Negative electrode for lithium secondary battery including a pattern, and lithium secondary battery including the negative electrode

Abstract

The present application relates to a negative electrode for a lithium secondary battery including a pattern, 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. 10-2022-0175723, filed with the Korean Intellectual Property Office on December 15, 2022, and all of its content is incorporated herein by reference.

[0002] This application relates to a negative electrode for a lithium secondary battery including a pattern, and a lithium secondary battery including the negative electrode.

Background Art

[0003] Due to the rapid increase in the use of fossil fuels, the demand for alternative and clean energy has been increasing. As part of this, the fields of power generation and power storage using electrochemical reactions are the most actively studied.

[0004] Currently, a typical example of an electrochemical device using such electrochemical energy is a secondary battery, and its usage areas are showing a trend of increasing more and more.

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

[0006] Generally, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions emitted from the positive electrode, and silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, recently, with the demand for high-density energy batteries, research has been actively conducted on methods to increase the capacity by using silicon-based compounds such as Si / C and SiOx, which have a capacity more than 10 times greater than that of graphite-based materials, as the negative electrode active material. However, in the case of silicon-based compounds, which are high-capacity materials, although the capacity is large compared to conventionally used graphite, there is a problem that the volume rapidly expands during the charging process, cutting off the conductive path and degrading the battery characteristics.

[0008] Therefore, in order to solve the problems when using silicon-based compounds as the negative electrode active material, various solutions have been discussed, such as a solution to adjust the driving potential, additionally, a method of further coating a thin film on the active material layer, a solution to suppress the volume expansion itself, such as a method of adjusting the particle size of the silicon-based compound, or various solutions to prevent the conductive path from being cut off. However, in the case of the above solutions, there is a risk of degrading the battery performance, so there are limitations in their application, and there are still limitations in the commercialization of the production of negative electrode batteries with a high content of silicon-based compounds.

[0009] That is, the negative electrode using a silicon-based active material must be applied in order to maximize the capacity characteristics and satisfy the performance of rapid charging. However, as described above, there is no method derived that can solve the problems caused by the volume expansion of the silicon-based active material itself. In particular, research has been conducted on adjusting the degree of volume expansion by using a conductive material and a binder together for the negative electrode that should contain a high content of the silicon-based active material. However, since the conductive material and the binder are contained in a small amount compared to the active material and the adjustment of their content part is very limited, there are many limitations when changing the composition and content.

[0010] Therefore, in order to improve the capacity performance, even when using a silicon-based active material as the negative electrode active material, research is needed to prevent the volume expansion of the silicon active material due to the insertion and desorption of lithium during charge and discharge.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] Regarding the negative electrode that should contain a high content of silicon-based active material, research has been conducted to adjust its volume expansion using a conductive material and a binder together. However, compared to the active material, the conductive material and the binder are contained in a small amount, and the adjustment of their content part is very limited. Therefore, there are many restrictions when changing the composition and content.

[0013] As a result, in the negative electrode containing a silicon-based active material, it has been found by research that introducing a pattern into the negative electrode active material layer can solve the above-mentioned problems when the pattern fills a predetermined volume.

[0014] Therefore, the present application relates to a negative electrode for a lithium secondary battery including a pattern capable of solving the above-mentioned problems, and a lithium secondary battery including the negative electrode.

Means for Solving the Problems

[0015] One embodiment of the present specification provides a negative electrode for a lithium secondary battery including 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, wherein the negative electrode active material layer includes a pattern part and satisfies the following formula 1. [Formula 1] 5 ≦ [B / (A + B)] × 100(%) ≦ 30 In the above formula 1, A means the volume of the negative electrode active material layer excluding the pattern part, B means the volume of the pattern part.

[0016] One embodiment of the present application provides a lithium secondary battery including a positive electrode; the 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 for a lithium secondary battery of the present invention contains a silicon-based active material and targets high capacity and high energy density. At this time, since the silicon-based active material is contained in a high content in the negative electrode active material layer, the volume expansion degree during charge and discharge can be a problem. In the case of the negative electrode for a lithium secondary battery according to the present application, the negative electrode active material layer includes a pattern portion, and in particular, the volume of the pattern portion and the negative electrode active material layer satisfies the relationship of the above-mentioned formula 1.

[0018] That is, instead of adjusting the composition of the negative electrode active material layer, the composition is maintained, and the physical volume relationship is adjusted to solve volume expansion. Eventually, when using a silicon-based negative electrode, in order for the volume expansion rate of the negative electrode active material layer to satisfy a range where there is no problem in use (less than 5 to 10%), the volume of the pattern portion is set, and its ratio is adjusted to the range of the above-mentioned formula 1.

[0019] As a result, the negative electrode including the negative electrode active material layer satisfying the above formula 1 has less volume expansion due to charge and discharge, and the life characteristics of the lithium secondary battery can be maximized. In addition, it can have the characteristics of high density and high capacity, which are the advantages of the silicon-based negative electrode, and can provide a lithium secondary battery with excellent rapid charging performance.

[0020] In the case of the above-described configuration, there are also advantageous effects not only for a stacked type pouch battery but also when winding into cylindrical and rectangular roll-shaped batteries. The above configuration has no difference in volume expansion even when the formation charging speed is increased compared to existing conditions. In addition, not only the expansion in the xy direction but also the change in thickness in the z direction can be reduced.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0022] Before explaining the present invention, first, some terms are defined. In this specification, when a certain part "includes" a certain component, this means that, unless otherwise stated to the contrary, it does not exclude other components, but may further include other components.

[0023] In this specification, "p~q" means "greater than or equal to p and less than or equal to q". In this specification, the "specific surface area" is measured by the BET method. Specifically, it is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-miniII manufactured by BEL Japan. That is, in the present application, the BET specific surface area can mean the specific surface area measured by the above measurement method.

[0024] In this specification, "Dn" means the particle size distribution and means 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. On the other hand, the average particle size may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), and the difference in the diffraction pattern due to the particle size when the particles pass through the laser beam is measured to calculate the particle size distribution.

[0025] In one embodiment of the present application, the particle size or the particle diameter can mean the average diameter or the representative diameter of each individual particle constituting the metal powder.

[0026] In this specification, the meaning that a polymer contains a certain monomer in monomer units means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted to be the same as the polymer containing the monomer in monomer units.

[0027] In this specification, it is understood that the term "polymer" is used in a broad sense including copolymers unless otherwise specified as "homopolymer".

