Anode for lithium secondary battery, method for producing 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. 10-2022-0076797, filed with the Korean Intellectual Property Office on June 23, 2022, 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 the use of fossil fuels has led to an increased 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] At present, a representative 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] As technological development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among such secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. In addition, research into a method for manufacturing a high-density electrode with a higher energy density per unit volume as an electrode for such high-capacity lithium secondary batteries is being actively conducted.

[0006] In general, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and removes lithium ions from the positive electrode. Silicon-based particles having a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, in recent years, in response to the demand for high-density energy batteries, active research has been conducted into methods of increasing capacity by using silicon-based compounds such as Si / C and SiOx, which have a capacity 10 times larger than that of graphite-based materials, as negative electrode active materials. However, in the case of silicon-based compounds, which are high-capacity materials, they are materials with a large capacity compared to conventionally used graphite and have excellent capacity characteristics, but their volume expands rapidly during charging, cutting off the conductive path and reducing battery characteristics, resulting in a decrease in capacity from the beginning. In addition, when silicon-based negative electrodes undergo repeated charge and discharge cycles, lithium ions are not uniformly charged in the depth direction of the negative electrode, and reactions proceed on the surface, accelerating surface deterioration, so performance needs to be improved in terms of battery cycles.

[0008] In addition, when making an anode using silicon-based active material, it is important that the pore structure of the anode is simple, and it is known that the higher the tortuosity of an anode using silicon-based active material, the better the diffusion resistance. However, if the porosity is infinitely increased to improve the tortuosity, the contact points with the anode current collector layer decrease, and the adhesion with the anode current collector layer decreases, causing detachment and other problems, resulting in a decrease in life characteristics.

[0009] Various studies are being conducted to solve the above problems, but there are limitations to their application because they may actually reduce battery performance, and there are still limitations to the commercialization of negative electrode batteries with a high content of silicon-based compounds. As the ratio of silicon-based active material contained in the silicon-based active material layer increases, reactions with lithium ions are concentrated on the surface of the negative electrode, causing damage to the silicon-based active material on the surface side, resulting in a problem of reduced life characteristics.

[0010] Therefore, even when a silicon-based compound is used as the active material, it is necessary to develop a lithium secondary battery that improves the tortuosity of the negative electrode during charge and discharge cycles and also has excellent adhesion to the negative electrode current collector layer. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2009-080971 A Summary of the Invention [Problem to be solved by the invention]

[0012] The present application relates to a negative electrode for a lithium secondary battery, which uses a silicon-based active material in the negative electrode, and which is capable of improving cycle performance by improving the tortuosity and further improving the adhesive strength with a negative electrode current collector layer to prevent deterioration of the electrode surface during charge and discharge cycles, and a method for manufacturing the negative electrode for a lithium secondary battery, and a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0013] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, the negative electrode including a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer; wherein the first negative electrode active material layer has a porosity of 40% or less and the porosity of the second negative electrode active material layer is higher than that of the first negative electrode active material layer, the first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material; a first negative electrode conductive material; and a first negative electrode binder, the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material; a second negative electrode conductive material; and a second negative electrode binder, the first negative electrode conductive material includes two or more types of conductive materials, and the second negative electrode conductive material includes one type of conductive material.

[0014] In yet another embodiment, a method for manufacturing a negative electrode for a lithium secondary battery includes the steps of: preparing a negative electrode current collector layer; applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition to a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer to form a second negative electrode active material layer, The present invention provides a method for producing a negative electrode for a lithium secondary battery, wherein a porosity of a material layer is higher than a porosity of the first negative electrode active material layer, the first negative electrode active material layer comprises a first negative electrode active material layer composition including a first negative electrode active material; a first negative electrode conductive material; and a first negative electrode binder, and the second negative electrode active material layer comprises a second negative electrode active material layer composition including a second negative electrode active material; a second negative electrode conductive material; and a second negative electrode binder, wherein the first negative electrode conductive material includes two or more types of conductive materials, and the second negative electrode conductive material includes one type of conductive material.

[0015] Finally, 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 disposed between the positive electrode and the negative electrode; and an electrolyte. Effect of the Invention

[0016] According to one embodiment of the present invention, the negative electrode for a lithium secondary battery has a double layer structure, and the porosity of the first negative electrode active material layer is 40% or less, and the porosity of the second negative electrode active material layer is higher than that of the first negative electrode active material layer. By constructing the negative electrode in this way as a double layer, the porosity of the first negative electrode active material layer in contact with the negative electrode current collector layer can be reduced within a certain range, and the contact points with the negative electrode current collector layer can be increased to improve adhesion and enhance life characteristics, and the porosity of the second negative electrode active material layer can be increased within a certain range to improve the negative electrode tortuosity and improve diffusion resistance.

[0017] That is, the present invention adjusts the arrangement in the negative electrode active material layer according to the average particle size of the silicon-based active material, and has the above-mentioned characteristics, thereby making it possible to maintain the high capacity characteristic, which is an advantage of a negative electrode containing a silicon-based active material, and also to prevent the electrode from being detached, thereby improving the life characteristics.

[0018] In addition, a negative electrode for a lithium secondary battery according to one embodiment of the present invention is characterized in that a first negative electrode conductive material contained in the first negative electrode active material layer includes two or more types of conductive materials, and a second negative electrode conductive material contained in the second negative electrode active material layer includes one type of conductive material.

[0019] As described above, by adjusting the porosity of the first and second layers in a lithium secondary battery and incorporating a specific conductive material in the first and second layers, the battery has the advantage of having excellent output characteristics at a high C-rate, with more points at which charging and discharging can be performed, without significantly affecting the life characteristics of existing lithium secondary batteries.

