Negative electrode for a lithium secondary battery with improved rapid charging performance and lithium secondary battery comprising the same

Abstract

The present invention relates to a negative electrode for a secondary battery, a method for manufacturing the same, and a secondary battery comprising said negative electrode, wherein the negative electrode comprises: a current collector; a first negative active material layer located on said current collector and comprising a water-based binder; and a second negative active material layer located on said first negative active material layer and comprising a non-water-based binder.

Description

Technology Field

[0001] The present invention relates to a negative electrode for a secondary battery with improved rapid charging performance and a secondary battery including the same. Background Technology

[0002] As high-capacity cells are required to improve the driving range of electric vehicles, silicon-based active materials are being actively considered as cathode materials. However, due to the characteristics of silicon-based active materials, it is difficult to secure rapid charging performance because of issues such as increased cathode resistance and degraded lifespan caused by Si expansion during charging and discharging.

[0003] Accordingly, it is required to improve rapid charging characteristics and secure lifespan characteristics by optimizing the type and content of the binder, thereby ensuring improved energy density and excellent electrochemical properties. The problem to be solved

[0004] The present invention includes a negative electrode active material comprising a graphite-based active material and a silicon-based active material, and aims to solve the problem that it is difficult to secure a long lifespan due to the degradation of lifespan characteristics and rapid charging performance caused by the application of Si in conventional negative electrode structures.

[0005] In this invention, electrochemical characteristics are secured by using different types of binders for the upper and lower layers of the electrode. Additionally, by using a non-aqueous binder in the upper layer of the cathode, the resistance of the cathode is reduced compared to the use of an aqueous binder; as resistance is improved even during high-rate charging, long-term rapid charging performance can be secured. means of solving the problem

[0006] One embodiment of the present invention provides a negative electrode for a secondary battery comprising: a current collector; a first negative active material layer located on the current collector and comprising a water-based binder; and a second negative active material layer located on the first negative active material layer and comprising a non-water-based binder.

[0007] The above-mentioned water-based binder may include at least one of a styrene butadiene rubber (SBR)-based binder and a carboxymethylcellulose (CMC)-based binder.

[0008] The above-mentioned non-aqueous binder may include a polyvinylidene fluoride (PVdF)-based binder.

[0009] At least one of the first negative electrode active material layer and the second negative electrode active material layer may include a carbon-based active material and a silicon-based active material.

[0010] The second negative electrode active material layer may contain a carbon-based active material and a silicon-based active material in a weight ratio of 70:30 to 95:5.

[0011] The above aqueous binder may be included in an amount of 2 to 4 weight% with respect to the total weight of the first cathode active material layer, and the above non-aqueous binder may be included in an amount of 0.7 to 3.2 weight% with respect to the total weight of the second cathode active material layer.

[0012] The first cathode active material layer may not contain a non-aqueous binder.

[0013] The second cathode active material layer may not contain an aqueous binder.

[0014] The weight ratio of the above water-based binder and the above non-water-based binder may be 5:95 to 95:5.

[0015] Loading amount (g / cm²) of the first negative electrode active material layer above 2 ) and the loading amount (g / cm²) of the second cathode active material layer. 2 The ratio of ) can be 5:95 to 95:5.

[0016] The ratio of the thickness of the first cathode active material layer to the thickness of the second cathode active material layer may be 5:95 to 95:5.

[0018] Another embodiment provides a secondary battery comprising: a cathode; an anode; a separator located between the cathode and the anode; and an electrolyte. Effects of the invention

[0019] By improving the rapid charging characteristics of secondary batteries and securing lifespan characteristics, it is possible to achieve improved energy density and excellent electrochemical characteristics.

[0020] In the present invention, interfacial adhesion between the current collector and the negative electrode active material layer is improved, processability / appearance defects such as electrode detachment are improved, and rapid charging performance can be enhanced. Brief explanation of the drawing

[0021] FIG. 1 is a schematic cross-sectional view of a negative electrode for a secondary battery according to one embodiment. Specific details for implementing the invention

[0022] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Specific details for implementing the present invention will be described in detail below with reference to the attached drawings. Regardless of the drawings, identical reference numerals refer to identical components, and "and / or" includes each of the mentioned items and all combinations of one or more.

