Lithium-ion 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] This 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 advancement of technologies such as electric vehicles, energy storage systems (ESS), and portable electronic devices, the demand for lithium-ion batteries as an energy source is rapidly increasing.

[0003] In devices requiring large capacities, such as electric vehicles and energy storage systems, batteries are used in the form of modules and / or packs, each containing multiple secondary battery cells. In such battery modules and / or packs, if one secondary battery cell ignites or explodes due to internal or external factors, a phenomenon called thermal runway propagation occurs, where heat, flames, and high-pressure gases propagate to adjacent cells. This can cause a chain reaction of explosions in adjacent cells, posing a significant safety problem.

[0004] On the other hand, in the electric vehicle sector, there is a demand for cells with high energy density to extend the driving range on a single charge. For this reason, in recent years, cells have been developed for lithium secondary batteries for electric vehicles that use high-nickel NCM cathode active material with a nickel content of 80 mol% or more and / or Si-based anode active material, which have excellent capacity characteristics. However, in the case of such cells, there is a problem that they have high explosion pressure during thermal runaway, so thermal runaway propagation occurs rapidly and safety is inferior.

[0005] Conventionally, techniques such as inserting fire-resistant insulation materials into modules have been applied to prevent heat transfer to adjacent cells. However, when fire-resistant insulation materials are inserted into modules, the energy density decreases, which leads to problems such as a reduction in the vehicle's mileage.

[0006] Therefore, there is a need to develop lithium-ion secondary batteries that have high energy density and suppress thermal runaway propagation. [Overview of the project] [Problems that the invention aims to solve]

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

[0008] In one aspect, the present invention relates to a lithium secondary battery comprising 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 3.68V or higher. The following formula (1) represents V, which was measured after fully charging the four lithium secondary batteries to 4.35V, stacking them, and manufacturing a test module. T The present invention provides a lithium secondary battery having a power consumption of 4Ah / sec or less, preferably 1 to 4Ah / sec, and more preferably 2 to 4Ah / sec. Formula (1):V T =C total / t In formula (1) above, C total is the total discharge capacity of the test module, and t is the time it takes from the point when the voltage of the outermost lithium secondary battery in the test module becomes 0 after heating and igniting the outermost lithium secondary battery in the test module until the voltage of all lithium secondary batteries in the test module becomes 0. On the other hand, the total discharge capacity of the test module is the sum of the values ​​obtained by measuring the discharge capacity of each lithium secondary battery in the test module after CC-CV charging and CC discharging at 25°C, 0.33C, and a voltage range of 2.5V to 4.35V.

[0009] Here, the lithium secondary battery in the test module can have a size of 100 mm in width and 300 mm in length.

[0010] Also, the heating of the lithium secondary battery can be performed by attaching a mica heater with a size of 260 mm × 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.

[0011] Here, the positive electrode active material can contain 50% by weight or more, preferably 70% by weight or more, more preferably 90% - 100% of single-particle lithium nickel-based oxide with a Ni content of 70 mol% or less in the total positive electrode active material. More preferably, the positive electrode active material can consist of single-particle lithium nickel-based oxide with a Ni content of 70 mol% or less.

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

[0013] The single-particle lithium nickel-based oxide can 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.

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

[0015] On the other hand, the anode active material can consist of a carbon-based anode 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 containing a first negative electrode active material, and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second negative electrode active material, wherein the first and second negative electrode active materials may consist of carbon-based negative electrode active materials, and the first and second negative electrode active materials may be natural graphite, artificial graphite, or a combination thereof. Preferably, the weight ratio of artificial graphite to the total weight of negative electrode active material in the second negative electrode active material layer may be higher than the weight ratio of artificial graphite to the total weight of negative electrode active material in the first negative electrode active material layer.

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

number

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

[0019] The weight of the electrolyte per unit capacity of the lithium secondary battery can 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 that represents the thermal transition rate. T Because the thermal energy flow rate is low, at 4Ah / sec or less, even if thermal runaway occurs in one unit cell, the transmission of flames and / or heat to adjacent cells is minimal, resulting in excellent thermal runaway safety.