[0020] That is, the negative electrode for a lithium secondary battery according to the present invention is mainly characterized in that it has a double-layer structure in order to maximize the capacity characteristics by using a silicon-based active material and simplify the pore structure, with each layer satisfying a specific porosity range, and a specific conductive material is used in each layer so as to increase the number of points at which charging and discharging can be performed, thereby providing excellent output characteristics. [Brief description of the drawings]

[0021] [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 PREFERRED EMBODIMENTS

[0022] Before describing the present invention, some terms will first be defined.

[0023] In this specification, when a part is said to "comprise" a certain component, this means that it may further include other components, rather than excluding other components, unless specifically stated to the contrary.

[0024] In this specification, "p to q" means a range of "not less than p and not more than q".

[0025] 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 (77K) using a BELSORP-mini II manufactured by BEL Japan Co., Ltd. That is, in this application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0026] In this specification, "Dn" means particle size distribution, and refers to the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. Meanwhile, the 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 measuring device (e.g., Microtrac S3500), and the difference in the diffraction pattern due to the particle size when the particles pass through a laser beam is measured to calculate the particle size distribution.

[0027] In this specification, when a polymer contains a certain monomer as a monomer unit, it means that the monomer is involved in a polymerization reaction and is contained as a repeating unit in the polymer. In this specification, when a polymer contains a monomer, this is interpreted as the same as when a polymer contains a monomer as a monomer unit.

[0028] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers, unless otherwise specified as a "homopolymer."

[0029] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various polymerization degrees that are commercially available for molecular weight measurement as standard substances. In this specification, the molecular weight means the weight average molecular weight unless otherwise specified.

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings in order to enable those skilled in the art to easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the following description.

[0031] One embodiment of the present specification provides a negative electrode for a lithium secondary battery, the negative electrode including a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer; wherein the first negative electrode active material layer has a porosity of 40% or less and the porosity of the second negative electrode active material layer is higher than that of the first negative electrode active material layer, the first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material; a first negative electrode conductive material; and a first negative electrode binder, the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material; a second negative electrode conductive material; and a second negative electrode binder, the first negative electrode conductive material includes two or more types of conductive materials, and the second negative electrode conductive material includes one type of conductive material.

[0032] The negative electrode for a lithium secondary battery according to the present application is characterized in that it is configured as a double layer in which a first negative electrode active material layer and a second negative electrode active material layer satisfy a specific porosity range and use a certain amount of a specific conductive material, in order to obtain the advantages of an electrode using a high content of silicon particles in a single layer of active material, while resolving the disadvantages of having such an electrode, such as the problem of simplifying the negative electrode pore structure, the problem of improving adhesion to the negative electrode current collector layer, and the problem of output characteristics.

[0033] In general, it is important to increase the porosity of the negative electrode to simplify the negative electrode structure, but in the case of silicon-based negative electrodes, the porosity cannot be infinitely increased due to the problem of volume expansion, and if the porosity is increased alone, there is a problem of reduced life. Therefore, the present application is characterized in that the porosity of the upper layer is increased to improve the tortuosity of the negative electrode, and the porosity range of the lower layer is reduced to ensure life characteristics. In addition, the first negative electrode active material layer and the second negative electrode active material layer are further characterized in that the number of points at which charging and discharging can be performed is increased without significantly affecting the life characteristics of existing lithium secondary batteries, and the output characteristics are excellent at high C-rates.

[0034] 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. Specifically, a negative electrode for a lithium secondary battery 100 including a first negative electrode active material layer 20 and a second negative electrode active material layer 10 on one side of a negative electrode current collector layer 30 can be seen. Although FIG. 1 shows that the first negative electrode active material layer is formed on one side, it may be included on both sides of the negative electrode current collector layer.

[0035] The negative electrode for a lithium secondary battery of the present invention will be described in more detail below.

[0036] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, comprising: a negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on a side of the first negative electrode active material layer opposite to a side in contact with the negative electrode current collector layer.

[0037] 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 has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with surface treatment such as carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, fine irregularities can be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0038] In one 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.

[0039] However, the thickness can be variously deformed according to the type and use of the negative electrode used, and is not limited thereto.

[0040] In one embodiment of the present application, the first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material, a first negative electrode conductive material, and a first negative electrode binder, and the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder.

[0041] In one embodiment of the present application, the first negative electrode active material and the second negative electrode active material include a silicon-based active material including silicon particles having a distribution of silicon particle sizes of 0.01 μm or more and 50 μm or less, and the D50 particle size of the silicon-based active material included in the first negative electrode active material layer is smaller than or the same as the D50 particle size of the silicon-based active material included in the second negative electrode active material layer, providing a negative electrode for a lithium secondary battery.

[0042] In one embodiment of the present application, the silicon-based active material includes at least one selected from the group consisting of SiOx (0 < x < 2), SiOx (x = 0), SiC, and Si alloys, providing a negative electrode for a lithium secondary battery.

[0043] In one embodiment of the present application, the silicon-based active material includes at least one 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 SiOx (x = 0) may be included in an amount of 95 parts by weight or more.

[0044] In one embodiment of the present application, the silicon-based active material includes at least one 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 SiOx (x = 0) is included in an amount of 95 parts by weight or more, preferably 97 parts by weight or more, more preferably 99 parts by weight or more, and may be included in an amount of 100 parts by weight or less.

[0045] In one embodiment of the present application, particularly pure silicon (Si) particles may be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material can mean including pure Si particles (SiOx (x = 0)) that are not combined with other particles or elements within the above range when based on 100 parts by weight of the total silicon-based active material as described above.

[0046] In one embodiment of the present application, the silicon-based active material may consist of SiOx (x = 0).

