Patent Application
20250140912
This application claims under 35 U.S.C. § 119(a) the benefit of priority to Korean Patent Application No. 10-2023-0144602 filed on Oct. 26, 2023, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a sulfide-based solid electrolyte having an argyrodite-type crystal structure. More particularly, it relates to a sulfide-based solid electrolyte having an argyrodite-type crystal structure which is doped with an element having an oxidation number of 4 and a transition metal having an oxidation number of 6 so as to improve moisture stability and ionic conductivity of the sulfide-based solid electrolyte.
Lithium ion batteries are widely used in various apparatuses requiring energy storage. They require various battery characteristics, such as a high energy density, long cycle life, rapid charging and discharging, and high-temperature and low-temperature driving performance, depending on the field of application.
Recently, use of fossil fuels is avoided to solve environmental problems caused by carbon dioxide (CO2), and there is a great interest in electric vehicles using secondary batteries in the automobile industry. When a currently developed lithium ion battery is used, an electric vehicle may travel about 400 km on a single charge, but problems, such as instability at a high temperature and fires, still exist. In order to solve these problems, many companies are developing next-generation secondary batteries competitively.
All-solid-state batteries, which are attracting attention as a next-generation secondary battery, include all elements formed of solid, and have advantages, such a low risk of fire and explosion and high mechanical strength, as compared to lithium ion batteries using flammable organic solvents as electrolyte solutions.
As a solid electrolyte for all-solid-state batteries, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or the like may be used, and preferably, a sulfide-based solid electrolyte having high lithium ion conductivity may be used.
However, the sulfide-based solid electrolyte has high moisture reactivity when exposed to the atmosphere and thus generates toxic hydrogen sulfide (H2S) gas, and therefore, has poor stability in the air. Further, the sulfide-based solid electrolyte has an unstable interface due to contact between a cathode material or an anode material and the sulfide-based solid electrolyte and thus has low-efficiency life characteristics, and may not avoid interfacial resistance between the electrode and the solid electrolyte.
In an effort to solve these problems, various research on not only improvement in ionic conductivity of sulfide-based solid electrolytes but also improvement in moisture reactivity and interfacial stability of all-solid-state batteries is underway.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
The present disclosure has been made in an effort to solve the above-described problems associated with the prior art, and it is an object of the present disclosure to minimize generation of toxic hydrogen sulfide (H2S) gas through suppression of hydrolysis between a sulfide-based solid electrolyte and moisture (H2O).
It is another object of the present disclosure to improve interfacial stability between a sulfide-based solid electrolyte and an electrode through improvement in ionic conductivity of the sulfide-based solid electrolyte.
In one aspect, the present disclosure provides a sulfide-based solid electrolyte expressed as Chemical Formula below.
Li5+2x+yAxSbyB1-x-yS5-zSezX Chemical Formula 1:
Here, A is an element having an oxidation number of 4, B is a transition metal having an oxidation number of 6, X is at least one selected from Cl, Br, I, and combinations thereof, 0<x<1, 0<y<1, 0<x+y<1, and 0<x<5.
In a preferred embodiment, the element having the oxidation number of 4 may include one selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and combinations thereof.
In another preferred embodiment, the transition metal having the oxidation number of 6 may include one selected from the group consisting of tungsten (W), molybdenum (Mo), and a combination thereof.
In still another preferred embodiment, the sulfide-based solid electrolyte may have an argyrodite-type crystal structure.
In yet another preferred embodiment, the element having the oxidation number of 4 and the transition metal having the oxidation number of 6 may be located at 4b sites of the argyrodite-type crystal structure.
In still yet another preferred embodiment, 1-x-y configured to indicate an amount of the transition metal having the oxidation number of 6 may be greater than 0 but less than 0.5.
In a further preferred embodiment, z may be greater than 0 but less than 3.5.
In another further preferred embodiment, the sulfide-based solid electrolyte may belong to a space group F-43m.
In still another further preferred embodiment, selenium (Se) may be substituted for at least some of sulfur (S).
Other aspects and preferred embodiments of the disclosure are discussed infra.
The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof illustrated in the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present disclosure, and wherein:
It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes, will be determined in part by the particular intended application and use environment.
In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing.
The above-described objects, other objects, advantages and features of the present disclosure will become apparent from the descriptions of embodiments given hereinbelow with reference to the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed herein and may be implemented in various different forms. The embodiments are provided to make the description of the present disclosure thorough and to fully convey the scope of the present disclosure to those skilled in the art.
