JPWO2009038037A1 - Heat-resistant positive electrode mixture and all-solid lithium secondary battery using the same - Google Patents

Abstract

A heat-resistant positive electrode mixture comprising a compound represented by the following formula (1) and a sulfide-based solid electrolyte. LiNixM1-xO2 (1) (wherein x is a number satisfying 0.1 <x <0.9, and M is an element selected from the group consisting of Fe, Co, Mn, and Al.)

Description

  The present invention relates to a heat-resistant positive electrode mixture and an all-solid lithium secondary battery using the same.

  In recent years, there has been an increasing demand for lithium ion secondary batteries used in personal digital assistants, portable electronic devices, small household power storage devices, motorcycles powered by motors, electric vehicles, hybrid electric vehicles, and the like.

In the lithium ion secondary battery, an organic electrolytic solution is used as an electrolyte. Although organic electrolytes exhibit high ionic conductivity, they are liquid and flammable, so there are concerns about safety such as leakage and ignition.
As a method for ensuring the safety of a lithium ion secondary battery, an all-solid secondary battery using an inorganic solid electrolyte instead of an organic electrolyte has been studied.

In the secondary battery, it is necessary to ensure sufficient electron conduction, electron transfer and ion conduction at the electrolyte-positive electrode active material interface.
In the case of a secondary battery using an organic electrolyte, the organic electrolyte penetrates into the positive electrode, and the electron conduction of the positive electrode active material and the ionic conduction of the electrolyte occur sufficiently, and the electron conduction, electron transfer and ionic conduction are sufficient. It can be secured. On the other hand, in an all-solid-state secondary battery, a positive electrode mixture (a mixture of a positive electrode active material and a solid electrolyte) used as a positive electrode has few contact surfaces between the solid electrolyte and the positive electrode active material, and performs electron conduction, electron transfer and ion conduction. It was difficult to secure enough.

In order to ensure sufficient electron conduction, electron transfer and ion conduction, it is preferable to increase the contact area between the solid electrolyte and the positive electrode active material.
As a method for increasing the contact area, a high-density molded body made of a positive electrode mixture can be prepared. In the case of a powder such as a positive electrode mixture, a high-density molded body can be produced by casting using a slurry, or applying the slurry and then compacting with a roll press or the like. However, in order to obtain a molded body by these methods, it is necessary to remove the solvent in the slurry by drying or baking (Patent Document 1), and the positive electrode mixture contained in the slurry is thermally stable at the solvent removal temperature. Needed. A positive electrode active material widely used in current lithium secondary batteries includes LiCoO _2, but LiCoO ₂ is a compound with poor thermal stability.

  Patent Document 2 discloses a solid electrolyte made of sulfide-based crystallized glass that exhibits high lithium ion conductivity even at room temperature. However, the electrolyte described in Patent Document 1 is industrially disadvantageous because it requires a large amount of expensive lithium. In addition, the electrolyte described in Patent Document 2 is subjected to heat treatment at 500 ° C. or higher in the manufacturing process. The heat treatment requires special equipment and is industrially disadvantageous.

Non-Patent Document 1 discloses an all-solid lithium secondary battery that exhibits good cycle characteristics. The all-solid lithium secondary battery described in Non-Patent Document 1 uses a sulfide-based glass electrolyte having an amorphous structure in a solid electrolyte and a positive electrode mixture. Sulfide-based glass electrolytes are thermally unstable when used as positive electrode composites. Therefore, the all-solid lithium secondary battery disclosed in Non-Patent Document 1 cannot be used for applications that require heat resistance.
JP 2006-248876 A JP 2002-109955 A Material Integration Vol.15 No.6 2002 25-30

  An object of the present invention is to provide a heat-resistant positive electrode mixture having thermal and temporal stability.

According to the present invention, the following positive electrode mixture and the like are provided.
1. A heat-resistant positive electrode mixture comprising a compound represented by the following formula (1) and a sulfide solid electrolyte having a crystallinity of 50% or more.
LiNi _x M _1-x O ₂ (1)
(In the formula, x is a number satisfying 0.1 <x <0.9, and M is an element selected from the group consisting of Fe, Co, Mn, and Al.)
2. A heat-resistant positive electrode mixture comprising a compound represented by the following formula (2) and a sulfide solid electrolyte having a crystallinity of 50% or more.
_{LiNi x M 1-x-y} L y O 2 (2)
(Where x is a number satisfying 0.1 <x <0.9, y is a number satisfying 0.01 <y <0.9, and x and y are 0 <1-xy. It is a number that satisfies
M and L are elements selected from the group consisting of Fe, Co, Mn, and Al, and are different from each other. )
3. The heat-resistant positive electrode mixture according to 1 or 2, wherein the sulfide-based solid electrolyte contains at least lithium (Li), phosphorus (P), and sulfur (S).
4). The sulfide-based glass solid electrolyte in which the sulfide-based solid electrolyte contains lithium (Li), phosphorus (P) and sulfur (S) is heat-treated at a temperature of 180 ° C. to 210 ° C. for 3 to 240 hours, or from 210 ° C. 4. The heat-resistant positive electrode mixture according to any one of 1 to 3, which is a sulfide-based crystallized glass solid electrolyte that has been heat-treated at a temperature of 330 ° C. or lower for 0.1 to 240 hours.
5. In the X-ray diffraction (CuKα: λ = 1.5418４), the sulfide-based solid electrolyte is 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0.3 deg, 21. Any one of 1 to 4 having diffraction peaks at 8 ± 0.3 deg, 23.8 ± 0.3 deg, 25.9 ± 0.3 deg, 29.5 ± 0.3 deg, 30.0 ± 0.3 deg Heat-resistant positive electrode composite.
The liquid mixture which consists of a heat-resistant positive electrode compound material in any one of 6.1-5, and a solvent.
The positive electrode obtained from the heat-resistant positive electrode compound material in any one of 7.1-5.
An all solid lithium battery comprising the positive electrode according to 8.7.
An all solid lithium battery obtained by further heat-treating the all solid lithium battery according to 9.8.
A device comprising the all-solid-state lithium battery according to 10.8 or 9.
11. The compound represented by the formula (1) or (2) has an average primary particle diameter of 0.01 to 30 μm, and the sulfide solid electrolyte has an average primary particle diameter of 0.01 to 30 μm. The heat-resistant positive electrode composite material according to any one of the above.
12 The average primary particle diameter X of the compound represented by the formula (1) or (2) and the average primary particle diameter Y of the sulfide electrolyte are heat resistance according to any one of 1 to 5 satisfying the formula (3). Positive electrode composite.
X ≧ Y (3)

