Negative electrode active material, negative electrode for lithium secondary battery including same, and lithium secondary battery

Abstract

The present invention relates to a negative electrode active material, a negative electrode for a lithium secondary battery, including same, and a lithium secondary battery. The negative electrode active material includes a silicon-based active material; and graphite, wherein the graphite includes natural graphite and artificial graphite, an absolute value of a ratio of a difference in average particle diameter (D50) size of the natural graphite with respect to the artificial graphite is 10% or less, and an absolute value of a ratio of a difference in average particle diameter (D50) size of the silicon-based active material with respect to the artificial graphite is 40% or less.

Description

Negative active material, negative electrode for lithium secondary battery and lithium secondary battery containing same

[0001] This application claims the benefit of Korean Patent Application No. 10-2024-0073588 filed with the Korean Intellectual Property Office on June 5, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present application relates to a negative electrode active material, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery.

[0003] Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and as part of this, the most actively researched field is power generation and storage using electrochemical reactions.

[0004] A representative example of an electrochemical device that currently utilizes this electrochemical energy is the secondary battery, and its application area is gradually expanding.

[0005] The recent rapid proliferation of battery-powered electronic devices, including mobile phones, laptops, electric vehicles, power tools, and vacuum cleaners, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity and / or high-output secondary batteries. In particular, lithium secondary batteries, with their lightweight design and high energy density, are attracting attention as power sources for electronic devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0006] Lithium secondary batteries produce electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated between the positive and negative electrodes, which are made of active materials capable of intercalating and deintercalating lithium ions, while charging an organic electrolyte or polymer electrolyte between them.

[0007] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and deintercalates lithium ions from the positive electrode. A material with a high discharge capacity can be used as the negative electrode active material.

[0008] As a cathode active material constituting the cathode of a lithium secondary battery, a metal oxide such as LiCoO2, LiMnO2, LiMn2O4 or LiNiO2 is used, and as a cathode active material constituting the anode, a carbon-based material such as metal lithium, graphite or activated carbon, or silicon oxide (SiO x ) are being used. Among the above negative active materials, metallic lithium was mainly used in the early days, but as the charge and discharge cycle progressed, lithium atoms grew on the surface of metallic lithium, damaging the separator and destroying the battery. Therefore, carbon-based materials are mainly used recently.

[0009] Graphite is mainly used as an anode active material in lithium secondary batteries, but because graphite has a low capacity per unit mass of 372 mAh / g, it is difficult to increase the capacity of lithium secondary batteries. Accordingly, non-carbonaceous anode materials with higher energy density than graphite, such as silicon, tin, and their oxides, are being developed to increase the capacity of lithium secondary batteries. However, these non-carbonaceous anode materials have a large capacity, but low initial efficiency, which causes a large amount of lithium consumption during initial charge and discharge, and a large irreversible capacity loss.

[0010] Recently, in response to the demand for high-density energy batteries, research is actively being conducted on methods to increase capacity by using silicon compounds such as Si / C or SiOx, which have a capacity more than 10 times greater than graphite materials, as anode active materials. However, in the case of silicon compounds, which are high-capacity materials, although the capacity is large compared to the graphite used in the past, there is a problem that the volume expands rapidly during the charging process, which cuts off the conductive path and deteriorates the battery characteristics.

[0011] Accordingly, in order to secure appropriate capacity and stability of the cathode, a method of manufacturing an electrode by mixing graphite with a silicon-based active material with high specific capacity in an appropriate ratio is being attempted.

[0012] However, even though a method of combining silicon-based active materials and graphite is used in the negative electrode, the particle sizes of the graphite material and silicon-based active material are different, which causes a problem in that the dispersibility of each active material within the electrode is reduced, and as a result, slurry clumping occurs, which actually causes a problem in that the life performance is reduced.

[0013] Therefore, even when using a silicon-based active material as an anode active material to improve capacity performance, research is needed to improve the dispersibility of the aforementioned anode active material.

[0014] <Prior Art Literature>

[0015] (Patent Document 1) Japanese Patent Publication No. 2009-080971

[0016] The present inventors have conducted research on improving the dispersibility of the mixed negative electrode active material of the silicon-based active material and graphite mentioned above, and have found that, in particular, when the average particle diameter (D50) of the graphite material and the silicon-based active material used as the negative electrode active material is adjusted, the dispersibility of the active material within the electrode can be improved, and clusters of the silicon-based active material can be prevented, thereby realizing optimal battery performance, leading to the present invention.

[0017] One embodiment of the present invention provides a negative electrode active material, wherein the negative electrode active material comprises a silicon-based active material; and graphite, wherein the graphite comprises natural graphite and artificial graphite, and wherein the ratio of the difference in average particle diameter (D50) size between the natural graphite and the artificial graphite is 10% or less in absolute value, and the ratio of the difference in average particle diameter (D50) size between the artificial graphite and the silicon-based active material is 40% or less in absolute value.

[0018] Another embodiment of the present invention provides an anode for a lithium secondary battery, comprising: a cathode current collector layer; and a cathode active material layer provided on one or both sides of the cathode current collector layer, wherein the cathode active material layer includes the cathode active material described above.

[0019] Finally, it is an object to provide a lithium secondary battery comprising: a positive electrode; an anode for the aforementioned lithium secondary battery; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0020] In the case of the negative electrode active material according to one embodiment of the present invention, the ratio of the difference in the average particle diameter (D50) size between the artificial graphite and natural graphite is controlled to an absolute value of 10% or less, and the ratio of the difference in the average particle diameter (D50) size between the artificial graphite and the silicon-based active material is controlled to an absolute value of 40% or less. In this way, by controlling the average particle diameter (D50) of the negative electrode active material included in the negative electrode, the dispersibility of the negative electrode active material in the negative electrode slurry can be improved, and the negative electrode manufactured thereby has the characteristic of improving the dispersibility of different or more types of active materials in the electrode, thereby suppressing local volume expansion and stress concentration phenomenon, and improving the life characteristics of the electrode.

