JPH04269461A - All-solid-state lithium secondary battery - Google Patents

Abstract

PURPOSE:To provide a full-solid lithium secondary battery using a solid electrolyte which substantially has no possibility of an internal short-circuit by reducing the electron conductivity of the solid electrolyte. CONSTITUTION:A full-solid lithium secondary battery is formed by using, as a component, a solid electrolyte prepared by quenching an oxyacid salt lithium ion conductive solid electrolyte or a molten material forming it in oxygen atmosphere and making the valence of a transition metal forming the oxyacid monovalent.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an all-solid-state lithium secondary battery, and more particularly to an all-solid-state lithium secondary battery using a solid electrolyte.

0002

[Prior Art] All-solid-state batteries using solid electrolytes are attracting a lot of attention as they achieve high reliability without worrying about leakage, and those using lithium are particularly promising as batteries with high capacity. There is. A LiI-Al2O3-based lithium ion conductive solid electrolyte has already been used as a solid electrolyte when configuring a power source for driving a cardiac pacemaker. However, there are few examples of such lithium ion conductive solid electrolytes being used as practical devices, and this is due to the low ionic conductivity of the lithium ion conductive solid electrolytes. In order to overcome these problems, oxyacid-based lithium ion conductive solid electrolytes, typified by Li4SiO4-Li3VO4, have been proposed as solid electrolytes having relatively high ionic conductivity. This solid electrolyte is produced by solid ionics (Kodansha 1986), in which a predetermined amount of each raw material is mixed, sealed in a glass tube in an inert gas atmosphere such as argon, heated and melted, and then allowed to cool naturally or rapidly cooled in liquid nitrogen. Published in 2015, page 77).

0003

[Problem to be solved by the invention] However, the solid electrolyte synthesized by this method has high electronic conductivity,
For example, solid-state batteries made using these have the problem of large so-called self-discharge, in which the voltage decreases over time, especially when placed in a high-temperature atmosphere. The present invention solves these problems and aims to provide an all-solid-state lithium secondary battery with extremely low self-discharge.

0004

[Means for Solving the Problems] In order to solve the above-mentioned problems, the all-solid-state lithium secondary battery of the present invention provides an oxyacid-based lithium ion battery in which the valence of the transition metal constituting the oxyacid is monovalent. A conductive solid electrolyte is a constituent element, and a solid electrolyte manufactured by rapidly cooling an oxyacid-based lithium ion conductive solid electrolyte or a melt of the raw materials constituting it in an oxygen atmosphere is a constituent element. .

[0005]

[Operation] In order to solve the above problem, the inventors discovered that when a melt of an oxyacid-based lithium ion conductive solid electrolyte is rapidly cooled in an oxygen atmosphere, the electronic conductivity decreases significantly, and at the same time, the ionic conductivity increases. I found something to do. This is considered to be based on the following effects.

[0006] In other words, when the lithium ion conductive solid electrolyte represented by Li4SiO4-Li3VO4 is manufactured according to the manufacturing method described in the conventional technology, it has a slight non-stoichiometric composition in the oxygen-acid part of its composition. Therefore, the transition metals such as V that form the oxyacid have a mixed valence, and electrons conduct hopping through the mixed valence portion, which is thought to produce the electronic conductivity of the solid electrolyte. For example, the above-mentioned Li4SiO4-Li3VO4 is melted in an inert gas atmosphere such as argon or in a glass sealed tube, and when it is naturally cooled or rapidly cooled in liquid nitrogen, the valence of V becomes a mixture of tetravalent and pentavalent, Electron conductivity occurs through this route. However, when this melt is rapidly cooled in an oxygen atmosphere, the valence of V is unified to 5, and the electronic conductivity due to the above-mentioned hopping disappears.

[0007]

[Embodiment] An all-solid-state lithium secondary battery according to an embodiment of the present invention will be described in detail below with reference to the drawings.

(Example 1) In FIG. 1, Li2CO3
, SiO2, V2O5 powder at a molar ratio of 17:4:3, dispersed in n-hexane, and heated at 600°C in dry air.
After heating for 3 hours, allow to cool to room temperature. Then, put this in a glassy carbon container 1, and then add 1 liter of oxygen.
The conditioning material is melted by heating to about 700° C. in an infrared image furnace 2 flowing with argon gas containing vol%. This is dropped onto a rotating roller 3 coated with titanium on the surface and having a sufficient heat capacity, whereby the melt is rapidly cooled at a cooling rate of 105° C./sec and collected in a glass container 4. The rotating roller 3 where the melt is rapidly cooled and the atmosphere around it are maintained in an oxygen atmosphere by oxygen introduced from the oxygen inlet 5. Finally, this was pulverized in a dry air atmosphere to obtain a lithium ion conductive solid electrolyte A represented by the compositional formula 0.4Li4SiO4-0.6Li3VO4. As a comparative example, powders of Li2CO3, SiO2, and V2O5 were quantitatively determined at a molar ratio of 17:4:3, dispersed in n-hexane, heated in dry air at 600°C for 3 hours, allowed to cool to room temperature, and pulverized. The fine powder obtained by
The product was pressure-molded at a pressure of Obtained. Note that all the atmospheric gases used in the above manufacturing process have a purity of 99.99% or higher. In addition, in this example, the cooling rate of the melt was 105°C/
Although it was performed at 105 to 107° C./second, similar effects can be produced.

