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

Abstract

The invention provides a negative electrode for a lithium secondary battery and a lithium secondary battery including the same. A negative electrode for a lithium secondary battery according to an embodiment of the present disclosure includes 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 including first pores, and a second negative electrode active material layer formed on the first negative electrode active material layer and including artificial graphite and second pores, the difference between the aspect ratio of the first air hole and the aspect ratio of the second air hole is 0.5-3.0, so that the structural stability, the service life characteristic and the rapid charging performance of the negative electrode for the lithium secondary battery can be improved.

Description

Technical Field

[0001] The disclosed matter of the present application 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, and with the development of the information communication and display industries, it is widely used as a power source for portable electronic communication devices such as portable cameras, mobile phones, and laptop computers. In addition, recently, battery packs including secondary batteries have also been developed and applied as power sources for eco-friendly vehicles such as electric vehicles.

[0003] As secondary batteries, for example, lithium secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc. can be cited. Among them, lithium secondary batteries are actively developed and applied because of their high working voltage and energy density per unit weight, and their advantages in charging speed and weight reduction.

[0004] Recently, as the application targets of lithium secondary batteries have expanded, lithium secondary batteries with high capacity and output are currently being developed. For example, a silicon-based material with high capacity can be included in the negative electrode active material.

[0005] However, due to the volume expansion rate and low conductivity of silicon, the life characteristics of the electrode may be damaged during rapid charging. Summary of the Invention

[0006] Technical Problem

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

[0008] According to one aspect of the present disclosure, a lithium secondary battery with improved life characteristics can be provided.

[0009] Technical Solution

[0010] The negative electrode for a lithium secondary battery according to an exemplary embodiment of the present disclosure includes: 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 including first pores; and a second negative electrode active material layer formed on the first negative electrode active material layer, including artificial graphite and second pores, and the difference between the first pore major axis ratio defined by Formula 1 and the second pore major axis ratio defined by Formula 2 is 0.5 to 3.0.

[0011] [Formula 1]

[0012] First pore major axis ratio = PZ1 / PX1

[0013] [Formula 2]

[0014] Second pore major axis ratio = PZ2 / PX2

[0015] In Formulas 1 and 2, PX1 is the ratio of the length in the first direction of the first pores measured for the first negative electrode active material layer by 3D X-ray Microscopy (XRM) to the sum of the length in the first direction, the length in the second direction perpendicular to the first direction on a plane, and the length in the third direction perpendicular to the first and second directions.

[0016] PZ1 is the ratio of the length in the third direction of the first pores measured for the first negative electrode active material layer by XRM to the sum of the length in the first direction, the length in the second direction, and the length in the third direction.

[0017] PX2 is the ratio of the length in the first direction of the second pores measured for the second negative electrode active material layer by XRM to the sum of the length in the first direction, the length in the second direction, and the length in the third direction.

[0018] PZ2 is the ratio of the length in the third direction of the second pores measured for the second negative electrode active material layer by XRM to the sum of the length in the first direction, the length in the second direction, and the length in the third direction.

[0019] In some embodiments, the difference between the first pore aspect ratio and the second pore aspect ratio may be from 1.0 to 2.5.

[0020] In some embodiments, the second pore aspect ratio may be greater than the first pore aspect ratio.

[0021] In some embodiments, the first direction may represent the extending direction of the longer side of the negative electrode when observed in the plane direction, the second direction may represent the extending direction of the shorter side of the negative electrode when observed in the plane direction, and the third direction may represent the thickness direction of the negative electrode.

[0022] 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.

[0023] In some embodiments, the first pore aspect ratio may be the average of the first pore aspect ratios of the respective plurality of first pores, and the second pore aspect ratio may be the average of the second pore aspect ratios of the respective plurality of second pores.

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

[0025] [Formula 3]

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

[0027] [Formula 4]

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

[0029] In Formulas 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] In some embodiments, the first negative electrode active material layer may include natural graphite.

[0033] In some embodiments, the natural graphite may include a carbon coating formed on the surface portion.

[0034] In some embodiments, the carbon coating may include amorphous carbon.

[0035] In some embodiments, the first Raman peak height ratio defined by the following Formula 5 of the first negative electrode active material layer may be 2.5 to 3.6 times the second Raman peak height ratio defined by the following Formula 6 of the second negative electrode active material layer.

[0036] [Formula 5]

[0037] First Raman peak height ratio = ID1 / IG1

[0038] [Formula 6]

[0039] Second Raman peak height ratio = ID2 / IG2

[0040] In Formulas 5 and 6, ID1 is the maximum height of the peak in the wave number range of 1300 cm -1 to 1500 cm -1 of the Raman spectrum of the first negative electrode active material layer, and IG1 is the maximum height of the peak in the wave number range of 1500 cm -1 to 1700 cm -1 of the Raman spectrum of the first negative electrode active material layer. ID2 is the maximum height of the peak in the wave number range of 1300 cm -1 to 1500 cm -1The maximum height of the peak within the wavenumber range, and IG2 is 1500 cm of the Raman spectrum of the second negative electrode active material layer -1 to 1700 cm -1 The maximum height of the peak within the wavenumber range.

[0041] In some embodiments, the first Raman peak height ratio may be from 0.25 to 0.6.

[0042] In some embodiments, the second Raman peak height ratio may be from 0.03 to 0.2.

[0043] The lithium secondary battery according to an exemplary embodiment of the present disclosure includes the negative electrode for a lithium secondary battery described above and a positive electrode opposite to the negative electrode.

