Negative electrode active material, method for preparing negative electrode active material, negative electrode composition, negative electrode for lithium secondary battery comprising same, and lithium secondary battery comprising negative electrode

Abstract

The present invention is characterized in that the negative electrode active material contains a silicon-based active material having a specific surface area of 5 m2 / g or more, the silicon-based active material is porous and has internal pores, the tap density of the silicon-based active material is 0.2 g / cm3 or more and 0.8 g / cm3 or less, and the silicon-based active material contains a compound selected from the group consisting of SiOx (x = 0) and SiOx (0lt; xlt; 2), and the content of SiOx (x = 0) is 70 parts by weight or more based on 100 parts by weight of the silicon-based active material.

Description

Technical Field

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2023-0143044, filed with the Korean Intellectual Property Office on October 24, 2023, the entire contents of which are incorporated herein by reference.

[0002] This application relates to a negative electrode active material, a method for preparing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery comprising the negative electrode, and a lithium secondary battery comprising the negative electrode. Background Technology

[0003] As the use of fossil fuels increases rapidly, the demand for alternative or clean energy sources continues to grow, and as part of this trend, the most active area of ​​research is in the field of power generation and energy storage using electrochemical reactions.

[0004] Currently, representative examples of electrochemical devices using this type of electrochemical energy include secondary batteries, and their applications are expanding.

[0005] With the technological advancements and increasing demands of mobile devices, the need for secondary batteries as energy sources is rapidly growing. Among these secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and are widely used. Furthermore, methods for preparing high-density electrodes with even higher energy density per unit volume, used as electrodes for such high-capacity lithium-ion batteries, have been actively researched.

[0006] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material for inserting and deintercalating lithium ions from the positive electrode, and silicon-based particles with high discharge capacity can be used as the negative electrode active material.

[0007] In particular, with the increasing demand for high-density energy batteries in recent years, there is a growing need for materials such as Si / C or SiO2, which have a capacity more than 10 times higher than graphite-based materials. x The method of using silicon-based compounds as negative electrode active materials to improve capacity has been actively studied. However, although silicon-based compounds, as high-capacity materials, have higher capacity than graphite used in related technologies, they have the problem of rapid volume expansion during charging, which breaks the conductive path and leads to the degradation of battery characteristics.

[0008] Therefore, in order to solve the problems when using silicon-based compounds as negative electrode active materials, measures such as adjusting the driving potential and suppressing the volume expansion of the material itself, such as methods for further coating the active material layer with a thin film and adjusting the particle size of silicon-based compounds, as well as various measures to prevent the breakage of the conductive path, have been discussed. However, the application of these measures has limitations because the performance of the battery may be degraded, which limits the commercialization of batteries with negative electrodes containing high silicon-based compounds.

[0009] Furthermore, in the case of Si anode active materials, studies have found that wider grain boundaries, i.e. smaller grain size, are more beneficial to the performance characteristics of secondary batteries because grain boundaries act as diffusion paths for lithium.

[0010] However, since this method cannot completely suppress volume changes, research is needed to more effectively mitigate silicon volume changes in order to improve battery life performance.

[0011] Therefore, there is a need to study a silicon-based active material that can prevent damage to the conductive path caused by the volume expansion of silicon compounds, even when the silicon-based active material is used as a negative electrode active material to improve capacity performance.

[0012] <Related Technical Documents>

[0013] (Patent Document 1) Japanese Patent Application No. 2009-080971 Summary of the Invention

[0014] Technical issues

[0015] The study found that by etching the surface of the pulverized silicon-based active material itself with an alkaline solution, a porous silicon-based active material with internal pores can be obtained. In particular, it was confirmed that because the specific surface area and tap density can be adjusted within a certain range by changing the etching conditions, a uniform reaction occurs in the lithium insertion / deintercalation reaction and stress on the silicon-based active material is reduced.

[0016] This application relates to a negative electrode active material capable of solving the above-mentioned problems, a method for preparing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery containing the negative electrode, and a lithium secondary battery containing the negative electrode.

[0017] Technical solution

[0018] One exemplary embodiment of this specification provides a negative electrode active material, the negative electrode active material comprising a specific surface area of ​​5 m² 2 The silicon-based active material has a density of 0.2 g / cm³ or higher, wherein the silicon-based active material has a porous structure including internal pores.3 above and 0.8 g / cm 3 below, and the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, contains 70 parts by weight or more of SiO x (x = 0).

[0019] Another exemplary embodiment provides a method for preparing a negative electrode active material, the method comprising: pulverizing a silicon raw material; and forming a silicon-based active material by exposing the pulverized silicon to a corrosion solution to corrode the pulverized silicon, wherein the corrosion solution is an alkaline solution.

[0020] Yet another exemplary embodiment aims to provide a negative electrode composition, the negative electrode composition comprising: a negative electrode active material according to the present application; a negative electrode conductive material; and a negative electrode binder.

[0021] Yet another exemplary embodiment aims to provide a negative electrode for a lithium secondary battery, the negative electrode comprising: a negative electrode current collector layer; and a negative electrode active material layer provided on one surface or both surfaces of the negative electrode current collector layer, wherein the negative electrode active material layer contains the negative electrode composition according to the present application or a cured product thereof.

[0022] Finally, a lithium secondary battery is provided, the lithium secondary battery comprising: a positive electrode; a 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.

[0023] Advantageous Effects

[0024] The negative electrode active material according to an exemplary embodiment of the present invention is characterized in that, on the basis of the existing pulverization treatment method, a corrosion process is further carried out by treatment with an alkaline solution to adjust the specific surface area, pore morphology and tapped density of the silicon-based active material. When the silicon-based active material is corroded in an alkaline solution, anisotropic corrosion occurs, wherein the corrosion rate varies according to the crystal plane direction, and the silicon-based active material according to the present application can be formed by exposing polycrystalline silicon with randomly distributed crystal planes therein to an alkaline solution.

[0025] The negative electrode active material of the present invention includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2) as the silicon-based active material, and its main feature is that, based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of SiO x(x=0) (i.e., having pure Si active material), and by adjusting the surface area of ​​the silicon-based active material to a specific range to solve the problem of volume expansion with charging and discharging as a result.

[0026] That is, by using silicon-based active materials with a surface area that meets the scope of this invention, particularly those with an internal pore morphology and a larger surface area than particles of the same size, uniform lithium insertion and extraction reactions can be achieved, relieving internal stress within the particles and reducing particle micronization. Furthermore, the negative electrode active material of this invention is characterized by volume expansion into the internal pores during charging, thereby reducing the overall volume change of the particles and improving battery life. Attached Figure Description

[0027] Figure 1 This is a diagram showing the preparation process of the silicon active material according to Example 1 of this application.

[0028] Figure 2 A diagram illustrating the stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of this application.

