Low-expansion silicon-carbon composite with improved electrical conductivity, preparation method therefor, and silicon anode material comprising same

Abstract

The present invention relates to a silicon-carbon composite used as an anode material for a secondary battery, a method for preparing same, and an anode material using same, and, more specifically, to a low-expansion silicon-carbon composite, a preparation method therefor, and an anode material using same, the composite having a carbon coating layer formed on the surface of a carbon-silicon composite particle so as to minimize, when the composite is applied as an anode material for a secondary battery, an increase in volume of the composite, so as to increase long-term stability, and having a specific heteroelement doped into the carbon coating layer of the composite so as to improve electrical conductivity.

Description

Low-expansion silicon-carbon composite with improved electrical conductivity, method for producing the same, and silicon anode material comprising the same

[0001] The negative electrode material of a lithium-ion battery and / or an all-solid-state battery has a problem in that volume expansion occurs due to lithium ions being inserted into the negative electrode material by repeated operation of the battery, and the lifespan of the battery is shortened due to side reactions with the electrolyte component. The present invention relates to a low-expansion silicon-carbon composite that minimizes volume expansion and side reactions with the electrolyte component through the formation of a carbon coating layer, while improving the problem of reduced electrical conductivity due to the formation of a carbon coating layer, a method for producing the same, and a silicon negative electrode material including 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, such as lithium secondary batteries and all-solid-state batteries, are 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 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 charging and discharging, increasing its volume by up to 300%. This causes silicon, one of the anode components, to fragment during charging and discharging, resulting in significantly reduced mechanical stability.

[0005] Additionally, the introduction of carbon materials as a support for the above silicon-based negative electrode material is being attempted and developed.

[0006] Carbon materials are materials composed of carbon, one of the most abundant resources on Earth. Carbon materials are extremely lightweight, strong, and possess excellent electrical and thermal conductivity, making them a key material widely used in fields such as hydrogen vehicles, aviation, secondary batteries, and high-end consumer goods. Carbon materials can be manufactured from a variety of raw materials, including coconut shells, polyacrylonitrile, rayon, and pitch. However, carbon materials manufactured from solid raw materials like coconut shells are difficult to control in terms of molecular weight and composition (Korean Patent Application Publication No. 10-2019-0093960).

[0007] On the other hand, pitch, a viscoelastic solid polymer extracted from crude oil or plants, has the advantages of high yield when converted into carbon materials, low cost of raw materials, and its molecular structure is closer to the graphite structure than other raw materials, which reduces the energy required for heat treatment (U.S. Patent Nos. 4,242,196 and 4,340,464).

[0008] In particular, pyrolysis fuel oil (PFO), naphtha cracking bottom oil (NCB), vacuum residue (VR), and fluid catalytic cracking decant oil (FCC-DO), which are obtained as by-products in the petroleum refining process, have a high content of aromatic compounds and a low content of impurities such as sulfur and nitrogen, and therefore pitch manufactured from them is attracting attention as a material for carbon materials.

[0009] However, carbon supports based on pitch derived from fuel oil (PFO) have a relatively high content of metal impurities, making them unsuitable for use as anode materials in secondary batteries. If these residual metal impurities are high, they can react with the electrolyte of a secondary battery to generate gases, increasing the risk of fire and explosion. Furthermore, various chemical side reactions caused by the metal impurities can increase the irreversible capacity, thereby reducing charge-discharge efficiency. Consequently, their application as anode materials in secondary batteries is limited.

[0010] The negative electrode material of a lithium-ion battery and / or an all-solid-state battery has a problem in that volume expansion occurs due to lithium ions being inserted into the negative electrode material by repeated operation of the battery, and the lifespan of the battery is shortened due to side reactions with the electrolyte components. The present invention aims to provide a silicon-carbon composite that achieves minimization of volume expansion and side reactions by forming a specific carbon coating layer on the surface of carbon-silicon composite particles and the composite particles with an optimal thickness so as to minimize such volume expansion and side reactions, and improves electrical conductivity lowered by the carbon coating layer, a method for manufacturing the same, a silicon negative electrode material using the same, and a lithium-ion battery and / or an all-solid-state battery to which the negative electrode material is applied.

[0011] The low-expansion silicon-carbon composite of the present invention, which has improved electrical conductivity to solve the above problem, comprises: carbon-silicon composite particles; and a carbon coating layer doped with a heterogeneous element, boron, is formed on the outermost surface of the carbon-silicon composite particles.

