Anode for lithium secondary battery, method for manufacturing anode for lithium secondary battery, and lithium secondary battery including anode

Abstract

The present application relates to a negative electrode for a lithium secondary battery, a method for producing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2023-0090369, filed with the Korean Intellectual Property Office on July 12, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode for a lithium secondary battery, a method for producing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode. [Background technology]

[0003] The rapid increase in fossil fuel use has led to an increasing demand for alternative and clean energy, and one of the most actively researched fields in this area is power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005] With technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used. In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. The negative electrode active material may be silicon-based particles that have a high discharge capacity.

[0007] In particular, with the recent demand for high-density energy batteries, Si / C and SiO, which have capacities 10 times larger than those of graphite-based materials, have been used as negative electrode active materials.x Active research is being conducted into methods of increasing capacity by incorporating silicon-based compounds such as these. However, while silicon-based compounds, which are high-capacity materials, have superior capacitance characteristics compared to conventionally used graphite, they rapidly expand in volume during charging, disrupting the conductive path and reducing battery performance, resulting in a decrease in capacity from the beginning. Furthermore, with silicon-based anodes, lithium ions are not uniformly charged throughout the anode depth during repeated charge and discharge cycles, and reactions occur on the surface, accelerating surface degradation. Therefore, performance improvements are needed in terms of battery cycles.

[0008] While the above advantages necessitate the use of silicon-based anodes, in addition to the above problems, silicon-based anodes also have the drawback of being susceptible to thermal runaway. That is, when a lithium secondary battery is operated, an exothermic reaction occurs during the intermetallic alloy reaction, which accelerates thermal runaway and poses a risk of explosion.

[0009] To solve this problem, various researches have been conducted, such as a method of using a two-layer negative electrode active material layer and a method of improving the negative electrode active material to prevent thermal runaway. However, there are limitations to their application because they may actually reduce the performance of the battery. In addition, there are still limitations to the commercialization of the production of negative electrode batteries with a high content of silicon-based compounds. Therefore, a method that can dramatically solve the problem of thermal runaway in silicon-based active materials has not yet been found.

[0010] Therefore, it is necessary to develop a negative electrode for a lithium secondary battery that can secure capacity characteristics and energy density using a silicon-based negative electrode and can solve the problem of thermal runaway. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0012] When applying a silicon-based anode to ensure capacity characteristics and energy density, it was found that the degree of Li-Si-Cu alloy formation reaction can be controlled by forming a coating layer containing LTO (lithium titanium oxide) on one or both sides of the anode current collector layer.

[0013] That is, when a cell is exposed to high temperatures, decomposition readily proceeds, and the resulting alloy formation between Si and Cu accelerates the exothermic reaction, resulting in thermal runaway, which has been a problem. However, the present applicant has discovered that the above problem can be solved by uniformly coating one or both sides of the negative electrode current collector layer with lithium titanium oxide. As a result, the present application relates to a negative electrode for a lithium secondary battery that can prevent thermal runaway, a method for manufacturing a negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0014] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; wherein one or both sides of the negative electrode current collector layer comprise a coating layer, the coating layer comprising a coating layer composition, and the coating layer comprises 95 parts by weight or more of lithium titanium oxide represented by the following Formula 1, based on 100 parts by weight of the coating layer composition:

[0015] [Formula 1] Li a Ti b O c In the formula 1, a is an integer from 1 to 4, b is an integer from 1 to 5; c is an integer from 2 to 14.

[0016] In another embodiment, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including: preparing a negative electrode current collector layer; forming a coating layer on one or both surfaces of the negative electrode current collector layer; and forming a negative electrode active material layer on the negative electrode current collector layer on which the coating layer has been formed, wherein the step of forming the coating layer includes the steps of electrolyzing lithium titanium oxide represented by Formula 1 to form it in an ionic state; and reducing the lithium titanium oxide in the ionic state on the surface of the negative electrode current collector layer.

[0017] Finally, in one embodiment of the present application, there is provided a lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte. [Effects of the Invention]

[0018] According to one embodiment of the present invention, a negative electrode for a lithium secondary battery includes a coating layer on one or both sides of a negative electrode current collector layer, and is characterized in that the coating layer contains 95 parts by weight or more of lithium titanium oxide based on 100 parts by weight of a coating layer composition.

[0019] Conventional lithium titanium oxide coating involves mixing a binder and conductive material together and coating them on the negative electrode current collector layer. However, in this case, when the cell is exposed to high temperatures, decomposition easily progresses, and the formation of an alloy between Si and Cu after decomposition cannot be controlled, accelerating the exothermic reaction and causing problems.

