Negative electrode having improved safety against internal short circuit, secondary battery comprising same, and secondary battery system for same

Abstract

The present invention relates to a negative electrode, a secondary battery comprising same, and a secondary battery system for same. The negative electrode comprises, in a coating layer, aluminum-containing particles having specific components and a conductive material, and thus can implement a predetermined volume resistivity. Such negative electrodes allow a certain amount of current to leak, while implementing appropriate insulation on the surface of the negative electrode in the event of an internal short circuit, and thus can prevent the internal short circuit from causing a meltdown and / or rapid heat generation in a secondary battery.

Description

A cathode with improved safety against internal short circuits, a secondary battery including the same, and a secondary battery system therefor

[0001] The present invention relates to a cathode having improved safety against internal short circuits, a secondary battery including the same, and a secondary battery system therefor.

[0002] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2024-0013054, dated January 29, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] Lithium secondary batteries generate electrical energy through oxidation and reduction reactions that occur when lithium ions intercalate and deintercalate at the positive and negative electrodes. Lithium secondary batteries are manufactured by using materials capable of reversibly intercalating and deintercalating lithium ions as active materials for the positive and negative electrodes, and filling the space between the positive and negative electrodes with an organic or polymer electrolyte.

[0005] Lithium secondary batteries, like these, charge and discharge through electrochemical reactions that involve the insertion, removal, and movement of ions between the active materials in the positive and negative electrodes. Repeated charging and discharging of these batteries can lead to overheating due to electrical misuse (overcharging) or other hazardous factors. If this condition persists, the lithium secondary battery can be destroyed or explode, potentially causing fatal harm to the user. Therefore, safety measures are essential.

[0006] For example, conventional secondary batteries utilize a porous separator installed between the positive and negative electrodes as a safety measure. When the internal temperature of the case rises above a safe temperature, the porous separator responds by closing its pores and blocking ion movement between the two electrodes, thereby suppressing electrochemical reactions and ensuring safety (shutdown phenomenon).

[0007] However, if the temperature inside the conventional secondary battery rises excessively beyond the temperature release rate of the case due to unevenness of the separator or other internal short-circuit causes, the separator itself melts before the shutdown phenomenon occurs, losing its function of insulating the positive and negative electrodes. In addition, if the positive and negative electrodes are short-circuited, a chain reaction (melt down) such as decomposition of the negative active material and electrolyte, decomposition of the positive active material, etc. occurs, and then a thermal runaway phenomenon occurs. This thermal runaway phenomenon not only causes an explosion of the secondary battery in which the short-circuit occurred, but also induces a meltdown phenomenon in secondary batteries adjacent to the secondary battery in question, which has the problem of causing additional explosions.

[0008] The meltdown phenomenon is induced by internal short circuits occurring between electrodes in a secondary battery, between electrodes and their current collectors, and / or between current collectors. Specifically, when a short circuit occurs due to contact between the positive electrode current collector (or the positive electrode surface) and the negative electrode, the resistance of the shorted portion rapidly increases heat generation, leading to a thermal runaway phenomenon in a short period of time. Therefore, to ensure battery stability, a means is needed to prevent, guard against, and / or counteract this phenomenon.

[0009]

[0010] [Prior Art Literature]

[0011] Republic of Korea Patent Publication No. 10-2011-0067565

[0012] Republic of Korea Patent Publication No. 10-2021-0054930

[0013]

[0014] The purpose of the present invention is to provide a lithium secondary battery-related technology capable of ensuring battery safety in the event of an internal short circuit in a lithium secondary battery.

[0015]

[0016] To solve the above-mentioned problem,

[0017] The present invention,

[0018] A negative electrode active layer provided on at least one surface of a negative electrode current collector and including a negative electrode active material; and

[0019] Including a coating layer positioned on the above cathode active layer,

[0020] The above coating layer includes aluminum-containing particles and a conductive material,

[0021] The above aluminum-containing particles provide a cathode exceeding 50 parts by weight based on the total weight of the coating layer.

[0022] At this time, the cathode is about 1.0 × 10 -4 It can have a volume resistivity in the range of Ω·cm or more and less than about 1.0 Ω·cm.

[0023] Additionally, the aluminum-containing particles may include a metal compound represented by the following chemical formula 1:

[0024] [Chemical Formula 1]

[0025] Al p O q (OH) r

[0026] In chemical formula 1,

[0027] p is an integer from 1 to 10, q is an integer from 0 to 20, and p≤q,

[0028] r is an integer from 1 to 5.

[0029] For example, the aluminum-containing particles may include one or more of boehmite, pseudoboehmite, diaspore, akdalaite, and aluminum trihydroxide.

[0030] In addition, the aluminum-containing particles have an average particle diameter (D) in the range of 0.1 ㎛ to 3.0 ㎛ 50 ) can have.

[0031] In addition, the conductive material may include at least one of natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, summer black, graphene, and carbon nanotubes.

[0032] Additionally, the conductive agent may be included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the total aluminum-containing particles.

[0033] In addition, the coating layer may further include 5 to 15 parts by weight of a dispersant based on 100 parts by weight of the total aluminum-containing particles.

[0034] Here, the dispersant may include a dispersant containing one or more carboxylic acids.

[0035] Additionally, the coating layer may further include 5 parts by weight or less of a binder based on the total 100 parts by weight.

[0036] The above binder may include at least one of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyalkyl acrylate, polyamide (PA), and polystyrene (PS).

[0037] Furthermore, the average thickness of the coating layer may be in the range of 1.5 to 20 μm, and at this time, the thickness ratio of the coating layer to the negative electrode active layer may be in the range of 0.05 to 0.3.

[0038]

[0039] In addition, the present invention,

[0040] A secondary battery is provided, comprising: a positive electrode; a negative electrode according to the present invention described above; and a separator disposed between the positive electrode and the negative electrode.

[0041]

[0042] Furthermore, the present invention,

[0043] A plurality of cell assemblies each including n secondary batteries according to the present invention described above (wherein 3≤n≤100 is an integer),

[0044] A charging and discharging unit that electrically couples each of the above-mentioned multiple cell assemblies to individually charge or discharge them,

[0045] A sensing unit that is electrically coupled to the electrodes of each secondary battery included in the above-described multiple cell assemblies and individually measures at least one of the voltage and current of the secondary battery during charging and discharging of each secondary battery, and

[0046] A control unit electrically coupled to the charging / discharging unit and the sensing unit to control charging or discharging of each cell assembly;

[0047] The above control unit provides a secondary battery system that stops charging or discharging of a cell assembly including the secondary battery when the current amount measured by the sensing unit satisfies a predetermined value.

[0048] At this time, the control unit may perform a step of selecting a cell assembly in which an error rate between the average current flow of a plurality of cell assemblies and the current flow of an individual cell assembly is 5% or more; a step of determining that an internal short circuit has occurred in the secondary battery when the current flow measured by the sensing unit based on the applied current flow of each secondary battery is 0.5% or more lower among the individual secondary batteries provided in the selected cell assembly; and a step of stopping charging or discharging of a cell assembly including the secondary battery determined to have occurred due to an internal short circuit.

[0049] Additionally, the sensing unit may further include a temperature measurement sensor for measuring the temperature of each secondary battery provided in the cell assembly.

[0050]

[0051] The cathode according to the present invention can implement a predetermined volume resistance by including aluminum-containing particles of a specific component and a conductive material in a coating layer located on the outermost surface of the cathode. Such a cathode can implement appropriate insulation properties on the cathode surface in the event of an internal short circuit while allowing a predetermined current to leak, thereby preventing meltdown and / or rapid overheating of a secondary battery due to an internal short circuit.

[0052] In addition, the secondary battery system according to the present invention can prevent meltdown phenomenon and rapid heat generation in the event of an internal short circuit by including the secondary battery of the present invention described above, and can quickly determine an internal short circuit through a predetermined current leaked from the secondary battery, so that operation can be preemptively controlled before thermal runaway of the secondary battery occurs, thereby improving safety issues caused by an internal short circuit.

[0053]

[0054] Figure 1 is a structural diagram schematically showing the configuration of a secondary battery system according to the present invention.

[0055] Figure 2 is a graph showing the change in voltage and temperature of the battery at the negative electrode of the lithium secondary battery of Comparative Example 1 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface.

[0056] Figure 3 is a graph showing the change in voltage and temperature of the battery at the negative electrode of the lithium secondary battery of Example 1 when an internal short circuit occurs due to contact between the positive electrode collector and the negative electrode surface.

[0057] Figure 4 is a cross-sectional view showing the electrode assembly structure of a secondary battery manufactured in an experimental example for a safety test of a secondary battery according to the present invention.

[0058]

[0059] The present invention can be modified in various ways and has many embodiments, and specific embodiments will be described in detail in the detailed description.

[0060] However, this is not intended to limit the present invention to a specific embodiment, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

[0061] In the present invention, it should be understood that terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0062] Additionally, in the present invention, “current flow” means the amount of electricity flowing through an electrode when charging or discharging a secondary battery, which can be quantified as current and / or voltage.

