Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and a non-aqueous electrolyte solution, wherein the negative electrode active material comprises a silicon-carbon composite, and the non-aqueous electrolyte solution comprises a lithium salt and an organic solvent containing a cyclic carbonate-based compound, a linear carbonate-based compound, and a compound represented by chemical formula 1.

Description

lithium secondary battery

[0001] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0194812 filed December 23, 2024 and Korean Patent Application No. 10-2025-0188710 filed December 2, 2025, the entire contents of which are incorporated herein.

[0002] The present invention relates to a lithium secondary battery with improved high voltage and high temperature characteristics.

[0003] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive and negative electrodes include an active material capable of lithium ion intercalation and deintercalation.

[0004] The electrode of a lithium secondary battery is manufactured by applying an electrode slurry containing an electrode active material, a conductive material, and a binder onto an electrode current collector, drying it, rolling the electrode until it reaches a desired thickness, and vacuum drying it.

[0005] With the recent increase in demand for electric vehicles and the like, there is a growing need for batteries with high energy density and excellent rapid charging performance. Accordingly, there are active attempts to apply Si-based anode active materials as cathode materials, which have a large theoretical capacity and a fast reaction rate with lithium ions, resulting in superior rapid charging performance.

[0006] However, compared to carbon-based anode active materials, silicon-based anode active materials exhibit greater volume change during charging and discharging, leading to swelling and a deterioration in long-term lifespan characteristics. Consequently, silicon oxide (SiO), which shows relatively less volume change among silicon-based anode active materials, has been primarily used to date. However, silicon oxide-based anode active materials have lower capacity characteristics compared to other silicon-based anode active materials, such as Si or Si-C composites, which limits the increase in energy density.

[0007] The present invention aims to overcome the aforementioned limitations by applying a Si-C composite as the negative electrode active material and replacing a portion of the electrolyte solvent with a sulfonamide-based compound, thereby providing a lithium secondary battery having excellent high-temperature durability even at high voltages.

[0008] [1] The present invention is a lithium secondary battery comprising a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and a non-aqueous electrolyte, and

[0009] The above-mentioned negative electrode active material comprises a silicon-carbon composite, and

[0010] The present invention provides a lithium secondary battery comprising the above-mentioned non-aqueous electrolyte, a lithium salt; and an organic solvent comprising a cyclic carbonate-based compound, a linear carbonate-based compound, and a compound represented by the following chemical formula 1.

[0011] [Chemical Formula 1]

[0012]

[0013] In the above chemical formula 1,

[0014] R1 is a fluorine atom, a carbon-1 to carbon-10 alkyl group substituted with one or more fluorines, or a carbon-1 to carbon-10 alkoxy group substituted with one or more fluorines, and R2 and R3 are independently hydrogen, a carbon-1 to carbon-10 alkyl group, or a carbon-6 to carbon-20 aryl group.

[0015] [2] The present invention provides a lithium secondary battery according to [1], wherein the silicon-carbon composite has a structure in which Si is deposited within a carbon matrix.

[0016] [3] The present invention provides a lithium secondary battery, wherein the negative electrode active material in [1] or [2] further comprises a carbon-based negative electrode active material.

[0017] [4] The present invention provides a lithium secondary battery, wherein, in [3] the negative electrode active material comprises the silicon-carbon composite and the carbon-based negative electrode active material in a weight ratio of 1:99 to 30:70.

[0018] [5] The present invention provides a lithium secondary battery in which, in at least one of [1] to [4], the positive active material comprises a lithium nickel-based oxide having the composition of the following formula A.

[0019] Li 1+x (Ni a Co b Mn c M d )O2

[0020] In the above chemical formula A,

[0021] M is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0022] x, a, b, c, and d are -0.20≤x≤0.20, 0.50≤a<1, 0, respectively. <b<0.50, 0<c<0.50, 0≤d≤0.10, a+b+c+d=1을 만족한다.

[0023] [6] The present invention provides a lithium secondary battery in which, in at least one of [1] to [5], the positive active material comprises a lithium nickel-based oxide having a nickel content of 80 mol% or more among all metals excluding lithium.

[0024] [7] The present invention provides a lithium secondary battery in which, in at least one of [1] to [6], the positive active material comprises a single-particle lithium nickel-based oxide.

[0025] [8] The present invention provides a lithium secondary battery in which, in at least one of [1] to [7], the compound represented by Formula 1 is selected from the group consisting of one or more compounds represented by Formulas 1-1 to 1-5.

[0026] [Chemical Formula 1-1]

[0027]

[0028] [Chemical Formula 1-2]

[0029]

[0030] [Chemical Formula 1-3]

[0031]

[0032] [Chemical Formula 1-4]

[0033]

[0034] [Chemical Formula 1-5]

[0035]

[0036] In the above chemical formulas 1-1 to 1-5,

[0037] R2 and R3 are as defined in Chemical Formula 1 above.

[0038] [9] The present invention provides a lithium secondary battery in which, in at least one of [1] to [8], the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound is 2.0 to 5.0.

[0039]

[0010] The present invention provides a lithium secondary battery in which, in at least one of [1] to [9], the content of the compound represented by Formula 1 is 5 volume% to 40 volume% based on the total volume of the organic solvent.

[0040]

[0011] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0010] , the content of the cyclic carbonate compound is 10 volume% to 45 volume% based on the total volume of the organic solvent.

[0041]

[0012] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0011] , the content of the linear carbonate-based compound is 30 volume% to 80 volume% based on the total volume of the organic solvent.

[0042]

[0013] The present invention provides a lithium secondary battery, wherein, in at least one of [1] to

[0012] , the non-aqueous electrolyte further comprises one or more additives selected from the group consisting of cyclic carbonate-based additives, sulfon-based additives, and sulfate-based additives.

[0043]

[0014] The present invention provides a lithium secondary battery having a charge cut-off voltage of 4.30V or higher in at least one of [1] to

[0013] .

[0044] The lithium secondary battery according to the present invention can exhibit high energy density by including a Si-C composite with excellent capacity characteristics as a negative electrode active material.

[0045] The lithium secondary battery according to the present invention includes a sulfonamide-based compound with excellent oxidation stability as an electrolyte solvent, so the decomposition reaction of the electrolyte occurring during high temperature and / or high voltage operation is suppressed, thereby enabling excellent lifespan and resistance characteristics.

[0046] In addition, since a sulfate-based film with the characteristic of promoting the reduction reaction of oxidizing gas is formed on the cathode by the sulfonyl group contained in the above sulfonamide-based compound, the effects of enhanced high-temperature durability and reduced gas generation can be realized.

[0047] Figure 1 is a scanning electron microscope image of a single-particle positive electrode active material.

[0048] Figure 2 is a scanning electron microscope image of a pseudo-single particle cathode active material.

[0049] Figure 3 is a scanning electron microscope image of a secondary particle positive electrode active material.

[0050] The present invention will be described in more detail below.

[0051]

[0052] In the present invention, "single particle type" refers to a particle composed of 30 or fewer nodules, and is a concept that includes a single particle composed of one nodule and a pseudo-single particle which is a composite of 2 to 30 nodules. Fig. 1 shows a scanning electron microscope image of a positive electrode active material in a single particle form, and Fig. 2 shows a scanning electron microscope image of a positive electrode active material in a pseudo-single particle form.