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

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

[0024] Furthermore, because the lithium secondary battery according to the present invention has excellent thermal runaway safety, when manufacturing modules using it, there is no need to use a large amount of fire-resistant insulation material, and a relatively high energy density can be achieved per unit volume.

[0025] The lithium secondary battery according to the present invention can be designed to use a single-particle type positive electrode active material with 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, not only is it excellent in thermal runaway safety due to the low thermal transition rate, but it can also be driven stably at a high voltage of 4.35V or higher, and high capacity can be achieved.

[0026] The lithium secondary battery according to the present invention can 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 met, the explosion pressure during thermal runaway is reduced, further improving thermal runaway safety.

[0027] Furthermore, the lithium secondary battery according to the present invention minimizes 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 drawing]

[0028] [Figure 1] This is a scanning electron microscope image of a single-particle cathode active material. [Figure 2] This is a scanning electron microscope image of a pseudo-single-particle cathode active material. [Figure 3] This is a scanning electron microscope image of a secondary particle cathode active material. [Modes for carrying out the invention]

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

[0030] The terms and words used herein and in the claims should not be interpreted in a manner limited to their general or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0031] In this invention, "single-particle type" refers to a particle consisting of 30 or fewer nodules, and is a concept that includes single particles consisting of one nodule and pseudo-single particles which are composites of 2 to 30 nodules. Figure 1 shows a scanning electron microscope image of a positive electrode active material in single-particle form, and Figure 2 shows a scanning electron microscope image of a positive electrode active material in pseudo-single-particle form.

[0032] The aforementioned "nodule" is a subparticle unit that constitutes a single particle or a pseudo-single particle, and can be a single crystal without crystalline grain boundaries, or a polycrystalline material in which no grain boundaries appear to exist when observed with a scanning electron microscope at a field of view of 5,000 to 20,000 times magnification.

[0033] In this invention, "secondary particles" refer to particles formed by the aggregation of multiple primary particles, for example, tens to hundreds of primary particles. Specifically, secondary particles can be aggregates of 50 or more primary particles. Figure 3 shows a scanning electron microscope (SEM) image of a positive electrode active material in secondary particle form.

[0034] In this invention, "particle" is a concept that includes one or all of the following: single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

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

[0036] In this invention, "average particle size D 50 "50% of the volume of the cumulative particle size distribution of the powder being measured" refers to the particle size corresponding to 50% of the cumulative volume, 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 introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and after irradiating it with ultrasound at approximately 28 kHz with an output of 60 W to obtain a volume cumulative particle size distribution graph, the particle size corresponding to 50% of the cumulative volume can be determined to measure it.

[0037] In this invention, "loading amount (mAh / cm²)" 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 is measured for the punched-out electrode, 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 of electrode per unit area W1 - Weight of electrode current collector per unit area W2) / 2

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

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

[0042] The inventors of this invention have diligently conducted research to develop a lithium secondary battery with high energy density and superior safety. As a result, they have discovered that when a lithium secondary battery is designed to satisfy specific conditions, the thermal transition rate measured in a test module manufactured by stacking four fully charged lithium secondary batteries can minimize the propagation of thermal runaway to adjacent cells even if thermal runaway occurs in a unit cell in the module and / or pack state, thereby achieving high energy density. This led to the completion of the present invention.

[0043] Specifically, the lithium secondary battery according to the present invention is a lithium secondary battery comprising 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 3.68V or higher, and the V expressed by the following formula (1) was measured after manufacturing a test module by stacking four of the lithium secondary batteries that had been fully charged to 4.35V. T The current rate is 4Ah / sec or less, preferably 1Ah / sec to 4Ah / sec, and more preferably 2Ah / sec to 4Ah / sec.

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

[0045] In formula (1) above, C total is the total discharge capacity of the test module, and t is the time it takes from the point when the voltage of the outermost lithium secondary battery in the test module becomes 0 after heating and igniting the outermost lithium secondary battery in the test module until the voltage of all lithium secondary batteries in the test module becomes 0.

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

[0047] On the other hand, the total discharge capacity of the test module is the sum of the values ​​obtained by charging and discharging each lithium secondary battery in the test module at 25°C, 0.33C, and a voltage range of 2.5V to 4.35V, and measuring their discharge capacities.