[0044] Technical effects

[0045] According to one embodiment of the present disclosure, the structural stability, life characteristics, and fast charging performance of the negative electrode for a lithium secondary battery can be improved. In addition, the cost can be reduced.

[0046] According to one embodiment of the present disclosure, the structural stability and fast charging life characteristics can be improved simultaneously. In addition, the energy density of the secondary battery can be improved or maintained.

[0047] The negative electrode for a lithium secondary battery of the present disclosure and the lithium secondary battery including the same can be widely applied to electric vehicles, battery charging stations, and other green technology fields using batteries such as solar power generation and wind power generation that use batteries. The negative electrode for a lithium secondary battery of the present disclosure and the lithium secondary battery including the same can be used for environmentally friendly (eco - friendly), electric vehicles (Electric Vehicle), hybrid vehicles, etc. that prevent climate change by suppressing air pollution and greenhouse gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 To show a cross - sectional view of the negative electrode for a lithium secondary battery according to an exemplary embodiment;

[0049] Figure 2 and Figure 3 Are respectively a plan view and a cross - sectional view showing a lithium secondary battery according to an exemplary embodiment. DETAILED DESCRIPTION

[0050] Embodiments of the present disclosure provide a negative electrode for a lithium secondary battery (hereinafter may be simply referred to as "negative electrode") including a plurality of negative electrode active material layers. In addition, a lithium secondary battery (hereinafter may be simply referred to as "secondary battery") including the negative electrode is provided.

[0051] Hereinafter, embodiments of the present disclosure will be described in detail. However, this is only for illustration, and the present disclosure is not limited to the specific embodiments illustrated.

[0052] Figure 1 To show a cross-sectional view of a negative electrode for a lithium secondary battery according to an exemplary embodiment.

[0053] Refer to Figure 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.

[0054] For example, the negative electrode current collector 110 may include a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a 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 110 may be 10 μm to 50 μm.

[0055] On at least one surface of the negative electrode current collector 110, a first negative electrode active material layer 120 including first pores may be formed.

[0056] In some embodiments, the first negative electrode active material layer 120 may include natural graphite. Thereby, the adhesion and capacity characteristics between the negative electrode current collector 110 and the first negative electrode active material layer 120 can be improved.

[0057] According to one embodiment, the first negative electrode active material layer 120 may be formed to directly contact the negative electrode current collector 110.

[0058] Based on the total weight of the first negative electrode active material layer 120, the content of natural graphite may be 40% by weight or more, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0059] Based on the total weight of the first negative electrode active material layer 120, the content of natural graphite may be 99% by weight or less, 95% by weight or less, 90% by weight or less, or 85% by weight or less.

[0060] In one embodiment, the negative electrode active material contained in the first negative electrode active material layer 120 may be substantially composed of natural graphite.

[0061] In an exemplary embodiment, a second negative electrode active material layer 130 including artificial graphite and second pores may be formed on the first negative electrode active material layer 120. Thereby, the life characteristics and fast charging performance of the negative electrode 100 can be improved.

[0062] According to one embodiment, the second negative electrode active material layer 130 may be formed to directly contact the first negative electrode active material layer 120.

[0063] Based on the total weight of the second negative electrode active material layer 130, the content of artificial graphite can be 40% by weight or more, 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, or 90% by weight or more.

[0064] Based on the total weight of the second negative electrode active material layer 130, the content of artificial graphite can be 99% by weight or less, 95% by weight or less, 90% by weight or less, or 85% by weight or less.

[0065] In one embodiment, the negative electrode active material contained in the second negative electrode active material layer 130 may be substantially composed of artificial graphite.

[0066] 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. Thereby, the capacity characteristics of the secondary battery can be improved.

[0067] For example, the silicon-based active material may include Si, SiO x (0 < x < 2), metal-doped SiO x (0 < x < 2), silicon-carbon composite, etc. The metal may include lithium and / or magnesium, and metal-doped SiO x (0 < x < 2) may include metal silicate.

[0068] According to one embodiment, the silicon-based active material may not be included in the first negative electrode active material layer 120, and the silicon-based active material may be included in the second negative electrode active material layer 130. Thereby, while improving the capacity characteristics of the secondary battery, the life characteristics can be maintained or improved.

[0069] 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.

[0070] For example, the negative electrode 100 may include a first negative electrode active material layer 120 containing natural graphite and a second negative electrode active material layer 130 containing artificial graphite, thereby improving the structural stability, life characteristics, and fast charging performance and reducing costs.

[0071] In an exemplary embodiment, the difference between the first pore aspect ratio defined by Formula 1 and the second pore aspect ratio defined by Formula 2 is 0.5 to 3.0, and may be 1.0 to 2.5 in some embodiments.

[0072] [Formula 1]

[0073] First pore aspect ratio = PZ1 / PX1

[0074] [Formula 2]

[0075] Second pore major axis ratio = PZ2 / PX2

[0076] In Formula 1 and Formula 2, PX1 is the ratio of the length of the first pore in the first direction measured by 3D X-ray Microscopy (XRM) for the first negative electrode active material layer 120 to the sum of the length in the first direction, the length in the second direction perpendicular to the first direction in the plane, and the length in the third direction perpendicular to the first direction and the second direction.

[0077] PZ1 is the ratio of the length of the first pore in the third direction measured by XRM for the first negative electrode active material layer 120 to the sum of the length in the first direction, the length in the second direction, and the length in the third direction.