[0021] Specifically, by limiting the average particle size of the silicon-based active material and artificial graphite as described above, the silicon-based active material has a smaller particle size than the graphite-based active material, and when the negative electrode slurry is mixed and the electrode is coated while the particle sizes are different, a phenomenon occurs where the silicon-based active material, which has a smaller particle size than the graphite-based active material, locally forms clusters. The clusters of the silicon-based active material undergo a large volume change during the charge / discharge process compared to the surrounding graphite-based active material, which acts as a factor accelerating the deterioration of the electrode. Therefore, it is necessary to control the difference in the average particle size of the silicon-based active material and artificial graphite as described above.

[0022] Likewise, in the case of natural graphite and artificial graphite in graphite-based active materials, the average particle size is controlled as in the present application, and through such control, the active material in the electrode is evenly distributed, thereby preventing local stress generation, reaction promotion, and deterioration during the operation of the battery, and has the characteristic of being able to manufacture a uniformly distributed electrode.

[0023] That is, rather than simply controlling the average particle size of the silicon-based active material and graphite, or controlling the average particle size of the artificial graphite and natural graphite within the graphite alone, the above-mentioned problem can be solved by controlling the difference value between the average particle size of the silicon-based active material and the artificial graphite and the artificial graphite and natural graphite contained within the graphite.

[0024] Figure 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.

[0025] Figure 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application.

[0026] <Explanation of symbols>

[0027] 10: Negative current collector layer

[0028] 20: Negative active material layer

[0029] 30: Membrane

[0030] 40: Positive active material layer

[0031] 50: Positive current collector layer

[0032] 100: Cathode for lithium secondary batteries

[0033] 200: Cathode for lithium secondary batteries

[0034] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0035] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0036] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0037] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0038] Furthermore, when we say that a part of a layer or the like is "above" or "on" another part, this includes not only cases where it is "directly above" that part, but also cases where there is another part in between. Conversely, when we say that a part is "directly above" another part, it means that there is no other part in between. Furthermore, when we say that a part is "above" or "on" a reference part, it means that it is located above or below that reference part, and does not necessarily mean that it is located "above" or "on" in the direction opposite to gravity.

[0039] In this specification, "specific surface area" is measured by the BET method, and specifically, it can be measured by removing gas (degassing) from a measurement target at 130°C for 2 hours and performing N2 absorption / desorption at 77K using BET measuring equipment (BEL-SORP-mini, Nippon Bell). That is, the BET specific surface area in this specification can mean the specific surface area of ​​the particle itself measured by the above measurement method.

[0040] In this specification, the average length or diameter of the challenge material can be measured using SEM or TEM.

[0041] In this specification, "Dn" means particle size distribution, and means the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. That is, D50 is the particle size (average particle size) at the 50% point of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at the 90% point of the cumulative distribution of particle numbers according to particle size, and D10 is the particle size at the 10% point of the cumulative distribution of particle numbers according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the difference in diffraction pattern according to particle size is measured when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0042] In the present application, the “Dn” of the active material in the negative electrode can be measured by confirming the size of the active material contained in the negative electrode after the final charge / discharge after manufacturing the negative electrode, and specifically, in the case of the average particle diameter (D50), when the cross-section of the negative electrode active material layer is continuously cut after manufacturing the negative electrode and the final charge / discharge, this can be measured in the electrode cross-section. At this time, a 3D imaging technique can be utilized, and specifically, a 3D image can be obtained by stacking images of cross-sections obtained continuously, and through this, it is possible to compare the average particle diameters of active materials in the battery after charge / discharge.

[0043] In one embodiment of the present application, particle size or particle diameter may mean the average diameter or representative diameter of each grain forming the metal powder.

[0044] As used herein, the term "a polymer comprises a monomer as a monomer unit" means that the monomer participates in a polymerization reaction and is included as a repeating unit within the polymer. As used herein, "a polymer comprises a monomer" is interpreted to mean that the polymer comprises the monomer as a monomer unit.

[0045] In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers unless 'homopolymer' is specified.

[0046] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-converted 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 materials. In this specification, molecular weight means weight average molecular weight unless otherwise specified.

[0047] Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice it. However, the present invention can be implemented in various different forms and is not limited to the following description.

[0048] One embodiment of the present invention provides a negative electrode active material, wherein the negative electrode active material comprises a silicon-based active material; and graphite, wherein the graphite comprises natural graphite and artificial graphite, and wherein the ratio of the difference in average particle diameter (D50) size between the natural graphite and the artificial graphite is 10% or less in absolute value, and the ratio of the difference in average particle diameter (D50) size between the artificial graphite and the silicon-based active material is 40% or less in absolute value.

[0049] The negative electrode according to the present application includes natural graphite, artificial graphite, and silicon-based active materials. Artificial graphite has a relatively slow rate of change, but high structural stability, and natural graphite has a relatively large volume change compared to artificial graphite, but has a high rate of change, so the two graphites have different properties. When constructing a graphite electrode using these properties, the two graphites are blended and used to compensate for the difference in properties, and in particular, the present application constructs an electrode using a silicon-based active material together to compensate for the relatively low specific capacity of graphite.

[0050] When using one type of active material, there is no major problem, but when using multiple types of active materials at the same time, differences in particle size occur, and materials with small particle sizes form clusters within the electrode, causing local unevenness. At this time, the volume change of the Si-based active material forming the cluster is accompanied by a larger volume expansion than that of the surrounding graphite-based active material, which causes local stress and structural changes within the electrode, as well as loss of conductivity, resulting in problems such as increased internal resistance of the electrode and decreased lifespan.

[0051] The present application recognizes the above problems and, in response to the application of artificial graphite, natural graphite, and silicon-based active materials simultaneously, is characterized by controlling the particle size relationship of natural graphite and silicon-based active materials based on artificial graphite. In other words, it has the characteristic of being able to control the occurrence of local unevenness according to the particle size relationship of each active material.

[0052] In the present application, the negative active material includes a silicon-based active material and graphite.

[0053] In the present application, the silicon-based active material is Si, SiOx (0 <x<2), Si / C, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함할 수 있다.

[0054] In the present application, when the silicon-based active material is Si, the content of Si in the silicon-based active material may be 98% or more, 99% or more, and specifically 100%.