[0028] 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 monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard substances. In this specification, the molecular weight means the weight average molecular weight unless otherwise specified.

[0029] Hereinafter, with reference to the drawings, a detailed description will be given so that a person having ordinary knowledge in the technical field to which the present invention pertains can easily implement the present invention. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0030] One embodiment of this specification provides a negative electrode for a lithium secondary battery, including 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, wherein the negative electrode active material layer includes a pattern portion and satisfies the following formula 1. [Formula 1] 5 ≦ [B / (A + B)] × 100 (%) ≦ 30 In the above formula 1, A means the volume of the negative electrode active material layer excluding the pattern portion, B means the volume of the pattern portion.

[0031] FIG. 3 is a diagram showing a structure in which the active material layer of the negative electrode for a lithium secondary battery according to an embodiment of the present application is patterned. Specifically, A means the volume of the negative electrode active material layer excluding the pattern portion, and B indicates the volume of the pattern portion in the negative electrode active material layer.

[0032] In the present application, the pattern portion can be defined as a plain portion region that does not have the negative electrode active material layer in the negative electrode active material layer. That is, the pattern portion is a portion on the upper part of the negative electrode current collector layer that does not have the negative electrode active material layer, and is separated by a partition wall or other substances, which is different from a structure in which the negative electrode active material layer has a pattern form.

[0033] In the present invention, a negative electrode including a negative electrode active material layer that satisfies the above-described formula 1 has less volume expansion due to charge and discharge, and the life characteristics of the lithium secondary battery can be maximized. Also, it can have the characteristics of high density and high capacity, which are the advantages of a silicon-based negative electrode, and can provide a lithium secondary battery with excellent rapid charging performance. The pattern portion in the present invention can play the above-described role only when the negative electrode active material layer is not formed. When a partition wall is formed and separated, the portion blocked by the partition wall cannot accommodate volume expansion unlike the pattern portion of the present invention, so the above-described effect of relaxing volume expansion is lost.

[0034] In one embodiment of the present application, the formula 1 may be 5 ≤ [B / (A + B)]×100(%) ≤ 30, specifically, it can satisfy the range of 6 ≤ [B / (A + B)]×100(%) ≤ 25, and more specifically, 10 ≤ [B / (A + B)]×100(%) ≤ 25.

[0035] This application is characterized in that instead of adjusting the composition of the negative electrode active material layer, the composition is maintained and the physical volume relationship is adjusted to solve volume expansion. Eventually, when using a silicon-based negative electrode, in order to satisfy that the volume expansion rate of the negative electrode active material layer is within a range where there is no problem in use (less than 5 to 10%), the volume of the pattern portion is set and the ratio is adjusted to the range of the aforementioned formula 1.

[0036] When the range of the aforementioned formula 1 is satisfied, not only in the case of a stack-type pouch battery, but also when winding into cylindrical and rectangular roll-shaped batteries, volume expansion can be solved and advantageous effects can be achieved. Also, even if the formation charging speed is increased compared to the existing conditions, there is no difference in volume expansion, and not only the expansion in the xy direction but also the change in thickness in the z direction can be reduced.

[0037] In one embodiment of this application, the aforementioned formula 1 means the volume ratio of the pattern portion to the total volume of the negative electrode active material layer, and the unit of formula 1 can be expressed in %.

[0038] In one embodiment of this application, the aforementioned negative electrode active material layer provides a negative electrode for a lithium secondary battery that satisfies the following formula 2. [Formula 2] [{(x + x1)(y + y1)(z + z1)-xyz} / xyz]×100(%) < 50% In the aforementioned formula 2, x, y, and z are, respectively, the overall width, overall length, and overall thickness of the negative electrode active material layer including the pattern portion after the manufacture of the negative electrode for the lithium secondary battery, x1, y1, and z1 respectively mean the length changes in the x, y, and z directions immediately after 1 / 3C CC - CV charging (0.05C cut-off) up to 4.2V and then 1 / 3C CC discharging up to 2.5V after the manufacture of the negative electrode for the lithium secondary battery.

[0039] The aforementioned formula 2 satisfies [Formula 2] < 50%, specifically, [Formula 2] < 48%, [Formula 2] < 45%, and can satisfy 5% < [Formula 2], 10% < [Formula 2], 15% < [Formula 2], 20% < [Formula 2], 25% < [Formula 2].

[0040] That is, the above formula 2 can represent the volume expansion rate after the activation process (i.e., after 1 / 3C CC-CV charging to 4.2V (0.05C cut-off) once and then 1 / 3C CC discharging to 2.5V) with respect to the total volume of the negative electrode active material layer of the lithium secondary battery in the fresh state. By including the pattern portion that satisfies the range of the above formula 1 in the negative electrode active material layer, it can have the characteristic of satisfying the range of the above formula 2.

[0041] Specifically, the above formula 2 can be confirmed in FIG. 3. x is the length in the TD direction and represents the total width of the negative electrode active material layer, y is the length in the MD direction and represents the total length of the negative electrode active material layer, and z represents the thickness of the negative electrode active material layer. At this time, x1, y1, and z1 respectively represent the amounts of length change in the x, y, and z directions after the above-mentioned activation process after the production of the negative electrode for the lithium secondary battery.

[0042] In one embodiment of the present application, the negative electrode active material layer provides a negative electrode for a lithium secondary battery that satisfies the following formula 3. [Formula 3] [{(x + x2)(y + y2)(z + z2)-xyz} / xyz]×100(%) < 100% In the above formula 3, x, y, and z are respectively the total width, total length, and total thickness of the negative electrode active material layer including the pattern portion after the production of the negative electrode for the lithium secondary battery, x2, y2, and z2 respectively represent the length changes in the x, y, and z directions after 1C CC-CV charging to 4.2V (0.05C cut-off) and then performing 0.5C CC discharging to 3.0V for 300 cycles after the production of the negative electrode for the lithium secondary battery.

[0043] The above formula 3 can satisfy [Formula 3] < 100%, specifically, [Formula 3] < 97%, [Formula 3] < 95%, and can also satisfy 50% < [Formula 3], 55% < [Formula 3], 60% < [Formula 3].

[0044] That is, Formula 3 can represent the volume expansion rate after 300 cycles (i.e., after performing 300 cycles of 1C CC-CV charging (0.05C cut-off) up to 4.2V and then 0.5C CC discharging up to 3.0V) with respect to the total volume of the negative electrode active material layer in the fresh state. By including the pattern portion that satisfies the range of Formula 1 described above, the negative electrode active material layer has the characteristic that the range of Formula 3 can be satisfied.

