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

Abstract

A negative electrode composition, a negative electrode for a lithium secondary battery including the same, a lithium secondary battery, and a method for manufacturing the negative electrode composition are provided. The negative electrode composition includes a silicon-carbon composite, graphite, and a negative electrode conductive material, where the silicon-carbon composite has a larger BET specific surface area than the graphite.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0136399, filed on October 21, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present description relates to a negative electrode composition, a negative electrode for a lithium secondary battery including the same, a lithium secondary battery, and a method for producing the negative electrode composition. [Background technology]

[0003] Recently, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, as well as power tools and vacuum cleaners, the demand for rechargeable batteries that are small and lightweight yet have relatively high capacity and / or high output has been rapidly increasing. In particular, lithium rechargeable batteries have been attracting attention as a driving power source for electronic devices due to their light weight and high energy density. Accordingly, research and development efforts to improve the performance of lithium rechargeable batteries have been actively pursued.

[0004] Lithium secondary batteries have an organic or polymer electrolyte between a positive electrode and a negative electrode, which contain active materials that allow for the intercalation and deintercalation of lithium ions. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted into and extracted from the positive and negative electrodes.

[0005] The positive electrode active material of a lithium secondary battery is a metal oxide such as LiCoO2, LiMnO2, LiMn2O4, or LiNiO2, and the negative electrode active material is a carbon-based material such as metallic lithium, graphite, or activated carbon, or silicon oxide (SiO xAmong the negative electrode active materials, metallic lithium was primarily used in the early days, but as charge and discharge cycles progressed, lithium atoms grew on the surface of the metallic lithium, damaging the separator and destroying the battery. Therefore, carbon-based materials have recently become the norm.

[0006] Graphite is commonly used as the negative electrode active material for lithium secondary batteries, but its low capacity per unit mass of 372 mAh / g makes it difficult to achieve high capacity in lithium secondary batteries. To address this issue, non-carbon-based negative electrode materials, such as silicon, tin, and their oxides, have been developed to have higher energy densities than graphite. However, while these non-carbon-based negative electrode materials offer high capacity, they suffer from low initial efficiency, resulting in significant lithium consumption during initial charge / discharge cycles and significant irreversible capacity loss.

[0007] In particular, silicon-based active materials undergo transient volume changes during battery operation, resulting in a reduction in battery life. Therefore, there is a need to develop a negative electrode that can effectively improve battery life characteristics while using silicon-based negative electrode active materials. Summary of the Invention [Problem to be solved by the invention]

[0008] One aspect of the present description relates to a lithium secondary battery, the types of active materials and conductive materials constituting a negative electrode composition, and battery performance provided by an active material having a specific relationship regarding the BET specific surface area value. [Means for solving the problem]

[0009] In one example, the present disclosure provides a negative electrode composition and a negative electrode for a lithium secondary battery including the same, wherein the negative electrode composition includes a silicon-carbon composite, graphite, and a negative electrode conductive material, and the BET specific surface area of the silicon-carbon composite is greater than the BET specific surface area of the graphite.

[0010] The graphite includes natural graphite and artificial graphite, and the BET specific surface area of the natural graphite is larger than the BET specific surface area of the artificial graphite.

[0011] In one example, the present description also provides a lithium secondary battery including the negative electrode and a method for producing the negative electrode composition.

[0012] In yet another example, the present disclosure provides a battery module and a battery pack including the lithium secondary battery. [Effects of the Invention]

[0013] According to another example of the present disclosure, when a silicon-carbon composite, which is a high-capacity material, is used as the negative electrode composition to fabricate a high-capacity battery, satisfying the interrelationship between the BET specific surface areas of the silicon-carbon composite and the graphite can improve the shortened life span of conventional secondary batteries, enable rapid charging, and provide excellent electrode adhesion.

[0014] When the silicon-carbon composite, graphite, and single-walled carbon nanotubes (SWCNTs) are used together as a conductive material in the negative electrode composition, the conductive paths between the negative electrode active material particles can be improved, thereby improving the capacity, efficiency, and lifespan of the battery. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following provides a more detailed explanation of this description to aid in understanding it. The terms and words used in this description and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as having meanings and concepts consistent with the technical idea of the present invention.

[0016] The terms used in this description are merely used to describe exemplary embodiments and are not intended to limit the description. The singular expressions include the plural expressions unless the context clearly indicates otherwise.

[0017] It should be understood that in this description, the terms "comprises," "includes," or "has" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0018] Furthermore, when a part such as a layer is said to be "on" or "above" another part, this does not only mean that it is "directly above" that part, but also includes cases where there is another part in between. Conversely, when a part is said to be "directly above" another part, it means that there is no other part in between. Furthermore, being "on" or "above" a reference part means being above or below the reference part, and does not necessarily mean being "above" or "above" the direction opposite to gravity.

[0019] In this description, the "specific surface area" is measured by the BET method, which can be measured by degassing the measurement object at 130°C for 2 hours using a BET measurement device (BEL-SORP-mini, Nippon Bell) and then performing N2 absorption / desorption at 77 K. That is, in this description, the BET specific surface area can refer to the specific surface area of the particle itself measured by the above measurement method.

[0020] In this description, the average length or diameter of the conductive material can be measured using SEM or TEM.

[0021] In this description, "pore size" may refer to the size of the pores in the particles themselves, and can be measured using a formula based on the BJH (Barrett-Joyer-Halenda) method through nitrogen adsorption. After deriving the pore area according to the pore size using the BELSORP-mini II model from BEL Japan, the pore size showing the largest pore area was used as the representative. The BJH method can be used, and the measured values are plotted with the X axis representing the pore diameter (Dp / nm) and the Y axis representing dVp / dDp (cm). 3 g -1 nm -1 )

[0022] In this description, "pore volume" may refer to the volume of the pores of the particle itself, and can be measured using a calculation formula based on the absorption / desorption isotherm method through nitrogen adsorption. After deriving an N2 adsorption / desorption isotherm graph using the BELSORP-mini II model from BEL Japan, the volume where P / P0 (close to 1) is highest in adsorption was used as a representative value. The absorption / desorption isotherm method can be used, and the plot of measured values has the X axis representing pressure (P / P0) and the Y axis representing Va / cm. 3 (STP)g -1 is.

[0023] Negative electrode composition An example of a negative electrode composition according to the present description includes a silicon-carbon composite, graphite, and a negative electrode conductive material, wherein the BET specific surface area of the silicon-carbon composite is larger than the BET specific surface area of the graphite.

[0024] When the silicon-carbon composite and the graphite satisfy the mutual relationship of the BET specific surface area, the life of the secondary battery is improved, rapid charging is possible, and electrode adhesion is excellent.

