JP2001093535A - Solid electrolyte cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that an internal resistance of a cell is high and charging-discharging property is deteriorated since and adhesion strength between an electrode and a solid electrolyte is small. SOLUTION: The solid electrolyte cell is formed by arranging solid electrolyte between a pair of positive an negative electrodes comprising an active substance containing transition metal element, the transition metal element included in the positive electrode active substance is diffused in the solid electrolyte of the positive electrode side and the transition metal element included in the negative electrode active substance is diffused in the solid electrolyte of the negative electrode side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid electrolyte battery, and more particularly to a solid electrolyte battery having an improved interface between an electrode and a solid electrolyte.

[0002]

2. Description of the Related Art With the recent remarkable development of portable devices typified by portable telephones and personal computers, demand for batteries as power sources has been rapidly increasing. In particular, lithium ion batteries are batteries that use lithium, which has a low atomic weight and a large ionization energy, and are therefore being actively studied as batteries that can obtain high energy densities. It has been used. These lithium-ion batteries are roughly classified into cylindrical type and square type.In both cases, the positive electrode and the negative electrode are inserted through a separator into a battery case. The structure has been injected and sealed.

In the above-mentioned lithium ion battery, lithium cobalt oxide (LiCoO ₂ ) and lithium manganate (LiMn ₂ O ₄ ) are generally used as a positive electrode active material. Further, a carbon material such as coke and carbon fiber is used for the negative electrode active material. LiCoO listed here
₂ and LiMn ₂ O _{4 have} a charge / discharge voltage of about 4V. On the other hand, the charge / discharge potential of the carbon material is around 0V. Therefore, a lithium ion battery achieves a high voltage of about 3.5 V by combining these positive electrode active materials and negative electrode active materials.

[0004] In recent years, with the demand for thin, light and small electronic devices such as video photographing devices, notebook personal computers, and portable information terminals such as portable telephones, the above-mentioned organic electrolytic solution has been required. Instead, a polymer electrolyte battery in which a polymer electrolyte and an organic electrolyte are mixed between a pair of positive and negative electrodes has attracted attention. However, these lithium ion batteries or polymer electrolyte batteries use a liquid for the electrolyte, and thus cannot eliminate the problem of liquid leakage at all.
Further, when an abnormality such as a short circuit occurs in the battery, there is a risk that the organic electrolyte solution reacts and the battery is ignited. for that reason,
In order to ensure battery safety, development of a lithium battery formed of a nonflammable solid is desired.

In order to solve such a problem, lithium batteries using an inorganic solid electrolyte have been actively developed.

[0006] In particular, sodium ion conductive solid electrolyte
(A NASICON-based material)
In recent years, lithium ion conductive crystalline solid electrolytes have been
× 10 ^-3~ 1 × 10^-FourS ・ cm^-1Lithium ion conduction
Solid electrolytes having a high modulus have been proposed.

For example, Japanese Patent Application Laid-Open No. 5-299101 discloses
Is Li_{1+ (4-n) x}M_xTi_2-x(PO _Four)_Three(M is monovalent or
Is a divalent cation, n = 1 when M is monovalent, and M is divalent
Where n = 2, and x is 0.1 to 0.5)
1 × 10 by sintering^-3~ 1 × 10
^-FourS ・ cm^-1Lithium ion conductivity can be obtained
ing. Further, in Japanese Patent Application Laid-Open No. 10-97811,
P of a given composition ratio_TwoO_Five, SiO_Two, TiO_Two, Al_TwoO_Three,
Li_TwoAfter melt molding O etc., heat treatment_{1 + x + y}A
l_xTi_2-yP_3-yO₁₂(0 ≦ x ≦ 0.4, 0 <y ≦ 0.
By depositing 6), 1.0 × 10^-3~ 2.0
× 10^-3S ・ cm^-1Having a lithium ion conductivity of
Propose body electrolytes.

Japanese Patent Application Laid-Open No. 6-111831 discloses a solid electrolyte in which a positive electrode comprising MnO ₂ or a composite oxide of an alkali metal and manganese and a solid electrolyte are integrally formed, and the solid electrolyte is MnO ₂ or an alkali. By forming a Li ₂ MnO ₃ layer formed on the surface of the positive electrode by reacting a lithium compound with a composite oxide of metal and manganese, the contact area of the interface between the positive electrode and the solid electrolyte is small, and the internal resistance of the battery is reduced. Since it is small, it proposes that it has excellent charge / discharge characteristics.

