Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery having improved safety during thermal runaway, the lithium secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the lithium secondary battery has a nominal voltage of 3.68 V or more, and when a test module is manufactured by stacking four of the lithium secondary batteries fully charged up to 4.35 V and then measured for VT, which is represented by the following equation (1), the measurement value is 4 Ah / sec or less. Equation (1): VT = Ctotal / t, wherein Ctotal is the total discharge capacity of the test module; and t is the time taken from the moment when the voltage of the lithium secondary battery placed at the outermost part of the test module reaches 0 V after being ignited by heating, until the voltage of all lithium secondary batteries within the test module reaches 0 V.

Description

lithium secondary battery

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

[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] For devices requiring large capacities, such as electric vehicles and energy storage devices, batteries are typically implemented in module and / or pack configurations, each equipped with multiple secondary battery cells. If a single secondary battery cell in such a module and / or pack ignites or explodes due to internal or external factors, this can result in a phenomenon known as thermal runway propagation, in which heat, flames, and high-pressure gases spread to adjacent cells. This can lead to a chain reaction of explosions in adjacent cells, posing a significant safety risk.

[0004] Meanwhile, in the electric vehicle field, cells with high energy densities are in demand to extend single-charge driving ranges. Accordingly, cells utilizing high-nickel NCM cathode active materials with nickel contents of 80 mol% or more and / or Si-based anode active materials, which offer excellent capacity characteristics, are being developed for lithium secondary batteries for electric vehicles. However, these cells have the disadvantage of high explosive pressure in the event of thermal runaway, which rapidly propagates the thermal runaway, compromising safety.

[0005] In the past, a technology was applied to insert refractory insulation materials into modules to prevent heat transfer to neighboring cells. However, when refractory insulation materials are inserted into modules, there are problems such as a decrease in energy density, which reduces the driving range of the vehicle.

[0006] Therefore, there is a need for the development of a lithium secondary battery with high energy density and suppressed thermal runaway propagation.

[0007] The present invention is intended to solve the above problems, and to provide a lithium secondary battery that has a low heat transfer rate during thermal runaway and can be stably operated at high voltage to achieve high energy density.

[0008] In one aspect, the present invention is a lithium secondary battery comprising a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the lithium secondary battery has a nominal voltage of 3.68 V or more,

[0009] The four lithium secondary batteries were fully charged to 4.35 V, stacked, and then a test module was manufactured, and the V represented by the following formula (1) was measured. T A lithium secondary battery having a current of 4 Ah / sec or less, preferably 1 to 4 Ah / sec, more preferably 2 to 4 Ah / sec is provided.

[0010] Equation (1): V T = C total / t

[0011] In the above equation (1), the C total is the total discharge capacity of the test module, and t is the time taken from the time when the voltage of the lithium secondary battery placed at the outermost end of the test module becomes 0 after heating and igniting one lithium secondary battery placed at the outermost end of the test module until the voltage of all lithium secondary batteries in the test module becomes 0. Meanwhile, the total discharge capacity of the test module is a value obtained by measuring the discharge capacity by CC-CV charging each lithium secondary battery in the test module at 0.33C at 25°C in a voltage range of 2.5 V to 4.35 V, and then CC discharging them.

[0012] At this time, the lithium secondary battery in the test module may have a size of 100 mm in width and 300 mm in length.

[0013] In addition, heating of the lithium secondary battery can be performed by attaching a mica heater measuring 260 mm x 90 mm connected to a PID controller (Proportional-Integral-Derivative controller) to the lithium secondary battery and heating it with an output of 300 W.

[0014] At this time, the positive electrode active material may include a single particle lithium nickel-based oxide having a Ni content of 70 mol% or less in an amount of 50 wt% or more, preferably 70 wt% or more, and more preferably 90% to 100% of the total positive electrode active material. More preferably, the positive electrode active material may be composed of a single particle lithium nickel-based oxide having a Ni content of 70 mol% or less.

[0015] The above single particle lithium nickel oxide may include 30 or fewer nodules, and the average particle diameter of the nodules may be 0.8 µm to 4.0 µm.

[0016] The above single particle lithium nickel oxide may be represented by the following [chemical formula 1].

[0017] [Chemical Formula 1]

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

[0019] In the above [chemical formula 1], M1 includes 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≤0.2이다.

[0020] 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.

[0021] Meanwhile, the negative electrode active material may be composed of a carbon-based negative electrode active material.

