Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: a positive electrode comprising a positive electrode active material; a negative electrode comprising a negative electrode active material; and a non-aqueous electrolyte, wherein the positive electrode active material comprises a single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 70 mol% based on the total metals excluding lithium, and a Co-containing coating layer provided on a surface of the lithium nickel-based oxide, and the non-aqueous electrolyte comprises a lithium salt and an organic solvent comprising a compound represented by chemical formula 1, a linear carbonate-based compound, and a cyclic carbonate-based compound including ethylene carbonate.

Description

lithium secondary battery

[0001] The present application claims the benefit of priority based on Korean Patent Application No. 10-2024-0194810 filed December 23, 2024 and Korean Patent Application No. 10-2025-0164721 filed November 4, 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] With the advancement of technologies such as electric vehicles, energy storage systems (ESS), and portable electronic devices, the demand for lithium secondary batteries as an energy source is rapidly increasing.

[0004] Recently, in the electric vehicle sector, there has been a demand for cells with high energy density to extend driving range per charge. Accordingly, lithium-ion batteries containing high-nickel (High-Ni) cathode active materials, which improve capacity by increasing the nickel content, have been developed. However, since high-nickel cathode active materials have a high unit cost, their application poses a problem of increasing production costs for secondary batteries and electric vehicles. Furthermore, while increasing the nickel content in the cathode active material improves initial capacity characteristics, the highly reactive Ni... 4+ There is a problem in that the excessive generation of ions causes the structure of the positive electrode active material to collapse, which increases the degradation rate of the positive electrode active material and reduces lifespan characteristics and battery safety.

[0005] To address these issues, technologies are being developed to secure energy density by applying cathode active materials with a relatively lower Ni content compared to high-nickel cathode active materials and operating at higher voltages than conventional methods. However, operating lithium-ion batteries at high voltages presents a problem in that side reactions with the electrolyte increase, leading to increased gas generation and cell degradation, which in turn degrades lifespan characteristics.

[0006] Therefore, developing lithium-ion batteries that have high energy density, excellent lifespan characteristics, and low manufacturing costs is an important task.

[0007] The present invention aims to solve the above-mentioned problems by applying a single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 70 mol% as a positive electrode active material, and by 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 voltage.

[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 positive electrode active material comprises a single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 70 mol% among the total metals excluding lithium; and a coating layer containing a Co element provided on the surface of the lithium nickel-based oxide.

[0010] The present invention provides a lithium secondary battery comprising the above-mentioned non-aqueous electrolyte comprising a lithium salt; and an organic solvent comprising a cyclic carbonate-based compound including ethylene carbonate, 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, wherein the single-particle lithium nickel-based oxide of [1] is a single particle consisting of one nodule, a pseudo-single particle consisting of a complex of 2 to 30 nodules, or a combination thereof.

[0016] [3] The present invention provides a lithium secondary battery, wherein, in [1] or [2], the lithium nickel-based oxide has the composition of the following formula A.

[0017] [Chemical Formula A]

[0018] Li 1+x (Ni a Co b Mn c M d )O2

[0019] In the above chemical formula A,

[0020] 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

[0021] x, a, b, c, and d are -0.20≤x≤0.20, 0.50≤a≤0.70, and 0, respectively. <b<0.50, 0<c<0.50, 0≤d≤0.10, a+b+c+d=1을 만족한다.

[0022] [4] The present invention provides a lithium secondary battery in which, in [3], a, b, c, and d of the formula A satisfy 0.55≤a≤0.65, 0.05≤b≤0.15, 0.25≤c≤0.35, and 0≤d≤0.10, respectively.

[0023] [5] The present invention provides a lithium secondary battery in which, in at least one of [1] to [4], the content of Co element in the coating layer is 1 mol% to 5 mol% based on the total molar amount of the positive electrode active material.

[0024] [6] The present invention is, in at least one of [1] to [5], the D of the positive active material. 50 This provides a lithium secondary battery with a thickness of 1㎛ to 10㎛.

[0025] [7] The present invention provides a lithium secondary battery in which, in at least one of [1] to [6], 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] [8] The present invention provides a lithium secondary battery in which, in at least one of [1] to [7], the content of the cyclic carbonate compound is 5 volume% to 40 volume% based on the total volume of the organic solvent.

[0039] [9] The present invention provides a lithium secondary battery in which, in at least one of [1] to [8], the content of the linear carbonate compound is 20 volume% to 90 volume% based on the total volume of the organic solvent.

[0040]

[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 1 volume% to 40 volume% based on the total volume of the organic solvent.

[0041]

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

[0010] , the ratio of the total volume of the linear carbonate compound and the compound represented by Formula 1 to the volume of the cyclic carbonate compound is 2.0 to 6.0.

[0042]

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

[0011] , the non-aqueous electrolyte further comprises one or more lithium salt-based additives selected from the group consisting of lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium difluorophosphate, and lithium difluorobisoxalatephosphate.

[0043]

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

[0012] , the non-aqueous electrolyte further comprises a compound represented by the following chemical formula 2.

[0044] [Chemical Formula 2]

[0045]

[0046] In the above chemical formula 2,

[0047] A is a heterocyclic group having 3 to 5 carbon atoms or a heteroaryl group having 3 to 5 carbon atoms, and

[0048] Rk is an alkylene group having 1 to 3 carbon atoms.

[0049]

[0014] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0013] , the negative electrode active material comprises a carbon-based negative electrode active material.

[0050]

[0015] The present invention provides a lithium secondary battery in which, in at least one of [1] to

[0014] , the lithium secondary battery has a charge cut-off voltage of 4.35V or higher.

[0051] The lithium secondary battery according to the present invention includes a Co coating layer as a positive electrode active material and uses a single-particle lithium nickel-based oxide having a nickel content of 50 mol% to 70 mol%, so that even when operated under a high voltage of 4.35V or higher, rapid degradation of the positive electrode active material does not occur, and thus excellent lifespan characteristics can be exhibited.

[0052] The lithium secondary battery according to the present invention includes a sulfonamide-based compound with excellent oxidation stability as an electrolyte solvent, so that the oxidative decomposition reaction occurring at the anode interface during high temperature and / or high voltage operation is suppressed, thereby exhibiting excellent resistance characteristics.

[0053] Figure 1 is a scanning electron microscope image of a single-particle positive electrode active material.

[0054] Figure 2 is a scanning electron microscope image of a pseudo-single particle cathode active material.

[0055] Figure 3 is a scanning electron microscope image of a secondary particle positive electrode active material.

[0056] Figure 4 is a scanning electron microscope image of the positive electrode active material used in Example 1.

[0057] Figure 5 is a scanning electron microscope image of the positive electrode active material used in Example 6.

[0058] The present invention will be described in more detail below.

[0059]

[0060] 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.

[0061] The above “nodule” is a sub-particle 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.

[0062] 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.

[0063] In the present invention, the term “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.

