Negative electrode for lithium metal secondary battery and manufacturing method for the same

Abstract

To provide a negative electrode for a lithium metal secondary battery having a lithium-containing metal layer with high wettability toward an electrolyte, and a manufacturing method for the same in an industrially advantageous manner.SOLUTION: The manufacturing method for a negative electrode for a lithium metal secondary battery includes pressing, against the surface of a lithium-containing metal layer, a texture transfer material that has a plurality of depressions with diameters ranging from 2 μm to 20 μm and depths of 12 μm or less. The lithium-containing metal layer is disposed on at least one surface of a negative electrode current collector in a laminate structure. This pressing process forms surface irregularities on the lithium-containing metal layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a lithium metal secondary battery and a method for producing the same. [Background technology]

[0002] In recent years, research and development into secondary batteries that contribute to energy efficiency has been conducted to ensure that many people have access to affordable, reliable, sustainable, and advanced energy. Lithium metal secondary batteries are known as high-capacity secondary batteries. Lithium metal secondary batteries use lithium ions as a charge transfer medium. During charging, lithium ions are deposited on a lithium-containing metal layer at the negative electrode to form a lithium metal layer. During discharging, the lithium ions released from the lithium metal layer are absorbed into the positive electrode.

[0003] A known negative electrode for a lithium metal secondary battery is a laminated negative electrode having a negative electrode current collector and a lithium layer disposed on at least one surface of the negative electrode current collector. For this laminated negative electrode, it has been investigated to provide irregularities on the surface of the lithium layer (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-272726 Summary of the Invention [Problem to be solved by the invention]

[0005] Improving high-rate characteristics is one of the challenges facing secondary battery technology. In particular, improving the high-rate characteristics of lithium metal secondary batteries immediately after manufacture is also effective for shortening the charge rate time during aging. To improve the reactivity of the lithium metal-containing layer of a lithium metal secondary battery negative electrode, it is effective to form irregularities on the surface of the lithium metal-containing layer to improve the wettability of the lithium metal-containing layer to the electrolyte. To improve the wettability of the lithium metal-containing layer, it is necessary to form fine irregularities. However, according to the inventor's research, when fine irregularities are formed on the surface of the lithium metal-containing layer by pressing an irregularity transfer material against the surface of the lithium metal-containing layer, the lithium metal-containing layer may adhere to the surface of the irregularity transfer material, resulting in partial loss of the lithium metal-containing layer. Furthermore, the lithium metal-containing layer peeled off from the irregularity transfer material may curl, with a cross section bent into a semicircular shape, making it difficult to use as a lithium metal secondary battery negative electrode.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a negative electrode for a lithium metal secondary battery having a lithium-containing metal layer that has high wettability with an electrolyte solution, and a manufacturing method for industrially advantageously manufacturing the negative electrode for a lithium metal secondary battery, which will ultimately contribute to energy efficiency. [Means for solving the problem]

[0007] In response to the above-mentioned problems, the present inventors have found that by pressing a texture transfer material having a plurality of recesses each having a predetermined diameter and depth onto a lithium-containing metal layer laminated on the surface of a negative electrode current collector, the lithium-containing metal layer on which the texture is formed has high wettability with organic solvents used as electrolytes in lithium metal secondary batteries, and have completed the present invention.

[0008] (1) A method for producing a negative electrode for a lithium metal secondary battery, comprising: pressing a texture transfer material having a plurality of recesses, each having a diameter of 2 μm or more and a depth of 12 μm or less, onto a surface of a laminate having a negative electrode current collector and a lithium-containing metal layer disposed on at least one surface of the negative electrode current collector, on the surface of the lithium-containing metal layer side of the laminate; and forming textures on the surface of the lithium-containing metal layer.

[0009] According to the method for producing a negative electrode for a lithium metal secondary battery (1), the size of the recesses arranged on the surface of the irregularity transfer material is within the above-mentioned range, so that the releasability between the lithium-containing metal layer and the irregularity transfer material is high, and the lithium-containing metal is less likely to adhere to the irregularity transfer material after the lithium-containing metal layer is pressed against it. Furthermore, the lithium-containing metal layer having irregularities formed on its surface has high wettability with the electrolyte. Therefore, a negative electrode for a lithium metal secondary battery having a lithium-containing metal layer that has high wettability with the electrolyte can be produced industrially advantageously.

[0010] (2) The method for producing a negative electrode for a lithium metal secondary battery according to (1), wherein the diameter of the recesses of the unevenness transfer material is in the range of 2 μm to 15 μm.

[0011] According to the method for producing a negative electrode for a lithium metal secondary battery (2), the releasability between the lithium-containing metal layer and the pattern transfer material is further improved.

