Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery having excellent low-temperature lifespan characteristics. The lithium secondary battery of the present invention comprises: an anode comprising an anode mixture layer that includes a first anode active material, a second anode active material, an anode conductive material and an anode binder; a cathode comprising a cathode mixture layer that includes a cathode active material, a cathode conductive material and a cathode binder; and an electrolyte. CFC defined in relation (1) is 0.38 to 1.962. Relation (1): CFC = 100×Wc - {(D50, a1×D50, a2×L×RN / P×1010) / MWC} In relation (1), Wc is the ratio of the weight of the anode conductive material to the total weight of the anode mixture layer, MWC is the weight value of 1 mole of carbon measured in units of g, D50, a1 is the D50 value of the first anode active material measured in units of m, D50, a2 is the D50 value of the second anode active material measured in units of m, L is the weight value of the anode active material per unit area of the anode mixture layer disposed on a cross-section of the anode, measured in units of g / 25cm2, and RN / P is the ratio of the capacity of the anode to the capacity of the cathode.

Description

lithium secondary battery

[0001] The present invention relates to a lithium secondary battery, and more particularly, to a high-voltage lithium secondary battery having excellent low-temperature life characteristics.

[0002] With the advancement of technology in electric vehicles, energy storage systems (ESS), and portable electronic devices, the demand for lithium secondary batteries as an energy source is rapidly increasing.

[0003] Meanwhile, in the electric vehicle field, cells with high energy densities are required to extend single-charge driving ranges. Consequently, research is being conducted to increase the active material content within the electrode composite layer. To increase the active material content, components other than the active material, such as the conductive agent and / or binder, must be reduced. However, a reduced conductive agent content leads to reduced electrical conductivity, which increases internal cell resistance. Furthermore, lithium plating occurs at low temperatures, which rapidly degrades cell capacity.

[0004] Therefore, there is a need for the development of a lithium secondary battery that has high energy density while suppressing cell degradation at low temperatures.

[0005] The present invention is intended to solve the above problems, and to provide a lithium secondary battery that can be stably operated at high voltage to achieve high energy density and has excellent low-temperature lifespan characteristics.

[0006] In one aspect, the present invention provides a lithium secondary battery comprising: a negative electrode including a negative electrode active material including a first negative electrode active material and a second negative electrode active material, a negative electrode composite layer including a negative electrode conductive material and a negative electrode binder; a positive electrode including a positive electrode composite layer including a positive electrode active material, a positive electrode conductive material and a positive electrode binder; and an electrolyte, wherein the CFC defined by the following formula (1) is 0.38 to 1.962, preferably 0.39 to 1.962, more preferably 0.40 to 1.962.

[0007] Equation (1): CFC = 100×W c - {(D 50, a1 × D 50, a2 ×L×R N / P ×10 10 ) / MW C}

[0008] In the above equation (1), W c MW is the ratio of the weight of the cathode conductive material to the total weight of the cathode composite layer. C is the weight of 1 mole of carbon measured in grams, D 50, a1 D of the first negative electrode active material measured in m 50 value, D 50, a2 D of the second negative electrode active material measured in m 50 The value is , and L is g / 25cm 2 The value of the weight of the negative active material per unit area of ​​the negative electrode composite layer placed on the cross-section of the above negative electrode measured in units, R N / P is the ratio of the cathode capacity to the anode capacity.

[0009] In the above equation (1), the W c may be 0.001 to 0.05, preferably 0.002 to 0.03, more preferably 0.003 to 0.03.

[0010] In the above formula (1), L may be 0.2 to 0.5, preferably 0.3 to 0.4, and more preferably 0.3 to 0.35.

[0011] In the above equation (1), the RN / P may be 1.05 to 1.10, preferably 1.06 to 1.09, more preferably 1.07 to 1.08.

[0012] The first negative electrode active material and the second negative electrode active material may each independently be a graphite-based material, and preferably, the first negative electrode active material may be artificial graphite, and the second negative electrode active material may be natural graphite.

[0013] Meanwhile, D of the first negative electrode active material 50 The D of the second negative electrode active material may be 10㎛ to 30㎛, preferably 10㎛ to 20㎛. 50 The silver may be 5㎛ to 25㎛, preferably 5㎛ to 20㎛.

[0014] The above negative conductive material may be a point-shaped conductive material.

[0015]

[0016] Meanwhile, the positive electrode active material may include a single-particle lithium nickel-based oxide having a nickel content of 70 mol% or less. In this case, the single-particle lithium nickel-based oxide may include 30 or fewer nodules, and the average particle diameter of the nodules may be 0.8 μm to 4.0 μm.

[0017] Preferably, the single particle lithium nickel oxide may be represented by the following [chemical formula 1].

[0018] [Chemical Formula 1]

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

[0020] In the above [chemical formula 1], M 1It contains one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and -0.1≤x≤0.1, 0.5≤a≤0.7, 0 <b<0.5, 0<c<0.5, 0≤d≤0.2이다.

[0021] The above single particle lithium nickel oxide may further include a coating layer on its surface including one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

[0022] The lithium secondary battery according to the present invention may have an energy density of 260 Wh / kg or more and a charge cut-off voltage of 4.35 V or more.

[0023] The lithium secondary battery according to the present invention is characterized in that the CFC, which is a relationship between the particle size of the negative electrode active material, the negative electrode cross-sectional loading amount, the negative electrode conductive material, and the N / P ratio, is designed to satisfy a specific range. When the lithium secondary battery according to the present invention satisfies the CFC value defined by Equation (1) in the range of 0.38 to 1.962, degradation due to lithium plating at low temperatures is suppressed, and the life characteristics can be significantly improved.

[0024] Meanwhile, the lithium secondary battery according to the present invention can use a single particle type positive electrode active material having a nickel content of 70 mol% or less, preferably 50 to 70 mol%, as a positive electrode active material, and in this case, it can be stably operated at a high voltage of 4.35 V or higher, thereby realizing a high energy density.

[0025] Figure 1 is a scanning electron microscope photograph of a single-particle positive electrode active material.

[0026] Figure 2 is a scanning electron microscope photograph of a pseudo-single particle positive electrode active material.

[0027] Figure 3 is a scanning electron microscope photograph of a secondary particle-type positive electrode active material.

[0028] Hereinafter, the present invention will be described in more detail.

[0029] Terms or words used in this specification and the scope of the claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0030] In the present invention, "D 50 "It refers to the particle size corresponding to 50% of the volume accumulation amount of the volume accumulation particle size distribution of the powder to be measured, and can be measured using the laser diffraction method. For example, after dispersing the powder to be measured in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves of about 28 kHz at an output of 60 W, obtaining a volume accumulation particle size distribution graph, and then calculating the particle size corresponding to 50% of the volume accumulation amount.