[0012] As a preferred embodiment of the present invention, the carbon-silicon composite particle comprises a porous carbon support including a surface layer and a core layer; and silicon (Si).

[0013] As a preferred embodiment of the present invention, the carbon coating layer may include a carbide of a coating agent including a boron precursor and pitch, which are heterogeneous element doping agents.

[0014] As a preferred embodiment of the present invention, the boron precursor may include at least one selected from boric acid, boron oxide, and phenylboronic acid.

[0015] As a preferred embodiment of the present invention, the pitch may be manufactured based on petroleum residue.

[0016] As a preferred embodiment of the present invention, the carbon coating layer may have an average thickness of 10 to 190 nm.

[0017] As a preferred embodiment of the present invention, the carbon coating layer doped with the heterogeneous element of the silicon-carbon composite of the present invention can have a heterogeneous element content that satisfies the following equation 1 when analyzed by XPS.

[0018] [Formula 1]

[0019] 0.1% ≤ (A / C)×100(%) ≤ 9.1%

[0020] In Equation 1, A is the atomic% value of boron (B) in the carbon coating layer analyzed by XPS, and C is the atomic% value of carbon (C) in the carbon coating layer analyzed by XPS.

[0021] As a preferred embodiment of the present invention, the porous carbon support includes mesopores having a diameter of 2 nm to 50 nm, and the ratio of the volume of the mesopores of the surface layer to the volume of the entire mesopores of the porous carbon support may be 0.5 to 0.76.

[0022] As a preferred embodiment of the present invention, the porous carbon support may have a ratio of the volume of mesopores to the volume of the total pores of 0.1 or more.

[0023] As a preferred embodiment of the present invention, the porous carbon support may have a surface porosity greater than a deep porosity.

[0024] As a preferred embodiment of the present invention, the low-expansion silicon-carbon composite of the present invention can satisfy a volume expansion reduction rate of 25% or more calculated based on the following equation 2.

[0025] [Formula 2]

[0026] Volume expansion reduction rate (%) = {(DE) / D} × 100(%)

[0027] In Equation 2, D is the volume of the carbon-silicon composite particles without a carbon coating layer, and E is the volume of the low-expansion silicon-carbon composite doped with a heterogeneous element. The volumes of D and E are the volumes of the negative electrode materials measured after the carbon-silicon composite particles without a carbon coating layer and the low-expansion silicon-carbon composite doped with a heterogeneous element were applied as negative electrode materials for a half-cell for a lithium-ion battery, respectively, and the half-cell was operated for 50 cycles. At this time, the negative electrode materials of the carbon-silicon composite particles without a carbon coating layer and the low-expansion silicon-carbon composite doped with a heterogeneous element have the same size before the half-cell operation.

[0028] As a preferred embodiment of the present invention, in the silicon-carbon composite of the present invention, the change rate (%) of the fluorine atom content in the negative electrode material measured by the volume expansion reduction rate can satisfy the following equation 3.

[0029] [Formula 3]

[0030] 5% ≤ {(HG) / G}×100(%) ≤20%

[0031] In Equation 3, G is the fluorine (F) content (in wt%) in the surface of the negative electrode material manufactured from carbon-silicon composite particles without a carbon coating layer for which the volume expansion reduction rate was measured, and H is the fluorine content (in wt%) in the surface of the negative electrode material manufactured from a low-expansion silicon-carbon composite doped with a heterogeneous element for which the volume expansion reduction rate was measured.

[0032]

[0033] In addition, the purpose of the present invention relates to a method for producing a low-expansion silicon-carbon composite doped with a heterogeneous element as described above, wherein the low-expansion silicon-carbon composite can be provided by performing a process including: a first step of preparing carbon-silicon composite particles; a second step of performing dry or wet coating of a coating agent including a boron precursor and pitch on the surface of the carbon-silicon composite particles to produce carbon-silicon composite particles coated with the coating agent; and a third step of performing a carbonization treatment on the carbon-silicon composite particles coated with the coating agent to produce a composite in which a carbon coating layer doped with a heterogeneous element is formed on the outermost surface of the carbon-silicon composite particles.

[0034] As a preferred embodiment of the present invention, the coating amount of the coating agent coated on the carbon-silicon composite particles in the second step may be 2.0 to 23.0 parts by weight based on 100 parts by weight of the carbon-silicon composite particles.

[0035] As a preferred embodiment of the present invention, the two-step dry coating can be performed by a mechanofusion method.

