Anode for lithium secondary batteries and lithium secondary batteries containing the anode.

Abstract

A negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes: a first negative electrode active material layer comprising a first negative electrode active material and a first binder comprising an acrylate-styrene-butadiene copolymer; and a second negative electrode active material layer disposed on the first negative electrode material layer, the second negative electrode active material layer comprising a second negative electrode active material and a second binder comprising an acrylate-styrene-butadiene copolymer. The peak intensity ratio of the first negative electrode active material according to the Raman spectrum is less than the peak intensity ratio of the second negative electrode active material according to the Raman spectrum, and the peak intensity ratio according to the Raman spectrum is expressed as I. D / I G .

Description

[0001] Cross-reference and priority claims of related applications

[0002] This application claims priority to Korean Patent Application No. 10-2020-0078448, filed with the Korean Intellectual Property Office (KIPO) on June 26, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode. Background Technology

[0004] With the development of information and display technologies, rechargeable and dischargeable secondary batteries have been widely used as power sources for portable electronic devices such as portable cameras, mobile phones, and portable computers. Recently, battery packs including secondary batteries have been developed and are being used as power sources for environmentally friendly vehicles, such as hybrid electric vehicles.

[0005] Secondary batteries include, for example, lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Lithium-ion batteries have attracted attention due to their high operating voltage, energy density per unit weight, high charging rate, and compact size.

[0006] For example, a lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator layer (separator); and an electrolyte immersing the electrode assembly. The lithium secondary battery may further include a casing having, for example, a pouch shape.

[0007] For example, a lithium secondary battery may include: a negative electrode comprising, for example, a carbon-based material capable of adsorbing and releasing lithium ions; a positive electrode formed of a lithium-containing oxide; and a non-aqueous electrolyte comprising a lithium salt dissolved in an organic solvent.

[0008] Amorphous or crystalline carbon can be used as a negative electrode active material, and crystalline carbon may be advantageous from a high capacity perspective. Examples of crystalline carbon include natural graphite and synthetic graphite.

[0009] For example, Korean Patent Application Publication No. 10-2005-0004930 discloses a negative electrode active material including artificial graphite, which may not provide sufficient discharge capacity and power. Summary of the Invention

[0010] According to one aspect of the present invention, a negative electrode for a lithium secondary battery with improved fast charging performance is provided.

[0011] According to one aspect of the present invention, a lithium secondary battery is provided, comprising a negative electrode for use in a lithium secondary battery.

[0012] According to an exemplary embodiment, the negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer includes: a first negative electrode active material layer comprising a first negative electrode active material and a first binder comprising an acrylate-styrene-butadiene copolymer; and a second negative electrode active material layer disposed on the first negative electrode material layer. The second negative electrode active material layer comprises a second negative electrode active material and a second binder comprising an acrylate-styrene-butadiene copolymer. The peak intensity ratio of the first negative electrode active material according to the Raman spectrum is less than the peak intensity ratio of the second negative electrode active material according to the Raman spectrum, and the peak intensity ratio according to the Raman spectrum is expressed as I. D / I G .

[0013] In some implementations, the peak intensity ratio of the first negative electrode active material according to the Raman spectrum can be in the range of 0.1-0.4.

[0014] In some implementations, the peak intensity ratio of the second negative electrode active material according to the Raman spectrum can be in the range of 0.4-1.5.

[0015] In some embodiments, the ratio of the peak intensity ratio of the second negative electrode active material according to the Raman spectrum to the peak intensity ratio of the first negative electrode active material according to the Raman spectrum can be in the range of 1.5-5.

[0016] In some embodiments, the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the first adhesive may be less than the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the second adhesive.

[0017] In some embodiments, the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer in the first adhesive may be 5-30% by weight, and the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer in the second adhesive may be 45-90% by weight.

[0018] In some embodiments, the ratio of the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the second adhesive to the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the first adhesive can be greater than 1 and equal to or less than 10.

[0019] In some implementations, the content of the first binder may be less than 1.5% by weight, based on the total weight of the first negative electrode active material layer.

[0020] In some implementations, the content of the second binder can be 1-3% by weight, based on the total weight of the second negative electrode active material layer.

