Anode active material for lithium secondary battery, secondary battery comprising same, and manufacturing method thereof

Abstract

The present invention relates to an anode active material for a lithium secondary battery and a manufacturing method thereof, the anode active material comprising a silicon-based substrate and a coating layer coated on the surface of the silicon-based substrate, wherein: the coating layer comprises a carbon layer and one or more nano-carbon beads; the carbon layer and the nano-carbon beads contain sulfur; and the content of the coating material in the coating layer may be 0.10-1.50 weight%.

Description

Negative active material for lithium secondary battery, secondary battery including same, and method for manufacturing same

[0001] The present invention relates to a battery, and more particularly, to a negative electrode active material for a lithium secondary battery, a secondary battery including the same, and a method for manufacturing the same.

[0002] Social concern over the depletion of fossil fuels and the resulting environmental pollution is growing, and eco-friendly energy sources are attracting attention as a solution. Among these eco-friendly energy sources, interest in electric energy is growing, and lithium secondary batteries are particularly gaining attention.

[0003] Lithium secondary batteries are widely used in small applications such as mobile phones and laptops, as well as medium- to large-scale applications such as electric vehicles and energy storage systems. As the application scope of lithium secondary batteries expands, the development of new materials for high capacity and high output is becoming increasingly important. However, considering ways to improve electrochemical properties, such as extending the efficient use time in small applications and enhancing energy performance in medium- to large-scale applications such as electric vehicles, improving electrochemical properties remains a technical challenge to be addressed. Specifically, the anode material in a lithium secondary battery stores lithium ions and is a factor related to the battery's capacity and lifespan. Various carbon-based materials, including artificial graphite, natural graphite, and hard carbon, which enable lithium insertion and deintercalation, have been used as anode materials. Graphite has a low discharge voltage of 0.2 V compared to lithium, but batteries using graphite as an anode active material exhibit a high discharge voltage of 3.6 V, providing advantages in energy density for lithium secondary batteries. Additionally, it is the most widely used because it guarantees a long lifespan of lithium secondary batteries due to its excellent reversibility.

[0004] The above natural graphite has the advantage of being inexpensive and exhibiting electrochemical properties similar to those of artificial graphite, making it highly useful as an anode material. However, natural graphite has a plate-like shape, resulting in a large surface area and exposed edges, which can cause electrolyte penetration or decomposition when applied as an anode active material. This can cause the edges to peel off or break, resulting in a significant irreversible reaction. In addition, when manufacturing this into an electrode plate, the graphite material is flatly pressed and oriented on the current collector, making it difficult for the electrolyte to be impregnated, which can deteriorate the charge-discharge characteristics.

[0005] Research into new anode materials to overcome the limitations of graphite continues, and interest in silicon-based anode materials is growing in particular. Silicon is not only abundant worldwide, but also boasts a high theoretical capacity of approximately 4,200 mAh / g compared to graphite, a low reaction potential with lithium, and the advantage of being an environmentally friendly material.

[0006] However, since the silicon-based negative electrode material is used by mechanically crushing bulk silicon, it has an irregular shape, and the irregular shape causes irregular expansion and contraction of the volume during the charging and discharging process of the silicon, which leads to a decrease in battery performance, and when manufacturing the electrode, an uneven electrode is manufactured, which can lead to a decrease in battery performance.

[0007] To solve the above-mentioned problems, efforts are needed to suppress side reactions of the negative electrode material with the electrolyte and further improve conductivity.

[0008] The technical problem to be solved by the present invention is to provide a negative electrode active material that suppresses side reactions with an electrolyte and further improves conductivity.

[0009] Another technical problem to be solved by the present invention is to provide a method for manufacturing a negative electrode active material having the aforementioned advantages.

[0010] According to one embodiment of the present invention, a negative active material includes a silicon-based base material and a coating layer coated on the surface of the silicon-based base material, the coating layer includes a carbon layer and at least one nanocarbon bead, the carbon layer and the nanocarbon beads include sulfur, and the content of the coating material may be 0.10 to 1.50 wt% based on 100 wt% of the total active material.

[0011] According to one embodiment, the negative active material can satisfy the following equation 1.

[0012] <Formula 1>

[0013] 0.50 ≤ coating material content [wt%] × BET specific surface area [m 2 / g] ≤ 9.50

[0014] According to one embodiment, the negative active material can satisfy the following equation 2.

[0015] <Formula 2>

[0016] 1.40 ≤ Average particle diameter of secondary particles (D50) [㎛] × coating material content [wt%] ≤ 15.0

[0017] According to one embodiment, the negative active material can satisfy the following equation 3.

[0018] <Formula 3>

[0019] 2.0 ≤ (sulfur content [wt%] / coating material content [wt%]) × 100 ≤ 120.0

[0020] In one embodiment, the negative active material may include 0.03 to 0.3 wt% of the sulfur. In one embodiment, the D10 particle size of the secondary particles may be 2.0 to 6.5 μm. In one embodiment, the average particle size (D50) of the secondary particles may be 6.7 to 9.5 μm.

[0021] In one embodiment, the D90 particle size of the secondary particles may be 10.6 to 15.7 μm. In one embodiment, the Span value ((D90-D10) / D50) of the secondary particles may be 0.80 to 1.40. In one embodiment, the silicon-based matrix may be silicon alone, silicon oxide, silicon nitride, silicon sulfide, silicon carbide, silicon-metal alloy, and combinations thereof.