  According to the present invention, it is possible to provide a heat-resistant positive electrode mixture having thermal and temporal stability.

It is a schematic sectional drawing which shows one Embodiment of the all-solid-state lithium battery which concerns on this invention. It is an X-ray diffraction spectrum chart of the sulfide type solid electrolyte produced in the manufacture example. It is a figure which shows the measurement result of the powder X-ray diffraction of the crystallized glass electrolyte produced in the manufacture example. It is a figure which shows the measurement result of the ion conductivity of the molded object for ion conductivity measurement produced in Example 1. FIG. It is a figure which shows the measurement result of the ion conductivity of the molded object for ion conductivity measurement produced in the comparative example 1. FIG.

The positive electrode mixture of the first aspect of the present invention comprises a compound represented by the following formula (1) and a sulfide-based solid electrolyte. The compound represented by the following formula (1) is preferably LiNi _0.8 Co _0.2 O ₂ .
LiNi _x M _1-x O ₂ (1)
(In the formula, x is a number satisfying 0.1 <x <0.9, and M is an element selected from the group consisting of Fe, Co, Mn, and Al.)

The positive electrode mixture of the second aspect of the present invention comprises a compound represented by the following formula (2) and a sulfide-based solid electrolyte. The compounds represented by the following (2) are preferably LiNi _0.8 Co _0.15 Al _0.05 O ₂ and LiNi _1/3 Co _1/3 Mn _1/3 O ₂ .
_{LiNi x M 1-x-y} L y O 2 (2)
(Where x is a number satisfying 0.1 <x <0.9, y is a number satisfying 0.01 <y <0.9, and x and y are 0 <1-xy. It is a number that satisfies
M and L are elements selected from the group consisting of Fe, Co, Mn, and Al, and are different from each other. )

  In place of the compound represented by the formula (1) or (2), a part of the transition metal of the formula (1) or (2) may be replaced with Al, Ti, V, Cr, Mn, Fe, Cu, Zn, A compound substituted with another metal such as Mg, Ga, Zr, Nb, or Si may be used.

  The sulfide-based solid electrolyte preferably contains at least lithium (Li), phosphorus (P), and sulfur (S), such as lithium sulfide and diphosphorus pentasulfide, or lithium sulfide and simple phosphorus and simple sulfur, and further sulfide It can be produced from raw materials such as lithium, diphosphorus pentasulfide, simple phosphorus and / or simple sulfur. The sulfide-based solid electrolyte may be further subjected to a flame retardant treatment.

The sulfide-based solid electrolyte preferably has a crystallinity of 50% or more and 100% or less. When the degree of crystallinity of the sulfide-based solid electrolyte is less than 50%, the thermal stability of the positive electrode mixture is poor, and sufficient battery performance cannot be exhibited due to low lithium ion conductivity. There is a fear.
The crystallinity can be measured by using an NMR spectrum apparatus. Specifically, the Gaussian curve using measured solid ³¹ PNMR spectrum of sulfide-based solid electrolyte, the obtained solid ³¹ PNMR spectrum, the resonance lines observed in 70～120Ppm, the nonlinear least square method And the degree of crystallinity can be measured by determining the area ratio of each curve.

  A preferred sulfide-based solid electrolyte can be produced from lithium sulfide and diphosphorus pentasulfide and / or simple phosphorus and simple sulfur.

As lithium sulfide, those commercially available without particular limitation can be used, but those having high purity are preferred.
Preferably, the lithium sulfide has a total content of lithium salts of sulfur oxides of preferably 0.15% by mass or less, more preferably 0.1% by mass or less, and a content of lithium N-methylaminobutyrate. It is 0.15 mass% or less, More preferably, it is 0.1 mass% or less. When the total content of the lithium salt of sulfur oxide is 0.15% by mass or less, the solid electrolyte obtained by the melt quenching method or the mechanical milling method becomes a glassy electrolyte (fully amorphous). That is, when the total content of the lithium salt of sulfur oxide exceeds 0.15% by mass, the obtained electrolyte may be a crystallized product from the beginning, and the ionic conductivity of the crystallized product is low. Further, even if this crystallized product is subjected to a heat treatment, the crystallized product is not changed, and there is a possibility that a sulfide-based solid electrolyte having high ion conductivity cannot be obtained.