[0031] In the present invention, "single-particle type" means a particle formed by an aggregation of 30 or fewer sub-particles. The sub-particle unit constituting the single-particle type particle is called a nodule. Single-particle type particles include single particles composed of one nodule and pseudo-single particles which are complexes of 2 to 30 nodules. Fig. 1 shows a scanning electron microscope image of a single-particle type positive electrode active material, and Fig. 2 shows a scanning electron microscope image of a pseudo-single-particle type positive electrode active material.

[0032] The above "nodule" is a sub-particle unit that constitutes a single particle and a pseudo-single particle, and may be a single crystal without a crystalline grain boundary, or a polycrystal with no apparent grain boundary when observed under a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0033] In the present invention, "secondary particle type" refers to a particle formed by an aggregation of more than 30 sub-particles. To distinguish them from the sub-particles constituting single-particle particles, the sub-particles constituting the secondary particles are referred to as "primary particles." Figure 3 illustrates a scanning electron microscope (SEM) image of a secondary particle type positive electrode active material.

[0034] In the present invention, “particle” is a concept including any one or all of a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0035] In the present invention, the average particle diameter (D) of the nodules or primary particles mean ) means the arithmetic mean value calculated after measuring the particle size of nodules or primary particles observed in scanning electron microscope images.

[0036]

[0037] The inventors of the present invention have conducted repeated research to develop a lithium secondary battery having excellent low-temperature life characteristics, and as a result, have discovered that when the CFC, which is a relationship between the particle size of the negative electrode active material, the negative electrode cross-sectional loading amount, the negative electrode conductive material, and the N / P ratio, satisfies the range of 0.38 to 1.962, degradation due to lithium plating at low temperatures is suppressed, and the low-temperature life characteristics are significantly improved, thereby completing the present invention.

[0038]

[0039] Specifically, a lithium secondary battery according to the present invention comprises: an anode including a first anode active material and a second anode active material, an anode composite layer including a cathode conductive material and a cathode binder; a cathode including a cathode composite layer including a cathode active material, a cathode conductive material and a cathode binder; and an electrolyte, wherein the CFC defined by the following formula (1) is 0.38 to 1.962, preferably 0.39 to 1.962, and more preferably 0.40 to 1.962.

[0040] Equation (1): CFC = 100×W c - {(D 50, a1 × D 50, a2 ×L×R N / P ×10 10 ) / MW C}

[0041] In the above equation (1), W c MW is the ratio of the weight of the cathode conductive material to the total weight of the cathode composite layer. C is the weight of 1 mole of carbon measured in grams, D 50, a1 D of the first negative electrode active material measured in m 50 value, D 50, a2 D of the second negative electrode active material measured in m 50 The value is , and L is g / 25cm 2 The value of the weight of the negative active material per unit area of ​​the negative electrode composite layer placed on the cross-section of the above negative electrode measured in units, R N / P is the ratio of the cathode capacity to the anode capacity.

[0042] When a lithium secondary battery is designed so that the CFC value satisfies the above range, the low-temperature life characteristics are significantly improved. When the CFC is less than 0.38 or more than 1.962, lithium plating occurs during low-temperature charge / discharge, causing a rapid decrease in cell capacity. In general, since Li ions have low conductivity at low temperatures, the resistance increases during low-temperature charge / discharge, which prevents lithium ions from being completely inserted into the negative electrode in the high-voltage region during charging and may accumulate on the surface of the negative electrode, resulting in lithium plating. However, when the negative electrode is designed so that the CFC is 0.38 to 1.962 by controlling the weight of the negative electrode conductive material in the negative electrode composite layer, the particle size and content of the negative electrode active material, and the N / P ratio as in the present invention, the electronic and ionic conductivities of the negative electrode increase, improving lithium mobility. As a result, the internal electrode resistance and lithium plating are reduced, thereby improving the low-temperature life characteristics.

[0043]

[0044] Meanwhile, the ratio W of the weight of the cathode conductive material to the total weight of the cathode composite layer c may be 0.001 to 0.05, preferably 0.002 to 0.03, more preferably 0.003 to 0.03. W c When the above range is satisfied, the electrical conductivity and capacity characteristics of the cathode are excellent. W c If it is too small, the battery conductivity of the negative electrode decreases, the internal resistance of the cell increases, and lithium plating may occur at low temperatures, and W c If it is too large, the cathode capacity may decrease.

[0045] The above MW C is the weight value of 1 mole of carbon measured in grams, which is 12.

[0046] Meanwhile, the above L is the unit area (25 cm) of the cathode composite layer placed on the cross-section of the cathode. 2) by weight of the negative electrode active material, it may be 0.2 to 0.5, preferably 0.3 to 0.4, more preferably 0.3 to 0.35. When L satisfies the above range, the ratio of the negative electrode conductive material and the negative electrode active material is appropriately maintained, so that lithium plating can be effectively suppressed during low-temperature charge / discharge, and high energy density can be realized.

[0047] Also, R, the ratio of cathode capacity to anode capacity N / P may be 1.05 to 1.10, preferably 1.06 to 1.09, and more preferably 1.07 to 1.08. If the negative electrode capacity is too small relative to the positive electrode capacity, lithium plating may occur, and if it is too large, the energy density may decrease.

[0048] Above W c , D 50, a1 , D 50, a2 , L, R N / P is a unitless number that does not include units.

[0049]

[0050] Hereinafter, each component of the lithium secondary battery according to the present invention will be described in more detail.

[0051]

[0052] cathode

[0053] A lithium secondary battery according to the present invention comprises an anode comprising a first anode active material, a second anode active material, a cathode conductive material, and a cathode binder. Specifically, the anode comprises an anode current collector, and a cathode composite layer formed on at least one surface of the anode current collector, wherein the anode composite layer comprises an anode active material, a cathode conductive material, and a cathode binder. The anode active material comprises a first anode active material and a second anode active material.

[0054] The negative electrode 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., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0055]

[0056] Meanwhile, the first negative electrode active material and the second negative electrode active material may each independently be graphite-based materials such as natural graphite, artificial graphite, etc. Preferably, the first negative electrode active material may be artificial graphite, and the second negative electrode active material may be natural graphite.

[0057] The graphite-based materials for the first negative electrode active material and the second negative electrode active material may or may not independently include a coating layer formed on the surface of the graphite-based negative electrode active material. The coating layer may be a carbon coating layer.