[0064] 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.

[0065]

[0066] As a result of repeated research to develop a lithium secondary battery that has relatively low manufacturing costs and excellent high-temperature durability even at high voltages, the inventors discovered that by applying a single-particle lithium nickel-based oxide containing a Co coating layer as the positive electrode active material and having a Ni content of 50 mol% to 70 mol%, and replacing part of the electrolyte solvent with a sulfonamide-based compound, excellent high-temperature life characteristics and high-temperature storage characteristics can be achieved even when operating at high voltages, and thus completed the present invention.

[0067] Specifically, due to the low oxidation stability of Ni, as the Ni content in the cathode active material increases, the adverse reactivity with the electrolyte on the surface of the active material increases. Therefore, in this invention, energy density is improved by increasing the driving voltage instead of increasing the Ni content. Mid-nickel cathode active materials with a Ni content of 50 mol% to 70 mol% have superior durability and lower cost compared to high-nickel cathode active materials with a nickel content exceeding 70 mol%, thus ensuring performance stability and reducing manufacturing costs.

[0068] However, when a lithium secondary battery containing a mid-nickel cathode active material with a Ni content of 50 mol% to 70 mol% is operated at high voltage, the oxidation state of nickel fluctuates rapidly during the insertion / extraction of Li ions, which causes the potential distribution within and between particles to become non-uniform. This potential non-uniformity leads to localized electrochemical instability, which not only exacerbates side reactions in the electrolyte but also increases gas generation and transition metal leaching due to oxidative decomposition reactions of the electrolyte at the cathode interface, thereby increasing resistance and potentially degrading the long-term performance of the battery.

[0069] Therefore, the present invention aims to suppress side reactions at the anode interface to the maximum extent by enhancing oxidation stability through the application of a single-particle form of a cathode active material that includes a Co coating layer. In particular, the Co coating layer can contribute to the structural stability and output enhancement of the cathode active material and assist in the uniform insertion and extraction of lithium ions. However, even in this case, limitations still exist regarding side reactions with the electrolyte, cobalt leaching, and structural stability under high voltage. In particular, single-particle cathode active materials have limitations in improving output characteristics.

[0070] Accordingly, the inventors replaced a portion of the electrolyte solvent with a sulfonamide-based compound. As a result, compared to conventional carbonate-based organic solvents, it was confirmed that the effect of reducing side reactions on the electrode surface while increasing lithium ion mobility resulted in reduced gas generation and improved electrochemical stability.

[0071] Specifically, the sulfonamide compound represented by Chemical Formula 1 of the present invention has a low donor number and minimizes coordination with Li ions, thereby increasing the participation rate of the solvation structure of ethylene carbonate, which has the effect of stably increasing the mobility of lithium ions. Accordingly, it can contribute to the improvement of the output performance of the battery.

[0072] In addition, the above sulfonamide compounds have low nucleophilicity (i.e., low electron donor number) and therefore do not participate much in the dissociation reaction of lithium ions in the electrolyte, so decomposition reactions do not occur easily, which can contribute to reducing the amount of gas generated. Even if decomposition occurs, the decomposition products are sulfite-based or sulfate-based compounds with excellent high-voltage stability, which is advantageous for high-voltage operation.

[0073] In addition, the above-mentioned sulfonamide compound contributes to the formation of a dense and uniform CEI film on the anode, and since the CEI film is formed before high-voltage operation, it can play a role in improving the stability of the Co coating layer during subsequent high-voltage operation.

[0074] Therefore, a lithium secondary battery to which the above electrolyte is applied has a low resistance increase rate and can simultaneously exhibit excellent lifespan characteristics and durability.

[0075]

[0076] The following describes each component constituting the present invention in more detail.

[0077]

[0078] anode

[0079] 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.

[0080] 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.

[0081] The above positive active material may include a lithium nickel-based oxide having a Ni content of 50 mol% to 70 mol%, preferably 52 mol% to 68 mol%, and more preferably 55 mol% to 65 mol% among the total metals excluding lithium.

[0082] As the nickel content in lithium nickel-based oxides increases, the reactivity of Ni increases. 4+As the number of ions increases, the structural stability of the cathode active material decreases during charging and discharging, leading to rapid cathode degradation. This phenomenon is further exacerbated during high-voltage operation. In contrast, lithium nickel-based oxides with a Ni content of 50 mol% to 70 mol% exhibit higher structural stability at high voltages compared to lithium nickel-based oxides with a nickel content of 80 mol% or higher; therefore, the degradation of lifespan characteristics during high-voltage operation can be minimized. However, if the Ni content is less than 50 mol%, not only do capacity characteristics deteriorate, but it also becomes difficult to realize the output improvement effect resulting from the improvement of the solvation structure of the compound represented by Chemical Formula 1 described earlier. Specifically, since the total amount of nickel contributing to the change in oxidation state during the charging and discharging process decreases, a strong oxidation potential field is not sufficiently formed. Consequently, desolvation—which breaks the bond between lithium ions and the solvent—does not proceed smoothly, leading to a degradation of output characteristics. Nevertheless, since a certain level of oxidation potential exists at the interface between the cathode and the electrolyte, it can lead to non-uniform oxidative decomposition of the electrolyte and additives. Consequently, local side effects may increase and performance degradation may be accelerated.

[0083] Accordingly, it is preferable that the Ni content of the lithium nickel-based oxide is 50 mol% to 70 mol%.

[0084] Specifically, the lithium nickel-based oxide may be a lithium transition metal oxide containing nickel, manganese, and cobalt, and more specifically, may have the composition of the following chemical formula A.

[0085] [Chemical Formula A]

[0086] Li 1+x (Ni a Co b Mn c M d )O2

[0087] In the above chemical formula A,

[0088] 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

[0089] x, a, b, c, and d are -0.20≤x≤0.20, 0.50≤a≤0.70, and 0, respectively. <b<0.50, 0<c<0.50, 0≤d≤0.10, a+b+c+d=1을 만족한다.

[0090] 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.

[0091] The above 'a' represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, 0.50 <a<0.70, 0.52≤a≤0.68, 또는 0.55≤a≤0.65일 수 있다. a가 상기 범위를 만족할 때, 고전압에서 안정적으로 구동되어 고용량 및 고수명 특성을 구현할 수 있다.

[0092] 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, 0.05≤b≤0.30 또는 0.05≤b≤0.15일 수 있다.

[0093] 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, 0.05≤c≤0.30 또는 0.25≤c≤0.35일 수 있다.

[0094] 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. When elements are included, the structural stability of lithium nickel-based oxide particles is improved, enabling superior lifespan characteristics during high-voltage operation.

[0095] 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, or 0 <d≤0.10일 수 있다. M When the molar ratio of the elements satisfies the above range, both the structural stability and capacity of the positive active material can be excellent.

