Lithium secondary battery and method for manufacturing lithium secondary battery

Abstract

The present invention addresses the problem of providing a means for enhancing rapid charging performance in a lithium-deposition-type lithium secondary battery comprising a negative electrode intermediate layer. The above problem that the present invention addresses is resolved by providing, to at least a portion of the negative electrode intermediate layer, a recess part that is recessed from a solid electrolyte layer side to a negative electrode current collector side.

Description

Lithium secondary battery and method of manufacturing the same

[0001] The present invention relates to a lithium secondary battery and a method for manufacturing a lithium secondary battery.

[0002] In recent years, research and development of all-solid-state lithium secondary batteries using oxide- or sulfide-based solid electrolytes has been actively pursued. Solid electrolytes are materials primarily composed of ionic conductors capable of ion conduction in a solid state. Therefore, all-solid-state lithium secondary batteries have the advantage that, in principle, they do not encounter the various problems associated with flammable organic electrolytes that are common in conventional liquid-based lithium secondary batteries. Furthermore, the use of high-potential, high-capacity positive electrode materials and high-capacity negative electrode materials generally leads to significant improvements in the battery's power density and energy density.

[0003] One type of all-solid-state lithium secondary battery is known as a so-called lithium deposition type, in which lithium metal is deposited on a negative electrode current collector during charging. In such lithium deposition type all-solid-state lithium secondary batteries, ionization of lithium metal during discharging causes voids in the lithium metal, which can lead to a decrease in discharge capacity. Therefore, in lithium deposition type all-solid-state lithium secondary batteries, a restraining pressure is generally applied in the stacking direction to suppress the generation of voids.

[0004] Japanese Patent Application Publication No. 2020-191202 (corresponding to the specification of U.S. Patent Application Publication No. 2020 / 0373609) discloses a technology in which an Ag-containing anode active material layer (anode intermediate layer) is provided between an anode current collector and a solid electrolyte layer. By adopting such a configuration, Li precipitates as a Li(Ag) alloy containing Ag as a solid solution during the charging process. Furthermore, during the discharging process, only Li dissolves from the Li(Ag) alloy, leaving the Ag that was solid-solved, which is believed to suppress the occurrence of voids.

[0005] However, the inventors have conducted research and found that a lithium deposition type lithium secondary battery having a negative electrode intermediate layer may not provide sufficient rapid charging performance.

[0006] Therefore, an object of the present invention is to provide a means for improving the rapid charging performance of a lithium deposition type lithium secondary battery having a negative electrode intermediate layer.

[0007] The present inventors have conducted extensive research in light of the above-described problems and have found that the above-described problems can be solved by providing a recess in at least a part of the negative electrode intermediate layer that is recessed from the solid electrolyte layer side toward the negative electrode current collector side, thereby completing the present invention.

[0008] That is, one aspect of the present invention relates to a lithium secondary battery including a power generating element in which a positive electrode having a positive electrode active material layer containing a positive electrode active material, a solid electrolyte layer containing a solid electrolyte, and a negative electrode having an anode current collector and an anode intermediate layer formed on the surface of the anode current collector facing the solid electrolyte layer, and in which lithium metal precipitates during charging, are stacked in this order. The lithium secondary battery is characterized in that the anode intermediate layer has a first recess that is recessed from the solid electrolyte layer side toward the anode current collector side.

[0009] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (stacked-type secondary battery) according to one embodiment of the present invention. FIG. 2A is an enlarged cross-sectional view of a cell layer of a stacked-type secondary battery according to one embodiment of the present invention. FIG. 2A corresponds to the configuration of the evaluation cell produced in Example 1. FIG. 2B is a cross-sectional view for illustrating lithium deposition in the cell layer shown in FIG. 2A. FIG. 3 is an enlarged cross-sectional view of a cell layer illustrating a modified stacked-type secondary battery according to the present invention. FIG. 3 corresponds to the configuration of the evaluation cell produced in Example 2. FIG. 4A is an enlarged cross-sectional view of a cell layer illustrating a modified stacked-type secondary battery according to the present invention. FIG. 4A corresponds to the configuration of the evaluation cell produced in Example 3. FIG. 4B is an enlarged plan view of a negative electrode intermediate layer in the modified example shown in FIG. 4A. FIG. 5 is an enlarged cross-sectional view of a cell layer illustrating a modified stacked-type secondary battery according to the present invention. FIG. 5 corresponds to the configuration of the evaluation cell produced in Example 4. FIG. 6 is an enlarged cross-sectional view of a cell layer illustrating a modified stacked-type secondary battery according to the present invention. FIG. 6 corresponds to the configuration of the evaluation cell produced in Example 5. FIG. 7 is an enlarged cross-sectional view of a cell layer showing a modified example of a stacked secondary battery according to the present invention. FIG. 7 corresponds to the configuration of the evaluation cell produced in Example 6. FIG. 8 is an enlarged cross-sectional view of a cell layer showing a modified example of a stacked secondary battery according to the present invention. FIG. 8 corresponds to the configuration of the evaluation cell produced in Example 7. FIG. 9 is an enlarged cross-sectional view of a cell layer showing a modified example of a stacked secondary battery according to the present invention. FIG. 9 corresponds to the configuration of the evaluation cell produced in Example 8. FIG. 10 is an enlarged cross-sectional view of a cell layer showing an example of a stacked secondary battery not according to the present invention. FIG. 10 corresponds to the configuration of the evaluation cell produced in Comparative Example 1.

[0010] One aspect of the present invention is a lithium secondary battery including a power generating element in which a positive electrode having a positive electrode active material layer containing a positive electrode active material, a solid electrolyte layer containing a solid electrolyte, and a negative electrode current collector and a negative electrode having a negative electrode intermediate layer formed on a surface of the negative electrode current collector facing the solid electrolyte layer, the negative electrode intermediate layer having a first recess recessed from the solid electrolyte layer side toward the negative electrode current collector. This aspect enables improved rapid charging performance in a lithium deposition-type lithium secondary battery including a negative electrode intermediate layer.

[0011] Hereinafter, a lithium secondary battery according to one embodiment of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and duplicated explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the sake of explanation and may differ from the actual proportions.

