Patent Description:
Currently, the lithium secondary battery market has been extended not only to small-sized IT devices, but also to medium/large-sized markets such as electric vehicles and ESS systems. Such a lithium secondary battery is required to have high instantaneous output, excellent reversibility during charging and discharging, high energy density, and excellent reproducibility and stability. Flexibility in shape and processing also plays an important role in order to cope with the trend to be more compact and thinner. In particular, as the lithium secondary battery market becomes gradually medium/large-sized, there is a growing need to manufacture a secondary battery by packaging or modularizing plural cells rather than to manufacture a secondary battery with one cell.

However, using an explosive liquid electrolyte to package and enlarge it is the same as creating a gunpowder where you never know when it will explode. In <NUM> addition, lithium secondary batteries using liquid electrolytes have the risk of explosion when the temperature rises, and thus requires expensive safety devices such as a vent cap or a positive temperature coefficient (PTC) device. The use of these safety devices is a cause of lowering the energy density of the lithium secondary battery and increasing the manufacturing cost of the battery. Therefore, the use of expensive safety devices has a disadvantage in terms of the energy density and the manufacturing cost of the secondary batteries, in both small-capacity batteries used in portable electronic devices and large-capacity batteries such as power sources for electric vehicles. In particular, for the commercialization of large-capacity batteries such as electric vehicles batteries, it is required to develop a solid-state batteries that can secure the stability of secondary batteries without using expensive safety devices as they have excellent stability.

Lithium ion conductive ceramics, which may be called a starting point of developing a solid electrolyte, may be largely divided into sulfide-based and oxide-based ceramics. The sulfide-based solid electrolyte is relatively easy to synthesize and has ductility compared to the oxide-based solid electrolyte and thus, does not require high heat treatment during processing. The sulfide-based solid electrolyte also exhibits high conductivity. For example, thio-LISICON(Li<NUM>Ge<NUM>P<NUM>S<NUM>) shows the conductivity of <NUM>/cm, and LGPS(Li<NUM>GeP<NUM>S<NUM>) shows the conductivity of <NUM>/cm. However, the sulfide-based solid electrolyte has a fatal disadvantage of having a severe odor and being unstable in air and water, so the need for a stable oxide-based solid electrolyte is emerging. Representative oxide-based solid electrolytes include LATP(Li<NUM>+xAlxTi<NUM>-x(PO<NUM>)<NUM>) (<NUM> < x < <NUM>), LAGP (Li<NUM>+xAlxGe<NUM>-x(PO<NUM>)<NUM>) (<NUM> < x < <NUM>), Li<NUM>La<NUM>Zr<NUM>O<NUM> (LLZO), etc. Among them, the LATP and the LAGP are good for commercialization because they have excellent ionic conductivity and are stable in the atmosphere. Most of these oxide-based solid electrolytes are prepared by a solid phase method, so the particles are uneven and the crystallinity varies greatly depending on the heat treatment temperature.

(Patent Document <NUM>) <CIT> <CIT> discloses methods for preparing ceramic solid electrolytes. "<NPL>, disclose a method for preparing those electrolytes.

In a conventional method for synthesizing a ceramic solid electrolyte, the ceramic solid electrolyte is prepared by mixing raw material particles by a solid phase method, mixing the mixture by ball-milling in a dry state, and then heating the mixture. The ceramic solid electrolyte prepared by this way has low ionic conductivity because it has uneven particle distribution and various shapes of particles. An object of the present invention is to prepare a ceramic solid electrolyte having even particle distribution, even particle shape, and excellent crystallinity by improving the conventional method for synthesizing the ceramic solid electrolyte.

Conventional ceramic solid electrolytes have uneven particle distribution and particle shape, which makes dispersion uneven, lowers the ionic conductivity, and reduces the electrochemical properties of the battery when manufactured as an electrolyte. Accordingly, the present invention provides ceramic solid electrolyte particles having spherical shapes and even distribution by mixing raw materials using water as a solvent and applying a rotary concentration method or a spray method. When the ceramic particles prepared above are made into an electrolyte and applied to a battery, it is possible to exhibit excellent electrochemical properties.

According to the present invention, it is possible to prepare a high-performance ceramic electrolyte having even particle shape and distribution.

The specific content of the present invention will be described in more detail. However, this is to present an embodiment of the present invention as an example. The present invention is not limited by the following description. The present invention is only defined by the following claims to be described below.

In one embodiment of the present invention, the oxide-based conductive ceramic electrolyte may be prepared by mixing raw materials of the ceramic solid electrolyte in an equivalent ratio using distilled water as a solvent, mixing the mixture in a solution state for <NUM> hours by ball-milling, drying first by adding a rotary concentration method or a spray method, drying second at <NUM>, heating first at <NUM> for <NUM> hours, and heating second at <NUM> for <NUM> hours.

The solid electrolyte LATP may be represented by the following Chemical Formula <NUM>.

[Chemical Formula <NUM>]     Li<NUM>+xAlxTi<NUM>-x(PO<NUM>)<NUM> (<NUM> < x < <NUM>).