[0096] The above lithium nickel-based oxide may have a manganese content that is higher than the cobalt content. Specifically, a, b, c, and d of the above chemical formula A may satisfy 0.55≤a≤0.65, 0.05≤b≤0.15, 0.25≤c≤0.35, and 0≤d≤0.10, respectively. When the manganese content is higher than the cobalt content in this way, positive charges are distributed relatively evenly on the anode surface compared to cases where the cobalt and manganese contents are equal or the cobalt content is higher. Accordingly, the degree of reaction participation of the electrolyte on the anode surface increases, and the solvation of lithium ions is effectively achieved.

[0097] Specifically, since the oxidation number of manganese is +4 and that of cobalt is +3, a higher manganese content leads to an increase in the positive charge on the anode surface. This increase in positive charge strengthens electrostatic attraction, causing solvent molecules within the electrolyte to surround lithium ions more stably. When solvation is effectively achieved in this way, the mobility of lithium ions within the electrolyte can be improved.

[0098] Meanwhile, the molar ratio of nickel to the molar ratio of manganese among all metals excluding lithium in the lithium nickel-based oxide (i.e., the a / c value of Formula 1) may be 1 to 3, preferably 1.2 to 2.8, and more preferably 1.5 to 2.5. In addition, the molar ratio of nickel to the molar ratio of cobalt among all metals excluding lithium in the lithium nickel-based oxide (i.e., the a / b value of Formula 1) may be 3 to 10, preferably 4 to 8, and more preferably 5 to 7. In this case, it may contribute to stabilizing the solvation structure described above.

[0099] In particular, since the lithium secondary battery according to the present invention includes a single-particle type positive electrode active material, the surface area is smaller compared to the case where a secondary particle type positive electrode active material of the same particle size is included, so the reaction with the electrolyte at the surface of the positive electrode may be limited, but this can be compensated for by adjusting the composition as described above.

[0100] The above-mentioned 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 above-mentioned lithium nickel-based oxide may be a single-particle lithium nickel-based oxide containing 30 or fewer nodules.

[0101] 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.

[0102] The above single-particle lithium nickel-based oxide preferably comprises 30 or fewer nodules, preferably 1 to 25, and more preferably 1 to 15 nodules. If the number of nodules constituting the lithium nickel-based oxide exceeds 30, particle breakage increases during electrode manufacturing, and the occurrence of internal cracks due to volume expansion / contraction of nodules during charging and discharging increases, which may reduce the effect of improving high-temperature life characteristics and high-temperature storage characteristics.

[0103] 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.

[0104] The above positive active material is D 50This 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.

[0105]

[0106] The positive electrode active material of the present invention comprises a coating layer containing a Co element provided on the surface of the lithium nickel-based oxide. The coating layer may be provided on a part or the whole of the surface of the lithium nickel-based oxide. Specifically, the coating layer may be formed in a film or membrane form distinct from an island form, and more specifically, it may be provided on an area of ​​90% or more, preferably 95% or more, of the total surface area of ​​the lithium nickel-based oxide.

[0107] When the Co element is coated on the surface of a lithium nickel-based oxide, a layered LCO-like phase (specifically, Li e CoO2, 0 <e<1) 형태로 존재하게 되며, 이는 전지의 출력 특성 개선에 기여할 수 있다. 단입자형 양극 활물질은 전극 표면에서 부반응성이 낮아 고온 내구성이 우수한 장점이 있지만, Li 이온의 이동성이 낮아 출력 특성 면에서는 한계가 있으므로 Co 원소를 포함하는 코팅층을 형성함으로써, 단입자형 양극 활물질의 한계점을 보완하는 효과가 있다.

[0108] In addition, since the Co element is coated in an LCO-like phase form, it has superior coverage characteristics compared to other elements coated in a salt form such as tungsten (W), fluorine (F), boron (B), and phosphorus (P), thus preventing non-uniform electrochemical reactions and having an excellent effect in improving long-term high-temperature durability.

[0109] In addition, since the Co coating layer contains an LCO-like phase, it maintains a stable structure compared to nickel, where the oxidation state changes randomly, and accordingly, can induce a homogeneous reaction in terms of maintaining the c-axis structure.

[0110] However, as explained above, the Co coating layer has the limitation of being unstable at high voltage. The significance of the present invention lies in overcoming this limitation by introducing a compound represented by Chemical Formula 1 to form a reinforced CEI film on the Co coating layer.

[0111] The above coating layer can be formed by mixing the Co-containing raw material and the lithium nickel-based oxide and heat treating. The above cobalt-containing raw material may be one or more selected from Co3O4, Co(OH)2, Co2O3, Co3(PO4)2, CoF3, Co(OCOCH3)2·4H2O, Co(NO3)·6H2O, Co(SO4)2·7H2O, and CoC2O4, and preferably may be Co(OH)2.

[0112] The above Co-containing raw material can be mixed in an amount of 1 mol% to 5 mol% relative to the total molar amount of the lithium nickel-based oxide.

[0113] The content of the Co element in the coating layer may be 1 mol% to 5 mol%, preferably 2 mol% to 4 mol%, and more preferably 2.5 mol% to 3.5 mol%, based on the total molar amount of the cathode active material. Although the above-described effects are achieved when the Co coating layer is formed, if it is formed excessively, the coating is applied in a non-uniform form, making it impossible to improve uniform output characteristics. Furthermore, since it may be difficult to observe the stability improvement effect resulting from the use of single-particle lithium nickel-based oxide, it is preferable that the content be within the above range. The formation of the coating layer can be confirmed through scanning electron microscopy (SEM), and the content of the Co element in the coating layer can be determined through XRD analysis of the LCO-like phase (specifically Li) present on the surface of the cathode active material.e CoO2, 0 <e<1)의 피크 강도를 확인하거나 ICP 분석을 통해 양극 활물질 내 Co 함량을 측정한 후 리튬 니켈계 산화물에 포함된 Co 함량을 차감하는 방법으로 측정될 수 있다.

[0114] In addition to the Co-containing coating layer, the lithium nickel-based oxide may further include a coating layer on its surface containing one or more elements selected from the group consisting of 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.

[0115]

[0116] A single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 70 mol% among all metals excluding the lithium mentioned above may be included in the total positive active material layer in an amount of more than 50 weight%, preferably 55 weight% or more, more preferably 60 weight% or more, even more preferably 70 weight% or more, and even more preferably 100 weight% of the total positive active material. When the proportion of the single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 70 mol% among the total weight of the positive active material satisfies the above range, excellent lifespan characteristics can be obtained even when operating at high voltage.

[0117] The above positive active material layer may include a positive active material other than a single-particle lithium nickel-based oxide with a nickel content of 50 mol% to 70 mol%, that is, a lithium nickel-based oxide with a nickel content exceeding 70 mol% or a secondary-particle lithium nickel-based oxide, but if the proportion of the lithium nickel-based oxide with a nickel content exceeding 70 mol% or the secondary-particle lithium nickel-based oxide is 50 weight% or more of the total positive active material, the lifespan characteristics may be degraded when operating at high voltage.

