Silicon-carbon-containing electrode material and lithium secondary battery comprising same

Abstract

A silicon-carbon-containing electrode material according to an embodiment of the present invention comprises: a porous carbon structure; and a silicon-containing coating layer formed on the porous carbon structure, in which the volume ratio of micropores having a pore diameter of 2 nm or less in the total pore volume is more than 50% and less than 90%. Therefore, the life characteristics and efficiency of the lithium secondary battery can be improved.

Description

Technical Field

[0001] The present invention relates to a silicon-carbon electrode material and a lithium secondary battery including the electrode material. More specifically, the present invention relates to a silicon-carbon electrode material including a porous carbon material and a lithium secondary battery including the electrode material. Background Art

[0002] A secondary battery is a battery that can be repeatedly charged and discharged. With the development of the information communication and display industries, secondary batteries are widely used as power sources for portable electronic communication devices such as portable cameras, mobile phones, and laptop computers. As a power source for eco-friendly vehicles such as electric vehicles, a battery pack including a secondary battery is also being applied.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc. Among them, lithium secondary batteries have a high operating voltage and energy density per unit weight, and are advantageous for charging speed and weight reduction.

[0004] For example, a lithium secondary battery may include: an electrode assembly including a positive electrode, a negative electrode, and a separator (diaphragm); and an electrolytic solution impregnating the electrode assembly. The lithium secondary battery may further include an exterior material for accommodating the electrode assembly and the electrolytic solution, such as a pouch-type exterior material.

[0005] In order to manufacture a lithium secondary battery with higher capacity and power, silicon and carbon can be compounded and used as a negative electrode material. For example, silicon can improve the capacity characteristics of the battery, and carbon can act as a support for silicon. Summary of the Invention

[0006] (I) Technical Problems to be Solved

[0007] One technical problem of the present invention is to provide a silicon-carbon electrode material having improved life characteristics and efficiency.

[0008] One technical problem of the present invention is to provide a method for preparing the silicon-carbon electrode material.

[0009] One technical problem of the present invention is to provide a lithium secondary battery having improved life characteristics and efficiency.

[0010] (II) Technical Solutions

[0011] The silicon-carbon electrode material according to an exemplary embodiment may include: a porous carbon structure; and a silicon-containing coating formed on the porous carbon structure, wherein, in the total pore volume, the volume ratio of micropores having a pore diameter of 2 nm or less may be more than 50% and less than 90%.

[0012] In some embodiments, in the total pore volume of the electrode material, the volume ratio of micropores with a pore diameter of 2 nm or less can be 55% to 80%.

[0013] In some embodiments, in the total pore volume of the electrode material, the volume ratio of mesopores with a pore diameter exceeding 2 nm and 50 nm or less can be 8% to 48%, and the volume ratio of macropores with a pore diameter exceeding 50 nm can be 1.5% to 10%.

[0014] In some embodiments, the total pore volume of the electrode material can be 0.02 cm 3 / g to 0.2 cm 3 / g.

[0015] In some embodiments, the ratio of the total pore volume of the electrode material to the total pore volume of the porous carbon structure can be 0.15 or less.

[0016] In some embodiments, the specific surface area of the electrode material can be 60 m 2 / g to 320 m 2 / g.

[0017] In some embodiments, the ratio of the specific surface area of the electrode material to the specific surface area of the porous carbon structure can be 0.1 or less.

[0018] In some embodiments, in the total weight of the electrode material, the content of silicon can be 30% by weight to 80% by weight.

[0019] In some embodiments, the peak intensity ratio of the Raman spectrum measured from the silicon-containing coating defined by the following formula 1 can be 0.5 or less.

[0020] [Formula 1]

[0021] Peak intensity ratio of Raman spectrum = I c-Si / I a-Si

[0022] In formula 1, I c-Si can be the peak intensity of the silicon-containing coating in the region of the Raman spectrum with a wavelength of 515 nm -1 , and I a-Si can be the peak intensity of the silicon-containing coating in the region of the Raman spectrum with a wavelength of 480 nm -1 .

[0023] In some embodiments, the ratio of the peak intensity (I D ) of the D band to the peak intensity (I G ) of the G band of the Raman spectrum obtained from the porous carbon structure can be 1 to 1.3.

[0024] In a method for preparing a silicon-carbon electrode material according to an exemplary embodiment, a polymer precursor solution may be formed. The polymer precursor contained in the polymer precursor solution may be polymerized to form a polymer gel. The polymer gel may be dried and carbonized to form a bulk carbon structure. The bulk carbon structure may be pulverized to form a porous carbon structure. A silicon-containing coating may be formed on the porous carbon structure to obtain a silicon-carbon electrode material. In the total pore volume of the electrode material, the volume ratio of micropores having a pore diameter of 2 nm or less may be more than 50% and less than 90%.

[0025] In some embodiments, the silicon-containing coating may be formed by a deposition process under temperature conditions of 400 °C to 800 °C and pressure conditions of 700 torr to 800 torr.

[0026] In some embodiments, the deposition process may include supplying a silicon precursor and a carrier gas, and the flow rate ratio of the silicon precursor to the carrier gas may be 1 / 50 to 1 / 3.

[0027] A lithium secondary battery according to an exemplary embodiment may include: a negative electrode including the silicon-carbon electrode material according to the above embodiment; and a positive electrode disposed opposite to the negative electrode.

[0028] (III) Advantageous Effects

[0029] A silicon-carbon electrode material according to an exemplary embodiment may include: a porous carbon structure; and a silicon-containing coating formed on the porous carbon structure.

[0030] In the total pore volume of the electrode material, the volume ratio of micropores having a pore diameter of 2 nm or less may be more than 50% and less than 90%. Accordingly, the contact between silicon and the electrolyte may be minimized, thereby improving the life characteristics and efficiency of the lithium secondary battery.

[0031] The electrode material may be widely applied to green technology fields such as electric vehicles, battery charging stations, other battery-utilizing solar power generation, and wind power generation. In addition, the lithium secondary battery may be used for eco-friendly electric vehicles, hybrid vehicles, etc. that prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 and Figure 2 are a schematic plan view and a schematic cross-sectional view respectively showing a lithium secondary battery according to an exemplary embodiment.

[0033] Figure 3 is a flowchart showing a method for preparing a silicon-carbon-containing electrode material according to an exemplary embodiment.

[0034] Figures 4 to 8 are diagrams respectively showing pore distribution diagrams of the silicon-carbon-containing electrode materials according to Examples 1 to 5.

[0035] Figures 9 to 14 are diagrams respectively showing pore distribution diagrams of the silicon-carbon-containing electrode materials according to Comparative Examples 1 to 6.

[0036] Description of Reference Numerals

[0037] 100: positive electrode 105: positive electrode current collector

[0038] 107: positive electrode lead 110: positive electrode active material layer

[0039] 120: negative electrode active material layer 125: negative electrode current collector

[0040] 127: negative electrode lead 130: negative electrode

[0041] 140: separator 150: electrode assembly

[0042] 160: housing Detailed Description of Embodiments

[0043] Embodiments of the present invention provide a silicon-carbon-containing electrode material, the silicon-carbon-containing electrode material comprising: a porous carbon structure; and a silicon-containing coating formed on the porous carbon structure. Embodiments of the present invention can provide a negative electrode for a lithium secondary battery and a lithium secondary battery including the electrode material.

