Negative electrode for lithium secondary battery and lithium secondary battery comprising same

Abstract

A negative electrode for a lithium secondary battery according to an embodiment of the present invention comprises: a negative electrode current collector; and a negative electrode active material layer provided on at least one surface of the negative electrode current collector and including a negative electrode active material and a conductive material, in which an electrode peak intensity ratio of the negative electrode active material layer obtained by analysis of a distribution function (PDF) is 1.1 to 2.7.

Description

Technical Field

[0001] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same. 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 camcorders, mobile phones, and laptop computers. In addition, in recent years, battery packs including secondary batteries are being developed and used as power sources for eco-friendly vehicles such as electric vehicles.

[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. Therefore, they are actively developed and applied.

[0004] In recent years, with the expansion of the application targets of lithium secondary batteries, lithium secondary batteries with higher capacity and power are being developed. For example, high-capacity silicon and carbon can be compounded and used as a negative electrode active material.

[0005] However, since the volume expansion rate of the negative electrode including the silicon-carbon composite negative electrode active material increases, repeated charge and discharge may cause a reduction in life characteristics. Summary of the Invention

[0006] (I) Technical Problem to be Solved

[0007] According to one aspect of the present invention, a negative electrode for a lithium secondary battery having improved life characteristics and power characteristics can be provided.

[0008] According to another aspect of the present invention, a lithium secondary battery having improved life characteristics and power characteristics can be provided.

[0009] (II) Technical Solution

[0010] The negative electrode for a lithium secondary battery according to an exemplary embodiment of the present invention includes: a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including a negative electrode active material and a conductive material, wherein an electrode peak intensity ratio defined by the following formula 1 is 1.1 to 2.7.

[0011] [Formula 1]

[0012] Electrode peak intensity ratio = Ip2 / Ip1

[0013] In Formula 1, Ip1 is the maximum height of the peak in the range of 3.4 Å to 4.1 Å of the PDF spectrum obtained by performing pair distribution function (PDF) analysis on the negative electrode active material layer, and Ip2 is the maximum height of the peak in the range of 4.1 Å to 4.9 Å of the PDF spectrum.

[0014] In some embodiments, the electrode peak intensity ratio can be 2.13 to 2.64.

[0015] In some embodiments, the negative electrode active material may include composite particles, and the composite particles include: carbon-based particles including pores; and a silicon-containing coating formed on the surface of the carbon-based particles.

[0016] In some embodiments, the particle peak distance defined by the following Formula 2 of the composite particles can be 0.6 Å or less.

[0017] [Formula 2]

[0018] Particle peak distance (Å) = p4 - p3

[0019] In Formula 2, p3 is the central peak value of the peak with the maximum height in the range of 3.4 Å to 4.1 Å of the PDF spectrum obtained by performing PDF analysis on the composite particles, and p4 is the central peak value of the peak with the maximum height in the range of 4.1 Å to 4.9 Å of the PDF spectrum obtained by performing PDF analysis on the composite particles.

[0020] In some embodiments, the particle peak distance can be 0.56 Å to 0.59 Å.

[0021] In some embodiments, the particle peak intensity ratio defined by the following Formula 3 of the composite particles can be 0.1 to 0.35.

[0022] [Formula 3]

[0023] Particle peak intensity ratio = Ip4 / Ip3

[0024] In Formula 3, Ip3 is the maximum height of the peak in the range of 3.4 Å to 4.1 Å of the PDF spectrum obtained by performing PDF analysis on the composite particles, and Ip4 is the maximum height of the peak in the range of 4.1 Å to 4.9 Å of the PDF spectrum obtained by performing PDF analysis on the composite particles.

[0025] In some embodiments, the particle peak intensity ratio can be 0.15 to 0.28.

[0026] In some embodiments, the size of the pores of the carbon-based particles can be 0.1 nm to 10 nm.

[0027] In some embodiments, the size of the pores of the carbon-based particles may be from 1 nm to 5 nm.

[0028] In some embodiments, the composite particles may further comprise a carbon coating formed on the silicon-containing coating.

[0029] In some embodiments, the content of the composite particles may be from 5% by weight to 40% by weight relative to the total weight of the negative electrode active material layer.

[0030] In some embodiments, the content of the composite particles may be from 10% by weight to 30% by weight relative to the total weight of the negative electrode active material layer.

[0031] In some embodiments, the negative electrode active material may further comprise a graphite-based active material, and the graphite-based active material comprises at least one selected from artificial graphite and natural graphite.

[0032] In some embodiments, the conductive material may comprise single-walled carbon nanotubes (SWCNT).

[0033] The lithium secondary battery according to an exemplary embodiment of the present invention includes: the negative electrode for a lithium secondary battery as described above; and a positive electrode disposed opposite to the negative electrode.

[0034] (III) Beneficial effects

[0035] According to one embodiment of the present invention, the power characteristics and life characteristics of the secondary battery can be improved.

[0036] According to one embodiment of the present invention, the physical stability and chemical stability of the composite particles can be improved.

[0037] According to one embodiment of the present invention, the capacity retention rate of the secondary battery can be improved.

[0038] The negative electrode for a lithium secondary battery of the present invention and the lithium secondary battery including the same can be widely applied to green technology fields such as electric vehicles, battery charging stations, other battery-utilizing solar power generation, and wind power generation. The negative electrode for a lithium secondary battery of the present invention and the lithium secondary battery including the same can be used for eco-friendly electric vehicles (EVs), hybrid vehicles, etc. that prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1is a schematic cross-sectional view showing a composite particle according to an exemplary embodiment.

[0040] Figure 2 and Figure 3 are a schematic plan view and a schematic cross-sectional view respectively showing a lithium secondary battery according to an exemplary embodiment.

[0041] Figure 4 is the PDF spectrogram obtained by analyzing the distribution function (PDF) in Example 3.

[0042] Figure 5 is the PDF spectrogram obtained by PDF analysis in Comparative Example 1.

[0043] Figure 6 is the PDF spectrogram obtained by PDF analysis in Comparative Example 3. Detailed Description

[0044] Embodiments of the present invention provide a negative electrode for a lithium secondary battery including a negative electrode active material layer (hereinafter, may be simply referred to as "negative electrode"). In addition, a lithium secondary battery including the negative electrode (hereinafter, may be simply referred to as "secondary battery") is provided.

[0045] 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.

[0046] In an exemplary embodiment, the negative electrode may include: a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector and containing a negative electrode active material and a conductive material.

[0047] For example, the negative electrode current collector may include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a foam nickel, a foam copper, a polymer substrate coated with a conductive metal, etc. These may be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector may be 10 μm to 50 μm.

[0048] In an exemplary embodiment, the negative electrode active material may include composite particles including a carbon-based particle and a silicon (Si)-containing coating. Hereinafter, with reference to Figure 1 , the detailed configuration of the composite particles will be described. For example, the negative electrode active material may include a plurality of the composite particles.

