JP2018005985A - Positive electrode mixture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode mixture by which a lithium ion battery with a high discharge voltage can be obtained.SOLUTION: A positive electrode mixture comprises: a solid electrolyte including a lithium element, a phosphorus element and a sulfur element, and at least one element M selected from a group consisting of Si, Sn, Pb, Sb, B, Al, Ga, In, Ti, Zr, V and Nb, and having peaks at, at least 2θ=20.1±0.5° and 23.9±0.5° in powder X-ray diffraction measurement with Cu Kα rays; and a positive electrode active material including a sulfur element.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode mixture, a positive electrode, and a lithium ion battery.

Since the conventional lithium ion battery uses an electrolytic solution containing an organic solvent as an electrolyte, there is a risk of liquid leakage and a risk of ignition. Therefore, an all-solid lithium ion battery using a solid electrolyte that does not use a solvent has been studied.
In addition, in order to increase the capacity and output of an all-solid-state battery, development of electrode composites used for electrodes is being promoted. For example, a positive electrode mixture including a solid electrolyte containing a Li element or Na element, an S element, and a halogen element selected from the group consisting of I, Br, Cl, and F, and a sulfur-based active material is proposed. (See Patent Document 1).

JP 2014-11033 A

By using the positive electrode mixture described in Patent Document 1, a lithium ion battery having a high discharge voltage can be obtained while using a sulfur-based active material having a high capacity. However, further improvements have been sought.
The subject of this invention is providing the positive electrode compound material from which the lithium ion battery with a high discharge voltage is obtained.

According to the present invention, the following positive electrode mixture and the like are provided.
1. Elemental lithium, elemental phosphorus and elemental sulfur;
And at least one element M selected from the group consisting of Si, Sn, Pb, Sb, B, Al, Ga, In, Ti, Zr, V and Nb,
In a powder X-ray diffraction measurement using CuKα rays, a solid electrolyte having peaks at least 2θ = 20.1 ± 0.5 ° and 23.9 ± 0.5 °;
And a positive electrode active material containing a sulfur element.
2. 2. The positive electrode mixture according to 1, wherein the solid electrolyte further contains a halogen element.
3. The positive electrode mixture according to 1 or 2, wherein the element M is Si.
4). Furthermore, the positive electrode compound material in any one of 1-3 containing an electroconductive substance.
5. 5. The positive electrode mixture according to 4, wherein the positive electrode active material and the conductive material are combined.
6). 6. The positive electrode mixture according to 4 or 5, wherein the conductive substance is porous carbon having pores.
The positive electrode containing the positive electrode compound material in any one of 7.1-6.
A lithium ion battery having the positive electrode according to 8.7.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode compound material from which the lithium ion battery with a high discharge voltage is obtained can be provided.

The positive electrode mixture of the present invention includes the following solid electrolyte and a positive electrode active material containing a sulfur element.
Solid electrolyte:
Lithium element (Li), phosphorus element (P) and sulfur element (S);
And at least one element M selected from the group consisting of Si, Sn, Pb, Sb, B, Al, Ga, In, Ti, Zr, V and Nb,
In powder X-ray diffraction measurement using CuKα rays, there are peaks at least at 2θ = 20.1 ± 0.5 ° and 23.9 ± 0.5 °.
The solid electrolyte does not contain germanium element (Ge).

In the powder X-ray diffraction measurement, having the above-mentioned peak indicates that the solid electrolyte is Li _4-x Ge _1-x P _x S ₄ (x is 0 <x <1) system thiolithic region II (thio-LISICON) It shows that it contains a region II) type crystal structure or a crystal structure similar to this type.

The elemental composition of the solid electrolyte used in the present invention preferably satisfies the following formula (1).
_{Li a M b P c S d} X e (1)
(Wherein M is at least one element selected from the group consisting of Si, Sn, Pb, Sb, B, Al, Ga, In, Ti, Zr, V and Nb. X is I, Cl, (At least one element selected from the group consisting of Br and F. a to e indicate the composition ratio of each element.)

In the formula (1), a is preferably 8 ≦ a ≦ 12, and particularly preferably 9 ≦ a ≦ 11.
b and c are b> 0 and c> 0, preferably 2 ≦ b + c ≦ 4, and particularly preferably 2.5 ≦ b + c ≦ 3.5.
d is preferably 10 ≦ d ≦ 14, and particularly preferably 11 ≦ d ≦ 13.
e is preferably 0 ≦ e ≦ 0.5, and particularly preferably 0.2 ≦ e ≦ 0.4.

In the formula (1), M is preferably Si. When M is Si, in the formula (1), a is preferably 8 ≦ a ≦ 12, and particularly preferably 9 ≦ a ≦ 11.
b and c are b> 0 and c> 0, preferably 2 ≦ b + c ≦ 4, and particularly preferably 2.5 ≦ b + c ≦ 3.5.
d is preferably 10 ≦ d ≦ 14, and particularly preferably 11 ≦ d ≦ 13.
e is preferably 0 <e <0.5, and particularly preferably 0.2 ≦ e ≦ 0.4.
X is preferably F, Cl, Br or I, and particularly preferably Cl.
a to e can be controlled by adjusting the mixing ratio of the solid electrolyte raw materials.

