JP2000285910A - Lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve charging rate of active material and battery energy density by forming a positive electrode active material body and/or a negative electrode active material body from a sintered body of a metal oxide and solid electrolyte where conductive particles are dispersed. SOLUTION: As metal oxide used for a positive electrode active material body and a negative electrode active material body, composite oxide such as lithium manganese composite oxide, oxide such as titan oxide, and their derivative are used. As solid electrolyte, an oxide-based or sulfide-based amorphous solid electrolyte is used. The metal oxide and the solid electrolyte are preferably mixed in volume ratio of about 65:35-97:3. As conductive particle to be dispersed, metal particle such as Pt, acetylene black, or natural graphite is used. Volume ratio of this conductive particle is preferably 50% in order to form a continuous network in the solid electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium battery, and more particularly, to a lithium battery having an improved electrode.

[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. LiCo listed here
The charge and discharge voltage of O ₂ and LiMn ₂ O ₄ is 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.

In general, a lithium ion battery is coated with a binder, for example, polytetrafluoroethylene, polyvinylidene fluoride, or the like by adding a conductive agent such as acetylene black or graphite and a solvent, if necessary, to the positive electrode or the negative electrode. After preparing the liquid, this coating liquid is coated on an aluminum or copper metal foil called a current collector by a coating method such as an extrusion method or a doctor blade method, and dried and cut to form a sheet. It is common. In addition, if necessary, a coating liquid applied to a metal foil may be pressed and compressed by a roll press device in order to increase the filling density of the electrode before cutting.

[0005]

However, the electrode formed on the current collector by coating requires a binder for binding particles that do not directly contribute to the electrode reaction, and furthermore, the packing density of the electrode. Even if the roll is pressed and compressed by a roll press device to improve the volume, the volume occupied by the substantial active material in the electrode, that is, the active material filling rate is limited to 30 to 60% and does not increase. There is a problem.

Accordingly, when the coating type electrode is used, the capacity of the battery is reduced, and as a result, the energy density of the battery is reduced. The same applies to pressure-formed pellet-shaped electrodes, such as coin-shaped batteries, and there is a problem that the active material filling rate cannot be increased because of containing a binder.

Japanese Patent Application Laid-Open No. 8-138724 discloses that a positive electrode and a negative electrode are obtained by pressing a mixture of a glassy solid electrolyte powder and an active material powder, and the glassy solid electrolyte powder is pressed with these. It has been proposed to press-mold the solid electrolyte in between. That is, the positive electrode and the negative electrode obtained by press-molding a mixture of the glassy solid electrolyte powder and the active material powder were those in which the contact state between the solid electrolyte and the active material was point contact between the powder inside the electrode, but the softened glass By the solid electrolyte, the bonding state becomes surface contact, the contact area between the active material and the solid electrolyte increases, the intercalation / deintercalation reaction of lithium ions easily occurs, and the impedance in the electrode is reduced. That you can do it.

However, when a metal oxide is used as the electrode active material, there is a problem that the electron conductivity of the active material itself is low and the impedance inside the electrode is still high.

On the other hand, a lithium ion battery using a carbon material for the negative electrode active material body is expected to have a high energy density because the charge / discharge potential of the carbon material is around 0 V. May be deposited on the surface of the negative electrode to cause an internal short circuit, and cannot be said to have sufficient safety.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-mentioned problems of the conventional lithium battery, and has solved the conventional problems of low active material filling rate and low battery energy density. The purpose is to provide.

Another object of the present invention is to provide a lithium battery which has solved the conventional problem that the contact area between the active material and the solid electrolyte is small and the impedance inside the electrode cannot be reduced.

It is a further object of the present invention to provide a lithium battery which solves the conventional problem that when a carbon material is used as the negative electrode active material, lithium metal may precipitate on the surface of the negative electrode and cause an internal short circuit.

[0013]

In order to achieve the above object, a lithium battery according to the present invention is characterized in that an electrolyte is interposed between a positive electrode active material body and a negative electrode active material body. The material and / or the negative electrode active material were formed of a sintered body of a metal oxide and a solid electrolyte in which conductive particles were dispersed.

In the above-mentioned lithium battery, it is desirable that the conductive particles are metal powder and / or carbon powder.

The metal oxide may be a lithium manganese composite oxide, manganese dioxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium vanadium composite oxide,
Lithium titanium composite oxide, titanium oxide, niobium oxide,
It is desirable to be composed of one or more of vanadium oxide, tungsten oxide or a derivative thereof.