[0118] 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).

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126]

[0127] cathode

[0128] 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.

[0129] It is preferable that the above cathode is not lithium metal.

[0130] 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 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.

[0131] The above negative electrode active material is a carbonaceous material such as artificial graphite, natural graphite, graphitized carbon fiber, or amorphous carbon; a metallic material capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO k (0 <k< 2), SnO2, 바나듐 산화물, 리튬 바나듐 산화물과 같이 리튬을 도프 및 탈도프할 수 있는 금속 산화물; 또는 Si-C 복합체 또는 Sn-C 복합체과 같이 상기 금속질 물질과 탄소질 재료를 포함하는 복합물 등을 들 수 있으며, 이들 중 어느 하나 또는 둘 이상의 혼합물이 사용될 수 있다.

[0132] The above-mentioned cathode active material may include a carbon-based cathode active material, and preferably may be composed of 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. For example, the above-mentioned carbon-based cathode active material may include 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 2:8 to 8:2, more preferably 2:8 to 4:6.

[0133] D of the above carbon-based cathode active material 50 The size may be 2㎛ to 30㎛, preferably 5㎛ to 30㎛.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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.

[0140] 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.

[0141]

[0142] Non-aqueous electrolyte

[0143] 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.

[0144]

[0145] (1) Lithium salt

[0146] The non-aqueous electrolyte of the present invention includes a lithium salt.

[0147] 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.

[0148] 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.

[0149] 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.

[0150]

[0151] (2) Organic solvent

[0152] The above-mentioned non-aqueous electrolyte comprises an organic solvent comprising a cyclic carbonate compound including ethylene carbonate, a linear carbonate compound, and a compound represented by the following chemical formula 1.

[0153] [Chemical Formula 1]

[0154]

[0155] In the above chemical formula 1,

[0156] 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.

[0157] 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 4.35V 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 4.35V 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 and CH4, while exhibiting excellent electrochemical and chemical stability and not reducing the degree of dissociation of the lithium salt.

[0158] Based on the total volume of the organic solvent, the content of the compound represented by Chemical Formula 1 may be 1 volume% or more, 3 volume% or more, 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 1 volume% to 40 volume%, preferably 5 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 carbonate-based solvent is insufficient, so the dissociation of lithium ions does not occur sufficiently, making it difficult to achieve performance in high-power systems.

[0159] 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.

[0160] 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.

[0161] 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, specifically one or more selected from the group consisting of compounds represented by the following chemical formulas 1-1 to 1-3, more specifically one or more selected from the group consisting of compounds represented by the following chemical formulas 1-1 and 1-2, and even more specifically, a compound represented by the following chemical formula 1-1.

[0162] The compound represented by the following chemical formula 1-1 has a structure substituted with one F, and since the electron-pulling effect is localized, it does not significantly affect the charge distribution or polarity of the entire compound. In addition, as the donor number is formed at an appropriately low level, the interaction with Li ions is not excessively suppressed, which is desirable in that the mechanism for ethylene carbonate and linear carbonate to coordinate centrally with Li ions within the solvation structure can be maintained.

[0163] On the other hand, in structures with three or more substituted F groups, such as those in Chemical Formulas 1-2 to 1-5 below, the electron pulling effect becomes concentrated only at the terminals, and the charge distribution within the compound may become non-uniform compared to the structure in Chemical Formula 1-1. Consequently, the probability of the compound represented by Chemical Formula 1 binding unevenly around the lithium ion increases, and thus the possibility of forming an unstable solvation structure compared to the structure in Chemical Formula 1-1 also increases.

[0164] Since side reactions at the electrode interface can be prevented as the solvation structure becomes more stable, it is most desirable for the compound represented by Chemical Formula 1 to have the structure of Chemical Formula 1-1.

[0165] [Chemical Formula 1-1]

[0166]

[0167] [Chemical Formula 1-2]

[0168]

[0169] [Chemical Formula 1-3]

[0170]

[0171] [Chemical Formula 1-4]

[0172]

[0173] [Chemical Formula 1-5]

[0174]

[0175] 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.

[0176] 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, more specifically one or more selected from the group consisting of compounds represented by the following chemical formulas 1-A and 1-B, and even more specifically, it may be the compound represented by the following chemical formula 1-A.

[0177] [Chemical Formula 1-A]

[0178]

[0179] [Chemical Formula 1-B]

[0180]

[0181] [Chemical Formula 1-C]

[0182]

[0183] [Chemical Formula 1-D]

[0184]

[0185] [Chemical Formula 1-E]

[0186]

[0187]

[0188] The above cyclic carbonate compound includes ethylene carbonate. Preferably, the above cyclic carbonate compound may consist of ethylene carbonate, that is, may not include any other cyclic carbonate compounds other than ethylene carbonate.

[0189] The above organic solvent includes ethylene carbonate along with the compound represented by Chemical Formula 1. Through this combination, gas generation resulting from the decomposition of the cyclic carbonate-based solvent can be minimized, the destruction of the SEI film on the surface of the negative electrode active material can be prevented, and the oxidation stability, chemical stability, and electrochemical stability of the non-aqueous electrolyte can be improved. Furthermore, lithium transition metal oxides used as positive electrode active materials are subject to structural instability and increased carbon dioxide gas generation depending on conditions such as the content of the internally contained transition metal and high-voltage operation, which causes problems such as increased cell resistance and lithium precipitation. However, when using the combination of the compound represented by Chemical Formula 1 and ethylene carbonate described above, the carbon dioxide generated at the positive electrode is reduced at the negative electrode, thereby significantly reducing the amount of gas generated within the cell. Therefore, a lithium secondary battery to which the above-described non-aqueous electrolyte is applied is desirable as it prevents an increase in resistance, improves lifespan performance, and possesses excellent durability.

[0190] If cyclic carbonates other than ethylene carbonates, specifically fluorine-substituted ethylene carbonates (such as fluoroethylene carbonates), are used, it is not desirable because they inhibit the reduction of CO2 due to their higher reducing power than CO2. In this regard, it may be desirable that fluorine-substituted ethylene carbonates, such as fluoroethylene carbonates, are not included in the non-aqueous electrolyte, or at least be added in small amounts.

[0191] Based on the total volume of the organic solvent, the content of the cyclic carbonate-based compound may be 5 volume% or more, 10 volume% or more, 15 volume% or more, or 20 volume% or more. Additionally, based on the total volume of the organic solvent, the content of the cyclic carbonate-based compound may be 40 volume% or less, 35 volume% or less, 30 volume% or less, or 25 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-based compound may be 5 volume% to 40 volume%, specifically 10 volume% to 30 volume%, and more specifically 15 volume% to 25 volume%. When within this range, the viscosity of the organic solvent is appropriately controlled, the dissociation, migration, and transport of the lithium salt can be carried out smoothly, and there is an effect of improving the long-term cycle performance of the battery due to the reinforcement of the SEI layer.