[0044] According to an exemplary embodiment, the electrode material can be used as a negative electrode material for a lithium secondary battery. The use of the electrode material is not limited to the negative electrode material, and the electrode material can be used as a material having conductivity or charge storage characteristics for various electrical devices, electronic devices, and electrochemical devices.

[0045] In this specification, a micropore may refer to a pore having a diameter of 0.01 nm or more and 2 nm or less, a mesopore may refer to a pore having a diameter exceeding 2 nm and 50 nm or less, and a macropore may refer to a pore having a diameter exceeding 50 nm.

[0046] Hereinafter, embodiments of the present invention will be described in detail. However, these are merely exemplary embodiments, and the present invention is not limited to the specific embodiments described exemplarily.

[0047] <Silicon-Carbon-Containing Electrode Material>

[0048] A silicon-carbon electrode material according to an exemplary embodiment may include: a porous carbon structure; and a silicon-containing coating formed on the porous carbon structure, wherein, in the total pore volume, the volume ratio of micropores having a pore diameter of 2 nm or less may be more than 50% and less than 90%.

[0049] In some embodiments, the porous carbon structure may include a carbonized polymer. For example, the porous carbon structure may include a carbide material. The carbonized polymer may refer to a material generated by converting a polymer into a carbon-rich structure through a carbonization process. The carbonization process may be a process of heating the polymer in an oxygen-free state to remove non-carbon elements and leave a carbonized residue. The carbide material may be composed of carbon and a metal element or a metalloid element. Examples of the carbide material may include tungsten carbide (WC), silicon carbide (SiC), titanium carbide (TiC), etc.

[0050] In some embodiments, the porous carbon structure may include a plurality of pores. The pores may be formed from the surface of the porous carbon structure and extend into the interior of the porous carbon structure.

[0051] For example, the cross-section of the porous carbon structure may be circular or may randomly change from the circular shape. The silicon-containing coating may be partially formed on the pores and the surface of the porous carbon structure, and may also be formed as a plurality of discontinuous islands or patterns.

[0052] In some embodiments, the total pore volume of the porous carbon structure may be 0.8 cm 3 / g to 1.2 cm 3 / g, 0.85 cm 3 / g to 1.1 cm 3 / g, 0.9 cm 3 / g to 1.05 cm 3 / g or 0.95 cm 3 / g to 1 cm 3 / g. Within the above range, a sufficient silicon-containing coating can be formed inside the pores, and the capacity characteristics of the battery can be improved.

[0053] In some embodiments, the specific surface area of the porous carbon structure may be 650 m 2 / g to 2200 m 2 / g, 1200 m 2 / g to 2150 m 2 / g, 1700 m 2 / g to 2100 m 2 / g or 1800 m 2from / g to 2100 m 2 / g. Within the above range, the silicon deposition area can be fully ensured, and the stability of the electrode material can be improved.

[0054] In some embodiments, the silicon-containing coating can be formed on the surface of the porous carbon structure. For example, the silicon-containing coating can be formed simultaneously on the outer surface and the inner surface of the pores of the porous carbon structure.

[0055] In one embodiment, the pores of the above porous carbon structure can be at least partially filled with the silicon-containing coating. For example, the pores can be completely filled with the silicon-containing coating, or can be partially filled with the silicon-containing coating.

[0056] When the pores are partially filled with the silicon-containing coating, the internal space of the pores can further include the remaining space other than the part filled with the silicon-containing coating.

[0057] In some embodiments, the silicon-containing coating can be formed by a deposition process (e.g., chemical vapor deposition (CVD) process).

[0058] For example, a silicon precursor can be supplied to the porous carbon structure having the above pores. The silicon particles separated from the silicon precursor can be deposited on the porous carbon structure to form the silicon-containing coating.

[0059] For example, the silicon particles can be deposited on the outer wall of the porous carbon structure, and can also be substantially uniformly deposited on the inner wall of the pores. Therefore, a silicon-containing coating with a uniform cross-section can be formed on the entire surface of the porous carbon structure.

[0060] When the proportion of the pores filled with the silicon-containing coating in the pores contained in the porous carbon structure increases, the specific surface area increased by the pores can be fully utilized, thereby improving the capacity characteristics of the battery.

[0061] For example, the electrode material can include micropores, and can further include mesopores and macropores.

[0062] In some embodiments, in the total pore volume of the electrode material, the volume ratio of micropores with a pore diameter of 2 nm or less can be more than 50% and less than 90%. For example, in the total pore volume of the electrode material, the volume ratio of micropores can be 50.5% to 80%, 55% to 80%, 55% to 75%, 55% to 70%, or 55% to 60%.

[0063] When the volume ratio of micropores in the total pore volume of the electrode material is 50% or less, the contact between silicon and the electrolyte increases, so that the formation of the solid electrolyte interface phase (SEI) may increase. Therefore, the electrolyte may be depleted, and the initial efficiency and life characteristics of the lithium secondary battery may deteriorate.

[0064] When the volume ratio of micropores in the total pore volume of the electrode material is 90% or more, it may be difficult for the silicon precursor to deposit on the inner wall of the pores of the porous carbon structure, and condensation may occur between the silicon precursors on the outer surface of the porous carbon structure, so that aggregation of silicon particles may occur. Therefore, the capacity characteristics of the battery may deteriorate.

[0065] In some embodiments, in the total pore volume of the electrode material, the volume ratio of mesopores with a pore diameter exceeding 2 nm and 50 nm or less may be 8% to 48%, for example, it may be 15% to 48%, 20% to 45%, 30% to 40% or 30% to 35%.

[0066] In some embodiments, in the total pore volume of the electrode material, the volume ratio of macropores with a pore diameter exceeding 50 nm may be 1.5% to 10%, for example, it may be 1.7% to 9.9%, 2.0% to 9.8%, 2.5% to 9.7% or 3% to 9.5%.

[0067] Within the above ranges of the volume ratio of mesopores and the volume ratio of macropores, the silicon-containing coating can be sufficiently formed inside the pores included in the porous carbon structure, and aggregation of silicon particles can be suppressed. Therefore, the capacity characteristics of the lithium secondary battery can be improved.

[0068] In some embodiments, the total pore volume of the electrode material may be 0.02 cm 3 / g to 0.2 cm 3 / g, for example, it may be 0.03 cm 3 / g to 0.16 cm 3 / g, 0.04 cm 3 / g to 0.10 cm 3 / g or 0.04 cm 3 / g to 0.06 cm 3 / g. Within the above range, generation of cracks due to excessive increase in pore volume can be prevented.

[0069] In some embodiments, the ratio of the total pore volume of the electrode material to the total pore volume of the porous carbon structure may be 0.15 or less, for example, it may be 0.1 or less, 0.01 to 0.15 or 0.01 to 0.1. Within the above range, the specific surface area of the electrode material can be sufficiently ensured.