[0045] Specifically, Formula 3 can be confirmed in FIG. 3. x is the length in the TD direction and represents the total width of the negative electrode active material layer, y is the length in the MD direction and represents the total length of the negative electrode active material layer, and z is the thickness of the negative electrode active material layer. At this time, x2, y2, and z2 respectively represent the amounts of change in length in the x, y, and z directions after undergoing the aforementioned 300 cycles after the manufacture of the negative electrode for the lithium secondary battery.

[0046] In one embodiment of the present application, the negative electrode active material layer provides a negative electrode for a lithium secondary battery that satisfies the following Formula 4. [Formula 4] 5 ≦ xyz - {(xi × n)yz + x(yj × m)z - nmxiyj} ≦ 30 In Formula 4, x, y, and z are respectively the total width, total length, and total thickness of the negative electrode active material layer including the pattern portion after the manufacture of the negative electrode for the lithium secondary battery, n is the number of patterns in the x direction, m is the number of patterns in the y direction, xi represents the width of the pattern, yj represents the length of the pattern, i is an integer from 1 to n, j is an integer from 1 to m.

[0047] FIG. 3 corresponds to the case where the pattern portion is formed with a 2D pattern. At this time, n is the number of patterns in the x direction. When n is 3, i can be represented by an integer from 1 to 3, and x1, x2, and x3 can respectively represent the widths of the respective patterns. Similarly, m is the number of patterns in the y direction. When m is 3, j is an integer from 1 to 3, and y1, y2, and y3 can respectively represent the lengths of the respective patterns.

[0048] The formula 4 can represent the volume obtained by excluding the volume of the pattern portion included in the negative electrode active material layer based on the total volume of the negative electrode active material layer, and can represent the volume of the actually provided negative electrode active material layer. That is, when the formula 4 is less than the aforementioned range, the capacity characteristics may not be ensured. When it exceeds the aforementioned range, volume expansion cannot be controlled, and instead, there is a problem that the life characteristics deteriorate.

[0049] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the pattern portion includes one or more selected from the group consisting of a 1D pattern; a 2D pattern; a V pattern; and a U pattern.

[0050] Here, the 1D pattern can mean that a pattern is formed only in the length or width direction in the negative electrode active material layer, and the 2D pattern can mean that a pattern is formed in both the length and width directions in the negative electrode active material layer. Also, in the case of the V and U patterns, it can mean forming a V-shaped or U-shaped pattern in the shape of the formed pattern.

[0051] In the present application, there is provided a negative electrode for a lithium secondary battery, wherein the negative electrode active material layer includes a negative electrode active material layer composition, and the negative electrode active material layer composition includes a silicon-based active material; a negative electrode conductive material; and a negative electrode binder.

[0052] At this time, the silicon-based active material can be used as the negative electrode active material. The negative electrode active material layer composition according to one embodiment of the present invention solves the conventional problems by using a negative electrode active material layer having the above-described pattern portion even when a silicon-based active material is used.

[0053] In one embodiment of the present application, the silicon-based active material may include one or more selected from the group consisting of SiOx (x = 0), SiOx (0 < x < 2), SiC, and Si alloy.

[0054] The active material of the present invention includes a silicon-based active material. The silicon-based active material may be SiOx, Si / C, or Si. SiOx may include a compound represented by SiOx (0 ≦ x < 2). In the case of SiO2, since it does not react with lithium ions and cannot store lithium, x is preferably within the above range. The silicon-based active material may be Si / C or Si composed of a composite of Si and C. Also, two or more of the above-described silicon-based active materials may be mixed and used. The negative electrode active material may further include a carbon-based active material together with the above-described silicon-based active material. The carbon-based active material can contribute to improving the cycle characteristics or battery life performance excellent in the negative electrode or secondary battery of the present invention.

[0055] Generally, it is known that a silicon-based active material has a capacity 10 times or more higher than that of a carbon-based active material. Accordingly, when the silicon-based active material is applied to a negative electrode, it is expected that an electrode having a high level of energy density can be realized even with a thin thickness.

[0056] 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 included in an amount of 70 parts by weight or more.

[0057] 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 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 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.

[0058] The silicon-based active material according to the present application contains 70 parts by weight or more of the SiOx (x = 0) based on 100 parts by weight of the silicon-based active material. When compared with a silicon-based active material using a SiOx (0 <x <2) series as a main material, it has a disadvantage that the theoretical capacity is significantly reduced compared to the silicon-based active material of the present application. That is, when using an active material of the SiOx (0 <x <2) series, no matter what treatment is performed on the active material itself, it is impossible to realize the same conditions as the charge and discharge capacity compared to the case of having the silicon-based active material of the present invention.

[0059] In one embodiment of the present application, the silicon-based active material may use pure silicon (Si) as the silicon-based active material. Using pure silicon (Si) as the silicon-based active material may mean, as described above, that pure Si particles (SiOx (x = 0)) not bonded to other particles or elements are included within the above range when the silicon-based active material is based on 100 parts by weight in total.

[0060] When the silicon-based active material is compared with the conventionally used graphite-based active material, the capacity is significantly higher, and the attempt to apply it has increased. However, the volume expansion rate is high during the charge and discharge process, and it has been limited to cases such as when a small amount is mixed with the graphite-based active material and used.

[0061] Therefore, in order to improve the capacity performance, the present invention manufactures a negative electrode including a pattern portion satisfying the above-described formula 1 in order to solve the problems of maintaining the conductive path due to the volume expansion and maintaining the bonding of the conductive material, binder, and active material while using a high content of the silicon-based active material as the negative electrode active material.

[0062] On the one hand, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically, it may be 5.5 μm to 8 μm, and more specifically, it may be 6 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. As a result, the dispersion of the particles constituting the negative electrode slurry becomes smooth. In addition, since the size of the silicon-based negative electrode active material has a value equal to or greater than the lower limit value of the above range, the contact area between the silicon particles and the conductive material by the composite composed of the conductive material and the binder in the negative electrode slurry is excellent, and the possibility of maintaining the conductive network is increased, and the capacity retention rate is increased. 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 smoothly formed, whereby it is possible to prevent the phenomenon of non-uniform current density during charge and discharge.

