JP2017199539A - Solid electrolyte structure, lithium battery, and method of manufacturing solid electrolyte structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte structure low in interface resistance and hardly causing a short circuit between electrodes.SOLUTION: A solid electrolyte structure includes a solid electrolyte substrate containing a lithium ion conductive solid electrolyte and a lithium carbonate layer formed on a surface of the solid electrolyte substrate. Particles of the solid electrolyte exposed on the surface of the solid electrolyte substrate have a size of 10 μm or less, and the lithium carbonate layer has a thickness of 100 nm or less.SELECTED DRAWING: Figure 2

Description

  The technique disclosed by this specification is related with a solid electrolyte structure.

  In recent years, with the spread of electronic devices such as personal computers and mobile phones, the spread of electric vehicles, and the expansion of the use of natural energy such as sunlight and wind power, the demand for high-performance batteries is increasing. Especially, utilization of the all-solid-state lithium ion secondary battery by which all the battery elements are comprised is anticipated. All-solid lithium ion secondary batteries are safer than conventional lithium ion secondary batteries that use organic electrolytes in which a lithium salt is dissolved in an organic solvent, because there is no risk of leakage or ignition of organic electrolytes. In addition, since the exterior can be simplified, the energy density per unit mass or unit volume can be improved.

The electrolyte layer of the all solid lithium ion secondary battery is formed by a solid electrolyte structure including a lithium ion conductive solid electrolyte. Examples of the lithium ion conductive solid electrolyte include a solid electrolyte having a garnet-type crystal structure or a garnet-type similar crystal structure containing at least Li (lithium), La (lanthanum), Zr (zirconium), and O (oxygen). (For example, Li ₇ La ₃ Zr ₂ O ₁₂ (hereinafter referred to as “LLZ”)).

  In an all-solid-state lithium ion secondary battery, since the electrolyte layer and the electrode are both solid, the contact resistance at the interface between the electrolyte layer and the electrode tends to be higher than that of a conventional lithium ion secondary battery. In addition, in an all-solid-state lithium ion secondary battery, when a DC voltage is applied at a relatively high current density during charging, lithium ions that have moved to the negative electrode side through the electrolyte layer are deposited in a protruding shape on the negative electrode surface. There is a possibility that protruding lithium penetrates the electrolyte layer and short-circuits between the electrodes (for example, see Non-Patent Document 1).

Yaoyu Ren, et al., "Direct observation of lithium dendrites in-situ garnet-type lithium-ion solid-electrolyte chemistry," "Electronic observation of lithium dendrites in garnet-type lithium ion solid electrolyte" Electrochemistry Communications), Elsevier BV, The Netherlands, May 15, 2015, No. 57, p. 27-30

  Thus, as a solid electrolyte structure used for an electrolyte layer of an all-solid-state lithium ion secondary battery, a solid electrolyte structure having low interface resistance with an electrode and hardly causing a short circuit between the electrodes is required. In addition, such a subject is a subject common not only to the solid electrolyte structure used for the electrolyte layer of an all-solid-state lithium ion secondary battery but the solid electrolyte structure containing the solid electrolyte which has lithium ion conductivity.

  In this specification, the technique which can solve the subject mentioned above is disclosed.

  The technology disclosed in the present specification can be realized as, for example, the following forms.

(1) A solid electrolyte structure disclosed in the present specification includes a solid electrolyte substrate including a lithium ion conductive solid electrolyte, and a lithium carbonate layer formed on a surface of the solid electrolyte substrate. In the body, the size of the particles of the solid electrolyte exposed on the surface of the solid electrolyte substrate is 10 μm or less, and the thickness of the lithium carbonate layer is 100 nm or less. When this solid electrolyte structure is used for a solid electrolyte layer of a battery, the solid electrolyte particles are exposed on the surface of the solid electrolyte substrate, and the size of the exposed solid electrolyte particles is relatively small, 10 μm or less. The specific surface area of the solid electrolyte substrate becomes relatively large. As a result, the current bias in the contact surface between the solid electrolyte layer and the electrode (negative electrode) is reduced, and the amount of lithium deposited on the electrode (negative electrode) is reduced. As a result, occurrence of a short circuit due to local lithium deposition can be suppressed. In addition, since the specific surface area of the solid electrolyte substrate is relatively large, the interface resistance between the solid electrolyte layer and the electrode (at least one of the negative electrode and the positive electrode) can be reduced. In addition, the lithium ion conductivity is extremely low (about 1 / 100,000 or less of the solid electrolyte layer), and the thickness of the lithium carbonate layer is relatively thin, 100 nm or less, so between the solid electrolyte layer and the electrode (negative electrode) in the first place. Resistance becomes smaller. In addition, variation in resistance between the solid electrolyte layer and the electrode (negative electrode) is reduced. As a result, the current bias between the solid electrolyte layer and the electrode (negative electrode) is reduced (that is, local current concentration is suppressed), and the amount of lithium deposition on the electrode (negative electrode) is reduced. . As a result, occurrence of a short circuit due to local lithium deposition can be suppressed. Further, since the lithium carbonate layer having extremely low lithium ion conductivity is relatively thin, the interface resistance between the solid electrolyte layer and the electrode (at least one of the negative electrode and the positive electrode) can be reduced.

(2) In the solid electrolyte structure, the solid electrolyte may have a garnet-type crystal structure or a garnet-type similar crystal structure containing at least Li, La, Zr, and O. According to the present solid electrolyte structure, lithium ion conductivity can be sufficiently provided. In addition, according to the present solid electrolyte structure, it is possible to effectively suppress the occurrence of a short circuit due to local lithium precipitation and to effectively reduce the interface resistance between the solid electrolyte layer and the electrode. Can do.

(3) In the solid electrolyte structure, the solid electrolyte includes at least one of Mg and A (A is at least one element selected from the group consisting of Ca, Sr, and Ba). Also good. According to the present solid electrolyte structure, further improved lithium ion conductivity can be provided. In addition, according to the present solid electrolyte structure, it is possible to effectively suppress the occurrence of a short circuit due to local lithium precipitation and to effectively reduce the interface resistance between the solid electrolyte layer and the electrode. Can do.

(4) The lithium battery disclosed in the present specification is a lithium battery including a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode. It is formed by a solid electrolyte structure. According to this lithium battery, the interface resistance between the solid electrolyte layer and the electrode can be lowered, and the occurrence of a short circuit between the electrodes can be suppressed.

(5) In the lithium battery, in the pond, the negative electrode may include at least one of an Li metal and an Li alloy that are electrode active materials. According to this lithium battery, the interface resistance between the solid electrolyte layer and the electrode can be lowered, and the occurrence of a short circuit between the electrodes can be suppressed.

(6) In the lithium battery, at least one of the positive electrode and the negative electrode may include an electrode active material and a sulfide solid electrolyte. According to this lithium battery, the interface resistance between the solid electrolyte layer and the electrode can be lowered, and the occurrence of a short circuit between the electrodes can be suppressed.

(7) A manufacturing method disclosed in the present specification includes a solid electrolyte substrate including a lithium ion conductive solid electrolyte, and a lithium carbonate layer formed on a surface of the solid electrolyte substrate, and the solid electrolyte substrate In the method for producing a solid electrolyte structure in which the size of the particles of the solid electrolyte expressed on the surface of the solid electrolyte structure is 10 μm or less, a step of preparing the solid electrolyte structure, and the pH of the solid electrolyte structure is 1 or more, 14 And a cleaning step of immersing in the following cleaning liquid. According to this manufacturing method, the thickness of the lithium carbonate layer formed on the surface of the solid electrolyte substrate can be made 100 nm or less, the occurrence of a short circuit due to local lithium deposition can be suppressed, The interface resistance between the electrolyte layer and the electrode can be reduced.