Using the lithium ion conductive solid electrolyte A thus prepared and the lithium ion conductive solid electrolyte B prepared by a conventionally known manufacturing method as constituent elements, an all-solid-state secondary battery C of this example and a battery D of a comparative example were prepared, respectively. Created. In Figure 2, 6
and 8 is 3 ton/cm after mixing 100 mg of the battery active material represented by MoS2 and 100 mg of the solid electrolyte.
A positive electrode and a negative electrode were created by pressure molding at a pressure of 2, 7 is a solid electrolyte layer made of 500 mg of the solid electrolyte, and 9 is a lead terminal made of metal nickel, and the side surfaces of the positive electrode 6 and negative electrode 8 are Bonded with carbon paste. The positive electrode 6, the electrolyte layer 7, and the negative electrode 8 were bonded together by placing the whole in a mold with a diameter of 10 mm and applying a pressure of 3 ton/cm2. Finally, a sealing layer 10 was formed using epoxy resin to seal the entire structure, resulting in batteries C and D of this example. In the above configuration, battery C of the example
Solid electrolyte A was used for battery D of the comparative example, and solid electrolyte B was used for battery D of the comparative example.

Batteries C and D prepared as described above were subjected to a voltage holding test by storage in a high temperature atmosphere. The test was conducted by charging the battery at room temperature for 24 hours at 3 volts, placing it in a constant temperature bath kept at 100° C., and evaluating the decrease in battery voltage depending on the number of days of storage.

As is clear from FIG. 3, the battery C of this embodiment, which has electrolyte A produced by rapidly cooling a melt in an oxygen atmosphere, is different from electrolyte B produced by a conventional manufacturing method. Compared to Battery D of Comparative Example, which has the following components, the decrease in holding voltage due to high-temperature storage was significantly reduced.

Furthermore, V constituting solid electrolytes A and B
When the valence of V was confirmed by XPS (X-ray optical spectroscopy), it was found that in the sample of solid electrolyte B,
In contrast, in the sample of solid electrolyte A, about 50 at% of tetravalent V was present, whereas in the sample of solid electrolyte A, it was 1 at%, which is the detection limit of XPS.
We confirmed the following and obtained results that prove the factors described in the above-mentioned effects.

In this example, the melt of the raw materials constituting the solid electrolyte was quenched in an oxygen atmosphere, but even if a solid electrolyte prepared according to the conventional manufacturing method was melted and quenched in an oxygen atmosphere, Needless to say, it produces a similar effect.

(Example 2) In this example, 0.6Li4Ge, which is an oxyacid-based lithium ion conductive solid electrolyte, was used.
Taking O4-0.4Li3VO4 as an example, the all-solid-state lithium secondary battery of this example will be described. Well, the synthesis is
The same manufacturing apparatus as shown in FIG. 1 of Example 1 was used.

Powders of Li2CO3, GeO2, and V2O5 were quantitatively dispersed in n-hexane at a molar ratio of 9:3:1, heated in dry air at 600° C. for 3 hours, and then allowed to cool to room temperature. Thereafter, this is placed in a container 1 made of glassy carbon, and then heated to about 700° C. in an infrared image furnace 2 in which argon gas containing 1% by volume of oxygen is flowed to melt the adjustment material. this,
The molten material is dropped onto a rotating roller 3 coated with titanium on the surface and having sufficient heat capacity.
The sample is rapidly cooled at a cooling rate of 0.05°C/second and collected in a glass container 4. The rotating roller 3 where the melt is rapidly cooled and the atmosphere around it are heated by oxygen introduced from the oxygen inlet 5.
It is kept in an oxygen atmosphere. Finally, this was pulverized in a dry air atmosphere to obtain a lithium ion conductive solid electrolyte E. As a comparative example, Li2CO3, GeO
2. V2O5 powder was quantitatively determined at a molar ratio of 9:3:1, dispersed in n-hexane, heated in dry air at 600°C for 3 hours, cooled to room temperature, and crushed to obtain a fine powder of 3 tons.
The product was pressure-molded at a pressure of on/cm2, sealed in a quartz glass container, sintered at 800°C for 1 hour, allowed to cool to room temperature, and crushed in a dry air atmosphere to form a lithium ion conductive solid. Electrolyte F was obtained. Note that all the atmospheric gases used in the above manufacturing process have a purity of 99.99% or higher. Further, in this example, the cooling rate of the molten material was 105°C/sec, but a similar effect can be produced by cooling the melt at 105°C to 107°C/sec.

