Method for preparing negative electrode composition for secondary battery

Abstract

A method for preparing a negative electrode active material for a secondary battery according to exemplary embodiments of the present disclosure comprises a step of mixing a first binder containing at least one of carboxymethyl cellulose including an acyclic hemiacetal functional group and a salt thereof, and a second binder containing at least one of carboxymethyl cellulose including no acyclic hemiacetal functional group and a salt thereof, wherein the weight average molecular weights of the first and second binders are 300,000 g / mol (exclusive) to 3,500,000 g / mol (exclusive).

Description

Method for producing a negative electrode composition for a secondary battery

[0001] The disclosure of the present application relates to a method for producing a negative electrode composition for a secondary battery, a negative electrode for a secondary battery produced using the same, and a secondary battery including the same.

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

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

[0004] Recently, as the scope of secondary battery applications expands, development of manufacturing methods for secondary battery anodes with higher reliability and process stability is underway. For example, the resistance, adhesive strength, and lifespan characteristics of the anode and secondary battery can deteriorate depending on factors such as the order of raw material input and the type of raw material used during the anode manufacturing process.

[0005] According to one aspect of the present disclosure, a method for producing a negative electrode composition for a secondary battery having improved dispersibility, stability, and adhesiveness and reduced resistance can be provided.

[0006] According to one aspect of the present disclosure, a negative electrode for a secondary battery having improved stability and lifespan characteristics and reduced resistance can be provided.

[0007] According to one aspect of the present disclosure, a secondary battery having improved stability and lifespan characteristics and reduced resistance can be provided.

[0008] A method for manufacturing a negative electrode composition according to embodiments of the present disclosure comprises mixing a first binder comprising at least one of carboxymethylcellulose and a salt thereof comprising an acyclic hemiacetal functional group; and a second binder comprising at least one of carboxymethylcellulose and a salt thereof not comprising the acyclic hemiacetal functional group, wherein the weight average molecular weights of the first and second binders are greater than 300,000 g / mol and less than 3,500,000 g / mol.

[0009] In some embodiments, the first binder and the second binder may be mixed in a weight ratio of 10:90 to 90:10.

[0010] In some embodiments, the first binder and the second binder may be mixed in a weight ratio of 20:80 to 80:20.

[0011] In some embodiments, the first binder and the second binder may be mixed in a powder state.

[0012] In some embodiments, the viscosity of the first and second binders may be from 550 cP to 14,500 cP.

[0013] In some embodiments, the method may further include mixing and kneading a first solvent after mixing the first and second binders to form a first preliminary composition having a solids content of 50 wt% to 75 wt%.

[0014] In some embodiments, the method may further include mixing a second solvent after forming the first preliminary composition to form a second preliminary composition having a solids content of 40 wt% to 65 wt%.

[0015] In some embodiments, the third preliminary composition may further include mixing a third binder with the second solvent, or mixing the third binder after mixing the second solvent.

[0016] In some embodiments, the first binder may include a carboxycellulose-based compound comprising a repeating unit of the following chemical formula 1, and the second binder may not include a carboxycellulose-based compound comprising a repeating unit of the following chemical formula 1:

[0017] [Chemical Formula 1]

[0018]

[0019] In the above chemical formula 1, M1 and M2 are each independently Na or Li, at least one of R1 to R4 is a group represented by the following chemical formula 2, the others are each independently H or a group represented by the following chemical formula 2, and n is an integer.

[0020] [Chemical Formula 2]

[0021]

[0022] In the above chemical formula 2, R5 is -CH0, -CH2CHO, -COCH3, or -CH2COCH3, and *- indicates a bonding position bonded to oxygen.

[0023] In some embodiments, R5 in the above formula 2 may be -CH0 or -COCH3.

[0024] In some embodiments, the second binder powder may include a cellulose-based compound comprising repeating units of the following formula 3:

[0025] [Chemical Formula 3]

[0026]

[0027] In the above chemical formula 3, M4 and M5 are each independently Na or Li, and n is an integer.

[0028] In some embodiments, a negative electrode active material in powder form is mixed with the first and second binders, and the negative electrode active material may include at least one of natural graphite, artificial graphite, and a silicon-based active material.

[0029] In some embodiments, the first and second solvents may each independently include at least one selected from the group consisting of water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, and t-butanol.

[0030] A negative electrode according to embodiments of the present disclosure comprises: a negative electrode current collector; and a negative electrode active material layer formed from a negative electrode composition manufactured by the method for manufacturing a negative electrode composition for a secondary battery described above, the negative electrode current collector being disposed on at least one surface thereof.

[0031] A secondary battery according to embodiments of the present disclosure includes the above-described negative electrode for a secondary battery; and a positive electrode opposite the negative electrode.

[0032] According to one embodiment of the present disclosure, a negative electrode composition for a secondary battery having improved dispersibility, stability, and adhesiveness and reduced resistance can be manufactured.

[0033] According to one embodiment of the present disclosure, the life characteristics and output characteristics of a negative electrode for a secondary battery manufactured using the negative electrode composition can be improved.

[0034] According to one embodiment of the present disclosure, the life characteristics and output characteristics of a secondary battery including the negative electrode can be improved.

[0035] The method for manufacturing the negative electrode composition for a secondary battery of the present disclosure, the negative electrode, and the secondary battery can be widely applied in green technology fields such as electric vehicles, battery charging stations, and other fields utilizing batteries, such as solar power generation and wind power generation. The method for manufacturing the negative electrode composition for a secondary battery of the present disclosure, the negative electrode, and the secondary battery can be used in eco-friendly electric vehicles, hybrid vehicles, etc., which suppress air pollution and greenhouse gas emissions and thus prevent climate change.

[0036] FIG. 1 is a schematic flowchart illustrating a method for manufacturing a negative electrode composition for a secondary battery according to exemplary embodiments.

[0037] FIG. 2 is a schematic flowchart illustrating a method for manufacturing a negative electrode composition for a secondary battery according to other exemplary embodiments.

[0038] Figures 3 and 4 are schematic plan views and cross-sectional views, respectively, showing secondary batteries according to exemplary embodiments.

[0039] Embodiments of the present disclosure provide a method for manufacturing an anode composition for a secondary battery (hereinafter, abbreviated as "anode composition"). An anode composition manufactured using the method for manufacturing the anode composition is provided. An anode for a secondary battery and a secondary battery manufactured using the anode composition are also provided.

