Lithium-ion battery

Abstract

本発明は、熱暴走時安全性が向上したリチウム二次電池に関し、正極活物質を含む正極と、負極活物質を含む負極と、電解質とを含み、公称電圧が3.68V以上であり、下記式(1)で表されるVPが4mbar·Ah-1·sec-1以下であるリチウム二次電池に関する。式(1):VP=ΔP / (tmax×C)前記式(1)中、前記ΔPは、前記リチウム二次電池を4.35Vまで充電した後、不活性雰囲気のチャンバ内に配置し、前記リチウム二次電池を加熱して爆発させた後、測定したチャンバ内の最大圧力Pmaxとチャンバの初期圧力P0との差であり、前記tmaxは、前記Pmaxに逹するのにかかる時間であり、前記Cは、前記リチウム二次電池を25℃で0.33Cで2.5V~4.35Vの電圧範囲で、CC-CV充電およびCC放電して測定した放電容量である。

Description

[Technical Field]

[0001] This invention relates to lithium secondary batteries, and more particularly to thermal runaway of Regarding lithium-ion batteries with improved safety. [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] For devices requiring large capacities, such as electric vehicles and energy storage devices, modules and / or packs consisting of multiple secondary battery cells are used. battery This is being used. battery In a module and / or pack, if one secondary battery cell ignites or explodes due to internal or external factors, a thermal runway propagation phenomenon occurs, where heat, flames, and high-pressure gases propagate to other 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 need for cells with high energy density to extend the driving range on a single charge. Therefore, recent years For lithium secondary batteries used in electric vehicles, cells have been developed that utilize high-nickel NCM positive electrode active material with a nickel content of 80 mol% or more and / or Si-based negative electrode active material, which offer excellent capacity characteristics. However, such cells have a problem in that they have high explosion pressure during thermal runaway, leading to rapid thermal runaway propagation and inferior safety.

[0005] Conventionally, in order to prevent heat transfer to adjacent cells, techniques such as inserting a refractory heat insulating material into a module or a pack have been applied. However, when a refractory heat insulating material is inserted into a module or a pack, there are problems such as a decrease in energy density, which in turn leads to a decrease in the driving range of the vehicle.

[0006] Therefore, there is a need to develop a lithium secondary battery that has a high energy density and suppresses thermal runaway propagation.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention is for solving the above problems, and aims to provide a lithium secondary battery in which thermal runaway propagation is suppressed because the explosion pressure is small during thermal runaway, which can be stably driven at a high voltage and can achieve a high energy density.

Means for Solving the Problems

[0008] In one aspect, the present invention is a lithium secondary battery including a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, and an electrolyte, wherein the lithium secondary battery has a nominal voltage of 3.68 V or more, and V represented by the following formula (1) P is 4 mbar·Ah -1 ·sec -1 or less, preferably 1 to 4 mbar·Ah -1 ·sec -1 , more preferably 2 to 4 mbar·Ah -1 ·sec -1 and provides a lithium secondary battery. 、 Formula (1): V =ΔP / (t P ×C) max In the formula (1), the ΔP is the maximum pressure P in the chamber measured after charging the lithium secondary battery to 4.35 V and then placing it in a chamber in an inert atmosphere and heating and exploding the lithium secondary battery and to the max and、 This is the difference from the initial pressure P0 of the chamber, and the aforementioned t max P max to reach This is the time required to do so, and C is the time required to heat the lithium secondary battery at 25°C 、 0.33C 、 Voltage range of 2.5V to 4.35V C This is the discharge capacity measured by C-CV charging and CC discharge. Here, CC means constant current and CV means constant voltage.

[0009] Here, the chamber may be equipped with a pressure sensor, which can measure pressure changes inside the chamber. The volume of the chamber may be 100L to 140L, and the inert atmosphere may be, for example, a nitrogen atmosphere.

[0010] Furthermore, the lithium secondary battery is heated by a 260mm x 90mm mica heater connected to a PID controller (Proportional-Integral-Derivative controller) that heats the lithium secondary battery. attachment This can be done by heating with a power output of 300W.

[0011] According to one embodiment, the chamber may be equipped with a pressure sensor, which can measure pressure changes inside the chamber. The volume of the chamber is 100 L, the inert gas is nitrogen, and the lithium secondary battery is heated by a 260 mm x 90 mm mica heater connected to a PID controller (Proportional-Integral-Derivative controller). Installed Alternatively, this can be done by heating with a 300W output.

[0012] On the other hand, the lithium secondary battery may have, for example, an overall width of 50 mm to 300 mm, an overall length of 50 mm to 1,000 mm, and a thickness of 2 mm to 40 mm, preferably an overall width of 50 mm to 200 mm, an overall length of 100 mm to 800 mm, and a thickness of 2 mm to 30 mm, more preferably an overall width of 50 mm to 200 mm, an overall length of 200 mm to 500 mm, and a thickness of 5 mm to 15 mm, but is not limited thereto. According to one embodiment, the lithium secondary battery may have an overall width of 100 mm, an overall length of 300 mm, and a thickness of 8.5 mm. P This is per 1Ah of the discharge capacity of a lithium secondary battery. of This indicates the rate of change in explosion pressure, depending on the dimensions of the lithium secondary battery. That's strange It's not something that transforms.

