Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery including a positive electrode, a separator, and a negative electrode, wherein the positive electrode includes a positive electrode active material and a positive electrode conductive material, the negative electrode includes a negative electrode active material and a negative electrode conductive material, the positive electrode active material includes a lithium composite transition metal compound including nickel (Ni) and cobalt (Co), the negative electrode active material includes silicon oxide, artificial graphite, and natural graphite, the positive electrode conductive material includes a dot-like conductive material, a linear conductive material, and a sheet-like conductive material, and the negative electrode conductive material includes a dot-like conductive material, a linear conductive material, and a sheet-like conductive material.

Description

[Technical Field]

[0001] This specification claims the benefit of the filing date of Korean Patent Application No. 10-2022-0129606 filed with the Korean Intellectual Property Office on October 11, 2022, and Korean Patent Application No. 10-2023-0129061 filed with the Korean Intellectual Property Office on September 26, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery. [Background technology]

[0003] Secondary batteries are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs), which are powered by an electrical drive source.

[0004] Such secondary batteries have the primary advantage of dramatically reducing the use of fossil fuels, as well as the advantage of not producing any by-products associated with energy use, and are therefore attracting attention as a new energy source that is environmentally friendly and can improve energy efficiency.

[0005] In general, a secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, etc. Furthermore, the electrodes such as the positive electrode and the negative electrode may have an electrode active material layer provided on a current collector.

[0006] As secondary batteries become more widely used, various battery performances are being sought. While attempts to improve battery performance have been made to optimize the composition of electrode active material layers, the selection or combination of materials may improve some battery performance, but may actually degrade other performance. Therefore, research is needed to select or combine materials appropriately depending on the secondary battery performance to be improved. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a lithium secondary battery with improved resistance characteristics. [Means for solving the problem]

[0008] One embodiment of the present invention comprises: A lithium secondary battery including a positive electrode, a separator, and a negative electrode, the positive electrode includes a positive electrode active material and a positive electrode conductive material, the negative electrode includes a negative electrode active material and a negative electrode conductive material, the positive electrode active material includes a lithium composite transition metal compound including nickel (Ni) and cobalt (Co), The negative electrode active material includes silicon oxide, artificial graphite, and natural graphite, the positive electrode conductive material includes a dot-shaped conductive material, a linear conductive material, and a sheet-shaped conductive material; The negative electrode conductive material includes a dot-shaped conductive material, a linear conductive material, and a sheet-shaped conductive material. [Effects of the Invention]

[0009] According to the embodiments described in this specification, the positive electrode and the negative electrode use specific types of active materials and contain point-like conductive materials, linear conductive materials, and sheet-like conductive materials as conductive materials, thereby improving the conductivity of both the positive electrode and the negative electrode, significantly improving the cell resistance characteristics, and providing an improved rapid charging effect. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a graph showing the resistance value depending on the state of charge (SOC) of the batteries produced in Examples 1 to 3 and Comparative Examples 1 to 6. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in more detail below to facilitate understanding of the present invention. The present invention may be realized in various different forms and is not limited to the embodiments described herein. In this regard, the terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are 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 describe their invention.

[0012] It will be understood that in this specification, the terms "comprise," "provide," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0013] Furthermore, when a part such as a layer is said to exist "on" or "above" another part, this includes not only the case where it exists "directly above" the other part, but also the case where there is another part between them. Conversely, when a part is said to exist "directly above" another part, it means that there is no other part between them. Furthermore, being "on" or "above" a reference part means being located above or below the reference part, and does not necessarily mean being located "above" or "above" the direction opposite to gravity.

[0014] A lithium secondary battery according to one embodiment of the present specification includes a positive electrode, a separator, and a negative electrode, wherein the positive electrode includes a positive electrode active material and a positive electrode conductive material, the negative electrode includes a negative electrode active material and a negative electrode conductive material, the positive electrode active material includes a lithium composite transition metal compound including nickel (Ni) and cobalt (Co), and the negative electrode active material includes silicon oxide, artificial graphite, and natural graphite. In addition, the positive electrode conductive material includes a dot-like conductive material, a linear conductive material, and a sheet-like conductive material, and the negative electrode conductive material includes a dot-like conductive material, a linear conductive material, and a sheet-like conductive material.

