ANODE FOR A SECONDARY BATTERY, SECONDARY BATTERY THAT INCLUDES THIS

Abstract

Anode for secondary battery, comprising: an anode current collector; and a first anode active material layer that is formed on the anode current collector and a first silicon-based active material and a first conductive material comprising a single-walled carbon nanotube; and a second anode active material layer formed on top of the first anode active material layer, containing a second silicon-based active material and a second conductive material comprising a multi-walled carbon nanotube, wherein the single-walled carbon nanotube has a Raman R value of 0.01 to 0.1, where the Raman R value represents a ratio of a D-band peak intensity (Id) to a G-band peak intensity (Ig), wherein the content of the first silicon-based active material, based on the total weight of the first anode active material layer, is greater than the content of the second silicon-based active material, based on the total weight of the second anode active material layer, and where the content of the single-walled carbon nanotube is 0.02 to 0.2 wt.%, based on the total weight of the first anode active material layer, and the content of the multi-walled carbon nanotube is 0.2 to 0.5 wt.%, based on the total weight of the second anode active material layer.

Description

[BACKGROUND OF THE INVENTION] 1. Field of the invention

[0001] The present invention relates to an anode for a secondary battery and a secondary battery comprising the anode, and in particular to an anode for a secondary battery comprising a silicon-based anode active material, and a secondary battery comprising the same. 2. Description of the state of the art

[0002] A secondary battery is a battery that can be repeatedly charged and discharged and has become widely used in portable electronic communication devices such as camcorders, mobile phones, and laptops with the development of the information, communication, and display industries. Examples of secondary batteries include lithium-ion batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and the like. Among these, lithium-ion batteries offer high operating voltage and high energy density per unit weight, and are advantageous in terms of charging speed and low weight. For these reasons, lithium-ion batteries have been actively developed and used as a power source.

[0003] The lithium secondary battery can comprise an electrode assembly including a cathode, an anode, and a separator; and an electrolyte in which the electrode assembly is impregnated. The lithium secondary battery can further comprise, for example, a pocket-shaped outer casing in which the electrode assembly and the electrolyte are housed.

[0004] Since the application area of ​​the lithium secondary battery has recently expanded from a small electronic device to a large device, such as a hybrid vehicle, sufficient capacity and output characteristics cannot be implemented by the existing lithium secondary battery.

[0005] In the case of an electric vehicle (EV) powered solely by a battery, for example, the high energy consumption rate and quantity imposes a limitation on ensuring sufficient driving time compared to the available secondary battery.

[0006] Accordingly, the development of a lithium secondary battery capable of ensuring high rate and high capacity characteristics is required.

[0007] For example, Korean patent publication no. 2017-0099748 discloses an electrode arrangement for a lithium secondary battery and a lithium secondary battery containing it, but there is a limitation regarding ensuring a sufficiently high rate and sufficient capacity characteristics. US 2015 / 0280221 A1 discloses a multilayer anode for a secondary battery in which the silicon-based active material is mainly contained in the upper (outer) composite anode layer and the graphite-based active material is mainly contained in the lower (inner) composite anode layer. CN 107946561 A discloses only an anode with a single-layer structure containing conductive materials including graphene, carbon black, SWCNT, and MWCNT, as well as a silicon-based active material.WO 2020 / 177624 A1 discloses an anode active material multilayer structure containing a conductive material, wherein the content of conductive material in the upper (outer) active material layer is lower than the content of conductive material in the lower (inner) active material layer. [SUMMARY OF THE INVENTION]

[0008] One object of the present invention is to provide an anode for a secondary battery with stable electrical properties.

[0009] Another object of the present invention is to provide a secondary battery that includes an anode with stable electrical properties.

[0010] To solve the above problems, according to one aspect of the present invention, an anode for a secondary battery according to independent claim 1 is provided, comprising: an anode current collector; and a first anode active material layer formed on the anode current collector, comprising a first silicon-based active material and a first conductive material comprising a single-walled carbon nanotube, wherein the single-walled carbon nanotube has a Raman R value (a D-band peak intensity (Id) / a G-band peak intensity (Ig)) of 0.01 to 0.1.

[0011] In exemplary embodiments, the content of the first silicon-based active material can be 5 wt.% or more, based on the total weight of the first anode active material layer.

[0012] In exemplary embodiments, the single-walled carbon nanotube can have a length of 5 µm or more.

[0013] In exemplary embodiments, the single-walled carbon nanotube can have a diameter of 1.2 to 2 nm.

