Anode composition, anode for lithium secondary battery including the same, and lithium secondary battery including the anode

Abstract

The present application relates to a negative electrode composition, 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. 10-2022-0113646, filed with the Korean Intellectual Property Office on September 7, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, 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 as part of this, the most actively researched field is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that uses 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 increase, the demand for secondary batteries as energy sources 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 released from the positive electrode. Silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, with the recent demand for high-density energy batteries, active research is being conducted into methods of increasing capacity using silicon-based compounds such as Si / C and SiOx as anode active materials, which have a capacity more than 10 times greater than that of graphite-based materials.However, while silicon-based compounds, which are high-capacity materials, have a higher capacity than conventionally used graphite, they suffer from the problem of rapid volume expansion during charging, which breaks the conductive path and reduces battery performance.

[0008] Therefore, in order to solve the problems associated with using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as methods for controlling the driving potential, methods for additionally coating a thin film on the active material layer, methods for suppressing volume expansion itself, such as methods for controlling the particle size of the silicon-based compound, or methods for preventing the conductive path from being broken. However, these methods have limitations in their application because they may actually degrade battery performance, and there are still limitations in the commercialization of negative electrode batteries with a high content of silicon-based compounds.

[0009] Therefore, in the process of preparing a silicon-based anode to maximize capacity characteristics, research is needed into anode compositions that can prevent the volume expansion, destruction of conductive paths, and surface cracking that occur during charging and discharging. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0011] Silicon-based negative electrodes use negative electrode binders to suppress volume expansion due to charging and discharging, and various types of negative electrode conductive materials are used to maintain the conductive path, but the problems of volume expansion due to charging and discharging and life characteristics have yet to be solved.

[0012] As a result of research to improve the above problems, it has been found that when a conductive material having a certain composition is included as the conductive material and the content of the binder is adjusted, it can be controlled.

[0013] Therefore, the present application relates to a negative electrode composition capable of solving the above problems, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Means for Solving the Problems

[0014] One embodiment of the present specification is a negative electrode composition including a silicon-based active material; a linear conductive material; and a negative electrode binder, wherein the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and includes 90 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material, the linear conductive material includes SWCNT; and MWCNT, includes 80 parts by weight or more and 95 parts by weight or less of the silicon-based active material based on 100 parts by weight of the negative electrode composition, and includes 3 parts by weight or more and 10 parts by weight or less of the negative electrode binder based on 100 parts by weight of the silicon-based active material.

[0015] Another embodiment provides a negative electrode for a lithium secondary battery, including a negative electrode current collector layer; and a negative electrode active material layer including the negative electrode composition according to the present application formed on one or both surfaces of the negative electrode current collector layer.

[0016] Finally, a lithium secondary battery is provided, 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.

Advantages of the Invention

[0017] The negative electrode composition according to the present application solves the above-mentioned problem by including a silicon-based active material and a linear conductive material to increase the capacity of the negative electrode. Specifically, it uses MWCNTs, which can form a short-range conductive network, and SWCNTs, which can increase the long-range conductive network and the rigidity of the binder. The conductive material satisfying the above composition increases the proportion of active material in the negative electrode composition and increases the solid content of the negative electrode slurry, thereby improving the performance of the cell itself.

[0018] In addition, in order to ensure the conductive network as described above and to prevent problems caused by the volume expansion of the silicon-based active material, a certain amount of binder is contained based on the silicon-based active material.

[0019] That is, the negative electrode composition according to the present invention is characterized in that, in a negative electrode that uses a silicon-based active material to maximize capacity, the ratio of the silicon-based active material contained therein is specified, and the weight part of the negative electrode binder that can effectively suppress volume expansion and relaxation according to the ratio, and the composition of the linear conductive material that can ensure a conductive network and suppress rigidity are optimized.

[0020] A primary object of the present invention is to maintain the advantages of using a silicon-based active material when a negative electrode composition having the above-described composition and content is applied to a negative electrode, while resolving problems such as reduced life characteristics and disconnection of the conductive network. [Brief explanation 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. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[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 otherwise specified.

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

[0026] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point of the cumulative particle number distribution corresponding to the particle size. That is, D50 is the particle size (median particle size) at the 50% point of the cumulative particle number distribution corresponding to the particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution corresponding to the particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution corresponding to the particle size. Meanwhile, the median particle size 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 particle size distribution is calculated by measuring the difference in diffraction patterns corresponding to the particle size when the particles pass through a laser beam.

[0027] In one embodiment of the present application, the particle size or particle size may refer to the average diameter or typical diameter of individual grains that make up the particle.

[0028] In this specification, 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. In this specification, when it is said that a polymer contains a monomer, this is interpreted in the same way as the polymer containing the monomer as a monomer unit.

[0029] In this specification, unless otherwise specified, the term "polymer" is understood to be used in a broad sense including copolymers.

[0030] In this specification, the weight-average molecular weight (Mw) and the number-average molecular weight (Mn) are the polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using various degrees of polymerization of monodisperse polystyrene polymers (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, unless otherwise specified, the molecular weight means the weight-average molecular weight.

[0031] Hereinafter, a detailed description will be given with reference to the drawings so that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention may be realized in various different forms and is not limited to the following description.

[0032] One embodiment of this specification provides a negative electrode composition containing a silicon-based active material; a linear conductive material; and a negative electrode binder, wherein the silicon-based active material contains one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), contains 90 parts by weight or more of SiOx (x = 0) based on 100 parts by weight of the silicon-based active material, the linear conductive material contains SWCNT; and MWCNT, contains 80 parts by weight or more and 95 parts by weight or less of the silicon-based active material based on 100 parts by weight of the negative electrode composition, and contains 3 parts by weight or more and 10 parts by weight or less of the negative electrode binder based on 100 parts by weight of the silicon-based active material.

