Anode active material, anode composition, anode for lithium secondary battery including the same, and lithium secondary battery including the anode

Abstract

The present application relates to a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0091113 filed with the Korean Intellectual Property Office on July 13, 2023, and Korean Patent Application No. 10-2024-0091946 filed with the Korean Intellectual Property Office on July 11, 2024, the entire contents of which are incorporated herein by reference.

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

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

[0004] Currently, a typical example of an electrochemical element that uses such electrochemical energy is a secondary battery, and the range of its use is tending to expand more and more.

[0005]

[0003] As technological development and demand for mobile devices increase, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life, and low self-discharge rate, have been commercialized and widely used.

[0004] In addition, active research is being conducted on methods for manufacturing high-density electrodes with higher energy density per unit volume as electrodes for such high-capacity lithium secondary batteries.

[0006] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material that inserts and extracts lithium ions from the positive electrode. Silicon-based particles with a large discharge capacity can be used as the negative electrode active material.

[0007] In particular, with the recent demand for high-density energy batteries, Si / C and SiO, which have capacities 10 times larger than graphite-based materials, are being used as negative electrode active materials. x However, while silicon-based compounds, which are high-capacity materials, have a higher capacity than conventional graphite, they suffer from a problem of rapid volume expansion during charging, which can disrupt the conductive path and reduce battery performance.

[0008] Therefore, in order to solve the problems when using silicon-based compounds as negative electrode active materials, various methods have been discussed, such as methods for controlling the driving potential, methods for additionally coating a thin film on the active material layer, methods for suppressing volume expansion itself, such as methods for controlling the particle size of the silicon-based compound, or methods for preventing the conductive path from being broken. However, these methods have limitations in their application because they may actually degrade battery performance, and there are still limitations in the commercialization of negative electrode batteries with a high content of silicon-based compounds.

[0009] To prevent the volume change during charging and discharging, a method of improving performance by forming a coating layer of carbon or oxide film on the surface of the silicon-based active material has been mainly studied. However, this method also has the problem that the sudden volume change that occurs at the interface between the coating layer and the silicon-based active material during charging and discharging causes cracks in the coating layer, exposing the silicon-based active material to the surface, which actually reduces cycle performance.

[0010] In particular, when the material of the coating layer is non-conductive, the resistance drops sharply.

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

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-080971 Summary of the Invention [Problem to be solved by the invention]

[0013] As a result of research into solving the problem of volume expansion of silicon-based active materials, it was found that when a coating layer having a specific active material phase and inactive material phase is included on the surface of the silicon-based active material, and in particular when the active material phase and inactive material phase form a double concentration gradient, it is possible to mitigate the volume change that occurs during charging and discharging, minimize the occurrence of cracks in the coating film, and suppress side reactions.

[0014] Therefore, the present application relates to a negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode, which can solve the above-mentioned problems. [Means for solving the problem]

[0015] One embodiment of the present specification provides an anode active material including a silicon-based active material and a coating layer surrounding at least a portion of an outer surface of the silicon-based active material, wherein the coating layer includes an active material phase and a non-active material phase, the non-active material phase in the coating layer has a concentration gradient in which the concentration decreases from the outer surface of the coating layer to the interior of the coating layer, and the active material phase in the coating layer has a concentration gradient in which the concentration increases from the outer surface of the coating layer to the interior of the coating layer.

[0016] Another embodiment provides a negative electrode composition including a negative electrode active material according to the present application, a negative electrode conductive material, and a negative electrode binder.

[0017] Another embodiment provides a negative electrode for a lithium secondary battery, comprising: 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 comprises the negative electrode composition according to the present application or a cured product thereof.

[0018] Finally, there is provided a lithium secondary battery comprising a positive electrode, a negative electrode for a lithium secondary battery according to the present application, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. [Effects of the Invention]

[0019] In the case of an anode active material according to one embodiment of the present invention, a coating layer having a specific active material phase and a non-active material phase is included on the surface of a silicon-based active material. In particular, the active material phase and the non-active material phase form a double concentration gradient, which reduces volume changes that occur during charge and discharge, minimizes cracking in the coating film, and suppresses side reactions.

[0020] When such a negative electrode active material is used, the initial capacity efficiency and cycle capacity retention rate can be improved by forming a coating layer having a specific double concentration gradient. In addition, in the case of a coating material with low conductivity, the resistance increase rate can be suppressed due to the relatively low coating material concentration.

[0021] That is, unlike conventional batteries that include a coating layer of carbon or oxide film, the concentration of silicon-based active material gradually increases toward the inside of the coating film, which prevents the coating layer from cracking and suppresses volume expansion and side reactions, thereby improving cycle life performance. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing a laminated structure of a negative electrode for a lithium secondary battery according to an embodiment of the present application. [Figure 2] FIG. 1 is a diagram showing a stack structure of a lithium secondary battery according to an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0023] Before describing the present invention, some terms will first be defined.

[0024] In this specification, unless otherwise specified, when a part "comprises" a certain component, it does not mean that it may further include other components, but does not exclude other components.

[0025] In this specification, "p to q" means a range of "not less than p and not more than q."

[0026] In this specification, the "specific surface area" is measured by the BET method, and specifically, is calculated from the amount of nitrogen gas adsorption at liquid nitrogen temperature (77 K) using a BELSORP-mino II manufactured by BEL Japan Co., Ltd. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above-mentioned measurement method.