[0070] In some embodiments, the specific surface area of the electrode material can be 60 m 2 / g to 320 m 2 / g. For example, it can be 61 m 2 / g to 200 m 2 / g, 62 m 2 / g to 180 m 2 / g or 62 m 2 / g to 100 m 2 / g. Within the above range, a uniform silicon-containing coating can be formed on the entire surface of the porous carbon structure.

[0071] In some embodiments, the ratio of the specific surface area of the electrode material to the specific surface area of the porous carbon structure can be 0.1 or less. For example, it can be 0.05 or less, 0.01 to 0.1, or 0.01 to 0.05. Within the above range, silicon can be uniformly deposited inside the pores of the porous carbon structure.

[0072] For example, the above total pore volume and the distribution (volume ratio) of micropores, mesopores, and macropores can be measured using nitrogen adsorption / desorption according to the standards specified in ISO15901-2 and ISO 15901-3.

[0073] By condensing gas in the pores of a solid through nitrogen adsorption, the porosity and pore diameter distribution of the material can be determined. As the pressure increases, nitrogen can first condense in the pores with the smallest diameter, and the pressure can increase until the saturation point where all pores are filled with liquid is reached. After that, the nitrogen pressure can be gradually reduced so that the liquid evaporates from the system. The pore volume and pore distribution can be measured through the isotherms of nitrogen adsorption and desorption and the hysteresis analysis between them.

[0074] For example, the above specific surface area can refer to the surface area per unit mass calculated by measuring the physical adsorption of gas molecules on the solid surface according to the ISO 9277 standard and using the Brunauer-Emmett-Teller (BET) theory.

[0075] In some embodiments, in the total weight of the electrode material, the silicon content can be 30 wt% to 80 wt%. For example, it can be 40 wt% to 76 wt%, 48.5 wt% to 70 wt%, or 50 wt% to 60 wt%. Therefore, the stability and energy density of the electrode material can be improved.

[0076] In some embodiments, the peak intensity ratio of the Raman spectrum measured from the silicon-containing coating defined by the following formula 1 may be 0.5 or less, for example, it may be 0.4 or less. Within the above range, the proportion of the amorphous structure of silicon can be increased, and thus the structural stability of the electrode material can be improved.

[0077] [Formula 1]

[0078] Peak intensity ratio of Raman spectrum = I c-Si / I a-Si

[0079] In formula 1, I c-Si may be the peak intensity of the silicon-containing coating in the region of the Raman spectrum with a wavelength of 515 nm -1 , and I a-Si may be the peak intensity of the silicon-containing coating in the region of the Raman spectrum with a wavelength of 480 nm -1 .

[0080] For example, in formula 1, I c-Si may represent the proportion of silicon with a crystalline structure (Cristalline-Si), and in formula 1, I a-Si may represent the proportion of silicon with an amorphous structure (Amorphrous-Si).

[0081] In some embodiments, the ratio of the peak intensity I D of the D band to the peak intensity I G of the G band in the Raman spectrum obtained from the porous carbon structure may be 1 to 1.3, for example, it may be 1.05 to 1.25, 1.1 to 1.25, 1.15 to 1.22, or 1.2 to 1.22. Within the above range, the defects of the carbon-based material can be reduced, and thus the stability of the electrode material can be improved.

[0082] In the Raman spectrum obtained by Raman spectroscopic analysis of the porous carbon structure, the peak intensity (I G ) of the G band may be the peak intensity in the wavenumber region of about 1540 cm -1 to about 1620 cm -1 , and the peak intensity (I D ) of the D band may be the peak intensity in the wavenumber region of about 1300 cm -1 to about 1420 cm -1 .

[0083] The G band is a peak that can be commonly found in graphite-based materials. For example, when carbon atoms form a hexagonal crystal structure, the G band can appear. The D band is caused by a vibration mode with symmetry and cannot be observed in a perfect lattice structure. For example, when the hexagonal crystal structure is not well-developed or there are defects, the D band can appear.

[0084] For example, the peak intensity (I D ) of the above-mentioned D band and the peak intensity (I G ) of the G band can be the average value of the values obtained at 3 to 100 positions within a selected partial area of the carbon and through Raman spectroscopy analysis, and can vary according to changes in the thickness, uniformity, and structural stability of the carbon-based material.

[0085] The Raman spectroscopy analysis can be carried out using a Raman spectrometer of a type well-known in the art. For example, the laser wavelength of the Raman spectrometer can be, for example, about 532 nm to about 785 nm, the laser power can be about 5 mW to about 90 mW, the laser exposure time can be about 3 seconds to about 20 seconds, and the number of scans can be 1 to 10 times.

[0086] Figure 3 is a flowchart showing a method for preparing a silicon-carbon electrode material according to an exemplary embodiment.

[0087] Referring to Figure 3 , for example, in step S10, a polymer precursor solution can be prepared. The polymer precursor solution can exist in a sol state.

[0088] For example, a polymer precursor for forming the matrix within the porous carbon structure can be dissolved in a polar solvent or a proton solvent such as water. The polymer precursor can include an amine group-containing compound, an alcohol group-containing compound, a carbonyl group-containing compound, etc.

[0089] For example, the polymer precursor can include a phenolic compound, a polyol, an alkylamine, an aromatic amine, an aldehyde group-containing compound, a ketone group-containing compound, a carboxylic acid group-containing compound, an ester group-containing compound, urea, an acyl halide, an isocyanate group-containing compound, etc. These can be used alone or in combination of two or more.

[0090] In some embodiments, as the polymer precursor, a first precursor and a second precursor that are different from each other can be used simultaneously. For example, the first precursor can include a phenolic compound, and the second precursor can include an aldehyde group-containing compound. In one embodiment, the first precursor can include resorcinol, and the second precursor can include formaldehyde.

[0091] In one embodiment, the molar ratio of the second precursor to the first precursor can be adjusted within the range of 1 to 3. For example, it can be adjusted to the range of 1 to 2.5 or 1 to 2.

[0092] For example, in step S20, polymerization can be carried out in the polymer precursor solution to form a polymer gel.

[0093] Forming the gel (gelation) may refer to the dispersed polymer particles of the polymer precursor connecting to each other to form a continuous network.

[0094] According to an exemplary embodiment, a polymerization catalyst and / or a polymerization initiator can be added to the polymer precursor solution and polymerization can be carried out. Thus, a polymer gel can be formed while generating a polymer in the solution.

[0095] In one embodiment, the polymerization catalyst may comprise a basic compound. For example, the polymerization catalyst may comprise hydroxides of alkali metals or alkaline earth metals; carbonates of alkali metals or alkaline earth metals; ammonium-based compounds such as ammonium carbonate, ammonium bicarbonate, ammonium acetate, ammonium hydroxide, etc.; amine-based compounds such as diethylamine, triethylamine, triethanolamine, ethylenediamine, hexamethylenetetramine, etc. These can be used alone or in combination of two or more.