[0040] Hereinafter, embodiments of the present disclosure will be described in detail. However, these are merely exemplary and the present disclosure is not limited to the specific embodiments described as examples.

[0041]

[0042] <Method for producing a cathode composition>

[0043] FIG. 1 is a schematic flowchart illustrating a method for manufacturing a negative electrode composition for a secondary battery according to exemplary embodiments.

[0044] The method for manufacturing the negative electrode composition for the secondary battery includes mixing (step S10) a first binder including at least one of carboxymethyl cellulose and a salt thereof including an acyclic hemiacetal functional group; and a second binder including at least one of carboxymethyl cellulose and a salt thereof not including the acyclic hemiacetal functional group.

[0045] The above hemiacetal functional group means a group including carbon in which one hydroxyl group and one ether bond (-O-) are bonded, formed by an acyclic hemiacetal reaction of at least one free hydroxyl group contained in carboxymethylcellulose or a salt thereof with an aldehyde compound.

[0046] The weight average molecular weight of the first and second binders is greater than 300,000 g / mol and less than 3,500,000 g / mol.

[0047] Accordingly, the dispersibility between active materials within the negative electrode composition is improved, and the internal resistance and capacity characteristics of the negative electrode and secondary battery manufactured therefrom can be improved.

[0048] The first binder has a fast dissolution rate when mixed into a solvent in the future, thereby better dispersing the negative electrode active materials, and the second binder has a relatively slow dissolution rate, thereby further improving the stability of the negative electrode composition being manufactured.

[0049] In addition, if the weight average molecular weight of the first and second binders is too small, the dissolution rate becomes too fast, which reduces the stability of the negative electrode composition, and if the weight average molecular weight is too large, the dissolution rate becomes too slow, which may cause aggregation between the negative electrode active materials.

[0050] The above first binder powder may include a product formed by a reaction of at least one free hydroxyl group (-OH) of carboxymethyl cellulose (CMC) and / or a salt thereof with an aldehyde compound to form an acyclic hemiacetal (hereinafter, abbreviated as a hemiacetal reaction). The metal included in the salt may be an alkali metal, and may be, for example, lithium, sodium, calcium, or the like.

[0051] Specifically, the above-mentioned free hydroxyl group and the -CHO group of the above-mentioned aldehyde compound react to form a direct bond between one hydroxyl group and one ether bond (-O-) on the same carbon.

[0052] A group containing carbon in which one hydroxyl group and one ether bond (-O-) are formed by the above hemiacetal reaction can be defined as a hemiacetal functional group.

[0053] That is, the product may be carboxymethylcellulose and / or a salt thereof in a form in which the hydroxyl group participating in the hemiacetal reaction is substituted with the hemiacetal functional group.

[0054] The above first binder powder may include carboxymethylcellulose and / or a salt thereof, which includes a hemiacetal functional group derived from a hemiacetal reaction of at least one of the free hydroxyl groups with an aldehyde compound.

[0055] Compared to a composition using only CMC and / or a salt thereof in which the hydroxyl group is not substituted by the hemiacetal functional group described above, the negative electrode composition according to the embodiments of the present disclosure can more effectively improve the dispersibility of negative electrode active materials in the negative electrode composition by including a compound including the hemiacetal functional group due to the repulsive force between ether bonds. Accordingly, the life characteristics and low resistance characteristics of a secondary battery including a negative electrode to which the negative electrode composition manufactured by the above manufacturing method is applied can be improved.

[0056] For example, the carboxymethyl cellulose and / or salt thereof containing the hemiacetal functional group can be prepared by mixing and heating CMC and / or salt thereof etherified only with methyl carboxylic acid and / or salt thereof and an aldehyde compound. The aldehyde compound may include a monoaldehyde compound and / or a dialdehyde compound. The aldehyde compound may include, for example, glyoxal, methyl glyoxal, etc.

[0057] Carboxymethylcellulose or a salt thereof containing the above hemiacetal functional group can be represented, for example, by the following chemical formula A.

[0058] [Chemical Formula A]

[0059]

[0060] In the above chemical formula A, the CMC represents a repeating unit constituting the main chain of carboxymethyl cellulose or a salt thereof, and the functional group bonded to the CMC represents a hemiacetal functional group. The R may be, for example, an alkyl group, or an alkyl group including an aldehyde group or a ketone group at the terminal, etc.

[0061] In some embodiments, the first binder may include a carboxycellulose-based compound including a repeating unit of the following chemical formula 1, and the second binder may not include a carboxycellulose-based compound including a repeating unit of the following chemical formula 1.

[0062] [Chemical Formula 1]

[0063]

[0064] In the above chemical formula 1, M1 and M2 are each independently Na or Li, at least one of R1 to R4 is a group represented by the following chemical formula 2, the others are each independently H or a group represented by the following chemical formula 2, and n is an integer.

[0065] [Chemical Formula 2]

[0066]

[0067] In the above chemical formula 2, R5 is -CH0, -CH2CHO, -COCH3, or -CH2COCH3, and *- indicates a bonding position bonded to oxygen.

[0068] In some embodiments, R5 in the above formula 2 may be -CH0 or -COCH3.

[0069] In some embodiments, the hemiacetal functional group may be, for example, a group represented by the following chemical formula A-1 or A-2.

[0070]

[0071] In the above chemical formula A-1 or A-2, *- indicates a bonding position where the hemiacetal functional group is bonded to the main chain of carboxymethylcellulose or its salt, and is the same as the position where the free hydroxyl group was bonded before the hemiacetal reaction proceeded.

[0072] Accordingly, the first binder powder may include a compound including a repeating unit of the chemical formula 1, wherein any one, two, three or four of R1 to R4 in the chemical formula 1 are groups represented by the chemical formula 2.

[0073] The above M1 and the above M2 may be identical to each other.

[0074] In the above chemical formula 1, -OCH2COOM1 and -OCH2COOM2, M1 and M2 can each exist in the form of carboxylic acid salts by ionic bonding, and -OCH2COO - M1 + and -OCH2COO - M2 + can exist in the form of

[0075] The above n may be, for example, 300 to 15000 or 500 to 10000.

[0076] In some embodiments, one or two of R1 to R4 may be a group represented by the above formula 2, and the remainder may be H.

