Anode for lithium secondary battery with improved safety against internal short circuit, lithium secondary battery including same, and lithium secondary battery system therefor

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, a lithium secondary battery including the same, and a lithium secondary battery system therefor. The negative electrode for a lithium secondary battery includes specific silicon-containing particles and aluminum-containing particles, thereby achieving a predetermined volume resistance. As a result, a lithium secondary battery including the same can achieve suitable insulation properties on the negative electrode surface during an internal short circuit, allowing a predetermined current to leak, thereby preventing meltdown and / or rapid heat generation of the lithium secondary battery due to the internal short circuit.

Description

[Technical Field]

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

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0078158, filed June 19, 2023, and Korean Patent Application No. 10-2024-0013412, filed January 29, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference. [Background technology]

[0003] Lithium secondary batteries generate electrical energy through oxidation and reduction reactions that occur when lithium ions are intercalated / deintercalated between the positive and negative electrodes. Lithium secondary batteries are manufactured by using materials capable of reversibly intercalating / deintercalating lithium ions as the active materials for the positive and negative electrodes and charging an organic or polymer electrolyte between the positive and negative electrodes.

[0004] Such lithium secondary batteries are charged and discharged through electrochemical reactions in which ions are inserted, removed, and transferred between the active materials of the two electrodes, but secondary batteries that are repeatedly charged and discharged can generate heat due to electrical misuse (overcharging) and other dangerous factors. If this condition continues, the lithium secondary battery may break down and explode, causing fatal damage to the user, so safety measures are essential. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Korean Patent Publication No. 10-2011-0067565 [Patent Document 2] Korean Patent Publication No. 10-2021-0054930 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a lithium secondary battery-related technology that can ensure the safety of the battery when an internal short circuit occurs in the lithium secondary battery. [Means for solving the problem]

[0007] To solve the above problem, In one embodiment, the present invention comprises: 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 located on the negative electrode active layer, the coating layer comprises silicon-containing particles, aluminum-containing particles, and a dispersant; Volume resistivity is 1.0×10 -4 The present invention provides a negative electrode for a lithium secondary battery having a resistance of Ω·cm or more and 1.0 Ω·cm or less.

[0008] At this time, the negative electrode has a capacity of 3.0×10 -3 Ω·cm~9.0×10 -1 It may have a volume resistivity of Ω·cm.

[0009] The silicon-containing particles contained in the coating layer may include particles in which the ratio of silicon element to oxygen element is 1:0.5 to 2.0.

[0010] The silicon-containing particles have an average particle size (D 50 ) and the aluminum-containing particles have an average particle size (D 50 ).

[0011] The silicon-containing particles may also include a carbon layer on the surface.

[0012] The aluminum-containing particles contained in the coating layer may include a metal compound represented by the following Chemical Formula 1:

[0013] [Chemical formula 1] Al p O q (OH) r

[0014] In Chemical Formula 1, p is an integer of 1 to 10, q is an integer of 0 to 20, and p≦q; r is an integer of 1 to 5.

[0015] As one example, the aluminum-containing particles may include one or more of boehmite, pseudoboehmite, diaspore, akdalaite, and aluminum trihydroxide.

[0016] The coating layer may contain, based on the total weight, 1 to 30% by weight of silicon-containing particles, 30 to 89% by weight of aluminum-containing particles, and 10 to 40% by weight of a dispersant.

[0017] Meanwhile, the dispersant contained in the coating layer may include a first dispersant containing one or more carboxylic acids and a second dispersant containing one or more amino groups.

[0018] The coating layer may further include one or more binders selected from the group consisting of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyalkyl acrylate, polyamide (PA), and polystyrene (PS).

[0019] In one embodiment, the present invention further comprises: There is provided a lithium secondary battery comprising a positive electrode, the negative electrode according to the present invention as described above, and a separator disposed between the positive electrode and the negative electrode.

[0020] In this case, the positive electrode may include a positive electrode active layer on a positive electrode current collector, the positive electrode active layer including one or more positive electrode active materials selected from compounds represented by the following Formulas 2 and 3:

[0021] [Chemical formula 2] Life a M 1 1-a XO4

[0022] [Chemical formula 3] Li x [Ni y Co z Mn w M 2 v ]O2

[0023] In the above Chemical Formula 2 and Chemical Formula 3, M 1 is one or more elements selected from 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; X is one or more of P, Si, S, As, and Sb; a is 0 <a≦1.0であり、 M 2 is one or more elements selected from 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; x, y, z, w, and v are in the ranges 1.0≦x≦1.30, 0≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, and y+z+w+v=1, respectively.

[0024] Furthermore, in one embodiment, the present invention provides a plurality of cell assemblies each including n (where n is an integer of 3≦n≦100) lithium secondary batteries according to the present invention; a charging / discharging unit electrically coupled to each of the plurality of cell assemblies to charge or discharge the cell assemblies individually; a sensing unit electrically coupled to an electrode of each of the lithium secondary batteries included in the plurality of cell assemblies, and configured to individually measure at least one of a voltage and a current of each of the lithium secondary batteries when the lithium secondary batteries are charged or discharged; and a control unit electrically connected to the charging / discharging unit and the sensing unit to control charging or discharging of each cell assembly; The control unit provides a lithium secondary battery system that stops charging or discharging the cell assembly including the lithium secondary battery when the amount of current measured by the sensing unit meets a predetermined value.

[0025] Here, the control unit: A step of selecting cell assemblies having an error rate of 5% or more between an average current flow rate of the plurality of cell assemblies and the current flow rate of each individual cell assembly; determining that an internal short circuit has occurred in each lithium secondary battery when the amount of current measured by the sensing unit is lower than the amount of current applied to the lithium secondary battery by 0.5% or more for each individual lithium secondary battery included in the selected cell assembly; and A step may be performed of stopping charging or discharging of the cell assembly including the lithium secondary battery in which it is determined that an internal short circuit has occurred.

[0026] The sensing unit may further include a temperature sensor for measuring the temperature of each lithium secondary battery included in the cell assembly.

[0027] In one embodiment, the present invention further comprises: In the lithium secondary battery system according to the present invention, a step of selecting cell assemblies having an error rate of 5% or more between an average current flow rate of the plurality of cell assemblies and the current flow rate of each individual cell assembly; determining that an internal short circuit has occurred in each lithium secondary battery when the amount of current measured by the sensing unit is lower than the amount of current applied to the lithium secondary battery by 0.5% or more for each individual lithium secondary battery included in the selected cell assembly; and A method for operating a lithium secondary battery system is provided, which includes a step of stopping charging or discharging of a cell assembly including a lithium secondary battery in which it has been determined that an internal short circuit has occurred. [Effects of the Invention]

[0028] The negative electrode for a lithium secondary battery according to the present invention includes specific silicon-containing particles and aluminum-containing particles, and thus can achieve a predetermined volume resistance. As a result, a lithium secondary battery including these particles can achieve suitable insulation on the negative electrode surface during an internal short circuit, allowing a predetermined current to leak, thereby preventing meltdown and / or rapid heat generation of the lithium secondary battery due to an internal short circuit.

[0029] Furthermore, the lithium secondary battery system according to the present invention includes the lithium secondary battery of the present invention described above, and is not only capable of preventing a meltdown phenomenon and rapid heat generation in the event of an internal short circuit, but also capable of quickly detecting an internal short circuit through a predetermined current leaked from the lithium secondary battery, thereby preemptively controlling the operation of the lithium secondary battery before thermal runaway occurs, thereby improving safety issues due to an internal short circuit. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a structural diagram illustrating a schematic configuration of a lithium secondary battery system according to the present invention. [Figure 2] 1 is a block diagram showing a hardware configuration embodying a control device 140 included in the lithium secondary battery system according to the present invention. FIG. [Figure 3] 1 is a cross-sectional view showing an electrode assembly structure of a lithium secondary battery manufactured in an experimental example for a safety test of the lithium secondary battery according to the present invention; [Figure 4] 1 is a graph showing the voltage at the negative electrode provided in the lithium secondary battery of Comparative Example 1 and the temperature change of the battery when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. [Figure 5]10 is a graph showing the voltage and temperature changes of the negative electrode provided in the lithium secondary battery of Comparative Example 5 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. [Figure 6] 10 is a graph showing the voltage at the negative electrode provided in the lithium secondary battery of Example 2 and the temperature change of the battery when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. [Figure 7] 1 is a graph showing the change in charge-discharge capacity of the lithium secondary batteries of Examples 5 and 6 and Comparative Example 1 after 400 charge-discharge cycles. [Figure 8] 1 is a graph showing changes in coulombic efficiency of the lithium secondary batteries of Examples 5 and 6 and Comparative Example 1 after 400 charge / discharge cycles. DETAILED DESCRIPTION OF THE INVENTION

[0031] Because the present invention is susceptible to various modifications and embodiments, specific embodiments will be described in detail.

[0032] However, this is not intended to limit the invention to any particular embodiment, but rather to be understood as including all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0033] In the present invention, the terms "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and may be understood as not precluding the presence or possibility of addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0034] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion therebetween. Furthermore, in the present application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0035] In addition, in the present invention, the term "amount of current flowing" refers to the amount of electricity flowing through the electrodes when the lithium secondary battery is charged or discharged, and this can be quantified as a current and / or a voltage.

[0036] In addition, in the present invention, D 50 can be defined as the particle size corresponding to 50% of the cumulative volume on the particle size distribution curve (graph curve of particle size distribution diagram). 50 can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0037] As used in this specification, the terms "about," "approximately," and "substantially" are used to mean a range of or approximation to a numerical value or degree, taking into account inherent manufacturing and material tolerances, and are used to prevent an infringer from unfairly using the disclosure content in which precise or absolute numerical values ​​provided to aid in the understanding of the present invention are mentioned.