[0029] Figure 3 A diagram illustrating the stacked structure of a lithium secondary battery according to an exemplary embodiment of this application.

[0030] <Explanation of reference numerals and symbols in the attached drawings>

[0031] 10: Negative electrode current collector layer

[0032] 20: Negative electrode active material layer

[0033] 30: Diaphragm

[0034] 40: Positive electrode active material layer

[0035] 50: Positive current collector layer

[0036] 100: Negative electrode for lithium secondary batteries

[0037] 200: Positive electrode for lithium secondary batteries Detailed Implementation

[0038] Before describing the present invention, some terms will be defined.

[0039] In this specification, when a part “contains” a constituent element, unless otherwise specifically stated, this does not mean that other constituent elements are excluded, but rather that other constituent elements may also be included.

[0040] In this specification, "p to q" refers to the range of "above p and below q".

[0041] In this specification, "specific surface area" is measured by the BET method, specifically calculated using a BELSORP-mini II manufactured by BEL Japan from the amount of nitrogen adsorbed at liquid nitrogen temperature (77 K). That is, in this application, BET specific surface area can refer to the specific surface area measured by the aforementioned method.

[0042] In this specification, "D" n "" refers to particle size distribution, specifically the particle size at the n% point of the cumulative particle number distribution based on particle size. That is, D 50 D is the particle size (average particle size) at the 50% point of the cumulative particle number distribution based on particle size. 90 It is the particle size at the 90% point of the cumulative particle number distribution based on particle size, and D 10 This refers to the particle size at the 10% point of the cumulative distribution of particle numbers based on particle size. Alternatively, the average particle size can be measured using laser diffraction. Specifically, after dispersing the powder to be tested in a dispersion medium, the resulting dispersion is introduced into a commercially available laser diffraction particle size measurement device (e.g., Microtrac S3500) to measure the change in the diffraction pattern as the particles pass through the laser beam, thereby calculating the particle size distribution.

[0043] In one exemplary embodiment of this application, particle size or particle diameter may refer to the average or representative diameter of the individual particles forming the metal powder.

[0044] In this specification, the fact that a polymer contains monomers as monomeric units means that the monomers participate in the polymerization reaction and are therefore included in the polymer as repeating units. In this specification, when a polymer contains monomers, it is interpreted in the same way as when the polymer contains monomers as monomeric units.

[0045] In this specification, "polymer" is understood to be used in a broad sense, including copolymers, unless otherwise stated as "homogeneous polymer".

[0046] In this specification, the weight-average molecular weight (M) w ) and number-average molecular weight (M n The molecular weight is the weight-average molecular weight of polystyrene measured by gel permeation chromatography (GPC) using commercially available monodisperse polystyrene polymers (standard samples) of various degrees of polymerization as standard materials. In this specification, unless otherwise stated, molecular weight refers to weight-average molecular weight.

[0047] The invention will now be described in detail with reference to the accompanying drawings to enable those skilled in the art to readily implement it. However, the invention can be implemented in various different forms and is not limited to the following description.

[0048] One exemplary embodiment of the present specification provides a negative electrode active material, the negative electrode active material comprising a silicon-based active material having a specific surface area of 5 m 2 / g or more, wherein the silicon-based active material has a porous structure including internal pores, and the tapped density of the silicon-based active material is 0.2 g / cm 3 or more and 0.8 g / cm 3 or less, and the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, contains 70 parts by weight or more of SiO x (x = 0).

[0049] The negative electrode active material of the present invention includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2) as the silicon-based active material, and its main feature is that, based on 100 parts by weight of the silicon-based active material, it contains 70 parts by weight or more of SiO x (x = 0) (i.e., having a pure Si active material), and by adjusting the surface area, pore morphology and bulk density of the silicon-based active material to a specific range to solve the problem of volume expansion during charge and discharge caused thereby.

[0050] That is, the silicon-based active material has a grain size of generally several hundred to several millimeters due to its high crystallinity, and the silicon-based active material according to the present application is characterized in that a porous structure including internal pores is formed in the corresponding silicon-based active material through etching treatment, and the specific surface area can be increased to improve reaction uniformity and reduce volume change, thereby improving the service life performance of the battery.

[0051] By using a silicon-based active material whose surface area meets the scope of the present invention, particularly having an internal pore morphology and a larger surface area than particles having the same particle size, it is possible to achieve uniform lithium insertion and extraction reactions, relieve the stress inside the particles, and reduce the pulverization of the particles. In addition, the negative electrode active material of the present invention is characterized in that during the charging process, the volume expands into the internal pores, thereby reducing the volume change of the entire particle and also improving the service life of the battery.

[0052] In one exemplary embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, may contain 70 parts by weight or more of SiO x (x = 0).

[0053] In one exemplary embodiment of this application, the silicon-based active material includes SiO2. x (x=0), and based on 100 parts by weight of silicon-based active material, it can contain more than 70 parts by weight of SiO. x (x=0).

[0054] In another exemplary embodiment, based on 100 parts by weight of silicon-based active material, SiO x The content of (x=0) can be 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more, and the SiO x The content of (x=0) can be 100 parts by weight or less, preferably 99 parts by weight or less, and more preferably 95 parts by weight or less.

[0055] In one exemplary embodiment of this application, pure silicon (Si) particles can be used as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material means that, as described above, based on a total of 100 parts by weight of silicon-based active material, pure Si particles (SiOx (x=0)) that are not bound to other particles or elements are included in the above range.

[0056] In one exemplary embodiment of this application, the silicon-based active material can be based on 100 parts by weight of silicon-based active material having 100 parts by weight of SiO x It is composed of silicon-based particles (x=0).

[0057] In one exemplary embodiment of this application, a negative electrode active material is provided, wherein the silicon-based active material may contain metal impurities, and in this case, the impurities are metals that are typically contained in the silicon-based active material, specifically, the content of metal impurities in the silicon-based active material is less than 0.1 parts by weight.

[0058] Because silicon-based active materials have significantly higher capacity than graphite-based active materials used in related technologies, attempts to apply silicon-based active materials have been increasing. However, these attempts are limited to situations such as mixing small amounts of silicon-based active materials with graphite-based active materials and using them, because silicon-based active materials have a high volume expansion rate during charge and discharge.

[0059] Therefore, in order to solve the above-mentioned problems, this invention, while using silicon-based active materials only as negative electrode active materials to improve capacity performance, changes the method of preparing silicon-based active materials to adjust the specific surface area, pore morphology and bulk density of the silicon-based active materials themselves, rather than adjusting the composition of conductive materials and binders, thereby solving the existing problems.

[0060] In one exemplary embodiment of this application, the negative electrode active material may contain a specific surface area of ​​5 m². 2 Silicon-based active materials of / g or higher.

[0061] In this application, the specific surface area of ​​the silicon-based active material can be 15 m². 2 / g or more and 80 m 2 / g or less.

