TW202414882A - Solid electrolyte for solid-state battery - Google Patents

Abstract

The present invention relates to a solid electrolyte for a fully solid battery. According to an embodiment of the present invention, the solid electrolyte for a fully solid battery is formed of an oxide containing Li, K and Bi.

Description

Solid electrolyte for all-solid-state batteries

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

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

As a secondary battery, lithium-ion batteries using liquid electrolytes are the most widely used. However, when external impact is applied to the battery, there is a risk of liquid electrolyte leakage, so additional parts and devices are required to ensure safety.

Recently, in order to improve the safety of secondary batteries, the development of all-solid batteries using solid electrolytes as electrolytes has been actively carried out. As solid electrolytes for all-solid batteries, there are polymer electrolytes, oxide electrolytes, sulfide electrolytes, etc. Among them, sulfide solid electrolytes have the highest ionic conductivity, but there is a problem of generating hydrogen sulfide gas when reacting with water. Polymer electrolytes have the advantages of relatively simple processes and the ability to use existing lithium-ion battery processes, but have the disadvantage of significantly low ionic conductivity.

Compared with sulfide-based electrolytes, oxide-based electrolytes have the advantage of superior safety. In addition, oxide-based electrolytes generally require a high sintering temperature of 1,000°C or more, which may increase manufacturing costs.

[The problem the invention is trying to solve]

The present invention is used to solve the above-mentioned known technical problems, and its subject is to provide a solid electrolyte that can be sintered at a low temperature and has excellent ionic conductivity. [Technical means for solving the problem]

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

The solid electrolyte for a fully solid battery according to an embodiment of the present invention can satisfy 0.2≤(Li+K)/Bi＜1 based on the molar ratio of each component. In addition, the solid electrolyte for a fully solid battery according to an embodiment of the present invention can satisfy 0.2≤(Li+K)/Bi≤0.6 based on the molar ratio of each component.

The solid electrolyte for a fully solid battery according to an embodiment of the present invention can satisfy 0.1≤Li＜0.5 based on the molar ratio. In addition, the solid electrolyte for a fully solid battery according to an embodiment of the present invention can satisfy 0.10≤K≤0.15 based on the molar ratio.

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

According to one embodiment of the present invention, the softening point of the solid electrolyte for the all-solid-state battery can be 540°C to 600°C.

According to an embodiment of the present invention, the Half-ball temperature of the solid electrolyte for the all-solid-state battery can be 550°C to 660°C.

In addition, the solid electrolyte for the all-solid-state battery according to the present invention can further have other additional structures within the scope of not damaging the technical concept of the present invention. [Effect of the invention]

According to one embodiment of the present invention, the solid electrolyte for the all-solid-state battery includes Li, K and Bi, which enables low-temperature sintering and has excellent ionic conductivity.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings to the extent that a person having ordinary knowledge in the technical field to which the present invention belongs can easily implement.

In order to clearly explain the present invention, the description of the parts not related to the present invention is omitted, and the same reference symbols are marked on the same components throughout the specification. It should be understood that the specific shapes, structures and characteristics described in the specification can be changed from one embodiment to other embodiments without departing from the concept and scope of the present invention, and the position or configuration of individual components can also be changed without departing from the concept and scope of the present invention.

Therefore, the detailed description given below is not to be interpreted in a limiting sense, but it should be understood that the scope of the present invention includes the scope claimed in the claims of the patent application and all scopes equivalent thereto.

FIG. 1 is a diagram schematically showing a cross section of a 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 can be in contact with the anode (11) and the cathode (12) respectively. The anode (11) and the cathode (12) can have an anode active material layer and a cathode active material layer respectively, and the anode active material layer and the cathode active material layer can be in contact with the solid electrolyte layer (13) respectively.

The anode (11) and the cathode (12) can be bonded to the solid electrolyte layer (13) by sintering. That is, the anode (11), the cathode (12) and the solid electrolyte layer (13) can be sintered into one body.

In FIG1 , a fully solid-state battery (10) is illustrated as including a single layer of an anode (11), a cathode (12), and a solid electrolyte layer (13), but the present invention is not limited thereto, and the fully solid-state battery may be constructed in a form in which the anode, cathode, and solid electrolyte layer are each formed of a plurality of layers. Alternatively, a so-called stacked fully solid-state battery may be constructed in which a plurality of anodes, cathodes, and solid electrolyte layers are alternately stacked.

According to one embodiment of the present invention, the solid electrolyte layer (13) includes an oxide-based electrolyte as a solid electrolyte.

