Method for producing all-solid-state battery

Abstract

Provided is a means for more reliably enabling short-circuit to be suppressed in a lithium deposition-type all-solid-state battery. The present invention provides a method for producing an all-solid-state battery including a power generating element having: a positive electrode formed as a result of a positive electrode active material layer that contains a positive electrode active material capable of absorbing and releasing lithium ions being disposed on a surface of a positive electrode current collector; a negative electrode that has a negative electrode current collector and in which a lithium metal is deposited on the negative electrode current collector during charging; a solid electrolyte layer that is disposed between the positive electrode and the negative electrode and that contains a solid electrolyte; and a negative electrode intermediate layer that is disposed between the negative electrode current collector and the solid electrolyte layer and that contains a material capable of absorbing and releasing lithium ions and at least one type of lithium-reactive material selected from the group consisting of metals alloyable with lithium. The method includes: a first charging step for charging an uncharged all-solid-state battery precursor having the same configuration as the all-solid-state battery until a capacity C1 [mAh / cm2] is reached; and a second charging step for charging, from a capacity C2 [mAh / cm2], the all-solid-state battery precursor that has been subjected to the first charging step. In the method, 0.8×Cx [mAh / cm2] ≤ C1 [mAh / cm2] ≤ C2 [mAh / cm2] and I1 [mA / cm2] < I2 [mA / cm2] are satisfied, where Cx [mAh / cm2] is the capacity of the lithium-reactive material contained per unit area of the negative electrode intermediate layer in plan view of the power generating element, I1 [mA / cm2] is the maximum value of the current density in the first charging step, and I2 [mA / cm2] is the minimum value of the current density in the second charging step.

Description

Manufacturing method for all-solid-state batteries

[0001] The present invention relates to a method for manufacturing an all-solid-state battery.

[0002] In recent years, research and development on all-solid-state secondary batteries using oxide- or sulfide-based solid electrolytes has been actively conducted. Solid electrolytes are materials primarily composed of ionic conductors that can conduct ions in a solid state. Therefore, all-solid-state secondary batteries have the advantage that, in principle, they do not encounter the various problems associated with flammable organic electrolytes that are present in conventional liquid-based lithium secondary batteries.

[0003] One type of all-solid-state battery is known as a lithium deposition type, in which lithium metal is deposited on the negative electrode current collector during the charging process. During the charging process of a lithium deposition type all-solid-state secondary battery, lithium metal is deposited between the solid electrolyte layer and the negative electrode current collector. Repeated charge and discharge cycles cause lithium metal to deposit in the gaps in the solid electrolyte, potentially forming dendrites, which are branched crystals of lithium. Because dendrites can cause short circuits in all-solid-state batteries and the resulting capacity loss, methods for suppressing dendrite growth are being investigated.

[0004] Japanese Patent Application Laid-Open Publication No. 2019-96610 discloses a technology for providing an anode active material layer (anode intermediate layer) between an anode current collector and a solid electrolyte layer, the anode active material layer containing an anode active material (e.g., amorphous carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, or zinc) that forms an alloy or compound with lithium. This configuration allows lithium metal to precipitate between the anode active material layer and the anode current collector during charging. According to this document, the anode active material layer functions as a protective layer for the lithium metal layer and inhibits dendrite growth from the lithium metal layer, thereby preventing short circuits and capacity loss in all-solid-state batteries.

[0005] However, the inventors have conducted studies and found that even if the techniques described in the above documents are applied, there are cases in which short circuits in all-solid-state batteries cannot be sufficiently suppressed.

[0006] Therefore, an object of the present invention is to provide a means for more reliably suppressing short circuits in a lithium deposition-type all-solid-state battery.

[0007] One aspect of the present invention is a method for producing an all-solid-state battery including a power generating element having: a positive electrode including a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions and disposed on the surface of a positive electrode current collector; a negative electrode having a negative electrode current collector and in which lithium metal is deposited on the negative electrode current collector during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a negative electrode intermediate layer interposed between the negative electrode current collector and the solid electrolyte layer and containing at least one selected from the group consisting of a material capable of absorbing and releasing lithium ions and a metal capable of alloying with lithium. The production method includes the steps of: charging a solid-state battery precursor having the same configuration as the all-solid-state battery and in an uncharged state with a capacity C １ [mAh / cm ２ a first charging step of charging the all-solid-state battery precursor after the first charging step to a capacity C ２ [mAh / cm ２ and a second charging step of charging the negative electrode intermediate layer from C. When the power generating element is viewed from above, the capacity of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer is C. ｘ [mAh / cm ２ ], and the maximum value of the current density in the first charging step is I １ [mA / cm ２ ], and the minimum value of the current density in the second charging step is I ２ [mA / cm ２ ], 0.8 × C ｘ [mAh / cm ２ ]≦C １ [mAh / cm ２ ]≦C ２ [mAh / cm ２ ] and I １ [mA / cm ２ ]<I ２ [mA / cm ２ ] is satisfied.

[0008] 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.