[0078] PX2 is the ratio of the length of the second pore in the first direction measured by XRM for the second negative electrode active material layer 130 to the sum of the length in the first direction, the length in the second direction, and the length in the third direction.

[0079] PZ2 is the ratio of the length of the second pore in the third direction measured by XRM for the second negative electrode active material layer 130 to the sum of the length in the first direction, the length in the second direction, and the length in the third direction.

[0080] The term "first direction" used in this specification may represent the extending direction of the longer side of the negative electrode 100 when observed in the plane direction and / or Figure 1 the first direction of

[0081] The term "second direction" used in this specification may represent the extending direction of the shorter side of the negative electrode 100 when observed in the plane direction. The second direction may represent a direction perpendicular to the first direction in the same plane and / or Figure 1 the second direction of

[0082] The term "third direction" used in this specification may represent a direction perpendicular to the first direction and the second direction, the thickness direction of the negative electrode 100, and / or Figure 1 the third direction of

[0083] The first pore major axis ratio may be the ratio of the length of the first pore included in the first negative electrode active material layer 120 in the third direction to the length in the first direction.

[0084] The second pore major axis ratio may be the ratio of the length of the second pore included in the second negative electrode active material layer 130 in the third direction to the length in the first direction.

[0085] Since the difference between the major axis ratios of the first pores and the second pores is included in the above range, the structural stability can be improved by the first negative electrode active material layer 120 within an appropriate range, and the fast charging characteristics and output characteristics can be enhanced by the second negative electrode active material layer 130.

[0086] When the difference between the major axis ratios of the first pores and the second pores exceeds 3.0, the energy density and life characteristics of the second negative electrode active material layer 130 may be reduced.

[0087] When the difference between the major axis ratios of the first pores and the second pores is less than 0.5, the adhesion and stability of the first negative electrode active material layer 120 may be reduced.

[0088] For example, XRM can be used to obtain 3D modeling images of samples of the negative electrode active material layers 120 and 130. The major axis ratios of the first pores and the second pores can be measured by analyzing the 3D modeling images with analysis software.

[0089] For example, the major axis ratio of the first pores can be measured in a region of the first negative electrode active material layer 120 that is more than about 10 μm away from the negative electrode current collector 110. For example, the major axis ratio of the second pores can be measured in a region that is more than about 10 μm away from the outermost surface of the second negative electrode active material layer 130. Thereby, the measurement accuracy can be improved and the reliability can be enhanced.

[0090] In some embodiments, the major axis ratio of the second pores may be greater than that of the first pores. Thus, a morphology in which the second pores are sufficiently aligned in the thickness direction (e.g., the third direction) of the negative electrode 100 is included, so that the fast charging life characteristics can be improved. In this case, the difference between the major axis ratios of the first pores and the second pores may be a value obtained by subtracting the major axis ratio of the first pores from that of the second pores.

[0091] In some embodiments, the first negative electrode active material layer 120 may include a plurality of first pores, and the second negative electrode active material layer 130 may include a plurality of second pores.

[0092] For example, the major axis ratio of the first pores may be an average of the major axis ratio values measured for each of the plurality of first pores by XRM. For example, the major axis ratio of the second pores may be an average of the major axis ratio values measured for each of the plurality of second pores by XRM.

[0093] 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 may be 1.4 to 1.8 in some embodiments.

[0094] [Formula 3]

[0095] First porosity (%) = (VP1 / VL1) * 100

[0096] [Formula 4]

[0097] Second porosity (%) = (VP2 / VL2) * 100

[0098] In Formulas 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.

[0099] For example, VL1, VP1, VL2, and VP2 can be measured by XRM.

[0100] For example, VL1 can 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 can be the total volume of the second negative electrode active material layer 130 including the total volume of the plurality of second pores.

[0101] Within the porosity range, the structural stability can be improved within an appropriate range by the first negative electrode active material layer 120, and the fast charging characteristics and output characteristics can be improved by the second negative electrode active material layer 130.

[0102] For example, since the second negative electrode active material layer 130 has greater porosity than the first negative electrode active material layer 120, the structural stability and fast charging life characteristics can be improved simultaneously, and the energy density can be improved or maintained.

[0103] For example, XRM can be used to obtain 3D modeling images of the samples of the negative electrode active material layers 120 and 130. The first porosity and the second porosity can be measured by analyzing the 3D modeling images with analysis software.

[0104] For example, the first porosity can be measured in a region of the first negative electrode active material layer 120 that is more than about 10 μm away from the negative electrode current collector 110. For example, the second porosity can be measured in a region that is more than about 10 μm away from the outermost surface of the second negative electrode active material layer 130. Thereby, the measurement accuracy can be improved and the reliability can be enhanced.

[0105] In some embodiments, the first porosity can be 15% to 25%. Within this range, the adhesion between the first negative electrode active material layer 120 and the negative electrode current collector 110 is improved and the capacity characteristics can be maintained or improved.

[0106] In some embodiments, the second porosity may be from 25% to 40%. Within this range, the fast charging performance and output characteristics of the second negative electrode active material layer 130 are improved and the energy density can be maintained or improved.

[0107] 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 portion. Thereby, the output characteristics and life characteristics of the negative electrode 100 can be improved.

[0108] According to one embodiment, the carbon coating may include amorphous carbon. Thereby, the structural stability of natural graphite can be further improved.

