Lithium metal secondary battery and aging method thereof

Abstract

To provide a lithium metal secondary battery and an aging method for the lithium metal secondary battery that can shorten an aging time.SOLUTION: A lithium metal secondary battery includes an electrode stack in which a positive electrode layer, a separator, and a negative electrode layer are stacked in this order, and an electrolyte. The negative electrode layer is a lithium-containing metal layer, and a plurality of protrusions are arranged on the surface of the separator on the negative electrode layer side or on the surface of the negative electrode layer on the separator side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a lithium metal secondary battery and an aging method thereof. [Background technology]

[0002] In recent years, research and development has been conducted on secondary batteries that contribute to energy efficiency, ensuring that more people have access to affordable, reliable, sustainable, and advanced energy. Known examples of such secondary batteries include lithium secondary batteries that use a lithium-containing compound as the positive electrode active material in the positive electrode layer, and that transfer lithium ions from the positive electrode active material to the negative electrode layer during charging and from the negative electrode layer to the positive electrode active material during discharging. Since lithium is present in the positive electrode active material immediately after production, lithium secondary batteries with such a configuration typically undergo aging, including a charging process (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2024-500687 Summary of the Invention [Problem to be solved by the invention]

[0004] In the field of secondary battery technology, shortening the aging time is one of the challenges. Known lithium secondary batteries use a lithium-containing metal layer as the negative electrode layer, and during charging, lithium ions are deposited on the lithium-containing metal layer to form a lithium metal layer. However, according to the inventors' studies, when a high-concentration electrolyte solution with an electrolyte concentration of 1.0 to 2.5 mol / L is used in a lithium metal secondary battery, the separator first retains a sufficient amount of electrolyte, and then the electrolyte solution is difficult to transfer to the surface of the lithium metal negative electrode, and it takes a long time for the electrolyte solution to fully wet the entire surface of the negative electrode. High-concentration electrolyte solutions are being considered, particularly for large-sized lithium metal secondary batteries for automotive use, making it difficult to shorten the aging time.

[0005] The present invention has been made in view of the above, and aims to provide a lithium metal secondary battery and an aging method for a lithium metal secondary battery that can shorten the aging time, thereby contributing to improved energy efficiency. [Means for solving the problem]

[0006] The present inventors have found that, in order to solve the above problems, it is effective to arrange a plurality of protrusions on the surface of the separator of a lithium metal secondary battery facing the negative electrode layer or on the surface of the negative electrode layer facing the separator, and have completed the present invention.

[0007] (1) A lithium metal secondary battery comprising: an electrode laminate in which a positive electrode layer, a separator, and a negative electrode layer are laminated in this order; and an electrolyte; wherein the negative electrode layer is a lithium-containing metal layer, and a plurality of protrusions are disposed on the surface of the separator facing the negative electrode layer or on the surface of the negative electrode layer facing the separator.

[0008] In the lithium metal secondary battery (1), the protrusions form a gap between the separator and the negative electrode layer. This allows the lithium negative electrode to be wetted first, and then the electrolyte moves to the separator, allowing the electrolyte to penetrate both the separator and the negative electrode layer. This shortens the time it takes for the lithium metal negative electrode to be sufficiently wetted with the electrolyte compared to conventional batteries. This shortens the retention time after injection of the electrolyte, and shortens the total aging time.

[0009] (2) The lithium metal secondary battery according to (1), wherein the convex portion is disposed on the surface of the separator on the negative electrode layer side.

[0010] In the lithium metal secondary battery (2), convex portions are formed on the surface of the separator facing the negative electrode layer, increasing the wettability of the negative electrode layer. This stabilizes the negative electrode potential. After the negative electrode potential stabilizes, if the lithium metal secondary battery is constrained, the convex portions collapse and the gaps disappear. When the battery is initially charged in this constrained state, lithium ions are deposited on the negative electrode, strengthening the bond between the lithium foil and the deposited lithium. This improves discharge characteristics.

[0011] (3) The lithium metal secondary battery according to (2), wherein the separator has a functional layer on the surface on the negative electrode layer side, and the protrusions are disposed on the surface of the functional layer.

[0012] According to the lithium metal secondary battery of (3), by providing a functional layer on the surface of the separator on the negative electrode layer side, the characteristics of the lithium metal secondary battery can be further improved.

