Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery with improved stability during thermal runaway, which includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, and has a nominal voltage of 3.68 V or more. Four of the lithium secondary batteries, which have been fully charged by charging to 4.35 V, were stacked to produce a test module, and the V represented by the following formula (1) was measured. T is 4 Ah / sec or less. Formula (1):V T =C total / t In the formula (1), the C total is the total discharge capacity of the test module, and t is the time it takes from the time when the voltage of one lithium secondary battery placed at the outermost side of the test module becomes 0 to the time when the voltages of all lithium secondary batteries in the test module become 0 after heating and igniting the lithium secondary battery.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery with improved safety during thermal runaway. [Background technology]

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

[0003] In devices requiring large capacity, such as electric vehicles and energy storage devices, batteries in the form of modules and / or packs each containing multiple secondary battery cells are used. If one secondary battery cell in such a battery module and / or pack catches fire or explodes due to internal or external factors, a thermal runway propagation phenomenon occurs in which heat, flames, high-pressure gas, etc. spread to other adjacent cells, causing a chain reaction of explosions among the adjacent cells and creating a major safety issue.

[0004] Meanwhile, in the field of electric vehicles, cells with high energy density are required to extend the driving distance per charge. To this end, in recent years, lithium secondary batteries for electric vehicles have been developed that use high-nickel NCM cathode active materials with nickel contents of 80 mol% or more and / or Si-based anode active materials, which have excellent capacity characteristics. However, such cells have a problem of poor safety due to the high explosion pressure during thermal runaway, which leads to rapid thermal runaway propagation.

[0005] Conventionally, a technique of inserting fireproof insulation into the module has been applied to prevent heat transfer between adjacent cells, but inserting fireproof insulation into the module reduces the energy density, which in turn reduces the vehicle's mileage.

[0006] Therefore, there is a need to develop a lithium secondary battery that has a high energy density and in which the propagation of thermal runaway is suppressed. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve the above problems, and aims to provide a lithium secondary battery that has a low thermal transition rate during thermal runaway, can be stably operated at high voltage, and can achieve high energy density. [Means for solving the problem]

[0008] In one aspect, the present invention provides a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, wherein the lithium secondary battery has a nominal voltage of 3.68 V or more; Four of the lithium secondary batteries were fully charged to 4.35 V, and then stacked to produce a test module. The V T The present invention provides a lithium secondary battery having a capacity of 4 Ah / sec or less, preferably 1 to 4 Ah / sec, and more preferably 2 to 4 Ah / sec. Formula (1):V T =C total / t In the formula (1), the C total is the total discharge capacity of the test module, and t is the time it takes from the moment the voltage of the outermost lithium secondary battery in the test module becomes 0 after heating and igniting one of the lithium secondary batteries in the test module, until the voltages of all the lithium secondary batteries in the test module become 0. Meanwhile, the total discharge capacity of the test module is the sum of the discharge capacities measured by CC-CV charging and CC discharging each lithium secondary battery in the test module at 25°C, 0.33C, and in the voltage range of 2.5V to 4.35V.

[0009] Here, the lithium secondary battery in the test module may have a size of 100 mm wide and 300 mm long.

[0010] In addition, the lithium secondary battery may be heated by attaching a mica heater of 260 mm x 90 mm size connected to a PID controller (Proportional-Integral-Derivative controller) to the lithium secondary battery and heating it with an output of 300 W.

[0011] The positive electrode active material may contain 50% by weight or more, preferably 70% by weight or more, more preferably 90% to 100% of a single-particle lithium nickel-based oxide having an Ni content of 70 mol% or less, based on the total weight of the positive electrode active material.More preferably, the positive electrode active material may consist of a single-particle lithium nickel-based oxide having an Ni content of 70 mol% or less.

[0012] The single-particle lithium nickel-based oxide may include 30 or less nodules, and the average particle size of the nodules may be 0.8 μm to 4.0 μm.

[0013] The single particle type lithium nickel-based oxide may be represented by the following [Chemical Formula 1]. [Chemical formula 1] Li 1+x [Ni a Co b Mn c M 1 d ]O2 In the above [Chemical Formula 1], M 1 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≦0.2である。

[0014] The single-particle lithium nickel-based oxide may further include a coating layer on its surface, the coating layer containing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

[0015] Meanwhile, the negative electrode active material may be a carbon-based negative electrode active material.

[0016] Preferably, the negative electrode includes a negative electrode current collector, a first negative electrode active material layer formed on the negative electrode current collector and including a first negative electrode active material, and a second negative electrode active material layer formed on the first negative electrode active material layer and including a second negative electrode active material, the first negative electrode active material and the second negative electrode active material being carbon-based negative electrode active materials, and the first negative electrode active material and the second negative electrode active material being natural graphite, artificial graphite, or a combination thereof. Preferably, the weight ratio of the artificial graphite to the total weight of the negative electrode active materials in the second negative electrode active material layer may be higher than the weight ratio of the artificial graphite to the total weight of the negative electrode active materials in the first negative electrode active material layer.

[0017] The electrolyte may contain an organic solvent and a lithium salt, and the content W of the imide-based lithium salt in the total lithium salt may be I can satisfy the following formula (2). Formula (2):

number

[0018] The content of LiN(CF3SO2)2 in the total lithium salts contained in the electrolyte is W LiFSI When satisfies the above range, the propagation of flame and / or heat to adjacent cells during thermal runaway can be minimized.

[0019] The weight of the electrolyte per unit capacity of the lithium secondary battery may be 1.0 g / Ah to 3.0 g / Ah.