[0192] 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.

[0193] Based on the total volume of the organic solvent, the content of the linear carbonate-based compound may be 20 volume% or more, 25 volume% or more, 30 volume% or more, 40 volume% or more, 45 volume% or more, 50 volume% or more, or 55 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, or 65 volume% or less. The above numerical ranges can be combined with one another without limitation. Specifically, based on the total volume of the organic solvent, the content of the linear carbonate-based compound may be 20 volume% to 90 volume%, specifically 40 volume% to 85 volume%, and more specifically 50 volume% to 70 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.

[0194] The ratio of the total volume of the linear carbonate compound and the compound represented by Formula 1 to the volume of the cyclic carbonate compound, i.e., (volume of linear carbonate compound + volume of compound represented by Formula 1) / volume of cyclic carbonate, may be 2.0 to 6.0, preferably 3.0 to 4.0, and more preferably 3.5 to 4.5. If the ratio of the total volume of the linear carbonate compound and the compound represented by Formula 1 to the volume of the cyclic carbonate compound is too small, the electrolyte viscosity may increase and the ionic conductivity may decrease; if it is too large, the durability of the SEI layer may decrease and long-term cycle performance may be degraded; therefore, it is desirable that it be within the above range.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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).

[0199] 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).

[0200] 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.

[0201]

[0202] (3) Additives

[0203] The above-mentioned non-aqueous electrolyte may further include additives as needed.

[0204] The above-mentioned non-aqueous electrolyte may further include one or more lithium salt-based additives selected from the group consisting of lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium difluorophosphate (LiDFP), and lithium difluorobisoxalate phosphate (LiDFOP), and preferably may include lithium bis(oxalate)borate (LiBOB). The lithium salt-based additive is a compound different from the lithium salt included in the above-mentioned non-aqueous electrolyte, and when included in the non-aqueous electrolyte, it has the effect of stabilizing the film formed on the anode and cathode to improve high-temperature life characteristics.

[0205] The content of the lithium salt-based additive may be 0.05% to 5% by weight, preferably 0.1% to 1% by weight, and more preferably 0.3% to 0.8% by weight, based on the total weight of the non-aqueous electrolyte. If the content of the lithium salt-based additive is too low, a sufficient electrode film cannot be formed during the activation process, so the above effect may be negligible; and if the lithium salt-based additive is excessive, swelling problems may occur due to gas generated from unnecessary reactions, so it is desirable to be within the above range.

[0206] The above-mentioned non-aqueous electrolyte may further include a compound represented by the following chemical formula 2.

[0207] [Chemical Formula 2]

[0208]

[0209] In the above chemical formula 2,

[0210] A is a heterocyclic group having 3 to 5 carbon atoms or a heteroaryl group having 3 to 5 carbon atoms, and

[0211] Rk is an alkylene group having 1 to 3 carbon atoms.

[0212] Since the compound represented by Chemical Formula 2 above contains a propargyl functional group, when included in the electrolyte, it undergoes reductive decomposition through a radical reaction, thereby forming a SEI film of a PEO (poly(ethylene oxide))-based polymer component on the surface of the cathode. This not only improves the high-temperature durability of the cathode itself but also has the effect of preventing the electrodeposition of transition metals on the cathode surface. Furthermore, since the propargyl group has the property of adsorbing metal ions, it can function to prevent the leaching of impurities by adsorbing them onto the surface of metallic impurities contained in the anode, and to suppress internal short circuits by preventing the leached metal ions from precipitating on the cathode. In addition, the compound represented by Chemical Formula 2 can inhibit the generation of HF by binding with PF5, an electrolyte decomposition product, thereby preventing the destruction of the CEI (cathode electrolyte interphase) film formed on the surface of the anode and inhibiting further decomposition of the electrolyte.

[0213] In one embodiment of the present invention, A of Formula 2 may be a nitrogen-containing heteroaryl group having 3 to 5 carbon atoms, and preferably may be an imidazole group.

[0214] As a preferred example, the compound represented by the above chemical formula 2 can be represented by the following chemical formula 2-1.

[0215] [Chemical Formula 2-1]

[0216]

[0217] In the above chemical formula 2-1,

[0218] Rk is as defined in Chemical Formula 2 above.

[0219] In one embodiment of the present invention, Rk of Formula 2 may be a straight-chain or branched-chain alkylene group having 1 to 3 carbon atoms, preferably a straight-chain alkylene group having 1 to 3 carbon atoms, more preferably a methylene group.

[0220] As a preferred example, the compound represented by the above chemical formula 2 may be represented by the following chemical formula 2-A.

[0221] [Chemical Formula 2-A]

[0222]

[0223] The content of the compound represented by Chemical Formula 2 above may be 0.05% to 5% by weight, preferably 0.05% to 1% by weight, and more preferably 0.1% to 0.5% by weight, based on the total weight of the non-aqueous electrolyte. Considering that if the content of the compound represented by Chemical Formula 2 above is excessive, it may participate excessively in the decomposition reaction at the interface between the electrode and the electrolyte and cause the film resistance to become excessively large, thereby increasing the resistance of the battery, it is preferable that the content of the compound represented by Chemical Formula 2 above be 5% by weight or less.

[0224] In addition to this, 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, phosphorus-based additives, nitrile-based additives, amine-based additives, silane-based additives, and benzene-based additives.

[0225] 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.

[0226] 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).

[0227] 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).

[0228] 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.

[0229] 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).

[0230] 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.

[0231] The above benzene-based additive may be one or more selected from the group consisting of monofluorobenzene, difluorobenzene, trifluorobenzene, and tetrafluorobenzene.

[0232] The content of each of the above-mentioned cyclic carbonate-based additive, sulfone-based additive, sulfate-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, based on the total weight of the above-mentioned non-aqueous electrolyte.

[0233] In particular, when the above-mentioned cyclic carbonate-based additive is included, its content must be 5% by weight or less, and it is undesirable if it is included in an amount exceeding 5% by weight based on the total weight of the non-aqueous electrolyte, as this can act as an organic solvent. For example, in the case of fluoroethylene carbonate (FEC), when used in an amount of 5% by weight or less, it can contribute to the stabilization of the interface between the electrode and the electrolyte by forming a dense LiF-based film through reductive decomposition during the initial operation. However, when used in an amount exceeding 5% by weight, the remaining FEC that does not participate in film formation easily undergoes defluorination, increasing HF, which can cause etching of the electrode surface and local side reactions. As a result, the increase in interfacial resistance and the consequent performance degradation may be accelerated, and this problem can be particularly exacerbated during high-voltage operation.

[0234]

[0235] Separator

[0236] 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.

[0237] 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.

[0238] 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.