[0013] The aforementioned V P This refers to the capacity of lithium secondary batteries and the explosion pressure. 、 and explosion speed degree This is a relational expression. The unit cell is V within the specified range. P By designing to satisfy this condition, the propagation of flame and / or heat to adjacent cells during thermal runaway can be minimized, thereby suppressing the thermal runaway transition.

[0014] Here, the positive electrode active material is a material other than lithium. All Gold Single-particle lithium nickel oxide having a Ni content of 70 mol% or less relative to the genus. , positive extremely active material whole It may contain 50% by weight or more, preferably 70% by weight or more, and more preferably 90% to 100% by weight of the positive electrode active material. Even more preferably, the positive electrode active material may contain a material other than lithium. All Gold Among the genera of It can consist solely of single-particle lithium nickel oxide with a Ni content of 70 mol% or less.

[0015] The aforementioned single-particle lithium nickel oxide contains 30 or fewer nodules, and the average particle size of the nodules is... teeth The particle size can be between 0.8 μm and 4.0 μm.

[0016] The aforementioned single-particle lithium nickel 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 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 -0.1 ≤ x ≤ 0.1, 0.5 ≤ a ≤ 0.7, 0 <b<0.5、0<c<0.5、0≦d≦0.2である。

[0017] 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.

[0018] On the other hand, the negative electrode active material can consist of a carbon-based negative electrode active material.

[0019] 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 negative electrode active material and the second negative electrode active material may be carbon-based negative electrode active materials, and the first negative electrode active material and the second negative electrode active material may be natural graphite or artificial graphite. 、 Or it may be a combination of these. Preferably, the weight ratio of artificial graphite to the total weight of the negative electrode active material in the second negative electrode active material layer. teeth , 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 No need .

[0020] The electrolyte may include an organic solvent and a lithium salt. , Tium salts whole among of Content of imide-based lithium salts WI The following equation (2) can be satisfied. Formula (2):

number

[0021] Electrolytes Tari Tium salts whole Of these, the content of imide-based lithium salts such as LiN(CF3SO2)2 is W I If the above range is met, adjacent cells during thermal runaway to The propagation of flames and / or heat can be minimized.

[0022] Weight of electrolyte per unit capacity of the lithium secondary battery teeth, It can be between 1.0g / Ah and 3.0g / Ah.

[0023] The aforementioned lithium secondary battery of Charging cutoff voltage teeth The voltage can be 4.35V or higher, preferably 4.35V to 5V, and more preferably 4.35V to 4.5V. [Effects of the Invention]

[0024] The lithium secondary battery according to the present invention, when fully charged and experiencing thermal runaway, has a low explosion pressure, so even if an explosion occurs in one unit cell, the explosion will not affect adjacent cells. to It exhibits minimal flame and / or heat propagation, resulting in superior thermal runaway safety.

[0025] 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.

[0026] 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.

[0027] Furthermore, because the lithium secondary battery according to the present invention has excellent thermal runaway safety, when using the lithium secondary battery as a unit cell to manufacture a module or pack, 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.

[0028] The lithium secondary battery according to the present invention can be designed to use a single-particle type positive electrode active material in which the nickel content is 70 mol% or less, preferably 50 to 70 mol%, relative to the total number of moles of metals other than lithium, 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 the explosion pressure reduced during thermal runaway, resulting in excellent thermal runaway safety, but it can also be stably driven at a high voltage of 4.35V or higher, enabling high capacity.

[0029] 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.

[0030] Furthermore, the lithium secondary battery according to the present invention adjusts the content of imide-based lithium salt in the electrolyte according to the Ni content of the positive electrode active material, thereby preventing thermal transfer to adjacent cells during thermal runaway. of Make it possible to minimize it doing . [Brief explanation of the drawing]

[0031] [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]

[0032] The present invention will be described in more detail below.

[0033] Terms and words used in this specification and in the claims are, general It should not be interpreted in a way that is limited to its literal or dictionary meaning, and the inventors is In accordance with the principle that terms can be appropriately defined to best describe the invention, the terms should be interpreted to have meanings and concepts consistent with the technical idea of ​​this invention.

[0034] In this invention, "single particle type" and This 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 cathode active material in single particle form, and Figure 2 shows a scanning electron microscope image of a cathode active material in pseudo-single particle form.

[0035] The aforementioned "nodule" constitutes a single particle and a pseudo-single particle. Sub It is a single crystal that is a particle unit and does not have a crystalline grain boundary, or 、 Using a scanning electron microscope te5 When observed at a field of view of 000x to 20000x, it can be determined that the material is a polycrystalline material in which no grain boundaries appear to exist in appearance.

[0036] In this invention, "secondary particles" and This refers 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 cathode active material in secondary particle form.

[0037] In this invention, "particle" refers to a single particle, a pseudo-single particle, a primary particle, or a nodule. 、 This concept includes one or all of the following: and secondary particles.

[0038] In the present invention, the average particle size (D) of the nodule or primary particle mean ) After measuring the particle size of the nodule or primary particle observed in the scanning electron microscope image to This refers to the calculated arithmetic mean.