[0015] The present inventors have discovered that when the above-mentioned active materials are used in the positive electrode and the negative electrode, and when dot-like conductive materials, linear conductive materials, and sheet-like conductive materials are added to the positive electrode and dot-like conductive materials, linear conductive materials, and sheet-like conductive materials are added to the negative electrode, the cell resistance can be significantly improved, and have completed the present invention.

[0016] According to one embodiment, the lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) may contain nickel in an amount of 80 mol % or more, for example, 80 mol % or more but less than 100 mol %, of the metals other than lithium. When the nickel content is high, the efficiency of the positive electrode can be increased, and a high energy density of the battery can be achieved.

[0017] According to one embodiment, the lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) may further contain at least one of manganese and aluminum. Specifically, the lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) may be represented by the following Chemical Formula 1:

[0018] [Chemical formula 1] Li a Ni (1-x-y) Co x M1 y M2 w O2 In Chemical Formula 1, 1.0≦a≦1.5, 0 <x≦0.2、0≦y≦0.2、0≦w≦0.1、0<x+y≦0.2であり、 M1 is one or more metals selected from Mn and Al; M2 is one or more metallic elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

[0019] According to one embodiment, the positive electrode may contain 90 to 100 parts by weight of the lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) based on 100 parts by weight of the positive electrode active material.

[0020] In one embodiment of the present specification, the silicon oxide is SiO x (0 < x < 2).

[0021] The silicon oxide may be included in an amount of 1 to 40 parts by weight, for example, 1 to 20 parts by weight, based on 100 parts by weight of the negative electrode active material.

[0022] As the silicon oxide, SiO x (0 < x < 2), the active material may be silicon oxide composite particles containing SiO x (0 < x < 2) and pores.

[0023] The SiO x (0 < x < 2) corresponds to a matrix within the silicon oxide composite particles. The SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the x corresponds to the number ratio of O to Si contained in the SiO x (0 < x < 2). When the silicon oxide composite particles contain the SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0024] The silicon oxide composite particles may further contain at least one of a Mg compound and a Li compound. The Mg compound and the Li compound may correspond to a matrix within the silicon oxide composite particles.

[0025] The Mg compound and / or the Li compound may be present inside and / or on the surface of the SiO x (0 < x < 2). The initial efficiency of the battery can be improved by the Mg compound and / or the Li compound.

[0026] The Mg compound may include at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The Mg silicate may include at least one of Mg2SiO4 and MgSiO3. The Mg silicide may include Mg2Si. The Mg oxide may include MgO.

[0027] In one embodiment of the present specification, the Mg element may be contained at 0.1% to 20% by weight, or may be contained at 0.1% to 10% by weight, based on 100% by weight of the total weight of the silicon oxide. Specifically, the Mg element may be contained at 0.5% to 8% by weight, or 0.8% to 4% by weight. When the above range is satisfied, the Mg compound can be contained in an appropriate content in the silicon oxide, so that the volume change of the silicon oxide during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0028] The Li compound may include at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may include at least one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may include Li7Si2. The Li oxide may include Li2O.

[0029] In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be classified into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate may exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 in the silicon oxide composite particles, and the amorphous lithium silicate is Li a Si b Oc It may be in the form of (2≦a≦4, 0<b≦2, 2≦c≦5), and is not limited to the above form.

[0030] In one embodiment of the present specification, the Li element may be contained in an amount of 0.1% to 20% by weight, or may be contained in an amount of 0.1% to 10% by weight, based on 100% by weight of the total weight of the silicon oxide active material. Specifically, the Li element may be contained in an amount of 0.5% to 8% by weight, and more specifically, may be contained in an amount of 0.5% to 4% by weight. When the above range is satisfied, the Li compound can be contained in a suitable content in the silicon oxide active material, so that the volume change of the negative electrode active material during charging and discharging of the battery can be easily suppressed, and the discharge capacity and initial efficiency of the battery can be improved.

[0031] The content of the Mg element or Li element can be confirmed by ICP (inductively coupled plasma) analysis. For the ICP analysis, after accurately collecting a certain amount (about 0.01 g) of the negative electrode active material, it is transferred to a platinum crucible, and nitric acid, hydrofluoric acid, and sulfuric acid are added and completely decomposed on a hot plate. Then, using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300), at the wavelength specific to the Mg element or Li element, the intensity of the standard solution prepared using a standard solution (5 mg / kg) is measured to create a reference calibration curve. Then, the pretreated sample solution and the blank sample are introduced into the instrument, the intensity of each is measured to calculate the actual intensity, and after calculating the concentration of each component with respect to the created calibration curve, it is converted so that the total of the whole becomes the theoretical value, and the content of the Mg element or Li element of the manufactured silicon oxide active material can be analyzed.

