Lithium secondary battery, and battery module and battery pack comprising same

Abstract

The present invention relates to a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode comprises a lithium nickel-based active material, the negative electrode comprises a silicon-based active material, the electrolyte comprises a carbonate-based solvent, an amide-based solvent, and a lithium salt, the lithium salt comprises a lithium salt containing a fluorine-based anion and a sulfonylimide-based lithium salt, the amide-based solvent is contained in an amount of more than 10 vol % and 25 vol % or less on the basis of 100 vol % of the solvent contained in the electrolyte, and the molar ratio of the sulfonylimide-based lithium salt is more than 10 mol % and less than 50 mol % on the basis of 100 mol % of the lithium salt.

Description

Lithium secondary battery, battery module and battery pack including the same

[0001] The present application claims the benefit of the filing dates of Patent No. 10-2025-0026295 filed with the Korean Intellectual Property Office on February 28, 2025 and Patent No. 10-2026-0035947 filed with the Korean Intellectual Property Office on February 26, 2026, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery, a battery module including the same, and a battery pack.

[0003] Secondary batteries are widely applied not only to portable devices but also to electric vehicles (EVs) and hybrid electric vehicles (HEVs) powered by electric driving sources.

[0004] These secondary batteries are attracting attention as a new energy source for improving eco-friendliness and energy efficiency, as they not only have the primary advantage of being able to drastically reduce the use of fossil fuels but also the advantage of not generating any by-products from the use of energy.

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

[0006] Conventional lithium-ion batteries have been developed to achieve high capacity and high energy density by using active materials with high specific capacity and increasing the weight per unit area and current density of the electrode layers formed on the current collector by increasing the content of the positive and negative electrode layers coated on the current collector. In addition, to enhance user convenience, there was a need to secure not only high energy density characteristics but also rapid charging performance.

[0007] However, conventional electrolytes have a tendency to decompose at high temperatures, which limits their operation in the high-temperature range advantageous for rapid charging; in particular, this limits their application to pouch batteries with non-rigid casings. Therefore, various studies are being conducted to optimize electrolytes to reduce charging time while ensuring durability at high temperatures.

[0008] The present invention aims to provide a lithium secondary battery that can be used even in high-temperature regions to reduce charging time.

[0009] One embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode comprises a lithium nickel-based active material and the negative electrode comprises a silicon-based active material, the electrolyte comprises a carbonate-based solvent, an amide-based solvent, and a lithium salt, wherein the lithium salt comprises a lithium salt containing a fluorine-based inorganic anion and a sulfonylimide-based lithium salt, and the amide-based solvent is included in an amount greater than 10 vol% and less than or equal to 25 vol% based on 100 vol% of the solvent included in the electrolyte, and the molar ratio of the sulfonylimide-based lithium salt is greater than 10 mol% and less than 50 mol% based on 100 mol% of the lithium salt.

[0010] According to one embodiment of the present invention, a lithium secondary battery is provided in which the ratio of D80 to D60 is 10 or less, where D60 is the slope (% / day) of the capacity retention rate according to the storage period at 60°C in the SOC100 state and D80 is the slope (% / day) of the capacity retention rate according to the storage period at 80°C.

[0011] According to one embodiment of the present invention, a lithium secondary battery is provided in which the ratio of R80 to R60 is 35 or less, where R60 is the slope (% / day) of the increase in resistance according to a storage period of 60°C in an SOC100 state and R80 is the slope (% / day) of the increase in resistance according to a storage period of 80°C.

[0012] According to one embodiment of the present invention, a battery module comprising a lithium secondary battery according to the above embodiment is provided.

[0013] According to one embodiment of the present invention, a battery pack comprising a lithium secondary battery according to the above embodiment is provided.

[0014] According to one embodiment of the present invention, a battery pack including a battery module according to the above embodiment is provided.

[0015] According to the embodiments described in this specification, a lithium secondary battery having an electrolyte composition ratio optimized for reducing charging time is provided by using a carbonate-based solvent and an amide-based solvent as an electrolyte in a specific ratio, and adjusting the ratio of a lithium salt containing a fluorine-based inorganic anion and a sulfonylimide-based lithium salt.

[0016] Hereinafter, the present invention will be described in more detail to aid in understanding the invention. The present invention may be embodied in various different forms and is not limited to the embodiments described herein. In this case, terms or words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0017] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] Furthermore, when it is said that a part, such as a layer, is "above" or "on" another part, this includes not only the case where it is "directly above" the other part, but also the case where there is another part in between. Conversely, when it is said that a part is "directly above" another part, it means that there is no other part in between. Also, saying that a part is "above" or "on" a reference part means that it is located above or below the reference part, and it does not necessarily mean that it is located "above" or "on" facing the opposite direction of gravity.