[0109] In some embodiments, the first Raman peak height ratio defined by the following formula 5 of the first negative electrode active material layer may be 2.5 to 3.6 times the second Raman peak height ratio defined by the following formula 6 of the second negative electrode active material layer 130. Within this range, the amorphous characteristics of the first negative electrode active material layer 120 and the second negative electrode active material layer 130 can be appropriately adjusted, thereby improving the life characteristics, fast charging characteristics, and output characteristics.

[0110] [Formula 5]

[0111] First Raman peak height ratio = ID1 / IG1

[0112] [Formula 6]

[0113] Second Raman peak height ratio = ID2 / IG2

[0114] In Formulas 5 and 6, ID1 is the maximum height of the peak within the wavenumber range of 1300 cm -1 to 1500 cm -1 of the Raman spectrum of the first negative electrode active material layer 120 (for example, the D band of the Raman spectrum). IG1 is the maximum height of the peak within the wavenumber range of 1500 cm -1 to 1700 cm -1 of the Raman spectrum of the first negative electrode active material layer 120 (for example, the G band of the Raman spectrum). ID2 is the maximum height of the peak within the wavenumber range of 1300 cm -1 to 1500 cm -1 of the Raman spectrum of the second negative electrode active material layer 130. IG2 is the maximum height of the peak within the wavenumber range of 1500 cm -1 to 1700 cm -1 of the Raman spectrum of the second negative electrode active material layer 130.

[0115] For example, the first Raman peak height ratio and the second Raman peak height ratio can represent the degree of amorphousness. For example, the higher the first Raman peak height ratio and the second Raman peak height ratio, the higher the amorphous characteristics of the first negative electrode active material layer 120 and the second negative electrode active material layer 130 can be.

[0116] In some embodiments, the first Raman peak height ratio can be from 0.25 to 0.6. Within this range, cracking (crack) of the first negative electrode active material layer 120 can be suppressed and excessive reduction of crystallinity can be suppressed.

[0117] In some embodiments, the second Raman peak height ratio can be from 0.03 to 0.2. Within this range, the resistance of the negative electrode 100 decreases and stability can be improved.

[0118] Figure 2 and Figure 3 are a plan view and a cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. For example, Figure 3 is a cross-sectional view taken along the I-I' line of Figure 2 in the thickness direction.

[0119] Figure 2 and Figure 3 The structures shown are illustrated for convenience of explanation, and the structure of the lithium secondary battery according to the embodiments of the present disclosure is not limited thereto.

[0120] Referring to Figure 2 and Figure 3 , the lithium secondary battery may include the negative electrode 100 described above and a positive electrode 150 configured to face the negative electrode 100.

[0121] 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.

[0122] 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 from 10 μm to 50 μm.

[0123] 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 inserting and extracting lithium ions.

[0124] 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).

[0125] 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.

[0126] [Chemical Formula 1]

[0127] Li x Ni a M b O 2+z

[0128] In Chemical Formula 1, 0.9 ≤ x ≤ 1.2, 0.5 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.5, and -0.5 ≤ z ≤ 0.1. As described above, M may include Co, Mn, and / or Al.

[0129] The bonding relationship included in the layered structure or the crystal structure of the positive electrode active material represented by Chemical Formula 1 does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn may be used together with Ni as the main active elements of the positive electrode active material. The provision of Chemical Formula 1 is for expressing the bonding relationship of the main active elements and should be understood to include the introduction and substitution of additional elements.

[0130] In one embodiment, an auxiliary element for enhancing the chemical stability of the positive electrode active material or the layered structure / crystal structure may be further included on the basis of the main active elements. 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.

[0131] 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 be used, for example, like Al, as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn.

[0132] For example, 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 1-1.

[0133] [Chemical Formula 1-1]

[0134] Li x Ni a M1 b1 M2 b2 O 2+z

[0135] In Chemical Formula 1-1, M1 may include Co, Mn, and / or Al. M2 may include the above-mentioned auxiliary elements. In Chemical Formula 1-1, 0.9 ≤ x ≤ 1.2, 0.5 ≤ a ≤ 0.99, 0.01 ≤ b1 + b2 ≤ 0.5, and -0.5 ≤ z ≤ 0.1.

[0136] 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 auxiliary element may be used as the coating element or the doping element. For example, one or more combinations of the above elements may be used alone as the coating element or the doping element.

[0137] The coating element or the doping element may be present on the surface of the lithium nickel metal oxide particles or may penetrate through the surface of the lithium nickel metal oxide particles and be included in the bonding structure shown in Chemical Formula 1 or Chemical Formula 1-1.

[0138] 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.

[0139] Ni may be provided as a transition metal related to the output and capacity of the lithium secondary battery. Therefore, by using a high-nickel (High-Ni) composition for the positive electrode active material as described above, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0140] 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. According to an exemplary embodiment, not only the conductivity can be maintained by including Co, but also the life stability and capacity retention characteristics can be improved by Mn.

[0141] The content of Ni in the NCM-based lithium oxide (for example, the mole fraction of Ni in the total moles of nickel, cobalt, and manganese) may be 0.5 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.

[0142] In some embodiments, the positive electrode active material may also 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) active material (for example, LiFePO4).

[0143] In some embodiments, the positive electrode active material may include, for example, a lithium-rich layered oxide (LLO) / over-lithiated oxide (OLO) active material having a chemical structure or crystal structure represented by Chemical Formula 2, an Mn-rich active material, a Co-less active material, and the like. These may be used alone or in combination of two or more.