[0032] In one embodiment of the present specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon oxide composite particles. The carbon layer imparts electrical conductivity to the silicon oxide composite particles, thereby improving the initial efficiency, life characteristics, and capacity characteristics of a secondary battery including a negative electrode active material containing the silicon oxide composite particles. The total weight of the carbon layer may be 5 wt % to 40 wt % based on 100 wt % of the total weight of the silicon oxide composite particles.

[0033] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0034] The average particle size (D50) of the silicon oxide active material may be 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically 4 μm to 10 μm. When the average particle size (D50) of the silicon oxide active material is within this range, side reactions between the silicon oxide composite particles and the electrolyte are controlled, and the discharge capacity and initial efficiency of the battery can be effectively achieved.

[0035] In this specification, the average particle size (D50) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve of the particles. The average particle size (D50) can be measured, for example, using a laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0036] In one embodiment of the present specification, the artificial graphite and the natural graphite may be included in an amount of 60 parts by weight or more and 99 parts by weight or less of the carbon-based active material based on 100 parts by weight of the negative electrode active material. The artificial graphite and the natural graphite may be included in a weight ratio of 1:9 to 9:1, for example, 2:8 to 8:2, specifically 3:7 to 7:3.

[0037] According to one embodiment, the positive electrode conductive material includes dot-like conductive materials, linear conductive materials, and sheet-like conductive materials, and the negative electrode conductive material includes dot-like conductive materials, linear conductive materials, and sheet-like conductive materials. According to this embodiment, it is sufficient that both the positive electrode and the negative electrode include dot-like conductive materials, linear conductive materials, and sheet-like conductive materials, and these do not need to be of the same type or composition. The dot-like conductive materials, linear conductive materials, and sheet-like conductive materials included in the positive electrode and the negative electrode may be the same type or different types.

[0038] The total amount of the dot-like conductive material, linear conductive material, and sheet-like conductive material may be 0.1 to 5 parts by weight based on 100 parts by weight of each of the positive electrode active material layer and the negative electrode active material layer. For example, it may be preferably 0.2 to 2 parts by weight, or 0.2 to 4.5 parts by weight. When the dot-like conductive material, linear conductive material, and sheet-like conductive material are mixed in the amounts described above, the sheet-like conductive material, when mixed with the binder, fills the pores between the active material particles, improving physical contact between the active materials, reducing interfacial resistance, and improving adhesion between the lower positive electrode active material and the current collector. Furthermore, the linear conductive material and sheet-like conductive material improve the conductive path, increasing electrical conductivity and improving diffusion resistance. Therefore, improving resistance at the interface between the current collector and the active material layer can improve cell resistance and high-temperature durability.

[0039] The dot-like conductive material refers to a conductive material having a spherical particle shape and a diameter (D50) in the range of 10 nm to 500 nm, and examples thereof include graphite such as natural graphite and artificial graphite; and carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; and the dot-like conductive material may contain any one or more of these.

[0040] The linear conductive material refers to a conductive material having an elliptical particle shape and an aspect ratio (ratio of length to diameter) in the range of 50 to 650, and examples thereof include conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes (CNTs) such as single-walled carbon nanotubes and multi-walled carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives, and the linear conductive material may contain any one or more of these.

[0041] The sheet-like conductive material means a conductive material having a two-dimensional axis and an aspect ratio of 1:1 to 1:10, and examples thereof include graphene and graphite.

[0042] According to one embodiment, the positive electrode conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer containing the positive electrode active material. The negative electrode conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the negative electrode active material layer containing the negative electrode active material. This range has the advantage of further increasing the degree of improvement in cell resistance by improving electrical conductivity within the electrode.

[0043] According to one embodiment, the content ratio of the dot-like conductive material, the linear conductive material, and the sheet-like conductive material contained in the positive electrode conductive material or the negative electrode conductive material may be 0.3 parts by weight to 2 parts by weight of the dot-like conductive material, 0.01 parts by weight to 1 part by weight of the linear conductive material, and 0.5 parts by weight to 3 parts by weight of the sheet-like conductive material, based on 100 parts by weight of the positive electrode active material layer or the negative electrode active material layer.