[0055] In the present application, when the silicon-based active material is the remainder excluding Si, the content of Si based on 100 parts by weight of the silicon-based active material may include 40 parts by weight or more and 80 parts by weight or less. That is, the content of the Si element itself in the silicon-based active material may satisfy the above range.

[0056] In the present application, the Si / C may be expressed as a silicon carbon composite.

[0057] In this specification, the silicon-carbon composite is a composite of Si and C, and is distinct from silicon carbide, denoted as SiC. Since the silicon carbide does not electrochemically react with lithium, all performances, including lifespan, may be measured as 0.

[0058] The above silicon-carbon composite may be a composite of silicon and graphite, and may also form a structure in which a core composed of silicon and graphite is surrounded by graphene or amorphous carbon. The silicon in the silicon-carbon composite may be nano-silicon. For example, the nano-silicon may be silicon having a particle size ranging from 1 nm to 999 nm.

[0059] In the present application, the graphite includes natural graphite and artificial graphite.

[0060] In the present application, the ratio of the difference in average particle diameter (D50) between the artificial graphite and the natural graphite may be an absolute value of 10% or less.

[0061] In another embodiment, the ratio of the difference in average particle diameter (D50) between the artificial graphite and the natural graphite may be 10% or less in absolute value, preferably 9% or less, more preferably 8.5% or less, and may be 1% or more or 3% or more.

[0062] In the present application, the ratio of the difference in average particle diameter (D50) size between the artificial graphite and the silicon-based active material may be an absolute value of 40% or less.

[0063] In another embodiment, the ratio of the difference in average particle diameter (D50) size between the artificial graphite and the silicon-based active material may be 40% or less in absolute value, preferably 38% or less, more preferably 35% or less, and may be 1% or more, 5% or more, 10% or more, or 20% or more.

[0064] The present application is characterized by controlling the average particle diameters of the silicon-based active material, artificial graphite, and the artificial graphite and natural graphite contained within the graphite as described above. By satisfying the above range, the three types of active materials included in the negative electrode slurry can exhibit uniform dispersion without forming individual clusters. Accordingly, local reaction promotion, stress concentration, and electrode deterioration due to different reactivity with lithium ions can be improved, and the lifespan of the manufactured negative electrode can be improved accordingly.

[0065] Specifically, the reason for limiting the particle size difference between the silicon-based active material and the artificial graphite as described above is that the silicon-based active material has a smaller particle size than the graphite material, and when the slurry is mixed and the electrode is coated in a state where the particle sizes are different, the silicon-based active material with smaller particle sizes locally forms clusters, and since these clusters of the silicon-based active material have a larger volume change during the charge / discharge process than the surrounding graphite material, they act as a factor accelerating the deterioration of the electrode, and this is to prevent this phenomenon. At this time, the particle sizes of the silicon-based active material and the entire graphite were not compared, but the particle sizes of the artificial graphite among graphite were compared, which has a similar meaning to comparing the particle sizes of the entire graphite.

[0066] In the present application, the absolute value ratio of the difference in the average particle diameter (D50) between the artificial graphite and the natural graphite can be calculated as |{(AB) / A}| x 100%, where the average particle diameter of the artificial graphite is defined as A and the average particle diameter of the natural graphite is defined as B.

[0067] In the present application, the absolute value ratio of the difference in the average particle diameter (D50) between the artificial graphite and the silicon-based active material can be calculated as |{(AC) / A}| x 100%, where the average particle diameter of the artificial graphite is defined as A and the average particle diameter of the silicon-based active material is defined as C.

[0068] That is, when the average particle size of the silicon-based active material or natural graphite is within a certain range, larger or smaller than that of artificial graphite, and included within a certain ratio, the aforementioned effect can be achieved.

[0069] In the present application, the average particle diameter (D50) of the silicon-based active material may be 1 ㎛ or more and 10 ㎛ or less.

[0070] In another embodiment, the average particle diameter (D50) of the silicon-based active material can satisfy a range of 1 ㎛ or more and 10 ㎛ or less, 2 ㎛ or more and 10 ㎛ or less, or 4 ㎛ or more and 10 ㎛ or less.

[0071] In the present application, the average particle diameter (D50) of the graphite may be 5 ㎛ or more and 20 ㎛ or less.

[0072] In another embodiment, the average particle diameter (D50) of the graphite may be 5 µm or more and 20 µm or less, preferably 6 µm or more and 18 µm or less, and more preferably 7 µm or more and 17 µm or less.

[0073] In the present application, the average particle diameter (D50) of the natural graphite may be 5 µm or more and 20 µm or less, and the average particle diameter (D50) of the artificial graphite may be 5 µm or more and 20 µm or less.

[0074] In another embodiment, the average particle diameter (D50) of the natural graphite may be 5 µm or more and 20 µm or less, preferably 7 µm or more and 17 µm or less, and more preferably 9 µm or more and 15 µm or less.

[0075] In another embodiment, the average particle diameter (D50) of the artificial graphite may be 5 µm or more and 20 µm or less, preferably 8 µm or more and 18 µm or less, and more preferably 10 µm or more and 16 µm or less.

[0076] In the present application, the average particle size of the graphite may refer to the average particle size (D50) of the entire average of artificial graphite and natural graphite contained in the graphite. In this case, the present application does not compare the particle size of the silicon-based active material with that of the entire graphite, but rather compares it with the particle size of artificial graphite among graphite, but this has a similar meaning to comparing it with the particle size of the entire graphite.

[0077] In the present application, the average particle diameters of the silicon-based active material and the graphite can be used without limitation as long as they satisfy the above-mentioned average particle diameter difference, but in particular, when using the silicon-based active material and graphite having the above-mentioned average particle diameter range, the silicon-based active material can be prevented from forming local clusters within the electrode, and thus, negative reactions such as local stress generation, promotion of reaction with lithium ions, and rapid deterioration of the active material due to the silicon-based active material having a large volume change during the charge / discharge process compared to the surrounding graphite material can be suppressed.