[0025] According to one example, the graphite includes at least one of natural graphite and artificial graphite, and when the graphite includes both the natural graphite and the artificial graphite, the BET specific surface area of the natural graphite is larger than the BET specific surface area of the artificial graphite. The graphite may include only natural graphite or only artificial graphite. Preferably, the graphite includes both natural graphite and artificial graphite.

[0026] When artificial graphite has a smaller BET specific surface area than natural graphite, it is possible to obtain the same or greater electrode adhesive strength even with less binder used, compared to when artificial graphite has a larger BET specific surface area than natural graphite.

[0027] Since artificial graphite consumes a relatively large amount of binder compared to natural graphite, when the artificial graphite has a smaller BET specific surface area than the natural graphite, it can exhibit an effect of improving electrode adhesive strength.

[0028] In addition, since the silicon-carbon composite has a relatively low reactivity with lithium ions, it is advantageous for the silicon-carbon composite to have a larger BET specific surface area than the natural graphite in order to facilitate the insertion and desorption of lithium ions.

[0029] Therefore, by satisfying the above-mentioned BET specific surface area relationship, when the same amount of binder is used, the electrode adhesion strength is improved and smooth intercalation and deintercalation of lithium ions is improved, thereby improving the life characteristics and fast charging performance of the secondary battery.

[0030] According to one example of the present disclosure, the BET specific surface area of the silicon-carbon composite is 1 m 2 or more larger than the BET specific surface area of the natural graphite. 2 / g~9m 2 / g large.

[0031] Since silicon has lower electrical conductivity than graphite, the reactivity of silicon-carbon composites with lithium ions is relatively low. Therefore, if the BET specific surface area, which corresponds to the reactive area of the silicon-carbon composite, is larger than that of natural graphite within the above range, it is advantageous for smooth insertion and desorption of lithium ions.

[0032] The BET specific surface area of the silicon-carbon composite is 1.2 m2 larger than the BET specific surface area of the natural graphite. 2 / g or more, 1.5m 2 / g or more, 1.7m 2 / g or more, or 1.9m 2 The BET specific surface area of the silicon-carbon composite is 8.7 m / g or more larger than the BET specific surface area of the natural graphite. 2 / g or less, 8.4m 2 / g or less, 8.2m 2 / g or less, or 8m 2 / g or less.

[0033] According to one example of the present disclosure, the BET specific surface area of the silicon-carbon composite is 2 m 2 or more times larger than the BET specific surface area of the artificial graphite. 2 / g~10m 2 / g large.

[0034] Since the electrical conductivity of silicon is lower than that of graphite, if the BET specific surface area corresponding to the reaction area of the silicon-carbon composite is larger than that of artificial graphite within the above range, it is advantageous for smooth insertion and desorption of lithium ions.

[0035] The BET specific surface area of the silicon-carbon composite is 2.2 m2 larger than the BET specific surface area of the artificial graphite. 2 / g or more, 2.5m 2 / g or more, 2.7m 2 / g or more, or 2.9m 2 / g or more.

[0036] The BET specific surface area of the silicon-carbon composite is 9.7 m or less than the BET specific surface area of the artificial graphite. 2 / g or less, 9.4m 2 / g or less, 9.2m2 / g or less, or 9m 2 / g or less.

[0037] According to one example of the present disclosure, the BET specific surface area of the natural graphite is 0.1 m less than the BET specific surface area of the artificial graphite. 2 / g~2m 2 / g large.

[0038] Within this range, when the BET specific surface area of natural graphite is large, the BET specific surface area of artificial graphite, which consumes a relatively large amount of binder, becomes relatively small, and when the same amount of binder is used, the electrode adhesive strength can be improved.

[0039] The BET specific surface area of the natural graphite is 0.2 m less than the BET specific surface area of the artificial graphite. 2 / g or more, or 0.3m 2 The BET specific surface area of the natural graphite is 1.9 m / g or more larger than the BET specific surface area of the artificial graphite. 2 / g or less, 1.8m 2 / g or less, or 1.7m 2 / g or less.

[0040] Natural graphite has a BET specific surface area of 1.5m 2 / g or more 3.5m 2 / g or less, which can improve electrode adhesion. Artificial graphite and silicon-carbon composites affect fast charging and lifespan performance, and their BET specific surface areas are 0.1 m 2 / g or more 2.5m 2 / g or less, 3m 2 / g or more 15m 2 / g or less.

[0041] If the artificial graphite has a larger BET specific surface area than the natural graphite, when an electrode is fabricated using the negative electrode composition, the binder in the electrode may be consumed in greater amounts, resulting in a decrease in electrode adhesion. Also, if the BET specific surface area of the silicon-carbon composite is smaller than that of the natural graphite, lithium insertion and / or desorption from the silicon-carbon composite may be difficult, resulting in a decrease in lifespan and fast charging performance.

[0042] In this description, the silicon-carbon composite is a composite of Si and C, and Si and C (graphite) are present, respectively. For example, the peaks of Si and C can be observed by elemental analysis methods such as XRD or NMR. In this description, the silicon-carbon composite can be expressed as Si / C. The silicon-carbon composite can be composed of Si and C that are not bonded to each other, but may contain additional components as necessary. For example, the silicon-carbon composite may or may not contain silicon carbide, expressed as SiC. When the silicon-carbon composite contains silicon carbide, its content is 3 wt % or less. The silicon-carbon composite may exist in a crystalline state, an amorphous state, or a mixture thereof. According to one example, the C in the silicon-carbon composite may exist in an amorphous state.

[0043] According to one example, the silicon-carbon composite may be a composite of silicon and graphite, or may have a structure in which a core of silicon and graphite is surrounded by graphene or amorphous carbon, etc. In the silicon-carbon composite, the silicon may be nanosilicon.

[0044] According to one example, the silicon-carbon composite includes porous carbon particles and silicon located on the surface or in the internal pores of the porous carbon particles.

[0045] According to one example, the silicon-carbon composite can be manufactured by a method including forming silicon on the surface and in the internal pores of porous carbon-based particles.

[0046] The porous carbon-based particles can be prepared by a method known in the art, for example, by carbonizing organic materials such as petroleum-based materials, polymers, etc., or by chemically treating and then carbonizing natural materials such as palm bark, etc. In another example, the porous carbon-based particles can be prepared by a method including a step of etching carbon-based particles having internal pores to expand the internal pores of the carbon-based particles.

[0047] The step of expanding the internal pores of the carbon-based particles may be performed in a nitrogen (N2), oxygen (O2), or air atmosphere, and the flow rate of the oxygen (O2) or oxygen-containing air may be controlled to 0.1 L / min to 10 L / min.