[0039] In this invention, "average particle size D 50 "50% of the volume cumulative particle size distribution of the powder being measured represents the particle size corresponding to 50% of the volume cumulative amount, and can be measured using the laser diffraction method. For example, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W. hand After obtaining a volume-cumulative particle size distribution graph, the particle size corresponding to 50% of the volume-cumulative amount can be determined to measure it.

[0040] In this invention, "loading amount (mAh / cm²)" 2 ) 」 It can be measured as follows:

[0041] 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.

[0042] 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

[0043] 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.

[0044] In this invention, the "porosity (%)" can be calculated by 1 - (density of the electrode / true density of the electrode).

[0045] 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 such that the change in explosion pressure relative to the unit capacity of the lithium secondary battery cell during thermal runaway in a fully charged state satisfies a specific range, even if thermal runaway occurs in a unit cell in a module and / or pack state, the propagation of thermal runaway to adjacent cells can be minimized, thereby achieving high energy density. This led to the completion of the present invention.

[0046] 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 is represented by the following formula (1) V P However, 4 mbar·Ah -1 sec -1 The following is preferably 1 mbar·Ah -1 sec -1 ~4mbar·Ah -1 sec -1 , more preferably 2 mbar·Ah -1 sec -1 ~4mbar·Ah -1 sec -1 That is the case.

[0047] Formula (1):V P =ΔP / (t max ×C)

[0048] In formula (1) above, ΔP is calculated after the lithium secondary battery has been charged to 4.35V, placed in a chamber with an inert atmosphere, and heated to the point of explosion. to The maximum pressure P measured in the chamber max and 、 This is the difference from the initial pressure P0 of the chamber, and the aforementioned t max Pmax to reach This is the time required to do so, and C is the lithium secondary battery, 25 ℃、 0.33C 、 This is the discharge capacity measured by CC-CV charging and CC-discharging within a voltage range of 2.5V to 4.35V.

[0049] Here, the volume of the chamber can be 100 L to 140 L, and the inert atmosphere can be, for example, a nitrogen atmosphere.

[0050] Furthermore, the lithium secondary battery is heated by a 260mm x 90mm mica heater connected to a PID controller (Proportional-Integral-Derivative controller) that heats the lithium secondary battery. attachment This can be done by heating with a power output of 300W.

[0051] On the other hand, the lithium secondary battery may have, for example, an overall width of 50 mm to 300 mm, an overall length of 50 mm to 1,000 mm, and a thickness of 2 mm to 40 mm, preferably an overall width of 50 mm to 200 mm, an overall length of 100 mm to 800 mm, and a thickness of 2 mm to 30 mm, more preferably 、 The overall width can be 50mm to 200mm, the overall length 200mm to 500mm, and the thickness 5mm to 15mm, but is not limited to these dimensions. According to one embodiment, the lithium secondary battery can have an overall width of 100mm, an overall length of 300mm, and a thickness of 8.5mm. P This is per 1Ah of the discharge capacity of a lithium secondary battery. of This indicates the rate of change in explosion pressure, depending on the dimensions of the lithium secondary battery. That's strange It's not something that transforms.

[0052] The aforementioned ΔP represents the maximum value of the explosion pressure generated when a lithium secondary battery explodes, and the aforementioned t max This is until the explosion pressure reaches its maximum during a lithium secondary battery explosion. to This indicates the time required.

[0053] According to our research, when an explosion occurs in one of the unit cells, the greater the explosion pressure, the faster the explosion velocity, and the larger the battery capacity, the greater the thermal runaway propagation to adjacent cells.

[0054] Therefore, in this invention, the capacity of the lithium secondary battery and the explosion pressure 、 and the relationship between the explosion velocity and V P By designing the cells so that they satisfy a specific range, the propagation of heat and / or flames to adjacent cells is minimized in the event of thermal runaway, thereby preventing chain reactions of fire and / or explosions. Specifically, the V P 4 mbar·Ah -1 sec -1 The following conditions can be met to achieve a significant improvement in thermal runaway propagation:

[0055] On the other hand, V P This includes the capacity of the lithium secondary battery, the design of the positive electrode (e.g., the type of positive electrode active material, the composition of the positive electrode). 、 (and loading amount, etc.), negative electrode design (e.g., type of negative electrode active material, negative electrode composition) 、 (and loading amount, etc.) 、 and / or is affected by 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 P V increases. Also, if the amount of electrolyte and / or the content of imide-based lithium salt in the lithium secondary battery increases, P Therefore, when designing lithium secondary batteries, these factors should be appropriately adjusted to achieve the desired V P It is possible to manufacture lithium secondary batteries that have a value.