[0047] The negative electrode for a lithium secondary battery according to the present application includes the above-described silicon-based active material in a first negative electrode active material layer and a second negative electrode active material layer, and specifically includes pure silicon particles containing 95 parts by weight or more of SiOx (x = 0). At this time, since a high content of pure silicon particles is included, the capacity characteristics are excellent, and in order to solve the problem of reduced life characteristics due to the pore structure simplification caused thereby, by including the second negative electrode active material layer according to the present invention, the above problem is solved.

[0048] On the other hand, 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 the above 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 smooth dispersion of the particles constituting the negative electrode slurry. In addition, when the size of the first negative electrode active material is equal to or greater than the above lower limit range, the contact area between the silicon particles and the conductive material is excellent due to the complex of the conductive material and the binder in the negative electrode slurry, and the conductive network is more likely to be maintained, thereby increasing the capacity retention rate. On the other hand, when the average particle size satisfies the above range, silicon particles that are too large are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the current density non-uniformity phenomenon during charging and discharging.

[0049] In particular, the negative electrode for a lithium secondary battery according to the present application satisfies that the porosity of the first negative electrode active material layer is 40% or less, and the porosity of the second negative electrode active material layer is higher than the porosity of the first negative electrode active material layer.

[0050] The porosity control affects the overall composition and content of the first and second negative electrode active material layer compositions, and is mainly influenced by the D50 particle size of the silicon-based active material contained in the first and second negative electrode active material layer compositions and the type of conductive material, etc. That is, as one method for implementing the porosity, active materials with different particle sizes can be arranged, and the particle size can be controlled by adjusting the content of the conductive material.

[0051] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, in which the silicon-based active material contained in the first negative electrode active material layer has a D50 particle size of 5 μm or less, and the silicon-based active material contained in the second negative electrode active material layer has a D50 particle size of 5 μm or more.

[0052] In still another embodiment, the D50 particle size of the silicon-based active material contained in the first negative electrode active material layer may be 5 μm or less, and may be 0.5 μm or more, preferably 1 μm or more, and more preferably 3 μm or more.

[0053] In another embodiment, the D50 particle size of the silicon-based active material contained in the second negative electrode active material layer may be in the range of 5 μm or more, preferably 6 μm or more, more preferably 7 μm or more, and 15 μm or less, preferably 10 μm or less.

[0054] In one embodiment of the present application, the first negative electrode active material layer may have a porosity of 40% or less, preferably 35% or less, and may be 10% or more, preferably 20% or more.

[0055] In one embodiment of the present application, the second negative electrode active material layer may have a porosity of 42% or more, preferably 45% or more, and may be 90% or less, preferably 80% or less.

[0056] By satisfying the above-mentioned particle size distribution and porosity ranges, the negative electrode for a lithium secondary battery according to the present application has the following characteristics: the porosity of the surface portion (second negative electrode active material layer) satisfies the above-mentioned range; the porosity of the surface portion (second negative electrode active material layer) satisfies the above-mentioned range; the porosity of the portion (first negative electrode active material layer) that comes into contact with the negative electrode current collector satisfies the above-mentioned range; and the adhesion to the negative electrode current collector layer is improved, thereby increasing the adhesion even with continued charge / discharge cycles, thereby enhancing the life characteristics.

[0057] 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~80.0m2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET surface area is measured according to DIN 66131 (using nitrogen).

[0058] In one embodiment of the present application, the silicon-based active material can be, for example, in crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or shard particles. Alternatively, but less preferably, the silicon particles may have a fibrous structure or be in the form of a silicon-containing film or coating.

[0059] In one embodiment of the present application, the silicon-based active material may have a non-spherical morphology, and the sphericity 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.

[0060] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter.

[0061] [Formula 1] 4πA / P 2

[0062] In one embodiment of the present application, the first negative electrode active material may be 80 parts by weight or less based on 100 parts by weight of the first negative electrode active material layer composition, and the second negative electrode active material may be 80 parts by weight or more based on 100 parts by weight of the second negative electrode active material layer composition.

[0063] In yet another embodiment, the first negative electrode active material may be 80 parts by weight or less, 60 parts by weight or more, preferably 65 parts by weight or more, and most preferably 70 parts by weight or more, based on 100 parts by weight of the first negative electrode active material layer composition.

[0064] In yet another embodiment, the second negative electrode active material may be 80 parts by weight or more, preferably 85 parts by weight or more, and more preferably 88 parts by weight or more, based on 100 parts by weight of the second negative electrode active material layer composition, and may be 100 parts by weight or less, preferably 95 parts by weight or less.

[0065] The first negative electrode active material layer composition and the second negative electrode active material layer composition according to the present application have the effect of improving capacity characteristics by using a silicon-based active material with extremely high capacity in the above-mentioned range, and in particular, by adjusting the range of the first negative electrode active material contained in the first negative electrode active material layer to the above-mentioned 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.

[0066] In the past, it was common to use only graphite-based compounds as negative electrode active materials, but in recent years, as the demand for high-capacity batteries has increased, attempts to mix silicon-based compounds to increase capacity have been increasing. However, silicon-based compounds have a limitation in that their volume expands rapidly during the charge / discharge process, damaging the conductive path formed in the negative electrode active material layer and reducing the performance of the battery.

[0067] In addition, when a silicon-based active material of a certain particle size is included within the above range in order to adjust the porosity range as described above, the conductive path cannot be secured due to volume expansion during charging and discharging, resulting in a decrease in output characteristics and therefore a decrease in life characteristics.

[0068] Therefore, in one embodiment of the present application, the first negative electrode conductive material includes two or more conductive materials, and the second negative electrode conductive material includes one conductive material, thereby solving the above-mentioned problems.

