Anode active material, anode including said anode active material, secondary battery including said anode, and method for producing said anode active material

Abstract

The present invention relates to a negative electrode active material, a negative electrode including the negative electrode active material, a secondary battery including the negative electrode, and a method for producing the negative electrode active material.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2021-0159927, filed with the Korean Intellectual Property Office on November 19, 2021, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a negative electrode active material, a negative electrode including the negative electrode active material, a secondary battery including the negative electrode, and a method for producing the negative electrode active material. [Background technology]

[0003] In recent years, with the rapid spread of battery-powered electronic devices such as mobile phones, laptops, and electric vehicles, the demand for secondary batteries that are small, lightweight, and have relatively high capacity has been rapidly increasing. In particular, lithium secondary batteries, which are lightweight and have high energy density, have attracted attention as power sources for portable devices. For this reason, active research and development efforts are being made to improve the performance of lithium secondary batteries.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. The positive electrode and the negative electrode may have active material layers formed on current collectors, each containing a positive electrode active material and a negative electrode active material. Generally, the positive electrode uses a lithium-containing metal oxide such as LiCoO2 or LiMn2O4 as the positive electrode active material, and the negative electrode uses a lithium-free carbon-based active material or a silicon-based active material as the negative electrode active material.

[0005] Silicon-based negative electrode active materials have been attracting attention due to their higher capacity and superior fast charging characteristics compared to carbon-based active materials. However, silicon-based active materials have the disadvantage of low initial efficiency due to their large irreversible capacity caused by large volume expansion / contraction during charging / discharging.

[0006] To overcome this, a commonly known approach is to maximize the performance of secondary batteries containing silicon-based active materials by doping silicon particles with a Group 13 or 15 element. However, because the doping of the element involves directly adding a doping source to the raw material or chemically synthesizing the element, the total content of the doping element contained in the silicon particles can be freely adjusted, but the doping element is uniformly distributed throughout the silicon particles. While increasing the total content of the doping element has the effect of improving the battery cycle, it also has the problem of reducing the discharge capacity.

[0007] Therefore, there is a need to develop a method for improving the discharge capacity, efficiency, and lifespan of silicon-based active materials. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent No. 10-1308948 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention relates to a negative electrode active material, a negative electrode including the negative electrode active material, a secondary battery including the negative electrode, and a method for producing the negative electrode active material. [Means for solving the problem]

[0010] One embodiment of the present invention provides an anode active material having a silicon-based composite including: silicon-based particles; and one or more elements selected from the group consisting of B and P distributed within the silicon-based particles; wherein the silicon-based particles include 95 parts by weight or more of Si based on a total of 100 parts by weight of the silicon-based particles, and the element has a concentration gradient that increases from the center to the surface of the silicon-based composite.

[0011] One embodiment of the present invention provides a method for producing a negative electrode active material, the method including the steps of: preparing metallic silicon; preparing a doping source including one or more compounds selected from the group consisting of a B-containing compound and a P-containing compound; and mixing the metallic silicon and the doping source, followed by heat treatment at a temperature equal to or higher than the boiling point of the doping source.

[0012] One embodiment of the present invention provides a negative electrode comprising the negative electrode active material. One embodiment of the present invention provides a secondary battery including the negative electrode. [Effects of the Invention]

[0013] The anode active material according to the present invention includes a silicon-based composite in which silicon particles are doped with B or P, and the doping element has a concentration gradient that increases from the center to the surface of the silicon-based composite. This maximizes the diffusion of Li ions on the composite surface while minimizing capacity loss, resulting in a superior initial discharge capacity compared to a uniformly doped active material.

[0014] In addition, the method for manufacturing an anode active material according to the present invention diffuses atoms from a doping source into adjacent silicon particles having micron-sized units, and as described above, the doping element can have a concentration gradient from high to low from the surface to the interior. Furthermore, since it is not a chemical synthesis method, it has the advantage of being easy to mass-produce. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present specification will be explained in more detail below. In this specification, when a part "comprises" a certain component, this means that it may further include other components, rather than excluding other components, unless otherwise specified.

[0016] In this specification, when a member is said to be located "on" another member, this includes not only the case where the member is in contact with the other member, but also the case where another member is present between the two members.

[0017] The terms and words used in this specification should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0018] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0019] In this specification, the crystallinity of the structure contained in the negative electrode active material may be confirmed by X-ray diffraction analysis. The X-ray diffraction analysis may be performed using an XRD (X-ray diffraction) analysis device (product name: D4-endavor, manufacturer: Bruker), and in addition to the above device, any device commonly used in the art may be appropriately adopted.

[0020] In this specification, the presence or absence of elements in the negative electrode active material and the content of the elements can be confirmed by ICP analysis, which can be performed using an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300).

[0021] In this specification, the average particle size (D 50 The average particle size (D) can be defined as the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve (graph curve of particle size distribution diagram). 50 ) can be measured, for example, by using a laser diffraction method. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0022] Preferred embodiments of the present invention will be described in detail below. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0023] negative electrode active material One embodiment of the present invention provides an anode active material having a silicon-based composite including: silicon-based particles; and one or more elements selected from the group consisting of B and P distributed within the silicon-based particles; wherein the silicon-based particles include 95 parts by weight or more of Si based on a total of 100 parts by weight of the silicon-based particles, and the element has a concentration gradient that increases from the center to the surface of the silicon-based composite.

[0024] Generally, silicon particles are doped with B or P to maximize the performance of secondary batteries containing silicon-based negative electrode active materials. However, because the B or P doping is performed by directly adding the doping source to the raw material or by chemical synthesis, the total content of the doping element contained in the silicon particles can be freely adjusted, but the doping element is uniformly distributed throughout the silicon particles. Increasing the total content of the doping element improves the battery cycle life, but also reduces the discharge capacity.

[0025] To address this issue, the present invention provides an anode active material in which a doping element is concentrated on the surface of silicon particles, thereby maximizing lithium ion diffusion on the surface of the silicon particles and minimizing capacity loss. Therefore, a secondary battery including the anode active material has improved initial efficiency, resistance performance, and / or lifespan characteristics while minimizing the loss of battery discharge capacity.

[0026] In one embodiment of the present invention, the silicon-based composite includes silicon-based particles; and one or more elements selected from the group consisting of B and P distributed within the silicon-based particles. Further, the element has a concentration gradient that increases from the center to the surface of the silicon-based composite.