[0144] [Chemical Formula 2]

[0145] p[Li2MnO3]·(1-p)[Li q JO2]

[0146] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0147] 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 160 and then dried and rolled to form the positive electrode active material layer 170. The coating may include processes such as gravure coating, slot die coating, multi-layer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, and the like. The positive electrode active material layer 170 may further include a binder and may selectively further include a conductive material, a thickening agent, and the like.

[0148] Solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran may be used.

[0149] The binder may include polyvinylidene fluoride (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.

[0150] In one embodiment, a PVDF series 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 170 can be reduced, and the amount of the positive electrode active material can be relatively increased. Thereby, the output characteristics and capacity characteristics of the secondary battery can be improved.

[0151] The conductive material may be added to improve the conductivity of the positive electrode active material layer 170 and / or the mobility of lithium ions or electrons. For example, the conductive material may include carbon series 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 series conductive materials including perovskite substances such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3. These may be used alone or in combination of two or more.

[0152] The positive electrode paste may further include a thickener and / or a dispersant, etc. In one embodiment, the positive electrode paste may include a thickener such as carboxymethyl cellulose (CMC).

[0153] A first negative electrode active material layer 120 may be formed on at least one surface of the 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.

[0154] The above-mentioned first negative electrode active material can be mixed in a solvent to prepare a first negative electrode paste. The first negative electrode paste can be coated / deposited on at least one surface of the negative electrode current collector 110 and then dried and rolled to manufacture the first negative electrode active material layer 120. The coating can include processes such as gravure coating, slot die coating, multi-layer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, casting, etc.

[0155] The above-mentioned second negative electrode active material can be mixed in a solvent to prepare a second negative electrode paste. The second negative electrode paste can be coated / deposited on the first negative electrode active material layer 120 and then dried and rolled to manufacture the second negative electrode active material layer 130. The coating can be carried out by using a process substantially the same as the above coating process of the first negative electrode active material layer 120.

[0156] The first negative electrode active material layer 120 and the second negative electrode active material layer 130 can further include a binder, and can selectively further include a conductive material, a thickening agent, etc.

[0157] The solvent contained in the negative electrode paste can include water, pure water, deionized water, distilled water, ethanol, isopropyl alcohol, methanol, acetone, n-propanol, and tert-butanol, etc. These solvents can be used alone or in combination of two or more.

[0158] The above substances can be used as the binder, conductive material, and thickening agent when manufacturing the positive electrode 150.

[0159] In some embodiments, a styrene-butadiene-rubber (SBR) based binder, carboxymethyl cellulose (CMC), polyacrylic acid based binder, poly(3,4-ethylenedioxythiophene) (PEDOT) based binder, etc. can be used as the negative electrode binder. These can be used alone or in combination of two or more.

[0160] In an exemplary embodiment, a separator 140 can be disposed between the positive electrode 150 and the negative electrode 100. The separator 140 can be configured to prevent an electrical short circuit between the positive electrode 150 and the negative electrode 100 and allow ion flow. For example, the thickness of the separator can be 10 μm to 20 μm.

[0161] For example, the separator 140 may include a porous polymer film or a porous non-woven fabric.

[0162] The porous polymer film 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.

[0163] The porous non-woven fabric may include high melting point glass fibers, polyethylene terephthalate fibers, etc.

[0164] The separator 140 may also include a ceramic-based material. For example, inorganic particles may be coated on or dispersed in the polymer film to improve heat resistance.

[0165] The separator 140 may have a single-layer or multi-layer structure including the above polymer film and / or non-woven fabric.

[0166] According to an exemplary embodiment, an electrode unit is defined by a positive electrode 150, a negative electrode 100, and a separator 140, and a plurality of electrode units 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 by winding, stacking, z-folding, stack-folding, etc.

[0167] The electrode assembly 180 may be accommodated in a case 190 together with an electrolyte to form a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte may be used as the electrolyte.

[0168] The non-aqueous electrolyte includes a lithium salt as an electrolyte and an organic solvent. The lithium salt is represented, for example, as Li + X - , and as the negative ion (X - ) of the lithium salt, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 -, (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - etc.

[0169] 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, ethylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (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, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc. These can be used alone or in combination of two or more.

[0170] The non-aqueous electrolyte may further include additives. The additives may include, for example, cyclic carbonate compounds, fluorinated carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc. These can be used alone or in combination of two or more.

[0171] The cyclic carbonate compounds may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0172] The fluorinated cyclic carbonate compounds may include fluoroehtylenecarbonate (FEC), etc.

[0173] The sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0174] The cyclic sulfate compounds may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0175] The cyclic sulfite compounds may include ethylene sulfite, buthylene sulfite, etc.

[0176] The phosphate compounds may include lithium difluoro bis-oxalatophosphate, lithium difluoro phosphate, etc.

[0177] The borate compounds may include lithium bis(oxalate) borate, etc.

[0178] In some embodiments, a solid electrolyte may also be used to replace the above non-aqueous electrolyte. In this case, the lithium secondary battery may be manufactured in the form of an all-solid-state battery. Additionally, a solid electrolyte layer may be disposed between the positive electrode 150 and the negative electrode 100 to replace the above separator 140.

[0179] The solid electrolyte may include a sulfide-based electrolyte. As non-limiting examples, 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 (where m and n are positive numbers, and Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (where p and q are positive numbers, and M is P, Si, Ge, B, Al, Ga or In), Li7-xPS 6- 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.

