All-solid-state battery

Abstract

Provided is a means, in a lithium deposition-type all-solid-state battery, for making an internal short circuit of the battery less likely to occur, even after repeated charge / discharge cycles. The problem, in said all-solid-state battery provided with a lithium deposition-type power generation element, can be solved by arranging a negative electrode intermediate layer, which contains a carbon material and a solid electrolyte, adjacent to a negative electrode current collector-side surface of the solid electrolyte layer.

Description

All solid state battery

[0001] The present invention relates to an all-solid-state battery.

[0002] In recent years, research and development on all-solid-state 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 batteries have the advantage that, in principle, they do not encounter the various problems associated with flammable organic electrolytes, as occurs in conventional liquid-based batteries that use nonaqueous electrolytes.

[0003] One type of all-solid-state secondary battery is known as a lithium deposition type, in which lithium metal is deposited on a negative electrode current collector during charging. In such lithium deposition type all-solid-state secondary batteries, dendrites derived from the deposited lithium metal are formed on the negative electrode during charging, which may cause an internal short circuit in the battery.

[0004] As a technology intended to address such problems, for example, Japanese Patent Laid-Open Publication No. 2019-96610 discloses a technology in which a negative electrode active material layer containing a negative electrode active material such as amorphous carbon and a binder is disposed between a negative electrode current collector and a solid electrolyte layer. According to this document, with the above-described configuration, lithium is absorbed into the negative electrode active material layer during the battery charging process, and then lithium metal is precipitated between the negative electrode active material layer and the negative electrode current collector.

[0005] However, in the course of investigations by the present inventors, it was found that, according to the technology described in the above document, lithium metal may actually be precipitated between the negative electrode active material layer and the solid electrolyte layer during the charging process of the battery, and that this lithium metal precipitation may cause the generation of dendrites and the resulting internal short circuit.

[0006] Therefore, an object of the present invention is to provide a means for making it difficult for an internal short circuit to occur in a lithium deposition type all-solid-state battery even as charge / discharge cycles progress.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by disposing a negative electrode intermediate layer containing a carbon material and a solid electrolyte in a position corresponding to the negative electrode active material layer in the above-mentioned document in an all-solid-state battery including a lithium deposition-type power generating element, thereby completing the present invention.

[0008] That is, one embodiment of the present invention is an all-solid-state 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 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 first solid electrolyte; and a negative electrode intermediate layer present adjacent to a surface of the solid electrolyte layer facing the negative electrode current collector and containing a carbon material and a second solid electrolyte.

[0009] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (stacked-type secondary battery) according to one embodiment of the present invention.

[0010] One embodiment of the present invention is an all-solid-state 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 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 first solid electrolyte; and a negative electrode intermediate layer adjacent to a surface of the solid electrolyte layer facing the negative electrode current collector and containing a carbon material and a second solid electrolyte. The all-solid-state battery according to this embodiment is less likely to develop an internal short circuit even as charge-discharge cycles progress.

[0011] 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.

[0012] FIG. 1 is a cross-sectional view schematically illustrating the overall structure of a stacked-type (internal parallel connection type) all-solid-state lithium secondary battery (hereinafter also simply referred to as a "stacked-type secondary battery") according to one embodiment of the present invention. FIG. 1 shows a cross section of the stacked-type secondary battery during charging. The stacked-type secondary battery 10a shown in FIG. 1 has a structure in which a substantially rectangular power-generating element 21, where charge and discharge reactions actually proceed, is sealed inside a laminate film 29, which is a battery exterior. The power-generating element 21 has a structure in which a negative electrode, a solid electrolyte layer 17, and a positive electrode are stacked. The negative electrode has a structure in which a negative electrode current collector 11' and a negative electrode active material layer 13 made of lithium metal deposited on the surface of the negative electrode current collector 11' are stacked. A negative electrode intermediate layer 14 is disposed adjacent to the surface of the negative electrode active material layer 13 facing the solid electrolyte layer 17. 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 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.

[0013] The main components of the all-solid-state battery according to this embodiment will be described below.

