KR20190030252A - Method for producing solid electrolyte and solide electrolyte produced by the method - Google Patents

Abstract

The present invention relates to a method for manufacturing a solid electrolyte and a solid electrolyte manufactured therefrom. A manufacturing process is simple since no separate raw material synthesis process is performed, and the relative sintering density of the solid electrolyte is increased by adding zirconia powder, thereby increasing the strength and ion conductivity. The method comprises the steps of: mixing alpha-alumina (α-Al_2O_3), sodium carbonate (Na_2CO_3), and magnesium hydroxide (Mg(OH)_2) with a solvent and performing ball milling; and mixing the ball-milled mixture with granular zirconia powder to manufactured slurry.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing a solid electrolyte and a solid electrolyte produced therefrom,

The present invention relates to a process for producing a solid electrolyte and a solid electrolyte produced therefrom.

Sodium-sulfur (NAS) secondary batteries have been recognized for their stability and reliability and are being applied to large-capacity power storage systems. Since the sodium-sulfur secondary battery is a high-temperature battery operating at 250-350 ° C, it is not affected by the surrounding environment. In addition, sodium-sulfur secondary cells are free from irregular charge-discharge damage and are suitable for application to wind power or solar power generation systems. Sodium-sulfur secondary batteries generally employ a solid electrolyte formed of beta-alumina (beta "-Al ₂ O ₃ ). The beta-alumina solid electrolyte has a low output power of the battery and a loss of power It is necessary to have a low specific resistivity and a high mechanical strength.

However, the beta alumina solid electrolyte has a problem that the densification is hindered and the performance is deteriorated due to dry precipitation and segregation phenomenon of Na ₂ O that occurs during the spray drying process. Particularly, the insoluble beta-alumina solid electrolyte has a high resistivity value, resulting in poor ionic conductivity and a relatively low mechanical strength.

Beta alumina powder for the production of beta-alumina solid electrolyte has been prepared by solid-phase reaction method in which powders of oxides such as Al ₂ O ₃ and Na ₂ O are mixed with a phase stabilizer of Li ₂ O series, . Beta alumina powder by the conventional method is formed into a typical plate-like powder. That is, the beta alumina powder has a hexagonal plate-like shape, and Na ^{2 +} ions that transfer ions in the powder have anisotropy due to the orientation according to the previous drawing which is a plane perpendicular to the C axis. Therefore, when a plate-like beta alumina powder is press-molded into a tubular shape to form a tubular-shaped alumina solid electrolyte, the powder is vertically oriented in the pressing direction, making ion conduction between the anode materials difficult, There arises a problem that the resistance of the beta-alumina solid electrolyte becomes extremely high as compared with the axial direction. In addition, the plate-like beta-alumina powder has a problem that the resistivity is made high and the mechanical strength is remarkably deteriorated.

Korean Patent No. 10-1404045

It is an object of the present invention to provide a method of manufacturing a solid electrolyte in which the manufacturing process is simplified since there is no sodium beta alumina powder synthesis step. It is another object of the present invention to provide a solid electrolyte improved in physical properties such as sintering density, sodium ion conductivity and sodium corrosion by adding zirconia.

In order to solve the above problems,

Alpha-alumina _{(α-Al 2 O 3)} , sodium carbonate (Na ₂ CO ₃₎ and the step of ball milling is mixed with magnesium hydroxide (Mg (OH) ₂₎ a solvent; And

And mixing the ball milled mixture and the granular zirconia powder to prepare a slurry.

Further, according to the present invention,

Alpha-alumina _{(α-Al 2 O 3)} , sodium carbonate (Na ₂ CO _3), and provides a solid electrolyte containing a magnesium hydroxide (Mg (OH) _2), and zirconia.

The method of the present invention improves the sintering density and ion conductivity of the solid electrolyte by adding zirconia powder and improves the stability of the sodium secondary battery by increasing the strength of the solid electrolyte.

In addition, the method for producing the solid electrolyte of the present invention is advantageous in terms of process economics by a simple method by removing the sodium beta alumina powder synthesis process.

FIG. 1 is an image of a method for producing a solid electrolyte according to the present invention.
2 is a graph showing the XRD analysis results of the solid electrolyte according to the present invention.
3 is a graph showing the " fraction " and the relative sintered density of the solid electrolyte according to the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.

In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Therefore, the configurations shown in the embodiments described herein are merely the most preferred embodiments of the present invention and are not intended to represent all of the technical ideas of the present invention. Therefore, various equivalents And variations.

The present invention relates to a method for producing a solid electrolyte.

