JP2013211238A - Lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery having a large electric capacity and good cycle characteristics, and to provide an anode used for the same.SOLUTION: The anode is manufactured of an anode mixture having a weight per unit area of 8.5 mg/cmor less, and the anode mixture contains an anode active material and a solid electrolyte.

Description

  The present invention relates to a lithium ion battery.

  In the current lithium ion battery, an organic electrolyte is mainly used as an electrolyte. Although organic electrolytes exhibit high ionic conductivity, the electrolytes are liquid and flammable, so there are concerns about risks such as leakage and ignition when used as batteries. Therefore, development of a safer solid electrolyte is expected as an electrolyte for next-generation lithium ion batteries.

In order to solve this problem, a sulfide-based solid electrolyte containing sulfur (S) element, lithium (Li) element and phosphorus (P) element as main components has been developed, and a battery using this sulfide-based solid electrolyte As an all-solid-state lithium battery was developed.
However, the conventional all-solid lithium battery has a problem that the discharge capacity decreases when the charge / discharge cycle is repeated (see Patent Document 1), and it is required to improve the cycle characteristics.

Moreover, the negative electrode used for the all-solid-state lithium battery has a defect that there are many carbons (C) and its electric capacity is small (see Patent Document 1).
In order to eliminate such drawbacks, there is a method of using silicon for the negative electrode.
However, an all-solid lithium battery using silicon for the negative electrode has a drawback in that the electric capacity decreases when charging and discharging are repeated.

JP 2006-32232 A

  An object of the present invention is to provide a lithium ion battery having a large electric capacity and good cycle characteristics, and a negative electrode used therefor.

According to the present invention, the following lithium ion batteries and the like are provided.
1. A negative electrode manufactured by a negative electrode mixture having a basis weight of 8.5 mg / cm ² or less, wherein the negative electrode mixture includes a negative electrode active material and a solid electrolyte.
2. A negative electrode comprising a negative electrode active material and a solid electrolyte, wherein the total weight per unit area of the negative electrode active material and the solid electrolyte is 8.3 mg / cm ² or less.
3. A negative electrode comprising a negative electrode active material, a solid electrolyte, and a binder, wherein the total weight per unit area of the negative electrode active material, the solid electrolyte, and the binder is 8.5 mg / cm ² or less.
4). A lithium ion battery comprising a negative electrode mixture having a basis weight of 8.5 mg / cm ² or less, wherein the negative electrode mixture includes a negative electrode layer containing a negative electrode active material and a solid electrolyte, and an electrolyte layer containing a solid electrolyte.
5. A negative electrode layer including a negative electrode active material and a solid electrolyte, wherein the total weight per unit area of the negative electrode active material and the solid electrolyte is 8.3 mg / cm ² or less; and an electrolyte layer including a solid electrolyte. Lithium ion battery.
6). An electrolyte comprising a negative electrode active material, a solid electrolyte, and a binder, wherein the negative electrode active material, the solid electrolyte, and the binder have a total weight per unit area of negative electrode of 8.5 mg / cm ² or less, and a solid electrolyte A lithium-ion battery comprising a layer.
7). 5. The lithium ion battery according to 4, wherein the weight per unit area of the negative electrode mixture is 0.05 mg / cm ² or more and 8.0 mg / cm ² or less.
8). The negative active material to the total weight of the negative electrode per unit area of the solid electrolyte 0.05 mg / cm ² or more and 7.8 mg / cm ² or less, a lithium ion battery according to 5.
9. 7. The lithium ion battery according to 6, wherein a total weight per unit area of the negative electrode active material, the solid electrolyte, and the binder is 0.05 mg / cm ² or more and 8.0 mg / cm ² or less.
10. The lithium ion battery according to any one of 4 to 9, wherein the solid electrolyte is a lithium ion conductive inorganic solid electrolyte that satisfies a composition represented by the following formula (1).
Li _a M _b P _c S _d (1)
(In Formula (1), M represents an element selected from the group consisting of B, Zn, Si, Cu, Ga, and Ge. Ad represents the composition ratio of each element, and a: b: c: d. Satisfies 1-12: 0 to 0.2: 1: 2-9.)
11. The lithium ion battery according to any one of 4 to 10, wherein the negative electrode mixture includes a negative electrode active material composed of at least one of silicon, tin, indium, aluminum, and lithium.
12 The lithium ion battery according to any one of 4 to 11, wherein the negative electrode active material has an average particle size of 100 μm or less.
A device comprising the lithium ion battery according to any one of 13.4 to 12.

  According to the present invention, a lithium ion battery having a large electric capacity and good cycle characteristics and a negative electrode used therefor can be obtained.

It is a figure which shows the relationship between the test cycle frequency | count of the lithium ion battery produced by the Example and the comparative example, and a capacity | capacitance maintenance factor.

The first lithium ion battery of the present invention is manufactured from a negative electrode mixture having a basis weight of 8.5 mg / cm ² or less. The negative electrode mixture includes a negative electrode layer containing a negative electrode active material and a solid electrolyte, and a solid electrolyte. And an electrolyte layer.
The second lithium ion battery of the present invention includes a negative electrode active material and a solid electrolyte, and the total weight of the negative electrode active material and the solid electrolyte per unit area of the negative electrode layer is 8.3 mg / cm ² or less. A negative electrode layer and an electrolyte layer containing a solid electrolyte are provided.
The third lithium ion battery of the present invention includes a negative electrode active material, a solid electrolyte, and a binder, and the total weight of the negative electrode active material, the solid electrolyte, and the binder per unit area of the negative electrode layer is 8.5 mg / The negative electrode layer which is cm < ² > or less and the electrolyte layer containing a solid electrolyte are provided.