[0239]

[0240] lithium secondary battery

[0241] The lithium secondary battery according to the present invention may have a charge cut-off voltage (full charge voltage) of 4.3V or higher, preferably 4.35V or higher, and may be 4.8V or lower, 4.6V or lower, or 4.5V or lower. 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, there is a problem in that if the driving voltage increases, side reactions with the electrolyte during charging and discharging increase, and structural collapse of the positive electrode active material occurs rapidly, causing the lifespan characteristics to deteriorate rapidly. 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, by applying a single-particle lithium nickel-based oxide having a Co coating layer as the positive electrode active material and a Ni content of 50 mol% to 70 mol%, excellent lifespan characteristics can be maintained even when the charge cut-off voltage is 4.35V or higher.

[0242] 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 4.35V or higher by using a specific positive active material and an electrolyte solvent.

[0243] 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.

[0244] 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.

[0245] 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.

[0246] In addition, the present invention provides a pack cell assembly.

[0247] 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.

[0248] 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.

[0249]

[0250] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0251] <Examples and Comparative Examples: Manufacture of Lithium Secondary Batteries>

[0252] Example 1.

[0253] (1) Preparation of positive electrode active material

[0254] Ni 0.6 Co 0.1 Mn 0.3 A precursor having a composition represented by (OH)2 and LiOH were introduced into a Henschel mixer (700L) and mixed for 20 minutes at a center speed of 400 rpm. At this time, LiOH was introduced in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1.05:1. The mixed powder was placed in an alumina crucible measuring 330 mm × 330 mm and calcined at a temperature of 850°C for 10 hours under an oxygen atmosphere to form Li[Ni 0.6 Co 0.1 Mn 0.3 A lithium nickel-based oxide having the composition of ]O2 was prepared. Subsequently, 3 mol% of Co(OH)2 was added relative to the total molar amount of the lithium nickel-based oxide, and the mixture was calcined again at a temperature of 750°C for 10 hours to form a Co coating layer, thereby D 50 A positive electrode active material with a particle size of 3.8 μm was prepared. A photograph of the prepared positive electrode active material observed using a scanning electron microscope is attached in Fig. 4. Through Fig. 4, it can be confirmed that a single-particle positive electrode active material was prepared. Based on the total moles of the prepared positive electrode active material, the content of the Co element in the coating layer was 3 mol%.

[0255]

[0256] (2) Preparation of non-aqueous electrolyte

[0257] A non-aqueous electrolyte was prepared by dissolving LiPF6 to a concentration of 1.0 M in an organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and the compound represented by Chemical Formula 1-A in a volume ratio of 20:60:20, and then adding the compound represented by Chemical Formula 2-A and lithium bis(oxalateto)borate (LiBOB). Based on the total weight of the non-aqueous electrolyte, the content of the compound represented by Chemical Formula 2-A was 0.1 wt% and the content of LiBOB was 0.5 wt%.

[0258]

[0259] (3) Manufacturing of lithium secondary batteries

[0260] An anode slurry (solid content 75.5 wt%) was prepared by adding the above-prepared anode active material, 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 97.74:0.7:1.56. The anode slurry was applied to one side of an Al thin film with a thickness of 15 μm, and a cathode active material layer (thickness: 136.6 μm) was formed by drying and roll pressing, and this was used as the anode.

[0261] A cathode slurry (solid content 26 wt%) was prepared by adding a mixture of artificial graphite and natural graphite in a weight ratio of 8:2 as a cathode active material, carbon black as a conductive material, and styrene-butadiene rubber-carboxymethylcellulose (SBR-CMC) as a binder in a weight ratio of 96.15:1.55:2.3 to distilled water as a solvent. The cathode slurry was applied to one side of a Cu thin film with a thickness of 15 μm, and a cathode active material layer (thickness: 179.8 μm) was formed by drying and roll pressing, and this was used as a cathode.

[0262] 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.

[0263]

[0264] Example 2.

[0265] 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 20:75:5.

[0266]

[0267] Example 3.

[0268] 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 20:70:10.

[0269]

[0270] Example 4.

[0271] A lithium secondary battery was manufactured in the same manner as in Example 1, except that 1 mol% of Co(OH)2 was added relative to the total molar amount of lithium nickel-based oxide when forming the coating layer of the positive electrode active material.

[0272]

[0273] Example 5.

[0274] 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 20:50:30.

[0275]

[0276] Example 6.

[0277] (1) Preparation of positive electrode active material

[0278] Ni 0.6 Co 0.2 Mn 0.2 A precursor having a composition represented by (OH)2 and LiOH were introduced into a Henschel mixer (700L) and mixed for 20 minutes at a center speed of 400 rpm. At this time, LiOH was introduced in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1.05:1. The mixed powder was placed in an alumina crucible measuring 330 mm × 330 mm and calcined at a temperature of 800°C for 10 hours under an oxygen atmosphere to produce Li[Ni 0.6 Co 0.2 Mn 0.2 A lithium nickel-based oxide having the composition of ]O2 was prepared. Subsequently, 3 mol% of Co(OH)2 was added relative to the total molar amount of the lithium nickel-based oxide, and the mixture was calcined again at a temperature of 750°C for 10 hours to form a Co coating layer, thereby D 50 A positive electrode active material with a particle size of 3.8 μm was prepared. A photograph of the prepared positive electrode active material observed using a scanning electron microscope is attached in Fig. 5. Through Fig. 5, it can be confirmed that a single-particle positive electrode active material was prepared. Based on the total moles of the prepared positive electrode active material, the content of the Co element in the coating layer was 3 mol%.

[0279]

[0280] (2) Preparation of non-aqueous electrolyte

[0281] A non-aqueous electrolyte was prepared using the same method as in Example 1 above.

[0282]

[0283] (3) Manufacturing of lithium secondary batteries

[0284] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured positive electrode active material was used.

[0285]

[0286] Example 7.

[0287] 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 a compound represented by the chemical formula 1-B were mixed in a volume ratio of 20:60:20.

[0288]

[0289] Comparative Example 1.

[0290] The above Li[Ni that does not form a Co coating layer 0.6 Co 0.1 Mn 0.3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a lithium nickel-based oxide having the composition of ]O2 was used as the positive active material.

[0291]

[0292] Comparative Example 2.

[0293] 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 20:80 when preparing the non-aqueous electrolyte.

[0294]

[0295] Comparative Example 3.

[0296] (1) Preparation of positive electrode active material

[0297] Ni 0.6 Co 0.1 Mn 0.3 A precursor having a composition represented by (OH)2 and LiOH were introduced into a Henschel mixer (700L) and mixed for 20 minutes at a center speed of 400 rpm. At this time, LiOH was introduced in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1.05:1. The mixed powder was placed in an alumina crucible measuring 330 mm × 330 mm and calcined at a temperature of 650°C for 8 hours under an oxygen atmosphere to form Li[Ni 0.6 Co 0.1 Mn 0.3A lithium nickel-based oxide having the composition of ]O2 was prepared. Subsequently, 3 mol% of Co(OH)2 was added relative to the total molar amount of the lithium nickel-based oxide, and the mixture was calcined again at a temperature of 750°C for 10 hours to form a Co coating layer, thereby D 50 A positive active material with a particle size of 15 μm and in the form of secondary particles was prepared. Based on the total moles of the prepared positive active material, the content of the Co element in the coating layer was 3 mol%.

