Negative electrode active material, method for producing a negative electrode active material, negative electrode composition, negative electrode for lithium secondary battery containing the same, and lithium secondary battery containing the negative electrode

Abstract

This application relates to a negative electrode active material, a method for producing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit as of the filing date of Korean Patent Application No. 10-2023-0143044, filed with the Korean Intellectual Property Office on 24 October 2023, and all its contents are incorporated herein by reference.

[0002] This application relates to a negative electrode active material, a method for producing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery containing the negative electrode. [Background technology]

[0003] The rapid increase in the use of fossil fuels has led to a growing demand for alternative and clean energy sources, and one of the most actively researched areas in this field is the generation and storage of electricity using electrochemical reactions.

[0004] Currently, a typical example of an electrochemical element that utilizes such electrochemical energy is the secondary battery, and its range of applications is steadily expanding.

[0005] With the development of technologies related to mobile devices and the increasing demand, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium-ion batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have become commonplace and are widely used. Furthermore, research is actively being conducted on methods for manufacturing high-density electrodes with even higher energy density per unit volume for use in such high-capacity lithium-ion batteries.

[0006] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator membrane. The negative electrode contains a negative electrode active material that inserts and de-inserts lithium ions released from the positive electrode, and silicon-based particles with a high discharge capacity may be used for the negative electrode active material.

[0007] In particular, with the recent demand for high-density energy batteries, Si / C and SiO2, which have more than 10 times the capacity of graphite-based materials, are being used as negative electrode active materials. x Active research is being conducted on methods to increase capacity by using silicon-based compounds such as the one shown. However, while silicon-based compounds are high-capacity materials and have a larger capacity than the graphite used conventionally, they have the problem of rapidly expanding in volume during the charging process, disrupting the conductive path and degrading battery performance.

[0008] Therefore, in order to resolve the problems that arise when using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as adjusting the driving potential, further coating a thin film on the active material layer, suppressing volume expansion itself by adjusting the particle size of the silicon-based compound, or preventing the conduction path from being interrupted. However, in the case of the aforementioned methods, there is a possibility that the performance of the battery may actually decrease, so there are limitations to their application, and the commercialization of negative electrode batteries with a high content of silicon-based compounds remains limited.

[0009] Furthermore, in the case of Si negative electrode active materials, the grain boundaries act as diffusion pathways for lithium. Therefore, research has revealed that wider grain boundaries, i.e., smaller grain sizes, are advantageous for the performance characteristics of secondary batteries.

[0010] However, even these methods cannot completely suppress volume changes, and research is needed to more effectively mitigate silicon volume changes in order to improve battery life.

[0011] Therefore, even when using silicon-based active materials as negative electrode active materials to improve capacity performance, research is needed on the silicon-based active materials themselves that can prevent damage to the conductive path due to volume expansion of silicon-based compounds. [Prior art documents] [Patent Documents]

[0012] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2009-080971 Summary of the Invention Problems to be Solved by the Invention

[0013] Through research, it has been found that the pulverized silicon-based active material itself can be surface-etched through an alkali solution treatment to obtain a porous silicon-based active material having internal pores. In particular, when the etching conditions are changed, the specific surface area range and tap density can be adjusted within a predetermined range, so that during the lithium insertion / desorption reaction, the reaction occurs uniformly and the stress received by the silicon-based active material is reduced.

[0014] This application relates to a negative electrode active material, a method for manufacturing a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode, which can solve the above-mentioned problems. Means for Solving the Problems

[0015] One embodiment of this specification includes a silicon-based active material having a specific surface area of 5 m 2 / g or more. The silicon-based active material has a porous structure including internal pores, and the tap density of the silicon-based active material is 0.2 g / cm 3 or more and 0.8 g / cm 3 or less. The silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of SiO x (x = 0), and provides a negative electrode active material. [[ID=I41]]

[0016] In another embodiment, a method for manufacturing a negative electrode active material includes a step of pulverizing a silicon raw material; and a step of exposing the pulverized silicon to an etching solution to etch the pulverized silicon to form a silicon-based active material, wherein the etching solution is an alkaline solution.

[0017] In another embodiment, a negative electrode composition including the negative electrode active material according to the present application, a negative electrode conductive material, and a negative electrode binder is provided.

[0018] In another embodiment, a negative electrode for a lithium secondary battery includes a negative electrode current collector layer; and a negative electrode active material layer provided on one or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer includes the negative electrode composition according to the present application or a cured product thereof.

[0019] Finally, a lithium secondary battery including a positive electrode, the negative electrode for a lithium secondary battery according to the present application, a separator provided between the positive electrode and the negative electrode, and an electrolyte is provided.

Effects of the Invention

[0020] In the case of the negative electrode active material according to an embodiment of the present invention, in addition to the conventional pulverization processing method, the specific surface area, pore morphology, and tap density of the silicon-based active material are adjusted through the process of etching through alkaline solution treatment. When the silicon-based active material is etched in an alkaline solution, anisotropic etching with different etching rates along the crystal plane directions is performed, and polycrystalline silicon with randomly distributed crystal planes is exposed to the alkaline solution to form the silicon-based active material according to the present application.

[0021] The negative electrode active material of the present invention includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2). Based on 100 parts by weight of the silicon-based active material, the SiO xThe main feature of this invention is that it contains 70 parts by weight or more of (x=0), i.e., a pure silicon (Pure Si) active material, while solving the problem of volume expansion due to charging and discharging, which is a problem associated with such materials, by adjusting the surface area of ​​the silicon-based active material to a predetermined range.

