Secondary battery manufacturing method and secondary battery

Abstract

To provide a manufacturing method of a secondary battery capable of reducing an electric resistance difference between an inner mixture layer and an outer mixture layer of an anode, and the secondary battery.SOLUTION: A manufacturing method of a secondary battery comprising a wound electrode body 1 includes: a first coating step of coating a first surface of an anode collector foil 11, which is positioned inside if wound, with a first mixture containing a first positive material; a second coating step of coating a second surface of the anode collector foil 11, which is positioned outside if wound, with a second mixture containing a second positive material; and a winding step of winding the anode collector foil 11 coated with the first positive material and the second positive material. Variations in a particle size of the first positive material with which the first surface of the anode collector foil 11 are smaller than variations in a particle size of the second positive material with which the second surface of the anode collector foil 11 is coated.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a secondary battery including a wound-type electrode assembly, and to a secondary battery. [Background technology]

[0002] Currently, secondary batteries such as lithium-ion batteries are used in electric vehicles, hybrid vehicles, plug-in hybrid vehicles, etc. Among secondary batteries, there is a wound-type secondary battery that includes an electrode assembly formed by stacking and winding a positive electrode sheet, a negative electrode sheet, and a separator.

[0003] In a wound secondary battery, the density of the active material in the inner composite layer of the negative electrode located on the inside in the wound state is higher than the density of the active material in the outer composite layer of the negative electrode located on the outside, and therefore the electrical resistance of the inner composite layer is higher than the electrical resistance of the outer composite layer, which causes a difference in electrical resistance between the inner composite layer and the outer composite layer, resulting in the problem that a substance that provides an intercalator (e.g., lithium) is likely to precipitate.

[0004] In this regard, the secondary battery disclosed in Patent Document 1 is configured so that the electrode density of the inner composite layer of the negative electrode is lower than that of the outer composite layer of the negative electrode, so that the electrode densities of the inner composite layer and the outer composite layer of the negative electrode are the same when the negative electrode current collector is wound. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-130317 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the particle size of each active material contained in the composite layer usually varies, and the specific surface area is not uniform, resulting in variation in resistance within the composite layer. Therefore, there is a problem that the difference in electrical resistance between the inner composite layer and the outer composite layer of the negative electrode cannot be sufficiently suppressed by simply making the densities of the inner composite layer and the outer composite layer the same, as in the secondary battery disclosed in Patent Document 1.

[0007] The present invention is intended to solve such problems, and aims to provide a method for manufacturing a secondary battery that can reduce the difference in electrical resistance between the inner composite layer and the outer composite layer of the negative electrode, and a secondary battery. [Means for solving the problem]

[0008] A method for manufacturing a secondary battery including a wound electrode assembly according to one aspect of the present invention includes the steps of: a first coating step of coating a first surface of the negative electrode current collector foil, the first surface being located on the inner side when the negative electrode current collector foil is wound, with a first composite material containing a first active material; a second coating step of coating a second surface of the negative electrode current collector foil, the second surface being located on the outer side when the negative electrode current collector foil is wound, with a second composite material containing a second active material; a winding step of winding the negative electrode current collector foil coated with the first active material and the second active material; Including, The variation in particle size of the first active material coated on the first surface of the negative electrode current collector foil is smaller than the variation in particle size of the second active material coated on the second surface of the negative electrode current collector foil.

[0009] A first value indicative of the particle size variation of the first active material can be derived by subtracting from a second value indicative of the particle size variation of the second active material the difference between the second value and the first value.

[0010] In addition, the difference between the particle diameters D10 and D90 of the first active material, which corresponds to the first value, is within a range of 4.0 to 9.5 μm, The difference between the particle diameters D10 and D90 of the second active material, which corresponds to the second value, can be within the range of 5.0 to 11.0 μm.

[0011] Furthermore, it is preferable that the particle size of the first active material applied to the first surface of the negative electrode current collector foil is substantially uniform.

[0012] Furthermore, the first composite and the second composite can be configured so that, when the electrode body is wound, the density of the first active material coated on the first surface of the negative electrode current collector foil and the density of the second active material coated on the second surface of the negative electrode current collector foil are substantially the same.