[0077] In some embodiments, at least one of R2 and R4 may be a group represented by the above formula 2, and the other may be H.

[0078] In some embodiments, the first binder powder may include a compound in which among R1 to R4 in the chemical formula 1, R2 is a group represented by the chemical formula 2, and the remainder is H. The first binder powder may be, for example, a compound in which among R1 to R4, R2 is a group represented by the chemical formula 2, and the remainder is H.

[0079] In some embodiments, the first binder powder may include a compound in which R2 among R1 to R4 is a group represented by the above chemical formula 2 and the rest are H; and a compound in which R4 among R1 to R4 is a group represented by the above chemical formula 2 and the rest are H.

[0080] The compound including the repeating unit represented by the above chemical formula 1 may be, for example, a compound represented by the following chemical formula 1-1, but is not limited thereto.

[0081] [Chemical Formula 1-1]

[0082]

[0083] In the above chemical formula 1-1, M1, M 2, R1 to R4 and n refer to the contents described above in chemical formula 1. R E1 and R E2 are each independently H or CH2COOM3, M3 is Na or Li, and n is an integer. For example, R E1 is hydrogen and R E2 It can be CH2COOM3.

[0084] As a non-limiting example, M1 to M3 may be identical to each other.

[0085] In some embodiments, the second binder powder may include a cellulose-based compound comprising repeating units of the following formula 3:

[0086] [Chemical Formula 3]

[0087]

[0088] In the above chemical formula 3, M4 and M5 are Na or Li, and n is an integer. The n may be, for example, 300 to 15000 or 500 to 10000.

[0089] The compound including the repeating unit represented by the above chemical formula 3 may be, for example, a compound represented by the following chemical formula 3-1.

[0090] [Chemical Formula 3-1]

[0091]

[0092] In the above chemical formula 3-1, M4 and M5 are each independently Na or Li, and R E3 and R E4 One of them is H and the other is CH2COOM6, M6 is Na or Li, and n is an integer. The n can be, for example, 300 to 15000 or 500 to 10000. For example, R E3 is H and R E4 It can be CH2COOM6.

[0093] As a non-limiting example, M4 to M6 may be identical to each other.

[0094] In one embodiment, the first binder may be comprised of at least one of carboxymethylcellulose and a salt thereof comprising an acyclic hemiacetal functional group, and the second binder may be comprised of at least one of carboxymethylcellulose and a salt thereof not comprising an acyclic hemiacetal functional group.

[0095] In some embodiments, the mixing of the first and second binders may be performed using a mixer. For example, the mixer may be an automatic mixer driven by current. For example, a mixer manufactured by Primix may be used. As a non-limiting example, the mixer may be a 2000L PD mixer, a Planetary Despa & Mixer, etc.

[0096] The above mixer can be driven at the above constant speed through changes in the maximum driving current until the cathode slurry production is completed.

[0097] In some embodiments, the first binder and the second binder may be mixed in a powder state.

[0098] The first and second binders may be introduced into the mixer in a solid state. The first and second binder powders may not be introduced into the mixer in the form of a binder solution in which they are mixed in advance. Accordingly, the phenomenon of solvent shock, in which swelling occurs on the surface of the aggregates in which the first binder powder is aggregated and the first solvent cannot penetrate, can be further suppressed. Accordingly, the dispersibility of the negative active material and the first and second binders, the lifespan characteristics of the secondary battery, and the internal resistance can be further improved. For example, the introduction of the first solvent may be performed 1 to 20 seconds after the introduction of the negative active material powder and the first and second binder powders is completed.

[0099] In some embodiments, the first binder and the second binder may be mixed in a weight ratio of 10:90 to 90:10.

[0100] In some embodiments, the first binder and the second binder may be mixed in a weight ratio of 20:80 to 80:20, for example, in a weight ratio of 30:70 to 70:30 or 40:60 to 60:40. Accordingly, the stability of the negative electrode composition can be secured while improving the dispersibility of the negative electrode active materials in the negative electrode composition.

[0101] In some embodiments, the viscosity of the first and second binders may be 550 cP to 14,500 cP, for example, 2000 cP to 10000 cP or 3000 cP to 9000 cP. The viscosity refers to a viscosity measured in an aqueous solution state having a concentration of 1.2 wt%. The viscosity may be measured, for example, at room temperature. In this case, the aqueous solution having a concentration of 1.2 wt% may be formed by dissolving the first binder powder or the second binder powder in water at a concentration of 1 wt%, respectively.

[0102] In some embodiments, the weight average molecular weight of the first and second binders may be 500,000 g / mol to 3,000,000 g / mol, 1,200,000 g / mol to 2,700,000 g / mol, or 1,500,000 g / mol to 2,500,000 g / mol. Accordingly, the dissolution rate of the first binder powder can be controlled so as not to become too fast or the dissolution rate of the second binder powder to become too slow, thereby further improving the dispersibility of the negative electrode active materials in the negative electrode composition and sufficiently ensuring the stability of the negative electrode composition.

[0103] FIG. 2 is a schematic flowchart illustrating a method for manufacturing a negative electrode composition for a secondary battery according to other exemplary embodiments.

[0104] In some embodiments, the method may further include mixing and kneading a first solvent after mixing the first and second binders to form a first preliminary composition having a solid content of 50 wt% to 75 wt% (step S20).

[0105] In some embodiments, the method may further include mixing a second solvent after forming the first preliminary composition to form a second preliminary composition having a solids content of 40 wt% to 65 wt%.

[0106] In some embodiments, the method may further include forming a third binder composition by mixing a third binder with the second solvent or by mixing the third binder after mixing the second solvent (step S30).

[0107] The third binder may include a styrene-butadiene rubber (SBR) binder, a styrene-acrylate binder, a polyacrylic acid binder, a poly(3,4-ethylenedioxythiophene, PEDOT) binder, etc. These may be used alone or in combination of two or more.

[0108] The input form of the above third binder can be input in solid or liquid form and is not particularly limited.

[0109] In some embodiments, when no other components are further mixed, the third preliminary composition may be a cathode composition manufactured by the manufacturing method.

[0110] The above-described negative active material powder (hereinafter abbreviated as “negative active material”) may include a material capable of adsorbing and desorbing lithium ions. For example, the negative active material may be a carbon-based material such as crystalline carbon, amorphous carbon, a carbon composite, or carbon fiber; lithium metal; a lithium alloy; a silicon (Si)-containing material, or a tin (Sn)-containing material. These may be used alone or in combination of two or more. The amorphous carbon may include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers (MPCF), or the like.

