JPH1186863A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve charging/discharging characteristics by using an electrochemically active metal for a positive electrode current collector, and using an organic compound with high affinity to the metal ions for a positive electrode active material. SOLUTION: An electrochemically active metal having a metal dissolution- deposition reaction accompanied by a charging/discharging, e.g. copper, is used for a positive electrode current collector. A positive electrode material preferably has a proper complex forming constant for metal ions and the functional group expected with electrochemical oxidation reduction. The positive electrode material having low molecular weight, small electrochemical equivalent, and a proper oxidation reduction potential is preferably used in view of increasing the battery energy density. Dithizone, 8-oxyquinoline, 1-(2-pyridylazo)-2-naphthol, N-benzoyl-N-phenylhydroxylamine, or a phenanthroline derivatives are used with respect to copper ions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION As communication devices such as computers and mobile phones become smaller and lighter, there is a demand for higher energy density of secondary batteries as power sources. The present invention relates to a secondary battery having a small size and a large charge / discharge capacity, in particular, a lithium-based secondary battery using a positive electrode containing an organic compound capable of forming a specific complex with a metal ion that is electrochemically activated. It relates to batteries.

[0002]

2. Description of the Related Art Lead secondary batteries include lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, lithium secondary batteries, and lithium ion batteries. Lithium-based secondary batteries have attracted attention as the flower shape of next-generation secondary batteries due to their large theoretical capacity, and are being actively studied for improvement.

[0003] As a positive electrode active material of a lithium secondary battery, a lithium salt of a transition metal oxide such as cobalt, nickel, manganese, and vanadium is mainly used, and by controlling the composition and structure thereof, high energy density can be achieved. Is measured. However, the capacity of the positive electrode is far below the theoretical capacity of lithium metal, and is inferior to the capacity of a carbon material for a negative electrode that intercalates lithium ions. Attempts to utilize an organic compound having a large theoretical capacity as a positive electrode active material have also been disclosed in U.S. Pat.
7 ・ Although it is scattered in JP-A-5-74459, it is unsatisfactory in any of voltage output, stability of charge / discharge cycle, current density, etc.

[0004]

Many organic compounds are attractive as positive electrode active materials because of their large theoretical capacities, but because of their poor conductivity and slow oxidation-reduction reaction, However, problems such as voltage drop, low current density, and deterioration of characteristics at room temperature were observed. As means for overcoming these problems, attempts have been made to add a carbon material or the like as a conductive agent or to combine it with another material, but there have been few satisfactory cases.

[0005]

SUMMARY OF THE INVENTION In order to overcome the above-mentioned problems, the present invention actively utilizes a current collector dissolution-precipitation reaction which has been conventionally attempted to avoid as much as possible in the process of manufacturing a battery. This aims to solve the above problem.
That is, it is intended to realize a secondary battery having excellent characteristics by using a metal that is electrochemically active for the positive electrode current collector and using an organic compound having high affinity for ions of the metal as the positive electrode active material. Is what you do.

[0006] Silver or copper is known as an electrode-reactive metal in which its own dissolution reaction takes place when charged near a potential difference of 4 V like a lithium secondary battery. It has hardly been used as a current collector. However, at the time of discharge, metal deposition, which is a reverse reaction, is reversibly recognized to some extent. Therefore, in order to enhance the reversibility, an organic compound having a high affinity for the metal ion was selected as the positive electrode in the present invention for the purpose of preventing the metal ion eluted at the time of charging from being dissipated by diffusion and trapping the metal ion near the electrode. Naturally, it is considered that the complex formation reaction and its reverse reaction and the oxidation-reduction reaction of the organic compound itself proceed conjugately in the positive electrode with charge / discharge to realize a high capacity.

The positive electrode current collector used in the present invention is not particularly limited as long as it is electrochemically active, that is, a metal dissolution-precipitation reaction accompanying charge / discharge is observed. However, copper is preferred in terms of cost. Examples of such a current collector include, in addition to a pure metal foil, an alloy foil containing the metal as a main component, and a clad foil of another metal which is electrochemically inactive with the metal. it can. Also,
Titanium and stainless steel coated with the metal are also candidates. Examples of the coating method include methods such as vapor deposition, sputtering, and plating, and the method is not particularly limited.

