Negative electrode and rechargeable lithium battery comprising same

Abstract

Provided are a negative electrode and a rechargeable lithium battery comprising same, wherein the negative electrode includes: a current collector; and a negative electrode active material layer located on the current collector and composed of a silicon-based negative electrode active material and a polymer having a potential band of 1.5 V or less with respect to Li, the negative electrode having a binding force of 1.0 gf / mm or more and an electrical conductivity of 1.0 S / m to 6.0 S / m.

Description

Anode and lithium secondary battery containing the same

[0001] It relates to a negative electrode and a lithium secondary battery including the same.

[0002] The recent rapid proliferation of battery-powered electronic devices, such as mobile phones, laptops, and electric vehicles, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity lithium secondary batteries. Accordingly, active research and development is underway to improve the performance of lithium secondary batteries.

[0003] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode that contain active materials capable of intercalating and deintercalating lithium ions, and an electrolyte, and produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated / deintercalated from the positive electrode and the negative electrode.

[0004] One embodiment provides a cathode exhibiting high electrical conductivity and stable battery performance.

[0005] Another embodiment provides a lithium secondary battery comprising the above negative electrode.

[0006] According to one embodiment, a negative electrode is provided, comprising: a current collector; and a negative electrode active material layer positioned on the current collector and made of a polymer and silicon-based negative electrode active material having a potential band with respect to Li of 1.5 V or less, wherein the negative electrode has an adhesive strength of 1.0 gf / mm or more and an electrical conductivity of 1.0 S / m to 6.0 S / m.

[0007] According to another embodiment, a lithium secondary battery is provided, which includes the negative electrode, a positive electrode including a positive electrode active material, and a non-aqueous electrolyte.

[0008] Specific details of other implementation examples are included in the detailed description below.

[0009] The cathode according to one embodiment can exhibit high electrical conductivity and stable battery performance.

[0010] Figures 1 to 4 are cross-sectional views schematically showing a lithium secondary battery according to one embodiment.

[0011] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention. The present invention is defined solely by the scope of the claims set forth below.

[0012] Unless otherwise specified herein, when a part such as a layer, film, region, plate, etc. is said to be "on top of" another part, this includes not only cases where it is "directly on top of" the other part, but also cases where there is another part in between.

[0013] Unless otherwise specified herein, the singular may also include the plural. In addition, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0014] As used herein, “combination thereof” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the components.

[0015] Unless otherwise defined herein, the particle size may be the average particle size. In addition, the particle size refers to the average particle size (D50), which means the diameter of particles with a cumulative volume of 50% by volume in a particle size distribution. The average particle size (D50) can be measured by a method well known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) photograph or a scanning electron microscope (SEM) photograph. Alternatively, the average particle size (D50) value can be obtained by measuring with a measuring device that utilizes dynamic light-scattering, performing data analysis to count the number of particles for each particle size range, and calculating from the counted number. Alternatively, the average particle size (D50) value can be obtained by measuring with a laser diffraction method. When measuring by laser diffraction, more specifically, after the particles to be measured are dispersed in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasonic waves of approximately 28 kHz at an output of 60 W, and the average particle size (D50) based on 50% of the particle size distribution in the measuring device can be calculated.

[0016] According to one embodiment, a negative electrode includes a current collector and a negative electrode active material layer positioned on the current collector and made of a polymer and silicon-based negative electrode active material having a potential band with respect to Li of 1.5 V or less. The negative electrode may have a binding force of 1.0 gf / mm or more and an electrical conductivity of 1.0 S / m to 6.0 S / m.

[0017] The above negative electrode active material layer includes only a silicon-based negative electrode active material and a polymer having a potential band of 1.5 V or less with respect to Li.

[0018] The above polymer may have a potential band with respect to Li of 1.5 V or less, and may have a potential band with respect to Li of 1.5 V or less and 0.1 V or more.

[0019] The polymer having the above potential band can serve as a conductive material that accepts lithium ions, and can also serve as a binder that effectively bonds silicon-based negative electrode active materials to each other, thereby suppressing volume expansion of the negative electrode active materials and improving their lifespan characteristics. Furthermore, the polymer can also serve as an active material that reacts with lithium ions and participates in charge-discharge reactions.