[0013] (4) The lithium metal secondary battery according to any one of (1) to (3), wherein the projections have an average diameter in the range of 100 μm or more and 300 μm or less and an average height in the range of 0.5 μm or more and 1.5 μm or less.

[0014] In the lithium metal secondary battery (4), the average diameter and average height of the protrusions are within the above ranges, so that gaps through which the electrolyte can penetrate can be more stably formed between the separator and the negative electrode layer, thereby shortening the time for the electrolyte to penetrate.

[0015] (5) The lithium metal secondary battery according to any one of (1) to (4), wherein the average distance between adjacent protrusions is within the range of 100 μm to 1 mm.

[0016] In the lithium metal secondary battery (5), since the average spacing between the protrusions is within the above range, gaps through which the electrolyte can penetrate can be more stably formed between the separator and the negative electrode layer, further shortening the time for the electrolyte to penetrate.

[0017] (6) The lithium metal secondary battery according to any one of (1) to (5), wherein the area occupancy of the convex portions is in the range of 5% to 10%.

[0018] In the lithium metal secondary battery (6), the area occupancy of the protrusions is within the above range, so that lithium ions are uniformly charged without variation, improving durability. Furthermore, if the protrusions are made of a resin suitable for the electrolyte, the dissolution rate of the protrusions in the electrolyte increases, making it less likely that the resin will remain between the negative electrode layer and the separator, resulting in uneven coating of the negative electrode layer and the separator with the resin.

[0019] (7) A method for aging a lithium metal secondary battery according to claim 1 or 2, comprising the step of charging the lithium metal secondary battery in a state where the surface of the separator is aligned with the direction of gravity.

[0020] According to the aging method for a lithium metal secondary battery (7), the lithium metal secondary battery is positioned so that the surface of the separator is aligned with the direction of gravity. Therefore, the electrolyte penetrates between the separator and the negative electrode layer through the gaps formed by the protrusions due to capillary action. This results in uniform wettability of the negative electrode layer, uniform potential of the negative electrode layer, and a shorter impregnation retention time. This allows for a higher charge rate during aging. Therefore, this aging method for a lithium metal secondary battery allows for a shorter aging time. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a lithium metal secondary battery and an aging method for a lithium metal secondary battery that can shorten the aging time. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a cross-sectional view showing a lithium metal secondary battery according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a portion A in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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.

[0024] Fig. 1 is a cross-sectional view showing a lithium metal secondary battery according to one embodiment of the present invention, and Fig. 2 is an enlarged cross-sectional view of a portion A in Fig. 1.

[0025] As shown in FIGS. 1 and 2, a lithium metal secondary battery 100 includes an electrode stack 40 in which a positive electrode layer 10, a separator 20, and a negative electrode layer 30 are stacked in this order, and an electrolyte solution 50. A positive electrode current collector (not shown) is disposed on the surface of the positive electrode layer 10 opposite the separator 20 side. A negative electrode current collector (not shown) is disposed on the surface of the negative electrode layer 30 opposite the separator 20 side. The electrode stack 40 and the electrolyte solution 50 are housed in an exterior body (not shown). The exterior body includes a positive electrode tab connected to the positive electrode current collector and a negative electrode tab connected to the negative electrode current collector.

[0026] The positive electrode layer 10 includes a positive electrode active material. As the positive electrode active material, a compound containing lithium can be used. Examples of the positive electrode active material include lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), and LiNi p Mn q Co r 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 M y Examples of such positive electrode layer 10 include a hetero-element-substituted Li-Mn spinel represented by O4 (x+y=2, M=at least one selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate (an oxide containing Li and Ti), and lithium metal phosphate (LiMPO4, M=at least one selected from Fe, Mn, Co, and Ni). The positive electrode layer 10 may contain various additives used as materials for positive electrode layers, such as a binder and a conductive additive.

[0027] The separator 20 has a functional layer 25 on the surface on the negative electrode layer 30 side, and protrusions 21 are arranged on the surface of the functional layer 25.

[0028] The separator 20 is not particularly limited, but may be any known material used as a separator for lithium metal secondary batteries, such as 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 thickness of the separator 20 is not particularly limited, but may be, for example, in the range of 10 μm to 15 μm, or in the range of 10 μm to 12 μm.