[0063] In addition, in this specification, "average particle diameter (D 50 )" means the particle diameter at which the integrated value is 50% in the particle diameter distribution of the particles, and is also called the median diameter. The above average particle diameter can be measured by a method commonly applied in the art. For example, the above average particle diameter can be measured using a particle size analyzer or an analysis device using a laser diffraction scattering particle size distribution measurement method, but is not limited thereto.

[0064]

[0065] Hereinafter, the present invention will be described in more detail.

[0066]

[0067] cathode

[0068] The present invention,

[0069] A negative electrode active layer provided on at least one surface of a negative electrode current collector and including a negative electrode active material; and

[0070] Including a coating layer positioned on the above cathode active layer,

[0071] The above coating layer includes aluminum-containing particles and a conductive material,

[0072] The above aluminum-containing particles provide a cathode exceeding 50 parts by weight based on 100 parts by weight of the entire coating layer.

[0073]

[0074] The negative electrode according to the present invention may be an negative electrode applicable to a secondary battery (specifically, a lithium secondary battery). The negative electrode has a structure in which a negative electrode active layer containing a negative electrode active material and a coating layer are sequentially laminated on a negative electrode current collector.

[0075] At this time, the negative electrode may have a coating layer including aluminum-containing particles and a conductive material on the surface of the negative electrode active layer including a carbon-based negative electrode active material, thereby having a predetermined volume resistance. Specifically, the coating layer may have a density of 1.0 × 10 -4 It can have a volume resistivity in the range of Ω·cm or more, more specifically 1.0 × 10 -4 It may be in the range of Ω·cm or more and less than 1.0 Ω·cm. For example, the coating layer may have a thickness of 5.0 × 10 -4 Ω·cm or less but less than 1.0 Ω·cm; 1.0 × 10 -3 Ω·cm or more but less than 1.0 Ω·cm; 3.0 × 10 -3 Ω·cm or more but less than 1.0 Ω·cm; 1.0 × 10 -2 Ω·cm or more but less than 1.0 Ω·cm; 3.0 × 10 -3 Ω·cm or more but less than 1.0 Ω·cm; 3.0 × 10 -3 Ω·cm to 9.0 × 10 -1 Ω·cm; 5.0 × 10 -2 Ω·cm to 9.0 × 10 -1 Ω·cm; 6.0 × 10 -2 Ω·cm to 8.0 × 10 -1 Ω· -1 ·cm; 8.0 × 10 -2 Ω·cm to 5.0 × 10 -1 Ω·cm; 4.0 × 10 -2Ω·cm to 2.0 × 10 -1 Ω·cm; 5.0 × 10 -2 Ω·cm to 1.5 × 10 -1 Ω·cm; 8.0 × 10 -2 Ω·cm to 1.0 × 10 -1 Ω·cm; 7.0 × 10 -2 Ω·cm to 9.0 × 10 -2 Ω·cm; 7.0 × 10 -2 Ω·cm to 4.5 × 10 -1 Ω·cm; 7.0 × 10 -2 Ω·cm to 3.0 × 10 -1 Ω·cm; 8.0 × 10 -2 Ω·cm to 2.0 × 10 -1 Ω·Ω·cm; 1.0 × 10 -1 Ω·cm to 9.0 × 10 -1 Ω·cm; 1.0 × 10 -1 Ω·cm to 5.0 × 10 -1 Ω·cm; 2.0 × 10 -1 Ω·cm to 8.0 × 10 -1 Ω·cm; or 5.0 × 10 -1 It can have a volume resistivity in the range of Ω·cm to 1.0 Ω·cm.

[0076] If the volume resistance of the above-mentioned negative electrode exceeds 1.0 Ω·cm, an internal short circuit, especially an internal short circuit due to contact between the negative electrode surface and the positive electrode current collector (and / or positive electrode active layer), may occur on the surface of the negative electrode, causing a significant reduction in the amount of current applied to the outside of the electrode or preventing it from flowing completely. Accordingly, the short circuit current of the secondary battery is blocked, but it is not easy to selectively detect and respond to an internally short-circuited secondary battery in a short period of time in a device including a plurality of secondary batteries, such as a battery module or pack. In addition, in order to respond to an internal short circuit, the cell assembly including the secondary battery in which the internal short circuit occurred must be separated and / or removed from the secondary battery system, which is a problem of low economic efficiency. In addition, if the volume resistance of the above-mentioned negative electrode exceeds 1.0 × 10-4 If it is less than Ω·cm, sufficient insulation is not achieved on the cathode surface in the event of an internal short circuit, causing a meltdown phenomenon such as decomposition of the cathode active material and electrolyte, decomposition of the cathode active material, and consequently, a problem of ignition occurs.

[0077] That is, the negative electrode of the present invention has a volume resistivity satisfying the above-described range, thereby providing an appropriate resistance to the negative electrode surface in the event of an internal short circuit, thereby implementing a predetermined insulation property at the short circuit point. Accordingly, the heat generation of the secondary battery in the event of an internal short circuit can be significantly reduced, thereby delaying the occurrence of a meltdown phenomenon. In addition, by suppressing the heat generation of the secondary battery in which an internal short circuit has occurred, additional heat generation and / or a meltdown phenomenon in an adjacent secondary battery can be prevented, thereby securing time to respond to (or deal with) a problem caused by an internal short circuit. In addition, by allowing a significantly low amount of current (i.e., leakage current) to flow at the internal short circuit point of the secondary battery, abnormal operation such as an internal short circuit can be easily determined / diagnosed, thereby providing an advantage in that it is easy to respond to abnormal operation of the secondary battery.

[0078] In order to satisfy the volume resistance of the above-described range, the cathode according to the present invention can control the components forming the coating layer, the content of each component, the mixing form and size of each component, the thickness ratio of the cathode active layer and the coating layer, etc.

[0079] Specifically, the coating layer does not function as a resistive layer during normal operation of the secondary battery, so that overvoltage does not occur during charging and discharging, and in the event of abnormal operation such as an internal short circuit, it functions as a resistive layer that prevents direct current flow between the negative electrode active layer and the positive electrode active layer and / or the negative electrode active layer and the positive electrode current collector due to their contact, while allowing a small amount of current to leak. To this end, the coating layer may have a form coated on the negative electrode active layer so as to cover the entire exposed surface of the negative electrode active layer, and in some cases, it may be selectively disposed only on the edge and / or end surface of the negative electrode active layer that is easy to contact with the positive electrode current collector (and / or the positive electrode active layer, etc.), or it may be selectively disposed only in the center of the negative electrode active layer that can come into contact with the positive electrode current collector (and / or the positive electrode active layer, etc.) when the separator is damaged by an external force.

[0080] In addition, the coating layer can implement a volume resistance to the extent that it can prevent current from directly flowing due to contact between the negative electrode active layer and the positive electrode active layer and / or the negative electrode active layer and the positive electrode current collector when an internal short circuit occurs by including aluminum-containing particles and a conductive material, but allows a predetermined amount of current to leak.

[0081] "Aluminum-containing particles" refers to particles containing aluminum element (Al) as a main component among metal components. Specifically, in the present invention, the aluminum-containing particles are particles containing a metal compound represented by the following chemical formula 1:

[0082] [Chemical Formula 1]

[0083] Al p O q (OH) r

[0084] In chemical formula 1,

[0085] p is an integer from 1 to 10, q is an integer from 0 to 20, and p≤q,

[0086] r is an integer from 1 to 5.

[0087] Typically, a cathode having a coating layer on a cathode active layer has a structure in which a metal oxide such as silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), or zirconium oxide (ZrO2) is included in the coating layer for the purpose of blocking the movement of current in the event of an internal short circuit. However, since the above-described metal oxides have high insulating properties, a coating layer including them completely blocks current leaking into and / or out of the battery in the event of an internal short circuit.

[0088] However, the present invention includes a conductive material in the form of particles having aluminum oxide hydroxide crystals as in Chemical Formula 1 in the coating layer, thereby providing insulation to the surface of the coating layer when an internal short circuit occurs, and at the same time allowing a very small amount of current to leak into and / or out of the battery. In addition, the aluminum-containing particles have the advantage of being inexpensive to manufacture, thereby increasing economic feasibility in mass production of secondary batteries.

[0089] These aluminum-containing particles include boehmite (γ-AlO(OH)), pseudoboehmite (AlO(OH)), diaspore (α-AlO(OH)), and akdalaite (Al 10 O 14 (OH)2) and aluminum trihydroxide.

[0090] In addition, the aluminum-containing particles have an average particle diameter (D) in the range of 0.1 ㎛ to 3.0 ㎛ 50) may have. Specifically, the aluminum-containing particles have an average particle diameter (D) in the range of 0.1 ㎛ to 2.0 ㎛; 0.1 ㎛ to 0.9 ㎛; 0.5 ㎛ to 1.5 ㎛; 0.3 ㎛ to 0.9 ㎛; 0.5 ㎛ to 0.9 ㎛; 0.3 ㎛ to 0.7 ㎛; 0.4 ㎛ to 0.8 ㎛; 0.1 ㎛ to 0.7 ㎛; 0.1 ㎛ to 0.5 ㎛; 0.2 ㎛ to 0.4 ㎛; or 0.25 ㎛ to 0.35 ㎛ 50 ) can have.