[0056] On the other hand, the lithium secondary battery of Nominal Voltage teeth, The voltage can be 3.68V or higher, preferably 3.68V to 3.80V, and more preferably 3.69V to 3.75V. Here, the nominal voltage is the voltage when the lithium secondary battery is discharged. Okeru This refers to the average voltage. The energy density of a lithium secondary battery is determined during discharge. Okeru Since it is calculated by multiplying the average voltage and average current, a higher nominal voltage results in increased energy density. Conventional lithium secondary batteries using lithium nickel cobalt manganese oxide as the positive electrode active material typically have a charge cutoff voltage of 4.25V, in which case the nominal voltage is 3.6V. In contrast, the present invention achieves high energy density by raising the charge cutoff voltage to 4.35V or higher and the nominal voltage to 3.68V or higher. Specifically, the lithium secondary battery according to the present invention can have an energy density of 500Wh / L or more, preferably 500Wh / L to 800Wh / L.

[0057] Preferably, the lithium secondary battery of Charging cut-off voltage (full charge voltage) teeth The voltage is preferably 4.35V or higher, more 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 positive electrode 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 of the positive electrode active material increases. However, as the drive voltage increases, during charging and discharging... ni There is a problem in that side reactions with the dissolution increase, causing rapid structural collapse of the positive electrode active material 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, when lithium nickel cobalt manganese oxides are conventionally used as positive electrode active materials, the charge cut-off voltage teeth It was generally around 4.25V. However, in this invention, by applying a lithium nickel-based oxide with a Ni content of 70 mol% or less and having a single-particle form as the positive electrode active material, it is possible to maintain excellent life characteristics even when the charge cut-off voltage is 4.35V or higher.

[0058] The components of the lithium secondary battery according to the present invention will be described in more detail below.

[0059] 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 is a material other than lithium. All Gold Among the genera of Ni content: 70 mol% below This is a single-particle lithium nickel oxide. correct extremely active material whole It may contain 50% or more by weight of it.

[0060] 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 is 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 includes a positive electrode active material. In addition, the positive electrode active material layer may further include a positive electrode conductive material and a positive electrode binder.

[0061] The positive electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium, silver etc. on the surface of aluminum or stainless steel. of Surface-treated items, etc. of use do It is possible. Also, the positive electrode current collector is usually 3 μm It can have a thickness of ~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 films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics. obtain .

[0062] 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%.

[0063] 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, and thereby reducing the explosion pressure during thermal runaway.

[0064] In the case of lithium nickel oxides in secondary particle form, where 50 to several hundred primary particles aggregate, the large contact area with the electrolyte leads to numerous side reactions with the electrolyte, generating gas 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 present inside the lithium secondary battery, the explosion pressure increases during thermal runaway. 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. Therefore, compared to secondary particles, there are fewer side reactions with the electrolyte, and consequently, the amount of gas generated is significantly less. Consequently, when single-particle lithium nickel oxides are used as the positive electrode active material, the explosion pressure decreases during thermal runaway. 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 therefore, the effect of reducing the explosion pressure during thermal runaway decreases.

[0065] 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%.

[0066] Specifically, the single-particle lithium nickel oxide is made of nickel, manganese 、 It can also be a lithium transition metal oxide containing cobalt, and can be represented, for example, by the following [Chemical Formula 1].

[0067] [Chemical formula 1] Li 1+x [Ni a Co b Mn c M 1 d ]O2

[0068] 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 are Ti, Mg, Al, Zr 、 It may include one or more selected from the group consisting of and Y, and more preferably Ti, Mg, Al, Zr 、 It may include two or more types selected from the group consisting of and Y.

[0069] 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 crystal structure is formed. obtain .

[0070] The above a is a lithium other than lithium in lithium nickel oxide. All Gold Among the genera of This indicates the molar ratio of nickel, 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.

[0071] The above b is a lithium other than lithium in lithium nickel oxide. All Gold Among the genera of This shows the molar ratio of cobalt, 0 <b<0.5、0.05≦b≦0.4 、 Alternatively, 0.1 ≤ a ≤ 0.4 can be the case.

[0072] The aforementioned c is a lithium other than lithium in lithium nickel oxide. All Gold Among the genera of Shows the molar ratio of manganese, 0 <c<0.5、0.05≦c≦0.4 、 Alternatively, 0.1 ≤ c ≤ 0.4 can be the case.

[0073] The above d is a lithium other than lithium in the lithium nickel oxide. All Gold Among the genera of M 1 The molar ratio of the elements is shown, with 0≦d≦0.2 and 0≦d≦0.1. 、 or 0 <d≦0.1であることができる。M 1 When the molar ratio of the elements satisfies the above range, the structural stability and capacity of the positive electrode active material teeth It is possible to excel at everything.

[0074] 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.

[0075] 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 Ti, Mg, Al, Zr, Y 、 It may contain two or more elements selected from the group consisting of and W.

[0076] 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.

[0077] On the other hand, the nodule of Average particle size teeth, The average particle size of the nodule 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 nodule satisfies the above range, particle cracking during electrode manufacturing can be minimized, and the increase in resistance can be suppressed more effectively. Here, the average particle size of the nodule and This 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.

[0078] On the other hand, the lithium nickel-based oxide of D 50 teeth 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 50 If 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, and the output characteristics deteriorate, which is a problem. 。

[0079] On the other hand, the single-particle lithium nickel oxide having a nickel content of 70 mol% or less is used within the positive electrode active material layer. The correct extremely active material whole Of the total weight of the positive electrode active material, it may contain 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 When the ratio of single-particle lithium nickel oxides with a nickel content of 70 mol% or less satisfies the aforementioned range, excellent thermal runaway safety is observed.

