Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising a positive electrode, a separator, and a negative electrode, wherein the negative electrode contains a silicon-based active material and has a resistivity represented by formula 1 of 100% to 140%.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0098788, filed on July 28, 2023, and all contents disclosed in the documents of that Korean patent application 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 electrical sources.

[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, making them environmentally friendly and drawing attention as a new energy source for improving 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. In addition, 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 the use of secondary batteries increases, various battery performances are being demanded, and therefore attempts are being made to develop types of materials or combinations of materials that can improve battery performance. 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 an improved lifespan. [Means for solving the problem]

[0008] One embodiment of the present invention comprises: a positive electrode, a separator, and a negative electrode; the negative electrode contains a silicon-based active material, Provided is a lithium secondary battery having a resistivity represented by the following formula 1 in the range of 100% to 140%: [Formula 1] [SOC 5% discharge resistor] / [SOC 50% discharge resistor] x 100-100 The SOC 5% discharge resistance and SOC 50% discharge resistance are the resistances measured at 25°C when a 2.5C discharge pulse is applied for 10 seconds at a state of charge (SOC) of 5% and 50%, respectively.

[0009] According to one embodiment of the present invention, the lithium secondary battery has a resistivity represented by the following formula 2 in the range of 90% to 110%: [Formula 2] [SOC5% discharge resistance] / [SOC20% discharge resistance]×100-100 The SOC 5% discharge resistance and SOC 20% discharge resistance are the resistances measured at 25°C when a 2.5C discharge pulse is applied for 10 seconds at a state of charge (SOC) of 5% and 20%, respectively.

[0010] According to one embodiment of the present invention, the positive electrode is 50 The first positive electrode active material and D 50 The second positive electrode active material has a particle size of 6 μm or less.

[0011] According to one embodiment of the present invention, the negative electrode active material includes a silicon-based active material and a carbon-based active material. [Effects of the Invention]

[0012] According to the embodiments described herein, by using a silicon-based active material as the negative electrode active material, a high-capacity cell can be realized, and at the same time, by satisfying the resistivity according to a specific state of charge (SOC), the depth of use of the silicon-based active material can be controlled, thereby improving the lifespan performance of the battery. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in more detail below to facilitate understanding of the present invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this regard, the terms and words used in the specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as having meanings and concepts consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concepts of terms in order to best describe his or her invention.

[0014] As used herein, terms such as "comprises," "provides," or "having" are intended to specify the presence of stated features, numbers, steps, components, or combinations thereof, but are understood not to preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0015] Furthermore, when a part such as a layer is said to be "on" another part, this does not only mean that it is "directly on top" of that other part, but also includes cases where there is another part between them. Conversely, when a part is said to be "directly above" another part, it means that there is no other part between them. Furthermore, being "on" a reference part means being located above or below the reference part, and does not necessarily mean being "on" in the opposite direction of gravity.

[0016] A lithium secondary battery according to one embodiment of the present specification includes a positive electrode, a separator, and a negative electrode, wherein the negative electrode includes a silicon-based active material and has a resistivity represented by the following formula 1 in the range of 100% to 140%:

[0017] [Formula 1] [SOC 5% discharge resistor] / [SOC 50% discharge resistor] x 100-100

[0018] The SOC 5% discharge resistance and SOC 50% discharge resistance are resistances measured when a 2.5C discharge pulse is applied to the lithium secondary battery for 10 seconds at 25°C and a state of charge (SOC) of 5% and 50%, respectively.

[0019] The resistivity represented by the formula 1 may be 100% to 140%, or 105% to 130%, or 110% to 120%, or 110% to 115%.

[0020] The inventors have found that NCM (nickel-cobalt-manganese)-based cathode materials, especially those with a cobalt hydroxide coating layer for surface protection and improved low-resistance performance, exhibit low resistance at the end of discharge. However, when NCM-based cathode materials are used with silicon-based anode materials, the kinetic load on the anode increases, increasing the depth of use of the silicon-based active material and resulting in reduced battery life. The present invention can improve battery life by achieving a specific discharge resistance ratio for a specific state of charge. Specifically, the present invention has demonstrated that the depth of use of the silicon-based active material in the anode can be controlled by increasing the discharge resistance at a low state of charge relative to the discharge resistance at 50% state of charge, thereby improving battery life.

