Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: a positive electrode including a positive current collector and a positive active material layer located on the positive current collector; a non-aqueous electrolyte; and a negative electrode; wherein the positive active material layer comprises lithium transition metal oxide particles, and the lithium transition metal oxide particles comprise 60 mol% or more of nickel (Ni) atoms with respect to 100 mol% of total transition metal atoms, and the non-aqueous electrolyte comprises a polyethylene glycol-based polymer with reduced water content.

Description

Technology Field

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

[0002] With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly rising. Among these secondary batteries, lithium secondary batteries, which exhibit high energy density and operating potential, long cycle life, and low self-discharge rate, have been commercialized and are widely used.

[0003] Furthermore, with the recent increase in interest in environmental issues, much research is being conducted on electric vehicles (EVs) and hybrid electric vehicles (HEVs) that can replace fossil fuel-using vehicles, such as gasoline and diesel cars, which are one of the major causes of air pollution.

[0004] Lithium-ion batteries that can be used in such electric vehicles, hybrid electric vehicles, etc., require high energy density, the ability to deliver high output in a short time, and long lifespan characteristics for long-term use.

[0005] Conventional layered lithium cobalt oxide (LiCoO2) is widely used as the cathode material for lithium secondary batteries, but it has limitations such as poor structural stability, low energy density, and poor price competitiveness due to the resource limitations of cobalt.

[0006] Accordingly, nickel-based cathode active materials are being considered because they are relatively abundant, low-cost, and capable of achieving high energy density. Although higher nickel content enables the realization of higher energy density, they suffer from problems such as rapid degradation of cycle characteristics during long-term use, swelling caused by gas generation within the battery in high-temperature environments, and reduced thermal safety due to low chemical stability.

[0007] Conventionally, the development of related technologies was pursued following the discovery that adding a certain amount of polyethylene glycol-based polymer additives to the electrolyte suppresses side reactions on the surface of the cathode active material. However, polyethylene glycol-based polymers possess high hygroscopicity due to the inclusion of hydrophilic hydroxyl groups, which can introduce moisture into the battery. This moisture introduces side reactions, such as the generation of hydrogen fluoride (HF), by reacting with the lithium salt (LiPF6) in the electrolyte. Furthermore, it causes problems by disrupting the cathode structure and decomposing the SEI (solid-electrolyte interphase) layer of the anode, thereby accelerating gas generation within the battery.

[0008] Accordingly, there is a need for lithium secondary batteries capable of preventing the risk of swelling and explosion caused by gas generation within the battery, as well as the degradation of lifespan characteristics. The problem to be solved

[0009] One aspect of the present invention aims to provide a lithium secondary battery that includes a high-nickel cathode active material with a high nickel content, while preventing the risk of swelling and battery explosion caused by gas generation within the battery and the degradation of lifespan characteristics in high-temperature environments. means of solving the problem

[0010] One embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive current collector and a positive active material layer located on the positive current collector; a non-aqueous electrolyte; and a negative electrode; wherein the positive active material layer comprises lithium transition metal oxide particles, and the lithium transition metal oxide particles comprise 60 mol% or more of nickel (Ni) atoms with respect to 100 mol% of total transition metal atoms, and the non-aqueous electrolyte comprises a polyethylene glycol-based polymer with reduced water content.

[0011] The electrode density of the above anode may be 3.3 g / cc or more and 4.2 g / cc or less, and specifically may be 3.5 g / cc or more and 3.8 g / cc or less.

[0012] The above lithium transition metal oxide particles may contain 80 mol% or more or 88 mol% or more of nickel (Ni) atoms relative to 100 mol% of total transition metal atoms.

[0013] The above-mentioned polyethylene glycol-based polymer with reduced moisture content may have a moisture content reduced by 50% or more compared to the polyethylene glycol-based polymer before the moisture content was reduced.

[0014] After charging the above lithium secondary battery to 4.2V in CC mode (Constant Current) with a current rate of 0.3C at 25℃ and then switching to CV mode (Constant Voltage) to complete charging under a 1 / 20C current cut-off condition, and storing it at 60℃ for one week, the amount of carbon dioxide generated may be 50% or less of the total amount of gas generated in the battery, which is 100% by volume.

[0015] After charging the above lithium secondary battery to 4.2V in CC mode (Constant Current) with a current rate of 0.3C at 25℃ and then switching to CV mode (Constant Voltage) to complete charging under a 1 / 20C current cut-off condition, and storing it at 60℃ for one week, the amount of carbon dioxide generated in the battery may be reduced by more than 45% compared to the amount of carbon dioxide generated when the polyethylene glycol-based polymer is not added to the above non-aqueous electrolyte.

[0016] The moisture content of the above-mentioned non-aqueous electrolyte may be 3.0 ppm or less.

[0017] The water content of the above-mentioned non-aqueous electrolyte may be reduced by 5 to 30% compared to the case where a polyethylene glycol-based polymer with no reduced water content is added.

[0018] The hydrogen fluoride (HF) content of the above-mentioned non-aqueous electrolyte may be 130 ppm or less.

[0019] The hydrogen fluoride (HF) content of the above-mentioned non-aqueous electrolyte may be reduced by 10 to 90% compared to the case where a polyethylene glycol-based polymer with no reduced water content is added.

[0020] A crack may exist on the surface of the lithium transition metal oxide particle, and the polyethylene glycol-based polymer may be located in the crack.

[0021] The above polyethylene glycol-based polymer may be located between the lithium transition metal oxide particles or on the surface of the lithium transition metal oxide particles.

[0022] At least a portion of the above polyethylene glycol-based polymer may form a coordination bond with at least a portion of the above lithium transition metal oxide.

[0023] The above polyethylene glycol-based polymer may include a compound represented by the following chemical formula 1.

[0024] [Chemical Formula 1]

[0025]

[0026] In the above Chemical Formula 1, n is an integer from 5 to 100, and R 1 is hydrogen, or a C1 to C4 linear or branched alkyl group, and R 2 is hydrogen, or a linear or branched C1 to C4 alkyl group.

[0027] The number average molecular weight (M) of the above polyethylene glycol-based polymer n ) may be 50g / mol or more and 2000g / mol or less.

[0028] The above polyethylene glycol-based polymer may include polyethylene glycol (PEG), polyethylene glycol dimethyl ether (PEGDME), or a mixture thereof.

[0029] The above polyethylene glycol-based polymer may include polyethylene glycol dimethyl ether (PEGDME).

[0030] The content of the polyethylene glycol-based polymer relative to the total 100% by weight of the above-mentioned non-aqueous electrolyte may be 0.1% by weight or more and 10% by weight or less.

[0031] The above positive active material layer may comprise lithium transition metal oxide particles represented by the following chemical formula 2:

[0032] [Chemical Formula 2]

[0033] Li a Ni 1-x-y-z Co x Mn y M z O b

[0034] In the above chemical formula 2, 0.5≤a≤1.3, 1.9≤b≤2.1, 0≤x≤0.4, 0≤y≤0.4, and 0≤x+y+z≤0.4, M is one or more substances selected from Al, Mg, Zr, and B, and 0≤z≤0.2.