[0038] In conventional secondary batteries, a porous separator placed between the positive and negative electrodes is used as an example of a safety measure. When the temperature inside the case rises above a safe temperature, this porous separator closes its pores in response to the temperature, blocking the movement of ions between the two electrodes and suppressing the electrochemical reaction, thereby achieving safety (shutdown phenomenon).

[0039] However, in conventional secondary batteries, if the internal temperature of the battery rises excessively beyond the temperature release rate of the case due to separator non-uniformity or other internal short circuits, the separator itself melts before shutting down, losing its ability to insulate the positive and negative electrodes. Furthermore, if the positive and negative electrodes are short-circuited, a chain reaction (meltdown) occurs, including decomposition of the negative electrode active material and electrolyte, and decomposition of the positive electrode active material, eventually leading to thermal runaway. This thermal runaway phenomenon can not only cause the secondary battery where the short circuit occurred to explode, but can also induce meltdown in adjacent secondary batteries, causing additional explosions.

[0040] A meltdown phenomenon occurs when an internal short circuit occurs due to contact between electrodes included in a secondary battery, or between electrodes and their current collectors and / or between current collectors. In particular, when a short circuit occurs due to contact between a positive electrode current collector (or the surface of the positive electrode) and a negative electrode, the resistance of the short circuited area causes a rapid increase in the amount of heat generated, leading to a thermal runaway phenomenon in a short period of time. Therefore, in order to ensure the stability of lithium secondary batteries, measures are needed to prevent, prevent, and / or respond to such a thermal runaway phenomenon.

[0041] The present invention will now be described in more detail.

[0042] <Anode for lithium secondary batteries> In one embodiment, the present invention comprises: a negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a negative electrode active material; and a coating layer located on the negative electrode active layer, the coating layer comprises silicon-containing particles, aluminum-containing particles, and a dispersant; Volume resistivity is 1.0×10 -4 The present invention provides a negative electrode for a lithium secondary battery having a resistance of Ω·cm or more and 1.0 Ω·cm or less.

[0043] The negative electrode for a lithium secondary battery according to the present invention has a structure in which a negative electrode active layer containing a negative electrode active material and a coating layer are sequentially stacked on a negative electrode current collector.

[0044] In this case, the negative electrode may have a coating layer containing silicon-containing particles and aluminum-containing particles on the surface of a negative electrode active layer containing a carbon-based negative electrode active material, and may have a predetermined volume resistivity. -4 It may have a volume resistivity of Ω·cm or more, more specifically, 1.0×10 -3 For example, the coating layer may have a resistance of 5.0×10 -3 Ω·cm~1.0Ω·cm, 1.0×10 -3 Ω·cm~1.0Ω·cm, 3.0×10 -3 Ω·cm~1.0Ω·cm, 1.0×10 -2 Ω·cm~1.0Ω·cm, 3.0×10 -3 Ω·cm~9.0×10 -1 Ω·cm, 5.0×10 -2 Ω·cm~9.0×10 -1 Ω·cm, 6.0×10 -2 Ω·cm~8.0×10 -1 Ω·cm, 8.0×10 -2 Ω·cm~5.0×10 -1 Ω·cm, 4.0×10 -2 Ω·cm~2.0×10 -1 Ω·cm, 5.0×10 -2 Ω·cm~1.5×10 -1 Ω·cm, 8.0×10 -2 Ω·cm~1.0×10 -1 Ω·cm, 7.0×10 -2 Ω·cm~9.0×10 -2 Ω·cm, 7.0×10 -2 Ω·cm~4.5×10 -1 Ω·cm, 7.0×10 -2 Ω·cm~3.0×10 -1 Ω·cm, 8.0×10 -2 Ω·cm~2.0×10 -1 Ω·cm, 1.0×10 -1 Ω·cm~9.0×10 -1 Ω·cm, 1.0×10-1 Ω·cm~5.0×10 -1 Ω·cm, 2.0×10 -1 Ω·cm~8.0×10 -1 Ω·cm, or 5.0×10 -1 It may have a volume resistivity of Ω·cm to 1.0 Ω·cm.

[0045] If the volume resistivity of the negative electrode exceeds 1.0 Ω·cm, excessive resistance may occur on the negative electrode surface in the event of an internal short circuit, particularly an internal short circuit caused by contact between the negative electrode surface and the positive electrode current collector (and / or positive electrode active layer), resulting in a significant reduction or complete cessation of current flow externally to the electrode. While this may interrupt the short-circuit current of the lithium secondary battery, it is difficult to quickly and selectively detect and address an internally shorted lithium secondary battery within a device containing multiple lithium secondary batteries, such as a battery module or pack. Furthermore, addressing an internal short circuit requires separating and / or removing the cell assembly containing the lithium secondary battery with the internal short circuit from the lithium secondary battery system, which is uneconomical. Furthermore, if the volume resistivity of the negative electrode is below the lower limit of the above range, sufficient insulation may not be achieved on the negative electrode surface in the event of an internal short circuit, resulting in meltdown, such as decomposition of the negative electrode active material and the electrolyte, or decomposition of the positive electrode active material, resulting in fire.

[0046] That is, the anode of the present invention has a volume resistivity within the above range, thereby providing suitable resistance to the anode surface during an internal short circuit and providing insulation at the short circuit site. This significantly reduces heat generation in the lithium secondary battery during an internal short circuit, thereby delaying the occurrence of a meltdown. Furthermore, by suppressing heat generation in the lithium secondary battery in which an internal short circuit has occurred, additional heat generation and / or meltdown in adjacent lithium secondary batteries can be prevented, thereby providing time to address (or treat) the problem caused by the internal short circuit. Furthermore, by allowing a significantly reduced amount of current (i.e., leakage current) to flow at the internal short circuit site of the lithium secondary battery, abnormal operation such as an internal short circuit can be easily identified / diagnosed, thereby providing the advantage of facilitating response to abnormal operation of the lithium secondary battery.

[0047] In the negative electrode according to the present invention, the components constituting the coating layer, the content of each component, the mixed form and size of each component, the thickness ratio of the negative electrode active layer to the coating layer, etc. may be controlled to satisfy the volume resistivity within the above range.

[0048] Specifically, the coating layer does not function as a resistance layer during normal operation of the lithium secondary battery, preventing overvoltage during charge and discharge. Furthermore, during abnormal operation, such as an internal short circuit, the coating layer functions as a resistance layer to prevent 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 contact therebetween, while also allowing a small amount of current to leak. To this end, the coating layer may be coated on the negative electrode active layer to cover the entire exposed surface of the negative electrode active layer. In some cases, the coating layer may be selectively disposed only on the edge and / or end surfaces of the negative electrode active layer that are likely to come into contact with the positive electrode current collector (and / or positive electrode active layer), or only on the center of the negative electrode active layer that may come into contact with the positive electrode current collector (and / or positive electrode active layer) if the separator is damaged by external force.

[0049] In addition, the coating layer includes silicon-containing particles and aluminum-containing particles, and may have a volume resistance that prevents direct current flow 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 during an internal short circuit, while allowing a predetermined current to leak.

[0050] The term "silicon-containing particles" refers to particles containing silicon (Si) as a primary component among metal components. Examples of such silicon-containing particles include silicon particles, silicon carbide particles, and silicon oxide particles, and preferably include oxidized silicon oxide particles. In this case, the silicon-containing particles contain silicon and oxygen, and the molar ratio thereof may be 1:0.5-2.0, 1:0.5-1.5, 1:0.8-1.2, or 1:0.9-1.1.

[0051] The silicon-containing particles are not particularly limited in form as long as the molar ratio of silicon and oxygen in the particles satisfies the above range. For example, the silicon-containing particles may be silicon monoxide (SiO q , where 0.8≦q≦1.2) particles.

[0052] In the present invention, by controlling the elemental ratio of silicon and oxygen elements (i.e., the molar ratio of the elements) as described above, the volume resistivity of the coating layer composed of silicon-containing particles can be controlled to satisfy the above-mentioned predetermined range, thereby imparting insulating properties to the surface of the coating layer in the event of an internal short circuit and simultaneously allowing an extremely small amount of current to leak into and / or outside the battery.

[0053] Specifically, when the proportion of silicon element is higher than the proportion of oxygen element, the insulating properties are reduced, causing excessive leakage current at the internal short circuit point, which increases the resistance at the internal short circuit point and causes a rapid rise in the temperature of the lithium secondary battery.Furthermore, when the proportion of silicon element is lower than the proportion of oxygen element, the band gap of the silicon-containing particles increases, completely blocking leakage current in the event of an internal short circuit, making it difficult to selectively identify / diagnose the lithium secondary battery in which an internal short circuit has occurred.

[0054] Meanwhile, the silicon-containing particles have a chemical structure that allows for lithium ion insertion during charging of a lithium secondary battery, and have been used as a silicon-based negative electrode active material in a conventional negative electrode active layer. However, when the silicon-containing particles are applied to the coating layer of the present invention, the surface area into which lithium ions are inserted may be significantly reduced due to the low content compared to when the silicon-containing particles are applied to the negative electrode active layer. This means that the resistance of the silicon-containing particles to lithium insertion in the coating layer increases. Therefore, when the silicon-containing particles are applied to the coating layer of the present invention, it may be difficult for them to insert lithium ions, as with typical silicon-based negative electrode active materials, during charging of a lithium secondary battery.