[0048] The step of expanding the internal pores of the carbon-based particles may be performed at a temperature ranging from 400° C. to 1200° C. for 30 minutes to 4 hours.

[0049] The pore characteristics of the resulting porous carbon-based particles may vary depending on the conditions for expanding the internal pores of the carbon-based particles.

[0050] The step of forming the silicon may be performed using a chemical vapor deposition method, in which silicon nanoparticles are deposited on the surfaces and / or in the pores of the carbon-based particles with expanded pores, thereby forming silicon in the form of a film, islands, or a mixture thereof.

[0051] The silicon nanoparticles may be crystalline, semi-crystalline, amorphous, or a combination thereof.

[0052] According to additional examples of the present description, the negative electrode composition may include graphite, which may include natural graphite and synthetic graphite.

[0053] According to one example, the natural graphite may satisfy the specific surface area relationship. Also, the natural graphite may satisfy the above condition while having a sphericity of 0.7 or more, or 0.9 or more.

[0054] In this description, sphericity may be the value obtained by dividing the circumference of a circle having the same area as the projected image by the perimeter of the projected image when a particle is projected, and specifically, it can be expressed by the following Equation 1. The sphericity can be determined from an SEM image or measured using a flow analyzer such as a Sysmex FPIA3000 manufactured by Malvern. In addition, the crystal size can be confirmed by XRD analysis. [Formula 1] Sphericity = Circumference of a circle with the same area as the image of the particle projected / Perimeter of the projected image

[0055] The natural graphite refers to graphite that is naturally produced, and examples thereof include scaled graphite, flake graphite, and soil graphite. Natural graphite is abundant, inexpensive, and has the advantages of high theoretical capacity and compaction density, enabling high output.

[0056] The natural graphite may be selected to satisfy the sphericity by checking the particle shape using an SEM and a particle shape analyzer.

[0057] According to one example, the artificial graphite may satisfy the specific surface area relationship. Also, the artificial graphite may satisfy the above condition while having a sphericity of 0.95 or less, or 0.9 or less.

[0058] The artificial graphite may be selected to satisfy the sphericity by checking the particle shape using an SEM and a particle shape analyzer.

[0059] The silicon-carbon composite, natural graphite, and artificial graphite have a particulate form. The average particle size (D50) of the silicon-carbon composite may be 1 μm or more, for example, 1 μm to 15 μm, 2 μm to 14 μm, or 3 μm to 13 μm. When the average particle size (D50) of the silicon-carbon composite is in the range of more than 1 μm but less than 15 μm, volume expansion and contraction during charge and discharge are reduced, improving life performance. Furthermore, an excessive increase in specific surface area is prevented, thereby preventing side reactions with the electrolyte as the cycle progresses, improving life performance. The average particle size (D50) of the natural graphite and artificial graphite is not particularly limited, but may be 1 μm or more, for example, 1 μm to 35 μm, 3 μm to 30 μm, or 5 μm to 25 μm.

[0060] In this description, the "average particle size (D50)" can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. The average particle size (D50) can be measured, for example, using a laser diffraction method. The laser diffraction method generally allows measurement of particle sizes from the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0061] The average particle size (D50) can be measured using a Microtrac device (manufacturer: Microtrac Model: S3500) with water and Triton-X100 dispersant. The average particle size (D50) of the positive electrode active material can be measured at a refractive index of 1.5 to 1.7, and that of the negative electrode active material can be measured at a refractive index of 1.97 or 2.42. For example, the particles can be dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer. Ultrasound of about 28 kHz is irradiated at an output of 60 W to obtain a volume cumulative particle size distribution graph, and the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0062] According to a further example of the present disclosure, the negative electrode conductive material may include single-walled carbon nanotubes (SWCNTs). The term "SWCNTs" refers to a tubular carbon structure composed of a single carbon layer. When the conductive material in the negative electrode composition includes the single-walled carbon nanotubes (SWCNTs), the charge / discharge capacity and / or lifespan of the battery may be improved. The single-walled carbon nanotubes (SWCNTs) effectively connect the conductive paths between particles, thereby preventing the loss of the conductive paths due to the swelling of the silicon-based negative electrode active material. As a result, when the single-walled carbon nanotubes (SWCNTs) are included, the lifespan of the battery may be improved.

[0063] According to an example, the negative electrode composition may include an additional conductive material other than the single-walled carbon nanotubes, such as carbon black or multi-walled carbon nanotubes (MWCNTs).

[0064] In this description, the length of a carbon nanotube refers to the length of the long axis passing through the center of the carbon nanotube unit, and the diameter of a carbon nanotube refers to the length of the short axis passing through the center of the unit and perpendicular to the long axis.

[0065] The average length of the single-walled carbon nanotubes (SWCNTs) may be 0.1 μm to 50 μm, 0.5 μm to 25 μm, or 0.5 μm to 20 μm. The average length may be 5 μm to 15 μm. The lower limit of the average length may be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, or 8 μm, and the upper limit may be 50 μm, 30 μm, 25 μm, 20 μm, 15 μm, 14 μm, 13 μm, 12 μm, 11 μm, or 10 μm.

[0066] When single-walled carbon nanotubes (SWCNTs) having such an average length are used together with the silicon-carbon composite and the graphite, the conductive paths between the particles are more easily connected, thereby improving the conductivity, strength, and / or electrolyte storage stability of the negative electrode. On the other hand, if the length of the carbon nanotubes is too short, it may be difficult to efficiently form conductive paths, resulting in reduced conductivity, and if the length of the carbon nanotubes is too long, it may be difficult to disperse the carbon nanotubes.

[0067] The average length of the single-walled carbon nanotubes (SWCNTs) can be calculated from the average value of the results of SEM observation.

[0068] The average diameter of the single-walled carbon nanotubes (SWCNTs) may be 1 nm to 20 nm, or 1.5 nm to 15 nm. In another example, the average diameter may be 1.5 nm to 5 nm. The lower limit of the average diameter may be 1 nm, 1.5 nm, or 2 nm, and the upper limit may be 20 nm, 18 nm, 16 nm, 14 nm, 12 nm, 10 nm, 8 nm, 6 nm, or 4 nm.

[0069] Single-walled carbon nanotubes (SWCNTs) that satisfy this range have flexible properties, and therefore have the effect of preventing the contact between negative electrode active material particles from being easily broken even when physically damaged. On the other hand, if the diameter of the carbon nanotubes (SWCNTs) is too large, the density of the electrode may decrease, and if the diameter of the carbon nanotubes (SWCNTs) is too small, dispersion may be difficult, which may reduce the processability of the dispersion.

