Anode for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide an anode for a lithium secondary battery having improved life-span properties, and a lithium secondary battery including the same.SOLUTION: An anode for a lithium secondary battery includes: an anode current collector; a first anode active material layer disposed on at least one surface of the anode current collector and including a first anode active material including a graphite-based active material; and a second anode active material layer disposed on the first anode active material layer and including a second anode active material including composite particles including silicon, where the tortuosity (T2) of the second anode active material layer is 2.32 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[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.

Background Art

[0002] A secondary battery is a battery that can be repeatedly charged and discharged, and is widely applied as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook computers with the development of the information communication and display industries. Recently, a battery pack including a secondary battery has also been developed and applied as a power source for environmentally friendly vehicles such as electric vehicles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc. Among them, lithium secondary batteries have been actively developed and applied because of their high operating voltage and energy density per unit weight, and advantages in charging speed and weight reduction.

[0004] Recently, while the application range of lithium secondary batteries is expanding, the development of lithium secondary batteries with higher capacity and output is underway. 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 during rapid charging of the electrode may deteriorate.

Summary of the Invention

Problems to be Solved by the Invention

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

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

Means for Solving the Problems

[0008] The 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 disposed on at least one surface of the negative electrode current collector and containing a first negative electrode active material, and a second negative electrode active material layer disposed on the first negative electrode active material layer and containing a second negative electrode active material. The first negative electrode active material includes a graphite-based active material, the second negative electrode active material includes composite particles containing silicon, and the degree of curvature (T2) of the second negative electrode active material layer obtained by analysis with an X-ray microscope (XRM) is 2.32 or less.

[0009] In some embodiments, the degree of curvature (T2) of the second negative electrode active material layer can be defined by the following formula 1. [Formula 1] T2 = L P2 / L 2 In formula 1, L P2 is the average flow path length through which lithium ions pass when permeating the second negative electrode active material layer in the thickness direction, and L 2 is the thickness of the second negative electrode active material layer.

[0010] In some embodiments, the composite particles can include carbon-based particles and a silicon-containing coating formed on the surface of the carbon-based particles.

[0011] In some embodiments, the carbon-based particles can include at least one selected from the group consisting of activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fibers, carbon black, graphite, porous carbon, pyrolyzed cryogel, pyrolyzed xerogel, and pyrolyzed aerogel.

[0012] In some embodiments, the content of the composite particles relative to the total weight of the first negative electrode active material and the second negative electrode active material may be 2% by weight to 30% by weight.

[0013] In some embodiments, the content of the composite particles with respect to the total weight of the first negative electrode active material and the second negative electrode active material may be 4.5 wt% to 24 wt%.

[0014] In some embodiments, the second negative electrode active material may further include a graphite-based active material.

[0015] In some embodiments, the content of the composite particles with respect to the total weight of the second negative electrode active material may be 4 wt% to 40 wt%.

[0016] In some embodiments, the content of the composite particles with respect to the total weight of the second negative electrode active material may be 9 wt% to 40 wt%.

[0017] In some embodiments, the graphite-based active material may include at least one of artificial graphite and natural graphite.

[0018] In some embodiments, the degree of bending (T1) of the first negative electrode active material layer obtained by analysis with an X-ray microscope (XRM) may be greater than the degree of bending (T2) of the second negative electrode active material layer.

[0019] In some embodiments, the degree of bending (T1) of the first negative electrode active material layer can be defined by the following formula 2. [Formula 2] T1 = L P1 / L 1 In Formula 2, L P1 is the average flow path length through which lithium ions pass when permeating the first negative electrode active material layer in the thickness direction, and L 1 is the thickness of the first negative electrode active material layer.

[0020] In some embodiments, the degree of bending (T1) may be 2.34 to 3.0.

[0021] In some embodiments, the ratio of the degree of bending (T1) of the first negative electrode active material layer to the degree of bending (T2) of the second negative electrode active material layer may be 1.03 to 1.44.

[0022] In some embodiments, the first negative electrode active material may not include the composite particles.

[0023] In some embodiments, the first negative electrode active material layer may be disposed directly on the negative electrode current collector, and the second negative electrode active material layer may be disposed directly on the first negative electrode active material layer.

[0024] The lithium secondary battery according to an exemplary embodiment includes the negative electrode for a lithium secondary battery described above and a positive electrode disposed to face the negative electrode.

Advantages of the Invention

[0025] According to one embodiment of the present disclosure, the life characteristics during rapid charging can be improved.

[0026] According to one embodiment of the present disclosure, both the electron mobility and the lithium ion mobility in the negative electrode can be improved.

[0027] The negative electrode for a lithium secondary battery and the lithium secondary battery including the same according to the present disclosure can be widely applied in the fields of green technologies such as electric vehicles, battery charging stations, and other solar power generation and wind power generation using batteries. The negative electrode for a lithium secondary battery and the lithium secondary battery including the same according to the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, etc. for suppressing air pollution and greenhouse gas emissions to prevent climate change.

Brief Description of the Drawings

[0028]

Figure 1

Figure 2

Figure 3

Figure 4

[0029] Embodiments of the present disclosure provide a negative electrode for a lithium secondary battery including a negative electrode active material layer having a multilayer structure (hereinafter, may be abbreviated as "negative electrode"). Further, a lithium secondary battery including the negative electrode (hereinafter, may be abbreviated as "secondary battery") is provided.

[0030] Hereinafter, embodiments of the present disclosure will be described more specifically. However, these embodiments are merely illustrative of the present disclosure and do not limit the present disclosure.

[0031] FIG. 1 is a schematic cross-sectional view showing a negative electrode for a lithium secondary battery according to an exemplary embodiment.

[0032] 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.

[0033] 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, and the like. These can be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector 110 may be 5 μm to 50 μm.

