Negative electrode composition, negative electrode for lithium secondary battery, comprising same, and lithium secondary battery comprising negative electrode

Abstract

The present application relates to a negative electrode composition, a negative electrode for a lithium secondary battery, comprising same, and a lithium secondary battery comprising the negative electrode. A point-type conductive material is included as a negative electrode conductive material included the negative electrode composition, and the central particle diameter of the negative electrode conductive material satisfies 30% to 60% of the central particle diameter of a silicon-based active material, thereby improving the quality of an electrode through improvement of dispersability and improving lifespan performance through securement of a pore structure.

Description

Negative electrode composition, negative electrode for lithium secondary battery including same, and lithium secondary battery including negative electrode

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0100220, filed with the Korean Intellectual Property Office on August 1, 2023, the entire contents of which are incorporated herein by reference.

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

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

[0006] 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. Silicon particles with a high discharge capacity can be used as the negative electrode active material.

[0007] In particular, with the recent 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.

[0008] Accordingly, in order to solve the problems when using a silicon-based compound as an anode active material, various methods are being discussed, such as a method for controlling the driving potential, a method for additionally coating a thin film on the active material layer, a method for controlling the particle size of the silicon-based compound, a method for suppressing the volume expansion itself, or a method for preventing the conductive path from being cut off. However, the above methods may actually lower the performance of the battery, so there are limitations in their application, and there are still limitations in the commercialization of anode batteries with a high silicon-based compound content.

[0009] In addition, research results on the aforementioned problem have revealed that, in the case of silicon-based active materials, the smaller the crystal grain size and the smaller the particle size, the better the life performance. However, when the crystal grain size of silicon-based active materials is reduced or the particle size is micron-sized to improve the life performance, there is a problem that the coating condition on the electrode does not improve, and the particle size of silicon-based active materials becomes relatively small due to particle agglomeration, making it difficult to achieve a relatively uniform dispersion.

[0010] Due to the above problems, the electrode coating condition is poor, and as a result, the electrode adhesion is reduced, and when the cycle is repeated, detachment from the current collector occurs, which causes a rapid drop in life performance, or the detachment phenomenon makes it difficult to use.

[0011] Therefore, when using a silicon-based active material as a negative electrode active material to improve capacity performance, research is needed on a method to solve the above-mentioned problems.

[0012] <Prior Art Literature>

[0013] (Patent Document 1) Japanese Patent Publication No. 2009-080971

[0014] As a result of research on a method to improve the life performance of a negative electrode containing a silicon-based active material, it was found that the aforementioned problem can be solved by using a silicon-based active material of several microns in size and a point-shaped conductive material having a central particle diameter of a certain ratio to the particle size of the silicon-based active material rather than the point-shaped conductive material of several tens of nm that was used previously.

[0015] In other words, when using a dot-shaped conductor of several tens of nm in size as in the past, or a linear conductor such as a carbon nanotube, or a combination of a linear conductor and a planar conductor, it becomes difficult to secure pores within the electrode, and when charging / discharging is performed, the pores within the electrode are blocked due to side reactions, blocking the movement path of Li ions, which increases resistance and leads to a decrease in cell performance.

[0016] However, it was found that the lifespan of the electrode is the best when the silicon-based active material has a particle size of several microns, and accordingly, it was found that by controlling the center particle size of the dot-shaped conductive material used together, the quality of the electrode can be improved through improved dispersibility and the lifespan performance can be improved through securing a pore structure.

[0017] Accordingly, the present application relates to a negative electrode composition capable of solving the above-mentioned problems, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

[0018] One embodiment of the present specification is a negative electrode composition comprising a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material is SiOx (x=0), SiOx (0 <x≤2) 및 금속 불순물로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 실리콘계 활물질 100 중량부 기준 상기 SiOx (x=0)를 90 중량부 이상 포함하고, 상기 음극 도전재는 점형 도전재를 포함하며, 상기 음극 도전재의 중심 입경은 상기 실리콘계 활물질의 중심 입경 대비 30% 이상 60% 이하인 것인 음극 조성물을 제공한다.