[0009] One aspect of the present invention is a method for producing an all-solid-state battery including a power generating element having: a positive electrode including a positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions and disposed on the surface of a positive electrode current collector; a negative electrode having a negative electrode current collector and in which lithium metal is deposited on the negative electrode current collector during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; and a negative electrode intermediate layer interposed between the negative electrode current collector and the solid electrolyte layer and containing at least one selected from the group consisting of a material capable of absorbing and releasing lithium ions and a metal capable of alloying with lithium. The production method includes the steps of: charging a solid-state battery precursor having the same configuration as the all-solid-state battery and in an uncharged state with a capacity C １ [mAh / cm ２ a first charging step of charging the all-solid-state battery precursor after the first charging step to a capacity C ２ [mAh / cm ２ and a second charging step of charging the negative electrode intermediate layer from C. When the power generating element is viewed from above, the capacity of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer is C. ｘ [mAh / cm ２ ], and the maximum value of the current density in the first charging step is I １ [mA / cm ２ ], and the minimum value of the current density in the second charging step is I ２ [mA / cm ２ ], 0.8 × C ｘ [mAh / cm ２ ]≦C １ [mAh / cm ２ ]≦C ２ [mAh / cm ２ ] and I １ [mA / cm ２ ]<I ２ [mA / cm ２ According to the manufacturing method of this embodiment, it is possible to more reliably suppress short circuits in a lithium deposition type all-solid-state battery.

[0010] Hereinafter, first, the overall structure of the all-solid-state battery manufactured by the manufacturing method according to the present embodiment will be described with reference to the attached drawings, and then the manufacturing method according to the present embodiment will be described. Note that the technical scope of the present invention should be determined based on the description of the claims, and is not limited to only the following embodiments.

[0011] 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′, a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11′, and a negative electrode intermediate layer 14 containing silver nanoparticles and carbon black and disposed between the negative electrode active material layer 13 and the solid electrolyte layer 17 are stacked. 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". The negative electrode, solid electrolyte layer, and positive electrode are laminated in this order, with the negative electrode intermediate layer 14 and the adjacent positive electrode active material layer 15 facing each other with the solid electrolyte layer 17 interposed therebetween. As a result, adjacent negative electrodes, solid electrolyte layers, and positive electrodes constitute one unit cell layer 19. Therefore, the stacked secondary battery 10a shown in FIG. 1 can be said to have a structure in which a plurality of unit cell layers 19 are laminated 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 electrode and positive electrode) are attached to the negative electrode current collector 11' and the positive electrode current collector 11", respectively, and are structured so as to be sandwiched between the ends of the laminate film 29 and extended to the outside of the laminate film 29. A constraining 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.

[0012] The main components of the all-solid-state battery according to this embodiment will be described below.

[0013] [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. There are no particular limitations 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 limitations on the thickness of the current collector, but an example is 10 to 100 μm.

[0014] [Negative Electrode Active Material Layer] The all-solid-state battery according to this embodiment is a so-called lithium deposition type battery 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.

[0015] [Negative Electrode Intermediate Layer] The negative electrode intermediate layer is a layer interposed between the negative electrode active material layer and the solid electrolyte layer, and contains a lithium-reactive material, such as a material capable of absorbing and releasing lithium ions during charging or a metal capable of alloying with lithium during charging.

[0016] The material capable of absorbing and releasing lithium ions is not particularly limited, but a carbon material is preferred. 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, 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.

[0017] 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.

[0018] The lithium-reactive material may be used alone or in combination of two or more. A preferred embodiment of using two or more materials in combination is a combination of a material capable of absorbing and releasing lithium ions and a metal capable of alloying with lithium. This ensures sufficient strength and lithium ion conductivity of the negative electrode intermediate layer. More specifically, it is preferable to use nanoparticles made of In, Si, Sn, or Ag in combination with carbon black, and it is more preferable to use nanoparticles made of Ag in combination with carbon black. When using a material capable of absorbing and releasing lithium ions in combination with a metal capable of alloying with lithium, the blending ratio (mass ratio) of the material capable of absorbing and releasing lithium ions to the metal capable of alloying with lithium is not particularly limited, but is preferably 10:1 to 1:1, more preferably 5:1 to 2:1.

[0019] The content of the lithium-reactive material in the negative electrode intermediate layer (when two or more materials are used in combination, this refers to the total content of those materials; the same applies hereinafter) is not particularly limited, but is preferably in the range of 50 to 100 mass%, more preferably in the range of 70 to 100 mass%, even more preferably in the range of 85 to 100 mass%, and particularly preferably in the range of 90 to 100 mass%.

[0020] The negative electrode intermediate layer may be composed solely of a lithium reactive material as long as a freestanding film can be produced using only the lithium reactive material, but may also contain a binder as necessary. The type of binder is not particularly limited, and binders known in the art can be appropriately used. Examples include polyvinylidene fluoride (PVDF) (including compounds in which hydrogen atoms are substituted with other halogen elements), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose.

[0021] The binder content in the negative electrode intermediate layer is not particularly limited, but is preferably in the range of 1 to 15 mass%, more preferably in the range of 5 to 10 mass%. If the binder content is 1 mass% or more, a negative electrode intermediate layer with sufficient strength can be formed. If the binder content is 15 mass% or less, a negative electrode intermediate layer with sufficient lithium ion conductivity can be formed.

[0022] The thickness of the negative electrode intermediate layer is not particularly limited, but is preferably 1 to 50 μm, more preferably 5 to 40 μm, and even more preferably 10 to 30 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 50 μm or less, a decrease in energy density can be suppressed.

