Negative electrode sheet and manufacturing method thereof

Abstract

To provide a negative electrode sheet that improves the battery performance and has excellent resistance to Li deposition.SOLUTION: A negative electrode sheet 40 includes a negative electrode current collector 41, a first active material region 42A arranged on the negative electrode current collector 41 and having a hard carbon content of 0 mass% or more and less than 50 mass%, and second active material region 42B arranged on the negative electrode current collector 41 alternately with the first active material region 42A in the in-plane direction of the negative electrode current collector 41, having a hard carbon content of 50 mass% or more and 100 mass% or less, and protruding from the upper surface of the first active material regions 42A.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a negative electrode sheet and a method for producing a negative electrode sheet. [Background technology]

[0002] It is known that in secondary batteries, the negative electrode active material contains hard carbon (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses that a carbon material in which a graphitizable carbon material and a non-graphitizable carbon material are mixed is used as the negative electrode active material of a lithium ion secondary battery.

[0004] Incidentally, in a secondary battery having a negative electrode active material containing hard carbon, it is preferable to provide a negative electrode sheet that not only improves the performance of the battery but also has excellent resistance to Li precipitation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-176448 A Summary of the Invention [Problem to be solved by the invention]

[0006] In consideration of the above, an object of the present invention is to provide a negative electrode sheet that improves battery performance and has excellent resistance to Li deposition. [Means for solving the problem]

[0007] A negative electrode sheet according to a first aspect of the present invention comprises a negative electrode current collector, first active material regions disposed on the negative electrode current collector and having a hard carbon content of 0 mass % or more and less than 50 mass %, and second active material regions disposed on the negative electrode current collector alternately with the first active material regions in an in-plane direction of the negative electrode current collector, the hard carbon content being 50 mass % or more and 100 mass % or less, and protruding from an upper surface of the first active material regions.

[0008] In a second aspect of the present invention, there is provided a negative electrode sheet according to the first aspect of the present invention, wherein the second active material region protrudes from the upper surface of the first active material region by an amount of 5 μm or more.

[0009] A manufacturing method of a negative electrode sheet according to a third aspect of the present invention includes an arrangement step of arranging, on a negative electrode current collector, first active material regions having a hard carbon content of 0 mass % or more and less than 50 mass %, and second active material regions arranged alternately with the first active material regions in an in-plane direction of the negative electrode current collector, the second active material regions having a hard carbon content of 50 mass % or more and 100 mass % or less, and being harder than the first active material regions, and a pressing step of pressing the negative electrode current collector on which the first active material regions and the second active material regions are arranged.

[0010] In a negative electrode sheet of a fourth aspect of the present invention, in the negative electrode sheet of the third aspect of the present invention, the arranging step includes a first arranging step of arranging the first active material region on the negative electrode current collector, and a second arranging step of arranging the second active material region on the negative electrode current collector on which the first active material region is arranged. Effect of the Invention

[0011] In the negative electrode sheet of the first aspect of the present invention, the negative electrode current collector has second active material regions arranged alternately with the first active material regions in the in-plane direction of the negative electrode current collector and protruding from the upper surface of the first active material regions, so that unevenness is formed on the surface of the active material regions. Therefore, compared with the case where the active material regions are formed flat, the area of ​​the active material regions exposed to the electrolyte is increased. As a result, the input / output performance is improved, and the battery performance can be improved. Moreover, by including the first active material region having a hard carbon content of 0 mass% or more and less than 50 mass%, and the second active material region having a hard carbon content of 50 mass% or more and 100 mass% or less, the second active material region forming the protrusions is formed of a material having a hard carbon content of 50 mass% or more and 100 mass% or less. Here, hard carbon is a material having excellent Li deposition resistance because it has a high negative electrode potential compared to graphite and the like. Therefore, it is possible to obtain a negative electrode sheet having excellent Li deposition resistance while improving the battery performance.

