Negative electrode active material, negative electrode material comprising same, and secondary battery comprising same

Abstract

The present invention relates to a negative electrode active material and, more particularly, to: a negative electrode active material having high energy density, excellent solid electrolyte interphase (SEI) forming properties, and low lithium ion diffusion resistance; a negative electrode material comprising same; and a secondary battery using same.

Description

Negative active material, negative electrode material containing the same, and secondary battery containing the same

[0001] The present invention relates to an anode active material having high energy density, excellent SEI (solid electrolyte interphase) formation, and low lithium ion diffusion resistance, an anode material for a lithium ion secondary battery including the same, and a lithium ion secondary battery using the same.

[0002] With the recent development of the information and communication industry, demand for electronic devices has been rapidly increasing, and with the revitalization of the electric vehicle market, demand for batteries used in these electronic devices and electric vehicles has also increased significantly.

[0003] Secondary batteries, including lithium secondary batteries and all-solid-state batteries containing liquid electrolytes, are the most widely used for these applications due to their high energy density and minimal self-discharge when not in use. Secondary batteries generally consist of a positive electrode, a negative electrode, and an electrolyte (liquid or solid). Carbon-based materials such as graphite are widely used as the negative electrode active material.

[0004] Recently, attempts have been made to use silicon-based anode active materials to improve the capacity of secondary batteries. Silicon, with its theoretically very high energy density, is attracting attention as a next-generation battery anode material to replace graphite. However, it reacts with lithium during charge and discharge, increasing its volume by up to 300%. This causes the silicon anode material to fracture during charge and discharge, resulting in significantly poor mechanical stability.

[0005] To solve these problems, a composite obtained by forming a silicon layer on a porous carbon support with excellent electrical conductivity has been proposed. However, since conventional carbon supports mainly have micropores, there is a problem that deposition does not reach the deep pores well when chemical vapor deposition (CVD) or the like is performed in a subsequent process, and the silicon crystals formed on the carbon support are large, so the phenomenon of fracture due to volume expansion cannot be sufficiently resolved.

[0006] In addition, there have been various attempts to improve the properties of existing negative electrode active materials composed of silicon and carbon supports as negative electrode materials, but existing negative electrode active materials have problems such as poor SEI (solid electrolyte interphase) formation within the cell of a lithium-ion secondary battery and high lithium-ion diffusion resistance.

[0007] [Prior Art Literature]

[0008] [Patent Document]

[0009] (Patent Document 001) Korean Patent Registration No. 10-2500979 (Announcement Date: February 17, 2023)

[0010] (Patent Document 002) Korean Patent Registration No. 10-2496671 (Announcement Date: February 8, 2023)

[0011] (Patent Document 003) Korean Patent Publication No. 10-2020-0058972 (Published on May 28, 2020)

[0012] The present invention has been devised to overcome the above-described problems, and by controlling the pore characteristics of a carbon-silicon composite that serves as a support for an anode active material, and introducing a pitch coating and a conductive material into the carbon-silicon composite with controlled pore characteristics in a specific manner, an anode active material has been completed that improves low SEI formation and high lithium ion diffusion resistance, which are problems of existing anode active materials. That is, the present invention aims to provide an anode active material, an anode material comprising the same, and a secondary battery using the same.

[0013] The present invention for solving the above-described problem comprises a silicon composite as a negative active material and a carbon layer formed on the silicon composite, wherein the carbon layer includes a conductive material.

[0014] As a preferred embodiment of the present invention, the conductive material may include at least one selected from SUPER-P, VGCF (vapor grown carbon fibers), and Mxnene particles represented by the following chemical formula 1.

[0015] [Chemical Formula 1]

[0016] A x B y C z

[0017] In the above chemical formula 1, A may be Ti, Nb or Ta, B may be Si, Ge, Sn or Al, C may be a carbon atom or a nitrogen atom, x may be 3 or 4, y may be 0 or 1, and z may be 2 or 3.

[0018] As a preferred embodiment of the present invention, in the chemical formula 1, A may be Ti, C may be a carbon atom, x may be 3 or 4, y may be 0, and z may be 2 or 3.

[0019] As a preferred embodiment of the present invention, the conductive material may be included in an amount of 0.1 to 8.0 wt% based on the total weight of the negative electrode active material.

[0020] As a preferred embodiment of the present invention, the carbon layer may be formed by dry coating petroleum-based pitch on a silicon composite.

[0021] As a preferred embodiment of the present invention, the dry coating may be performed under conditions of 3,000 to 10,000 rpm.

[0022] As a preferred embodiment of the present invention, the carbon layer may be included in an amount of 5.0 to 15.0 wt% based on the total weight of the negative electrode active material.

[0023] As a preferred embodiment of the present invention, the silicon composite may be a carbon-silicon composite including a porous carbon support; and silicon formed on the porous carbon support.

[0024] As a preferred embodiment of the present invention, the energy density of the negative active material may be 1450.0 mAh / g or more.

[0025]

[0026] Another object of the present invention is to provide a negative electrode material comprising the negative electrode active material described above.

[0027] In addition, another object of the present invention is to provide a secondary battery including the negative electrode material described above.

[0028] As a preferred embodiment of the present invention, the secondary battery may be a lithium secondary battery or an all-solid-state battery.

[0029] The negative electrode active material of the present invention has excellent SEI (solid electrolyte interphase) formation within the cell of a lithium ion secondary battery, low lithium ion diffusion resistance, and high energy density. When this is introduced as a negative electrode material of a lithium ion secondary battery, a lithium ion secondary battery having excellent charge capacity, discharge capacity, and / or initial ICE (initial concentration efficiency) and improved life characteristics can be provided.

[0030] FIGS. 1A to 1D each show the results of measuring the charge / discharge capacity and initial efficiency (ICE) of a secondary battery cell conducted in Experimental Example 2. FIG. 1A shows the results of measuring Comparative Example 1, FIG. 1B shows the results of measuring Example 1, FIG. 1C shows the results of measuring Example 2, and FIG. 1D shows the results of measuring Comparative Example 2.