[0022] In other words, by using a silicon-based active material whose surface area satisfies the range of the present invention, it becomes possible to have a larger surface area compared to particles with the same particle size, particularly those with internal pores. This enables uniform lithium insertion and extraction reactions, relieves stress within the particles, and reduces particle pulverization. Furthermore, during charging, volume expansion occurs in the internal pores, mitigating the overall volume change of the particles and improving battery life. [Brief explanation of the drawing]

[0023] [Figure 1] This figure shows the manufacturing process of a silicon active material according to Example 1 of this application. [Figure 2] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 3] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of this application. [Modes for carrying out the invention]

[0024] Before describing the present invention, let us first define some terms.

[0025] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0026] In this specification, "p~q" means "p or greater and q or less".

[0027] In this specification, "specific surface area" is measured by the BET method, specifically calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using a BELSORP-mini II manufactured by BEL Japan. In other words, in this application, BET specific surface area can mean the specific surface area measured by the above measurement method.

[0028] In this specification, "Dn" refers to the particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution by particle size. That is, D50 is the particle size (central particle size) at the 50% point of the cumulative particle number distribution by particle size, D90 is the particle size at the 90% point of the cumulative particle number distribution by particle size, and D10 is the particle size at the 10% point of the cumulative particle number distribution by particle size. On the other hand, the central particle size may be measured using the laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac S3500), and the particle size distribution is calculated by measuring the difference in diffraction patterns due to particle size as the particles pass through the laser beam.

[0029] In one embodiment of this application, particle size may refer to the average diameter or representative diameter of each individual particle constituting the metal powder.

[0030] In this specification, the meaning of a polymer containing a monomer as a monomer unit means that the monomer participates in the polymerization reaction and is included as a repeating unit within the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted as being equivalent to the polymer containing a monomer as a monomer unit.

[0031] In this specification, the term "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise specified as "homopolymer."

[0032] In this specification, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are the molecular weights in terms of polystyrene measured by Gel Permeation Chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as the standard substance. In this specification, the molecular weight means the weight average molecular weight unless otherwise specified.

[0033] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention belongs to easily implement the present invention, a detailed description will be given with reference to the drawings. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0034] One embodiment of this specification has a silicon-based active material with a specific surface area of 5 m 2 / g or more. The silicon-based active material has a porous structure including internal pores, and the tap density of the silicon-based active material is 0.2 g / cm 3 or more and 0.8 g / cm 3 or less. The silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of SiO x (x = 0), providing a negative electrode active material.

[0035] The negative electrode active material of the present invention includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2) as the silicon-based active material. Based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of SiO x (x = 0). That is, while having a pure silicon (Pure Si) active material, the main feature is that the problem of volume expansion due to charge and discharge, which is a problem caused by this, is solved by adjusting the surface area, pore morphology, and volume density of the silicon-based active material within a predetermined range.

[0036] That is, the silicon-based active material has high crystallinity, and the general grain size has several hundred to several millimeters. The silicon-based active material according to the present application forms a porous structure including internal pores by etching treatment on the silicon-based active material, increases the specific surface area, improves the uniformity of the reaction, relaxes the volume change, and has the characteristic that the life performance of the battery can be improved.

[0037] By using a silicon-based active material whose surface area of the silicon-based active material satisfies the scope of the present invention, particularly, it has an internal pore morphology and has a larger surface area than particles having the same particle size. Thereby, a uniform insertion and desorption reaction of lithium is possible, the stress inside the particles can be relaxed, and the pulverization of the particles can be reduced. Also, during charging, volume expansion proceeds in the internal pores, relaxing the volume change of the entire particle, and having the characteristic that the life of the battery can also be improved.

[0038] In one embodiment of the present application, the silicon-based active material is SiO x (x = 0) and SiO x (0 < x < 2), and includes one or more selected from the group consisting of, based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may contain 70 parts by weight or more.

[0039] In one embodiment of the present application, the silicon-based active material contains SiO x (x = 0), and based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may contain 70 parts by weight or more.

[0040] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiO x (x = 0) may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0041] In one embodiment of this application, pure silicon (Si) particles may be used as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material means that, as described above, when based on 100 parts by weight of the total silicon-based active material, pure Si particles (SiO) that are not bonded with other particles or elements are used. x This can mean that (x=0) is included in the aforementioned range.

[0042] In one embodiment of this application, the silicon-based active material is SiO2 based on 100 parts by weight of silicon-based active material. x It may consist of silicon-based particles having 100 parts by weight of (x=0).

[0043] In one embodiment of this application, the silicon-based active material may contain metallic impurities, in which case the impurities are metals that can be commonly found in silicon-based active materials, and specifically, the content of metallic impurities in the silicon-based active material is 0.1 parts by weight or less, providing a negative electrode active material.

[0044] In the case of silicon-based active materials, the capacity is significantly higher compared to conventionally used graphite-based active materials, and attempts to apply them are increasing. However, the volume expansion rate during the charge-discharge process is high, so their use is limited to cases where they are mixed in small amounts with graphite-based active materials.

[0045] Therefore, in the present invention, in order to improve capacity performance, while using only silicon-based active material as the negative electrode active material, the problems described above were resolved not by adjusting the composition of the conductive material and binder, but by changing the manufacturing method of the silicon-based active material, thereby adjusting the specific surface area, pore morphology, and volume density of the silicon-based active material itself.

[0046] In one embodiment of this application, the negative electrode active material has a specific surface area of ​​5 m². 2 It may contain silicon-based active material in amounts of / g or more.

[0047] In this application, the silicon-based active material has a specific surface area of ​​15 m². 2 / g or more 80m 2 It may be less than / g.

