JP2001155777A - Lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium battery which can improve the lithium ion conductivity and increase the current density of the electrolyte, and to solve the problem that an organic solvent or a lithium salt as carrier of the lithium ion must be included. SOLUTION: A lithium ion battery including a solid electrolyte layer inserted between a pair of electrodes, characterized in that the electrodes and the solid electrolyte layer comprise a non-protonic solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a lithium battery.

[0002]

2. Description of the Related Art Lithium-ion batteries are widely used in mobile phones, notebook computers, etc., taking advantage of their characteristics such as high energy density, low self-discharge and long-term storage. . These lithium ion batteries use lithium cobaltate (LiCoO ₂ ) or lithium manganate (Li) as a positive electrode active material.
Mn ₂ O ₄ ) is generally used, and a carbon material such as coke or carbon fiber is used as the negative electrode active material.

[0003] In general, a lithium ion battery includes the above-mentioned positive electrode active material or negative electrode active material, a conductive agent such as acetylene black or graphite, and a binder such as polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE). Coated on aluminum foil or copper foil, spirally wound through a separator made of polypropylene or polyethylene or a combination of them, inserted into a battery case, sealed with an organic electrolyte solution The structure has been.

The components of these organic electrolytes are an aprotic solvent and an electrolyte salt, and the aprotic solvents include propylene carbonate (PC), dimethoxyethane (DME), ethylene carbonate (EC), and dimethyl carbonate (DMC). ), Diethyl carbonate (DE
C) is used alone or in a mixed state, and as electrolyte salts, LiClO ₄ , LiAsF ₆ , LiBF ₄ , L
iPF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N and the like are used.

[0005] In recent years, with the demand for thinner and smaller electronic equipment such as portable information communication terminals such as mobile phones and notebook personal computers, polymer electrolytes have been used in place of the above-mentioned organic electrolytes. Attention has been paid to lithium batteries using an electrolyte.

[0006] The polymer electrolyte is a mixture of a polymer having a donor type polar group represented by polyethylene oxide (PEO) and polypropylene oxide (PPO) and an electrolyte salt, and can form a thin electrolyte layer. It is expected that the energy density will be improved. Alternatively, since there is no fear of liquid leakage and corrosion and no volatile aprotic solvent is used, there is little danger of explosion and ignition, so that battery characteristics and safety can be improved.

However, the aforementioned polymer electrolyte is
There is a problem that the ionic conductivity is lower than that of the organic electrolyte, and the gel electrolyte in which the organic electrolyte is mixed with the polymer electrolyte has an ionic conductivity comparable to that of the organic electrolyte. It has been done.

[0008] When such a gel electrolyte is used, it is difficult to keep the electrical contact between the solid electrolyte layer and the electrode layer ideally. For example, Japanese Patent Application Laid-Open No. A monomer composition obtained by polymerizing a monomer composition by mixing a salt and a solvent is laminated on the positive electrode active material layer, a part of the monomer composition is impregnated in the positive electrode active material layer, and the positive electrode active material layer is impregnated. The positive electrode active material layer and the polymer solid electrolyte are sufficiently adhered to each other by polymerizing the monomer composition laminated on the surface of the positive electrode active material and forming a polymer solid electrolyte in close contact with the positive electrode active material layer. It has been proposed to do so.

In Japanese Patent Application Laid-Open No. HEI 8-111233, the resistance of the interface between the positive electrode and the solid electrolyte in which both ends or one end of the main chain of polyether, polythioether or polyacrylate are chemically bonded to the surface of the positive electrode oxide, and It has been proposed to reduce the interface resistance between the positive electrode active material particles.

In Japanese Patent Application Laid-Open No. Hei 8-315855, a mixture of an organic compound having a polymerizable functional group, an organic solvent, and a lithium salt is sandwiched between both electrodes, and thereafter, the polymerization is completed. Proposals have been made to prevent the generation of an interface between the electrode and the electrode and to prevent separation of the solid electrolyte and the electrode.