[0021] According to one embodiment, the resistivity of the formula 1 may be in the range of 100% to 120%, or may be in the range of 100% to 115%.

[0022] According to one embodiment, the lithium secondary battery may have a resistivity in the range of 90% to 110%, as represented by the following formula 2: [Formula 2] [SOC5% discharge resistance] / [SOC20% discharge resistance]×100-100 The SOC 5% discharge resistance and SOC 20% discharge resistance are the resistances measured at 25°C when a 2.5C discharge pulse is applied for 10 seconds at a state of charge (SOC) of 5% and 20%, respectively.

[0023] The resistivity represented by the formula 2 may be 90% to 110%, or 90% to 100%, or 90% to 98%, or 92% to 96%.

[0024] In this embodiment, the discharge resistance at 20% state of charge is relatively lower than the discharge resistance at 5% state of charge. Therefore, by controlling only the discharge resistance at 5% state of charge, the depth of use of the silicon-based active material can be limited.

[0025] In one embodiment, the silicon-based active material includes at least one of silicon oxide, silicon-metal complex, and silicon-carbon composite. x (0≦x<2), SiM y (M is a metal, 1≦y≦4) and a Si / C composite. The silicon-based active material may be one type only, or two or more types may be used together. When both of the two negative electrode active material layers contain a silicon-based active material, the two negative electrode active material layers may use the same type of silicon-based active material, or different types or different combinations of silicon-based active materials.

[0026] When the negative electrode active material layer contains a silicon-based active material, the silicon-based active material may be contained in an amount of 1 part by weight to 10 parts by weight based on 100 parts by weight of the total negative electrode active material.

[0027] In one embodiment of the present specification, the negative electrode active material layer containing the silicon-based active material may further contain a carbon-based active material. In this case, the carbon-based active material may include at least one of artificial graphite and natural graphite. Based on 100 parts by weight of the total negative electrode active material contained in the negative electrode active material layer, the carbon-based active material may be included in an amount of 90 parts by weight to 99 parts by weight.

[0028] As the silicon-based active material, SiO x (0≦x<2) contains SiO xIt may be a silicon-based composite particle containing (0 < x < 2) and pores.

[0029] The above SiO x (0 < x < 2) corresponds to a matrix within the silicon-based composite particle. The above SiO x (0 < x < 2) may be in a form containing Si and SiO2, and the Si may form a phase. That is, the above x corresponds to the number ratio of O to Si contained in the above SiO x (0 < x < 2). When the silicon-based composite particle contains the above SiO x (0 < x < 2), the discharge capacity of the secondary battery can be improved.

[0030] The silicon-based composite particle may further contain at least one of a Mg compound and a Li compound. The Mg compound and the Li compound can correspond to a matrix within the silicon-based composite particle. [[ID=十七]]

[0031] The above Mg compound and / or Li compound may be present inside and / or on the surface of the above SiO x (0 < x < 2). The initial efficiency of the battery can be improved by the above Mg compound and / or Li compound.

[0032] The above Mg compound may contain at least one selected from the group consisting of Mg silicate, Mg silicide, and Mg oxide. The above Mg silicate may contain at least one of Mg2SiO4 and MgSiO3. The above Mg silicide may contain Mg2Si. The above Mg oxide may contain MgO.

[0033] In one embodiment of the present specification, the Mg element may be contained in an amount of 0.1% to 20% by weight, or 0.1% to 10% by weight, based on 100% by weight of the total silicon-based active material. Specifically, the Mg element may be contained in an amount of 0.5% to 8% by weight or 0.8% to 4% by weight. When the above range is satisfied, the Mg compound is contained in an appropriate content in the silicon-based active material, so that the volume change of the silicon-based active material can be easily suppressed during charging and discharging of the battery, and the discharge capacity and initial efficiency of the battery can be improved.

[0034] The Li compound may contain at least one selected from the group consisting of Li silicate, Li silicide, and Li oxide. The Li silicate may contain at least one of Li2SiO3, Li4SiO4, and Li2Si2O5. The Li silicide may contain Li7Si2. The Li oxide may contain Li2O.