[0016]

When the electrode active material body is formed of a sintered body of a metal oxide and a solid electrolyte, the filling rate of the active material is improved, and a wide contact area between the active material and the solid electrolyte in the electrode can be secured. Since the conductive metal particles and carbon particles are dispersed in the solid electrolyte, the impedance in the electrode can be reduced, and the energy density of the battery can be improved. In general, the charge / discharge potential of a metal oxide is higher than the charge / discharge potential of a carbon material. Therefore, in principle, no lithium deposition reaction occurs, and the reliability of the battery is improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the lithium battery of the present invention will be described. FIG. 1 is a cross-sectional view showing a configuration example of a coin-type lithium battery according to the present invention. In FIG. 1, 1 is a positive electrode can, 2 is a positive electrode current collecting layer, 3 is a positive electrode active material body, 5 is an electrolyte, 6 is a negative electrode active material body, 7 is a negative electrode current collecting layer,
8 is a negative electrode can.

The positive electrode current collecting layer 2 is arranged for bonding and current collection to the positive electrode can 1 and the positive electrode active material member 3, and is made of, for example, a polyimide adhesive containing a carbon material.

The positive electrode active material body 3 is obtained by mixing and sintering a metal oxide serving as a positive electrode active material and a solid electrolyte.
It consists of a solid electrolyte in which conductive particles are dispersed.
The negative electrode active material member 6 is obtained by mixing and sintering a metal oxide having a charge / discharge potential lower than the charge / discharge potential of the positive electrode active material in the positive electrode active material member 3 as a negative electrode active material and a solid electrolyte. Yes, it consists of a solid electrolyte in which conductive particles are dispersed.

The positive electrode active material 3 and the negative electrode active material 6
As the metal oxide used for, 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,
Lithium titanium composite oxide, titanium oxide, niobium oxide,
Vanadium oxide, tungsten oxide, and derivatives thereof are given. Here, there is no clear distinction between the positive electrode active material and the negative electrode active material, and the charge and discharge potentials of the two types of compounds are compared to each other, and those showing a noble potential are used for the positive electrode, and those showing a noble potential are used for the negative electrode. Thus, a battery having an arbitrary voltage can be formed.

As the solid electrolyte used for the positive electrode active material 3 and the negative electrode active material 6, for example, Li ₂ O—B ₂ O ₃ −
P ₂ O _{5 system, Li 2 O-B 2 O} 3 -ZnO -based oxide-based amorphous solid _{electrolyte, LiI-Li 2 S-P} 2 S 5 and Li
_{3 PO 4 -Li 2 S-Si} 2 S sulfide-based amorphous solid electrolytes such as, _{or, Li 3 PO 4 -Li 2 S} -SiS
And an amorphous electrolyte in which a metal oxide and a sulfide are mixed.

The metal oxide and the solid electrolyte have a volume ratio of 6
It is mixed at about 5:35 to 97: 3. If the amount of the metal oxide is too large, the contact area between the active material and the solid electrolyte decreases, and the impedance in the electrode decreases.
On the other hand, when the amount of the solid electrolyte is too large, there is a problem that the active material filling rate decreases and the battery energy density decreases.

The conductive particles dispersed in the solid electrolyte used for the positive electrode active material member 3 and the negative electrode active material member 6 include metal particles of Pt, Rh, Pd, Au, and Ru, acetylene black, Ketjen black, and natural metal. One or more of graphite, artificial graphite, and the like are used.

It is necessary that the conductive particles form a continuous network in the solid electrolyte in order to impart electronic conductivity. The conductive particles in the solid electrolyte preferably occupy 50% or more by volume.

The electrolyte 5 may be liquid or solid as long as it has ion conductivity. The electrolyte 5 includes an organic electrolyte in which a desired electrolyte salt is dissolved in an organic solvent, a solid polymer electrolyte in which an electrolyte salt is dissolved in an ion-conductive polymer material, a gel electrolyte in which these are combined, and an inorganic electrolyte. An inorganic solid electrolyte made of a material can be used. When an organic electrolyte is used for the electrolyte 5, a separator (not shown) for separating the positive electrode active material member 3 and the negative electrode active material member 6 is required.

Examples of the organic solvent used in the organic electrolyte include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, gamma-butyrolactone, sulfolane, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, and the like.
Tetrahydrofuran, 2-methyltetrahydrofuran,
One or a mixture of two or more solvents selected from dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate can be used.