[0053] The above "nodule" is a sub-grain unit constituting a single particle and a pseudo-single particle, and may be a single crystal that does not have crystalline grain boundaries, or a polycrystalline material that does not appear to have grain boundaries when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope.

[0054] In the present invention, "secondary particle" refers to a particle formed by the aggregation of a plurality of primary particles, for example, tens to hundreds of primary particles. Specifically, the secondary particle may be an aggregate of more than 30 primary particles. FIG. 3 shows a scanning electron microscope (SEM) image of a positive electrode active material in the form of a secondary particle.

[0055] In the present invention, "particle" is a concept that includes any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0056] In the present invention, "D 50"This refers to the particle size corresponding to 50% of the volume cumulative amount of the volume cumulative particle size distribution of the powder to be measured, and can be measured using the laser diffraction method. For example, the powder to be measured can be measured by dispersing it in a dispersion medium, introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasound of about 28 kHz at an output of 60 W, obtaining a volume cumulative particle size distribution graph, and then determining the particle size corresponding to 50% of the volume cumulative amount.

[0057]

[0058] As a result of repeated research to develop a lithium secondary battery with excellent high voltage and high temperature characteristics while including a silicon-carbon composite (Si-C composite) as the negative electrode active material, the inventors discovered that by replacing a portion of the electrolyte solvent with a sulfonamide-based compound and controlling the compositional ratio between the sulfonamide-based compound and the carbonate-based compound to satisfy specific conditions, excellent high-temperature life characteristics and high-temperature storage characteristics can be achieved even during high-voltage operation, and thus completed the present invention.

[0059] Specifically, silicon-based anode active materials undergo a larger volume change during charging and discharging compared to carbon-based anode active materials, making it difficult to maintain a stable SEI layer under high temperature and high voltage conditions. In addition, silicon-based anode active materials have a large active surface area and high chemical reactivity, making them more susceptible to side reactions that occur as electrolyte components oxidize at high temperature and high voltage.

[0060] Accordingly, in the present invention, a portion of the electrolyte solvent was replaced with a sulfonamide-based compound, and it was confirmed that this resulted in film reinforcement and improved high-temperature lifespan due to the formation of a sulfate-based film. The sulfonyl groups contained in the sulfonamide-based compound cause a sulfate-based film to form on the surface of the cathode, and said sulfate-based film has excellent durability, which not only improves the high-temperature durability of the cell but also contributes to reducing gas generation by promoting the reduction reaction of oxidizing gases present within the cell.

[0061] Meanwhile, among silicon-based negative electrode active materials, the volume expansion phenomenon during charging and discharging can be mitigated by the carbon matrix of the Si-C composite, so the sulfate-based film can be maintained more stably in a negative electrode containing a Si-C composite compared to a negative electrode containing SiO or Si.

[0062]

[0063] The following describes each component constituting the present invention in more detail.

[0064]

[0065] cathode

[0066] A lithium secondary battery according to the present invention comprises a negative electrode comprising a negative electrode active material. Specifically, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material. In addition, the negative electrode active material layer may further comprise a negative electrode conductive material and a negative electrode binder in addition to the negative electrode active material.

[0067] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0068] The above-mentioned negative electrode active material comprises a silicon-carbon composite. The silicon-carbon composite is a material having a structure in which Si is deposited within a carbon matrix, and due to the contribution of carbon, metallic Si and silicon oxide (SiO₂) x Compared to ), it has the advantage of having a smaller degree of volume expansion and higher electrical conductivity, resulting in excellent initial efficiency.

[0069] Specifically, the silicon-carbon composite can be formed by depositing silicon onto porous carbon-based particles using a silane gas. Additionally, if necessary, the silicon-carbon composite may further include a carbon layer on its surface. Conductivity is improved by the carbon layer, and the initial efficiency, lifespan characteristics, and capacity characteristics of the secondary battery can be enhanced.

[0070] In addition, the silicon-carbon composite can be manufactured through the steps of: depositing silicon onto porous carbon particles via chemical vapor deposition (CVD); and forming a carbon layer on the surface of the porous carbon particles on which the silicon is deposited.

[0071] Compared to embedded silicon-carbon composites, which have a structure in which Si is embedded within a carbon matrix, or powdered silicon-carbon composites manufactured by grinding Si or SiO to obtain porous silicon particles and forming a carbon layer thereon, these deposition-type silicon-carbon composites effectively buffer volume expansion and strengthen the electrical network, thereby providing excellent effects in improving the structural stability and rapid charging performance of the battery.

[0072] The weight ratio of silicon to carbon in the silicon-carbon composite may be 1:99 to 30:70, preferably 2:98 to 20:80, more preferably 3:97 to 15:85, and even more preferably 5:95 to 10:90. It is desirable for the ratio of silicon to carbon to be within the above range, as this allows for the realization of high capacity characteristics due to Si, while also enabling the mitigation of volume expansion, improvement of electrical conductivity, and increase in initial efficiency through the contribution of carbon.

[0073] The grain size of the silicon-carbon composite may be 30 nm or less, preferably 3 nm to 20 nm, more preferably 7 nm to 15 nm.

[0074] D of the above silicon-carbon composite 50 The µm can be 3 µm to 15 µm, preferably 5 µm to 12 µm, more preferably 6 µm to 10 µm.

[0075] The above-mentioned cathode active material may further include a carbon-based cathode active material. The above-mentioned carbon-based cathode active material may include, for example, natural graphite, artificial graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, or a combination thereof, and preferably may include natural graphite and artificial graphite. For example, the above-mentioned carbon-based cathode active material may be a mixture of natural graphite and artificial graphite, in which case the weight ratio of natural graphite to artificial graphite may be 1:9 to 9:1, preferably 1:9 to 5:5, more preferably 1:9 to 3:7.

[0076] D of the above carbon-based cathode active material 50 The size may be 2㎛ to 30㎛, preferably 5㎛ to 30㎛.

[0077] The above-mentioned negative electrode active material may include the silicon-carbon composite and the carbon-based negative electrode active material in a weight ratio of 30:70 to 1:99, preferably 20:80 to 2:98, and more preferably 10:90 to 3:97. Although a higher content of the silicon-carbon composite is advantageous for realizing high energy density and improving rapid charging performance, it is expensive and may lead to reduced lifespan due to volume expansion during charging and discharging; therefore, it is desirable to mix the carbon-based negative electrode active material, which has high structural stability and is relatively inexpensive, within the above range.

[0078] Meanwhile, in addition to the silicon-carbon composite and carbon-based cathode active material, the above-mentioned negative electrode active material may further include one or more selected from the group consisting of silicon-based materials; metals or alloys of these metals and lithium; metal composite oxides; materials capable of doping and undoping lithium; lithium metals; and transition metal oxides.

[0079] The above silicon-based material is Si, SiO x(0 <x<2) 및 Si-Y 합금(상기 Y는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 전이금속, 희토류 원소 및 이들의 조합 중 선택되는 원소이며, Si는 될 수 없음.)으로 이루어진 군에서 선택된 1종 이상일 수 있다.

[0080] The above metal or alloy of these metals and lithium may be a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn; or an alloy of these metals and lithium.

[0081] The above metal composite oxides are PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1) and Sn x Me 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8)로 이루어진 군에서 선택된 1종 이상일 수 있다.

[0082] The materials capable of doping and dedoping the above lithium may be one or more selected from the group consisting of Sn, SnO2, and Sn-Y (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn).