[0029] The functional layer 25 may be, for example, a conductive layer having electrical conductivity. If the functional layer 25 is a conductive layer, electrons are supplied to the functional layer 25 side during charging, promoting the formation of lithium nuclei in the functional layer 25. This makes it possible to suppress short circuits caused by dendrites and a decrease in the density of the active material layer of the negative electrode layer in a charged state. The electrical conductivity of the conductive layer is, for example, 1.0 × 10 1 S / cm or more 1.0×10 5 The surface resistivity of the conductive layer may be in the range of 200 Ω / cm or less. 2 The following may also be used. As the material for the conductive layer, for example, conductive materials such as metals and carbon nanotubes (CNTs) can be used. Examples of metals include Cu, Zn, Ti, and Sn. These conductive materials may be used alone or in combination of two or more.

[0030] The protrusions 21 have the function of forming a gap between the separator 20 and the negative electrode layer 30, thereby facilitating penetration of the electrolyte solution 50 between the separator 20 and the negative electrode layer 30. There are no particular limitations on the shape of the protrusions 21, and they may be, for example, columnar, granular, or have a trapezoidal cross section.

[0031] The diameter (D in FIG. 2) of the protrusions 21 is not particularly limited, but may be in the range of 100 μm to 300 μm in average diameter. The height (H in FIG. 2) of the protrusions 21 is not particularly limited, but may be in the range of 50 nm to 3 μm in average height, or in the range of 0.5 μm to 1.5 μm in average height. When the average diameter and average height of the protrusions 21 are within the above ranges, gaps through which the electrolyte solution 50 can penetrate can be more stably formed between the separator 20 and the negative electrode layer 30.

[0032] The interval (L in FIG. 2) between adjacent protrusions 21 is not particularly limited, but may be within a range of 100 μm or more and 1 mm or less on average. The interval between protrusions 21 is the distance between one protrusion 21 and the nearest protrusion 21 to that protrusion 21. When the average interval between protrusions 21 is within the above range, a gap through which the electrolyte solution 50 can permeate can be more stably formed between the separator 20 and the negative electrode layer 30.

[0033] The area occupation ratio of the protrusions 21 is not particularly limited, but may be within a range of 5% to 10%. The area occupation ratio of the protrusions 21 is the percentage of the area occupied by the protrusions 21 with respect to the surface area of ​​the separator 20. When the area occupation ratio of the protrusions 21 is within the above range, it is possible to form gaps that allow easy penetration of the electrolyte solution while maintaining lithium ion conductivity between the separator 20 and the negative electrode layer 30.

[0034] The average diameter, average height, average spacing and area occupancy of the protrusions 21 can be measured by observing the surface of the separator 20 with an SEM (scanning electron microscope).

[0035] The material of the protrusions 21 is not particularly limited, and for example, resin, metal, carbon, or ceramic can be used. Examples of resin include PVDF, polyethylene (PE), polypropylene (PP), polyethylene glycol (PEG), polyethylene oxide (PEO), and acrylic resin. The resin may be one that gradually dissolves in the electrolyte solution 50. As the protrusions 21 dissolve, the distance between the separator 20 and the negative electrode layer 30 becomes constant. After the negative electrode layer 30 is sufficiently wetted with the electrolyte solution 50, the lithium metal secondary battery 100 may be temporarily heated to promote the dissolution of the protrusions 21. The material of the protrusions 21 may be the same as the material of the functional layer 25.

[0036] For example, sputtering or coating can be used as a method for forming the protrusions 21 on the separator 20. The coating method is a method in which a dispersion liquid in which material particles of the protrusions 21 are dispersed is applied in a pattern to the surface of the separator 20 and then dried. For example, a gravure method can be used as a method for applying the dispersion liquid.

[0037] The negative electrode layer 30 is a lithium-containing metal layer. The lithium-containing metal layer is made of elemental lithium or a lithium alloy. The lithium alloy includes a metal that forms an alloy with lithium. Examples of metals that form an alloy with lithium include Mg, Au, Ag, In, Ge, Sn, Pb, Al, and Zn.