[0027] In this specification, "Dn" refers to particle size distribution, and refers to the particle size at the n% point in the cumulative particle number distribution according to particle size. That is, D50 is the particle size (average particle size) at the 50% point in the cumulative particle number distribution according to particle size, D90 is the particle size at the 90% point in the cumulative particle number distribution according to particle size, and D10 is the particle size at the 10% point in the cumulative particle number distribution according to particle size. Meanwhile, the average particle size can be measured using the laser diffraction method. Specifically, the powder to be measured is dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac S3500). The particle size distribution is calculated by measuring the difference in the diffraction pattern according to particle size when the particles pass through a laser beam.

[0028] In one embodiment of the present application, the particle size or particle size may refer to the average diameter or typical diameter of the individual particles that make up the metal powder.

[0029] As used herein, when a polymer contains a certain monomer as a monomer unit, it means that the monomer participates in a polymerization reaction and is contained as a repeating unit in the polymer. As used herein, when a polymer contains a monomer, it is interpreted in the same way as when a polymer contains the monomer as a monomer unit.

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

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

[0032] The present invention will now be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the present invention, although the present invention may be embodied in various different forms and is not limited to the following description.

[0033] One embodiment of the present specification provides an anode active material including a silicon-based active material and a coating layer surrounding at least a portion of an outer surface of the silicon-based active material, wherein the coating layer includes an active material phase and a non-active material phase, the non-active material phase in the coating layer has a concentration gradient in which the concentration decreases from the outer surface of the coating layer to the interior of the coating layer, and the active material phase in the coating layer has a concentration gradient in which the concentration increases from the outer surface of the coating layer to the interior of the coating layer.

[0034] In the case of an anode active material according to one embodiment of the present invention, a coating layer having a specific active material phase and a non-active material phase is included on the surface of a silicon-based active material. In particular, the active material phase and the non-active material phase form a double concentration gradient, which reduces volume changes that occur during charge and discharge, minimizes cracking in the coating film, and suppresses side reactions.

[0035] When a concentration gradient is not formed as in the present application (that is, when the coating layer is a non-active material phase and the inside of the active material consists of an active material phase), during charging and discharging, the degree of volume expansion at the interface between the coating layer and the active material varies sharply, resulting in a decrease in structural stability, and the coating layer may crack and cause side reactions. However, in the present invention, a concentration gradient is formed in the coating layer, the degree of volume expansion at the interface can be reduced, the volume of the active material changes gradually, the safety of the coating layer can be enhanced, the coating layer can be prevented from cracking, and side reactions can be reduced.

[0036] In addition, the present application includes a coating layer having a specific active material phase and a non-active material phase on the surface of a silicon-based active material. In particular, by forming a double concentration gradient between the active material phase and the non-active material phase, unlike the conventional case where a silicon-based active material includes a coating layer of carbon or an oxide film or these form a concentration gradient, it can alleviate the volume change that occurs during charge and discharge, minimize crack generation in the coating film, suppress side reactions, improve the initial capacity efficiency and cycle capacity retention rate, and also suppress the resistance increase rate. In particular, when the coating layer of the silicon-based active material has only a concentration gradient of the non-active material phase, that is, when there is no coating layer of the active material phase, for example, when the silicon-based active material does not have a concentration gradient due to a doping element coating layer, the relaxation effect of the resistance increase due to the formation of the coating layer cannot be expected.

[0037] In one 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, it may contain 70 parts by weight or more of SiO x (x = 0).

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

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

[0040] In one embodiment of the present application, the silicon-based active material is SiO x It may further contain (0 < x < 2).

[0041] In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiO x It may contain 70 parts by weight or more, preferably 80 parts by weight or more, more preferably 90 parts by weight or more of (x = 0), and may contain 100 parts by weight or less, preferably 99 parts by weight or less, more preferably 95 parts by weight or less.

[0042] In one embodiment of the present application, particularly, pure silicon (Si) particles may be used as the silicon-based active material. Using pure silicon (Si) particles as the silicon-based active material means that, as described above, when based on 100 parts by weight of the total amount of the silicon-based active material, pure Si particles (SiO x [[ID=​​​​​​​​​In one embodiment of the present application, the silicon-based active material may contain metal impurities. In this case, the impurities may be metals that may be generally contained in silicon-based active materials, and specifically, may be contained in an amount of 0.1 parts by weight or less based on 100 parts by weight of the silicon-based active material.

[0045] Meanwhile, the average particle size (D50) of the silicon-based active material of the present invention may be 5 μm to 10 μm, specifically 5.5 μm to 8 μm, and more specifically 6 μm to 7 μm. If the average particle size is less than 5 μm, the specific surface area of ​​the particles increases excessively, resulting in an excessive increase in the viscosity of the negative electrode slurry. As a result, the particles constituting the negative electrode slurry are not dispersed smoothly. Furthermore, if the size of the silicon-based active material is excessively small, the contact area between the silicon particles and the conductive material decreases due to the complex of the conductive material and the binder in the negative electrode slurry, increasing the possibility of the conductive network being broken, resulting in a decrease in capacity retention. On the other hand, if the average particle size exceeds 10 μm, excessively large silicon particles are present, resulting in an uneven negative electrode surface, which causes non-uniform current density during charge and discharge. Furthermore, if the silicon particles are excessively large, the phase stability of the negative electrode slurry becomes unstable, resulting in a decrease in processability. This results in a decrease in the capacity retention of the battery.

[0046] In one embodiment of the present application, the silicon-based active material generally has a characteristic BET specific surface area. The BET specific surface area of ​​the silicon-based active material is preferably 0.01 m 2 / g~150.0m 2 / g, more preferably 0.1m 2 / g~100.0m 2 / g, particularly preferably 0.2m 2 / g~80.0m 2 / g, most preferably 0.2m 2 / g~18.0m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (using nitrogen).