[0083] The above transition metal oxide may be a lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, or a combination thereof.

[0084] The above-mentioned negative electrode active material may be included in an amount of 80% to 98% by weight, preferably 90% to 98% by weight, and more preferably 93% to 98% by weight, based on the total weight of the negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, excellent energy density can be achieved.

[0085] The above-mentioned cathode conductive material is used to impart conductivity to the cathode, and in the battery being constructed, it may be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; carbon-based structures such as carbon fibers or carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides 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.

[0086] The above-mentioned cathode conductive material may typically be included in an amount of 0.1 to 10 weight%, preferably 0.25 to 8 weight%, and more preferably 0.25 to 5 weight% based on the total weight of the cathode active material layer.

[0087] The above-mentioned cathode binder serves to improve adhesion between cathode active material particles and adhesion between the cathode active material and the cathode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0088] The above-mentioned cathode binder may be included in an amount of 1 to 10 weight%, preferably 1 to 8 weight%, more preferably 1 to 5 weight% based on the total weight of the positive active material layer.

[0089] The above cathode can be manufactured according to a conventional cathode manufacturing method. For example, it can be manufactured by mixing a cathode active material, a cathode binder, and / or a cathode conductive material in a solvent to prepare a cathode slurry, applying the cathode slurry onto a cathode current collector, and then drying and rolling, or by casting the cathode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto a cathode current collector.

[0090] As solvents for the cathode slurry, solvents commonly used in the relevant technical field may be used; for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc., may be used individually or as a mixture of two or more. The amount of the solvent used is sufficient if it is sufficient to dissolve or disperse the cathode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that provides excellent thickness uniformity when coated for subsequent anode manufacturing.

[0091]

[0092] anode

[0093] A lithium secondary battery according to the present invention comprises a positive electrode comprising a positive electrode active material. Specifically, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material. In addition, the positive electrode active material layer may further comprise a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material.

[0094] The above positive current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the positive current collector to increase the adhesion of the positive active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0095] The above positive active material may include a lithium nickel-based oxide having a Ni content of 60 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably greater than 80 mol% and less than or equal to 95 mol% among the total metals excluding lithium.

[0096] Specifically, the positive electrode active material may include a lithium nickel-based oxide containing nickel, manganese, and cobalt, and more specifically, may include a lithium nickel-based oxide having the composition of the following chemical formula A.

[0097] [Chemical Formula A]

[0098] Li 1+x (Ni a Co b Mn c M d )O2

[0099] In the above chemical formula A,

[0100] M is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0101] x, a, b, c, and d are -0.20≤x≤0.20, 0.50≤a<1, 0, respectively. <b<0.50, 0<c<0.50, 0≤d≤0.10, a+b+c+d=1을 만족한다.

[0102] The above 1+x represents the lithium molar ratio in the lithium nickel-based oxide, and may be -0.10≤x≤0.10, 0≤x≤0.10, or 0≤x≤0.07. When 1+x satisfies the above range, a stable layered crystal structure can be formed.

[0103] The above a represents the molar ratio of nickel among all metals excluding lithium in the lithium nickel-based oxide, and may be 0.60≤a<1, 0.70≤a<1, 0.80≤a<1, or 0.82≤a<1. When a satisfies the above range, high energy density is exhibited, making it possible to achieve high capacity.

[0104] The above b represents the molar ratio of cobalt among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <b<0.40, 0<b<0.30, 0.03≤b≤0.15 또는 0.05≤b≤0.12일 수 있다. b가 상기 범위를 만족할 때, 양호한 저항 특성 및 출력 특성을 구현할 수 있다.

[0105]

[0106] The above c represents the molar ratio of manganese among the total metals excluding lithium in the lithium nickel-based oxide, where 0 <c<0.40, 0<c<0.30, 0.03≤c≤0.15 또는 0.05≤c≤0.12일 수 있다. c가 상기 범위를 만족할 때, 양극 활물질의 구조 안정성이 우수하게 나타난다.

[0107] M may be one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and preferably may be Al. When elements are included, the structural stability of lithium nickel-based oxide particles is improved, enabling superior lifespan characteristics during high-voltage operation.

[0108] The above d represents the molar ratio of element M among the total metals excluding lithium in the lithium nickel-based oxide, where 0≤d≤0.10, 0≤d≤0.05, 0≤d≤0.03, or 0 <d≤0.03일 수 있다.

[0109] The above lithium nickel-based oxide may further include a coating layer on its surface comprising one or more elements selected from the group consisting of Co, Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo. In this case, contact between the electrolyte and the lithium nickel-based oxide is suppressed by the coating layer, thereby reducing the leaching of transition metals or gas generation caused by side reactions with the electrolyte, and thus further improving stability during thermal runaway.

[0110]

[0111] The above-mentioned positive electrode active material may include a single-particle lithium nickel-based oxide. The single-particle lithium nickel-based oxide may be a single particle consisting of one nodule, a pseudo-single particle which is a complex of two to thirty nodules, or a combination thereof. That is, the lithium nickel-based oxide may be a single-particle lithium nickel-based oxide containing 30 or fewer nodules.

[0112] In the case of lithium nickel-based oxides in the form of secondary particles aggregated from more than 30 to hundreds of primary particles, side reactions with the electrolyte occur frequently due to the large contact area with the electrolyte, and gas is generated during these side reactions. Under high temperature and / or high voltage conditions, the amount of gas generated and side reactions with the electrolyte increase further, causing the performance of the lithium secondary battery to degrade rapidly. In contrast, single-particle lithium nickel-based oxides have a small number of nodules constituting the particles, and consequently, fewer interfaces within the particles, resulting in a small contact area with the electrolyte. Therefore, compared to secondary particles, side reactions with the electrolyte are less frequent, and consequently, the amount of gas generated is significantly lower. Thus, when single-particle lithium nickel-based oxides are applied as cathode active materials, the degradation of lifespan characteristics can be minimized under high temperature and / or high voltage conditions.

[0113] The above nodules may have an average particle size of 0.1 μm to 10 μm, preferably 0.5 μm to 8 μm, and more preferably 1 μm to 5 μm. When the average particle size of the nodules satisfies the above range, particle breakage during electrode manufacturing is minimized, and the increase in resistance can be suppressed more effectively. At this time, the average particle size of the nodules refers to a value obtained by measuring the particle sizes of the nodules observed in the SEM image obtained by analyzing the positive electrode active material powder with a scanning electron microscope, and then calculating the arithmetic mean of the measured values.

[0114] The above positive active material is D 50 This can be 1㎛ to 10㎛, preferably 2㎛ to 8㎛, more preferably 3㎛ to 5㎛. D of the positive active material 50 If this is too small, processability during electrode manufacturing decreases, and electrolyte impregnation decreases, which may increase electrochemical properties, and D 50 If this is too large, there is a problem that resistance increases and output characteristics deteriorate, so it is desirable to be within the above range.

[0115] In addition to the lithium nickel-based oxide, the above-mentioned positive electrode active material may further include conventional positive electrode active materials used in lithium secondary batteries, such as LCO (LiCoO2), LNO (LiNiO2), LMO (LiMnO2, LiMn2O4), LiCoPO4, and LFP (LiFePO4).