As the electrolyte salt, for example, LiClO_Four,
LiBF_Four, LiPF₆, LiCF _ThreeSO_Three, LiN
(CF_ThreeSO_Two)_Two, LiN (C_TwoF_FiveSO_Two)_TwoSuch
Can be mentioned.

As the separator, for example, a nonwoven fabric made of polyolefin fiber or a microporous film made of polyolefin fiber can be used. Here, as polyolefin fiber,
For example, polypropylene fiber, polyethylene fiber and the like can be mentioned.

As the ion conductive polymer material, for example, a polymer having an ethylene oxide skeleton represented by polyethylene oxide, a polymer having a propylene oxide skeleton represented by propylene oxide, or a mixture or copolymer thereof is used. No. As the electrolyte salt in this case, the same one as the above-mentioned organic electrolyte can be used.

As the inorganic solid electrolyte, for example, 30Li
_{I-41Li 2 O-29P 2} O 5 and Li ₂ O-35B ₂
O ₃ -25LiNbO ₃ oxide-based amorphous solid electrolytes such _{as, 45LiI-37Li 2 S-18P} 2 S 5 and 1Li
Such as _{3 PO 4 -63Li 2 S-36Si} 2 S sulfide-based amorphous solid electrolyte, and the like.

The negative electrode current collecting layer 7 is arranged for bonding and current collecting between the negative electrode active material body 6 and the negative electrode can 8 made of, for example, stainless steel, and is made of, for example, a conductive adhesive containing silver.

The positive electrode can 1 containing the above-mentioned positive electrode active material 3 and the negative electrode can 8 containing the negative electrode active material 6 are caulked via an insulating packing 4 and sealed.

The lithium battery to which the present invention is applied may be a primary battery or a secondary battery as long as the cathode active material body and / or the anode active material body is composed of a mixture with a solid electrolyte powder. It may be. Battery shape is cylindrical,
It is not limited to a square type, a button type, a coin type, a flat type and the like.

[0034]

[Example] [Example] LiMn ₂ O ₄ as a positive electrode active material
The following shows a battery using Li ₄ Ti ₅ O ₁₂ as the negative electrode active material, Li ₂ O—B ₂ O ₃ —ZnO glass as the solid electrolyte mixed with the electrode active material, and graphite as the conductive particles. .

Lithium hydroxide and manganese dioxide are mixed such that the molar ratio of Li to Mn is 1: 2, and this mixture is heated and fired at 800 ° C. for 20 hours in the air to form a lithium manganese composite oxide (LiMn). ₂ O ₄ ) was adjusted. Lithium hydroxide and titanium dioxide are mixed such that the molar ratio of Li and Ti is 4: 5, and this mixture is heated and synthesized at 850 ° C. for 15 hours in the air to obtain a lithium-titanium composite oxide (Li ₄ Ti). ₅ O ₁₂ ) was adjusted. Commercially available Li ₂ O—B ₂ O ₃ —ZnO glass as the solid electrolyte and natural graphite as the conductive particles were used.

The cathode active material body 3 is composed of LiMn ₂ O ₄ and LiMn ₂ O _4.
2 O-B ₂ O ₃ -ZnO and natural graphite 8: 1 were weighed at 1 weight ratio, pressure-molding such that the mixture to a diameter 17 mm, the product form of the positive electrode active material body Obtained.

The green compact was fired at 550 ° C. in the atmosphere to produce a sintered electrode. The produced positive electrode active material had a diameter of 15 mm and a thickness of 1.0 mm.

Similarly, the negative electrode active material body 6 is made of Li ₄ Ti ₅ O
₁₂ and _{Li 2 O-B 2 O 3} -ZnO and natural graphite 8: 1:
And weighed to a weight ratio of 1.
mm to obtain a formed negative electrode active material body. The formed body was fired at 550 ° C. in the atmosphere to produce a sintered body. The prepared negative electrode active material had a diameter of 1
It was 5.5 mm and 1.2 mm in thickness.

The electrolytic solution was prepared by dissolving lithium perchlorate (LiClO ₄ ) as an electrolyte in propylene carbonate so that its concentration was 1 mol / l.

The positive electrode active material body 3 is housed and mounted in the positive electrode can 1 via the positive electrode current collecting layer 2 made of a conductive adhesive, and the separator made of a polypropylene nonwoven fabric impregnated with the electrolytic solution 4 is used as the positive electrode active material. Placed on body 3. On the other hand, on the negative electrode side, similarly to the positive electrode side, the negative electrode active material body 6 was housed and mounted in the negative electrode can 8 via the negative electrode current collector layer 7 made of a conductive adhesive.