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

[0049] Here, the lithium secondary battery in the test module may have dimensions of 100 mm in width and 300 mm in height.

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

[0051] According to the inventors' research, as described above, V measured by manufacturing a test module T When manufacturing battery modules and battery packs using lithium secondary batteries designed to have a thermal runaway rate of 4 Ah / sec or less, it has been found that the rate at which heat and / or flame propagates to adjacent cells is significantly reduced, and even if thermal runaway occurs in one unit cell, the occurrence of a chain reaction fire and / or explosion can be suppressed to the greatest extent possible.

[0052] On the other hand, V T This is affected by the discharge capacity of the lithium secondary battery, the design of the positive electrode (e.g., type of positive electrode active material, composition of the positive electrode, and loading amount), the design of the negative electrode (e.g., type of negative electrode active material, composition of the negative electrode, and loading amount), and / or the design of the electrolyte (e.g., electrolyte content, type and content of lithium salts, type of additives, etc.). For example, if the content of positive electrode active material with a high nickel content increases in the positive electrode, or if the negative electrode contains Si-based negative electrode active material, V T V increases. Also, if the capacity of the lithium secondary battery increases or the amount of electrolyte in the lithium secondary battery increases, V will increase. T Therefore, when designing lithium secondary batteries, these factors should be appropriately adjusted to achieve the desired V T It is possible to manufacture lithium secondary batteries that have a value.

[0053] On the other hand, the nominal voltage of the lithium secondary battery can be 3.68V or higher, preferably 3.68V to 3.80V, and more preferably 3.69V to 3.75V. 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 results in increased energy density. The nominal voltage of a conventional lithium secondary battery using lithium nickel cobalt manganese oxide as the positive electrode active material was around 3.6V, but in the present invention, a high energy density can be achieved by increasing the charge cut-off voltage to make the nominal voltage 3.68V or higher. Specifically, the lithium secondary battery according to the present invention can have an energy density of 500Wh / L or higher, preferably 500Wh / L to 800Wh / L.

[0054] Preferably, the charge cut-off voltage (full charge voltage) of the lithium secondary battery is 4.35V or higher, preferably 4.35V to 5V, and more preferably 4.35V to 4.5V. When the charge cut-off voltage satisfies the above range, the capacity of the active material increases, the nominal voltage increases, and a 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 charging and discharging, leading to a rapid collapse of the positive electrode active material structure and a rapid deterioration of its lifespan characteristics. This problem is more pronounced in high-nickel lithium nickel cobalt manganese oxides with a high nickel content. Therefore, conventionally, when lithium nickel cobalt manganese oxide is used as the positive electrode active material, the charge cut-off voltage has generally been around 4.3V. However, in this invention, by applying a lithium nickel-based oxide having a Ni content of 70 mol% or less and having a single-particle form as the positive electrode active material, excellent life characteristics can be maintained even when the charge cut-off voltage is 4.35V or higher.

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

[0056] The components of the lithium secondary battery according to the present invention will be described in more detail below.

[0057] positive electrode The lithium secondary battery according to the present invention includes a positive electrode containing 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, and the positive electrode active material layer contains a 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 with surface treatments such as carbon, nickel, titanium, or silver can be used. The positive electrode current collector can also typically have 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 adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0059] On the other hand, 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%.

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

[0061] In the case of lithium nickel oxides in secondary particle form, where more than 30 to several hundred primary particles aggregate, the large contact area with the electrolyte leads to many side reactions with the electrolyte, and gas is generated during these side reaction processes. Under high temperature and / or high voltage conditions, the amount of gas generated increases significantly, and if a large amount of gas is contained inside the lithium secondary battery, the explosion pressure increases during thermal runaway, and the greater the explosion pressure, the faster the heat and flame propagate to adjacent cells. In contrast, single-particle lithium nickel oxides have fewer nodules constituting the particles, resulting in fewer interfaces within the particles and a smaller contact area with the electrolyte. Compared to secondary particles, there are fewer side reactions with the electrolyte, and consequently, the amount of gas generated is significantly less. Therefore, when single-particle lithium nickel oxides are used as positive electrode active materials, the explosion pressure decreases during thermal runaway, and the thermal transition rate also decreases. However, even when single-particle lithium nickel oxides are used, if the nickel content in the lithium nickel oxide is high, the reduction in gas generation is small, and this reduces the effect of reducing explosion pressure and thermal transition rate during thermal runaway.

