Anode for secondary battery with optimized binder distribution and secondary battery including the same

Abstract

To provide an anode for a nonaqueous electrolyte secondary battery, capable of alleviating peeling of an anode mixture layer from an anode current collector as well as improving battery performance.SOLUTION: An anode for a nonaqueous electrolyte secondary battery includes: an anode current collector; and an anode mixture layer formed on the anode current collector, and containing an anode active material, a conductive material, a rubber-based binder, and a water-soluble polymer-based binder. The anode mixture layer contains, relative to a total weight thereof, 1.0-2.5 wt.% of the rubber-based binder and 0.5-1.5 wt.% of the water-soluble polymer-based binder. When the anode mixture layer is divided into ten equal parts in a thickness direction based on the current collector, a ratio (CA / CB) of a content ratio (CA) of the rubber-based binder at intervals of parts 0 to 3 to a total content of the rubber-based binder to a content ratio (CB) of the water-soluble polymer-based binder at intervals of the parts 0 to 3 to a total content of the water-soluble polymer-based binder is greater than 1.0, and a ratio CA / CB at intervals of parts 7 to 10 is smaller than 1.0.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a secondary battery, and more specifically to a technology for improving the battery performance by improving the binder distribution in the negative electrode of the secondary battery. [Background technology]

[0002] Mobile information terminals such as mobile phones, laptops, and tablet PCs are rapidly becoming more compact and lightweight while offering increased functionality. Non-aqueous electrolyte secondary batteries with high energy density and capacity are widely used as the driving power sources for these devices.

[0003] Carbon materials are widely used as negative electrode active materials for non-aqueous electrolyte secondary batteries. However, there is a growing demand for new high-capacity non-aqueous electrolyte secondary batteries, and interest in silicon materials, which have a larger discharge capacity than carbon materials, is growing.

[0004] As a technique relating to non-aqueous electrolyte secondary batteries using silicon materials, Japanese Patent No. 6128481 discloses a non-aqueous electrolyte secondary battery including a negative electrode plate in which a negative electrode active material layer comprising a negative electrode active material and a binder is formed on a negative electrode substrate, the negative electrode active material comprising a silicon oxide and a carbonaceous material, the mass of the silicon oxide being 1 to 20 mass% relative to the sum of the masses of the silicon oxide and the carbonaceous material, the ratio O / Si of oxygen atoms to silicon atoms of the silicon oxide being 0.5 to 1.5, the binder comprising binder A made of a rubber binder having a double bond and binder B made of a water-soluble polymer compound, the binder A being distributed so that it is more abundant on the negative electrode substrate side than on the surface side of the negative electrode active material layer, and the binder B being present at least around the silicon oxide.

[0005] The above patent document limits the distribution of each of binder A and binder B in a negative electrode plate containing SiOx, but does not mention the relative contents of these binders. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6128481 Summary of the Invention [Problem to be solved by the invention]

[0007] In the negative electrode of a non-aqueous electrolyte secondary battery, rubber-based binders and water-soluble polymer-based binders are typically used to maintain the binding strength between negative electrode active materials and between the negative electrode active material and the negative electrode current collector. However, by optimizing the distribution of each binder at each electrode position in consideration of the influence of each binder on binding, the quality and performance of the product can be improved compared to when the same binder content is used. [Means for solving the problem]

[0008] The present invention relates to a negative electrode for a non-aqueous electrolyte secondary battery, including a negative electrode current collector and a negative electrode mixture layer formed by coating a negative electrode active material, a conductive material, a rubber-based binder, and a water-soluble polymer-based binder on the negative electrode current collector, the negative electrode mixture layer including 1.0 to 2.5 wt % of the rubber-based binder and 0.5 to 1.5 wt % of the water-soluble polymer-based binder relative to the total weight of the negative electrode mixture layer, and the negative electrode mixture layer has a ratio (C A ) and the ratio of the content of water-soluble polymer binder in the range of 0 to 3 to the total content of water-soluble polymer binder (C B ) and the ratio (C A / C B ) exceeds 1.0 and is in the range of 7 to 10. A / C B The present invention provides a negative electrode for a non-aqueous electrolyte secondary battery, in which the value of the non-aqueous electrolyte ratio is less than 1.0.

[0009] The rubber binder content in the range of 0-3 is preferably higher than the content in the range of 7-10.