[0111] The above crystalline carbon may include graphitic carbon such as natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0112] The lithium metal may include pure lithium metal and / or lithium metal having a protective layer formed thereon for suppressing dendrite growth, etc. In one embodiment, a lithium metal-containing layer deposited or coated on an anode current collector may be used as the anode active material layer. In one embodiment, a lithium thin film layer may be used as the anode active material layer.

[0113] Elements included in the above lithium alloy include aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, etc. These may be used alone or in combination of two or more.

[0114] The above silicon-containing material can provide increased capacity characteristics. The above silicon-containing material is Si, SiO x (0 <x<2), 금속 도핑된 SiO x (0 <x<2), 실리콘-탄소 복합체 등을 포함할 수 있다.

[0115] The above metal may include lithium and / or magnesium, and the metal-doped SiO x (0 <x<2)는 금속 실리케이트를 포함할 수 있다.

[0116] In some embodiments, a negative electrode active material in powder form is mixed with the first and second binders, and the negative electrode active material may include at least one of natural graphite, artificial graphite, and a silicon-based active material.

[0117] For example, the ratio of the total content of the natural graphite and / or artificial graphite and the content of the silicon-based active material among the negative active materials may be 90:10 to 99:1 or 95:5 to 99:1.

[0118] In some embodiments, the negative active material comprises natural graphite and SiO. x (0 <x<2)를 포함할 수 있다.

[0119] In some embodiments, the first solvent may begin to be added before the addition of the negative active material powder and the first and second binder powders is completed. For example, the first solvent may begin to be added together with the first and second binder powders when the addition of the first and second binder powders is 3 / 4 complete, but is not limited thereto.

[0120] In some embodiments, the first and second solvents may each independently include at least one selected from the group consisting of water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, and t-butanol.

[0121] In some embodiments, the first and second solvents may be the same.

[0122] As non-limiting examples, additional components such as conductive agents, thickeners, dispersants, etc. that can be further added to the cathode composition may be added to the mixer at any time.

[0123] By adjusting the amount of the above-described components, the solid content or viscosity of the cathode composition can be controlled according to the technical purpose.

[0124] The solid content of the above cathode composition may be, for example, 40 wt% to 65 wt%, 45 wt% to 63 wt%, 50 wt% to 61 wt%, or 52 wt% to 60 wt%.

[0125] For example, based on the total content of the solid content included in the negative electrode composition, the total amount of the negative electrode active material can be appropriately adjusted within a range of 80 wt% to 98.9 wt%, the total amount of the binder can be appropriately adjusted within a range of 1.0 wt% to 10 wt%, for example, 1.1 wt% to 10 wt%, and the total amount of other components such as the conductive material can be appropriately adjusted within a range of 0.1 wt% to 10 wt%.

[0126] The viscosity of the above cathode composition at 23°C may be, for example, 6000 cP to 15000 cP, 7000 cP to 13000 cP, 8000 cP to 11000 cP, 8500 cP to 10000 cP, or 9000 cP to 9500 cP.

[0127]

[0128] <Cathode for secondary batteries and secondary batteries>

[0129] Figures 3 and 4 are schematic plan views and cross-sectional views, respectively, illustrating secondary batteries according to exemplary embodiments. For example, Figure 4 is a cross-sectional view taken along line I-I' of Figure 3 in the thickness direction.

[0130] The structures illustrated in FIGS. 3 and 4 are examples for convenience of explanation, and the structure of the secondary battery according to embodiments of the present disclosure is not limited thereto.

[0131] Referring to FIGS. 3 and 4, the secondary battery may include a negative electrode (130) manufactured using the above-described negative electrode composition and a positive electrode (100) opposite the negative electrode (130).

[0132] The cathode (130) can be formed from a cathode composition manufactured by the above-described manufacturing method.

[0133] For example, a method for manufacturing a negative electrode for a secondary battery including the above-described manufacturing method may be provided. The method for manufacturing a negative electrode for a secondary battery may include applying the above-described negative electrode composition to at least one surface of a negative electrode current collector (125), drying, and rolling.

[0134] The cathode (130) can be formed by applying the cathode composition to at least one surface of the cathode current collector (125), drying, and rolling.

[0135] The positive electrode (100) may include a positive electrode current collector (105) and a positive electrode active material layer (110) formed on at least one surface of the positive electrode current collector (105).

[0136] The positive electrode current collector (105) may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector (105) may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. For example, the thickness of the positive electrode current collector (105) may be 10 μm to 50 μm.

[0137] The positive electrode active material layer (110) may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0138] According to exemplary embodiments, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0139] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 4.

[0140] [Chemical Formula 4]

[0141] Li x Ni a M b O 2+z

[0142] In chemical formula 4, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b≤0.5, -0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0143] The chemical structure represented by Chemical Formula 4 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn can serve as the main active element of the positive electrode active material together with Ni. Chemical Formula 4 is provided to express the bonding relationship of the above main active elements and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0144] In one embodiment, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the positive electrode active material or the layered structure / crystal structure. The auxiliary elements may be incorporated into the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 4.

[0145] The auxiliary element may include at least one selected from the group consisting of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may also function as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn, for example, Al.

[0146] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 4-1.

[0147] [Chemical Formula 4-1]

[0148] Li x Ni a M1 b1 M2 b2 O 2+z

[0149] In Chemical Formula 4-1, M1 may include Co, Mn, and / or Al. M2 may include the auxiliary elements described above. In Chemical Formula 4-1, 0.9≤x≤1.2, 0.5≤a≤0.99, 0.01≤b1+b2≤0.5, -0.5≤z≤0.1 may be satisfied.

[0150] The above-described positive electrode active material may further include a coating element or doping element. For example, elements substantially identical to or similar to the above-described auxiliary elements may be used as the coating element or doping element. For example, the above-described elements may be used singly or in combination of two or more.

[0151] The above coating element or doping element may be present on the surface of the lithium-nickel metal oxide particle, or may penetrate through the surface of the lithium-nickel metal composite oxide particle and be included in the bonding structure represented by the above chemical formula 4 or chemical formula 4-1.

[0152] The above positive electrode active material may include a nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content may be used.