[0019] In the present specification, the presence or absence and content of elements within the active material of the anode or cathode can be confirmed through ICP analysis, and ICP analysis can be performed using an inductively coupled plasma emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0020] In this specification, "average particle size (D 50 )" can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The above average particle size (D 50 ) can be measured using the laser diffraction method. For example, the average particle size (D) of the positive electrode active material 50 The measurement method of ) involves dispersing particles of the positive electrode active material in a dispersion medium, introducing them into a commercially available laser diffraction particle size measuring device (e.g., HORIBA LA-960), irradiating them with ultrasound of approximately 28 kHz at an output of 60 W, and then measuring the average particle size (D) corresponding to 50% of the volume accumulation amount of in the measuring device. 50 ) can be produced.

[0021] In this specification, "single particle" is a concept contrasted with a secondary particle form formed by the aggregation of tens to hundreds of primary particles, and means composed of 10 or fewer primary particles. Specifically, in the present invention, a single particle may be a single particle composed of one primary particle, or it may be a particle form formed by the aggregation of several primary particles.

[0022] In this specification, "primary particle" refers to the smallest unit of particle recognized when observing an active material through a scanning electron microscope, and "secondary particle" refers to a secondary structure formed by the aggregation of tens to hundreds of primary particles.

[0023] According to one embodiment of the present specification, the present invention comprises a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode comprises a lithium nickel-based active material and the negative electrode comprises a silicon-based active material, the electrolyte comprises a carbonate-based solvent, an amide-based solvent, and a lithium salt, wherein the lithium salt comprises a lithium salt containing a fluorine-based inorganic anion and a sulfonylimide-based lithium salt, and wherein the amide-based solvent is included in an amount greater than 10 vol% and less than or equal to 25 vol% based on 100 vol% of the solvent included in the electrolyte, and the molar ratio of the sulfonylimide-based lithium salt is greater than 10 mol% and less than 50 mol% based on 100 mol% of the lithium salt.

[0024] In one embodiment of the present specification, the amide-based solvent may be included in an amount greater than 10 vol%, 13 vol% or more, or 15 vol% or more based on 100 vol% of the solvent included in the electrolyte, 25 vol% or less, 23 vol% or less, or 20 vol% or less, or greater than 10 vol% and 25 vol% or less, 13 vol% or more, 23 vol% or less, or 15 vol% or more and 20 vol% or less.

[0025] If the above amide-based solvent is included in an amount exceeding the above range, the ionic conductivity decreases due to the increase in the viscosity of the electrolyte, which may lead to an increase in resistance. On the other hand, if the amide-based solvent is included in an amount below the above range, durability may be compromised in high-temperature environments.

[0026] In one embodiment of the present specification, the carbonate-based solvent may include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and propylene carbonate (PC).

[0027] In particular, among the above carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate can be used as high-viscosity organic solvents because they have a high dielectric constant and effectively dissociate lithium salts. Additionally, if low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed with these cyclic carbonates in appropriate proportions, an electrolyte with high electrical conductivity can be produced and used.

[0028] In one embodiment of the present specification, the amide-based solvent may include one or more of formamide, dimethylformamide, dimethylsulfamoylfluoride, and diethylsulfamoylfluoride.

[0029] The above-mentioned amide-based solvent has a high dielectric constant, which allows it to dissolve lithium ions well; its high polarity increases compatibility with electrolyte salts; and it possesses high thermal stability. However, if the amide-based solvent is used alone, its high viscosity results in high viscosity during battery operation, which is disadvantageous from the perspective of rapid charging. In contrast, when a carbonate-based solvent and an amide-based solvent are mixed in an appropriate ratio, not only can the electrolyte salt be dissolved more effectively, but an electrolyte with high thermal stability can also be obtained while appropriately controlling viscosity.

[0030] In one embodiment of the present specification, the molar ratio of the sulfonylimide-based lithium salt may be greater than 10 mol%, 13 mol% or more, 15 mol% or more, or 20 mol% or more based on 100 mol% of the lithium salt; less than 50 mol%, 48 mol% or less, 45 mol% or less, or 40 mol% or less; greater than 10 mol% and less than 50 mol%, 13 mol% or more and 48 mol% or less, 15 mol% or more and 45 mol% or less, or 20 mol% or more and 40 mol% or less. If the molar ratio of the sulfonylimide-based lithium salt exceeds the above range, resistance increases due to gas generation, and a vent risk may occur when applied to a pouch battery. On the other hand, if the molar ratio of lithium bisfluorosulfonylimide (LiFSI) is below the above range, the high-temperature stability of the electrolyte is inferior, and salt decomposition within the electrolyte is promoted during the rapid charging process, which may result in inferior durability.