[0298]

[0299] (2) Preparation of non-aqueous electrolyte

[0300] A non-aqueous electrolyte was prepared using the same method as in Example 1 above.

[0301]

[0302] (3) Manufacturing of lithium secondary batteries

[0303] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured positive electrode active material was used.

[0304]

[0305] Comparative Example 4.

[0306] (1) Preparation of positive electrode active material

[0307] Ni 0.8 Co 0.1 Mn 0.1 A precursor having a composition represented by (OH)2 and LiOH were introduced into a Henschel mixer (700L) and mixed for 20 minutes at a center speed of 400 rpm. At this time, LiOH was introduced in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1.05:1. The mixed powder was placed in an alumina crucible measuring 330 mm × 330 mm and calcined at a temperature of 900°C for 8 hours under an oxygen atmosphere to produce Li[Ni 0.8 Co 0.1 Mn 0.1A lithium nickel-based oxide having the composition of ]O2 was prepared. Subsequently, 3 mol% of Co(OH)2 was added relative to the total molar amount of the lithium nickel-based oxide, and the mixture was calcined again at a temperature of 750°C for 10 hours to form a Co coating layer, thereby D 50 A positive electrode active material with a particle size of 3.1 μm was prepared. A photograph of the prepared positive electrode active material observed using a scanning electron microscope is attached in Fig. 5. Through Fig. 5, it can be confirmed that a single-particle positive electrode active material was prepared. Based on the total moles of the prepared positive electrode active material, the content of the Co element in the coating layer was 3 mol%.

[0308]

[0309] (2) Preparation of non-aqueous electrolyte

[0310] A non-aqueous electrolyte was prepared using the same method as in Example 1 above.

[0311]

[0312] (3) Manufacturing of lithium secondary batteries

[0313] A lithium secondary battery was manufactured in the same manner as in Example 5, except that the above-manufactured positive electrode active material was used.

[0314]

[0315] Comparative Example 5.

[0316] A lithium secondary battery was manufactured in the same manner as in Example 1, except that when forming the coating layer of the positive electrode active material, Li2WO4 containing 3 mol% of W element relative to the total molar amount of the lithium nickel-based oxide was added in the form dissolved in isopropanol, stirred, and then calcined at a temperature of 650°C for 6 hours to form a Li2WO4 coating layer.

[0317]

[0318] Comparative Example 6.

[0319] (1) Preparation of positive electrode active material

[0320] Ni 1 / 3 Co 1 / 3 Mn1 / 3 A precursor having a composition represented by (OH)2 and LiOH were introduced into a Henschel mixer (700L) and mixed for 20 minutes at a center speed of 400 rpm. At this time, LiOH was introduced in an amount such that the molar ratio of Li:(Ni+Co+Mn) was 1.05:1. The mixed powder was placed in an alumina crucible measuring 330 mm × 330 mm and calcined at a temperature of 800°C for 15 hours under an oxygen atmosphere to produce Li[Ni 1 / 3 Co 1 / 3 Mn 1 / 3 A lithium nickel-based oxide having the composition of ]O2 was prepared. Subsequently, 3 mol% of Co(OH)2 was added relative to the total molar amount of the lithium nickel-based oxide, and the mixture was calcined again at a temperature of 750°C for 10 hours to form a Co coating layer, thereby D 50 A single-particle cathode active material with a particle size of 3.2 μm was prepared. Based on the total moles of the prepared cathode active material, the content of the Co element in the coating layer was 3 mol%.

[0321]

[0322] (2) Preparation of non-aqueous electrolyte

[0323] A non-aqueous electrolyte was prepared using the same method as in Example 1 above.

[0324]

[0325] (3) Manufacturing of lithium secondary batteries

[0326] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the above-manufactured positive electrode active material was used.

[0327]

[0328] Comparative Example 7.

[0329] A lithium secondary battery was manufactured in the same manner as in Example 1, except that an organic solvent was used to mix fluoroethylene carbonate (FEC), EMC, and a compound represented by the chemical formula 1-A in a volume ratio of 20:60:20 when preparing the non-aqueous electrolyte.

[0330]

[0331] <Experimental Example>

[0332] Experimental Example 1: Evaluation of Resistance and Life After High-Temperature Cycling

[0333] 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 4.35V at 0.33C at 45℃ using an electrochemical charge / discharger under CC-CV (0.05C cut off) conditions, 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.

[0334] Each of the batteries for which the initial resistance measurement was completed was charged at 45°C at 0.33C to 4.35V under CC-CV (0.05C cut off) conditions, and then discharged at 0.33C to 2.5V to measure the initial discharge capacity.

[0335] 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.

[0336] - Capacity retention rate (%) = (Discharge capacity after 400 cycles / Initial discharge capacity) × 100

[0337] - Resistance increase rate (%) = {(Resistance after 400 cycles - Initial resistance) / Initial resistance} × 100

[0338]

[0339] Experimental Example 2: Evaluation of Resistance and Lifespan After High-Temperature Storage

[0340] 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 4.35V at 0.33C at 25℃ using an electrochemical charge / discharger under CC-CV (0.05C cut off) conditions, 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.

[0341] Each of the batteries for which the initial resistance measurement was completed was charged at 25°C at 0.33C to 4.35V under CC-CV (0.05C cut off) conditions, and then discharged at 0.33C to 2.5V to measure the initial discharge capacity.

[0342] 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.

[0343] - Capacity retention rate (%) = (Discharge capacity after 20 weeks of storage / Initial discharge capacity) × 100

[0344] - Resistance increase rate (%) = {(Resistance after 20 weeks of storage - Initial resistance) / Initial resistance} × 100