[0096] The molar ratio of the phenolic compound (for example, resorcinol) as the first precursor to the polymerization catalyst can be adjusted within the range of 100 to 1000. For example, it can be adjusted to the range of 150 to 700, 150 to 600, 150 to 500, 200 to 700, 200 to 600 or 200 to 500.

[0097] For example, the polymerization initiator may include azobisisobutyronitrile (AIBN), t-butylperacetate, benzoyl peroxide (BPO), acetyl peroxide, lauroyl peroxide, etc.

[0098] The polymerization temperature for forming the polymer gel can be in the range of about 70 °C to 100 °C, and the polymerization time can be 1 day to 4 days or 2 days to 3 days.

[0099] For example, in step S30, a bulk carbon structure can be formed by drying and carbonization.

[0100] According to an exemplary embodiment, by drying, the solvent (for example, water) in the polymer gel can be removed, and pores can be formed in the space where the solvent is removed. The dried polymer can be carbonized to form a bulk carbon structure containing pores.

[0101] In some embodiments, the carbonization can be carried out under anaerobic conditions or in an inert gas (e.g., N2 or Ar) atmosphere. The carbonization can be carried out at a temperature above 700 °C, for example, at a temperature of 800 °C to 1200 °C, 800 °C to 1100 °C, or 850 °C to 1000 °C.

[0102] In some embodiments, the bulk carbon structure can be pulverized to form a plurality of porous carbon structures.

[0103] For example, in step S40, silicon can be deposited on the porous carbon structure to form a silicon-containing coating, thereby obtaining a silicon-carbon electrode material.

[0104] In some embodiments, the silicon-containing coating can be formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD) using a silicon precursor. The silicon precursor can include a silane compound (e.g., SiH4).

[0105] For example, in the case of the CVD process, the silicon precursor can be supplied together with a carrier gas such as N2 and / or Ar.

[0106] In some embodiments, the ratio of the flow rate of the silicon precursor to the flow rate of the carrier gas can be 1 / 50 to 1 / 3, for example, 1 / 20 to 1 / 3 or 1 / 10 to 1 / 3. Within the above range, a silicon coating can be easily formed without causing pore blockage.

[0107] In some embodiments, the flow rate of the silicon precursor can be adjusted according to the amount of the porous carbon structure loaded in the deposition chamber.

[0108] For example, the silicon precursor can be injected so that the space velocity (SV) defined by Equation 2 remains within an appropriate range.

[0109] [Equation 2]

[0110]

[0111] In Equation 2, the carbon volume can be calculated based on the density of the porous carbon structure.

[0112] For example, the space velocity (SV) of the silicon precursor can be 100 h -1 (h -1 ) to 3000 h -1 、500 h -1 to 3000 h -1 or 750 h -1 to 2500 h-1 Within the above range, the silicon deposition efficiency can be increased according to the amount of the porous carbon structure loaded in the deposition chamber.

[0113] In some embodiments, the CVD process can be carried out within a temperature range of 400°C to 800°C. For example, the CVD process can be carried out within a temperature range of 425°C to 750°C or 425°C to 700°C.

[0114] In some embodiments, the CVD process can be carried out within a pressure range of 700 Torr to 800 Torr. For example, the CVD process can be carried out within a pressure range of 720 Torr to 780 Torr or 740 Torr to 780 Torr.

[0115] In some embodiments, the CVD process can be carried out for 1000 minutes to 2000 minutes. For example, the CVD process can be carried out for 1200 minutes to 1950 minutes, 1300 minutes to 1900 minutes, 1400 minutes to 1850 minutes, or 1500 minutes to 1800 minutes.

[0116] In one embodiment, the electrode material can be made to have characteristics such as a micropore volume ratio, mesopore volume ratio, macropore volume ratio, total pore volume, specific surface area, etc. within the above ranges.

[0117] According to an exemplary embodiment, the above characteristics can be obtained by adjusting a combination of conditions including the flow rate and space velocity (SV) of the silicon precursor, deposition temperature, deposition pressure, deposition time, etc.

[0118] For example, in the total pore volume of the electrode material, the volume ratio of micropores with a pore diameter of 2 nm or less can be more than 50% and less than 90%.

[0119] In some embodiments, a carbon coating can be further formed on the silicon-containing coating. The carbon coating can be formed by deposition using a gas such as methane or by solution coating using a monomer / polymer solution, etc.

[0120] In one embodiment, the carbon coating can contain a polymer having improved elastic properties such as an acrylonitrile-based polymer. For example, it can also contain conductive polymers such as polypyrrole, polyaniline, polythiophene, poly 3,4-ethylenedioxythiophene, etc.

[0121] In one embodiment, the hydrocarbon precursor can also be pyrolyzed or polymerized in an inert gas or an anaerobic atmosphere to form a carbon coating. The hydrocarbon precursor can be an alkane such as methane, ethane, or propane, an alkene such as ethylene or propylene, an alkyne such as acetylene, etc.

[0122] <Lithium secondary battery>

[0123] Figure 1 and Figure 2 are a schematic plan view and a schematic cross-sectional view, respectively, showing a lithium secondary battery according to an exemplary embodiment. Figure 2 is a cross-sectional view taken along the I-I' line of Figure 1 .

[0124] Referring to Figure 1 and Figure 2 , the lithium secondary battery may include an electrode assembly, and the electrode assembly may include a positive electrode 100 and a negative electrode 130. The electrode assembly 150 may further include a separator 140 interposed between the positive electrode 100 and the negative electrode 130. The electrode assembly 150 may be accommodated in a case 160 together with an electrolytic solution containing an electrolyte and immersed in the electrolytic solution.

[0125] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110, and the positive electrode active material layer 110 is provided on at least one surface of the positive electrode current collector 105.

[0126] For example, the positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector is not limited thereto, but for example, the positive electrode current collector may be 10 μm to 50 μm.

[0127] For example, the positive electrode active material may include a compound capable of reversibly inserting and extracting lithium ions.

[0128] For example, the positive electrode active material may include a lithium metal oxide containing metal elements such as nickel, cobalt, manganese, and aluminum.

[0129] According to an exemplary embodiment, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0130] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following Chemical Formula 1.

[0131] [Chemical Formula 1]

[0132] Li x Ni a M b O 2+z

[0133] In Chemical Formula 1, 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.4, and -0.5 ≤ z ≤ 0.1. As described above, M may include Co, Mn, and / or Al.

[0134] The chemical structure represented by Chemical Formula 1 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and Mn may be provided together with Ni as the main active elements of the positive electrode active material. Chemical Formula 1 is provided to represent the bonding relationship of the main active elements, and it should be understood that Chemical Formula 1 is a formula including the introduction and substitution of additional elements.

[0135] In one embodiment, in addition to including the main active elements, auxiliary elements for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may be further included. The auxiliary elements may be mixed together into the layered structure / crystal structure to form a bond, and it should be understood that this case is also included within the scope of the chemical structure represented by Chemical Formula 1.

[0136] The auxiliary elements may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary elements may act as auxiliary active elements that contribute to the capacity / power activity of the positive electrode active material together with Co or Mn, such as Al.