[0116] The above positive active material may be included in an amount of 80% to 98% by weight, preferably 90% to 98% by weight, and more preferably 93% to 98% by weight, based on the total weight of the positive active material layer. When the content of the positive active material satisfies the above range, excellent energy density can be achieved.

[0117] Next, the above-mentioned positive electrode conductive material is used to impart conductivity to the positive electrode, and in the battery being constructed, it can be used without special limitations as long as it has electronic conductivity without causing chemical changes. Specific examples include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; carbon-based structures such as carbon fibers or carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more of these may be used.

[0118] The above-mentioned positive conductive material may typically be included in an amount of 0.1 to 10 weight%, preferably 0.5 to 8 weight%, and more preferably 0.5 to 5 weight% based on the total weight of the positive active material layer.

[0119] The above-mentioned 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), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more may be used.

[0120] The above anode binder may be included in an amount of 1% to 10% by weight, preferably 1% to 8% by weight, and more preferably 1% to 5% by weight, based on the total weight of the anode active material layer.

[0121] The above anode may be manufactured according to a conventional anode manufacturing method. For example, the above anode may be manufactured by mixing an anode active material, an anode binder, and / or an anode conductive material in a solvent to prepare an anode slurry, applying the anode slurry onto an anode current collector, and then drying and rolling, or by casting the anode slurry onto a separate support and then laminating the film obtained by peeling it off from the support onto an anode current collector.

[0122] Meanwhile, solvents commonly used in the relevant technical field may be used as solvents for the anode slurry; for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc., may be used individually or as a mixture of two or more. The amount of the solvent used is sufficient if it is sufficient to dissolve or disperse the anode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that exhibits excellent thickness uniformity when coated for anode manufacturing thereafter.

[0123]

[0124] Non-aqueous electrolyte

[0125] A lithium secondary battery according to the present invention comprises a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a lithium salt and an organic solvent, and may optionally further comprise an additive.

[0126]

[0127] (1) Lithium salt

[0128] The non-aqueous electrolyte of the present invention includes a lithium salt.

[0129] The above lithium salts may be those commonly used in electrolytes for lithium secondary batteries without limitation, and specifically, the above lithium salts are Li as cations + It includes, and as anion, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , B 10 Cl 10 - , AlCl4 - , AlO2 - , PF6 - , CF3SO3 - , CH3CO2 - , CF3CO2 - , AsF6 - , SbF6 - , CH3SO3 - , (CF3CF2SO2)2N - , (CF3SO2)2N - , (FSO2)2N - , BF2C2O4 - , BC4O8 - , BF2C2O4CHF-, PF4C2O4 - , PF2C4O8 - , PO2F2 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , C4F9SO3 - , CF3CF2SO3 - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , CF3(CF2)7SO3 - and SCN - It may include one or more selected from the.

[0130] Specifically, the lithium salt is from the group consisting of LiPF6, LiClO4, LiBF4, LiN(FSO2)2(LiFSI), LiTFSI, lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), LiSO3CF3, LiPO2F2, lithium bis(oxalate)borate (LiBOB), lithium difluoro(oxalate)borate (LiFOB), lithium difluoro(bisoxalato)phosphate (LiDFOP), lithium tetrafluoro(oxalate)phosphate (LiTFOP), and lithium fluoromalonato(difluoro)borate (LiFMDFB). It may be any one or more selected, and preferably LiPF6.

[0131] In one embodiment of the present invention, the concentration of the lithium salt in the non-aqueous organic solution containing the lithium salt and the organic solvent, that is, the mixed solution of the lithium salt and the organic solvent, may be 0.5 M to 4.0 M, specifically 1.0 M to 2.0 M. When the concentration of the lithium salt is within the above range, it is possible to appropriately form viscosity and surface tension while sufficiently securing the effects of improving low-temperature output and improving cycle characteristics.

[0132]

[0133] (2) Organic solvent

[0134] The above-mentioned non-aqueous electrolyte comprises an organic solvent comprising a cyclic carbonate compound, a linear carbonate compound, and a compound represented by the following chemical formula 1.

[0135] [Chemical Formula 1]

[0136]

[0137] In the above chemical formula 1,

[0138] R1 is a fluorine atom, a carbon-1 to carbon-10 alkyl group substituted with one or more fluorines, or a carbon-1 to carbon-10 alkoxy group substituted with one or more fluorines, and R2 and R3 are independently hydrogen, a carbon-1 to carbon-10 alkyl group, or a carbon-6 to carbon-20 aryl group.

[0139] Conventional non-aqueous electrolytes for lithium secondary batteries generally contained carbonate-based solvents as organic solvents. However, carbonate-based solvents decompose rapidly at high potentials of 4.30V or higher, generating a large amount of gas and side reactions. In contrast, the compound represented by Chemical Formula 1 has relatively high oxidation stability even at high potentials of 4.30V or higher, thereby minimizing the generation of gas and side reactions caused by electrolyte decomposition. Furthermore, due to its structural characteristics, the compound represented by Chemical Formula 1 does not generate gases such as CO2 or CH4, while exhibiting excellent electrochemical and chemical stability and not reducing the degree of dissociation of the lithium salt. In addition, the compound represented by Chemical Formula 1 causes a sulfate-based film to form at the negative electrode, and this film promotes the reduction reaction of oxidizing gases, contributing to the reduction of gas generation.

[0140] Based on the total volume of the organic solvent, the content of the compound represented by Chemical Formula 1 may be 5 volume% or more, 8 volume% or more, 10 volume% or more, 15 volume% or more, 18 volume% or more, or 20 volume% or more. Additionally, based on the total volume of the organic solvent, the content of the compound represented by Chemical Formula 1 may be 40 volume% or less, 35 volume% or less, 32 volume% or less, 30 volume% or less, 25 volume% or less, 22 volume% or less, or 20 volume% or less. The above numerical ranges may be combined with one another without limitation. Specifically, based on the total volume of the organic solvent, the content of the compound represented by Chemical Formula 1 may be 5 volume% to 40 volume%, preferably 10 volume% to 30 volume%, and more preferably 15 volume% to 25 volume%. If the content of the compound represented by Chemical Formula 1 in the organic solvent is too low, the improvement effect described above is negligible, and if it is too high, the initial resistance may increase excessively.

[0141] In the compound represented by the above chemical formula 1, R1 may be a fluorine atom (F), an alkyl group having 1 to 10 carbon atoms substituted with one or more fluorines, or an alkoxy group having 1 to 10 carbon atoms substituted with one or more fluorines; specifically, it may be a fluorine atom, an alkyl group having 1 to 5 carbon atoms substituted with one or more fluorines, or an alkoxy group having 1 to 5 carbon atoms substituted with one or more fluorines; more specifically, it may be a fluorine atom, an alkyl group having 1 to 3 carbon atoms substituted with one or more fluorines, or an alkoxy group having 1 to 3 carbon atoms substituted with one or more fluorines; more specifically, it may be a fluorine atom, CF3-*, CF3CF2-*, CF3O-*, or CF3CF2O-*; more specifically, it may be a fluorine atom, CF3-*, or CF3O-*; more specifically, it may be a fluorine atom or CF3-*; and more specifically, it may be a fluorine atom. In the above, "*" may indicate a connection site.