In general, sodium beta-alumina is widely used as a solid electrolyte in sodium secondary batteries such as sodium-sulfur batteries. Sodium beta-alumina coexists with a-alumina and beta " -alumina. Theoretically, beta / -Al < " > -alumina crystal phase fraction is theoretically higher than that of a- Of the ionic conductivity.

On the other hand, the conventional sodium beta alumina solid electrolyte has a disadvantage in that it involves a process of synthesizing relatively bulky MgO-Al ₂ O ₃ so that it can be dispersed well before the ball milling process.

However, in the method of manufacturing a solid electrolyte according to the present invention, the synthesis process is simplified by adding the powdery α-Al ₂ O ₃ , Na ₂ CO ₃ and Mg (OH) ₂ raw materials in the ball milling process, Can be reduced.

In addition, zirconia powder is added as an additive to increase the relative sintering density of the solid electrolyte to improve the strength as well as to improve the corrosion resistance to the sodium solution.

The present invention, alpha-alumina _{(α-Al 2 O 3)} , sodium carbonate (Na ₂ CO ₃₎ and the step of ball milling is mixed with magnesium hydroxide (Mg (OH) ₂₎ a solvent; And

And mixing the ball milled mixture and the granular zirconia powder to prepare a slurry.

Wherein the ball milling is alpha-alumina _{(α-Al 2 O 3)} , sodium carbonate (Na ₂ CO ₃₎ and the initial raw material of magnesium hydroxide (Mg (OH) ₂₎ may be added in powder form, of the respective raw materials Mixing and grinding. Generally, the initial raw materials are synthesized and synthesized in the form of a bulky granule. In the method of manufacturing the solid electrolyte according to the present invention, the process is simplified by omitting the synthesis process.

Further, in the ball milling step, the solvent may be methanol or acetone. By using methanol or acetone as a solvent as described above, it is easier to mix and grind and establish a more accurate composition than to perform ball milling using water as a solvent.

In one example, the ball milling step may be performed for 1 to 15 hours. Specifically, the ball milling step may be performed for 3 to 12 hours or 5 to 10 hours.

In the method for producing a solid electrolyte of the present invention, it is possible to perform a step of drying in a drying oven after ball milling. The drying step may be performed for 15 to 55 hours. Specifically, the drying step may be carried out for 20 to 50 hours or 24 to 48 hours.

In the method for producing a solid electrolyte of the present invention, a ball milled mixture and granular zirconia powder may be mixed to prepare a slurry. The zirconia powder serves to increase the sintered density of the solid electrolyte to form a dense microstructure, thereby improving the strength. detailed

In one example, the amount of zirconia powder in the step of preparing the slurry may be 0.1 to 15 wt%. Specifically, the content of the zirconia powder may be 0.5 to 13% by weight or 1 to 10% by weight. If the content of the zirconia powder is more than 15% by weight, it is possible to reduce the ion conductivity of the solid electrolyte by decreasing the? "- phase fraction.

In one example, the particle size of zirconia on the particles may range from 40 to 90 mu m on average. Specifically, the particle diameter of the zirconia on the particles may be in the range of 45 to 85 mu m or 40 to 80 mu m on average.

In one example, a binder or dispersant may be added in the step of preparing the slurry. Specifically, the binder may include polyvinyl alcohol (PVA), and the dispersant may include ammonium polymethacrylate. The content of the binder and the dispersant may be independently from 0.1 to 1% by weight.

The method for producing a solid electrolyte of the present invention may include a step of putting the slurry prepared through the step of manufacturing slurry into a spray dryer to prepare granules. Specifically, the temperature of the inlet of the spray dryer may be in the range of 150 to 200 ° C, and the temperature of the outlet of the spray dryer may be in the range of 100 to 150 ° C.

The method for producing a solid electrolyte of the present invention may include a step of forming the slurry into a tubular shape through cold isostatic pressing (CIP) after the step of producing the slurry. Specifically, in the step of molding into a tube shape, the prepared granules may be filled in a molding mold and a pressure of 100 to 450 MPa may be applied in a vacuum state.

The method for producing a solid electrolyte of the present invention may include a step of sintering after the step of forming into a tube shape. The sintering step serves to induce phase transition so that the initial raw material is sodium beta alumina.

In one example, the sintering may be performed at a temperature in the range of 1500 < 0 > C to 1800 < 0 > C. Specifically, the sintering may be performed at a temperature ranging from 1550 캜 to 1750 캜 or from 1600 캜 to 1700 캜. In addition, the sintering step may be performed for 5 minutes to 60 minutes. Specifically, the sintering step may be performed for 15 to 45 minutes.