[0023] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which the present invention pertains. Throughout the specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components. Furthermore, the singular form includes the plural form unless specifically stated otherwise in the text.

[0024] In this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" or "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between.

[0026] One embodiment of the present invention provides a negative electrode for a secondary battery.

[0027] FIG. 1 is a schematic cross-sectional view of a negative electrode for a secondary battery according to one embodiment. Referring to FIG. 1, the negative electrode (10) for a secondary battery comprises a current collector (11); a first negative active material layer (13) located on the current collector and comprising a water-based binder; and a second negative active material layer (15) located on the first negative active material layer and comprising a non-water-based binder.

[0028] The above current collector (11) may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof, but is not limited thereto.

[0029] The first negative active material layer (13) is located on the current collector (11) and includes a water-based binder and a negative active material, and may additionally include a thickening material and / or a conductive material as needed (optional).

[0030] The above-mentioned water-based binder may include at least one of a styrene butadiene rubber (SBR)-based binder and a carboxymethyl cellulose (CMC)-based binder. For example, one or more types of cellulose-based compounds, specifically carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof (such as Na, K, or Li as alkali metals), such as styrene-butyl rubber or styrene-butyl acrylate copolymer, may be mixed and used, but the present invention is not limited thereto. By including a water-based binder in the negative electrode active material layer located on the current collector, the negative electrode swelling can be improved and the adhesion between the current collector and the negative electrode active material layer can be enhanced. Specifically, when using the above-mentioned SBR system, etc., the binder is mixed into the slurry in a particulate form, so there is no substantial effect on the increase in slurry viscosity, and the binder is easily dispersed, so there is no problem with the formation of an insulating region (layer) due to binder clumping, and since it has good spreadability with the current collector and can be applied uniformly in the width direction, the adhesion between the current collector and the active material layer can be improved.

[0031] Meanwhile, in one example of the present invention, the first negative active material layer (13) may not include a non-aqueous binder. Accordingly, the above-described effect can be further improved.

[0032] The above-mentioned thickening agent is intended to impart viscosity to create a stable solution, and conventionally known thickening agents may be used.

[0033] The above conductive material is used to impart conductivity to the cathode and is not particularly limited as long as it is a conventional electronically conductive material that does not cause chemical changes within the battery. For example, a material selected from the group consisting of natural graphite, synthetic graphite, carbon black, acetylene black, ketjenblack, carbon fiber, carbon nanotube, and combinations thereof may be used, but is not limited thereto.

[0035] The second cathode active material layer (15) is located on the first cathode active material layer (13) and includes a non-aqueous binder and a cathode active material, and may additionally include a conductive material as needed (optional).

[0036] The above-mentioned non-aqueous binder may be an NMP (N-Methyl-2-Pyrrolidone)-based binder or a polyvinylidene fluoride (PVdF)-based binder, and may include, for example, at least one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride-co-tetrafluoroethylene, polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-co-trifluorochloroethylene, and polyvinylidene fluoride-co-ethylene, but the present invention is not limited thereto. Including a non-aqueous binder in the negative electrode active material layer located on the electrode surface allows the non-aqueous binder to be sufficiently wetted by the electrolyte, enabling the movement of Li ions, which can be advantageous under high-rate conditions such as rapid charging. However, non-aqueous binders, particularly PVdF-based binders, have the disadvantage of increasing swelling and decreasing adhesion compared to CMC / SBR-based binders, but in the case of the present invention, these problems can be improved by using a CMC / SBR-based binder in the first negative electrode active material layer.

[0037] Meanwhile, in one example of the present invention, the second negative active material layer (15) may not include an aqueous binder. Accordingly, the above-described effect can be further improved.

[0038] The above conductive material may be a conductive material that can be used in the first cathode active material layer, and may be a conductive material that is the same as or different from that used in the first cathode active material layer.

[0040] At least one of the first negative active material layer (13) and the second negative active material layer (15) may include a carbon-based active material and a silicon-based active material. For example, the first negative active material layer and the second negative active material layer may each independently include a carbon-based active material and a silicon-based active material. Accordingly, a high-capacity and high-energy-density battery can be manufactured, and rapid charging performance can be secured by suppressing the increase in negative resistance and improving the degradation of lifespan characteristics due to Si expansion during charging and discharging.

