Lithium secondary battery

Abstract

A lithium secondary battery according to one embodiment includes: a positive electrode including a first positive electrode active material and a second positive electrode active material; and a negative electrode including a first negative electrode active material and a second negative electrode active material. A specific capacity value of the first positive electrode active material is greater than a specific capacity value of the second positive electrode active material, a specific capacity value of the first negative electrode active material is greater than a specific capacity value of the second negative electrode active material, and an R value of the lithium secondary battery according to Formula 1 below is 0.1 to 35. [Formula 1] R = X / Y, in Formula 1, X is the content ratio of the positive electrode active material, and Y is the content ratio of the negative electrode active material.

Description

Technical Field

[0001] The invention relates to a lithium secondary battery. Background Art

[0002] In recent years, research on environmentally friendly vehicles such as electric vehicles (EVs) that can replace fossil fuel-based vehicles, which are one of the main causes of air pollution, has been actively carried out. As a power source for such environmentally friendly vehicles, lithium secondary batteries with high discharge voltage and power stability are mainly used.

[0003] Generally, a lithium secondary battery includes a positive electrode and a negative electrode, and the capacity, energy density, stability, life characteristics, etc. of the secondary battery finally manufactured may be different according to the type and content of the active material contained in the positive electrode and the negative electrode. For example, the energy density and stability of the active material may be in a trade-off relationship with each other, and the capacity and degree of degradation of the finally manufactured electrode may be different according to the type of active material used.

[0004] Therefore, it is necessary to develop a lithium secondary battery having the above characteristics improved and excellent performance. Summary of the invention

[0005] Technical issues to be solved

[0006] An object of one aspect of the present invention is to effectively suppress the difference in the degree of deterioration between the positive electrode and the negative electrode.

[0007] Another object of the present invention is to balance the usage capacity ratio of the positive electrode and the negative electrode in a lithium secondary battery.

[0008] Another object of the present invention is to provide a lithium secondary battery having excellent life characteristics and high energy density.

[0009] Technical Solution

[0010] According to a specific embodiment, a lithium secondary battery includes: a positive electrode, the positive electrode includes a first positive electrode active material and a second positive electrode active material; and a negative electrode, the negative electrode includes a first negative electrode active material and a second negative electrode active material. The specific capacity value of the first positive electrode active material is greater than the specific capacity value of the second positive electrode active material, the specific capacity value of the first negative electrode active material is greater than the specific capacity value of the second negative electrode active material, and the R value of the lithium secondary battery according to the following formula 1 is 0.1 to 35.

[0011] [Formula 1]

[0012] R=X / Y

[0013] In Formula 1, X is the content ratio of the positive electrode active material according to Formula 2 below, and Y is the content ratio of the negative electrode active material according to Formula 3 below.

[0014] [Formula 2]

[0015] X=C X1 / C X2

[0016] In Formula 2, C X1 is the weight ratio of the first positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material, C X2 is the weight ratio of the second positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material.

[0017] [Formula 3]

[0018] Y=C Y1 / C Y2

[0019] In Formula 3, C Y1 is the weight ratio of the first negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material, C Y2 is the weight ratio of the second negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material.

[0020] The first negative electrode active material may include at least one of natural graphite, a silicon-based active material, and a metal-based active material.

[0021] The second negative electrode active material may include at least one of artificial graphite and a low-crystalline carbon-based active material.

[0022] The first negative electrode active material may include a silicon-based active material.

[0023] The second negative electrode active material may include artificial graphite.

[0024] The R value may be 0.62 to 33.

[0025] According to another specific embodiment, a lithium secondary battery includes: a positive electrode, the positive electrode includes a first positive electrode active material and a second positive electrode active material; and a negative electrode, the negative electrode includes a first negative electrode active material and a second negative electrode active material. The specific capacity value of the first positive electrode active material is greater than the specific capacity value of the second positive electrode active material, the first negative electrode active material includes natural graphite, the second negative electrode active material includes artificial graphite, and the R value of the lithium secondary battery according to Formula 1 is 0.1 to 35.

[0026] The R value may be 0.25 to 9.

[0027] In any of the above embodiments, the R value may be from 0.8 to 1.2.