[0020] The charge cutoff voltage of the lithium secondary battery can be 4.35V or higher, preferably 4.35V to 5V, and more preferably 4.35V to 4.5V. [Effects of the Invention]

[0021] The lithium secondary battery according to the present invention has a V T Since the discharge current is low at 4 Ah / sec or less, even if thermal runaway occurs in one unit cell, there is little propagation of flame and / or heat to adjacent cells, providing excellent thermal runaway safety.

[0022] Furthermore, the lithium secondary battery according to the present invention has a high nominal voltage of 3.68 V or more, and therefore can achieve a high energy density.

[0023] Furthermore, the lithium secondary battery according to the present invention can be driven at a high voltage of 4.35 V or more and can achieve a high capacity even when a positive electrode active material with a relatively low nickel content is used.

[0024] In addition, since the lithium secondary battery according to the present invention has excellent thermal runaway safety, when a module is manufactured using the same, it is not necessary to use a large amount of fireproof insulating material, and a relatively high energy density per unit volume can be achieved.

[0025] The lithium secondary battery according to the present invention may be designed to use a single particle type positive electrode active material having a nickel content of 70 mol% or less, preferably 50 to 70 mol%, as the positive electrode active material, and a carbon-based negative electrode active material as the negative electrode active material. In this case, the thermal transition rate is low, which not only provides excellent thermal runaway safety, but also allows stable operation at a high voltage of 4.35 V or more, thereby achieving high capacity.

[0026] The lithium secondary battery according to the present invention may be designed so that the weight of the electrolyte per unit capacity is 1.0 g / Ah to 3.0 g / Ah. When the weight of the electrolyte is satisfied, the explosion pressure during thermal runaway is reduced, and thermal runaway safety is further improved.

[0027] In addition, the lithium secondary battery according to the present invention can minimize thermal transfer to adjacent cells during thermal runaway by adjusting the content of imide-based lithium salt in the electrolyte according to the Ni content of the positive electrode active material. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a scanning electron microscope photograph of a single particle positive electrode active material. [Figure 2] 1 is a scanning electron microscope photograph of a pseudo-single particle positive electrode active material. [Figure 3] 1 is a scanning electron microscope photograph of a secondary particle positive electrode active material. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will be described in more detail below.

[0030] The terms and words used in this specification and claims should not be interpreted in a limited way to their general or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their inventions.

[0031] In the present invention, the term "single particle type" refers to particles consisting of 30 or less nodules, and is a concept that includes a single particle consisting of one nodule and a quasi-single particle that is a composite of 2 to 30 nodules. Figure 1 shows a scanning electron microscope photograph of a positive electrode active material in the single particle form, and Figure 2 shows a scanning electron microscope photograph of a positive electrode active material in the quasi-single particle form.

[0032] The "nodule" is a sub-particle unit constituting a single particle or a quasi-single particle, and may be a single crystal having no crystalline grain boundary, or a polycrystal having no apparent grain boundary when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope.

[0033] In the present invention, the term "secondary particles" refers to particles formed by agglomeration of a plurality of primary particles, for example, tens to hundreds of primary particles. Specifically, the secondary particles may be aggregates of 50 or more primary particles. FIG. 3 shows a scanning electron microscope (SEM) photograph of a positive electrode active material in the form of secondary particles.

[0034] In the present invention, the term "particle" is a concept that includes any one or all of a single particle, a quasi-single particle, a primary particle, a nodule, and a secondary particle.

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

[0036] In the present invention, the "average particle size D 50 " means the particle size corresponding to 50% of the volume cumulative amount in 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 is dispersed in a dispersion medium, introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W to obtain a volume cumulative particle size distribution graph, and the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0037] In the present invention, the term "loading amount (mAh / cm 2 ) can be measured as follows:

[0038] First, the electrode to be measured is punched out to a unit area size and its weight W1 is measured. Then, the weight W2 of the electrode current collector of the punched out electrode is measured, and the weight W of the electrode active material layer is calculated using the following mathematical formula 1.

[0039] Mathematical formula 1: Weight of electrode active material layer W = (Weight per unit area of ​​electrode W1 - Weight per unit area of ​​electrode current collector W2) / 2

[0040] Then, the weight of the electrode active material per unit area, Wa, is calculated by multiplying the weight W of the electrode active material layer by the weight ratio of the electrode active material to the total weight of the electrode active material layer, and the loading amount can be calculated by multiplying Wa by the specific capacity (unit: mAh) of the electrode active material.

[0041] In the present invention, the "porosity (%)" can be calculated by 1-(electrode density / electrode true density).

[0042] As a result of extensive research into the development of a lithium secondary battery having high energy density and excellent safety, the inventors have discovered that when a lithium secondary battery is designed so that the thermal transition rate measured in a test module manufactured by stacking four fully charged lithium secondary batteries satisfies certain conditions, even if thermal runaway occurs in a unit cell in a module and / or pack state, the propagation of thermal runaway to adjacent cells can be minimized, thereby achieving high energy density, and have completed the present invention.

[0043] Specifically, the lithium secondary battery according to the present invention is a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, and the lithium secondary battery has a nominal voltage of 3.68 V or more. Four of the lithium secondary batteries fully charged to 4.35 V were stacked to manufacture a test module, and the V T The current is 4 Ah / sec or less, preferably 1 Ah / sec to 4 Ah / sec, and more preferably 2 Ah / sec to 4 Ah / sec.

[0044] Formula (1):V T =C total / t

[0045] In the formula (1), the C total is the total discharge capacity of the test module, and t is the time it takes from the time when the voltage of one lithium secondary battery placed at the outermost side of the test module becomes 0 to the time when the voltages of all lithium secondary batteries in the test module become 0 after heating and igniting the lithium secondary battery.