[0020] Since the above polymer has a great effect in suppressing volume expansion, it can be more effective when used together with an active material that has a great volume expansion during charge and discharge, such as a silicon-based negative electrode active material.

[0021] Since the negative active material layer according to one embodiment includes a polymer capable of suppressing volume expansion, high capacity can be effectively obtained by using a silicon-based active material without deterioration of lifespan due to volume expansion, and capacity can also be obtained from the polymer.

[0022] In addition, since the polymer acts as a conductive material and a binder, the negative active material according to one embodiment can be composed only of a silicon-based active material and a polymer without the need to use an additional conductive material and binder.

[0023] Examples of the polymers include polythiophene, poly(3,4-methylenedioxythiophene), polypyrrole, or combinations thereof. These polymers are environmentally friendly polymers.

[0024] In one embodiment, the polymer content may be 30 wt% to 85 wt%, 35 wt% to 85 wt%, or 39 wt% to 81 wt%, based on 100 wt% of the total weight of the negative electrode active material layer. When the polymer content is within the above range, a more excellent bonding force can be exhibited, volume expansion of the silicon-based active material can be more effectively suppressed, better life characteristics and better ionic conductivity can be exhibited, and an anode exhibiting appropriate charge / discharge efficiency and better electrical conductivity can be implemented.

[0025] The content of the silicon-based active material may be 15 wt% to 70 wt%, 15 wt% to 65 wt%, or 19 wt% to 61 wt%, based on 100 wt% of the total weight of the negative electrode active material layer. When the content of the silicon-based active material is within the above range, a higher capacity may be exhibited.

[0026] The above silicon-based negative electrode active material may include a silicon-based material and an amorphous carbon coating layer positioned on the silicon-based material.

[0027] In one embodiment, the silicon-based material is Si, SiO x (0 <x≤2) 또는 이들의 조합일 수 있다. 상기 Si은 Si 나노 입자일 수 있다.

[0028] In another embodiment, the silicon-based negative electrode active material may include an assembly of at least one silicon nanoparticle and an amorphous carbon coating layer positioned on the surface of the assembly.

[0029] The particle size of the above silicon nanoparticles may be 10 nm to 1,000 nm, and according to another embodiment, 10 nm to 200 nm, or 20 nm to 150 nm. When the particle size of the silicon nanoparticles is within the above range, excessive volume expansion occurring during charge and discharge can be suppressed, and disconnection of the conductive path due to particle fragmentation during charge and discharge can be prevented.

[0030] In the above amorphous carbon coating layer, the amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or a combination thereof. The thickness of the amorphous carbon coating layer may be 1 nm to 2 μm, 1 nm to 500 nm, 10 nm to 300 nm, or 20 nm to 200 nm. When the thickness of the amorphous carbon coating layer is within the above range, silicon volume expansion during charge and discharge can be well suppressed.

[0031] When the silicon-carbon composite includes silicon nanoparticles and an amorphous carbon coating layer, the content of the silicon nanoparticles may be 30 wt% to 70 wt%, or 40 wt% to 65 wt%, based on 100 wt% of the total silicon-carbon composite. In addition, the content of the amorphous carbon coating layer may be 30 wt% to 70 wt%, or 35 wt% to 60 wt%, based on 100 wt% of the total silicon-carbon composite.

[0032] The current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof.

[0033] According to one embodiment, the negative electrode may have an adhesive strength of 1.0 gf / mm or more, and may also be 1.0 gf / mm to 3.5 gf / mm, 1.2 gf / mm to 3.3 gf / mm, or 1.5 gf / mm to 3.0 gf / mm. In one embodiment, the adhesive strength of the negative electrode refers to the adhesive strength between the current collector and the negative electrode active material layer. When the adhesive strength of the negative electrode is within the above range, it may exhibit better life characteristics and lower expansion rate. In one embodiment, the adhesive strength may be obtained by measuring the 180° peel strength using a tensile strength tester after attaching a double-sided tape to the negative electrode. The double-sided tape may be a double-sided tape coated with an acrylic adhesive, and may be, for example, 3M 9346 paper double-sided tape.