[0014] According to the invention, the anode active material layer comprises: a first anode active material layer formed on the anode current collector and containing a first silicon-based active material and a first conductive material comprising the single-walled carbon nanotube; and a second anode active material layer formed on the first anode active material layer and containing a second silicon-based active material and a second conductive material comprising a multi-walled carbon nanotube.

[0015] According to the invention, the content of the first silicon-based active material, based on the total weight of the first anode active material layer, is greater than the content of the second silicon-based active material, based on the total weight of the second anode active material layer.

[0016] In exemplary embodiments, the content of the first silicon-based active material can be 5 wt.% or more, based on the total weight of the first anode active material layer, and the content of the second silicon-based active material can be less than 5 wt.%, based on the total weight of the second anode active material layer.

[0017] According to the invention, the content of the single-walled carbon nanotube is 0.02 to 0.2 wt.%, based on the total weight of the first anode active material layer, and the content of the multi-walled carbon nanotube is 0.2 to 0.5%, based on the total weight of the second anode active material layer.

[0018] According to another aspect of the present invention, a secondary battery is provided comprising: the anode for a secondary battery; a cathode; and a separating membrane arranged between the anode and the cathode.

[0019] According to one embodiment of the present disclosure, the anode active material layer can comprise the silicon-based active material and the single-walled carbon nanotube with a Raman R-value within a specific range. In this case, if an electrical short circuit occurs in the anode due to anode swelling during charging and discharging of the battery by enclosing the silicon-based active material, the increase in resistance due to the electrical short circuit can be minimized by the single-walled carbon nanotube. This can improve the lifetime characteristics of the secondary battery by effectively preventing heat generation due to the increased resistance.

[0020] According to the present invention, the anode comprises the first anode active material layer, including the single-walled carbon nanotube, and the second anode active material layer, including the multi-walled carbon nanotube. In this case, an increase in the anode's resistance can be effectively prevented by the first anode active material layer with the single-walled carbon nanotube, and the interfacial resistance can be reduced by the second anode active material layer with the multi-walled carbon nanotube. This further improves the electrochemical safety of the secondary battery. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0021] The above and other tasks, features and other advantages of the present invention will become clearer from the following detailed description in conjunction with the accompanying drawings, in which: Fig.Figure 1 is a schematic cross-sectional view representing a secondary battery according to an embodiment of the present invention; and Fig. Figure 2 is a schematic cross-sectional view representing an anode for a secondary battery according to another embodiment of the present invention. [DETAILED DESCRIPTION OF THE INVENTION]

[0022] Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, these embodiments are merely an example, and the present invention is not limited to the specific embodiments described as examples.

[0023] Fig. Figure 1 is a schematic cross-sectional view representing a secondary battery according to an embodiment of the present invention, and Fig.Figure 2 is a schematic cross-sectional view representing an anode for a secondary battery according to another embodiment of the present invention.

[0024] Referring to Fig. 1 can comprise a lithium secondary battery 10, an electrode arrangement 150 and a housing 160 in which the electrode arrangement 150 is housed.

[0025] The electrode arrangement 150 can comprise a cathode 100, an anode 130 and a separating membrane 140 arranged between the cathode 100 and the anode 130.

[0026] The cathode 100 can comprise a cathode current collector 105 and a cathode active material layer 110, which is arranged on at least one surface of the cathode current collector 105 and comprises a cathode active material.

[0027] The cathode active material may include a compound that can reversibly intercalate and deintercalate lithium ions.

[0028] In one embodiment, the cathode-active material layers 110 can be formed on both surfaces (e.g., upper and lower surfaces) of the cathode current collector 105. For example, the cathode-active material layers 110 can be applied to the upper and lower surfaces of the cathode current collector 105, respectively, and can be applied directly to the surfaces of the cathode current collector 105.

[0029] The cathode 100 can be produced by coating the cathode current collector 105 with a cathode slurry, followed by drying and rolling (or pressing) the same. The cathode slurry can be produced by mixing the cathode active material with a binder, a conductive material and / or a dispersant in a solvent, followed by stirring.

[0030] The cathode current collector 105 can comprise a metallic material that exhibits no reactivity in the charging / discharging voltage range of the secondary battery 10 and facilitates the application and adhesion of the electrode active material. For example, the cathode current collector 105 can comprise stainless steel, nickel, aluminum, titanium, copper, zinc, or an alloy thereof, and preferably comprises aluminum or an aluminum alloy.

[0031] The cathode active material layer 110 can comprise a lithium metal oxide as the cathode active material. For example, the cathode active material can comprise a lithium transition metal composite oxide particle.

[0032] In some embodiments, the cathode active material may comprise a lithium (Li)-nickel (Ni)-based oxide. For example, the lithium transition metal composite oxide particle may include nickel and may further contain at least one of cobalt (Co) and manganese (Mn).