[0014] [Current Collector] The current collector (negative electrode current collector, positive electrode current collector) has the function of mediating the movement of electrons from the electrode active material layer (negative electrode active material layer, positive electrode active material layer). There are no particular restrictions on the material that constitutes the current collector. Examples of materials that can be used for the current collector include metals such as aluminum, nickel, iron, stainless steel, titanium, and copper, as well as conductive resins. There are also no particular restrictions on the thickness of the current collector, but an example is 10 to 100 μm.

[0015] [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 charging. The layer of lithium metal deposited on the negative electrode current collector during charging is the negative electrode active material layer of the all-solid-state battery according to this embodiment. Therefore, the thickness of the negative electrode active material layer increases as the charging process progresses, and decreases as the discharging process progresses. The negative electrode active material layer need not be present during full discharge, but in some cases, a negative electrode active material layer containing a certain amount of lithium metal may be present during full discharge. 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. In addition, in the all-solid-state battery according to this embodiment, the negative electrode intermediate layer (described later) contains a solid electrolyte, thereby reducing the likelihood of internal short circuits occurring in the battery even as charge-discharge cycles progress. This is because lithium metal is less likely to deposit between the solid electrolyte layer and the negative electrode intermediate layer during charging. Therefore, in a preferred embodiment of the all-solid-state battery according to this aspect, lithium metal does not precipitate between the solid electrolyte layer and the negative electrode intermediate layer during charging.

[0016] [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). In this specification, the solid electrolyte contained in the solid electrolyte layer is referred to as the "first solid electrolyte," and the solid electrolyte contained in the negative electrode intermediate layer (described later) is referred to as the "second solid electrolyte." Therefore, the order of "first" and "second" itself has no meaning; these terms are merely used to distinguish the locations where the solid electrolyte is present. The solid electrolyte (first solid electrolyte) contained in the solid electrolyte layer is not particularly limited, and any known solid electrolyte in the art can be appropriately used. Examples include sulfide solid electrolytes and oxide solid electrolytes. This solid electrolyte exhibits excellent lithium ion conductivity, and is therefore preferably a sulfide solid electrolyte containing an S element, more preferably a sulfide solid electrolyte containing a Li element, an M element, and an S element, wherein the M element contains at least one element selected from the group consisting of P, Si, Ge, Sn, Ti, Zr, Nb, Al, Sb, Br, Cl, and I, and even more preferably a sulfide solid electrolyte containing an S element, a Li element, and a P element. An example is 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. ４ These sulfide solid electrolytes are preferably used because they have excellent lithium ion conductivity.

[0017] The ionic conductivity (e.g., Li ion conductivity) of the sulfide solid electrolyte at room temperature (25°C) is, for example, 1 × 10 －５ S / cm or more, and preferably 1×10 －４ The ionic conductivity of the solid electrolyte can be measured by an AC impedance method.

[0018] Examples of the shape of the solid electrolyte include particulate shapes such as spherical shapes and oval spherical shapes, thin films, etc. When the solid electrolyte is particulate, its average particle size (D50) is not particularly limited, but is preferably 0.01 μm or more and 40 μm or less, more preferably 0.1 μm or more and 20 μm or less, and even more preferably 0.5 μm or more and 10 μm or less.

[0019] The content of the solid electrolyte in the solid electrolyte layer is preferably 50 to 100 mass %, more preferably 90 to 100 mass %.

[0020] The solid electrolyte layer may further contain a binder in addition to the solid electrolyte. The binder is not particularly limited, and known binders can be used as appropriate. For example, the binders described below for the negative electrode intermediate layer can be similarly used. The content of the binder in the solid electrolyte layer is not particularly limited, and is, for example, 1 to 10 mass %.

[0021] The thickness of the solid electrolyte layer varies depending on the intended configuration of the all-solid-state battery, but is usually 0.1 to 1000 μm, and preferably 10 to 100 μm.

[0022] [Positive Electrode Active Material Layer] The positive electrode active material layer essentially contains a positive electrode active material, and may contain a solid electrolyte, a binder, and a conductive additive as needed.

[0023] The type of the positive electrode active material contained in the positive electrode active material layer is not particularly limited, but first, a lithium-containing positive electrode active material can be mentioned. Examples of the lithium-containing positive electrode active material include 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 , Li２ MnSiO ４ , Li ４ Ti ５ O １２ Among them, Li(Ni-Mn-Co)O ２ and those in which a portion of these transition metals has been replaced with other elements (hereinafter also referred to simply as "NMC composite oxides") are preferably used as the positive electrode active material. If these lithium-containing positive electrode active materials are used as the positive electrode active material, no active material need be placed on the negative electrode side during battery production. However, some negative electrode active material (such as lithium metal) may be placed.