[0028] In any of the above embodiments, the values ​​of X and Y in Formula 1 may be 0.1 to 9, respectively.

[0029] In any of the above embodiments, the value of X in Formula 1 may be 0.3 to 1, and the value of Y in Formula 1 may be 0.1 to 2.

[0030] In any of the above embodiments, the first positive electrode active material may include at least any one of a layered active material and a spinel active material.

[0031] In any of the above embodiments, the second positive electrode active material may include an olivine-type active material.

[0032] In any one of the above embodiments, the first positive active material may be represented by the following Chemical Formula 1.

[0033] [Chemical formula 1]

[0034] Li z Ni a Co b Mn c O2

[0035] In the chemical formula 1, 0.5≤a≤0.98, 0≤b≤0.5, 0≤c≤0.5, and 1≤z≤1.5.

[0036] The second positive active material may be represented by the following Chemical Formula 2.

[0037] [Chemical formula 2]

[0038] LiMePO4

[0039] In the chemical formula 2, Me is one or more elements selected from the group consisting of Co, Ni, Fe and Mn.

[0040] Beneficial Effects

[0041] According to a specific embodiment of the present invention, the imbalance in the degree of degradation of the positive electrode and the negative electrode can be effectively alleviated.

[0042] According to another specific embodiment of the present invention, the usage capacity ratio of the positive electrode and the negative electrode can be kept balanced.

[0043] According to another specific embodiment of the present invention, a lithium secondary battery having excellent lifespan characteristics and high energy density can be provided. DETAILED DESCRIPTION

[0044] Hereinafter, specific embodiments of the present invention will be described in detail. However, specific embodiments of the present invention may be modified into various other forms, and their scope is not limited to the specific embodiments described below. In addition, specific embodiments of the present invention may not only be defined and applied by the composition of the specific embodiments described below, but may also be selectively combined with all or part of each specific embodiment to achieve various modifications.

[0045] Lithium secondary battery

[0046] According to a specific embodiment, a lithium secondary battery includes: a positive electrode, the positive electrode includes a first positive electrode active material and a second positive electrode active material; and a negative electrode, the negative electrode includes a first negative electrode active material and a second negative electrode active material. The specific capacity value of the first positive electrode active material is greater than the specific capacity value of the second positive electrode active material, the specific capacity value of the first negative electrode active material is greater than the specific capacity value of the second negative electrode active material, and the R value of the lithium secondary battery according to the following formula 1 is 0.1 to 35.

[0047] [Formula 1]

[0048] R=X / Y

[0049] In Formula 1, X is the content ratio of the positive electrode active material according to Formula 2 below, and Y is the content ratio of the negative electrode active material according to Formula 3 below.

[0050] [Formula 2]

[0051] X=C X1 / C X2

[0052] In Formula 2, C X1 is the weight ratio of the first positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material, C X2 is the weight ratio of the second positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material.

[0053] [Formula 3]

[0054] Y=C Y1 / C Y2

[0055] In Formula 3, C Y1is the weight ratio of the first negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material, C Y2 is the weight ratio of the second negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material.

[0056] As described above, the energy density and stability of the active material may be in a trade-off relationship, and the capacity and degree of degradation of the final manufactured electrode may be different from each other depending on the type of active material used. For example, compared with active materials with olivine structure such as lithium iron phosphate (LFP)-based positive electrode active materials, active materials with layered structures or spinel structures such as nickel-cobalt-manganese (NCM)-based positive electrode active materials have relatively larger specific capacity values, but due to insufficient structural stability, structural degradation may progress relatively faster during battery use.

[0057] In this regard, when active materials are mixed (blended) and used so that the positive electrode contains two or more active materials with different properties, the degree of deterioration of the positive electrode may differ according to the mixing ratio of the active materials. In addition, when a negative electrode that is not suitable for the active material mixing ratio and degree of deterioration of the positive electrode containing the mixed active material is used to manufacture a secondary battery, the degree of deterioration of the positive electrode and the negative electrode in the secondary battery differs from each other, so that the balance of the use capacity ratio may not be maintained, which may lead to a reduction in the life characteristics and long-term performance of the secondary battery.