[0010] C in the interval between 0 and 3 A / C B is in the range of 1.02 to 1.50, and C in the interval between 7 and 10 A / C B is preferably in the range of 0.50 to 0.98, and C in the range of 0 to 3 A / C B is in the range of 1.07 to 1.48, and C in the interval between 7 and 10 A / C B is more preferably in the range of 0.52 to 0.95.

[0011] The rubber binder may have a content in the range of 0 to 3 that is higher than the overall average content, and a content in the range of 7 to 10 that is lower than the overall average content.

[0012] The rubber-based binder may be at least one selected from the group consisting of styrene butadiene rubber (SBR), fluorine-based rubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, and silane-based rubber.

[0013] The water-soluble polymer binder may be at least one selected from the group consisting of carboxymethyl cellulose, cellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylate, and derivatives thereof.

[0014] The negative electrode active material may be at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, and silicon oxide, and the conductive material may be at least one selected from the group consisting of acetylene carbon black, ketjen black, carbon nanotubes, graphene, and graphite.

[0015] The negative electrode mixture layer has a C in the range of 3 to 5. A / C B C in the interval between 5 and 7 when the value is greater than 1.0 A / C B may be less than 1.0.

[0016] Furthermore, the present invention provides a non-aqueous electrolyte secondary battery including the above-mentioned negative electrode. [Effects of the Invention]

[0017] The negative electrode according to the present invention can alleviate the peeling phenomenon between the negative electrode mixture layer and the negative electrode current collector, and can also improve the battery performance. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram schematically illustrating the concept of lithium ion diffusion according to the content distribution of a rubber-based binder in the thickness direction of a negative electrode mixture layer. [Figure 2] 2(a) and 2(b) are graphs showing the ratio of the content in each section to the average SBR and CMC content in all sections (C / Cavg) and CA / CB in Comparative Example 1. [Figure 3] 1( a) and 1(b) are graphs showing the ratio of the content in each section (C / Cavg) and CA / CB to the average SBR and CMC content in all sections in Example 1. [Figure 4] 1 is a photograph showing the penetration of distilled water into the inside of the electrode and the resulting peeling phenomenon in an electrode peeling experiment using distilled water penetration into the negative electrode surfaces of Comparative Example 1 and Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention relates to a non-aqueous electrolyte secondary battery including a negative electrode mixture layer formed by applying a negative electrode active material, a rubber-based binder, and a water-soluble polymer-based binder onto a negative electrode current collector.

[0020] Specifically, the negative electrode provided by the present invention includes a negative electrode current collector and a negative electrode mixture layer formed by coating a negative electrode active material, a conductive material, a rubber-based binder, and a water-soluble polymer-based binder on the negative electrode current collector.

[0021] The binder basically serves to maintain the binding strength between the negative electrode active materials and between the active materials and the negative electrode current collector. The negative electrode mixture layer contains 1.0 to 2.5 wt % of a rubber-based binder and 0.5 to 1.5 wt % of a water-soluble polymer-based binder based on the total weight of the negative electrode mixture layer.

[0022] If the total content of the rubber-based binder in the negative electrode mixture layer is less than 1.0 wt %, the bonding strength between the negative electrode active materials may be reduced, and cracks may easily occur during drying or rolling due to insufficient ductility of the negative electrode mixture layer. If the total content of the rubber-based binder exceeds 2.5 wt %, the movement of electrons and lithium ions within the battery may be hindered, resulting in a significant increase in cell resistance.

[0023] The rubber-based binder is not particularly limited, but may be at least one selected from the group consisting of styrene butadiene rubber (SBR), fluorine-based rubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, and silane-based rubber.

[0024] On the other hand, if the content of the water-soluble polymer binder in the negative electrode mixture layer is less than 0.5 wt%, not only will the binding strength between the negative electrode active materials be reduced, but the viscosity of the slurry will also be reduced, resulting in problems such as reduced phase stability of the slurry and increased edge thickness during coating. Furthermore, if the content of the water-soluble polymer binder exceeds 1.5 wt%, not only will the viscosity of the slurry increase excessively, reducing coating workability, but it will also be difficult to uniformly dissolve the polymer binder, resulting in problems such as the formation of microgels.

[0025] The water-soluble polymer binder may be at least one selected from the group consisting of carboxymethyl cellulose (CMC), cellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylate, and derivatives thereof.

