Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery which comprises a cathode, a separator and an anode, the anode including a silicon-based active material, and which has a resistance ratio, represented by formula 1, of 100% to 140%.

Description

lithium secondary battery

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0098788, filed on July 28, 2023, the entire disclosure of which is incorporated herein by reference.

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

[0003] Secondary batteries are widely used not only in portable devices but also in electric vehicles (EVs) and hybrid electric vehicles (HEVs) that are driven by electrical power sources.

[0004] These secondary batteries are attracting attention as a new energy source for environmental friendliness and energy efficiency because they not only have the primary advantage of being able to drastically reduce the use of fossil fuels, but also have the advantage of producing no byproducts from energy use.

[0005] Typically, a secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, and the like. In addition, 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 utility of secondary batteries increases, the demand for diverse battery performance is increasing. Therefore, efforts are being made to develop materials or combinations of materials that can improve battery performance.

[0007] The present invention seeks to provide a lithium secondary battery with improved lifespan.

[0008] One embodiment of the present invention is

[0009] Containing an anode, a separator and a cathode,

[0010] The above negative electrode contains a silicon-based active material,

[0011] A lithium secondary battery is provided, wherein the resistance ratio represented by the following equation 1 is within a range of 100% to 140%:

[0012] [Formula 1]

[0013] [SOC 5% discharge resistance] / [SOC 50% discharge resistance] X 100 - 100

[0014] SOC 5% discharge resistance and SOC 50% discharge resistance are the resistances measured when a 2.5 C discharge pulse is applied for 10 seconds at 5% and 50% state of charge (SOC) respectively at 25℃.

[0015] According to one embodiment of the present invention, the lithium secondary battery has a resistance ratio expressed by the following equation 2 within a range of 90% to 110%:

[0016] [Formula 2]

[0017] [SOC 5% discharge resistance] / [SOC 20% discharge resistance] X 100 - 100

[0018] SOC 5% discharge resistance and SOC 20% discharge resistance are the resistances measured when a 2.5 C discharge pulse is applied for 10 seconds at 5% and 20% state of charge (SOC) respectively at 25℃.

[0019] According to one embodiment of the present invention, the positive electrode is D 50 The first positive electrode active material having a diameter of 9 ㎛ or more and D 50 It includes a second positive electrode active material having a size of 6 μm or less.

[0020] 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.

[0021] According to the embodiments described herein, a high-capacity cell can be realized by using a silicon-based active material as a negative active material, and the life performance of the battery can be improved by controlling the depth of use of the silicon-based active material by satisfying the resistance ratio according to a specific state of charge (SOC).

[0022] Hereinafter, the present invention will be described in more detail to facilitate understanding. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this regard, terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Rather, they should be interpreted in the sense and concept that aligns with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention.

[0023] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0024] Furthermore, when we say that a part of a layer or the like is "above" or "on" another part, this includes not only cases where it is "directly above" that part, but also cases where there is another part in between. Conversely, when we say that a part is "directly above" another part, it means that there is no other part in between. Furthermore, when we say that a part is "above" or "on" a reference part, it means that it is located above or below that reference part, and does not necessarily mean that it is located "above" or "on" in the direction opposite to gravity.

[0025] 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 is characterized in that the resistance ratio expressed by the following formula 1 is in the range of 100% to 140%.

[0026] [Formula 1]

[0027] [SOC 5% discharge resistance] / [SOC 50% discharge resistance] X 100 - 100

[0028] SOC 5% discharge resistance and SOC 50% discharge resistance are the resistances measured when a 2.5 C discharge pulse is applied for 10 seconds at 5% and 50% state of charge (SOC) respectively at 25℃.

[0029] The resistance ratio represented by the above formula 1 may be 100% to 140%, or may be 105% to 130%, or may be 110% to 120%, or may be 110% to 115%.

