JP5780322B2 - Sulfide solid electrolyte material and lithium solid state battery - Google Patents

Description

  The present invention relates to a sulfide solid electrolyte material having high Li ion conductivity.

  With the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones in recent years, development of batteries that are used as power sources has been regarded as important. Also in the automobile industry and the like, development of high-power and high-capacity batteries for electric vehicles or hybrid vehicles is being promoted. Currently, lithium batteries are attracting attention among various batteries from the viewpoint of high energy density.

  Since lithium batteries currently on the market use an electrolyte containing a flammable organic solvent, it is possible to install safety devices that suppress the temperature rise during short circuits and to improve the structure and materials to prevent short circuits. Necessary. In contrast, a lithium battery in which the electrolyte is changed to a solid electrolyte layer to make the battery completely solid does not use a flammable organic solvent in the battery, so the safety device can be simplified, and manufacturing costs and productivity can be reduced. It is considered excellent. Furthermore, a sulfide solid electrolyte material is known as a solid electrolyte material used for such a solid electrolyte layer.

Since the sulfide solid electrolyte material has high Li ion conductivity, it is useful for increasing the output of the battery, and various studies have been made heretofore. For example, Non-Patent Document 1 discloses a LiI—Li ₂ S—P ₂ S ₅ -based amorphous material obtained by a mechanical milling method. In Non-Patent Document _{2, LiI-Li 2 S-} P 2 S 5 based amorphous material obtained by mechanical milling method is disclosed. In Non-Patent Document 3, using _{LiI-Li 2 S-P 2} S 5 based sulfide solid electrolyte material to the anode side, the cathode side be used other solid electrolyte materials have been disclosed.

Further, in Patent Document 1, and Li 2 _{S-P 2} S ₅ based lithium ion conductor crystal glass, battery using the same as a solid electrolyte is disclosed. Patent Document 2 discloses a nonaqueous electrolyte battery in which a combination of solid electrolytes is selected as a specific combination in order to suppress a reaction between a positive electrode active material and a solid electrolyte.

JP 2005-228570 A JP 2003-217663 A

Naoko Torui and two others, “Synthesis of LiI-Li2S-P2S5 Amorphous Materials by Mechanical Milling and Their Lithium Ion Conduction Properties”, Abstracts of Solid State Ionics Conference, Vol. 23, p. Issued 26-27, 2003 Rene Mercier et al., “SUPERIONIC CONDUCTION IN Li2S-P2S5-LiI -GLASSES”, Solid State Ionics 5 (1981), 663-666 Kazunori Takada et al., “Solid-state lithium battery with graphite anode”, Solid State Ionics 158 (2003), 269-274

  Conventionally, a sulfide solid electrolyte material having high Li ion conductivity has been demanded. This invention is made | formed in view of the said situation, and makes it a main objective to provide the sulfide solid electrolyte material with high Li ion conductivity.

  In order to solve the above problems, in the present invention, a sulfide solid electrolyte material having an ionic conductor having an ortho composition and LiI is a glass having a glass transition point. A solid electrolyte material is provided.

  According to the present invention, since it has LiI (LiI component), it is Li-rich and a sulfide solid electrolyte material having high Li ion conductivity can be obtained. Furthermore, since this sulfide solid electrolyte material has high amorphousness to such an extent that it has a glass transition point, it can increase Li ion conductivity.

  In the said invention, it is preferable that content of the said LiI exists in the range of 10 mol%-30 mol%.

  In the said invention, it is preferable that the said ion conductor contains Li, X (X is P, Si, Ge, Al, or B), and S. It is because it can be set as the sulfide solid electrolyte material with high Li ion conductivity.

  In the said invention, it is preferable that the said ion conductor contains Li, P, and S.

  Further, in the present invention, a sulfide solid electrolyte material having an ionic conductor having an ortho composition and LiI, wherein the ionic conductor contains oxygen (O). An electrolyte material is provided.

  According to the present invention, since it has LiI (LiI component), it is Li-rich and a sulfide solid electrolyte material having high Li ion conductivity can be obtained. Furthermore, since this ionic conductor contains oxygen, this sulfide solid electrolyte material can suppress a decrease in chemical stability due to the influence of LiI.

In the above invention, the oxygen of the ion conductor is preferably derived from a Li 2 _O. This is because oxygen is easily introduced.

  In the said invention, it is preferable that the said ion conductor contains Li, X (X is P, Si, Ge, Al, or B), S, and O. It is because it can be set as the sulfide solid electrolyte material with high Li ion conductivity.

  In the said invention, it is preferable that the said ion conductor contains Li, P, S, and O.

  In the present invention, a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte formed between the positive electrode active material layer and the negative electrode active material layer A positive electrode active material layer having a potential of 2.8 V (vs Li) or higher, an ionic conductor having an ortho composition, and a sulfide solid having LiI A lithium solid state battery comprising an electrolyte material is provided.

  According to the present invention, since the positive electrode active material layer contains the sulfide solid electrolyte material having LiI (LiI component), a high output lithium solid state battery can be obtained.

  In the said invention, it is preferable that the said ion conductor contains Li, X (X is P, Si, Ge, Al, or B), and S. It is because it can be set as the sulfide solid electrolyte material with high Li ion conductivity.

  In the said invention, it is preferable that the said ion conductor contains Li, P, and S.

  In the present invention, a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte formed between the positive electrode active material layer and the negative electrode active material layer A lithium solid state battery, wherein at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains the sulfide solid electrolyte material described above I will provide a.

  According to the present invention, since a sulfide solid electrolyte material having LiI (LiI component) is contained, a high output lithium solid state battery can be obtained. Furthermore, since the sulfide solid electrolyte material contains an ionic conductor containing oxygen (O), it is possible to suppress a decrease in chemical stability due to the influence of LiI. As a result, a lithium solid state battery in which an increase in reaction resistance is suppressed can be obtained.

  In the said invention, it is preferable that the said positive electrode active material layer contains the said positive electrode active material whose electric potential is 2.8V (vs Li) or more, and the said sulfide solid electrolyte material.

  In this invention, there exists an effect that the sulfide solid electrolyte material with high Li ion conductivity can be obtained.

It is a schematic sectional drawing which shows an example of the lithium solid battery of this invention. It is a result of the X-ray-diffraction measurement with respect to the sulfide solid electrolyte material obtained in Examples 1-1 and 1-2 and Comparative Examples 1-1 to 1-3. It is a result of the differential thermal analysis with respect to the sulfide solid electrolyte material obtained in Example 1-2 and Comparative Example 1-3. It is a result of Li ion conductivity measurement with respect to the sulfide solid electrolyte material obtained in Examples 1-1 and 1-2. It is a result of the Raman spectroscopic measurement with respect to the sulfide solid electrolyte material obtained in Example 1-1, 1-2. It is a result of the cyclic voltammetry measurement with respect to the sulfide solid electrolyte material obtained in Example 1-2. It is a result of evaluation of charging / discharging cycle characteristics with respect to the lithium solid state battery obtained in Example 2 and Comparative Example 2. It is the result of evaluation of reaction resistance measurement with respect to the lithium solid battery obtained in Example 2 and Comparative Example 2. It is a result of Li ion conductivity measurement with respect to the sulfide solid electrolyte material obtained in Examples 3-1 to 3-6. It is the result of evaluation of reaction resistance measurement with respect to the lithium solid state battery obtained in Example 4, Comparative Examples 4-1, 4-2, and Reference Example 4.

  Hereinafter, the sulfide solid electrolyte material and the lithium solid battery of the present invention will be described in detail.

A. First, the sulfide solid electrolyte material of the present invention will be described. The sulfide solid electrolyte material of the present invention can be roughly divided into two embodiments. Hereinafter, the sulfide solid electrolyte material of the present invention will be described separately for the first embodiment and the second embodiment.