[0055] Furthermore, the silicon-containing particles can effectively impart insulation to the coating layer surface during an internal short circuit while simultaneously preventing minute current leakage into and / or outside the battery. However, the silicon-containing particles are expensive to manufacture, and when used alone, they must be applied to the coating layer at a high content of 50 wt.% or more in order to prevent minute current leakage into and / or outside the battery while providing insulation to the coating layer surface. Therefore, the present invention is characterized in that the coating layer contains specific aluminum-containing particles together with the silicon-containing particles.

[0056] "Aluminum-containing particles" refers to particles containing aluminum (Al) as a primary component among metal components. The aluminum-containing particles according to the present invention are inexpensive to produce and have low electrical conductivity, and therefore, when applied alone to a coating layer, they are characterized by a significantly low effect of causing minute current leakage inside and / or outside the battery. However, when the aluminum-containing particles are mixed with silicon-containing particles at a predetermined weight ratio and applied to a coating layer, they exhibit the same or superior effect as when the silicon-containing particles are used alone in the coating layer, which is advantageous in terms of economy in mass production.

[0057] Such aluminum-containing particles may be particles comprising a metal compound represented by the following Chemical Formula 1:

[0058] [Chemical formula 1] Al p O q (OH) r

[0059] In Chemical Formula 1, p is an integer of 1 to 10, q is an integer of 0 to 20, and p≦q; r is an integer of 1 to 5.

[0060] Aluminum oxide (Al2O3), which is conventionally used in the insulating layer of electrodes and contains aluminum as a metallic component and oxygen as a non-metallic component, completely blocks current leakage inside and / or outside the battery when an internal short circuit occurs when it is applied to a coating layer together with silicon-containing particles. However, the present invention includes aluminum-containing particles in the coating layer in the form of particles having aluminum oxide hydroxide crystals, as shown in Chemical Formula 1, together with silicon-containing particles, thereby imparting insulation to the coating layer surface during an internal short circuit while preventing minute amounts of current from leaking inside and / or outside the battery.

[0061] Such aluminum-containing particles include boehmite (γ-AlO(OH)), pseudoboehmite (AlO(OH)), diaspore (α-AlO(OH)), akdalaite (Al 10 O 14 Examples of the particles include particles containing one or more of aluminum trihydroxide ((OH)2) and aluminum trihydroxide.

[0062] The silicon-containing particles can be controlled to have a specific particle size. Specifically, the silicon-containing particles have an average particle size (D 50), more specifically, the average particle size (D 50 ).

[0063] The silicon-containing particles have an average particle size (D 50 If the average particle diameter (D) of the silicon-containing particles is less than the above range, the silicon-containing particles tend to penetrate into the negative electrode active layer disposed below the coating layer. This increases the electrical resistance at the interface between the negative electrode active layer and the coating layer, which can degrade the electrical performance of the lithium secondary battery during normal operation. 50 ) exceeds the above range, it is difficult to form a uniform coating layer, and the average thickness of the coating layer becomes too thick to form a uniform coating layer, resulting in a problem of reduced energy density of the negative electrode.

[0064] The aluminum-containing particles have an average particle size (D 50 Specifically, the aluminum-containing particles may have an average particle size (D) of 0.1 μm to 2.0 μm, 0.1 μm to 0.9 μm, 0.5 μm to 1.5 μm, 0.3 μm to 0.9 μm, 0.5 μm to 0.9 μm, 0.3 μm to 0.7 μm, 0.4 μm to 0.8 μm, 0.1 μm to 0.7 μm, 0.1 μm to 0.5 μm, 0.2 μm to 0.4 μm, or 0.25 μm to 0.35 μm. 50 ).

[0065] The aluminum-containing particles have an average particle size (D 50 If the average particle diameter (D) of the aluminum-containing particles is less than the above range, the aluminum-containing particles may be contained in the coating layer in a non-uniformly aggregated form due to a decrease in dispersibility. This may result in a problem of a decrease in the electrical properties of the coating layer. In addition, the average particle diameter (D) of the aluminum-containing particles may be less than the above range. 50 If the thickness (T) of the coating layer exceeds the above range, it is difficult to make the coating layer thin, which limits the energy density of the negative electrode.

[0066] In addition, the silicon-containing particles may include a carbon layer on the surface to improve the energy density and energy efficiency of the negative electrode during normal operation of the lithium secondary battery. The carbon layer may be formed by uniformly mixing the silicon-containing particles with carbon particles, with the carbon particles physically or chemically adsorbed to the surface of the silicon-containing particles. In some cases, the carbon layer may be formed by depositing carbon atoms on the surface of the silicon-containing particles. The carbon layer may improve the electrical conductivity of the particle surface while suppressing volume expansion of the silicon-containing particles. As a result, although the insulating properties of the coating layer may be somewhat reduced during an internal short circuit of the lithium secondary battery, the charge / discharge capacity and efficiency during normal operation of the lithium secondary battery may be improved and volume change of the negative electrode may be minimized.

[0067] The carbon layer may have an average thickness of 1 nm to 1,000 nm, specifically 100 nm to 1,000 nm, 200 nm to 1,000 nm, 500 nm to 1,000 nm, 800 nm to 1,000 nm, 10 nm to 200 nm, 10 nm to 90 nm, 10 nm to 70 nm, 10 nm to 50 nm, or 10 nm to 30 nm.

[0068] The coating layer may also include a dispersant along with the silicon-containing particles and the aluminum-containing particles, which allows the silicon-containing particles and the aluminum-containing particles to be uniformly dispersed within the coating layer without agglomeration.

[0069] Specifically, the dispersant may include a first dispersant that interacts with the metals contained in the silicon-containing particles and the aluminum-containing particles to stabilize the particle surfaces and thereby prevent particle aggregation, and a second dispersant that helps each particle dispersed by the first dispersant to maintain its dispersed state.

[0070] In this case, the first dispersant may include one or more carboxylic acids, and the second dispersant may include one or more amino groups.

[0071] For example, the first dispersant may be a tricarboxylic acid such as citric acid, methane tricarboxylic acid, ethane tricarboxylic acid, benzene-1,3,5-tricarboxylic acid, or 5-sulfo-1,2,4-benzenetricarboxylic acid; 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, or benzene-1,2,4,5-tetracarboxylic acid. tetracarboxylic acids such as benzene-1,2,3,4,5-pentacarboxylic acid; pentacarboxylic acids such as benzene-1,2,3,4,5-pentacarboxylic acid; or hexacarboxylic acids such as benzene-1,2,3,4,5,6-hexacarboxylic acid (benzene-1,2,3,4,5,6-hexacarboxylic acid mellitic acid).

[0072] The second dispersant may include ethylenediamine, piperazine, hexamethylenediamine, 1,3-diaminopropane, bishexamethylenetriamine, diethylenetriamine, and the like.

[0073] Furthermore, because the electrical properties of the coating layer are significantly affected by the silicon-containing particles, the dispersant contained in the coating layer can be present in a predetermined ratio relative to the weight of the silicon-containing particles. Specifically, the dispersant can be present in the coating layer in a weight ratio of 50% to 500% relative to the total weight of the silicon-containing particles, and more specifically, can be present in the coating layer in a weight ratio of 80% to 500%, 50% to 90%, 110% to 190%, 110% to 300%, 150% to 250%, or 180% to 220% relative to the total weight of the silicon-containing particles. By adjusting the dispersant content within the above ranges, the present invention can prevent aggregation of the silicon-containing particles due to a small amount of dispersant while preventing degradation of the electrical properties of the coating layer due to an excessive amount of dispersant.

[0074] The first dispersant and the second dispersant contained in the dispersant may be contained in the dispersant in a weight ratio of 1:0.5 to 2.0, specifically 1:0.5 to 1.2, 1:0.8 to 1.2, or 1:1.1 to 2.0. By adjusting the content ratio of the first dispersant and the second dispersant as described above, the present invention can uniformly disperse not only silicon-containing particles but also aluminum-containing particles in the coating layer.

[0075] Furthermore, the coating layer may contain silicon-containing particles, aluminum-containing particles, and a dispersant in predetermined content ratios, for example, 1 wt % to 30 wt % of silicon-containing particles, 30 wt % to 89 wt % of aluminum-containing particles, and 10 wt % to 40 wt % of a dispersant, based on the total weight of the coating layer.

[0076] As one example, the coating layer may contain, based on the total weight, 10 to 20 wt % of silicon-containing particles, 50 to 65 wt % of aluminum-containing particles, and 25 to 30 wt % of a dispersant (first dispersant:second dispersant=1:1 (wt. / wt.)).

[0077] As another example, the coating layer may contain, based on the total weight, 21 to 30 wt % of silicon-containing particles, 50 to 64 wt % of aluminum-containing particles, and 15 to 20 wt % of a dispersant (first dispersant:second dispersant=1:1 (wt. / wt.)).

[0078] As another example, the coating layer may contain, relative to the total weight, 5 to 15 wt % of silicon-containing particles, 65 to 85 wt % of aluminum-containing particles, and 10 to 20 wt % of a dispersant (first dispersant:second dispersant=1:1 (wt. / wt.)).

[0079] By controlling the content ratios of each component contained in the coating layer as described above, the present invention can provide a coating layer in which silicon-containing particles and aluminum-containing particles are uniformly dispersed in the anode. Furthermore, the coating layer can be highly stable, thereby preventing damage to the coating layer during the anode manufacturing process or battery assembly process. Furthermore, by controlling the content ratios of each component contained in the coating layer as described above, the volume resistivity of the anode can be easily controlled within a predetermined range according to the present invention.

[0080] Furthermore, the coating layer may further include one or more binders selected from styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyalkyl acrylate, polyamide (PA), and polystyrene (PS).