[0022] Preferably, the negative electrode comprises: a negative current collector; a first negative active material layer formed on the negative current collector and including a first negative active material; and a second negative active material layer formed on the first negative active material layer and including a second negative active material, wherein the first negative active material and the second negative active material may be made of a carbon-based negative active material, and the first negative active material and the second negative active material may be natural graphite, artificial graphite, or a combination thereof. Preferably, the weight ratio of artificial graphite to the total weight of the negative active material in the second negative active material layer may be higher than the weight ratio of artificial graphite to the total weight of the negative active material in the first negative active material layer.

[0023] The above electrolyte may include an organic solvent and a lithium salt, and the content of the imide-based lithium salt among the total lithium salts is W. I This equation (2) can be satisfied.

[0024] Equation (2):

[0025]

[0026] In the above formula (2), a is the mol% of Ni among the total metal excluding lithium of the positive electrode active material.

[0027] Content of LiN(CF3SO2)2 among the total lithium salts contained in the electrolyte W LiFSI When this above range is satisfied, the propagation of flame and / or heat to neighboring cells during thermal runaway can be minimized.

[0028] The electrolyte weight per unit capacity of the lithium secondary battery may be 1.0 g / Ah to 3.0 g / Ah.

[0029] The above lithium secondary battery may have 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.

[0030] The lithium secondary battery according to the present invention has a heat transfer rate of V T Even if thermal runaway occurs in one unit cell, the spread of flame and / or heat to neighboring cells is minimal, resulting in excellent thermal runaway safety, as the current is less than 4Ah / sec.

[0031] In addition, the lithium secondary battery according to the present invention can realize high energy density because the nominal voltage is as high as 3.68 V or higher.

[0032] In addition, the lithium secondary battery according to the present invention can be operated at a high voltage of 4.35 V or higher and can achieve high capacity even when a cathode active material with a relatively low nickel content is applied.

[0033] In addition, since the lithium secondary battery according to the present invention has excellent thermal runaway safety, when manufacturing a module using the same, there is no need to use a large amount of refractory insulating material, and thus a relatively high energy density per same volume can be achieved.

[0034] The lithium secondary battery according to the present invention can 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 a positive electrode active material, and a carbon-based negative electrode active material as a negative electrode active material. In this case, not only is the thermal runaway safety excellent due to a low heat transfer rate, but it can also be stably operated at a high voltage of 4.35 V or higher, thereby realizing a high capacity.

[0035] The lithium secondary battery according to the present invention can be designed so that the electrolyte weight per unit capacity is 1.0 g / Ah to 3.0 g / Ah, and when the electrolyte weight is satisfied, the electrolyte can be prevented from acting as fuel during thermal runaway and an increase in explosive pressure can be suppressed.

[0036] In addition, the lithium secondary battery according to the present invention can minimize heat transfer to neighboring cells during thermal runaway by controlling the content of an imide-based lithium salt in the electrolyte according to the Ni content of the positive electrode active material.

[0037] Figure 1 is a scanning electron microscope photograph of a single-particle positive electrode active material.

[0038] Figure 2 is a scanning electron microscope photograph of a pseudo-single particle positive electrode active material.

[0039] Figure 3 is a scanning electron microscope photograph of a secondary particle positive electrode active material.

[0040] Hereinafter, the present invention will be described in more detail.

[0041] Terms or words used in this specification and 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.

[0042] In the present invention, "single particle type" means a particle composed of 30 or fewer nodules, and is a concept that includes a single particle composed of one nodule and a pseudo-single particle which is a composite of 2 to 30 nodules. Fig. 1 shows a scanning electron microscope image of a positive electrode active material in the form of a single particle, and Fig. 2 shows a scanning electron microscope image of a positive electrode active material in the form of a pseudo-single particle.

[0043] 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.

[0044] In the present invention, "secondary particle" refers to a particle formed by the agglomeration of multiple primary particles, for example, tens to hundreds. Specifically, the secondary particle may be an agglomerate of more than 30 primary particles. Figure 3 illustrates a scanning electron microscope (SEM) image of a positive electrode active material in the form of secondary particles.

[0045] 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.

[0046] 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.

[0047] In the present invention, "average particle diameter 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.

[0048] In the present invention, “loading amount (mAh / cm 2 ) can be measured as follows:

[0049] First, the electrode to be measured is punched out to a unit area size, and then its weight W1 is measured. Then, the weight W2 of the electrode current collector in the punched electrode is measured, and then the weight W of the electrode active material layer is calculated using the following mathematical equation 1.