[0036] As a preferred embodiment of the present invention, the mechanofusion method can perform coating for 5 to 30 minutes under conditions of a blade rotation speed of 500 to 5000 rpm of the mechanofusion equipment.

[0037] As a preferred embodiment of the present invention, the wet coating in the second step can be performed by mixing the coating solution containing the coating agent and THF with the carbon-silicon composite particles, and then removing the THF.

[0038] As a preferred embodiment of the present invention, the carbon-silicon composite particles of step 1 may be manufactured by performing a process including step 1-1 of preparing a porous carbon support having mesopores with a diameter of 2 nm to 50 nm and a ratio of the volume of the mesopores of the surface layer to the volume of the entire mesopores of 0.5 to 0.76; and step 1-2 of depositing silicon (Si) on the porous carbon support.

[0039] As a preferred embodiment of the present invention, the deposition in steps 1 and 2 can be performed at a temperature of 300°C to 600°C and under a silane (SiH4) gas atmosphere of 50 sccm to 500 sccm.

[0040]

[0041] Another object of the present invention is to provide a silicon anode material characterized by including the low-expansion silicon-carbon composite described above.

[0042] In addition, another object of the present invention is to provide a lithium ion battery and / or an all-solid-state battery including a silicon negative electrode material.

[0043] The low-expansion silicon-carbon composite doped with a heterogeneous element of the present invention has low expansion properties by suppressing volume expansion due to insertion of lithium ions into the composite due to the presence of a carbon coating layer with an optimal thickness, and also has the effect of suppressing and preventing the formation of a side-reaction layer by minimizing side reactions with electrolyte components. In addition, the electrical conductivity is improved by doping the carbon coating layer with a heterogeneous element, so that the reduction in electrical conductivity due to the formation of the carbon coating layer can be prevented or improved. When the silicon-carbon composite with these characteristics is applied as a silicon anode material for a secondary battery, a secondary battery (lithium ion battery and / or all-solid-state battery) using the same can secure increased charge-discharge efficiency and high long-term stability.

[0044] The porous carbon support described above can be provided as a silicon anode material, preferably a silicon anode material for secondary batteries, by silane coating or deposition treatment. The porous carbon support according to the present invention can deposit a sufficient amount of silicon (Si) within the pores of the porous support by including mesopores within a predetermined range.

[0045] The content of the deposited silicon may be 10 wt% or more based on the weight of the total particles. The content of the deposited silicon may be a value obtained by analysis using an energy dispersive spectrometer (EDS). The content of the deposited silicon may be 10 wt% or more, 15 wt% or more, 20 wt% or more, 25 wt% or more, or 30 wt% or more, but is not limited thereto. In addition, the content of the deposited silicon may be 60 wt% or less, 58 wt% or less, 56 wt% or less, 54 wt% or less, 52 wt% or less, or 50 wt% or less, but is not limited thereto. If the content of the deposited silicon is too low, the electric capacity may be reduced. In addition, if the content of the deposited silicon is too large, the problem caused by the volume expansion of the silicon during charge and discharge may not be solved, which may cause structural damage to the negative electrode material and deteriorate the cycle characteristics.

[0046]

[0047] The silicon-carbon composite of the present invention described above can be applied as a battery negative electrode material, and the battery negative electrode material can have improved mechanical strength along with high electrical capacity and excellent cycle characteristics.

[0048] The method for manufacturing the above-mentioned battery negative electrode material is not particularly limited, and can be manufactured using a general method for manufacturing battery negative electrode materials. For example, the above-mentioned battery negative electrode material can be manufactured by mixing a low-expansion silicon-carbon composite, an active material, a conductive material, a binder, etc., and coating / drying / rolling the mixture onto a component such as an electrode current collector, but is not limited thereto.

[0049] The present invention also relates to a battery comprising the aforementioned battery negative electrode material. The battery comprising the battery negative electrode material according to the present invention is a secondary battery, and may be a lithium-ion battery or an all-solid-state battery, but is not limited thereto.

[0050]

[0051] The lithium ion battery may specifically include a positive electrode, a negative electrode, a separator, and an electrolyte. At this time, the negative electrode may include the above-described battery negative electrode material. The positive electrode may use a material usable in a lithium ion battery, and may include, for example, one or more positive electrode active materials selected from doped or undoped lithium nickel oxide, lithium cobalt oxide, lithium cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium nickel cobalt aluminum oxide, and a positive electrode current collector selected from aluminum, stainless steel, nickel, titanium, platinum, or an alloy thereof, but is not limited thereto. In addition, the separator may use a typical separator usable in a lithium ion battery. The separator may include, for example, one or more selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, and polytetrafluoroethylene (PTFE), but is not limited thereto.