[0022] In one embodiment, the carbon layer may be an amorphous carbon layer. In one embodiment, the carbon layer may have a thickness of 1.0 to 10 nm. In one embodiment, the at least one nanocarbon bead may be configured as at least one cluster. In one embodiment, the at least one nanocarbon bead may have at least one of a spherical shape and an oval shape.

[0023] According to another embodiment of the present invention, a method for manufacturing an anode active material for a lithium secondary battery includes a step of uniformly mixing a silicon-based coating material and a sulfur-containing coating material, and a step of carbonizing the mixed result by heat treatment, wherein the coating material may be included in an amount of 1 to 8 parts by weight based on 100 parts by weight of the coating material. In one embodiment, the method for manufacturing an anode active material for a lithium secondary battery may satisfy the following equation 4.

[0024] <Formula 4>

[0025] 0.37 ≤ (sulfur content [wt%] / content of coating material before carbonization [wt%]) × 100 ≤ 25.0

[0026] In one embodiment, the silicon-based coating material may include silicon alone, silicon oxide, silicon nitride, silicon sulfide, silicon carbide, silicon-metal alloy, and combinations thereof. In one embodiment, the sulfur-containing coating material may be coal tar or petroleum pyrolyzed oil (PFO).

[0027] According to one embodiment, the negative electrode active material includes a carbon layer including sulfur and at least one nanocarbon bead as a coating layer, thereby providing a negative electrode material that suppresses side reactions with an electrolyte and further improves conductivity.

[0028] According to another embodiment of the present invention, a lithium secondary battery is provided that includes a negative electrode active material having the above advantages.

[0029] According to another embodiment of the present invention, a method for providing a negative electrode active material having the above advantages is provided.

[0030] FIG. 1a and FIG. 1b are SEM and TEM photographs of a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0031] FIGS. 2a and 2b are SEM and TEM photographs of a negative electrode active material for a lithium secondary battery according to a comparative example of the present invention, and FIGS. 2c and 2d are SEM and TEM photographs of a negative electrode active material for a lithium secondary battery according to another comparative example of the present invention.

[0032] FIGS. 3A to 3D are SEM-EDAM photographs of a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0033] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising," as used herein, specifies particular features, regions, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0035] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0036] In this specification, D1O means the particle size at 10% by volume in the cumulative size-distribution curve, D50 means the particle size at 50% by volume, and D90 means the particle size at 90% by volume.

[0037] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0038] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0039] FIG. 1a and FIG. 1b are SEM and TEM photographs of a negative electrode active material for a lithium secondary battery according to one embodiment of the present invention.

[0040] Referring to FIGS. 1A and 1B, a negative active material for a lithium secondary battery according to one embodiment of the present invention includes a silicon-based base material and a coating layer coated on the surface of the silicon-based base material, and the coating layer may include at least one of a carbon layer and nanocarbon beads. Specifically, the nanocarbon beads may be arranged on the carbon layer.

[0041] The above silicon-based matrix may be silicon alone, silicon oxide, silicon nitride, silicon sulfide, silicon carbide, silicon-metal alloy, and combinations thereof. Specifically, in the case of silicon oxide, SiO X It can be, and in the case of silicon carbide, it can be a Si-C composite.

[0042] The coating layer may be at least partially coated on the surface of the silicon base material by a coating material. The coating layer may be coated on part or all of the surface of the silicon base material. Specifically, the nanocarbon beads may be coated on part or all of the coating layer.

[0043] In one embodiment, the coating layer may contain 0.10 to 1.50 wt% of a coating material in the negative active material. The coating material may be, for example, coal tar, pyrolyzed fuel oil (PFO), and a combination thereof. Specifically, the content of the coating material may be included in the negative active material at 0.20 to 1.46 wt%. The content of the coating material refers to the content of the coating material in the negative active material after a carbonization process at a predetermined temperature range, for example, a temperature of 900°C or higher.

[0044] If the content of the coating material exceeds the upper limit, the amorphous carbon layer is formed thickly, which inhibits the movement of lithium ions and causes irreversibility, which causes the battery's charging efficiency and initial capacity to decrease and its lifespan to deteriorate. If the content of the coating material exceeds the lower limit, the amorphous carbon layer becomes insufficient, which causes a high specific surface area and fails to secure sufficient electrical conductivity, which causes the initial efficiency and initial capacity to decrease and the lifespan to deteriorate.

[0045] In one embodiment, the coating layer may include a carbon layer and at least one nanocarbon bead. The carbon layer and the nanocarbon beads may be coated from a coating material, for example, a coal tar-derived coating material. The carbon layer may be a layered coating layer having a high carbon content. The nanocarbon beads may be in the form of granules having a high carbon content.

[0046] In one embodiment, the carbon layer and nanocarbon beads may include sulfur. Since the carbon layer and nanocarbon beads include sulfur, the sulfur doped into the carbon lattice provides extra electrons, thereby increasing the electron concentration and thus improving electrical conductivity.

[0047] In one embodiment, the carbon layer and nanocarbon beads may include a sulfur content of 0.03 to 0.3 wt% based on 100 wt% of the total negative active material composition. Specifically, the sulfur content may include 0.03 to 0.25 wt%. When the sulfur content exceeds the upper limit, the amorphous carbon layer containing sulfur is formed thickly, thereby inhibiting the movement of lithium ions and causing irreversibility, which lowers the initial efficiency and initial capacity of the battery and deteriorates the lifespan of the battery. When the sulfur content exceeds the lower limit, the amorphous carbon layer containing sulfur is formed in small amounts, which exposes the surface of the base material, causing a high specific surface area and failing to secure sufficient electrical conductivity, which lowers the initial efficiency and initial capacity of the battery and deteriorates the lifespan.