[0009]

Conventionally, in the case of a battery using a solid electrolyte, the connection between the electrode and the solid electrolyte is often formed only by pressure welding, and the contact area between the electrode and the solid electrolyte and the bonding strength are weak. Therefore, the resistance at these interfaces is increased, the internal resistance of the battery is increased, and the charge and discharge characteristics are inferior. In particular, there has been a problem that as the charge / discharge current increases, the voltage drop due to the internal resistance of the battery increases, and the current density is limited.

[0010] Further, many crystalline solid electrolytes have anisotropy in the ion conduction path, so that the grain boundary resistance in the solid electrolyte becomes a problem. Therefore, a sintered body is often used as the crystalline solid electrolyte.
No. 01 proposes to improve this problem.
However, the problem of the ion conduction path also applies to the interface between the electrode and the solid electrolyte, and there is a problem that contact only by pressure welding increases the resistance of the interface.

JP-A-6-111831 proposes to improve the interface resistance between an electrode and a solid electrolyte, but this method involves forming MnO ₂ by sputtering or Li ₂
The formation of MnO ₃ has a problem that the process is complicated, such as the reaction between MnO ₂ and LiOH.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has a problem in that the bonding strength between an electrode and a solid electrolyte is weak, the internal resistance as a battery is large, and the charge / discharge characteristics are poor. It is an object of the present invention to provide a solid electrolyte battery that has solved the problems.

[0013]

According to another aspect of the present invention, there is provided a solid electrolyte battery having a solid electrolyte disposed between a pair of positive and negative electrodes made of an active material containing a transition metal element. The transition metal element included in the active material of the positive electrode was diffused in the solid electrolyte on the negative side, and the transition metal element included in the active material of the negative electrode was diffused in the solid electrolyte on the negative electrode side.

Further, the solid electrolyte is lithium (L
It is preferable that the solid electrolyte is a crystalline solid electrolyte having lithium ion conductivity containing i), titanium (Ti), phosphorus (P) and oxygen (O).

Further, the active material of the positive electrode is Li _{1 + x} Mn _2-x
O ₄ (0 ≦ x ≦ 0.2) or LiMn _2-y Me _y O ₄ (M
e = Ni, Cr, Cu, Zn, 0 <y ≦ 0.6), and the active material of the negative electrode is Li ₄ Ti ₅ O ₁₂ or Li ₄ M
Desirably, it consists of n ₅ O ₁₂ .

[0016]

In the solid electrolyte battery of the present invention, the transition metal element contained in the active material of the positive electrode diffuses into the solid electrolyte on the positive electrode side,
Since the transition metal element contained in the active material of the negative electrode is diffused in the solid electrolyte on the negative electrode side, the bonding between the electrode and the solid electrolyte is strengthened. Therefore, the internal resistance of the battery can be reduced by increasing the contact area of the interface. When the transition metal element in the active material of the electrode diffuses into the solid electrolyte, the active material structure near the interface is likely not to maintain the original crystal structure, but according to the present invention, there is no effect. Was confirmed.

[0017]

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 a lithium battery according to the present invention. In FIG. 1, 1 is a package, 2 is a pair of electrodes, 2a is a positive electrode, 2b is a negative electrode, 3 is a solid electrolyte layer, 4 is a positive electrode current collector, and 5 is a negative electrode current collector.

The material of the package 1 is not limited as long as it can maintain airtightness. For example, a laminate made of aluminum, 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 current collection of the positive electrode 2a or the negative electrode 2b, and is made of a metal foil such as aluminum (Al), nickel (Ni), copper (Cu). Can be used.

The active material of the positive electrode 2a 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) is selected. The active material of the negative electrode 2b is Li ₄ Ti ₅ O ₁₂ , L
One of i ₄ Mn ₅ O ₁₂ is selected. 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. 1 to
A battery with a voltage of 3.5 V can be configured.

