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

Abstract

A negative electrode for a lithium secondary battery, according to embodiments of the present disclosure, comprises: a negative electrode current collector; a first negative electrode active material layer formed on at least one surface of the negative electrode current collector; and a second negative electrode active material layer which is formed on the first negative electrode active material layer and includes artificial graphite, wherein the first Raman peak area ratio of the first negative electrode active material layer is 1 to 2 and the second Raman peak area ratio of the second negative electrode active material layer is 0.2 to 0.5.

Description

Anode for a lithium secondary battery and a lithium secondary battery comprising the same

[0001] The disclosure of the present application relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0002] Secondary batteries, which can be repeatedly charged and discharged, are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, thanks to the advancements in the information and communication and display industries. Furthermore, battery packs containing secondary batteries are being developed and applied as power sources for eco-friendly vehicles such as electric vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, and nickel-hydrogen batteries. Among these, lithium secondary batteries are being actively developed and applied due to their high operating voltage and energy density per unit weight, and their advantages in charging speed and weight reduction.

[0004] Recently, as the application scope of lithium secondary batteries expands, development of lithium secondary batteries with higher capacity and output is underway. For example, high-capacity silicon-based materials may be incorporated into the negative electrode active material.

[0005] However, the life characteristics of the electrode during rapid charging may be degraded depending on the volume expansion rate and low conductivity of silicon.

[0006] According to one aspect of the present disclosure, a negative electrode for a lithium secondary battery having improved life characteristics can be provided.

[0007] According to one aspect of the present disclosure, a lithium secondary battery having improved life characteristics can be provided.

[0008] According to exemplary embodiments of the present disclosure, a negative electrode for a lithium secondary battery comprises: a negative electrode current collector; a first negative electrode active material layer formed on at least one surface of the negative electrode current collector; and a second negative electrode active material layer formed on the first negative electrode active material layer and including artificial graphite, wherein a first Raman peak area ratio defined by the following Equation 1 of the first negative electrode active material layer is 1 to 2, and a second Raman peak area ratio defined by the following Equation 2 of the second negative electrode active material layer is 0.2 to 0.5.

[0009] [Formula 1]

[0010] First Raman peak area ratio = AD1 / AG1

[0011] [Formula 2]

[0012] Second Raman peak area ratio = AD2 / AG2

[0013] In Equations 1 and 2, AD1 is the Raman spectral spectrum of the first negative active material layer at 1320 cm -1 1390 cm inland -1 is the area of ​​the peak having the maximum height in the wavenumber range. AG1 is the area of ​​the Raman spectroscopy spectrum of the first negative active material layer at 1575 cm -1 1590 cm in height -1 is the area of ​​the peak with the maximum height in the frequency range.

[0014] AD2 is 1320 cm of the Raman spectroscopy spectrum of the second negative active material layer. -1 1390 cm inland -1 is the area of ​​the peak having the maximum height in the wavenumber range. AG2 is the area of ​​the Raman spectroscopy spectrum of the second negative active material layer at 1575 cm -1 1590 cm in height -1 is the area of ​​the peak with the maximum height in the frequency range.

[0015] In some embodiments, the first Raman peak area ratio may be 3 to 5 times the second Raman peak area ratio.

[0016] In some embodiments, the first Raman peak area ratio may be 1.2 to 1.5.

[0017] In some embodiments, the second Raman peak area ratio may be 0.3 to 0.4.

[0018] In some embodiments, the thickness of the second negative electrode active material layer may be 30% to 70% of the sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer.

[0019] In some embodiments, the thickness of the second negative electrode active material layer may be 40% to 60% of the sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer.

[0020] In some embodiments, the first negative active material layer may include natural graphite.

[0021] In some embodiments, the natural graphite may include a carbon coating formed on a surface.

[0022] In some embodiments, the carbon coating may comprise amorphous carbon.

[0023] In some embodiments, the first negative electrode active material layer may include a plurality of first pores, and the second negative electrode active material layer may include a plurality of second pores.

[0024] In some embodiments, the ratio of the second porosity of the second negative electrode active material layer, defined by Equation 4 below, to the first porosity of the first negative electrode active material layer, defined by Equation 3 below, may be 1.2 to 2.0.

[0025] [Formula 3]

[0026] 1st porosity (%) = (VP1 / VL1)*100

[0027] [Formula 4]

[0028] Second porosity (%) = (VP2 / VL2)*100

[0029] In Equations 3 and 4, VL1 is the volume of the first negative electrode active material layer, VP1 is the total volume of the plurality of first pores, VL2 is the volume of the second negative electrode active material layer, and VP2 is the total volume of the plurality of second pores.

[0030] In some embodiments, the first porosity may be 15% to 25%.

[0031] In some embodiments, the second porosity may be 25% to 40%.

[0032] A lithium secondary battery according to exemplary embodiments of the present disclosure includes the above-described negative electrode for a lithium secondary battery, and a positive electrode opposite to the negative electrode.

[0033] According to one embodiment of the present disclosure, the structural stability, life characteristics, and rapid charging performance of a negative electrode for a lithium secondary battery can be improved. In addition, for example, costs can be reduced.

[0034] According to one embodiment of the present disclosure, excessive crystallinity degradation can be prevented while crack generation in the negative active material layer is suppressed.

[0035] According to one embodiment of the present disclosure, stability can be improved while reducing the resistance of the cathode.

[0036] The anode for a lithium secondary battery of the present disclosure and the lithium secondary battery comprising the same can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other battery-based solar and wind power generation. The anode for a lithium secondary battery of the present disclosure and the lithium secondary battery comprising the same can be used in eco-friendly electric vehicles, hybrid vehicles, etc., which prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0037] FIG. 1 is a schematic cross-sectional view showing a negative electrode for a lithium secondary battery according to exemplary embodiments.