[0062] Furthermore, in the case of single-particle lithium nickel oxides with a relatively low nickel content, the structural stability at high voltages is higher compared to lithium nickel oxides with a high nickel content or those with a secondary particle form, thus minimizing the degradation of life characteristics when driven at high voltages. Specifically, the higher the nickel content in the lithium nickel oxide, the more reactive the Ni... +4The increased ion content reduces the structural stability of the positive electrode active material during charging and discharging, leading to rapid degradation of the positive electrode. This phenomenon worsens under high-voltage operation. Therefore, in this 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 degradation of the active material under 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 around 50 mol% to 70 mol%.

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

[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 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. 1 When elements are included, the structural stability of lithium nickel oxide particles is improved, and better life characteristics can be achieved when driven at high voltage. Preferably, the M 1 The elements may include one or more selected from the group consisting of Ti, Mg, Al, Zr, and Y, and more preferably two or more selected from the group consisting of Ti, Mg, Al, Zr, and Y.

[0066] The aforementioned 1+x represents the lithium molar ratio within the lithium nickel oxide and can 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 crystalline structure can be formed.

[0067] The above-mentioned 'a' represents the molar ratio of nickel among all metals other than lithium in the lithium nickel oxide, and can 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 driven stably at high voltage, achieve high capacity, reduce explosion pressure during thermal runaway, and have excellent thermal runaway safety.

[0068] The above b represents the molar ratio of cobalt among all metals other than lithium in the lithium nickel oxide, and 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 aforementioned c represents the molar ratio of manganese among all metals other than lithium in the lithium nickel oxide, and 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 above d is M, which is the total metal other than lithium in the lithium nickel oxide. 1 This indicates the molar ratio of elements, where 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 aforementioned range, the structural stability and capacity of the positive electrode active material can all be excellent.

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

[0072] When a coating layer is present on the surface of a lithium nickel oxide, the coating layer suppresses contact between the electrolyte and the lithium nickel oxide, thereby reducing the elution of transition metals and the generation of gases due to side reactions with the electrolyte, and thus further improving safety during thermal runaway. Preferably, the coating layer may contain 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, it may contain 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 oxide preferably contains 30 or fewer nodules, preferably 1 to 25, and more preferably 1 to 15. This is because if the number of nodules constituting the lithium nickel oxide exceeds 30, particle cracking increases during electrode manufacturing, and the occurrence of internal cracks due to volume expansion / contraction of nodules increases during charging and discharging, which can reduce the improvement effect on high-temperature lifetime characteristics and high-temperature storage characteristics.

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

[0075] On the other hand, the D of the lithium nickel oxide 50 The particle size can be 2.0 μm to 10.0 μm, preferably 2.0 μm to 8.0 μm. More preferably, it is about 3.0 μm to 7.0 μm. D of lithium nickel oxide 50If it is too small, the processability during electrode manufacturing will decrease, electrolyte impregnation will decrease, and electrochemical properties may increase. 50 If the value is too large, the resistance increases, which leads to a decrease in output characteristics.

[0076] On the other hand, the single-particle lithium nickel oxide having a nickel content of 70 mol% or less may be present in the positive electrode active material layer in an amount of more than 50% by weight, preferably 55% by weight or more, more preferably 60% by weight or more, even more preferably 70% by weight or more, and even more preferably 100% by weight of the total positive electrode active material. When the ratio of the single-particle lithium nickel 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 observed.

[0077] The positive electrode active material layer may contain a portion of a positive electrode active material other than single-particle lithium nickel oxide with a nickel content of 70 mol% or less, i.e., lithium nickel oxide in secondary particle form and / or single-particle lithium nickel oxide with a nickel content exceeding 70 mol%. However, if the proportion of secondary particles and / or lithium nickel oxide with a nickel content exceeding 70 mol% exceeds 50% by weight of the total positive electrode active material, the improvement in thermal runaway safety is minimal and undesirable.

