Lithium secondary battery

Abstract

To provide means of reducing an internal resistance of a battery in a lithium secondary battery in which a lithium-containing alloy layer is disposed on a negative electrode.SOLUTION: A lithium secondary battery includes a power generation element including a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a lithium-containing alloy as a negative electrode active material disposed on a surface of a negative electrode current collector, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer and containing the solid electrolyte. The negative electrode active material layer includes a lithium-containing alloy layer containing a lithium-containing alloy having a substantially uniform composition. At least a part of the surface of the lithium-containing alloy layer on the solid electrolyte layer side is formed of the lithium-containing alloy, and the lithium-containing alloy layer has not yet been subjected to charge / discharge treatment.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery. [Background technology]

[0002] In recent years, much research and development has been done on lithium secondary batteries that use oxide- or sulfide-based solid electrolytes, which are materials primarily composed of ionic conductors that allow ions to be conducted in a solid state.

[0003] One type of lithium secondary battery is known in which an alloy layer made of an alloy of lithium and another metal is disposed between a solid electrolyte layer and a negative electrode current collector during battery manufacturing. For example, Patent Document 1 discloses a solid-state battery in which an aluminum layer in contact with the solid electrolyte layer, a lithium layer, and an aluminum-lithium alloy layer disposed between the aluminum layer and the lithium layer are disposed between the solid electrolyte layer and the negative electrode current collector. Patent Document 1 also discloses a method for manufacturing such a solid-state battery, in which a stack of a positive electrode layer, a solid electrolyte layer, an aluminum plate, and a lithium plate is laminated in this order using a roll press or the like. Patent Document 1 suggests that alloying occurs at the interface between the aluminum plate and the lithium plate during the pressure-welding of the stack, and that this alloying also progresses with repeated charge and discharge. This configuration is said to suppress the decrease in discharge capacity associated with repeated charge and discharge compared to when a powdered aluminum-lithium alloy is used for the negative electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 151376 Summary of the Invention [Problem to be solved by the invention]

[0005] However, according to the investigations of the present inventors, it has been found that in a lithium secondary battery having the configuration disclosed in Patent Document 1, the internal resistance of the battery may be high, and in particular, the reaction resistance of the metal (alloy) layer constituting the negative electrode may be high.

[0006] Therefore, an object of the present invention is to provide a means for reducing the internal resistance of a lithium secondary battery having a lithium-containing alloy layer disposed on the negative electrode. [Means for solving the problem]

[0007] The present inventors have conducted extensive research in view of the above-mentioned problems, and have found that the above-mentioned problems can be solved by including in the negative electrode a lithium-containing alloy layer containing a lithium-containing alloy having a substantially uniform composition before charge / discharge treatment of the battery, and by arranging the lithium-containing alloy layer so that at least a part of the lithium-containing alloy layer is in contact with the solid electrolyte layer, 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 having a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a lithium-containing alloy as a negative electrode active material disposed on the surface of a negative electrode current collector, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer and containing a solid electrolyte. The lithium secondary battery is characterized in that the negative electrode active material layer includes a lithium-containing alloy layer containing a lithium-containing alloy having a substantially uniform composition, and at least a portion of the surface of the lithium-containing alloy layer facing the solid electrolyte layer is made of the lithium-containing alloy, and the lithium secondary battery is in a state prior to charge / discharge treatment.

[0009] Another aspect of the present invention relates to a method for manufacturing a lithium secondary battery including a power generating element having a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a lithium-containing alloy as a negative electrode active material disposed on the surface of a negative electrode current collector, and a solid electrolyte layer containing a solid electrolyte interposed between the positive electrode active material layer and the negative electrode active material layer. The manufacturing method includes a pressurizing step of pressing the solid electrolyte layer, a first metal layer made of a metal capable of alloying with lithium, a lithium metal layer made of lithium metal, and a second metal layer made of a metal capable of alloying with lithium, in the stacking direction of the stack (1), to compress and bond the layers together, and is characterized in that at least a portion of the first metal layer is alloyed with lithium up to the surface facing the solid electrolyte layer by the pressurizing step. [Effects of the Invention]

[0010] According to the present invention, in a lithium secondary battery having a lithium-containing alloy layer disposed on the negative electrode, the internal resistance of the battery can be reduced. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view that schematically illustrates the overall structure of a stacked-type (internal parallel connection type) lithium secondary battery (stacked-type secondary battery) according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of a cell layer that constitutes the stacked secondary battery shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view showing an embodiment of a method for manufacturing a lithium secondary battery according to an aspect of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing another embodiment of the method for producing a lithium secondary battery according to an aspect of the present invention. [Figure 5]Figure 5 is a graph showing the results of recording the change in cell voltage relative to the change in capacity when a constant current of 1 mA / cm2 was applied to the evaluation cell (symmetric cell) prepared in Experimental Example 1 at a temperature of 25°C and a confining pressure of 20 MPa in the stacking direction until a capacity of 1.24 mAh / cm2 was reached (the same test was performed three times). [Figure 6] FIG. 6 is a graph showing the results of recording the change in cell voltage relative to the change in capacity when a constant current of 1 mA / cm2 was applied to the evaluation cell (symmetric cell) prepared in Comparative Experimental Example 1 at a temperature of 25°C and a confining pressure of 20 MPa in the stacking direction until a capacity of 1.24 mAh / cm2 was reached (the results of the same test performed four times are shown). [Figure 7] 7A and 7B are micrographs taken with a scanning electron microscope (SEM) of the cross section of one electrode of the evaluation cells fabricated in Experimental Example 1 and Comparative Experimental Example 1. Fig. 7A is from Experimental Example 1, and Fig. 7B is from Comparative Experimental Example 1. [Figure 8] FIG. 8 is a graph showing the results of recording the change in cell voltage versus the change in capacity when a constant current of 1 mA / cm2 was applied to the evaluation cells produced in Experimental Example 2 and Comparative Experimental Example 2 under a confining pressure of 20 MPa in the stacking direction at a temperature of 25°C until a capacity of 2.45 mAh / cm2 was reached. DETAILED DESCRIPTION OF THE INVENTION