[0033] In the case of the negative electrode composition according to the present application, in a negative electrode applying a silicon-based active material to maximize the capacity, the ratio of the silicon-based active material contained is specified, and the weight part of the negative electrode binder capable of effectively suppressing the volume expansion and relaxation in accordance with the ratio, and the composition of the linear conductive material capable of suppressing the securing and rigidity of the conductive network are optimized as the main features.

[0034] Hereinafter, the negative electrode composition according to the present application will be described in detail.

[0035] In one embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 <x <2), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be contained in an amount of 90 parts by weight or more.

[0036] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be contained in an amount of 90 parts by weight or more, preferably 92 parts by weight or more, more preferably 93 parts by weight or more, and may be contained in an amount of 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0037] In one embodiment of the present application, the silicon-based active material may be SiOx (x = 0).

[0038] In one embodiment of the present application, particularly pure silicon (Si) may be used as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material means that, as described above, when based on 100 parts by weight of the entire silicon-based active material, it may mean containing pure Si particles (SiOx (x = 0)) not bonded to other particles or elements within the above range.

[0039] In one embodiment of the present application, the crystal grain size of the silicon-based active material may be 200 nm or less.

[0040] In another embodiment, the crystal grain size of the silicon-based active material may be 200 nm or less, preferably 130 nm or less, more preferably 110 nm or less, even more preferably 100 nm or less, specifically 95 nm or less, more specifically 91 nm or less. The crystal grain size of the silicon-based active material may be 10 nm or more, preferably 15 nm or more.

[0041] The silicon-based active material has the above-described crystal grain size, and the crystal grain size of the silicon-based active material can be adjusted by changing the process conditions during the manufacturing process. By satisfying the above-described range, the crystal grain boundaries are widely distributed, allowing lithium ions to be uniformly inserted during lithium ion insertion, reducing the stress exerted on silicon particles during lithium ion insertion and thereby mitigating particle cracking. As a result, the negative electrode has the characteristic of improving its life stability. If the crystal grain size exceeds the above-described range, the crystal grain boundaries within the particles are narrowly distributed, causing lithium ions to be non-uniformly inserted within the particles, resulting in increased stress due to ion insertion and particle cracking.

[0042] In one embodiment of the present application, the silicon-based active material may include a crystalline structure having a crystal grain distribution of 1 nm or more and 200 nm or less, and the area ratio of the crystalline structure may be 5% or less based on the total area of ​​the silicon-based active material.

[0043] In another embodiment, the area ratio of the crystalline texture may be 5% or less, 3% or less, or 0.1% or more, based on the total area of ​​the silicon-based active material.

[0044] That is, the silicon-based active material according to the present application has a crystal grain size of 200 nm or less, and the size of each crystal structure is small, so that the above-mentioned area ratio can be satisfied, and thus the distribution of the grain boundaries can be widened, thereby achieving the above-mentioned effects.

[0045] In one embodiment of the present application, the silicon-based active material may contain 20 or more crystalline structures.

[0046] In another embodiment, the number of crystalline structures contained in the silicon-based active material may be 20 or more, 30 or more, or 35 or more, and may satisfy the range of 60 or less, or 50 or less.

[0047] That is, as described above, when the crystal grain size of the silicon-based active material satisfies the above range and the number of crystalline structures satisfies the above range, the strength of the silicon-based active material itself will have an appropriate range, and when contained in an electrode, flexibility can be imparted and volume expansion can be efficiently suppressed.

[0048] In this application, the term "crystal grain" refers to a collection of irregularly shaped crystal particles of microscopic size in a metal or material, and the term "crystal grain size" may refer to the diameter of the observed crystal grain. That is, in this application, the term "crystal grain size" refers to the size of a domain that shares the same crystal orientation within a particle, and is a different concept from the grain size or particle size, which represent the size of a substance.

[0049] In one embodiment of the present application, the crystal grain size can be calculated from the FWHM (Full Width at Half Maximum) value by XRD analysis. The remaining values ​​except for L are measured by XRD analysis of the silicon-based active material, and the crystal grain size can be measured according to the Debye-Scherrer equation, since FWHM and crystal grain size are inversely proportional to each other. In this case, the Debye-Scherrer equation is as shown in the following equation 1-1.

[0050] [Formula 1-1] FWHM=Kλ / LCosθ

[0051] In the formula 1-1, L is the crystal grain size, K is a constant, θ is the Bragg angle, and λ is the wavelength of the X-ray.

[0052] Furthermore, the crystal grains have various shapes and can be measured three-dimensionally. Generally, the crystal grain size can be measured by the commonly used circle method or diameter measurement method, but is not limited thereto.

[0053] The diameter measurement method involves drawing 5 to 10 equilibrium lines, each with a length of L mm, on a micrograph of the target particle, counting the number of crystal grains z on the lines, and averaging them. Only those grains that fit completely are counted, and those that do not fit are excluded. If the number of lines is P and the magnification is V, the average grain size can be calculated using the following formula 1-2.

[0054] [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(μm)

[0055] The circle method is a method in which a circle of a specified diameter is drawn on a micrograph of the target particle, and then the average area of ​​the crystal grains is calculated from the number of crystal grains that fit within the circle and the number of crystal grains that cross the boundary line, and can be calculated using the following formula 1-3.

[0056] [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)V 2 )(μm 2 )

[0057] In the above formulas 1-3, Fm is the average particle area, Fk is the measured area on the photograph, z is the number of particles that fit within the circle, n is the number of particles that span the arc, and V is the magnification of the microscope.