(8) In the above manufacturing method, the pH of the cleaning liquid may be 7 or more and 13 or less. According to this production method, the thickness of the lithium carbonate layer formed on the surface of the solid electrolyte substrate can be made 100 nm or less while suppressing the components constituting the solid electrolyte layer from eluting into the cleaning liquid.

  The technology disclosed in the present specification can be realized in various forms. For example, a solid electrolyte structure including a solid electrolyte, a lithium battery including an electrolyte layer formed by the solid electrolyte structure, or It can be realized in the form of an all-solid lithium battery, a manufacturing method thereof, a cleaning method, or the like.

It is explanatory drawing which shows roughly the cross-sectional structure of the all-solid-state lithium ion secondary battery 102 in this embodiment. It is explanatory drawing which shows roughly the cross-sectional structure of the electrolyte layer 112 of this embodiment. It is explanatory drawing which shows roughly the cross-sectional structure of the electrolyte layer 112a of a 1st comparative example. FIG. 4 is an explanatory diagram schematically showing a cross-sectional configuration of the electrolyte layer 112b of the second comparative example. It is a flowchart which shows the manufacturing method of the all-solid-state battery 102 of this embodiment. It is explanatory drawing which shows the evaluation result of a washing | cleaning liquid. It is the photograph which observed the cross section of the sample which has not been wash | cleaned by FE-SEM. It is the photograph which observed the cross section of the washing implementation sample by distilled water by FE-SEM. It is the photograph which observed the cross section of the washing implementation sample by 0.1M nitric acid by FE-SEM. It is explanatory drawing which shows the evaluation result about the interface resistance which made 1st sample S1 for evaluation. It is explanatory drawing which shows the evaluation result about the interface resistance which made 2nd evaluation sample S2 object. It is explanatory drawing which shows the evaluation result about the short circuit characteristic for 2nd sample for evaluation S2. It is explanatory drawing which shows the outline | summary and evaluation result of 3rd performance evaluation. It is explanatory drawing which shows the calculation method of the average value (expressed particle average size AS) of the particle size PS of the solid electrolyte 202 exposed on the surface of the solid electrolyte substrate 203. FIG.

A. Embodiment:
A-1. Configuration of all solid state battery 102:
FIG. 1 is an explanatory view schematically showing a cross-sectional configuration of an all-solid lithium ion secondary battery (hereinafter referred to as “all-solid battery”) 102 in the present embodiment. FIG. 1 shows XYZ axes orthogonal to each other for specifying the direction. In this specification, for convenience, the positive Z-axis direction is referred to as the upward direction, and the negative Z-axis direction is referred to as the downward direction. The same applies to FIG.

  The all-solid-state battery 102 includes a battery main body 110, a first current collecting member 154 disposed on one side (upper side) of the battery main body 110, and a second disposed on the other side (lower side) of the battery main body 110. Current collecting member 156. The first current collecting member 154 and the second current collecting member 156 are substantially flat plate-shaped members having conductivity. For example, stainless steel, Ni (nickel), Ti (titanium), Fe (iron), Cu ( Copper), Al (aluminum), a conductive metal material selected from these alloys, a carbon material, and the like. In the following description, the first current collecting member 154 and the second current collecting member 156 are collectively referred to as a current collecting member.

  The battery body 110 is a secondary battery in which battery elements are all made of solid, and include an electrolyte layer 112, a positive electrode 114 disposed on one side (upper side) of the electrolyte layer 112, and the other side (lower side) of the electrolyte layer 112. A negative electrode 116 disposed on the side). In the following description, the positive electrode 114 and the negative electrode 116 are collectively referred to as electrodes.

The electrolyte layer 112 has a substantially flat plate shape and includes a lithium ion conductive solid electrolyte 202. As the solid electrolyte 202 contained in the electrolyte layer 112, for example, an oxide-based solid electrolyte is used. More specifically, for example, oxide solid electrolytes shown in the following (1) and (2) are used as the solid electrolyte 202.
(1) A solid electrolyte having a garnet-type crystal structure or a garnet-type similar crystal structure containing at least Li (lithium), La (lanthanum), Zr (zirconium), and O (oxygen) (for example, Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ))
(2) At least one of Mg (magnesium) and A (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)) with respect to LLZ. Solid electrolyte with element substitution (for example, LLZ with Mg and Sr element substitution (hereinafter referred to as “LLZ-MgSr”))

The positive electrode 114 has a substantially flat plate shape and includes a positive electrode active material 214 and a solid electrolyte 204 as a lithium ion conduction aid. As the positive electrode active material 214, for example, S _{(sulfur), TiS 2, LiCoO 2,} LiMn 2 O 4, LiFePO 4 or the like is used. Examples of the solid electrolyte 204 included in the positive electrode 114 include a sulfide-based solid electrolyte (for example, Li ₂ S—P ₂ S ₅ system, LiI—Li ₂ S—P ₂ S ₅ system, LiI—Li ₂ S). -B ₂ S ₃ type, or _{LiI-Li 2} S-SiS 2 system solid electrolyte, Chiorishikon, and _Li 10 _GeP 2 _{S 12} or the like) is used. The positive electrode 114 may further contain an electron conduction auxiliary agent (for example, conductive carbon, Ni (nickel), Pt (platinum), Ag (silver)).

The negative electrode 116 has a substantially flat plate shape, and includes a negative electrode active material 216 and a solid electrolyte 206 as a lithium ion conduction aid. As the negative electrode active material 216, for example, Li metal, Li—Al alloy, Li ₄ Ti ₅ O ₁₂ , carbon, Si (silicon), SiO, or the like is used. Examples of the solid electrolyte 206 included in the negative electrode 116 include a sulfide-based solid electrolyte (for example, Li ₂ S—P ₂ S ₅ system, LiI—Li ₂ S—P ₂ S ₅ system, LiI—Li ₂ S). -B ₂ S ₃ type, or _{LiI-Li 2} S-SiS 2 system solid electrolyte, Chiorishikon, and _Li 10 _GeP 2 _{S 12} or the like) is used. The negative electrode 116 may further contain an electron conduction aid (for example, conductive carbon, Ni, Pt, Ag).

A-2. Detailed configuration of the electrolyte layer 112:
FIG. 2 is an explanatory diagram schematically showing a cross-sectional configuration of the electrolyte layer 112 of the present embodiment. 2 shows an enlarged cross-sectional configuration of the electrolyte layer 112 in the X1 portion of FIG. 1 (that is, near the boundary with the negative electrode 116). As shown in FIG. 2, the electrolyte layer 112 includes a solid electrolyte substrate 203 containing the particles of the solid electrolyte 202 described above, and a lithium carbonate layer 222 formed on the surface of the solid electrolyte substrate 203. The lithium carbonate layer 222 is a layer of a substance generated by a reaction between lithium contained in the solid electrolyte 202 and carbon dioxide in the atmosphere. The lithium ion conductivity of the lithium carbonate layer 222 is extremely low (about 1 / 100,000 or less of the electrolyte layer 112). The electrolyte layer 112 including the solid electrolyte substrate 203 and the lithium carbonate layer 222 corresponds to the solid electrolyte structure in the claims.

  Here, in the electrolyte layer 112 of the present embodiment, particles of the solid electrolyte 202 are exposed on the surface of the solid electrolyte substrate 203, and the average size PS (hereinafter referred to as “table”) of the particles of the solid electrolyte 202 that are exposed. The average particle size AS ”) is relatively small at 10 μm or less. Furthermore, in the electrolyte layer 112 of the present embodiment, the thickness LT of the lithium carbonate layer 222 formed on the surface of the solid electrolyte substrate 203 is relatively thin at 100 nm or less. Therefore, in the all-solid-state battery 102 using the electrolyte layer 112 of the present embodiment, the interface resistance between the electrolyte layer 112 and the electrodes 114 and 116 can be lowered and the electrodes 114, Generation | occurrence | production of the short circuit between 116 can be suppressed. A method for calculating the size PS of the solid electrolyte 202 particles exposed on the surface of the solid electrolyte substrate 203 and the average particle size AS of the solid electrolyte substrate 203 will be described later.