[0012] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. FIG. 1 shows a cross section of the stacked-type secondary battery during charging. The stacked-type secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular power generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior. The power generating element 21 has a structure in which a negative electrode, a solid electrolyte layer 17, and a positive electrode are stacked. The negative electrode has a structure in which a negative electrode current collector 11′ and a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11′ are stacked. A negative electrode intermediate layer 14 is disposed so as to contact the negative electrode active material layer 13 and the solid electrolyte layer 17, respectively. The negative electrode intermediate layer 14 has a first recess (not shown) recessed from the solid electrolyte layer 17 side toward the negative electrode current collector 11′ side. The positive electrode has a structure in which a positive electrode active material layer 15 is disposed on the surface of a positive electrode current collector 11". As a result, the negative electrode current collector 11', the negative electrode active material layer 13, the negative electrode intermediate layer 14, the solid electrolyte layer 17, the positive electrode active material layer 15, and the positive electrode current collector 11" constitute one unit cell layer 19. Therefore, it can be said that the stacked secondary battery 10a shown in FIG. 1 has a structure in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel. A negative electrode current collector 25 and a positive electrode current collector 27 that are electrically connected to the respective electrodes (negative and positive electrodes) are attached to the negative electrode current collector 11′ and the positive electrode current collector 11″, respectively, and are configured to be sandwiched between the ends of the laminate film 29 and extend to the outside of the laminate film 29. A restraining pressure is applied to the stacked secondary battery 10a in the stacking direction of the power generating element 21 by a pressure member (not shown). Therefore, the volume of the power generating element 21 is kept constant.

[0013] FIG. 2A is an enlarged cross-sectional view of a cell layer 19 of a stacked secondary battery according to one embodiment of the present invention. As shown in FIG. 2A , the cell layer 19 constituting the stacked secondary battery 10 a according to this embodiment has a positive electrode composed of a positive electrode current collector 11″ and a positive electrode active material layer 15 disposed on the surface thereof. A solid electrolyte layer 17 containing a solid electrolyte is disposed on the surface of the positive electrode active material layer 15 opposite the positive electrode current collector 11″. A negative electrode composed of a negative electrode current collector 11′ and a negative electrode intermediate layer 14 disposed on the surface thereof is disposed on the surface of the solid electrolyte layer 17 opposite the positive electrode active material layer 15 such that the solid electrolyte layer 17 and the negative electrode intermediate layer 14 are in contact with each other. Note that FIG. 2A shows a cross section of the stacked secondary battery in a fully discharged state, and the negative electrode active material layer 13 is not present in the negative electrode. In the embodiment shown in FIG. 2A , the negative electrode intermediate layer 14 has a first recess recessed from the solid electrolyte layer 17 side toward the negative electrode current collector 11′ side. A gap H exists between the first recess and the solid electrolyte layer 17. In this specification, the term "first recess" refers to a region in the negative electrode intermediate layer that is thinner than the average thickness of the outer peripheral edge, and has an area of ​​0.001 mm when the power generating element is viewed in plan from the stacking direction. ２ or more. Furthermore, the "flat portion" refers to a region other than the recessed portion or the protruding portion described below. The thickness of the negative electrode intermediate layer at the outer peripheral edge may vary slightly, but is preferably substantially uniform, and uniformity is preferred. "Substantially uniform" refers to a thickness error from the average thickness being within a range of ±5%. With this configuration, the stress due to the restraining pressure in the stacking direction is reduced in the first recessed portion, thereby reducing the lithium diffusion resistance. This reduces the lithium diffusion resistance throughout the cell, and as a result, the rapid charging performance can be improved.

[0014] The mechanism by which the lithium secondary battery according to the present embodiment exhibits the above-described effects is not completely clear, and without being bound by any theory, the following mechanism is speculated. The lithium secondary battery according to the present embodiment is a so-called lithium deposition type in which lithium metal is deposited on the negative electrode current collector during the charging process. In such lithium deposition type lithium secondary batteries, it is known that the lithium metal deposited during the charging process ionizes during the discharging process, causing voids in the lithium metal, which can cause a decrease in discharge capacity. Therefore, in order to suppress the formation of such voids, a confining pressure is generally applied in the stacking direction of the battery in lithium deposition type lithium secondary batteries. The first recesses in the negative electrode intermediate layer experience low stress due to the confining pressure, which makes it easy for gaps to form at the interface between the solid electrolyte and the negative electrode intermediate layer, resulting in high lithium reaction resistance. On the other hand, the flat portions without irregularities experience high stress compared to the first recesses, which provides good contact at the interface between the solid electrolyte and the negative electrode intermediate layer, resulting in low lithium reaction resistance. Therefore, as shown in FIG. 2B , it is presumed that in the initial stage of lithium deposition, lithium is first deposited on the flat portion, and then lithium deposition proceeds from the lithium deposited on the flat portion toward the first recess. When the present inventors analyzed the cell resistance using electrochemical impedance spectroscopy (EIS), they found no difference in the resistance component related to the lithium reaction resistance throughout the cell between cases where the first recess was provided and cases where the first recess was not provided. On the other hand, it was found that the lithium diffusion resistance throughout the cell was significantly reduced when the first recess was provided. This is presumably because, when lithium deposition proceeds from the lithium deposited on the flat portion during the initial stage of lithium deposition, the horizontal lithium diffusion resistance toward the first recess, where stress is low, is reduced. Thus, it is presumed that, in the lithium secondary battery according to this embodiment, the provision of the first recess reduces the lithium diffusion resistance throughout the cell, resulting in improved rapid charging performance.

[0015] The main components of the lithium secondary battery according to this embodiment will be described below.

[0016] [Current Collector] The current collector (negative electrode current collector, positive electrode current collector) has the function of mediating the movement of electrons from the electrode active material layer (negative electrode active material layer, positive electrode active material layer). There are no particular restrictions on the material that constitutes the current collector. Examples of materials that can be used for the current collector include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular restrictions on the thickness of the current collector, but an example is 10 to 100 μm.

[0017] [Negative Electrode Active Material Layer] The lithium secondary battery according to this embodiment is a so-called lithium deposition type in which lithium metal is deposited on the negative electrode current collector during the charging process. The layer of lithium metal deposited on the negative electrode current collector during this charging process is the negative electrode active material layer of the lithium secondary battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and the thickness of the negative electrode active material layer decreases as the discharging process progresses. Although the negative electrode active material layer does not need to be present during full discharge, in some cases, a negative electrode active material layer composed of a certain amount of lithium metal may be present during full discharge. Furthermore, the thickness of the negative electrode active material layer (lithium metal layer) during full charge is not particularly limited, but is typically 0.1 to 1000 μm.

[0018] [Negative Electrode Intermediate Layer] The negative electrode intermediate layer is a layer interposed between the negative electrode current collector and the solid electrolyte layer, and typically contains a carbon material and / or a metal material and a binder. By providing such a negative electrode intermediate layer, the precipitation and growth of lithium dendrites are suppressed. The negative electrode intermediate layer as a whole is preferably conductive. The volume resistivity of the negative electrode intermediate layer is not particularly limited, but is preferably 10 ２ In this specification, the volume resistivity of the negative electrode intermediate layer is a value measured using an electrode resistance measurement system (manufactured by Hioki E.E. Corporation, product name: RM2610).

[0019] The negative electrode intermediate layer preferably contains a carbon material. By containing the carbon material in the negative electrode intermediate layer, the precipitation and growth of lithium dendrites can be suppressed. Specific examples of the carbon material include carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNT), graphite, hard carbon, etc. Among these, the carbon material preferably contains at least one selected from the group consisting of carbon black, and more preferably contains at least one selected from the group consisting of acetylene black, Ketjen Black (registered trademark), furnace black, channel black, and thermal lamp black.