[0035] The above positive active material layer may further include lithium transition metal oxide particles represented by the following chemical formula 3:

[0036] [Chemical Formula 3]

[0037] Li a Ni 1-x-y-z Co x Mn y M z O b

[0038] In Chemical Formula 3, 0.5≤a≤1.3, 1.9≤b≤2.1, 0.25≤x≤0.55, 0.25≤y≤0.55, and 0.5≤x+y+z≤0.8, M is one or more substances selected from Al, Mg, Zr, and B, and 0≤z≤0.2. Effects of the invention

[0039] A lithium secondary battery according to one embodiment of the present invention includes a high-nickel cathode active material having a high nickel content, and provides a lithium secondary battery capable of preventing the risk of swelling and battery explosion caused by gas generation within the battery and the degradation of lifespan characteristics in a high-temperature environment.

[0040] Accordingly, high energy density of the lithium secondary battery can be realized, and at the same time, the stability and lifespan characteristics of the battery according to charging and discharging can be significantly improved. Specific details for implementing the invention

[0041] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which the present invention pertains. Throughout the specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Furthermore, the singular form includes the plural form unless specifically stated otherwise in the text.

[0042] In this specification, when a part such as a layer, film, region, plate, etc. is described as being “on” or “on” another part, this includes not only cases where it is “immediately on” another part, but also cases where there is another part in between.

[0043] In addition, the terms “on” and “on” in this specification mean being located above or below the target part, and do not necessarily mean being located on the upper side with respect to the direction of gravity.

[0044] In this specification, "room temperature" means 25°C unless specifically defined otherwise.

[0046] To increase the energy density of lithium secondary batteries, high-capacity cathode active materials must be used and rolled to a higher density to generate a large amount of energy per unit volume. To increase the capacity of NCM-based cathode active materials, the nickel content in the cathode active material must be increased; however, as the nickel content increases, it becomes chemically unstable and prone to reacting with the electrolyte. For example, when exposed to a high-temperature environment of 40°C or higher, a large amount of carbon dioxide (CO2) is generated due to the reaction between the high-nickel cathode active material and the electrolyte, which can increase the amount of gas generated within the battery.

[0047] Furthermore, if the positive electrode is rolled to a higher density to increase the energy density of the battery, the particles of the positive active material may break during the rolling process, causing numerous cracks to occur within the positive active material. These cracks can accelerate side reactions with the electrolyte, which can rapidly increase the amount of gas generated within the battery in a high-temperature environment.

[0048] These gases seep between unit cells, causing the lithium secondary battery to swell. Consequently, this can lead to increased resistance due to the increased distance between interfaces, such as electrodes and separators, and furthermore, a rapid decline in battery lifespan. Additionally, severe gas generation increases the internal pressure of the pouch, which can significantly raise the risk of battery explosion.

[0049] When a cathode containing a high-nickel cathode active material is included, carbon dioxide generated at the cathode is the main cause of increased gas generation in the battery, and in order to prevent such problems, it is necessary to suppress the generation of carbon dioxide at the cathode.

[0050] One embodiment of the present invention is intended to solve the above-mentioned problems that occur when a high-nickel-based cathode active material is included in a lithium secondary battery, and may include a polyethylene glycol-based polymer with reduced water content as an additive to the high-nickel-based cathode active material and the electrolyte.

[0051] The effect of reducing the amount of carbon dioxide generated by mixing a polyethylene glycol-based polymer with reduced water content into the electrolyte is very significantly realized in a lithium secondary battery including a high-nickel cathode as in one embodiment of the present invention.

[0052] Specifically, one embodiment of the present invention provides a lithium secondary battery comprising: a positive electrode including a positive current collector and a positive active material layer located on the positive current collector; a non-aqueous electrolyte; and a negative electrode; wherein the positive active material layer comprises lithium transition metal oxide particles, and the lithium transition metal oxide particles comprise 60 mol% or more of nickel (Ni) atoms with respect to 100 mol% of total transition metal atoms, and the non-aqueous electrolyte comprises a polyethylene glycol-based polymer with reduced water content.

[0053] A lithium secondary battery of one embodiment of the present invention comprises lithium transition metal oxide particles in a positive electrode active material layer, and the lithium transition metal oxide particles may comprise a high-nickel positive electrode active material comprising 60 mol% or more of nickel atoms with respect to 100 mol% of total transition metal atoms.

[0054] At the same time, the non-aqueous electrolyte may contain a polyethylene glycol-based polymer with reduced water content, thereby suppressing the generation of carbon dioxide caused by the reaction between the electrolyte and the high-nickel cathode active material layer, which is chemically unstable and highly reactive.

[0055] Accordingly, it is possible to prevent problems such as the absorption of gases containing carbon dioxide between the unit cells of a lithium secondary battery, which causes swelling of the lithium secondary battery, reduces battery stability, and degrades battery life characteristics due to electrolyte depletion and electrode degradation.

[0056] Hereinafter, a lithium secondary battery of one embodiment of the present invention will be described in more detail.

[0057] Anode and non-aqueous electrolyte

[0058] A positive electrode of a lithium secondary battery according to one embodiment of the present invention comprises a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, wherein the positive electrode active material layer comprises lithium transition metal oxide particles, and the lithium transition metal oxide particles comprise 60 mol% or more of nickel (Ni) atoms with respect to 100 mol% of total transition metal atoms.

[0059] That is, the positive electrode of a lithium secondary battery according to one embodiment of the present invention corresponds to a high-nickel positive electrode containing 60 mol% or more of nickel atoms among the transition metal atoms in the positive electrode active material layer. More specifically, it may contain 70 mol% or more, 80 mol% or more, or 88 mol% or more of nickel atoms. The upper limit of the molar ratio of nickel atoms may be 100 mol% or less, or 95 mol% or less, although not limited thereto. Accordingly, a high energy density of the lithium secondary battery can be realized.

[0060] Meanwhile, a non-aqueous electrolyte of one embodiment of the present invention comprises a polyethylene glycol-based polymer with reduced water content.

[0061] A lithium secondary battery of one embodiment of the present invention is a high-nickel cathode and includes a polyethylene glycol-based polymer with reduced water content in the non-aqueous electrolyte. Therefore, as described above, problems such as electrolyte depletion, swelling of the battery due to the generation of carbon dioxide, and reduction of battery capacity can be improved.

[0062] Specifically, the lithium transition metal oxide particles of the positive electrode active material layer are crushed by the pressure received during the rolling process performed during the manufacturing of the positive electrode, causing cracks to form on the surface. A polyethylene glycol-based polymer with reduced water content contained in the non-aqueous electrolyte is positioned in the cracks, thereby blocking excessive contact with the electrolyte on the surface within the cracks. Accordingly, the generation of gases such as carbon dioxide caused by the reaction between the high-nickel positive electrode active material layer and the electrolyte can be suppressed, swelling can be prevented, the stability of the battery can be improved, and the deterioration of the battery's lifespan can be prevented.

[0063] In addition, the polyethylene glycol-based polymer can be located not only in the cracks of the lithium transition metal oxide particles but also between the lithium transition metal oxide particles or on the surface of the lithium transition metal oxide particles, thereby preventing excessive contact between the lithium transition metal oxide particles and the electrolyte.

[0064] For example, in a lithium secondary battery according to one embodiment, at least a portion of the polyethylene glycol-based polymer may form a coordination bond with at least a portion of the lithium transition metal oxide. Accordingly, the polyethylene glycol may surround the lithium transition metal oxide, and for example, when the lithium transition metal oxide includes a lithium-nickel-manganese-cobalt-based oxide, at least a portion of the polyethylene glycol-based polymer may form a coordination bond with the Ni+2 valence ion of the lithium transition metal oxide. Accordingly, there is an advantage in that the occurrence of cation mixing as described below is significantly reduced. In addition, the generation of gases such as carbon dioxide due to the reaction between the positive electrode active material layer and the electrolyte is suppressed, swelling is prevented, battery stability is improved, and the battery life is improved.