[0021] In some embodiments, the first peak intensity ratio of the first negative electrode active material, as measured by X-ray diffraction, can be in the range of 0.001-0.012, and the first peak intensity ratio of the second negative electrode active material, as measured by X-ray diffraction, can be in the range of 0.013-0.05. The first peak intensity ratio measured by X-ray diffraction is expressed as I(110) / I(002) obtained in the X-ray diffraction analysis.

[0022] In some embodiments, the second peak intensity ratio of the first negative electrode active material, as measured by X-ray diffraction, can be in the range of 0.1 to 0.35, and the second peak intensity ratio of the second negative electrode active material, as measured by X-ray diffraction, can be in the range of 0.4 to 1.0. The second peak intensity ratio measured by X-ray diffraction is expressed as I(110) / I(004) obtained in the X-ray diffraction analysis.

[0023] In some implementations, the thickness of the second negative electrode active material layer can be 3%-70% of the total thickness of the negative electrode active material layer.

[0024] According to an exemplary embodiment, a lithium secondary battery includes a negative electrode according to the embodiment described above and a positive electrode opposite to the negative electrode.

[0025] The negative electrode for a lithium secondary battery according to an exemplary embodiment may include a negative electrode current collector, a first negative electrode active material layer disposed on the negative electrode current collector, and a second negative electrode active material layer disposed on the first negative electrode active material layer. A battery including a negative electrode may have improved power and capacity characteristics, such as charge / discharge power and fast charging characteristics.

[0026] For example, the first negative electrode active material layer may include a first negative electrode active material and a first binder, and the second negative electrode active material layer may include a second negative electrode active material and a second binder. For example, the peak intensity ratio (I0.05) of the first negative electrode active material according to the Raman spectrum... D / I G The ratio of the peak intensity of the second negative electrode active material to that of the second negative electrode active material, based on the Raman spectrum, can be less than that of the second negative electrode active material (I). D / I G ).

[0027] In this configuration, the first negative electrode active material layer disposed on the negative electrode current collector may include a first negative electrode active material with a large basal plane area and may have enhanced adhesion to the negative electrode current collector. The second negative electrode active material layer disposed on the first negative electrode active material layer may include a second negative electrode active material with a large edge plane ratio, which may be advantageous from the perspective of lithium-ion intercalation. Therefore, the second negative electrode active material layer can have low resistance.

[0028] Therefore, it is possible to achieve a negative electrode active material layer with excellent adhesion to the negative electrode current collector and low resistance characteristics. Attached Figure Description

[0029] Figure 1 A schematic cross-sectional view illustrating the construction of a lithium secondary battery according to an exemplary embodiment.

[0030] Figure 2 A schematic cross-sectional view illustrating the construction of a negative electrode for a lithium secondary battery according to an exemplary embodiment. Detailed Implementation

[0031] According to an exemplary embodiment of the present invention, the negative electrode for a lithium secondary battery may include a negative electrode current collector, a first negative electrode active material layer with high adhesion, and a second negative electrode active material layer with low resistance characteristics. The negative electrode for the lithium secondary battery may have improved adhesion between the negative electrode current collector and the negative electrode active material layer, and may provide enhanced fast-charging performance of the lithium secondary battery.

[0032] The invention will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that such embodiments described with reference to the drawings are provided to further understand the spirit of the invention and do not limit the subject matter to be protected as disclosed in the detailed description and the appended claims.

[0033] Figure 1 A schematic cross-sectional view illustrating the construction of a lithium secondary battery according to an exemplary embodiment.

[0034] Reference Figure 1 The lithium secondary battery 100 may include a negative electrode 200 (hereinafter simply referred to as the negative electrode), a positive electrode 300, and a separator layer 400 between the negative electrode 200 and the positive electrode 300 for use in the lithium secondary battery.

[0035] The electrode assembly may be defined by a negative electrode 200, a positive electrode 300, and a separator layer 400. The lithium secondary battery 100 may also include a battery case in which the electrode assembly is inserted, and a non-aqueous electrolyte injected into the battery case.

[0036] There are no particular limitations on the shape of the lithium secondary battery of the present invention. It can be cylindrical (using a can), square, pouch, or coin-shaped, etc.

[0037] For example, the negative electrode 200 may include a negative electrode current collector 210 and a negative electrode active material layer 220.