[0058] In the lithium secondary battery according to the above specific embodiment, considering the active material mixing ratio, degree of deterioration, etc. of the positive electrode containing active materials with different specific capacity values ​​in a mixed manner, the negative electrode also contains active materials with different specific capacity values ​​in a mixed manner. Specifically, the positive electrode contains a first positive electrode active material with a relatively large specific capacity value and a second positive electrode active material with a relatively small specific capacity value, and the negative electrode contains a first negative electrode active material with a relatively large specific capacity value and a second negative electrode active material with a relatively small specific capacity value.

[0059] Therefore, the lithium secondary battery can effectively alleviate the imbalance of the degradation degree and usage capacity ratio of the two electrodes by including a negative electrode with an active material mixing ratio suitable for the positive electrode containing mixed active materials and a degradation degree, so the life characteristics, energy density, etc. of the secondary battery can be excellent.

[0060] The first negative electrode active material may include at least one of natural graphite, silicon-based active material, and metal-based active material, and the second negative electrode active material may include at least one of artificial graphite and low-crystallinity carbon-based active material. At this time, when the first negative electrode active material includes natural graphite and the second negative electrode active material includes artificial graphite, the natural graphite may be natural graphite having a larger specific capacity value than artificial graphite.

[0061] The silicon-based active material is not particularly limited as long as it is an active material having a larger specific capacity value than the second negative electrode active material. Exemplarily, the silicon-based active material may be selected from at least one of silicon (Si), silicon oxide (SiO x ; 0 < x ≤ 2), the silicon oxide doped with metal or coated with carbon, and silicon-carbon composite (Si-C).

[0062] The metal-based active material is not particularly limited as long as it is an active material having a larger specific capacity value than the second negative electrode active material. Exemplarily, the metal-based active material may be selected from at least one of tin (Sn), tin oxide (SnO x ; 0 < x ≤ 2), and lithium metal (Li-metal).

[0063] The low-crystallinity carbon-based active material is not limited as long as it is an active material having a smaller specific capacity value than the first negative electrode active material. Exemplarily, the low-crystallinity carbon-based active material may be selected from at least one of soft carbon and hard carbon.

[0064] In the lithium secondary battery, the first negative electrode active material may include a silicon-based active material, and the second negative electrode active material may include artificial graphite. In this case, the content of the silicon-based active material in the active materials contained in the negative electrode of the lithium secondary battery may be 3 to 15% by weight, and the content of artificial graphite may be 85 to 97% by weight. In addition, in this case, the R value may be 0.62 to 33.

[0065] A lithium secondary battery according to another specific embodiment includes: a positive electrode including a first positive electrode active material and a second positive electrode active material; and a negative electrode including a first negative electrode active material and a second negative electrode active material. The specific capacity value of the first positive electrode active material is greater than that of the second positive electrode active material, the first negative electrode active material includes natural graphite, the second negative electrode active material includes artificial graphite, and the R value of the lithium secondary battery according to Formula 1 is 0.1 to 35.

[0066] In the lithium secondary battery according to the above-mentioned specific embodiment, considering the active material mixing ratio, degree of deterioration, etc. of the positive electrode containing active materials with different specific capacity values ​​in a mixed manner, the negative electrode also contains natural graphite and artificial graphite in a mixed manner. Specifically, in the lithium secondary battery according to the specific embodiment, the first negative electrode active material contains natural graphite, and the second negative electrode active material contains artificial graphite. At this time, the specific capacity values ​​of the natural graphite and the artificial graphite may be the same or different. That is, the natural graphite may be a natural graphite having a specific capacity value greater than or equal to that of artificial graphite, and may also be a natural graphite having a relatively small specific capacity value.

[0067] Hereinafter, the R value according to the above-mentioned formula 1 will be specifically described.

[0068] The R value is the ratio between the content ratio (X) of the positive electrode active material and the content ratio (Y) of the negative electrode active material in a lithium secondary battery that uses a positive electrode and a negative electrode that contain active materials with different properties from each other in a mixed manner, and refers to the value obtained by dividing the content ratio (X) of the positive electrode active material by the content ratio (Y) of the negative electrode active material.