[0050] 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

[0051] Then, the weight of the electrode active material per unit area Wa is calculated by multiplying the weight ratio of the electrode active material to the total weight of the electrode active material layer by the weight W 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.

[0052] In the present invention, “porosity (%)” can be calculated as 1 - (electrode density / electrode true density).

[0053]

[0054] The present inventors have conducted repeated research to develop a lithium secondary battery with high energy density and excellent safety, and as a result, they have found that if a lithium secondary battery is designed so that the heat transfer rate measured in a test module manufactured by stacking four lithium secondary batteries in a fully charged state satisfies a specific condition, even if thermal runaway occurs in a unit cell in a module and / or pack state, the propagation of thermal runaway to neighboring cells can be minimized, and high energy density can be achieved, thereby completing the present invention.

[0055]

[0056] Specifically, the lithium secondary battery according to the present invention is a lithium secondary battery including a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the lithium secondary battery has a nominal voltage of 3.68 V or higher, and after manufacturing a test module by stacking four of the lithium secondary batteries fully charged to 4.35 V, the V represented by the following formula (1) is measured. T It is 4 Ah / sec or less, preferably 1 to 4 Ah / sec, more preferably 2 to 4 Ah / sec.

[0057] Equation (1): V T = C total / t

[0058] In the above equation (1), the C total is the total discharge capacity of the test module, and t is the time taken from the time when the voltage of the lithium secondary battery placed at the outermost end of the test module becomes 0 after heating and igniting one lithium secondary battery placed at the outermost end of the test module until the voltage of all lithium secondary batteries in the test module becomes 0.

[0059] Since the voltage of a unit cell (lithium secondary battery) drops to 0 when thermal runaway occurs, the above t represents the time it takes for the thermal runaway occurring in the outermost unit cell to propagate to all unit cells in the test cell.

[0060] 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 0.33C at 25°C in a voltage range of 2.5 V to 4.35 V.

[0061] Above V T is the discharge capacity of the entire test module divided by the time it takes for thermal runaway to propagate throughout the test module, and is a value that can represent the heat transfer rate during thermal runaway.

[0062] At this time, the lithium secondary battery in the test module may have a size of 100 mm in width and 300 mm in length.

[0063] In addition, heating of the lithium secondary battery can be performed by attaching a mica heater measuring 260 mm x 90 mm connected to a PID controller (Proportional-Integral-Derivative controller) to the lithium secondary battery and heating it with an output of 300 W.

[0064] According to the research of the present inventors, the test module was manufactured as described above and measured V T When manufacturing a battery module or battery pack using a lithium secondary battery designed to have a current of 4 Ah / sec or less, it was found that the rate of heat and / or flame propagation to neighboring cells was significantly reduced, so that even if thermal runaway occurred in one unit cell, the occurrence of a chain reaction of fire and / or explosion could be suppressed to the greatest extent possible.

[0065] Meanwhile, the above V T is affected by the discharge capacity of the lithium secondary battery, the cathode design (e.g., the type of cathode active material, the cathode composition and loading amount, etc.), the anode design (e.g., the type of anode active material, the anode composition and loading amount, etc.) and / or the electrolyte design (e.g., the electrolyte content, the type and content of lithium salt, the type of additive, etc.). For example, when the content of a cathode active material with a high nickel content in the cathode increases, or when a Si-based anode active material is included in the anode, V T This increases. Also, when the capacity of the lithium secondary battery increases or the amount of electrolyte in the lithium secondary battery increases, V T increases. Therefore, when designing a lithium secondary battery, these factors should be appropriately adjusted to achieve the desired V T A lithium secondary battery having a value can be manufactured.

[0066]

[0067] Meanwhile, the lithium secondary battery may have a nominal voltage of 3.68 V or higher, preferably 3.68 V to 3.80 V, and more preferably 3.69 V to 3.75 V. At this time, the nominal voltage refers to the average voltage value during discharge of the lithium secondary battery. Since the energy density of the lithium secondary battery is calculated by the product of the average voltage and the average current during discharge, the energy density increases when the nominal voltage is high. The nominal voltage of a conventional lithium secondary battery using a lithium nickel cobalt manganese oxide as a positive electrode active material was at the level of 3.6 V, but in the present invention, the charge cut-off voltage is increased to make the nominal voltage 3.68 V or higher, thereby realizing 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.