[0012] In the negative electrode sheet according to the second embodiment of the present invention, the amount of protrusion of the second active material region from the top surface of the first active material region is set to 5 μm or more, thereby increasing the area of ​​the active material region exposed to the electrolyte. This improves input / output performance and improves battery performance. On the other hand, if the amount of protrusion of the second active material region from the top surface of the first active material region is set to less than 5 μm, the improvement in input / output performance is slight.

[0013] In the method for producing a negative electrode sheet according to the third aspect of the present invention, the method includes an arrangement step of arranging a first active material region on a negative electrode current collector and a second active material region that is arranged alternately with the first active material region in the in-plane direction of the negative electrode current collector and is harder than the first active material region, and a pressing step of pressing the negative electrode current collector on which the first active material region and the second active material region are arranged, so that in the pressing step, the first active material region that is more easily crushed than the second active material region forms a recess, and the second active material region that is less easily crushed than the first active material region forms a protrusion. Therefore, the surface of the active material region is uneven, and the area of ​​the active material region exposed to the electrolyte is increased. As a result, the input / output performance is improved, and the battery performance can be improved. Moreover, by including the first active material region having a hard carbon content of 0% by mass or more and less than 50% by mass and the second active material region having a hard carbon content of 50% by mass or more and 100% by mass or less, the second active material region that forms the protrusion is formed of a material having a hard carbon content of 50% by mass or more and 100% by mass or less. Here, hard carbon is a material with excellent Li-precipitation resistance because it has a higher negative electrode potential than graphite, etc. Therefore, it is possible to improve the performance of the battery and to provide a negative electrode sheet with excellent Li-precipitation resistance.

[0014] In the manufacturing method of the negative electrode sheet according to the fourth aspect of the present invention, the arranging step includes a first arranging step of arranging the first active material region on the negative electrode current collector, and a second arranging step of arranging the second active material region on the negative electrode current collector on which the first active material region is arranged, so that the second active material region is arranged after the first active material region. Therefore, even if the second active material region is arranged so as to cover the first active material region, a convex portion is not formed by the first active material region, but is formed by the second active material region. As a result, it is possible to manufacture a negative electrode sheet that improves the performance of the battery and has excellent resistance to Li precipitation. [Brief description of the drawings]

[0015] [Figure 1] 1 is an exploded perspective view showing a secondary battery according to an embodiment; [Diagram 2] FIG. 2 is a perspective view showing a partially developed state of the wound body according to the embodiment. [Diagram 3] 2 is a cross-sectional view showing a schematic view of a wound body according to the embodiment, showing a cross section taken along line SS in FIG. 1. [Figure 4] 1 is a graph showing the relationship between the hard carbon content and the density difference before and after pressing. [Diagram 5] FIG. 2 is an enlarged cross-sectional view showing a negative electrode sheet according to the embodiment. [Figure 6] 13 is a graph showing the relationship between the width of a second active material region and the resistance ratio. [Figure 7] 4A to 4C are cross-sectional views showing a method for producing a negative electrode sheet. [Figure 8] 4A to 4C are cross-sectional views showing a method for producing a negative electrode sheet. [Figure 9] FIG. 2 is a perspective view, partially in cross section, showing a method for producing a negative electrode sheet. [Figure 10] 1 is a graph showing the relationship between the gap and the height difference before and after pressing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, a secondary battery according to an embodiment will be described with reference to the drawings. In the embodiment, for example, a lithium-ion secondary battery will be described as a secondary battery used as an on-board power source for electric vehicles, hybrid vehicles, etc. In each drawing, the arrow UP indicates the upper side in the vertical direction of the battery cell 10, the arrow FR indicates the front side in the front-rear direction of the battery cell 10, the arrow LH indicates the left side in the horizontal direction of the battery cell 10, and the arrow D indicates the width direction D of the wound body 30.

[0017] [Configuration of battery cell 10] As shown in FIG. 1, a battery cell 10 as a lithium ion secondary battery includes a lid assembly 20, a wound body 30, and a battery case 12.

[0018] (Lid Assembly 20) The lid assembly 20 has a negative external terminal 22 and a positive external terminal 23 on the upper surface of the lid member 21. The lid assembly 20 has a negative current collector terminal 24 and a positive current collector terminal 25 on the lower surface of the lid member 21.