In the lithium ion battery of the present invention, the basis weight of the negative electrode mixture, which is a material for producing the negative electrode layer, is 8.5 mg / cm ² or less, or the total of the negative electrode active material and the solid electrolyte contained in the negative electrode layer is 8.3 mg. / Cm ² or less, or the total of the negative electrode active material, the solid electrolyte, and the binder contained in the negative electrode layer is 8.5 mg / cm ² or less. In addition, the basis weight of the negative electrode mixture which is a material for manufacturing the negative electrode layer, the total of the negative electrode active material and the solid electrolyte contained in the negative electrode layer, and the lower limit of the total of the negative electrode active material, the solid electrolyte and the binder contained in the negative electrode layer are Although it does not restrict | limit, 0.01 mg / cm < ² > can be made into a minimum. By using such a negative electrode layer, it is possible to suppress a decrease in electric capacity that occurs when the charge / discharge cycle is repeated.

The basis weight of the negative electrode mixture is preferably 0.05 mg / cm ² or more and 8.0 mg / cm ² or less, more preferably 0.1 mg / cm ² or more and 7.5 mg / cm ² or less.
The total weight per negative electrode layer per unit area of the negative electrode active material and the solid electrolyte is preferably, 0.05 mg / cm ² or more 7.8 mg / cm ² or less, more preferably, 1.0 mg / cm ² or more 7.3mg / Cm ² or less.
Further, the total weight per unit area of the negative electrode active material, the solid electrolyte, and the binder is preferably 0.05 mg / cm ² or more, 8.0 mg / cm ² or less, more preferably 0.1 mg / cm ² or more 7 0.5 mg / cm ² or less.

When the basis weight of the negative electrode mixture is greater than 8.5 mg / cm ² , or the total weight per unit area of the negative electrode active material and the solid electrolyte is greater than 8.3 mg / cm ² , or the negative electrode active If the total weight of the substance, the solid electrolyte, and the binder per unit area of the negative electrode layer is greater than 8.5 mg / cm ² , the negative electrode layer becomes thick and the cycle characteristics deteriorate. On the other hand, the weight per unit area of the negative electrode mixture, the total weight per unit area of the negative electrode active material and the solid electrolyte, or the total weight per unit area of the negative electrode active material, the solid electrolyte, and the binder is 0. If it is less than 01 mg / cm ² , the electric capacity may be lowered.

  The “weight per unit area” referred to in the present invention is a weight obtained by converting the weight of the negative electrode mixture, which is a material for manufacturing the negative electrode layer, per unit area of the negative electrode layer to be manufactured. The "total weight per unit area of the negative electrode active material and the solid electrolyte contained in the negative electrode layer" means the total weight of the negative electrode active material and the solid electrolyte contained in the manufactured negative electrode layer. It is the weight converted per area. Accordingly, when the weight of the negative electrode mixture or the total weight of the negative electrode active material and the solid electrolyte per unit area of the negative electrode layer increases, the negative electrode layer becomes thicker, and the weight of the negative electrode mixture, or the negative electrode active material and the solid electrolyte When the total weight per unit area of the negative electrode layer becomes smaller, the negative electrode layer becomes thinner.

  The negative electrode mixture constituting the negative electrode layer includes a negative electrode active material and a solid electrolyte. In addition, the negative electrode mixture may include a conductive additive, a binder (binder), and the like. The current collector and the conductive layer formed on the current collector are not included.

In the present invention, the negative electrode active material is a material capable of inserting and removing lithium ions, and those known as negative electrode active materials in the battery field can be used.
The negative electrode active material is preferably composed of at least one of silicon (Si), tin (Sn), indium (In), aluminum (Al), and lithium (Li). The negative electrode active material is more preferably at least one of silicon and tin, or an alloy of silicon and tin, and more preferably silicon.

In the present invention, the negative electrode active material is preferably a powder, and the average particle size is preferably 100 μm or less. Although a minimum is not specifically limited, For example, it is 100 micrometers or less and 1 nm or more. More preferably, the average particle diameter of the negative electrode active material is 30 μm or less and 10 nm or more.
By using the negative electrode active material powder having an average particle size of 100 μm or less, the contact between the solid electrolyte particles and the negative electrode active material particles is maintained well, and sufficient reaction sites can be secured.
On the other hand, a negative electrode layer manufactured using a negative electrode mixture manufactured using a negative electrode active material having an average particle size of less than 1 nm is likely to be cracked, which may make it difficult to manufacture the negative electrode layer.
The average particle size is preferably measured by a laser diffraction particle size distribution measuring method.

Negative electrode active material powder having an average particle size of 100 μm or less is obtained by pulverizing a lump of metal or alloy and coarse particles using a mortar, ball mill, bead mill, jet mill, planetary ball mill, vibration ball mill, sand mill, cutter mill, etc. Can be obtained by sieving.
The pulverization may be performed by either wet pulverization or dry pulverization, and the implementation means is not limited to the above.
In addition to the above, a powder having an average particle size of 100 μm or less can be obtained by using a method of reducing metal ions in a liquid phase, a method of rapidly cooling molten metal, a physical method of electron beam evaporation, or the like.

  A negative electrode active material can be used in the quantity of 10 weight%-95 weight% of negative electrode compound material total weight, for example. Preferably, it is 30% to 90% by weight of the total weight of the negative electrode mixture, and more preferably 45% to 85% by weight of the total weight of the negative electrode mixture.

  The negative electrode layer can be produced by a known method. For example, it can be produced by a coating method or an electrostatic method (electrostatic spray method, electrostatic screen method, etc.).