[0081] The coating layer according to the present invention may contain only silicon-containing particles, aluminum-containing particles, and a dispersant, but may also contain one or more binders described above to enhance adhesion between the particles of the coating layer. In this case, the binder may be contained in an amount of 0.1 to 10 parts by weight relative to 100 parts by weight of the entire coating layer, specifically, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight relative to 100 parts by weight of the entire coating layer.

[0082] The coating layer may have an average thickness of 1.5 μm to 30 μm, which may be greater than the average particle size of the silicon-containing particles. Specifically, the coating layer may have an average thickness of 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 11 μm to 14 μm. The average thickness of the coating layer may be measured by a method commonly used in the art for measuring the thickness of a thin film, and may refer to the average of any of a plurality of values ​​measured in this manner, or the intermediate value between the maximum and minimum values ​​measured.

[0083] The thickness ratio of the coating layer to the negative electrode active layer may be 0.05 to 0.3, specifically 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.

[0084] 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 to the coating layer. Here, the volume resistance of the coating layer can be controlled by the components constituting the coating layer, the content of each component, the mixed 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 less than the above-mentioned lower limit, the volume resistance of the negative electrode may decrease, and the insulating properties may be significantly reduced in the event of an internal short circuit. Furthermore, if the thickness of the negative electrode active layer is equal to or less than the coating layer and the thickness ratio of the coating layer to the negative electrode active layer is greater than the above-mentioned upper limit, the volume resistance of the negative electrode may significantly increase. Therefore, although the short-circuit current of a lithium secondary battery is interrupted in the event of an internal short circuit, there are limitations, such as the difficulty and economical nature of selectively detecting and responding to an internally shorted lithium secondary battery in a device containing multiple lithium secondary batteries, such as a battery module or pack.

[0085] That is, by adjusting the thickness ratio of the coating layer to the negative electrode active layer within the above range, the present invention can realize a high energy density of the negative electrode and minimize the volume expansion rate of the negative electrode during normal operation of the lithium secondary battery. Furthermore, the negative electrode has the advantage of preventing a significant increase in resistance due to excessive thickness during an internal short circuit and physically protecting the negative electrode surface.

[0086] Meanwhile, the negative electrode active layer included in the negative electrode includes a carbon-based negative electrode active material, which may include a carbon-based negative electrode active material commonly used in the art. For example, the carbon-based negative electrode active material refers to a material primarily composed of carbon atoms, and 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, and preferably includes natural graphite or a mixture of natural graphite and artificial graphite.

[0087] The carbon-based negative electrode active material is preferably a spherical graphite granule formed by the aggregation of multiple flake graphite particles. Examples of flake graphite include natural graphite, artificial graphite, mesophase calcined carbon (bulk mesophase) made from tar or pitch, and graphitized cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.). A graphite granule assembled from multiple pieces of highly crystalline natural graphite is particularly preferred. Each graphite granule may be formed by the aggregation of 2 to 100, preferably 3 to 20, flake graphite particles.

[0088] The carbon-based negative electrode active material has an average particle size (D 50 Specifically, the average particle size (D 50 ) can be shown.

[0089] In addition, the negative electrode active layer may further include, in addition to the carbon-based negative electrode active material as the main component, a conductive material, a binder, other additives, and the like, as needed.

[0090] The conductive material may include, but is not limited to, one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, and the like.

[0091] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0092] The content of the conductive material may be 0.1 to 10 parts by weight, specifically 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, based on 100 parts by weight of the total negative electrode active layer. By controlling the content of the conductive material within the above range, the present invention can prevent a low content of conductive material from increasing the resistance of the negative electrode and reducing the charge capacity. Furthermore, it can prevent problems such as a decrease in the content of the negative electrode active material due to an excessive amount of conductive material, thereby reducing the charge capacity, or a decrease in fast charge characteristics due to an increase in the loading amount of the negative electrode active layer.

[0093] The binder is a component that aids in bonding between the negative electrode active material and the conductive material, etc., and between the negative electrode active material and the current collector, and may be suitably used within a range that does not degrade 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.

[0094] The content of the binder may be 0.1 to 10 parts by weight, specifically 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, based on 100 parts by weight of the total negative electrode active layer. By controlling the content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent a decrease in adhesive strength of the active layer due to a low content of binder or a decrease in electrical properties of the electrode due to an excessive amount of binder.

[0095] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery, and examples thereof include copper, stainless steel, nickel, titanium, calcined carbon, etc. In the case of copper or stainless steel, it may also be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector is preferably 1 to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0096] <Lithium secondary battery> In one embodiment, the present invention further comprises: There is provided a lithium secondary battery comprising a positive electrode, the negative electrode according to the present invention, and a separator disposed between the positive electrode and the negative electrode.

[0097] The lithium secondary battery according to the present invention includes an electrode assembly having a structure in which a separator is disposed between a positive electrode and the above-described negative electrode of the present invention, and the electrode assembly is inserted into a battery case, and then an electrolyte composition is injected and sealed.

[0098] In this case, the negative electrode has the same structure as the negative electrode for a lithium secondary battery according to the present invention, and therefore a detailed description thereof will be omitted.

[0099] In addition, the positive electrode includes a positive electrode mixture layer prepared by applying a positive electrode slurry containing a positive electrode active material onto a positive electrode current collector, drying the slurry, and pressing the slurry. The positive electrode mixture layer may further include a conductive material, a binder, other additives, and the like, as needed.

[0100] Here, the positive electrode active material is a material that can undergo an electrochemical reaction on a positive electrode current collector and may include at least one lithium metal oxide represented by the following Formula 2 and Formula 3, which are capable of reversibly intercalating and deintercalating lithium ions:

[0101] [Chemical formula 2] Life a M 1 1-a XO4

[0102] [Chemical formula 3] Li x [Ni y Co z Mn w M 2 v ]O2

[0103] In the above Chemical Formula 2 and Chemical Formula 3, M 1 is one or more elements selected from 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; X is one or more of P, Si, S, As, and Sb; a is 0 <a≦1.0であり、 M 2 is one or more elements selected from 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; x, y, z, w, and v are in the ranges 1.0≦x≦1.30, 0≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, and y+z+w+v=1, respectively.

[0104] The compounds represented by Chemical Formula 2 and Chemical Formula 3 are lithium metal oxides that are used in the industry as positive electrode active materials for lithium secondary batteries. Among them, 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 the advantage of being suitable for medium- to large-sized secondary batteries for power storage in the transportation field such as electric vehicles (EVs) and energy storage systems (ESSs) due to its high energy density and performance such as output.

[0105] In this case, the lithium metal oxide represented by chemical formula 3 is LiNi 0.8 Co 0.1 Mn 0.1O2, 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 It may contain O2 etc.

[0106] Although the charge / discharge capacity of the lithium composite metal oxide increases with increasing nickel (Ni) content, it also exhibits low chemical and structural stability, which can lead to the problem of a high risk of fire due to the tendency for exothermic reactions to occur. In particular, the exothermic reactions can occur when a short-circuit current flows inside the battery. Therefore, the lithium secondary battery according to the present invention has an advantage of improving safety by incorporating a coating layer with a predetermined volume resistivity into the negative electrode, which suppresses exothermic reactions during an internal short circuit caused by contact between the negative electrode surface and the positive electrode current collector (and / or the positive electrode active layer) and significantly reduces current leakage, thereby preventing subsequent problems that may occur after an internal short circuit.

[0107] On the other hand, the compounds represented by the above chemical formula 2 include LiFePO4, LiFe 0.8 Mn 0.2 PO4, LiFe 0.7 Mn 0.3 PO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn 0.7 It may contain PO4 etc.

[0108] The positive electrode active material may be included in an amount of 85 parts by weight or more, specifically 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more, based on the weight of the positive electrode active layer.

[0109] The positive electrode active layer may further include a conductive material, a binder, and other additives in addition to the positive electrode active material.

[0110] In this case, the conductive material is used to improve the electrical performance of the positive electrode, and may be a conductive material commonly used in the art. Specifically, the conductive material may include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, denka black, ketjen black, Super P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0111] The conductive material may be contained in an amount of 0.1 to 5 parts by weight, specifically 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, based on the weight of each positive electrode active layer.

[0112] The binder functions to bind the positive electrode active material, the positive electrode additive, and the conductive material together, and any material having this function may be used without particular limitation. Specifically, the binder may include one or more resins 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.

[0113] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 1 to 5 parts by weight, based on the weight of each positive electrode active layer.

[0114] The total thickness of the positive electrode active layer is not particularly limited, but may be specifically 50 μm to 300 μm, more specifically 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.

[0115] The positive electrode may use a current collector that has high conductivity and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used. In the case of aluminum or stainless steel, it may also be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the current collector may be preferably 3 to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0116] 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. It may be any material commonly used in the art, but is not particularly limited thereto. Specifically, it may contain one or more polymers selected from the group consisting of chemically resistant and hydrophobic polypropylene, polyethylene, and polyethylene-propylene copolymer. The separator may be in the form of a porous polymer substrate, such as a sheet or nonwoven fabric containing the above-mentioned polymers. In some cases, it may be in the form of a composite separator, in which organic or inorganic particles are coated on the porous polymer substrate with an organic binder. The separator may have an average pore diameter of about 0.01 μm to 10 μm and an average thickness of about 5 μm to 300 μm.

[0117] Meanwhile, the lithium secondary battery according to the present invention is not particularly limited, but may be a secondary battery having a stack type, a zigzag type, or a zigzag-stack type electrode assembly in which the positive electrode current collector (and / or positive electrode active layer) and the negative electrode active layer are relatively likely to come into contact with each other. As one example, the lithium secondary battery according to the present invention may be a pouch type secondary battery or a prismatic type secondary battery.