[0038] The negative electrode current collector 210 may include copper or copper alloys; stainless steel, nickel, titanium or their alloys; copper or stainless steel with surface treatments such as carbon, nickel, titanium, silver, etc.

[0039] For example, the negative electrode active material, binder, solvent, and optionally conductive agent, dispersant, etc., can be mixed or stirred to form a slurry. The slurry can be coated onto the current collector and pressed to form a negative electrode active material layer 220.

[0040] Solvents may include non-aqueous solvents. Non-aqueous solvents may include, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0041] Conductive agents can include carbon-based conductive materials.

[0042] Please refer to the following Figure 2 The composition, properties and structure of the negative electrode active material layer 220 are described in more detail.

[0043] For example, the positive electrode 300 may include a positive electrode current collector 310 and a positive electrode active material layer 320. For example, the positive electrode 300 may be manufactured by coating the positive electrode active material onto the positive electrode current collector 310.

[0044] The positive current collector 310 may include aluminum or aluminum alloy; stainless steel, nickel, titanium or alloys thereof; aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, silver, etc.

[0045] Positive electrode active materials widely used in related technologies can be used to form the positive electrode active material layer 320. In one embodiment, the positive electrode active material may include a lithium composite oxide comprising at least one of cobalt, manganese, and nickel. For example, a compound represented by the following chemical formula can be used as a lithium composite oxide.

[0046] Li x Mn 1-y M y A2

[0047] Li x Mn 1-y M y O 2-z X z

[0048] Lix Mn2O 4-z X z

[0049] Li x Mr 2-y M y M' z A4

[0050] Li x Co 1-y M y A2

[0051] Li x Co 1-y M y O 2-z X z

[0052] Li x Ni 1-y M y A2

[0053] Li x Ni 1-y M y O 2-z X z

[0054] Li x Ni 1-y Co y O 2-z X z

[0055] Li x Ni 1-y-z Co y M z A α

[0056] Li x Ni 1-y-z Co y M z O 2-α X α

[0057] Li x Ni 1-y-z Mr y M z A α

[0058] Li x Ni 1-y-z Mr y M z O 2-α X

[0059] In the above chemical formulas, 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2.2, and M and M' can be the same as or different from each other. M and M' can be selected from Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V and rare earth metals, A can be selected from O, F, S and P, and X can be selected from F, S and P.

[0060] For example, the positive electrode active material, binder, solvent, and optionally conductive agent, dispersant, etc., can be mixed or stirred to form a slurry. The slurry can be coated on the positive electrode current collector 310, dried, and pressed to form the positive electrode active material layer 320.

[0061] Solvents may include non-aqueous solvents. Non-aqueous solvents may include, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0062] Adhesives may include organic adhesives, such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or water-based adhesives, such as styrene-butadiene rubber (SBR).

[0063] For example, adhesives can be used with thickeners such as carboxymethyl cellulose (CMC).

[0064] Conductive agents can include carbon-based conductive materials.

[0065] For example, the membrane layer 400 may comprise a porous polymer membrane made of a polyolefin-based polymer, such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer. The membrane layer 400 may also be formed of a nonwoven fabric, including high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0066] The separator layer 400 can be applied to the battery by winding, laminating, stacking, folding, etc.

[0067] For example, non-aqueous electrolyte solutions may include lithium salts and organic solvents.

[0068] Lithium salts, commonly used in electrolytes for lithium secondary batteries, can be used, and can be derived from Li + X - Show.

[0069] Lithium Salt X - The anions may include, for example, 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 - (CF3CF2SO2)2N - wait.

[0070] Organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These organic solvents may be used alone or in combination.

[0071] Figure 2 A schematic cross-sectional view illustrating the construction of a negative electrode for a lithium secondary battery according to an exemplary embodiment.

[0072] Reference Figure 2 According to an exemplary embodiment, the negative electrode for a lithium secondary battery may include a negative electrode current collector 210, a first negative electrode active material layer 222 disposed on the negative electrode current collector 210, and a second negative electrode active material layer 224 disposed on the first negative electrode active material layer 222.

[0073] For example, the first negative electrode active material layer 222 may include a first negative electrode active material and a first adhesive comprising an acrylate-styrene-butadiene copolymer. For example, the second negative electrode active material layer 224 may include a second negative electrode active material and a second adhesive comprising an acrylate-styrene-butadiene copolymer.