[0153] Ni can be provided as a transition metal associated with the output and capacity of a lithium secondary battery. Therefore, by employing a high-content (High-Ni) composition as described above in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0154] However, as the Ni content increases, the long-term storage stability and lifespan stability of the cathode or secondary battery may relatively deteriorate, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, the inclusion of Co can maintain electrical conductivity, while improving lifespan stability and capacity retention characteristics through Mn.

[0155] The content of Ni (e.g., the mole fraction of nickel among the total moles of nickel, cobalt, and manganese) in the NCM-based lithium oxide may be 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0156] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0157] In some embodiments, the positive electrode active material may include, for example, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide) active material, a Mn-rich active material, a Co-less active material, etc. having a chemical structure or crystal structure represented by Chemical Formula 5. These may be used alone or in combination of two or more.

[0158] [Chemical Formula 5]

[0159] p[Li2MnO3]·(1-p)[Li q JO2]

[0160] In chemical formula 5, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B 중 적어도 하나의 원소를 포함할 수 있다.

[0161] The positive electrode active material can be mixed in a solvent to prepare a positive electrode slurry. The positive electrode slurry can be coated on at least one surface of a positive electrode current collector (105), and then dried and rolled to prepare a positive electrode active material layer (110). The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. The positive electrode active material layer (110) can further include a binder and optionally can further include a conductive material and / or a thickener.

[0162] As the above solvent, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. can be used.

[0163] The above binder may include polyvinylidenefluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. These may be used alone or in combination of two or more.

[0164] In one embodiment, a PVDF-based binder may be used as the positive electrode binder. In this case, the amount of binder used to form the positive electrode active material layer (110) may be reduced, while the amount of positive electrode active material may be relatively increased. Accordingly, the output characteristics and capacity characteristics of the secondary battery may be improved.

[0165] The conductive material may be added to enhance the conductivity and / or mobility of lithium ions or electrons of the positive electrode active material layer (110). For example, the conductive material may include a carbon-based conductive material such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), carbon fiber, etc., and / or a metal-based conductive material including a perovskite material such as tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc. These may be used alone or in combination of two or more.

[0166] The positive electrode slurry may further include a thickener and / or a dispersant. In one embodiment, the positive electrode slurry may include a thickener such as carboxymethyl cellulose (CMC).

[0167] A cathode composition can be manufactured by a manufacturing method according to exemplary embodiments.

[0168] The negative electrode (130) may include a negative electrode current collector (125) and a negative electrode active material layer (120) formed using a negative electrode composition manufactured by a manufacturing method according to exemplary embodiments, and disposed on at least one surface of the negative electrode current collector (125). The negative electrode composition manufactured by the manufacturing method according to exemplary embodiments may have a negative electrode slurry form. The negative electrode active material layer (120) may be formed by applying and drying the above-described negative electrode composition on at least one surface of the negative electrode current collector (125), and may be formed, for example, by applying, drying, and rolling the above-described negative electrode composition.

[0169] For example, the negative electrode current collector (125) may include copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, etc. These may be used alone or in combination of two or more. For example, the thickness of the negative electrode current collector (125) may be 10 μm to 50 μm.

[0170] The negative electrode active material layer (120) may include the above-described negative electrode active material. For example, the negative electrode active material may include a plurality of negative electrode active material particles.

[0171] After the above-described negative electrode composition is coated / deposited on a negative electrode current collector (125), drying and rolling can be performed to manufacture a negative electrode active material layer (120). The coating can include methods such as gravure coating, slot die coating, multilayer simultaneous die coating, imprinting, doctor blade coating, dip coating, bar coating, and casting. The negative electrode active material layer (120) can optionally further include a conductive agent, a thickener, and the like.

[0172] The above-described materials that can be used in manufacturing the anode (100) as the above-described conductive agent and thickener can be used.

[0173] In exemplary embodiments, a separator (140) may be interposed between the anode (100) and the cathode (130). The separator (140) may be configured to prevent electrical short-circuiting between the anode (100) and the cathode (130) and to allow ion flow. For example, the thickness of the separator may be 10 μm to 20 μm.

[0174] For example, the separator (140) may include a porous polymer film or a porous nonwoven fabric.

[0175] The above porous polymer film may include a polyolefin polymer such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. These may be used alone or in combination of two or more.

[0176] The above porous nonwoven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, etc.

[0177] The separator (140) may include a ceramic material. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0178] The separator (140) may have a single-layer or multi-layer structure including the above-described polymer film and / or non-woven fabric.

[0179] According to exemplary embodiments, an electrode cell is defined by an anode (100), a cathode (130), and a separator (140), and a plurality of electrode cells may be stacked to form an electrode assembly (150) in the form of, for example, a jelly roll. For example, the electrode assembly (150) may be formed through winding, stacking, z-folding, stack-folding, etc. of the separator (140).

[0180] An electrode assembly (150) may be housed together with an electrolyte within a case (160) to define a lithium secondary battery. According to exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

[0181] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent, and the lithium salt is, for example, Li+ X - is expressed as and the anion of the lithium salt (X - ) as F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Examples include:

[0182] Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, vinylene carbonate, methylacetate (MA), ethyl acetate (EA), n-propylacetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), fluoroethyl acetate (FEA), difluoroethyl acetate (DFEA), trifluoroethyl acetate (TFEA), dibutyl ether, Tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethyl alcohol, isopropyl alcohol, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, gamma-butyrolactone, and propylene sulfite can be used. These can be used alone or in combination of two or more.

[0183] The above non-aqueous electrolyte may further include additives. The additives may include, for example, cyclic carbonate compounds, fluorine-substituted carbonate compounds, sultone compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc. These may be used alone or in combination of two or more.

[0184] The above cyclic carbonate compound may include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), etc.

[0185] The above fluorine-substituted cyclic carbonate compound may include fluoroethylene carbonate (FEC), etc.

[0186] The above sultone compounds may include 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, etc.

[0187] The above cyclic sulfate compound may include 1,2-ethylene sulfate, 1,2-propylene sulfate, etc.

[0188] The above cyclic sulfite compound may include ethylene sulfite, butylene sulfite, etc.

[0189] The above phosphate compound may include lithium difluoro bis-oxalato phosphate, lithium difluoro phosphate, etc.

[0190] The above borate compound may include lithium bis(oxalate) borate, etc.