[0038] The electrolytic solution 50 includes an organic solvent and an electrolyte. Examples of the organic solvent include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, hydrofluoroethers, aromatic ethers, sulfones, cyclic esters, chain carboxylic acid esters, and nitriles. Examples of the cyclic carbonates include ethylene carbonate, propylene carbonate, vinylene carbonate, and fluoroethylene carbonate. Examples of the chain carbonates include dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 4-methyl-1,3-dioxolane. Examples of the 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.

[0039] 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 may be, for example, within a range of 1.0 to 4.0 mol / L, or within a range of 1.0 to 2.5 mol / L.

[0040] The aging method for the lithium metal secondary battery 100 of this embodiment includes, for example, a step of leaving the lithium metal secondary battery 100 stationary and allowing the electrolyte solution 50 to penetrate between the separator 20 and the negative electrode layer 30 (hereinafter, this step may be referred to as a standing step), and an initial charging step of charging the lithium metal secondary battery 100 after the standing step.

[0041] In the standing step, it is preferable to position the lithium metal secondary battery 100 so that the surface of the separator 20 is aligned with the direction of gravity, i.e., so that the stacking direction of the electrode stack 40 is perpendicular to the direction of gravity. When the lithium metal secondary battery 100 is left standing in this position, the electrolyte solution 50 accumulates below the direction of gravity of the lithium metal secondary battery 100. When the separator 20 comes into contact with the electrolyte solution 50 accumulated below the direction of gravity, the electrolyte solution 50 penetrates between the separator 20 and the negative electrode layer 30 through gaps formed by the protrusions 21 due to capillary action. This shortens the penetration time until the electrolyte solution 50 sufficiently penetrates between the separator 20 and the negative electrode layer 30.

[0042] In the standing step, a load may be applied in the stacking direction of the electrode stack 40 of the lithium metal secondary battery 100. The applied load may be, for example, in the range of 0.001 MPa or more and 0.05 MPa or less. The time for leaving the lithium metal secondary battery 100 in the standing step may be, for example, 5 hours or less.

[0043] In the initial charging step, similar to the standing step described above, the lithium metal secondary battery 100 is positioned so that the surface of the separator 20 is aligned with the direction of gravity. By performing the initial charging with the lithium metal secondary battery 100 positioned in this manner, the separator 20 comes into contact with the electrolyte solution 50 pooled downward in the direction of gravity, which facilitates the electrolyte solution 50 permeating between the separator 20 and the negative electrode layer 30 through the gaps formed by the protrusions 21 due to capillary action. This increases the amount of electrolyte solution 50 between the separator 20 and the negative electrode layer 30. This allows for a high charge rate in the initial charging step. The charge rate may be, for example, in the range of 0.05 C or more and 0.3 C or less.

[0044] In the initial charging step, a load may be applied in the stacking direction of the electrode stack 40 of the lithium metal secondary battery 100. By applying a load, the internal resistance of the lithium metal secondary battery 100 decreases, and therefore the charge rate can be increased. The applied load may be, for example, in the range of 0.001 MPa or more and 1.00 MPa or less.

[0045] In the lithium metal secondary battery 100 of this embodiment configured as described above, the convex portions 21 are disposed on the surface of the separator 20 facing the negative electrode layer 30. The convex portions 21 form gaps between the separator 20 and the negative electrode layer 30, facilitating penetration of the electrolyte solution 50 between the separator 20 and the negative electrode layer 30. This shortens the time it takes for the electrolyte solution 50 to fully penetrate between the separator 20 and the negative electrode layer 30 immediately after the lithium metal secondary battery 100 is manufactured. This shortens the aging time. Furthermore, the convex portions formed on the surface of the separator 20 facing the negative electrode layer 30 enhance the wettability of the negative electrode layer 30. Even after lithium ions are deposited on the negative electrode layer 30 during charging, the gaps formed between the separator 20 and the negative electrode layer 30 are maintained. This improves discharge characteristics. Furthermore, the lithium metal secondary battery 100 of this embodiment has a functional layer 25 on the surface facing the negative electrode layer 30, further improving the characteristics of the lithium metal secondary battery 100.