In Japanese Patent Application Laid-Open No. 3-37971,
LiI, Li-β-Al in organic polymer solid electrolyte
Inorganic solid electrolytes such as ₂ O ₃ , Li ₃ N, and LiI-Al ₂ O ₃ are dispersed to improve ionic conductivity and have flexibility, withstand voltage, and a highly reliable thin battery has been proposed. ing.

[0012] In Japanese Patent Application Laid-Open No. 9-50816,
Li ₂ in the polymer electrolyte mixed with solute and electrolyte salt
_{CO 3, CoCO 3, NiCO 3} , by dispersing the metal carbonate such as MgCO _3, mechanical properties, together with the workability is excellent, and high chemical stability composite solid electrolyte have been proposed in the interface with the anode I have.

However, these methods still have a problem that the lithium ion conductivity of the electrolyte is low and the current density is low, and it is necessary to contain a large amount of the main lithium ion conductor, that is, the organic solvent and the lithium salt.

Further, the development of a solid electrolyte battery using an inorganic compound for the solid electrolyte is also in progress. For example, in JP-A-8-148180, a compound comprising a transition metal oxide and a transition metal sulfide as a positive electrode active material is used as a positive electrode, a lithium ion conductive glass solid electrolyte containing Li ₂ S, and a metal alloyed with lithium. It has been proposed that an all-solid lithium battery having a negative electrode as a negative electrode does not generate dendrites or drop off an active material in the negative electrode, and has an excellent charge / discharge cycle life. However, in this proposal, since the positive electrode and the solid electrolyte contain a sulfide-based compound, there are problems such as high reactivity with moisture.

In Japanese Patent Application Laid-Open No. 5-299101, Li _{1+ (4-n)} M _x Ti having excellent lithium ion conductivity is disclosed.
_A lithium battery excellent in high-rate discharge characteristics has been proposed by using a sintered _2-x (PO ₄ ) ₃ as a solid electrolyte. However, even in the case of an all-solid lithium battery using an oxide inorganic solid electrolyte as described above, there are problems such as inferior energy density and discharge current density as compared with a conventional secondary battery using a non-aqueous solvent as an electrolyte. And it has not been put to practical use.

Even if the lithium ion conductivity of the inorganic solid electrolyte is improved, the characteristics of the battery are not improved because of the interfacial resistance between particles and the interfacial resistance between the electrode and the solid electrolyte. Even if each material has sufficient characteristics, sufficient characteristics cannot be obtained due to high interface resistance.

The present invention has been made in view of such problems of the prior art, and has a low lithium ion conductivity of an electrolyte and a low current density. For example, an organic solvent or a lithium salt which is a lithium ion conductor is used. An object of the present invention is to provide a lithium battery that has solved the conventional problem that it needs to be included.

[0018]

According to a first aspect of the present invention, there is provided a lithium battery having a solid electrolyte layer sandwiched between a pair of electrodes. The solid electrolyte layer contains an aprotic solvent.

In the above-mentioned lithium battery, it is preferable that the electrode is made of an electrode active material and a solid electrolyte, and the solid electrolyte layer is made of the same material as the solid electrolyte.

In the above lithium battery, it is preferable that the solid electrolyte layer is made of an oxide crystallized glass having lithium ion conductivity.

In the above-mentioned lithium battery, it is preferable that the aprotic solvent comprises one or more of propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, and diethyl carbonate.

In the above lithium battery, the active material of the electrode is Li _{1 + x} Mn _2-x O ₄ (0 ≦ x ≦ 0.2), LiMn _2-y
Me _y O ₄ (Me = Ni, Cr, Cu, Zn, 0 <y ≦
0.6), Li ₄ Ti ₅ O ₁₂ and at least one selected from the group consisting of Li ₄ Mn ₅ O ₁₂ .