[0038] FIGS. 2 and 3 are schematic plan views and cross-sectional views, respectively, showing lithium secondary batteries according to exemplary embodiments.

[0039] Figure 4 is a cross-section of the cathode of Example 1 measured using a scanning electron microscope (SEM).

[0040] Figure 5 is a cross-section of the cathode of Example 2 measured by SEM.

[0041] Figure 6 is a cross-section of the cathode of Comparative Example 1 measured by SEM.

[0042] Figure 7 is a Raman spectroscopy spectrum of each of the first negative electrode active material layer and the second negative electrode active material layer of Example 1.

[0043] Embodiments of the present disclosure provide a negative electrode for a lithium secondary battery (hereinafter, abbreviated as "negative electrode") comprising a plurality of negative electrode active material layers. In addition, a lithium secondary battery (hereinafter, abbreviated as "secondary battery") comprising the negative electrode is provided.

[0044] Hereinafter, embodiments of the present disclosure will be described in detail. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0045] FIG. 1 is a schematic cross-sectional view showing a negative electrode for a lithium secondary battery according to exemplary embodiments.

[0046] Referring to FIG. 1, the negative electrode (100) may include a negative electrode current collector (110), a first negative electrode active material layer (120), and a second negative electrode active material layer (130).

[0047] For example, the negative electrode current collector (110) may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, 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 (125) may be 10 μm to 50 μm.

[0048] A first negative electrode active material layer (120) can be formed on at least one surface of the negative electrode current collector (110).

[0049] In some embodiments, the first negative electrode active material layer (120) may include natural graphite. Accordingly, the adhesion and capacity characteristics between the negative electrode current collector (110) and the first negative electrode active material layer (120) may be improved.

[0050] According to one embodiment, the first negative electrode active material layer (120) may be formed to be in direct contact with the negative electrode current collector (110).

[0051] The content of natural graphite relative to the total weight of the first negative electrode active material layer (120) may be 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0052] The content of natural graphite relative to the total weight of the first negative electrode active material layer (120) may be 99 wt% or less, 95 wt% or less, 90 wt% or less, or 85 wt% or less.

[0053] In one embodiment, the negative electrode active material included in the first negative electrode active material layer (120) may be substantially composed of natural graphite.

[0054] In exemplary embodiments, a second negative electrode active material layer (130) including artificial graphite may be formed on the first negative electrode active material layer (120). Accordingly, the life characteristics and rapid charging performance of the negative electrode (100) may be improved.

[0055] According to one embodiment, the second negative electrode active material layer (130) may be formed to be in direct contact with the first negative electrode active material layer (120).

[0056] The content of artificial graphite relative to the total weight of the second negative electrode active material layer (130) may be 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, or 90 wt% or more.

[0057] The content of artificial graphite relative to the total weight of the second negative electrode active material layer (130) may be 99 wt% or less, 95 wt% or less, 90 wt% or less, or 85 wt% or less.

[0058] In one embodiment, the negative electrode active material included in the second negative electrode active material layer (130) may be substantially composed of artificial graphite.

[0059] In some embodiments, at least one of the first negative electrode active material layer (120) and the second negative electrode active material layer (130) may further include a silicon-based active material. Accordingly, the capacity characteristics of the secondary battery may be improved.

[0060] For example, the above silicon-based active material is Si, SiO x (0 <x<2), 금속 도핑된 SiO x (0 <x<2), 실리콘-탄소 복합체 등을 포함할 수 있다. 상기 금속은 리튬 및 / 또는 마그네슘을 포함할 수 있으며, 금속 도핑된 SiO x (0 <x<2)는 금속 실리케이트를 포함할 수 있다.

[0061] According to one embodiment, the first negative electrode active material layer (120) may not include the silicon-based active material, and the second negative electrode active material layer (130) may include the silicon-based active material. Accordingly, the capacity characteristics of the secondary battery may be improved, while the life characteristics may be maintained or improved.

[0062] In some embodiments, the first negative electrode active material layer (120) and the second negative electrode active material layer (130) may include different negative electrode active materials.

[0063] For example, the negative electrode (100) can be made of a first negative electrode active material layer (120) including natural graphite and a second negative electrode active material layer (130) including artificial graphite, thereby improving structural stability, life characteristics, and rapid charging performance while reducing costs.

[0064] In exemplary embodiments, the first Raman peak area ratio defined by the following Equation 1 of the first negative electrode active material layer (120) may be 1 to 2, and the second Raman peak area ratio defined by the following Equation 2 of the second negative electrode active material layer (130) may be 0.2 to 0.5.

[0065] [Formula 1]

[0066] First Raman peak area ratio = AD1 / AG1

[0067] [Formula 2]

[0068] Second Raman peak area ratio = AD2 / AG2

[0069] In Equations 1 and 2, AD1 is 1320 cm of the Raman spectroscopy spectrum of the first negative active material layer (120). -1 1390 cm inland -1 is the area of ​​the peak having the maximum height in the wavenumber range (e.g., D band of the Raman spectral spectrum). AG1 is the area of ​​the peak having the maximum height in the Raman spectral spectrum of the first negative active material layer (130) at 1575 cm -1 1590 cm in height -1 is the area of ​​the peak having the maximum height in the wavenumber range (e.g., G band of Raman spectroscopy spectrum). AD2 is the area of ​​the peak having the maximum height in the Raman spectroscopy spectrum of the second negative active material layer (130) at 1320 cm -1 1390 cm inland -1 is the area of ​​the peak having the maximum height in the wavenumber range. AG2 is the area of ​​the Raman spectroscopy spectrum of the second negative active material layer (130) at 1575 cm-1 1590 cm in height -1 is the area of ​​the peak with the maximum height in the frequency range.

