Lithium secondary battery with improved safety against internal short circuits and lithium secondary battery system therefor

Abstract

The present invention relates to a lithium secondary battery and a lithium secondary battery system therefor, wherein the lithium secondary battery includes a negative electrode having a predetermined volume resistivity, thereby enabling a predetermined current to flow while providing insulation to the negative electrode surface in the event of an internal short circuit, thereby preventing meltdown and / or rapid heat generation in the lithium secondary battery due to an internal short circuit. Furthermore, a lithium secondary battery system according to the present invention includes the lithium secondary battery of the present invention and is capable of preventing meltdown and rapid heat generation in the event of an internal short circuit. This allows the system to preemptively control operation of the lithium secondary battery before thermal runaway occurs, thereby preventing additional meltdown and / or thermal runaway in adjacent lithium secondary batteries, thereby advantageously alleviating safety issues due to internal short circuits.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery with improved safety against internal short circuits and a lithium secondary battery system therefor.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0026060, filed February 27, 2023, and all contents disclosed in the documents of said Korean patent application 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 and deintercalated between the positive and negative electrodes. Lithium secondary batteries are manufactured by using materials capable of reversibly intercalating and deintercalating lithium ions as the active materials for the positive and negative electrodes, and filling the space between the positive and negative electrodes with an organic or polymer electrolyte solution.

[0004] Such lithium secondary batteries are charged and discharged through electrochemical reactions in which ions are released, inserted, 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] In order to solve the above-mentioned problems, in one embodiment, the present invention comprises: a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; In the negative electrode, a negative electrode active layer including a carbon-based negative electrode active material and a coating layer including silicon-containing particles are sequentially disposed on a negative electrode current collector, The volume resistance of the negative electrode is approximately 1.0 × 10 -4 We provide a lithium secondary battery with a resistance of Ω·cm to 1.0 Ω·cm.

[0008] For example, the negative electrode has a capacitance of about 8.0×10 -3 Ω·cm~9.0×10 -1 It may have a volume resistivity of Ω·cm.

[0009] The silicon-containing particles may include particles in which the ratio of silicon element to oxygen element is about 1:0.5 to 1.5.

[0010] The silicon-containing particles have an average particle size (D 50 ) and may include a carbon layer on the surface.

[0011] The coating layer may contain about 70 parts by weight or more of silicon-containing particles and about 30 parts by weight or less of binder, based on 100 parts by weight of the entire coating layer.

[0012] The coating layer may have an average thickness of about 1.5 μm to 30 μm, and the thickness ratio of the coating layer to the negative electrode active layer may be about 0.01 to 0.3.

[0013] Furthermore, 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 the compounds represented by the following Chemical Formula 1 and Chemical Formula 2:

[0014] [Chemical formula 1] Life a M 1 1-a XO4

[0015] [Chemical formula 2] Li x [Ni y Co z Mn w M 2 v ]O2

[0016] In the above Chemical Formula 1 and Chemical Formula 2, 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.

[0017] In one embodiment, the present invention further comprises: 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 connected 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 lithium secondary battery; 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.

[0018] the control unit selects cell assemblies having an error rate of about 5% or more between an average amount of current passing through the plurality of cell assemblies and an amount of current passing through an 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 about 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 has been determined that an internal short circuit has occurred.

[0019] The sensing unit may further include a temperature sensor for measuring the temperature of each lithium secondary battery included in the cell assembly.

[0020] In another embodiment, the present invention provides A step of selecting cell assemblies having an error rate of about 5% or more between an average amount of current passing through the plurality of cell assemblies and an amount of current passing through an 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 about 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.

[0021] Furthermore, in another embodiment, the present invention provides A step of selecting cell assemblies having an error rate of about 5% or more between an average amount of current passing through the plurality of cell assemblies and an amount of current passing through an 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 about 0.5% or more for each individual lithium secondary battery included in the selected cell assembly; and A non-transitory computer-readable recording medium is provided that stores a program for executing a method for operating a lithium secondary battery system, the method including 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.

[0022] In another embodiment, the present invention provides a negative electrode active layer including a carbon-based negative electrode active material and a coating layer including silicon-containing particles on a negative electrode current collector; The silicon-containing particles contained in the coating layer include particles having a silicon to oxygen ratio of about 1:0.5 to 1.5, The volume resistance of the negative electrode is approximately 1.0 × 10 -4 We provide a negative electrode for lithium secondary batteries with a resistance of Ω·cm to 1.0 Ω·cm.

[0023] The silicon-containing particles have a carbon layer on the surface and an average particle size (D 50 ) may be.

[0024] The coating layer may contain about 70 parts by weight or more of silicon-containing particles and about 30 parts by weight or less of binder, based on 100 parts by weight of the entire coating layer.

[0025] The coating layer may have an average thickness of about 1.5 μm to 30 μm, and the thickness ratio of the coating layer to the thickness of the negative electrode active layer may be about 0.01 to 0.3. [Effects of the Invention]

[0026] The lithium secondary battery according to the present invention includes a negative electrode having a predetermined volume resistivity, and thus, in the event of an internal short circuit, a predetermined current can be leaked while achieving suitable insulation on the surface of the negative electrode, thereby preventing meltdown and / or sudden heat generation of the lithium secondary battery due to an internal short circuit.

