Patent Application
20240204246
The present invention relates to a sulfide-based solid electrolyte composition, which has good stability against water and has ion conductivity sufficient to be applied to an all-solid-state battery, and a preparation method thereof.
Oxide solid electrolytes represented by NASICON and β/β″-alumina have properties of easily diffusing Na+ ions, and thus, are applied to commercial energy storage systems in high-temperature environments (245° C. to 300° C.).
The room-temperature ionic conductivity (σion) of such an oxide solid electrolyte may reach a level close to the ionic conductivity of a liquid electrolyte. However, such high room-temperature ionic conductivity may be obtained when a densified pellet is sintered at a high temperature (1200° C. to 1600° C.) that reduces grain boundary resistance, which makes it difficult for the oxide solid electrolyte to be applied to commercial secondary batteries for everyday use.
In contrast, a sulfide-based solid-phase electrolyte does not require a high-temperature sintering process, and a low modulus of elasticity of a soft sulfide enables the manufacturing of a battery by an industrially applicable method (e.g., cold pressing). However, a sulfide-based solid-phase electrolyte previously developed has room for improvement in terms of various properties.
The purpose of the invention is to provide a solid electrolyte composition excellent in stability against water and ion conductivity, and a method for preparing the composition.
According to an aspect of the invention, there is provided a solid electrolyte composition including a material represented by [Formula 1] below.
NaaZnbGacSd Formula 1
According to another aspect of the invention, there is provided a method for preparing a solid electrolyte composition including a material represented by [Formula 1] below, wherein the method includes
NaaZnbGacSd [Formula 1]
A solid electrolyte composition according to the invention has good ion conductivity to be applied to an all-solid-state battery.
In addition, the solid electrolyte composition according to the invention is not substantially decomposed or forms a hydrate in a humid atmosphere or in water, thereby facilitating water-phase synthesis or water-phase processing.
In addition, the solid electrolyte composition according to the invention does not undergo continuous decomposition at the interface in a Na alloying/dealloying reaction and has good cycle properties.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present application pertains may easily practice the embodiments. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
In addition, in order to clearly describe the present invention, parts irrelevant to the description are omitted in the drawings, and like reference numerals designate like elements throughout the specification.
Throughout the present specification, when a part is referred to as “including” another component, it means the part may further include other components, rather than excluding other components, unless specifically stated otherwise.
The terms “about,” “substantially,” and the like used herein are used in a sense that is close to a numerical value presented with a manufacturing and material tolerance specific to a stated meaning, and is used to prevent an unscrupulous person from abusing a disclosure in which an exact or absolute value is stated in order to facilitate the understanding of the invention.
In addition, the term “a step ˜ing,” or “a step of ˜,” as used throughout the specification, does not mean “a step for ˜.”
Throughout the present specification, the description of “A and/or B” means “A or B, or A and B.”
A solid electrolyte composition according to the present invention is characterized by including a material represented by [Formula 1] below.
NaaZnbGacSd Formula 1
When the contents of Na, Zn, and Ga described in [Formula 1] above are out of the above range, it is difficult to obtain ion conductivity sufficient to be applied to a solid electrolyte of an all-solid-state battery, so that it is preferable to maintain the above range.
The Na content (a) is more preferably 2.725 to 2.875, even more preferably 2.75 to 2.85, and most preferably 2.775 to 2.825.
The Zn content (b) is more preferably 0.725 to 0.875, even more preferably 0.75 to 0.85, and most preferably 0.775 to 0.825.
The Ga content (c) is more preferably 1.125 to 1.275, even more preferably 1.15 to 1.25, and most preferably 1.175 to 1.225.
In the solid electrolyte composition, the space group of the material represented by [Formula 1] above may be I41/acd.
In the solid electrolyte composition, the ion conductivity σion at room temperature (25° C.) of the material represented by [Formula 1] above may be 0.1 mScm−1 or greater. In addition, the ion conductivity σion at room temperature (25° C.) of the solid electrolyte composition may be 0.15 mScm−1 or greater, 0.2 mScm−1 or greater, 0.25 mScm−1 or greater, or most preferably 0.3 mScm−1 or greater.