[0035] In one embodiment of the present invention, the Li compound may include a form of lithium silicate. The lithium silicate is represented by Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and can be divided into crystalline lithium silicate and amorphous lithium silicate. The crystalline lithium silicate can exist in the form of at least one lithium silicate selected from the group consisting of Li2SiO3, Li4SiO4, and Li2Si2O5 in the silicon-based composite particles, and the amorphous lithium silicate may be in the form of Li a Si b O c (2 ≤ a ≤ 4, 0 < b ≤ 2, 2 ≤ c ≤ 5), and is not limited to the above form.

[0036] In one embodiment of the present specification, the Li element may be contained in an amount of 0.1 wt % to 20 wt %, or 0.1 wt % to 10 wt %, based on a total of 100 wt % of the silicon-based active material. In another embodiment, the Li element may be contained in an amount of 0.5 wt % to 8 wt %, and in another embodiment, the Li element may be contained in an amount of 0.5 wt % to 4 wt %. When the above range is satisfied, the Li compound can be contained in the silicon-based active material at an appropriate content, which can easily suppress volumetric changes of the negative electrode active material during charge and discharge of the battery, thereby improving the discharge capacity and initial efficiency of the battery.

[0037] The Mg or Li element content can be confirmed by inductively coupled plasma (ICP) analysis. For the ICP analysis, a fixed amount (approximately 0.01 g) of the negative electrode active material is accurately separated and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the mixture is completely decomposed on a hot plate. Then, an inductively coupled plasma optical emission spectrometry (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution (5 mg / kg) prepared at the wavelength specific to Mg or Li, creating a reference calibration curve. The pretreated sample solution and the base sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentrations of each component are calculated using the created calibration curve, and the total is converted to a theoretical value. The Mg or Li element content of the resulting silicon-based active material can then be analyzed.

[0038] In one embodiment of the present specification, a carbon layer may be provided on the surface and / or inside the pores of the silicon-based composite particles. The carbon layer imparts electrical conductivity to the silicon-based composite particles, thereby improving the initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including a negative electrode active material containing the silicon-based composite particles. The total weight of the carbon layer may be 5 wt % to 40 wt % based on 100 wt % of the total silicon-based composite particles.

[0039] In one embodiment of the present specification, the carbon layer may contain at least one of amorphous carbon and crystalline carbon.

[0040] The average particle size (D 50 ) may be 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically 4 μm to 10 μm. When the above range is satisfied, side reactions between the silicon-based composite particles and the electrolyte are controlled, and the discharge capacity and initial efficiency of the battery can be effectively achieved.

[0041] 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 using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0042] The active material containing Si / C as the silicon-based active material is a composite of Si and C and is distinguished from silicon carbide, which is abbreviated as SiC. The silicon carbon composite may be a composite of silicon and graphite, or may have a structure in which a core of silicon and graphite is surrounded by graphene or amorphous carbon. In the silicon carbon composite, the silicon may be nanosilicon. The average particle size (D 50 ) may be 2 μm to 15 μm, specifically 3 μm to 12 μm, and more specifically 4 μm to 10 μm. A carbon layer may be provided on the surface of the active material containing Si / C.

[0043] In one embodiment of the present specification, the negative electrode includes a current collector and a negative electrode active material layer, and 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, 90 parts by weight or more and 99.9 parts by weight or less, 95 parts by weight or more and 99.9 parts by weight or less, or 98 parts by weight or more and 99.9 parts by weight or less, in 100 parts by weight of the negative electrode active material layer.

[0044] In one embodiment of the present specification, the positive electrode is 50 The positive electrode active material may have a particle size of 9 μm or more.

[0045] In one embodiment of the present specification, the positive electrode has a composition of D 50 The positive electrode active material having a particle size of 9 μm or more may be contained in an amount of 30 to 75 parts by weight, for example 50 to 60 parts by weight.

[0046] In one embodiment of the present specification, the positive electrode is 50 The positive electrode active material may have a particle size of 6 μm or less.