[0078] On the other hand, the positive electrode active material can be included in an amount of 80% to 98% by weight, preferably 90% to 98% by weight, and more preferably 93% to 98% by weight, relative to the total weight of the positive electrode active material layer. When the content of the positive electrode active material satisfies the above range, an 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 particular limitations as long as it does not cause chemical changes and has electronic conductivity in the battery that is constructed. 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, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers 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. Of these, one or more can be used.

[0080] The positive electrode conductive material can typically be included 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, relative to the total weight of the positive electrode active material layer.

[0081] Next, the positive electrode binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used.

[0082] The positive electrode binder may be present in an amount of 1% to 10% by weight, preferably 1% to 8% by weight, and more preferably 1% to 5% by weight, relative to 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 produce a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling it; or by casting the positive electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto the positive electrode current collector.

[0084] On the other hand, as the solvent for the positive electrode slurry, solvents commonly used in the art can be used, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water, which can be used individually or in combination of two or more. The amount of solvent used should be such that it dissolves or disperses the positive electrode active material, conductive material, and binder, and has a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness and manufacturing yield of the slurry.

[0085] On the other hand, the loading amount of the positive electrode according to the present invention is 0.5 mAh / cm². 2 ~10mAh / cm 2 Preferably 2mAh / cm² 2 ~8mAh / cm 2 , more preferably 2.5 mAh / cm² 2 ~6mAh / cm 2 This is possible. When the positive electrode loading amount satisfies the above range, thermal runaway safety and capacity characteristics are further improved.

[0086] Furthermore, the positive electrode can have a porosity of 10% to 50%, preferably 15% to 45%, and more preferably 15% to 30%. When the positive electrode porosity satisfies the above range, the electrolyte impregnation is improved, and even better capacity characteristics can be achieved.

[0087] negative electrode The lithium secondary battery according to the present invention includes a negative electrode containing 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, and the negative electrode active material layer contains a 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 with surface treatments such as carbon, nickel, titanium, or silver, and aluminum-cadmium alloys can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in various forms such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0089] On the other hand, the negative electrode active material may consist of 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 contain natural graphite and artificial graphite, in which case the weight ratio of natural graphite to artificial graphite may be 1:9 to 9:1, preferably 2:8 to 8:2.

[0090] In recent years, in order to achieve high capacity, there has been a tendency to use Si-based negative electrode active materials such as SiO, Si, and Si-C composites, which have high theoretical capacity, as negative electrode active materials. However, according to the inventors' research, it has been found that when Si-based negative electrode active materials are included, the explosion pressure increases during thermal runaway, which accelerates 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 contain Si-based negative electrode active materials as the negative electrode active material.

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

[0092] The negative electrode active material can be included in an amount of 80% to 98% by weight, preferably 90% to 98% by weight, and more preferably 93% to 98% by weight, relative to the total weight of the negative electrode active material layer. When the content of the negative electrode active material satisfies the above range, an excellent energy density can be achieved.

[0093] Next, the negative electrode conductive material is used to impart conductivity to the negative electrode and can be used without particular limitations in the battery it is constructed from, as long as it does not cause chemical changes and has electronic conductivity. 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, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers 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. One of these alone or a mixture of two or more can be used.

[0094] The negative electrode conductive material can typically be included 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 plays a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, of which one or more may be used.

[0096] The negative electrode binder may be present in an amount of 1% to 10% by weight, preferably 1% to 8% by weight, and more preferably 1% to 5% by weight, relative to the total weight of the negative electrode active material layer.

[0097] On the other hand, in the lithium secondary battery according to the present invention, the negative electrode active material layer may be a single-layer structure or a multilayer 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 the negative electrode current collector and containing a first negative electrode active material, and a second negative electrode active material layer formed on the first negative electrode active material layer and containing a second negative electrode active material. Here, the first negative electrode active material and the second negative electrode active material may consist of carbon-based negative electrode active materials, such as natural graphite, artificial graphite, or a combination thereof.

