Negative electrode for lithium secondary battery, method for manufacturing negative electrode for lithium secondary battery, and lithium secondary battery including negative electrode

Abstract

The present application relates to a negative electrode for a secondary battery; a method for producing a negative electrode for a lithium secondary battery; and a lithium secondary battery including the negative electrode, the negative electrode of the lithium secondary battery being characterized by including a negative electrode current collector layer and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, one or both surfaces of the negative electrode current collector layer containing a coating layer, the coating layer containing a coating layer composition, and the coating layer contains 95 parts by weight or more of the lithium titanium oxide represented by Formula 1 per 100 parts by weight of the coating layer composition. [Formula 1] LiaTibOc (In Formula 1, a is an integer of 1 to 4, b is an integer of 1 to 5, and c is an integer of 2 to 14).

Description

[0001] Cross - reference to related applications

[0002] This application claims priority and the benefit of Korean Patent Application No. 10 - 2023 - 0090369, filed on July 12, 2023, with the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. Technical field

[0003] This application relates to an anode for a lithium secondary battery, a method of manufacturing the anode for a lithium secondary battery, and a lithium secondary battery including the anode. Background art

[0004] Due to the rapid growth in the use of fossil fuels, the demand for the use of alternative or clean energy sources is increasing, and as part of this, the field that is being most actively studied is the field of power generation and power storage using electrochemical reactions.

[0005] Currently, secondary batteries are representative examples of electrochemical devices that utilize such electrochemical energy, and their range of use tends to gradually expand.

[0006] With the development of technology and the increasing demand for mobile devices, the demand for secondary batteries as an energy source has increased sharply. Among these secondary batteries, lithium secondary batteries with high energy density, high voltage, long cycle life, and low self - discharge rate have been commercialized and widely used. In addition, methods for manufacturing high - density electrodes with higher energy density per unit volume as electrodes for such high - capacity lithium secondary batteries are being actively studied.

[0007] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material for intercalating and deintercalating lithium ions that migrate from the positive electrode, and silicon - based particles with high discharge capacity can be used as the negative electrode active material.

[0008] In particular, in response to the demand for high - density energy batteries in recent years, methods for improving the capacity by using silicon - based compounds (such as Si / C or SiOx) with a capacity more than 10 times that of graphite - based materials as the negative electrode active material in combination are being actively studied. However, when compared with graphite commonly used, the capacity characteristics of silicon - based compounds as high - capacity materials are excellent in themselves, but during the charging process, rapid volume expansion occurs, disconnecting the conduction path and causing deterioration of battery characteristics, and thus the capacity decreases from the initial stage. In addition, for silicon - based anodes, when the charge - discharge cycle is repeated, lithium ions cannot be uniformly charged in the depth direction of the negative electrode, and the reaction occurs on the surface, accelerating surface deterioration. Therefore, in terms of battery cycling, performance improvement is required.

[0009] In addition, due to the above advantages, it is necessary to use a silicon-based negative electrode. However, in addition to the above problems, the silicon-based negative electrode also has the disadvantage of being prone to thermal runaway. That is, when the silicon-based negative electrode operates in a lithium secondary battery, an exothermic reaction occurs due to the alloying reaction between metals, which accelerates thermal runaway and poses a risk of explosion.

[0010] To solve this problem, various methods are being studied, such as adopting a double-layer negative electrode active material layer and improving the negative electrode active material to prevent thermal runaway. However, these methods may instead reduce the battery performance, thereby limiting their application and hindering the commercialization of negative electrode batteries with a higher content of silicon compounds. In addition, no method has been developed that can significantly solve the thermal runaway problem of silicon-based active materials.

[0011] Therefore, it is necessary to develop a negative electrode for a lithium secondary battery that can ensure capacity characteristics and energy density while solving the problem of thermal runaway by using a silicon-based negative electrode.

[0012] Prior art documents

[0013] (Patent Document 1) Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention

[0014] [Technical Problem]

[0015] When applying a silicon-based negative electrode to ensure capacity characteristics and energy density, it has been found that if a coating layer containing LTO is formed on one surface or both surfaces of the negative electrode current collector layer, the degree of the alloy formation reaction of Li-Si-Cu can be controlled.

[0016] That is, when the battery cell is exposed to high temperature, it is prone to decomposition, and the exothermic reaction is accelerated due to the formation of an alloy of Si and Cu after decomposition, resulting in the problem of thermal runaway. However, the applicant has found that when lithium titanate oxide is uniformly coated on one surface or both surfaces of the negative electrode current collector layer, the above problems can be solved. Therefore, the present application relates to a negative electrode for a lithium secondary battery capable of preventing thermal runaway, a method for manufacturing the negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

[0017] [Technical Solution]

[0018] An exemplary embodiment of the present specification provides a negative electrode for a lithium secondary battery, which includes: a negative electrode current collector layer; and a negative electrode active material layer provided on one surface or both surfaces of the negative electrode current collector layer; wherein, one surface or both surfaces of the negative electrode current collector layer include a coating layer, and the coating layer includes a coating layer composition, and based on 100 parts by weight of the coating layer composition, it includes 95 parts by weight or more of lithium titanate oxide represented by Formula 1.

[0019] [Formula 1]

[0020] Li a Ti b O c

[0021] In Formula 1,

[0022] a is an integer from 1 to 4,

[0023] b is an integer from 1 to 5, and

[0024] c is an integer from 2 to 14.

[0025] Another exemplary embodiment provides a method for manufacturing a negative electrode for a lithium secondary battery, the method comprising: preparing a negative electrode current collector layer; forming a coating layer on one surface or both surfaces of the negative electrode current collector layer; and forming a negative electrode active material layer on the top surface of the negative electrode current collector layer on which the coating layer is formed, wherein the formation of the coating layer includes electrolyzing the lithium titanate oxide represented by the above Formula 1 to make it in an ionic state; and reducing the lithium titanate oxide in the ionic state on the surface of the negative electrode current collector layer.

[0026] Finally, the exemplary embodiment of the present application provides a lithium secondary battery, which includes: a positive electrode; the negative electrode for a lithium secondary battery of the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0027] [Advantageous Effects]

[0028] The negative electrode for a lithium secondary battery according to the exemplary embodiment of the present invention includes a coating layer on one surface or both surfaces of the negative electrode current collector layer, and in particular, based on 100 parts by weight of the coating layer composition, it includes 95 parts by weight or more of lithium titanate oxide.