1. First Embodiment The sulfide solid electrolyte material of the first embodiment is a sulfide solid electrolyte material having an ionic conductor having an ortho composition and LiI, and is a glass having a glass transition point. To do.

  According to the first embodiment, since it has LiI (LiI component), it is Li-rich and can be a sulfide solid electrolyte material having high Li ion conductivity. Furthermore, since the sulfide solid electrolyte material of the first embodiment is highly amorphous to such an extent that it has a glass transition point, Li ion conductivity can be increased. In addition, according to the first embodiment, since the ionic conductor has an ortho composition, a sulfide solid electrolyte material that is hardly deteriorated (for example, oxidative decomposition) can be obtained.

FIG. 1 of Non-Patent Document 1 describes xLiI · 75Li ₂ S · 25P ₂ S ₅ based amorphous material (amorphous material). This amorphous body has an ion conductor having an ortho composition of 75Li ₂ S · 25P ₂ S ₅ and LiI. However, the amorphous body usually means that the periodicity as a crystal is not observed in X-ray diffraction measurement or the like, and the amorphous body has a wide range. For this reason, some amorphous materials have high or low amorphous properties. Here, in Non-Patent Document 1, although it is described that an amorphous body is synthesized by a mechanical milling method, the details are not clear and there is no special description, so that it is normal dry mechanical milling. It is guessed.

  As described in Comparative Example 1-3 described later, in the case of dry mechanical milling, a glassy sulfide solid electrolyte material having a glass transition point cannot be obtained. The reason is probably that in dry mechanical milling, the raw material composition adheres to the wall surface of a container or the like and it is difficult to make it sufficiently amorphous. On the other hand, the sulfide solid electrolyte material of the first embodiment can be obtained, for example, by performing wet mechanical milling as described later. In the wet mechanical milling, since the raw material composition can be prevented from sticking to the wall surface of a container or the like, it can be sufficiently amorphized. Therefore, a solid electrolyte material having a high degree of amorphousness to the extent that it has a glass transition point can be obtained. The glass in the strict sense refers to an amorphous body and a glass transition point observed. In Non-Patent Document 1, the term “amorphous” is used, but the term “glass” is not used. Moreover, when comparing glass and amorphous materials other than glass, there is generally no index for determining which has higher Li ion conductivity.

(1) Sulfide solid electrolyte material The sulfide solid electrolyte material of the first embodiment is characterized by being a glass having a glass transition point. The presence or absence of a glass transition point can be confirmed by differential thermal analysis (DTA). The fact that the sulfide solid electrolyte material is an amorphous material can be determined by X-ray diffraction (XRD) measurement using CuKα rays.

  One feature of the sulfide solid electrolyte material of the first embodiment is that it includes an ionic conductor having an ortho composition and LiI. Since the sulfide solid electrolyte material is glass, LiI is usually present in a state of being incorporated into the structure of an ionic conductor having an ortho composition. Therefore, it is preferable that the sulfide solid electrolyte material does not have a LiI peak in XRD measurement using CuKα rays. The LiI peak usually appears at 2θ = 26 °, 30 °, 43 °, and 51 °. Further, the content of LiI is not particularly limited as long as it is a ratio capable of obtaining a glass having a glass transition point. For example, it is preferably 34 mol% or less, and 30 mol% or less. Is more preferable. On the other hand, the content of LiI is, for example, preferably 1 mol% or more, more preferably 5 mol% or more, and further preferably 10 mol% or more. This is because if the content of LiI is too small, it may not contribute to the improvement of Li ion conductivity.

The ionic conductor has an ortho composition. Here, ortho generally refers to one having the highest degree of hydration among oxo acids obtained by hydrating the same oxide. In the first embodiment, the crystal composition to which Li ₂ S (and Li ₂ O) is added most in the sulfide is referred to as an ortho composition. For example, Li ₃ PS ₄ corresponds to the ortho composition in the Li ₂ S—P ₂ S ₅ system, Li ₃ AlS ₃ corresponds to the ortho composition in the Li ₂ S—Al ₂ S ₃ system, and Li ₂ S—B _2. In the S ₃ system, Li ₃ BS ₃ corresponds to the ortho composition, in the Li ₂ S—SiS ₂ system, Li ₄ SiS ₄ corresponds to the ortho composition, and in the Li ₂ S—GeS ₂ system, Li ₄ GeS _{4 corresponds} to the ortho composition. Applicable. In the first embodiment, part of sulfur (S) in the ortho composition may be substituted with oxygen (O).

In the first embodiment, “having an ortho composition” includes not only a strict ortho composition but also a composition in the vicinity thereof. Specifically, the main component is an anion structure having an ortho composition (PS ₄ ³⁻ structure, SiS ₄ ⁴⁻ structure, GeS ₄ ⁴⁻ structure, AlS ₃ ³⁻ structure, BS ₃ ³⁻ structure). The ratio of the anion structure of the ortho composition is preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, based on the total anion structure in the ion conductor, 90 mol % Or more is particularly preferable. The ratio of the anion structure of the ortho composition can be determined by Raman spectroscopy, NMR, XPS, or the like.

  The composition of the ion conductor is not particularly limited, but preferably contains Li, X (X is P, Si, Ge, Al, or B), and S. It is because it can be set as the sulfide solid electrolyte material with high Li ion conductivity. X is particularly preferably P. X may contain two or more of the above elements.

Further, the sulfide solid electrolyte material of the first embodiment is a raw material composition containing Li ₂ S, a sulfide of X (X is P, Si, Ge, Al, or B), and LiI. It is preferable that it is crystallized.

Li ₂ S contained in the raw material composition preferably has few impurities. This is because side reactions can be suppressed. Examples of the method for synthesizing Li ₂ S include the method described in JP-A-7-330312. Furthermore, Li ₂ S is preferably purified using the method described in WO2005 / 040039. On the other hand, examples of the sulfide of X contained in the raw material composition include P ₂ S ₃ , P ₂ S ₅ , SiS ₂ , GeS ₂ , Al ₂ S ₃ , B ₂ S _{3 and the} like.

Also, the sulfide solid electrolyte material is preferably substantially free of Li 2 _S. It is because it can be set as the sulfide solid electrolyte material with little hydrogen sulfide generation amount. Li ₂ S reacts with water to generate hydrogen sulfide. For example, when the proportion of Li ₂ S contained in the raw material composition is large, Li ₂ S tends to remain. “Substantially free of Li ₂ S” can be confirmed by X-ray diffraction. Specifically, when it does not have a Li ₂ S peak (2θ = 27.0 °, 31.2 °, 44.8 °, 53.1 °), it is determined that it does not substantially contain Li ₂ S. can do.

Moreover, it is preferable that the said sulfide solid electrolyte material does not contain bridge | crosslinking sulfur substantially. It is because it can be set as the sulfide solid electrolyte material with little hydrogen sulfide generation amount. “Bridged sulfur” refers to bridged sulfur in a compound obtained by reacting Li ₂ S with the sulfide of X described above. For example, Li ₂ S and _P 2 _{S 5} is bridging sulfur reactions to become _{S 3} PS-PS 3 structure corresponds. Such bridging sulfur easily reacts with water and easily generates hydrogen sulfide. Furthermore, “substantially free of bridging sulfur” can be confirmed by measurement of a Raman spectrum. For example, in the case of a Li ₂ S—P ₂ S ₅ sulfide solid electrolyte material, the peak of the S ₃ P—S—PS ₃ structure usually appears at 402 cm ⁻¹ . Therefore, it is preferable that this peak is not detected. Moreover, the peak of PS ₄ ³⁻ structure usually appears at 417 cm ⁻¹ . In a first embodiment, the intensity _{I 402} at 402 cm ^-1 is preferably smaller than the intensity _{I 417} at 417 cm ^-1. More specifically, the strength I ₄₀₂ is preferably 70% or less, more preferably 50% or less, and even more preferably 35% or less with respect to the strength I ₄₁₇ . As for the sulfide solid electrolyte material other than Li 2 _{S-P 2} S ₅ based, to identify the unit containing the crosslinking sulfur, by measuring the peak of the unit, are substantially free of bridging sulfur It can be judged that there is no.