[0048] In one embodiment, the sulfur content relative to the content of the coating material may be 0.02 to 1.20. The sulfur content relative to the content of the coating material refers to a value obtained by dividing the sulfur content by the content of the coating material remaining in the negative electrode active material that has undergone the carbonization process.

[0049] If the content of the coating material exceeds the upper limit, the amorphous carbon layer is formed thickly, which inhibits lithium ion (Li) movement and causes irreversibility, which lowers the initial efficiency and initial capacity of the battery, and thus causes a problem of deterioration in the life of the battery. If the content of the coating material exceeds the lower limit, the amorphous carbon layer is formed insufficiently, exposing the surface of the base material, which causes a high specific surface area and fails to secure sufficient electrical conductivity, which lowers the initial efficiency and initial capacity and causes a problem of deterioration in the life of the battery.

[0050] In one embodiment, the carbon layer may be an amorphous carbon coating layer. In one embodiment, the carbon layer may have a thickness in the range of 1.0 to 10 nm. Specifically, the carbon layer may have a thickness in the range of 1.0 to 8.0 nm. When the thickness of the carbon layer exceeds the upper limit, there is a problem that the amorphous layer acts as a resistor, thereby inhibiting the movement of lithium ions and causing irreversibility, which lowers the initial efficiency and initial capacity, thereby causing a deterioration in the battery life, and when the thickness of the carbon layer exceeds the lower limit, the surface of the base material is exposed due to the insufficiency of the amorphous carbon layer, which causes a high specific surface area, and since sufficient conductivity is not secured, sufficient electrical conductivity is not secured, which lowers the initial efficiency and initial capacity, and thus, there is a problem that the battery life is deteriorated.

[0051] In one embodiment, the nanocarbon beads may be composed of at least one cluster. The cluster refers to a group of grains, and the nanocarbon beads may have a shape of not only a single grain but also a group of grains.

[0052] In one embodiment, at least one nanocarbon bead may have at least one shape of spherical and oval. The at least one nanocarbon bead may have a particle diameter of 2.0 nm to 1.0 μm. Specifically, the particle diameter of the nanocarbon bead may be 3.0 nm to 0.9 μm. If the particle diameter of the nanocarbon bead exceeds the upper limit, dispersion of the coating material is not easy, resulting in the formation of an uneven particle size and an uneven amorphous coating, thereby deteriorating battery performance. If the particle diameter of the nanocarbon bead exceeds the lower limit, there is a problem in that the initial efficiency decreases as the specific surface area increases.

[0053] In one embodiment, at least one of the nanocarbon beads may be disposed on at least one of the silicon-based matrix and the carbon layer. Specifically, the nanocarbon beads may be disposed on the silicon-based matrix, may be disposed on the carbon layer, or may be disposed in part on the silicon-based matrix and in part on the carbon layer.

[0054] In one embodiment, the negative active material of the present invention may be composed of at least one secondary particle, and the D10 of the secondary particle may be 2.0 to 6.5 μm. Specifically, the D10 may be 2.3 to 6.3 μm. More specifically, the D10 may be 2.3 to 4.0 μm. When the range of the D10 exceeds the lower limit, the fine particle content increases, which causes a problem in that contact is not easy, and there is a problem in that the electrochemical characteristics of the battery deteriorate.

[0055] In one embodiment, the D50 of the secondary particles may be 6.5 to 10 μm. Specifically, the D50 may be 6.7 to 9.5 μm. More specifically, the D50 may be 6.7 to 9.1 μm.

[0056] If the above D50 range exceeds the upper limit, there is a problem that the electrochemical characteristics of the battery deteriorate due to the deterioration of characteristics that can affect the electrode quality, such as the dispersion problem with the graphite when producing a mixed electrode with graphite. If the above D50 range exceeds the lower limit, there is a problem that the yield decreases during the pulverization process.

[0057] In one embodiment, the D90 of the secondary particles may be 10.0 to 16.0 μm. Specifically, the D90 may be 10.6 to 15.7 μm.

[0058] If the above D90 range exceeds the upper limit, when manufacturing a mixed electrode with graphite, there is a problem of dispersion with the graphite and an increase in the diffusion time of lithium ions, which deteriorates the electrochemical characteristics of the battery. If the above D90 range exceeds the lower limit, it is related to the above D50, and there is a problem in the pulverization process to implement it.

[0059] In one embodiment, the Span value ((D90-D10) / D50) of the secondary particle may be in the range of 0.80 to 1.40. Specifically, the Span value may be in the range of 0.86 to 1.39. More specifically, the Span value may be in the range of 1.20 to 1.39. Even more specifically, the Span value may be in the range of 1.26 to 1.39.

[0060] The above Span value refers to the narrowness and breadth between the minimum and maximum values ​​in the average value of the particle size distribution using laser diffraction. Specifically, the Span value refers to the difference between D90 and D10 for the average particle size (D50). When the Span value satisfies 0.9 to 1.3, there is an advantage in implementing an anode active material with excellent battery characteristics due to uniform dispersion during electrode production. Specifically, the Span value may satisfy the above range when D50 is in the range of 6.7 to 9.1 ㎛.