For the solid electrolyte used in the present invention, two or more raw materials (compounds or simple substances) are selected and reacted so that the solid electrolyte contains the elements (Li, P, S and element M) which are essential as a whole. Can be manufactured.
The raw material containing lithium element is preferably at least one of lithium compounds such as lithium sulfide (Li ₂ S), lithium oxide (Li ₂ O), lithium carbonate (Li ₂ CO ₃ ), and lithium metal alone. . As the lithium compound, lithium sulfide (Li ₂ S) is particularly preferable.

Examples of the raw material containing phosphorus element and / or sulfur element include phosphorus sulfide such as diphosphorus trisulfide (P ₂ S ₃ ) and diphosphorus pentasulfide (P ₂ S ₅ ), and sodium phosphate (Na ₃ PO ₄ ). It is preferable that they are at least one of phosphorus compounds, such as zinc sulfide (ZnS), phosphorus simple substance, or sulfur simple substance. Of these, phosphorus sulfide is preferable. These raw materials can be used without particular limitation as long as they are industrially produced and sold.

As a raw material containing the element M, a sulfide or halide of the element M is preferable. Examples of the sulfide include silicon sulfide (SiS ₂ ), boron sulfide (B ₂ S ₃ ), gallium sulfide (Ga ₂ S ₃ ), tin sulfide (SnS or SnS ₂ ), aluminum sulfide (Al ₂ S ₃ ), and the like. Is mentioned.
As a halide, the halogen containing compound represented by Formula (2) mentioned later is mentioned.

  The raw material preferably further contains at least one halogen element such as fluorine (F), chlorine (Cl), bromine (Br) and iodine (I), and more preferably at least one of chlorine, bromine and iodine. For example, a halogen-containing compound represented by the following formula (2) is preferable.

M ′ _l −X _m (2)
In the formula (2), M ′ is sodium (Na), lithium (Li), boron (B), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), arsenic (As), Selenium (Se), tin (Sn), antimony (Sb), tellurium (Te), lead (Pb), or bismuth (Bi) are shown, lithium (Li) or phosphorus (P) is preferable, and lithium is particularly preferable.
X is a halogen element selected from fluorine, chlorine, bromine and iodine.
L is an integer of 1 or 2, and m is an integer of 1 to 10.

Specific examples of the halogen-containing compound represented by the above formula (2) include sodium halides such as NaI, NaF, NaCl and NaBr, lithium halides such as LiF, LiCl, LiBr and LiI, BCl ₃ and BBr. ₃ , boron halides such as BI ₃ , aluminum halides such as AlF ₃ , AlBr ₃ , AlI ₃ , AlCl ₃ , SiF ₄ , SiCl ₄ , SiCl ₃ , Si ₂ Cl ₆ , SiBr ₄ , SiBrCl ₃ , SiBr ₂ Cl _2, SiI ₄ halides such as _{silicon, PF 3, PF 5, PCl} 3, PCl 5, POCl 3, PBr 3, POBr 3, PI 3, P 2 Cl 4, phosphorus halides such as P 2 _{I 4,} SF ₂ , halogeno such as SF ₄ , SF ₆ , S ₂ F ₁₀ , SCl ₂ , S ₂ Cl ₂ , S ₂ Br ₂ Arsenic halides such as sulfur nitride, AsF ₃ , AsCl ₃ , AsBr ₃ , AsI ₃ , AsF ₅ , selenium halides such as SeF ₄ , SeF ₆ , SeCl ₂ , SeCl ₄ , Se ₂ Br ₂ , SeBr ₄ , SnF ₄ , SnCl ₄ , SnBr ₄ , SnI ₄ , SnF ₂ , SnCl ₂ , SnBr ₂ , SnI ₂ , tin halides such as SbF ₃ , SbCl ₃ , SbBr ₃ , SbI ₃ , SbF ₅ , SbCl _5, etc. , TeF ₄ , Te ₂ F ₁₀ , TeF ₆ , TeCl ₂ , TeCl ₄ , TeBr ₂ , TeBr ₄ , TeI _{4 and the} like tellurium halides, PbF ₄ , PbCl ₄ , PbF ₂ , PbCl ₂ , PbBr ₂ , PbBr _2, etc. of lead _{halide, BiF 3, BiCl 3, BiBr} 3, BiI 3 , etc. Ha Gen bismuth, and the like.

Among the halogen-containing compounds, lithium halides such as lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus pentachloride (PCl ₅ ), phosphorus trichloride (PCl ₃ ), and five odors Phosphorus halides such as phosphorus bromide (PBr ₅ ) and phosphorus tribromide (PBr ₃ ) are preferred. Among these, lithium halides such as lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), and phosphorus tribromide (PBr ₃ ) are preferable, and lithium chloride (LiCl) and lithium bromide (LiBr) are preferable. ) And lithium halides such as lithium iodide (LiI) are more preferable. As the halogen-containing compound, one of the above compounds may be used alone, or two or more thereof may be used in combination, that is, at least one of the above compounds can be used.

As a combination of raw materials, for example, the following combinations are preferable.
Lithium sulfide, sulfur compound of element M and phosphorus sulfide / lithium sulfide, sulfur compound of element M, phosphorus sulfide and halogen or a compound containing a halogen element (lithium halide is preferred)
Among _them, Li _{2 S,} it is preferable to use a _{P 2} S 5, SiS 2 and halogenated lithium (LiCl, etc.).