In the case of a Li ₂ S—P ₂ S ₅ -based sulfide solid electrolyte material, the ratio of Li ₂ S and P ₂ S ₅ to obtain the ortho composition is Li ₂ S: P ₂ S ₅ = 75 on a molar basis. : 25. The same applies to the Li ₂ S—Al ₂ S ₃ -based sulfide solid electrolyte material and the Li ₂ S—B ₂ S ₃ -based sulfide solid electrolyte material. On the other hand, in the case of a Li ₂ S—SiS ₂ -based sulfide solid electrolyte material, the ratio of Li ₂ S and SiS ₂ to obtain the ortho composition is Li ₂ S: SiS ₂ = 66.7: 33.3 on a molar basis. It is. The same applies to the case of a Li ₂ S—GeS ₂ -based sulfide solid electrolyte material.

The raw material composition is, when containing Li ₂ S and _P 2 _{S 5,} the proportion of Li ₂ S to the total of Li ₂ S and _P 2 _{S 5} is preferably in the range of 70 mol% 80 mol% 72 mol% to 78 mol% is more preferable, and 74 mol% to 76 mol% is more preferable. Incidentally, the raw material composition is, when containing Li ₂ S and _Al 2 _{S 3,} which is the same when containing Li ₂ S and _B 2 _{S 3.} On the other hand, the raw material composition is, when containing Li ₂ S and SiS _2, the ratio of Li ₂ S to the total of Li ₂ S and SiS ₂ is in the range of 62.5mol% ~70.9mol% Is preferable, it is more preferable that it is in the range of 63 mol% to 70 mol%, and it is more preferable that it is in the range of 64 mol% to 68 mol%. The same applies when the raw material composition contains Li ₂ S and GeS ₂ .

Examples of the shape of the sulfide solid electrolyte material of the first embodiment include particles. The average particle diameter of the particulate sulfide solid electrolyte material is preferably in the range of 0.1 μm to 50 μm, for example. The sulfide solid electrolyte material preferably has high Li ion conductivity, and the Li ion conductivity at room temperature is preferably 1 × 10 ⁻⁴ S / cm or more, for example, 1 × 10 ⁻³ S. / Cm or more is more preferable.

  The sulfide solid electrolyte material of the first embodiment can be used for any application that requires Li ion conductivity. Especially, it is preferable that the said sulfide solid electrolyte material is what is used for a battery. Furthermore, when using the said sulfide solid electrolyte material for a battery, you may use for a positive electrode active material layer (positive electrode body), may be used for a negative electrode active material layer (negative electrode body), and may be used for an electrolyte layer.

(2) Manufacturing method of sulfide solid electrolyte material Next, the manufacturing method of the sulfide solid electrolyte material of 1st embodiment is demonstrated. The method for producing the sulfide solid electrolyte material of the first embodiment is not particularly limited as long as it is a method capable of obtaining the sulfide solid electrolyte material described above. As a method for producing the sulfide solid electrolyte material, for example, a raw material composition containing Li ₂ S, a sulfide of X (X is P, Si, Ge, Al, or B), and LiI, The manufacturing method which has the synthetic | combination process made amorphous by wet mechanical milling can be mentioned.

  Mechanical milling is not particularly limited as long as the raw material composition is mixed while applying mechanical energy, and examples thereof include a ball mill, a vibration mill, a turbo mill, a mechanofusion, and a disk mill. Among these, a ball mill is preferable, and a planetary ball mill is particularly preferable. This is because a desired sulfide solid electrolyte material can be obtained efficiently.

  Various conditions of mechanical milling are set so that a desired sulfide solid electrolyte material can be obtained. For example, when a planetary ball mill is used, a raw material composition and grinding balls are added, and the treatment is performed at a predetermined number of revolutions and time. In general, the higher the number of rotations, the faster the production rate of the sulfide solid electrolyte material, and the longer the treatment time, the higher the conversion rate from the raw material composition to the sulfide solid electrolyte material. The rotation speed of the base plate when performing the planetary ball mill is preferably in the range of, for example, 200 rpm to 500 rpm, and more preferably in the range of 250 rpm to 400 rpm. Further, the treatment time when performing the planetary ball mill is preferably in the range of 1 hour to 100 hours, and more preferably in the range of 1 hour to 50 hours.

  The liquid used for wet mechanical milling preferably has a property of not generating hydrogen sulfide by the reaction with the raw material composition. Hydrogen sulfide is generated when protons dissociated from liquid molecules react with a raw material composition or a sulfide solid electrolyte material. Therefore, it is preferable that the liquid has an aprotic property that does not generate hydrogen sulfide. In addition, aprotic liquids can be broadly classified into polar aprotic liquids and nonpolar aprotic liquids.

  The polar aprotic liquid is not particularly limited. For example, ketones such as acetone; nitriles such as acetonitrile; amides such as N, N-dimethylformamide (DMF); dimethyl sulfoxide (DMSO) And the like.

  An example of a nonpolar aprotic liquid is alkane that is liquid at room temperature (25 ° C.). The alkane may be a chain alkane or a cyclic alkane. The chain alkane preferably has, for example, 5 or more carbon atoms. On the other hand, the upper limit of the carbon number of the chain alkane is not particularly limited as long as it is liquid at room temperature. Specific examples of the chain alkane include pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, and paraffin. The chain alkane may have a branch. On the other hand, specific examples of the cyclic alkane include cyclopentane, cyclohexane, cycloheptane, cyclooctane, and cycloparaffin.

  Other examples of nonpolar aprotic liquids include aromatic hydrocarbons such as benzene, toluene and xylene; chain ethers such as diethyl ether and dimethyl ether; cyclic ethers such as tetrohydrofuran; chloroform Alkyl halides such as methyl chloride and methylene chloride; esters such as ethyl acetate; fluorinated benzene, heptane fluoride, 2,3-dihydroperfluoropentane, 1,1,2,2,3,3 Fluorine compounds such as 4-heptafluorocyclopentane can be exemplified. In addition, the addition amount of the said liquid is not specifically limited, What is necessary is just a quantity which can obtain a desired sulfide solid electrolyte material.

2. Second Embodiment Next, a second embodiment of the sulfide solid electrolyte material of the present invention will be described. The sulfide solid electrolyte material of the second embodiment is a sulfide solid electrolyte material having an ionic conductor having an ortho composition and LiI, wherein the ionic conductor contains oxygen (O). It is what.

  According to the second embodiment, since it has LiI (LiI component), it is Li-rich and can be a sulfide solid electrolyte material having high Li ion conductivity. Furthermore, since the ionic conductor contains oxygen (O), the sulfide solid electrolyte material of the second embodiment can suppress a decrease in chemical stability due to the influence of LiI. Further, according to the second embodiment, since the ionic conductor has an ortho composition, it is possible to obtain a sulfide solid electrolyte material which is hardly deteriorated (for example, oxidative decomposition). In addition, the sulfide solid electrolyte material of the second embodiment may be glass, unlike the sulfide solid electrolyte material of the first embodiment described above, and may be an amorphous body excluding glass, It may have crystallinity or may be completely crystalline.

(1) Sulfide solid electrolyte material The sulfide solid electrolyte material of the second embodiment is characterized in that an ionic conductor having an ortho composition contains oxygen (O). O contained in the ionic conductor is usually present at the position of S in an anion structure (for example, PS ₄ ^3- structure) having an ortho composition composed of only S. Specific examples include PS ₃ O ³⁻ , PS ₂ O ₂ ³⁻ _, PSO ₃ ^{3− and the} like. Moreover, it can be confirmed by NMR, Raman spectroscopy, XPS, etc. that the ionic conductor has O. In particular, when the ionic conductor has P, it is preferably measured by ³¹ P MAS NMR. The oxygen in the ion conductor is preferably derived from an oxygen-containing compound, and more preferably derived from Li ₂ O. This is because a sulfide solid electrolyte material having high chemical stability can be obtained.