[0029] In the prior art, lithium titanate oxide is mixed with a binder and a conductive material, and the mixture is coated on the negative electrode current collector layer. In this case, when the battery cell is exposed to high temperature, decomposition easily occurs, and the formation of an alloy of Si and Cu cannot be controlled after decomposition, accelerating the exothermic reaction and causing significant problems.

[0030] However, according to the present application, based on 100 parts by weight of the coating layer composition, it includes 95 parts by weight or more of lithium titanate oxide. The melting point of lithium titanate oxide itself is above 1500 °C and it exhibits high thermal stability, so it can be stable even at high temperatures and can prevent and control the alloy formation reaction of Li-Si-Cu, thereby solving the inherent thermal stability problem of silicon-based negative electrodes.

[0031] In addition, the negative electrode for a lithium secondary battery of the present application is formed by electrolysis, so that the coating layer contains 95 parts by weight or more of lithium titanate oxide without using a binder or a conductive material. That is, lithium titanate oxide is electrolyzed to make it in an ionic state, and then it is reduced on the surface of the negative electrode current collector to form a coating layer. By this manufacturing method, a coating layer made of lithium titanate oxide can be formed, so that the thermal runaway problem of the silicon-based negative electrode can be solved.

[0032] As a result, the negative electrode for a lithium secondary battery of the present invention maximizes the capacity characteristics and energy density by using a silicon-based active material, and uses a coating layer containing lithium titanate oxide through a specific manufacturing process to solve the thermal runaway problem, thereby ensuring output characteristics, life, and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a diagram showing the laminated structure of the negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application.

[0034] <DESCRIPTION OF THE REFERENCE NUMERALS>

[0035] 10: negative electrode active material layer

[0036] 20: coating layer

[0037] 30: negative electrode current collector layer

[0038] 100: negative electrode for a lithium secondary battery DETAILED DESCRIPTION

[0039] Before describing the present invention, some terms are first defined.

[0040] In this specification, when a part "includes", "contains", or "has" a component, unless otherwise specifically described, this does not mean excluding another component, but means that another component can also be included.

[0041] In this specification, "p to q" represents a range of "p or more and q or less".

[0042] In this specification, the "specific surface area" is measured by the BET method, and specifically, it is calculated from the nitrogen adsorption amount at the liquid nitrogen temperature (77K) by using BELSORP-mino II available from BEL Japan, Inc. That is, in the present application, the BET specific surface area may refer to the specific surface area measured by the above measurement method.

[0043] In this specification, "Dn" refers to the particle size distribution and is the particle size at the n% point in the cumulative distribution of the number of particles according to the particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative distribution of the number of particles according to the particle size, D90 is the particle size at the 90% point in the cumulative distribution of the number of particles according to the particle size, and D10 is the particle size at the 10% point in the cumulative distribution of the number of particles according to the particle size. Note that the particle size distribution can be measured by the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium, and then the resulting dispersion is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S 3500). When a laser beam passes through the particles, the difference in the diffraction pattern according to the particle size is measured, and then the particle size distribution is calculated.

[0044] In this specification, the description "the polymer contains a specific monomer as a monomer unit" means that the monomer participates in the polymerization reaction and is included in the polymer as a repeating unit. In this specification, when the polymer contains a monomer, it should be interpreted in the same way as when the polymer contains the monomer as a monomer unit.

[0045] In this specification, it should be understood that unless otherwise specified as "homopolymer", the term "polymer" is used in a broad sense including copolymers.

[0046] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are the molecular weights in terms of polystyrene measured by gel permeation chromatography (GPC) while using commercially available monodisperse polystyrene polymers (standard samples) with various degrees of polymerization as standard materials.

[0047] In this specification, unless otherwise specifically described, the molecular weight refers to the weight average molecular weight.

[0048] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0049] An exemplary embodiment of this specification provides a negative electrode for a lithium secondary battery, which includes: a negative electrode current collector layer; and a negative electrode active material layer provided on one surface or both surfaces of the negative electrode current collector layer; wherein one surface or both surfaces of the negative electrode current collector layer include a coating layer, and the coating layer contains a coating layer composition, and based on 100 parts by weight of the coating layer composition, contains 95 parts by weight or more of a lithium titanium oxide represented by Formula 1.

[0050] [Formula 1]

[0051] Li a Ti b Oc

[0052] In Formula 1,

[0053] a is an integer from 1 to 4,

[0054] b is an integer from 1 to 5, and

[0055] c is an integer from 2 to 14.

[0056] According to the present application, based on 100 parts by weight of the coating composition, it contains more than 95 parts by weight of lithium titanium oxide. The melting point of lithium titanium oxide itself is above 1500 °C and it exhibits high thermal stability. Therefore, it can be stable even at high temperatures and can prevent and control the alloy formation reaction of Li-Si-Cu, thereby solving the inherent thermal stability problem of the silicon-based negative electrode.

[0057] Figure 1 FIG. is a diagram showing the laminated structure of the negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, it can be seen that the negative electrode 100 for a lithium secondary battery includes a coating layer 20 and a negative electrode active material layer 30 on one surface of the negative electrode current collector layer 10. Figure 1 It shows that the negative electrode active material layer and the coating layer are formed on one surface, but the negative electrode active material layer and the coating layer can also be formed on both surfaces of the negative electrode current collector layer. In the case where coating layers are included on both surfaces, when at least one coating layer contains the coating composition of the present application, the other coating layer can be a coating layer used in the art.

[0058] Hereinafter, the negative electrode for a lithium secondary battery of the present invention will be described in more detail.

[0059] In an exemplary embodiment of the present application, the thickness of the negative electrode current collector layer is generally 1 μm to 100 μm. There is no particular limitation on such a negative electrode current collector layer as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector layer may have fine unevenness formed on the surface to enhance the adhesion of the negative electrode active material, and can be used in various forms, such as a film, sheet, foil, net, porous body, foam body or non-woven fabric body.

[0060] More specifically, the negative electrode current collector layer may contain copper.

[0061] In an exemplary embodiment of the present application, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less.