  FIG. 3 is an explanatory diagram schematically showing a cross-sectional configuration of the electrolyte layer 112a of the first comparative example, and FIG. 4 is an explanatory diagram schematically showing a cross-sectional configuration of the electrolyte layer 112b of the second comparative example. is there. In the electrolyte layer 112 a of the first comparative example shown in FIG. 3, the surface of the solid electrolyte substrate 203 is polished to have a flat shape, and particles of the solid electrolyte 202 are not exposed on the surface of the solid electrolyte substrate 203. Note that the thickness LT of the lithium carbonate layer 222 in the electrolyte layer 112a of the first comparative example shown in FIG. 3 is substantially the same as the thickness LT of the lithium carbonate layer 222 in the electrolyte layer 112 of the embodiment shown in FIG. .

  In the electrolyte layer 112b of the second comparative example shown in FIG. 4, the exposed particle average size AS (average value of the size PS of each particle of the solid electrolyte 202 exposed on the surface of the solid electrolyte substrate 203) is shown in FIG. It is larger than the exposed particle average size AS in the electrolyte layer 112 of the embodiment shown. Further, in the electrolyte layer 112b of the second comparative example shown in FIG. 4, the thickness LT of the lithium carbonate layer 222 is thicker than the thickness LT of the lithium carbonate layer 222 in the electrolyte layer 112 of the embodiment shown in FIG.

  In the electrolyte layer 112a of the first comparative example shown in FIG. 3, since the solid electrolyte 202 particles are not exposed on the surface of the solid electrolyte substrate 203, the specific surface area of the solid electrolyte substrate 203 becomes extremely small. As a result, the contact area between the electrolyte layer 112a and the negative electrode 116 (or positive electrode 114) becomes extremely small, and the interface resistance between the electrolyte layer 112a and the negative electrode 116 (or positive electrode 114) becomes extremely large. Further, in the electrolyte layer 112a of the first comparative example, when the all solid state battery 102 is charged, the current is concentrated at a small contact portion between the electrolyte layer 112a and the negative electrode 116. As a result, lithium is intensively deposited on the surface of the negative electrode 116 at the contact point, and the deposited lithium becomes a protrusion and penetrates the electrolyte layer 112a to the positive electrode 114, which may cause a short circuit between the electrodes 114 and 116. There is.

  Further, in the electrolyte layer 112b of the second comparative example shown in FIG. 4, the exposed particle average size AS (the average value of the sizes PS of the particles of the solid electrolyte 202 exposed on the surface of the solid electrolyte substrate 203) is relatively high. Since it is large, the specific surface area of the solid electrolyte substrate 203 is relatively small. As a result, the contact area between the electrolyte layer 112b and the negative electrode 116 (or positive electrode 114) becomes relatively small, and the interface resistance between the electrolyte layer 112b and the negative electrode 116 (or positive electrode 114) becomes relatively large. In addition, in the electrolyte layer 112b of the second comparative example, the thickness LT of the lithium carbonate layer 222 is relatively thick. From this point also, the interface resistance between the electrolyte layer 112b and the negative electrode 116 (or the positive electrode 114) is relatively high. growing. In the electrolyte layer 112b of the second comparative example, when the all-solid battery 102 is charged, the current is concentrated at a small contact portion between the electrolyte layer 112b and the negative electrode 116. As a result, lithium is intensively deposited on the surface of the negative electrode 116 at the contact location, and the deposited lithium becomes a protrusion and penetrates the electrolyte layer 112b to the positive electrode 114, which may cause a short circuit between the electrodes 114 and 116. There is.

  Furthermore, in the electrolyte layer 112b of the second comparative example, the exposed particle average size AS is relatively large, and thus the lithium carbonate layer 222 in the direction (vertical direction) in which the electrolyte layer 112b and the negative electrode 116 (or the positive electrode 114) face each other. Variation in the distance from the electrode side surface to the surface of the solid electrolyte substrate 203 (hereinafter referred to as “the coating length LC of the lithium carbonate layer 222”) becomes relatively large. That is, the difference (LC2-LC1) between the coating length LC2 of the lithium carbonate layer 222 at a position near the boundary between the particles of the solid electrolyte 202 and the coating length LC1 of the lithium carbonate layer 222 at a position near the center of the particles of the solid electrolyte 202. 4), the electrolyte layer 112b of the second comparative example shown in FIG. 4 is larger than the electrolyte layer 112 of the embodiment shown in FIG. If the variation in the coating length LC of the lithium carbonate layer 222 is relatively large, the current during charging of the all-solid-state battery 102 is concentrated in a portion where the coating length LC of the lithium carbonate layer 222 is short (that is, a portion with low electrical resistance). There is a possibility that lithium concentrates on the surface of the negative electrode 116 at the location, and the deposited lithium becomes a protrusion and penetrates the electrolyte layer 112b to the positive electrode 114, thereby causing a short circuit between the electrodes 114 and 116.

  On the other hand, in the electrolyte layer 112 of the present embodiment, the particles of the solid electrolyte 202 are exposed on the surface of the solid electrolyte substrate 203, and the exposed particle average size AS (the size PS of the particles of the solid electrolyte 202 to be exposed) The average value) is relatively small at 10 μm or less. Therefore, in the electrolyte layer 112 of this embodiment, the specific surface area of the solid electrolyte substrate 203 is relatively large, and as a result, the contact area between the electrolyte layer 112 and the electrodes 114 and 116 is relatively large. Therefore, the interface resistance between the electrolyte layer 112 and the electrodes 114 and 116 can be made relatively small. In addition, in the electrolyte layer 112 of the present embodiment, the thickness LT of the lithium carbonate layer 222 formed on the surface of the solid electrolyte substrate 203 is relatively thin at 100 nm or less. The interface resistance with the electrodes 114 and 116 becomes relatively small.

  In the electrolyte layer 112 of this embodiment, the specific surface area of the solid electrolyte substrate 203 is relatively large, the contact area between the electrolyte layer 112 and the electrodes 114 and 116 is relatively large, and the coating length of the lithium carbonate layer 222 is also large. Since the variation in LC is relatively small, current bias in the plane of the interface between the electrolyte layer 112 and the electrodes 114 and 116 is suppressed when the all-solid battery 102 is charged. As a result, the uneven deposition of lithium on the surface of the negative electrode 116 is suppressed, and the occurrence of a short circuit between the electrodes 114 and 116 is suppressed.

  Note that the particles of the solid electrolyte 202 are exposed on the surface of the solid electrolyte substrate 203. In other words, in the cross section of the solid electrolyte substrate 203 parallel to the Z direction, the length of the surface of the solid electrolyte substrate 203 is This is longer than the width of solid electrolyte substrate 203 (the length in the direction perpendicular to the Z direction). For example, when actual measurement was performed using a sample having an average exposed particle size AS of 4.5 μm, the width of the solid electrolyte substrate 203 was 115.9 μm, whereas the length of the surface of the solid electrolyte substrate 203 was 124.m. It was 4 μm and about 1.07 times. Note that the length of the surface of the solid electrolyte substrate 203 can be measured by approximating the irregular curve of the particles with a short straight line and adding up the lengths of the straight lines. In addition, dust that adheres to holes or surfaces deeper than the average exposed particle size AS is excluded from measurement.