[0065] In one embodiment of the present invention, the electrode density of the positive electrode of a lithium secondary battery may be 3.3 g / cc or higher and 4.2 g / cc or lower. When such electrode density is satisfied, the effect of reducing the amount of gas, such as carbon dioxide, by mixing a polyethylene glycol-based polymer into the electrolyte is more significantly realized. Specifically, when the electrode density of a high-nickel positive electrode is 3.3 g / cc or higher, a relatively large amount of carbon dioxide is generated. When the electrode density is 3.3 g / cc or higher and 4.2 g / cc or lower, a polyethylene glycol-based polymer with reduced water content is added to the electrolyte, thereby significantly reducing the amount of carbon dioxide generated. More specifically, the electrode density of the positive electrode may be 3.5 g / cc or higher and 3.8 g / cc or lower. If the electrode density of the positive electrode is too low, there is a disadvantage in that high energy density cannot be satisfied. If the electrode density of the positive electrode is too high, it may be difficult to achieve the density with general rolling equipment as excessive pressure is required during the rolling process, and furthermore, it may be difficult to control the amount of carbon dioxide generated due to increased cracking of the positive electrode active material particles.

[0066] In a lithium secondary battery of one embodiment of the present invention, the electrode density of the positive electrode is the total weight of the positive electrode active material layer divided by the total volume, and can be calculated, for example, by punching the electrode to a certain size and measuring the mass and volume of the part excluding the current collector.

[0067] The moisture content of the polyethylene glycol-based polymer with reduced moisture content may be reduced by 50% by weight or more and 99.9% by weight or less compared to the moisture content of the polyethylene glycol-based polymer before the reduction in moisture content, for example, 60% by weight or more and 99.5% by weight or less, preferably 70% by weight or more and 99.5% by weight or less, more preferably 80% by weight or more and 99.5% by weight or less, or 95% by weight or more and 99.5% by weight or less. The polyethylene glycol-based polymer has the characteristic of high hygroscopicity as it contains hydrophilic hydroxyl groups, and can introduce moisture (H2O) into the battery. The introduced moisture reacts with the lithium salt (LiPF6) of the electrolyte to produce hydrogen fluoride (HF). HF spontaneously reacts with the electrode active material, which exhibits weak basicity, causing the electrode active material components to leach out and form lithium fluoride (LiF) on the surface of the positive electrode active material, which can lead to an increase in electrical resistance within the electrode and a decrease in battery life due to gas generation. Accordingly, the present invention can improve the aforementioned problem by reducing the moisture content of the polyethylene glycol-based polymer.

[0068] Meanwhile, regarding the reduction of the moisture content of the polyethylene glycol-based polymer, for example, the polyethylene glycol-based polymer solution is introduced into a moisture adsorbent and left for 6 to 18 hours, preferably 10 to 14 hours, to obtain a polyethylene glycol-based polymer with reduced moisture content, but the present invention is not limited thereto. As a non-limiting example, the moisture adsorbent may be 1 to 10 Å molecular sieves, preferably 1 to 8 Å molecular sieves, and more preferably 2 to 6 Å molecular sieves.

[0070] In one embodiment of the present invention, the amount of carbon dioxide generated among the total amount of gas generated within the battery after high-temperature storage may be 55% or less, preferably 50% or less, more preferably 40% or less, and most preferably 35% or less. This is a result of the amount of carbon dioxide generated being reduced compared to before the addition of a polyethylene glycol-based polymer with reduced moisture content into the electrolyte, thereby realizing excellent lifespan characteristics of the lithium secondary battery and simultaneously improving battery stability by preventing swelling of the battery. The lower limit may be, for example, 5% or more.

[0071] Here, high-temperature storage can be performed, for example, by charging a lithium secondary battery that has completed the formation process to 4.2V in CC mode (Constant Current) with a current rate of 0.3C in a 25℃ room temperature chamber, and then switching to CV mode (Constant Voltage) to complete charging under a 1 / 20C current cut-off condition, and then storing it in a convection oven at 60℃ for one week.

[0072] After such high-temperature storage, the lithium secondary battery is placed in a vacuum acrylic box, and a hole is made in the battery to achieve pressure equilibrium inside and outside the battery. Then, the total amount of gas (V, mL) generated after high-temperature storage can be calculated based on 1 atmosphere according to the following mathematical formula 1.

[0073] [Mathematical Formula 1]

[0074] 1atm x V = (P1-P0) x (V1-V0)

[0075] (P0 is the pressure of the acrylic box in a vacuum (atm), P1 is the pressure of the acrylic box after pressure equilibrium is achieved between the inside and outside of the battery (atm), V1 is the volume of the acrylic box (mL), and V0 is the volume of the lithium secondary battery immediately after the formation process is completed (mL).)

[0076] The amount of carbon dioxide generated after high-temperature storage can be obtained by collecting gas from inside the acrylic box, calculating the proportion of carbon dioxide in the total gas through gas chromatography analysis, and multiplying this by the total amount of gas calculated above.

[0077] Gas chromatography analysis may be performed using the Agilent 7890A GC-TCD device, but is not limited to this.

[0078] In a lithium secondary battery of one embodiment of the present invention, the effect of reducing the generation of gases such as carbon dioxide by mixing a polyethylene glycol-based polymer with reduced water content into the electrolyte is very significantly realized in a lithium secondary battery including a high-nickel cathode as in the present invention.

[0079] Specifically, the amount of carbon dioxide generated after high-temperature storage of a lithium secondary battery of one embodiment of the present invention may be reduced by more than 45% compared to the amount of carbon dioxide generated when the polyethylene glycol-based polymer is not added to the non-aqueous electrolyte. More specifically, it may be reduced by 55% or more and 90% or less, or by 75% or more and 90% or less.

[0080] Here, the high-temperature storage conditions and the method for calculating the amount of carbon dioxide generated are as described above.

[0081] Through this, as the amount of carbon dioxide generated within the battery is reduced, swelling is prevented, which can improve battery stability and prevent a decrease in battery life.

[0082] A lithium secondary battery of one embodiment of the present invention may have a significantly reduced moisture content of the non-aqueous electrolyte within the battery measured by disassembling the battery after the formation process, and specifically, the moisture content may be 3.0 ppm or less, 2.9 ppm or less, or 2.8 ppm or less, preferably 2.5 ppm or less, 2.4 ppm or less, or 2.3 ppm or less, more preferably less than 2.3 ppm, 2.2 ppm or less, or 2.1 ppm or less.

[0083] The moisture content of the non-aqueous electrolyte in such a battery may be reduced by 5% or more and 30% or less, 10% or more and 25% or less, or 10% or more and 20% or less compared to the moisture content when a polyethylene glycol-based polymer with no reduced moisture content is added.

[0084] Meanwhile, the moisture content of the polyethylene glycol-based polymer and the moisture content of the electrolyte may be in weight units.

[0085] In addition, a lithium secondary battery of one embodiment of the present invention may have a significantly reduced hydrogen fluoride (HF) content in the non-aqueous electrolyte within the battery, measured by disassembling the battery after the formation process, and specifically, the hydrogen fluoride content may be 130 ppm or less, 5 ppm or more and 120 ppm or less, 10 ppm or more and 100 ppm or less, 15 ppm or more and 80 ppm or less, 20 ppm or more and 70 ppm or less, or 25 ppm or more and 60 ppm or less.