Further, when the content of lithium N-methylaminobutyrate is 0.15% by mass or less, a deteriorated product of lithium N-methylaminobutyrate does not deteriorate the cycle performance of the lithium battery.
When lithium sulfide with reduced impurities is used, a high ion conductive electrolyte can be obtained.

The method for producing lithium sulfide used in the solid substance is not particularly limited as long as it is a method that can reduce at least the impurities.
For example, it can also be obtained by purifying lithium sulfide produced by the following method.
Among the following production methods, the method a or b is particularly preferable.
a. A method in which lithium hydroxide and hydrogen sulfide are reacted at 0 to 150 ° C. in an aprotic organic solvent to produce lithium hydrosulfide, and this reaction solution is then desulfurized at 150 to 200 ° C. -330312).
b. A method of directly producing lithium sulfide by reacting lithium hydroxide and hydrogen sulfide at 150 to 200 ° C. in an aprotic organic solvent (Japanese Patent Laid-Open No. 7-330312).
c. A method of reacting lithium hydroxide and a gaseous sulfur source at a temperature of 130 to 445 ° C. (Japanese Patent Laid-Open No. 9-283156).

There is no restriction | limiting in particular as a purification method of the lithium sulfide obtained as mentioned above. Preferable purification methods include, for example, International Publication No. WO2005 / 40039.
Specifically, the lithium sulfide obtained as described above is washed at a temperature of 100 ° C. or higher using an organic solvent.
The organic solvent used for washing is preferably an aprotic polar solvent, and more preferably, the aprotic organic solvent used for lithium sulfide production and the aprotic polar organic solvent used for washing are the same. .
Examples of the aprotic polar organic solvent preferably used for washing include aprotic polar organic compounds such as amide compounds, lactam compounds, urea compounds, organic sulfur compounds, cyclic organophosphorus compounds, Or it can use suitably as a mixed solvent. In particular, N-methyl-2-pyrrolidone (NMP) is selected as a good solvent.

The amount of the organic solvent used for washing is not particularly limited, and the number of times of washing is not particularly limited, but is preferably 2 or more. Cleaning is preferably performed under an inert gas such as nitrogen or argon.
The washed lithium sulfide is dried at a temperature equal to or higher than the boiling point of the organic solvent used for washing for 5 minutes or more, preferably about 2 to 3 hours or more under an inert gas stream such as nitrogen under normal pressure or reduced pressure. Thus, lithium sulfide used in the present invention can be obtained.

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

The mixing molar ratio of the lithium sulfide to diphosphorus pentasulfide or simple phosphorus and simple sulfur is usually 50:50 to 80:20, preferably 60:40 to 75:25.
Particularly preferably, it is about Li ₂ S: P ₂ S ₅ = 68: 32 to 74:26 (molar ratio).

The sulfide-based solid electrolyte may be a mixture of a sulfide-based glass solid electrolyte and a sulfide-based crystallized glass solid electrolyte as long as the overall crystallinity is 50% or more.
As a method for producing a sulfide-based glass solid electrolyte, there are a melt quenching method and a mechanical milling method (MM method).
In the case of the melt quenching method, P ₂ S ₅ and Li ₂ S mixed in a predetermined amount in a mortar and pelletized are placed in a carbon-coated quartz tube and vacuum-sealed. After reacting at a predetermined reaction temperature, a sulfide-based glass solid electrolyte is obtained by putting it in ice and rapidly cooling it.
The reaction temperature at this time is preferably 400 ° C to 1000 ° C, more preferably 800 ° C to 900 ° C.
Moreover, reaction time becomes like this. Preferably it is 0.1 to 12 hours, More preferably, it is 1 to 12 hours.
The quenching temperature of the reactant is usually 10 ° C. or less, preferably 0 ° C. or less, and the cooling rate is usually about 1 to 10,000 K / sec, preferably 10 to 10,000 K / sec.

In the case of the MM method, a sulfide-based glass solid electrolyte is obtained by mixing a predetermined amount of P ₂ S ₅ and Li ₂ S in a mortar and reacting them for a predetermined time by a mechanical milling method.
The mechanical milling method using the above raw materials can be reacted at room temperature. According to the MM method, since a glass solid electrolyte can be produced at room temperature, there is an advantage that a glass solid electrolyte having a charged composition can be obtained without thermal decomposition of raw materials.
Further, the MM method has an advantage that the glass solid electrolyte can be made into fine powder simultaneously with the production of the glass solid electrolyte.
In the MM method, various types such as a rotating ball mill, a rolling ball mill, a vibrating ball mill, and a planetary ball mill can be used.

As conditions for the MM method, for example, when a planetary ball mill is used, the rotational speed is set to several tens to several hundreds of revolutions / minute, and the treatment may be performed for 0.5 hours to 100 hours.
Although specific examples of the sulfide-based glass solid electrolyte by the melt quenching method and the MM method have been described above, manufacturing conditions such as temperature conditions and processing time can be appropriately adjusted according to the equipment used.

Thereafter, the obtained sulfide-based glass solid electrolyte is heat-treated at a predetermined temperature to produce a sulfide-based crystallized glass solid electrolyte.
The heat treatment temperature for producing the sulfide-based crystallized glass solid electrolyte is preferably 180 ° C to 330 ° C, more preferably 200 ° C to 320 ° C, and particularly preferably 210 ° C to 310 ° C.
If it is lower than 180 ° C., it may be difficult to obtain a crystallized glass having a high degree of crystallinity, and if it is higher than 330 ° C., a crystallized glass having a low degree of crystallinity may be produced.
The heat treatment time is preferably from 3 to 240 hours, particularly preferably from 4 to 230 hours, when the temperature is from 180 ° C to 210 ° C. Moreover, in the case of temperature higher than 210 degreeC and 330 degrees C or less, 0.1 to 240 hours are preferable, 0.2 to 235 hours are especially preferable, Furthermore, 0.3 to 230 hours are preferable.
When the heat treatment time is shorter than 0.1 hour, it may be difficult to obtain a crystallized glass with a high degree of crystallinity, and when it is longer than 240 hours, a crystallized glass with a low degree of crystallinity may be produced.