[0180] In one embodiment, the solid electrolyte may also include oxide-based amorphous solid electrolytes such as Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0181] As Figure 2 and Figure 3 shown, each electrode tab (positive electrode tab and negative electrode tab) may protrude from the positive electrode current collector 160 and the negative electrode current collector 110 belonging to each electrode unit and extend to one side of the housing 190. The electrode tab may be welded to the one side of the housing 190 to form electrode leads (positive electrode lead 157 and negative electrode lead 107) extending or exposed to the outside of the housing 190.

[0182] The lithium secondary battery may be manufactured, for example, in a cylindrical, rectangular, pouch-type or coin-type using a can.

[0183] The embodiments of the present disclosure will be further described below with reference to specific experimental examples. The experimental examples include examples and comparative examples that merely illustrate the present disclosure and do not limit the scope of the appended claims. It will be obvious to those of ordinary skill in the art that various changes and modifications can be made to the examples within the scope and technical concept of the present disclosure, and these variations and modifications are naturally within the scope of the appended claims.

[0184] Examples 1 to 12, Comparative Examples 6 and 7

[0185] (1) Manufacturing the negative electrode

[0186] 1) Manufacturing the first negative electrode active material layer

[0187] Prepare a first negative electrode paste by mixing 93.4% by weight of natural graphite, 3% by weight of artificial graphite as a conductive material, 2.4% by weight of styrene-butadiene rubber (SBR) as a binder, and 1.2% by weight of carboxymethyl cellulose (CMC) as a thickener.

[0188] Coat the first negative electrode paste on a copper current collector and dry and roll it to form a first negative electrode active material layer.

[0189] 2) Manufacturing the second negative electrode active material layer

[0190] Prepare a second negative electrode paste by mixing 95.4% by weight of artificial graphite, 3% by weight of artificial graphite as a conductive material, 0.4% by weight of styrene-butadiene rubber (SBR) as a binder, and 1.2% by weight of carboxymethyl cellulose (CMC) as a thickener.

[0191] Coat the second negative electrode paste on the first negative electrode active material layer and dry and roll it to form a negative electrode including a second negative electrode active material layer.

[0192] During the formation of the first negative electrode active material layer and the second negative electrode active material layer, a negative electrode was manufactured by comprehensively adjusting variables such as rolling time, pressure, and loading amount so that the first pore aspect ratio, the second pore aspect ratio, the first porosity, the second porosity, the first Raman peak height ratio, and the second Raman peak height ratio were adjusted as shown in Tables 1 and 2 below.

[0193] (2) Manufacturing a lithium half-cell

[0194] Manufacture a lithium half-cell including the negative electrode and using lithium metal as the counter electrode (positive electrode).

[0195] Specifically, a lithium coin half-cell of CR2016 (diameter 20 mm, thickness 1.6 mm) specification was constructed by inserting a separator (polyethylene, thickness 20 μm) between the negative electrode and lithium metal (thickness 1 mm).

[0196] The lithium metal / separator / negative electrode assembly was placed in a coin cell plate, and after injecting the electrolyte, the cap was covered and clamped. The electrolyte used was a substance obtained by forming a 1 M LiPF6 solution with a mixed solvent of EC / EMC (3:7; volume ratio) and adding 2.0% by volume of fluoroethylene carbonate (FEC) to the total volume of the electrolyte. After clamping, it was impregnated for 3 h to 24 h, and then charged and discharged for three cycles at 0.1 C (charging condition: CC-CV 0.1 C 0.01 V 0.01 C cut-off (CUT-OFF), discharging condition: CC 0.1 C 1.5 V cut-off (CUT-OFF)).

[0197] Comparative Example 1

[0198] A negative electrode and a lithium half-cell were fabricated in the same manner as in Example 1, except that an equal amount of artificial graphite was used instead of natural graphite in the first negative electrode active material layer.

[0199] Comparative Example 2

[0200] A negative electrode and a lithium half-cell were fabricated in the same manner as in Example 1, except that the first negative electrode active material layer was not formed and the second negative electrode active material layer was directly formed on the copper current collector.

[0201] Comparative Example 3

[0202] A negative electrode and a lithium half-cell were fabricated in the same manner as in Example 1, except that the first negative electrode active material layer was not formed, the second negative electrode active material layer was directly formed on the copper current collector, and an equal amount of natural graphite was used instead of artificial graphite in the second negative electrode active material layer.

[0203] Comparative Example 4

[0204] A negative electrode and a lithium half-cell were fabricated in the same manner as in Example 1, except that an equal amount of natural graphite was used instead of artificial graphite in the second negative electrode active material layer.

[0205] Comparative Example 5

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

[0207] Experimental Example

[0208] (1) Measuring the first pore major axis ratio, the second pore major axis ratio, the first porosity, and the second porosity

[0209] Samples were prepared by cutting the negative electrodes fabricated according to the above-described examples and comparative examples. Portions of the samples other than regions with a thickness of approximately 10 μm adjacent to the copper current collector in the first negative electrode active material layer and regions with a thickness of approximately 10 μm adjacent to the outer surface in the second negative electrode active material layer were analyzed.

[0210] The samples were introduced into an XRM (Zeiss Xradia 620 versa, manufactured by Zeiss) to obtain 3D modeling images.

[0211] The XRM measurement conditions were as follows:

[0212] i) Source condition: 50 kV, 4.5 W

[0213] ii) Voxel size: 300 nm

[0214] The lengths in the first direction, second direction, and third direction of the plurality of first pores included in the first negative electrode active material layer and the plurality of second pores included in the second negative electrode active material layer were measured by analyzing the 3D modeling images using analysis software (Matdict Material Characterization, manufactured by GeoDict Software).