[0086] The hydrogen fluoride content of the non-aqueous electrolyte in such a battery may be reduced by 10% or more and 90% or less, 20% or more and 80% or less, or 50% or more and 70% or less compared to the hydrogen fluoride content when a polyethylene glycol-based polymer with no reduced water content is added to the non-aqueous electrolyte.

[0087] In a lithium secondary battery of one embodiment of the present invention, the polyethylene glycol-based polymer may mean not only a polymer containing only -OCH2CH2 repeating units, but also a polymer containing 50 mol% or more, 60 mol% or more, or 70 mol% or more of -OCH2CH2 repeating units within the total repeating units.

[0088] For example, a polymer comprising 50 mol% of repeating units derived from ethylene glycol and 50 mol% of repeating units derived from propylene glycol may also be included in the polyethylene glycol-based polymer included in the lithium secondary battery of one embodiment of the present invention.

[0089] As a specific example, the above polyethylene glycol-based polymer may include one represented by Chemical Formula 1.

[0090] [Chemical Formula 1]

[0091]

[0092] In Chemical Formula 1, n is an integer from 5 to 100, and R 1 is hydrogen, or a C1 to C4 linear or branched alkyl group, and R 2 can be hydrogen, or a linear or branched C1 to C4 alkyl group.

[0093] Here, the linear or branched alkyl group of C1 to C4 may be, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or t-butyl.

[0094] The above polyethylene glycol-based polymer may more specifically include polyethylene glycol (PEG), polyethylene glycol monomethyl ether (mPEG), polyethylene glycol dimethyl ether (PEGDME), or a mixture thereof.

[0095] More specifically, polyethylene glycol dimethyl ether (PEGDME) may be included. While including polyethylene glycol dimethyl ether may result in improved lifespan characteristics, the present invention is not necessarily limited thereto.

[0096] The number average molecular weight (M) of the above polyethylene glycol-based polymer nThe range may be 50 g / mol or more and 2000 g / mol or less. More specifically, it may be 100 g / mol or more and 1000 g / mol or less, preferably 200 g / mol or more and 900 g / mol or less. When this range is satisfied, the polyethylene glycol-based polymer can be easily positioned in the cracks of the lithium transition metal oxide, and the generation of carbon dioxide due to side reactions between the anode and the electrolyte can be suppressed, which is desirable.

[0097] In a lithium secondary battery of one embodiment of the present invention, the content of the polyethylene glycol-based polymer with respect to a total of 100% by weight of the non-aqueous electrolyte may be 0.1% by weight or more and 10% by weight or less. If the content of the polyethylene glycol-based polymer is too low, the effect of suppressing carbon dioxide generation during high-temperature storage may be reduced, and if it is too high, the viscosity of the electrolyte increases, thereby reducing lithium ion mobility and consequently increasing the resistance of the battery.

[0098] More specifically, the content of the polyethylene glycol-based polymer may be 0.1% by weight or more and 5% by weight or less, 0.5% by weight or more and 3% by weight or less, or 0.5% by weight or more and 2% by weight or less, based on 100% by weight of the total non-aqueous electrolyte.

[0099] In a lithium secondary battery of one embodiment of the present invention, the positive active material layer may include lithium transition metal oxide particles represented by the following chemical formula 2.

[0100] [Chemical Formula 2]

[0101] Li a Ni 1-x-y-z Co x Mn y M z O b

[0102] In the above chemical formula 2, 0.5≤a≤1.3, 1.9≤b≤2.1, 0≤x≤0.4, 0≤y≤0.4, and 0≤x+y+z≤0.4, M is one or more materials selected from Al, Mg, Zr, and B, and 0≤z≤0.2.

[0103] In Chemical Formula 2, x, y, and z may more specifically be 0≤x≤0.3, 0≤y≤0.3, 0≤z≤0.1, and 0≤x+y+z≤0.3, and more specifically 0≤x≤0.2, 0≤y≤0.2, 0≤z≤0.08, and 0≤x+y+z≤0.2, or 0≤x≤0.12, 0≤y≤0.12, 0≤z≤0.05, and 0≤x+y+z≤0.12.

[0104] High energy density of lithium secondary batteries can be achieved by including such high-nickel cathode active materials. Meanwhile, as the content of Ni among transition metals increases, a phenomenon called cation mixing occurs during the charge-discharge process in which the positions of Li+1 ions and Ni+2 ions within the layered structure of the cathode active material are swapped, causing the structure to collapse. Consequently, the cathode active material may undergo side reactions with the electrolyte or exhibit leaching of transition metals. This occurs because the sizes of Li+1 ions and Ni+2 ions are similar. Ultimately, through these side reactions, the depletion of the electrolyte inside the secondary battery and the structural collapse of the cathode active material easily degrade the performance of the battery. At the same time, gas generation due to the side reactions increases the internal pressure of the cell, which can cause safety issues.

[0105] Recognizing these problems, by using an electrolyte with a polyethylene glycol-based polymer having reduced water content in the positive active material of Formula 2 according to one embodiment of the present invention, a coordination compound is formed in which the Ni 2+ ions of the positive active material and a part of the polyethylene glycol-based polymer are coordinately bonded, thereby suppressing the cation mixing phenomenon between Li +1 ions and Ni 2+ ions while securing the amount of nickel transition metal required to secure the capacity of the positive active material.

[0106] In addition, the positive electrode active material layer may further include lithium transition metal oxide particles represented by the following chemical formula 3.

[0107] [Chemical Formula 3]

[0108] Li a Ni 1-x-y-z Co x Mn y M z O b

[0109] In Chemical Formula 3, 0.5≤a≤1.3, 1.9≤b≤2.1, 0.25≤x≤0.55, 0.25≤y≤0.55, and 0.5≤x+y+z≤0.8, M is one or more substances selected from Al, Mg, Zr, and B, and 0≤z≤0.2.

[0110] That is, the lithium transition metal oxide particles represented by Chemical Formula 2 may be included alone in the positive electrode active material layer, or a mixture of lithium transition metal oxide particles represented by Chemical Formula 2 and lithium transition metal oxide particles represented by Chemical Formula 3 may be included.

[0111] When a mixture of lithium transition metal oxide particles represented by Chemical Formula 2 and lithium transition metal oxide particles represented by Chemical Formula 3 is included, the mixing ratio of the two can be determined such that the mole fraction of nickel atoms among the transition metal atoms in the total lithium transition metal oxide is 60% or more.

[0112] Although not necessarily limited to this, it may be beneficial from the perspective of improving energy density to include lithium transition metal oxide particles represented by the above chemical formula 2.

[0114] The other components of the anode and non-aqueous electrolyte are described below.

[0115] The above-mentioned positive electrode can be manufactured by preparing a slurry by mixing and stirring a solvent, an positive electrode binder and a conductive material with a positive electrode active material as needed, applying the slurry to a positive electrode current collector, drying it, and then rolling it to form a layer of positive electrode active material on the positive electrode current collector.

[0116] Al or Cu may be used as the anode current collector, but is not limited thereto.

[0117] The above-mentioned positive binder serves to adhere positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0118] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotube, metal powders such as copper, nickel, aluminum, and silver, metal fibers, etc., and one or more types of conductive materials such as polyphenylene derivatives can be used, but are not limited thereto.