A battery G of this example and a battery H of a comparative example were respectively manufactured using the lithium ion conductive solid electrolyte E thus prepared and F manufactured by a conventionally known manufacturing method as constituent elements. In FIG. 4, 11 and 13
After mixing 100 mg of the battery active material represented by the chemical formula TiS2 and 100 mg of the solid electrolyte, the
It is an electrode created by pressure molding at a pressure of 2.
12 is a solid electrolyte layer made of 500 mg of the solid electrolyte, and 14 is a lead terminal made of metal nickel,
It was adhered to the side surfaces of the positive electrode 11 and negative electrode 13 using carbon paste. The positive electrode 11, the electrolyte layer 12, and the negative electrode 13 were bonded together by placing the whole in a mold with a diameter of 10 mm and applying a pressure of 3 ton/cm2. Finally, a sealing layer 15 was formed using epoxy resin to seal the entire structure, resulting in batteries G and H of this example. In the above configuration, solid electrolyte E was used in battery G of the present example, and solid electrolyte F was used in battery H of the comparative example.

Batteries G and H prepared as described above were subjected to a voltage holding test by storage in a high temperature atmosphere. The test was conducted by charging the battery at room temperature for 24 hours at 3 volts, placing it in a constant temperature bath kept at 100° C., and evaluating the decrease in battery voltage depending on the number of days of storage.

As is clear from FIG. 5, the battery G of this embodiment, which has an electrolyte E produced by rapidly cooling a melt in an oxygen atmosphere, is different from the electrolyte F produced by a conventional manufacturing method. Compared to Battery H of Comparative Example, which had the following components, the drop in holding voltage due to high-temperature storage was significantly reduced.

Furthermore, W constituting solid electrolytes E and F
When the valence of was confirmed by XPS (X-ray optical spectroscopy), it was found that in the solid electrolyte F sample, about 50 atomic percent of pentavalent W was present compared to the hexavalent W, whereas in the solid electrolyte E sample, Among them, it was confirmed that the concentration was below 1 atomic %, which is the detection limit of XPS, and results were obtained that proved the factors described in the above-mentioned effect.

In this example, the melt of the raw materials constituting the solid electrolyte was quenched in an oxygen atmosphere, but even if a solid electrolyte prepared according to the conventional manufacturing method was melted and quenched in an oxygen atmosphere, Needless to say, it produces a similar effect.

In the above examples, 0.4Li4SiO4-0 was used as the oxyacid-based lithium ion conductive solid electrolyte.
．． 6Li3VO4 and 0.6Li4GeO4-0.4L
Although the effects of this example have been described using an all-solid lithium secondary battery using i3VO4 as an electrolyte, it is not necessary to limit the material to this material in particular, and any known oxyacid-based lithium ion conductive solid electrolyte may be used. Needless to say, it is also effective in manufacturing.

[0022]

【Effect of the invention】
As is clear from the above description of the embodiments, by following the all-solid-state lithium secondary battery of the present invention, it is possible to obtain an all-solid-state lithium secondary battery with extremely low self-discharge.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the concept of the configuration of an apparatus for producing an oxyacid-based lithium ion conductive solid electrolyte, which is a component of an all-solid-state lithium secondary battery according to an embodiment of the present invention.

[Fig. 2] Cross-sectional view showing the configuration of all-solid-state secondary batteries C and D of Example 1

[Figure 3] Graph showing the characteristics of all-solid-state secondary batteries C and D

[Fig. 4] Cross-sectional view showing the structure of all-solid-state secondary batteries G and H of Example 2

[Figure 5] Graph showing the characteristics of all-solid-state secondary batteries G and H

[Explanation of symbols]

1 Glassy carbon container 2 Infrared image furnace 3 Rotating roller 4 Glass container 5 Oxygen inlet

Claims (2)

[Claims] 1. An all-solid-state lithium secondary battery comprising an oxyacid-based lithium ion conductive solid electrolyte in which the transition metal constituting the oxyacid has a single valence. 2. An all-solid-state lithium secondary battery comprising an oxyacid-based lithium ion conductive solid electrolyte or a solid electrolyte produced by rapidly cooling a melt of raw materials constituting the same in an oxygen atmosphere.