[0012] One aspect of the present invention is a lithium secondary battery including a power generating element including a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a lithium-containing alloy as a negative electrode active material disposed on the surface of a negative electrode current collector, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer and containing a solid electrolyte, wherein the negative electrode active material layer includes a lithium-containing alloy layer having a substantially uniform composition, and at least a portion of the surface of the lithium-containing alloy layer facing the solid electrolyte layer is made of the lithium-containing alloy, and the lithium secondary battery is in a state prior to charge / discharge treatment. According to this aspect, the internal resistance of the lithium secondary battery can be reduced in the lithium-containing alloy layer disposed on the negative electrode.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the dimensional proportions in the drawings are exaggerated for the convenience of explanation and may differ from the actual proportions.

[0014] Fig. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) 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 before charge / discharge treatment (i.e., in a state where no charge / discharge treatment has been performed).

[0015] The stacked 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. Here, the power generating element 21 has a configuration in which a negative electrode, a solid electrolyte layer 17, and a positive electrode are stacked. More specifically, the negative electrode has a structure in which a negative electrode current collector 11′ and a negative electrode active material layer 13 arranged on the surface of the negative electrode current collector 11′ are stacked. Furthermore, the positive electrode has a structure in which a positive electrode active material layer 15 is arranged 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 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, the stacked secondary battery 10a shown in FIG. 1 can also be said to have a configuration in which a plurality of unit cell layers 19 are stacked and electrically connected in parallel.

[0016] Fig. 2 is an enlarged cross-sectional view of a cell layer 19 constituting the stacked secondary battery 10a shown in Fig. 1. In this embodiment, the negative electrode active material layer 13 has a lithium-containing alloy layer (LiAl alloy layer) 13a with a substantially uniform composition located on the solid electrolyte layer 17 side, and an Al metal layer 13b located on the negative electrode current collector 11' side, as shown in Fig. 2. Here, the interface between the LiAl alloy layer 13a and the Al metal layer 13b constituting the negative electrode active material layer 13 shown in Fig. 2 is not clear, and the composition of the LiAl alloy layer 13a and the composition of the Al metal layer 13b change continuously at this interface.

[0017] 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.

[0018] <Lithium secondary battery> The main components of the lithium secondary battery according to this embodiment will be described below.

[0019] [Current collector] The current collectors (negative electrode current collector, positive electrode current collector) function to mediate the transfer of electrons from the electrode active material layers (negative electrode active material layer, positive electrode active material layer). There are no particular limitations on the material that constitutes the current collectors. Examples of materials that can be used for the current collectors include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular limitations on the thickness of the current collectors, but an example is 10 to 100 μm.

[0020] [Negative electrode active material layer] The negative electrode active material layer 13 of the lithium secondary battery according to this embodiment includes a lithium-containing alloy layer 13a having a substantially uniform composition before charge / discharge treatment of the battery. The "lithium-containing alloy layer" is an alloy layer composed of an alloy of lithium and a metal other than lithium. The lithium-containing alloy layer having a substantially uniform composition means that lithium atoms and metal atoms other than lithium atoms are dissolved in each other and exhibit a uniform composition except for the inclusion of inevitable impurities. In this embodiment, it is sufficient that a portion of the lithium-containing alloy layer has a substantially uniform composition; it is not essential that the entire lithium-containing alloy layer has a substantially uniform composition. However, from the viewpoint of uniformity of the battery reaction, it is preferable that the entire lithium-containing alloy layer has a substantially uniform composition.

[0021] The metal other than lithium contained in the lithium-containing alloy layer 13a is not particularly limited, and any metal can be used as long as it can be alloyed with lithium and does not adversely affect the performance of the battery. In a preferred embodiment, the lithium-containing alloy contains an alloy of lithium and one or more metals selected from the group consisting of indium, aluminum, silicon, tin, magnesium, gold, silver, and zinc. Among these, the lithium-containing alloy more preferably contains an alloy of lithium and indium and / or aluminum, and even more preferably contains an alloy of lithium and aluminum from the viewpoint of a low standard electrode potential during alloying.

[0022] In this embodiment, it is essential that at least a portion of the surface of the lithium-containing alloy layer 13a constituting the negative electrode active material layer 13 facing the solid electrolyte layer 17 is composed of a lithium-containing alloy having a substantially uniform composition. The presence of a lithium-containing alloy having a substantially uniform composition on the surface of the lithium-containing alloy layer facing the solid electrolyte layer facilitates smooth lithium ion conduction during the charge and discharge process of the battery, thereby effectively contributing to reducing the internal resistance of the battery. Furthermore, the larger the area of ​​the portion of the lithium-containing alloy layer facing the solid electrolyte layer where the lithium-containing alloy having a substantially uniform composition is present, the lower the reaction resistance of lithium ions and the greater the effect of reducing the internal resistance. Therefore, the area of ​​the portion of the lithium-containing alloy layer facing the solid electrolyte layer where the lithium-containing alloy having a substantially uniform composition is present is preferably 50% or more, more preferably 80% or more, even more preferably 90% or more, particularly preferably 95% or more, and most preferably 100%. That is, as in the embodiment shown in FIG. 2, it is most preferable that the entire surface of the lithium-containing alloy layer facing the solid electrolyte layer is composed of a lithium-containing alloy having a substantially uniform composition.

[0023] The thickness of the lithium-containing alloy layer 13a before the charge / discharge treatment of the battery is not particularly limited and is set in consideration of the capacity of the positive electrode and the capacity of the entire battery, but is preferably 50 to 1000 μm, more preferably 50 to 500 μm, even more preferably 50 to 300 μm, and particularly preferably 100 to 200 μm.