This sulfide-based crystallized glass solid electrolyte has 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0.3 deg in X-ray diffraction (CuKα: λ = 1.5418４). 21.8 ± 0.3 deg, 23.8 ± 0.3 deg, 25.9 ± 0.3 deg, 29.5 ± 0.3 deg, 30.0 ± 0.3 deg.
A solid electrolyte having such a crystal structure has extremely high lithium ion conductivity.

  In the positive electrode mixture of the present invention, an electrically conductive substance may be appropriately added as a conductive additive so that electrons move smoothly in the active material. The electrically conductive substance is not particularly limited, but a conductive substance such as acetylene black, carbon black, or carbon nanotube or a conductive polymer such as polyaniline, polyacetylene, or polypyrrole is used alone or in combination. Can do.

  The positive electrode composite of the present invention can be produced by mixing the compound represented by the above formula (1) or formula (2) and a sulfide-based solid electrolyte. The mixing ratio of the compound represented by formula (1) or formula (2) and the sulfide-based solid electrolyte (compound represented by formula (1) or formula (2): sulfide-based solid electrolyte weight ratio) is preferably Is 50-90: 50-10.

The average primary particle size of the compound represented by the formula (1) or (2) is preferably 0.01 to 30 μm, and particularly preferably 0.1 to 20 μm. Similarly, the average primary particle size of the sulfide-based solid electrolyte is preferably 0.01 to 30 μm, and particularly preferably 0.1 to 20 μm. Thereby, battery performance, that is, charge / discharge efficiency is improved, and improvement in performance can be expected.
Moreover, it is preferable that the average primary particle diameter X of the compound represented by the formula (1) or (2) and the average primary particle diameter Y of the sulfide-based electrolyte satisfy the formula (3).
X ≧ Y (3)
Thereby, the contact area between the positive electrode material and the electrolyte is maximally improved, and the battery performance, that is, the output characteristics is improved.
The average primary particle size means a value measured with a laser diffraction particle size distribution measuring device [SEISHIN LASER MICRON SIZER LMS-30 (manufactured by Seishin Enterprise)].

The positive electrode composite of the present invention is excellent in thermal and temporal stability. Accordingly, the positive electrode composite of the present invention is used for automobiles used in the vicinity of a battery including a reflow process in manufacturing thereof, a battery including a reflow process, and a high-temperature engine, such as casting molding using slurry. It can be suitably used for a battery or the like.
The positive electrode composite of the present invention has the advantage that the restrictions on battery manufacturing conditions and installation locations can be greatly relaxed due to its excellent thermal and temporal stability.

The positive electrode of an all-solid-state lithium battery can be formed by apply | coating the liquid mixture which consists of a positive electrode compound material and a solvent of this invention.
In the mixed solution, the positive electrode mixture of the present invention is not dissolved in a solvent. Since the specific gravity of the positive electrode mixture of the present invention is usually larger than the specific gravity of the solvent, it is usually precipitated in the above mixed solution, but when forming the positive electrode, the positive electrode mixture is uniformly dispersed by stirring or the like. It is preferable to use a mixed liquid.

  The solvent used in the mixed solution is preferably a solvent having low reactivity with the positive electrode mixture, but by treating the positive electrode mixture surface so that the positive electrode mixture does not react with the solvent, for example, by coating the surface of the positive electrode mixture, A solvent having high reactivity with the material can also be used.

The solvent is preferably an organic solvent, more preferably a hydrocarbon organic solvent, such as hexane, heptane, toluene, xylene, decalin, and the like.
Of these solvents, hexane, toluene, and xylene, which are low-boiling solvents, are preferable in consideration of the drying process after coating, but it is difficult to use a low-boiling solvent having a high evaporation rate in consideration of maintaining the mixed liquid. , Toluene, xylene and the like are preferable.

  The solvent used in the mixed solution is preferably dehydrated to reduce the water content. The water content of the solvent is usually 30 ppm or less, preferably 10 ppm or less, more preferably 1.0 ppm or less.

You may further add a binder to the liquid mixture which consists of a positive electrode compound material and a solvent.
The binder is not particularly limited as long as the reactivity with the positive electrode mixture is low, preferably a thermoplastic resin and a thermosetting resin, more preferably polysiloxane, polyalkylene glycol, polytetrafluoroethylene (PTFE), Polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), styrene butadiene rubber / carboxymethyl cellulose (SBR / CMC), polyethylene oxide (PEO), branched PEO, polyphenylene oxide (PPO), PEO-PPO copolymer, branched PEO -PPO copolymer, alkylborane-containing polyether.
The binder is particularly preferably SBR or polyalkylene glycol from the viewpoint of ease of sheet formation, prevention of increase in interface resistance and prevention of reduction in charge / discharge capacity.

The all solid lithium battery of the present invention includes a positive electrode made of the positive electrode mixture of the present invention, a negative electrode, and a solid electrolyte layer made of a sulfide-based solid electrolyte sandwiched between the positive electrode and the negative electrode.
The sulfide-based solid electrolyte contained in the solid electrolyte layer may be the same as or different from the sulfide-based solid electrolyte contained in the positive electrode mixture, and is preferably the same.

