JP3502170B2 - All-solid lithium battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an all solid lithium battery using a lithium ion conductive solid electrolyte as an electrolyte.

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as personal computers and mobile phones, the demand for batteries as a power source thereof has become very large. In particular,
BACKGROUND ART A lithium secondary battery is being put to practical use as a battery that can obtain a high energy density because lithium has a small atomic weight and a large ionization energy.

However, since an ordinary lithium battery uses an organic electrolyte solution in which an electrolyte is dissolved in an organic solvent as an electrolyte, there is no danger of ignition or the like when an unexpected situation such as a short circuit of the battery occurs. I can't. One of the methods for improving the safety of a lithium battery is to use a solid electrolyte, which is an incombustible material, as an electrolyte, and to configure the battery only with an incombustible material. Research and development is being carried out in various fields.

As electrode active materials used in all-solid-state lithium batteries, transition metal sulfides such as TiS ₂ and transition metal oxides such as WO ₃ have been studied. These substances are
A material that can electrochemically move lithium ions in and out of ion sites in a crystal lattice, such as TiS.
The battery reaction when ₂ is the positive electrode active material and metallic lithium is the negative electrode active material is represented by (Chemical Formula 1). Thus, the entry and exit of ions to and from the ion site in the crystal lattice of these substances becomes an electrode reaction during battery operation.

[0005]

[Chemical 1]

[0006]

[Chemical 2]

[0007]

[Chemical 3]

[0008]

However, these electrode active materials have a problem that the battery capacity becomes low because the crystal structure is changed by a certain amount or more of lithium ions entering and leaving the ion site. Was.
In the above titanium disulfide (TiS ₂ ), LixTiS ₂ is 0
In the range of ≤x≤1, lithium ions can be electrochemically taken in and out, and this reaction exhibits high reversibility, but when the lithium ions are intercalated to a composition of x> 1, a crystal phase transition occurs. If this phase transition occurs, it becomes impossible to smoothly deintercalate lithium ions again. That is, the above Li / Ti
If the S ₂ battery is continuously discharged up to the range of x> 1 in (Chemical Formula 1), it becomes difficult to maintain the initial performance even if the battery is charged again. Further, in the case of LixCoO ₂ , it has been reported that when deintercalating lithium ions to the range of x <0.5, the crystal structure also changes and it becomes difficult to reintercalate lithium ions again.

The fact that the reversibility of the reaction is impaired by these crystalline phase transitions means that the amount of lithium ions that can be taken in and out with the charge and discharge of the battery is limited to the range in which the phase transition does not occur. There was a problem that the capacity was limited to low ones.

An object of the present invention is to solve the above problems and provide a high capacity all-solid-state lithium battery.

[0011]

Means for Solving the Problems An amorphous lithium ion conductive solid electrolyte mainly comprising sulfide is used as a solid electrolyte layer, which comprises a positive electrode, a negative electrode and a solid electrolyte, and a non-active material is used as an active material of the positive electrode. An all-solid-state lithium battery is constructed using an electrode containing a compound in a crystalline state.

Further, lithium cobalt oxide, lithium nickel oxide or lithium manganate is used as the amorphous compound. Further, as the lithium ion conductive solid electrolyte, a lithium ion conductive solid electrolyte composed of a substance mainly containing lithium sulfide and silicon sulfide is used.

Further, as the lithium ion conductive solid electrolyte, at least one compound selected from lithium oxide or lithium oxyacid salt and a lithium ion conductive solid electrolyte composed of lithium sulfide and silicon sulfide are used.

[0014]

[Function] The amorphous material has a more disordered structure than the crystalline material, and thus has more ion sites. Therefore, more lithium ions can be taken in and out without causing a phase transition. That is, when a battery using an amorphous material as an electrode active material is discharged to a certain voltage, the discharge capacity becomes larger than that using a crystalline material.