[0061] If the above Span value exceeds the upper limit, the particle size distribution becomes too wide, making it difficult to achieve uniform dispersion. If the above Span value exceeds the lower limit, the particle size distribution becomes narrow, making it difficult to maintain uniform contact between particles.

[0062] In one embodiment, a negative active material for a lithium secondary battery may satisfy the following equation 1.

[0063] <Formula 1>

[0064] 0.50 ≤ coating material content [wt%] × BET specific surface area [m2 / g] ≤ 9.50

[0065]

[0066] The content of the coating material after carbonization in the above formula 1 refers to the content of the coating material in the final product, and refers to the content of the coating material after carbonization. The above formula 1 can confirm the relationship between the appropriate coating material content of the negative active material and the BET specific surface area.

[0067] The above equation 1 can satisfy 0.50 to 9.50. Specifically, the above equation 1 can satisfy 0.80 to 6.40, and more specifically, 0.88 to 6.38.

[0068] If the value of the above equation 1 exceeds the upper limit, it means that the amorphous carbon layer is thick, and accordingly, there is a problem that the movement of lithium ions is inhibited, irreversibility occurs, the initial efficiency and initial capacity of the battery are reduced, and the lifespan is deteriorated. If the value of the above equation 2 exceeds the lower limit, there is a problem that the surface of the base material is exposed due to the insufficiency of the amorphous carbon layer, causing a high specific surface area, and sufficient electrical conductivity is not secured, so the initial efficiency and initial capacity are reduced, and the lifespan is deteriorated.

[0069]

[0070] According to one embodiment of the present invention, a negative active material for a lithium secondary battery can satisfy the following equation 2.

[0071] <Formula 2>

[0072] 1.40 ≤ Average particle diameter of secondary particles (D50) [㎛] × coating material content [wt%] ≤ 15.0

[0073]

[0074] In the above formula 2, D50 refers to the D50 of the secondary particle, and the coating material content refers to the content of the coating material after carbonization. The above formula 2 can satisfy a range of 1.40 to 15.0. Specifically, the above formula 2 can satisfy a range of 14.1 to 13.6.

[0075] If the upper limit of the above equation 3 is exceeded, the central particle diameter becomes large or the particle distribution is uneven, which affects the electrode quality, such as the problem of dispersion with graphite, when manufacturing a mixed electrode with graphite, and makes it difficult to derive normal electrochemical properties. If the lower limit of the above equation 3 is exceeded, the surface of the base material is exposed due to insufficient amorphous carbon layer, causing a high specific surface area, and there is a problem that sufficient electrical conductivity is not secured, resulting in a decrease in the initial efficiency and initial capacity, and a deterioration in the battery life.

[0076]

[0077] In one embodiment, a negative electrode active material for a lithium secondary battery may satisfy the following equation 3.

[0078] <Formula 3>

[0079] 2.0 ≤ (sulfur content [wt%] / coating material content [wt%]) × 100 ≤ 120.0

[0080]

[0081] The above equation 3 represents the percentage of sulfur content relative to the content of the coating material after carbonization. The above equation 3 can satisfy 2.0 to 120.0. Specifically, the above equation 3 can satisfy 2.05 to 118.6.

[0082] If the upper limit of the above equation 3 is exceeded, the amorphous carbon layer is insufficient, exposing the surface of the base material, causing a high specific surface area and failing to secure sufficient electrical conductivity, which causes a problem of reduced initial efficiency and initial capacity and deterioration of the lifespan when applied to a battery. If the lower limit of the above equation 3 is exceeded, the amorphous carbon layer is formed thickly, which inhibits the movement of lithium ions and causes irreversibility, which causes a problem of reduced initial efficiency and initial capacity of the battery and deterioration of the lifespan.

[0083] In one embodiment, the negative active material for a lithium secondary battery may have an expansion ratio of 60.0% or less. Specifically, the expansion ratio may have an expansion ratio in the range of 40.0 to 60.0%. More specifically, the expansion ratio may have an expansion ratio in the range of 44.0 to 58.0%.

[0084] The above expansion ratio refers to the percentage of the value obtained by dividing (thickness of electrode after 50 cycles - thickness of Cu current collector) - (thickness of fresh electrode - thickness of Cu current collector) by (thickness of fresh electrode - thickness of Cu current collector). If the above expansion ratio exceeds the upper limit, excessive expansion of the negative electrode material occurs, causing deformation of the electrode structure constituting the inside of the cell, resulting in poor stability and hindering smooth movement of lithium ions, which in turn deteriorates the battery life.

[0085] According to one embodiment of the present invention, a method for manufacturing an anode active material for a lithium secondary battery comprises the steps of uniformly mixing a silicon-based coating material and a sulfur-containing coating material, and the steps of heat-treating the mixed resultant material to carbonize it. The silicon-based coating material is identical to the silicon-based base material described above, as long as it does not contradict it.

[0086] The sulfur-containing coating material may be a sulfur-containing material, for example, coal tar. The sulfur-containing coating material may be in a powder, liquid, or gaseous state, and specifically, may be a sulfur-containing liquid material.

[0087] In one embodiment, the coating material may have a surface tension of 25 to 45 dyne / cm, specifically, 30 to 40 dyne / cm, at room temperature. The silicon-based base material, which is the coating material, may have a higher surface tension than the coating material, for example, 65 to 75 dyne / cm. Accordingly, due to the difference in surface tension between the coating material and the coating material, the coating material may be uniformly coated on the surface of the coating material, and the remaining coating material after coating on the surface forms a spherical or elliptical shape in the carbonization process to lower the surface energy, thereby forming nanocarbon beads.