The active material of the electrode is transition gold.
It is desirable that the oxide be a lithium oxide containing a group element. Money
When lithium metal is used for the negative electrode, a battery with higher voltage can be obtained.
However, when the solid electrolyte and metallic lithium come into contact,
The solid electrolyte undergoes a reduction reaction, resulting in characteristics as a solid electrolyte
This is because there is a possibility of damaging it. Lithium ion battery
Coke and carbon fiber, which are commonly used in
A high battery is obtained. However, these carbon materials are
Poor wettability with organic compounds and difficult to diffuse into solid electrolyte
Problem that bonding with the solid electrolyte becomes insufficient
There is. Therefore, as the active material of the electrode, solid electrolytic
Lithium oxide containing transition metal that easily diffuses
Is desirable. In the case of solid electrolyte batteries,
Data and organic electrolytes are not used.
There is a limit in allowing the electrodes to expand and contract. Accordingly
The active material of the electrode used in the present invention includes a charge / discharge reaction
Li with small expansion and contraction accompanying_{1 + x}Mn_2-xO_Four(0 ≦ x
≦ 0.2), LiMn_2-yMe _yO_Four(Me = Ni, C
r, Cu, Zn, 0 <y ≦ 0.6), Li_FourTi_FiveO₁₂Ma
Or Li_FourMn_FiveO₁₂It is desirable that

Here, the transition metal element contained in the active material and the transition metal element diffused into the solid electrolyte are manganese (Mn) and titanium (Ti). LiMn _2-y
Me _y O ₄ (Me = Ni, Cr, Cu, Zn, 0 <y ≦
The electrode active material represented by the formula (0.6) contains transition metal elements other than manganese and titanium (Me in the above chemical formula). However, even if these transition metal elements diffuse together with manganese in the solid electrolyte, there is a problem. There is no.

The method of forming the electrodes 2 (2a, 2b) is as follows: (1) A slurry is prepared by dispersing an active material in water or a solvent in which a molding aid is dissolved, and this slurry is coated on a base film. (2) a method in which the active material is powdered directly or granulated and charged into a metal mold, and then subjected to pressure molding with a press machine, followed by firing;
(3) A method in which the granulated powder is press-formed by a roll press machine, processed into a sheet shape, and then cut and fired. The granulation of (2) and (3) is (1)
The wet granulation using granulation from the slurry described in the above method or the dry granulation using no solvent may be used. Also,
In the method (2), a molding aid may not be used.

As a molding aid usable here, a general organic binder for granulating ceramics can be used.

As the base 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.

The solid electrolyte 3 is made of a known lithium ion
Conductive solid electrolytes can be used. In particular, lithium (L
i), titanium (Ti), phosphorus (P) and oxygen (O) elements
Crystalline solid-state electrodes with lithium ion conductivity containing iodine
Desirably degraded, Li _{1 + x}M_xTi_2-x(P
O_Four)_Three(Where M is Al, Sc, Y, La), Li_{1 + x}
Ti_{2- x}(PO_Four)_Three, Li_0.5-3xR_{0.5 + x}TiO_Three(here
And R is La, Pr, Nd, Sm), Li_{1 + x + y}Al_xTi
_2-xSi_yP_3-yO₁₂, Li_{1+ (4-n)}M_xTi_2-x(PO_Four)_Three
(M is a monovalent or divalent cation).

Inorganic solid electrolytes are roughly classified into crystalline and non-crystalline. A non-crystalline oxide-based solid electrolyte has a lithium ion conductivity of 1 × 10 at room temperature.
^-6 S · cm ⁻¹ , and a solid electrolyte that sufficiently satisfies the characteristics has not been found. The sulfide-based solid electrolyte has a lithium ion conductivity of 1 × 10 ⁻³ S · cm at room temperature.
^-1, which is comparable to that of organic electrolytes, but has problems such as hygroscopicity. Furthermore, during the heat treatment, the amorphous solid electrolyte reacts with the active material of the electrode, and often forms a reaction product at the interface between the electrode and the solid electrolyte. Become. Therefore, it is desirable that the solid electrolyte used is a crystalline solid electrolyte.

The method for forming the solid electrolyte 3 is the same as the method for forming the electrode 2 described above.

The electrode 2 and the solid electrolyte 3 are not only baked alone, but also processed by stacking the sintered solid electrolyte 3 while sandwiching it between the formed positive electrode 2a and negative electrode 2b. I do not care.