[0062] In another exemplary embodiment, the specific surface area of ​​the silicon-based active material can be 5 m². 2 / g or more, preferably 8 m 2 / g or more, preferably 12 m 2 / g or more, specifically 13 m 2 / g or more, more specifically 15 m 2 / g or more. The specific surface area of ​​silicon-based active materials can be 200 m². 2 / g or less, 150 m 2 / g or less, 100 m 2 / g and 95 m 2 / g or less, and can meet the preferred 90 m 2 / g or less, more preferably 80 m 2 The specific surface area is in the range below / g. Specific surface area can be measured according to DIN 66131 (using nitrogen).

[0063] In one exemplary embodiment of this specification, the silicon-based active material comprises a (220) crystal plane and a (111) crystal plane, wherein the specific surface area of ​​the (220) crystal plane can be 1 m². 2 / g or more and 30 m 2 / g or less, and the specific surface area of ​​the (111) crystal plane can be 0.1 m 2 / g or more and 5 m 2 / g or less.

[0064] The silicon-based active material of this application is subjected to an alkaline etching process after being crushed. 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.

[0065] In this case, as described above, the specific surface area of ​​the (220) crystal plane can be 1 m². 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, and 10 m 2 / g or more and 25 m 2 / g or less, and the (111) crystal plane can satisfy 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, and 0.8 m 2 / g or more and 3 m 2 Specific surface area below / g.

[0066] As described above, the present invention is characterized in that the specific surface area of ​​the crystal face meets the above-mentioned range, and during the process of manufacturing the electrode using etched silicon-based active material, the distribution of the exposed (220) face increases and the lithium ion mobility increases, thereby improving the battery life retention rate.

[0067] In this application, the specific surface area of ​​the (220) crystal plane and the specific surface area of ​​the (111) crystal plane can be measured as follows.

[0068] In this case, it can be assumed that since the corrosion is carried out under conditions that only corrode the silicon surface, the sphericity and mass of the silicon particles do not change before and after corrosion; and the (111) surface is hardly corroded, so the surface area does not change.

[0069] Before etching, the morphology of silicon particles is simplified into a three-dimensional shape, and the area ratio of the upper / lower surface (111 facet) and the side surface (220 facet) is determined by the sphericity value. Then, the specific surface area of ​​each crystal facet is derived from the specific surface area measurement. Subsequently, the increased specific surface area of ​​the (220) facet can be determined from the specific surface area measurement after etching.

[0070] Furthermore, the crystal plane ratio can be expressed by calculating the area ratio, which is obtained by integrating the intensity of the peaks corresponding to each plane after XRD measurement.

[0071] In this application, the specific surface areas of the (220) and (111) crystal planes are values ​​measured by the BET method. Specifically, in this application, an alkaline solution is used for etching so that the (111) plane is not etched, and the specific surface area of ​​the (220) crystal plane is calculated by subtracting the surface area of ​​the (111) plane alone from the specific surface area obtained by the BET method, the surface area of ​​the (111) plane being obtained from the value calculated by the specific surface area before etching and the crystal plane ratio.

[0072] The silicon-based active material has the aforementioned surface area, and the specific surface area and pore morphology of the silicon-based active material can be adjusted by changing the process conditions, particularly the corrosion conditions, during the preparation process described below. That is, when the negative electrode active material is prepared using the preparation method according to this application, the negative electrode active material has a larger surface area than particles of the same particle size due to its surface roughness. In this case, because the bonding strength between the negative electrode active material and the binder is improved by satisfying the aforementioned range, the negative electrode active material has the characteristic of mitigating electrode cracks caused by repeated charge-discharge cycles. When the surface area of ​​the silicon-based active material is below the aforementioned range, pores are not sufficiently formed, making it difficult to expect uniform reactions during charge-discharge and failing to effectively buffer volume expansion. Furthermore, when the content exceeds the aforementioned range, the problem is that the battery life is shortened due to excessive side reactions with the electrolyte.

[0073] Furthermore, during the lithium-ion intercalation process, lithium ions can enter uniformly, which reduces the stress applied during lithium-ion intercalation into silicon particles, thereby mitigating particle cracking. As a result, the negative electrode exhibits characteristics that improve the stability of its lifespan. When the surface area size is smaller than the aforementioned range, even when the particles have the same particle size, a smooth surface is formed, leading to decreased bonding strength with the binder and resulting in electrode cracking. In this case, the uneven intercalation of lithium ions into the particles causes high stress due to ion intercalation, further contributing to particle cracking.

[0074] In one exemplary embodiment of this application, the negative electrode active material is characterized by having a porous structure containing internal pores formed by corrosion, rather than having an externally uneven morphology.

[0075] Compared to silicon-based active materials with uneven surface morphology, the active material with internal pores, as described in this application, is characterized by a significantly increased specific surface area and further improved reaction uniformity, thereby reducing stress and micronization. Furthermore, as volume expansion propagates into the internal pores, these pores buffer volume changes, mitigating overall particle volume variations and resulting in improved lifetime retention compared to silicon-based active materials with uneven surface morphology.

[0076] In one exemplary embodiment of this application, the tap density of the silicon-based active material can be 0.2 g / cm³. 3 Above and 0.8 g / cm 3 the following.

[0077] In another exemplary embodiment, the tap density of the silicon-based active material can be 0.2 g / cm³. 3 Above and 0.8 g / cm 3The preferred value is 0.25 g / cm³. 3 Above and 0.78 g / cm 3 The following is more preferably 0.35 g / cm³. 3 Above and 0.77 g / cm 3 the following.

[0078] In this application, tap density refers to the value obtained by filling a container with silicon powder, measuring the apparent volume of particles obtained by vibrating the container under predetermined conditions, and dividing the mass of the silicon powder by the apparent volume.

[0079] The tap density can be adjusted within the aforementioned range according to the degree of corrosion during the preparation of the silicon-based active material. Specifically, in the case of the silicon-based active material according to this application, when pores are uniformly formed by corrosion to have an internal pore morphology, the tap density decreases while satisfying the aforementioned specific surface area range. However, when the silicon-based active material is formed with an uneven surface, although the specific surface area can increase to a certain extent, the tap density also increases, and structures such as pores cannot be formed in the particles, limiting the increase in specific surface area. In other words, compared to silicon-based active materials with an uneven surface, the active material, while satisfying the tap density in this application, is characterized by a larger increase in specific surface area, further improved reaction uniformity, thereby achieving stress reduction and reduced micronization.

[0080] In one exemplary embodiment of this application, the silicon-based active material may comprise silicon-based particles with a particle size distribution of 0.01 μm or more and 30 μm or less.