[0031] In one embodiment of the present specification, the lithium salt containing the fluorine-based inorganic anion may include any one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), and lithium hexafluoroarsenate (LiAsF6), and specifically may be lithium hexafluorophosphate (LiPF6).

[0032] In one embodiment of the present specification, the sulfonylimide-based lithium salt may include any one of lithium bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), and lithium bispentafluoroethanesulfonylimide (LiBETI), and specifically may be lithium bisfluorosulfonylimide (LiFSI).

[0033] In one embodiment of the present invention, the concentration of the lithium salt may be 0.8 M to 1.4 M. Specifically, the concentration of the lithium salt may be 0.8 M or more, 0.9 M or more, or 1.0 M or more, 1.4 M or less, 1.35 M or less, or 1.3 M or less, or 0.8 M or more and 1.35 M or less, 0.9 M or more and 1.3 M or less, or 1.0 M or more and 1.3 M or less.

[0034] In one embodiment of the present invention, the lithium salt may be included in an amount of 10 to 15 parts by weight based on 100 parts by weight of the electrolyte. Specifically, the weight of the lithium salt may be 10 parts by weight or more, 11 parts by weight or more, or 12 parts by weight or more; 15 parts by weight or less, 14.5 parts by weight or less, or 14 parts by weight or less; or 10 parts by weight or more and 14.5 parts by weight or less, 11 parts by weight or more and 14 parts by weight or less, or 12 parts by weight or more and 14 parts by weight or less.

[0035] If the concentration of lithium salt in the electrolyte exceeds the above range, the viscosity increases and the ion conductivity decreases, which may result in disadvantages in terms of rapid charging performance, and if it is below the above range, appropriate electrical conductivity cannot be obtained.

[0036] In one embodiment of the present specification, the ionic conductivity of the electrolyte may be 6.5 mS / cm or higher. Specifically, the ionic conductivity of the electrolyte may be 8 mS / cm or higher, or 10 mS / cm or higher.

[0037] In addition to the components of the above electrolyte, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, haloalkylene carbonate compounds such as fluoroethylene carbonate and difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0038]

[0039] <Polar>

[0040] In one embodiment of the present specification, the anode may include a lithium composite transition metal compound containing nickel (Ni) as a lithium nickel-based active material. The lithium composite transition metal compound may further include at least one of cobalt, manganese, and aluminum. The lithium composite transition metal compound may contain 80 mol% or more of nickel among 100 mol% of metals excluding lithium. Specifically, the lithium composite transition metal compound may contain 85 mol% or more, 90 mol% or more, or 95 mol% or more of nickel among 100 mol% of metals excluding lithium, and may contain less than 100 mol%, 98 mol% or less, or 96 mol% or less.

[0041] In one embodiment of the present specification, the positive active material may comprise a plurality of positive active materials having different nickel contents.

[0042] In one embodiment of the present specification, the positive active material has an average particle size (D 50 ) may be less than 7㎛. Specifically, the above-mentioned positive active material has an average particle size (D 50) may be less than 7㎛, 6.5㎛ or less, or 6㎛ or less, greater than 2.8㎛ and 3㎛ or more, or 3.3㎛ or more, 2.8㎛ or more and less than 7㎛, 3㎛ or more and 6.5㎛ or less, or 3.3㎛ or more and 6㎛ or less.

[0043] In one embodiment of the present specification, the positive active material may include single particles or secondary particles, but is not limited thereto.

[0044] In one embodiment of the present specification, the lithium nickel-based active material may be a single particle or a secondary particle, for example, a single particle. When the lithium nickel-based active material is a single particle, the occurrence of microcracks is suppressed, and structural stability during the charge-discharge process is improved. As a result, electrical and mechanical degradation within the electrode is mitigated, which has the advantage of improving cycle life and high-temperature stability.

[0045] In one embodiment of the present specification, the anode has an average particle size (D 50 ) may include multiple different positive active materials.

[0046] In one embodiment of the present specification, the anode may include an anode active material layer, and based on 100 parts by weight of the anode active material layer, the anode active material may include 80 parts by weight or more, 90 parts by weight or more, or 95 parts by weight or more, and may include less than 100 parts by weight, 98 parts by weight or less, or 96 parts by weight or less.

[0047] The above-described positive electrode may further include a positive current collector in addition to the aforementioned positive active material layer, wherein the positive active material layer is formed on at least one surface of the positive current collector.

[0048] In the above-mentioned positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc., may be used, and specifically, aluminum foil may be used. In addition, the above-mentioned positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0049] The above-described positive active material layer may include a positive conductive material and a positive binder together with the positive active material described above.