[0041] The carbon-based active material may be selected from one or more of artificial graphite, natural graphite, and hard carbon, and the silicon-based active material may be Si, SiO x (0 <x<2), Si-Q 합금(상기 Q는 알칼리 금속, 알칼리 토금속, 13족 원소, 14족 원소, 15족 원소, 16족 원소, 전이금속, 희토류 원소 및 이들의 조합으로 이루어진 군에서 선택되는 원소이며, Si은 아님), Si-탄소 복합체, 또한 이들 중 적어도 하나와 SiO2의 혼합물일 수 있다.

[0042] In addition, the first cathode active material layer (13) may contain a carbon-based active material and a silicon-based active material in a weight ratio of 60:40 to 95:5, preferably 70:30 to 95:5, and more preferably 70:30 to 90:10, but the present invention is not limited thereto.

[0043] Specifically, the second negative electrode active material layer (15) may contain a carbon-based active material and a silicon-based active material in a weight ratio of 70:30 to 95:5, preferably a weight ratio greater than 70:30 and less than 95:5 or a weight ratio of 75:25 to 95:5, and more preferably a weight ratio of 80:20 to 95:5. In the weight ratio range of the carbon-based and silicon-based active materials, electrode swelling and DCIR increase can be suppressed and the rapid charging life characteristics of the battery can be further improved.

[0044] In the first cathode active material layer and the second cathode active material layer, the cathode active material comprising the carbon-based active material and the silicon-based active material may be included in an amount of 90 to 99 weight% with respect to the total weight of the first cathode active material layer and in an amount of 90 to 99 weight% with respect to the total weight of the second cathode active material layer, but the present invention is not limited thereto.

[0045] The above-mentioned aqueous binder may be included in an amount of 2 to 4 weight% with respect to the total weight of the first cathode active material layer, preferably 2.5 to 3.5 weight%, and more preferably 2.6 to 3 weight%. Accordingly, the above-described effect can be further improved.

[0046] The above-mentioned non-aqueous binder may be included in an amount of 0.7 to 3.2 weight% with respect to the total weight of the second cathode active material layer, preferably 1 to 3 weight%, and more preferably 2 to 3 weight%. Accordingly, the above-described effect can be further improved.

[0047] In addition, specifically, the weight ratio of the aqueous binder and the non-aqueous binder may be 5:95 to 95:5, preferably 20:80 to 95:5, 40:60 to 95:5, or 40:60 to 90:10, and more preferably 45:55 to 90:10, 40:60 to 80:20, 45:55 to 80:20, 55:45 to 85:15, or 60:40 to 80:20. Accordingly, short circuits between the first and second cathode active material layers and the collector (suppressing reduced adhesion / increased swelling) can be minimized, and deterioration effects such as side reactions of the electrolyte in the second cathode active material layer can be suppressed, as well as rapid charging life can be significantly improved by sufficiently suppressing the expansion of silicon particles during rapid charging and discharging.

[0048] The above-mentioned thickening agent may be included in an amount of 0.1 to 5 weight%, preferably 0.1 to 3 weight%, and more preferably 0.1 to 1.5 weight% with respect to the total weight of the first negative electrode active material layer, but the present invention is not limited thereto.

[0049] The conductive material may be included in an amount of 0.1 to 10 weight%, preferably 0.1 to 5 weight%, based on the total weight of the first negative electrode active material layer, and in an amount of 0.1 to 10 weight%, preferably 0.1 to 5 weight%, based on the total weight of the second negative electrode active material layer, but the present invention is not limited thereto.

[0051] Loading amount of the first cathode active material layer (loading g / cm²) 2 ) and the loading amount (g / cm²) of the second cathode active material layer. 2 The ratio of ) may be 5:95 to 95:5, preferably 20:80 to 95:5, 40:60 to 95:5 or 40:60 to 90:10, more preferably 45:55 to 90:10, 40:60 to 80:20, 45:55 to 80:20, 55:45 to 85:15 or 60:40 to 80:20.

