JP2013030440A - Solid electrolyte and lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte with high conductivity including a sulfide-based solid electrolyte of an Li-P-S system and an Li-P-S-O system.SOLUTION: A solid electrolyte of the present invention includes a sulfide-based solid electrolyte represented by composition formula: LiPSO(0.01≤x≤1.42 and 0.01≤z≤1.55 ), and the sulfide-based solid electrolyte has peaks of X-ray diffraction around diffraction angles (2θ/CuKα) of at least 12.9°, 14.4°, 15.2°, 18.0°, 20.5-22.0°, 24.2°, 25.0°, 28.0° and 30.6°. Another solid electrolyte of the present invention includes a sulfide-based solid electrolyte represented by composition formula: LiPS(0.06≤x≤0.08), and the sulfide-based solid electrolyte has peaks of X-ray diffraction around diffraction angles (2θ/CuKα) of at least 13.3°, 14.75°, 15.3°, 18.0°, 21.0-21.7°, 24.2°, 25.4°, 28.4° and 30.6°.

Description

  The present invention relates to a solid electrolyte including a sulfide-based solid electrolyte and a lithium battery including the solid electrolyte.

  2. Description of the Related Art In recent years, as information electronic devices such as mobile phones, notebook personal computers, and tablet personal computers have been improved in performance, high-performance storage batteries for driving these information electronic devices for a long time with a single charge are desired. In addition, hybrid vehicles and electric vehicles are rapidly spreading due to the reduction of greenhouse gases and rising gasoline prices, and high output and high capacity storage batteries for driving the motors mounted on these vehicles are desired. Yes. Currently, lithium batteries are mainly used as batteries that satisfy such requirements.

  Currently, flammable organic solvents are used as electrolytes for lithium batteries because of their high ionic conductivity, wide potential window, and low cost. However, since the energy density of the lithium battery is very high, it is desirable to use a flame retardant material as the electrolyte of the lithium battery in order to further improve the safety of the lithium battery. Inorganic solid electrolytes are attracting attention as such flame-retardant materials.

Inorganic solid electrolytes include amorphous or crystalline inorganic electrolytes such as nitrides, oxides, and sulfides. As a sulfide-based glass solid electrolyte, a three-component glassy solid electrolyte of lithium sulfide, germanium disulfide and lithium iodide (Patent Document 1), or a lithium ion conductive sulfide represented by the general formula Li ₂ -X A solid electrolyte (Patent Document 2) in which lithium phosphate is present in glass is known. These ionic conductivities are at the 10 ⁻⁴ S / cm level. Furthermore, a crystalline material having a basic structure of SiS ₄ , PO ₄ , PS ₄ , and PN ₄ tetrahedrons is searched for aiming at high ion conductivity as a crystalline material, not amorphous, and Li ₂ S—GeS ₂ —Ga. _An ion conductivity of 10 ⁻⁵ to 10 ⁻⁴ S / cm has been reported for a ₂ S ₃ solid electrolyte (Patent Document 3).

Among solid electrolytes, a sulfide solid electrolyte called thio-LISICON (LIthium SuperIonic CONductor) is known as a solid electrolyte having a very high lithium ion conductivity. Among them, the ion conductivity of Li _3.25 Ge _0.25 P _0.75 S ₄ is 2.2 × 10 ⁻³ S / cm, which is the highest among the sulfide-based thiolysicons (see, for example, Non-Patent Document 1). In addition, Li-PS-based and Li-PS-O-based sulfide-based solid electrolytes have been reported as sulfide-based thiolysicons that do not contain metal elements other than lithium in order to improve electrolyte stability. (For example, see Non-Patent Documents 2 and 3).

Japanese Examined Patent Publication No. 6-70906 Japanese Patent No. 3184517 Japanese Patent No. 3744665

R. Kanno and M. Murayama, "Lithium Ionic Conductor Thio-LISICON The Li2S-GeS2-P2S5 System", Journal of The Electrochemical Society, 148 (7), A742-A746 (2001) M. Murayama, N. Sonoyama, A. Yamada and R. Kanno, "Material design of new lithium ionic conductor, Thio-LISICON, in the Li2S-P2S5 System", Solid State Ionics, 170, 173-180 (2004) K. Takeda, M Osada, N. Ohta, T. Inada, A. Kajiyama, H. Sasaki, S. Kondo, M. Watanabe and T Sasaki, "Lithium ion conductive oxysulfide, Li3PO4-Li3PS4", Solid State Ionics, 176 , 2355-2359 (2005)

  However, the conductivity of these sulfide-based solid electrolytes is still lower than the conductivity of combustible organic solvents currently used. The present invention has high conductivity among Li-PS-based and Li-PS-O-based sulfide-based solid electrolytes containing no metal element other than lithium in order to improve the stability of the electrolyte. The aim is to develop new solid electrolytes that may have.