[0031] Figure 2 is a shape graph of a Nyquist plot measured by EIS in Experimental Example 3.

[0032] Each of FIGS. 3a to 3d is an EIS measurement result of a secondary battery cell performed in Experimental Example 3. FIG. 3a is a measurement result for Comparative Example 1, FIG. 3b is a measurement result for Example 1, FIG. 3c is a measurement result for Example 2, and FIG. 3d is a measurement result for Comparative Example 2.

[0033] Hereinafter, the present invention will be described in more detail.

[0034] Silicon, which is conventionally used as an anode active material, has a high theoretical capacity of 4,000 to 4,200 mAh / g. However, as the silicon content as an anode active material increases, its conductivity decreases compared to carbon-based materials, and there are problems in that the volume change occurring in the charge / discharge reaction is severe, causing electrical insulation of silicon particles or excessively high electrical resistance due to contact resistance. In order to overcome these shortcomings, the anode active material according to the present invention includes a silicon composite and a carbon layer formed on the silicon composite, wherein the carbon layer includes a conductive material.

[0035] In addition, the negative active material introducing the specific conductive agent is manufactured by mixing a porous silicon composite (a carbon-silicon composite without a carbon layer formed) and the conductive agent, followed by dry coating with petroleum pitch, preferably Hosokawa dry coating, and then carbonization. In addition, the Hosokawa dry coating can be performed under conditions of 3,000 to 10,000 rpm, preferably under conditions of 4,000 to 8,000 rpm.

[0036] In the above Hosokawa dry coating, the rotation speed affects the shear force, which affects the stress between the parent particles and the interfacial bonding between the parent particles. The higher the rotation speed, the stronger the compressive stress and shear force are generated, which provides mechanical energy to the particle surface, causing the coating particles (parent particles) to interfacially bond with the surface of the parent particles. In other words, the carbon layer formed by the parent particle, the carbon-silicon composite, the conductive material, and the petroleum pitch is more strongly bonded. This means that the diffusion speed of lithium ions is high during the manufacture of secondary batteries, thereby increasing the amount of active lithium and thus the capacity. However, if the rotation speed is too high and the compressive stress and shear force are too high, exceeding the particle strength of the parent particles to be coated, the particles may be pulverized or worn, which may significantly reduce the theoretical capacity as an anode active material. Therefore, it is preferable to perform dry coating within the above rotation speed range.

[0037]

[0038] [Silicone complex]

[0039] The above silicon composite may use a carbon-silicon composite.

[0040] The carbon-silicon composite comprises a porous carbon support; and the formed silicon of the porous carbon support.

[0041] The porous carbon support of the above carbon-silicon composite may have a mesopore volume ratio of 2 to 50 nm in pore size of 10 to 80%, preferably 30 to 60%, and more preferably 40 to 50%, based on the pore volume. If the mesopore volume ratio of the porous carbon support is less than 10%, there may be too many micropores, so that a relatively large amount of silicon source may be deposited on the outside, and if the mesopore volume ratio of the porous carbon support exceeds 80%, the hardness of the particles is insufficient, so that when an electrode is manufactured using the same, there is a concern that the structure of the electrode may collapse.

[0042] In addition, the porous carbon support may have an average particle size of 1 to 20 μm. Preferably, the porous carbon support may have an average particle size of 3 to 20 μm, more preferably, an average particle size of 3 to 10 μm. When the average particle size of the porous carbon support is less than 1 μm, the silicon source cannot sufficiently penetrate into the pores and is deposited only on the outside of the particles, and when the average particle size of the porous carbon support exceeds 20 μm, it is difficult for the silicon source to sufficiently deposit into the pores.

[0043] Additionally, the porous carbon support may have a BET surface area of ​​300 to 3,000 m2 / g. Preferably, the porous carbon support may have a BET surface area of ​​300 to 1,500 m2 / g, more preferably, a BET surface area of ​​500 to 1,500 m2 / g. When the BET surface area of ​​the porous carbon support is less than 300 m2 / g, there may be too many macropores and thus a lack of effective pores, and when the BET surface area of ​​the porous carbon support exceeds 3,000 m2 / g, there may be too many micropores and thus a large amount of silicon source may be deposited on the outside of the particles.

[0044] In addition, the porous carbon support may have a tap density of 0.05 to 0.60 g / ml. Preferably, the porous carbon support may have a tap density of 0.05 to 0.50 g / ml, more preferably, a tap density of 0.1 to 0.4 g / ml. When the tap density of the porous carbon support is less than 0.05 g / ml, process control may be difficult during deposition of the silicon source, resulting in a decrease in yield. When the tap density of the porous carbon support exceeds 0.60 g / ml, uniform coating may be difficult during deposition of the silicon source.

[0045] When the above porous carbon support is introduced into a porous silicon composite, stress caused by volume expansion of silicon can be alleviated.

[0046]

[0047] [Method for manufacturing a porous carbon support]

[0048] The above porous carbon support may be manufactured by performing a process including: (a) a step of synthesizing pitch by thermal decomposition and polycondensation of a petroleum-based raw material, (b) a step of solidifying and pulverizing the pitch to obtain pitch in the form of pellets or powder, (c) a step of stabilizing the pitch, (d) a step of carbonizing the stabilized pitch to obtain a carbonized body, and (e) a step of activating the carbonized body to obtain a porous carbon support.

[0049] In step (a), pitch can be synthesized by thermal decomposition and polycondensation of petroleum-based raw materials.

[0050] In a specific embodiment of the present invention, the petroleum-based raw material may include at least one selected from the group consisting of pyrolysis fuel oil (PFO), naphtha cracking residue (NCB), ethylene cracker bottom oil (EBO), vacuum residue (VR), de-asphalted oil (DAO), atmospheric residue (AR), fluid catalytic cracking (RFCC-DO) oil, residue fluid catalytic cracking decant oil (RFCC-DO), and heavy aromatic oil. In a preferred specific embodiment of the present invention, the petroleum-based raw material may include pyrolysis fuel oil.