[0118] <Lithium secondary battery system> Furthermore, in one embodiment, the present invention provides a plurality of cell assemblies each including n (where n is an integer of 3≦n≦100) lithium secondary batteries according to the present invention; a charging / discharging unit electrically coupled to each of the plurality of cell assemblies to charge or discharge the same; a sensing unit electrically coupled to an electrode of each lithium secondary battery included in the plurality of cell assemblies, and configured to individually measure at least one of a voltage and a current of each lithium secondary battery when the lithium secondary battery is charged or discharged; and a control unit electrically connected to the charging / discharging unit and the sensing unit to control charging or discharging of each cell assembly; The control unit provides a lithium secondary battery system that stops charging or discharging the cell assembly including the lithium secondary battery when the amount of current measured by the sensing unit meets a predetermined value.

[0119] 1 is a schematic diagram showing the configuration of a lithium secondary battery system according to the present invention. Referring to FIG. 1, the lithium secondary battery system 10 according to the present invention includes a plurality of cell assemblies 110, each including n (where n is an integer such that 3≦n≦100) lithium secondary batteries 111 according to the present invention, a charging / discharging unit 120 electrically coupled to each of the cell assemblies 110 and charging or discharging the cell assemblies 110 individually, a sensing unit 130 electrically coupled to electrodes of each of the lithium secondary batteries 111 included in the cell assemblies 110 and measuring the voltage and / or current flowing through each of the secondary batteries 111 individually during charging or discharging of the lithium secondary batteries, and a control unit 140 electrically coupled to the charging / discharging unit 120 and the sensing unit 130 and controlling the charging or discharging of each of the cell assemblies 110.

[0120] The lithium secondary battery system 10 is configured to individually measure and monitor the voltage and / or current flowing through n lithium secondary batteries 111 constituting a cell assembly 110 when the secondary batteries are being charged or discharged, thereby determining whether an internal short circuit has occurred in the secondary battery 111, and to immediately stop charging or discharging only the cell assembly 110 including the lithium secondary battery 111 if an internal short circuit is determined to have occurred.

[0121] Specifically, conventional secondary battery systems have developed technologies for diagnosing internal short circuits in secondary batteries by measuring changes in battery temperature during charging and / or discharging, or by measuring changes in the state of charge (SOC) due to self-discharge during an internal short circuit. However, when an internal short circuit occurs in an actual secondary battery, thermal runaway progresses within a short period of time due to a meltdown phenomenon. However, these technologies have limitations in that the diagnostic accuracy is low or the diagnostic process is complicated, it takes a long time to recognize an internal short circuit, and it is difficult to respond to thermal runaway.

[0122] However, the lithium secondary battery system 10 according to the present invention includes the lithium secondary battery 111 according to the present invention. The lithium secondary battery includes a negative electrode having a coating layer with a predetermined volume resistivity on the surface of the negative electrode active layer. This allows for suitable insulation on the negative electrode surface and significantly reduced leakage current to flow through the negative electrode during an internal short circuit due to contact between the positive electrode current collector (or positive electrode active layer) and the negative electrode surface. While conventional lithium secondary batteries experience a flow voltage and current approaching 0 V and 0 A due to leakage current during an internal short circuit, the lithium secondary battery 111 according to the present invention generates a predetermined flow current with only a small amount of leakage current removed from the applied current. This allows for highly accurate detection and / or determination of an internal short circuit in the lithium secondary battery 111 within a significantly shorter time. Furthermore, the lithium secondary battery 111 significantly reduces heat, such as short-circuit heat, generated during an internal short circuit, thereby delaying the occurrence of a meltdown. Furthermore, since the heat from the lithium secondary battery in which an internal short circuit has occurred can be prevented from causing additional heat generation and / or meltdown in adjacent lithium secondary batteries, time can be secured to respond (or treat) to prevent thermal runaway in the lithium secondary battery in which an internal short circuit has occurred.

[0123] To this end, the sensing unit 130 is electrically connected to the lithium secondary batteries 111 separately from the charge / discharge unit 120, and can measure the electrical properties flowing through the electrodes, particularly the negative electrodes, of the secondary batteries in real time for each lithium secondary battery when the lithium secondary batteries 111 are charged or discharged. Here, the "electrical properties" refer to properties of electricity flowing through the electrodes, particularly the negative electrodes, of the lithium secondary batteries, and can include current flow, voltage flow, etc. The measured electrical properties can be transmitted to the control unit 140.

[0124] As one example, the sensing unit 130 may individually measure one or more of the energizing voltage and energizing current of each lithium secondary battery 111. The lithium secondary battery system 10 according to the present invention includes the above-described lithium secondary battery 111 according to the present invention in a cell assembly, and even if an internal short circuit occurs, insulation is realized on the surface of the negative electrode, and a predetermined energizing current in which a small amount of leakage current is eliminated is applied. Therefore, whether or not an internal short circuit has occurred in each lithium secondary battery 111 can be quickly diagnosed based on a change in one or more of the energizing current and the energizing voltage.

[0125] The sensing unit 130 may include means commonly used in the art for measuring electrical properties flowing through each lithium secondary battery 111. For example, the sensing unit 130 may include a current measurement sensor for measuring a current flowing through the lithium secondary battery 111, a voltage measurement sensor for measuring a voltage flowing through the lithium secondary battery 111, etc.

[0126] The sensing unit 130 may further include a temperature sensor (not shown) inside the cell assembly 110 for measuring the temperature of each lithium secondary battery 111 included in the cell assembly 110. The current flowing through a lithium secondary battery may increase when the temperature of the secondary battery rises. Such a rise in temperature of the secondary battery may occur due to an overload caused by a change in the load connected to the system; the opening or closing of a transformer or capacitor; or excessive current flowing during operation of an electric motor. The sensing unit 130 may further include a temperature sensor for measuring the temperature of each lithium secondary battery 111 to reflect changes in the current flowing due to a rise in the temperature of the secondary battery in addition to an internal short circuit of the lithium secondary battery, thereby further reducing the error rate when determining an internal short circuit.

[0127] Furthermore, the control unit 140 is electrically coupled to the charge / discharge unit 120 and the sensing unit 130. The control unit 140 monitors the electrical properties of each lithium secondary battery 111 in real time during charging and / or discharging of each cell assembly 110, detects and / or determines whether or not an internal short circuit has occurred in each lithium secondary battery 111 based on changes in the electrical properties, and controls charging or discharging of the cell assembly 110 including the lithium secondary battery 111 in which an internal short circuit has occurred.

[0128] As one example, the control unit 140 monitors the electrical properties of each lithium secondary battery 111 transmitted in real time from the sensing unit 130, and if there is a change in the transmitted electrical properties, determines whether the amount of change meets a predetermined value; if it meets the predetermined value, individually controls the charging or discharging of the cell assembly 110 including the lithium secondary battery 111 via the charging / discharging unit 120.

[0129] Specifically, the control unit 140 first receives the individual current amounts for all of the lithium secondary batteries 111 included in the lithium secondary battery system 10 from the sensing unit 130, and then calculates the current amounts for each cell assembly 110 including the lithium secondary batteries 111 and the average current amount of the plurality of cell assemblies 110, i.e., the average current amount A of the cell assemblies 110, from the received individual current amounts for the lithium secondary batteries 111. Here, the current amount may refer to a current voltage and / or a current, and may reflect a correction value according to the temperature of each lithium secondary battery measured by a temperature sensor of the sensing unit 130. Furthermore, the average current amount A of the plurality of cell assemblies 110 may be the average current amount of all of the cell assemblies included in the lithium secondary battery system, or in some cases, the average current amount of some of the all of the cell assemblies.

[0130] The calculated average current A of the cell assemblies 110 can be compared individually with the current of each cell assembly 110 to initially screen out cell assemblies 110 with an error rate of 5% or more, specifically 7% or more, 10% or more, 5-20%, or 5-15%. The initial screening refers to a process of screening out cell assemblies 110 that include lithium secondary batteries that are recognized as having problems from among all lithium secondary batteries. The initial screening can shorten the time required to monitor the preset applied current amount and the current amount of each individual lithium secondary battery during charging and discharging for all lithium secondary batteries, thereby enabling quicker detection of an internal short circuit in the lithium secondary battery system.

[0131] Furthermore, voltage differences between the n lithium secondary batteries included in each cell assembly may occur during charging and discharging. These voltage differences may occur due to the manufacturing process of each lithium secondary battery or external factors. The voltage differences between the cells may affect the capacity and lifespan of the lithium secondary batteries and may lead to overcharging and / or over-discharging of individual lithium secondary batteries. To prevent this, cell balancing may be performed. Cell balancing may be performed by applying minute currents to a circuit structure applied to the lithium secondary battery system. However, this may induce deviations in the amount of current flowing between the lithium secondary batteries. Therefore, the accuracy of internal short-circuit detection can be improved by setting the error rate between the average current flow amount A and the current flow amount of each lithium secondary battery to 5% or more.

[0132] Next, the control unit 140 may determine that an internal short circuit has occurred in an individual lithium secondary battery 111 included in the initially screened cell assembly 110 if the current flow rate of the individual lithium secondary battery is lower than a preset applied current flow rate by 0.5% or more when the lithium secondary battery 111 is charged or discharged.