[0070] In Equations 1 and 2, 1000 cm when measuring AD1, AD2, AG1 and AG2 -1 and 1800 cm -1 The peak height at the wave point can be set as the base height and the peak area can be measured.

[0071] For example, the ratio of the first and second Raman peak areas may indicate the degree of amorphousness. For example, the higher the ratio of the first and second Raman peak areas, the higher the amorphousness of the first and second negative electrode active material layers (120, 130).

[0072] In the above first and second Raman peak area ratio ranges, crack occurrence in the first negative electrode active material layer (120) can be suppressed, excessive crystallinity degradation can be prevented, and stability can be improved while the resistance of the negative electrode (100) is reduced.

[0073] The area of ​​a Raman peak may have a technically different meaning than the intensity or height of a Raman peak in the same wavenumber range. For example, in a Raman spectrum, two peaks of the same height may have different peak areas. Accordingly, the Raman peak area ratio may contain more information about the physical properties of the measured object than the Raman peak intensity ratio or the Raman peak height ratio.

[0074] In some embodiments, the first Raman peak area ratio may be 1.2 to 1.5 or 1.28 to 1.38. Accordingly, the structural stability of the first negative active material layer (120) may be further improved.

[0075] In some embodiments, the second Raman peak area ratio may be 0.3 to 0.4 or 0.32 to 0.38. Accordingly, the resistance of the cathode (100) may be further reduced.

[0076] In some embodiments, the first Raman peak area ratio may be 3 to 5 times, or 3.5 to 4.5 times, the second Raman peak area ratio. In this range, the amorphous characteristics of the first negative active material layer (120) and the second negative active material layer (130) may be appropriately controlled, thereby improving the life characteristics, rapid charging characteristics, and output characteristics.

[0077] In some embodiments, the thickness (L2) of the second negative electrode active material layer (130) may be 30% to 70% or 40% to 60% of the sum of the thickness (L1) of the first negative electrode active material layer (120) and the thickness (L2) of the second negative electrode active material layer (130). In this range, the capacity characteristics, structural stability, and rapid charge / discharge characteristics of the negative electrode (100) may be improved while an increase in resistance may be suppressed.

[0078] The thickness (L1) of the first negative electrode active material layer (120) may be the shortest distance from the point where the first negative electrode active material layer (120) contacts the negative electrode current collector (110) to the point where it contacts the second negative electrode active material layer (130). The thickness (L2) of the second negative electrode active material layer (130) may be the shortest distance from the point where the second negative electrode active material layer (130) contacts the first negative electrode active material layer (120) to the outermost surface of the second negative electrode active material layer (130).

[0079] In some embodiments, the natural graphite included in the first negative electrode active material layer (120) may include a carbon coating formed on the surface. Accordingly, the output characteristics and life characteristics of the negative electrode (100) may be improved.

[0080] In one embodiment, the carbon coating may include amorphous carbon. Accordingly, the structural stability of natural graphite is further improved and the resistance is reduced, so that the first Raman peak area ratio can be adjusted to an appropriate range.

[0081] In some embodiments, the first negative active material layer (120) may include a plurality of first pores, and the second negative active material layer (130) may include a plurality of second pores.

[0082] In some embodiments, the ratio of the second porosity defined by Equation 4 below of the second negative electrode active material layer (130) to the first porosity defined by Equation 3 below of the first negative electrode active material layer (120) may be 1.2 to 2.0, and in some embodiments, may be 1.4 to 1.8.

[0083] [Formula 3]

[0084] 1st porosity (%) = (VP1 / VL1)*100

[0085] [Formula 4]

[0086] Second porosity (%) = (VP2 / VL2)*100

[0087] In Equations 3 and 4, VL1 is the volume of the first negative electrode active material layer (120), VP1 is the total volume of the plurality of first pores, VL2 is the volume of the second negative electrode active material layer (130), and VP2 is the total volume of the plurality of second pores.

[0088] For example, VL1, VP1, VL2 and VP2 of Equations 3 and 4 can be measured via 3D X-ray microscopy (XRM).

[0089] For example, VL1 in Equation 3 may be the total volume of the first negative electrode active material layer (120) including the total volume of the plurality of first pores, and VL2 in Equation 4 may be the total volume of the second negative electrode active material layer (130) including the total volume of the plurality of second pores.

[0090] Within the above porosity range, structural stability improvement by the first negative electrode active material layer (120) and rapid charging characteristics and output characteristics improvement by the second negative electrode active material layer (130) can be implemented together within an appropriate range.

[0091] For example, if the second negative electrode active material layer (130) has greater porosity than the first negative electrode active material layer (120), structural stability and rapid charge life characteristics can be improved together, and energy density can be improved or maintained.

[0092] For example, a 3D modeling image of a negative active material layer (120, 130) sample can be acquired using XRM. The first porosity and the second porosity can be measured by analyzing the 3D modeling image using analysis software.

[0093] For example, the first porosity can be measured in a region spaced apart from the negative current collector (110) of the first negative active material layer (120) by about 10 μm or more. For example, the second porosity can be measured in a region spaced apart from the outermost surface of the second negative active material layer (130) by about 10 μm or more. Accordingly, the accuracy of the measurement can be improved and the reliability can be enhanced.

[0094] In some embodiments, the first porosity may be 15% to 25%. In this range, the adhesion between the first negative electrode active material layer (120) and the negative electrode current collector (110) may be improved, while the capacity characteristics may be maintained or improved.

[0095] In some embodiments, the second porosity may be 25% to 40%. Within this range, the energy density may be maintained or improved while the rapid charging performance and output characteristics of the second negative active material layer (130) are improved.

[0096] Figures 2 and 3 are schematic plan views and cross-sectional views, respectively, illustrating a lithium secondary battery according to exemplary embodiments. For example, Figure 3 is a cross-sectional view taken along line I-I' of Figure 2 in the thickness direction.

