Method of preparing sulfide-based solid electrolyte for all-solid battery having argyrodite-type crystal structure

Abstract

Disclosed is a method of preparing a sulfide-based solid electrolyte for an all-solid battery having an argyrodite-type crystal structure through a solution process. The method including obtaining a precursor solution by dissolving lithium sulfide, phosphorus sulfide and a halogen compound in a solvent, obtaining a precursor powder by removing the solvent from the precursor solution. Solid electrolyte for an all-solid battery can be produced by such method.

Claims

1. A method of preparing a sulfide-based solid electrolyte for an all-solid battery, comprising: obtaining a precursor solution by admixing lithium sulfide, phosphorus sulfide and a halogen compound in a solvent; obtaining a precursor powder by removing at least a portion of the solvent from the precursor solution; and thermally treating the precursor powder, wherein the solvent is removed by subjecting the precursor solution in a vacuum atmosphere to first drying at a temperature ranging from about 25 C. to less than about 50 C. for about 1 hr to 3 hr, second drying at a temperature ranging from about 50 C. to less than about 100 C. for about 1 hr to 3 hr, third drying at a temperature ranging from about 100 C. to less than about 150 C. for about 1 hr to 3 hr, fourth drying at a temperature ranging from about 150 C. to less than about 200 C. for about 1 hr to 3 hr, and/or fifth drying at a temperature ranging from about 200 C. to less than about 250 C. for about 1 hr to 3 hr, two or more of the first drying to the fifth drying are performed under continuous or non-continuous heating.

2. The method of claim 1, wherein solid electrolyte crystals are grown during or after thermally treating the precursor powder.

3. The method of claim 2, wherein the grown solid electrolyte crystals comprise an argyrodite-type crystal structure.

4. The method of claim 1, wherein the lithium sulfide comprises lithium sulfide (Li.sub.2S), and the phosphorus sulfide comprises phosphorus pentasulfide (P.sub.2S.sub.5).

5. The method of claim 1, wherein the halogen compound is selected from the group consisting of lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI) and combinations thereof.

6. The method of claim 1, wherein the solvent is selected from the group consisting of ethanol, propanol, butanol, dimethyl carbonate, ethyl acetate, tetrahydrofuran, 1,2-dimethoxyethane, propylene glycol dimethyl ether, acetonitrile and combinations thereof.

7. The method of claim 1, wherein the solvent is removed by drying after obtaining the precursor solution.

8. The method of claim 1, wherein the solvent is removed by drying the precursor solution in a vacuum atmosphere at a temperature ranging from about 25 C. to about 250 C. for about 5 hr to about 15 hr.

9. The method of claim 1, wherein the precursor powder is thermally treated at a temperature of about 400 C. to 600 C. for about 1 hr to 5 hr.

10. The method of claim 9, wherein the precursor powder is thermally treated by elevating a temperature from room temperature to about 150 C. at a rate of about 2.5 C./min-10 C./min, from about 150 C. to about 250 C. at a rate of about 2.5 C./min-5 C./min, from about 250 C. to about 400 C. at a rate of about 1 C./min-2.5 C./min, and/or from about 400 C. to about 550 C. at a rate of about 1 C./min.

11. The method of claim 1, wherein the sulfide-based solid electrolyte comprises the argyrodite-type crystal structure, as represented by Chemical Formula 1:
[Chemical Formula 1] Li.sub.6PS.sub.5X, wherein X is Cl, Br or I.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an exemplary process of preparing an exemplary sulfide-based solid electrolyte for an exemplary all-solid battery having an argyrodite-type crystal structure according to an exemplary embodiment of the present invention;

(2) FIG. 2 shows the results of Raman spectroscopy of crystals of an exemplary precursor powder obtained in step S2 of Example according to an exemplary embodiment of the present invention;

(3) FIG. 3 shows the results of X-ray diffraction spectroscopy of an exemplary sulfide-based solid electrolyte prepared in Example according to an exemplary embodiment of the present invention; and

(4) FIG. 4 shows the results of measurement of discharge capacity through charge-discharge testing of an all-solid battery of Preparation Example according to the present invention.

