All-solid-state lithium ion secondary battery

Abstract

The present invention addresses the problem of providing an all-solid-state lithium ion secondary battery which is excellent in terms of battery performance by improving bonding of lithium metal and a solid electrolyte that is composed of a high-density crystal body. In order to solve the problem, an all-solid-state lithium ion secondary battery according to the present invention includes: a negative electrode that is composed of lithium metal; a solid electrolyte that is composed of a lithium-containing crystal body; an ionic liquid that contains a lithium salt; and a positive electrode. The negative electrode and the solid electrolyte are bonded to each other, and the surface roughness of the bonding surface of the solid electrolyte and the negative electrode is 0.19 μm or less. It is preferable that the crystal body is a single crystal body. The single crystal body is represented by a chemical formula such as Li7-xLa3Zr2-xTaxO12 (0.2≤x≤1) or Li7-y-zLa3Zr2-y-zTayNbzO12 (0≤y≤0.8, 0.2≤z≤1, 0.2≤y+z≤1).

Description

All-solid-state lithium-ion secondary battery

[0001] The present application relates to an all-solid-state lithium-ion secondary battery containing a crystalline material with high density and lithium ion conductivity as an electrolyte.

[0002] In recent years, all-solid-state batteries have been developed from the viewpoints of safety, lifespan, and output. Lithium-containing garnet crystals are known to have high density and excellent lithium ion conductivity, making them suitable as solid electrolytes for all-solid-state lithium-ion secondary batteries (see Patent Document 1). However, it is not easy to achieve a good bond between the high-density crystals serving as the solid electrolyte and the lithium metal serving as the negative electrode. For this reason, all-solid-state lithium-ion secondary batteries using high-density crystals as the solid electrolyte and exhibiting excellent performance have not yet been put to practical use.

[0003] Patent No. 6278433

[0004] The present application has been made in view of the above circumstances, and an object of the present application is to provide an all-solid-state lithium-ion secondary battery having excellent battery performance by improving the bonding between a solid electrolyte made of a high-density crystalline body and lithium metal.

[0005] The all-solid-state lithium ion secondary battery of the present application is an all-solid-state lithium ion secondary battery having a negative electrode made of lithium metal, a solid electrolyte made of a lithium-containing crystal, and a positive electrode, in which the negative electrode and the solid electrolyte are joined together, and the surface roughness of the joint surface of the solid electrolyte with the negative electrode is 0.19 μm or less.

[0006] The method for manufacturing an all-solid-state lithium-ion secondary battery of the present application is a method for manufacturing an all-solid-state lithium-ion secondary battery in which a positive electrode includes a positive electrode mixture and a positive electrode current collector, and the positive electrode mixture and a solid electrolyte are bonded via an ionic liquid, and includes a positive electrode-side bonding step of applying the ionic liquid to the positive electrode mixture and then bonding the solid electrolyte and the positive electrode mixture via the ionic liquid.

[0007] In the all-solid-state lithium ion secondary battery of the present invention, the surface roughness of the joint surface of the solid electrolyte with the negative electrode is 0.19 μm or less, thereby providing an all-solid-state lithium ion secondary battery with excellent battery performance in which the solid electrolyte and the negative electrode are in close contact with each other.

[0008] FIG. 1 is a structural schematic diagram of an all-solid-state lithium-ion secondary battery according to a second embodiment; FIG. 2 is an oscillation photograph of the single crystal of Example 1 obtained by single crystal X-ray diffraction measurement; Nyquist plot of the single crystal of Example 1; Graph showing the results of a charge-discharge cycle test of the all-solid-state lithium-ion secondary battery of Example 2; Graph showing the charge-discharge of the all-solid-state lithium-ion secondary batteries of Example 2 and Comparative Example 1; Graph showing the results of a charge-discharge cycle test of the all-solid-state lithium-ion secondary batteries of Example 2 and Comparative Example 2; Graph showing the temperature dependence of charge-discharge of the all-solid-state lithium-ion secondary battery of Example 2 and the liquid lithium-ion secondary battery of the Reference Example; Nyquist plots of the solid electrolyte of the all-solid-state lithium-ion secondary battery of Example 2 and the glass filter of the liquid lithium-ion secondary battery of the Reference Example during charging; Graph showing the results of a long-term charge-discharge cycle test of the all-solid-state lithium-ion secondary battery of Example 2.