[0024] In this embodiment, as shown in FIG. 2, the negative electrode active material layer 13 preferably further includes a metal layer 13b made of a metal other than lithium, adjacent to both the lithium-containing alloy layer 13a and the negative electrode current collector 11′. This configuration further promotes alloying of the lithium-containing alloy layer 13a, thereby increasing the proportion of the lithium-containing alloy in contact with the solid electrolyte layer. The metal constituting the metal layer 13b made of a metal other than lithium is not particularly limited, and any metal can be used as long as it can be alloyed with lithium and does not adversely affect battery performance. The metal may be the same as or different from the metal constituting the lithium-containing alloy layer 13a together with lithium. However, from the viewpoints of achieving better battery performance and low-cost and easy manufacturing, the metal constituting the metal layer 13b made of a metal other than lithium is preferably the same as the metal constituting the lithium-containing alloy layer 13a together with lithium.

[0025] When metal layer 13b made of a metal other than lithium is present, the thickness of metal layer 13b is not particularly limited, but is preferably 10 to 100 μm, more preferably 20 to 70 μm, even more preferably 30 to 60 μm, and particularly preferably 40 to 50 μm.

[0026] [Negative electrode intermediate layer] In the lithium secondary battery according to this embodiment, a negative electrode intermediate layer may be interposed between the negative electrode active material layer and the solid electrolyte layer. The negative electrode intermediate layer contains a lithium-reactive material and, if necessary, a binder, and is a layer that suppresses decomposition of the solid electrolyte constituting the solid electrolyte layer and promotes uniform migration of lithium ions toward the negative electrode. Examples of the lithium-reactive material include carbon materials and metal materials that can occlude lithium ions during charging.

[0027] Specific examples of carbon materials capable of absorbing lithium ions during charging 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, carbon black is preferred, and at least one selected from the group consisting of acetylene black, Ketjen Black (registered trademark), furnace black, channel black, and thermal lamp black is more preferred.

[0028] Furthermore, it is more preferable that the metal material as the lithium-reactive material contains a metal that can be alloyed with lithium during charging. Examples of metals that can be alloyed with lithium include In, Al, Si, Sn, Mg, Au, Ag, and Zn. Among these, In, Si, Sn, and Ag are preferred, and Ag is more preferred.

[0029] When the carbon material is in a particulate form, its average particle diameter (average primary particle diameter) is, for example, 10 nm to 200 nm, preferably 15 nm to 150 nm, and more preferably 20 nm to 100 nm. When the metal is in a particulate form, its average particle diameter is, for example, 10 nm to 500 nm, preferably 20 nm to 300 nm, more preferably 30 nm to 200 nm, and even more preferably 40 nm to 100 nm. In this specification, the average particle diameter of the carbon material and metal particles refers to the 50% cumulative diameter (D) of the particle diameters of the particles (the maximum distance between any two points on the outline of the observed 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). 50 )

[0030] The lithium-reactive material may be used alone or in combination of two or more. A preferred embodiment of using two or more in combination is to use the above-mentioned carbon material in combination with a metal capable of forming an alloy with lithium. This ensures sufficient mechanical strength and lithium ion conductivity of the negative electrode intermediate layer. When the above-mentioned carbon material and the metal capable of forming an alloy with lithium are used in combination, the compounding ratio (mass ratio) between them is not particularly limited, but the carbon material:metal capable of forming an alloy with lithium (mass ratio) is preferably 10:1 to 1:1, and more preferably 5:1 to 2:1.

[0031] The negative electrode intermediate layer may further contain a binder in addition to the lithium-reactive material. The type of binder is not particularly limited, and binders known in the art can be appropriately used. Examples include fluorine-based resins such as polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements) and polytetrafluoroethylene (PTFE), as well as styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC). Among these, the binder of the negative electrode intermediate layer preferably contains a fluorine-based resin, and particularly preferably contains PVDF.

[0032] The thickness of the negative electrode intermediate layer is not particularly limited, but is preferably 1 to 30 μm, more preferably 1 to 20 μm, even more preferably 1 to 10 μm, and particularly preferably 1 to 5 μm. When the thickness of the negative electrode intermediate layer is 1 μm or more, the function of the negative electrode intermediate layer can be fully exhibited. When the thickness of the negative electrode intermediate layer is 30 μm or less, a decrease in energy density can be suppressed.

[0033] [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 adopted. Examples include LPS (Li2S-P2S5), Li6PS5X (where X is Cl, Br, or I), and Li7P3S 11 , Li 3.2 P0.96 Examples of suitable sulfide solid electrolytes include sulfide solid electrolytes such as S and Li3PS4. 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 during charge and discharge. These solid electrolytes may be used alone or in combination of two or more. Of course, solid electrolytes other than those mentioned above may also be used.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] [Cathode 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 FIG. 1 . However, if the positive electrode active material layer 15 itself has a certain degree of conductivity, it may constitute a positive electrode without using a positive electrode current collector. The type of positive electrode active material contained in the positive electrode active material layer is not particularly limited, and examples include lithium-free positive electrode active materials and lithium-containing positive electrode active materials.

[0038] (Lithium-free positive electrode active material) In this specification, the term "lithium-free positive electrode active material" refers to a positive electrode active material that does not contain lithium element. Examples of the lithium-free positive electrode active material include, but are not limited to, transition metal oxides, transition metal fluorides, and sulfur-based positive electrode active materials.

[0039] Specific examples of transition metal oxides and transition metal fluorides include titanium oxide (TiO2), niobium oxide (Nb2O3), tungsten oxide (WO3), iron(II) fluoride (FeF2), vanadium pentoxide (VO5), iron oxide (FeO X ), manganese dioxide (MnO2), etc.

