JPH06243868A - Manufacture of secondary battery - Google Patents

Abstract

PURPOSE:To enhance a Coulomb efficiency, and thereby make an energy density high by assembling a secondary battery after each electrode composed of carbon material is charged/discharged in advance, and thereby eliminating the generation of decomposed gas and byproducts within the battery. CONSTITUTION:After a carbon electrode produced through specified manufacturing processes, is charged/discharge in advance, it is assembled in a battery as an anode or a cathode, so that a secondary battery is thereby made up. This constitution thereby eliminates the generation of decomposed gas and byproducts at the time of initial charging/discharging, can make a Coulomb efficiency equal to or more than 95%, and also can make an energy density high. Besides, a fiber structural body is desirable as carbon material, the kind of raw material and its manufacture are not particularly specified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a secondary battery using an electrode containing carbonaceous material.

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as video cameras and notebook computers, demand for small and high capacity secondary batteries has increased. Most of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte, but the battery voltage is low at about 1.2 V, and it is difficult to improve the energy density. Therefore, a lithium secondary battery using lithium metal for the negative electrode has been studied.

However, in a secondary battery in which lithium metal is used as the negative electrode, lithium tends to grow into dendrites due to repeated charging / discharging, resulting in short circuits and shortened life. Therefore, there has been proposed a secondary battery in which various carbonaceous materials are used for the negative electrode and used by doping and dedoping with lithium ions. Further, such various carbonaceous materials can be used as a positive electrode after being doped with anions. Secondary batteries using electrodes made by doping lithium ions or anions into the above carbonaceous materials are disclosed in JP-A-57-208079 and JP-A-58.
-93176, JP-A-58-192266, JP-A-62-90863, and JP-A-62-12.
Japanese Laid-Open Patent Publication No. 2066 and Japanese Laid-Open Patent Publication No. 3-66856 are known.

[0004]

However, a secondary battery using a carbonaceous material as an electrode has a problem that the ratio of the amount of discharged electricity to the amount of electricity required for the first charge after fabrication of the battery (Coulomb efficiency) is small. Have It is known that the initial Coulombic efficiency is very small, 40-80%, depending on the type of carbon material, and reaches 90% or more after several times of charge / discharge. In particular, using a carbonaceous material as the negative electrode,
In the lithium ion secondary battery utilizing the doping or dedoping of lithium ions on the carbon negative electrode,
The small Coulombic efficiency is a big problem. In this lithium ion secondary battery, the lithium ions doped into the carbon negative electrode are supplied from the positive electrode via the electrolytic solution.
If the Coulomb efficiency at the first time is low, it is necessary to add an extra positive electrode by the amount of extra lithium not used after the second time. For this reason, the volume or weight of the battery is increased, and the energy density is disadvantageous.

The reason why the Coulomb efficiency of the first charge and discharge is low is that the functional group on the carbon surface decomposes the solvent or the electrolyte, the functional group on the carbon surface itself is decomposed, or the part of the carbonaceous material that is not easily dedoped. There are various reasons such as the fact that it is doped with alkali metal ions. In any case, it is accompanied by decomposition gas and by-products. For this reason, the generation of such gas and by-product has been a big problem as in the case where an excessive amount of positive electrode has to be charged.

The present invention is intended to solve these drawbacks of the prior art, and suppresses generation of decomposition gas and by-products and low Coulombic efficiency at the time of first charge / discharge, thereby improving energy density. It is an object of the present invention to provide a method for manufacturing the secondary battery described above.

[0007]

The present invention has the following constitution in order to solve the above problems.

"A secondary battery comprising at least one electrode composed of an electrode containing carbonaceous material and an electrolytic solution, which is charged and discharged in advance and then assembled as a secondary battery. Method. ”The secondary battery of the present invention is characterized in that an electrode made of a carbonaceous material is charged and discharged in advance before being assembled as a battery and then assembled as a secondary battery. The method is not particularly limited.