[0034] The first negative electrode active material layer 120 including a first negative electrode active material containing a graphite-based active material can be disposed on at least one surface of the negative electrode current collector 110. According to one embodiment, the first negative electrode active material layer 120 can be in direct contact with the negative electrode current collector 110.

[0035] In some embodiments, the graphite-based active material can include artificial graphite and / or natural graphite. Thereby, the adhesion between the negative electrode current collector 110 and the first negative electrode active material layer 120 can be improved, and the electron mobility can be enhanced.

[0036] The content of the graphite-based active material with respect to the total weight of the first negative electrode active material 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.

[0037] The content of the graphite-based active material with respect to the total weight of the first negative electrode active material may be 99 wt% or less, 95 wt% or less, 90 wt% or less, or 85 wt% or less. In this case, the first negative electrode active material may further include a silicon-containing active material or the like.

[0038] In one embodiment, the first negative electrode active material can be substantially composed of the graphite-based active material.

[0039] In an exemplary embodiment, a second negative electrode active material layer 130 containing a composite particle can be disposed on the first negative electrode active material layer 120. According to one embodiment, the second negative electrode active material layer 130 can be in direct contact with the first negative electrode active material layer 120.

[0040] For example, the composite particle can include silicon (Si).

[0041] FIG. 2 is a schematic cross-sectional view showing a composite particle according to an exemplary embodiment.

[0042] In FIG. 2, for convenience of explanation, the shape of the composite particle is schematically shown, but the structure and shape of the composite particle of the present disclosure are not limited to those shown in FIG. 2. For example, the cross-section of the carbon-based particle may be randomly changed from circular. Also, the silicon-containing coating may be partially formed on the pores and surface of the carbon-based particle, or may be formed in a plurality of discontinuous islands or patterns.

[0043] Referring to FIG. 2, the composite particles 50 can include carbon-based particles 60 containing a plurality of pores 65 and a silicon-containing coating 70.

[0044] According to some embodiments, the pores 65 of the carbon-based particles 60 can relieve the volume expansion of silicon contained in the silicon-containing coating 70. Thereby, while adopting the relatively high capacity characteristics of silicon, cracks due to the difference between the volume expansion rate of carbon (for example, about 150% by volume or less) and the volume expansion rate of silicon (for example, about 400% by volume or more) during charge and discharge can be prevented. Therefore, gas generation due to the side reaction between the negative electrode active material and the electrolyte can be suppressed, and the life characteristics of the secondary battery can be improved.

[0045] The pores 65 of the carbon-based particles 60 can include a shape that indents from the outermost part of the carbon-based particles 60 into the inside of the carbon-based particles 60. For example, the pores 65 can include open pores that open to the outside of the carbon-based particles 60.

[0046] As used herein, the terms "surface of the carbon-based particles" and / or "surface of the carbon-based particles 60" can represent the outer surface 62 of the carbon-based particles 60, the inner surface 67 of the pores 65, or the outer surface 62 of the carbon-based particles 60 and the inner surface 67 of the pores 65. The inner surface 67 of the pores 65 can represent the surface of the pores 65 that indents into the inside of the carbon-based particles 60.

[0047] The silicon-containing coating 70 can be formed on at least a part of the outer surface 62 of the carbon-based particles 60. The silicon-containing coating 70 can be formed on at least a part of the inner surface 67 of the pores 65 of the carbon-based particles 60. The silicon-containing coating 70 can be formed on at least a part of the outer surface 62 of the carbon-based particles 60 and at least a part of the inner surface 67 of the pores 65.

[0048] In some embodiments, the carbon-based particles 60 can include activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fibers, carbon black, graphite, porous carbon, pyrolyzed cryogel, pyrolyzed xerogel, pyrolyzed aerogel, etc. These can be used alone or in combination of two or more.

[0049] In some embodiments, the carbon-based particles 60 can include an amorphous structure or a crystalline structure.

[0050] In some embodiments, the size of the pores 65 of the carbon-based particles 60 may be 0.1 nm to 20 nm, 0.5 nm to 15 nm, or 1 nm to 10 nm. Within this range, excessive deposition of silicon can be prevented, and the generation of cracks in the negative electrode active material during charge and discharge of the secondary battery can be further suppressed.

[0051] The size of the pores 65 can mean the diameter of the entrance of the pores 65 formed on the surface portion of the carbon-based particles 60.

[0052] In some embodiments, the silicon-containing coating 70 can include silicon. In one embodiment, the silicon-containing coating 70 can further include SiO x (0 < x < 2).

[0053] In one embodiment, the silicon-containing coating 70 may not include silicon carbide (SiC). Thereby, the capacity characteristics of the secondary battery can be improved. According to an exemplary embodiment, by adjusting the temperature and time during silicon deposition, the formation of silicon carbide can be suppressed.

[0054] In some embodiments, the second negative electrode active material may further include a graphite-based active material. The graphite-based active material may further include artificial graphite and / or natural graphite. The graphite-based active material can improve the life characteristics and structural stability of the negative electrode.

[0055] The content of the composite particles 50 with respect to the total weight of the second negative electrode active material (for example, the total weight of the plurality of composite particles 50 and the graphite-based active material) may be 3% by weight or more, 5% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more, 35% by weight or more, 40% by weight or more, or 45% by weight or more.

[0056] The content of the composite particles with respect to the total weight of the second negative electrode active material may be 90% by weight or less, 85% by weight or less, 80% by weight or less, 75% by weight or less, 70% by weight or less, 65% by weight or less, 60% by weight or less, 55% by weight or less, or 50% by weight or less.

[0057] In one embodiment, the second negative electrode active material can be substantially composed of the composite particles 50 and the graphite-based active material.

[0058] In an exemplary embodiment, the degree of bending (T2) of the second negative electrode active material layer 130 obtained by analysis with an X-ray microscope (XRM) may be 2.32 or less. In some embodiments, the degree of bending (T2) of the second negative electrode active material layer 130 may be 2.29 or less, or 2.09 or less. In some embodiments, the degree of bending (T2) may be 1 to 2.32, 1 to 2.29, or 1 to 2.09.

