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. 10-2023-0143031, 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, research is actively being conducted on methods to increase capacity by using silicon-based compounds such as Si / C and SiOx, which have more than 10 times the capacity of graphite-based materials, as negative electrode active materials. However, while silicon-based compounds are high-capacity materials, they have the problem that, although they have a larger capacity than conventionally used graphite, their volume expands rapidly 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 size, are advantageous for the performance characteristics of secondary batteries.

[0010] However, when conventional metallic grade silicon (MG-Si) is cast and pulverized to produce negative electrode active material, the pulverized silicon-based active material itself is in the form of a plate, and the plate surface consists of 111 crystal planes. These planes have low lithium ion mobility, and when applied to batteries, this results in a reduced battery life retention rate, causing problems.

[0011] Therefore, in order to improve the performance of the capacity, even when a silicon-based active material is used as the negative electrode active material, research on the silicon-based active material itself that can prevent the conductive path from being damaged due to the volume expansion of the silicon-based compound is necessary.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0013] When the surface of the pulverized silicon-based active material itself is etched through an alkali solution treatment to etch the crystal plane, the lithium ion mobility can be adjusted. In particular, when the etching conditions are changed, the specific surface area of the 111 plane and the 220 plane in the silicon-based active material can be adjusted. As a result, it was confirmed that during the insertion / desorption reaction of lithium, the reaction occurs uniformly and the stress received by the silicon-based active material is reduced.

[0014] Therefore, the present application relates to a negative electrode active material, a method for manufacturing the 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 that can solve the above problems.

Means for Solving the Problems

[0015] One embodiment of the present specification includes a silicon-based active material including a 220 crystal plane and a 111 crystal plane, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) is included in an amount of 70 parts by weight or more, the specific surface area of the 220 crystal plane is 1 m 2 / g or more and 30 m 2 / g or less, and the specific surface area of the 111 crystal plane is 0.1 m2 5 m or more per g 2 Provided is a negative electrode active material that is 5 m or less per g.

[0016] In another embodiment, a method for producing a negative electrode active material includes: pulverizing a silicon raw material; and 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 including 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 is provided.

[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] The negative electrode active material of the present invention includes, as a silicon-based active material, one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2). Based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) is included in an amount of 70 parts by weight or more. That is, while having a Pure Si active material, etching through an alkaline solution is performed on a conventional pulverization processing method. As a result, the lateral surface of the pulverized plate-shaped silicon-based active material can be selectively etched to increase the sphericity of the particles. In particular, the specific surface area of the (111) crystal plane is reduced, enabling uniform reaction during the insertion and desorption reactions of lithium during charge and discharge. The stress received by the silicon-based active material is reduced, and cracking of the particles can be alleviated, thereby improving the electrode life retention rate.

[0021] In particular, this application is characterized by controlling the crystal grain direction distribution to satisfy the range of formula 1 when manufacturing a silicon-based active material as described above. That is, when MG-Si is simply crushed as in the conventional method, the crystal grain size of the active material exceeds 200 nm to 300 nm and has a plate-like shape, resulting in a relatively large proportion of 111 crystal planes. In this case, the 111 crystal planes have a lower lithium mobility than the 220 crystal planes, and lithium cannot enter and exit uniformly during lithium insertion and deinsertion reactions. However, the silicon-based active material according to this application contains a large proportion of 220 crystal planes, unlike existing materials, so that lithium can enter and exit uniformly during lithium insertion and deinsertion reactions, thereby mitigating the cracking phenomenon of silicon on the electrode surface, and thereby enhancing the lifespan characteristics of the electrode. [Brief explanation of the drawing]

[0022] [Figure 1] This figure shows a stacked structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. [Figure 2] This figure shows a stacked structure of a lithium secondary battery according to one embodiment of this application. [Figure 3] This diagram illustrates a method for calculating crystal grain size. [Figure 4] This figure shows the unit structure of the silicon-based active material relating to this application. [Figure 5] This figure shows the 220th and 111th faces of the silicon-based active material related to this application. [Figure 6] This diagram compares the densities of 220-plane and 111-plane silicon-based active materials. [Figure 7] This figure shows the etching process related to this application. [Modes for carrying out the invention]

[0023] Before describing the present invention, let us first define some terms.

[0024] In this specification, when a part "includes" a component, this means that, unless otherwise stated, it may include other components rather than excluding them.

[0025] In this specification, "p~q" means "p or greater and q or less".

[0026] 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 BELSORP-mino 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.

[0027] 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 also 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.

[0028] 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.

[0029] In this specification, the meaning that a polymer contains a certain monomer in monomer units means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In this specification, when a polymer is said to contain a monomer, this is interpreted to be the same as the polymer containing the monomer in monomer units.

[0030] In this specification, the term "polymer" is understood to be used in a broad sense including copolymers unless expressly stated as "homopolymer".

[0031] In this specification, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) are the polystyrene-equivalent molecular weights measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymers of various degrees of polymerization (standard samples) commercially available for molecular weight measurement as standard substances. In this specification, the molecular weight means the weight-average molecular weight unless otherwise specified.

[0032] Hereinafter, for those with ordinary knowledge in the technical field to which the present invention belongs to be able to easily implement the present invention, it will be described in detail with reference to the drawings. However, the present invention can be embodied in various different forms and is not limited to the following description.