[0191] In some embodiments, a solid electrolyte may be used instead of the non-aqueous electrolyte described above. In this case, the lithium secondary battery may be manufactured in the form of an all-solid-state battery. Furthermore, a solid electrolyte layer may be placed between the positive electrode (100) and negative electrode (130) instead of the separator (140) described above.

[0192] The solid electrolyte may include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte may include Li2S-P2S5, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are positive numbers, Z is Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q , (p, q are positive numbers, M is P, Si, Ge, B, Al, Ga, or In), Li7-xPS6-xCl x (0≤x≤2), Li7-xPS6-xBr x (0≤x≤2), Li7-xPS6-xI x (0≤x≤2) etc. These can be used alone or in combination of two or more.

[0193] In one embodiment, the solid electrolyte may include an oxide-based amorphous solid electrolyte, such as, for example, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li2O-B2O3-ZnO, etc.

[0194] As illustrated in FIGS. 2 and 3, electrode tabs (positive electrode tabs and negative electrode tabs) may protrude from the positive electrode collector (105) and negative electrode collector (125) belonging to each electrode cell and extend to one side of the case (160). The electrode tabs may be fused together with the one side of the outer case (160) to form electrode leads (positive electrode leads (107) and negative electrode leads (127)) that extend or are exposed to the outside of the outer case (160).

[0195] The above lithium secondary battery can be manufactured in a cylindrical, square, pouch or coin shape using, for example, a can.

[0196]

[0197] The embodiments of the present disclosure described above include the following aspects and can be implemented through at least one of the following aspects.

[0198] A method for producing a negative electrode composition for a secondary battery according to a first aspect of the present disclosure comprises mixing a first binder comprising at least one of carboxymethyl cellulose and a salt thereof comprising an acyclic hemiacetal functional group; and a second binder comprising at least one of carboxymethyl cellulose and a salt thereof not comprising the acyclic hemiacetal functional group, wherein the weight average molecular weights of the first and second binders are greater than 300,000 g / mol and less than 3,500,000 g / mol.

[0199] In the first aspect, according to the second aspect, the first binder and the second binder can be mixed in a weight ratio of 10:90 to 90:10.

[0200] In the second aspect, according to the third aspect, the first binder and the second binder can be mixed in a weight ratio of 20:80 to 80:20.

[0201] In any one of the first to third aspects, according to the fourth aspect, the first binder and the second binder can be mixed in a powder state.

[0202] In any one of the first to fourth aspects, according to the fifth aspect, the viscosity of the first and second binders may be 550 cP to 14,500 cP.

[0203] In any one of the first to fifth aspects, according to the sixth aspect, the method may further include mixing and kneading a first solvent after mixing the first and second binders to form a first preliminary composition having a solid content of 50 wt% to 75 wt%.

[0204] In the sixth aspect, according to the seventh aspect, after forming the first preliminary composition, the method may further include mixing a second solvent to form a second preliminary composition having a solid content of 40 wt% to 65 wt%.

[0205] In the seventh aspect, according to the eighth aspect, a step of forming a third preliminary composition may further be included by mixing a third binder with the second solvent or by mixing the third binder after mixing the second solvent.

[0206] In any one of the first to eighth aspects, according to the ninth aspect, the first binder may include a carboxycellulose-based compound including a repeating unit of the chemical formula 1, and the second binder may not include a carboxycellulose-based compound including a repeating unit of the chemical formula 1.

[0207] In the ninth aspect, according to the tenth aspect, R5 in the chemical formula 2 may be -CH0 or -COCH3.

[0208] In any one of the first to tenth aspects, according to the eleventh aspect, the second binder powder may include a cellulose compound including a repeating unit of the chemical formula 3.

[0209] In any one of the first to eleventh aspects, according to the twelfth aspect, a negative electrode active material in powder form is mixed together with the first and second binders, and the negative electrode active material may include at least one of natural graphite, artificial graphite, and a silicon-based active material.

[0210] In the eighth aspect, according to the thirteenth aspect, the first and second solvents may each independently include at least one selected from the group consisting of water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, and t-butanol.

[0211] A negative electrode for a secondary battery according to a 14th aspect of the present disclosure comprises: a negative electrode current collector; and a negative electrode active material layer formed from a negative electrode composition manufactured by a method for manufacturing a negative electrode composition according to any one of the first to 13th aspects, the negative electrode current collector being disposed on at least one surface thereof.

[0212] A secondary battery according to the 15th aspect of the present disclosure comprises: a negative electrode for a secondary battery according to the 14th aspect; and a positive electrode opposite to the negative electrode.

[0213]

[0214] Hereinafter, embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope and technical idea of ​​the present disclosure, and it is also natural that such changes and modifications fall within the scope of the appended claims.

[0215]

[0216] Manufacturing example

[0217] Manufacturing Example 1

[0218] 250 g of CMC-Na (weight average molecular weight: 1,500,000, degree of substitution (DS): 0.9) containing a repeating unit represented by the above chemical formula 3, 3.5 g of methylglyoxal, and 0.5 g of oxalic acid were added to 500 g of ethanol solution, stirred at 60°C for 180 minutes, and dried to prepare a first binder powder (compound a).

[0219] The compound a above includes a repeating unit represented by the chemical formula 1 above, M1 and M2 in the chemical formula 1 are Na, R2 among R1 to R4 is a group represented by the chemical formula 2 above, the rest are H, and R5 in the chemical formula 2 above is CH3.

[0220] Manufacturing Example 2

[0221] A first binder powder (compound b) was prepared in the same manner as in Manufacturing Example 1, except that an equivalent amount of glyoxal was added instead of methylglyoxal.

[0222] The compound b above includes a repeating unit represented by the chemical formula 1, M1 and M2 in the chemical formula 1 are Na, R2 among R1 to R4 is a group represented by the chemical formula 2, the rest are H, and R5 in the chemical formula 2 is H.

[0223] Manufacturing Example 3

[0224] A first binder powder (compound c) was prepared in the same manner as in Manufacturing Example 1, except that 250 g of CMC-Na (weight average molecular weight: 300,000, degree of substitution (DS): 0.9) was used.

[0225] Manufacturing Example 4

[0226] A first binder powder (compound d) was prepared in the same manner as in Manufacturing Example 1, except that 250 g of CMC-Na (weight average molecular weight: 3,500,000, degree of substitution (DS): 0.9) was used.