[0046] When thermal runaway occurs, the voltage of the unit cell (lithium secondary battery) drops to 0, so the t represents the time it takes for the thermal runaway that occurs in the outermost unit cell to propagate to all unit cells in the test cell.

[0047] Meanwhile, the total discharge capacity of the test module is the sum of the discharge capacities measured by charging and discharging each lithium secondary battery in the test module at 25° C., 0.33 C, and in the voltage range of 2.5 V to 4.35 V.

[0048] The above V T is a value obtained by dividing the discharge capacity of the entire test module by the time it takes for thermal runaway to propagate throughout the entire test module, and is a value that can represent the thermal transition speed during thermal runaway.

[0049] Here, the lithium secondary battery in the test module may have a size of 100 mm wide and 300 mm long.

[0050] In addition, the lithium secondary battery may be heated by attaching a mica heater of 260 mm x 90 mm size connected to a PID controller (Proportional-Integral-Derivative controller) to the lithium secondary battery and heating it with an output of 300 W.

[0051] According to the research of the present inventors, as described above, the V T It has been found that when battery modules or battery packs are manufactured using lithium secondary batteries designed to have a discharge capacity of 4 Ah / sec or less, the speed at which heat and / or flames propagate to adjacent cells is significantly reduced, and even if thermal runaway occurs in one unit cell, the occurrence of a chain reaction of fires and / or explosions can be minimized.

[0052] On the other hand, the V T is affected by the discharge capacity of the lithium secondary battery, the design of the positive electrode (e.g., the type of positive electrode active material, the composition of the positive electrode, and the loading amount), the design of the negative electrode (e.g., the type of negative electrode active material, the composition of the negative electrode, and the loading amount), and / or the design of the electrolyte (e.g., the electrolyte content, the type and content of the lithium salt, the type of additive, etc.). For example, when the content of the positive electrode active material with a high nickel content increases in the positive electrode or when the negative electrode contains a Si-based negative electrode active material, V T In addition, V increases when the capacity of the lithium secondary battery increases or when the amount of electrolyte in the lithium secondary battery increases. T Therefore, when designing a lithium secondary battery, these factors must be adjusted appropriately to achieve the desired V T It is possible to manufacture lithium secondary batteries having high electrical resistance.

[0053] Meanwhile, the nominal voltage of the lithium secondary battery may be 3.68 V or higher, preferably 3.68 V to 3.80 V, and more preferably 3.69 V to 3.75 V. Here, the nominal voltage refers to the average voltage value during discharge of the lithium secondary battery. Since the energy density of a lithium secondary battery is calculated by multiplying the average voltage and average current during discharge, a higher nominal voltage increases the energy density. While the nominal voltage of conventional lithium secondary batteries using lithium nickel cobalt manganese-based oxides as the positive electrode active material was around 3.6 V, the present invention increases the charge cut-off voltage to 3.68 V or higher, thereby achieving a high energy density. Specifically, the lithium secondary battery according to the present invention may have an energy density of 500 Wh / L or higher, preferably 500 Wh / L to 800 Wh / L.

[0054] Preferably, the charge cut-off voltage (full charge voltage) of the lithium secondary battery is 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 is within this range, the capacity of the active material increases, the nominal voltage increases, and high energy density can be achieved. Generally, as the charge cut-off voltage increases, the capacity exhibited by the positive electrode active material increases. However, as the charge cut-off voltage increases, side reactions with the electrolyte increase during charge and discharge, causing rapid structural collapse of the positive electrode active material and rapid deterioration of life characteristics. This problem is more pronounced in high-nickel lithium-nickel-cobalt-manganese oxides with a high nickel content. Therefore, in the past, when lithium-nickel-cobalt-manganese oxides were used as positive electrode active materials, the charge cut-off voltage was generally around 4.3 V. However, in the present invention, by using a lithium nickel-based oxide having a single particle form and a Ni content of 70 mol % or less as the positive electrode active material, it is possible to maintain excellent life characteristics even when the charge cut-off voltage is 4.35 V or more.

[0055] The lithium secondary battery according to the present invention includes a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, and the positive electrode active material may contain 50% by weight or more of a single-particle lithium nickel-based oxide in which the Ni content of all metals other than lithium is 70 mol % or less.

[0056] Each component of the lithium secondary battery according to the present invention will now be described in more detail.

[0057] positive electrode The lithium secondary battery according to the present invention includes a positive electrode including a positive electrode active material. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on at least one surface of the positive electrode current collector, the positive electrode active material layer including the positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer may further include a positive electrode conductive material and a positive electrode binder.

[0058] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesive strength of the positive electrode active material. It can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0059] Meanwhile, in the present invention, the positive electrode active material can contain a single particle type lithium nickel-based oxide having an Ni content of 70 mol % or less, preferably 50 mol % to 70 mol %.

[0060] As described above, when a single particle lithium nickel-based oxide having a relatively low nickel content is used as a positive electrode active material, side reactions with the electrolyte are suppressed under high temperature and high voltage conditions, reducing gas generation. As a result, the explosion pressure during thermal runaway is reduced, and the rate at which heat and / or flames are transferred to adjacent cells is reduced.