[0052] The negative electrode of the lithium ion battery may include the above-described battery negative electrode material. The negative electrode may include a negative electrode current collector and a battery negative electrode material, and the negative electrode current collector may include one or more selected from aluminum, stainless steel, nickel, titanium, platinum, or an alloy thereof, but is not limited thereto.

[0053] The electrolyte of the above lithium ion battery may include, but is not limited to, an organic liquid electrolyte, an inorganic liquid electrolyte, a polymer electrolyte, or a molten inorganic electrolyte usable in a lithium ion battery.

[0054] The above-mentioned all-solid-state battery may specifically include a positive electrode, a negative electrode, and a solid electrolyte, and may further include a separator as needed, but is not limited thereto. The positive electrode may include the above-mentioned positive electrode active material, and may include a positive electrode current collector as needed, but is not limited thereto.

[0055] The above negative electrode may include a battery negative electrode material according to the present invention. The negative electrode may have a single-layer structure including the battery negative electrode material, or may further include a negative electrode current collector as needed, but is not limited thereto.

[0056] The solid electrolyte may optionally use a solid electrolyte usable in an all-solid-state battery. The solid electrolyte may be, for example, at least one selected from the group consisting of a Garnet-type, a Nasicon-type, a LISICON-type, a perovskite-type, and a LiPON-type, but is not limited thereto.

[0057] 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.

[0058] [Example]

[0059] Preparation Example 1: Preparation of a porous carbon support

[0060] 300 g of petroleum residue oil (YNCC, HTC PFO (pyrolysis fuel oil)) was introduced into a reactor equipped with a stirrer, and pyrolysis and polycondensation were performed at 450°C for 3 hours while supplying nitrogen at a flow rate of 100 ml / min. During this time, the stirrer was rotated at a speed of 200 rpm to mix the reactants. The polymerized pitch was solidified and pelletized to obtain solid pitch pellets with an average particle size of 1 to 30 mm.

[0061] After crushing the solid pitch pellets obtained above, they were placed in a rotary kiln with three zones to sequentially perform stabilization, carbonization, and activation. The conditions for stabilization, carbonization, and activation are as shown in Table 1 below.

[0062] The activated carbonized body, after the above activation, was pulverized using a pulverizer (NETZSCH, air jet mill) to produce a porous carbon support.

[0063]

[0064] Preparation examples 2-3

[0065] A porous carbon support was manufactured in the same manner as Preparation Example 1, except that the carbonization and activation conditions were changed as shown in Table 1 below.

[0066] Step Condition Preparation Example 1 Preparation Example 2 Preparation Example 3 Stabilization temperature (℃) 310 310 310 Hours (hr) 222 Atmosphere Air Air Air Carbonization temperature (℃) 900 900 1000 Hours (hr) 111 Atmosphere Nitrogen Nitrogen Nitrogen Activation temperature (℃) 900 900 1000 Hours (hr) 323 Water vapor flow rate (ml / min) 10 10 10

[0067] Table 2 below shows the measured physical properties of the manufactured porous carbon supports. The specific surface area of ​​the porous carbon supports was measured using a Belsorp mini II according to ASTM D4820-93. The tap density of the carbon supports was measured using a tap density analyzer (Electrolab, ETD-1020x) according to ASTM B527. The average particle size of the carbon supports was measured using a particle size analyzer (Horiba, Laser Particle Analyzer, LA-960V2) according to ASTM E112.

[0068]

[0069] Preparation Example 1 Preparation Example 2 Preparation Example 3 Average particle size (㎛) 9.2 16.3 47.20 Specific surface area (m 2 / g)1240.91417.7988.6Tap density (g / ml)0.590.360.43Micropore (%)72.860.823.9Mesopore (%)25.131.162.1Macropore (%)2.48.12.5Mesopore ratio of surface layer0.660.630.51

[0070]

[0071] Example 1: Preparation of carbon-silicon composite particles and low-expansion silicon-carbon composites doped with heterogeneous elements.

[0072] (1) Manufacturing of carbon-silicon (C-Si) composite particles

[0073] Carbon-silicon composite particles were prepared using the porous carbon support manufactured in Preparation Example 1. 18 g of the porous carbon support of Preparation Example 1 was placed in a rotary kiln, and silane (SiH4) gas was injected to deposit the porous carbon support.