[0034] According to one embodiment, the cathode may have an electrical conductivity of 1.0 S / m to 6.0 S / m, and may also have an electrical conductivity of 1.5 S / m to 5.5 S / m, 2.0 S / m to 5.0 S / m, or 3.0 S / m to 6.0 S / m. When the electrical conductivity of the cathode is within the above range, it may exhibit better efficiency and output characteristics.

[0035] <Method for manufacturing cathode>

[0036] A cathode according to an embodiment can be manufactured by the following process.

[0037] A negative electrode active material layer composition is prepared by adding a polymer and silicon-based negative electrode active material having a potential band of 1.5 V or less with respect to Li to a solvent. The solvent may be an organic solvent, for example, N-methyl pyrrolidone.

[0038] The negative electrode is manufactured by applying, drying, and rolling the negative electrode active material layer composition to a current collector.

[0039] The above coating, drying and rolling processes can be performed under general cathode manufacturing conditions, and there is no need to limit them.

[0040] Lithium secondary battery

[0041] Another embodiment provides a lithium secondary battery comprising a negative electrode, a positive electrode, and an electrolyte according to the above embodiment.

[0042] [anode]

[0043] The above positive electrode may include a current collector and a positive electrode active material layer formed on the current collector.

[0044] The above-described positive electrode active material layer includes a positive electrode active material and may further include a binder and / or a conductive material. For example, the positive electrode may further include an additive that can function as a sacrificial positive electrode.

[0045] As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used. Specifically, one or more of a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0046] The above composite oxide may be a lithium transition metal composite oxide, and specific examples thereof include lithium nickel-based oxide, lithium cobalt-based oxide, lithium manganese-based oxide, lithium iron phosphate-based compound, cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0047] As an example, a compound represented by any one of the following chemical formulas may be used: Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Mn 2-b X b O 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05); Li a Ni 1-b-c Co b X c O 2-α D α(0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2); Li a Ni b Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1); Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8, 0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5); Li (3-f) Fe2(PO4)3(0≤f≤2); Li a FePO4(0.90≤a≤1.8).

[0048] In the above chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0049] For example, the cathode active material may be a high-nickel cathode active material in which the nickel content is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less, based on 100 mol% of metals excluding lithium in the lithium transition metal composite oxide. The high-nickel cathode active material can realize high capacity and thus can be applied to high-capacity, high-density lithium secondary batteries.

[0050] In the above positive electrode, the content of the positive electrode active material may be 90 wt% to 98 wt% based on the total weight of the positive electrode active material layer. The contents of the binder and the conductive agent may each be 1 wt% to 5 wt% based on the total weight of the positive electrode active material layer.

[0051] The above binder serves to adhere the positive electrode active material particles well to each other and also to adhere the positive electrode active material well to the current collector. Representative examples of the binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0052] The conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive can be used in the battery. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0053] Al may be used as the above current collector, but is not limited thereto.

[0054] [Electrolyte]

[0055] The above electrolyte comprises a non-aqueous organic solvent and a lithium salt.

[0056] The above non-aqueous organic solvent acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0057] As the above non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent can be used.

[0058] Examples of the carbonate solvent that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. Examples of the ester solvent that can be used include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methylpropionate, ethylpropionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. Examples of the ether solvents that can be used include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, examples of the ketone solvents that can be used include cyclohexanone. Examples of the alcohol solvents that can be used include ethyl alcohol and isopropyl alcohol, and examples of the aprotic solvents that can be used include nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, an aromatic ring, or an ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; and sulfolanes.

[0059] The above non-aqueous organic solvents can be used alone or in combination of two or more.

[0060] In addition, when using a carbonate solvent, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0061] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery, enabling the basic operation of a lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. Representative examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2) (x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0062] [Separator]

[0063] Depending on the type of lithium secondary battery, a separator may be present between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films comprising two or more layers thereof. Furthermore, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0064] The above separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof, positioned on one or both sides of the porous substrate.

[0065] The above porous substrate may be a polymer film formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyarylether ketone, polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more thereof.

[0066] The organic material may include a polyvinylidene fluoride polymer or a (meth)acrylic polymer.