[0097] Referring to FIGS. 2 and 3, the lithium secondary battery may include the above-described negative electrode (100) and the positive electrode (150) arranged to face the negative electrode (100).

[0098] The positive electrode (150) may include a positive electrode current collector (160) and a positive electrode active material layer (170) formed on at least one surface of the positive electrode current collector (160).

[0099] The positive electrode current collector (160) may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector (160) may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector (160) may be 10 μm to 50 μm.

[0100] The positive electrode active material layer (170) may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0101] According to exemplary embodiments, 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).

[0102] In some embodiments, 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.

[0103] [Chemical Formula 1]

[0104] Li x Ni a M b O 2+z

[0105] In Chemical Formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, -0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0106] 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 includes Co and / or Mn, and Co and / or Mn can serve as the main active element of the positive electrode active material together with Ni. Chemical Formula 1 is provided to express the bonding relationship of the above main active elements and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0107] In one embodiment, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the positive electrode active material or the layered structure / crystal structure. The auxiliary elements may be incorporated into the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0108] The auxiliary element may include, for example, at least one selected from the group consisting 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, and Zr. The auxiliary element may also act as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn, for example, Al.

[0109] 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.

[0110] [Chemical Formula 1-1]

[0111] Li x Ni a M1 b1 M2 b2 O 2+z

[0112] In Chemical Formula 1-1, M1 may include Co, Mn, and / or Al. M2 may include the auxiliary elements described above. 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 may be satisfied.

[0113] The above-described positive electrode active material may further include a coating element or doping element. For example, elements substantially identical to or similar to the above-described auxiliary elements may be used as the coating element or doping element. For example, the above-described elements may be used singly or in combination of two or more.

[0114] The above coating element or doping element may be present on the surface of the lithium-nickel metal oxide particle, or may penetrate through the surface of the lithium-nickel metal composite oxide particle and be included in the bonding structure represented by the above chemical formula 1 or chemical formula 1-1.

[0115] The above positive electrode active material may include a nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content may be used.

[0116] Ni can be provided as a transition metal associated with the output and capacity of a lithium secondary battery. Therefore, by employing a high-content (High-Ni) composition as described above in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0117] However, as the Ni content increases, the long-term storage stability and lifespan stability of the cathode or secondary battery may relatively deteriorate, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, the inclusion of Co can maintain electrical conductivity, while improving lifespan stability and capacity retention characteristics through Mn.

[0118] The content of Ni (e.g., the mole fraction of nickel among the total moles of nickel, cobalt, and manganese) in the NCM-based lithium oxide 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.

[0119] In some embodiments, the positive electrode active material may 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., LiFePO4).

[0120] In some embodiments, the positive electrode active material may include, for example, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide) active material, a Mn-rich active material, a Co-less 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.

[0121] [Chemical Formula 2]

[0122] p[Li2MnO3]·(1-p)[Li q JO2]

[0123] In chemical formula 2, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B로 구성된 그룹으로부터 선택되는 적어도 하나의 원소를 포함할 수 있다.

[0124] The positive electrode active material can be mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry can be coated on at least one surface of a positive electrode current collector (160), and then dried and rolled to prepare a positive electrode active material layer (170). The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. The positive electrode active material layer (170) can further include a binder and optionally can further include a conductive agent, a thickener, etc.

[0125] As the above solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used.

[0126] The above binder may include polyvinylidenefluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0127] In one embodiment, a PVDF-based binder may be used as the positive electrode binder. In this case, the amount of binder used to form the positive electrode active material layer (170) may be reduced, while the amount of positive electrode active material may be relatively increased. Accordingly, the output characteristics and capacity characteristics of the secondary battery may be improved.

[0128] The conductive material may be added to enhance the conductivity and / or mobility of lithium ions or electrons of the positive electrode active material layer (170). For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, etc., and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc. These may be used alone or in combination of two or more.

[0129] The positive electrode slurry may further include a thickener and / or a dispersant. In one embodiment, the positive electrode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0130] A first negative electrode active material layer (120) may be formed on at least one surface of a negative electrode current collector (110), and a second negative electrode active material layer (130) may be formed on the first negative electrode active material layer (120).

[0131] The first negative electrode active material described above can be mixed in a solvent to prepare a first negative electrode slurry. The first negative electrode slurry can be coated / deposited on at least one surface of a negative electrode current collector (110), and then dried and rolled to prepare a first negative electrode active material layer (120). The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting.

[0132] The second negative electrode active material described above can be mixed in a solvent to prepare a second negative electrode slurry. The second negative electrode slurry can be coated / deposited on the first negative electrode active material layer (120), and then dried and rolled to prepare a second negative electrode active material layer (130). The coating can be performed using a method substantially the same as the above-described coating method for the first negative electrode active material layer (120).

[0133] The first and second negative electrode active material layers (120, 130) may further include a binder and optionally further include a conductive agent, a thickener, etc.

[0134] The solvent included in the cathode slurry may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, etc. These may be used alone or in combination of two or more.

[0135] The above-described materials that can be used in manufacturing the anode (150) as the binder, conductive agent and thickener can be used.

[0136] In some embodiments, a styrene-butadiene rubber (SBR)-based binder, a carboxymethyl cellulose (CMC)-based binder, a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene, PEDOT)-based binder, or the like may be used as the negative electrode binder. These may be used alone or in combination of two or more.

[0137] In exemplary embodiments, a separator (140) may be interposed between the anode (150) and the cathode (100). The separator (140) may be configured to prevent electrical short-circuiting between the anode (150) and the cathode (100) and to allow ion flow. For example, the thickness of the separator may be 10 μm to 20 μm.

[0138] For example, the separator (140) may include a porous polymer film or a porous nonwoven fabric.

