Solid electrolyte for all-solid-state battery

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 one embodiment of the present invention is made of an oxide containing Li, K and Bi.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte for all-solid-state batteries.

Background Art

[0002] Recently, the use of secondary batteries has increased significantly in various fields, ranging from IT devices such as mobile phones to electric vehicles and energy storage devices.

[0003] As secondary batteries, lithium-ion batteries using liquid electrolytes are most widely used. However, liquid electrolytes pose a risk of leakage when the battery is subjected to external shocks, and accordingly, additional components and devices are required to ensure safety.

[0004] Recently, in order to improve the safety of secondary batteries, the development of all-solid-state batteries using solid electrolytes as electrolytes has been actively underway. As solid electrolytes for all-solid-state batteries, there are polymer-based electrolytes, oxide-based electrolytes, sulfide-based electrolytes, etc. Among these, sulfide-based solid electrolytes have the highest ionic conductivity, but have the problem of generating hydrogen sulfide gas by reacting with moisture. Polymer-based electrolytes have the advantage that the process is relatively simple and the existing lithium-ion battery process can be used, but have the disadvantage that the ionic conductivity is significantly low.

[0005] Oxide-based electrolytes have the advantage of being safer than sulfide-based electrolytes, but have relatively low ionic conductivity. In addition, oxide-based electrolytes generally require a high sintering temperature of 1,000 °C or higher, and accordingly, the manufacturing cost can increase significantly.

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a solid electrolyte for all-solid-state batteries that can be sintered at a low temperature and has excellent ionic conductivity in order to solve the problems of the above-described prior art.

Means for Solving the Problems

[0007] The solid electrolyte for all-solid-state batteries according to one embodiment of the present invention is composed of an oxide containing Li, K, and Bi.

[0008] The solid electrolyte for all-solid-state batteries according to one embodiment of the present invention can satisfy 0.2 ≤ (Li + K) / Bi < 1 based on the molar ratio of each component. Also, the solid electrolyte for all-solid-state batteries according to one embodiment of the present invention can satisfy 0.2 ≤ (Li + K) / Bi ≤ 0.6 based on the molar ratio of each component.

[0009] The solid electrolyte for all-solid-state batteries according to one embodiment of the present invention can satisfy 0.1 ≤ Li < 0.5 based on the molar ratio. Also, the solid electrolyte for all-solid-state batteries according to one embodiment of the present invention can satisfy 0.10 ≤ K ≤ 0.15 based on the molar ratio.

[0010] The solid electrolyte for all-solid-state batteries according to one embodiment of the present invention can have a bismuth oxide crystal structure.

[0011] The solid electrolyte for all-solid-state batteries according to one embodiment of the present invention can have a softening point of 540°C to 600°C.

[0012] The solid electrolyte for all-solid-state batteries according to one embodiment of the present invention can have a Half-ball temperature of 550°C to 660°C.

[0013] In addition to this, the solid electrolyte for all-solid-state batteries according to the present invention can further include other additional configurations as long as it does not harm the technical idea of the present invention.

Advantages of the Invention

[0014] According to one embodiment of the present invention, since the solid electrolyte for all-solid-state batteries contains Li, K, and Bi, it can have excellent ionic conductivity while enabling low-temperature sintering.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0016] Hereinafter, with reference to the attached drawings, preferred embodiments of the present invention will be described in detail to such an extent that those having ordinary knowledge in the technical field to which the present invention pertains can easily implement them.

[0017] In order to clearly explain the present invention, descriptions of parts not related to the present invention are omitted, and the same reference numerals will be given to the same components throughout the specification. It should be understood that the specific shapes, structures, and characteristics described in the specification can be changed and embodied from one embodiment to another without departing from the spirit and scope of the present invention, and the positions or arrangements of individual components can also be changed without departing from the spirit and scope of the present invention.

[0018] Therefore, the detailed description to be described later is not made in a limiting sense, and the scope of the present invention should be understood to include the scope claimed by the claims of the claims and all ranges equivalent thereto.

[0019] FIG. 1 is a drawing schematically showing a cross section of an all-solid-state battery.

