JP5189304B2 - Glass ceramic and method for producing the same - Google Patents

Description

  The present invention relates to a glass ceramic and a manufacturing method thereof. More specifically, the present invention relates to a glass ceramic suitable as a solid electrolyte used in a lithium ion secondary battery and a method for producing the same.

In recent years, the demand for secondary batteries such as high-performance lithium batteries used in personal digital assistants, portable electronic devices, small household power storage devices, motorcycles powered by motors, electric vehicles, hybrid electric vehicles, etc. has increased. Yes.
As the applications for use expand, further improvements in safety and performance of secondary batteries are required.
In order to ensure the safety of the lithium battery, it is effective to use an inorganic solid electrolyte instead of the organic solvent electrolyte.

  As the inorganic solid electrolyte, it is known that a heat-treated sulfide glass mainly composed of lithium element, phosphorus element and sulfur element has high ionic conductivity (for example, see Patent Document 1).

  Further, Patent Document 2 contains lithium (Li), phosphorus (P), and sulfur (S) elements as constituents as a solid electrolyte, and in X-ray diffraction (CuKα: λ = 1.5418Å), 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0.3 deg, 21.8 ± 0.3 deg, 23.8 ± 0.3 deg, 25.9 ± 0.3 deg, 29. A lithium ion conductive sulfide-based crystallized glass having diffraction peaks at 5 ± 0.3 deg and 30.0 ± 0.3 deg is disclosed. Those exhibiting these X-ray diffraction peaks exhibit particularly high ionic conductivity.

In order to increase the content of crystals useful for improving ion conductivity, it is conceivable to increase the heat treatment conditions. However, in this case, there is a problem that Li ₄ P ₂ S _6, which is an unfavorable crystal component, is generated for improving ion conductivity.

In general, sulfide-based solid electrolytes use lithium sulfide (Li ₂ S) and diphosphorus pentasulfide (P ₂ S ₅ ) as starting materials, and a sulfide glass is produced from these mixtures by mechanical milling or melt quenching. And it is manufactured by heat-treating this.
In this production method, the content of the high ion conductive crystal is limited, and the Li ₄ P ₂ S ₆ crystal is present in a considerable content.
Therefore, the development of glass ceramics that improve the ion conductivity by increasing the content of crystals contributing to the improvement of ion conductivity while suppressing the formation of crystals of Li ₄ P ₂ S ₆ has been required.
JP 2002-109955 A JP 2005-228570 A

The present invention has been made in view of the above-described problems, and an object thereof is to provide a glass ceramic having a high content of high ion conductive crystals and a low content of Li ₄ P ₂ S ₆ crystals. .

As a result of intensive studies, the present inventors have found that the ionic conductivity increases when there are many crystals giving peaks at 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm in the solid ³¹ P-NMR spectrum. The present invention has been completed.
According to the present invention, the following glass ceramic and the manufacturing method thereof can be provided.
1. A glass ceramic containing a lithium (Li) element, a phosphorus (P) element, and a sulfur (S) element, wherein the solid ³¹ P-NMR spectrum of the glass ceramic is 90.9 ± 0.4 ppm and 86.5 ±. It has a peak due to crystals at a position of 0.4 ppm, the ratio (x _c ) of the crystals in the glass ceramic is 50 mol% to 100 mol%, and Li ₄ P ₂ S _{6 in the} glass ceramic is Glass ceramic which is 10 mol% or less.
2. A glass ceramic having a crystal ratio (x _c ) of 90 mol% to 100 mol% and a content ratio of lithium (Li) element, phosphorus (P) element, and sulfur (S) element of 7: 3: 11 in atomic ratio .
3. The solid ³¹ P-NMR spectrum is 10.9 or 2 which heat-treats a sulfide glass containing a seed crystal having peaks due to crystals at positions of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm. Glass ceramic manufacturing method.
4). 4. The method for producing a glass ceramic according to 3, wherein the sulfide glass containing the seed crystal is obtained by subjecting sulfide glass to a preheat treatment.
5. 4. The method for producing a glass ceramic according to 3, wherein the sulfide glass containing the seed crystal is a mixture in which 1-50 wt% of glass ceramic powder is blended with sulfide glass powder.