Examples of the method for producing a solid electrolyte from the raw materials include a method not using a solvent and a method using a solvent.
As a method not using a solvent, there are a method of applying mechanical energy and a method of applying thermal energy. The method of giving mechanical energy is, for example, a dry mechanical milling method using a mill. A method for applying thermal energy is, for example, a melt quenching method.
As a method using a solvent, a wet mechanical milling method in which a raw material and a solvent are put into a mill, a method of bringing a raw material into contact with a hydrocarbon solvent (WO2009 / 047977), a method of bringing a raw material into contact with a hydrocarbon solvent, and pulverization synthesis Examples include a method of alternately performing means (Japanese Patent Laid-Open No. 2010-140893), and a method of performing a pulverization synthesis step after a step of contacting a raw material in a solvent (PCT / JP2012 / 005992).

  The solvent may be a polar solvent or a nonpolar solvent. Nonpolar solvents include hydrocarbon solvents. Examples of the hydrocarbon solvent include aliphatic hydrocarbon solvents and aromatic hydrocarbon solvents, and mixing in an aromatic hydrocarbon solvent is preferable. As the aromatic hydrocarbon solvent, alkylbenzene is preferable. As the alkylbenzene, toluene is preferable.

  As a specific production example, for example, Nature energy 30, 1-5 (2016) Yuki Kato et. al. Can be referred to.

The positive electrode active material used in the present invention is an active material containing a sulfur element as a constituent element.
For example, elemental sulfur (S), titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), iron sulfide (FeS, FeS ₂ ), copper sulfide (CuS), nickel sulfide (Ni ₃ S ₂ ), lithium sulfide, Compounds containing sulfur elements such as organic disulfide compounds and carbon sulfide compounds can be used.

Organic disulfide compounds and carbon sulfide compounds are exemplified below.

In formulas (A) to (C), X is a substituent, n and m are each independently an integer of 1 to 2, and p and q are each independently an integer of 1 to 4.
In formula (D), Z is -S- or -NH-, respectively, and n is an integer of 2 to 300 repetitions.

Of the above, elemental sulfur or lithium sulfide having a high theoretical capacity is preferred.
The sulfur is not particularly limited, but is preferably a simple sulfur having a purity of 95% by weight or more, more preferably a simple sulfur having a purity of 96% by weight or more, and particularly preferably a sulfur having a purity of 97% by weight or more. It is a simple substance.
If the purity of sulfur is 95% by weight or more, the irreversible capacity of a battery manufactured using this sulfur can be reduced.
Examples of the crystal system of simple sulfur include α sulfur (orthorhombic system), β sulfur (monoclinic system), γ sulfur (monoclinic system), amorphous sulfur, and the like. But they can be used together.

Examples of lithium sulfide include Li ₂ S, Li ₂ S ₂ , Li ₂ S ₄ , and Li ₂ S ₈ . Of these, Li ₂ S is preferable.

  In the positive electrode mixture of the present invention, as the positive electrode active material, it is sufficient to include at least one of sulfur and a compound containing a sulfur atom. When only the elemental sulfur is included, when only the compound containing a sulfur atom is included, elemental sulfur and It may contain both compounds containing sulfur atoms. In these cases, two or more kinds of elemental sulfur may be contained, or a compound containing two or more kinds of sulfur atoms may be contained.

The positive electrode mixture of the present invention preferably contains a conductive substance in addition to the above-described solid electrolyte and positive electrode active material.
The conductive material is a material having an electric conductivity of 1.0 × 10 ³ S / m or more, preferably a material having 1.0 × 10 ⁴ S / m or more, more preferably 1.0 × 10 ^5. It is a substance of S / m or more.
The conductive substance preferably has pores. By having the pores, the positive electrode active material can be included in the pores, the contact area between the positive electrode active material and the conductive material can be increased, and the specific surface area of the positive electrode active material can be increased.
The shape of the conductive material is not particularly limited, and may be a particulate conductive material, a plate-shaped conductive material, or a rod-shaped conductive material. For example, the plate-like conductive material may be graphene, the rod-like conductive material may be, for example, carbon nanotubes, etc., and the particulate conductive material may have a large surface area, a large pore volume, and an electronic conductivity. Examples include ketjen black and activated carbon, which have high properties.

Examples of the conductive substance include carbon, metal powder, and metal compound. Carbon is preferred. When the positive electrode mixture of the present invention contains carbon as a conductive substance, since carbon has high conductivity and is light, a battery having a high energy density per weight can be obtained.
More preferably, the conductive material is porous carbon having pores.
Examples of the porous carbon that is a conductive substance include carbon blacks such as ketjen black, acetylene black, denka black, thermal black, and channel black; and carbons such as graphite, carbon fiber, and activated carbon. These may be used alone or in combination of two or more.