[0227]

[0228] Example

[0229] Example 1

[0230] (1) Preparation of cathode composition

[0231] Compound a was used as the first binder powder, and CMC-Na (weight average molecular weight: 1,500,000, degree of substitution (DS): 0.9) used in Manufacturing Example 1 was used as the second binder powder. Compound a was a compound including a repeating unit represented by the above chemical formula 1, and CMC-Na was a compound including a repeating unit represented by the above chemical formula 3.

[0232] The planetary mixer of the mixer (Primix, 2000L class PD mixer) was set and maintained at the maximum operating speed, and natural graphite as a negative active material, carbon black as a conductive material, and first binder powder and second binder powder were fed into the mixer.

[0233] After that, water was added as the first solvent to the mixer and kneaded to form the first preliminary composition.

[0234] Afterwards, SBR was added to the mixer and water was added to prepare a cathode composition in the form of a slurry.

[0235] Based on the total solid content of the manufactured negative electrode composition, the weight ratio of natural graphite, carbon black, first binder powder, second binder powder, and SBR was 96.8:0.5:0.24:0.96:1.5. The total solid content of the negative electrode composition was 54 wt%.

[0236]

[0237] Examples 2 to 8 and Comparative Examples 1 to 5

[0238] A negative electrode composition was prepared in the same manner as in Example 1, except that the weight ratio, viscosity, and weight average molecular weight of the first and second binders were changed as shown in Table 1 below.

[0239] First binderSecond binderWeight ratio of first and second bindersFirst and second bindersViscosityWeight average molecular weightExample 1 Compound aCMC-Na20:803000cP1,500,000g / molExample 2 Compound aCMC-Na40:603000cP1,500,000g / molExample 3 Compound aCMC-Na50:503000cP1,500,000g / molExample 4 Compound aCMC-Na60:403000cP1,500,000g / molExample 5 Compound aCMC-Na80:203000cP1,500,000g / molExample 6 Compound bCMC-Na50:503000cP1,500,000g / molExample 7 Compound aCMC-Na10:903000cP1,500,000g / molExample 8 Compound aCMC-Na90:103000cP1,500,000g / molComparative Example 1-CMC-Na0:1003000cP1,500,000g / molComparative Example 2 Compound a-100:03000cP1,500,000g / molComparative Example 3 Compound aCMC-Na50:50500cP300,000g / molComparative Example 4 Compound aCMC-Na50:5015000cP3,500,000g / molComparative Example 5-CMC-Na0:10020000cP4,000,000g / mol

[0240]

[0241] (2) Manufacturing of secondary batteries

[0242] A secondary battery was manufactured as follows using the negative electrode composition according to the above-described examples and comparative examples.

[0243] The above negative electrode composition was coated, dried, and rolled on a copper current collector to manufacture a negative electrode.

[0244] LiNi as positive electrode active material 0.8 Co 0.1 Mn 0. A slurry-type positive electrode composition was prepared by mixing O2, carbon black as a conductive agent, and PVDF as a binder in a mass ratio of 95:3:2. The positive electrode slurry was coated, dried, and rolled onto an aluminum current collector to prepare a positive electrode.

[0245] The 43 positive electrode sheets and the 44 negative electrode sheets were notched to a predetermined size, stacked, and a separator (polyethylene, 25 ㎛ thick) was interposed between the positive and negative electrodes to form an electrode cell. Then, the tab portions of the positive and negative electrodes were welded. The welded positive electrode / separator / negative electrode assembly was placed in a pouch and sealed on three sides except for the electrolyte injection portion. At this time, the part with the electrode tab was included in the sealing portion. The electrolyte was injected through the electrolyte injection portion, and the electrolyte injection portion was also sealed, followed by impregnation for 12 hours or more to manufacture a secondary battery.

[0246] The electrolyte was prepared using a 1M LiPF6 solution prepared using a mixed solvent of EC / EMC (25 / 75; volume ratio), to which 1 wt% of vinylene carbonate (VC) and 0.5 wt% of 1,3-propenesultone (PRS) were added based on the total weight of the solution.

[0247] Pre-charging was performed on the above lithium secondary battery at a current (5 A) corresponding to 0.25 C for 36 minutes. Degassing was performed after 1 hour, aging was performed for more than 24 hours, and then chemical charge / discharge was performed (charge condition CC-CV 0.2 C 4.2 V 0.05 C CUT-OFF, discharge condition CC 0.2 C 2.5 V CUT-OFF).

[0248]

[0249] Experimental example

[0250] (1) Measurement of negative electrode adhesion

[0251] For the cathodes of the above-described examples and comparative examples, the adhesive strength was measured through a 90° peel test. The measuring equipment used was the DS2-N model from IMADA.

[0252] Specifically, the cathode was cut to a length of 18 mm to prepare a sample. A tape was attached to the sample, and the force (90°) required to remove the tape was measured and expressed in units of N / 18 mm.

[0253] The results are shown in Table 2 below.

[0254] (2) Internal resistance measurement

[0255] The internal resistance of the secondary batteries of the above-described examples and comparative examples was measured using a 200A class charger / discharger from Wonik PNE.

[0256] Specifically, a current equivalent to 1C was applied for 10 seconds at SOC50% and the direct current internal resistance (DCIR) was measured.

[0257] The results are shown in Table 2 below.

[0258] (3) Capacity maintenance rate evaluation

[0259] For the lithium half-cells of the examples and comparative examples, charging (CC-CV 0.33C 4.2V 0.05C CUT-OFF) and discharging (CC 0.33C 2.5V CUT-OFF) were performed 800 times each in a chamber maintained at 25°C, and the discharge capacity at 800 times was divided by the discharge capacity at 1 time and multiplied by 100 to evaluate the capacity retention rate.

[0260] The results are shown in Table 2 below.