[0023] [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. ４These sulfide solid electrolytes are preferably used because they have excellent lithium ion conductivity and a low bulk modulus, allowing them to follow the volume change of the electrode active material during charge and discharge.

[0024] The content of the solid electrolyte in the solid electrolyte layer is preferably 50 to 100 mass %, more preferably 90 to 100 mass %.

[0025] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte.

[0026] The thickness of the solid electrolyte layer varies depending on the configuration of the intended all-solid-state battery, but is usually 0.1 to 1000 μm, and preferably 10 to 40 μm.

[0027] [Positive Electrode Active Material Layer] The positive electrode active material layer essentially contains a positive electrode active material, and may contain a binder and a conductive additive as needed.

[0028] The type of the positive electrode active material contained in the positive electrode active material layer is not particularly limited, but may be LiCoO ２ , LiMnO ２ , LiNiO ２ , LiVO ２ , Li(Ni-Mn-Co)O ２ Layered 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 Among them, Li(Ni-Mn-Co)O ２ Also, those in which part of these transition metals has been replaced with other elements (hereinafter also simply referred to as "NMC composite oxides") are preferably used as the positive electrode active material.

[0029] In addition, a sulfur-based positive electrode active material is also one of the preferred embodiments. Examples of the sulfur-based positive electrode active material include particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and any material can be used as long as it is capable of releasing lithium ions during charging and absorbing lithium ions during discharging by utilizing the oxidation-reduction reaction of sulfur.

[0030] The content of the positive electrode active material in the positive electrode active material layer is preferably 50 to 100% by mass, more preferably 55 to 95% by mass, and even more preferably 60 to 90% by mass.

[0031] The thickness of the positive electrode active material layer varies depending on the configuration of the intended all-solid-state battery, but is usually 0.1 to 1000 μm, preferably 1 to 100 μm, and more preferably 10 to 40 μm.

[0032] Next, the manufacturing method according to this embodiment will be described. The all-solid-state battery manufactured by the manufacturing method according to this embodiment has undergone an initial charging step. Herein, the structure to which the initial charging step is applied is referred to as an "all-solid-state battery precursor." This "all-solid-state battery precursor" has the same configuration as the all-solid-state battery manufactured by the manufacturing method according to this embodiment (specifically, it essentially includes the above-described positive electrode current collector, positive electrode active material layer, solid electrolyte layer, negative electrode intermediate layer, and negative electrode current collector). The manufacturing method according to this embodiment is broadly divided into Stage 1, in which an all-solid-state battery precursor having the above-described configuration is prepared, and Stage 2, in which the all-solid-state battery precursor is subjected to an initial charging. Furthermore, the initial charging step performed in Stage 2 essentially includes a first charging step and a second charging step (details of which will be described later). This initial charging step charges the battery from the uncharged state after Stage 1 to, for example, a fully charged state. After this initial charging step, an optional discharging step may be further performed. The manufacturing method according to the present embodiment is characterized in Step 2, in which an initial charging step (and a discharging step as necessary) is performed on the all-solid-state battery precursor. Meanwhile, the method for producing the all-solid-state battery precursor in Step 1 is not particularly limited, and therefore a detailed description of Step 1 will be omitted.

[0033] [Initial Charging Step (First Charging Step and Second Charging Step)] In the step 2 of the manufacturing method according to the present embodiment, the capacity C １ [mAh / cm ２ ], and the all-solid-state battery precursor that has undergone the first charging step is charged to a capacity C ２ [mAh / cm ２ In the first charging step and the second charging step, when the power generating element is viewed from above, the capacity of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer is set to C ｘ [mAh / cm ２ ], and the maximum current density in the first charging step is I １ [mA / cm ２ ], and the minimum current density in the second charging step is I ２ [mA / cm ２ ], the formula 1: 0.8 × C ｘ [mAh / cm ２ ]≦C １ [mAh / cm ２ ]≦C ２ [mAh / cm ２ ], and Formula 2: I １ [mA / cm ２ ]<I ２ [mA / cm ２ By including these steps, a more reliable effect of suppressing short circuits can be achieved in a lithium deposition type all-solid-state battery. Although the detailed mechanism is not clear, the present inventors speculate as follows. Note that the following mechanism is merely speculation, and the technical scope of the present invention is not limited thereby.