In the solid electrolyte composition, the material represented by [Formula 1] above may be substantially inert to moisture or water.
In the solid electrolyte composition, the crystal structure of the material represented by [Formula 1] above may be a tetragonal phase.
A method for preparing a solid electrolyte composition according to the invention is to prepare the aforementioned solid electrolyte composition, and
NaaZnbGacSd Formula 1
In the method for preparing a solid electrolyte composition, any of various known methods for mixing powder may be used as the mixing method.
In the method for preparing the solid electrolyte composition, it is preferable that the step (b) is performed at 700° C. to 800° C. for 12 hours to 48 hours.
When the heating temperature is lower than 700° C., the raw materials may remain in the raw material state even after a synthesis process since the synthesis is not achieved due to a low heating temperature, and when higher than 800° C., there is a possibility in that the solid electrolyte is synthesized in a different phase rather than a tetragonal phase, so that it is preferable to maintain the range of 700° C. to 800° C.
When the heating time is less than 12 hours, smooth synthesis of a reactant is degraded due to insufficient heating time, and when greater than 48 hours, a chemical reaction may occur between the reactant and a quartz tube, thereby producing a synthesized product different from the solid electrolyte, so that it is preferable to maintain the heating time in the range of 12 hours to 48 hours.
In the method for preparing the solid electrolyte composition, a process of pelletizing the solid electrolyte composition prepared through the step (c) by pressing the solid electrolyte composition at −20° C. to 200° C., and 300 MPa to 400 MPa, for 1 minute to 10 minutes may be further included.
Raw materials used for synthesis in all embodiments had a purity of 99% or greater and were used as purchased without any further purification.
Each raw material was prepared in the following composition ratio in about 1 g of a reactant.
First, a stainless steel ball (10 mm) and about 1 g of the reactant were placed together in a stainless steel pot for a ball mill grinder (PULVERISETTE 23, FRISTCH) to be ground for 5 minutes at a frequency of 40 Hz, and then the ground powder was put into a quartz tube.
The entire process was performed in a glove box filled with argon. Each quartz tube was closed with a quartz stopper, taken out of the glove box, and immediately connected to a vacuum sealer (NBD-DXZ-02, Nobody Sci. Tech. Co.). Thereafter, the sealed tube was placed in a box furnace, heated (5° C./min) to a temperature of 750° C., and maintained for 12 hours, and then the quartz tube was taken out and slowly cooled (−5° C./h) to 400° C. and then naturally cooled to room temperature to synthesize a solid electrolyte composition.
Through the above, a material having the composition of Na2.8Zn0.8Ga1.2S4 was obtained.
Each raw material was prepared in the following composition ratio in about 1 g of a reactant.
A material having the composition of Na2.85Zn0.85Ga1.15S4 was obtained through the same process as in Example 1 by using the above raw materials.
Each raw material was prepared in the following composition ratio in about 1 g of a reactant.
A material having the composition of Na2.9Zn0.9Ga1.1S4 was obtained through the same process as in Example 1 by using the above raw materials.
Each raw material was prepared in the following composition ratio in about 1 g of a reactant.
A material having the composition of Na2.7Zn0.7Ga1.3S4 was obtained through the same process as in Example 1 by using the above raw materials.
Each raw material was prepared in the following composition ratio in about 1 g of a reactant.
A material having the composition of Na3ZnGaS4 was obtained through the same process as in Example 1 by using the above raw materials.
Each raw material was prepared in the following composition ratio in about 1 g of a reactant.
A material having the composition of Na2.95Zn0.95Ga1.05S4 was obtained through the same process as in Example 1 by using the above raw materials.
Each raw material was prepared in the following composition ratio in about 1 g of a reactant.