[0027] Furthermore, the lithium secondary battery system according to the present invention includes the lithium secondary battery of the present invention described above, and can prevent a meltdown phenomenon and rapid heat generation in the event of an internal short circuit. Therefore, the operation of the lithium secondary battery can be preemptively controlled before thermal runaway occurs, and additional meltdown phenomena and / or thermal runaway occurring in adjacent lithium secondary batteries and / or cell assemblies including the same can be prevented, thereby providing the advantage of improving safety issues due to internal short circuits. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a structural diagram illustrating a schematic configuration of a lithium secondary battery system according to the present invention. [Figure 2] 2 is a structural diagram illustrating a control unit of the lithium secondary battery system according to the present invention; FIG. [Figure 3] 1 shows a scanning electron microscope (SEM) image of a cross-sectional structure of a negative electrode provided in the lithium secondary batteries prepared in Examples 2 and 3 and a thickness of a coating layer measured. [Figure 4] 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 5] 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 6]10 is a graph showing the voltage and temperature changes of the negative electrode provided in the lithium secondary battery of Comparative Example 3 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. [Figure 7] 10 is a graph showing the voltage and temperature changes of the negative electrode provided in the lithium secondary battery of Comparative Example 4 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. [Figure 8] 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. DETAILED DESCRIPTION OF THE INVENTION

[0029] In some of the accompanying drawings, corresponding components are given the same reference numerals. Those skilled in the art will understand that the drawings illustrate elements simply and clearly and are not necessarily drawn to scale. For example, to facilitate understanding of the various embodiments, the dimensions of some elements shown in the drawings may be exaggerated relative to other elements. Furthermore, elements of known technology that are useful or essential in commercially viable embodiments may not be depicted from time to time so as not to obscure the spirit of the various embodiments of the present invention.

[0030] Since the present invention can be modified in various ways and can have various embodiments, the embodiments will be described in detail in the detailed description.

[0031] However, this is not intended to limit the invention to the embodiments, but can be understood as including all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0032] In the present invention, terms such as "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 additional possibility of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0033] 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 this 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.

[0034] In addition, in the present invention, the term "amount of current flowing" refers to the amount of electricity that flows through the electrodes when the lithium secondary battery is charged or discharged, and this can be quantified as a current and / or a voltage.

[0035] As used herein, 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 infringers from unfairly using disclosure content that refers to precise or absolute numerical values ​​provided to aid in the understanding of the present invention.

[0036] In 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, the porous separator responds by closing its pores and blocking ion movement between the electrodes (shutdown phenomenon), thereby suppressing the electrochemical reaction and ensuring safety.

[0037] However, if the temperature inside the battery rises excessively beyond the temperature release rate of the case due to unevenness of the separator or other internal short circuits, the separator itself will melt 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) will occur, 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 not only causes the explosion of the secondary battery where the short circuit occurred, but also induces meltdown in neighboring secondary batteries, causing additional explosions.

[0038] The meltdown phenomenon is induced by an internal short circuit caused by contact between electrodes contained in a secondary battery, between electrodes and the current collectors of the electrodes, and / or between current collectors. When the contact occurs between the positive electrode current collector (or the positive electrode surface) and the negative electrode, the resistance of the short circuited area causes a sudden increase in the amount of heat generated, leading to a thermal runaway phenomenon in a short period of time. Therefore, in order to achieve battery stability, measures are needed to prevent, prevent, and / or respond to this.

[0039] To address these issues, the present invention proposes a lithium secondary battery in which the surface resistance of the negative electrode is improved by applying a suitable insulating coating to the surface of the negative electrode active material. As a result of the improved surface resistance of the negative electrode, the lithium secondary battery according to the present invention has improved safety in various aspects, such as preventing hard shorts between the positive electrode current collector and the negative electrode active material.

[0040] The present invention will now be described in more detail.

[0041] <Lithium secondary battery>

[0042] In one embodiment, the present invention comprises: a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; In the negative electrode, a negative electrode active layer including a carbon-based negative electrode active material and a coating layer including silicon-containing particles are sequentially disposed on a negative electrode current collector, The volume resistance of the negative electrode is approximately 1.0 × 10 -4 We provide a lithium secondary battery with a resistance of Ω·cm to 1.0 Ω·cm.

[0043] The lithium secondary battery according to the present invention includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode assembly is inserted into a battery case, and then an electrolyte composition is injected into the battery case, which is then sealed.

[0044] The negative electrode has a structure in which a negative electrode active layer including a carbon-based negative electrode active material and a coating layer including silicon-containing particles are sequentially stacked on at least one surface of a negative electrode current collector.