[0261] Weight-average molecular weight of the first and second binders, evaluation results, adhesive strength (N / 18mm), internal resistance (mΩ), capacity Retention rate (%) Example 1 20: 80 1,500,000 g / mol 0.53 1.11 287.1 Example 2 40: 60 1,500,000 g / mol 0.51 1.04 389.0 Example 3 50: 50 1,500,000 g / mol 0.49 1.02 389.9 Example 4 60: 40 1,500,000 g / mol 0.45 0.99 591.2 Example 5 80: 20 1,500,000 g / mol 0.42 0.99 290.9 Example 6 50: 50 1,500,000 g / mol 0.49 1.02 289.7 Example 7 10: 90 1,50 0,000g / mol 0.50 1.44 87 0.3 Example 8 9 0: 10 1,500,000g / mol 0.35 1.24 47 2.8 Comparative Example 10: 100 1,500,000g / mol 0.53 1.56 16 0.8 Comparative Example 2 100: 01,500,000g / mol 0.32 1.52 36 1.1 Comparative Example 3 50: 50 300,000g / mol 0.33 1.62 06 0.2 Comparative Example 4 50: 50 3,500,000g / mol 0.63 1.59 368.6 Comparative Example 50: 100 4,000,000g / mol 0.64 1.63 60.2

[0262]

[0263] Referring to Table 2, in the secondary batteries according to the examples, the adhesive strength and capacity retention rate were improved and the internal resistance was reduced.

[0264] In the secondary battery according to the comparative examples, in which the negative electrode composition containing the first binder or the second binder alone, or the first and second binders are mixed, and the weight average molecular weight is less than 300,000 g / mol or more than 3,500,000 g / mol, the capacity retention rate is lowered to 68.6% or less, and the internal resistance is increased to 1.523 mΩ or more.

[0265] In the secondary batteries according to Examples 1 to 6 in which the weight ratio of the first and second binders was 20:80 to 80:20, the capacity retention rate was further improved and the internal resistance was further reduced.

[0266] The negative electrode compositions manufactured in Comparative Examples 1 and 2 using only a second binder that did not contain a hemiacetal functional group showed significantly reduced dispersibility between active materials, resulting in a secondary battery employing the composition having a very low capacity retention rate and a very high internal resistance. Even when a compound having a high weight average molecular weight, such as in Comparative Example 2, was used, only the adhesive strength increased excessively, and the capacity retention rate and internal resistance of the secondary battery were still evaluated to be deteriorated.

[0267] In the negative electrode composition manufactured in Comparative Example 3 using only the first binder containing a hemiacetal functional group, stability was reduced and it acted as an obstacle to Li insertion / de-insertion, resulting in an increase in internal resistance and a low capacity retention rate.

[0268] In Comparative Example 4, where the weight average molecular weights of the first and second binder powders were too small, the slurry stability was reduced, resulting in a phenomenon similar to that of Comparative Example 2, resulting in an increase in internal resistance and a low capacity retention rate.

[0269] In Comparative Example 5, where the weight average molecular weight of the first and second binder powders was too small, the dissolution rate in the solvent was too slow, so that dispersion between the active materials did not proceed smoothly, and a phenomenon similar to Comparative Example 1 occurred, resulting in an increase in internal resistance and a low capacity retention rate.

Claims

1. A step of mixing a first binder comprising at least one of carboxymethyl cellulose and a salt thereof containing an acyclic hemiacetal functional group; and a second binder comprising at least one of carboxymethyl cellulose and a salt thereof not containing the acyclic hemiacetal functional group, A method for producing a negative electrode composition for a secondary battery, wherein the weight average molecular weight of the first and second binders is more than 300,000 g / mol and less than 3,500,000 g / mol.

2. A method for producing a negative electrode composition for a secondary battery, wherein the first binder and the second binder are mixed in a weight ratio of 10:90 to 90:10 in the first paragraph.

3. A method for producing a negative electrode composition for a secondary battery, wherein the first binder and the second binder are mixed in a weight ratio of 20:80 to 80:20 in the second paragraph.

4. A method for producing a negative electrode composition for a secondary battery, wherein the first binder and the second binder are mixed in a powder state in the first paragraph.

5. A method for producing a negative electrode composition for a secondary battery, wherein the viscosity of the first and second binders in the first paragraph is 550 cP to 14,500 cP.

6. A method for producing a negative electrode composition for a secondary battery, further comprising the step of mixing and kneading a first solvent after mixing the first and second binders in the first paragraph to form a first preliminary composition having a solid content of 50 wt% to 75 wt%.

7. A method for producing a negative electrode composition for a secondary battery, further comprising the step of forming a second preliminary composition having a solid content of 40 wt% to 65 wt% by mixing a second solvent after forming the first preliminary composition in the sixth paragraph.

8. A method for producing a negative electrode composition for a secondary battery, further comprising the step of forming a third preliminary composition by mixing a third binder with the second solvent in the seventh paragraph or mixing the third binder after mixing the second solvent.

9. A method for producing a negative electrode composition for a secondary battery, wherein in paragraph 1, the first binder comprises a carboxycellulose-based compound comprising a repeating unit of the following chemical formula 1, and the second binder does not comprise a carboxycellulose-based compound comprising a repeating unit of the following chemical formula 1: [Chemical Formula 1] (In the chemical formula 1 above, M1 and M2 are each independently Na or Li, at least one of R1 to R4 is a group represented by the chemical formula 2 below, the others are each independently H or a group represented by the chemical formula 2 below, and n is an integer) [Chemical formula 2] (In the above chemical formula 2, R5 is -CH0, -CH2CHO, -COCH3, or -CH2COCH3, and *- indicates a bonding position bonded to oxygen).

10. A method for producing a negative electrode composition for a secondary battery, wherein in paragraph 9, R5 in the chemical formula 2 is -CH0 or -COCH3.

11. A method for producing a negative electrode composition for a secondary battery, wherein the second binder powder comprises a cellulose-based compound including a repeating unit of the following chemical formula 3: [Chemical Formula 3] (In the above chemical formula 3, M4 and M5 are each independently Na or Li, and n is an integer).

12. A method for producing a negative electrode composition for a secondary battery, wherein, in the first paragraph, a negative electrode active material in a powder form is mixed with the first and second binders, and the negative electrode active material includes at least one of natural graphite, artificial graphite, and a silicon-based active material.

13. A method for producing a negative electrode composition for a secondary battery, in claim 8, wherein the first and second solvents each independently include at least one selected from the group consisting of water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, and t-butanol.

14. Negative current collector; and A negative electrode for a secondary battery, comprising a negative electrode active material layer formed from a negative electrode composition manufactured by the manufacturing method of claim 1, and disposed on at least one surface of the negative electrode current collector.

15. A negative electrode for a secondary battery according to Article 14; and A secondary battery comprising a positive electrode opposite to the negative electrode.

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