[0040] Examples of sulfur-based positive electrode active materials include particles or thin films of organic or inorganic sulfur compounds. Any material can be used as long as it utilizes the oxidation-reduction reaction of sulfur to release lithium ions during charging and absorb lithium ions during discharging. Examples of organic sulfur compounds include disulfide compounds, sulfur-modified polyacrylonitrile, sulfur-modified polyisoprene, rubeanic acid (dithiooxamide), and polycarbonate, as typified by the compounds described in International Publication No. 2010 / 044437. Among these, disulfide compounds, sulfur-modified polyacrylonitrile, and rubeanic acid are preferred, with sulfur-modified polyacrylonitrile being particularly preferred. Disulfide compounds containing dithiobiurea derivatives, thiourea groups, thioisocyanates, or thioamide groups are more preferred. On the other hand, inorganic sulfur compounds are preferred due to their excellent stability. Specific examples include sulfur (S), S-carbon composites, TiS2, TiS3, TiS4, NiS, NiS2, CuS, FeS2, MoS2, and MoS3. Among these, S, S-carbon composites, TiS2, TiS3, TiS4, FeS2, and MoS2 are preferred, with S, S-carbon composites, TiS2, and FeS2 being more preferred. Here, the term "S-carbon composite" refers to a composite containing sulfur powder and a carbon material, which are combined by heat treatment or mechanical mixing. More specifically, the composite may be one in which sulfur is distributed on the surface or within the pores of the carbon material, one in which sulfur and the carbon material are uniformly dispersed at the nano-level and aggregated to form particles, one in which the carbon material is distributed on the surface or within fine sulfur powder, or a combination of these.

[0041] In some cases, two or more types of lithium-free positive electrode active materials may be used in combination. Of course, lithium-free positive electrode active materials other than those mentioned above may also be used.

[0042] (Lithium-containing positive electrode active material) In this specification, the lithium-containing positive electrode active material refers to a positive electrode active material containing lithium element. The lithium-containing positive electrode active material is not particularly limited, but may be a layered rock salt type active material such as LiCoO2, LiMnO2, LiNiO2, LiVO2, Li(Ni-Mn-Co)O2, Li(Ni-Co-Al)O2, LiMn2O4, LiNi 0.5 Mn 1.5 Examples of oxide active materials include spinel-type active materials such as LiFePO4 and LiMnPO4, olivine-type active materials such as LiFeSiO4 and LiMnSiO4, and Si-containing active materials such as LiFeSiO4 and LiMnSiO4. 12 Examples include:

[0043] In some cases, two or more kinds of lithium-containing positive electrode active materials may be used in combination. Of course, lithium-containing positive electrode active materials other than those mentioned above may also be used.

[0044] The positive electrode active material may be in the form of, for example, particles (spherical, fibrous), thin film, etc. When the positive electrode active material is in the form of particles, the average particle diameter (D50) is, for example, preferably in the range of 1 nm to 100 μm, more preferably in the range of 10 nm to 50 μm, still more preferably in the range of 100 nm to 20 μm, and particularly preferably in the range of 1 to 20 μm.

[0045] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably within the range of 40 to 100 mass %, and more preferably within the range of 50 to 90 mass %, for example.

[0046] The positive electrode active material layer may further contain at least one of a solid electrolyte, a conductive additive, and a binder, as necessary. The specific forms of the solid electrolyte and the binder are the same as those described above, and therefore detailed description is omitted here. The solid electrolyte that can be used in the positive electrode active material layer is the same as that described in the solid electrolyte layer. The binder that can be used in the positive electrode active material layer is the same as that described in the negative electrode intermediate layer.

[0047] Examples of conductive additives include, but are not limited to, 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 (CNTs), and carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). Furthermore, particulate ceramic materials or resin materials coated with the above-mentioned metal materials by plating or the like can also be used as conductive additives.

[0048] 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.

[0049] In a preferred embodiment of the lithium secondary battery according to the present invention, the positive electrode active material contains a lithium-free positive electrode active material before the battery is charged and discharged. In this case, since the lithium-free positive electrode active material cannot release lithium ions, the lithium secondary battery according to the present invention is used for charging and discharging in which the initial charging and discharging process is a discharge process. Here, if the positive electrode active material does not contain a lithium-free positive electrode active material and the initial charging and discharging process is a charging process, alloying of the lithium-containing alloy layer may progress during this initial charging and discharging process. Therefore, even in a battery in which the internal resistance of the battery increases when the initial charging and discharging process is a discharging process, the problem of increased internal resistance may not be significantly manifested if the initial charging and discharging process is a charging process. Therefore, the lithium secondary battery according to the present invention is preferable because the effect of reducing the internal resistance of the battery is more significantly manifested when the initial charging and discharging process is a discharging process.

[0050] [Positive and negative current collector plates] The material constituting the current collector plates (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 plates. 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 and negative leads] Although not shown, the current collectors (11", 11') and the current collector plates (27, 25) may be electrically connected via positive and negative electrode leads. Materials used in known lithium ion secondary batteries may be used as the constituent materials of the positive and negative electrode leads. The parts removed from the exterior are preferably covered with a heat-resistant, insulating heat-shrinkable tube or the like to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting products (e.g., automobile parts, particularly electronic devices).

[0052] [Battery exterior materials] As the battery exterior material, a known metal can case can be used, or 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 to these. 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 devices 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] 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.

[0054] 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.

[0055] Furthermore, the lithium secondary battery according to this embodiment may or may not 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).

[0056] 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.