[0063] In one embodiment of the present application, the silicon-based active material usually has a specific BET surface area. The BET surface area of the silicon-based active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, particularly preferably 0.2 m 2 / g to 80.0 m 2 / g, most preferably 0.2 m 2 / g to 18.0 m 2 / g. The BET surface area is measured in accordance with DIN 66131 (using nitrogen).

[0064] In one embodiment of the present application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure, or may exist in the form of a silicon-containing thin film or coating, but this is not so preferable.

[0065] In one embodiment of the present application, the silicon-based active material may be 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

[0066] In another embodiment, the silicon-based active material may contain 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, and may be 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

[0067] The negative electrode active material layer composition according to the present application uses a specific conductive material and binder that can control the volume expansion rate during the charge and discharge process even when using a silicon-based active material with a significantly high capacity within the above range, and has a pattern portion that satisfies the range of the above-described formula 1, thereby not degrading the performance of the negative electrode and having excellent output characteristics during charging and discharging.

[0068] In one embodiment of the present application, the silicon-based active material may have a non-spherical form, and its 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.

[0069] In the present application, the sphericity is determined by the following formula 1-1, where A is the area and P is the boundary line. [Formula 1-1] 4πA / P 2

[0070] Conventionally, it has been common to use only graphite-based compounds as the negative electrode active material. However, recently, as the demand for high-capacity batteries has increased, attempts have been made to mix and use silicon-based compounds to increase the capacity. However, in the case of silicon-based compounds, even if the characteristics of the silicon-based active material itself are adjusted according to the present application, there is a risk that the volume will rapidly expand during the charge / discharge process and damage the conductive paths formed in the negative electrode active material layer.

[0071] Therefore, in one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0072] In one embodiment of the present application, the dot-shaped conductive material can be used to improve the conductivity of the negative electrode, and means a dot-shaped or spherical conductive material that does not induce a chemical change and has conductivity. Specifically, the dot-shaped 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 derivative. Preferably, it may include carbon black in terms of embodying high conductivity and excellent dispersibility.

[0073] In one embodiment of the present application, the BET specific surface area of the dot-shaped conductive material may be 40 m 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 / g or less.

[0074] In one embodiment of the present application, the dot-shaped conductive material can satisfy a functional group content (Volatile matter) of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, more preferably 0.01% or more and 0.1% or less.

[0075] Particularly when the functional group content of the dot-shaped conductive material satisfies the above range, the functional groups present on the surface of the dot-shaped conductive material exist, and when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, in the present invention, by using silicon particles and a specific binder, the functional group content of the dot-shaped conductive material can be reduced, thereby having an excellent effect on improving dispersibility.

[0076] In one embodiment of the present application, it is characterized by including a dot-shaped conductive material having a functional group content within the above range together with a silicon-based active material, and the adjustment of the functional group content can be adjusted by the degree of heat treatment of the dot-shaped conductive material.

[0077] In one embodiment of the present application, the particle size of the dot-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0078] In one embodiment of the present application, the negative electrode conductive material may include a planar conductive material. The planar conductive material can play a role in increasing the surface contact between silicon particles in the negative electrode to improve conductivity, and at the same time suppressing the interruption of the conductive path due to volume expansion. The planar conductive material may be expressed as a plate-shaped conductive material or a bulk-type conductive material.

[0079] In one embodiment of the present application, the planar conductive material may be provided in a form that binds to the surface of the silicon-based particles. Specifically, it may be provided in a form in which the -OH group or -O on the surface of the silicon-based particles binds to the hydrophilic group of the planar conductive material.

[0080] In one embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and preferably may be plate-shaped graphite.

[0081] In one embodiment of the present application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, specifically, it may be 3 μm to 6 μm, and more specifically, it may be 4 μm to 5 μm. When the above range is satisfied, since the particle size is sufficient, dispersion becomes easy while preventing the viscosity of the negative electrode slurry from rising too much. Therefore, when dispersing using the same equipment and time, the dispersion effect is excellent.

[0082] In one embodiment of the present application, the planar conductive material may have a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0083] In one embodiment of the present application, as the planar conductive material, a high specific surface area planar conductive material with a high BET specific surface area; or a low specific surface area planar conductive material may be used.

[0084] In one embodiment of the present application, as the planar conductive material, a high specific surface area planar conductive material; or a low specific surface area planar conductive material may be used without limitation. However, in particular, since the planar conductive material according to the present application may be affected to some extent by dispersion in terms of electrode performance, it is particularly preferable to use a low specific surface area planar conductive material that does not cause problems in dispersion.

[0085] In one embodiment of the present application, the planar conductive material may have a BET specific surface area of 1 m 2 / g or more.

[0086] In another embodiment, the planar conductive material may have a BET specific surface area of 1 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, more preferably 5 m 2 / g or more and 250 m 2 / g.

[0087] The planar conductive material according to the present application may use a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area.

[0088] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area is 50 m 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 / g or less.

[0089] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area is 1 m 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, more preferably 5 m 2 / g or more and 25 m 2 / g or less.

[0090] In addition, as the conductive material, there may be a linear conductive material such as a carbon nanotube. The carbon nanotube may be a bundled carbon nanotube. The bundled carbon nanotube may include a plurality of carbon nanotube unit bodies. Specifically, here, the 'bundle type' refers to a secondary shape of a bundle or rope in which a plurality of carbon nanotube unit bodies are arranged in parallel with substantially the same orientation of the longitudinal axis of the carbon nanotube unit body or twisted, unless otherwise mentioned. The carbon nanotube unit body has a graphite sheet having a nanosize diameter in a cylindrical shape and has an sp2 bonding structure. At this time, depending on the angle and structure around which the graphite sheet is wound, it can exhibit the characteristics of a conductor or a semiconductor. The bundled carbon nanotube can be uniformly dispersed during the production of the negative electrode compared to the entangled type carbon nanotube, and can smoothly form a conductive network in the negative electrode, improving the conductivity of the negative electrode.

[0091] Exemplarily, the linear conductive material may be a single-walled carbon nanotube (SWCNT) having a large BET specific surface area, linearity, a very small diameter, and a very long length. A linear conductive material such as SWCNT cannot be stretched through dispersion and has a strong ability to return to its original form while being dried. As a result, since a linear conductive material such as SWCNT has a strong force to return to its original form when dried, it generally exists in a form that wraps or connects the negative electrode active material and secondary aggregates. The joining method can be adsorbed by van der Waals forces.