[0068]

[0069] Preferably, the lithium secondary battery has a charge cut-off voltage (full charge 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, the capacity of the active material increases, and the nominal voltage increases, thereby realizing high energy density. In general, as the charge cut-off voltage increases, the capacity developed from the positive electrode active material increases. However, there is a problem in that when the charge cut-off voltage increases, side reactions with the electrolyte increase during charge and discharge, and the structural collapse of the positive electrode active material occurs rapidly, resulting in rapid deterioration of the life characteristics. This problem is more prominent 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 the positive electrode active material, the charge cut-off voltage was generally around 4.3 V. However, in the present invention, by applying a lithium nickel-based oxide having a Ni content of 70 mol% or less and a single particle form as a positive electrode active material, it is possible to maintain excellent life characteristics even when the charge cut-off voltage is 4.35 V or higher.

[0070]

[0071] A lithium secondary battery according to the present invention comprises: a positive electrode including a positive electrode active material; a positive electrode including a negative electrode active material; a negative electrode including a negative electrode active material; and an electrolyte, wherein the positive electrode active material may include a single-particle lithium nickel-based oxide having a Ni content of 70 mol% or more among all metals excluding lithium, at 50 wt% or more of the total positive electrode active material.

[0072]

[0073] Hereinafter, each component of the lithium secondary battery according to the present invention will be described in more detail.

[0074]

[0075] anode

[0076] A lithium secondary battery according to the present invention comprises a positive electrode comprising a positive electrode active material. Specifically, the positive electrode comprises a positive electrode current collector, a positive electrode active material layer formed on at least one surface of the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode active material. Furthermore, the positive electrode active material layer may further comprise a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material.

[0077] 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.

[0078]

[0079] 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%.

[0080] 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 as a result, the explosion pressure during thermal runaway is reduced, thereby reducing the rate at which heat and / or flame is transferred to neighboring cells.

[0081] In the case of secondary particle-type lithium nickel-based oxides in which more than 30 to hundreds of primary particles are aggregated, side reactions with the electrolyte frequently occur because the contact area with the electrolyte is large, and gas is generated during the side reactions. The amount of gas generated significantly increases under high temperature and / or high voltage conditions, and if a large amount of gas is contained inside the lithium secondary battery, the explosion pressure increases during thermal runaway, and the higher the explosion pressure, the faster the heat or flame spreads to the neighboring cells. 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, resulting in less side reactions with the electrolyte than secondary particles, and consequently, the amount of gas generated is also significantly less. Therefore, when single-particle lithium nickel-based oxides are applied as cathode active materials, the explosion pressure during thermal runaway decreases, and the heat transfer rate also decreases. However, even when single-particle lithium nickel oxide is applied, if the nickel content in the lithium nickel oxide is high, the reduction in gas generation is small, and accordingly, the effect of reducing the explosion pressure and heat transfer rate during thermal runaway is low.

[0082]

[0083] 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. +4As 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%.

[0084]

[0085] 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].

[0086] [Chemical Formula 1]

[0087] Li 1+x [Ni a Co b Mn c M 1 d ]O2

[0088] 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.

[0089] 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.

[0090] The above a represents the molar ratio of nickel among the total 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 to realize high capacity, and the explosion pressure is reduced in the event of thermal runaway, thereby exhibiting excellent thermal runaway safety.

[0091] 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≤a≤0.4일 수 있다.

[0092] 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.

[0093] 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.

[0094]

[0095] 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.

[0096] 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 effect of transition metal dissolution or gas generation due to side reactions with the electrolyte, and thus further improving stability during thermal runaway. 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.

[0097]

[0098] 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.

[0099]

[0100] 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.

[0101]

[0102] Meanwhile, the lithium nickel oxide is D50 It may be 2.0㎛ to 10.0㎛, preferably 2.0㎛ to 8.0㎛. More preferably, it is preferably about 3.0㎛ to 7.0㎛. 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.

[0103]

[0104] Meanwhile, the single-particle lithium nickel-based oxide having a nickel content of 70 mol% or less may be included 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 still 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 in the total weight of the positive electrode active material satisfies the above range, excellent thermal runaway safety is exhibited.

[0105] 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 effect of improving thermal runaway safety is minimal, which is not desirable.

[0106]

[0107] Meanwhile, the positive electrode active material may be included in an amount of 80 wt% to 98 wt%, preferably 90 wt% to 98 wt%, and more preferably 93 wt% to 98 wt%, 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.

[0108]

[0109] 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.