[0057] <Method for manufacturing lithium secondary batteries> Next, a method for manufacturing a lithium secondary battery according to another embodiment of the present invention will be described. This embodiment of the present invention relates to a method for manufacturing a lithium secondary battery including a power generating element having a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode having a negative electrode active material layer containing a lithium-containing alloy as a negative electrode active material disposed on the surface of a negative electrode current collector, and a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer and containing a solid electrolyte. The manufacturing method includes a pressurizing step in which a laminate (1) including the solid electrolyte layer, a first metal layer made of a metal capable of alloying with lithium, a lithium metal layer made of lithium metal, and a second metal layer made of a metal capable of alloying with lithium is pressed in the stacking direction of the laminate (1) to compress and bond the layers together. The pressurizing step is characterized in that at least a portion of the first metal layer is alloyed with lithium up to the surface facing the solid electrolyte layer. This manufacturing method allows the lithium secondary battery according to the embodiment of the present invention to be manufactured. However, the technical scope of the lithium secondary battery according to one embodiment of the present invention is not limited to those manufactured by the manufacturing method.

[0058] One of the features of the method for producing a lithium secondary battery according to this embodiment is that it includes a predetermined pressurizing step. This pressurizing step produces a laminate of a negative electrode active material layer and a solid electrolyte layer. The laminate may further include a negative electrode current collector and / or a negative electrode intermediate layer. Components other than the laminate can be produced as appropriate by referring to conventionally known knowledge.

[0059] (Pressure process) In the pressurizing step, first, a laminate (1) is prepared in which a solid electrolyte layer, a first metal layer made of a metal capable of alloying with lithium, a lithium metal layer made of lithium metal, and a second metal layer made of a metal capable of alloying with lithium are stacked in this order. At this time, the laminate (1) may further include a negative electrode current collector. In the pressurizing step, the laminate (1) prepared above is then pressed in the stacking direction to compress the layers together.

[0060] 3A and 3B are cross-sectional views showing an embodiment of a method for manufacturing a lithium secondary battery according to an aspect of the present invention. As shown in Fig. 3A, a laminate (1) 101 according to this embodiment has a configuration in which a solid electrolyte layer 17, a first aluminum metal layer 200a, a lithium metal layer 200b, a second aluminum metal layer 200c, and a negative electrode current collector 11' are laminated.

[0061] In this embodiment, pressure is applied in the stacking direction of the laminate (1) 101 shown in FIG. 3(a) to compress the layers. As a result, alloying progresses between the first aluminum metal layer 200a, the lithium metal layer 200b, and the second aluminum metal layer 200c, resulting in a solid electrolyte layer-negative electrode laminate 100 as shown in FIG. 3(b). This solid electrolyte layer-negative electrode laminate 100 is a component of the unit cell layer 19 shown in FIG. 2. In this solid electrolyte layer-negative electrode laminate 100, the entire surface of the first aluminum metal layer 200a shown in FIG. 3(a) is alloyed with lithium up to the surface on the solid electrolyte layer 17 side by the pressure applied in the above-mentioned pressurizing step. However, the entire surface of the first aluminum metal layer 200a does not have to be alloyed with lithium up to the surface on the solid electrolyte layer 17 side, as long as at least a portion of the first aluminum metal layer 200a is alloyed with lithium up to the surface on the solid electrolyte layer 17 side. Such a solid electrolyte layer-negative electrode laminate 100 can function as a battery by disposing a positive electrode on the exposed surface of the solid electrolyte layer 17. Furthermore, if a lithium-containing alloy is present on the surface of the lithium-containing alloy layer facing the solid electrolyte layer, lithium ion conduction can proceed smoothly during the charge and discharge process of the battery, which can effectively contribute to reducing the internal resistance of the battery.

[0062] The thickness of each metal layer constituting the laminate (1) described above is not particularly limited and can be appropriately set taking into account the composition and thickness of the lithium-containing alloy layer in the negative electrode of the resulting battery, the thickness of the metal layer, such as the aluminum metal layer, etc. Here, the thickness of the first metal layer (aluminum metal layer 200a shown in FIG. 3a) depends on the type of metal constituting the first metal layer, but is preferably a thickness that will not cause fracture due to stress generated by protrusions present on the surface of the solid electrolyte layer to which the first metal layer is in contact. This configuration can prevent short circuits caused by fracture of the first metal layer during compression bonding in the pressing step. To determine the thickness of the first metal layer that satisfies this requirement, for example, the indentation depth at which the first metal layer fractures when the thickness of the first metal layer is changed can be obtained in advance using a nanoindentation method, and the thickness of the first metal layer can be set so that the indentation depth is greater than the maximum surface roughness of the solid electrolyte layer. For example, the thickness of the first metal layer is, for example, 5 to 30 μm, preferably 10 to 25 μm, and more preferably 15 to 20 μm. The thickness of the lithium metal layer is, for example, 20 to 500 μm, preferably 50 to 300 μm, and more preferably 50 to 150 μm. The thickness of the second metal layer is, for example, 50 to 500 μm, preferably 70 to 300 μm, and more preferably 100 to 200 μm.

[0063] There are no particular limitations on the means for carrying out the pressurizing step, and conventionally known knowledge can be referred to as appropriate. The pressurizing step can be carried out using, for example, a uniaxial press or a roll press. There are also no particular limitations on the pressure applied in the stacking direction of the laminate (1) in the pressurizing step, as long as it is a pressure that can press-bond the layers together and promote alloying. As an example, the pressure applied in the stacking direction of the laminate (1) is preferably 50 to 250 MPa, more preferably 100 to 200 MPa.

[0064] In the above-described embodiment, a negative electrode current collector 11′ is further disposed on the laminate (1). Although the pressurizing step may be performed in a state where the negative electrode current collector 11′ is not disposed on the laminate (1), performing the pressurizing step in a state where the negative electrode current collector 11′ is disposed can prevent peeling of the negative electrode current collector 11′ and an increase in internal resistance resulting from peeling.

[0065] In addition, in the method for producing a lithium secondary battery according to this embodiment, the pressurizing step preferably includes pressurizing the laminate (1) from outside the battery outer casing while the laminate (1) is sealed inside the battery outer casing as shown in Fig. 1. With this configuration, the laminate (1) is not exposed to the outside and is not able to function as a battery, which can significantly improve safety during production. When performing this pressurizing step, it is necessary to arrange a positive electrode active material layer and, if necessary, a positive electrode current collector on the side of the solid electrolyte layer opposite the negative electrode.