[0052] In addition, the ratio of the thickness of the first cathode active material layer to the thickness of the second cathode active material layer may be 5:95 to 95:5, preferably 20:80 to 95:5, 40:60 to 95:5 or 40:60 to 90:10, more preferably 45:55 to 90:10, 40:60 to 80:20, 45:55 to 80:20, 55:45 to 85:15 or 60:40 to 80:20.

[0053] When the ratio of the loading amount of the above-mentioned negative active material layer and / or the ratio of the thickness of the negative active material layer falls within the range described above, rapid charging performance due to DC-IR reduction is improved, and interfacial adhesion (interface between the first and second active material layers and / or interface between the active material layer and the current collector) due to the suppression of swelling of the active material layer can be significantly improved.

[0055] Another embodiment of the present invention provides a secondary battery comprising: a cathode; an anode; a separator located between the cathode and the anode; and an electrolyte.

[0056] The above cathode is as described above.

[0057] The above positive electrode includes a current collector and a positive electrode active material layer formed by applying a positive electrode slurry containing a positive electrode active material onto the current collector.

[0058] The above-mentioned current collector may use the aforementioned negative current collector, and it is acceptable to use materials known in the relevant technical field, but the present invention is not limited thereto.

[0059] The above-mentioned positive active material layer comprises a positive active material and may further comprise a binder and a conductive material as needed (optional). The positive active material may be any positive active material known in the art, and, for example, it is preferable to use a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof, but the present invention is not limited thereto.

[0060] The above binder and conductive material may use the cathode binder and cathode conductive material described above, and it is acceptable to use materials known in the relevant technical field, but the present invention is not limited thereto.

[0061] The above separator may be selected from, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a nonwoven or woven fabric. For example, polyolefin-based polymer separators such as polyethylene and polypropylene may be mainly used in lithium secondary batteries, and separators coated with a composition containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength. Optionally, they may be used in a single-layer or multi-layer structure, and while it is acceptable to use separators known in the relevant art field, the present invention is not limited thereto.

[0062] The above electrolyte contains an organic solvent and a lithium salt.

[0063] The above organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move. For example, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvents may be used. The above organic solvent may be used alone or as a mixture of two or more types. When two or more types are mixed, the mixing ratio can be appropriately adjusted according to the desired battery performance. Meanwhile, it is acceptable to use organic solvents known in the relevant technical field, but the present invention is not limited thereto.

[0064] The above lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions within the battery, enabling the operation of a basic lithium secondary battery and promoting the movement of lithium ions between the positive and negative electrodes. Examples of the above lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO3C2F5)2, LiN(CF3SO2)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, and LiN(C x F 2x+1 SO2)(C y F 2y+1 Examples include SO2)(x and y are natural numbers), LiCl, LiI, LiB(C2O4)2, or combinations thereof, but the present invention is not limited thereto.

[0065] The concentration of the lithium salt can be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0066] In addition, the above electrolyte may additionally include pyridine, triethyl phosphate, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc., as needed to improve charge / discharge characteristics and flame retardancy characteristics. In some cases, it may additionally include halogen-containing solvents such as carbon tetrachloride and trifluoroethylene to impart non-flammability, and may additionally include FEC (fluoro-ethylene carbonate), PRS (propene sulfone), FPC (fluoro-propylene carbonate), etc., to improve high-temperature storage characteristics.

[0067] The above secondary battery may be a lithium secondary battery.

[0068] A method for manufacturing a secondary battery according to the present invention to achieve the above-mentioned purpose may be manufactured by sequentially stacking a manufactured negative electrode, a separator, and a positive electrode to form an electrode assembly, placing the manufactured electrode assembly into a cylindrical battery case or a prismatic battery case, and then injecting an electrolyte. Alternatively, the battery may be manufactured by stacking the electrode assembly, impregnating it with an electrolyte, placing the resulting product into a battery case, and sealing it.

[0069] The battery case used in the present invention may be one commonly used in the field, and there are no restrictions on the external shape according to the application of the battery; for example, it may be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0070] The secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells. Preferred examples of the medium-to-large device include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, but are not limited to these.

[0072] A method for manufacturing a secondary battery according to the present invention to achieve the above-mentioned purpose may be manufactured by sequentially stacking a manufactured negative electrode, a separator, and a positive electrode to form an electrode assembly, placing the manufactured electrode assembly into a cylindrical battery case or a prismatic battery case, and then injecting an electrolyte. Alternatively, the battery may be manufactured by stacking the electrode assembly, impregnating it with an electrolyte, placing the resulting product into a battery case, and sealing it.