However, the following problem occurs when an organic electrolyte solution in which an electrolyte is dissolved in an organic solvent is used as the electrolyte layer. In the organic electrolytic solution, lithium ions are in a state of being solvated with the organic solvent, and solvent molecules move in and out of the amorphous material as lithium ions move in and out. Since the size of the organic solvent molecule is larger than that of lithium ion, the amorphous structure is likely to change. For this reason, the structure of the amorphous material changes in a stable direction every time the solvent molecules repeatedly flow in and out due to repeated charging and discharging, and finally it crystallizes, making it impossible to generate a high capacity. Therefore, a solid electrolyte having no organic solvent molecules is preferable as the electrolyte, and a solid electrolyte mainly composed of sulfide has high ionic conductivity, and thus the all-solid-state lithium battery configured can operate at a large current. Is preferable.

Further, as the compound in the amorphous state, lithium cobalt oxide, lithium nickel oxide or lithium manganate is preferably used since it serves as an electrode of high voltage and high capacity.

When using the electrode active material exhibiting a high potential as described above, it is necessary to use a solid electrolyte having a high decomposition voltage as the lithium ion conductive solid electrolyte. Since a solid electrolyte composed of a substance containing lithium sulfide and silicon sulfide shows a high decomposition voltage, a lithium ion conductive solid electrolyte composed of a substance containing lithium sulfide and silicon sulfide is preferably used as the lithium ion conductive solid electrolyte. .

A lithium ion conductive solid electrolyte composed of at least one compound selected from lithium oxide or lithium oxyacid salt and a lithium ion conductive solid electrolyte composed of a substance containing lithium sulfide and silicon sulfide is a sulfide. A part of sulfur in the glass structure is replaced with oxygen, and a more stable glass skeleton is formed. As a result, it becomes stable even for an electrode active material showing a high potential. Therefore, as the lithium ion conductive solid electrolyte, a lithium ion conductive solid electrolyte composed of at least one compound selected from lithium oxide or lithium oxyacid salt and a substance containing lithium sulfide and silicon sulfide is preferably used.

[0019]

The present invention will be described in detail below with reference to examples and reference examples.

Reference Example 1 In this reference example, amorphous vanadium oxide was used as a compound mainly composed of amorphous as a positive electrode active material, and a lithium ion conductive solid electrolyte mainly composed of sulfide was used as a solid electrolyte. A lithium ion conductive amorphous solid electrolyte represented by 0.6Li ₂ S-0.4SiS ₂ was used, and metallic lithium was used as a negative electrode active material to construct an all-solid-state lithium battery as described below. evaluated.

First, amorphous vanadium oxide was synthesized as follows. Vanadium oxide (V
₂ O ₅ ) was a commercially available reagent special grade. This vanadium oxide was put into a platinum crucible and melted in an oxygen stream at 800 ° C., and then rapidly cooled by a twin roller to be an amorphous state.

Next, a lithium ion conductive solid electrolyte 0.6Li ₂ S-0.4SiS ₂ mainly composed of sulfide was synthesized as follows.

Lithium sulfide (Li ₂ S) and silicon sulfide (SiS ₂ ) were mixed at a molar ratio of 3: 2, and the mixture was put into a glassy carbon crucible. The crucible was put in a vertical furnace and heated to 950 ° C. in an argon stream to make the mixture in a molten state. After heating for 2 hours, the melt was rapidly cooled by a twin roller to obtain a lithium ion conductive amorphous solid electrolyte represented by 0.6Li ₂ S-0.4SiS ₂ .

The thus obtained 0.6Li ₂ S-0.
4SiS ₂ and amorphous vanadium oxide were mixed at a weight ratio of 1: 1 and carbon fiber was added as a conductive material at a weight ratio of 2% to obtain a positive electrode material.

As the negative electrode, metallic lithium foil (thickness 1 m
m) was punched into a size of 10 mmφ.

A cross-sectional view of the all-solid-state lithium battery constructed in FIG. 1 is shown. The positive electrode 1 obtained above and the negative electrode 2 made of a metallic lithium foil were mixed with a solid electrolyte (0.6Li ₂ S-0.4Si).
The S ₂ ) layer 3 was pressed integrally into a cylindrical shape of 10 mmφ. However, the positive electrode weight at that time was 100 mg.
Then, the positive electrode lead 4 and the negative electrode lead 5 were adhered with a carbon paste 6, and the whole was resin-sealed 7 to obtain an all-solid-state lithium battery according to this reference example.