[0033] In some embodiments, the cathode active material or the lithium transition metal composite oxide particle may further comprise a coating element or a doping element. For example, the coating element or doping element may comprise Al, Ti, Ba, Zr, Si, B, Mg, P, Sr, W, La, or an alloy or oxide thereof. These may be used alone or in combination with two or more of them. The cathode active material or the lithium transition metal composite oxide particle is passivated by the coating or doping element, which may further improve its stability and lifetime against the penetration of an external object.

[0034] In some embodiments, the lithium transition metal composite oxide particles can be represented by the formula 1 below. Li x Ni 1-y M y O 2+z [Formula 1]

[0035] In formula 1, x and y can lie in the range 0.9 ≤ x ≤ 1.2 and 0 ≤ y ≤ 0.7, and z can lie in the range -0.1 ≤ z ≤ 0.1. M can be at least one element selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, and Zr.

[0036] For example, nickel (Ni) can be provided as a metal associated with the capacity of the lithium secondary battery. The higher the nickel content, the better the capacity and performance of the lithium secondary battery. However, if the nickel content is increased too much, the lifetime can be reduced, which can be detrimental to mechanical and electrical stability. Cobalt (Co), for example, can be a metal associated with the conductivity or resistance of the lithium secondary battery. In one embodiment, M comprises manganese (Mn), and Mn can be provided as a metal associated with the mechanical and electrical stability of the lithium secondary battery. Through an interaction between the nickel, cobalt, and manganese described above, the capacity, performance, low resistance, and lifetime stability of the cathode active material layer 110 can be jointly improved.

[0037] In some embodiments, the nickel content in the cathode active material can be 80 mol% or more, and preferably 85 mol% or more, based on a total number of transition metal atoms. Accordingly, it is possible to implement a high-capacity, high-performance lithium secondary battery.

[0038] For example, a cathode slurry can be prepared by mixing the cathode active material with a binder, a conductive material, and / or a dispersant in a solvent, followed by stirring. The cathode slurry can be applied to the cathode current collector 105, followed by compression and drying, to produce the cathode active material layer 110.

[0039] The binder may, for example, be an organic binder such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or an aqueous binder such as styrene-butadiene rubber (SBR), and may be used together with a thickening agent such as carboxymethylcellulose (CMC).

[0040] For example, a PVDF-based binder can be used to form the cathode. In this case, the amount of binder required to form the cathode active material layer can be reduced, thereby improving the performance and capacity of the secondary battery.

[0041] The conductive material may be included to facilitate electron transfer between the active material particles. For example, the conductive material may be a carbon-based conductive material such as graphite, carbon black, graphene, or carbon nanotubes, and / or a metal-based conductive material such as tin, tin oxide, titanium oxide, or a perovskite material such as LaSrCoO3 and LaSrMnO3, etc.

[0042] In some embodiments, the electrode of the cathode 100 can have a density of 3.0 to 3.9 g / cm³. 3 exhibit and preferably from 3.2 to 3.8 g / cm³ 3 .

[0043] According to exemplary embodiments, the cathode active material layer 110 can have a multilayer structure.

[0044] Referring to the Fig. 1 and Fig.2 The anode 130 comprises an anode current collector 125 and an anode active material layer 120 formed on at least one surface of the anode current collector 125. According to exemplary embodiments, the anode active material layers 120 can be formed on both surfaces (e.g., upper and lower surfaces) of the anode current collector 125. The anode active material layers 120 can be applied to the upper and lower surfaces of the anode current collector 125, respectively. For example, the anode active material layers 120 can come into direct contact with the surfaces of the anode current collector 125.

[0045] The anode current collector 125 can, for example, comprise gold, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, and preferably comprises copper or a copper alloy.

[0046] In one embodiment of the present disclosure, the anode active material layer 120 can comprise an anode active material capable of intercalating and deintercalating lithium ions, a conductive material, and a binder. The anode active material can comprise a silicon-based active material, and the conductive material can comprise a single-walled carbon nanotube.

[0047] According to the invention, the single-walled carbon nanotube exhibits a Raman R value of approximately 0.01 to 0.1. The Raman R value represents a peak intensity ratio (Id / Ig) that is represented by measuring a peak intensity (Ig) near a G-band (approximately 1,580 cm⁻¹) and a peak intensity (Id) near a D-band (approximately 1,350 cm⁻¹) in Raman spectrum analysis.