[0073] The battery case used in the present invention may be one commonly used in the field, and there are no restrictions on the external shape according to the application of the battery; for example, it may be a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin shape.

[0074] The secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but can also preferably be used as a unit cell in a medium-to-large battery module comprising a plurality of battery cells. Preferred examples of the medium-to-large device include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, but are not limited to these.

[0076] The present invention will be described in detail below through examples, but these are intended to explain the invention in more detail and the scope of the present invention is not limited by the following examples.

[0077] Examples

[0078] (Examples 1-5)

[0079] <Manufacturing of the Cathode>

[0080] A first cathode slurry was prepared by adding water to 94 wt% of an active material mixed with artificial graphite and SiO in a weight ratio of 90:10, 3 wt% of a carbon black conductive material, 1.7 wt% of an SBR-based binder (SBR, manufacturer: Hansol Chem), and 1.3 wt% of CMC.

[0081] A second cathode slurry was prepared by adding NMP to 94 wt% of an active material mixed in a weight ratio of artificial graphite:SiO₂ 90:10, 3.0 wt% of a carbon black conductive material, and 3 wt% of a PVdF-based binder (PVdF, manufacturer: kureha).

[0082] A first cathode slurry prepared was applied to one side of a copper current collector (8㎛ thick copper foil) using a slot die and dried, and then applied to the other side in the same way and dried. Subsequently, a second cathode slurry was applied to both sides of the copper current collector coated with the first cathode slurry in the same manner and dried.

[0083] At this time, the coating amounts of the first cathode slurry and the second cathode slurry were adjusted so that the ratio of the loading amounts of each cathode active material layer was as shown in Table 1 below.

[0084] A cathode having a current collector, a first cathode active material layer, and a second cathode active material layer was manufactured by rolling the cathode after drying was completed.

[0085] Manufacturing of the anode

[0086] Li[Ni as a positive electrode active material 0.88 Co 0.1 Mn 0.02 A slurry was prepared by mixing ]O2, carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder in a weight ratio of 96.5:2:1.5. The slurry was uniformly coated onto an aluminum foil 12 μm thick and vacuum dried to produce a positive electrode for a secondary battery.

[0087] Manufacturing of secondary batteries

[0088] An anode and a cathode were each notched to a predetermined size and laminated, and a separator (polyethylene, thickness 13 μm) was interposed between the anode and the cathode to form an electrode cell, after which the tab portions of the anode and the cathode were welded. The welded assembly of the anode / separator / cathode was placed inside a pouch, and three sides were sealed, excluding the surface for electrolyte injection. At this time, the portion containing the electrode tabs was included in the sealed portion.

[0089] Electrolyte was injected through the remaining surface excluding the sealing part, and after sealing the remaining surface, it was impregnated for at least 12 hours.

[0090] The electrolyte used was prepared by dissolving 1M LiPF6 in a mixed solvent of EC / EMC / DEC (25 / 45 / 30; volume ratio) and then adding 1 wt% vinylene carbonate (VC), 0.5 wt% 1,3-propensulfone (PRS), and 0.5 wt% lithium bis(oxalateto)borate (LiBOB).

[0091] Subsequently, pre-charging was performed for 36 minutes with a current corresponding to 0.25C. After 1 hour, degassing was performed, and after aging for more than 24 hours, formation charge and discharge were carried out (charging conditions CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharging conditions CC 0.2C 2.5V CUTOFF).

[0092] Afterwards, standard charging and discharging were performed (charging conditions CC-CV 0.33C 4.2V 0.05C CUT-OFF, discharging conditions CC 0.33C 2.5V CUT-OFF).

[0093] (Examples 6-7)

[0094] A cathode, a positive electrode, and a secondary battery were manufactured in the same manner as in Example 4, except that when preparing the second cathode slurry, an active material mixed with artificial graphite and SiO₂ in a weight ratio of 70:30 (Example 6) or an active material mixed with artificial graphite and SiO₂ in a weight ratio of 95:5 (Example 7) was used.