[0049] In some embodiments, the negative electrode active material may include the composite particles and a graphite-based active material. For example, the graphite-based active material may include artificial graphite and / or natural graphite.

[0050] In the total weight of the negative electrode active material (e.g., the total weight of multiple composite particles and graphite-based active material), the content of the composite particles can be 3 wt% or more, 5 wt% or more, 10 wt% or more, 15 wt% or more, 20 wt% or more, 25 wt% or more, 30 wt% or more, 35 wt% or more, 40 wt% or more, or 45 wt% or more.

[0051] In the total weight of the negative electrode active material, the content of the composite particles can be 90 wt% or less, 85 wt% or less, 80 wt% or less, 75 wt% or less, 70 wt% or less, 65 wt% or less, 60 wt% or less, 55 wt% or less, or 50 wt% or less.

[0052] In one embodiment, the negative electrode active material can substantially consist of the composite particles and the graphite-based active material.

[0053] In an exemplary embodiment, the electrode peak intensity ratio defined by the following formula 1 of the negative electrode active material layer can be 1.1 to 2.7. In some embodiments, the electrode peak intensity ratio can be 2.13 to 2.64. The electrode peak intensity ratio can be measured by pair distribution function (PDF) analysis.

[0054] [Formula 1]

[0055] Electrode peak intensity ratio = Ip2 / Ip1

[0056] In formula 1, Ip1 is the maximum height of the peak in the range of 3.4 Å to 4.1 Å of the PDF spectrum obtained by performing PDF analysis on the negative electrode active material layer, and Ip2 is the maximum height of the peak in the range of 4.1 Å to 4.9 Å of the PDF spectrum.

[0057] For example, the electrode peak intensity ratio can correspond to the degree of dispersion of the peaks of the PDF spectra of carbon atoms and silicon atoms contained in the negative electrode active material layer.

[0058] Within the above range of the electrode peak intensity ratio, the crystallinity and amorphousness of the carbon component (e.g., carbon-based particles and / or graphite-based active material) and the silicon component of the negative electrode active material layer can be adjusted. Therefore, the power characteristics and life characteristics of the secondary battery can be improved.

[0059] The scattering data for the PDF analysis can be collected, for example, at beam line 1C of the Pohang Light Source (PLS-II) of the Pohang Accelerator Laboratory (PAL). In addition to the beam line 1C, other devices capable of measuring the scattering data can also be used.

[0060] For example, a negative electrode sample including a negative electrode active material layer can be fixed, and using high-energy X-rays (22.003 KeV) with a wavelength (λ) of 0.56356 Å, two-dimensional (2D) scanning can be performed within a range of 5 - 80 degrees (2θ) with a step size of 0.017 degrees to measure the scattering data. The scattering data can include 2D scattering images.

[0061] The 2D scattering images are integrated by software (e.g., Dioptas), and thus one-dimensional (1D) scattering intensity data can be obtained. During the process of obtaining the 1D scattering intensity data, when the current collector is bonded to the composite particles 50, the diffraction peak of the current collector can be flattened.

[0062] For example, by collecting X-rays scattered in the atmosphere, background data can be obtained.

[0063] For example, by applying the 1D scattering intensity data, the background data, the wavelength used, and the chemical composition to software (e.g., PDFgetX3), a structure function S(Q) can be obtained. In this case, the relative intensity of the background data with respect to the 1D scattering intensity data (background scale) can be set to 1.0, and the range of Q can be set to 0.1 to 12.0.

[0064] Performing a Fourier transform on the S(Q) can obtain the G(r) function. By showing the variation of G(r) according to the interatomic distance (r), the PDF spectrum can be obtained.

[0065] P1 and p2 in Equation 1 can be measured by drawing a baseline parallel to the horizontal axis (r) based on the lowest vertical axis (G(r)) height within the range of 0 Å to 6 Å of the r in the PDF spectrum, and then obtaining the central peak value of the peak with the maximum height based on the baseline.

[0066] In some embodiments, the secondary battery including the negative electrode can be charged and discharged during formation and then discharged to 2.2 V, and the secondary battery can be disassembled to obtain the negative electrode active material layer, and the obtained negative electrode active material layer can be used as an object to measure the electrode peak intensity ratio. Therefore, the physical properties of the substantially driven negative electrode active material layer can be measured.

[0067] Figure 1 It is a schematic cross-sectional view of a composite particle according to an exemplary embodiment.

[0068] For ease of explanation, Figure 1schematically shows the shape of the composite particles, but the structure / shape of the composite particles of the present invention is not limited to Figure 1 the structure / shape shown in. For example, the cross-section of the carbon-based particles may randomly change from circular. In addition, the silicon-containing coating may be partially formed on the pores and surface of the carbon-based particles, and may also be formed as a plurality of discontinuous islands or patterns.

[0069] Referring to Figure 1 , as described above, the composite particle 50 may include a carbon-based particle 60 and a silicon-containing coating 70.

[0070] In an exemplary embodiment of the present invention, the carbon-based particle 60 may include pores 65. For example, the carbon-based particle 60 may be a porous particle including a plurality of pores.

[0071] In some embodiments, the carbon-based particle 60 may include activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fibers, carbon black, graphite, porous carbon, cryogel, xerogel, aerogel, etc. These may be used alone or in combination of two or more.

[0072] In some embodiments, the carbon-based particle 60 may include an amorphous structure or a crystalline structure.

[0073] According to one embodiment, the carbon-based particle 60 may include an amorphous structure. In this case, the durability of the negative electrode active material can be increased, thereby suppressing the generation of cracks during charge and discharge or external impact. Therefore, the life characteristics of the secondary battery can be improved.

[0074] The silicon-containing coating 70 may be formed on the surface of the carbon-based particle 60 including the pores 65. For example, the volume expansion of the silicon contained in the silicon-containing coating 70 can be alleviated through the pores 65. Therefore, the relatively high capacity characteristics of silicon can be utilized, and at the same time, cracks caused by the difference in the volume expansion rate of carbon (e.g., below about 150% by volume) and the volume expansion rate of silicon (e.g., above about 400% by volume) during charge and discharge of the battery can be prevented. Therefore, the generation of gas caused by the side reaction between the negative electrode active material and the electrolyte can be suppressed, and the life characteristics of the secondary battery can be improved.

[0075] The pores 65 of the carbon-based particle 60 may include a shape that bends inward from the outermost part of the carbon-based particle 60 to the inside of the carbon-based particle 60. For example, the pores 65 may include pores (open pores) that open to the outside of the carbon-based particle 60.

[0076] As used herein, the term "surface of the carbon-based particles" and / or "surface of the carbon-based particles 60" may refer to the outer surface 62 of the carbon-based particles 60, the inner surface 67 of the pores 65, or both the outer surface 62 of the carbon-based particles 60 and the inner surface 67 of the pores 65.