[0062] In another exemplary embodiment, the thickness of the negative electrode current collector layer may be 1 μm or more and 100 μm or less, specifically 2 μm or more and 50 μm or less, and more specifically 5 μm or more and 25 μm or less.

[0063] However, the thickness can be variously changed according to the type and use of the negative electrode used, and is not limited thereto.

[0064] In the case of the negative electrode for a lithium secondary battery in the prior art, the negative electrode active material layer is directly coated on one surface of the negative electrode current collector layer. In particular, the silicon-based active material layer exhibits excellent capacity characteristics, but is affected by low stability due to the above-mentioned thermal runaway problem, making it difficult to be applied to lithium secondary batteries.

[0065] Therefore, the negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application includes a coating layer on one surface or both surfaces of the negative electrode current collector layer, and in particular, the coating layer includes a coating layer composition, and based on 100 parts by weight of the coating layer composition, includes 95 parts by weight or more of lithium titanium oxide.

[0066] In an exemplary embodiment of the present application, based on 100 parts by weight of the coating layer composition, the coating layer may include 95 parts by weight or more, preferably 97 parts by weight or more, more preferably 99 parts by weight or more of lithium titanium oxide, and includes 100 parts by weight or less of lithium titanium oxide.

[0067] In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the coating layer composition consists of lithium titanium oxide. The fact that the coating layer composition consists of lithium titanium oxide may mean that based on 100 parts by weight of the coating layer composition, 100 parts by weight of lithium titanium oxide is included.

[0068] In the prior art, lithium titanium oxide, a binder, and a conductive material are mixed together and applied to facilitate coating. When driving a lithium secondary battery and the battery cell is exposed to high temperature, if the content of lithium titanium oxide is low due to the inclusion of a binder and a conductive material together, decomposition is likely to occur. This causes the negative electrode current collector layer and the negative electrode active material layer to come into contact with each other, and after decomposition, an Si-Cu alloy is formed, which accelerates the exothermic reaction and leads to the thermal runaway problem.

[0069] However, the coating layer according to an exemplary embodiment of the present application includes lithium titanium oxide within the above-mentioned range. In particular, the melting point of lithium titanium oxide is 1500 °C or more, so even in the case of a battery cell runaway, direct contact between the negative electrode active material layer and the negative electrode current collector layer can be minimized, thereby delaying and suppressing the alloy reaction of Si-Cu and enhancing thermal stability.

[0070] Therefore, the lithium titanium oxide of the exemplary embodiments of the present application, especially the lithium titanium oxide having a spinel or garnet structure, has a high melting point of over 1500 °C. A coating layer composed of the lithium titanium oxide having a spinel or garnet structure is directly coated on the Cu foil used as the negative electrode current collector layer, which can inhibit the alloy formation reaction between Li and Si, and thus inhibit thermal runaway.

[0071] In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the coating layer is 0.1 μm or more and 5 μm or less.

[0072] In another exemplary embodiment, the thickness of the coating layer may be 0.1 μm or more and 5 μm or less, preferably 0.5 μm or more and 4 μm or less, and more preferably 1 μm or more and 3 μm or less.

[0073] The thickness of the coating layer is within the above range. If the thickness is less than this range, the negative electrode current collector layer and the negative electrode active material layer may come into contact with each other in the case of thermal runaway, making it difficult to control thermal runaway. If the thickness exceeds this range, problems with negative electrode capacity and rapid charging may occur. That is, when the thickness is within this range, the capacity and rapid charging performance of the negative electrode can be ensured, and at the same time, thermal runaway can be easily prevented.

[0074] In an exemplary embodiment of the present application, the lithium titanium oxide can be represented by the above formula 1.

[0075] In the present application, a is an integer from 1 to 4, specifically an integer from 2 to 4, or an integer of 3 or 4.

[0076] In the present application, b is an integer from 1 to 5, specifically an integer from 3 to 5, or an integer of 4 or 5.

[0077] In the present application, c is an integer from 2 to 14, an integer from 5 to 13, or an integer from 8 to 12.

[0078] In an exemplary embodiment of the present application, the lithium titanium oxide may be represented by Li4Ti5O 12 represented.

[0079] In the present application, the lithium titanium oxide is applied to a high-voltage lithium secondary battery, and due to the above composition, it has the advantages of ensuring thermal stability and being beneficial to the operation of high-voltage battery cells.

[0080] In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the melting point of the lithium titanium oxide is 1500 °C or more.

[0081] In another exemplary embodiment, the melting point of the lithium titanium oxide may be 1500 °C or higher, preferably 1510 °C or higher, more preferably 1515 °C or higher, and 2000 °C or lower.

[0082] Since the melting point of the lithium titanium oxide is within this range, in the case of thermal runaway, the coating layer maintains its shape without melting, thereby preventing direct contact between the negative electrode current collector layer and the negative electrode active material layer and ensuring the stability of the battery cell. In this case, the melting point as described above can be controlled by changing the composition and structure of the lithium titanium oxide, and specifically, can be determined by the content of Ti contained in the lithium titanium oxide. That is, Ti acts as the central atom in the lithium titanium oxide, and as the Ti content increases, the melting point can also increase.

[0083] In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided, in which the lithium titanium oxide has a spinel or garnet structure.

[0084] In the present application, the spinel structure may refer to having oxygen ions arranged in a cubic close-packed manner and cations occupying octahedral and tetrahedral sites.

[0085] In spinel structure compounds, O (oxygen) ions form octahedrons similar to those in layered structure compounds, and transition metal ions are present inside the octahedrons. Li ions and metal ions are present in tetrahedral and octahedral positions respectively, and Li ions are inserted into octahedral sites. Such a structural feature provides a three-dimensional Li ion diffusion channel for spinel structure compounds. Due to this three-dimensional Li ion diffusion channel, spinel structure compounds have the advantage of allowing Li ions to be embedded in all directions, but due to the complex Li ion diffusion channel, the Li ion diffusion rate is relatively low within the spinel structure compared to layered structure compounds.

[0086] The lithium titanium oxide of the exemplary embodiment of the present application has a spinel structure, resulting in a lower interlayer voltage. Therefore, dendrites are not formed, and lithium ions can be stably absorbed. In addition, the lithium titanium oxide is very suitable for application in the negative electrode of a lithium secondary battery due to its excellent thermal stability, chemical stability, and mechanical strength.