[0070] The average diameter of the single-walled carbon nanotubes (SWCNTs) can be calculated from the average value observed by TEM.

[0071] The BET specific surface area of the single-walled carbon nanotubes is 200 m 2 / g~2,000m 2 / g, and in some instances, 250m 2 / g~1,500m 2 When single-walled carbon nanotubes (SWCNTs) that satisfy the above range are used, even if a small amount of conductive material is used, dispersion is easy and particles can be effectively connected.

[0072] The single-walled carbon nanotubes (SWCNTs) may be included in an amount of 0.01 to 5 parts by weight, specifically 0.01 to 4 parts by weight, 0.01 to 3 parts by weight, 0.01 to 2 parts by weight, 0.01 to 1 part by weight, or 0.05 to 0.5 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0073] When the content range is satisfied, it is possible to easily connect a conductive path between silicon-based negative electrode active material particles including the silicon-carbon composite and graphite.

[0074] According to additional examples of the present description, the BET specific surface area of the silicon-carbon composite is greater than the BET specific surface area of the natural graphite, which is greater than the BET specific surface area of the artificial graphite.

[0075] According to one example, the specific surface area is measured by the BET method, which can be measured by degassing the measurement object at 130° C. for 2 hours using a BET measurement device (BEL-SORP-mini, Nippon Bell) and then performing N2 absorption / desorption at 77 K. That is, in this description, the BET specific surface area can refer to the specific surface area of the particles themselves measured by the above measurement method.

[0076] According to one example, the negative electrode conductive material may include single-walled carbon nanotubes (SWCNTs).

[0077] In the case of the negative electrode composition according to one example of the present disclosure, when a silicon-based active material, which is a high-capacity material, is used to manufacture a high-capacity battery, the composition contains a silicon-carbon composite, natural graphite, artificial graphite, and single-walled carbon nanotubes (SWCNTs) having the above-mentioned contents, and the interrelationship between the BET specific surface areas of the silicon-carbon composite, the natural graphite, and the artificial graphite is satisfied, thereby improving the shortened lifespan of conventional secondary batteries, enabling rapid charging, and exhibiting excellent electrode adhesion.

[0078] In addition, by using the silicon-carbon composite, graphite, and single-walled carbon nanotubes (SWCNTs) as a conductive material together in the negative electrode composition having the above content, the conductive paths between the negative electrode active material particles can be improved, thereby improving the capacity, efficiency, and lifespan of the battery.

[0079] In one example of the present disclosure, a negative electrode composition is provided in which the total pore volume (total pore V) of the silicon-carbon composite is equal to or greater than the total pore volume of the natural graphite, and the total pore volume of the natural graphite is equal to or greater than the total pore volume of the artificial graphite.

[0080] Pore volume, like the BET specific surface area, can affect electrode adhesion and smooth lithium ion intercalation and deintercalation. That is, when the pore volume of natural graphite is equal to or greater than that of artificial graphite, binder consumption can be relatively reduced, improving electrode adhesion with the same amount of binder. Furthermore, when the pore volume of a silicon-carbon composite is equal to or greater than that of natural graphite, smooth lithium ion intercalation and deintercalation from the silicon-carbon composite is facilitated, resulting in improved battery life and fast charging performance.

[0081] According to a further example of the present description, the silicon-carbon composite, natural graphite, and artificial graphite in the negative electrode composition may contain pores.

[0082] According to one example, the pore volume may refer to the volume of the pores of the particle itself, and can be measured by a calculation formula based on the absorption / desorption isotherm method through nitrogen adsorption. Specifically, after deriving an N2 adsorption / desorption isotherm graph using the BELSORP-mini II model from BEL Japan, the volume at the point where P / P0 (close to 1) is highest in adsorption is taken as the representative volume. The absorption / desorption isotherm method can be used, and the measured values are plotted with the X axis representing pressure (P / P0) and the Y axis representing Va / cm. 3 (STP)g -1 is.

[0083] According to one example, the pore volume (total pore V) of the silicon-carbon composite is 4 to 11 cm 3 / g, the pore volume (total pore V.) of the natural graphite is 2 to 8 cm 3 / g, and the pore volume (total pore V.) of the artificial graphite is 0.1 to 4 cm 3 / g or less.

[0084] The pore volume of the silicon-carbon composite is 1 cm larger than the pore volume of the natural graphite. 3 / g~8cm 3 / g large.

[0085] The pore volume of the silicon-carbon composite may be the same as the pore volume of the natural graphite.

[0086] The pore volume of the silicon-carbon composite is 4 cm 2 larger than the pore volume of the artificial graphite. 3 / g~11cm 3 / g large.

[0087] The pore volume of the natural graphite is 1 cm 2 or more times larger than the pore volume of the artificial graphite. 3 / g~6cm 3 / g large.

[0088] The pore volume of the natural graphite may be the same as the pore volume of the artificial graphite.

[0089] When the pore volumes (total pore V) of the silicon-carbon composite, the natural graphite, and the artificial graphite satisfy the above ranges, the secondary battery may have the characteristics of improved life span, rapid charging, and excellent electrode adhesion.

[0090] In one example of the present disclosure, there is provided a negative electrode composition, wherein the pore intensity of the silicon-carbon composite having a size of 2 nm to 200 nm is equal to or greater than the pore intensity of the natural graphite, and the pore intensity of the natural graphite is equal to or greater than the pore intensity of the artificial graphite.

[0091] According to one example, the pore size may refer to the size of the pores in the particles themselves, and may be measured by a calculation formula according to the BJH (Barrett-Joyer-Halenda) method through a nitrogen adsorption method. Specifically, the pore area according to the pore size is calculated using a BELSORP-mini II model from BEL Japan, and the pore size showing the largest pore area is used as the representative. The BJH method may be used, and the measured values may be plotted with the X axis representing the pore diameter (Dp / nm) and the Y axis representing the pore diameter (dVp / dDp) (cm). 3 g -1 nm -1 )

[0092] When the above range is satisfied, the secondary battery can be improved in terms of its life span, can be rapidly charged, and has excellent electrode adhesion.

[0093] In one example of the present description, the natural graphite has a BET specific surface area of 1.5 m 2 / g or more 3.5m 2 / g or less, and the artificial graphite has a BET specific surface area of 0.1 m 2 / g or more 2.5m 2 / g or less.

[0094] The natural graphite has a BET specific surface area of 1.5m 2 / g or more 3.5m 2 / g or less, 1.5m 2 / g or more 3.3m 2 / g or less, 1.5m 2 / g or more 3m 2 / g or less, 1.5m 2 / g or more 2.8m 2 / g or less, or 1.5m 2 / g or more 2.5m 2 / g or less.