[0047] In one embodiment of the present application, silicon-based active material can be, for example, in crystalline or amorphous form, and is preferably non-porous.Silicon particles are preferably spherical or shard particles.Alternatively, but less advantageously, silicon particles can have a fibrous structure or be in the form of silicon-containing film or coating.

[0048] In one embodiment of the present application, the silicon-based active material may have a non-spherical shape, and the sphericity is, for example, 0.9 or less, for example, 0.7 to 0.9, for example, 0.8 to 0.9, for example, 0.85 to 0.9.

[0049] In this application, the circularity is determined by the following formula 1-1, where A is the area and P is the perimeter.

[0050] [Formula 1-1] 4πA / P 2

[0051] Silicon-based active materials have significantly higher capacities than conventionally used graphite-based active materials, and attempts to use them are increasing. However, because of their high volume expansion during the charge / discharge process, their use is limited to mixing small amounts with graphite-based active materials.

[0052] Therefore, in the present invention, in order to improve capacity performance, only a silicon-based active material is used as the negative electrode active material, and the above-mentioned problems are solved by forming a coating layer having a double concentration gradient on the surface of the silicon-based active material, as described below, rather than adjusting the composition of the conductive material and binder to solve the above-mentioned problems.

[0053] In one embodiment of the present application, there is provided a negative electrode active material, wherein the coating layer includes an active material phase and a non-active material phase, the non-active material phase in the coating layer has a concentration gradient in which the concentration decreases from the outer surface to the interior of the coating layer, and the active material phase in the coating layer has a concentration gradient in which the concentration increases from the outer surface to the interior of the coating layer.

[0054] In the present application, the active material phase specifically means a phase that chemically reacts with lithium ions and participates in the electrode reaction, and the non-active material phase means a phase that does not react with lithium ions and does not participate in the electrode reaction.

[0055] In one embodiment of the present application, the inactive material phase provides a negative electrode active material represented by the following formula 1:

[0056] [Formula 1] Si x A 100-x In the formula 1, A is an O or C element, x means the atomic weight percentage value, and is 20 or more and 100 or less.

[0057] In one embodiment of the present application, there is provided a negative electrode active material, wherein the active material phase includes a silicon composite, the silicon composite includes silicon and a doping element contained in the silicon, and the doping element includes one or more selected from the group consisting of B and P.

[0058] In one embodiment of the present application, there is provided a negative electrode active material, wherein the doping element is contained in an amount of 0.01 parts by weight to 10 parts by weight, based on 100 parts by weight of the silicon composite.

[0059] In another embodiment, the doping element may be present in an amount of 0.01 to 10 parts by weight, preferably 0.02 to 8 parts by weight, more preferably 0.05 to 5 parts by weight, based on 100 parts by weight of the silicon composite.

[0060] As described above, by including the doping element in the active material phase in the above-mentioned weight parts, when the doping element is included in a negative electrode in the future, the conductivity can be increased and the resistance increase rate can be suppressed.

[0061] In one embodiment of the present application, the negative electrode active material satisfies the following formula 2:

[0062] [Formula 2] 10≦Ratio of silicon inside the negative electrode active material (at%)−Ratio of silicon on the surface of the negative electrode active material (at%)≦60 In one embodiment of the present application, the proportion of silicon inside the negative electrode active material refers to the proportion of silicon in the silicon-based active material or in a region in contact with the silicon-based active material in the coating layer, more specifically, the proportion of silicon in the region in contact with the silicon-based active material in the coating layer.

[0063] In one embodiment of the present application, the proportion of silicon on the surface of the negative electrode active material refers to a region of the silicon-based active material in contact with the coating layer, or a region of the coating layer on the opposite side to the silicon-based active material, more specifically, a region of the coating layer on the opposite side to the silicon-based active material.

[0064] In one embodiment of the present application, the negative electrode active material includes a silicon-based active material and a coating layer surrounding at least a portion of the outer surface of the silicon-based active material, and in this case, the coating layer may satisfy the following formula 3:

[0065] [Formula 3] 10≦Ratio of silicon inside the coating layer (at%) - Ratio of silicon on the surface of the coating layer (at%)≦60

[0066] That is, the negative electrode active material according to the present application forms a concentration gradient in the coating layer, and the negative electrode active material as a whole may satisfy formula 2, and specifically formula 3.

[0067] In one embodiment of the present application, the proportion of silicon inside the coating layer may refer to the proportion of silicon in a region in contact with or close to the silicon-based active material in the coating layer, and the proportion of silicon on the surface of the coating layer may refer to the proportion of silicon in a region on the opposite side of the coating layer that is in contact with the silicon-based active material.

[0068] In the present application, the thickness of the coating layer may be more than 0% and not more than 50% of the particle size (D50) of the silicon-based active material, preferably more than 0% and not more than 45%, and more preferably 5% or more and not more than 40%.

[0069] The particle size (D50) of the silicon-based active material means an average particle size or an average particle diameter. When the particle size falls within the above range, the ratio of the active material phase to the inactive material phase is appropriate, and the silicon-based active material has the characteristics of excellent capacity efficiency and a reduced resistance increase rate.

[0070] One embodiment of the present application provides a negative electrode composition comprising the negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0071] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode active material is 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

[0072] In another embodiment, the amount of the negative electrode active material may be 40 parts by weight or more, preferably 60 parts by weight or more, more preferably 65 parts by weight or more, and even more preferably 70 parts by weight or more, based on 100 parts by weight of the negative electrode composition, and may be 95 parts by weight or less, preferably 90 parts by weight or less, and more preferably 85 parts by weight or less.

[0073] The negative electrode composition according to the present application is characterized in that, even when a negative electrode active material having a significantly high capacity is used within the above range, the negative electrode active material has a specific specific surface area that can suppress the volume expansion rate during charge and discharge, and therefore, even when the negative electrode active material is contained within the above range, the negative electrode performance is not reduced and excellent output characteristics during charge and discharge are achieved.