[0074] In an exemplary embodiment, the peak intensity ratio (I0.05) of the first negative electrode active material according to the Raman spectrum D / I G The ratio of the peak intensity of the second negative electrode active material to that of the second negative electrode active material, based on the Raman spectrum, can be less than that of the second negative electrode active material (I). D / I G ).

[0075] For example, the negative electrode active material may include graphite-based particles. Graphite-based particles can refer to particles whose surface at least partially can be graphite. Graphite particles may include artificial graphite and natural graphite. Artificial graphite can be prepared by graphitizing graphite precursors at temperatures above 150°C, preferably about 2800°C to 3200°C. Graphite precursors may include coke, mesophase carbon, such as mesophase microspheres and bulk mesophase. Natural graphite may include flake natural graphite, bulk-type natural graphite, and spherical natural graphite obtained by grinding, assembling, and spheroidizing flake natural graphite.

[0076] For example, graphite-based particles can be prepared by chemical or physical processing. Non-limiting examples of chemical or physical processing include crushing, classifying, assembling, lamination, compression, compounding, mixing, coating, oxidation, deposition, mechanochemical processing, chamfering, spheroidizing, curvature, annealing, etc.

[0077] Based on the peak intensity ratio (I) of Raman spectroscopy D / I G In the measurement, mapping can be performed at multiple points on the negative electrode (200), thereby allowing measurement of the D-band intensity (I) of the negative electrode active material at each point. D ) and G-band strength (I G ). After that, the D-band strength (I) can be... D ) relative to G-band intensity (I G The average value of the ratios of (I) is used as the peak intensity ratio (I) D / I G ).

[0078] For example, the D-band can represent the 1300 to 1420 cm⁻¹ range of the spectrum measured using a Raman spectrometer at an excitation wavelength of 532 nm. -1 The peak intensity in the region. For example, the G band can represent the peak intensity in the region from 1540 to 1620 cm⁻¹ of a spectrum measured using a Raman spectrometer at an excitation wavelength of 532 nm. -1 Peak intensity at that location.

[0079] For example, when based on the peak intensity ratio (I) of the Raman spectrum D / I G As the basal plane of the negative electrode active material decreases, its length may increase. Conversely, as the peak intensity ratio (I) of the Raman spectrum decreases... D / I G As the diameter increases, the area of ​​the exposed end face in the negative electrode active material may increase.

[0080] In some embodiments, the first negative electrode active material layer 222 disposed on the negative electrode current collector 210 may include a negative electrode active material having a relatively long base surface, and the second negative electrode active material layer 224 disposed on the first negative electrode active material layer 222 may include a negative electrode active material having a relatively large exposed end face area.

[0081] For example, a negative electrode active material with a relatively large exposed end-face area in the second negative electrode active material layer 224 can easily undergo lithium-ion intercalation. Therefore, the low resistance characteristics of the second negative electrode active material layer 224 can be improved.

[0082] Furthermore, the negative electrode active material having a relatively long base surface in the first negative electrode active material layer 222 can easily enhance the adhesion between the first negative electrode active material layer 222 and the negative electrode current collector.

[0083] For example, the peak intensity ratio (I) of the first negative electrode active material according to the Raman spectrum D / I G The value can be approximately 0.1-0.4. For example, in the peak intensity ratio (I... D / I G Within the aforementioned range, the crystal length of the first negative electrode active material can be increased. Therefore, the adhesion of the first negative electrode active material layer 222, which includes the first negative electrode active material, can be further improved.

[0084] For example, the peak intensity ratio (I) of the second negative electrode active material according to the Raman spectrum. D / I G The ratio can be approximately 0.4-1.5. For example, the peak intensity ratio (I0.05) of the second negative electrode active material can be... D / I GWithin the aforementioned range, the exposed end face area of ​​the second negative electrode active material can be increased. Therefore, lithium ion intercalation can be easily achieved through the second negative electrode active material, thereby further improving the low resistance characteristics of the second negative electrode active material layer 224 including the second negative electrode active material.

[0085] For example, if the peak intensity ratio (I) of the second negative electrode active material according to the Raman spectrum D / I G If the value exceeds 1.5, the high-temperature storage characteristics, fast-charging life characteristics, and normal life characteristics may deteriorate.

