Separator for nonaqueous electrolyte battery and nonaqueous electrolyte battery

Abstract

To prevent a separator of a nonaqueous electrolyte battery having a silicon-based negative electrode from peeling off from the negative electrode.SOLUTION: A separator 5 for a nonaqueous electrolyte battery includes a first layer 51 in contact with a silicon-based negative electrode 3, and a second layer 52 in contact with the first layer and interposed between the silicon-based negative electrode and a positive electrode 4, the second layer having a higher elastic modulus than the first layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The technology disclosed herein relates to a separator for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery. [Background technology]

[0002] Patent Document 1 describes a conventional separator for a non-aqueous electrolyte battery. The conventional separator includes a substrate and a particle layer on a main surface of the substrate. The particle layer has a convex pattern. When the negative electrode expands due to charging of the non-aqueous electrolyte battery, the particle layer presses the separator, positive electrode, and negative electrode, thereby preventing the structure of the electrode stack from shifting. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 187607 Summary of the Invention [Problem to be solved by the invention]

[0004] Silicon-based negative electrodes enable non-aqueous electrolyte batteries to achieve high capacity. However, silicon-based negative electrodes expand and contract significantly during charging and discharging. The separator in contact with the silicon-based negative electrode cannot keep up with the large expansion and contraction of the silicon-based negative electrode, which can lead to the separator peeling off from the silicon-based negative electrode. Separation of the separator can lead to an internal short circuit in the non-aqueous electrolyte battery.

[0005] The technology disclosed herein prevents the separator of a nonaqueous electrolyte battery equipped with a silicon-based negative electrode from peeling off from the negative electrode. [Means for solving the problem]

[0006] A separator with a low elastic modulus can accommodate the large expansion and contraction of the silicon-based negative electrode and prevent the separator from peeling off from the silicon-based negative electrode. However, a separator with a low elastic modulus has difficulty in ensuring the strength required for the separator.

[0007] To ensure the strength of the separator, it is possible to provide a coating on the separator. For example, aluminum oxide (alumina) is an example of such a coating. However, such a coating has a relatively high electrical resistance, which adversely affects the performance of non-aqueous electrolyte batteries.

[0008] Therefore, the inventors of the present invention have designed the separator in contact with the silicon-based negative electrode to be a two-layer separator made of two materials with different elastic moduli.

[0009] Specifically, the technology disclosed herein relates to a separator for a non-aqueous electrolyte battery. a first layer in contact with the silicon-based negative electrode; and a second layer that is in contact with the first layer and is interposed between the silicon-based negative electrode and the positive electrode, the second layer having a higher elastic modulus than the first layer.

[0010] The first layer of the separator is in contact with the silicon-based negative electrode. The first layer has a relatively low modulus of elasticity. Here, a low modulus of elasticity can be rephrased as a low Young's modulus of the material constituting the first layer. The first layer is relatively soft. Even if the silicon-based negative electrode expands and contracts significantly during charging and discharging of the nonaqueous electrolyte battery, the first layer can follow the expansion and contraction of the silicon-based negative electrode. Peeling of the first layer from the silicon-based negative electrode is suppressed.

[0011] The separator includes a second layer. The second layer is in contact with the first layer. More specifically, the second layer is interposed between the silicon-based negative electrode and the positive electrode. The second layer has a relatively high elastic modulus. A high elastic modulus can also be said to mean that the Young's modulus of the material constituting the second layer is high. The second layer has a relatively high rigidity, making it easier to ensure strength than the first layer.

[0012] A separator comprising a soft first layer and a high-strength second layer can ensure the strength required for a separator in a non-aqueous electrolyte battery while suppressing peeling from the silicon-based negative electrode. By combining a soft first layer with a high-strength second layer, the separator strength can be ensured without increasing the overall thickness of the separator. Reducing the separator thickness is advantageous for increasing the capacity of non-aqueous electrolyte batteries.

[0013] The first layer may be polypropylene (PP).

[0014] The first layer may be made of polyamide (PA).

[0015] Polypropylene (PP) or polyamide (PA) can prevent peeling from the silicon-based negative electrode.

[0016] The second layer may be polyethylene terephthalate (PET).

[0017] The second layer may be made of polystyrene (PS).

[0018] Polyethylene terephthalate (PET) or polystyrene (PS) can ensure the strength required for the separator of a non-aqueous electrolyte battery when combined with the first layer made of polypropylene (PP) or polyamide (PA) described above.

[0019] The silicon-based negative electrode may include silicon monoxide (SiO), and the positive electrode may include lithium (Li).