[0044] The positive electrode and the negative electrode may be of the same type or different types.

[0045] According to one embodiment, the negative electrode may include a current collector and a negative electrode active material layer provided on the current collector.

[0046] The negative electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 80 parts by weight or more and 90 parts by weight or less, relative to 100 parts by weight of the negative electrode active material layer.

[0047] According to one embodiment of the present specification, the negative electrode active material layer may further contain a negative electrode binder in addition to the negative electrode active material and the negative electrode conductive material.

[0048] The negative electrode binder may improve adhesion between negative electrode active material particles and between the negative electrode active material particles and the negative electrode current collector. Any material known in the art may be used as the negative electrode binder. Non-limiting examples of the negative electrode binder include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or various copolymers thereof.

[0049] The negative electrode binder may be included in an amount of 0.1 parts by weight to 20 parts by weight, for example, preferably 0.3 parts by weight to 20 parts by weight, more preferably 0.5 parts by weight to 10 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0050] In one embodiment of the present specification, the negative electrode active material layer may have a thickness of 5 μm or more and 500 μm or less.

[0051] In one embodiment of the present specification, the negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but is not limited thereto.

[0052] In one embodiment of the present specification, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the lithium composite transition metal compound containing nickel (Ni) and cobalt (Co). The positive electrode active material layer may have a thickness of 20 μm to 500 μm.

[0053] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive, and may be, for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may typically have a thickness of 1 to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material, and may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0054] In one embodiment, the positive electrode active material may be contained in an amount of 80 parts by weight to 99.9 parts by weight, preferably 80 parts by weight to 99 parts by weight, relative to 100 parts by weight of the positive electrode active material layer.

[0055] According to a further embodiment of the present specification, the positive electrode active material layer may further include a positive electrode binder.

[0056] The positive electrode binder may serve to improve adhesion between positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector. Any positive electrode binder known in the art may be used, and non-limiting examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination.

[0057] The positive electrode binder may be included in an amount of 0.1 parts by weight to 50 parts by weight, for example, preferably 0.3 parts by weight to 35 parts by weight, more preferably 0.5 parts by weight to 20 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0058] The positive and negative electrodes can be fabricated by a conventional method for fabricating positive and negative electrodes, except for using the positive and negative electrode active materials and conductive materials described above. Specifically, they can be fabricated by coating a composition for forming an active material layer containing the active material and, optionally, a binder and conductive material, on a current collector, followed by drying and rolling. The types and contents of the positive and negative electrode active materials, binder, and conductive material are as described above. The solvent may be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of solvent used should be sufficient to dissolve or disperse the active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to provide a viscosity that allows excellent thickness uniformity when applied to fabricate positive and negative electrodes. Alternatively, the positive electrode and the negative electrode can be produced by casting the active material layer-forming composition on a separate support, peeling the composition from the support, and laminating the resulting film on a current collector.

[0059] The positive electrode and the negative electrode may further contain additional additives as needed, such as a thickener, such as sodium carboxymethyl cellulose (Na-CMC), lithium carboxymethyl cellulose (Li-CMC), or cellulose nanofiber (CNF).

[0060] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferred that the separator exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification. Specifically, porous polymer films, such as those made from polyolefin 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, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0061] Examples of the electrolyte include, but are not limited to, 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 manufacturing lithium secondary batteries.

[0062] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0063] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0064] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be used more preferably.

[0065] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0066] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0067] A lithium secondary battery according to one embodiment of the present invention includes an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte.

[0068] According to a further embodiment of the present invention, there is provided a battery module including the above-described lithium secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and therefore can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0069] The lithium secondary battery according to the embodiment of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, as well as portable devices such as mobile phones, laptops, and digital cameras. For example, 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); or power storage systems.

[0070] Below, preferred examples are presented to help understand the present invention, but these examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0071] Example 1 Anode active materials (SiO included 5 parts by weight based on 100 parts by weight of the total anode active materials) including SiO and carbon-based active materials (including artificial graphite and natural graphite), three conductive materials (including carbon black, CNT, and graphene), a binder (SBR), and a thickener (CMC) were added to a distilled water solvent in a weight ratio of 95:2:2:1 to form anode slurry. The anode slurry was coated onto a 15 μm-thick copper foil to a dry thickness of 130 μm and then dried to prepare anodes.