[0069] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the first negative electrode conductive material includes at least one selected from the group consisting of a dot-like conductive material, a linear conductive material, and a planar conductive material, and the second negative electrode conductive material includes a linear conductive material.

[0070] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the first negative electrode conductive material includes at least two selected from the group consisting of a dot-like conductive material, a linear conductive material, and a sheet-like conductive material, and the second negative electrode conductive material includes a linear conductive material.

[0071] In one embodiment of the present application, the first negative electrode conductive material includes at least two selected from the group consisting of a dot-like conductive material, a linear conductive material, and a sheet-like conductive material, and the second negative electrode conductive material may be composed of a linear conductive material.

[0072] That is, the active material layer region (first negative electrode active material layer) in contact with the negative electrode current collector of the negative electrode for a lithium secondary battery contains two or more types of conductive materials, increasing the number of points at which charging and discharging are possible and providing excellent output characteristics at a high C-rate. At the same time, the second negative electrode active material layer contains a small amount of one type of linear conductive material to ensure a conductive path and maximize the content of silicon-based active material.

[0073] In one embodiment of the present application, the first negative electrode conductive material comprises a dot-shaped conductive material, a linear conductive material, and a sheet-shaped conductive material.

[0074] In one embodiment of the present application, the first negative electrode conductive material comprises a linear conductive material and a sheet conductive material.

[0075] In one embodiment of the present application, the first negative electrode conductive material and the second negative electrode conductive material may be made of any material that can be 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.

[0076] 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 to the negative electrode and has conductivity without inducing 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 may preferably include carbon black in that it realizes high conductivity and has excellent dispersibility.

[0077] In one embodiment of the present application, the dot-shaped 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.

[0078] In one embodiment of the present application, the particle diameter 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.

[0079] 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 suppress discontinuity of the conductive path due to volume expansion, and can be expressed as a plate-type conductive material or a bulk-type conductive material.

[0080] 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 be preferably platelet graphite.

[0081] 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. If the range is satisfied, the sufficient particle size makes it easy to disperse without causing an excessive increase in viscosity of the negative electrode slurry. Therefore, when dispersing using the same equipment and time, the dispersion effect is excellent.

[0082] 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.

[0083] 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.

[0084] In one embodiment of the present application, the sheet conductive material may be a high-specific surface area sheet conductive material or a low-specific surface area sheet conductive material without any restrictions. However, the sheet conductive material in the present application may be affected to some extent by dispersion in terms of electrode performance, and it may be particularly preferable to use a low-specific surface area sheet conductive material that does not cause dispersion problems.

[0085] In one embodiment of the present application, the sheet conductive material has a BET specific surface area of ​​5 m 2 / g or more.

[0086] 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.

[0087] In another embodiment, the sheet conductive material is a high specific surface area sheet conductive material having 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.

[0088] 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.

[0089] 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 include a plurality of carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in the form of a bundle or rope in which a plurality of carbon nanotube units are arranged in a line with the longitudinal axes of the carbon nanotube units substantially aligned in the same direction or are entangled. The carbon nanotube units have a graphite sheet with a nano-sized diameter and a cylindrical shape with an sp2 bond structure. In this case, the graphite sheet may exhibit conductive or semiconductive properties depending on the angle and structure of the graphite sheet. The bundled carbon nanotubes can be uniformly dispersed during the manufacture of the negative electrode compared to entangled type carbon nanotubes, and can smoothly form a conductive network in the negative electrode, thereby improving the conductivity of the negative electrode.

[0090] In one embodiment of the present application, the first negative electrode conductive material may be present in an amount of 1 part by weight or more and 40 parts by weight or less based on 100 parts by weight of the first negative electrode active material layer composition.

[0091] In another embodiment, the first negative electrode conductive material may be 1 part by weight or more and 40 parts by weight or less, preferably 10 parts by weight or more and 30 parts by weight or less, and more preferably 15 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the first negative electrode active material layer composition.

[0092] In one embodiment of the present application, the second negative electrode conductive material may be present in an amount of 0.01 parts by weight or more and 5 parts by weight or less based on 100 parts by weight of the second negative electrode active material layer composition.

[0093] In yet another embodiment, the second negative electrode conductive material may be 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 second negative electrode active material layer composition.

[0094] In one embodiment of the present application, the first 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.

[0095] In one embodiment of the present application, the dot-shaped conductive material may be in the range 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 first negative electrode conductive material.

[0096] In one embodiment of the present application, the sheet conductive material may be in the range 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 first negative electrode conductive material.

[0097] In one embodiment of the present application, the linear conductive material may be in the range 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 first negative electrode conductive material.

[0098] In one embodiment of the present application, the first negative electrode conductive material may include a linear conductive material and a planar conductive material.

[0099] In one embodiment of the present application, the first negative electrode conductive material may include a linear conductive material and a sheet conductive material, and the ratio of the linear conductive material:sheet conductive material may satisfy 0.01:1 to 0.1:1.

[0100] In one embodiment of the present application, the first negative electrode conductive material particularly includes a linear conductive material and a planar conductive material, and by satisfying the above-mentioned composition and ratio, respectively, the battery does not have a significant effect on the life characteristics of existing lithium secondary batteries, and the number of points at which charging and discharging are possible increases, resulting in excellent output characteristics at a high C-rate.

[0101] The first and second negative electrode conductive materials according to the present application have a completely different structure from the positive electrode conductive material applied to the positive electrode. That is, the first and second negative electrode conductive materials according to the present application serve to capture the contact points between the silicon-based active materials, which have a very large volume expansion of the electrodes due to charging and discharging, and the positive electrode conductive material serves to provide some conductivity while acting as a buffer having a shock-absorbing function when rolled, and has a completely different structure and role from the negative electrode conductive material of the present invention.