[0137] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following Chemical Formula 1-1.

[0138] [Chemical Formula 1-1]

[0139] Li x Ni a M1 b1 M2 b2 O 2+z

[0140] In Chemical Formula 1-1, M1 may include Co, Mn, and / or Al. M2 may include the above-mentioned auxiliary elements. In Chemical Formula 1-1, 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b1 + b2 ≤ 0.4, and -0.5 ≤ z ≤ 0.1.

[0141] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially the same as or similar to the above-mentioned auxiliary element may be used as the coating element or the doping element. For example, one or a combination of two or more of the above elements may be used as the coating element or the doping element.

[0142] The coating element or the doping element may be present on the surface of the lithium-nickel metal oxide particles or penetrate through the surface of the lithium-nickel metal oxide particles and be included in the bonding structure represented by Chemical Formula 1 or Chemical Formula 1-1.

[0143] The positive electrode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content may be used.

[0144] Nickel may be provided as a transition metal related to the power and capacity of the lithium secondary battery. Therefore, as described above, by using a high-content (high-nickel (High-Ni)) composition for the positive electrode active material, a positive electrode with a high capacity and a lithium secondary battery with a high capacity can be provided.

[0145] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or the secondary battery may be relatively reduced, and the side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, the conductivity can be maintained by including Co, and the life stability and capacity retention characteristics can be improved by Mn.

[0146] The content of Ni in the NCM-based lithium oxide (for example, the mole fraction of Ni in the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0147] In some embodiments, the positive electrode active material may further include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (for example, LiFePO4).

[0148] In some embodiments, the positive electrode active material may include, for example, an Mn-rich based active material, a Li rich layered oxide (LLO) / Over Lithiated Oxide (OLO) based active material, or a Co-less based active material having a chemical structure or crystal structure represented by the following Chemical Formula 2.

[0149] [Chemical Formula 2]

[0150] p[Li2MnO3]·(1-p)[Li q JO2]

[0151] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0152] For example, the positive electrode active material may be dispersed in a solvent to prepare a positive electrode mixture. The positive electrode mixture may be coated on the positive electrode current collector 105 and then dried and calendered to manufacture the positive electrode 100. The coating process may be performed by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc., and is not limited thereto. The positive electrode mixture may further include a binder, and may optionally further include a conductive material, a thickening agent, etc.

[0153] Non-limiting examples of the solvent used to prepare the positive electrode mixture may include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0154] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder may be used as the positive electrode binder.

[0155] The conductive material can be added to enhance the conductivity of the positive electrode mixture layer and / or the mobility of lithium ions or electrons. For example, the conductive material can include carbon-based conductive materials such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, etc. and / or metal-based conductive materials including perovskite materials such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc.

[0156] As the thickener, for example, carboxymethyl cellulose (CMC) can be used.

[0157] The negative electrode 130 can include a negative electrode current collector 125 and a negative electrode active material layer 120 on the negative electrode current collector 125.

[0158] For example, the negative electrode active material layer 120 can contain a negative electrode active material and a negative electrode binder, and can further contain a conductive material.

[0159] For example, the negative electrode 130 can be manufactured as follows: the negative electrode active material, the negative electrode binder, and the conductive material are mixed in a solvent and stirred to prepare a negative electrode slurry, and then the negative electrode slurry is coated on the negative electrode current collector 125 and dried and calendered to manufacture the negative electrode 130.

[0160] The coating process can be carried out by methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, rod coating, casting, etc., and is not limited thereto.

[0161] For example, the negative electrode current collector 125 can include gold, stainless steel, nickel, aluminum, titanium, copper, or their alloys. As an example, the negative electrode current collector 125 can include copper or a copper alloy. The negative electrode current collector is not limited thereto, but for example, the negative electrode current collector can be 10 μm to 50 μm.

[0162] For example, the negative electrode active material layer 120 can contain a silicon-carbon-containing electrode material according to the above exemplary embodiments as the negative electrode active material. In some embodiments, the negative electrode active material can further contain a graphite-based active material such as artificial graphite or natural graphite.

[0163] In some embodiments, in the total weight of the negative electrode active material contained in the negative electrode active material layer 120, the content of the silicon-carbon electrode material according to the above exemplary embodiments may be 5% by weight or more, 10% by weight or more, 20% by weight or more, 30% by weight or more, 40% by weight or more, or 50% by weight or more, and may be 95% by weight or less, 90% by weight or less, 80% by weight or less, or 70% by weight or less.

[0164] In one embodiment, the negative electrode active material contained in the negative electrode active material layer 120 may be composed of the content of the silicon-carbon electrode material according to the above exemplary embodiments. Therefore, the initial efficiency, capacity characteristics, and life characteristics of the lithium secondary battery can be improved.

[0165] For example, with respect to the total weight of the negative electrode active material layer 120, the content of the negative electrode active material contained in the negative electrode active material layer 120 may be 60% by weight to 99% by weight. For example, it may be 70% by weight to 98% by weight or 80% by weight to 98% by weight.

[0166] Non-limiting examples of the solvent for the negative electrode mixture may include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, and the like.

[0167] The negative electrode binder and the conductive material may be substantially the same or similar substances as the above positive electrode binder and conductive material.

[0168] For example, the negative electrode binder may use a styrene-butadiene rubber (SBR)-based binder, a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene) (PEDOT)-based binder, etc., and may be used together with a thickener such as carboxymethyl cellulose (CMC).

[0169] In one embodiment, the separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. The separator can prevent a short circuit between the positive electrode and the negative electrode and can maintain the flow of ions. According to the embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present invention is not limited thereto.

[0170] For example, the separator 140 may include a porous polymer membrane made of a polyolefin-based polymer such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer.

[0171] For example, the separator 140 may include a non-woven fabric formed of glass fibers with a high melting point, polyethylene terephthalate fibers, etc.

[0172] For example, a battery cell may be formed by including a positive electrode 100, a negative electrode 130, and a separator 140. In addition, a plurality of battery cells may be stacked to form an electrode assembly 150. For example, the electrode assembly 150 may be formed by winding, stacking, z-folding, or stack-folding of the separator 140.

[0173] The electrode assembly 150 and the electrolyte are accommodated in a housing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte may use a non-aqueous electrolyte.

[0174] The non-aqueous electrolyte may contain a lithium salt as an electrolyte and an organic solvent. The lithium salt may be represented, for example, by Li + X - As the anion (X - ) of the lithium salt, examples may include F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO -, (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - etc.

[0175] The organic solvent may include an organic compound that has sufficient solubility for the lithium salt and the additive and is non-reactive in the battery. As the organic solvent, it may include, for example, at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.

[0176] As the organic solvent, for example, propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc. These can be used alone or in combination of two or more.

[0177] The non-aqueous electrolyte may further contain an additive. The additive may include, for example, a cyclic carbonate group compound, a fluorine-substituted carbonate group compound, a sultone group compound, a cyclic sulfate group compound, a cyclic sulfite group compound, a phosphate group compound, and a borate group compound.