[0020] Referring to FIG. 1, the all-solid-state battery 10 includes a positive electrode 11, a negative electrode 12, and a solid electrolyte layer 13. The solid electrolyte layer 13 is disposed between the positive electrode 11 and the negative electrode 12 and can be in contact with the positive electrode 11 and the negative electrode 12 respectively. The positive electrode 11 and the negative electrode 12 can each include 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 can each be in contact with the solid electrolyte layer 13.

[0021] The positive electrode 11 and the negative electrode 12 can each be joined to the solid electrolyte layer 13 by sintering. That is, the positive electrode 11, the negative electrode 12, and the solid electrolyte layer 13 can be integrally sintered.

[0022] In FIG. 1, the all-solid-state battery 10 is illustrated in a form including one layer each of the positive electrode 11, the negative electrode 12, and the solid electrolyte layer 13, but the present invention is not limited thereto, and the all-solid-state battery may be configured in a form in which the positive electrode, the negative electrode, and the solid electrolyte layer each include a plurality of layers. Or it may be configured as a so-called laminated all-solid-state battery in a form in which a plurality of the positive electrode, the negative electrode, and the solid electrolyte layer are alternately laminated.

[0023] The solid electrolyte layer 13 according to an embodiment of the present invention includes an oxide-based electrolyte as the solid electrolyte.

[0024] As the oxide-based solid electrolyte, a NASICON (Nasicon) type such as LAGP and a garnet type solid electrolyte such as LLZO are known, and through continuous research and development, the ionic conductivity of such oxide-based solid electrolytes has reached 10 -4 S / cm level is known to have been improved.

[0025] However, there is a limit to further improving the ionic conductivity with the NASICON type and garnet type oxide-based solid electrolytes. Moreover, these oxide-based solid electrolytes are sintered at a high temperature of 1,000 °C or higher. As described above, although a certain degree of excellent ionic conductivity can be obtained, an increase in manufacturing cost associated with high-temperature sintering is inevitable.

[0026] In one embodiment of the present invention, through a new oxide-based solid electrolyte that overcomes the limitations of such conventional oxide-based solid electrolytes, excellent ionic conductivity is ensured while reducing the sintering temperature.

[0027] According to one embodiment of the present invention, the solid electrolyte for an all-solid-state battery can be composed of an oxide containing Li, K, and Bi. In one embodiment, the solid electrolyte for an all-solid-state battery can have a bismuth oxide crystal structure.

[0028] In the composition forming the solid electrolyte, Bi forms a crystal structure and is a low-temperature component that serves to lower the sintering temperature.

[0029] In the composition forming the solid electrolyte, Li and K can function as network modifiers and can increase the lattice constant of the bismuth oxide crystal structure. Along with this, since a wider movement path for Li ions can be ensured in the crystal structure, the ionic conductivity can be improved.

[0030] Thus, the solid electrolyte according to one embodiment of the present invention is composed of an oxide containing Li, K, and Bi, so that Bi functions as the main composition of the crystal structure, and Li and K can play a role in widening the flow path of Li ions and lowering the sintering temperature.

[0031] According to one embodiment of the present invention, the components forming the solid electrolyte can have a specific composition range.

[0032] The solid electrolyte according to one embodiment of the present invention can satisfy the following relational expression based on the molar ratio of each component.

[0033] 2 ≦ (Li + K) / Bi < 1

[0034] Preferably, the solid electrolyte according to one embodiment of the present invention can satisfy the following relational expression based on the molar ratio of each component.

[0035] (2) 0.2 ≦ (Li + K) / Bi ≦ 0.6

[0036] When the molar ratio of the alkali components (Li and K) of the solid electrolyte and the molar ratio of Bi satisfy the above relational expression, the ionic conductivity can be remarkably improved.

[0037] The solid electrolyte according to an embodiment of the present invention can further satisfy the following relational expression based on the molar ratio.

[0038] (3) 0.10 ≦ Li < 0.5

[0039] (4) 0.10 ≦ K ≦ 0.15

[0040] When the molar ratio of the alkali components (Li and K) of the solid electrolyte satisfies the above range, the ionic conductivity can be improved.

[0041] The sintering temperature of the solid electrolyte according to an 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 shows an ionic conductivity of about 2.4×10 -4 ~ about 5.8×10 -4 S / cm at room temperature.