[0069] The content ratio (X) of the positive electrode active material is the weight ratio (C) of the first positive electrode active material relative to the total weight of the first positive electrode active material and the second positive electrode active material. X1 ) and the weight ratio of the second positive electrode active material (C X2 ) and refers to the weight ratio of the first positive electrode active material (C X1 ) divided by the weight ratio of the second positive electrode active material (C X2 ) value.

[0070] The content ratio (Y) of the negative electrode active material is the weight ratio (C) of the first negative electrode active material relative to the total weight of the first negative electrode active material and the second negative electrode active material. Y1 ) and the weight ratio of the second negative electrode active material (C Y2 ), and refers to the weight ratio of the first negative electrode active material (C Y1 ) divided by the weight ratio of the second negative electrode active material (C Y2 ) value.

[0071] The R value of the lithium secondary battery according to the above specific embodiment may be 0.1 to 35, specifically, it may be 0.1 or more, 0.2 or more, 0.25 or more, 0.4 or more, or 0.62 or more, and may be 33 or less, 11 or less, 10 or less, 9 or less, or 4 or less. The R value of the lithium secondary battery according to one specific embodiment may be 0.1 to 11, 0.2 to 10, 0.25 to 9, or 0.4 to 4. The R value of the lithium secondary battery according to another specific embodiment may be 0.62 to 33.

[0072] The lithium secondary battery according to the above specific embodiment includes a positive electrode and a negative electrode using active materials with different characteristics from each other in a mixed manner, and the ratio between the content ratio (X) of the positive electrode active material and the content ratio (Y) of the negative electrode active material can be substantially the same. That is, in the lithium secondary battery according to the above specific embodiment, the R value can be 0.8 to 1.2. Specifically, in the lithium secondary battery according to the above specific embodiment, the R value can be 0.9 to 1.1, and can be substantially 1.0. When the ratio between the content ratio (X) of the positive electrode active material and the content ratio (Y) of the negative electrode active material in the lithium secondary battery is substantially the same, the difference in the degree of deterioration of the positive and negative electrodes can be effectively alleviated, so that the usage capacity ratio of the positive and negative electrodes can be kept more balanced, thereby significantly improving the life characteristics and long-term performance of the secondary battery.

[0073] In the lithium secondary battery according to the above specific embodiment, the weight ratio of the first positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material (C X1 ) and the weight ratio of the second positive electrode active material (C X2 ) may be 0.1 to 0.9 respectively. In addition, the weight ratio of the first negative electrode active material relative to the total weight of the first negative electrode active material and the second negative electrode active material (C Y1 ) and the weight ratio of the second negative electrode active material (C Y2 ) can be 0.1 to 0.9 respectively.

[0074] Specifically, relative to the total weight of the first positive electrode active material and the second positive electrode active material, the weight ratio of the first positive electrode active material (C X1 ) may be 0.1 to 0.5, and the weight ratio of the second positive electrode active material (C X2 ) may be 0.5 to 0.9. In addition, relative to the total weight of the first negative electrode active material and the second negative electrode active material, the weight ratio of the first negative electrode active material (C Y1 ) may be 0.1 to 0.5, and the weight ratio of the second negative electrode active material (C Y2 ) can be from 0.5 to 0.9.

[0075] In the lithium secondary battery according to the above specific embodiment, the X value and the Y value of Formula 1 may be 0.1 to 9, respectively. Specifically, the X value and the Y value of Formula 1 may be 0.1 to 1.5, 0.1 to 1, 0.2 to 1, 0.3 to 0.7 or 0.3 to 0.5, respectively. Specifically, the X value of Formula 1 may be 0.3 to 1, and the Y value of Formula 1 may be 0.1 to 2. More specifically, the X value of Formula 1 may be 0.3 to 0.7, and the Y value of Formula 1 may be 0.1 to 1.

[0076] When the contents of the first positive electrode active material, the second positive electrode active material, the first negative electrode active material and the second negative electrode active material in the lithium secondary battery are adjusted as described above, the degradation of the electrode can be alleviated due to the excellent stability, thereby providing a lithium secondary battery with improved life characteristics and excellent energy density.