[0012] (3) The method for producing a negative electrode for a lithium metal secondary battery according to (1) or (2), wherein the recess is conical or hemispherical.

[0013] According to the method for producing a negative electrode for a lithium metal secondary battery (3), since the recesses have no sharp edges, the lithium-containing metal layer is less likely to be damaged when pressed against the lithium-containing metal layer, and no protrusions with edges are formed on the surface of the resulting negative electrode for a lithium metal secondary battery. Therefore, a battery using the resulting negative electrode for a lithium metal secondary battery can prevent lithium deposition due to current concentration at the edges of the lithium-containing metal layer, thereby preventing micro-short circuits within the battery and suppressing the occurrence of voltage drop defects.

[0014] (4) The method for producing a negative electrode for a lithium metal secondary battery according to any one of (1) to (3), wherein the texture transfer material is formed of any one of Al, Ti, Ni, W, and carbon.

[0015] According to the method for producing a negative electrode for a lithium metal secondary battery of (4), even if the material of the pattern transfer material is mixed into the negative electrode of the lithium metal secondary battery, a short circuit is unlikely to occur.

[0016] (5) The method for producing a negative electrode for a lithium metal secondary battery according to any one of (1) to (4), wherein the thickness of the lithium-containing metal layer is t (unit: μm) and the depth of the recess is D (unit: μm), satisfying the relationship D≦t−2.

[0017] According to the method for producing a negative electrode for a lithium metal secondary battery (5), the thickness of the portion of the lithium-containing metal layer where the irregularities are not formed is 2 μm or more after the irregularities are formed, which increases the strength of the lithium-containing metal layer after the irregularities are formed.

[0018] (6) The method for producing a negative electrode for a lithium metal secondary battery according to any one of (1) to (5), wherein when the irregularity transfer material is pressed against the surface of the lithium-containing metal layer side, an organic solvent or a structure is interposed between the surface of the lithium-containing metal layer side and the irregularity transfer material.

[0019] According to the method for producing a negative electrode for a lithium metal secondary battery (6), the releasability between the lithium-containing metal layer and the pattern transfer material is further improved.

[0020] (7) The method for producing a negative electrode for a lithium metal secondary battery according to any one of (1) to (6), wherein the concave-convex transfer material is a plate-like body, and the concave portions are arranged on at least one surface of the plate-like body.

[0021] According to the method for producing a negative electrode for a lithium metal secondary battery (7), since the irregularity transfer material is a plate-like body, irregularities can be efficiently formed on the lithium-containing metal layer of the laminate adjusted to a predetermined size.

[0022] (8) The method for producing a negative electrode for a lithium metal secondary battery according to any one of (1) to (6), wherein the concave-convex transfer material is a roll-shaped body, and the concave portions are arranged on at least a part of the surface of the roll-shaped body.

[0023] According to the method for producing a negative electrode for a lithium metal secondary battery (8), since the irregularity transfer material is in a roll form, irregularities can be continuously formed on the lithium-containing metal layer of the long laminate in a roll-to-roll manner.

[0024] (9) The method for producing a negative electrode for a lithium metal secondary battery according to any one of (1) to (8), wherein the laminate has the lithium-containing metal layers laminated on both sides of the negative electrode current collector, and the unevenness transfer material is pressed simultaneously against each of the lithium-containing metal layers laminated on both sides of the negative electrode current collector.

[0025] According to the method for producing a negative electrode for a lithium metal secondary battery of (9), the irregularity transfer material is pressed simultaneously against the lithium-containing metal layers laminated on both sides of the negative electrode current collector, so that the lithium-containing metal layers are unlikely to deform.

[0026] (10) The method for producing a negative electrode for a lithium metal secondary battery according to any one of (1) to (9), wherein the pressure with which the unevenness transfer material is pressed against the surface on the lithium-containing metal layer side is in the range of 5 MPa or more and 25 MPa or less.

[0027] According to the method for producing a negative electrode for a lithium metal secondary battery (10), the pressure when pressing the unevenness transfer material is within the above range, so that unevenness can be reliably formed on the surface of the lithium-containing metal layer while maintaining the releasability between the lithium-containing metal layer and the unevenness transfer material.

[0028] (11) A laminate having a negative electrode current collector and a lithium-containing metal layer disposed on at least one surface of the negative electrode current collector, wherein the lithium-containing metal layer has, on its surface, protrusions having a diameter of 2 μm or more and 20 μm or less and a height of 12 μm or less, and a contact angle at 25°C of 20 degrees or less with respect to a liquid having a viscosity at 25°C of 5 mPaS or more and 12 mPaS or less.