[0092] In one embodiment of the present application, the negative electrode conductive material may be 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

[0093] In another embodiment, the negative electrode conductive material may contain 10 parts 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, more preferably 10 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the negative electrode active material layer composition.

[0094] In one embodiment of the present application, the negative electrode conductive material may include a planar conductive material and a linear conductive material.

[0095] In one embodiment of the present application, the negative electrode conductive material may contain 80 parts by weight or more and 99.9 parts by weight or less of the planar conductive material; and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0096] In another embodiment, the negative electrode conductive material may contain 80 parts by weight or more and 99.9 parts by weight or less of the planar conductive material, preferably 85 parts by weight or more to 99.9 parts by weight or less, more preferably 95 parts by weight or more to 98 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0097] In another embodiment, the negative electrode conductive material may contain 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material, preferably 0.1 parts by weight or more and 15 parts by weight or less, more preferably 2 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the negative electrode conductive material.

[0098] In one embodiment of the present application, when the negative electrode conductive material includes a planar conductive material and a linear conductive material and satisfies the respective compositions and ratios, it does not significantly affect the life characteristics of conventional lithium secondary batteries. In particular, when including a planar conductive material and a linear conductive material, there are more points where charging and discharging are possible, resulting in excellent output characteristics at a high C-rate and a reduction in the amount of gas generated at high temperatures.

[0099] The negative electrode conductive material according to the present application has a completely different configuration from the positive electrode conductive material applied to the positive electrode. That is, in the case of the negative electrode conductive material according to the present application, it plays a role of controlling the contacts between silicon-based active materials with very large volume expansion of the electrode during charging and discharging. The positive electrode conductive material plays a role of imparting partial conductivity while acting as a buffer with a buffering effect when rolled, and its configuration and role are completely different from those of the negative electrode conductive material of the present invention.

[0100] Also, the negative electrode conductive material according to the present application is applied to silicon-based active materials and has a completely different configuration from the conductive materials applied to graphite-based active materials. That is, the conductive material used in an electrode having a graphite-based active material simply has smaller particles than the active material, and thus has the characteristics of improving output characteristics and imparting partial conductivity, and its configuration and role are completely different from those of the negative electrode conductive material applied together with silicon-based active materials as in the present invention.

[0101] In one embodiment of the present application, the planar conductive material used as the aforementioned negative electrode conductive material generally has a structure and role different from those of the carbon-based active material used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and means a material processed into a spherical or dot-like form in order to facilitate the storage and release of lithium ions.

[0102] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like form and can be represented by plate graphite. That is, it is a material included to maintain a conductive path within the negative electrode active material layer, and does not play a role in storing and releasing lithium, but means a material for ensuring a conductive path in a planar form within the negative electrode active material layer.

[0103] That is, in the present application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate shape and used as a substance for securing a conductive path, rather than serving as a material for storing or releasing lithium. At this time, the negative electrode active material contained together has high capacity characteristics for storing and releasing lithium and plays a role of being able to store and release all lithium ions transmitted from the positive electrode.

[0104] On the other hand, in the present application, the use of a carbon-based active material as an active material means that it is processed into a dot-like or spherical shape and used as a material for storing or releasing lithium.

[0105] In one embodiment of the present application, the negative electrode binder may include at least any one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and substances in which hydrogen thereof is substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0106] According to an embodiment of the present application, the negative electrode binder plays a role in controlling the silicon-based active material and the negative electrode conductive material in order to prevent the twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. If the above role is satisfied, any general negative electrode binder can be applied. Specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0107] In one embodiment of the present application, based on 100 parts by weight of the negative electrode active material layer composition, the negative electrode binder may be included in an amount of 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and may also be included in an amount of 5 parts by weight or more and 10 parts by weight or more.

[0108] Compared with the conventional carbon-based negative electrode, when a Si-based negative electrode is used, an aqueous binder may be applied in the above parts by weight, and a dot-shaped conductive material with a low functional group content may be used. Due to the above characteristics, the dot-shaped conductive material has hydrophobicity and has excellent bonding strength with the conductive material / binder.

[0109] In one embodiment of the present application, the negative electrode active material layer can form a negative electrode for a lithium secondary battery by coating a negative electrode slurry containing the negative electrode active material layer composition on one or both sides of a negative electrode current collector.

[0110] In one embodiment of the present application, the negative electrode for a lithium secondary battery can be formed by applying and drying a negative electrode slurry containing the negative electrode composition on one or both sides of a negative electrode current collector layer.

[0111] In one embodiment of the present application, the negative electrode slurry may include a negative electrode active material layer composition and a slurry solvent.

[0112] In one embodiment of the present application, the content of the solid component of the negative electrode slurry can satisfy 5% or more and 40% or less.

[0113] In another embodiment, the content of the solid component of the negative electrode slurry can satisfy the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0114] The content of the solid component of the negative electrode slurry may mean the content of the negative electrode active material layer composition contained in the negative electrode slurry, or may mean the content of the negative electrode active material layer composition based on 100 parts by weight of the negative electrode slurry.

[0115] When the content of the solid component of the negative electrode slurry satisfies the above range, during the formation of the negative electrode active material layer, the viscosity is appropriate, the agglomeration phenomenon of the particles of the negative electrode composition is minimized, and the negative electrode active material layer can be efficiently formed.

[0116] In one embodiment of the present application, the slurry solvent can be used without limitation as long as it can disperse the above-mentioned negative electrode composition. Specifically, water or NMP may be used.

[0117] FIG. 1 is a diagram showing the laminated structure of a negative electrode for 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 can be confirmed on one surface of the negative electrode current collector layer 10. FIG. 1 shows that the negative electrode active material layer is formed on one surface, but it may be included on both surfaces of the negative electrode current collector layer.

[0118] 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 surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. Further, fine irregularities may be formed on the surface to strengthen the binding force of the negative electrode active material, and it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0119] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

[0120] However, the thickness may vary diversely depending on the type and use of the negative electrode used, and is not limited thereto.

[0121] In one embodiment of the present application, the porosity of the negative electrode active material layer can satisfy the range of 10% or more and 60% or less.

[0122] In another embodiment, the porosity of the negative electrode active material layer can satisfy the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0123] 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, by including the silicon-based active material and conductive material according to the present application in specific compositions and content portions, the above range is satisfied, and thereby the electrode has appropriate ranges of electrical conductivity and resistance.