[0081] The fact that silicon-based active materials contain silicon particles with a particle size distribution of 0.01 μm or larger and 30 μm or smaller means that they contain a large number of individual silicon particles with particle sizes in the above range, and the number of silicon particles contained is unlimited.

[0082] When silicon particles have a spherical shape, the particle size of silicon particles can be expressed as the diameter of the silicon particles. However, even in the case of other non-spherical shapes, the particle size can be measured by comparison with the case of spherical shapes, and the particle size of a single silicon particle can usually be measured by measurement methods in the art.

[0083] On the other hand, the average particle size (D) of the silicon-based active material of the present invention 50The particle size can be from 3 μm to 10 μm, specifically from 5.5 μm to 8 μm, and more specifically from 6 μm to 7 μm. When the average particle size is within the above range, the viscosity of the negative electrode slurry is formed within a suitable range because the specific surface area of ​​the particles is within a suitable range. Therefore, it is beneficial to disperse the particles constituting the negative electrode slurry. In addition, the size of the silicon-based active material has a value equal to or greater than the lower limit range, and because the composite material of conductive material and binder in the negative electrode slurry provides excellent contact area between silicon particles and conductive material, the possibility of a continuous conductive network is increased, thereby improving the capacity retention rate. On the other hand, when the average particle size meets the above range, excessively large silicon particles are eliminated, thereby forming a smooth negative electrode surface, thus preventing uneven current density during charging and discharging.

[0084] In one exemplary embodiment of this application, the silicon-based active material may exist, for example, in a crystalline or amorphous form, and is preferably not porous. The silicon particles are preferably spherical or fragmented. Alternatively, but less preferably, the silicon particles may also have a fibrous structure or exist in the form of a silicon-containing film or coating.

[0085] In one exemplary embodiment of this application, a negative electrode composition is provided, the negative electrode composition comprising: a negative electrode active material; a negative electrode conductive material; and a negative electrode binder.

[0086] In one exemplary embodiment of this application, a negative electrode composition is provided, wherein the content of negative electrode active material is 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0087] In another exemplary embodiment, based on 100 parts by weight of the negative electrode composition, the content of the negative electrode active material can be 40 parts by weight or more, preferably 60 parts by weight or more, more preferably 65 parts by weight or more, and even more preferably 70 parts by weight or more, and the content can be 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0088] The negative electrode composition according to this application is characterized in that, even when using a silicon-based active material with very high capacity within the above-mentioned range, by using a negative electrode active material that meets a specific specific surface area size and can suppress the volume expansion rate during charging and discharging, the performance of the negative electrode does not deteriorate and the output characteristics during charging and discharging are excellent, even if the content of the silicon-based active material is within the above-mentioned range.

[0089] In related technologies, graphite-based compounds are typically used as the negative electrode active material. However, in recent years, with the increasing demand for high-capacity batteries, there have been more attempts to mix and use silicon-based active materials to improve capacity. However, in the case of silicon-based active materials, as mentioned above, even if the properties of the silicon-based active material itself are adjusted, its volume will expand rapidly during charging and discharging, which may cause damage to the conductive paths formed in the negative electrode active material layer in some cases.

[0090] Therefore, in one exemplary 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.

[0091] In one exemplary embodiment of this application, a dot-shaped conductive material can be used to enhance the conductivity of the negative electrode, and refers to a conductive material with a dot-shaped or spherical shape that has conductivity without causing chemical change. Specifically, the dot-shaped conductive material can 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 cracking black, conductive fibers, fluorocarbons, aluminum powder, nickel powder, zinc oxide, potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably includes carbon black for achieving high conductivity and excellent dispersibility.

[0092] In one exemplary embodiment of this application, the dot-shaped conductive material may have a diameter of 40 μm. 2 / g or more and 70 m 2 / g or less, preferably 45 m 2 / g or more and 65 m 2 / g or less, more preferably 50 m 2 / g or more and 60 m 2 BET specific surface area below / g.

[0093] In one exemplary embodiment of this application, the functional group content (volatile substances) of the dot-shaped conductive material can be 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.

[0094] Specifically, when the functional group content of the dot-shaped conductive material meets the above-mentioned range, functional groups exist on the surface of the dot-shaped conductive material, so that when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, in this invention, because a specific silicon-based active material is used, the functional group content of the dot-shaped conductive material can be reduced, thus the present invention has an excellent effect on improving dispersibility.

[0095] In one exemplary embodiment of this application, the material is characterized by comprising, in addition to a silicon-based active material, a dot-shaped conductive material having a functional group content within the aforementioned range, and the functional group content can be adjusted according to the degree of heat treatment of the dot-shaped conductive material.

[0096] In one exemplary embodiment of this application, the particle size of the dot-shaped conductive material can be from 10 nm to 100 nm, preferably from 20 nm to 90 nm, and more preferably from 20 nm to 60 nm.

[0097] In one exemplary embodiment of this application, the conductive material may include a planar conductive material.

[0098] Planar conductive materials can be used to improve conductivity by increasing the surface contact between silicon particles in the negative electrode, while suppressing the interruption of conductive paths due to volume expansion. Planar conductive materials can be described as plate-shaped conductive materials or bulk-shaped conductive materials.

[0099] In one exemplary embodiment of this application, the planar conductive material may include at least one selected from the group consisting of plate graphite, graphene, graphene oxide and graphite flakes, and may preferably be plate graphite.

[0100] In one exemplary embodiment of this application, the planar conductive material may have an average particle size (D) of 2 μm to 7 μm, specifically 3 μm to 6 μm, more specifically 3.5 μm to 5 μm. 50 When the average particle size meets the above range, sufficient particle size promotes dispersion without causing an excessive increase in the viscosity of the negative electrode slurry. Therefore, when using the same equipment and time to disperse the particles, the dispersion effect is excellent.

[0101] In one exemplary embodiment of this application, a negative electrode composition is provided, wherein the planar conductive material D 10 For particles larger than 0.5 μm and smaller than 2.0 μm, D 50 It is above 2.5 μm and below 3.5 μm, and D 90 It is between 6.5 μm and 15.0 μm.

[0102] In one exemplary embodiment of this application, as a planar conductive material, 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 can be used.

[0103] In one exemplary embodiment of this application, a planar conductive material with a high specific surface area or a low specific surface area can be used without limitation. However, in particular, the planar conductive material according to this application may affect the electrode performance to some extent due to the dispersion effect, so it may be particularly desirable to use a planar conductive material with a low specific surface area that does not cause dispersion problems.

[0104] In one exemplary embodiment of this application, the planar conductive material may have a diameter of 0.25 μm. 2 BET specific surface area above / g.

[0105] In another exemplary embodiment, the planar conductive material may have a 1 m 2 / g or more and 500 m 2 / g or less, preferably 5 m 2 / g or more and 300 m 2 / g or less, preferably 5 m 2 / g or more and 250 m 2 BET specific surface area below / g.