As a method for diffusing the transition metal element of the active material into the solid electrolyte 3, the positive electrode 2 a fired independently,
Using the solid electrolyte 3 and the negative electrode 2b, the solid electrolyte 3 is
and a method in which the laminated body is heat-treated by sandwiching the solid electrolyte 3 and a method in which the sintered body of the solid electrolyte 3 is similarly laminated and heat-treated in the formed positive electrode 2a and the negative electrode 2b. Here, examples of the heat treatment method include a heat treatment at normal pressure and a heat treatment with pressurization. In particular, the heat treatment by pressurizing has an effect that the transition metal element of the active material of the electrode with respect to the solid electrolyte 3 is rapidly diffused, and the time of the heat treatment can be shortened.

The solid electrolyte 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.

[0033]

EXAMPLES [Example] Lithium hydroxide and manganese dioxide were mixed so that the molar ratio of Li and Mn was 1.1: 1.9, and this mixture was heated and fired at 650 ° C. in the air for 15 hours. The lithium manganese composite oxide (Li
_1.1 Mn _1.9 O ₄ ) was synthesized and used as an active material of the positive electrode. Next, lithium hydroxide and manganese dioxide were converted to Li and Mn.
And the mixture was heated and calcined at 600 ° C. in the air for 15 hours to synthesize a lithium manganese composite oxide (Li ₄ Mn ₅ O ₁₂ ).
This was used as the active material of the negative electrode.

The obtained active materials were dispersed in a solvent in which a molding aid was dissolved to prepare a slurry. Next, the slurry was formed into a green tape shape by a doctor blade method to obtain a formed electrode. The thickness at this time is about 50 μm
Met.

As the solid electrolyte 3, the main crystal phase is Li
_{1 + x + y} using _{Al x Ti 2-x Si y} P 3-y O 12 crystalline solid electrolyte represented by. The slurry was prepared by dispersing the powdery solid electrolyte in a solvent in which a molding aid was dissolved.
This slurry was formed into a green tape by a doctor blade method to obtain a solid electrolyte formed form. The thickness at this time was about 70 μm. Next, apply this green tape to 3
It was cut into a size of 5 cm × 35 cm and fired at a temperature of 1250 ° C. for 3 hours to obtain a sintered body of the solid electrolyte 3. The thickness of the sintered body at this time is about 55 μm, and is 28 cm × 28 cm
It was the size of.

The obtained shaped bodies of the positive electrode and the negative electrode obtained above were cut into a size of 25 cm × 25 cm, laminated with a solid electrolyte sintered body sandwiched therebetween, and subjected to pressure heat treatment.
A laminate of a-solid electrolyte 3-negative electrode 2b was obtained. The pressure heat treatment is performed by removing the binder at a temperature of 350 ° C. for 1 hour and then performing a pressure load of 5.4 MPa at a temperature of 550 ° C. for 20 minutes. At this time, the positive electrode and the negative electrode of the laminate had a thickness of 28 μm and a size of 25 mm × 25 mm, and contraction only in the thickness direction was confirmed.

The positive electrode current collector 4 was joined to the positive electrode 2a of the laminate, and the negative electrode current collector 5 was similarly joined to the negative electrode 2b and mounted on the aluminum laminate of the package 1. The aluminum laminate was prepared by cutting two pieces having a size of 35 mm × 35 mm, sandwiching the laminated body in which the current collectors were joined, and thermocompression-bonding the outer periphery of the aluminum laminate to obtain the 35 mm × 35 mm shown in FIG. A 35 mm square solid electrolyte battery was assembled.

Further, the interface of the cross section of the solid electrolyte battery is denoted by E
Analysis by PMA confirmed that the manganese (Mn) element was present near the interface between the solid electrolyte 3 and the positive electrode 2a and the negative electrode 2b. No manganese element was detected in the center of the solid electrolyte 3. This confirmed that the manganese element in the electrode active material was diffused into the solid electrolyte.

COMPARATIVE EXAMPLE The method for synthesizing the active material for the positive electrode and the active material for the negative electrode and the method for firing the solid electrolyte were the same as in the example. The thickness of the obtained solid electrolyte is about 5
It was 3 μm.