[0178] The cyclic carbonate group compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0179] The fluorine-substituted carbonate group compound may include fluoroethylene carbonate (FEC), etc.

[0180] The sulfone group-containing compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0181] The cyclic sulfate group-containing compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0182] The cyclic sulfite group-containing compound may include ethylene sulfite, butylene sulfite, etc.

[0183] The phosphate group-containing compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0184] The borate group-containing compound may include lithium bis(oxalate) borate, etc.

[0185] As Figure 1 shown, the tab (positive tab or negative tab) may protrude from the positive current collector 105 and the negative current collector 125 belonging to each battery cell, respectively, and extend to one side of the housing 160. The tabs may be fused together and connected to the electrode leads (positive lead 107 or negative lead 127) extending to the outside of the housing 160.

[0186] For example, the lithium secondary battery may be made into a cylindrical shape using a can, a prismatic shape, a pouch type, a coin shape, etc.

[0187] Hereinafter, with reference to specific experimental examples, the embodiments of the present invention will be further described. The examples and comparative examples included in the experimental examples are only used to illustrate the present invention and are not used to limit the claims. Various changes and modifications can be made to the examples within the scope and technical idea of the present invention, which is obvious to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0188] Example 1

[0189] Formation of the silicon-containing coating

[0190] Using a carbon structure with an average pore size of 1.9 nm, a specific surface area of 2052 m 2 / g, and a total pore volume of 0.98 cm 3 / g, a silicon-containing coating was formed on the porous carbon structure through a CVD process using SiH4 as a precursor.

[0191] Specifically, as described above, the carbon structure was loaded into a CVD chamber, and a CVD process was carried out under the conditions of a temperature of 425 °C, a pressure of 760 Torr, a LHSV = 31.5 h considering the ratio of SiH4 to the carbon structure -1 , a SiH4 / N2 volume ratio = 0.02, and a deposition time of 1800 minutes, thereby preparing a silicon-carbon electrode material.

[0192] Manufacture of the negative electrode

[0193] 70 wt% of the silicon-carbon electrode material prepared as described above as the negative electrode active material, 15 wt% of Super P as the conductive material, and 15 wt% of polyacrylic acid (PAA) as the binder were mixed to obtain a negative electrode slurry. The Super P is conductive carbon black provided by TIMCAL, a subsidiary of the French multinational company Imerys S.A. The primary particle size of the conductive carbon black is about 50 nm, the secondary particle size is about 150 nm to 200 nm, and the specific surface area is 62 m 2 / g, and the main components are: carbon content > 99%, ash content < 0.05%.

[0194] The negative electrode slurry was coated on a copper substrate and dried and calendered to manufacture a negative electrode with a mixture density of 1.5 g / cubic centimeter (cc).

[0195] Manufacture of a lithium half-cell (Li-half cell)

[0196] A lithium secondary battery was manufactured including the negative electrode manufactured as described above and using lithium metal (Li metal) as the counter electrode (positive electrode).

[0197] Specifically, a separator (polyethylene, thickness 20 μm) was disposed between the negative electrode and the lithium metal (thickness 1 mm) to form a lithium coin-type half-cell (coin half-cell).

[0198] Example 2

[0199] The same carbon structure as in Example 1 was used, and a silicon-containing coating was formed on the porous carbon structure through a CVD process using SiH4 as a precursor.

[0200] Specifically, as described above, the carbon structure is loaded into the CVD chamber, and the CVD process is carried out under the conditions of a temperature of 410 °C, a pressure of 760 Torr, and a LHSV = 0.11 h considering the ratio of SiH4 to the carbon structure -1 , a SiH4 / N2 volume ratio of 0.15, and a deposition time of 1800 minutes to prepare a silicon-carbon electrode material.

[0201] A secondary battery is manufactured by the same method as in Example 1, except that the silicon-carbon electrode material prepared by the above method is used.

[0202] Example 3

[0203] The same carbon structure as in Example 1 is used, and a silicon-containing coating is formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0204] Specifically, as described above, the carbon structure is loaded into the CVD chamber, and the CVD process is carried out under the conditions of a temperature of 410 °C, a pressure of 760 Torr, and a LHSV = 0.11 h considering the ratio of SiH4 to the carbon structure -1 , a SiH4 / N2 volume ratio of 0.3, and a deposition time of 1800 minutes to prepare a silicon-carbon electrode material.

[0205] A secondary battery is manufactured by the same method as in Example 1, except that the silicon-carbon electrode material prepared by the above method is used.

[0206] Example 4

[0207] The same carbon structure as in Example 1 is used, and a silicon-containing coating is formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0208] Specifically, as described above, the carbon structure is loaded into the CVD chamber, and the CVD process is carried out under the conditions of a temperature of 350 °C, a pressure of 760 Torr, and a LHSV = 0.11 h considering the ratio of SiH4 to the carbon structure -1 , a SiH4 / N2 volume ratio of 0.11, and a deposition time of 2520 minutes to prepare a silicon-carbon electrode material.

[0209] A secondary battery is manufactured by the same method as in Example 1, except that the silicon-carbon electrode material prepared by the above method is used.

[0210] Example 5

[0211] The same carbon structure as in Example 1 is used, and a silicon-containing coating is formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0212] Specifically, as described above, the carbon structure is loaded into the CVD chamber, and the LHSV = 0.11 h is considered in terms of the ratio of SiH4 to the carbon structure at a temperature of 370 °C and a pressure of 760 Torr. -1 The CVD process is carried out under the conditions of SiH4 / N2 volume ratio = 0.12 and a deposition time of 2160 minutes, so as to prepare the silicon-carbon-containing electrode material.

[0213] A secondary battery is manufactured by the same method as in Example 1, except that the silicon-carbon-containing electrode material prepared by the above method is used.

[0214] Comparative Example 1

[0215] Preparation of Porous Carbon Structure

[0216] Resorcinol and formaldehyde are mixed in a molar ratio of 1:2 in water to prepare a polymer precursor solution. The mixture of resorcinol and formaldehyde is mixed with water in a weight ratio of 1:10. Sodium carbonate as a catalyst is added to the polymer precursor solution. The molar ratio of resorcinol to the catalyst is adjusted to 500. Then, polymerization is carried out at 80 °C for 3 days to form a polymer gel.

[0217] After polymerization, the polymer gel is completely dried below 60 °C and then carbonized at a temperature of 850 °C in an N2 atmosphere. The carbonized product is pulverized to prepare a porous carbon structure.

[0218] Formation of Silicon-Containing Coating

[0219] The obtained carbon structure is used, and a silicon-containing coating is formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0220] Specifically, as described above, the carbon structure is loaded into the CVD chamber, and the LHSV = 20.0 h is considered in terms of the ratio of SiH4 to the carbon structure at a temperature of 500 °C and a pressure of 760 Torr. -1 The CVD process is carried out under the conditions of SiH4 / N2 volume ratio = 0.1 and a deposition time of 2880 minutes, so as to prepare the silicon-carbon-containing electrode material.

[0221] A secondary battery is manufactured by the same method as in Example 1, except that the silicon-carbon-containing electrode material prepared by the above method is used.