[0045] In addition, the negative electrode may have a predetermined volume resistivity by providing a coating layer containing silicon-containing particles on the surface of a negative electrode active layer containing a carbon-based negative electrode active material. For example, the coating layer may have a volume resistivity of about 1.0×10 -4 It may have a volume resistivity of Ω·cm or greater, or a volume resistivity of about 1.0×10 -4 For example, the coating layer may have a resistance of about 8.0×10 -3 Ω·cm~9.0×10 -1 Ω·cm, 7.0×10 -2 Ω·cm~9.0×10 -2 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.

[0046] If the volume resistivity of the negative electrode exceeds 1.0 Ω·cm, excessive resistance occurs 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 complete cessation of current flow. This allows the lithium secondary battery to block short-circuit current, making the secondary battery highly safe. However, it is difficult to selectively detect and respond to an internally shorted lithium secondary battery in a relatively short period of time within a device containing multiple lithium secondary batteries, such as a battery module or pack. In this case, responding to an internal short circuit requires separating and / or removing the cell assembly containing the lithium secondary battery in question from the lithium secondary battery system, which reduces economic viability.

[0047] In addition, the volume resistance of the negative electrode is 1.0 × 10 -4 If the electrical resistance is less than Ω·cm, sufficient insulation is not achieved on the surface of the negative electrode during an internal short circuit, which can lead to meltdowns such as decomposition of the negative electrode active material and electrolyte, and decomposition of the positive electrode active material.

[0048] 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 lower 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 relatively easy response to abnormal operation of the lithium secondary battery.

[0049] In order to satisfy the volume resistivity within the above range, the components constituting the coating layer, the content of each component, the mixed form and size of each component, and the thickness ratio of the negative electrode active layer to the coating layer may be controlled.

[0050] For example, 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.

[0051] The coating layer may contain silicon-containing particles as a primary component and may further contain a binder for forming the silicon-containing particles into a coating layer. For example, the coating layer may contain approximately 70 parts by weight or more of silicon-containing particles and approximately 30 parts by weight or less of a binder, based on 100 parts by weight of the total coating layer. In one embodiment, the silicon-containing particles may be present in an amount of approximately 85 parts by weight or more, 90 parts by weight or more, 95 parts by weight or more, 80 to 99 parts by weight, 90 to 99 parts by weight, 85 to 95 parts by weight, or 90 to 95 parts by weight, and the binder may be present in an amount of 15 parts by weight or less, 10 parts by weight or less, 5 parts by weight or less, 1 to 20 parts by weight, 1 to 10 parts by weight, 5 to 15 parts by weight, or 5 to 10 parts by weight.

[0052] By adjusting the contents of the silicon-containing particles and binder within the above-mentioned ranges, the coating layer of the present invention can prevent a reduction in the leakage current of the coating layer due to an excessive binder content, while preventing a phenomenon in which an excessive silicon-containing particle content reduces the morphological stability of the coating layer and damages the coating layer.

[0053] The binder may be any polymeric compound capable of fixing the silicon-containing particles without impairing the electrical properties of the coating layer. For example, the binder may include at least one selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylamide, 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.

[0054] The binder not only firmly fixes the silicon-containing particles contained in the coating layer but also has adhesive strength with the negative electrode active layer on which the coating layer is formed, thereby improving the durability of the negative electrode.

[0055] The silicon-containing particles contained in the coating layer may be oxidized silicon particles. For example, the silicon-containing particles may contain silicon and oxygen, and the ratio thereof may be approximately 1:0.5-1.5, 1:0.8-1.2, or 1:0.9-1.1.

[0056] The silicon-containing particles are not particularly limited in form as long as the elemental 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.

[0057] In the present invention, by controlling the elemental ratio of silicon and oxygen (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 fall within the above-mentioned predetermined range. As a result, the lithium secondary battery of the present invention can impart predetermined insulation properties to the surface of the coating layer of the negative electrode during an internal short circuit, while at the same time allowing an extremely small amount of current to leak into the battery.

[0058] For example, if the proportion of silicon is higher than the proportion of oxygen, insulation is 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 temperature of the lithium secondary battery. Also, if the proportion of silicon is lower than the proportion of oxygen, 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.

[0059] Meanwhile, the silicon-containing particles have a chemical structure that allows for lithium ion insertion during charging of a lithium secondary battery, and thus 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 used in the coating layer of the present invention, the surface area into which lithium ions are inserted may be significantly reduced due to a lower content ratio compared to when the silicon-containing particles are used in the negative electrode active layer. This means that the resistance of the silicon-containing particles to lithium insertion occurring in the coating layer increases. Therefore, when the silicon-containing particles are used in the coating layer of the present invention, it may be difficult for the silicon-containing particles to insert lithium ions, as with typical silicon-based negative electrode active materials, during charging of a lithium secondary battery.

[0060] The silicon-containing particles have an average particle size (D 50 For example, the silicon-containing particles may have an average particle size (D) of about 1 μm to 10 μm, 1 μm to 5 μm, 1 μm to 3 μm, 3 μm to 9 μm, 3 μm to 7 μm, 10 μm to 20 μm, 15 μm to 20 μm, 14 μm to 19 μm, 5 μm to 15 μm, 5 μm to 10 μm, 5 μm to 8 μm, 7.5 μm to 10 μm, 5 μm to 7.5 μm, 6 μm to 8 μm, or 6 μm to 7 μm. 50 ).