[0048] In another embodiment, the silicon-based active material has a specific surface area of ​​5 m². 2 / g or more, preferably 8m 2 / g or more, comfortably, 12m 2 / g or more, specifically 13m 2 / g or more, more specifically, 15m 2 The silicon-based active material may be greater than or equal to / g. 2 / g or less, 150m 2 / g or less, 100m 2 / g or less, 95m 2 It may be less than / g, preferably 90m 2 / g or less, more preferably 80m 2 The range of less than or equal to / g may be satisfied. The specific surface area can be measured (using nitrogen) according to DIN 66131.

[0049] In one embodiment of this specification, the silicon-based active material comprises 220 crystal planes and 111 crystal planes, wherein the specific surface area of ​​the 220 crystal plane is 1 m². 2 / g or more 30m 2 The amount is less than or equal to / g, and the specific surface area of ​​the 111 crystal plane is 0.1m². 2 / g or more 5m 2 It may be less than / g.

[0050] The silicon-based active material according to this application is pulverized by a base etching process described later, and then undergoes an etching process. When the silicon-based active material is exposed to an alkaline solution under specific conditions, anisotropic etching occurs along the crystal plane direction, resulting in more etching of the 220 crystal planes.

[0051] In this case, as described above, the specific surface area of ​​the 220 crystal plane is 1 m 2 / g or more 30m 2 / g or less, preferably 5m2 / g or more 25m 2 / g or less, 10m 2 / g or more 25m 2 It may be less than or equal to / g, and the specific surface area of ​​the 111 crystal plane is 0.1m². 2 / g or more 5m 2 Less than or equal to / g, preferably 0.5m 2 / g or more 4m 2 / g or less, 0.8m 2 / g or more 3m 2 The condition of being less than or equal to / g may also be met.

[0052] As described above, when the specific surface area of ​​the crystal planes satisfies the aforementioned range, the distribution of the exposed 220 planes increases when manufacturing electrodes with etched silicon-based active material, resulting in higher lithium ion mobility and improved battery life retention.

[0053] In this application, the specific surface area of ​​the 220 crystal plane and the specific surface area of ​​the 111 crystal plane may be measured as follows.

[0054] In this application, since etching is performed under conditions that only etch the surface of the silicon, the degree of sphericity and mass of the silicon particles before and after etching do not change, and the 111 surface is hardly etched, so it can be assumed that the surface area does not change.

[0055] Before etching, the morphology of the silicon particles is simplified into a three-dimensional figure, and the area ratio of the top / bottom surface (111 facets) to the side surface (220 facets) is determined from the degree of spheroidization value. Subsequently, the specific surface area of ​​each crystal face is derived from the specific surface area measurements. After that, the increased specific surface area of ​​the 220 facet can be determined from the etching specific surface area measurements.

[0056] Furthermore, the proportion of crystal planes can be expressed by calculating the area ratio obtained by integrating the intensity of the peaks corresponding to each plane after XRD measurement.

[0057] In this application, the specific surface areas of the 220 crystal plane and the 111 crystal plane are values ​​measured by BET. In particular, since etching is performed through an alkaline solution in this application, the 111 plane is not etched, and the specific surface area of ​​the 220 crystal plane is calculated by subtracting the surface area of ​​only the 111 plane from the value calculated by the ratio of the specific surface area before etching to the crystal plane, using the specific surface area obtained by BET.

[0058] The silicon-based active material has the aforementioned surface area, and the specific surface area and pore morphology of the silicon-based active material can be adjusted by changing the manufacturing process conditions, particularly the etching conditions, which will be described later. That is, when the negative electrode active material is manufactured using the manufacturing method according to this application, the rough surface results in a larger surface area than particles of the same particle size. In this case, the above range is satisfied, and the bonding strength with the binder is increased, which has the characteristic of mitigating electrode cracks caused by repeated charge-discharge cycles. If the surface area of ​​the silicon-based active material is less than the above range, pores will not be sufficiently formed, and a uniform reaction cannot be expected during charge and discharge, making it impossible to effectively buffer volume expansion. Furthermore, if it exceeds the above range, there is a problem in that the battery life is actually reduced due to excessive side reactions with the electrolyte.

[0059] Furthermore, when lithium ions are inserted, they are inserted uniformly, reducing the stress applied when inserting lithium ions into silicon particles, thereby mitigating particle cracking. As a result, the life stability of the negative electrode can be improved. If the surface area is smaller than the aforementioned range, even with the same particle size, the surface is formed smoothly, reducing the bonding force with the binder, leading to electrode cracking. In this case, lithium ions are inserted non-uniformly into the particles, resulting in high stress due to ion insertion and causing particle cracking.

[0060] In one embodiment of this application, the negative electrode active material is characterized in that it has a porous structure including internal pores through etching, rather than having an external uneven morphology.

[0061] Compared to silicon-based active materials with surface irregularities, the form with internal pores, as in this application, allows for a greater increase in specific surface area, thereby improving reaction uniformity and achieving stress relaxation and reduced pulverization. Furthermore, as volume expansion progresses within the internal pores, the internal pores act as a buffer, mitigating the overall volume change of the particles. This results in a higher lifespan compared to silicon-based active materials with surface irregularities.

[0062] In one embodiment of this application, the tap density of the silicon-based active material is 0.2 g / cm³. 3 More than 0.8g / cm 3 The following is also acceptable.

[0063] In another embodiment, the tap density of the silicon-based active material is 0.2 g / cm³. 3 More than 0.8g / cm 3 Preferably, 0.25 g / cm³ 3 More than 0.78g / cm 3 More preferably, 0.35 g / cm³ 3 More than 0.77g / cm 3 The following is also acceptable.

[0064] In this application, the tap density refers to the value obtained by measuring the apparent volume of particles obtained by vibrating a container under predetermined conditions after filling it with silicon powder, and then dividing the mass of the silicon powder added by the apparent volume.