[0020] However, the present application contains 95 parts by weight or more of lithium titanium oxide based on 100 parts by weight of the coating layer composition. The lithium titanium oxide itself has a melting point of 1500°C or higher, making it highly thermally stable and stable even at high temperatures. This prevents and controls the Li-Si-Cu alloy formation reaction, thereby resolving the chronic thermal stability problem of silicon-based negative electrodes.

[0021] In addition, the negative electrode for a lithium secondary battery according to the present application is characterized in that the coating layer is formed by electrolysis so as to contain 95 parts by weight or more of lithium titanium oxide without the use of a binder or conductive material. That is, lithium titanium oxide is electrolyzed into an ionized state and then reduced on the surface of the negative electrode current collector to form the coating layer. This manufacturing method allows the formation of a coating layer made of lithium titanium oxide, thereby solving the problem of thermal runaway in silicon-based negative electrodes.

[0022] That is, the negative electrode for a lithium secondary battery according to the present invention is characterized in that it maximizes capacity characteristics and energy density by using a silicon-based active material, and also ensures output characteristics, lifespan, and stability by using a coating layer containing lithium titanium oxide in a specific manufacturing process to solve the problem of thermal runaway. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0024] Before describing the present invention, some terms will first be defined.

[0025] In this specification, when a part is said to "comprise" a certain component, unless otherwise specified, this does not mean that it excludes other components, but that it may further include other components.

[0026] In this specification, "p to q" means a range of "not less than p and not more than q."

[0027] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan Co., Ltd. That is, in this application, the BET specific surface area can mean the specific surface area measured by the above measurement method.

[0028] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution by particle size. Meanwhile, particle size distribution can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The difference in diffraction patterns due to particle size when the particles pass through a laser beam is measured, and the particle size distribution is calculated.

[0029] As used herein, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. As used herein, when a polymer contains a monomer, this is interpreted as meaning that the polymer contains the monomer as a monomer unit.

[0030] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless specifically referred to as a "homopolymer."

[0031] In this specification, the weight-average molecular weight (Mw) and water-average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) with various degrees of polymerization that are commercially available for molecular weight measurement as standard substances.

[0032] In this specification, unless otherwise specified, the molecular weight means the weight average molecular weight.

[0033] DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be embodied in various different forms and is not limited to the following description.

[0034] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; wherein one or both sides of the negative electrode current collector layer comprise a coating layer, the coating layer comprising a coating layer composition, and the coating layer comprises 95 parts by weight or more of lithium titanium oxide represented by the following Formula 1, based on 100 parts by weight of the coating layer composition:

[0035] [Formula 1] Li a Ti b O c In the formula 1, a is an integer from 1 to 4, b is an integer from 1 to 5; c is an integer from 2 to 14.

[0036] The present application is characterized by containing 95 parts by weight or more of lithium titanium oxide based on 100 parts by weight of the coating layer composition. The lithium titanium oxide itself has a melting point of 1500°C or higher and is highly thermally stable, making it stable even at high temperatures. It can also prevent and control the Li-Si-Cu alloy formation reaction, thereby resolving the chronic thermal stability problem of silicon-based anodes.

[0037] FIG. 1 is a diagram showing the layer structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode for a lithium secondary battery 100 can be seen, including a coating layer 20 and a negative electrode active material layer 10 on one side of a negative electrode current collector layer 30. While FIG. 1 shows the negative electrode active material layer and coating layer formed on one side, they may be formed on both sides of the negative electrode current collector layer. When coating layers are formed on both sides, at least one coating layer may include a coating layer composition according to the present application, and the remaining coating layers may be coating layers commonly used in the art.

[0038] The negative electrode for a lithium secondary battery of the present invention will be described in more detail below.

[0039] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surfaces treated with carbon, nickel, titanium, silver, or the like, and aluminum-cadmium alloys can be used. Furthermore, the surface can be provided with fine irregularities to strengthen the bonding strength of the negative electrode active material, and the negative electrode current collector layer can be used in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0040] More specifically, the negative electrode current collector layer may contain copper.

[0041] In one embodiment of the present application, the negative electrode current collector layer may have a thickness of 1 μm or more and 100 μm or less.

[0042] In another 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, more specifically 5 μm or more and 25 μm or less.

[0043] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0044] In the case of conventional negative electrodes for lithium secondary batteries, a negative electrode active material layer is directly coated on one side of the negative electrode current collector layer. In particular, silicon-based active material layers are characterized by excellent capacity characteristics, but have the problem of poor stability due to the aforementioned thermal runaway problem, making them difficult to apply to lithium secondary batteries.

[0045] Accordingly, in the case of the negative electrode for a lithium secondary battery according to the present application, a coating layer is provided on one or both sides of the negative electrode current collector layer, and in particular, the coating layer includes a coating layer composition and includes 95 parts by weight or more of lithium titanium oxide based on 100 parts by weight of the coating layer composition.