[0058] The carbon coating layer may be formed by providing one or more materials selected from the group consisting of coal-tar pitch, rayon, and polyacrylonitrile-based resins or precursors of the materials to the surface of the graphite-based material, and then pyrolyzing them. Preferably, the carbon coating layer includes soft carbon, and may be formed by a sintering and pyrolysis process of the coal-tar pitch. The heat treatment process for forming the carbon coating layer may be performed at a temperature range of 1000°C to 4000°C. At this time, if the heat treatment process is performed at less than 1000°C, it may be difficult to form a uniform carbon coating layer, and if it is performed at a temperature exceeding 4000°C, there is a problem that the carbon coating layer is excessively formed during the process. The first negative electrode active material and the second negative electrode active material are D 50 This may be the same or different. D of the first negative electrode active material and the second negative electrode active material 50 In this different case, the first negative electrode active material has a D greater or less than the second negative electrode active material. 50 can have

[0059] Meanwhile, D of the first negative electrode active material 50 The size of the second negative electrode active material may be 10 μm to 30 μm, preferably 10 μm to 20 μm. In addition, the D of the second negative electrode active material 50 The D of the first negative electrode active material and the second negative electrode active material may be 5 ㎛ to 25 ㎛, preferably 5 ㎛ to 20 ㎛. 50 When the above range is satisfied, the CFC value is likely to satisfy the range of the present invention, and the difference in particle size of each negative electrode active material facilitates packing between particles, thereby reducing internal voids, and accordingly, the electrode orientation is reduced during rolling, thereby obtaining the effect of suppressing electrode expansion during charge and discharge.

[0060] Meanwhile, in the present invention, the first negative electrode active material and the second negative electrode active material may be mixed in a weight ratio of 90:10 to 50:50, preferably 90:10 to 60:40, and more preferably 90:10 to 70:30. When the mixing ratio of the first negative electrode active material and the second negative electrode active material satisfies the above range, the electrochemical performance is more excellent.

[0061] Meanwhile, the content of the entire negative electrode active material including the first negative electrode active material and the second negative electrode active material may be about 80 wt% to 98 wt%, preferably about 90 wt% to 98 wt%, and more preferably about 93 wt% to 98 wt%, based on the total weight of the negative electrode composite layer. When the content of the negative electrode active material satisfies the above range, excellent energy density can be achieved.

[0062]

[0063] Next, the negative electrode conductive material is used to provide conductivity to the negative electrode, and in the battery to be constructed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0064] Preferably, the negative electrode conductive material may be a dot-shaped conductive material. A dot-shaped conductive material refers to a conductive material in the form of particles that come into contact with the active material in the form of dots. Specific examples of dot-shaped conductive materials include, but are not limited to, carbon particles such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and porous carbon. Since a dot-shaped conductive material has a low molecular weight and excellent dispersibility, when used, the conductive material is uniformly dispersed in the negative electrode slurry, thereby reducing the viscosity, and thus improving the coatability of the negative electrode slurry.

[0065] The above negative electrode conductive material may be typically included in an amount of 0.1 to 5 wt%, preferably 0.2 to 3 wt%, and more preferably 0.3 to 3 wt%, based on the total weight of the negative electrode active material layer. If the content of the negative electrode conductive material is too low, the electrical conductivity of the negative electrode may decrease, which may cause lithium plating during low-temperature operation, and if the content of the negative electrode conductive material is too high, the content of the negative electrode active material may decrease, which may result in a decrease in capacity characteristics.

[0066] The above negative electrode binder serves to improve adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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 may be used alone or a mixture of two or more thereof.

[0067] The above negative electrode binder may be included in an amount of 1 to 10 wt%, preferably 1 to 8 wt%, and more preferably 1 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0068]

[0069] The above negative electrode can be manufactured according to a conventional negative electrode manufacturing method. For example, the negative electrode can be manufactured by mixing a negative electrode active material, a negative electrode binder, and / or a negative electrode conductive material in a solvent to manufacture a negative electrode slurry, applying the negative electrode slurry onto a negative electrode current collector, and then drying and rolling, or by casting the negative electrode slurry onto a separate support, peeling the support, and laminating the resulting film onto a negative electrode current collector.

[0070] Meanwhile, solvents commonly used in the art may be used as solvents for the negative electrode slurry, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water, which may be used alone or in combination of two or more. The amount of the solvent used is sufficient to dissolve or disperse the negative electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0071]

[0072] anode

[0073] A lithium secondary battery according to the present invention comprises a positive electrode comprising a positive electrode active material, a positive electrode conductive material, and a positive electrode binder. 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, a positive electrode conductive material, and a positive electrode binder.

[0074] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0075]

[0076] Meanwhile, in the present invention, the positive electrode active material may include a single particle lithium nickel-based oxide having a Ni content of 70 mol% or less, preferably 50 mol% to 70 mol%.

[0077] When a single particle lithium nickel oxide having a relatively low nickel content as described above is used as a cathode active material, side reactions with the electrolyte are suppressed under high temperature and high voltage conditions, gas generation is reduced, and excellent life characteristics can be realized.

[0078] In the case of secondary particle-type lithium nickel-based oxides in which 40 to hundreds of primary particles are aggregated, side reactions with the electrolyte frequently occur because the contact area with the electrolyte is large, and gases are generated during the side reactions. In particular, the amount of gas generated further increases under high temperature and / or high voltage conditions, which causes rapid cell degradation. In contrast, single-particle lithium nickel-based oxides have a smaller number of nodules constituting the particles, which reduces the intra-particle interface and thus the contact area with the electrolyte. Therefore, side reactions with the electrolyte are less than secondary particles, and the amount of gas generated is also significantly less. Therefore, when single-particle lithium nickel-based oxides are applied as a cathode active material, excellent cycle characteristics can be obtained even under high voltage and high temperature conditions.

[0079] In addition, in the case of single particle lithium nickel oxides with relatively low nickel content, the structural stability at high voltage is higher than that of lithium nickel oxides with high nickel content or secondary particle form, so that the degradation of life characteristics during high voltage operation can be minimized. Specifically, the higher the nickel content in the lithium nickel oxide, the more reactive Ni becomes. +4 As the number of ions increases, the structural stability of the positive electrode active material decreases during charge and discharge, causing positive electrode degradation to occur rapidly. This phenomenon becomes more severe during high voltage operation. Therefore, in the present invention, by applying a lithium nickel-based oxide with a low Ni content of 70 mol% or less, it is possible to suppress the reduction in lifespan due to active material degradation during high voltage operation. However, if the Ni content is too low, the capacity characteristics deteriorate, so the Ni content of the lithium nickel-based oxide is preferably about 50 mol% to 70 mol%.

[0080]

[0081] Specifically, the single-particle lithium nickel-based oxide may be a lithium transition metal oxide containing nickel, manganese, and cobalt, and may be, for example, represented by the following [chemical formula 1].

