KR20180051717A - Lithium-Ion Conducting Composite Solid Electrolyte For Lithium Battery, Method Of Manufacturing The Same, And Lithium Battery Comprising The Same - Google Patents

Abstract

The present invention relates to a lithium ion conductive composite solid electrolyte, a manufacturing method thereof, and a lithium battery including the same. More specifically, the present invention relates to a composite solid electrolyte exhibiting high lithium ion conductivity, in which a heterogeneous sulfide-based solid electrolyte material such as amorphous y[Li_4SnS_4]_(1-y)[x(LiI)_(1-x)(LiBH_4)] (0 < x, y (the number of moles) < 1) or the like is combined with an oxide-based lithium ion conductive solid electrolyte, to eliminate a sintering process of high heat treatment temperature and to increase the density of solid electrolyte pellets and reduce grain boundary resistance, such that high lithium ion conductivity is exhibited, and to a manufacturing method thereof and a lithium battery including the same.

Description

TECHNICAL FIELD The present invention relates to a lithium ion conductive composite solid electrolyte, a method for producing the lithium ion conductive composite solid electrolyte, and a lithium battery including the lithium ion conductive composite solid electrolyte.

The present invention relates to a lithium ion conductive composite solid electrolyte, and more particularly, to a lithium ion conductive solid electrolyte which comprises an amorphous heterogeneous sulfide based solid electrolyte material complexed with an oxide-based lithium ion conductive solid electrolyte to eliminate a sintering process at a high heat treatment temperature, The present invention relates to a composite solid electrolyte exhibiting high lithium ion conductivity by increasing electrolyte pellet density and grain boundary resistance.

Recently, lithium batteries have been actively studied for efficient use of energy, and various efforts are being made to use them as energy sources for electric vehicles and electric power storage as well as small-sized mobile electronic devices.

The commercialized lithium ion secondary battery uses a liquid electrolyte based on an organic electrolyte. However, in the case of an organic electrolyte, the risk of explosion / fire is very high. To improve the safety of the battery, an organic liquid electrolyte is replaced with an inorganic- The need to do so has been increasing.

A pre-solid secondary battery in which an inorganic-based solid electrolyte is used instead of a liquid electrolyte does not use a flammable organic electrolytic solution, and has excellent safety because there is no risk of electrolyte leakage or ignition. However, in the case of all the solid batteries, the anode, the solid electrolyte, and the cathode are all in a solid state, and it is difficult for them to come into close contact with each other, so that the resistance at each interface and the battery cell becomes very large, and the lithium ion conductivity of the solid electrolyte It is difficult to increase the output of the battery.

There an inorganic solid electrolyte material may be divided into sulfide and oxide-based material, in the case of the Yellow River water system materials, but shows an oxide-based contrast high lithium ion conductive property, hygroscopicity is strong and is a sulfide of hydrogen (H ₂ S) toxic gas There is a high possibility of occurrence. Oxide-based solid electrolyte _{LLZO (Li a La 3 Zr 2} O 12), pages lobe _{LLTO (Li 3a La (2 /} 3a) □ (1 / 3-2a) having a tree structure having the garnet configuration Sky material _{TiO 3), LATP (Li 1} + a Al a Ti 2-a (PO 4) 3) and the like, the oxide-based solid electrolyte is a sulfide-based solid electrolyte compared to water, chemical, physical and mechanical stability having a NASICON structure And has attracted much attention as a solid electrolyte material due to its high bulk ion conduction property.

However, most of the oxide-based solid electrolyte materials have a high grain boundary resistance, so that the total lithium ion conductivity is low, so there is a problem in using the powder directly as a solid electrolyte of a battery. In order to solve this problem, the pellet is produced by sintering the solid electrolyte powder and then the sintering process (heat treatment) at a high temperature (800 ° C ~ 1400 ° C) is used to lower the grain boundary resistance by increasing the bonding force and pellet density between solid electrolyte particles. In this case, not only a cost problem due to the high-temperature heat treatment process such as the sintering process but also a restriction on the selection of the electrode and the component material for the battery configuration is imposed.

Therefore, in order to develop a high-performance pre-solid lithium secondary battery, there is a need for a technique capable of increasing the lithium ion conductivity by reducing the grain boundary resistance of the solid electrolyte by eliminating the sintering process in the production of the solid electrolyte.