[0102] In addition, the first and second negative electrode conductive materials according to the present application are applied to silicon-based active materials and have a completely different structure from conductive materials applied to graphite-based active materials. That is, the conductive material used in electrodes having graphite-based active materials has smaller particles than the active material, and therefore has the properties of improving output characteristics and imparting some electrical conductivity, and has a completely different structure and role from the first negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0103] In one embodiment of the present application, the first and second negative electrode binders 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, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen of these substances is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0104] The first and second negative electrode binders according to one embodiment of the present application serve to hold down the active material and conductive material in order to prevent twisting and structural deformation of the negative electrode structure during volume expansion and relaxation of the first and second negative electrode active materials. Any common binder can be used as long as it fulfills the above-mentioned role, and specifically, a water-based binder can be used, and more specifically, a PAM-based binder can be used.

[0105] In one embodiment of the present application, the amount of the first and second negative electrode binders is 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, based on 100 parts by weight of the first and second negative electrode active material layer compositions, and may be 5 parts by weight or more, or 10 parts by weight or more.

[0106] In particular, in the present application, the first negative electrode binder may be included in an amount of 10 parts by weight or more based on 100 parts by weight of the first negative electrode active material layer composition, and the second negative electrode binder may be included in an amount of 10 parts by weight or less based on 100 parts by weight of the second negative electrode active material layer composition.

[0107] In one embodiment of the present application, based on 100 parts by weight of the first negative electrode active material layer composition, the first negative electrode binder may be included in an amount of 10 parts by weight or more, preferably 12 parts by weight or more, more preferably 15 parts by weight or more, and may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less.

[0108] In one embodiment of the present application, based on 100 parts by weight of the second negative electrode active material layer composition, the second negative electrode binder may be included in an amount of 10 parts by weight or less, 1 part by weight or more, preferably 3 parts by weight or more, and most preferably 5 parts by weight or more.

[0109] In particular, when the content of the first negative electrode binder contained in the first negative electrode active material layer is increased to 10 parts by weight or more and the content of the second negative electrode binder is decreased to 10 parts by weight or less, the total binder content can be maintained within a certain range, and in particular, the binder content on the negative electrode current collector layer side can be increased to further strengthen the adhesive strength with the negative electrode current collector layer, thereby further improving the life characteristics of the lithium secondary battery.

[0110] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, in which an adhesive strength of a surface of the first negative electrode active material layer in contact with the negative electrode current collector layer satisfies 100 gf / 5 mm or more and 500 gf / 5 mm or less under conditions of 25° C. and normal pressure.

[0111] In still another embodiment, the adhesive strength of the surface of the first negative electrode active material layer in contact with the negative electrode current collector layer may satisfy, at 25° C. and normal pressure conditions, 100 gf / 5 mm or more and 500 gf / 5 mm or less, preferably 300 gf / 5 mm or more and 450 gf / 5 mm or less, and more preferably 350 gf / 5 mm or more and 430 gf / 5 mm or less.

[0112] In particular, in the negative electrode according to the present application, the content of the negative electrode binder in the first negative electrode active material layer composition is adjusted to a certain range or more, thereby improving the adhesive strength as described above.

[0113] In addition, even if the silicon-based active material expands and contracts repeatedly due to repeated charging and discharging of the negative electrode, the application of a negative electrode binder with a specific composition maintains the conductive network, preventing discontinuities and suppressing increases in resistance.

[0114] The adhesive strength was measured at 90° and a speed of 5 mm / s using a peel strength tester with 3M 9070 tape. Specifically, one surface of the negative electrode active material layer of the negative electrode for lithium secondary battery was attached to one surface of a slide glass (3M 9070 tape) to which an adhesive film was attached. Then, the negative electrode was attached by rolling it back and forth 5 to 10 times with a 2 kg rubber roller, and the adhesive strength (peeling strength) was measured at an angle of 90° and a speed of 5 mm / s. In this case, the adhesive strength can be measured under conditions of 25°C and normal pressure.

[0115] Specifically, the adhesive strength was measured on a 5 mm x 15 cm electrode at 25°C and normal pressure.

[0116] In one embodiment of the present application, normal pressure may mean pressure in a state where no specific pressure is applied or reduced, and may be used in the same sense as atmospheric pressure. Generally, it may be expressed as 1 atmosphere.

[0117] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the first negative electrode active material layer has a thickness of 10 μm or more and 200 μm or less, and the second negative electrode active material layer has a thickness of 10 μm or more and 100 μm or less.

[0118] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, in which the loading amount (a) of the first negative electrode active material layer composition is at least twice the loading amount (b) of the second negative electrode active material layer composition.

[0119] In another embodiment, the loading amount (a) of the first negative electrode active material layer composition may be in the range of 2.0 to 10 times, preferably 2.2 to 6 times, the loading amount (b) of the second negative electrode active material layer composition.

[0120] The loading amount may refer to the weight of a composition for forming a negative electrode active material layer, and specifically, the loading amount of a composition may have the same meaning as the loading amount of a slurry including the composition.

[0121] In one embodiment of the present application, the loading amount (a) of the first negative electrode active material layer composition is 2 mg / cm 2 More than 5mg / cm 2 Less than 2.2 mg / cm, preferably 2.2 mg / cm 2 More than 4mg / cm 2 The following ranges may be satisfied:

[0122] In one embodiment of the present application, the loading amount (b) of the second negative electrode active material layer composition is 0.5 mg / cm 2 More than 1.5mg / cm 2 Less than 0.8 mg / cm, preferably 0.8 mg / cm 2 More than 1.3mg / cm 2 The following ranges may be satisfied:

[0123] The first negative electrode active material layer composition and the second negative electrode active material layer composition have the loading amounts, so that the ratio of the active materials contained in the first negative electrode active material layer and the second negative electrode active material layer can be adjusted. That is, the amount of the first negative electrode active material contained in the first negative electrode active material layer can be adjusted to optimize the capacity characteristics, and the amount of the second negative electrode active material contained in the second negative electrode active material layer can be adjusted to suppress the surface reaction of the negative electrode without deteriorating the capacity characteristics, thereby improving the life characteristics.