[0026] Meanwhile, the negative electrode mixture layer of the present invention includes, based on the solid content weight, a negative electrode active material and a conductive material in addition to the rubber-based binder and the water-soluble polymer-based binder. The negative electrode active material and the conductive material are typically contained in amounts used to form the negative electrode mixture layer, and are not particularly limited in the present invention.

[0027] The negative electrode active material may be a graphite-based material, a non-graphite-based material, or a silicon oxide. Examples of the graphite-based material include natural graphite and artificial graphite, and examples of the non-graphite-based material include soft carbon and hard carbon. These may be used alone or in combination.

[0028] Examples of the conductive material include acetylene carbon black, ketjen black, carbon nanotubes, graphene, graphite, etc. Needless to say, any one of these can be used alone, or two or more of them can be used in combination.

[0029] The negative electrode mixture layer is produced by adding water to a mixture of the above-described negative electrode active material, conductive material, rubber-based binder, and water-soluble polymer-based binder to form a slurry, and then applying the resulting slurry to a negative electrode current collector and drying it. The amount of water, for example, distilled water, used to prepare the slurry may be in the range of 40 to 60 wt. % based on the total weight of the slurry, although the amount is not particularly limited.

[0030] In the negative electrode mixture layer obtained by the present invention, the water-soluble polymer binder and the rubber binder bind the negative electrode active material to each other and also to the negative electrode current collector.

[0031] Although the water-soluble polymer binder has a high affinity for moisture, when exposed to moisture, it absorbs moisture and causes swelling. If such a water-soluble polymer binder is present in a relatively large amount at the interface between the negative electrode mixture layer and the negative electrode current collector, some of the bonds acting between the negative electrode active material, the binder, and the negative electrode current collector may be replaced by bonds acting between moisture and the binder, thereby resulting in a decrease in the binding strength between the negative electrode active material and the negative electrode current collector. This decrease in binding strength may cause delamination between the negative electrode current collector and the negative electrode mixture layer when the negative electrode current collector is filled with an electrolyte.

[0032] On the other hand, rubber-based binders have low moisture affinity and do not significantly cause the problem of decreased binding strength due to moisture adsorption. Therefore, it is preferable to use a rubber-based binder rather than a water-soluble polymer-based binder in the section close to the negative electrode current collector to improve the binding strength between the substrate, i.e., the negative electrode current collector, and the negative electrode active material.

[0033] However, the rubber-based binder is present non-uniformly among the negative electrode active materials in the form of small particles. If a large amount of such rubber-based binder is present in the negative electrode mixture layer, particularly on the surface of the negative electrode mixture layer, it may clog the gaps among the negative electrode active materials, thereby inhibiting the diffusion of lithium ions transferred from the positive electrode into the negative electrode.

[0034] The concept of lithium ion diffusion depending on the content distribution of the rubber-based binder is shown in Figure 1. As shown in Figure 1, when a large amount of rubber-based binder is distributed on the surface of the negative electrode mixture layer, it hinders the transport of lithium ions, causing a problem of inhibiting the diffusion of lithium ions into the negative electrode.

[0035] As a result, the battery resistance may increase, and during high-rate charging, the precipitation of lithium salts from the surface of the electrode may reduce charge-discharge efficiency. However, if the amount of rubber-based binder present on the surface is small, lithium ions can easily diffuse into the inside of the negative electrode, preventing such problems.

[0036] As described above, since the rubber-based binder and the water-soluble polymer-based binder each have different influences on binding and battery performance, by taking these influences into consideration and optimizing the distribution of each binder for each electrode position, both the quality and performance of the product can be improved.

[0037] Therefore, the present invention provides a negative electrode in which the role of a rubber-based binder is increased in the vicinity of the current collector in the negative electrode mixture layer to mitigate the peeling phenomenon between the mixture layer and the current collector, and the role of a water-soluble polymer-based binder is increased on the surface of the mixture layer to improve battery performance, within the range that does not inhibit the bonding force between the active materials.