DETAILED DESCRIPTION

(5) The above and other aspects, features and advantages of the present invention will be more clearly understood from the following exemplary embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed herein, but may be modified into different forms. These embodiments are provided to thoroughly explain the invention and to sufficiently transfer the spirit of the present invention to those skilled in the art.

(6) Throughout the drawings, the same reference numerals will refer to the same or like elements. For the sake of clarity of the present invention, the dimensions of structures are depicted as being larger than the actual sizes thereof. It will be understood that, although terms such as first, second, etc. may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a first element discussed below could be termed a second element without departing from the scope of the present invention. Similarly, the second element could also be termed a first element. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise.

(7) It will be further understood that the terms comprise, include, have, etc. when used in this specification specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Also, it will be understood that when an element such as a layer, film, area, or sheet is referred to as being on another element, it can be directly on the other element, or intervening elements may be present therebetween. In contrast, when an element such as a layer, film, area, or sheet is referred to as being under another element, it can be directly under the other element, or intervening elements may be present therebetween.

(8) Unless otherwise specified, all numbers, values, and/or representations that express the amounts of components, reaction conditions, polymer compositions, and mixtures used herein are taken to mean that these numbers are approximations including various uncertainties of the measurements that essentially occur in obtaining these values among others, and thus should be understood to be modified by the term about in all cases. Furthermore, when a numerical range is disclosed in this specification, such a range is continuous and includes all values from the minimum value of said range to the maximum value thereof, unless otherwise indicated. Moreover, when such a range refers to an integer, all integers including the minimum value to the maximum value are included unless otherwise indicated.

(9) In the present specification, when a range is described for a variable, it will be understood that the variable includes all values including the end points described within the stated range. For example, the range of 5 to 10 will be understood to include any subranges, such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, and the like, as well as individual values of 5, 6, 7, 8, 9 and 10, and will also be understood to include any value between the valid integers within the stated range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, 6.5 to 9, and the like. Also, for example, the range of 10% to 30% will be understood to include any subranges, such as 10% to 15%, 12% to 18%, 20% to 30%, etc., as well as all integers including values of 10%, 11%, 12%, 13% and the like and up to 30%, and will also be understood to include any value between the valid integers within the stated range, such as 10.5%, 15.5%, 25.5%, and the like.

(10) Further, unless specifically stated or obvious from context, as used herein, the term about is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. About can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from the context, all numerical values provided herein are modified by the term about.

(11) It is understood that the term vehicle or vehicular or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles.

(12) FIG. 1 shows an exemplary process of preparing an exemplary sulfide-based solid electrolyte for an exemplary all-solid battery having an argyrodite-type crystal structure according to an exemplary embodiment of the present invention. With reference thereto, the preparation method of the present invention may include obtaining a precursor solution by dissolving materials such as raw materials for a solid electrolyte in a solvent (S1), obtaining a precursor powder by removing the solvent from the precursor solution (S2) and growing solid electrolyte crystals by thermally treating the precursor powder (S3).

(13) Obtaining the precursor solution (S1) may include dissolving the raw materials for a solid electrolyte in a solvent.

(14) The raw materials may include lithium sulfide, phosphorus sulfide and a halogen compound.

(15) The lithium sulfide may include lithium sulfide (Li.sub.2S), and the phosphorus sulfide may include phosphorus pentasulfide (P.sub.2S.sub.5).

(16) The halogen compound may be selected from the group consisting of lithium bromide (LiBr), lithium chloride (LiCl), lithium iodide (LiI) and combinations thereof.

(17) The solvent may be a polar solvent, which is able to dissolve the lithium sulfide, phosphorus sulfide and halogen compound, and may be specifically selected from the group consisting of ethanol, propanol, butanol, dimethyl carbonate, ethyl acetate, tetrahydrofuran, 1,2-dimethoxyethane, propylene glycol dimethyl ether, acetonitrile and combinations thereof.

(18) The composition of the raw materials is not particularly limited, and may vary so as to be suitable for the composition of the desired sulfide-based solid electrolyte.