In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the drawings, the dimensions of structures may be exaggerated compared to the actual dimensions thereof, for clarity of description. In the following description of the embodiments, terms, such as “first” and “second”, may be used to describe various elements but do not limit the elements. These terms are used only to distinguish one element from other elements. For example, a first element may be named a second element, and similarly, a second element may be named a first element, without departing from the scope and spirit of the disclosure. Singular expressions may encompass plural expressions, unless they have clearly different contextual meanings.
In the following description of the embodiments, terms, such as “including,”,“comprising,” and “having,” are to be interpreted as indicating the presence of characteristics, numbers, steps, operations, elements or parts stated in the description or combinations thereof, and do not exclude the presence of one or more other characteristics, numbers, steps, operations, elements, parts or combinations thereof, or possibility of adding the same. In addition, it will be understood that, when a part, such as a layer, a film, a region or a plate, is said to be “on” another part, the part may be located “directly on” the other part or other parts may be interposed between the two parts. In the same manner, it will be understood that, when a part, such as a layer, a film, a region or a plate, is said to be “under” another part, the part may be located “directly under” the other part or other parts may be interposed between the two parts.
All numbers, values and/or expressions representing amounts of components, reaction conditions, polymer compositions and blends used in the description are approximations in which various uncertainties in measurement generated when these values are obtained from essentially different things are reflected and thus it will be understood that they are modified by the term “about”, unless stated otherwise. In addition, it will be understood that, if a numerical range is disclosed in the description, such a range includes all continuous values from a minimum value to a maximum value of the range, unless stated otherwise. Further, if such a range refers to integers, the range includes all integers from a minimum integer to a maximum integer, unless stated otherwise.
In the following description of the embodiments, it will be understood that, when the range of a variable is stated, the variable includes all values within the stated range including stated end points of the range. For example, it will be understood that a range of “5 to 10” includes not only values of 5, 6, 7, 8, 9 and 10 but also arbitrary subranges, such as a subrange of 6 to 10, a subrange of 7 to 10, a subrange of 6 to 9, and a subrange of 7 to 9, and arbitrary values between integers which are valid within the scope of the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. Further, for example, it will be understood that a range of “10% to 30%” includes not only all integers including values of 10%, 11%, 12%, 13%, . . . 30% but also arbitrary subranges, such as a subrange of 10% to 15%, a subrange of 12% to 18%, and a subrange of 20% to 30%, and arbitrary values between integers which are valid within the scope of the stated range, such as 10.5%, 15.5%, and 25.5%.
A great deal of research on sulfide-based solid electrolytes is underway around the world due to high lithium ion conductivity and electrochemical stability thereof. The sulfide-based solid electrolytes are classified into a crystalline type and a non-crystalline type depending on presence or absence of a crystal structure. There are a thio-LiSiCON-type crystal structure, an LGPS-type crystal structure, and an argyrodite-type crystal structure as representative examples of the crystalline type, and the non-crystalline type may have a glass structure or a glass-ceramic structure depending on a heat treatment temperature.
The argyrodite-type crystal structure is one of a solid electrolyte which has the same crystal structure as argyrodite having composition Ag8GeS6 and exhibits lithium ion conductivity. As representative examples of an electrolyte having a Li-argyrodite structure having lithium ion (Li+) conductivity used in all-solid-state batteries, Li7PS6 and Li6PS5X (X being Cl, Br, or I) are known.
Li5+2x+yAxSbyB1-x-yS5-zSezX Chemical Formula 1:
In chemical formula 1, A is an element having an oxidation number of 4, B is a transition metal having an oxidation number of 6, and X is at least one selected from Cl, Br, I, and combinations thereof, 0<x<1, 0<y<1, 0<x+y<1, and 0<x<5.
The sulfide-based solid electrolyte according to the present disclosure may have an argyrodite-type crystal structure. Referring to
The conventional sulfide-based solid electrolyte Li6PS5X (X being Cl, Br, or I) having the argyrodite-type crystal structure includes tetrahedrons PS43- in the crystal structure, and phosphorus (P) may be located at the centers of the tetrahedrons. Referring to this, in the present disclosure, the sites of phosphorus (P) of the conventional sulfide-based solid electrolyte Li6PS5X having the argyrodite-type crystal structure may be substitutionally doped with the elements A and B and antimony (Sb).