[0059] In some embodiments, the degree of bending (T2) can be defined by the following formula 1.

[0060] [Formula 1] T2 = L P2 / L 2

[0061] In Formula 1, L P2is the average flow path length through which lithium ions permeate in the thickness direction of the second negative electrode active material layer 130, and L 2 is the thickness of the second negative electrode active material layer 130. L P2 and L 2 may have the same unit.

[0062] In one embodiment, L P2 can represent the average distance of the path formed by connecting the pores contained in the second negative electrode active material layer 130.

[0063] As used herein, the term "thickness direction" can represent the thickness direction of each of the negative electrode current collector 110, the first negative electrode active material layer 120, and the second negative electrode active material layer 130, or the direction in which the negative electrode current collector 110, the first negative electrode active material layer 120, and the second negative electrode active material layer 130 are laminated.

[0064] For example, a 3D image can be obtained by the analysis of the X-ray microscope, and a 3D modeling image can be obtained by analysis software (e.g., Matdict Material Characterization, manufactured by GeoDict Software). Also, the tortuosity (T2) can be measured by the analysis software.

[0065] For example, the greater the tortuosity, the more complex the path formed by the pore structure in the negative electrode active material layer may become, or the number of bends may increase. Therefore, from the tortuosity, the movement path of the liquid (e.g., the electrolyte of the lithium secondary battery) in the negative electrode active material layer and the degree of diffusion of lithium ions can be estimated.

[0066] For example, the greater the tortuosity, the longer the movement path of lithium ions in the negative electrode active material layer may become. For example, the smaller the tortuosity, the easier the movement of lithium ions, and the output characteristics and life characteristics can be improved.

[0067] For example, tortuosity can represent the ratio of the actual migration distance of a substance permeating through the inside to the thickness of the negative electrode active material layer. For example, when the thicknesses of the electrode layers are equal, if the migration distance of lithium ions is relatively short, the tortuosity can become relatively small. In this case, the lithium ion mobility of the negative electrode active material layer increases, and the rapid charging performance can be improved.

[0068] Within the range of the tortuosity (T2), the lithium ion mobility of the second negative electrode active material layer 130 provided as the outermost layer of the negative electrode 100 can be improved. Thereby, lithium ions can be smoothly moved to the negative electrode current collector 110, and the life characteristics during rapid charging can be improved.

[0069] Theoretically, since the migration distance of lithium ions is equal to or greater than the thickness of the negative electrode active material layer, the tortuosity (T2) can be 1 or more.

[0070] In some embodiments, the tortuosity (T1) of the first negative electrode active material layer 120 obtained by X-ray microscope analysis may be greater than the tortuosity (T2) of the second negative electrode active material layer 130.

[0071] In some embodiments, the tortuosity (T1) can be defined by the following formula 2.

[0072] [Formula 2] T1 = L P1 / L 1

[0073] In Formula 2, L P1 is the average flow path length that lithium ions pass through when permeating through the first negative electrode active material layer 120 in the thickness direction, and L 1 is the thickness of the first negative electrode active material layer 120. L P1 and L 1 may have the same unit.

[0074] In one embodiment, L P1It can represent the average distance of the paths formed by connecting the pores included in the first negative electrode active material layer 120.

[0075] A 3D image can be obtained by the analysis of the X-ray microscope, and a 3D modeling image can be obtained by analysis software (e.g., Matdict Material Characterization, manufactured by GeoDict Software). Also, the tortuosity (T1) can be measured by the analysis software.

[0076] For example, 3D images of samples of the negative electrode active material layers 120, 130 can be obtained using an X-ray microscope (e.g., Zeiss Xradia 620 versa, manufactured by Zeiss). After analyzing the 3D image with analysis software (e.g., Matdict Material Characterization, manufactured by GeoDict Softerage) to obtain a 3D modeling image consisting of the negative electrode active material and the pore structure, the tortuosities (T1, T2) of the negative electrode active material layers 120, 130 can be measured.

[0077] By relatively greatly adjusting the tortuosity (T1) of the first negative electrode active material layer 120 adjacent to the negative electrode current collector 110, the contact between the first negative electrode active material and the conductive material can be increased around the negative electrode current collector 110, and the electron transfer path can be increased. Thereby, the mobility of electrons by the negative electrode active material can be improved.

[0078] By relatively slightly adjusting the tortuosity (T2) of the second negative electrode active material layer 130, the mobility of lithium ions toward the negative electrode current collector 110 can be improved. Thereby, both the electron mobility and the lithium ion mobility in the negative electrode 100 can be improved.

[0079] In some embodiments, the tortuosity (T1) of the first negative electrode active material layer 120 may be 2.34 to 3.0. In the above range, the electron mobility is improved around the negative electrode current collector 110, and appropriate lithium ion mobility can be maintained.

[0080]

[0080] In some embodiments, the ratio of the degree of bending (T1) of the first negative electrode active material layer 120 to the degree of bending (T2) of the second negative electrode active material layer 130 may be 1.0 to 1.45, 1.01 to 1.44, 1.03 to 1.44, 1.2 to 1.44, or 1.24 to 1.44. Within the above range, both the electron mobility and ion mobility of the negative electrode with the multilayer structure can be improved, and the capacity retention rate can be enhanced.

[0081]

[0080] For example, by the above-described analysis method, the degree of bending (T1) of the first negative electrode active material layer 120 and the degree of bending (T2) of the second negative electrode active material layer can be measured respectively.

[0082]

[0080] In some embodiments, the degree of bending (T1) and / or the degree of bending (T2) can be adjusted according to the content of the composite particles 50 with respect to the total weight of the first negative electrode active material and the second negative electrode active material, the content of the composite particles 50 with respect to the total weight of the second negative electrode active material, the types of the first negative electrode active material and the second negative electrode active material, and the like.