[0077] In the lithium secondary battery according to the above specific embodiment, the first positive electrode active material may include at least any one of a layered active material and a spinel active material, and the second positive electrode active material may include an olivine active material. Exemplarily, the first positive electrode active material may include lithium-transition metal oxides such as lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4) or lithium nickel oxide (LiNiO2), or lithium-transition metal composite oxides in which a part of these transition metals is replaced by other transition metals. In addition, exemplarily, the first positive electrode active material may include an NCM-based positive electrode active material or an LLO (Li rich layered oxides (LLOs), over-lithiated oxides (Over Lithiated Oxides), over-lithiated layered oxides (Over-lithiated layered oxide, OLO))-based positive electrode active material.

[0078] In the lithium secondary battery according to the above specific embodiment, the first positive electrode active material may be represented by the following Chemical Formula 1, and the second positive electrode active material may be represented by the following Chemical Formula 2.

[0079] [Chemical formula 1]

[0080] Li z Ni a Co b Mn c O2

[0081] In the chemical formula 1, 0.5≤a≤0.98, 0≤b≤0.5, 0≤c≤0.5, and 1≤z≤1.5.

[0082] [Chemical formula 2]

[0083] LiMePO4

[0084] In the chemical formula 2, Me is one or more elements selected from the group consisting of Co, Ni, Fe and Mn.

[0085] Exemplarily, the second positive electrode active material may be a lithium iron phosphate (LFP)-based positive electrode active material represented by the chemical formula LiFePO 4 .

[0086] In the lithium secondary battery according to the above specific embodiment, when the positive electrode and the negative electrode each contain three or more active materials having different characteristics from each other, two active materials selected therefrom can satisfy the above characteristics. That is, in the lithium secondary battery according to the above specific embodiment, when the positive electrode contains three or more active materials, two optional active materials therefrom can respectively satisfy the characteristics of the first positive electrode active material and the second positive electrode active material, and when the negative electrode contains three or more active materials, two optional active materials therefrom can respectively satisfy the characteristics of the first negative electrode active material and the second negative electrode active material.

[0087] Exemplarily, when the positive electrode includes three or more active materials having different characteristics from each other, the active material having the first large specific capacity value and the active material having the second large specific capacity value can respectively satisfy the characteristics of the first positive electrode active material and the second positive electrode active material. In addition, when the negative electrode includes three or more active materials having different characteristics from each other, the active material having the first large specific capacity value and the active material having the second large specific capacity value can respectively satisfy the characteristics of the first negative electrode active material and the second negative electrode active material.

[0088] In the lithium secondary battery according to the above specific embodiment, the positive electrode and the negative electrode may each include a current collector and a mixture layer formed on at least one side of the current collector.

[0089] The type, thickness, etc. of the positive electrode current collector and the negative electrode current collector are not particularly limited. For example, the positive electrode current collector may use aluminum foil (Al-Foil), and the negative electrode current collector may use copper foil (Cu-Foil). In addition, for example, the thickness of the positive electrode current collector and the negative electrode current collector may be 10-50 μm, respectively.

[0090] The positive electrode mixture layer and the negative electrode mixture layer are active layers containing active materials that substantially participate in the electrochemical reaction of the secondary battery. The positive electrode mixture layer may contain the above-mentioned first positive electrode active material and the second positive electrode active material, and the negative electrode mixture layer may contain the above-mentioned first negative electrode active material and the second negative electrode active material.

[0091] The positive electrode mixture layer and the negative electrode mixture layer may each further contain a conductive material. The conductive material is not particularly limited, and illustratively, may be at least one selected from the following: graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotubes (CNTs); metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. When the positive electrode mixture layer further contains a conductive material, illustratively, the content of the conductive material may be 0.1-5% by weight based on the total weight of the positive electrode mixture layer. In addition, when the negative electrode mixture layer further contains a conductive material, illustratively, the content of the conductive material may be 0.1-5% by weight based on the total weight of the negative electrode mixture layer.