[0088] In one embodiment, the coating material may be included in an amount of 1 to 8 parts by weight per 100 parts by weight of the coating material. Specifically, the coating material may be included in an amount of 2 to 7 parts by weight per 100 parts by weight of the coating material, and more specifically, the coating material may be included in an amount of 3 to 5 parts by weight per 100 parts by weight of the coating material.

[0089] If the upper limit of the above range is exceeded, agglomeration or agglomeration between particles is induced, which causes an increase in particle size, and the nano carbon amorphous layer is formed thickly, and the thick formation of the amorphous layer inhibits the movement of lithium ions and causes irreversibility, which reduces the initial efficiency and initial capacity, and causes a deterioration in the lifespan. If the lower limit of the above range is exceeded, the amorphous carbon layer is insufficient, exposing the surface of the base material, causing a high specific surface area, and not securing sufficient electrical conductivity, which causes a problem of a decrease in the initial efficiency and initial capacity, and a deterioration in the lifespan.

[0090] In one embodiment, the step of uniformly mixing the silicon-based coating material and the sulfur-containing coating material may be performed by a dry mixing step. The dry mixing step may be a mechanical mixing treatment, and the mechanical mixing treatment may be performed by selecting any one method from among ball milling, mechanofusion milling, shaker milling, planetary milling, attritor milling, disk milling, shape milling, nauta milling, nobilta milling, Planetary, 3D-mixer, V-mixer, Mechano-Fusion, Hybridizer, Pate Mixer, or a combination thereof.

[0091] The step of carbonizing the mixed result by heat treating the result in which the coating material and the coating material are mixed may be carbonized on the surface of the coating material while heat treating the result.

[0092] In one embodiment, the step of carbonizing the mixed result by heat treatment may be performed in a range of 800 to 1,000°C. Specifically, the range may be performed in a range of 850 to 950°C.

[0093] If heat treatment is performed in a range outside the upper limit of the above range, there is a problem that the crystal grain growth of Si occurs, thereby reducing the battery capacity and efficiency, and if heat treatment is performed in a range outside the lower limit of the above range, there is a problem that it is difficult to achieve uniform amorphization of the coating material.

[0094] In one embodiment, a method for manufacturing a negative electrode active material for a lithium secondary battery can satisfy the following equation 4.

[0095] <Formula 4>

[0096] 0.37 ≤ (sulfur content [wt%] / content of coating material before carbonization [wt%]) × 100 ≤ 25.0

[0097]

[0098] The above formula 4 refers to the sulfur content [wt%] relative to the content [wt%] of the coating material before carbonization. The above formula 4 may be 0.37 to 25.0, specifically, the above formula 4 may be 0.43 to 24.9.

[0099] If the range of the above equation 4 exceeds the upper limit, the surface of the base material is exposed due to the insufficient amorphous carbon layer, causing a high specific surface area, and insufficient electrical conductivity is not secured, which causes a decrease in the initial efficiency and initial capacity, and a deterioration in the lifespan. If the range of the above equation 4 exceeds the lower limit, the amorphous layer acts as a resistor, which reduces the movement of lithium ions, and causes irreversibility, which causes a decrease in the initial efficiency and initial capacity, and a deterioration in the lifespan of the battery.

[0100] According to another embodiment of the present invention, a lithium secondary battery may include a negative electrode including the above-described negative electrode active material, a positive electrode including the above-described positive electrode active material, a separator positioned between the negative electrode and the positive electrode, and an electrolyte. The description of the negative electrode active material is the same as the description of the negative electrode active material for a lithium secondary battery described above, to the extent that it does not contradict the description.

[0101] The above anode is LiCoO2, LiNiO2, LiNi x Mn y O2, Li 1+z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al zAny one of the group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, LiFeO2, LiFePO4, and combinations thereof, wherein x is 0.3 to 0.8, y is 0.1 to 0.45, and z may independently be 0 to 0.2. The positive electrode may be more specifically LiFePO4, LiCoO2, NCM811, and NCM622. The negative electrode may use the above-described active material for a lithium secondary battery, or an negative electrode active material manufactured through a method for manufacturing a precursor of the negative electrode active material.

[0102] The above separation membrane may be a conventional porous polymer film used as a separator in the past, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / propylene copolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, used alone or in a laminated manner, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., may be used, and these are non-limiting examples.

[0103] In the above electrolyte, lithium salts that can be included as the electrolyte can be used without limitation as those commonly used in electrolytes for lithium secondary batteries, and for example, the anion of the lithium salt may be F - , Cl - , Br - , 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 - It can be any one selected from the group consisting of .

[0104] In the above electrolyte, as the organic solvent, those commonly used in electrolytes for lithium secondary batteries can be used without limitation, and representative examples thereof include one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more thereof.

[0105] The above lithium secondary battery may be placed in a battery case. The battery case may be, as non-limiting examples, any one of a cylindrical shape using a can, a square shape, a pouch shape, and a coin shape.