[0019] In another embodiment, there is provided an anode for a lithium secondary battery, comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer comprises a negative electrode composition according to the present application or a cured product thereof.

[0020] Finally, a lithium secondary battery is provided, including: a cathode; an anode for a lithium secondary battery according to the present application; a separator provided between the cathode and the anode; and an electrolyte.

[0021] In the case of a negative electrode composition according to one embodiment of the present invention, the central particle size of the silicon-based active material is maintained at a micro size, and a dot-shaped conductive material is included as a negative electrode conductive material to solve the problem of uniform dispersion and the problem of electrode coating state, and the central particle size of the dot-shaped conductive material is optimized in comparison with the central particle size of the silicon-based active material.

[0022] That is, the negative electrode conductive material includes a dot-shaped conductive material, and the central particle diameter of the negative electrode conductive material satisfies a range of 30% to 60% of the central particle diameter of the silicon-based active material, thereby improving the quality of the electrode through improved dispersibility and improving the life performance through securing a pore structure.

[0023] 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.

[0024] Figure 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application.

[0025] Figure 3 is a diagram illustrating the concept of sphericity.

[0026] Figure 4 is a diagram showing a lithium ion path when the dot-shaped conductive material of the present application is used.

[0027] Figure 5 is a diagram showing the lithium ion path when linear and / or planar conductive materials are used.

[0028] <Explanation of symbols>

[0029] 10: Negative current collector layer

[0030] 20: Negative active material layer

[0031] 30: Membrane

[0032] 40: Positive active material layer

[0033] 50: Positive current collector layer

[0034] 100: Cathode for lithium secondary batteries

[0035] 200: Cathode for lithium secondary batteries

[0036] 1: Silicon-based active material

[0037] 2: Dot-shaped challenger

[0038] 3: Linear or planar conductive material

[0039] 4: Lithium ion pathway

[0040] Before explaining the present invention, some terms are first defined.

[0041] When a part of this specification is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise stated.

[0042] In this specification, ‘p to q’ means a range of ‘p or more and q or less.’

[0043] In this specification, "specific surface area" is measured by the BET method, and specifically, is calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan. That is, in this application, the BET specific surface area may mean the specific surface area measured by the above measurement method.

[0044] 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, center 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.

[0045] 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.

[0046] 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.

[0047] In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers unless 'homopolymer' is specified.

[0048] 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.

[0049] 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.

[0050] One embodiment of the present specification is a negative electrode composition comprising a silicon-based active material; a negative electrode conductive material; and a negative electrode binder, wherein the silicon-based active material is SiOx (x=0), SiOx (0 <x≤2) 및 금속 불순물로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 실리콘계 활물질 100 중량부 기준 상기 SiOx (x=0)를 90 중량부 이상 포함하고, 상기 음극 도전재는 점형 도전재를 포함하며, 상기 음극 도전재의 중심 입경은 상기 실리콘계 활물질의 중심 입경 대비 30% 이상 60% 이하인 것인 음극 조성물을 제공한다.

[0051] The above-mentioned negative electrode conductive material includes a dot-shaped conductive material, and the central particle diameter of the above-mentioned negative electrode conductive material satisfies a range of 30% to 60% of the central particle diameter of the above-mentioned silicon-based active material, thereby improving the quality of the electrode through improved dispersibility and improving the life performance through securing a pore structure.

[0052] In one embodiment of the present application, the silicon-based active material is SiOx (x=0) and SiOx (0 <x≤2) 및 금속 불순물로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 실리콘계 활물질 100 중량부 기준 상기 SiOx (x=0)를 90 중량부 이상 포함할 수 있다.

[0053] In one embodiment of the present application, the silicon-based active material includes SiOx (x=0), and may include 95 parts by weight or more of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[0054] In another embodiment, the silicon-based active material may contain 95 parts by weight or more, preferably 96 parts by weight or more, more preferably 98 parts by weight or more, of the SiOx (x=0) based on 100 parts by weight of the silicon-based active material, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 98 parts by weight or less.