FIG. 1 is a schematic sectional view showing an embodiment of an all solid lithium battery according to the present invention.
In the all solid lithium battery 1, a solid electrolyte layer 20 is sandwiched between a pair of electrodes composed of a positive electrode 10 and a negative electrode 30 made of the positive electrode mixture of the present invention. Current collectors 40 and 42 are provided on the positive electrode 10 and the negative electrode 30, respectively.

  The positive electrode 10 is made of the positive electrode mixture of the present invention, and can be produced by forming the positive electrode mixture of the present invention in a film shape on at least a part of the solid electrolyte layer 20. As the film forming method, in addition to the method of forming the mixture of the positive electrode mixture and the solvent of the present invention described above, for example, a blast method, an aerosol deposition method, a cold spray method, a sputtering method, a vapor phase growth, for example A method, a pressure press method, a thermal spraying method, or the like can also be used. By forming a film by such a method, the porosity of the electrode material layer can be further reduced, and electron conduction, electron transfer and ion conduction can be improved.

The solid electrolyte layer 20 can be manufactured by forming a sulfide-based solid electrolyte into a film by, for example, a blast method or an aerosol deposition method. Also, a sulfide-based solid electrolyte can be formed by a cold spray method, a sputtering method, a vapor deposition method (chemical vapor deposition: CVD), a thermal spraying method, or the like.
Further, there is a method in which a solution in which a sulfide-based solid electrolyte is mixed with a solvent and a binder (binder, polymer compound, etc.) is applied and applied, and then the solvent is removed to form a film. Also, the solid electrolyte itself, solid electrolyte and binder (binder, polymer compound, etc.) and support (materials and compounds to reinforce the strength of the solid electrolyte layer and prevent short circuit of the solid electrolyte itself) are mixed -It is also possible to form a film by pressing the combined electrolyte under pressure.
A suitable thickness and width differ depending on the use of the battery, and it is necessary to consider a combination with the positive electrode material and the negative electrode material. Therefore, an optimal film forming method may be appropriately selected according to the use.

Although a solvent will not be specifically limited if it does not have a bad influence on the performance of solid electrolyte, For example, a non-aqueous solvent is mentioned.
Examples of the non-aqueous solvent include solvents used in electrolyte solutions such as dry heptane, toluene, hexane, tetrahydrofuran (THF), N methylpyrrolidone, acetonitrile, dimethoxyethane, and dimethyl carbonate, and preferably have a water content. The solvent is 100 ppm or less, more preferably 50 ppm or less.

As the binder, a thermoplastic resin or a thermosetting resin can be used. For example, polysiloxane, polyalkylene glycol, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer ( FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer ( ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene -Chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer Combined or (Na ⁺ ) ion crosslinked body of the material, ethylene-methacrylic acid copolymer or (Na ⁺ ) ion crosslinked body of the material, ethylene-methyl acrylate copolymer or (Na ⁺ ) ion crosslinked of the material Body, ethylene-methyl methacrylate copolymer, or (Na ⁺ ) ion-crosslinked body of the material.

  Among these, polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE) are preferable.

The negative electrode 30 can be produced in the same manner as the positive electrode 10. As a negative electrode material used for preparation of the negative electrode 30, what is used as a negative electrode active material in the battery field | area 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 include fibers, vapor grown carbon fibers, natural graphite, and non-graphitizable carbon. Or it may be a mixture thereof. Preferably, it is artificial graphite. Moreover, the metal itself of metal lithium, metal indium, metal aluminum, or metal silicon, or the alloy which combined these metals with another element or compound can be used as a negative electrode material.
In the present invention, since the solid electrolyte layer 20 is composed of a sulfide-based solid electrolyte, even when metallic lithium or graphite is used for the negative electrode material, the negative electrode and the solid electrolyte layer do not react, and good battery performance can be exhibited.

  The negative electrode material may be mixed with a conductive additive and / or a sulfide solid electrolyte in the same manner as the positive electrode mixture. The sulfide solid electrolyte used for the negative electrode material is preferably the same as the sulfide solid electrolyte used for the solid electrolyte layer.

As the current collectors 40 and 42, a plate or foil made of copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, indium, lithium, or an alloy thereof, or the like Can be used.
The current collectors 40 and 42 may be the same as or different from each other. For example, a copper foil may be used for the current collector 40 and an aluminum foil may be used for the current collector 42.

An all-solid lithium battery can be manufactured by bonding and joining the battery members described above. As a method of joining, there are a method of laminating each member, pressurizing and pressure bonding, a method of pressing through two rolls (roll to roll), and the like.
Moreover, you may join to the joining surface through the active material which has ion conductivity, and the adhesive material which does not inhibit ion conductivity.
In joining, heat fusion may be performed as long as the crystal structure of the solid electrolyte does not change.

Moreover, it is preferable that the all-solid lithium battery produced by the above-described method can be further heat-treated to obtain a high-power battery. The heating temperature during the heat treatment is preferably 100 ° C. or higher. Moreover, heat processing time is 0.1 to 10 hours normally.
The heat treatment of the all-solid lithium battery includes a case where only the battery element portion including only the negative electrode, the solid electrolyte formed body, and the positive electrode is heat-treated. Also, it does not include heat treatment such as safety devices and lapping.