[0042] Examples

[0043] (Example 1)

[0044] Li 2 O 10 mol%, K 2 O 12.5 mol% and Bi 2 O 3 77.5 mol% were mixed to prepare a precursor powder for the production of the solid electrolyte. After mixing the precursor powder, it was put into a melting furnace and melted at a temperature of about 1,000°C for about 30 minutes. Thereafter, the homogenized melt was poured onto a quenching roller and cooled to room temperature. After pulverizing this and sieving it, fine particles having a size of 10 μm or less were obtained. Finally, the fine particles thus obtained were sintered at about 500°C for about 6 hours to produce a solid electrolyte.

[0045] (Additional Examples and Comparative Examples)

[0046] Li 2 O and Bi 2 O 3 Precursor powders were prepared by varying the composition ratios of Li , O and Bi , O , and 3 , and melted at a temperature of 800°C to 1,200°C for about 30 minutes according to the composition ratios. Thereafter, fine particles were obtained through the same process as in Example 1, and sintered at about 500°C for about 6 hours respectively to produce solid electrolytes.

[0047] The solid electrolyte composition ratios according to the respective examples and comparative examples described above are as shown in Table 1.

[0048]

Table 1

[0049] Figure 2 shows a triangular chart illustrating the composition ranges of the solid electrolytes according to the examples and comparative examples of the present invention. 1 to 4 in Figure 2 correspond to Examples 1 to 4, and 5 to 9 correspond to Comparative Examples 1 to 5.

[0050] Referring to Figure 2, Examples 1 to 4, Comparative Example 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-ceramic structure. And Comparative Example 1 is located at the boundary between the bismuth oxide crystal structure and the lithium-bismuth oxide crystal structure.

[0051] Figure 3 shows an XRD graph of the solid electrolyte according to an example (Example 3) of the present invention, and Figures 4 and 5 show XRD graphs of the solid electrolytes according to the comparative examples (Comparative Examples 2 and 4) of the present invention.

[0052] Referring to FIG. 3, it can be confirmed that the solid electrolyte according to the embodiment of the present invention has a single-phase bismuth oxide crystal structure. On the contrary, 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).

[0053] 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 as described in Table 2.

[0054]

Table 2

[0055] 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 the half-ball temperature shows 660°C or lower. Thus, since the solid electrolyte according to the embodiment of the present invention has excellent low-temperature characteristics compared to conventional oxide-based solid electrolytes, low-temperature sintering is possible.

[0056] Also, the solid electrolytes according to Examples 1 to 4 of the present invention have a very excellent ionic conductivity of 2.4×10 -4 ~5.8×10 -4 S / cm. In comparison, the solid electrolytes according to the comparative examples show low-temperature characteristics similar to those of the examples, but the ionic conductivity is 0.97×10 -6 ~1.7×10 -5 S / cm, showing a significant difference from the examples of the present invention.

[0057] Thus, it can be confirmed that the solid electrolytes according to Examples 1 to 4 of the present invention have excellent ionic conductivity while being capable of low-temperature sintering.

[0058] As described above, the present invention has been explained by specific examples such as specific components. However, the above examples are merely provided to assist in a more general understanding of the present invention, and the present invention is not limited thereto. Those having ordinary knowledge in the technical field to which the present invention pertains can make various modifications and variations from such descriptions.

[0059] Therefore, the idea of the present invention should not be defined as being limited to the above-described examples, and it can be said that not only the claims described below but also all those equivalently or equivalently modified to the claims belong to the scope of the idea of the present invention.

Claims

1. A solid electrolyte for an all-solid-state battery, composed of an oxide containing Li, K, and Bi, wherein, based on the molar ratio of each component, 0.2 ≤ (Li + K) / Bi < 1 is satisfied, the solid electrolyte for an all-solid-state battery.

2. The solid electrolyte for an all-solid-state battery according to Claim 1, wherein, based on the molar ratio of each component, 0.2 ≤ (Li + K) / Bi ≤ 0.6 is satisfied.

3. The solid electrolyte for an all-solid-state battery according to Claim 1, wherein, based on the molar ratio, 0.1 ≤ Li < 0.5 is satisfied.

4. The solid electrolyte for an all-solid-state battery according to Claim 1, wherein, based on the molar ratio, 0.10 ≤ K ≤ 0.15 is satisfied.

5. The solid electrolyte for an all-solid-state battery according to Claim 1, which has a bismuth oxide crystal structure.

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