[0046] According to the aging method for the lithium metal secondary battery 100 of this embodiment, the lithium metal secondary battery 100 of this embodiment is arranged so that the surface of the separator 20 is aligned with the direction of gravity, which makes it easier for the electrolyte solution 50 to permeate between the separator 20 and the negative electrode layer 30. This shortens the permeation time of the electrolyte solution 50. Furthermore, the amount of electrolyte solution 50 between the separator 20 and the negative electrode layer 30 increases. This makes it possible to increase the charge rate in the initial charge step. Therefore, according to the aging method for the lithium metal secondary battery 100 of this embodiment, the aging time can be shortened.

[0047] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. For example, in the lithium metal secondary battery 100 of this embodiment, the protrusions 21 are disposed on the separator 20, but the position of the protrusions 21 is not limited thereto. The protrusions 21 may be disposed on the surface of the negative electrode layer 30 facing the separator 20.

[0048] In the aging method for the lithium metal secondary battery 100 of this embodiment, a standing step is performed, but if the electrolyte solution 50 has sufficiently penetrated between the separator 20 and the negative electrode layer 30 immediately after the production of the lithium metal secondary battery 100, the standing step may be omitted. [Example]

[0049] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the contents of the following examples.

[0050] [Example 1] (Fabrication of separator with convex portions) A polyolefin porous separator and a resin particle dispersion in which resin particles were dispersed in a solvent were prepared. The surface of the porous separator was corona-treated. The resin particle dispersion was pattern-coated on the corona-treated porous separator surface using a gravure method, and then dried to produce a separator with protrusions.

[0051] (Preparation of positive electrode) Acetylene black (AB) as an electron conductive material, polyvinylidene fluoride (PVDF) as a binder, and polyvinylpyrrolidone (PVP) as a dispersant 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 resulting 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. The resulting positive electrode paste was then applied to an aluminum 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 resulting positive electrode plate was punched out to a size of 30 mm x 40 mm to form a positive electrode.

[0052] (Preparation of negative electrode) A 10 μm thick copper foil (negative electrode current collector, electrical conductivity: 6.5 × 10 6 A clad material was prepared by bonding a 20 μm-thick lithium foil (negative electrode layer) to a 100 μm-thick aluminum foil (sintered body / cm). This clad material was punched out to a size of 34 mm × 44 mm to form a negative electrode.

[0053] (Preparation of electrolyte) An electrolyte solution was prepared by dissolving LiFSI in 1,2-dimethoxyethane (DME) at a concentration of 4 mol / L.

[0054] (Fabrication of lithium metal secondary batteries) The convex surface of the separator with convex portions was placed on the negative electrode layer (lithium foil) of the negative electrode, and the positive electrode mixture layer of the positive electrode was placed on the surface opposite the convex portion of the separator 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.

[0055] [Examples 2 and 3] A lithium metal secondary battery was fabricated in the same manner as in Example 1, except that the acrylic resin particle dispersion was applied in a different pattern.

[0056] [Example 4] A lithium metal secondary battery was fabricated in the same manner as in Example 1, except that a separator with convex portions having a functional layer was used as the separator with convex portions. The separator with convex portions having a functional layer was fabricated as follows.

[0057] A 0.08 μm thick conductive porous copper layer was formed on one surface of a polyolefin porous separator by RF sputtering. The surface of the conductive porous copper layer was then corona treated, and a resin particle dispersion was pattern-coated onto the layer by gravure coating, followed by drying.

[0058] [Comparative Example 1] A lithium metal secondary battery was fabricated in the same manner as in Example 1, except that a commercially available separator was used instead of the separator with convex portions.

[0059] [evaluation] (separator) (Evaluation of the properties of the convex parts of a separator with convex parts) The surfaces of the separators with protrusions produced in Examples 1 to 4 were observed using an SEM to measure the average diameter, average height, average spacing, and area occupancy. The results are shown in Table 1 below. The average diameter, average height, and average spacing are values ​​measured for 100 protrusions.

[0060] [Table 1]

[0061] (Aging evaluation) The lithium metal secondary batteries fabricated in Examples 1 to 4 and Comparative Example 1 were subjected to a standing step and an initial charging step under the conditions shown in Table 2 below. In the initial charging step, charging was performed at 0.1 C to 4.30 V. Comparative Examples 1-1, 1-2, and 1-3 use the lithium metal secondary battery fabricated in Comparative Example 1, but the conditions for the standing step and the initial charging step were changed. Reference Example 1 uses the lithium metal secondary battery fabricated in Example 4, but the conditions for the standing step and the initial charging step were changed. In Table 2, the "vertical" battery arrangement means that the lithium metal secondary battery was arranged so that the surface of the separator was aligned with the direction of gravity, and the "horizontal" battery arrangement means that the lithium metal secondary battery was arranged so that the surface of the separator was perpendicular to the direction of gravity. Aging evaluation was performed on 56 lithium metal secondary batteries.