  The all solid lithium battery of the present invention can be either a secondary battery or a primary battery, and can be used in devices such as watches, mobile phones, personal computers, automobiles, and generators. In particular, since the all solid lithium battery of the present invention is highly safe, the degree of design freedom of the apparatus can be increased by using the all solid lithium battery of the present invention.

Among the above-described devices, the automobile includes an electric automobile whose driving source is an electric motor, and a hybrid electric automobile using a combination of an electric motor and an internal combustion engine as a driving source, and these automobiles require a large current and a large voltage.
The all-solid-state lithium battery of the present invention can extract more power by connecting in series and / or in parallel to form a battery cell. By connecting a plurality of battery cells in series and / or parallel to form a battery module (battery pack, battery unit), a battery that satisfies the large current and large voltage required by the automobile can be obtained.
[Example]

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

(2) Purification of lithium sulfide After decanting NMP in the 500 mL slurry reaction solution (NMP-lithium sulfide slurry) obtained in (1) above, 100 mL of dehydrated NMP was added and stirred at 105 ° C. for about 1 hour. . 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 (NMAB) Was quantified by ion chromatography. As a result, the total content of sulfur oxides was 0.13% by mass, and LMAB was 0.07% by mass.

(3) Production of sulfide-based solid electrolyte Li ₂ S and P ₂ S ₅ (manufactured by Aldrich) produced above were used as starting materials. 250 g of the mixture adjusted to a molar ratio of 70:30 was placed in a SUS container (capacity: 6.7 L) filled with zirconia balls, and 200 hours under a dry atmosphere at a dew point of −40 ° C. or lower and at room temperature. A mechanical milling treatment was performed by applying mechanical energy of 1 kJ / kg · s by a vibration mill to obtain a sulfide-based solid electrolyte powder of white yellow powder.
Powder X-ray diffraction measurement was performed on the obtained powder (CuKα: λ = 1.5418Å). The obtained chart is shown in FIG. From this chart, it was confirmed that the peak of the raw material crystal completely disappeared and the sulfide-based solid electrolyte powder was vitrified. The obtained sulfide-based glass solid electrolyte (amorphous glass electrolyte) had a crystallinity of 0%.

The obtained amorphous glass electrolyte powder was sealed in a SUS tube in an argon atmosphere, and subjected to a firing treatment at 300 ° C. for 2 hours to produce a sulfide-based crystallized glass solid electrolyte (crystallized glass electrolyte). .
The average primary particle diameter of the obtained crystallized glass electrolyte was 3 μm. The average primary particle size was measured with a laser diffraction particle size distribution analyzer SEISHIN LASER MICRON SIZER LMS-30 (manufactured by Seishin Enterprise). The average primary particle diameter of a positive electrode active material (for example, LiNi _0.8 Co _0.2 O ₂ ) described later was also measured in the same manner.

  The crystallized glass electrolyte produced above was subjected to powder X-ray diffraction measurement (CuKα: λ = 1.5418Å). The obtained crystallized glass electrolyte has 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0.3 deg, 21.8 ± 0.3 deg, 23.8 ± 0.3 deg. 25.9 ± 0.3 deg, 29.5 ± 0.3 deg, 30.0 ± 0.3 deg. The obtained results are shown in FIG.

Moreover, it confirmed that the crystallinity degree of the obtained crystallized glass electrolyte was 50% or more. The crystallinity, using JNM-CMXP302NMR apparatus (manufactured by JEOL Ltd.), to measure the solid ³¹ PNMR spectrum under the following conditions, the obtained solid ³¹ PNMR spectrum, is observed in 70~120ppm The resonance lines were separated into Gaussian curves using a non-linear least square method and calculated from the area ratio of each curve.

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

Example 1
LiNi _0.8 Co _0.2 O ₂ was prepared based on “Solid State Communications, Vol. 90, No. 7, p.439-442, 1994” (average primary particle size: 10 μm). This LiNi _0.8 Co _0.2 O ₂ and the crystallized glass electrolyte prepared in the production example were mixed at a weight ratio of 1: 1 to obtain a positive electrode mixture. The positive electrode mixture was pulverized in a mortar for 5 minutes, filled with about 0.3 g of the positive electrode mixture in a tablet molding machine, and a pressure of 4 to 6 MPa was applied to obtain a positive electrode mixture molded body. Further, about 10 mg of a mixture obtained by mixing carbon graphite (manufactured by TIMCAL, SFG-15) as an electrode and the crystallized glass electrolyte prepared in the production example at a weight ratio of 1: 1 was placed on both sides of the molded body, and the tablet was again formed. By applying pressure with a molding machine, an AC impedance measurement molded body (diameter: about 10 mm, thickness: about 2 mm) composed of an electrode, a positive electrode mixture molded body, and an electrode was produced.

AC impedance measurement was performed on the obtained AC impedance measurement molded body. In the AC impedance method, the first measurement is performed at room temperature (28.9 ° C), the temperature is increased to 190 ° C, the temperature is decreased to room temperature (26.6 ° C), and the second measurement is performed. It was. The results are shown in FIG.
As is clear from FIG. 4, the measurement curve before the temperature increase and the measurement curve after the temperature increase did not greatly change the resistance component even after the high temperature of 190 ° C., and the shapes of the curves almost coincided. That is, it was confirmed that the positive electrode mixture of the present invention was excellent in thermal stability.