The conductive material is preferably a conductive material having pores, and the pore volume is 0.1 cc / g or more and 5.0 cc / g or less. The pore volume is more preferably 0.1 cc / g or more and 4.5 cc / g or less, and particularly preferably 0.75 cc / g or more and 3.9 cc / g or less. The conductive substance is preferably a conductive substance having pores and having an average pore diameter of 100 nm or less. The average pore diameter is more preferably 0.1 nm to 100 nm, still more preferably 0.1 nm to 25 nm, and most preferably 0.5 nm to 17 nm.
Since the conductive material has pores, the positive electrode active material can be inserted into the pores of the conductive material, and the contact state between the conductive material and the positive electrode active material can be improved. The electron conductivity of can be increased. In addition, when the conductive material and the positive electrode active material are combined, it is easy to form a composite by having pores, and the electron conductivity of the positive electrode mixture can be increased.
If the pore capacity of the conductive material is less than 0.1 cc / g, the positive electrode active material content inside the conductive material may not be increased, making it difficult to obtain a lithium ion battery having a high electric capacity. There is a risk. On the other hand, when the pore capacity of the conductive material is more than 5.0 cc / g, there is a possibility that sufficient electron conductivity cannot be ensured even if it is combined with the positive electrode active material.
When the average pore diameter of the conductive material is less than 0.1 nm, it may be difficult to impregnate the positive electrode active material in the pores. On the other hand, when the average pore diameter of the conductive material is more than 100 nm, the positive electrode active material impregnated in the pores may not function sufficiently as the active material.

The specific surface area of the conductive material is preferably 10 m ² / g or more and 5000 m ² / g or less. For example, in order for the sulfur-porous carbon composite obtained by combining sulfur and porous carbon to ensure a contact area with the solid electrolyte, the porous carbon should have a large specific surface area. Since the average pore diameter is small, it is difficult to contain sulfur in the pores. If the specific surface area of the porous carbon is small, the contact with sulfur is not sufficient and the electron conductivity cannot be secured, and there is a possibility that sulfur does not sufficiently function as an active material. Therefore, the BET specific surface area of the porous carbon is preferably 10 m ² / g or more and 5000 m ² / g or less. More preferably, ^{50 m} 2 / g or more 4500 m ² / g or less, more preferably ^70m 2 / g or more 4000 m ² / g or less, and most preferably not more than 100 m ² / g or more 3500 m ² / g.

The BET specific surface area, pore diameter, pore volume and average pore diameter of the conductive material can be measured by the following methods. Hereinafter, although the case where a conductive substance is porous carbon is demonstrated to an example, the following measuring method is not limited to the case where a conductive substance is porous carbon.
The BET specific surface area, the pore diameter, the pore volume and the average pore diameter can be determined using a nitrogen adsorption isotherm obtained by adsorbing nitrogen gas to the porous carbon at a liquid nitrogen temperature. it can.
Specifically, the specific surface area can be determined by the Brenauer-Emmet-Telle (BET) method using a nitrogen adsorption isotherm. Further, the pore diameter and pore volume can be determined by the Barret-Joyner-Halenda (BJH) method using a nitrogen adsorption isotherm (adsorption side). The average pore diameter is calculated from the total pore volume and the BET specific surface area assuming that the pore structure is cylindrical.
As a measuring apparatus, it can measure using the specific surface area and pore distribution measuring apparatus (Autosorb-3) made from Quantachrome, for example. Examples of the pretreatment for measurement include heating and evacuation at 200 ° C. for 3 hours.

In the present invention, the positive electrode active material and the conductive material are preferably in contact with each other. In order to bring the positive electrode active material and the conductive material into contact with each other, it is preferable to integrate them by a mechanical action such as mechanical milling or to combine the positive electrode active material and the conductive material as described below. More preferably, it is a positive electrode active material-conductive material composite. “Positive electrode active material-conductive material composite” is a positive electrode active material deposited on the surface of the conductive material, dissolved in the positive electrode active material and brought into contact with the surface of the conductive material and then solidified The positive electrode active material is synthesized in the presence of a conductive material and integrated with the conductive material. For example, the positive electrode active material and the conductive material are integrated by a mechanical action such as mechanical milling. Does not include
The surface of the conductive material includes the surface of the pore when the conductive material has pores.
As the positive electrode active material-conductive material complex, it is preferable that the conductive material has pores, and the positive electrode active material exists in the pores.

  In the positive electrode active material-conductive material composite in which the positive electrode active material and the conductive material are combined, the content of the positive electrode active material is, for example, 5 to 90% by weight, preferably 40 to 90% by weight, More preferably, it is 50-80 weight%.

  The positive electrode mixture of the present invention means, for example, the above-described solid electrolyte, or a solid electrolyte precursor that becomes the solid electrolyte by heating or the like (for example, glass, a mixture of glass and glass ceramics, or a mixture of these and a raw material compound) And the positive electrode active material described above can be manufactured by integrating them by a mechanical action such as mechanical milling. Specifically, by kneading machines, planetary ball mills, rolling ball mills, vibrating ball mills, vertical roller mills such as ring roller mills, high speed rotating mills such as hammer mills and cage mills, and airflow mills such as jet mills. It can manufacture by processing by the method of mixing, the wet mixing in a fill mix etc., the dry mixing in a mechano-fusion, etc.