[0095] The artificial graphite has a BET specific surface area of 0.1 m 2 / g or more 2.2m 2 / g or less, 0.1m 2 / g or more 2m 2 / g or less, 0.1m2 / g or more 1.8m 2 / g or less, 0.1m 2 / g or more 1.5m 2 / g or less, 0.3m 2 / g or more 2.5m 2 / g or less.

[0096] When the natural graphite and artificial graphite satisfy the BET specific surface area range, the negative electrode composition contains two types of graphite other than the silicon-carbon composite, which have different specific surface areas. This allows the use of the silicon-carbon composite as the negative electrode active material to have increased battery capacity and excellent output characteristics at a high C-rate, and can alleviate the problem of reduced lifespan of the negative electrode and secondary battery that may occur due to large volume changes in silicon-based particles.

[0097] The natural graphite can improve electrode adhesion within this BET specific surface area range, while the artificial graphite can affect fast charge and life performance within this BET specific surface area range. Furthermore, if the artificial graphite has a larger BET specific surface area than the natural graphite, fabricating an electrode from the negative electrode composition may consume more binder in the electrode, resulting in a decrease in electrode adhesion.

[0098] In one example of the present description, there is provided a negative electrode composition in which the negative electrode conductive material comprises single-walled carbon nanotubes (SWCNTs), and in which, based on 100 parts by weight of the total content of the silicon-carbon composite, graphite, and single-walled carbon nanotubes in the negative electrode composition, the silicon-carbon composite is contained in an amount of 0.5 parts by weight to 50 parts by weight; the graphite is contained in an amount of 45 parts by weight to 99 parts by weight; and the single-walled carbon nanotubes (SWCNTs) are contained in an amount of 0.01 parts by weight to 5 parts by weight, and based on 100 parts by weight of the graphite, the natural graphite is contained in an amount of 10 parts by weight to 70 parts by weight; and the artificial graphite is contained in an amount of 30 parts by weight to 90 parts by weight.

[0099] According to additional examples of the present description, the negative electrode composition can include a silicon-carbon composite; graphite; and a negative electrode conductive material, wherein the graphite can include natural graphite and artificial graphite, and the negative electrode conductive material can include single-walled carbon nanotubes (SWCNTs).

[0100] According to a further example of the present description, the negative electrode composition may contain 0.5 to 50 parts by weight of the silicon-carbon composite; 45 to 99 parts by weight of the graphite; and 0.01 to 5 parts by weight of the single-walled carbon nanotubes (SWCNTs), based on a total of 100 parts by weight of the silicon-carbon composite, graphite, and single-walled carbon nanotubes.

[0101] In one example, based on 100 parts by weight of the total content of the silicon-carbon composite, graphite, and single-walled carbon nanotubes in the negative electrode composition, the silicon-carbon composite may be present in an amount of 1 to 40 parts by weight, 2 to 30 parts by weight, 3 to 20 parts by weight, 4 to 10 parts by weight, or 5 to 10 parts by weight. The graphite may be present in an amount of 50 to 99 parts by weight, 55 to 99 parts by weight, 60 to 99 parts by weight, 65 to 99 parts by weight, 70 to 99 parts by weight, or 75 to 95 parts by weight. The single-walled carbon nanotubes (SWCNTs) may be present in an amount of 0.01 to 4 parts by weight, 0.01 to 3 parts by weight, 0.01 to 2 parts by weight, 0.01 to 1 part by weight, or 0.05 to 0.5 parts by weight.

[0102] According to a further example of the present description, the natural graphite may be included in an amount of 10 to 70 parts by weight; and the artificial graphite may be included in an amount of 30 to 90 parts by weight, based on 100 parts by weight of the graphite.

[0103] For example, based on 100 parts by weight of the graphite, the natural graphite may be 11 to 68 parts by weight; and the artificial graphite may be 32 to 89 parts by weight.

[0104] When the silicon-carbon composite content range is satisfied within the anode composition content range, capacity characteristics can be improved, when the graphite content range is satisfied, fast charging performance and anode adhesion strength can be improved, and when the single-walled carbon nanotube (SWCNT) content range is satisfied, battery efficiency and life performance can be improved. As a result, the secondary battery can have the characteristics of improved lifespan, increased charge and discharge points, and excellent output characteristics at high C-rates.

[0105] In one example of the present description, a negative electrode composition is provided that further includes a binder.

[0106] The binder may improve adhesion between negative electrode active material particles and between the negative electrode active material particles and the negative electrode current collector. The negative electrode binder may be any binder known in the art, and non-limiting examples thereof include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen is substituted with Li, Na, or Ca, or various copolymers thereof.

[0107] The binder may be included in an amount of 10% or less, preferably 1% to 5%, based on 100 parts by weight of the negative electrode composition. For example, the binder may be included in an amount of 9% or less, 8% or less, 7% or less, 6% or less, or 5% or less, based on 100 parts by weight of the negative electrode composition. The binder may be included in an amount of 0.5% or more, or 1% or more, based on 100 parts by weight of the negative electrode composition.

[0108] Method for producing negative electrode composition One example of the present description is a method for producing a negative electrode composition, comprising: adding water to a negative electrode conductive material and mixing them to form a first mixture; and mixing a silicon-carbon composite and graphite with the first mixture to form a second mixture, wherein the BET specific surface area of the silicon-carbon composite is greater than the BET specific surface area of the graphite.

[0109] According to an additional example of the present description, the method of making the negative electrode composition may include mixing the silicon-carbon composite and graphite together with the negative electrode conductive material.

[0110] According to one example, the graphite includes at least one of natural graphite and artificial graphite, and when the graphite includes both the natural graphite and the artificial graphite, the BET specific surface area of the natural graphite is larger than the BET specific surface area of the artificial graphite. Preferably, the graphite includes both the natural graphite and the artificial graphite.

[0111] In one example of the present description, there is provided a method for producing a negative electrode composition, wherein the negative electrode conductive material comprises single-walled carbon nanotubes (SWCNTs), and the negative electrode composition contains, based on 100 parts by weight of the total content of the silicon-carbon composite, graphite, and single-walled carbon nanotubes, 0.5 parts by weight to 50 parts by weight of the silicon-carbon composite; 45 parts by weight to 99 parts by weight of the graphite; and 0.01 parts by weight to 5 parts by weight of the single-walled carbon nanotubes (SWCNTs), and based on 100 parts by weight of the graphite, the negative electrode composition contains 10 parts by weight to 70 parts by weight of the natural graphite; and 30 parts by weight to 90 parts by weight of the artificial graphite.