The present invention employs the following configuration in order to solve the above problems.
(1) The solid electrolyte of the invention of claim 1 includes a sulfide-based solid electrolyte represented by a composition formula Li _{3 + 5x} P _1-x S _4−z O _z , and 0.01 ≦ x ≦ 1.42. Yes, and 0.01 ≦ z ≦ 1.55.
(2) The invention according to claim 2 is the solid electrolyte according to claim 1, wherein 0.02 ≦ x ≦ 1.11 and 0.20 ≦ z ≦ 1.20.
(3) The invention according to claim 3 is the solid electrolyte according to claim 2, further satisfying 0.03 ≦ x ≦ 0.09 and satisfying 0.25 ≦ z ≦ 1.00.
(4) The invention of claim 4 is the solid electrolyte according to any one of claims 1 to 3, wherein the sulfide-based solid electrolyte is a powder of Cu-Kα rays having an X-ray wavelength of 1.5418 angstroms. In X-ray diffraction measurement, at least 12.9 °, 14.4 °, 15.2 °, 18.0 °, 20.5 to 22.0 °, 24.2 °, 25.0 °, 28.0 It has a characteristic peak near the diffraction angle (2θ) of 30.6 °.
(5) The solid electrolyte of the invention of claim 5 includes a sulfide-based solid electrolyte represented by a composition formula Li _{3 + 5x} P _1-x S ₄ , wherein 0.06 ≦ x ≦ 0.08, In the powder X-ray diffraction measurement by Cu-Kα ray having an X-ray wavelength of 1.5418 Å, the system solid electrolyte is at least 13.3 °, 14.75 °, 15.3 °, 18.0 °, 21.0 It has characteristic peaks in the vicinity of diffraction angles (2θ) of ˜21.7 °, 24.2 °, 25.4 °, 28.4 °, and 30.6 °.
(6) The invention of claim 6 is the solid electrolyte according to any one of claims 1 to 5, and does not include Li ₂ S and γ-Li ₃ PS ₄ .
(7) A lithium battery according to a seventh aspect of the invention includes the solid electrolyte according to any one of the first to sixth aspects.

  ADVANTAGE OF THE INVENTION According to this invention, the solid electrolyte with high electroconductivity containing the sulfide type solid electrolyte of a Li-PS system and a Li-PS-O system can be obtained.

FIG. 1 is a Li ₂ S—P ₂ S ₅ —P ₂ O ₅ -based ternary composition diagram showing the composition range of the sulfide-based solid electrolyte of the present invention. FIG. 2 is a schematic view showing a cross section of a lithium battery in one embodiment of the present invention. FIG. 3 is a ternary composition diagram of the Li ₂ S—P ₂ S ₅ —P ₂ O ₅ system showing the composition ranges of Examples, Comparative Examples, and Reference Examples. FIG. 4 is an X-ray diffraction pattern of a sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. along the line ₁ . FIG. 5 is an X-ray diffraction pattern of a sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. along the line 2. FIG. 6 is an X-ray diffraction pattern of a sulfide-based solid electrolyte of a sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4-z O _z synthesized at 700 ° C. along the line _3. . FIG. 7 is an X-ray diffraction pattern of a sulfide-based solid electrolyte of a sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4-z O _z synthesized at 700 ° C. along the line _4. . FIG. 8 is an X-ray diffraction pattern of a sulfide-based solid electrolyte of a sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4-z O _z synthesized at 900 ° C. along the line _1. . FIG. 9 shows a composition formula Li _{3 + 5x} P ₁₋ which was synthesized at 900 ° C. and annealed at 530 ° C. or 700 ° C. when x was 0.07 and z was 0.40. ₂ is an X-ray diffraction pattern of a sulfide-based solid electrolyte of _x S _4−z O _z . FIG. 10 is an X-ray diffraction pattern of a sulfide-based solid electrolyte having a composition formula of Li _{3 + 5x} P _1-x S ₄ synthesized at 615 ° C. or 700 ° C. when the value of x is 0.07. . FIG. 11 is a graph showing the electrical conductivity of the sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. along the line ₁ . FIG. 12 is a graph showing the conductivity of a sulfide-based solid electrolyte having a composition of Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. along the line ₂ . FIG. 13 is a graph showing the electrical conductivity of a sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. along the line ₃ . FIG. 14 is a graph showing the electrical conductivity of a sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. along the line ₄ . FIG. 15 is a graph showing the electrical conductivity of a sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 900 ° C. along the line ₁ . FIG. 16 shows a sulfide-based solid of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 900 ° C., where the value of x is 0.07 and the value of z is 0.40. It is a figure which shows the DTA curve of electrolyte. FIG. 17 shows a sulfide-based solid of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C., where the value of x is 0.07 and the value of z is 0.50. It is a figure which shows the CV curve of electrolyte.

As a result of intensive studies, the inventor includes a sulfide-based solid electrolyte represented by a composition formula Li _{3 + 5x} P _1−x S _4−z O _z , and 0.01 ≦ x ≦ 1.42. Including a conductivity of a solid electrolyte _satisfying 0.01 ≦ z ≦ 1.55 and a sulfide-based solid electrolyte represented by a composition formula Li _{3 + 5x} P _1-x S ₄ , and 0.06 ≦ x ≦ 0.08 In the powder X-ray diffraction measurement by Cu-Kα ray having an X-ray wavelength of 1.5418 Å, the sulfide-based solid electrolyte is at least 13.3 °, 14.75 °, 15.3 °, 18. The conductivity of the solid electrolyte having characteristic peaks in the vicinity of diffraction angles (2θ) of 0 °, 21.0 to 21.7 °, 24.2 °, 25.4 °, 28.4 °, 30.6 ° I found it high and came up with the present invention. Hereinafter, although the detail of this invention is demonstrated, this invention is not limited to the following embodiment.