[0065] The tap density can be adjusted to the aforementioned range in the manufacturing process of the silicon-based active material described later, depending on the degree of etching. That is, in the case of the silicon-based active material according to this application, when etching results in an internal pore morphology and the pores are formed uniformly, the tap density decreases while satisfying the aforementioned specific surface area range. However, when the silicon-based active material is formed in an uneven morphology, the specific surface area can be increased to some extent, but the tap density also increases together, making it impossible to form pore-like structures inside the particles, thus limiting the increase in specific surface area. In other words, compared to silicon-based active materials with an uneven surface morphology, when the tap density is satisfied, as in this application, the specific surface area can be increased to a larger level, which can further improve the uniformity of the reaction, thereby achieving stress relaxation and reduced pulverization.

[0066] In one embodiment of this application, the silicon-based active material may include silicon-based particles having a particle size distribution of 0.01 μm to 30 μm.

[0067] The fact that the silicon-based active material contains silicon-based particles having a particle size distribution of 0.01 μm to 30 μm means that it contains a large number of individual silicon-based particles having particle sizes within the range, and the number of silicon-based particles included is not limited.

[0068] The particle size of the silicon-based particles can be expressed by their diameter if they are spherical, but even if they have other shapes that are not spherical, the particle size can be measured in a way that is more efficient than in the case of spherical particles, and the particle size of individual silicon-based particles can be measured using methods commonly used in this industry.

[0069] On the other hand, the average particle size (D50 particle size) of the silicon-based active material in the present invention may be 3 μm to 10 μm, more specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. When the average particle size falls within the above range, the specific surface area of ​​the particles falls within an appropriate range, and the viscosity of the negative electrode slurry is formed within an appropriate range. This allows for smooth dispersion of the particles constituting the negative electrode slurry. Furthermore, when the size of the silicon-based active material is greater than or equal to the lower limit of the above range, the contact area between the silicon particles and the conductive material is excellent due to the composite of the conductive material and the binder in the negative electrode slurry, increasing the likelihood of a sustained conductive network and increasing the capacity retention rate. On the other hand, when the average particle size satisfies the above range, excessively large silicon particles are excluded, and the surface of the negative electrode is formed smoothly, thereby preventing the phenomenon of uneven current density during charging and discharging.

[0070] In one embodiment of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably non-porous. The silicon particles are preferably spherical or multi-piece particles. Alternatively, the silicon particles may have a fibrous structure, or exist in the form of a silicon-containing thin film or coating, but these are less preferred.

[0071] One embodiment of this application provides a negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0072] In one embodiment of this application, the negative electrode composition is provided, wherein the negative electrode active material is 40 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0073] In another embodiment, the negative electrode active material may be 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 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0074] The negative electrode composition according to this application uses a negative electrode active material that satisfies a specific crystal grain size that allows the volume expansion rate to be controlled during the charge-discharge process even when a silicon-based active material with significantly high capacity is used within the aforementioned range, and has the characteristic of not degrading the performance of the negative electrode even when included within the aforementioned range, and having excellent output characteristics during charging and discharging.

[0075] Traditionally, graphite-based compounds were commonly used as the negative electrode active material. However, with the increasing demand for high-capacity batteries, there has been a growing trend to mix in silicon-based active materials to increase capacity. However, as mentioned above, even if the properties of the silicon-based active material itself are adjusted, there is a problem in some cases where its volume expands rapidly during the charge / discharge process, damaging the conductive paths formed within the negative electrode active material layer.

[0076] Therefore, in one embodiment of this application, the negative electrode conductive material may include one or more selected from the group consisting of point conductive materials, planar conductive materials, and linear conductive materials.

[0077] In one embodiment of this application, the point-shaped conductive material can be used to improve conductivity in the negative electrode and means a point-shaped or spherical conductive material that is conductive without inducing a chemical change. Specifically, the point-shaped conductive material may be at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably contains carbon black in terms of embodying high conductivity and having excellent dispersibility.

[0078] In one embodiment of this application, the point conductive material has a BET specific surface area of ​​40 m². 2 / g or more 70m 2 It may be less than or equal to / g, preferably 45m 2 / g or more 65m 2 / g or less, more comfortably, 50m 2 / g or more 60m 2 It may be less than / g.

[0079] In one embodiment of this application, the point-shaped conductive material may 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.

[0080] In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, functional groups are present on the surface of the dot-shaped conductive material, and when water is used as the solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, the present invention makes it possible to reduce the functional group content of the dot-shaped conductive material by using a specific silicon-based active material, thereby having an outstanding effect on improving dispersibility.

[0081] In one embodiment of this application, a silicon-based active material is provided along with a point-type conductive material having a functional group content within the aforementioned range, wherein the functional group content can be adjusted by the degree to which the point-type conductive material is heat-treated.

[0082] In one embodiment of this application, the particle size of the dot-like conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0083] In one embodiment of this application, the conductive material may include a planar conductive material.

[0084] The planar conductive material can improve conductivity by increasing surface contact between silicon particles within the negative electrode, and at the same time suppress the disruption of the conductive path due to volume expansion. The planar conductive material may also be described as a plate-type conductive material or a bulk-type conductive material.

[0085] In one embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate-type graphite, graphene, graphene oxide, and graphite flakes, and preferably plate-type graphite.

[0086] In one embodiment of this application, the average particle size (D50) of the planar conductive material may be 2 μm to 7 μm, more specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the above range is satisfied, the particle size is sufficient, making dispersion easy while preventing the viscosity of the negative electrode slurry from increasing too much. Therefore, the dispersion effect is superior when dispersion is performed using the same equipment and time.

[0087] In one embodiment of this application, a negative electrode composition is provided in which the planar conductive material has 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.

[0088] In one embodiment of this application, the planar conductive material may be a planar conductive material with a high specific surface area and a high BET specific surface area; or a planar conductive material with a low specific surface area.