[0020] The combination of a negative electrode containing silicon monoxide (SiO) and a positive electrode containing lithium (Li) is advantageous for increasing the capacity of nonaqueous electrolyte batteries. On the other hand, a negative electrode containing silicon monoxide (SiO) expands and contracts significantly during charging and discharging of the nonaqueous electrolyte battery. The separator having the first and second layers described above can prevent peeling from the negative electrode and ensure strength in nonaqueous electrolyte batteries equipped with a negative electrode containing silicon monoxide (SiO).

[0021] The nonaqueous electrolyte battery disclosed herein comprises: The separator described above; The battery includes a silicon-based negative electrode and a positive electrode separated by the separator.

[0022] This non-aqueous electrolyte battery can achieve a high capacity.

[0023] The positive electrode may be in contact with the second layer.

[0024] That is, the separator is sandwiched between the positive electrode and the silicon-based negative electrode, and the separator having the first and second layers can prevent the positive electrode from being affected by the expansion and contraction of the silicon-based negative electrode.

[0025] The separator may have a third layer interposed between the second layer and the positive electrode.

[0026] The second layer of the separator does not need to be in direct contact with the positive electrode. The third layer may have a specific function, such as heat resistance. [Effects of the Invention]

[0027] The separator for a nonaqueous electrolyte battery and the nonaqueous electrolyte battery described above can prevent the separator from peeling off from the silicon-based negative electrode. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a cross-sectional view of a nonaqueous electrolyte battery. [Figure 2] FIG. 2 is an enlarged view of a portion of the nonaqueous electrolyte battery. [Figure 3] FIG. 3 shows the properties of materials that can be used for the first and second layers of the separator. [Figure 4] FIG. 4 is an enlarged view of a portion of a nonaqueous electrolyte battery according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of a separator for a nonaqueous electrolyte battery and a nonaqueous electrolyte battery will be described with reference to the drawings. The separator for a nonaqueous electrolyte battery and the nonaqueous electrolyte battery described here are merely examples.

[0030] (Overall structure of secondary battery) FIG. 1 schematically shows the overall structure of a nonaqueous electrolyte battery 1. The nonaqueous electrolyte battery 1 of FIG. 1 is a battery cell in which a power generating element 2 is housed in a container 10. The nonaqueous electrolyte battery 1 is, for example, a lithium-ion battery. The container 10 is formed into a bag shape by folding one laminate material 11 or by stacking two laminate materials 11. The laminate material 11 has, for example, a three-layer structure in which a metal layer is sandwiched between resin layers. The metal layer is, for example, aluminum or stainless steel. The resin layer is, for example, polypropylene (PP) or polyethylene (PE). The container 10 is sealed with the power generating element 2 and electrolyte housed therein. The nonaqueous electrolyte battery 1 is a so-called pouch-type battery. Note that the nonaqueous electrolyte batteries to which the separator disclosed herein can be applied are not limited to pouch-type batteries.

[0031] The power generating element 2 has a negative electrode 3 and a positive electrode 4. The negative electrodes 3 and positive electrodes 4 are immersed in an electrolyte inside a container 10. The negative electrodes 3 and positive electrodes 4 are alternately stacked. The number of negative electrodes 3 and positive electrodes 4 is arbitrary. For example, the number of negative electrodes 3 may be greater than the number of positive electrodes 4. The power generating element 2 is an electrode laminate. Note that, hereinafter, the direction in which the negative electrodes 3 and positive electrodes 4 are stacked may be referred to as the stacking direction.

[0032] The negative electrode 3 has a negative electrode current collector 31. The negative electrode current collector 31 is a thin plate extending in a direction perpendicular to the stacking direction. A first end of the negative electrode current collector 31, i.e., the left end in FIG. 1 , protrudes outward from the first opening 12 of the container 10.

[0033] A negative electrode active material is applied to a first surface and a second surface of a negative electrode current collector 31 located inside the container 10. The first surface is the upper surface of the negative electrode current collector 31 in FIG. 1, and the second surface is the lower surface of the negative electrode current collector 31 in FIG. 1. The negative electrode active material forms a negative electrode composite part 32 on the negative electrode current collector 31. The negative electrode 3 is configured to include the negative electrode current collector 31 and the negative electrode composite part 32.

[0034] The negative electrode 3 is a silicon-based negative electrode. That is, the negative electrode active material contains silicon. Here, the negative electrode active material contains silicon monoxide (SiO). A silicon-based negative electrode is advantageous for increasing the capacity of the nonaqueous electrolyte battery 1.