[0072] The conductive material used in the negative electrode active material layer was prepared by mixing a dot-like conductive material (carbon black), a linear conductive material (CNT), and a sheet-like conductive material (graphene) in a weight ratio of 0.95:0.05:1.0 based on 100 parts by weight of the negative electrode active material.

[0073] Ni-based cathode active material (Li1.0 Ni 0.86 Co 0.08 Mn 0.06 A positive electrode active material layer-forming composition including a positive electrode slurry prepared by dissolving O2, a conductive material (including carbon black, CNT, and graphene), and a binder (PVDF) in a methylpyrrolidone (NMP) solvent at a weight ratio of 97.0:1:2 was coated onto a 12 μm-thick aluminum foil to a dry thickness of 120 μm, and then dried to prepare a positive electrode.

[0074] The conductive material used in the positive electrode active material layer was prepared by mixing a dot-like conductive material (carbon black), a linear conductive material (CNT), and a sheet-like conductive material (graphene) in a weight ratio of 0.35:0.05:0.6 based on 100 parts by weight of the positive electrode active material.

[0075] The positive and negative electrodes were stacked with a separator interposed therebetween, and an electrolyte solution having a composition of 1M LiPF6, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 3 / 7), and vinylene carbonate (VC) / propane sultone (PS) (containing 3 parts by weight and 1.5 parts by weight, respectively, based on 100 parts by weight of the electrolyte) was injected to prepare a battery.

[0076] The fabricated batteries were set to each SOC (%), and the resistance characteristics were measured under pulse discharge conditions of 2.5 C for 10 seconds. The results are shown in Figure 1.

[0077] Example 2 Ni-based cathode active material (Li 1.0 Ni 0.86 Co 0.08 Mn 0.06A cathode was manufactured by coating a cathode active material layer-forming composition including a cathode slurry prepared by dissolving a 93.5:4.5:2 weight ratio of carbon black (O2), a conductive material (including carbon black, CNT, and graphene), and a binder (PVDF) in a methylpyrrolidone (NMP) solvent onto a 12 μm-thick aluminum foil to a dry thickness of 120 μm and then drying the coated aluminum foil. The cathode was manufactured in the same manner as in Example 1, except that the conductive material used in the cathode active material layer was prepared by mixing a dot-like conductive material (carbon black), a linear conductive material (CNT), and a sheet-like conductive material (graphene) in a weight ratio of 0.2:1.2:3.1 based on 100 parts by weight of the cathode active material.

[0078] Example 3 A negative electrode was fabricated by dissolving a negative electrode active material (including SiO and a carbon-based active material (including artificial graphite and natural graphite) in an amount of 5 parts by weight based on 100 parts by weight of the total negative electrode active material), three conductive materials (including carbon black, CNT, and graphene), a binder (SBR), and a thickener (CMC) in a distilled water solvent in a weight ratio of 90:7:2:1 to form a negative electrode slurry. The negative electrode was then coated onto a 15 μm-thick copper foil to a dry thickness of 130 μm and dried to form a negative electrode. The negative electrode was fabricated in the same manner as in Example 1, except that the conductive material used in the negative electrode active material layer was prepared by mixing a dot-like conductive material (carbon black), a linear conductive material (CNT), and a sheet-like conductive material (graphene) in a weight ratio of 2.5:1.2:3.3 based on 100 parts by weight of the negative electrode active material.

[0079] Comparative Example 1 The same procedure as in Example 1 was carried out, except that the dot-like conductive material was used alone for both the positive electrode and the negative electrode.

[0080] Comparative Example 2 The same procedure as in Example 1 was carried out, except that linear conductive materials were used alone for both the positive and negative electrodes.

[0081] Comparative Example 3 The same procedure as in Example 1 was carried out, except that the sheet-shaped conductive material was used alone for both the positive electrode and the negative electrode.

[0082] Comparative Example 4 The same procedure as in Example 1 was carried out, except that dot-shaped conductive materials and linear conductive materials were used as the negative electrode conductive materials.

[0083] Comparative Example 5 The same procedure as in Example 1 was carried out, except that a linear conductive material and a sheet-shaped conductive material were used as the negative electrode conductive material.