[0089] In one embodiment of this application, the planar conductive material may be any planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area without limitation. In particular, the planar conductive material according to this application may be affected to some extent by dispersion in terms of electrode performance, and it is especially preferable to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0090] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​0.25 m². 2 It may be more than / g.

[0091] In another embodiment, the planar conductive material has a BET specific surface area of ​​1 m². 2 / g or more 500m 2 It may be less than / g, preferably 5m 2300 m / g or more 2 5 m / g or less, more preferably 2 250 m / g or more 2 It may be 5 m / g or less

[0092] The planar conductive material according to the present application may use a high specific surface area planar conductive material or a low specific surface area planar conductive material

[0093] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area is 50 m 2 / g or more and 500 m / g or less, preferably 2 80 m / g or more 2 300 m / g or more 2 300 m / g or less, more preferably 2 100 m / g or more 2 300 m / g or less, and may satisfy the range

[0094] In another embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area is 1 m 2 / g or more and up to 40 m / g 2 5 m / g or less, preferably 2 30 m / g or more 2 5 m / g or less, more preferably 2 25 m / g or more 2 It may satisfy the range of 25 m / g or less

[0095] Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundle-type carbon nanotubes. The bundle-type carbon nanotubes may contain multiple carbon nanotube units. Specifically, unless otherwise specified, "bundle type" here refers to a secondary shape in which multiple carbon nanotube units are arranged in parallel with substantially the same orientation along their longitudinal axes, or are twisted into a bundle or rope. The carbon nanotube units have a graphite sheet that is cylindrical with a nanoscale diameter and has an sp2 bond structure. In this case, the properties of a conductor or semiconductor can be exhibited depending on the angle and structure in which the graphite sheet is wound. Compared to entangled type carbon nanotubes, the bundle-type carbon nanotubes can be uniformly dispersed during the manufacture of the negative electrode, smoothly forming a conductive network within the negative electrode and improving the conductivity of the negative electrode.

[0096] In one embodiment of this application, the negative electrode conductive material is provided in an amount of 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0097] In another embodiment, the negative electrode conductive material may be present in an amount of 0.1 parts by weight or more and 20 parts by weight or less, preferably 1 part by weight or more and 20 parts by weight or less, more preferably 5 parts by weight or more and 15 parts by weight or less, and most preferably 6 parts by weight or more and 13 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0098] The negative electrode conductive material described in this application has a completely different structure from the positive electrode conductive material applied to the positive electrode. Specifically, the negative electrode conductive material described in this application plays a role in controlling the contact points between silicon-based active materials, which experience very large volume expansion of the electrodes due to charging and discharging. The positive electrode conductive material, on the other hand, plays a role in providing partial conductivity while acting as a buffer during rolling, and its structure and role are completely different from the negative electrode conductive material of the present invention.

[0099] Furthermore, the negative electrode conductive material described in this application is applied to silicon-based active materials and has a completely different structure from conductive materials applied to graphite-based active materials. In other words, conductive materials used in electrodes with graphite-based active materials simply have particles that are smaller than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity. This is completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials, as in the present invention.

[0100] In one embodiment of this application, the planar conductive material used as the anode conductive material has a different structure and role from the carbon-based active material typically used as the anode active material. Specifically, the carbon-based active material used as the anode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form to facilitate the storage and release of lithium ions.

[0101] On the other hand, planar conductive materials used as negative electrode conductive materials are substances having a planar or plate-like form, and can be represented as plate-type graphite. In other words, they are substances included to maintain conductive pathways within the negative electrode active material layer, and do not play a role in lithium storage and release, but rather substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0102] In other words, in this 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 to secure a conductive path that does not serve the role of storing or releasing lithium. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release and plays a role in storing and releasing all lithium ions transmitted from the positive electrode.

[0103] On the other hand, in this application, the use of a carbon-based active material as the active material means that it was processed into a point-like or spherical shape and used as a substance that plays a role in storing or releasing lithium.

[0104] In other words, in one embodiment of this application, the carbon-based active material, artificial graphite or natural graphite, is punctate and has a BET specific surface area of ​​0.1 m². 2 / g or more 4.5m 2 The range of less than or equal to / g may also be satisfied. In addition, plate-type graphite, which is a planar conductive material, is planar and has a BET specific surface area of ​​5m². 2 It may be more than / g.

[0105] In one embodiment of this application, the negative electrode binder may contain at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which the hydrogen atoms of these are substituted with Li, Na, or Ca, or may contain a variety of copolymers thereof.

[0106] The negative electrode binder according to one embodiment of this application plays a role in controlling the active material and conductive material in order to prevent twisting and structural deformation of the negative electrode structure during the volume expansion and relaxation of the silicon-based active material. Any ordinary binder can be used as long as it fulfills the above role, and specifically, an aqueous binder may be used, and more specifically, a PAM-based binder may be used.

[0107] In one embodiment of this 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, based on 100 parts by weight of the negative electrode composition, and may also be 5 parts by weight or more, or 10 parts by weight or more.

[0108] One embodiment of this application provides a method for producing a negative electrode active material, comprising the steps of: grinding a silicon raw material; and exposing the ground silicon to an etching solution and etching the ground silicon to form a silicon-based active material, wherein the etching solution is an alkaline solution.

[0109] Traditionally, silicon ingots were manufactured by crushing them using physical force. In this manufacturing method, the crystal grain size generally exceeds 200 nm, the surface is smooth, and the surface area is 5 m². 2 The value will be less than / g. When silicon-based active materials are simply manufactured using conventional methods, there is a disadvantage in that the surface area cannot be controlled, making it difficult to ensure the lifetime stability of the negative electrode.