[0222] Comparative Example 2

[0223] The carbon structure prepared by the same method as in Comparative Example 1 is used, and a silicon-containing coating is formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0224] Specifically, as described above, the porous carbon structure is loaded into the CVD chamber, and the CVD process is carried out under the conditions of a temperature of 390 °C, a pressure of 760 Torr, and a LHSV = 21.0 h considering the ratio of SiH4 to the carbon structure -1 、SiH4 / N2 volume ratio = 0.03, and a deposition time of 2160 minutes to prepare a silicon-carbon electrode material.

[0225] A secondary battery is manufactured by the same method as in Example 1, except that the silicon-carbon electrode material prepared by the above method is used.

[0226] Comparative Example 3

[0227] The same carbon structure as that used in Example 1 is used, and a silicon-containing coating is formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0228] Specifically, as described above, the carbon structure is loaded into the CVD chamber, and the CVD process is carried out under the conditions of a temperature of 350 °C, a pressure of 760 Torr, and a LHSV = 0.11 h considering the ratio of SiH4 to the carbon structure -1 、SiH4 / N2 volume ratio = 0.3, and a deposition time of 2520 minutes to prepare a silicon-carbon electrode material.

[0229] A secondary battery is manufactured by the same method as in Example 1, except that the silicon-carbon electrode material prepared by the above method is used.

[0230] Comparative Example 4

[0231] Formation of silicon-containing coating

[0232] A carbon structure with an average pore size of 4.0 nm, a specific surface area of 1657 m 2 / g, and a total pore volume of 2.06 cm 3 / g recorded in Table 1 below is used, and a silicon-containing coating is formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0233] Specifically, as described above, the carbon structure is loaded into the CVD chamber, and the CVD process is carried out under the conditions of a temperature of 500 °C, a pressure of 760 Torr, and a LHSV = 31.5 h considering the ratio of SiH4 to the carbon structure -1 、SiH4 / N2 volume ratio = 0.1, and a deposition time of 600 minutes to prepare a silicon-carbon electrode material.

[0234] A secondary battery is manufactured by the same method as in Example 1, except that the silicon-carbon electrode material prepared by the above method is used.

[0235] Comparative Example 5

[0236] A carbon structure with an average pore size of 2.5 nm, a specific surface area of 1729 m 2 / g, and a total pore volume of 1.12 cm 3 / g was used. A silicon-containing coating was formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0237] Specifically, as described above, the carbon structure was loaded into the CVD chamber, and the CVD process was carried out under the conditions of a temperature of 500 °C, a pressure of 760 Torr, LHSV = 31.5 h considering the ratio of SiH4 to the carbon structure -1 , SiH4 / N2 volume ratio = 0.1, and a deposition time of 600 minutes to prepare a silicon-carbon electrode material.

[0238] A secondary battery was manufactured by the same method as in Example 1, except that the silicon-carbon electrode material prepared by the above method was used.

[0239] Comparative Example 6

[0240] A carbon structure with an average pore size of 2.5 nm, a specific surface area of 1729 m 2 / g, and a total pore volume of 1.12 cm 3 / g was used. A silicon-containing coating was formed on the porous carbon structure by a CVD process using SiH4 as a precursor.

[0241] Specifically, as described above, the carbon structure was loaded into the CVD chamber, and the CVD process was carried out under the conditions of a temperature of 500 °C, a pressure of 760 Torr, LHSV = 42.0 h considering the ratio of SiH4 to the carbon structure -1 , SiH4 / N2 volume ratio = 0.1, and a deposition time of 600 minutes to prepare a silicon-carbon electrode material.

[0242] A secondary battery was manufactured by the same method as in Example 1, except that the silicon-carbon electrode material prepared by the above method was used.

[0243] The physical properties of the porous carbon structures and silicon-carbon electrode materials prepared according to the examples and comparative examples were measured / evaluated as follows.

[0244] (1) Measurement of the total pore volume / volume ratio of micropores, mesopores, and macropores

[0245] The total pore volume, and the distribution (volume ratio) of micropores, mesopores, and macropores in the total pore volume were measured at 77 K using nitrogen adsorption according to ISO 15901-2 and ISO 15901-3 standards and by the t-plot method. Specifically, a 3-Flex Adsorption Analyzer from Micromeritics Instrument Corporation was used.

[0246] The distribution (volume ratio) of micropores, mesopores, and macropores in the total pore volume measured according to the above method is shown in Table 2 below, and the measurement results of the silicon-containing carbon electrode materials of Examples 1 to 5 and Comparative Examples 1 to 6 are shown in the form of pore distribution diagrams in Figures 4 to 8 and Figures 9 to 14 below.

[0247] (2) Measurement of average pore size

[0248] The pore size of the porous carbon structure was measured using a 3-Flex Adsorption Analyzer from Micromeritics. Specifically, the maximum peak position of the Barrett-Joyner-Halenda (BJH) pore size distribution curve obtained from the nitrogen isothermal adsorption and desorption curve (nitrogen gas sorption isotherm) of the porous carbon structure samples used in the examples and comparative examples was measured to measure the pore size of the porous carbon structure.

[0249] (3) Measurement of specific surface area

[0250] The specific surface area was calculated as the surface area per unit mass by measuring the physical adsorption of gas molecules on the solid surface using a 3-Flex Adsorption Analyzer system according to ISO 9277 standard.

[0251] (4) Measurement of silicon content

[0252] The content of silicon in the total weight of the silicon-containing carbon electrode material was measured using an ICP-OES analyzer. Specifically, the sample was placed in a PP tube, nitric acid and a small amount of hydrofluoric acid were added and dissolved overnight. After the sample was dissolved, it was stored refrigerated, then the hydrofluoric acid was neutralized with saturated boric acid water and diluted with ultrapure water. After that, the residual carbon was removed with a 0.45 μm syringe filter and analyzed.

[0253] (5) Measurement of the peak intensity ratio (I c-Si / I a-Si ) of Raman spectrum

[0254] For the silicon-carbon electrode materials prepared according to the above-described examples and comparative examples, the Raman spectrum of the silicon-containing coating was measured using a 532 nm laser Raman analyzer (Laser Raman Spectroscopy). The peak intensity (I -1 ) of the silicon-containing coating in the region with a wavelength of 515 nm c-Si and the peak intensity (I -1 ) of the silicon-containing coating in the region with a wavelength of 480 nm a-Si ) in the Raman spectrum obtained by the measurement were determined. The measured peak intensities were substituted into Equation 1 to calculate the peak intensity ratio (I c-Si / I a-Si ) of the Raman spectrum.

[0255] (6) Measurement of the ratio of the peak intensity (I D ) of the D band to the peak intensity (I G ) of the G band in the Raman spectrum

[0256] The I D / I G value of the porous carbon structure contained in the silicon-carbon electrode materials prepared according to the above-described examples and comparative examples was measured under the following conditions. Specifically, three positions on the surface of the silicon-carbon electrode material were selected, and the I D / I G value was obtained as the average of the corresponding values.