[0061] 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.

[0062] The coating layer containing the silicon-containing particles may have an average thickness of about 1.5 μm to 30 μm, which may be greater than the average particle size of the silicon-containing particles. For example, the coating layer may have an average thickness of about 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. In this case, 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 mean the average of any three or more measured values, or the intermediate value between the maximum and minimum values ​​among the measured values.

[0063] The thickness ratio of the coating layer to the negative electrode active layer may be approximately 0.05 to 0.3, for example, approximately 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.

[0064] 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. The volume resistance of the coating layer can be controlled by the components constituting the coating layer, the content of each component, the mixing form and size of each component, etc., as described above. However, even if the volume resistance of the coating layer is controlled, if the thickness of the negative electrode active layer is excessively thicker than the coating layer and the thickness ratio of the coating layer to the negative electrode active layer is less than the above-mentioned lower limit, the electrical performance of the negative electrode may be improved, but 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 smaller 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 increase significantly, and the short-circuit current of the lithium secondary battery may be interrupted in the event of an internal short circuit. However, this has limitations, such as difficulty in selectively detecting and responding to an internally shorted lithium secondary battery in a device including multiple lithium secondary batteries, such as a battery module or pack, within a relatively short period of time, resulting in low economic viability.

[0065] Therefore, 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 relatively 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.

[0066] Furthermore, the silicon-containing particles may include a carbon layer on their surfaces 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 onto the surfaces of the silicon-containing particles. In some cases, the carbon layer may be formed by depositing carbon atoms onto the surfaces 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 in 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 average thickness of the carbon layer may be approximately 1 nm to 1,000 nm, for example, approximately 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] 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. For example, the carbon-based negative electrode active material may include at least one of natural graphite and artificial graphite, and in one embodiment, may include natural graphite or a mixture of natural graphite and artificial graphite.

[0069] The carbon-based negative electrode active material may be a spherical graphite granule formed by the aggregation of a plurality of 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.). For example, the carbon-based negative electrode active material may be assembled using a plurality of highly crystalline natural graphite particles. Each graphite granule may be formed by the aggregation of approximately 2 to 100, e.g., 3 to 20, flake graphite particles.

[0070] The carbon-based negative electrode active material has an average particle size (D 50 ), for example, an average particle size (D) of about 0.5 μm to 15 μm, 0.5 μm to 10 μm, 5 μm to 20 μm, 10 μm to 20 μm, 12 μm to 18 μm, 2 μm to 7 μm, 0.5 μm to 5 μm, or 1 μm to 3 μm. 50 ) can be shown.

[0071] 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.

[0072] The conductive material may include one or more of carbon black, acetylene black, ketjen black, carbon nanotubes, carbon fibers, and the like.

[0073] For example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0074] The content of the conductive material may be about 0.1 to 10 parts by weight, for example, about 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.

[0075] 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. For example, 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.

[0076] The content of the binder may be about 0.1 to 10 parts by weight, for example, about 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.

[0077] The negative electrode current collector is not particularly limited as long as it has relatively 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 may be preferably in the range of about 1 μm to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0078] Furthermore, 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 positive electrode slurry, and pressing the positive electrode slurry. The positive electrode slurry may further include a conductive material, a binder, other additives, and the like, as needed.

[0079] The positive electrode active material is a material capable of undergoing an electrochemical reaction on a positive electrode current collector, and may include one or more lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2, which are capable of reversibly intercalating and deintercalating lithium ions:

[0080] [Chemical formula 1] Life a M 1 1-a XO4

[0081] [Chemical formula 2] Li x [Ni y Co z Mn w M 2 v ]O2

[0082] In the above Chemical Formula 1 and Chemical Formula 2, 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.

[0083] The compounds represented by Chemical Formula 1 and Chemical Formula 2 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 2 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.

[0084] The compound represented by the above chemical formula 1 includes LiFePO4, LiFe 0.8 Mn 0.2 PO4, LiFe 0.7 Mn 0.3 PO4, LiFe 0.5 Mn 0.5PO4, etc. In addition, although the charge / discharge capacity of the lithium composite metal oxide increases as the nickel (Ni) content increases, the lithium composite metal oxide exhibits low chemical and structural stability, which can easily cause an exothermic reaction, resulting in a high risk of fire. For example, the exothermic reaction 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 an exothermic reaction 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), while significantly reducing current leakage and preventing subsequent problems after an internal short circuit.

[0085] The lithium metal oxide represented by chemical formula 2 is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 It may contain O2 etc.

[0086] The positive electrode active material may be included in an amount of about 85 parts by weight or more, for example, about 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.

[0087] The positive electrode active layer may further include a conductive material, a binder, and other additives in addition to the positive electrode active material.

[0088] 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. For example, 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.