[0120] The above-mentioned non-aqueous electrolyte may include a non-aqueous organic solvent and a lithium salt together with the polyethylene glycol-based polymer described above.

[0121] Non-aqueous organic solvents serve as a medium through which ions involved in the electrochemical reactions of the battery can move.

[0122] The above-mentioned non-aqueous organic solvent and lithium salt may include materials commonly used in the field of lithium secondary battery technology and are not limited to specific materials.

[0123] For example, the above-mentioned non-aqueous organic solvent may include carbonates, esters, ethers, or ketones alone or as a mixture thereof, but it may be preferable to select from cyclic carbonate solvents, linear carbonate solvents, and mixtures thereof, and it may be preferable to use a mixture of cyclic carbonate solvents and linear carbonate solvents. The above-mentioned cyclic carbonate solvent has high polarity and can sufficiently dissociate lithium ions, but it has the disadvantage of having high viscosity and low ionic conductivity. Therefore, the characteristics of a lithium secondary battery can be optimized by mixing the above-mentioned cyclic carbonate solvent with a linear carbonate solvent that has low polarity but low viscosity.

[0124] The above-mentioned cyclic carbonate-based solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and mixtures thereof, and the above-mentioned linear carbonate-based solvent may be selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, methylisopropyl carbonate, ethylpropyl carbonate, and mixtures thereof.

[0125] The above-mentioned non-aqueous organic solvent is a mixed solvent of a cyclic carbonate-based solvent and a linear carbonate-based solvent, wherein the volume ratio of the linear carbonate solvent to the cyclic carbonate solvent may be 1:1 to 9:1, and preferably, may be mixed in a volume ratio of 1.5:1 to 4:1.

[0126] The above lithium salts are not limited to but include LiPF6, LiBF4, LiClO4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, LiN(CF3SO2)2, LiN(SO3C2F5)2, LiCF3SO3, LiC4F9SO3, LiC6H5SO3, LiSCN, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 It may be one or more selected from the group consisting of SO2)(where x and y are natural numbers), LiCl, LiI, and LiB(C2O4)2.

[0127] The concentration of the lithium salt may be 0.1 M or higher and 2.0 M or lower, and more specifically, 0.7 M or higher and 1.6 M or lower. If the concentration of the lithium salt is less than 0.1 M, the conductivity of the electrolyte decreases, and the performance of the electrolyte deteriorates; if it exceeds 2.0 M, the viscosity of the electrolyte increases, and the mobility of lithium ions may decrease. The lithium salt acts as a source of lithium ions within the battery, enabling the basic operation of a lithium secondary battery.

[0129] cathode

[0130] In a lithium secondary battery of one embodiment of the present invention, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, and the negative electrode active material layer may comprise a negative electrode active material.

[0131] The above cathode can be manufactured by preparing a slurry by mixing and stirring a solvent, a cathode binder and a conductive material with a cathode active material as needed, applying the slurry to a cathode current collector, compressing it, and drying it to form a cathode active material layer on the cathode current collector.

[0132] The cathode is described in detail below, but the present invention is not limited thereto.

[0133] The above negative electrode active material may include a material capable of reversibly inserting / extracting lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide.

[0134] The material capable of reversibly inserting / extracting the above lithium ions is a carbon material, and any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries may be used. Specific examples may include crystalline carbon such as amorphous, plate-like, flake-like, spherical, or fibrous natural graphite or artificial graphite, amorphous carbon such as soft carbon or hard carbon, or combinations thereof.

[0135] The above lithium metal alloy may be an alloy of lithium with metals such as Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, or Sn.

[0136] The materials capable of doping and dedoping the above lithium are Si and SiO x (0 < x < 2), may be a Si-C complex, Sn, SnO2, or Sn-C complex.

[0137] The above transition metal oxide may be vanadium oxide or lithium vanadium oxide.

[0138] The above-mentioned cathode binder serves to effectively bond the cathode active material particles to each other and also to effectively bond the cathode active material to the cathode current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

[0139] Examples of the above-mentioned water-insoluble binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0140] Examples of the above-mentioned water-soluble binders include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and an olefin copolymer having 2 to 8 carbon atoms, a copolymer of (meth)acrylic acid and an alkyl ester of (meth)acrylate, or a combination thereof.

[0141] When a water-soluble binder is used as the above-mentioned cathode binder, a cellulose-based compound capable of imparting viscosity may be further included. As this cellulose-based compound, one or more types such as carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. Na, K, or Li may be used as the alkali metal.

[0142] The above conductive material is used to impart conductivity to the electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube; metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum, silver; conductive polymers such as polyphenylene derivatives; or conductive materials including mixtures thereof.

[0143] The above-mentioned cathode current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0145] Separator and lithium secondary battery

[0146] A lithium secondary battery of one embodiment of the present invention may further include a separator between the positive electrode and the negative electrode. The separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof, and may be made of a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator, but is not particularly limited.

[0147] In addition, to increase the stability of the lithium secondary battery, a separator may be used in which an inorganic material-containing layer including ceramic particles such as alumina is coated on one or both sides of the above-mentioned separator. However, the present invention is not limited thereto.

[0148] A lithium secondary battery of one embodiment of the present invention can be of any shape, such as coin type, button type, sheet type, stacked type, cylindrical type, flat type, or prismatic type, and can be manufactured by assembling the above-described positive electrode, negative electrode, non-aqueous electrolyte, and separator according to what is known in the art to suit the desired battery shape.

[0150] Preferred embodiments and comparative examples of the present invention are described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0151] Preparation Example 1: Method for preparing a polyethylene glycol-based polymer with reduced moisture content

[0152] The prepared PEGDME (100% solution, manufacturer: Sigma Aldrich) was placed in 4Å molecular sieves (product name: 208590, manufacturer: Merck) and left for 12 hours to reduce moisture. The moisture content of the PEGDME was 4064.6 ppm before moisture reduction and 70.7 ppm after moisture reduction.

[0154] Preparation Example 2: Method for manufacturing a lithium secondary battery

[0155] (1) An anode slurry was prepared by mixing 95 parts by weight of NCM-based anode active material particles, 2.0 parts by weight of carbon black conductive material, 1.0 parts by weight of graphite-based conductive material, 2.0 parts by weight of PVDF binder, and n-methyl-2-pyrrolidone (NMP) as a solvent. This was applied to a 12 µm thick aluminum film with a mass per area of ​​20 mg / cm² 2An anode coated electrode was manufactured by applying it and passing it through a hot air drying oven at 120°C. The anode coated electrode manufactured above was rolled using a roll press rolling facility to achieve a density of 3.6 g / cc or more to manufacture a final anode electrode.

[0156] A cathode slurry was prepared by adding 5 parts by weight of a graphite-based conductive material, 1.2 parts by weight of carboxymethylcellulose, 1.5 parts by weight of styrene-butadiene rubber, and pure water to 92.3 parts by weight of a cathode active material, which is a mixture of natural graphite and artificial graphite in a certain ratio. This was uniformly coated onto a 6 μm copper thin film and passed through a hot air drying oven at 120°C to produce a cathode coated electrode. The cathode coated electrode produced above was sufficiently rolled using a roll press rolling facility to produce a final cathode electrode.