[0034] The all-solid-state battery precursor produced in Step 1 is in an uncharged state (a state in which lithium is not contained in the lithium reactive material contained in the negative electrode intermediate layer (more specifically, a state in which lithium is not occluded in a material capable of absorbing and releasing lithium ions, and a state in which lithium is not alloyed in a metal capable of alloying with lithium)). Here, lithium ions move from the positive electrode to the negative electrode for the first time in the initial charging step of Step 2 (more specifically, the first charging step). At this time, the lithium reactive material contained in the negative electrode intermediate layer reacts electrochemically with the lithium ions. After reacting with the lithium ions, the lithium reactive material has lithium ion conductivity, and therefore, by carrying out the charging step of Step 2, lithium ions can move in the negative electrode intermediate layer. Then, when the lithium reactive material contained in the negative electrode intermediate layer has completely reacted with the lithium ions, deposition of lithium metal begins on the negative electrode current collector side of the negative electrode intermediate layer. Details of Equations 1 and 2 will be described later. In summary, in the first charging step of the manufacturing method according to the present embodiment, at least 80% of the total amount of lithium ions with which the lithium reactive material contained in the negative electrode intermediate layer can react is supplied to the negative electrode (the technical significance of Equation 1). This allows a sufficient amount of lithium reactive material to react with the lithium ions, imparting lithium ion conductivity to the negative electrode intermediate layer. Furthermore, in the first charging step, charging is performed at a relatively low charge density (low rate) compared to the second charging step (the technical significance of Equation 2). This suppresses localized reactions between the lithium reactive material and lithium ions. As a result, lithium ion conductivity is uniformly imparted to the negative electrode intermediate layer in the first charging step, and the lithium metal (negative electrode active material layer) deposited in the subsequent second charging step becomes more uniform. Furthermore, because the strength of the negative electrode intermediate layer is also uniform, even if micro-dendrites are formed in the lithium metal (negative electrode active material layer), their growth is suppressed. Therefore, a more reliable short-circuit suppression effect can be achieved in a lithium deposition-type all-solid-state battery. In the first charging step and the second charging step, which will be described in detail below, only the relative relationship of the current densities is specified, not the absolute values ​​of the current densities.This is because the required current density varies depending on the configuration of the target all-solid-state battery, and therefore the essence of the present invention cannot be expressed using the absolute value of the current density.

[0035] Formula 1 and Formula 2 will be explained in detail below. Formula 1: 0.8 × C ｘ [mAh / cm ２ ]≦C １ [mAh / cm ２ ]≦C ２ [mAh / cm ２ Formula 2: I １ [mA / cm ２ ]<I ２ [mA / cm ２ In Formula 1, C ｘ [mAh / cm ２ ] represents the capacity of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer when the power generating element is viewed in plan view. In other words, when an all-solid-state battery precursor in an uncharged state is charged, theoretically, the amount of charge required for all of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer to react with lithium ions is the capacity C ｘ [mAh / cm ２ In this specification, the capacitance C ｘ [mAh / cm ２ The value of [capacity per unit mass] is calculated by multiplying the capacity per unit mass of each material of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer by the mass of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer. The capacity per unit mass of each material is determined by the following method. 0.1 g of sample A, which is the lithium reactive material to be measured, is weighed out, placed in an SLD sleeve (Φ10), and clamped at both ends with hard Cr-plated SLD pins. The pellet A is prepared by pressing at room temperature (25°C) for 1 minute at a pressure of 390 MPa. In addition, Li as a solid electrolyte is used. ６ P.S. ５0.1 g of Cl was weighed out, and a solid electrolyte pellet was prepared in the same manner as above. SUS foil as a current collector, pellet A, a solid electrolyte pellet, lithium metal as a counter electrode, and SUS foil as a current collector were sequentially stacked to prepare a capacity measurement half cell. A confining pressure of 3 MPa was applied in the stacking direction of the capacity measurement half cell using a pressure member, and a current of 1.5 [mA / cm] was applied at a temperature of 60°C. ２ ], lithium ions are transferred from the lithium metal to pellet A. The behavior of the cell voltage at this time is measured, and the current capacity [mAh] of the lithium reactive material is determined from this behavior. The cutoff voltage differs depending on the type of lithium reactive material, but the point at which the cell voltage drops sharply is taken as the cutoff voltage. The time T (h) from the start of charging to cutoff and the constant charging current of 1.5 [mA / cm ２ ] divided by the mass (0.1 g) of sample A used in the measurement is the capacity per unit mass of sample A [mA / (g cm ２ ) )]. The mass M (g) of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer and the capacity per unit mass of each material calculated above [mA / (g cm ２ ) )] is expressed as C ｘ [mAh / cm ２ When two or more types of lithium reactive materials are contained in the negative electrode intermediate layer, the capacity per unit mass is determined for each material by the above method, and the product of this and the mass of each material contained per unit area of ​​the negative electrode intermediate layer is calculated. Then, the products calculated for all materials are summed to obtain the capacity C ｘ [mAh / cm ２ ] can be obtained.

[0036] In Formula 1, C １ is the capacity of the all-solid-state battery precursor at the end of the first charging step [mAh / cm ２ ]. ２ is the capacity of the all-solid-state battery precursor at the start of the second charging step (unit: [mAh / cm ２ The capacity of the uncharged all-solid-state battery precursor is 0 [mAh / cm ２ ].