[0019] (Wound body 30) As shown in FIG. 2, the wound body 30 has a power generating section 31 , a negative electrode current collecting section 32 , and a positive electrode current collecting section 33 .

[0020] As shown in FIG. 2 and FIG. 3, the wound body 30 is formed in a flat shape by winding a negative electrode sheet 40, a positive electrode sheet 50, and two separators 45 in a stacked state.

[0021] The power generation section 31 is formed by stacking a region of the positive electrode sheet 50 coated with a positive electrode active material, a region of the negative electrode sheet 40 coated with a negative electrode active material, and a separator 45. The power generation section 31 has a function of storing electrical energy of the battery cells 10.

[0022] The negative electrode current collecting part 32 is not coated with a negative electrode active material, and is formed by winding a negative electrode sheet 40. The positive electrode current collecting part 33 is not coated with a positive electrode active material, and is formed by winding a positive electrode sheet 50.

[0023] <Negative electrode sheet 40> As shown in FIG. 3, the negative electrode sheet 40 has a negative electrode active material layer 42 disposed on both sides of a long strip-shaped negative electrode current collector 41.

[0024] The negative electrode active material layer 42 includes first active material regions 42A that form recesses and second active material regions 42B that form protrusions, forming projections and recesses on the surface of the negative electrode active material layer 42.

[0025] Hard carbon (HC) and graphite (e.g., natural graphite) are contained in a predetermined ratio in the negative electrode active material forming the negative electrode active material layer 42. Here, the content of hard carbon in the entire negative electrode active material composed of hard carbon and graphite is defined as the hard carbon content.

[0026] Fig. 4 is a graph showing the relationship between the hard carbon ratio and the density difference before and after pressing. As shown in Fig. 4, when the hard carbon content of the negative electrode active material is 0 mass% or more and less than 50 mass%, a density difference occurs before and after pressing. On the other hand, when the hard carbon content of the negative electrode active material is 50 mass% or more and 100 mass% or less, almost no density difference occurs before and after pressing.

[0027] That is, when the hard carbon content of the negative electrode active material is 0% by mass or more and less than 50% by mass, the thickness decreases after pressing, whereas when the hard carbon content of the negative electrode active material is 50% by mass or more and 100% by mass or less, the thickness does not change after pressing.

[0028] For this reason, the first active material region 42A forming the recesses preferably has a hard carbon content of 0% by mass or more and less than 50% by mass, and the second active material region 42B forming the protrusions preferably has a hard carbon content of 50% by mass or more and 100% by mass or less.

[0029] 5, the first active material regions 42A extend in the winding direction of the wound body 30 and are formed as convex stripes lower than the second active material regions 42B. A plurality of first active material regions 42A are arranged at equal intervals along the width direction D. The first active material regions 42A and the second active material regions 42B are arranged alternately in the in-plane direction of the negative electrode current collector 41. The first active material regions 42A and the second active material regions 42B are arranged alternately in the width direction D.

[0030] The second active material regions 42B extend in the winding direction of the wound body 30 and are formed as protrusions taller than the first active material regions 42A. A plurality of second active material regions 42B are arranged at equal intervals along the width direction D. The second active material regions 42B and the first active material regions 42A are arranged alternately in the in-plane direction of the negative electrode current collector 41. The second active material regions 42B and the first active material regions 42A are arranged alternately in the width direction D.

[0031] The second active material region 42B is formed to protrude upward from the upper surface of the first active material region 42A. From the viewpoint of improving battery performance, the amount of protrusion T of the second active material region 42B from the upper surface of the first active material region 42A is preferably 5 μm or more.

[0032] When the protrusion amount T is 5 [μm], the width W1 in the width direction D of the first active material region 42A is 10 [μm], and the width W2 in the width direction D of the second active material region 42B is 50 to 100 [μm], the resistance ratio relative to a negative electrode active material layer without unevenness becomes small as shown in Fig. 6. Also, when the protrusion amount T is 5 [μm], the width W1 in the width direction D of the first active material region 42A is 10 [μm], and the width W2 in the width direction D of the second active material region 42B is 71 [μm], the resistance ratio relative to a negative electrode active material layer without unevenness becomes a minimum value.