[0110] The above-mentioned positive electrode conductive material may be included in an amount of typically 0.1 to 10 wt%, preferably 0.5 to 8 wt%, and more preferably 0.5 to 5 wt%, based on the total weight of the positive electrode active material layer.

[0111]

[0112] 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.

[0113] The above positive 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.

[0114]

[0115] 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.

[0116] 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.

[0117]

[0118] Meanwhile, the positive electrode according to the present invention has a loading amount of 0.5 to 10 mAh / cm 2 , preferably 2 to 8 mAh / cm 2 , more preferably 2.5 to 6 mAh / cm 2 When the anode loading amount satisfies the above range, the thermal runaway safety and capacity characteristics are more excellent.

[0119] Additionally, the anode may have a porosity of 10% to 50%, preferably 15% to 45%, and more preferably 15% to 30%. When the anode porosity satisfies the above range, electrolyte impregnation properties are improved, thereby realizing better capacity characteristics.

[0120]

[0121] cathode

[0122] A lithium secondary battery according to the present invention comprises an anode comprising an anode active material. Specifically, the anode comprises an anode current collector, and an anode active material layer formed on at least one surface of the anode current collector, wherein the anode active material layer comprises the anode active material. In addition, the anode active material layer may further comprise an anode conductive material and an anode binder in addition to the anode active material.

[0123] 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.

[0124]

[0125] Meanwhile, the negative electrode active material may be composed of a carbon-based negative electrode active material, and the carbon-based negative electrode active material 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, and in this case, the weight ratio of the natural graphite: artificial graphite may be 1:9 to 9:1, preferably 2:8 to 8:2.

[0126] Recently, there has been a trend to apply Si-based negative electrode active materials such as SiO, Si, and Si-C composites with high theoretical capacities as negative electrode active materials to implement high capacity. However, according to the research of the present inventors, when Si-based negative electrode active materials are included, the explosion pressure increases during thermal runaway, which accelerates the heat propagation speed and reduces thermal runaway safety. Therefore, it is preferable that the lithium secondary battery according to the present invention not include Si-based negative electrode active materials as negative electrode active materials.

[0127] The above carbon-based negative electrode active material has an average particle diameter D50 This may be 2㎛ to 30㎛, preferably 5㎛ to 30㎛.

[0128] The above negative active material may be included in an amount of 80 wt% to 98 wt%, preferably 90 wt% to 98 wt%, and more preferably 93 wt% to 98 wt%, based on the total weight of the negative active material layer. When the content of the negative active material satisfies the above range, excellent energy density can be achieved.

[0129]

[0130] 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.

[0131] The above negative electrode conductive material may be included in an amount of typically 0.1 to 10 wt%, preferably 0.25 to 8 wt%, and more preferably 0.25 to 5 wt%, based on the total weight of the negative electrode active material layer.

[0132]

[0133] 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.

[0134] 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.

[0135]

[0136] 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. At this time, the first negative electrode active material and the second negative electrode active material may be made of a carbon-based negative electrode active material, and may be, for example, natural graphite, artificial graphite, or a combination thereof.

[0137]

[0138] Meanwhile, when the negative electrode active material layer is a multilayer structure composed of two or more layers, each layer may have different types and / or contents of the negative electrode active material, binder, and / or conductive material.

[0139] 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) may be formed to be 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 may be formed to be 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.

[0140] Alternatively, the weight ratio of the conductive material to the total weight of the second negative electrode active material layer (upper layer) may be formed to be higher than the weight ratio of the conductive material to the total weight of the first negative electrode active material layer (upper layer).

[0141] By forming the negative 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 active material layer contains a high proportion of natural graphite and the second negative active material layer contains a high proportion of artificial graphite, the effect of reducing the heat transfer rate during thermal runaway can be further improved.

[0142]

[0143] 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.

[0144] 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.

[0145]

[0146] Meanwhile, the negative electrode according to the present invention has a loading amount of 0.5 to 10 mAh / cm 2 , preferably 2 to 8 mAh / cm 2 , more preferably 2.5 to 6.5 mAh / cm 2 When the cathode loading amount satisfies the above range, the thermal runaway safety and capacity characteristics are more excellent.

[0147] Additionally, the cathode may have a porosity of 15% to 50%, preferably 20% to 40%, and more preferably 20% to 35%. When the cathode porosity satisfies the above range, even better capacity characteristics can be realized.

[0148]

[0149] electrolyte

[0150] The electrolyte may include an organic solvent and a lithium salt.