[0083]

[0080] The degree of bending (T1) and / or the degree of bending (T2) can also be adjusted according to the formation conditions of the composite particles 50. For example, the degree of bending (T1) and / or the degree of bending (T2) can also be adjusted according to the porosity, pore size, density, and firing conditions of the carbon-based particles contained in the composite particles 50; the thickness, density, and heat treatment conditions of the silicon-containing coating, and the like.

[0084]

[0080] According to one embodiment, the degree of bending (T1) and / or the degree of bending (T2) can be adjusted according to the presence or absence of magnetic orientation and the conditions of magnetic orientation by applying a magnetic field during the manufacture of the negative electrode 100.

[0085]

[0080] For example, by using the composite particles 50, the capacity characteristics can be improved and the degree of bending (T2) can be reduced to improve the rapid filling performance.

[0086] In some embodiments, the content of the composite particles 50 with respect to the total weight of the first negative electrode active material and the second negative electrode active material may be 2 wt% to 30 wt%. In one embodiment, the content of the composite particles 50 with respect to the total weight of the first negative electrode active material and the second negative electrode active material may be 4.5 wt% to 24 wt%. Within the above range, the life characteristics, output characteristics, and life characteristics during rapid charging can be improved.

[0087] In some embodiments, the content of the composite particles 50 with respect to the total weight of the second negative electrode active material may be 4 wt% to 40 wt%. In one embodiment, the content of the composite particles 50 with respect to the total weight of the second negative electrode active material may be 9 wt% to 40 wt%. Within the above range, the degree of bending (T2) of the second negative electrode active material layer 130 can be reduced. Thereby, the lithium ion mobility of the negative electrode 100 can be improved, and the life characteristics during rapid charging can be improved.

[0088] According to some embodiments, the first negative electrode active material may not contain the composite particles 50. Thereby, the proportion of the graphite-based active material in the first negative electrode active material layer 120 is increased, and the electron conductivity and structural stability of the negative electrode 100 can be improved.

[0089] According to some embodiments, the first negative electrode active material layer 120 can be directly disposed on the negative electrode current collector 110, and the second negative electrode active material layer 130 can be directly disposed on the first negative electrode active material layer 120.

[0090] FIG. 3 and FIG. 4 are a schematic plan view and a cross-sectional view showing a lithium secondary battery according to an exemplary embodiment, respectively. For example, FIG. 4 is a cross-sectional view taken along the thickness direction along "I-I'" in FIG. 3.

[0091] Referring to FIGS. 3 and 4, the lithium secondary battery can include the above-described negative electrode 100 and a positive electrode 150 disposed to face the negative electrode 100.

[0092] The positive electrode 150 can 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.

[0093] The positive electrode current collector 160 can include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector 160 can also include carbon, nickel, titanium, aluminum or stainless steel surface-treated with silver. For example, the thickness of the positive electrode current collector 160 may be 5 μm to 50 μm.

[0094] The positive electrode active material layer 170 can include a positive electrode active material. The positive electrode active material can include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0095] According to an exemplary embodiment, the positive electrode active material can include a lithium-nickel metal oxide. The lithium-nickel metal oxide can further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0096] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide can include a layered structure or crystal structure represented by the following Chemical Formula 1.

[0097] [Chemical Formula 1] Li x Ni a M b O 2+z

[0098] In Chemical Formula 1, 0.9 ≦ x ≦ 1.2, 0.6 ≦ a ≦ 0.99, 0.01 ≦ b ≦ 0.4, and -0.5 ≦ z ≦ 0.1 may be satisfied. As described above, M can include Co, Mn, and / or Al.

[0099] The chemical structure represented by Chemical Formula 1 shows the bonding relationships contained within the layered 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 be provided as the main active elements of the positive electrode active material together with Ni. Chemical Formula 1 is provided to represent the bonding relationships of the main active elements and should be understood as a formula that includes the introduction and substitution of additional elements.

[0100] In one embodiment, in addition to the main active elements, the positive electrode active material or the layered / crystal structure may further include auxiliary elements for improving the chemical stability. The auxiliary elements can be incorporated together within the layered / crystal structure to form bonds. Also in this case, it should be understood that they are included within the scope of the chemical structure represented by Chemical Formula 1.

[0101] The auxiliary elements can 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 elements can also act as auxiliary active elements that contribute to the capacity / output activity of the positive electrode active material together with Co or Mn, such as Al.

[0102] For example, the positive electrode active material or the lithium-nickel metal oxide can include a layered or crystal structure represented by the following Chemical Formula 1-1.

[0103] [Chemical Formula 1-1] Li x Ni a M1 b1 M2 b2 O 2+z

[0104] In Chemical Formula 1-1, M1 can include Co, Mn, and / or Al, and M2 can include the aforementioned auxiliary elements. In Chemical Formula 1-1, 0.9 ≦ x ≦ 1.2, 0.6 ≦ a ≦ 0.99, 0.01 ≦ b1 + b2 ≦ 0.4, and -0.5 ≦ z ≦ 0.1 may be satisfied.

[0105] The positive electrode active material can further include a coating element or a doping element. For example, an element substantially the same as or similar to the aforementioned auxiliary element can be used as the coating element or the doping element. For example, the aforementioned elements can be used alone or in combination of two or more as the coating element or the doping element.

[0106] The coating element or the doping element may be present on the surface of the lithium-nickel metal oxide particles, and may penetrate from the surface of the lithium-nickel metal oxide particles and be included in the bonding structure represented by Chemical Formula 1 or Chemical Formula 1-1.

[0107] The positive electrode active material can include a nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, an NCM-based lithium oxide with an increased nickel content can be used.