[0215] The ratios (PX1, PX2) of the length in the first direction to the sum of the lengths in the first direction, second direction, and third direction were calculated.

[0216] The ratios (PZ1, PZ2) of the length in the third direction to the sum of the lengths in the first direction, second direction, and third direction were calculated.

[0217] The values of the aspect ratios of the first pores were calculated by substituting the PX1 and PZ1 values of the plurality of first pores into Equation 1, and the average value of the aspect ratios of the first pores was used as the aspect ratio of the first pores for evaluation.

[0218] The PX2 and PZ2 values of multiple second pores were respectively substituted into Equation 2 to calculate the aspect ratio values of the second pores, and the average of the aspect ratio values of the second pores was used as the aspect ratio of the second pores and evaluated.

[0219] The difference between the aspect ratio of the first pore and the aspect ratio of the second pore was converted to an absolute value.

[0220] The first porosity of the first negative electrode active material layer and the second porosity of the second negative electrode active material layer were measured by analyzing the 3D modeling image with the analysis software.

[0221] The ratio of the second porosity to the first porosity was calculated.

[0222] (2) Measuring the first Raman peak height ratio and the second Raman peak height ratio

[0223] Samples were prepared by cutting the negative electrodes manufactured according to the above-mentioned examples and comparative examples.

[0224] The second Raman peak height ratio was measured for the second negative electrode active material layer, which is the outermost layer of the sample, using a 532 nm Laser Raman Spectroscopy (model: Invia, manufacturer: RENISHAW).

[0225] The measurement method of the specific Raman analyzer is as follows:

[0226] i) Turn on the power of the Raman analyzer.

[0227] ii) Open the Spectral acquisition setup window.

[0228] iii) Select 'Static' as the Grating Scan Type and enter 1000 (RamanShift(cm -1 )) as the central value.

[0229] iv) In the Configuration, select 532nm edge as the Laser, select 1800 / mm (vis) as the Grating, and select Renishaw 1024 StramLine CCD as the Detector.

[0230] v) In the acquisition condition settings, set the exposure time ( / s) to 10, the objective to 50, the accumulation to 5, and the laser power ( / %) to 10.

[0231] vi) Place the sample on the sample stage and confirm the measurement site, then obtain the Raman spectrum of the sample.

[0232] In the Raman spectrum, the peak intensity ID2 of the band with a wavenumber of 1300 cm -1 to 1500 cm -1 (e.g., D band) and the peak intensity IG2 of the band with a wavenumber of 1500 cm -1 to 1700 cm -1 (e.g., G band) were measured. The measured peak intensities were used in Equation 6 to calculate the second Raman peak height ratio.

[0233] The second negative electrode active material layer was partially removed by repeatedly pasting and peeling 3M tape on the upper surface of the sample, and the first Raman peak height ratio was measured for the first negative electrode active material layer with the second negative electrode active material layer partially removed using the same equipment and the same method as for measuring the second Raman peak height ratio.

[0234] In the Raman spectrum, the peak intensity ID1 of the band with a wavenumber of 1300 cm -1 to 1500 cm -1 (e.g., D band) and the peak intensity IG1 of the band with a wavenumber of 1500 cm -1 to 1700 cm -1 (e.g., G band) were measured. The measured peak intensities were used in Equation 5 to calculate the first Raman peak height ratio.

[0235] The multiple of the first Raman peak height ratio relative to the second Raman peak height ratio was calculated.

[0236] (3) Evaluating the capacity retention rate during fast charging

[0237] The lithium half-cells fabricated according to the described examples and comparative examples were charged at a charging rate (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 in a step charging manner until the depth of discharge (DOD) reached 77.2% within 20 minutes, and then discharged at 1C. The rapid charging evaluation was carried out by repeating the cycle of the above charging and discharging. After setting a 10-minute waiting time between charge-discharge cycles and repeating 300 cycles, the discharge capacity after 300 cycles was divided by the discharge capacity after one cycle and multiplied by 100 to evaluate the capacity retention rate.

[0238] (4) Evaluating the increase rate of the resistance (DCIR)

[0239] The lithium half-cells fabricated according to the above examples and comparative examples were repeatedly charged and discharged in the same method as in Experimental Example (3) to measure the resistance (DCIR).

[0240] After one cycle and 300 cycles, the discharged lithium half-cells were charged according to the rapid charging conditions of Experimental Example (3), discharged at 0.3C until the depth of discharge (DOD) reached 50%, and then discharged at 1C for 30 seconds. The resistance (DCIR) was calculated by measuring the voltage (V) decreased within 10 seconds during the discharge.

[0241] The resistance after 300 cycles was divided by the resistance after one cycle and multiplied by 100 to evaluate the resistance increase rate.

[0242] The measurement and evaluation results are shown in Table 1 and Table 2 below.

[0243]

Table 1

[0244]

[0245]

Table 2

[0246]

[0247] Referring to Table 1 and Table 2, compared with the comparative examples, in the examples where the difference between the first pore major axis ratio and the second pore major axis ratio is 0.5 to 3.0, the rapid charging capacity retention rate is improved and the resistance increase rate is reduced.

[0248] In Examples 7 and 8 where the ratio of the second porosity to the first porosity exceeds 1.2 to 2.0, the rapid charging capacity retention rate decreases relatively and the resistance increase rate increases relatively.