[0027] The silicon-based particles may include one or more selected from the group consisting of Si and SiO x (0 < x ≤ 2). The SiO x (0 < x ≤ 2) may be a composite including amorphous SiO2 and crystalline Si as silicon oxide particles.

[0028] In one embodiment of the present invention, the silicon-based particles may contain 95 parts by weight or more of Si based on 100 parts by weight in total of the silicon-based particles. Specifically, it may contain 96 parts by weight or more, 96.5 parts by weight or more, 97 parts by weight or more, or 97.5 parts by weight or more. Also, the higher the upper limit of the Si content, the better, and the upper limit may be 100 parts by weight or less, 99.9 parts by weight or less, 99.5 parts by weight or less, 99 parts by weight or less, or 98.5 parts by weight or less.

[0029] In one embodiment of the present invention, as the silicon-based particles, particularly pure silicon (Si) may be used. Using pure silicon (Si) as the silicon-based particles means that, as described above, when the silicon-based particles are based on 100 parts by weight in total, it may mean including pure Si particles (SiO x (x = 0)) within the above range without being combined with other particles or elements.

[0030] In one embodiment of the present invention, based on 100 parts by weight in total of the silicon-based particles, O may be contained at less than 5 parts by weight. Specifically, it may be contained at less than 4 parts by weight, or less than 3.5 parts by weight. The lower limit of the oxygen atom may be 0 parts by weight or more, 0.5 parts by weight or more, 1 part by weight or more, 1.5 parts by weight or more, or 2 parts by weight or more.

[0031] In one embodiment of the present invention, based on 100 parts by weight of the total silicon-based composite, the O content may be 3 parts by weight or less. Specifically, it may be 0 parts by weight or more and 3 parts by weight or less, 0.1 parts by weight or more and 3 parts by weight or less, 0.5 parts by weight or more and 3 parts by weight or less, 1 part by weight or more and 3 parts by weight or less, 1.5 parts by weight or more and 3 parts by weight or less, 2 parts by weight or more and 3 parts by weight or less, 2.1 parts by weight or more and 2.9 parts by weight or less. The upper limit of the O content may be 3 parts by weight, 2.9 parts by weight, 2.8 parts by weight, 2.6 parts by weight, or 2.5 parts by weight. The lower limit of the O content may be 0 parts by weight, 0.1 parts by weight, 0.5 parts by weight, 1 part by weight, 1.5 parts by weight, 2 parts by weight, or 2.3 parts by weight.

[0032] The above-mentioned oxygen content can be measured by XRF analysis. Specifically, using a multi-channel fluorescence X-ray analyzer manufactured by Shimadzu Corporation, after putting a powdery sample into a sample cup and scanning with X-rays, the characteristic fluorescence X-ray corresponding to the elements generated from the sample is analyzed. The spectrum of the sample can be analyzed on software to know the content of each element, and the proportion of oxygen in the total sample weight can also be confirmed in the same way.

[0033] The silicon-based particles may be primary particles composed of one lump, or secondary particles formed by granulating the primary particles.

[0034] In one embodiment of the present invention, the Si corresponds to a matrix within the silicon-based particles. The Si may exist in the form of SiO x (x = 0). That is, the silicon-based particles may mean particles composed only of Si, or particles further containing Si and trace amounts of SiO[[ID=*15]] x (0 < x ≦ 2).

[0035] It should be noted that there seems to be an incomplete formula in the original text at "SiO " and "SiO ", which may affect the full understanding of the content. But the translation is done as accurately as possible based on the provided text.Doping the silicon particles with B or P expands the framework of the Si matrix, further facilitating the movement of Li ions, thereby enabling ions to move easily into the particles. In addition, doping increases the electrical conductivity of the Si particles, which have low conductivity, improving charge / discharge performance.

[0036] The doping element may be present in a form that substitutes for Si atoms present in the conventional silicon-based particles before doping, and thus the lattice structure of the conventional Si matrix can be expanded by the substituted doping element.

[0037] The element may be present with a concentration gradient that increases from the center to the surface of the silicon-based composite. The term "having an increasing concentration gradient" refers to both continuous and discontinuous increases in the element concentration. In this case, the distance Ra from the center to the surface of the silicon-based composite is used as a reference. The concentration of the doping element can be measured using the region from the center to 0.25 Ra (first region), the region from 0.25 Ra to 0.5 Ra (second region), the region from 0.5 Ra to 0.75 Ra (third region), and the region from 0.75 Ra to the surface (fourth region) as references to determine whether or not a concentration gradient exists. In one example, if the concentration of an element in the third and fourth regions as a whole is higher than the concentration of the element in the first and second regions as a whole, it is considered to have a concentration gradient that increases from the center to the surface. In another example, if the concentration of an element in the second region is higher than the concentration of the element in the first region, the concentration of an element in the third region is higher than the concentration of the element in the second region, and the concentration of an element in the fourth region is higher than the concentration of the element in the third region, it is considered to have a concentration gradient that increases from the center to the surface.

[0038] When the concentration of the doping element has a concentration gradient that increases from the center to the surface of the silicon-based composite, the doping element is distributed intensively on the surface of the silicon-based composite, and thus the diffusion of lithium ions on the surface of the silicon-based composite can be maximized without increasing the doping amount, thereby improving cycle performance and minimizing the decrease in battery capacity.

[0039] In one embodiment of the present invention, the one or more elements selected from the group consisting of B and P may be included in an amount of 0.1 to 50 parts by weight, based on 100 parts by weight of the total silicon-based composite. Specifically, the amount may be 0.5 to 25 parts by weight, 0.5 to 22 parts by weight, or 1 to 21 parts by weight, and more specifically, 1 to 10 parts by weight, 2 to 6 parts by weight, or 3 to 5 parts by weight. When the negative electrode active material includes the element(s) in the above ranges, sufficient diffusion paths for lithium ions can be formed on the surface of the silicon-based particles while minimizing capacity loss of the negative electrode active material, thereby achieving the effect of maximizing battery capacity while increasing lifespan.

[0040] The content of these elements can be confirmed by ICP analysis. Specifically, a certain amount (approximately 0.01 g) of negative electrode active material is taken and transferred to a platinum crucible. Nitric acid, hydrofluoric acid, and sulfuric acid are added and the mixture is completely decomposed on a hot plate. Then, an inductively coupled plasma optical emission spectrometer (ICPAES, Perkin-Elmer 7300) is used to measure the intensity of a standard solution prepared using a standard solution (5 mg / kg) at the characteristic wavelength of the element to be analyzed, and a reference calibration curve is created. The pretreated sample solution and a blank sample are then introduced into the instrument, and their respective intensities are measured to calculate the actual intensities. The concentrations of each component are calculated by comparing them with the created calibration curve, and the total is converted to a theoretical value, allowing the content of the elements contained in the negative electrode active material to be analyzed.