[0038] More specifically, when the negative electrode mixture layer of the present invention is divided into 10 equal parts in the thickness direction based on the current collector, the rubber binder content ratio (C A ) and the content ratio of water-soluble polymer binder (C B ) ratio (C A / C B ) exceeds 1.0 and is in the range of 7 to 10. A / C B is preferably less than 1.0. More preferably, in the range of 0 to 3, A / C B may be in the range of 1.02 to 1.50, more preferably 1.07 to 1.48, and C in the interval between 7 and 10 A / C B may be in the range of 0.50 to 0.98, and more preferably 0.52 to 0.95. In this case, the content ratio of the rubber binder or the water-soluble polymer binder, C A or C B means the value obtained by dividing the content of each binder contained in the corresponding section by the content of all binders contained in the entire section.

[0039] The reason for limiting each range to between 0 and 3 and between 7 and 10 is that the quality and performance of the product to be improved in the present invention are related to the properties near the interfaces on both sides of the mixture layer, and the desired level of properties can be fully achieved even if the above conditions are satisfied only in these ranges.

[0040] In this case, it is preferable that the content of the rubber binder in the section between 0 and 3 is higher than that in the section between 7 and 10. Also, it is preferable that the content in the section between 0 and 3 is higher and the content in the section between 7 and 10 is lower than the average content of the rubber binder in the entire section. Otherwise, it is preferable that the content of the rubber binder in the section between 0 and 3 is higher and the content in the section between 7 and 10 is lower than the average content of the rubber binder in the entire section. A / C B is over 1.0, and in the range between 7 and 10, C A / C B In order to simultaneously satisfy a distribution in which the viscosity of the water-soluble polymer binder is less than 1.0, it is necessary to increase the range of change in the content of the water-soluble polymer binder in each section. However, unlike water-insoluble rubber-based binders, the viscosity of the slurry produced from the water-soluble polymer binder can change significantly depending on the content change, which increases the possibility of defects occurring in the coating process, in which the viscosity of the slurry must be kept constant.

[0041] Furthermore, in the range of 3 to 5, the content ratio of the rubber binder (C A ) and the content ratio of water-soluble polymer binder (C B ) ratio (C A / C B ) exceeds 1.0 and C in the interval between 5 and 7 A / C B may be less than 1.0.

[0042] According to the present invention, in the binder distribution within the anode mixture layer, the rubber-based binder content is controlled to be higher in the vicinity of the anode current collector than in the surface of the anode mixture layer, and the water-soluble polymer-based binder content is controlled to be higher in the surface of the anode mixture layer than in the vicinity of the anode current collector, thereby alleviating the peeling phenomenon between the anode mixture layer and the anode current collector and improving battery performance.

[0043] The formation of the negative electrode mixture layer is not particularly limited. For example, as described above, a negative electrode mixture layer-forming slurry (slurry 1) having a binder content suitable for the range of 0 to 3 and a negative electrode mixture layer-forming slurry (slurry 2) having a binder content suitable for the range of 7 to 10 can be prepared, and then these can be used as a negative electrode current collector. Slurry 1 and slurry 2 can be simultaneously or sequentially applied to a copper foil and then dried at the same time to form the negative electrode mixture layer. Alternatively, the negative electrode mixture layer can be prepared by applying and drying the slurry 1, and then applying and drying slurry 2. [Example]

[0044] Example The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0045] Example 1 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.8%, 1.2%, 96%, and 1%, respectively, and then distilled water was added to make the solid content weight about 50%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0046] Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.2%, 1.2%, 96.6%, and 1%, respectively, and then distilled water was added to make the solid content weight about 52%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 2.

[0047] The negative electrode slurry 1 was applied to one surface of a copper foil (thickness: 8 μm) to a thickness of 60 μm to form a first mixture layer, and then the negative electrode slurry 2 was applied to the first mixture layer to a thickness of 60 μm to form a second mixture layer.

[0048] As a result, a structure of a first mixture layer in the range of 0 to 5 and a second mixture layer in the range of 5 to 10 in the thickness direction based on the surface of the copper foil was formed, and then dried in a drying oven formed with four zones under the following conditions.

[0049] Temperature of 100℃, wind speed 0.42m / s, drying time 20 seconds Temperature in zone 2: 110°C, wind speed: 0.47 m / s, drying time: 20 seconds Temperature in zone 3: 115°C, air speed: 0.50 m / s, drying time: 20 seconds Temperature of 4 zones: 125°C, wind speed: 0.77m / s, drying time: 20 seconds

[0050] Thereafter, the first and second mixture layers were rolled to produce a negative electrode having a final thickness of 80 μm.