[0086] In some implementations, the peak intensity ratio (I2) of the second negative electrode active material according to the Raman spectrum D / I G The ratio of peak intensity to the first anode active material based on Raman spectroscopy (I) D / I G The ratio can be approximately 1.5-5.

[0087] For example, in peak intensity ratio (I D / I G Within this ratio range, a negative electrode active material layer with low resistance and improved adhesion to the negative electrode current collector can be effectively achieved.

[0088] In some embodiments, the first peak intensity ratio of the first negative electrode active material, represented by I(110) / I(002) and measured by X-ray diffraction, can be about 0.001-0.012. The first peak intensity ratio I(110) / I(002) of the second negative electrode active material, measured by X-ray diffraction, can be about 0.013-0.05.

[0089] In some embodiments, the second peak intensity ratio of the first negative electrode active material, represented by I(110) / I(004) and measured by X-ray diffraction, can be about 0.1-0.35, and the second peak intensity ratio of the second negative electrode active material, represented by I(110) / I(004) and measured by X-ray diffraction, can be about 0.4-1.0.

[0090] For example, the first peak intensity ratio I(110) / I(002) and the second peak intensity ratio I(110) / I(004) measured by X-ray diffraction can be calculated from the values ​​of the peak intensity of the carbon 002 plane (I(002)), the carbon 004 plane (I(004)) and the carbon 110 plane (I(110)) measured in an X-ray diffraction apparatus under the following measurement conditions.

[0091] [Measurement Conditions]

[0092] Target: Copper

[0093] X-ray power: 40kV, 100mA

[0094] Measurement range: 2θ = 20° to 80°

[0095] Step angle: 0.02°

[0096] Counting time per step: 3 seconds

[0097] For example, if the first peak intensity ratio I(110) / I(002) of the first negative electrode active material is about 0.001-0.012, or the second peak intensity ratio I(110) / I(004) of the first negative electrode active material is about 0.1-0.35, then the negative electrode active material can have a crystal structure with a large crystal length.

[0098] The first negative electrode active material with a crystal structure having a large crystal length can be included in the first negative electrode active material layer 222. High capacity can be achieved by the negative electrode active material layer 220, and the adhesion between the negative electrode current collector 210 and the negative electrode active material layer 220 can be improved.

[0099] For example, if the first peak intensity ratio I(110) / I(002) of the second negative electrode active material is about 0.013-0.05, or the second peak intensity ratio I(110) / I(004) of the second negative electrode active material is about 0.4-1.0, then the area of ​​the exposed end face of the second negative electrode active material can be increased, and the second negative electrode active material can have an amorphous structure.

[0100] Lithium-ion intercalation can be effectively achieved using a second negative electrode active material with a large end-face area and an amorphous structure. Therefore, the low-resistance characteristics of the second negative electrode active material layer 224 can be further improved.

[0101] In some embodiments, the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the first adhesive can be smaller than the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the second adhesive.

[0102] For example, in the first adhesive, the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer can be from about 5% to 30% by weight, while in the second adhesive, the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer is from about 45% to 90% by weight.

[0103] For example, if the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer in the second adhesive is about 45% to 90% by weight, the low resistance characteristics of the negative electrode active material layer 220 can be improved. If the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer in the first adhesive is about 5% to 30% by weight, the adhesion between the negative electrode active material layer 220 and the negative electrode current collector 210 can be improved.

[0104] For example, the first negative electrode active material layer 222 disposed on the negative electrode current collector 210 may include an acrylate-styrene-butadiene copolymer having repeating units derived from acrylate monomers in an amount of about 5% to 30% by weight, thereby improving the adhesion between the negative electrode current collector 210 and the first negative electrode active material layer 222.

[0105] For example, the second negative electrode material layer 224 disposed on the first negative electrode active material layer 222 may include an acrylate-styrene-butadiene copolymer having repeating units derived from acrylate monomers in an amount of about 45% to 90% by weight, thereby improving the low resistance characteristics of the negative electrode active material layer 220.

[0106] Therefore, a negative electrode active material layer 220 with improved fast charging and low resistance characteristics and improved adhesion to the negative electrode current collector 210 can be effectively achieved.

[0107] In some embodiments, the content of the first binder may be less than about 1.5% by weight, based on the total weight of the first negative electrode active material layer 222. For example, within the above range, the increase in resistance of the negative electrode active material layer 220 due to the relatively low content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer can be effectively prevented.