[0047] In one embodiment of the present specification, the positive electrode has a composition of D 50 The positive electrode active material may contain 20 to 100 parts by weight of a particle size of 6 μm or less.

[0048] In one embodiment of the present specification, the positive electrode is 50 Positive electrode active material with a diameter of 9 μm or more and D 50 The positive electrode active material may have a particle size of 6 μm or less.

[0049] In one embodiment of the present specification, the positive electrode has a composition of D 50 The positive electrode active material may contain more than 0 parts by weight and not more than 80 parts by weight of a positive electrode active material having a diameter of 9 μm or more, 50 The positive electrode active material may contain 20 parts by weight or more and less than 100 parts by weight of a particle size of 6 μm or less.

[0050] In one embodiment of the present specification, the positive electrode has a composition of D 50The positive electrode active material may contain 30 parts by weight or more and 75 parts by weight or less of a particle diameter of 9 μm or more, 50 The positive electrode active material may contain 25 parts by weight or more and 70 parts by weight or less of a particle size of 6 μm or less.

[0051] In one embodiment of the present specification, the positive electrode has a composition of D 50 The positive electrode active material may contain 40 parts by weight or more and 70 parts by weight or less of a particle diameter of 9 μm or more, 50 The positive electrode active material may contain 30 parts by weight or more and 60 parts by weight or less of a particle size of 6 μm or less.

[0052] In one embodiment of the present specification, the positive electrode may include a lithium composite transition metal compound containing nickel (Ni) and cobalt (Co) as an active material. The lithium composite transition metal compound may further include at least one of manganese and aluminum. The lithium composite transition metal compound may include, among metals other than lithium, nickel in an amount of 60 mol% or more, 60 mol% or more but less than 100 mol%, 60 mol% to 80 mol%, or 80 mol% or more, for example, 80 mol% or more but less than 100 mol%.

[0053] According to an additional embodiment of the present specification, the negative electrode active material layer may further include a negative electrode binder in addition to the negative electrode active material.

[0054] 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. The negative electrode binder may be any binder known in the art, and non-limiting examples thereof may 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, polytetrafluoroethylene, 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.

[0055] The negative electrode binder may be included in an amount of 0.1 to 20 parts by weight, for example, 0.3 to 20 parts by weight, or 0.5 to 10 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0056] The negative electrode active material layer may not contain a conductive material, but may further contain a conductive material if necessary. The conductive material contained in the negative electrode active material layer is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. Examples of the conductive material include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; conductive tubes such as 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. The content of the conductive material in the negative electrode active material layer may be 0.01 to 20 parts by weight, preferably 0.03 to 18 parts by weight, per 100 parts by weight of the negative electrode active material layer.

[0057] In one embodiment of the present specification, the negative electrode active material layer may have a thickness of 90 μm or more and 150 μm or less.

[0058] 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, calcined carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, transition metals that adsorb carbon well, such as copper and nickel, can be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0059] In one embodiment of the present specification, the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector and containing the positive electrode active material. The positive electrode active material layer may have a thickness of 20 μm to 500 μm.

[0060] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector typically has a thickness of 1 to 500 μm, and fine irregularities can be formed on the collector surface to enhance adhesion of the positive electrode active material. It can be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0061] 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, 90 parts by weight to 99.9 parts by weight, 95 parts by weight to 99.9 parts by weight, or 98 parts by weight to 99.9 parts by weight in 100 parts by weight of the positive electrode active material layer.

[0062] According to an additional embodiment of the present specification, the positive electrode active material layer according to the above embodiment may further include a positive electrode binder and a conductive material.

[0063] 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. The positive electrode binder may be any binder known in the art, and non-limiting examples thereof include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, 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.

[0064] The positive electrode binder may be included in an amount of 0.1 to 50 parts by weight, for example, 0.3 to 35 parts by weight, or 0.5 to 20 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0065] The conductive material contained in the positive electrode active material layer is used to impart conductivity to the electrode. Any conductive material can be used without particular limitations as long as it has electronic conductivity and does not cause chemical changes within the battery. Specific examples include graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or 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. These materials may be used alone or in combination. Specifically, in one embodiment, the conductive material may include one or more of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0066] The conductive material may be included in an amount of 0.1 parts by weight to 10 parts by weight, for example, 0.1 parts by weight to 7 parts by weight, or 0.1 parts by weight to 5 parts by weight, based on 100 parts by weight of the composition for a positive electrode active material layer.