  One feature of the sulfide solid electrolyte material of the second embodiment is that it includes an ionic conductor having an ortho composition and LiI. In the second embodiment, it is preferable that at least a part of LiI is present in a state of being incorporated into the structure of an ionic conductor having an ortho composition. The content of LiI is not particularly limited, but is preferably in the range of 1 mol% to 60 mol%, more preferably in the range of 5 mol% to 50 mol%, for example, and 10 mol% to 40 mol. More preferably, it is in the range of%.

The ionic conductor has an ortho composition. As described above, Li ₃ PS ₄ corresponds to the ortho composition in the Li ₂ S—P ₂ S ₅ system, Li ₃ AlS ₃ corresponds to the ortho composition in the Li ₂ S—Al ₂ S ₃ system, and Li ₂ S. -B ₂ in S ₃ system _Li 3 BS ₃ corresponds to an ortho _composition, Li 2 S-SiS the _{2-based Li} 4 SiS ₄ corresponds to an ortho _composition in Li 2 S-GeS ₂ system _Li 4 GeS ₄ Corresponds to ortho composition. In the second embodiment, part of sulfur (S) in the ortho composition is substituted with oxygen (O).

  The composition of the ionic conductor is not particularly limited, but should contain Li, X (X is P, Si, Ge, Al, or B), S, and O. Is preferred. It is because it can be set as the sulfide solid electrolyte material with high Li ion conductivity. X is particularly preferably P.

The sulfide solid electrolyte material of the second embodiment contains Li ₂ S, Li ₂ O, a sulfide of X (X is P, Si, Ge, Al, or B), and LiI. It is preferable to use a raw material composition. The sulfides of Li ₂ S and X contained in the raw material composition are as described above.

In the case of a Li ₂ S—Li ₂ O—P ₂ S ₅ -based sulfide solid electrolyte material, the ratio of Li ₂ S, Li ₂ O, and P ₂ S ₅ to obtain the ortho composition is on a molar basis (Li _{2 S + Li 2 O):} P 2 S 5 = 75: 25. The same applies to Li ₂ S—Li ₂ O—Al ₂ S ₃ -based sulfide solid electrolyte materials and Li ₂ S—Li ₂ O—B ₂ S ₃ -based sulfide solid electrolyte materials. On the other hand, in the case of a Li ₂ S—Li ₂ O—SiS ₂ -based sulfide solid electrolyte material, the ratio of Li ₂ S, Li ₂ O and SiS ₂ to obtain the ortho composition is (Li ₂ S + Li ₂ O) on a molar basis. ): SiS ₂ = 66.7: 33.3. The same applies to the case of a Li ₂ S—Li ₂ O—GeS ₂ -based sulfide solid electrolyte material.

The raw material composition _is, when containing Li 2 S, Li ₂ O and _{P 2 S 5, Li 2 S} , Li 2 S and Li ₂ O ratio of to the total of Li ₂ O and _P 2 _{S 5} is, 70 mol % To 80 mol% is preferable, 72 mol% to 78 mol% is more preferable, and 74 mol% to 76 mol% is more preferable. Incidentally, the raw material composition _is, when containing Li ₂ S, Li 2 O and _Al 2 _{S 3,} which is the same when containing Li ₂ S, Li 2 O and _B 2 _{S 3.} On the other hand, the raw material composition _is, when containing Li 2 S, Li ₂ O and _{SiS 2, Li 2 S, Li} 2 S and Li ₂ O ratio of to the total of Li ₂ O and SiS ₂ is, 62.5Mol % To 70.9 mol% is preferable, 63 mol% to 70 mol% is more preferable, and 64 mol% to 68 mol% is more preferable. The same applies to the case where the raw material composition contains Li ₂ S, Li ₂ O, and GeS ₂ .

Further, Li ₂ O ratio of to the sum of Li ₂ S and Li ₂ O is, preferably for example in the range of 1 mol% 40 mol%, and more preferably in the range of 4mol% ~27mol%. If the proportion of Li ₂ O is too small, it may not be possible to contribute to the improvement of the chemical stability of the sulfide solid electrolyte material, and if the proportion of Li ₂ O is too large, the Li ion conductivity may be greatly reduced. Because there is sex.

In addition, the content of Li ₂ O in the sulfide solid electrolyte material of the second embodiment is preferably in the range of, for example, 1 mol% to 30 mol%, and more preferably in the range of 3 mol% to 20 mol%. .

  Since other matters regarding the sulfide solid electrolyte material of the second embodiment are the same as the matters described in “1. First embodiment”, description thereof is omitted here.

(2) Manufacturing method of sulfide solid electrolyte material Next, the manufacturing method of the sulfide solid electrolyte material of 2nd embodiment is demonstrated. The method for producing the sulfide solid electrolyte material of the second embodiment is not particularly limited as long as it is a method capable of obtaining the sulfide solid electrolyte material described above. As an example of the method for producing the sulfide solid electrolyte material, Li ₂ S, Li ₂ O, a sulfide of X (X is P, Si, Ge, Al, or B), and LiI are contained. The manufacturing method which has the synthetic | combination process which amorphizes a raw material composition can be mentioned.

  Examples of the amorphization method include mechanical milling and melt quenching, and mechanical milling is preferable among them. This is because processing at room temperature is possible, and the manufacturing process can be simplified. The mechanical milling may be dry mechanical milling or wet mechanical milling, but the latter is preferred. This is because the raw material composition can be prevented from adhering to the wall surface of a container or the like, and a sulfide solid electrolyte material with higher amorphousness can be obtained.

  Moreover, in said manufacturing method, you may perform the heat processing process which heat-processes with respect to the sulfide solid electrolyte material obtained at the synthesis | combination process. This is because a crystalline sulfide solid electrolyte material can be obtained. The heating temperature is preferably a temperature equal to or higher than the crystallization temperature.

On the other hand, as another example of the method for producing the sulfide solid electrolyte material, a raw material containing Li ₂ S, a sulfide of X (X is P, Si, Ge, Al, or B), and LiI A first amorphization step for amorphizing the composition, and a second amorphous material that is amorphized by adding Li ₂ O to the material obtained by the first amorphization step. The manufacturing method which has a conversion process can be mentioned. By adding Li ₂ O in the second amorphization step, the chemical stability of the sulfide solid electrolyte material can be improved efficiently. In the above manufacturing method, LiI is added in the first amorphization step, but LiI may be added in the second amorphization step. Furthermore, in the above manufacturing method, a heat treatment step of performing heat treatment on the sulfide solid electrolyte material obtained in the second amorphization step may be performed.

B. Next, the lithium solid state battery of the present invention will be described. The lithium solid state battery of the present invention can be roughly divided into two embodiments. Hereinafter, the lithium solid state battery of the present invention will be described separately for the first embodiment and the second embodiment.

1. First Embodiment A lithium solid state battery according to a first embodiment includes a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, the positive electrode active material layer, and the negative electrode active material layer. A lithium solid state battery having a solid electrolyte layer formed therebetween, wherein the positive electrode active material layer has a positive electrode active material having a potential of 2.8 V (vs Li) or more, and an ionic conductor having an ortho composition And a sulfide solid electrolyte material having LiI.