The conventional organic electrolyte solution imparts lithium ion conductivity to the electrolyte by dissolving the electrolyte salt in an aprotic solvent. In the present invention, an aprotic solvent containing no electrolyte salt is used. Only improves the battery characteristics, and it is considered that lithium ions move by an unconventional conduction mechanism.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the lithium battery of the present invention will be described. FIG. 1 is a sectional view showing a configuration example of the lithium battery according to the present invention. In FIG. 1, 1
Denotes a package, 2 denotes a pair of electrodes, 2a denotes a positive electrode, 2b denotes a negative electrode, 3 denotes a solid electrolyte layer, 4 denotes a positive electrode current collector, and 5 denotes a negative electrode current collector.

The material of the package 1 is not limited as long as it can maintain airtightness. For example, an aluminum laminate, a metal such as nickel or aluminum, or a shrink case can be used.

The positive electrode current collector 4 or the negative electrode current collector 5 is provided for collecting the current of the positive electrode 2a or the negative electrode 2b, and uses a metal foil such as aluminum (Al), nickel (Ni), copper (Cu). be able to.

The positive electrode 2a is made of a powder of a positive electrode active material, and if necessary, a solid electrolyte powder of the same material as the solid electrolyte layer is mixed. The negative electrode 2b is made of a negative electrode active material powder, and a solid electrolyte powder of the same material as the solid electrolyte layer is mixed as needed. When the positive or negative electrode active material and the solid electrolyte powder are mixed, the lithium ion conductivity in the electrode is expected to be improved.However, when the mixing amount of the solid electrolyte powder is excessive, the positive electrode or the positive electrode that contributes to the charge / discharge reaction of the battery is improved. The amount per volume or weight of the negative electrode active material decreases, and the energy density as a battery decreases. Therefore, the amount of the positive electrode or negative electrode active material in the electrode is desirably 40% by weight or more. Further, a conductive agent and a binder are added to the positive electrode 2a and the negative electrode 2b as needed.

As the electrode active material used for the positive electrode 2a and the negative electrode 2b, for example, lithium manganese composite oxide, manganese dioxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium vanadium composite oxide Oxides, lithium titanium composite oxides, titanium oxide, niobium oxide, vanadium oxide, tungsten oxide, and the like, and their inducers can be used. Among the above transition metal oxides, particularly L
i _{1 + x} Mn _2-x O ₄ (0 ≦ x ≦ 0.2), LiMn _{2 -y} Me
_y O ₄ (Me = Ni, Cr, Cu, Zn, 0 <y ≦ 0.6
), Li ₄ Ti ₅ O ₁₂ , or Li ₄ Mn ₅ O ₁₂ , a crystalline system in which the volume change of the active material during charging / discharging is small is a spinel-based active material and shows good cycle characteristics. It is. Here, there is no clear distinction between the positive electrode active material and the negative electrode active material, and those showing a noble potential by comparing the charge and discharge potentials of the two compounds are shown as the positive electrode, and those showing the noble potential are shown as the negative electrode. It can be used to form a battery of any voltage.

Solid electrolyte powder used for the solid electrolyte layer 3,
The solid electrolyte powder to be mixed with the positive electrode 2a or the negative electrode _{2b, 30LiI-41Li 2 O-} 29P 2 O 5, 40
_{Li 2 O-35B 2 O 5} -25LiNbO 3, 25Li 2 O
_{-25Al 2 O 3 -50SiO 2, 40Li} 2 O-6Y 2 O 3
-54SiO ₂ or 65LiNbO ₂ -35SiO
₂ or an oxide-based amorphous solid electrolyte such as Li _{1 + x} M _x Ti _2-x
(PO ₄ ) ₃ (where M is Al, Sc, Y, La), Li
_{1 + x} Ti _2-x (PO ₄ ) ₃ , Li _0.5-3x R _{0.5 + x} TiO ₃ (where R is La, Pr, Nd, Sm), Li _{1 + x + y} Al _x T
An oxide-based crystallized glass such as i _2-x Si _y P _{3 -y} O ₁₂ can be used. The solid electrolyte powder is preferably an oxide crystallized glass from the viewpoint of ionic conductivity.