[0066] Furthermore, in the method for producing a lithium secondary battery according to this embodiment, it is preferable to further include, after the pressurizing step, measuring the diffusion resistance in the stacking direction of the laminate (1) to confirm the quality of the laminate (1). By including such a diffusion resistance measuring step, it is possible to eliminate unit cell layers of poor quality, thereby improving the yield of finished batteries. Note that there are no particular limitations on the means for measuring the diffusion resistance, and for example, electrochemical impedance spectroscopy (EIS) can be used to measure the diffusion resistance of the negative electrode active material layer from the diffusion resistance component at 1 Hz or less, thereby confirming the quality.

[0067] Here, a process may be performed in which a cell layer including a positive electrode, a solid electrolyte layer, and a negative electrode is preliminarily fabricated into a large sheet, and the sheet is then cut to a desired size. However, if the cell layer is in a state capable of functioning as a battery, there is a possibility that a short circuit will occur between the positive and negative electrodes when the cell layer is cut. Furthermore, the SOC of a cell layer in which the negative electrode includes a lithium-containing alloy is often at or near 100%, posing a significant risk of a short circuit. In this regard, the manufacturing method according to the present embodiment enables the cell layer to function as a battery by undergoing a pressurizing step. Therefore, even if a step of cutting to a desired size is performed in the state of the laminate (1), for example, the occurrence of the above-mentioned short circuit can be effectively prevented. In other words, the manufacturing method according to the present embodiment has the advantage of improving the flexibility of the battery manufacturing process while further improving safety during manufacturing.

[0068] 4A and 4B are cross-sectional views showing another embodiment of the method for manufacturing a lithium secondary battery according to an aspect of the present invention. As shown in Fig. 4A, in this embodiment, first, a laminate (2) 102 having a configuration in which a solid electrolyte layer 17 and a first aluminum metal layer 200a are laminated is prepared.

[0069] Next, in this embodiment, pressure is applied in the stacking direction of the laminate (2) 102 shown in FIG. 4(a) to compress and bond the layers together. As a result, the solid electrolyte layer 17 and the first aluminum metal layer 200a are firmly bonded together. In this way, by undergoing a step of previously bonding the solid electrolyte layer and the first metal layer, it is possible to increase the area of ​​the bonding interface between them. As a result, it is possible to further reduce the internal resistance of the lithium secondary battery.

[0070] The pressure applied in the stacking direction of the laminate (2) is not particularly limited, but from the viewpoint of further increasing the area of ​​the bonding interface, it is preferably greater than the pressure applied in the stacking direction of the laminate (1). For example, the pressure applied in the stacking direction of the laminate (2) is preferably 260 to 500 MPa, more preferably 300 to 400 MPa.

[0071] In this embodiment, the lithium metal layer 200b, the second aluminum metal layer 200c, and the negative electrode current collector 11' are laminated on the laminate of the solid electrolyte layer 17 and the first aluminum metal layer 200a obtained above in the same manner as in the above-described embodiment, and then a pressurizing step is carried out. Note that the operations after this pressurizing step can be carried out in the same manner as in the above-described embodiment.

[0072] 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 manufacturing method according to claim 6 having the features of claim 7; a manufacturing method according to claim 6 or 7 having the features of claim 8; a manufacturing method according to any one of claims 6 to 8 having the features of claim 9; a manufacturing method according to claim 9 having the features of claim 10; and a manufacturing method according to any one of claims 6 to 10 having the features of claim 11. [Example]

[0073] The present invention will be described in more detail below with reference to experimental examples. However, the technical scope of the present invention is not limited to the following experimental examples. In the following, the operations were carried out in a glove box with a dew point of -68°C or less. Furthermore, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0074] [Experimental Example 1] (Fabrication of solid electrolyte layer) Argyrodite-type sulfide solid electrolyte (Li6PS5Cl, average particle size (D 50 A pellet-shaped solid electrolyte layer (700 μm thick) was produced by compacting powder of 0.8 μm in an environment of 25° C. Here, the pressing conditions for the powder compaction were a pressure equivalent to 400 MPa for 1 minute.

[0075] (Fabrication of an evaluation cell containing a LiIn alloy layer) A laminate was prepared by placing indium foil (20 μm thick) on both sides of the solid electrolyte layer prepared above. A pressure of 400 MPa was applied in the stacking direction of the laminate for 1 second. Next, a lithium foil (200 μm thick), an indium foil (300 μm thick), and a stainless steel foil (50 μm thick) serving as a current collector were placed in this order from the indium foil side to obtain a laminate. A pressure of 100 MPa was then applied in the stacking direction of this laminate for 1 second to prepare an evaluation cell (symmetric cell) in which LiIn alloy layers were placed on both sides of the solid electrolyte layer. Observation of the cross section of this evaluation cell using a scanning electron microscope (SEM) revealed that the entire interface between the LiIn alloy layers constituting the electrodes on both sides of the solid electrolyte layer and the solid electrolyte layer was composed of LiIn alloy, as shown in Figure 2. Furthermore, due to the above preparation method, it was confirmed that a metal layer (In metal layer) composed of indium was interposed between the LiIn alloy layer and the current collector (stainless steel foil) so as to be adjacent to both of them.

[0076] (Evaluation of overvoltage of evaluation cell) At a temperature of 25°C, a confining pressure of 20 MPa was applied in the stacking direction to the evaluation cell fabricated above, and a current of 1 mA / cm 2 A constant current of 1.24mAh / cm 2 A voltage was applied until the capacity reached 100 kJ / s. Figure 5 is a graph showing the recorded results of the change in cell voltage versus the change in capacity during the above test (each graph shows the results of three identical tests). Note that, since a symmetric cell was used as the evaluation cell, the potential difference between the two electrodes before the test began was 0 V. Therefore, the change in cell voltage shown in Figure 5 is the change in the voltage (i.e., overvoltage) applied between the two electrodes during the above test. Furthermore, according to Ohm's law, the smaller this overvoltage, the smaller the reaction resistance of the symmetric cell.