  Further, if the thickness LT of the lithium carbonate layer 222 formed on the surface of the solid electrolyte substrate 203 is relatively thin, such as 100 nm or less, the increase in interface resistance due to the presence of the lithium carbonate layer 222 is negligible. In addition, since a very thin lithium carbonate layer 222 exists on the surface of the solid electrolyte substrate 203, holes and scratches on the surface of the solid electrolyte substrate 203 are filled with the lithium carbonate layer 222, thereby short-circuiting between the electrodes 114 and 116. Occurrence is better suppressed. In this respect, the thickness of the lithium carbonate layer 222 is preferably, for example, 5 nm or more.

  The solid electrolyte 202 included in the electrolyte layer 112 preferably has a garnet-type crystal structure or a garnet-type similar crystal structure containing at least Li, La, Zr, and O. In this way, sufficient lithium ion conductivity can be secured. In addition, the occurrence of a short circuit between the electrodes 114 and 116 due to local lithium deposition can be effectively suppressed, and the interface resistance between the electrolyte layer 112 and the electrodes 114 and 116 can be effectively reduced. Can do. In addition to this, the solid electrolyte 202 included in the electrolyte layer 112 may contain at least one of Mg and A (A is at least one element selected from the group consisting of Ca, Sr, and Ba). preferable. In this way, further improved lithium ion conductivity can be ensured. In addition, the occurrence of a short circuit between the electrodes 114 and 116 due to local lithium deposition can be further effectively suppressed, and the interface resistance between the electrolyte layer 112 and the electrodes 114 and 116 can be further effectively reduced. can do.

  In addition, the electrolyte layer 112 of the present embodiment is suitable for application to an all solid state battery including a positive electrode and a negative electrode. According to the all solid state battery, the interface resistance between the electrolyte layer 112 and the electrode can be lowered, and the occurrence of a short circuit between the electrodes can be suppressed.

  Moreover, the electrolyte layer 112 of this embodiment is suitable for application to the all-solid-state battery 102 provided with the negative electrode 116 containing at least one of Li metal which is an electrode active material, and Li alloy. In the all-solid-state battery 102 including the negative electrode 116 containing at least one of Li metal and Li alloy, the occurrence of a short circuit between the electrodes 114 and 116 due to local deposition of lithium tends to be a problem, but the electrolyte layer of the present embodiment. If 112 is applied, the occurrence of a short circuit between the electrodes 114 and 116 can be suppressed.

  In addition, the electrolyte layer 112 of the present embodiment is suitable for application to the all-solid battery 102 in which at least one of the positive electrode 114 and the negative electrode 116 contains a sulfide solid electrolyte. By applying to such an all-solid battery 102, the interface resistance between the electrolyte layer 112 and the electrodes 114 and 116 can be drastically reduced.

A-3. Manufacturing method of all-solid battery 102:
FIG. 5 is a flowchart showing a method for manufacturing the all solid state battery 102 of the present embodiment. First, raw material particles of the solid electrolyte 202 are prepared by pulverizing and mixing the raw material powder of the solid electrolyte 202 for the electrolyte layer 112 (S110). The composition of the raw material powder of the solid electrolyte 202 is appropriately set according to the composition of the solid electrolyte 202 to be produced. Specific examples of the blending of the raw material powder are described in the section “A-4. Performance Evaluation” described later.

  Next, the electrolyte layer 112 is produced by firing the prepared raw material particles of the solid electrolyte 202 (S120). That is, by firing the raw material particles of the solid electrolyte 202, a solid electrolyte substrate 203 which is a sintered body is formed. Further, lithium contained in the solid electrolyte 202 near the surface of the solid electrolyte substrate 203 and carbon dioxide in the atmosphere , A lithium carbonate layer 222 is generated on the surface of the solid electrolyte substrate 203, and as a result, an electrolyte layer 112 (see FIG. 2) having a structure including the solid electrolyte substrate 203 and the lithium carbonate layer 222 is formed. The The exposed particle average size AS can be controlled by adjusting the firing temperature and firing time at this time. Specific examples of the firing temperature and firing time are described in the section “A-4. Performance Evaluation” described later.

  Next, the surface of the electrolyte layer 112 is cleaned by impregnating the electrolyte layer 112 in a cleaning solution (S130). By this cleaning process, a part of the lithium carbonate layer 222 formed on the surface of the solid electrolyte substrate 203 constituting the electrolyte layer 112 is removed, and the thickness LT of the lithium carbonate layer 222 is reduced. As the cleaning liquid, a liquid having a pH of 1 or more and 14 or less (for example, nitric acid having a predetermined concentration, distilled water, a liquid after the electrolyte layer 112 is taken out after impregnated with distilled water (hereinafter referred to as “distilled water”). Etc.))) is used. The thickness LT of the lithium carbonate layer 222 can be controlled by adjusting the pH of the cleaning liquid and the impregnation time in the cleaning process. Specific examples of the cleaning liquid and the impregnation time are described in the section “A-4. Performance Evaluation” described later. In addition, the exposed particle average size AS is not significantly changed by the washing step.

  Next, the washed electrolyte layer 112 is dried (S140). The electrolyte layer 112 is dried by, for example, wiping, natural drying, drying in the air, drying in an inert gas, or vacuum drying.

  Next, the electrodes 114 and 116 and the current collecting members 154 and 156 are joined to the dried electrolyte layer 112 (S150). The joining of these members is realized by, for example, stacking these members and performing a heat treatment in a state where a predetermined load is applied in the stacking direction. Through the above steps, the all-solid-state battery 102 having the configuration shown in FIG. 1 is manufactured.

A-4. Performance evaluation:
A plurality of samples of the electrolyte layer 112 were prepared and performance evaluation was performed. The performance evaluation will be described below.

A-4-1. Preparation of a sample of the electrolyte layer 112:
(Preparation of LLZ-MgSr sintered body)
Composition: Li _6.95 Mg _0.15 La _2.75 Sr _0.25 Zr _2.0 O ₁₂ Li ₂ CO ₃ , MgO, La (OH) ₃ , SrCO ₃ , ZrO ₂ were weighed so as to be . At that time, considering the volatilization of Li during firing, Li ₂ CO ₃ was further added so as to be about 15 mol% in terms of element. This raw material was put into a nylon pot together with zirconia balls, and pulverized and mixed in an organic solvent with a ball mill for 15 hours. After mixing, the slurry was dried and calcined on an MgO plate at 1100 ° C. for 10 hours. Note that the composition of the powder after calcining may deviate somewhat from the above composition. A binder was added to the calcined powder, and the mixture was pulverized and mixed with a ball mill in an organic solvent for 15 hours. After mixing, the slurry was dried to obtain LLZ-MgSr powder. The obtained LLZ-MgSr powder was press-molded with a die having a diameter of 14 mm so as to have a thickness of about 1.5 mm, and 1.5 (t) using a cold isostatic pressing machine (CIP). / Cm ² ) hydrostatic pressure was applied to obtain a molded body. The obtained molded body was fired under a predetermined firing condition (firing temperature and firing time) in an inert gas atmosphere to obtain a LLZ-MgSr sintered body. The LLZ-MgSr sintered body corresponds to the solid electrolyte substrate 203 constituted by the solid electrolyte 202 particles. Moreover, the lithium carbonate layer 222 is produced | generated when the lithium contained in the solid electrolyte 202 and the carbon dioxide in air | atmosphere react with the surface of a LLZ-MgSr sintered compact (solid electrolyte substrate 203). The structure constituted by the LLZ-MgSr sintered body (solid electrolyte substrate 203) and the lithium carbonate layer 222 corresponds to the electrolyte layer 112 (see FIG. 2).

In addition, when the produced LLZ-MgSr sintered body was pulverized and the main crystal phase was identified by XRD, the crystal structure of the LLZ-MgSr sintered body was an LLZ cubic crystal having high ion conductivity. Further, both surfaces of the LLZ-MgSr sintered body are polished and subjected to gold vapor deposition to obtain a measurement sample, and lithium ions are obtained by an alternating current impedance method (using 1470E and 1255B manufactured by Solartron) for the obtained measurement sample. When the conductivity was measured, it was 1.4 × 10 ⁻³ (S / cm).