[0078] In the present application, the reason for limiting the difference in particle size between natural and artificial graphite to a certain level is the same as described above. If a difference in particle size occurs, the active material is not evenly distributed within the electrode, which may cause local stress, reaction acceleration, deterioration, etc. during the operation of the battery. Accordingly, in order to manufacture a uniform electrode, all active materials must have a difference in particle size within the scope of the present application.

[0079] In one embodiment of the present application, the weight ratio of the silicon-based active material:graphite based on 100 parts by weight of the negative electrode active material may be 5:95 to 40:60.

[0080] In another embodiment, the weight ratio of the silicon-based active material:graphite based on 100 parts by weight of the negative active material can be 5:95 to 40:60, preferably 7:93 to 35:75, and more preferably 10:90 to 30:70.

[0081] In the present application, the ratio of silicon-based active material and graphite in the negative active material is characterized by satisfying the above range. Silicon-based active material is known to have excellent capacity characteristics, but when applied in high content due to volume expansion during charging and discharging, life performance may be reduced due to volume expansion, and when included in low content, it may be difficult to improve capacity characteristics. Therefore, by having the above content, it has the characteristic of improving life characteristics along with capacity characteristics.

[0082] In the present application, the weight ratio of the artificial graphite:natural graphite based on 100 parts by weight of the graphite may be 60:40 to 80:20.

[0083] In another embodiment, the weight ratio of the artificial graphite:natural graphite based on 100 parts by weight of the graphite can be satisfied as 60:40 to 80:20, preferably 65:35 to 78:22, and more preferably 70:30 to 75:25.

[0084] Graphite can be either synthetic or natural. Synthetic graphite has been shown to have superior cell characteristics compared to natural graphite, leading to a reduction in the use of natural graphite and an increase in the use of synthetic graphite. However, from a cost perspective, synthetic graphite requires coke to be calcined and graphitized, resulting in high processing costs. Therefore, if the above range is met, it can offer the advantage of improved cell characteristics while minimizing cost.

[0085] In the present application, the negative electrode active material may be comprised of artificial graphite, natural graphite, and silicon-based active material in a small weight ratio in that order.

[0086] In the present application, the average particle diameter (D50) of the artificial graphite may be larger than the average particle diameter (D50) of the natural graphite, and the average particle diameter (D50) of the natural graphite may be larger than the average particle diameter (D50) of the silicon-based active material.

[0087] In the present application, based on the average particle diameter (D50) of artificial graphite having the highest weight ratio in the negative active material, the relationship of average particle diameter (D50) of artificial graphite > natural graphite > silicon-based active material can be satisfied.

[0088] In the present application, based on the average particle diameter (D50) of artificial graphite having the highest weight ratio in the negative active material, the relationship of natural graphite > artificial graphite > average particle diameter (D50) of silicon-based active material can be satisfied.

[0089] In the present application, the relationship of artificial graphite > natural graphite > average particle diameter (D50) of silicon-based active material is satisfied based on the average particle diameter (D50) of artificial graphite having the highest weight ratio in the negative electrode active material, and the average particle diameter of the natural graphite based on the average particle diameter of the artificial graphite is in a range having a difference of 10% or less, and the average particle diameter of the silicon-based active material based on the average particle diameter of the artificial graphite may be smaller in a range of 20% or more and 40% or less.

[0090] In the present application, the average particle diameter (D50) of the artificial graphite having the highest weight ratio in the negative active material is based on the relationship of natural graphite > artificial graphite > average particle diameter (D50) of the silicon-based active material, and the average particle diameter of the artificial graphite based on the average particle diameter of the natural graphite is in a range having a difference of 10% or less, and the average particle diameter of the silicon-based active material based on the average particle diameter of the artificial graphite may be smaller in a range of 20% or more and 40% or less.

[0091] That is, if the average particle size values ​​of artificial graphite and natural graphite satisfy the difference value described above, the average particle size of artificial graphite may be larger or smaller than that of natural graphite.

[0092] In the present application, a negative electrode composition including the above negative electrode active material is provided.

[0093] In the present application, the negative electrode composition may further include, in addition to the silicon-based active material, a negative electrode conductive material; and a negative electrode binder.

[0094] That is, in the present application, the negative electrode composition including the negative electrode active material may further include a negative electrode conductive material and a negative electrode binder.

[0095] At this time, the cathode composition and the cathode slurry are different from each other, and when the cathode composition includes a slurry solvent, it can be expressed as a cathode slurry.

[0096] In the present application, the negative electrode active material may be included in an amount of 90 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0097] In another embodiment, the negative active material may be 90 parts by weight or more, 91 parts by weight or more, 92 parts by weight or more, and 95 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0098] By including a negative electrode active material in the above range, it has the characteristics of being able to secure the capacity characteristics and energy density of the negative electrode.

[0099] Previously, graphite compounds were typically used solely as negative electrode active materials. However, with the increasing demand for high-capacity batteries, attempts to mix silicon-based active materials to increase capacity have been increasing. However, even if the properties of silicon-based active materials themselves are adjusted as described above, the rapid expansion of volume during the charge / discharge process can cause some problems, damaging the conductive path formed within the negative electrode active material layer.

[0100] Therefore, in one embodiment of the present application, the negative electrode conductive material may include at least one selected from the group consisting of a dot-shaped conductive material, a planar conductive material, and a linear conductive material.

[0101] In one embodiment of the present application, the dot-shaped conductive material may be used to improve conductivity of the negative electrode, and refers to a dot-shaped or spherical conductive material having conductivity without causing chemical change. 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, paneth black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of implementing high conductivity and excellent dispersibility.

[0102] In one embodiment of the present application, the dot-shaped conductive material has a BET specific surface area of ​​40 m 2 / g or more than 70m 2 / g or less, preferably 45m 2 / g or more than 65m 2 / g or less, more preferably 50m 2 / g or more than 60m 2 / g can be less.

[0103] In one embodiment of the present application, the dot-shaped conductive material can satisfy a volatile matter content of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less.

[0104] In particular, 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, so that when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed within the solvent. In particular, in the present invention, the functional group content of the dot-shaped conductive material can be reduced by using a specific silicon-based active material, thereby having an excellent effect in improving dispersibility.

[0105] 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 functional group content can be controlled by adjusting the degree of heat treatment of the dot-shaped conductive material.