[0041] In one embodiment of the present invention, when the distance from the center to the surface of the silicon-based composite is Ra, the concentration of the B or P element in a region (fourth region) extending from the center of the silicon-based composite toward the surface at a point where Ra is 0.75 Ra may be higher than the concentration of the B or P element in the remaining regions. Specifically, the concentration may be 10% to 10,000%, more specifically, 50% to 5,000% higher. In another embodiment, the concentration may be 100% to 1,000%, 100% to 800%, 100% to 700%, 100% to 600%, or 100% to 500% higher. In this case, the concentration of an element in a specific region may refer to the weight percent of the element based on the total weight of the specific region. When the element has the above-described concentration gradient, lithium ion diffusion on the surface of the silicon-based composite can be maximized without increasing the doping amount of the element, thereby improving cycle performance and minimizing battery capacity loss.

[0042] In one embodiment of the present invention, when the distance from the center to the surface of the silicon-based composite is Ra, the concentration of the B or P element contained in the region (fourth region) from the point where 0.75 Ra is measured from the center to the surface of the silicon-based composite may be 20% to 1,000% higher than the concentration of the B or P element contained in the region (third region) from the point where 0.5 Ra is measured from the center to the surface of the silicon-based composite to the point where 0.75 Ra is measured from the center to the surface of the silicon-based composite. Specifically, the concentration may be 50% to 800% higher, more specifically, 70% to 600% higher, even more specifically, 100% to 600% higher, or even more specifically, 100% to 500% higher. When the element has the above concentration gradient, lithium ion diffusion on the surface of the silicon-based composite can be maximized without increasing the doping amount of the element, thereby improving cycle performance and minimizing battery capacity loss.

[0043] In one embodiment of the present invention, when the distance from the center to the surface of the silicon-based composite is Ra, the concentration of the B or P element contained in the region (fourth region) from the point where the Ra is 0.75 Ra from the center to the surface of the silicon-based composite may be 2 to 6 times higher than the concentration of the B or P element contained in the region (third region) from the point where the Ra is 0.5 Ra from the center to the surface of the silicon-based composite to the point where the Ra is 0.75 Ra from the center to the surface of the silicon-based composite. Specifically, the concentration may be 2.3 to 5 times higher, and more specifically, the concentration may be 2.5 to 4 times, or 2.5 to 3.5 times higher. When the elements have the above-mentioned concentration gradient, an optimal concentration gradient is achieved, and lithium ion diffusion on the surface of the silicon-based composite can be maximized without increasing the doping amount of the element, thereby improving cycle performance and minimizing battery capacity loss.

[0044] In one embodiment of the present invention, when the distance from the center to the surface of the silicon-based composite is Ra, the concentration of the B or P element contained in the region (third region) from the point where the Ra is 0.5 Ra in the direction from the center to the surface of the silicon-based composite to the point where the Ra is 0.75 Ra in the direction from the center to the surface of the silicon-based composite may be 2.5 to 5 times higher than the concentration of the B or P element contained in the region (second region) from the point where the Ra is 0.25 Ra in the direction from the center to the surface of the silicon-based composite to the point where the Ra is 0.5 Ra in the direction from the center to the surface of the silicon-based composite. Specifically, the concentration may be 3 to 5 times higher, and more specifically, the concentration may be 3.5 to 4.5 times higher. When the elements have the above-mentioned concentration gradient, an optimal concentration gradient is achieved, and lithium ion diffusion on the surface of the silicon-based composite can be maximized without increasing the doping amount of the element, thereby improving cycle performance and minimizing battery capacity loss.

[0045] In this specification, the distance Ra from the center to the surface of the silicon-based composite can be calculated as the radius when the silicon-based composite is converted into a sphere having the same cross-sectional area. Furthermore, the center of the silicon-based composite can refer to the center of gravity of the silicon-based composite.

[0046] In one embodiment of the present invention, the concentration of the B or P element in a region corresponding to 40% by volume of the total volume of the silicon-based composite from the center toward the surface of the silicon-based composite may be higher than the concentration of the B or P element in a region corresponding to the remaining 60% by volume. When the doping element is distributed on the surface of the silicon-based composite within the above range, the diffusion of lithium ions on the surface of the silicon-based particle can be maximized without increasing the doping amount of the element, thereby improving cycle performance and minimizing the decrease in battery capacity.

[0047] In one embodiment of the present invention, the concentration of the B or P element in a region corresponding to the remaining 60% by volume of the silicon-based composite, measured from the center toward the surface, may be 10% to 10,000% higher than the concentration in a region corresponding to 40% by volume of the total volume of the silicon-based composite. Specifically, the concentration may be 50% to 5,000% higher, and more specifically, 100% to 1,000% higher. In another embodiment, the concentration may be 100% to 800% higher, more specifically, 100% to 600% higher, and even more specifically, 100% to 500% higher. When the elements have such a concentration gradient, lithium ion diffusion on the surface of the silicon-based composite can be maximized without increasing the doping amount of the element, thereby improving cycle performance and minimizing battery capacity loss.

[0048] In one embodiment of the present invention, the weight of the B or P element contained in the region (fourth region) extending from the center of the silicon-based composite toward the surface at a point where the surface roughness is 0.75 Ra to the surface may be higher than the weight of the B or P element contained in the remaining region. Specifically, the weight may be 50% to 2,000% higher, more specifically, 70% to 1,500% higher, even more specifically, 100% to 1,300% higher, or even more specifically, 200% to 1,000% higher. In this case, the remaining region may refer to the region extending from the center of the silicon-based composite toward the surface at a point where the surface roughness is 0.75 Ra. When the elements have such a weight difference depending on the region of the silicon-based composite, lithium ion diffusion on the surface of the silicon-based composite can be maximized without increasing the doping amount of the elements, thereby improving cycle performance and minimizing battery capacity loss.

[0049] In one embodiment of the present invention, the lower limit of the content of the doping element (B or P element) in the second region may be 0.05 wt %. Specifically, the content of the doping element in the second region may be 0.05 wt % to 5 wt %, 0.05 wt % to 3.5 wt %, or 0.1 wt % to 3 wt %.