[0110] However, the method for producing the negative electrode active material according to this application includes an etching step as shown in Figure 1, which allows for the formation of silicon particles, thereby obtaining a silicon-based active material that satisfies the surface area requirements of this application. That is, as can be seen in Figure 1, when exposed to an alkaline solution, the surface of the silicon-based active material undergoes anisotropic etching with different etching rates depending on the crystal plane orientation, and it can be confirmed that this etching leads to the formation of a porous structure on the surface and inside.

[0111] In one embodiment of this application, the step of exposing the pulverized silicon to an etching solution and etching the pulverized silicon to form a silicon-based active material may include a step of exposing the pulverized silicon to the etching solution and then stirring it at a temperature of 20°C to 120°C for 30 minutes to 50 hours.

[0112] By stirring and etching the silicon at the aforementioned time and temperature, the surface area range and tap density specified in this application can be satisfied.

[0113] In one embodiment of this application, the alkaline solution is OH - It may also be a solution that generates a substance and creates an aqueous solution with a pH above 7.

[0114] In another embodiment, the alkaline solution may be LiOH, NaOH, or KOH.

[0115] In one embodiment of this application, the concentration of the alkaline solution may be 0.001 M (mol / L) or more and 10 M (mol / L) or less.

[0116] The process of etching through an alkaline solution of the aforementioned concentration allows for the fulfillment of desired specific surface area and tap density.

[0117] One embodiment of this application may include the steps of: grinding a silicon raw material; exposing the ground silicon to an etching solution and etching the ground silicon to form a silicon-based active material; adding an acid solution to the silicon-based active material to neutralize it; and vacuum filtration.

[0118] As described above, an acid solution can be added to a solution containing an etched silicon-based active material to neutralize it, and then the silicon-based active material and the solution can be separated by vacuum filtration or centrifugation.

[0119] In this application, the acid solution is H + Any substance that generates a compound and causes a neutralization reaction with a base may be used without limitation; specifically, it may be HCl, HNO3, or H2SO4.

[0120] The process may further include the step of drying the silicon-based active material in a drying oven to remove moisture. In this case, the drying temperature of the drying oven may be between 40°C and 100°C.

[0121] One embodiment of this application provides a negative electrode for a lithium secondary battery, comprising a negative electrode current collector layer; and a negative electrode active material layer formed on one or both sides of the negative electrode current collector layer, the negative electrode composition according to this application or a cured product thereof.

[0122] Figure 2 shows a laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery can be seen, which includes a negative electrode active material layer 20 on one surface of a negative electrode current collector layer 10. Figure 2 shows that the negative electrode active material layer is formed on one surface, but it may also be included on both sides of the negative electrode current collector layer.

[0123] In one embodiment of this application, the negative electrode for the lithium secondary battery may 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.

[0124] In this case, the negative electrode slurry may contain the aforementioned negative electrode composition and slurry solvent.

[0125] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0126] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

[0127] The solid content of the negative electrode slurry may mean the content of the negative electrode composition contained in the negative electrode slurry, or it may mean the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0128] When the solid content of the negative electrode slurry satisfies the aforementioned range, the viscosity is appropriate during the formation of the negative electrode active material layer, minimizing the caking phenomenon of the particles of the negative electrode composition, and enabling efficient formation of the negative electrode active material layer.

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

[0130] In one embodiment of this application, the negative electrode current collector layer typically has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be made of materials such as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or aluminum-cadmium alloy. Furthermore, fine irregularities may be formed on the surface to strengthen the bonding force of the negative electrode active material, and it may be used in various forms such as film, sheet, foil, net, porous body, foam, or nonwoven fabric.

[0131] In one embodiment of this 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.

[0132] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited to this.

[0133] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0134] In another embodiment, the porosity of the negative electrode active material layer may be in the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

[0135] The aforementioned porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the aforementioned range is satisfied by including the silicon-based active material and conductive material according to this application in specific composition and content portions, thereby ensuring that the electrical conductivity and resistance of the electrode are within an appropriate range.

[0136] One embodiment of this application provides a lithium secondary battery comprising a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separation membrane provided between the positive electrode and the negative electrode; and an electrolyte.

[0137] Figure 3 shows a stacked structure of a lithium secondary battery according to one embodiment of the present application. Specifically, it shows that a negative electrode 100 for a lithium secondary battery, including a negative electrode active material layer 20, can be seen on one side of a negative electrode current collector layer 10, and a positive electrode 200 for a lithium secondary battery, including a positive electrode active material layer 40, can be seen on one side of a positive electrode current collector layer 50, and that the negative electrode 100 and the positive electrode 200 for a lithium secondary battery are formed in a stacked structure with a separation membrane 30 in between.

[0138] A secondary battery according to one embodiment of this specification may, in particular, include the negative electrode for lithium secondary batteries described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, a detailed explanation will be omitted.

[0139] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and containing the positive electrode active material.

[0140] In the positive electrode, the positive electrode current collector is not particularly limited as long as it has conductivity while not inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment of aluminum or stainless steel surfaces with carbon, nickel, titanium, silver, etc. may be used. Further, the positive electrode current collector may usually have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive force of the positive electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0141] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; chemical formula Li 1+c1 Mn 2-c1 O4 (0 ≦ c1 ≦ 0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 M c2 O2 (where 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) represented by Ni-site type lithium nickel oxide; chemical formula LiMn 2-c3 M c3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01 ≦ c3 ≦ 0.1) or lithium manganese composite oxide represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); examples include LiMn2O4 in which a part of Li in the chemical formula is substituted with an alkaline earth metal ion, but it is not limited thereto. The positive electrode may be Li metal (Li-metal).

[0142] The positive electrode active material layer may also include a positive electrode conductive material and a positive electrode binder, along with the positive electrode active material described above.

