Negative electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

Description

[Technical field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0176315 filed on December 15, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same. [Background technology]

[0003] With the rapid development of the electronics, communications, and computer industries, the application of energy storage technology is expanding to camcorders, mobile phones, laptops, PCs, and even electric vehicles. In response to this, lightweight, long-lasting, and reliable high-performance secondary batteries are being developed.

[0004] Lithium secondary batteries have been attracting attention as a battery that can meet such needs.

[0005] A lithium secondary battery is constructed by stacking or winding an electrode assembly including a positive electrode, a negative electrode, and a separator between them, and housing the electrode assembly in a battery case into which an electrolyte is injected. The lithium secondary battery produces electrical energy by oxidation / reduction reactions occurring when lithium ions are inserted / extracted from the positive electrode and the negative electrode.

[0006] Among lithium secondary batteries, lithium-sulfur batteries, which use sulfur-based materials as the positive electrode active material, have recently been attracting attention. Sulfur, the main material of the positive electrode active material, has the advantages of being very abundant, non-toxic, and low weight per atom. In addition, the theoretical discharge capacity of lithium-sulfur batteries is 1675mAh / g-sulfur, and the theoretical energy density is 2,600Wh / kg, which is much higher than the theoretical energy densities of other battery systems currently being researched (Ni-MH battery: 450Wh / kg, Li-FeS battery: 480Wh / kg, Li-MnO2 battery: 1,000Wh / kg, Na-S battery: 800Wh / kg), making it the most promising battery currently being developed.

[0007] FIG. 1 is a cross-sectional view of a conventional lithium secondary battery (100). Referring to FIG. 1, a separator (130) is interposed between a positive electrode (110) and a negative electrode (120). The size of the negative electrode (120) is larger than the size of the positive electrode (110), and the negative electrode (120) is located in a region corresponding to the positive electrode (110), so that the negative electrode (120) and the positive electrode (110) are in contact with each other with the separator (130) in between. Since the size of the negative electrode (120) is larger than the size of the positive electrode (110), there is an area (A) of the negative electrode (120) that is not in contact with the positive electrode (110). The negative electrode (120) may be lithium metal.

[0008] The charge and discharge reactions of the lithium secondary battery (100) occur only in the area where the negative electrode (120) and the positive electrode (110) are in contact with each other with the separator (130) sandwiched therebetween. When the charge and discharge reactions of the lithium secondary battery (100) are repeatedly performed, the porosity of the lithium metal of the negative electrode (120) gradually increases and the rigidity weakens. As a result, the lithium metal is released from the area (A) that is not in contact with the positive electrode (110) at the edge of the negative electrode (120). If the released lithium metal pieces move freely inside the pouch cell and an external force is applied to the lithium secondary battery (100), the released lithium metal pieces may cause a short circuit of the lithium secondary battery (100).

[0009] Therefore, there is a need to develop lithium secondary batteries that can solve the above problems. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Republic of Korea Patent Publication No. 100-2017-0124075 Summary of the Invention [Problem to be solved by the invention]

[0011] In order to solve the above problems, the present inventors have conducted extensive research and found that by changing the structure of the negative electrode for a lithium secondary battery, it is possible to prevent lithium metal from being detached from a region of the negative electrode that is not in contact with the positive electrode via a separator, and thus completed the present invention.

[0012] Therefore, an object of the present invention is to provide a negative electrode for a lithium secondary battery that can prevent the elimination of lithium metal.

[0013] Another object of the present invention is to provide a lithium secondary battery including the negative electrode for lithium secondary batteries. [Means for solving the problem]

[0014] In order to achieve the above objectives, The present invention comprises a first layer comprising a lithium metal sheet; a second layer formed on the upper surface of the first layer and including a lithium metal sheet and a negative electrode current collector surrounding an outer peripheral surface of the lithium metal sheet; and a third layer formed on an upper surface of the second layer and including a lithium metal sheet; and

[0015] In an embodiment of the present invention, the negative electrode current collector may have edge widths in the vertical and horizontal directions, which are the same or different from each other.

[0016] In one embodiment of the present invention, the negative electrode current collector may have an area that is 10 to 30% of the area of ​​the second layer.