[0080] The positive electrode active material layer may contain 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%, but the ratio of secondary particles and / or lithium nickel oxide with a nickel content exceeding 70 mol% That is correct extremely active material whole If the amount exceeds 50% by weight, the improvement in thermal runaway safety is minimal and undesirable.

[0081] 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.

[0082] Next, the positive electrode conductive material is used to impart conductivity to the positive 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 and 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; and conductive wisps such as zinc oxide and potassium titanate. mosquito; Examples include conductive metal oxides such as titanium dioxide; or conductive polymers such as polyphenylene derivatives, and one of these can be used alone or as a mixture of two or more. obtain .

[0083] The positive electrode conductive material is typically 0.1% of the total weight of the positive electrode active material layer. weight% ~10% by weight, preferably 0.5% by weight to 8% by weight, more preferably 0.5% by weight weight% It can be included in an amount of approximately 5% by weight.

[0084] Next, the positive electrode binder plays a role in improving adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), PolyExamples include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more is used. obtain .

[0085] The positive electrode binder is 1 in proportion to the total weight of the positive electrode active material layer. weight% ~10% by weight, preferably 1 weight% ~8% by weight, more preferably 1% by weight weight% It can contain up to 5% by weight.

[0086] The positive electrode is manufactured by a conventional method for manufacturing positive electrodes. do This is possible. For example, the positive electrode may consist of a positive electrode active material and a positive electrode binder. 、 and / or a positive electrode slurry is produced by mixing positive electrode conductive material in a solvent, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling it. do or 、 The positive electrode slurry can be cast onto another support, and the resulting film, obtained by peeling it off the support, can be laminated onto the positive electrode current collector.

[0087] On the other hand, the solvent for the positive electrode slurry is a solvent commonly used in the relevant technical field. of for There are For example, one of the following can be used: dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc. in,Alternatively, two or more types can be mixed and used. The amount of solvent used will be determined considering the coating thickness of the slurry and the manufacturing yield, and will be the amount of the positive electrode active material and conductive material. 、 and dissolve or disperse the binder, after that Therefore, when coating for the manufacture of the positive electrode, it has a viscosity that can exhibit excellent thickness uniformity. Na That level is sufficient.

[0088] On the other hand, the positive electrode according to the present invention of Loading amount teeth, 0.5 mAh / cm 2 ~10mAh / cm 2 , preferably 2 mAh / cm 2 ~8mAh / cm 2 , more preferably 2.5 mAh / cm 2 ~6mAh / cm 2 This is possible. When the positive electrode loading amount satisfies the aforementioned range, thermal runaway safety and capacity characteristics are further improved.

[0089] 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.

[0090] 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 is 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 includes a negative electrode active material. In addition, the negative electrode active material layer may further include a negative electrode conductive material and a negative electrode binder.

[0091] 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, or a surface of copper or stainless steel with carbon, nickel, titanium, silver, etc. of Surface-treated materials, aluminum-cadmium alloys, etc. of for There are It is possible. Also, the negative electrode current collector is usually 3 μm It can have a thickness of ~500 μm, and, similar to the positive electrode current collector, it can also form fine irregularities 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. obtain .

[0092] On the other hand, the negative electrode active material can consist of a carbon-based negative electrode active material, such as natural graphite, artificial graphite, graphitized carbon fiber, amorphous carbon, soft carbon, or hard carbon. 、 Alternatively, a combination of these may be included. For example, the carbon-based negative electrode active material may include natural graphite and artificial graphite, in which case the weight ratio of natural graphite to artificial graphite may be 1:9 to 9:1, preferably 2:8 to 8:2.

[0093] recent years To achieve high capacity, there is a tendency to apply Si-based anode active materials such as SiO, Si, and Si-C composites, which have high theoretical capacity, as anode active materials. but However, according to the inventors' research, it has been observed that when a Si-based negative electrode active material is included, the explosion pressure increases during thermal runaway. Therefore, it is preferable that the lithium secondary battery according to the present invention does not contain a Si-based negative electrode active material as the negative electrode active material.

[0094] The carbon-based negative electrode active material of Average particle size D 50 teeth, The particle size can be 2 μm to 30 μm, preferably 5 μm to 30 μm.

[0095] 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.

[0096] 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 configured in, as long as it does not cause a chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, etc. nine Examples include carbon-based materials such as carbon fibers 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, and one of these alone or a mixture of two or more is used. obtain .

[0097] The aforementioned negative electrode conductive material is typically 0.1 in weight relative to the total weight of the negative electrode active material layer. weight% ~10% by weight, preferably 0.25% by weight to 8% by weight, more preferably 0.25% by weight weight% It can be included in an amount of approximately 5% by weight.

[0098] The aforementioned negative electrode binder plays a role in improving 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), PolyExamples include vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these alone or a mixture of two or more is used. obtain .

[0099] The aforementioned negative electrode binder is negative electrode With respect to the total weight of the active material layer, weight% ~10% by weight, preferably 1 weight% ~8% by weight, more preferably 1% by weight weight% It can contain up to 5% by weight.