In order to obtain a plurality of samples having different average particle size AS (average size of particle size PS of solid electrolyte 202 exposed on the surface), a plurality of LLZ-MgSr sintered bodies were obtained by varying the firing conditions described above. Was made. The relationship between the firing conditions and the exposed particle average size AS in the obtained sample was as follows.
(1) Firing condition 1: 1050 ° C., 3 hours—expressed particle average size AS: about 4.5 μm
(2) Firing condition 2: 1100 ° C., 4 hours—expressed particle average size AS: about 10 μm
(3) Firing condition 3: 1200 ° C., 10 hours—expressed particle average size AS: about 200 μm

  Further, in order to obtain a sample in which the particles of the solid electrolyte 202 are not exposed on the surface, a sample obtained by polishing the surface of the LLZ-MgSr sintered body obtained by the firing condition 1 with # 2000 abrasive paper in the atmosphere, And the sample grind | polished similarly in the glove box of argon atmosphere was produced.

(Cleaning of LLZ-MgSr sintered body)
In order to remove part of the lithium carbonate layer 222 formed on the surface of the produced LLZ-MgSr sintered body (solid electrolyte substrate 203) and adjust the thickness LT of 222, each LLZ-MgSr sintered body Washing was performed. Here, various cleaning liquids were evaluated in order to investigate suitable cleaning liquids for cleaning the LLZ-MgSr sintered body. FIG. 6 is an explanatory view showing the evaluation result of the cleaning liquid. FIG. 6 shows the types of cleaning liquids used, their pH values, and the results of ICP elemental analysis of the cleaning liquid after cleaning (the ranks A to G in the order of decreasing contents of Li, La, and Zr). Attached evaluation results), the presence or absence of the shape change of the LLZ-MgSr sintered body after cleaning, and the determination results are shown.

  As shown in FIG. 6, the cleaning liquid includes nitric acid having a concentration of 1 to 3 M (molar: mol / L), nitric acid having a concentration of 0.8 M, nitric acid having a concentration of 0.1 M, distilled water, and a LLZ-MgSr sintered body. The liquid after the LLZ-MgSr sintered body was taken out after impregnated with distilled water was used. The pH of nitric acid with a concentration of 1 to 3 M and nitric acid with a concentration of 0.8 M is less than 1, the pH of 0.1 M nitric acid is about 1, the pH of distilled water is about 7, and the pH of the solution after washing with distilled water is The pH was about 13. About each cleaning liquid, about 0.5 g of LLZ-MgSr sintered pellets are immersed in about 30 ml of an aqueous solution for 5 minutes, and then distilled water is added to the surface of the LLZ-MgSr sintered body taken out of the liquid. The surface liquid was removed by pouring, the moisture was wiped off, and vacuum drying was performed for about 1 hour.

  When each LLZ-MgSr sintered body after cleaning was visually observed, in a case where nitric acid having a concentration of 1 to 3 M was used as a cleaning liquid, a shape change was observed in the LLZ-MgSr sintered body, and many of the sintered bodies were observed. It is considered that the portion was dissolved in the cleaning liquid. Therefore, nitric acid having a concentration of 1 to 3 M was determined to be rejected (x). Further, in the case of using nitric acid having a concentration of 0.8M as the cleaning liquid, the shape of the LLZ-MgSr sintered body is maintained visually. However, when the ICP elemental analysis of the cleaning liquid after cleaning was performed, LLZ-MgSr was analyzed. It was confirmed that Li, La, and Zr, which are the main components of the sintered body, were eluted in a large amount (2 ppm or more) in the cleaning liquid. Therefore, nitric acid with a concentration of 0.8 M was determined to be slightly inappropriate (Δ). From these results, it can be said that the pH of the cleaning liquid is preferably 1 or more.

  In the case where nitric acid having a concentration of 0.1 M was used as the cleaning liquid, the shape of the LLZ-MgSr sintered body was maintained, and the elution of the main component of the LLZ-MgSr sintered body into the cleaning liquid was relatively small (Li 1 to 2 ppm for La, 0.1 to 1 ppm for La, and less than 0.1 ppm for Zr). Therefore, nitric acid with a concentration of 0.1 M was determined to be acceptable (◯). Moreover, in the case where distilled water (pH = 7) or distilled water-washed liquid (pH = 13) was used as the cleaning liquid, the elution of the main component of the LLZ-MgSr sintered body in the cleaning liquid was less (Li 1-2 ppm, and La and Zr are below the detection limit). Therefore, distilled water and a solution after washing with distilled water were determined to be acceptable (◯). From these results, it can be said that the pH of the cleaning liquid is more preferably 7 or more and 13 or less. In the ICP elemental analysis of the cleaning liquid after cleaning in the case where distilled water was used as the cleaning liquid, Zr and La were below the detection limit, and only Li elution was detected. From this, it is considered that the reason why the pH of the solution after washing with distilled water becomes higher than the pH of distilled water is mainly due to elution of Li.

(Surface observation and analysis)
Surface observation and analysis were performed on the samples of the produced LLZ-MgSr sintered bodies. Specifically, (1) a sample that has not been cleaned, (2) a sample that has been cleaned with distilled water, (3) a sample that has been cleaned with 0.1 M nitric acid, and (4) a sample that has been surface polished in the atmosphere. When the crystal phase present on the surface was identified by XRD measurement, a LLZ cubic peak and a lithium carbonate peak were observed in all samples.

  Also, among the samples of the LLZ-MgSr sintered body produced by firing under the firing condition 1 described above (with the exposed particle average size AS being 4.5 μm), (1) a sample that has not been cleaned, (2) FIGS. 7 to 9 show photographs of cross-sections observed with FE-SEM for each of the cleaning sample with distilled water and (3) the cleaning sample with 0.1 M nitric acid. In the uncleaned sample (FIG. 7), it was observed that a large amount of heterogeneous material (lithium carbonate layer 222) was present on the surface of the LLZ-MgSr sintered body (solid electrolyte substrate 203). When the thickness LT of the lithium carbonate layer 222 was measured, the thickness was approximately 200 nm to 500 nm, and the variation was relatively large. When the average of the thickness LT of the lithium carbonate layer 222 was determined from the 1000 × field image, it was about 400 nm.

  On the other hand, it was confirmed that the heterogeneous material (lithium carbonate layer 222) was removed to a different degree in the cleaning sample with distilled water (FIG. 8) and the cleaning sample with 0.1M nitric acid (FIG. 9). It was. When the thickness LT of the lithium carbonate layer 222 was measured, it was about 100 nm in the sample subjected to washing with distilled water. In addition, measurement was not possible with 0.1 M nitric acid-washed sample, but the etching process was repeated at intervals of several nanometers to the range of about 30 nm in the thickness direction, and elemental analysis (XPS analysis) was performed. However, since the range in which the ratio of Li, C, and O is different from that in the internal LLZ was present in the region of about 15 to 20 nm or less, it was confirmed that the lithium carbonate layer 222 of 20 nm or less was also present in this sample. It was done.

  Although not shown in the drawings, the thickness LT of the lithium carbonate layer 222 was about 100 nm in the sample subjected to washing with the distilled water-washed solution, like the sample washed with distilled water. For samples polished in the atmosphere, the thickness LT of the lithium carbonate layer 222 is about 200 nm, and for samples polished in the glove box, the lithium carbonate layer is washed in the same manner as the sample washed with 0.1 M nitric acid. The thickness LT of 222 was 20 nm or less.

