maintenance rate The capacity retention rate was calculated using the following formula, and the results are shown in Table 1 below.

[0181] Capacity retention rate (%) = {(discharge capacity after N cycles / discharge capacity after 1 cycle)} × 100

[0182] In the above formula, N is an integer of 1 or more.

[0183] (2) Resistance increase rate After one charge / discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charge / discharge device, and after adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference in voltage before and after the pulse application.

[0184] After N cycles of charge and discharge (N is an integer of 1 or more), the resistance after N cycles was calculated using the same method as above, and the resistance increase rate was calculated using the following formula. The results are shown in Table 1 below.

[0185] Resistance increase rate (%) = (resistance after N cycles - initial resistance) / initial resistance x 100 (In the above formula, N is an integer of 1 or more)

[0186] [Table 1]

[0187] Referring to Table 1, it can be seen that the secondary batteries of Examples 1 to 3, which are secondary batteries having the features of the present invention, have a high capacity retention rate and a low resistance increase rate even after multiple charge-discharge cycles. In particular, the secondary battery of Example 2 has significantly excellent life and resistance characteristics even after 900 charge-discharge cycles.

[0188] However, the secondary batteries of Comparative Examples 1 and 2 exhibit a very low capacity retention rate and an excessively high resistance increase rate. N / E P It can be confirmed that the combination of the above significantly improves the life performance and resistance characteristics of the secondary battery.

Claims

1. a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an electrolyte; the positive electrode includes a positive electrode active material, The positive electrode active material includes 15 wt % or more of a first positive electrode active material in a single particle form, the negative electrode includes a carbon-based active material and a silicone-based active material, The weight E of the electrolyte impregnated in the positive electrode Ｐ Weight E of the electrolyte impregnated in the negative electrode Ｎ The proportion of E Ｎ / E Ｐ A secondary battery having a resistance of 0.9 or more.

2. The average particle size (D ５０ 2. The secondary battery according to claim 1, wherein the average particle diameter is 0.1 μm to 5 μm.

3. The secondary battery of claim 1 , wherein the first positive electrode active material comprises a lithium composite transition metal oxide represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ１ Ni ｂ１ Co ｃ１ M １ ｄ１ M ２ ｅ１ O ２ (In the above Chemical Formula 1, M １ is Mn, Al, or a combination thereof; M ２ is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, a1, b1, c1, d1, and e1 are atomic fractions of each independent element, 0.8≦a1≦1.3, 0.8≦b1<1, 0<c1<0.2, 0<d1<0.2, 0≦e1≦0.1, and b1+c1+d1+e1=1.)

4. The secondary battery of claim 1 , wherein the positive electrode active material further comprises a second positive electrode active material in the form of secondary particles.

5. The secondary battery of claim 4 , wherein the second positive electrode active material comprises a lithium composite transition metal oxide represented by the following Chemical Formula 2: [Chemical formula 2] Li ａ２ Ni ｂ２ Co ｃ２ M ３ ｄ２ M ４ ｅ２ O ２ (In the above Chemical Formula 1, M ３ is Mn, Al, or a combination thereof; M ４ is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, a2, b2, c2, d2, and e2 are atomic fractions of each independent element, 0.8≦a2≦1.3, 0.8≦b2<1, 0<c2<0.2, 0<d2<0.2, 0≦e2≦0.1, and b2+c2+d2+e2=1.)

6. 5. The secondary battery according to claim 4, wherein a weight ratio of the first positive electrode active material to the second positive electrode active material is 15:85 to 99:

1.

7. The average particle size (D ５０ ) is the average particle size (D ５０ 5. The secondary battery according to claim 4, wherein the capacitance is greater than 1 / 2.

8. The average particle size (D ５０ ) of the second positive electrode active material relative to the average particle size (D ５０ 5. The secondary battery according to claim 4, wherein the ratio of 0.1 to 0.5 is 1.1 or more.

9. The average particle size (D ５０ 5. The secondary battery according to claim 4, wherein the thickness of the first electrode is 6 μm to 30 μm.

10. 2. The secondary battery according to claim 1, wherein the positive electrode has a porosity of 18% to 32%.

11. 2. The secondary battery according to claim 1, wherein the carbon-based active material comprises at least one selected from the group consisting of graphite, hard carbon, soft carbon, carbon black, graphene, and fibrous carbon.

12. The silicone-based active material is SiO ｘ The secondary battery according to claim 1 , comprising a silicone-based compound represented by (0≦x<2).

13. 2. The secondary battery according to claim 1, wherein the weight ratio of the carbon-based active material to the silicone-based active material is 60:40 to 99:

1.

14. 2. The secondary battery according to claim 1, wherein the porosity of the negative electrode is 20% to 40%.

15. The secondary battery according to claim 1, wherein the N / P ratio calculated by the following mathematical formula C is 1.0 to 1.2: [Mathematical formula C] N / P ratio={(discharge capacity per unit area of ​​the negative electrode) / (discharge capacity per unit area of ​​the positive electrode)}.

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