[0082] [Chemical Formula 1]

[0083] Li 1+x [Ni a Co b Mn c M 1 d ]O2

[0084] In the above [chemical formula 1], M 1 It may contain one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo. M 1 When the element is included, the structural stability of lithium nickel-based oxide particles is improved, so that better life characteristics can be realized when driving at high voltage. Preferably, the M 1 The element may include at least one selected from the group consisting of Ti, Mg, Al, Zr and Y, and more preferably, at least two selected from the group consisting of Ti, Mg, Al, Zr and Y.

[0085] The above 1+x represents the lithium molar ratio in the lithium nickel-based oxide, and may be -0.1≤x≤0.1, 0≤x≤0.1, or 0≤x≤0.07. When 1+x satisfies the above range, a stable layered crystal structure can be formed.

[0086] The above a represents the molar ratio of nickel among all metals excluding lithium in the lithium nickel-based oxide, and may be 0.5≤a≤0.7, 0.55≤a≤0.7, or 0.55≤a≤0.65. When a satisfies the above range, it can be stably operated at high voltage and achieve high capacity.

[0087] The above b represents the molar ratio of cobalt among all metals excluding lithium in the lithium nickel oxide, and is 0. <b<0.5, 0.05≤b≤0.4 또는 0.1≤b≤0.4일 수 있다.

[0088] The above c represents the molar ratio of manganese among all metals excluding lithium in lithium nickel oxide, and is 0. <c<0.5, 0.05≤c≤0.4 또는 0.1≤c≤0.4일 수 있다.

[0089] The above d is M of all metals except lithium in lithium nickel oxide. 1 It represents the molar ratio of elements, 0≤d≤0.2, 0≤d≤0.1 or 0 <d≤0.1일 수 있다. M 1 When the molar ratio of the elements satisfies the above range, both the structural stability and capacity of the positive electrode active material can be excellent.

[0090]

[0091] Meanwhile, the single particle lithium nickel oxide may further include a coating layer on its surface including one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

[0092] When a coating layer exists on the surface of a lithium nickel-based oxide, contact between the electrolyte and the lithium nickel-based oxide is suppressed by the coating layer, thereby reducing the elution of transition metals or gas generation due to side reactions with the electrolyte, and thus further improving the life characteristics. Preferably, the coating layer may include two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and more preferably, may include two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, and W.

[0093]

[0094] Meanwhile, it is preferred that the single particle lithium nickel-based oxide comprises no more than 30 nodules, preferably 1 to 25 nodules, 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 internal cracks occur more frequently due to volume expansion / contraction of the nodules during charge / discharge, which may deteriorate the effect of improving high-temperature life characteristics and high-temperature storage characteristics.

[0095]

[0096] Meanwhile, the average particle size of the nodules may be 0.8 µm to 4.0 µm, preferably 0.8 µm to 3 µm, and more preferably 1.0 µm to 3.0 µm. When the average particle size of the nodules satisfies the above range, particle breakage is minimized during electrode manufacturing, and resistance increase can be more effectively suppressed. At this time, the average particle size of the nodules refers to a value obtained by measuring the particle sizes of nodules observed in SEM images obtained by analyzing the positive electrode active material powder with a scanning electron microscope, and then calculating the arithmetic mean of the measured values.

[0097]

[0098] Meanwhile, the single-particle lithium nickel-based oxide having a nickel content of 70 mol% or less may be included in an amount of 50 wt% or more, preferably 70 wt% or more, and more preferably 100 wt%, of the total positive electrode active material in the positive electrode active material layer. When the proportion of the single-particle lithium nickel-based oxide having a nickel content of 70 mol% or less of the total weight of the positive electrode active material satisfies the above range, it can be stably operated at high voltage.

[0099] The above-described positive electrode active material layer may include a positive electrode active material other than a single-particle lithium nickel-based oxide having a nickel content of 70 mol% or less, i.e., a lithium nickel-based oxide in the form of secondary particles and / or a single-particle lithium nickel-based oxide having a nickel content exceeding 70 mol%. However, if the proportion of the secondary particles and / or the lithium nickel-based oxide having a nickel content exceeding 70 mol% is 50 wt% or more of the entire positive electrode active material, the life characteristics may be deteriorated when driven at high voltage.

[0100]

[0101] Meanwhile, the positive electrode active material is D 50 It may be 3.0㎛ to 8.0㎛, preferably 3.0㎛ to 7.5㎛. More preferably, it is preferably about 3.5㎛ to 7.5㎛. D of lithium nickel-based oxide 50 If this is too small, the processability during electrode manufacturing may be poor, the electrolyte impregnation may be poor, and the electrochemical properties may increase. 50 If this is too large, there is a problem that the resistance increases and the output characteristics deteriorate.

[0102]

[0103] Meanwhile, the positive electrode active material may be included in an amount of 93 wt% to 99 wt%, preferably 95 wt% to 98 wt%, and more preferably 95 wt% to 97 wt%, based on the total weight of the positive electrode active material layer, i.e., the total amount of the positive electrode active material, the positive electrode conductive material, and the positive electrode binder. When the content of the positive electrode active material satisfies the above range, a high energy density can be realized.

[0104]

[0105] Next, the positive electrode conductive material is used to provide conductivity to the positive electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any particular limitation. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, carbon nanotube, etc.; metal powder or metal fiber such as copper, nickel, aluminum, silver, etc.; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, etc., and one of these may be used alone or a mixture of two or more may be used.

[0106] Preferably, the positive electrode conductive material may include a linear conductive material and a point-shaped conductive material. When a linear conductive material and a point-shaped conductive material are used together as the positive electrode conductive material, excellent conductivity can be achieved with only a small amount of the conductive material, thereby increasing the positive electrode active material content within the positive electrode.

[0107] At this time, the linear conductive material means a conductive material that makes line contact with the active material, and the point-shaped conductive material means a conductive material that makes point contact with the active material.

[0108] Examples of the linear conductive material include, but are not limited to, fibrous carbon materials such as carbon fibers and carbon nanotubes, and metal fibers such as copper, nickel, aluminum, and silver, and various conductive materials in the form of fibers can be used.

[0109] As the above-mentioned point-shaped conductive material, carbon particles such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, porous carbon, etc. can be used, but are not limited thereto.

[0110] The above-mentioned positive electrode conductive material may typically be included in an amount of 0.5 to 2 wt%, preferably 0.5 to 1.8 wt%, and more preferably 0.8 to 1.8 wt%, based on the total weight of the positive electrode active material layer, i.e., the total weight of the positive electrode active material, the positive electrode conductive material, and the positive electrode binder. When the content of the positive electrode conductive material satisfies the above range, the positive electrode conductivity is excellent, and the content of the active material in the positive electrode can be increased to realize a high capacity.

[0111] Next, the positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, 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 may be used alone or a mixture of two or more thereof may be used.