[0029] According to the negative electrode for lithium metal secondary batteries (11), the size of the convex portions arranged on the surface is within the above-mentioned range, so that the releasability from the pattern transfer material is high. Furthermore, the contact angle at 25°C with a liquid having a viscosity of 5 mPaS to 12 mPaS at 25°C, which corresponds to the electrolyte solution of a typical lithium metal secondary battery, or the organic solvent or mixed solvent thereof that constitutes the electrolyte solution, is low at 20° or less, and the wettability is high. Therefore, a lithium metal secondary battery using the negative electrode for lithium metal secondary batteries (11) not only has improved wettability of the negative electrode with the electrolyte solution, shortens the aging time, but also reduces the internal resistance of the battery and improves the charging characteristics, particularly at high rates. Therefore, it is a lithium metal secondary battery that is particularly compatible with rapid charging. [Effects of the Invention]

[0030] According to the present invention, it is possible to provide a negative electrode for a lithium metal secondary battery having a lithium-containing metal layer that has high wettability with respect to an electrolytic solution, and a manufacturing method by which the negative electrode for a lithium metal secondary battery can be manufactured industrially advantageously. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a cross-sectional view showing an example of the configuration of an electrode stack using a negative electrode for a lithium metal secondary battery according to one embodiment of the present invention. [Figure 2] 1 is a schematic diagram showing an example of an apparatus for manufacturing a negative electrode for a lithium metal secondary battery that can be used in a method for manufacturing a negative electrode for a lithium metal secondary battery according to one embodiment of the present invention. [Figure 3]FIG. 2 is a schematic diagram showing another example of an apparatus for manufacturing a negative electrode for a lithium metal secondary battery that can be used in the method for manufacturing a negative electrode for a lithium metal secondary battery according to one embodiment of the present invention. [Figure 4] 1 is an SEM photograph of the surface of the unevenness transfer material produced in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below are merely examples of the present invention, and the present invention is not limited to the following.

[0033] The negative electrode according to one embodiment of the present invention is for use in a lithium metal secondary battery. The lithium metal secondary battery includes an electrode stack in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, an electrolyte solution, and an exterior housing that accommodates the electrode stack and the electrolyte solution.

[0034] Fig. 1 is a cross-sectional view showing an electrode laminate using a negative electrode for a lithium metal secondary battery according to one embodiment of the present invention. As shown in Fig. 1, the electrode laminate 1 is a laminate in which a plurality of positive electrodes 10 and a plurality of negative electrodes 20 are alternately stacked with separators 30 interposed therebetween.

[0035] The positive electrode 10 includes a positive electrode current collector 11 and positive electrode active material layers 12 laminated on both sides of the positive electrode current collector 11. Examples of materials for the positive electrode current collector 11 include aluminum, aluminum alloys, stainless steel, nickel, iron, and titanium.

[0036] The positive electrode active material layer 12 contains a positive electrode active material. The positive electrode active material is a lithium compound that releases lithium ions during discharge and absorbs lithium ions during charge. Examples of the lithium compound that can be used include layered active materials, spinel-type active materials, and olivine-type active materials. Specific examples of the positive electrode active material include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium-nickel-manganese cobalt oxide (NMC:LiNi p Mn q Cor O2(p+q+r=1)), LiNi p Al q Co r O2 (p+q+r=1), lithium manganese oxide (LiMn2O4), Li 1+x Mn 2-x-y Examples of such an element-substituted Li-Mn spinel are MO4 (x+y=2, M=at least one selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (oxide containing Li and Ti), and lithium metal phosphate (LiMPO4, M=at least one selected from Fe, Mn, Co, and Ni). The positive electrode active material layer 12 may further contain a conductive additive and a binder.

[0037] The negative electrode 20 has a negative electrode current collector 21 and lithium-containing metal layers 22 laminated on both sides of the negative electrode current collector 21. Examples of materials for the negative electrode current collector 21 include copper, copper alloys, nickel, and stainless steel.

[0038] Lithium ions are deposited on the surface of the lithium-containing metal layer 22 during charging, forming a lithium metal layer, and lithium from the lithium metal layer is released during discharging. Therefore, the thickness of the negative electrode 20 changes with charging and discharging. The lithium-containing metal layer 22 has protrusions on its surface, each having a diameter of 2 μm to 20 μm and a height of 12 μm or less. The lithium-containing metal layer 22 has a contact angle of 20 degrees or less at 25°C with a liquid having a viscosity of 5 mPaS to 12 mPaS at 25°C. The liquid having a viscosity of 5 mPaS to 12 mPaS at 25°C is, for example, an electrolyte used in a lithium metal secondary battery using the negative electrode 20. The contact angle may be 10 degrees or less, or may be 5 degrees or less. The thickness of the lithium-containing metal layer 22 other than the protrusions may be 2 μm or more. The lithium-containing metal layer 22 can be made of lithium or a metal that forms an alloy with lithium. Examples of metals that form alloys with lithium include Mg, Si, Au, Ag, In, Ge, Sn, Pb, Al, and Zn.