[0077] For example, a silicon-containing coating 70 may be formed on at least a portion of the outer surface 62 of the carbon-based particles 60.

[0078] For example, a silicon-containing coating 70 may be formed on at least a portion of the inner surface 67 of the pores 65 of the carbon-based particles 60.

[0079] For example, a silicon-containing coating 70 may be formed on at least a portion of the outer surface 62 of the carbon-based particles 60 and at least a portion of the inner surface 67 of the pores 65.

[0080] In some embodiments, the silicon-containing coating 70 may comprise amorphous silicon. Accordingly, the stability of the composite particles can be improved, and the life characteristics of the secondary battery can be enhanced.

[0081] According to one embodiment, the silicon-containing coating 70 may not comprise crystalline silicon. Accordingly, the stability of the composite particles can be further improved, and the life characteristics of the secondary battery can be further enhanced.

[0082] In some embodiments, the peak distance of the composite particles 50 measured by PDF analysis and defined by Equation 2 below may be 0.6 Å or less, and in some embodiments, the peak distance may be 0.56 Å to 0.59 Å or 0.57 Å to 0.59 Å.

[0083] [Equation 2]

[0084] Particle peak distance (Å) = p4 - p3

[0085] In Equation 2, p3 is the center peak value of the peak with the maximum height in the range of 3.4 Å to 4.1 Å of the PDF spectrum obtained by performing PDF analysis on the composite particles 50, and p4 is the center peak value of the peak with the maximum height in the range of 4.1 Å to 4.9 Å of the PDF spectrum obtained by performing PDF analysis on the composite particles 50.

[0086] For example, the particle peak distance may correspond to the distance between silicon atoms comprised in the silicon-containing coating 70.

[0087] Within the above particle peak distance range, the distance between silicon atoms comprised in the silicon-containing coating 70 can be maintained at an appropriate level, thereby improving the stability and amorphousness of silicon. Accordingly, the physical and chemical stabilities of the composite particles 50 can be improved, and the capacity retention rate during charge and discharge of the secondary battery can be enhanced.

[0088] In some embodiments, the particle peak intensity ratio of the composite particles 50 measured by PDF analysis and defined by the following Equation 3 may be from 0.1 to 0.35. According to one embodiment, the particle peak intensity ratio may be from 0.13 to 0.29 or from 0.15 to 0.28.

[0089] [Equation 3]

[0090] Particle peak intensity ratio = Ip4 / Ip3

[0091] In Equation 3, Ip3 is the maximum height of the peak in the range of 3.4 Å to 4.1 Å of the PDF spectrum obtained by performing PDF analysis on the composite particles 50, and Ip4 is the maximum height of the peak in the range of 4.1 Å to 4.9 Å of the PDF spectrum obtained by performing PDF analysis on the composite particles 50.

[0092] For example, the particle peak intensity ratio may correspond to the degree of dispersion of the peaks of the PDF spectrum of the silicon atoms contained in the silicon-containing coating 70.

[0093] Within the above peak intensity ratio range, the silicon atoms can each have an appropriate degree of amorphousness and can be uniformly coated on the surface of the carbon-based particles 60. Therefore, the life characteristics of the secondary battery can be improved.

[0094] In some embodiments, the size of the pores 65 of the carbon-based particles 60 may be from 0.1 nm to 10 nm, from 0.5 nm to 8 nm, or from 1 nm to 5 nm. Within the above range, excessive deposition of silicon can be prevented, thereby further suppressing the generation of cracks in the negative electrode active material during charge and discharge of the secondary battery.

[0095] The size of the pores 65 may refer to the diameter of the entrances of the pores 65 formed in the surface portion of the carbon-based particles 60.

[0096] In some embodiments, the silicon-containing coating 70 may contain silicon and may optionally further contain SiO x (0 < x < 2).

[0097] According to one embodiment, the composite particles 50 may not contain silicon carbide. In this case, the capacity characteristics and life characteristics of the negative electrode active material can be improved.

[0098] In some embodiments, the composite particles 50 may further include a carbon coating (not shown) formed on the silicon-containing coating 70. Therefore, contact between the silicon of the negative electrode active material and water can be prevented. Therefore, reduction in the discharge capacity and capacity efficiency of the secondary battery can be suppressed until the negative electrode is formed after the preparation of the negative electrode active material.

[0099] In some embodiments, a carbon coating may also be formed on portions of the surface of the carbon-based particles 60 where the silicon-containing coating 70 is not formed. For example, the carbon coating may entirely cover the carbon-based particles 60 and the silicon-containing coating 70. Accordingly, the mechanical stability and chemical stability of the negative electrode active material can be improved.

[0100] In one embodiment, the carbon coating may include at least one of carbon and a conductive polymer. For example, the carbon may include amorphous carbon. For example, the conductive polymer may include polyacetylene, polyaniline, polypyrrole, polythiophene, etc.

[0101] In some embodiments, the content of the composite particles 50 may be 5 wt% to 40 wt%, or may be 10 wt% to 30 wt% relative to the total weight of the negative electrode active material layer. Within the above range, the volume expansion of silicon can be reduced, thereby improving the life characteristics of the secondary battery.

[0102] The conductive material included in the negative electrode active material layer may include carbon nanotubes.

[0103] In some embodiments, the conductive material may include single-walled carbon nanotubes (SWCNT). Accordingly, the power characteristics and life characteristics of the secondary battery can be improved.

[0104] In some embodiments, the content of the conductive material may be 0.05 wt% to 3 wt% or 0.1 wt% to 1 wt% relative to the total weight of the negative electrode active material layer. Within the above range, the resistance of the negative electrode active material layer can be reduced, and the life characteristics can be improved.

[0105] Hereinafter, a method for preparing the above composite particles 50 according to an exemplary embodiment will be provided.

[0106] In an exemplary embodiment, carbon-based particles 60 including pores 65 may be prepared.

[0107] In some embodiments, the primary carbon-based particles and an additive may be mixed and first calcined and washed to form the carbon-based particles 60.

[0108] In one embodiment, the primary carbon-based particles may include at least one selected from glucose, sucrose, cellulose, petroleum-based pitch, coal-based pitch, biomass, and resol oligomer.

[0109] In some embodiments, the additive may be provided as a chemical etchant or a hard template.

[0110] In one embodiment, the chemical etchant may include potassium hydroxide (KOH), potassium acetate, potassium carbonate (K 2 CO 3 ), sodium hydroxide (NaOH), sodium carbonate (Na 2 CO 3 ), ammonia water (NH 4 OH), sulfuric acid (H 2 SO 4 ), etc., and / or acidic chemicals. These can be used alone or in combination of two or more. For example, the reaction of the primary carbon-based particles and the additive can be carried out by a chemical activation method.