[0074] While graphite-based compounds have traditionally been used exclusively as negative electrode active materials, attempts to incorporate silicon-based active materials into negative electrode active materials have been increasing in recent years in response to the growing demand for high-capacity batteries. However, even if the properties of silicon-based active materials are adjusted as described above, their volume can rapidly expand during charge and discharge, potentially damaging the conductive paths formed in the negative electrode active material layer.

[0075] Therefore, in one embodiment of the present application, the negative electrode conductive material may include one or more selected from the group consisting of dot-shaped conductive materials, sheet-shaped conductive materials, and linear conductive materials.

[0076] In one embodiment of the present application, the dot-like conductive material refers to a dot-like or spherical conductive material that can be used to improve the conductivity of a negative electrode, does not cause chemical changes, and has conductivity. Specifically, the dot-like 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 includes carbon black, which achieves high conductivity and excellent dispersibility.

[0077] In one embodiment of the present application, the point-like conductive material has a BET specific surface area of ​​40 m 2 / g or more 70m 2 / g or less, preferably 45m 2 / g or more 65m 2 / g or less, more preferably 50m 2 / g or more 60m 2 / g or less.

[0078] In one embodiment of the present application, the dot-like conductive material may have 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.

[0079] In particular, when the content of functional groups in the dot-like conductive material satisfies the above range, the functional groups are present on the surface of the dot-like conductive material, and when water is used as a solvent, the dot-like conductive material can be smoothly dispersed in the solvent. In particular, by using a specific silicon-based active material, the present invention can reduce the content of functional groups in the dot-like conductive material, thereby achieving an excellent effect of improving dispersibility.

[0080] In one embodiment of the present application, the silicon-based active material is characterized by including a dot-like conductive material having a functional group content within the above range, and the content of the functional group can be adjusted depending on the degree of heat treatment of the dot-like conductive material.

[0081] In one embodiment of the present application, the particle size of the dotted conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

[0082] In one embodiment of the present application, the conductive material may include a sheet-shaped conductive material.

[0083] The sheet-like conductive material can improve conductivity by increasing surface contact between silicon particles in the negative electrode and can also prevent the conductive path from being broken due to volume expansion. The sheet-like conductive material can be referred to as a plate-like conductive material or a bulk-like conductive material.

[0084] In one embodiment of the present application, the sheet-like conductive material may include at least one selected from the group consisting of platelet graphite, graphene, graphene oxide, and graphite flakes, and may preferably be platelet graphite.

[0085] In one embodiment of the present application, the average particle size (D50) of the sheet-like conductive material may be 2 μm to 7 μm, specifically 3 μm to 6 μm, and more specifically 3.5 μm to 5 μm. When the above range is satisfied, the sufficient particle size does not cause an excessive increase in viscosity of the negative electrode slurry and dispersion is easy. Therefore, when dispersion is performed using the same device and for the same time, the dispersion effect is excellent.

[0086] In one embodiment of the present application, the sheet-shaped conductive material provides a negative electrode composition having a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less.

[0087] In one embodiment of the present application, the sheet-shaped conductive material may be a sheet-shaped conductive material having a high BET specific surface area, or a sheet-shaped conductive material having a low specific surface area.

[0088] In one embodiment of the present application, the sheet-like conductive material can be a sheet-like conductive material with a high specific surface area or a sheet-like conductive material with a low specific surface area, without any restrictions. However, since dispersion of the sheet-like conductive material according to the present application can have some effect on electrode performance, it is particularly preferable to use a sheet-like conductive material with a low specific surface area in which dispersion does not cause problems.

[0089] In one embodiment of the present application, the sheet-shaped conductive material has a BET specific surface area of ​​0.25 m 2 / g or more.

[0090] In another embodiment, the sheet-shaped conductive material has a BET specific surface area of ​​1 m 2 / g or more 500m 2 / g or less, preferably 5m 2 / g or more 300m 2 / g or less, more preferably 5m 2 / g or more 250m 2 / g or less.

[0091] The sheet-shaped conductive material according to the present application may be a sheet-shaped conductive material with a high specific surface area or a sheet-shaped conductive material with a low specific surface area.

[0092] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a high specific surface area, and a BET specific surface area of ​​50 m 2 / g or more 500m 2 / g or less, preferably 80m 2 / g or more 300m 2 / g or less, more preferably 100m 2 / g or more 300m 2 / g or less.

[0093] In another embodiment, the sheet-shaped conductive material is a sheet-shaped conductive material having a low specific surface area, and a BET specific surface area of ​​1 m 2 / g or more 40m 2 / g or less, preferably 5m 2 / g or more 30m 2 / g or less, more preferably 5m 2 / g or more 25m 2 / g or less.

[0094] Other conductive materials include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include multiple carbon nanotube units. Specifically, unless otherwise specified, the term "bundle type" refers to a secondary shape in which multiple carbon nanotube units are arranged side by side or entangled with their longitudinal axes aligned in substantially the same direction, forming a bundle or rope-like structure. The carbon nanotube units each have a cylindrical graphite sheet with a nanometer-sized diameter and an sp2 bonding structure. Depending on the curved angle and structure of the graphite sheet, the carbon nanotube unit may exhibit conductive or semiconductive properties. Compared to entangled carbon nanotubes, the bundled carbon nanotubes can be more uniformly dispersed during negative electrode fabrication, smoothly forming a conductive network within the negative electrode, thereby improving the conductivity of the negative electrode.