[0139] The above porous polymer film may include a polyolefin polymer such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. These may be used alone or in combination of two or more.

[0140] The above porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0141] The separator (140) may include a ceramic material. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0142] The separator (140) may have a single-layer or multi-layer structure including the above-described polymer film and / or non-woven fabric.

[0143] According to exemplary embodiments, an electrode cell is defined by an anode (150), a cathode (100), and a separator (140), and a plurality of electrode cells may be stacked to form an electrode assembly (180) in the form of, for example, a jelly roll. For example, the electrode assembly (180) may be formed through winding, stacking, z-folding, stack-folding, or the like of the separator (140).

[0144] An electrode assembly (180) may be housed together with an electrolyte within a case (190) to define a lithium secondary battery. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0145] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - is expressed as and the anion of the lithium salt (X - ) as 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 - Examples include:

[0146] Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methylacetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, Tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite can be used. These can be used alone or in combination of two or more.

[0147] The above non-aqueous electrolyte may further include additives. The additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc. These may be used alone or in combination of two or more.

[0148] The above cyclic carbonate compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0149] The above fluorine-substituted cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0150] The above sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0151] The above cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0152] The above cyclic sulfite compound may include ethylene sulfite, butylene sulfite, etc.

[0153] The above phosphate compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0154] The above borate compound may include lithium bis(oxalate) borate, etc.

[0155] In some embodiments, a solid electrolyte may be used instead of the non-aqueous electrolyte described above. In this case, the lithium secondary battery may be manufactured in the form of an all-solid-state battery. Furthermore, a solid electrolyte layer may be positioned between the positive electrode (150) and negative electrode (100) instead of the separator (140) described above.

[0156] The solid electrolyte may include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte may include Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are positive numbers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , (p, q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li7-xPS6-xCl x (0≤x≤2), Li7-xPS6-xBr x (0≤x≤2), Li7-xPS6-xI x (0≤x≤2) etc. These can be used alone or in combination of two or more.

[0157] In one embodiment, the solid electrolyte may include an oxide-based amorphous solid electrolyte, such as, for example, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0158] As illustrated in FIGS. 2 and 3, electrode tabs (positive electrode tabs and negative electrode tabs) may protrude from the positive electrode collector (160) and negative electrode collector (110) belonging to each electrode cell and extend to one side of the case (190). The electrode tabs may be fused together with the one side of the case (190) to form electrode leads (positive electrode lead (157) and negative electrode lead (107)) that extend or are exposed to the outside of the case (190).

[0159] The above lithium secondary battery can be manufactured in a cylindrical, square, pouch or coin shape using, for example, a can.

[0160] The embodiments of the present disclosure described above include the following aspects and can be implemented through at least one of the following aspects.

[0161] According to a first aspect of the present disclosure, a negative electrode for a lithium secondary battery comprises: a negative electrode current collector; a first negative electrode active material layer formed on at least one surface of the negative electrode current collector; and a second negative electrode active material layer formed on the first negative electrode active material layer and including artificial graphite, wherein a first Raman peak area ratio defined by the following formula 1 of the first negative electrode active material layer is 1 to 2, and a second Raman peak area ratio defined by the following formula 2 of the second negative electrode active material layer is 0.2 to 0.5.

[0162] [Formula 1]

[0163] First Raman peak area ratio = AD1 / AG1

[0164] [Formula 2]

[0165] Second Raman peak area ratio = AD2 / AG2

[0166] In Equations 1 and 2, AD1 is the Raman spectral spectrum of the first negative active material layer at 1320 cm -1 1390 cm inland -1 is the area of ​​the peak having the maximum height in the wavenumber range. AG1 is the area of ​​the Raman spectroscopy spectrum of the first negative active material layer at 1575 cm -1 1590 cm in height -1 is the area of ​​the peak with the maximum height in the frequency range.

[0167] AD2 is 1320 cm of the Raman spectroscopy spectrum of the second negative active material layer. -1 1390 cm inland -1 is the area of ​​the peak having the maximum height in the wavenumber range. AG2 is the area of ​​the Raman spectroscopy spectrum of the second negative active material layer at 1575 cm -1 1590 cm in height -1 is the area of ​​the peak with the maximum height in the frequency range.

[0168] In the first aspect, according to the second aspect, the first Raman peak area ratio may be 3 to 5 times the second Raman peak area ratio.

[0169] In the first aspect or the second aspect, according to the third aspect, the first Raman peak area ratio may be 1.2 to 1.5.

[0170] In any one of the first to third aspects, according to the fourth aspect, the second Raman peak area ratio may be 0.3 to 0.4.

[0171] In any one of the first to fourth aspects, according to the fifth aspect, the thickness of the second negative electrode active material layer may be 30% to 70% of the sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer.

[0172] In any one of the first to fifth aspects, according to the sixth aspect, the thickness of the second negative electrode active material layer may be 40% to 60% of the sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer.

[0173] In any one of the first to sixth aspects, according to the seventh aspect, the first negative electrode active material layer may include natural graphite.

[0174] In the seventh aspect, according to the eighth aspect, the natural graphite may include a carbon coating formed on the surface.

[0175] In the eighth aspect, according to the ninth aspect, the carbon coating may include amorphous carbon.

[0176] In the first aspect or the ninth aspect, according to the tenth aspect, the first negative electrode active material layer may include a plurality of first pores, and the second negative electrode active material layer may include a plurality of second pores.

[0177] In the above 10th aspect, according to the 11th aspect, the ratio of the second porosity defined by the following formula 4 of the second negative electrode active material layer to the first porosity defined by the following formula 3 of the first negative electrode active material layer may be 1.2 to 2.0.