[0151] 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 C2 to C20 linear, branched, or cyclic hydrocarbon group, 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 a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0152]

[0153] 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 include at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2(LiFSI), LiCl, LiI, and LiB(C2O4)2. Preferably, the lithium salt may include a phosphate lithium salt such as LiPF6, an imide lithium salt such as LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, or a combination thereof. At this time, 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, and specifically, the content of the imide-based lithium salt in the total weight of the lithium salt W I It is desirable that the following equation (2) be satisfied.

[0154] Equation (2):

[0155]

[0156] In the above formula (2), a is the molar % of Ni among the total metal excluding lithium of the positive electrode active material, and a may be 70 or less, preferably 50 to 70, and more preferably 55 to 70.

[0157] When the content a of Ni in the positive electrode active material and the content of the imide lithium salt in the electrolyte satisfy the conditions of the above formula (2), the transfer of thermal runaway to neighboring cells can be minimized when ignition or thermal runaway occurs.

[0158] Meanwhile, it is preferable to use the concentration of the lithium salt within the range of 0.1 to 3.0 M, preferably 0.1 to 2.0 M, and more preferably 0.5 to 1.5 M. 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.

[0159]

[0160] 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.

[0161]

[0162] Meanwhile, 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 the explosion pressure and causing rapid heat transfer. On the other hand, if the amount of electrolyte per unit capacity is too small, the electrolyte may be rapidly consumed during the activation and battery operation processes, resulting in a deterioration in the life characteristics.

[0163]

[0164] separator

[0165] 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 ceramic components or polymeric materials may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0166]

[0167] 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.

[0168] 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 a plurality of battery modules are provided.

[0169] According to another embodiment of the present invention, a battery pack is provided comprising a plurality of lithium secondary batteries according to the present invention as unit cells. The battery pack may not include a battery module.

[0170] Additionally, the present invention provides a pack cell assembly.

[0171] According to one embodiment, the battery module may include 10 to 50 unit cells, preferably 16 to 36 unit cells. The battery pack may include 10 to 1,000 unit cells, preferably 10 to 500 unit cells.

[0172] 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.

[0173] 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.

[0174]

[0175] Example 1

[0176] <Cathode manufacturing>

[0177] Positive electrode active material: Positive electrode conductive material: PVDF binder were mixed in a weight ratio of 97: 1: 2 in N-methylpyrrolidone to prepare a positive electrode slurry. At this time, D was used as the positive electrode active material. 50 This 4.0㎛ single particle 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.

[0178] The above cathode slurry was applied on an aluminum current collector sheet, dried, and then rolled to obtain a loading of 4.0 mAh / cm 2 And, a cathode having a porosity of 25% was manufactured.

[0179]

[0180] <Cathode Manufacturing>

[0181] Negative active material: Negative conductive material: Styrene-butadiene rubber (SBR): Carboxymethyl cellulose (CMC) were mixed in a weight ratio of 96: 1: 2: 1 in water to prepare a negative electrode slurry. At this time, graphite was used as the negative active material, and carbon black was used as the negative electrode conductive material.

[0182] The negative electrode slurry was applied on a copper current collector sheet, dried, and rolled to obtain a loading of 4.5 mAh / cm. 2 And, a cathode with a porosity of 30% was manufactured.

[0183]

[0184] <Lithium secondary battery manufacturing>

[0185] 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 so that the amount of electrolyte per unit capacity was 2.0 g / Ah, thereby manufacturing a lithium secondary battery cell. At this time, the electrolyte was manufactured by dissolving a lithium salt (LiPF6 100 wt%) in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7 so as to have a concentration of 1.0 M.

[0186]

[0187] Example 2

[0188] D as a cathode active material 50 This 3.7㎛ single particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]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.

[0189]

[0190] Example 3

[0191] D as a cathode active material 50 This 3.6㎛ single particle Li[Ni 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 100% of O2 was used.

[0192]

[0193] Example 4

[0194] A positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that LiPF6:LiFSI was mixed in a weight ratio of 60:40 as a lithium salt when manufacturing a lithium secondary battery.

[0195]

[0196] Example 5

[0197] A positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 2, except that LiPF6:LiFSI was mixed in a weight ratio of 60:40 as a lithium salt when manufacturing a lithium secondary battery.

[0198]

[0199] Example 6

[0200] A positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 3, except that LiPF6:LiFSI was mixed in a weight ratio of 80:20 as a lithium salt when manufacturing a lithium secondary battery.