Korean Registered Patent No. 10-1508423 Korea Patent No. 10-1236059

SUMMARY OF THE INVENTION It is an object of the present invention to provide an oxide-based lithium ion conductive solid electrolyte which can be applied to a lithium battery, which is amorphous y [Li ₄ SnS ₄ ] (1-y) [x (LiI) Based solid electrolyte materials such as LiBH ₄ (LiBH ₄ ) (0 <x, y (molar number) <1), thereby eliminating the sintering process at a high heat treatment temperature and increasing the density of solid electrolyte pellets And a composite solid electrolyte exhibiting high lithium ion conductivity by reducing the grain boundary resistance.

(1-x) (LiBH ₄ )] (0 < x, y (number of moles) &gt;) of the amorphous structure y [Li ₄ SnS ₄ ] 1). &Lt; / RTI &gt;

In addition,

1) preparing Li ₄ SnS ₄ (LSS) crystallized through a solid phase method by mixing Li ₂ S (lithium sulfide), S (sulfur) and SnS (tin sulfide) in a molar ratio of 2: 1: 1;

2) dissolving the crystallized Li ₄ SnS ₄ (LSS) of the step 1) in a solvent, followed by drying and heat-treating the amorphous Li ₄ SnS ₄ powder; And

3) Amorphous Li ₄ SnS ₄ powder of the step 2) is mixed with LiI and LiBH ₄ to form an amorphous y [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) ] (0 < x, y (moles) < 1) powder.

A lithium ion conductive solid electrolyte comprising an amorphous structure y [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y Of the present invention.

The present invention also relates to a method for producing _a sulfide-based solid electrolyte, which comprises reacting an LLTO (Li _3a La _{(2/3-a)) (1 / 3-2a)} TiO ₃ having a perovskite structure as an oxide- A lithium ion conductive composite solid electrolyte comprising a complex of [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y do.

In addition,

1) reacting a metal nitrate with a chelating agent as a starting material to prepare a sol and a gel; and subjecting the gel to thermal decomposition, heat treatment, and pulverization to prepare LLTO powder;

2) Li ₄ SnS ₄ (LSS) crystallized through the solid phase method is dissolved in a solvent, and amorphous Li ₄ SnS ₄ powder is produced through a drying and a heat treatment process, and then mixed with LiI and LiBH ₄ to form y [Li (LSS-LiI-LiBH ₄ ) powder having a composition of 0 <x, y (mole number) <1> ₄ SnS ₄ ] (1-y) [x LiI 1-x LiBH ₄ ]. And

3) mixing the LLTO and the LSS-LiI-LiBH ₄ and press-molding them.

In addition, the present invention _{y [Li 4 SnS 4] (} 1-y) [x (LiI) (1-x) (LiBH 4)] (0 <x, y ( molar amount) of the amorphous structure in accordance with the present invention < 1). &Lt; / RTI &gt;

In addition, the present invention relates to a method for producing _a sulfide-based solid electrolyte, which comprises reacting an LLTO (Li _3a La _{(2/3-a)) (1 / 3-2a)} TiO ₃ having a perovskite structure as an oxide- A lithium ion conductive composite solid electrolyte comprising a complex of [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y A lithium battery is provided.

The lithium ion conductive composite solid electrolyte according to the present invention is an amorphous y [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1- x) (LiBH ₄ )], thereby eliminating the sintering process at a high heat treatment temperature, increasing the density of the solid electrolyte pellets and reducing the grain boundary resistance, thereby exhibiting high lithium ion conductivity. Such a lithium ion conductive composite solid electrolyte makes it possible to provide a lithium battery with high output and high performance at the time of use, thereby providing a lithium battery which does not require a sintering process and is excellent in ion conductivity.

1 is a graph showing an X-ray diffraction pattern of solid electrolyte pellets prepared in Example 1, Comparative Example 1 and Comparative Example 3. FIG.
FIG. 2 is a photograph of a composite solid electrolyte powder and pellet prepared in Example 1, and a composite solid electrolyte powder obtained through a scanning electron microscope (SEM) and an energy dispersive spectroscopy (EDS) experiment.
3 is a graph showing the impedance spectra of the composite solid electrolyte pellets prepared in Examples 1, 3, 5, and 10.
4 is a graph showing the impedance spectrum of the composite solid electrolyte pellet prepared in Comparative Example 1, Comparative Example 2, and Comparative Example 3. FIG.

Hereinafter, the present invention will be described in detail.

The present invention relates to a lithium ion battery including an amorphous structure y [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y Thereby providing a conductive solid electrolyte.