[0033] One embodiment of this specification includes a silicon-based active material including the 220 crystal plane and the 111 crystal plane, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 < x < 2), based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of the SiOx (x = 0), and the specific surface area of the 220 crystal plane is 1 m 2 / g or more and 30 m 2 / g or less, and the specific surface area of the 111 crystal plane is 0.1 m 2 / g or more and 5 m 2 / g or less, and provides a negative electrode active material.

[0034] Figure 4 shows the unit structure of the silicon-based active material according to the present application. It includes crystal planes. Specifically, the 220 plane and the 111 plane of the silicon-based active material can be confirmed in Figure 5. Figure 6 corresponds to a diagram comparing the densities of the 220 plane and the 111 plane of the silicon-based active material. Specifically, as can be confirmed, when the density and direction of the 220 plane and the 111 plane are confirmed, it can be confirmed that the 220 plane with a lower particle density within the same area is more advantageous when Li moves because the particle density is smaller on the 220 plane.

[0035] In one embodiment of the present application, the specific surface area of the 220 crystal plane is 1 m 2 / g or more and 30 m 2 / g or less, and the specific surface area of the 111 crystal plane is 0.1 m 2 / g or more and 5 m 2 / g or less, and a negative electrode active material is provided.

[0036] The silicon-based active material according to the present application is pulverized by an etching process described later and undergoes an etching process. However, when the silicon-based active material is exposed to an alkaline solution under specific conditions, anisotropic etching occurs along the crystal plane direction, so the 220 crystal plane is etched more.

[0037] At this time, as described above, the specific surface area of the 220 crystal plane is 1 m 2 / g or more and 30 m 2 / g or less, preferably 5 m 2 / g or more and 25 m 2 / g or less, 10 m 2 / g or more and 25 m 2 / g or less may also be acceptable. The specific surface area of the 111 crystal plane is 0.1 m 2 / g or more and 5 m 2 / g or less, preferably 0.5 m 2 / g or more and 4 m 2 / g or less, 0.8 m 2 / g or more and 3 m 2 / g or less may also satisfy the requirement.

[0038] 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.

[0039] 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.

[0040] In this application, since etching is performed under conditions that etch only the surface of the silicon, the degree of spheroidization and mass of the silicon particles before and after etching remain unchanged, and the 111 plane is hardly etched, so it can be assumed that the surface area does not change.

[0041] Before etching, the morphology of the silicon particles is simplified into a three-dimensional figure, and the area ratio of the top / bottom (111 faces) and side (220 faces) is determined from the degree of spheroidization value. Then, the specific surface area of ​​each crystal face is derived from the specific surface area measurements. Subsequently, the increased specific surface area of ​​the 220 face can be determined from the etched specific surface area measurements.

[0042] 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.

[0043] 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 was 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.

[0044] In this application, the silicon-based active material provides a negative electrode active material that satisfies the following formula 1.

[0045] [Formula 1] 45 ≤ (X / Y) × 100 In the above formula 1, Y represents the proportion of 111 crystal planes within the silicon-based active material. X represents the proportion of 220 crystal planes within the silicon-based active material.

[0046] As described above, this application is characterized by controlling the crystal grain orientation distribution that satisfies the range of formula 1 when manufacturing a silicon-based active material. That is, when MG-Si is simply crushed as in the conventional method, the crystal grain size of the active material exceeds 200 nm, it has a plate-like shape, and a relatively large proportion of 111 crystal planes are formed. In this case, the 111 crystal planes have a lower lithium mobility than the 220 crystal planes, and lithium cannot enter and exit uniformly during lithium insertion and deinsertion reactions. However, the silicon-based active material according to this application contains a large proportion of 220 crystal planes, unlike the conventional method, so that lithium can enter and exit uniformly during lithium insertion and deinsertion reactions, thereby mitigating the cracking phenomenon of silicon on the electrode surface, and thereby enhancing the life characteristics of the electrode.

[0047] In one embodiment of this application, the silicon-based active material comprises one or more selected from the group consisting of spherical silicon-based active material and plate-type silicon-based active material, and the negative electrode active material is provided containing 80 parts by weight or more of spherical silicon-based active material based on 100 parts by weight of the silicon-based active material.

[0048] In another embodiment, the silicon-based active material comprises one or more selected from the group consisting of spherical silicon-based active material and plate-shaped silicon-based active material, and based on 100 parts by weight of the silicon-based active material, it may contain 80 parts by weight or more, 85 parts by weight or more, 90 parts by weight or more, or 100 parts by weight or less, 99 parts by weight or less, or 95 parts by weight or less of the spherical silicon-based active material.

[0049] In this application, the plate-shaped silicon-based active material can mean an active material in which the 111 crystal plane of the silicon-based active material is developed and has a broad planar form rather than a spherical shape, and the spherical silicon-based active material can mean one having spherical particles in which the 220 crystal plane of the silicon-based active material is more developed than the plate-shaped silicon-based active material and does not have a broad and extensive planar form.

[0050] That is, the silicon-based active material may have a spherical form, and its sphericity is, for example, 0.8 or more, for example, 0.8 to 0.95, for example, 0.9 to 0.95, for example, 0.93 to 0.95.

[0051] In one embodiment of this application, X means the ratio of the 220 crystal plane in the silicon-based active material, means the ratio when based on the entire surface of the silicon-based active material, and X may satisfy 30 to 60, preferably 35 to 60, more preferably 35 to 55.