Usually, the electrodes, the electrolytic solution, the form of the battery, and the charging / discharging conditions such as current, voltage and time may be charged and discharged by the same method as that of the secondary battery, but different methods may be used in some cases. . When gas is generated by the first charge / discharge as described above, it is desirable to charge / discharge after considering a mechanism for discharging the gas. The number of times of charging / discharging performed in advance may usually be once, but in some cases it is also preferable to repeat several times until no side reaction occurs or the Coulombic efficiency stabilizes. Further, in the case of a (lithium) ion battery utilizing the doping and dedoping of an alkali metal ion such as lithium ion, it is possible to charge and discharge by using an alkali metal as a counter electrode.

The carbonaceous material used in the electrode of the present invention can be used without any particular limitation on the raw materials and manufacturing method. Raw materials include coke and pitch such as petroleum and coal, plants such as wood, low molecular weight organic compounds such as natural gas and lower hydrocarbons, polyacrylonitrile, synthetic polymers such as phenol resin and furfuryl alcohol resin. , These are 700 to 30 depending on raw materials and uses
A carbonaceous material is obtained through a treatment of carbonization or graphitization, which is performed by firing at 00 ° C. Natural graphite can also be used. The properties of carbonaceous matter include density and crystal thickness (L
c), crystal plane spacing (d002), electric resistance, strength, elastic modulus, etc., which should be appropriately determined according to the intended electrode characteristics of the secondary battery, and are not particularly limited. Absent.

It is a preferred embodiment that the carbonaceous material is in the form of a fiber or a fiber structure. As the carbon fiber, PAN-based carbon fiber obtained from polyacrylonitrile (PAN), pitch-based carbon fiber obtained from pitch of coal or petroleum, cellulose-based carbon fiber obtained from cellulose, gas obtained from gas of low molecular weight organic substance Examples include phase-grown carbon fiber, but in addition,
Carbon fibers obtained by firing polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol, etc. may be used. Among these carbon fibers, it is preferable to appropriately select carbon fibers satisfying the characteristics according to the characteristics of the electrode and the battery in which the carbon fibers are used.

When the carbonaceous electrode of the present invention is used as a negative electrode of a (lithium) ion secondary battery utilizing doping or dedoping of alkali metal ions such as lithium ions, PAN-based carbon fiber, pitch Carbon-based fibers and vapor-grown carbon fibers are preferred. In particular, PAN-based carbon fibers and pitch-based carbon fibers are preferable in that lithium ion doping is good. Among them, "Torayca" T series or "Torayca" manufactured by Toray Industries, Inc.
PAN-based carbon fibers such as M series and pitch-based carbon fibers obtained by firing mesophase pitch coke are more preferably used.

When the above-mentioned carbon fiber is used for an electrode, it is a preferable electrode form to dispose the carbon fiber in a uniaxial direction or to form a cloth-like or felt-like structure. Examples of the fabric-like or felt-like structure include woven fabric, knitted fabric,
Examples thereof include braids, laces, nets, felts, papers, non-woven fabrics, mats, etc., but woven fabrics, felts, mats and the like are preferable from the viewpoint of the properties of carbon fibers and electrode characteristics.

The diameter of the carbon fiber when the carbon fiber is used for the electrode of the present invention should be determined so that each form can be easily adopted, but preferably the carbon fiber having a diameter of 0.01 to 1000 μm is used, and 0.1 ˜10 μm is more preferred.
It is also preferable to use several kinds of carbon fibers having different diameters.

When the carbonaceous electrode of the present invention is used in an ion secondary battery utilizing doping or dedoping of alkali metal ions such as lithium ions, a cation-doped carbon electrode is used for the negative electrode. However, a carbon electrode doped with anions may be used for the positive electrode, or a material other than the carbon electrode may be used for the positive electrode. When an electrode made of carbonaceous material is used for the positive electrode, it does not have to have the same properties as the carbonaceous material of the negative electrode, and carbonaceous material according to the required positive electrode characteristics may be used. Further, when using other than the carbon electrode for the positive electrode,
It is preferable to use an inorganic compound such as metal or metal oxide, or an organic polymer compound as the positive electrode. In this case, when an inorganic compound such as a metal or a metal oxide is used for the positive electrode, it becomes a positive electrode active material by cation doping and dedoping, but in the case of an organic polymer compound, it is positive electrode active by anion doping and dedoping. Various doping modes are adopted depending on the substance, such as being a substance, and these are appropriately selected according to the positive electrode characteristics of the battery. As such a positive electrode, an inorganic compound such as a transition metal oxide or a transition metal chalcogen containing an alkali metal, polyacetylene, polyparaphenylene, polyphenylene vinylene,
Examples of the positive electrode used in ordinary secondary batteries include conjugated polymers such as polyaniline, polypyrrole, and polythiophene, crosslinked polymers having disulfide bonds, and thionyl chloride. Among these, (lithium)
In the case of the positive electrode of the ion secondary battery, transition metal oxides such as cobalt, manganese, molybdenum, vanadium, chromium, iron, copper and titanium and transition metal chalcogens are preferably used.