[0143] In this case, the positive electrode conductive material is used to impart conductivity to the electrode and can be used without particular limitations as long as it does not cause chemical changes in the battery that is constructed and has electronic conductivity. 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, thermal black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used.

[0144] Furthermore, the positive electrode binder plays a role in improving adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one or more of these may be used.

[0145] The separation membrane separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. It can be used without particular limitations as long as it is a membrane typically used in secondary batteries, but it is especially preferable to have low resistance to ion movement of the electrolyte and excellent moisture-retaining capacity for the electrolyte. Specifically, porous polymer films, such as those made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof, may be used. Alternatively, ordinary porous nonwoven fabrics, such as those made from high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separation membranes containing ceramic components or polymeric substances to ensure heat resistance or mechanical strength may be used, and they may be selectively used in single-layer or multi-layer structures.

[0146] Examples of the aforementioned electrolytes 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.

[0147] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0148] As the non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate may be used.

[0149] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are suitable for use because they are high-viscosity organic solvents with high dielectric constants that readily dissociate lithium salts. Furthermore, by mixing such cyclic carbonates with linear carbonates with low viscosity and low dielectric constant, such as dimethyl carbonate and diethyl carbonate, in appropriate proportions, electrolytes with high electrical conductivity can be produced, making them even more suitable for use.

[0150] The metal salt may be a lithium salt, and the lithium salt is a substance that is easily soluble in the non-aqueous electrolyte, for example, the anion of the lithium salt may be F - Cl - , I - NO3 - , N(CN)2 - BF4 - ClO4 - PF6 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - CF3SO3 -CF3CF2SO3 - (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - You may use one or more selected from the group consisting of the following:

[0151] In addition to the components of the electrolyte, the electrolyte may further contain one or more additives for the purpose of improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride.

[0152] 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. Because the battery module and battery pack include the secondary battery having high capacity, high rate characteristics and cycle characteristics, they can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems. [Examples]

[0153] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments 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 of the present description and the technical concept, and such variations and modifications naturally fall within the scope of the claims.

[0154] <Manufacturing example> <Manufacturing of the negative electrode active material in Example 1> Silicon powder was added to a 0.1M KOH aqueous solution in a mass ratio of 30:1, and etching was performed by stirring at 40°C for 3 hours using a hot plate and a stirring magnet. After neutralization with the addition of 0.1M HCl, the mixture was filtered under reduced pressure to obtain a silicon-based active material.

[0155] Subsequently, the material was dried in a 60°C drying oven to obtain an etched porous silicon-based active material.

[0156] <Manufacturing of the negative electrode active material in Comparative Example 1> In Example 1, pulverized silicon powder that had not undergone etching treatment was used.

[0157] <Manufacturing of the negative electrode active material in Comparative Example 2> After MG-Si silicon blocks were converted into silane gas at high temperatures, they were deposited onto a substrate after a chemical reaction. Subsequently, silicon-based active material was grown through the generation of crystal nuclei to produce the silicon-based active material.

[0158] The negative electrode active materials described above satisfied the physical properties shown in Table 1.

[0159] [Table 1]

[0160] For reference, Comparative Examples 3 and 4 were obtained by adjusting the concentration of the etching solution. In Comparative Example 3, a silicon-based active material was produced by etching using a 0.01 M KOH aqueous solution at 40°C for 3 hours. In Comparative Example 4, a silicon-based active material was produced by etching using a 1 M KOH aqueous solution at 40°C for 3 hours.

[0161] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by adding the silicon-based active material, negative electrode conductive material, and polyacrylamide as a binder in a weight ratio of 80:10:10 to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 25% by weight).

[0162] Specifically, the conductive material is carbon black (specific surface area: 45 m²). 2 The values ​​were per gram (30 nm to 50 nm in diameter).

[0163] As for the specific mixing method, the negative electrode conductive material, binder, and water were dispersed using a homomixer at 2500 rpm for 30 minutes, and then the silicon-based active material was added and dispersed at 2500 rpm for another 30 minutes to produce the negative electrode slurry.

[0164] As the negative electrode current collector layer, the negative electrode slurry is applied to both sides of a copper current collector (thickness: 8 μm) at a rate of 85 mg / 25 cm². 2 The material was coated with the specified load, rolled (roll press), 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 then used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0165] <Manufacturing of secondary batteries> As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2A cathode slurry was prepared by adding O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for cathode slurry formation (solid content concentration 78% by weight).

[0166] As the positive electrode current collector, 537 mg / 25 cm of the positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm). 2 The cathode was manufactured by coating with the specified load, rolling (roll press), and drying in a vacuum oven at 130°C for 10 hours to form a cathode active material layer (thickness: 65 μm) (cathode thickness: 77 μm, porosity: 26%).

[0167] A polyethylene separation membrane was interposed between the positive electrode and the negative electrodes of the above-mentioned examples and comparative examples, and an electrolyte was injected to manufacture a lithium secondary battery.

[0168] The aforementioned electrolyte was prepared by adding vinylene carbonate at a concentration of 3% by weight relative to the total weight of the electrolyte to an organic solvent mixture of fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90, and adding LiPF6 as a lithium salt at a concentration of 1M.

[0169] <Example of experiment> Experimental Example 1: Monocell Life Performance Results The secondary batteries containing the negative electrodes manufactured in the above examples and comparative examples were evaluated for their lifespan using an electrochemical charger / discharger, and their capacity retention rate was assessed. The secondary batteries underwent in-situ cycle testing at 4.2-3.0V and 1C / 0.5C. During the test, the capacity retention rate was measured every 50 cycles by charging / discharging at 0.33C / 0.33C (4.2-3.0V).