[0111] In one embodiment, the hard template may include silica, polystyrene, etc. These can be used alone or in combination of two or more. The hard template can be provided, for example, as an additive for forming pores. For example, the size of the pore 65 can be adjusted according to the particle size of the hard template.

[0112] In one embodiment, the first calcination can be carried out at 600 °C to 900 °C. Within the above range, the size and / or volume of the pore 65 can be appropriately controlled.

[0113] In one embodiment, the washing can be carried out by adding an acidic solution or a basic solution to the mixture. For example, the acidic solution may include hydrochloric acid (HCl) solution, sulfuric acid (H 2 SO 4 ) solution, etc. For example, the basic solution may include NaOH solution, etc.

[0114] In an exemplary embodiment, the carbon-based particles 60 and the silicon-containing gas can be calcined together (for example, the second calcination) to form the composite particles 50, and the composite particles 50 include a silicon-containing coating 70 formed on the surface of the carbon-based particles 60. For example, the silicon-containing gas may include silane gas and an inert gas. For example, the inert gas may include argon (Ar) gas.

[0115] In some embodiments, the volume of the silane gas relative to the total volume of the silicon-containing gas can be 10% by volume to 70% by volume, 20% by volume to 70% by volume, 20% by volume to 50% by volume, or 30% by volume to 50% by volume. Within the above range, the domain size of the silicon contained in the silicon-containing coating 70 before the heat treatment can be reduced. Therefore, the grain size of the silicon after the heat treatment can be reduced.

[0116] In some embodiments, the second calcination can be carried out at 400 °C to 600 °C. Within the above range, the grain size of the silicon contained in the silicon-containing coating 70 before the heat treatment can be reduced. Therefore, the mechanical stability of the negative electrode active material during the rolling process or repeated charge and discharge of the secondary battery can be improved.

[0117] Figure 2 and Figure 3 are a schematic plan view and a schematic cross-sectional view respectively showing a lithium secondary battery according to an exemplary embodiment. For example, Figure 3 is a cross-sectional view taken along the Figure 2 I-I' line in the thickness direction.

[0118] The lithium secondary battery may include the above-mentioned negative electrode 130 and a positive electrode 100 disposed opposite to the negative electrode 130.

[0119] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 formed on at least one surface of the positive electrode current collector 105.

[0120] The positive electrode current collector 105 may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector 105 may further include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector 105 may be 10 μm to 50 μm.

[0121] The positive electrode active material layer 110 may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly inserting and extracting lithium ions.

[0122] 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).

[0123] 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.

[0124] [Chemical Formula 1]

[0125] Li x Ni a M b O 2+z

[0126] 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.

[0127] The bonding relationship included in the layered structure or crystal structure of the positive electrode active material is represented by the chemical structure represented by Chemical Formula 1, and other additional elements are not excluded. For example, M may include Co and / or Mn, and Co and / or Mn may be provided together with Ni as the main active element of the positive electrode active material. Chemical Formula 1 is provided to represent the bonding relationship of the main active element, and it should be understood that Chemical Formula 1 is a formula including the introduction and substitution of additional elements.

[0128] In one embodiment, in addition to including the main active element, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may be further included. The auxiliary element may be mixed into the layered structure / crystal structure together 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.

[0129] The auxiliary element may include, for example, at least one selected from 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, and Zr. The auxiliary element may act as an auxiliary active element that contributes to the capacity / power activity of the positive electrode active material together with Co or Mn, such as Al.

[0130] 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.

[0131] [Chemical Formula 1-1]

[0132] Li x Ni a M1 b1 M2 b2 O 2+z

[0133] In Chemical Formula 1-1, M1 may include Co, Mn, and / or Al. M2 may include the above-mentioned auxiliary element. In Chemical Formula 1-1, 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b1 + b2 ≤ 0.4, -0.5 ≤ z ≤ 0.1.

[0134] 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.

[0135] The coating element or 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.

[0136] 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.

[0137] Ni may be provided as a transition metal related to the power and capacity of the lithium secondary battery. Thus, 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 high-capacity lithium secondary battery can be provided.

[0138] 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.

[0139] The content of Ni in the NCM-based lithium oxide (e.g., the mole fraction of Ni in the total moles of nickel, cobalt, and manganese) may be 0.5 or more, 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.

[0140] 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 (e.g., LiFePO 4 )

[0141] In some embodiments, the positive electrode active material may include, for example, a lithium-rich layered oxide (LLO) / over-lithiated oxide (OLO)-based active material, a manganese-rich-based active material, a cobalt-less-based active material, etc., having a chemical structure or crystal structure represented by Chemical Formula 2. These may be used alone or in combination of two or more.

[0142] [Chemical Formula 2]

[0143] p[Li 2 MnO 3 ·(1-p)[Liq JO 2

[0144] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may contain at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0145] The positive electrode active material may be mixed in a solvent to prepare a positive electrode paste. The positive electrode paste may be coated on at least one surface of the positive electrode current collector 105 and then dried and calendered to prepare the positive electrode active material layer 110. The coating may include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc. The positive electrode active material layer 110 may further contain a binder, and may optionally further contain a conductive material, a thickening agent, etc.

[0146] The solvent may be N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0147] The binder may include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) copolymer, polyacrylonitrile, polymethylmethacrylate, nitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0148] In one embodiment, a PVDF-based binder may be used as the positive electrode binder. In this case, the amount of the binder used to form the positive electrode active material layer 110 may be reduced, and the amount of the positive electrode active material may be relatively increased. Therefore, the power characteristics and capacity characteristics of the secondary battery may be improved.

[0149] ​The conductive material can be added to enhance the conductivity of the positive electrode active material layer 110 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 such as perovskite materials including tin, tin oxide, titanium oxide, LaSrCoO 3 , LaSrMnO 3 and the like. These can be used alone or in combination of two or more.

[0150] The positive electrode paste can further include a thickener and / or a dispersant, etc. In one embodiment, the positive electrode paste can include a thickener such as carboxymethyl cellulose (CMC).

[0151] As described above, the negative electrode 130 can include a negative electrode current collector 125 and a negative electrode active material layer 120 formed on at least one surface of the negative electrode current collector 125.

[0152] The above-mentioned negative electrode active material and conductive material can be mixed with a solvent to prepare a negative electrode paste. The negative electrode paste can be coated / deposited on the negative electrode current collector 125 and then dried and calendered to prepare the negative electrode active material layer 120. The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, knife coating, dip coating, rod coating, casting, etc. The negative electrode active material layer 120 can further include an adhesive, and can optionally further include a conductive material, a thickener, etc.

[0153] The solvent contained in the negative electrode paste can include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, tert-butanol, etc. These can be used alone or in combination of two or more.

[0154] As the adhesive and thickener, the above-mentioned substances that can be used in the manufacture of the positive electrode 100 can be used.