Next, the positive electrode can 1 and the negative electrode can 8 were caulked via the insulating packing 4 to assemble a coin-type lithium battery having an outer diameter of 20 mm and a thickness of 3.3 mm as shown in FIG. .

[Comparative Example] L produced in the same manner as in the example
iMn ₂ O ₄ and Li ₂ O—B ₂ O ₃ —ZnO were weighed at a weight ratio of 9: 1, and the mixture was weighed 17 mm.
To obtain a formed form of the positive electrode active material body. The prepared negative electrode active material body had a diameter of 15 mm and a thickness of 0.1 mm.
9 mm.

Further, Li ₄ Ti ₅ O ₁₂ and Li ₂ O—B ₂
O ₃ -ZnO was weighed so as to have a weight ratio of 9: 1, and this mixture was subjected to pressure molding so as to have a diameter of 17 mm to obtain a formed form of a negative electrode active material body. The prepared negative electrode active material body had a diameter of 15 mm and a thickness of 1 mm.

Hereinafter, a coin-type lithium battery was manufactured in the same manner as in the example. The manufactured coin-type lithium battery had a diameter of 20 mm and a thickness of 2.9 mm.

The above-described battery capacity measurement was performed. In addition,
The discharge capacity of the battery was 2.8 V at the end-of-charge voltage and 2
After the battery was charged at a constant current of mA and left for 1 hour, the battery was discharged at a constant current of 2.0 mA to a constant current of 2.0 V. Further, the ratio of the positive electrode and the negative electrode active material to the theoretical capacity was determined.

As a result, in the battery of the above example, the discharge capacity was 41 mAh, and the ratio to the theoretical capacity was 88%. On the other hand, in the battery of the comparative example, the discharge capacity was 28 mAh, and the ratio to the theoretical capacity was 55%. This indicates that the conductive particles are dispersed in the solid electrolyte mixed with the electrode active material body, so that the impedance in the electrode can be reduced and the energy density of the battery can be improved.

It should be noted that the present invention is not limited to the above-described embodiment, but can be implemented with appropriate modifications without departing from the scope of the invention.

[0048]

As described above, according to the lithium battery of the present invention, the positive electrode active material and / or the negative electrode active material are sintered with the solid electrolyte in which conductive particles are dispersed and the metal oxide. Since it is formed of a solid body, the filling rate of the active material is improved, the contact area between the active material in the electrode and the solid electrolyte can be secured widely, the impedance in the electrode can be reduced, and the energy density of the battery can be reduced. Can be improved.

[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]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode can, 2 ... Positive electrode collector layer, 3 ... Positive electrode active material body, 4 ... Insulating packing, 5 ... Electrolyte,
6 ... negative electrode active material body, 7 ... negative electrode current collecting layer, 8 ...
Negative electrode can

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H01M 10/40 H01M 10/40 Z (72) Inventor Ei Higuchi 3-5 Kodai, Seikacho, Soraku-gun, Kyoto Prefecture Address Kyocera Co., Ltd. Central Research Laboratory (72) Inventor Makoto Osaki 3-5 Kyodai, Seika-cho, Soraku-gun, Kyoto Prefecture 72 Kyocera Co., Ltd. 5-5 Kyocera Corporation Central Research Laboratory (72) Inventor Toru Hara 3-5 Koikadai, Seika-cho, Soraku-gun, Kyoto Prefecture F-term in Kyocera Corporation Central Research Laboratory 5H003 AA02 BA01 BB05 BC01 5H014 AA02 AA06 BB01 EE10 5H015 AA01 AA02 AA07 CC01 DD01 EE06 EE12 EE13 5H029 AJ03 AK02 AK03 AL02 AL03 AM03 AM04 AM05 AM07 AM12 BJ03 CJ02 DJ08 DJ09 DJ16 EJ01 EJ04 EJ05

Claims (3)

[Claims] 1. In a lithium battery having an electrolyte interposed between a positive electrode active material and a negative electrode active material, conductive particles are dispersed in the positive electrode active material and / or the negative electrode active material. A lithium battery formed of a sintered body of a solid electrolyte and a metal oxide. 2. The lithium battery according to claim 1, wherein the conductive particles are metal powder and / or carbon powder. 3. The metal oxide is a lithium manganese composite oxide, manganese dioxide, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium vanadium composite oxide, lithium titanium composite oxide, 3. The lithium battery according to claim 1, comprising one or more of titanium oxide, niobium oxide, vanadium oxide, tungsten oxide, and derivatives thereof.