[0091] The above aluminum-containing particles have an average particle diameter (D 50 ) is less than the above-described range, the dispersibility of the aluminum-containing particles is reduced, so that the aluminum-containing particles may be included in the coating layer in an unevenly aggregated form. Accordingly, there is a problem that the electrical properties of the coating layer are reduced. In addition, the average particle diameter (D) of the aluminum-containing particles 50 ) If the above-described range is exceeded, it is difficult to thin the coating layer, so there is a limit to the reduction in the energy density of the cathode.

[0092] Additionally, the coating layer includes a conductive material along with aluminum-containing particles to achieve a predetermined volume resistance. The conductive material prevents high resistance from being added to the coating layer, while also improving the energy density and energy efficiency of the negative electrode during normal operation of the secondary battery.

[0093] The above-mentioned conductive material may include graphite-based materials such as natural graphite and artificial graphite; carbon black-based materials such as acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, and summer black; graphene; and carbon nanotubes, alone or in combination of two or more.

[0094] The above coating layer can control the volume resistance of the cathode within a predetermined range by including aluminum-containing particles and a conductive material in a predetermined amount.

[0095] Specifically, the aluminum-containing particles may be included in an amount exceeding 50 parts by weight based on 100 parts by weight of the entire coating layer, and the conductive material may be included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the entire aluminum-containing particles.

[0096] More specifically, the coating layer may contain aluminum-containing particles in an amount of 55 parts by weight or more; 60 parts by weight or more; 70 parts by weight or more; 80 parts by weight or more; 90 parts by weight or more; 95 parts by weight or more; 55 parts by weight to 99.99 parts by weight; 70 parts by weight to 99.99 parts by weight; 80 parts by weight to 99.99 parts by weight; 90 parts by weight to 99.99 parts by weight; 95 parts by weight to 99.99 parts by weight; or 99 parts by weight to 99.99 parts by weight, based on the total of 100 parts by weight.

[0097] In addition, the conductive agent may be included in an amount of 0.01 to 4.5 parts by weight, 0.01 to 4.0 parts by weight, 0.01 to 3.0 parts by weight, 0.01 to 2.5 parts by weight, 0.01 to 2.0 parts by weight, 0.01 to 1.5 parts by weight, 0.01 to 1.0 parts by weight, 0.05 to 0.9 parts by weight, 0.05 to 2 parts by weight, 0.1 to 4 parts by weight, or 0.05 to 0.5 parts by weight, based on 100 parts by weight of the total aluminum-containing particles.

[0098] The present invention allows for easy control of the volume resistance of the negative electrode within a predetermined range by controlling the content within the aforementioned range, such that aluminum-containing particles are included as the main component of the coating layer and a small amount of a conductive agent is included. In addition, by controlling the content of the aluminum-containing particles and the conductive agent within the aforementioned range, the electrical performance resistance of the negative electrode due to the coating layer can be prevented, thereby effectively improving high-temperature safety while maintaining the electrical performance of the negative electrode.

[0099] In addition, the coating layer may include a dispersant along with aluminum-containing particles and a conductive agent. The dispersant serves to uniformly disperse the aluminum-containing particles and the conductive agent within the coating layer without agglomeration.

[0100] Specifically, the dispersant may include a dispersant that stabilizes the particle surface by interacting with elements contained in the aluminum-containing particles and the conductive material, respectively, thereby preventing agglomeration of the particles. To this end, the dispersant may include one or more carboxylic acids.

[0101] For example, the dispersant may be a tricarboxylic acid such as citric acid, methane tricarboxylic acid, ethane tricarboxylic acid, benzene-1,3,5-tricarboxylic acid, 5-sulfo-1,2,4-benzenetricarboxylic acid, etc.; Tetracarboxylic acids such as ethane-1,1,2,2-tetracarboxylic acid, propane-1,1,2,3-tetracarboxylic acid, butane-1,2,3,4-tetracarboxylic acid, cyclopentane-1,2,3,4-tetracarboxylic acid, and benzene-1,2,4,5-tetracarboxylic acid; It may include a pentacarboxylic acid such as benzene-1,2,3,4,5-pentacarboxylic acid or a hexacarboxylic acid such as benzene-1,2,3,4,5,6-hexacarboxylic acid (mellitic acid).

[0102] In addition, since the electrical properties of the coating layer are greatly influenced by the aluminum-containing particles, the dispersant contained in the coating layer may be contained in the coating layer within a predetermined range. Specifically, the dispersant may be contained in an amount of 5 to 15 parts by weight based on 100 parts by weight of the total aluminum-containing particles, and more specifically, may be contained in an amount of 5 to 12 parts by weight, 8 to 12 parts by weight, 5 to 10 parts by weight, 10 to 15 parts by weight, or 9 to 11 parts by weight based on 100 parts by weight of the total aluminum-containing particles.

[0103] The present invention can prevent aluminum-containing particles from agglomerating due to a small amount of dispersant by controlling the content of the dispersant within the above range, while preventing the electrical properties of the coating layer from deteriorating due to an excessive amount of dispersant.

[0104] Furthermore, the coating layer may further include a binder to strengthen the adhesion between the aluminum-containing particles and the conductive material. The binder is not particularly limited as long as it is applied to the active layer of the positive and / or negative electrodes, but may preferably include at least one of butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyalkyl acrylate, polyamide (PA), and polystyrene (PS).

[0105] At this time, the binder may be included in an amount of 5 parts by weight or less based on 100 parts by weight of the entire coating layer, and specifically, may be included in an amount of 0.1 parts by weight to 5 parts by weight, 0.1 parts by weight to 4 parts by weight, 0.1 parts by weight to 3 parts by weight, 0.1 parts by weight to 2 parts by weight, 0.1 parts by weight to 1 part by weight, or 1 part by weight to 3 parts by weight.

[0106] Furthermore, the coating layer may contain aluminum-containing particles, a conductive agent, and a dispersant in a predetermined content ratio. For example, the coating layer may contain, based on 100 parts by weight of the total, 85 to 99 parts by weight of aluminum-containing particles; 0.01 to 5 parts by weight of a conductive agent; and 0.99 to 10 parts by weight or less of a dispersant.

[0107] For example, the coating layer may include 90 to 91 parts by weight of aluminum-containing particles; 0.05 to 0.15 parts by weight of a conductive agent; and 8.85 to 9.95 parts by weight of a dispersant, based on 100 parts by weight of the total.

[0108] The present invention can include a coating layer in which aluminum-containing particles and a conductive agent are uniformly dispersed in the negative electrode by controlling the content ratio of each component contained in the coating layer as described above. In addition, since the coating layer can achieve high morphological stability, the coating layer can be prevented from being damaged during the manufacturing process of the negative electrode or the assembly process of the battery. In addition, by controlling the content ratio of each component contained in the coating layer as described above, the volume resistance of the negative electrode can be easily controlled within a predetermined range according to the present invention.

[0109] Meanwhile, the average thickness of the coating layer may be in the range of 1.5 µm to 30 µm, and the average thickness may be greater than the average particle diameter of the aluminum-containing particles. Specifically, the average thickness of the coating layer may be 1.5 µm to 20 µm; 1.5 µm to 10 µm; 1.5 µm to 5 µm; 1.5 µm to 3 µm; 3 µm to 9 µm; 3 µm to 7 µm; 5 µm to 25 µm; 5 µm to 20 µm; 5 µm to 18 µm; 5 µm to 15 µm; 5 µm to 10 µm; 5 µm to 8 µm; 10 µm to 20 µm; 11 µm to 19 µm; 8 µm to 13 µm; 10 µm to 15 µm; 14 µm to 19 µm; 15 µm to 18 µm; 12 µm to 16 µm; Or, it may have an average thickness in the range of 11㎛ to 14㎛. In this case, the average thickness of the coating layer may be measured by a method commonly applied in the art to measure the thickness of a thin film. The average thickness may mean an average of any multiple values ​​measured in this way, or may mean a middle value between the largest and smallest values ​​among the measured values.

[0110] Additionally, the coating layer may have a thickness ratio to the negative electrode active layer in the range of 0.05 to 0.3, specifically, in the range of 0.05 to 0.2; 0.05 to 0.1; 0.05 to 0.09; 0.07 to 0.12; 0.1 to 0.2; 0.15 to 0.25; or 0.15 to 0.2.

[0111] The volume resistance of the negative electrode according to the present invention may be affected by i) the volume resistance of the coating layer and ii) the thickness ratio of the negative electrode active layer and the coating layer. Here, the volume resistance of the coating layer can be controlled through the components constituting the coating layer, the content of each component, the mixing form and size of each component, etc. as described above. However, even if the volume resistance of the coating layer is controlled, if the thickness of the negative electrode active layer is excessively thicker than the coating layer and the thickness ratio of the coating layer to the negative electrode active layer is smaller than the lower limit described above, the volume resistance of the negative electrode may decrease, which may significantly deteriorate the insulation in the event of an internal short circuit. In addition, if the thickness of the negative electrode active layer is equal to or smaller than the coating layer and the thickness ratio of the coating layer to the negative electrode active layer is larger than the upper limit described above, the volume resistance of the negative electrode significantly increases. Therefore, although the short-circuit current of the secondary battery is blocked in the event of an internal short circuit, it is not easy to selectively detect and respond to an internally short-circuited secondary battery in a short period of time in a device including a plurality of secondary batteries, such as a battery module or pack, and there is a limitation in that the economic feasibility is low.