[0249] In Examples 11 and 12 where the ratio of the height of the first Raman peak exceeds 2.5 to 3.6 times the ratio of the height of the second Raman peak, the rapid charging capacity retention rate decreases relatively, and the resistance increase rate increases relatively.

[0250] Compared with the examples, in Comparative Example 1 where only artificial graphite is included in the first negative electrode active material layer and the second negative electrode active material layer, and in Comparative Example 4 where only natural graphite is included in the first negative electrode active material layer and the second negative electrode active material layer, the rapid charging capacity retention rate decreases, and the resistance increase rate increases.

[0251] Compared with the examples, in Comparative Example 5 where artificial graphite is included in the first negative electrode active material layer and natural graphite is included in the second negative electrode active material layer, the rapid charging capacity retention rate decreases, and the resistance increase rate increases.

Claims

1. A negative electrode for a lithium secondary battery, comprising: Negative current collector: a first negative electrode active material layer formed on at least one side of the negative electrode current collector and comprising first pores; and The second negative electrode active material layer is formed on the first negative electrode active material layer and includes artificial graphite and second pores. The difference between the first pore aspect ratio defined by the following formula 1 and the second pore aspect ratio defined by the following formula 2 is 0.5 to 3.0, [Formula 1] The first pore aspect ratio = PZ1 / PX1 [Formula 2] Second pore aspect ratio = PZ2 / PX2 In Formula 1 and Formula 2, PX1 is a ratio of the length of the first pore in the first direction measured by a 3D X-ray microscope to the sum of the length in the first direction, the length in the second direction perpendicular to the first direction on a plane, and the length in the third direction perpendicular to the first direction and the second direction of the first pore in the first negative electrode active material layer. PZ1 is a ratio of the length of the first pore in the third direction to the sum of the length in the first direction, the length in the second direction, and the length in the third direction, measured by a 3D X-ray microscope on the first negative electrode active material layer. PX2 is a ratio of the length of the second pore in the first direction to the sum of the length in the first direction, the length in the second direction, and the length in the third direction measured by a 3D X-ray microscope for the second negative electrode active material layer, PZ2 is a ratio of the length of the second pore in the third direction to the sum of the length in the first direction, the length in the second direction, and the length in the third direction, measured by a 3D X-ray microscope on the second negative electrode active material layer. 2 . The negative electrode for a lithium secondary battery according to claim 1 , wherein a difference between the first pore aspect ratio and the second pore aspect ratio is 1.0 to 2.

5. 3 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the second pore aspect ratio is greater than the first pore aspect ratio.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein the first direction represents the extending direction of the longer side of the negative electrode when viewed in a planar direction, the second direction represents the extending direction of the shorter side of the negative electrode when viewed in a planar direction, and the third direction represents the thickness direction of the negative electrode. 5 . The 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. 6 . The negative electrode for a lithium secondary battery according to claim 5 , wherein the first pore aspect ratio is an average of the first pore aspect ratios of the plurality of first pores, and the second pore aspect ratio is an average of the second pore aspect ratios of the plurality of second pores.

7. The negative electrode for a lithium secondary battery according to claim 5, wherein a ratio of a second porosity of the second negative electrode active material layer defined by the following formula 4 to a first porosity of the first negative electrode active material layer defined by the following formula 3 is 1.2 to 2.0, [Formula 3] First porosity (%) = (VP1 / VL1)*100 [Formula 4] Second porosity (%) = (VP2 / VL2)*100 In Formula 3 and Formula 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. 8 . The negative electrode for a lithium secondary battery according to claim 7 , wherein the first porosity is 15% to 25%. 9 . The negative electrode for a lithium secondary battery according to claim 7 , wherein the second porosity is 25% to 40%. 10 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the first negative electrode active material layer comprises natural graphite. 11 . The negative electrode for a lithium secondary battery according to claim 10 , wherein the natural graphite includes a carbon coating layer formed on a surface thereof. 12 . The negative electrode for a lithium secondary battery according to claim 11 , wherein the carbon coating layer comprises amorphous carbon.

13. The negative electrode for a lithium secondary battery according to claim 1, wherein a first Raman peak height ratio defined by the following formula 5 of the first negative electrode active material layer is 2.5 to 3.6 times a second Raman peak height ratio defined by the following formula 6 of the second negative electrode active material layer, [Formula 5] The first Raman peak height ratio = ID1 / IG1 [Formula 6] The second Raman peak height ratio = ID2 / IG2 In Formula 5 and Formula 6, ID1 is the Raman spectrum of the first negative electrode active material layer at 1300 cm -1 Up to 1500cm -1 IG1 is the maximum peak height within the wavenumber range of 1500 cm-1 of the Raman spectrum of the first negative electrode active material layer. -1 Up to 1700cm -1 The maximum height of the peak in the wave number range is ID2 is the 1300 cm-1 Raman spectrum of the second negative electrode active material layer. -1 Up to 1500cm -1 IG2 is the maximum peak height within the wavenumber range of 1500 cm-1 of the Raman spectrum of the second negative electrode active material layer. -1 Up to 1700cm -1 The maximum height of the peak within the wavenumber range. 14 . The negative electrode for a lithium secondary battery according to claim 13 , wherein the first Raman peak height ratio is 0.25 to 0.

6. 15 . The negative electrode for a lithium secondary battery according to claim 13 , wherein the second Raman peak height ratio is 0.03 to 0.

2.

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

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