Among them, Li<NUM>Al<NUM>Ti<NUM>(PO<NUM>)<NUM> is preferable.

Step <NUM> for preparing the LATP ceramic solid electrolyte may be a step of preparing a solid electrolyte precursor by adding and mixing lithium chloride, aluminum nitrate, ammonium phosphate, and titanium butoxide in distilled water. The lithium chloride is LiCl, the aluminum nitrate is Al(NO<NUM>)<NUM>·<NUM><NUM>O, the ammonium phosphate is NH<NUM>H<NUM>PO<NUM>, and the titanium butoxide is Ti(OC<NUM>H<NUM>)<NUM>.

Step <NUM> may be a step for mixing the solid electrolyte precursor with a ball-mill. The speed of the ball-mill may be <NUM> RPM to <NUM> RPM, preferably <NUM> to <NUM> RPM.

Step <NUM> may be a step for drying first by a rotary concentration method or a spray method. The temperature of the rotary concentration method may be <NUM> to <NUM>, preferably <NUM> to <NUM>. The temperature of the spray method may be <NUM> to <NUM>, preferably <NUM> to <NUM>.

Step <NUM> may be a step for drying second in a dryer at <NUM> for at least <NUM> hours to completely remove the distilled water solvent.

Step <NUM> may be a step for calcining first ceramic particles in a heat treatment device and firing second the ceramic particles. The first calcining temperature may be <NUM> to <NUM>, preferably <NUM> to <NUM>. The second firing temperature may be <NUM> to <NUM>, preferably <NUM> to <NUM>. The calcining and firing time may be <NUM> to <NUM> hours, preferably <NUM> to <NUM> hours. The ceramic particles may be calcined at <NUM> for <NUM> hours and then fired at <NUM> for <NUM> hours.

The heat treatment may be performed by starting from room temperature. The solid electrolyte ceramic particles may be made into a powder form with a mortar.

The solid electrolyte LAGP may be represented by the following Chemical Formula <NUM>.

[Chemical Formula <NUM>]     Li<NUM>+xAlxGe<NUM>-x(PO<NUM>)<NUM> (<NUM> < x < <NUM>).

Among them, Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> is preferable.

Step <NUM> for preparing the LAGP ceramic solid electrolyte particles may be a step of preparing a solid electrolyte precursor by adding and mixing lithium chloride, aluminum nitrate, ammonium phosphate, and germanium oxide in distilled water. The lithium chloride is LiCl, the aluminum nitrate is Al(NO<NUM>)<NUM>·<NUM><NUM>O, the ammonium phosphate is NH<NUM>H<NUM>PO<NUM>, and the germanium oxide is GeO<NUM>.

The synthesis of an LATP solid electrolyte was performed by calculating the chemical equivalent ratio of LiCl, Al(NO<NUM>)<NUM>·<NUM><NUM>O, NH<NUM>H<NUM>PO<NUM>, and Ti(OC<NUM>H<NUM>)<NUM>, capable of forming Li<NUM>Al<NUM>Ti<NUM>(PO<NUM>)<NUM> (LiCl <NUM> mole molecular weight = <NUM>/mol, Al(NO<NUM>)<NUM>·<NUM><NUM>O <NUM> mole molecular weight = <NUM>/mol, NH<NUM>H<NUM>PO<NUM> <NUM> mole molecular weight = <NUM>/mol, Ti(OC<NUM>H<NUM>)<NUM> <NUM> mole molecular weight = <NUM>/mol), and then each <NUM> mol was added to <NUM> of distilled water. Thereafter, zirconia balls of <NUM> and <NUM> in diameter were prepared in a ratio of <NUM>:<NUM>, and then added in a <NUM> container prepared so that a volume ratio of the mixed sample and the zirconia balls was <NUM>:<NUM>. The rotary speed of the ball milling was <NUM> to <NUM> RPM, and the ball milling was performed for <NUM> hours. After ball milling, the zirconia balls were removed from the sample. Then, the sample was dried first by a rotary concentration method or a spray method, put in an evaporation dish and then sufficiently dried second at <NUM> for <NUM> hours. Then, the dried sample was pulverized in a mortar to form a powder form. Then, the sample was heat treated as follows. The temperature was raised from room temperature to <NUM>. Then, the sample was heat treated for <NUM> hours to calcine the sample and cooled naturally until <NUM> or less. Thereafter, the sample was heat treated at <NUM> for <NUM> hours to fire the sample and then pulverized to prepare a powdered LATP solid electrolyte.

Although the preferred Example of the present invention has been described as above, the present invention is not limited to the Example, and various modifications are possible by those skilled in the art within the scope of the technical idea of the present invention.

A method of preparing the LATP solid electrolyte was illustrated in <FIG>. As in the prior art, a sample obtained by ball-milling and mixing without using a distilled water solvent and then heat-treating is referred to as Sample <NUM>, a sample obtained by ball-milling and mixing using a distilled water solvent, drying the solvent, and then heat-treating is referred to as Sample <NUM>, a sample obtained by ball-milling and mixing using a distilled water solvent, drying first the solvent by a rotary concentration method, drying second the solvent in an oven, and then heat-treating is referred to as Sample <NUM>, and a sample obtained by ball-milling and mixing using a distilled water solvent, drying first the solvent by spraying, drying second the solvent in an oven, and then heat-treating is referred to as Sample <NUM>. Samples <NUM> to <NUM> are summarized in Table <NUM> below.