When the solid electrolyte precursor that becomes the solid electrolyte by heating or the like is used, the solid electrolyte precursor may be heated as necessary when integrated by mechanical action or after integration. For example, when the solid electrolyte precursor contains glass, the heating temperature is preferably Tg or more and (Tc + 100 ° C.) or less (Tg: glass transition temperature, Tc: crystallization temperature). If it is less than Tg, crystallization may be very slow. If it exceeds (Tc + 100 ° C.), the electrolyte may be deteriorated and the ionic conductivity may be lowered. More preferably, it is (Tg + 5 ° C.) or more and (Tc + 90 ° C.) or less, and more preferably (Tg + 10 ° C.) or more and (Tc + 80 ° C.) or less.
For example, the heating temperature is 150 ° C. or higher and 360 ° C. or lower, preferably 160 ° C. or higher and 350 ° C. or lower, more preferably 180 ° C. or higher and 310 ° C. or lower, more preferably 180 ° C. or higher and 290 ° C. or lower, Especially preferably, it is 190 degreeC or more and 270 degrees C or less.

The heating time is preferably 0.005 minutes or more and 10 hours or less. More preferably, it is 0.005 minutes or more and 5 hours or less, and particularly preferably 0.01 minutes or more and 3 hours or less. If it is less than 0.005 minutes, heating may be insufficient. If it exceeds 10 hours, the electrolyte may deteriorate and the ionic conductivity may decrease.
There is no specific specification for the temperature raising method. The temperature may be raised slowly to a predetermined temperature or heated rapidly.

The heat treatment is preferably performed in an environment with a dew point of −40 ° C. or less, and more preferably in an environment with a dew point of −60 ° C. or less.
The pressure at the time of heating may be a normal pressure or a reduced pressure.
The atmosphere may be in the air or an inert atmosphere.
Furthermore, you may heat in a solvent as it describes in Unexamined-Japanese-Patent No. 2010-186744.

  The mixing ratio of the positive electrode active material and the solid electrolyte or solid electrolyte precursor is not particularly limited. However, when there are too many positive electrode active materials, an ion conduction path is difficult to be formed in the composite material, resulting in a decrease in voltage and a decrease in utilization rate of the active material. On the other hand, when the amount of the positive electrode active material is small, the electric capacity becomes small. Therefore, the weight ratio of the positive electrode active material to the solid electrolyte or solid electrolyte precursor (positive electrode active material: solid electrolyte) is preferably 20:80 to 90:10, more preferably 30:70 to 80:20, still more preferably. Is 40:60 to 75:25, most preferably 50:50 to 70:30.

In the positive electrode mixture of the present invention, a binder resin, a conductive material (conductive auxiliary agent), other positive electrode active materials, etc. are added in addition to the above-described solid electrolyte and positive electrode active material and, if necessary, a conductive material. May be.
Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing resins such as fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, Natural butyl rubber (NBR) or the like can be used alone or as a mixture of two or more. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used.
As the conductive assistant, the above-described conductive substances can be used.

The positive electrode mixture of the present invention is suitable as a material for forming a positive electrode of a lithium ion battery. The positive electrode of the present invention is produced using the positive electrode mixture of the present invention as a raw material, or contains a positive electrode mixture. A known method or a method developed in the future can be adopted as a method for producing the positive electrode. For example, the positive electrode mixture of the present invention can be formed by a method of press-molding by a usual method to form a sheet-like electrode. Moreover, it can also manufacture by forming into a film by the electrostatic method or the apply | coating method.
The thickness of the positive electrode can be appropriately adjusted according to the required performance of the lithium ion battery.

  The lithium ion battery of the present invention only needs to have a positive electrode obtained from the above-described positive electrode mixture of the present invention, and other components such as a solid electrolyte layer, a negative electrode, and a current collector can be used. .

The solid electrolyte layer is a layer made of a solid electrolyte. As the solid electrolyte, a known solid electrolyte such as a polymer-based solid electrolyte, an oxide-based solid electrolyte, or a sulfide-based solid electrolyte can be used. Preferably, it is a solid electrolyte used with the positive electrode mixture of the present invention described above.
The thickness of the solid electrolyte layer is preferably 0.001 mm or more and 1 mm or less.

It is preferable that a negative electrode layer contains a negative electrode active material, an electrolyte, and a conductive support agent. Moreover, the binder may be included. The formation method and thickness are the same as in the case of the positive electrode.
As the negative electrode active material, a material capable of inserting and desorbing lithium ions, and a material known as a negative electrode active material in the battery field can be used.
For example, carbon materials, specifically artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolytic vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon Examples thereof include fibers, vapor-grown carbon fibers, natural graphite, and non-graphitizable carbon. Or it may be a mixture thereof. Preferably, it is artificial graphite.
Also, an alloy in combination with a metal itself such as metallic lithium, metallic indium, metallic aluminum, metallic silicon, or another element or compound can be used as the negative electrode material. Among these, silicon, tin, and lithium metal having a high theoretical capacity are preferable.
About an electrolyte and a conductive support agent, the same thing as the positive electrode mixture and the solid electrolyte layer mentioned above can be used.

  As the current collector, a plate-like body, a foil-like body, a mesh-like body, or the like made of stainless steel, gold, platinum, copper, zinc, nickel, tin, aluminum, or an alloy thereof can be used.

  The lithium ion battery of the present invention can be produced by a known method, for example, by a coating method or an electrostatic method (an electrostatic spray method, an electrostatic screen method, etc.).

