KR102595766B1 - Solid electrolyet for solid-state battery - Google Patents

Abstract

The present invention relates to a solid electrolyte for an all-solid-state battery. The solid electrolyte for an all-solid-state battery according to an embodiment of the present invention is composed of oxides containing Li, K, and Bi.

Description

Solid electrolyte for all-solid-state battery {SOLID ELECTROLYET FOR SOLID-STATE BATTERY}

The present invention relates to a solid electrolyte for an all-solid-state battery.

Recently, the use of secondary batteries has increased significantly in various fields, from IT devices such as mobile phones to electric vehicles and energy storage devices.

As secondary batteries, lithium-ion batteries using liquid electrolyte are most widely used. However, liquid electrolyte has a risk of leakage when external shock is applied to the battery, and thus additional parts and devices are needed to ensure safety.

Recently, in order to improve the safety of secondary batteries, development of all-solid-state batteries that use solid electrolytes as electrolytes is actively underway. Solid electrolytes in all-solid-state batteries include polymer electrolytes, oxide electrolytes, and sulfide electrolytes. Among these, sulfide-based solid electrolytes have the highest ionic conductivity, but have the problem of generating hydrogen sulfide gas when they react with moisture. Polymer electrolytes have the advantage of having a relatively simple process and being able to use existing lithium-ion battery processes, but have the disadvantage of having significantly low ionic conductivity.

Oxide-based electrolytes have the advantage of being safer than sulfide-based electrolytes, but their ionic conductivity is relatively low. Additionally, oxide-based electrolytes generally require a high sintering temperature of 1,000°C or more, which can significantly increase manufacturing costs.

The present invention is intended to solve the problems of the prior art described above, and its purpose is to provide a solid electrolyte for an all-solid-state battery that can be sintered at low temperatures and has excellent ionic conductivity.

The solid electrolyte for an all-solid-state battery according to an embodiment of the present invention is composed of oxides containing Li, K, and Bi.

The solid electrolyte for an all-solid-state battery according to an embodiment of the present invention may satisfy 0.2≤(Li+K)/Bi<1 based on the molar ratio of each component. Additionally, the solid electrolyte for an all-solid-state battery according to an embodiment of the present invention may satisfy 0.2≤(Li+K)/Bi≤0.6 based on the molar ratio of each component.

The solid electrolyte for an all-solid-state battery according to an embodiment of the present invention may satisfy 0.1≤Li<0.5 based on the molar ratio. Additionally, the solid electrolyte for an all-solid-state battery according to an embodiment of the present invention may satisfy 0.10≤K≤0.15 based on the molar ratio.

The solid electrolyte for an all-solid-state battery according to an embodiment of the present invention may have a bismuth oxide crystal structure.

The solid electrolyte for an all-solid-state battery according to an embodiment of the present invention may have a softening point of 540°C to 600°C.

The solid electrolyte for an all-solid-state battery according to an embodiment of the present invention may have a half-ball temperature of 550°C to 660°C.

In addition to this, the solid electrolyte for an all-solid-state battery according to the present invention may further include other additional components without impairing the technical spirit of the present invention.

According to one embodiment of the present invention, the solid electrolyte for an all-solid-state battery contains Li, K, and Bi, thereby enabling low-temperature sintering and having excellent ionic conductivity.

1 is a diagram schematically showing a cross section of an all-solid-state battery.
Figure 2 shows a triangular diagram showing the composition range of solid electrolytes according to examples and comparative examples of the present invention.
Figure 3 shows an XRD graph of a solid electrolyte according to an embodiment of the present invention.
Figures 4 and 5 show XRD graphs of solid electrolytes according to comparative examples of the present invention.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail so that a person skilled in the art can easily implement the present invention.

In order to clearly explain the present invention, descriptions of parts unrelated to the present invention have been omitted, and like reference numerals are assigned to like components throughout the specification. The specific shape, structure, and characteristics described in the specification may be changed and implemented from one embodiment to another without departing from the spirit and scope of the present invention, and the location or arrangement of individual components may also be implemented within the spirit and scope of the present invention. It should be understood as something that can be changed without deviating from it.

Accordingly, the detailed description described below is not to be taken in a limiting sense, and the scope of the present invention should be taken to encompass the scope of the claims and all equivalents thereof.

1 is a diagram schematically showing a cross section of an all-solid-state battery.

Referring to FIG. 1, the all-solid-state battery 10 includes an anode 11, a cathode 12, and a solid electrolyte layer 13. The solid electrolyte layer 13 is disposed between the anode 11 and the cathode 12 and may be in contact with the anode 11 and the cathode 12, respectively. The positive electrode 11 and the negative electrode 12 may each have a positive electrode active material layer and a negative electrode active material layer, and the positive electrode active material layer and the negative electrode active material layer may each be in contact with the solid electrolyte layer 13.

The anode 11 and the cathode 12 may each be bonded to the solid electrolyte layer 13 by sintering. That is, the anode 11, cathode 12, and solid electrolyte layer 13 can be sintered as one piece.