[0157] After punching out a positive electrode and a negative electrode to a certain size, a jelly roll was manufactured by sequentially laminating them with a separator coated with ceramic powder on polyethylene resin. The manufactured jelly roll was inserted into a pouch formed to an appropriate size, positive and negative electrode tabs were welded, and a carbonate-based electrolyte (electrolyte 1) was injected. After the electrolyte injection was completed, the lithium-ion battery underwent an initial charging and room-temperature aging process, followed by a second aging process at a high temperature of 40°C to 45°C. The final lithium-ion battery was manufactured by completing a single formation charge-discharge process on the lithium-ion battery after the high-temperature aging was finished. Each formation condition was identical and was performed under charging (CC: 0.1C, 4.1V cut off, CV: 4.1V, 0.05C cut off) and discharging (CC: 0.1C, 2.5V cut off) conditions.

[0158] (2) PEGDME with a number average molecular weight of 500 and reduced water content according to Preparation Example 1 was added to electrolyte 1 at a concentration of 1 wt% and stirred sufficiently (electrolyte 2). A lithium-ion battery was prepared in the same manner as in (1) above, except that electrolyte 2 was used instead of electrolyte 1.

[0160] Discharge capacity and energy density per unit volume

[0161] The manufactured lithium-ion battery was charged to 4.2V in CC mode (Constant Current) with a current rate of 0.3C in a 25℃ room temperature chamber, and then the charging was completed by switching to CV mode (Constant Voltage) with a current cut-off condition of 1 / 20C. After a rest period of 30 minutes, it was discharged to 2.5V in CC mode, and the discharge capacity was measured. The energy density per unit volume was calculated by multiplying the measured discharge capacity by the average voltage during discharge and dividing by the volume of the lithium-ion battery cell.

[0163] Amount of gas generated after high-temperature storage

[0164] The manufactured lithium-ion battery was charged to 4.2V in CC mode with a current rate of 0.3C in a 25℃ room temperature chamber, and then switched to CV mode to complete charging under a 1 / 20C current cut-off condition. The lithium-ion battery, after being fully charged, was stored in a 60℃ convection oven for one week.

[0165] After high-temperature storage was completed, the lithium-ion battery was inserted into a sealed acrylic box under vacuum conditions, a hole was punctured in the pouch with a syringe needle, and the pressure inside and outside the battery was equalized before checking the pressure in the acrylic box.

[0166] At this time, the pressure was set to P1 (atm), the initial vacuum pressure of the acrylic box was set to P0 (atm), the volume of the acrylic box was set to V1 (mL), and the volume of the fresh cell immediately after the formation process was set to V0 (mL). The total volume (V, mL) occupied by gas at 1 atm was calculated using the following formula.

[0167] 1atm x V = (P1-P0) x (V1-V0)

[0168] About 20 mL of the gas generated at this time was collected and analyzed using gas chromatography (Gas chromatography, manufacturer: Agilent, model name: 7890A GC-TCD) to determine the proportion of carbon dioxide in the total amount of gas.

[0169] Finally, the total amount of carbon dioxide generated inside the lithium-ion battery was calculated by multiplying the total gas volume by the proportion of carbon dioxide measured through gas chromatography analysis.

[0171] Capacity retention rate after 200 charge-discharge cycles at 45℃

[0172] The manufactured lithium-ion battery was charged to 4.2V in CC mode with a current rate of 1.0C in a 45℃ high-temperature chamber, and then switched to CV mode to complete charging under a 1 / 20C current cut-off condition. After a rest period of 30 minutes, the battery was discharged to 2.5V in CC mode, and after another rest period of 30 minutes, the charging process was repeated 200 times. At this time, the ratio of the 200th discharge capacity to the initial discharge capacity was calculated and set as the capacity retention rate [%] after 200 cycles.

[0174] [Example 1]

[0175] A lithium-ion battery was manufactured according to the method for manufacturing a lithium secondary battery of Manufacturing Example 2 described above by mixing 70 wt% of an NCM-based cathode active material having a Ni content of 83 mol% and 30 wt% of an NCM-based cathode active material having a Ni content of 50 mol% among the total molar amounts of Ni, Co, and Mn. At this time, the final Ni content of the cathode active material was calculated to be 73.1 mol%.

[0176] For the manufactured lithium-ion battery, the 0.3C discharge capacity, the total amount of gas generated after high-temperature storage, the proportion of carbon dioxide in the total gas, the amount of carbon dioxide, and the capacity retention rate after 200 charge-discharge cycles at 45℃ were measured according to the method described above.

[0177] [Example 2]

[0178] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that only an NCM-based cathode active material with a Ni content of 80 mol% was used.

[0179] [Example 3]

[0180] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that only an NCM-based cathode active material with a Ni content of 83 mol% was used.

[0181] [Example 4]

[0182] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that only an NCM-based cathode active material with a Ni content of 88 mol% was used.

[0183] [Example 5]

[0184] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that only an NCM-based cathode active material with a Ni content of 60 mol% was used.

[0185] [Example 6]

[0186] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that the anode rolling density was set to 3.3 g / cc.

[0187] [Example 7]

[0188] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that the anode rolling density was set to 2.98 g / cc.

[0189] [Example 8]

[0190] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that after the initial charging and room temperature aging processes were performed on the lithium-ion battery after the electrolyte injection was finished, the process of charging to 4.0V to 4.1V at a 0.1C rate and the process of secondary aging at a high temperature of 40 to 45℃ were omitted, and the formation charge / discharge process was completed.

[0191] [Example 9]

[0192] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that an electrolyte containing polyethylene glycol dimethyl ether with a number average molecular weight of 500 at a concentration of 3% by weight was used instead of electrolyte 2.

[0193] [Comparative Example 1]

[0194] A lithium-ion battery was manufactured and evaluated in the same manner as in Example 1, except that only an NCM-based cathode active material with a Ni content of 50 mol% was used.

[0195] The total amount of gas, the proportion of carbon dioxide in the total gas, the amount of carbon dioxide, the reduction in carbon dioxide after the addition of PEGDME, and the capacity retention rate after 200 charge-discharge cycles at 45°C, as measured in Examples 1 to 8 and Comparative Example 1 above, are summarized in Tables 1 to 3 below.

[0196] division Example 1 Example 2 Example 3 Example 4 Design and performance Cathode Active Material #1 (Content, Weight%) Ni83 (70) Ni80 (100) Ni83 (100) Ni88 (100) Cathode Active Material #2 (Content, Weight%) Ni50 (30) - - - Anode active material Ni content (mol%) 73.1 80 83 88 anode density (g / cc) 3.61 3.74 3.7 3.63 Energy density per unit volume (Wh / L) 606 646 657 675 High-temperature aging process in Mars 4.0V 40℃ 24hr aging 4.1V 45℃ 24hr aging 4.1V 40℃ 24hr aging 4.0V 45℃ 24hr aging (1) No additives Gas (mL) after 1 week of storage in buffer cell at 60℃ 120.04 168.96 170.61 175.29 CO2 (mL) after buffer cell storage at 60℃ for 1 week 85.2 129.85 136.15 132.05 CO2 / Total gas(%) 71% 77% 80% 75% Capacity retention rate (%) at 45℃ and 1C for 200 cycles 84% 85% 83% 83% (2) Addition of moisture-reduced PEGDME Gas (mL) after 1 week of storage in buffer cell at 60℃ 38.14 55.12 60.52 62.56 CO2 (mL) after buffer cell storage at 60℃ for 1 week 11.26 21.41 22.45 23.72 CO2 / Total gas(%) 30 39 37 38 CO2 reduction (%) upon PEGDME addition 87 84 84 82 Capacity retention rate (%) at 45℃ and 1C for 200 cycles 95% 95% 95% 95%