[0020] The negative electrode intermediate layer preferably contains a metal material instead of or in addition to the carbon material. By including a metal material in the negative electrode intermediate layer, lithium metal can be more uniformly deposited on the current collector surface. Specific examples of metal materials include indium (In), aluminum (Al), silicon (Si), tin (Sn), magnesium (Mg), gold (Au), silver (Ag), zinc (Zn), nickel (Ni), copper (Cu), and alloys containing at least one of these. Among these, the metal material preferably contains at least one selected from the group consisting of In, Al, Si, Sn, Mg, Au, Ag, and Zn, more preferably at least one selected from the group consisting of Ag, Mg, Zn, and Al, even more preferably at least one selected from the group consisting of Ag, Mg, and Zn, and particularly preferably Ag.

[0021] The shapes of the carbon material and the metal material are not particularly limited, but are preferably particulate. The average primary particle size of the carbon particles is, for example, 200 nm or less, preferably 150 nm or less, more preferably 100 nm or less, even more preferably 80 nm or less, even more preferably 60 nm or less, even more preferably 50 nm or less, and particularly preferably 45 nm or less. The lower limit of the average primary particle size of the carbon particles is not particularly limited, but is preferably 10 nm or more, more preferably 20 nm or more, and even more preferably 25 nm or more. The average primary particle size of the metal particles is, for example, 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, and particularly preferably 80 nm or less. The lower limit of the average primary particle size of the metal particles is not particularly limited, but is, for example, 10 nm or more, preferably 20 nm or more, even more preferably 30 nm or more, and even more preferably 40 nm or more. When the average primary particle size of the carbon particles and / or the average primary particle size of the metal particles is within the above range, the rapid charging performance can be further improved. In this specification, the average primary particle size of the particles refers to the 50% cumulative diameter (D50) of the particle diameters of the particles observed in several to several tens of fields of view when the cross section of a layer containing the particles is observed with a scanning electron microscope (SEM) (the maximum distance among the distances between any two points on the outline of the observed particles).

[0022] When the negative electrode intermediate layer contains carbon particles and metal particles, the mass ratio of the carbon particles to the metal particles (carbon particles:metal particles) is preferably 10:1 to 1:1, more preferably 5:1 to 2:1, and even more preferably 4:1 to 2.5:1. The volume ratio of the carbon particles to the metal particles (carbon particles:metal particles) is preferably 99:1 to 70:30, and more preferably 95:5 to 75:25. When the compounding ratio (mass ratio or volume ratio) of the carbon particles to the metal particles is within the above range, rapid charging performance can be further improved.

[0023] The content of the carbon material and / or metal material in the negative electrode intermediate layer is not particularly limited, but is preferably 80 to 100 mass %, more preferably 82 to 99 mass %, and even more preferably 84 to 95 mass %, relative to 100 mass % of the total solid content in the negative electrode intermediate layer. When the content of the carbon material and / or metal material is within the above range, rapid charging performance can be further improved.

[0024] The negative electrode intermediate layer preferably contains a binder in addition to a carbon material and / or a metal material. The type of binder is not particularly limited, and binders known in the art can be appropriately used. Examples include styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), and carboxymethyl cellulose (CMC). Among these, styrene-butadiene rubber, tetrafluoroethylene, and polyvinylidene fluoride are preferred, and tetrafluoroethylene and polyvinylidene fluoride are more preferred. These binders may be used alone or in combination of two or more.

[0025] The content of the binder in the negative electrode intermediate layer is not particularly limited, but is preferably 8 to 20 mass %, more preferably 10 to 18 mass %, and even more preferably 12 to 16 mass %, relative to 100 mass % of the total solid content in the negative electrode intermediate layer. When the binder content is within the above range, rapid charging performance can be further improved.

[0026] The thickness of the negative electrode intermediate layer is preferably 1 μm to 20 μm, more preferably 1 μm to 15 μm, and even more preferably 1 μm to 10 μm. When the thickness of the negative electrode intermediate layer is within the above range, it is possible to prevent a decrease in charge / discharge capacity while suppressing the precipitation and growth of lithium dendrites.

[0027] The lithium secondary battery according to this embodiment is characterized in that the negative electrode intermediate layer has a first recess recessed from the solid electrolyte layer side toward the negative electrode current collector side. The shape of the first recess when the power generating element is viewed in plan from the stacking direction is not particularly limited and may be any shape, such as circular, elliptical, semicircular, semi-elliptical, triangular, rectangular, polygonal, or irregular. The inner wall surface of the first recess in the negative electrode intermediate layer may be configured parallel to the stacking direction, or may be a tapered surface widening from the bottom of the first recess toward the surface on the solid electrolyte side.

[0028] It is sufficient that at least one first recess is formed in the negative electrode intermediate layer. From the viewpoint of further improving the rapid charging performance, the number of first recesses is preferably 3 to 100, more preferably 5 to 70, and even more preferably 10 to 50.

[0029] The size of one first recess must be 0.001 mm. ２ The size of one first recess is 0.001 mm ２ If the size of each first recess is less than 0.005 mm, the effect of the present invention may not be sufficiently obtained. ２ It is preferable that the thickness is 0.01 mm or more. ２ More preferably, it is 0.015 mm or more. ２ More preferably, it is 0.15 mm or more. ２ The upper limit of the size of one first recess is not particularly limited, but from the viewpoint of maintaining the strength of the negative electrode intermediate layer, it is particularly preferred that the upper limit be 1 mm or more. ２ Preferably, it is 0.5 mm or less. ２ That is, according to a preferred embodiment of the present invention, the size of one first recess is 0.001 to 1 mm ２ It is preferable that the thickness is 0.005 to 1 mm. ２ More preferably, it is 0.01 to 1 mm ２ More preferably, it is 0.015 to 1 mm ２ It is particularly preferable that the thickness is 0.15 to 0.5 mm. ２When the size of the first recess is within the above range, the strength of the negative electrode intermediate layer can be maintained while the rapid charging performance can be further improved.

[0030] When the power generating element is viewed from above in the stacking direction, the ratio of the total area of ​​the first recesses in the negative electrode intermediate layer to the area surrounded by the outer peripheral edge of the negative electrode intermediate layer (100%) is preferably more than 0% and less than 50%, more preferably 0.05% to 45%, and even more preferably 0.1% to 40%. When the area ratio of the first recesses is within the above range, rapid charging performance can be further improved.

[0031] In the negative electrode intermediate layer, the ratio of the distance (depth) from the surface on the solid electrolyte side to the bottom of the first recess is preferably 25% or more, more preferably 50% or more, even more preferably 60% or more, particularly preferably 75% or more, and most preferably 90% or more, relative to 100% of the thickness of the negative electrode intermediate layer. When the ratio of the distance (depth) from the surface on the solid electrolyte side to the bottom of the first recess is within the above range, rapid charging performance can be further improved.