[0124] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be a pre-lithiated negative electrode.

[0125] In one embodiment of the present application, there is provided 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; applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and applying a second negative electrode active material layer composition to a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer to form a second negative electrode active material layer, The present invention provides a method for producing a negative electrode for a lithium secondary battery, wherein a porosity of a material layer is 40% or less, the first negative electrode active material layer comprises a first negative electrode active material layer composition including a first negative electrode active material, a first negative electrode conductive material, and a first negative electrode binder, and the second negative electrode active material layer comprises a second negative electrode active material layer composition including a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder, wherein the first negative electrode conductive material includes two or more types of conductive materials, and the second negative electrode conductive material includes one type of conductive material.

[0126] In the method for manufacturing the negative electrode, the composition and content in each step may be the same as those described above.

[0127] In one embodiment of the present application, a step of forming a first negative electrode active material layer by coating a first negative electrode active material layer composition on one or both sides of the negative electrode current collector layer is provided.

[0128] That is, the step is a step of forming an active material layer on a negative electrode current collector layer, which may mean a step of forming an active material layer on a surface (lower layer) in contact with the current collector layer in a double layer structure.

[0129] In one embodiment of the present application, applying the first negative electrode active material layer composition includes applying and drying a first negative electrode slurry including the first negative electrode active material layer composition; and a negative electrode slurry solvent.

[0130] In this case, the solid content of the first negative electrode slurry may be in the range of 10% to 40%.

[0131] In one embodiment of the present application, forming the first negative electrode active material layer may include mixing the first negative electrode slurry; and coating the mixed first negative electrode slurry on one or both sides of the negative electrode current collector layer, and the coating may be performed using a coating method commonly used in the art.

[0132] In one embodiment of the present application, a step of forming a second negative electrode active material by coating a second negative electrode active material layer composition on a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer is provided.

[0133] That is, the step refers to a step of forming a second negative electrode active material layer on the first negative electrode active material layer, and may refer to a step of forming an active material layer on a surface (upper layer) away from a current collector layer in a double layer structure.

[0134] In one embodiment of the present application, applying the second negative electrode active material layer composition includes applying and drying a second negative electrode slurry including the second negative electrode active material layer composition; and a negative electrode slurry solvent.

[0135] In this case, the solid content of the second negative electrode slurry may be in the range of 10% to 40%.

[0136] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, wherein the forming of the second negative electrode active material layer includes: mixing the second negative electrode slurry; and coating the mixed second negative electrode slurry on a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer.

[0137] The coating may be performed using any coating method commonly used in the art.

[0138] The description of the forming of the first negative electrode active material layer may be similarly applied to the forming of the second negative electrode active material layer.

[0139] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, wherein the step of forming the second negative electrode active material layer on the first negative electrode active material layer includes a wet on dry process or a wet on wet process.

[0140] In one embodiment of the present application, the wet-on-dry process may refer to a process of applying a first negative electrode active material layer composition, completely drying the composition, and applying a second negative electrode active material layer composition thereon, and the wet-on-wet process refers to a process of applying a first negative electrode active material layer composition, without drying the composition, and applying a second negative electrode active material layer composition thereon.

[0141] In particular, the wet on dry process involves coating a first negative electrode active material layer composition, completely drying it, and then coating a second negative electrode active material layer composition on top of it, and through this process, the first negative electrode active material layer and the second negative electrode active material layer can have a clear boundary, which allows the compositions contained in the first negative electrode active material layer and the second negative electrode active material layer to be formed as a double layer without being mixed.

[0142] In one embodiment of the present application, the negative electrode slurry solvent may be used without limitation as long as it can dissolve the first negative electrode active material layer composition and the second negative electrode active material layer composition, and specifically, water or NMP may be used.

[0143] In one embodiment of the present application, there is provided a method for manufacturing a negative electrode for a lithium secondary battery, the method including a step of pre-lithiating a negative electrode in which a first negative electrode active material layer and a second negative electrode active material layer are formed on the negative electrode current collector, the step of pre-lithiating the negative electrode including a lithium electrolytic plating process; a lithium metal transfer process; a lithium metal deposition process; or a stabilized lithium metal powder (SLMP) coating process.

[0144] 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 provided between the positive electrode and the negative electrode; and an electrolyte.

[0145] A secondary battery according to an embodiment of the present specification may include the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator and an electrolyte interposed between the positive electrode and the negative electrode, and the negative electrode is the same as the negative electrode described above. The negative electrode has been described above, so a detailed description thereof will be omitted.

[0146] 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.

[0147] In the positive electrode, the positive electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has conductivity, and for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can usually have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to increase the adhesive force of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0148] 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), 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, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 Mc2 O2 (wherein 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); 2-c3 M c3 Examples of the lithium manganese composite oxide include, but are not limited to, lithium manganese composite oxide represented by Li2Mn3MO8 (wherein 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 (wherein 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 replaced with an alkaline earth metal ion. The positive electrode may be Li metal.

[0149] 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.

[0150] 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 has electronic conductivity without causing chemical changes in the battery that is constructed.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; or conductive polymers such as polyphenylene derivatives, and the like, and one or more of these may be used alone or in mixture.

[0151] The positive electrode binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesive strength 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, or various copolymers thereof, and one or more of these may be used alone or in combination.