[0067] The above inorganic materials are Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, It may include inorganic particles selected from, but not limited to, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0068] The organic and inorganic substances may be mixed and present in one coating layer, or a coating layer including an organic substance and a coating layer including an inorganic substance may be present in a laminated form.

[0069] Lithium secondary batteries can be classified into cylindrical, square, pouch, coin, etc. types according to their shapes. FIGS. 1 to 4 are schematic diagrams illustrating lithium secondary batteries according to one embodiment, wherein FIG. 1 can be said to be a cylindrical battery, FIG. 2 a square battery, and FIGS. 3 and 4 a pouch battery. Referring to FIGS. 1 to 4, a lithium secondary battery (100) may include an electrode assembly (40) having a separator (30) interposed between a positive electrode (10) and a negative electrode (20), and a case (50) in which the electrode assembly (40) is built. The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). The lithium secondary battery (100) may include a sealing member (60) that seals the case (50) as shown in FIG. 1. In addition, in FIG. 2, the lithium secondary battery (100) may include a positive lead tab (11), a positive terminal (12), a negative lead tab (21), and a negative terminal (22). As in FIGS. 3 and 4, the lithium secondary battery (100) may include electrode tabs (70), i.e., a positive tab (71) and a negative tab (72), which serve as electrical paths for inducing current formed in the electrode assembly (40) to the outside.

[0070] Hereinafter, examples and comparative examples of the present invention will be described. The following examples are merely exemplary of the present invention, and the present invention is not limited to the following examples.

[0071] (Example 1)

[0072] A slurry for a negative electrode active material layer was prepared by mixing 19 wt% of a silicon-carbon composite and 81 wt% of polythiophene (potential band of 0.5 V vs. Li) in a water solvent.

[0073] The silicon-carbon composite was used as an assembly having a soft carbon coating layer in which silicon nanoparticles having an average particle diameter (D50) of 100 nm were assembled. At this time, the content of silicon nanoparticles was 54 wt% with respect to the total weight of the silicon-carbon composite, the content of the soft carbon was 46 wt%, and the thickness of the soft carbon coating layer was 100 nm.

[0074] A negative electrode including a negative electrode active material layer was manufactured by coating, drying, and rolling the above negative electrode active material layer slurry on a Cu foil current collector.

[0075] A half-cell was manufactured using the above-described negative electrode, lithium metal counter electrode, and electrolyte. The electrolyte used was ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 20:10:70) containing 1.5 M LiPF6 dissolved therein.

[0076] (Example 2)

[0077] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that a slurry for the negative electrode active material layer was manufactured by mixing 20 wt% of a silicon-carbon composite and 80 wt% of polythiophene in a water solvent.

[0078] (Example 3)

[0079] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that a slurry for the negative electrode active material layer was manufactured by mixing 30 wt% of a silicon-carbon composite and 70 wt% of polythiophene in a water solvent.

[0080] (Example 4)

[0081] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that a slurry for the negative electrode active material layer was manufactured by mixing 40 wt% of a silicon-carbon composite and 60 wt% of polythiophene in a water solvent.

[0082] (Example 5)

[0083] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that a slurry for the negative electrode active material layer was manufactured by mixing 50 wt% of a silicon-carbon composite and 50 wt% of polythiophene in a water solvent.

[0084] (Example 6)

[0085] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that a slurry for the negative electrode active material layer was manufactured by mixing 60 wt% of a silicon-carbon composite and 40 wt% of polythiophene in a water solvent.

[0086] (Example 7)

[0087] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that a slurry for the negative electrode active material layer was manufactured by mixing 61 wt% of a silicon-carbon composite and 39 wt% of polythiophene in a water solvent.

[0088] (Example 8)

[0089] SiO x (x is 2) A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that a negative electrode active material layer slurry was manufactured by mixing 20 wt% of (x is 2) and 80 wt% of polythiophene in a water solvent.

[0090] (Comparative Example 1)

[0091] A slurry for a negative electrode active material layer was prepared by mixing 97 wt% of the mixed negative electrode active material of the Si-carbon composite and polythiophene of Example 1 above (mixing ratio of Si-carbon composite:polythiophene=15:85 by weight), 1 wt% of carbon black, 1 wt% of styrene-butadiene rubber, and 1 wt% of carboxymethyl cellulose in a water solvent.