[0106] 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.

[0107] In one embodiment of the present application, the conductive material may include a planar conductive material.

[0108] The above-mentioned planar conductive material can improve conductivity by increasing planar contact between silicon particles within the cathode, and at the same time, suppress the disconnection of conductive paths due to volume expansion. The above-mentioned planar conductive material can be expressed as a plate-shaped conductive material or a bulk conductive material.

[0109] 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 may preferably be plate-shaped graphite.

[0110] In one embodiment of the present application, the average particle diameter (D50) of the surface-shaped conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the above range is satisfied, dispersion is easy without causing excessive viscosity increase of the negative electrode slurry due to sufficient particle size. Therefore, the dispersion effect is excellent when dispersion is performed using the same equipment and time.

[0111] In one embodiment of the present application, the surface-shaped conductive material provides a negative electrode composition having 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.

[0112] In one embodiment of the present application, the planar conductive material may be a high-specific surface area planar conductive material having a high BET surface area; or a low-specific surface area planar conductive material.

[0113] In one embodiment of the present application, a high surface area surface conductive material or a low surface area surface conductive material may be used without limitation as the surface conductive material, but in particular, since the surface conductive material according to the present application may be affected to some extent by dispersion in electrode performance, it may be particularly preferable to use a low surface area surface conductive material that does not cause dispersion problems.

[0114] In one embodiment of the present application, the surface-shaped conductive material has a BET specific surface area of ​​0.25 m 2 / g can be more than that.

[0115] In another embodiment, the surface-shaped conductive material has a BET surface area of ​​1 m 2 / g or more than 500m 2 / g or less, preferably 5m 2 / g or more than 300m 2 / g or less, more preferably 5m 2 / g or more than 250m 2 / g can be less.

[0116] The planar conductive material according to the present application may be a planar conductive material with a high specific surface area; or a planar conductive material with a low specific surface area.

[0117] In another embodiment, the surface-shaped conductive material is a high surface area surface-shaped conductive material, and has a BET surface area of ​​50 m 2 / g or more than 500m 2 / g or less, preferably 80m 2 / g or more than 300m 2 / g or less, more preferably 100m 2 / g or more than 300m 2 / g can satisfy the range below.

[0118] In another embodiment, the surface-shaped conductive material is a low surface area surface-shaped conductive material, and has a BET surface area of ​​1 m 2 / g or more than 40m 2 / g or less, preferably 5m 2 / g or more than 30m 2 / g or less, more preferably 5m 2 / g or more than 25m 2 / g can satisfy the range below.

[0119] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the term "bundle type" herein refers to a secondary shape in the form of a bundle or rope, in which a plurality of carbon nanotube units are arranged in a substantially identical orientation with their longitudinal axes aligned in parallel or entangled, unless otherwise specified. The carbon nanotube units have a cylindrical shape of a graphite sheet with a nano-sized diameter and an sp2 bonding structure. At this time, the graphite sheets may exhibit conductor or semiconductor properties depending on the angle and structure at which they are rolled. The above bundled carbon nanotubes can be uniformly dispersed during the manufacture of a cathode compared to entangled type carbon nanotubes, and can smoothly form a conductive network within the cathode, thereby improving the conductivity of the cathode.

[0120] In one embodiment of the present application, a negative electrode composition is provided in which the negative electrode conductive material is present in an amount of 0.1 parts by weight or more and 5 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0121] In another embodiment, the negative electrode conductive material may be included in an amount of 0.1 to 5 parts by weight, preferably 0.2 to 3 parts by weight, more preferably 0.2 to 2 parts by weight, and most preferably 0.2 to 1 part by weight, based on 100 parts by weight of the negative electrode composition.

[0122] In particular, in one embodiment of the present application, since the negative electrode conductive material includes a linear conductive material and satisfies the above composition and ratio, it does not have a significant effect on the life characteristics of an existing lithium secondary battery, and the number of points at which charging and discharging are possible increases, resulting in excellent output characteristics at a high C-rate.

[0123] The negative electrode conductive material according to the present application has a completely separate composition from the positive electrode conductive material applied to the positive electrode. That is, the negative electrode conductive material according to the present application serves to secure the contact between silicon-based active materials, which undergo a significant volume expansion of the electrode due to charging and discharging, and the positive electrode conductive material serves to provide some conductivity while acting as a buffer during rolling, and is completely different in composition and role from the negative electrode conductive material of the present invention.

[0124] In addition, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different composition from the conductive material applied to a graphite-based active material. 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 some conductivity, and is completely different in composition and role from the negative electrode conductive material applied together with a silicon-based active material as in the present invention.

[0125] In one embodiment of the present application, the planar conductive material used as the aforementioned negative electrode conductive material has a structure and function different from those of carbon-based active materials generally used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material processed into a spherical or dot-shaped form to facilitate the storage and release of lithium ions.

[0126] On the other hand, the planar conductive material used as the negative electrode conductive material is a material having a planar or plate-like shape, and can be expressed as plate-like graphite. In other words, it refers to a material included to maintain a conductive path within the negative electrode active material layer, and is not a material that plays a role in storing and releasing lithium, but rather a material that secures a conductive path in a planar shape within the negative electrode active material layer.

[0127] 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-shaped form and used as a material that secures a conductive path rather than a role for storing or releasing lithium. In this case, the included negative electrode active material has high capacity characteristics for lithium storage and release, and serves to store and release all lithium ions delivered from the positive electrode.

[0128] On the other hand, in the present application, the use of graphite as an active material means that it is processed into a dot or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0129] That is, in one embodiment of the present application, the graphite, artificial graphite or natural graphite, is in the form of dots and has a BET specific surface area of ​​0.1 m 2 / g or more than 4.5 m 2 / g or less can be satisfied. In addition, the plate-shaped graphite, which is a planar conductive material, has a BET surface area of ​​5 m in the form of a planar surface. 2 / g can be more than that.

[0130] 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), fluoroelastomer, polyacrylic acid, and a material in which hydrogens thereof are substituted with Li, Na, Ca, or the like, and may also include various copolymers thereof.