[0051] In a specific embodiment of the present invention, the petroleum-based raw material may contain an aromatic compound in an amount of 10 to 90 wt%. Preferably, the petroleum-based raw material may contain an aromatic compound in an amount of 20 to 80 wt%, more preferably 30 to 70 wt%. When the content of the aromatic compound in the petroleum-based raw material satisfies the above range, even if the solid pitch pellets described below are stabilized, carbonized, and activated without separately pulverizing, a porous carbon support having controlled pore characteristics can be obtained.

[0052] In a specific embodiment of the present invention, the aromatic compound may be a compound having 1 to 4 aromatic rings. Specifically, the aromatic compound may include at least one selected from the group consisting of substituted or unsubstituted benzene, naphthalene, phenanthrene, indene, biphenyl, anthracene, tetralin, and fluorene. In this case, even if the solid pitch pellets described below are stabilized, carbonized, and activated without separately pulverizing, a porous carbon support having controlled pore characteristics can be obtained.

[0053] In a specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum-based raw material can be carried out at a temperature of 350 to 500°C. In a preferred specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum-based raw material can be carried out at a temperature of 400 to 500°C. In a more preferred specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum-based raw material can be carried out at a temperature of 430 to 470°C. When the temperature of the thermal decomposition and polycondensation of the petroleum-based raw material is 350 to 500°C, a pitch containing a large amount of relatively low molecular weight components can be produced, and in the activation process of step (e) described below, components having relatively small molecular weights are vaporized first, thereby sufficiently forming mesopores in the carbon support. If the thermal decomposition and polycondensation temperature of petroleum-based raw materials is less than 350°C, it is difficult to manufacture pitch that is solid at room temperature, and if this temperature exceeds 500°C, the pitch contains a lot of relatively high molecular weight components, making it difficult to manufacture a carbon support having mesopores.

[0054] In a specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum raw material may be performed under an atmosphere of an oxidizing gas, an inert gas, or a mixture thereof. In a preferred specific embodiment of the present invention, the oxidizing gas may be oxygen, ozone, or a combination thereof, the inert gas may be nitrogen, helium, neon, argon, or a combination thereof, and the mixture thereof may be air, but is not particularly limited thereto.

[0055] When an oxidizing gas is used during the thermal decomposition and polycondensation of petroleum-based raw materials, a pitch with a high softening point can be produced, but it is difficult to perform the thermal decomposition and polycondensation at high temperatures. When an inert gas is used during the thermal decomposition and polycondensation of petroleum-based raw materials, thermal decomposition and polycondensation can be performed at high temperatures, but it is difficult to produce a pitch with a relatively high softening point. When a mixed gas of an oxidizing gas and an inert gas is used during the thermal decomposition and polycondensation of petroleum-based raw materials, thermal decomposition and polycondensation can be performed at relatively high temperatures, thereby producing a pitch with a relatively high softening point.

[0056] In a specific embodiment of the present invention, the gas may be supplied at a flow rate of 10 to 800 ml / min during the thermal decomposition and polycondensation of a petroleum-based raw material. In a preferred specific embodiment of the present invention, the gas may be supplied at a flow rate of 100 to 500 ml / min during the thermal decomposition and polycondensation of a petroleum-based raw material. When the flow rate of the gas is less than 10 ml / min, the yield of the pitch increases, but the low molecular weight component increases too much, which is disadvantageous for subsequent processes (e.g., stabilization). When the flow rate of the gas exceeds 800 ml / min, the yield of the pitch may decrease.

[0057] In a specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum-based raw material can be carried out for 1 to 10 hours. In a preferred embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum-based raw material can be carried out for 2 to 8 hours. In a more preferred embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum-based raw material can be carried out for 2 to 7 hours. If the thermal decomposition and polycondensation time of the petroleum-based raw material is less than 1 hour, it is difficult to produce a pitch having a high softening point, and if the thermal decomposition and polycondensation time of the petroleum-based raw material exceeds 10 hours, an excessive amount of quinoline-insoluble components may be produced.

[0058] In a specific embodiment of the present invention, the thermal decomposition and polycondensation of the petroleum-based raw material may be performed under stirring. The stirring conditions for the petroleum-based raw material are not particularly limited, but, for example, a stirrer rotating at 10 to 500 rpm may be used.

[0059] In a specific embodiment of the present invention, the pitch synthesized in step (a) may have a softening point of 200 to 350°C. In a preferred embodiment of the present invention, the pitch may have a softening point of 200 to 330°C. In a more preferred embodiment of the present invention, the pitch may have a softening point of 200 to 300°C. Since the pitch manufactured according to the present invention has a high softening point, when used as a precursor for manufacturing a carbon support, the stabilization process is easy, and a high yield can be obtained after carbonization and activation.

[0060] In a specific embodiment of the present invention, the yield of the pitch synthesized in step (a) may be 10 to 50 wt%. In a preferred embodiment of the present invention, the yield of the pitch may be 15 to 50 wt%. In a more preferred embodiment of the present invention, the yield of the pitch may be 30 to 50 wt%.

[0061] In a specific embodiment of the present invention, a step of pretreating the petroleum-based raw material may be performed prior to step (a). By removing low-boiling-point components contained in the petroleum-based raw material through the pretreating step, a pitch having a higher softening point can be produced.

[0062] In a specific embodiment of the present invention, the pretreatment step may be performed at a temperature equal to or lower than the thermal decomposition and polycondensation temperature of the petroleum-based raw material in step (a), but is not particularly limited to this condition. Specifically, the pretreatment step may be performed at 250 to 450°C, preferably 250 to 400°C, and more preferably 300 to 400°C.

[0063] In a specific embodiment of the present invention, the pretreatment step may be performed for a time equal to or shorter than the thermal decomposition and polycondensation time of the petroleum-based raw material in step (a), but is not particularly limited to this condition. Specifically, the pretreatment step may be performed for 1 to 8 hours, preferably 1 to 6 hours, and more preferably 1 to 5 hours.