[0050] In one embodiment of the present invention, the lower limit of the content of the doping element in the third region may be 0.05 wt % or 0.1 wt %, or more specifically, the content of the doping element in the third region may be 0.1 wt % to 15 wt % or less, or 0.5 wt % to 12 wt %.

[0051] In one embodiment of the present invention, the lower limit of the content of the doping element in the fourth region may be 1 wt %. Specifically, the content of the doping element in the fourth region may be 1 wt % to 40 wt % or less, 2 wt % to 35 wt %, or 3 wt % to 30 wt %.

[0052] If the content of the doping element in each region does not satisfy the above range, doping cannot be smoothly performed inside the silicon-based particles, and the doping element is located only on the surface of the particles, resulting in a problem that the doped material is easily removed during a washing process of the active material due to a small doping amount, or the discharge capacity is reduced due to excessive doping.

[0053] In one embodiment of the present invention, when the distance from the center to the surface of the silicon-based composite is Ra, the concentration of the O element contained in a region (fourth region) from the point where the Ra is 0.75 Ra from the center to the surface of the silicon-based composite may be 1.1 to 10 times higher than the concentration of the O element contained in a region (third region) from the point where the Ra is 0.5 Ra from the center to the surface of the silicon-based composite to the point where the Ra is 0.75 Ra from the center to the surface of the silicon-based composite. Specifically, the concentration may be 1.2 to 8 times, 1.2 to 5 times, or 1.3 to 3 times higher. If the O element concentration in the fourth region is distributed beyond the above range, O is excessively distributed on the surface of the silicon-based composite, resulting in problems such as reduced initial efficiency and capacity retention.

[0054] In one embodiment of the present invention, when the distance from the center to the surface of the silicon-based composite is Ra, the concentration of the O element contained in a region (third region) from a point where the Ra is 0.5 Ra from the center to the surface of the silicon-based composite to a point where the Ra is 0.75 Ra from the center to the surface of the silicon-based composite may be 1.2 to 10 times higher than the concentration of the O element contained in a region (second region) from a point where the Ra is 0.25 Ra from the center to the surface of the silicon-based composite to a point where the Ra is 0.5 Ra from the center to the surface of the silicon-based composite. Specifically, the concentration may be 1.2 to 8 times, 1.5 to 5 times, or 1.7 to 3 times higher.

[0055] In one embodiment of the present invention, the Si crystal grains may be 5 nm to 1,000 nm. Specifically, they may be 10 nm to 500 nm, 50 nm to 300 nm, 100 nm to 300 nm, 150 nm to 300 nm, or 180 nm to 300 nm. More specifically, they may be 180 nm to 260 nm. When the Si crystal grains satisfy the above range, Li ions are more uniformly diffused into the Si crystal grains, preventing accelerated deterioration of the material and maintaining a stable structure of the Si particles during charge and discharge, thereby improving the cell life.

[0056] In one embodiment of the present invention, a carbon layer may be provided on at least a portion of the surface of the silicon-based composite. In this case, the carbon layer may be partially coated on at least a portion of the surface, i.e., the surface of the composite, or may be coated on the entire surface of the composite. The carbon layer imparts conductivity to the negative electrode active material, thereby improving the initial efficiency, life characteristics, and capacity characteristics of the secondary battery.

[0057] Specifically, the carbon layer may include crystalline carbon or amorphous carbon, and preferably includes amorphous carbon.

[0058] The crystalline carbon may further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0059] The amorphous carbon may be a carbon-based material formed by using at least one carbide or hydrocarbon selected from the group consisting of tar, pitch, and other organic substances as a source in a chemical vapor deposition process.

[0060] The carbonized organic material may be a carbonized organic material selected from carbonized sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and combinations thereof.

[0061] The hydrocarbon may be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The aliphatic or alicyclic hydrocarbon of the substituted or unsubstituted aliphatic or alicyclic hydrocarbon may be methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, hexane, or the like. The aromatic hydrocarbon of the substituted or unsubstituted aromatic hydrocarbon may be benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, phenanthrene, or the like.

[0062] Specifically, the carbon layer may be formed by disposing a carbonaceous precursor on the silicon-based composite and then heat-treating the resulting composite. The carbonaceous precursor may be graphene or graphite for producing crystalline carbon, or may be a carbonaceous material formed by using at least one carbide selected from the group consisting of tar, pitch, and other organic substances for producing amorphous carbon, or a hydrocarbon such as methane, ethane, or acetylene as a source in a chemical vapor deposition process.

[0063] In one embodiment of the present invention, the carbon layer may be included in an amount of 0.1 to 50 parts by weight, specifically 0.5 to 10 parts by weight or 20 parts by weight, more specifically 2 to 4 parts by weight, based on 100 parts by weight of the total negative electrode active material. When the amount is within the above range, side reactions can be reduced by coating the surface of the negative electrode active material, and a decrease in capacity and efficiency can be prevented by increasing electrical conductivity.

[0064] The average particle size (D 50) may be 0.5 μm to 50 μm, specifically 2 μm to 20 μm, more specifically 2 μm to 10 μm, and even more specifically 2 μm to 7 μm. When the above range is satisfied, the structural stability of the active material during charge and discharge can be ensured. In addition, the level of volume expansion / contraction, which occurs when the particle size is excessively large, can be prevented, and the decrease in initial efficiency due to the occurrence of side reactions caused by the large surface area compared to the volume, which occurs when the particle size is excessively small, can be prevented.

[0065] The particle size of the negative active material can be adjusted by methods such as, but not limited to, a ball mill, a jet mill, or air classification.

[0066] Method for producing negative electrode active material One embodiment of the present invention provides a method for producing a negative electrode active material, the method including the steps of: preparing metallic silicon; preparing a doping source including one or more compounds selected from the group consisting of a B-containing compound and a P-containing compound; and mixing the metallic silicon and the doping source, followed by heat treatment at a temperature equal to or higher than the boiling point of the doping source.

[0067] Generally, methods for maximizing the performance of secondary batteries containing silicon-based negative electrode active materials by doping silicon-based particles with B or P elements have been known. Conventionally, the doping of B or P elements has been achieved by directly adding the doping source to a liquid silicon raw material or by chemical synthesis. When preparing negative electrode active materials using these methods, the doping element is uniformly distributed throughout the silicon particles. However, while increasing the total content of the doping element improves battery cycle life, it also reduces discharge capacity.