[0030] The present inventors have discovered that although NCM cathode materials, especially NCM cathode materials with a Co hydroxide coating layer added for surface protection and low-resistance performance improvement, have low-resistance characteristics at the end of discharge, when NCM cathode materials are used together with silicon-based anode materials, the kinetic burden of the anode increases, and the depth of use of the silicon-based active material increases, which may lead to a decrease in battery life. In the present invention, battery life performance can be improved by satisfying the ratio of discharge resistance according to a specific state of charge. Specifically, in the present invention, it was discovered that the depth of use of the silicon-based active material of the anode can be controlled by increasing the discharge resistance at a low state of charge with respect to the discharge resistance at a 50% state of charge, thereby improving battery life performance.

[0031] According to one embodiment, the resistance ratio of the above formula 1 may be within a range of 100% to 120%, and may be within a range of 100% to 115%.

[0032] According to one embodiment, the lithium secondary battery may have a resistance ratio within a range of 90% to 110% as expressed by the following equation 2:

[0033] [Formula 2]

[0034] [SOC 5% discharge resistance] / [SOC 20% discharge resistance] X 100 - 100

[0035] SOC 5% discharge resistance and SOC 20% discharge resistance are the resistances measured when a 2.5 C discharge pulse is applied for 10 seconds at 5% and 20% state of charge (SOC) at 25℃.

[0036] The resistance ratio represented by the above formula 2 may be 90% to 110%, or may be 90% to 100%, or may be 90% to 98%, or may be 92% to 96%.

[0037] In the above implementation, the discharge resistance at 20% of the charge state is relatively low compared to the discharge resistance at 5% of the charge state, and thus, the depth of use of the silicon-based active material can be limited by controlling only the discharge resistance at 5% of the charge state.

[0038] In one embodiment, the silicon-based active material includes at least one of silicon oxide, silicon metal complex, and silicon carbon composite. Specifically, the silicon-based active material includes at least one of SiOx (0≤x<2), SiMy (M is metal, 1≤y≤4), and Si / C. The silicon-based active material may include only one type, or two or more types may be included together. When both negative electrode active material layers include silicon-based active materials, the same type of silicon-based active material may be used in the two-layered negative electrode active material layers, or different types or different combinations of silicon-based active materials may be used.

[0039] When the above negative electrode active material layer includes a silicon-based active material, the silicon-based active material may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the total negative electrode active material.

[0040] In one embodiment of the present specification, the negative electrode active material layer including the silicon-based active material may further include 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 included in the negative electrode active material layer, the carbon-based active material may be included in an amount of 90 parts by weight or more and 99 parts by weight or less.

[0041] The active material containing SiOx (0≤x<2) as the above silicon-based active material is SiO x (0 <x<2) 및 기공을 포함하는 실리콘계 복합 입자일 수 있다.

[0042] The above SiO x (0 <x<2)는 상기 실리콘계 복합 입자 내에서 매트릭스(matrix)에 해당한다. 상기 SiO x (0 <x<2)는 Si 및 SiO2가 포함된 형태일 수 있으며, 상기 Si는 상(phase)을 이루고 있을 수도 있다. 즉, 상기 x는 상기 SiO x (0 <x<2) 내에 포함된 Si에 대한 O의 개수비에 해당한다. 상기 실리콘계 복합 입자가 상기 SiO x (0 <x<2)를 포함하는 경우, 이차 전지의 방전 용량이 개선될 수 있다.

[0043] The above silicon-based composite particles may further include 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-based composite particles.

[0044] The above Mg compound and / or Li compound is SiO x (0 <x<2)의 내부 및 / 또는 표면에 존재할 수 있다. 상기 Mg 화합물 및 / 또는 Li 화합물에 의해 전지의 초기 효율이 개선될 수 있다.

[0045] The above 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.

[0046] In one embodiment of the present specification, the Mg element may be included in an amount of 0.1 wt% to 20 wt%, or 0.1 wt% to 10 wt%, based on 100 wt% of the total silicon-based active material. Specifically, the Mg element may be included in an amount of 0.5 wt% to 8 wt% or 0.8 wt% to 4 wt%. When the above range is satisfied, the Mg compound can be included in an appropriate amount in the silicon-based active material, so that 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.

[0047] 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.