<FIG> are SEM photographs of LATP ceramic particles according to the above process. Sample <NUM> (<FIG>) has an irregular particle shape and a wide particle distribution of <NUM> to <NUM> micrometers. Sample <NUM> (<FIG>) contains some irregularly shaped particles, but is generally even, and the particle distribution is <NUM>-<NUM> micrometers. Sample <NUM> (<FIG>) has a very even particle shape and has a particle distribution of <NUM> to <NUM> micrometers. Sample <NUM> (<FIG>) has a very even particle shape and has a particle distribution of <NUM> to <NUM> micrometers.

The synthesized Li<NUM>Al<NUM>Ti<NUM>(PO<NUM>)<NUM> was analyzed at a scanning speed of <NUM>°/min for an XRD analysis <NUM> theta section of <NUM>° to <NUM>°. The analyzed results were shown in <FIG>. It can be seen that the LATP is synthesized in a NASICON structure.

The ionic conductivities of Samples <NUM> to <NUM> are shown in Table <NUM>.

As the particles are more even and the distribution is better, the ionic conductivity is increased.

The synthesis of an LAGP solid electrolyte was performed by calculating the chemical equivalent ratio of LiCl, Al(NO<NUM>)<NUM>. <NUM><NUM>O, NH<NUM>H<NUM>PO<NUM>, and GeO<NUM>, capable of forming Li<NUM>Al<NUM>Ge<NUM>(PO<NUM>)<NUM> (LiCl <NUM> mole molecular weight = <NUM>/mol, Al(NO<NUM>)<NUM>·<NUM><NUM>O <NUM> mole molecular weight = <NUM>/mol, NH<NUM>H<NUM>PO<NUM> <NUM> mole molecular weight = <NUM>/mol, GeO<NUM> <NUM> mole molecular weight = <NUM>/mol), and then each <NUM> mol was added to <NUM> of distilled water.

Thereafter, zirconia balls of <NUM> and <NUM> in diameter were prepared in a ratio of <NUM>:<NUM>, and then added in a <NUM> container prepared so that a volume ratio of the mixed sample and the zirconia balls was <NUM>:<NUM>. The rotary speed of the ball milling was <NUM> to <NUM> RPM, and the ball milling was performed for <NUM> hours. After ball milling, the zirconia balls were removed from the sample. Then, the sample was dried first by a rotary concentration method or a spray method, put in an evaporation dish and then sufficiently dried second at <NUM> for <NUM> hours. Then, the dried sample was pulverized in a mortar to form a powder form. Then, the sample was heat treated as follows. The temperature was raised from room temperature to <NUM>. Then, the sample was heat treated for <NUM> hours to calcine the sample and cooled naturally until <NUM> or less. Thereafter, the sample was heat treated at <NUM> for <NUM> hours to fire the sample and then pulverized to prepare a powdered LATP solid electrolyte.

<FIG> are SEM photographs of particles of LAGP synthesized by methods of Samples <NUM> to <NUM>. The particles synthesized through first solvent drying by adding rotary concentration method (Sample <NUM>) shows the best particle characteristic.

Claim 1:
A method for preparing a ceramic solid electrolyte selected from Li<NUM>+xAlxTi<NUM>-x(PO<NUM>)<NUM> (LATP) and Li<NUM>+xAlxGe<NUM>-x(PO<NUM>)<NUM> (LAGP), comprising mixing raw materials of the ceramic solid electrolyte with a ball-mill using distilled water as a solvent, drying the distilled water, and then high temperature heat-treating,
wherein drying comprises drying first the solvent by rotary concentrating or by spraying, and drying second the solvent in a dryer to completely remove the distilled water solvent,
wherein the temperature of drying first the distilled water is <NUM> to <NUM> when the drying first is by rotary concentrating,
the temperature of drying first the distilled water is <NUM> to <NUM> when the drying first is by spraying, and
wherein in the high temperature heat-treating process, first, the ceramic particles are calcined, and second, the ceramic particles are fired, wherein the temperature of calcining the ceramic particles is <NUM> to <NUM> and the temperature of firing the ceramic particles is <NUM> to <NUM>,
wherein the mixing is carried out in the distilled water,
wherein the raw materials are LiCl, Al(NO<NUM>)<NUM>·<NUM><NUM>O, NH<NUM>H<NUM>PO<NUM> and Ti(OC<NUM>H<NUM>)<NUM> when the ceramic solid electrolyte is LATP, or the raw materials are LiCl, Al(NO<NUM>)<NUM>·<NUM><NUM>O, NH<NUM>H<NUM>PO<NUM> and GeO<NUM> when the ceramic solid electrolyte is LAGP, and wherein <NUM> < x < <NUM>.