The solid electrolyte is preferably in the form of pellets.

The solid electrolyte is composed of Li ₄ SnS ₄ (LSS) is prepared and dissolved in a solvent, and amorphous Li ₄ SnS ₄ powder is prepared through drying and low-temperature heat treatment, and then mixed with LiI and LiBH ₄ to form y [Li ₄ SnS ₄ ] ) [x (LiI) (1-x) (LiBH ₄ )] (LSS-LiI-LiBH ₄ ) powder.

The present invention also relates to a method for producing _a sulfide-based solid electrolyte, which comprises reacting an LLTO (Li _3a La _{(2/3-a)) (1 / 3-2a)} TiO ₃ having a perovskite structure as an oxide- A lithium ion conductive composite solid electrolyte comprising a complex of [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y do.

The oxide-based solid electrolyte and the sulfide-based solid electrolyte among the complex solid electrolytes are preferably combined in a weight ratio of 9: 1 to 1: 1.

The solid electrolyte is preferably in the form of pellets.

The oxide-based solid electrolyte among the complex solid electrolytes may further include a general oxide solid electrolyte including a sintering process in addition to the LLTO solid electrolyte. For example, oxide such as LLZO (Li _a La ₃ Zr ₂ O ₁₂ ) having a garnet structure and Li _{1 + a} Al _a Ti _2-a (PO ₄ ) ₃ (0.1? A? 0.5) I can. But the present invention is not limited to these and can be used as long as it can be used in the technical field.

The oxide-based solid electrolyte may be prepared by reacting a metal nitrate with a chelating agent as a starting material to prepare a sol and a gel, and then subjecting the gel to thermal decomposition, heat treatment, and pulverization to produce LLTO powder.

The sulfide-based solid electrolyte is a Li ₄ SnS ₄ (LSS) was dissolved in after manufacture solvent drying and _{y [Li 4 SnS 4] (} 1-y) over a low heat treatment step after producing the Li ₄ SnS ₄ powder of amorphous through LiI and LiBH ₄ and mix [x ( LiI) (1-x) (LiBH ₄ )] (LSS-LiI-LiBH ₄ ) powder.

This oxide-based material, LLTO, and the sulfide, LSS-LiI-LiBH ₄ , are mixed with each other and pressure-molded to produce a composite solid electrolyte in the form of a pellet.

Composite solid electrolyte according to the present invention has a particle size of 1 ~ 200 ㎛, to form a pellet of 100 ~ 1000 ㎛ ^{thickness, 1.0 × 10 -6 ~ 1.0 ×} 10 -3 to have ionic conductivity in S / cm at room temperature have.

The present invention also provides a method for producing the composite solid electrolyte according to the present invention.

The method comprises the steps of preparing an LLTO solid electrolyte powder based on a sol-gel method, dissolving amorphous LSS-LiI-LiBH ₄ A step of preparing a solid electrolyte powder, and a step of mixing the oxide-based solid electrolyte and the sulfide-based solid electrolyte powder and press-molding them to prepare a composite solid electrolyte in the form of a pellet.

Specifically,

1) reacting a metal nitrate with a chelating agent as a starting material to prepare a sol and a gel; and subjecting the gel to thermal decomposition, heat treatment, and pulverization to prepare LLTO powder;

2) Li ₄ SnS ₄ (LSS) crystallized through the solid phase method is dissolved in a solvent, and amorphous Li ₄ SnS ₄ powder is produced through a drying and a heat treatment process, and then mixed with LiI and LiBH ₄ to form y [Li (LSS-LiI-LiBH ₄ ) powder having a composition of 0 <x, y (mole number) <1> ₄ SnS ₄ ] (1-y) [x LiI 1-x LiBH ₄ ]. And

3) mixing the LLTO and the LSS-LiI-LiBH ₄ and press-molding them.

In the above method, LLTO and LSS-LiI-LiBH ₄ are preferably mixed in a weight ratio of 9: 1 to 1: 1 in step 3).

In the above-described method, it is preferable to produce pellet form through pressure molding in step 3).