[0074] During silane gas coating, the pressure was atmospheric pressure, and the deposition was performed for 1 hour at a temperature of 475°C and a flow rate of 300 sccm to produce carbon-silicon composite particles. The physical properties of the produced carbon-silicon composite particles are shown in Table 3 below.

[0075] (2) Manufacturing of low-expansion silicon-carbon (Si-C) composites doped with boron, a heterogeneous element.

[0076] A coating agent was prepared by mixing 3 wt% of boric acid, a boron precursor, and 97 wt% of pitch derived from petroleum residue.

[0077] For 100 parts by weight of the carbon-silicon composite particles manufactured previously, 22 parts by weight of the coating agent was introduced into the reactor of a mechanofusion device, and then coating was performed for 15 minutes under conditions of a blade rotation speed of 2,700 rpm to manufacture carbon-silicon composite particles coated with the coating agent.

[0078] Next, the carbon-silicon composite particles coated with the coating agent were placed in an electric furnace, heated at 5°C / min to 700°C, carbonization was performed at 700°C for 2 hours, and then slowly cooled to 25°C, thereby forming a carbon coating layer doped with a heterogeneous element, boron (B), with a thickness of 100 nm on the surface of the carbon-silicon composite particles, thereby manufacturing a low-expansion silicon-carbon composite.

[0079]

[0080] Comparative Example 1: Low-expansion Si-C composite having an undoped carbon coating layer

[0081] A silicon-carbon composite was manufactured using the same method as in Example 1, but using only pitch derived from petroleum residue as a coating agent, a low-expansion silicon-carbon composite was manufactured under the same conditions.

[0082]

[0083] Comparative Example 2

[0084] Comparative Example 2 produced C-Si composite particles in the same manner as Example 1, except that graphite having a diameter of 17.08 μm was used instead of the porous carbon support of Preparation Example 1, and the deposition was performed for 47 minutes at a flow rate of 100 sccm during silane gas deposition.

[0085] And, each of the C-Si composite particles of Comparative Example 2 was manufactured into a low-expansion Si-C composite having a carbon coating layer of the same thickness formed using mechanofusion equipment in the same manner as Example 1.

[0086] At this time, the thickness of the carbon coating layer was measured through TEM analysis after cutting the cross-section.

[0087] Classification Example 1 Comparative Example 1 Comparative Example 2 C-Si composite particles (after Si deposition) Average particle size (㎛) 6.10 6.14 17.08 Specific surface area (m 2 / g)82.798.75.4Tab density (g / ml)0.6130.620.96Si content (wt%)43.845.05.7Low expansion Si-C composite coating agentCoating amount9 parts by weight (based on 100 parts by weight of C-Si composite particles)Carbon coating layer thickness100 nm100 nm100 nm

[0088]

[0089] Examples 2 to 4 and Comparative Example 3

[0090] After manufacturing carbon-silicon (C-Si) composite particles in the same manner as in Example 1, a coating agent was coated and carbonized using the mechanofusion method under the same conditions to manufacture a silicon-carbon (Si-C) composite, but the coating amount was changed to form a low-expansion C-Si composite having a carbon coating layer having a thickness as shown in Table 4 below, and Examples 2 to 4 and Comparative Example 3 were performed, respectively.

[0091] Low-expansion Si-C composite Example 2 Example 3 Example 4 Comparative Example 3 Coating amount (weight parts) based on 100 parts by weight of C-Si composite particles 714250 Carbon coating layer thickness 100 nm 120 nm 200 nm 0 Average particle size (㎛) 6.0 5 5.98 7.10 5.97 Tap density (g / ml) 0.62 5 0.72 7 0.70 10.62

[0092]

[0093] Examples 5 to 8

[0094] After manufacturing carbon-silicon (C-Si) composite particles in the same manner as in Example 1, a coating agent was coated and carbonized using a mechanofusion method under the same conditions, thereby manufacturing a silicon-carbon (Si-C) composite having a boron-doped carbon coating layer having the same thickness as in Example 1. However, the content of the boron precursor in the coating agent was changed from Example 1, and the boron precursor, boric acid, was used in amounts of 1 wt%, 5 wt%, 20 wt%, and 31 wt% in the coating agent, respectively. Using these coating agents, the coating agents were manufactured, and Examples 5 to 8 were performed, respectively.

[0095]

[0096] Experimental Example 1: XPS Analysis

[0097] XPS analysis was performed on the carbon coating layer of the composites manufactured in Examples 1 and 5 to 8, and the results are shown in Table 5 below.