[0092] The positive electrode mixture layer and the negative electrode mixture layer may each further include a binder. The binder is not particularly limited. Exemplarily, the binder contained in the positive electrode mixture layer may be selected from at least one of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), carboxymethyl cellulose (CMC), ethyl cellulose, acrylic resin, styrene-butadiene rubber (SBR) and polytetrafluoroethylene (PTFE). In addition, exemplarily, the binder contained in the negative electrode mixture layer may be selected from at least one of the following: styrene-butadiene rubber (SBR), fluorine-based rubber, ethylene-propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, silane-based rubber and other rubber-based binders; and cellulose-based binders such as carboxymethyl cellulose (CMC), hydroxypropyl methylcellulose, methyl cellulose or their alkali metal salts (Na, K or Li). When the positive electrode mixture layer further includes a binder, exemplarily, the content of the binder may be 0.1-5% by weight based on the total weight of the positive electrode mixture layer. In addition, when the negative electrode mixture layer further includes a binder, illustratively, the content of the binder may be 0.1-5 wt % based on the total weight of the negative electrode mixture layer.

[0093] In the lithium secondary battery according to the above specific embodiment, a separator may not be included between the positive electrode and the negative electrode, and a separator may be further included. When the lithium secondary battery further includes a separator, the separator may be a polyolefin-based polymer separator such as polyethylene, polypropylene, glass fiber, polyester, polytetrafluoroethylene, or a combination thereof, and may be in the form of a non-woven fabric or a woven fabric. In addition, the separator may be coated with a composition comprising a ceramic component, etc. to ensure heat resistance or mechanical strength, and may optionally be composed of a single layer or a multilayer structure. As the separator, a separator having the above-mentioned compound, structure, etc. may be applied, but is not limited thereto.

[0094] The lithium secondary battery according to the above specific embodiment may further include a solid electrolyte. That is, the lithium secondary battery may include a solid electrolyte between the positive electrode and the negative electrode without including a separator. The solid electrolyte is not particularly limited, and illustratively, the solid electrolyte may be an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or a polymer-based solid electrolyte.

[0095] Hereinafter, the method for manufacturing the lithium secondary battery according to the above specific embodiment will be described in detail.

[0096] The method for manufacturing the lithium secondary battery according to the above specific embodiment is not particularly limited. For example, in the case of a positive electrode, a positive electrode slurry containing the above first positive electrode active material and the second positive electrode active material is coated on a positive electrode collector by a method such as rod coating, casting or spraying, and the positive electrode slurry is dried at 100-140° C., thereby a positive electrode having a positive electrode mixture layer formed on the surface of the positive electrode collector can be manufactured.

[0097] In addition, in the case of a negative electrode, a negative electrode slurry containing the above-mentioned first negative electrode active material and the second negative electrode active material is coated on a negative electrode collector by a method such as rod coating, casting or spraying, and the negative electrode slurry is dried at 80-120° C., thereby forming a negative electrode having a negative electrode mixture layer formed on the surface of the negative electrode collector.

[0098] The positive electrode slurry and the negative electrode slurry may each further include a solvent. For example, the solvent may be dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water. At this time, considering the coating thickness of the slurry, the manufacturing yield, etc., the amount of the solvent used is not particularly limited as long as it is sufficient to dissolve or disperse the components of the slurry and make the slurry have a viscosity that can show excellent thickness uniformity when applied to the current collector.

[0099] When the lithium secondary battery according to the above specific embodiment does not further include a solid electrolyte, the lithium secondary battery may be manufactured by inserting a secondary battery cell including the above positive electrode and negative electrode into a battery case and then injecting an electrolyte.

[0100] The battery housing may be a battery housing commonly used in the art. Exemplarily, the battery housing may be cylindrical, prismatic, soft-pack or coin-shaped, specifically soft-pack. In addition, the battery housing may be a structure stacked with an insulating layer, an adhesive layer, a metal film, and the like. The metal film may include aluminum (Al) or the like to ensure the mechanical strength of the housing and block moisture and oxygen.

[0101] The electrolyte may include an organic solvent and a lithium salt. The organic solvent acts as a medium that allows the ions involved in the electrochemical reaction of the battery to move. For example, the following solvents may be used alone or in combination with two or more of the following solvents: carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents or aprotic solvents, and the mixing ratio when two or more solvents are mixed can be appropriately adjusted according to the desired battery performance. The lithium salt is a substance that is dissolved in an organic solvent and acts as a source of lithium ions in the battery, can realize the basic operation of a lithium secondary battery and promote the movement of lithium ions between the positive electrode and the negative electrode. As the lithium salt, a known substance may be used at a concentration suitable for the purpose. The electrolyte may further include a known solvent as needed to improve charge and discharge characteristics and flame retardant properties, etc., and may include a known additive.