[0197] division Example 5 Example 6 Example 7 Example 8 Design and performance Cathode Active Material #1 (Content, Weight%) Ni60 (100) Ni83 (70) Ni83 (70) Ni83 (70) Cathode Active Material #2 (Content, Weight%) - Ni50 (30) Ni50 (30) Ni50 (30) Anode active material Ni content (mol%) 60 73.1 73.1 73.1 anode density (g / cc) 3.69 3.3 2.98 3.61 Energy density per unit volume (Wh / L) 557 554 500 606 High-temperature aging process in Mars 4.0V 45℃ 24hr aging 4.0V 40℃ 24hr aging 4.1V 45℃ 24hr aging 4.0V 45℃ aging X (1) No additives Gas (mL) after 1 week of storage in buffer cell at 60℃ 100.03 75.4 42.3 149.68 CO2 (mL) after buffer cell storage at 60℃ for 1 week 64.8 35.8 8.1 112.87 CO2 / Total gas(%) 65% 47% 19% 75% Capacity retention rate (%) at 45℃ and 1C for 200 cycles 89% 90% 96% 89% (2) Addition of moisture-reduced PEGDME Gas (mL) after 1 week of storage in buffer cell at 60℃ 41.21 40.98 38.24 84.94 CO2 (mL) after buffer cell storage at 60℃ for 1 week 9.8 8.12 4.24 45.24 CO2 / Total gas(%) 24 20 11 53 CO2 reduction (%) upon PEGDME addition 85 77 48 60 Capacity retention rate (%) at 45℃ and 1C for 200 cycles 96 96 95 94

[0198] division Example 9 Comparative Example 1 Design and performance Cathode Active Material #1 (Content, Weight%) Ni83 (70) Ni50 (100) Cathode Active Material #2 (Content, Weight%) Ni50 (30) - Anode active material Ni content (mol%) 73.1 50 anode density (g / cc) 3.61 3.69 Energy density per unit volume (Wh / L) 606 537 High-temperature aging process in Mars 4.0V 45℃ 24hr aging 4.0V 40℃ 24hr aging (1) No additives Gas (mL) after 1 week of storage in buffer cell at 60℃ 120.04 54.2 CO2 (mL) after buffer cell storage at 60℃ for 1 week 85.2 18.6 CO2 / Total gas(%) 71% 34% Capacity retention rate (%) at 45℃ and 1C for 200 cycles 84% 97% (2) Addition of moisture-reduced PEGDME Gas (mL) after 1 week of storage in buffer cell at 60℃ 48.64 42.26 CO2 (mL) after buffer cell storage at 60℃ for 1 week 9.24 10.26 CO2 / Total gas(%) 19% 24% CO2 reduction (%) upon PEGDME addition 89 45 Capacity retention rate (%) at 45℃ and 1C for 200 cycles 95 96

[0199] As shown in Tables 1 to 3 above, Examples 1 to 9 of the present invention demonstrate that by adding PEGDME with reduced moisture content to a high-nickel anode of 60 mol% or more, the amount of carbon dioxide generated after high-temperature storage is significantly reduced, and the capacity retention rate after 200 charge-discharge cycles at 45°C is greatly improved. In addition, as the amount of carbon dioxide generated decreases, battery stability can be improved.

[0200] More specifically, in the case of Examples 1 to 6 and Example 9 of the present invention, the amount of carbon dioxide generated after high-temperature storage is large compared to Example 7, which has a small anode density, and Comparative Example 1, which includes a low-nickel anode, before the addition of PEGDME with reduced moisture content (see amount of carbon dioxide generated in the case of no additive), and the effect of reducing the amount of carbon dioxide generated by adding PEGDME with reduced moisture content in Examples 1 to 6 and Example 9 is prominent.

[0201] In addition, when comparing Examples 1 to 5 and Example 9 with Example 6, it can be seen that when the anode density exceeds 3.3 g / cc, the amount of carbon dioxide generated before the addition of PEGDME with reduced moisture content is high, and thus, when the anode density exceeds 3.3 g / cc, the effect of reducing the amount of carbon dioxide generated by the addition of PEGDME with reduced moisture content is prominent.

[0202] In addition, in the case of Examples 1 to 6 and Example 9 of the present invention, the amount of carbon dioxide generated among the total amount of gas generated after high-temperature storage following the addition of PEGDME with reduced moisture content is 50% or less, and in this case, it can be confirmed that the lifespan characteristics are further improved compared to Example 8.

[0203] In addition, in the case of Examples 1 to 6 and Example 9 of the present invention, it can be confirmed that the amount of carbon dioxide generated is reduced by more than 45% compared to before addition by adding PEGDME with reduced moisture content.

[0204] In addition, when PEGDME with reduced moisture content was added, the effect of improving lifespan characteristics was relatively excellent.

[0206] [Example 10]

[0207] For a lithium-ion battery prepared by adding PEGDME with reduced moisture content to the electrolyte in Example 1, the initial DC resistance, capacity retention rate, capacity recovery rate, cell thickness change rate, electrolyte moisture content, and electrolyte hydrogen fluoride (HF) content were measured according to the following method and are listed in Table 4 below.

[0209] Initial DC Resistance (DC-IR)

[0210] The manufactured lithium-ion battery was charged to 4.2V in CC mode with a current of 1.0C rate in a 45℃ high-temperature chamber, and then switched to CV mode to complete charging with a current cut-off condition of 1 / 20C.

[0211] Next, the DC resistance is calculated from the difference in current and voltage when different currents are applied. In the initial fully charged state, a constant current discharge of 10A was performed for 10 seconds, followed by a constant current discharge of 1A for 10 seconds, and then a constant current discharge of 10A for 4 seconds. The initial DC resistance was calculated using the equation ΔR = ΔV / ΔI from the data at 18 seconds and 23 seconds.

[0213] Capacity retention, capacity recovery, and cell thickness change at 60℃

[0214] The manufactured lithium-ion battery was charged to 4.2V in CC mode with a current of 1.0C rate in a 45℃ high-temperature chamber, and then switched to CV mode to complete charging under a 1 / 20C current cut-off condition. Subsequently, after leaving it at 60℃ for one week, the change in thickness, retention capacity, and recovery capacity were measured, and the results are shown in Table 4 below.

[0215] For thickness change, the thickness of the battery was measured before leaving it for 0 days, and the thickness was measured again using the same method after leaving it for one week to calculate the rate of change (%).

[0216] Capacity retention was calculated by storing the lithium-ion battery at 60°C for one week and then performing a 0.2C, 2.5V cutoff discharge, thereby determining the ratio of the discharge capacity after storage to the discharge capacity after one discharge (0 days).

[0217] The capacity recovery rate was measured by storing the lithium secondary battery at 60°C for one week, charging it to 4.2V in CC mode with a current rate of 1.0C, then switching to CV mode and completing the charge under a 1 / 20C current cut-off condition, followed by discharging with a 0.2C, 2.5V cut-off, and measuring the discharge capacity, and calculating the ratio of the discharge capacity to the initial capacity before storage.