[0095] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material is 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

[0096] In another embodiment, the negative electrode conductive material may be included in an amount of 0.1 parts by weight to 40 parts by weight, preferably 0.2 parts by weight to 30 parts by weight, more preferably 0.4 parts by weight to 25 parts by weight, and most preferably 0.4 parts by weight to 10 parts by weight, based on 100 parts by weight of the negative electrode composition.

[0097] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material includes a sheet-shaped conductive material and a linear conductive material.

[0098] In one embodiment of the present application, there is provided a negative electrode composition, wherein the negative electrode conductive material comprises 80 parts by weight or more and 99.9 parts by weight or less of the sheet-like conductive material and 0.1 parts by weight or more and 20 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0099] In another embodiment, the negative electrode conductive material may contain 80 parts by weight or more and 99.9 parts by weight or less, preferably 85 parts by weight or more and 99.9 parts by weight or less, and more preferably 95 parts by weight or more and 98 parts by weight or less of the sheet-like conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0100] In another embodiment, the negative electrode conductive material may contain 0.1 parts by weight or more and 20 parts by weight or less, preferably 0.1 parts by weight or more and 15 parts by weight or less, and more preferably 0.2 parts by weight or more and 5 parts by weight or less of the linear conductive material, based on 100 parts by weight of the negative electrode conductive material.

[0101] In one embodiment of the present application, the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, and by satisfying the above-mentioned composition and proportions, the battery does not have a significant effect on the life characteristics of conventional lithium secondary batteries. In particular, when the negative electrode conductive material includes a sheet-like conductive material and a linear conductive material, the battery has the following characteristics: there are more points at which charging and discharging are possible, output characteristics are excellent at a high C-rate, and the amount of high-temperature gas generated is reduced.

[0102] In one embodiment of the present application, the negative electrode conductive material may be made of a linear conductive material.

[0103] 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 migration within the electrode.

[0104] In one embodiment of the present application, when the negative electrode conductive material includes only a linear conductive material, the negative electrode conductive material may be included in an amount of 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.

[0105] The negative electrode conductive material according to the present 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 the present application serves to form a contact between the silicon-based active material, which experiences a large volume expansion of the electrode upon charging and discharging, while the positive electrode conductive material serves to act as a buffer during rolling and to impart some conductivity, and thus has a completely different structure and role from the negative electrode conductive material of the present invention.

[0106] Furthermore, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from conductive materials applied to graphite-based active materials. That is, conductive materials used in electrodes having graphite-based active materials simply have smaller particles than the active material, and therefore have the properties of improving output characteristics and imparting some conductivity, and are completely different in structure and role from negative electrode conductive materials applied together with silicon-based active materials as in the present invention.

[0107] In one embodiment of the present application, the sheet-like conductive material used as the negative electrode conductive material has a structure and function different from that of a carbon-based active material generally used as a 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 dotted shape to facilitate the storage and release of lithium ions.

[0108] In contrast, the sheet-like conductive material used as the negative electrode conductive material is a material having a sheet or plate shape and can be expressed as plate-like graphite. That is, it is a material contained in the negative electrode active material layer to maintain a conductive path, and does not play a role in storing and releasing lithium, but refers to a material in a sheet shape to ensure a conductive path inside the negative electrode active material layer.

[0109] That is, in this application, the term "platy graphite is used as a conductive material" means that it is processed into a sheet or plate 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 contained therein has high capacity characteristics for storing and releasing lithium, and serves to store and release all lithium ions transferred from the positive electrode.

[0110] In contrast, in the present application, the term "carbon-based active material is used as an active material" means that the carbon-based active material is processed into a dotted or spherical shape and used as a material that stores or releases lithium.

[0111] That is, in one embodiment of the present application, the carbon-based active material, artificial graphite or natural graphite, is dot-shaped and has a BET specific surface area of ​​0.1 m 2 / g or more 4.5m 2 The sheet-shaped conductive material, plate-shaped graphite, may be in the form of a sheet and have a BET specific surface area of ​​5 m 2 / g or more.

[0112] In one embodiment of the present application, the negative electrode binder may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and substances in which hydrogen is substituted with Li, Na, Ca, or the like, or may include various copolymers thereof.

[0113] The negative electrode binder according to one embodiment of the present application plays a role in holding the active material and the conductive material together to prevent distortion and deformation of the negative electrode structure when the volume of the silicon-based active material expands and relaxes. As long as the binder fulfills the above role, any common binder can be used. Specifically, a water-based binder may be used, and more specifically, a PAM-based binder may be used.

[0114] In one embodiment of the present application, the amount of the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, and more preferably 20 parts by weight or less, based on 100 parts by weight of the negative electrode composition, or may be 5 parts by weight or more, or 10 parts by weight or more.

[0115] One embodiment of the present 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 surfaces of the negative electrode current collector layer, the negative electrode active material layer including the negative electrode composition according to the present application or a cured product thereof.

[0116] 1 is a diagram showing the laminated structure of a negative electrode for a lithium secondary battery according to one embodiment of the present application. Specifically, a negative electrode for a lithium secondary battery 100 can be seen, which includes a negative electrode active material layer 20 on one side of a negative electrode current collector layer 10. While FIG. 1 shows the negative electrode active material layer formed on one side, it may be formed on both sides of the negative electrode current collector layer.

[0117] In one embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by applying a negative electrode slurry containing the negative electrode composition to one or both surfaces of a negative electrode current collector layer and drying the applied slurry.

[0118] In this case, the negative electrode slurry may include the above-described negative electrode composition and a slurry solvent.

[0119] In one embodiment of the present application, the solid content of the negative electrode slurry may be 5% or more and 40% or less.

[0120] In another embodiment, the solid content of the negative electrode slurry may be in the range of 5% to 40%, preferably 7% to 35%, more preferably 10% to 30%.