[0092] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that the negative electrode active material layer slurry was used.

[0093] (Comparative Example 2)

[0094] SiO x (x is 2) and 97 wt% of a mixed negative active material of polythiophene (mixing ratio of Si-carbon composite: polythiophene = 15:85 by weight), 1 wt% of carbon black, 1 wt% of styrene-butadiene rubber, and 1 wt% of carboxymethyl cellulose were mixed in a water solvent to prepare a negative active material layer slurry.

[0095] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that the negative electrode active material layer slurry was used.

[0096] (Comparative Example 3)

[0097] A slurry for a negative electrode active material layer was prepared by mixing 78 wt% of the Si-carbon composite negative electrode active material of Example 1, 19 wt% of polythiophene, 1 wt% of carbon black conductive material, 1 wt% of styrene-butadiene rubber binder, and 1 wt% of carboxymethyl cellulose thickener in a water solvent.

[0098] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that the negative electrode active material layer slurry was used.

[0099] (Comparative Example 4)

[0100] SiO x (x is 2) 78 wt% of negative active material, 19 wt% of polythiophene, 1 wt% of carbon black conductive agent, 1 wt% of styrene-butadiene rubber binder, and 1 wt% of carboxymethyl cellulose thickener were mixed in a water solvent to prepare a negative active material layer slurry.

[0101] A negative electrode and a half-cell were manufactured in the same manner as in Example 1, except that the negative electrode active material layer slurry was used.

[0102] Si-carbon composite or SiO included in the negative electrode active material layer of the above Examples 1 to 8 and the above Comparative Examples 1 to 4 xThe content of (x is 2) (Si-based material content) and the content of polythiophene are summarized and shown in Table 1 below.

[0103] Experimental Example 1) Evaluation of Bonding Strength

[0104] The bonding strength of the negative electrodes manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 was measured as follows.

[0105] First, the manufactured cathode was cut into a size of 25 mm in width and 100 mm in length and prepared. Double-sided tape (double-sided tape coated with acrylic adhesive, 3M 9346 double-sided tape for paper) with a size of 20 mm in width and 40 mm in length was attached to an acrylic plate with a size of 40 mm in width and 100 mm in length. After attaching the prepared electrode on the double-sided tape, it was lightly pressed 5 times with a hand roller, and it was mounted on a UTM (20 kgf Load cell), and about 25 mm of one side of the cathode was peeled off, and the cathode was fixed to the upper clip of the tensile strength tester, and the tape attached to one side of the cathode was fixed to the lower clip, and the 180° peeling strength was measured while peeling at a speed of 100 mm / min. The results are shown in Table 1 as the bonding strength.

[0106] Experimental Example 2) Electrical Conductivity Evaluation

[0107] The electrical conductivity of the cathodes manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 was measured as follows.

[0108] After sampling the cathode to 10Φ (diameter 10 mm), the electrical resistance was measured using an electric impedance spectroscopy meter at room temperature (25°C) with a torque of 10 N·m applied. At this time, a frequency of 500 kHz to 50 mHz was scanned using an amplitude of 50 mV at the open circuit potential.

[0109] The results are shown in Table 1 below.

[0110] Experimental Example 3) Evaluation of Life Characteristics

[0111] The half-cells manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 were charged and discharged 50 times at 1C in the range of 0.01 V to 1.5 V. The charge and discharge method and cut-off conditions were as follows.

[0112] Charging: Constant current / constant voltage, 0.01V / 0.01C cutoff

[0113] Discharge: Constant current, 1.5 V cutoff

[0114] The ratio of the 50-cycle discharge capacity to the 1-cycle discharge capacity was calculated. The results are shown in Table 1 below.

[0115] Experimental Example 4) Expansion Rate Evaluation

[0116] The half-cells manufactured in Examples 1 to 8 and Comparative Examples 1 to 4 were charged and discharged 50 times at 1C, so that the SOC (State of Charge) reached 100 (a state in which the battery is charged to 100% of its total charge capacity when charged and discharged at 0.01 V to 1.5 V, i.e., a fully charged state).