For comparison, an all-solid-state lithium battery was obtained in the same manner as above except that vanadium oxide that was not made amorphous was used in place of the above amorphous vanadium oxide.

To compare the performance of these batteries, 2
The batteries were discharged to 2.0 V with a constant current of 0 μA, and the discharge capacities were compared. FIG. 2 shows the discharge curve obtained for each battery.

As a result, the one using amorphous vanadium oxide as the electrode active material showed a larger discharge capacity.

As described above, according to this reference example, a high capacity all-solid-state lithium battery was obtained.

Reference Example 2 This Reference Example is the same as Reference Example 1 except that amorphous LiV ₂ O ₅ was used in place of the amorphous vanadium oxide used in Reference Example 1 as the compound mainly composed of amorphous. An all-solid-state lithium battery according to this reference example was constructed by the above method.

Amorphous LiV ₂ O ₅ was obtained by immersing the amorphous vanadium oxide obtained in Reference Example 1 in n-butyllithium diluted with cyclohexane, washing with cyclohexane and drying under reduced pressure.

For comparison, the amorphous LiV ₂ O ₅ obtained above is heated to 600 ° C. in an argon atmosphere and crystallized to obtain crystalline LiV ₂ O ₅ , which is then converted into amorphous LiV ₂ O ₅ . Used instead, an all-solid-state lithium battery was constructed.

The performance of these batteries was evaluated by a charge / discharge test conducted at a constant current of 20 μA in the voltage range of 3.5V to 2.0V. As a result, the all-solid-state lithium battery using amorphous LiV ₂ O ₅ showed a larger charge / discharge capacity.

As described above, according to this reference example, it was found that a high capacity all-solid-state lithium battery can be obtained.

Reference Example 3 In this Reference Example, instead of the amorphous vanadium oxide used in Reference Example 1 as a compound mainly composed of amorphous material,
Reference example 1 except that amorphous molybdenum oxide was used
An all-solid-state lithium battery according to the present invention was constructed in the same manner as in. For comparison, an all-solid-state lithium battery was constructed using crystalline molybdenum oxide.

As the amorphous molybdenum oxide, a commercially available reagent grade molybdenum oxide (MoO ₃ ) was put in a platinum crucible and melted at 900 ° C. in an oxygen stream, and then rapidly cooled by a twin roller to be in an amorphous state. .

As a result of comparing the discharge capacities of these all-solid-state lithium batteries in the same manner as in Reference Example 1, the one using amorphous molybdenum oxide as the electrode active material showed a larger discharge capacity.

As described above, according to this reference example, it was found that a high capacity all-solid-state lithium battery can be obtained.

Reference Example 4 This Reference Example is the same as Reference Example 1 except that amorphous tungsten oxide was used in place of the amorphous vanadium oxide used in Reference Example 1 as the compound mainly composed of amorphous. The method constituted an all-solid-state lithium battery according to the invention. For comparison, an all-solid-state lithium battery was constructed using crystalline tungsten oxide.

Amorphous tungsten oxide was synthesized by the quenching device shown in FIG. First, commercially available reagent grade tungsten oxide (WO ₃ ) was added to 2 mm × 2 mm × 10 mm
Was pressed into a rectangular parallelepiped shape. This pressure-molded body was set at position 8 in FIG. This sample was heated and melted by the light 11 emitted from the light source 10 of the light collecting furnace 9. Further, the melt 12 was rapidly cooled by a twin roller 13 to obtain amorphous tungsten oxide.

Using the thus-obtained amorphous tungsten oxide and non-amorphous tungsten oxide, an all-solid-state lithium battery was constructed, and the discharge capacities thereof were compared by the same method as in Reference Example 1. FIG. 4 shows the charge / discharge curves obtained for each battery.

As a result, the use of amorphous tungsten oxide as the electrode active material showed a larger discharge capacity.

As described above, according to this reference example , it was found that a high capacity all-solid-state lithium battery can be obtained.

Reference Example 5 In Reference Example 1, except that amorphous titanium oxide was used in place of the amorphous vanadium oxide used in Reference Example 1 as the compound mainly composed of amorphous, An all-solid-state lithium battery according to the present invention was constructed in the same manner. For comparison, an all-solid-state lithium battery was constructed using crystalline titanium oxide.