  According to the present invention, a glass ceramic having high ion conductivity can be provided.

The glass ceramic of the present invention contains a lithium (Li) element, a phosphorus (P) element, and a sulfur (S) element, and is characterized by satisfying the following conditions (1) to (3).
(1) Solid ³¹ P-NMR spectrum of glass ceramic has peaks due to crystals at 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm.
(2) The ratio (x _c ) of crystals that give rise to the peak of (1) in the glass ceramic is 50 mol% to 100 mol%.
(3) Li ₄ P ₂ S _{6 in the} glass ceramic is 10 mol% or less.

The two peaks of condition (1) are observed when a high ion conductive crystal component is present in the glass ceramic. Specifically, it is a peak caused by P ₂ S ₇ ^4- or PS ₄ ^3- in the crystal.

Condition (2) is used to define the ratio x _c of the crystal occupied in the glass ceramic.
When a high ion conductive crystal component is present in a predetermined amount or more, specifically 50 mol% or more in the glass ceramic, lithium ions move mainly through the high ion conductive crystal. Therefore, the lithium ion conductivity is improved as compared with the case of moving a non-crystalline portion (glass portion) in the glass ceramic or a crystal lattice (for example, P ₂ S ₆ ⁴⁻ ) that does not exhibit high ion conductivity. The ratio _{x c} is preferably 65mol% ~100mol%. More preferably, it is 90 mol%-100 mol%, Most preferably, it is 95 mol%-100 mol%.
The ratio x _c of the crystal can be controlled by adjusting the heat treatment time and temperature of the sulfide glass as a raw material.

Condition (3), the crystalline component to decrease the ionic conductivity in a glass ceramic, in particular, defines an content of Li ₄ P ₂ S _6. In the conventional sulfide-based glass ceramic, when the content ratio of the crystal that generates the peak in the condition (2) is increased, a crystal of Li ₄ P ₂ S ₆ is also generated. Therefore, the improvement in ionic conductivity is improved by Li ₄ P ₂ S. It was suppressed by ₆ crystals.
In the present invention, the content of Li ₄ P ₂ S ₆ crystals is suppressed to a predetermined amount or less, specifically 10 mol% or less, preferably 0 to 5 mol%, so that the ionic conductivity of the glass ceramic is improved. .

The measurement method of the content of each crystal is a solid-state ^{31 P-NMR} spectrum, the resonance lines observed in 70～120Ppm, separated into a Gaussian curve using non-linear least squares method, from the area ratio of each curve calculate. In the solid ³¹ P-NMR spectrum, the peaks at 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm are peaks due to the high ion conductive crystal, and the peak at 108.5 ± 0.6 ppm is It is a peak resulting from the crystal of Li ₄ P ₂ S ₆ . For details, refer to Japanese Patent Application No. 2005-356889.
Moreover, the glass ceramic whose content ratio of a lithium (Li) element, a phosphorus (P) element, and a sulfur (S) element is 7: 3: 11 by atomic ratio is preferable.

  The glass ceramic of this invention can be manufactured by heat-processing the sulfide type glass which contains each element of lithium (Li), phosphorus (P), and sulfur (S), and also contains a seed crystal, for example.

For example, Li ₂ S and P ₂ S ₅ can be used as the raw material for the sulfide glass.
As Li ₂ S, those commercially available without particular limitation can be used, but those having high purity are preferred. For example, the Li 2 _S obtained by reacting lithium hydroxide with hydrogen sulfide in an aprotic organic solvent, an organic solvent, those purified by washing with 100 ° C. or higher temperature can be preferably used.
Specifically, in the manufacturing method disclosed in Japanese Patent Laid-Open No. 7-330312, it is preferable to produce Li ₂ S, it is obtained by purification of the Li ₂ S by the method described in International Publication WO2005 / No. 40039 preferable.