[0117] After performing charge and discharge cycles, the battery was disassembled to obtain the negative electrode. The thickness of the negative electrode before charge and discharge (initial thickness) and after 50 charge and discharge cycles (post-charge and discharge thickness) were measured. From these results, the expansion ratio was calculated according to Equation 1 below. The results are shown in Table 1 below.

[0118] [Formula 1]

[0119] Expansion ratio (%) = {(thickness after charge and discharge - initial thickness) / initial thickness} * 100

[0120] Si-based material (wt%)Polythiophene (wt%)Bonding strength (gf / mm)Electrical conductivity (S / m)Capacity retention rate (%)Expansion rate (%)Example 119813.015.795.34.5Example 220802.725.595.94.9Example 330702.474.996.75.3Example 440601.954.598.25.8Example 550501.524.097.86.1Example 660401.233.696.96.5Example 761391.013.496.36.9Example 820802.525.396.15.0Comparative example 114.682.43.212.593.24.2Comparative example 214.682.43.122.292.74.1Comparative example 378190.811.792.38.8Comparative example 478190.751.392.18.3

[0121] As shown in Table 1 above, Si-carbon composite or SiO x (x is 2), it can be seen that the batteries of Examples 1 to 8 including a negative electrode made of polythiophene exhibit excellent bonding strength, electrical conductivity, capacity retention and low expansion rate. On the other hand, Si-carbon composite or SiO x (x is 2), it can be seen that Comparative Examples 1 and 2, which contain polythiophene, carbon black, styrene-butadiene rubber and carboxymethyl cellulose, exhibit high bonding strength and low expansion ratio, but low electrical conductivity and capacity retention.

[0122] In particular, Si-carbon composites or SiO x (x is 2), polythiophene, carbon black, styrene-butadiene rubber and carboxymethyl cellulose, and comparative examples 3 and 4 containing a small amount of polythiophene, can be seen to exhibit very low adhesive strength, very low electrical conductivity, low capacity retention and very high expansion ratio.

[0123] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. Current collector; and A negative electrode including a negative electrode active material layer positioned on the current collector and made of a polymer and silicon-based negative electrode active material having a potential band of 1.5 V or less with respect to Li, A cathode having an adhesive strength of 1.0 gf / mm or more and an electrical conductivity of 1.0 S / m to 6.0 S / m.

2. In paragraph 1, The above polymer is a cathode having a potential of 1.5 V or less and 0.1 V or more with respect to Li.

3. In paragraph 1, The above polymer is a cathode comprising polythiophene, poly(3,4-methylenedioxythiophene), polypyrrole or a combination thereof.

4. In paragraph 1, A negative electrode having a polymer content of 30 to 85 wt% based on 100 wt% of the total negative electrode active material layer.

5. In paragraph 1, A negative electrode having a polymer content of 35 wt% to 85 wt% based on 100 wt% of the total negative electrode active material layer.

6. In paragraph 1, A negative electrode having a content of the above silicon-based active material of 15 to 70 wt% based on 100 wt% of the total negative electrode active material layer.

7. In paragraph 1, A negative electrode having a content of the above silicon-based active material of 15 to 65 wt% based on 100 wt% of the total negative electrode active material layer.

8. In paragraph 1, The above silicon-based negative electrode active material is a negative electrode including a silicon-based material and an amorphous carbon coating layer positioned on the silicon-based material.

9. In paragraph 8, The above silicon-based material is a cathode made of Si nanoparticles.

10. In paragraph 8, The above silicon-based material is Si, SiO x (0 <x≤2) 또는 이들의 조합인 음극.

11. In paragraph 1, The above silicon-based negative electrode active material is a negative electrode comprising an assembly in which at least one silicon nanoparticle is assembled and an amorphous carbon coating layer positioned on the surface of the assembly.

12. In paragraph 8, The above amorphous carbon is a cathode that is soft carbon, hard carbon, mesophase pitch carbide, calcined coke or a combination thereof.

13. In paragraph 1, A cathode having a bonding force of 1.0 gf / mm to 3.5 gf / mm.

14. In paragraph 1, A cathode having an electrical conductivity of 1.5 S / m to 5.5 S / m.

15. The cathode of any one of paragraphs 1 to 14; a cathode comprising a cathode active material; and non-aqueous electrolyte A lithium secondary battery comprising:

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