(Sulfide-based solid electrolyte)
The sulfide-based solid electrolyte of the present invention will be described with reference to the ternary composition diagram of the Li ₂ S—P ₂ S ₅ —P ₂ O ₅ system in FIG. In FIG. 1, “●” indicates the composition of Examples described later, “■” indicates the composition of Comparative Examples described later, and “▲” indicates the composition of Non-Patent Document 3 described above. 2 shows the composition of a Li—P—S—O-based sulfide solid electrolyte.

The sulfide-based solid electrolyte of the present invention is represented by Li _{3 + 5x} P _1−x S _4−z O _z , 0.01 ≦ x ≦ 1.42, and 0.01 ≦ z ≦ 1.55. It is preferable that When the value of x is smaller than 0.01, the ratio of Li ₇ PS ₆ and γ-Li ₃ PS ₄ contained in the sulfide-based solid electrolyte is increased, and the conductivity of the solid electrolyte may be decreased, If the value of x is larger than 1.55, the proportion of Li ₂ S contained in the sulfide-based solid electrolyte increases, and the conductivity of the solid electrolyte may decrease. When the value of z is smaller than 0.01, the ratio of Li ₇ PS ₆ , β-Li ₃ PS ₄ and γ-Li ₃ PS ₄ contained in the sulfide-based solid electrolyte increases, and the solid electrolyte In some cases, the electrical conductivity decreases, and when the value of z is greater than 1.55, the ratio of Li ₇ PS ₆ contained in the sulfide-based solid electrolyte increases, and the electrical conductivity of the solid electrolyte may decrease. is there. When the values of x and z are within the range of 0.01 ≦ x ≦ 1.42 and 0.01 ≦ z ≦ 1.55, a new phase (PN: described later) contained in the sulfide-based solid electrolyte is included. The ratio of (New Phase) increases and the conductivity of the solid electrolyte increases.

In the ternary composition diagram of the Li ₂ S—P ₂ S ₅ —P ₂ O ₅ system in FIG. 1, the ranges of 0.01 ≦ x ≦ 1.42 and 0.01 ≦ z ≦ 1.55 , B, C, and D.

When the sulfide-based solid electrolyte of the present invention is represented by Li _{3 + 5x} P _1−x S _4−z O _z , 0.02 ≦ x ≦ 1.11 and 0.20 ≦ z ≦ 1. More preferably, it is 20. When the values of x and z are 0.02 ≦ x ≦ 1.11 and 0.20 ≦ z ≦ 1.20, the ratio of Li ₂ S and γ-Li ₃ PS ₄ decreases and the sulfide system The ratio of the below-mentioned novel phase (PN) contained in the solid electrolyte is further increased, and the conductivity of the solid electrolyte is increased. In the ternary composition diagram of the Li ₂ S—P ₂ S ₅ —P ₂ O ₅ system in FIG. 1, the ranges of 0.02 ≦ x ≦ 1.11 and 0.20 ≦ z ≦ 1.20 , F, G, and H.

When the sulfide-based solid electrolyte of the present invention is expressed as Li _{3 + 5x} P _1-x S _4−z O _z , 0.03 ≦ x ≦ 0.09 and 0.25 ≦ z ≦ 1. More preferably, it is 00. When the values of x and z are 0.03 ≦ x ≦ 0.09 and 0.25 ≦ z ≦ 1.00, the ratio of Li ₂ S and γ-Li ₃ PS ₄ decreases and the sulfide system The ratio of the below-mentioned novel phase (PN) contained in the solid electrolyte is further increased, and the conductivity of the solid electrolyte is increased. In the ternary composition diagram of the Li ₂ S—P ₂ S ₅ —P ₂ O ₅ system in FIG. 1, the ranges of 0.03 ≦ x ≦ 0.09 and 0.25 ≦ z ≦ 1.00 are represented by the symbol I , J, K, and L.

The conductivity is about 1 × 10 ⁻⁴ S / cm or more and the Li—P—S—O-based sulfide solid electrolyte described in Non-Patent Document 3 (the maximum value of the conductivity is 7.3 × 10 ^{− 5} S / cm), the sulfide-based solid electrolyte of the present invention is represented by Li _{3 + 5x} P _1-x S _4-z O _z , and when x = 0.07, It is preferable that 0.20 ≦ z ≦ 1.00. When z = 50, 0.03 ≦ x ≦ 0.07 is preferable.

Since the ratio of Li ₂ S and γ-Li ₃ PS ₄ is low and the conductivity of the sulfide-based solid electrolyte can be increased, the sulfide-based solid electrolyte of the present invention has Li _{3 + 5x} P _1-x S. It is shown in _4-z O z, if an x = 0.07, further preferably 0.40 ≦ z ≦ 0.60.

The new phase (PN) is at least 12.9 °, 14.4 °, 15.2 °, 18.0 °, 20 in the powder X-ray diffraction measurement by Cu-Kα ray having an X-ray wavelength of 1.5418 Å. It has characteristic peaks in the vicinity of diffraction angles (2θ) of 0.5 to 22.0 °, 24.2 °, 25.0 °, 28.0 °, and 30.6 °. Therefore, the sulfide-based solid electrolyte of the present invention has the above-mentioned characteristic peak in powder X-ray diffraction measurement with Cu-Kα rays having an X-ray wavelength of 1.5418 angstroms. The new layer (PN) is presumed to have a crystal structure similar to Li _3.33 Ge _0.33 P _0.66 S ₄ from the diffraction angle (2θ) of its characteristic peak.