[0024] In addition, a preferred embodiment is to use a lithium-free positive electrode active material, such as a sulfur-based positive electrode active material, as the positive electrode active material. Examples of sulfur-based positive electrode active materials include particles or thin films of organic sulfur compounds or inorganic sulfur compounds, and any material can be used as long as it can release lithium ions during charging and absorb lithium ions during discharging using the oxidation-reduction reaction of sulfur. If these lithium-free positive electrode active materials are used as the positive electrode active material, it is necessary to place an active material such as lithium metal on the negative electrode side (between the negative electrode current collector and the negative electrode intermediate layer) during battery production.

[0025] The content of the positive electrode active material in the positive electrode active material layer is not particularly limited, but is preferably, for example, 30 to 99 mass %, more preferably 40 to 90 mass %, and even more preferably 45 to 80 mass %.

[0026] The positive electrode active material layer preferably further contains a solid electrolyte. The specific form of the solid electrolyte contained in the positive electrode active material layer may be the same as that described in the solid electrolyte layer section. A sulfide solid electrolyte is preferably used because it has excellent lithium ion conductivity and a low bulk modulus, allowing it to follow the volumetric changes of the positive electrode active material that occur during charging and discharging. The content of the solid electrolyte in the positive electrode active material layer is not particularly limited, but is, for example, 1 to 70% by mass, preferably 10 to 60% by mass, and more preferably 20 to 55% by mass.

[0027] The binder used in the positive electrode active material layer is not particularly limited, and any known binder can be used as appropriate. For example, the binder described below for the negative electrode intermediate layer can be used. The content of the binder in the positive electrode active material layer is not particularly limited, and is, for example, 1 to 10 mass %.

[0028] The conductive additive used in the positive electrode active material layer is not particularly limited, and may be, for example, carbon such as carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.). The content of the conductive additive in the positive electrode active material layer is not particularly limited, and is, for example, 10 to 30 mass%.

[0029] The thickness of the positive electrode active material layer varies depending on the intended configuration of the all-solid-state battery, but is usually 0.1 to 1000 μm, and preferably 10 to 300 μm.

[0030] [Negative electrode intermediate layer] The negative electrode intermediate layer is a layer adjacent to the surface of the solid electrolyte layer facing the negative electrode current collector, and contains a carbon material and a solid electrolyte (second solid electrolyte). The negative electrode intermediate layer is preferably conductive as a whole. The volume resistivity of the negative electrode intermediate layer is not particularly limited, but is preferably 10 ２ In this specification, the volume resistivity of the negative electrode intermediate layer is a value measured using an electrode resistance measurement system (manufactured by Hioki E.E. Corporation, product name: RM2610).

[0031] The carbon material contained in the negative electrode intermediate layer is preferably at least one selected from the group consisting of carbon materials capable of absorbing lithium ions. By including a carbon material capable of absorbing lithium ions in the negative electrode intermediate layer, the precipitation and growth of lithium dendrites can be further suppressed. Specific examples of carbon materials capable of absorbing lithium ions include carbon black (specifically, acetylene black, Ketjen Black (registered trademark), furnace black, channel black, thermal lamp black, etc.), carbon nanotubes (CNT), graphite, hard carbon, etc. Among these, the carbon material preferably includes at least one selected from the group consisting of carbon black, and more preferably includes at least one selected from the group consisting of acetylene black, Ketjen Black (registered trademark), furnace black, channel black, and thermal lamp black. In a preferred embodiment, the negative electrode intermediate layer includes at least one type of carbon particles containing the above-mentioned carbon material capable of absorbing lithium ions. This can effectively contribute to improving the rate characteristics of the all-solid-state battery.