[0087] In addition, in an exemplary embodiment of the present application, the lithium titanium oxide has a spinel structure and a melting point of 1500 °C or higher, preferably 1510 °C or higher, more preferably 1515 °C or higher, and 2000 °C or lower. For example, the melting point of the lithium titanium oxide having a spinel structure may be 1520 °C.

[0088] The lithium titanium oxide having a spinel structure according to an exemplary embodiment of the present application has a high melting point, and a coating layer composed of the lithium titanium oxide having a spinel structure is directly coated on a Cu foil used as a negative electrode current collector layer, so that the alloy formation reaction between Li and Si can be inhibited, thereby inhibiting thermal runaway.

[0089] In an exemplary embodiment of the present application, the negative electrode active material layer contains a negative electrode active material layer composition, and the negative electrode active material layer composition contains a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0090] In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloys.

[0091] In an exemplary embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the content of SiOx (x = 0) may be 95 parts by weight or more.

[0092] In an exemplary embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the content of SiOx (x = 0) may be 95 parts by weight or more, preferably 97 parts by weight or more, more preferably 99 parts by weight or more, and 100 parts by weight or less.

[0093] In an exemplary embodiment of the present application, pure silicon (Si) particles may be particularly used as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material may mean that, based on 100 parts by weight of the total amount of the silicon-based active material as described above, pure Si particles (SiOx (x = 0)) not combined with other particles or elements are included within the above range.

[0094] In an exemplary embodiment of the present application, the silicon-based active material may be composed of SiOx (x = 0).

[0095] The negative electrode for a lithium secondary battery of the present application includes the above silicon-based active material in the negative electrode active material layer, and specifically, contains pure silicon particles containing 95 parts by weight or more of SiOx (x = 0). In this case, when a high content of pure silicon particles is included, the capacity characteristics are excellent, and the coating layer of the present invention is included to solve the resulting thermal runaway problem.

[0096] Note that the average particle size (D50) of the silicon-based active material of the present invention can be 3 μm to 10 μm, specifically 4 μm to 8 μm, and more specifically 5 μm to 7 μm. When the average particle size is within the above range, the specific surface area of the particles is within a suitable range, such that the viscosity of the negative electrode paste is formed within a suitable range. Therefore, the particles constituting the negative electrode paste are smoothly dispersed. In addition, when the value of the size of the first negative electrode active material is equal to or greater than the lower limit value of the range, due to the composite formed by the conductive material and the binder in the negative electrode paste, the contact area between the silicon particles and the conductive material is excellent, so the possibility of maintaining the conductive network increases, thereby increasing the capacity retention rate. Note that when the average particle size satisfies the above range, excessive silicon particles are excluded, so the surface of the negative electrode is smoothly formed. Therefore, uneven current density during charging and discharging can be prevented.

[0097] In the negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application, the porosity of the negative electrode active material layer satisfies 50% or more.

[0098] In an exemplary embodiment of the present application, the porosity of the negative electrode active material layer can be 50% or more, preferably 60% or more, and can satisfy 90% or less, preferably 80% or less.

[0099] The above porosity control affects the overall composition and content of the negative electrode active material layer composition, but mainly affects the D50 particle size of the silicon-based active material contained in the negative electrode active material layer composition.

[0100] In an exemplary embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the D50 particle size of the silicon-based active material contained in the negative electrode active material layer is 5 μm or more.

[0101] By respectively satisfying the ranges of the particle size distribution and the porosity, the negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application satisfies the porosity within the range, simplifies the pore structure, thereby improving the diffusion resistance by reducing the phenomenon of concentrated reaction of lithium ions with the silicon-based active material on the surface.

[0102] In an exemplary embodiment of the present application, the silicon-based active material generally has a unique BET specific surface area. The BET specific surface area of the silicon-based active material is preferably 0.1 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, and most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET specific surface area is measured according to DIN 66131 (using nitrogen).

[0103] In an exemplary embodiment of the present application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or fragmented particles. Alternatively, less preferably, the silicon particles may also have a fibrous structure or may exist in the form of a silicon-containing film or coating layer.

[0104] In an exemplary embodiment of the present application, the silicon-based active material may have a non-spherical shape, and its sphericity (roundness) is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, and for example, 0.85 to 0.9.

[0105] In the present application, the sphericity (roundness) is determined by Equation 2 below, where A is the area and P is the perimeter.

[0106] [Equation 2]

[0107] 4πA / P 2

[0108] In an exemplary embodiment of the present application, based on 100 parts by weight of the negative electrode active material layer composition, the content of the silicon-based active material may be 80 parts by weight or more.

[0109] In another exemplary embodiment, based on 100 parts by weight of the negative electrode active material layer composition, the content of the silicon-based active material may be 80 parts by weight or more, preferably 85 parts by weight or more, and 99 parts by weight or less, preferably 97 parts by weight or less, more preferably 95 parts by weight or less.

[0110] The negative electrode active material layer composition of the present application uses a silicon-based active material with a significantly higher capacity within the above range, improving the capacity characteristics. In particular, the range of the silicon-based active material contained in the negative electrode active material layer is adjusted to the above range, thereby solving the problems of surface deterioration, life characteristics, and ensuring a conductive path during the charge and discharge processes without deteriorating the capacity performance of the negative electrode.

[0111] In the prior art, usually only graphite-based compounds are used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, in order to increase the capacity, attempts to use silicon-based compounds in combination have also increased. However, the limitation of silicon-based compounds is that their volume expands rapidly during the charge / discharge process, resulting in damage to the conductive path formed in the negative electrode active material layer, thereby deteriorating the performance of the battery.

[0112] In addition, in order to adjust the porosity range as described above, when a silicon-based active material having a certain particle size is included within the above range, a conductive path cannot be ensured due to volume expansion during charging and discharging, so the output characteristics deteriorate, and the life characteristics deteriorate accordingly.

[0113] Therefore, in an exemplary embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a planar conductive material.

[0114] In an exemplary embodiment of the present application, the negative electrode conductive material may be used without limitation with materials commonly used in the art, and specifically, the negative electrode conductive material is selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0115] In an exemplary embodiment of the present application, the dot-shaped conductive material refers to a conductive material that can be used to improve the conductivity of the negative electrode, has conductivity without causing chemical changes, and has a dot shape or a spherical shape. Specifically, the dot-shaped conductive material may be one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and in terms of high conductivity and excellent dispersibility, carbon black may be preferably included.