[0050] At this time, the above-mentioned positive conductive material is used to impart conductivity to the electrode, and in the battery being constructed, any material that has electronic conductivity without causing chemical changes can be used without special limitations. 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, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxide such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0051] In one embodiment of the present invention, carbon nanotubes may be used as the positive electrode conductive material, and specifically, multi-wall carbon nanotubes may be used.

[0052] The content of the conductive material in the positive active material layer may be 0.01 to 20 parts by weight, preferably 0.03 to 18 parts by weight, relative to 100 parts by weight of the negative active material layer.

[0053] In addition, the anode binder serves to improve adhesion between anode active material particles and adhesion between the anode active material and the anode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-coHFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, hydrogenated nitrile rubber (HNBR), or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0054] The anode binder may be included in an amount of 0.1 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the anode active material layer, for example, 0.3 parts by weight or more and 20 parts by weight or less, or 0.5 parts by weight or more and 10 parts by weight or less.

[0055] The above positive active material layer can be formed by applying a positive slurry containing a binder and / or a conductive material together with a lithium nickel-based active material in the form of a single particle to at least one surface of a positive current collector, and then drying and rolling.

[0056] An anode slurry according to one embodiment of the present invention may further include a solvent for forming an anode slurry. Specifically, the solvent for forming an anode slurry may include methylpyrrolidone (NMP), etc., in terms of facilitating the dispersion of components.

[0057]

[0058] <Cathode>

[0059] A cathode according to one embodiment of the present invention comprises a cathode active material layer, and the cathode active material layer comprises a silicon-based active material.

[0060] According to one embodiment of the present invention, the negative electrode active material layer may further include a carbon-based active material.

[0061] The above-described cathode may further include a cathode current collector in addition to the aforementioned cathode active material layer, wherein the cathode active material layer is formed on at least one surface of the cathode current collector. The cathode active material layer comprises the silicon-based active material and the carbon-based active material. Furthermore, the cathode active material layer may further include a binder and / or a conductive material.

[0062] In one embodiment, the silicon-based active material comprises at least one of silicon oxide, silicon metal complex, and silicon carbon complex. Specifically, the silicon-based active material comprises at least one of SiOx (0≤x<2), SiMy (M is a metal, 1≤y≤4), and Si / C. The silicon-based active material may comprise only one type or two or more types together. When both negative electrode active material layers comprise silicon-based active materials, the silicon-based active material of the same type may be used in the two active material layers, or silicon-based active materials of different types or different combinations may be used.

[0063] 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, 이차전지의 방전 용량이 개선될 수 있다.

[0064] The above silicon carbon composite is a composite of Si and C, wherein Si and C (e.g., graphite) are present respectively. In this specification, the above silicon carbon composite may be denoted as Si / C. The above silicon carbon composite may consist of Si and C that are not bonded to each other, but may include additional components as necessary. For example, the above silicon carbon composite may or may not include silicon carbide denoted as SiC. If the above silicon carbon composite includes silicon carbide, its content is 10 weight% or less. The above silicon carbon composite may exist in a crystalline, amorphous, or mixed state. According to one example, C in the above silicon carbon composite may exist in an amorphous state. The average particle size (D) of the active material containing the above Si / C 50 The ) may be 2㎛ or more, 3㎛ or more, or 4㎛ or more, 15㎛ or less, 12㎛ or less, or 10㎛ or less, 2㎛ to 15㎛, specifically 3㎛ to 12㎛, and more specifically 4㎛ to 10㎛. 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 realized.

[0065] 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 imparted to the silicon-based composite particles, and the initial efficiency, lifespan characteristics, and battery capacity characteristics of a secondary battery including a negative electrode active material comprising the silicon-based composite particles may be improved. The total weight of the carbon layer may be included in an amount of 5% to 40% by weight based on 100% by weight of the total silicon-based composite particles.

[0066] In one embodiment of the present specification, the carbon layer may include at least one of amorphous carbon and crystalline carbon.

[0067] According to one embodiment of the present invention, the carbon-based active material may be used without particular limitation, and representative examples include crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite and artificial graphite, and examples of amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke. The graphite may be natural graphite, artificial graphite, or a mixture thereof.

[0068] According to one embodiment of the present specification, a silicon-based active material may be included in an amount of 1 to 15 parts by weight based on 100 parts by weight of total negative electrode active material included in the negative electrode active material layer. For example, the silicon-based active material may be included in an amount of 1 part by weight or more, 3 parts by weight or more, or 5 parts by weight or more, 15 parts by weight or less, 13 parts by weight or less, or 10 parts by weight or less, or 1 to 13 parts by weight, or 5 to 13 parts by weight.

[0069] According to one embodiment of the present specification, based on 100 parts by weight of 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 85 parts by weight or more, 87 parts by weight or more, or 90 parts by weight or more, 99 parts by weight or less, 97 parts by weight or less, or 95 parts by weight or less, or 85 parts by weight or more and 99 parts by weight or less, 87 parts by weight or more, 97 parts by weight or less, or 90 parts by weight or more and 95 parts by weight or less.