[0061] In the case of lithium nickel-based oxides in the form of secondary particles, consisting of an aggregate of more than 30 to several hundred primary particles, the large contact area with the electrolyte causes many side reactions with the electrolyte, resulting in the generation of gas during these side reactions. Under high temperature and / or high voltage conditions, the amount of gas generated significantly increases. If a large amount of gas is present inside a lithium secondary battery, the explosion pressure increases during thermal runaway. The greater the explosion pressure, the faster the heat and flames propagate to adjacent cells. In contrast, single-particle lithium nickel-based oxides have fewer nodules constituting the particles, resulting in fewer interfaces within the particles and a smaller contact area with the electrolyte. This reduces side reactions with the electrolyte compared to secondary particles, resulting in significantly less gas generation. Therefore, when single-particle lithium nickel-based oxides are used as a positive electrode active material, the explosion pressure and thermal transition rate during thermal runaway are also reduced. However, even when single-particle lithium nickel-based oxides are used, if the nickel content in the lithium nickel-based oxide is high, the reduction in gas generation is small, thereby reducing the effectiveness of reducing the explosion pressure and thermal transition rate during thermal runaway.

[0062] In addition, single particle type lithium nickel oxide with a relatively low nickel content has higher structural stability at high voltages than lithium nickel oxide with a high nickel content or secondary particle form, which can minimize the deterioration of life characteristics during high voltage operation. Specifically, the higher the nickel content in the lithium nickel oxide, the more reactive Ni +4The amount of ions increases, which reduces the structural stability of the positive electrode active material during charge and discharge, resulting in rapid deterioration of the positive electrode. This phenomenon becomes even more severe during high-voltage operation. Therefore, in the present invention, by using 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 deterioration of the active material during high-voltage operation. However, if the Ni content is too low, the capacity characteristics will deteriorate, so the Ni content of the lithium-nickel-based oxide is preferably approximately 50 mol% to 70 mol%.

[0063] Specifically, the single particle lithium nickel-based oxide may be a lithium transition metal oxide containing nickel, manganese, and cobalt, and may be represented by the following [Chemical Formula 1], for example.

[0064] [Chemical formula 1] Li 1+x [Ni a Co b Mn c M 1 d ]O2

[0065] In the above [Chemical Formula 1], M 1 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. 1 When the element is contained, the structural stability of the lithium nickel-based oxide particles is improved, and better life characteristics can be realized during high voltage operation. 1 The element may include one or more elements selected from the group consisting of Ti, Mg, Al, Zr, and Y, and more preferably may include two or more elements selected from the group consisting of Ti, Mg, Al, Zr, and Y.

[0066] The 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 this range, a stable layered crystal structure may be formed.

[0067] The a represents the molar ratio of nickel to all metals other than 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 the a satisfies this range, the battery can be stably driven at high voltage, achieving high capacity, and exhibiting excellent thermal runaway safety due to reduced explosion pressure during thermal runaway.

[0068] The b represents the molar ratio of cobalt to all metals other than lithium in the lithium nickel-based oxide, and is 0 <b<0.5、0.05≦b≦0.4、または0.1≦a≦0.4であることができる。

[0069] The c represents the molar ratio of manganese to all metals other than lithium in the lithium nickel-based oxide, and is 0 <c<0.5、0.05≦c≦0.4、または0.1≦c≦0.4であることができる。

[0070] The d is M of all metals other than lithium in the lithium nickel-based oxide. 1 Indicates the molar ratio of elements, and is 0≦d≦0.2, 0≦d≦0.1, or 0 <d≦0.1であることができる。M 1 When the molar ratio of the elements satisfies the above range, the positive electrode active material can have excellent structural stability and capacity.

[0071] Meanwhile, the single particle lithium nickel-based oxide may further include a coating layer on its surface, the coating layer including one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

[0072] When a coating layer is present on the surface of the lithium nickel-based oxide, the coating layer prevents contact between the electrolyte and the lithium nickel-based oxide, thereby reducing the elution of transition metals and the generation of gas due to side reactions with the electrolyte, thereby further improving safety during thermal runaway. Preferably, the coating layer contains 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, two or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, and W.

[0073] On the other hand, the single-particle lithium nickel-based oxide preferably contains 30 or less 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 cracking increases during electrode production, and the occurrence of internal cracks due to volume expansion / contraction of the nodules during charge / discharge increases, which may reduce the effect of improving high-temperature life characteristics and high-temperature storage characteristics.

[0074] 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 this range, particle cracking during electrode fabrication can be minimized, and an increase in resistance can be more effectively suppressed. Here, the average particle size of the nodules refers to a value obtained by measuring the particle size of each nodule observed in an SEM image obtained by analyzing the positive electrode active material powder using a scanning electron microscope, and then calculating the arithmetic mean of the measured values.

[0075] On the other hand, the D of the lithium nickel oxide 50 The diameter of the lithium nickel oxide is 2.0 μm to 10.0 μm, preferably 2.0 μm to 8.0 μm, and more preferably about 3.0 μm to 7.0 μm. 50If D is too small, the processability during electrode manufacturing may be reduced, the electrolyte impregnation may be reduced, and the electrochemical properties may increase. 50 If is too large, the resistance increases and the output characteristics deteriorate.

[0076] Meanwhile, the single-particle lithium nickel-based oxide having a nickel content of 70 mol% or less may be contained in an amount of more than 50 wt%, preferably 55 wt% or more, more preferably 60 wt% or more, even more preferably 70 wt% or more, and even more preferably 100 wt% of the total weight of the positive electrode active material in the positive electrode active material layer. When the ratio of the single-particle lithium nickel-based oxide having a nickel content of 70 mol% or less to the total weight of the positive electrode active material satisfies the above range, excellent thermal runaway safety is exhibited.

[0077] The positive electrode active material layer may contain 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 secondary particle lithium nickel-based oxide and / or a single particle lithium nickel-based oxide having a nickel content of more than 70 mol%. However, if the ratio of the secondary particles and / or the lithium nickel-based oxide having a nickel content of more than 70 mol% is 50 wt% or more of the total positive electrode active material, the effect of improving thermal runaway safety is small, which is not preferable.