[0046] In one embodiment of the present application, the coating layer composition may contain 95 parts by weight or more of lithium titanium oxide, preferably 97 parts by weight or more of lithium titanium oxide, and more preferably 99 parts by weight or more, or 100 parts by weight or less, based on 100 parts by weight of the coating layer composition.

[0047] The present application provides a negative electrode for a lithium secondary battery, wherein the coating layer composition is composed of lithium titanium oxide. The coating layer composition being composed of lithium titanium oxide may mean that the coating layer composition contains 100 parts by weight of lithium titanium oxide, based on 100 parts by weight of the coating layer composition.

[0048] Previously, to ensure ease of coating, lithium titanium oxide was mixed with binders and conductive materials before application. When the cell is exposed to high temperatures during operation of a lithium secondary battery, if the lithium titanium oxide content is low, including the binder and conductive materials, it easily decomposes. After decomposition, the negative electrode current collector layer and the negative electrode active material layer come into contact to form a Si-Cu alloy, which accelerates the exothermic reaction and causes thermal runaway.

[0049] However, the coating layer according to the present application is characterized by containing lithium titanium oxide in the above range, as described above. In particular, since the melting point of lithium titanium oxide is 1500°C or higher, direct contact between the negative electrode active material layer and the negative electrode current collector layer can be prevented to the greatest extent possible even if cell runaway begins, and thermal stability is ensured by delaying and suppressing the Si-Cu alloy reaction.

[0050] Therefore, the lithium titanium oxide according to the present application, particularly the lithium titanium oxide having a spinel or garnet structure, has a high melting point of 1500°C or more, and the coating layer made of the lithium titanium oxide having a spinel or garnet structure is directly coated on the Cu foil, which is the negative electrode current collector layer, to suppress the alloy formation reaction between Li and Si, thereby suppressing the thermal runaway phenomenon.

[0051] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness of the coating layer is 0.1 μm or more and 5 μm or less.

[0052] In another 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.

[0053] The thickness of the coating layer is within the above range. If the thickness is less than this range, contact between the negative electrode current collector layer and the negative electrode active material layer may occur during thermal runaway, making it difficult to control thermal runaway. If the thickness is greater than this range, problems may occur with negative electrode capacity and fast charging. In other words, by having the thickness within this range, negative electrode capacity and fast charging performance can be ensured and thermal runaway can be easily prevented.

[0054] In one embodiment of the present application, the lithium titanium oxide can be represented by Formula 1 above.

[0055] In the present application, a is an integer of 1 to 4, specifically, a is an integer of 2 to 4, and may be an integer of 3 or 4.

[0056] In the present application, b is an integer of 1 to 5, specifically an integer of 3 to 5, and may be an integer of 4 to 5.

[0057] In the present application, c is an integer of 2 to 14, and may be an integer of 5 to 13, or may be an integer of 8 to 12.

[0058] In one embodiment of the present application, the lithium titanium oxide is Li4Ti5O 12 It may also be expressed as:

[0059] In the present application, the lithium titanium oxide is applied to high-voltage lithium secondary batteries, and by having the above-described composition, it has advantages in ensuring thermal stability and in driving high-voltage cells.

[0060] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the melting point of the lithium titanium oxide is 1500° C. or higher.

[0061] In another 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 may be 2000°C or lower.

[0062] The melting point range allows the lithium titanium oxide to maintain its shape without melting during thermal runaway, preventing direct contact between the negative electrode current collector layer and the negative electrode active material layer, thereby ensuring cell stability. The melting point can be adjusted by modifying the composition and structure of the lithium titanium oxide, and more specifically, can be determined by the Ti content of the lithium titanium oxide. In other words, Ti acts as the central atom in the lithium titanium oxide, and the melting point increases as the Ti content increases.

[0063] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the lithium titanium oxide has a spinel structure or a garnet structure.

[0064] In this application, a spinel structure can mean that it consists of a cubic close-packed arrangement of oxygen ions with cations occupying all of the octahedral and tetrahedral sites.

[0065] In spinel structure compounds, O ions form octahedra, just like in layer structure compounds, with transition metal ions present inside. Li ions and metal ions are present in tetrahedral and octahedral positions, respectively, with Li ions inserted into the octahedral positions. Due to this structural feature, spinel structure compounds have three-dimensional Li ion diffusion pathways. Spinel structure compounds have the advantage that Li ions can be inserted into the three-dimensional Li ion diffusion pathways from various directions, but due to the complex Li ion diffusion pathways, the Li ion diffusion rate inside the spinel structure is relatively slower than that of layer structure compounds.