[0039] The separator 30 may be, for example, a porous sheet or a nonwoven fabric sheet. Examples of materials for the porous sheet include polyolefins such as polyethylene and polypropylene, aramid, polyimide, and fluororesin. Examples of materials for the nonwoven fabric sheet include glass fiber and cellulose fiber. The separator 30 preferably has a contact angle of 30 degrees or less at 25°C with a liquid having a viscosity of 5 mPaS to 12 mPaS at 5°C. That is, the separator 30 preferably has low wettability with respect to the electrolyte or solvent, similar to that of the lithium-containing metal layer 22. If the contact angle of the separator 30 with respect to the electrolyte is 40 degrees to 60 degrees, micro-short circuits may be more likely to occur.

[0040] The electrolytic solution contains an organic solvent and an electrolyte. Examples of the organic solvent include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, hydrofluoroethers (HFEs), aromatic ethers, sulfones, cyclic esters, chain carboxylic acid esters, and nitriles. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane. Examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, and diethyl ether. Examples of hydrofluoroethers include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl)ether, and 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane. Examples of aromatic ethers include anisole. Examples of sulfones include sulfolane and methylsulfolane. Examples of cyclic esters include γ-butyrolactone. Examples of chain carboxylic acid esters include acetate esters, butyrate esters, and propionate esters. Examples of nitriles include acetonitrile and propionitrile. The organic solvents may be used alone or in combination of two or more.

[0041] The electrolyte is a source of lithium ions, which are a charge transfer medium, and contains a lithium salt. Examples of lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(CF3SO2)2 (LiTFSI), LiN(FSO2)2 (LiFSI), and LiBC4O8. The lithium salts may be used alone or in combination of two or more. The concentration of the electrolyte is, for example, within the range of 1.0 to 4.0 mol / L.

[0042] The exterior body is expandable and contractible in accordance with changes in the thickness of the negative electrode 20 due to charging and discharging. A laminate film can be used as the material of the exterior body. As the laminate film, a laminate film having a three-layer structure in which an inner resin layer, a metal layer, and an outer resin layer are laminated in this order from the inside can be used. The outer resin layer can be, for example, a polyamide (nylon) layer or a polyethylene terephthalate (PET) layer, the metal layer can be, for example, an aluminum layer, and the inner resin layer can be, for example, a polyethylene layer or a polypropylene layer.

[0043] Next, a method for producing the negative electrode for a lithium metal secondary battery according to this embodiment will be described.

[0044] In the method for manufacturing a negative electrode for a lithium metal secondary battery according to this embodiment, a concave-convex transfer material having a plurality of recesses on its surface is pressed against the surface of a laminate having a negative electrode current collector and a lithium-containing metal layer, on the side of the lithium-containing metal layer, to form concaves and convexes on the surface of the lithium-containing metal layer. The concaves of the concave-convex transfer material have a diameter of 2 μm to 20 μm and a depth of 12 μm or less. The diameter of the concaves may be in the range of 2 μm to 15 μm or in the range of 5 μm to 15 μm. The depth of the concaves may be in the range of 2 μm to 15 μm or in the range of 4 μm to 12 μm. The depth of the concaves may satisfy the relationship D≦t−2, where t (unit: μm) is the thickness of the lithium-containing metal layer and D (unit: μm). The shape of the concaves of the concave-convex transfer material may be, for example, conical or hemispherical. The pitch of the concaves may be, for example, in the range of 4 μm to 50 μm. Such a concave-convex transfer material having recesses can be produced, for example, by forming recesses on the surface of a plate-like substrate by laser processing. Examples of materials that can be used for the plate-like substrate include Al, Ti, Ni, W, and carbon.

[0045] When the texture transfer material is pressed against the surface of the lithium-containing metal layer, an organic solvent or structure may be interposed between the surface of the lithium-containing metal layer and the texture transfer material. The organic solvent or structure may act as a release agent. The organic solvent may have an ether bond or a carbonate ester bond. Examples of solvents having an ether bond include DME (1,2-dimethoxyethane) and DEE (1,2-dimethoxyethane). Examples of solvents having a carbonate ester bond include dimethyl carbonate. The structure may be arranged in the form of a layer on the surface of the texture transfer material. Examples of the structure include fluororesin and DLC (diamond-like carbon). These act as release agents when arranged in the form of a layer on the surface of the texture transfer material.