[0100] 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 and artificial graphite. 、 Or it could be a combination of these.

[0101] On the other hand, if the negative electrode active material layer has a multilayer structure composed of two or more layers, each layer In negative electrode active material, binder 、 and / or the types and / or amounts of conductive materials may differ from one another.

[0102] 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.

[0103] Alternatively, the weight ratio of the conductive material to the total weight of the second negative electrode active material layer (upper layer) is set to the weight of the first negative electrode active material layer ( bottom The weight ratio of the conductive material to the total weight of the layer can be made higher.

[0104] In this way, by forming the negative electrode active material layer in a multilayer structure and varying the composition of each layer, the performance characteristics of the battery can be improved. For example, the first negative electrode active material layer In the heavens The ratio of natural graphite is increased, and the second negative electrode active material layer In people When a high proportion of graphite is formed, it reduces the explosion pressure during thermal runaway. of It can be improved further.

[0105] The aforementioned negative electrode is manufactured by a conventional negative electrode manufacturing method. do This is possible. For example, the negative electrode may consist of a negative electrode active material and a negative electrode binder. 、 and / or a negative electrode slurry is produced by mixing a negative electrode conductive material in a solvent, applying the negative electrode slurry onto a negative electrode current collector, and then drying and rolling it. do or 、 The negative electrode slurry is cast onto another support, and the resulting film, obtained by peeling it off the support, is then laminated onto the negative electrode current collector. do It is possible.

[0106] On the other hand, the solvent for the negative electrode slurry is a solvent commonly used in the relevant technical field. of for There areFor example, one of the following can be used: dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc. in, Alternatively, two or more types can be mixed and used. The amount of solvent used will be determined considering the slurry coating thickness and manufacturing yield, and the negative electrode active material, conductive material 、 and dissolve or disperse the binder, after that Therefore, when coating for the manufacture of the positive electrode, it has a viscosity that can exhibit excellent thickness uniformity. Na That level is sufficient.

[0107] On the other hand, the negative electrode according to the present invention of Loading amount teeth , 0.5 mAh / cm 2 ~10mAh / cm 2 , preferably 2 mAh / cm 2 ~8mAh / cm 2 , more preferably 2.5 mAh / cm 2 ~6.5mAh / cm 2 This is possible. When the negative electrode loading amount satisfies the above range, thermal runaway safety and capacity characteristics are further improved.

[0108] 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.

[0109] electrolyte The electrolyte may include an organic solvent and a lithium salt.

[0110] 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; R-CN (where R is a linear or branched chain of C2-C20). 、 Nitriles such as hydrocarbon groups with a cyclic structure (which may include double-bonded aromatic rings or ether bonds); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes, etc. of use do This is possible. Among them, carbonate-based solvents are preferred, and cyclic carbonates (for example, ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery are preferred. low High viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate) 、 A mixture of (or diethyl carbonate, etc.) is more preferable.

[0111] The lithium salt as The lithium salt can be any compound that can provide lithium ions for use in lithium secondary batteries, without any particular limitations. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, or LiAl O 4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2 ( The lithium salt may include one or more selected from the group consisting of 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.

[0112] For example, the lithium salt can be a phosphate-based lithium salt such as LiPF6 used alone, or a mixture of the phosphate-based lithium salt and the imide-based lithium salt can be used.

[0113] When using a mixture of phosphate-based lithium salt and imide-based lithium salt, of the total weight of the lithium salt of The content of the imide-based lithium salt can be appropriately adjusted according to the Ni content in the positive electrode active material. Specifically, of the total weight of the lithium salt of Content of imide-based lithium salts W I It is preferable that the following equation (2) is satisfied.

[0114] Formula (2):

number

[0115] In formula (2) above, a is a positive electrode active material other than lithium. All Gold Among the genera ofThis is the molar percentage of Ni, and the above a can be 70 or less, preferably 50 to 70, and more preferably 55 to 70.

[0116] 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), thermal runaway transition to adjacent cells occurs in the event of ignition or thermal runaway. of It can be minimized.

[0117] On the other hand, the concentration of the lithium salt is 0.1 M ~3.0M, preferably 0.1 M ~2.0M, fer0.5 M It is preferable to use it within a range of ~1.5M. When the lithium salt concentration falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively. Possible .

[0118] 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), and lithium difluorobisoxalate phosphate. Lithium tetrafluorooxalate phosphate (LiTFOP), lithium methyl sulfate (LiMS), lithium ethyl sulfate (LiES), propane sultone (PS), propensultone (PRS), succinonitrile (SN), adiponitrile (AND), 1,3,6-hexanetricarbonitrate (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) and other additives may be used alone or in combination, but are not limited thereto. The additive may be used in amounts of 0.1% of the total weight of the electrolyte. weight% ~10% by weight, preferably 0.1 weight% It can contain up to 5% by weight.

[0119] On the other hand, the electrolyte can 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 volume is too high, during thermal runaway, the electrolyte can act as fuel, increasing the explosion pressure and potentially leading to rapid thermal transition. On the other hand, if the amount of electrolyte per unit volume is too low, the electrolyte will be consumed quickly during the activation and battery operation processes, potentially reducing its lifespan.