[0066] The lithium titanium oxide according to the present invention has a spinel structure, has a low interlayer voltage, does not form dendrites, and can absorb lithium ions. It also has excellent thermal stability, chemical stability, and mechanical strength, making it suitable for use as a negative electrode for lithium secondary batteries.

[0067] Also, in one embodiment of the present application, the lithium titanate has a spinel structure and may have a melting point of 1500 °C or higher, preferably 1510 °C or higher, more preferably 1515 °C or higher, and may be 2000 °C or lower. The lithium titanate having the spinel structure may have a melting point of 1520 °C as an example.

[0068] The lithium titanate having the spinel structure according to the present application has a high melting point, and the coating layer made of the lithium titanate having the spinel structure is directly coated on a Cu foil which is a negative electrode current collector layer, suppressing the alloy formation reaction between Li and Si and suppressing the thermal runaway phenomenon.

[0069] In one embodiment of the present application, the negative electrode active material layer includes a negative electrode active material layer composition containing a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

[0070] In the present application, the silicon-based active material is SiO x (x = 0), SiO x (0 < x < 2), SiC, and Si alloy, and provides a negative electrode for a lithium secondary battery containing one or more selected from the group consisting of.

[0071] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may be contained in 95 parts by weight or more.

[0072] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) is 95 parts by weight or more, preferably SiO x(x=0) is contained in an amount of 97 parts by weight or more, more preferably 99 parts by weight or more, and may be contained in an amount of 100 parts by weight or less.

[0073] In one embodiment of the present application, the silicon-based active material may be, in particular, pure silicon (Si) particles. The use of pure silicon (Si) as the silicon-based active material means, as described above, that pure silicon (SiO ) particles not bonded to other particles or elements, based on 100 parts by weight of the total silicon-based active material. x (x=0)) can be included in the range.

[0074] In one embodiment of the present application, the silicon-based active material is SiO x (x=0).

[0075] The negative electrode for a lithium secondary battery according to the present application contains the above-mentioned silicon-based active material in the negative electrode active material layer, and specifically, SiO x The battery contains pure silicon particles containing 95 parts by weight or more of (x=0). In this case, when the pure silicon particles are contained in a high content, the capacity characteristics are excellent, and the problem of thermal runaway caused by this is solved by including the coating layer according to the present invention.

[0076] Meanwhile, the average particle size (D50) of the silicon-based active material of the present invention may 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 this range, the specific surface area of ​​the particles is within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the first negative electrode active material is equal to or greater than the lower limit of the range, the contact area between the silicon particles and the conductive material is improved by the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of maintaining the conductive network and improving the capacity retention rate. Meanwhile, when the average particle size is within this range, excessively large silicon particles are excluded, resulting in a smooth negative electrode surface, thereby preventing non-uniform current density during charge and discharge.

[0077] In the negative electrode for a lithium secondary battery according to the present application, the porosity of the negative electrode active material layer satisfies 50% or more.

[0078] In one embodiment of the present application, the porosity of the negative electrode active material layer may be 50% or more, preferably 60% or more, and may be 90% or less, preferably 80% or less.

[0079] The adjustment of the porosity affects the overall composition and content of the negative electrode active material layer composition, and is mainly influenced by the D50 particle size of the silicon-based active material contained in the negative electrode active material layer composition.

[0080] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the silicon-based active material contained in the negative electrode active material layer has a D50 particle size of 5 μm or more.

[0081] By satisfying the above-mentioned particle size distribution and porosity ranges, the negative electrode for a lithium secondary battery according to the present application satisfies the above-mentioned porosity ranges and simplifies the pore structure, thereby improving the phenomenon in which the reaction between lithium ions and silicon-based active material is concentrated only on the surface, thereby improving diffusion resistance.

[0082] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET surface area of ​​the silicon-based active material is preferably less than 0.01 m 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET surface area is determined according to DIN 66131 (using nitrogen).

[0083] In one embodiment of the present application, the silicon-based active material may be present, for example, in a crystalline or amorphous form, and is preferably not porous. Preferably, the silicon particles are spherical or shard-like particles. Alternatively, but less preferably, the silicon particles may have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0084] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and the circularity thereof is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0085] In this application, the circularity is determined by the following formula 2, where A is the area and P is the perimeter.

[0086] [Formula 2] 4πA / P 2

[0087] In one embodiment of the present application, the silicon-based active material may be included in an amount of 80 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0088] In another embodiment, the silicon-based active material may be contained in an amount of 80 parts by weight or more, preferably 85 parts by weight or more, based on 100 parts by weight of the negative electrode active material layer composition, and may be contained in an amount of 99 parts by weight or less, preferably 97 parts by weight or less, and more preferably 95 parts by weight or less.