[0201]

[0202] Comparative Example 1

[0203] D as a cathode active material 50 This 8.6㎛ 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 manufactured in the same manner as in Example 1, except that 100% of O2 was used.

[0204]

[0205] Comparative Example 2

[0206] D as a cathode active material 50 This 3.6㎛ single particle 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.

[0207]

[0208] Comparative Example 3

[0209] D as a cathode active material 50 This 3.6㎛ single particle Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01]O2 was used at 100% and graphite:SiO was mixed at a weight ratio of 95:5 as the negative electrode active material, and a positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1.

[0210]

[0211] Comparative Example 4

[0212] D as a cathode active material 50 This 3.3㎛ single particle 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 manufactured in the same manner as in Example 1, except that 100% of O2 was used.

[0213]

[0214] Comparative Example 5

[0215] D as a cathode active material 50 This 3.7㎛ single particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 and D 50 This 8.6㎛ secondary particle-shaped Li[Ni 0.80 Co 0.10 Mn 0.10 ]O2 was mixed in a weight ratio of 5:5 and used to manufacture a positive electrode, a negative electrode, and a lithium secondary battery in the same manner as in Example 1.

[0216]

[0217] Comparative Example 6

[0218] D as a cathode active material 50 This 3.6㎛ single particle Li[Ni 0.70 Co 0.10 Mn 0.20 ]O2 and D 50 This 7.8㎛ secondary particle-shaped Li[Ni 0.70 Co 0.10 Mn 0.20]O2 was mixed in a weight ratio of 5:5 and used to manufacture a positive electrode, a negative electrode, and a lithium secondary battery in the same manner as in Example 1.

[0219]

[0220] Comparative Example 7

[0221] D as a cathode active material 50 This 3.6㎛ single particle Li[Ni 0.70 Co 0.10 Mn 0.20 ]O2 and D 50 This 7.8㎛ secondary particle-shaped Li[Ni 0.70 Co 0.10 Mn 0.20 ]O2 was mixed in a weight ratio of 25:75 and used to manufacture a positive electrode, a negative electrode, and a lithium secondary battery in the same manner as in Example 1.

[0222]

[0223] Comparative Example 8

[0224] A positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that graphite:SiO was mixed in a weight ratio of 95:5 as the negative electrode active material.

[0225]

[0226] Comparative Example 9

[0227] A positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 2, except that graphite:SiO was mixed in a weight ratio of 95:5 as the negative electrode active material.

[0228]

[0229] Comparative Example 10

[0230] A positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 3, except that graphite:SiO was mixed in a weight ratio of 95:5 as the negative electrode active material.

[0231]

[0232] Comparative Example 11

[0233] A positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that LiPF6:LiFSI was mixed in a weight ratio of 50:50 as a lithium salt when manufacturing a lithium secondary battery.

[0234]

[0235] Comparative Example 12

[0236] A positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 3, except that LiPF6:LiFSI was mixed in a weight ratio of 70:30 as a lithium salt when manufacturing a lithium secondary battery.

[0237]

[0238] Experimental Example 1

[0239] The discharge capacity (C) of each lithium secondary battery cell manufactured in Examples 1 to 6 and Comparative Examples 1 to 12 was measured by charging and discharging at 0.33C in a voltage range of 2.5 V to 4.35 V. 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 total was calculated as 4C.

[0240] After heating and igniting one lithium secondary battery cell placed at the outermost end of the test module, the time taken from the point when the voltage of the lithium secondary battery placed at the outermost end became 0 until the voltage of all lithium secondary batteries within the test module became 0 was measured. At this time, the voltage of each lithium secondary battery was measured using a data logger.

[0241] The measurement results are shown in [Table 1] and Fig. 1.

[0242] Unit cell capacity C(Ah)Test module capacity (Ah)t (sec)V T(Ah / sec) Example 1 4116454.30 3.02 Example 2 4116453.77 3.05 Example 3 4116451.41 3.19 Example 44116442.38 3.87 Example 5 4116441.88 3.92 Example 6 4116441.56 3.95 Comparative Example 14116433.204.94 Comparative Example 24116435.96 4.56 Comparative Example 34116421.137.76 Comparative Example 44116419.368.47 Comparative Example 5 4116434.97 4.69 Comparative Example 64116440.244.08 Comparative Example Comparative Example 74116439.864.11 Comparative Example 84116438.334.28 Comparative Example 94116437.784.34 Comparative Example 104116436.704.47 Comparative Example 114116439.614.14 Comparative Example 124116439.234.18

[0243] Experimental Example 2

[0244] Each of the lithium secondary battery cells manufactured in Examples 1 to 6 and Comparative Examples 1 to 12 was stacked in groups of 16 to manufacture a battery module. Then, the unit cell positioned at the outermost part of each battery module was heated with a heating device, and the time from the time a flame was generated until the battery module was completely burned was measured.