According to the first embodiment, since the positive electrode active material layer contains the sulfide solid electrolyte material having LiI (LiI component), a high-power lithium solid state battery can be obtained. Conventionally, LiI was considered to decompose near 2.8 V, and therefore, a sulfide solid electrolyte material having LiI has not been used for the positive electrode active material layer. For example, Non-Patent Document 3 page 270 describes that LiI—Li ₂ S—P ₂ S ₅ cannot be combined with a positive electrode active material such as LiCoO ₂ . Further, paragraphs [0028] and [0029] of Patent Document 2 describe that the potential at which the oxidation reaction of LiI occurs is low and cannot be combined with the positive electrode active material. Furthermore, according to the Nernst equation, LiI undergoes an oxidation reaction at 2.8V.
E = ΔU _elec /γF=270.29×10 ³ /1×96450=2.8 V (vs Li)

  However, as described in (Evaluation of oxidative decomposition) in [Evaluation 1] of Examples described later, even if a positive electrode active material layer contains a sulfide solid electrolyte material having LiI, LiI is not unexpectedly decomposed. It was confirmed. The reason is not yet clear, but it is considered that LiI is stabilized by the interaction with the ionic conductor.

FIG. 1 is a schematic cross-sectional view showing an example of the lithium solid state battery of the first embodiment. A lithium solid battery 10 shown in FIG. 1 includes a positive electrode active material layer 1 containing a positive electrode active material, a negative electrode active material layer 2 containing a negative electrode active material, and between the positive electrode active material layer 1 and the negative electrode active material layer 2. The solid electrolyte layer 3 formed on the cathode, the positive electrode current collector 4 for collecting current of the positive electrode active material layer 1, the negative electrode current collector 5 for collecting current of the negative electrode active material layer 2, and these members are housed. A battery case 6 is provided. In the first embodiment, the positive electrode active material layer 1 contains a positive electrode active material having a potential of 2.8 V (vs Li) or higher, an ionic conductor having an ortho composition, and a sulfide solid electrolyte material having LiI. It is a great feature to do. In particular, in the first embodiment, it is preferable that the positive electrode active material layer 1, the negative electrode active material layer 2, and the solid electrolyte layer 3 contain the sulfide solid electrolyte material.
Hereinafter, the lithium solid state battery of the first embodiment will be described for each configuration.

(1) Positive electrode active material layer The positive electrode active material layer in the first embodiment includes a positive electrode active material having a potential of 2.8 V (vs Li) or higher, an ionic conductor having an ortho composition, and a sulfide solid electrolyte having LiI. Material.

(I) Sulfide solid electrolyte material The sulfide solid electrolyte material in the first embodiment is the sulfide solid electrolyte material described in "A. Sulfide solid electrolyte material 1. First embodiment" (with a glass transition point). Not only glass) but also an amorphous body excluding glass, crystallinity, or complete crystallinity. In the first embodiment, it is preferable that at least a part of LiI is present in a state of being incorporated into the structure of an ionic conductor having an ortho composition. The content of LiI is not particularly limited, but is preferably in the range of 1 mol% to 60 mol%, more preferably in the range of 5 mol% to 50 mol%, for example, and 10 mol% to 40 mol. More preferably, it is in the range of%. The ionic conductor having the ortho composition is the same as that described in “A. Sulfide Solid Electrolyte Material 1. First Embodiment”, and is not described here.

  Further, the content of the sulfide solid electrolyte material in the positive electrode active material layer is, for example, in the range of 0.1% by volume to 80% by volume, in particular, in the range of 1% by volume to 60% by volume, in particular, 10% by volume. It is preferable to be in the range of% to 50% by volume.

(Ii) Positive electrode active material The positive electrode active material in the first embodiment is not particularly limited as long as it has a potential of 2.8 V (vs Li) or higher. For example, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , rock salt layer type active materials such as LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , spinel type activities such as LiMn ₂ O ₄ , Li (Ni _0.5 Mn _1.5 ) O ₄ Examples thereof include olivine-type active materials such as substances, LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCuPO _{4, and the} like. Si-containing oxides such as Li ₂ FeSiO ₄ and Li ₂ MnSiO ₄ may be used as the positive electrode active material. Furthermore, the potential of the positive electrode active material is preferably higher, for example, 3.0 V (vs Li) or higher.

  Examples of the shape of the positive electrode active material include a particle shape, and among them, a spherical shape or an elliptical shape is preferable. Moreover, when a positive electrode active material is a particle shape, it is preferable that the average particle diameter exists in the range of 0.1 micrometer-50 micrometers, for example. Further, the content of the positive electrode active material in the positive electrode active material layer is, for example, preferably in the range of 10% by volume to 99% by volume, and more preferably in the range of 20% by volume to 99% by volume.

(Iii) Positive electrode active material layer The positive electrode active material layer in the first embodiment may further contain at least one of a conductive material and a binder in addition to the positive electrode active material and the sulfide solid electrolyte material. . Examples of the conductive material include acetylene black, ketjen black, and carbon fiber. Examples of the binder include fluorine-containing binders such as PTFE and PVDF. The thickness of the positive electrode active material layer is preferably in the range of 0.1 μm to 1000 μm, for example.

(2) Negative electrode active material layer Next, the negative electrode active material layer in the first embodiment will be described. The negative electrode active material layer in the first embodiment is a layer containing at least a negative electrode active material, and may further contain at least one of a solid electrolyte material, a conductive material and a binder as necessary. .

  In the first embodiment, the solid electrolyte material contained in the negative electrode active material layer is preferably the sulfide solid electrolyte material described in the above “(1) Positive electrode active material layer (i) Sulfide solid electrolyte material”. . This is because a high output battery can be obtained. The content of the sulfide solid electrolyte material in the negative electrode active material layer is, for example, in the range of 0.1% by volume to 80% by volume, especially in the range of 1% by volume to 60% by volume, in particular, 10% by volume to It is preferably within the range of 50% by volume.

  Examples of the negative electrode active material include a metal active material and a carbon active material. Examples of the metal active material include In, Al, Si, and Sn. On the other hand, examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Further, the content of the negative electrode active material in the negative electrode active material layer is, for example, preferably in the range of 10% by volume to 99% by volume, and more preferably in the range of 20% by volume to 99% by volume. The conductive material and the binder are the same as those used for the positive electrode active material layer described above. The thickness of the negative electrode active material layer is preferably in the range of 0.1 μm to 1000 μm, for example.

(3) Solid electrolyte layer Next, the solid electrolyte layer in the first embodiment will be described. The solid electrolyte layer in the first embodiment is a layer formed between the positive electrode active material layer and the negative electrode active material layer, and is a layer composed of a solid electrolyte material. The solid electrolyte material contained in the solid electrolyte layer is not particularly limited as long as it has Li ion conductivity.

  In the first embodiment, the solid electrolyte material contained in the solid electrolyte layer is preferably the sulfide solid electrolyte material described in the above “(1) Positive electrode active material layer (i) Sulfide solid electrolyte material”. This is because a high output battery can be obtained. The content of the sulfide solid electrolyte material in the solid electrolyte layer is not particularly limited as long as a desired insulating property can be obtained. For example, within the range of 10% by volume to 100% by volume, It is preferably within the range of 50% to 100% by volume. In particular, in the first embodiment, it is preferable that the solid electrolyte layer is composed only of the sulfide solid electrolyte material.

  The solid electrolyte layer may contain a binder. This is because a solid electrolyte layer having flexibility can be obtained by containing a binder. Examples of the binder include fluorine-containing binders such as PTFE and PVDF. The thickness of the solid electrolyte layer is, for example, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 0.1 μm to 300 μm.

(4) Other configurations The lithium solid state battery of the first embodiment has at least the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer described above. Furthermore, it usually has a positive electrode current collector for collecting current of the positive electrode active material layer and a negative electrode current collector for collecting current of the negative electrode active material layer. Examples of the material for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. Among them, SUS is preferable. On the other hand, examples of the material for the negative electrode current collector include SUS, copper, nickel, and carbon. Among them, SUS is preferable. In addition, the thickness and shape of the positive electrode current collector and the negative electrode current collector are preferably appropriately selected according to the use of the lithium solid state battery. Moreover, the battery case of a common lithium solid battery can be used for the battery case used for the first embodiment. Examples of the battery case include a SUS battery case.