[0068] To address this issue, the present invention provides a method for manufacturing an anode active material in which micron-sized metallic silicon particles are mixed with a doping source and then heat-treated to distribute the doping element intensively on the surface of the silicon particles. The anode active material manufactured by this method maximizes lithium ion diffusion on the surface of the silicon-based composite and minimizes capacity loss, thereby minimizing the decrease in battery discharge capacity, while improving initial efficiency, resistance performance, and / or life characteristics. Furthermore, this manufacturing method does not require temperatures high enough to melt silicon, and the reaction conditions are milder than conventional methods. Since it is not a chemical synthesis method, it is easy to mass-produce.

[0069] The metal silicon refers to a silicon raw material with a Si purity of 99% or more. Generally, metal silicon used in the relevant field may be appropriately adopted and used.

[0070] In one example, the metallurgical silicon may be obtained by inducing a reduction reaction of silica sand (SiO2) using a thermal reduction reaction with carbon in an electric furnace, producing liquid Si, and then cooling it.

[0071] In one embodiment of the present invention, the method may further include the step of crushing and classifying the metallurgical silicon after the step of preparing the metallurgical silicon.

[0072] The crushing and classification of the metallurgical silicon may be performed before the step of mixing the metallurgical silicon with a doping source (described later) and heat-treating the mixture. If the crushing and classification are not performed before the heat-treatment step, there is a problem that the doping itself is not performed properly because there is a limit to the diffusion of the foreign element into the silicon when doping with the foreign element. Therefore, by crushing and classifying the silicon to a micro-size level, the foreign element can be diffused into the silicon and distributed at an appropriate level. Furthermore, by crushing and classifying the metallurgical silicon first, the doping source and silicon can be mixed uniformly, and the foreign element can be uniformly doped into each silicon.

[0073] The metal silicon may be pulverized using a jet mill or a ball mill using a physical collision method.

[0074] The classification of the metallurgical silicon may be carried out using a dry classification method (air classifier) ​​or a wet classification method (hydrocyclone). For example, it may be carried out using an air classification method.

[0075] D of the crushed and classified silicon metal 50 The particle size may be 1 μm to 20 μm, specifically 2 μm to 10 μm, and more specifically 2 μm to 7 μm. By satisfying the above range, particle cracking due to charge and discharge is minimized, thereby suppressing side reactions as much as possible and improving the life performance of the cell.

[0076] The compound containing B may be at least one selected from the group consisting of H3BO3 (boric acid) and BN (boron nitride).

[0077] The P-containing compound may be at least one selected from the group consisting of H3PO4 (phosphoric acid) and P2O5 (phosphorus pentoxide).

[0078] The heat treatment may be performed at a temperature below the melting point of metallic silicon, specifically at a temperature below 1414°C. The heat treatment may be carried out at a temperature equal to or higher than the boiling point of the doping source.

[0079] The heat treatment may be carried out at 300°C to 1,400°C. Specifically, it may be carried out at 400°C to 1,000°C, 500°C to 1,000°C, or 600°C to 1,000°C, more specifically, at 700°C to 900°C for 2 to 5 hours. For example, the heat treatment may be carried out at 700°C to 900°C for 3 hours under Ar gas purging conditions.

[0080] If the heat treatment temperature is higher than the above range, the silicon particles melt and the doping occurs in the liquid state, resulting in a uniform distribution of the doping element throughout the silicon. Therefore, if the doping amount is increased to achieve the desired cycle characteristics, the discharge capacity may actually decrease. Furthermore, the higher the heat treatment temperature, the larger the Si crystal grains become, which may reduce the electrochemical performance of the silicon-based composite doped with the element.

[0081] On the other hand, when the heat treatment temperature is within the above range, the doping source evaporates but the silicon does not melt. Therefore, atoms from the doping source can be diffused into adjacent silicon particles to dope the element, and the silicon-based Complex Since the doping element is distributed with a concentration gradient on the surface of the battery, even a small amount of doping can easily improve cycle characteristics and minimize capacity loss. In addition, it can easily prevent insufficient doping due to an excessively low heat treatment temperature.

[0082] For example, when B2O3 (melting point = 450°C, boiling point = 1860°C) is used as a doping source, if heat treatment is performed at a temperature below the melting point of metal silicon (approximately 1400°C), B2O3 exists in a liquid state, so B2O3 diffuses only near the surface of the metal silicon particles, resulting in a very small amount of doping or the surface being oxidized.In contrast, if heat treatment is performed at a temperature above the boiling point of B2O3 (1860°C), the silicon particles melt and react in a liquid state, so the desired doping concentration gradient is not achieved. Silicon-based composites The problem is that it is difficult to obtain

[0083] The temperature rise condition during the heat treatment may be 1° C. / min to 10° C. / min, specifically 3° C. / min to 7° C. / min, or 4° C. / min to 6° C. / min.

[0084] In one embodiment of the present invention, the method may further include forming a carbon layer on at least a portion of the silicon-based composite formed after the step of mixing the metal silicon and the doping source and then heat-treating the mixture.

[0085] The carbon layer may be formed by chemical vapor deposition (CVD) using a hydrocarbon gas or by carbonizing a carbon source material.

[0086] Specifically, the silicon-based particles may be placed in a reactor, and then a hydrocarbon gas may be subjected to chemical vapor deposition (CVD) at 900°C to 1,100°C. The hydrocarbon gas may be at least one hydrocarbon gas selected from the group consisting of methane, ethane, propane, and acetylene, and the heat treatment may be performed at 900°C to 1,100°C.

[0087] negative electrode The negative electrode according to an embodiment of the present invention may include the negative electrode active material described above. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer may include the negative electrode active material. Furthermore, the negative electrode active material layer may further include a binder and / or a conductive material.

[0088] The negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that easily adsorbs carbon, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 6 μm to 20 μm, but is not limited thereto.

[0089] The 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, polytetrafluoroethylene, 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.

[0090] The conductive material is not particularly limited as long as it does not induce chemical changes in the battery and is conductive, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0091] secondary battery A secondary battery according to an embodiment of the present invention may include the negative electrode according to the embodiment 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 solution, 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.

[0092] 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.

[0093] The positive electrode current collector in the positive electrode is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like may be used. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and the surface of the current collector may be provided with fine irregularities to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0094] 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; or a compound having the chemical formula Li 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 O2 (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and 0.01≦c2≦0.5 is satisfied); 2-c3 M c3 Examples of the lithium manganese composite oxide 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 satisfies 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); or LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion. The positive electrode may be lithium metal (Li-metal).