[0089] The negative electrode active material layer composition according to the present application has the effect of improving capacity characteristics by using a silicon-based active material with extremely high capacity within the above range, and in particular, by adjusting the range of the silicon-based active material contained in the negative electrode active material layer to the above range, the problems of surface deterioration during charging and discharging, problems with life characteristics, and problems with ensuring conductive paths are solved without reducing the capacity performance of the entire negative electrode.

[0090] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based compounds into negative electrode active materials to increase capacity have recently been increasing in response to growing demand for high-capacity batteries. However, silicon-based compounds have a limitation in that their volume rapidly expands during charging and discharging, damaging the conductive paths formed within the negative electrode active material layer and thereby degrading battery performance.

[0091] In addition, when a silicon-based active material of a certain particle size is contained within the above range in order to adjust the porosity range as described above, there is a problem that the conductive path is not secured due to volume expansion during charging and discharging, resulting in a decrease in output characteristics and therefore a decrease in life characteristics.

[0092] Therefore, in one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of dot-like conductive materials, linear conductive materials, and planar conductive materials.

[0093] In one embodiment of the present application, the negative electrode conductive material may be any material commonly used in the art without limitation, and may be selected from the group consisting of dot-shaped conductive materials, planar conductive materials, and linear conductive materials.

[0094] In one embodiment of the present application, the dot-like conductive material refers to a dot-like or spherical conductive material that can be used to improve the conductivity of a negative electrode and that exhibits conductivity without undergoing a chemical change. Specifically, the dot-like conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black, which realizes high conductivity and excellent dispersibility.

[0095] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0096] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0097] In one embodiment of the present application, the planar conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode, and at the same time, can prevent the conductive path from being disconnected due to volume expansion, and can be referred to as a plate-like conductive material or a bulk-like conductive material.

[0098] In one embodiment of the present application, the sheet conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may preferably be platelet graphite.

[0099] In one embodiment of the present application, the average particle size (D50) of the sheet conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 4 μm to 5 μm. When the average particle size satisfies the above range, the sufficient particle size facilitates dispersion without excessively increasing the viscosity of the negative electrode slurry. Therefore, when dispersing using the same device and time, the dispersion effect is excellent.

[0100] In one embodiment of the present application, the sheet conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 1.5 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 7.0 μm or more and 15.0 μm or less.

[0101] In one embodiment of the present application, the sheet conductive material may be a sheet conductive material having a high BET specific surface area; or a sheet conductive material having a low specific surface area.

[0102] In one embodiment of the present application, the sheet conductive material may be a sheet conductive material with a high specific surface area or a sheet conductive material with a low specific surface area without any restrictions. However, since the sheet conductive material of the present application may be affected to some extent by dispersion in terms of electrode performance, it may be particularly preferable to use a sheet conductive material with a low specific surface area that does not pose a dispersion problem.

[0103] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0104] In another embodiment, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0105] In another embodiment, the sheet conductive material is a sheet conductive material having a high specific surface area, and a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0106] In another embodiment, the sheet conductive material is a sheet conductive material having a low specific surface area, and a BET specific surface area of ​​5 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0107] Other conductive materials include linear conductors such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a bundle- or rope-like secondary shape in which a plurality of carbon nanotube monomers are arranged side by side with the longitudinal axes of the carbon nanotube monomers substantially aligned in the same direction or are entangled. The carbon nanotube units have graphite sheets in the form of cylinders with nano-sized diameters, and sp 2 The bundled carbon nanotubes have a bonding structure. Depending on the angle and structure of the graphite plane wrapping, they can exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0108] In one embodiment of the present application, the negative electrode conductive material may be included in an amount of 0.01 parts by weight to 40 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0109] In another embodiment, the negative electrode conductive material may be included in an amount of 0.01 parts by weight to 40 parts by weight, preferably 0.1 parts by weight to 30 parts by weight, and more preferably 0.5 parts by weight to 25 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0110] In one embodiment of the present application, when the negative electrode conductive material contains only linear conductive material, the amount may be 0.01 parts by weight or more and 5 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

[0111] In another embodiment, when the negative electrode conductive material includes only a linear conductive material, the linear conductive material may be included in an amount of 0.01 parts by weight or more and 5 parts by weight or less, preferably 0.03 parts by weight or more and 3 parts by weight or less, and more preferably 0.1 parts by weight or more and 2 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0112] In one embodiment of the present application, the negative electrode conductive material includes dot-like conductive material; sheet-like conductive material; and linear conductive material, and the dot-like conductive material:sheet-like conductive material:linear conductive material may satisfy a ratio of 1:1:0.01 to 1:1:1.

[0113] In one embodiment of the present application, the dot-like conductive material may be contained in an amount of 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, based on 100 parts by weight of the negative electrode conductive material.