In the present invention, the electrolyte layer and the negative electrode layer include a solid electrolyte. The solid electrolytes used for the electrolyte layer and the negative electrode layer may be the same or different.
Solid electrolytes include polymer-based solid electrolytes, oxide-based solid electrolytes, and sulfide-based solid electrolytes.

(1) Polymer-based solid electrolyte The polymer-based solid electrolyte of the present invention is not particularly limited. For example, as disclosed in Japanese Patent Application Laid-Open No. 2010-262860, materials used as polymer electrolytes such as fluororesin, polyethylene oxide, polyacrylonitrile, polyacrylate, derivatives thereof, and copolymers thereof can be used.
As a fluororesin, what contains vinylidene fluoride (VdF), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), these derivatives, etc. as a structural unit is mentioned, for example. Specifically, binary copolymers such as homopolymers such as polyvinylidene fluoride (PVdF), polyhexafluoropropylene (PHFP), and polytetrafluoroethylene (PTFE), copolymers of VdF and HFP, and 3 Examples thereof include an original copolymer.

(2) Oxide-based solid electrolyte The oxide-based solid electrolyte has a crystal having a perovskite structure such as LiN, LISICON, Thio-LISICON, La _0.55 Li _0.35 TiO ₃ or a NASICON type structure. LiTi ₂ P ₃ O ₁₂ and these crystallized electrolytes can be used.

(3) Sulfide-based solid electrolyte A lithium ion conductive inorganic solid electrolyte satisfying the composition represented by the following formula (1) is preferable.
Li _{a Mb} P _c S _d (1)
In the formula (1), M represents an element selected from the group consisting of B, Zn, Si, Cu, Ga, and Ge.
a to d indicate the composition ratio (molar ratio) of each element, and a: b: c: d satisfies 1 to 12: 0 to 0.2: 1: 2 to 9. Preferably, b is 0, more preferably the ratio of a, c and d (a: c: d) is a: c: d = 1 to 9: 1: 3-7, more preferably a: c: d = 1.5-4: 1: 3.25-4.5.
The composition ratio of each element can be controlled by adjusting the blending amount of the raw material compound when producing the solid electrolyte.

  The sulfide-based solid electrolyte may be amorphous (vitrified), crystallized (glass ceramics), or only partially crystallized. Here, when crystallized, the ion conductivity may be higher than that of glass. In that case, it is preferable to crystallize.

As the crystal structure, for example, Li ₇ PS ₆ structure, Li ₄ P ₂ S ₆ structure, Li ₃ PS ₄ structure, Li ₄ SiS ₄ structure, Li ₂ SiS ₃ structure disclosed in JP 2002-109955 A, The Li ₇ P ₃ S ₁₁ structure disclosed in Japanese Patent Application Laid-Open No. 2005-228570 and International Publication No. 2007/065539 is preferable.
Here, the Li ₇ P ₃ S ₁₁ structure has 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0. 0 in X-ray diffraction (CuKα: λ = 1.5418４). It has diffraction peaks at 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.
This is because the above-described crystal structure has higher ionic conductivity than the amorphous body.

  The crystallized portion of the sulfide-based solid electrolyte may be composed of only one crystal structure or may have a plurality of crystal structures. The crystallization method will be described later.

The degree of crystallinity of the sulfide-based solid electrolyte (the degree of crystallinity of the crystal structure having higher ionic conductivity than that of the amorphous body) is preferably 50% or more, and more preferably 60% or more. This is because when the crystallinity of the sulfide-based solid electrolyte is less than 50%, the effect of increasing the ionic conductivity by crystallization is reduced.
The degree of crystallinity can be measured by using an NMR spectrum apparatus. Specifically, a solid ³¹ P-NMR spectrum of a sulfide-based solid electrolyte was measured, and the resonance line observed at 70-120 ppm was separated into a Gaussian curve using a nonlinear least square method. It can be measured by determining the area ratio of each curve.

Method for producing the sulfide-based solid electrolyte, the raw material of the sulfide-based solid electrolyte, _Li 2 S (lithium _sulfide), P 2 _{S 3} (trisulfide _{diphosphorus), P} 2 _{S 5} (phosphorus pentasulfide), SiS ₂ (silicon sulfide), Li ₄ SiO ₄ (lithium orthosilicate), Al ₂ S ₃ (aluminum sulfide), simple phosphorus (P), simple sulfur (S), silicon (Si), GeS ₂ (germanium sulfide), B ₂ S ₃ (diarsenic trisulfide), Li ₃ PO ₄ (lithium phosphate), Li ₄ GeO ₄ (lithium germanate), LiBO ₂ (lithium metaborate), LiAlO ₃ (lithium aluminate), or the like may be used. it can. Preferred raw materials for sulfide-based solid electrolytes are Li ₂ S (lithium sulfide) and P ₂ S ₅ (diphosphorus pentasulfide).
Hereinafter, a sulfide-based solid electrolyte using Li ₂ S (lithium sulfide) and P ₂ S ₅ (diphosphorus pentasulfide) as a raw material for the sulfide-based solid electrolyte will be described.

As lithium sulfide, those commercially available without particular limitation can be used, but those having high purity are preferred.
Lithium sulfide can be manufactured by the method of Unexamined-Japanese-Patent No. 7-330312, Unexamined-Japanese-Patent No. 9-283156, Unexamined-Japanese-Patent No. 2010-163356, and Unexamined-Japanese-Patent No. 2011-84438, for example.
For example, in Japanese Patent Application Laid-Open No. 2010-163356, lithium hydroxide and hydrogen sulfide are reacted at 70 ° C. to 300 ° C. in a hydrocarbon organic solvent to produce lithium hydrosulfide, and then this reaction solution is desulfurized. Lithium sulfide is synthesized by hydrogenation.
In JP 2011-84438 A, lithium hydroxide and hydrogen sulfide are reacted at 10 ° C. to 100 ° C. in an aqueous solvent to produce lithium hydrosulfide, and then this reaction solution is dehydrosulfurized. To synthesize lithium sulfide.