[0089] The conductive material may be contained in an amount of about 0.1 to 5 parts by weight based on the weight of each positive electrode active layer, for example, about 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.

[0090] 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. For example, 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. As one example, the binder may include polyvinylidene fluoride.

[0091] The binder may be contained in an amount of about 1 to 10 parts by weight, for example, about 2 to 8 parts by weight, or 1 to 5 parts by weight, based on the weight of each positive electrode active layer.

[0092] The total thickness of the positive electrode active layer may be, for example, about 50 μm to 300 μm, or about 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.

[0093] The positive electrode may use a current collector that has high conductivity without inducing 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 in the range of about 3 μm to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0094] 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 made of any material commonly used in the art, including, for example, one or more of the following polymers: polypropylene, polyethylene, and polyethylene-propylene copolymer, which are chemically resistant and hydrophobic. 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, the separator 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.

[0095] Meanwhile, the lithium secondary battery according to the present invention 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 have a relatively high contact possibility. For example, the lithium secondary battery according to the present invention may be a pouch type secondary battery or a prismatic type secondary battery.

[0096] <Lithium secondary battery system>

[0097] 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; 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.

[0098] 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 between 3 and 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 individually charging or discharging the cell assemblies; a sensing unit 130 electrically coupled to electrodes of each lithium secondary battery 111 included in the cell assemblies 110 and individually measuring the voltage and / or current flowing through each secondary battery 111 during charging or discharging of the lithium secondary batteries; 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 cell assembly 110; and the plurality of cell assemblies 110. Here, the cell assemblies 110 may be a secondary battery module or a secondary battery pack including a plurality of cells. In this case, each lithium secondary battery 111 included in the cell assembly 110 may include a positive electrode 111a and a negative electrode 111b, and the secondary battery module or secondary battery pack 150 may include a positive terminal 112a and a negative terminal 112b electrically connected to the positive electrode 111a and the negative electrode 111b of each lithium secondary battery 111.

[0099] 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.

[0100] The control unit 140 according to an embodiment disclosed in the present invention may include an MCU 142, a memory 144, a communication I / F (interface) 146, and an input / output I / F 148. 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 performs the functions of the control unit 140.

[0101] 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, RAM, DRAM, SRAM, etc. may be used for the memory 144. As the non-volatile memory, ROM, PROM, EAROM, EPROM, EEPROM, flash memory, etc. may be used for the memory 144. The examples of the memory 144 listed above are merely illustrative and are not limited thereto.

[0102] The communication I / F 146 is configured to transmit and receive various data to and from a server and may be any of various devices supporting wired or wireless communication. For example, programs and various data for operating the control unit 140 may be transmitted and received via wired or wireless communication from a separately provided external server via the communication I / F 146. The input / output I / F 148 may provide an interface for connecting an input device (not shown) such as a keyboard, mouse, or touch panel and an output device (not shown) such as a display to the MCU 142, thereby transmitting and receiving data.

[0103] 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 the cell assembly 110 when the secondary batteries are being charged or discharged, thereby detecting an internal short circuit in the secondary battery 111, and to immediately stop charging or discharging only the cell assembly 110 including the lithium secondary battery 111 when an internal short circuit is detected.

[0104] For example, 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 occurs in a relatively short time due to a meltdown phenomenon. However, these technologies have limitations in that the accuracy of diagnosis is low or the diagnostic process is complicated, it takes a relatively long time to recognize an internal short circuit, and it is difficult to respond to thermal runaway.

[0105] However, the lithium secondary battery system 10 according to the present invention includes the lithium secondary battery 111 described above. 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 favorable 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 near-zero voltage and near-zero current due to leakage current during an internal short circuit, the lithium secondary battery 111 according to the present invention allows for a predetermined current to flow with minimal leakage current lost. This allows for relatively accurate detection and / or determination of an internal short circuit in the lithium secondary battery 111 within a significantly shorter time period. Furthermore, the lithium secondary battery 111 significantly reduces heat, such as short-circuit heat, generated by an internal short circuit, thereby delaying the occurrence of a meltdown. Furthermore, since it is possible to prevent additional heat generation and / or meltdown of adjacent lithium secondary batteries due to the heat of the lithium secondary battery in which an internal short circuit has occurred, it is possible to ensure time for response (or treatment) to prevent thermal runaway of the lithium secondary battery in which an internal short circuit has occurred.

[0106] 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.

[0107] 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.

[0108] 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 flowing current, a voltage measurement sensor for measuring a flowing voltage, etc.

[0109] 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.

[0110] Furthermore, the control unit 140 is electrically coupled to the charging / discharging unit 120 and the sensing unit 130, respectively, and monitors the electrical properties of each lithium secondary battery 111 in real time when each cell assembly 110 is charged and / or discharged, and individually detects and / or determines internal short circuits in the lithium secondary batteries 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.

[0111] 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.

[0112] 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.