The positive electrode material used in the present invention is appropriately selected from a group of organic compounds classified into a precipitation reagent, a colorimetric reagent, a titration reagent, an extraction reagent, a metal indicator, a gravimetric analysis reagent, and the like for a target metal ion. You can choose. The criteria for selection are:
It is desirable to have not only an appropriate complex formation constant for the metal ion but also a functional group expected to undergo electrochemical redox. Further, from the viewpoint of increasing the energy density of the battery, a battery having a small molecular weight or electrochemical equivalent and having a suitable oxidation-reduction potential is desirable.

As a suitable example, quinolinol derivatives 1- (2) represented by dithizone or the like for silver ions and dithizone-8-oxyquinoline for copper ions.
-Pyridylazo) -2-naphthol; a phenylhydroxyamine derivative represented by N-benzoyl-N-phenylhydroxyamine; a phenanthroline derivative.

At the time of forming the positive electrode, an organic compound appropriately selected may be used as a ligand as it is, or may be used as a complex with the metal ion prepared in advance. As an alternative to preparing the complex in advance, a salt of the metal ion of interest may be mixed with the positive electrode slurry containing the organic compound.

As the conductive polymer used as a part of the positive electrode of the present invention, polyaniline, polypyrrole, polythiophene, polyacetylene and their derivatives can be used, but polyaniline and its derivatives are particularly preferable. Although there is no particular limitation on the binder polymer for forming the positive electrode of the present invention, polyvinylidene fluoride is preferably used. Further, addition of a carbon material or the like as a conductive agent is not avoided.

[0012] The electrolyte solution may include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF or a mixture of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, sulfolane, dimethoxyethane, tetrahydrofuran, and γ-butyrolactone. ₆ ,
A lithium salt selected from LiCF ₃ SO ₃ or the like can be dissolved and used. The nonaqueous electrolyte can be used as it is via an appropriate separator, or can be used as a polymer gel electrolyte in combination with a polyacrylonitrile polymer or the like. In addition, a solid electrolyte such as LiI, Li ₃ N—LiI—B ₂ O ₃ , and LiAl ₂ O _3, or a polymer electrolyte in which a lithium salt is supported on polyethylene oxide or the like can be used according to the purpose.

[0013] A lithium secondary battery can be constructed using a lithium foil or a lithium alloy foil for the negative electrode. Further, it is considered that a lithium ion battery can be formed by using a carbon material supporting lithium ions or the like as a negative electrode.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments. [Example 1] Dithizone of Tokyo Chemical Industry Co., Ltd. and polyvinylidene fluoride (PVDF, KF polymer) of Kureha Chemical Industry Co., Ltd. were mixed at a weight ratio of about 3: 1, and N-methylpyrrolidone (NMP) was mixed. In addition, a positive electrode slurry was prepared. This slurry was applied on a silver foil (thickness, 50 μm) of Furuuchi Chemical Co., Ltd., and was preliminarily dried at 85 ° C. and further dried by heating under vacuum at 85 ° C. to remove NMP.
A positive electrode was prepared. Organic electrolyte is propylene carbonate (PC) / ethylene carbonate (EC), PC:
1M LiBF dissolved in a mixed solvent of EC = 1.33: 1 (weight ratio)
4 was used. A mixture of 1 part by weight of a polyacrylonitrile polymer of Nippon Exlan Industrial Co., Ltd. and 3.3 parts by weight of the above organic electrolyte was heated to 120 ° C. to form a sol. This sol was cooled to −20 ° C. to obtain a sheet-like polymer gel electrolyte, which was returned to room temperature and used. The negative electrode is a lithium foil (thickness, 2
And a stainless steel foil (SUS-3) manufactured by Furuuchi Chemical Co., Ltd. as a negative electrode current collector and a positive electrode lead.
02; thickness, 50 microns). A flat lithium secondary battery (battery A) is obtained by combining these battery members and crimping a pair of slide glasses as a support.
Was built. FIG. 1 shows a schematic diagram of the battery of the present invention.