[0064] Additionally, in step (b), the pitch can be solidified and pulverized to obtain a pitch in the form of pellets or powder.

[0065] The liquid pitch obtained in step (a) is solidified, for example, by extrusion and cooling, and pelletized into a desired size to obtain solid pitch pellets. The process of extruding, cooling, and pelletizing the liquid pitch to obtain solid pitch pellets can be performed using commercially available equipment. For example, this process can be performed using a double-belt cooler & flaker from IPCO, but is not particularly limited to this equipment.

[0066] The pitch pellets obtained in step (b) have an average particle size of 1 to 30 mm, preferably 5 to 25 mm. When the average particle size of the pitch pellets is within this range, a porous carbon support can be manufactured through stabilization, carbonization, and activation described below without separately pulverizing the pitch pellets.

[0067] However, if necessary, the pitch pellets obtained in step (b) may be further crushed or pulverized and classified. The pitch pellets can be further finely divided through crushing or pulverization, and the particle size distribution of the pitch pellets can be made uniform through classification. Here, classification may be performed by dry classification, wet classification, or classification using a sieve. By crushing or pulverizing and classification, powdered pitch having an average particle size of 50 to 500 μm can be obtained.

[0068] And, in step (c), a step of stabilizing the pitch can be performed.

[0069] First, the pitch obtained in step (b) is subjected to primary oxidation to stabilize the carbon structure of the pitch.

[0070] In a specific embodiment of the present invention, the stabilization of the pitch may be performed in an oxidizing gas atmosphere. In a preferred embodiment of the present invention, the stabilization of the pitch may be performed in an air atmosphere, but is not particularly limited thereto.

[0071] In a specific embodiment of the present invention, the stabilization of the pitch may be performed at a temperature of 100 to 500°C, preferably 150 to 300°C. When the stabilization of the pitch is performed at this temperature, the carbon structure within the pitch changes from thermoplastic to thermosetting, so that the structure can be stably maintained during the subsequent carbonization process. At this time, the heating rate may be 2 to 10°C / min. If the heating rate is too slow, productivity may be poor, and if the heating rate is excessively fast, uniform stabilization treatment may be difficult.

[0072] In a specific embodiment of the present invention, the stabilization of the pitch can be performed at a pressure of 0.1 to 10 bar, preferably 0.5 to 5 bar. When the stabilization of the pitch is performed at a pressure within this range, the structure of the pitch can be sufficiently stabilized, including the carbon within the pitch.

[0073] In a specific embodiment of the present invention, the stabilization of the pitch can be performed under conditions of a flow rate of an oxidizing gas, preferably air, of 0.1 to 500 ml / min, preferably 1 to 300 ml / min. When the stabilization of the pitch is performed under these oxidizing gas flow rates, the structure of the pitch, including the carbon within the pitch, can be sufficiently stabilized.

[0074] In a specific embodiment of the present invention, the pitch stabilization may be performed for 1 to 10 hours, preferably 2 to 8 hours. If the pitch stabilization is performed for this period of time, the structure of the pitch, including the carbon within the pitch, can be sufficiently stabilized.

[0075] And, in step (d), the stabilized pitch is carbonized to obtain a carbonized body. Through carbonization of the pitch, other functional groups contained in the pitch are removed, and a carbonized body composed of substantially pure carbon can be obtained.

[0076] In a specific embodiment of the present invention, the carbonization of the pitch may be performed under an inert gas atmosphere. In a preferred embodiment of the present invention, the carbonization of the pitch may be performed under a nitrogen or argon atmosphere, but is not particularly limited thereto.

[0077] In a specific embodiment of the present invention, carbonization of the pitch may be performed at a temperature of more than 700°C and less than or equal to 1,000°C, preferably 800 to 900°C. If the temperature during carbonization of the pitch is lower than this range, carbonization may not be sufficiently achieved, and if the temperature during carbonization of the pitch is higher than this range, the carbonization yield may decrease.

[0078] In a specific embodiment of the present invention, the carbonization of the pitch can be performed under conditions of a flow rate of an inert gas, preferably nitrogen, of 0.1 to 30 ml / min, preferably 0.1 to 10 ml / min. When the carbonization of the pitch is performed under these inert gas flow rates, the pitch can be sufficiently carbonized.

[0079] In a specific embodiment of the present invention, the carbonization of the pitch may be performed for 0.5 to 5 hours, preferably 1 to 3 hours. If the carbonization of the pitch is performed for this period of time, the pitch can be sufficiently carbonized.

[0080] And, in step (e), the carbonized body (carbonized pitch) is activated to obtain a porous carbon support. By activating the carbonized body, pores are formed in the pitch pellets, thereby obtaining a porous carbon support.

[0081] In a specific embodiment of the present invention, the activation of the carbonized body may be performed in an oxidizing gas atmosphere. In a preferred embodiment of the present invention, the activation of the carbonized body may be performed in a steam atmosphere, but is not particularly limited thereto.

[0082] In a specific embodiment of the present invention, activation of the carbonized body can be performed at a temperature of more than 700°C and less than or equal to 1,000°C, preferably 800 to 900°C. When activation of the carbonized body is performed at this temperature, a porous carbon support in which micropores and mesopores are sufficiently formed can be obtained.

[0083] In a specific embodiment of the present invention, activation of the carbonized body can be performed at a pressure of 0.1 to 10 bar, preferably 0.1 to 5 bar. When activation of the carbonized body is performed at this pressure, a porous carbon support in which micropores and mesopores are sufficiently formed can be obtained.

[0084] In a specific embodiment of the present invention, the activation of the carbonized body can be performed under conditions of a flow rate of an oxidizing gas, preferably water vapor, of 0.1 to 100 ml / min, preferably 0.1 to 50 ml / min. When the activation of the carbonized body is performed under these oxidizing gas flow rates, a porous carbon support in which micropores and mesopores are sufficiently formed can be obtained.