[0098] Content of boron precursor in the coating agent (weight%) Element content (atomic%) in the carbon coating layer of the composite Formula 1, (boron / carbon) × 100 Boron (B) Carbon (C) Example 13 Weight % 0.48 46.79 1.03 Example 51 Weight % 0.18 47.11 0.38 Example 65 Weight % 0.72 46.53 1.55 Example 720 Weight % 2.96 45.25 6.54 Example 831 Weight % 4.13 44.08 9.37

[0099]

[0100] Experimental Example 2: Electrochemical Evaluation of Secondary Batteries

[0101] Half coin cells were manufactured using each of the Si-C composites manufactured in Examples 1 to 8 and Comparative Examples 1 to 3 (Manufacturing Examples 1 to 8 and Comparative Manufacturing Examples 1 to 3).

[0102] Low-expansion C-Si composite: A slurry was prepared by mixing a conductive material and a binder in a ratio of 8:1:1. At this time, the conductive material used was super-P, and the binder used was a mixture of styrene butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) in a weight ratio of 5:5.

[0103] Next, the slurry was uniformly applied to copper foil and dried in an 80°C oven for approximately 1 hour. After the primary drying, the slurry was roll-pressed and dried in a 120°C vacuum oven for approximately 6 hours and 30 minutes to manufacture a negative electrode plate.

[0104] A half coin cell was manufactured using the above-mentioned negative electrode and lithium foil as a counter electrode. A porous polyethylene film was used as a separator, and a CR2032 half coin cell (half cell) was manufactured under the conditions shown in Table 7 below.

[0105] The electrolyte was prepared by dissolving 1.3 M LiPF6 in a solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:5:2, and dissolving 10 wt% fluoro-ethylene carbonate (FEC), 0.2 wt% lithium tetrafluoroborate (LiBF4), 0.5 wt% vinylene carbonate (VC), and 1 wt% propane sulton (PS) additives (see Table 6).

[0106] Composition (AM:CM:BM) 8:1:1 Area capacity (mAh / cm 2)1 Electrolyte 1.3M LiPF6 EC / EMC / DMC 3:5:2, FEC 10%, LiBF4 0.2%, 0.5% VC, 1% PS Cut-off voltage (V) Formation: 0.005 ~ 1.5, Cycle test: 0.005 ~ 1.5 C-rate (C) Formation: 0.1 ~ 0.1. 0.01 C cut-off (CV) at 0.005 V

[0107] In Table 6 above, AM, CM, and BM represent active material (carbon-silicon composite particles), conductor (Super P carbon black), and binder (styrene-butadiene rubber / carboxymethyl cellulose 5:5), respectively, and EC, EMC, DMC, FEC, VC, and PS represent ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, vinylene carbonate, and propane sultone, respectively.

[0108] Electrochemical analysis was performed on the manufactured half coin cell under the following conditions.

[0109] Cut off voltage (V): 0.005 - 1.5V (Formation), 0.005 - 1.2V(Cycle)

[0110] Formation C-rate (C): 0.1C lithiation, 0.1C delithiation

[0111] Cycle C-rate (C): 0.5C lithiation, 0.5C delithiation

[0112] In addition, the volume expansion reduction rate of the low-expansion silicon-carbon composite after operating the half-cell for 50 cycles was measured according to Equation 1 below.

[0113] The change rate (%) of fluorine atom content in the negative electrode material, which measured the volume expansion reduction rate, was measured using Equation 2 and is shown in Table 8 below.

[0114] [Formula 2]

[0115] Volume expansion reduction rate (%) = {(DE) / D}×100(%)

[0116] In Equation 2, D is the volume of the carbon-silicon composite particle without a carbon coating layer, E is the volume of the silicon-carbon composite, and the volumes of D and E are the volumes of the negative electrode materials measured after the carbon-silicon composite particle without a carbon coating layer and the silicon-carbon composite, respectively, were applied as negative electrode materials for a half-cell for a lithium-ion battery and the half-cell was operated for 40 cycles. At this time, the negative electrode materials of the carbon-silicon composite particle without a carbon coating layer and the silicon-carbon composite before the half-cell operation have the same size.

[0117] [Formula 3]

[0118] Fluorine atom (F) content (%) in the cathode material = {(HG) / G}×100(%)

[0119] In Equation 3, G is the fluorine (F) content (weight %) in the surface of the negative electrode material manufactured from carbon-silicon composite particles without a carbon coating layer for which the volume expansion reduction rate was measured, and H is the fluorine content (weight %) in the surface of the negative electrode material manufactured from the silicon-carbon composite for which the volume expansion reduction rate was measured.