[0052] In one embodiment of this application, Y means the ratio of the 111 crystal plane in the silicon-based active material, means the ratio when based on the entire surface of the silicon-based active material, and Y may satisfy 50 to 80, preferably 55 to 80, more preferably 55 to 75.

[0053] In one embodiment of this application, the silicon-based active material may further include various crystal planes.

[0054] In one embodiment of this application, the silicon-based active material includes one or more selected from the group consisting of SiOx (x = 0) and SiOx (0 <x <2), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0055] In one embodiment of this application, the silicon-based active material includes SiOx (x = 0), and based on 100 parts by weight of the silicon-based active material, the SiOx (x = 0) may be included in an amount of 70 parts by weight or more.

[0056] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx(x=0) may be included in an amount of 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0057] In one embodiment of this application, the silicon-based active material may be one that particularly contains pure silicon (Si) particles. Using pure silicon (Si) particles as the silicon-based active material means, as described above, that when the silicon-based active material is based on 100 parts by weight of the total, it may contain pure Si particles (SiOx(x=0)) that are not bonded with other particles or elements within the range described above.

[0058] In one embodiment of this application, the silicon-based active material may consist of silicon-based particles having 100 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[0059] In one embodiment of this application, the silicon-based active material may contain metallic impurities, in which case the impurities may be metals that can be commonly found in silicon-based active materials, specifically, 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0060] In the case of silicon-based active materials, the capacity is significantly higher compared to conventionally used graphite-based active materials, and there are increasing attempts to apply them. 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.

[0061] 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 conventional problems described above were solved by adjusting the crystal grain size or surface area of ​​the silicon-based active material itself, rather than by adjusting the composition of the conductive material and binder.

[0062] In one embodiment of this application, the crystal grain size of the silicon-based active material may be 500 nm or less.

[0063] In another embodiment, the crystal grain size of the silicon-based active material may be 300 nm or less, preferably 250 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, specifically 100 nm or less, and more specifically 80 nm or less. The crystal grain size of the silicon-based active material may also be in the range of 20 nm or more, preferably 60 nm or more.

[0064] The silicon-based active material has the aforementioned grain size, and the grain size of the silicon-based active material can be adjusted by changing the process conditions during the manufacturing process. In this case, by filling the aforementioned range and ensuring a wide distribution of grain boundaries, lithium ions can be inserted uniformly, reducing the stress applied during lithium ion insertion into silicon particles, thereby mitigating particle cracking. As a result, the lifetime stability of the negative electrode can be improved. If the grain size exceeds the aforementioned range, the grain boundaries within the particles become narrowly distributed. In this case, lithium ions are inserted non-uniformly within the particles, resulting in high stress due to ion insertion and causing particle breakage.

[0065] In one embodiment of this application, the silicon-based active material includes a crystalline structure having a grain distribution of 1 nm to 500 nm, and the area ratio of the crystalline structure is 5% or less based on the total area of ​​the silicon-based active material.

[0066] In another embodiment, the area ratio of the crystal structure may be 5% or less, 3% or less, or 0.1% or more, based on the total area of ​​the silicon-based active material.

[0067] In other words, the silicon-based active material relating to this application has a crystal grain size of 500 nm or less, and the size of each individual crystal structure is formed to be small, thereby satisfying the aforementioned area ratio. As a result, the distribution of crystal grain boundaries can be broadened, and the aforementioned effects can be achieved.

[0068] One embodiment of this application provides a negative electrode active material in which the number of crystal structures contained in the silicon-based active material is three or more.

[0069] In another embodiment, the number of crystal structures contained in the silicon-based active material may be 3 or more, 5 or more, 10 or more, and may satisfy the range of 60 or less, or 50 or less.

[0070] In other words, as described above, when the silicon-based active material satisfies the aforementioned range in terms of crystal grain size and the number of crystal structures satisfies the aforementioned range, the strength of the silicon-based active material itself becomes appropriate, allowing it to provide flexibility when contained within an electrode and to efficiently suppress volume expansion.

[0071] In this application, "crystal grain" refers to a crystalline particle in a metal or material that consists of an aggregate of irregularly shaped particles of microscopic size, and "crystal grain size" may refer to the particle size of the observed crystal grain particles. In other words, in this application, "crystal grain size" refers to the size of domains within a particle that share the same crystal orientation, and is a concept different from particle size or particle size, which expresses the size of a substance.

[0072] In one embodiment of this application, the grain size can be calculated using the FWHM (Full Width at Half Maximum) value by XRD analysis. Specifically, Figure 3 shows how to calculate the grain size. In Figure 3, the remaining value excluding L is measured by XRD analysis of the silicon-based active material, and the grain size can be measured by the Debey-Scherrer equation, which states that FWHM and grain size are inversely proportional. In this case, the Debey-Scherrer equation is as shown in Equation 1-1 below.

[0073] [Formula 1-1] FWHM = (Kλ) / (LCosθ)

[0074] In the above formula 1-1, L is the grain size, K is a constant, θ is the Bragg angle, and λ is the wavelength of the X-ray.

[0075] Furthermore, the shape of the crystal grains can be varied and measured three-dimensionally. Generally, the crystal grain size can be measured using the commonly used circle method or diameter measurement method, but is not limited to these methods.