[0037] "0.8 x C" in Equation 1 ｘ[mAh / cm ２ ]≦C １ [mAh / cm ２ ]" is the capacity C of the all-solid-state battery precursor at the end of the first charging step １ is the capacity C of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer ｘ 80% of (0.8 x C ｘ This means that the first charging step is carried out so that the capacitance is equal to or greater than 0.8×C. ｘ [mAh / cm ２ ]>C １ [mAh / cm ２ ], the second charging step (charging at a relatively high rate) is initiated in a state in which the reaction between the lithium reactive material contained in the negative electrode intermediate layer and lithium ions has not progressed sufficiently. In such a case, the lithium ion conductivity of the negative electrode intermediate layer may become non-uniform, or the strength of the negative electrode intermediate layer may become non-uniform. As a result, there is a risk that the growth of dendrites from the lithium metal (negative electrode active material layer) may not be sufficiently suppressed. From this perspective, the "0.8 × C ｘ [mAh / cm ２ ]≦C １ [mAh / cm ２ ]" 0.8 × C ｘ It is preferable that the coefficient of 0.8 is closer to 1. That is, it is preferable to set "0.9 × C ｘ ≦C １ ", and more preferably "0.95 × C ｘ ≦C １ ", and more preferably "0.98 x C ｘ ≦C １ ", and particularly preferably "1 x C ｘ ≦C １ " (units omitted). On the other hand, from the viewpoint of shortening the charging time in the manufacturing process, it is preferable that the time required for the first charging step is shorter. Therefore, from this viewpoint, "0.8 × C ｘ =C １ " is preferable. More preferably, "0.9 × C ｘ =C １ ", and more preferably "0.95 × C ｘ =C １", and more preferably "0.98 x C ｘ =C １ ", and particularly preferably "1 x C ｘ =C １ " (units omitted).

[0038] "C" in Equation 1 １ [mAh / cm ２ ]≦C ２ [mAh / cm ２ ]" is the capacity C of the all-solid-state battery precursor at the start of the second charging step ２ is the capacity C of the all-solid-state battery precursor at the end of the first charging step １ From the viewpoint of shortening the charging time in the manufacturing process, it is preferable that no other charging step and / or discharging step is included between the first charging step and the second charging step. That is, it is preferable that the second charging step is performed following the first charging step (however, a rest step may be included between the first charging step and the second charging step). In this case, the above relationship is expressed as "C １ =C ２ "

[0039] Thus, in one embodiment, Equation 1 preferably becomes "0.9 x C ｘ =C １ =C ２ ", and more preferably "0.95 × C ｘ =C １ =C ２ ", and more preferably "0.98 x C ｘ =C １ =C ２ ", and particularly preferably "1 x C ｘ =C １ =C ２ " (units omitted).

[0040] In Formula 2, I １ is the maximum value of the current density in the first charging step (unit: [mA / cm ２ The current density in the first charging step may be constant or may vary. From the viewpoint of shortening the charging time in the manufacturing process, the current density in the first charging step is constant (i.e., the current density is I １It is preferable that the temperature remains constant.

[0041] In Formula 2, I ２ is the minimum value of the current density in the second charging step (unit [mA / cm ２ The current density in the second charging step may be constant or may vary. From the viewpoint of shortening the charging time in the manufacturing process, the current density in the second charging step is constant (i.e., the current density is I ２ It is preferable that the temperature remains constant.

[0042] In the manufacturing method according to the present embodiment, the maximum value I of the current density in the first charging step １ It is preferable that the following formula 3 is further satisfied: Formula 3: I １ [mA / cm ２ ]<8×I ｘ [mA / cm ２ In Formula 3, I ｘ is the capacitance C ｘ [mAh / cm ２ ] The current density (unit [mA / cm ２ ]), where C ｘ is the same as defined in the above formula 1, and I １ is the same as the definition described in the above formula 2. Therefore, in other words, the capacity C of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer is ｘ This means that the first charging step is performed at a current density such that it takes longer than 1 / 8 hour (7.5 minutes) to charge the negative electrode intermediate layer. By performing the first charging step at such a low rate, lithium ion conductivity is imparted more uniformly to the negative electrode intermediate layer, and the lithium metal (negative electrode active material layer) deposited thereafter becomes more uniform. In addition, since the strength in the negative electrode intermediate layer also becomes more uniform, even if minute dendrites are generated in the lithium metal (negative electrode active material layer), their growth is suppressed. Therefore, it is possible to further suppress short circuits in lithium deposition-type all-solid-state batteries. From the same perspective, the maximum current density I in the first charging step １ and the maximum value I of the current density in the second charging step ２More preferably, the following formula 4 is further satisfied, and even more preferably, the following formula 5 is further satisfied. Formula 4: I １ [mA / cm ２ ]≦5×I ｘ [mA / cm ２ Formula 5: I ２ [mA / cm ２ ]≦10×I ｘ [mA / cm ２ ].

[0043] In the manufacturing method according to the present embodiment, as long as the first charging step and the second charging step are included in step 2, other charging steps may be included. However, from the viewpoint of shortening the charging time in the manufacturing process, it is preferable not to include other charging steps and / or discharging steps between the first charging step and the second charging step or after the second charging step. That is, in the first charging step, the all-solid-state battery precursor is not charged to an uncharged state (capacity 0 [mAh / cm ２ ]) to the capacity C １ [mAh / cm ２ ], and then in a second charging step, the all-solid-state battery precursor is charged to a capacity C １ (=C ２ ) [mAh / cm ２ (However, a rest step may be included between the first charging step and the second charging step.) Furthermore, it is more preferable to charge the battery to a fully charged state (SOC 100%) by the second charging step.