[0067] The positive and negative electrodes may be fabricated according to conventional methods for fabricating positive and negative electrodes, except for the above description. Specifically, they may be fabricated by coating a composition for forming an active material layer containing the active material and, optionally, a binder and a 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 a 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, and to provide a viscosity that allows excellent thickness uniformity during subsequent coating for fabricating positive and negative electrodes, taking into account the coating thickness and manufacturing yield of the slurry. Alternatively, the positive electrode and the negative electrode may 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.

[0068] 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 limitations. In particular, a separator that exhibits low resistance to electrolyte ion movement and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be used in a single-layer or multi-layer structure.

[0069] Examples of the electrolyte 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 manufacturing lithium secondary batteries, but are not limited to these.

[0070] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0071] Examples of the non-aqueous organic solvent that may be used include non-proton organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-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.

[0072] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate can be used because they are high-viscosity organic solvents with high dielectric constants that allow them to dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte with high electrical conductivity can be prepared, and therefore can be used.

[0073] 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:

[0074] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or 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.

[0075] An additional embodiment of the present invention provides a battery module including the aforementioned secondary battery as a unit cell, and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, excellent rate-limiting characteristics, and excellent cycle characteristics, 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.

[0076] The secondary battery according to the embodiment of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, 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, 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, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0077] Below, preferred examples are presented to help understand the present invention, but the above 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 is natural that such changes and modifications fall within the scope of the appended claims.

[0078] Examples 1 to 2 and Comparative Examples 1 to 5 <Cel production> Example 1 Positive electrode production A lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn) in an atomic ratio of 84:8:8 as the positive electrode active material and doped with aluminum (Al), a conductive material (CNT), and a binder (PVDF) were added to a methylpyrrolidone (NMP) solvent in a weight ratio of 97:1:2 to prepare a positive electrode slurry (the solid content of the positive electrode slurry was 70 parts by weight of the total positive electrode slurry).

[0079] The prepared positive electrode slurry was coated on an Al current collector, dried, and then rolled at room temperature to prepare a positive electrode.

[0080] The positive electrode active material is D 50 The positive electrode active material having a diameter of 9.7 μm and D50 The positive electrode active material has a particle size of 4.3 μm and the positive electrode active material has a particle size of 4.3 μm. The positive electrode active material contains the positive electrode active material having a particle size of 4.3 μm and the positive electrode active material having ...

[0081] Negative electrode production For the negative electrode active material layer, negative electrode active materials including Mg-doped SiO active material and carbon-based active material (artificial graphite and natural graphite in a weight ratio of 8:2) (the Mg-doped SiO active material was included in an amount of 5 parts by weight based on 100 parts by weight of the total negative electrode active material), conductive material (carbon black), binder (SBR), and thickener (Li-CMC) were added to a distilled water solvent in a weight ratio of 96:1:2:1 to prepare a negative electrode slurry (the solid content of the negative electrode slurry was 50 parts by weight of the total negative electrode slurry).

[0082] The negative electrode active material layer slurry prepared above was coated on a Cu current collector, dried, and then rolled at room temperature to prepare a negative electrode.

[0083] Cell production A separator was interposed between the prepared positive and negative electrodes, and the resulting assembly was assembled. An electrolyte was then injected and activated as follows to prepare a cell.

[0084] - Electrolyte composition: 1M LiPF6, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 3 / 7), vinylene carbonate (VC) / propane sultone (PS, propane sultone) (contained in the electrolyte at 3 parts by weight and 1.5 parts by weight, respectively) - Activation: 0.1C, 3 hours. After charging, high temperature / normal temperature aging, degassing

[0085] Example 2. The positive electrode active material is D 50 The positive electrode active material has a diameter of 9.7 μm and D 50 An electrode and a cell were fabricated in the same manner as in Example 1, except that the cathode active material having a particle size of 4.3 μm was included in a weight ratio of 6:4.