[0108] There is no particular limitation on the lower limit of the content of the first binder. The first binder may be included in an amount sufficient to maintain the function of the electrode, and the content of the first binder may be, for example, more than about 0.1% by weight based on the total weight of the first negative electrode active material layer 222.

[0109] In some embodiments, the content of the second binder can be from about 1% to 3% by weight, based on the total weight of the second negative electrode active material layer 224. For example, within the above range, the low resistance characteristics of the negative electrode active material layer 220 can be effectively achieved.

[0110] In some embodiments, the ratio of the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer included in the second adhesive to the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the first adhesive can be greater than about 1 and less than or equal to 10.

[0111] For example, within the aforementioned range of repeating units derived from acrylate monomers between the first adhesive and the second adhesive, a negative electrode active material layer 220 with enhanced adhesion to the negative electrode current collector 210 and low resistance can be effectively achieved.

[0112] In some embodiments, the acrylate-styrene-butadiene copolymer included in the first adhesive or the second adhesive may have a core-shell structure. In this case, the core of the acrylate-styrene-butadiene copolymer may include styrene and / or butadiene, and the shell of the acrylate-styrene-butadiene copolymer may include acrylate.

[0113] In some embodiments, the first or second negative electrode active material layer may further comprise at least one material selected from polyvinylidene fluoride and / or carboxymethyl cellulose as a sub-binder. For example, the sub-binder can further improve the adhesion of the first negative electrode active material layer or the low resistance characteristics of the second negative electrode active material layer.

[0114] In some embodiments, the thickness of the second negative electrode active material layer 224 can be about 3% to 70% of the total thickness of the negative electrode active material layer 220. For example, within this thickness range of the second negative electrode active material layer 224, the improved low resistance characteristics can be achieved more effectively by the negative electrode active material layer 220.

[0115] Preferred embodiments are presented below to describe the invention in more detail. However, the following examples are merely illustrative, and those skilled in the art will clearly understand that various changes and modifications can be made within the scope and spirit of the invention. Such changes and modifications should be included within the appended claims.

[0116] Example 1

[0117] <Negative electrode>

[0118] Artificial graphite with a single-particle structure, serving as the first negative electrode active material, is mixed with an acrylate-styrene-butadiene copolymer containing 25% acrylate monomers, serving as the first binder. The mixture is then dispersed in deionized distilled water to prepare a first negative electrode slurry. The first negative electrode slurry is coated onto one surface of a copper foil current collector to form a first negative electrode active material layer. Based on the total weight of the first negative electrode active material layer, the content of the first binder is 1% by weight. The peak intensity ratio (I0.05) of the first negative electrode active material is measured by Raman spectroscopy. D / I G The value is 0.28.

[0119] The 1360 cm⁻¹ of the spectrum was measured using a Raman spectrometer at an excitation wavelength of 532 nm. -1 Peak intensity at I D The 1580 cm⁻¹ spectrum was obtained by using a Raman spectrometer at an excitation wavelength of 532 nm. -1 Peak intensity at I G .

[0120] The intensity ratio of the first peak, I(110) / I(002), measured by X-ray diffraction analysis of the first negative electrode active material is 0.007, and the intensity ratio of the second peak, I(110) / I(004), measured by X-ray diffraction analysis of the first negative electrode active material is 0.173.

[0121] Artificial graphite with an assembly-type particle structure, serving as the second negative electrode active material, is mixed with an acrylate-styrene-butadiene copolymer containing 55% acrylate monomers, serving as the second binder. The mixture is then dispersed in deionized distilled water to prepare a second negative electrode slurry. The second negative electrode slurry is coated onto one surface of the first negative electrode active material layer to form a second negative electrode material layer. Based on the total weight of the second negative electrode active material layer, the content of the second binder is 2% by weight. The peak intensity ratio (Ig) of the second negative electrode active material is measured by Raman spectroscopy. D / I G The value is 0.69.

[0122] The intensity ratio of the first peak, I(110) / I(002), measured by X-ray diffraction analysis of the second negative electrode active material is 0.014, and the intensity ratio of the second peak, I(110) / I(004), measured by X-ray diffraction analysis of the second negative electrode active material is 0.363.