[0076] The aforementioned diameter measurement method involves drawing 5 to 10 equilibrium lines, each with a length of L mm, on a micrograph of the target particle. The number of crystal grains z along each line is then counted and averaged to determine the average grain size. In this process, only grains that are completely within the line are counted, while those overlapping are excluded. If the number of lines is P and the magnification is V, the average grain size can be calculated using the following equation 1-2.

[0077] [Formula 1-2] Dm=(L*P*10 3 ) / (zV)(μm)

[0078] Furthermore, the circle method involves drawing a circle of a predetermined diameter on a micrograph of the target particles, and then determining the average area of ​​the crystal grains by the number of crystal grains that fall within the circle and the number of crystal grains that fall on the boundary. This can be calculated using the following equations 1-3.

[0079] [Formula 1-3] Fm=(Fk*10 6 ) / ((0.67n+z)V 2 )(μm 2 )

[0080] In equations 1-3 above, Fm represents the average particle area, Fk represents the measurement area on the photograph, z represents the number of particles inside the circle, n represents the number of particles along the arc, and V represents the microscope magnification.

[0081] In one embodiment of this application, the negative electrode active material has a surface area of ​​0.25 m². 2 It may also contain silicon-based active material in a quantity of / g or more.

[0082] In another embodiment, the silicon-based active material has a surface area of ​​0.25 m². 2 / g or more, preferably 0.28m 2 / g or more, more preferably 0.30m 2 / g or more, specifically 0.31m 2 / g or more, more specifically, 0.32m 2 The silicon-based active material may be 3 m² or more. 2 Less than or equal to / g, preferably 2.5m 2 Less than or equal to / g, more preferably 2.2m 2 It can satisfy a range of less than or equal to / g. Surface area (using nitrogen) can be measured according to DIN 66131.

[0083] The silicon-based active material has the aforementioned surface area, and the size of the surface area of ​​the silicon-based active material can be adjusted by changing the process conditions in the manufacturing process 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 compared to particles with the same particle size, and in this case, the bonding force with the binder is increased by satisfying the aforementioned range, which has the characteristic of mitigating electrode cracks caused by repeated charge-discharge cycles.

[0084] Furthermore, when lithium ions are inserted, they are inserted uniformly, reducing the stress on the silicon particles during insertion, 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.

[0085] 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.

[0086] 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.

[0087] When the silicon-based particles are spherical, the particle size can be expressed by their diameter. However, even when they are not spherical, the particle size can be measured in a way that is more efficient than when they are spherical, and the particle size of individual silicon-based particles can be measured using methods commonly used in this industry.

[0088] 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 is 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 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.

[0089] In one embodiment of this application, the silicon-based active material typically has a characteristic BET surface area. The BET surface area of ​​the silicon-based active material is preferably 0.01 to 150.0 m². 2 / g, more preferably 0.1~100.0m 2 / g, particularly preferably 0.2 to 80.0m 2 / g, most preferably 0.2 to 18.0m 2 The value is / g. BET surface area is measured according to DIN 66131 (using nitrogen).

[0090] 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.

[0091] In one embodiment of this application, the present invention provides a negative electrode composition in which the silicon-based active material is 60 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

[0092] In another embodiment, the silicon-based active material may contain 60 parts by weight or more, preferably 65 parts by weight or more, more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may also contain 95 parts by weight or less, preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

[0093] 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 using a silicon-based active material with significantly high capacity within the aforementioned range, and has the characteristic of not degrading the performance of the negative electrode even when including the aforementioned range, and having excellent output characteristics during charging and discharging.

[0094] 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, a problem can sometimes occur where the volume expands rapidly during the charge / discharge process, damaging the conductive paths formed within the negative electrode active material layer.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] In particular, when the functional group content of the dot-shaped conductive material satisfies the aforementioned range, functional groups present on the surface of the dot-shaped conductive material allow for smooth dispersion of the dot-shaped conductive material in the solvent when water is used. Specifically, in the present invention, by using a specific silicon-based active material, the functional group content of the dot-shaped conductive material can be reduced, thereby having an outstanding effect on improving dispersibility.

[0100] 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 of heat treatment of the point-type conductive material.

[0101] 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.

[0102] In one embodiment of this application, the conductive material may include a planar conductive material.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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 the electrode performance due to dispersion effects, and it is especially preferable to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0109] In one embodiment of this application, the planar conductive material has a BET specific surface area of ​​1 m². 2 It may be more than / g.

[0110] 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 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g is also acceptable.

[0111] The planar conductive material according to this application may be a planar conductive material with a high specific surface area; or a planar conductive material with a low specific surface area.

[0112] In another embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area is 50 m². 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 Less than / g, more comfortably, 100m 2 / g or more 300m 2 The range of / g or less may also be satisfied.

[0113] 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 m². 2 / g or more 40m2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 The range of / g or less may also be satisfied.

[0114] 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.

[0115] In one embodiment of this application, the negative electrode conductive material is provided in an amount of 10 to 40 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0116] In another embodiment, the negative electrode conductive material may contain 0.1 parts by weight or more and 40 parts by weight or less, preferably 0.2 parts by weight or more and 30 parts by weight or less, more preferably 0.4 parts by weight or more and 25 parts by weight or less, and most preferably 0.4 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the negative electrode composition.

[0117] In one embodiment of this application, a negative electrode composition is provided in which the negative electrode conductive material includes a planar conductive material and a linear conductive material.