Further, another sulfide-based solid electrolyte of the present invention does not contain P ₂ O ₅ , is represented by Li _{3 + 5x} P _1-x S ₄ , 0.06 ≦ x ≦ 0.08, and X-ray In powder X-ray diffraction measurement using Cu—Kα ray at a wavelength of 1.5418 angstrom, at least 13.3 °, 14.75 °, 15.3 °, 18.0 °, 21.0 to 21.7 °, 24 It is preferable to have characteristic peaks in the vicinity of diffraction angles (2θ) of .2 °, 25.4 °, 28.4 °, and 30.6 °. That is, the sulfide-based solid electrolyte of the present invention is represented by Li _{3 + 5x} P _1-x S ₄ , 0.06 ≦ x ≦ 0.08, and preferably includes the novel layer (PN). When the value of x is 0.06 ≦ x ≦ 0.08, the ratio of the new phase (PN) contained in the sulfide-based solid electrolyte is further increased, and the conductivity of the solid electrolyte is increased. In the ternary composition diagram of the Li ₂ S—P ₂ S ₅ —P ₂ O ₅ system in FIG. 1, the range of 0.06 ≦ x ≦ 0.08 is between the line segments indicated by the symbols M and N. It is a range.

The sulfide-based solid electrolyte of the present invention preferably does not contain Li ₂ S and γ-Li ₃ PS ₄ . That is, in the sulfide-based solid electrolyte of the present invention, it is preferable that Li ₂ S and γ-Li ₃ PS ₄ are not detected in powder X-ray diffraction measurement with Cu-Kα rays having an X-ray wavelength of 1.5418 angstroms. This is because if the sulfide-based solid electrolyte contains Li ₂ S and γ-Li ₃ PS ₄ , the conductivity of the solid electrolyte may be reduced.

  The solid electrolyte of the present invention may include other solid electrolytes in addition to the above-described sulfide-based solid electrolyte as long as the high conductivity due to the above-described sulfide-based solid electrolyte is not inhibited.

  In this specification, the conductivity is the ionic conductivity of Li ions. The ionic conductivity of the sulfide-based solid electrolyte is measured by, for example, a known alternating current impedance method.

The solid electrolyte of the present invention can be obtained, for example, by mixing raw materials such as Li ₂ S, P ₂ S ₅ , P ₂ O ₅ , LiPO ₄ and then firing at 650 to 1000 ° C. After firing at 650 to 1000 ° C., the fired sample may be quenched using water or the like. Further, after firing at 650 to 1000 ° C., the fired sample may be slowly cooled to room temperature. A sample fired at 650 to 1000 ° C. may be further annealed at 500 to 800 ° C.

(Lithium battery)
The lithium battery of the present invention will be described with reference to FIG. FIG. 2 is a schematic view showing a cross section of a lithium battery in one embodiment of the present invention. A lithium battery 1 according to an embodiment of the present invention includes a solid electrolyte 2, a negative electrode 3, a positive electrode 4, a current collector 5, and an insulating part 6 according to the present invention. The material used for the negative electrode 3 will not be specifically limited if it is the material conventionally used as the negative electrode of a lithium battery. For example, Li, In, C, or the like can be used as a material used for the negative electrode 3. The material used for the positive electrode 4 is not particularly limited as long as it is a material conventionally used as a positive electrode of a lithium battery. For example, LiCoO ₂ , TiS, LiMn ₂ O ₄ or the like can be used as the material used for the positive electrode 4. The material used for the current collector 5 and the insulating part 6 is not particularly limited as long as it is a material conventionally used as a current collector and an insulating part of a lithium battery. For example, stainless steel or the like can be used as a material used for the current collector 5, and polycarbonate or the like can be used as a material used for the insulating portion 6. In addition, although the lithium battery 1 in one Embodiment of this invention mentioned above is a bulk type lithium battery, the lithium battery comprised by a thin film may be sufficient as the lithium battery of this invention.

  Hereinafter, the present invention will be described in more detail with reference to examples. Note that the following examples do not limit the present invention.

(Sample preparation)
Starting materials Li ₂ S, P ₂ S ₅ and P ₂ O ₅ were weighed in a glove box in an argon atmosphere and mixed for 10 minutes using an agate mortar to prepare a mixed sample. However, in Example 20 and Example 21 described later, the starting materials were mixed using a vibration mill. The sample was put in a pelleter, and a pressure of 20 MPa was applied to the pelleter using a uniaxial press machine to form a φ13 mm pellet. The pellet was put into a carbon-coated quartz tube, and the quartz tube was sealed at an internal pressure of 10 Pa. Then, the quartz tube containing the pellets was heated to 615 ° C., 700 ° C. or 900 ° C. at 5 ° C./min, and held for 1 hour. And the quartz tube hold | maintained at the said temperature for 1 hour was thrown into water, and the baked pellet was rapidly cooled and the sample was produced. Some samples were quenched and then annealed at 530 ° C. or 700 ° C. for 1 hour. A plurality of samples having different values of x and z in the composition formula Li _{3 + 5x} P _1-x S _4−z O _z were prepared.

(Powder X-ray diffraction measurement)
In order to identify the crystals contained in the prepared sample, powder X-ray diffraction measurement was performed using a powder X-ray diffraction apparatus Ulima-IV (manufactured by Rigaku Corporation) and Smart Lab (manufactured by Rigaku Corporation). For powder X-ray diffraction measurement, Cu-Kα rays having an X-ray wavelength of 1.5418 angstroms were used. Powder X-ray diffraction measurement was performed at a diffraction angle (2θ) in the range of 10 to 100 °.