[0152] The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator that is generally used in secondary batteries can be used without any particular restrictions. In particular, a separator that has low resistance to ion movement of the electrolyte and excellent electrolyte humidification ability is preferred. Specifically, a porous polymer film, for example, 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, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymeric substance may be used to ensure heat resistance or mechanical strength, and may be selectively used in a single layer or multilayer structure.

[0153] 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 the manufacture of lithium secondary batteries, but are not limited to these.

[0154] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0155] Examples of the non-aqueous organic solvent include aprotic 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, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0156] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, are preferably used because they are high-viscosity organic solvents with high dielectric constants and good dissociation of 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 produced, and therefore these can be used more preferably.

[0157] The metal salt may 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 may 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:

[0158] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, and aluminum trichloride for the purposes of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0159] 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 the battery pack include the secondary battery having high capacity, high rate-limiting characteristics, and high 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.

[0160] Below, preferred examples are presented to aid in understanding the present invention. However, these examples are intended to illustrate the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical ideas of the present description. Naturally, such changes and modifications fall within the scope of the appended claims.

[0161] <Example> <Production of negative electrodes> Example 1: Preparation of negative electrode Preparation of the first negative electrode active material layer A first negative electrode active material layer composition was prepared by mixing silicon-based active material Si (average particle size (D50): 5 μm), first conductive material, second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10. The first negative electrode slurry was prepared by adding the mixture to distilled water as a solvent for forming a negative electrode slurry (solid concentration 25 wt%).

[0162] The first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material is SWCNT.

[0163] The mixing method was as follows: the first conductive material, the second conductive material, the binder and the water were dispersed using a homomixer at 2500 rpm for 30 minutes, the active material was then added, and the mixture was dispersed at 2500 rpm for 30 minutes to prepare a slurry.

[0164] The first negative electrode slurry was applied at 2.75 mg / cm on both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector. 2 The coated layer was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a first negative electrode active material layer (thickness: 33 μm) (porosity: 35%).

[0165] Preparation of second negative electrode active material layer A second negative electrode active material layer composition was prepared by mixing silicon-based active material Si (average particle size (D50): 5 μm), SWCNT, and binder polyacrylamide in a weight ratio of 89:1:10. The second negative electrode slurry was prepared by adding the mixture to distilled water as a solvent for forming a negative electrode slurry (solid concentration 25 wt%).

[0166] The mixing method was as follows: the SWCNTs, binder and water were dispersed using a homomixer at 2500 rpm for 30 minutes, the active material was then added, and the mixture was dispersed at 2500 rpm for 30 minutes to prepare a slurry.

[0167] The second negative electrode slurry was applied to the first negative electrode active material layer at a concentration of 1 mg / cm. 2 The coated layer was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a second negative electrode active material layer (thickness: 15 μm) (porosity: 45%).

[0168] As a result, a negative electrode was produced in which a first negative electrode active material layer and a second negative electrode active material layer were laminated in this order on a negative electrode current collector layer.

[0169] A negative electrode was prepared in the same manner as in Example 1, except that the composition and content were changed as shown in Table 1 below. In Table 1 below, the third conductive material was carbon black C (specific surface area: 58 m 2 / g, average particle size (D50): 37 nm).

[0170] [Table 1]

[0171] <Secondary battery manufacturing> LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2O2 (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 a positive electrode slurry to prepare a positive electrode slurry (solid concentration 78 wt%).

[0172] The positive electrode current collector was an aluminum current collector (thickness: 12 μm) and the positive electrode slurry was applied to both sides at 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 of positive electrode: 77 μm, porosity: 26%).

[0173] An electrolyte was injected between the positive electrode and the negative electrode of Example 1 via a polyethylene separator to prepare a secondary battery.

[0174] The electrolyte was prepared by adding 3% by weight of vinylene carbonate based on the total weight of the electrolyte to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) were mixed in a volume ratio of 10:90, and LiPF6 was added as a lithium salt at a concentration of 1M.

[0175] Monocells were prepared in the same manner as above, except that the negative electrodes of the Examples and Comparative Examples were used, and the life characteristics were evaluated in the range of 4.2-3.0V.

[0176] Experimental example 1: Life characteristic evaluation The secondary batteries including the negative electrodes prepared in the Examples and Comparative Examples were subjected to a life evaluation using an electrochemical charger / discharger to evaluate the capacity retention rate. The secondary batteries were subjected to a cycle test at 4.2-3.0 V, 1 C / 0.5 C, and the number of cycles at which the capacity retention rate reached 80% was measured.

[0177] Capacity retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at 1st cycle)} X100

[0178] The results are shown in Table 2 below.

[0179] Experimental example 2: Resistance increase rate measurement evaluation In the test of Experimental Example 1, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles, and then the resistance was measured by discharging at 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0180] For the resistance increase rate measurement evaluation, data at 250 cycles was calculated, and the results are shown in Table 2 below.

[0181] [Table 2]

[0182] According to one embodiment of the present invention, a negative electrode for a lithium secondary battery has a double layer structure, and satisfies that a porosity of a first negative electrode active material layer is 40% or less, and a porosity of a second negative electrode active material layer is higher than that of the first negative electrode active material layer.

[0183] As can be seen from Example 1 in Table 2, by forming the negative electrode in a double layer, the porosity of the first negative electrode active material layer in contact with the negative electrode current collector layer can be reduced within a certain range to increase the number of contact points with the negative electrode current collector layer, improving adhesion and enhancing life characteristics, and the porosity of the second negative electrode active material layer can be increased within a certain range to improve the tortuosity of the negative electrode, improving the diffusion resistance. In particular, by adjusting the porosity of the first and second layers in a lithium secondary battery as described above and incorporating a specific conductive material into the first and second layers, it was confirmed that the battery has the characteristics of having many points where charging and discharging are possible and excellent output characteristics at a high C rate without significantly affecting the life characteristics of existing lithium secondary batteries.