Since this Li ₂ S manufacturing method can obtain high-purity lithium sulfide by simple means, the raw material cost of sulfide glass can be reduced. In addition, the above purification method is economically advantageous because it can remove sulfur oxide, lithium N-methylaminobutyrate (hereinafter referred to as LMAB), and the like, which are impurities contained in Li ₂ S, by a simple treatment. .
Incidentally, the total amount of sulfur oxides contained in the Li ₂ S, preferably 0.15 mass% or less, LMAB is preferably not more than 0.1 mass%.

P ₂ S ₅ can be used without particular limitation as long as it is industrially manufactured and sold. In place of P ₂ S ₅ , elemental phosphorus (P) and elemental sulfur (S) in a corresponding molar ratio can also be used. Simple phosphorus (P) and simple sulfur (S) can be used without particular limitation as long as they are industrially produced and sold.

The mixing ratio of the raw materials is not particularly limited and may be appropriately adjusted, but is preferably about Li ₂ S: P ₂ S ₅ = 7: 3 (molar ratio).

Examples of the method for producing sulfide glass include a melt quenching method and a mechanical milling method (hereinafter, sometimes referred to as MM method).
Specifically, in the case of the melt quenching method, P ₂ S ₅ and Li ₂ S mixed in a predetermined amount in a mortar and pelletized are placed in a carbon-coated quartz tube and vacuum sealed. After reacting at a predetermined reaction temperature, the glass is put into ice and quenched to obtain a sulfide glass.
The reaction temperature at this time is preferably 400 ° C to 1000 ° C, more preferably 800 ° C to 900 ° C.
Moreover, reaction time becomes like this. Preferably it is 0.1 to 12 hours, More preferably, it is 1 to 12 hours.

Further, in the case of the MM method, sulfide glass is obtained by mixing a predetermined amount of P ₂ S ₅ and Li ₂ S in a mortar and reacting for a predetermined time by a mechanical milling method.
In the MM method, it is preferable to use a ball mill. Specifically, it is preferable to use a planetary ball mill. In the planetary ball mill, since the base plate revolves while the pot rotates, very high impact energy can be generated efficiently.
As conditions for the MM method, for example, when a planetary ball mill is used, the rotational speed is set to several tens to several hundreds of revolutions / minute, and the treatment may be performed for 0.5 hours to 100 hours.
Although specific examples of the sulfide glass by the melt quenching method and the MM method have been described above, manufacturing conditions such as temperature conditions and processing time can be appropriately adjusted according to the equipment used.

  Examples of a method for producing a sulfide glass containing a seed crystal include the following methods (1) and (2).

(1) Method of generating seed crystal by pre-heat treatment of sulfide glass manufactured by the above method In this method, a seed crystal is generated by pre-heat treatment of sulfide glass. In the past, glass ceramics were produced by heat-treating sulfide glass. However, in this method, prior to heat treatment for converting to glass ceramic (referred to as main heat treatment), pre-heat treatment of sulfide glass is performed in advance. It is used for heat treatment. A seed crystal can be generated in the sulfide glass by the preliminary heat treatment.
The heating temperature in the preliminary heat treatment is 190 ° C to 280 ° C, preferably 200 ° C to 260 ° C. The treatment time is 10 minutes to 10 days, preferably 30 minutes to 10 days.
After the preliminary heat treatment, the heat treatment is performed after cooling to room temperature.

In the sulfide glass containing a seed crystal obtained by the preliminary heat treatment, the presence of the seed crystal can be confirmed by a solid ³¹ P-NMR spectrum. That is, it can be confirmed by the peaks caused by the crystals at the positions of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm. The content of seed crystals in the sulfide glass is 1 mol% to 50 mol%, preferably 5 mol% to 30 mol%.