[0108] Ni can be provided as a transition metal related to the output and capacity of the lithium secondary battery. Thereby, by adopting the composition with a high content (High-Ni) as described above for the positive electrode active material, a positive electrode with a high capacity and a lithium secondary battery with a high capacity can be provided.

[0109] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or the secondary battery may relatively decrease, and the side reaction with the electrolyte may also increase. In contrast, according to an exemplary embodiment, by including Co, the electrical conductivity can be maintained, and by Mn, the life stability and capacity retention characteristics can be improved.

[0110] The content of Ni in the NCM-based lithium oxide (for example, the molar fraction of Ni in the total number of 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.

[0111] In some embodiments, the cathode 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-based (LFP) active material (for example, LiFePO 4 ).

[0112] In some embodiments, the cathode active material may include, for example, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide)-based active material, an Mn-rich-based active material, a Co-less-based active material, etc., having a chemical structure or crystal structure represented by Chemical Formula 2. These can be used alone or in combination of two or more.

[0113] [Chemical Formula 2] p[Li 2 MnO 3 ·(1-p)[Li q JO 2

[0114] In Chemical Formula 2, 0 < p < 1 and 0.9 ≤ q ≤ 1.2, and J can include at least one element of Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0115] ​The positive electrode active material can be mixed in a solvent to produce a positive electrode slurry. After coating the positive electrode slurry on at least one surface of the positive electrode current collector 160, it can be dried and rolled to produce the 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, casting, etc. The positive electrode active material layer 170 can further include a binder, and can selectively further include a conductive material, a thickener, etc.

[0116] As the solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used.

[0117] The binder can include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These can be used alone or in combination of two or more.

[0118] In one embodiment, a PVDF-based binder can be used as the positive electrode binder. In this case, the amount of the binder for forming 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.

[0119] The conductive material can be added to enhance the conductivity of the positive electrode active material layer 170 and / or the mobility of lithium ions or electrons. For example, the conductive material can include carbon-based conductive materials such as graphite, carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, VGCF (vapor-grown carbon fiber), carbon fibers, etc. and / or metals such as tin, tin oxide, titanium oxide, LaSrCoO 3 、LaSrMnO 3 and perovskite materials such as LaSrMnO can be included in the metal-based conductive material. These can be used alone or in combination of two or more.

[0120] The positive electrode slurry can further include a thickening agent and / or a dispersing agent, etc. In one embodiment, the positive electrode slurry can include a thickening agent such as carboxymethyl cellulose (CMC).

[0121] A first negative electrode active material layer 120 can be formed on at least one surface of the negative electrode current collector 110, and a second negative electrode active material layer 130 can be formed on the first negative electrode active material layer 120.

[0122] The first negative electrode active material described above can be mixed in a solvent to produce a first negative electrode slurry. After coating / vapor depositing the first negative electrode slurry on at least one surface of the negative electrode current collector 110, it can be dried and rolled to produce the 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, casting, etc.

[0123] The above-described second negative electrode active material can be mixed in a solvent to produce a second negative electrode slurry. After coating / vapor depositing the second negative electrode slurry on the first negative electrode active material layer 120, it can be dried and rolled to produce a second negative electrode active material layer 130. The coating method can include substantially the same type of method as the above-described coating method of the first negative electrode active material layer 120.

[0124] In one embodiment, the above-described first negative electrode slurry can be applied on at least one surface of the negative electrode current collector 110, and after applying the second negative electrode slurry on the first negative electrode slurry, it can be dried and rolled simultaneously.

[0125] The first and second negative electrode active material layers 120 and 130 can further include a binder, and can selectively further include a conductive material, a thickener, and the like.

[0126] Solvents included in the negative electrode slurry can include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, and the like. These can be used alone or in combination of two or more.

[0127] As the binder, conductive material, and thickener, the above-described substances that can be used during the manufacture of the positive electrode 150 can be used.

[0128] In some embodiments, as the negative electrode binder, a styrene-butadiene-rubber (SBR)-based binder, carboxymethyl cellulose (CMC), a polyacrylic acid-based binder, a poly(3,4-ethylenedioxythiophene) (PEDOT)-based binder, and the like can be used. These can be used alone or in combination of two or more.

[0129] In an exemplary embodiment, a separator 140 can be interposed 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 the flow of ions. For example, the thickness of the separator may be 10 μm to 20 μm.

[0130] For example, the separator 140 can include a porous polymer film or a porous nonwoven fabric.

[0131] The porous polymer film can include polyolefin-based polymers such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers. These can be used alone or in combination of two or more.

[0132] The porous nonwoven fabric can include high melting point glass fibers, polyethylene terephthalate fibers, and the like.

[0133] The separator 140 can also include a ceramic-based material. For example, inorganic particles can be coated on the polymer film or dispersed in the polymer film to improve heat resistance.

[0134] The separator 140 can have a single-layer or multi-layer structure including the aforementioned polymer film and / or nonwoven fabric.

[0135] According to an exemplary embodiment, an electrode cell is defined by a positive electrode 150, a negative electrode 100, and a separator 140, and a plurality of electrode cells can be stacked to form, for example, a jelly roll type electrode assembly 180. For example, the electrode assembly 180 can be formed by winding, stacking, Z-folding, stack-folding, etc. of the separator 140.

[0136] A lithium secondary battery can be defined by housing the electrode assembly 180 together with an electrolytic solution in a case 190. According to an exemplary embodiment, a non-aqueous electrolytic solution can be used as the electrolytic solution.

[0137] The non-aqueous electrolytic solution contains a lithium salt as an electrolyte and an organic solvent. The lithium salt is represented by, for example, Li + X - , and as the anion (X - ) of the lithium salt, F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , BF 4 - , ClO 4 - , PF 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , CF 3 SO 3- , CF 3 CF 2 SO 3 - , (CF 3 SO 2 ) 2 N - , (FSO 2 ) 2 N - , CF 3 CF 2 (CF 3 ) 2 CO - , (CF 3 SO 2 ) 2 CH - , (SF 5 ) 3 C - , (CF 3 SO 2 ) 3 C - , CF 3 (CF 2 ) 7 SO 3 - , CF 3 CO 2 - , CH 3 CO 2 - , SCN - , and (CF 3 CF 2 SO 2 ) 2 N - etc. can be mentioned.