[0051] Example 2 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.8%, 1.3%, 95.9%, and 1%, respectively, and then distilled water was added to make the solid content weight about 52%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0052] Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.2%, 1.3%, 96.5%, and 1%, respectively, and then distilled water was added to make the solid content weight about 52%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 2.

[0053] Thereafter, a negative electrode having a negative electrode mixture layer on the surface of the copper foil was produced in the same manner as in Example 1.

[0054] Example 3 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.8%, 1.2%, 96%, and 1%, respectively, and then distilled water was added to make the solid content weight about 50%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0055] Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 0.8%, 1.2%, 97%, and 1%, respectively, and then distilled water was added to make the solid content approximately 50% by weight. The mixture was mixed for 100 minutes to prepare negative electrode slurry 2.

[0056] Thereafter, a negative electrode having a negative electrode mixture layer on the surface of the copper foil was produced in the same manner as in Example 1.

[0057] Example 4 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.8%, 1.2%, 96%, and 1%, respectively, and then distilled water was added to make the solid content weight about 50%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0058] Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 0.8%, 1.2%, 97%, and 1%, respectively, and then distilled water was added to make the solid content approximately 50% by weight. The mixture was mixed for 100 minutes to prepare negative electrode slurry 2.

[0059] The negative electrode slurry 1 was applied to one surface of a copper foil (thickness: 8 μm) to a thickness of 60 μm, and then dried in a drying oven having four sections under the following conditions to form a first mixture layer.

[0060] Temperature in zone 1: 130°C, wind speed: 2.01 m / s, drying time: 10 seconds Temperature in zone 2: 140°C, wind speed: 2.01 m / s, drying time: 10 seconds Temperature in zone 3: 140°C, wind speed: 0.60 m / s, drying time: 10 seconds Temperature of 4 zones: 150°C, wind speed: 1.01 m / s, drying time: 10 seconds

[0061] Next, negative electrode slurry 2 was applied to the first mixture layer to a thickness of 60 μm, and then, similar to the formation of the first mixture layer, it was dried under the same conditions in a drying oven formed with four zones to form a second mixture layer.

[0062] As a result, a structure was formed in which the first mixture layer was in the 0 to 5 section and the second mixture layer was in the 5 to 10 section in the thickness direction based on the surface of the copper foil.

[0063] Thereafter, the first and second mixture layers were rolled to produce a negative electrode having a final thickness of 80 μm.

[0064] Example 5 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.6%, 1.2%, 96.2%, and 1%, respectively, and then distilled water was added to make the solid content approximately 50% by weight. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0065] Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.4%, 1.2%, 96.4%, and 1%, respectively, and then distilled water was added to make the solid content weight about 50%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 2.

[0066] The negative electrode slurry 1 was applied to one surface of a copper foil (thickness: 8 μm) to a thickness of 60 μm, and then dried in a drying oven having four sections under the following conditions to form a first mixture layer.

[0067] Temperature in zone 1: 130°C, wind speed: 2.01 m / s, drying time: 10 seconds Temperature in zone 2: 140°C, wind speed: 2.01 m / s, drying time: 10 seconds Temperature in zone 3: 140°C, wind speed: 0.60 m / s, drying time: 10 seconds Temperature of 4 zones: 150°C, wind speed: 1.01 m / s, drying time: 10 seconds

[0068] Next, negative electrode slurry 2 was applied to the first mixture layer to a thickness of 60 μm, and then, similar to the formation of the first mixture layer, it was dried under the same conditions in a drying oven formed with four zones to form a first mixture layer.

[0069] As a result, a structure was formed in which the first mixture layer was in the range of 0 to 5 and the second mixture layer was in the range of 5 to 10 in the thickness direction based on the surface of the copper foil.

[0070] Thereafter, the first and second mixture layers were rolled to produce a negative electrode having a final thickness of 80 μm.

[0071] Comparative Example 1 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.5%, 1.2%, 96.3%, and 1%, respectively, and then distilled water was added to make the solid content weight about 50%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0072] The negative electrode slurry 1 was applied to one side of a copper foil (thickness 8 μm) to a thickness of 120 μm, and then dried in a drying oven formed into four zones under the following conditions to form a first mixture layer having a thickness range of 0 to 10 μm.