[0178] [Formula 3]

[0179] 1st porosity (%) = (VP1 / VL1)*100

[0180] [Formula 4]

[0181] Second porosity (%) = (VP2 / VL2)*100

[0182] In Equations 3 and 4, VL1 is the volume of the first negative electrode active material layer, VP1 is the total volume of the plurality of first pores, VL2 is the volume of the second negative electrode active material layer, and VP2 is the total volume of the plurality of second pores.

[0183] In the above eleventh aspect, according to the twelfth aspect, the first porosity may be 15% to 25%.

[0184] In any one of the first to twelfth aspects, in some embodiments according to the thirteenth aspect, the second porosity may be 25% to 40%.

[0185] A lithium secondary battery according to a 14th aspect of the present disclosure includes a negative electrode for a lithium secondary battery according to any one of the first to 13th aspects, and a positive electrode opposite to the negative electrode.

[0186] Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the embodiments are possible within the scope and technical idea of ​​the present disclosure, and such changes and modifications are included in the appended claims.

[0187] Examples 1 to 15 and Comparative Examples 6 to 9

[0188] (1) Cathode manufacturing

[0189] 1) Manufacturing of the first negative electrode active material layer

[0190] A first negative electrode slurry was prepared by mixing 93.4 wt% of natural graphite, 3 wt% of artificial graphite as a conductive material, 2.4 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.2 wt% of carboxymethyl cellulose (CMC) as a thickener.

[0191] The first negative electrode slurry was coated, dried, and rolled on a copper current collector to form a first negative electrode active material layer.

[0192] 2) Manufacturing of the second negative electrode active material layer

[0193] A second negative electrode slurry was prepared by mixing 95.4 wt% of artificial graphite as a conductive material, 3 wt% of artificial graphite as a conductive material, 0.4 wt% of styrene-butadiene rubber (SBR) as a binder, and 1.2 wt% of carboxymethyl cellulose (CMC) as a thickener.

[0194] The second negative electrode slurry was coated, dried, and rolled on the first negative electrode active material layer to form a negative electrode including the second negative electrode active material layer.

[0195] By comprehensively changing variables such as rolling time and pressure, loading amount, etc. during the formation of the first and second negative electrode active material layers, a negative electrode was manufactured and selected in which the first Raman peak area ratio, the second Raman peak area ratio, the thickness of the second negative electrode active material layer relative to the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer, the first porosity, and the second porosity were controlled as shown in Tables 1 and 2 below.

[0196] (2) Manufacturing of lithium half cells

[0197] A lithium half-cell was manufactured including the above negative electrode and using lithium metal (Li metal) as a counter electrode (anode).

[0198] Specifically, a lithium coin half-cell of CR2016 (diameter 20 mm, thickness 1.6 mm) standard was formed by interposing a separator (polyethylene, thickness 20 ㎛) between the negative electrode and lithium metal (thickness 1 mm).

[0199] The combination of lithium metal / separator / cathode was placed in a coin cell plate, and after pouring the electrolyte, the plate was clamped after covering with a cap. The electrolyte was a 1 M LiPF6 solution formed using a mixed solvent of EC / EMC (3:7; volume ratio) with 2.0 vol% of fluoroethylene carbonate (FEC) added to the total volume of the electrolyte. After clamping, it was impregnated for 3 to 24 hours, and then 3 cycles of charge and discharge were performed at 0.1 C (charge conditions: CC-CV 0.1 C 0.01 V 0.01 C CUT-OFF, discharge conditions: CC 0.1 C 1.5 V CUT-OFF).

[0200] Example 16

[0201] A negative electrode and a lithium half-cell were manufactured in the same manner as in Example 1, except that an amorphous carbon coating was performed on the surface of the natural graphite of the first negative electrode active material layer.

[0202] Comparative Example 1

[0203] A negative electrode and a lithium half-cell were manufactured in the same manner as in Example 1, except that the second negative electrode active material layer was formed directly on the copper current collector without forming the first negative electrode active material layer.

[0204] The thickness of the second negative electrode active material layer of Comparative Example 1 was substantially the same as the total thickness of the first negative electrode active material layer and the second negative electrode active material layer of Example 1.

[0205] Comparative Example 2

[0206] A negative electrode and a lithium half-cell were manufactured in the same manner as in Comparative Example 1, except that an equivalent amount of natural graphite was used instead of artificial graphite in the second negative electrode active material layer.

[0207] Comparative Example 3

[0208] A negative electrode and a lithium half-cell were manufactured in the same manner as in Example 1, except that an equivalent amount of natural graphite was used instead of artificial graphite in the second negative electrode active material layer.

[0209] Comparative Example 4

[0210] A negative electrode and a lithium half-cell were manufactured in the same manner as in Example 1, except that an equivalent amount of artificial graphite was used instead of natural graphite in the first negative electrode active material layer.

[0211] Comparative Example 5

[0212] A negative electrode and a lithium half-cell were manufactured in the same manner as in Example 1, except that an equivalent amount of artificial graphite was used instead of natural graphite in the first negative electrode active material layer, and an equivalent amount of natural graphite was used instead of artificial graphite in the second negative electrode active material layer.

[0213]

[0214] Experimental example

[0215] (1) Measurement of the first Raman peak area ratio and the second Raman peak area ratio

[0216] Samples were prepared by cutting the cathodes manufactured according to the above-described examples and comparative examples.

[0217] The second Raman peak area ratio was measured for the second negative electrode active material layer, which is the outermost layer of the above sample, using a 532 nm laser Raman analyzer (Laser Raman Spectroscopy) (Model name: Invia, Manufacturer: RENISHAW).

[0218] The specific Raman analyzer measurement method was as follows.

[0219] i) Turn on the power of the Raman analyzer.

[0220] ii) Open the Spectral acquisition setup window.

[0221] iii) Select ‘Static’ as the Grating Scan Type and enter 1500 (Raman Shift (cm-1)) as the Center value.