[0138] Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite. These can be used alone or in combination of two or more.

[0139] The non-aqueous electrolyte can further contain an additive. The additive can include, for example, cyclic carbonate compounds, fluorine-substituted 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.

[0140] The cyclic carbonate compounds can include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0141] The fluorine-substituted carbonate compounds can include fluoroehtylene carbonate (FEC), etc.

[0142] The sultone compounds can include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0143] The cyclic sulfate compounds can include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0144] The cyclic sulfite compounds can include ethylene sulfite, butylene sulfite, etc.

[0145] The phosphate-based compound can include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, and the like.

[0146] The borate-based compound can include lithium bis(oxalate)borate and the like.

[0147] In some embodiments, a solid electrolyte can be used instead of the aforementioned non-aqueous electrolyte. In this case, the lithium secondary battery can be manufactured in the form of an all-solid-state battery. Also, a solid electrolyte layer may be disposed between the positive electrode 150 and the negative electrode 100 instead of the aforementioned separator 140.

[0148] The solid electrolyte can include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte is Li 2 S-P 2 S 5 、Li 2 S-P 2 S 5 -LiCl、Li 2 S-P 2 S 5 -LiBr、Li 2 S-P 2 S 5 -LiCl-LiBr、Li 2 S-P 2 S 5 -Li 2 O、Li 2 S-P 2 S 5 -Li 2 O-LiI、Li 2 S-SiS 2 、Li 2 S-SiS 2 -LiI、Li 2 S-SiS 2 -LiBr、Li 2 S-SiS 2 -LiCl、Li 2 S-SiS2 -B 2 S 3 -LiI, Li 2 S - SiS 2 -P 2 S 5 -LiI, Li 2 S - B 2 S 3 , Li 2 S - P 2 S 5 -Z m S n (m, n are positive numbers, and Z is Ge, Zn, or Ga.), Li 2 S - GeS 2 , Li 2 S - SiS 2 -Li 3 PO 4 , Li 2 S - SiS 2 -Li p MO q (p, q are positive numbers, and M is P, Si, Ge, B, Al, Ga, or In.), Li 7 -xPS 6 -xCl x (0 ≤ x ≤ 2), Li 7 -xPS 6 -xBr x (0 ≤ x ≤ 2), Li 7 -xPS 6 -xI x (0 ≤ x ≤ 2) etc. can be included. These can be used alone or in combination of two or more.

[0149] In one embodiment, the solid electrolyte is, for example, Li 2 O - B 2 O 3 -P 2 O 5 , Li 2 O - SiO 2 , Li 2 O - B 2 O 3 , Li 2 O - B 2 O 3 and can also include oxide - based amorphous solid electrolytes such as -ZnO.

[0150] As shown in FIG. 3, electrode tabs (a positive electrode tab and a negative electrode tab) can protrude from the positive electrode current collector 160 and the negative electrode current collector 110 belonging to each electrode cell, respectively, and extend to one side portion of the case 190. The electrode tabs can be fused together with the one side portion of the case 190 to form electrode leads (a positive electrode lead 157 and a negative electrode lead 107) extending or exposed outside the case 190.

[0151] The lithium secondary battery can be manufactured, for example, in a cylindrical shape, a square shape, a pouch type, or a coin type using a can.

[0152] Hereinafter, specific examples are presented to assist in understanding the present invention. However, these examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It is obvious to those skilled in the art that various changes and modifications can be made within the scope of the present invention and the scope of the technical idea, and it is natural that these variations and modifications belong to the scope of the appended claims.

[0153] Example 1 (1) Manufacture of the first negative electrode active material layer 95.5% by weight of artificial graphite as the first negative electrode active material, 1% by weight of carbon nanotubes (CNT) as the conductive material, 2% by weight of styrene-butadiene rubber (SBR) as the binder, and 1.5% by weight of carboxymethyl cellulose (CMC) as the thickener were mixed to obtain a first negative electrode slurry.

[0154] (2) Formation of the second negative electrode active material layer 1) Manufacture of composite particles Manufacture of carbon-based particles i) Synthesis of resol oligomer: Phenol and formaldehyde were mixed at a molar ratio of 1:2, 1.5% by weight of triethylamine was added, and the reaction was carried out under the conditions of 85 ° C., 4 hours, and 160 rpm (stirring). ii) Suspension stabilization of resol oligomer: After dispersing 1 g of polyvinyl alcohol (PVA) in an aqueous dispersion medium, it was added to the resol oligomer. iii) Curing of resol oligomer: 3 g of hexamethylenetetramine (HMTA) was added as a curing agent, and the reaction was carried out under the conditions of 98 °C, 12 hours, and 400 rpm (stirring). iv) Obtaining carbon material: The cured resol oligomer was classified using a sieve and then washed with H 2 O. v) Removing unreacted monomers and oligomers from the washed resol oligomer using ethanol and drying it. vi) Carbonization and activation: The dried resol oligomer was calcined at 900 °C for 1 hour under a nitrogen atmosphere. During the calcination, CO 2 gas was introduced at a rate of 1 L / min, and carbonized at 900 °C to produce porous carbon-based particles.

[0155] Formation of silicon-containing coating Silane gas was injected into the porous carbon-based particles into a CVD coater at a flow rate of 50 mL / min to 100 mL / min, heated to 550 °C at a heating rate of 5 °C / min to 20 °C / min, and then held for about 120 minutes to produce composite particles containing a silicon-containing coating.

[0156] 2) Formation of the second negative electrode active material layer The composite particles and artificial graphite were mixed at a weight ratio of 4:6 and used as the second negative electrode active material.