[0118] In one embodiment of this application, the negative electrode conductive material is provided, comprising 80 to 99.9 parts by weight of the planar conductive material and 0.1 to 20 parts by weight of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material, as a negative electrode conductive material.

[0119] In another embodiment, the negative electrode conductive material may include 80 to 99.9 parts by weight of the planar conductive material, preferably 85 to 99.9 parts by weight, and more preferably 95 to 98 parts by weight, based on 100 parts by weight of the negative electrode conductive material.

[0120] In another embodiment, the negative electrode conductive material may include 0.1 to 20 parts by weight, preferably 0.1 to 15 parts by weight, and more preferably 0.2 to 5 parts by weight, of the linear conductive material based on 100 parts by weight of the negative electrode conductive material.

[0121] In one embodiment of this application, the negative electrode conductive material includes a planar conductive material and a linear conductive material, each satisfying the aforementioned composition and proportion, without significantly affecting the life characteristics of a conventional lithium secondary battery. In particular, when a planar conductive material and a linear conductive material are included, the number of charge and discharge points increases, resulting in excellent output characteristics at a high C-rate and a reduction in the amount of high-temperature gas generated.

[0122] In one embodiment of this application, the negative electrode conductive material may be a linear conductive material.

[0123] In particular, when linear conductive materials are used alone, the tortuosity of the electrode, which is a problem with silicon-based negative electrodes, can be simplified, improving the electrode structure and thereby reducing the resistance to lithium ion movement within the electrode.

[0124] In one embodiment of this application, when the negative electrode conductive material includes a linear conductive material alone, the negative electrode conductive material may contain 0.1 parts by weight or more and 5 parts by weight or less, preferably 0.2 parts by weight or more and 3 parts by weight or less, and more preferably 0.4 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the negative electrode composition.

[0125] 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.

[0126] 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.

[0127] In one embodiment of this application, the planar conductive material used as the negative electrode conductive material has a different structure and role from the carbon-based active material typically used as the negative electrode active material. Specifically, the carbon-based active material used as the negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or point-like form to facilitate the storage and release of lithium ions.

[0128] 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 storing or releasing lithium; they are substances that secure conductive pathways in a planar manner within the negative electrode active material layer.

[0129] In other words, in this application, the use of plate-shaped graphite as a conductive material means that it was processed into a planar or plate-shaped form and used as a material to secure a conductive path for lithium that does not play a role in storage or release. 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.

[0130] 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.

[0131] 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.

[0132] 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 substances are substituted with Li, Na, or Ca, or may contain a variety of copolymers thereof.

[0133] 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.

[0134] 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.

[0135] 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 step of exposing the ground silicon to an etching solution and etching the ground silicon to form a silicon-based active material includes a step of stirring the ground silicon at a temperature of 20°C to 120°C for 1 to 30 minutes after exposure to the etching solution, and the etching solution is an alkaline solution.

[0136] Figure 7 shows the etching process according to this application. Specifically, the pulverized silicon is etched through an alkaline solution, and anisotropic etching occurs as a result of this etching, allowing for rapid etching of the lateral surface of the silicon-based active material, thereby satisfying the relationship between the range and specific surface area of ​​Equation 1 described above.

[0137] In particular, in the case of this application, etching is performed under conditions where the etching rate of the 220 surface is higher than that of the 111 surface. The 220 surface is more sensitive to temperature and concentration conditions than the 111 surface, which affects the etching rate. However, if the etching time is set as described above, the specific surface area of ​​the 111 surface and the 220 surface can be adjusted as in this application.

[0138] 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.

[0139] In another embodiment, the alkaline solution may be LiOH, NaOH, or KOH.

[0140] In one embodiment of this application, the concentration of the alkaline solution may be 0.001 M (mole / L) or more and 10 M (mole / L) or less.

[0141] The etching process using an alkaline solution of the aforementioned concentration allows for the fulfillment of the desired specific surface area.

[0142] 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.

[0143] As described above, an acid solution can be added to the solution containing the 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.

[0144] 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.

[0145] 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.

[0146] In this application, the degree of spheroidization and mass of the silicon-based active material after exposure to the etching solution may be the same as that of the silicon-based active material after exposure to the etching solution, in the step of exposing the pulverized silicon to an etching solution and etching the pulverized silicon to form a silicon-based active material.

[0147] In other words, the manufacturing method described in this application performs etching under conditions that etch only the surface of the silicon, so the 111 surface is hardly etched, and thus exhibits the characteristics described above.

[0148] 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.

[0149] Figure 1 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 1 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.

[0150] 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.

[0151] In this case, the negative electrode slurry may contain the aforementioned negative electrode composition and slurry solvent.

[0152] In one embodiment of this application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0153] 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%.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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 20 μm or more and 500 μm or less.

[0159] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited to this.

[0160] In one embodiment of this application, the porosity of the negative electrode active material layer may be in the range of 10% to 60%.

[0161] 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%.

[0162] The aforementioned porosity is varied by 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 compositions and content portions, thereby ensuring that the electrical conductivity and resistance of the electrode are within an appropriate range.

[0163] 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.

[0164] Figure 2 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.

[0165] 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.

[0166] 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.