Can using the production method of the present invention to produce the composite solid electrolyte powder, and 100 ~ 1000 ㎛ pellets of thickness having a size of 1 ~ 200 ㎛ particles, at room temperature, ^{1.0 × 10 -6 ~ 1.0 × 10} -3 S / cm The composite solid electrolyte having an ionic conductivity of &lt; RTI ID = 0.0 &gt;

In addition, the present invention _{y [Li 4 SnS 4] (} 1-y) [x (LiI) (1-x) (LiBH 4)] (0 <x, y ( molar amount) of the amorphous structure in accordance with the present invention < 1). &Lt; / RTI &gt;

The present invention also relates to a method for producing _a sulfide-based solid electrolyte, which comprises reacting an LLTO (Li _3a La _{(2/3-a)) (1 / 3-2a)} TiO ₃ having a perovskite structure as an oxide- A lithium ion conductive composite solid electrolyte comprising a complex of [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y A lithium battery is provided.

The lithium battery may include a positive electrode including a positive electrode active material, and a solid electrolyte interposed between the negative electrode including the negative electrode active material. In addition, the positive electrode and the negative electrode layer may further include the solid electrolyte described above, thereby reducing the interfacial resistance between the positive electrode and the solid electrolyte in contact with the negative electrode, thereby reducing the cell resistance.

The lithium battery may have a structure that further includes a solid electrolyte layer between the anode and the solid electrolyte and between the anode and the solid electrolyte. The additional solid electrolyte membrane improves the chemical stability of the conventional solid electrolyte and can improve the adhesion between the electrode and the solid electrolyte.

The positive electrode active material can be used without limitation as long as it is commonly used in a lithium battery. For _{example, LiCoO 2, LiMnO 2, LiMn} 2 O 4, LiNi 1 - x Mn x O2 (0 <x <1), LiNi 1 -x- y Co x Mn y O 2 (0 <x <0.5, 0 <y <0.5), lithium transition metal oxide of LiFePO ₄ , TiS ₂ , FeS ₂ , transition metal sulfide, and the like.

The negative electrode active material can be used without limitation as long as it is commonly used in a lithium battery. For example, at least one selected from the group consisting of a lithium metal, a metal capable of alloying with lithium, a metal oxide, and a carbon-based material. For example, examples of the metal capable of being alloyed with lithium include Si, Sn, Al, Ge, Pb and Bi. Examples of the metal oxide include lithium titanium oxide, SnO ₂ , SiO _x to be. The carbon-based material may be crystalline carbon, amorphous carbon, or a mixture thereof.

The lithium battery is also suitable for applications requiring high safety and high capacity such as an electric vehicle and can be used in a hybrid vehicle by being combined with a conventional internal combustion engine, a fuel cell, a supercapacitor and the like. In addition, the lithium battery can be used for all other purposes such as mobile compact IT products such as mobile phones and portable computers.

A preferred embodiment of the present invention is as follows. The following embodiments are illustrative of the technical features of the present invention, and the present invention is not limited to these embodiments.

< Example  1>

As a starting material Li precursor, LiNO _3, La precursor of _{La (NO 3) 3 6H 2} O, Ti precursor of _{Ti [OCH (CH3) 2]} 4 (titanium isopropoxide) to Li _{0. 29} La _{0 . 57} is TiO ₃ so as to obtain a molar ratio between Li, La, Ti 0.29: were prepared by weighing a 1: 0.57. The starting materials were dissolved in ethylene glycol, citric acid (HOC (COOH) (CH ₂ COOH) ₂ ) was added to the solution, and the solution was heated to 60 ° C to prepare a sol Respectively. At this time, citric acid corresponding to three times the molar amount of the entire metal nitrate was added. The solution was heated to 270 DEG C to prepare a gel and pyrolyzed. After completion of the heat treatment at 900 캜 for 3 hours, a solid electrolyte powder was prepared. The powder was milled by wet milling at 220 rpm for 12 hours by adding zirconia balls and ethanol. The powder was collected, dried at 80 ° C. for 24 hours, and filtered through a 100 μm mesh to obtain a fine LLTO powder having a size of 100 nm to 5 μm.

Li ₂ S (lithium sulfide), S (Sulfur) and SnS (Tin sulfide) were weighed in a molar ratio of 2: 1: 1 as a starting material of the sulfide-based solid electrolyte. Thereafter, the powder was pressurized to 300 MPa to prepare pellets, and then subjected to vacuum heat treatment at 550 ° C. for 48 h to obtain crystallized Li ₄ SnS ₄ (LSS) powder. 0.4 mol of Li ₄ SnS ₄ was dissolved in a methanol solution, and the mixture was stirred at 50 ° C. for 6 hours. After vacuum drying at room temperature, methanol was volatilized to obtain amorphous Li ₄ SnS ₄ powder. Then, the Li ₄ SnS ₄ powder was subjected to vacuum heat treatment at 200 ° C. for 5 hours ₄ SnS ₄ powder was obtained. Amorphous Li ₄ SnS ₄ and LiI thus obtained were mixed in a molar ratio of 0.6: 0.4 to obtain an amorphous 0.6 [Li ₄ SnS ₄ ] 0.4 (LiI) solid electrolyte powder.