[0112] In one example of the present description, the BET specific surface area of the silicon-carbon composite is 1 m 2 or more larger than the BET specific surface area of the natural graphite. 2 / g~9m 2 / g, and the BET specific surface area of the silicon-carbon composite is 2 m / s greater than the BET specific surface area of the artificial graphite. 2 / g~10m 2 / g, and the BET specific surface area of the natural graphite is 0.1 m / g larger than the BET specific surface area of the artificial graphite. 2 / g~2m 2 / g even larger.

[0113] In the examples described herein, the BET specific surface areas of the silicon-carbon composite, the natural graphite, and the artificial graphite are the same as those described above for the negative electrode composition.

[0114] negative electrode One example of the present disclosure provides a negative electrode for a lithium secondary battery, comprising: a current collector; and a negative electrode active material layer including the above-described negative electrode composition formed on one or both surfaces of the current collector.

[0115] According to an additional example of the present description, the current collector is not particularly limited as long as it is conductive as a negative electrode current collector without inducing chemical changes in the battery. For example, the current collector may be copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like. A transition metal that easily adsorbs carbon, such as copper or nickel, may also be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but is not limited thereto.

[0116] According to a further example of the present disclosure, a negative electrode active material layer containing the negative electrode composition according to the above example may be formed on one or both surfaces of the current collector. According to one example, the thickness of the negative electrode active material layer may be 20 μm or more and 500 μm or less.

[0117] According to a further example of the present disclosure, the negative electrode for a lithium secondary battery may be prepared by a conventional negative electrode preparation method. The negative electrode composition may be coated on a current collector, and the coating may be dried and rolled. The types and contents of the negative electrode active material, conductive material, and binder may be the same as those described above.

[0118] The solvent may be a solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and may be used alone or in combination. The amount of solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder, taking into account the coating thickness of the slurry and the production yield, and to provide a viscosity that allows excellent thickness uniformity when applied to fabricate the negative electrode. Alternatively, the negative electrode may be fabricated by casting the active material layer-forming composition on a separate support, peeling it off from the support, and laminating the resulting film on a current collector.

[0119] Lithium secondary battery One example of the present description provides a lithium secondary battery including: a positive electrode; a negative electrode for a lithium secondary battery according to one or more of the above examples; and a separator between the positive electrode and the negative electrode.

[0120] According to this additional example, the negative electrode is the same as the negative electrode according to the previous example. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0121] According to a further example of the present description, the positive electrode includes a positive electrode current collector and a positive electrode active material layer including a positive electrode composition formed on the current collector. The current collector may be a positive electrode current collector.

[0122] According to one example, the positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode composition. The positive electrode composition may include the positive electrode active material.

[0123] The positive electrode current collector in the positive electrode is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. 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. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and the surface of the current collector may be formed with fine irregularities to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0124] For example, the thickness of the negative electrode active material layer may be 20 μm or more and 500 μm or less, and the thickness of the positive electrode active material layer may be 90% to 110%, for example 95% to 105%, of the thickness of the negative electrode active material layer, or these thicknesses may be the same.

[0125] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 Mc3 Examples of the lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and 0.01≦c3≦0.1), or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be metallic lithium (Li-metal).

[0126] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0127] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that is conductive without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination.

[0128] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0129] According to an additional example of the present description, the lithium secondary battery can include a separator between the positive electrode and the negative electrode.

[0130] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitations. In particular, a separator with low resistance to electrolyte ion movement and excellent electrolyte humidification capacity is preferred. Specifically, a porous polymer film, such as 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, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymer material may be used, and may be selectively used in a single-layer or multi-layer structure.

[0131] According to one example of the present description, the lithium secondary battery can include an electrolyte.

[0132] Examples of the electrolytic solution include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0133] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0134] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0135] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed in an appropriate ratio with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, an electrolyte having high conductivity can be prepared, and therefore such cyclic carbonates can be used even more preferably.

[0136] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl -, I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0137] In addition to the components of the electrolytic solution, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0138] In one example of the present description, the lithium secondary battery is a cylindrical battery.

[0139] According to one example, the cylindrical battery may mean that the battery itself, which includes an assembly including a positive electrode, a negative electrode, a separator, and an electrolyte, has a cylindrical shape, and may include a cylindrical can, a battery assembly provided inside the cylindrical can, and a top cap.

[0140] In one example of the present disclosure, a battery module including the lithium secondary battery is provided.

[0141] In one example of the present description, a battery pack is provided that includes a battery module according to the above-described example.

[0142] A further example of the present description provides a battery module and a battery pack including the same, each including the cylindrical battery as a unit cell. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0143] The lithium secondary battery according to the present embodiment stably exhibits excellent discharge capacity, output characteristics, and cycle performance, and can be used not only in portable devices such as mobile phones, laptops, and digital cameras, but also 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. For example, the battery module or battery pack can be used as a power source for one or more medium- to large-sized devices, such as power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0144] Example Below, preferred examples are presented to help understand the present description, but these examples are merely illustrative of the present description, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of the present description, and it is natural that such changes and modifications fall within the scope of the attached claims.

[0145] <Examples and Comparative Examples> Example 1 Anode manufacturing A negative electrode composition containing a silicon-carbon composite, graphite, and a negative electrode conductive material was prepared. The negative electrode composition contained 10 parts by weight of the silicon-carbon composite, graphite, and a negative electrode conductive material, based on 100 parts by weight of the total content of the silicon-carbon composite, graphite, and a negative electrode conductive material. The negative electrode composition contained 10 parts by weight of the silicon-carbon composite, 89.5 parts by weight of graphite (artificial graphite:natural graphite = 89:11 weight ratio), and 0.5 parts by weight of single-walled carbon nanotubes. Based on 100 parts by weight of the negative electrode composition, 1.15 parts by weight of styrenebutadiene rubber (SBR) and 1 part by weight of carboxymethyl cellulose (CMC) were used as binders. The negative electrode conductive material was added in the form of a CNT pre-dispersion containing 0.09 parts by weight of a dispersant and 0.06 parts by weight of single-walled CNTs, based on 100 parts by weight of the negative electrode composition. The BET specific surface areas of the artificial graphite, natural graphite, and silicon-carbon composite in the composition were each 0.8 m. 2 / g, 1.8m 2 / g, 6.8m 2 / g.

[0146] That is, the silicon-carbon composite, graphite, and binders, carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), were added to a single-walled carbon nanotube pre-dispersion liquid using distilled water as a dispersion medium and CMC (carboxymethyl cellulose) as a dispersant, followed by stirring. Then, distilled water was added to prepare a negative electrode composition (solid content = 50 parts by weight).