[0058] In one embodiment of the present application, the silicon-based active material has a surface area of ​​0.25 m 2 / g or more.

[0059] In another embodiment, the silicon-based active material has a surface area of ​​0.25 m 2 / g or more, preferably 0.28m 2 / g or more, more preferably 0.30m 2 / g or more, specifically 0.31m 2 / g or more, more specifically 0.32m 2 The silicon-based active material may have a surface area of ​​3 m / g or more. 2 / g or less, preferably 2.5m 2 / g or less, more preferably 2.2m 2 The surface area can be measured according to DIN 66131 (using nitrogen).

[0060] The silicon-based active material has the above surface area, and the size of the surface area of ​​the silicon-based active material can be adjusted by changing the process conditions in the manufacturing process and the growth conditions of the silicon-based active material. That is, when the silicon-based active material is manufactured by the manufacturing method of the present application, the rough surface has a larger surface area than particles having the same particle size, and in this case, by satisfying the above range, the bonding strength with the binder is increased, thereby having the characteristic of being able to mitigate cracks in the electrode due to repeated charge-discharge cycles.

[0061] Furthermore, lithium ions are uniformly inserted during lithium ion insertion, reducing the stress applied to silicon particles during lithium ion insertion, thereby mitigating particle cracking. As a result, the negative electrode has the advantage of improving its life stability. If the surface area is less than the above range, even with the same particle size, the surface will be smooth, reducing the binding strength with the binder and causing cracks in the electrode. In this case, lithium ions will be non-uniformly inserted into the particles, resulting in greater stress due to ion insertion and particle cracking.

[0062] In one embodiment of the present application, the silicon-based active material satisfies the range of the following formula 2-1.

[0063] [Formula 2-1] X1 / Y1≦0.960

[0064] In the formula 2-1, X1 is the actual area of ​​the silicon-based active material, Y1 means the area of ​​a spherical particle of the silicon-based active material having the same perimeter.

[0065] The formula 2-1 can be measured using a particle analyzer. Specifically, the silicon-based active material according to the present application is scattered onto a glass plate by air injection, and then a shadow image of the scattered silicon-based active material particles is taken, and the shapes of 10,000 silicon-based active material particles in the image are measured. In this case, the formula 2-1 is a value representing the average for 10,000 particles. The formula 2-1 according to the present application can be measured from the image, and the formula 2-1 can be expressed as the sphericity of the silicon-based active material. The sphericity can be calculated using the formula [4π * actual area of ​​silicon-based active material / (boundary)]. 2 ] can also be expressed as

[0066] In one embodiment of the present application, the sphericity of the silicon-based active material may be, for example, 0.960 or less, for example, 0.957 or less, or 0.8 or more, for example, 0.9 or more, specifically 0.93 or more, more specifically 0.94 or more, for example, 0.941 or more.

[0067] In one embodiment of the present application, the silicon-based active material satisfies the range of the following formula 2-2.

[0068] [Formula 2-2] X2 / Y2≦0.995

[0069] In the formula 2-2, Y2 is the actual perimeter of the silicon-based active material, X2 is the perimeter of the circumscribing figure of the silicon-based active material.

[0070] The formula 2-2 can be measured using a particle analyzer. Specifically, the silicon-based active material according to the present application is scattered onto a glass plate by air injection, and then a shadow image of the scattered silicon-based active material particles is taken. The shapes of 10,000 silicon-based active material particles in the image can be measured. In this case, the formula 2-2 represents an average value for 10,000 particles. The formula 2-2 according to the present application can be measured from the image, and the formula 2-2 can be expressed as the convexity of the silicon-based active material.

[0071] In one embodiment of the present application, the range of X2 / Y2≦0.996, preferably X2 / Y2≦0.995, may be satisfied, or the range of 0.8≦X2 / Y2, preferably 0.9≦X2 / Y2, more preferably 0.95≦X2 / Y2, specifically 0.98≦X2 / Y2 may be satisfied.

[0072] The smaller the value of the formula 2-1 or 2-2, the greater the roughness of the silicon-based active material. When a silicon-based active material having such a range is used, the bonding strength with the binder increases, thereby providing the characteristic that cracks in the electrode due to repeated charge-discharge cycles can be alleviated.

[0073] In one embodiment of the present application, the silicon-based active material may contain silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less.

[0074] The silicon-based active material containing silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less means that the silicon-based active material contains a plurality of individual silicon-based particles having particle sizes within the range, and the number of silicon-based particles contained is not limited.

[0075] The particle size of the silicon-based particles may be expressed as their diameter if they are spherical. However, even if the particles are not spherical but have other shapes, the particle size can be measured in comparison with the spherical shape, and the particle size of each silicon-based particle can be measured by a method generally used in the art.

[0076] Meanwhile, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size is within this range, the specific surface area of ​​the particles falls 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 silicon-based active material is equal to or greater than the lower limit of the range, the composite of the conductive material and the binder in the negative electrode slurry provides an excellent contact area between the silicon particles and the conductive material, increasing the likelihood of maintaining a conductive network and improving capacity retention. On the other hand, 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 one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 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 specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0078] In one embodiment of the present application, the silicon-based active material may be, for example, in crystalline or amorphous form, and is preferably non-porous.The silicon particles are preferably spherical or shard particles.Alternatively, but less advantageously, the silicon particles may also have a fibrous structure or be in the form of a silicon-containing film or coating.

[0079] In one embodiment of the present application, the silicon-based active material may be included in an amount of 80 parts by weight to 95 parts by weight based on 100 parts by weight of the negative electrode composition.