The tube-shaped solid electrolyte produced through the sintering step has an average height of 130 to 200 mm, an outer diameter of 15 to 35 mm, and an average diameter of 1 to 8 mm. Specifically, the height of the solid electrolyte ranges from 150 to 180 mm on average, the outer diameter ranges from 20 to 30 mm on average, and the difference between the inner diameter and outer diameter can range from 2 to 6 mm on average.

In addition, the relative sintering density of the tube-shaped solid electrolyte produced through the sintering step may be 93% or more. Specifically, the relative sintering density of the solid electrolyte may be 94% or more, 95% or more, 96% or more. The upper limit value of the relative sintering density is not particularly limited, but may be, for example, 100% or less and 99% or less.

In addition, the? -? - phase fraction of the tube-shaped solid electrolyte produced through the sintering step may be 60% or more. Specifically, the? -? Phase fraction of the solid electrolyte may be 61% or more or 62% or more. The upper limit value of the? "- phase fraction is not particularly limited, but may be, for example, 100% or less and 99% or less.

The present invention is also directed to solid electrolytes.

A solid electrolyte according to the invention may comprise alpha-alumina _{(α-Al 2 O 3)} , sodium carbonate (Na ₂ CO _3), magnesium hydroxide (Mg (OH) _2), and zirconia.

In one example, the solid electrolyte according to the present invention may be in the form of a tube. Specifically, the height of the tubular solid electrolyte ranges from 130 to 200 mm on average and the outer diameter can range from 15 to 35 mm on average. More specifically, the height of the tubular solid electrolyte ranges from 150 to 180 mm on average and the outer diameter can range from 20 to 30 mm on average. In addition, the difference between the inner diameter and the outer diameter of the tubular solid electrolyte may be in the range of 1 to 8 mm on average, and specifically in the range of 2 to 6 mm on average.

In one example, the relative sintered density of the solid electrolyte according to the present invention may be at least 93%. Specifically, the relative sintering density of the solid electrolyte may be 94% or more, 95% or more, 96% or more. The upper limit value of the relative sintering density is not particularly limited, but may be, for example, 100% or less and 99% or less.

The? -? - phase fraction of the solid electrolyte according to the present invention may be at least 60%. Specifically, the? -? - phase fraction of the solid electrolyte may be at least 61% or at least 62%. The upper limit value of the? "- phase fraction is not particularly limited, but may be, for example, 100% or less and 99% or less.

Best Mode for Carrying Out the Invention Hereinafter, the present invention will be described in more detail with reference to examples and drawings based on the above description. The following examples are intended to illustrate the invention and are not intended to limit the scope of the invention.

Example  One

103.66 g of α-Al ₂ O _{3 as} raw material powder, 21.55 g of sodium carbonate (Na ₂ CO ₃ ) and 5.38 g of magnesium hydroxide (Mg (OH) ₂ ) were mixed with methanol in a solvent and subjected to a ball milling process Respectively. Ball milled and dried in a drying oven for 24 hours. 1% by weight of PVA (polyvinyl alcohol), 1% by weight of ammonium polymethacrylate and 1% by weight of zirconia powder were added to the dried raw material powder to prepare a slurry. The prepared slurry was introduced into a spray dryer having an inlet temperature of 200 ° C and an outlet temperature of 120 ° C to prepare raw material powder granules.

The prepared granules were uniformly packed in a polyurethane molding mold, packed, vacuum packed, and a pressure of 200 MPa was applied to prepare a tube shaped molded article. The formed tube was sintered at 1650 ° C for 30 minutes using a magnesia crucible to prepare a sodium beta alumina solid electrolyte.

Example  2

A sodium beta alumina solid electrolyte was prepared in the same manner as in Example 1, except that zirconia powder was added in an amount of 3 wt%.

Example  3

A sodium beta alumina solid electrolyte was prepared in the same manner as in Example 1 except that zirconia powder was added in an amount of 5% by weight.

Example  4

A sodium beta alumina solid electrolyte was prepared in the same manner as in Example 1 except that zirconia powder was added in an amount of 10% by weight.

Comparative Example  One

A sodium beta alumina solid electrolyte was prepared in the same manner as in Example 1, except that zirconia powder was not added.

Experimental Example  One

X-ray diffraction (XRD) was measured on the sodium beta alumina solid electrolyte prepared in Examples 1 to 4 to examine the phase relationship of the sodium beta alumina solid electrolyte according to the present invention. The results are shown in Fig.

As shown in FIG. 2, zirconia peaks were confirmed at 30 ° and it was confirmed that as the content of zirconia increased, the intensity of peaks also increased. In addition, NaAlO ₂ and a-alumina peaks were not confirmed.