The mixed LLTO and sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 (LiI) were weighed at a ratio of 90:10 by weight and then mixed and pressed at 300 MPa to prepare a pellet-shaped solid electrolyte.

< Example  2>

A composite solid electrolyte pellet was prepared in the same manner as in Example 1 except that the LLTO and the sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 (LiI) were weighed and weighed at a ratio of 80:20 by weight .

< Example  3>

A composite solid electrolyte pellet was prepared in the same manner as in Example 1 except that the mixed LLTO and the sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 (LiI) were weighed at a weight ratio of 70:30 and then mixed .

< Example  4>

A composite solid electrolyte pellet was prepared in the same manner as in Example 1 except that the LLTO and the sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 (LiI) were weighed at a weight ratio of 60:40 and then mixed .

< Example  5>

A composite solid electrolyte pellet was prepared in the same manner as in Example 1, except that the LLTO and the sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 (LiI) were weighed and weighed at a ratio of 50:50 by weight .

< Example  6>

The LLTO powder preparation and the amorphous LSS preparation method are the same as in <Example 1>. LiI and LiBH ₄ were weighed and mixed at a molar ratio of 0.25: 0.75 and mixed with an amorphous LSS in a molar ratio of 0.4: 0.6 to form amorphous 0.6 [Li ₄ SnS ₄ ] 0.4 [0.25 (LiI) 0.75 (LiBH ₄ ) An electrolyte powder was obtained.

Were weighed and weighed at a ratio of 90:10 in weight ratio with the dispersed LLTO and sulfide-based electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 [0.25 (LiI) 0.75 (LiBH ₄ )] and then mixed and pressed at 300 MPa to form pellets A solid electrolyte was prepared.

< Example  7>

The results are shown in Tables 1 and 2, except that the LLTO and the sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 [0.25 (LiI) 0.75 (LiBH ₄ )] were weighed and weighed at a weight ratio of 80:20. The composite solid electrolyte pellets were prepared in the same manner.

< Example  8>

Except that the LLTO and the sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 [0.25 (LiI) 0.75 (LiBH ₄ )] were weighed and weighed at a weight ratio of 70:30 and then mixed. The composite solid electrolyte pellets were prepared in the same manner.

< Example  9>

Except that the mixture was weighed and weighed at a ratio of 60:40 in weight ratio with the dispersed LLTO and the sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 [0.25 (LiI) 0.75 (LiBH ₄ ) To prepare a composite solid electrolyte pellet.

< Example  10>

Except that the mixture was weighed and weighed at a ratio of 50:50 in weight ratio with the dispersed LLTO and the sulfide electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 [0.25 (LiI) 0.75 (LiBH ₄ ) To prepare a composite solid electrolyte pellet.

< Comparative Example  1>

The LLTO powder prepared in Example 1 was press-formed at 300 MPa to prepare a solid electrolyte pellet.

< Comparative Example  2>

The pellet prepared in Comparative Example 1 was sintered at 1200 ^o C for 6 hours to prepare a pellet-shaped solid electrolyte sintered body.

< Comparative Example  3>

The amorphous Li ₄ SnS ₄ prepared in Example 1 The powder was press-molded at 300 MPa to prepare a solid electrolyte pellet.

< Evaluation example  1> X-ray diffraction experiment

X-ray diffraction experiments were conducted to understand the crystal structure of the solid electrolyte prepared in Example 1, Comparative Example 1 and Comparative Example 3.