[0147] The negative electrode composition was applied to a copper (Cu) metal thin film, which was a negative electrode current collector, having a thickness of 15 μm, and dried. The temperature of the circulating air was 60° C. Then, the composition was rolled and dried in a vacuum oven at 130° C. for 12 hours to prepare a negative electrode having a negative electrode active material layer disposed on the negative electrode current collector.

[0148] In this case, the weight of the CMC added to the binder: the weight of the CMC added to the dispersant was 1.14:0.06. The average length of the single-walled carbon nanotube units in the negative electrode active material layer was 10 μm, and the average diameter was 2 nm.

[0149] <Examples 2 to 23> A negative electrode was prepared in the same manner as in Example 1, except that the BET specific surface areas of the artificial graphite, natural graphite, and silicon-carbon composite contained in the negative electrode composition, and their respective weight ratios based on a total of 100 parts by weight of the silicon-carbon composite, graphite, and single-walled carbon nanotubes in the negative electrode composition, are shown in Table 1 below.

[0150] <Comparative Examples 1 to 6> A negative electrode was prepared in the same manner as in Example 1, except that the BET specific surface areas of the artificial graphite, natural graphite, and silicon-carbon composite contained in the negative electrode composition, and the weight ratios thereof, based on 100 parts by weight of the total content of the silicon-carbon composite, graphite, and single-walled carbon nanotubes in the negative electrode composition, are shown in Table 1 below. <Reference Examples 1 and 2> A negative electrode was fabricated in the same manner as in Example 1, except that multi-walled carbon nanotubes (MWCNTs) and carbon black were used instead of the single-walled carbon nanotubes contained in the negative electrode composition.

[0151] The negative electrodes prepared in the examples and comparative examples are as shown in Table 1 below.

[0152] [Table 1]

[0153] The pore volumes of the materials used in Examples 1 and 23 and Comparative Examples 1, 2 and 6 are shown in Table 2 below.

[0154] [Table 2]

[0155] The specific surface area was measured using a BET measuring device (BEL-SORP-mini, Nippon Bell) by degassing at 130°C for 2 hours and then performing N2 absorption / desorption at 77K.

[0156] The pore volume was determined by deriving an N adsorption / desorption isotherm graph using the BELSORP-mini II model from BEL Japan, and the volume at the point where P / P (close to 1) was highest during adsorption was used as a representative value.

[0157] Experimental example Anodes and lithium secondary batteries including the same were fabricated using the anode active materials of the Examples and Comparative Examples, respectively.

[0158] Life (capacity retention rate) characteristic evaluation The manufactured batteries were charged and discharged to evaluate the capacity retention rate, which is shown in Table 3 below.

[0159] The first and second cycles were charged and discharged at 0.1 C, and from the third cycle onwards, the charge and discharge was carried out at 0.5 C. The 300th cycle was completed in a charged state (with lithium in the negative electrode).

[0160] Charging conditions: CC (constant current) / CV (constant voltage) (4.25V / 0.05C current cut-off) Discharge condition: CC (constant current) condition 2.5V

[0161] The capacity retention rates were calculated as follows: Capacity retention rate (%) = (100th discharge capacity / 1st discharge capacity) × 100

[0162] Table 3 below shows values for energy density (based on Example 1, %) and capacity retention rate (300 cycles, %) for Examples 1 to 23, Comparative Examples 1 to 6, and Reference Examples 1 and 2.

[0163] Li-plating time evaluation 1.4875cm 2 The lithium (Li) metal thin film cut into a circular shape was used as the positive electrode. A porous polyethylene separator was placed between the positive electrode and the negative electrode, and an electrolyte solution of 1M LiPF6 dissolved in a 7:3 volumetric mixture of methyl ethyl carbonate (EMC) and ethylene carbonate (EC) with 0.5 parts by weight of vinylene carbonate was dissolved was injected to fabricate a lithium coin half-cell.

[0164] After the first charge / discharge cycle was completed, the Li-plating time was measured under a 1.8C charge condition. Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.5V

[0165] Electrode adhesion evaluation Each negative electrode was punched out to a size of 20 mm x 150 mm and fixed to the center of a glass slide using tape. The negative electrode current collector was then peeled off using a UTM to measure the 180-degree peel strength. The peel strength was measured for at least five negative electrodes and averaged to determine the evaluation. The results are shown in Table 3 below.

[0166] [Table 3]

[0167] The negative electrode composition according to the present disclosure includes a silicon-carbon composite, graphite, and a negative electrode conductive material. The graphite includes natural graphite and artificial graphite. The BET specific surface area of the silicon-carbon composite is greater than that of the natural graphite, which in turn is greater than that of the artificial graphite. The negative electrode composition satisfies the interrelationship between the BET specific surface areas of the silicon-carbon composite, the natural graphite, and the artificial graphite when using a high-capacity silicon-based active material to fabricate a high-capacity battery. This improves the lifespan reduction of conventional secondary batteries, enables fast charging, and provides excellent electrode adhesion. Table 3 shows that the Li plating point in the Examples is at a higher SOC% than the Comparative Examples, indicating that lithium is deposited more slowly during charging. This indicates that the fast charging performance is excellent because lithium is deposited more slowly during charging.

[0168] In addition, the silicon-carbon composite, graphite, and single-walled carbon nanotubes (SWCNTs) used as a conductive material in the negative electrode composition can improve the conductive paths between particles of the negative electrode active material, thereby improving the capacity, efficiency, and lifespan of the battery.

[0169] Natural graphite has a BET specific surface area of 1.5m 2 / g or more 3.5m 2 / g or less, which can improve electrode adhesion. Artificial graphite and silicon-carbon composites affect fast charging and lifespan performance, and their BET specific surface areas are 0.1 m 2 / g or more 2.5m 2 / g or less, 3m 2 / g or more 15m 2 / g or less.

[0170] If the artificial graphite has a larger BET specific surface area than natural graphite, the binder in the electrode may be consumed in greater amounts when fabricating an electrode using the negative electrode composition, which may result in reduced electrode adhesion. Also, if the BET specific surface area of the silicon-carbon composite is smaller than that of natural graphite, it may be difficult to insert and / or extract lithium from the silicon-carbon composite, which may result in reduced lifespan and fast charging performance.

[0171] Examples 1 to 23 are cases where a negative electrode composition satisfying a specific specific surface area ratio was used, and it can be confirmed that the life performance, rapid charging, and electrode adhesive strength are all excellent.