[0257] i) Tap density of the silicon-carbon electrode material: 0.99 g / cm 3

[0258] ii) Electrode density: 1.3 g / cm 3

[0259] iii) Raman spectrometer: inVia, Renishaw (UK)

[0260] iv) Argon ion laser wavelength: 532 nm

[0261] v) Exposure time: 20 seconds, number of accumulations: 10 times

[0262] The results of the physical property evaluation of the porous carbon structures prepared according to the examples and comparative examples were recorded in Table 1 below, and the results of the physical property evaluation of the silicon-carbon electrode materials prepared according to the examples and comparative examples were recorded in Tables 2 and 3 below.

[0263] [Table 1]

[0264]

[0265] [Table 2]

[0266]

[0267] [Table 3]

[0268]

[0269] Experimental Example

[0270] The performance of secondary batteries using silicon-carbon electrode materials prepared according to the examples and comparative examples was measured / evaluated as follows.

[0271] (1) Measurement of charge capacity and discharge capacity

[0272] For each secondary battery of the examples and comparative examples, CC / CV charging was performed at a rate of 0.1C (C-rate) at 25 °C (0.01V, 0.01C cut-off), and the discharge capacity was measured after CC discharge at a rate of 0.1C (1.5V cut-off). Specifically, each battery was charged at a constant current (0.1C rate) until the set voltage reached 4.2V. After that, the charging was switched to the constant voltage mode, and the current gradually decreased to 0.01C. The discharge process of the battery was carried out at a constant current rate of 0.1C. During the discharge process of the battery, the voltage gradually decreased while maintaining a constant current flow, and when the voltage decreased to 1.5V, the discharge was stopped. The entire charge and discharge evaluation was carried out at a temperature of 25 °C.

[0273] (2) Evaluation of initial efficiency

[0274] The initial efficiency was calculated by calculating the ratio of the discharge capacity measured in (1) to the charge capacity as a percentage.

[0275] (3) Measurement of capacity retention rate (life characteristics) during repeated charge and discharge

[0276] For each secondary battery of the examples and comparative examples, CC / CV charging at a rate of 0.1C (0.01V, 0.01C cut-off) and CC discharge at a rate of 0.1C (1.5V cut-off) were repeated 50 times at 25 °C. The capacity retention rate was evaluated by the percentage of the value obtained by dividing the discharge capacity of the 50th cycle by the discharge capacity of the 1st cycle.

[0277] The evaluation results in Experimental Examples 1 to 3 are shown in Table 4 below.

[0278] [Table 4]

[0279]

[0280] Referring to Tables 1 to 4, compared with the batteries of Comparative Examples 1 to 6 manufactured using silicon-carbon electrode materials with a volume ratio of micropores in the total pore volume of 50% or less or exceeding 90%, the batteries of Examples 1 to 5 manufactured using silicon-carbon electrode materials with a volume ratio of micropores in the total pore volume exceeding 50% and less than 90% have improved charge capacity, discharge capacity, initial efficiency, and capacity retention rate.

Claims

1. A silicon-carbon electrode material comprising: Porous carbon structures; and a silicon-containing coating formed on the porous carbon structure, in, In the total pore volume, the volume ratio of micropores having a pore diameter of 2 nm or less is more than 50% and less than 90%.

2. The silicon-carbon electrode material according to claim 1, wherein The volume ratio of micropores having a pore diameter of 2 nm or less in the total pore volume is 55% to 80%.

3. The silicon-carbon electrode material according to claim 1, wherein In the total pore volume, the volume ratio of mesopores having a pore diameter of more than 2 nm and less than 50 nm is 8% to 48%, and the volume ratio of macropores having a pore diameter of more than 50 nm is 1.5% to 10%.

4. The silicon-carbon electrode material according to claim 1, wherein The total pore volume is 0.02 cm 3 / g to 0.2cm 3 / g.

5. The silicon-carbon electrode material according to claim 1, wherein The ratio of the total pore volume of the silicon-carbon electrode material to the total pore volume of the porous carbon structure is 0.15 or less.

6. The silicon-carbon electrode material according to claim 1, wherein The specific surface area of ​​the silicon-carbon electrode material is 60 m 2 / g to 320m 2 / g.

7. The silicon-carbon electrode material according to claim 1, wherein The ratio of the specific surface area of ​​the silicon-carbon electrode material to the specific surface area of ​​the porous carbon structure is 0.1 or less.

8. The silicon-carbon electrode material according to claim 1, wherein The content of silicon is 30 wt % to 80 wt % in the total weight of the silicon-carbon electrode material.

9. The silicon-carbon electrode material according to claim 1, wherein The peak intensity ratio of the Raman spectrum measured from the silicon-containing coating layer defined by the following formula 1 is 0.5 or less, [Formula 1] The peak intensity ratio of Raman spectrum = I c-Si / I a-Si In formula 1, I c-Si The wavelength in Raman spectroscopy is 515nm -1 The peak intensity of the silicon-containing coating in the region of a-Si The wavelength in Raman spectroscopy is 480nm -1 The peak intensity of the silicon-containing coating in the region of .

10. The silicon-carbon electrode material according to claim 1, wherein The peak intensity I of the D band of the Raman spectrum obtained from the porous carbon structure is D The peak intensity of the G band I G The ratio is 1 to 1.

3.

11. A method for preparing a silicon-carbon electrode material, comprising the following steps: forming a polymer precursor solution; polymerizing the polymer precursor contained in the polymer precursor solution to form a polymer gel; drying and carbonizing the polymer gel to form a bulk carbon structure; crushing the bulk carbon structure to form a porous carbon structure; as well as forming a silicon-containing coating on the porous carbon structure to obtain a silicon-carbon electrode material, Among them, in the total pore volume of the silicon-carbon electrode material, the volume ratio of micropores with a pore diameter of 2 nm or less is more than 50% and less than 90%.

12. The method for preparing a silicon-carbon electrode material according to claim 11, wherein: The silicon-containing coating is formed by a deposition process at a temperature of 400° C. to 800° C. and a pressure of 700 torr to 800 torr.

13. The method for preparing a silicon-carbon electrode material according to claim 12, wherein: The deposition process includes supplying a silicon precursor and a carrier gas, and a ratio of a flow rate of the silicon precursor to a flow rate of the carrier gas is 1 / 50 to 1 / 3.

14. A lithium secondary battery comprising: A negative electrode, the negative electrode comprising the silicon-carbon electrode material according to claim 1; as well as A positive electrode is arranged opposite to the negative electrode.

15. A lithium secondary battery comprising a negative electrode, the negative electrode comprising a silicon-carbon electrode material, in, The silicon-carbon electrode material comprises: a porous carbon structure; and a silicon-containing coating, wherein the silicon-containing coating is formed on the porous carbon structure. In the total pore volume of the silicon-carbon electrode material, the volume ratio of micropores with a pore diameter of 2 nm or less is more than 50% and less than 90%, The ratio of the specific surface area of ​​the silicon-carbon electrode material to the specific surface area of ​​the porous carbon structure is 0.1 or less.

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