[0116] In an exemplary embodiment of the present application, the BET specific surface area of the dot-shaped conductive material may be 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0117] In an exemplary embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, more preferably 20 nm to 60 nm.

[0118] In an exemplary embodiment of the present application, the planar conductive material can improve the conductivity by increasing the surface contact between silicon particles in the negative electrode. At the same time, the disconnection of the conductive path caused by volume expansion is suppressed, and it can be represented as a flaky conductive material or a massive conductive material.

[0119] In an exemplary embodiment of the present application, the planar conductive material may include one or more selected from the group consisting of flaky graphite, graphene, graphene oxide, and graphite flakes, and may be preferably flaky graphite.

[0120] In an exemplary embodiment of the present application, the average particle size (D50) of the planar conductive material may be from 2 μm to 7 μm, specifically from 3 μm to 6 μm, and more specifically from 4 μm to 5 μm. When the above range is satisfied, the sufficient particle size results in easy dispersion without causing an excessive increase in the viscosity of the negative electrode paste. Therefore, when dispersion is carried out using the same equipment and time, the dispersion effect is excellent.

[0121] In an exemplary embodiment of the present application, a negative electrode composition is provided, wherein D10 of the planar conductive material is 0.5 μm or more and 1.5 μm or less, D50 is 2.5 μm or more and 3.5 μm or less, and D90 is 7.0 μm or more and 15.0 μm or less.

[0122] In an exemplary embodiment of the present application, for the planar conductive material, a planar conductive material having a high BET specific surface area or a planar conductive material having a low specific surface area may be used.

[0123] In an exemplary embodiment of the present application, there is no limitation on using a planar conductive material having a high specific surface area or a planar conductive material having a low specific surface area for the planar conductive material. However, particularly, the electrode performance of the planar conductive material of the present application may be affected by the dispersion effect to a certain extent. Therefore, it is particularly preferred to use a planar conductive material having a low specific surface area that does not cause dispersion problems.

[0124] In an exemplary embodiment of the present application, the BET specific surface area of the planar conductive material may be 5 m 2 / g or more.

[0125] In another exemplary embodiment, the BET specific surface area of the planar conductive material may be 5 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g or less.

[0126] In another exemplary embodiment, the planar conductive material is a planar conductive material having a high specific surface area, and the BET specific surface area may satisfy 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, and more preferably 100 m 2 / g or more and 300 m2 less than / g.

[0127] In another exemplary embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area can satisfy 5 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, and more preferably 5 m 2 / g or more and 25 m 2 / g or less.

[0128] Other conductive materials may include linear conductive materials, such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may contain a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundled" herein refers to a secondary shape of a bundle or rope, in which a plurality of carbon nanotube units are arranged side by side or entangled in an orientation such that the longitudinal axes of the carbon nanotube units are substantially the same. The carbon nanotube units have a graphite sheet layer with a nanoscale diameter of a cylindrical shape and have an sp2 bonding structure. In this case, the characteristics of a conductor or a semiconductor can be exhibited according to the winding angle and structure of the graphite sheet layer. Compared with entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during the manufacturing process of the negative electrode and can more smoothly form a conductive network in the negative electrode to improve the conductivity of the negative electrode.

[0129] In an exemplary embodiment of the present application, based on 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode conductive material may be 0.01 part by weight or more and 40 parts by weight or less.

[0130] In another exemplary embodiment, based on 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode conductive material may be 0.01 part by weight or more and 40 parts by weight or less, preferably 0.1 part by weight or more and 30 parts by weight or less, and more preferably 0.5 part by weight or more and 25 parts by weight or less.

[0131] In an exemplary embodiment of the present application, when the negative electrode conductive material only contains a linear conductive material, based on 100 parts by weight of the negative electrode active material layer composition, the content of the linear conductive material may be 0.01 part by weight or more and 5 parts by weight or less.

[0132] In another exemplary embodiment, when the negative electrode conductive material only contains a linear conductive material, based on 100 parts by weight of the negative electrode active material layer composition, the content of the linear conductive material may be 0.01 part by weight or more and 5 parts by weight or less, preferably 0.03 part by weight or more and 3 parts by weight or less, and more preferably 0.1 part by weight or more and 2 parts by weight or less.

[0133] In an exemplary embodiment of the present application, the negative electrode conductive material includes a dot-shaped conductive material, a planar conductive material, and a linear conductive material, and the ratio of the dot-shaped conductive material: planar conductive material: linear conductive material may be 1:1:0.01 to 1:1:1.

[0134] In an exemplary embodiment of the present application, based on 100 parts by weight of the negative electrode conductive material, the content of the dot-shaped conductive material may be 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less.

[0135] In an exemplary embodiment of the present application, based on 100 parts by weight of the negative electrode conductive material, the content of the planar conductive material may be 1 part by weight or more and 60 parts by weight or less, preferably 5 parts by weight or more and 50 parts by weight or less, and more preferably 10 parts by weight or more and 50 parts by weight or less.

[0136] In an exemplary embodiment of the present application, based on 100 parts by weight of the negative electrode conductive material, the content of the linear conductive material may be 0.01 part by weight or more and 10 parts by weight or less, preferably 0.05 part by weight or more and 8 parts by weight or less, and more preferably 0.1 part by weight or more and 5 parts by weight or less.

[0137] In an exemplary embodiment of the present application, the negative electrode conductive material may include a linear conductive material and a planar conductive material.

[0138] In an exemplary embodiment of the present application, the negative electrode conductive material may include a linear conductive material and a planar conductive material, and the ratio of the linear conductive material to the planar conductive material may be 0.01:1 to 0.1:1.

[0139] In an exemplary embodiment of the present application, since the negative electrode conductive material particularly includes a linear conductive material and a planar conductive material and respectively satisfies the above compositions and ratios, the life characteristics of the existing lithium secondary battery are not significantly affected, and the number of points where charging and discharging can be performed increases, so the output characteristics at a high C rate are excellent.

[0140] The structure of the negative electrode conductive material of the present application is completely different from that of the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material of the present application serves to maintain the contact between silicon-based active materials with a very large volume expansion of the electrode caused by charging and discharging, while the positive electrode conductive material serves as a buffer during rolling and confers some conductivity, and is completely different from the negative electrode conductive material of the present invention in terms of structure and function.