[0121] The solid content of the negative electrode slurry refers to the content of the negative electrode composition contained in the negative electrode slurry, and may refer to the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

[0122] When the solid content of the negative electrode slurry satisfies the above range, the viscosity during the formation of the negative electrode active material layer is suitable, and particle aggregation of the negative electrode composition is minimized, thereby enabling the negative electrode active material layer to be efficiently formed.

[0123] In one embodiment of the present application, the slurry solvent can be any solvent that can dissolve the negative electrode composition, and specifically, water or N-methyl-2-pyrrolidone (NMP) may be used.

[0124] In one embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. Such a negative electrode current collector layer is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy may be used. Furthermore, the surface may be formed with fine irregularities to strengthen the binding force of the negative electrode active material, and the negative electrode current collector layer may be used in various forms such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0125] In one embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, and the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

[0126] However, the thickness may vary depending on the type and application of the negative electrode used, and is not limited thereto.

[0127] In one embodiment of the present application, the porosity of the negative electrode active material layer may be in the range of 10% or more and 60% or less.

[0128] In another embodiment, the porosity of the negative electrode active material layer may 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.

[0129] The porosity varies depending on the composition and content of the silicon-based active material, conductive material, and binder contained in the negative electrode active material layer. In particular, the silicon-based active material and conductive material according to the present application are contained in specific compositions and content portions to satisfy the above range, thereby providing an electrode with suitable ranges of electrical conductivity and resistance.

[0130] One embodiment of the present application provides a lithium secondary battery including 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.

[0131] 2 is a diagram showing a laminated structure of a lithium secondary battery according to one embodiment of the present application. Specifically, a lithium secondary battery anode 100 including an anode active material layer 20 on one side of an anode current collector layer 10 can be seen, and a lithium secondary battery cathode 200 including a cathode active material layer 40 on one side of a cathode current collector layer 50 can be seen, and the lithium secondary battery anode 100 and lithium secondary battery cathode 200 are shown stacked with a separator 30 interposed therebetween.

[0132] A secondary battery according to an embodiment of the present specification may include, in particular, the negative electrode for a lithium secondary battery described above. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the negative electrode has been described above, detailed description thereof will be omitted.

[0133] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0134] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance the adhesive strength of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0135] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; a lithium iron oxide such as LiFe3O4; 1+c1 Mn 2-c1 O4 (0≦c1≦0.33), lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, V2O5, and Cu2V2O7; chemical formula LiNi 1-c2 M c2 Ni-site type lithium nickel oxide represented by the chemical formula LiMnO2 (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.3 is satisfied); 2-c3 M c3 Examples of suitable lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfying 0.01≦c3≦0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); and LiMn2O4, in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be Li metal.

[0136] The positive electrode active material layer may contain a positive electrode conductive material and a positive electrode binder in addition to the above-described positive electrode active material.

[0137] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be any material that has electronic conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0138] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used singly or in combination.

[0139] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. It is particularly preferable that the separator exhibits low resistance to electrolyte ion migration and excellent electrolyte humidification. Specifically, porous polymer films, such as those made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. To ensure heat resistance or mechanical strength, a separator coated with a ceramic component or a polymeric material may be used, and may be selectively used as a single-layer or multi-layer structure.

[0140] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries.

[0141] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0142] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0143] In particular, among the carbonate organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, can be preferably used as high-viscosity organic solvents, because they have a high dielectric constant and dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and therefore such cyclic carbonates can be more preferably used.

[0144] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0145] In addition to the constituent components of the electrolyte, the electrolyte may further include one or more additives, such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, in order to improve the life characteristics of the battery, suppress a decrease in battery capacity, and improve the discharge capacity of the battery.

[0146] According to one embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and therefore can be used as a power source for medium- to large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0147] Below, preferred examples are presented to help understand the present invention. However, the following examples are merely for the purpose of illustrating the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, and it is natural that such changes and modifications fall within the scope of the appended claims. [Example]

[0148] <Production example> <Production of silicon-based active materials> Example 1 The P-doped silicon microparticles were subjected to rapid thermal treatment in an oxidizing atmosphere to produce a negative electrode active material with a P and O concentration gradient in the coating layer.

[0149] Specifically, silicon particles with a D50 of 5 μm were uniformly mixed with P2O5 particles in a mass ratio of 10:1, and then heat-treated in an Ar atmosphere to produce P-doped silicon particles. At this time, Ar was flowed at 1000 sccm and maintained at 900°C for 10 hours.

[0150] The P-doped silicon particles were then rapidly oxidized in a 100% oxygen atmosphere to form an oxide concentration gradient in the surface coating layer. The heating and cooling processes for rapid oxidation were performed in an Ar atmosphere, and oxidation was carried out at 700°C for 1 hour while flowing oxygen at 500 sccm. The coating layer was 50 nm thick, and the compositional difference between the active material phase inside and outside the coating layer was 20%.

[0151] <Example 2> The surface of P-doped silicon microparticles was etched and coated with C to produce a negative electrode active material with a P and C concentration gradient in the coating layer.

[0152] P-doped silicon was prepared in the same manner as in Example 1, and the silicon-based active material was etched with a 1.0 M KOH solution to form pores on the surface. The porosity tended to decrease from the surface to the interior. The surface of the silicon-based active material was then coated with C using chemical vapor deposition (CVD), filling the pores with C and creating a concentration gradient within the coating layer. The chemical vapor deposition was performed at 800°C for 2 hours while flowing acetylene gas at a rate of 40 mL / min. The coating layer was 50 nm thick, and the compositional difference between the exterior and interior of the coating layer was 16%.