[0017] In one embodiment of the present invention, the surface of the negative electrode current collector in contact with the lithium metal sheets of the first to third layers may include an uneven structure.

[0018] In one embodiment of the present invention, the negative electrode current collector may have a thickness of 1 to 10 μm.

[0019] In one embodiment of the present invention, the negative electrode current collector may have a thickness of 1 to less than 5 μm.

[0020] In one embodiment of the present invention, the first to third layers may be the same in size.

[0021] In one embodiment of the present invention, the thickness of the negative electrode current collector and the thickness of the second layer of lithium metal sheet may be the same.

[0022] In one embodiment of the present invention, the first layer may have a thickness of 10 to 50 μm, the third layer may have a thickness of 10 to 50 μm, and the negative electrode for a lithium secondary battery may have a thickness of 21 to 110 μm.

[0023] In one embodiment of the present invention, the negative electrode for a lithium secondary battery may be a negative electrode for a lithium-sulfur battery.

[0024] The present invention also provides a battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, The size of the negative electrode is larger than the size of the positive electrode, The negative electrode provides a lithium secondary battery which is the negative electrode of the present invention.

[0025] In one embodiment of the present invention, the size of the lithium metal sheet of the second layer of the negative electrode may be smaller than or equal to that of the positive electrode.

[0026] In one embodiment of the present invention, the lithium secondary battery may be a lithium-sulfur battery. Effect of the Invention

[0027] The negative electrode for a lithium secondary battery of the present invention can prevent lithium metal from being detached from an area of ​​the separator that is not in contact with the positive electrode, thereby minimizing loss of energy density and improving safety. [Brief description of the drawings]

[0028] [Figure 1] FIG. 1 is a cross-sectional view of a conventional lithium secondary battery. [Diagram 2] 1 is a side view of a negative electrode for a lithium secondary battery according to an embodiment of the present invention. [Diagram 3] 1 is a cross-sectional view of a negative electrode for a lithium secondary battery according to an embodiment of the present invention. [Figure 4] FIG. 2 is a plan view of a second layer of a negative electrode for a lithium secondary battery according to an embodiment of the present invention. [Diagram 5] 1 is a cross-sectional view of a lithium secondary battery according to an embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in order to enable those skilled in the art to easily carry out the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0030] In order to clearly describe the present invention, parts that are not relevant to the description will be omitted, and the same reference numerals will be used throughout the specification to refer to the same or similar components.

[0031] Furthermore, the terms and words used in this specification and the claims should not be interpreted limited to their ordinary or dictionary meanings, but should be interpreted with a meaning and concept that is consistent with the technical idea of ​​the present invention, based on the principle that an inventor can appropriately define the concept of a term in order to best describe his or her invention.

[0032] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may, however, be embodied in various different forms and should not be construed as limited to the embodiments set forth herein.

[0033] The present invention comprises a first layer (121) comprising a lithium metal sheet; a second layer (122) formed on the upper surface of the first layer and including a lithium metal sheet (124) and a negative electrode current collector (125) surrounding the outer periphery of the lithium metal sheet; and The present invention relates to a negative electrode (120) for a lithium secondary battery, comprising a third layer (123) formed on the upper surface of the second layer and comprising a lithium metal sheet.

[0034] FIG. 2 is a side view of a negative electrode 120 for a lithium secondary battery according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view of the negative electrode 120 for a lithium secondary battery according to an embodiment of the present invention.

[0035] 2 and 3, the negative electrode (120) for a lithium secondary battery according to the present invention includes first to third layers (121, 122, 123) which are stacked one on top of the other.

[0036] The first layer (121) and the third layer (123) may each include a lithium metal sheet, and preferably consist of a lithium metal sheet.

[0037] FIG. 4 is a plan view of a second layer 122 of a negative electrode 120 for a lithium secondary battery according to one embodiment of the present invention.

[0038] 4, the second layer 122 may include a lithium metal sheet 124 and a negative electrode current collector 125 surrounding the outer periphery of the lithium metal sheet 124. That is, the negative electrode current collector 125 may be hollow in the center, and the lithium metal sheet 124 may be located in the hollow space.