[0167] In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surfaces treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector may also have a thickness of 3 to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it may be used in various forms such as film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0168] 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; lithium iron oxide such as LiFe3O4; or a compound with the chemical formula Li 1+c1 Mn 2-c1 Lithium manganese oxides such as O4 (0 ≤ c1 ≤ 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, Cu2V2O7; chemical formula LiNi 1-c2 Ni-site type lithium nickel oxide represented as Mc2O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, satisfying 0.01 ≤ c2 ≤ 0.6); chemical formula LiMn 2-c3 M c3 Lithium manganese composite oxides represented as O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, satisfying 0.01 ≤ c3 ≤ 0.6) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion, etc., are examples but are not limited to these. The positive electrode may be Li-metal.

[0169] In one embodiment of this application, the positive electrode active material comprises a lithium composite transition metal compound containing nickel (Ni), cobalt (Co), and manganese (Mn), wherein the lithium composite transition metal compound comprises single particles or secondary particles, and the average particle size (D50) of the single particles may be 1 μm or more.

[0170] For example, the average particle size (D50) of the single particle may be 1 μm or more and 12 μm or less, 1 μm or more and 8 μm or less, 1 μm or more and 6 μm or less, greater than 1 μm and 12 μm or less, greater than 1 μm and 8 μm or less, or greater than 1 μm and 6 μm or less.

[0171] Even when the single particle is formed with a small particle size (average particle size (D50) of 1 μm or more and 12 μm or less), it may exhibit excellent particle strength. For example, the single particle may have a strength of 650 kgf / cm². 2 When rolled with this force, the particle strength can be 100-300 MPa. This allows the single particle to have a strength of 650 kgf / cm². 2 Even when rolled with strong force, the phenomenon of increased fine particles within the electrode due to particle cracking is mitigated, thereby improving the battery's lifespan characteristics.

[0172] The single particle can be produced by mixing a transition metal precursor and a lithium raw material and firing the mixture. The secondary particle may be produced by a different method than that of the single particle, and its composition may be the same as or different from that of the single particle.

[0173] The method for forming the single particles is not particularly limited, but generally, they may be formed by increasing the firing temperature and over-firing, or they may be produced by using additives such as grain growth promoters that are useful for over-firing, or by changing the starting material.

[0174] For example, the firing is carried out at a temperature at which a single particle can be formed. To form this, the firing must be carried out at a higher temperature than when secondary particles are produced. For example, if the precursor composition is the same, the firing must be carried out at a temperature about 30°C to 100°C higher than when secondary particles are produced. The firing temperature for forming the single particle may vary depending on the metal composition in the precursor. For example, when attempting to form a single particle of a high-nickel (High-Ni) NCM-based lithium composite transition metal oxide with a nickel (Ni) content of 80 mol% or more, the firing temperature may be 700°C to 1000°C, preferably about 800°C to 950°C. When the firing temperature meets the above range, a positive electrode active material containing a single particle with excellent electrochemical properties can be produced. If the firing temperature is below 790°C, a positive electrode active material containing a lithium composite transition metal compound in secondary particle form can be produced. If it exceeds 950°C, excessive firing may occur, preventing the proper formation of a layered crystal structure and potentially reducing the electrochemical properties.

[0175] In this specification, the term "single particle" is used to distinguish it from a secondary particle formed by the aggregation of tens or hundreds of primary particles, and is a concept that includes a single particle consisting of one primary particle and an agglomeration of 30 or fewer primary particles, known as an agglomeration of single particles.

[0176] Specifically, in this invention, a single particle may be a single particle consisting of one primary particle or an aggregate of 30 or fewer primary particles in an analogous-single particle form, and a secondary particle may be in a form in which several hundred primary particles are aggregated.

[0177] In one embodiment of this application, the lithium composite transition metal compound, which is the positive electrode active material, further contains secondary particles, wherein the average particle size (D50) of the single particles is smaller than the average particle size (D50) of the secondary particles.

[0178] In this invention, a single particle may be a single particle consisting of one primary particle or an aggregate of 30 or fewer primary particles in an analogous-single particle form, and a secondary particle may be in a form in which several hundred primary particles are aggregated.

[0179] The aforementioned lithium-complex transition metal compounds may further contain secondary particles. Secondary particles refer to forms formed by the aggregation of primary particles and can be distinguished from the concept of single particles, which includes a single primary particle, a single particle, or an analogous-single-particle form that is an aggregate of 30 or fewer primary particles.

[0180] The particle size (D50) of the secondary particles may be 1 μm to 20 μm, 2 μm to 17 μm, preferably 3 μm to 15 μm. The specific surface area (BET) of the secondary particles is 0.05 m². 2 / g~10m 2 It may be / g, preferably 0.1m 2 / g~1m 2 It may be / g, and more preferably 0.3m 2 / g~0.8m 2 / g is also acceptable.

[0181] In an additional embodiment of this application, the secondary particles are aggregates of primary particles, and the average particle size (D50) of the primary particles is 0.5 μm to 3 μm. Specifically, the secondary particles may be in the form of aggregates of several hundred primary particles, and the average particle size (D50) of the primary particles may be 0.6 μm to 2.8 μm, 0.8 μm to 2.5 μm, or 0.8 μm to 1.5 μm.

[0182] When the average particle size (D50) of the primary particles satisfies the aforementioned range, a single-particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size (D50) of the primary particles is too small, the number of aggregated primary particles forming lithium nickel oxide particles increases, reducing the effect of suppressing particle cracking during rolling. If the average particle size (D50) of the primary particles is too large, the lithium diffusion path within the primary particles becomes longer, increasing resistance and potentially degrading the output characteristics.