[0085] In a specific embodiment of the present invention, the activation of the carbonized body may be performed for 0.5 to 5 hours, preferably 1 to 3 hours. When the activation of the carbonized body is performed for this period of time, a porous carbon support in which micropores and mesopores are sufficiently formed can be obtained.

[0086] In a specific embodiment of the present invention, the stabilization, carbonization, and activation of steps (c) to (e) above can each be performed in a microwave-assisted heating furnace. In a preferred embodiment of the present invention, the stabilization, carbonization, and activation of steps (c) to (e) above can all be performed in a microwave-assisted heating furnace. A microwave-assisted heating furnace is preferred because it can increase the temperature of the pitch itself without increasing the external temperature of the pitch, but is not particularly limited thereto.

[0087] In a specific embodiment of the present invention, the above steps (c) to (e) can be performed continuously in a single device. In a preferred embodiment of the present invention, the above steps (c) to (e) can be performed continuously in a single rotary kiln, but the device is not particularly limited thereto. By performing the above steps (c) to (e) continuously in a single device, process optimization can be achieved.

[0088] In a specific embodiment of the present invention, the porous carbon support obtained in step (e) may be further pulverized or ground and classified. Through pulverization or grounding, the porous carbon support can be further finely divided, and through classification, the particle size distribution of the porous carbon support can be made uniform. Here, classification may be performed by dry classification, wet classification, or classification using a sieve.

[0089]

[0090] [silicon]

[0091] In the present invention, silicon in the carbon-silicon composite composition may refer to a silicon portion formed by a Si-Si bond, and for example, a carbon-silicon composite may be obtained by forming silicon on a porous carbon support.

[0092] The silicon may include crystalline silicon particles. At this time, the size of the silicon crystals may be on the nanoscale. Specifically, the average size of the silicon crystals may be 10 nm or less. Preferably, the average size of the silicon crystals may be 8 nm or less, 5 nm or less, 3 nm or less, or 1 nm or less. When the average size of the silicon crystals satisfies the above range, the size of the stress due to the volume expansion of the silicon is reduced, so the life characteristics of the negative electrode active material may be improved.

[0093] Meanwhile, the silicon may be 10 to 90 wt% of the total weight of the carbon-silicon composite, and preferably 15 to 85 wt%. If the silicon is less than 10 wt% of the total weight of the carbon-silicon composite, the electric capacity may decrease, and if it exceeds 90 wt%, the problem caused by volume expansion of silicon during charge and discharge may not be resolved, which may cause structural damage to the negative electrode material and deteriorate cycle characteristics.

[0094]

[0095] [Method for producing carbon-silicon composites (or porous silicon composites)]

[0096] The carbon-silicon composite (or porous silicon composite) described above can be manufactured by a manufacturing method including a step of forming silicon on the surface and inside the pores of a porous carbon support to obtain a carbon-silicon composite.

[0097] In a specific embodiment of the present invention, the step of forming silicon on the surface and within the pores of the porous carbon support can be performed using a device (e.g., a rotary kiln) and a method (e.g., chemical vapor deposition (CVD)) known in the art to which the present invention pertains. Specifically, silicon can be formed on the surface and within the pores of the porous carbon support by supplying a silicon source to the porous carbon support and performing CVD.

[0098] In a specific embodiment of the present invention, the silicon source may include at least one selected from silane (SiH4), dichlorosilane (SiH2Cl2), silicon tetrafluoride (SiF4), silicon tetrachloride (SiCl4), methylsilane (CH3SiH3), and disilane (Si2H6), but is not particularly limited thereto.

[0099] CVD of a silicon source can be performed at a temperature of 300 to 700°C. For example, CVD of a silicon source can be performed at a temperature of 400 to 600°C, 400 to 500°C, or 400 to 450°C, but is not particularly limited to this range. In addition, CVD can be performed at atmospheric pressure, and may be performed under a low vacuum of about 10 Torr if necessary. In addition, the deposition can be performed under a silane (SiH4) gas atmosphere of, for example, 50 sccm or more and 500 sccm or less.

[0100]

[0101] [Carbon layer]

[0102] The carbon layer is formed on the silicon composite, and the carbon layer can be formed in the internal pores and / or the external surface of the carbon-silicon composite, which is the silicon composite.

[0103] By forming the above carbon layer, better electrical conductivity can be secured and the specific surface area can be appropriately controlled, so that when this complex is used as a negative electrode active material of a secondary battery, the capacity retention rate of the secondary battery can be further improved.

[0104] The electrical conductivity of a negative electrode active material is a critical factor in facilitating electron transfer during electrochemical reactions. If the carbon-silicon composite used as the negative electrode active material contains insufficient carbon, its electrical conductivity may be insufficient. Therefore, by including an additional carbon layer in the carbon-silicon composite, the charge-discharge capacity, initial charge efficiency, and capacity retention rate of a secondary battery can be improved, while providing superior electrical conductivity, suppressing electrolyte side reactions, and further enhancing the performance of the secondary battery.

[0105] The thickness of the above carbon layer may be 1 nm to 1 ㎛, preferably 3 to 150 nm, and more preferably 5 to 100 nm. When the thickness of the carbon layer is within this range, the effect of improving conductivity can be obtained while suppressing a decrease in the capacity of the secondary battery.

[0106] In addition, the carbon layer may include at least one selected from pitch, graphene, carbon nanotubes, carbon nanofibers, and graphite, and may preferably be a carbon layer formed by performing a dry coating process and carbonization treatment with petroleum-based pitch. In addition, the dry coating may be performed under conditions of 3,000 to 10,000 rpm, preferably under conditions of 4,000 to 8,000 rpm.