[0112] That is, the present invention can realize a high energy density of the negative electrode by controlling the thickness ratio of the coating layer to the negative electrode active layer within the above-described range, and can minimize the volume expansion rate of the negative electrode during normal operation of the secondary battery. In addition, the negative electrode has the advantage of physically protecting the negative electrode surface while preventing a significant increase in resistance due to excessive thickness in the event of an internal short circuit.

[0113]

[0114] Meanwhile, the negative electrode active layer included in the negative electrode may include a carbon-based negative electrode active material, and the carbon-based negative electrode active material may include a carbon-based negative electrode active material commonly applied in the art. For example, the carbon-based negative electrode active material refers to a material containing carbon atoms as a main component, and the carbon-based negative electrode active material may include at least one selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, and Ketjen black. Specifically, the carbon-based negative electrode active material may include at least one of natural graphite and artificial graphite, but preferably, it may include natural graphite or a mixture of natural graphite and artificial graphite.

[0115] In addition, it is preferable that the carbon-based negative electrode active material is a spherical graphite assembly formed by aggregating a plurality of flake-shaped graphite. Examples of the flake-shaped graphite include, in addition to natural graphite and artificial graphite, mesophase calcined carbon (bulk mesophase) using tar and pitch as raw materials, and graphitized coke (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.), and in particular, one assembled using a plurality of highly crystalline natural graphites is preferable. In addition, one graphite assembly can be formed by aggregating 2 to 100, preferably 3 to 20, flake-shaped graphite.

[0116] In addition, the carbon-based negative electrode active material has an average particle diameter (D) in the range of 0.5 μm to 20 μm. 50 ) can be represented, and specifically, the average particle diameter (D) in the range of 0.5 ㎛ to 15 ㎛; 0.5 ㎛ to 10 ㎛; 1 ㎛ to 15 ㎛; 5 ㎛ to 20 ㎛; 10 ㎛ to 20 ㎛; 12 ㎛ to 18 ㎛; 2 ㎛ to 7 ㎛; 0.5 ㎛ to 5 ㎛; or 1 ㎛ to 3 ㎛ 50 ) can be expressed.

[0117] In addition, the negative electrode active layer may optionally further include a conductive agent, a binder, other additives, etc., as needed, along with the carbon-based negative electrode active material as the main component.

[0118] The above-mentioned challenge material may include one or more of carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0119] For example, the cathode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. alone or in combination as a conductive material.

[0120] At this time, the content of the conductive material may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, and specifically, may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight. By controlling the content of the conductive material within the above range, the present invention can prevent the resistance of the negative electrode from increasing due to a low content of the conductive material, thereby reducing the charging capacity, and can prevent the problem of the content of the negative electrode active material decreasing due to an excessive amount of the conductive material, thereby reducing the charging capacity, or the problem of the rapid charging characteristics from decreasing due to an increase in the loading amount of the negative electrode active layer.

[0121] In addition, the binder may be appropriately applied as a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and may be applied within a range that does not deteriorate the electrical properties of the electrode. Specifically, the binder may include at least one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber, and fluororubber.

[0122] The content of the binder may be 0.1 to 10 parts by weight based on 100 parts by weight of the entire negative electrode active layer, and specifically, may be 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight. By controlling the content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent the adhesive strength of the active layer from being lowered due to a low content of binder or the electrical properties of the electrode from being lowered due to an excessive amount of binder.

[0123] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used. In the case of copper or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the negative electrode current collector can be appropriately applied in the range of 1 to 500 ㎛ in consideration of the conductivity and total thickness of the negative electrode to be manufactured.

[0124]

[0125] secondary batteries

[0126] In addition, the present invention,

[0127] A secondary battery is provided, comprising: a positive electrode; a negative electrode according to the present invention described above; and a separator disposed between the positive electrode and the negative electrode.

[0128]

[0129] The secondary battery according to the present invention may be a lithium secondary battery. The secondary battery includes an electrode assembly having a structure in which a separator is arranged between the positive electrode and the negative electrode of the present invention described above, and has a structure in which the electrode assembly is inserted into a battery case and then an electrolyte composition is injected and sealed.

[0130] At this time, since the negative electrode has the same configuration as the configuration of the negative electrode for a secondary battery according to the present invention described above, a detailed description thereof is omitted.

[0131] In addition, the positive electrode has a positive electrode composite layer manufactured by applying, drying, and pressing a positive electrode slurry containing a positive electrode active material on a positive electrode current collector, and the positive electrode composite layer may optionally further include a conductive material, a binder, other additives, etc., as needed.

[0132] Here, the positive electrode active material is a material capable of causing an electrochemical reaction on the positive electrode collector, and may include at least one lithium metal oxide represented by the following chemical formulas 2 and 3, which is capable of reversibly intercalating and deintercalating lithium ions:

[0133] [Chemical Formula 2]

[0134] LiFe a M 1 1-a XO4

[0135] [Chemical Formula 3]

[0136] Li x [Ni y Co zMnwM 2 v ]O2

[0137] In the above chemical formulas 2 and 3,

[0138] M 1 is at least one element among W, Cu, Fe, V, Cr, Co, Ni, Mn, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0139] X is one or more of P, Si, S, As, and Sb,

[0140] a is 0 <a≤1.0이고,

[0141] M 2 is at least one element among W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo,

[0142] x, y, z, w, and v are 1.0≤x≤1.30, 0≤y<1, 0≤z≤1, 0≤w≤1, 0≤v≤0.1, respectively, but y+z+w+v=1.

[0143]

[0144] Each compound represented by the above Chemical Formula 2 and Chemical Formula 3 is a lithium metal oxide used in the art as a cathode active material for secondary batteries. Among these, the lithium composite metal oxide represented by Chemical Formula 3 is a ternary lithium oxide mainly composed of nickel (Ni), cobalt (Co), and manganese (Mn), and has a high energy density, making it suitable for use in medium and large secondary batteries for transportation such as electric vehicles (EVs) or power storage such as energy storage systems (ESSs) in terms of performance such as output.

[0145] At this time, the lithium metal oxide represented by chemical formula 3 is LiNi 0.8 Co0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 May include O2, etc.

[0146] The lithium composite metal oxide has an increased charge / discharge capacity as the nickel (Ni) content increases, but it exhibits low chemical and structural stability, so there is a problem that an exothermic reaction is likely to occur, which increases the possibility of ignition. In particular, the exothermic reaction may occur when a short-circuit current flows inside the battery. Accordingly, the secondary battery according to the present invention introduces a coating layer that satisfies a predetermined volume resistivity into the negative electrode, thereby suppressing the exothermic reaction in the event of an internal short circuit due to contact between the negative electrode surface and the positive electrode current collector (and / or positive electrode active layer), while allowing a significantly small amount of current to leak, thereby preventing problems that occur continuously after the internal short circuit, thereby improving safety.

[0147] Meanwhile, compounds represented by the chemical formula 2 include LiFePO4, LiFe 0.8 Mn 0.2 PO4, LiFe 0.7 Mn 0.3 PO4.0 LiFe 0.5 Mn 0.5 May include PO4, etc.

[0148] In addition, the positive electrode active material may be included in an amount of 85 parts by weight or more based on 100 parts by weight of the entire positive electrode active layer, and specifically, may be included in an amount of 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0149] In addition, the positive electrode active layer may further include a conductive agent, a binder, other additives, etc., along with the positive electrode active material.

[0150] At this time, the conductive material is used to improve the electrical performance of the anode, and can be applied as a material commonly used in the art, but specifically, it can include at least one of graphite compounds such as natural graphite and artificial graphite; carbon black such as acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, and summer black; graphene; and carbon nanotubes.

[0151] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight based on 100 parts by weight of the entire positive electrode active layer, and specifically, may be included in an amount of 0.1 to 4 parts by weight; 2 to 4 parts by weight; 1.5 to 5 parts by weight; 1 to 3 parts by weight; 0.1 to 2 parts by weight; or 0.1 to 1 part by weight.

[0152] In addition, the binder serves to bind the positive electrode active material, the positive electrode additive, and the conductive material to each other, and any binder having this function may be used without particular limitation. Specifically, the binder may include at least one resin selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

[0153] In addition, the binder may be included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the entire positive electrode active layer, specifically 2 to 8 parts by weight; or 1 to 5 parts by weight.

[0154] The total thickness of the above-mentioned positive electrode active layer is not particularly limited, but may be specifically in the range of 50 µm to 300 µm, and more specifically in the range of 100 µm to 200 µm; 80 µm to 150 µm; 120 µm to 170 µm; 150 µm to 300 µm; 200 µm to 300 µm; or 150 µm to 190 µm.