[0133] Generally, when an internal short circuit occurs in a lithium secondary battery, leakage current occurs at the short point, and therefore, when measured, the passing current and passing voltage may be close to 0 A and 0 V, respectively. However, in the lithium secondary battery system according to the present invention, the coating layer on the negative electrode of the secondary battery not only provides a predetermined insulation property to the surface of the negative electrode in the event of an internal short circuit, but also allows a predetermined current to pass through. The current may be lower than the amount of current applied that is preset for charging or discharging the lithium secondary battery, since it is a small amount of current lost due to leakage at the internal short point from the applied current. Such a deviation between the preset applied current amount and the passed current amount may be 0.5% or more of the preset applied current amount, 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 to 90%, 5 to 50%, 10 to 30%, 50 to 90%, 0.5 to 20%, 0.5 to 10%, 0.5 to 5%, 0.5 to 3%, 5 to 10%, or 0.5 to 20%.

[0134] In order to stop charging or discharging the lithium secondary battery 111 determined to have an internal short circuit, the control unit 140 can send a charge or discharge stop signal to the charging / discharging unit 120 to stop charging or discharging the cell assembly 110 including the lithium secondary battery 111. When the charging / discharging unit 120 receives the charge or discharge stop signal from the control unit 140, it can selectively stop charging or discharging the cell assembly 110 including the lithium secondary battery 111. By controlling charging or discharging on a cell assembly basis when an internal short circuit occurs in a lithium secondary battery, the present invention can shorten the response time compared to responding to an internal short circuit on a lithium secondary battery basis, and can also improve the maintenance efficiency during normal use of the lithium secondary battery system.

[0135] Meanwhile, the cell assembly 110 may include two or more lithium secondary batteries 111 of the present invention, specifically 2 to 100, 2 to 50, 2 to 30, 5 to 20, 3 to 5, 5 to 20, or 10 to 20 lithium secondary batteries 111.

[0136] The plurality of lithium secondary batteries 111 may be electrically connected in series, in parallel, or in a mixed series-parallel configuration.

[0137] For example, n lithium secondary batteries may be connected in parallel and installed inside a cell assembly. The lithium secondary battery system according to the present invention controls charge / discharge on a cell assembly basis when an internal short circuit occurs. When n lithium secondary batteries are electrically connected in parallel inside a cell assembly, the charge / discharge of a lithium secondary battery that has experienced an internal short circuit can be individually and additionally controlled. Another advantage is that when an internal short circuit occurs in any one of the lithium secondary batteries, the charge or discharge of each lithium secondary battery can be controlled.

[0138] The cell assembly 110 may be a battery module or a battery bank depending on the number of lithium secondary batteries included therein and the type and / or shape of the housing containing them. When including a plurality of such cell assemblies 110, the secondary battery pack 150 may refer to a battery pack or an energy storage system.

[0139] In addition, the charging / discharging unit 120 is electrically connected to each of the plurality of cell assemblies 110 individually and has the function of charging or discharging each cell assembly 110. To this end, the charging / discharging unit 120 may be electrically connected to an external power source PS (power source) for charging the cell assembly 110 and an electric load EL (electric load) for using the power stored in the cell assembly 110.

[0140] Here, the types of the external power source PS and the electric load EL are not particularly limited as long as they are of a type normally applied to a product to which the lithium secondary battery system 10 is applied.

[0141] As one example, the external power source PS is a means capable of supplying constant current or constant voltage charging power to each of the cell assemblies 110, and when the lithium secondary battery system 10 is applied to an electric vehicle (EV), it may include a charging station for the electric vehicle (EV), or in some cases, a separate power source or auxiliary battery included inside the electric vehicle (EV).

[0142] In addition, the electric load EL is a means for discharging the lithium secondary battery 111 provided in the cell assembly 110 using the power stored in the cell assembly 110, and when the lithium secondary battery system 10 is applied to an electric vehicle (EV), it may be an inverter and an electric motor applied to the EV. The inverter may function to convert DC current provided from the cell assembly 110 included in the lithium secondary battery system 10 into AC current, and the electric motor may be driven using the AC power provided from the inverter.

[0143] In addition, the lithium secondary battery system 10 according to the present invention may further include an input / output unit (not shown) for inputting charge / discharge conditions to the control unit 140 and allowing a user to check the results determined by the control unit 140.

[0144] The lithium secondary battery system 10 may change the applied voltage and current conditions during charging and / or discharging depending on the type and use environment of the electric load EL electrically coupled to the charging / discharging unit 120. In order to input the changed charging / discharging conditions to the control unit 140, the input / output unit may include user input means commonly used in the art, such as a keyboard, a mouse, a barcode recognizer, a voice recognizer, a touch screen, etc., but is not limited thereto.

[0145] In addition, the input / output unit may include, but is not limited to, output means commonly used in the industry, such as a display device such as a monitor or touch screen, or an audio output device, to inform the user of whether or not an internal short circuit has occurred, the time of occurrence, and the location of the lithium secondary battery 111 and / or cell assembly 110 in which an internal short circuit has been determined to have occurred, when the control unit 140 determines that an internal short circuit has occurred in the cell assembly 110.

[0146] FIG. 2 is a block diagram showing a hardware configuration that embodies the control unit 140 included in the lithium secondary battery system according to the present invention.

[0147] The control unit 140 according to the present invention may include an MCU 142 , a memory 144 , a communication I / F 146 , and an input / output I / F 148 .

[0148] The MCU 142 is a microcontroller unit, which is a processor that executes various programs stored in the memory 144, processes various data used in such programs, and enables the control unit 140 to function.

[0149] The memory 144 may store operation data of various programs related to the operation of the lithium secondary battery system for the operation of the control unit 140. A plurality of such memories 144 may be provided as needed. The memory 144 may be a volatile memory or a non-volatile memory. As the volatile memory, the memory 144 may use RAM, DRAM, SRAM, etc. As the non-volatile memory, the memory 144 may use ROM, PROM, EAROM, EPROM, EEPROM, flash memory, etc. The examples of the memory 144 listed above are merely illustrative and are not limited thereto.

[0150] The communication I / F 146 may be configured to transmit and receive various data to and from a server and may be any device capable of supporting wired or wireless communication. For example, the communication I / F 146 may transmit and receive programs and various data for operating the control unit 140 from a separately provided external server via wired or wireless communication.

[0151] In addition, the input / output I / F 148 may provide an interface that connects input devices (not shown) such as a keyboard, mouse, or touch panel and output devices such as a display (not shown) to the MCU 142, enabling data to be transmitted and received.

[0152] Furthermore, the lithium secondary battery system 10 according to the present invention, having the above-described configuration, has excellent safety against internal short circuits and 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 powered by battery-type motors; 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; electric golf carts; and energy storage systems (ESS). More specifically, examples of such devices include, but are not limited to, hybrid electric vehicles (HEVs).

[0153] However, the electronic or electrical devices and / or any other related devices or components described herein may be embodied using any suitable hardware, firmware (e.g., application-specific integrated circuits), software, or a combination of software, firmware, and hardware. For example, various components of these devices may be formed on a single integrated circuit (IC) chip or on separate IC chips. Also, various components of these devices may be embodied 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 embodied, for example, by traces or conductive elements on a PCB or other type of circuit carrier. The conductive elements may include, for example, metallization, such as surface metallizations, and / or pins, and may include conductive polymers or ceramics. Electrical energy may also be transmitted via wireless connections, for example, using electromagnetic radiation or light.

[0154] Additionally, the various components of these devices may be processes or threads running on one or more processors, executing within one or more computing devices, executing computer program instructions, and interacting with other system components to perform the various functions described herein. The computer program instructions are stored in memory, which may be embodied 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 storage media, such as CD-ROMs, flash drives, etc.

[0155] Additionally, those skilled in the art should recognize that the functionality of various computing devices may be combined or integrated into a single computing device, or the functionality of a particular computing device may be distributed across one or more other computing devices without departing from the scope of exemplary embodiments of the present invention.

[0156] The lithium secondary battery system according to the present invention, having the above-described configuration, can apply a predetermined current when an internal short circuit occurs, thereby preemptively controlling charge and / or discharge before thermal runaway occurs in the lithium secondary battery where the short circuit occurs. Furthermore, since the system can prevent additional meltdown and / or thermal runaway from occurring in an adjacent lithium secondary battery, the system can be advantageously applied to a battery module or battery pack using a plurality of lithium secondary batteries.

[0157] <Operation method of lithium secondary battery system> In one embodiment, the present invention further comprises: In the lithium secondary battery system according to the present invention, a step of selecting cell assemblies having an error rate of 5% or more between an average current flow rate of the plurality of cell assemblies and the current flow rate of each individual cell assembly; determining that an internal short circuit has occurred in each lithium secondary battery when the amount of current measured by the sensing unit is lower than the amount of current applied to the lithium secondary battery by 0.5% or more for each individual lithium secondary battery included in the selected cell assembly; and A method for operating a lithium secondary battery system is provided, which includes a step of stopping charging or discharging of a cell assembly including a lithium secondary battery in which it has been determined that an internal short circuit has occurred.

[0158] The method for operating the lithium secondary battery system refers to a method for driving the lithium secondary battery system of the present invention. The driving method has the same configuration as that of the lithium secondary battery system described above, and therefore a detailed description thereof will be omitted.

[0159] The present invention will be described in more detail below with reference to examples and experimental examples.

[0160] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0161] Examples 1 to 8 and Comparative Examples 1-8. Manufacturing of lithium secondary batteries

[0162] Cathode manufacturing LiNi with a particle size of 5 μm is used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2 was prepared and mixed with N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 with a carbon-based conductive material and polyvinylidene fluoride as a binder to form a slurry, which was then cast onto an aluminum sheet, dried in a vacuum oven at 120°C, and rolled to produce a cathode.