[0032] The average particle size (average primary particle size) of the carbon particles is not particularly limited, but is, for example, 200 nm or less, preferably 150 nm or less, and more preferably 100 nm or less. There is no particular limit on the lower limit of the average particle size of the carbon particles, but it is, for example, 10 nm or more, preferably 15 nm or more, and more preferably 20 nm or more. In this specification, the average particle size of the particles refers to the 50% cumulative diameter (D50) of the particle diameters of the particles observed in several to several tens of fields of view when the cross section of a layer containing the particles is observed using a scanning electron microscope (SEM) (the maximum distance between any two points on the outline of the observed particles). There is no particular limit on the content of the carbon material in the negative electrode intermediate layer, but it is, for example, 50 to 90 mass%, preferably 60 to 80 mass%, and more preferably 65 to 77 mass%.

[0033] The negative electrode intermediate layer essentially contains a solid electrolyte (second solid electrolyte). The specific form of the solid electrolyte contained in the negative electrode intermediate layer can be the same as that described in the solid electrolyte layer section. A sulfide solid electrolyte is preferably used because of its excellent lithium ion conductivity. The content of the solid electrolyte in the negative electrode intermediate layer is not particularly limited, but is, for example, 5 to 34% by mass, preferably 8 to 25% by mass, and more preferably 10 to 20% by mass, relative to 100% by mass of the total amount of the negative electrode intermediate layer.

[0034] The negative electrode intermediate layer may further contain at least one metal material. Examples of such metal materials include indium (In), aluminum (Al), silicon (Si), tin (Sn), magnesium (Mg), gold (Au), silver (Ag), zinc (Zn), nickel (Ni), copper (Cu), and alloys containing at least one of these. When the negative electrode intermediate layer contains these metal materials, the metal material preferably contains at least one selected from the group consisting of In, Al, Si, Sn, Mg, Au, Ag, and Zn, more preferably contains at least one selected from the group consisting of Ag, Mg, Zn, and Al, even more preferably contains at least one selected from the group consisting of Ag, Mg, and Zn, and particularly preferably contains Ag. The average primary particle diameter of the metal particles is, for example, 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, and particularly preferably 80 nm or less. There is no particular lower limit to the average primary particle size of the metal particles, but it is, for example, 10 nm or more, preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more.

[0035] However, from the viewpoint of further enhancing the effects of the all-solid-state battery according to this embodiment, the content of the metallic material capable of being alloyed with lithium in the negative electrode intermediate layer is preferably as small as possible, for example, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, particularly preferably 0.5% by mass or less, and most preferably 0% by mass, relative to 100% by mass of the total amount of the negative electrode intermediate layer (i.e., it is most preferable that the negative electrode intermediate layer does not contain a metallic material capable of being alloyed with lithium). This is because a small content of the metallic material capable of being alloyed with lithium in the negative electrode intermediate layer allows lithium ions that migrate from the positive electrode to the negative electrode side during charging to reach the surface of the negative electrode current collector without being captured by the negative electrode intermediate layer, thereby more reliably depositing lithium metal between the negative electrode current collector and the negative electrode intermediate layer. The smaller the content of all metal materials in the negative electrode intermediate layer, the better. For example, the content of all metal materials is preferably 5 mass% or less, more preferably 3 mass% or less, even more preferably 1 mass% or less, particularly preferably 0.5 mass% or less, and most preferably 0 mass% relative to 100 mass% of the total amount of the negative electrode intermediate layer (i.e., it is most preferable that the negative electrode intermediate layer does not contain any metal materials).

[0036] The negative electrode intermediate layer preferably further contains a binder. The type of binder is not particularly limited, and binders known in the art can be appropriately used. Examples of binders include polyvinylidene fluoride (PVDF), compounds in which hydrogen atoms of PVDF are substituted with other halogen elements, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC). Among these, the binder preferably contains polyvinylidene fluoride (PVDF) or styrene-butadiene rubber (SBR). The content of the binder in the negative electrode intermediate layer is not particularly limited, but is, for example, 8 to 20% by mass, preferably 10 to 18% by mass, and more preferably 12 to 16% by mass.

[0037] The proportion of the total mass of the carbon material, the solid electrolyte (second solid electrolyte), and the binder relative to the total mass (100% by mass) of the negative electrode intermediate layer is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, particularly preferably 99% by mass or more, and most preferably 100% by mass.