(5) Lithium solid state battery The lithium solid state battery of the first embodiment may be a primary battery or a secondary battery, but among them, a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful, for example, as a vehicle-mounted battery. Examples of the shape of the lithium solid state battery of the first embodiment include a coin type, a laminate type, a cylindrical type, and a square type.

  Moreover, the manufacturing method of the lithium solid state battery of the first embodiment is not particularly limited as long as it is a method capable of obtaining the above-described lithium solid state battery, and is the same method as a general method for manufacturing a lithium solid state battery. Can be used. As an example of a method for producing a lithium solid state battery, a power generation element is manufactured by sequentially pressing a material constituting the positive electrode active material layer, a material constituting the solid electrolyte layer, and a material constituting the negative electrode active material layer, A method of storing the power generation element in the battery case and caulking the battery case can be exemplified.

2. Second Embodiment Next, a second embodiment of the lithium solid state battery of the present invention will be described. The lithium solid state battery of the second embodiment is formed between a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and the positive electrode active material layer and the negative electrode active material layer. A solid lithium battery having a solid electrolyte layer, wherein at least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains the sulfide solid electrolyte material described above. Is.

  According to the second embodiment, since the sulfide solid electrolyte material having LiI (LiI component) is contained, a high output lithium solid state battery can be obtained. Furthermore, since the sulfide solid electrolyte material contains an ionic conductor containing oxygen (O), it is possible to suppress a decrease in chemical stability due to the influence of LiI. As a result, a lithium solid state battery in which an increase in reaction resistance is suppressed can be obtained.

  Similarly to FIG. 1 described above, the lithium solid state battery of the second embodiment includes a positive electrode active material layer 1 containing a positive electrode active material, a negative electrode active material layer 2 containing a negative electrode active material, a positive electrode active material layer 1 and A solid electrolyte layer 3 formed between the negative electrode active material layers 2, a positive electrode current collector 4 for collecting current of the positive electrode active material layer 1, and a negative electrode current collector 5 for collecting current of the negative electrode active material layer 2. And a battery case 6 for housing these members. In the second embodiment, at least one of the positive electrode active material layer 1, the negative electrode active material layer 2, and the solid electrolyte layer 3 is a sulfide solid described in “A. Sulfide solid electrolyte material 2. Second embodiment”. The main feature is that it contains an electrolyte material. In particular, in the second embodiment, the positive electrode active material layer 1, the negative electrode active material layer 2, and the solid electrolyte layer 3 preferably contain the sulfide solid electrolyte material.

  In the second embodiment, it is preferable that at least the positive electrode active material layer 1 contains the sulfide solid electrolyte material. This is because, as described above, the sulfide solid electrolyte material having LiI has not been used for the positive electrode active material layer. Furthermore, in the second embodiment, the potential of the positive electrode active material is not particularly limited, but is preferably 2.8 V (vs Li) or more, for example. Further, other matters relating to the lithium solid state battery of the second embodiment are the same as the matters described in the above-mentioned “B. Lithium solid state battery 1. First embodiment”.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1-1]
As starting materials, lithium sulfide (Li ₂ S), diphosphorus pentasulfide (P ₂ S ₅ ) and lithium iodide (LiI) were used. Next, in a glove box under an Ar atmosphere (dew point −70 ° C.), Li ₂ S and P ₂ S ₅ have a molar ratio of 75Li ₂ S · 25P ₂ S ₅ (Li ₃ PS ₄ , ortho composition). Weighed as follows. Next, LiI was weighed so that LiI was 10 mol%. 2 g of this mixture is put into a planetary ball mill container (45 cc, made of ZrO ₂ ), dehydrated heptane (moisture content of 30 ppm or less, 4 g) is added, and further ZrO ₂ balls (φ = 5 mm, 53 g) are added, The container was completely sealed (Ar atmosphere). This container was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling was performed 40 times with a base plate rotation speed of 500 rpm and a one-hour treatment and a 15-minute pause. Thereafter, the obtained sample was dried on a hot plate so as to remove heptane to obtain a sulfide solid electrolyte material. The composition of the obtained sulfide solid electrolyte material was 10LiI · 90 (0.75Li ₂ S · 0.25P ₂ S ₅ ).

[Example 1-2]
A sulfide solid electrolyte material was obtained in the same manner as in Example 1-1 except that the LiI ratio was changed to 30 mol%. The composition of the obtained sulfide solid electrolyte material was 30LiI · 70 (0.75Li ₂ S · 0.25P ₂ S ₅ ).

[Comparative Examples 1-1 and 1-2]
A sulfide solid electrolyte material was obtained in the same manner as in Example 1-1 except that the ratio of LiI was changed to 35 mol% and 40 mol%, respectively. The composition of the obtained sulfide solid electrolyte material is 35LiI · 65 (0.75Li ₂ S · 0.25P ₂ S ₅ ) and 40LiI · 60 (0.75Li ₂ S · 0.25P ₂ S ₅ ), respectively. there were.

[Comparative Example 1-3]
The Li ₂ S—P ₂ S ₅ —LiI-based amorphous material described in Non-Patent Document 1 was reproduced as faithfully as possible. Non-Patent Document 1 does not describe wet mechanical milling at all, and therefore, normal dry mechanical milling is used. First, lithium sulfide (Li ₂ S), diphosphorus pentasulfide (P ₂ S ₅ ) and lithium iodide (LiI) were used as starting materials. Next, in a glove box under an Ar atmosphere (dew point −70 ° C.), Li ₂ S and P ₂ S ₅ have a molar ratio of 75Li ₂ S · 25P ₂ S ₅ (Li ₃ PS ₄ , ortho composition). Weighed as follows. Next, LiI was weighed so that LiI was 30 mol%. 1 g of this mixture was put into a container of a planetary ball mill (45 cc, made of ZrO ₂ ), and ZrO ₂ balls (φ = 10 mm, 10 pieces) were further charged to completely seal the container (Ar atmosphere). This container was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling was performed 40 times at a base plate rotation speed of 370 rpm for 1 hour and 15 minutes. Thereby, a sulfide solid electrolyte material was obtained. The composition of the obtained sulfide solid electrolyte material was 30LiI · 70 (0.75Li ₂ S · 0.25P ₂ S ₅ ).

[Evaluation 1]
(X-ray diffraction measurement)
X-ray diffraction (XRD) measurement using CuKα rays was performed on the sulfide solid electrolyte materials obtained in Examples 1-1 and 1-2 and Comparative Examples 1-1 to 1-3. For XRD measurement, RINT Ultimate III manufactured by Rigaku was used. The result is shown in FIG. As shown in FIG. 2A, in Examples 1-1 and 1-2, a halo pattern was obtained, and it was confirmed to be an amorphous body. On the other hand, in Comparative Example 1-2, a LiI peak was confirmed in the vicinity of 2θ = 26 ° and was not amorphous. In Comparative Example 1-1, a slight LiI peak was observed in the vicinity of 2θ = 26 °, and it was determined that the material was not amorphous. On the other hand, as shown in FIG. 2B, in Comparative Example 1-3, a halo pattern was obtained, and it was confirmed to be an amorphous material.