[0222] iv) In Configuration, 532 nm edge was selected as Laser, 1800 / mm(vis) as Grating, and Renishaw 1024 StramLine CCD as Detector.

[0223] v) In the Acquisition conditions, Exposure time was set to 10 s, Objective to 50, Accumulation to 5, Laser power to 5% (1.5 mW), and Focus level to 0%.

[0224] vi) After placing the sample on the sample stage and confirming the measurement location, the Raman spectrum of the sample was acquired.

[0225] In the Raman spectrum, the wavenumber is 1320 cm -1 1390 cm inland -1 Area (AD2) of the peak with maximum height in the in-band (e.g., D band) and wavenumber 1575 cm -1 1590 cm in height -1 The area (AG2) of the peak with the maximum height in the in-band (e.g., G band) was measured. The measured peak intensities were applied to Equation 2 to calculate the second Raman peak area ratio.

[0226] The second negative electrode active material layer was partially removed by repeatedly attaching and detaching 3M tape to the upper surface of the sample. The 3M tape was repeatedly attached and detached until the negative electrode current collector was visible, and a portion of the first negative electrode active material layer was separated while still attached to the 3M tape.

[0227] The first Raman peak area ratio was measured for the separated first negative active material layer using the same equipment and method as the second Raman area height ratio measurement. Specifically, in the Raman spectroscopy spectrum, the wavenumber was 1320 cm -1 1390 cm inland -1Area (AD1) of the peak with maximum height in the in-band (e.g., D band) and wavenumber 1575 cm -1 1590 cm in height -1 The area (AG1) of the peak with the maximum height in the in-band (e.g., G band) was measured. The measured peak intensities were applied to Equation 1 to calculate the first Raman peak area ratio.

[0228] The ratio of the area of ​​the first Raman peak was calculated to be several times greater than the ratio of the area of ​​the second Raman peak.

[0229] (2) Measurement of first and second porosity

[0230] Samples were prepared by cutting the negative electrodes manufactured according to the above-described examples and comparative examples. Analysis was performed on the samples, excluding an approximately 10 μm thick region adjacent to the copper current collector in the first negative electrode active material layer and an approximately 10 μm thick region adjacent to the outer surface in the second negative electrode active material layer.

[0231] The above sample was placed into XRM (Zeiss Xradia 620 versa, Zeiss) to obtain a 3D modeling image.

[0232] The XRM measurement conditions were as follows.

[0233] i) Source condition: 50 kV, 4.5 W

[0234] ii) Voxel size: 300 nm

[0235] The above 3D modeling image was analyzed using analysis software (Matdict Material Characterization, GeoDict Software Co., Ltd.) to measure the first porosity defined by Equation 3 of the first negative electrode active material layer and the second porosity defined by Equation 4 of the second negative electrode active material layer.

[0236] The ratio of the second porosity to the first porosity was calculated.

[0237] (3) Capacity retention rate evaluation during rapid charging

[0238] The lithium half-cells manufactured according to the above-described examples and comparative examples were charged to a depth of discharge (DOD) of 77.2% within 20 minutes using a step-by-step charge method at a C-rate of 3.25C / 3.0C / 2.75C / 2.5C / 2.25C / 2.0C / 1.75C / 1.5C / 1.25C / 1.0C / 0.75C / 0.5C, and then discharged at 1C. The charge and discharge were considered as one cycle, and the cycles were repeated to conduct a rapid charge evaluation. After repeating 300 cycles with a waiting time of 10 minutes between charge and discharge cycles, the discharge capacity after 300 cycles was divided by the discharge capacity after 1 cycle and multiplied by 100 to evaluate the capacity retention rate.

[0239] (4) Evaluation of resistance (DCIR) increase rate

[0240] For lithium half-cells manufactured according to the above-described examples and comparative examples, rapid charging and discharging were repeated in the same manner as in Experimental Example (3), and resistance (DCIR) was measured.

[0241] After 1 cycle and 300 cycles, each discharged lithium half-cell was charged at 1C to reach 50% of DOD according to the rapid charging conditions of Experimental Example (3), and then discharged at 1C for 30 seconds. The resistance (DCIR) was calculated by measuring the voltage decrease (V) for 10 seconds during the discharge.

[0242] The resistance after 300 cycles was divided by the resistance after 1 cycle and multiplied by 100 to evaluate the resistance increase rate.

[0243] The measurement and evaluation results are shown in Tables 1 and 2 below.

[0244] Ratio of the first Raman peak area ratio to the second Raman peak area ratio Ratio of the first Raman peak area to the second Raman peak area ratio Thickness of the second negative electrode active material layer to the total thickness of the first and second negative electrode active material layers (%) Example 11.28 0.32 4.00 50 Example 21.5 0.40 3.75 70 Example 31.6 10.46 3.50 50 Example 41.94 0.42 4.61 50 Example 51.03 0.22 4.68 50 Example 61.15 0.39 2.95 50 Example 71.99 0.39 5.0 350 Example 81.33 0.41 3.20 30 Example 91.29 0.35 3.69 40 Example 101.200.274.4460Example 111.320.324.1370Example 121.060.224.8220Example 131.850.493.7880Example 141.050.353.0050Example 151.870.384.9250Example 161.320.314.2650Comparative Example 1-0.41-100Comparative Example 2-1.49-100Comparative Example 31.471.451.0150Comparative Example 40.390.400.97550Comparative Example 50.331.310.2550Comparative Example 60.970.273.5950Comparative Example 72.030.464.4150Comparison Example 81.130.186.2850Comparison Example 91.840.533.4750

[0245]