[0142] Additionally, R2 and R3 may independently be hydrogen, an alkyl group having 1 to 10 carbon atoms, or an aryl group having 6 to 20 carbon atoms; specifically, they may independently be an alkyl group having 1 to 10 carbon atoms; more specifically, they may independently be an alkyl group having 1 to 5 carbon atoms; even more specifically, they may independently be an alkyl group having 1 to 3 carbon atoms; even more specifically, they may independently be a methyl group or an ethyl group; and even more specifically, they may each be a methyl group.

[0143] The compound represented by the above chemical formula 1 may be one or more selected from the group consisting of compounds represented by the following chemical formulas 1-1 to 1-5, more specifically one or more selected from the group consisting of compounds represented by the following chemical formulas 1-1 to 1-3, and more specifically a compound represented by the following chemical formula 1-1.

[0144] [Chemical Formula 1-1]

[0145]

[0146] [Chemical Formula 1-2]

[0147]

[0148] [Chemical Formula 1-3]

[0149]

[0150] [Chemical Formula 1-4]

[0151]

[0152] [Chemical Formula 1-5]

[0153]

[0154] At this time, in the above chemical formulas 1-1 to 1-5, R2 and R3 are as defined in the above chemical formula 1.

[0155] The compound represented by the above chemical formula 1 may be one or more selected from the group consisting of compounds represented by the following chemical formulas 1-A, 1-B, 1-C, 1-D, and 1-E, specifically one or more selected from the group consisting of compounds represented by the following chemical formulas 1-A, 1-B, and 1-C, and more specifically, may be the compound represented by the following chemical formula 1-A.

[0156] [Chemical Formula 1-A]

[0157]

[0158] [Chemical Formula 1-B]

[0159]

[0160] [Chemical Formula 1-C]

[0161]

[0162] [Chemical Formula 1-D]

[0163]

[0164] [Chemical Formula 1-E]

[0165]

[0166]

[0167] The above cyclic carbonate compound may be one or more selected from the group consisting of ethylene carbonate, fluoroethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate; more specifically, it may be one or more selected from the group consisting of ethylene carbonate and fluoroethylene carbonate; and even more specifically, it may be ethylene carbonate.

[0168] Based on the total volume of the organic solvent, the content of the cyclic carbonate compound may be 5 volume% or more, 10 volume% or more, 15 volume% or more, 20 volume% or more, or 25 volume% or more. Additionally, based on the total volume of the organic solvent, the content of the cyclic carbonate compound may be 45 volume% or less, 40 volume% or less, or 35 volume% or less. The above numerical ranges may be combined without limitation. Specifically, based on the total volume of the organic solvent, the content of the cyclic carbonate compound may be 5 volume% to 45 volume%, specifically 10 volume% to 40 volume%, and more specifically 20 volume% to 35 volume%; when within this range, the viscosity of the organic solvent is appropriately controlled, and the dissociation, migration, and transport of the lithium salt can be carried out smoothly.

[0169] The above linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and specifically may be one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate, more specifically may be one or more selected from the group consisting of ethylmethyl carbonate, dimethyl carbonate, and diethyl carbonate in terms of further improving the oxidation stability of the organic solvent, and more specifically may be ethylmethyl carbonate.

[0170] Based on the total volume of the organic solvent, the content of the linear carbonate-based compound may be 15 volume% or more, 30 volume% or more, 40 volume% or more, 45 volume% or more, or 50 volume% or more. Additionally, based on the total volume of the organic solvent, the content of the linear carbonate-based compound may be 90 volume% or less, 85 volume% or less, 80 volume% or less, 75 volume% or less, 70 volume% or less, 65 volume% or less, or 60 volume% or less. The above numerical ranges can be combined without limitation. Specifically, based on the total volume of the organic solvent, the content of the linear carbonate-based compound may be 15 volume% to 90 volume%, specifically 30 volume% to 70 volume%, and more specifically 50 volume% to 60 volume%, and when within the above range, it is possible to realize a non-aqueous electrolyte having excellent oxidation stability while appropriately controlling the viscosity of the organic solvent.

[0171] In addition, the present invention confirmed that by controlling the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound, the viscosity of the organic solvent is controlled to an appropriate level and the degree of dissociation of the lithium salt is improved, thereby improving the ionic conductivity. Specifically, the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound may be 2.0 to 5.0.

[0172] When the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound is less than 2, that is, when the cyclic carbonate compound is included in excess compared to the linear carbonate compound and the sulfonamide compound, there is a problem in which the viscosity of the organic solvent becomes excessively high, and gas generation due to the decomposition of ethylene carbonate is intensified. In addition, when the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound is greater than 4, that is, when the linear carbonate compound and the sulfonamide compound are included in excess compared to the cyclic carbonate compound, there is a problem in which the degree of dissociation of the lithium salt decreases, and the ionic conductivity decreases rapidly.

[0173] Specifically, the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound may be 2.1 or more, 2.2 or more, or 2.3 or more. Additionally, the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound may be 4.6 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.8 or less, or 2.5 or less. The above numerical ranges may be combined without limitation. Specifically, the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound may be 2.0 to 4.0, preferably 2.0 to 3.0, and more preferably 2.0 to 2.5.

[0174] Meanwhile, the above organic solvent may additionally include, without limitation, organic solvents commonly used in non-aqueous electrolytes as needed. For example, the above organic solvent may additionally include at least one organic solvent selected from linear ester compounds, cyclic ester compounds, ether compounds, glycine compounds, and nitrile compounds.

[0175] The above linear ester compound may specifically be at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0176] In addition, the above-mentioned cyclic ester compound may specifically be at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0177] The above ether-based compound may be at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methylpropyl ether, ethyl propyl ether, 1,3-dioxolane (DOL), and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL).

[0178] The above glame-based compound has a higher dielectric constant and lower surface tension compared to the above linear carbonate-based compound and is a solvent with low reactivity with metal, and may be at least one selected from the group consisting of dimethoxyethane (glame, DME), diethoxyethane, digylme, triglyme, and tetraglyme (TEGDME).

[0179] The above nitrile-based solvent may be at least one selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0180]

[0181] (3) Additives

[0182] The above-mentioned non-aqueous electrolyte may further include additives as needed.

[0183] The above-mentioned non-aqueous electrolyte may further include one or more additives selected from the group consisting of cyclic carbonate-based additives, sulfonate-based additives, sulfate-based additives, lithium salt-based additives, phosphorus-based additives, nitrile-based additives, amine-based additives, silane-based additives, and benzene-based additives, and preferably may further include one or more additives selected from the group consisting of cyclic carbonate-based additives, sulfonate-based additives, and sulfate-based additives, and more preferably may include cyclic carbonate-based additives, sulfonate-based additives, and sulfate-based additives.

[0184] The above-mentioned cyclic carbonate-based additive may be one or more selected from the group consisting of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate (FEC), and specifically may be vinylene carbonate.

[0185] The above sulfone-based additive is a material capable of forming a stable SEI film by a reduction reaction on the cathode surface, and may be one or more selected from the group consisting of 1,3-propane sulfone (PS), 1,4-butane sulfone, ethene sulfone, 1,3-propene sulfone (PRS), 1,4-butene sulfone, and 1-methyl-1,3-propene sulfone, and specifically may be 1,3-propane sulfone (PS).

[0186] The above sulfate-based additive is a material capable of forming a stable SEI film that is electrically decomposed on the cathode surface and does not crack even during high-temperature storage, and may be one or more selected from the group consisting of ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate (MTMS).