A-4-2. First performance evaluation result:
As the first performance evaluation, the electrolyte layer 112 (the structure formed by the above-described LLZ-MgSr sintered body and the lithium carbonate layer 222), the electrodes 114 and 116, and the current collecting members 154 and 156 are joined. A first evaluation sample S1 of the all-solid-state battery 102 was produced, and the interface resistance was evaluated. In addition, since it is for evaluation of interfacial resistance, as the electrodes 114 and 116, those containing a sulfide-based solid electrolyte but not containing an electrode active material were used.

(Preparation of first evaluation sample S1)
All operations were performed in an argon atmosphere glove box. Li ₂ S · P ₂ S ₅ (molar ratio 80:20) glass was used as the sulfide-based solid electrolyte material. The sulfide-based solid electrolyte powder and the SUS (stainless steel) current collector powder are put into a mold in order, and are pressure-molded at 360 MPa. The diameter is 10 mm, and the thickness (the thickness of the sulfide-based solid electrolyte portion) is 0. Two sheets of approximately 3 mm green compacts were produced. The obtained sulfide-based solid electrolyte green compact and the above-described electrolyte layer 112 (structure composed of the LLZ-MgSr sintered body and the lithium carbonate layer 222) were combined with a SUS current collector / sulfide-based solid. The layers were laminated in the order of electrolyte green compact / electrolyte layer 112 / sulfide-based solid electrolyte green compact / SUS current collector. This laminated body was fixed by applying a load of about 50 MPa in the laminating direction, and heat-treated at 190 ° C. to 220 ° C. for 3 hours. Then, it cooled to room temperature and obtained 1st sample S1 for evaluation.

(Evaluation of interface resistance)
For each first evaluation sample S1, the interface resistance was measured by the AC impedance method. FIG. 10 is an explanatory diagram showing an evaluation result of the interface resistance for the first evaluation sample S1. FIG. 10 shows each range of the exposed particle average size AS (where no particles are exposed on the surface of the polished body) (4.5 μm or less, 4.5 μm to 10 μm or less, 10 μm to 200 μm or less). And each range of thickness LT of lithium carbonate layer 222 (20 nm or less, greater than 20 nm and less than or equal to 100 nm, greater than 100 nm and less than or equal to 200 nm, greater than 200 nm and less than or equal to 400 nm). The evaluation results based on the interfacial resistance values (evaluation results with ranks A to D in ascending order of interfacial resistance) are described. Of the polished bodies, the lithium carbonate layer 222 having a thickness LT of “˜20 nm” was polished in a glove box in an argon atmosphere, and the lithium carbonate layer 222 had a thickness LT of “100 to 200 nm”. Is polished in the air (the same applies to FIGS. 11 and 12).

As shown in FIG. 10, in the sample S1 in which the average exposed particle size AS is 10 μm or less and the thickness LT of the lithium carbonate layer 222 is about 100 nm or less, the interface resistance is relatively low (100Ω / cm ² or less), Sample S1 having an average exposed particle size AS of 4.5 μm or less resulted in particularly low interface resistance (50 Ω / cm ² or less). From this, the interface resistance between the electrolyte layer 112 formed of the LLZ-MgSr sintered body and the electrodes 114 and 116 including the sulfide-based solid electrolyte is expressed by particles, and the exposed particle average size AS is It can be said that when the thickness LT of the lithium carbonate layer 222 is 10 nm or less and the thickness LT of the lithium carbonate layer 222 is 100 nm or less, the average particle size AS is 4.5 μm or less.

A-4-3. Second performance evaluation result:
As the second performance evaluation, the electrolyte layer 112 (the structure formed by the above-described LLZ-MgSr sintered body and the lithium carbonate layer 222), the electrodes 114 and 116, and the current collecting members 154 and 156 are joined. Then, a second evaluation sample S2 of the all-solid battery 102 was produced, and the interface resistance and the short-circuit characteristics were evaluated. In the second evaluation sample S2, Li metal foil was used as the electrodes 114 and 116.

(Production of second evaluation sample S2)
All operations were performed in an argon atmosphere glove box. As the electrode material, Li metal foil (thickness 0.1 mm, manufactured by Honjo Metal) was used. Li metal foil was punched with a punch, and two Li metal foils having a diameter of 10 mm and a thickness of 0.1 mm were produced. The obtained Li metal foil and the above-described electrolyte layer 112 (structure composed of the LLZ-MgSr sintered body and the lithium carbonate layer 222) were combined with the SUS current collector / Li metal foil / electrolyte layer 112 / Li. The metal foil / SUS current collector was laminated in this order. This laminate was fixed by applying a load of about 1 MPa in the laminating direction, and heat-treated at 170 ° C. for 2 hours. Then, it cooled to room temperature and obtained 2nd sample S2 for evaluation.

(Evaluation of interface resistance)
About each 2nd sample S2 for evaluation, interface resistance was measured by the alternating current impedance method. FIG. 11 is an explanatory diagram showing an evaluation result of the interface resistance for the second evaluation sample S2. In FIG. 11, each range of the exposed particle average size AS (where no particles are exposed on the surface of the abrasive body) (4.5 μm or less, 4.5 μm to 10 μm or less, 10 μm to 200 μm or less) And each range of thickness LT of lithium carbonate layer 222 (20 nm or less, greater than 20 nm and less than or equal to 100 nm, greater than 100 nm and less than or equal to 200 nm, greater than 200 nm and less than or equal to 400 nm). The evaluation results based on the interfacial resistance values (evaluation results with ranks A to D in ascending order of interfacial resistance) are described.

As shown in FIG. 11, in the sample S2 in which the average particle size AS is 10 μm or less and the thickness LT of the lithium carbonate layer 222 is 100 nm or less, the interface resistance is relatively low (25Ω / cm ^2). The following results were obtained: Sample S2 having an average exposed particle size AS of 4.5 μm or less had a particularly low interface resistance (10 Ω / cm ² or less). From this, as for the interface resistance of the electrolyte layer 112 comprised by the LLZ-MgSr sintered compact, and the electrodes 114 and 116 comprised by Li metal foil, particle | grains have exposed, and exposed particle | grain average size AS is It can be said that when the thickness LT of the lithium carbonate layer 222 is 10 nm or less and the thickness LT of the lithium carbonate layer 222 is 100 nm or less, the average particle size AS is 4.5 μm or less.

(Evaluation of short circuit characteristics)
With respect to each second evaluation sample S2, a DC voltage application test was carried out to check whether or not there was a short circuit between the electrodes by continuously applying a DC voltage for 500 seconds. At this time, the current density with respect to the area of the junction interface between the electrolyte layer 112 and the electrodes 114 and 116 is gradually increased under the condition of 25 ° C. (0.01, 0.02, 0.04, 0.06, 0.08, 0.1,..., ² mA / cm ² was selected as appropriate) and the evaluation was performed. FIG. 12 is an explanatory diagram showing an evaluation result of the short-circuit characteristic for the second evaluation sample S2. FIG. 12 shows the evaluation results based on the presence / absence of a short circuit at each current density (evaluation results with ranks A to D in the order in which short circuits hardly occur) for each second evaluation sample S2 similar to FIG. Has been.

As shown in FIG. 12, the sample S2 in which the average particle size AS is 10 μm or less and the thickness LT of the lithium carbonate layer 222 is 100 nm or less results in no short circuit even at a relatively high current density ( In the sample S2 in which the average particle size AS is 4.5 μm or less, no short-circuit occurs even at a higher current density (1 mA / cm ² , 0.5 A / cm ² or more and no short circuit to 1 mA / cm ^{2 or} less). cm ² or more, no short circuit up to 1.5 mA / cm ² ). From this, the possibility of the occurrence of a short circuit in the all-solid-state battery 102 including the electrolyte layer 112 formed of the LLZ-MgSr sintered body and the electrodes 114 and 116 formed of Li metal foil is expressed by particles. When the average particle size AS is 10 μm or less and the thickness LT of the lithium carbonate layer 222 is 100 nm or less, the average particle size AS is low, and when the average particle size AS is 4.5 μm or less, the average particle size AS is further decreased. I can say that.