[0170] Capacity retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0171] [Table 2]

[0172] Experimental Example 2: Monocell Resistance Change In Experimental Example 1, during the test, the capacity retention rate was measured by charging / discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles. Then, the resistance was measured by discharging with a 2.5C pulse using SOC50, and the resistance increase rate was compared and analyzed.

[0173] For the measurement and evaluation of the aforementioned resistance increase rate, data was calculated for 200 cycles, and the results are shown in Table 3 below.

[0174] [Table 3]

[0175] As can be seen in Tables 2 and 3 above, in Examples 1 to 4, when the silicon-based active material is etched in an alkaline solution, anisotropic etching occurs in which the etching rate differs depending on the orientation of the crystal plane, and the surface area of ​​the silicon-based active material satisfies the range of a silicon-based active material that meets the requirements of the present invention.

[0176] In particular, the experiments confirmed that the particles have internal pores and a larger surface area than particles of the same particle size, which enables uniform lithium insertion and extraction reactions, relieves stress within the particles, reduces pulverization, and, during charging, promotes volume expansion in the internal pores, mitigating the overall volume change of the particles and improving battery life.

[0177] In Examples 1 to 4, all specimens have an internally porous structure. Specifically, in Example 1, the etching concentration and temperature conditions were kept the same, but the etching time was changed to form Examples 2 to 4. As can be seen in Table 1, the specific surface area and tap density can be adjusted by adjusting the etching time, and increasing the etching time tended to increase the specific surface area and decrease the tap density.

[0178] In Comparative Example 1, where the etching process was not performed as in Example 1, it was confirmed that the material had the same specific surface area and tap density as the pulverized simple silicon-based active material. In Comparative Example 2, although the specific surface area was increased compared to Comparative Example 1, it differed from the embodiment of the present invention in that it had an external uneven structure, and it was confirmed that the tap density also increased accordingly. In other words, it was confirmed that the tap density of Comparative Example 2 was significantly increased compared to Examples 1 to 4.

[0179] Comparative Example 3 uses the same manufacturing process as Example 1, but corresponds to a case where the tap density is below the lower limit of the present invention, while Comparative Example 4 is the same as Example 1, but corresponds to a case where the tap density exceeds the upper limit of the present invention. In both cases, the concentration of the etching solution was adjusted. In Comparative Example 3, it was confirmed that the mechanical properties were weakened due to the excessive development of fine pores within the particles, resulting in a decrease in volume retention. In Comparative Example 4, it was confirmed that internal pores were not sufficiently formed, resulting in an inferior volume retention rate.

[0180] In summary, Comparative Examples 1 to 4 show that when the surface area range and tap density of the present invention are not met, the specific surface area is small, the uniformity of the reaction decreases, and consequently, the stress relaxation and pulverization reduction capabilities decrease. Furthermore, compared to the examples in which volume expansion proceeds in the internal pores, the above experiments confirmed that volume expansion could not be controlled, the overall volume change increased, and the volume retention rate decreased significantly. [Explanation of symbols]

[0181] 10 ···Negative electrode current collector layer 20...Negative electrode active material layer 30...Separation membrane 40...Cathode active material layer 50 ···Positive electrode current collector layer 100 ···Negative electrode for lithium secondary batteries 200 ···Positive electrode for lithium secondary batteries

Claims

1. Specific surface area is 5 m ２ Contains silicon-based active material in amounts of / g or more, The aforementioned silicon-based active material has a porous structure including internal pores. The tap density of the aforementioned silicon-based active material is 0.2 g / cm³. ３ 0.8g / cm or more ３ The following: The aforementioned silicon-based active material is SiO ｘ (x=0) and SiO ｘ It comprises one or more selected from the group consisting of (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, the SiO ｘ A negative electrode active material containing 70 parts by weight or more of (x=0).

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

3. The silicon-based active material has a specific surface area of ​​15 m². ２ / g or more 80m ２ The negative electrode active material according to claim 1, wherein the amount is less than or equal to / g.

4. The negative electrode active material according to claim 1, wherein the D50 particle size of the silicon-based active material is 3 μm or more and 10 μm or less.

5. The step of crushing the silicon raw material; and A step of exposing pulverized silicon to an etching solution and etching the pulverized silicon to form a silicon-based active material; A method for producing a negative electrode active material, comprising: The etching solution is an alkaline solution, and this is a method for producing a negative electrode active material.

6. The alkaline solution generates OH － and is a solution that creates an aqueous solution with a pH exceeding 7. The method for producing a negative electrode active material according to claim 5.

7. The step of exposing the pulverized silicon to an etching solution and etching the pulverized silicon to form a silicon-based active material is as follows: A method for producing a negative electrode active material according to claim 5, comprising the step of exposing the pulverized silicon to an etching solution and then stirring it at a temperature of 20°C to 120°C for 30 minutes to 50 hours.

8. The method for producing a negative electrode active material according to claim 5, wherein the concentration of the alkaline solution is 0.001 M (mol / L) or more and 10 M (mol / L) or less.

9. A negative electrode composition comprising a negative electrode active material; a negative electrode conductive material; and a negative electrode binder according to any one of claims 1 to 4.

10. The negative electrode composition according to claim 9, wherein the negative electrode active material is 40 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

11. The negative electrode composition according to claim 9, wherein the negative electrode conductive material is 20 parts by weight or less based on 100 parts by weight of the negative electrode composition.

12. 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, The negative electrode for a lithium secondary battery comprises the negative electrode composition or a cured product thereof according to claim 9, wherein the negative electrode active material layer includes the negative electrode composition or a cured product thereof according to claim 9.

13. The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less. The negative electrode for a lithium secondary battery according to claim 12, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

14. positive electrode; A negative electrode for a lithium secondary battery according to claim 12; A separation membrane provided between the positive electrode and the negative electrode; and Electrolyte; Lithium-ion batteries, including lithium-ion batteries.

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