(Measurement of conductivity)
After putting the pulverized sample in a room temperature cell, a pressure of 5 MPa was applied to the room temperature cell to produce a pellet. After gold powder was dispersed on both sides of the pellet, a pressure of 15 MPa was applied to the pellet to form electrodes on both sides of the pellet to prepare a measurement sample. An impedance / gain phase analyzer Solatron 1260 (manufactured by Solartron) was used to measure the conductivity of the measurement sample. AC impedance measurement was performed under the conditions of a measurement range of 1 Hz to 10 MHz, a measurement temperature of 25 ° C., an AC voltage of 50 to 100 mV, and an integration time of 2 seconds, and the conductivity of the sample was measured.

(Measurement of thermal stability)
In order to examine the thermal stability of the sample, differential thermal measurement was performed using a differential type differential thermal balance Thermo Plus EVO II TG8120 (manufactured by Rigaku Corporation). Sample preparation for measurement was performed in a glove box in an argon atmosphere. A sample for measurement was prepared by packing 10 mg of the ground sample in a SUS pan and sealing it at 10 MPa. Further, Al ₂ O ₃ was packed in a SUS pan and sealed at 10 MPa to prepare a reference sample. The sample for measurement was heated up to 700 ° C. or 900 ° C. at 10 ° C./min, and then the temperature was lowered to room temperature at 10 ° C./min.

(Cyclic voltammetry)
To examine the electrochemical stability of the sample, cyclic voltammetry (CV) of the sample was measured. For the measurement of CV, an Au electrode and a Li electrode were used.

Results (sample preparation)
Samples of Examples and Comparative Examples were prepared along Lines 1 to 4 in the ternary composition diagram of the Li ₂ S—P ₂ S ₅ —P ₂ O ₅ system in FIG. Line ₁ is a line segment when the value of z is changed with the value of x being 0.07 in the composition formula Li _{3 + 5x} P _1−x S _4−z O _z . Line2, in the composition formula _{Li 3 + 5x P 1-x} S 4-z O z, as 0.40 the value of z, which is a line segment when changing the value of x. Line ₃ is a line segment when the value of x is changed with the value of z being 0.50 in the composition formula Li _{3 + 5x} P _1−x S _4−z O _z . Line ₄ is a line segment when the value of x is changed with the value of z being 0.80 in the composition formula Li _{3 + 5x} P _1−x S _4−z O _z . As a reference example, the sample described in Non-Patent Document 3 is indicated by “▲”. The composition of the prepared sample described in Non-Patent Document 3 is in line with Line5. Line ₅ is a line segment when the value of x is changed with the value of x being 0 in the composition formula Li _{3 + 5x} P _1−x S _4−z O _z . As in FIG. 1, “●” in FIG. 3 indicates the composition of the example, and “■” indicates the composition of the comparative example. Table 1 shows the lines on the ternary composition diagram to which the prepared samples and reference examples belong, the synthesis temperature, the values of x and z in the composition formula Li _{3 + 5x} P _1−x S _4−z O _z, and the annealing temperature. Shown in

(Powder X-ray diffraction measurement)
FIG. 4 shows the result of the powder X-ray diffraction measurement of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. with the composition along Line 1. In the examples, the value of x is 0.07, and the values of z are 0.00, 0.20, 0.30, 0.40, 0.50, 0.60, 0.80 and 1. 00. FIG. 4 also shows a rhombus mark indicating the diffraction angle of the characteristic peak of the new phase, the characteristic peak of Li ₇ PS ₆ , so that the crystal identified by powder X-ray diffraction measurement can be recognized. bars showing the diffraction angles, illustrating the γ-Li ₃ PS ₄ X-ray diffraction pattern, β-Li ₃ PS ₄ X-ray diffraction pattern of X-ray diffraction pattern and β-Li ₃ PO _4.

In Examples 1 to 8 (z = 0.00 to 1.00), Li ₇ PS ₆ was detected. In the case of Example 1 (z = 0.00), in addition to β-Li ₃ PS ₄ and γ-Li ₃ PS ₄ , 12.9 °, 14.4 °, 15.2 °, 18.0 °, A new phase with characteristic peaks at diffraction angles (2θ) of 20.5 to 22.0 °, 24.2 °, 25.0 °, 28.0 ° and 30.6 ° was detected. In Example 2 (z = 0.20), β-Li ₃ PS ₄ was not detected, and γ-Li ₃ PS ₄ became the main phase. In Examples 3 and 4 (z = 0.30 and 0.40), γ-Li ₃ PS ₄ was still present. In Examples 5 and 6 (z = 0.50 and 0.60), γ-Li ₃ PS ₄ was not detected, and the only crystals detected were the new phase and Li ₇ PS ₆ . In Example 5 (z = 0.50), the solid electrolyte closest to the compound having a new phase as a single layer was obtained. The diffraction angle (2θ) of the characteristic peak of the new phase shifted to the low angle side or the high angle side as the value of z increased from 0.40. The diffraction angle (2θ) of the characteristic peak of the new phase was shifted to the lowest angle side in Example 6 (z = 0.60), and the diffraction angle (2θ) was shifted to the highest angle side in Example 7 (z = 0.80). In Example 5 (z = 0.50), the ratio of the new phase was the highest. In Examples 7 and 8 (z = 0.80 and 1.00), β-Li ₃ PO ₄ was detected in addition to the new phase. In Examples 7 and 8 (z = 0.80 and 1.00), the ratio of Li ₇ PS ₆ and β-Li ₃ PO ₄ was high.