[0055] In one embodiment of the present application, in particular, pure silicon (Si) particles may be used as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material may mean that, based on 100 parts by weight of the total silicon-based active material, pure Si particles (SiOx (x=0)) not combined with other particles or elements are included within the above range.

[0056] In one embodiment of the present application, the silicon-based active material may be formed of silicon-based particles having 100 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[0057] In one embodiment of the present application, the silicon-based active material may contain a metal impurity, and at this time, the impurity may be a metal that may be generally contained in the silicon-based active material, and specifically, may contain 0.1 part by weight or less based on 100 parts by weight of the silicon-based active material.

[0058] Meanwhile, the central particle diameter of the silicon-based active material of the present invention may be 1.5 μm or more and 15 μm or less. In this case, the central particle diameter of the silicon-based active material may mean the average particle diameter and may be expressed as D50.

[0059] In the present application, the central particle diameter of the silicon-based active material may be specifically 2 μm to 8 μm, and more specifically 3 μm to 6 μm. If the average particle diameter is less than the above range, the specific surface area of ​​the particles increases excessively, causing the viscosity of the negative electrode slurry to increase excessively. Accordingly, the particles constituting the negative electrode slurry are not smoothly dispersed. In addition, if the size of the silicon-based active material is excessively small, the contact area between the silicon particles and the conductive material is reduced by the composite composed of the conductive material and the binder in the negative electrode slurry, increasing the possibility of the conductive network being disconnected, thereby lowering the capacity retention rate. On the other hand, if the average particle diameter exceeds the above range, excessively large silicon particles are present, making the surface of the negative electrode unsmooth, resulting in uneven current density during charge and discharge. In addition, if the silicon particles are excessively large, the phase stability of the negative electrode slurry becomes unstable, thereby degrading the processability. Consequently, the capacity retention rate of the battery is lowered.

[0060] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET surface area of ​​the silicon-based active material is preferably 0.01 m 2 / g to 150.0 m 2 / g, more preferably 0.1 m 2 / g to 100.0 m 2 / g, especially 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. BET surface area is measured according to DIN 66131 (using nitrogen).

[0061] In one embodiment of the present application, the silicon-based active material may exist in a crystalline or amorphous form, for example, and is preferably non-porous. The silicon particles are preferably spherical or fragment-shaped. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or be present in the form of a silicon-containing film or coating.

[0062] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape 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.

[0063] In the present application, the circularity is determined by the following equation 1-1, where A is the area and P is the boundary line.

[0064] [Formula 1-1]

[0065] 4πA / P 2

[0066] In the case of silicon-based active materials, compared to the existing graphite-based active materials, the capacity is significantly higher, so attempts to apply it are increasing. However, because the volume expansion rate is high during the charge / discharge process, it is limited to cases where a small amount is mixed with the graphite-based active material and used.

[0067] Therefore, in the case of the present invention, in order to improve capacity performance, only a silicon-based active material is used as the negative electrode active material, and in order to solve the above-described problem, the particle size ratio with the negative electrode conductive material described below is optimized.

[0068] In one embodiment of the present application, a negative electrode composition is provided in which the silicon-based active material is at least 40 parts by weight based on 100 parts by weight of the negative electrode composition.

[0069] In another embodiment, the silicon-based active material may be included in an amount of 40 parts by weight or more, preferably 60 parts by weight or more, more preferably 65 parts by weight or more, and even more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be included in an amount of 95 parts by weight or less, preferably 90 parts by weight or less, and even more preferably 85 parts by weight or less.

[0070] The negative electrode composition according to the present application uses a negative electrode active material that satisfies a specific size capable of controlling 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 uses the negative electrode conductive material and negative electrode binder described below together so that the performance of the negative electrode is not deteriorated even within the above range, and has the characteristic of excellent output characteristics during charge and discharge.

[0071] 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.