(Differential thermal analysis)
Differential thermal analysis (DTA) was performed on the sulfide solid electrolyte materials obtained in Example 1-2 and Comparative Example 1-3. For DTA, TGA / SDTA851e manufactured by METTLER was used. The result is shown in FIG. As shown in FIG. 3, in Example 1-2, a glass transition was confirmed at about 70 ° C. On the other hand, in Comparative Example 1-3, a clear glass transition was not confirmed. Since the sulfide solid electrolyte material obtained in Example 1-2 is an amorphous material as shown in FIG. 2A and has a glass transition point as shown in FIG. It was glass in meaning. On the other hand, in Comparative Example 1-3, even an amorphous body was not a glass in a strict sense. In Example 1-2, since wet mechanical milling is used, the raw material composition can be prevented from adhering to the wall surface of the container, and a more solid sulfide solid electrolyte material is considered to have been obtained. It is done. Moreover, when comparing the crystallization behavior, Example 1-2 using wet mechanical milling has a sharper peak than Comparative Example 1-3 using dry mechanical milling, and thus the molecular structure is more uniform. It was suggested that

(Li ion conductivity measurement)
For the sulfide solid electrolyte materials obtained in Examples 1-1 and 1-2, Li ion conductivity (normal temperature) was measured by the AC impedance method. Li ion conductivity was measured as follows. 100 mg of the sample added to the support tube (made by Macor) was sandwiched between electrodes made of SKD. Thereafter, the sample was compacted at a pressure of 4.3 ton / cm ² , and impedance measurement was performed while restraining the sample at 6 Ncm. Solartron 1260 was used for measurement, and the measurement conditions were an applied voltage of 5 mV and a measurement frequency range of 0.01 MHz to 1 MHz. The result is shown in FIG. FIG. 4 also shows the results of FIG. 2 of Non-Patent Document 1. As shown in FIG. 4, the sulfide solid electrolyte material obtained in Examples 1-1 and 1-2 has higher Li ion conductivity than the sulfide solid electrolyte material described in Non-Patent Document 1. Was confirmed.

(Raman spectroscopy measurement)
Raman spectroscopic measurements were performed on the sulfide solid electrolyte materials obtained in Examples 1-1 and 1-2. For Raman spectroscopic measurement, Nanofinder SOLAR T II manufactured by Tokyo Instruments was used. The result is shown in FIG. As shown in FIG. 5, the sulfide solid electrolyte materials obtained in Examples 1-1 and 1-2 were confirmed to have a PS ₄ ^3- structure peak in the vicinity of 420 cm ⁻¹ . The peak of the _P 2 _S ^{7 4-} structures containing bridging sulfur (410Cm around ^-1) did not have.

(Verification of oxidative degradation)
Cyclic voltammetry (CV) was performed on the sulfide solid electrolyte material (30LiI · 70 (0.75Li ₂ S · 0.25P ₂ S ₅ )) obtained in Example 1-2. A cell composed of Li / sulfide solid electrolyte material / SUS was prepared as an evaluation cell. This evaluation cell is a cell having a bipolar structure in which Li is used for the reference electrode and the counter electrode, and SUS is used for the working electrode. The potential scanning speed was 5 mV / s, and the potential range was −0.3 V to 10 V. The result is shown in FIG. As shown in FIG. 6, the oxidation-reduction current corresponding to the dissolution and precipitation of Li was confirmed, but the oxidation decomposition reaction of LiI could not be confirmed. From this, it was confirmed that when the ionic conductor having the ortho composition is doped with LiI, the oxidative decomposition of LiI does not occur.

  In addition, since the conventional amorphous sulfide solid electrolyte material had only a melting and quenching method, it was difficult to synthesize an ortho-composition sulfide solid electrolyte material. Since the decomposition potential of LiI is thermodynamically 2.7 V and the amorphous bond is strong, it has been conventionally used for batteries using a high potential positive electrode active material because LiI undergoes oxidative decomposition. The idea that it was not possible was spreading. In recent years, mechanical milling has been established as a new amorphization method, and it has become possible to synthesize ortho-sulfide solid electrolyte materials (amorphous materials), but the idea that LiI undergoes oxidative decomposition has spread. The ionic conductor having an ortho composition has not been doped with LiI. However, as described above, the present inventors have found a new finding that when an ionic conductor having an ortho composition is doped with LiI, oxidative decomposition of LiI does not occur.

[Example 2]
LiCoO ₂ (positive electrode active material) coated with the sulfide solid electrolyte material (30LiI · 70 (0.75Li ₂ S · 0.25P ₂ S ₅ )) obtained in Example 1-2 and LiNbO ₃ having a thickness of 7 nm ) In a weight ratio of positive electrode active material: sulfide solid electrolyte material = 7: 3 to obtain a positive electrode mixture. Next, the sulfide solid electrolyte material obtained in Example 1-2 and graphite (negative electrode active material) were mixed at a weight ratio of negative electrode active material: sulfide solid electrolyte material = 5: 5. I got the material. Next, the sulfide solid electrolyte material obtained in Example 1-2 was prepared as a solid electrolyte layer forming material. A positive electrode composite material 16.2 mg, a solid electrolyte layer forming material 65 mg, and a negative electrode composite material 12 mg were put into a cylinder and cold pressed at a pressure of 4.3 ton / cm ² to obtain a lithium solid state battery.

[Comparative Example 2]
First, except that the ratio of Li ₂ S and P ₂ S ₅ was changed to a molar ratio of 67Li ₂ S · 33P ₂ S ₅ , the sulfide solid electrolyte material was changed in the same manner as in Comparative Example 1-3. Obtained (dry mechanical milling). The composition of the obtained sulfide solid electrolyte material was 30LiI · 70 (0.67Li ₂ S · 0.33P ₂ S ₅ ).
Next, the sulfide solid electrolyte material used for the positive electrode mixture, the negative electrode mixture, and the solid electrolyte layer forming material was converted into the sulfide solid electrolyte material (30LiI · 70 (0.67Li ₂ S · 0) obtained above. A lithium solid state battery was obtained in the same manner as in Example 2 except that it was changed to .33P ₂ S ₅ )).

[Evaluation 2]
(Evaluation of charge / discharge cycle characteristics)
Using the lithium solid state batteries obtained in Example 2 and Comparative Example 2, the charge / discharge cycle characteristics were evaluated. Constant current charge / discharge measurement was performed in the range of 3V to 4.1V with respect to the lithium solid state battery. The charge / discharge rate was 0.1 C, and the temperature was 25 ° C. The result is shown in FIG. As shown in FIG. 7, it was confirmed that in Example 2, the reduction in discharge capacity was smaller than that in Comparative Example 2 even when charging and discharging were repeated. As in Comparative Example 2, when a sulfide solid electrolyte material having bridging sulfur was used, the sulfide solid electrolyte material was oxidized and decomposed. On the other hand, as in Example 2, when a sulfide solid electrolyte material having no bridging sulfur was used, oxidative decomposition of the sulfide solid electrolyte material did not occur, and the discharge capacity could be maintained at a high value. It is considered a thing.

(Reaction resistance measurement)
Reaction resistance measurements were performed using the lithium solid state batteries obtained in Example 2 and Comparative Example 2. After adjusting the potential of the lithium solid state battery to 3.96 V, the reaction resistance of the battery was calculated by performing complex impedance measurement. In addition, reaction resistance was calculated | required from the diameter of the circular arc of an impedance curve. The result is shown in FIG. As shown in FIG. 8, it was confirmed that the reaction resistance of Example 2 was significantly smaller than that of Comparative Example 2. As in Comparative Example 2, when a sulfide solid electrolyte material having bridging sulfur was used, the sulfide solid electrolyte material was oxidatively decomposed, and thus it was considered that the reaction resistance was increased. On the other hand, as in Example 2, when a sulfide solid electrolyte material having no bridging sulfur was used, the oxidative decomposition of the sulfide solid electrolyte material did not occur and the reaction resistance did not increase. it is conceivable that. From the results of the oxidative decomposition verification, the charge / discharge cycle characteristics evaluation, and the reaction resistance measurement described above, it has been suggested that the decomposition of LiI, which has been a concern in the past, does not occur, but that the decomposition of crosslinked sulfur actually occurs. It was done.