[0114] In one embodiment of the present application, the sheet conductive material may be contained in an amount of 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, based on 100 parts by weight of the negative electrode conductive material.

[0115] In one embodiment of the present application, the linear conductive material may be contained in an amount of 0.01 parts by weight or more and 10 parts by weight or less, preferably 0.05 parts by weight or more and 8 parts by weight or less, and more preferably 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0116] In one embodiment of the present application, the negative electrode conductive material may include a linear conductive material and a planar conductive material.

[0117] In one embodiment of the present application, the negative electrode conductive material may include linear conductive material and sheet conductive material, and the ratio of the linear conductive material to the sheet conductive material may satisfy 0.01:1 to 0.1:1.

[0118] In one embodiment of the present application, the negative electrode conductive material particularly includes a linear conductive material and a planar conductive material, and by satisfying the above-mentioned compositions and proportions, the battery is not significantly affected in terms of the life characteristics of conventional lithium secondary batteries, and more points are available for charging and discharging, resulting in excellent output characteristics at a high C rate.

[0119] The negative electrode conductive material according to the present application has a completely different structure from the positive electrode conductive material used in the positive electrode. That is, the negative electrode conductive material according to the present application serves to secure the contact points between the silicon-based active materials, which undergo a very large volume expansion of the electrodes upon charging and discharging, while the positive electrode conductive material serves to provide a buffer during rolling and also to impart some conductivity, and therefore has a completely different structure and role from the negative electrode conductive material of the present invention.

[0120] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and providing some conductivity, and are completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0121] In one embodiment of the present application, the negative electrode binder may be included in an amount of 1 part by weight to 20 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0122] In another embodiment, the negative electrode binder may be included in an amount of 1 part by weight to 20 parts by weight, preferably 2 parts by weight to 15 parts by weight, and more preferably 3 parts by weight to 15 parts by weight, based on 100 parts by weight of the negative electrode active material layer composition.

[0123] In one 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, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0124] The negative electrode binder according to one embodiment of the present application fulfills the role of capturing the active material and conductive material to prevent distortion and deformation of the negative electrode structure during volume expansion and relaxation of the negative electrode silicon-based active material. Any common binder can be used as long as it fulfills this role. Specifically, an aqueous binder can be used, and more specifically, a PAM-based binder may be used.

[0125] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, 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.

[0126] One embodiment of the present application provides a method for manufacturing a negative electrode for a lithium secondary battery, the method including the steps of: preparing a negative electrode current collector layer; forming a coating layer on one or both sides of the negative electrode current collector layer; and forming a negative electrode active material layer on the negative electrode current collector layer on which the coating layer has been formed, wherein the step of forming the coating layer includes the steps of electrolyzing lithium titanium oxide that satisfies the range of Formula 1 to form it in an ionic state; and reducing the lithium titanium oxide in the ionic state on the surface of the negative electrode current collector layer.

[0127] By forming the coating layer by electrolysis as described above, unlike conventional methods, it is possible to uniformly coat without containing materials such as conductive materials and binders, thereby satisfying the aforementioned lithium titanium oxide content requirement. That is, while conventional methods have reduced the lithium titanium oxide content and increased the conductive material and binder contents to ensure ease of coating, the present application uses an increased lithium titanium oxide content to prevent thermal runaway, making it possible to easily coat using the aforementioned manufacturing method.

[0128] In one embodiment of the present application, the step of forming the coating layer is more specifically performed by dissolving and dispersing the lithium titanium oxide powder in an electrolyte solution, electrolyzing it to form ions, and then laminating and reducing the resulting mixture on a negative electrode current collector (e.g., Cu foil), i.e., by heating at 60°C to 80°C and pressing the resulting mixture, the coating layer can be formed independently without a conductive material or binder.

[0129] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by coating one or both surfaces of a current collector with a negative electrode slurry including the negative electrode active material layer composition.

[0130] More specifically, the step of forming the anode active material layer on the anode current collector layer on which the coating layer is formed includes the steps of: preparing an anode active material layer composition including a silicon-based active material; an anode conductive material; and an anode binder; adding a slurry solvent to the anode active material layer composition to form an anode slurry; and applying the anode slurry to the anode current collector layer on which the coating layer is formed.

[0131] In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition; and a slurry solvent.

[0132] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0133] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0134] The solid content of the negative electrode slurry may refer to the content of the negative electrode active material layer composition contained in the negative electrode slurry, and may refer to the content of the negative electrode active material layer composition based on 100 parts by weight of the negative electrode slurry.

[0135] When the solid content of the negative electrode slurry satisfies the above range, the viscosity is appropriate during the formation of the negative electrode active material layer, and the agglomeration of particles of the negative electrode composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0136] In one embodiment of the present application, there is provided a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to the present application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0137] A secondary battery according to an embodiment of the present specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0138] 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 including the positive electrode active material.