[0048] If the single-walled carbon nanotube meets the Raman R-value range specified above, the anode active material layer 120, including the single-walled carbon nanotube, exhibits fewer structural defects and a high degree of crystallinity, thus further improving electrical conductivity. Furthermore, if the single-walled carbon nanotube meets the length and diameter specifications described below, the effects described above can be further enhanced, enabling the implementation of a secondary battery with excellent electrochemical properties.

[0049] In some embodiments, the single-walled carbon nanotube can have a length of 5 µm or more, 20 µm or more, or 50 µm or more. In this case, a conductive material network can be easily formed by the single-walled carbon nanotube, and an increase in resistance caused by the electrical short circuit can be more effectively prevented. This makes it possible to implement a secondary battery with excellent electrochemical properties.

[0050] In some embodiments, the single-walled carbon nanotube can have a length of 200 µm or less, or 100 µm or less. If its length falls within the above range, aggregation of the single-walled carbon nanotube in the anode slurry can be prevented, and improved dispersing power can be ensured. However, it is not necessarily limited to this, and an upper limit for the length of the single-walled carbon nanotube can be appropriately adjusted according to the types of anode active material, binder, and dispersion medium mixed with the anode slurry during its manufacture.

[0051] In some embodiments of the present disclosure, the content of the single-walled carbon nanotube can be about 0.02 to 0.2 wt.%, based on the total weight of the anode active material layer 120. Preferably, according to the present disclosure, the content of the single-walled carbon nanotube can be about 0.05 to 0.15 wt.%, based on the total weight of the anode active material layer 120.

[0052] For example, if the content of the single-walled carbon nanotube meets the above range, an increase in resistance caused by enclosing a large amount of silicon-based active material can be effectively prevented, and thus the lifetime characteristics of the secondary battery can be further improved.

[0053] In one embodiment, the single-walled carbon nanotube can have a diameter of 0.5 to 10 nm, preferably 1 to 5 nm, and even more preferably 1.2 to 2 nm. In this case, it is possible to more effectively prevent an increase in resistance caused by enclosing a large amount of the silicon-based active material.

[0054] In one embodiment, the conductive material may also include materials that are essentially the same or similar to those used to form the cathode 100.

[0055] The silicon-based active material can contain SiOx (0 <x<2) oder SiOx enthaltend eine Lithiumverbindung (0<x<2) umfassen. Die Li-Verbindung enthaltende SiOx kann Lithiumsilikat enthaltendes SiOx sein. Das Lithiumsilikat kann in mindestens einem Teil der SiOx-Partikel (0 < x < 2) vorhanden sein, beispielsweise kann es innerhalb und / oder auf einer Oberfläche der SiOx-Partikel (0 < x < 2) vorhanden sein. In einer Ausführungsform kann das Lithiumsilikat Li2SiO3, Li2Si2O5, Li4SiO4, Li4Si3O8 und dergleichen umfassen.

[0056] The silicon-based active material may also include a silicon-carbon compound, such as silicon carbide (SiC), a silicon oxide-carbon compound, or a silicon-silicon oxide-carbon compound.

[0057] In one embodiment of the present disclosure, the silicon-based active material content can be 5 wt.% (“wt.%) or more, based on the total weight of the anode active material layer. For example, the silicon-based active material content can be 5 wt.% to 40 wt.%, based on the total weight of the anode active material layer. If the silicon-based active material content meets the above range, the performance and capacity of the lithium-ion battery can be further improved, and a high-energy cell can be implemented more easily.

[0058] For example, during charging and discharging of the battery, the swelling of the silicon-based active material increases due to repeated deintercalation and intercalation of lithium ions, potentially leading to an electrical short circuit between the anode active materials and thus reducing the battery's stability. However, in the present invention, the increase in resistance due to the electrical short circuit can be effectively reduced by the stable network of conductive material formed by the single-walled carbon nanotube, and the battery's lifetime characteristics can be further improved.

[0059] In one embodiment, the anode active material may further comprise at least one of a carbon-based active material and an active lithium composite material.

[0060] The carbon-based active material can include a graphite-based active material and a non-graphite-based active material. The graphite-based active material can include at least one natural graphite and one synthetic graphite.

[0061] The non-graphite-based active material may include at least one of hard and soft carbons, carbon nanotubes, carbon fibers, coke, and pitch.

[0062] For example, synthetic graphite and hard carbon can comprise primary and / or secondary particle forms.

[0063] Synthetic graphite has a relatively superior lifespan compared to natural graphite, and because natural graphite has a larger specific surface area than synthetic graphite, it has a relatively low resistance, which can be advantageous in terms of performance improvement. For example, synthetic and natural graphite can be mixed and used together.