[0124] In one embodiment of the present application, a lithium secondary battery is provided, which includes 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.

[0125] FIG. 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 can be confirmed on one surface of a negative electrode current collector layer 10, and a positive electrode 200 for a lithium secondary battery including a positive electrode active material layer 40 can be confirmed on one surface of a positive electrode current collector layer 50. It shows that the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are laminated with a separator 30 interposed therebetween.

[0126] A secondary battery according to an embodiment of the present specification may particularly 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 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, a specific description thereof will be omitted.

[0127] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0128] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of aluminum or stainless steel may be used. Further, the positive electrode current collector may usually 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 force of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc.

[0129] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 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-c2Ni-site type lithium nickel oxide represented by Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01 ≦ c2 ≦ 0.6); chemical formula LiMn 2-c3 M c3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and 0.01 ≦ c3 ≦ 0.6) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include LiMn2O4 in which part of Li in the chemical formula is substituted with alkaline earth metal ions, but are not limited thereto. The positive electrode may be metallic lithium (Li-metal).

[0130] In one embodiment of the present application, the positive electrode active material includes a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), the lithium composite transition metal compound includes single particles or secondary particles, and the average particle size (D50) of the single particles may be 1 μm or more.

[0131] 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.

[0132] The single particles may be formed with a small particle size having an average particle size (D50) of 1 μm or more and 12 μm or less, and may have excellent particle strength. For example, when the single particles are rolled with a force of 650 kgf / cm 2 they can have a particle strength of 100 MPa to 300 MPa. Thereby, even when the single particles are rolled with a strong force of 650 kgf / cm 2 the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, and the life characteristics of the battery are improved.

[0133] The single particles can be manufactured by mixing a transition metal precursor and a lithium raw material and then firing them. The secondary particles may be manufactured by a method different from that of the single particles, and their composition may be the same as or different from that of the single particles.

[0134] The method for forming the single particles is not particularly limited. Generally, they may be formed by increasing the firing temperature to overfire, using additives such as a particle growth promoter useful for overfiring, or changing the starting materials, etc.

[0135] For example, the firing is carried out at a temperature capable of forming single particles. To form these, firing should be carried out at a temperature higher than that during the production of secondary particles. For example, when the composition of the precursor is the same, firing needs to be carried out at a temperature about 30 °C to 100 °C higher than that during the production of secondary particles. The firing temperature for forming the single particles may vary depending on the metal composition in the precursor. For example, when attempting to form a high-content nickel (High-Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more into single particles, the firing temperature may be 700 °C to 1000 °C, preferably 800 °C to 950 °C. When the firing temperature satisfies the above range, a cathode active material containing single particles with excellent electrochemical properties can be manufactured. When the firing temperature is less than 790 °C, a cathode active material containing a lithium composite transition metal compound in the form of secondary particles can be manufactured. When it exceeds 950 °C, it may be overfired and a layered crystal structure cannot be sufficiently formed, resulting in a possible decrease in electrochemical properties.

[0136] In this specification, the single particles are terms used to distinguish from the secondary particles formed by the aggregation of dozens to hundreds of conventional primary particles, and include the concept of single particles composed of one primary particle and similar-single particle forms that are aggregates of 30 or fewer primary particles.

[0137] Specifically, in the present invention, the single particle may be a single particle composed of one primary particle or an agglomerate of 30 or fewer primary particles in a similar-single particle form, and the secondary particle may be in a form in which several hundred primary particles are aggregated.

[0138] In one embodiment of the present application, the lithium composite transition metal compound as the positive electrode active material further includes secondary particles, and the average particle size (D50) of the single particle is smaller than the average particle size (D50) of the secondary particle.

[0139] In the present invention, the single particle may be a single particle composed of one primary particle or an agglomerate of 30 or fewer primary particles in a similar-single particle form, and the secondary particle may be in a form in which several hundred primary particles are aggregated.

[0140] The above-described lithium composite transition metal compound may further include secondary particles. The secondary particle means a form formed by aggregation of primary particles, and can be distinguished from the concept of a single particle including a single primary particle, a single particle, or an agglomerate of 30 or fewer primary particles in a similar-single particle form.

[0141] The particle size (D50) of the secondary particle may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particle may be 0.05 m 2 / g to 10 m 2 / g, preferably 0.1 m 2 / g to 1 m 2 / g, more preferably 0.3 m 2 / g to 0.8 m 2 / g.

[0142] In an additional embodiment of the present application, the secondary particles are aggregates of primary particles, and the average particle diameter (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in a form in which several hundred primary particles are aggregated, and the average particle diameter (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.

[0143] When the average particle diameter (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 diameter (D50) of the primary particles is too small, the number of aggregated primary particles forming lithium nickel-based oxide particles increases, and the effect of suppressing particle cracking during rolling decreases. If the average particle diameter (D50) of the primary particles is too large, the lithium diffusion path inside the primary particles becomes long, the resistance increases, and the output characteristics may deteriorate.

[0144] According to an additional embodiment of the present application, the average particle diameter (D50) of the single particles is characterized by being smaller than the average particle diameter (D50) of the secondary particles. Thereby, even if the single particles are formed with a small particle diameter, their particle strength is excellent, and thus the phenomenon of an increase in fine particles in the electrode due to particle cracking can be alleviated, and the life characteristics of the battery can be improved.

[0145] In one embodiment of the present application, the average particle diameter (D50) of the single particles is smaller than the average particle diameter (D50) of the secondary particles.

[0146] For example, the average particle diameter (D50) of the single particles may be 1 μm to 16 μm smaller than the average particle diameter (D50) of the secondary particles, may be 1.5 μm to 15 μm smaller, or may be 2 μm to 14 μm smaller.

[0147] 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, even if the single particles are formed with a small particle size, they have excellent particle strength. As a result, the phenomenon of an increase in fine particles in the electrode due to particle cracking is alleviated, and there is an effect of improving the life characteristics and energy density of the battery.

[0148] According to an additional embodiment of the present application, the single particles are contained in an amount of 15 parts by weight to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material. The single particles may be contained in an amount of 20 parts by weight to 100 parts by weight, or 30 parts by weight to 100 parts by weight with respect to 100 parts by weight of the positive electrode active material.

[0149] For example, the single particles may be contained 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 with respect to 100 parts by weight of the positive electrode active material. The single particles may be contained in an amount of 100 parts by weight or less with respect to 100 parts by weight of the positive electrode active material.