[0155] In addition, the positive electrode can be used as a positive electrode current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used, and in the case of aluminum or stainless steel, a material surface-treated with carbon, nickel, titanium, silver, etc. can also be used. In addition, the average thickness of the current collector can be appropriately applied in the range of 3 to 500 ㎛, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0156] Meanwhile, the separator interposed between the positive and negative electrodes of each unit cell is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the art, but specifically, one containing at least one polymer selected from the group consisting of polypropylene, polyethylene, and polyethylene-propylene copolymers having chemical resistance and hydrophobicity can be used. The separator may have a porous polymer substrate form such as a sheet or non-woven fabric containing the above-described polymer, and in some cases, may have a composite separator form in which organic or inorganic particles are coated on the porous polymer substrate using an organic binder. In addition, the separator may have an average pore diameter of 0.01 to 10 μm, and an average thickness of 5 to 300 μm.

[0157] Meanwhile, the secondary battery according to the present invention is not particularly limited, but may be a secondary battery having a stacked, zigzag, or zigzag-stacked electrode assembly having a relatively high possibility of contact between the positive electrode current collector (and / or positive electrode active layer) and the negative electrode active layer. For example, the secondary battery according to the present invention may be a pouch-type secondary battery or a square-shaped secondary battery.

[0158]

[0159] secondary battery system

[0160] Furthermore, the present invention,

[0161] A plurality of cell assemblies each including n secondary batteries according to the present invention (wherein 3≤n≤100 is an integer),

[0162] A charging / discharging unit that electrically couples multiple cell assemblies and individually charges or discharges them,

[0163] A sensing unit that is electrically connected to the electrodes of each secondary battery included in a plurality of cell assemblies and individually measures at least one of the voltage and current of the secondary battery during charging and discharging of each secondary battery, and

[0164] It includes a control unit that controls charging or discharging of each cell assembly by electrically connecting to the charging / discharging unit and the sensing unit,

[0165] The above control unit provides a secondary battery system that stops charging or discharging of a cell assembly including the secondary battery when the current amount measured by the sensing unit satisfies a predetermined value.

[0166]

[0167] FIG. 1 is a schematic diagram of a configuration of a secondary battery system according to the present invention. Referring to FIG. 1, a secondary battery system (10) according to the present invention includes a plurality of cell assemblies (110) each including n (wherein 3≤n≤100 is an integer) of the secondary batteries (111) of the present invention described above; a charging / discharging unit (120) electrically coupled to each of the plurality of cell assemblies (110) to individually charge or discharge them; a sensing unit (130) electrically coupled to an electrode of each secondary battery (111) included in the plurality of cell assemblies (110) to individually measure a current voltage and / or current of each secondary battery (111) when charging / discharging the secondary battery; and a control unit (140) electrically coupled to the charging / discharging unit (120) and the sensing unit (130) to control charging or discharging of each cell assembly (110).

[0168] The secondary battery system (10) can individually measure and monitor the voltage and / or current of n secondary batteries (111) constituting a cell assembly (110) when charging or discharging the secondary battery, thereby determining an internal short circuit of the secondary battery (111), and has a configuration that immediately stops only the charging or discharging of the cell assembly (110) including the secondary battery (111) when an internal short circuit is determined.

[0169] Specifically, conventional secondary battery systems have developed technologies to diagnose internal short circuits within secondary batteries by measuring temperature changes in the battery during charging and / or discharging, or through changes in the state of charge (SOC) caused by self-discharge in the event of an internal short circuit. However, when an internal short circuit actually occurs in a secondary battery, thermal runaway occurs within a short period of time due to the meltdown phenomenon. However, the above technologies have limitations in that the accuracy of the diagnosis is low, or the diagnosis process is complicated, so it takes a long time to recognize the internal short circuit, making it difficult to respond to thermal runaway.

[0170] However, the secondary battery system (10) according to the present invention includes the secondary battery (111) of the present invention mentioned above, and the secondary battery has a negative electrode having a coating layer having a predetermined volume resistance on the surface of the negative electrode active layer, so that when an internal short circuit occurs due to contact between the positive electrode current collector (or the positive electrode active layer) and the negative electrode surface, it is possible to allow a remarkably low amount of leakage current to flow in the negative electrode while implementing appropriate insulation on the negative electrode surface. Accordingly, when an internal short circuit occurs, the current voltage and current of conventional secondary batteries are close to 0 V and 0 A, respectively, due to the leakage current, but in the secondary battery (111) according to the present invention, a predetermined current flows with a very small amount of leakage current lost from the applied current, so that the internal short circuit of the secondary battery (111) can be detected and / or determined with high accuracy in a remarkably short time by using this. In addition, the secondary battery (111) can significantly reduce heat generated by internal short circuits, such as short circuit heat, thereby delaying the occurrence of a meltdown phenomenon. Furthermore, since the heat of the secondary battery in which an internal short circuit has occurred can prevent additional heat generation and / or meltdown of adjacent secondary batteries, it is possible to secure response (or processing) time to prevent thermal runaway of the secondary battery in which an internal short circuit has occurred.

[0171] To this end, the sensing unit (130) is electrically coupled to the secondary battery (111) separately from the charging / discharging unit (120), so that the electrical properties flowing through the secondary battery electrodes, particularly the negative electrodes, can be measured for each secondary battery in real time when the secondary battery (111) is being charged or discharged. Here, the 'electrical properties' are properties for electricity flowing through the electrodes of the secondary battery, particularly the negative electrodes, and may include current flow, current flow voltage, etc. The electrical properties measured in this way can be transmitted to the control unit (140).

[0172] For example, the sensing unit (130) can individually measure at least one of the voltage and current of each secondary battery (111). The secondary battery system (10) according to the present invention includes the secondary battery (111) of the present invention described above in a cell assembly, so that even if an internal short circuit occurs, a predetermined current is applied while a trace amount of leakage current is lost while insulation is implemented on the surface of the negative electrode, so that it is possible to individually and quickly diagnose whether an internal short circuit of the secondary battery (111) occurs through a change in at least one of the voltage and current.

[0173] The sensing unit (130) may include means commonly applied in the art to measure electrical properties flowing in each secondary battery (111). For example, the sensing unit (130) may include a current measuring sensor for measuring current flow, a voltage measuring sensor for measuring voltage flow, etc.

[0174] In addition, the sensing unit (130) may further include a temperature measuring sensor (not shown) for measuring the temperature of each secondary battery (111) provided in the cell assembly (110) inside the cell assembly (110). The current of the secondary battery may increase when the temperature of the secondary battery rises. This increase in the temperature of the secondary battery may occur when an overload is caused by a change in the load connected to the system; when a transformer or condenser is turned on or off; or when excessive current flows during the operation of an electric motor. The sensing unit (130) may further include a temperature measuring sensor for measuring the temperature of each secondary battery (111) in order to reflect a change in the current due to a temperature rise of the secondary battery in addition to an internal short circuit of the secondary battery, thereby further reducing the error rate when determining an internal short circuit.

[0175] Furthermore, the control unit (140) is electrically coupled to the charging and discharging unit (120) and the sensing unit (130), respectively. The control unit (140) monitors the electrical properties of each secondary battery (111) in real time when each cell assembly (110) is charged and / or discharged, and individually detects and / or determines an internal short circuit of the secondary battery (111) through a change in the electrical properties, and controls the charging or discharging of the cell assembly (110) including the secondary battery (111) in which the internal short circuit has occurred.

[0176] For example, the control unit (140) monitors the electrical properties of each secondary battery (111) transmitted in real time from the sensing unit (130), and when there is a change in the transmitted electrical properties, determines whether the amount of change satisfies a predetermined value; and when the predetermined value is satisfied, individually controls the charging or discharging of the cell assembly (110) including the secondary battery (111) through the charging / discharging unit (120).

[0177] Specifically, the control unit (140) first receives the individual current flow amounts for all secondary batteries (111) included in the secondary battery system (10) from the sensing unit (130), and calculates the current flow amounts of each cell assembly (110) including them and the average value of the current flow amounts of the plurality of cell assemblies (110), i.e., the average current flow amount (A) of the cell assembly (110), from the received individual current flow amounts of the secondary batteries (111). Here, the current flow amount may mean a current flow voltage and / or a current flow, and may be a correction value reflected according to the temperature of each secondary battery measured by the temperature measurement sensor of the sensing unit (130). In addition, the average current flow amount (A) of the plurality of cell assemblies (110) may be the average current flow amount of all cell assemblies included in the secondary battery system, and in some cases, may be the average current flow amount of a part of the cell assemblies of the entire cell assemblies.

[0178] The average current flow (A) of the cell assemblies (110) thus calculated and the current flow of each cell assembly (110) are individually compared to select cell assemblies (110) having an error rate of 5% or more, specifically 7% or more; 10% or more; 5 to 20%; or 5 to 15%. The primary selection refers to a process of selecting cell assemblies including secondary batteries that are recognized as having a problem among all secondary batteries. The primary selection can shorten the time required to monitor the preset applied current flow and the current flow of each secondary battery during charging and discharging for all secondary batteries, and thus can provide speed in determining an internal short circuit in the secondary battery system.