[0112] The above positive electrode binder may be included in an amount of 0.5 wt% to 5 wt%, preferably 1 wt% to 4 wt%, and more preferably 1 wt% to 3 wt%, based on the total weight of the positive electrode active material layer.

[0113]

[0114] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method. For example, the positive electrode can be manufactured by mixing a positive electrode active material, a positive electrode binder, and / or a positive electrode conductive material in a solvent to manufacture a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling the resulting film, or by casting the positive electrode slurry onto a separate support, and then peeling the resulting film from the support and laminating the resulting film onto a positive electrode current collector.

[0115] Meanwhile, solvents commonly used in the art may be used as the solvent for the positive electrode slurry, and examples thereof include dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water, which may be used alone or in combination of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder in consideration of the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0116]

[0117] electrolyte

[0118] The electrolyte may include an organic solvent and a lithium salt.

[0119] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a straight or branched hydrocarbon group having a C2 to C20 chain or a hydrocarbon group having a C3 inner ring structure and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and in terms of increasing the charge-discharge performance of the battery, a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0120]

[0121] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 3.0M, preferably 0.1 to 2.0M, and more preferably 0.5 to 1.5M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0122]

[0123] In addition to the electrolyte components, the electrolyte may additionally include additives for the purposes of improving the life characteristics of the battery, suppressing battery capacity reduction, and improving the discharge capacity of the battery. For example, the additives include various additives used in the art, such as fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene sulfate (ESa), lithium difluorophosphate (LiPO2F2), lithium bisoxalato borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxalato borate (LiDFOB), lithium difluorobisoxalatophosphate (LiDFBP), lithium tetrafluorooxalato phosphate (LiTFOP), lithium methylsulfate (LiMS), lithium ethylsulfate (LiES), propanesultone (PS), propenesultone (PRS), succinonitrile (SN), adiponitrile (AND), 1,3,6-hexanetricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), Ethyldi(pro-2-yl-1-yl)phosphate (EDP), 5-methyl-5-propazyloxylcarbonyl-1,3-dioxane-2-one (MPOD), etc. can be used alone or in combination, but are not limited thereto. The above additives can be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte.

[0124]

[0125] separator

[0126] The lithium secondary battery according to the present invention may further include a separator between the positive electrode and the negative electrode, if necessary. The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used as a separator in lithium secondary batteries may be used without particular limitation. In particular, a separator having low resistance to electrolyte ion movement and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. Additionally, a coated separator containing a ceramic component or polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0127]

[0128] The lithium secondary battery of the present invention as described above can operate stably at high voltage to achieve high energy density, and has excellent life characteristics at low temperatures.

[0129] Preferably, the lithium secondary battery according to the present invention has a charge cut-off voltage of 4.35 V or higher, preferably 4.35 V to 5 V, and more preferably 4.35 V to 4.5 V. When the charge cut-off voltage satisfies the above range during operation, a high energy density can be realized. Specifically, the lithium secondary battery according to the present invention may have an energy density of 260 Wh / kg or higher, preferably 260 Wh / kg to 330 Wh / kg, and more preferably 270 Wh / kg to 320 Wh / kg.

[0130] The capacity of a lithium secondary battery is affected not only by the type of active material used but also by the operating voltage range. In particular, when lithium nickel cobalt manganese oxide is used as the cathode active material, higher capacity can be achieved as the operating voltage increases. However, as the operating voltage increases, side reactions with the electrolyte during charge and discharge increase, and the structural collapse of the cathode active material occurs rapidly, rapidly deteriorating the battery's lifespan. This problem is more pronounced in high-nickel lithium nickel cobalt manganese oxides with a high nickel content. However, when lithium nickel oxides with a nickel content of 70 mol% or less and a single-particle form are used as the cathode active material, the battery can operate stably even at high voltages of 4.35 V or higher, thereby achieving high energy density.

[0131]

[0132] 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 be operated at high voltage to achieve high energy density, and has excellent safety in the event of thermal runaway, making it particularly useful in the electric vehicle field.

[0133] According to another embodiment of the present invention, a battery module including a lithium secondary battery according to the present invention as a unit cell and a battery pack including the same are provided.

[0134] The above battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0135]

[0136] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0137]

[0138] Example 1

[0139] <Cathode Manufacturing>

[0140] Negative active material: Negative conductive material: Styrene-butadiene rubber (SBR): Carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 96.15: 0.5: 2.3: 1.05 to prepare a negative electrode slurry. At this time, the negative electrode active material is D 50 This 16㎛ artificial graphite and D 50 This 18㎛ natural graphite was mixed and used in a weight ratio of 8:2, and Super C 65 was used as the negative electrode conductive material.

[0141] The cathode slurry is placed on a copper current collector sheet at a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3415 g / 25 cm 2 This was applied, dried, and rolled to manufacture a cathode.

[0142]

[0143] <Cathode manufacturing>

[0144] Positive electrode active material: Positive electrode conductive material: PVDF binder were mixed in a weight ratio of 97:1.2:1.8 in N-methylpyrrolidone to prepare a positive electrode slurry (solid content 75 wt%). At this time, single particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 was used 100%, and carbon nanotubes and acetylene black were mixed in a weight ratio of 2:1 as the anode conductive material.

[0145] The above cathode slurry is placed on an aluminum current collector sheet, and the ratio of the cathode capacity to the cathode capacity (R) N / P ) was applied so that the ratio was 1.07, dried, and rolled to manufacture the anode.

[0146]

[0147] <Lithium secondary battery manufacturing>

[0148] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured as described above, and the electrode assembly was inserted into a battery case, and then an electrolyte was injected to manufacture a lithium secondary battery cell.

[0149] At this time, the electrolyte was prepared by dissolving LiPF61.0M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and then adding 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of propane sultone (PS), 1 wt% of ethylene sulfate (ESa), 1 wt% of lithium difluorophosphate, and 0.2 wt% of LiBF4 as additives.

[0150]

[0151] Example 2

[0152] A lithium secondary battery was manufactured in the same manner as Example 1, except that carbon nanotubes were used solely as a cathode conductive material.

[0153]

[0154] Example 3

[0155] When manufacturing the cathode, the cathode slurry is applied to 25 cm of one side of the copper collector. 2 The weight of the negative active material per area (L) is 0.3175 g / 25 cm 2 This is applied so that, when manufacturing the anode, the anode slurry is applied so that the ratio of the anode capacity to the cathode capacity (R) N / P) was applied so that the ratio of the positive electrode active material to the positive electrode active material was 1.072, and a lithium secondary battery was manufactured using the same method as Example 1, except that carbon nanotubes and acetylene black were mixed in a weight ratio of 5:1 as the positive electrode active material.