[0107]

[0108] In addition, the present invention may include the carbon layer in an amount of 5.0 to 15.0 wt%, preferably 7.0 to 13.0 wt%, and more preferably 8.5 to 12.5 wt%, based on the total weight of the negative electrode active material. At this time, if the carbon layer content is less than 5.0 wt% based on the total weight of the negative electrode active material, there may be a problem in that the effect of suppressing side reactions between silicon particles and electrolytes is minimal, and if the carbon layer content exceeds 15.0 wt%, the ion transfer rate may decrease, the amount of active lithium may decrease, and there may be a problem in that the overall capacity of a secondary battery including the same may decrease.

[0109]

[0110] [Challenge]

[0111] The negative active material of the present invention comprises the silicon composite described above and the carbon layer, and includes the conductive material in the carbon layer.

[0112] The above-mentioned conductive material may include at least one selected from SUPER-P, VGCF (vapor grown carbon fibers) and Mxnene particles represented by the following chemical formula 1, and preferably may include the above-mentioned Mxnene particles.

[0113] [Chemical Formula 1]

[0114] A x B y C z

[0115] In the above chemical formula 1, A may be Ti, Nb or Ta, and preferably may be Ti. And, B in the above chemical formula 1 may be Si, Ge, Sn or Al, and preferably may be Si or Al. And, in the above chemical formula 1, C may be a carbon atom or a nitrogen atom, and preferably may be a carbon atom. And, x may be 3 or 4, y may be 0 or 1, z may be 2 or 3, and preferably x may be 3 or 4, y may be 0, z may be 2 or 3, and more preferably x may be 3, y may be 0, and z may be 2.

[0116] The negative active material of the present invention may contain the conductive material in an amount of 0.1 to 8.0 wt%, preferably 0.5 to 5.0 wt%, and more preferably 2.0 to 4.0 wt%, based on the total weight of the negative active material. At this time, if the conductive material content is less than 0.1 wt% based on the total weight of the negative active material, the effect of reducing lithium ion diffusion resistance due to its use may be insignificant, and thus the effect of improving energy density may be insignificant. In addition, if the conductive material content exceeds 8.0 wt%, the relative amount of the negative active material may decrease due to excessive use, which may cause a problem of reducing capacity and lowering energy density. Therefore, it is preferable to contain the conductive material in the negative active material within the above wt% range.

[0117]

[0118] The negative active material of the present invention described above may have an energy density of 1450.0 mAh / g or more, preferably an energy density of 1480.0 mAh / g or more, and more preferably, an energy density of 1490.0 mAh / g or more.

[0119] The upper limit of the energy density is not particularly limited, but in one or more embodiments, it may be, but is not limited to, 2000 mAh / g or less, 1950 mAh / g or less, 1900 mAh / g or less, 1850 mAh / g or less, 1800 mAh / g or less, 1750 mAh / g or less, 1700 mAh / g or less, 1650 mAh / g or less, or 1600 mAh / g or less.

[0120]

[0121] The negative electrode active material described above can be applied as a negative electrode material for a lithium-ion secondary battery, and by using this, a lithium-ion secondary battery with excellent charge-discharge efficiency and improved life characteristics can be manufactured.

[0122]

[0123] Hereinafter, the present invention will be described in more detail through examples, but the following examples do not limit the scope of the present invention, and should be interpreted as helping to understand the present invention.

[0124] [Example]

[0125] Comparative Example 1: Preparation of negative electrode active material

[0126] As a negative electrode active material, a carbon-silicon composite (Hanwha SKPC-1) containing 67 wt% of a porous carbon support and 33 wt% of silicon disposed on the surface and inside the pores of the porous carbon support was prepared as a negative electrode active material.

[0127] The above porous carbon support has an average particle size of 6.5 μm, a BET specific surface area of ​​1015.65 m2 / g, and a tap density of 0.36 g / ml.

[0128] The carbon-silicon composite, which is a negative active material, has a volume ratio of mesopores with a pore size of 2 to 50 nm of about 42.0 to 43.0%.

[0129]

[0130] Comparative Example 2: Preparation of negative electrode active material

[0131] The carbon-silicon composite (porous silicon composite) of Comparative Example 1 was subjected to Hosokawa dry coating treatment at a speed of 7,000 rpm for 10 minutes with petroleum pitch, and then carbonized to form a carbon layer, thereby manufacturing a silicon composite as a negative electrode active material.

[0132]

[0133] Example 1: Preparation of negative electrode active material

[0134] The carbon-silicon composite (porous silicon composite) of Comparative Example 1 was mixed with MXene particles represented by the following chemical formula 1-1, and then subjected to Hosokawa dry coating treatment at a speed of 7,000 rpm for 10 minutes with petroleum pitch, followed by carbonization treatment to produce a negative electrode active material in which a carbon layer including MXene particles was formed on the silicon composite.

[0135] The manufactured negative active material contains 10 wt% of a carbon layer and 3 wt% of MXene particles out of a total of 100 wt%.

[0136] [Chemical Formula 1-1]

[0137] A x B y C z

[0138] In chemical formula 1-1, A is Ti, C is a carbon atom, x is 3, y is 0, and z is 2.

[0139]

[0140] Example 2: Preparation of negative electrode active material

[0141] The carbon-silicon composite (silicon composite) of Comparative Example 1 was mixed with MXene particles represented by the following Chemical Formula 1-1, and then subjected to Hosokawa dry coating treatment at a speed of 4,000 rpm for 10 minutes with a petroleum pitch, followed by carbonization treatment to produce a negative electrode active material in which a carbon layer including MXene particles was formed on the silicon composite.

[0142] The manufactured negative active material contains 10 wt% of a carbon layer and 3 wt% of MXene particles out of a total of 100 wt%.

[0143] [Chemical Formula 1-1]

[0144] A x B y C z

[0145] In chemical formula 1-1, A is Ti, C is a carbon atom, x is 3, y is 0, and z is 2.

[0146]

[0147] Examples 3 to 5

[0148] A negative electrode active material was manufactured in the same manner as in Example 1, but the amount of MXene particles used was changed, and negative electrode active materials having different MXene particle contents were manufactured as shown in Table 1 below, and Examples 3 to 5 were performed.