Amorphous titanium oxide was obtained by hydrolyzing titanium isopropoxide (Ti [OCH (CH ₃ ) ₂ ] ₄ ). Amorphous titanium oxide is obtained by subjecting the amorphous titanium oxide thus obtained to 800
Obtained by heating at ℃ for 24 hours.

Using the thus obtained amorphous titanium oxide and crystalline titanium oxide, an all-solid-state lithium battery was constructed and the performance was the same as in Reference Example 1 except that the discharge end voltage was 0.5V. As a result of comparing the discharge capacities by the method, the one using amorphous titanium oxide showed a larger discharge capacity.

As described above, according to this reference example , it was found that a high capacity all-solid-state lithium battery can be obtained.

Example 1 In this example, amorphous vanadium oxide used in Reference Example 1 was replaced with amorphous lithium cobalt oxide represented by LiCoO ₂ as a compound mainly composed of amorphous. An all-solid-state lithium battery according to the present invention was constructed. For comparison, an all-solid-state lithium battery was constructed using crystalline lithium cobalt oxide.

First, crystalline LiCoO ₂ was synthesized by mixing cobalt oxide (Co ₃ O ₄ ) and lithium carbonate (Li ₂ CO ₃ ) and firing at 900 ° C. in the atmosphere. Next, in order to amorphize this crystalline lithium cobalt oxide, it was finely pulverized by a planetary ball mill until a halo appeared in an X-ray diffraction image.

Amorphous LiCoO ₂ obtained in this way
Further, an all-solid-state lithium battery according to the present invention and an all-solid-state lithium battery for comparison were constructed in the same manner as in Reference Example 1 except that crystalline LiCoO ₂ was used as the positive electrode active material.

The characteristics of these all-solid-state lithium batteries were the same as those of Reference Example 2 except that the charge / discharge voltage range was 4.4 V to 2.5 V.
It was evaluated by the same charge and discharge test.

The discharge curve obtained is shown in FIG. As a result, it was found that the all-solid-state lithium battery using amorphous lithium cobalt oxide as the electrode active material has a higher discharge capacity, and that the present invention can provide a high-capacity all-solid-state lithium battery.

Example 2 In this example, instead of the lithium cobalt oxide represented by LiCoO ₂ used in Example 1 as the transition metal oxide, an amorphous nickel acid represented by LiNiO ₂ was used. In the same manner as in Example 1 except that lithium was used, an all-solid-state lithium battery according to the present invention and an all-solid-state lithium battery for comparison were formed by using crystalline lithium nickelate, and their characteristics were evaluated. .

However, crystalline LiNiO ₂ was synthesized by mixing nickel oxide (NiO) and lithium hydroxide (LiOH) and firing at 1000 ° C. in the atmosphere. The crystalline lithium nickel oxide thus obtained was finely pulverized in the same manner as in Example 1.

The characteristics of the thus-obtained all-solid-state lithium battery were evaluated in the same manner as in Example 1. As a result, the one using amorphous lithium nickel oxide as the electrode active material showed a higher discharge capacity. According to the present invention, it has been found that a high capacity all-solid-state lithium battery can be obtained.

Example 3 In this example, instead of the lithium cobalt oxide represented by LiCoO ₂ used in Example 1 as the transition metal oxide, an amorphous compound represented by LiMn ₂ O ₄ was used. An all-solid-state lithium battery according to the present invention and a comparative all-solid-state lithium battery using crystalline lithium manganate were constructed in the same manner as in Example 1 except that lithium manganate was used. evaluated.

However, crystalline LiMn ₂ O ₄ was synthesized by mixing manganese dioxide (MnO ₂ ) and lithium carbonate (Li ₂ CO ₃ ) and firing at 800 ° C. in the atmosphere,
Amorphous lithium nickel oxide was obtained by finely pulverizing the crystalline lithium manganate thus obtained in the same manner as in Example 1.