[0044] In the manufacturing method according to the present embodiment, in order to more reliably suppress a short circuit in a lithium deposition type all-solid-state battery, in the initial charging step of stage 2, charging is performed only by the first charging step and the second charging step described above; ｘ =C １ =C ２ and it is particularly preferable that the current density in the first charging step and the current density in the second charging step are each constant. That is, according to one embodiment, the initial charging step performed on an all-solid-state battery precursor that has the same configuration as the all-solid-state battery and is in an uncharged state satisfies a capacity C ｘ [mAh / cm ２a first charging step of charging the all-solid-state battery precursor after the first charging step to a capacity C ｘ [mAh / cm ２ and a second charging step of charging from a current density of 0.1 V to a current density of 0.2 V, wherein the current density in the first charging step is constant and the current density in the second charging step is constant.

[0045] In the manufacturing method according to this embodiment, it is more preferable to perform charging while applying a confining pressure to the all-solid-state battery precursor during the first charging step and the second charging step. That is, in the manufacturing method according to this embodiment, it is preferable that the all-solid-state battery precursor further includes a confining member that confines the power-generating element in the stacking direction, and that the first charging step and the second charging step are performed under a confining pressure of 0.1 MPa or more in the stacking direction of the power-generating element. By performing charging while applying a confining pressure in this manner, more uniform lithium ion conductivity is imparted to the negative electrode intermediate layer, and the lithium metal (negative electrode active material layer) deposited thereafter becomes more uniform. Furthermore, since the strength in the negative electrode intermediate layer becomes more uniform, even if micro-dendrites are generated in the lithium metal (negative electrode active material layer), their growth is suppressed. Therefore, it is possible to further suppress short circuits in lithium-precipitation-type all-solid-state batteries. From this perspective, the confining pressure is more preferably 0.2 MPa or more, even more preferably 1.0 MPa or more, and particularly preferably 3.0 MPa or more.

[0046] [Discharging Step] The manufacturing method according to the present embodiment may further include a discharging step of discharging the all-solid-state battery precursor that has been subjected to the first charging step and the second charging step, as necessary. When performing such a discharging step, the capacity of the all-solid-state battery precursor is 0.8×C ｘ [mAh / cm ２It is preferable to carry out the discharge step so that the capacitance is not less than 0.9×C. By carrying out the discharge step under such conditions, the subsequent charge step can be carried out while maintaining the negative electrode intermediate layer formed in the first charge step described above (i.e., in a state in which lithium is retained in the negative electrode intermediate layer and lithium ion conductivity is ensured). This makes it possible to make the lithium metal (negative electrode active material layer) deposited in the subsequent charge step more uniform. Furthermore, since the strength in the negative electrode intermediate layer also becomes more uniform, even if minute dendrites are generated in the lithium metal (negative electrode active material layer) in the subsequent charge step, their growth is suppressed. Therefore, a more reliable short-circuit suppression effect can be achieved in a lithium deposition-type all-solid-state battery. From this perspective, it is possible to achieve a more reliable short-circuit suppression effect in a lithium deposition-type all-solid-state battery precursor when the capacity of the all-solid-state battery precursor is 0.9×C. ｘ [mAh / cm ２ ] (more preferably 0.95 × C ｘ It is particularly preferable that the value is not less than 0.98×C ｘ Most preferably not less than 1×C ｘ It is more preferable to carry out a discharge step (so that the discharge voltage is not less than 100 V).

[0047] The following embodiments are also included within the scope of the present invention: a manufacturing method according to claim 1 having the features of claim 2; a manufacturing method according to claim 1 having the features of claim 3; a manufacturing method according to any one of claims 1 to 3 having the features of claim 4; a manufacturing method according to any one of claims 1 to 4 having the features of claim 5; a manufacturing method according to any one of claims 1 to 5 having the features of claim 6; and a manufacturing method according to any one of claims 1 to 6 having the features of claim 7.

[0048] <Example of Preparation of Evaluation Cell Precursor> [Evaluation Cell Precursor A] (Preparation of Positive Electrode) In a glove box with an argon atmosphere having a dew point of −68° C. or less, LiNi as a positive electrode active material was ０．８ Mn ０．１ Co ０．１ O ２ , acetylene black as a conductive additive, and Li as a solid electrolyte. ６ P.S. ５The mixture was mixed in an agate mortar and then further stirred and mixed in a planetary ball mill. Two parts by mass of styrene-butadiene rubber (SBR) as a binder was added to 100 parts by mass of the resulting mixed powder, and mesitylene was added as a solvent and mixed to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied to the surface of an aluminum foil as a positive electrode current collector, dried, and pressed to obtain a positive electrode having a positive electrode active material layer (50 μm thick) on the surface of the positive electrode current collector.

[0049] (Preparation of Solid Electrolyte Layer) In a glove box with an argon atmosphere having a dew point of −68° C. or less, Li as a solid electrolyte was ６ P.S. ５ A solid electrolyte slurry was prepared by adding 2 parts by mass of SBR as a binder to 100 parts by mass of Cl, and adding mesitylene as a solvent and mixing them. The solid electrolyte slurry was applied to the surface of a stainless steel foil as a support and dried to obtain a solid electrolyte layer (thickness: 30 μm).