[0072] Previously, linear or planar conductive materials were mainly used in negative electrodes using silicon-based active materials. However, in the case of linear conductive materials, the tendency for the negative electrode pores to become clogged as the amount of conductive material increased became more serious, which increased the pore resistance and caused performance problems. In addition, although the planar conductive material itself could form surface contact, there was a problem that the ion migration path was damaged due to the negative electrode rolling. In other words, the role of the negative electrode conductive material is to enable conductivity by creating contact points between particles, but if this blocks the pore structure within the electrode and hinders the migration path of ions within the electrolyte, the resistance increases.

[0073] Specifically, this can be confirmed in Fig. 5. In contrast to Fig. 4, Fig. 5 uses linear and / or planar conductive materials, making it difficult to secure pores within the electrode, and when charging / discharging is performed, the pores within the electrode are blocked due to side reactions, blocking the lithium ion movement path, which increases resistance and leads to deterioration of cell performance.

[0074] Therefore, in one embodiment of the present application, the negative electrode conductive material may include a dot-shaped conductive material. When using a dot-shaped conductive material as described above, it is easy to secure an ion migration path, and thus the effect is superior to using a linear or planar conductive material. Specifically, as can be seen in Fig. 4, by using a dot-shaped conductive material having the characteristics described below, the pores of the negative electrode become larger, thereby securing a lithium ion migration path, and thus reducing the resistance increase rate.

[0075] In one embodiment of the present application, a cathode composition is provided in which the sphericity of the dot-shaped conductive material is expressed by the following formula 1.

[0076] [Formula 1]

[0077] 0.7 ≤ X1 / Y1 ≤ 0.96

[0078] In the above equation 1,

[0079] X1 is the orthogonal projection area of ​​the point-shaped challenge material,

[0080] Y1 represents the area of ​​a circle that has the same circumference as the orthogonal projection of the point-shaped challenge material.

[0081] The above equation 1 can be measured using a particle analyzer. Specifically, the dot-shaped conductive material according to the present application is scattered on a glass plate by spraying air, and the shapes of 10,000 dot-shaped conductive material particles in the photograph taken by projecting the scattered dot-shaped conductive material particles can be measured. At this time, equation 1 is a value expressing the average for 10,000 particles. Equation 1 according to the present application can be measured from the above image, and equation 1 can be expressed as the sphericity of the dot-shaped conductive material. The concept of sphericity is illustrated in Fig. 3. The sphericity is expressed by the equation [4π* spherical projection area of ​​silicon-based active material / (spherical projection perimeter of silicon-based active material)]. 2 ] may also be displayed.

[0082] In another expression, X1 may represent the actual area of ​​the point-shaped conductive material, and Y1 may represent the area of ​​a spherical particle with the same perimeter as the point-shaped conductive material.

[0083] In one embodiment of the present application, the sphericity of the dot-shaped conductive material may be, for example, 0.960 or less, for example, 0.957 or less. The sphericity of the dot-shaped conductive material may be 0.7 or more, for example, 0.85 or more, specifically 0.9 or more, more specifically 0.91 or more, for example, 0.92 or more.

[0084] As described above, the point-shaped conductive material satisfies the sphericity of the above formula 1, and differs from the planar or linear conductive material in the range of the above formula 1.

[0085] In one embodiment of the present application, the dot-shaped conductive material may have an ID / IG of 0.01 or more and 1.5 or less when measured by Raman spectroscopy.

[0086] In another embodiment, the dot-shaped conductive material may have an ID / IG of 0.01 or more and 1.5 or less, 0.02 or more and 1.3 or less, and more specifically, 0.03 or more and 1.05 or less, when measured by Raman spectroscopy.

[0087] The above ID / IG may refer to an index for identifying a defect in the structure, and the extent to which a defect exists in a point-like conductive material can be identified through raman spectroscopy measurement, and a point-like conductive material that satisfies the above raman spectroscopy range will have excellent life performance when the battery is operated in the future.

[0088] 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 carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] In the embodiment of the present application, the central particle diameter of the negative electrode conductive material may be 0.45 μm or more and 9 μm or less, preferably the central particle diameter may be 0.6 μm or more and 3 μm or less, and more preferably the particle diameter may be 0.90 μm or more and 1.8 μm or less.