[0095] 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.

[0096] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it does not cause chemical changes in the battery that is constructed and has electronic conductivity. Specific examples include graphite such as natural graphite 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, and the like, and one or more of these may be used alone or in combination.

[0097] The positive electrode binder improves adhesion between positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. One or more of these may be used alone or in combination.

[0098] The separator separates the negative electrode and positive electrode and provides a path for lithium ion migration. Any separator typically used in secondary batteries can be used without particular limitations. It is particularly preferable that the separator exhibits low resistance to ion migration in the electrolyte and has excellent electrolyte humidification capacity. 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 coated separator containing a ceramic component or a polymeric material may be used, and it may be selectively used as a single-layer or multi-layer structure.

[0099] Examples of the electrolytic solution include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries. Specifically, the electrolytic solution may contain a non-aqueous organic solvent and a metal salt.

[0100] 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.

[0101] In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are preferably used as high-viscosity organic solvents, 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 solution having high electrical conductivity can be prepared, and therefore these cyclic carbonates are even more preferably used.

[0102] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - , and (CF3CF2SO2)2N - One or more selected from the group consisting of:

[0103] In addition to the 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 derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, and improving the discharge capacity of the battery.

[0104] According to another 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 can be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. [Example]

[0105] Below, preferred examples are presented to help understand the present invention. However, the above examples are merely illustrative of 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. It goes without saying that such changes and modifications fall within the scope of the appended claims.

[0106] Example 1 Example 1-1 Silica sand (SiO2) was subjected to a thermal reduction reaction using carbon in an electric furnace, and then liquid silicon was produced. Specifically, a high current of 10,000A or more was passed through a graphite electrode to produce liquid silicon at 2,000°C. The silicon was then gradually cooled to room temperature, and the cooled silicon mass was used as the raw material and coarsely crushed and air-classified to produce silicon in liquid state. 50 Metallic silicon powder with a particle size of 5 μm was obtained. A 120 g mixture of 60 g of metallic silicon powder (Si powder) and 60 g of H3BO3 powder as a doping source (1:1 weight ratio) was heated in a reactor at a reaction temperature of 500°C under an Ar gas environment. The temperature was increased at 5°C / min. After cooling to room temperature at 5°C / min, the reacted powder was collected. To remove unreacted doping source, the powder was mixed with water and then washed three times at 6,000 rpm for 5 minutes using a centrifuge. The supernatant was discarded, and the mixture collected at the bottom was collected and dried in an oven at 60°C. Finally, a sieving process was performed using a 325 mesh filter to remove particle agglomerates that occurred during the heat treatment. Silicon-based composite A negative electrode active material was produced.

[0107] Example 1-2 A negative electrode active material was prepared in the same manner as in Example 1-1, except that the reaction temperature was 700°C.

[0108] Examples 1-3 A negative electrode active material was prepared in the same manner as in Example 1-1, except that the reaction temperature was 900°C.

[0109] Examples 1-4 A negative electrode active material was prepared in the same manner as in Example 1-1, except that H3PO4 was used instead of H3BO3.

[0110] Comparative Example 1-1 Silica sand (SiO2) was subjected to a thermal reduction reaction using carbon in an electric furnace, and then liquid-state Si was produced. Specifically, a high current of 10,000A or more was passed through a graphite electrode to produce liquid-state Si at 2,000°C. After adding H3BO3 (boric acid) to the liquid-state Si at 2,000°C so that the B content was 5 wt% of the total, the silicon was gradually cooled to room temperature. The cooled silicon block doped with B was then used as the raw material and coarsely crushed and air-classified to produce D. 50 A negative electrode active material powder having a particle size of 5 μm was obtained, and then a sieving process was finally performed using a filter having a 325 mesh size to prepare a B-doped negative electrode active material.

[0111] Comparative Example 1-2 A P-doped negative active material was prepared in the same manner as in Comparative Example 1-1, except that H3PO4 was used instead of H3BO3 so that the P content was 5 wt% of the total.

[0112] Comparative Examples 1-3 A negative electrode active material was prepared in the same manner as in Example 1-1, except that B2O3 was used instead of H3BO3. The compositions of the negative electrode active materials prepared in the examples and comparative examples are as shown in Table 1 below.

[0113] [Table 1]

[0114] The compounds prepared in the above examples and comparative examples Silicon-based compositesThe concentrations of elements in each region are as shown in Table 2 below.

[0115] [Table 2]

[0116] The types and total contents of the elements were confirmed by ICP analysis using an inductively coupled plasma optical emission spectrometer (ICP-OES, AVIO 500, manufactured by Perkin-Elmer 7300).

[0117] The concentration gradient of the element is Silicon-based composites The cross section of the active material was cut and then measured by SEM EDS analysis. Specifically, the cross section of the active material was cut by ion milling, and the element content of the cross section was confirmed by SEM EDS (Energy-dispersive X-ray spectroscopy). The SEM measurement image was analyzed to measure the element concentration in each section.

[0118] The aforementioned Silicon-based composites The distance Ra from the center to the surface is Silicon-based composites The radius was calculated by converting it into a sphere with the same cross-sectional area. Silicon-based composites The center of Silicon-based composites Measurements were taken based on the center of gravity.

[0119] The aforementioned Silicon-based composites The size of the Si crystal grains contained in the silicon dioxide powder can be confirmed by X-ray diffraction analysis, which was performed using an X-ray diffraction (XRD) analyzer (product name: D4-Endeavor, manufacturer: Bruker). Specifically, the powder sample was placed in a holder and measured using a Cu Kα X-ray. The size of the crystal grains was calculated by fitting the XRD results using the Scherrer equation, and the crystal grains were measured based on the Si(111) plane (2θ=28.4°~28.5°).

[0120] <Experimental Example 1: Evaluation of discharge capacity, initial efficiency, and life (capacity retention rate) characteristics> Negative electrodes and secondary batteries were manufactured using the negative electrode active materials of the examples and comparative examples, respectively.

[0121] Anode manufacturing Average particle size (D 50 A negative electrode slurry containing the negative electrode active material produced in Example 1-1 having a particle size of 5 μm, single-walled carbon nanotubes, plate-shaped artificial graphite, carbon black as a conductive material, a polyacrylamide polymer as a binder, and water as a solvent was prepared.