[0032] The first recess of the negative electrode intermediate layer preferably has a hole penetrating from the solid electrolyte layer side to the negative electrode current collector side in at least a portion thereof (FIG. 3). This configuration further reduces stress in the first recess, thereby further improving rapid charging performance.

[0033] In the negative electrode intermediate layer, the outer periphery of the first recess preferably has a first protrusion (14a in FIGS. 4A and 4B) protruding from the negative electrode current collector side toward the solid electrolyte layer side. Herein, the term "first protrusion" refers to a region in the negative electrode intermediate layer that is thicker than the average thickness of the outer periphery. Furthermore, the term "outer periphery of the first recess" refers to a range of 100 μm from the outer periphery of the first recess. This configuration further reduces the lithium diffusion resistance in the flat portion and the first recess, thereby further improving rapid charging performance. According to the mechanism described above, it is believed that the stress due to the restraining pressure in the stacking direction decreases in the order of the first protrusion, the flat portion, and the first recess. Therefore, in the initial stage of lithium deposition, lithium deposits first in the first protrusion. Lithium deposition begins at the first protrusion, and then proceeds to the flat portion and the first recess. It is presumed that rapid charging performance improves due to the reduced horizontal lithium diffusion resistance.

[0034] When the negative electrode intermediate layer has the first convex portion, the ratio of the maximum thickness to the minimum thickness at the outer periphery of the first concave portion is preferably 2 or more ( FIG. 5 ). This configuration further reduces the lithium diffusion resistance in the flat portion and the first concave portion, thereby further improving the rapid charging performance.

[0035] The first convex portions of the negative electrode intermediate layer preferably have a tapered shape ( FIG. 9 ). Here, the tapered shape may be a shape that widens from the solid electrolyte side to the negative electrode current collector side. This configuration increases the stress on the tip portions of the first convex portions, further reducing the lithium diffusion resistance in the flat portions and the first concave portions, thereby further improving the rapid charging performance.

[0036] When the negative electrode intermediate layer has first convex portions, it is preferable that second concave portions corresponding to the first convex portions of the negative electrode intermediate layer are formed in the solid electrolyte layer described below ( FIGS. 4A , 5 , and 9 ). This configuration improves ionic conductivity in the second concave portions, thereby further improving rapid charging performance.

[0037] In the above-described embodiments of FIGS. 2A , 3 , 4A , 5 , and 9 , voids H exist in the first recesses. However, embodiments in which the voids H are filled with a solid electrolyte layer, as described below, as in the embodiments shown in FIGS. 6 to 8 , are also preferred. That is, in a lithium secondary battery according to a preferred embodiment of the present invention, the solid electrolyte layer has second convex portions corresponding to the first recesses of the negative electrode intermediate layer. This configuration further reduces lithium diffusion resistance in the flat portions, thereby further improving rapid charging performance. The embodiment shown in FIG. 6 is similar to the embodiment shown in FIG. 2A except for the second convex portions corresponding to the first recesses of the negative electrode intermediate layer. The embodiment shown in FIG. 7 is similar to the embodiment shown in FIG. 5 except for the second convex portions corresponding to the first recesses of the negative electrode intermediate layer. The embodiment shown in FIG. 8 is similar to the embodiment shown in FIG. 7 except for the fact that the density of the flat portions (regions D1) of the solid electrolyte corresponding to the flat portions of the negative electrode intermediate layer is higher than the density of the second convex portions of the solid electrolyte. With this configuration, the lithium diffusion resistance in the flat portion is further reduced, and the rapid charging performance can be further improved.

[0038] [Solid Electrolyte Layer] The solid electrolyte layer is interposed between the negative electrode and the positive electrode and contains a solid electrolyte (usually as a main component). The solid electrolyte contained in the solid electrolyte layer is not particularly limited, and any solid electrolyte known in the art can be appropriately used. As an example, LPS (Li ２ S-P ２ S ５ ), Li ６ P.S. ５ X (wherein X is Cl, Br or I), Li ７ P ３ S １１ , Li ３．２ P ０．９６ S and Li ３ P.S. ４Examples of sulfide solid electrolytes include sulfide solid electrolytes such as those listed above. These sulfide solid electrolytes are preferably used because they have excellent lithium ion conductivity and a low bulk modulus, allowing them to follow the volume changes of the electrode active material that accompany charge and discharge. These solid electrolytes may be used alone or in combination of two or more. Of course, solid electrolytes other than those listed above may also be used.

[0039] The content of the solid electrolyte in the solid electrolyte layer is preferably 50% by mass or more and 100% by mass or less, and more preferably 90% by mass or more and 99% by mass or less.

[0040] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The binder that can be used in the solid electrolyte layer is the same as that described above for the negative electrode intermediate layer.

[0041] The thickness of the solid electrolyte layer varies depending on the intended configuration of the lithium secondary battery, but is usually 0.1 μm or more and 1000 μm or less, and preferably 10 μm or more and 40 μm or less.

[0042] [Positive Electrode Active Material Layer] The positive electrode active material layer essentially contains a positive electrode active material, and may contain a solid electrolyte, a binder, and / or a conductive additive as necessary. The positive electrode active material layer is typically disposed on the surface of a positive electrode current collector as shown in Figure 1. However, if the positive electrode active material layer 15 itself has a certain degree of conductivity, the positive electrode active material layer itself can constitute the positive electrode without using a positive electrode current collector.

[0043] The type of positive electrode active material contained in the positive electrode active material layer is not particularly limited, but a lithium-containing metal oxide is preferred. That is, according to a preferred embodiment of the present invention, the positive electrode active material contains at least one selected from lithium-containing metal oxides. According to a more preferred embodiment of the present invention, the positive electrode active material is composed of only at least one selected from lithium-containing metal oxides. A specific example of the lithium-containing metal oxide is LiCoO ２ , LiMnO ２ , LiNiO ２ , Li(Ni-Mn-Co)O ２Layered rock salt active materials such as LiMn ２ O ４ , LiNi ０．５ Mn １．５ O ４ Spinel-type active materials such as LiFePO ４ , LiMnPO ４ Olivine type active materials such as Li ２ FeSiO ４ , Li ２ MnSiO ４ Examples of oxide active materials other than those mentioned above include Si-containing active materials such as Li ４ Ti ５ O １２ , LiVO ２ Among them, Li(Ni-Mn-Co)O ２ Also, those in which part of these transition metals has been replaced with other elements (NMC composite oxides) are preferably used as the positive electrode active material.

[0044] In addition, a sulfur-based positive electrode active material is also a preferred embodiment. Examples of the sulfur-based positive electrode active material include organic sulfur compounds and inorganic sulfur compounds, and any material can be used as long as it can release lithium ions during charging and absorb lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur. In some cases, two or more types of positive electrode active materials may be used in combination.