[0050] (Preparation of Negative Electrode Intermediate Layer) Silver nanoparticles and carbon black nanoparticles were weighed and mixed in a mass ratio of 1:3. 0.5 parts by mass of SBR as a binder was added to 5 parts by mass of the obtained mixture, and mesitylene 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 and dried to obtain a negative electrode intermediate layer (thickness 10 μm). When the power generating element is viewed in plan, the capacity C of the mixture of silver nanoparticles and carbon black nanoparticles contained per unit area of ​​the negative electrode intermediate layer is Ｘ is 0.5 [mAh / cm ２ ]. 0.5 [mAh / cm ２ ]Current density I required for charging in 1 hour ｘ is 0.5 [mA / cm ２ ].

[0051] (Preparation of Evaluation Cell Precursor) A positive electrode active material layer formed on the surface of an aluminum foil (positive electrode current collector) and a solid electrolyte layer formed on the surface of a stainless steel foil were stacked so that the exposed surface of the positive electrode active material layer and the exposed surface of the solid electrolyte layer faced each other, and then transferred by cold isostatic pressing (CIP). After peeling off the stainless steel foil adjacent to the solid electrolyte layer, the solid electrolyte layer and the negative electrode intermediate layer formed on the surface of the stainless steel foil (negative electrode current collector) were stacked so that the exposed surface of the solid electrolyte layer and the exposed surface of the negative electrode intermediate faced each other, and then transferred by cold isostatic pressing (CIP). Finally, an aluminum positive electrode tab and a nickel negative electrode tab were bonded to the aluminum foil (positive electrode current collector) and the stainless steel foil (negative electrode current collector), respectively, using an ultrasonic welder. The resulting laminate was placed inside an aluminum laminate film and vacuum sealed to obtain an evaluation cell precursor A, which is a lithium deposition-type all-solid-state battery precursor.

[0052] [Evaluation Cell Precursor B] Evaluation cell precursor B was obtained in the same manner as the evaluation cell precursor A, except that no negative electrode intermediate layer was provided (i.e., in the above (Production of evaluation cell precursor) a stainless steel foil (negative electrode current collector) on which no negative electrode intermediate layer was formed was superposed on the exposed surface of the solid electrolyte layer).

[0053] <Example of Initial Charging of Evaluation Cell Precursor> The evaluation cell precursor prepared above was subjected to the following initial charging at a temperature of 60° C. while applying a restraining pressure of 3 MPa in the stacking direction using a pressure member.

[0054] [Example 1] A constraining pressure of 3 MPa was applied to the evaluation cell precursor A in the stacking direction using a pressure member, and a pressure of 3.0 [mA / cm ２ ](= 6 × I ｘ ) at a constant current of 0.5 [mAh / cm ２ ](1×C ｘ ) (first charging step). ２ ](=12×I ｘ The battery was charged at a constant current of 0.5 [mAh / cm 2 ] until the voltage reached 4.3 V (second charging step), and the charge capacity at this time was measured. ２The sum of the charge capacity in the first charging step and the charge capacity in the second charging step was defined as the charge capacity in the first charging step.

[0055] [Examples 2 to 7, Comparative Examples 2 and 3] Evaluation cell precursor A was initially charged in the same manner as in Example 1, except that the confining pressure, the current density in the first charging step, and / or the current density in the second charging step were changed to the values ​​shown in Table 1. In this way, evaluation cell A after charging was obtained.

[0056] Comparative Example 1 A pressure of 1.5 [mA / cm ] was applied to the evaluation cell precursor B using a pressure member in the stacking direction while applying a restraining pressure of 3 MPa. ２ ](=3×I ｘ ) at a constant current of 0.5 [mAh / cm ２ ] was charged (first charging step). ２ ](=8×I ｘ The battery was charged at a constant current of 0.5 [mAh / cm 2 ] until the voltage reached 4.3 V (second charging step), and the charge capacity at this time was measured. ２ The charge capacity in the first charge was calculated by adding the charge capacity in the second charge step to the charge capacity in the first charge step. In this way, a charged evaluation cell B was obtained.

[0057] <Evaluation of Charge / Discharge Efficiency and Rate Characteristics> The charge / discharge efficiency and rate characteristics of each evaluation cell were evaluated under the following conditions.

[0058] First, after the initial charge, each evaluation cell was charged at 6.0 [mA / cm ２ The battery was discharged at a constant current of 1000 kJ / s until the voltage reached 2.5 V, and the discharge capacity of the initial discharge was measured. The percentage of the discharge capacity of the initial discharge relative to the charge capacity of the initial charge was calculated, and the resulting value was taken as the charge-discharge efficiency.

[0059] Subsequently, after the initial charge and discharge, each evaluation cell was charged at 60°C with a current of 0.55 [mA / cm ２ The battery was charged at a constant current of 0.55 [mA / cm 2 ] until the voltage reached 4.3 V, and the charge capacity at this time was measured. ２The battery was then discharged at a constant current of 5.5 [mA / cm 2 ] at a temperature of 60° C. until the voltage reached 2.5 V. ２ The battery was charged at a constant current of 5.5 [mA / cm 2 ] until the voltage reached 4.3 V, and the charge capacity at this time was measured. ２ The battery was discharged at a constant current of 0.55 [mA / cm 2 ] until the voltage reached 2.5 V. ２ ] to the charge capacity at 5.5 [mA / cm ２ The ratio of the charge capacity at each charge capacity was calculated, and the obtained value was taken as the charge capacity ratio. The larger the charge capacity ratio, the better the rate characteristics.