[0073] Temperature of 100℃, wind speed 0.42m / s, drying time 20 seconds Temperature in zone 2: 110°C, wind speed: 0.47 m / s, drying time: 20 seconds Temperature in zone 3: 115°C, air speed: 0.50 m / s, drying time: 20 seconds Temperature of 4 zones: 125°C, wind speed: 0.77m / s, drying time: 20 seconds

[0074] The mixture layer thus prepared was rolled to prepare a negative electrode having a final thickness of 80 μm.

[0075] Comparative Example 2 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.5%, 1.3%, 96.2%, and 1%, respectively, and then distilled water was added to make the solid content weight about 52%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0076] The negative electrode slurry 1 was applied to one surface of a copper foil (thickness 8 μm) to a thickness of 120 μm, and then dried under the same conditions as in Comparative Example 1 to form a first mixture layer having a thickness range of 0 to 10 μm.

[0077] The first mixture layer thus prepared was rolled to prepare a negative electrode having a final thickness of 80 μm.

[0078] Comparative Example 3 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 0.8%, 1.2%, 97%, and 1%, respectively, and then distilled water was added to make the solid content approximately 50% by weight. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0079] The negative electrode slurry 1 was applied to one surface of a copper foil (thickness 8 μm) to a thickness of 120 μm, and then dried under the same conditions as in Comparative Example 1 to form a first mixture layer having a thickness range of 0 to 10 μm.

[0080] The first mixture layer thus prepared was rolled to prepare a negative electrode having a final thickness of 80 μm.

[0081] Comparative Example 4 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.8%, 1.2%, 96%, and 1%, respectively, and then distilled water was added to make the solid content weight about 50%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0082] Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 1.2%, 1.2%, 96.6%, and 1%, respectively, and then distilled water was added to make the solid content weight about 52%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 2.

[0083] The negative electrode slurry 1 was applied to one surface of a copper foil (thickness: 8 μm) to a thickness of 60 μm to form a first mixture layer, and then the negative electrode slurry 2 was applied to the first mixture layer to a thickness of 60 μm to form a second mixture layer.

[0084] As a result, a structure of a first mixture layer in the range of 0 to 5 and a second mixture layer in the range of 5 to 10 in the thickness direction based on the surface of the copper foil was formed, and then dried in a drying oven formed with four zones under the following conditions.

[0085] Temperature in zone 1: 130°C, wind speed: 2.01 m / s, drying time: 10 seconds Temperature in zone 2: 140°C, wind speed: 2.01 m / s, drying time: 10 seconds Temperature in zone 3: 140°C, wind speed: 0.60 m / s, drying time: 10 seconds Temperature of 4 zones: 150°C, wind speed: 1.01 m / s, drying time: 10 seconds

[0086] Thereafter, the first and second mixture layers were rolled to produce a negative electrode having a final thickness of 80 μm.

[0087] Comparative Example 5 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) were mixed as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material in weight ratios of 1.4%, 1.6%, 96%, and 1%, respectively, and then distilled water was added to make the solid content approximately 50% by weight, followed by mixing for 100 minutes.

[0088] However, the viscosity was too high to obtain a slurry, and the subsequent process for manufacturing the negative electrode was discontinued.

[0089] Comparative Example 6 Styrene butadiene rubber (SBR, A) and carboxymethyl cellulose (CMC, B) as binders, artificial graphite as a negative electrode active material, and carbon black as a conductive material were mixed in weight ratios of 2%, 0.4%, 96.6%, and 1%, respectively, and then distilled water was added to make the solid content weight about 50%. The mixture was mixed for 100 minutes to prepare negative electrode slurry 1.

[0090] The negative electrode slurry 1 was applied to one side of a copper foil (thickness 8 μm) to a thickness of 120 μm. However, due to the low viscosity of the slurry, the slurry did not stably form a coating layer on the copper foil, and the subsequent process for manufacturing the negative electrode was discontinued.

[0091] Measurement of binder distribution in the mixture layer The binder distribution in the thickness direction of the mixture layers of the negative electrodes produced in Examples 1 to 5 and Comparative Examples 1 to 4 was measured. The results are shown in Table 1.

[0092] The binder distribution measurement was carried out by staining the negative electrode mixture layer with OsO4, cutting the cross section of the electrode, and performing SEM-EDAX analysis.

[0093] In the SEM analysis, the distribution of Os elements in the cross section of the mixture layer indicates the distribution of the rubber-based binder, and the distribution of Na elements indicates the distribution of the water-soluble binder.