[0094] In the embodiment of the present application, the central particle diameter of the dot-shaped conductive material may be 0.45 μm or more and 9 μm or less, preferably the central particle diameter may be 0.6 μm or more and 3 μm or less, and more preferably the particle diameter may be 0.90 μm or more and 1.8 μm or less.

[0095] In the present application, the negative electrode conductive material having a center particle diameter of 1 μm or less based on 100 parts by weight of the negative electrode conductive material may be included in an amount of 5 parts by weight or less.

[0096] The present application is characterized by using a cathode conductive material having the above-mentioned central particle diameter range, rather than a dot-shaped conductive material of several tens of nm in size used in the production of conventional Pure Si electrodes.

[0097] In the case of point-shaped conductive materials, unlike linear conductive materials and planar conductive materials, the aforementioned problem can be solved by using a conductive material having a spherical shape, and when using point-shaped conductive materials, it is easy to secure an ion movement path, so the effect is superior to using the linear conductive material or planar conductive material.

[0098] That is, the negative electrode conductive material includes a dot-shaped conductive material, and since the central particle diameter of the negative electrode conductive material satisfies the above range compared to the central particle diameter of the silicon-based active material, the electrode quality is improved through improved dispersibility, and the life performance is improved through securing a pore structure.

[0099] In one embodiment of the present application, the dot-shaped conductive material may be included in an amount of 95 parts by weight or more, 96 parts by weight or more, 98 parts by weight or more, and 100 parts by weight or less, based on 100 parts by weight of the cathode conductive material.

[0100] In one embodiment of the present application, the negative conductive material may be formed of a dot-shaped conductive material.

[0101] In one embodiment of the present application, a negative electrode composition is provided in which the center particle diameter of the negative electrode conductive material is 30% or more and 60% or less compared to the center particle diameter of the silicon-based active material.

[0102] In one embodiment of the present application, the negative electrode conductive material may further include at least one selected from the group consisting of a planar conductive material and a linear conductive material.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] Other linear conductive materials may include 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, unless otherwise stated, 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. The carbon nanotube units have a cylindrical 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 curling angle and structure. 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.

[0115] 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 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0116] In another embodiment, the negative electrode conductive material may include 1 part by weight or more and 20 parts by weight or less, preferably 3 parts by weight or more and 15 parts by weight or less, more preferably 5 parts by weight or more and 15 parts by weight or less, and most preferably 8 parts by weight or more and 13 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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 or spherical shape and used as a material that plays a role in storing or releasing lithium.

[0123] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is in a dot-like shape 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.

[0124] 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.

[0125] In one embodiment of the present application, a negative electrode composition is provided in which the negative electrode binder includes an aqueous binder, and the aqueous binder includes at least one selected from the group consisting of polyacrylic acid (PAA) and polyacrylamide (PAM).

[0126] 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.

[0127] In one embodiment of the present application, the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and may be 5 parts by weight or more, or 10 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0128] In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, including: 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 formed on one or both sides of the negative electrode current collector layer.

[0129] 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.

[0130] 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.

[0131] At this time, the cathode slurry may include the cathode composition described above; and a slurry solvent.

[0132] In one embodiment of the present application, the solid content of the cathode slurry can satisfy 5% or more and 40% or less.

[0133] 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.

[0134] 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] However, the thickness can be varied depending on the type and purpose of the cathode used and is not limited thereto.

[0140] 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.

[0141] 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.

[0142] 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, the silicon-based active material and conductive material according to the present application are included in a specific composition and content portion to satisfy the above range, and accordingly, the electrode is characterized by having an appropriate range of electrical conductivity and resistance.

[0143] In one embodiment of the present application, a lithium secondary battery is provided, comprising: 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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 c2Ni-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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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 an ethylene homopolymer, a propylene 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. 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.

[0153] Examples of the above 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.

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

[0155] 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.

[0156] 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.

[0157] 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 can be used.