[0095] (Comparative Examples 1~2)

[0096] A cathode, a positive electrode, and a secondary battery were manufactured in the same manner as in Example 1, except that the coating amounts of the first cathode slurry and the second cathode slurry were adjusted so that the ratio of the loading amounts of each cathode active material layer was as shown in Table 1 below.

[0097] (Comparative Example 3)

[0098] A negative electrode, a positive electrode, and a secondary battery were manufactured in the same manner as in Example 1, except that a negative electrode slurry was prepared by adding water to 94 wt% of an active material mixed in a weight ratio of artificial graphite:SiO₂ 90:10, 3 wt% of a carbon black conductive material, 1 wt% of an SBR-based binder (SBR, manufacturer: Hansol Chem), 1 wt% of a PVdF-based binder (PVdF, manufacturer: Kureha), and 1 wt% of CMC, and the prepared negative electrode slurry was coated onto a copper current collector.

[0100] Evaluation example

[0101] Cathode Swelling Analysis

[0102] The cathodes prepared according to Examples 1 to 7 and Comparative Examples 1 to 2 were charged to SOC 100 (0.2C CC / CV charging 4.2V 0.05C cut), and the cathode thickness was measured after disassembling the cell.

[0103] Analysis of secondary battery output characteristics (DC-IR)

[0104] The output characteristics of each secondary battery prepared according to Examples 1 to 7 and Comparative Examples 1 to 2 were evaluated. For the output characteristic evaluation, the secondary batteries of the examples and comparative examples were charged (0.3C CC / CV charge 4.2V 0.05C cut), rested for 10 minutes, and discharged (0.3C CC discharge SOC50 cut). They were then rested for 1 hour at the set SOC, discharged at 1C for 10 seconds, and then rested again for 10 seconds.

[0105] At this time, the difference between the voltage after the discharge ends and the voltage after the 10-second rest is divided by the current to calculate the resistance (DCIR), and the result is shown in Table 1 below.

[0106] *Evaluation of rapid charging life characteristics

[0107] The secondary batteries prepared according to Examples 1 to 7 and Comparative Examples 1 to 2 are charged in Step 1 at a 2.0C c-rate (SOC 8-50 range) and in Step 2 at a 0.5C c-rate (SOC 51-80 range), and then discharged at a 1 / 3C c-rate to a constant temperature (25) set within the DOD72 (SOC 8-80) range. A rapid charging evaluation was conducted in a chamber that maintains this. After repeating 100 cycles with a 10-minute rest time between charge and discharge cycles, the discharge capacity retention rate after rapid charging was measured, and the results are shown in Table 1 below.

[0108] Loading amount (g / cm²) 2 )ratio(%) Second layer artificial graphite: SiO (weight ratio) Electrode swelling (%) DCIR (mohm) Fast charging life (%) Comparative Example 1 100:0 - 30.7 1.080 80 Comparative Example 2 0:100 90:10 35.0 1.050 75 Example 1 10:90 90:10 33.5 1.060 81 Example 2 30:70 90:10 32.7 1.060 84 Example 3 50:50 90:10 31.2 1.070 86 Example 4 70:30 90:10 31.2 1.070 91 Example 5 90:10 90:10 31.2 1.074 87 Example 6 70:30 70:30 32.0 1.078 85 Example 7 70:30 95:5 31.0 1.070 89

[0109] (In Table 1 above, the loading amount ratio is the loading amount of the first cathode active material layer : the loading amount of the second cathode active material layer.)

[0110] In the case of Examples 1 to 5, the first negative electrode active material layer (current collector portion) was used with a CMC / SBR-based binder to minimize short circuits between the negative electrode active material layer and the current collector (suppressing reduced adhesion / increased swelling), and the rapid charging life characteristics were improved by applying a PVdF-based binder to the second negative electrode active material layer (electrode surface portion) with high reactivity.

[0111] On the other hand, it was confirmed that when only CMC / SBR-based binders were used (Comparative Example 1) or only PVdF-based binders were used (Comparative Example 2), DCIR increased or the decrease in adhesion strength and increase in swelling could not be suppressed, resulting in a deterioration of the rapid filling life.