[0080] In another embodiment, the silicon-based active material may be included in an amount of 80 parts by weight or more, preferably 83 parts by weight or more, more preferably 85 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 95 parts by weight or less, preferably 93 parts by weight or less, more preferably 91 parts by weight or less.

[0081] The negative electrode composition according to the present application uses a silicon-based active material with a significantly high capacity within the above-mentioned range. That is, if the amount exceeds the above-mentioned range, the life characteristics cannot be ensured even when using the combination of the linear conductive material and binder of the present invention, and the cell performance evaluation results in poor results. On the other hand, if the amount is less than the above-mentioned range, although the life characteristics can be ensured, the capacity characteristics and energy density are significantly reduced, and when a negative electrode with the same capacity is produced, the thickness of the active material layer increases and the fast charging performance also deteriorates.

[0082] The present application uses a silicon-based active material in the above range that can control volume expansion and maximize capacity characteristics, and is characterized by optimizing the contents of the linear conductive material and binder described below.

[0083] The battery contains a certain amount of specific carbonaceous materials that can suppress the volume expansion rate during charging and discharging and do not cause any problems with capacity characteristics, resulting in high capacity characteristics and improved electrode life characteristics.

[0084] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, 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.

[0085] In this application, the circularity is determined by the following formula 1, where A is the area and P is the perimeter.

[0086] [Formula 1] 4πA / P 2

[0087] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into batteries to increase capacity have been increasing in recent years as demand for high-capacity batteries has grown. However, even if the properties of silicon-based active materials are partially adjusted as described above, their volume can rapidly expand during charge / discharge processes, potentially damaging the conductive paths formed in the negative electrode active material layer.

[0088] Therefore, in one embodiment of the present application, the negative electrode conductive material includes a linear conductive material, and the linear conductive material may include SWCNTs and MWCNTs.

[0089] Generally, conventional silicon-based negative electrodes may contain both dot-shaped conductive materials and sheet-shaped conductive materials, but the conductive materials of the present application are characterized by containing only linear conductive materials, and the linear conductive materials include SWCNTs and MWCNTs.

[0090] The dot-like conductive material can be used to improve the conductivity of the negative electrode, and refers to a spherical or dot-like conductive material that does not undergo chemical changes and has conductivity. 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 achieves high conductivity and excellent dispersibility.

[0091] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and can also prevent the conductive path from being broken due to volume expansion, and can be referred to as a plate-like conductive material or a bulk-like conductive material. The sheet-like conductive material may include at least one selected from the group consisting of plate-like graphite, graphene, graphene oxide, and graphite flakes, and is preferably plate-like graphite.

[0092] First, when carbon black is used as a dot-like conductive material in a silicon-based anode, it has the advantage of being inexpensive in terms of processing cost, but to fulfill its function, it must be included in a high proportion in the anode composition. The need to use such a high proportion of dot-like conductive material has led to the problem of gas generation at high temperatures, which reduces the stability of the anode.

[0093] In addition, plate-shaped graphite, which is used as a sheet-type conductive material, is reasonably priced, has suitable rigidity, and is soft enough to act as a buffer when rolling a silicon-based negative electrode. It also has a high specific surface area, which allows it to form a conductive network between active materials. However, since a sheet-type conductive material must be contained in a certain amount relative to the silicon-based active material used, there are limitations on the amount of silicon-based active material that can be contained in the negative electrode active material, despite the above-mentioned properties. As a result, there is a problem in that it is not possible to maximize capacity characteristics.

[0094] Furthermore, there have been attempts to solve certain problems by appropriately combining the aforementioned point-like conductive materials and sheet-like conductive materials, but the above-mentioned problems of point-like conductive materials and sheet-like conductive materials have still not been solved.

[0095] However, the negative electrode conductive material according to the present application is characterized in that it contains only linear conductive materials, and in particular, the linear conductive materials contain SWCNTs and MWCNTs.

[0096] In the present application, the SWCNTs have a specific surface area of ​​900 m2 / g~1500m 2 / g and the mean diameter may be 50 nm or more and 450 nm or less.

[0097] In one embodiment of the present application, the SWCNTs may have a mean diameter of 50 nm or more and 450 nm or less, a length of 5 μm or more and 20 μm or less, and an average aspect ratio of 15 to 100.

[0098] SWCNTs are long and have a high specific surface area, making them ideal for forming a conductive network between silicon-based active materials. However, they are very expensive, and if too much SWCNT is used, the stiffness decreases due to the inclusion of the SWCNT dispersant.

[0099] In the present application, the MWCNTs have a specific surface area of ​​100 m 2 / g~500m 2 / g and the mean diameter may be 10 nm or more and 20 nm or less.

[0100] In the present application, the MWCNTs may have a mean diameter of 10 nm or more and 20 nm or less, a length of 300 nm or more and 1000 nm or less, and an average aspect ratio of 15 to 100.

[0101] Although MWCNTs have a smaller specific surface area and are shorter in length than SWCNTs, they are superior in performance to the point-like conductive materials and sheet-like conductive materials.

[0102] In this application, SWCNTs have a high specific surface area and a large aspect ratio, while MWCNTs are used in a bundled form and are located on the surface of the silicon-based active material, making it difficult to connect the active material layers. That is, SWCNTs are used for long-distance connections, while MWCNTs are used for mixing with the particle surface and binder composite.