[0131] The negative electrode binder according to one embodiment of the present application serves to hold the active material and conductive material in order to prevent distortion and structural deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. If the above-mentioned role is satisfied, all general binders can be applied, and specifically, an aqueous binder can be used, and more specifically, a PAM-based binder can be used.

[0132] In one embodiment of the present application, the negative electrode binder may be in an amount of 1 part by weight or more and 10 parts by weight or less, preferably 2 parts by weight or more and 9 parts by weight or less, and more preferably 2 parts by weight or more and 8 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0133] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, which includes a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer includes a negative electrode active material according to the present application.

[0134] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, comprising: a negative electrode current collector layer; and a negative electrode active material layer including a negative electrode composition according to the present application, or a cured product thereof, or a dried product thereof, formed on one or both sides of the negative electrode current collector layer.

[0135] Fig. 1 is a diagram showing a laminated structure of an anode for a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode (100) including an anode active material layer (20) on one surface of an anode current collector layer (10) can be confirmed, and although Fig. 1 shows that the anode active material layer is formed on one surface, it can be included on both surfaces of the anode current collector layer.

[0136] In one embodiment of the present application, the negative electrode for the lithium secondary battery can be formed by applying and drying a negative electrode slurry containing the negative electrode composition to one or both sides of a negative electrode current collector layer.

[0137] At this time, the cathode slurry may include the cathode composition described above; and a slurry solvent.

[0138] In one embodiment of the present application, the solid content of the cathode slurry can satisfy 5% or more and 40% or less.

[0139] In another embodiment, the solid content of the cathode slurry can satisfy a 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.

[0140] The solid content of the above cathode slurry may mean the content of the cathode composition included in the cathode slurry, and may mean the content of the cathode composition based on 100 parts by weight of the cathode slurry.

[0141] When the solid content of the above negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer, thereby minimizing particle agglomeration of the negative electrode composition, and thus has the characteristic of efficiently forming the negative electrode active material layer.

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

[0143] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. The negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding strength of the negative electrode active material can be strengthened by forming fine unevenness on the surface, and can be used in various forms such as a film, sheet, foil, net, porous body, foam, non-woven fabric, etc.

[0144] 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 5 μm or more and 500 μm or less.

[0145] However, the thickness can be varied depending on the type and purpose of the cathode used and is not limited thereto.

[0146] In one embodiment of the present application, the porosity of the negative electrode active material layer can satisfy a range of 10% or more and 60% or less.

[0147] In another embodiment, the porosity of the negative electrode active material layer can satisfy a 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.

[0148] The above porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder included in the negative electrode active material layer, and in particular, by including the silicon-based active material and conductive material according to the present application in a specific composition and content portion, the above range is satisfied, and accordingly, the electrode is characterized by having an appropriate range of electrical conductivity and resistance.

[0149] In one embodiment of the present application, a lithium secondary battery is provided, including: a positive electrode; an anode for a lithium secondary battery according to the present application; a separator provided between the positive electrode and the negative electrode; and an electrolyte.

[0150] In the present application, the negative electrode active material layer may further include a negative electrode conductive material and a negative electrode binder.

[0151] In the present application, the negative electrode active material may be included in an amount of 90 parts by weight or more based on 100 parts by weight of the composition included in the negative electrode active material layer.

[0152] In the present application, the negative electrode conductive material may be 0.1 parts by weight or more and 5 parts by weight or less based on 100 parts by weight of the composition included in the negative electrode active material layer, and the negative electrode binder may be 1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the composition included in the negative electrode active material layer.

[0153] At this time, the composition included in the negative electrode active material layer may be the negative electrode composition described above.

[0154] FIG. 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery negative electrode (100) including a negative electrode active material layer (20) on one surface of a negative electrode current collector layer (10) can be confirmed, and a lithium secondary battery positive electrode (200) including a positive electrode active material layer (40) on one surface of a positive electrode current collector layer (50) can be confirmed, and it is shown that the lithium secondary battery negative electrode (100) and the lithium secondary battery positive electrode (200) are formed in a laminated structure with a separator (30) interposed therebetween.

[0155] A secondary battery according to one embodiment of the present specification may particularly include the negative electrode for a lithium secondary battery as 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, wherein the negative electrode is identical to the negative electrode described above. Since the negative electrode has been described above, a detailed description thereof will be omitted.

[0156] The above 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.

[0157] In the above positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the current collector to increase the adhesive strength of the positive electrode active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0158] The above positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; or a compound having the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4(0≤c1≤0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≤c2≤0.3); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxide represented by O2 (wherein, M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≤c3≤0.1) or Li2Mn3MO8 (wherein, M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4, etc., in which a part of Li in the chemical formula is replaced with an alkaline earth metal ion, but is not limited thereto. The positive electrode may be Li-metal.

[0159] The above-described 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.

[0160] At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used.

[0161] In addition, the positive electrode binder plays a role of improving the adhesion between positive electrode active material particles and the adhesiveness between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0162] The separator is used to separate the negative electrode and the positive electrode and to provide a passage for lithium ions. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

[0163] 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.

[0164] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0165] As the above non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolan, formamide, dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolan derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyrropionate, ethyl propionate, etc. can be used.

[0166] In particular, among the above carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents with high dielectric constants and thus can be preferably used because they easily dissociate lithium salts. In addition, when low-viscosity, low-dielectric constant linear carbonates such as dimethyl carbonate and diethyl carbonate are mixed and used in an appropriate ratio with these cyclic carbonates, an electrolyte with high electrical conductivity can be produced, so that they can be used even more preferably.

[0167] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte, for example, the anion of the lithium salt is 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.

[0168] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine 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 battery capacity decrease, and improving the discharge capacity of the battery.

[0169] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus 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.

[0170] In one embodiment of the present application, the lithium secondary battery is a cylindrical battery.

[0171] For example, the cylindrical battery may mean that the battery itself has a cylindrical shape and includes an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte, and may be specifically composed of a cylindrical can, a battery assembly provided inside the cylindrical can, and a top cap.

[0172] In one embodiment of the present application, a battery module including the lithium secondary battery is provided.

[0173] In one embodiment of the present application, a battery pack including a battery module according to the above-described embodiment is provided.