[0102] Example

[0103] <Manufacturing of Secondary Battery>

[0104] 1. Example 1 to Example 3

[0105] 95 wt% of the NCM-based positive electrode active material (Li(Ni 0.5 Co 0.2 Mn 0.3 )O2) and LFP-based positive active materials (LiFePO4) as a mixed positive active material of the first positive active material and the second positive active material, 2 wt% of a conductive material (carbon black), and 3 wt% of a binder (polyvinylidene fluoride; PVDF) were added to an N-methylpyrrolidone (NMP) solvent to prepare a slurry, and the slurry was heated at 16 mg / cm 2 The positive electrode was prepared by coating on an aluminum foil having a thickness of 20 μm and then drying at 135° C. In addition, 95 wt % of a mixed negative electrode active material including natural graphite and artificial graphite as a first negative electrode active material and a second negative electrode active material, 2 wt % of a conductive material (carbon black), and 3 wt % of a binder (carboxymethyl cellulose; CMC) were added to distilled water to prepare a slurry, and the slurry was heated at 8 mg / cm 2 The negative electrode was manufactured by coating on a copper foil having a thickness of 10 μm and then drying at 115° C. Thereafter, a polyolefin separator was inserted between the positive electrode and the negative electrode to manufacture the secondary battery cells of Examples 1 to 3.

[0106] At this time, the mixed positive electrode active material and the mixed negative electrode active material were mixed at a weight ratio shown in Table 1 below, and the X value, Y value, and R value according to the following Formulas 1 to 3 were calculated.

[0107] [Formula 1]

[0108] R=X / Y

[0109] In Formula 1, X is the content ratio of the positive electrode active material according to Formula 2 below, and Y is the content ratio of the negative electrode active material according to Formula 3 below.

[0110] [Formula 2]

[0111] X=C X1 / C X2

[0112] In Formula 2, C X1 is the weight ratio of the first positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material, C X2 is the weight ratio of the second positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material.

[0113] [Formula 3]

[0114] Y=C Y1 / C Y2

[0115] In Formula 3, C Y1 is the weight ratio of the first negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material, C Y2 is the weight ratio of the second negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material.

[0116] 2. Comparative Example 1 and Comparative Example 2

[0117] Secondary battery cells of Comparative Examples 1 and 2 were manufactured in the same manner as in Examples 1 to 3, except that, as shown in Table 1 below, only natural graphite or artificial graphite was included as the negative electrode active material.

[0118] <Evaluation of Secondary Batteries - Capacity Retention Rate>

[0119] The secondary battery cell manufactured as described above is placed in a soft pack for a secondary battery, and then an electrolyte solution in which 1M LiPF6 is dissolved in a solvent mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) is injected and sealed to manufacture a soft pack type lithium secondary battery. The prepared soft pack type lithium secondary battery is used as a secondary battery sample of the embodiment and the comparative example.

[0120] For the secondary battery manufactured as described above, the capacity retention rate in the range of discharge depth (DOD) 100 (state of charge (SOC) 0-100) was evaluated in a chamber maintained at 25°C. Under constant current / constant voltage (CC / CV) conditions, the battery was charged at 0.3C to a voltage corresponding to SOC 100 and then cut off at 0.05C. Then, under constant current (CC) conditions, the battery was discharged at 0.3C to a voltage corresponding to SOC 0, and its discharge capacity was measured. After repeating the above steps for 500 cycles, the discharge capacity retention rate relative to the initial discharge capacity was measured as a percentage (%) according to the following formula 4, and the results are shown in the following Table 1.

[0121] [Formula 4]

[0122]

[0123] [Table 1]

[0124]

[0125]

[0126] Referring to Table 1, as a lithium secondary battery using a positive electrode containing active materials having different characteristics in a mixed manner, in the secondary batteries of Examples 1 to 3 in which the negative electrode also uses a negative electrode containing active materials having different characteristics in a mixed manner, the capacity retention rate value is relatively high, and therefore excellent life characteristics are exhibited.