[0086] Comparative Example 1 The positive electrode active material is D 50Electrodes and cells were fabricated in the same manner as in Example 1, except that the electrode contained only positive electrode active material having a particle size of 4.3 μm.

[0087] Comparative Example 2 The positive electrode active material is D 50 The positive electrode active material having a diameter of 9.7 μm and D 50 An electrode and a cell were fabricated in the same manner as in Example 1, except that the cathode active material having a particle size of 4.3 μm was included in a weight ratio of 25:75.

[0088] Comparative Example 3. The positive electrode active material is D 50 The positive electrode active material having a diameter of 9.7 μm and D 50 An electrode and a cell were fabricated in the same manner as in Example 1, except that the cathode active material having a particle size of 4.3 μm was included in an 8:2 weight ratio.

[0089] Comparative Example 4. An electrode and a cell were fabricated in the same manner as in Example 1, except that the negative electrode contained only a carbon-based active material (artificial graphite and natural graphite in a weight ratio of 8:2) as the negative electrode active material.

[0090] Comparative Example 5. The negative electrode contains only a carbon-based active material (containing artificial graphite and natural graphite in a weight ratio of 8:2) as a negative electrode active material, and the positive electrode active material is D 50 Electrodes and cells were fabricated in the same manner as in Example 1, except that only the positive electrode active material having a particle size of 4.3 μm was included.

[0091] Experimental example 1. Room temperature (25°C) SOC 50% resistance performance Resistance was measured by applying a 2.5 C discharge pulse to the cell for 10 seconds at 25°C and 50% state of charge (SOC).

[0092] Experimental example 2: SOC 20% resistance performance at room temperature (25°C) Resistance was measured by applying a 2.5 C discharge pulse to the cell for 10 seconds at 25°C and 20% state of charge (SOC).

[0093] Experimental example 3: SOC 5% resistance performance at room temperature (25°C) Resistance was measured by applying a 2.5 C discharge pulse to the cell for 10 seconds at 25°C and 5% state of charge (SOC).

[0094] Experimental Example 4: Room temperature (25°C) cycle performance The fabricated cells were subjected to charge-discharge cycling at room temperature (25°C) by constant current / constant voltage (CC / CV) charging at 0.33C to 4.2V (0.05C cutoff), followed by 0.33C constant current (CC) discharge (2.5V cutoff). After 300 cycles, the discharge capacity was measured. After charging as described above, the cells were set to 50% SOC at 0.33C discharge, and then pulse discharged at 2.5C for 10 seconds, measuring the resistance and the capacity retention (capacity after 300 cycles / initial capacity x 100%). The results are shown in Table 1 below.

[0095] The measured values ​​of the batteries fabricated in the examples and comparative examples are shown in Table 1 below.

[0096] [Table 1]

[0097] As can be seen from the results of Examples 1 and 2 in Table 1, when the resistivity represented by Equation 1 satisfies the range of 100% to 140% and the resistivity represented by Equation 2 satisfies the range of 90% to 110%, it can be confirmed that the capacity retention rate after cycles at room temperature (25°C) shows a high value of around 95%.

[0098] In contrast, when the resistivity is lower than that shown by Equation 1 and Equation 2, as in Comparative Examples 1 and 2, it can be confirmed that the capacity retention rate after room temperature (25°C) cycling is a low value of around 70%.

[0099] When the resistivity represented by Equation 1 and Equation 2 is excessively high as in Comparative Example 3, the capacity retention rate after room temperature (25°C) cycling is as high as 97%, ensuring longevity performance. However, the resistance at SOC 20% also increases, which may adversely affect battery output performance.

[0100] Comparative Examples 4 and 5 correspond to cases where the negative electrode is made of only a carbon-based active material. When the negative electrode does not contain a silicon-based active material and contains only a carbon-based active material, it can be confirmed that the proportion of the positive electrode material has little effect on the room-temperature life performance.

Claims

1. a positive electrode, a separator, and a negative electrode; the negative electrode contains a silicon-based active material, The resistivity represented by the following formula 1 is in the range of 100% to 140%, [Formula 1] [SOC 5% discharge resistance] / [SOC 50% discharge resistance] x 100 - 100 The SOC 5% discharge resistance and the SOC 50% discharge resistance are the resistances measured when a 2.5 C discharge pulse is applied to the lithium secondary battery for 10 seconds at 25°C and at a state of charge (SOC) of 5% and 50%, respectively.