[Example 3-1]
First, lithium sulfide (Li ₂ S), lithium oxide (Li ₂ O), diphosphorus pentasulfide (P ₂ S ₅ ), and lithium iodide (LiI) were used as starting materials. Next, a predetermined amount of Li ₂ S, P ₂ S ₅ and LiI was weighed in a glove box under an Ar atmosphere (dew point −70 ° C.). 2 g of this mixture is put into a planetary ball mill container (45 cc, made of ZrO ₂ ), dehydrated heptane (moisture content of 30 ppm or less, 4 g) is added, and further ZrO ₂ balls (φ = 5 mm, 53 g) are added, The container was completely sealed (Ar atmosphere). This container was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling for 1 hour and 15 minutes of rest was performed 20 times at a base plate rotation speed of 370 rpm. Next, a predetermined amount of Li ₂ O was added to the obtained sample, and mechanical milling was performed again under the same conditions. Thereafter, the obtained sample was dried on a hot plate so as to remove heptane to obtain a sulfide solid electrolyte material. The composition of the obtained sulfide solid electrolyte material was 30LiI · 70 (0.69Li ₂ S · 0.06Li ₂ O · 0.25P ₂ S ₅ ).

[Examples 3-2 to 3-6]
The ratio of LiI is xLiI · (100−x) (0.69Li ₂ S · 0.06Li ₂ O · 0.25P ₂ S ₅ ) so that x = 10, 20, 40, 43, and 60, respectively. The sulfide solid electrolyte material was obtained like Example 3-1, except having changed into.

[Comparative Example 3-1]
Except that Li ₂ O and Li ₂ were not used and Li ₂ S and P ₂ S ₅ were weighed at a molar ratio (ortho composition) of 75Li ₂ S · 25P ₂ S ₅ , the same as in Example 3-1. A sulfide solid electrolyte material was obtained. The composition of the obtained sulfide solid electrolyte material was 75Li ₂ S · 25P ₂ S ₅ .

[Comparative Example 3-2]
First, lithium sulfide (Li ₂ S), lithium oxide (Li ₂ O), and diphosphorus pentasulfide (P ₂ S ₅ ) were used as starting materials. Next, Li ₂ S and P ₂ S ₅ were weighed so as to have a molar ratio of 69Li ₂ S · 25P ₂ S ₅ in a glove box under an Ar atmosphere (dew point −70 ° C.). 2 g of this mixture is put into a planetary ball mill container (45 cc, made of ZrO ₂ ), dehydrated heptane (moisture content of 30 ppm or less, 4 g) is added, and further ZrO ₂ balls (φ = 5 mm, 53 g) are added, The container was completely sealed (Ar atmosphere). This container was attached to a planetary ball mill (P7 made by Fritsch), and mechanical milling was performed 20 times with a base plate rotation speed of 500 rpm and a 1-hour treatment and a 15-minute pause. Li ₂ O was added to the obtained sample so as to be 6 mol%, and mechanical milling was performed again under the same conditions. Thereafter, the obtained sample was dried on a hot plate so as to remove heptane to obtain a sulfide solid electrolyte material. The composition of the obtained sulfide solid electrolyte material was 69Li ₂ S · 6Li ₂ O · 25P ₂ S ₅ .

[Example 4]
The sulfide solid electrolyte material used for the positive electrode mixture, the negative electrode mixture, and the solid electrolyte layer forming material was the same as the sulfide solid electrolyte material (30LiI · 70 (0.69Li ₂ S · A lithium solid state battery was obtained in the same manner as in Example 2 except that it was changed to 0.06Li ₂ O · 0.25P ₂ S ₅ )).

[Comparative Examples 4-1 and 4-2]
The sulfide solid electrolyte materials used in the positive electrode mixture, the negative electrode mixture, and the solid electrolyte layer forming material were respectively converted into sulfide solid electrolyte materials (75Li ₂ S · 25P ₂ S ₅ obtained in Comparative Example 3-1. ) And the sulfide solid electrolyte material (69Li ₂ S · 6Li ₂ O · 25P ₂ S ₅ ) obtained in Comparative Example 3-2, a lithium solid state battery was obtained in the same manner as in Example 4. It was.

[Reference Example 4]
The sulfide solid electrolyte material used for the positive electrode mixture, the negative electrode mixture, and the solid electrolyte layer forming material was the same as the sulfide solid electrolyte material (30LiI · 70 (0.75Li ₂ S · A lithium solid state battery was obtained in the same manner as in Example 4 except that it was changed to 0.25P ₂ S ₅ )).

[Evaluation 3]
(Li ion conductivity measurement)
For the sulfide solid electrolyte material obtained in Examples 3-1 to 3-6, the Li ion conductivity (normal temperature) was measured by the AC impedance method. The measurement method is the same as described above. The result is shown in FIG. For reference, the results of the sulfide solid electrolyte materials obtained in Examples 1-1 and 1-2 are also shown in FIG. As shown in FIG. 9, Examples 3-1 to 3-6 doped with both LiI and Li ₂ O have Li ion conductivity higher than those of Examples 1-1 and 1-2 doped with only LiI. It was confirmed that it would be higher. The reason why the Li ion conductivity is improved by doping both LiI and Li ₂ O is not yet clear, but the mixed anion effect (the effect of improving the conductivity by mixing different anions) occurs. There is a possibility.

(Reaction resistance measurement)
Using the lithium solid state batteries obtained in Example 4, Comparative Examples 4-1 and 4-2, and Reference Example 4, reaction resistance was measured. The method for measuring reaction resistance is the same as described above. The result is shown in FIG. As shown in FIG. 10, the reaction resistance of Reference Example 4 was slightly increased as compared with Comparative Example 4-1. In consideration of the fact that the reference example 4 is obtained by doping LiI with respect to the comparative example 4-1, the chemical stability of the sulfide solid electrolyte material may be reduced by doping with LiI. It is done. In addition, the reaction resistance of Comparative Example 4-2 increased compared to Comparative Example 4-1. In consideration of the fact that Comparative Example 4-2 is doped with Li ₂ O, it is possible that the Li ion conductivity of the sulfide solid electrolyte material was lowered by doping with Li ₂ O.

On the other hand, in Example 4, the reaction resistance was significantly reduced as compared with Comparative Example 4-1. This is considered as follows. That is, Li ion doping improves the Li ion conductivity of the sulfide solid electrolyte material, suppresses the disadvantages of Li ₂ O doping (reduction in Li ion conductivity), and Li ₂ O doping reduces the sulfide solid electrolyte material. This is probably because the chemical stability was improved and the defects (decrease in chemical stability) of LiI doping were suppressed. That is, by doping both LiI and Li 2 _O, is considered a synergistic effect occurs which mutually complement each other's shortcomings.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode active material layer 2 ... Negative electrode active material layer 3 ... Solid electrolyte layer 4 ... Positive electrode collector 5 ... Negative electrode collector 6 ... Battery case 10 ... Lithium solid battery

Claims (5)

A sulfide solid electrolyte material containing Li, X (X is P, Si, Ge, Al, or B), S and O, and having an ortho-composition and LiI, The conductor contains oxygen ,
A sulfide solid electrolyte material characterized by not having Li ₂ S and bridging sulfur . _2. The sulfide solid electrolyte material according to claim 1, wherein oxygen of the ionic conductor is derived from Li ₂ O. 3.   3. The sulfide solid electrolyte material according to claim 1, wherein the ion conductor contains Li, P, S, and O. 4. A lithium solid state battery having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer Because
At least one of the positive electrode active material layer, the negative electrode active material layer, and the solid electrolyte layer contains the sulfide solid electrolyte material according to any one of claims 1 to 3. Lithium solid state battery. 5. The lithium solid state battery according to claim 4 , wherein the positive electrode active material layer contains the positive electrode active material having a potential of 2.8 V (vs Li) or more and the sulfide solid electrolyte material.

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