[0064] In one embodiment, the carbon-based material can comprise the non-graphite-based active material or minute carbon particles. These minute carbon particles can include carbon black, Super P, and the like. The high-speed properties of the anode active material can be enhanced by the carbon-based material.

[0065] In one embodiment, an anode slurry can be prepared by mixing and stirring the anode active material with a binder, a conductive material, and / or a dispersant in a solvent. The anode slurry can be applied (coated) to the anode current collector 125, followed by compression and drying to produce the anode active material layer 120.

[0066] Materials that are essentially the same or similar to those used to form the cathode 100 can be used as binders to form the anode.

[0067] In some embodiments, the binder for forming the anode 130 may, for example, comprise styrene-butadiene rubber (SBR) or an acrylic binder to achieve consistency with the carbon-based active material and may be used together with a thickening agent such as carboxymethylcellulose (CMC).

[0068] In one embodiment, the anode active material layer 120 can have a density of 1.4 to 1.9 g / cm³ 3 exhibit.

[0069] In some embodiments, the anode 130 can have a larger area (e.g., a contact surface with the separating membrane 140) and / or volume than the cathode 100. This allows lithium ions generated by the cathode 100 to migrate smoothly to the anode 130 without precipitating in the middle, thus further improving the performance and capacity characteristics.

[0070] Referring to Fig. 2 The anode active material layer 120 of the present invention has a multilayer structure.

[0071] According to the invention, the anode active material layer 120 comprises a first anode active material layer 122 formed on the anode current collector 125, and comprising a first silicon-based active material and a first conductive material comprising single-walled carbon nanotubes, and a second anode active material layer 124 formed on the first anode active material layer 122, and comprising a second silicon-based active material and a second conductive material comprising multi-walled carbon nanotubes.

[0072] For example, if the anode active material layer 120 comprises the first anode active material layer 122 and the second anode active material layer 124 with different types of carbon nanotubes, an increase in the resistance of the anode 130 due to repeated charging can be effectively prevented by the single-walled carbon nanotube contained in the first anode active material layer 122, and the interfacial resistance between the separating membrane 140 and the anode 130 can be reduced by the multi-walled carbon nanotube contained in the second anode active material layer 124. Accordingly, the internal resistance of the secondary battery can be reduced, further improving its fast-charging characteristics and stability.

[0073] According to the invention, the content of the first silicon-based active material, based on the total weight of the first anode active material layer 122, is greater than the content of the second silicon-based active material, based on the total weight of the second anode active material layer 124.

[0074] According to some exemplary embodiments, the content of the first silicon-based active material, based on the total weight of the first anode active material layer 122, may be 5 wt.% or more, and the content of the second silicon-based active material may be less than 5 wt.%, based on the total weight of the second anode active material layer 124.

[0075] For example, if the content ranges of the first silicon-based active material and the second silicon-based active material meet the above conditions or ranges, and the content of the first silicon-based active material is increased, even if the saturation from the first anode active material layer 122 is increased, it is possible to effectively prevent an increase in resistance due to the electrical short circuit through the single-walled carbon nanotube contained in the first anode active material layer 122.

[0076] Furthermore, since the content of the second silicon-based active material contained in the second anode active material layer 124 is lower than the content of the first silicon-based active material, an electrical short circuit due to swelling of the second anode active material layer 124 can be effectively prevented, even when including the multi-walled carbon nanotube, and the interfacial resistance with the separating membrane 140 can be reduced by the multi-walled carbon nanotube.

[0077] According to the invention, the content of the single-walled carbon nanotube is 0.02 to 0.2 wt.%, based on the total weight of the first anode active material layer 122, and the content of the multi-walled carbon nanotube is 0.2 to 0.5 wt.%, based on the total weight of the second anode active material layer 124.

[0078] If the contents of the single-walled carbon nanotube and the multi-walled carbon nanotube meet the above ranges, the resistance increases due to the swelling of the anode 130 and the interfacial resistance between the anode 130 and the separating membrane 140 can be prevented, so that the fast charging characteristics and the lifetime characteristics of the secondary battery can be further improved.

[0079] In one embodiment, the same length and diameter of the single-walled carbon nanotube, as described above, can be applied to it.

[0080] In one embodiment, the multi-walled carbon nanotube can have a length of 1 to 100 µm and preferably 10 to 50 µm.

[0081] In one embodiment, the multi-walled carbon nanotube can have a length of 5 to 50 nm, preferably 5 to 20 nm and even more preferably 8 to 17 nm.

[0082] If the length and diameter of the multi-walled carbon nanotube meet the above requirements, an increase in interfacial resistance can be more effectively prevented with the 140 separation membrane.