(2) Method of blending powder of sulfide glass with powder of glass ceramic as crystal part to 1 to 50 wt%, preferably 5 to 30 wt% A predetermined amount of glass ceramic powder is added as a seed crystal.
As the glass ceramic to be added, a heat-treated sulfide glass can be used.
The heating temperature during the heat treatment is preferably 190 ° C to 260 ° C. The treatment time is preferably 30 minutes to 10 days.

The glass ceramic to be added has peaks due to crystals at positions of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm in the solid ³¹ P-NMR spectrum, and the proportion of crystals in the glass ceramic _{(x c)} is intended preferably 20mol% ~100mol%. By adding such a glass ceramic, it is possible to further increase the preferred crystal ratio (x _c ) in the obtained glass ceramic.

Subsequently, the above-described sulfide glass containing the seed crystal is heat-treated at a predetermined temperature (main heat treatment) to produce the glass ceramic of the present invention.
The heat treatment temperature for forming the glass ceramic is preferably 260 ° C to 400 ° C, more preferably 300 ° C to 360 ° C.
When the temperature is lower than 260 ° C., it may be difficult to obtain a crystal with high ion conductivity. When the temperature is higher than 400 ° C., a crystal with low ion conductivity may be generated.
The heat treatment time is preferably 30 minutes to 5 hours when the temperature is 260 ° C. or higher and 320 ° C. or lower. Moreover, in the case of the temperature higher than 320 degreeC and 400 degrees C or less, 0.1 minute-30 minutes are preferable.
If the heat treatment time is too short, it may be difficult to obtain crystals with high ion conductivity, and if it is too long, crystals with low ion conductivity may be formed.

The glass ceramic of the present invention is a nonflammable inorganic solid having a decomposition voltage of at least 10 V or more. In addition, while maintaining the characteristic that the lithium ion transport number is 1, it exhibits extremely high lithium ion conductivity of 10 ⁻³ S / cm level at room temperature. Therefore, it is extremely suitable as a material for a solid electrolyte of a lithium battery. Moreover, it is a solid electrolyte excellent in heat resistance.

Production Example 1
(1) Production of lithium sulfide (Li ₂ S) Lithium sulfide was produced according to the method of the first aspect (two-step method) of JP-A-7-330312. Specifically, N-methyl-2-pyrrolidone (NMP) 3326.4 g (33.6 mol) and lithium hydroxide 287.4 g (12 mol) were charged into a 10 liter autoclave equipped with a stirring blade, and 300 rpm, 130 The temperature was raised to ° C. After the temperature rise, hydrogen sulfide was blown into the liquid at a supply rate of 3 liters / minute for 2 hours. Subsequently, this reaction solution was heated in a nitrogen stream (200 cc / min) to dehydrosulfide a part of the reacted hydrogen sulfide. As the temperature increased, water produced as a by-product due to the reaction between hydrogen sulfide and lithium hydroxide started to evaporate, but this water was condensed by the condenser and extracted out of the system. While water was distilled out of the system, the temperature of the reaction solution rose, but when the temperature reached 180 ° C., the temperature increase was stopped and the temperature was kept constant. After the dehydrosulfurization reaction was completed (about 80 minutes), the reaction was completed to obtain lithium sulfide.

(2) Purification of lithium sulfide After decanting NMP in the 500 mL slurry reaction solution (NMP-lithium sulfide slurry) obtained in (1) above, 100 mL of dehydrated NMP was added and stirred at 105 ° C. for about 1 hour. did. NMP was decanted at that temperature. Further, 100 mL of NMP was added, stirred at 105 ° C. for about 1 hour, NMP was decanted at that temperature, and the same operation was repeated a total of 4 times. After completion of the decantation, lithium sulfide was dried at 230 ° C. (temperature higher than the boiling point of NMP) under a nitrogen stream for 3 hours under normal pressure. The impurity content in the obtained lithium sulfide was measured.

Incidentally, lithium sulfite _(Li 2 _SO 3), the content of each sulfur oxide lithium sulfate _(Li 2 SO ₄₎ and lithium thiosulfate _{(Li 2 S 2 O 3)} , and N- methylamino acid lithium (LMAB) Was quantified by ion chromatography. As a result, the total content of sulfur oxides was 0.13% by mass, and LMAB was 0.07% by mass.