Here, the sulfide-based solid electrolyte according to the present disclosure may be configured such that the elements A and B and antimony (Sb) may be substituted for all phosphorus (P) of the conventional sulfide-based solid electrolyte having the composition Li6PS5X. Therefore, the sulfide-based solid electrolyte according to the present disclosure may not include phosphorus (P).
Further, referring to
According to the present disclosure, as the transition metal B having the oxidation number of 6 and a large ionic radius is substituted for the sites of phosphorus (P), a crystal lattice volume may be increased. As the crystal lattice volume is increased, activation energy with respect to migration of lithium ions in the crystal lattice may be reduced, and thereby, lithium ion conductivity may be increased.
Further, the transition metal B substituted for the sites of phosphorus (P) may induce occurrence of vacancies in the crystal lattice. Occurrence of vacancies may facilitate formation of a cubic phase, and the cubic phase has sufficient migration paths of lithium ions (Li+) and may thus facilitate 3D fast conduction. Thereby, improvement in lithium ion conductivity of the sulfide-based solid electrolyte may be promoted.
Here, 1-x-y indicating the amount of the transition metal B in the sulfide-based solid electrolyte may be greater than 0 but less than 1. Preferably, 1-x-y may be greater than 0 but less than 0.5. When 1-x-y indicating the amount of the transition metal B in the sulfide-based solid electrolyte is less than 0.5, lithium ion conductivity of the sulfide-based solid electrolyte may be further improved.
Further, the transition metal B reacts with sulfur (S) and thus forms BS2 during a process of generating H2S gas through reaction between moisture (H2O) present in the air and the sulfide-based solid electrolyte, thereby being capable of suppressing generation of toxic hydrogen sulfide gas.
In one embodiment, the element A having the oxidation number of 4 may include a group 4 element on the periodic table. Preferably, the element A may include at least one selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and combinations thereof. Further, the transition metal B having the oxidation number of 6 may include at least one selected from the group consisting of tungsten (W), molybdenum (Mo), and a combination thereof.
z indicating the amount of selenium (Se) in the sulfide-based solid electrolyte may be greater than 0 but less than 5. Preferably, z may be greater than 0 but less than 3.5. When z indicating the amount of selenium (Se) in the sulfide-based solid electrolyte is less than 3.5, generation of H2S gas caused by hydrolysis may be further suppressed. Here, selenium (Se) may be substituted for at least some of sulfur (S).
Further, the sulfide-based solid electrolyte according to the present disclosure may belong to, for example, a cubic crystal system, and more concretely, may belong to the space group F-43m.
Hereinafter, the present disclosure will be described in more detail through the following Examples and Comparative Examples. The following Examples and Comparative Examples serve merely to exemplarily describe the present disclosure, and are not intended to limit the scope and spirit of the disclosure.
Migration paths of lithium ions (Li+) in sulfide-based solid electrolytes having the argyrodite-type crystal structure were predicted using molecular dynamics simulation.
Concretely, molecular dynamics simulation of a sulfide-based solid electrolyte having composition Li6.5Si0.5Sb0.5S5I, which does not include a transition metal having an oxidation number of 6 and selenium (Se), was executed, and simulation results are shown in
Further, molecular dynamics simulation of a sulfide-based solid electrolyte having composition Li6.25Si0.5Sb0.25W0.25S5I, which does not include selenium (Se), was executed, and simulation results are shown in
Moreover, molecular dynamics simulation of a sulfide-based solid electrolyte having composition Li6.5Si0.75W0.25S4.75Se0.25I, which includes a transition metal having an oxidation number of 6 and selenium (Se) but does not include antimony (Sb), was executed, and simulation results are shown in
Referring to
Lithium ion conductivities of sulfide-based solid electrolytes having various compositions, activation energies (Ea) required for migration of lithium ions, and energies above hull (Ehull) of the sulfide-based solid electrolytes were calculated using a molecular dynamics calculation method through machine learning, and are set forth in Table 1 below.
The energy above hull (Ehull) is an index to evaluate synthesis possibility of a material, it is determined that synthesis possibility of the material is higher as the energy above hull (Ehull) is closer to 0, and it is generally evaluated that it is possible to synthesize the material when the energy above hull (Ehull) is 100 or less.
80% ionic conductivity (80% IC) was calculated by Equation below.