[0083] In some embodiments, the length of the single-walled carbon nanotube can be greater than the length of the multi-walled carbon nanotube. In this case, the electrochemical properties of the secondary battery can be ensured more reliably.

[0084] In one embodiment, the first anode active material layer 122 can be produced by coating the anode current collector 125 with the first anode slurry, which comprises the first silicon-based active material, wherein the first conductive material contains the single-walled carbon nanotube, a binder, and a solvent, followed by drying and rolling. Furthermore, the second anode active material layer 124 can be produced by coating the first anode active material layer 122 with the second anode slurry, which comprises the second silicon-based active material, wherein the second conductive material contains the multi-walled carbon nanotube, a binder, and a solvent, followed by drying and rolling.

[0085] In one embodiment, the first anode slurry is applied to the anode current collector 125, and the second anode slurry can further be applied to the applied first anode slurry, and then the applied first anode slurry and the second anode slurry can be dried and rolled to prepare the first anode active material layer 122 and the second anode active material layer 124.

[0086] In some embodiments, the loading weight ratio of the second anode slurry to the first anode slurry can be 0.25 to 1.25 and preferably 0.5 to 1.

[0087] Referring to Fig.1. The separating membrane 140 can be arranged between the cathode 100 and the anode 130. The separating membrane 140 can comprise a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer.

[0088] The separation membrane 140 can comprise a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber or the like.

[0089] The separating membrane 140 can extend in the second direction between the cathode 100 and the anode 130 and can be folded and wound in one thickness direction of the lithium secondary battery. Several cathodes 100 and anodes 130 can be laminated in the thickness direction with the separating membrane 140 positioned between them.

[0090] An electrode cell is formed by the cathode 100, the anode 130, and the separating membrane 140, and multiple electrode cells are laminated to form, for example, the electrode assembly 150. The electrode assembly 150 can be formed by winding, laminating, or folding (e.g., Z-folding) the separating membrane 140.

[0091] The electrode assembly 150 is housed in the casing 160, and an electrolyte can be injected into the casing 160 along with the electrode assembly. The casing 160 can, for example, be in the form of a bag, a can, or the like.

[0092] A non-aqueous electrolyte can be used as the electrolyte, according to the exemplary embodiments.

[0093] The non-aqueous electrolyte comprises a lithium salt of an electrolyte and an organic solvent, and the lithium salt is, for example, Li + X - represented, and as the anion (X-) of the lithium salt, F -, Cl - , Br, I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - , etc., can be mentioned as examples.

[0094] Examples of organic solvents that can be used include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulforan, γ-butyrolactone, propylene sulfite, tetrahydrofuran, and the like. These compounds can be used alone or in combination with two or more of them.

[0095] Electrode tabs (a cathode tab and an anode tab) each project from the cathode current collector 105 and the anode current collector 125 belonging to each electrode cell and may extend to one side of the outer casing 160. The electrode tabs may be fused to one side of the outer casing 170 to form electrode leads (a cathode lead and an anode lead) that extend to or are exposed on one outside of the outer casing 170.

[0096] The cathode conductor and the anode conductor can be formed on the same side of the lithium secondary battery or housing 160, or they can be formed on opposite sides.

[0097] For example, the cathode connection can be formed at one end of the housing 160 and the anode connection can be formed at the other end of the housing 160, which faces one end.

[0098] The lithium secondary battery can be manufactured, for example, in a cylindrical shape using a can, a square shape, a pouch shape, or a coin shape.

[0099] Specific experimental examples are proposed below to facilitate understanding of the present invention. However, these examples serve only to illustrate the present invention, and it will be obvious to the person skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. Such changes and modifications are duly included in the appended claims. Reference examples 1 to 6 and comparison examples 1 to 3(1) Preparation of the cathode

[0100] A cathode slurry was prepared by Li[Ni 0.88 Co 0.09 Mn 0.03]O2 as the active cathode material, soot as the conductive material and polyvinylidene fluoride (PVdF) as the binder were mixed in a weight ratio of 98.5:0.5:1.

[0101] The produced cathode slurry was uniformly applied to an aluminum foil, followed by drying and rolling processes to produce a cathode. (2) Preparation of the anode

[0102] An anode active material, a conductive material and a binder were mixed according to the composition and weight ratio shown in Table 1 below and dispersed in water to produce an anode slurry.

[0103] A single-walled carbon nanotube (OCSiAI Co., SW-CNT, with a length of more than 5 µm and a diameter of 1.2 to 2 nm) or a multi-walled carbon nanotube (MW-CNT, with a length of 10 to 50 µm and a diameter of 8 to 17 nm) can be used as the conductive material.