Example 1
(1) Production of sulfide-based glass containing seed crystal (a) Production of sulfide-based glass Li ₂ S and P ₂ S ₅ (manufactured by Aldrich) produced in the above production example were used as starting materials. About 1 g of a mixture prepared at a molar ratio of 70:30 (Li: P: S = 7: 3: 11) and 10 alumina balls having a diameter of 10 mm were placed in a 45 mL alumina container, and a planetary ball mill (Fritchsch: Model No. P-7) In nitrogen, at room temperature (25 ° C.), with a rotational speed of 370 rpm and mechanical milling for 20 hours, a sulfide-based glass that is a white yellow powder is obtained. Obtained.

As a result of performing powder X-ray diffraction measurement on the obtained powder (CuKα: λ = 1.5418 、), this chart shows a broad shape peculiar to an amorphous body. It was confirmed that (amorphization).

(B) Production of glass ceramic (seed crystal) to be added A part of the sulfide glass produced in the above (a) was heat-treated at 220 ° C. for 10 days to obtain a glass ceramic.
With respect to this glass ceramic, a solid ³¹ P-NMR spectrum was measured, and a ratio (x _c ) of crystals observed at peaks of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm was calculated. As a result, _{x c} was 66 mol%.

The measurement conditions for the solid ³¹ P-NMR spectrum are as follows.
Apparatus: JNM-CMXP302 NMR apparatus manufactured by JEOL Ltd. Observation nucleus: ³¹ P
Observation frequency: 121.339 MHz
Measurement temperature: Room temperature Measurement method: MAS method Pulse sequence: Single pulse 90 ° Pulse width: 4 μs
Magic angle rotation speed: 8600Hz
Wait time until the next pulse application after FID measurement: 100-2000s
(Set to be more than 5 times the maximum spin-lattice relaxation time)
Number of integrations: 64 times Chemical shifts were determined using (NH ₄ ) ₂ HPO ₄ (chemical shift 1.33 ppm) as an external reference.
In order to prevent deterioration due to moisture in the air during sample filling, the sample was filled into a hermetic sample tube in a dry box in which dry nitrogen was continuously flowed.

Further, the crystallinity _{x c} for solid ³¹ P-NMR spectrum, the resonance lines observed in 70～120Ppm, separated into a Gaussian curve using non-linear least square method was calculated from the area ratio of each curve.

(C) Mixing step 90 wt% of the sulfide-based glass manufactured in (a) above and 10 wt% of the glass ceramic (seed crystal) manufactured in (b) above were mixed. This mixture was pulverized and mixed with a ball mill to obtain a sulfide-based glass containing seed crystals.

(2) Heat treatment step The sulfide-based glass containing the seed crystal produced in (c) of (1) above was treated at 300 ° C. for 2 hours to produce a glass ceramic.
With respect to this glass ceramic, a solid ³¹ P-NMR spectrum was measured, and a ratio (x _c ) of crystals observed at peaks of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm was calculated. As a result, _{x c} was 95 mol%. Moreover, the content rate of the crystal of Li ₄ P ₂ S ₆ (calculated from the peak of 108.5 ± 0.6 ppm) was 1 mol%.
When indexing was performed by JADE (software: MDI Inc.) from the powder X-ray diffraction result of this glass ceramic, it was confirmed that it was a triclinic Li ₇ P ₃ S ₁₁ crystal.
This glass ceramic was shaped into a pellet and its ionic conductivity (25 ° C., hereinafter the same) was measured and found to be 6 × 10 ⁻³ S / cm.

Example 2
(1) Manufacture of sulfide-based glass containing seed crystals The sulfide-based glass manufactured in (1) (a) of Example 1 is preheated at 200 ° C. for 2 hours to contain seed crystals. Sulfide glass was obtained.
For this seed crystal-containing sulfide-based glass, a solid ³¹ P-NMR spectrum was measured, and the ratio of crystals observed at peaks of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm (x _c ) was calculated. did. As a result, _{x c} was 10mol%.