[0098] On the other hand, if the negative electrode active material layer has a multilayer structure composed of two or more layers, the type and / or content of the negative electrode active material, binder, and / or conductive material may differ 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 made 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, the performance characteristics of the battery can be improved by forming the negative electrode active material layer in a multilayer structure and varying the composition of each layer. For example, if the proportion of natural graphite is increased in the first negative electrode active material layer and the proportion of synthetic graphite is increased in the second negative electrode active material layer, the effect of reducing explosion pressure during thermal runaway can be further improved.

[0102] The negative electrode can be manufactured by 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 produce a negative electrode slurry, applying the negative electrode slurry onto a negative electrode current collector, and then drying and rolling it; or by casting the negative electrode slurry onto another support, peeling it off the support, and laminating the resulting film onto a negative electrode current collector.

[0103] On the other hand, as the solvent for the negative electrode slurry, solvents commonly used in the art can be used, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, and water, either individually or in combination of two or more. The amount of solvent used should be such that it dissolves or disperses the negative electrode active material, conductive material, and binder, and has a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness and manufacturing yield of the slurry.

[0104] On the other hand, the loading amount of the negative electrode according to the present invention is 0.5 mAh / cm². 2 ~10mAh / cm 2 Preferably 2mAh / cm² 2 ~8mAh / cm 2 , more preferably 2.5 mAh / cm² 2 ~6.5mAh / cm 2 This is possible. When the negative electrode loading amount satisfies the above range, thermal runaway safety and capacity characteristics are further improved.

[0105] Furthermore, the negative electrode can 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 aforementioned organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned organic solvents 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; dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group of C2-C20, and may include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0108] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, without any particular limitations. Specifically, the lithium salt may include one or more selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2(LiFSI), LiCl, LiI, or LiB(C2O4)2. Preferably, the lithium salt may include phosphate-based lithium salts such as LiPF6, imide-based lithium salts such as LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, or combinations 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 of the imide-based lithium salt in the total weight of the lithium salt W I It is preferable that the following equation (2) is satisfied.

[0109] Formula (2):

number

[0110] In formula (2) above, a is the mole percent of Ni among 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 Ni content a in the positive electrode active material and the imide-based lithium salt content in the electrolyte satisfy the conditions of formula (2), the thermal runaway transition to adjacent cells can be minimized in the event of ignition or thermal runaway.

[0112] On the other hand, the concentration of the lithium salt is preferably within the range of 0.1 M to 3.0 M, more 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 falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0113] The electrolyte may further contain additives in addition to the constituent components of the electrolyte, for the purpose of improving the battery's lifespan characteristics, suppressing the decrease in battery capacity, and improving the battery's discharge capacity. 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 bisoxalate borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium difluorobisoxalate phosphate (LiDFBP), and lithium tetrafluorooxalate phosphate (LiTF). The following can be used individually or in combination, but are not limited to: OP), lithium methyl sulfate (LiMS), lithium ethyl sulfate (LiES), propanesultone (PS), propensultone (PRS), succinonitrile (SN), adiponitrile (AND), 1,3,6-hexanetricarbonite (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), ethyldi(pro-2-i-1-nyl)phosphate (EDP), 5-methyl-5-propargyloxylcarbonyl-1,3-dioxan-2-one (MPOD), etc. The additives can be present in an amount of 0.1% to 10% by weight, preferably 0.1% to 5% by weight, relative to the total weight of the electrolyte.

[0114] On the other hand, the electrolyte can be contained 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 high, during thermal runaway, the electrolyte acts as fuel, increasing the explosion pressure, which can cause a rapid thermal transition. On the other hand, if the amount of electrolyte per unit capacity is too low, the electrolyte is consumed quickly during the activation and battery operation processes, which can reduce the lifespan characteristics.

[0115] Separator 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 in lithium secondary batteries can be used without particular limitations, and those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as porous polymer films made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

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

[0117] According to another embodiment of the present invention, 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 are provided.

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

[0119] Furthermore, the present invention provides a pack cell assembly.

[0120] According to one embodiment, the battery module may contain 10 to 50, preferably 16 to 36, unit cells. The battery pack may contain 10 to 1,000, preferably 10 to 500, unit cells.