FIG. 5 shows the result of the powder X-ray diffraction measurement of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. with the composition along Line 2. The values of x in the examples were 0.07 and 0.105, respectively, and the value of z was 0.40. FIG. 5 also shows a rhombus mark indicating the diffraction angle of the characteristic peak of the novel phase and the characteristic peak of Li ₇ PS ₆ so that the crystal identified by powder X-ray diffraction measurement can be recognized. The bar line which shows a diffraction angle is shown. The diffraction angle of the strongest characteristic peak of Li ₂ S was also shown.

The main phases of Examples 4 and 9 (x = 0.07 and 0.105) were new phases. As the value of x increased, the proportion of Li ₇ PS ₆ increased. In Example 9 (x = 0.105), a characteristic peak of Li ₂ S as a starting material was detected. Therefore, if the value of x increases to about 0.1 regardless of the amount of oxygen, there is a possibility that the solid solution limit of Li ₂ S will be reached.

FIG. 6 shows the result of the powder X-ray diffraction measurement of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. with the composition along Line 3. The values of x in the examples were 0.03, 0.05, 0.07, and 0.08, respectively, and the value of z was 0.50. FIG. 6 also shows a rhombus mark indicating the diffraction angle of the characteristic peak of the novel phase, the characteristic peak of Li ₇ PS ₆ , so that the crystal identified by powder X-ray diffraction measurement can be recognized. bars having a diffraction angle and an X-ray diffraction pattern of γ-Li ₃ PS _4.

In all Examples 10, 11 and 5 (x = 0.03, 0.05 and 0.07), the main phase was a new phase. Li ₇ PS ₆ was detected in all Examples 10, 11 and 5 (x = 0.03, 0.05, and 0.07). In Example 10 (x = 0.03), the proportion of γ-Li ₃ PS ₄ was high, but the proportion of γ-Li ₃ PS ₄ decreased as the value of x increased from 0.03. As the value of x increased from 0.03 to 0.05, the diffraction angle (2θ) of the characteristic peak of the new phase shifted to the higher angle side. From this, it can be seen that when the value of x increases from 0.03 to 0.05, the lattice of the new phase is reduced. However, even when the value of x increased from 0.05 to 0.07, the diffraction angle (2θ) of the characteristic peak of the new phase did not change. Further, when the value of x increased from 0.05 to 0.07, the ratio of Li ₇ PS ₆ and γ-Li ₃ PS ₄ decreased.

FIG. 7 shows the result of the powder X-ray diffraction measurement of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1−x S _4−z O _z synthesized at 700 ° C. with the composition along Line 4. The values of x in Examples and Comparative Examples were 0.03, 0.05, 0.07, 0.09, and 0.333, respectively, and the value of z was 0.80. FIG. 7 also shows a rhombus mark indicating the diffraction angle of the characteristic peak of the novel phase, the characteristic peak of Li ₇ PS ₆ , so that the crystal identified by powder X-ray diffraction measurement can be recognized. bars showing the diffraction angle, an X-ray diffraction pattern of γ-Li ₃ PS ₄ X-ray diffraction pattern and β-Li ₃ PO _4.

Li ₇ PS ₆ and β-Li in all Examples 12, 13, 7 and 14 (x = 0.03, 0.05, 0.07 and 0.09) and Comparative Example 1 (x = 0.333) ₃ PO ₄ was detected. In Examples 12, 13, 7 and 14 (x = 0.03, 0.05, 0.07 and 0.09), the main phase was a new phase. In Examples 12, 13, and 14 (x = 0.03, 0.05, and 0.09), γ-Li ₃ PS ₄ was detected. In Example 14 (x = 0.09) and Comparative Example 1 (x = 0.333), Li ₂ S as a starting material was detected. From this, it is surmised that the solid solution limit of Li ₂ S exists in the range where the value of x is larger than 0.07 and 0.09 or less on Line4.

FIG. 8 shows the result of the powder X-ray diffraction measurement of the sulfide solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 900 ° C. with the composition along Line 1. In the examples, the value of x was 0.07, and the values of z were 0.20, 0.40, and 0.80, respectively. FIG. 8 also shows a rhombus mark indicating the diffraction angle of the characteristic peak of the new phase, the characteristic peak of Li ₇ PS ₆ , so that the crystal identified by powder X-ray diffraction measurement can be recognized. bars having a diffraction angle and an X-ray diffraction pattern of β-Li ₃ PS _4.

The main phase of all Examples 15-17 (z = 0.20, 0.40 and 0.80) was a novel phase. In Example 16 (z = 0.40), the proportion of β-Li ₃ PS ₄ was high. In Examples 15 and 17 (z = 0.20 and 0.80), the proportion of β-Li ₃ PS ₄ Was very small. As the value of z increased, the proportion of Li ₇ PS ₆ decreased, and when the value of z reached 0.80 (Example 17), Li ₇ PS ₆ was not detected. As the value of z increased from 0.40 to 0.80, the diffraction angle (2θ) of the characteristic peak of the new phase shifted to the higher angle side.