[0035] The negative electrode 3 has a separator 5. The separator 5 is interposed between the negative electrode 3 and the positive electrode 4. The separator 5 separates the negative electrode mixture portion 32 of the negative electrode 3 from the positive electrode mixture portion 42 of the positive electrode 4. The separator 5 is, for example, a porous material that is permeable to ionic substances. The separator 5 covers at least the main surface of the negative electrode mixture portion 32 of the negative electrode 3. The structure of the separator 5 will be described in detail later.

[0036] The positive electrode 4 has a positive electrode current collector 41. The positive electrode current collector 41 is a thin plate extending in a direction perpendicular to the stacking direction. A second end of the positive electrode current collector 41, i.e., the right end in FIG. 1 , protrudes outward from a second opening 13 of the container 10. The second opening 13 is an opening on the opposite side to the first opening 12 in the direction perpendicular to the stacking direction. Note that the protruding direction of the positive electrode current collector 41 is not limited to the opposite side to the negative electrode current collector 31.

[0037] A positive electrode active material is applied to a first surface and a second surface of a positive electrode current collector 41 located inside the container 10. The positive electrode active material forms a positive electrode composite part 42 to which the positive electrode current collector 41 is connected. The positive electrode active material is a metal oxide containing lithium (Li). The positive electrode current collector 41 and the positive electrode composite part 42 constitute a positive electrode 4.

[0038] As described above, the negative electrodes 3 and the positive electrodes 4 are stacked alternately. The negative electrode mixture portion 32 and the positive electrode mixture portion 42 are stacked in the stacking direction inside the container 10 with the separator 5 interposed therebetween. The area of ​​the negative electrode mixture portion 32 may be larger than the area of ​​the positive electrode mixture portion 42, for example.

[0039] The first opening 12 of the container 10 is sealed with resin 6. The resin 6 is located between the laminate material 11 and the negative electrode current collector 31 and between the negative electrode current collectors 31. Similarly, the second opening 13 is sealed with resin 6. The resin 6 is located between the laminate material 11 and the positive electrode current collector 41 and between the positive electrode current collectors 41.

[0040] The multiple negative electrode current collectors 31 are not connected inside the container 10, but individually protrude outside the container 10. Similarly, the multiple positive electrode current collectors 41 are not connected inside the container 10, but individually protrude outside the container 10. Because the connection space between the negative electrode current collectors 31 and the positive electrode current collectors 41 inside the container 10 can be omitted, the areas of the negative electrode composite portion 32 and the positive electrode composite portion 42 can be increased accordingly. This allows the energy density of the nonaqueous electrolyte battery 1 to be increased.

[0041] The structure of the nonaqueous electrolyte battery 1 described above is an example, and the nonaqueous electrolyte battery to which the separator disclosed herein can be applied is not limited to the structure described above.

[0042] (Separator structure) Next, the structure of the separator 5 will be described in detail with reference to Fig. 2. Fig. 2 shows a cross section of one negative electrode 3, one separator 5, and one positive electrode 4 included in the power generating element 2.

[0043] Separator 5 includes first layer 51. First layer 51 contacts negative electrode 3, more precisely, main surface 321 of negative electrode mixture portion 32. Main surface 321 of negative electrode mixture portion 32 is the surface that faces positive electrode mixture portion 42 with separator 5 interposed therebetween.

[0044] The separator 5 includes a second layer 52. The second layer 52 is a layer that contacts the first layer 51 in the stacking direction. The separator 5 has a two-layer structure consisting of the first layer 51 and the second layer 52. The second layer 52 is interposed between the negative electrode 3 and the positive electrode 4. The positive electrode 4, more precisely, the main surface 421 of the positive electrode mixture portion 42, is in contact with the second layer 52. The main surface 421 of the positive electrode mixture portion 42 is the surface that faces the negative electrode mixture portion 32 with the separator 5 interposed therebetween.

[0045] The first layer 51 and the second layer 52 are made of materials with different properties. The second layer 52 has a higher elastic modulus than the first layer 51. In other words, the second layer 52 has a higher Young's modulus than the first layer 51.

[0046] The first layer 51 may be made of polyolefin, more specifically, polypropylene (PP). The first layer 51 may also be made of polyamide (PA), i.e., nylon. The modulus of elasticity of the first layer 51 is relatively low. In the separator 5, the first layer 51 is relatively soft.