[0078] The positive electrode active material may be contained in an amount of 80% by weight to 98% by weight, preferably 90% by weight to 98% by weight, and more preferably 93% by weight to 98% by weight, based on the total weight of the positive electrode active material layer. When the content of the positive electrode active material satisfies the above range, excellent energy density can be achieved.

[0079] Next, the positive electrode conductive material is used to impart conductivity to the positive electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the battery that is constructed and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotube, and other carbon-based materials; 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; and conductive polymers such as polyphenylene derivatives. Among these, one type may be used alone or a mixture of two or more types may be used.

[0080] The positive electrode conductive material can usually be contained in an amount of 0.1 to 10% by weight, preferably 0.5 to 8% by weight, and more preferably 0.5 to 5% by weight, based on the total weight of the positive electrode active material layer.

[0081] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0082] The positive electrode binder can be contained 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 positive electrode active material layer.

[0083] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode. 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 prepare a positive electrode slurry, applying the positive electrode slurry to a positive electrode current collector, drying, and rolling the slurry, or by casting the positive electrode slurry on a separate support, peeling it off from the support, and laminating the resulting film on the positive electrode current collector.

[0084] Meanwhile, the solvent for the positive electrode slurry may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, which may be used alone or in combination. The amount of the solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is applied to produce a positive electrode, taking into consideration the coating thickness and production yield of the slurry.

[0085] Meanwhile, the loading of the positive electrode according to the present invention is 0.5 mAh / cm 2 ~10mAh / cm 2 , preferably 2 mAh / cm 2 ~8mAh / cm 2 , more preferably 2.5 mAh / cm 2 ~6mAh / cm 2 When the positive electrode loading amount satisfies the above range, thermal runaway safety and capacity characteristics are further improved.

[0086] The positive electrode may have a porosity of 10% to 50%, preferably 15% to 45%, and more preferably 15% to 30%. When the positive electrode porosity is within this range, the electrolyte impregnation property is improved, and even more excellent capacity characteristics can be achieved.

[0087] negative electrode The lithium secondary battery according to the present invention includes a negative electrode including a negative electrode active material. Specifically, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, the negative electrode active material layer including the negative electrode active material. In addition to the negative electrode active material, the negative electrode active material layer may further include a negative electrode conductive material and a negative electrode binder.

[0088] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, etc., can be used. The negative electrode current collector typically has a thickness of 3 μm to 500 μm. As with the positive electrode current collector, the surface of the current collector can be formed with fine irregularities to strengthen the binding force of the negative electrode active material. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0089] Meanwhile, the negative electrode active material may be a carbon-based negative electrode active material, which may include, for example, natural graphite, artificial graphite, graphitized carbon fiber, amorphous carbon, soft carbon, hard carbon, or a combination thereof. More preferably, the carbon-based negative electrode active material may include natural graphite and artificial graphite, in which case the weight ratio of the natural graphite to the artificial graphite may be 1:9 to 9:1, preferably 2:8 to 8:2.

[0090] In recent years, there has been a trend toward using Si-based negative electrode active materials, such as SiO, Si, and Si-C composites, which have high theoretical capacities, as negative electrode active materials in order to achieve high capacity. However, research by the present inventors has shown that when a Si-based negative electrode active material is included, the explosion pressure increases during thermal runaway, which in turn increases the heat propagation rate and reduces thermal runaway safety. Therefore, it is preferable that the lithium secondary battery according to the present invention does not include a Si-based negative electrode active material as the negative electrode active material.

[0091] The average particle size D of the carbon-based negative electrode active material 50 The thickness can be 2 μm to 30 μm, preferably 5 μm to 30 μm.

[0092] The negative electrode active material may be contained in an amount of 80% by weight to 98% by weight, preferably 90% by weight to 98% by weight, and more preferably 93% by weight 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 this range, excellent energy density can be achieved.

[0093] The negative electrode conductive material is used to impart conductivity to the negative electrode, and can be any material that does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, carbon nanotubes, and other carbon-based materials; metal powders or fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These materials may be used alone or in combination.

[0094] The negative electrode conductive material can usually be contained in an amount of 0.1 to 10% by weight, preferably 0.25 to 8% by weight, and more preferably 0.25 to 5% by weight, relative to the total weight of the negative electrode active material layer.

[0095] The negative electrode binder serves to improve adhesion between particles of the negative electrode active material and between the negative electrode active material and the negative electrode current collector. Specific examples of the negative electrode binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0096] The negative electrode binder may be contained 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 negative electrode active material layer.

[0097] Meanwhile, in the lithium secondary battery according to the present invention, the negative electrode active material layer may have a single layer structure or a multi-layer structure of two or more layers. For example, the negative electrode may include a first negative electrode active material layer formed on at least one surface of a negative electrode current collector and including a first negative electrode active material, and a second negative electrode active material layer formed on the first negative electrode active material layer and including a second negative electrode active material. Here, the first negative electrode active material and the second negative electrode active material may be carbon-based negative electrode active materials, such as natural graphite, artificial graphite, or a combination thereof.

[0098] On the other hand, when the negative electrode active material layer has a multilayer structure composed of two or more layers, the types and / or contents of the negative electrode active material, binder, and / or conductive material may differ from one another in each layer.

[0099] For example, the weight ratio of natural graphite to the total weight of the negative electrode active material in the first negative electrode active material layer (lower layer) can be made higher than the weight ratio of natural graphite to the total weight of the negative electrode active material in the second negative electrode active material layer (upper layer), and the weight ratio of artificial graphite to the total weight of the negative electrode active material in the second negative electrode active material layer can be made higher than the weight ratio of artificial graphite to the total weight of the negative electrode active material in the first negative electrode active material layer.