[0157] 95.5 wt% of the second negative electrode active material, 1 wt% of CNT as a conductive material, 2 wt% of SBR as a binder, and 1.5 wt% of CMC as a thickener were mixed to obtain a second negative electrode slurry.

[0158] The first negative electrode slurry and the second negative electrode slurry were sequentially coated on a copper current collector, dried, and rolled to form a negative electrode including a first negative electrode active material layer and a second negative electrode active material layer. The ratio (volume ratio) of the loading amounts of the first negative electrode slurry and the second negative electrode slurry was adjusted to 5:5.

[0159] (3) Manufacture of Lithium Half-Cell A lithium half-cell was manufactured using the negative electrode produced by the above method and lithium metal as the counter electrode (positive electrode).

[0160] Specifically, a lithium coin half-cell (coin half-cell) of CR2016 (diameter 20 mm, thickness 1.6 mm) standard was constructed with a separator (polyethylene, thickness 20 μm) interposed between the manufactured negative electrode and lithium metal (thickness 1 mm).

[0161] The combination of lithium metal / separator / negative electrode was placed in a coin cell plate, covered with a cap after injecting the electrolyte solution, and clamped.

[0162] In the production of the electrolyte solution, a 1M LiPF solution was formed using a mixed solvent of EC / EMC (volume ratio of 3:7), and 2.0 volume% of fluoroethylene carbonate (FEC) was added to the total volume of the electrolyte solution. After clamping, it was impregnated for 3 to 24 hours, and then charged and discharged at 0.1C for 3 cycles (charging conditions: CC-CV 0.1C 0.01V 0.01C CUT-OFF, discharging conditions: CC 0.1C 1.5V CUT-OFF). 6 After clamping, it was impregnated for 3 to 24 hours, and then charged and discharged at 0.1C for 3 cycles (charging conditions: CC-CV 0.1C 0.01V 0.01C CUT-OFF, discharging conditions: CC 0.1C 1.5V CUT-OFF).

[0163] Examples 2 to 13, 17 and Comparative Example 3 Negative electrodes and lithium half-cells were manufactured in the same manner as in Example 1, except that the content of the composite particles with respect to the total weight of the first negative electrode active material and the second negative electrode active material, the content of the composite particles with respect to the total weight of the second negative electrode active material, and the ratio of the loading amounts of the first negative electrode active material layer and the second negative electrode active material layer were adjusted as shown in Table 1 below.

[0164] Example 14 A laminate in which the first negative electrode slurry and the second negative electrode slurry were sequentially coated on a current collector was passed between a pair of neodymium magnets with a magnetic field of 3000 Gauss formed 3 cm apart from each other for 30 seconds to apply a magnetic field (magnetic orientation), and then a negative electrode and a lithium half-cell were produced in the same manner as in Example 1 except for drying and rolling.

[0165] Example 15 A laminate in which the first negative electrode slurry and the second negative electrode slurry were sequentially coated on a current collector was passed between a pair of neodymium magnets with a magnetic field of 3000 Gauss formed 10 cm apart from each other for 30 seconds to apply a magnetic field (magnetic orientation), and then a negative electrode and a lithium half-cell were produced in the same manner as in Example 1 except for drying and rolling.

[0166] Example 16 A laminate in which the first negative electrode slurry and the second negative electrode slurry were sequentially coated on a current collector was passed between a pair of neodymium magnets with a magnetic field of 3000 Gauss formed 10 cm apart from each other for 60 seconds to apply a magnetic field (magnetic orientation), and then a negative electrode and a lithium half-cell were produced in the same manner as in Example 1 except for drying and rolling.

[0167] Comparative Example 1 A negative electrode and a lithium half-cell were produced in the same manner as in Example 1 except that a mixture of composite particles and artificial graphite (weight ratio 2:8) was used as the first negative electrode active material and the second negative electrode active material.

[0168] Comparative Example 2 A negative electrode and a lithium half-cell were produced in the same manner as in Example 1 except that only artificial graphite was used as the second negative electrode active material.

[0169] Comparative Examples 4 and 5 A negative electrode and a lithium half-cell were produced in the same manner as in Example 1 except that SiOx (0 < x < 2), which is a silicon-based active material, was used instead of the composite particles produced as described above.

[0170] The content of the composite particles with respect to the total weight of the first negative electrode active material and the second negative electrode active material, the content of the composite particles with respect to the total weight of the second negative electrode active material, and the ratio (volume ratio) of the load amounts of the first negative electrode active material layer and the second negative electrode active material layer, and the magnetic field application are shown in Table 1 below. In the magnetic field application of Table 1, ○ means that a magnetic field was applied, and X means that no magnetic field was applied.

[0171] In Table 1, the contents described in Comparative Example 4 and Comparative Example 5 indicate the content of SiOx (0 < x < 2).

[0172]

Table 1

[0173] Experimental Example (1) Measurement of tortuosity The negative electrodes manufactured according to the above-described Examples and Comparative Examples were cut into a size of 3 mm × 10 mm to prepare samples.

[0174] The samples were put into an X-ray microscope (Zeiss Xradia 620 versa, manufactured by Zeiss) to obtain 3D images of the negative electrodes.

[0175] The measurement conditions of the X-ray microscope were as follows. i) Source condition: 60 kV, 4.5 W ii) Voxel size: 350 nm

[0176] The measured 3D images were used with analysis software (GeoDict Software, manufactured by Math 2 Market) to obtain 3D modeling images composed of the negative electrode active material and the pore structure.

[0177] Regarding the 3D modeling image, the tortuosity (T1) of the first negative electrode active material layer and the tortuosity (T2) of the second negative electrode active material layer were measured using the Diffudict Module (manufactured by GeoDict Software, Math 2 Market) function in the analysis software.