The compositional formula Li _{3 + 5x} P _1-x S ₄₋ was synthesized at 900 ° C. and annealed at 530 ° C. or 700 ° C. when x was 0.07 and z was 0.40. the results of the _z O _z powder X-ray diffraction measurement of the sulfide-based solid electrolyte shown in Fig. FIG. 9 also shows a rhombus mark indicating the diffraction angle of the characteristic peak of the novel phase, the characteristic peak of Li ₇ PS ₆ , so that the crystal identified by powder X-ray diffraction measurement can be recognized. bars having a diffraction angle and an X-ray diffraction pattern of β-Li ₃ PS _4. Furthermore, in order to be able to compare with the result of the powder X-ray diffraction measurement of the sulfide-based solid electrolyte having the same composition before the annealing treatment, the composition formula Li _{3 + 5x} P _1-x S of the same composition synthesized at 900 ° C. The result of the powder X-ray diffraction measurement of the sulfide type solid electrolyte of No. ₄ was also shown.

By performing the annealing treatment, the main phase of Examples 18 and 19 (annealing temperatures = 530 ° C. and 700 ° C.) became β-Li ₃ PS ₄ , and the ratio of the new phase was significantly reduced.

The composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 615 ° C. or 700 ° C. of the composition when the value of x is 0.07 and the value of z is 0.00, that is, FIG. 10 shows the results of powder X-ray diffraction measurement of the sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S ₄ synthesized at 615 ° C. or 700 ° C. in the case where the value of x is 0.07. Shown in FIG. 10 also shows a rhombus mark indicating the diffraction angle of the characteristic peak of the novel phase, the characteristic peak of Li ₇ PS ₆ , so that the crystal identified by powder X-ray diffraction measurement can be recognized. bars having a diffraction angle and an X-ray diffraction pattern of γ-Li ₃ PS _4.

In Examples 20 and 21 (synthesis temperatures 615 ° C. and 700 ° C.), in addition to Li ₇ PS ₆ and γ-Li ₃ PS ₄ , 13.3 °, 14.75 °, 15.3 °, 18.0 ° Novel phases with characteristic peaks at diffraction angles (2θ) of 21.0-21.7 °, 24.2 °, 25.4 °, 28.4 ° and 30.6 ° were detected.

Summarizing the above results, the prepared sample and the line on the ternary composition diagram to which the reference example belongs, the synthesis temperature, the values of x and z in the composition formula Li _{3 + 5x} P _1−x S _4−z O _z and The detected crystals are shown in Table 2.

(Measurement of conductivity)
FIG. 11 shows the measurement results of the conductivity of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1-x S _4-z O _z synthesized at 700 ° C. with the composition along Line ₁ . The conductivity is 6.0 × 10 ^{−5 in} the range of z value of 0.00 or more and 0.30 or less (Examples 1 to 3) in which a low-conductivity γ-Li ₃ PS ₄ phase exists. It was as low as S / cm or less. However, when the value of z became 0.40 or more and the main phase changed to a new phase, the conductivity became 9.1 × 10 ⁻⁵ S / cm or more (Examples 4 to 8). The highest conductivity among sulfide-based solid electrolytes synthesized at 700 ° C. with a composition along Line 1 is 2.1 × 10 ⁻⁴ S / cm when the value of z is 0.80. (Example 7). In Example 7 (z = 0.80), more Li ₇ PS ₆ and γ-Li ₃ PS ₄ were present than in Examples 4 and 6 (z = 0.40 and 0.60). Nevertheless, the conductivity of Example 7 (z = 0.80) is high because the lattice size of the new phase of Example 7 (z = 0.80) is similar to that of Examples 4 and 6 (z = 0.40 and 0). .60) is smaller than that of Example 60 (z = 0.80), which is considered to be suitable for ion conduction.

FIG. 12 shows the measurement results of the conductivity of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1-x S _4-z O _z synthesized at 700 ° C. with the composition along Line 2. The conductivity is 2.1 × 10 ⁻⁴ S / cm in Example 4 (x = 0.07), and 4.92 × 10 ⁻⁵ S / cm in Example 9 (x = 0.105). cm. The low conductivity of Example 9 (x = 0.105) is presumed to be due to the increase in the proportion of Li ₇ PS _{6 and} the remaining starting material Li ₂ S.

FIG. 13 shows the measurement results of the conductivity of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. with the composition along Line ₃ . The conductivity is 1.06 × 10 ⁻⁴ S / cm in Example 10 (x = 0.03), and 1.35 × 10 ⁻⁴ S / cm in Example 11 (x = 0.05). cm, and in Example 5 (x = 0.07), it was 9.11 × 10 ⁻⁵ S / cm. Thus, when the value of z is 0.50, the conductivity of the order of about 10 ⁻⁴ S / cm is considered to be related to the fact that the main phase is a new phase.

FIG. 14 shows the measurement results of the conductivity of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. with the composition along Line ₄ . The conductivity was highest at 2.1 × 10 ⁻⁴ S / cm in Example 7 (x = 0.07). However, in Examples 12 to 14 (x = 0.03, 0.05 and 0.09) and Comparative Example 1 (x = 0.333), the conductivity is on the order of 10 ⁻⁵ S / cm, which is low. It was. This is because in Example 7 (x = 0.07), the ratio of the new phase is high, and Examples 12-14 (x = 0.03, 0.05 and 0.09) and Comparative Example 1 (x = 0). .333) is considered to be due to the high proportion of crystals with low conductivity such as Li ₇ PS ₆ , γ-Li ₃ PS ₄ , and Li ₂ S.