[0013] A secondary battery including a wound electrode assembly according to one aspect of the present invention comprises: The negative electrode sheet included in the electrode assembly includes a current collecting foil and an active material coated on both sides of the current collecting foil, When the negative electrode sheet is wound, the variation in particle size of the first active material located inside the current collector foil is smaller than the variation in particle size of the second active material located outside the current collector foil. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a method for manufacturing a secondary battery that can reduce the difference in electrical resistance between the inner and outer composite layers of the negative electrode, and the secondary battery. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a diagram showing an example of an electrode body included in a secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a cross-sectional view of a negative electrode sheet according to one embodiment of the present invention. [Figure 3] FIG. 10 is a graph showing the relationship between the variation in particle size of the negative electrode active material and the lithium deposition resistance of the inner and outer mixture layers. [Figure 4] 1A to 1C are diagrams illustrating an example of a method for manufacturing a secondary battery according to an embodiment of the present invention. [Figure 5] FIG. 1 is a diagram showing the results of performance evaluation of a secondary battery according to one embodiment of the present invention and the results of performance evaluation of two types of secondary batteries according to the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a diagram showing an example of an electrode body 1 included in a secondary battery according to an embodiment of the present invention. The electrode body 1 is housed in a battery case (not shown) of the secondary battery. The width direction shown in the drawing refers to the width direction of the electrode body 1. Furthermore, the stacking direction refers to the stacking direction of the electrode sheets included in the electrode body 1.

[0017] The electrode assembly 1 is formed by stacking a positive electrode sheet, a negative electrode sheet, and a separator, winding them, and flattening them. As shown in Fig. 1, the electrode assembly 1 has two curved portions 2 and 3 at its top and bottom.

[0018] The positive electrode sheet includes a current collector foil (aluminum, etc.) and a composite material. The positive electrode composite material is composed of a slurry containing an active material (lithium cobalt oxide, etc.), a conductive agent, and a binder. The negative electrode sheet includes a current collector foil (copper, etc.) and a composite material. The negative electrode sheet is formed by coating both sides of the current collector foil with the composite material. The negative electrode composite material is composed of a slurry containing an active material (graphite, etc.), a conductive agent, and a binder. The separator is an insulating material that insulates the positive electrode sheet and the negative electrode sheet, and is placed between the positive electrode sheet and the negative electrode sheet.

[0019] FIG. 2 is a cross-sectional view of a negative electrode sheet 10 according to one embodiment of the present invention. FIG. 2 shows cross sections of the curved portion of the negative electrode sheet 10 before and after winding. The negative electrode sheet 10 includes a current collector foil 11 and composite layers 12 and 13 formed by coating both sides of the current collector foil 11 with a composite material. The current collector foil 11 corresponds to the negative electrode current collector foil. Hereinafter, the composite layer 12 located inside the current collector foil 11 when the negative electrode sheet 10 is wound will be referred to as the inner composite layer 12, and the active material contained in the inner composite layer 12 will be referred to as the first active material. Furthermore, the composite layer 13 located outside the current collector foil 11 when the negative electrode sheet 10 is wound will be referred to as the outer composite layer 13, and the active material contained in the outer composite layer 13 will be referred to as the second active material.

[0020] Negative electrode sheet 10 is configured so that the variation in particle size of the first active material is smaller than the variation in particle size of the second active material when negative electrode sheet 10 is wound. In this embodiment, the variation in particle size of the first active material is determined so that inner composite layer 12 and outer composite layer 13 have the same resistance to lithium deposition.

[0021] The difference between two particle sizes in the particle size distribution of the first active material contained in the inner composite layer 12 (specifically, particle size distribution measured by laser diffraction scattering; the same applies below) can be used as a value indicating the particle size variation of the first active material in the inner composite layer 12. This value corresponds to the first value. For example, the difference between the D10 and D90 particle sizes of the first active material can be used as the first value. Note that the first value may also be defined using other particle sizes, such as D20 and D80 particle sizes.

[0022] Similarly, the difference between two particle sizes in the particle size distribution of the second active material contained in outer composite layer 13 can be used as a value indicating the particle size variation of the second active material in outer composite layer 13. This value corresponds to the second value. For example, the difference between the D10 and D90 particle sizes of the second active material can be used as the second value. Note that the second value may also be defined using other particle sizes, such as D20 and D80 particle sizes.

[0023] Specifically, the difference DF between the second value and the first value is calculated based on Equation 1. Then, the first value can be derived by subtracting the difference DF from the second value.

number

[0024] 3 is a diagram showing the relationship between the particle size variation of the negative electrode active material and the lithium deposition resistance of the inner composite layer 12 and the outer composite layer 13. The lithium deposition resistance of the inner composite layer 12 and the outer composite layer 13 is represented by the reaction resistance of the negative electrode. In the example shown in FIG. 3, the difference between the particle sizes D10 and D90 of the negative electrode active material is used as a value indicating the particle size variation of the negative electrode active material.

[0025] 3, the lithium deposition resistance of the inner composite layer 12 is lower than that of the outer composite layer 13. Furthermore, the difference X between the lithium deposition resistance of the inner composite layer 12 and the lithium deposition resistance of the outer composite layer 13 is constant regardless of the variation in particle size of the negative electrode active material. In this embodiment, the variation in particle size of the first active material is determined so that the level of lithium deposition resistance of the inner composite layer 12 is the same as the level of lithium deposition resistance of the outer composite layer 13.