Experimental Example  2

The phase fraction, relative sintered density and resistivity of the sodium beta alumina solid electrolyte prepared in Examples 1 to 4 and Comparative Example 1 were measured in order to analyze phase analysis of the sodium beta alumina solid electrolyte according to the present invention , And the measured results are shown in Table 1 and FIG.

Sintering temperature.
( ^o C) Sintering time
(min.) Relative sintering density
(%, theor.) β "- phase fraction
(%) Resistivity
(Ω · cm) Comparative Example 1 1650 30 92 60 - Example 1 1650 30 96.3 63 13.5 Example 2 1650 30 96.6 61 10.4 Example 3 1650 30 97.8 60 14.7 Example 4 1650 30 99.3 60 14.8

At this time, the peaks obtained by XRD (Rigaku Rint 2000, Cu Kα-radiation, Japan) measurement were JCPDS Card 10-173 for α-alumina phase, 31-1263 for β-alumina phase, β " The data of 31-1262 were analyzed with reference.

In the present invention, the phase is divided into three phases: a-alumina, beta -alumina and beta "-alumina. In the present invention, The relative fraction is calculated by Equation (1) below. ≪ EMI ID = 1.0 >

[Equation 1]

The detailed peak calculation at each phase is shown in Equation 2 below.

&Quot; (2) "

I _{α (104) (113)} : X-ray intensity of the (104) and (113) faces of α-Al ₂ O ₃

_{I β (012) (026)} (017): β-Al 2 O 3 in (012), X-ray intensity of the (017), (026)

I? _{1011 ) (2010)} : X-ray intensity of β-Al ₂ O ₃ (10 11 ) and (20 10 )

(012), (017), (026) crystal planes (JCPDS file 31-1263) of? -Alumina, (104) and Peaks of (10 11 ) and (20 10 ) crystal faces of βalumina (JCPDS file 31-1262) were used.

The sintered density was measured by the Archimedes method (ASTM 373-88), and the impedance was measured using IM6 equipment of Zahner-Electric Co., and the specific resistance value was obtained. The impedance was measured using a silver electrode at a frequency of 1 Hz to 3 MHz at 350 ° C.

As can be seen from Table 1, as the zirconia content of the solid electrolytes of Examples 1 to 4 was increased, the relative sintered density was increased and the " - " phase fraction was almost maintained as compared with the solid electrolyte of Comparative Example 1, Is attributed to the toughening effect and contributes to the increase of the sintered density, but it can be said to be effective in maintaining the? "- phase fraction by not producing a side reaction such as sodium zirconate. However, the addition of a large amount of zirconia resulted in an increase in the grain boundary resistance for sodium ion conduction and an increase in the resistivity of the solid electrolyte due to the distribution of zirconia in the beta alumina crystal grain boundaries. Therefore, it was confirmed that the addition of the proper amount of 3 wt% zirconia powder exhibited the lowest specific resistance value due to the increase of the sintering density remarkably while maintaining the phase fraction.

Claims (11)

Alpha-alumina _{(α-Al 2 O 3)} , sodium carbonate (Na ₂ CO ₃₎ and the step of ball milling is mixed with magnesium hydroxide (Mg (OH) ₂₎ a solvent; And
And mixing the ball milled mixture and the granular zirconia powder to prepare a slurry.
The method according to claim 1,
In the ball milling step, the solvent comprises at least one of methanol and acetone.
The method according to claim 1,
Wherein a particle diameter of the zirconia on the particles is in the range of 40 to 90 mu m on average.
The method according to claim 1,
A method for producing a solid electrolyte, comprising the steps of: after slurry preparation, shaping into a tubular form through cold isostatic pressing (CIP).
5. The method of claim 4,
And sintering after the step of forming into a tube shape.
6. The method of claim 5,
Wherein the step of sintering is performed at a temperature in the range of 1500 ° C to 1800 ° C.
Alpha-alumina _{(α-Al 2 O 3)} , sodium carbonate (Na ₂ CO _3), magnesium hydroxide (Mg (OH) ₂₎ and the solid electrolyte comprises zirconia.
8. The method of claim 7,
Wherein the solid electrolyte is in the form of a tube.
9. The method of claim 8,
Wherein the tubular solid electrolyte has an average height ranging from 130 to 200 mm and an outer diameter ranging from 15 to 35 mm on average.
9. The method of claim 8,
Wherein a difference between an inner diameter and an outer diameter of the tubular solid electrolyte is in the range of 1 to 8 mm on average.
9. The method of claim 8,
Wherein the tubular solid electrolyte has a relative sintering density of 93% or more.

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