[0120] After initial 50 cycles of operation, half-cell low-expansion C-Si composite recharge capacity (mAh / g) discharge capacity (mAh / g) ICE (%) volume expansion reduction rate (%) change in F content in anode material (%) retention rate compared to initial capacity (%) manufacturing example 1 embodiment 1 1886 156 282.83 412.83 7.7 manufacturing example 2 embodiment 2 1843 1520 82.52 818.7 31.2 manufacturing example 3 embodiment 3 1874 1545 82.53 017.53 5.7 manufacturing example 4 embodiment 4 1622 1312 80.93 510.7 40. 1 Manufacturing Example 5 Example 5 1864151981.52810.236.8 Manufacturing Example 6 Example 6 1866152681.83611.535.9 Manufacturing Example 7 Example 7 1701134779.23218.932.1 Manufacturing Example 8 Example 8 1781142780.13322.831.5 Comparative Manufacturing Example 1 Comparative Example 1 1883151380.33210.136.7 Comparative Manufacturing Example 2 Comparative Example 2 1407129491.7233.822.5 Comparative Manufacturing Example 3 Comparative Example 3 1810149682.60021.7

[0121] Looking at the electrochemical evaluation results of the secondary battery (half cell) in Table 7 above, it was confirmed that the secondary battery using the low-expansion C-Si composite of the present invention as the negative electrode material had a high volume expansion reduction rate of 25% or more after 50 cycles of operation, and as a result, the initial capacity retention rate was very high at 30.0% or more.

[0122] In contrast, in the case of comparative manufacturing example 1, which introduced a low-expansion silicon-carbon composite manufactured using only pitch as a coating agent as a cathode material, there was a problem of lowering ICE and life characteristics.

[0123] In addition, Comparative Manufacturing Example 2, which introduced Comparative Example 2 using graphite as a porous carbon support as a cathode material, showed a low volume expansion reduction rate (inhibition effect).

[0124] In addition, in the case of Comparative Manufacturing Example 3, which introduced Comparative Example 3 without forming a coating layer as a negative electrode material, there was no effect of suppressing volume expansion, and there was a problem that the retention rate compared to the initial capacity was relatively very low compared to the manufacturing examples.

[0125] In addition, in the case of Manufacturing Example 4, which introduced the negative electrode material of Example 4 manufactured by coating with a coating amount exceeding 23 parts by weight, 25 parts by weight, it had a high volume expansion reduction rate and a high initial capacity retention rate, but there was a problem of a decrease in capacity.

[0126] In addition, in the case of Manufacturing Example 8, which introduced the negative electrode material of Example 8 manufactured using a boron precursor content in the coating agent of 31 wt%, which is more than 30 wt%, there was a problem that the retention rate was relatively low compared to the initial capacity when compared to Manufacturing Example 1 (Example 1, 3 wt%), Manufacturing Example 6 (Example 6, 5 wt%), and Manufacturing Example 7 (Example 7, 20 wt%).

[0127] Through the experimental results of Table 7 above, it was confirmed that the negative electrode material of the present invention can secure low volume expansion rate and long-term performance stability by minimizing volume expansion of the negative electrode material (silicon-carbon composite) due to lithium ion insertion and minimizing the formation of a side reaction layer formed by the reaction of F in the electrolyte and the negative electrode material component.

[0128]

[0129] Experimental Example 3: Electrochemical Evaluation of All-Solid-State Batteries

[0130] Manufacturing Example 9 was performed by manufacturing an all-solid-state battery using the carbon-silicon composite manufactured in Example 1.

[0131] The solid electrolyte used was sulfide-based argyrodite with a diameter of 5 μm, and was manufactured into pellets by applying a pressure of 130 MPa.

[0132] The low-expansion silicon-carbon composite manufactured in Manufacturing Example 1: solid electrolyte: conductive material were mixed in a ratio of 50:40:10, applied onto the manufactured pellets, and a pressure of 440 MPa was applied to manufacture a laminate. The solid electrolyte used was an argyrodite sulfide-based solid electrolyte having a diameter of 1 μm, and the conductive material used was VGCF.

[0133] An all-solid-state battery compression cell was manufactured by using the above-manufactured laminate and a 1t (1mm) thick lithium metal as a counter electrode and applying a force of 50kgf using a torque wrench.