The electrolytic solution used in the secondary battery of the present invention is not particularly limited, and a conventional electrolytic solution can be used.
For example, an acid or alkaline aqueous solution, a non-aqueous solvent, etc. may be mentioned. Among these, as the solvent used for the electrolytic solution of the above (lithium) ion secondary battery, propylene carbonate, ethylene carbonate, γ-butyrolactone, N-methylpyrrolidone, acetonitrile, N, N
-Dimethylformamide, dimethylsulfoxide, tetrahydrofuran, 1,3-dioxolane, methyl formate, sulfolane, oxazolidone, thionyl chloride, 1,
2-dimethoxyethane, diethyl carbonate, derivatives and mixtures of these are preferably used. As the electrolyte contained in the electrolytic solution, alkali metal, particularly lithium halide, perchlorate, thiocyanate, borofluoride, phosphorus fluoride, arsenic fluoride, aluminum fluoride, trifluoromethane sulfate, etc. It is preferably used.

The shape and method of forming the carbonaceous electrode used in the present invention should be appropriately determined according to the shape of the carbonaceous material and the characteristics of the secondary battery, and are not particularly limited. For example, when the carbonaceous material is a powder, it is prepared by using a polymer such as Teflon, polyvinylidene fluoride, or polypropylene as a binder and pressure-bonding it on a metal net or applying slurry or pressure-bonding it on a metal foil. .
When the carbonaceous material is a fiber, the electrodes are uniaxially arranged as described above, or formed into a structure such as a woven fabric and bundled or knitted with a conductive fiber such as a metal or a conductive polymer to form an electrode. Created as.

The secondary battery using the electrode of the present invention can be used as a video camera, a personal computer, a word processor, a radio-cassette, by utilizing the features of light weight, high capacity and high energy density.
It is widely applicable to portable small electronic devices such as mobile phones.

[0019]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 (1) Preparation of carbon electrode and charging / discharging A commercially available pitch coke "LPC-A" (manufactured by Nippon Steel Chemical Co., Ltd.) powder and Teflon powder were mixed in a weight ratio of 90/10. Thus mixed and pressure-molded together with the nickel mesh of the collecting electrode to obtain 10 mg of a carbon electrode. Using this electrode as a working electrode, metallic lithium is used for the counter electrode and the reference electrode, and 1 is used for the electrolytic solution.
A beaker-type cell was made using MLiClO ₄ / propylene carbonate.

In this cell, 100 mA / weight of carbon
After doping lithium ions to 0 V (vs. Li ⁺ / Li) with respect to the reference electrode with a current of g, similarly 1.5 V (vs.
Charge / discharge was completed by dedoping up to Li ⁺ / Li).

(2) Preparation of positive electrode Commercially available lithium carbonate (Li ₂ CO ₃ ) and basic cobalt carbonate
(2CoCO ₃ .3Co (OH) ₂ ) was weighed so that the molar ratio was Li / Co = 1/1, mixed in a ball mill, and heat-treated at 900 ° C. for 20 hours to obtain LiCoO ₂ . This is crushed with a ball mill, artificial graphite is used as the conductive material, and Teflon (PTF) is used as the binding material.
E) and LiCoO ₂ / artificial graphite / PTFE ＝ 80/15 /
The mixture was mixed so as to be 5 and pressure-molded together with the nickel mesh of the collecting electrode to obtain 20 mg of a positive electrode.