[0077] As shown in Figure 5, the overvoltage of the evaluation cell prepared above was small and stable. Therefore, the reaction resistance of the evaluation cell was small, and it is expected that the internal resistance of a lithium secondary battery can be reduced by applying an electrode containing this LiIn alloy layer to the negative electrode of the lithium secondary battery.

[0078] [Comparative Experiment Example 1] (Fabrication of an evaluation cell containing a LiIn alloy layer) A laminate was obtained by arranging indium foil (300 μm thick), lithium foil (200 μm thick), and stainless steel foil (50 μm thick) as a current collector on both sides of the solid electrolyte layer prepared in Experimental Example 1 described above, in that order from the solid electrolyte layer side. A pressure of 100 MPa was then applied to this laminate in the stacking direction for 1 second to prepare an evaluation cell (symmetric cell) in which LiIn alloy layers were arranged on both sides of the solid electrolyte layer. Observation of the cross section of this evaluation cell using a scanning electron microscope (SEM) revealed that the LiIn alloy layers arranged on both sides of the solid electrolyte layer did not reach the interface with the solid electrolyte layer, and the entire interface was composed of indium.

[0079] (Evaluation of overvoltage of evaluation cell) The overvoltage of the evaluation cell prepared above was evaluated using the same method as in Experimental Example 1. Figure 6 is a graph showing the results of recording the change in cell voltage versus the change in capacity during the above test (each showing the results of the same test performed four times).

[0080] As shown in Figure 6, the overvoltage of the evaluation cell prepared above was significantly higher than that of Experimental Example 1, and increased as the test progressed. Therefore, the reaction resistance of this evaluation cell was high, and it is thought that even if this electrode were used as the negative electrode of a lithium secondary battery, the internal resistance of the lithium secondary battery would not be reduced.

[0081] 7(a) and 7(b) show micrographs of the cross sections of one electrode of the evaluation cells fabricated in Experimental Example 1 and Comparative Experimental Example 1, observed using a scanning electron microscope (SEM). As shown in Fig. 7(a), almost the entire surface of the lithium-containing alloy layer (LiIn alloy layer) 13a constituting the electrode of Experimental Example 1, facing the solid electrolyte layer 17, was composed of the lithium-containing alloy (LiIn alloy). In contrast, as shown in Fig. 7(b), the surface of the lithium-containing alloy layer (LiIn alloy layer) 13a constituting the electrode of Comparative Experimental Example 1, facing the solid electrolyte layer 17, did not reach the solid electrolyte layer, and a metal layer (In metal layer 13c) derived from the raw materials was interposed between the lithium-containing alloy layer (LiIn alloy layer) 13a and the solid electrolyte layer 17.

[0082] [Experimental Example 2] (Fabrication of an evaluation cell containing a LiAl alloy layer) On one side of the solid electrolyte layer prepared in Experimental Example 1, aluminum foil (15 μm thick), lithium foil (200 μm thick), aluminum foil (100 μm thick), and stainless steel foil (50 μm thick) as a current collector were arranged in this order from the solid electrolyte layer side to obtain a laminate. Next, a pressure of 200 MPa was applied to this laminate in the stacking direction for 1 second, thereby disposing a LiAl alloy layer as a working electrode on one side of the solid electrolyte layer. Furthermore, a pressure of 400 MPa was applied to this laminate in the stacking direction for 1 second, with an indium foil (20 μm thick) arranged on the other side of the solid electrolyte layer. Next, lithium foil (200 μm thick), indium foil (300 μm thick), and stainless steel foil (50 μm thick) as a current collector were arranged in this order from the indium foil side to obtain a laminate. Next, a pressure of 100 MPa was applied to this laminate in the stacking direction for 1 second, thereby disposing a LiIn alloy layer as a counter electrode, thereby producing an evaluation cell. When the cross section of this evaluation cell was observed using a scanning electron microscope (SEM), it was found that the entire interface between the LiAl alloy layer constituting the working electrode disposed on one side of the solid electrolyte layer and the solid electrolyte layer was made of LiAl alloy, as shown in Figure 2. It was also confirmed that due to the above-mentioned manufacturing method, a metal layer made of aluminum (Al metal layer) was present on the surface of the LiAl alloy layer opposite the solid electrolyte layer.

[0083] (Evaluation of overvoltage of evaluation cell) At a temperature of 25°C, a confining pressure of 20 MPa was applied in the stacking direction to the evaluation cell fabricated above, and a current of 1 mA / cm 2 A constant current of 3.12mAh / cm 2 The current was applied until the capacity reached 1000 kJ / s. In this experiment, the current was applied so that lithium ions migrated from the LiAl alloy layer of the working electrode to the counter electrode (i.e., the discharge process proceeds when the working electrode is negative and the counter electrode is positive). Figure 8 shows a graph showing the results of recording the change in cell voltage versus the change in capacity during the above test.

[0084] As shown in Figure 8, the overvoltage of the evaluation cell fabricated above was small and stable. Therefore, the reaction resistance of the evaluation cell was small, and it is expected that the internal resistance of a lithium secondary battery can be reduced by applying an electrode containing this LiAl alloy layer to the negative electrode of the lithium secondary battery.