[0153] Example 3 The B-doped silicon microparticles were subjected to rapid thermal treatment in an oxidizing atmosphere to produce a negative electrode active material with a B and O concentration gradient in the coating layer.

[0154] Specifically, silicon particles with a D50 of 5 μm were uniformly mixed with B2O3 particles in a mass ratio of 10:1, followed by heat treatment in a CO2 atmosphere to produce B-doped silicon particles. CO2 was flowed at 1000 sccm, and the mixture was maintained at 700°C for 24 hours. Rapid oxidation was then performed in the same manner as in Example 1 to produce an anode active material with a concentration gradient in the coating layer. The coating layer was 50 nm thick, and the compositional difference between the active material phase outside and inside the coating layer was 20%.

[0155] Example 4 The surface of the B-doped silicon microparticles was etched and coated with C to produce a negative electrode active material having a concentration gradient of B and C in the coating layer.

[0156] B-doped silicon particles were prepared in the same manner as in Example 3, and a negative active material having a concentration gradient in the coating layer was prepared by chemical vapor deposition in the same manner as in Example 2. The coating layer had a thickness of 50 nm, and the composition difference between the active material phase inside and outside the coating layer was 16%.

[0157] <Example 5> By subjecting P-doped silicon microparticles to rapid thermal treatment in an oxidizing atmosphere, a negative electrode active material was produced in which the coating layer had a P and O concentration gradient and the thickness of the coating layer exceeded 50% of the silicon particle size.

[0158] Specifically, P-doped silicon particles were prepared in the same manner as in Example 1, and an oxidation process was performed in the same manner as in Example 1, except that the oxidation process was performed at 1200°C for 10 hours, to prepare a negative electrode active material.

[0159] <Comparative Example 1> Undoped silicon microparticles were gradually oxidized to prepare a negative electrode active material having a coating layer without a concentration gradient.

[0160] Specifically, silicon particles with a D50 of 5 μm were used, and the heating, heat treatment, and cooling processes were all carried out in an air atmosphere. The heating rate was 5°C / min, and cooling was carried out naturally.

[0161] The low oxygen concentration and heat treatment temperature allowed the oxidation process to proceed slowly, and sufficient oxygen diffusion resulted in the formation of a coating layer without a concentration gradient. The coating layer was made of SiO2 and had a thickness of 50 nm.

[0162] <Comparative Example 2> After ball milling the MG-silicon, a silicon-based active material without a coating layer was produced by HF etching.

[0163] Specifically, a wet milling method was used using n-hexane as a solvent, and zirconia (ZrO2) balls were used. The mass ratio of silicon precursor to balls was 1:40, and the milling was carried out for 30 minutes. The active material was then placed in a 0.03M HF solution and stirred at 200 rpm for 30 minutes to remove the surface oxide layer. The D50 of the produced negative electrode active material was 5 μm.

[0164] <Comparative Example 3> Silicon microparticles were doped with phosphorus from the surface to produce a negative electrode active material with a doping element concentration gradient.

[0165] That is, P-doped silicon particles were produced in the same manner as in Example 1, but without undergoing an oxidation process, and a coating layer consisting of a non-active material phase was not present. In this case, the composition difference of the doping element between the surface and the interior of the active material was 0.3%.

[0166] <Comparative Example 4> Undoped silicon microparticles were subjected to rapid thermal treatment in an oxidizing atmosphere to produce a negative electrode active material with a concentration gradient of Si and O in the coating layer.

[0167] Specifically, silicon particles with a D50 of 5 μm were rapidly oxidized in a 100% oxygen atmosphere to form an oxide concentration gradient in the surface coating layer. The heating and cooling processes for rapid oxidation were carried out in an Ar atmosphere, and oxidation was carried out at 700°C for 1 hour while flowing oxygen at 500 sccm. The coating layer was 50 nm thick, and the compositional difference between the inside and outside of the coating layer was 20%.

[0168] <Production of negative electrodes> The negative electrode active material containing the silicon-based active material, the first conductive material, the second conductive material, and polyacrylamide as a binder were added to distilled water as a solvent for forming a negative electrode slurry in a weight ratio of 80:9.6:0.4:10 to prepare a negative electrode slurry (solid concentration 25 wt %).

[0169] Specifically, the first conductive material is plate-shaped graphite (specific surface area: 17 m 2 / g, average particle size (D50): 3.5 μm), and the second conductive material was SWCNT.

[0170] As a 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 30 minutes to prepare a negative electrode slurry.

[0171] The negative electrode current collector layer was made of a copper current collector (thickness: 8 μm) and the negative electrode slurry was applied to both sides of the copper current collector at a rate of 85 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a negative electrode active material layer (thickness: 33 μm), which was used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity: 40.0%).

[0172] <Secondary battery manufacturing> LiNi as the positive electrode active material 0.6 Co 0.2 Mn 0.2 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 were added in a weight ratio of 97:1.5:1.5 to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry (solid concentration: 78 wt%).

[0173] The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) at a rate of 537 mg / 25 cm. 2 The coated layer was rolled and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode active material layer (thickness: 65 μm) to prepare a positive electrode (thickness: 77 μm, porosity: 26%).

[0174] A polyethylene separator was interposed between the positive electrode and the negative electrode of each of the examples and comparative examples, and an electrolyte was injected into the separator to prepare a lithium secondary battery.

[0175] The electrolyte was an organic solvent made by mixing fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) in a volume ratio of 10:90, to which 3 wt % vinylene carbonate was added based on the total weight of the electrolyte, and LiPF6 was added as a lithium salt at a concentration of 1M.