The lithium sulfide preferably has a total lithium oxide lithium salt content of 0.15% by mass or less, more preferably 0.1% by mass or less, and a lithium N-methylaminobutyrate content. The content is preferably 0.15% by mass or less, more preferably 0.1% by 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). On the other hand, if the total content of the lithium salt of sulfur oxide exceeds 0.15% by mass, the obtained electrolyte may become a crystallized product from the beginning, and the ionic conductivity of this 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.
In addition, 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 ion battery. When lithium sulfide with reduced impurities is used, a high ion conductive electrolyte can be obtained.

The lithium sulfide described in JP-A-7-330312 and JP-A-9-283156 preferably contains a lithium salt of sulfur oxide and the like, and thus is preferably purified.
On the other hand, since lithium sulfide produced by the method for producing lithium sulfide described in JP 2010-163356 A has a very small content of lithium salt of sulfur oxide, etc., production of a sulfide-based solid electrolyte without purification. You may use for.
As a preferable purification method, for example, the purification method described in International Publication No. 2005/40039 and the like can be mentioned. Specifically, the lithium sulfide obtained as described above is washed at a temperature of 100 ° C. or higher using an organic solvent.

As long as diphosphorus pentasulfide (P ₂ S ₅ ) is industrially manufactured and sold, it can be used without particular limitation.

  The ratio (molar ratio) of lithium sulfide to diphosphorus pentasulfide is usually 50:50 to 80:20, preferably 60:40 to 78:22, and particularly preferably 68:32 to 76:24.

As a method for producing a sulfide-based glass solid electrolyte, there are a melt quenching method, a mechanical milling method (MM method), a slurry method in which raw materials are reacted in an organic solvent, and the like.
(A) Melting and quenching method The melting and quenching method is described in, for example, Japanese Patent Application Laid-Open No. 6-279049 and International Publication No. 2005/119706.
Specifically, a mixture of P ₂ S ₅ and Li ₂ S in a predetermined amount in a mortar and pelletized is 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 is preferably 400 ° C to 1000 ° C, more preferably 800 ° C to 900 ° C. The reaction time is preferably 0.1 hour to 12 hours, more preferably 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.

(B) Mechanical milling method The mechanical milling method is described in, for example, JP-A-11-134937, JP-A-2004-348972, and JP-A-2004-34897.
Specifically, a predetermined amount of P ₂ S ₅ and Li ₂ S are mixed in a mortar and reacted for a predetermined time using, for example, various ball mills to obtain a sulfide-based glass solid electrolyte.
The MM 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 may be set to several tens to several hundreds of revolutions / minute, and the treatment may be performed for 0.5 hours to 100 hours.
Further, as described in JP 2010-90003 A, balls of a ball mill may be used by mixing balls having different diameters.
Further, as described in JP2009-110920A and JP2009-2111950A, an organic solvent may be added to the raw material to form a slurry, and the slurry may be mechanically milled.
Moreover, you may adjust the temperature in the mill in the case of a mechanical milling process as described in Unexamined-Japanese-Patent No. 2010-30889.
It is preferable that the raw material be 60 ° C. or higher and 160 ° C. or lower during mechanical milling.

(C) Slurry method The slurry method is described in International Publication No. 2004/093099 and International Publication No. 2009/047977.
Specifically, a sulfide-based glass solid electrolyte is obtained by reacting a predetermined amount of P ₂ S ₅ particles and Li ₂ S particles in an organic solvent for a predetermined time. Here, as described in Japanese Patent Application Laid-Open No. 2010-140893, in order to advance the reaction, the slurry containing the raw material may be reacted while being circulated between the bead mill and the reaction vessel.
Further, as described in International Publication No. 2009/047977, when the raw material lithium sulfide is pulverized in advance, the reaction can proceed efficiently.
In addition, as described in JP2011-270191A, a polar solvent having a solubility parameter of 9.0 or more (eg, methanol, diethylcarnate, acetonitrile) in order to increase the specific surface area of the raw material lithium sulfide. It may be immersed in a predetermined time.

The reaction temperature is preferably 20 ° C. or higher and 80 ° C. or lower, more preferably 20 ° C. or higher and 60 ° C. or lower. The reaction time is preferably 1 hour or longer and 16 hours or shorter, more preferably 2 hours or longer and 14 hours or shorter.
It is preferable that the raw materials lithium sulfide and phosphorous pentasulfide be in a solution or slurry form by the addition of an organic solvent. Usually, the amount of the raw material (total amount) added to 1 liter of the organic solvent is about 0.001 kg or more and 1 kg or less. Preferably they are 0.005 kg or more and 0.5 kg or less, Especially preferably, they are 0.01 kg or more and 0.3 kg.

The organic solvent is not particularly limited, but an aprotic organic solvent is particularly preferable.
Examples of the aprotic organic solvent include an aprotic organic solvent (for example, a hydrocarbon organic solvent), an aprotic polar organic compound (for example, an amide compound, a lactam compound, a urea compound, an organic sulfur compound, and a cyclic organic phosphorus). A compound or the like) can be suitably used as a single solvent or a mixed solvent.
As the hydrocarbon-based organic solvent, saturated hydrocarbons, unsaturated hydrocarbons, or aromatic hydrocarbons can be used as the hydrocarbon-based solvent that is the solvent.
Examples of the saturated hydrocarbon include hexane, pentane, 2-ethylhexane, heptane, decane, and cyclohexane.
Examples of the unsaturated hydrocarbon include hexene, heptene, cyclohexene and the like.
Aromatic hydrocarbons include toluene, xylene, decalin, 1,2,3,4-tetrahydronaphthalene and the like.
Of these, toluene and xylene are particularly preferable.