[0039] Thus, referring to FIG. 2, in a side view of a negative electrode (120) for a lithium secondary battery according to one embodiment of the present invention, the second layer (122) may show only a negative electrode current collector (125), and referring to FIG. 5, in a cross-sectional view of a negative electrode (120) for a lithium secondary battery according to one embodiment of the present invention, the second layer (122) may show both a negative electrode current collector (125) and a lithium metal sheet (124).

[0040] The area of ​​the negative electrode current collector (125) is smaller than the area of ​​the lithium metal sheet (124) since it exists only on the outer peripheral surface of the lithium metal sheet (124), and may preferably have an area of ​​10 to 30%, more preferably 10 to 20%, of the area of ​​the second layer (122).

[0041] In addition, the edge widths of the negative electrode current collector (125) in the vertical and horizontal directions may be the same or different from each other. When the edge widths of the negative electrode current collector (125) in the vertical and horizontal directions are W1, W2, W3, and W4, respectively, they may be the same or different from each other, and may be preferably defined by any of the following formulas 1 to 3.

[0042] [Formula 1] W1=W2=W3=W4 [Formula 2] W1 ≠ W2 ≠ W3 ≠ W4 [Formula 3] (W1=W2) ≠ (W3=W4)

[0043] In the formulas 1 to 3, W1 is the vertical width of the upper edge, W2 is the vertical width of the lower edge, W3 is the horizontal width of the left edge, and W4 is the horizontal width of the right edge.

[0044] Preferably, the edge width of the negative electrode current collector (125) may be the same as that of Equation 1.

[0045] The thickness of the negative electrode current collector (125) may be 1 to 10 μm, preferably 1 to less than 5 μm. A thickness of less than 1 μm is too thin, and the negative electrode current collector (125) cannot be manufactured to have a thickness of less than 1 μm. If the thickness exceeds 10 μm, the weight of the negative electrode (120) for the lithium secondary battery becomes heavy, and the energy density of the lithium secondary battery (100) may decrease.

[0046] The lithium metal sheet (124) and the negative electrode current collector (125) constituting the second layer (122) may have the same thickness. If the lithium metal sheet (124) is thinner than the negative electrode current collector (125), the lithium metal sheets of the first layer (121) and the third layer (123) will only contact the negative electrode current collector (125) of the second layer (122) and will not contact the lithium metal sheet (124), resulting in space. In the lithium secondary battery (100) including the negative electrode (120), the negative electrode (120) will not contribute to the capacity development of the lithium secondary battery (100), and the total energy density of the lithium secondary battery (100) may be reduced. Furthermore, if the thickness of the lithium metal sheet (124) is greater than the thickness of the negative electrode current collector (125), the lithium metal sheets of the first layer (121) and the third layer (123) will only be in contact with the lithium metal sheet (124) of the second layer (122) and will not be able to contact the negative electrode current collector (125), resulting in gaps, which may reduce the conductivity of the negative electrode current collector (125).

[0047] The second layer (122) may be manufactured by placing a lithium metal sheet on one or both sides of the negative electrode current collector (125) and rolling it, but the present invention is not limited thereto.

[0048] The first to third layers (121, 122, 123) may have the same size.

[0049] In addition, the negative electrode current collector (125) may have an uneven structure on the surface of the first to third layers (121, 122, 123) that comes into contact with the lithium metal sheet.

[0050] The unevenness may be formed in a regular or irregular manner, for example, the unevenness may be formed in a shape similar to a polygonal column protruding or receding from the surface, more specifically, the unevenness may be formed in a gear-like shape protruding or receding.

[0051] Specifically, the lower surface of the negative electrode current collector (125) may have an uneven structure since it is in contact with the upper surface of the lithium metal sheet of the first layer (121). Also, the upper surface of the negative electrode current collector (125) may have an uneven structure since it is in contact with the lower surface of the lithium metal sheet of the third layer (123). Also, since the lithium metal sheet (124) of the second layer (122) is located inside the negative electrode current collector (125), the inner peripheral surface of the negative electrode current collector (125) in contact with it may have an uneven structure.