[0046] The pressure with which the unevenness transfer material is pressed against the surface on the lithium-containing metal layer side is not particularly limited, but may be in the range of 5 MPa to 25 MPa. The unevenness transfer material may be in the form of a plate or a roll.

[0047] FIG. 2 is a schematic diagram showing an example of an apparatus for manufacturing a negative electrode for a lithium metal secondary battery that can be used in the method for manufacturing a negative electrode for a lithium metal secondary battery according to one embodiment of the present invention.

[0048] The lithium metal secondary battery negative electrode manufacturing apparatus 100 shown in FIG. 2 includes a pair of press rolls 110 and a texture-forming laminate 120. A negative electrode material laminate 20a is used as the negative electrode raw material. The negative electrode material laminate 20a includes a negative electrode current collector material 21a and a lithium-containing metal layer material 22a laminated on both sides of the negative electrode current collector material 21a. The negative electrode material laminate 20a is adjusted to the size of the lithium metal secondary battery negative electrode to be manufactured. The texture-forming laminate 120 is a laminate in which a plate-shaped texture-transfer material 122 is placed on the surface of the lithium-containing metal layer material 22a of the negative electrode material laminate 20a so that the surface on the recessed side is in contact with the surface. The plate-shaped texture-transfer material 122 is a plate-shaped body with recesses arranged on at least one surface. A release plate 121 is arranged on the surface of the plate-shaped texture-transfer material 122 opposite the recessed side. For example, a copper plate can be used as the release plate 121. By pressing the unevenness-forming laminate 120 with a pair of press rolls 110, unevenness is simultaneously formed on the surface of the lithium-containing metal layer material 22a laminated on both sides of the negative electrode current collector material 21a.

[0049] FIG. 3 is a schematic diagram showing an example of an apparatus for manufacturing a negative electrode for a lithium metal secondary battery that can be used in the method for manufacturing a negative electrode for a lithium metal secondary battery according to one embodiment of the present invention.

[0050] The lithium metal secondary battery negative electrode manufacturing apparatus 200 shown in FIG. 3 has a pair of roll-shaped irregularity transfer materials 210. The roll-shaped irregularity transfer material 210 is a roll-shaped body having recesses on at least a portion of its surface. A long lithium-containing metal layer material sheet 20b is used as the negative electrode raw material. The long lithium-containing metal layer material sheet 20b has a long negative electrode current collector material sheet 21b and a long lithium-containing metal layer material sheet 22b laminated on both sides of the long negative electrode current collector material sheet 21b. By passing the long lithium-containing metal layer material sheet 20b between the pair of roll-shaped irregularity transfer materials, irregularities are simultaneously formed on each surface of the long lithium-containing metal layer material sheet 22b laminated on both sides of the long negative electrode current collector material sheet 21b. This results in a long, textured negative electrode material laminate sheet 20c having a long negative electrode current collector material sheet 21c and a long, textured lithium-containing metal layer material sheet 22c laminated on both sides of the long negative electrode current collector material sheet 21c. The obtained long, textured negative electrode material laminate sheet 20c is adjusted to a predetermined size and used as a negative electrode for a lithium metal secondary battery.

[0051] According to the method for manufacturing a negative electrode for a lithium metal secondary battery of this embodiment configured as described above, the size of the recesses arranged on the surface of the recessed portion transfer material (plate-shaped recessed portion transfer material 122, roll-shaped recessed portion transfer material 210) is within the above-mentioned range, so that the releasability between the lithium-containing metal layer and the recessed portion transfer material is high, and the lithium-containing metal is less likely to adhere to the recessed portion transfer material after the lithium-containing metal layer is pressed against it. Furthermore, the lithium-containing metal layer having the recessed portions formed on its surface has high wettability with the electrolyte. Therefore, a negative electrode for a lithium metal secondary battery having a lithium-containing metal layer that has high wettability with the electrolyte can be manufactured industrially advantageously.