[0104] The Raman R values ​​for SW-CNT and MW-CNT shown in Table 1 below represent a peak intensity ratio (Id / Ig) determined by measuring a G-band (approximately 1,580 cm⁻¹) peak intensity (Ig) and a D-band (approximately 1,350 cm⁻¹) peak intensity (Id) in Raman spectrum analysis. The Raman R values ​​were measured using the Renishaw inVia.

[0105] The anode slurry was applied to a thin copper film (thickness: 6 µm), followed by drying and rolling to a density of 1.7 g / cm³. 3 , in order to produce an anode with a thickness of 133 µm. [TABLE 1] Area Conductive material Anode activated material binder type R-value Salary (Weight %) Content (wt.%) of artificial graphite Salary (wt.%) of SiOx(0 <x<2) SBR / CMC content (1.5:1.3 weight ratio) (wt%) Reference example 1 SW-CNT 0.03 0.1 91.1 6 2.8 Reference example 2 SW-CNT 0.02 0.02 91.18 6 2.8 Reference example 3 SW-CNT 0.03 0.2 91.0 6 2.8 Reference example 4 SW-CNT 0.03 0.01 91.19 6 2.8 Reference example 5 SW-CNT 0.03 0.21 90.99 6 2.8 Reference example 6 SW-CNT 0.1 0.1 91.1 6 2.8 Comparative example 1 MW-CNT 1.1 0.5 90.7 6 2.8 Comparative example 2 SW-CNT 0.2 0.1 91.1 6 2.8 Comparative example 3 MW-CNT 1.1 0.5 97.50 - 2.8 (3) Production of secondary batteries

[0106] The cathode and anode were arranged with an intermediate polyethylene (PE) membrane (13 µm) to form an electrode cell, and the electrode cells were laminated to create an electrode assembly. The electrode assembly 150 was housed in a bag, and electrode strip sections were fused together. An electrolyte was then injected, and the bag was sealed to create a secondary battery.

[0107] After preparing a 1M LiPF6 solution with a mixed solvent of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (EC / EMC / DEC, 25 / 45 / 30; volume ratio), 1 wt% vinylene carbonate (VC), based on a total amount by weight of the electrolyte, 0.5 wt% of 1,3-propensultone (PRS) and 0.5 wt% lithium bis(oxalato)borate (LiBOB) were added to use it as an electrolyte solution. Examples 7 to 10

[0108] Synthetic graphite, SiOx (0 <x<2), das einwandige Kohlenstoff-Nanoröhrchen (SW-CNT) und das SBR / CMC wurden in einem Gewichtsverhältnis von 89,1:8:0,1:2,8 gemischt und in Wasser dispergiert, um eine erste Anodenaufschlämmung herzustellen.

[0109] Then, an anode active material, a conductive material and a binder were mixed according to the composition and weight ratio from Table 2 below and dispersed in water to produce a second anode slurry.

[0110] The first anode slurry was applied to a thin copper film (thickness: 6 µm), and then a second anode slurry was applied over the first. The loading weight ratio of the first and second anode slurries was 1:1.

[0111] Afterwards, the applied first anode slurry and the second anode slurry were dried and then concentrated to a density of 1.7 g / cm³. 3 rolled to produce an anode with a thickness of 133 µm. [TABLE 2] Area Conductive material Anode activated material binder type R-value Salary (Weight %) Content (wt.%) of artificial graphite Salary (wt.%) of SiOx (0 <x<2) SBR / CMC content (1.5:1.3 weight ratio) (wt%) Example 7 MW-CNT 1.1 0.5 92.7 4 2.8 Example 8 MW-CNT 1.1 0.2 93.0 4 2.8 Example 9 MW-CNT 1.1 0.1 93.1 4 2.8 Example 10 SW-CNT 0.03 0.1 93.1 4 2.8 Experimental example(1) Electrode resistance (Ωcm)

[0112] The electrode resistances (Ωcm) of the anodes of the examples and the comparison examples were measured.

[0113] A hioki XF057 probe unit was used as measuring equipment, and the measurement conditions were in the range of 100 µA current and 0.5 V voltage, and the number of pin contacts was 500. (2) Evaluation of the fast cycle at room temperature

[0114] The lithium secondary batteries according to the examples, reference examples and comparison examples were repeatedly subjected to 200 charge / discharge cycles with step current values ​​(2C, 1.75C, 1.5C, 1.25C, 1C, 0.75C and 0.5C) in an interval of 0.25C from 2C to 0.5C at room temperature (25°C), by charging under 4.2 V cut-off conditions, followed by 10 minutes of standing and discharging at a constant current of 0.5C under 2.5 V cut-off conditions, followed by 10 minutes of standing.