[0155] In some embodiments, the negative electrode adhesive can use styrene-butadiene-rubber (SBR)-based adhesives, carboxymethyl cellulose (CMC), polyacrylic acid-based adhesives, poly(3,4-ethylenedioxythiophene) (PEDOT)-based adhesives, etc. These can be used alone or in combination of two or more.

[0156] In an exemplary embodiment, the separator 140 may be disposed between the positive electrode 100 and the negative electrode 130. The separator 140 may be arranged to prevent a short circuit between the positive electrode 100 and the negative electrode 130 and to allow the flow of ions. For example, the thickness of the separator may be from 10 μm to 20 μm.

[0157] For example, the separator 140 may include a porous polymer membrane or a porous nonwoven fabric.

[0158] The porous polymer membrane may include polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. These may be used alone or in combination of two or more.

[0159] The porous nonwoven fabric may include glass fibers with a high melting point, polyethylene terephthalate fibers, etc.

[0160] The separator 140 may also include a ceramic-based material. For example, inorganic particles may be coated on or dispersed in the polymer membrane to improve heat resistance.

[0161] The separator 140 may have a single-layer or multi-layer structure including the above polymer membrane and / or nonwoven fabric.

[0162] According to an exemplary embodiment, the battery cell is defined by the positive electrode 100, the negative electrode 130, and the separator 140, and an electrode assembly 150 in the form of, for example, a jelly roll may be formed by laminating a plurality of battery cells. For example, the electrode assembly 150 may be formed by winding, stacking, z-folding, stack-folding, etc. of the separator 140.

[0163] The electrode assembly 150 and the electrolyte are accommodated in the housing 160, thereby defining a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte may be used for the electrolyte.

[0164] The non-aqueous electrolyte may include 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, F - , Cl - , Br- , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 , PF 4 - , (CF 3 ) 3 , PF 3 - , (CF 3 ) 4 , PF 2 - , (CF 3 ) 5 , PF - , (CF 3 ) 6 , P - , CF 3 , SO 3 - , CF 3 , CF 2 , SO 3 - , (CF 3 , SO 2 ) 2 , N - , (FSO 2 ) 2 , N - , CF 3 , CF 2 , (CF 3 ) 2 , CO - , (CF 3 , SO 2 ) 2 , CH - , (SF 5 ) 3 , C - , (CF 3 , SO 2 ) 3 , C - , CF 3 , (CF 2 ) 7 , SO 3 - , CF 3 , CO 2- , CH 3 CO 2 - , SCN - and (CF 3 CF 2 SO 2 ) 2 N - etc.

[0165] 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. can be used. These can be used alone or in combination of two or more.

[0166] The non-aqueous electrolyte may further contain an additive. The additive may include, for example, a cyclic carbonate-based compound, a fluorine-substituted carbonate-based compound, a sultone-based compound, a cyclic sulfate-based compound, a cyclic sulfite-based compound, a phosphate-based compound, a borate-based compound, etc. These may be used alone or in combination of two or more.

[0167] The cyclic carbonate-based compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0168] The fluorine-substituted carbonate-based compound may include fluoroethylenecarbonate (FEC), etc.

[0169] The sultone-based compound may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0170] The cyclic sulfate-based compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0171] The cyclic sulfite-based compound may include ethylene sulfite, butylene sulfite, etc.

[0172] The phosphate-based compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0173] The borate-based compound may include lithium bis(oxalate) borate, etc.

[0174] In some embodiments, a solid electrolyte may be used to replace the above non-aqueous electrolyte. In this case, the lithium secondary battery may be made in the form of an all-solid-state battery. And, a solid electrolyte layer may be disposed between the positive electrode 100 and the negative electrode 130 to replace the above separator 140.

[0175] The solid electrolyte may include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte may include Li 2 S-P 2 S 5 、Li 2 S-P 2 S 5 -LiCl、Li 2 S-P 2 S 5 -LiBr、Li 2 S-P 2 S 5 -LiCl-LiBr、Li 2 S-P 2 S 5 -Li 2 O、Li 2 S-P 2 S 5 -Li 2 O-LiI、Li 2 S-SiS 2 、Li 2 S-SiS 2 -LiI、Li 2 S-SiS 2 -LiBr、Li 2 S-SiS 2 -LiCl、Li 2 S-SiS 2 -B 2 S 3 -LiI、Li 2 S-SiS 2 -P 2 S 5 -LiI、Li 2 S-B 2 S 3 、Li 2 S-P 2 S 5 -Z m S n (m and n are positive numbers, Z is Ge, Zn or Ga), Li 2 S-GeS 2 、Li 2 S-SiS 2 -Li 3 PO 4 、Li 2 S-SiS 2 -Li p MO q (p and q are positive numbers, M is P, Si, Ge, B, Al, Ga or In), Li7 -xPS 6 -xCl x (0 ≤ x ≤ 2), Li 7 -xPS 6 -xBr x (0 ≤ x ≤ 2), Li 7 -xPS 6 -xI x (0 ≤ x ≤ 2), etc. These can be used alone or in combination of two or more.

[0176] In one embodiment, the solid electrolyte may further contain, for example, Li 2 O - B 2 O 3 -P 2 O 5 、Li 2 O - SiO 2 、Li 2 O - B 2 O 3 、Li 2 O - B 2 O 3 -ZnO and other oxide - based amorphous solid electrolytes.

[0177] Such as Figure 2 and Figure 3 As shown, the tabs (the positive tab and the negative tab) can respectively protrude from the positive current collector 105 and the negative current collector 125 belonging to each battery cell and extend to one side of the housing 160. The tabs can be fused to the said one side of the housing 160 to form electrode leads (the positive lead 107 and the negative lead 127) extending to the outside of the housing 160 or exposed to the outside of the housing 160.

[0178] The lithium secondary battery can be made into, for example, a cylindrical, prismatic, pouch - type or coin - type using a can, etc.

[0179] 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 for illustrating 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 are obvious to those skilled in the art, and such variations and modifications are naturally within the scope of the claims.

[0180] Example 1

[0181] Preparation of carbon - based particles

[0182] Dry-mix asphalt and potassium acetate in a weight ratio of 5:5 and conduct the first calcination at 800 °C for 2 hours. Wash the mixture after the first calcination with an excessive amount of 0.5 M HCl aqueous solution to prepare carbon-based particles containing pores. Prepare the carbon-based particles by making the specific volume of the pores of the carbon-based particles 0.6 cm 3 / g.

[0183] Formation of silicon-containing coating

[0184] Inject a silicon-containing gas containing silane gas and argon into a CVD coater at a flow rate of 50 mL / min to 100 mL / min. The content of silane gas is 50 vol% relative to the total volume of the silicon-containing gas. Heat up to 550 °C at a heating rate of 5 °C / min to 20 °C / min and then hold for about 120 minutes to prepare composite particles containing a silicon-containing coating.