[0033] In other words, when the protrusion amount T is 5 [μm] and the width W1 in the width direction D of the first active material region 42A is 10 [μm], the battery performance is improved when the width W2 in the width direction D of the second active material region 42B is 50 to 100 [μm], and further, the battery performance is most improved when the width W2 in the width direction D of the second active material region 42B is 71 [μm].

[0034] The width W1 of the first active material region 42A in the width direction D may be set to 10 μm or more, or may be set to less than 10 μm.

[0035] <Positive electrode sheet 50> 3, in the positive electrode sheet 50, positive electrode active material layers 52 are disposed on both sides of a long strip-shaped positive electrode collector 51. At one end of the positive electrode sheet 50 in the width direction D, the positive electrode active material is not applied, and the positive electrode collector 51 is exposed.

[0036] (Separator 45) The separator 45 is formed of an insulating material such as polypropylene, polyethylene, etc. The separator 45 is disposed between the positive electrode sheet 50 and the negative electrode sheet 40, and insulates the positive electrode sheet 50 from the negative electrode sheet 40.

[0037] (Battery case 12) The battery case 12 is made of, for example, aluminum, and is formed in the shape of a rectangular box that is long in the left-right direction and has an open top.

[0038] With the wound body 30, the negative electrode current collector terminal 24, and the positive electrode current collector terminal 25 housed inside the battery case 12, the lid member 21 is attached, for example, by laser welding, so as to cover the opening of the battery case 12.

[0039] [Method of manufacturing the negative electrode sheet 40] The negative electrode sheet 40 is manufactured through a first arrangement step, a second arrangement step, and a pressing step.

[0040] (1st placement process) 7, in the first arrangement step, the first active material regions 42A in a slurry state before hardening are arranged, for example, by a gravure roll, on the surface of the negative electrode current collector 41. As a result, the first active material regions 42A are arranged at equal intervals along the width direction D.

[0041] (Second placement process) 8, in the second arrangement step, the second active material regions 42B in a slurry state before curing are arranged on the surface of the negative electrode current collector 41 between the first active material regions 42A arranged in the first arrangement step, for example by a gravure roll, so as to be at the same height as the first active material regions 42A. As a result, the second active material regions 42B are arranged alternately with the first active material regions 42A along the width direction D, with the same height as the first active material regions 42A. Thereafter, the first active material regions 42A and the second active material regions 42B are dried by a drying device such as a heater, and the liquid portion of the slurry is volatilized and cured.

[0042] The cured second active material region 42B has a higher hard carbon content than the cured first active material region 42A, and is hard and resistant to deformation (crushing) by an external force.

[0043] (Pressing process) In the pressing step, as shown in FIG. 9, the negative electrode current collector 41 having the first active material region 42A and the second active material region 42B arranged thereon is pressed using a pressing device 60.

[0044] The press device 60 includes a first roller 61 and a second roller 62 that faces the first roller 61 with a gap (gap) G therebetween. The negative electrode current collector 41 is transported between the first roller 61 and the second roller 62 and is pressed.

[0045] Fig. 10 is a graph showing the relationship between gap G and the height difference before and after pressing. As shown in Fig. 10, it can be seen that the smaller the gap G is, the larger the height difference before and after pressing is for the cured first active material region 42A. On the other hand, for the cured second active material region 42B, even if the gap G is changed, the process difference before and after pressing hardly changes at all. In other words, when the protrusion amount T is 5 [μm] or more, the gap G needs to be 33 [μm] or less.

[0046] By the press processing using press device 60, hardened second active material region 42B, which is less likely to deform, is not crushed by hardened first active material region 42A, while hardened first active material region 42A, which is more likely to deform, is crushed by hardened second active material region 42B. As a result, unevenness is formed on the surface of negative electrode active material layer 42.