[0150] When the single particles within the above range are included, excellent battery characteristics can be exhibited in combination with the negative electrode material described above. In particular, when the single particles are 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 fabricating the electrode can be alleviated, and thereby the life characteristics of the battery can be improved.

[0151] 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 with respect 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 with respect to 100 parts by weight of the positive electrode active material. The secondary particles may be 0 parts by weight or more with respect to 100 parts by weight of the positive electrode active material.

[0152] 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 positive electrode active material includes secondary particles, its components may be the same as those exemplified for the above-described single-particle positive electrode active material, or may be other components, and the single-particle form can mean an aggregated form.

[0153] In one embodiment of the present application, among 100 parts by weight of the positive electrode active material layer, 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 still more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0154] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder together with the positive electrode active material described above.

[0155] At this time, the positive electrode conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without particular limitation as long as it has electron conductivity without causing a chemical change. 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 powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Among these, one kind alone or a mixture of two or more kinds may be used.

[0156] In addition, the positive electrode binder plays a role in improving the adhesion between the positive electrode active material particles and the adhesion force between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene 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. Among these, one kind alone or a mixture of two or more kinds may be used.

[0157] The separator separates the negative electrode and the positive electrode and provides a migration path for lithium ions. Usually, any separator that can be used in a secondary battery can be used without particular limitation. In particular, those with low resistance to the ion migration of the electrolyte and excellent moisture retention ability of the electrolyte solution are preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as a polyethylene homopolymer, a polypropylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may be used. Further, a coated separator containing a ceramic component or a polymer substance to ensure heat resistance or mechanical strength may be used, and it may be selectively used in a single-layer or multi-layer structure.

[0158] 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 the manufacture of lithium secondary batteries. Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt.

[0159] 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, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc.

[0160] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and can preferably be used because they can well dissociate lithium salts. By mixing linear carbonates with low viscosities and low dielectric constants such as dimethyl carbonate and diethyl carbonate with such cyclic carbonates in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, so they can be more preferably used.

[0161] The metal salt may be a lithium salt. The lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, 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 may be used.

[0162] In addition to the constituent components of the electrolyte, 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, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the capacity reduction of the battery, improving the discharge capacity of the battery, etc.

[0163] 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. Since the battery module and the battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they may be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

Examples

[0164] Hereinafter, preferred embodiments are presented to assist in understanding the present invention. However, these embodiments are merely illustrative of the description, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope of the description and the scope of the technical idea. It is natural that such variations and modifications belong to the scope of the claims.

[0165] [Production Example] [Manufacture of Negative Electrode] As a silicon-based active material, Si (average particle size (D50): 5 μm), a first conductive material, a second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry at a weight ratio of 80:10:0.4:9.6 to produce a negative electrode slurry (solid content concentration: 25% by weight).

[0166] The first conductive material was plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0167] As a mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed at 2500 rpm for 30 minutes using a homo mixer, then the active material was added, and thereafter, it was dispersed at 2500 rpm for 30 minutes to produce a slurry.

[0168] As a negative electrode current collector, the negative electrode slurry was coated on both sides of a copper current collector (thickness: 8 μm) at a loading amount of 85 mg / 25 cm 2 and rolled, and dried in a vacuum oven at 130 °C for 10 hours to form a negative electrode active material layer, which was used as the negative electrode (void ratio of the negative electrode: 40.0%).

[0169] Thereafter, a pattern was formed on the negative electrode active material layer using a laser. The form and information of the pattern are as shown in Table 1 below. At this time, the volume (A + B) of the entire negative electrode active material layer was formed to be the same, and experiments were conducted by only changing the volume of the pattern part.

[0170]

Table 1

[0171] In Table 1, Comparative Example 1 corresponds to the case where it is manufactured in the same manner as the production of the negative electrode for the secondary battery, except that no pattern is formed.

[0172] Experimental Example 1. Initial Discharge Capacity Evaluation For the secondary battery including the negative electrode manufactured in the above Examples and Comparative Examples, the initial discharge capacity was measured at 4.2 - 3.0V 0.33C / 0.33C using an electrochemical charge and discharge device.

[0173] Experimental Example 2: Monocell Normal Temperature Life Characteristic Evaluation For the secondary battery including the negative electrode manufactured in the above Examples and Comparative Examples, life evaluation was performed using an electrochemical charge and discharge device, and the capacity retention rate was evaluated. The secondary battery was subjected to a cycle test at 4.2 - 3.0V, 1C / 0.5C, and the number of cycles at which the capacity retention rate reached 80% was measured. Capacity Retention Rate (%) = {(Discharge Capacity at the Nth Cycle) / (Discharge Capacity at the First Cycle)} × 100

[0174] Experimental Example 3. Resistance Increase Rate Measurement Evaluation In Experimental Example 2, during the test, after charging and discharging at 0.33C / 0.33C (4.2 - 3.0V) every 50 cycles to measure the capacity retention rate, discharging was performed at 2.5C pulse at SOC50 to measure the resistance, and the resistance increase rate was compared and analyzed. For the above resistance increase rate measurement evaluation, data at 150 cycles were calculated respectively.

[0175] Experimental Example 4. Cell Swelling Evaluation For the cell evaluated in Experimental Example 2, after formation in the 150 - cycle discharge (3.0V) state, the overall thickness increase rate of the comparison cell was calculated.

[0176] Experimental Example 5. Pore Resistance Evaluation Coin symmetric cells were fabricated using the negative electrodes produced in the above Examples and Comparative Examples, and the pore resistance was calculated by measuring in the range of 300 kHz to 300 mHz at 25°C using EIS. The evaluation results of Experimental Examples 1 to 5 were respectively described in Table 2 below.

[0177]

Table 2

[0178] The negative electrode for a lithium secondary battery of the present invention contains a silicon-based active material and targets high capacity and high energy density. At this time, the silicon-based active material is contained in a high content in the negative electrode active material layer, and thus, the volume expansion degree may become a problem during charge and discharge. At this time, in the case of the negative electrodes of Examples 1 to 4, the negative electrode active material layer includes a pattern portion, and in particular, it can be confirmed that the volume of the pattern portion and the negative electrode active material layer satisfies the relationship of Formula 1 described above.

[0179] It can be confirmed that the negative electrode including the negative electrode active material layer satisfying Formula 1 has less volume expansion due to charge and discharge, and the life characteristics of the lithium secondary battery can be maximized. Also, it can have the characteristics of high density and high capacity, which are the advantages of the silicon-based negative electrode, and it can be confirmed that it has the characteristic of being able to provide a lithium secondary battery with excellent rapid charging performance.