Hereinafter, the present invention will be described in more detail with reference to examples.
The evaluation method is as follows.
(1) X-ray diffraction (XRD) measurement From the solid electrolyte powder produced in each example, a circular pellet having a diameter of 10 mm and a height of 0.1 to 0.3 cm was molded to prepare a sample. This sample was measured using an airtight holder for XRD without being exposed to air. The 2θ position of the diffraction peak was determined by the centroid method using the XRD analysis program JADE.
The measurement was performed under the following conditions using a powder X-ray diffraction measurement device SmartLab manufactured by Rigaku Corporation.
Tube voltage: 45kV
Tube current: 200 mA
X-ray wavelength: Cu-Kα ray (1.5418mm)
Optical system: Parallel beam method Slit configuration: Solar slit 5 °, entrance slit 1 mm, light receiving slit 1 mm
Detector: Scintillation counter Measurement range: 2θ = 10-60 °
Step width, scan speed: 0.02 °, 1 ° / min

(2) Ionic conductivity measurement The solid electrolyte was filled in a tablet molding machine, and a pressure of 22 MPa was applied to obtain a molded body. Carbon was placed on both sides of the molded body as an electrode, and pressure was again applied with a tablet molding machine to prepare a molded body for measurement (diameter of about 10 mm, thickness of 0.1 to 0.2 cm). The ion conductivity of this molded body was measured by AC impedance measurement. The conductivity value was a value at 25 ° C.

Example 1
(1) Synthesis of lithium sulfide (Li ₂ S) In a 500 mL separable flask equipped with a stirrer, 200 g of lithium hydroxide anhydride (manufactured by Honjo Chemical Co., Ltd.) dried under an inert gas was charged. The temperature was raised under a nitrogen stream, and the internal temperature was maintained at 200 ° C. Nitrogen gas was switched to hydrogen sulfide gas (manufactured by Sumitomo Seika Co., Ltd.), the flow rate was 500 mL / min, and lithium hydroxide anhydride and hydrogen sulfide were reacted.
The water generated by the reaction was condensed and collected by a condenser. When the reaction was performed for 6 hours, 144 mL of water was recovered. The reaction was further continued for 3 hours, but no generation of water was observed.
The produced powder was collected and measured for purity and X-ray diffraction. The purity was 98.5%, and the peak pattern of lithium sulfide was confirmed by X-ray diffraction measurement.

(2) Production of solid electrolyte In a glove box filled with nitrogen, lithium sulfide (0.3891 g, 8.47 × 10 ⁻³ mol) synthesized in the above (1), diphosphorus pentasulfide (P ₂ S ₅ , 0.2934 g, 1.32 × 10 ⁻³ mol), silicon sulfide (SiS ₂ , 0.2942 g, 3.19 × 10 ⁻³ mol), and lithium chloride (LiCl, 0.0233 g, 0.55 × 10 ^{− 3} mol) and 15 Zr ₂ O balls having a diameter of 10 mm as grinding media were charged into a stainless steel 45 mL pot and sealed. Elemental composition of the whole material is _{Li 10 Si 1.8 P 1.5 S 12.3} Cl 0.3.
The pot was taken out of the glove box and mounted on a heated planetary ball mill (manufactured by Ito Seisakusho: rotation radius 0.075 m, reverse rotation direction of rotation and revolution 1). While milling at a rotational speed of 350 rpm, the temperature was raised to 250 ° C., and the treatment was performed for 30 hours after the temperature was raised.
From the X-ray diffraction measurement of the obtained powder, it was confirmed that it had peaks at 2θ = 20.1 ± 0.5 ° and 23.9 ± 0.5 °. The ion conductivity σ was 1.3 × 10 ⁻³ S / cm.

(3) Preparation of composite of positive electrode active material and conductive material 0.500 g of sulfur (manufactured by Aldrich, purity 99.998%) and 0.214 g of porous carbon (Ketjen Black (KB) EC600JD, manufactured by Lion) After mixing in a mortar, the mixture was placed in a hermetic stainless steel container and heat-treated in an electric furnace. The heating conditions were from room temperature to 150 ° C. at 10 ° C./minute, held at 150 ° C. for 6 hours, then heated to 300 ° C. at 10 ° C./minute, held for 2.75 hours, then naturally cooled, A complex was obtained.
In addition, the pore capacity | capacitance of the pore whose pore diameter of ketjen black is 100 nm or less was 2.7 cc / g, the average pore diameter was 12.7 nm, and the BET specific surface area was 1365 m ² .

(4) Production of positive electrode composite material 0.5 g of the solid electrolyte powder synthesized in (2) above and 0.5 g of the composite produced in (3) above were put in a mill pot, and a planetary ball mill (manufactured by Fritsch: Model No. P-7) was subjected to mechanical milling for 5 hours at room temperature (25 ° C.) in argon at room temperature (25 ° C.) to obtain a positive electrode mixture.