[0187] The above lithium salt-based additive may be one or more selected from the group consisting of lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium difluorophosphate (LiDFP), and lithium difluorobisoxalate phosphate (LiDFOP).

[0188] The above-mentioned phosphorus additive may be a phosphate-based or phosphite-based compound, and specifically, may be one or more selected from the group consisting of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite, tris(2,2,2-trifluoroethyl)phosphate, and tris(trifluoroethyl)phosphite.

[0189] The above nitrile-based additive may be one or more selected from the group consisting of succinonitrile (SN), adiponitrile (ADN), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, ethylene glycol bis(2-cyanoethyl) ether (ASA3), 1,3,6-hexane tricarbonitrile (HTCN), 1,4-disiano 2-butene (DCB), and 1,2,3-tris(2-cyanoethyl)propane (TCEP).

[0190] The above amine-based additive may be one or more selected from the group consisting of triethanolamine and ethylenediamine, and the above silane-based compound may be tetravinylsilane.

[0191] The above benzene-based additive may be one or more selected from the group consisting of monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0192] The content of each of the above-mentioned cyclic carbonate-based additive, sulfone-based additive, sulfate-based additive, lithium salt-based additive, phosphorus-based additive, nitrile-based additive, amine-based additive, silane-based additive, and benzene-based additive may be 0.05% to 5% by weight, preferably 0.1% to 3% by weight, and more preferably 0.3% to 1% by weight, based on the total weight of the above-mentioned non-aqueous electrolyte. If the content of each additive is less than 0.05% by weight, the effect of improving the high-temperature storage characteristics and high-temperature life characteristics of the battery is negligible, and if it exceeds 5% by weight, there is a possibility that excessive side reactions may occur in the electrolyte during charging and discharging of the battery. In particular, if the above-mentioned additives for forming the SEI film are added in excess, they may not decompose sufficiently at high temperatures and may remain as unreacted substances or precipitates in the electrolyte at room temperature. Consequently, the lifespan or resistance characteristics of the battery may be degraded, so it is desirable to be within the above range.

[0193]

[0194] Separator

[0195] The lithium secondary battery according to the present invention may further include a separator between the positive electrode and the negative electrode as needed. The separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator commonly used as a separator in a lithium secondary battery may be used without special limitations, and it is particularly desirable that it has low resistance to ion movement in a non-aqueous electrolyte and excellent electrolyte moisture retention capacity.

[0196] For example, the above separator may include a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof; or a porous nonwoven fabric made of a high melting point glass fiber, a polyethylene terephthalate fiber, etc. as a substrate.

[0197] In addition, a coating layer containing ceramic components and / or polymer materials may be formed on at least one surface of the above substrate to ensure heat resistance or mechanical strength.

[0198]

[0199] lithium secondary battery

[0200] In the lithium secondary battery according to the present invention, it is preferable that the charge cut-off voltage (full charge voltage) be 4.30V or higher, preferably 4.30V to 5V, and more preferably 4.30V to 4.50V. When the charge cut-off voltage satisfies the above range, the capacity of the positive electrode active material increases, and the nominal voltage increases, thereby enabling the realization of high energy density. Generally, as the charge cut-off voltage increases, the capacity of the positive electrode active material increases. However, if the driving voltage increases, side reactions with the electrolyte during charging and discharging increase, structural collapse of the positive electrode active material occurs rapidly, leading to rapid degradation of lifespan characteristics and insufficient utilization of the capacity of the negative electrode active material. Such problems are more pronounced in high-nickel lithium nickel-cobalt-manganese oxides with a high nickel content. Therefore, conventionally, when lithium nickel-cobalt-manganese oxides were used as positive electrode active materials, the charge cut-off voltage was generally around 4.25V. However, in the present invention, a silicon-carbon composite is applied as the negative electrode active material and a non-aqueous electrolyte containing a solvent with excellent oxidation stability is introduced, thereby enabling excellent lifespan characteristics to be maintained even when the charge cut-off voltage is 4.30V or higher.

[0201] The lithium secondary battery according to the present invention is capable of realizing excellent high-temperature life characteristics and high-temperature storage characteristics even when the charge cut-off voltage is high at 4.30V or higher by using a specific negative electrode active material and an electrolyte solvent.

[0202] The lithium secondary battery according to the present invention can be usefully applied to portable devices such as mobile phones, laptop computers, and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs). The lithium secondary battery according to the present invention can achieve high energy density by operating at high voltage and can be particularly useful in the electric vehicle field because it exhibits excellent safety in the event of thermal runaway.

[0203] According to another embodiment of the present invention, a battery module comprising a lithium secondary battery according to the present invention as a unit cell and a battery pack comprising a plurality of battery modules are provided.

[0204] According to another embodiment of the present invention, a battery pack comprising a plurality of lithium secondary batteries according to the present invention as unit cells is provided. The battery pack may not include a battery module.

[0205] In addition, the present invention provides a pack cell assembly.

[0206] According to one embodiment, the battery module may include 10 to 50, preferably 16 to 36 unit cells. The battery pack may include 10 to 1,000, preferably 10 to 500 unit cells.

[0207] The above 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.

[0208]

[0209] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention.

[0210] <Examples and Comparative Examples: Manufacture of Lithium Secondary Batteries>

[0211] Example 1.

[0212] (1) Preparation of non-aqueous electrolyte

[0213] A non-aqueous electrolyte was prepared by dissolving LiPF6 to a volume ratio of 1.0 M in an organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and a compound represented by the chemical formula 1-A in a volume ratio of 30:50:20, and then adding vinylene carbonate (VC), 1,3-propane sulfone (PS), and ethylene sulfate (ESA). At this time, the content of VC, PS, and ESA was added such that it was 0.5 wt% each based on the total weight of the non-aqueous electrolyte.

[0214]

[0215] (2) Manufacturing of lithium secondary batteries

[0216] Li[Ni 0.83 Co 0.08 Mn 0.08 Al 0.01 A positive active material having the composition of ]O2 (D 50 A positive electrode slurry with a solid content of 60.0 wt% was prepared by adding carbon nanotubes as a conductive material and polyvinylidene fluoride as a binder to N-methyl-2-pyrrolidone (NMP), a solvent, in a weight ratio of 97:1.2:1.8 (=3.4 μm). The positive electrode slurry was applied to both sides of an aluminum current collector with a thickness of 15 μm, dried at 130°C, and then placed between two rolling rolls to produce a positive electrode.

[0217] Meanwhile, a mixture of a Si-C composite and graphite in a weight ratio of 5:95 was prepared as the negative electrode active material. In this case, the Si-C composite has a structure in which Si is deposited within a carbon matrix; specifically, a composite prepared by depositing silicon onto porous carbon particles via CVD deposition and forming a carbon layer on the surface of the silicon-deposited porous carbon particles was used. The weight ratio of Si to C in the Si-C composite is 8:92, the grain size is 7 to 15 nm, and D 50 The thickness is 8.5 μm. The graphite used was a mixture of artificial graphite and natural graphite in a weight ratio of 8:2. A cathode slurry with a solid content of 26 wt% was prepared by mixing the cathode active material, styrene-butadiene rubber-carboxymethylcellulose (SBR-CMC) as a binder, and carbon black as a conductive agent in distilled water in a weight ratio of 97.7:0.5:1.8. The cathode slurry was applied to both sides of a copper current collector with a thickness of 10 μm, dried at 130°C, and then placed between two rolling rolls to roll and produce a cathode.