[0163] Anode manufacturing A graphite mixture consisting of natural graphite (average particle size: 10±1 μm) and artificial graphite (average particle size: 8±1 μm) mixed in a 2:8 weight ratio was prepared as the negative electrode active material, carbon black was used as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were used as binders. 95 parts by weight of the graphite mixture, 1 part by weight of carbon black, 1.5 parts by weight of CMC, and 2.5 parts by weight of SBR were mixed with water to a solids content of 50% to prepare a negative electrode slurry.

[0164] Separately, aluminum-containing particles such as boehmite (average particle size (D 50 The silicon-containing particles (200-400 nm) and the first dispersant, citric acid, were added to water and mixed for 10 minutes to disperse the particles. Then, the second dispersant, ethylenediamine, was added to the dispersion and dispersed. Finally, the silicon-containing particles were added to the dispersion and mixed for 20-30 minutes to prepare a coating slurry. At this time, the following information was recorded: i) the content of each component, ii) the type of silicon-containing particles, and iii) the particle size (D) of the silicon-containing particles contained in the coating slurry.50 ) were adjusted as shown in Table 1 below.

[0165] After the negative electrode slurry and coating slurry were prepared, they were simultaneously cast onto a copper sheet (thickness: 10 μm) being transported roll-to-roll (transport speed: 5 m / min) using a dual die coater. The negative electrode slurry and coating slurry were cast to average thicknesses of 100-200 μm and 5-20 μm, respectively, along the direction of copper sheet transport. The copper sheet onto which the slurries were simultaneously cast was dried in a vacuum oven at 120°C and then rolled to produce a negative electrode (thickness ratio of the coating layer to the negative electrode active layer: approximately 0.17). The volume resistivity of the fabricated negative electrode was measured. The volume resistivity was measured using a volume resistivity tester (model: XF057) equipped with 46 probes. Specifically, a constant current was applied while the 46 probes were in contact with the surface of the negative electrode active layer, and the potential distribution generated on the surface was measured at multiple points. The total thickness of the negative electrode active layer and coating layer and the measured potential values ​​were then used to perform an inverse analysis of the potential distribution using the finite volume method to calculate the volume resistance of the negative electrode. The measurement results are shown in Table 1.

[0166] Lithium secondary battery manufacturing A separator made of polypropylene with a thickness of 18 μm was placed between the previously prepared positive and negative electrodes, and the resulting product was inserted into a pouch-type case. An electrolyte composition was then injected to assemble a 1 Ah-class lithium secondary battery.

[0167] [Table 1]

[0168] Comparative Example 8. Manufacture of a lithium secondary battery A lithium secondary battery was fabricated in the same manner as in Example 2, 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 μm) to the negative electrode active layer was about 0.02. The volume resistance of the negative electrode was 2.397×10 -4The resistance was Ω·cm.

[0169] Examples 9 to 16 and Comparative Examples 9 to 16. Production of lithium secondary battery systems Using the lithium secondary batteries produced in Examples 1 to 8 and Comparative Examples 1 to 8, a lithium secondary battery system having the configuration shown in FIG. 1 was fabricated.

[0170] Specifically, ten lithium secondary batteries each manufactured in Examples 1 to 8 and Comparative Examples 1 to 8 were prepared, and five of each lithium secondary battery were arranged in the thickness direction of the battery and then fixed together to fabricate two cell assemblies 110. A charging / discharging unit 120 and a sensing unit 130 were electrically connected in parallel to the positive electrode 111a and negative electrode 111b of each lithium secondary battery included in the cell assembly. Here, the charging / discharging unit 120 had separate ports to allow electrical connection to an external power source PS and an electrical load EL. The sensing unit 130 included a current sensor for measuring the current flowing through the negative electrode 111b and a temperature sensor for measuring the surface temperature of each lithium secondary battery.

[0171] In addition, the charging / discharging unit 120 and the sensing unit 130 are each electrically connected to the 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 included in the cell assembly 110, and outputting whether an internal short circuit has occurred during charging / discharging; the time when the internal short circuit has occurred; and the position of the lithium secondary battery 111 determined to have an internal short circuit among the lithium secondary batteries of the cell assembly.

[0172] An external power source PS and an electrical load EL were connected to each port of the charging / discharging unit 120, and the cell assembly was charged / discharged. During the charging / discharging process of the cell assembly, the sensing unit 130 measured the current flowing through the negative electrode of each lithium secondary battery and the surface temperature of the lithium secondary battery in real time, and transmitted the results to the control unit 140. Thereafter, pressure was applied to the surface of any one of the plurality of lithium secondary batteries 111 included in the cell assembly 110, inducing an internal short circuit in that lithium secondary battery 111.

[0173] When an internal short circuit occurs in the lithium secondary battery 111, the sensing unit 130 measures the current flowing through the lithium secondary battery 111 and the surface temperature of each lithium secondary battery included in the cell assembly 110, and transmits the measured current flowing through the lithium secondary battery 111 and the surface temperature of each lithium secondary battery to the control unit 140. The control unit 140 calculates the average value of each transmitted current flowing through the lithium secondary battery 111 and obtains the average current flowing through the lithium secondary battery 111 by applying a correction value corresponding to the measured temperature of each lithium secondary battery to the calculated average value.

[0174] The control unit 140 compared the calculated average current flow A with the transmitted current value of each lithium secondary battery, and initially screened out lithium secondary batteries with an error rate of 5 to 10%. The control unit 140 diagnosed an internal short circuit in a lithium secondary battery with a current flowing 0.5 to 5% lower than a preset applied current during charging or discharging of the screened lithium secondary batteries. The control unit 140 also sent an electrical signal to the charging / discharging unit 120 to stop charging / discharging of the cell assembly 110 including the lithium secondary battery diagnosed as having an internal short circuit, thereby stopping charging / discharging of the cell assembly 110. In this regard, in the lithium secondary battery system of the embodiment, charging / discharging of the cell assembly was stopped before the lithium secondary battery ignited, while in the lithium secondary battery system of the comparative example, the lithium secondary battery ignited before charging / discharging of the cell assembly was stopped.

[0175] Thereafter, the control unit 140 transmits to the input / output unit whether an internal short circuit has occurred during charging / discharging, the time when the internal short circuit has occurred, and the position of the lithium secondary battery 111 in which it is determined that an internal short circuit has occurred among the lithium secondary batteries of the cell assembly, and the input / output unit outputs the transmitted information on the touch screen.

[0176] Experimental Example 1 In order to evaluate the performance of the lithium secondary battery system according to the present invention during an internal short circuit, the following experiment was carried out.

[0177] Specifically, as shown in FIG. 3, a separator having a perforated shape 211c-1 at the center was used, and a positive electrode having no positive active layer formed at the center was used 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. Except for this, a 1 Ah-class pouch-type lithium secondary battery (N / P ratio = approximately 1.07) for experiment was fabricated in the same manner as in Examples 1 to 8 and Comparative Examples 1 to 8.

[0178] Each lithium secondary battery was fully charged, and the center of the pouch-type lithium secondary battery was pressurized at 1 MPa to induce an internal short circuit. The current flow voltage and surface temperature of the lithium secondary battery were then measured for 100 seconds. This internal short circuit induction experiment was repeated a total of three times.

[0179] The energization voltage and surface temperature of the lithium secondary battery were measured 100 seconds after the internal short circuit occurred, and the average values ​​were calculated to confirm whether the lithium secondary battery ignited after the internal short circuit occurred and the time required for the battery temperature to reach its maximum value. The results are shown in Table 2 below. Furthermore, the voltage and temperature changes over time for Example 2, Comparative Example 1, and Comparative Example 5 are shown in Figures 4 to 6.

[0180] Separately, a lithium secondary battery system was fabricated in Example 9 using cell assemblies each including one 1 Ah pouch-type lithium secondary battery for experimentation fabricated previously and nine pouch-type lithium secondary batteries fabricated in Examples 1 to 8 and Comparative Examples 1 to 8. An internal short circuit was induced in the experimental lithium secondary battery while charging and discharging the fabricated lithium secondary battery system. At this time, the applied voltage during charging and discharging of the system was adjusted to 4.2 V.

[0181] Next, it was confirmed whether the lithium secondary battery system had diagnosed an internal short circuit in the experimental lithium secondary battery and whether the location of the lithium secondary battery in which the internal short circuit occurred had been confirmed. The results are shown in Table 2 below.

[0182] [Table 2]

[0183] 4 is a graph showing the voltage and temperature changes at the negative electrode of Comparative Example 1, i.e., a lithium secondary battery not having the coating of the present invention applied to the negative electrode surface, when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. In Comparative Example 1, the voltage changes rapidly, and the resulting high current generation causes a rapid rise in temperature around 5 seconds, which may lead to ignition.

[0184] 5 is a graph showing the voltage and temperature changes at the negative electrode of the lithium secondary battery of Comparative Example 5 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. In Comparative Example 5, a coating layer containing an insulating material (specifically, SiO2) is provided on the negative electrode surface, and there is almost no change in voltage over time. As a result, no current flows and there is almost no change in temperature, even when the battery is compressed at 1 mPa. In this case, no fire occurs, but there is no temperature change, which creates the problem of not being able to detect any abnormalities in the cell.

[0185] FIG. 6 is a graph showing the voltage and battery temperature changes at the negative electrode of the lithium secondary battery of Example 2 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. Example 2 is an example of a lithium secondary battery in which a coating layer with a predetermined volume resistivity is provided on the negative electrode. As shown in FIG. 6, the voltage graph at the top shows a slight change in voltage over time, resulting in the generation of a predetermined small current. In contrast, the temperature graph at the bottom shows a small change within a range that does not cause a fire. That is, Example 2 shows a case in which a small current flows during an internal short circuit, making it possible to quickly detect the internal short circuit.