[0052] In the method for producing a negative electrode for a lithium metal secondary battery of this embodiment, if the recesses of the irregularity transfer material are conical or hemispherical, the recesses are not angular, and therefore, when pressed against the lithium-containing metal layer, defects are unlikely to occur in the lithium-containing metal layer. In the method for producing a negative electrode for a lithium metal secondary battery of this embodiment, if the irregularity transfer material is formed from the above-mentioned material, short circuits are unlikely to occur even when it is mixed into the negative electrode of a lithium metal secondary battery. In the method for producing a negative electrode for a lithium metal secondary battery of this embodiment, if the thickness t of the lithium-containing metal layer and the depth D of the recesses of the irregularity transfer material satisfy the above relationship, the thickness of the lithium-containing metal layer in the portion where the irregularities are not formed after the irregularity transfer material is formed will be 2 μm or more. This increases the strength of the lithium-containing metal layer after the irregularity transfer material is formed. In the method for producing a negative electrode for a lithium metal secondary battery of this embodiment, if an organic solvent or structure is interposed between the surface of the lithium-containing metal layer and the irregularity transfer material when pressing the irregularity transfer material against the surface of the lithium-containing metal layer, the releasability of the lithium-containing metal layer and the irregularity transfer material is further improved.

[0053] In the method for producing a negative electrode for a lithium metal secondary battery of this embodiment, when the unevenness transfer material is a plate-shaped unevenness transfer material 122, unevenness can be efficiently formed on the lithium-containing metal layer of a laminate adjusted to a predetermined size. In the method for producing a negative electrode for a lithium metal secondary battery of this embodiment, when the unevenness transfer material is a roll-shaped unevenness transfer material 210, unevenness can be formed on the lithium-containing metal layer of a long laminate by roll-to-roll.

[0054] In the manufacturing method of the negative electrode for a lithium metal secondary battery of this embodiment, when the pressure for pressing the unevenness transfer material is within the above range, unevenness can be reliably formed on the surface of the lithium-containing metal layer while maintaining the releasability between the lithium-containing metal layer and the unevenness transfer material.

[0055] The lithium metal secondary battery negative electrode obtained by the method for producing a lithium metal secondary battery negative electrode of this embodiment has high releasability from the pattern transfer material because the size of the convex portions arranged on the surface is within the above range. Furthermore, the contact angle at 25°C with a liquid having a viscosity of 5 mPaS to 12 mPaS at 25°C is low (20° or less), so the electrode has high wettability with the electrolyte. Therefore, lithium metal secondary batteries using the lithium metal secondary battery negative electrode of this embodiment have improved high-rate performance.

[0056] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments.

[0057] For example, although a non-aqueous solvent-type lithium metal secondary battery containing an electrolyte solution has been described as a lithium metal secondary battery using the negative electrode for a lithium metal secondary battery of this embodiment, the present invention is not limited thereto. The negative electrode for a lithium metal secondary battery of the present invention may also be used in a solid electrolyte-type lithium metal secondary battery. Furthermore, although the negative electrode 20 has a lithium-containing metal layer 22 laminated on both surfaces of the negative electrode current collector 21, the negative electrode 20 may have a lithium-containing metal layer 22 laminated on one surface of the negative electrode current collector 21. [Example]

[0058] The present invention will be described with reference to examples, but the present invention is not limited to these examples.

[0059] [Example 1] (Preparation of negative electrode) A concave-convex transfer material was produced by forming recesses with a diameter of 15 μm and a depth of 12 μm at a pitch of 20 μm on the surface of a Ti substrate using laser processing. Figure 4 shows an SEM (scanning electron microscope) photograph of the surface of the obtained concave-convex transfer material. The SEM photograph in Figure 4 shows that the recesses on the surface of the concave-convex transfer material are conical.

[0060] A Li-Cu laminate was prepared by laminating a Li foil on one surface of a Cu negative electrode current collector. DEE (1,2-diethoxyethane) was dropped onto the Li foil of the Li-Cu laminate. The surface of the Li foil of the Li-Cu laminate was then placed on the recessed portion of the above-mentioned texture transfer material, and sandwiched between 20 μm-thick release copper foils to obtain a texture-forming laminate in which the release copper foil, Li-Cu laminate, texture transfer material, and release copper foil were laminated in this order. The obtained texture-forming laminate was pressed at a pressure of 25 MPa using a roll press to achieve a compression ratio of 30%. The release copper foil and texture transfer material were peeled off from the pressed texture-forming laminate to obtain a textured Li-Cu laminate in which the texture was transferred to the surface of the Li layer.

[0061] (Preparation of positive electrode) Acetylene black (AB) as an electron conductive material and polyvinylidene fluoride (PVDF) as a binder were premixed with N-methyl-2-pyrrolidone (NMP) as a dispersion solvent, and the mixture was wet mixed in a planetary mixer to obtain a premixed slurry. 0.8 Co 0.1 Mn 0.1 The obtained premixed slurry was mixed with O2 (NCM811) and dispersed using a planetary mixer to obtain a positive electrode paste. NCM811 had a median diameter of 12 μm. Next, the obtained positive electrode paste was applied to an Al positive electrode current collector, dried, pressed with a roll press, and then dried in a vacuum at 120°C to form a positive electrode plate equipped with a positive electrode active material layer. The obtained positive electrode plate was punched out to a size of 30 mm x 40 mm to form a positive electrode.