[0048] In one embodiment of the present invention, the Li compound may include a lithium silicate form. The lithium silicate may include Li a Si b O c(2≤a≤4, 0 <b≤2, 2≤c≤5)로 표시되며, 결정질 리튬 실리케이트와 비정질 리튬 실리케이트로 구분될 수 있다. 상기 결정질 리튬 실리케이트는 상기 실리콘계 복합 입자 내에서 Li2SiO3, Li4SiO4및 Li2Si2O5로 이루어진 군에서 선택된 적어도 1종의 리튬 실리케이트의 형태로 존재할 수 있으며, 비정질 리튬 실리케이트는 Li a Si b O c (2≤a≤4, 0 <b≤2, 2≤c≤5)의 형태일 수 있고, 상기 형태에 한정되지는 않는다.

[0049] In one embodiment of the present specification, the Li element may be included in an amount of 0.1 wt% to 20 wt%, or 0.1 wt% to 10 wt%, based on 100 wt% of the total silicon-based active material. In another embodiment, the Li element may be included in an amount of 0.5 wt% to 8 wt%, and in yet another embodiment, the Li element may be included in an amount of 0.5 wt% to 4 wt%. When the above range is satisfied, the Li compound may be included in an appropriate amount in the silicon-based active material, so that a change in the volume 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.

[0050] The content of the above Mg element or Li element can be confirmed through ICP analysis. For the ICP analysis, a certain amount (approximately 0.01 g) of the negative active material is precisely aliquoted, transferred to a platinum crucible, and completely decomposed on a hot plate by adding nitric acid, hydrofluoric acid, and sulfuric acid. Thereafter, an inductively coupled plasma electroluminescence spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution prepared using a standard solution (5 mg / kg) at the wavelength unique to the Mg element or Li element, thereby creating a reference calibration curve. Thereafter, the pretreated sample solution and blank sample are introduced into the device, and the respective intensities are measured to calculate the actual intensity, and the concentration of each component is calculated against the created calibration curve, and then the content of the Mg element or Li element of the manufactured silicon-based active material can be analyzed by converting so that the sum of the entire values ​​becomes the theoretical value.

[0051] 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. By the carbon layer, conductivity is provided to the silicon-based composite particles, and the initial efficiency, life characteristics, and battery capacity characteristics of a secondary battery including a negative active material including the silicon-based composite particles may be improved. The total weight of the carbon layer may be comprised in an amount of 5 wt% to 40 wt% based on a total of 100 wt% of the silicon-based composite particles.

[0052] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0053] The average particle diameter (D) of the above silicon-based composite particles 50) may be 2 ㎛ to 15 ㎛, specifically 3 ㎛ to 12 ㎛, and more specifically 4 ㎛ to 10 ㎛. When the above range is satisfied, the side reaction between the silicon-based composite particles and the electrolyte is controlled, and the discharge capacity and initial efficiency of the battery can be effectively implemented.

[0054] In this specification, the average particle diameter (D 50 ) can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve. The average particle size (D 50 ) can be measured, for example, using a laser diffraction method. The laser diffraction method can generally measure particle diameters from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0055] The above silicon-based active material, which includes Si / C, is a composite of Si and C and is distinct from silicon carbide, which is denoted as SiC. The silicon-carbon composite may be a composite of silicon and graphite, and may form a structure in which a core composed of silicon and graphite is surrounded by graphene or amorphous carbon. In the silicon-carbon composite, the silicon may be nano silicon. The average particle diameter (D) of the active material including the Si / C 50 ) may be 2 ㎛ to 15 ㎛, specifically 3 ㎛ to 12 ㎛, and more specifically 4 ㎛ to 10 ㎛. A carbon layer may be provided on the surface of the active material including the Si / C.

[0056] 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 included 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, among 100 parts by weight of the negative electrode active material layer.

[0057] In one embodiment of the present specification, the anode is D 50 It may include a positive electrode active material having a size of 9 ㎛ or more.

[0058] In one embodiment of the present specification, the positive electrode is D based on 100 parts by weight of the positive electrode active material. 50 The positive electrode active material having a diameter of 9 ㎛ or more may be included in an amount of 30 to 75 parts by weight, for example, 50 to 60 parts by weight.