The experimental results are shown in Fig. As shown in FIG. 1, it was confirmed that Li _0.29 La _0.57 TiO ₃ (LLTO) had a pure perovskite structure free from impurities. &Lt; Comparative Example 3 > In the case of the crystalline Li ₄ SnS ₄ (LSS) was dissolved in a solvent and then subjected to a reheat treatment at a low temperature (200 ° C.), only a diffraction peak having a low crystallinity was observed only at 27 ° and 47 °. In the case of <Example 1> in which amorphous LSS, LiI and LLTO were mixed, the LLTO crystalline peak having a weight ratio of 90 was found to be large, and the amorphous LSS showed small characteristic diffraction peaks. The amount of mixed LiI was not so large and the characteristic peak of LiI was not observed well. It was found that no characteristic peaks were observed other than the LSS and LLTO diffraction peaks, and it was confirmed that chemical side reactions did not occur when the LLTO and LSS-LiI composite solid electrolytes were mixed, and they were simply mixed with different types of solid electrolyte powders .

< Evaluation example  2> Scanning electron microscope ( SEM ) And energy dispersive spectroscopy (EDS) experiments

Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) experiments were conducted to characterize the surface properties of the composite solid electrolyte prepared in Example 1.

The experimental results are shown in Fig. The weight of LLTO and sulfide-based electrolyte 0.6 [Li ₄ SnS ₄ ] 0.4 (LiI) distributed in Example 1 was weighed at a ratio of 90:10, and the mixed powder was press-molded at 300 MPa to produce pellets (See the powder and pellet picture of FIG. 2), surface SEM and EDS analyzes of the powder before pelletization were performed. It can be seen that the particle size of the dispersed LLTO powder is 5 μm or less, and it is confirmed that the components of Ti of LLTO and the S and Sn components of Li ₄ SnS ₄ are uniformly dispersed. From the result that the LLTO and LSS-LiI composite solid electrolyte powders were uniformly dispersed, it was judged that the solid electrolytes were uniformly dispersed in the pellet solid electrolytes.

< Evaluation example  3> Impedance measurement experiment and ion conductivity calculation

AC impedance measurement method was used to measure ion conductivity of composite solid electrolyte. To this end, Au was coated on both sides of the solid electrolyte pellet to make a blocking interface that ions could not pass through. Then, an AC voltage was applied to both sides of the sintered body at a voltage amplitude of 5 mV and a frequency range of 700 kHz to 0.1 Hz "He said. The resistance of the intersection of the half circle of the impedance trace with the real axis is measured by the fitting method and the thickness and area of the specimen are substituted into the following equation to calculate the total ion conductivity of the solid electrolyte.

? (S cm ^-1 ) = 1 / (R) * (L / A)

(R: resistance value obtained from fitting, A: pellet area, L: pellet thickness)  

Impedance openings obtained from Example 1, Example 3, Example 5 and Example 10, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are shown in Figs. 3 and 7 4, and the ionic conductivity values of the solid electrolytes prepared in Examples 2, 4, 6, 7, 8, and 9, which were measured in the same manner, are shown in Table 1.

Ionic conductivity measurement results of composite solid electrolyte pellets division Ion conductivity (S / cm) Example 1 3.0 x 10 ^-6 Example 2 1.5 x 10 ^-5 Example 3 2.6 x 10 ^-5 Example 4 8.3 × 10 ^-5 Example 5 1.8 × 10 ^-4 Example 6 4.3 × 10 ^-6 Example 7 2.1 x 10 ^-5 Example 8 1.8 x 10 ^-5 Example 9 7.5 × 10 ^-5 Example 10 1.4 x 10 ^-4 Comparative Example 1 6.3 × 10 ^-7 Comparative Example 2 1.1 × 10 ^-4 Comparative Example 3 3.4 x 10 ^-5

In the case of <Comparative Example 1>, when the pellet was produced without the sintering process at a high temperature of the LLTO powder, the ionic conductivity value was very low as 6.3 × 10 ^-7 S / cm. In the case of Comparative Example 2, when the pellet produced in Comparative Example 1 was sintered at a high temperature of 1200 ° C, the ion conductivity value was measured as 1.1 × 10 ^-4 S / cm, which was several hundred times . However, it can be seen that a high-temperature heat treatment process is required to increase the ionic conductivity of the oxide-based solid electrolyte LLTO. Comparative Example 3 In the case of phosphorus amorphous LSS, the ion conductivity value was found to be lower than that of Comparative Example 2 which was sintered at 3.4 × 10 ^-5 S / cm.