[0127] Therefore, it is judged that when the positive electrode and the negative electrode each contain active materials having different characteristics from each other in a mixed manner and adjust the content ratio so that the R value according to Formula 1 is 0.1 to 35 by considering the respective active material characteristics, the life characteristics of the secondary battery can be improved to an excellent level.

Claims

1. A lithium secondary battery, comprising: A positive electrode, the positive electrode comprising a first positive electrode active material and a second positive electrode active material; as well as a negative electrode, the negative electrode comprising a first negative electrode active material and a second negative electrode active material, The specific capacity of the first positive electrode active material is greater than the specific capacity of the second positive electrode active material. The specific capacity value of the first negative electrode active material is greater than the specific capacity value of the second negative electrode active material, The lithium secondary battery has an R value of 0.1 to 35 according to the following Formula 1, [Formula 1] R=X / Y In Formula 1, X is the content ratio of the positive electrode active material according to Formula 2 below, and Y is the content ratio of the negative electrode active material according to Formula 3 below, [Formula 2] X=C X1 / C X2 In Formula 2, C X1 is the weight ratio of the first positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material, C X2 is the weight ratio of the second positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material, [Formula 3] Y=C Y1 / C Y2 In Formula 3, C Y1 is the weight ratio of the first negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material, C Y2 is the weight ratio of the second negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material.

2. The lithium secondary battery according to claim 1, wherein The first negative electrode active material includes at least one of natural graphite, a silicon-based active material, and a metal-based active material, and the second negative electrode active material includes at least one of artificial graphite and a low-crystalline carbon-based active material.

3. The lithium secondary battery according to claim 1, wherein The first negative electrode active material includes a silicon-based active material, and the second negative electrode active material includes artificial graphite.

4. The lithium secondary battery according to claim 3, wherein: The R value is 0.62 to 33.

5. A lithium secondary battery comprising: A positive electrode, the positive electrode comprising a first positive electrode active material and a second positive electrode active material; as well as a negative electrode, the negative electrode comprising a first negative electrode active material and a second negative electrode active material, The specific capacity of the first positive electrode active material is greater than the specific capacity of the second positive electrode active material. The first negative electrode active material comprises natural graphite, The second negative electrode active material comprises artificial graphite, The lithium secondary battery has an R value of 0.1 to 35 according to the following Formula 1, [Formula 1] R=X / Y In Formula 1, X is the content ratio of the positive electrode active material according to Formula 2 below, and Y is the content ratio of the negative electrode active material according to Formula 3 below, [Formula 2] X=C X1 / C X2 In Formula 2, C X1 is the weight ratio of the first positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material, C X2 is the weight ratio of the second positive electrode active material to the total weight of the first positive electrode active material and the second positive electrode active material, [Formula 3] Y=C Y1 / C Y2 In Formula 3, C Y1 is the weight ratio of the first negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material, C Y2 is the weight ratio of the second negative electrode active material to the total weight of the first negative electrode active material and the second negative electrode active material.

6. The lithium secondary battery according to claim 5, wherein: The R value is 0.25 to 9.

7. The lithium secondary battery according to claim 1 or 5, wherein: The R value is 0.8 to 1.

2.

8. The lithium secondary battery according to claim 1 or 5, wherein: The values ​​of X and Y in Formula 1 are 0.1 to 9, respectively.

9. The lithium secondary battery according to claim 1 or 5, wherein: The value of X in Formula 1 is 0.3 to 1, and the value of Y in Formula 1 is 0.1 to 2.

10. The lithium secondary battery according to claim 1 or 5, wherein: The first positive electrode active material includes at least one of a layered active material and a spinel active material, and the second positive electrode active material includes an olivine active material.

11. The lithium secondary battery according to claim 1 or 5, wherein: The first positive electrode active material is represented by the following chemical formula 1, and the second positive electrode active material is represented by the following chemical formula 2: [Chemical formula 1] Li z Ni a Co b Mr c O2 In the chemical formula 1, 0.5≤a≤0.98, 0≤b≤0.5, 0≤c≤0.5, 1≤z≤1.5, [Chemical formula 2] LiMePO4 In the chemical formula 2, Me is one or more elements selected from the group consisting of Co, Ni, Fe and Mn.

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