[0174] A further embodiment of the present invention provides a battery module including the aforementioned cylindrical battery as a unit cell and a battery pack including the same. The battery module and battery pack include the secondary battery having high capacity, high rate characteristics, and cycle characteristics, and thus 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.

[0175] The lithium secondary battery according to the embodiments of the present invention stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and therefore can be used as a power source for portable devices such as mobile phones, laptop computers, and digital cameras, as well as 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. For example, the battery module or battery pack can be used as a power source for any one or more medium- to large-sized devices selected from the group consisting of power tools; electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0176] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0177] <Manufacturing Example>

[0178] <Example 1>

[0179] Manufacturing of cathode

[0180] An anode composition was prepared, comprising 15 parts by weight of Si / C, 85 parts by weight of graphite (artificial graphite: natural graphite = 80:20 weight ratio) and 0.001 parts by weight of single-walled carbon nanotubes, based on 100 parts by weight of the total content of the anode active material in the anode composition, and 2.5 parts by weight of SBR (styrenebutadiene rubber) as a binder, 1.1 parts by weight of CMC (carboxymethyl cellulose), and further comprising 0.108 parts by weight of a CNT pre-dispersion liquid including 0.06 parts by weight of a dispersant and 0.04 parts by weight of single-walled CNTs, based on 100 parts by weight of the anode composition. At this time, the average particle diameters (D50) of the artificial graphite, natural graphite and silicon carbon composite in the composition were prepared to be 12.4 μm, 11.4 μm and 9.39 μm, respectively.

[0181] Distilled water was used as a dispersion medium, and the silicon carbon composite, graphite, carboxymethyl cellulose (CMC) as a binder, and styrene butadiene rubber (SBR) were added to a single-walled carbon nanotube dispersion using carboxymethyl cellulose (CMC) as a dispersant, stirred, and then distilled water was added to prepare a negative electrode composition (solid content = 50 parts by weight).

[0182] The above negative electrode composition was applied to a copper (Cu) metal thin film, which is a negative electrode current collector, with a thickness of 15 ㎛, and dried. The temperature of the circulating air at this time was 60°C. Subsequently, the negative electrode was rolled (roll pressed) and dried in a vacuum oven at 130°C for 12 hours, thereby manufacturing a negative electrode in which a negative electrode active material layer was disposed on the negative electrode current collector.

[0183] At this time, the weight of CMC added as a binder among the CMC: the weight of CMC added as a dispersant = 1.14:0.06. The average length of the single-walled carbon nanotube units in the negative active material layer was 10 μm, and the average diameter was 2 nm.

[0184] In the above negative electrode, it was manufactured in the same manner as in Example 1, except that the average particle size was adjusted as shown in Table 1 below.

[0185] Silicon-based active material (㎛) Artificial graphite (㎛) Natural graphite (㎛) Difference in absolute value of average particle size between silicon-based active material and artificial graphite (%) (based on artificial graphite) Difference in absolute value of average particle size between artificial graphite and natural graphite (%) (based on artificial graphite) Example 19.39 12.41 1.42 4.27% 8.06% Example 29.39 12.41 2.02 4.27% 3.22% Example 39.86 12.41 1.42 0.48% 8.06% Example 49.86 12.41 2.02 0.48% 3.22% Example 59.15 10.81 0.11 5.28% 6.48% Example 6 10.01 3.01 2.42 3.08% 4.62% Comparative example 19.3916.81744.11%1.19%Comparative example 29.3916.811.444.11%32.14%Comparative example 39.3912.41724.27%37.10%Comparative example 46.5312.411.447.34%8.06%

[0186] (2) Manufacturing of the anode

[0187] A cathode slurry was prepared by adding a cathode active material (Li(NiaCobMnc)O2, where NCM excluding lithium (Li) and oxygen (O2) has a ratio of Ni:Co:Mn=60 / 10 / 30, satisfying the ratio (a:b:c=0.60:0.10:0.30)), a cathode conductive agent (LB.CNT), and a binder (PVdF) in a weight ratio of 97.0:1.56:1.44 to a solvent (N-methylpyrrolidone, NMP). The cathode slurry was applied to and dried on an aluminum (Al) thin film, which is a cathode current collector, with a thickness of 12 μm, and then rolled using a roll press to prepare a cathode.

[0188] (3) Manufacturing of secondary batteries

[0189] An electrode assembly was manufactured by interposing a compressible thin film separator (PE 9um) ceramic coating 3um / 3um between the positive and negative electrodes. After positioning the electrode assembly inside a case, an electrolyte was injected into the case to manufacture a lithium secondary battery.

[0190] <Experimental Example>

[0191] Cell resistance evaluation and life evaluation

[0192] The internal resistance of the manufactured battery was evaluated and is shown in Table 2 below. The 1st and 2nd cycles were charged and discharged at 0.1C, and the 3rd and 4th cycles were charged and discharged at 0.33C. After that, the battery was partially charged to 50% of the SOC based on the discharge capacity of the 4th cycle, and then a discharge current of 2.5C was applied, and the internal resistance of the battery was calculated through the voltage change (HPPC test).

[0193] In addition, the life performance of the manufactured batteries was evaluated and is shown in Table 2 below. Each battery was 45 o Charge and discharge were performed at a charge rate of 3.0C and a discharge rate of 0.5C in C.

[0194] Table 2 below describes the internal resistance of the batteries of Examples 1 to 6 and Comparative Examples 1 to 4 in comparison. This describes the internal resistance of the batteries of Comparative Examples 1 to 4 relatively when the internal resistance of the battery of Example 1 is set to 1.0.

[0195] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Battery Internal Resistance 1.000.990.980.980.960.991.071.031.171.01 Lifespan (300 cycles @ 45℃, %) 96.196.296.196.396.596.094.694.893.995.5

[0196] In the case of Examples 1 to 6 according to the present application, by limiting the average particle diameter of the silicon-based active material and the graphite-based active material (artificial graphite) to the range of the present application, it can be seen that the silicon-based active material has a smaller particle diameter than the graphite-based active material, and when the negative electrode slurry is mixed and the electrode is coated in a state where the particle diameters are different, the phenomenon in which the silicon-based active material, which has a smaller particle diameter than the graphite-based active material, forms a local cluster is controlled. In addition, in the case of natural graphite and artificial graphite in the graphite-based active material, the average particle diameter is controlled as in Examples 1 to 6, and through the control, the active material in the electrode is evenly dispersed, so that it is possible to prevent local stress generation, reaction promotion, and deterioration during the operation of the battery, and it can be seen that a uniformly dispersed electrode can be manufactured.