2. 2. The lithium secondary battery according to claim 1, wherein the resistivity represented by Formula 1 is in the range of 100% to 120%.

3. The resistivity represented by the following formula 2 is in the range of 90% to 110%, [Formula 2] [SOC5% discharge resistance] / [SOC20% discharge resistance] x 100-100 2. The lithium secondary battery according to claim 1, wherein the SOC 5% discharge resistance and the SOC 20% discharge resistance are resistances measured when a 2.5 C discharge pulse is applied to the lithium secondary battery for 10 seconds at 25° C. and at a state of charge (SOC) of 5% and 20%, respectively.

4. The positive electrode contains 100 parts by weight of the positive electrode active material. ５０ 2. The lithium secondary battery according to claim 1, comprising 30 to 75 parts by weight of a positive electrode active material having a particle size of 9 μm or more.

5. The positive electrode is D ５０ A positive electrode active material having a diameter of 9 μm or more and D ５０ The lithium secondary battery according to claim 1 , comprising a positive electrode active material having a particle size of 6 μm or less.

6. 2. The lithium secondary battery according to claim 1, wherein the positive electrode contains, as a positive electrode active material, a lithium composite oxide containing at least one of cobalt, manganese, and aluminum, and having a nickel content of 60 mol % or more out of 100 mol % of metals excluding lithium.

7. 2. The lithium secondary battery according to claim 1, wherein the negative electrode contains a silicon-based active material and a carbon-based active material as negative electrode active materials.

8. 2. The lithium secondary battery according to claim 1, wherein the negative electrode contains 1 to 10 parts by weight of a silicon-based active material based on 100 parts by weight of a total of negative electrode active materials.

9. The lithium secondary battery according to claim 1 , wherein the silicon-based active material includes at least one of a silicon oxide, a silicon-metal complex, and a silicon-carbon composite.

10. The lithium secondary battery according to claim 7 , wherein the carbon-based active material includes at least one of artificial graphite and natural graphite.

11. 2. The lithium secondary battery according to claim 1, wherein the resistivity represented by Formula 1 is in the range of 100% to 115%.

12. 4. The lithium secondary battery according to claim 3, wherein the resistivity represented by formula 2 is in the range of 90% to 100%.

13. 4. The lithium secondary battery according to claim 3, wherein the resistivity represented by formula 2 is in the range of 90% to 98%.

14. 4. The lithium secondary battery according to claim 3, wherein the resistivity represented by formula 2 is in the range of 92% to 96%.

15. The above D ５０ The positive electrode active material having a particle size of 9 μm or more is contained in an amount of more than 0 part by weight and not more than 80 parts by weight based on 100 parts by weight of the positive electrode active material, ５０ The lithium secondary battery according to claim 5 , wherein the positive electrode active material having a particle size of 6 μm or less is contained in an amount of 20 parts by weight or more and less than 100 parts by weight based on 100 parts by weight of the positive electrode active material.

16. The above D ５０ The positive electrode active material having a particle size of 9 μm or more is contained in an amount of 30 to 75 parts by weight based on 100 parts by weight of the positive electrode active material, ５０ 6. The lithium secondary battery according to claim 5, wherein the positive electrode active material having a particle size of 6 μm or less is contained in an amount of 25 to 70 parts by weight based on 100 parts by weight of the positive electrode active material.

17. 7. The lithium secondary battery according to claim 6, wherein the nickel content is 60 mol % to 80 mol % of 100 mol % of metals excluding lithium.

18. 7. The lithium secondary battery according to claim 6, wherein the nickel content is 80 mol % or more and less than 100 mol % of 100 mol % of metals excluding lithium.

19. 7. The lithium secondary battery according to claim 6, wherein the nickel content is 60 mol % or more and less than 100 mol % of 100 mol % of metals excluding lithium.

20. The lithium secondary battery according to claim 9 , wherein the silicon carbon composite comprises nanosilicon.

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