[0178] Specifically, in the settings of the tortuosity analysis software, the Computation Direction of the Percolation path was set in the Z direction (thickness direction). Subsequently, in the 3D modeling image, the tortuosity of the first negative electrode active material layer and the second negative electrode active material layer was measured respectively.

[0179] (2) Evaluation of the capacity retention rate (life characteristics) during rapid charging The lithium half-cells manufactured according to the above-described examples and comparative examples were charged by a step-by-step charging method at C-rates 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 so that the Depth of Discharge (DOD) reached 72% within 35 minutes, and then discharged at 1 / 3C. The above charging and discharging were regarded as one cycle, and the evaluation of rapid charging was carried out while repeating the cycle.

[0180] A waiting time of 10 minutes was provided during the charge-discharge cycle, and 200 cycles were repeated. After that, the discharge capacity after 200 cycles was divided by the discharge capacity after 1 cycle and shown as a percentage.

[0181] The results of the measurement and evaluation are shown in Table 2 below. In the capacity retention rate during rapid charging, N / A indicates the case where the capacity retention rate drops sharply before 200 cycles and it is difficult to use the battery.

[0182] Table 2 shows the ratio (T1 / T2) of the tortuosity (T1) of the first negative electrode active material layer to the tortuosity (T2) of the second negative electrode active material layer.

[0183]

Table 2

[0184] Referring to Table 1 and Table 2, in the examples where the degree of bending (T2) of the second negative electrode active material layer is 2.32 or less, the capacity retention rate during rapid charging was generally improved compared to the comparative examples.

[0185] In Examples 8 and 9 where the content of the composite particles with respect to the total weight of the first negative electrode active material and the second negative electrode active material is outside the range of 2% by weight to 30% by weight, the degree of bending (T2) increased relatively, and the capacity retention rate during rapid charging decreased compared to other examples.

[0186] In Examples 10 and 11 where the content of the composite particles with respect to the total weight of the second negative electrode active material is outside the range of 4% by weight to 40% by weight, the degree of bending (T2) increased relatively, and the capacity retention rate during rapid charging decreased compared to other examples.

[0187] In Example 12 where the degree of bending (T1) is less than 2.34, the capacity retention rate during rapid charging decreased compared to other examples.

[0188] In Example 13 where the degree of bending (T1) exceeds 3.0, the capacity retention rate during rapid charging decreased compared to other examples.

[0189] In Examples 14 to 16 where a magnetic field was applied, the degree of bending (T2) decreased and the capacity retention rate improved.

[0190] In Example 17 where the degree of bending (T1) of the first negative electrode active material layer is smaller than the degree of bending (T2) of the second negative electrode active material layer, the capacity retention rate during rapid charging decreased compared to other examples.

Claims

1. A negative electrode current collector; a first negative electrode active material layer disposed on at least one surface of the negative electrode current collector and including a first negative electrode active material; a second negative electrode active material layer disposed on the first negative electrode active material layer and including a second negative electrode active material; the first negative electrode active material includes a graphite-based active material, and the second negative electrode active material includes composite particles including silicon; The second negative electrode active material layer has a tortuosity of 2.32 or less as determined by an X-ray microscope (XRM) analysis.

2. The negative electrode for a lithium secondary battery according to claim 1 , wherein the tortuosity of the second negative electrode active material layer is defined by the following formula 1: [Formula 1] T2=L Ｐ２ / L ２ (In formula 1, T2 is the bending degree of the second negative electrode active material layer, L Ｐ２ is the average flow path length through which lithium ions pass when penetrating the second negative electrode active material layer in the thickness direction, and L ２ is the thickness of the second negative electrode active material layer.)

3. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the composite particles include carbon-based particles and a silicon-containing coating formed on a surface of the carbon-based particles.

4. 4. The negative electrode for a lithium secondary battery according to claim 3, wherein the carbon-based particles include at least one selected from the group consisting of activated carbon, carbon nanotubes, carbon nanowires, graphene, carbon fibers, carbon black, graphite, porous carbon, pyrolyzed cryogel, pyrolyzed xerogel, and pyrolyzed aerogel.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein a content of the composite particles is 2% by weight to 30% by weight based on a total weight of the first negative electrode active material and the second negative electrode active material.

6. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein a content of the composite particles is 4.5% by weight to 24% by weight based on a total weight of the first negative electrode active material and the second negative electrode active material.

7. The negative electrode of claim 1 , wherein the second negative electrode active material further comprises a graphite-based active material.

8. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein a content of the composite particles is 4% by weight to 40% by weight based on a total weight of the second negative electrode active material.

9. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein a content of the composite particles is 9% by weight to 40% by weight based on a total weight of the second negative electrode active material.

10. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the graphite-based active material includes at least one of artificial graphite and natural graphite.

11. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein a degree of curvature of the first negative electrode active material layer obtained by analysis with an X-ray microscope (XRM) is greater than the degree of curvature of the second negative electrode active material layer.

12. The negative electrode for a lithium secondary battery according to claim 11 , wherein the tortuosity of the first negative electrode active material layer is defined by the following Formula 2: [Formula 2] T1=L Ｐ１ / L １ (In formula 2, T1 is the bending degree of the first negative electrode active material layer, L Ｐ１ is the average flow path length through which lithium ions pass when penetrating the first negative electrode active material layer in the thickness direction, and L １ is the thickness of the first negative electrode active material layer.)

13. 13. The negative electrode for a lithium secondary battery according to claim 12, wherein the tortuosity of the first negative electrode active material layer is 2.34 to 3.

0.

14. 12. The negative electrode for a lithium secondary battery according to claim 11, wherein a ratio of a tortuosity of the first negative electrode active material layer to a tortuosity of the second negative electrode active material layer is 1.03 to 1.

44.

15. The negative electrode for a lithium secondary battery according to any one of claims 1 to 14, a positive electrode disposed opposite the negative electrode.

Images