[0179] In addition, the n secondary batteries included in each cell assembly may have a voltage difference between cells during charging and discharging. Such a voltage difference between cells may be caused by the manufacturing process of each secondary battery or external factors. The voltage difference between cells may affect the capacity and lifespan of the secondary battery and may cause overcharging and / or overdischarging of individual secondary batteries, so cell balancing may be performed to prevent this. Cell balancing may be performed by applying a microcurrent to the circuit structure applied to the secondary battery system. In this case, a deviation in the current flow rate between the secondary batteries may be induced. Therefore, by setting the error rate between the average current flow rate (A) and the current flow rate of each secondary battery to 5% or more, the accuracy of determining an internal short circuit can be further improved.

[0180] Next, the control unit (140) can determine an internal short circuit of the secondary battery if the current capacity of the individual secondary battery is 0.5% or more lower than the preset current capacity when charging or discharging the secondary battery (111) included in the primarily selected cell assembly (110).

[0181] In general, when an internal short circuit occurs in a secondary battery, a leakage current occurs at the short circuit point, so that the current and voltage may be close to 0A and 0V, respectively, when measured. However, in the secondary battery system according to the present invention, not only is a predetermined insulation realized on the surface of the negative electrode when an internal short circuit occurs due to the coating layer of the negative electrode provided in the secondary battery, but a predetermined current may also be passed. Since the current is a small amount of current that has leaked from the internal short circuit point in the applied current, it may be lower than the preset applied current amount for charging or discharging the secondary battery. The deviation between the preset applied current amount and the current amount may be 0.5% or more of the preset applied current amount, and specifically, 0.5% or more; 1% or more; 2% or more; 3% or more; 5% or more; 10% or more; 15% or more; 20% or more; 30% or more; 50% or more; 70% or more; 5~90%; 5~50%; 10~30%; 50~90%; 0.5~20%; 0.5~10%; 0.5~5%; 0.5~3%; 5~10%; or 0.5~20%.

[0182] The control unit (140) may send a charge or discharge stop signal to the charge / discharge unit (120) to stop charging or discharging of the cell assembly (110) including the secondary battery (111) in order to stop charging or discharging of the secondary battery (111) determined to have an internal short circuit. When the charge / discharge unit (120) receives the charge or discharge stop signal from the control unit (140), the charge / discharge unit (120) may selectively stop charging or discharging of the cell assembly (110) including the secondary battery (111). The present invention controls charging or discharging in units of cell assemblies when an internal short circuit of a secondary battery occurs, thereby reducing the response time compared to when responding to an internal short circuit at the secondary battery level, and also increasing the maintenance efficiency during normal use of the secondary battery system.

[0183] Meanwhile, the cell assembly (110) may include two or more secondary batteries (111) of the present invention, and specifically, may include 2 to 100; 2 to 50; 2 to 30; 5 to 20; 3 to 5; 5 to 20; or 10 to 20 secondary batteries (111).

[0184] These multiple secondary batteries (111) can be electrically connected in series, parallel, or a series-parallel combination.

[0185] For example, n secondary batteries can be connected in parallel and mounted inside a cell assembly. The secondary battery system according to the present invention controls charging / discharging on a cell assembly basis when an internal short circuit occurs. However, when n secondary batteries provided inside a cell assembly are electrically connected in parallel, there is an advantage in that the charging / discharging of the secondary battery in which an internal short circuit occurs among the n secondary batteries can be individually additionally controlled.

[0186] If an internal short circuit occurs in any secondary battery, there is an advantage in that the charging or discharging of each secondary battery can be controlled.

[0187] In addition, the cell assembly (110) may be a battery module or a battery bank, depending on the number of secondary batteries contained therein or the shape and / or type of the housing containing them. In addition, when a plurality of such cell assemblies (110) are included (150), it may refer to a battery pack or an energy storage system.

[0188] In addition, the charging / discharging unit (120) has a function of individually electrically coupling with a plurality of cell assemblies (110) to charge or discharge each cell assembly (110), and for this purpose, it can be electrically coupled with an external power source (PS) for charging the cell assemblies (110) and an electric load (EL) for using the power stored in the cell assemblies (110).

[0189] Here, the types of the external power source (PS) and electric load (EL) are not particularly limited as long as they are commonly applied to products to which the secondary battery system (10) is applied.

[0190] For example, the external power source (PS) is a means for supplying charging power of constant current or constant voltage to each of the cell assemblies (110). When the secondary battery system (10) is applied to an electric vehicle (EV), it may include a charging station for the electric vehicle (EV), and in some cases, it may include a separate power source or auxiliary battery included inside the electric vehicle (EV).

[0191] In addition, the electric load (EL) is a means for discharging secondary batteries (111) provided in the cell assembly (110) using the power stored in the cell assembly (110), and when the secondary battery system (10) is applied to an electric vehicle (EV), it may be an inverter and an electric motor applied to the electric vehicle (EV). The inverter may perform a function of converting direct current provided from the cell assembly (110) included in the secondary battery system (10) into alternating current, and the electric motor may be driven using alternating current provided from the inverter.

[0192] In addition, the secondary battery system (10) according to the present invention may further include an input / output unit (not shown) so that the charging / discharging conditions can be input to the control unit (140) and the user can check the results determined by the control unit (140).

[0193] The secondary battery system (10) above can change the applied voltage or applied current conditions during charging and / or discharging depending on the type of electrical load (EL) electrically connected to the charging and / or discharging unit (120) or the usage environment. In order to input the changed charging / discharging conditions into the control unit (140), the input / output unit may include, but is not limited to, a user input means such as a keyboard, mouse, barcode reader, voice reader, or touch screen commonly applied in the art.

[0194] In addition, the input / output unit may include, but is not limited to, an output means such as a display device such as a monitor or touch screen, or an audio output device commonly used in the art, in order to inform the user of whether an internal short circuit has occurred; the time of occurrence; and the location of the secondary battery (111) and / or the cell assembly (110) where an internal short circuit has occurred, when the control unit (140) determines that an internal short circuit has occurred.

[0195]

[0196] Furthermore, since the secondary battery system (10) according to the present invention has the above-described configuration and thus has excellent safety against internal short circuits, it can be used as a power source for medium- to large-sized devices that require high energy density and high safety against internal short circuits. Specific examples of such medium- to large-sized devices include power tools that are powered by an electric motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (Escooters); electric golf carts; and energy storage systems (ESSs), and more specifically, hybrid electric vehicles (HEVs) are mentioned, but are not limited thereto.

[0197] Meanwhile, the electronic or electrical devices and / or any other related devices or components described herein may be implemented using any suitable hardware, firmware (e.g., application-specific integrated circuits), software, or a combination of software, firmware, and hardware. For example, the various components of these devices may be formed on a single integrated circuit (IC) chip or on individual IC chips. Furthermore, the various components of these devices may be implemented on a flexible printed circuit film, a tape carrier package (TCP), a printed circuit board (PCB), or a single substrate. The electrical connections or interconnections described herein may be implemented, for example, by wiring or conductive elements on a PCB or other type of circuit carrier. The conductive elements may include metallizations, such as surface metallizations, and / or pins, and may include conductive polymers or ceramics. Additionally, electrical energy can be transmitted wirelessly, for example, using electromagnetic radiation or light.

[0198] Additionally, various components of these devices may be processes or threads that execute on one or more processors to perform the various functions described herein, execute computer program instructions within one or more computing devices, and interact with other system components. The computer program instructions are stored in memory, which may be implemented in the computing device using standard memory devices, such as random access memory (RAM). The computer program instructions may also be stored on other non-transitory computer-readable media, such as CD-ROMs, flash drives, etc.

[0199] Additionally, those skilled in the art should recognize that the functions of various computing devices may be combined or integrated into a single computing device, or that the functions of a particular computing device may be distributed across one or more other computing devices without departing from the scope of the exemplary embodiments of the present invention.

[0200]

[0201] The secondary battery system according to the present invention, having the above-described configuration, can apply a predetermined current in the event of an internal short circuit, thereby preemptively controlling charging and / or discharging before thermal runaway occurs in the secondary battery in which the short circuit has occurred. Furthermore, since it can prevent additional meltdown and / or thermal runaway occurring in adjacent secondary batteries, it can be usefully applied to battery modules or battery packs in which multiple secondary batteries are applied.

[0202]

[0203] Hereinafter, the present invention will be described in more detail through examples and experimental examples.

[0204] However, the following examples and experimental examples are only illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0205]

[0206] Examples 1 to 8 and Comparative Examples 1 to 3. Manufacturing of secondary batteries

[0207] Manufacturing of anodes

[0208] LiNi with a particle size of 5㎛ as a cathode active material 0.8 Co 0.1 Mn 0.1 O2 was prepared, and a slurry was formed by mixing carbon-based materials and polyvinylidene fluoride as a binder with N-methyl pyrrolidone (NMP) in a weight ratio of 94:3:3, casting it on an aluminum sheet, drying it in a vacuum oven at 120°C, and then rolling it to manufacture a cathode.