Examples of the conductive agent include acetylene black, graphite, Ketjen black, RuO ₂ , SnO ₂ doped with Sb ₂ O _3, and SnO ₂ doped In ₂ O ₃ .

As the binder, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTF)
E), polyolefins, polyimides and the like.

As a method of forming the positive electrode 2a, the negative electrode 2b, and the solid electrolyte 3, each powder is dispersed in the binder dispersed in a solvent to form a slurry, and the slurry is applied on a base film. dry. At this time, the positive electrode 2a, the negative electrode 2b, and the solid electrolyte 3 are formed and cut, and then laminated by thermocompression bonding or the like, or the positive electrode 2a or the negative electrode 2b
Is formed, dried, the solid electrolyte 3 is formed thereon, dried, and then the negative electrode 2b or the positive electrode 2a is formed thereon. Further, there is a method in which the powder is put into a mold and pressed by a press machine, or a method in which the granulated powder is pressed and formed by a roll press to form a sheet.

Here, as the substrate film, for example, resin films such as polyethylene terephthalate, polypropylene, polyethylene and tetrafluoroethylene, and metal foils such as aluminum, stainless steel and copper can be used.

As the aprotic solvent contained in the positive electrode 2a-solid electrolyte 3-negative electrode 2b, propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxy Examples of the solvent include one or more of ethane (DME), dimethyl carbonate (DMC), and diethyl carbonate (DEC).

As a method of including an aprotic solvent in the laminate of the positive electrode 2a, the solid electrolyte 3 and the negative electrode 2b, a method of dipping the laminate into an aprotic solvent, or a method of directly impregnating the laminate with an aprotic solvent And the like. The amount of the aprotic solvent to be contained in the laminate is not particularly limited, but is preferably 0.1 cc or more per 1 cm ² because it is necessary to wet the powder forming the laminate moderately.

In an all-solid-state battery containing no aprotic solvent, lithium ions rely only on migration in bulk. In the lithium battery of the present invention, however, the lithium ion of the aprotic solvent that wets the particle surface is not used. It is assumed that ions are moving at the interface.

The lithium battery to which the present invention is applied may be a primary battery or a secondary battery. The battery shape is not limited to a cylindrical type, a square type, a button type, a coin type, a flat type and the like.

[0038]

EXAMPLES Example 1 Lithium hydroxide and manganese dioxide were mixed so that the molar ratio of Li and Mn was 1: 2.
This mixture was heated and baked at 900 ° C. in the air for 15 hours to obtain a lithium manganese composite oxide (LiMn _2).
O ₄ ) was synthesized and used as a positive electrode active material. Next, lithium hydroxide and manganese dioxide are mixed such that the molar ratio of Li and Mn is 4: 5.
By heating and baking at 0 ° C. for 15 hours, a lithium manganese composite oxide (Li ₄ Mn ₅ O ₁₂ ) was synthesized and used as a negative electrode active material.

This LiMn ₂ O ₄ was mixed with Li _{1 + x + y} Al _x Ti _2-x Si _y P _{3- y} O ₁₂ as a solid electrolyte powder in a volume ratio of 8: 2. Acetylene black and polyvinylidene fluoride (PVd
F) was mixed at a ratio of 82: 8: 10 by weight. The polyvinylidene fluoride (PVdF) used was previously dissolved in N-methylpyrrolidone. Furthermore, polyvinylidene fluoride (PV
A slurry was formed by adding and mixing 12 g of dF). After this slurry was applied on aluminum (Al) by a doctor blade method, polyvinylidene fluoride (PVdF) was dried to form a sheet.

Further, the solid electrolyte powder Li _{1 + x + y} Al _x Ti
_2-x Si _y P _3-y O ₁₂ with polyvinylidene fluoride (PVd
F) was mixed at a weight ratio of 9: 1. As described above, polyvinylidene fluoride (PVdF) used was previously dissolved in N-methylpyrrolidone (NMP). Further, about 15 g of N-methylpyrrolidone (NMP) was added to this mixture and mixed to form a slurry. The slurry was applied on the above-described positive electrode by a doctor blade method, laminated, and dried to obtain a laminate of the positive electrode 2a and the solid electrolyte 3.