[0070] In one embodiment of the present specification, the cathode comprises a current collector and a cathode active material layer, and the cathode active material in 100 parts by weight of the cathode active material layer 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.

[0071] According to further embodiments of the present specification, the negative electrode active material layer may additionally include a negative electrode binder in addition to the negative electrode active material.

[0072] The above-mentioned cathode binder can serve to improve the adhesion between cathode active material particles and the adhesion between the cathode active material particles and the cathode current collector. The above-mentioned cathode binder may be those known in the art, and non-limiting examples may include at least one selected from the group consisting of polyvinylidenefluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), hydrogenated nitrile rubber (HNBR), fluororubber, polyacrylic acid, and materials in which the hydrogens thereof are substituted with Li, Na, or Ca, etc., and various thereof It may include copolymers.

[0073] The above-mentioned cathode binder may be included in an amount of 0.1 parts by weight or more and 20 parts by weight or less based on 100 parts by weight of the cathode active material layer, for example, 0.1 parts by weight or more, 0.3 parts by weight or more, or 0.5 parts by weight or more, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less, or 0.3 parts by weight or more and 20 parts by weight or less, or 0.5 parts by weight or more and 10 parts by weight or less.

[0074] The above-mentioned negative electrode active material layer may not include a conductive material, but may include a conductive material as needed. The conductive material included in the above-mentioned negative electrode active material layer is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, Farnes black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0075] In one embodiment of the present invention, carbon nanotubes may be used as the cathode conductive material, and specifically, single-wall carbon nanotubes may be used.

[0076] The content of the conductive material in the above-mentioned cathode active material layer may be 0.01 to 20 parts by weight, preferably 0.03 to 18 parts by weight, relative to 100 parts by weight of the cathode active material layer.

[0077] 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.

[0078] In one embodiment of the present specification, the negative current collector may be conductive without causing chemical changes in the battery, and is not particularly limited. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used as the current collector. Specifically, transition metals that adsorb carbon well, such as copper and nickel, may be used as the current collector, and specifically, copper foil may be used. The thickness of the current collector may be 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0079] The above-described anode and cathode may be manufactured according to conventional methods for manufacturing anodes and cathodes, except for using the description above. Specifically, they may be manufactured by applying a composition for forming an active material layer, comprising the above-described active material and optionally a binder and a conductive material, onto a current collector, followed by drying and rolling. At this time, the types and contents of the anode and cathode active materials, binder, and conductive material are as described above. The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one of these alone or a mixture of two or more may be used. The amount of solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder, taking into account the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity during subsequent coating for the manufacture of anodes and cathodes. Alternatively, the anode and cathode may be manufactured by casting the composition for forming the active material layer onto a separate support and then laminating the film obtained by peeling off from the support onto a current collector.

[0080]

[0081] Separator and Secondary Battery

[0082] In one embodiment of the present specification, the lithium secondary battery comprises a positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0083] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used in secondary batteries can be used without special restrictions, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte wettability. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure. Specifically, the above-mentioned separation membrane may be coated with a composition comprising inorganic particles and a binder on a porous polymer film, and more specifically, the inorganic particles may include alumina oxide (Al2O3), and the binder may be any one of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyacrylonitrile, and polyacrylic acid.

[0084] According to one embodiment of the present invention, the thickness of the separator may be 5㎛ to 20㎛. Specifically, it may be 5㎛ to 15㎛, or 10㎛ to 15㎛.

[0085] According to one embodiment of the present invention, the thickness of the porous polymer film may be 3 µm to 15 µm. Specifically, it may be 3 µm to 12 µm, or 5 µm to 10 µm.

[0086] According to one embodiment of the present specification, when the slope (% / day) of the capacity retention rate according to the storage period at 60°C in the SOC 100 state of the lithium secondary battery is denoted as D60 and the slope (% / day) of the capacity retention rate according to the storage period at 80°C is denoted as D80, the ratio of D80 to D60 may be 10 or less. Specifically, the ratio of D80 to D60 may be 9 or less or 8 or less.

[0087] In this specification, the capacity retention rate may refer to the ratio of the capacity being maintained to the capacity at the beginning of life based on a discharge capacity of 0.33C.

[0088] According to one embodiment of the present specification, when the slope (% / day) of the resistance increase rate according to the storage period at 60°C in the SOC 100 state of the lithium secondary battery is denoted as R60 and the slope (% / day) of the resistance increase rate according to the storage period at 80°C is denoted as R80, the ratio of R80 to R60 may be 35 or less. Specifically, the ratio of R80 to R60 may be 34.5 or less or 34 or less.