[0094] At this time, in Table 1, C A indicates the ratio of SBR contained in a predetermined section (sections 0 to 3 and 7 to 10 in the thickness direction from the current collector) to the total SBR content, and C B indicates the ratio of the CMC content contained in a given section (sections 0 to 3 and 7 to 10 in the thickness direction from the current collector) to the total CMC content, and C A / C B is the C included in the specified sections (sections 0 to 3 and 7 to 10 in the thickness direction from the current collector). B C against A The ratio of

[0095] Furthermore, in Example 1 and Comparative Example 1, the ratio of the content in each section to the average SBR content and the CMC content of all sections (C / C avg ) and C A / C B are shown in Figures 2 and 3, respectively. In Figures 2 and 3, (a) shows C / C avg (b) is the graph of C A / C B This is a graph of

[0096] Current collector adhesion measurement To measure the adhesive strength between the mixture layer and the current collector in the electrodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 4, an 18 mm wide 3M tape was attached to each electrode and a 90-degree peel test was performed.

[0097] The load value when the mixture layer and the current collector separated was measured, and the adhesive strength of the current collector was calculated by dividing this by the width of the tape. The values ​​are shown in Table 1.

[0098] Measurement of electrode peeling The electrodes produced in Examples 1 to 5 and Comparative Examples 1 to 4 were cut into pieces measuring 5 cm x 5 cm, and the four corners were fixed with tape.

[0099] About 1 ml of distilled water was dropped onto the mixture layer of the electrode, and then the mixture was left for 30 minutes.

[0100] It was visually observed whether or not the distilled water had penetrated into the mixture layer and caused peeling between the mixture layer and the current collector, and the presence or absence of peeling is shown in Table 1 as ○ (peeled) or × (not peeled).

[0101] Battery charge / discharge efficiency measurement Batteries were fabricated using the electrodes produced in Examples 1 to 5 and Comparative Examples 1 to 4.

[0102] Each of the prepared batteries was charged in a CC (Constant Current) mode at 1.5 C until the voltage reached 4.2 V, and the charge capacity was confirmed.

[0103] Thereafter, the battery was discharged in a CC (Constant Current) mode at 0.3 C until the voltage reached 2.5 V, and the discharge capacity was confirmed.

[0104] The charge / discharge efficiency was calculated by dividing the discharge capacity measured in this way by the charge capacity, and the calculation results are shown in Table 1.

[0105] [Table 1]

[0106] As can be seen from the results of Table 1 and Figures 2 and 3, in the range of 0 to 3 close to the current collector side, the SBR content ratio (C A ) is the CMC content ratio (C B ) is larger than (C A / C B The electrodes of Examples 1 to 5, in which the CMC content ratio (C > 1) was high, had excellent charge-discharge efficiency and did not experience peeling of the electrode in distilled water. However, in the case of Comparative Examples 1 and 2, in the range of 0 to 3 near the current collector, A ) is the SBR content ratio (C B), which resulted in electrode peeling due to binder swelling caused by water. An electrode peeling experiment using distilled water penetration was conducted on the negative electrode surfaces of Comparative Example 1 and Example 1. Photographs of the distilled water penetration into the electrodes of Example 1 and Comparative Example 1 were taken, and the photographs are shown in FIG. 4.

[0107] 4, in the case of Comparative Example 1, the high CMC content resulted in easy penetration of distilled water, but in the case of Example 1, distilled water did not easily penetrate. This shows that in the case of the present invention, peeling of the electrode from the current collector due to water penetration can be suppressed.

[0108] The negative electrodes of Comparative Examples 1 to 4 showed lower charge-discharge efficiency than the negative electrodes of Examples 1 to 5. In the case of Comparative Examples 1 to 4, in the section 7 to 10 on the negative electrode surface side, the SBR content ratio (C A ) is high, but this is thought to be because the large amount of SBR particles fills the surface voids of the active material, preventing lithium ions from expanding into the inside of the negative electrode.

[0109] Therefore, in the negative electrodes of Examples 1 to 5 according to the present invention, even if the same content of binder is used, optimizing the distribution of each binder for each electrode position can contribute to improving not only the quality of the product but also its performance.