[0134] Electrochemical analysis was performed on the manufactured all-solid-state battery compression cell under the following conditions.

[0135] Cut off voltage (V): 0.005 - 1.5V (Formation), 0.005 - 1.0V(Cycle)

[0136] Formation C-rate (C): 0.1C lithiation, 0.1C delithiation

[0137] Cycle C-rate (C): 0.3C lithiation, 0.3C delithiation

[0138] After 50 cycles of operation, C-rate, charge capacity (mAh / g), discharge capacity (mAh / g), ICE (%), initial capacity retention rate (%), manufacturing example 90.1C1523124781.977.1

[0139]

[0140] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments and the attached drawings, but is intended to be defined by the appended claims. Accordingly, those skilled in the art will appreciate that various substitutions, modifications, and alterations may be made without departing from the technical spirit of the present invention as defined in the claims, and such modifications are also within the scope of the present invention.

Claims

1. Carbon-silicon composite particles; and a carbon coating layer doped with a heterogeneous element is formed on the outermost surface of the carbon-silicon composite particles; The above carbon-silicon composite particles include a porous carbon support including a surface layer and a deep layer; and silicon (Si); A low-expansion silicon-carbon composite with improved electrical conductivity, characterized in that the above heterogeneous element comprises boron (B).

2. A low-expansion silicon-carbon composite with improved electrical conductivity, characterized in that the carbon coating layer comprises a carbide of a coating agent including a boron precursor and pitch in the first paragraph.

3. A low-expansion silicon-carbon composite with improved electrical conductivity, characterized in that the carbon coating layer in the first paragraph has an average thickness of 10 to 190 nm.

4. In the second paragraph, the pitch is a low-expansion silicon-carbon composite with improved electrical conductivity, characterized in that it is manufactured based on petroleum residue.

5. A low-expansion silicon-carbon composite with improved electrical conductivity, characterized in that in the second paragraph, the boron precursor comprises at least one selected from boric acid, boron oxide, and phenylboronic acid.

6. In the first paragraph, the carbon coating layer doped with the heterogeneous element is characterized in that the content of the heterogeneous element satisfies the following equation 1 when analyzed by XPS, and is a low-expansion silicon-carbon composite with improved electrical conductivity; [Formula 1] 0.1% ≤ (A / C)×100(%) ≤ 9.1% In Equation 1, A is the atomic% value of boron (B) in the carbon coating layer analyzed by XPS, and C is the atomic% value of carbon (C) in the carbon coating layer analyzed by XPS.

7. Step 1: Preparing carbon-silicon composite particles; Step 2: performing dry or wet coating of a coating agent including a boron precursor and pitch on the surface of the carbon-silicon composite particles to manufacture carbon-silicon composite particles coated with the coating agent; and A method for producing a low-expansion silicon-carbon composite with improved electrical conductivity, characterized by performing a process including the step of: carbonizing carbon-silicon composite particles coated with the above coating agent to produce a composite in which a carbon coating layer doped with a heterogeneous element is formed on the outermost surface of the carbon-silicon composite particles.

8. In paragraph 7, A method for producing a low-expansion silicon-carbon composite with improved electrical conductivity, characterized in that the coating amount of the coating agent coated on the carbon-silicon composite particles in the above 2 steps is 2.0 to 23.0 parts by weight per 100 parts by weight of the carbon-silicon composite particles.

9. In paragraph 7, the two-step dry coating is performed using the mechanofusion method. The above mechanofusion method is a method for manufacturing a low-expansion silicon-carbon composite with improved electrical conductivity, characterized in that coating is performed for 5 to 30 minutes under conditions of a blade rotation speed of 500 to 5,000 rpm of a mechanofusion device.

10. In the 7th paragraph, the carbon-silicon composite particles of step 1, Step 1-1 of preparing a porous carbon support including mesopores with a diameter of 2 nm to 50 nm and having a ratio of the volume of the mesopores in the surface layer to the volume of the entire mesopores of 0.5 to 0.76; and A method for manufacturing a low-expansion silicon-carbon composite with improved electrical conductivity, characterized in that the composite is manufactured by performing a process including step 1-2 of depositing silicon (Si) on the porous carbon support.

11. A silicon anode material characterized by comprising a silicon-carbon composite selected from any one of claims 1 to 6.

12. A lithium ion battery comprising the silicon negative electrode material of clause 11.

13. An all-solid-state battery comprising the silicon negative electrode material of clause 11.