[0122] The negative electrode slurry was applied to a copper (Cu) metal thin film, which was a negative electrode current collector, with a thickness of 20 μm, and dried. At this time, the temperature of the circulating air was 60°C. Then, the negative electrode was manufactured by rolling and drying in a vacuum oven at 130°C for 12 hours (loading: 8.55 mAh / cm). 2 ).

[0123] In the manufactured negative electrode, the weight ratio of the negative electrode active material, the single-walled carbon nanotubes, the plate-shaped artificial graphite, the conductive material, and the binder was 70:0.21:10:10:9.79.

[0124] In addition, the negative electrodes of Examples 1-2 to 1-4 and Comparative Examples 1-1 to 1-3 were manufactured in the same manner, except that the negative electrode active materials of Examples 1-2 to 1-4 and Comparative Examples 1-1 to 1-3 were used instead of the negative electrode active material of Example 1-1.

[0125] Secondary battery manufacturing A lithium metal foil was prepared as the positive electrode. A porous polyethylene separator was interposed between the negative electrode and positive electrode of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-3 produced above, and an electrolyte solution was injected to produce coin-shaped half cells of Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-3.

[0126] The electrolyte used was a solution in which ethyl methyl carbonate (EMC) and ethylene carbonate (EC) were mixed in a volume ratio of 7:3, vinylene carbonate (VC) was dissolved at 0.5 wt %, and LiPF6 was dissolved at a concentration of 1M.

[0127] Evaluation of discharge capacity, initial efficiency, and capacity retention The manufactured batteries were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and the results are shown in Table 3 below.

[0128] The first and second cycles were charged and discharged at 0.1 C, and the third to 49th cycles were charged and discharged at 0.5 C. Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.0V voltage cut-off

[0129] The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of the first charge / discharge. - Discharge capacity of negative active material (mAh / g) = Measured discharge capacity / Loading amount of negative active material - Charge capacity of negative active material (mAh / g) = measured charge capacity / loading amount of negative active material Initial efficiency (%) = (discharge capacity of negative electrode active material (mAh / g) / charge capacity of negative electrode active material (mAh / g)) × 100 The capacity retention rate was calculated as follows. -Capacity retention rate (%) = (49th discharge capacity / 1st discharge capacity) x 100

[0130] [Table 3]

[0131] According to one embodiment of the present invention Silicon-based compositesis characterized in that B or P has a concentration gradient that increases from the center to the surface of the negative electrode active material.

[0132] It can be seen from Table 3 above that Examples 1-1 to 1-4 are excellent in all of discharge capacity, initial efficiency, and capacity retention rate.

[0133] In contrast, in Comparative Examples 1-1 and 1-2, the negative electrode active material is doped uniformly with B and P, and there is no concentration gradient in the negative electrode active material.

[0134] Although the total content of the doping elements in Comparative Example 1-1 was higher than that in Example 1-1, it was confirmed that the initial efficiency and capacity retention rate were reduced because the doping elements were uniformly present in the active material.

[0135] Although the total content of the doping elements in Comparative Example 1-2 was higher than that in Example 1-4, it was confirmed that the initial efficiency and capacity retention rate decreased because the doping elements were uniformly present in the active material.

[0136] Comparative Examples 1-3 used B2O3 as a doping source. Because the boiling point of B2O3 is 1860°C, B2O3 reacts in a liquid state during the reaction at 500°C. This prevents the doping of the doping element from smoothly reaching the interior of the silicon-based particles, resulting in the doping element remaining only on the particle surface. Therefore, the active material of Comparative Example 3 does not have a concentration gradient that increases from the particle center to the surface, and B2O3 is concentrated only on the particle surface, resulting in the problem of the doped material being easily removed during the cleaning process of the negative electrode active material. Furthermore, excessive O distribution was observed, resulting in reduced initial efficiency and capacity retention.

[0137] In contrast, in Examples 1-1 to 1-4, the doping source reacts in a gaseous state to form a silicon-based compound in a solid state. ComplexIt was confirmed that the doping occurs with an appropriate concentration gradient inside the negative electrode, and oxygen is removed while the doping occurs, resulting in almost no oxygen in the negative electrode active material, which improves the initial efficiency and capacity retention rate.

[0138] <Example 2> Example 2-1 Silica sand (SiO2) was subjected to a thermal reduction reaction using carbon in an electric furnace, and then liquid silicon was produced. Specifically, a high current of 10,000A or more was passed through a graphite electrode to produce liquid silicon at 2,000°C. The silicon was then gradually cooled to room temperature, and the cooled silicon mass was used as the raw material and coarsely crushed and air-classified to produce silicon in liquid state. 50 A metallurgical silicon powder with a particle size of 5 μm was obtained. A 120 g mixture of metallurgical silicon powder (Si powder) and H3BO3 powder as a doping source (60 g each, 1:1 by weight) was heated in a reactor at 500°C under an Ar gas atmosphere. The temperature was increased at 5°C / min. After cooling to room temperature at 5°C / min, the reacted powder was collected. To remove unreacted doping source, the powder was mixed with water and centrifuged at 6,000 rpm for 5 minutes, three times. The supernatant was discarded, and the mixture collected at the bottom was collected and dried in an oven at 60°C. A final sieving process was performed using a 325 mesh filter to remove particle agglomerates that occurred during the heat treatment, producing the negative electrode active material.

[0139] Example 2-2 A 120g mixture of 60g of metal silicon powder (Si powder) and 60g of H3BO3 powder (doping source) (weight ratio: 1:1) was heated in a reactor at a reaction temperature of 500°C in an Ar gas environment. The temperature increase rate was 7°C / min.

[0140] Example 2-3 A 120g mixture of 60g of metal silicon powder (Si powder) and 60g of H3BO3 powder (doping source) (weight ratio: 1:1) was heated in a reactor at a reaction temperature of 500°C in an Ar gas environment. The temperature increase rate was 3°C / min.

[0141] Comparative Example 2-1 Silica sand (SiO2) was subjected to a thermal reduction reaction using carbon in an electric furnace, and then liquid Si was produced. Specifically, a high current of 10,000A or more was passed through a graphite electrode to produce liquid Si at 2,000°C. H3BO3 (boric acid) was added to the liquid Si at 2,000°C so that the B content was 4.12 wt% of the total, and then the silicon was gradually cooled to room temperature. The cooled silicon ingot doped with B was then coarsely crushed and air-classified to produce D. 50 A negative electrode active material powder having a particle size of 5 μm was obtained, and then a sieving process was finally performed using a filter having a 325 mesh size to prepare a B-doped negative electrode active material.