[0059] In one embodiment of the present specification, the anode is D 50 It may include a positive electrode active material having a size of 6 μm or less.

[0060] In one embodiment of the present specification, the positive electrode is D based on 100 parts by weight of the positive electrode active material. 50 The positive electrode active material having a diameter of 6 ㎛ or less may be included in an amount of 20 to 100 parts by weight.

[0061] In one embodiment of the present specification, the anode is D 50 This positive electrode active material having a diameter of 9 ㎛ or more and D 50 It may include a positive electrode active material having a size of 6 μm or less.

[0062] In one embodiment of the present specification, the positive electrode is D based on 100 parts by weight of the positive electrode active material. 50 It may contain more than 0 parts by weight and less than 80 parts by weight of a positive electrode active material having a diameter of 9 ㎛ or more, and D 50 The positive electrode active material having a diameter of 6 ㎛ or less may be included in an amount of 20 parts by weight or more and less than 100 parts by weight.

[0063] In one embodiment of the present specification, the positive electrode is D based on 100 parts by weight of the positive electrode active material. 50 It may contain 30 parts by weight or more and 75 parts by weight or less of a positive electrode active material having a diameter of 9 ㎛ or more, and D 50 The positive electrode active material having a size of 6 ㎛ or less may be included in an amount of 25 parts by weight or more and 70 parts by weight or less.

[0064] In one embodiment of the present specification, the positive electrode is D based on 100 parts by weight of the positive electrode active material. 50 It may contain 40 parts by weight or more and 70 parts by weight or less of a positive electrode active material having a diameter of 9 ㎛ or more, and D 50 The positive electrode active material having a size of 6 ㎛ or less may be included in an amount of 30 parts by weight or more and 60 parts by weight or less.

[0065] In one embodiment of the present specification, the positive electrode may include a lithium composite transition metal compound including 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 nickel among metals other than lithium in an amount of 60 mol% or more, 60 mol% or more but less than 100 mol%, 60 mol% to 80 mol%, 80 mol% or more, for example, 80 mol% or more but less than 100 mol%.

[0066] 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.

[0067] The above negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material particles and the negative electrode current collector. The above-mentioned negative electrode binder may be one known in the art, and non-limiting examples thereof include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and a material in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0068] The above negative electrode binder may be included in an amount of 0.1 to 20 parts by weight based on 100 parts by weight of the negative electrode active material layer, for example, 0.3 to 20 parts by weight, or 0.5 to 10 parts by weight.

[0069] The negative electrode active material layer may not include a conductive material, but may further include a conductive material as needed. The conductive material included in the negative electrode active material layer is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black; conductive fibers such as carbon fiber or 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 may be used. The content of the conductive material in the negative electrode active material layer may be 0.01 to 20 parts by weight, and preferably 0.03 to 18 parts by weight, based on 100 parts by weight of the negative electrode active material layer.

[0070] In one embodiment of the present specification, the thickness of the negative electrode active material layer may be 90 μm or more and 150 μm or less.

[0071] In one embodiment of the present specification, the negative electrode current collector may be any conductive material that does not cause a chemical change in the battery, and is not particularly limited thereto. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that adsorbs carbon well, 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 the thickness of the current collector is not limited thereto.

[0072] 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 including the positive electrode active material. The thickness of the positive electrode active material layer may be 20 μm or more and 500 μm or less.

[0073] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 1 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesive strength of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0074] In one embodiment, the positive electrode active material may be included in 100 parts by weight of the positive electrode active material layer 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.

[0075] According to an additional embodiment of the present specification, the positive electrode active material layer according to the above-described embodiment may further include a positive electrode binder and a conductive material.

[0076] The above-described positive electrode binder can serve to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material particles and the positive electrode current collector. Those known in the art can be used as the positive electrode binder, and non-limiting examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0077] The positive electrode binder may be included in an amount of 0.1 to 50 parts by weight based on 100 parts by weight of the positive electrode active material layer, for example, 0.3 to 35 parts by weight, or 0.5 to 20 parts by weight.