[0185] Prepare the composite particles by making the silicon content 45 wt% relative to the total weight of the composite particles.

[0186] Formation of negative electrode

[0187] Mix 95.6 wt% of the negative electrode active material composed of 15 wt% of the composite particles and 80.6 wt% of artificial graphite, 0.1 wt% of SWCNT as a conductive material, 2.8 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener to obtain a negative electrode slurry.

[0188] Coat the negative electrode slurry on a copper substrate and dry and calender it to manufacture a negative electrode.

[0189] Manufacture of lithium half-cell

[0190] Manufacture a lithium half-cell that includes the negative electrode and uses lithium metal as the counter electrode (positive electrode).

[0191] Specifically, place a separator (polyethylene, thickness 20 μm) between the negative electrode and the lithium metal (thickness 1 mm) to form a CR2016 (diameter 20 mm, thickness 1.6 mm) specification lithium coin-type half-cell.

[0192] Place the combination of lithium metal / diaphragm / negative electrode into a coin cell plate, inject the electrolyte, then cover it with a cap and clamp it. The electrolyte used is an electrolyte formed by using a mixed solvent of EC / EMC (3:7; volume ratio) to form a 1M LiPF 6 solution and adding 2.0% by volume of fluoroethylene carbonate (FEC) relative to the total volume of the electrolyte. After clamping, immerse it for 3 to 24 hours, and then perform charge and discharge 3 cycles at 0.1C (charging condition: CC-CV 0.1C 0.01V 0.01C cut-off (CUT-OFF), discharging condition: CC 0.1C 1.5V cut-off).

[0193] Manufacture of lithium secondary battery

[0194] Mix LiNi 0.88 Co 0.1 Mn 0.02 O 2 which is used as the positive electrode active material, carbon black which is used as the conductive material, and polyvinylidene fluoride (PVDF) which is used as the binder in a weight ratio of 96.5:2:1.5 to prepare the positive electrode slurry.

[0195] Coat the positive electrode slurry evenly on an aluminum current collector (thickness: 12μm), and perform vacuum drying and calendering to manufacture the positive electrode.

[0196] Cut the positive electrode and the negative electrode into specified sizes respectively and stack them. Place a diaphragm (polyethylene, thickness 13μm) between the positive electrode and the negative electrode to form an electrode core, and then weld the tab parts of the positive electrode and the negative electrode respectively. Put the welded positive electrode / diaphragm / negative electrode assembly into a soft package and seal three sides except the electrolyte injection surface. At this time, make the part with the tab included in the sealed part. Inject the electrolyte through the electrolyte injection surface and seal the electrolyte injection surface, and then immerse it for more than 12 hours to manufacture the lithium secondary battery.

[0197] The electrolyte used is an electrolyte prepared as follows: Prepare a 1M LiPF 6 solution by using a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio), and add 1% by weight of vinylene carbonate (VC), 0.5% by weight of 1,3 - propanesultone (PRS), and 0.5% by weight of lithium bis(oxalate)borate (LiBOB) relative to the total weight of the solution.

[0198] The lithium secondary battery is pre-charged at a current corresponding to 0.25C for 36 minutes. Degassing is performed 1 hour later, and it is aged for more than 24 hours, and then formation charge and discharge are carried out (charging conditions: CC / CV 0.2C 4.2V cut-off at 0.05C, discharging conditions: CC 0.2C cut-off at 2.5V).

[0199] After that, standard charge and discharge are carried out (charging conditions: CC / CV 0.5C 4.2V cut-off at 0.05C, discharging conditions: CC 0.5C cut-off at 2.5V).

[0200] Example 2 and Example 3

[0201] The negative electrode, lithium half-cell, and lithium secondary battery are manufactured by the same method as in Example 1, except that the content of silane gas relative to the total volume of the silicon-containing gas is changed as shown in Table 1 below.

[0202] Example 4

[0203] The carbon-based particles formed with a silicon-containing coating are placed in a thermal CVD chamber, and a mixed gas of ethylene gas and argon gas is supplied while performing heat treatment at a temperature below 600°C to prepare composite particles with a carbon coating formed on the silicon-containing coating.

[0204] Except for the above content, the negative electrode, lithium half-cell, and lithium secondary battery are manufactured by the same method as in Example 1.

[0205] Example 5

[0206] The negative electrode, lithium half-cell, and lithium secondary battery are manufactured by the same method as in Example 1, except that an equal amount of a dispersion of silica with an average particle size of 6 nm is added to replace potassium acetate, and washing is performed with a 0.5M NaOH aqueous solution instead of an HCl aqueous solution.

[0207] Example 6

[0208] The negative electrode, lithium half-cell, and lithium secondary battery are manufactured by the same method as in Example 1, except that an equal amount of a dispersion of silica with an average particle size of 3 nm is added to replace potassium acetate, and washing is performed with a 0.5M NaOH aqueous solution instead of an HCl aqueous solution, and the content of silane gas relative to the total volume of the silicon-containing gas is changed as shown in Table 1 below.

[0209] Example 7

[0210] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that an equal amount of a dispersion of silica with an average particle size of 6 nm was added in place of potassium acetate, and washing was performed with 0.5 M aqueous NaOH solution instead of aqueous HCl solution, and the content of silane gas relative to the total volume of silicon-containing gas was changed as shown in Table 1 below.

[0211] Example 8

[0212] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that a negative electrode active material composed of 95.6 wt% of a mixture of 5 wt% composite particles and 90.6 wt% artificial graphite, 0.1 wt% of SWCNT as a conductive material, 2.8 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0213] Example 9

[0214] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that a negative electrode active material composed of 95.6 wt% of a mixture of 10 wt% composite particles and 85.6 wt% artificial graphite, 0.1 wt% of SWCNT as a conductive material, 2.8 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0215] Example 10

[0216] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that a negative electrode active material composed of 89.5 wt% of a mixture of 30 wt% composite particles and 59.5 wt% artificial graphite, 0.1 wt% of SWCNT as a conductive material, 8.9 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0217] Example 11

[0218] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that a negative electrode active material composed of 85.6 wt% of a mixture of 40 wt% composite particles and 45.6 wt% artificial graphite, 0.1 wt% of SWCNT as a conductive material, 12.8 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0219] Example 12

[0220] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 11, except that 0.1 wt% of multi-walled carbon nanotubes (MWCNT) was used as the conductive material.

[0221] Example 13

[0222] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that 95.6 wt% of a negative electrode active material composed of 3 wt% of composite particles and 92.6 wt% of artificial graphite, 0.1 wt% of SWCNT as the conductive material, 2.8 wt% of styrene-butadiene rubber (SBR) as the binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as the thickener were mixed to obtain a negative electrode slurry.