In Figure 1, the all-solid-state battery 10 is shown as including one layer each of the anode 11, the cathode 12, and the solid electrolyte layer 13, but the present invention is not limited thereto and includes the anode, the cathode, and the solid electrolyte layer. An all-solid-state battery may be constructed in a form in which the solid electrolyte layer is each composed of a plurality of layers. Alternatively, it may be configured as a so-called stacked all-solid-state battery in which a plurality of anodes, cathodes, and solid electrolyte layers are alternately stacked.

The solid electrolyte layer 13 according to an embodiment of the present invention includes an oxide-based electrolyte as a solid electrolyte.

As oxide-based solid electrolytes, Nasicon-type solid electrolytes such as LAGP and Garnet-type solid electrolytes such as LLZO are known, and through continuous research and development, the ionic conductivity of these oxide-based solid electrolytes has increased to 10 ^-4 S/. It is known to have improved to the cm level.

However, there is a limit to further improving ionic conductivity with the oxide-based solid electrolytes of the Nasicon type and Garnet type. In addition, these oxide-based solid electrolytes are sintered at a high temperature of 1,000°C or higher, so even if a certain degree of excellent ionic conductivity can be obtained as described above, an increase in manufacturing cost due to high temperature sintering cannot be avoided.

In one embodiment of the present invention, excellent ionic conductivity is secured while lowering the sintering temperature through a new oxide-based solid electrolyte that overcomes the limitations of the conventional oxide-based solid electrolyte.

According to one embodiment of the present invention, a solid electrolyte for an all-solid-state battery may be made of oxide containing Li, K, and Bi. In one embodiment, the solid electrolyte for an all-solid-state battery may have a bismuth oxide crystal structure.

In the composition of the solid electrolyte, Bi forms a crystal structure and plays a role in lowering the sintering temperature as a temperature lowering component.

Li and K in the composition of the solid electrolyte can function as a network modifier and increase the lattice constant of the bismuth oxide crystal structure. Accordingly, a wider movement path for Li ions can be secured in the crystal structure, thereby improving ionic conductivity.

In this way, the solid electrolyte according to an embodiment of the present invention is made of an oxide containing Li, K, and Bi, so that Bi functions as the main composition of the crystal structure and Li and K widen the flow path of Li ions to lower the sintering temperature. It can play a lowering role.

According to one embodiment of the present invention, the components constituting the solid electrolyte may have a specific composition range.

The solid electrolyte according to an embodiment of the present invention may satisfy the following relational equation based on the molar ratio of each component.

(1) 0.2≤(Li+K)/Bi<1

Preferably, the solid electrolyte according to an embodiment of the present invention may satisfy the following relational equation based on the molar ratio of each component.

(2) 0.2≤(Li+K)/Bi≤0.6

When the molar ratio of the alkaline components (Li and K) of the solid electrolyte and the molar ratio of Bi satisfy the above relational equation, ionic conductivity can be significantly improved.

The solid electrolyte according to an embodiment of the present invention may further satisfy the following relational equation based on the molar ratio.

(3) 0.10≤Li<0.5

(4) 0.10≤K≤0.15

When the molar ratio of the alkaline components (Li and K) of the solid electrolyte satisfies the above range, ionic conductivity can be improved.

The sintering temperature of the solid electrolyte according to one embodiment of the present invention is about 500°C to about 600°C. When the solid electrolyte according to an embodiment of the present invention is sintered at the above temperature, ^it exhibits an ionic conductivity of about ^2.4

Example

(Example 1)

A precursor powder for producing a solid electrolyte was prepared by mixing 10 mol% of Li ₂ O, 12.5 mol% of K ₂ O, and 77.5 mol% of Bi ₂ O ₃ . After mixing the precursor powder, it was placed in a melting furnace and melted at a temperature of about 1,000°C for about 30 minutes. Afterwards, the homogenized melt was poured into a quenching roller and cooled to room temperature, pulverized, and then sieved to obtain fine particles with a size of 10 ㎛ or less. Finally, the fine particles thus obtained were sintered at about 500°C for about 6 hours to prepare a solid electrolyte.

(Additional Examples and Comparative Examples)

Precursor powders were prepared by varying the composition ratios of Li ₂ O and Bi ₂ O ₃ and melted at a temperature of 800°C to 1,200°C for about 30 minutes depending on the composition ratio. Then, fine particles were obtained through the same process as in Example 1, respectively. A solid electrolyte was prepared by sintering at about 500°C for about 6 hours.

The solid electrolyte composition ratio according to each Example and Comparative Example described above is as shown in Table 1. In Table 1, R means Li or K, and R ₂ O/Bi ₂ O ₃ means the ratio of Li ₂ O and K ₂ O to Bi ₂ O ₃ .

division Solid electrolyte composition (mol%) R ₂ O/Bi ₂ O ₃ Li ₂ O _K2O Bi ₂ O ₃ Example 1 10 12.5 77.5 0.29 Example 2 15 12.5 72.5 0.38 Example 3 18 12.5 69.5 0.44 Example 4 25 12.5 62.5 0.6 Comparative Example 1 37.5 12.5 50 One Comparative Example 2 50 12.5 37.5 1.67 Comparative Example 3 62.5 12.5 25 3 Comparative Example 4 75 12.5 12.5 7 Comparative Example 5 85 12.5 2.5 39

Figure 2 shows a triangular diagram showing the composition range of solid electrolytes according to examples and comparative examples of the present invention. In Figure 2, ① to ④ correspond to Examples 1 to 4, and ⑤ to ⑨ correspond to Comparative Examples 1 to 5.