The hydrocarbon solvent is preferably dehydrated in advance. Specifically, the water content is preferably 100 ppm by weight or less, and particularly preferably 30 ppm by weight or less.
In addition, you may add another solvent to a hydrocarbon type solvent as needed. Specific examples include ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran, alcohols such as ethanol and butanol, esters such as ethyl acetate, and halogenated hydrocarbons such as dichloromethane and chlorobenzene.

  Manufacturing conditions such as temperature conditions, processing time, and charge for the melt quenching method, MM method and slurry method can be appropriately adjusted according to the equipment used.

A method for producing a sulfide-based solid electrolyte (glass ceramic) is disclosed in Japanese Patent Application Laid-Open No. 2005-228570, International Publication No. 2007/065539, and Japanese Patent Application Laid-Open No. 2002-109955.
Specifically, the sulfide-based solid electrolyte (glass) obtained above is heat-treated at a predetermined temperature to produce a sulfide-based crystallized glass (glass ceramic) solid electrolyte.
The heating is preferably performed in an environment having a dew point of −40 ° C. or less, and more preferably in an environment having a dew point of −60 ° C. or less.
Moreover, the pressure at the time of a heating may be a normal pressure, and may be under pressure reduction.
The atmosphere may be air or an inert atmosphere.
Furthermore, you may heat in a solvent as it describes in Unexamined-Japanese-Patent No. 2010-186744.

For example, the heat treatment temperature for producing a glass ceramic having a Li ₇ P ₃ S ₁₁ structure is preferably 180 ° C. or higher and 330 ° C. or lower, more preferably 200 ° C. or higher and 320 ° C. or lower, and particularly preferably 210 ° C. or higher and 310 ° C. or lower. is there. When the temperature is lower than 180 ° C., it may be difficult to obtain a crystallized glass having a high degree of crystallinity.
In the case of a temperature of 180 ° C. or higher and 210 ° C. or lower, the heat treatment time is preferably 3 hours or longer and 240 hours or shorter, and particularly preferably 4 hours or longer and 230 hours or shorter. When the temperature is higher than 210 ° C. and lower than or equal to 330 ° C., it is preferably 0.1 hours or longer and 240 hours or shorter, particularly preferably 0.2 hours or longer and 235 hours or shorter, and more preferably 0.3 hours or longer and 230 hours or shorter. .
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 generated.

In addition, regarding the heating conditions for forming the Li ₇ PS ₆ crystal structure, the Li ₄ P ₂ S ₆ crystal structure, the Li ₃ PS ₄ crystal structure, the Li ₄ SiS ₄ crystal structure, and the Li ₂ SiS ₃ crystal structure, for example, Crystallized glass having the above crystal structure can be produced by the method disclosed in JP-A No. 2002-109955.

The average particle size of the sulfide-based solid electrolyte is preferably 0.01 μm or more and 1000 μm or less, more preferably 0.01 μm or more and 500 μm or less, and further preferably 1 μm or more and 250 μm or less.
The average particle size is preferably measured by a laser diffraction particle size distribution measuring method.

  In the negative electrode layer, the solid electrolyte can be used, for example, in an amount of 5 wt% to 90 wt% of the total weight of the negative electrode mixture. Preferably, it is 10% by weight to 70% by weight of the negative electrode composite material weight, and more preferably 15% by weight to 55% by weight of the negative electrode composite material weight.

  The lithium ion battery of the present invention has the above-described negative electrode layer and an electrolyte layer containing a solid electrolyte, and other constituent members can employ known materials and configurations for lithium ion batteries. Usually, a lithium ion battery has an electrolyte layer between a positive electrode layer and a negative electrode layer.

The positive electrode layer usually contains a positive electrode active material, and a mixture of the positive electrode active material and a solid electrolyte (positive electrode mixture) can be used. Furthermore, you may contain a conductive support agent and a binder (binder). As the positive electrode active material, a material capable of inserting and desorbing lithium ions, and a material known as a positive electrode active material in the battery field can be used.
For example, V ₂ O ₅ , LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1, 0 <b <1, 0 < c <1, a + b + c = 1), LiNi _1-Y Co _{Y 2} O ₂ , LiCo _1-Y Mn _{Y 2} O ₂ , LiNi _1-Y Mn _{Y 2} O ₂ (where 0 ≦ Y <1), Li (Ni _{a Co b Mn c) O 4 (} 0 <a <2,0 <b <2,0 <c <2, a + b + c = 2), LiMn 2-Z Ni Z O 4, LiMn 2-Z Co Z O 4 ( wherein And 0 <Z <2), LiCoPO ₄ , and LiFePO ₄ .
As a positive electrode material, what is used as a positive electrode active material in the battery field | area can be used. For example, in the sulfide system, titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), iron sulfide (FeS, FeS ₂ ), copper sulfide (CuS), nickel sulfide (Ni ₃ S ₂ ), and the like can be used. Preferably, TiS ₂ can be used.

In the oxide system, bismuth oxide (Bi ₂ O ₃ ), bismuth leadate (Bi ₂ Pb ₂ O ₅ ), copper oxide (CuO), vanadium oxide (V ₆ O ₁₃ ), lithium cobalt oxide (LiCoO ₂ ) Lithium nickelate (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), and the like can be used. It is also possible to use a mixture of these. Preferably, lithium cobaltate can be used.