[0158] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, 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.

[0159] One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. The battery module and 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.

[0160] 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.

[0161] <Manufacturing Example>

[0162] <Manufacturing of the cathode>

[0163] A negative electrode slurry was prepared by adding Si as a silicon-based active material, carbon black C as a point-shaped conductive material, and polyacrylamide as a binder to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 80:10:10 (solid content concentration 25 wt%).

[0164] As a specific mixing method, the dot-shaped conductive material, binder, and water were dispersed using a homogenous mixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for 30 minutes to produce a negative electrode slurry.

[0165] The negative electrode slurry is applied at 85 mg / 25 cm on both sides of a copper current collector (thickness: 8 μm) as a negative electrode current collector layer. 2 The coating was carried out with a loading amount of , rolled (roll pressed), and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was used as a negative electrode (thickness of negative electrode: 41 μm, porosity of negative electrode: 40.0%).

[0166] At this time, the central particle diameter of the silicon-based active material and the central particle diameter of the dot-shaped conductive material satisfied the ranges shown in Table 1 below.

[0167] Central particle diameter of point-shaped conductive materialSphericity of point-shaped conductive materialCentral particle diameter of silicon-based active materialCentral particle diameter of point-shaped conductive material / Central particle diameter of silicon-based active material x 100%Example 10.9 μm0.953 μm30%Example 21.8 μm0.903 μm60%Example 31.5 μm0.915 μm30%Example 43 μm0.895 μm60%Comparative example 10.09 μm0.933 μm3%Comparative example 22.1 μm0.903 μm70%Comparative example 33 μm0.8915 μm20%Comparative example 42 μm0.902 μm100%Comparative example 510 μm0.865 μm200%

[0168] In the above Table 1, the change in the central particle diameter of the silicon-based active material and the central particle diameter of the dot-shaped conductive material can be controlled within the above range through classification, and specifically, the central particle diameter of the above Table 1 was controlled by controlling the grinding time, deposition time, and temperature before classification.

[0169] Comparative Example 6

[0170] In the above Example 1, a negative electrode was manufactured in the same manner as in the above Example 1, except that “carbon black C: carbon nanotubes as linear conductive material were used in a weight ratio of 7:3” instead of carbon black C as a dot-shaped conductive material.

[0171] <Comparative Example 7>

[0172] In the above Example 1, a negative electrode was manufactured in the same manner as in the above Example 1, except that “carbon black C: carbon nanotubes as linear conductive material were used in a weight ratio of 5:5” instead of carbon black C as a dot-shaped conductive material.

[0173] Comparative Example 8

[0174] In the above Example 1, a negative electrode was manufactured in the same manner as in the above Example 1, except that “carbon black C: carbon nanotubes as linear conductive material were used in a weight ratio of 3:7” instead of carbon black C as a dot-shaped conductive material.

[0175] <Comparative Example 9>

[0176] In the above Example 1, a negative electrode was manufactured in the same manner as in the above Example 1, except that “carbon nanotubes as a linear conductive material” were used instead of carbon black C as a dot-shaped conductive material.

[0177] <Manufacturing of secondary batteries>

[0178] LiNi as a cathode active material 0.6 Co 0.2 Mn 0.2 O2 (average particle size (D50): 15㎛), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a cathode slurry at a weight ratio of 97:1.5:1.5 to prepare a cathode slurry (solid content concentration: 78 wt%).

[0179] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12㎛) as a positive electrode collector at a density of 537mg / 25cm. 2 A positive electrode was manufactured by coating with a loading amount, rolling, and drying in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) (positive electrode thickness: 77 μm, porosity 26%).

[0180] A lithium secondary battery was manufactured by interposing a polyethylene separator between the positive electrode and the negative electrode of the above examples and comparative examples and injecting an electrolyte.

[0181] The above electrolyte was an organic solvent containing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90, vinylene carbonate added at 3 wt% based on the total weight of the electrolyte, and LiPF6 added at a concentration of 1 M as a lithium salt.