[0183] According to an additional embodiment of this application, the average particle size (D50) of the single particle is smaller than the average particle size (D50) of the secondary particle. As a result, even if the single particle is formed with a small particle size, it can have excellent particle strength, thereby mitigating the phenomenon of increased fine particles in the electrode due to particle cracking, and thereby improving the battery life characteristics.

[0184] In one embodiment of this application, the average particle size (D50) of the single particle is 1 μm to 18 μm smaller than the average particle size (D50) of the secondary particle.

[0185] For example, the average particle size (D50) of the single particle may be 1 μm to 16 μm smaller, 1.5 μm to 15 μm smaller, or 2 μm to 14 μm smaller than the average particle size (D50) of the secondary particle.

[0186] When the average particle size (D50) of a single particle is smaller than the average particle size (D50) of secondary particles, for example, when the above range is satisfied, the single particle can have excellent particle strength even if it is formed with a small particle size. This mitigates the phenomenon of increasing fine particles in the electrode due to particle cracking, resulting in improved battery life characteristics and improved energy density.

[0187] According to additional embodiments of this application, the single particle is included in an amount of 15 to 100 parts by weight per 100 parts by weight of the positive electrode active material. The single particle may also be included in an amount of 20 to 100 parts by weight, or 30 to 100 parts by weight per 100 parts by weight of the positive electrode active material.

[0188] For example, the single particle may be present in an amount of 15 parts by weight or more, 20 parts by weight or more, 25 parts by weight or more, 30 parts by weight or more, 35 parts by weight or more, 40 parts by weight or more, or 45 parts by weight or more, per 100 parts by weight of the positive electrode active material. The single particle may be present in an amount of 100 parts by weight or less, per 100 parts by weight of the positive electrode active material.

[0189] When a single particle within the aforementioned range is included, it can be combined with the aforementioned negative electrode material to exhibit excellent battery characteristics. In particular, when the single particle is 15 parts by weight or more, the phenomenon of increased fine particles in the electrode due to particle cracking during the rolling process after electrode fabrication can be mitigated, thereby improving the battery's lifespan characteristics.

[0190] In one embodiment of this application, the lithium composite transition metal compound may further contain secondary particles, the amount of which may be 85 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 80 parts by weight or less, 75 parts by weight or less, or 70 parts by weight or less per 100 parts by weight of the positive electrode active material. The amount of which may be 0 parts by weight or more per 100 parts by weight of the positive electrode active material.

[0191] When the above range is satisfied, the aforementioned effect due to the presence of a single-particle positive electrode active material can be maximized. If a secondary-particle positive electrode active material is included, its components may be the same as those exemplified in the single-particle positive electrode active material described above, or they may be other components, and may represent a form in which the single-particle form is aggregated.

[0192] In one embodiment of this application, in 100 parts by weight of the positive electrode active material layer, the positive electrode active material may be included in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 90 parts by weight or more and 99.9 parts by weight or less, more preferably 95 parts by weight or more and 99.9 parts by weight or less, and even more preferably 98 parts by weight or more and 99.9 parts by weight or less.

[0193] 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.

[0194] 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.

[0195] 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.

[0196] 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.

[0197] 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.

[0198] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0199] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidone, 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 derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc. may be used.

[0200] Among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate which are cyclic carbonates are high-viscosity organic solvents with high dielectric constants and can preferably be used because they can well dissociate lithium salts. If linear carbonates with low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate are mixed with such cyclic carbonates at an appropriate ratio, an electrolyte having high electric conductivity can be produced, and thus they can be more preferably used.

[0201] A lithium salt may be used as the metal salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 -CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2) 2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - You may use one or more selected from the group consisting of the following:

[0202] 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.

[0203] 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 power sources 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]

[0204] 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.

[0205] <Manufacturing example> <Manufacturing of the negative electrode active material in Example 1> Silicon powder was added to a 2M KOH aqueous solution, and etching was performed by stirring at 60°C for 30 minutes using a hot plate and a stirring magnet. After neutralization with 2M HCl, the mixture was filtered under reduced pressure to obtain a silicon-based active material.

[0206] Subsequently, the silicon-based active material was dried in a 60°C drying oven to obtain a surface that had been etched.

[0207] <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.

[0208] The manufacturing process was the same as in Example 1, except that the silicon-based active material was formed under the conditions shown in Table 1 below.

[0209] [Table 1]

[0210] <Manufacturing of negative electrodes> A negative electrode slurry was prepared by adding the aforementioned silicon-based active material, a first conductive material, a second conductive material, and polyacrylamide as a binder in a weight ratio of 80:9.6:0.4:10 to distilled water as a solvent for forming the negative electrode slurry (solid content concentration 25% by weight).

[0211] Specifically, the first conductive material is a plate-shaped graphite (specific surface area: 17 m²). 2The second conductive material was SWCNT, with a particle size of 3.5 μm (d / g) and an average particle size of 3.5 μm.

[0212] As for the specific mixing method, the first conductive material, the second conductive material, the 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.

[0213] 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%).

[0214] <Manufacturing of secondary batteries> As the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 A 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).

[0215] 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%).

[0216] 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.

[0217] 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.

[0218] Experimental Example 1: Evaluation of Monocell Lifespan 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), and the results are shown in Table 2.