[0062] The OCV (circuit voltage) of the lithium metal secondary battery after the initial charging step was measured and its coefficient of variation was calculated. The results are shown in Table 2. The OCV coefficient of variation is preferably 0.30% or less.

[0063] For the lithium metal secondary batteries after the initial charging process, those whose post-aging voltage dropped to around 1.9 V after 6 hours were deemed defective, and all others were deemed good. The yield ratio was calculated as the percentage of good batteries out of the total number of lithium metal secondary batteries that underwent aging evaluation. The results are shown in Table 2. The yield ratio is preferably 0.9 or higher.

[0064] The lithium metal secondary battery after the initial charging step was discharged to 2.65 V at a discharge rate of 1 C. The ratio of the discharge capacity to the charge capacity in the initial charging step was calculated and used as the initial capacity. The results are shown in Table 2.

[0065] [Table 2]

[0066] The results in Table 2 confirm that in Examples 1 to 4, in which lithium metal secondary batteries with convex portions arranged on the surface of the separator facing the negative electrode layer were aged while being positioned so that the surface of the separator was perpendicular to the direction of gravity, the aged batteries had a low coefficient of variation of OCV and high yield ratios and initial capacities, even when the battery was left standing for a short period of 5 hours during the standing process. In contrast, for lithium metal secondary batteries using a separator without convex portions, when the battery was left standing for a long period of 48 hours during the standing process, the aged batteries had a low coefficient of variation of OCV and high yield ratios and initial capacities, similar to Examples 1 to 4 (Comparative Example 1-1). However, when the battery was left standing for a short period of 5 hours during the standing process, the aged batteries had an increased coefficient of variation of OCV and low yield ratios (Comparative Examples 1-2 and 1-3). This was due to insufficient penetration of the electrolyte between the separator and the negative electrode layer. Furthermore, even in the case of a lithium metal secondary battery in which a convex portion is arranged on the surface of the negative electrode layer side of the separator, if the separator surface is arranged perpendicular to the direction of gravity and the battery is left standing for 5 hours in the standing process, it was confirmed that the OCV coefficient of variation of the battery after aging increases and the yield ratio decreases (Reference Example 1). [Explanation of symbols]

[0067] 10 Positive electrode layer 20 Separator 21 Convex part 25 Functional Layers 30 negative electrode layer 40 Electrode laminate 50 Electrolyte 100 Lithium metal secondary battery

Claims

1. an electrode stack in which a positive electrode layer, a separator, and a negative electrode layer are stacked in this order; and an electrolyte solution; The negative electrode layer is a lithium-containing metal layer, A lithium metal secondary battery, wherein a plurality of protrusions are arranged on the surface of the separator facing the negative electrode layer or on the surface of the negative electrode layer facing the separator.

2. 2. The lithium metal secondary battery according to claim 1, wherein the convex portion is disposed on a surface of the separator facing the negative electrode layer.

3. 3. The lithium metal secondary battery according to claim 2, wherein the separator has a functional layer on a surface thereof facing the negative electrode layer, and the protrusions are disposed on the surface of the functional layer.

4. 3. The lithium metal secondary battery according to claim 1, wherein the projections have an average diameter in the range of 100 μm to 300 μm and an average height in the range of 0.5 μm to 1.5 μm.

5. 3. The lithium metal secondary battery according to claim 1, wherein the average distance between adjacent projections is in the range of 100 μm to 1 mm.

6. 3. The lithium metal secondary battery according to claim 1, wherein the area occupancy of the protrusions is in the range of 5% to 10%.

7. 3. A method for aging a lithium metal secondary battery according to claim 1 or 2, comprising: A method for aging a lithium metal secondary battery, comprising the step of charging the lithium metal secondary battery in a state where the surface of the separator is aligned with the direction of gravity.

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