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

After decanting NMP in the 500 mL slurry reaction solution (NMP-lithium sulfide slurry) obtained above, 100 mL of dehydrated NMP was added and stirred at 105 ° C. for about 1 hour. NMP was decanted at that temperature. Further, 100 mL of NMP was added, stirred at 105 ° C. for about 1 hour, NMP was decanted at that temperature, and the same operation was repeated a total of 4 times. After completion of the decantation, lithium sulfide was dried at 230 ° C. (temperature higher than the boiling point of NMP) under a nitrogen stream for 3 hours under normal pressure. The impurity content in the obtained lithium sulfide was measured.
Incidentally, lithium sulfite _(Li 2 _SO 3), the content of each sulfur oxide lithium sulfate _(Li 2 SO ₄₎ and lithium thiosulfate _{(Li 2 S 2 O 3)} , and N- methylamino acid lithium (LMAB) Was quantified by ion chromatography. As a result, the total content of sulfur oxides was 0.13% by weight, and LMAB was 0.07% by weight.

(2) Production of solid electrolyte As raw materials, 0.306 g (6.66 × 10 ⁻³ mol) of lithium sulfide synthesized in (1) above, 0.494 g (2.22 ×) of diphosphorus pentasulfide (manufactured by Aldrich) 10 ⁻³ mol) and 0.200 g (1.49 × 10 ⁻³ mol) of lithium iodide (Aldrich) were used.
The mixed powder and 10 zirconia balls having a diameter of 10 mm were put into a planetary ball mill (Fritsch Co., Ltd. model number P-7) alumina pot and completely sealed. This operation was performed in a glove box under an argon atmosphere with a dew point of -80 ° C or lower.
For the first few minutes, the planetary ball mill was rotated at a low speed (85 rpm) to sufficiently mix the mixed powder. Thereafter, the rotational speed of the planetary ball mill was gradually increased to 370 rpm. Mechanical milling was performed for 20 hours at a rotational speed of the planetary ball mill at 370 rpm. As a result of evaluating the mechanically milled powder by X-ray diffraction measurement, it was confirmed that it was sulfide glass (electrolyte precursor).
In addition, it confirmed that a solid electrolyte (glass ceramic) was producible by heat-processing an electrolyte precursor at 230 degreeC for 2 hours.

(3) Preparation of positive electrode composite material 0.5 g of the electrolyte precursor powder prepared in the above (2) and 0.5 g of the composite prepared in Example 1 (2) were put in a mill pot, and a planetary ball mill (Fritsch Product: Model No. P-7) was mechanically milled for 5 hours at room temperature (25 ° C.) in argon at a rotational speed of 370 rpm.
0.5 g of the mixture after the mechanical milling treatment was quickly sandwiched between two stainless steel plates previously heated to 210 ° C. in an oven controlled at a temperature of 210 ° C. and left for 10 minutes. The sample reaches 210 ° C. in about 2 minutes by being sandwiched between heated metal plates. Then, it air-cooled and obtained the positive electrode compound material.

Comparative Example 2
(1) Preparation of solid electrolyte It manufactured with the method based on Example 1 of international publication gazette WO07 / 0666539.
Specifically, 0.325 g (0.00707 mol) of lithium sulfide synthesized in Comparative Example 1 (1) and 0.675 g (0.00303 mol) of diphosphorus pentasulfide (manufactured by Aldrich) were used as raw materials. Was the same as in Comparative Example 1.
As a result of evaluating the mechanically milled white yellow powder by X-ray diffraction measurement, it was confirmed that it was vitrified (sulfide glass).
0.5 g of the obtained sulfide glass was put into a SUS container and set in an oven controlled at a temperature of 300 ° C. in advance. The mixture was allowed to stand for 2 hours and then air-cooled to obtain a solid electrolyte (glass ceramic).

(2) Production of positive electrode composite material 0.5 g of the solid electrolyte produced in the above (1) and 0.5 g of the composite produced in Example 1 (2) were put in a mill pot, and a planetary ball mill (manufactured by Fritsch: Model No. P-7) was subjected to mechanical milling for 5 hours at room temperature (25 ° C.) in argon at room temperature (25 ° C.) to obtain a positive electrode mixture.

[Evaluation of discharge voltage]
Lithium ion batteries were produced using the positive electrode composites produced in the above Examples and Comparative Examples, and the discharge voltage (V ₁₀ ) 10 seconds after the start of discharge was evaluated.
Specifically, 60 mg of the solid electrolyte (glass ceramics) produced in Comparative Example 2 (1) was put into a plastic cylinder having a diameter of 10 mm and subjected to pressure molding. Thereafter, 6.9 mg of the positive electrode mixture was charged into the cylinder, and pressure-molded again to obtain a laminate of the positive electrode and the solid electrolyte. An indium foil (thickness 0.3 mm, diameter 9.5 mm) and a lithium foil (thickness 0.2 mm, diameter 9.5 mm) are put on the solid electrolyte side, and a three-layer structure of a positive electrode, a solid electrolyte layer, and a negative electrode A lithium ion battery was produced.
The produced lithium ion battery was subjected to a constant current charge / discharge test at a charge / discharge current density of 0.500 mA / cm ² , a charge / discharge potential range of 0.7-2.2 V, and a charge / discharge temperature of 25 ° C. Then, after charging at a current density of 0.500mA / cm ² to 2.2V, the same test was conducted with a discharge current density of 10 mA / cm ^2. When discharging at a current density of 10 mA / cm ² , the discharge voltage (V ₁₀ ) 10 seconds after the start of discharge was evaluated. The measurement results are shown in Table 1.