In addition, Li _x CoO ₂ , Li _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x FePO ₄ , Li _x CoPO ₄ , Li _x Mn _1/3 Ni _1/3 Co _1/3 O ₂ , Li _x Mn _{1 .5} Ni _0.5 O ₂ and the like can also be used (X is 0.1 to 0.9.)

In addition to the above, niobium selenide (NbSe ₃ ), organic disulfide compounds, carbon sulfide compounds, sulfur, metallic indium and the like 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.

  Examples of the solid electrolyte include those similar to the solid electrolyte used in the above-described electrolyte layer.

  The positive electrode layer can be produced by a known method. For example, it can be produced by a coating method or an electrostatic method (electrostatic spray method, electrostatic screen method, etc.).

A conductive additive can be added to the negative electrode layer and the positive electrode layer. The conductive auxiliary agent should just have electroconductivity. The conductivity of the conductive auxiliary agent is preferably 1 × 10 ³ S / cm or more, more preferably 1 × 10 ⁵ S / cm or more.
Examples of the conductive aid include substances selected from carbon materials, metal powders and metal compounds, and mixtures thereof.

Specific examples of conductive aids include carbon, nickel, copper, aluminum, indium, silver, cobalt, magnesium, lithium, chromium, gold, ruthenium, platinum, beryllium, iridium, molybdenum, niobium, osnium, rhodium, tungsten and zinc. A substance containing at least one element selected from the group consisting of: More preferably, it is a simple substance of carbon, carbon, nickel, copper, silver, cobalt, magnesium, lithium, ruthenium, gold, platinum, niobium, osnium or rhodium having a high conductivity, simple substance, mixture or compound.
Specific examples of the carbon material include carbon black such as ketjen black, acetylene black, denka black, thermal black and channel black, graphite, carbon fiber, activated carbon and the like. These can be used alone or in combination of two or more.
Among these, acetylene black, denka black, and ketjen black having high electron conductivity are preferable.

  In the negative electrode layer, the conductive additive can be used, for example, in an amount of 60 wt% to 0.5 wt% of the total weight of the negative electrode mixture. Preferably, it is 50% by weight to 1.5% by weight of the negative electrode composite material weight, and more preferably 40% by weight to 2.5% by weight of the negative electrode composite material weight.

  A binder (binder) can be added to the negative electrode layer, the positive electrode layer, and the electrolyte layer.

  As the binder, polyethylene-based and vinylidene fluoride-based are preferable, and polyvinylidene fluoride, polyethylene glycol, polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polysiloxy acid, vinylidene fluoride-hexafluoropropylene copolymer. Etc.

Preferably, the binder is a polymer having a unit of the following formula (10) or a unit of the formula (11).
_{- [OCH 2 CH 2] n} - ··· (10)
_{- [CH 2 -CF 2] n} - ··· (11)
The weight average molecular weight is preferably 10,000 to 100,000. The weight average molecular weight is measured by gel permeation chromatography (GPC).

More preferably, it is represented by the following formula.
_{R 20 - [OCH 2 CH 2} ] n -H
R ₂₁ — [CH ₂ —CF ₂ ] _n —R _{21 ′}
R ₂₀ , R ₂₁ and R _{21 ′} are each a linear or branched hydrocarbon group, a group having a cyclic structure, or a functional group, and the hydrocarbon group and the group having a cyclic structure may include a functional group. Good.

（式中、Ｒ_１〜Ｒ_４は、それぞれ、Ｈ、Ｆ、ＣＦ_３、ＣＨ_２ＣＦ_３、ＣＦ_２ＣＦ_３、ＣＦ_２ＣＦ_２ＣＦ_３、ＯＣＦ_２ＣＦ_２ＣＦ_３、ＯＣＦ_３又はＣｌであり、Ｒ_１〜Ｒ_４は少なくとも１つは、Ｆ、ＣＦ_３、ＣＨ_２ＣＦ_３、ＣＦ_２ＣＦ_３、ＣＦ_２ＣＦ_２ＣＦ_３、ＯＣＦ_２ＣＦ_２ＣＦ_３又はＯＣＦ_３である。） Further, the binder used in the present invention is preferably a resin containing the following structural unit A in the molecular skeleton.

(Wherein R _{1 to} R ₄ are H, F, CF ₃ , CH ₂ CF ₃ , CF ₂ CF ₃ , CF ₂ CF ₂ CF ₃ , OCF ₂ CF ₂ CF ₃ , OCF ₃ or Cl, respectively. And at least one of R _{1 to} R ₄ is F, CF ₃ , CH ₂ CF ₃ , CF ₂ CF ₃ , CF ₂ CF ₂ CF ₃ , OCF ₂ CF ₂ CF _3, or OCF ₃ ).

Preferably, a copolymer having a structure derived from vinylidene fluoride (R ₁ = F, R ₂ = F, R ₃ = H, R ₄ = H), polyvinylidene fluoride (PVDF), tetrafluoroethylene (TEF) A copolymer or a homopolymer having a structure derived from (R ₁ = F, R ₂ = F, R ₃ = F, R ₄ = F), a structure derived from hexafluoropropylene (HFP) (R ₁ = F , R ₂ = F, R ₃ = CF ₃ , R ₄ = F).
Specific examples include PVDF-HFP, PVDF-HFP-TEF, PVDF-TEF, TEF-HFP, and the like.