[0045] These positive electrode active materials may be used alone or in combination of two or more. Of course, positive electrode active materials other than those mentioned above may also be used.

[0046] The shape of the positive electrode active material may be, for example, particulate (spherical, fibrous), thin film, etc. When the positive electrode active material is particulate, its average particle diameter (D ５０ ) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, even more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm. ５０ The value of can be measured by a laser diffraction scattering method.

[0047] The content of the positive electrode active material is not particularly limited, but from the viewpoint of energy density, it is, for example, 50% by mass or more and 99% by mass or less, preferably 70% by mass or more and 99% by mass or less, and more preferably 80% by mass or more and 99% by mass or less, relative to the total mass of the positive electrode active material layer.

[0048] The positive electrode active material layer may further contain a solid electrolyte, a binder, and / or a conductive additive in addition to the positive electrode active material. Here, the solid electrolyte that can be used in the positive electrode active material layer is the same as that described for the solid electrolyte layer above. The binder that can be used in the positive electrode active material layer is the same as that described for the negative electrode intermediate layer above. Examples of conductive additives include metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals, carbon fibers (specifically, vapor-grown carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNT), and carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), but are not limited thereto. Furthermore, a conductive additive can also be used in which particulate ceramic materials or resin materials are coated with the above-mentioned metal materials by plating or the like.

[0049] The thickness of the positive electrode active material layer varies depending on the configuration of the intended lithium secondary battery, but is, for example, 0.1 μm or more and 1000 μm or less, preferably 30 μm or more and 300 μm or less, more preferably 50 μm or more and 200 μm or less, and even more preferably 70 μm or more and 150 μm or less.

[0050] [Positive current collector plate and negative current collector plate] The material constituting the current collector plate (25, 27) is not particularly limited, and known highly conductive materials conventionally used as current collector plates for secondary batteries can be used. Metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferred as constituent materials of the current collector plate. From the viewpoints of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. The positive current collector plate 27 and the negative current collector plate 25 may be made of the same material or different materials.

[0051] [Positive Electrode Lead and Negative Electrode Lead] Although not shown in the drawings, the current collectors (11", 11') and the current collector plates (27, 25) may be electrically connected via a positive electrode lead or a negative electrode lead. As the constituent materials of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly adopted. Note that the portion removed from the exterior is preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like so as to prevent contact with peripheral devices or wiring, etc., causing electrical leakage and affecting products (for example, automobile parts, particularly electronic devices, etc.).

[0052] [Battery Exterior Material] As the battery exterior material, a known metal can case can be used. Alternatively, a bag-shaped case using an aluminum-containing laminate film 29 that can cover the power generating element as shown in FIG. 1 can be used. The laminate film can be, for example, a three-layer laminate film formed by laminating PP, aluminum, and nylon in this order, but is not limited thereto. A laminate film is desirable from the viewpoint of achieving high output and excellent cooling performance, making it suitable for use in batteries for large equipment such as EVs and HEVs. Furthermore, an aluminum-containing laminate film is more preferable as the exterior material because it allows for easy adjustment of the collective pressure applied to the power generating element from the outside.

[0053] The lithium secondary battery according to the present embodiment has a configuration in which a plurality of unit cell layers are connected in parallel, and therefore has high capacity and excellent cycle durability, and is therefore suitable for use as a driving power source for EVs and HEVs.

[0054] Although one embodiment of the lithium secondary battery of the present invention has been described above, the present invention is not limited to the configuration described in the above embodiment, and can be modified as appropriate based on the claims.

[0055] For example, the type of battery to which the lithium secondary battery according to the present invention is applied includes a bipolar battery including a bipolar electrode having a positive electrode active material layer electrically coupled to one surface of a current collector and a negative electrode active material layer electrically coupled to the opposite surface of the current collector.

[0056] Furthermore, the lithium secondary battery according to the present embodiment does not have to be an all-solid-state type. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolytic solution). There is no particular limitation on the amount of liquid electrolyte (electrolytic solution) that can be contained in the solid electrolyte layer, but it is preferably an amount that allows the shape of the solid electrolyte layer formed by the solid electrolyte to be maintained and prevents leakage of the liquid electrolyte (electrolytic solution).

[0057] <Method for manufacturing lithium secondary battery> According to another aspect of the present invention, there is provided a method for manufacturing a lithium secondary battery including a power generating element in which a positive electrode having a positive electrode active material layer containing a positive electrode active material, a solid electrolyte layer containing a solid electrolyte, and a negative electrode current collector and a negative electrode having a negative electrode intermediate layer formed on the surface of the negative electrode current collector facing the solid electrolyte layer, where lithium metal precipitates during charging, are stacked in this order. The method is characterized by comprising the steps of forming a negative electrode intermediate layer precursor 1 on the surface of a substrate (hereinafter also referred to as the "negative electrode intermediate layer precursor 1 forming step"), forming a first recess in the exposed surface of the negative electrode intermediate layer precursor 1 to form a negative electrode intermediate layer precursor 2 (hereinafter also referred to as the "negative electrode intermediate layer precursor 2 forming step"), and overlapping a solid electrolyte layer precursor on the exposed surface of the negative electrode intermediate layer precursor 2 and applying pressure in the stacking direction (hereinafter also referred to as the "negative electrode intermediate layer forming step").

[0058] Hereinafter, each step of the method for producing a lithium secondary battery according to this embodiment will be described.

[0059] [Step of Forming Negative Electrode Intermediate Layer Precursor 1] The substrate functions as a support when forming the negative electrode intermediate layer precursor 1. The substrate may also serve as a negative electrode current collector in a lithium secondary battery. When the substrate also serves as a negative electrode current collector, the materials described above in the section [Current Collector] can be used as the substrate.

[0060] A method for forming the negative electrode intermediate layer precursor 1 on the surface of the substrate includes coating the surface of the substrate with a negative electrode active material layer slurry in which materials constituting the negative electrode intermediate layer (carbon material and / or metal material and binder) are dispersed in a dispersion medium, and then drying the coating.

[0061] [Step of Forming Negative Electrode Intermediate Layer Precursor 2] The method for forming the first recess in the exposed surface of the negative electrode intermediate layer precursor 1 formed on the surface of the substrate is not particularly limited, but an example is a method of removing at least a portion of the negative electrode intermediate layer precursor 1 from the exposed surface by, for example, scratching the exposed surface with a pointed tool. In this case, by scratching until the substrate is exposed, the aforementioned hole can be provided in the first recess of the negative electrode intermediate layer. Alternatively, the first recess may be formed by pressing a hard member against the exposed surface and compressing it.

[0062] When the first recess is formed by removing at least a portion of the negative electrode intermediate layer precursor 1 from the exposed surface, it is preferable to form the first protrusion by placing the at least a portion on the outer periphery of the first recess, which makes it easy to form the first protrusion.