[0009] The all-solid-state lithium-ion secondary battery of the first embodiment of the present application includes a negative electrode, a solid electrolyte, and a positive electrode. The negative electrode is bonded to the solid electrolyte. The negative electrode is made of lithium metal. More specifically, the negative electrode is a lithium metal foil. The solid electrolyte is made of a crystalline body. A crystalline body has a higher ionic conductivity than a sintered body. Therefore, a solid electrolyte made of a crystalline body is excellent as a component of an all-solid-state battery. The crystalline body of the first embodiment contains lithium and has a high lithium ion conductivity.

[0010] Since the lithium ion conductivity is improved, it is preferable that the density of this lithium-containing crystalline body is high. Ultimately, it is preferable that the lithium-containing crystalline body is a lithium-containing single crystal. The joining surface of the solid electrolyte where the solid electrolyte is joined to the negative electrode is smooth. Specifically, the surface roughness of this joining surface is preferably 0.19 μm or less, more preferably 0.17 μm or less, and even more preferably 0.16 μm or less. The surface roughness is the arithmetic mean surface roughness Ra value calculated by contacting a short needle using a microprofile measuring instrument (Surfcorder SE 4000, manufactured by Kosaka Laboratory Co., Ltd.).

[0011] The surface of the solid electrolyte to be bonded to the negative electrode is preferably a mirror surface. The mirror surface of the solid electrolyte means that the surface has a surface roughness of 0.16 μm or less. Since the lithium ion conductivity is high, the lithium-containing single crystal has a high conductivity of Li. ７－ｘ La ３ Zr ２－ｘ Ta ｘ O １２ (0.2≦x≦1), Li ７－ｙ－ｚ La ３ Zr ２－ｙ－ｚ Ta ｙ Nb ｚ O １２ (0≦y≦0.8, 0.2≦z≦1, 0.2≦y+z≦1), Li ７－３ｐ Al ｐ La ３ Zr ２ O １２ (0.1≦p≦0.3), Li ７－３ｑ Ga ｑ La ３ Zr ２ O １２ (0.1≦q≦0.3), or Li ７－３ｒ－ｓ－ｔ Ga ｒ La ３ Zr ２－ｓ－ｔ Ta ｓ Nb ｔ O １２ (0.02≦r<0.5, 0≦s≦1.0, 0≦t≦1.0, 0.05≦s+t≦1.0), and Li ７－ｘ La ３ Zr ２－ｘ Ta ｘ O １２ It is more preferable that (0.2≦x≦1). The method for obtaining these lithium-containing single crystals is not particularly limited, but it is preferable to grow them by the Czochralski method (Cz method), and it is more preferable to obtain them in the same manner as the method in the examples described later.

[0012] Chemical formula Li ７－ｘ La ３ Zr ２－ｘ Ta ｘ O １２ The compound represented by (0.2≦x≦1) is Li ６．４ La ３ Zr １．４ Ta０．６ O １２ , Li ６．５ La ３ Zr １．５ Ta ０．５ O １２ , and Li ６．６ La ３ Zr １．６ Ta ０．４ O １２ The compound represented by the formula Li is preferably one or more compounds selected from the group consisting of these compounds. ７－ｙ－ｚ La ３ Zr ２－ｙ－ｚ Ta ｙ Nb ｚ O １２ The compound represented by (0≦y≦0.8, 0.2≦z≦1, 0.2≦y+z≦1) is Li ６．４ La ３ Zr １．４ Ta ０．３ Nb ０．３ O １２ , Li ６．５ La ３ Zr １．５ Ta ０．２５ Nb ０．２５ O １２ , and Li ６．５５ La ３ Zr １．５５ Nb ０．４５ O １２ Examples of the compound include compounds represented by the following formula:

[0013] Chemical formula Li ７－３ｐ Al ｐ La ３ Zr ２ O １２ The compound represented by (0.1≦p≦0.3) is Li ６．７ Al ０．１ La ３ Zr ２ O １２ and Li ６．２５ Al ０．２５ La ３ Zr ２ O １２ Examples of compounds include those represented by the chemical formula Li ７－３ｑ Ga ｑ La ３ Zr ２ O １２The compound represented by (0.1≦q≦0.3) is Li ６．７ Ga ０．１ La ３ Zr ２ O １２ and Li ６．２５ Ga ０．２５ La ３ Zr ２ O １２ Examples of the compound include compounds represented by the following formula:

[0014] Chemical formula Li ７－３ｒ－ｓ－ｔ Ga ｒ La ３ Zr ２－ｓ－ｔ Ta ｓ Nb ｔ O １２ The compound represented by (0.02≦r<0.5, 0≦s≦1.0, 0≦t≦1.0, 0.05≦s+t≦1.0) is Li ６ Ga ０．２５ La ３ Zr １．７５ Ta ０．２５ O １２ , Li ６ Ga ０．２５ La ３ Zr １．７５ Nb ０．２５ O １２ , Li ６ Ga ０．２５ La ３ Zr １．７５ Ta ０．１２５ Nb ０．１２５ O １２ , Li ６．１２５ Ga ０．１２５ La ３ Zr １．５ Ta ０．２５ Nb ０．２５ O １２ , and Li ５．５５ Ga ０．４ La ３ Zr １．７５ Ta ０．１２５ Nb ０．１２５ O １２ In addition, the lithium-containing crystal preferably has a garnet structure, since it has high lithium ion conductivity and no grain boundaries.

[0015] The positive electrode includes a positive electrode mixture and a positive electrode current collector. More specifically, the positive electrode mixture is provided on the positive electrode current collector. The positive electrode mixture includes, for example, a positive electrode active material, a conductive additive, and a binder. The positive electrode active material is LiFePO ４ (LFP), LiCoO ２ , and LiNi ０．５ Mn １．５ O ４ Lithium phosphate complex compounds and lithium complex oxides such as LiFePO are preferred. ４ (LFP) is used. Examples of the conductive additive include carbon-based materials such as carbon nanotubes (CNT), preferably carbon-based materials, and more preferably carbon nanotubes (CNT). Examples of the binder include resin-based materials such as polyvinylidene fluoride (PVDF), polyacrylic acid, and polyimide, and preferably polyvinylidene fluoride (PVDF). Examples of the positive electrode current collector include aluminum foil. The positive electrode mixture is bonded to the solid electrolyte.

[0016] The content of the positive electrode active material contained in the positive electrode mixture is preferably 85% by mass or more and 100% by mass or less, more preferably 90% by mass and 98% by mass or less, of the total amount of the positive electrode mixture. The content of the conductive additive contained in the positive electrode mixture is preferably 0.5% by mass or more and 10% by mass or less, more preferably 1.0% by mass or more and 5.0% by mass or less, of the total amount of the positive electrode mixture. The content of the binder contained in the positive electrode mixture is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.5% by mass or more and 3.0% by mass or less, of the total amount of the positive electrode mixture. By setting the content of each material in the positive electrode mixture within the above-mentioned ranges, the effect of improving battery characteristics according to the present invention tends to be more effective and reliable.