σexp.=σcalc.Xc7.14 Equation:
Here, Xc indicates a degree of crystallinity, and 0.8 is substituted thereinto in the case of a 80% crystal structure. σcalc. indicates a calculated lithium ion conductivity, i.e., a bulk ionic conductivity (BIC).
In general, it may be determined that, when 80% ionic conductivity of a solid electrolyte is 1 mS/cm or more, there is a possibility of commercialization of the solid electrolyte. Referring to Table 1, the bulk ionic conductivities of sulfide-based solid electrolytes having phosphorus (P) were calculated to be low.
In order to evaluate moisture stabilities of sulfide-based solid electrolytes according to the present disclosure, hydrogen sulfide gas generation energies of the sulfide-based solid electrolytes were calculated using Density Functional Theory (DFT). A calculation process is as follows.
Cproducts(SE,H2O,x)=x·C(SE)+(1−x)C(H2O) Reaction Formula 1:
Ereaction(SE,H2O,x)=Eeq(Cproducts(SE,H2O,x))−E(Cproducts(SE,H2O,x)) Reaction Formula 2:
Here, eq indicates a phase equilibria state among the products acquired from the reaction formula (1).
The hydrogen sulfide gas generation energies Eg of the solid electrolytes SE and the reaction formulas used to calculate the hydrogen sulfide gas generation energies Eg are set forth in Table 2 below.
As the gas generation energy decreases, generation of hydrogen sulfide gas is easier in hydrolysis of the sulfide-based solid electrolyte. That is, as the gas generation energy increases, generation of hydrogen sulfide gas may be suppressed and moisture stability may be increased.
Referring to Table 2, the gas generation energies of the sulfide-based solid electrolytes doped with an element having an oxidation number of 4 or a transition metal having an oxidation number of 6 were calculated to be higher. It is predicted that tungsten (W) and molybdenum (Mo) reacted with sulfur (S) to form WS2 and MoS2, and thereby, generation of H2S gas was suppressed.
Interfacial reaction energies between a cathode active material and a coating composition thereof generally included in a cathode and sulfide-based solid electrolytes having various compositions were calculated through computer simulation. A detailed calculation method is as follows.
xC
a+(1−x)Cb→Cequil Equation eq1:
(Ca and Cb=compositions of two phases in contact, Cequil=low phase equilibrium energy, and 0<x<1)
ΔE[Ca,Cb]=min{Epd[xCa+(1−x)Cb]−xE[Ca]−(1−x)E[Cb]} Equation eq2:
(Epd: a combination of reaction products having the lowest energy in xCa+(1−x)Cb)
Related energy calculated using DFT may be acquired from the database of the materials project, and a function to find the minimum value is in the materials project.
Equation eq3 was derived using Equation eq2 in order to describe a phenomenon in a battery cell.
ϕpd[C,μLi]=min{Epd[c+μLi]−nLi[c]μLi} Equation eq3:
ϕpd[c, μLi] indicates the composition c having the lowest energy in μLi, in the same manner as Epd. Here, lithium potential determined from a calculated average cathode voltage is used.
In Equation eq4, electric potential on the interface is changed by causing the electrolyte to be in equilibrium with the external lithium potential and to react with the cathode, and interfacial stability is determined by a μLi function. The magnitude of Δϕ determines thermodynamic stability.
Δϕpd[ccathode,celectrode,μLi]=min{ϕpd[Xc
Finally, interfacial reaction energy between the electrolyte and the cathode may be confirmed using Δϕ.
The interfacial reaction energies of the sulfide-based solid electrolytes having various compositions were calculated through the above process, and are set forth in Table 3 below.
Referring to Table 3, it may be confirmed that the interfacial reaction energies of the sulfide-based solid electrolytes according to the present disclosure are higher than the conventional argyrodite-type sulfide-based solid electrolyte (Li6PS5Cl). Thereby, it is predicted that, it is difficult to cause decomposition reaction in the sulfide-based solid electrolytes according to the present disclosure, and thus, stability on the interfaces of the sulfide-based solid electrolytes according to the present disclosure may be increased.
As is apparent from the above description, the present disclosure provides a sulfide-based solid electrolyte having an argyrodite-type crystal structure which includes an element having an oxidation number of 4 and a transition metal having an oxidation number of 6 so as to improve both ionic conductivity and moisture stability of the sulfide-based solid electrolyte in a balanced way.
The disclosure has been described in detail with reference to preferred embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2023-0144602 | Oct 2023 | KR | national |