A material having the composition of Na2.6Zn0.6Ga1.4S4 was obtained through the same process as in Example 1 by using the above raw materials.
Each raw material was prepared in the following composition ratio in about 1 g of a reactant.
A material having the composition of Na2.5Zn0.5Ga1.5S4 was obtained through the same process as in Example 1 by using the above raw materials.
XRD analysis was performed on the solid electrolyte compositions synthesized by Examples 1 to 4 and Comparative Examples 1 to 4. The XRD peaks in
From the results of comparing the crystal structures through X-ray diffraction, it has been confirmed that crystals with a space group I41/acd were synthesized in a tetragonal phase up to x values of 0 (Comparative Example 1), 0.5 (Comparative Example 2), 1.0 (Example 3), 1.5 (Example 2), 2.0 (Example 1), and 3.0 (Example 4) in Na3−xZn1−xGa1+xS4. Among these, Example 4 had a relatively weak peak intensity, thereby exhibiting a relatively low level of crystallinity, which appears to be due to the inclusion of some amorphous phases.
Meanwhile, when the x value was 0.40 (Comparative Example 3) and 0.50 (Comparative Example 4), an impurity peak corresponding to the NaGaS2 phase began to appear, and the decrease in peak intensity was greater compared to Example 4. From the above, it can be seen that a pure phase of Na3−xZn1−xGa1+xS4 can only be obtained when the x value is from 0 to 0.30, and when the x value is 0.30, some amorphous phases may be contained. When the x value was 0.40 and 0.50, it was confirmed that synthesis was achieved in a form containing an impurity phase and an amorphous phase.
In order to analyze the electrochemical properties of the Na3−xZn1−xGa1+XS4 composition synthesized according to Examples 1 to 4 and Comparative Examples 1 to 4, a cell was manufactured as follows.
First, 200 mg of the composition was ground in a hand grinding manner, and then disposed between stainless steel disks. The powder was pelletized under a pressure of 300 MPa in a polyoxymethylene (POM) mold. The thickness of the prepared pellet was about 500 μm and the area thereof was about 1.33 cm2.
In addition, by using a polyether ether ketone (PEEK) mold and a hot press (200° C., 10 min, YLJ-HP60-LD, MTI Corp.), hot-pressed pellets were also prepared.
The EIS spectrum was recorded by applying a sine wave of ±10.0 mV within the frequency range of 2 MHz to 0.1 Hz (SP2, One A-Tech). An automatic WBCS 3000 battery cycler (One A-Tech) was used for voltage and constant current studies.
As confirmed in
However, the resistance began to increase when the x value was greater than 0.30, and gradually increased to 1.12 kΩ when the x value was 0.30 (Example 4), 1.75 kΩ when the x value was 0.40 (Comparative Example 3), and 4.06 kΩ when the x value was 0.50 (Comparative Example 4). The increase in resistance that occurs when the x value is greater than 0.30, despite the increase in vacancy, appears to be due to the generation of an amorphous phase and/or the generation of an impurity phase.
Nevertheless, it can be seen from the results of Example 1 to Example 4 that the introduction of vacancies through proper adjustment of the Zn/Ga ratio greatly contributes to the improvement of ion conductivity (Sion) If not controlled in such a manner, the ion conductivity (Sion) becomes too low to be used as a solid electrolyte.
In addition, in the synthesized composition, temperature dependence of the ion conductivity (Sion) between −20° C. to +60° C. was investigated.
As confirmed in
In Na3ZnGaS4, which is Comparative Example 1, the steepest slope gradually became gentler with the introduction of vacancies until the x value was 0.20, but the slope slightly increased again from the x value of 0.30. That is, the solid electrolyte compositions according to Examples 1 to 4 exhibit relatively good temperature dependence properties compared to that of Comparative Example 1.
As confirmed in
The Na2.8Zn0.8Ga1.2S4 composition, which is Example 1, has the highest ion conductivity of 0.08 mScm−1, and the lowest activation energy (EA) value of 0.32 eV, so that it can be seen that the composition is the most preferable example of a solid electrolyte composition.