[0246] First porosity (%) Second porosity (%) Non-rapid charging capacity retention rate (%, 300 cyc) Resistance increase rate (%, 300 cyc) Example 120.128.31.4198100 Example 219.727.51.4097101 Example 321.029.81.4297101 Example 421.230.31.4396102 Example 521.529.21.3696101 Example 625.131.01.2493104 Example 714.828.01.8992104 Example 823.532.51.3895101 Example 921.627.91.2996101Example 1022.028.81.3196102Example 1124.131.01.2994102Example 1224.832.11.2990105Example 1315.828.11.7892102Example 1424.829.41.1989105Example 1515.431.12.0290104Example 1619.529.61.5298100Comparative Example 1-24.2-72106Comparative Example 2-26.7-87117Comparative Example 319.420.21.0478122Comparative Example 432.036.81.1571113Comparative Example 530.919.20.6274107Comparative Example 626.329.51.1285107Comparative Example 714.228.42.0083106Comparative Example 824.446.01.8984107Comparative Example 914.926.71.7984108

[0247]

[0248] Fig. 4 is a cross-section of the cathode of Example 1 measured by a scanning electron microscope (SEM). Fig. 5 is a cross-section of the cathode of Example 2 measured by SEM. Fig. 6 is a cross-section of the cathode of Comparative Example 1 measured by SEM.

[0249] Referring to FIGS. 4 to 6, the second negative electrode active material layer contains relatively more pores than the first negative electrode active material layer.

[0250] Figure 7 is a Raman spectroscopy spectrum of each of the first negative electrode active material layer and the second negative electrode active material layer of Example 1.

[0251] Referring to Tables 1 and 2, in examples in which the first Raman peak area ratio was 1 to 2 and the second Raman peak area ratio was 0.2 to 0.5, the rapid charge capacity retention rate was improved and the resistance increase rate was reduced compared to the comparative examples.

[0252] In Examples 6 and 7, where the first Raman peak area ratio was 3 to 5 times greater than the second Raman peak area ratio, the rapid charge capacity retention rate was relatively reduced and the resistance increase rate was increased.

[0253] In Examples 12 and 13, where the thickness of the second negative electrode active material layer was 30% to 70% of the sum of the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer, the rapid charge capacity retention rate was relatively reduced and the resistance increase rate was increased.

[0254] In Examples 14 and 15, where the ratio of the second porosity to the first porosity was outside of 1.2 to 2.0, the rapid charge capacity retention rate was relatively lowered and the resistance increase rate was increased.

Claims

1. Negative current collector; A first negative electrode active material layer formed on at least one surface of the negative electrode current collector; and A second negative electrode active material layer formed on the first negative electrode active material layer and including artificial graphite, A negative electrode for a lithium secondary battery, wherein the first Raman peak area ratio defined by the following formula 1 of the first negative electrode active material layer is 1 to 2, and the second Raman peak area ratio defined by the following formula 2 of the second negative electrode active material layer is 0.2 to 0.5: [Formula 1] 1st Raman peak area ratio = AD1 / AG1 [Formula 2] Second Raman peak area ratio = AD2 / AG2 (In Equations 1 and 2, AD1 is 1320 cm of the Raman spectrum of the first negative electrode active material layer. -1 1390 cm inland -1 is the area of ​​the peak having the maximum height in the waveband of AG1, and AG1 is the Raman spectroscopy spectrum of the first negative active material layer at 1575 cm -1 1590 cm inland -1 is the area of ​​the peak having the maximum height in the frequency range, AD2 is 1320 cm of the Raman spectrum of the second negative electrode active material layer. -1 1390 cm inland -1 is the area of ​​the peak having the maximum height in the waveband of AG2, and AG2 is the Raman spectroscopy spectrum of the second negative active material layer at 1575 cm -1 1590 cm inland -1 is the area of ​​the peak with the maximum height in the frequency range).

2. A negative electrode for a lithium secondary battery according to claim 1, wherein the first Raman peak area ratio is 3 to 5 times the second Raman peak area ratio.

3. A negative electrode for a lithium secondary battery according to claim 1, wherein the first Raman peak area ratio is 1.2 to 1.

5.

4. A negative electrode for a lithium secondary battery according to claim 1, wherein the second Raman peak area ratio is 0.3 to 0.

4.

5. A negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the second negative electrode active material layer is 30% to 70% of the sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer.

6. A negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the second negative electrode active material layer is 40% to 60% of the sum of the thickness of the first negative electrode active material layer and the thickness of the second negative electrode active material layer.

7. A negative electrode for a lithium secondary battery according to claim 1, wherein the first negative electrode active material layer comprises natural graphite.

8. A negative electrode for a lithium secondary battery according to claim 7, wherein the natural graphite includes a carbon coating formed on a surface portion.

9. A negative electrode for a lithium secondary battery according to claim 8, wherein the carbon coating includes amorphous carbon.

10. A negative electrode for a lithium secondary battery according to claim 1, wherein the first negative electrode active material layer includes a plurality of first pores, and the second negative electrode active material layer includes a plurality of second pores.

11. In claim 10, a negative electrode for a lithium secondary battery, wherein a ratio of the second porosity of the second negative electrode active material layer, defined by the following formula 4, to the first porosity of the first negative electrode active material layer, defined by the following formula 3, is 1.2 to 2.0: [Formula 3] 1st porosity (%) = (VP1 / VL1)*100 [Formula 4] Second porosity (%) = (VP2 / VL2)*100 (In Equations 3 and 4, VL1 is the volume of the first negative electrode active material layer, VP1 is the total volume of the plurality of first pores, VL2 is the volume of the second negative electrode active material layer, and VP2 is the total volume of the plurality of second pores).

12. A negative electrode for a lithium secondary battery according to claim 11, wherein the first porosity is 15% to 25%.

13. A negative electrode for a lithium secondary battery according to claim 11, wherein the second porosity is 25% to 40%.

14. A negative electrode for a lithium secondary battery according to claim 1; and A lithium secondary battery comprising a positive electrode opposite to the negative electrode.

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