The electrodes were formed in the following procedure. The active materials for the positive electrode and the negative electrode obtained above were dispersed in N-methyl-2-pyrrolidone in which polyvinylidene fluoride was dissolved to prepare a slurry. The obtained slurry was applied on an aluminum foil by a doctor blade method, and N-methyl-2-pyrrolidone was removed to obtain a positive electrode and a negative electrode.
Further, roll pressure was applied for the purpose of improving the powder filling rate of the obtained electrode. The thickness of each of the obtained electrodes was 30 μm.

The obtained electrode is cut into a size of 25 mm × 25 mm, and the obtained sintered body of the solid electrolyte is laminated so as to be sandwiched therebetween. About 1 which is near the melting point of vinylidene
Heated at a temperature of 70 ° C.

From the obtained laminate, a rectangular solid electrolyte battery was assembled in the same manner as in the example. Further, the distribution state of the manganese element in the solid electrolyte was confirmed by EPMA in the same manner as in the example, but the presence of the manganese element was not confirmed at any place.

(Evaluation) Using the thus obtained rectangular solid electrolyte battery, the charging condition was set to 10
0 μA / cm ² , 200 μA / cm ² , 500 μA / cm
^The above-mentioned rectangular solid electrolyte battery is charged to 1.5 V with a current of ² , and after the voltage reaches 1.5 V, charging is stopped and 5
After that, the battery was discharged to the voltage of 0.5 V with the same current as that at the time of charging, then charged again to 1.5 V, and after reaching this voltage, the charging was stopped and held for 5 minutes. went.

Table 1 shows the results. The numbers in the table indicate the discharge capacity for each discharge current, and the unit is mAh.

[0045]

[Table 1]

As described above, the solid electrolyte battery in which the transition metal element contained in the active material of the electrode is diffused in the solid electrolyte has a higher charge / discharge characteristic than the solid electrolyte battery in which the electrode is merely adhered to the solid electrolyte. It turns out that it is excellent. In particular, it is remarkable that the decrease in the discharge capacity is small even when the discharge current increases.

This is because, in the solid electrolyte battery of the present invention, the transition metal element contained in the active material of the positive electrode diffuses into the solid electrolyte on the positive electrode side, and the transition metal element contained in the active material of the negative electrode diffuses into the solid electrolyte on the negative electrode side. Is presumed to be due to the fact that the bonding between the electrode and the solid electrolyte is strengthened due to the diffusion of, the resistance at the interface between the electrode and the solid electrolyte is reduced, and as a result, the internal resistance is reduced.

[0048]

As described above, according to the solid electrolyte battery of the present invention, the transition metal element contained in the active material of the positive electrode diffuses into the solid electrolyte on the positive electrode side, and the active material of the negative electrode flows into the solid electrolyte on the negative electrode side. Since the transition metal element contained in the substance is diffused, the bonding between the electrode and the solid electrolyte is strengthened. As a result, the internal contact resistance of the battery can be reduced by increasing the contact area of the interface, and a solid electrolyte battery having excellent charge / discharge characteristics can be 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.

[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 BB05 BC01 BC06 BD00 5H024 AA02 CC04 CC07 FF23 HH00 5H029 AJ01 AK03 AL03 AM12 BJ04 DJ17 HJ02

Claims (3)

[Claims] 1. A solid electrolyte battery comprising a solid electrolyte disposed between a pair of positive and negative electrodes made of an active material containing a transition metal element, wherein the solid electrolyte on the positive electrode side is included in the active material of the positive electrode. Wherein the transition metal element contained in the active material of the negative electrode is diffused into the solid electrolyte on the negative electrode side. 2. The method according to claim 1, wherein the solid electrolyte is a crystalline material having lithium ion conductivity including lithium (Li), titanium (Ti), phosphorus (P) and oxygen (O) elements. The solid electrolyte battery according to any one of the preceding claims. 3. The positive electrode active material is Li _{1 + x} Mn _2-x O _4.
(0 ≦ x ≦ 0.2) or LiMn _2-y Me _y O ₄ (Me
= Ni, Cr, Cu, Zn, 0 <y ≦ 0.6), and the active material of the negative electrode is Li ₄ Ti ₅ O ₁₂ or Li ₄ M
3. The solid electrolyte battery according to claim 1, comprising n ₅ O ₁₂ .