[0110] When the SBR content is low, as in Comparative Example 3, the adhesion to the current collector is significantly reduced, and peeling of the electrode mixture layer or negative electrode active material from the current collector is a problem. Although Comparative Example 3 does not use a negative electrode slurry with a controlled binder distribution, it is easy to predict that when the SBR content is excessively low, the adhesion to the current collector will be significantly reduced even if the binder content is controlled in each section.

[0111] Meanwhile, Comparative Example 4 uses the same anode slurries 1 and 2 as in Example 1, but the drying conditions are different from those in Example 1. As can be seen from the results of Comparative Example 4 and Example 1, even though the same anode slurries are used, the distribution of the binder present in each section in the thickness direction of the anode mixture layer differs depending on the drying conditions.

[0112] These results show that by controlling the drying process, it is possible to manufacture a negative electrode having a negative electrode mixture layer in which the binder content in each section is controlled, as in the present invention.

Claims

1. a negative electrode current collector; and a negative electrode mixture layer formed on the negative electrode current collector and including a negative electrode active material, a conductive material, a rubber-based binder, and a water-soluble polymer-based binder, The negative electrode mixture layer contains 1.0 to 2.5 wt % of a rubber-based binder and 0.5 to 1.5 wt % of a water-soluble polymer-based binder based on the total weight of the negative electrode mixture layer, When the negative electrode mixture layer is divided into 10 equal parts in the thickness direction based on the negative electrode current collector, the content of the rubber-based binder contained in the negative electrode mixture layer in the section between 0 and 5 on the negative electrode current collector side is higher than the content of the rubber-based binder contained in the negative electrode mixture layer in the section between 5 and 10 on the surface side, The negative electrode mixture layer in the section between 0 and 5 on the negative electrode current collector side has a rubber-based binder content greater than a water-soluble polymer-based binder content, The ratio of the rubber binder content of the negative electrode mixture layer in the range of 0 to 3 to the total content of the rubber binder (C Ａ ) is 29 to 41%.

2. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the rubber-based binder in the negative electrode mixture layer in the surface side section between 5 and 10 is less than the content of the water-soluble polymer-based binder.

3. The ratio of the rubber binder content of the negative electrode mixture layer in the range of 0 to 5 on the negative electrode current collector side to the total content of the rubber binder (C Ａ ) and the ratio of the content of the water-soluble polymer binder in the negative electrode mixture layer on the negative electrode current collector side to the total content of the water-soluble polymer binder (C Ｂ ) ratio (C Ａ / C Ｂ ) exceeds 1.0, and C in the section between 5 and 10 on the surface side Ａ / C Ｂ 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the value of σ is less than 1.

0.

4. The ratio of the rubber binder content in the range of 0 to 3 to the total content of the rubber binder (C Ａ ) and the ratio of the content of the water-soluble polymer binder in the range of 0 to 3 to the total content of the water-soluble polymer binder (C Ｂ ) ratio (C Ａ / C Ｂ ) is in the range of 1.04 to 1.46, and C in the interval between 7 and 10 Ａ / C Ｂ 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the value of ρ is in the range of 0.53 to 0.

97.

5. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the rubber binder has a content in the range of 0 to 3 more than the content in the range of 7 to 10.

6. 2. The negative electrode for a nonaqueous electrolyte secondary battery according to claim 1, wherein the rubber-based binder is at least one selected from the group consisting of styrene-butadiene rubber (SBR), fluorine-based rubber, ethylene-propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, and silane-based rubber.

7. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the water-soluble polymer binder is at least one selected from the group consisting of carboxymethyl cellulose, cellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylate, and derivatives thereof.

8. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, and silicon oxide.

9. 2. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive material is at least one selected from the group consisting of acetylene carbon black, carbon nanotubes, graphene, and graphite.

10. The negative electrode mixture layer has a C in the range of 3 to 5. Ａ / C Ｂ C in the interval between 5 and 7, where C is greater than 1.0 Ａ / C Ｂ The negative electrode for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the value of the negative electrode is less than 1.

0.

11. A non-aqueous electrolyte secondary battery comprising the negative electrode according to claim 1 .

12. The negative electrode mixture layer has a C in the range of 3 to 5. Ａ / C Ｂ C in the interval between 5 and 7, where C is greater than 1.0 Ａ / C Ｂ The nonaqueous electrolyte secondary battery according to claim 11 , wherein the ρ is less than 1.0.

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