[0139] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on the collector surface to enhance adhesion of the positive electrode active material. For example, it can be used in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0140] 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) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 Mc2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of the lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (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); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0141] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-mentioned positive electrode active material.

[0142] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the constructed battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0143] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0144] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator that exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may be used, and may be used in a single-layer or multi-layer structure.

[0145] Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries, but are not limited to these.

[0146] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0147] Examples of the non-aqueous organic solvent that can be used include non-proton organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0148] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferably used because they are high-viscosity organic solvents with high dielectric constants and can effectively dissociate lithium salts. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore, such a mixture is more preferably used.

[0149] The metal salt can be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt can be 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 - One or more selected from the group consisting of:

[0150] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0151] The lithium secondary battery according to the present invention is useful in portable devices such as mobile phones, laptops, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs), and is particularly suitable as a component battery of medium- to large-sized battery modules. Accordingly, the present invention also provides a medium- to large-sized battery module including the above-described lithium secondary battery as a unit cell.

[0152] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and battery pack include the secondary battery having a large capacity and excellent rate-limiting and cycle characteristics, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0153] Below, preferred examples are shown to aid in understanding the present invention. However, the above examples are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims.

[0154] <Example> <Production of negative electrodes> Example 1: Preparation of negative electrode A negative electrode active material layer composition was prepared using silicon-based active material Si (average particle size (D50): 8 μm), single-walled carbon nanotubes (SWCNTs), and polyacrylamide as a binder in a weight ratio of 89:1:10. This was added to distilled water as a solvent for forming a negative electrode slurry to produce a negative electrode slurry (solid concentration 25 wt%).

[0155] The mixing method was as follows: SWCNT, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the active material was added and dispersed at 2500 rpm for 30 minutes to prepare a slurry.

[0156] Lithium titanium oxide was electrolyzed into an ionized state and then reduced to form a coating layer (2 μm) on the surface of an 8 μm-thick Cu foil current collector as a negative electrode current collector. Then, the negative electrode slurry was applied at a rate of 2.75 mg / cm to the negative electrode current collector layer on which the coating layer was formed. 2The coated film was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm) to prepare a negative electrode (porosity: 55%).

[0157] The same preparation as in Example 1 was carried out, except that the coating layer was changed as shown in Table 1 below.

[0158] [Table 1]

[0159] In Table 1, Comparative Example 1 corresponds to the case where no coating layer was formed, and Comparative Example 2 corresponds to the case where Li4Ti5O 12 The lithium titanium oxides in Examples 1 to 3, 5, and Comparative Example 2 were prepared by mixing Denka black and PVdF in a ratio of 94:4:2, adding NMP as a solvent, and coating the slurry on the surface of an 8 μm thick Cu foil current collector as a negative electrode current collector. Comparative Example 3 corresponds to a case where carbon was coated on the surface of an 8 μm thick Cu foil current collector as a negative electrode current collector. In Table 1, the lithium titanium oxides in Examples 1 to 3, 5, and Comparative Example 2 were Li4Ti5O with a spinel structure. 12 In Example 4, Li4Ti5O with a garnet structure is used. 12 In Example 6, Li4Ti5O with NASICON structure was used. 12 was used.

[0160] <Secondary battery manufacturing> LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added in a weight ratio of 97:1.5:1.5 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%).

[0161] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) at a rate of 537 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to prepare a positive electrode (thickness: 77 μm, porosity: 26%).

[0162] A polyethylene separator was interposed between the positive electrode and the negative electrode of each of the Examples and Comparative Examples, and an electrolyte was injected thereinto to prepare a lithium secondary battery.

[0163] The electrolyte was prepared by adding 3 wt% vinylene carbonate (based on the total weight of the electrolyte) to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) were mixed in a volume ratio of 10:90, and LiPF6 was added as a lithium salt at a concentration of 1M.

[0164] <Experimental Example> Experimental example 1: Safety evaluation results Safety evaluation was carried out on the secondary batteries including the negative electrodes produced in the examples and comparative examples.

[0165] The safety assessment was carried out using the CTCP (cell to cell propagation) (closed system) method, which involves stacking four cells (SOC100) in a jig that simulates a module, and artificially applying extreme heat to the first cell using a heating pad to induce thermal runaway in the cell.

[0166] The cell adjacent to the pad was defined as No. 1, and the cell furthest from it was defined as No. 4. The time from when the voltage of No. 1 reached 0V to when the voltage of No. 4 reached V=0 was considered the total time of CTCP (Cell to cell propagation), and the longer this time, the higher the stability was evaluated. The results are shown in Table 2 below.