[0038] The thickness of the negative electrode intermediate layer is not particularly limited, but is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. When the thickness of the negative electrode intermediate layer is 30 μm or less, the path of lithium ions moving through the negative electrode intermediate layer during charging is not too long, so that the resistance during charging can be kept low. In addition, the energy density of the all-solid-state battery can be improved. The lower limit of the thickness of the negative electrode intermediate layer is not particularly limited, but from the viewpoint of ensuring the strength of the negative electrode intermediate layer, it is preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more.

[0039] Although one embodiment of the all-solid-state 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.

[0040] For example, the type of battery to which the all-solid-state lithium secondary battery according to the present invention is applied also 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.

[0041] The following embodiments are also included within the scope of the present invention: an all-solid-state battery according to claim 1 having the features of claim 2; an all-solid-state battery according to claim 1 or 2 having the features of claim 3; an all-solid-state battery according to claim 3 having the features of claim 4; an all-solid-state battery according to any one of claims 1 to 4 having the features of claim 5; an all-solid-state battery according to any one of claims 1 to 5 having the features of claim 6; an all-solid-state battery according to any one of claims 1 to 5 having the features of claim 7; and an all-solid-state battery according to any one of claims 1 to 7 having the features of claim 8.

[0042] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Note that the following operations were performed in a glove box. Furthermore, the instruments and devices used in the glove box were thoroughly dried beforehand.

[0043] <Examples of Preparation of Evaluation Cells> [Example 1] (Preparation of Negative Electrode Intermediate Layer) After weighing out a carbon material (acetylene black, DENKA BLACK Li-100 (manufactured by Denka Co., Ltd.)) and a sulfide solid electrolyte powder into a glass sample bottle, a toluene solution of styrene butadiene rubber was added. Next, toluene was added until a predetermined viscosity was reached, and the mixture was mixed for 5 minutes using an ultrasonic mixer. The resulting slurry was then applied to a 10 μm thick stainless steel (SUS430) foil using a 15 μm thick applicator and dried overnight in vacuum at room temperature to obtain a negative electrode intermediate layer (thickness 15 μm). The materials were weighed so that the compounding ratio of the constituent materials in the resulting negative electrode intermediate layer was carbon material: sulfide solid electrolyte: styrene butadiene rubber = 76:10:14 (mass ratio).

[0044] (Preparation of Evaluation Cell) 100 mg of sulfide solid electrolyte was weighed, placed in a Macol tube, sandwiched between hard Cr-plated SLD pins, and pressed at room temperature for 1 second at a pressure of 200 MPa to obtain an electrolyte pellet. Next, a 0.02 mm thick indium foil was placed on one side of the electrolyte pellet, and the negative electrode intermediate layer prepared above was placed on the other side, and pressed at room temperature for 1 minute at a pressure of 400 MPa. Then, a 0.15 mm thick lithium foil, a 0.3 mm thick indium foil, and a 10 μm thick stainless steel (SUS430) foil as a current collector were placed in this order on the indium foil. Meanwhile, a 10 μm thick stainless steel (SUS430) foil was placed on the negative electrode intermediate layer as a current collector, and pressed at room temperature for 1 second at a pressure of 100 MPa to prepare an evaluation cell (lithium symmetric cell). The confining pressure during cell assembly was 3 MPa.

[0045] Example 2 A test cell of this example was produced using the same method as in Example 1 described above, except that the components were weighed so that the compounding ratio of the constituent materials in the obtained negative electrode intermediate layer was carbon material: sulfide solid electrolyte: styrene-butadiene rubber = 68.8:17.2:14 (mass ratio).

[0046] Example 3 A test cell of this example was produced using the same method as in Example 1 described above, except that the materials were weighed so that the compounding ratio of the constituent materials in the obtained negative electrode intermediate layer was carbon material: sulfide solid electrolyte: styrene-butadiene rubber = 66:20:14 (mass ratio).

[0047] Comparative Example 1 A test cell of this comparative example was produced using the same method as in Example 1 described above, except that the components were weighed so that the blending ratio of the constituent materials in the resulting negative electrode intermediate layer was carbon material: sulfide solid electrolyte: styrene-butadiene rubber = 86:0:14 (mass ratio) (no sulfide solid electrolyte was blended).