[0156]

[0157] Example 4

[0158] <Cathode Manufacturing>

[0159] Negative active material: Negative conductive material: Styrene-butadiene rubber (SBR): Carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 94.65: 2: 2.3: 1.05 to prepare a negative electrode slurry. At this time, the negative electrode active material was D 50 This 13.5㎛ artificial graphite and D 50 This 9㎛ natural graphite was mixed and used in a weight ratio of 8:2, and Super C 65 was used as the negative electrode conductive material.

[0160] The cathode slurry is placed on a copper current collector sheet at a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3513g / 25cm 2 This was applied, dried, and rolled to manufacture a cathode.

[0161]

[0162] <Cathode manufacturing>

[0163] Positive electrode active material: Positive electrode conductive material: PVDF binder were mixed in a weight ratio of 97:1.2:1.8 in N-methylpyrrolidone to prepare a positive electrode slurry (solid content 75 wt%). At this time, single particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 was used 100%, and carbon nanotubes and acetylene black were mixed in a weight ratio of 2:1 as the anode conductive material.

[0164] The above cathode slurry is placed on an aluminum current collector sheet, and the ratio of the cathode capacity to the cathode capacity (R)N / P ) was applied so that the value was 1.0945, dried, and rolled to manufacture the anode.

[0165]

[0166] <Lithium secondary battery manufacturing>

[0167] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured as described above, and the electrode assembly was inserted into a battery case, and then an electrolyte was injected to manufacture a lithium secondary battery cell.

[0168] At this time, the electrolyte was prepared by dissolving LiPF61.0M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and then adding 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of propane sultone (PS), 1 wt% of ethylene sulfate (ESa), 1 wt% of lithium difluorophosphate, and 0.2 wt% of LiBF4 as additives.

[0169]

[0170] Example 5

[0171] Negative active material: Negative conductive material: Styrene-butadiene rubber (SBR): Carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 95.90: 0.75: 2.3: 1.05 to prepare a negative electrode slurry. At this time, the negative electrode active material is D 50 This 16㎛ artificial graphite and D 50 This 18㎛ natural graphite was mixed and used in a weight ratio of 8:2, and Super C 65 was used as the negative electrode conductive material.

[0172] The cathode slurry is placed on a copper current collector sheet at a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3391 g / 25 cm 2 This was applied, dried, and rolled to manufacture a cathode.

[0173]

[0174] <Cathode manufacturing>

[0175] Positive electrode active material: Positive electrode conductive material: PVDF binder were mixed in a weight ratio of 97:1.2:1.8 in N-methylpyrrolidone to prepare a positive electrode slurry (solid content 75 wt%). At this time, single particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 was used 100%, and carbon nanotubes and acetylene black were mixed in a weight ratio of 2:1 as the anode conductive material.

[0176] The above cathode slurry is placed on an aluminum current collector sheet, and the ratio of the cathode capacity to the cathode capacity (R) N / P ) was applied so that the concentration was 1.0730, dried, and rolled to manufacture the anode.

[0177]

[0178] <Lithium secondary battery manufacturing>

[0179] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured as described above, and the electrode assembly was inserted into a battery case, and then an electrolyte was injected to manufacture a lithium secondary battery cell.

[0180] At this time, the electrolyte was prepared by dissolving LiPF61.0M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and then adding 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of propane sultone (PS), 1 wt% of ethylene sulfate (ESa), 1 wt% of lithium difluorophosphate, and 0.2 wt% of LiBF4 as additives.

[0181]

[0182] Example 6

[0183] Negative active material: Negative conductive material: Styrene-butadiene rubber (SBR): Carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 95.65: 1: 2.3: 1.05 to prepare a negative electrode slurry. At this time, the negative electrode active material is D 50 This 17.6㎛ artificial graphite and D 50 This 18㎛ natural graphite was mixed and used in a weight ratio of 8:2, and Super C 65 was used as the negative electrode conductive material.

[0184] The cathode slurry is placed on a copper current collector sheet at a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3512 g / 25 cm 2 This was applied, dried, and rolled to manufacture a cathode.

[0185]

[0186] <Cathode manufacturing>

[0187] Positive electrode active material: Positive electrode conductive material: PVDF binder were mixed in a weight ratio of 97:1.2:1.8 in N-methylpyrrolidone to prepare a positive electrode slurry (solid content 75 wt%). At this time, single particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 was used 100%, and carbon nanotubes and acetylene black were mixed in a weight ratio of 2:1 as the anode conductive material.

[0188] The above cathode slurry is placed on an aluminum current collector sheet, and the ratio of the cathode capacity to the cathode capacity (R) N / P ) was applied so that the concentration was 1.0950, dried, and rolled to manufacture the anode.

[0189]

[0190] <Lithium secondary battery manufacturing>

[0191] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured as described above, and the electrode assembly was inserted into a battery case, and then an electrolyte was injected to manufacture a lithium secondary battery cell.

[0192] At this time, the electrolyte was prepared by dissolving LiPF61.0M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and then adding 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of propane sultone (PS), 1 wt% of ethylene sulfate (ESa), 1 wt% of lithium difluorophosphate, and 0.2 wt% of LiBF4 as additives.

[0193]

[0194] Example 7

[0195] Negative active material: Negative conductive material: Styrene-butadiene rubber (SBR): Carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 95.40: 1.25: 2.3: 1.05 to prepare a negative electrode slurry. At this time, the negative electrode active material was D 50 This 16㎛ artificial graphite and D 50 This 18㎛ natural graphite was mixed and used in a weight ratio of 8:2, and Super C 65 was used as the negative electrode conductive material.

[0196] The cathode slurry is placed on a copper current collector sheet at a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3182 g / 25 cm 2 This was applied, dried, and rolled to manufacture a cathode.

[0197]

[0198] <Cathode manufacturing>

[0199] Positive electrode active material: Positive electrode conductive material: PVDF binder were mixed in a weight ratio of 97:1.2:1.8 in N-methylpyrrolidone to prepare a positive electrode slurry (solid content 75 wt%). At this time, single particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 was used 100%, and carbon nanotubes and acetylene black were mixed in a weight ratio of 2:1 as the anode conductive material.

[0200] The above cathode slurry is placed on an aluminum current collector sheet, and the ratio of the cathode capacity to the cathode capacity (R) N / P ) was applied so that the ratio was 1.058, dried, and rolled to manufacture the anode.

[0201]

[0202] <Lithium secondary battery manufacturing>

[0203] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured as described above, and the electrode assembly was inserted into a battery case, and then an electrolyte was injected to manufacture a lithium secondary battery cell.

[0204] At this time, the electrolyte was prepared by dissolving LiPF61.0M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and then adding 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of propane sultone (PS), 1 wt% of ethylene sulfate (ESa), 1 wt% of lithium difluorophosphate, and 0.2 wt% of LiBF4 as additives.