[0047] [Effect] However, when projections and recesses are formed on the surface of the active material region, Li ions may concentrate on the projections, resulting in the precipitation of Li metal.

[0048] The negative electrode sheet 40 according to the embodiment has a negative electrode current collector 41, first active material regions 42A arranged on the negative electrode current collector 41 and having a hard carbon content of 0 mass % or more and less than 50 mass %, and second active material regions 42B arranged on the negative electrode current collector 41 alternately with the first active material regions 42A in the in-plane direction of the negative electrode current collector 41, having a hard carbon content of 50 mass % or more and 100 mass % or less, and protruding from an upper surface of the first active material regions 42A (see FIG. 3 ).

[0049] Negative electrode current collector 41 has second active material regions 42B arranged alternately with first active material regions 42A in the in-plane direction of negative electrode current collector 41 and protruding from the upper surfaces of first active material regions 42A, so that unevenness is formed on the surface of the active material region. Therefore, compared with the case where the active material region is formed flat, the area of ​​the active material region exposed to the electrolyte is increased. As a result, input / output performance is improved, and battery performance can be improved.

[0050] Moreover, by including the first active material region 42A having a hard carbon content of 0% by mass or more and less than 50% by mass and the second active material region 42B having a hard carbon content of 50% by mass or more and 100% by mass or less, the second active material region 42B forming the protrusions is formed of a material having a hard carbon content of 50% by mass or more and 100% by mass or less. Here, hard carbon is a material having excellent Li deposition resistance because it has a high negative electrode potential compared to graphite and the like. Therefore, it is possible to obtain a negative electrode sheet 40 that improves the performance of the battery and has excellent Li deposition resistance.

[0051] In the negative electrode sheet 40 according to this embodiment, the amount of protrusion of the second active material region 42B from the upper surface of the first active material region 42A is set to 5 μm or more (see FIG. 5).

[0052] By setting the difference in thickness between the first active material region 42A and the second active material region 42B to 5 μm or more, the area of ​​the active material region exposed to the electrolyte is increased. This improves input / output performance, and improves battery performance. On the other hand, if the difference in thickness between the first active material region 42A and the second active material region 42B is set to less than 5 μm, the improvement in input / output performance is slight.

[0053] A manufacturing method of the negative electrode sheet 40 according to the embodiment includes an arrangement step of arranging, on a negative electrode current collector 41, first active material regions 42A having a hard carbon content of 0% or more and less than 50% by mass and second active material regions 42B arranged alternately with the first active material regions 42A in the in-plane direction of the negative electrode current collector 41, the second active material regions 42B having a hard carbon content of 50% or more and 100% by mass or less and being harder than the first active material regions 42A, and a pressing step of pressing the negative electrode current collector 41 on which the first active material regions 42A and the second active material regions 42B are arranged (see FIGS. 7 to 9).

[0054] The method includes a step of arranging the first active material regions 42A and the second active material regions 42B, which are arranged alternately with the first active material regions 42A in the in-plane direction of the negative electrode current collector 41 and are harder than the first active material regions 42A, on the negative electrode current collector 41, and a pressing step of pressing the negative electrode current collector 41 on which the first active material regions 42A and the second active material regions 42B are arranged, so that in the pressing step, the first active material regions 42A, which are more easily crushed than the second active material regions 42B, form recesses, and the second active material regions 42B, which are less easily crushed than the first active material regions 42A, form protrusions. Therefore, unevenness is formed on the surface of the active material regions, and the area of ​​the active material regions exposed to the electrolyte is increased. As a result, the input / output performance is improved, and the battery performance can be improved.

[0055] Moreover, by setting the hard carbon content of the second active material region 42B forming the protrusions to be 50 mass % or more and 100 mass % or less, the protrusions are formed of a material with excellent Li-precipitation resistance, which improves the battery performance and allows the manufacture of a negative electrode sheet 40 with excellent Li-precipitation resistance.