[0223] Example 14

[0224] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that 95.6 wt% of a negative electrode active material composed of 45 wt% of composite particles and 50.6 wt% of artificial graphite, 0.1 wt% of SWCNT as the conductive material, 2.8 wt% of styrene-butadiene rubber (SBR) as the binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as the thickener were mixed to obtain a negative electrode slurry.

[0225] Comparative Example 1

[0226] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that an equal amount of a dispersion of silica with an average particle size of 50 nm was added in place of potassium acetate, and washing was carried out with 0.5 M NaOH aqueous solution in place of HCl aqueous solution.

[0227] Comparative Example 2

[0228] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that an equal amount of a dispersion of silica with an average particle size of 100 nm was added in place of potassium acetate, and washing was carried out with 0.5 M NaOH aqueous solution in place of HCl aqueous solution.

[0229] Comparative Example 3

[0230] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that 82.7 wt% of a negative electrode active material, which was a mixture of 50 wt% of composite particles and 32.7 wt% of artificial graphite, 0.1 wt% of SWCNT as a conductive material, 15.7 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0231] Comparative Example 4

[0232] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that 79.5 wt% of a negative electrode active material, which was a mixture of 75 wt% of composite particles and 4.5 wt% of artificial graphite, 0.1 wt% of SWCNT as a conductive material, 18.9 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0233] Comparative Example 5

[0234] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that 95.6 wt% of artificial graphite as a negative electrode active material, 0.1 wt% of SWCNT as a conductive material, 2.8 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0235] Comparative Example 6

[0236] The negative electrode, lithium half-cell, and lithium secondary battery were fabricated in the same manner as in Example 1, except that 80.7 wt% of a negative electrode active material, which was a mixture of 40 wt% of composite particles and 40.7 wt% of artificial graphite, 5 wt% of carbon black as a conductive material, 12.8 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.5 wt% of carboxymethyl cellulose (CMC) as a thickener were mixed to obtain a negative electrode slurry.

[0237] Experimental Example

[0238] (1) Measurement of the pore size of the carbon-based particles

[0239] The pore size of the carbon-based particles prepared according to the above-mentioned examples and comparative examples was measured using a surface area analyzer (ASAP-2420) 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 samples obtained from the examples and comparative examples was measured to measure the pore size of the carbon-based particles.

[0240] (2) Pair distribution function (PDF) analysis of the composite particles

[0241] PDF analysis was performed on the composite particles prepared according to the above-mentioned examples and comparative examples to obtain a PDF spectrum with the PDF function G(r) on the vertical axis and r (Å) corresponding to the distance between atoms on the horizontal axis. Specifically, the scattering data used for the PDF analysis was collected at beamline 1C of the Pohang Light Source (PLS-II) at the Pohang Accelerator Laboratory (PAL).

[0242] The sample of the composite particles was added to a capillary, and high-energy X-rays with a wavelength (λ) of 0.56356 Å (22.003 KeV) were used to measure the scattering data including 2D scattering images in the range of 5 - 80 degrees (2θ) with a step size of 0.017 degrees.

[0243] The 2D scattering images were integrated by software (Dioptas) to obtain 1D scattering intensity data. During the process of obtaining the 1D scattering intensity data, when the current collector was adhered to the composite particles, the diffraction peak of the current collector was flattened.

[0244] Background data can be obtained by collecting X-rays scattered in a hollow capillary.

[0245] The 1D scattering intensity data, the background data, the wavelength used, and the chemical composition were applied to software (PDFgetX3) to obtain the structure function S(Q). During the process of obtaining the S(Q), the relative intensity (background ratio) of the background data with respect to the 1D scattering intensity data was set to 1.0, and the range of Q was set to 0.1 to 12.0.

[0246] The G(r) function was obtained by performing a Fourier transform on the S(Q), and the PDF spectrum was obtained by showing the variation of G(r) according to the interatomic distance (r).

[0247] Taking the vertical axis (G(r)) height at r = 0 Å of the PDF spectrum as a reference, draw a baseline parallel to the horizontal axis (r). Then, taking the baseline as a reference, obtain the central peak value of the peak with the maximum height in the range of 3.4 Å to 4.1 Å and designate it as p3, and obtain the central peak value of the peak with the maximum height in the range of 4.1 Å to 4.9 Å and designate it as p4. Substitute the p3 and the p4 into Equation 2 to calculate the particle peak distance.

[0248] Take the peak height of the p3 as Ip3, and take the peak height of the p4 as Ip4. Substitute the Ip3 and the Ip4 into Equation 3 to calculate the particle peak intensity ratio.

[0249] (3) PDF analysis of the negative electrode

[0250] After the lithium half-cell manufactured according to the above-mentioned examples and comparative examples is formed and charged and discharged, it is discharged to 2.2 V. Disassemble the lithium half-cell to obtain the negative electrode active material layer, and perform PDF analysis on the obtained negative electrode active material layer to obtain a PDF spectrum with the vertical axis being the PDF function G(r) and the horizontal axis being r (Å) corresponding to the distance between atoms.

[0251] Specifically, the scattering data used for the PDF analysis is collected at beamline 1C of the Pohang Light Source (PLS-II) of the Pohang Accelerator Laboratory (PAL).

[0252] Stand and fix the negative electrode perpendicular to the X-ray incident direction, and use high-energy X-rays (22.003 KeV) with a wavelength (λ) of 0.56356 Å to measure the scattering data including the 2D scattering image in the range of 5 - 80 degrees (2θ) with a step size of 0.017 degrees.

[0253] Integrate the 2D scattering image through software (Dioptas) to obtain 1D scattering intensity data. During the process of obtaining the 1D scattering intensity data, when the current collector is adhered to the composite particles, flatten the diffraction peak of the current collector.

[0254] By collecting the X-rays scattered in the atmosphere, background data can be obtained.

[0255] Apply the 1D scattering intensity data, the background data, the wavelength used, and the chemical composition to software (PDFgetX3) to obtain the structure function S(Q). During the process of obtaining the S(Q), the relative intensity (background ratio) of the background data with respect to the 1D scattering intensity data is set to 1.0, and the range of Q is set to 0.1 to 12.0.

[0256] The G(r) function is obtained by performing a Fourier transform on the S(Q), and the PDF spectrum is obtained by showing the variation of G(r) according to the interatomic distance (r).

[0257] Based on the lowest vertical axis (G(r)) height in the r range of 0 Å to 6 Å of the PDF spectrum, a baseline parallel to the horizontal axis (r) is drawn. Then, based on this baseline, the central peak value of the peak with the maximum height in the range of 3.4 Å to 4.1 Å is obtained as p1, and the central peak value of the peak with the maximum height in the range of 4.1 Å to 4.9 Å is obtained as p2.