[0106] As the planar conductive material according to this application, a planar conductive material with a high specific surface area or a planar conductive material with a low specific surface area can be used.

[0107] In yet another exemplary embodiment, the planar conductive material is a planar conductive material with a high specific surface area, and the BET specific surface area can meet 50 m². 2 / g or more and 500 m 2 / g or less, preferably 80 m 2 / g or more and 300 m 2 / g or less, more preferably 100 m 2 / g or more and 300 m 2 The range below / g.

[0108] In yet another exemplary embodiment, the planar conductive material is a planar conductive material with a low specific surface area, and the BET specific surface area can meet the requirement of 1 m². 2 / g or more and 40 m 2 / g or less, preferably 5 m 2 / g or more and 30 m 2 / g or less, preferably 5m 2 / g or more and 25 m 2 The range below / g.

[0109] Other conductive materials could be linear conductive materials such as carbon nanotubes. Carbon nanotubes can be bundled carbon nanotubes. Bundled carbon nanotubes can contain multiple carbon nanotube units. Specifically, unless otherwise stated, the term "bundled" as used herein refers to a secondary shape in the form of a bundle or rope, wherein multiple carbon nanotube units are arranged side-by-side or intertwined with substantially the same orientation along the longitudinal axis of the carbon nanotube units. Within the carbon nanotube unit, the graphite sheet is cylindrical with a diameter on the nanometer scale and has sp... 2 Bonded structure. In this case, carbon nanotube units can exhibit conductor or semiconductor properties depending on the structure and angle of the graphite sheet winding. Compared to entangled carbon nanotubes, bundled carbon nanotubes can be uniformly dispersed during the preparation of the negative electrode, and the conductivity of the negative electrode can be improved by smoothly forming a conductive network in the negative electrode.

[0110] In an exemplary embodiment of this application, a negative electrode composition is provided, wherein the content of the negative electrode conductive material is less than 20 parts by weight based on 100 parts by weight of the negative electrode composition.

[0111] In another exemplary embodiment, based on 100 parts by weight of the negative electrode composition, the content of the negative electrode conductive material can be 0.1 parts by weight or more and 20 parts by weight or less, preferably 1 part by weight or more and 20 parts by weight or less, more preferably 5 parts by weight or more and 15 parts by weight or less, and most preferably 6 parts by weight or more and 13 parts by weight or less.

[0112] The negative electrode conductive material according to this application has a completely different structure from the positive electrode conductive material used in the positive electrode. That is, the negative electrode conductive material according to this application is used to capture the contact points between silicon-based active materials where the volume expansion of the electrode is very large due to charging and discharging, while the positive electrode conductive material is used to act as a buffer during rolling while imparting partial conductivity, and its structure and function are completely different from the negative electrode conductive material of this invention.

[0113] Furthermore, the negative electrode conductive material according to this application is applied to silicon-based active materials and has a completely different structure from the conductive material applied to graphite-based active materials. That is, the conductive material used for electrodes with graphite-based active materials has only particles that are smaller than the active material, thereby improving output characteristics and imparting partial conductivity, and its structure and function are completely different from the negative electrode conductive material used together with silicon-based active materials in this invention.

[0114] In one exemplary embodiment of this application, the planar conductive material used as the negative electrode conductive material has a structure and function different from that of carbon-based active materials typically used as negative electrode active materials. Specifically, the carbon-based active material used as the negative electrode active material can be artificial graphite or natural graphite, and refers to materials that are processed into spherical or dot-like shapes and used to promote the storage and release of lithium ions.

[0115] Conversely, planar conductive materials used as negative electrode conductive materials are materials with planar or plate-like shapes, and can be described as plate-like graphite. That is, planar conductive materials are materials included to maintain the conductive path in the negative electrode active material layer, and refer to materials that ensure the conductive path in a planar form in the negative electrode active material layer, rather than playing a role in storing and releasing lithium.

[0116] That is, in this application, the fact that plate-shaped graphite is used as a conductive material means that the plate-shaped graphite is processed into a planar or plate-like shape and used as a material to ensure a conductive path rather than to store or release lithium. In this case, the negative electrode active material included together has high capacity characteristics for lithium storage and release, and plays the role of storing and releasing all lithium ions transported from the positive electrode.

[0117] Conversely, in this application, the fact that carbon-based active materials are used as active materials means that the carbon-based active materials are processed into dots or spheres and used as materials for storing or releasing lithium.

[0118] That is, in one exemplary embodiment of this application, the artificial or natural graphite, as a carbon-based active material, is dot-shaped, and its BET specific surface area can meet the requirement of 0.1 m². 2 / g or more and 4.5 m 2 The range is below / g. Furthermore, the plate-shaped graphite, as a planar conductive material, is in a planar form, and its BET specific surface area can be 5 m². 2 / g or more.

[0119] In one exemplary embodiment of this application, the negative electrode adhesive may include at least one selected from the group consisting of: polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials wherein the hydrogen atoms therein are replaced by Li, Na, Ca, etc., and may also include various copolymers thereof.

[0120] The negative electrode adhesive according to the exemplary embodiments of this application serves to support the active material and the conductive material to prevent the distortion and structural deformation of the negative electrode structure when the silicon-based active material undergoes volume expansion and mitigation. When the above functions are satisfied, all common adhesives can be applied, specifically, water-based adhesives can be used, and more specifically, PAM-based adhesives can be used.

[0121] In one exemplary embodiment of this application, based on 100 parts by weight of the negative electrode composition, the content of the negative electrode binder can be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and the content can be 5 parts by weight or more and 10 parts by weight or more.

[0122] An exemplary embodiment of this application provides a method for preparing a negative electrode active material, the method comprising:

[0123] The silicon raw material was crushed; and

[0124] Silicon-based active materials are formed by exposing pulverized silicon to an etching solution to corrode the pulverized silicon.

[0125] The corrosive solution is an alkaline solution.

[0126] In related technologies, negative electrode active materials are prepared by physically crushing silicon blocks. When negative electrode active materials are prepared as described above, the grain size is typically greater than 200 nm and the surface is smooth, resulting in a specific surface area of ​​less than 5 m². 2 The value of / g. When silicon-based active materials are simply prepared using related technologies, the surface area cannot be controlled, which makes it difficult to ensure the stability of the negative electrode's lifespan.

[0127] However, the method for preparing the negative electrode active material according to the present invention can be achieved by including, for example Figure 1 The etching steps shown are used to form silicon particles, thus obtaining a silicon-based active material that meets the surface area dimensions according to this application. That is, as... Figure 1 It can be confirmed that during exposure to alkaline solutions, the corrosion rate of silicon-based active materials varies with the crystal plane orientation and anisotropic corrosion occurs, resulting in the formation of porous structures on the surface and inside as the corrosion progresses.