[0142] The total doping weight of the doping elements in Examples 2-1 to 2-3 and Comparative Example 2-1 is the same, 4.12 parts by weight based on 100 parts by weight of the total negative electrode active material.

[0143] [Table 4]

[0144] <Experimental Example 2: Evaluation of discharge capacity, initial efficiency, and life (capacity retention rate) characteristics> Negative electrodes and secondary batteries were manufactured using the negative electrode active materials of the examples and comparative examples, respectively.

[0145] Anode manufacturing Average particle size (D 50A negative electrode slurry containing the negative electrode active material produced in Example 2-1 having a particle size of 5 μm, single-walled carbon nanotubes, plate-shaped artificial graphite, carbon black as a conductive material, a polyacrylamide polymer as a binder, and water as a solvent was prepared.

[0146] The negative electrode slurry was applied to a copper (Cu) metal thin film, which was a negative electrode current collector, with a thickness of 15 μm, and dried. At this time, the temperature of the circulating air was 60°C. Then, the negative electrode was manufactured by rolling and drying in a vacuum oven at 130°C for 12 hours (loading: 9.5 mAh / cm). 2 ).

[0147] In the manufactured negative electrode, the weight ratio of the negative electrode active material, the single-walled carbon nanotubes, the plate-shaped artificial graphite, the conductive material, and the binder was 70:0.21:10:10:9.79.

[0148] In addition, negative electrodes of Examples 2-2 to 2-3 and Comparative Example 2-1 were manufactured in the same manner, except that the negative electrode active materials of Examples 2-2 to 2-3 and Comparative Example 2-1 were used instead of the negative electrode active material of Example 2-1.

[0149] Secondary battery manufacturing A lithium metal foil was prepared as the positive electrode. A porous polyethylene separator was interposed between the negative electrode and positive electrode of Examples 2-1 to 2-3 and Comparative Example 2-1 prepared above, and an electrolyte solution was injected to prepare coin-shaped half cells of Examples 2-1 to 2-3 and Comparative Example 2-1.

[0150] The electrolyte used was a solution in which fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7, and LiPF6 was dissolved at a concentration of 1M. Evaluation of discharge capacity, initial efficiency, and capacity retention The manufactured batteries were charged and discharged to evaluate the discharge capacity, initial efficiency, and capacity retention rate, and the results are shown in Table 5 below.

[0151] The first and second cycles were charged and discharged at 0.1 C, and the third to 49th cycles were charged and discharged at 0.5 C. Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off) Discharge condition: CC (constant current) condition 1.0V voltage cut-off

[0152] The discharge capacity (mAh / g) and initial efficiency (%) were derived from the results of the first charge / discharge. - Discharge capacity of negative active material (mAh / g) = Measured discharge capacity / Loading amount of negative active material - Charge capacity of negative active material (mAh / g) = measured charge capacity / loading amount of negative active material Initial efficiency (%) = (discharge capacity of negative electrode active material (mAh / g) / charge capacity of negative electrode active material (mAh / g)) × 100

[0153] The capacity retention rate was calculated as follows. -Capacity retention rate (%) = (49th discharge capacity / 1st discharge capacity) x 100

[0154] [Table 5]

[0155] The negative electrode active material according to one embodiment of the present invention is characterized by a concentration gradient in which B or P increases from the center to the surface of the negative electrode active material, and it was found that when a concentration gradient is provided as in Examples 2-1 to 2-3, the discharge capacity, initial efficiency, and capacity retention rate are significantly improved compared to Comparative Example 2-1, which does not have a concentration gradient. In particular, when a concentration gradient is provided as in Example 2-1, it was confirmed that the initial efficiency and capacity retention rate are significantly improved simultaneously.

Claims

1. Silicon-based particles; and one or more elements selected from the group consisting of B and P distributed within the silicon-based particles, The silicon-based particles contain 95 parts by weight or more of Si based on a total of 100 parts by weight of the silicon-based particles, The element has a concentration gradient that increases from the center to the surface of the silicon-based composite.

2. The negative electrode active material of claim 1 , wherein the silicon-based composite has an O content of 3 parts by weight or less, based on a total of 100 parts by weight of the silicon-based composite.

3. 2. The negative electrode active material of claim 1, wherein the at least one element selected from the group consisting of B and P is included in an amount of 0.1 to 50 parts by weight based on a total of 100 parts by weight of the silicon-based composite.

4. 2. The negative electrode active material according to claim 1, wherein a concentration of the element contained in a region from a point at which the distance from the center of the silicon-based composite to the surface is 0.75Ra in a surface direction from the center of the silicon-based composite to the surface has a higher value than a concentration of the element contained in the remaining region, when a distance from the center of the silicon-based composite to the surface is Ra.

5. 2. The negative electrode active material according to claim 1, wherein, when a distance from the center of the silicon-based composite to the surface is defined as Ra, a concentration of the element contained in a region from a point at which the distance from the center of the silicon-based composite to the surface is 0.75 Ra has a value that is 20% to 1,000% higher than a concentration of the element contained in a region from a point at which the distance from the center of the silicon-based composite to the surface is 0.5 Ra to a point at which the distance from the center of the silicon-based composite to the surface is 0.75 Ra.

6. 2. The negative electrode active material according to claim 1, wherein the Si crystal grains are 5 nm to 1,000 nm.

7. D of the negative electrode active material ５０ The negative electrode active material according to claim 1, wherein the average particle size is 0.5 μm to 50 μm.

8. providing metallurgical silicon; providing a doping source comprising one or more compounds selected from the group consisting of B-containing compounds and P-containing compounds; After mixing the metal silicon and the doping source, heat treatment is performed at a temperature equal to or higher than the boiling point of the doping source and lower than the melting point of the metal silicon. A method for producing a negative electrode active material, comprising:

9. The method of claim 8 , further comprising the steps of crushing and classifying the metallurgical silicon after the step of preparing the metallurgical silicon.

10. D of the crushed and classified metallurgical silicon ５０ The method for producing a negative electrode active material according to claim 9, wherein the thickness is 0.5 μm to 50 μm.

11. The method for producing a negative electrode active material according to claim 8, wherein the heat treatment is performed at 300°C to 1,400°C.

12. A negative electrode comprising the negative electrode active material according to any one of claims 1 to 7.

13. A secondary battery comprising the negative electrode according to claim 12.

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