[0113] The calculated average current A of the cell assemblies 110 is compared individually with the current of each cell assembly 110, and cell assemblies 110 having an error rate of about 5% or more, for example, about 7% or more, 10% or more, 5 to 20%, or 5 to 15%, can be initially screened out. The initial screening is a process of screening out cell assemblies 110 including lithium secondary batteries that are recognized as having a problem from all lithium secondary batteries, and can shorten the time required to monitor the preset applied current amount and the current amount of each individual lithium secondary battery when charging and discharging all lithium secondary batteries, thereby improving the speed of determining an internal short circuit in the lithium secondary battery system.

[0114] Furthermore, voltage differences between the n lithium secondary batteries included in each cell assembly may occur during charging and discharging. Such voltage differences may arise due to the manufacturing process of each lithium secondary battery or external factors, and 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 about 5% or more.

[0115] 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 selected cell assembly 110 if the current flow rate of the individual lithium secondary battery is lower than a preset applied current flow rate by about 0.5% or more when the lithium secondary battery 111 is charged or discharged.

[0116] Generally, when an internal short circuit occurs in a lithium secondary battery, leakage current occurs at the short circuit point, and the measured current and 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 during an internal short circuit, but also allows a predetermined current to flow. This current may be lower than the applied current 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 circuit point from the applied current. Such a deviation between the preset applied current amount and the passed current amount may be about 0.5% or more of the preset applied current amount, for example, about 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%, or 5 to 10%.

[0117] 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.

[0118] Meanwhile, the cell assembly 110 may include two or more lithium secondary batteries 111 of the present invention, for example, 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.

[0119] The plurality of lithium secondary batteries 111 may be electrically connected in series, in parallel, or in a mixed series-parallel configuration.

[0120] 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 an internal short circuit can be individually and additionally controlled. Another advantage is that when an internal short circuit occurs in any of the lithium secondary batteries, the charge or discharge of each lithium secondary battery can be controlled.

[0121] The cell assembly 110 may be called a battery module or a battery bank depending on the number of lithium secondary batteries contained therein and the type and / or shape of the housing containing them. When a plurality of such cell assemblies 110 are included (150), it may refer to a battery pack or an energy storage system.

[0122] In addition, the charging / discharging unit 120 is electrically connected to the plurality of cell assemblies 110 individually and has the function of charging or discharging each cell assembly 110, and for this purpose, it can be electrically connected to an external power source PS for charging the cell assembly 110 and an electrical load EL for using the power stored in the cell assembly 110.

[0123] 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 that is normally applied to a product to which the lithium secondary battery system 10 is applied.

[0124] 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).

[0125] 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 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.

[0126] 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.

[0127] 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 charger / discharger 120. In order to input the changed charge / discharge conditions to the controller 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, or a touch screen.

[0128] In addition, the input / output unit may include output means, such as a display device such as a monitor or touch screen, or an audio output device, commonly used in the industry, to inform the user of whether an internal short circuit has occurred, the time of occurrence, and the location of the lithium secondary battery 111 and / or the 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.

[0129] Furthermore, the lithium secondary battery system 10 according to the present invention has the above-described configuration and is therefore excellent in 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. Examples of such medium- to large-sized devices include power tools powered by electric 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), including hybrid electric vehicles (HEVs).

[0130] 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.

[0131] Additionally, various components of these devices may be implemented within one or more computing devices, running on one or more processors to perform various functions described herein. Additionally, such various components may be processes or threads that execute computer program instructions and interact with other system components. 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.

[0132] 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 the exemplary embodiments of the present invention.

[0133] 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 in which the short circuit occurs. Furthermore, since the lithium secondary battery system can prevent additional meltdown and / or thermal runaway from occurring in an adjacent lithium secondary battery, the lithium secondary battery system can be usefully applied to battery modules, battery packs, etc., using a plurality of lithium secondary batteries.

[0134] The present invention will be described in more detail below with reference to examples and experimental examples.

[0135] 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.

[0136] Examples 1 to 5 and Comparative Examples 1 to 5. Production of lithium secondary batteries

[0137] Cathode manufacturing

[0138] 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 polyvinylidene fluoride as a carbon-based conductive material and binder in N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 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 positive electrode.

[0139] Anode manufacturing

[0140] A graphite mixture of natural graphite (average particle size: 10±1 μm) and artificial graphite (average particle size: 8±1 μm) in a 2:8 weight ratio was prepared as the negative electrode active material, along with carbon black as the conductive material and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) as the binder. 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 produce a negative electrode slurry.

[0141] Separately, silicon-containing particles, styrene butadiene rubber (SBR), and carbon black as a conductive material were added to water and mixed for 20 to 30 minutes to prepare a coating slurry. At this time, the following information was collected: 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.

[0142] The negative electrode slurry and coating slurry were prepared and 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 μm to 200 μm and 5 μm to 20 μm, respectively, along the direction of transport of the copper sheet. 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).