[0100] Alternatively, the weight ratio of the conductive material to the total weight of the second negative electrode active material layer (upper layer) can be higher than the weight ratio of the conductive material to the total weight of the first negative electrode active material layer (lower layer).

[0101] In this way, by forming the negative electrode active material layer in a multilayer structure and varying the composition of each layer, the performance characteristics of the battery can be improved. For example, if the first negative electrode active material layer has a high ratio of natural graphite and the second negative electrode active material layer has a high ratio of artificial graphite, the effect of reducing explosion pressure during thermal runaway can be further improved.

[0102] The negative electrode can be manufactured by a conventional method for manufacturing a negative electrode. 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 prepare a negative electrode slurry, applying the negative electrode slurry to a negative electrode current collector, drying, and rolling the negative electrode slurry, or by casting the negative electrode slurry on a separate support, peeling it from the support, and laminating the resulting film on the negative electrode current collector.

[0103] Meanwhile, the solvent for the negative electrode slurry may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, which may be used alone or in combination. The amount of solvent used should be sufficient to dissolve or disperse the negative electrode active material, conductive material, and binder, and to provide a viscosity that allows excellent thickness uniformity when the slurry is subsequently applied to produce a positive electrode, taking into consideration the coating thickness and manufacturing yield of the slurry.

[0104] Meanwhile, the loading of the negative electrode according to the present invention is 0.5 mAh / cm 2 ~10mAh / cm 2 , preferably 2 mAh / cm 2 ~8mAh / cm 2 , more preferably 2.5 mAh / cm 2 ~6.5mAh / cm 2 When the negative electrode loading amount satisfies the above range, thermal runaway safety and capacity characteristics are further improved.

[0105] The negative electrode may have a porosity of 15% to 50%, preferably 20% to 40%, and more preferably 20% to 35%. When the negative electrode porosity satisfies the above range, better capacity characteristics can be achieved.

[0106] electrolyte The electrolyte may include an organic solvent and a lithium salt.

[0107] The organic solvent may be any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred.

[0108] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries without particular limitation. Specifically, the lithium salt may include one or more selected from the group consisting of LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(CF, SO) (LiFSI), LiCl, LiI, or LiB(CO) . Preferably, the lithium salt may include a phosphate-based lithium salt such as LiPF, an imide-based lithium salt such as LiN(CF, SO), LiN(CF, SO), or LiN(CF, SO), or a combination thereof. Here, the content of the imide-based lithium salt in the total weight of the lithium salt can be appropriately adjusted according to the Ni content in the positive electrode active material. Specifically, the content W I It is preferable that satisfies the following formula (2).

[0109] Formula (2):

number

[0110] In the formula (2), a represents the mole percent of Ni in all metals other than lithium in the positive electrode active material, and a can be 70 or less, preferably 50 to 70, and more preferably 55 to 70.

[0111] When the content a of Ni in the positive electrode active material and the content a of the imide-based lithium salt in the electrolyte satisfy the condition of the above formula (2), the thermal runaway transition to adjacent cells can be minimized in the event of fire or thermal runaway.

[0112] On the other hand, the concentration of the lithium salt is preferably in the range of 0.1 M to 3.0 M, preferably 0.1 M to 2.0 M, and more preferably 0.5 M to 1.5 M. When the concentration of the lithium salt is within this range, the electrolyte has appropriate conductivity and viscosity, and therefore can exhibit excellent electrolyte performance, allowing lithium ions to migrate effectively.

[0113] In addition to the constituent components of the electrolyte, the electrolyte may further contain additives for the purpose of improving the life characteristics of the battery, suppressing the decrease in the capacity of the battery, improving the discharge capacity of the battery, etc. For example, the additives may 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 bis(oxalato)borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium tetrafluorooxalatophosphate (LiTF Examples of additives that can be used alone or in combination include, but are not limited to, lithium methyl sulfate (LiMS), lithium ethyl sulfate (LiES), propane sultone (PS), propene sultone (PRS), succinonitrile (SN), adiponitrile (AND), 1,3,6-hexanetricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), ethyl di(prop-2-yn-1-yl)phosphate (EDP), and 5-methyl-5-propargyloxylcarbonyl-1,3-dioxan-2-one (MPOD). The additives may be included in an amount of 0.1 wt % to 10 wt %, preferably 0.1 wt % to 5 wt %, based on the total weight of the electrolyte.

[0114] The electrolyte may be included in an amount of 1.0 g / Ah to 3.0 g / Ah, preferably 1.5 g / Ah to 2.5 g / Ah, and more preferably 1.8 g / Ah to 2.5 g / Ah per unit capacity of the lithium secondary battery. If the amount of electrolyte per unit capacity is too large, the electrolyte may act as fuel during thermal runaway, increasing explosion pressure and causing rapid thermal transition. On the other hand, if the amount of electrolyte per unit capacity is too small, the electrolyte may be consumed quickly during activation and battery operation, resulting in reduced lifespan.

[0115] Separator The lithium secondary battery according to the present invention may further include a separator between the positive and negative electrodes, if necessary. The separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator commonly used in lithium secondary batteries may be used without limitation. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity is preferred. Specifically, a porous polymer film, such as 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, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used in a single-layer or multi-layer structure.

[0116] The lithium secondary battery according to the present invention can be usefully applied to portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs), etc. The lithium secondary battery according to the present invention can be driven at a high voltage, can achieve high energy density, and has excellent safety in the event of thermal runaway, and therefore can be particularly useful in the electric vehicle field.

[0117] According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery according to the present invention as a unit cell, and a battery pack including a plurality of battery modules.

[0118] According to yet another embodiment of the present invention, there is provided a battery pack including a plurality of lithium secondary batteries according to the present invention as unit cells. The battery pack may not include a battery module.