[0120] 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 pathway for the movement of lithium ions. , As a separator in lithium secondary batteries usually Any suitable material can be used without particular restrictions, but materials that exhibit low resistance to ion movement of the electrolyte and have excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, and ethylene / hexene copolymers, are preferred. 、 and porous polymer films made from polyolefin polymers such as ethylene / methacrylate copolymers. 、 Alternatively, a laminated structure of two or more layers may be used. obtain Furthermore, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. In addition, 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.

[0121] 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.

[0122] 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. 、 A battery pack including multiple battery modules is also provided.

[0123] 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 is battery It does not need to include modules.

[0124] Furthermore, the present invention provides a pack cell assembly.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] The positive electrode slurry was applied onto an aluminum current collector sheet, dried, and then rolled to 、 produce a positive electrode with a loading amount of 4.0 mAh / cm 2 and a porosity of 25%.

[0130] <Manufacture of Negative Electrode> Negative electrode active material: negative electrode conductive material: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) were mixed in water at a weight ratio of 96:1:2:1 to produce a negative electrode slurry. Here, graphite was used as the negative electrode active material and carbon black was used as the negative electrode conductive material.

[0131] The negative electrode slurry was applied onto a copper current collector sheet, dried, and then rolled to produce a negative electrode with a loading amount of 4.5 mAh / cm 2 and a porosity of 30%.

[0132] <Manufacture of Lithium Secondary Battery> A separator was interposed between the positive electrode and the negative electrode manufactured as described above Let to manufacture an electrode assembly. After inserting the electrode assembly into a battery case, an electrolyte was injected so that the amount of electrolyte per unit capacity was 2.0 g / Ah, and a lithium secondary battery cell was manufactured. Here, as the electrolyte, an electrolyte manufactured by dissolving a lithium salt (LiPF6 100% by weight) at a concentration of 1.0 M in a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) mixed at a volume ratio of 3:7 was used. The dimensions of the lithium secondary battery cell were 100 mm in overall width, 300 mm in overall length 、 and 8.5 mm in thickness.

[0133] Example 2 As the positive electrode active material, except that single-particle type Li[Ni 50 with D 0.60 Co 0.10 Mn 0.30 O2 of 3.7 μm was used at 100%, the positive electrode, negative electrode 、 and lithium secondary battery were manufactured in the same manner as in Example 1.

[0134] Example 3 As the positive electrode active material, D 50 is 3.6 μm single-particle type Li[Ni 0.70 Co 0.10 Mn 0.20 O2 was used at 100%, and the positive electrode, negative electrode 、 and the lithium secondary battery were manufactured in the same manner as in Example 1.

[0135] Example 4 During the manufacture of the lithium secondary battery, as the lithium salt, LiPF6:LiFSI was mixed and used at a weight ratio of 60:40, and the positive electrode, negative electrode 、 and the lithium secondary battery were manufactured in the same manner as in Example 1.

[0136] Example 5 During the manufacture of the lithium secondary battery, as the lithium salt, LiPF6:LiFSI was mixed and used at a weight ratio of 60:40, and the positive electrode, negative electrode 、 and the lithium secondary battery were manufactured in the same manner as in Example 2.

[0137] Example 6 During the manufacture of the lithium secondary battery, as the lithium salt, LiPF6:LiFSI was mixed and used at a weight ratio of 80:20, and the positive electrode, negative electrode 、 and the lithium secondary battery were manufactured in the same manner as in Example 3.

[0138] Comparative Example 1 As the positive electrode active material, D 50 is 3.6 μm single-particle type Li[Ni 0.70 Co 0.10 Mn 0.20 O2 and D 50 is 7.8 μm secondary particle form Li[Ni 0.70 Co 0.10 Mn 0.20 O2 were mixed and used at a weight ratio of 5:5, and the positive electrode, negative electrode 、 and the lithium secondary battery were manufactured in the same manner as in Example 1.

[0139] Comparative Example 2 As the positive electrode active material, D 50 Single-particle Li[Ni 0.70 Co 0.10 Mn 0.20 ]O2 and D 50 Li[Ni 0.70 Co 0.10 Mn 0.20 The positive and negative electrodes were prepared in the same manner as in Example 1, except that O2 was mixed in a weight ratio of 25:75. 、 They also manufactured lithium-ion batteries.

[0140] Comparative Example 3 As the positive electrode active material, D 50 Single-particle Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 The positive and negative electrodes were prepared in the same manner as in Example 1, except that 100% O2 was used. 、 They also manufactured lithium-ion batteries.

[0141] Comparative Example 4 As the positive electrode active material, D 50 The single-particle Li[Ni 0.93 Co 0.05 Mn 0.01 Al 0.01 The positive and negative electrodes were prepared in the same manner as in Example 1, except that 100% O2 was used. 、 They also manufactured lithium-ion batteries.

[0142] Comparative Example 5 Except for using a mixture of graphite and SiO in a weight ratio of 95:5 as the negative electrode active material, the positive and negative electrodes were prepared in the same manner as in Example 1. 、 They also manufactured lithium-ion batteries.