Further, Li ₄ Mn ₅ O ₁₂ is slurried in the same manner as LiMn ₂ O ₄ as a positive electrode active material, applied to the solid electrolyte side of the laminate, laminated, and dried.
A laminate of the positive electrode 2a, the solid electrolyte 3, and the negative electrode 2b was obtained. The thickness of the obtained laminate was about 200 μm.

The obtained laminate is impregnated with propylene carbonate (PC) to bond the positive electrode current collector 4 to the positive electrode 2a of the laminate, and similarly, to bond the negative electrode current collector 5 to the negative electrode 2b. The package 1 was mounted on an aluminum laminate. The aluminum laminate was prepared by cutting two pieces having a size of 35 mm × 35 mm, sandwiching the laminate in which the current collectors were joined, and thermocompression-bonding the outer periphery of the aluminum laminate to obtain the 35 mm laminate shown in FIG. A × 35 mm square lithium battery was assembled.

Example 2 The method of synthesizing the positive electrode active material and the negative electrode active material, and the method of forming the positive electrode 2a, the solid electrolyte 3 and the negative electrode 2b were the same as in Example 1. The obtained positive electrode 2a-
The thickness of the solid electrolyte 3-negative electrode 2b was about 220 μm. The obtained laminated body was impregnated with a mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) (PC: DME = 1: 1 by volume), and thereafter, corners were formed in the same manner as in the example. -Type lithium battery was assembled.

[Comparative Example 1] The following comparative experiment was conducted in order to confirm the characteristics of a conventional lithium ion battery.

The method for synthesizing the positive electrode active material and the negative electrode active material was the same as in the example. Further, the solid electrolyte powder was not mixed with the positive electrode and the negative electrode, and the electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were used. The mixing ratio was 82: 8: 10 by weight. The method for producing the positive electrode and the negative electrode was performed in the same manner as in the example. The obtained positive electrode and negative electrode had a thickness of about 30 μm and a coating weight of about 0.048 g.

The resulting positive and negative electrodes were electrolyzed with a mixed solvent of propylene carbonate (PC) and dimethoxyethane (DME) (PC: DME = 1: 1 by volume) in which LiClO ₄ was dissolved at a concentration of 1 M / l. 0.3 as liquid
It was impregnated dropwise by cc. Further, a nonwoven fabric made of polypropylene was selected as a separator, and this was impregnated with the same mixed solvent as described above.

The positive electrode and the negative electrode impregnated with the electrolytic solution were overlapped with a separator interposed therebetween to form a positive electrode-electrolyte layer-negative electrode laminate.

Thereafter, a prismatic lithium battery was assembled in the same manner as in Example 1.

Comparative Example 2 A method for synthesizing a positive electrode active material and a negative electrode active material and a method for forming a positive electrode, a solid electrolyte, and a negative electrode were the same as those in Example 1. The thickness of the obtained positive electrode-solid electrolyte-negative electrode was about 180 m. Further, roll pressing was performed for the purpose of improving the filling rate of the laminate and the contact area of the powder. The obtained laminate was not impregnated with an aprotic solvent, and a prismatic lithium battery was assembled in the same manner as in the example. (Evaluation) Using the thus obtained rectangular lithium battery for evaluation, a redox reaction was confirmed with a potentiostat. FIG. 2 shows the result of the oxidation-reduction reaction according to Example 1, FIG. 3 shows the result of the oxidation-reduction reaction according to Example 2, FIG. 4 shows the result of the oxidation-reduction reaction according to Comparative Example 1, and FIG. 9 shows the results of the oxidation-reduction reaction according to Comparative Example 2. The measurement condition is that the voltage sweep speed is 10 ^-1 mV / sec.
The voltage range is 0 to 1.5 V in Example 1, Example 2 and Comparative Example 1, and 0 to 1.5 V in Comparative Example 2.
5V.