[0017] The all-solid-state lithium-ion secondary battery of the present application may further include an ionic liquid. The ionic liquid contains a lithium salt. Examples of the lithium salt include a salt composed of lithium ions and an anion of the ionic liquid. An all-solid-state lithium-ion secondary battery including an ionic liquid may be referred to as a quasi-solid-state lithium-ion secondary battery or a semi-solid-state lithium-ion secondary battery. However, in this application, a quasi-solid-state lithium-ion secondary battery including an ionic liquid between the solid electrolyte and the positive electrode is also referred to as an all-solid-state lithium-ion secondary battery.

[0018] 1 is a schematic diagram showing the structure of an all-solid-state lithium-ion secondary battery according to a second embodiment, which includes a small amount of ionic liquid only inside the positive electrode and at the interface on the solid electrolyte side. In the all-solid-state lithium-ion secondary battery according to the second embodiment, the ionic liquid is present inside the positive electrode mixture and between the positive electrode mixture and the solid electrolyte. In other words, the positive electrode mixture and the solid electrolyte are bonded together via the ionic liquid. The ionic liquid brings the positive electrode mixture and the solid electrolyte into close contact with each other, improving the battery performance of the all-solid-state lithium-ion secondary battery.

[0019] The cation of the ionic liquid is preferably a pyrrolidinium-based cation, aliphatic quaternary ammonium, or aliphatic quaternary phosphonium, which are stable against lithium metal, with pyrrolidinium-based cations being more preferred. Examples of anions in the ionic liquid include amide anions such as bis(fluorosulfonyl)amide, bis(trifluoromethylsulfonyl)amide, and fluorosulfonyl(trifluoromethylsulfonyl)amide, as well as borate anions. Amide anions are preferred, with bis(fluorosulfonyl)amide being more preferred. It is possible that an ionic liquid containing a lithium salt exists continuously between the negative electrode and the positive electrode through cracks in the solid electrolyte, and that this ionic liquid transports lithium ions, thereby operating the all-solid-state lithium-ion secondary battery. However, this possibility was refuted by the experimental results shown in the examples below.

[0020] The method for manufacturing an all-solid-state lithium-ion secondary battery according to the second embodiment includes an anode-side joining step and a cathode-side joining step. In the anode-side joining step, the anode and the solid electrolyte are joined. It is preferable to provide an anode-side polishing step prior to the anode-side joining step, in which the anode-side surface of the solid electrolyte is polished to a surface roughness of 0.19 μm or less. In the anode-side joining step, the anode is pressed against the anode-side surface of the solid electrolyte, thereby joining the anode to the solid electrolyte.

[0021] In the positive electrode side joining step, an ionic liquid is applied to the positive electrode mixture, and then the solid electrolyte and the positive electrode mixture are joined via the ionic liquid. That is, the solid electrolyte is pressed against the positive electrode mixture via the ionic liquid. The negative electrode side joining step and the positive electrode side joining step may be performed simultaneously. That is, the positive electrode, the ionic liquid, the solid electrolyte, and the negative electrode may be stacked, and pressure may be applied from both the outside of the positive electrode and the negative electrode to produce an integrated all-solid-state lithium-ion secondary battery.

[0022] <Solid electrolyte> (Li by Czochralski method (Cz method) ６．５ La ３ Zr １．５ Ta ０．５ O １２ Single crystal growth of raw material lithium carbonate Li ２ CO ３ , lanthanum oxide La ２ O ３ , zirconium oxide ZrO ２ , and tantalum oxide Ta ２ O ５ Li ２ CO ３ :La ２ O ３ : ZrO ２ :Ta ２ O ５ The powder sample was obtained by weighing and mixing the components in a molar ratio of 3.445:1.5:1.5:0.25. This molar ratio is the same as that of the composition of the target single crystal, Li ６．５ La ３ Zr １．５ Ta ０．５ O １２ Lithium is 1.06 times more abundant than Li ６．８９ La ３ Zr １．５ Ta ０．５ O１２ This is the molar ratio that results in the composition:

[0023] 120 g of this powder sample was filled into an alumina crucible and then fired at 850 °C for 4 hours as a calcination step to obtain a calcined powder. This calcined powder was filled into an iridium crucible with an inner diameter of 46 mm and a depth of 49 mm and set in a pulling-type single crystal growth furnace (manufactured by Technosearch, TCH-3) equipped with a high-frequency induction heating coil. In addition, a cylindrical iridium rod with a diameter of 5 mm and a length of 50 mm was set in the pulling section of this growth furnace. Nitrogen gas was circulated through this growth furnace at 3 L / min, creating a nitrogen atmosphere for the growth environment.

[0024] A current was passed through the high-frequency induction heating coil, and when the temperature of the bottom of the iridium crucible reached 1250°C, the calcined powder was melted. The iridium rod was rotated at 3 rpm and brought into contact with the melted portion. The iridium rod was then pulled up at 6 mm / h to form a thin, long Li crucible with a diameter of 2 mm and a length of 40 mm. ６．５ La ３ Zr １．５ Ta ０．５ O １２ Seed crystals were grown.

[0025] This seed crystal was processed into a cylindrical shape with a diameter of 2 mm and a length of 40 mm and set in the pulling section of the growth furnace. In the same manner as in the case of growing the seed crystal, the seed crystal rotated at 3 rpm was brought into contact with the molten part of the calcined powder in the iridium crucible. Thereafter, the seed crystal was pulled up at 2 mm / h while rotating at 3 rpm to produce a cylindrical Li single crystal with a diameter of 15 mm and a length of 80 mm, which is the single crystal of Example 1. ６．５ La ３ Zr １．５ Ta ０．５ O １２ Single crystals were grown.

[0026] (Li ６．５ La ３ Zr １．５ Ta ０．５ O １２ Evaluation of single crystal) Li ６．５ La ３ Zr １．５ Ta ０．５ O １２The single crystal was crushed to obtain single crystal grains of 0.05 mm square. The single crystal grains were attached to quartz glass pins, and the diffraction intensity was collected using a single crystal X-ray diffractometer (Rigaku Rapid-II). An example of the obtained vibration image is shown in Figure 1. As shown in Figure 1, the diffraction points in the vibration image are clear spots, indicating that Li ６．５ La ３ Zr １．５ Ta ０．５ O １２ It can be seen that a single crystal was obtained.

[0027] The lattice constant calculated from the collected diffraction intensity data was 12.9487(3) Å, which is the same as the previously reported garnet-type Li ６．５ La ３ Zr １．５ Ta ０．５ O １２ The single crystal structure was analyzed using the Jana2006 program, and the R value, which indicates the reliability of the analysis, was 1.34%. ６．５ La ３ Zr １．５ Ta ０．５ O １２ The single crystal was shown to have a garnet-type structure.

[0028] Also, cylindrical Li ６．５ La ３ Zr １．５ Ta ０．５ O １２ The single crystal was cut with a diamond cutter to prepare a single crystal plate with a diameter of 15 mm and a thickness of 1.2 mm. The surface of this single crystal plate was then polished with sandpaper. A 20 nm thick gold film was formed on both sides of this single crystal plate by sputtering, and the electrical resistance was measured using an AC impedance analyzer (Solartron, S1260). The resulting Nyquist plot is shown in Figure 3. The lithium ion conductivity calculated from the Nyquist plot in Figure 3 was 8.46 x 10 －４ S / cm, and the previously reported Li ６．５ La ３ Zr １．５ Ta ０．５ O １２ The lithium ion conductivity was in good agreement with that of the single crystal.