[0115] A percentage value (A2 / A1 × 100%) of a discharge capacity A2, measured after 200 executions of the charge / discharge cycle, up to a discharge capacity A1, measured after a single execution of the charge / discharge cycle, was calculated, and the results are shown in Table 3 below. (3) Evaluation of the cycle at high temperature (45°C)

[0116] The lithium secondary batteries of the examples, reference examples and comparison examples were repeatedly subjected to 200 charge / discharge cycles by charging at a constant current of 0.3C under 4.2V and 0.05C cutoff conditions, followed by 10 minutes of standing time and discharging at a constant current of 0.5C under 2.5V cutoff conditions, followed by 10 minutes of standing time.

[0117] A percentage value (B2 / B1 × 100%) of a discharge capacity B2, measured after 200 executions of the charge / discharge cycle, up to a discharge capacity B1, measured after a single execution of the charge / discharge cycle, was calculated, and the results are shown in Table 3 below. (4) Assessment of storage at high temperature (60°C)

[0118] The lithium secondary batteries of the examples, the reference examples and the comparison examples were charged to SOC (state of charge) 100% with a constant current of 0.3C under 4.2V and 0.05C cutoff conditions and then stored at a high temperature of 60°C for 8 weeks.

[0119] A percentage value (C2 / C1 × 100%) of a discharge capacity C2, measured after storage at high temperature, to a discharge capacity C1, measured before storage at high temperature, was calculated, and the results are shown in Table 3 below. [TABLE 3] Area Electrode resistance (Ωcm) Rated fast cycle (%) at room temperature (25°C) Rated cycle (%) at high temperature (45°C) Rated storage (%) at high temperature (60°C, 8 weeks) Reference Example 1 0.030 87 95 96 Reference Example 2 0.031 84 93 93 Reference example 3 0.034 86 96 97 Reference example 4 0.058 81 88 85 Reference example 5 0.047 80 91 82 Reference Example 6 0.065 81 90 89 Example 7 0.040 94 93 95 Example 8 0.038 92 94 93 Example 9 0.032 93 93 92 Example 10 0.036 87 94 95 Comparative example 1 0.078 79 86 90 Comparative example 2 0.052 80 84 88 Comparative example 3 0.043 76 92 94

[0120] Referring to Table 3 above, it can be confirmed that the lithium secondary batteries, according to the examples, exhibit excellent performance in terms of fast cycle properties at room temperature, cycle properties at high temperature, and storage properties at high temperature. [Description of reference symbols] 100 cathode 105 Cathode current collector 110 Cathode active material layer 130 anode 125 Anode current collector 120 anode active material layer 122 First anode active material layer 124 Second anode active material layer 140 separating membrane 150 electrode arrangement 160 cases

Claims

An anode for a secondary battery comprising: an anode current collector; and a first anode active material layer formed on the anode current collector and comprising a first silicon-based active material and a first conductive material comprising a single-walled carbon nanotube; and a second anode active material layer formed on the first anode active material layer and comprising a second silicon-based active material and a second conductive material comprising a multi-walled carbon nanotube, wherein the single-walled carbon nanotube has a Raman R value of 0.01 to 0.1, where the Raman R value represents a ratio of a D-band peak intensity (Id) to a G-band peak intensity (Ig).wherein the content of the first silicon-based active material, based on the total weight of the first anode active material layer, is greater than the content of the second silicon-based active material, based on the total weight of the second anode active material layer, and wherein the content of the single-walled carbon nanotube is 0.02 to 0.2 wt%, based on the total weight of the first anode active material layer, and the content of the multi-walled carbon nanotube is 0.2 to 0.5 wt%, based on the total weight of the second anode active material layer. Anode for a secondary battery according to claim 1, wherein the content of the first silicon-based active material, based on the total weight of the first anode active material layer, is 5 wt.% or more. Anode for a secondary battery according to claim 1, wherein the single-walled carbon nanotube has a length of 5 µm or more. Anode for a secondary battery according to claim 1, wherein the single-walled carbon nanotube has a diameter of 1.2 to 2 nm. Anode for a secondary battery according to claim 1, wherein the content of the first silicon-based active material is 5 wt.% or more, based on the total weight of the first anode active material layer, and the content of the second silicon-based active material is less than 5 wt.%, based on the total weight of the second anode active material layer. Secondary battery comprising: the anode for a secondary battery according to claim 1; a cathode; and a separating membrane arranged between the anode and the cathode.

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