[0121] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0122] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0123] Example 1 <Manufacturing of positive electrodes> A positive electrode slurry was prepared by mixing positive electrode active material, positive electrode conductive material, and PVDF binder in a weight ratio of 97:1:2 in N-methylpyrrolidone. Here, D was used as the positive electrode active material. 50 Single-particle Li[Ni 0.56 Co 0.12 Mn 0.32 100% O2 was used, and carbon nanotubes were used as the positive electrode conductive material.

[0124] The positive electrode slurry is applied to an aluminum current collector sheet, dried, and then rolled to produce a load of 4.0 mAh / cm². 2 Therefore, a positive electrode with a porosity of 25% was manufactured.

[0125] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by mixing negative electrode active material, negative electrode conductive material, styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in water in a weight ratio of 96:1:2:1. Here, graphite was used as the negative electrode active material, and carbon black was used as the negative electrode conductive material.

[0126] The negative electrode slurry was applied to a copper current collector sheet, dried, and then rolled, resulting in a loading volume of 4.5 mAh / cm². 2 Therefore, a negative electrode with a porosity of 30% was manufactured.

[0127] <Manufacturing of lithium-ion secondary batteries> An electrode assembly was manufactured by interposing a separator between the positive electrode and negative electrode manufactured as described above. After inserting the electrode assembly into a battery case, electrolyte was injected so that the amount of electrolyte per unit volume was 2.0 g / Ah to manufacture a lithium secondary battery cell. Here, the electrolyte used was prepared 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 to a concentration of 1.0 M.

[0128] Example 2 As the positive electrode active material, D 50 The single-particle Li[Ni 0.60 Co 0.10 Mn 0.30 The positive electrode, negative electrode, and lithium secondary battery were manufactured 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 Li[Ni 0.70 Co 0.10 Mn 0.20 The positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1, except that 100% O2 was used.

[0130] Example 4 The positive electrode, negative electrode, and 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 60:40 was used as the lithium salt during the manufacturing of the lithium secondary battery.

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

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

[0133] Comparative Example 1 As the positive electrode active material, except that D 50 is 8.6 μm secondary particle type Li[Ni 0.85 Co 0.06 Mn 0.08 Al 0.01 O2 was used at 100%, the positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1.

[0134] Comparative Example 2 As the positive electrode active material, except that D 50 is 3.6 μm single particle type Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 was used at 100%, the positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1.

[0135] Comparative Example 3 As the positive electrode active material, except that D 50 is 3.6 μm single particle type Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 O2 was used at 100%, and as the negative electrode active material, except that graphite:SiO was used by mixing at a weight ratio of 95:5, the positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1.

[0136] Comparative Example 4 As the positive electrode active material, except that D 50 is 3.3 μm single particle type Li[Ni [[ID=As the positive electrode active material, D 50 is a single-particle type Li[Ni 0.60 Co 0.10 Mn 0.30 O2 with D 50 is a secondary particle form of Li[Ni 0.80 Co 0.10 Mn 0.10 O2 with a weight ratio of 5:5 were mixed and used. Except for this, the positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1.

[0138] Comparative Example 6 [[ID=__]]As the positive electrode active material, D 50 is a single-particle type Li[Ni 0.70 Co 0.10 Mn 0.20 O2 with D 50 is a secondary particle form of Li[Ni 0.70 Co 0.10 Mn 0.20 O2 with a weight ratio of 5:5 were mixed and used. Except for this, the positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1.

[0139] Comparative Example 7 As the positive electrode active material, D 50 is a single-particle type Li[Ni 0.70 Co 0.10 Mn 0.20 O2 and, D 50 is a secondary particle form of Li[Ni 0.70 Co 0.10 Mn<00001l4O2 with a weight ratio of 25:75 were mixed and used. Except for this, the positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1. [[ID=6!]]

[0140] Comparative Example 8 As the negative electrode active material, graphite:SiO were mixed and used with a weight ratio of 95:5. Except for this, the positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 1.