[0052] The surface of the negative electrode current collector (125) in contact with the lithium metal sheets of the first to third layers (121, 122, 123) has an uneven structure, which may increase the bonding strength with the lithium metal sheets and may reduce the weight of the lithium secondary battery negative electrode (120).

[0053] The negative electrode current collector (125) is not particularly limited as long as it has high conductivity without causing any chemical change in the lithium secondary battery (100). For example, copper, stainless steel, aluminum, nickel, titanium, palladium, baked carbon, copper or stainless steel surface-treated with carbon, nickel, silver, etc., aluminum-cadmium alloy, etc. may be used.

[0054] The first layer (121) may have a thickness of 10 to 50 μm, and the third layer may have a thickness of 10 to 50 μm. The lithium secondary battery negative electrode (120) may have a thickness of 21 to 110 μm, and preferably has a thickness of 21 μm or more and less than 105 μm.

[0055] The negative electrode (120) for the lithium secondary battery may be manufactured by placing the first layer (121) on the lower surface of the second layer (122), placing the third layer (123) on the upper surface of the second layer (122), and rolling the resulting mixture, but this is not particularly limited in the present invention. Alternatively, the negative electrode (120) for the lithium secondary battery may be manufactured by placing lithium metal sheets on both sides of the negative electrode current collector (125) and rolling the resulting mixture, in which case the lithium metal sheet (124) is inserted into the negative electrode current collector (125) to form the second layer (122), and the remaining lithium metal sheet that is not inserted is present on the upper and lower surfaces of the second layer (122). The lithium metal sheet located on the lower surface may be the first layer (121), and the lithium metal sheet located on the upper surface may be the third layer (123).

[0056] The negative electrode 120 for a lithium secondary battery according to an embodiment of the present invention may be a negative electrode for a lithium-sulfur battery.

[0057] The present invention also relates to a battery comprising a positive electrode (110); a negative electrode (120); a separator (130) interposed between the positive electrode and the negative electrode; and an electrolyte (not shown), The size of the negative electrode (120) is larger than the size of the positive electrode (110), The negative electrode (120) relates to the lithium secondary battery (100) which is the negative electrode (120) of the present invention described above.

[0058] FIG. 5 is a cross-sectional view of a lithium secondary battery 100 according to an embodiment of the present invention.

[0059] Referring to FIG. 5, the lithium secondary battery (100) according to the present invention has a positive electrode (110) and a negative electrode (120) sandwiched between a separator (130).

[0060] The negative electrode (120) and the positive electrode (110) may be located in regions corresponding to each other.

[0061] In addition, since the size of the negative electrode (120) is larger than that of the positive electrode (110), the negative electrode (120) may have a region (A) that is not in contact with the positive electrode (110) and a region that is in contact with the positive electrode (110). The region that is in contact with the positive electrode (110) means that the positive electrode (110) and the negative electrode (120) are not in direct contact with each other, but are in contact with each other via a separator (130).

[0062] In this case, the size of the lithium metal sheet (124) of the second layer (122) of the negative electrode (120) may be smaller than or equal to that of the positive electrode (110).

[0063] The positive electrode (110) may be a positive electrode current collector (not shown) coated with a positive electrode active material, and the positive electrode active material may contain sulfur. Specifically, the sulfur may be inorganic sulfur (S8), Li-S n (n≧1), organic sulfur compounds and carbon-sulfur polymers [(C2S x ) n , x=2.5 to 50, n≧2], and preferably inorganic sulfur (S8). The positive electrode active material may be a sulfur-carbon composite containing a porous carbon material and sulfur in at least a part of the inside and the outside surface of the porous carbon material.

[0064] Therefore, the lithium secondary battery 100 according to an embodiment of the present invention may be a lithium-sulfur battery.