(19) The conditions for dissolving the raw materials in the solvent are not particularly limited, and for example, stirring may be performed at a temperature where degradation of the lithium sulfide, phosphorus compound and halogen compound or reaction therebetween does not occur for a period of time required to completely dissolve the raw materials in the solvent.

(20) The precursor powder may be obtained by removing the solvent from the precursor solution (S2).

(21) The precursor powder indicates a powder in which the raw materials are physically and chemically mixed, some of which are formed into crystals, which is described in detail in Example.

(22) Obtaining the precursor powder (S2) may include removing the solvent by drying the precursor solution immediately after obtaining the precursor solution. Here, the term immediately means without delay after confirmation of the dissolution of the raw materials in the solvent, and specifically indicates directly drying the solvent without additional reaction through continuous stirring of the precursor solution at a high temperature for a predetermined period of time. This is because the raw materials may sufficiently react under time and temperature conditions for drying the solvent.

(23) Obtaining the precursor powder (S2) may include removing the solvent by drying the precursor solution in a vacuum atmosphere at a temperature ranging from about 25 C. to about 250 C. for about 5 hr to 15 hr. If the drying conditions are less than about 25 C. and/or less than about 5 hr, the solvent may not be sufficiently removed, and the reaction of the raw materials may become insufficient. On the other hand, if the drying conditions is greater than about 250 C. and/or about 15 hr, the raw materials, especially phosphorus sulfide, may degrade.

(24) The drying of the precursor solution may be performed in a vacuum atmosphere through two or more continuous drying processes at different temperatures. Preferably, a first drying at a temperature ranging from about 25 C. to less than about 50 C. for about 1 hr to 3 hr, a second drying at a temperature ranging from about 50 C. to less than about 100 C. for 1 hr to 3 hr, a third drying at a temperature ranging from about 100 C. to less than about 150 C. for about 1 hr to 3 hr, a fourth drying at a temperature ranging from 150 C. to less than 200 C. for 1 hr to 3 hr, and/or a fifth drying at a temperature ranging from about 200 C. to less than about 250 C. for about 1 hr to 3 hr may be carried out.

(25) Here, the temperature for the first drying to the fifth drying may start from 25 C. and may be continuously or non-continuously elevated up to the range of about 200 C. to about 250 C. For example, non-continuous drying may be performed in such a manner that first drying at a temperature of about 25 C., the second drying at a temperature of about 50 C., the third drying at a temperature of about 100 C., the fourth drying at a temperature of about 150 C., and the fifth drying at a temperature of about 200 C. may be carried out, in which the temperature may be elevated as fast as possible from any one stage to the next stage. On the other hand, continuous drying may be performed in such a manner that the temperature may start from about 25 C. and is slowly elevated to about 50 C. for a preset period of time ranging from about 1 hr to 3 hr (first drying), and the temperature is slowly elevated from about 50 C. to about 100 C. for a preset period of time ranging from about 1 hr to 3 hr (second drying). The continuous or non-continuous heating conditions may be appropriately adjusted depending on the preset drying time.

(26) Thermally treating the precursor powder (S.sub.3) may include obtaining the sulfide-based solid electrolyte having an argyrodite-type crystal structure by growing crystals of the precursor powder formed during the drying of the precursor solution.

(27) The precursor powder may be thermally treated at a temperature of about 400 C. to 600 C. for about 1 hr to 5 hr. For example, thermal treatment may be conducted in a manner in which the temperature is elevated from room temperature to about 150 C. at a rate of about 2.5 C./min about-10 C./min, from about 150 C. to about 250 C. at a rate of 2.5 C./min to about 5 C./min, from about 250 C. to about 400 C. at a rate of about 1 C./min to about 2.5 C./min, and/or from about 400 C. to about 550 C. at a rate of about 1 C./min.

(28) If the conditions for thermal treatment are less than about 400 C. and/or less than about 1 hr, crystals may not be sufficiently grown. On the other hand, if the conditions for thermal treatment is greater than about 600 C. and/or about 5 hr, the solid electrolyte may degrade, thus reducing ion conductivity.