[0063] [Negative Electrode Intermediate Layer Forming Step] The solid electrolyte layer precursor can be formed by coating a solid electrolyte slurry, in which materials constituting the solid electrolyte layer (solid electrolyte and binder) are dispersed in a dispersion medium, onto the surface of a suitable support and drying the coating.

[0064] A solid electrolyte layer precursor is placed on the exposed surface of the anode intermediate layer precursor 2 having the first recess formed therein, and pressure is applied in the stacking direction. This allows a portion of the solid electrolyte layer precursor to fill the first recess, forming a second protrusion in the solid electrolyte layer that corresponds to the first recess of the anode intermediate layer. The density of the solid electrolyte layer can be controlled by changing the pressing method and pressing conditions when applying pressure in the stacking direction. More specifically, applying pressure using a cold isostatic press can make the density of the solid electrolyte layer uniform. Furthermore, applying pressure using a plate press can make the density of the solid electrolyte in the second protrusion (region D2 in FIG. 8 ) lower than the density of the solid electrolyte in the flat portion (region D1 in FIG. 8 ).

[0065] Alternatively, the solid electrolyte layer precursor may be pressed in advance and then placed on the exposed surface of the negative electrode intermediate layer precursor 2 on which the first recesses have been formed. This allows voids to be formed in the first recesses of the negative electrode intermediate layer.

[0066] When first convex portions are formed in the above-described negative electrode intermediate layer precursor 2 formation step, second concave portions corresponding to the first convex portions of the intermediate layer can be formed in the solid electrolyte layer by stacking the solid electrolyte layer precursors and applying pressure in the stacking direction.

[0067] The following embodiments are also included within the scope of the present invention: a lithium secondary battery according to claim 1 having the features of claim 2; a lithium secondary battery according to claim 1 or 2 having the features of claim 3; a lithium secondary battery according to any one of claims 1 to 3 having the features of claim 4; a lithium secondary battery according to any one of claims 1 to 4 having the features of claim 5; a lithium secondary battery according to any one of claims 1 to 5 having the features of claim 6; a lithium secondary battery according to claim 6 having the features of claim 7; a lithium secondary battery according to any one of claims 1 to 7 having the features of claim 8; a lithium secondary battery according to claim 6 having the features of claim 9; a lithium secondary battery according to claim 8 having the features of claim 10; and a lithium secondary battery according to claim 6 having the features of claim 11.

[0068] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. In the following, the preparation of the evaluation cell was carried out in a glove box in an argon atmosphere with a dew point of -68°C or less. In addition, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0069] <Example of Preparation of Evaluation Cell> [Example 1] (Preparation of Positive Electrode) NMC composite oxide (LiNi) ０．８ Mn ０．１ Co ０．１ O ２ ), carbon fiber as a conductive additive, and an argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５ Cl) were weighed out to a mass ratio of 85:15:5. These were mixed using an agate mortar and then further stirred and mixed using a planetary ball mill. 2 parts by mass of polytetrafluoroethylene (PTFE) as a binder was added to 100 parts by mass of the obtained mixed powder and mixed. The obtained mixture was layered on aluminum foil as a positive electrode current collector, pressed, and cut into a size of 21 mm × 21 mm, thereby obtaining a positive electrode having a positive electrode active material layer (thickness 100 μm) on the surface of the positive electrode current collector.

[0070] (Preparation of Solid Electrolyte Layer Precursor) Argyrodite-type sulfide solid electrolyte (Li ６ P.S. ５ A solid electrolyte slurry was prepared by adding 2 parts by mass of styrene butadiene rubber (SBR) as a binder to 100 parts by mass of ethylenediaminetetraacetic acid (ETA) (average particle diameter (D50): 0.8 μm), adding mesitylene as a solvent, and mixing the mixture. The solid electrolyte slurry was applied to the surface of a polyethylene terephthalate (PET) foil as a support, dried, and cut into a size of 25 mm × 25 mm to obtain a solid electrolyte layer precursor (thickness: 40 μm) formed on the surface of the support.

[0071] (Preparation of Negative Electrode Intermediate Layer) (1) Preparation of Negative Electrode Intermediate Layer Precursor Silver nanoparticles (average particle size (D50): 60 nm) and carbon black (DBP absorption: 175 mL / 100 g) were weighed and mixed to a mass ratio of Ag:C = 1:3. To 86 parts by mass of the resulting mixture, 14 parts by mass of polyvinylidene fluoride (PVDF) as a binder was added, and N-methyl-2-pyrrolidone (NMP) was added as a solvent and mixed to prepare a negative electrode intermediate layer slurry. The negative electrode intermediate layer slurry was applied to the surface of a stainless steel foil as a negative electrode current collector, dried, and cut into a size of 21 mm x 21 mm to obtain a negative electrode intermediate layer precursor (thickness 5 μm).

[0072] (2) Preparation of the Negative Electrode Intermediate Layer: The exposed surface of the negative electrode intermediate layer precursor opposite the surface in contact with the stainless steel foil (negative electrode current collector) was scratched with the tip corner of a spatula to peel off the surface layer of the exposed surface, and the peeled off portion was removed with tweezers. This resulted in the formation of first recesses, each of which had a semicircular shape with a diameter of 200 μm and a depth of 3 μm when viewed in plan from the stacking direction of the power generating element. Forty such first recesses were formed at approximately equal intervals on the exposed surface of the negative electrode intermediate layer, thereby obtaining a negative electrode intermediate layer formed on the surface of the stainless steel foil. The area of ​​the first recesses in the negative electrode intermediate layer was 0.142% of the 100% area surrounded by the outer periphery of the negative electrode intermediate layer.

[0073] (Preparation of Evaluation Cell) A cathode active material layer formed on the surface of an aluminum foil (cathode current collector) and a solid electrolyte layer precursor formed on the surface of a PET foil were stacked so that the exposed surface of the cathode active material layer and the exposed surface of the solid electrolyte layer precursor faced each other, and then bonded together by cold isostatic pressing (CIP; 700 MPa, 25°C, 1 minute). After peeling off the PET foil adjacent to the solid electrolyte layer precursor, the solid electrolyte layer precursor and a negative electrode intermediate layer formed on the surface of a stainless steel foil (anode current collector) were stacked so that the exposed surface of the solid electrolyte layer precursor and the exposed surface of the negative electrode intermediate layer faced each other, and then bonded together by cold isostatic pressing (CIP; 500 MPa, 80°C, 1 minute). Finally, a stainless steel positive electrode tab and a nickel negative electrode tab were joined to the aluminum foil (positive electrode current collector) and stainless steel foil (negative electrode current collector), respectively, using an ultrasonic welder. The resulting stack was placed inside an aluminum laminate film and vacuum-sealed to obtain an evaluation cell, which was a lithium deposition-type lithium secondary battery (Figure 2A).