[0245] Burning Time (sec) Example 1464 Example 2452 Example 3416 Example 4398 Example 5396 Example 6387 Comparative Example 1225 Comparative Example 2268 Comparative Example 3132 Comparative Example 4107 Comparative Example 5240 Comparative Example 6348 Comparative Example 7337 Comparative Example 8314 Comparative Example 9312 Comparative Example 10283 Comparative Example 11332 Comparative Example 12326

[0246] Through the above Table 2, V T A battery module using a lithium secondary battery of Examples 1 to 6 having a capacity of 4 Ah / sec or less as a unit cell is V T It can be confirmed that the time required for combustion is longer than that required for battery modules using lithium secondary batteries of Comparative Examples 1 to 12 exceeding 4 Ah / sec as unit cells, and thus the thermal runaway safety is superior.

Claims

1. A lithium secondary battery comprising a positive electrode including a positive active material; a negative electrode including a negative active material; and an electrolyte. The above lithium secondary battery has a nominal voltage of 3.68 V or higher, After manufacturing a test module by stacking four of the above lithium secondary batteries fully charged to 4.35 V, the V expressed by the following formula (1) was measured. T A lithium secondary battery having a capacity of 4 Ah / sec or less. Equation (1): V T = C total / t In the above equation (1), the C total is the total discharge capacity of the test module, and t is the time taken from the time when the voltage of the lithium secondary battery placed at the outermost end of the test module becomes 0 after heating and igniting one lithium secondary battery placed at the outermost end of the test module until the voltage of all lithium secondary batteries in the test module becomes 0.

2. In paragraph 1, A lithium secondary battery, wherein the positive electrode active material comprises a single particle lithium nickel oxide having a Ni content of 70 mol% or less, in an amount exceeding 50 wt% of the total positive electrode active material.

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

4. In paragraph 2, The above single particle lithium nickel oxide contains 30 or fewer nodules, A lithium secondary battery having an average particle diameter of the above nodules of 0.8 ㎛ to 4.0 ㎛.

5. In paragraph 2, 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], M1 includes 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.

6. In paragraph 2, A lithium secondary battery, wherein the single particle lithium nickel oxide further includes a coating layer on its surface, the coating layer including at least one element selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

7. In paragraph 1, A lithium secondary battery wherein the negative electrode active material is made of a carbon-based negative electrode active material.

8. In paragraph 1, The negative electrode comprises a negative current collector; a first negative active material layer formed on the negative current collector and including a first negative active material; and a second negative active material layer formed on the first negative active material layer and including a second negative active material. A lithium secondary battery wherein the first negative electrode active material and the second negative electrode active material are made of a carbon-based negative electrode active material.

9. In paragraph 8, A lithium secondary battery wherein the first negative electrode active material and the second negative electrode active material are natural graphite, artificial graphite, or a combination thereof.

10. In paragraph 9, A lithium secondary battery, wherein the weight ratio of artificial graphite to the total weight of the negative electrode active material in the second negative electrode active material layer is 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.

11. In paragraph 1, A lithium secondary battery having an electrolyte weight per unit capacity of 1.0 g / Ah to 3.0 g / Ah.

12. In paragraph 1, V expressed by equation (1) T A lithium secondary battery having a capacity of 1 to 4 Ah / sec.

13. In paragraph 1, The above electrolyte comprises an organic solvent and a lithium salt, Content of imide lithium salt among the total weight of the above lithium salt W I A lithium secondary battery satisfying the following equation (2). Equation (2): In the above formula (2), a is the mol% of Ni among the total metal excluding lithium of the positive electrode active material.

14. 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.

15. A battery module comprising a lithium secondary battery according to any one of claims 1 to 14 as a unit cell.

16. In paragraph 15, A battery module comprising 10 to 50 unit cells.

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

18. In paragraph 18, A battery pack comprising 10 to 1,000 unit cells.

19. A battery pack comprising the secondary battery module of claim 15.

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