[0258] The maximum height of the peak in the range of 3.4 Å to 4.1 Å of the PDF spectrum is taken as Ip1, and the maximum height of the peak in the range of 4.1 Å to 4.9 Å of the PDF spectrum is taken as Ip2. Substitute the Ip1 and Ip2 into Equation 1 to calculate the electrode peak intensity ratio.

[0259] Figure 4 is the PDF spectrum obtained by PDF analysis in Example 3.

[0260] Figure 5 is the PDF spectrum obtained by PDF analysis in Comparative Example 1.

[0261] Figure 6 is the PDF spectrum obtained by PDF analysis in Comparative Example 3.

[0262] (4) Measurement of Direct Current Internal Resistance (DCIR)

[0263] At room temperature (25 °C), the lithium batteries manufactured according to the above examples and comparative examples are charged (CC / CV 0.3C 4.2V 0.05C cut-off) and discharged (CC 0.3C 2.5V cut-off) twice. Then, they are discharged (CC 0.3C) to the point of SOC 50% in the charged (CC / CV 0.3C 4.2V 0.05C cut-off) state, and the DCIR (mΩ) at the point of SOC 50% for 10 seconds is measured.

[0264] (5) Measurement of Capacity Retention Rate

[0265] The lithium half-cells according to the examples and comparative examples are repeatedly charged (CC / CV 0.5C 0.01V 0.01C cut-off) and discharged (CC 0.1C 3.0V cut-off) 50 times, and the capacity retention rate is evaluated by the percentage of the value obtained by dividing the discharge capacity of the 50th time by the discharge capacity of the 1st time.

[0266] The measurement results and evaluation results are shown in Tables 1 and 2 below. The content of the composite particles in Table 1 is the content of the composite particles relative to the total weight of the negative electrode active material layer. The conductive material in Table 2 indicates the type of the conductive material and the content of the conductive material relative to the total weight of the negative electrode active material layer.

[0267] [Table 1]

[0268]

[0269] [Table 2]

[0270]

[0271] Referring to Tables 1 and 2, in the examples where the electrode peak intensity ratio according to Formula 1 is from 1.1 to 2.7, compared with the comparative examples, the resistance is overall reduced and the capacity retention rate is improved.

[0272] In the examples and comparative examples, the content of silicon relative to the total weight of the composite particles is substantially similar, but the measured physical properties and life characteristics of the composite particles are different according to the pore size and the concentration of silane gas.

[0273] In Example 4 where a carbon coating is further formed on the silicon-containing coating, the capacity retention rate is improved compared with other examples.

[0274] In Example 5 where the pore size of the carbon-based particles exceeds 10 nm, the capacity retention rate is reduced compared with other examples.

[0275] In Examples 6 and 7 where the particle peak intensity ratio according to Formula 3 is not within the range of 0.1 to 0.35, the capacity retention rate is reduced compared with other examples.

[0276] In Example 12 where SWCNT is not used as the conductive material, the capacity retention rate is reduced compared with other examples.

[0277] In Example 13 where the content of the composite particles relative to the total weight of the negative electrode active material layer is less than 5% by weight, the resistance increases compared with other examples.

[0278] In Example 14 where the content of the composite particles relative to the total weight of the negative electrode active material layer exceeds 40% by weight, the capacity retention rate is reduced compared with other examples.

Claims

1. A negative electrode for a lithium secondary battery, comprising: Anode current collector; as well as a negative electrode active material layer, the negative electrode active material layer being disposed on at least one side of the negative electrode current collector and comprising a negative electrode active material and a conductive material, The electrode peak intensity ratio of the negative electrode active material layer defined by the following formula 1 is 1.1 to 2.

7. [Formula 1] Electrode peak intensity ratio = Ip2 / Ip1 In Formula 1, Ip1 is the maximum height of a peak in the range of 3.4Å to 4.1Å of a PDF spectrum obtained by performing a PDF analysis on the negative electrode active material layer, and Ip2 is the maximum height of a peak in the range of 4.1Å to 4.9Å of the PDF spectrum.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein The electrode peak intensity ratio is 2.13 to 2.

64.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein The negative electrode active material comprises composite particles, and the composite particles comprise: a carbon-based particle comprising pores; and A silicon-containing coating is formed on the surface of the carbon-based particles.

4. The negative electrode for a lithium secondary battery according to claim 3, wherein The particle peak distance of the composite particles defined by the following formula 2 is less than 0.6 Å, [Formula 2] Particle peak distance (Å) = p4-p3 In Formula 2, p3 is the central peak of the peak with the maximum height in the range of 3.4Å to 4.1Å of the PDF spectrum obtained by performing PDF analysis on the composite particles, and p4 is the central peak of the peak with the maximum height in the range of 4.1Å to 4.9Å of the PDF spectrum obtained by performing PDF analysis on the composite particles.

5. The negative electrode for a lithium secondary battery according to claim 4, wherein The particle peak distance is 0.56Å to 0.59Å.

6. The negative electrode for a lithium secondary battery according to claim 3, wherein: The composite particles have a particle peak intensity ratio defined by the following formula 3 of 0.1 to 0.35: [Formula 3] Particle peak intensity ratio = Ip4 / Ip3 In Formula 3, Ip3 is the maximum height of the peak in the range of 3.4Å to 4.1Å of the PDF spectrum obtained by performing PDF analysis on the composite particles, and Ip4 is the maximum height of the peak in the range of 4.1Å to 4.9Å of the PDF spectrum obtained by performing PDF analysis on the composite particles.

7. The negative electrode for a lithium secondary battery according to claim 6, wherein: The particle peak intensity ratio is 0.15 to 0.

28.

8. The negative electrode for a lithium secondary battery according to claim 3, wherein The pores of the carbon-based particles have a size of 0.1 nm to 10 nm.

9. The negative electrode for a lithium secondary battery according to claim 3, wherein: The pores of the carbon-based particles have a size of 1 nm to 5 nm.

10. The negative electrode for a lithium secondary battery according to claim 3, wherein The composite particle further includes a carbon coating formed on the silicon-containing coating.

11. The negative electrode for a lithium secondary battery according to claim 3, wherein: The content of the composite particles is 5 wt % to 40 wt % relative to the total weight of the negative electrode active material layer.

12. The negative electrode for a lithium secondary battery according to claim 3, wherein: The content of the composite particles is 10 wt % to 30 wt % relative to the total weight of the negative electrode active material layer.

13. The negative electrode for a lithium secondary battery according to claim 3, wherein: The negative electrode active material further includes a graphite-based active material, and the graphite-based active material includes at least one selected from artificial graphite and natural graphite.

14. The negative electrode for a lithium secondary battery according to claim 1, wherein The conductive material comprises single-walled carbon nanotubes (SWCNTs).

15. A lithium secondary battery comprising: The negative electrode for a lithium secondary battery according to claim 1; as well as A positive electrode is arranged opposite to the negative electrode.

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