[0143] Comparative Example 6 The positive and negative electrodes were prepared 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. 、 They also manufactured lithium-ion batteries.

[0144] Comparative Example 7 The positive and negative electrodes were prepared 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. 、 They also manufactured lithium-ion batteries.

[0145] Comparative Example 8 As the positive electrode active material, D 50 Single-particle Li[Ni 0.86 Co 0.05 Mn 0.08 Al 0.01 Except for using 100% O2 and a mixture of graphite:SiO in a weight ratio of 95:5 as the negative electrode active material, the positive and negative electrodes were prepared in the same manner as in Example 1. 、 They also manufactured lithium-ion batteries.

[0146] Comparative Example 9 As the positive electrode active material, D 50 Single-particle Li[Ni 0.60 Co 0.10 Mn 0.30 ]O2 and D 50 Li[Ni 0.80 Co 0.10 Mn 0.10 The positive and negative electrodes were prepared in the same manner as in Example 1, except that O2 was mixed in a 5:5 weight ratio. 、 They also manufactured lithium-ion batteries.

[0147] Comparative Example 10 The positive and negative electrodes were manufactured in the same manner as in Example 1, except that a mixture of LiPF6 and LiFSI in a 50:50 weight ratio was used as the lithium salt during the manufacturing of the lithium secondary battery. 、 They also manufactured lithium-ion batteries.

[0148] Comparative Example 11 The positive and negative electrodes 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. 、 They also manufactured lithium-ion batteries.

[0149] Experimental Example 1 Each of the lithium secondary battery cells manufactured in Examples 1 to 6 and Comparative Examples 1 to 11 was charged in a CC-CV manner within a voltage range of 0.33 C、 from 2.5 V to 4.35 V, and then discharged in a CC manner. After that, the discharge capacity (C) was measured.

[0150] Thereafter, each of the lithium secondary batteries was placed in a chamber (chamber volume: 100 L) with a nitrogen (N2) atmosphere equipped with a pressure sensor. Then, a mica heater with a size of 260 mm × 90 mm connected to a PID controller (Proportional-Integral-Derivative controller) was attachment heated at an output of 300 W while causing an explosion, and the pressure inside the chamber was measured. The change in pressure ΔP and the time t max required to reach P max were measured. The measurement results of are shown in Table 1 below ] shown. <0OO0898>

[0151]

Table 1

[0152] Experimental Example 2<00009OO>Sixteen lithium secondary battery cells manufactured in Examples 1 to 6 and Comparative Examples 1 to 11 were stacked to manufacture battery modules. Thereafter, the unit cells arranged on the outermost side of each battery module were heated with a heating device, and the time from when a flame occurred until the battery module was completely burned was measured. [[ID=3Z]]

[0153]

Table 2

[0154] Referring to Table 2 above, for the battery modules using the lithium secondary batteries of Examples 1 to 6 where V P is 4 mbar·Ah -1 ·sec -1 or less as unit cells teeth , V P4 mbar·Ah -1 sec -1 Compared to the battery modules using lithium secondary batteries of Comparative Examples 1-11 as unit cells, the battery module that exceeded the limit of total fire damage. to The longer processing time confirms 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 aforementioned lithium secondary battery has a nominal voltage of 3.68V or higher. V is represented by the following formula (1) Ｐ 4 mbar・Ah －１ sec －１ The following is a lithium-ion battery. Equation (1): V Ｐ =ΔP / (t) ｍａｘ ×C) In the formula (1), ΔP is the maximum pressure P in the chamber measured after charging the lithium secondary battery to 4.35 V, placing it in a chamber with an inert atmosphere, heating the lithium secondary battery to cause an explosion, and then measuring it. ｍａｘ and the initial pressure P of the chamber ０ The difference between them, and the t ｍａｘ is the time required to reach the P ｍａｘ C is the discharge capacity measured by performing CC-CV charging and CC discharging on the lithium secondary battery at 25 °C at 0.33 C within a voltage range of 2.5 V to 4.35 V.

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

3. 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 the total metals other than lithium is 70 mol% or less.

4. The aforementioned single-particle lithium nickel oxide contains 30 or fewer nodules. The lithium secondary battery according to claim 2, wherein the average particle size of the nodule is 0.8 μm to 4.0 μm.

5. The lithium secondary battery according to claim 2, 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.

6. The lithium secondary battery according to claim 2, 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.

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

8. The negative electrode includes a negative electrode current collector, a first negative electrode active material layer formed on the negative electrode current collector and 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.

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

10. The lithium secondary battery according to claim 9, 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. The lithium secondary battery according to claim 1, wherein the weight of the electrolyte per unit capacity of the lithium secondary battery is 1.0 g / Ah to 3.0 g / Ah.

12. The electrolyte comprises an organic solvent and a lithium salt. Content W of the 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 the total metals other than lithium in the positive electrode active material.

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

14. The lithium secondary battery according to claim 1, wherein the lithium secondary battery has a charge cutoff voltage of 4.35V to 4.5V.

15. V represented by formula (1) above Ｐ However, 2-4 mbar / Ah －１ sec －１ The lithium secondary battery according to claim 1.

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 including the secondary battery module described in claim 16.

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