[0205]

[0206] Example 8

[0207] Negative active material: Negative conductive material: Styrene-butadiene rubber (SBR): Carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 94.90: 1.75: 2.3: 1.05 to prepare a negative electrode slurry. At this time, the negative electrode active material is D50 This 17.6㎛ artificial graphite and D 50 This 18㎛ natural graphite was mixed and used in a weight ratio of 8:2, and Super C 65 was used as the negative electrode conductive material.

[0208] The cathode slurry is placed on a copper current collector sheet at a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3460 g / 25 cm 2 This was applied, dried, and rolled to manufacture a cathode.

[0209]

[0210] <Cathode manufacturing>

[0211] Positive electrode active material: Positive electrode conductive material: PVDF binder were mixed in a weight ratio of 97:1.2:1.8 in N-methylpyrrolidone to prepare a positive electrode slurry (solid content 75 wt%). At this time, single particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 was used 100%, and carbon nanotubes and acetylene black were mixed in a weight ratio of 2:1 as the anode conductive material.

[0212] The above cathode slurry is placed on an aluminum current collector sheet, and the ratio of the cathode capacity to the cathode capacity (R) N / P ) was applied so that the ratio was 1.083, dried, and rolled to manufacture the anode.

[0213]

[0214] <Lithium secondary battery manufacturing>

[0215] An electrode assembly was manufactured by interposing a separator between the positive and negative electrodes manufactured as described above, and the electrode assembly was inserted into a battery case, and then an electrolyte was injected to manufacture a lithium secondary battery cell.

[0216] At this time, the electrolyte was prepared by dissolving LiPF61.0M in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and then adding 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of propane sultone (PS), 1 wt% of ethylene sulfate (ESa), 1 wt% of lithium difluorophosphate, and 0.2 wt% of LiBF4 as additives.

[0217]

[0218] Comparative Example 1

[0219] When preparing the negative electrode slurry, the negative electrode active material: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) is mixed in water at a weight ratio of 96.65:2.3:1.05 to prepare the negative electrode slurry, and the negative electrode slurry is applied on a copper current collector sheet with a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3205 g / 25 cm 2 The cathode was manufactured by applying this, and carbon nanotubes were used alone as the cathode conductive material during the manufacture of the cathode, and the cathode slurry was prepared by adding the ratio of the cathode capacity to the cathode capacity (R N / P ) was applied so that the ratio was 1.072, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0220]

[0221] Comparative Example 2

[0222] When preparing the negative electrode slurry, the negative electrode active material: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) is mixed in water at a weight ratio of 96.65:2.3:1.05 to prepare the negative electrode slurry, and the negative electrode slurry is applied on a copper current collector sheet with a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3375 g / 25 cm 2The cathode was manufactured by applying this, and when manufacturing the cathode, carbon nanotubes and acetylene black were mixed in a weight ratio of 5:1 as the cathode conductive material, and the cathode slurry was manufactured by mixing the cathode capacity to the cathode capacity (R N / P ) was applied so that it was 1.075, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0223]

[0224] Comparative Example 3

[0225] When preparing a negative electrode slurry, a negative electrode active material: a negative electrode conductive material: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) are mixed in water at a weight ratio of 96.4:0.25:2.3:1.05 to prepare a negative electrode slurry, and the negative electrode slurry is applied to a copper current collector sheet at a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3167 g / 25 cm 2 The cathode was manufactured by applying this, and when manufacturing the cathode, carbon nanotubes and acetylene black were mixed in a weight ratio of 5:1 as the cathode conductive material, and the cathode slurry was manufactured by mixing the cathode capacity to the cathode capacity (R N / P ) was applied so that the ratio was 1.072, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0226]

[0227] Comparative Example 4

[0228] When preparing a negative electrode slurry, a negative electrode active material: a negative electrode conductive material: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) are mixed in water at a weight ratio of 96.4:0.25:2.3:1.05 to prepare a negative electrode slurry, and the negative electrode slurry is applied to a copper current collector sheet at a thickness of 25 cm on one side of the copper current collector. 2 The weight of the negative active material per area (L) is 0.3428 g / 25 cm 2The cathode is manufactured by applying this, and carbon nanotubes are used solely as a cathode conductive material during the manufacture of the cathode, and the cathode slurry is prepared by mixing the cathode capacity with the ratio of the cathode capacity to the cathode capacity (R N / P ) was applied so that it became 1.070, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0229]

[0230] Comparative Example 5

[0231] When manufacturing the cathode, the cathode slurry is applied to 25 cm of one side of the copper collector. 2 The weight of the negative active material per area (L) is 0.3915 g / 25 cm 2 This is applied so that, when manufacturing the anode, the anode slurry is applied so that the ratio of the anode capacity to the cathode capacity (R) N / P ) was applied so that it became 1.3362, and a lithium secondary battery was manufactured in the same manner as in Example 1.

[0232]

[0233] Comparative Example 6

[0234] When manufacturing the cathode, the cathode slurry is applied to 25 cm of one side of the copper collector. 2 The weight of the negative active material per area (L) is 0.2986 g / 25 cm 2 This is applied so that, when manufacturing the anode, the anode slurry is applied so that the ratio of the anode capacity to the cathode capacity (R) N / P ) was applied so that it became 1.0010, and a lithium secondary battery was manufactured in the same manner as in Example 4.

[0235]

[0236] For each lithium secondary battery manufactured by Examples 1 to 8 and Comparative Examples 1 to 6, the CFC value expressed by the following formula (1) was calculated and shown in [Table 1] below. At this time, MW C was calculated as 12g.

[0237] Equation (1): CFC = 100×W c - {(D 50, a1×D 50, a2 ×L×R N / P ×10 10 ) / MW C}

[0238] In the above equation (1), W c MW is the ratio of the weight of the cathode conductive material to the total weight of the cathode composite layer. C is the weight of 1 mole of carbon measured in grams, D 50, a1 D of the first negative electrode active material measured in m 50 value, D 50, a2 D of the second negative electrode active material measured in m 50 The value is , and L is g / 25cm 2 The value of the weight of the negative active material per unit area of ​​the negative electrode composite layer placed on the cross-section of the above negative electrode measured in units, R N / P is the ratio of the cathode capacity to the anode capacity.