[0103] In one embodiment of the present application, there is provided a negative electrode composition in which the linear conductive material is contained in an amount of 0.5 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

[0104] In another embodiment, the linear conductive material may be contained in an amount of 0.5 parts by weight or more and 10 parts by weight or less, preferably 0.6 parts by weight or more and 8 parts by weight or less, and more preferably 0.6 parts by weight or more and 7 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

[0105] In one embodiment of the present application, the negative electrode conductive material includes a linear conductive material and satisfies the above-mentioned composition and ratio, which does not significantly affect the life characteristics of conventional lithium secondary batteries, increases the number of points at which charging and discharging are possible, and provides the characteristics of excellent output characteristics at a high C-rate.

[0106] In one embodiment of the present application, the MWCNT may be 0.3 parts by weight or more and 6 parts by weight or less, and the SWCNT may be 0.1 parts by weight or more and 1.5 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

[0107] In another embodiment, the MWCNT may be 0.3 parts by weight or more and 6 parts by weight or less, preferably 1.0 parts by weight or more and 5.5 parts by weight or less, and more preferably 2.0 parts by weight or more and 3.5 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

[0108] In another embodiment, the SWCNTs may be present in an amount of 0.3 parts by weight or more and 1.5 parts by weight or less, preferably 0.5 parts by weight or more and 1.0 part by weight or less, based on 100 parts by weight of the silicon-based active material.

[0109] That is, in the case of the linear conductive material according to the present application, SWCNT is not used alone, but rather, in order to solve the above-mentioned problems of cost and rigidity, MWCNT, which is an inferior material to SWCNT, is also included in the conductive network in the above-mentioned parts by weight. That is, by adjusting the parts by weight of the linear conductive material as described above and adjusting the ratio of SWCNT to MWCNT therein, it has been confirmed through research that it is advantageous in terms of cost and can exhibit effects equal to or superior to those when SWCNT is used alone.

[0110] As a result, compared to when dot-like and sheet-like conductive materials, including linear conductive materials, the silicon-based negative electrode active material can be contained in a higher content, thereby enabling the formation of good capacity characteristics. In addition, by using the above-mentioned combination of linear conductive materials, a conductive network can be secured even with a certain amount of volume expansion, and further, volume expansion can also be addressed by adjusting the negative electrode binder described below.

[0111] 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 form a contact between the silicon-based active materials, which undergo a very large volume expansion of the electrode upon charging and discharging, while the positive electrode conductive material serves to act as a buffer during rolling and to impart some conductivity, and therefore has a completely different structure and role from the negative electrode conductive material of the present invention.

[0112] 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 imparting 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.

[0113] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode binder includes one or more selected from the group consisting of a rubber-based binder and a water-based binder.

[0114] 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.

[0115] The negative electrode binder according to one embodiment of the present application plays a role in holding the active material and the conductive material together to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. As long as the binder fulfills the above role, any common binder can be used. Specifically, a water-based binder may be used, and more specifically, a PAM-based binder may be used.

[0116] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the negative electrode binder includes a water-based binder, and the negative electrode binder is present in an amount of 5 parts by weight or more and 15 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0117] In another embodiment, the amount of the negative electrode binder may be 5 parts by weight or more and 15 parts by weight or less, preferably 7 parts by weight or more and 13 parts by weight or less, and more preferably 9 parts by weight or more and 12 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0118] In one embodiment of the present application, the negative electrode binder may be included in an amount of 3 parts by weight to 10 parts by weight based on 100 parts by weight of the silicon-based active material.

[0119] In another embodiment, the amount of the negative electrode binder may be 3 parts by weight or more and 10 parts by weight or less, preferably 3.5 parts by weight or more and 9.5 parts by weight or less, and more preferably 4 parts by weight or more and 9 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

[0120] In the case of the negative electrode for a lithium secondary battery according to the present application, the silicon-based active material is used in the above-mentioned amount by weight to maximize capacity characteristics, and the volume expansion during charge and discharge is greater than when a conventional carbon-based active material is used as the main active material. Therefore, by including the above-mentioned amount of the negative electrode binder, the volume expansion of the highly rigid silicon-based active material during charge and discharge can be efficiently suppressed.

[0121] 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; and a negative electrode active material layer formed on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer comprising the negative electrode composition according to the present application.

[0122] 1 is a diagram showing a laminated 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 negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows a negative electrode active material layer formed on one side, it may also be formed on both sides of the negative electrode current collector layer.

[0123] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by applying a negative electrode slurry containing the negative electrode composition to one or both surfaces of a negative electrode current collector layer and drying the applied slurry.

[0124] In this case, the negative electrode slurry may include the above-described negative electrode composition and a slurry solvent.

[0125] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 55% or less.

[0126] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 55%, preferably 7% to 35%, and more preferably 10% to 30%.

[0127] The solid content of the negative electrode slurry refers to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0128] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is suitable, particle aggregation of the negative electrode composition is minimized, and the negative electrode active material layer can be efficiently formed. In addition, the negative electrode composition according to the present application includes a linear conductive material and a high content of a silicon-based active material, and is characterized by excellent fast charging performance and cell performance.

[0129] In one embodiment of the present application, the slurry solvent can be any solvent that can dissolve the negative electrode composition, and specifically, water, acetone, or NMP may be used.

[0130] 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 surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, the surface may be provided with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0131] 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 10 μm or more and 500 μm or less.

[0132] In the present application, the thickness of the negative electrode active material layer may refer to the thickness of a single layer of the negative electrode active material layer when the layer is formed on one surface of the negative electrode current collector layer.

[0133] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0134] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less.

[0135] In another embodiment, the porosity of the negative electrode active material layer may satisfy the range of 10% to 60%, preferably 20% to 50%, more preferably 30% to 45%.