Comparative Example 1
Except for using LiCoO ₂ instead of LiNi _0.8 Co _0.2 O _2, a molded article for AC impedance measurement was prepared in the same manner as in Example 1 and evaluated in the same manner as in Example 1. The results are shown in FIG.
As is clear from FIG. 5, the measurement curve before the temperature rise and the measurement curve after the temperature rise undergo a large resistance component change through a high temperature of 190 ° C., and the shapes of the curves are greatly different. That is, it was confirmed that the properties of the positive electrode mixture changed due to the high temperature.

Example 2
The crystallized glass electrolyte prepared in Production Example and LiNi _0.8 Co _0.2 O ₂ were mixed at a weight ratio of 2: 8 to obtain a positive electrode mixture. The positive electrode mixture was pulverized in a mortar for 5 minutes, and the pulverized positive electrode mixture was heat-treated at 150 ° C. for 30 minutes using a tube oven.

  A battery was produced using the heat-treated positive electrode mixture. Using a positive electrode composed of about 0.1 g of the positive electrode mixture, an electrolyte layer composed of about 0.2 g of the sulfide-based crystallized glass electrolyte prepared in the production example, and a negative electrode composed of an In sheet, the positive electrode, the electrolyte, and the negative electrode A battery consisting of three layers and having a thickness of about 1 mm and a diameter of about 16 mm was produced.

The charge / discharge characteristics of the produced battery were evaluated. The charge / discharge characteristic evaluation was performed using a charge / discharge automatic measuring device (manufactured by Toho Giken Co., Ltd.), with an upper limit voltage of 3.7 V, a lower limit voltage of 1.5 V, and a current density of 100 μA · cm ⁻² . As a result, the initial charge amount of the obtained battery was about 100 mAh / g.

Example 3
A battery was prepared in the same manner as in Example 2 except that the positive electrode mixture pulverized in a mortar was not heat-treated, and evaluated in the same manner as in Example 2. As a result, the initial charge amount of the obtained battery was about 80 mAh / g.
From Example 2 and Example 3, it was confirmed that the battery using the positive electrode mixture of the present invention does not cause a large change in charge / discharge characteristics even when the manufacturing process includes heat treatment.

Comparative Example 2
A battery was fabricated in the same manner as in Example 2 except that LiCoO ₂ was used instead of LiNi _0.8 Co _0.2 O ₂ , and evaluation was performed in the same manner as in Example 2. As a result, the initial charge amount of the obtained battery was about 35 mAh / g.

Comparative Example 3
A battery was prepared in the same manner as in Example 3 except that LiCoO ₂ was used instead of LiNi _0.8 Co _0.2 O ₂ , and evaluation was performed in the same manner as in Example 2. As a result, the initial charge amount of the obtained battery was about 70 mAh / g.
In Comparative Example 2 and Comparative Example 3, the initial charge amount is significantly reduced by performing the heat treatment. In the battery using LiCoO ₂ as the positive electrode mixture, LiNi _0.8 Co _0. It was confirmed that the thermal stability was inferior to the battery using ₂ O ₂ .

Comparative Example 4
A battery was produced in the same manner as in Example 2 except that the amorphous solid electrolyte produced in the production example was used in place of the crystallized glass electrolyte as the sulfide-based solid electrolyte used in the positive electrode mixture. Evaluation was performed in the same manner. As a result, the initial charge amount of the obtained battery was about 50 mAh / g.

Comparative Example 5
A battery was produced in the same manner as in Example 3 except that the amorphous solid electrolyte produced in the production example was used in place of the crystallized glass electrolyte as the sulfide-based solid electrolyte used in the positive electrode mixture. Evaluation was performed in the same manner. As a result, the initial charge amount of the obtained battery was about 120 mAh / g.
In Comparative Example 4 and Comparative Example 5, the initial charge amount significantly decreased by performing the heat treatment, and the battery using the amorphous glass electrolyte for the positive electrode mixture is a crystallized glass electrolyte for the positive electrode mixture. It was confirmed that the thermal stability was inferior compared to the battery using.

Example 4
A positive electrode mixture was prepared by mixing the crystallized glass electrolyte prepared in Production Example and LiNi _0.8 Co _0.2 O ₂ at a weight ratio of 1: 1, and stored in an inert atmosphere for 1 month. Thereafter, XRD measurement of the positive electrode mixture was performed. As a result, the diffraction peak of the positive electrode mixture did not change even when compared with the XRD pattern of LiNi _0.8 Co _0.2 O ₂ alone, and the positive electrode mixture of the present invention has excellent temporal stability. It was confirmed.
The measurement conditions for X-ray diffraction measurement (XRD) were as follows.
Device: Rigaku Ultima-III
X-ray: Cu-Kα ray (wavelength 1.5406mm, monochromatized with graphite monochromator)
2θ-θ reflection method, continuous scan (1.0 ° / min)
Sampling interval: 0.02 °
Slit DS, SS: 2/3 °, RS: 0.6 mm

Comparative Example 6
A positive electrode mixture was prepared by mixing the crystallized glass electrolyte prepared in Production Example and LiCoO ₂ at a weight ratio of 1: 1, and stored in an inert atmosphere for 1 month. Thereafter, XRD measurement of the positive electrode mixture was performed. As a result, it was confirmed that the diffraction peak of the positive electrode mixture was shifted to a lower angle side compared to the XRD pattern of LiCoO ₂ alone, and the lattice constant was changed. As a result, it was confirmed that the positive electrode mixture composed of the crystallized glass electrolyte and LiCoO ₂ was unstable over time as compared with the positive electrode mixture of the present invention.