[0128] In one exemplary embodiment of this application, forming a silicon-based active material by exposing pulverized silicon to an etching solution to etch the pulverized silicon may include: exposing the pulverized silicon to the resulting mixture, and then stirring the etching solution at a temperature of 20°C to 120°C for 30 minutes to 50 hours.

[0129] By etching silicon at the temperature described above and for the duration described above, the surface area range and tap density according to this application can be satisfied.

[0130] In one exemplary embodiment of this application, the alkaline solution may be one that generates OH- - It produces an aqueous solution with a pH greater than 7.

[0131] In another exemplary embodiment, the alkaline solution may be LiOH, NaOH, or KOH.

[0132] In one exemplary embodiment of this application, the concentration of the alkaline solution can be 0.001 M (mol / L) or more and 10 M (mol / L) or less.

[0133] By using an alkaline solution of the above concentration for the etching process, the present invention has the characteristics of satisfying the desired specific surface area and tap density.

[0134] An exemplary embodiment of this application may include: pulverizing silicon raw material; forming a silicon-based active material by exposing the pulverized silicon to an etching solution to etch the pulverized silicon; then adding an acid solution to the silicon-based active material to neutralize the silicon-based active material; and filtering under reduced pressure.

[0135] The solution containing the aforementioned corroded silicon-based active material can be neutralized by adding an acid solution, and then the silicon-based active material can be separated from the solution by vacuum filtration or centrifugation.

[0136] In this application, as an acid solution, H2 can be generated. + The acid solution can be any substance that can undergo a neutralization reaction with a base, without limitation, and the acid solution can specifically be HCl, HNO3, or H2SO4.

[0137] Subsequently, the method may further include drying the silicon-based active material in a drying oven to remove moisture.

[0138] In this case, the drying temperature of the drying oven can be above 40℃ and below 100℃.

[0139] In one exemplary embodiment of this application, a negative electrode for a lithium secondary battery is provided, comprising:

[0140] Negative current collector layer; and

[0141] A negative electrode active material layer is formed on one or both surfaces of the negative electrode current collector layer, the negative electrode active material layer comprising the negative electrode composition or a cured form thereof according to the present application.

[0142] Figure 2This diagram illustrates the stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of this application. Specifically, it can be confirmed that the negative electrode 100 for a lithium secondary battery includes a negative electrode active material layer 20 located on one surface of the negative electrode current collector layer 10, and Figure 2 The diagram shows a layer of negative electrode active material formed on one surface, but the negative electrode active material layer may be contained on both surfaces of the negative electrode current collector layer.

[0143] In one exemplary embodiment of this application, a negative electrode for a lithium secondary battery can be formed by coating a negative electrode slurry containing a negative electrode composition onto one or both surfaces of a negative electrode current collector layer and drying the negative electrode slurry.

[0144] In this case, the negative electrode slurry may contain: the above-described negative electrode composition; and a slurry solvent.

[0145] In an exemplary embodiment of this application, the solid content of the negative electrode slurry can be between 5% and 40%.

[0146] In another exemplary embodiment, the solid content of the negative electrode slurry can be in the range of 5% or more and 40% or less, preferably 7% or more and 35% or less, and more preferably 10% or more and 30% or less.

[0147] The solid content of the negative electrode slurry can refer to the content of the negative electrode composition contained in the negative electrode slurry, and it can also refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0148] When the solid content of the negative electrode slurry meets the above-mentioned range, the present invention has the following characteristics: because the viscosity is suitable during the formation of the negative electrode active material layer, the particle aggregation phenomenon of the negative electrode composition is minimized, thereby enabling the formation of the negative electrode active material layer efficiently.

[0149] In one exemplary embodiment of this application, the slurry solvent can be used without limitation, as long as the slurry solvent can dissolve the negative electrode composition; specifically, water or NMP can be used.

[0150] In one exemplary embodiment of this application, the negative electrode current collector layer typically has a thickness of 1 μm to 100 μm. There are no particular limitations on the negative electrode current collector layer, as long as it has high conductivity without causing chemical changes to the battery. For example, materials such as copper, stainless steel, aluminum, nickel, titanium, and sintered carbon can be used; copper or stainless steel with a surface treated with carbon, nickel, titanium, silver, etc.; aluminum-cadmium alloys, etc. Furthermore, the negative electrode current collector layer can also improve the bonding strength of the negative electrode active material by forming fine irregularities on its surface, and the negative electrode current collector layer can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0151] In one exemplary embodiment of this application, a negative electrode for a lithium secondary battery is provided, wherein the negative electrode current collector layer has a thickness of 1 μm or more and 100 μm or less, and the negative electrode active material layer has a thickness of 5 μm or more and 500 μm or less.

[0152] However, the thickness can be modified in various ways depending on the type and application of the negative electrode used, and is not limited to this.

[0153] In one exemplary embodiment of this application, the porosity of the negative electrode active material layer can be in the range of 10% or more and 60% or less.

[0154] In another exemplary embodiment, the porosity of the negative electrode active material layer can be in the range of 10% or more and 60% or less, preferably 20% or more and 50% or less, and more preferably 30% or more and 45% or less.

[0155] The porosity varies with the composition and content of the silicon-based active material, conductive material and binder contained in the negative electrode active material layer. In particular, when the silicon-based active material and conductive material according to this application are contained in a specific composition and content, the above range is satisfied. Therefore, the conductivity and resistance in the electrode have an appropriate range.

[0156] In one exemplary embodiment of this application, a lithium secondary battery is provided, the lithium secondary battery comprising: a positive electrode; a negative electrode for a lithium secondary battery according to this application; a separator disposed between the positive electrode and the negative electrode; and an electrolyte.

[0157] Figure 3 This is a diagram showing the stacked structure of a lithium secondary battery according to an exemplary embodiment of this application. Specifically, it can be seen that the negative electrode 100 for the lithium secondary battery includes a negative electrode active material layer 20 on one surface of the negative electrode current collector layer 10, and it can be seen that the positive electrode 200 for the lithium secondary battery includes a positive electrode active material layer 40 on one surface of the positive electrode current collector layer 50. It is shown that the negative electrode 100 and the positive electrode 200 for the lithium secondary battery are formed in a structure in which the electrodes are stacked with the separator 30 placed therebetween.

[0158] The secondary battery according to the exemplary embodiments of this specification may specifically include the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator between the positive and negative electrodes, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has already been described in detail, its specific description will be omitted.

[0159] 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 positive electrode active material.