[0136] The porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the silicon-based active material and conductive material according to the present application are contained in a specific composition and content, thereby satisfying the above range, and the electrode is characterized by having an appropriate range of electrical conductivity and resistance.

[0137] 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.

[0138] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery including a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10 can be seen, and a positive electrode 200 for a lithium secondary battery including a positive electrode active material layer 40 on one side of a positive electrode current collector layer 50 can be seen, and the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are stacked with a separator 30 interposed therebetween.

[0139] 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.

[0140] 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.

[0141] 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 whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0142] 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 Ni-site type lithium nickel oxide represented by the chemical formula LiMn 2-c3 M c3 Examples of suitable 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 satisfying 0.01≦c3≦0.6) 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.

[0143] In one embodiment of the present application, the positive electrode active material includes a lithium transition metal composite compound including nickel (Ni), cobalt (Co), and manganese (Mn), and the lithium transition metal composite compound includes single particles or secondary particles, and the single particles may have an average particle size (D50) of 1 μm or more.

[0144] For example, the average particle size (D50) of the single particles may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, more than 1 μm and 12 μm or less, more than 1 μm and 8 μm or less, or more than 1 μm and 6 μm or less.

[0145] The single particles can have excellent particle strength even when formed into small particle sizes with an average particle size (D50) of 1 μm or more and 12 μm or less. For example, the single particles can have a strength of 650 kgf / cm 2 The particle strength may be 100 to 300 MPa when the particle is rolled with a force of 650 kgf / cm. 2 Even if the electrode is rolled with a strong force, the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, thereby improving the life characteristics of the battery.

[0146] The single particles can be prepared by mixing a transition metal precursor and a lithium source material and calcining the mixture. The secondary particles can be prepared by a method different from that for the single particles, and the composition of the secondary particles can be the same as or different from that of the single particles.

[0147] The method for forming the single particles is not particularly limited, but may generally be formed by over-firing at an elevated firing temperature, or by using an additive such as a grain growth promoter that aids in over-firing, or by changing the starting material.

[0148] For example, the calcination is performed at a temperature that allows the formation of single particles. To achieve this, the calcination must be performed at a temperature higher than that used for the production of secondary particles. For example, when the precursor composition is the same, the calcination must be performed at a temperature about 30°C to 100°C higher than that used for the production of secondary particles. The calcination temperature for forming the single particles may vary depending on the metal composition of the precursor. For example, when forming a high-nickel (Ni) NCM-based lithium composite transition metal oxide having a nickel (Ni) content of 80 mol% or more into single particles, the calcination temperature may be about 700°C to 1000°C, preferably about 800°C to 950°C. When the calcination temperature satisfies the above range, a positive electrode active material including single particles with excellent electrochemical properties can be produced. When the calcination temperature is lower than 790°C, a positive electrode active material including a lithium composite transition metal compound in the form of secondary particles is produced. When the calcination temperature exceeds 950°C, excessive calcination may result in an inadequate formation of a layered crystal structure, resulting in poor electrochemical properties.

[0149] In this specification, the term "single particle" is used to distinguish it from conventional secondary particles formed by agglomeration of tens to hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and a quasi-single particle form that is an agglomeration of 30 or less primary particles.

[0150] Specifically, in the present invention, the single particle may be a single particle consisting of one primary particle or a quasi-single particle form which is an aggregate of 30 or less primary particles, and the secondary particle may be in the form of an aggregate of several hundred primary particles.

[0151] In one embodiment of the present application, the lithium transition metal composite compound serving as the positive electrode active material further includes secondary particles, and the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0152] In the present invention, the single particle may be a single particle consisting of one primary particle or a quasi-single particle form which is an aggregate of 30 or less primary particles, and the secondary particle may be an aggregate of several hundred primary particles.

[0153] The lithium transition metal composite compound may further include secondary particles. The secondary particles refer to a form formed by agglomeration of primary particles, and can be distinguished from the concept of single particles, which includes one primary particle, one single particle, or a similar-single particle form that is an agglomeration of 30 or less primary particles.

[0154] The particle diameter (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, and preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles may be 0.05 m 2 / g~10m 2 / g, preferably 0.1m 2 / g~1m 2 / g, more preferably 0.3m 2 / g~0.8m 2 / g.

[0155] In a further embodiment of the present application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0156] When the average particle size (D50) of the primary particles satisfies the above range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) of the primary particles is too small, the number of agglomerates of the primary particles forming the lithium nickel-based oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path within the primary particles becomes long, increasing resistance and potentially reducing output characteristics.

[0157] According to a further embodiment of the present invention, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles. As a result, the single particles can have excellent particle strength even when formed to a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, thereby improving the life characteristics of the battery.

[0158] In one embodiment of the present application, the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles by 1 μm to 18 μm.

[0159] For example, the average particle size (D50) of the single particles may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particles.

[0160] When the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles, for example, when the above range is satisfied, the single particles can have excellent particle strength even when formed to a small particle size, thereby mitigating the phenomenon of an increase in fine particles in the electrode due to particle cracking, and improving the life characteristics and energy density of the battery.

[0161] According to a further embodiment of the present application, the single particles are contained in an amount of 15 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material, or may be contained in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight relative to 100 parts by weight of the positive electrode active material.

[0162] For example, the single particles may be included in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, relative to 100 parts by weight of the positive electrode active material. The single particles may be included in an amount of 100 parts by weight or less, relative to 100 parts by weight of the positive electrode active material.

[0163] When the single particles are contained in the above range, excellent battery characteristics can be exhibited in combination with the above-mentioned negative electrode material. In particular, when the single particles are contained in an amount of 15 parts by weight or more, the phenomenon of an increase in fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery life characteristics.