As oxide-based solid electrolytes, sodium superionic conductor (Nasicon) type such as LAGP and garnet type such as LLZO are known, and it is known that the ionic conductivity of such oxide-based solid electrolytes has been improved to 10 ^-4 S/cm level through continuous research and development.

However, there is a limit to further improving the ionic conductivity of the above-mentioned sodium superionic conductor type and garnet type oxide-based solid electrolytes. Moreover, even if these oxide-based solid electrolytes can obtain a certain degree of excellent ionic conductivity as described above by sintering at a high temperature of more than 1,000°C, the increase in manufacturing costs caused by high temperature sintering cannot be avoided.

In one embodiment of the present invention, a new oxide-based solid electrolyte that overcomes the limitations of the known oxide-based solid electrolyte is used to reduce the sintering temperature and ensure very excellent ionic conductivity.

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

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

In the formation of the solid electrolyte composition, Li and K can act as network modifiers, which can increase the lattice constant of the bismuth oxide crystal structure. Therefore, in the aforementioned crystal structure, the migration path of Li ions can be wider, thereby improving the ionic conductivity.

Thus, by forming the solid electrolyte according to an embodiment of the present invention from an oxide containing Li, K and Bi, Bi functions as a main component of the crystal structure, and Li and K can play a role in expanding the migration path of Li ions to reduce the sintering temperature.

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

The solid electrolyte according to one embodiment of the present invention can satisfy the following relationship 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 can satisfy the following relationship 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 relationship, the ionic conductivity can be significantly improved.

The solid electrolyte according to one embodiment of the present invention can further satisfy the following relationship based on the molar ratio. (3) 0.10≤Li＜0.5 (4) 0.10≤K≤0.15

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.

The solid electrolyte according to one embodiment of the present invention is sintered at a temperature of about 500° C. to about 600° C. When sintered at the above temperature, the solid electrolyte according to one embodiment of the present invention exhibits an ionic conductivity of about 2.4×10 ^-4 to about 5.8×10 ^-4 S/cm at room temperature.

Embodiment

(Example 1)

10 mol% Li ₂ O, 12.5 mol% K ₂ O and 77.5 mol% Bi ₂ O ₃ were mixed to prepare the precursor powder for manufacturing the solid electrolyte. After the precursor powder was mixed, it was put into a furnace and melted at a temperature of about 1,100°C for about 30 minutes. After that, the homogenized melt was poured into a quenching roller and cooled to room temperature. After it was crushed, it was sieved to obtain particles with a size of less than 10μm. Finally, the particles obtained in this way were sintered at about 500°C for about 6 hours to produce a solid electrolyte.

(Additional Examples and Comparative Examples)

Precursor powders were prepared by setting different composition ratios of _Li2O and _Bi2O3 , and melted at 800°C to 1,200°C _for about 30 minutes according to the composition ratios. Then, microparticles were obtained by the same process as in Example 1, and sintered at about 500°C for about 6 hours to produce solid electrolytes.

The compositions of the solid electrolytes of the above-described embodiments and comparative examples are shown in Table 1.

[Table 1] Differentiation Composition of solid electrolyte (mol%) R ₂ O/Bi ₂ O _{3 Li2O K2O Bi2O3 ​} Embodiment 1 10 12.5 77.5 0.29 Embodiment 2 15 12.5 72.5 0.38 Embodiment 3 18 12.5 69.5 0.44 Embodiment 4 25 12.5 62.5 0.6 Comparison Example 1 37.5 12.5 50 1 Comparison Example 2 50 12.5 37.5 1.67 Comparison Example 3 62.5 12.5 25 3 Comparison Example 4 75 12.5 12.5 7 Comparison Example 5 85 12.5 2.5 39

Fig. 2 is a three-axis diagram showing the composition range of the solid electrolyte according to the embodiments and comparative examples of the present invention. ① to ④ in Fig. 2 correspond to embodiments 1 to 4, and ⑤ to ⑨ correspond to comparative examples 1 to 5.

2 , Examples 1 to 4, Comparative Example 2, and Comparative Examples 3 to 5 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. Moreover, Comparative Example 1 is located at the boundary between the bismuth oxide crystal structure and the lithium-bismuth oxide crystal structure.

FIG3 shows an XRD spectrum of a solid electrolyte according to an embodiment of the present invention (Embodiment 3), and FIG4 and FIG5 show XRD spectrums of solid electrolytes according to comparative examples (Comparative Examples 2 and 4) of the present invention.