Referring to Figure 2, Examples 1 to 4, Comparative Examples 2, and Comparative Examples 3 to 5 each have different crystal structures. Specifically, Examples 1 to 4 have a bismuth oxide crystal structure, Comparative Example 2 has a lithium-bismuth oxide crystal structure, and Comparative Examples 3 to 5 have a glass-bismuth oxide crystal structure. It has a ceramic (glass-ceramic) structure. And Comparative Example 1 is located at the boundary between the bismuth oxide crystal structure and the lithium oxide-bismuth oxide crystal structure.

Figure 3 shows an XRD graph of a solid electrolyte according to an example (Example 3) of the present invention, and Figures 4 and 5 show an indicates.

Referring to FIG. 3, it can be seen that the solid electrolyte according to an embodiment of the present invention has a single-phase bismuth oxide crystal structure. On the other hand, it can be confirmed that the solid electrolyte according to the comparative example has a lithium oxide-bismuth oxide crystal structure (see FIG. 4) or a glass-ceramic structure (see FIG. 5).

The results of measuring the crystal structure, softening point, half-ball temperature, and ionic conductivity of the solid electrolytes according to each Example and Comparative Example are shown in Table 2.

division crystal structure Yeonhwa branch
(℃) Half-ball temperature
(℃) ionic conductivity
(S/cm) Example 1 Bi ₂ O ₃ crystal structure 600 653 ^2.4 Example 2 Bi ₂ O ₃ crystal structure 570 600 ^4.0 Example 3 Bi ₂ O ₃ crystal structure 540 580 ^5.1 Example 4 Bi ₂ O ₃ crystal structure 540 554 ^5.8 Comparative Example 1 Bi ₂ O ₃ crystal structure 540 563 ^3.7 Comparative Example 2 Li ₂ OB ₂ O ₃ crystal structure 545 570 ^5.8 Comparative Example 3 Glass-ceramic structure 550 608 ^1.2 Comparative Example 4 Glass-ceramic structure 581 603 ^1.7 Comparative Example 5 Glass-ceramic structure 550 610 ^0.97

Referring to Table 2, the solid electrolytes according to Examples 1 to 4 of the present invention have a softening point of 600°C or lower and a half-ball temperature of 660°C or lower. As such, the solid electrolyte according to embodiments of the present invention has excellent low-temperature characteristics compared to the conventional oxide-based solid electrolyte, enabling low-temperature sintering.

In addition, the solid electrolytes according to Examples 1 to 4 of the present invention have very excellent ionic conductivity of 2.4 X 10 ^-4 to 5.8 X 10 ^-4 S/cm. In comparison, the solid electrolytes according to the comparative example show low temperature characteristics similar to ^those of the examples, but the ionic conductivity is ^0.97

In this way, it can be confirmed that the solid electrolytes according to Examples 1 to 4 of the present invention are capable of low-temperature sintering and have excellent ionic conductivity.

Although the present invention has been described above with reference to specific details such as specific components and limited examples, the examples are provided only to facilitate a more general understanding of the present invention, and the present invention is not limited thereto. Anyone with ordinary knowledge in the relevant technical field can make various modifications and variations from this description.

Accordingly, the spirit of the present invention should not be limited to the embodiments described above, and all modifications equivalent to or equivalent to the claims as well as the claims described below shall fall within the scope of the spirit of the present invention. will be.

10: All-solid-state battery
11: anode
12: cathode
13: solid electrolyte layer

Claims (8)

As a solid electrolyte for an all-solid-state battery,
It consists of oxides containing Li, K and Bi,
Based on the molar ratio of each component, satisfying 0.2≤(Li+K)/Bi<1,
Solid electrolyte for all-solid-state batteries. delete According to paragraph 1,
Based on the molar ratio of each component, satisfying 0.2≤(Li+K)/Bi≤0.6,
Solid electrolyte for all-solid-state batteries. According to paragraph 1,
Based on the molar ratio, satisfying 0.1≤Li<0.5,
Solid electrolyte for all-solid-state batteries. According to paragraph 1,
Based on the molar ratio, satisfying 0.10≤K≤0.15,
Solid electrolyte for all-solid-state batteries. According to paragraph 1,
Having a bismuth oxide crystal structure,
Solid electrolyte for all-solid-state batteries. According to paragraph 1,
A softening point of 540°C to 600°C,
Solid electrolyte for all-solid-state batteries. According to paragraph 1,
Half-ball temperature is 550℃ to 660℃,
Solid electrolyte for all-solid-state batteries.

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