[0089] In this specification, the resistance increase rate may refer to the ratio of the increase in resistance relative to the resistance in the initial state (Begin of Life) based on resistance when a pulse current of 2.5C is applied for 10 seconds in a state of 50% SOC.

[0090] Further embodiments of the present invention provide a battery module comprising the aforementioned secondary battery as a unit cell and a battery pack comprising the same. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability and cycle capability, they can be used as a power source for medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0091] Since the secondary battery according to the embodiments of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, it can be used as a power source for portable devices such as mobile phones, laptop computers, and digital cameras, as well as for medium-to-large 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 one or more medium-to-large devices, including a power tool; an electric vehicle (EV), a hybrid electric vehicle, and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0092]

[0093] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the above embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the description, and that such variations and modifications fall within the scope of the appended claims.

[0094]

[0095] Examples 1 to 3 and Comparative Examples 1 to 4

[0096] Cell Production

[0097] Example 1.

[0098] Anode fabrication

[0099] A cathode slurry was prepared by adding a single-particle lithium composite transition metal compound containing nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al) as cathode active materials in an atomic ratio of 83:8:8:1, a conductive material (MWCNT), and a binder (polyvinylidene fluoride (PVDF) + hydridized nitrile rubber (HNBR)) in a weight ratio of 97:1.2:1.8 to a methylpyrrolidone (NMP) solvent.

[0100] The anode slurry prepared above was applied onto an Al current collector, dried, and then rolled at room temperature to produce an anode.

[0101] D as the above positive active material 50 A single-particle cathode active material with a particle size of 6.0 μm was used.

[0102]

[0103] Cathode fabrication

[0104] A cathode active material layer was prepared by adding a cathode active material (8 parts by weight of silicon-carbon composite based on 100 parts by weight of total cathode active material) containing a silicon-based active material and a carbon-based active material (including artificial graphite and natural graphite in a weight ratio of 8:2), carbon black and single-walled carbon nanotubes (SWCNT) as conductive materials, a binder (SBR), and a thickener (Na-CMC) in a weight ratio of 96.56:0.472:0.028:1.8:1.14 to a distilled water solvent to prepare a cathode slurry.

[0105] The cathode active material layer slurry prepared above was coated onto a Cu current collector, dried, and then rolled at room temperature to produce a cathode.

[0106]

[0107] Cell production

[0108] A cell was fabricated by interposing a separator between the anode and cathode prepared above, assembling the cells, injecting an electrolyte, and activating them.

[0109] The above separator was prepared by applying a coating solution containing alumina oxide (Al2O3) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co HFP) onto an 8㎛ thick polyethylene (PE) film to a thickness of 4㎛ and drying it.

[0110] The above electrolyte composition was prepared by mixing diethyl carbonate, ethylmethyl carbonate, and dimethylsulfamoyl fluoride in a volume ratio of 20:60:20. In addition, LiPF6 and LiFSI salts were added as lithium salts in a molar ratio of 85:15 so that they were included at a molar concentration of 1.0 M based on the total electrolyte.

[0111] - Activation: 0.1C, 3hrs. Degas after high / room temperature aging following filling.

[0112]

[0113] Example 2.

[0114] A secondary battery was manufactured in the same manner as in Example 1, except that the molar ratio of LiPF6 salt and LiFSI salt was 7:3.

[0115]

[0116] Example 3.

[0117] A secondary battery was manufactured in the same manner as in Example 1, except that the molar ratio of LiPF6 salt and LiFSI salt was 6:4.

[0118]

[0119] Comparative Example 1.

[0120] A secondary battery was manufactured in the same manner as in Example 1, except that only a carbonate-based solvent was used as the solvent for the electrolyte.

[0121]

[0122] Comparative Example 2.

[0123] A secondary battery was manufactured in the same manner as in Example 1, except that the molar ratio of LiPF6 salt and LiFSI salt was 5:5.

[0124]

[0125] Comparative Example 3.

[0126] A secondary battery was prepared in the same manner as in Example 1, except that ethyl carbonate, ethyl methyl carbonate, and diethyl sulfamoyl fluoride were mixed in a volume ratio of 20:50:30 as the solvents for the electrolyte.

[0127]

[0128] Comparative Example 4.

[0129] A secondary battery was manufactured in the same manner as in Example 1, except that the molar ratio of LiPF6 salt and LiFSI salt was 9:1.

[0130]

[0131] Experimental Example 1. Evaluation of capacity retention rate when stored at 60℃

[0132] The discharge capacity was measured when stored for 4, 8, 12, and 16 weeks under conditions of 60°C at a state of charge (SOC) of 100%. Afterward, the capacity retention rate was calculated by comparing it with the initial state (BOL) discharge capacity of 0.33C.