[0026] For example, as shown in Figure 3, suppose the lithium deposition resistance of the first active material and the second active material of a secondary battery in which the first value indicating the particle size variation of the first active material is 9 μm and the second value indicating the particle size variation of the second active material is 9 μm is measured and the difference therebetween is X%. By substituting this X into Equation 1, the difference DF (1.0 μm) can be calculated.

[0027] Then, the first value (8 μm) can be derived by subtracting the difference DF from the second value (9 μm). In this way, the first value that equalizes the level of lithium deposition resistance of the inner composite layer 12 and the level of lithium deposition resistance of the outer composite layer 13 can be derived.

[0028] Furthermore, the negative electrode sheet 10 can be configured so that the density of the first active material and the density of the second active material are substantially the same when the negative electrode sheet 10 is wound. In this case, it is preferable to use the median particle size of the second active material as the particle size of the first active material.

[0029] 4 is a diagram showing an example of a method for manufacturing a secondary battery according to one embodiment of the present invention. The method for manufacturing a secondary battery includes a first coating step, a second coating step, and a winding step.

[0030] The first coating step is a step of coating a first composite material containing a first active material onto a first surface of negative electrode current collector foil 11, which is located on the inner side when negative electrode sheet 10 is wound. As a result, an inner composite material layer 12 is formed on negative electrode current collector foil 11.

[0031] The second coating step is a step of coating a second composite material containing a second active material on a second surface of the negative electrode current collector foil 11, which is located on the outer side when the negative electrode sheet 10 is wound. As a result, an outer composite material layer 13 is formed on the negative electrode current collector foil 11.

[0032] The winding step is a step of stacking and winding a positive electrode sheet, a negative electrode sheet 10, and a separator. In the winding step, the negative electrode current collector foil 11 coated with the first active material and the second active material is wound together with the positive electrode sheet and the separator.

[0033] 5 is a diagram showing the results of a performance evaluation of a secondary battery according to one embodiment of the present invention and two types of secondary batteries according to the prior art. In the performance evaluation, secondary batteries having graphite as the active material were used.

[0034] The secondary battery according to the first conventional technology was one in which the particle size variation of the first active material and the particle size variation of the second active material were the same, and the density of the first active material and the density of the second active material were the same. The densities of the first active material and the second active material were 1.000 g / cm 3 The thickness of each of inner mixture layer 12 and outer mixture layer 13 of the negative electrode was 28.0 μm.

[0035] In the secondary battery according to the first conventional technique, the difference in density between inner composite layer 12 and outer composite layer 13 of the negative electrode after winding was 0.2%. Also, the difference in electrical resistance between inner composite layer 12 and outer composite layer 13 of the negative electrode after winding was 5%.

[0036] The secondary battery according to the second prior art was one in which the particle size variations of the first and second active materials were the same, but the densities of the first and second active materials were different. The density of the first active material was 0.998 g / cm. 3 and the density of the second active material is 1.000 g / cm 3 That is, a secondary battery in which the density of the first active material was lower than the density of the second active material was used. The thickness of each of inner mixture layer 12 and outer mixture layer 13 of the negative electrode was 28.0 μm.

[0037] In the secondary battery according to the second conventional technique, the difference in density between the inner composite layer 12 and the outer composite layer 13 of the negative electrode after winding was substantially 0%. On the other hand, the difference in electrical resistance between the inner composite layer 12 and the outer composite layer 13 of the negative electrode after winding was 4.95%. This means that the difference in electrical resistance between the inner composite layer 12 and the outer composite layer 13 of the negative electrode cannot be sufficiently suppressed by simply making the densities of the inner composite layer 12 and the outer composite layer 13 of the negative electrode the same.

[0038] In a secondary battery according to one embodiment of the present invention, the difference in particle size between D10 and D90 of the first active material was 8 μm, and the difference in particle size between D10 and D90 of the second active material was 9 μm.

[0039] In the secondary battery according to one embodiment of the present invention, the difference in electrical resistance between the inner composite layer 12 and the outer composite layer 13 of the negative electrode after winding was substantially 0%. The results of this evaluation revealed that the secondary battery according to one embodiment of the present invention has a significantly lower difference in electrical resistance between the inner composite layer 12 and the outer composite layer 13 of the negative electrode after winding, compared to the secondary battery according to the above-mentioned conventional technology. This shows that the secondary battery according to one embodiment of the present invention has very excellent lithium deposition resistance.

[0040] In the method for manufacturing a secondary battery according to the embodiment described above, in a first coating step, a first composite material containing a first active material is applied to a first surface of the negative electrode current collector foil 11, which is located on the inner side when wound. Then, in a second coating step, a second composite material containing a second active material is applied to a second surface of the negative electrode current collector foil 11, which is located on the outer side when wound. The particle size variation of the first active material applied to the first surface of the negative electrode current collector foil 11 is smaller than the particle size variation of the second active material applied to the second surface of the negative electrode current collector foil 11.