[0106] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0107]

[0108] <Ingredient Characteristics>

[0109] The coating material of the present invention is a liquid material containing sulfur that is not measured by ASTM D3104 (softening point measurement method 1, softening point of 50°C or higher) or ASTM D36 (softening point measurement method 2, softening point of 30°C or higher) because liquid coal tar generated during the dry distillation of raw coal in a steel mill is fluid at room temperature, has a specific gravity of 1.1 to 1.3 g / cc, and has a fixed carbon content of 19 to 23% when carbonized at 900°C.

[0110] When the above liquid material is coated on a base material, which is a coating material, a carbon layer containing sulfur and nanocarbon beads (NCB) are formed on the surface of the base material due to the characteristics of the liquid.

[0111]

[0112] Manufacturing Process

[0113] As a process for manufacturing the negative electrode material of the present invention, in order to form the amorphous carbon layer of the negative electrode material and the nanocarbon beads, the coating process includes a step of uniformly dry mixing between a silicon-based coating material and a coating material, and a carbonization process of heat treatment at a temperature of 800 to 1,000°C after a dry dispersion process. The mixing and dispersion method is performed through a method such as a planetary, 3D-mixer, V-mixer, mechano-fusion, hybridizer, or paste mixer.

[0114]

[0115] <Example 1>

[0116] As the above silicon-based coating material, silicon oxide (SiO x ) was used, and liquid coal tar was used as the coating material. Specifically, the liquid coal tar was used as the silicon oxide (SiO x ) A negative electrode active material is manufactured by coating 1 part by weight based on 100 parts by weight and including a material carbonized at 900°C.

[0117]

[0118] <Example 2>

[0119] The above liquid coal tar is the silicon oxide (SiO x ) The negative active material was manufactured in the same manner as in Example 1, except that 4 parts by weight were coated based on 100 parts by weight.

[0120]

[0121] <Example 3>

[0122] The above liquid coal tar is the silicon oxide (SiO x ) The negative active material was manufactured in the same manner as in Example 1, except that 7 parts by weight were coated based on 100 parts by weight.

[0123]

[0124] <Example 4>

[0125] A silicon-carbon composite (Si-C Composite) was used as the silicon-based coating material, and liquid coal tar was used as the coating material. Specifically, a negative electrode active material including a material carbonized at 900°C by coating the liquid coal tar on the silicon-carbon composite was manufactured.

[0126]

[0127] <Example 5>

[0128] A negative active material was manufactured in the same manner as in Example 4, except that 4 parts by weight of the liquid coal tar was coated based on 100 parts by weight of the silicon-carbon composite (Si-C Composite).

[0129]

[0130] <Example 6>

[0131] A negative active material was manufactured in the same manner as in Example 4, except that 7 parts by weight of the liquid coal tar was coated based on 100 parts by weight of the silicon-carbon composite (Si-C Composite).

[0132]

[0133] <Comparative Example 1>

[0134] A negative active material was prepared in the same manner as in Example 1, except that the above liquid coal tar was not added as a coating material.

[0135]

[0136] Comparative Example 2

[0137] The above liquid coal tar is the silicon oxide (SiO x ) The negative active material was manufactured in the same manner as in Example 1, except that 9 parts by weight were coated based on 100 parts by weight.

[0138]

[0139] <Comparative Example 3>

[0140] The above liquid coal tar is the silicon oxide (SiO x ) The negative active material was manufactured in the same manner as in Example 1, except that 18 parts by weight was coated based on 100 parts by weight.

[0141]

[0142] Comparative Example 4

[0143] A negative active material was prepared in the same manner as in Example 4, except that the above liquid coal tar was not added as a coating material.

[0144]

[0145] Comparative Example 5

[0146] A negative active material was manufactured in the same manner as in Example 4, except that 9 parts by weight of the liquid coal tar was coated based on 100 parts by weight of the silicon-carbon composite (Si-C Composite).

[0147]

[0148] <Comparative Example 6>

[0149] The above solid pitch is the silicon oxide (SiO x ) The negative active material was manufactured in the same manner as in Example 1, except that 2 parts by weight was coated based on 100 parts by weight.

[0150]

[0151] Comparative Example 7

[0152] A negative active material was manufactured in the same manner as in Example 4, except that 2 parts by weight of the above-mentioned solid pitch was coated based on 100 parts by weight of the above-mentioned silicon-carbon composite (Si-C Composite).

[0153]

[0154] <Manufacturing of silicon-based single electrodes>

[0155] Silicon oxide (SiO) used as a coating material in Examples 1 to 3, Comparative Examples 1 to 3, and Comparative Example 6 X ) as a negative electrode active material, a method for manufacturing a silicon-based single electrode, wherein a negative electrode active material, a binder (PAA), and a conductive agent (Super P) are prepared and mixed so that the weight ratio of the negative electrode active material: binder: conductive agent is 75:24:1, respectively, to manufacture a slurry. The slurry is uniformly applied to a copper (Cu, about 10 ㎛ thick) current collector, pressed in a roll press, and then dried to manufacture a negative electrode. Specifically, the electrode is manufactured to have a loading amount of 2 to 3 mg / cm2 and an electrode density of 0.8 to 1.2 g / cc.

[0156] Lithium metal (Li-Metal) is used as the counter electrode, and 1 mol of LiPF6 solution is dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 3:7 as the electrolyte.

[0157] A CR 2032 half coin cell is manufactured using the above negative electrode, lithium metal, and electrolyte according to a conventional manufacturing method.