[0065] The lithium secondary battery (100) according to an embodiment of the present invention solves the problem of lithium metal detachment that occurs in conventional lithium secondary batteries. Specifically, the negative electrode (120) for the lithium secondary battery according to an embodiment of the present invention includes a lithium metal sheet (124) in a second layer (122) and a negative electrode current collector (125) surrounding the outer periphery of the lithium metal sheet (124). In a conventional lithium secondary battery (100), as the charge and discharge reactions are repeated, the porosity of the lithium metal gradually increases and the rigidity weakens, causing lithium metal to be released from the edge of the negative electrode (120), i.e., the region (A) where the negative electrode (120) does not contact the positive electrode (110). However, since the negative electrode (120) for a lithium secondary battery according to an embodiment of the present invention includes the negative electrode current collector (125) in the second layer (122), even if the rigidity of the lithium metal weakens as the charge and discharge are repeated, the negative electrode current collector (125) can prevent the release of the lithium metal. Therefore, the lithium secondary battery (100) according to an embodiment of the present invention can minimize the loss of energy density while ensuring safety. As the charging and discharging are repeated, lithium metal may be detached from the edges of the first layer (121) and the third layer (123) of the lithium secondary battery negative electrode (120). However, the negative electrode current collector (125) of the second layer (122) maintains the bond between the lithium metal sheets of the first to third layers, thereby solving the conventional problem.

[0066] On the other hand, a negative electrode in which a lithium metal sheet is laminated over the entire area of ​​a sheet-shaped negative electrode current collector is heavy in weight and may cause a loss in energy density in the lithium secondary battery. Also, a negative electrode consisting of only the second layer (122) of the present invention must be thicker than the second layer (122) of the present invention since only the second layer (122) must be used as the negative electrode, and therefore may be heavier than the negative electrode (120) for a lithium secondary battery of the present invention. Therefore, the negative electrode (120) for a lithium secondary battery according to one embodiment of the present invention may be more advantageous in terms of energy density.

[0067] Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the following claims also fall within the scope of the present invention. [Explanation of symbols]

[0068] 100: Lithium secondary battery 110: Positive electrode 120: Negative electrode 121: 1st layer 122: 2nd layer 123:Third layer 124: Lithium metal sheet 125: Negative electrode current collector 130: Separator

Claims

1. a first layer comprising a lithium metal sheet; a second layer formed on the upper surface of the first layer and including a lithium metal sheet and a negative electrode current collector surrounding an outer peripheral surface of the lithium metal sheet; a third layer formed on an upper surface of the second layer, the third layer including a lithium metal sheet.

2. The negative electrode current collector has edge widths in the vertical and horizontal directions, which are the same or different from each other. The negative electrode for a lithium secondary battery according to claim 1 .

3. The negative electrode current collector has an area of ​​10% to 30% of the area of ​​the second layer. The negative electrode for a lithium secondary battery according to claim 1 .

4. The surface of the negative electrode current collector in contact with the lithium metal sheets of the first to third layers includes an uneven structure. The negative electrode for a lithium secondary battery according to claim 1 .

5. The thickness of the negative electrode current collector is 1 μm or more and 10 μm or less. The negative electrode for a lithium secondary battery according to claim 1 .

6. The thickness of the negative electrode current collector is 1 μm or more and less than 5 μm. The negative electrode for a lithium secondary battery according to claim 5 .

7. The first to third layers are the same in size. The negative electrode for a lithium secondary battery according to claim 1 .

8. The thickness of the negative electrode current collector and the thickness of the second layer of lithium metal sheet are the same. The negative electrode for a lithium secondary battery according to claim 1 .

9. The first layer has a thickness of 10 μm or more and 50 μm or less, the third layer has a thickness of 10 μm or more and 50 μm or less, and the negative electrode for lithium secondary battery has a thickness of 21 μm or more and 110 μm or less. The negative electrode for a lithium secondary battery according to claim 1 .

10. The negative electrode for a lithium secondary battery is a negative electrode for a lithium-sulfur battery, The negative electrode for a lithium secondary battery according to claim 1 .

11. a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte solution, The size of the negative electrode is larger than the size of the positive electrode, The negative electrode of any one of claims 1 to 10, wherein the negative electrode is a lithium secondary battery.

12. The size of the lithium metal sheet of the second layer of the negative electrode is smaller than or equal to that of the positive electrode; The lithium secondary battery according to claim 11.

13. The lithium secondary battery is a lithium-sulfur battery. The lithium secondary battery according to claim 11.

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