Battery A was evaluated by charging and discharging in a constant charge-constant current discharge mode. The charge threshold voltage and the discharge threshold voltage were set to 4.4 and 2.0 V, respectively. Regarding the capacity of the positive electrode, although it cannot be accurately described because it is considered that some silver of the current collector functions as an active material, the capacity of the positive electrode active material calculated from the weight of the positive electrode mixture is not described. Charging equivalent to 160 mAh / g was performed, and charge / discharge characteristics were evaluated. FIG. 2 shows a charge / discharge pattern of the battery A in 10 to 15 cycles when charge / discharge was performed at 0.6 mA (current density; 0.15 mA / cm 2). As shown in FIG. 2, in the discharge pattern of this battery, although the potential was delayed in the early stage of the discharge and the potential gradually decreased after reaching the maximum value, the Coulomb efficiency was almost 100%.

Example 2 The dithizone used in Example 1 was 8-oxyquinoline from Wako Pure Chemical Industries, Ltd., and the positive electrode current collector was phosphor bronze foil (thickness, 20
Battery B was constructed in the same process as in Example 1 except that the battery B was used. The charge corresponding to 180 mAh / g was performed with respect to the apparent weight of the positive electrode active material calculated from the weight of the positive electrode mixture, and the charge / discharge characteristics were evaluated. In FIG. 3, 0.6 m
A shows a charge / discharge pattern of battery B in 20 to 25 cycles when charge / discharge was performed at A (current density; 0.15 mA / cm 2). As shown in FIG. 3, in the discharge pattern of this battery, a slight potential delay was observed at the beginning of discharge, and the potential gradually decreased after passing through the maximum value, but the Coulomb efficiency was almost 100%. .

Example 3 Example 8 was repeated except that the 8-oxyquinoline used in Example 2 was 1- (2-pyridylazo) -2-naphthol from Dojindo Laboratories Inc. Battery C was constructed in the same process. FIG. 4 shows a charge / discharge pattern (for 20 to 25 cycles) when the same evaluation as that of the battery B was performed. As shown in FIG. 4, in the discharge pattern of this battery, although the potential was delayed at the initial stage of the discharge and the potential gradually decreased after reaching the maximum value, the Coulomb efficiency was almost 100%.

Example 4 8-Oxyquinoline used in Example 2 was converted to N-benzoyl-
Battery D was constructed in the same manner as in Example 2, except that N-phenylhydroxyamine was used. FIG. 5 shows a charge / discharge pattern (for 20 to 25 cycles) when the same evaluation as that of the battery B was performed. As shown in FIG. 5, in the discharge pattern of this battery, although the potential was delayed in the early stage of the discharge and the potential gradually decreased after reaching the maximum value, the Coulomb efficiency was almost 100%.

Example 5 Dithizone and polyaniline from Tokyo Chemical Industry Co., Ltd., and polyvinylidene fluoride (PVDF, KF polymer) from Kureha Chemical Industry Co., Ltd. were mixed at a weight ratio of about 6: 3: 1. N-methylpyrrolidone (NM
P) was added to obtain an electrode agent slurry. This slurry was applied on an electrolytic copper foil (thickness, 12 microns) of Fukuda Metal Foil & Powder Co., Ltd., preliminarily dried at 85 ° C., and further dried by vacuum heating at 85 ° C. to remove NMP. A positive electrode was prepared. The polyaniline used in this example was
It was prepared by oxidative polymerization of aniline. Using this positive electrode, a battery E was constructed in the same manner as in Example 2. FIG. 6 shows the charge / discharge pattern (for 10 to 15 cycles) when the same evaluation as that of the battery B was performed. As shown in FIG. 6, the discharge pattern of this battery was flat and the potential rapidly decreased at the end of discharge, and the Coulomb efficiency was almost 100%.

Example 6 A battery F was constructed in the same manner as in Example 5, except that dithizone used in Example 5 was 8-oxyquinoline manufactured by Wako Pure Chemical Industries, Ltd. FIG. 7 shows the charge / discharge patterns (for 20 to 25 cycles) when the same evaluation as that of the battery E was performed. As shown in FIG. 7, the discharge pattern of this battery was flat and the potential rapidly decreased at the end of discharge, and the Coulomb efficiency was almost 100%.