[0141] In addition, the negative electrode conductive material of the present application is applied to silicon-based active materials, and its structure is completely different from that of the conductive material applied to graphite-based active materials. That is, since the conductive material for an electrode having a graphite-based active material only has smaller particles than the active material, the conductive material has the properties of improving output characteristics and imparting some conductivity, and is completely different from the negative electrode conductive material applied together with silicon-based active materials as described in the present invention in terms of structure and function.

[0142] In an exemplary embodiment of the present application, based on 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode binder may be 1 part by weight or more and 20 parts by weight or less.

[0143] In another exemplary embodiment, based on 100 parts by weight of the negative electrode active material layer composition, the content of the negative electrode binder may be 1 part by weight or more and 20 parts by weight or less, preferably 2 parts by weight or more and 15 parts by weight or less, and more preferably 3 parts by weight or more and 15 parts by weight or less.

[0144] In an exemplary embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen in the above materials is replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

[0145] The negative electrode binder of the exemplary embodiment of the present application serves to hold the active material and the conductive material to prevent the negative electrode structure from being distorted and structurally deformed when the volume of the negative electrode silicon-based active material expands and relaxes. When such a function is satisfied, all conventional binders can be applied. Specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

[0146] In an exemplary embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

[0147] An exemplary embodiment of the present application provides a method for manufacturing a negative electrode for a lithium secondary battery, the method comprising the following steps: preparing a negative electrode current collector layer; forming a coating layer on one or two surfaces of the negative electrode current collector layer; and forming a negative electrode active material layer on the top surface of the negative electrode current collector layer having the coating layer formed thereon, wherein the step of forming the coating layer includes electrolyzing the lithium titanium oxide represented by the above formula 1 to make it in an ionic state; and reducing the ionic state of the lithium titanium oxide on the surface of the negative electrode current collector layer.

[0148] As described above, different from the prior art, forming the coating layer by electrolysis enables uniform coating without including materials such as conductive materials and binders, thereby ensuring that the content of the above lithium titanium oxide is satisfied. That is, in the prior art, the content of lithium titanium oxide decreases and the content of conductive materials and binders increases to facilitate coating. However, in the present application, the content of lithium titanium oxide increases to prevent thermal runaway, and coating is facilitated by the above manufacturing method.

[0149] In the exemplary embodiment of the present application, the step of forming the coating layer more specifically includes: dissolving and dispersing lithium titanium oxide powder in an electrolyte solution, electrolyzing the solution to make the lithium titanium oxide in an ionic state, and then laminating and reducing the ionic state of the lithium titanium oxide on the negative electrode current collector (e.g., Cu foil) by heating and pressing at 60 °C to 80 °C, so that the coating layer can be formed alone without using a conductive material or a binder.

[0150] In the exemplary embodiment of the present application, a negative electrode slurry containing a negative electrode active material layer composition may be coated on one or two surfaces of the current collector to form a negative electrode for a lithium secondary battery.

[0151] More specifically, a method for manufacturing a negative electrode for a lithium secondary battery is provided, wherein the step of forming a negative electrode active material layer on the negative electrode current collector layer having the coating layer formed thereon includes: preparing a negative electrode active material layer composition containing a silicon-based active material, a negative electrode conductive material, and a negative electrode binder; forming a negative electrode slurry by including a slurry solvent in the negative electrode active material layer composition; and applying the negative electrode slurry to the top surface of the negative electrode current collector layer having the coating layer formed thereon.

[0152] In the exemplary embodiment of the present application, the negative electrode slurry may contain a negative electrode active material layer composition and a slurry solvent.

[0153] In the exemplary embodiment of the present application, the solid content of the negative electrode slurry may satisfy not less than 5% and not more than 40%.

[0154] In another exemplary embodiment, the solid content of the negative electrode paste may satisfy 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0155] The solid content of the negative electrode paste may represent the content of the negative electrode active material layer composition contained in the negative electrode paste, and may represent the content of the negative electrode active material layer composition based on 100 parts by weight of the negative electrode paste.

[0156] When the solid content of the negative electrode paste satisfies the above range, the viscosity is appropriate during the formation of the negative electrode active material layer, thereby minimizing the particle aggregation of the negative electrode composition to effectively form the negative electrode active material layer.

[0157] An exemplary embodiment of the present application provides a lithium secondary battery, which includes a positive electrode, a negative electrode for a lithium secondary battery of the present application, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0158] The secondary battery according to the exemplary embodiment of the present specification may particularly include the above-mentioned negative electrode for a lithium secondary battery. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the above-mentioned negative electrode. Since the negative electrode has been described above, its detailed description is omitted.

[0159] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing a positive electrode active material.

[0160] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the thickness of the positive electrode current collector may generally be 3 to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms, such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven fabric body.

[0161] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide, such as LiFe3O4; lithium manganese oxide, such as the chemical formula Li 1+c1 Mn 2-c1O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01 ≤ c2 ≤ 0.3) represents Ni-site type lithium nickel oxide; chemical formula LiMn 2-c3 M c3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which a part of Li in the chemical formula is replaced by alkaline earth metal ions, etc., but not limited thereto. The positive electrode can be Li metal.

[0162] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder together with the above positive electrode active material.

[0163] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitation as long as the positive electrode conductive material has electronic conductivity without causing chemical changes in the battery to be constructed. Specific examples may include graphite such as natural graphite and artificial graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, etc., and any one of them or a mixture of two or more of them can be used.

[0164] In addition, the positive electrode binder is used to improve the adhesion between the particles of the positive electrode active material and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene polymer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof, etc., and any one of them or a mixture of two or more of them can be used.

[0165] The separator is used to separate the negative electrode from the positive electrode and provide a migration path for lithium ions. Any separator can be used as this separator without particular limitation as long as it is commonly used in secondary batteries. In particular, a separator having a high water retention capacity for the electrolyte and a low resistance to the migration of electrolyte ions can be preferably used. Specifically, a porous polymer membrane can be used, for example, a porous polymer membrane made of polyolefin polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or having a laminated structure of two or more layers. In addition, conventional porous non-woven fabrics can be used, such as non-woven fabrics formed of high melting point glass fibers, polyethylene terephthalate fibers, etc. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multi-layer structure can be selectively used.