The characteristics of the thus-obtained all-solid-state lithium battery were evaluated in the same manner as in Example 1. As a result, the one using amorphous lithium manganate as the electrode active material showed a higher discharge capacity. According to the present invention, it has been found that a high capacity all-solid-state lithium battery can be obtained.

Reference Example 6 In this Reference Example, instead of the amorphous vanadium oxide used in Reference Example 1 as a compound mainly composed of amorphous material,
An all-solid-state lithium battery according to this reference example was constructed in the same manner as in reference example 1 except that amorphous molybdenum sulfide was used. For comparison, an all-solid-state lithium battery was constructed using crystalline molybdenum sulfide.

Amorphous molybdenum sulfide was obtained by finely pulverizing a commercially available reagent grade molybdenum sulfide (MoS ₂ ) in the same manner as in Example 1.

[0062] Using these all-solid-state lithium batteries the properties except that the end-of-discharge voltage was set to 1.0V results were examined in the same manner as in Reference Example 1, amorphous molybdenum sulfide as electrostatic electrode active material The one showed a larger discharge capacity.

As described above, according to this reference example, a high capacity all-solid-state lithium battery was obtained.

Reference Example 7 In this Reference Example, in place of 0.6Li ₂ S-0.4SiS ₂ used in Reference Example 1 as an electrolyte, one or more selected from lithium oxide or lithium oxyacid salt is used. 0.02Li ₃ PO ₄ -0.59Li ₂ S-0.39Si, which is one of sulfide-based lithium ion conductive solid electrolytes composed of certain compounds and lithium sulfide and silicon sulfide
An all-solid-state lithium battery according to this reference example and an all-solid-state lithium battery for comparison were constructed in the same manner as in Reference Example 1 except that the lithium ion conductive amorphous solid electrolyte represented by S ₂ was used.

When the discharge capacities of the thus obtained all-solid-state lithium secondary batteries were compared by the same method as in Reference Example 1, the one using amorphous vanadium oxide as the positive electrode active material showed a larger discharge capacity. Indicated.

As described above, according to this reference example, it was found that a high capacity all-solid-state lithium battery can be obtained.

Reference Example 8 In this Reference Example, in place of the 0.6Li ₂ S-0.4SiS ₂ used in Reference Example 1 as the electrolyte, one or more selected from lithium oxide or lithium oxyacid salt is used. 0.04Li ₄ SiO ₄ -0.58Li ₂ S-0.38S, which is one of sulfide-based lithium ion conductive solid electrolytes composed of lithium sulfide and silicon sulfide
An all-solid-state lithium battery according to this reference example and an all-solid-state lithium battery for comparison were constructed in the same manner as in Reference Example 1 except that the lithium ion conductive amorphous solid electrolyte represented by iS ₂ was used.

When the discharge capacities of the thus obtained all-solid-state lithium secondary batteries were compared by the same method as in Reference Example 1, the one using amorphous vanadium oxide as the electrode active material showed a larger discharge capacity. Indicated.

As described above, according to this reference example, a high capacity all-solid-state lithium battery was obtained.

Example 4 In this example, at least one selected from lithium oxide and lithium oxyacid salt was used as the electrolyte instead of 0.6Li ₂ S-0.4SiS ₂ used in Example 1. 0.02Li ₂ O-0.59Li ₂ S-0.39S, which is one of lithium ion conductive solid electrolytes mainly composed of a compound and a sulfide composed of lithium sulfide and silicon sulfide
An all-solid-state lithium battery according to the present invention using amorphous lithium cobalt oxide as the positive electrode active material in the same manner as in Example 1 except that the lithium ion conductive amorphous solid electrolyte represented by iS ₂ is used. , And an all-solid lithium battery for comparison using crystalline lithium cobalt oxide was constructed.

The characteristics of the thus-obtained all-solid-state lithium battery were compared in discharge capacity in the same manner as in Example 1. The larger discharge capacity was exhibited.

As described above, it was found that a high capacity all-solid-state lithium battery can be obtained according to the present invention.