[0074] [Example 2] The above "(2) Preparation of a Negative Electrode Intermediate Layer" was performed using the following method. The exposed surface of the negative electrode intermediate layer precursor opposite the surface in contact with the stainless steel foil was scratched with the tip corner of a spatula, and a portion of the negative electrode intermediate layer precursor was peeled off so as to penetrate from the exposed surface to the surface in contact with the stainless steel foil (negative electrode current collector). The peeled portion was then removed with tweezers. This resulted in the formation of first recesses (holes) that were semicircular in shape with a diameter of 200 μm and a depth of 5 μm when viewed in plan from the stacking direction of the power generating element. Forty such first recesses (holes) were formed at approximately equal intervals on the exposed surface of the negative electrode intermediate layer, thereby obtaining a negative electrode intermediate layer formed on the surface of the stainless steel foil. Except for this, the evaluation cell of this example was prepared using the same method as in Example 1 ( FIG. 3 ).

[0075] Example 3 The above-mentioned "(2) Preparation of a Negative Electrode Intermediate Layer" was performed using the following method. The exposed surface of the negative electrode intermediate layer precursor opposite the surface in contact with the stainless steel foil was scratched with the tip corner of a spatula, and a portion of the negative electrode intermediate layer precursor was peeled off so as to penetrate from the exposed surface to the surface in contact with the stainless steel foil (negative electrode current collector). The peeled portion was then removed with tweezers. This formed a first recess (hole) that had a semicircular shape with a diameter of 200 μm and a depth of 5 μm when viewed in plan from the stacking direction of the power generating element. Next, a protrusion was formed by placing the peeled portion on a portion of the outer periphery of the first recess (hole) so that it was in contact with a chord of the semicircle. Forty such pairs of first recesses (holes) and first protrusions were formed at approximately equal intervals on the exposed surface of the negative electrode intermediate layer, thereby obtaining a negative electrode intermediate layer formed on the surface of the stainless steel foil. Except for this, the evaluation cell of this example was produced using the same method as in Example 2. In the evaluation cell, the height of the first convex portion was 2.1 μm, and the ratio of the maximum thickness (7.1 μm) to the minimum thickness (5 μm) at the outer periphery of the first concave portion was 1.42 ( FIGS. 4A and 4B ).

[0076] [Example 4] An evaluation cell for this example was produced in the same manner as in Example 3 above (Production of evaluation cell), except that the cold isostatic pressing (CIP) conditions for bonding the exposed surface of the solid electrolyte layer precursor and the exposed surface of the negative electrode intermediate layer were 25°C, 100 MPa, and 1 minute. In the evaluation cell, the height of the first convex portion was 10 µm, and the ratio of the maximum thickness (15 µm) to the minimum thickness (5 µm) at the outer periphery of the first concave portion was 3 (Fig. 5).

[0077] [Example 5] An evaluation cell for this example was produced in the same manner as in Example 1, except that, in the above (production of an evaluation cell), the exposed surface of the positive electrode active material layer and the exposed surface of the solid electrolyte layer precursor were bonded together without CIP. In the evaluation cell, second protrusions (40 pieces, 3 μm high) corresponding to the first recesses (40 pieces, 3 μm deep) in the negative electrode intermediate layer were formed in the solid electrolyte layer ( FIG. 6 ).

[0078] Example 6 The above-mentioned "(2) Preparation of a Negative Electrode Intermediate Layer" was performed using the following method. The exposed surface of the negative electrode intermediate layer precursor opposite the surface in contact with the stainless steel foil (negative electrode current collector) was scratched with the tip corner of a spatula to peel off the surface of the exposed surface, and the peeled portion was removed with tweezers. This formed a first recess having a semicircular shape with a diameter of 200 μm and a depth of 3 μm when viewed in plan from the stacking direction of the power generating element. Next, a protrusion was formed by placing the peeled portion so that it contacted a portion of the outer periphery of the first recess (hole). Forty such pairs of first recesses (holes) and first protrusions were formed at approximately equal intervals on the exposed surface of the negative electrode intermediate layer, thereby obtaining a negative electrode intermediate layer formed on the surface of the stainless steel foil. Except for this, the evaluation cell of this example was prepared using the same method as in Example 5. In the evaluation cell, the solid electrolyte layer had 40 second protrusions (3 μm high) corresponding to the 40 first protrusions (3 μm deep) in the negative electrode intermediate layer, and 40 second protrusions (3.5 μm high) corresponding to the 40 first protrusions (3.5 μm high) in the negative electrode intermediate layer. The ratio of the maximum thickness (8.5 μm) to the minimum thickness (5 μm) at the outer periphery of the first protrusions was 1.7 ( FIG. 7 ).

[0079] [Example 7] An evaluation cell for this example was produced in the same manner as in Example 5 above (Production of evaluation cell), except that the exposed surface of the solid electrolyte layer precursor and the exposed surface of the negative electrode intermediate layer were bonded by plate pressing (500 MPa, 80°C, 1 minute) instead of CIP. In the evaluation cell, second convex portions (40 portions, 3 μm high) corresponding to the first concave portions (40 portions, 3 μm deep) of the negative electrode intermediate layer were formed in the solid electrolyte layer, and the density of the second convex portions was lower than the density of the flat portion ( FIG. 8 ).

[0080] [Example 8] After forming the first recesses (40) in the above "(2) Preparation of Negative Electrode Intermediate Layer," a laminate of stainless steel foil and a negative electrode intermediate layer precursor was subjected to cold isostatic pressing (CIP; 500 MPa, 80°C, 1 minute) to obtain a negative electrode intermediate layer with tapered first protrusions. Except for this, an evaluation cell for this example was prepared in the same manner as in Example 5. In the evaluation cell, the height of the first protrusions was 2.5 μm, and the ratio of the maximum thickness (7.5 μm) to the minimum thickness (5 μm) at the outer periphery of the first recesses was 1.5 ( FIG. 9 ).

[0081] [Comparative Example 1] An evaluation cell for this comparative example was produced in the same manner as in Example 1, except that the above "(2) Preparation of negative electrode intermediate layer" was not performed and the negative electrode intermediate layer precursor was used directly as the negative electrode intermediate layer (Fig. 10).

[0082] <Rapid Charge Test> (Conditioning Charge / Discharge) A positive electrode lead and a negative electrode lead were connected to the positive electrode current collector and the negative electrode current collector, respectively, of the evaluation cell (before the first charge) prepared above, and a conditioning charge / discharge was performed under the following conditions, followed by a rapid charge test. During this, the conditioning charge / discharge was performed while applying a restraining pressure of 3 MPa in the stacking direction of the evaluation cell using a pressure member.

[0083] (Conditioning charge / discharge conditions) Evaluation temperature: 333K (60°C) Voltage range: 2.5 to 4.25V Charging process (1): CC (cut off in 25 hours) Charging rate (1): 0.01C Charging process (2): CC (cut off at 4.25V) Charging rate (2): 0.05C Discharging process: CC Discharging rate: 0.1C (cut off at 2.5V) After charging and discharging, there was a 30-minute rest period.