[0133]

[0134] Experimental Example 2. Evaluation of capacity retention rate when stored at 80℃

[0135] The discharge capacity was measured when stored for 2, 4, and 6 days under conditions of 80°C at a state of charge (SOC) of 100%. Afterward, the capacity retention rate was calculated by comparing it with the initial state (BOL) discharge capacity of 0.33C.

[0136]

[0137] Experimental Example 3. Evaluation of resistance increase rate when stored at 60℃

[0138] After storing the batteries for 4, 8, 12, and 16 weeks at 60°C with a state of charge (SOC) of 100%, the resistance was measured when a pulse current of 2.5C was applied for 10 seconds at a state of charge of 50% to each battery. Then, the resistance increase rate was calculated by comparing it with the resistance when a pulse current of 2.5C was applied for 10 seconds at a state of charge of 50% from the initial state (BOL).

[0139]

[0140] Experimental Example 4. Evaluation of resistance increase rate when stored at 80℃

[0141] After storing the batteries for 2, 4, and 6 days at 80°C with a state of charge (SOC) of 100%, the resistance was measured when a pulse current of 2.5C was applied for 10 seconds at a state of charge of 50% for each battery. Then, the resistance increase rate was calculated by comparing it with the resistance when a pulse current of 2.5C was applied for 10 seconds at a state of charge of 50% in the initial state (BOL).

[0142]

[0143] The capacity retention rate and resistance increase rate of the batteries produced in the examples and comparative examples are listed in Table 1 below.

[0144] 60℃ Storage Condition 80℃ Storage Condition Duration of Slope (day) 285684112 Slope 246 Slope Example 1 Capacitance Retention Rate (%) 96.364 94.695 91.487 89.142 -0.0888 97.743 96.65 095.132 -0.785 8.835 Resistance Increase Rate (%) 0.927 2.867 4.388 88.25 30.084 4.687 89.23 6817.43 2.841 33.863 Example 2 Capacitance Retention Rate (%) 97.291 94.998 92.80 892.120 -0.085 98.18 96.73 95.23 -0.788 9.310 Resistance Increase Rate (%) 0.17 31.29 35.92 39.12 30.11 27.23 416.23 723.01 23.90 234.706 Example 3 Capacity Retention Rate (%) 96.28 094.278 90.50 088.35 1-0.098 597.62 196.198 94.019-0.968 39.835 Resistance Increase Rate (%) 0.748 3.24 36.45 69.58 30.10 67.85 612.598 23.12 33.70 634.913 Comparative Example 1 Capacity Retention Rate (%) 95.9 259 4.0 229 0.9 88 8.79 -0.0 87 96.5 19 4.9 29 1.9 3 -1.2 95 14.8 37 Resistance Increase Rate (%) -3.2 26 0.8 79 3.8 77 9.9 20.1 52 8.2 73 16.2 37 28.9 86 4.7 46 31.2 23 Comparative Example 2 Capacitance Retention Rate (%) 96.7 349 4.8 709 1.9 74 89.5 23 -0.0 8 89 6.8 249 5.8 79 2.9 1 -1.0 99 12.5 46 Resistance Growth Rate (%) -1.978 1.578 4.876 8.02 30.1197.134 18.26 332.560 5.440 45.744 Comparative Example 3 Capacity Retention Rate (%) 98.46 196.98 295.65 292.648 -0.067 98.145 96.48 795.888 -0.700 10.440 Resistance Growth Rate (%) 1.06 12.98 16.136 9.04 30.0968 8.245 13.468 22.88 43.69 3838.166 Comparative Example 4 Capacity Retention Rate (%) 96.03 293.1 2590.3 4787.095 -0.1 057 96.2 47 94.2 6090.1 25 -1.5 80614.957 Resistance Growth Rate (%) 0.8 123.0 125.4 359.7 350.1 04 267.8 5614.7 6024.8 124.06 739.009.

[0145]

[0146] As can be seen from the results of the examples and comparative examples in Table 1 above, the secondary battery in which the electrolyte composition satisfies the scope of the present invention did not show significant changes in terms of capacity retention rate and resistance increase rate even when the storage temperature condition increased.

[0147] Specifically, in the case of Examples 1 to 3, the decomposition of the electrolyte was suppressed even under high temperature conditions due to the appropriate ratio of amide-based solvent and sulfonylimide-based salt, and the LiFSI suppressed salt decomposition even at high temperatures, so that the ratio of the slopes of the capacity retention rate and resistance increase rate at 60°C storage conditions and the capacity retention rate and resistance increase rate at 80°C storage conditions satisfied values ​​of 10 or less and 35 or less, respectively.