[0084] Comparative Example 6 The same procedure as in Example 1 was carried out, except that dot-like conductive materials and sheet-like conductive materials were used as the negative electrode conductive materials.

[0085] 1 shows the resistance values ​​as a function of the state of charge (SOC) of the batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 6. It can be seen that Examples 1 to 3 exhibit superior resistance characteristics at all states of charge (SOC) compared to Comparative Examples 1 to 6. In this case, the resistance was measured by charging the manufactured cells at 0.33 C with constant current / constant voltage (CC / CV) up to 4.2 V (cutoff at 0.05 C) and discharging at 0.33 C with constant current (CC) (cutoff at 2.5 V) three times, then discharging at 0.33 C to set the SOC (%), and pulse discharging at 2.5 C for 10 seconds.

Claims

1. A lithium secondary battery including a positive electrode, a separator, and a negative electrode, the positive electrode includes a positive electrode active material and a positive electrode conductive material, the negative electrode includes a negative electrode active material and a negative electrode conductive material, The positive electrode active material includes a lithium composite transition metal compound including nickel (Ni) and cobalt (Co), The negative electrode active material includes silicon oxide, artificial graphite, and natural graphite, the positive electrode conductive material includes a dot-shaped conductive material, a linear conductive material, and a sheet-shaped conductive material; The negative electrode conductive material includes a dot-like conductive material, a linear conductive material, and a sheet-like conductive material.

2. 2. The lithium secondary battery according to claim 1, wherein the lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) contains 80 mol % or more of nickel among metals other than lithium.

3. The lithium secondary battery according to claim 1 , wherein the lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) further contains at least one of manganese and aluminum.

4. The lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) is represented by the following Chemical Formula 1: [Chemical formula 1] Li ａ Ni （１－ｘ－ｙ） Co ｘ M1 ｙ M2 ｗ O ２ In Chemical Formula 1, 1.0≦a≦1.5, 0<x≦0.2, 0≦y≦0.2, 0≦w≦0.1, 0<x+y≦0.2, M1 is one or more metals selected from Mn and Al; 2. The lithium secondary battery according to claim 1, wherein M2 is one or more metal elements selected from the group consisting of Ba, Ca, Zr, Ti, Mg, Ta, Nb, and Mo.

5. 2. The lithium secondary battery of claim 1, wherein the positive electrode comprises 90 to 100 parts by weight of the lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) based on 100 parts by weight of the positive electrode active material.

6. The silicon oxide is SiO ｘ 2. The lithium secondary battery according to claim 1, wherein x is 0<x<2.

7. 2. The lithium secondary battery of claim 1, wherein the silicon oxide is contained in an amount of 1 to 40 parts by weight based on 100 parts by weight of the negative electrode active material.

8. 2. The lithium secondary battery of claim 1, wherein the positive electrode conductive material is included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the positive electrode active material layer containing the positive electrode active material, and the negative electrode conductive material is included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the negative electrode active material layer containing the negative electrode active material.

9. 2. The lithium secondary battery according to claim 1, wherein the dot-like conductive material comprises at least one material selected from the group consisting of graphite and carbon black.

10. 2. The lithium secondary battery according to claim 1, wherein the linear conductive material comprises at least one selected from the group consisting of conductive fibers, conductive tubes, fluorocarbons, metal powders, conductive whiskers, conductive metal oxides, and polyphenylene derivatives.

11. 2. The lithium secondary battery according to claim 1, wherein the sheet-shaped conductive material comprises at least one selected from graphene and graphite, each having an aspect ratio of 1:1 to 1:

10.

12. 2. The lithium secondary battery according to claim 1, wherein a total amount of the dot-like conductive materials, the linear conductive materials, and the sheet-like conductive materials contained in the positive electrode conductive material or the negative electrode conductive material is 0.1 parts by weight to 5 parts by weight based on 100 parts by weight of a positive electrode active material layer containing the positive electrode active material or a negative electrode active material layer containing the negative electrode active material, respectively.

13. 2. The lithium secondary battery of claim 1, wherein, based on 100 parts by weight of each of the positive electrode active material layer containing the positive electrode active material and the negative electrode active material layer containing the negative electrode active material, the content of the dot-like conductive material is 0.3 parts by weight to 2 parts by weight, the content of the linear conductive material is 0.01 parts by weight to 1 part by weight, and the content of the sheet-like conductive material is 0.5 parts by weight to 3 parts by weight.

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