Meanwhile, in the case of the hot-pressed Na2.8Zn0.8Ga1.2S4 pellet (marked with an asterisk in
The stability of Na2.8Zn0.8Ga1.2S4, which is the composition according to Example 1, against moisture or water was evaluated. For comparison with the composition of Example 1, typical sulfide-based solid electrolyte compositions, Na3PS4 and Na3SbS4, were evaluated together.
Referring to
In contrast, Na2.8Zn0.8Ga1.2S4 and Na3SbS4, each of which is Example 1, exhibited an inert state except for some initial reactions, so that it can be seen that the stability thereof against N2 is good.
As confirmed in
In addition, no degradation in ion conductivity (Sion) was observed in the EIS spectrum measured after drying the immersed powder at 80° C.
In contrast, as confirmed in the internal image of
From the above, it can be seen that the Na2.8Zn0.8Ga1.2S4 composition according to Example 1 has properties of being substantially inert to water, and the properties means that it is possible to synthesize and/or process the composition according to Example 1 in an aqueous medium without having to perform dehydration treatment.
The possibility of using the Na2.8Zn0.8Ga1.2S4 composition according to Example 1 as a solid electrolyte was evaluated.
To this end, a symmetric Na2Sn|Na2.8Zn0.8Ga1.2S4|Na2Sn cell was manufactured.
The symmetric cell is manufactured by placing 30 mg of an Na2Sn alloy, which is prepared by performing mechanic synthesis using a ball mill grinder (PULVERISETTE 23, FRISTCH), into a polyoxymethylene (POM) mold of a cell, and then flattening the same. Thereafter, 200 mg of the solid electrolyte is added thereto and flattened again, and then 30 mg of Na2Sn is further added thereon to manufacture the cell.
In addition, a Na2Sn|Na2.8Zn0.8Ga1.2S4|TiS2 cell was manufactured, wherein a positive electrode was manufactured by dissolving 50% of Na2.8Zn0.8Ga1.2S4, 45% of TiS2, and 5% of CF in N-methyl-2-pyrrolidone, followed by vacuum drying the mixture at 150° C. Thereafter, 5 mg of the positive electrode material was placed into the polyoxymethylene (POM) mold of the cell, and 150 mg of the solid electrolyte was added thereto and then flattened, and then 30 mg of Na2Sn, which is a negative electrode material, was added and pressed under a pressure of 300 MPa.
The composition according to Example 1 showed good compatibility with the Na2Sn alloy (about 0.3 V vs. Na/Na+) As confirmed in
The voltage profile showed a slightly inclined behavior, which is commonly observed in all-solid-state cells of TiS2. The cell had an initial sodiation capacity of only 67 mAh/g, but the capacity was rapidly increased to 157 mAh/g during a subsequent desodiation process. Such a behavior appears to be due to a chemical reaction between Na2.8Zn0.8Ga1.2S4 and TiS2 during a physical contact such that each of the solid electrolyte and TiS2 is partially oxidized and reduced. Once oxidized, a decomposition product of Na2.8Zn0.8Ga1.2S4 appears to stabilize the interface without continuous decomposition. In fact, the capacity slowly decreased from 157 mAh/g to 136 mAh/g over the next 50 cycles (capacity retention rate was 87%), and the Coulomb efficiency was higher than 99.5%.
From the above results, it can be seen that the Na2.8Zn0.8Ga1.2S4 composition may be used as a solid electrolyte of an all-solid-state battery.
The foregoing description of the invention has been presented for purposes of illustration, and it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. Therefore, it should be understood that the embodiments described above are illustrative in all aspects and are not limiting. For example, each component described in a singular form may be distributed and implemented, and similarly, components described as being distributed may also be implemented in a combined form.
The scope of the invention is represented by the following claims rather than the above detailed description, and all changes and changed forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0174580 | Dec 2022 | KR | national |