[0164] In one embodiment of the present application, the lithium composite transition metal compound may further include secondary particles, and the secondary particles may be 85 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less relative to 100 parts by weight of the positive electrode active material. The secondary particles may be 0 parts by weight or more relative to 100 parts by weight of the positive electrode active material.

[0165] When the above range is satisfied, the above-described effects due to the presence of the single particle positive electrode active material can be maximized. When the secondary particle positive electrode active material is included, the components thereof may be the same as or different from those exemplified as the single particle positive electrode active material, and may refer to an aggregated form of single particles.

[0166] In one embodiment of the present application, the positive electrode active material may be contained in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less, relative to 100 parts by weight of the positive electrode active material layer.

[0167] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0168] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that 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; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0169] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder 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 binders may be used singly or in combination.

[0170] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and has excellent electrolyte humidification capacity. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminate structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, separators coated with ceramic components or polymeric substances may be used, and they may be selectively used as single-layer or multi-layer structures.

[0171] Examples of the electrolyte include, but are not limited to, 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.

[0172] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0173] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0174] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be used more preferably.

[0175] 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:

[0176] 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.

[0177] According to one embodiment of the present invention, there is provided 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 characteristics, and high cycle characteristics, and therefore 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. [Example]

[0178] Below, preferred examples are presented to help understand the present invention, but these examples are merely for the purpose of illustrating 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.

[0179] <Production example> <Production of negative electrodes> A negative electrode slurry was prepared by adding Si (average particle size (D50): 3.5 μm) as a silicon-based active material, SWCNT, MWCNT, and polyacrylamide (PAM) as a binder in the weight ratios shown in Table 1 below to distilled water as a solvent for forming a negative electrode slurry (solid concentration 28 wt%).

[0180] The SWCNTs have a BET specific surface area of ​​1000 to 1500 m 2 / g, the aspect ratio was 10,000 or more, and the average diameter was 1.0 μm or more. 2 / g level, the average diameter was 10 to 20 μm, and the number of walls was approximately 5 to 20.

[0181] As a specific mixing method, the SWCNTs, MWCNTs, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0182] The negative electrode current collector layer was made of a copper current collector (thickness: 26 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 87.7 mg / 25 cm. 2 The coated layer 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), which was used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0183] A negative electrode was prepared in the same manner as in Example 1, except that the weight parts were changed as shown in Table 1 below.

[0184] [Table 1]

[0185] In Table 1, the parts by weight are based on 100 parts by weight of the total negative electrode composition, and in Table 2 below, the parts by weight are based on 100 parts by weight of the negative electrode active material.

[0186] [Table 2]

[0187] <Comparative Example 7> A negative electrode active material layer composition was prepared by mixing Si (average particle size (D50): 3.5 μm) as a silicon-based active material, a first conductive material, a third conductive material, and polyacrylamide (PAM) as a binder in a weight ratio of 80:10:0.3:9.7. Distilled water was added as a solvent for forming a negative electrode slurry to produce a first negative electrode slurry (solid concentration: 45 wt%).

[0188] The first conductive material is carbon black C (specific surface area: 58 m 2 / g, diameter: 37 nm), and the third conductive material is a carbon nanotube.

[0189] The mixing method was as follows: the first conductive material, the third conductive material, the 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.

[0190] The negative electrode slurry was applied to both sides of a copper current collector (thickness: 30 μm) at a rate of 99.65 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 37 μm), which was used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0191] <Comparative Example 8> A negative electrode was manufactured in the same manner as in Comparative Example 7, except that the second conductive material was used instead of the first conductive material. The second conductive material was plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm).

[0192] <Comparative Example 9> A negative electrode active material layer composition was prepared using SiO (average particle size (D50): 3.5 μm) as a silicon-based active material, artificial graphite, a first conductive material, a third conductive material, and CMC:SBR as a binder in a weight ratio of 4.779:90.794:0.982:0.018:1.127:2.3. Distilled water was added as a solvent for forming a negative electrode slurry to produce a negative electrode slurry (solid concentration: 45 wt%).

[0193] The first conductive material is carbon black C (specific surface area: 58 m 2 / g, diameter: 37 nm), and the third conductive material is a carbon nanotube.

[0194] The mixing method was as follows: the first conductive material, the third conductive material, the 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.

[0195] The negative electrode slurry was applied to both sides of a copper current collector (thickness: 8 μm) at a rate of 9.312 mg / cm. 2 The coated layer was rolled and dried in a vacuum oven at 130° C. for 10 hours to form a negative electrode active material layer (thickness: 114 μm).

[0196] <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%).

[0197] 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%).

[0198] A polyethylene separator was interposed between the positive electrode and the negative electrode of Example 1, and an electrolyte was injected thereinto to produce the secondary battery of Example 1.

[0199] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) in a volume ratio of 30:70, to which vinylene carbonate was added in an amount of 3 wt % based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1 M.

[0200] Secondary batteries were fabricated in the same manner as above, except that the negative electrodes of the Examples and Comparative Examples were used.

[0201] Experimental example 1: Life evaluation of mono-cell The secondary battery fabricated as described above was subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate its capacity retention. The secondary battery was subjected to 300 cycles of charging (1.0 C cc / CV charging, 4.2 V, 0.05 C cut) and discharging (0.5 C CC discharge, 3.3 V cut) at room temperature (25°C), and the capacity retention was then confirmed.

[0202] The capacity retention rate at the 300th cycle was evaluated using the following formula, and the results are shown in Table 3 below.