[0167] [Table 2]

[0168] The negative electrode for a lithium secondary battery according to the present application is characterized in that the coating layer is formed by electrolysis to contain at least 95 parts by weight of lithium titanium oxide without any binder or conductive material. Specifically, lithium titanium oxide is electrolyzed to an ionized state and then reduced on the surface of the negative electrode current collector to form a coating layer. This manufacturing method allows the formation of a coating layer made of lithium titanium oxide, thereby resolving the problem of thermal runaway in silicon-based negative electrodes, as demonstrated in Examples 1 to 6. For reference, comparing Examples 1, 4, and 6, the effect of the melting point of the lithium titanium oxide can be compared. Example 4 was found to be superior to Example 1 in resolving the problem of thermal runaway. Example 6, which had a lower melting point than Example 1, was superior to the comparative example, but its thermal stability was inferior to Example 1. Furthermore, Example 5, which used a thicker coating layer than Example 1, was found to have a poorer thermal stability due to an increased cell resistance.

[0169] In Tables 1 and 2, Comparative Example 1 corresponds to a case where the lithium titanium oxide coating layer according to the present application was not used, Comparative Example 2 corresponds to a case where the lithium titanium oxide coating was formed by mixing a binder and a conductive material together and coating the mixture on the negative electrode current collector layer, and Comparative Example 3 corresponds to a case where a carbon coating was used instead of a lithium titanium oxide coating.

[0170] In the case of Comparative Examples 1 to 3, it was confirmed that when the cell was exposed to high temperatures, decomposition proceeded easily, and the alloy formation between Si and Cu after decomposition could not be controlled, accelerating the exothermic reaction and reducing thermal stability.

[0171] As a result, through the above experiments, it was found that in the case of the negative electrode for a lithium secondary battery according to the present invention, capacity characteristics and energy density are maximized by using a silicon-based active material, and output characteristics, lifespan, and stability are also ensured by using a coating layer containing lithium titanium oxide in a specific manufacturing process to solve the problem of thermal runaway. [Explanation of symbols]

[0172] 10 Negative electrode active material layer 20 coating layers 30 Negative electrode current collector layer 100 Negative electrode for lithium secondary battery

Claims

1. a negative electrode current collector layer; 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 include a coating layer; the coating layer comprises a coating layer composition; The coating layer composition contains 95 parts by weight or more of lithium titanium oxide represented by the following formula 1, based on 100 parts by weight of the coating layer composition: [Formula 1] Li ａ Ti ｂ O ｃ In the formula 1, a is an integer from 1 to 4, b is an integer from 1 to 5; a negative electrode for a lithium secondary battery, wherein c is an integer of 2 to 14;

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

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

4. 2. 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 higher.

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

6. the negative electrode active material layer includes a negative electrode active material layer composition including a silicon-based active material, a negative electrode conductive material, and a negative electrode binder; The silicon-based active material is SiO ｘ (x=0), SiO ｘ 2. The negative electrode for a lithium secondary battery according to claim 1, comprising at least one selected from the group consisting of (0<x<2), SiC, and a Si alloy.

7. The silicon-based active material is SiO ｘ (x=0) and SiO ｘ (0<x<2), and based on 100 parts by weight of the silicon-based active material, the SiO ｘ 7. The negative electrode for a lithium secondary battery according to claim 6, wherein (x=0) is contained in an amount of 95 parts by weight or more.

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

9. 7. The negative electrode for a lithium secondary battery according to claim 6, wherein the negative electrode conductive material comprises at least one material selected from the group consisting of a dot-like conductive material, a linear conductive material, and a sheet-like conductive material.

10. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

11. providing a negative electrode current collector layer; forming a coating layer on one or both surfaces of the negative electrode current collector layer; forming a negative electrode active material layer on the negative electrode current collector layer on which the coating layer is formed, The step of forming the coating layer includes the steps of electrolyzing lithium titanium oxide represented by the following formula 1 to form it into an ion state, and reducing the lithium titanium oxide in the ion state on the surface of the negative electrode current collector layer, [Formula 1] Li ａ Ti ｂ O ｃ In the formula 1, a is an integer from 1 to 4, b is an integer from 1 to 5; A method for producing a negative electrode for a lithium secondary battery, wherein c is an integer of 2 to 14.

12. The step of forming a negative electrode active material layer on the negative electrode current collector layer on which the coating layer is formed includes: preparing a negative electrode active material layer composition including a silicon-based active material, a negative electrode conductive material, and a negative electrode binder; adding a slurry solvent to the negative electrode active material layer composition to form a negative electrode slurry; and applying the negative electrode slurry onto the negative electrode current collector layer on which the coating layer is formed.

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

Images