[0182] <Experimental Example>

[0183] Experimental Example 1: Monocell Life Performance Results

[0184] The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were subjected to a life evaluation using an electrochemical charger / discharger, and the capacity retention rate was evaluated. The secondary batteries were subjected to an in-situ cycle test at 4.2-3.0 V 1C / 0.5C, and the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0 V) every 50 cycles during the test, and the results are recorded in Table 2.

[0185] Life retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at 1st cycle)} Х 100

[0186] Lifespan after 200 cycles (%) Example 188 Example 289 Example 388 Example 487 Comparative Example 178 Comparative Example 280 Comparative Example 362 Comparative Example 463 Comparative Example 575

[0187] Experimental Example 2: Changes in Monocell Resistance

[0188] In the above experimental example 1, the capacity retention rate was measured by performing 0.33C / 0.33C charge / discharge (4.2-3.0V) every 50 cycles during the test, and then the resistance increase rate was compared and analyzed by measuring the total resistance by discharging at 2.5C pulse at SOC50.

[0189] For the above resistance increase rate measurement evaluation, data at 200 cycles were calculated, and the results were as shown in Table 3 below.

[0190] Resistance increase rate (%) after 200 cycles Example 19 Example 27 Example 38 Example 48 Comparative Example 130 Comparative Example 221 Comparative Example 3103 Comparative Example 4100 Comparative Example 584

[0191] Experimental Example 3: Changes in Pore Resistance in the Electrode

[0192] For the cathodes of Example 1 and Comparative Examples 6 to 8, a coin symmetry cell was fabricated using two cathode electrodes to analyze the Li ion diffusion resistance excluding the influence of charge transfer, and EIS was measured. The frequency-dependent impedance data obtained through the measurement were fitted to compare and analyze the liquid diffusion resistance. The results of the Li ion diffusion resistance measurement within the electrodes are as shown in Table 4 below.

[0193] Pore ​​resistance (R pore, Ω) Example 11.5 Comparative Example 63 Comparative Example 74 Comparative Example 87 Comparative Example 915

[0194] As can be seen in Tables 2 and 3 above, when the life maintenance rate and resistance increase rate of the examples were confirmed, the central particle size of the silicon-based active material was maintained at a micro size, and a dot-shaped conductive material was included as the negative electrode conductive material to solve the problem of uniform distribution and the problem of electrode coating state, and the central particle size of the dot-shaped conductive material was optimized in comparison with the central particle size of the silicon-based active material, thereby confirming that the capacity maintenance rate was superior compared to the comparative example.

[0195] Specifically, as can be confirmed in Comparative Examples 1, 2, and 5, even if the central particle diameter of the silicon-based active material satisfies the range of the present invention, if the central particle diameter of the dot-shaped conductive material deviates from the particle diameter relationship and does not satisfy the particle diameter relationship, it can be confirmed that the life maintenance rate and the resistance increase rate are lower than those of the examples. In addition, when confirming the results of Comparative Examples 3 and 4, it can be confirmed that even if the central particle diameter of the dot-shaped conductive material is similar to that of the examples, if the central particle diameter of the silicon-based active material deviates from the particle diameter and does not satisfy the particle diameter relationship, the life maintenance rate and the resistance increase rate are lower than those of the examples.

[0196] For reference, in the case of Example 4, the particle size relationship between the dot-shaped conductive material and the silicon-based active material is satisfactory, but the particle size of the dot-shaped conductive material is somewhat increased, so there is no part that is inferior in terms of life performance and resistance increase rate compared to other examples in terms of performance, but there is a possibility that it is inferior to other examples in terms of design, such as energy density and electrode thickness. However, in this case, it also has superior characteristics in terms of life and resistance compared to other comparative examples 1 to 5.

[0197] In addition, in the past, linear or planar conductive materials were mainly used in negative electrodes using silicon-based active materials. However, in the case of linear conductive materials, the tendency for the negative electrode pores to become blocked worsened as the amount of conductive material increased, which increased the pore resistance and caused performance problems. In addition, although the planar conductive material itself could form surface contact, there was a problem that the ion movement path was damaged due to the negative electrode rolling. In other words, the role of the negative electrode conductive material is to enable conduction by creating contact points between particles, but if this blocks the pore structure within the electrode and hinders the movement path of ions within the electrolyte, the resistance increases.