In the case of Examples 1 to 5, when LLTO and amorphous 0.6LSS0.4LiI were mixed at different weight ratios, ionic conductivity increased as the mixing ratio of 0.6 [Li ₄ SnS ₄ ] 0.4 (LiI) It can be seen that it increases from 3.0 × 10 ^-6 S / cm to 1.8 × 10 ^-4 S / cm. In the case of Example 1, it was confirmed that ionic conductivity was increased four times or more as compared with that of Comparative Example 1 by mixing 0.6 LSS0.4LiI of 10 weight ratio. In Example 5, The ionic conductivity of the amorphous sulfide-based solid electrolyte, 0.6LSS0.4LiI, was uniformly mixed between the LLTO particles, indicating that the pellet density and bonding force between the LLTO and sulfide-based solid electrolytes And the ionic conductivity is improved by lowering the grain boundary resistance of the pellet. This is considered to be a phenomenon in which a soft sulfide-based solid electrolyte is uniformly dispersed between hard oxide particles.

(Example 6) to (Example 10) in which 0.6 [Li ₄ SnS ₄ ] 0.4 [0.25 (LiI) 0.75 (LiBH ₄ )] in which LiBH ₄ was added to LiI was mixed with LLTO, The ion conductivity value was increased similarly to Example 5, and the ion conductivity value was also significantly increased as compared with Comparative Example 1. In addition, From these results, it was found that LiBH ₄ is also effective for improving the ionic conductivity of composite solid electrolyte with LiI.

Claims (12)

A lithium ion conductive solid electrolyte comprising an amorphous structure y [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y .
The lithium ion conductive solid electrolyte according to claim 1, wherein the solid electrolyte is in the form of a pellet.
1) preparing Li ₄ SnS ₄ (LSS) crystallized through a solid phase method by mixing Li ₂ S (lithium sulfide), S (sulfur) and SnS (tin sulfide) in a molar ratio of 2: 1: 1;
2) dissolving the crystallized Li ₄ SnS ₄ (LSS) of the step 1) in a solvent, followed by drying and heat-treating the amorphous Li ₄ SnS ₄ powder; And
3) Amorphous Li ₄ SnS ₄ powder of the step 2) is mixed with LiI and LiBH ₄ to form an amorphous y [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) ] (0 < x, y (moles) < 1) powder.
A lithium ion conductive solid electrolyte comprising an amorphous structure y [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y &Lt; / RTI &gt;
(Li ₃ La _{(2/3-a)) (1 / 3-2a)} TiO ₃ having a perovskite structure as an oxide-based solid electrolyte, y [Li ₄ SnS ₄ ] (1-y) [x (LiI) (1-x) (LiBH ₄ )] (0 <x, y (number of moles) <1).
5. The lithium ion conductive composite solid electrolyte according to claim 4, wherein the oxide-based solid electrolyte and the sulfide-based solid electrolyte are compounded at a weight ratio of 9: 1 to 1: 1.
5. The lithium ion conductive composite solid electrolyte according to claim 4, wherein the oxide-based solid electrolyte further comprises an oxide-based solid electrolyte in addition to the LLTO solid electrolyte.
The oxide-based solid electrolyte according to claim 6, wherein the oxide-based solid electrolyte further comprises LLZO (Li _a La ₃ Zr ₂ O ₁₂ ) having a garnet structure or Li _{1 + a} Al _a Ti _{2 -a} (PO ₄ ) ₃ Lt; = a &lt; = 0.5). &Lt; / RTI &gt;
1) reacting a metal nitrate with a chelating agent as a starting material to prepare a sol and a gel; and subjecting the gel to thermal decomposition, heat treatment, and pulverization to prepare LLTO powder;
2) Li ₄ SnS ₄ (LSS) crystallized through the solid phase method is dissolved in a solvent, and amorphous Li ₄ SnS ₄ powder is produced through a drying and a heat treatment process, and then mixed with LiI and LiBH ₄ to form y [Li (LSS-LiI-LiBH ₄ ) powder having a composition of 0 <x, y (mole number) <1> ₄ SnS ₄ ] (1-y) [x LiI 1-x LiBH ₄ ]. And
3) mixing the LLTO and the LSS-LiI-LiBH ₄ and press-molding them.
The method of claim 8, wherein LLTO and LSS-LiI-LiBH ₄ are mixed in a weight ratio of 9: 1 to 1: 1 in step 3).
The method for producing a lithium ion conductive composite solid electrolyte according to claim 8, wherein the lithium ion conductive complex solid electrolyte is produced in a pellet form in the step 3).
7. A lithium battery comprising the solid electrolyte of claim 1 or claim 4.
12. The lithium battery according to claim 11, comprising a positive electrode comprising a positive electrode active material and a negative electrode including a negative electrode active material.

Images