[0078] The conductive material included in the positive electrode active material layer is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause chemical changes within the battery and has electronic conductivity. 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, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. Specifically, in one embodiment, the conductive material may include at least one of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0079] The above-mentioned conductive material may be included in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the composition for the positive electrode active material layer, for example, it may be included in an amount of 0.1 to 7 parts by weight, or 0.1 to 5 parts by weight.

[0080] The positive electrode and the negative electrode can be manufactured according to a conventional method for manufacturing positive and negative electrodes, except for using the above-described description. Specifically, the composition for forming an active material layer, which includes the above-described active material and optionally a binder and a conductive material, is applied to a current collector, followed by drying and rolling. At this time, the types and contents of the positive and negative electrode active materials, binders, and conductive materials are as described above. The solvent may be a solvent generally used in the relevant technical field, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water. One type alone or a mixture of two or more types thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during subsequent coating for manufacturing the positive and negative electrodes. Alternatively, the positive and negative electrodes may be manufactured by casting the composition for forming the active material layer on a separate support, then peeling the film from the support and laminating the resulting film on a current collector.

[0081] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, 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, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0082] Examples of the above 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 the manufacture of lithium secondary batteries.

[0083] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0084] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0085] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be used because they easily dissociate lithium salts. By mixing and using low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced and used.

[0086] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, as an anion of the lithium salt, at least one selected from the group consisting of 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- may be used. Can be.

[0087] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine 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 battery capacity decrease, and improving the discharge capacity of the battery.

[0088] A further 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, high rate characteristics, and cycle characteristics, and thus 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.

[0089] The secondary battery according to the embodiments of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as a power source for portable devices such as mobile phones, laptop computers, and digital cameras, as well as 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. For example, the battery module or battery pack can be used as a power source for any one or more medium- to large-sized devices selected from the group consisting of power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0090]

[0091] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0092] Examples 1 to 2 and Comparative Examples 1 to 5

[0093] Cell Production

[0094] Example 1.

[0095] Bipolar production

[0096] A cathode slurry was prepared by adding a lithium composite transition metal compound doped with aluminum (Al), a conductive agent (CNT), and a binder (PVDF) in a weight ratio of 97:1:2, containing nickel (Ni), cobalt (Co), and manganese (Mn) as cathode active materials in an atomic ratio of 84:8:8, to a methylpyrrolidone (NMP) solvent (the solid content of the cathode slurry was included as 70 parts by weight of the total cathode slurry).

[0097] The positive electrode slurry manufactured above was applied onto an Al current collector, dried, and then rolled at room temperature to manufacture a positive electrode.

[0098] The above positive electrode active material is D 50 This 9.7 ㎛ positive electrode active material and D 50 It contains a positive electrode active material of 4.3 μm in a weight ratio of 1:1.

[0099]

[0100] Cathode production

[0101] The negative electrode active material layer includes a negative electrode active material including a Mg-doped SiO active material and a carbon-based active material (including artificial graphite and natural graphite in a weight ratio of 8:2) (the Mg-doped SiO active material is 5 parts by weight based on 100 parts by weight of the total negative electrode active material), a conductive agent (carbon black), a binder (SBR), and a thickener (Li-CMC) in a weight ratio of 96:1:2:1 in distilled water to prepare a negative electrode slurry (the negative electrode slurry solid content is included as 50 parts by weight of the total negative electrode slurry).

[0102]

[0103] The negative electrode active material layer slurry manufactured above was applied onto a Cu current collector, dried, and then rolled at room temperature to manufacture a negative electrode.

[0104]

[0105] Cell production

[0106] A separator was inserted between the positive and negative electrodes manufactured above, assembled, and an electrolyte was injected and then activated to manufacture a cell.

[0107] - Electrolyte composition: 1M LiPF6, ethylene carbonate (EC) / ethyl methyl carbonate (EMC) (volume ratio 3 / 7), vinylene carbonate (VC) / propane sultone (PS, propane sultone) (included in the electrolyte at 3 parts by weight and 1.5 parts by weight, respectively)

[0108] - Activation: 0.1C, 3hrs. Degas after high temperature / room temperature aging after charging.

[0109]

[0110] Example 2.