[0197] Specifically, in the case of Example 2, the absolute difference (%) in the average particle diameters of artificial graphite and natural graphite decreased compared to Example 1, in the case of Example 3, the absolute difference (%) in the average particle diameters of the silicon-based active material and artificial graphite decreased compared to Example 1, and in the case of Example 4, the difference (%) in both cases decreased compared to Example 1. In such cases, when comparing examples, as the difference in absolute values ​​decreases, the increase in internal resistance decreases and also the lifespan tends to increase.

[0198] Likewise, Examples 5 and 6 have slightly changed the average particle diameters of the silicon-based active material and graphite (artificial graphite, natural graphite), and it can be confirmed that the effect is superior to that of the comparative example when the absolute value of the difference in the average particle diameter of the present invention is satisfied.

[0199] In the case of Comparative Examples 1 and 4, the difference in the average particle diameter (D50) of the silicon-based active material and the graphite (artificial graphite) is 40% or more, and in the case of Comparative Examples 2 and 3, the difference in the average particle diameter (D50) of natural graphite and artificial graphite is 10% or more in absolute value.

[0200] Specifically, Comparative Examples 1 and 4 are cases where the difference in average particle size between silicon and graphite exceeds the scope of the present application. In this case, silicon-based active materials with relatively small particle sizes form clusters within the graphite, resulting in local unevenness. Afterwards, when charge and discharge are repeated, it was confirmed that the volume of the silicon-based active materials forming the clusters changes significantly, increasing the internal resistance and, consequently, reducing the lifespan.

[0201] In Comparative Examples 2 and 3, not only was the difference in the average particle diameter of the silicon-based active material and artificial graphite large, but the difference in the average particle diameter (D50) of natural graphite and artificial graphite was also more than 10%, which means that the difference in particle diameter of each active material was large compared to Comparative Examples 1 and 4. This is a case where, in addition to the non-uniformity of the silicon-based active material that occurred in Comparative Examples 1 and 4, non-uniform dispersion also occurred between the natural graphite and artificial graphite, and it was confirmed that each active material formed a cluster, which resulted in relatively high internal resistance of the battery and a deteriorated lifespan.

[0202] Ultimately, it was confirmed that the active material within the electrode was not evenly distributed, resulting in increased resistance within the battery. This was confirmed again in a fast-charge cycle performed at 45°C, and it was confirmed that the examples meeting the above conditions exhibited superior life performance compared to Comparative Examples 1 to 4.

Claims

1. Contains silicon-based active material and graphite, The above graphite includes natural graphite and artificial graphite, The ratio of the difference in average particle diameter (D50) between the above artificial graphite and the above natural graphite is 10% or less in absolute value, A negative electrode active material having an absolute value of 40% or less in the ratio of the difference in average particle diameter (D50) size between the above artificial graphite and the above silicon-based active material.

2. In claim 1, The average particle diameter (D50) of the above silicon-based active material is 1 ㎛ or more and 10 ㎛ or less, A negative electrode active material having an average particle diameter (D50) of 5 ㎛ or more and 20 ㎛ or less.

3. In claim 1, The average particle size (D50) of the above natural graphite is 5㎛ or more and 20㎛ or less, The average particle diameter (D50) of the above artificial graphite is 5㎛ or more and 20㎛ or less, and is a negative electrode active material.

4. In claim 1, A negative electrode active material, wherein the weight ratio of the silicon-based active material:graphite is 5:95 to 40:60 based on 100 parts by weight of the negative electrode active material.

5. In claim 1, A negative electrode active material having a weight ratio of the artificial graphite:natural graphite of 60:40 to 80:20 based on 100 parts by weight of the above graphite.

6. In claim 1, The above silicon-based active material is Si, SiOx (0 <x<2), Si / C, 및 Si 합금으로 이루어진 군에서 선택되는 1 이상을 포함하는 것인 음극 활물질.

7. In claim 1, A negative electrode active material having a ratio of difference in average particle diameter (D50) between the above-mentioned artificial graphite and the above-mentioned natural graphite of an absolute value of 1% or more and 10% or less.

8. In claim 1, A negative electrode active material having an absolute value of 20% or more and 40% or less in the ratio of the difference in average particle diameter (D50) size between the above artificial graphite and the above silicon-based active material.

9. In claim 1, The average particle diameter (D50) of the above artificial graphite is larger than the average particle diameter (D50) of the above natural graphite, A negative electrode active material in which the average particle diameter (D50) of the above natural graphite is larger than the average particle diameter (D50) of the above silicon-based active material.

10. A negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, A negative electrode for a lithium secondary battery, wherein the negative electrode active material layer comprises a negative electrode active material according to any one of claims 1 to 9.

11. In claim 10, The thickness of the above negative electrode current collector layer is 1 μm or more and 100 μm or less, A negative electrode for a lithium secondary battery, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

12. In claim 10, A negative electrode for a lithium secondary battery, wherein the negative electrode active material layer further includes a negative electrode conductive material; and a negative electrode binder.

13. In claim 10, A negative electrode for a lithium secondary battery, wherein the negative electrode active material is included in an amount of 90 parts by weight or more based on 100 parts by weight of the composition included in the negative electrode active material layer.

14. In claim 12, Based on 100 parts by weight of the composition included in the above negative electrode active material layer, the negative electrode conductive material is 0.1 parts by weight or more and 5 parts by weight or less, A negative electrode composition, wherein the negative electrode binder is contained in an amount of 1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the composition included in the negative electrode active material layer.

15. Bipolar; A negative electrode for a lithium secondary battery according to claim 10; A separator provided between the anode and the cathode; and A lithium secondary battery comprising an electrolyte.

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