ｍは、一分子中の式（１）で示される繰返単位の数、ｎは一分子中の式（２）で示される繰返単位の数を示す。 Moreover, it is preferable that a binder has a repeating unit shown by Formula (1), and a repeating unit shown by Formula (2). (1) is a polymerized unit (VDF) based on vinylidene fluoride, and (2) is a polymerized unit (HFP) based on hexafluoropropylene.

m represents the number of repeating units represented by the formula (1) in one molecule, and n represents the number of repeating units represented by the formula (2) in one molecule.

If n is less than 10, it may not be dissolved in the nitrile solvent. When n is larger than 50, the characteristics of VDF are not exhibited and the adhesion may be poor. More preferably, it is m: n = 80-90: 20-10.
The number average molecular weight of the binder molecule is preferably 1,000 to 100,000.

  Specifically, examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), fluorine-containing resins such as fluorine rubber, Alternatively, thermoplastic resins such as polypropylene and polyethylene, ethylene-propylene-dienemer (EPDM), sulfonated EPDM, natural butyl rubber (NBR) and the like can be used alone or as a mixture of two or more. Polyvinylidene fluoride-hexafluoropropylene copolymer is particularly preferred. In addition, an aqueous dispersion of cellulose or styrene butadiene rubber (SBR), which is an aqueous binder, can also be used.

  The binder can be used, for example, in an amount of 30% by weight to 0.5% by weight of the total weight of the negative electrode mixture. Preferably, it is 20% by weight to 1.0% by weight of the negative electrode composite material weight, and more preferably 10% by weight to 1.5% by weight of the negative electrode composite material weight.

The lithium ion battery of the present invention preferably includes a current collector. The negative electrode current collector is provided on the side opposite to the electrolyte side of the negative electrode, and the positive electrode current collector is provided on the side opposite to the electrolyte side of the positive electrode.
As the current collector, a plate or foil made of copper, magnesium, stainless steel, titanium, iron, cobalt, nickel, zinc, aluminum, germanium, indium, lithium, or an alloy thereof can be used.

The lithium ion battery of the present invention can be manufactured by bonding and joining the above-described members. 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, this invention can provide the negative electrode layer demonstrated as a component of the said lithium ion battery independently as a negative electrode.

Production Example 1 [Production of lithium sulfide]
Production and purification of lithium sulfide were carried out in the same manner as in Examples of International Publication No. 2005/040039.
(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 for 2 hours at a supply rate of 3 liters / minute.
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 (LMAB) Was quantified by ion chromatography. As a result, the total content of sulfur oxides was 0.13% by mass, and LMAB was 0.07% by mass.
In the following production of the solid electrolyte, purified lithium sulfide was used.

Production Example 2 [Production of solid electrolyte]
Using the lithium sulfide produced in Production Example 1 (purified lithium sulfide), a solid electrolyte was produced and crystallized in the same manner as in Example 1 of International Publication No. 07/065539. Specifically, it was performed as follows.

0.6508 g (0.01417 mol) of lithium sulfide (purified lithium sulfide) produced in Production Example 1 and 1.3492 g (0.00607 mol) of diphosphorus pentasulfide (manufactured by Aldrich) were mixed well. Then, the mixed powder and 10 zirconia balls having a diameter of 10 mm were put into an alumina pot and completely sealed, and the alumina pot was filled with nitrogen to form a nitrogen atmosphere. This pot was attached to a planetary ball mill (manufactured by Fritsch: model number P-7).
Then, for the first few minutes, the planetary ball mill was rotated at a low speed (85 rpm) to sufficiently mix lithium sulfide and diphosphorus pentasulfide. 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 white yellow powder by X-ray measurement, it was confirmed that the powder was vitrified (sulfide glass). It was 220 degreeC when the glass transition temperature of this sulfide glass was measured by DSC (differential scanning calorimetry).
This sulfide glass was heated at 300 ° C. for 2 hours in a nitrogen atmosphere to produce a sulfide glass ceramic.
The obtained 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, 30.0 deg. A peak was observed.
The sulfide glass ceramic was particulate, and the average particle size was 190 μm (D50).

Example 1
(1) Production of negative electrode composite sheet 8.15 g of solid electrolyte (glass ceramics) powder produced in Production Example 2 and Si powder having an average diameter of 5 μm (manufactured by High Purity Chemical Laboratory, purity 99.9%) 3.49 g Were mixed lightly and 11.5 g of isobutyronitrile (manufactured by Kishida Chemical) was added. A solution in which 10% by weight of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) (manufactured by arkema, KYNER (registered trademark)) is dissolved in isobutyronitrile (manufactured by Kishida Chemical) as a binder therein. 3.59 g was added. Ten zirconia balls having a diameter of 10 mm were added, the alumina pot was completely sealed, and the pot was attached to a planetary ball mill. A slurry was obtained by performing mechanical milling at 370 rpm for 2 hours.
Apply a conductive primer (made by Nippon Graphite, product name: Bunny Height) on Al foil (Toyo Aluminum, 1N-30-H18, thickness 0.03 mm) to a thickness of 0.01 mm, and fully Dried. On this electroconductive primer layer, the negative electrode compound material layer was formed by apply | coating the slurry produced by the mechanical milling. The slurry coating amount was adjusted so that the solid content after removal of the solvent (corresponding to the weight of the negative electrode mixture) was 3.48 mg / cm ² per unit area (negative electrode composite weight per unit area). After coating, vacuum drying was performed at 150 ° C. for 3 hours to obtain a negative electrode mixture sheet (negative electrode layer).