[0048] <Evaluation Example of Evaluation Cell> (Measurement of AC Impedance) For the test cells (lithium symmetric cells) prepared above, AC impedance measurements were performed using an electrochemical measurement system (Model 1260A) manufactured by Solartron under conditions of a frequency range of 10 MHz to 0.05 Hz and a voltage amplitude of 10 mV. If an arc appeared in the Cole-Cole plot obtained as a result of the AC impedance measurement, the test cell was determined to be not short-circuited, and if no arc appeared, the test cell was determined to be short-circuited. Here, the appearance of an arc was confirmed in all of the test cells of Examples 1 to 3 and Comparative Example 1, so these test cells were determined to be not short-circuited.

[0049] (Charge-Discharge Cycle Test) A positive electrode lead and a negative electrode lead were connected to the positive electrode current collector and the negative electrode current collector, respectively, of the evaluation cell (lithium symmetric cell) prepared above, and a cycle charge-discharge test was performed while applying a restraining pressure of 3 MPa in the stacking direction of the evaluation cell using a pressure member. At this time, charge-discharge was performed using an electrochemical diagnostic device (VSP-300, manufactured by BioLogic) in a constant temperature bath set at 60°C using the following method.

[0050] First, the charging current density was set to 0.2 mA / cm ２ The initial charge was 6.4mAh / cm ２ The capacity was then charged to 0.1 V (vs. Li / Li ＋ ) and discharged (first cycle). After that, the battery was charged to a capacity corresponding to the discharge capacity exhibited in the previous cycle, and the cutoff voltage was again set to 0.1 V (vs. Li / Li ＋ ) and discharge cycle was repeated eight times (a total of nine cycles). The test cell was judged to have had a short circuit when unstable voltage behavior (noise) occurred during the charging process of the charge / discharge curve. The occurrence of a short circuit in each experimental example is shown in Table 1 below.

[0051] (Observation of Cross Section of Test Cell) The test cell (lithium symmetric cell) prepared above was subjected to the same charging process as the first cycle charging process of the charge-discharge cycle test described above, and then its cross section in the stacking direction was observed using a scanning electron microscope (SEM). As a result, in Examples 1 to 3, it was observed that lithium metal was precipitated only at the interface between the negative electrode current collector and the negative electrode intermediate layer. In contrast, in Comparative Example 1, it was also observed that lithium metal was precipitated between the solid electrolyte layer and the negative electrode intermediate layer.

[0052]

[0053] The results shown in Table 1 indicate that the inclusion of a solid electrolyte in addition to a carbon material as a constituent material of the negative electrode intermediate layer suppresses the occurrence of short circuits as charge-discharge cycles progress. As described above, in Comparative Example 1, lithium metal still precipitated between the solid electrolyte layer and the negative electrode intermediate layer during the charging process, whereas in the Examples, lithium metal precipitated only between the negative electrode current collector and the negative electrode intermediate layer during the charging process. This suggests that the occurrence of short circuits as charge-discharge cycles progressed was suppressed in the Examples by preventing the formation of lithium metal dendrites between the solid electrolyte layer and the negative electrode intermediate layer.

[0054] 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

1. An all-solid-state battery comprising 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 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 first solid electrolyte; and a negative electrode intermediate layer adjacent to a surface of the solid electrolyte layer facing the negative electrode current collector, the solid electrolyte layer containing a carbon material and a second solid electrolyte.

2. The all-solid-state battery according to claim 1, wherein the lithium metal does not precipitate between the solid electrolyte layer and the negative electrode intermediate layer during charging.

3. The all-solid-state battery according to claim 1 or 2, wherein the content of the second solid electrolyte in the negative electrode intermediate layer is 5 to 34 mass % relative to 100 mass % of the total amount of the negative electrode intermediate layer.

4. The all-solid-state battery according to claim 3, wherein the content of the second solid electrolyte in the negative electrode intermediate layer is 10 to 20 mass % relative to 100 mass % of the total amount of the negative electrode intermediate layer.

5. The all-solid-state battery according to claim 1 or 2, wherein the second solid electrolyte comprises a sulfide solid electrolyte.

6. The all-solid-state battery according to claim 1 or 2, wherein the positive electrode active material comprises a lithium-containing positive electrode active material.

7. The all-solid-state battery according to claim 1 or 2, wherein the positive electrode active material comprises a lithium-free positive electrode active material.

8. The all-solid-state battery according to claim 1 or 2, wherein the negative electrode intermediate layer does not contain a metal material capable of being alloyed with lithium.

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