[0218] An electrode assembly was manufactured by sequentially stacking the anode, a polyolefin-based porous separator coated with Al2O3, and the cathode. The assembled electrode assembly was housed in a battery case, and the manufactured non-aqueous electrolyte was injected to manufacture a lithium secondary battery.

[0219]

[0220] Example 2.

[0221] A lithium secondary battery was manufactured in the same manner as in Example 1, except that when preparing the non-aqueous electrolyte, an organic solvent was used in which EC, EMC, and the compound represented by the chemical formula 1-A were mixed in a volume ratio of 30:60:10.

[0222]

[0223] Example 3.

[0224] A lithium secondary battery was manufactured in the same manner as in Example 1, except that an organic solvent was used in which EC, EMC, and the compound represented by the chemical formula 1-A were mixed in a volume ratio of 20:60:20 when preparing the non-aqueous electrolyte.

[0225]

[0226] Example 4.

[0227] A lithium secondary battery was manufactured in the same manner as in Example 1, except that an organic solvent was used in which EC, EMC, and the compound represented by the chemical formula 1-A were mixed in a volume ratio of 18:60:22 when preparing the non-aqueous electrolyte.

[0228]

[0229] Comparative Example 1.

[0230] A lithium secondary battery was manufactured using the same method as in Example 1, except that an organic solvent was used in which EC and EMC were mixed in a volume ratio of 30:70 when preparing the non-aqueous electrolyte.

[0231]

[0232] Comparative Example 2.

[0233] A lithium secondary battery was manufactured in the same manner as in Example 1, except that an organic solvent was used in which EC, EMC, and the compound represented by the chemical formula 1-A were mixed in a volume ratio of 40:50:10 when preparing the non-aqueous electrolyte.

[0234]

[0235] Comparative Example 3.

[0236] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a compound represented by the following chemical formula B was used instead of the compound represented by the above chemical formula 1-A when preparing the non-aqueous electrolyte.

[0237] [Chemical Formula B]

[0238]

[0239]

[0240] Comparative Example 4.

[0241] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a mixture of SiO and graphite in a weight ratio of 5:95 was used as the negative electrode active material.

[0242]

[0243] Comparative Example 5.

[0244] A lithium secondary battery was manufactured in the same manner as Comparative Example 5, except that when preparing the non-aqueous electrolyte, an organic solvent was used in which EC, EMC and the compound represented by the chemical formula 1-A were mixed in a volume ratio of 30:60:10.

[0245]

[0246] Comparative Example 6.

[0247] A lithium secondary battery was manufactured using the same method as Comparative Example 5, except that an organic solvent was used in which EC and EMC were mixed in a volume ratio of 30:70 when preparing the non-aqueous electrolyte.

[0248]

[0249] Comparative Example 7.

[0250] A lithium secondary battery was manufactured in the same manner as in Example 1, except that a mixture of Si and graphite in a weight ratio of 5:95 was used as the negative electrode active material.

[0251]

[0252] Comparative Example 8.

[0253] A lithium secondary battery was manufactured in the same manner as Comparative Example 8, except that when preparing the non-aqueous electrolyte, an organic solvent was used in which EC, EMC, and the compound represented by the chemical formula 1-A were mixed in a volume ratio of 30:60:10.

[0254]

[0255] Comparative Example 9.

[0256] A lithium secondary battery was manufactured using the same method as Comparative Example 8, except that an organic solvent was used in which EC and EMC were mixed in a volume ratio of 30:70 when preparing the non-aqueous electrolyte.

[0257]

[0258] Comparative Example 10.

[0259] A lithium secondary battery was manufactured in the same manner as in Example 1, except that only graphite was used as the negative electrode active material and an organic solvent was used in which EC and EMC were mixed in a volume ratio of 30:70 when preparing the non-aqueous electrolyte.

[0260]

[0261] <Experimental Example>

[0262] Experimental Example 1. Performance evaluation after high-temperature cycling

[0263] (1) Resistance and lifespan evaluation

[0264] For each of the lithium secondary batteries manufactured in the above examples and comparative examples, after performing a formation process, the battery was charged to 4.3V at 0.33C at 45℃ under CC-CV (0.05C cut off) conditions using an electrochemical charge / discharger, discharged at 0.33C to reach an SOC of 50%, and then the initial resistance value was obtained by measuring the voltage drop that appeared while applying a discharge pulse of 2.5C constant current for 10 seconds.

[0265] Each of the batteries for which the initial resistance measurement was completed was charged at 45°C at 0.33C to 4.3V under CC-CV (0.05C cut off) conditions, and then discharged at 0.33C to 2.5V to measure the initial discharge capacity.

[0266] With the above charge / discharge defined as one cycle, the same charge / discharge was repeated for 400 cycles, and the capacity retention rate and resistance increase rate were calculated using the following formula. The measurement results are shown in Table 1 below.

[0267] - Capacity retention rate (%) = (Discharge capacity after 400 cycles / Initial discharge capacity) × 100

[0268] - Resistance increase rate (%) = {(Resistance after 400 cycles - Initial resistance) / Initial resistance} × 100

[0269]

[0270] (2) Measurement of gas generation amount

[0271] After transferring the above 400-cycle charged and discharged battery to a charging and discharging machine at room temperature (25℃), the gas collected inside the battery case was measured using a GC-TCD (gas chromatography-thermal conductivity detector), and the amount of gas generated was converted to mL / Ah by dividing it by the charge / discharge capacity and listed in Table 1 below.

[0272]

[0273] Experimental Example 2. Performance evaluation after high-temperature storage

[0274] (1) Resistance and lifespan evaluation

[0275] For each of the lithium secondary batteries manufactured in the above examples and comparative examples, an activation (formation) process was performed, and then the battery was charged to 4.3V at 0.33C at 25℃ under CC-CV (0.05C cut off) conditions using an electrochemical charge / discharger, discharged at 0.33C to reach SOC 50%, and then the initial resistance value was obtained by measuring the voltage drop that appeared while applying a discharge pulse of 2.5C constant current for 10 seconds.

[0276] Each of the batteries for which the initial resistance measurement was completed was charged at 25°C at 0.33C to 4.3V under CC-CV (0.05C cut off) conditions, and discharged at 0.33C to 2.5V to measure the initial discharge capacity.

[0277] Each of the batteries for which the initial discharge capacity measurement was completed was stored in a 60°C chamber for 20 weeks, and then the capacity retention rate and resistance increase rate were calculated using the following formula. The measurement results are shown in Table 1 below.

[0278] - Capacity retention rate (%) = (Discharge capacity after 20 weeks of storage / Initial discharge capacity) × 100

[0279] - Resistance increase rate (%) = {(Resistance after 20 weeks of storage - Initial resistance) / Initial resistance} × 100

[0280]

[0281] (2) Measurement of gas generation amount

[0282] After transferring the battery stored for 20 weeks as described above to a charging / discharging machine at room temperature (25℃), the gas collected inside the battery case was measured using a GC-TCD (gas chromatography-thermal conductivity detector), and the amount of gas generated was converted to mL / Ah by dividing it by the charge / discharge capacity and listed in Table 1 below.