[0084] The conditioning charge / discharge was performed using a charge / discharge tester, with the evaluation cell placed in a thermostatic chamber set to the evaluation temperature. During the charge process (1) (in which lithium metal precipitates on the negative electrode current collector), the cell was charged in constant current (CC) mode at 0.01 C for 25 hours. Then, during the charge process (2), the cell was charged in constant current (CC) mode at 0.05 C to 4.25 V. Then, during the discharge process (in which lithium metal dissolves on the negative electrode current collector), the cell was discharged in constant current (CC) mode at 0.1 C to 2.5 V. Here, 1 C refers to the current value at which the battery is fully charged (100% charged) after 1 hour of charging at that current value.

[0085] (Fast Charge Test) Evaluation temperature: 333K (60°C) Voltage range: 3.8 to 4.25V The fast charge test was performed using a charge / discharge tester, with the evaluation cell placed in a thermostatic chamber set to the above evaluation temperature. After CCCV charging to 15% SOC, CC charging was performed at 3.5C to the upper voltage limit. The charge capacity when CC charging was performed at 3.5C was measured and used as an index of fast charge performance. The results are shown in Table 1 below. Table 1 lists values ​​relative to the charge capacity value of Comparative Example 1, which is set to 100. The higher the charge capacity value, the better the fast charge performance.

[0086]

[0087] As shown in Table 1, according to the present invention, by providing a recess in the negative electrode intermediate layer that is recessed from the solid electrolyte layer side toward the negative electrode current collector side, it is possible to improve the rapid charging performance of a lithium deposition-type lithium secondary battery.

[0088] A comparison between Example 1 and Example 2 shows that rapid charging performance is further improved by providing holes in the first recesses that penetrate from the solid electrolyte layer side to the negative electrode current collector side. A comparison between Example 2 and Example 3 shows that rapid charging performance is further improved by providing first protrusions that protrude from the negative electrode current collector side to the solid electrolyte layer side on the outer periphery of the first recesses. A comparison between Example 3 and Example 4 shows that rapid charging performance is further improved by setting the ratio of the maximum thickness to the minimum thickness at the outer periphery of the first recesses to be 2 or more. A comparison between Example 1 and Example 5 shows that rapid charging performance is further improved by providing the solid electrolyte layer with second protrusions that correspond to the first recesses in the negative electrode intermediate layer. A comparison between Example 5 and Example 6 shows that rapid charging performance is further improved by providing the solid electrolyte layer with second protrusions that correspond to the first protrusions in the negative electrode intermediate layer. Comparing Example 1 with Example 8, it can be seen that rapid charging performance is further improved by providing a first convex portion that protrudes from the negative electrode current collector side toward the solid electrolyte layer side on the outer periphery of the first concave portion and by forming the first convex portion in a tapered shape.

[0089] REFERENCE SIGNS LIST 10a laminated secondary battery, 11' negative electrode current collector, 11" positive electrode current collector, 13 negative electrode active material layer, 14 negative electrode intermediate layer, 14a first convex portion, 15 positive electrode active material layer, 17 solid electrolyte layer, 17a second convex portion, 19 single cell layer, 21 power generating element, 25 negative electrode current collector, 27 positive electrode current collector, 29 laminate film H gap.

Claims

a positive electrode having a positive electrode active material layer containing a positive electrode active material; a solid electrolyte layer containing a solid electrolyte; and a negative electrode having a negative electrode current collector and a negative electrode intermediate layer formed on a surface of the negative electrode current collector facing the solid electrolyte layer, wherein lithium metal is deposited during charging; are stacked in this order, the negative electrode intermediate layer has a first recess recessed from the solid electrolyte layer side to the negative electrode current collector side.

2. The lithium secondary battery according to claim 1, wherein the negative electrode intermediate layer has a flat portion on which the first recessed portion or the first protruding portion protruding from the negative electrode current collector side toward the solid electrolyte layer side is not formed. 　 2 . The lithium secondary battery according to claim 1 , wherein a distance from a surface of the negative electrode intermediate layer facing the solid electrolyte to a bottom surface of the first recess is 25% or more relative to 100% of a thickness of the negative electrode intermediate layer. 　 2 . The lithium secondary battery according to claim 1 , wherein a distance from a surface of the negative electrode intermediate layer facing the solid electrolyte to a bottom surface of the first recess is 50% or more relative to 100% of a thickness of the negative electrode intermediate layer. 　 The lithium secondary battery according to claim 1 , wherein the negative electrode intermediate layer has a hole formed in at least a part of the first recess, the hole penetrating from the solid electrolyte layer side to the negative electrode current collector side. 　 The lithium secondary battery according to claim 1 , wherein the negative electrode intermediate layer has a first protrusion protruding from an outer periphery of the first recess toward the solid electrolyte layer from the negative electrode current collector side.

7. The lithium secondary battery according to claim 6, wherein the ratio of the maximum thickness to the minimum thickness at the outer periphery of the first recess is 2 or more. 　 The lithium secondary battery according to claim 1 , wherein the solid electrolyte layer has second convex portions corresponding to the first concave portions of the negative electrode intermediate layer. 　 The lithium secondary battery according to claim 6 , wherein the solid electrolyte layer has second recesses corresponding to the first protrusions of the negative electrode intermediate layer. 　 The lithium secondary battery according to claim 8 , wherein the density of the second protrusions is lower than the density of the flat portions in the solid electrolyte layer. 　 The lithium secondary battery according to claim 6 , wherein the first convex portion of the negative electrode intermediate layer has a tapered shape.

2. The lithium secondary battery according to claim 1, wherein, when the power-generating element is viewed in a plan view from the stacking direction, the total area of ​​the first recesses is greater than 0% and less than 50% of an area (100%) surrounded by the outer peripheral edge of the negative electrode intermediate layer. 　 a positive electrode having a positive electrode active material layer containing a positive electrode active material; a solid electrolyte layer containing a solid electrolyte; and a negative electrode having a negative electrode current collector and a negative electrode intermediate layer formed on a surface of the negative electrode current collector facing the solid electrolyte layer, wherein lithium metal is deposited during charging; a method for manufacturing a lithium secondary battery having a power generating element in which the above are stacked in this order, forming a negative electrode intermediate layer precursor 1 on the surface of a substrate; forming a first recess on an exposed surface of the negative electrode intermediate layer precursor (1) to form a negative electrode intermediate layer precursor (2); a solid electrolyte layer precursor is stacked on the exposed surface of the negative electrode intermediate layer precursor 2 and pressed in the stacking direction; The method for producing a lithium secondary battery comprising the steps of: 　 The first recess is formed by removing at least a portion of the negative electrode intermediate layer precursor 1 from an exposed surface, 14. The method for producing a lithium secondary battery according to claim 13, wherein after the at least a portion is placed on an outer periphery of the first recess to form a first protrusion, the solid electrolyte layer precursor is superimposed on an exposed surface of the negative electrode intermediate layer precursor 2 and pressed in the stacking direction.

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