[0062] (separator) A porous polyolefin film with a thickness of 20 μm was prepared as a separator. The contact angle of this separator with the following electrolyte at 25° C. was measured and found to be 26 degrees.

[0063] (Preparation of electrolyte) An electrolyte solution was prepared by dissolving LiFSI in 1,2-dimethoxyethane (DME) at a concentration of 2.5 mol / L. The viscosity of the obtained electrolyte solution was measured using a rotational viscometer and found to be 10 mPaS at 25°C.

[0064] (Fabrication of lithium metal secondary batteries) The textured Li-Cu laminate was punched out to a size of 34 mm x 44 mm to form a negative electrode. A separator was placed on the Li foil of the negative electrode, and then a positive electrode active material layer of the positive electrode was placed on the surface of the separator opposite the negative electrode side to produce an electrode laminate in this order. Next, tabs were attached to each of the positive electrode current collector and negative electrode current collector of the obtained electrode laminate. The electrode laminate with the attached tabs was placed in a laminate film bag, and after adding an electrolyte, the laminate film bag was sealed to produce a lithium metal secondary battery.

[0065] [Example 2] A negative electrode was produced in the same manner as in Example 1, except that the depth of the recesses in the concave-convex transfer material was set to 8 μm, and a lithium metal secondary battery was produced using the negative electrode.

[0066] [Example 3] A negative electrode was produced in the same manner as in Example 1, except that the depth of the recesses in the concave-convex transfer material was set to 4 μm, and a lithium metal secondary battery was produced using the negative electrode.

[0067] [Example 4] In preparing the negative electrode, the depth of the recesses in the unevenness transfer material was set to 4 μm, and the surface of the Li foil of the Li-Cu laminate was overlapped with the uneven portion of the unevenness transfer material without dropping DEE onto the Li foil of the Li-Cu laminate. An anode was prepared in the same manner as in Example 1, and a lithium metal secondary battery was prepared using the anode.

[0068] [Comparative Example 1] In preparing the negative electrode, a negative electrode was prepared in the same manner as in Example 1, except that a concave-convex transfer material was used in which recesses having a diameter of 1.0 μm and a depth of 20 μm were formed on the surface of a Ni base material by electrolysis. A lithium metal secondary battery was prepared using the negative electrode.

[0069] Comparative Example 2 In preparing the negative electrode, a negative electrode was prepared in the same manner as in Example 1, except that a concave-convex transfer material was used in which recesses having a diameter of 1.0 μm and a depth of 12 μm were formed on the surface of a Ni base material by electrolysis. A lithium metal secondary battery was prepared using the negative electrode.

[0070] Comparative Example 3 In preparing the negative electrode, a negative electrode was prepared in the same manner as in Example 1, except that the surface of a Ni base material was used as the texture transfer material, and recesses with a diameter of 1.0 μm and a depth of 5 μm were formed by electrolysis, and the compression ratio of the texture forming laminate was set to 15%. A lithium metal secondary battery was prepared using this negative electrode.

[0071] The materials of the substrates of the concave-convex transfer materials used in the production of the negative electrodes of Examples 1 to 4 and Comparative Examples 1 to 3, the processing method for forming the concave portions, the diameter and depth of the concave portions, the organic solvent (mold release agent), and the pressing conditions (pressure, compression ratio) are shown in Table 1 below.

[0072] [evaluation] The negative electrodes produced in Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated as follows. The results are shown in Table 2. 1) The adhesion of Li to the texture transfer material was visually observed. If there was no adhesion of Li, it meant that there was no damage to the Li foil of the negative electrode. 2) The negative electrode was placed on a flat plate and visually inspected for the occurrence of curling, i.e., the cross section is bent into a semicircular shape. In the production of lithium metal secondary batteries, the negative electrode that had curled was held down on both ends with tweezers and the separator and positive electrode were stacked on top of it. If the negative electrode did not curl, it meant that there was no gap between it and the flat plate and the negative electrode was flat. 3) The above electrolyte solution was dropped onto the surface of the Li foil of the negative electrode, and the contact angle of the electrolyte solution at 25° C. was measured.

[0073] The voltage (OCV) and AC resistance (ACR resistance) were measured at 1 kHz for the lithium metal secondary batteries produced in Examples 1 to 4 and Comparative Examples 1 to 3 before aging (immediately after production). The results are shown in Table 2 below.