(3) Preparation and Evaluation of Secondary Battery A carbon electrode which was previously charged and discharged in the above (1) was used as a negative electrode, and a porous polypropylene film (Celguard # 2500, manufactured by Daicel Chemical Industries, Ltd.) was used as a separator. Then, the positive electrode prepared in (2) above was overlaid to prepare a coin-type secondary battery. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used.
When this battery was charged and discharged, the Coulomb efficiency was 95%. Comparative Example 1 A secondary battery was prepared in the same manner as in Example 1, except that the carbon negative electrode was not previously charged and discharged. The Coulombic efficiency of this secondary battery was 70%, and gas generation was observed during charging and discharging.

Example 2 (1) Preparation of carbon electrode and charging / discharging A carbon electrode was prepared in the same manner as in Example 1 using powder of commercially available pitch coke "LPC-U" (manufactured by Nippon Steel Chemical Co., Ltd.). did. A beaker type cell was prepared by using this electrode as a reference electrode for metallic lithium, a counter electrode for the positive electrode prepared in Example 1 (2), and an electrolyte for propylene carbonate containing 1M lithium perchlorate.

In this cell, 100 mA / carbon weight
After doping lithium ions to 0 V (vs. Li ⁺ / Li) with respect to the reference electrode with a current of g, similarly 1.5 V (vs.
Charge / discharge was completed by dedoping up to Li ⁺ / Li).

(2) Preparation and Evaluation of Secondary Battery A carbon electrode which was previously charged and discharged in the above (1) was used as a negative electrode, and a porous polypropylene film (Celguard # 2500, manufactured by Daicel Chemical Industries, Ltd.) was used as a separator. Then, the positive electrode prepared in Example 1 (2) was overlaid to prepare a coin-type secondary battery. The electrolyte is 1M
Propylene carbonate containing lithium perchlorate was used. Coulomb efficiency is 95 when this battery is charged and discharged.
%Met. Example 3 (1) Preparation of carbon electrode and charging / discharging A commercially available pitch coke "M-coke" (manufactured by Nippon Mining Co., Ltd.) powder and polyvinylidene fluoride (PVdF) powder were used in a weight ratio of 90/10. The mixture was mixed and N-methylpyrrolidone was added to obtain a slurry. This slurry was applied to a copper foil, dried, and pressed. The counter electrode is a metallic lithium foil, the separator is a porous polypropylene film,
A coin-type secondary battery was prepared by using propylene carbonate containing 1M lithium perchlorate as the electrolytic solution.

In this cell, 100 mA / carbon weight
Charge and discharge were completed by doping lithium ions to the reference electrode up to 0 V with a current of g and then undoping to 1.5 V in the same manner.

(2) Preparation and Evaluation of Secondary Battery The carbon electrode charged and discharged in advance in the above (1) was taken out from the coin type secondary battery and washed, and then a porous polypropylene film (Celguard # 2500, Daicel Chemistry) was used. Example 1 through a separator manufactured by
The positive electrode prepared in (2) was overlaid and a coin-type secondary battery was prepared again. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used. When this battery was charged and discharged, the Coulomb efficiency was 95%.

Example 4 Commercially available PAN-based carbon fiber "Torayca" T300 (manufactured by Toray Industries, Inc.) was bundled with a Ni wire of a current collector, and this was used as a working electrode, and metallic lithium was used as a counter electrode and a reference electrode, and an electrolyte solution was used. 1M LiClO
_A beaker type cell was prepared using ₄ / propylene carbonate.

In this cell, 100 mA / carbon weight
After doping lithium ions to 0 V (vs. Li ⁺ / Li) with respect to the reference electrode with a current of g, similarly 1.5 V (vs.
Charge / discharge was completed by dedoping up to Li ⁺ / Li).

(2) Preparation and Evaluation of Secondary Battery Carbon fibers that had been charged and discharged in the above (1) were arranged on the Ni mesh of the current collector, and in Example 1 (2) through the separator. A coin type cell was prepared by stacking the prepared positive electrode. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used. When this battery was charged and discharged, the Coulombic efficiency was 96%.