[0160] In the positive electrode, there are no particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause chemical changes in the battery. For example, materials such as stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel with surfaces treated with carbon, nickel, titanium, silver, etc., can be used. Furthermore, the positive electrode current collector can typically have a thickness of 3 to 500 μm, and the adhesion of the positive electrode active material can be enhanced by forming fine irregularities on the surface of the current collector. For example, the positive electrode current collector can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0161] The positive electrode active material can be a commonly used positive electrode active material. Specifically, positive electrode active materials include: layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds replaced by one or more transition metals; lithium iron oxides such as LiFe3O4; and lithium manganese oxides such as Li 1+c1 Mn 2-c1 O4 (0≤c1≤0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5 and Cu2V2O7; such as LiNi 1-c2 M c2 O2 (where M is selected from at least one of the following groups: Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and c2 satisfies 0.01 ≤ c2 ≤ 0.3) represents a Ni-site type lithium nickel oxide; such as the chemical formula LiMn 2-c3 M c3 Lithium-manganese composite oxides represented by O2 (where M is selected from at least one of the following groups: Co, Ni, Fe, Cr, Zn, and Ta, and c3 satisfies 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is selected from at least one of the following groups: Fe, Co, Ni, Cu, and Zn); LiMn2O4 with Li partially replaced by alkaline earth metal ions, etc., but not limited to these. The positive electrode can be Li metal.

[0162] The positive electrode active material layer may include the positive electrode conductive material and the positive electrode binder together with the aforementioned positive electrode active material.

[0163] In this context, the positive electrode conductive material is used to provide conductivity to the electrode, and it can be used without particular restriction as long as the positive electrode conductive material has electronic conductivity without causing chemical changes in the battery to be constructed. Specific examples include: graphite such as natural or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, and carbon fibers; 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 any one or a mixture of two or more thereof can be used.

[0164] In addition, positive electrode binders are used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one or a mixture of two or more thereof may be used.

[0165] The separator separates the negative and positive electrodes and provides a path for lithium ions to move. It can be used without particular limitations, as long as it is typically used in secondary batteries. In particular, separators with excellent electrolyte retention and low resistance to electrolyte ion movement are preferred. Specifically, porous polymer membranes can be used, such as those formed from polyolefin polymers like ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers; or laminates of two or more layers thereof. Additionally, typical porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, separators coated with ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used as single-layer or multi-layer structures.

[0166] Examples of electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used to prepare lithium secondary batteries.

[0167] Specifically, electrolytes can contain non-aqueous organic solvents and metal salts.

[0168] As non-aqueous organic solvents, aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0169] In particular, among carbonate-based organic solvents, cyclic carbonates, as high-viscosity organic solvents, have high dielectric constants, thereby effectively dissociating lithium salts. Therefore, ethylene carbonate and propylene carbonate, as cyclic carbonates, are preferred. Furthermore, since cyclic carbonates can be mixed in appropriate proportions with low-viscosity and low-dielectric-constant linear carbonates such as dimethyl carbonate and diethyl carbonate to prepare electrolytes with high conductivity, such cyclic carbonates are even more preferred.

[0170] Lithium salts can be used as metal salts, as they are readily soluble in non-aqueous electrolytes. For example, one or more of the following groups can be used as the anion of lithium salts: 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 - .

[0171] In order to improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, in addition to the electrolyte components mentioned above, one or more additives such as: halogenated alkyl carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted... Zolpidemone, N,N-substituted imidazolidinyl ether, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0172] An exemplary embodiment of the present invention provides a battery module comprising the secondary battery as a unit cell and a battery pack comprising the same. Because the battery module and battery pack comprise a secondary battery having high capacity, high rate performance, and cycle characteristics, they can be used as a power source for medium to large-sized devices selected from the group consisting of: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0173] Preferred embodiments will be presented below to aid in understanding the invention, but these embodiments are provided merely to illustrate the invention, and it will be apparent to those skilled in the art that various alternatives and variations are possible within the scope and spirit of the invention, and naturally, such alternatives and variations also fall within the scope of the appended claims.

[0174] Invention Model

[0175] <Preparation Example>

[0176] <Preparation of the negative electrode active material in Example 1>

[0177] Silicon powder was added to a 0.1M KOH aqueous solution at a mass ratio of 1:30. The mixture was then stirred at 40°C for 3 hours using a heating plate and a magnetic stir bar to perform etching. 0.1M HCl was added to neutralize the mixture, and then the mixture was filtered under reduced pressure to obtain a silicon-based active material.

[0178] Then, the silicon-based active material is dried in a drying oven at 60°C to obtain the etched porous silicon-based active material.

[0179] <Preparation of negative electrode active material in Comparative Example 1>

[0180] In Example 1 above, pulverized silicon powder that had not undergone etching treatment was used.

[0181] <Preparation of negative electrode active material in Comparative Example 2>

[0182] After vaporizing MG-Si silicon blocks into silane gas at high temperature, a chemical reaction is carried out, and the gas is then deposited on a substrate. Silicon-based active materials are then grown through crystal nucleation to prepare silicon-based active materials.

[0183] The negative electrode active materials described above each satisfy the physical properties shown in Table 1.

[0184]

[0185] For reference, in Comparative Examples 3 and 4 above, the concentration of the etching solution was adjusted. In Comparative Example 3, a 0.01M KOH aqueous solution was used, and etching was performed at 40°C for 3 hours to prepare a silicon-based active material. In Comparative Example 4, a 1M KOH aqueous solution was used, and etching was performed at 40°C for 3 hours to prepare a silicon-based active material.

[0186] <Preparation of the negative electrode>

[0187] A negative electrode slurry (solid concentration of 25% by weight) was prepared by adding a negative electrode active material containing silicon-based active materials from Table 1, a negative electrode conductive material, and polyacrylamide as a binder in a weight ratio of 80:10:10 to distilled water, which was used as a solvent to form the negative electrode slurry.

[0188] Specifically, the negative electrode conductive material is carbon black (specific surface area: 45 m²). 2 / g, diameter: 30 to 50 nm).

[0189] As a specific mixing method, after dispersing the negative electrode conductive material, binder and water at 2500 rpm for 30 minutes using a homogenizer, a silicon-based active material is added, and the resulting mixture is then dispersed at 2500 rpm for 30 minutes to prepare a negative electrode slurry.

[0190] At 85 mg / 25 cm 2 The loading amount is coated with negative electrode slurry on both surfaces of a copper current collector (thickness: 8 μm) as the negative electrode current collector layer, and the copper current collector is rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (total thickness of negative electrode active material layer: 33 μm), which is used as the negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0191] Manufacturing of Secondary Batteries

[0192] By using LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2O2 (average particle size (D) 50 A positive electrode slurry (solid concentration of 78 wt%) was prepared by adding carbon black (product name: Super C65, manufacturer: Timcal) as a conductive material and polyvinylidene fluoride (PVdF) as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent used to form the positive electrode slurry in a weight ratio of 97:1.5:1.5.