[0219] Life retention rate (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the first cycle)} × 100

[0220] [Table 2]

[0221] Experiment Example 2: Evaluation of discharge resistance increase rate (after 200 cycles) at @SOC50 2.5C In Experimental Example 1, during the test, the battery was charged / discharged at 0.33C / 0.33C (4.2-3.0V) every 50 cycles to measure the capacitance retention rate. Then, at SOC50, the battery was discharged with a 2.5C pulse and the resistance was measured, and the resistance increase rate was compared and analyzed.

[0222] For the evaluation of the resistance increase rate mentioned above, data was calculated for 200 cycles, and the results are shown in Table 3 below.

[0223] [Table 3]

[0224] As can be seen in Tables 2 and 3 above, in Examples 1 to 7, in which the specific surface area of ​​the crystal planes according to this application was adjusted, it was confirmed that the lifetime evaluation and resistance increase rate were superior to those of Comparative Examples 1 to 4.

[0225] Specifically, as can be seen in Table 1 above, by adjusting the etching time, the specific surface area of ​​the 220 surfaces can be adjusted. This increases the distribution of the exposed 220 surfaces when manufacturing electrodes with the etched silicon-based active material, resulting in higher lithium ion mobility and improved battery life retention.

[0226] Comparative Example 1 is the case where no etching was performed, Comparative Example 2 is the case where the etching time was increased, and Comparative Example 3 is the case where the etching time was too short. In this case, Comparative Example 2 showed that the specific surface area of ​​the 220 plane exceeded the upper limit of the present application when the etching time was increased, resulting in a decrease in the mechanical properties of silicon and inferior characteristics in terms of lifetime retention rate and resistance increase rate due to an increase in side reactions. In the case of Comparative Example 3, etching was hardly performed and the specific surface area of ​​the 220 plane was below the range of the present application, and it was confirmed that the change in specific surface area was minute, similar to Comparative Example 1, and no improvement effect was observed. Finally, in the case of Comparative Example 4, the etching temperature was lowered to 20°C, and in this case, no etching was performed and the result was similar to Comparative Example 3.

[0227] This application describes a case where the specific surface area of ​​the crystal planes is adjusted. In the conventional case, when a relatively large proportion of 111 crystal planes are formed, the 111 crystal planes have lower lithium mobility than the 220 crystal planes, preventing uniform lithium movement during lithium insertion and removal reactions. However, the silicon-based active material according to this application increases the specific surface area of ​​the 220 crystal planes, allowing lithium to move uniformly during lithium insertion and removal reactions. This mitigates the silicon cracking phenomenon on the electrode surface, thereby enhancing the electrode's lifespan. [Explanation of Symbols]

[0228] 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. The silicon-based active material includes 220 crystal planes and 111 crystal planes, The silicon-based active material contains one or more selected from the group consisting of SiOx (x=0) and SiOx (0 < x < 2), and contains 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material. The specific surface area of ​​the aforementioned 220 crystal plane is 1 m ２ / g or more 30m ２ / g or less, The specific surface area of ​​the aforementioned 111 crystal plane is 0.1 m². ２ / g or more 5m ２ A negative electrode active material with a value of less than / g.

2. The silicon-based active material is the negative electrode active material according to claim 1, satisfying the following formula 1: [Formula 1] 45≦(X / Y)×100 In the above formula 1, Y represents the proportion of 111 crystal planes in the silicon-based active material. X represents the proportion of 220 crystal planes within the silicon-based active material.

3. The silicon-based active material comprises one or more selected from the group consisting of spherical silicon-based active material and plate-shaped silicon-based active material. The negative electrode active material according to claim 1, comprising 80 parts by weight or more of spherical silicon-based active material based on 100 parts by weight of the aforementioned silicon-based active material.

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 negative electrode active material according to claim 1, wherein the crystal grain size of the silicon-based active material is 500 nm or less.

6. The step of crushing the silicon raw material; and The step of exposing the 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 step of exposing the pulverized silicon to an etching solution and etching the pulverized silicon to form a silicon-based active material includes a step of stirring the pulverized silicon at a temperature of 20°C to 120°C for 1 to 30 minutes after exposure to the etching solution. The etching solution is an alkaline solution, and this is a method for producing a negative electrode active material.

7. The aforementioned alkaline solution is OH － A method for producing a negative electrode active material according to claim 6, wherein the solution generates and produces an aqueous solution with a pH exceeding 7.

8. The method for producing a negative electrode active material according to claim 6, wherein the concentration of the alkaline solution is 0.001 M (mole / L) or more and 10 M (mole / L) or less.

9. The method for producing a negative electrode active material according to claim 6, wherein the degree of spheroidization and mass of the pulverized silicon before exposure to the etching solution and the silicon-based active material after exposure to the etching solution are the same, in the step of exposing the pulverized silicon to an etching solution and etching the pulverized silicon to form a silicon-based active material.

10. 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 5.

11. The negative electrode composition according to claim 10, wherein the negative electrode active material is 60 parts by weight or more, based on 100 parts by weight of the negative electrode composition.

12. The negative electrode composition according to claim 10, wherein the negative electrode conductive material comprises one or more selected from the group consisting of point conductive material; planar conductive material; and linear conductive material.

13. 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 active material layer comprises the negative electrode composition described in claim 10 or a cured product thereof, wherein the negative electrode is a negative electrode for a lithium secondary battery.

14. 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 13, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less.

15. positive electrode; A negative electrode for a lithium secondary battery according to claim 13; 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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