[0239]

[0240] 100×WcD 50,a1 [m]D 50,a2 [m]L[g / 25cm 2 ]R N / P CFC Example 10.51.6×10 -5 1.8×10 -5 0.34151.07000.4123028 Example 20.51.6×10 -5 1.8×10 -5 0.34151.07000.4123028Example 30.51.6×10 -5 1.8×10 -5 0.31751.07200.4183136 Example 421.35×10 -5 9×10 -6 0.35131.09451.961069593 Example 50.751.6×10 -5 1.8×10 -5 0.33911.07300.662674968 Example 611.76×10 -5 1.8×10 -5 0.35121.09500.898475104Example 71.251.6×10 -5 1.8×10 -50.31821.05801.169202656Example 81.751.76×10 -5 1.8×10 -5 0.34601.08301.651074448Comparative example 101.6×10 -5 1.8×10 -5 0.32051.0720-0.08245824Comparative example 201.6×10 -5 1.8×10 -5 0.33751.0750-0.087075Comparative example 30.251.6×10 -5 1.8×10 -5 0.31671.07200.168519424Comparative example 40.251.6×10 -5 1.8×10 -5 0.34281.07000.16196896Comparative example 50.51.6×10 -5 1.8×10 -5 0.39151.33620.374450648Comparative example 621.35×10 -5 9×10 -6 0.29861.00101.969736517

[0241]

[0242] Experimental Example 1: Low-Temperature Characteristics Evaluation

[0243] Each lithium secondary battery manufactured by the above Examples 1 to 8 and Comparative Examples 1 to 6 was charged to 4.35 V at 0.2 C at -10°C, and then discharged to 2.5 V at 0.33 C, which constituted one cycle, and 50 charge-discharge cycles were performed, and then the capacity retention rate was measured using a cycler from PNE.

[0244] In addition, the energy density of each lithium secondary battery manufactured according to Examples 1 to 8 and Comparative Examples 1 to 6 was measured when driven in a voltage range of 2.5 V to 4.35 V. The measurement results are shown in Table 2.

[0245] Initial Capacity (Ah) Capacity after 50 cycles (Ah) Capacity retention rate after 50 cycles (%) Energy density (Wh / kg) Example 1 31.047 29.04 193.5 388 293.31 Example 2 31.36 329.33 793.54 0229 3.37 Example 3 28.75 125.95 790.28 2128 8.57 Example 4 31.05 129.126 93.80 0529 0.99 Example 5 30.93 428.41 491.85 36293.88 Example 6 31.279 28.19 290.1308 291.42 Example 728.65225.27688.2172288.59Example 830.85427.06587.7196292.24Comparative Example 128.05314.15550.4581286.54Comparative Example 231.10625.13180.7915285.46Comparative Example 329.35621.58273.5182291.67Comparative Example 430.84724.03477.9136288.72Comparative Example 527.60410.30837.3424271.21Comparative Example 627.40715.14755.2669291.62

[0246] As shown in Table 2 above, the lithium secondary batteries of Examples 1 to 8, in which the CFC satisfies the scope of the present invention, exhibited a high capacity retention rate of 87% or more after 50 cycles at a low temperature of -10°C, whereas the lithium secondary batteries of Comparative Examples 1 to 6, in which the CFC falls outside the scope of the present invention, exhibited a very low capacity retention rate of 37% to 80% after 50 cycles at a low temperature of -10°C.

Claims

1. A negative electrode including a negative electrode composite layer including a negative electrode active material including a first negative electrode active material and a second negative electrode active material, a negative electrode conductive material, and a negative electrode binder; A cathode comprising a cathode composite layer including a cathode active material, a cathode conductive material and a cathode binder; and Contains electrolytes, A lithium secondary battery having a CFC of 0.38 to 1.962, as defined by the following equation (1). Equation (1): CFC = 100×W c - {(D 50, a1 ×D 50, a2 ×L×R N / P ×10 10 ) / MW C } In the above equation (1), W c is the ratio of the weight of the cathode conductive material to the total weight of the cathode composite layer, MW C is the weight of 1 mole of carbon, measured in grams, D 50, a1 D of the first negative electrode active material measured in m 50 Value, D 50, a2 D of the second cathode active material measured in m 50 The value is , and L is g / 25cm 2 The value of the weight of the negative active material per unit area of ​​the negative electrode composite layer arranged on the cross-section of the above negative electrode measured in units, R N / P is the ratio of cathode capacitance to anode capacitance.

2. In paragraph 1, A lithium secondary battery wherein the first negative electrode active material and the second negative electrode active material are graphite-based materials.

3. In paragraph 1, The above first negative electrode active material is artificial graphite, A lithium secondary battery wherein the second negative electrode active material is natural graphite.

4. In paragraph 1, A lithium secondary battery, wherein the first negative electrode active material and the second negative electrode active material are included in a weight ratio of 90:10 to 50:

50.

5. In paragraph 1, A lithium secondary battery in which the above negative electrode conductive material is a point-shaped conductive material.

6. In paragraph 1, Above W c A lithium secondary battery having an electronegativity of 0.001 to 0.

05.

7. In paragraph 1, D of the above first negative electrode active material 50 is 10㎛ to 30㎛, D of the above second negative electrode active material 50 A lithium secondary battery having a particle size of 5㎛ to 25㎛.

8. In paragraph 1, A lithium secondary battery wherein L is 0.2 to 0.

5.

9. In paragraph 1, Above R N / P A lithium secondary battery having an electric potential of 1.05 to 1.

10.

10. In paragraph 1, A lithium secondary battery, wherein the positive electrode active material includes a single particle lithium nickel oxide having a nickel content of 70 mol% or less.

11. In paragraph 10, A lithium secondary battery, wherein the single particle lithium nickel-based oxide is contained in an amount of 50 wt% or more based on the total weight of the positive electrode active material.

12. In paragraph 10, The above single particle lithium nickel oxide contains 30 or fewer nodules, A lithium secondary battery having an average particle size of the above nodules of 0.8 ㎛ to 4.0 ㎛.

13. In paragraph 10, A lithium secondary battery, wherein the single particle lithium nickel oxide is represented by the following [chemical formula 1]. [Chemical Formula 1] Li 1+x [Ni a Co b Mr c M 1 d ]O2 In the above [chemical formula 1], M 1 It contains at least one element selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and -0.1≤x≤0.1, 0.5≤a≤0.7, 0 <b<0.5, 0<c<0.5, 0≤d≤0.2임.

14. In paragraph 10, A lithium secondary battery, wherein the single particle lithium nickel-based oxide further includes a coating layer on its surface, which includes at least one element selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

15. In paragraph 1, The above positive electrode active material is D 50 A lithium secondary battery having a diameter of 3.0 μm to 8 μm.

16. In paragraph 1, A lithium secondary battery, wherein the positive electrode conductive material includes a linear conductive material and a point-shaped conductive material.

17. In paragraph 1, The above lithium secondary battery is a lithium secondary battery having an energy density of 260 Wh / kg or more.

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

19. A battery module comprising the lithium secondary battery of claim 1.

20. An electric vehicle including the battery module of claim 19 as a power source.

Images