[0198] To confirm this, the change in pore resistance of the above Experimental Example 3 was measured, and this can be specifically confirmed in Table 4. Specifically, in the case of Comparative Examples 6 to 9, point-shaped and linear conductive materials were used, and when Comparative Examples 6 to 9 were compared, it was confirmed that as the amount of linear conductive material increased, the tendency for the cathode pores to be blocked worsened, and accordingly, the pore resistance increased. In addition, when the cathode of Example 1 was used, it was confirmed that the pore resistance was maintained low by using a specific point-shaped conductive material without including the linear conductive material.

[0199] This can also be confirmed in Fig. 5. In contrast to Fig. 4, Fig. 5 uses linear and / or planar conductive materials, making it difficult to secure pores within the electrode, and when charging / discharging is performed, the pores within the electrode are blocked due to side reactions, blocking the lithium ion movement path, which increases resistance and leads to deterioration of cell performance. Therefore, the present application includes a point-shaped conductive material as in the above embodiment, and as can be confirmed in Fig. 4, it is easy to secure an ion movement path, so it can be more effective compared to using the linear or planar conductive material.

Claims

1. A negative electrode composition comprising a silicon-based active material; a negative electrode conductive material; and a negative electrode binder; The above silicon-based active material is SiOx (x=0), SiOx (0 <x≤2) 및 금속 불순물로 이루어진 군에서 선택되는 1 이상을 포함하며, 상기 실리콘계 활물질 100 중량부 기준 상기 SiOx (x=0)를 90 중량부 이상 포함하고, The above negative conductive material includes a dot-shaped conductive material, A negative electrode composition wherein the center particle diameter of the negative electrode conductive material is 30% or more and 60% or less than the center particle diameter of the silicon-based active material.

2. In claim 1, A negative electrode composition comprising 95 parts by weight or more of the dot-shaped conductive material based on 100 parts by weight of the negative electrode conductive material.

3. In claim 1, A negative electrode composition wherein the central particle diameter of the above silicon-based active material is 1.5 μm or more and 15 μm or less.

4. In claim 1, A cathode composition wherein the center particle diameter of the cathode conductive material is 0.45 μm or more and 9 μm or less.

5. In claim 1, A negative electrode composition comprising 5 parts by weight or less of a negative electrode conductive material having a center particle diameter of 1 μm or less based on 100 parts by weight of the above negative electrode conductive material.

6. In claim 1, The sphericity of the above dot-shaped conductive material is expressed by the following formula 1: [Formula 1] 0.7 ≤ X1 / Y1 ≤ 0.96 In the above equation 1, X1 is the orthogonal projection area of ​​the point-shaped challenge material, Y1 represents the area of ​​a circle that has the same circumference as the orthogonal projection of the point-shaped challenge material.

7. In claim 1, The above-mentioned dot-shaped conductive material is a cathode composition comprising at least one selected from the group consisting of carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives.

8. In claim 1, The above negative binder includes an aqueous binder, A negative electrode composition wherein the above aqueous binder comprises at least one selected from the group consisting of polyacrylic acid (PAA) and polyacrylamide (PAM).

9. In claim 1, A negative electrode composition in which the silicon-based active material is at least 40 parts by weight based on 100 parts by weight of the negative electrode composition.

10. In claim 1, A cathode composition wherein the cathode conductive material is present in an amount of 1 part by weight or more and 20 parts by weight or less based on 100 parts by weight of the cathode composition.

11. 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 active material layer comprises a negative electrode composition according to any one of claims 1 to 10 or a cured product thereof.

12. In claim 11, 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.

13. Bipolar; A negative electrode for a lithium secondary battery according to claim 11; A separator provided between the anode and the cathode; and A lithium secondary battery comprising an electrolyte.

Images