[0029] <All-solid-state lithium-ion secondary battery and liquid lithium-ion secondary battery> An all-solid-state lithium-ion secondary battery and a liquid lithium-ion secondary battery were fabricated in an Ar gas-purged glove box by the following procedure. Charge-discharge measurements and electrochemical measurements of the lithium-ion secondary battery and the liquid lithium-ion secondary battery were carried out using an electrochemical analyzer (Bio-logic, VMP3). Unless otherwise specified, the charge-discharge measurements were carried out at a charge-discharge rate of 0.2 C (0.11 mA / cm). ２ )

[0030] (Fabrication of All-Solid-State Lithium-Ion Secondary Battery of Example 2) The single crystal of Example 1 was cut into a disk shape with a diameter of 12 mm and a thickness of 1.3 mm. One side of this disk-shaped single crystal was continuously polished using a variety of abrasive papers ranging from coarse No. 300 to fine No. 2000 or higher. The surface roughness of this polished surface was 0.16 μm. A positive electrode mixture material was applied to an Al current collector foil serving as a positive electrode current collector with a diameter of 11 mm and a thickness of 20 μm and dried to obtain a positive electrode. The positive electrode mixture material was composed of 95% by mass of LFP as a positive electrode active material, 2.5% by mass of carbon nanotubes (CNT) as a conductive additive, and 2.5% by mass of PVDF as a binder.

[0031] Lithium bis(fluorosulfonyl)amide (LiFSA) was dissolved in N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)amide (chemical formula below), an ionic liquid, to a concentration of 2 mol / L to obtain a lithium salt-containing ionic liquid.

[0032]

[0033] The polished surface of the disk-shaped single crystal was bonded to a 12 mm diameter, 0.3 mm thick Li foil (Honjo Metals) anode. 10 μL of lithium salt-containing ionic liquid was applied to the cathode mixture side of the cathode. The disk-shaped single crystal was placed so that the other surface of the disk-shaped single crystal was in contact with the cathode mixture, and the cathode and anode were pressed from the outside to obtain a 2032 coin-type all-solid-state lithium-ion secondary battery, which is the all-solid-state lithium-ion secondary battery of Example 2. At this time, the thickness of the cathode mixture was 30 μm.

[0034] (Fabrication of All-Solid-State Lithium-Ion Secondary Battery of Comparative Example 1) A coin-shaped all-solid-state lithium-ion secondary battery of Comparative Example 1 was obtained in the same manner as in Example 2, except that one surface of the disk-shaped single crystal of Example 2 was not polished. The surface roughness of the negative electrode side surface of the disk-shaped single crystal of Comparative Example 1 was 0.43 μm.

[0035] (Fabrication of All-Solid-State Lithium-Ion Secondary Battery of Comparative Example 2) An attempt was made to fabricate a coin-shaped all-solid-state lithium-ion secondary battery of Comparative Example 2 in the same manner as in Comparative Example 1, except that a slide glass (MATSUNAMI, S) having a thickness of 0.94 mm was used instead of the single crystal of Comparative Example 1.

[0036] (Fabrication of All-Solid-State Lithium-Ion Secondary Battery of Comparative Example 3) An attempt was made to fabricate a coin-shaped all-solid-state lithium-ion secondary battery of Comparative Example 3 in the same manner as in Comparative Example 2, except that the same slide glass as in Comparative Example 2, with a penetrating crack provided in the center, was used instead of the slide glass of Comparative Example 2.

[0037] (Fabrication of Liquid Lithium-Ion Secondary Battery of Reference Example) A coin-shaped liquid lithium-ion secondary battery of the Reference Example was obtained in the same manner as in Comparative Example 2, except that a glass filter (Advantec, GA-200) having a thickness of 0.74 mm was used instead of the slide glass of Comparative Example 2, and that this glass filter was impregnated with a sufficient amount of lithium salt-containing ionic liquid.