[0143] Scanning electron microscope analysis of the cross sections of the negative electrodes prepared in Examples 2 and 3 was performed, and the results are shown in Figures 3(A) and 3(B). The volume resistance of each prepared negative electrode was also measured. The volume resistance was measured using a volume resistance measuring device (model: XF057) equipped with 46 probes. Specifically, a constant current was applied with the 46 probes in contact with the surface of the negative electrode active layer, and the potential distribution generated on the surface was measured at multiple points. Subsequently, an inverse analysis of the potential distribution using the finite volume method was performed on the total thickness of the negative electrode active layer and coating layer and the measured potential values, and the volume resistance of the negative electrode was calculated. The measurement results are shown in Table 1.

[0144] Lithium secondary battery manufacturing

[0145] An 18 μm polypropylene separator was placed between the previously prepared positive and negative electrodes, and the resulting pouch-shaped case was then filled with an electrolyte composition to assemble a 1 Ah lithium secondary battery.

[0146] [Table 1]

[0147] Comparative Example 7. Manufacture of a lithium secondary battery

[0148] 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 about 4.375×10 -3 It was.

[0149] Examples 6 to 10 and Comparative Examples 8 to 14. Production of lithium secondary battery systems

[0150] Using the lithium secondary batteries produced in Examples 1 to 5 and Comparative Examples 1 to 7, a lithium secondary battery system having the configuration shown in FIG. 2 was fabricated.

[0151] For example, ten lithium secondary batteries each manufactured in Examples 1 to 5 and Comparative Examples 1 to 7 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 had 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.

[0152] 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.

[0153] 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 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.

[0154] 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.

[0155] 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 whose current flow amount was about 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.

[0156] 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.

[0157] Experimental example

[0158] 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.

[0159] 4 illustrates the structure of an electrode assembly 211 according to one embodiment, which includes a positive electrode 211a, a negative electrode 211b, and a separator 211c. The positive electrode 211a includes a positive electrode current collector 211a-1 and a positive electrode active layer 211a-2, and the negative electrode 211b includes a negative electrode current collector 211b-1, a negative electrode active layer 211b-2, and a coating layer 211b-3. According to one embodiment, as shown in FIG. 4, a separator 211c having a perforated shape 211c-1 at its center was used, and a positive electrode 211a-2 without a positive electrode active layer formed in its center was used, so that the positive electrode current collector 211a-1 and the negative electrode active layer 211b-2 contacted each other at the perforated portion of the separator 211c. An experimental 1 Ah pouch-type lithium secondary battery 211 (N / P ratio = approximately 1.07) was fabricated using the same method as in Examples 1 to 5 and Comparative Examples 1 to 7, except that the separator 211c had a perforated shape 211c-1 and the positive electrode 211a-2 did not have a positive electrode active layer formed in its center.

[0160] Each lithium secondary battery was fully charged, and the center of the pouch-type lithium secondary battery was pressurized with 1 MPa to induce an internal short circuit. The 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.

[0161] The current-carrying 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 it took for the battery temperature to reach its maximum value. The results are shown in Table 2 below. The changes in voltage and temperature over time are also shown in Figures 5 to 8.

[0162] 5 is a graph showing the voltage at the negative electrode and the temperature change of the battery in Comparative Example 1 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. In the case of this comparative example, the voltage changes rapidly, and the resulting relatively high current generates a rapid temperature rise around 5 seconds, which may lead to ignition.

[0163] Figure 6 is a graph showing the voltage and temperature changes at the negative electrode of a lithium secondary battery of Comparative Example 3 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. In the case of the comparative example shown in Figure 6, the ceramic on the negative electrode surface is coated with a small amount of conductive material, 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, for example, 1 MPa. However, although no fire occurs in this case, there is a problem in that there is no temperature change, making it difficult to detect abnormalities in the cell.

[0164] 7 is a graph showing the voltage and temperature changes at the negative electrode of the lithium secondary battery of Comparative Example 4 when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. That is, in this case too, there is a problem that the voltage drops suddenly in a fully charged state when an internal short circuit occurs, causing fire.

[0165] 8 is a graph showing the voltage and battery temperature changes in the negative electrode of the lithium secondary battery of Example 2 in multiple experiments when an internal short circuit occurs due to contact between the positive electrode current collector and the negative electrode surface. That is, when a coating layer containing SiO or carbon-coated SiO is provided on the negative electrode surface according to the present invention, the current (voltage) gradually leaks out relatively slowly at SOC100, and no fire occurs even in the event of an internal short circuit.

[0166] Separately, a lithium secondary battery system was fabricated in Example 6 using cell assemblies including one previously fabricated 1 Ah pouch-type lithium secondary battery for experimentation and nine pouch-type lithium secondary batteries fabricated in Examples 1 to 5 and Comparative Examples 1 to 7. An internal short circuit was induced in the experimental lithium secondary battery while charging and discharging the fabricated lithium secondary battery system. The applied voltage during charging and discharging of the system was adjusted to 4.2 V.

[0167] 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 an internal short circuit had occurred had been confirmed. The results are shown in Table 2 below.

[0168] [Table 2]

[0169] As shown in Table 2 and Figures 5 to 8, the lithium secondary battery according to the present invention has 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 at the same time, applying a small amount of current allows the temperature of the lithium secondary battery to be maintained below 90°C while maintaining a relatively high voltage. Furthermore, it was confirmed that a lithium secondary battery system including the 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 a small amount of current applied after an internal short circuit occurs.