(2) Production of Half Cell Using Negative Electrode Composite Material 60 mg of the inorganic solid electrolyte powder prepared in Production Example 2 was put into a ceramic cylinder having a diameter of 10 mm, and pressure-molded to obtain an electrolyte layer (electrolyte sheet).
Next, the negative electrode mixture sheet (weight per unit area: 3.48 mg / cm ² ) prepared in (1) was punched out into a circle using a punch having a diameter of 10 mm. The negative electrode composite material layer side of the punched sheet was pressure-molded so as to be in contact with the electrolyte layer to obtain a working electrode.
From the opposite side of the working electrode, a LiIn alloy foil was bonded and pressure-molded as a reference electrode and a counter electrode, and a half cell having a three-layer structure was produced. When the atomic ratio Li / In is 0.8 or less, the LiIn alloy can be used as a reference electrode because the Li desorption reaction potential is kept constant (0.62 V vs. Li / Li ⁺ ). Is possible.

(3) Cycle characteristic evaluation Cycle characteristic evaluation was performed about the produced half cell. 1.02 mA / cm ² and 0.01 Vvs. Li insertion was performed at a constant current (CC) up to Li / Li ⁺ , and Li insertion was performed at a constant voltage (CV) until the current reached 0.127 mA / cm ² at that voltage. Subsequently, at 1.02 mA / cm ² , 1.52 Vvs. Li desorption was performed at a constant current (CC) up to Li / Li ⁺ . The Li desorption cycle was repeated under these conditions, and the Li desorption capacity for each cycle was measured. The capacity retention rate was calculated by dividing the Li desorption capacity of each cycle by the initial Li desorption capacity. The relationship between the number of Li insertion / removal cycles and the capacity retention rate is shown in FIG.

Example 2
Evaluation was performed in the same manner as in Example 1 except that the basis weight of the negative electrode mixture was 2.46 mg / cm ² . The relationship between the number of Li insertion / removal cycles and the capacity retention rate is shown in FIG.

Comparative Example 1
Evaluation was performed in the same manner as in Example 1 except that the basis weight of the negative electrode mixture was 9.08 mg / cm ² . The relationship between the number of Li insertion / removal cycles and the capacity retention rate is shown in FIG.
As shown in FIG. 1, in Examples 1 and ² where the basis weight of the negative electrode mixture is 8.5 mg / cm ² or less, about 80% of the initial Li desorption capacity even after the Li desorption cycle is 40 cycles. In Comparative Example 1 in which the weight of the negative electrode mixture exceeded 8.5 mg / cm ² , the capacity decrease for each Li insertion / desorption cycle was lower than that in Example 1 and Example 2. It is remarkable. Thus, by using the negative electrode layer having a negative electrode composite weight of 8.5 mg / cm ² or less, it is possible to provide a negative electrode mixture having a high capacity retention rate and good cycle characteristics even when used repeatedly. it can.

  The lithium ion battery of the present invention can be used as a battery for various devices such as a portable information terminal, a portable electronic device, a small household power storage device, a motorcycle using a motor as a power source, an electric vehicle, and a hybrid electric vehicle.

Claims (13)

A negative electrode manufactured by a negative electrode mixture having a basis weight of 8.5 mg / cm ² or less, wherein the negative electrode mixture includes a negative electrode active material and a solid electrolyte. A negative electrode comprising a negative electrode active material and a solid electrolyte, wherein the total weight per unit area of the negative electrode active material and the solid electrolyte is 8.3 mg / cm ² or less. A negative electrode comprising a negative electrode active material, a solid electrolyte, and a binder, wherein the total weight per unit area of the negative electrode active material, the solid electrolyte, and the binder is 8.5 mg / cm ² or less. A lithium ion battery comprising a negative electrode mixture having a basis weight of 8.5 mg / cm ² or less, wherein the negative electrode mixture includes a negative electrode layer containing a negative electrode active material and a solid electrolyte, and an electrolyte layer containing a solid electrolyte. A negative electrode layer including a negative electrode active material and a solid electrolyte, wherein the total weight per unit area of the negative electrode active material and the solid electrolyte is 8.3 mg / cm ² or less; and an electrolyte layer including a solid electrolyte. Lithium ion battery. An electrolyte comprising a negative electrode active material, a solid electrolyte, and a binder, wherein the negative electrode active material, the solid electrolyte, and the binder have a total weight per unit area of negative electrode of 8.5 mg / cm ² or less, and a solid electrolyte A lithium-ion battery comprising a layer. The lithium ion battery according to claim 4, wherein a weight per unit area of the negative electrode mixture is 0.05 mg / cm ² or more and 8.0 mg / cm ² or less. The negative active material to the total weight of the negative electrode per unit area of the solid electrolyte 0.05 mg / cm ² or more and 7.8 mg / cm ² or less, a lithium ion battery according to claim 5. The lithium ion battery according to claim 6, wherein a total weight per unit area of the negative electrode active material, the solid electrolyte, and the binder is 0.05 mg / cm ² or more and 8.0 mg / cm ² or less. The lithium ion battery according to any one of claims 4 to 9, wherein the solid electrolyte is a lithium ion conductive inorganic solid electrolyte satisfying a composition represented by the following formula (1).
Li _a M _b P _c S _d (1)
(In Formula (1), M represents an element selected from the group consisting of B, Zn, Si, Cu, Ga, and Ge. Ad represents the composition ratio of each element, and a: b: c: d. Satisfies 1-12: 0 to 0.2: 1: 2-9.)   The lithium ion battery according to any one of claims 4 to 10, wherein the negative electrode composite material includes a negative electrode active material composed of at least one of silicon, tin, indium, aluminum, and lithium.   The lithium ion battery according to claim 4, wherein the negative electrode active material has an average particle size of 100 μm or less.   The apparatus provided with the lithium ion battery in any one of Claims 4-12.

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