[0148] However, in the case of Comparative Example 1, the weight ratio of the lithium salt satisfied the range of the present invention, and the ratio of the slope of the resistance increase rate satisfied a value of 35 or less; however, as a result that occurred because the resistance increase rate under storage conditions of 60°C and 80°C was greater than that of the example, the electrolyte decomposed and generated gas under high-temperature storage conditions because it did not contain an amide-based solvent, and consequently, the resistance increase rate was high and the capacity retention rate dropped sharply. In addition, in the case of Comparative Example 2, the LiFSI salt was excessively included, so gas was generated under high-temperature conditions, the resistance increased, and the capacity retention rate was poor.

[0149] In Comparative Example 3, the proportion of amide-based solvent in the electrolyte solvent was too high, which increased the viscosity of the electrolyte and consequently lowered the ionic conductivity, resulting in higher resistance compared to other examples and comparative examples. It can be confirmed that the ratio of the slopes of the capacity retention rate and resistance increase rate under storage conditions of 60°C and under storage conditions of 80°C is large.

[0150] In addition, Comparative Example 4 was a lithium salt, and the proportion of the sulfonylimide-based salt was too low, so the high-temperature stability of the electrolyte was inferior, and the decomposition of the salt in the electrolyte was promoted during the rapid charging process, so the ratio of the slopes of the capacity retention rate and resistance increase rate at 60°C storage conditions and the capacity retention rate and resistance increase rate at 80°C storage conditions was large.

Claims

1. A positive electrode; a negative electrode; a separator provided between the positive electrode and the negative electrode; and an electrolyte, comprising The above-mentioned positive electrode includes a lithium-nickel-based active material, and The above cathode includes a silicon-based active material, and The above electrolyte comprises a carbonate-based solvent; an amide-based solvent; and a lithium salt, and The above lithium salt comprises a lithium salt containing a fluorine-based inorganic anion; and a sulfonylimide-based lithium salt, and The above amide-based solvent is included in an amount of more than 10 vol% and less than or equal to 25 vol% based on 100 vol% of the solvent included in the electrolyte, and A lithium secondary battery in which the molar ratio of the above sulfonylimide-based lithium salt is greater than 10 mol% and less than 50 mol% based on 100 mol% of the above lithium salt.

2. A lithium secondary battery according to claim 1, wherein the carbonate-based solvent comprises one or more of ethylene carbonate (EC); dimethyl carbonate (DMC); diethyl carbonate (DEC); ethyl methyl carbonate (EMC); and propylene carbonate (PC).

3. A lithium secondary battery according to claim 1, wherein the amide-based solvent comprises one or more of formamide; dimethylformamide; dimethylsulfamoylfluoride; and diethylsulfamoylfluoride.

4. In claim 1, the lithium salt containing the fluorinated inorganic anion is lithium hexafluorophosphate (LiPF6), and The above sulfonylimide-based lithium salt is a lithium secondary battery in which lithium bisfluorosulfonylimide (LiFSI) is used.

5. A lithium secondary battery according to claim 1, wherein the concentration of the lithium salt is 0.8 M to 1.4 M.

6. A lithium secondary battery according to claim 1, wherein the ionic conductivity of the electrolyte is 6.5 mS / cm or higher.

7. A lithium secondary battery according to claim 1, wherein the positive electrode comprises a lithium nickel-based active material having a nickel content of 80 mol% or more of 100 mol% of metals excluding lithium, and comprising at least one of cobalt, manganese, and aluminum.

8. In claim 1, the lithium nickel-based active material is a single-particle lithium secondary battery.

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

10. A lithium secondary battery according to claim 1, wherein the negative electrode comprises 1 to 15 parts by weight of a silicon-based active material based on 100 parts by weight of a total negative electrode active material.

11. The lithium secondary battery according to claim 1, wherein the separator is a composition comprising inorganic particles and a binder coated on a porous polymer film.

12. A lithium secondary battery according to claim 11, wherein the thickness of the porous polymer film is 3 μm to 15 μm.

13. In Claim 1, A lithium secondary battery in which the ratio of D80 to D60 is 10 or less, where D60 is the slope (% / day) of the capacity retention rate according to the storage period at 60℃ in the SOC100 state and D80 is the slope (% / day) of the capacity retention rate according to the storage period at 80℃.

14. In Claim 1, A lithium secondary battery in which the ratio of R80 to R60 is 35 or less, where R60 is the slope (% / day) of the resistance increase rate according to a storage period of 60℃ in an SOC100 state and R80 is the slope (% / day) of the resistance increase rate according to a storage period of 80℃.

15. A battery module comprising a lithium secondary battery according to any one of claims 1 to 14.

16. A battery pack comprising a lithium secondary battery according to any one of claims 1 to 14.

17. A battery pack comprising the battery module of claim 15.