[0166] Examples of the electrolyte can include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, or molten-type inorganic electrolytes that can be used to manufacture lithium secondary batteries, but are not limited thereto.

[0167] Specifically, the electrolyte can contain a non-aqueous organic solvent and a metal salt.

[0168] As the non-aqueous organic solvent, for example, aprotic organic solvents (such as N-methyl-2-pyrrolidone), propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, or ethyl propionate can be used.

[0169] In particular, among carbonate organic solvents, ethylene carbonate and propylene carbonate as cyclic carbonates are high-viscosity organic solvents and can be preferably used because they have a high dielectric constant to dissociate lithium salts well. When the cyclic carbonate is mixed and used with a linear carbonate having a low viscosity and a low dielectric constant (such as dimethyl carbonate and diethyl carbonate) in a suitable proportion, an electrolyte having high conductivity can be prepared, and thus, it can be more preferably used.

[0170] A lithium salt can be used as the metal salt, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte. Among them, for example, as an anion of the lithium salt, one or more selected from the group consisting of F - 、Cl- , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - .

[0171] In addition to the above electrolyte components, for the purposes of improving the life characteristics of the battery, suppressing the reduction of the battery capacity, improving the discharge capacity of the battery, etc., the electrolyte may further contain one or more additives, such as haloalkyl carbonate compounds (such as vinylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoramide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0172] The lithium secondary battery of the present invention can be used in portable devices such as mobile phones, laptop computers and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs), and in particular, can preferably be used as a component battery of a medium and large-sized battery module. Therefore, the present invention provides a medium and large-sized battery module including the above lithium secondary battery as a unit battery.

[0173] Exemplary embodiments of the present invention provide a battery module including the above secondary battery as a unit cell, and a battery pack including the battery module. Since the battery module and the battery pack include a secondary battery having high capacity, high rate capacity, and high cycle characteristics, the battery module and the battery pack can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric energy storage systems.

[0174] Hereinafter, preferred embodiments will be provided to better understand the present invention. It is obvious to those skilled in the art that these embodiments are only for clarifying the present invention, and various modifications and changes can be made within the scope and technical idea of the present invention. These modifications and changes naturally fall within the scope of the claims contained herein.

[0175] Embodiments of the present invention

[0176] <Example>

[0177] <Preparation of negative electrode>

[0178] Example 1: Preparation of negative electrode

[0179] A negative electrode active material layer composition was prepared using Si (average particle diameter (D50): 8 μm) as a silicon-based active material, SWCNT, and polyacrylamide as a binder at a weight ratio of 89:1:10. The composition was added to distilled water as a solvent for forming the negative electrode slurry to prepare a negative electrode slurry (solid concentration: 25% by weight).

[0180] As a mixing method, SWCNT, binder, and water were dispersed at 2500 rpm for 30 minutes using a homogeneous mixer, and then the active material was added and dispersed therein at 2500 rpm for 30 minutes to manufacture the slurry.

[0181] Lithium titanate oxide was electrolyzed to make it in an ionic state, and then reduced on the surface of a Cu foil current collector with a thickness of 8 μm as a negative electrode current collector to form a coating layer (2 μm). Then, the negative electrode slurry was coated onto the negative electrode current collector layer formed with the coating layer at a loading amount of 2.75 mg / cm 2 and then roll-pressed and dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), thereby preparing a negative electrode (porosity: 55%).

[0182] A negative electrode was manufactured in the same manner as in Example 1, except that in Example 1, the coating layer was changed as shown in Table 1 below.

[0183] [Table 1]

[0184]

[0185] In Table 1, Comparative Example 1 corresponds to the case where no coating layer is formed, and Comparative Example 2 corresponds to the case where Li4Ti5O is mixed with Denka Black and PVF at a ratio of 94:4:2, NMP is added as a solvent, and the slurry is coated on the surface of a Cu foil current collector with a thickness of 8 μm as the negative electrode current collector. Comparative Example 3 corresponds to the case where carbon is coated on the surface of a Cu foil current collector with a thickness of 8 μm as the negative electrode current collector. In Table 1, the lithium titanate oxides of Examples 1 to 3, Example 5, and Comparative Example 2 have spinel-structured Li4Ti5O 12 , Comparative Example 2 corresponds to the case where Li4Ti5O, Denka Black and PVF are mixed at a ratio of 94:4:2, NMP is added as a solvent, and the slurry is coated on the surface of a Cu foil current collector with a thickness of 8 μm as the negative electrode current collector, and Comparative Example 3 corresponds to the case where carbon is coated on the surface of a Cu foil current collector with a thickness of 8 μm as the negative electrode current collector. In Table 1, the lithium titanate oxides of Examples 1 to 3, Example 5 and Comparative Example 2 have spinel-structured Li4Ti5O 12 , the lithium titanate oxide of Example 4 has garnet-structured Li4Ti5O 12 , and the lithium titanate oxide of Example 6 has NASICON-structured Li4Ti5O 12 .

[0186] <Preparation of Secondary Battery>

[0187] By adding LiNi 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black as a conductive material (product name: Super C65, manufacturer: Timcal), and polyvinylidene fluoride (PVdF) as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent for forming the positive electrode slurry to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0188] The positive electrode slurry was coated on both surfaces of an aluminum current collector (thickness: 12 μm) used as the positive electrode current collector at a loading amount of 537 mg / 25 cm 2 , and then roll-pressed and dried in a vacuum oven at 130 °C for 10 hours to form a positive electrode active material layer (thickness: 65 μm), thereby preparing a positive electrode (positive electrode thickness: 77 μm, porosity: 26%).

[0189] A lithium secondary battery was manufactured by disposing a polyethylene separator between the positive electrode and the negative electrode in Examples and Comparative Examples and injecting an electrolyte.

[0190] Vinylene carbonate was added to an organic solvent obtained by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) at a volume ratio of 10:90 in an amount of 3 wt% based on the total weight of the electrolyte, and LiPF6 as a lithium salt with a concentration of 1 M was added to obtain an electrolyte.

[0191] <Experimental Example>

[0192] Experimental Example 1: Safety Evaluation Results

[0193] Safety evaluations were conducted on secondary batteries containing the negative electrodes prepared in the examples and comparative examples.