[0074] [Table 1]

[0075] [Table 2]

[0076] The results in Tables 1 and 2 show that the negative electrodes of Examples 1 to 4, which were fabricated using a textured transfer material with recesses within the diameter and depth ranges of the present invention, were free of missing Li foil, flat, and easy to assemble. Furthermore, the voltage was high and the resistance was low, demonstrating high wettability with the electrolyte. Furthermore, by combining a negative electrode with a contact angle with the electrolyte of 20 degrees or less and a separator with a contact angle with the electrolyte of 30 degrees or less, and further using a negative electrode with a textured surface formed by the manufacturing method of the present invention, the wettability of the negative electrode was stabilized early. This enabled a reduction in the electrolyte impregnation time during aging and an improvement in the initial charge rate, thereby enabling a reduction in the aging time. Even if the aging time was shortened, it is expected that the yield of lithium metal secondary batteries after aging would be improved. [Explanation of symbols]

[0077] 1 Electrode laminate 10 positive electrode 11 Positive electrode current collector 12 Cathode active material layer 20 negative electrode 21 Negative electrode current collector 22 Lithium-containing metal layer 20a Negative electrode material laminate 21a Negative electrode current collector material 22a Lithium-containing metal layer material 20b Long negative electrode material laminate sheet 21b Long negative electrode current collector material sheet 22b Long lithium-containing metal layer material sheet 20c Long negative electrode material laminate sheet with concave and convex portions 21c Long negative electrode current collector material sheet 22c Long, textured lithium-containing metal layer material sheet 30 Separator 100 Lithium metal secondary battery negative electrode manufacturing equipment 110 Press Roll 120 Laminated body for forming unevenness 121 Release plate 122 Plate-shaped uneven transfer material 200 Lithium metal secondary battery negative electrode manufacturing equipment 210 Roll-shaped uneven transfer material

Claims

1. A method for manufacturing a negative electrode for a lithium metal secondary battery, comprising: pressing a texture transfer material, the material having a plurality of recesses each having a diameter of 2 μm or more and a depth of 12 μm or less, onto a surface of a laminate having a negative electrode current collector and a lithium-containing metal layer disposed on at least one surface of the negative electrode current collector, on the surface of the lithium-containing metal layer side of the laminate; and forming textures on the surface of the lithium-containing metal layer.

2. 2. The method for producing a negative electrode for a lithium metal secondary battery according to claim 1, wherein the diameter of the recesses of the unevenness transfer material is in the range of 2 μm to 15 μm.

3. 3. The method for producing a negative electrode for a lithium metal secondary battery according to claim 1, wherein the recesses are conical or hemispherical.

4. 3. The method for producing a negative electrode for a lithium metal secondary battery according to claim 1, wherein the patterning material is made of any one of Al, Ti, Ni, W, and carbon.

5. 3. The method for producing a negative electrode for a lithium metal secondary battery according to claim 1, wherein the thickness of the lithium-containing metal layer is t (unit: μm) and the depth of the recess is D (unit: μm), and the relationship D≦t−2 is satisfied.

6. 3. The method for producing a negative electrode for a lithium metal secondary battery according to claim 1, wherein when the unevenness transfer material is pressed against the surface of the lithium-containing metal layer side, an organic solvent or a structure is interposed between the surface of the lithium-containing metal layer side and the unevenness transfer material.

7. 3. The method for producing a negative electrode for a lithium metal secondary battery according to claim 1, wherein the concave-convex transfer material is a plate-like body, and the concave portions are arranged on at least one surface of the plate-like body.

8. 3. The method for producing a negative electrode for a lithium metal secondary battery according to claim 1, wherein the concave-convex transfer material is in the form of a roll, and the concave portions are arranged on at least a part of the surface of the roll.

9. 3. The method for manufacturing a negative electrode for a lithium metal secondary battery according to claim 1, wherein the laminate has the lithium-containing metal layers stacked on both sides of the negative electrode current collector, and the concave-convex transfer material is pressed simultaneously against each of the lithium-containing metal layers stacked on both sides of the negative electrode current collector.

10. 3. The method for producing a negative electrode for a lithium metal secondary battery according to claim 1, wherein the pressure at which the patterning material is pressed against the surface on the lithium-containing metal layer side is in the range of 5 MPa or more and 25 MPa or less.

11. A laminate having a negative electrode current collector and a lithium-containing metal layer disposed on at least one surface of the negative electrode current collector, the lithium-containing metal layer has, on its surface, protrusions having a diameter in the range of 2 μm to 20 μm and a height of 12 μm or less, and a contact angle at 25° C. of 20 degrees or less with a liquid having a viscosity at 25° C. of 5 mPaS to 12 mPaS or less.

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