[0176] <Experimental Example> <Experimental Example 1: Mono-cell life performance results> The secondary batteries including the negative electrodes prepared in the Examples and Comparative Examples were subjected to a lifespan evaluation using an electrochemical charger / discharger to evaluate the capacity retention. The secondary batteries were subjected to an in-situ cycle test at 4.2-3.0 V, 1 C / 0.5 C, and the capacity retention was measured every 50 cycles by charging / discharging at 0.33 C / 0.33 C (4.2-3.0 V). The results are shown in Table 1 below.

[0177] Lifetime retention rate (%) = {(discharge capacity at Nth cycle) / (discharge capacity at first cycle)} × 100

[0178] [Table 1]

[0179] <Experimental Example 2: Resistance change of mono cell> In Experimental Example 1, the capacity retention rate was measured by charging and discharging at 0.33C / 0.33C (4.2-3.0V) every 50 cycles during the test, and then the resistance was measured by discharging at 2.5C pulse at SOC50, and the resistance increase rate was compared and analyzed.

[0180] The data at 200 cycles for each of the resistance increase rates were calculated, and the results are shown in Table 2 below.

[0181] [Table 2]

[0182] In the case of an anode active material according to one embodiment of the present invention, a coating layer having a specific active material phase and a non-active material phase is provided on the surface of a silicon-based active material, and in particular, the active material phase and the non-active material phase form a dual concentration gradient, which mitigates volume changes that occur during charge and discharge, minimizes cracking in the coating film, and suppresses side reactions. This was confirmed through life evaluation and resistance evaluation. That is, the formation of a coating layer having a specific dual concentration gradient can improve initial capacity efficiency and cycle capacity retention, and in the case of a coating material with low conductivity, the relatively low coating material concentration can suppress the rate of resistance increase.

[0183] Comparative Example 1 is a silicon-based active material having a coating layer consisting only of a non-active material phase (SiO2), Comparative Example 2 is a case where there is no coating layer, Comparative Example 3 is a case where there is only a concentration gradient of the doping element and corresponds to a structure where there is no coating layer of the non-active material phase, and Comparative Example 4 is a case where there is only a concentration gradient of the non-active material phase (SiO2) and corresponds to a structure where there is no coating layer of the active material phase.

[0184] As can be seen from Tables 1 and 2, Comparative Examples 1 to 4 are inferior in lifespan and resistance characteristics, and although there may be some effect of increasing conductivity, it was confirmed that the performance is inferior to that of the Examples due to structural collapse and side reactions caused by volume expansion.

[0185] For reference, even if the coating layer contains an active material phase and a non-active material phase, and the non-active material phase in the coating layer does not result in the synthesis of a negative electrode active material having a concentration gradient in which the concentration increases from the outer surface to the inside of the coating layer, and even if such a structure is present, it is expected that the life and resistance will be reduced compared to the negative electrode active material having the configuration of the present invention. [Explanation of symbols]

[0186] 10 Negative electrode current collector layer 20...Negative electrode active material layer 30 Separator 40...Cathode active material layer 50 Positive electrode current collector layer 100 ···Negative electrode for lithium secondary battery 200 ···Positive electrode for lithium secondary battery

Claims

1. A negative electrode active material comprising: a silicon-based active material; and a coating layer surrounding at least a portion of an outer surface of the silicon-based active material, the coating layer includes an active material phase and a non-active material phase; the inactive material phase in the coating layer has a concentration gradient in which the concentration decreases from the outer surface of the coating layer to the interior of the coating layer, The active material phase in the coating layer has a concentration gradient in which the concentration increases from the outer surface of the coating layer to the interior of the coating layer.

2. The inactive material phase has the following formula 1: [Formula 1] Yes ｘ A １００－ｘ In the formula 1, A is an O or C element; x represents an atomic weight percentage value of 20 to 100; The negative electrode active material according to claim 1 , represented by the formula:

3. the active material phase comprises a silicon composite; The silicon composite includes silicon and a doping element contained in the silicon, The negative electrode active material according to claim 1 , wherein the doping element comprises at least one selected from the group consisting of B and P.

4. The negative electrode active material of claim 1 , wherein the thickness of the coating layer is more than 0% and not more than 50% of the particle size (D50) of the silicon-based active material.

5. The silicon-based active material is SiO ｘ (x=0), and based on 100 parts by weight of the silicon-based active material, the SiO ｘ The negative electrode active material according to claim 1 , comprising 70 parts by weight or more of (x=0).

6. The negative electrode active material of claim 3 , wherein the doping element is present in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the silicon composite.

7. The negative electrode active material is a compound represented by the following formula 2: [Formula 2] 10≦Ratio of silicon inside the negative electrode active material (at %)−Ratio of silicon on the surface of the negative electrode active material (at %)≦60 The negative electrode active material according to claim 1 , which satisfies the above formula:

8. A negative electrode composition comprising the negative electrode active material according to any one of claims 1 to 7, a negative electrode conductive material, and a negative electrode binder.

9. The negative electrode composition according to claim 8 , wherein the negative electrode active material is present in an amount of 40 parts by weight or more based on 100 parts by weight of the negative electrode composition.

10. The negative electrode composition according to claim 8 , wherein the negative electrode conductive material comprises a sheet-shaped conductive material and a linear conductive material.

11. 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, The negative electrode for a lithium secondary battery, wherein the negative electrode active material layer comprises the negative electrode composition according to claim 8 or a cured product thereof.

12. the thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less, 12. The negative electrode for a lithium secondary battery according to claim 11, wherein the thickness of the negative electrode active material layer is 5 μm or more and 500 μm or less.

13. A positive electrode and The negative electrode for a lithium secondary battery according to claim 11, a separator provided between the positive electrode and the negative electrode for the lithium secondary battery; Electrolytes, A lithium secondary battery comprising:

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