Comparative Example 2 Carbon fiber "Torayca" T300 was placed on the Ni mesh of the current collector without charging and discharging in advance, and was superposed on the positive electrode prepared in Example 1 (2) through the separator, A coin cell was created. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used. When this battery was charged and discharged, the Coulomb efficiency was 70%.

Example 5 Commercially available PAN-based carbon fiber "Torayca" M40 (Toray Industries, Inc.)
Was manufactured by bundling it with a Ni wire of a current collector, and using this as a working electrode, metallic lithium was used as a counter electrode and a reference electrode, and 1M LiClO ₄ / propylene carbonate was used as an electrolytic solution to prepare a beaker type cell.

In this cell, 100 mA / carbon weight /
After doping lithium ions to 0 V (vs. Li ⁺ / Li) with respect to the reference electrode with a current of g, similarly 1.5 V (vs.
Charge / discharge was completed by dedoping up to Li ⁺ / Li).

(2) Preparation and Evaluation of Secondary Battery The carbon fibers charged and discharged in advance in the above (1) were arranged on the Ni mesh of the current collector, and in Example 1 (2) through the separator. A coin type cell was prepared by stacking the prepared positive electrode. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used. When this battery was charged and discharged, the Coulombic efficiency was 96%.

Comparative Example 3 Carbon fiber "Torayca" M40 was placed on the Ni mesh of the current collector without charging and discharging in advance, and was superposed on the positive electrode prepared in Example 1 (2) through the separator, A coin cell was created. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used. When this battery was charged and discharged, the Coulomb efficiency was 85%.

Example 5 A commercially available PAN-based carbon fiber "Torayca" T300 (manufactured by Toray Industries, Inc.) and polyvinyl alcohol were used as a binder to prepare a mat electrode as a carbon fiber structure. Using this as a working electrode, lithium metal was used for the counter electrode and the reference electrode, and 1M LiClO ₄ / propylene carbonate was used for the electrolytic solution to prepare a beaker type cell.

In this cell, 100 mA / carbon weight /
After doping lithium ions to 0 V (vs. Li ⁺ / Li) with respect to the reference electrode with a current of g, similarly 1.5 V (vs.
Charge / discharge was completed by dedoping up to Li ⁺ / Li).

(2) Preparation and Evaluation of Secondary Battery The carbon fiber mat that had been charged and discharged in the above (1) was placed on the Ni mesh of the current collector, and in Example 1 (2) through the separator. A coin type cell was prepared by stacking the prepared positive electrode. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used. When this battery was charged and discharged, the Coulombic efficiency was 96%.

Comparative Example 4 A carbon fiber "Torayca" T300 mat electrode was placed on the Ni mesh of the current collector without charging and discharging in advance, and was overlaid with the positive electrode prepared in Example 1 (2) through the separator. Together, a coin cell was created. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used. When this battery was charged and discharged, the Coulomb efficiency was 70.
%Met.

[0041]

According to the present invention, when a carbonaceous electrode is charged and discharged in advance to prepare a secondary battery, decomposition gas and byproducts are not generated in the battery, and high Coulombic efficiency can be obtained. Therefore, it became unnecessary to charge an excessive amount of the positive electrode, and a secondary battery with high energy density was obtained.

Claims (7)

[Claims] 1. A secondary battery in which at least one electrode is composed of an electrode containing carbonaceous material and an electrolytic solution, which is assembled as a secondary battery after charging and discharging in advance. Production method. 2. The method for producing a secondary battery according to claim 1, wherein the carbonaceous electrode is carbon fiber. 3. The method for producing a secondary battery according to claim 1, wherein the carbonaceous electrode is a structure made of carbon fiber. 4. The method for manufacturing a secondary battery according to claim 3, wherein the structure is cloth or felt. 5. The method for manufacturing a secondary battery according to claim 1, wherein the electrode is used as a negative electrode. 6. The method for manufacturing a secondary battery according to claim 1, wherein the electrode is used as a positive electrode. 7. The method for producing a secondary battery according to claim 1, wherein the electrolytic solution is a non-aqueous electrolytic solution containing a lithium salt.