[0041] This allows the specific surface area of the first active material to be substantially uniform, thereby suppressing variations in resistance in the inner composite layer 12. Therefore, even when the negative electrode sheet 10 is wound, the difference in electrical resistance between the inner composite layer 12 and the outer composite layer 13 of the negative electrode can be reduced. This also suppresses the deposition of substances that provide intercalators (e.g., lithium). This effect occurs not only in the curved portions 2 and 3 of the negative electrode sheet 10 but also in the non-curved portions.

[0042] It is also preferable that the particle size of the first active material applied to the first surface of negative electrode current collector foil 11 be substantially uniform, which can improve the liquid circulation in inner mixture layer 12 of the negative electrode, i.e., the penetration of the electrolyte solution.

[0043] Furthermore, the difference in particle size between D10 and D90 of the first active material is preferably within a range of 4.0 to 9.5 μm, and the difference in particle size between D10 and D90 of the second active material is preferably within a range of 5.0 to 11.0 μm. This value assumes that the difference in particle size between the active material contained in outer composite layer 13 and the active material contained in inner composite layer 12 is 1.0 μm or more and 7.0 μm or less. If the difference in particle size is less than 1.0 μm or more, the effect of reducing the difference in electrical resistance between inner composite layer 12 and outer composite layer 13 of the negative electrode is not fully realized. Furthermore, if the difference in particle size is not less than 7.0 μm, the resistance of outer composite layer 13 is higher than that of inner composite layer 12. Therefore, by setting the difference in particle size between D10 and D90 of the first active material to within the range of 4.0 to 9.5 μm and the difference in particle size between D10 and D90 of the second active material to within the range of 5.0 to 11.0 μm, the resistance of the outer composite layer 13 and the inner composite layer 12 can be made equivalent.

[0044] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention. [Explanation of symbols]

[0045] 1 Electrode body 2 Curved section 3 Curved section 10 Negative electrode sheet 11 Negative electrode current collecting foil 12 Inner composite layer 13 Outer composite layer

Claims

1. A method for manufacturing a secondary battery including a wound electrode assembly, a first coating step of coating a first surface of the negative electrode current collector foil, the first surface being located on the inner side when the negative electrode current collector foil is wound, with a first composite material containing a first active material; a second coating step of coating a second surface of the negative electrode current collector foil, the second surface being located on the outer side when the negative electrode current collector foil is wound, with a second composite material containing a second active material; a winding step of winding the negative electrode current collector foil coated with the first active material and the second active material; Including, a variation in particle size of the first active material coated on a first surface of the negative electrode current collector foil is smaller than a variation in particle size of the second active material coated on a second surface of the negative electrode current collector foil; the first composite material and the second composite material are configured so that, when the electrode body is wound, the density of the first active material coated on the first surface of the negative electrode current collector foil and the density of the second active material coated on the second surface of the negative electrode current collector foil are the same. A method for manufacturing a secondary battery.

2. 2. The method for manufacturing a secondary battery according to claim 1, wherein the first value indicating the particle size variation of the first active material is derived by subtracting the difference between the second value indicating the particle size variation of the second active material and the first value from the second value indicating the particle size variation of the second active material.

3. the difference between the D10 and D90 particle sizes of the first active material, which corresponds to the first value, is within a range of 4.0 to 9.5 μm; 3. The method for producing a secondary battery according to claim 2, wherein a difference between D10 and D90 particle sizes of the second active material corresponding to the second value is within a range of 5.0 to 11.0 μm.

4. The method for manufacturing a secondary battery according to any one of claims 1 to 3, wherein the particle size of the first active material applied to the first surface of the negative electrode current collector foil is uniform.

5. A secondary battery having a wound electrode body, the negative electrode sheet included in the electrode body includes a current collecting foil, a first composite material coated on a first surface of the current collecting foil, and a second composite material coated on a second surface of the current collecting foil; When the negative electrode sheet is wound, a variation in particle size of the first active material in the first composite located inside the current collector foil is smaller than a variation in particle size of the second active material in the second composite located outside the current collector foil; the first composite material and the second composite material are configured so that the density of the first active material and the density of the second active material are the same when the negative electrode sheet is wound. Secondary battery.

6. a difference between D10 and D90 particle sizes of the first active material, which indicates a particle size variation of the first active material, is within a range of 4.0 to 9.5 μm; 6. The secondary battery according to claim 5, wherein a difference between particle diameters D10 and D90 of said second active material, which indicates a particle diameter variation of said second active material, is within a range of 5.0 to 11.0 μm.

7. The secondary battery according to claim 5 , wherein the particle size of the first active material applied to the current collector foil is uniform.

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