[0203] Capacity retention (%) = {(discharge capacity at 300th cycle / (discharge capacity at first cycle)}

[0204] [Table 3]

[0205] Experimental Example 2: Cycle resistance increase rate In Experimental Example 1, the capacity retention rate was measured by charging / discharging (4.2-3.0V) at 0.33C / 0.33C every 100 cycles during the test, and then the resistance was measured by discharging at 2.5C pulses at SOC50, and the resistance increase rate was compared and analyzed.

[0206] For the measurement and evaluation of the resistance increase rate, data at 200 cycles was calculated, and the results are shown in Table 4 below.

[0207] [Table 4]

[0208] As can be seen from Table 3, Examples 1 to 4 of the present invention exhibited superior performance compared to the comparative examples.

[0209] Specifically, in the case of Comparative Example 1, the conductive network was properly formed, but the binder content was so low that the connections between the networks were broken, resulting in a decrease in performance.

[0210] In Comparative Example 2, unlike Comparative Example 1, the binder ratio was very high, which appears to have reduced the degree of short circuiting of the interconnected structure between networks. However, the high ratio of the binder, which is a non-conductive material, increased the resistance, resulting in a decrease in performance.

[0211] Comparative Example 3 and Comparative Example 4 are cases where SWCNT or MWCNT is applied alone as the conductive material. Compared with Example 1, only the respective conductive material was excluded and there was no increase in the amount of the conductive material itself, resulting in weakened conductivity and degraded performance.

[0212] Comparative Examples 5 and 6 are cases where an active material in which Si and C are compounded is used. In the examples of the present application, all contain one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), and contain 90 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material, that is, it corresponds to the case of using pure Si (Pure Si). In the case of Comparative Examples 5 and 6, maximization of the capacity could not be achieved compared with the examples of the present application. The charging performance is a composite of graphite which is very inferior to Si, and since the condition that the evaluation charging C-rate is 1.0C is a very difficult condition to apply to the electrode, it is judged that problems such as lithium plating occurred, and also when using CMC:SBR as the binder, it is difficult to improve the performance in a silicon-based battery, and thus it is judged that the performance has rapidly deteriorated.

[0213] Comparative Examples 7 and 8 correspond to the case where carbon black which is a dot-like conductive material and plate-like graphite which is a sheet-like conductive material are applied. First, in the case of carbon black, the content of the added composition is high and the viscosity of the slurry becomes very high, affecting the dispersion of carbon black and SWCNT, and showing the above results. Also, when using plate-like graphite, since it is not a material that has a great influence on dispersion, there was no problem with the degree of dispersion, but the content of the conductive material increased, the composition ratio of the silicon-based active material decreased, and the electrode weight loading amount increased to achieve the same capacity, resulting in a thicker electrode and degraded performance. For reference, in Comparative Example 7, the thickness of the electrode increased along with the deterioration of the conductivity and dispersibility due to the conductive material, and the performance was even inferior to that of Comparative Example 8.

[0214] Finally, in Comparative Example 9, a significant decrease in performance was observed for the mixed electrode of SiO and graphite. This is believed to be the result of using graphite, which has significantly inferior charging performance compared to Si, as the main active material, and the fact that the estimated charging C-rate of 1.0C is a very difficult condition for a graphite electrode, leading to problems such as lithium plating, which resulted in a rapid decrease in performance. [Explanation of symbols]

[0215] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30 Separator 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. A negative electrode composition comprising: a silicon-based active material; a linear conductive material; and a negative electrode binder, The silicon-based active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and the silicon-based active material includes 90 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material; The linear conductive material includes SWCNT; and MWCNT, The negative electrode composition contains 80 parts by weight or more and 95 parts by weight or less of the silicon-based active material based on 100 parts by weight of the negative electrode composition, The negative electrode binder is contained in an amount of 3.5 parts by weight to 9.5 parts by weight based on 100 parts by weight of the silicon-based active material, A negative electrode composition that does not contain a point-like conductive material or a sheet-like conductive material.

2. The negative electrode composition according to claim 1 , wherein the silicon-based active material has a crystal grain size of 200 nm or less.

3. 2. The negative electrode composition according to claim 1, wherein the linear conductive material is present in an amount of 0.5 parts by weight to 10 parts by weight based on 100 parts by weight of the silicon-based active material.

4. The negative electrode composition according to claim 1 , wherein the MWCNT is 0.3 parts by weight or more and 6 parts by weight or less, and the SWCNT is 0.1 parts by weight or more and 1.5 parts by weight or less, based on 100 parts by weight of the silicon-based active material.

5. The MWCNT has a specific surface area of ​​100 m ２ / g to 500m ２ / g, The negative electrode composition according to claim 1 , wherein the mean diameter is 10 nm or more and 20 nm or less.

6. The SWCNT has a specific surface area of ​​900 m ２ / g~1500m ２ / g, The negative electrode composition according to claim 1 , wherein the mean diameter is 50 nm or more and 450 nm or less.

7. The negative electrode composition according to claim 1 , wherein the negative electrode binder comprises at least one selected from the group consisting of a rubber-based binder and a water-based binder.

8. a negative electrode current collector layer; and a negative electrode active material layer comprising the negative electrode composition according to any one of claims 1 to 7, formed on one or both surfaces of the negative electrode current collector layer; A negative electrode for a lithium secondary battery comprising:

9. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 9. The negative electrode for a lithium secondary battery according to claim 8, wherein the thickness of the negative electrode active material layer is 10 μm or more and 500 μm or less.

10. positive electrode; The negative electrode for a lithium secondary battery according to claim 8 ; a separator disposed between the positive electrode and the negative electrode; and Electrolyte; A lithium secondary battery comprising:

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