[0186] As shown in Table 2 and FIGS. 4 to 6, the lithium secondary batteries according to the embodiments of the present invention are provided with a coating layer having a predetermined volume resistivity on the surface of the negative electrode, thereby realizing insulation during an internal short circuit in the lithium secondary battery and simultaneously inducing a small amount of leakage current, thereby maintaining a conduction voltage of 3.0 V or higher, lower than the applied voltage of 4.2 V. It was also confirmed that the lithium secondary batteries according to the embodiments have a significantly low leakage current and maintain a battery temperature of 60° C. or lower. It was also confirmed that a lithium secondary battery system including such a lithium secondary battery can diagnose the presence or absence of an internal short circuit in the lithium secondary battery and accurately determine its location using the small amount of leakage current applied after an internal short circuit.

[0187] In contrast, the lithium secondary batteries of Comparative Examples 1, 4, 6, 7, and 8, which were not provided with a coating layer or had a coating layer with extremely low volume resistivity, showed a rapid temperature rise and ignition within several seconds upon an internal short circuit. It was also confirmed that such rapid thermal runaway made it impossible for the lithium secondary battery systems including the lithium secondary batteries of the Comparative Examples to determine whether or not an internal short circuit had occurred in the battery.

[0188] It was also confirmed that the lithium secondary batteries of Comparative Examples 3 and 5, in which the volume resistivity of the coating layer exceeded 1 Ω cm, were completely insulated, and no current leakage or temperature rise due to an internal short circuit occurred. Furthermore, it was shown that the lithium secondary battery system including the lithium secondary batteries of the above Comparative Examples was unable to determine i) whether or not an internal short circuit had occurred in the battery, and ii) the location of the internally shorted lithium secondary battery, in the event of an internal short circuit in the secondary battery.

[0189] These results demonstrate that the negative electrode for a lithium secondary battery according to the present invention, which contains specific silicon-containing particles and aluminum-containing particles, can achieve a desired volume resistance. Furthermore, a lithium secondary battery including the negative electrode can achieve suitable insulation on the negative electrode surface during an internal short circuit, allowing a desired current to leak, thereby preventing meltdown and / or rapid heat generation of the lithium secondary battery due to the internal short circuit and providing sufficient time to respond to the internal short circuit.

[0190] Furthermore, it can be seen that a lithium secondary battery system including the above-mentioned lithium secondary battery can determine with high accuracy and speed whether or not an internal short circuit has occurred in the lithium secondary battery and the location of the internally shorted lithium secondary battery by using the current applied during an internal short circuit.

[0191] Experimental Example 2 In order to evaluate the charge / discharge performance of the lithium secondary battery system according to the present invention, the following experiment was carried out.

[0192] Specifically, the lithium secondary batteries prepared in Examples 5 and 6 and Comparative Example 1 were activated by charging them at 25°C at a rate of 0.3 C to 4.2 V under CC-CV conditions and discharging them at a rate of 0.3 C to 2.5 V under CC conditions.

[0193] The activated lithium secondary batteries were then charged and discharged 400 times, and the charge / discharge capacity and coulombic efficiency of each lithium secondary battery were measured. The charging was performed under CC-CV conditions at 25°C at a 0.33 C-rate to 4.25 V, and the discharging was performed under CC conditions at a 0.5 C-rate to 3.0 V. The measurement results are shown in Figures 7 and 8.

[0194] 7 and 8, it can be seen that the lithium secondary batteries according to the present invention have excellent charge / discharge performance. Specifically, the lithium secondary batteries according to Examples 5 and 6 according to the present invention, despite having a coating layer with a predetermined volume resistivity on the surface of the negative electrode, exhibited equivalent charge / discharge capacities (FIG. 7) and coulombic efficiencies that were, on average, about 2% higher than the lithium secondary battery according to Comparative Example 1, which had no coating layer (FIG. 8).

[0195] These results show that the lithium secondary battery according to the present invention has a coating layer having a predetermined volume resistance on the negative electrode active layer, and therefore has excellent safety against internal short circuits as well as excellent charge / discharge performance.

[0196] Although the present invention has been described above with reference to preferred embodiments, it will be understood that a person skilled in the art or having ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0197] Therefore, the technical scope of the present invention is not limited to the content described in the Summary of the Invention of the specification, but can be defined by the claims. [Explanation of symbols]

[0198] 10: Lithium secondary battery system 110: Cell assembly 111: Lithium secondary battery 111a: Positive electrode of lithium secondary battery 111b: Negative electrode of lithium secondary battery 112a: Positive terminal 112b: Negative terminal 120: Charging / discharging unit 130: Sensing unit 140: Control unit 142: MCU 144: Memory 146: Communication I / F 148: Input / output I / F 150: Secondary battery pack PS: External power supply EL: Electric load 211: Experimental lithium secondary battery 211a-1: Positive electrode current collector 211a-2: Positive electrode active layer 211b-1: Negative electrode current collector 211b-2: Negative electrode active layer 211b-3: Negative electrode coating layer 211c: Separation membrane 211c-1: Penetration part of separation membrane

Claims

1. a negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a negative electrode active material; and a coating layer located on the negative electrode active layer, the coating layer comprises silicon-containing particles, aluminum-containing particles, and a dispersant; Volume resistance is 1.0 x 10 －４ A negative electrode for a lithium secondary battery having a resistivity of Ω·cm or more and 1.0 Ω·cm or less.

2. The negative electrode has a capacitance of 3.0×10 －３ Ω・cm~9.0×10 －１ 2. The negative electrode for a lithium secondary battery according to claim 1, having a volume resistivity of Ω·cm.

3. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the silicon-containing particles include particles having a silicon to oxygen ratio of 1:0.5 to 2.

0.

4. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the aluminum-containing particles include 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 of 1 to 10, q is an integer of 0 to 20, and p≦q; r is an integer of 1 to 5.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the aluminum-containing particles include at least one of boehmite, pseudoboehmite, diaspore, akdalite, and aluminum trihydroxide.

6. The silicon-containing particles have an average particle size (D ５０ ) The aluminum-containing particles have an average particle size (D ５０ 2. The negative electrode for a lithium secondary battery according to claim 1, comprising:

7. The negative electrode for a lithium secondary battery according to claim 1 , wherein the silicon-containing particles include a carbon layer on the surface thereof.

8. The coating layer has a weight of 1 to 30 wt. % silicon-containing particles; 30 to 89 wt. % aluminum-containing particles, and 2. The negative electrode for a lithium secondary battery according to claim 1, comprising 10 to 40% by weight of a dispersant.

9. The dispersant is a first dispersant comprising one or more carboxylic acids; and 10. The negative electrode for a lithium secondary battery according to claim 1, further comprising a second dispersant containing one or more amino groups.

10. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the coating layer further comprises at least one binder selected from the group consisting of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyalkyl acrylate, polyamide (PA), and polystyrene (PS).

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

12. 12. The lithium secondary battery of claim 11, wherein the positive electrode comprises a positive electrode active layer on a positive electrode current collector, the positive electrode active layer including one or more positive electrode active materials selected from compounds represented by the following Chemical Formula 2 and Chemical Formula 3: [Chemical formula 2] LiFe ａ M １ １－ａ XO ４ [Chemical formula 3] Li ｘ [Ni ｙ Co ｚ Mn ｗ M ２ ｖ ]O ２ In the above Chemical Formula 2 and Chemical Formula 3, M １ is one or more elements selected from 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; X is one or more of P, Si, S, As, and Sb; a is 0<a≦1.0, M ２ is one or more elements selected from 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; x, y, z, w, and v are in the ranges 1.0≦x≦1.30, 0≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, and y+z+w+v=1, respectively.

13. a plurality of cell assemblies each including n (where n is an integer of 3≦n≦100) lithium secondary batteries according to claim 11; a charging / discharging unit electrically coupled to each of the plurality of cell assemblies to charge or discharge the cell assemblies individually; a sensing unit electrically coupled to an electrode of each of the lithium secondary batteries included in the plurality of cell assemblies, and configured to individually measure at least one of a voltage and a current of each of the lithium secondary batteries when the lithium secondary batteries are charged or discharged; and a control unit electrically connected to the charging / discharging unit and the sensing unit to control charging or discharging of each cell assembly; The control unit stops charging or discharging the cell assembly including the lithium secondary battery when the amount of current measured by the sensing unit meets a predetermined value.

14. The control unit A step of selecting cell assemblies having an error rate of 5% or more between the average current flow rate of the plurality of cell assemblies and the current flow rate of each individual cell assembly; determining that an internal short circuit has occurred in each lithium secondary battery when the amount of current measured by the sensing unit is lower than the amount of current applied to the lithium secondary battery by 0.5% or more for each individual lithium secondary battery included in the selected cell assembly; and 14. The lithium secondary battery system according to claim 13, further comprising a step of stopping charging or discharging of a cell assembly including the lithium secondary battery in which it has been determined that an internal short circuit has occurred.

15. The lithium secondary battery system of claim 13 , wherein the sensing unit further comprises a temperature measurement sensor for measuring the temperature of each lithium secondary battery included in the cell assembly.

16. 14. The lithium secondary battery system according to claim 13, wherein a step of selecting cell assemblies having an error rate of 5% or more between an average current flow rate of the plurality of cell assemblies and the current flow rate of each individual cell assembly is performed. determining that an internal short circuit has occurred in each lithium secondary battery when the amount of current measured by the sensing unit is lower than the amount of current applied to the lithium secondary battery by 0.5% or more for each individual lithium secondary battery included in the selected cell assembly; and A method for operating a lithium secondary battery system, comprising the step of stopping charging or discharging of a cell assembly including a lithium secondary battery in which it has been determined that an internal short circuit has occurred.

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