[0149]

[0150] Examples 6 to 9

[0151] A negative electrode active material was manufactured in the same manner as in Example 1, but the amount of petroleum pitch used was changed, and a Hosokawa coating treatment was performed to manufacture negative electrode active materials having different carbon layer contents in the negative electrode active materials as shown in Table 1 below, and Examples 6 to 9 were performed.

[0152]

[0153] Experimental Example 1

[0154] The theoretical capacities of the negative active materials manufactured in Examples 1 to 9 and Comparative Examples 1 to 2 are shown in Table 1 below.

[0155] Classification Negative active material Inner Machin particle content (weight %) Negative active material Inner carbon layer content (weight %) Theoretical capacity (mAh) Comparative example 1001.664 Comparative example 2011.21.824 Example 13.010.02.160 Example 23.010.01.888 Example 35.010.01.612 Example 48.010.01.468 Example 59.010.01.414 Example 63.07.11.932 Example 73.012.81.816 Example 83.04.21.756 Example 93.015.81.668

[0156]

[0157] Experimental Example 2: Measurement of charge / discharge capacity and initial efficiency (ICE) of a secondary battery cell

[0158] After manufacturing lithium ion secondary battery cells using the negative active materials of Examples 1 to 9 and Comparative Examples 1 to 2, the charge / discharge capacity and initial efficiency (ICE) of the cells were measured, and the results are shown in Table 2 below. In addition, the measurement results for Examples 1 to 2 and Comparative Examples 1 to 2 are shown in Table 2 below and FIG. 1a (Comparative Example 1), FIG. 1b (Example 1), FIG. 1c (Example 2), and FIG. 1d (Comparative Example 2).

[0159] And, the measurement conditions are as shown in Table 2 below, and the measurement was performed by performing 2 cycles, and the results are shown in Table 3 below.

[0160] Charge Conditions CC Mode, CC-CV Mode: 0.1 C (Cutoff Voltage 0.005 V, Cutoff Current 0.01 C) Discharge Conditions CC Mode Conditions: 0.1 C (Cutoff Voltage 1.5 V)

[0161]

[0162] Cell numberCharge capacity (mAh)Discharge capacity (mAh)Initial efficiency (ICE, %)Comparative example 11.82641.635389.53Comparative example 21.76471.412880.06Example 11.90971.615784.61Example 21.76191.506785.51Example 31.55621.332685.64Example 41.42441.226386.12Example 51.38631.113480.33Example 61.88901.572883.26Example 71.79711.463381.43Example 81.70261.359779.89 Example 91.61541.249077.34

[0163]

[0164] Looking at Table 3 and Figure 1a, the ICE of the cell manufactured using Comparative Example 1, which is an anode active material without a pitch coating layer (carbon layer), was measured to be the best. However, this is a factor that reduces the lifespan because the degree of freedom of lithium ions increases and the resulting deformation of the carbon support during discharge has a significant impact.

[0165] And, looking at Examples 1 and 2 in Table 3 and FIGS. 1a to 1c, it can be confirmed that Example 2, which was performed at 4,000 rpm, was slightly superior to Example 1, which was performed at 7,000 rpm, in terms of ICE during coating. This does not mean that the 4,000 rpm process is superior to the 7,000 rpm process, because the pitch may not have been completely coated on the SiC support during the 4,000 rpm process. To confirm this, the capacity retention rate and the initial impedance change (EIS measurement) can be interpreted through a life evaluation of 50 cycles or more.

[0166] In addition, Example 5, which used 9.0 wt% of the Maxim particle content in the negative active material, which exceeded 8.0 wt%, had a problem in that the discharge capacity and initial efficiency were rather lower compared to Example 1 (3 wt%) and Example 4 (8 wt%).

[0167] In addition, each of Example 8, in which the carbon layer content in the negative active material was less than 5.0 wt%, and Example 9, in which the carbon layer content exceeded 15.0 wt%, had a problem of significantly reduced initial efficiency compared to Example 6 (7.1 wt%) and Example 7 (12.8 wt%).

[0168]

[0169] In addition, the theoretical capacity, discharge capacity, theoretical capacity realization rate, and energy density of the Si negative electrode material of each cell manufactured using Comparative Examples 1 to 2 and Examples 1 to 9 were measured, and the results are shown in Table 4 below.

[0170] ClassificationTheoretical capacity (mAh)Discharge capacity (mAh)Theoretical capacity realization rate (%)Si negative electrode materialEnergy density (mAh / g)Comparative example 11.6641.635398.271965.5Comparative example 21.8241.412877.461549.1Example 12.1601.615774.801496.0Example 21.8881.506779.801596.1Example 31.6121.332682.661461.1Example 41.4681.226383.531473.9Example 51.4141.113478.741220.8Example 61.9321.572881.401527.0 Example 71.8161.463380.571500.8 Example 81.7561.359777.431320.1 Example 91.6681.249074.881291.6

[0171]

[0172] Theoretical capacity is affected by how the actual battery is assembled, the movement of charges and lithium ions, and reactions with additives in the electrolyte.

[0173] The overall trend in Table 3 above shows that Examples 1 to 4, 6 and 7 showed excellent theoretical capacity realization rates and high energy densities overall.

[0174] However, Examples 5, 8 and 9 showed low theoretical capacity realization rates and energy densities.

[0175]

[0176] Experimental Example 3: EIS Evaluation

[0177] In order to measure the basic resistance, SEI, and diffusion resistance, which are indicators of battery performance through internal impedance measurement of a battery cell, EIS evaluation was performed under the conditions of Table 5 below, and the results are shown in Table 6 below and FIG. 3a (Comparative Example 1), FIG. 3b (Example 1), FIG. 3c (Example 2), and FIG. 3d (Comparative Example 2).

[0178] AC frequency range 100 kHz to 0.01 Hz Voltage limit conditions Lower limit -5 V, Upper limit 5 V Current limit conditions Automatic adjustment (Upper limit adjustment on EIS measuring equipment) Sinus Amplitude Va (Sine wave amplitude range) 5 mV

[0179] The shape of the Nyquist plot measured by EIS is shown in Figure 2, and its interpretation is as follows.