The relationship between the conductivity of the sulfide-based solid electrolyte of composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 700 ° C. and the crystals identified by powder X-ray diffraction measurement will be summarized. Li ₇ PS ₆ was detected in almost all compositions. When the value of x is 0.90 or more, Li ₂ S exceed solubility limit, is Li ₂ S detected in the sulfide-based solid electrolyte, the conductivity decreased greatly. When the value of z was 0.80 or more, β-Li ₃ PO ₄ was detected, but this crystal did not significantly affect the conductivity when 0.80 ≦ z ≦ 1.00. Also, the conductivity decreased in a manner that was difficult to increase with γ-Li ₃ PS ₄ .

FIG. 15 shows the measurement results of the conductivity of the sulfide-based solid electrolyte of the composition formula Li _{3 + 5x} P _1-x S _4−z O _z synthesized at 900 ° C. along the line ₁ . The conductivity is 1.24 × 10 ⁻⁴ S / cm in Example 15 (z = 0.20), and 2.64 × 10 ⁻⁴ S / cm in Example 16 (z = 0.40). cm, and in Example 17 (z = 0.80), it was 4.14 × 10 ⁻⁵ S / cm. When the value of z increased from 0.20 to 0.40, the conductivity increased because the ratio of Li ₇ PS ₆ was low and the ratio of β-Li ₃ PS ₄ having a high conductivity was high. It is believed that there is. In Example 17 (z = 0.80), the conductivity was low despite the fact that a sulfide-based solid electrolyte almost similar to the single phase of the new phase was obtained because the lattice of the new phase was extremely small. It is believed that there is.

The value of x was 0.07 and the conductivity of Example 18 synthesized at 900 ° C. and annealed at 530 ° C. when the value of z was 0.40 was 2.30 × 10 ⁻⁴ S / cm. The conductivity of Example 19 annealed at 700 ° C. was 1.14 × 10 ⁻⁴ S / cm. These values were smaller than 2.64 × 10 ⁻⁴ S / cm, which is the conductivity of Example 16 before annealing. Therefore, the conductivity of the sulfide-based solid electrolyte was lowered by the annealing treatment. From this result, it was found that the conductivity of the new phase was higher than that of β-Li ₃ PS ₄ .

The maximum value of the conductivity of the reference example is 7.3 × 10 ⁻⁵ S / cm of the reference example 4.

Summarizing the above results, the prepared sample and the line on the ternary composition diagram to which the reference example belongs, the synthesis temperature, the values of x and z in the composition formula Li _{3 + 5x} P _1−x S _4−z O _z and The conductivity is shown in Table 3.

  Table 4 shows the conductivity and the detected crystals.

(Measurement of thermal stability)
FIG. 16 shows the result of differential thermal measurement (DTA curve) of Example 16 synthesized at 900 ° C. in which the value of x is 0.07 and the value of z is 0.40. Endothermic peaks were observed around 500 ° C. and 600 ° C. during the temperature rising process, and exothermic peaks were observed around 560 ° C. during the temperature lowering process.

(Cyclic voltammetry)
FIG. 17 shows the CV measurement result of Example 5 synthesized at 700 ° C. in which the value of x is 0.07 and the value of z is 0.50. No oxidation / reduction peaks other than lithium dissolution / precipitation (Li → Li ⁺ + e ⁻ , Li ⁺ + e ⁻ → Li) were observed in the measured potential range. This indicates that this new phase is a substance having high electrochemical stability and a wide potential window.

DESCRIPTION OF SYMBOLS 1 Lithium battery 2 Solid electrolyte 3 Negative electrode 4 Positive electrode 5 Current collector 6 Insulation part

Claims (7)

A sulfide-based solid electrolyte represented by a composition formula Li _{3 + 5x} P _1-x S _4-z O _z ,
Solid electrolyte in which 0.01 ≦ x ≦ 1.42 and 0.01 ≦ z ≦ 1.55.   2. The solid electrolyte according to claim 1, wherein 0.02 ≦ x ≦ 1.11 and 0.20 ≦ z ≦ 1.20.   The solid electrolyte according to claim 2, wherein 0.03 ≦ x ≦ 0.09 and 0.25 ≦ z ≦ 1.00.   In the powder X-ray diffraction measurement by Cu-Kα ray having an X-ray wavelength of 1.5418 Å, the sulfide-based solid electrolyte is at least 12.9 °, 14.4 °, 15.2 °, 18.0 °, Any one of claims 1 to 3 having characteristic peaks in the vicinity of diffraction angles (2θ) of 20.5 to 22.0 °, 24.2 °, 25.0 °, 28.0 °, and 30.6 °. The solid electrolyte according to item. A sulfide-based solid electrolyte represented by a composition formula Li _{3 + 5x} P _1-x S ₄ ;
0.06 ≦ x ≦ 0.08,
The sulfide-based solid electrolyte has at least 13.3 °, 14.75 °, 15.3 °, 18.0 ° in powder X-ray diffraction measurement with Cu-Kα rays having an X-ray wavelength of 1.5418 angstroms, A solid electrolyte having characteristic peaks in the vicinity of diffraction angles (2θ) of 21.0 to 21.7 °, 24.2 °, 25.4 °, 28.4 °, 30.6 °. The solid electrolyte according to claim 1, which does not contain Li ₂ S and γ-Li ₃ PS ₄ .   The lithium battery containing the solid electrolyte of any one of Claims 1-6.

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