[0209]

[0210] Manufacturing of cathode

[0211] A mixed graphite was prepared as an anode active material by mixing natural graphite (average particle size: 10±1㎛) and artificial graphite (average particle size: 8±1㎛) in a weight ratio of 2:8, and carbon black was prepared as a conductive material and carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) were prepared as binders. Then, 95 parts by weight of the mixed graphite, 1 part by weight of the carbon black, 1.5 parts by weight of the carboxymethyl cellulose (CMC), and 2.5 parts by weight of the styrene butadiene rubber (SBR) were mixed with water to obtain a solid content of 50% to prepare a cathode slurry.

[0212] Separately, metal-containing particles and citric acid as a dispersant were added to water and mixed for 10 minutes to disperse them. After that, Super-P (trade name: super C-65) as a conductive agent was added to the prepared dispersion and mixed for 20 to 30 minutes to prepare a coating slurry. At this time, ① type of metal-containing particles included in the coating slurry, ② average particle diameter (D 50 ) and ③ the content based on 100 parts by weight of the entire coating layer, ④ the content of the conductive agent based on 100 parts by weight of the entire metal-containing particles, and ⑤ the content of the dispersant were adjusted as shown in Table 1 below.

[0213] When the cathode slurry and coating slurry were each prepared, each slurry was simultaneously cast on a copper foil (thickness: 10㎛) being transported roll-to-roll (transport speed: 5 m / min) using a dual die coater. At this time, the cathode slurry and coating slurry were cast so that the average thicknesses were 100 to 200 ㎛ and 10 to 20 ㎛, respectively, along the transport direction of the copper foil. The copper foil on which each slurry was simultaneously cast was dried in a vacuum oven at 120℃ and then rolled to manufacture the cathode (thickness ratio of the coating layer to the cathode active layer: approximately 0.17). ⑥ The volume resistivity of the manufactured cathode was measured. The volume resistivity was measured using a volume resistivity meter (model name: XF057) equipped with 46 probes. Specifically, a constant current was applied while the 46 probes were in contact with the surface of the cathode active layer to measure the potential distribution generated on the surface at multiple points. Afterwards, the volume resistance of the cathode was calculated by performing a back analysis of the potential distribution using the finite volume method for the total thickness of the cathode active layer and coating layer and the measured potential values. The measured results are shown in Table 1.

[0214]

[0215] Manufacturing of lithium secondary batteries

[0216] A separator made of 18 μm polypropylene was placed between the prepared positive and negative electrodes, inserted into a pouch-type case, and then an electrolyte composition was injected to assemble a 1 Ah-class lithium secondary battery.

[0217] Metal-containing particlesMetal-containing particles standard content⑥ Volume resistivity of cathode [Ω·cm]① Type② D 50 ③ Content based on 100 parts by weight of coating layer [parts by weight] ④ Conductive agent [parts by weight] ⑤ Dispersant [parts by weight] Example 1 Boehmite 300±100 nm 90.80.1108.284×10 -2 Example 2 Boehmite 300±100 nm 88.53 105.816×10 -1 Example 3 Boehmite 300±100 nm 83.310101.137×10-5 Example 4 Boehmite 300±100 nm 98.90.115.169×10 -2 Example 5 Boehmite 300±100 nm 83.30.1203.253×10 -1 Example 6 Boehmite 50±10 nm 90.80.1103.382×10 -2 Example 7 Boehmite 4±0.5㎛90.80.1106.927×10 -1 Example 8Al2O3300±100 nm90.80.110> 1Comparative Example 1Boehmite300±100 nm90.9010> 1Comparative Example 2Si300±100 nm90.80.1107.418×10 -5 Comparative example 3SiO2 300±100 nm 90.80.110> 1

[0218]

[0219] Example 9. Manufacturing of secondary batteries

[0220] A lithium secondary battery was manufactured using the same method as Example 1, except that the negative electrode active layer and the coating layer were formed so that the thickness ratio of the coating layer (average thickness: 1.5 ㎛) to the negative electrode active layer was approximately 0.02. At this time, the volume resistance of the negative electrode was 2.816 × 10 -5 It was Ω·cm.

[0221]

[0222] Examples 10-18 and Comparative Examples 4-6. Manufacturing of secondary battery systems

[0223] A secondary battery system having a configuration as shown in Fig. 1 was manufactured using the lithium secondary batteries manufactured in Examples 1 to 9 and Comparative Examples 1 to 3.

[0224] Specifically, 10 lithium secondary batteries each manufactured in Examples 1 to 9 and Comparative Examples 1 to 3 were prepared, and 5 of the prepared lithium secondary batteries were arranged in the thickness direction of the batteries, and then fixed to manufacture two cell assemblies (110). A charge / discharge unit (120) and a sensing unit (130) were individually electrically connected in parallel to the positive electrode (111a) and the negative electrode (111b) of each lithium secondary battery provided in the cell assemblies. Here, the charge / discharge unit (120) was provided with a separate port so that an external power source (PS) and an electric load (EL) could be electrically connected. The sensing unit (130) was provided with a current measuring sensor for measuring the conduction current of the negative electrode (111b) and a temperature measuring sensor for measuring the surface temperature of each lithium secondary battery.

[0225] In addition, the charging / discharging unit (120) and the sensing unit (130) are each electrically connected to a control unit (140), and the control unit (140) is equipped with a touch screen for inputting voltage and current conditions during charging and / or discharging of each lithium secondary battery provided in the cell assembly (110), and outputting whether an internal short circuit occurs during charging / discharging; the time when an internal short circuit occurs; and the location of the corresponding lithium secondary battery (111) among the lithium secondary batteries of the cell assembly in which an internal short circuit is determined to have occurred.

[0226] An external power source (PS) and an electric load (EL) were connected to each port of the above charging / discharging unit (120), and charging / discharging of the cell assembly was performed. During the charging / discharging process of the cell assembly, it was confirmed that the sensing unit (130) measured the current flowing from the negative electrode of each lithium secondary battery and the surface temperature of the lithium secondary battery in real time and transmitted the measured data to the control unit (140). Thereafter, the surface of any lithium secondary battery (111) among the plurality of lithium secondary batteries (111) provided in the cell assembly (110) was pressed to induce an internal short circuit of the corresponding lithium secondary battery (111).

[0227] When an internal short circuit occurs in a lithium secondary battery (111), the sensing unit (130) measures the current and surface temperature of each lithium secondary battery provided in the cell assembly (110) and transmits the measured current and surface temperature of the lithium secondary battery to the control unit (140). The control unit (140) calculates the average value of each received current and reflects a correction value according to the temperature of each measured lithium secondary battery to the calculated average value to obtain the average current (A).

[0228] The control unit (140) compares the thus calculated average current value (A) with the current value of each transmitted lithium secondary battery to primarily select a lithium secondary battery having an error rate of 5 to 10%, and diagnoses that an internal short circuit has occurred in a lithium secondary battery having a current amount that is 0.5 to 5% lower than a preset applied current when charging or discharging the selected lithium secondary battery. In addition, the control unit (140) sent an electrical signal to the charge / discharge unit (120) to stop charging / discharging of the cell assembly (110) including the lithium secondary battery diagnosed as having an internal short circuit, and accordingly, the charging / discharging of the cell assembly (110) was stopped. In this regard, in the lithium secondary battery system of the embodiment, charging / discharging of the cell assembly was stopped before ignition of the lithium secondary battery occurred, but in the lithium secondary battery system of the comparative example, ignition of the lithium secondary battery occurred before charging / discharging of the cell assembly was stopped.

[0229] Thereafter, the control unit (140) transmitted to the input / output unit whether an internal short circuit occurred during charging / discharging, the time of occurrence of an internal short circuit, and the location of the lithium secondary battery (111) in which an internal short circuit occurred among the lithium secondary batteries of the cell assembly was determined to have occurred, and the input / output unit output the transmitted information to the touch screen.

[0230]

[0231] Experimental Example 1.

[0232] In order to evaluate the performance of the secondary battery system according to the present invention in the event of an internal short circuit, the following experiment was conducted.

[0233] Specifically, as shown in Fig. 4, a separator having a perforated center (211c-1) was used, and a positive electrode was used in which a positive electrode active layer was not formed in the center so that the positive electrode current collector (211a-1) and the negative electrode active layer (211b-2) were in contact with each other at the perforated portion of the separator, and the same method as in Examples 1 to 9 and Comparative Examples 1 to 3 was performed to manufacture experimental 1 Ah-class pouch-type lithium secondary batteries (N / P ratio = approximately 1.07).

[0234] Each manufactured lithium secondary battery was fully charged, and the central portion of the pouch-type lithium secondary battery was pressurized to 1 MPa to induce an internal short circuit. The conduction voltage and surface temperature of the lithium secondary battery were measured for 100 seconds. This internal short circuit induction experiment was repeated a total of three times.