[0047] The second layer 52 may be polyester, more specifically, polyethylene terephthalate (PET). The second layer 52 may also be polystyrene (PS). The second layer 52 has a relatively high elastic modulus. In the separator 5, the second layer 52 is relatively hard. FIG. 3 shows the properties of materials that can be used for the first layer 51 and the second layer 52. The second layer 52 has a relatively high Young's modulus while ensuring high strength. Note that the materials that can be used for the first layer 51 and the second layer 52 are not limited to the materials shown in FIG. 3.

[0048] The negative electrode 3 of the nonaqueous electrolyte battery 1 is a silicon-based negative electrode, and the negative electrode 3 expands and contracts significantly as the nonaqueous electrolyte battery 1 is charged and discharged. The first layer 51 in contact with the negative electrode 3 has a low elastic modulus and is soft, so that even if the negative electrode 3 expands and contracts significantly, the first layer 51 can follow the expansion and contraction of the negative electrode 3. Peeling of the first layer 51 from the negative electrode 3 is suppressed.

[0049] Since it is easier to ensure strength for the second layer 52 than for the first layer 51, the separator 5 including the first layer 51 and the second layer 52 can ensure the strength required for the separator 5 of the nonaqueous electrolyte battery 1. The separator 5 including the first layer 51 and the second layer 52 can suppress the influence of expansion and contraction of the negative electrode 3 from affecting the positive electrode 4.

[0050] Furthermore, the separator 5 including the first layer 51 and the second layer 52 can ensure the necessary strength of the separator 5 without increasing the overall thickness of the separator 5. Reducing the thickness of the separator 5 is advantageous for increasing the energy density of the nonaqueous electrolyte battery 1 and achieving a high capacity of the nonaqueous electrolyte battery 1. The thickness of the first layer 51 and the thickness of the second layer 52 can be set to any appropriate thickness.

[0051] The combination of the material used for the first layer 51 and the material used for the second layer 52 can be selected arbitrarily from the materials exemplified above. Note that, in the combination of the material used for the first layer 51 and the material used for the second layer 52, the difference between the Young's modulus of the first layer 51 and the Young's modulus of the second layer 52 may not be too large. This is because if the difference between the Young's modulus of the first layer 51 and the Young's modulus of the second layer 52 is too large, peeling may occur between the first layer 51 and the second layer 52.

[0052] In a modified example of the nonaqueous electrolyte battery 1, the second layer 52 of the separator 5 and the positive electrode 4 are not necessarily in direct contact with each other. As shown in FIG. 4, the separator 5 may have a third layer 53 interposed between the second layer 52 and the positive electrode 4. The third layer 53 may be, for example, a layer having a heat resistance function. The layer having a heat resistance function may be made of, for example, aramid. The function of the third layer 53 is not limited to a heat resistance function. [Explanation of symbols]

[0053] 1. Non-aqueous electrolyte battery 3. Silicon-based negative electrode 4 Positive electrode 5 Separator 51 1st layer 52 2nd layer 53 3rd layer

Claims

1. a first layer in contact with the silicon-based negative electrode; a second layer in contact with the first layer and interposed between the silicon-based negative electrode and the positive electrode, the second layer having a higher elastic modulus than the first layer; Separator for non-aqueous electrolyte batteries.

2. The separator for a nonaqueous electrolyte battery according to claim 1, The first layer is polypropylene (PP). Separator for non-aqueous electrolyte batteries.

3. The separator for a nonaqueous electrolyte battery according to claim 1, The first layer is polyamide (PA). Separator for non-aqueous electrolyte batteries.

4. The separator for a nonaqueous electrolyte battery according to any one of claims 1 to 3, the second layer is polyethylene terephthalate (PET); Separator for non-aqueous electrolyte batteries.

5. The separator for a nonaqueous electrolyte battery according to any one of claims 1 to 3, the second layer is polystyrene (PS); Separator for non-aqueous electrolyte batteries.

6. The separator for a nonaqueous electrolyte battery according to claim 1, The silicon-based negative electrode contains silicon monoxide (SiO), and the positive electrode contains lithium (Li). Separator for non-aqueous electrolyte batteries.

7. The separator according to claim 1; A silicon-based negative electrode and a positive electrode separated by the separator. Non-aqueous electrolyte battery.

8. 8. The nonaqueous electrolyte battery according to claim 7, The positive electrode is in contact with the second layer. Non-aqueous electrolyte battery.

9. 8. The nonaqueous electrolyte battery according to claim 7, The separator has a third layer interposed between the second layer and the positive electrode. Non-aqueous electrolyte battery.

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