[0158]

[0159] <Manufacturing of silicon-based mixed electrodes>

[0160] A method for manufacturing a silicon-based mixed electrode including a silicon-carbon composite (Si-C Composite) used as a coating material in Examples 4 to 6, Comparative Examples 4 to 5, and Comparative Example 7 as a negative electrode active material, wherein the negative electrode active material, binder (SBR-CMC), and conductive material (Super P) are prepared so that the weight ratio of negative electrode active material: binder: conductive material is 96.1:2.9:1, and then added to distilled water and uniformly mixed to manufacture a slurry.

[0161] At this time, the negative electrode active material is a mixture containing 8% silicon and 92% spherical natural graphite, and has a capacity of about 440 to 450 mAh / g. The slurry is uniformly applied to a copper (Cu, about 10 ㎛ thick) current collector, and then pressed in a roll press and dried to manufacture the negative electrode. Specifically, the electrode has a loading amount of 7 to 8 mg / cm. 2 , and is manufactured to have an electrode density of 1.55 to 1.60 g / cc.

[0162] Lithium metal (Li-Metal) is used as the counter electrode, and 1 mol of LiPF6 solution is dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of 3:7 as the electrolyte.

[0163] A CR 2032 half coin cell is manufactured using the above negative electrode, lithium metal, and electrolyte according to a conventional manufacturing method.

[0164] Table 1 below shows the presence or absence of nanocarbon beads and the size of nanocarbon beads according to the content of the coating material, coating substance, and coating material.

[0165] Coating materialCoating materialCoating material contentCoating material content after carbonization at 900℃Sulfur contentPresence or absence of nanocarbon beadsNanocarbon bead size[Sulfur content (wt%)] / [Coating material content (wt%)] × 100-Equation 4[Sulfur content (wt%)] / [Coating material content after carbonization at 900℃] × 100-Equation 3(wt%)(wt%)(wt%)(nm)Example 1SiOxCoal Tar10.210.03O<1003.0014.29Example 2SiOxCoal Tar40.830.03O<1000.753.61Example 3SiOxCoal Tar71.460.03O<1000.432.05Example 4Si-CCoal Tar10.210.249O<10024.9118.57Example 5Si-CCoal Tar40.830.25O<1006.2530.12Example 6Si-CCoal Tar71.460. 254O<1003.6317.40Comparative Example 1SiOxCoal Tar000XX00Comparative Example 2SiOxCoal Tar91.870.034O<1000.381.81Comparative Example 3SiOxCoal Tar183.740.039O<1000.221.04Comparative Example 4Si-CCoal Tar000.22XX00Comparative Example 5Si-CCoal Tar91.870.256O<1002.8413.69Comparative Example 6SiOxPitch21.40XX00Comparative Example 7Si-CPitch21.40.22XX11.015.71

[0166] FIGS. 2a and 2b are SEM and TEM photographs of a negative electrode active material for a lithium secondary battery according to Comparative Example 2 of the present invention, and FIGS. 2c and 2d are SEM and TEM photographs of a negative electrode active material for a lithium secondary battery according to Comparative Example 6 of the present invention.

[0167] Referring again to FIGS. 1A and 1B, the negative electrode active material for a lithium secondary battery according to Example 2 of the present invention is shown in SEM and TEM photographs, and in the case of Example 2, it can be confirmed that a carbon layer and nanocarbon beads are formed.

[0168] Referring to FIGS. 2a and 2c, compared to FIGS. 1a and 1b, it can be confirmed that a carbon layer is formed, but nanocarbon beads are not formed, and accordingly, it can be confirmed that there is a disadvantageous effect in terms of initial capacity, initial efficiency, and mixing life.

[0169] Referring to FIGS. 3a to 3d, FIG. 3a shows mapping for Si, S, O, and C, FIG. 3b shows mapping for Si, FIG. 3c shows mapping for S, and FIG. 3d shows a spectrum for each element.

[0170] Referring to FIGS. 3A to 3D, the S content of the embodiments of the present invention can be more clearly confirmed. By including the S content within the scope of the present invention, nanocarbon beads can be appropriately formed.

[0171]

[0172] Looking at Table 2 below, we can see the characteristics of the negative electrode active materials for lithium secondary batteries according to the examples and comparative examples of Table 1. Specifically, the initial capacity, initial efficiency, and mixed lifespan are shown. In the case of a single electrode, the initial efficiency is calculated by multiplying (discharge capacity / charge capacity) × 100 by measuring once with a charge CC-CV of 0.1 C & 5 mV (0.005 C cutoff) and a discharge 0.1 C 1.5 V cut-off. In addition, in the case of a single electrode, the initial capacity is calculated by measuring three times with a charge CC-CV of 0.1 C & 5 mV (0.005 C cutoff) and a discharge 0.1 C 1.5 V cut-off, and then calculating the specific capacity (mAh / g) during discharge. Also, for the mixed electrode, the mixed lifespan is measured after 1 activation of charge CC-CV 0.1 C & 5 mV (0.005 C cutoff), discharge 0.1 C 1.5 V cutoff, and 50 cycles of charge CC-CV 0.5 C 1.0 V cutoff, (50 th Life discharge capacity / 1 stCalculate the life discharge capacity.

[0173] The particle size distribution of secondary particles D10, D50, and D90 was measured using laser diffraction.

[0174] The expansion ratio was evaluated as a percentage of the value obtained by dividing (thickness of electrode after 50 cycles - thickness of Cu current collector) - (thickness of fresh electrode - thickness of Cu current collector) by (thickness of fresh electrode - thickness of Cu current collector).