[0038] (Evaluation of All-Solid-State Lithium-Ion Secondary Battery and Liquid Lithium-Ion Secondary Battery) FIG. 4 shows the results of a charge-discharge cycle test at 35°C for the all-solid-state lithium-ion secondary battery of Example 2. As shown in FIG. 4, even in a low-temperature environment of 35°C, a practical battery capacity was maintained for 270 cycles or more. FIG. 5 also shows the charge-discharge cycles of the all-solid-state lithium-ion secondary battery of Example 2 at 30°C (dashed line) and the all-solid-state lithium-ion secondary battery of Comparative Example 1 at 35°C (solid line). In the all-solid-state lithium-ion secondary battery of Comparative Example 1, the resistance at the interface between the positive electrode and the solid electrolyte was significantly high, and therefore the discharge capacity per weight of the positive electrode active material (represented as "battery capacity per weight of positive electrode" in FIGS. 4 to 7) was only 15 mAh / g. In other words, unless the negative electrode side surface of the solid electrolyte was smooth, the battery characteristics of the all-solid-state lithium-ion secondary battery were insufficient.

[0039] 9 shows the results of a long-term charge-discharge cycle test at 35° C. conducted on the all-solid-state lithium-ion secondary battery of Example 2. As shown in Fig. 9, even after 800 or more charge-discharge cycles, the capacity retention rate exceeded 80%, demonstrating that the fabricated all-solid-state lithium-ion secondary battery has a long life.

[0040] 6 shows the results of a charge-discharge cycle test at 75°C for the all-solid-state lithium-ion secondary batteries of Example 2 and Comparative Example 2. As shown in FIG. 6, the all-solid-state lithium-ion secondary battery of Comparative Example 2 hardly provided any battery capacity and did not function as a lithium-ion secondary battery. Furthermore, the all-solid-state lithium-ion secondary battery of Comparative Example 3 also hardly provided any battery capacity. That is, it was confirmed that in the all-solid-state lithium-ion secondary battery of Example 2, the ionic liquid did not transport lithium ions through cracks in the solid electrolyte or the like to function as a lithium-ion secondary battery, but rather the solid electrolyte transported the lithium ions.

[0041] FIG. 7 shows the temperature dependence (30°C, 45°C, 70°C) of charge and discharge of the all-solid-state lithium-ion secondary battery of Example 2 with a solid line. In FIG. 7, charge and discharge at 70°C of the liquid lithium-ion secondary battery of the Reference Example are also shown with a dashed line. As shown in FIG. 7, the all-solid-state lithium-ion secondary battery of Example 2 was capable of charging and discharging the positive electrode at almost the theoretical capacity even at 30°C, which is near room temperature. Also, as shown in FIG. 7, the all-solid-state lithium-ion secondary battery of Example 2 was capable of charging and discharging the positive electrode at 70°C equivalent to that of the liquid lithium-ion secondary battery of the Reference Example. In other words, the all-solid-state lithium-ion secondary battery of the present application has battery characteristics similar to those of conventional liquid lithium-ion secondary batteries.

[0042] FIG. 8 is a Nyquist plot when using a solid electrolyte or a glass filter in the charged state shown in FIG. 7 . The solid electrolyte of the all-solid-state lithium-ion secondary battery of Example 2 is shown by a solid line, and the glass filter of the liquid lithium-ion secondary battery of Reference Example is shown by a dashed line. Measurements were performed under conditions of a frequency range of 500 kHz to 10 mHz and a voltage amplitude of ±10 mV. As shown in FIG. 8 , the impedance behavior during charging was highly dependent on temperature. Furthermore, the apex frequency of the arc indicating the interface resistance with the Li foil in the high-frequency range was more than one order of magnitude higher for the solid electrolyte of Example 2 (23 kHz) than for the glass filter of Reference Example (1.5 kHz). This result indicates that the reactivity of the Li foil interface is higher with Li than with the ionic liquid. ６．５ La ３ Zr １．５ Ta ０．５ O １２ This suggests that the single crystal is higher.