[0141] Comparative Example 9<0000`605>The positive electrode, negative electrode, and lithium secondary battery were manufactured in the same manner as in Example 2, except that graphite:SiO was used as the negative electrode active material in a weight ratio of 95:5.

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

[0143] Comparative Example 11 The positive electrode, negative electrode, and 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 during the manufacturing of the lithium secondary battery.

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

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

[0146] After heating and igniting one lithium secondary battery cell located on the outermost part of the test module, the time taken from the point when the voltage of the outermost lithium secondary battery became 0 until the voltage of all lithium secondary batteries in the test module became 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 Sixteen lithium secondary battery cells, each manufactured in Examples 1-6 and Comparative Examples 1-12, were stacked to produce battery modules. Subsequently, the outermost unit cell of each battery module was heated using a heating device, and the time from when a flame appeared until the battery module was completely burned was measured.

[0150] [Table 2]

[0151] Refer to Table 2 above, V T A battery module using lithium secondary batteries from Examples 1 to 6, where the current rate is 4Ah / sec or less, as the unit cell, has a V T Compared to battery modules using lithium secondary batteries with a capacitance exceeding 4Ah / sec as the unit cell (Comparative Examples 1-12), the time required for complete combustion is longer, confirming superior thermal runaway safety.

Claims

1. A lithium secondary battery comprising 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 aforementioned lithium secondary battery is 3.68V or higher. The positive electrode active material contains more than 50% by weight of single-particle lithium nickel oxide, in which the Ni content among all metals other than lithium is 50 mol% to 70 mol%, The V represented by the following formula (1) was measured after manufacturing a test module by stacking four of the aforementioned lithium secondary batteries, which had been fully charged to 4.35V. Ｔ A lithium secondary battery with a capacitance of 4Ah / sec or less. Equation (1): V Ｔ =C ｔｏｔａｌ / t In formula (1) above, C ｔｏｔａｌ θ is the total discharge capacity of the test module, and t is the time it takes from the point when the voltage of the outermost lithium secondary battery in the test module becomes 0 after heating and igniting the outermost lithium secondary battery in the test module until the voltage of all lithium secondary batteries in the test module becomes 0.

2. The lithium secondary battery according to claim 1, wherein the positive electrode active material consists of a single-particle lithium nickel oxide in which the Ni content of all metals other than lithium is 50 mol% to 70 mol%.

3. The aforementioned single-particle lithium nickel oxide contains 30 or fewer nodules. The lithium secondary battery according to claim 1, wherein the average particle size of the nodule is 0.8 μm to 4.0 μm.

4. The lithium secondary battery according to claim 1, 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 Mn ｃ M １ ｄ ]O ２ In the above [Chemical Formula 1], M １ It 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 satisfies -0.1 ≤ x ≤ 0.1, 0.5 ≤ a ≤ 0.7, 0 < b < 0.5, 0 < c < 0.5, and 0 ≤ d ≤ 0.

2.

5. The lithium secondary battery according to claim 1, wherein the single-particle lithium nickel oxide further comprises a coating layer on its surface containing one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo.

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

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

8. The lithium secondary battery according to claim 7, wherein the first negative electrode active material and the second negative electrode active material are natural graphite, artificial graphite, or a combination thereof.

9. The lithium secondary battery according to claim 8, 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.

10. 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.

11. V represented by equation (1) Ｔ The lithium secondary battery according to claim 1, wherein the capacitance is 1 Ah / sec to 4 Ah / sec.

12. The electrolyte comprises an organic solvent and a lithium salt. Content W of imide-based lithium salt in the total weight of the aforementioned lithium salt Ｉ However, the lithium secondary battery according to claim 1 satisfies the following formula (2). Formula (2): [Math 1] In formula (2) above, a is the mole percent of Ni among all metals other than lithium in the positive electrode active material.

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

14. The lithium secondary battery according to claim 4, wherein in the above [Chemical Formula 1], 0.55 ≤ a ≤ 0.

65.

15. In formula (2) above, W Ｉ The lithium secondary battery according to claim 12, wherein is greater than 0.

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

17. The battery module according to claim 16, wherein the battery module includes 10 to 50 unit cells.

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

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

20. A battery pack comprising the battery module described in claim 16.

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