[0060] The results are shown in Table 1 below. In Table 1, "-" indicates that measurement was not possible due to the occurrence of a short circuit.

[0061]

[0062] The results in Table 1 show that the present invention can more reliably suppress short circuits in lithium deposition-type all-solid-state batteries.

[0063] Comparing Example 1 and Example 3, I １ [mA / cm ２ ]≦5×I ｘ [mA / cm ２ ], the charge capacity ratio becomes larger (rate characteristics are improved). ２ [mA / cm ２ ]≦10×I ｘ [mA / cm ２ ] is further satisfied, the charge capacity ratio increases (rate characteristics improve). This is thought to be due to the fact that the growth of dendrites is further suppressed, thereby suppressing the increase in internal resistance caused by the reductive decomposition of the solid electrolyte. Furthermore, by comparing Example 2, Example 3, and Example 4, it is clear that I １ [mA / cm ２ ]≦5×I ｘ [mA / cm ２ ]and I ２ [mA / cm ２ ]≦10×I ｘ [mA / cm ２], the charge capacity ratio becomes even larger (rate characteristics are improved).

[0064] A comparison of Examples 4 to 7 reveals that as the confining pressure increases, the charge / discharge efficiency tends to increase and the charge capacity ratio also increases (rate characteristics improve). This is thought to be due to the fact that the electrochemical reaction between lithium ions and the lithium reactive material contained in the negative electrode intermediate layer proceeds more uniformly, improving the lithium conductivity of the negative electrode intermediate and uniformly depositing lithium metal between the negative electrode and the current collector.

[0065] 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, 15 positive electrode active material layer, 17 solid electrolyte layer, 19 single cell layer, 21 power generating element, 25 negative electrode current collector, 27 positive electrode current collector, 29 laminate film.

Claims

a positive electrode including a positive electrode active material layer disposed on a surface of a positive electrode current collector, the positive electrode active material layer containing a positive electrode active material capable of absorbing and releasing lithium ions; a negative electrode having a negative electrode current collector on which lithium metal is deposited during charging; a solid electrolyte layer interposed between the positive electrode and the negative electrode and containing a solid electrolyte; a negative electrode intermediate layer interposed between the negative electrode current collector and the solid electrolyte layer, the negative electrode intermediate layer including at least one lithium-reactive material selected from the group consisting of materials capable of absorbing and releasing lithium ions and metals capable of alloying with lithium; A method for manufacturing an all-solid-state battery including a power generating element having The capacity C １ [mAh / cm ２ a first charging step of charging the battery until The capacity C of the all-solid-state battery precursor that has undergone the first charging step ２ [mAh / cm ２ a second charging step of charging from and When the power generating element is viewed in plan, the capacity of the lithium reactive material contained per unit area of ​​the negative electrode intermediate layer is defined as C ｘ [mAh / cm ２ ], and the maximum value of the current density in the first charging step is I １ [mA / cm ２ ], and the minimum value of the current density in the second charging step is I ２ [mA / cm ２ ], 0.8 x C ｘ [mAh / cm ２ ]≦C １ [mAh / cm ２ ]≦C ２ [mAh / cm ２ ],and I １ [mA / cm ２ ]<I ２ [mA / cm ２ A method for manufacturing an all-solid-state battery that satisfies the following requirements. 　 Capacity C ｘ [mAh / cm ２ ]The current density required to charge for 1 hour is I ｘ [mA / cm ２ ], then I １ [mA / cm ２ ]<8×I ｘ [mA / cm ２ The method for producing an all-solid-state battery according to claim 1 , further satisfying the above condition. 　 Capacity C ｘ [mAh / cm ２ ]The current density required to charge for 1 hour is I ｘ [mA / cm ２ ], then I １ [mA / cm ２ ]≦5×I ｘ [mA / cm ２ The method for producing an all-solid-state battery according to claim 1 , further satisfying the above condition. 　 Capacity C ｘ [mAh / cm ２ ]The current density required to charge for 1 hour is I ｘ [mA / cm ２ ], then I ２ [mA / cm ２ ]≦10×I ｘ [mA / cm ２ The method for producing an all-solid-state battery according to claim 1 , further satisfying the above condition. 　 The initial charging step performed on an all-solid-state battery precursor having the same configuration as the all-solid-state battery and in an uncharged state is ｘ [mAh / cm ２ a first charging step of charging the battery until The capacity C of the all-solid-state battery precursor that has undergone the first charging step ｘ [mAh / cm ２ a second charging step of charging from consists only of The current density in the first charging step is constant, and The method for producing an all-solid-state battery according to claim 1 , wherein the current density in the second charging step is constant. 　 the all-solid-state battery precursor further includes a restraining member that restrains the power-generating element in a stacking direction, 3. The method for producing an all-solid-state battery according to claim 1, wherein the first charging step and the second charging step are performed in a state where a confining pressure in a stacking direction of the power-generating element is 0.1 MPa or more. 　 The all-solid-state battery precursor that has been subjected to the second charging step is charged to a capacity of 0.8×C ｘ [mAh / cm ２ The method for producing an all-solid-state battery according to claim 1 or 2, further comprising a discharging step of discharging the battery so that the charge / discharge voltage is not less than 100 V.