(29) The sulfide-based solid electrolyte having an argyrodite-type crystal structure prepared by the present invention may be represented by Chemical Formula 1:
Li.sub.6PS.sub.5X[Chemical Formula 1]

(30) In Chemical Formula 1, X is Cl, Br or L

EXAMPLE

(31) A better understanding of the present invention will be given through the following examples, which are merely set forth to illustrate, but are not to be construed as limiting the present invention.

ExamplePreparation of Sulfide-Based Solid Electrolyte

(32) (S1) 4.28 g of a lithium sulfide powder (made by Sigma Aldrich), 4.14 g of a phosphorus pentasulfide powder (made by Sigma Aldrich) and 1.57 g of a lithium chloride powder (made by Sigma Aldrich) were weighed and mixed. The resulting mixture was dissolved in 100 g of an acetonitrile solvent to give a precursor solution. The raw materials were stirred at room temperature until all the raw materials were dissolved.

(33) (S2) The precursor solution was dried in a vacuum at about 200 C. for about 12 hr, thus completely removing the acetonitrile solvent. Thereby, a precursor powder was obtained.

(34) (S3) The precursor powder was thermally treated at a temperature of about 550 C. for about 5 hr, thus obtaining a sulfide-based solid electrolyte.

Preparation ExampleManufacture of all-Solid Battery

(35) An all-solid battery, configured to include the above sulfide-based solid electrolyte and to include a cathode, an anode, and a solid electrolyte layer disposed between the cathode and the anode, was manufactured.

(36) (Solid electrolyte layer) A solid electrolyte layer having a thickness of 500 m was formed by subjecting the sulfide-based solid electrolyte of Example to compression molding.

(37) (Cathode) A cathode having a thickness of 30 m was formed on one side of the solid electrolyte layer using a powder comprising an active material (niobium-doped lithium nickel cobalt manganese-based active material, Nb-doped NCM-622), the sulfide-based solid electrolyte of Example and a conductive additive (Super C), which were mixed together. The amount of loaded active material for the cathode was 5.8 mg/cm.sup.2.

(38) (Anode) An anode was formed by attaching a piece of lithium foil having a thickness of 100 m to the remaining side of the solid electrolyte layer.

Test Example 1Raman Spectroscopy of Precursor Powder

(39) The crystals of the precursor powder obtained in step S2 of Example were analyzed through Raman spectroscopy. The results are shown in FIG. 2. The formation of PS.sub.4.sup.3 crystals on the precursor powder was confirmed. This means that a crystalline solid electrolyte can be obtained by the preparation method of the present invention.

Test Example 2X-Ray Diffraction Spectroscopy of Sulfide-Based Solid Electrolyte

(40) The sulfide-based solid electrolyte prepared in Example was subjected to X-ray diffraction spectroscopy. The results are shown in FIG. 3. The argyrodite crystal peaks were observed at 2=15.720, 18.16, 25.76, 30.28 and 31.64, from which the sulfide-based solid electrolyte was determined to have an argyrodite-type crystal structure.

Test Example 3Measurement of Lithium Ion Conductivity of Sulfide-Based Solid Electrolyte

(41) The sulfide-based solid electrolyte prepared in Example was subjected to compression molding to thus produce a molded measurement body (diameter of 13 mm, thickness of 0.6 mm). AC potential of 10 mV was applied to the molded body, and impedance was measured at a frequency sweep of 110.sup.6 to 100 Hz, and thus the lithium ion conductivity of the sulfide-based solid electrolyte was found to be very high, specifically 2.010.sup.3 S/cm. Therefore, according to the preparation method of the present invention, a sulfide-based solid electrolyte having high ion conductivity can be obtained.

Test Example 4Measurement of Discharge Capacity of all-Solid Battery

(42) The all-solid battery of Preparation Example was subjected to charge-discharge testing at a rate of 0.02 C under conditions of CC (constant current) of 2.0 V-3.58 V to thus measure the discharge capacity thereof. The results are shown in FIG. 4. The discharge capacity of the all-solid battery was about 160 mAh/g.

(43) Although preferred exemplary embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art will appreciate that the present invention may be embodied in other specific forms without changing the technical spirit or essential features. Thus, embodiments described above should be understood to be illustrative in every way and non-limiting.