[0123] Subsequently, drying and pressing processes are performed to prepare a negative electrode comprising a negative electrode active material layer with dimensions of 10cm×10cm×50μm.

[0124] The thickness of the first negative electrode active material layer is 40% of the total thickness of the negative electrode active material layer, and the thickness of the second negative electrode active material layer is 60% of the total thickness of the negative electrode active material layer.

[0125] Positive electrode

[0126] Li was mixed at a mass ratio of 46:2.5:1.5:50 as the positive electrode active material. 1.0 Ni 0.6 Co 0.2 Mn 0.2 O2, acetylene black (Denka Black) as a conductive material, PVDF as a binder, and N-methylpyrrolidone as a solvent were used to prepare the positive electrode slurry. The positive electrode slurry was coated onto an aluminum substrate, then dried and pressed to prepare the positive electrode.

[0127] <Battery Manufacturing>

[0128] The positive and negative electrodes obtained as described above are cut (notched) to appropriate dimensions and stacked, with a separator (polyethylene, thickness: 25 μm) inserted between them to form an electrode unit. Each tab portion of the positive and negative electrodes is welded. The welded positive / separator / negative electrode assembly is inserted into a flexible package, and the package is sealed on three sides except for the side where the electrolyte is injected. The tab portion is also included in the sealed portion. Electrolyte is injected through the electrolyte injection side, which is then also sealed. Subsequently, the above structure is impregnated for more than 12 hours.

[0129] The electrolyte was prepared by dissolving 1 M LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio), followed by the addition of 1.5 wt% vinylene carbonate and 0.5 wt% 1,3-propensultone (PRS).

[0130] The lithium secondary battery manufactured above was precharged by applying a precharge current (2.5A) corresponding to 0.25 C for 36 minutes. After 1 hour, the battery was degassed and aged for more than 24 hours, and then subjected to formation charge and discharge (charging conditions: CC-CV 0.2 C 4.2V 0.05C cutoff, discharging conditions: CC 0.2 C 2.5V cutoff).

[0131] Examples 2-14 and Comparative Example 1

[0132] As shown in Tables 1 and 2 below, the amounts and properties of the first binder and the first negative electrode active material contained in the first negative electrode active material layer, the amounts and properties of the second binder and the second negative electrode active material contained in the second negative electrode active material layer, and the thicknesses of the first negative electrode active material layer and the second negative electrode active material layer in Example 1 are changed to form a lithium secondary battery.

[0133] Comparative Example 2 and Comparative Example 3

[0134] The lithium secondary battery was manufactured using the same method as in Example 1, except that only a first negative electrode active material layer was formed on the copper foil current collector (Comparative Example 2) or only a second negative electrode active material layer was formed on the copper foil current collector (Comparative Example 3).

[0135] [Table 1]

[0136]

[0137]

[0138] [Table 2]

[0139]

[0140] Experimental Example

[0141] The adhesion and fast-charging performance of the negative electrode and lithium secondary battery prepared according to the examples and comparative examples were evaluated.

[0142] <Adhesion Analysis of the Negative Electrode>

[0143] The negative electrode prepared according to the examples and comparative examples was cut into pieces with a width of 18 mm and a length of 150 mm. An 18 mm wide tape was attached to the Cu foil of the negative electrode and thoroughly bonded using a roller with a 2 kg load. Double-sided tape was adhered to one side of a tensile testing machine, and the negative electrode active material layer was adhered to the double-sided tape. The tape attached to the copper foil was coupled to the opposite side of the tensile testing machine, and the adhesion force was measured.

[0144] <Evaluation of fast charging features>

[0145] A battery with a capacity of 10 Ah or more was manufactured using the negative electrode prepared according to the examples and comparative examples, and using the same positive electrode. A reference electrode was inserted between the positive and negative electrodes to obtain a three-electrode battery, and the potential of the negative electrode was confirmed during charging using this three-electrode battery.

[0146] While a three-electrode battery with a reference electrode inserted was charged to 4.2V at a constant current (CC) rate (C-rate) from 0.75C to 2.5C, the state of charge (SOC) point at which the CCV value of the negative electrode became constant below 0V for each charge rate was detected. This SOC point was designated as the discharge limit, and step-charging protocols for the embodiments and comparative examples were designed.