[0184] Incidentally, it was confirmed that in Examples 1 and 2, while maintaining the adhesive strength between the active material and the negative electrode current collector layer, the porosity of the surface portion that initially reacts with lithium is increased, improving the diffusion characteristics, and the resistance increase rate and life characteristics are improved.

[0185] In Examples 3 and 4, the diffusion characteristics were improved by applying large particle Si to the second negative electrode active material layer, but the volume expansion was somewhat large and the performance was inferior to Examples 1 and 2. However, even in this case, superior characteristics were shown compared to Comparative Examples 1 to 5.

[0186] Example 5 contains only dot-shaped conductive material, unlike Examples 1 to 4 and 6. Generally, silicon-based active materials are harder than conductive materials, and when SWCNTs are used, the conductive material content can be reduced compared to dot-shaped or planar conductive materials, which increases the silicon content and allows gentle rolling, making it easier to adjust the porosity range.

[0187] In addition, in the case of Examples 6 and 7, in addition to the characteristics of the present invention, the binder content was adjusted, i.e., the binder content in the first negative electrode active material layer was increased and the binder content in the second negative electrode active material layer was decreased, thereby preventing the detachment phenomenon and significantly improving the life performance.

[0188] In Comparative Examples 1 and 2, the adhesion between the active material and the current collector was somewhat poor, the diffusion characteristics of the surface portion were poor, and the resistance increased as the cycles proceeded, resulting in poorer life characteristics than in Examples. In particular, in the case of Comparative Example 5, it was confirmed that the contact with the negative electrode current collector layer was very poor, the initial resistance increased significantly, and cycle drop progressed rapidly. [Explanation of symbols]

[0189] 10...Second negative electrode active material layer 20...first negative electrode active material layer 30 Negative electrode current collector layer

Claims

1. Negative electrode current collector layer; a first negative electrode active material layer provided on one or both sides of the negative electrode current collector layer; and a second negative electrode active material layer provided on a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer; A negative electrode for a lithium secondary battery comprising: The first negative electrode active material layer has a porosity of 40% or less, the porosity of the second negative electrode active material layer is higher than the porosity of the first negative electrode active material layer, the first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material; a first negative electrode conductive material; and a first negative electrode binder; the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material; a second negative electrode conductive material; and a second negative electrode binder; The first negative electrode conductive material includes two or more conductive materials, The second negative electrode conductive material comprises one conductive material.

2. the first negative electrode active material and the second negative electrode active material each include a silicon-based active material containing silicon particles having a particle size distribution of 0.01 μm or more and 50 μm or less; 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the D50 particle size of the silicon-based active material contained in the first negative electrode active material layer is smaller than or equal to the D50 particle size of the silicon-based active material contained in the second negative electrode active material layer.

3. the silicon-based active material contained in the first negative electrode active material layer has a D50 particle size of 5 μm or less; 3. The negative electrode for a lithium secondary battery according to claim 2, wherein the silicon-based active material contained in the second negative electrode active material layer has a D50 particle size of 5 μm or more.

4. 3. The negative electrode for a lithium secondary battery according to claim 2, wherein the silicon-based active material comprises at least one selected from the group consisting of SiOx (0<x<2), SiOx (x=0), SiC, and a Si alloy.

5. 5. The negative electrode for a lithium secondary battery according to claim 4, wherein the silicon-based active material includes at least one selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and the silicon-based active material includes 95 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

6. The first negative electrode active material is 80 parts by weight or less based on 100 parts by weight of the first negative electrode active material layer composition, 2 . The negative electrode of claim 1 , wherein the second negative electrode active material is 80 parts by weight or more based on 100 parts by weight of the second negative electrode active material layer composition.

7. The first negative electrode conductive material includes at least one selected from the group consisting of a dot-shaped conductive material, a linear conductive material, and a sheet-shaped conductive material, The negative electrode for a lithium secondary battery according to claim 1 , wherein the second negative electrode conductive material comprises a linear conductive material.

8. The thickness of the first negative electrode active material layer is 10 μm or more and 200 μm or less, 2 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the second negative electrode active material layer has a thickness of 10 μm or more and 100 μm or less.

9. 2 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the loading amount (a) of the first negative electrode active material layer composition is at least twice as large as the loading amount (b) of the second negative electrode active material layer composition.

10. Providing a negative electrode current collector layer; applying a first negative electrode active material layer composition to one or both surfaces of the negative electrode current collector layer to form a first negative electrode active material layer; and forming a second negative electrode active material layer by applying a second negative electrode active material composition to a surface of the first negative electrode active material layer opposite to a surface in contact with the negative electrode current collector layer; A method for producing a negative electrode for a lithium secondary battery, comprising: The first negative electrode active material layer has a porosity of 40% or less, the porosity of the second negative electrode active material layer is higher than the porosity of the first negative electrode active material layer, the first negative electrode active material layer includes a first negative electrode active material layer composition including a first negative electrode active material; a first negative electrode conductive material; and a first negative electrode binder; the second negative electrode active material layer includes a second negative electrode active material layer composition including a second negative electrode active material; a second negative electrode conductive material; and a second negative electrode binder; The first negative electrode conductive material includes two or more conductive materials, the second negative electrode conductive material comprises one conductive material.

11. 11. The method of claim 10, wherein the forming of the second negative electrode active material layer on the first negative electrode active material layer comprises a wet on dry process or a wet on wet process.

12. Positive electrode; The negative electrode for a lithium secondary battery according to any one of claims 1 to 9; A separator disposed between the positive electrode and the negative electrode; and Electrolyte; A lithium secondary battery comprising:

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