[0345] Composition of organic solvent (volume%) (EMC + Chemical Formula 1) / EC volume ratio Cathode active material Experimental Example 1 Experimental Example 2 EC EMC Chemical Formula 1-A Composition Particle type Co Coating (mol%) Capacity retention rate (%) Resistance increase rate (%) Capacity retention rate (%) Resistance increase rate (%) Example 1 20 60 20 4.0 NCM 613 single particles 393.2 11.5 89.5 14.0 Example 2 20 75 5 4.0 NCM 613 single particles 392.7 19.5 88.7 18.5 Example 3 20 70 10 4.0 NCM 613 single particles 392.2 18.7 89.1 17.7 Example 4 20 60 20 4.0 NCM 613 single particles 192.5 17.5 87.9 20.4 Example 52050304.0NCM613 single particle 391.915.788.318.7 Example 6 2060204.0NCM622 single particle 381.729.280.528.3 Example 7 206020(Chemical Formula 1-B)4.0NCM613 single particle 384.324.785.423.9 Comparative Example 1 2060204.0NCM613 single particle -70.746.566.737.5 Comparative Example 2 2080-4.0NCM613 single particle 371.249.565.939.7 Comparative Example 3 2060204.0NCM6132 secondary particle 370.243.765.136.7 Comparative Example 4 2060204.0NCM811 Single Particle 366.550.265.542.1 Comparative Example 5 2060204.0NCM613 Single Particle 3 (W Coating) 68.551.267.944.1 Comparative Example 6 2060204.0NCM111 Single Particle 360.254.463.444.9 Comparative Example 7 20 (FEC) 60204.0NCM613 Single Particle 351.852.957.940.4

[0346] Through the results of Table 1 above, it can be confirmed that the lithium secondary batteries of Examples 1 to 6, which use a mixture of ethylene carbonate, a linear carbonate-based compound, and a compound represented by Chemical Formula 1 as the organic solvent of the non-aqueous electrolyte, and a single-particle lithium nickel-based oxide having a Ni content of 50 to 70 mol% and a Co coating layer as the positive electrode active material, maintain excellent lifespan and resistance characteristics even after high-temperature cycling and high-temperature storage.

[0347] Specifically, it can be confirmed that the lithium secondary batteries of Examples 1 to 7 have superior high-temperature cycle and storage performance compared to cases where a positive electrode active material without Co coating is used (Comparative Example 1), a non-aqueous electrolyte does not contain a compound represented by Chemical Formula 1 (Comparative Example 2), a positive electrode active material in the form of secondary particles is used (Comparative Example 3), a positive electrode active material with a high nickel composition having a Ni content of more than 70 mol% is used (Comparative Example 4), a positive electrode active material with W coating instead of Co coating is used (Comparative Example 5), a positive electrode active material with a low nickel composition having a Ni content of less than 50 mol% is used (Comparative Example 6), or fluoroethylene carbonate is used instead of ethylene carbonate (Comparative Example 7).

[0348] When using a low-nickel cathode active material as in Comparative Example 6, the total amount of nickel contributing to the change in oxidation state during the charge-discharge process decreases, so a strong oxidation potential field is not sufficiently formed. Consequently, desolvation, which breaks the bond between lithium ions and the solvent, does not occur smoothly, leading to a deterioration in output characteristics. Nevertheless, since a certain level of oxidation potential exists at the interface between the cathode and the electrolyte, it can lead to non-uniform oxidative decomposition of the electrolyte and additives. As a result, performance degradation may be accelerated as local side reactions increase.

[0349] As in Comparative Example 7, when FEC is used instead of EC as an organic solvent, the remaining FEC that does not participate in film formation easily undergoes defluorination, increasing HF, which can cause etching of the electrode surface and local side reactions. As a result, the increase in interfacial resistance and the resulting performance degradation may be accelerated, and this problem can be particularly exacerbated when operating at high voltage.

[0350] In addition, among Examples 1 to 7, it can be confirmed that the lithium secondary batteries of Examples 1 to 5 containing a positive electrode active material of NCM613 composition have superior high-temperature cycle and storage performance compared to the lithium secondary battery of Example 6 containing a positive electrode active material of NCM622 composition. This is because, as previously explained, when the manganese content is greater than the cobalt content, the reactivity on the surface of the positive electrode increases even in the form of a single particle, thereby increasing the effect of introducing the compound represented by Chemical Formula 1.

[0351] In addition, among Examples 1 to 7, it can be confirmed that the lithium secondary batteries of Examples 1 to 6, which use an electrolyte containing a compound represented by Formula 1-A as the organic solvent, exhibit superior high-temperature cycle and storage performance compared to the lithium secondary battery of Example 7, which uses an electrolyte containing a compound represented by Formula 1-B. This is due to the effect that Formula 1-A, having a structure substituted with one F, forms a solvation structure with a uniform and stable charge distribution compared to Formula 1-B, which has a structure substituted with three Fs.

Claims

1. A lithium secondary battery comprising a positive electrode including a positive active material; a negative electrode including a negative active material; and a non-aqueous electrolyte, and The above positive electrode active material comprises a single-particle lithium nickel-based oxide having a Ni content of 50 mol% to 70 mol% among the total metals excluding lithium; and a coating layer containing a Co element provided on the surface of the lithium nickel-based oxide. A lithium secondary battery comprising: a lithium salt; and an organic solvent comprising a cyclic carbonate compound including ethylene carbonate, a linear carbonate 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-mentioned single-particle lithium nickel-based oxide is a lithium secondary battery comprising a single particle consisting of one nodule, a pseudo-single particle which is a complex of 2 to 30 nodules, or a combination thereof.

3. In Claim 1, A lithium secondary battery in which the above lithium nickel-based oxide has 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≤0.70, and 0, respectively. <b<0.50, 0<c<0.50, 0≤d≤0.10, a+b+c+d=1을 만족한다.

4. In Claim 3, A lithium secondary battery in which a, b, c, and d of the above chemical formula A satisfy 0.55≤a≤0.65, 0.05≤b≤0.15, 0.25≤c≤0.35, and 0≤d≤0.10, respectively.

5. In Claim 1, A lithium secondary battery in which the content of Co element in the coating layer is 1 mol% to 5 mol% based on the total molar amount of the positive electrode active material.

6. In Claim 1, D of the above positive active material 50 A lithium secondary battery having a thickness of 1㎛ to 10㎛.

7. 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.

8. In Claim 1, A lithium secondary battery in which the content of the cyclic carbonate-based compound is 5 volume% to 40 volume% based on the total volume of the organic solvent.

9. In Claim 1, A lithium secondary battery in which the content of the linear carbonate-based compound is 20 volume% to 90 volume% based on the total volume of the organic solvent.

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

11. In Claim 1, A lithium secondary battery in which the ratio of the total volume of the linear carbonate compound and the compound represented by Formula 1 to the volume of the cyclic carbonate compound is 2.0 to 6.

0.

12. In Claim 1, A lithium secondary battery, wherein the above-mentioned non-aqueous electrolyte further comprises one or more lithium salt-based additives selected from the group consisting of lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium difluorophosphate, and lithium difluorobisoxalatephosphate.

13. In Claim 1, A lithium secondary battery wherein the above-mentioned non-aqueous electrolyte further comprises a compound represented by the following chemical formula 2: [Chemical Formula 2] In the above chemical formula 2, A is a heterocyclic group having 3 to 5 carbon atoms or a heteroaryl group having 3 to 5 carbon atoms, and Rk is an alkylene group having 1 to 3 carbon atoms.

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

15. In Claim 1, The above lithium secondary battery is a lithium secondary battery having a charge cut-off voltage of 4.35V or higher.

Images