[0283] Composition of organic solvent (volume%) Cathode active material (wt%) Experimental Example 1 Experimental Example 2 EC(a) EMC(b) Chemical formula 1-A (c) (b+c) / a Capacitance retention rate (%) Resistance increase rate (%) Gas generation rate (mL / Ah) Capacitance retention rate (%) Resistance increase rate (%) Gas generation rate (mL / Ah) Example 1 30 50 20 2.33 Si-C (5) + Graphite (95) 92.1 18.2 1.36 90.6 20.4 2.66 Example 2 30 60 10 2.33 91.5 20.7 1.5 788.4 21.8 2.87 Example 3 20 60 20 4.0 89.9 22.7 1.15 90.1 20.6 2.28 Example 41860224.5689.323.11.0989.621.12.22 Comparative Example 13070-2.3388.423.31.7485.824.63.48 Comparative Example 24050101.586.724.84.1882.928.07.89 Comparative Example 33050202.3385.926.21.8181.829.53.29 Comparative Example 43050202.33SiO (5) + Graphite (95)87.722.81.7088.123.52.96 Comparative Example 53060102.3388.521.11.7387.823.63.26 Comparative Example 63070-2.3389.920.51.6587.223.33.39 Comparative Example 73050202.33Si (5) +Graphite (95)85.123.81.5683.725.73.06 Comparative Example 83060102.3385.724.11.7284.924.33.23 Comparative Example 93070-2.3386.423.31.8683.326.83.81 Comparative Example 103070-2.33Graphite (100)90.221.81.5388.622.93.17

[0284] Through the results of Table 1 above, it can be confirmed that a lithium secondary battery using a mixture of cyclic carbonate compounds, linear carbonate compounds, and compounds represented by Chemical Formula 1 below as the organic solvent of the non-aqueous electrolyte, and a silicon-carbon composite as the negative electrode active material, maintains excellent lifespan and resistance characteristics even after high-temperature cycling and high-temperature storage, and also has a lower amount of gas generation.

[0285] Specifically, through a comparison of Examples 1 to 4 and Comparative Example 3, it can be confirmed that even if a sulfonamide-based compound is used, there is no effect of improving high-temperature performance when a compound with a structure containing a silyl group is used. Comparative Example 3 showed poor evaluation results even compared to Comparative Example 1, which did not use any sulfonamide-based compound, which means that sulfonamide-based compounds other than the structure of Formula 1 can actually degrade the high-temperature performance of a lithium secondary battery using a silicon-carbon composite as a negative electrode active material.

[0286] In addition, when examining the results of Experimental Example 1 of Comparative Examples 4 to 6 using SiO, it can be seen that Comparative Examples 4 and 5, which used an electrolyte containing a sulfonamide compound of Formula 1, have a lower capacity retention rate, a higher resistance increase rate, and a larger amount of gas generation compared to Comparative Example 6, which used an electrolyte not containing a sulfonamide compound of Formula 1.

[0287] In addition, when examining the results of Experimental Example 1 for Comparative Examples 7 to 9 using Si, it can be seen that Comparative Examples 7 and 8, which used an electrolyte containing a sulfonamide compound of Formula 1, have a lower capacity retention rate, a higher resistance increase rate, and a larger amount of gas generation compared to Comparative Example 9, which used an electrolyte not containing a sulfonamide compound of Formula 1.

[0288] On the other hand, in the case of Examples 1 to 4 and Comparative Example 1 using Si-C, it can be confirmed that the evaluation results of Experimental Examples 1 and 2 were superior for Examples 1 to 4 using an electrolyte containing a sulfonamide compound of Formula 1 compared to Comparative Example 1 using an electrolyte not containing a sulfonamide compound of Formula 1.

[0289] This result shows that a non-aqueous electrolyte containing a mixture of cyclic carbonate compounds, linear carbonate compounds, and a compound (c) represented by the following chemical formula 1 as an organic solvent has a significantly superior effect in improving high temperature and high voltage performance for a silicon-carbon composite among silicon-based cathodes.

Claims

1. A lithium secondary battery comprising a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and a non-aqueous electrolyte, and The above-mentioned negative electrode active material comprises a silicon-carbon composite, and A lithium secondary battery comprising: a lithium salt; and an organic solvent comprising a cyclic carbonate-based compound, a linear carbonate-based compound, and a compound represented by the following chemical formula 1; [Chemical Formula 1] In the above chemical formula 1, R1 is a fluorine atom, a carbon-1 to carbon-10 alkyl group substituted with one or more fluorines, or a carbon-1 to carbon-10 alkoxy group substituted with one or more fluorines, and R2 and R3 are independently hydrogen, a carbon-1 to carbon-10 alkyl group, or a carbon-6 to carbon-20 aryl group.

2. In Claim 1, The above silicon-carbon composite is a lithium secondary battery having a structure in which Si is deposited within a carbon matrix.

3. In Claim 1, A lithium secondary battery in which the above-mentioned negative electrode active material further comprises a carbon-based negative electrode active material.

4. In Claim 3, A lithium secondary battery in which the above negative electrode active material comprises the above silicon-carbon composite and the carbon-based negative electrode active material in a weight ratio of 1:99 to 30:

70.

5. In Claim 1, A lithium secondary battery wherein the positive active material comprises a lithium nickel-based oxide having the composition of the following chemical formula A: [Chemical Formula A] Li 1+x (Ni a Co b Mr c M d )O2 In the above chemical formula A, M is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, a, b, c, and d are -0.20≤x≤0.20, 0.50≤a<1, 0, respectively. <b<0.50, 0<c<0.50, 0≤d≤0.10, a+b+c+d=1을 만족한다.

6. In Claim 1, A lithium secondary battery in which the above-mentioned positive active material comprises a lithium nickel-based oxide having a nickel content of 80 mol% or more among the total metals excluding lithium.

7. In Claim 1, A lithium secondary battery in which the positive active material comprises a single-particle lithium nickel-based oxide.

8. In Claim 1, A lithium secondary battery wherein the compound represented by the above chemical formula 1 is one or more selected from the group consisting of compounds represented by the following chemical formulas 1-1 to 1-5: [Chemical Formula 1-1] [Chemical Formula 1-2] [Chemical Formula 1-3] [Chemical Formula 1-4] [Chemical Formula 1-5] In the above chemical formulas 1-1 to 1-5, R2 and R3 are as defined in Chemical Formula 1 above.

9. In Claim 1, A lithium secondary battery in which the ratio of the total volume of the linear carbonate compound and the sulfonamide compound to the volume of the cyclic carbonate compound is 2.0 to 5.

0.

10. In Claim 1, A lithium secondary battery having a content of the compound represented by Chemical Formula 1 of 5 volume% to 40 volume% based on the total volume of the organic solvent.

11. In Claim 1, A lithium secondary battery in which the content of the cyclic carbonate-based compound is 10 volume% to 45 volume% based on the total volume of the organic solvent.

12. In Claim 1, A lithium secondary battery in which the content of the linear carbonate-based compound is 30 volume% to 80 volume% based on the total volume of the organic solvent.

13. In Claim 1, A lithium secondary battery wherein the above-mentioned non-aqueous electrolyte further comprises one or more additives selected from the group consisting of cyclic carbonate-based additives, sulfonate-based additives, and sulfate-based additives.

14. In Claim 1, The above lithium secondary battery is a lithium secondary battery having a charge cut-off voltage of 4.30V or higher.

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