Reference Example 9 In this Reference Example, in order to confirm the chemical stability of the constructed all-solid-state lithium battery due to the difference in solid electrolyte, the solid electrolyte contains at least lithium oxide or lithium oxyacid salt. All-solid-state lithium batteries of Reference Examples 7 and 8 and Example 4 constituted by using one compound and a lithium ion solid electrolyte mainly composed of a sulfide composed of lithium sulfide and silicon sulfide, and Reference Examples 1 and 1 After storing the all-solid-state lithium battery composed of the above at 30 ° C. for 30 days, the impedance was measured.

As a result, the all-solid-state lithium batteries of Reference Examples 7 and 8 and Example 4 showed a smaller increase in impedance than the all-solid-state lithium batteries of Reference Example 1 and Example 1,
It was confirmed that the chemical stability was good. In particular, comparing the all-solid-state lithium batteries of Examples 4 and 1, the increase of impedance of Example 4 is much smaller than that of Example 1, and it is particularly stable to the electrode active material exhibiting a high potential. I understood it.

As described above, it was found from the results of this measurement that an all-solid-state lithium battery having good chemical stability can be obtained.

As described above, in the examples of the present invention, as the compound in the amorphous state, amorphous lithium nickelate, lithium cobaltate and lithium manganate, which are metal oxides, were used.

As the compounds in the amorphous state, only those obtained by the quenching method, the hydrolysis method of alkoxide, and the fine pulverization method have been described, but the amorphous compounds obtained by other methods. The same effect can be obtained by using the compound in the amorphous state, and the present invention is not limited to the compounds in the amorphous state obtained by the methods described in these examples.

In the examples of the present invention, only the case where metallic lithium was used as the negative electrode active material was explained, but the negative electrode active material may be a graphite-lithium compound, a lithium alloy such as Li-Al, or the like. The same effect can be obtained by using a substance other than metallic lithium, and the all-solid-state lithium battery of the present invention is not limited to the one using metallic lithium as the negative electrode active material.

In the embodiment of the present invention, as the solid electrolyte, 0.6Li ₂ S-0.4SiS ₂ , 0.0
Using such _{2Li 3 PO 4 -0.59Li 2 S-} 0.39SiS 2.

Further, in the examples of the present invention, the case where the amorphous compound was used as the positive electrode active material was described.

[0081]

As described above, according to the structure of the present invention, more lithium ions can be taken in and out without causing a phase transition, so that a high capacity all-solid-state lithium battery can be obtained. It was

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a lithium battery according to one reference example described in an example.

FIG. 2 is a discharge characteristic diagram of all-solid-state lithium batteries in one reference example and comparative example described in the examples.

FIG. 3 is a principle diagram of an apparatus for synthesizing a compound in an amorphous state in one reference example described in Examples.

FIG. 4 is a discharge characteristic diagram of all-solid-state lithium batteries in one reference example and comparative example described in the examples.

FIG. 5 is a discharge characteristic diagram of an all-solid-state lithium battery in one example and a comparative example of the present invention.

[Explanation of symbols]

1 positive electrode 2 Negative electrode 3 Solid electrolyte layer 4 Positive lead 5 Negative electrode lead 6 carbon paste 7 Sealing resin 8 samples 9 Light collecting furnace 10 light sources 11 light 12 Melt 13 twin rollers

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuya Iwamoto 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Shigeo Kondo 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. In-company (56) Reference JP-A-1-159970 (JP, A) JP-A-62-8452 (JP, A) JP-A-62-82665 (JP, A) JP-A-3-208256 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/36-10/40 H01M 4 / 02,4 / 58,6 / 18

Claims (2)

(57) [Claims] 1. A compound comprising a positive electrode, a negative electrode, and a solid electrolyte layer, wherein the solid electrolyte layer is an amorphous lithium ion conductive solid electrolyte containing sulfide as a main component, and the active material of the positive electrode is in an amorphous state. An all-solid-state lithium battery containing, wherein the compound in the amorphous state is lithium cobalt oxide, lithium nickel oxide or lithium manganate, and the lithium ion conductive solid electrolyte further contains lithium sulfide and silicon sulfide. An all-solid-state lithium battery comprising a substance. 2. The lithium ion conductive solid electrolyte,
The all-solid-state lithium battery according to claim 1, comprising at least one compound selected from lithium oxide or lithium oxyacid salt, and lithium sulfide and silicon sulfide.