[0235] The current-carrying voltage and surface temperature of the lithium secondary battery were measured 100 seconds after the internal short circuit, and their average values ​​were calculated. In addition, whether the lithium secondary battery caught fire after the internal short circuit was induced and the time it took for the battery temperature to reach the maximum were confirmed. The results are shown in Table 2 below. In addition, the voltage and temperature changes according to the elapsed time of Comparative Example 1 and Example 1 are shown in FIGS. 2 and 3, respectively.

[0236] Separately, a lithium secondary battery system manufactured in Example 10 was manufactured using a cell assembly each including one 1Ah-class experimental pouch-type lithium secondary battery manufactured previously and nine pouch-type lithium secondary batteries manufactured in Examples 1 to 9 and Comparative Examples 1 to 3. While performing charge and discharge of the manufactured lithium secondary battery system, an internal short circuit in the experimental lithium secondary battery was induced. At this time, the applied voltage during charge and discharge of the system was adjusted to 4.2 V.

[0237] Next, we examined whether the lithium secondary battery system could diagnose internal short circuits in experimental lithium secondary batteries and identify the locations of lithium secondary batteries where internal short circuits occurred. The results are presented in Table 2 below.

[0238] Internal short circuit induction test system of lithium secondary battery Whether internal short circuit exists Average current voltage [V] Average temperature Time required to reach maximum temperature Whether ignition occurs Example 14.10±0.05 39~42℃ Exceeding 60 seconds No ignition Example 23.70±0.10 45~50℃ Exceeding 60 seconds No ignition Example 30570~610℃ Approximately 20 seconds Ignition Example 43.90±0.10 30~50℃ Exceeding 60 seconds No ignition Example 54.00±0.10 30~45℃ Exceeding 60 seconds No ignition Example 63.80±0.10 30~50℃ Approximately 60 seconds No ignition Example 73.50±0.10 40~55℃ Approximately 45 seconds No ignition Example 84.21±0.0523~25℃-Non-ignition×Example 90550~580℃Approximately 10 seconds Ignition×Comparative example 14.21±0.0523~25℃-Non-ignition×Comparative example 20640~645℃Approximately 5 seconds Ignition×Comparative example 34.21±0.0525~27℃-Non-ignition×

[0239]

[0240] As shown in Table 2 and FIGS. 2 and 3, the lithium secondary battery of the embodiment according to the present invention was found to have insulation when an internal short circuit occurred in the lithium secondary battery, and at the same time, a small amount of leakage current was induced, so that the current voltage was lower than the applied voltage of 4.2 V but higher than 3.0 V. In addition, it was confirmed that the lithium secondary batteries of the embodiment had significantly low leakage current, so that the temperature of the battery was maintained at 60°C or lower. In addition, it was confirmed that the lithium secondary battery system including such a lithium secondary battery can diagnose whether an internal short circuit occurred in the lithium secondary battery by using a small amount of leakage current applied after an internal short circuit, and can also accurately determine the location thereof.

[0241] In contrast, the lithium secondary battery of the comparative example, which had a significantly lower volume resistivity of the coating layer, was found to rapidly increase in temperature within seconds of an internal short circuit, leading to ignition. Furthermore, due to this rapid thermal runaway, the lithium secondary battery system including the lithium secondary battery of the comparative example was found to be unable to determine whether the battery had an internal short circuit.

[0242] In addition, it was confirmed that the lithium secondary batteries of the comparative examples in which the volume resistivity of the coating layer exceeds 1 Ω·cm were completely insulated, and no current leakage or temperature rise occurred due to an internal short circuit. Furthermore, it was found that the lithium secondary battery system including the lithium secondary batteries of the comparative examples was unable to determine i) whether an internal short circuit occurred in the secondary battery and ii) the location of the internally shorted lithium secondary battery.

[0243]

[0244] From these results, it can be seen that the negative electrode according to the present invention can implement a predetermined volume resistance by including aluminum-containing particles of a specific component and a conductive material in a predetermined content ratio. In addition, it can be seen that the secondary battery including the same can implement appropriate insulation on the negative electrode surface in the event of an internal short circuit while allowing a predetermined current to leak, thereby preventing meltdown and / or rapid heating of the secondary battery due to an internal short circuit and providing time to respond to an internal short circuit.

[0245] Furthermore, it can be seen that a secondary battery system including the secondary battery can determine with high accuracy and speed whether there is an internal short circuit in the secondary battery and the location of the internally short-circuited lithium secondary battery by using the current applied when an internal short circuit occurs.

[0246]

[0247] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that the present invention can be variously modified and changed within a scope that does not depart from the technical scope of the present invention as set forth in the claims to be described below.

[0248] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the patent claims.

[0249]

[0250] [Explanation of symbols]

[0251] 10: Lithium secondary battery system

[0252] 110: Cell assembly 111: Lithium secondary battery

[0253] 111a: Cathode of lithium secondary battery 111b: Cathode of lithium secondary battery

[0254] 112a: positive terminal 112b: negative terminal

[0255] 120: Charging / Discharging section 130: Sensing section

[0256] 140: Control unit 150: Secondary battery pack

[0257] PS: External power EL: Electrical load

[0258] 211: Experimental lithium secondary battery

[0259] 211a-1: Cathode current collector 211a-2: Cathode active layer

[0260] 211b-1: Negative current collector 211b-2: Negative active layer

[0261] 211b-3: Cathode coating layer

[0262] 211c: Membrane 211c-1: Penetration of the membrane

Claims

1. A negative electrode active layer provided on at least one surface of a negative electrode current collector and including a negative electrode active material. And A coating layer positioned on the cathode active layer; The above coating layer includes aluminum-containing particles and a conductive material; The above aluminum-containing particles are a cathode having an amount exceeding 50 parts by weight based on 100 parts by weight of the entire coating layer.

2. In paragraph 1, The above cathode is about 1.0 × 10 -4 A cathode having a volume resistivity of Ω·cm or more and less than about 1.0 Ω·cm.

3. In paragraph 1, The above aluminum-containing particles are cathodes containing a metal compound represented by the following chemical formula 1: [Chemical Formula 1] Al p O q (OH) r In chemical formula 1, p is an integer from 1 to 10, q is an integer from 0 to 20, and p≤q, r is an integer from 1 to 5.

4. In paragraph 1, A cathode comprising the aluminum-containing particles at least one of boehmite, pseudoboehmite, diaspore, akdalaite, and aluminum trihydroxide.

5. In paragraph 1, The above aluminum-containing particles have an average particle diameter (D) of 0.1 ㎛ to 3.0 ㎛ 50 ) with a cathode.

6. In paragraph 1, The above-mentioned conductive material is a cathode comprising at least one of natural graphite, artificial graphite, carbon black, acetylene black, Denka black, Ketjen black, Super-P, channel black, furnace black, lamp black, summer black, graphene, and carbon nanotubes.

7. In paragraph 1, A cathode containing the above-mentioned conductive material in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the total aluminum-containing particles.

8. In paragraph 1, The above coating layer is a cathode further comprising 5 to 15 parts by weight of a dispersant based on 100 parts by weight of the total aluminum-containing particles.

9. In paragraph 8, The above dispersant is a cathode comprising a dispersant containing one or more carboxylic acids.

10. In paragraph 1, The above coating layer is a cathode further comprising 5 parts by weight or less of a binder based on the total 100 parts by weight.

11. In paragraph 10, The above binder is a negative electrode comprising at least one of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyalkyl acrylate, polyamide (PA), and polystyrene (PS).

12. In paragraph 1, The average thickness of the above coating layer is 1.5 to 20 μm, A cathode having a thickness ratio of the coating layer to the cathode active layer of 0.05 to 0.

3.

13. A secondary battery comprising a positive electrode, a negative electrode according to claim 1, and a separator disposed between the positive electrode and the negative electrode.

14. A plurality of cell assemblies each including n secondary batteries according to Article 13 (wherein 3≤n≤100 is an integer), A charging and discharging unit that electrically couples each of the above-mentioned multiple cell assemblies to individually charge or discharge them, A sensing unit that is electrically coupled to the electrodes of each secondary battery included in the above-described multiple cell assemblies and individually measures at least one of the voltage and current of the secondary battery during charging and discharging of each secondary battery, and A control unit electrically coupled to the charging / discharging unit and the sensing unit to control charging or discharging of each cell assembly; A secondary battery system in which the control unit stops charging or discharging of a cell assembly including the secondary battery when the current amount measured by the sensing unit satisfies a predetermined value.

15. In paragraph 14, The above control unit, A step of selecting a cell assembly in which the error rate between the average current capacity of multiple cell assemblies and the current capacity of an individual cell assembly is 5% or more; A step of determining that an internal short circuit has occurred in the secondary battery when the current amount measured by the sensing unit based on the approved current amount of each secondary battery is 0.5% or more lower than that of the individual secondary batteries provided in the selected cell assembly, and A secondary battery system that performs a step of stopping charging or discharging of a cell assembly including a secondary battery determined to have occurred due to an internal short circuit.

16. In paragraph 14, A secondary battery system wherein the sensing unit further includes a temperature measuring sensor for measuring the temperature of each secondary battery provided in the cell assembly.

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