(2) Heat treatment step The seed crystal-containing sulfide glass produced in (1) above was treated at 300 ° C. for 2 hours to produce a glass ceramic.
With respect to this glass ceramic, a solid ³¹ P-NMR spectrum was measured, and a ratio (x _c ) of crystals observed at peaks of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm was calculated. As a result, _{x c} was 95 mol%. The content of Li ₄ P ₂ S ₆ (calculated from the peak at 108.5 ± 0.6 ppm) was 1 mol%.
When indexing was performed by JADE (software: MDI Inc.) from the powder X-ray diffraction result of this glass ceramic, it was confirmed that it was a triclinic Li ₇ P ₃ S ₁₁ crystal.
This glass ceramic was shaped into a pellet and its ionic conductivity was measured and found to be 6 × 10 ⁻³ S / cm.

Comparative Example 1
The sulfide glass produced in (1) (a) of Example 1 was heat-treated at 200 ° C. for 3 hours to produce a glass ceramic.
With respect to this glass ceramic, a solid ³¹ P-NMR spectrum was measured, and a ratio (x _c ) of crystals observed at peaks of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm was calculated. As a result, _{x c} was 45 mol%. Moreover, the content rate (calculated from the peak of 108.5 ± 0.6 ppm) of Li ₄ P ₂ S ₆ was 0 mol%.
This glass ceramic was shaped into a pellet and its ionic conductivity was measured and found to be 6 × 10 ⁻⁴ S / cm.

Comparative Example 2
A glass ceramic was produced in the same manner as in Comparative Example 1 except that the heat treatment was performed at 340 ° C. for 40 minutes.
With respect to this glass ceramic, a solid ³¹ P-NMR spectrum was measured, and a ratio (x _c ) of crystals observed at peaks of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm was calculated. As a result, _{x c} was 60 mol%. The content of Li ₄ P ₂ S ₆ (calculated from the peak at 108.5 ± 0.6 ppm) was 15 mol%.
This glass ceramic was shaped into a pellet and its ionic conductivity was measured and found to be 7 × 10 ⁻⁴ S / cm.

The glass ceramic of the present invention is suitable for a solid electrolyte for a lithium secondary battery.
In addition, the all-solid-state lithium battery using the glass ceramic of the present invention is used in portable information terminals, portable electronic devices, small household electric power storage devices, motorcycles powered by motors, electric vehicles, hybrid electric vehicles, and the like. It can be used as a lithium secondary battery.

Claims (5)

A glass ceramic containing a lithium (Li) element, a phosphorus (P) element and a sulfur (S) element,
The solid ³¹ P-NMR spectrum of the glass ceramic has peaks due to crystals at the positions of 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm,
The ratio (x _c ) of the crystals in the glass ceramic is 65 mol% to 100 mol%,
Glass ceramic _Li 4 _P 2 _{S 6} occupied in the glass ceramic is less than 10 mol%. The ratio of the crystal _{(x c)} is 90mol% ~100mol%, lithium (Li) element content ratio of phosphorus (P) element and sulfur (S) element atomic ratio 7: 3:11 in a claim 2. The glass ceramic according to 1 . The sulfide glass containing a seed crystal having peaks due to crystals at positions 90.9 ± 0.4 ppm and 86.5 ± 0.4 ppm in the solid ³¹ P-NMR spectrum is heat-treated. The manufacturing method of the glass-ceramic of description.   The method for producing a glass ceramic according to claim 3, wherein the sulfide glass containing the seed crystal is obtained by subjecting sulfide glass to a preliminary heat treatment.   The method for producing a glass ceramic according to claim 3, wherein the sulfide glass containing the seed crystal is a mixture in which 1 to 50 wt% of a glass ceramic powder is blended with a sulfide glass powder.