[0172] On the other hand, Comparative Examples 1 and 3 to 6 are cases in which the specific specific surface area ratio of the negative electrode composition used herein is not satisfied. Since artificial graphite has a larger BET specific surface area than natural graphite, when an electrode is fabricated using the negative electrode composition, more binder in the electrode is consumed, which may result in a decrease in electrode adhesive strength and therefore a decrease in lifespan performance.

[0173] Comparative Example 2 is a case where the specific specific surface area ratio of the negative electrode composition used in this description is not satisfied, and the BET specific surface area of the silicon-carbon composite is smaller than the BET specific surface area of natural graphite, making it difficult to insert and / or extract lithium from the silicon-carbon composite, which may result in reduced life performance and fast charging performance.

[0174] Reference Examples 1 and 2 are cases in which multi-walled carbon nanotubes (MWCNTs) and carbon black are used as the negative electrode conductive material instead of the single-walled carbon nanotubes (SWCNTs) used in this description, and this may affect the battery life performance, fast charging performance, and electrode adhesion.

Claims

1. 1. A negative electrode composition comprising a silicon-carbon composite, graphite, and a negative electrode conductive material, The silicon-carbon composite has a BET specific surface area greater than the BET specific surface area of the graphite.

2. 2. The negative electrode composition according to claim 1, wherein the graphite includes at least one of natural graphite and artificial graphite, and when the graphite includes both the natural graphite and the artificial graphite, a BET specific surface area of the natural graphite is larger than a BET specific surface area of the artificial graphite.

3. The graphite includes the natural graphite, and the BET specific surface area of the silicon-carbon composite is 1 m larger than the BET specific surface area of the natural graphite. ２ / g~9m ２ The negative electrode composition according to claim 2 , wherein the Cr content is greater than 1 / g.

4. The graphite includes the artificial graphite, and the BET specific surface area of the silicon-carbon composite is 2 m2 larger than the BET specific surface area of the artificial graphite. ２ / g to 10m ２ The negative electrode composition according to claim 2 , wherein the Cr content is greater than 1 / g.

5. The graphite includes both the natural graphite and the artificial graphite, and the BET specific surface area of the natural graphite is 0.1 m or more smaller than the BET specific surface area of the artificial graphite. ２ / g to 2m ２ The negative electrode composition according to claim 2 , wherein the Cr content is greater than 1 / g.

6. 3. The negative electrode composition of claim 2, wherein the graphite includes both the natural graphite and the artificial graphite, and the pore volume of the silicon-carbon composite is the same as or larger than the pore volume of the natural graphite, and the pore volume of the natural graphite is the same as or larger than the pore volume of the artificial graphite.

7. The graphite includes both the natural graphite and the artificial graphite, and the natural graphite has a BET specific surface area of 1.5 m ２ / g or more 3.5m ２ / g or less, and the artificial graphite has a BET specific surface area of 0.1 m ２ / g or more 2.5m ２ The negative electrode composition according to claim 2 , wherein the SiO 2 content is 1 / g or less.

8. the negative electrode conductive material includes single-walled carbon nanotubes (SWCNTs), 10. The negative electrode composition of claim 1, wherein the silicon-carbon composite is included in an amount of 0.5 to 50 parts by weight, the graphite is included in an amount of 45 to 99 parts by weight, and the single-walled carbon nanotubes (SWCNTs) are included in an amount of 0.01 to 5 parts by weight, based on 100 parts by weight of a total amount of the silicon-carbon composite, graphite, and single-walled carbon nanotubes in the negative electrode composition.

9. 3. The negative electrode composition according to claim 2, wherein the graphite includes both the natural graphite and the artificial graphite, and the natural graphite is included in an amount of 10 parts by weight to 70 parts by weight, and the artificial graphite is included in an amount of 30 parts by weight to 90 parts by weight, based on 100 parts by weight of the graphite.

10. The negative electrode composition of claim 1 , further comprising a binder.

11. mixing a negative electrode conductive material and water to form a first mixture; and mixing the first mixture with a silicon-carbon composite and graphite to form a second mixture; A method for producing a negative electrode composition, comprising: The method for producing a negative electrode composition, wherein the silicon-carbon composite has a larger BET specific surface area than the graphite.

12. 12. The method for producing a negative electrode composition according to claim 11, wherein the graphite includes at least one of natural graphite and artificial graphite, and when the graphite includes both the natural graphite and the artificial graphite, a BET specific surface area of the natural graphite is larger than a BET specific surface area of the artificial graphite.

13. the negative electrode conductive material includes single-walled carbon nanotubes (SWCNTs), 12. The method of claim 11, wherein the silicon-carbon composite is included in an amount of 0.5 to 50 parts by weight, the graphite is included in an amount of 45 to 99 parts by weight, and the single-walled carbon nanotubes (SWCNTs) are included in an amount of 0.01 to 5 parts by weight, based on 100 parts by weight of a total amount of the silicon-carbon composite, graphite, and single-walled carbon nanotubes in the negative electrode composition.

14. 13. The method for producing a negative electrode composition according to claim 12, wherein the graphite includes both the natural graphite and the artificial graphite, and the natural graphite is included in an amount of 10 parts by weight to 70 parts by weight, and the artificial graphite is included in an amount of 30 parts by weight to 90 parts by weight, based on 100 parts by weight of the graphite.

15. The graphite includes the natural graphite, and the BET specific surface area of the silicon-carbon composite is 1 m larger than the BET specific surface area of the natural graphite. ２ / g~9m ２ The method for producing a negative electrode composition according to claim 12 , wherein the SiO 2 content is 0.015 wt % or more.

16. The graphite includes the artificial graphite, and the BET specific surface area of the silicon-carbon composite is 2 m2 larger than the BET specific surface area of the artificial graphite. ２ / g to 10m ２ The method for producing a negative electrode composition according to claim 12 , wherein the SiO 2 content is 0.015 wt % or more.

17. The graphite includes both the natural graphite and the artificial graphite, and the BET specific surface area of the natural graphite is 0.1 m or more smaller than the BET specific surface area of the artificial graphite. ２ / g to 2m ２ The method for producing a negative electrode composition according to claim 12 , wherein the SiO 2 content is 0.015 wt % or more.

18. a current collector; and A negative electrode active material layer comprising the negative electrode composition according to any one of claims 1 to 10, provided on one or both surfaces of the current collector. A negative electrode for a lithium secondary battery comprising:

19. positive electrode; A negative electrode for a lithium secondary battery according to claim 18; and a separator provided between the positive electrode and the negative electrode; A lithium secondary battery comprising:

20. 20. The lithium secondary battery according to claim 19, wherein the lithium secondary battery is a cylindrical battery.

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