[0194] The cell-to-cell propagation (closed system) method was used for the safety evaluation. This method corresponds to a method that includes stacking four cells (SOC 100) in a jig simulating a module and then artificially causing thermal runaway in the first cell by applying high temperature with a heating pad.

[0195] The cell adjacent to the pad was defined as No. 1, the cell farthest away was defined as No. 4, and the time from just before the voltage of No. 1 reached 0 V to when the voltage of No. 4 reached V = 0 was regarded as the total cell-to-cell propagation (CTCP) time, and it was evaluated that the longer this time, the higher the stability. The results are shown in Table 2 below.

[0196] [Table 2]

[0197] CTCP Time Example 1 60s Example 2 57s Example 3 70s Example 4 80s Example 5 50s Example 6 45s Comparative Example 1 34s Comparative Example 2 30s Comparative Example 3 30s

[0198] The negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application is formed by electrolysis, and thus contains 95 parts by weight or more of lithium titanate oxide in the coating layer without using a binder or a conductive material. That is, lithium titanate oxide is electrolyzed to make it in an ionic state, and then it is reduced on the surface of the negative electrode current collector to form a coating layer. As a result, as can be seen from Examples 1 to 6, by this manufacturing method, a coating layer made of lithium titanate oxide can be formed, and thus the thermal runaway problem of the silicon-based negative electrode can be solved. For reference, when comparing Examples 1, 4, and 6, the effects according to the melting point of lithium titanate oxide can be compared. In this case, it can be seen that Example 4 more effectively solves the thermal runaway problem compared to Example 1. In addition, it can be confirmed that since the melting point of Example 6 is lower than that of Example 1, although Example 6 is superior to the comparative example, it shows lower thermal stability compared to Example 1. Additionally, in Example 5 where the thickness of the formed coating layer is greater than that of Example 1, it can be confirmed that due to the increase in the resistance of the cell, the thermal stability is significantly reduced.

[0199] In Tables 1 and 2, Comparative Example 1 corresponds to the case where the lithium titanate oxide coating layer of the present application is not used, Comparative Example 2 corresponds to the case where lithium titanate oxide is mixed with a binder and a conductive material and the mixture is coated on the negative electrode current collector layer, and Comparative Example 3 corresponds to the case where carbon coating is used instead of lithium titanate oxide coating.

[0200] In the cases of Comparative Examples 1 to 3, it can be confirmed that when the cell is exposed to high temperature, decomposition easily occurs, and after decomposition, the formation of the alloy of Si and Cu cannot be controlled, accelerating the exothermic reaction and reducing the thermal stability.

[0201] As a result, it can be confirmed that through the tests described above, the negative electrode for a lithium secondary battery of the present invention maximizes capacity characteristics and energy density by using a silicon-based active material, and solves the thermal runaway problem by using a coating layer containing lithium titanate through a specific manufacturing process, thereby ensuring output characteristics, life, and stability.

Claims

1. A negative electrode for a lithium secondary battery, comprising: A negative electrode current collector layer; A negative electrode active material layer provided on one surface or both surfaces of the negative electrode current collector layer, Among them, One surface or both surfaces of the negative electrode current collector layer include a coating layer, and The coating layer contains a coating layer composition, and based on 100 parts by weight of the coating layer composition, contains 95 parts by weight or more of a lithium titanium oxide represented by Formula 1, [Formula 1] Li a Ti b O c In Formula 1, a is an integer from 1 to 4, b is an integer from 1 to 5, and c is an integer from 2 to 14.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein, The thickness of the coating layer is 0.1 μm or more and 5 μm or less.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein, The coating layer composition consists of a lithium titanium oxide.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein, The melting point of the lithium titanium oxide is 1500 °C or more.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein, The lithium titanium oxide has a spinel or garnet structure.

6. The negative electrode for a lithium secondary battery according to claim 1, wherein, The negative electrode active material layer contains a negative electrode active material layer composition, the negative electrode active material layer composition contains a silicon-based active material, a negative electrode conductive material, and a negative electrode binder, and Wherein, the silicon-based active material includes one or more selected from the group consisting of: SiOx, where x = 0; SiOx, where 0 < x < 2, SiC, and a silicon alloy.

7. The negative electrode for a lithium secondary battery according to claim 6, wherein, The silicon-based active material includes one or more selected from the group consisting of: SiOx, where x = 0; and SiOx, where 0 < x < 2, and based on 100 parts by weight of the silicon-based active material, the silicon-based active material contains 95 parts by weight or more of SiOx, where x = 0.

8. The negative electrode for a lithium secondary battery according to claim 6, wherein, Based on 100 parts by weight of the negative electrode active material layer composition, the content of the silicon-based active material is 80 parts by weight or more.

9. The negative electrode for a lithium secondary battery according to claim 6, wherein The negative electrode conductive material includes one or more selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a planar conductive material.

10. The negative electrode for a lithium secondary battery according to claim 1, wherein, The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and Wherein, the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

11. A method for manufacturing a negative electrode for a lithium secondary battery, the method comprising: Preparing a negative electrode current collector layer; Forming a coating layer on one surface or both surfaces of the negative electrode current collector layer; And Forming a negative electrode active material layer on the top surface of the negative electrode current collector layer having the coating layer formed thereon, Wherein, the formation of the coating layer includes electrolyzing the lithium titanium oxide represented by Formula 1 to make it in an ionic state; and reducing the ionic state of the lithium titanium oxide on the surface of the negative electrode current collector layer, [Formula 1] Li a Ti b O c In Formula 1, a is an integer from 1 to 4, b is an integer from 1 to 5, and c is an integer from 2 to 14.

12. The method according to claim 11, wherein, The process of forming the negative electrode active material layer on the top surface of the negative electrode current collector layer having the coating layer formed thereon includes: Preparing a negative electrode active material layer composition containing a silicon-based active material, a negative electrode conductive material, and a negative electrode binder; Forming a negative electrode slurry by including a slurry solvent in the negative electrode active material layer composition; and Applying the negative electrode slurry to the top surface of the negative electrode current collector layer having the coating layer formed thereon.

13. A lithium secondary battery, comprising: A positive electrode; The negative electrode for a lithium secondary battery according to any one of claims 1 to 10; A separator disposed between the positive electrode and the negative electrode; and An electrolyte.

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