A-4-4. Third performance evaluation result:
As the third performance evaluation, the electrolyte layer 112 (the structure formed by the above-described LLZ-MgSr sintered body and the lithium carbonate layer 222), the electrodes 114 and 116, and the current collecting members 154 and 156 are joined. Then, a third evaluation sample S3 (S3a to S3f) of the all-solid-state battery 102 was produced, and the interface resistance was evaluated. FIG. 13 is an explanatory diagram showing an outline of the third performance evaluation and an evaluation result.

(Preparation of third evaluation sample S3)
Third sample for evaluation S3a
All operations were performed in an argon atmosphere glove box. Li ₄ Ti ₅ O ₁₂ as a positive electrode active material 214, Li ₂ S · P ₂ S ₅ glass (molar ratio 80:20) as a sulfide-based solid electrolyte, and Ketjen black as an electron conduction aid A positive electrode mixture for forming the positive electrode 114 was obtained by mixing at a weight ratio of 3: 7: 1 to obtain a green compact. Further, a LiAl alloy (molar ratio 1: 1) as the negative electrode active material 216 and a Li ₂ S · P ₂ S ₅ glass (molar ratio 80:20) which is a sulfide-based solid electrolyte have a weight of 1: 1. The negative electrode mixture for forming the negative electrode 116 was obtained by combining in a ratio to obtain a green compact. The obtained positive electrode mixture and negative electrode mixture, and the electrolyte layer 112 described above (however, the exposed particle average size AS is 4.5 μm and the thickness LT of the lithium carbonate layer 222 is 20 nm or less), The layers were laminated in the order of SUS current collector / positive electrode mixture / electrolyte layer 112 / negative electrode mixture / SUS current collector. This laminated body was fixed by applying a load of about 50 MPa in the laminating direction, and heat-treated at 190 ° C. to 220 ° C. for 3 hours. Then, it cooled to room temperature and obtained 3rd sample S3a for evaluation.

Third evaluation sample S3b
In the above-described method for producing the third sample for evaluation S3a, the sintered body used as the electrolyte layer 112 is changed to an LLZ-MgSr sintered body polished in the air (that is, the surface of which 202 particles are not exposed). A third evaluation sample S3b was produced by the replaced method.

Third evaluation sample S3c
In the above-described method for producing the third evaluation sample S3a, the positive electrode mixture for forming the positive electrode 114 is composed of Li ₄ Ti ₅ O ₁₂ as the positive electrode active material 214 and ketjen black as the electron conduction aid. The negative electrode mixture for forming the negative electrode 116 was replaced with a green compact mixed at a weight ratio of 7: 1, and a compact of LiAl alloy (molar ratio 1: 1) as the negative electrode active material 216 was used. A third evaluation sample S3c was produced by the method replaced with. That is, in the third evaluation sample S3c, the electrodes 114 and 116 do not contain a sulfide-based solid electrolyte.

Third sample for evaluation S3d
In the above-described method for producing the third sample for evaluation S3c, the sintered body used as the electrolyte layer 112 is converted into an LLZ-MgSr sintered body polished in the air (that is, the surface of which 202 particles are not exposed). A third evaluation sample S3d was produced by the replaced method.

Third sample for evaluation S3e
In the above-described method for producing the third evaluation sample S3a, the third evaluation sample S3e was produced by replacing the sintered body used as the electrolyte layer 112 with an LLZ sintered body from the LLZ-MgSr sintered body. did. The method for producing the LLZ sintered body used for the third evaluation sample S3e is as follows.

The ratio of each component of Li, La, and Zr is Li: La: Zr = 7: 3: 2 (molar ratio) in the raw material powder, Li ₂ CO ₃ , La (OH) ₃ , ZrO ₂ In addition, since Li easily volatilizes during firing, 10% by mass of Li ₂ CO ₃ was added to the weighed Li ₂ CO ₃ in consideration of the volatile content of lithium. This raw material powder was put together with zirconia balls into an alumina pot, ground and mixed in a ball mill for 15 hours in ethanol, and further dried to obtain a blended material. The obtained blended material was calcined at 1100 ° C. for 10 hours in an alumina crucible to obtain a calcined material. A binder was added to the temporarily fired material, and the mixture was pulverized and mixed with a ball mill in an organic solvent for 15 hours and further dried to obtain an unfired material. The green material is put into a mold having a diameter of 10 mm, press-molded, and then a hydrostatic pressure of 1.5 t / cm ² is applied using a cold isostatic press (CIP) to obtain a molded body. It was. The compact was covered with a calcined powder having the same composition as the compact and fired at 1200 ° C. for 4 hours in an air atmosphere to obtain a lithium ion conductive LLZ sintered body having a diameter of 10 mm and a thickness of 1 mm. The average size (expressed particle average size AS) of the particles exposed on the surface of the LLZ sintered body was about 10 μm. This LLZ sintered body corresponds to the solid electrolyte substrate 203 constituted by the solid electrolyte 202 particles. Further, the lithium carbonate layer 222 is generated by reacting lithium contained in the solid electrolyte 202 with carbon dioxide in the atmosphere on the surface of the LLZ sintered body (solid electrolyte substrate 203). A structure constituted by the LLZ sintered body (solid electrolyte substrate 203) and the lithium carbonate layer 222 corresponds to the electrolyte layer 112 (see FIG. 2). Further, an X-ray diffraction pattern was obtained by analyzing the powder obtained by pulverizing the LLZ sintered body with an X-ray diffractometer (XRD), and the obtained X-ray diffraction pattern was compared with an ICDD card. It was confirmed that this LLZ sintered body almost coincided with the LLZ cubic ICDD card. Therefore, it can be judged that this LLZ sintered body has a garnet-type crystal structure or a garnet-type similar crystal structure.

  After the production of the LLZ sintered body, cleaning with nitric acid having a concentration of 0.1 M was performed. A third evaluation sample S3e was produced using the washed LLZ sintered body as the electrolyte layer 112.

Third evaluation sample S3f
In the above-described method for producing the third sample for evaluation S3e, the sintered body used as the electrolyte layer 112 was replaced with an LLZ sintered body polished in the air (that is, a surface on which 202 particles were not exposed). A third evaluation sample S3f was produced by the method.

(Evaluation results)
For each third evaluation sample S3, the interface resistance was measured by the AC impedance method. As shown in FIG. 13, when comparing the sample S3a and the sample S3b, the particles of the solid electrolyte 202 are not exposed on the surface of the LLZ-MgSr sintered body polished in the atmosphere, that is, the sintered body, and In the sample S3b using the electrolyte layer 112 composed of a sintered body in which the thickness LT of the lithium carbonate layer 222 exceeds about 100 nm, the interface resistance was 1162 Ω / cm ² whereas the average particle size of the exposed particles In the sample S3a using the electrolyte layer 112 composed of a LLZ-MgSr sintered body having a small AS of 4.5 μm and a thin lithium carbonate layer 222 having a thickness LT of 20 nm or less, the interface resistance is 22 Ω / cm ^2. And very low value. Similarly, when comparing the sample S3e and the sample S3f, even when the LLZ sintered body is used instead of the LLZ-MgSr sintered body, the electrolyte layer 112 constituted by the LLZ sintered body polished in the air. In the sample S3f using the material, the interface resistance was 1402 Ω / cm ² , whereas the exposed particle average size AS was as small as 4.5 μm, and the thickness LT of the lithium carbonate layer 222 was as thin as 20 nm or less. In the sample S3e using the electrolyte layer 112 composed of the sintered body, the interface resistance was a very low value of 52Ω / cm ² . In addition, when comparing the samples S3a and 3b with the samples S3e and 3f, it can be said that it is preferable to perform element substitution of Mg and Sr on LLZ because the interface resistance becomes lower.