[0175] The BET surface area was measured using the BET method (Surface area and Porosity Analyzer) of Micromeritics, ASAP2020.

[0176] Secondary particle D50 Secondary particle D10 Secondary particle D90 Span value (D90-D10 / D50) [Secondary particle D50] × [900℃ post-carbonization coating material content] - Equation 2 BET specific surface area Raman peak related data Initial capacity Expansion rate Initial efficiency Mixing life Post-carbonization coating material content x BET - Equation 1 (㎛) (㎛) (㎛) (-) (m 2 / g)R(Id / Ig)(mAh / g)(%)(%)(%)Example 16.72.310.61.241.414.211.06150246.282.175.20.88Example 26.92.510.81.205.732.121.08151444.383.276.81.76Example 39.56.314.50.8613.872.351.09149445.982 .474.23.43Example 48.93.215.61.391.876.521.42153857.585.676.51.37Example 59.13.715.571.307.555.251.5158551.286.278.24.36Example 69.33.915.651.2613.584.371.56157153.385.277.16.38Comparative Example 16. 52.110.41.2806.25X135851.876.146.20Comparative Example 29.95.715.81.0218.516.121.13143547.679.165.511.44Comparative Example 318.911.126.30.8070.695.691.19139653.278.155.521.28Comparative Example 48.61315.51.45010.85X154 275.283.261.10Comparative Example 59.54.115.71.2217.779.981.67151568.883.867.518.66Comparative Example 611.13.215.51.1115.546.84X143651.377.352.29.58Comparative Example 712.254.6224.31.6117.1510.21X151364.483.665.714.29

[0177] FIGS. 3A to 3D are SEM-EDAX photographs of a negative electrode active material for a lithium secondary battery according to an embodiment of the present invention. The present invention is not limited to the above-described embodiments and / or examples, but can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments and / or examples are exemplary in all respects and not restrictive.

Claims

1. Silicon-based base material; and Including a coating layer coated on the surface of the above silicone-based base material, The above coating layer comprises a carbon layer and at least one nano carbon bead, The above carbon layer and the above nanocarbon beads contain sulfur, A negative electrode active material for a lithium secondary battery, wherein the content of the coating material is 0.10 to 1.50 wt% based on 100 wt% of the total active material.

2. In paragraph 1, A negative active material for a lithium secondary battery satisfying the following equation 1. <Formula 1> 0.50 ≤ coating material content [wt%] × BET surface area [m 2 / g] ≤ 9.50 3. In paragraph 1, A negative active material for a lithium secondary battery satisfying the following equation 2. <Formula 2> 1.40 ≤ Average particle size of secondary particles (D50) [㎛] × coating material content [wt%] ≤ 15.0 4. In paragraph 1, A negative active material for a lithium secondary battery satisfying the following equation 3. <Formula 3> 2.0 ≤ (sulfur content [wt%] / coating material content [wt%]) × 100 ≤ 120.0 5. In paragraph 1, A negative active material for a lithium secondary battery, wherein the sulfur is contained in an amount of 0.03 to 0.3 wt%.

6. In paragraph 1, A negative active material for a lithium secondary battery having a D10 particle size of secondary particles of 2.0 to 6.5 ㎛.

7. In paragraph 1, A negative active material for a lithium secondary battery having an average particle diameter (D50) of 6.7 to 9.5 ㎛.

8. In paragraph 1, A negative active material for a lithium secondary battery having a D90 particle size of secondary particles of 10.6 to 15.7 ㎛.

9. In paragraph 1, A negative active material for a lithium secondary battery having a span value of secondary particles ((D90-D10) / D50) of 0.80 to 1.

40.

10. In paragraph 1, The above silicon-based matrix is ​​a negative electrode active material for a lithium secondary battery, which is silicon alone, silicon oxide, silicon nitride, silicon sulfide, silicon carbide, silicon-metal alloy, and a combination thereof.

11. In paragraph 1, The above carbon layer is an amorphous carbon layer, a negative electrode active material for a lithium secondary battery.

12. In paragraph 1, A negative electrode active material for a lithium secondary battery, wherein the carbon layer has a thickness of 1.0 to 10 nm.

13. In paragraph 1, A negative active material for a lithium secondary battery, wherein at least one of the above nanocarbon beads is composed of at least one cluster.

14. In paragraph 1, A negative active material for a lithium secondary battery, wherein at least one of the above nanocarbon beads has at least one of a spherical shape and an oval shape.

15. A step of uniformly mixing a silicon-based coating material and a coating material containing sulfur; and Including a step of carbonizing the mixed result by heat treatment, A method for producing a negative electrode active material for a lithium secondary battery, wherein the coating material comprises 1 to 8 parts by weight based on 100 parts by weight of the picocoating material.

16. In paragraph 15, A method for manufacturing a negative electrode active material for a lithium secondary battery satisfying the following equation 4. <Formula 4> 0.37 ≤ (sulfur content [wt%] / content of coating material before carbonization [wt%]) × 100 ≤ 25.0 17. In paragraph 15, The above silicon-based coating material is a method for producing an anode active material for a lithium secondary battery, the anode active material including silicon alone, silicon oxide, silicon nitride, silicon sulfide, silicon carbide, silicon-metal alloy and combinations thereof.

18. In paragraph 15, The above sulfur-containing coating material is a method for manufacturing an anode active material for a lithium secondary battery, which is coal tar or petroleum-based residual oil (PFO: pyrolyze).

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