[0119] The present invention also provides a pack cell assembly.

[0120] According to one embodiment, the battery module can include 10 to 50 unit cells, preferably 16 to 36 unit cells, and the battery pack can include 10 to 1,000 unit cells, preferably 10 to 500 unit cells.

[0121] The 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 (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0122] While the present invention may be embodied in various different forms, it is to be understood that the invention is not limited to the specific embodiments set forth herein, and that the invention may be embodied in various different forms without departing from the spirit or scope of the present invention.

[0123] Example 1 <Production of positive electrodes> The positive electrode active material, positive electrode conductive material, and PVDF binder were mixed in a weight ratio of 97:1:2 in N-methylpyrrolidone to prepare a positive electrode slurry. 50 Single particle type Li[Ni 0.56 Co 0.12 Mn 0.32 ]O2 was used 100%, and carbon nanotubes were used as the positive electrode conductive material.

[0124] The positive electrode slurry was applied to an aluminum current collector sheet, dried, and then rolled to obtain a current collector with a loading of 4.0 mAh / cm. 2 A positive electrode having a porosity of 25% was produced.

[0125] <Production of negative electrodes> Anode active material: anode conductive material: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) was mixed in water in a weight ratio of 96:1:2:1 to prepare anode slurry. Here, graphite was used as the anode active material, and carbon black was used as the anode conductive material.

[0126] The negative electrode slurry was applied to a copper current collector sheet, dried, and then rolled to a loading capacity of 4.5 mAh / cm. 2 A negative electrode having a porosity of 30% was produced.

[0127] <Lithium secondary battery manufacturing> A separator was interposed between the cathode and anode to prepare an electrode assembly, and the electrode assembly was inserted into a battery case. An electrolyte was then injected so that the amount of electrolyte per unit capacity was 2.0 g / Ah to prepare a lithium secondary battery cell. The electrolyte was prepared by dissolving lithium salt (LiPF6 100 wt%) to a concentration of 1.0 M in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0128] Example 2 As the positive electrode active material, D 50 Single particle type Li[Ni 0.60 Co 0.10 Mn 0.30 A positive electrode, a negative electrode, and a lithium secondary battery were produced in the same manner as in Example 1, except that 100% ]O2 was used.

[0129] Example 3 As the positive electrode active material, D 50 Single particle type Li[Ni 0.70 Co 0.10 Mn 0.20 A positive electrode, a negative electrode, and a lithium secondary battery were produced in the same manner as in Example 1, except that 100% ]O2 was used.

[0130] Example 4 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a mixture of LiPF6:LiFSI in a weight ratio of 60:40 was used as the lithium salt when manufacturing the lithium secondary battery.

[0131] Example 5 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 2, except that a mixture of LiPF6:LiFSI in a weight ratio of 60:40 was used as the lithium salt when manufacturing the lithium secondary battery.

[0132] Example 6 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 3, except that a mixture of LiPF6:LiFSI in a weight ratio of 80:20 was used as the lithium salt when manufacturing the lithium secondary battery.

[0133] Comparative Example 1 As the positive electrode active material, D 50 Secondary particle type Li[Ni 0.85 Co 0.06 Mn 0.08 Al 0.01 A positive electrode, a negative electrode, and a lithium secondary battery were produced in the same manner as in Example 1, except that 100% ]O2 was used.

[0134] Comparative Example 2 As the positive electrode active material, D 50 Single particle type Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 A positive electrode, a negative electrode, and a lithium secondary battery were produced in the same manner as in Example 1, except that 100% ]O2 was used.

[0135] Comparative Example 3 As the positive electrode active material, D 50 Single particle type Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 100% of ]O2 was used and a mixture of graphite and SiO in a weight ratio of 95:5 was used as the negative electrode active material.

[0136] Comparative Example 4 As the positive electrode active material, D 50 Single particle type Li[Ni 0.93 Co 0.05 Mn 0.01 Al 0.01 A positive electrode, a negative electrode, and a lithium secondary battery were produced in the same manner as in Example 1, except that 100% ]O2 was used.

[0137] Comparative Example 5 As the positive electrode active material, D 50 Single particle type Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 and D 50 Li[Ni] in the form of secondary particles with a particle size of 8.6 μm 0.80 Co 0.10 Mn 0.10 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 1, 2, and 3 were mixed in a weight ratio of 5:5.

[0138] Comparative Example 6 As the positive electrode active material, D 50 Single particle type Li[Ni 0.70 Co 0.10 Mn 0.20 ]O2 and D 50 Li[Ni] in the form of secondary particles with a particle size of 7.8 μm 0.70 Co 0.10 Mn 0.20 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that 1, 2, and 3 were mixed in a weight ratio of 5:5.

[0139] Comparative Example 7 As the positive electrode active material, D 50 Single particle type Li[Ni 0.70 Co 0.10 Mn 0.20 ]O2 and D 50 Li[Ni] in the form of secondary particles with a particle size of 7.8 μm 0.70 Co 0.10 Mn 0.20 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a mixture of 1, 2, and 3 was used in a weight ratio of 25:75.

[0140] Comparative Example 8 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a mixture of graphite and SiO in a weight ratio of 95:5 was used as the negative electrode active material.

[0141] Comparative Example 9 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 2, except that a mixture of graphite and SiO in a weight ratio of 95:5 was used as the negative electrode active material.

[0142] Comparative Example 10 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 3, except that a mixture of graphite and SiO in a weight ratio of 95:5 was used as the negative electrode active material.

[0143] Comparative Example 11 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that a mixture of LiPF6 and LiFSI in a weight ratio of 50:50 was used as the lithium salt when manufacturing the lithium secondary battery.