As a result, in Examples 1 and 2, a current associated with oxidation-reduction was obtained, and a current value almost equivalent to that of Comparative Example 1 using an organic electrolytic solution containing an electrolyte salt was obtained. It was also confirmed. Furthermore, the decrease in the current value is smaller than that in Comparative Example 1, and the lithium battery according to the present invention may have excellent cycle characteristics. In addition, it can be seen that, when compared with the all-solid-state battery of Comparative Example 2, it is significantly superior.

The lithium ion conduction mechanism in the lithium battery of the present invention is presumed to be attributable to the lithium ion conduction mechanism at the interface between the particle surface and the non-propylene solvent.

[0052]

As described above, according to the lithium battery of the first aspect, since the electrode and the solid electrolyte layer contain an aprotic solvent, an organic electrolyte solution in which an electrolyte salt is dissolved is used. Electrolyte characteristics equivalent to those of lithium-ion batteries can be obtained, and since they exhibit an unprecedented lithium-ion conduction mechanism and do not contain electrolyte salts, they do not cause decomposition of electrolyte salts due to overvoltage, and are highly reliable lithium batteries Is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of a lithium battery according to the present invention.

FIG. 2 is a graph showing an oxidation-reduction reaction according to Example 1 of the present invention.

FIG. 3 is a graph showing an oxidation-reduction reaction according to Example 2 of the present invention.

FIG. 4 is a graph showing an oxidation-reduction reaction according to Comparative Example 1.

FIG. 5 is a graph showing an oxidation-reduction reaction according to Comparative Example 2.

[Explanation of symbols]

1 ··· package, 2 ··· pair of electrodes, 2a ·
... Positive electrode, 2b ... Negative electrode, 3 ... Solid electrolyte layer, 4 ... Positive electrode current collector, 5 ... Negative electrode current collector

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinji Magome 3-5 Koikodai, Seika-cho, Soraku-gun, Kyoto Prefecture Inside the Central Research Laboratories of Kyocera Corporation (72) Inventor Toru Hara 3-cho, Koikadai, Soraku-gun, Kyoto 5 Kyocera Corporation Central Research Laboratory (72) Inventor Nobuyuki Kitahara 3-chome, Seika-cho, Soraku-gun, Kyoto Prefecture 5-5-2 Kyocera Corporation Central Research Laboratory (72) Inventor, Ei Higuchi Seika-cho, Kyoto 3-5-5 Kyocera Corporation Central Research Laboratory F term (reference) 5H003 AA01 AA10 BB05 BB12 BD03 5H014 AA02 EE10 HH01 5H029 AJ06 AJ07 AJ12 AK02 AK03 AL02 AL03 AM02 AM03 AM11 BJ02 BJ03 DJ16 HJ02

Claims (5)

[Claims] 1. A lithium battery having a solid electrolyte layer sandwiched between a pair of electrodes, wherein the electrode and the solid electrolyte layer contain an aprotic solvent. 2. The lithium battery according to claim 1, wherein the electrode comprises an electrode active material and a solid electrolyte, and the solid electrolyte layer comprises the same material as the solid electrolyte. 3. The lithium battery according to claim 1, wherein the solid electrolyte layer is made of an oxide crystallized glass having lithium ion conductivity. 4. The method according to claim 1, wherein the aprotic solvent comprises one or more of propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, and diethyl carbonate. The lithium battery according to claim 2 or 3. 5. The electrode according to claim 1, wherein the active material is Li _{1 + x} Mn _2-x O _4.
(0 ≦ x ≦ 0.2), LiMn _2-y Me _y O ₄ (Me = N
i, Cr, Cu, Zn, 0 <y ≦ 0.6), Li ₄ Ti ₅
O _12, and Li ₄ Mn ₅ claim 1, characterized in that it consists of at least one from O ₁₂ group consisting of selected, claim 2, lithium battery according to claim 3 or claim 4.