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 other hand, it can be confirmed that the solid electrolyte according to the comparative example has a lithium oxide-bismuth oxide crystal structure (see FIG4) or a glass-ceramic structure (see FIG5).

The measurement results of the crystal structure, softening point, half-ball temperature and ionic conductivity of the solid electrolyte according to each embodiment and comparative example are shown in Table 2.

[Table 2] Differentiation Crystal structure Softening point (℃) Half-ball temperature (℃) Ionic conductivity (S/cm) Embodiment 1 Bi ₂ O ₃ crystal structure 600 653 2.4× ^10-4 Embodiment 2 Bi ₂ O ₃ crystal structure 570 600 4.0× ^10-4 Embodiment 3 Bi ₂ O ₃ crystal structure 540 580 5.1×10 ^-4 Embodiment 4 Bi ₂ O ₃ crystal structure 540 554 5.8×10 ^-4 Comparison Example 1 Bi ₂ O ₃ crystal structure 540 563 3.7×10 ^-6 Comparison Example 2 Li ₂ OB ₂ O ₃ crystal structure 545 570 5.8×10 ^-5 Comparison Example 3 Glass-ceramic structure 550 608 1.2× ^10-6 Comparison Example 4 Glass-ceramic structure 581 603 1.7×10 ^-5 Comparison Example 5 Glass-ceramic structure 550 610 0.97×10 ^-6

2, the solid electrolytes of Examples 1 to 4 of the present invention have a softening point below 600°C, and the half-ball temperature shows below 660°C. Thus, compared with the conventional oxide-based solid electrolytes, the solid electrolytes of the embodiments of the present invention have excellent low-temperature characteristics, enabling low-temperature sintering.

Furthermore, the solid electrolytes according to Examples 1 to 4 of the present invention have very excellent ionic conductivity of 2.4×10 ^-4 to 5.8×10 ^-4 S/cm. In contrast, the solid electrolytes according to the comparative examples show similar low temperature characteristics to the examples, but the ionic conductivity is 0.97×10 ^-6 to 1.7×10 ^-5 S/cm, which is significantly different from the examples of the present invention.

Thus, it can be confirmed that the solid electrolytes according to Examples 1 to 4 of the present invention can be sintered at a low temperature and have excellent ionic conductivity.

The present invention has been described above using specific matters such as specific constituent elements and limited embodiments, but the aforementioned embodiments are only provided to help a more comprehensive understanding of the present invention, and the present invention is not limited thereto. Anyone with ordinary skills in the technical field to which the present invention belongs will understand that various modifications and variations can be made from such descriptions.

Therefore, the concept of the present invention should not be limited to the embodiments described above, and not only the scope of the patent application described later, but also those that are equivalent or equivalent to the scope of the patent application are within the scope of the concept of the present invention.

10: All-solid-state battery 11: Anode 12: Cathode 13: Solid electrolyte layer

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

FIG. 2 is a triaxial diagram showing the composition range of the solid electrolyte according to the embodiment and the comparative example of the present invention.

FIG3 shows an XRD spectrum of a solid electrolyte according to an embodiment of the present invention.

FIG. 4 and FIG. 5 show XRD spectra of the solid electrolyte according to the comparative example of the present invention.

10: All solid-state battery

11: Yang pole

12: cathode

13: Solid electrolyte layer

Claims (8)

A solid electrolyte for an all-solid-state battery is formed of oxides containing Li, K and Bi. A solid electrolyte for a fully solid-state battery as described in claim 1, wherein, based on the molar ratio of each component, 0.2≤(Li+K)/Bi＜1 is satisfied. A solid electrolyte for a fully solid-state battery as described in claim 2, wherein, based on the molar ratio of each component, 0.2≤(Li+K)/Bi≤0.6 is satisfied. A solid electrolyte for a fully solid-state battery as described in claim 2, wherein, based on the molar ratio, 0.1≤Li＜0.5 is satisfied. A solid electrolyte for a fully solid-state battery as described in claim 2, wherein, based on a molar ratio, 0.10≤K≤0.15 is satisfied. The solid electrolyte for an all-solid-state battery as described in claim 1, wherein the solid electrolyte for an all-solid-state battery has a bismuth oxide crystal structure. The solid electrolyte for an all-solid-state battery as described in claim 1, wherein the softening point of the solid electrolyte for an all-solid-state battery is 540°C to 600°C. The solid electrolyte for an all-solid-state battery as described in claim 1, wherein the Half-ball temperature of the solid electrolyte for an all-solid-state battery is 550°C to 660°C.

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