[0144] Comparative Example 12 A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 3, except that a mixture of LiPF6:LiFSI in a weight ratio of 70:30 was used as the lithium salt when manufacturing the lithium secondary battery.

[0145] Experimental Example 1 Each of the lithium secondary battery cells manufactured in Examples 1 to 6 and Comparative Examples 1 to 12 was charged and discharged at 0.33 C in a voltage range of 2.5 V to 4.35 V, and the discharge capacity C was measured. Then, four lithium secondary battery cells of each Example and Comparative Example were stacked to manufacture a test module. The total discharge capacity C of the test module was total was calculated at 4C.

[0146] One lithium secondary battery cell located at the outermost side of the test module was heated and ignited, and the time taken from when the voltage of the lithium secondary battery located at the outermost side reached 0 until the voltages of all the lithium secondary batteries in the test module reached 0 was measured. Here, the voltage of each lithium secondary battery was measured using a data logger.

[0147] The measurement results are shown in Table 1 below.

[0148] [Table 1]

[0149] Experimental Example 2 Battery modules were manufactured by stacking 16 of each of the lithium secondary battery cells manufactured in Examples 1 to 6 and Comparative Examples 1 to 12. Then, the unit cell arranged on the outermost side of each battery module was heated with a heating device, and the time from the time when a flame occurred until the battery module was completely burned down was measured.

[0150] [Table 2]

[0151] Referring to Table 2 above, V T The battery modules using the lithium secondary batteries of Examples 1 to 6, in which the V T Compared to the battery modules using the lithium secondary batteries of Comparative Examples 1 to 12, which have a capacity of over 4 Ah / sec, as unit cells, it takes a longer time to burn out, and it can be confirmed that this battery module has excellent safety against thermal runaway.

Claims

1. A lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, The nominal voltage of the lithium secondary battery is 3.68 V or more; Four of the lithium secondary batteries were charged to 4.35 V and fully charged, and stacked to produce a test module. The V Ｔ A lithium secondary battery having a capacity of 4 Ah / sec or less. Equation (1): V Ｔ =C ｔｏｔａｌ / t In the formula (1), the C ｔｏｔａｌ is the total discharge capacity of the test module, and t is the time it takes from the time when the voltage of the outermost lithium secondary battery in the test module becomes 0 after heating and igniting one of the lithium secondary batteries in the test module, until the voltages of all the lithium secondary batteries in the test module become 0.

2. 2. The lithium secondary battery according to claim 1, wherein the positive electrode active material contains more than 50% by weight of a single-particle lithium nickel-based oxide having an Ni content of 70 mol% or less based on the total weight of the positive electrode active material.

3. 2. The lithium secondary battery according to claim 1, wherein the positive electrode active material is a single-particle lithium nickel-based oxide having an Ni content of 70 mol % or less.

4. The single-particle lithium nickel-based oxide includes 30 or less nodules, 3. The lithium secondary battery according to claim 2, wherein the nodules have an average particle size of 0.8 μm to 4.0 μm.

5. The lithium secondary battery according to claim 2 , wherein the single particle lithium nickel-based oxide is represented by the following [Chemical Formula 1]: [Chemical formula 1] Li １＋ｘ [Ni ａ Co ｂ Mn ｃ M １ ｄ ]O ２ In the above [Chemical Formula 1], M １ 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.

2.

6. 3. The lithium secondary battery according to claim 2, wherein the single-particle lithium nickel-based oxide further comprises a coating layer on its surface, the coating layer containing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

7. 2. The lithium secondary battery according to claim 1, wherein the negative electrode active material is a carbon-based negative electrode active material.

8. the negative electrode includes a negative electrode current collector, a first negative electrode active material layer formed on the negative electrode current collector and including a first negative electrode active material, and a second negative electrode active material layer formed on the first negative electrode active material layer and including a second negative electrode active material, The lithium secondary battery according to claim 1 , wherein the first and second negative electrode active materials are carbon-based negative electrode active materials.

9. The lithium secondary battery according to claim 8 , wherein the first and second negative electrode active materials are natural graphite, artificial graphite, or a combination thereof.

10. 10. The lithium secondary battery of claim 9, wherein a weight ratio of the artificial graphite to a total weight of the negative electrode active material in the second negative electrode active material layer is higher than a weight ratio of the artificial graphite to a total weight of the negative electrode active material in the first negative electrode active material layer.

11. 2. The lithium secondary battery according to claim 1, wherein the weight of the electrolyte per unit capacity of the lithium secondary battery is 1.0 g / Ah to 3.0 g / Ah.

12. V represented by formula (1) Ｔ 2. The lithium secondary battery according to claim 1, wherein the capacity is 1 Ah / sec to 4 Ah / sec.

13. the electrolyte comprises an organic solvent and a lithium salt; The content W of the imide-based lithium salt in the total weight of the lithium salt Ｉ The lithium secondary battery according to claim 1, wherein satisfies the following formula (2): Formula (2): [Equation 1] In the formula (2), a represents the mole percentage of Ni in all metals other than lithium in the positive electrode active material.

14. 2. The lithium secondary battery according to claim 1, wherein the charge cutoff voltage of the lithium secondary battery is 4.35 V or higher.

15. A battery module including the lithium secondary battery according to claim 1 as a unit cell.

16. The battery module of claim 15, wherein the battery module includes 10 to 50 unit cells.

17. A battery pack including the lithium secondary battery according to any one of claims 1 to 14 as a unit cell.

18. 18. The battery pack according to claim 17, wherein the battery pack includes 10 to 1,000 unit cells.

19. A battery pack comprising the battery module according to claim 15.

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