[0147] The charging time of the comparative examples and embodiments was calculated using a step-charging scheme devised using a three-electrode battery, and the capacity retention rate was calculated by repeating the fast charge-1 / 3C discharge cycle 200 times with each step-charging scheme.

[0148] The results are shown in Table 3 below.

[0149] [Table 3]

[0150]

[0151]

[0152] Referring to Table 3, the second negative electrode active material layer includes a second binder containing repeating units derived from acrylate monomers within a specific content range and Raman spectral peak intensity ratios within a specific range (I0). D / I G In the embodiment of the second negative electrode active material, the fast charging performance of the negative electrode used in the lithium secondary battery is further improved, and the degradation of fast charging performance can be effectively prevented even after repeated fast charging and discharging.

[0153] Furthermore, the first negative electrode active material layer includes a first binder containing repeating units derived from acrylate monomers within a specific content range and a Raman spectral peak intensity ratio (I) within a specific range. D / I G In the embodiment of the first negative electrode active material, the adhesion between the first negative electrode active material layer and the negative electrode current collector is improved.

Claims

1. A negative electrode for a lithium secondary battery, comprising: Negative electrode current collector; A negative electrode active material layer disposed on the negative electrode current collector, wherein the negative electrode active material layer comprises: A first negative electrode active material layer, the first negative electrode active material layer comprising a first negative electrode active material and a first binder comprising an acrylate-styrene-butadiene copolymer; and A second negative electrode active material layer is disposed on the first negative electrode active material layer. The second negative electrode active material layer includes a second negative electrode active material and a second adhesive comprising an acrylate-styrene-butadiene copolymer. Wherein, the peak intensity ratio of the first negative electrode active material according to the Raman spectrum is less than the peak intensity ratio of the second negative electrode active material according to the Raman spectrum, and the peak intensity ratio according to the Raman spectrum is expressed as I. D / I G , The intensity ratio of the first peak of the first negative electrode active material, as measured by X-ray diffraction, is in the range of 0.001-0.

012. The intensity ratio of the first peak of the second negative electrode active material, as measured by X-ray diffraction, is in the range of 0.013-0.05, and The intensity ratio of the first peak, as measured by X-ray diffraction, is expressed as I(110) / I(002) obtained in the X-ray diffraction analysis. The intensity ratio of the second peak of the first negative electrode active material, as measured by X-ray diffraction, is in the range of 0.1-0.

35. The intensity ratio of the second peak of the second negative electrode active material, as measured by X-ray diffraction, is in the range of 0.4-1.0, and The intensity ratio of the second peak obtained by X-ray diffraction is expressed as I(110) / I(004) obtained in X-ray diffraction analysis.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein, The peak intensity ratio of the first negative electrode active material according to the Raman spectrum is in the range of 0.1-0.

4.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein, The peak intensity ratio of the second negative electrode active material according to the Raman spectrum is in the range of 0.4-1.

5.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein, The ratio of the peak intensity ratio of the second negative electrode active material according to the Raman spectrum to the peak intensity ratio of the first negative electrode active material according to the Raman spectrum is in the range of 1.5-5.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein, The content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the first adhesive is less than the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the second adhesive.

6. The negative electrode for a lithium secondary battery according to claim 5, wherein, In the first adhesive, the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer is 5-30% by weight, and in the second adhesive, the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer is 45-90% by weight.

7. The negative electrode for a lithium secondary battery according to claim 1, wherein, The ratio of the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the second adhesive to the content of repeating units derived from acrylate monomers in the acrylate-styrene-butadiene copolymer of the first adhesive is greater than 1 and equal to or less than 10.

8. The negative electrode for a lithium secondary battery according to claim 1, wherein, Based on the total weight of the first negative electrode active material layer, the content of the first adhesive is less than 1.5% by weight.

9. The negative electrode for a lithium secondary battery according to claim 1, wherein, Based on the total weight of the second negative electrode active material layer, the content of the second adhesive is 1-3 by weight.

10. The negative electrode for a lithium secondary battery according to claim 1, wherein, The thickness of the second negative electrode active material layer is 3%-70% of the total thickness of the negative electrode active material layer.

11. A lithium secondary battery, comprising: The negative electrode for a lithium secondary battery according to claim 1; and The positive electrode opposite to the negative electrode.

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