[0043] The present invention may also include the following aspects. [1] An all-solid-state lithium-ion secondary battery having a negative electrode made of lithium metal, a solid electrolyte made of a crystalline body containing lithium, and a positive electrode, wherein the negative electrode and the solid electrolyte are joined together, and the surface roughness of the joint surface of the solid electrolyte with the negative electrode is 0.19 μm or less. [2] The all-solid-state lithium-ion secondary battery in [1], wherein the crystalline body is a single crystalline body. [3] The all-solid-state lithium-ion secondary battery in [2], wherein the single crystalline body is a single crystalline body containing Li ７－ｘLa ３ Zr ２－ｘ Ta ｘ O １２ (0.2≦x≦1), Li ７－ｙ－ｚ La ３ Zr ２－ｙ－ｚ Ta ｙ Nb ｚ O １２ (0≦y≦0.8, 0.2≦z≦1, 0.2≦y+z≦1), Li ７－３ｐ Al ｐ La ３ Zr ２ O １２ (0.1≦p≦0.3), Li ７－３ｑ Ga ｑ La ３ Zr ２ O １２ (0.1≦q≦0.3), or Li ７－３ｒ－ｓ－ｔ Ga ｒ La ３ Zr ２－ｓ－ｔ Ta ｓ Nb ｔ O １２ (0.02≦r<0.5, 0≦s≦1.0, 0≦t≦1.0, 0.05≦s+t≦1.0). [4] The all-solid-state lithium-ion secondary battery according to any one of [1] to [3], wherein the joining surface is a mirror finish. [5] The all-solid-state lithium-ion secondary battery according to any one of [1] to [4], wherein the positive electrode comprises a positive electrode mixture and a positive electrode current collector, and the positive electrode mixture and the solid electrolyte are joined via an ionic liquid containing a lithium salt. [6] The method for manufacturing the all-solid-state lithium-ion secondary battery according to any one of [1] to [5], comprising a positive electrode-side joining step of applying the ionic liquid to the positive electrode mixture and then joining the solid electrolyte and the positive electrode mixture via the ionic liquid.

Claims

1. An all-solid-state lithium ion secondary battery having a negative electrode made of lithium metal, a solid electrolyte made of a lithium-containing crystal, and a positive electrode, wherein the negative electrode and the solid electrolyte are bonded together, and the surface roughness of the bonded surface of the solid electrolyte with the negative electrode is 0.19 μm or less.

2. The all-solid-state lithium ion secondary battery according to claim 1, wherein the crystal is a single crystal.

3. In claim 2, the single crystal body is Li ７－ｘ La ３ Zr ２－ｘ T ｘ O １２ (0.2≦x≦1), Li ７－ｙ－ｚ La ３ Zr ２－ｙ－ｚ T ｙ Nb ｚ O １２ (0≦y≦0.8, 0.2≦z≦1, 0.2≦y+z≦1), Li ７－３ｐ A ｐ La ３ Zr ２ O １２ (0.1≦p≦0.3), Li ７－３ｑ G ｑ La ３ Zr ２ O １２ (0.1≦q≦0.3), or Li ７－３ｒ－ｓ－ｔ G ｒ La ３ Zr ２－ｓ－ｔ T ｓ Nb ｔ O １２ An all-solid-state lithium-ion secondary battery represented by the chemical formula: (0.02≦r<0.5, 0≦s≦1.0, 0≦t≦1.0, 0.05≦s+t≦1.0).

4. The all-solid-state lithium ion secondary battery according to claim 1, wherein the joining surface is a mirror surface.

5. An all-solid-state lithium ion secondary battery according to any one of claims 1 to 4, wherein the positive electrode comprises a positive electrode mixture and a positive electrode current collector, and the positive electrode mixture and the solid electrolyte are bonded via an ionic liquid containing a lithium salt.

6. A method for producing an all-solid-state lithium ion secondary battery according to claim 5, comprising a positive electrode-side joining step of applying the ionic liquid to the positive electrode mixture and then joining the solid electrolyte and the positive electrode mixture via the ionic liquid.