Further, when comparing the sample S3c and the sample S3d, in the sample S3d using the electrolyte layer 112 composed of the LLZ-MgSr sintered body polished in the air, the interface resistance was 1 million Ω / cm ² or more. On the other hand, the sample S3c using the electrolyte layer 112 composed of the LLZ-MgSr sintered body having a small exposed particle average size AS of 4.5 μm and a thin lithium carbonate layer 222 having a thickness LT of 20 nm or less. Then, the interface resistance was about 250,000 Ω / cm ² , which was lower than that of the sample S3d. However, compared with the samples S3a and S3e in which the electrodes 114 and 116 include a sulfide-based electrolyte, the interface resistance is still high in the sample S3c. From this, it can be said that the electrolyte layer 112 of the present embodiment exhibits a greater effect of reducing the interface resistance when used by being joined to the electrodes 114 and 116 including the sulfide-based electrolyte.

  From these results, although the interfacial resistance is affected by the composition of the sintered body and the substance contained in the electrode, the particles are still exposed on the surface of the electrolyte layer 112, and the average particle size AS is 10 μm. It can be seen that a sample using a solid electrolyte structure in which the lithium carbonate layer 222 has a thickness LT as thin as 100 nm can reduce the interface resistance.

A-5. Calculation method of average particle size AS:
FIG. 14 is an explanatory diagram showing a method for calculating the average value PS of the solid electrolyte 202 particles exposed on the surface of the solid electrolyte substrate 203 (the average particle size AS expressed). FIG. 14 schematically shows a cross-sectional SEM image near the surface of the solid electrolyte substrate 203. As shown in FIG. 14, the size PS of each particle of the solid electrolyte 202 exposed on the surface of the solid electrolyte substrate 203 is a boundary point (neck point) NP with other particles adjacent to one side of the particle, It is a linear distance between the boundary point NP and another particle adjacent to the other side of the particle.

  Further, when calculating the average particle size AS, the sample is broken and evaluated by FE-SEM observation of a cross section obtained by ion beam cross-section. Specifically, a cross-sectional SEM image of the solid electrolyte substrate 203 is randomly acquired, the size PS of each particle of the solid electrolyte 202 exposed on the surface of the solid electrolyte substrate 203 is measured, and about 30 or more particles are measured. The average value of the measured values of the size PS is calculated as the expressed particle average size AS. For example, in the sample in which the above-described average particle size AS is calculated to be 4.5 μm, the size PS of about 20 particles can be measured in a field of view of 1000 times magnification. A double field of view photograph was obtained, and the average value of the size PS of each particle measured on the two photographs was calculated as the exposed particle average size AS.

  Moreover, when the SEM image of the surface of the solid electrolyte substrate 203 (electrolyte layer 112) can be acquired, the exposed particle average size AS may be calculated using the image of the surface. Specifically, three straight lines were drawn at equal intervals on the obtained SEM image of the surface (for example, 1000 times magnification), and the length of each particle on each straight line was measured as the particle size PS. A value obtained by dividing the total value of the particle sizes PS by the number of particles to be measured can be used as the exposed particle average size AS.

B. Variations:
The technology disclosed in the present specification is not limited to the above-described embodiment, and can be modified into various forms without departing from the gist thereof. For example, the following modifications are possible.

  The configuration of the all solid state battery 102 in the above embodiment is merely an example, and various changes can be made. For example, in the all-solid-state battery 102 of the above-described embodiment, the electrode active material and the electrolyte layer in the electrodes 114 and 116 are disposed between at least one of the electrolyte layer 112 and the positive electrode 114 and between the electrolyte layer 112 and the negative electrode 116. A protective layer for suppressing direct contact with the solid electrolyte 202 in 112 may be provided.

  Moreover, the material which forms each member in the said embodiment is an illustration to the last, and each member may be formed with another material. For example, in the above embodiment, LLZ or LLZ-MgSr, which is an oxide-based solid electrolyte, is used as the solid electrolyte 202 included in the electrolyte layer 112, but an element that can be substituted for LLZ (for example, Sn) (Elements such as (tin), Y (yttrium), Ga (gallium), Al (aluminum), Ta (tantalum), Nb (niobium), Ir (iridium), Bi (bismuth)). Good. Further, as the solid electrolyte 202, another oxide solid electrolyte (for example, LAGP or LZP) or an electrolyte other than the oxide solid electrolyte may be used.

  Moreover, in the said embodiment, although the sintered compact obtained by baking the particle | grains of the solid electrolyte 202 was used as the electrolyte layer 112, it is not restricted to this. For example, a green compact obtained by pressing and solidifying powder of the solid electrolyte 202 at a high pressure is used as the electrolyte layer 112, or an electrolyte layer in which particles of the solid electrolyte 202 are fixed using an electronic insulating adhesive (for example, a resin adhesive). 112 may be used. Alternatively, a plate-shaped solid electrolyte prepared in advance may be obtained, and the electrolyte layer 112 (solid electrolyte structure) may be manufactured by subjecting the plate-shaped solid electrolyte to a cleaning process.

 In the above embodiment, the solid electrolyte structure including the solid electrolyte substrate and the lithium carbonate layer of the present invention is used as the electrolyte layer 112 of the all-solid battery 102. However, the solid electrolyte structure of the present invention is described above. Is applicable to other uses. For example, the solid electrolyte structure of the present invention can be applied to a protective layer of an all-solid lithium ion secondary battery. The solid electrolyte structure of the present invention can also be applied to other primary or secondary batteries (for example, a lithium air battery or a lithium flow battery) using a solid electrolyte.

102: All-solid lithium ion secondary battery 110: Battery main body 112: Electrolyte layer 114: Positive electrode 116: Negative electrode 154: Current collecting member 156: Current collecting member 202: Solid electrolyte 203: Solid electrolyte substrate 204: Solid electrolyte 206: Solid electrolyte 214: Positive electrode active material 216: Negative electrode active material 222: Lithium carbonate layer

Claims (8)

A solid electrolyte substrate including a lithium ion conductive solid electrolyte;
A lithium carbonate layer formed on the surface of the solid electrolyte substrate;
In a solid electrolyte structure comprising:
The size of the solid electrolyte particles exposed on the surface of the solid electrolyte substrate is 10 μm or less,
A solid electrolyte structure, wherein the lithium carbonate layer has a thickness of 100 nm or less. The solid electrolyte structure according to claim 1,
The solid electrolyte has a garnet-type crystal structure or a garnet-type similar crystal structure containing at least Li, La, Zr, and O. The solid electrolyte structure according to claim 2,
The solid electrolyte structure contains at least one of Mg and A (A is at least one element selected from the group consisting of Ca, Sr, and Ba). In a lithium battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode,
The said solid electrolyte layer is a solid electrolyte structure as described in any one of Claim 1- Claim 3. The lithium battery characterized by the above-mentioned. The lithium battery according to claim 4,
The said negative electrode contains at least one of Li metal which is an electrode active material, and Li alloy, The lithium battery characterized by the above-mentioned. The lithium battery according to claim 4,
At least one of the positive electrode and the negative electrode contains an electrode active material and a sulfide-based solid electrolyte, and is a lithium battery. A solid electrolyte substrate including a lithium ion conductive solid electrolyte, and a lithium carbonate layer formed on the surface of the solid electrolyte substrate, and the size of the particles of the solid electrolyte exposed on the surface of the solid electrolyte substrate is In the method for producing a solid electrolyte structure having a size of 10 μm or less,
Preparing a solid electrolyte structure;
A cleaning step of immersing the solid electrolyte structure in a cleaning solution having a pH of 1 or more and 14 or less;
A manufacturing method comprising: In the manufacturing method of Claim 7,
The cleaning method has a pH of 7 or more and 13 or less.