[0180] In the case of Comparative Example 1, it is for a negative electrode having no pattern portion. As can be confirmed in Experimental Example 2, the life characteristics deteriorate. As can be confirmed in Experimental Example 3, the resistance increase rate is high. And as can be confirmed in Experimental Example 4, the cell swelling is high. This corresponds to the result that no pattern portion capable of preventing this is formed due to the volume expansion and relaxation of the silicon-based active material (especially, pure silicon (Pure Si)). In this case, it was confirmed that the life characteristics decreased rapidly.

[0181] In the case of Comparative Example 2, it corresponds to the case where the negative electrode active material layer has a pattern portion as in the invention of the present application, but the range is less than the range of Formula 1, that is, the volume of the pattern portion is smaller than the set volume of the present application. Also in this case, the same results as in Comparative Example 1 were shown. That is, it was confirmed that when forming the pattern portion with a volume less than the set volume, the life characteristics deteriorate to the same extent as when not forming the pattern portion.

[0182] In the case of Comparative Example 3, it corresponds to the case where the volume of the pattern portion is formed larger than the set volume of the present application. (That is, when exceeding the range of Formula 1) In this case, it was confirmed that the life characteristics showed results similar to those of the examples of the present application. However, as a result of securing an excessive pattern portion to control volume expansion, it was confirmed that the desired capacity could not be achieved in Experimental Example 1. That is, although pure silicon (Pure Si), which has better capacity characteristics than carbon-based active materials, is used for ensuring capacity characteristics and rapid charging, when forming a large pattern portion only to solve the life characteristics in this way, it was confirmed that the capacity characteristics deteriorated instead and it could not be used as a negative electrode.

[0183] Ultimately, when satisfying the range of Formula 1 described above, not only in the case of a stacked type pouch battery, but also when winding into cylindrical and rectangular roll-shaped batteries, volume expansion can be controlled, and it becomes advantageous for high energy density and high capacity characteristics. Also, it was confirmed by the above experimental examples that even when the formation charging speed is increased compared to existing conditions, there is no difference in volume expansion, and not only the expansion in the xy direction but also the change in thickness in the z direction can be reduced.

Explanation of Signs

[0184] 10 ··· Negative electrode current collector layer 20 ··· Negative electrode active material layer 30 ··· Separator 40 ··· Positive electrode active material layer 50 ··· Positive electrode current collector layer 60 ··· Pattern portion 100 ··· Negative electrode for lithium secondary battery 200 ··· Positive electrode for lithium secondary battery

Claims

1. 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; A negative electrode for a lithium secondary battery, comprising: The negative electrode active material layer includes a pattern portion and satisfies the following formula (1): A negative electrode for a lithium secondary battery: [Formula (1)] 5 ≤ [B / (A + B)] × 100 (%) ≤ 30 In Formula (1), A means the volume of the negative electrode active material layer excluding the pattern portion, B means the volume of the pattern portion.

2. The negative electrode active material layer satisfies the following formula (2): The negative electrode for a lithium secondary battery according to Claim 1: [Formula (2)] [{(x + x1)(y + y1)(z + z1) - xyz} / xyz] × 100 (%) < 50% In Formula (2), x, y, and z are the overall width, overall length, and overall thickness of the negative electrode active material layer including the pattern portion, respectively, after manufacturing the negative electrode for the lithium secondary battery, x1, y1, and z1 mean the length changes in the x, y, and z directions, respectively, after charging at 1 / 3 C CC - CV up to 4.2 V (0.05 C cut - off) and immediately discharging at 1 / 3 C CC up to 2.5 V after manufacturing the negative electrode for the lithium secondary battery.

3. The negative electrode active material layer satisfies the following formula (3): The negative electrode for a lithium secondary battery according to Claim 1: [Formula (3)] [{(x + x2)(y + y2)(z + z2) - xyz} / xyz] × 100 (%) < 100% In Formula (3), x, y, and z are the overall width, overall length, and overall thickness of the negative electrode active material layer including the pattern portion, respectively, after manufacturing the negative electrode for the lithium secondary battery, x2, y2, and z2 mean the length changes in the x, y, and z directions, respectively, after charging at 1 C CC - CV up to 4.2 V (0.05 C cut - off) and performing 300 cycles of discharging at 0.5 C CC up to 3.0 V after manufacturing the negative electrode for the lithium secondary battery.

4. The negative electrode active material layer satisfies the following formula (4): The negative electrode for a lithium secondary battery according to Claim 1: [Formula (4)] 5 ≤ xyz - {(xi × n)yz + x(yj × m)z - nmxiyj} ≤ 30 In Formula (4), x, y, and z are the overall width, overall length, and overall thickness of the negative electrode active material layer including the pattern portion, respectively, after manufacturing the negative electrode for the lithium secondary battery, n is the number of patterns in the x - direction, m is the number of patterns in the y - direction, xi means the width of the pattern, yj means the length of the pattern, i is an integer from 1 to n, j is an integer from 1 to m.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein the pattern portion includes one or more selected from the group consisting of a 1D pattern, a 2D pattern, a V pattern, and a U pattern.

6. The negative electrode active material layer includes a negative electrode active material layer composition, The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer composition includes a silicon-based active material, a negative electrode conductive material, and a negative electrode binder.

7. The negative electrode for a lithium secondary battery according to claim 6, wherein the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) is included in an amount of 70 parts by weight or more.

8. The negative electrode for a lithium secondary battery according to claim 6, wherein the silicon-based active material is included in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode active material layer composition.

9. The negative electrode conductive material includes a planar conductive material and a linear conductive material, The negative electrode for a lithium secondary battery according to claim 6, wherein based on 100 parts by weight of the negative electrode conductive material, the planar conductive material is included in an amount of 80 parts by weight or more and 99.9 parts by weight or less; and the linear conductive material is included in an amount of 0.1 parts by weight or more and 20 parts by weight or less.

10. The negative electrode for a lithium secondary battery according to claim 6, wherein the negative electrode conductive material is 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode active material layer composition.

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

12. A positive electrode; The negative electrode for a lithium secondary battery according to any one of claims 1 to 11; A separator provided between the positive electrode and the negative electrode; and An electrolyte; A lithium secondary battery comprising the same.

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