[0112] From the results of Example 4, which had the best rapid charging life, it was found that the most desirable active material layer loading ratio is 70:30. Although Examples 3 and 5 sufficiently suppressed the increase in electrode swelling, it was confirmed that the second negative electrode active material layer (upper layer) was undesirable because it failed to sufficiently control the expansion of silicon particles during rapid charging and discharging (Example 3) or increased DCIR (Example 5), resulting in a reduced rapid charging life.

[0113] In the case of Comparative Example 3, in which a cathode and a secondary battery were manufactured by mixing an aqueous binder (SBR) and a non-aqueous binder (PVdF) when preparing a cathode slurry, it was difficult to mix the binder solvents, so it could not be manufactured.

[0114] Comparing Examples 4, 6, and 7, in the case of Example 6, the swelling of the second negative electrode active material layer deteriorated due to the excessive mixing of SiO, and thus the rapid charging life was analyzed to have decreased somewhat; in the case of Example 7, although the electrode swelling and DCIR were improved, the rapid charging life was analyzed to have decreased somewhat due to the reduced amount of SiO active material mixed. Accordingly, it was found that the optimal weight ratio of artificial graphite to SiO in the second negative electrode active material layer in the present invention is less than 95:5 and greater than 70:30.

[0116] In the present invention, the PVDF binder is sufficiently wetted by the electrolyte to allow Li-ion movement, making it efficient in high-rate environments such as rapid charging. However, it was found that it is difficult to apply to anodes using SiOx due to the disadvantages of increased swelling and reduced adhesion compared to CMC / SBR. To solve this problem, in the embodiment of the present invention, a CMC / SBR-based binder is used for the current collector portion to minimize short circuits (reduced adhesion / increased swelling) between the active material and the current collector, and rapid charging characteristics can be secured by applying the PVDF binder to the electrode surface, where the reaction is high.

[0118] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be implemented in other specific forms without changing the technical concept or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. Explanation of the symbols

[0119] 10: Cathode 11: The whole house 13: First negative electrode active material layer 15: Second negative electrode active material layer

Claims

Claim 1 A current collector; a first negative active material layer located on the current collector and comprising a water-based binder; and a second negative active material layer located on the first negative active material layer and comprising a non-water-based binder, wherein the loading amount (g / cm²) of the first negative active material layer 2 ) and the loading amount (g / cm²) of the second cathode active material layer. 2 The ratio of ) is 55:45 to 85:15, and the non-aqueous binder is included in an amount of 0.7 to 3.2 weight% with respect to the total weight of the second negative electrode active material layer, for a negative electrode for a secondary battery. Claim 2 In claim 1, the aqueous binder comprises at least one of a styrene butadiene rubber (SBR)-based binder and a carboxymethylcellulose (CMC)-based binder, for a negative electrode for a secondary battery. Claim 3 In claim 1, the non-aqueous binder comprises a polyvinylidene fluoride (PVdF)-based binder, for a negative electrode for a secondary battery. Claim 4 In claim 1, at least one of the first negative electrode active material layer and the second negative electrode active material layer comprises a carbon-based active material and a silicon-based active material, for a negative electrode for a secondary battery. Claim 5 In claim 4, the second negative electrode active material layer comprises a carbon-based active material and a silicon-based active material in a weight ratio of 70:30 to 95:5, for a negative electrode for a secondary battery. Claim 6 A negative electrode for a secondary battery according to claim 1, wherein the aqueous binder is included in an amount of 2 to 4 weight% with respect to the total weight of the first negative electrode active material layer. Claim 7 In claim 1, the first negative electrode active material layer is a negative electrode for a secondary battery that does not include a non-aqueous binder. Claim 8 In claim 1, the second negative electrode active material layer is a negative electrode for a secondary battery that does not include a water-based binder. Claim 9 A negative electrode for a secondary battery according to claim 1, wherein the weight ratio of the aqueous binder to the non-aqueous binder is 5:95 to 95:

5. Claim 10 delete Claim 11 A negative electrode for a secondary battery according to claim 1, wherein the ratio of the thickness of the first negative electrode active material layer to the thickness of the second negative electrode active material layer is 5:95 to 95:

5. Claim 12 A secondary battery comprising: a negative electrode according to any one of claims 1 to 9 and 11; a positive electrode; a separator located between the negative electrode and the positive electrode; and an electrolyte.

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