[0111] The above positive electrode active material is D 50 This 9.7 ㎛ positive electrode active material and D 50 An electrode and a cell were manufactured in the same manner as in Example 1, except that the positive electrode active material having a diameter of 4.3 μm was included in a weight ratio of 6:4.

[0112]

[0113] Comparative Example 1.

[0114] The above positive electrode active material is D 50 An electrode and cell were manufactured in the same manner as in Example 1, except that only the positive electrode active material of 4.3 μm was included.

[0115] Comparative Example 2.

[0116] The above positive electrode active material is D 50 This 9.7 ㎛ positive electrode active material and D 50 An electrode and a cell were manufactured in the same manner as in Example 1, except that the positive electrode active material having a diameter of 4.3 μm was included in a weight ratio of 25:75.

[0117]

[0118] Comparative Example 3.

[0119] The above positive electrode active material is D 50 This 9.7 ㎛ positive electrode active material and D 50 An electrode and a cell were manufactured in the same manner as in Example 1, except that the positive electrode active material having a diameter of 4.3 μm was included in a weight ratio of 8:2.

[0120]

[0121] Comparative Example 4.

[0122] An electrode and cell were manufactured in the same manner as in Example 1, except that the negative electrode contained only a carbon-based active material (including artificial graphite and natural graphite in a weight ratio of 8:2) as the negative electrode active material.

[0123]

[0124] Comparative Example 5.

[0125] The above negative electrode contains only a carbon-based active material (including artificial graphite and natural graphite in a weight ratio of 8:2) as a negative electrode active material, and the above positive electrode active material is D 50 An electrode and cell were manufactured in the same manner as in Example 1, except that only positive electrode active materials having a diameter of 4.3 μm or less were included.

[0126]

[0127] Experimental Example 1. Resistance performance at 50% SOC at room temperature (25℃)

[0128] Resistance was measured by applying a 2.5 C discharge pulse for 10 seconds at 50% state of charge (SOC) at 25℃.

[0129]

[0130] Experimental Example 2. Resistance performance at 20% SOC at room temperature (25℃)

[0131] Resistance was measured by applying a 2.5 C discharge pulse for 10 seconds at 25℃ and 20% state of charge (SOC).

[0132]

[0133] Experimental Example 3. Resistance performance at 5% SOC at room temperature (25℃)

[0134] Resistance was measured by applying a 2.5 C discharge pulse for 10 seconds at 5% state of charge (SOC) at 25℃.

[0135]

[0136] Experimental Example 4. Cycle performance at room temperature (25℃)

[0137] The fabricated cell was cycled by constant current / constant voltage (CC / CV) charging (0.05C-cut) to 4.2 V at 0.33 C at room temperature (25℃) and constant current (CC) discharging (2.5V-cut) at 0.33 C. The discharge capacity was measured after 300 repetitions. After charging as above, the SOC was set to 50% with a 0.33 C discharge, and the resistance was measured by performing a 2.5 C 10-second pulse discharge to measure the capacity retention rate (capacity after 300 cycles / initial capacity x 100%). The results are shown in Table 2 below.

[0138]

[0139] The measurement values ​​of the batteries manufactured in the examples and comparative examples are listed in Table 1 below.

[0140] Experimental Example 1 Experimental Example 2 Experimental Example 3 Formula 1 Formula 2 Experimental Example 4 Initial SOC 50 resistance (mΩ) Initial SOC 20 resistance (mΩ) Initial SOC 5 resistance (mΩ) SOC5 / SOC50 X100-100 (%) SOC5 / SOC20 X100-100 (%) 25℃ cycle capacity retention (%) Example 11.361.502.88111.892.095.1 Example 21.361.492.92114.796.094.7 Comparative Example 11.281.412.5397.779.471.8 Comparative Example 21.311.502.6098.573.365.4 Comparative Example 31.351.543.29143.7113.697.0Comparative example 41.581.663.31108.899.094.1Comparative example 51.521.602.8084.474.593.3

[0141] As can be confirmed from the results of Examples 1 and 2 of Table 1 above, when the resistance ratio expressed by Equation 1 satisfies the range of 100% to 140% and the resistance ratio expressed by Equation 2 satisfies the range of 90% to 110%, it can be confirmed that the capacity retention rate after the room temperature (25°C) cycle shows a high value of approximately 95%.