Comparative Example 3
(1) Production of solid electrolyte Lithium sulfide and diphosphorus pentasulfide (manufactured by Aldrich) synthesized in Comparative Example 1 (1) were used as starting materials. About 1 g of a mixture adjusted to a molar ratio of 70:30 and 10 alumina balls having a diameter of 10 mm were placed in a 45 mL alumina container, and nitrogen was measured using a planetary ball mill (manufactured by Fritsch: Model No. P-7). A solid electrolyte (sulfide glass) as a white-yellow powder was obtained by performing mechanical milling for 20 hours at room temperature (25 ° C.) with a rotational speed of 370 rpm. It was 220 degreeC when the glass transition temperature was measured by DSC (differential scanning calorimetry).
The composition (Li _a P _b S _c ) of the solid electrolyte is a = 7, b = 3, c = 11. The produced solid electrolyte was heated at 300 ° C. for 2 hours under a nitrogen atmosphere. The obtained solid electrolyte (sulfide glass ceramic) was measured by X-ray diffraction. As a result, 2θ = 17.8, 18.2, 19.8, 21.8, 23.8, 25.9, 29.5, A peak was observed at 30.0 deg.

(2) Production of a composite of sulfur and a conductive substance 0.400 g of sulfur (manufactured by Aldrich, purity 99.998%) and 0.400 g of porous carbon (Ketjen Black (KB) EC600JD, manufactured by Lion) in a mortar After mixing, the mixture was placed in an airtight stainless steel container and heat-treated in an electric furnace. The heating conditions were from room temperature to 150 ° C. at 10 ° C./minute, held at 150 ° C. for 6 hours, then heated to 300 ° C. at 10 ° C./minute, held for 2.75 hours, then naturally cooled, A complex was obtained.

(3) Production of positive electrode composite material 0.5 g of the composite produced in (2) above and 0.5 g of the solid electrolyte (sulfide glass ceramic) powder produced in (1) above were placed in a mill pot, and a planetary ball mill (Fritsch Product: Model No. P-7) A positive electrode mixture was obtained by mechanical milling for 5 hours at 370 rpm in argon at room temperature (25 ° C.).

(4) Production of Lithium Ion Battery 50 mg of the sulfide-based solid electrolyte prepared above is put into a plastic cylinder having a diameter of 10 mm, pressure-molded, and 7.2 mg of the prepared positive electrode material is further charged and pressurized again. Molded. From the side opposite to the positive electrode material, indium foil (thickness 0.3 mm, 9.5 mmφ) and lithium foil (thickness 0.2 mm, 9.5 mmφ) are introduced, and the positive electrode, solid electrolyte layer, and negative electrode three layers A lithium ion battery was produced with a structure.
The produced lithium ion battery was subjected to a constant current charge / discharge test at a charge / discharge current density of 0.500 mA / cm ² , a charge / discharge potential range of 0.5-2.2 V, and a charge / discharge temperature of 25 ° C. In addition, this charge and discharge means the 1st charge and discharge after performing after battery preparation. The first discharge capacity was 1907 mAh / g, the first charge capacity was 1859 mAh / g, and the efficiency was 97%.

Comparative Example 4
The positive electrode mixture and lithium were prepared by the method described in Comparative Example 3 except that the solid electrolyte used for the positive electrode mixture and the solid electrolyte used for the solid electrolyte layer were thiolithicone Li _3.25 Ge _0.25 P _0.75 S _4. An ion battery was produced.
The produced lithium ion battery was subjected to a constant current charge / discharge test at a charge / discharge current density of 0.500 mA / cm ² , a charge / discharge potential range of 0.5-2.2 V, and a charge / discharge temperature of 25 ° C. In addition, this charge and discharge means the 1st charge and discharge after performing after battery preparation. The first discharge capacity was 1210 mAh / g, the first charge capacity was 571 mAh / g, and the efficiency was 47%.
From Comparative Examples 3 and 4, it can be seen that when the solid electrolyte is changed from Li ₇ P ₃ S ₁₁ to Li _3.25 Ge _0.25 P _0.75 S ₄ , the charge / discharge capacity and efficiency of the battery decrease.

  The positive electrode mixture of the present invention is suitable as a material for a positive electrode of a lithium ion battery. The lithium ion battery of the present invention can be used as a battery for a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle using a motor as a power source, an electric vehicle, a hybrid electric vehicle, or the like.

Claims (8)

Elemental lithium, elemental phosphorus and elemental sulfur;
And at least one element M selected from the group consisting of Si, Sn, Pb, Sb, B, Al, Ga, In, Ti, Zr, V and Nb,
In a powder X-ray diffraction measurement using CuKα rays, a solid electrolyte having peaks at least 2θ = 20.1 ± 0.5 ° and 23.9 ± 0.5 °;
And a positive electrode active material containing a sulfur element.   The positive electrode mixture according to claim 1, wherein the solid electrolyte further contains a halogen element.   The positive electrode mixture according to claim 1, wherein the element M is Si.   Furthermore, the positive electrode compound material in any one of Claims 1-3 containing an electroconductive substance.   The positive electrode mixture according to claim 4, wherein the positive electrode active material and the conductive material are combined.   The positive electrode mixture according to claim 4 or 5, wherein the conductive substance is porous carbon having pores.   A positive electrode comprising the positive electrode mixture according to claim 1.   A lithium ion battery having the positive electrode according to claim 7.