[0180] ① R ohm (Intercept): External electrolyte and composite resistance

[0181] ② R SEI (First semicircle): Charge transfer resistance in SEI formed on the surface of inner electrode particles

[0182] ③ R ct (Second semicircle): Charge resistance representing lithium ion redox reaction at the electrode material interface.

[0183] ④ Z w (45 o (Slope straight line): Chemical diffusion resistance of ions due to intercalation into the particle crystal structure

[0184] And, the EIS measurement results for the battery cells to which the negative active materials of Comparative Examples 1 to 2 and Examples 1 to 9 were applied are shown in Table 6 below.

[0185] Classification R ohm R SEI R CT Z WComparative Example 13.29023.3273.85311.00 Comparative Example 23.8196.27936.33514.18 Exemplary Example 12.82132.5914.24816.61 Exemplary Example 23.54034.2586.13412.82 Exemplary Example 33.62936.7274.69414.28 Exemplary Example 42.92249.8564.32817.28 Exemplary Example 53.13164.2588.64219.26 Exemplary Example 63.36825.6324.54511.85 Exemplary Example 73.56435.7255.46214.59 Exemplary Example 83.99811.5634.14512.14 Example 93.63145.28510.69416.32

[0186] The EIS measurement results in Table 6 are summarized as follows.

[0187] ① R ohm In relation to this, since the intercept value is the basic synthetic resistance of the electrolyte, separator, and battery components, it was not very significant because the same product was used.

[0188] ② R SEI In relation to , it is an indicator of the initial SEI formation by Formation, which is formed by reacting with the additive of the electrolyte on the interface of the negative electrode material during the first charging process, and this must be properly formed to prevent excessive side reactions with the electrolyte and protect the structural change of the negative electrode material. As a result of the measurement, it appears that a thicker SEI film layer was formed than the cell of Comparative Example 1, which is the standard for Examples 1 and 2, and this had two complementary relationships: a decrease in capacity and an increase in lifespan.

[0189] And, for the cells of Examples 1 and 2, R is influenced by the MXene particles. SEI It is judged to have MXene, a 2D material with very high electrical conductivity, and cations, i.e. Li +It has a strong property of inducing. Therefore, it is presumed that the initial lithium ion penetration rate into the negative electrode layer increased, and as a result, the SEI layer became enlarged as a result of the reaction by consuming lithium ions. It is believed that the initial ICE decrease was caused by the consumption of lithium ions due to the relatively enlarged formation of the SEI.

[0190] In the case of the cell of Comparative Example 2, SEI formation was insufficient compared to Comparative Example 1. This indicates that the initial lithium ions did not completely diffuse into the negative electrode layer, and it could be assumed that the coated carbon layer (pitch) was hindering the formation of SEI. The impedance difference of Comparative Example 2 was within the margin of error, and a significant comparison of the influence of SEI formation between the two samples was not possible.

[0191] ③ R CT In relation to this, the smaller the value related to the diffusion rate of lithium ions, the lower the diffusion resistance and the easier it is to diffuse.

[0192] The cells of Examples 1 and 2 are judged to be influenced by MXene, and the diffusion resistance is close to that of Comparative Example 1, where a carbon layer and a non-MXene-using negative electrode active material are applied. CT It was confirmed that it had a high diffusion resistance. In contrast, the cell of Comparative Example 2 had a very high diffusion resistance, and therefore, Comparative Example 2 is expected to show low efficiency at a high C-Rate, and the life maintenance rate according to the cycle evaluation is also expected to be low.

[0193] The overall trend of the measurement results in Table 6 above is that Examples 1 to 4, 6 and 7 are R SEI When I checked the numbers, it showed that they were formed properly overall, and overall R CT The lower the value, the lower the diffusion resistance tended to be.

[0194] However, Examples 5 and 8 showed inadequate SEI formation, and Example 9 showed adequate SEI formation but high diffusion resistance.

[0195]

[0196] The above illustrates and describes specific embodiments. However, the invention is not limited to the aforementioned embodiments, and those skilled in the art will readily appreciate that various modifications and implementations can be made without departing from the spirit and scope of the invention as set forth in the claims below.

Claims

1. Silicone composite; and A carbon layer formed on the above silicon composite; The above carbon layer is a negative electrode active material including a conductive material.

2. In the first paragraph, the conductive material comprises at least one selected from SUPER-P, VGCF (vapor grown carbon fibers), and Mxnene particles represented by the following chemical formula 1. [Chemical Formula 1] A x B y C z In the above chemical formula 1, A is Ti, Nb or Ta, B is Si, Ge, Sn or Al, C is a carbon atom or a nitrogen atom, x is 3 or 4, y is 0 or 1, and z is 2 or 3.

3. In the second paragraph, a negative electrode active material wherein A in the chemical formula 1 is Ti, C is a carbon atom, x is 3 or 4, y is 0, and z is 2 or 3.

4. In the first paragraph, the conductive material is included in an amount of 0.1 to 8.0 wt% based on the total weight of the negative electrode active material.

5. In the first paragraph, the carbon layer is a negative active material formed by dry coating petroleum-based pitch on a silicon composite.

6. A negative electrode active material according to claim 5, wherein the dry coating is performed under conditions of 3,000 to 10,000 rpm.

7. In the first paragraph, the carbon layer is included in an amount of 5.0 to 15.0 wt% based on the total weight of the negative electrode active material.

8. In the first paragraph, the silicon composite, porous carbon support; and A negative electrode active material, which is a carbon-silicon composite including silicon formed on the porous carbon support.

9. In the first paragraph, the energy density of the negative active material is 1450.0 mAh / g or more.

10. A negative electrode material comprising a negative electrode active material according to any one of claims 1 to 9.

11. A secondary battery comprising a negative electrode material according to Article 10.

12. In the 11th paragraph, the secondary battery is a lithium secondary battery or an all-solid-state battery.

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