[0085] [Comparative Experimental Example 2] (Fabrication of an evaluation cell containing a LiAl alloy layer) On one side of the solid electrolyte layer prepared in Experimental Example 1, aluminum foil (200 μm thick), lithium foil (100 μm thick), and stainless steel foil (50 μm thick) serving as a current collector were arranged in this order from the solid electrolyte layer side to obtain a laminate. Next, a pressure of 200 MPa was applied in the stacking direction of this laminate for 1 second to form a LiAl alloy layer serving as a working electrode on one side of the solid electrolyte layer. Furthermore, a pressure of 400 MPa was applied in the stacking direction of the laminate for 1 second to form a laminate with indium foil (20 μm thick) on the other side of the solid electrolyte layer. Next, lithium foil (200 μm thick), indium foil (300 μm thick), and stainless steel foil (50 μm thick) serving as a current collector were arranged in this order from the indium foil side to obtain a laminate. Next, a pressure of 100 MPa was applied in the stacking direction of this laminate for 1 second to form a LiIn alloy layer serving as a counter electrode, thereby producing an evaluation cell. When the cross section of this evaluation cell was observed using a scanning electron microscope (SEM), it was found that the LiAl alloy layer disposed on one side of the solid electrolyte layer did not reach the interface with the solid electrolyte layer, and the entire interface was composed of aluminum.

[0086] (Evaluation of overvoltage of evaluation cell) The overvoltage of the evaluation cell prepared above was evaluated using the same method as in Experimental Example 2. Figure 8 shows a graph showing the results of recording the change in cell voltage versus the change in capacity during the above test.

[0087] As shown in Figure 8, the evaluation cell prepared above exhibited a very large overvoltage, and the discharge process hardly progressed. Therefore, the reaction resistance of the evaluation cell was very large, and it is thought that even if an electrode including this LiAl alloy layer is used as the negative electrode of a lithium secondary battery, the internal resistance of the lithium secondary battery cannot be reduced. [Explanation of symbols]

[0088] 10a stacked secondary battery, 11' negative electrode current collector, 11” positive electrode current collector, 13 negative electrode active material layer, 13a lithium-containing alloy layer (LiAl alloy layer or LiIn alloy layer), 13b metal layer (Al metal layer or In metal layer), 13c metal layer (In metal layer), 15 positive electrode active material layer, 17 solid electrolyte layer, 19 cell layer, 21 power generation elements, 25 negative current collector plate, 27 positive current collector plate, 29 Laminating film, 100 solid electrolyte layer-negative electrode laminate, 101 laminate (1), 102 laminate (2), 200a: first aluminum metal layer (first metal layer); 200b lithium metal layer; 200c Second aluminum metal layer (second metal layer).

Claims

1. a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode active material layer containing a lithium-containing alloy as a negative electrode active material disposed on a surface of a negative electrode current collector; a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer and containing a solid electrolyte; a power generating element having a negative electrode active material layer including a lithium-containing alloy layer containing a lithium-containing alloy having a substantially uniform composition, at least a portion of a surface of the lithium-containing alloy layer facing the solid electrolyte layer being made of the lithium-containing alloy, the lithium secondary battery being before charge / discharge treatment.

2. 2. The lithium secondary battery according to claim 1, wherein the entire surface of said lithium-containing alloy layer on said solid electrolyte layer side is made of said lithium-containing alloy.

3. 3. The lithium secondary battery according to claim 1, wherein the negative electrode active material layer further includes a metal layer made of a metal other than lithium so as to be adjacent to both the lithium-containing alloy layer and the negative electrode current collector.

4. 3. The lithium secondary battery according to claim 1, wherein the positive electrode active material comprises a lithium-free positive electrode active material, and the first charge-discharge treatment is a discharge treatment.

5. 3. The lithium secondary battery according to claim 1, wherein the lithium-containing alloy comprises an alloy of lithium and one or more metals selected from the group consisting of indium, aluminum, silicon, tin, magnesium, gold, silver, and zinc.

6. a positive electrode having a positive electrode active material layer containing a positive electrode active material; a negative electrode having a negative electrode active material layer containing a lithium-containing alloy as a negative electrode active material disposed on a surface of a negative electrode current collector; a solid electrolyte layer interposed between the positive electrode active material layer and the negative electrode active material layer and containing a solid electrolyte; A method for manufacturing a lithium secondary battery having a power generating element having The method includes a pressurizing step of pressing a laminate (1) in a stacking direction of the laminate (1), in which the solid electrolyte layer, a first metal layer made of a metal capable of being alloyed with lithium, a lithium metal layer made of lithium metal, and a second metal layer made of a metal capable of being alloyed with lithium are stacked in this order, to pressure-bond each layer, the first metal layer is alloyed with lithium up to the surface on the solid electrolyte layer side by the pressurization in the pressurization step.

7. The pressurizing step includes: a laminate (2) including only the solid electrolyte layer and a first metal layer made of a metal capable of being alloyed with lithium is pressed in a stacking direction of the laminate (2) to compress and bond the layers together; a laminate (1) in which the laminate (2) in which each layer is pressure-bonded, a lithium metal layer made of lithium metal, and a second metal layer made of a metal that can be alloyed with lithium and is thicker than the first metal layer are laminated in this order, and the laminate (1) is pressed in the stacking direction of the laminate (1) to pressure-bond each layer; The method for producing the lithium secondary battery according to claim 6, comprising:

8. 8. The method for producing a lithium secondary battery according to claim 6, wherein the first metal layer has a thickness that does not cause fracture due to stress generated by a protrusion present on a surface of the solid electrolyte layer in contact with the first metal layer.

9. 8. The method for producing a lithium secondary battery according to claim 6, wherein the pressurizing step includes pressing the laminate (1), in which a negative electrode current collector is further disposed on a surface of the second metal layer opposite to the lithium metal layer, in a stacking direction of the laminate (1).

10. 10. The method for manufacturing a lithium secondary battery according to claim 9, wherein the pressurizing step includes pressurizing the laminate (1) from outside the battery outer casing while the laminate (1) is sealed inside the battery outer casing.

11. 8. The method for producing a lithium secondary battery according to claim 6, further comprising, after the pressing step, confirming the quality of the laminate (1) by measuring the diffusion resistance in the stacking direction of the laminate (1).

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