[0142] In contrast, as in Comparative Examples 1 and 2, when the resistance ratio is lower than that expressed by Equations 1 and 2, it can be confirmed that the capacity retention rate after the cycle at room temperature (25°C) shows a low value of around 70%.

[0143] As in Comparative Example 3, when the resistance ratios expressed by Equations 1 and 2 are excessively increased, the capacity retention rate after the cycle at room temperature (25°C) shows a high value of 97%, thereby ensuring life performance, but the resistance at SOC 20% also increases, which may adversely affect the battery output performance.

[0144] Comparative Examples 4 and 5 correspond to cases where the negative electrode is composed solely of a carbon-based active material. When the negative electrode contains only a carbon-based active material and no silicon-based active material, it can be confirmed that the ratio of positive electrode material has a minimal effect on room temperature life performance.

Claims

1. Contains a positive electrode, a separator, and a negative electrode; The above negative electrode contains a silicon-based active material, A lithium secondary battery having a resistance ratio expressed by the following equation 1 within a range of 100% to 140%: [Formula 1] [SOC 5% discharge resistance] / [SOC 50% discharge resistance] X 100 - 100 SOC 5% discharge resistance and SOC 50% discharge resistance are the resistances measured when a 2.5 C discharge pulse is applied for 10 seconds at 5% and 50% state of charge (SOC) respectively at 25℃.

2. A lithium secondary battery according to claim 1, wherein the resistance ratio represented by the above formula 1 is within a range of 100% to 120%.

3. A lithium secondary battery according to claim 1, wherein the resistance ratio represented by the following equation 2 is within a range of 90% to 110%. [Formula 2] [SOC 5% discharge resistance] / [SOC 20% discharge resistance] X 100 - 100 SOC 5% discharge resistance and SOC 20% discharge resistance are the resistances measured when a 2.5 C discharge pulse is applied for 10 seconds at 5% and 20% state of charge (SOC) respectively at 25℃.

4. In claim 1, the positive electrode is D based on 100 parts by weight of the positive electrode active material. 50 A lithium secondary battery comprising 30 to 75 parts by weight of a positive electrode active material having a diameter of 9 μm or more.

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

6. A lithium secondary battery according to claim 1, wherein the positive electrode comprises a lithium composite oxide having a nickel content of 60 mol% or more out of 100 mol% of metals other than lithium as a positive electrode active material and including at least one of cobalt, manganese, and aluminum.

7. A lithium secondary battery according to claim 1, wherein the negative electrode includes a silicon-based active material and a carbon-based active material as the negative electrode active material.

8. A 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 the total negative electrode active material.

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

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

11. A lithium secondary battery according to claim 1, wherein the resistance ratio represented by the above formula 1 is within a range of 100% to 115%.

12. A lithium secondary battery according to claim 3, wherein the resistance ratio represented by the above formula 2 is within a range of 90% to 100%.

13. A lithium secondary battery according to claim 3, wherein the resistance ratio represented by the above formula 2 is within a range of 90% to 98%.

14. A lithium secondary battery according to claim 3, wherein the resistance ratio represented by the above formula 2 is within a range of 92% to 96%.

15. In claim 5, the D 50 The positive electrode active material having a diameter of 9 ㎛ or more is included in an amount of more than 0 parts by weight and less than or equal to 80 parts by weight based on 100 parts by weight of the positive electrode active material, and the above D 50 A lithium secondary battery comprising a positive electrode active material having a diameter of 6 ㎛ or less 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. In claim 5, the D 50 The positive electrode active material having a diameter of 9 ㎛ or more is included in an amount of 30 to 75 parts by weight based on 100 parts by weight of the positive electrode active material, and the D 50 A lithium secondary battery comprising 25 to 70 parts by weight of a positive electrode active material having a diameter of 6 μm or less based on 100 parts by weight of the positive electrode active material.

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

18. A 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 other than lithium.

19. A 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 other than lithium.

20. A lithium secondary battery according to claim 9, wherein the silicon carbon composite is nano silicon.