[0193] The positive electrode slurry was prepared at 537 mg / 25 cm⁻¹ 2 The loading amount was coated on both surfaces of the aluminum current collector (thickness: 12 μm) used as the positive electrode current collector. The aluminum current collector was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (total thickness of the positive electrode active material layer: 65 μm), thereby preparing the positive electrode (positive electrode thickness: 77 μm, porosity: 26%).

[0194] Lithium secondary batteries were prepared by inserting a polyethylene separator between the positive electrode and the negative electrode of each embodiment and comparative example, and injecting electrolyte therein.

[0195] The electrolyte is obtained by adding 3% by weight of vinylene carbonate based on the total weight of the electrolyte to an organic solvent in which fluoroethylene carbonate (FEC) and diethyl carbonate (DEC) are mixed in a volume ratio of 10:90, and adding LiPF6 as a lithium salt at a concentration of 1 M.

[0196] <Experimental Example>

[0197] Experimental Example 1: Results of Single Cell Lifetime Performance

[0198] The lifespan and capacity retention of secondary batteries containing negative electrodes manufactured in the examples and comparative examples were evaluated using an electrochemical charge-discharge apparatus. The secondary batteries were subjected to in-situ cycle testing at 4.2–3.0 V 1C / 0.5C, and capacity retention was measured every 50 cycles by charging / discharging the secondary batteries at 0.33C / 0.33C (4.2–3.0 V).

[0199] Capacity retention (%) = {(Discharge capacity in the Nth cycle) / (Discharge capacity in the 1st cycle)} × 100

[0200]

[0201] Experiment Example 2: Changes in the resistance of a single cell

[0202] In Experiment 1, after measuring the capacity retention rate by charging and discharging the secondary battery at 0.33C / 0.33C (4.2–3.0V) every 50 cycles, the resistance was measured by discharging the secondary battery at a 2.5C pulse at SOC 50, and the resistance increase rate was compared and analyzed.

[0203] For the measurement and evaluation of the resistance increase rate, the data were calculated for 200 cycles, and the results are shown in Table 3 below.

[0204]

[0205] As can be confirmed from Tables 2 and 3 above, in the cases of Examples 1 to 4, when the silicon-based active material is etched in an alkaline solution, anisotropic corrosion occurs, wherein the corrosion rate varies according to the direction of the crystal face, and the surface area of ​​the silicon-based active material meets the requirements of the present invention.

[0206] Specifically, experiments have confirmed that silicon-based active materials have an internal pore morphology, which gives them a larger surface area than particles of the same size. This allows for uniform lithium insertion and extraction reactions, reducing stress within the particles and minimizing micronization. Furthermore, during charging, the volume expands into the internal pores to mitigate overall particle volume changes, thereby improving battery lifespan.

[0207] In Examples 1 to 4 above, all have an internal porous structure. Specifically, the corrosion concentration and temperature conditions are kept the same as in Example 1, but the corrosion time is changed to form Examples 2 to 4. As can be seen from Table 1 above, the specific surface area and tap density can be adjusted by adjusting the corrosion time, and there is a trend of increasing specific surface area and decreasing tap density as the corrosion time increases.

[0208] Comparative Example 1 is the case where the etching process was not performed in Example 1, and in this case, it can be confirmed that the specific surface area and tap density are the same as those of the pulverized silicon-based active material. Although Comparative Example 2 shows an increased specific surface area compared to Comparative Example 1, it differs from the embodiments of this application in that it has an external uneven structure, and it can be confirmed that the tap density is also increased. That is, it can be confirmed that the tap density of Comparative Example 2 is significantly increased compared to Examples 1 to 4.

[0209] Comparative Example 3 corresponds to the case in which the same preparation process as in Example 1 was performed, but the tap density was lower than the lower limit of the tap density of the present invention; and Comparative Example 4 corresponds to the case in which the same preparation process as in Example 1 was performed, but the tap density exceeded the upper limit of the tap density of the present invention. In both cases, the concentration of the etching solution was adjusted, and in the case of Comparative Example 3, it was confirmed that the capacity retention rate decreased because the mechanical properties were weakened due to the excessive development of micropores inside the particles; and in the case of Comparative Example 4, it was confirmed that the capacity retention rate deteriorated because the internal pores were not sufficiently formed.

[0210] Comparative Examples 1 to 4 show that when the surface area range and tap density of the present invention are not met, the smaller specific surface area leads to a deterioration in the uniformity of the reaction, thus reducing the ability to alleviate stress and decrease micronization. Furthermore, the above experiments confirm that, compared to the examples where volume expansion occurs in the internal pores, volume expansion is uncontrollable, and the overall volume change of the particles is increased, resulting in a significant decrease in capacity retention.

Claims

1. A negative electrode active material, said negative electrode active material comprising a specific surface area of ​​5 m² 2 Silicon-based active materials of / g or higher The silicon-based active material described herein has a porous structure containing internal pores. The tap density of the silicon-based active material is 0.2 g / cm³. 3 Above and 0.8 g / cm 3 Below, and The silicon-based active material includes one or more selected from the group consisting of SiO x (x = 0) and SiO x (0 < x < 2), and based on 100 parts by weight of the silicon-based active material, contains more than 70 parts by weight of SiO x (x = 0).

2. The negative electrode active material according to claim 1, wherein the silicon-based active material has a grain size of less than 200 nm.

3. The negative electrode active material according to claim 1, wherein the silicon-based active material has a 15 μm... 2 / g or more and 80m 2 Specific surface area below / g.

4. The negative electrode active material according to claim 1, wherein the silicon-based active material has a density of 3 μm or more and 10 μm or less. 50 granularity.

5. A method for preparing a negative electrode active material, the method comprising: The silicon raw material was crushed; and Silicon-based active materials are formed by exposing pulverized silicon to an etching solution to etch the pulverized silicon. The corrosive solution is an alkaline solution.

6. The method according to claim 5, wherein the alkaline solution generates OH-. - It produces an aqueous solution with a pH greater than 7.

7. The method of claim 5, wherein forming a silicon-based active material by exposing the pulverized silicon to an etching solution to etch the pulverized silicon comprises: The pulverized silicon was exposed to the etching solution, and the resulting mixture was stirred at a temperature of 20°C to 120°C for 30 minutes to 50 hours.

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

9. A negative electrode composition, said negative electrode composition comprising: The negative electrode active material according to any one of claims 1 to 4; Negative conductive material; and Negative electrode adhesive.

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

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

12. A negative electrode for a lithium secondary battery, the negative electrode comprising: Negative current collector layer; and A negative electrode active material layer, wherein the negative electrode active material layer is disposed on one or both surfaces of the negative electrode current collector layer. The negative electrode active material layer comprises the negative electrode composition or its cured form according to claim 9.

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

14. A lithium secondary battery, the lithium secondary battery comprising: positive electrode; The negative electrode for a lithium secondary battery according to claim 12; A membrane disposed between the positive electrode and the negative electrode; and Electrolytes.

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