[0170] On the other hand, the lithium secondary batteries of Comparative Examples 1, 2, 4, and 7, which did not have a coating layer or had a coating layer with extremely low volume resistance, were shown to experience a rapid rise in temperature and ignition within a few seconds in the event of an internal short circuit, and it was confirmed that such rapid thermal runaway made it impossible for the lithium secondary battery system to determine whether or not an internal short circuit had occurred in the battery.

[0171] It was also confirmed that the lithium secondary batteries of Comparative Examples 3, 5, and 6, in which the volume resistivity of the coating layer exceeded approximately 1 Ω cm, did not experience current leakage or temperature rise due to an internal short circuit. However, it was shown that these lithium secondary batteries were unable to determine i) the presence or absence of an internal short circuit in the battery, and ii) the location of the internally shorted lithium secondary battery, in a lithium secondary battery system in the event of an internal short circuit.

[0172] These results show that the lithium secondary battery according to the present invention includes a negative electrode having a predetermined volume resistivity, and is capable of not only providing insulation to the negative electrode surface during an internal short circuit but also allowing a predetermined current to flow, thereby preventing a meltdown phenomenon and / or rapid heat generation in the lithium secondary battery and providing time to respond to the internal short circuit.Furthermore, it is also found that a lithium secondary battery system including the same can determine with relatively high accuracy and speed whether or not an internal short circuit has occurred in the lithium secondary battery and the location of the short-circuited lithium secondary battery by using the current applied during an internal short circuit.

[0173] 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.

[0174] 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 is defined by the claims. [Explanation of symbols]

[0175] 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: Charge / discharge section 130: Sensing unit 140: Control unit 142:MCU 144: Memory 146: Communication I / F 148: Input / output interface 150: Secondary battery pack PS: External power supply EL: Electrical 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: Separation membrane penetration

Claims

1. a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; In the negative electrode, a negative electrode active layer including a carbon-based negative electrode active material and a coating layer including silicon-containing particles are sequentially disposed on a negative electrode current collector, The volume resistance of the negative electrode is 1.0×10 －４ A lithium secondary battery having a resistance of Ω·cm to 1.0 Ω·cm.

2. The negative electrode has a capacitance of 8.0×10 －３ Ω・cm~9.0×10 －１ 2. The lithium secondary battery according to claim 1, having a volume resistivity of Ω·cm.

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

5.

4. The silicon-containing particles have an average particle size (D ５０ 2. The lithium secondary battery according to claim 1, wherein

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

6. 2. The lithium secondary battery according to claim 1, wherein the coating layer comprises 70 parts by weight or more of silicon-containing particles and 30 parts by weight or less of a binder, based on 100 parts by weight of the entire coating layer.

7. the coating layer has an average thickness of 1.5 μm to 30 μm; 2. The lithium secondary battery according to claim 1, wherein the ratio of the thickness of the coating layer to the thickness of the negative electrode active layer is 0.01 to 0.

3.

8. The positive electrode includes 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 1 and Chemical Formula 2: [Chemical formula 1] LiFe ａ M １ １－ａ XO ４ [Chemical formula 2] Li ｘ [Ni ｙ Co ｚ Mn ｗ M ２ ｖ ]O ２ In the Chemical Formula 1 and the Chemical Formula 2, 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; 2. The lithium secondary battery according to claim 1, wherein 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, respectively, and y+z+w+v=1.

9. a plurality of cell assemblies each including n (where n is an integer of 3≦n≦100) lithium secondary batteries according to claim 1; 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 connected 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; 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.

10. 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 10. The lithium secondary battery system according to claim 9, 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.

11. The lithium secondary battery system of claim 9 , wherein the sensing unit further comprises a temperature measurement sensor for measuring the temperature of each lithium secondary battery included in the cell assembly.

12. A negative electrode for a lithium secondary battery, comprising a negative electrode active layer including a carbon-based negative electrode active material and a coating layer including silicon-containing particles on a negative electrode current collector, The silicon-containing particles contained in the coating layer include particles having a silicon to oxygen ratio of 1:0.5 to 1.5, The volume resistance of the negative electrode for a lithium secondary battery is 1.0×10 －４ A negative electrode for a lithium secondary battery having a resistance of Ω·cm to 1.0 Ω·cm.

13. The silicon-containing particles have a carbon layer on the surface and an average particle size (D ５０ 13. The negative electrode for a lithium secondary battery according to claim 12, comprising:

14. 13. The negative electrode for a lithium secondary battery according to claim 12, wherein the coating layer comprises 70 parts by weight or more of silicon-containing particles and 30 parts by weight or less of a binder, based on 100 parts by weight of the entire coating layer.

15. the coating layer has an average thickness of 1.5 μm to 30 μm; 13. The negative electrode for a lithium secondary battery according to claim 12, wherein a ratio of the thickness of the coating layer to the thickness of the negative electrode active layer is 0.01 to 0.3.

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