[0219] Measurement of electrolyte moisture content and HF content

[0220] 1. Method for measuring electrolyte moisture content (Karl-Fischer)

[0221] 1) Check if the Dirift value has stabilized, 2) Perform a blank test with the moisture meter: measure without inserting a sample and repeat until the result becomes 0, 3) Inject about 0.5g of electrolyte with a syringe and perform moisture titration.

[0222] 2. Method for Measuring Hydrofluoric Acid Content

[0223] 1) Fill a burette with 0.01N TEA / EMC titration solution, 2) Add 50ml of acetone and 10g of electrolyte to a beaker and input the actual amount of electrolyte added to perform the measurement, and 3) Once the measurement is completed, the analysis result is obtained automatically by the calculation method (see below).

[0224] HF = Titrate input volume (mL) * Titrate concentration * F (Standardization factor) * 20006.3 / Sample volume (g)

[0226] [Comparative Example 2]

[0227] A lithium-ion battery was prepared and evaluated in the same manner as in Example 10, except that PEGDME with no reduced moisture content was used.

[0228] Comparative Example 2 Example 10 Initial capacity (mAh) 1891 1900 Initial thickness (mm) 5.38 5.44 Thickness after storage (mm) (high-temperature storage) 5.70 5.55 Thickness change rate (%) 106 102 Retention capacity (mAh) 1740 1767 Dose retention rate (%) 92 93 Recovery capacity (mAh) 1759 1790 Dose recovery rate (%) 93 94 Electrolyte moisture content (ppm) 2.3 2.0 Electrolyte HF content (ppm) 135 50

[0229] Referring to Table 4 above, it can be seen that when using PEGDME with reduced moisture content, the electrolyte moisture content and HF content are reduced compared to PEGDME with no reduced moisture content, and battery performance is also improved.

[0231] Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

Claim 1 A lithium secondary battery comprising: a positive electrode including a positive current collector and a positive active material layer located on the positive current collector; a non-aqueous electrolyte; and a negative electrode; wherein the positive active material layer comprises lithium transition metal oxide particles, and the lithium transition metal oxide particles comprise 60 mol% or more of nickel (Ni) atoms relative to 100 mol% of total transition metal atoms, and the non-aqueous electrolyte comprises a polyethylene glycol-based polymer, the water content of the non-aqueous electrolyte is less than 2.3 ppm, and the content of the polyethylene glycol-based polymer relative to 100 weight% of the total non-aqueous electrolyte is 1 weight% or more and 10 weight% or less. Claim 2 A lithium secondary battery according to claim 1, wherein the electrode density of the positive electrode is 3.3 g / cc or more and 4.2 g / cc or less. Claim 3 A lithium secondary battery according to claim 2, wherein the electrode density of the positive electrode is 3.5 g / cc or more and 3.8 g / cc or less. Claim 4 A lithium secondary battery according to claim 1, wherein the lithium transition metal oxide particles contain 80 mol% or more of nickel (Ni) atoms with respect to 100 mol% of total transition metal atoms. Claim 5 A lithium secondary battery according to claim 1, wherein the lithium transition metal oxide particles contain 88 mol% or more of nickel (Ni) atoms with respect to 100 mol% of total transition metal atoms. Claim 6 A lithium secondary battery according to claim 1, wherein the polyethylene glycol-based polymer has a moisture content reduced by 50% or more compared to the polyethylene glycol-based polymer before the moisture content is reduced. Claim 7 A lithium secondary battery according to claim 1, wherein the amount of carbon dioxide generated is 50 volume% or less relative to the total amount of gas generated within the battery, after charging the lithium secondary battery to 4.2V in CC mode (Constant Current) with a current rate of 0.3C at 25℃, then switching to CV mode (Constant Voltage) with a current amount cut-off condition of 1 / 20C to complete charging, and then storing at 60℃ for one week. Claim 8 A lithium secondary battery according to claim 1, wherein the amount of carbon dioxide generated within the battery after charging to 4.2V in CC mode (Constant Current) with a current rate of 0.3C at 25℃, then switching to CV mode (Constant Voltage) with a current amount cut-off condition of 1 / 20C to complete charging, and then storing at 60℃ for one week, is reduced by more than 45% compared to the amount of carbon dioxide generated when the polyethylene glycol-based polymer is not added to the non-aqueous electrolyte. Claim 9 A lithium secondary battery according to claim 1, wherein the moisture content of the non-aqueous electrolyte is 2.0 ppm or less. Claim 10 A lithium secondary battery according to claim 1, wherein the water content of the non-aqueous electrolyte is reduced by 5 to 30% compared to the case where a polyethylene glycol-based polymer with no reduced water content is added. Claim 11 A lithium secondary battery according to claim 1, wherein the hydrogen fluoride (HF) content of the non-aqueous electrolyte is 130 ppm or less. Claim 12 A lithium secondary battery according to claim 1, wherein the hydrogen fluoride (HF) content of the non-aqueous electrolyte is reduced by 10 to 90% compared to the case where a polyethylene glycol-based polymer with no reduced water content is added. Claim 13 A lithium secondary battery according to claim 1, wherein a crack exists on the surface of the lithium transition metal oxide particle and the polyethylene glycol-based polymer is located in the crack. Claim 14 A lithium secondary battery according to claim 1, wherein the polyethylene glycol-based polymer is located between the lithium transition metal oxide particles or on the surface of the lithium transition metal oxide particles. Claim 15 A lithium secondary battery according to claim 1, wherein at least a portion of the polyethylene glycol-based polymer forms a coordination bond with at least a portion of the lithium transition metal oxide. Claim 16 In claim 1, the above-mentioned polyethylene glycol-based polymer comprises a compound represented by the following chemical formula 1, in a lithium secondary battery: [Chemical Formula 1] In the above Chemical Formula 1, n is an integer from 5 to 100, and R 1 is hydrogen, or a C1 to C4 linear or branched alkyl group, and R 2 is hydrogen, or a linear or branched C1 to C4 alkyl group. Claim 17 In claim 1, the number average molecular weight (M) of the polyethylene glycol-based polymer n A lithium secondary battery having a g / mol of 50 g / mol or more and 2000 g / mol or less. Claim 18 In claim 1, the polyethylene glycol-based polymer comprises polyethylene glycol (PEG), polyethylene glycol dimethyl ether (PEGDME), or a mixture thereof, in a lithium secondary battery. Claim 19 In claim 18, the above-mentioned polyethylene glycol-based polymer is a lithium secondary battery comprising polyethylene glycol dimethyl ether (PEGDME). Claim 20 delete Claim 21 In claim 1, the positive active material layer comprises lithium transition metal oxide particles represented by the following chemical formula 2, in a lithium secondary battery: [Chemical Formula 2]Li a Ni 1-x-y-z Co x Mn y M z O b In the above chemical formula 2, 0.5≤a≤1.3, 1.9≤b≤2.1, 0≤x≤0.4, 0≤y≤0.4, and 0≤x+y+z≤0.4, M is one or more substances selected from Al, Mg, Zr, and B, and 0≤z≤0.

2. Claim 22 A lithium secondary battery according to claim 1, wherein the positive electrode active material layer further comprises lithium transition metal oxide particles represented by the following chemical formula 3: [Chemical Formula 3]Li a Ni 1-x-y-z Co x Mn y M z O b In Chemical Formula 3, 0.5≤a≤1.3, 1.9≤b≤2.1, 0.25≤x≤0.55, 0.25≤y≤0.55, and 0.5≤x+y+z≤0.8, M is one or more substances selected from Al, Mg, Zr, and B, and 0≤z≤0.2.

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