Example 5
LiNi _0.8 Co _0.15 Al _0.05 O ₂ was prepared based on JP-A-10-316431 (average primary particle size: 5 μm). 70 mg of LiNi _0.8 Co _0.15 Al _0.05 O ₂ and the crystallized glass electrolyte prepared in Production Example of 30 mg were mixed in a mortar to obtain a positive electrode mixture.

200 mg of the crystallized glass electrolyte prepared in the production example was placed in a 15.5 mmφ mold and pressed three times at 154 MPa. Next, 100 mg of the positive electrode mixture was added and pressed three times at 530 MPa, and pellets of a laminate of the layer made of the crystallized glass electrolyte and the layer made of the positive electrode mixture were punched from the mold. The pellet was sandwiched between two titanium foils and placed in a battery cell. This battery cell was heated at 300 ° C. for 30 minutes to convert the crystallized glass electrolyte into glass ceramic.
An indium foil (15 mmφ, 0.1 mm thickness) was attached as a negative electrode from the opposite side of the positive electrode mixture of the laminate to prepare a battery.

The obtained battery was evaluated with a charge / discharge current density of 250 μA / cm ² , a cutoff upper limit voltage of 3.6 V, and a lower limit voltage of 1.5 V. As a result, the initial charge capacity was 165 mAh / g, and the discharge capacity was 115 mAh / g.

Comparative Example 7
A battery was fabricated in the same manner as in Example 5 except that LiCoO ₂ was used instead of LiNi _0.8 Co _0.15 Al _0.05 O ₂ . The obtained battery was evaluated with a charge / discharge current density of 250 μA / cm ² , a cutoff upper limit voltage of 3.9 V, and a lower limit voltage of 1.5 V. As a result, the obtained battery did not function as a secondary battery.

Example 6
Example 5 was repeated except that LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (average primary particle size: 10 μm) was used instead of LiNi _0.8 Co _0.15 Al _0.05 O _2. A battery was produced. The obtained battery was evaluated with a charge / discharge current density of 250 μA / cm ² , a cutoff upper limit voltage of 3.9 V, and a lower limit voltage of 1.5 V. As a result, the initial charge capacity was 135 mAh / g, and the discharge capacity was 95 mAh / g.

Example 7
A battery was fabricated in the same manner as in Example 5 except that the same LiNi _0.8 Co _0.2 O ₂ as in Example 1 was used instead of LiNi _0.8 Co _0.15 Al _0.05 O ₂ . The obtained battery was evaluated with a charge / discharge current density of 250 μA / cm ² , a cutoff upper limit voltage of 3.6 V, and a lower limit voltage of 1.5 V. As a result, the initial charge capacity was 145 mAh / g, and the discharge capacity was 105 mAh / g.

The positive electrode mixture of the present invention can be used for an all-solid lithium secondary battery.
The all-solid-state lithium secondary 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 (12)

A heat-resistant positive electrode mixture comprising a compound represented by the following formula (1) and a sulfide solid electrolyte having a crystallinity of 50% or more.
LiNi _x M _1-x O ₂ (1)
(In the formula, x is a number satisfying 0.1 <x <0.9, and M is an element selected from the group consisting of Fe, Co, Mn, and Al.) A heat-resistant positive electrode mixture comprising a compound represented by the following formula (2) and a sulfide solid electrolyte having a crystallinity of 50% or more.
_{LiNi x M 1-x-y} L y O 2 (2)
(Where x is a number satisfying 0.1 <x <0.9, y is a number satisfying 0.01 <y <0.9, and x and y are 0 <1-xy. It is a number that satisfies
M and L are elements selected from the group consisting of Fe, Co, Mn, and Al, and are different from each other. )   The heat-resistant positive electrode mixture according to claim 1 or 2, wherein the sulfide-based solid electrolyte contains at least lithium (Li), phosphorus (P), and sulfur (S).   The sulfide-based glass solid electrolyte in which the sulfide-based solid electrolyte contains lithium (Li), phosphorus (P) and sulfur (S) is heat-treated at a temperature of 180 ° C. to 210 ° C. for 3 to 240 hours, or from 210 ° C. The heat-resistant positive electrode composite material according to any one of claims 1 to 3, which is a sulfide-based crystallized glass solid electrolyte that has been heat-treated at a high temperature of 330 ° C or lower for 0.1 to 240 hours.   In the X-ray diffraction (CuKα: λ = 1.5418４), the sulfide-based solid electrolyte is 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0.3 deg, 21. Any one of claims 1 to 4 having a diffraction peak at 8 ± 0.3 deg, 23.8 ± 0.3 deg, 25.9 ± 0.3 deg, 29.5 ± 0.3 deg, 30.0 ± 0.3 deg. The heat-resistant positive electrode mixture described in 1.   The liquid mixture which consists of a heat-resistant positive electrode compound material and solvent in any one of Claims 1-5.   A positive electrode obtained from the heat-resistant positive electrode mixture according to claim 1.   An all solid lithium battery comprising the positive electrode according to claim 7.   An all solid lithium battery obtained by further heat-treating the all solid lithium battery according to claim 8.   An apparatus comprising the all solid lithium battery according to claim 8.   The average primary particle size of the compound represented by the formula (1) or (2) is 0.01 to 30 µm, and the average primary particle size of the sulfide-based solid electrolyte is 0.01 to 30 µm. The heat-resistant positive electrode mixture according to any one of -5. The average primary particle diameter X of the compound represented by the formula (1) or (2) and the average primary particle diameter Y of the sulfide-based electrolyte satisfy the formula (3). Heat-resistant positive electrode composite.
X ≧ Y (3)

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