[0056] In the manufacturing method of the negative electrode sheet 40 according to the embodiment, the arrangement process includes a first arrangement process of arranging the first active material region 42A on the negative electrode current collector 41, and a second arrangement process of arranging the second active material region 42B on the negative electrode current collector 41 on which the first active material region 42A is arranged (see Figures 7 and 8).

[0057] The arranging step includes a first arranging step of arranging the first active material region 42A on the negative electrode current collector 41, and a second arranging step of arranging the second active material region 42B on the negative electrode current collector 41 on which the first active material region 42A is arranged, so that the second active material region 42B is arranged after the first active material region 42A. Therefore, even if the second active material region 42B is arranged so as to cover the first active material region 42A, a convex portion is not formed by the first active material region 42A, but a convex portion is formed by the second active material region 42B. As a result, it is possible to manufacture a negative electrode sheet 40 that improves the performance of the battery and has excellent Li precipitation resistance.

[0058] The negative electrode sheet of the present invention has been described above based on the embodiment. However, the specific configuration is not limited to this embodiment, and design changes and the like are permitted as long as they do not deviate from the gist of the invention according to each claim of the claims.

[0059] In the embodiment, an example has been shown in which the first active material region 42A in a slurry state before curing is disposed on the surface of the negative electrode current collector 41, and then the second active material region 42B in a slurry state before curing is disposed on the surface of the negative electrode current collector 41. However, the second active material region 42B in a slurry state before curing may be disposed on the surface of the negative electrode current collector 41, and then the first active material region 42A in a slurry state before curing may be disposed, or the second active material region 42B in a slurry state before curing and the first active material region 42A in a slurry state before curing may be disposed simultaneously.

[0060] In the embodiment, an example has been shown in which the first active material region 42A in a slurry state before curing is disposed on the surface of the negative electrode current collector 41 by a gravure roll, and then the second active material region 42B in a slurry state before curing is disposed by a gravure roll so as to be at the same height as the first active material region 42A. However, normal coating may be performed in which the first active material region 42A in a slurry state before curing is disposed on the surface of the negative electrode current collector 41 by a gravure roll, and then the second active material region 42B in a slurry state before curing is supplied by a slurry supplying device.

[0061] In the embodiment, an example has been shown in which the negative electrode active material layers 42 are disposed on both sides of the negative electrode current collector 41. However, the negative electrode active material layer may be disposed on one side of the negative electrode current collector.

[0062] In the embodiment, an example has been shown in which the negative electrode sheet 40 is wound around the wound body 30. However, the negative electrode sheet may be laminated in a laminate-type electrode body.

[0063] In the embodiment, the negative electrode sheet constitutes a lithium ion secondary battery by way of example, but the negative electrode sheet may constitute other secondary batteries. [Explanation of symbols]

[0064] 40 Negative electrode sheet 41 Negative electrode current collector 42A 1st active material area 42B 2nd active material area

Claims

1. A negative electrode current collector; a first active material region disposed on the negative electrode current collector and having a hard carbon content of 0 mass % or more and less than 50 mass %; a second active material region disposed on the negative electrode current collector alternately with the first active material region in an in-plane direction of the negative electrode current collector, the second active material region having a hard carbon content of 50% by mass or more and 100% by mass or less and protruding from an upper surface of the first active material region; A negative electrode sheet having

2. The amount of protrusion of the second active material region from the top surface of the first active material region is set to 5 μm or more. The negative electrode sheet according to claim 1 .

3. a disposing step of disposing, on a negative electrode current collector, first active material regions having a hard carbon content of 0 mass % or more and less than 50 mass %, and second active material regions arranged alternately with the first active material regions in an in-plane direction of the negative electrode current collector, the hard carbon content of the second active material regions being 50 mass % or more and 100 mass % or less, and being harder than the first active material regions; a pressing step of pressing the negative electrode current collector on which the first active material region and the second active material region are disposed; A method for producing a negative electrode sheet comprising the steps of:

4. The disposing step includes a first disposing step of disposing the first active material region on the negative electrode current collector, and a second disposing step of disposing a second active material region on the negative electrode current collector on which the first active material region is disposed. The method for producing the negative electrode sheet according to claim 3 .

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