[Example 7] The dithizone used in Example 5 was replaced with 1- (2-pyridylazo) by Dojin Chemical Laboratory Co., Ltd.
Battery G was constructed in the same manner as in Example 5, except that -2-naphthol was used. FIG. 8 shows charge / discharge patterns (for 20 to 25 cycles) when the same evaluation as that of the battery E was performed. As shown in FIG. 8, the discharge pattern of this battery was flat and the potential rapidly decreased at the end of discharge, and the Coulomb efficiency was almost 100%.

Example 8 A battery was manufactured in the same manner as in Example 5, except that dithizone used in Example 5 was N-benzoyl-N-phenylhydroxyamine from Dojindo Laboratories. H was constructed. Charge / discharge pattern (20 to 25 cycles) when the same evaluation as that of battery E was performed
Is shown in FIG. As shown in FIG. 9, the discharge pattern of this battery was flat and the potential gradually decreased at the end of discharge, and the Coulomb efficiency was almost 100%.

Example 9 An aqueous solution in which cupric chloride was dissolved and a chloroform solution in which dithizone was dissolved were mixed, and the formed copper-dithizone complex was extracted and recovered in a chloroform layer. This complex was dried and used for the test. The copper-dithizone complex, activated carbon, polypyrrole, and polyvinylidene fluoride (PVDF, KF polymer) were mixed at a weight ratio of about 4: 4: 8: 1, and N-methylpyrrolidone (NM
P) was added to obtain an electrode agent slurry. This slurry was applied to a tin-copper alloy foil (tin content, 2%; thickness, 14 microns) of Fukuda Metal Foil & Powder Co., Ltd., preliminarily dried at 85 ° C., and further dried under vacuum at 85 ° C. NM
P was removed to prepare a positive electrode. The polypyrrole used in this example was prepared by oxidative polymerization of pyrrole. Using this positive electrode, a battery I was constructed in the same manner as in Example 2.
Charging corresponding to 160 mAh / g was performed with respect to the apparent weight of the positive electrode active material calculated from the weight of the positive electrode mixture, and the charge / discharge characteristics were evaluated. FIG. 10 shows that 0.4 mA (current density;
1 mA / cm 2) when charging and discharging at 10 mA
The charging / discharging pattern in 〜15 cycles was shown. FIG. 11 shows the cycle characteristics at 1 to 100 cycles.
It was shown to. The discharge pattern of this battery had a step in the middle. As shown in FIG. 11, the Coulomb efficiency was at least 100% for at least 100 cycles.

Example 10 A copper-dithizone complex, activated carbon, dithizone alone and polyaniline were mixed at a weight ratio of about 4: 4: 5: 3, and N-methylpyrrolidone (NM
P) was added to obtain an electrode agent slurry. This slurry was applied to a tin-copper alloy foil (tin content, 2%; thickness, 14 microns) of Fukuda Metal Foil & Powder Co., Ltd., preliminarily dried at 85 ° C., and further dried under vacuum at 85 ° C. NM
P was removed to prepare a positive electrode. Using this positive electrode, a battery J was constructed in the same manner as in Example 2. With respect to the apparent weight of the positive electrode active material calculated from the weight of the positive electrode mixture, 200 mAh /
g, and the charge / discharge characteristics were evaluated. FIG.
9 shows a charge / discharge pattern of the battery J in 10 to 15 cycles when charge / discharge was performed at 0.8 mA (current density; 0.2 mA / cm 2). FIG. 13 shows cycle characteristics in 1 to 100 cycles. The discharge pattern of this battery was flat and the potential rapidly decreased at the end of discharge. In addition, as shown in FIG.
Except for the cycles, the coulomb efficiency was stable at almost 100% for at least 100 cycles.

Example 11 8-oxyquinoline, polyaniline, and PVDF were mixed at a weight ratio of about 6: 3: 1, and N-methylpyrrolidone (NMP) was added to prepare an electrode agent slurry. The slurry was applied on a phosphor bronze foil (thickness, 20 microns) of Takeuchi Metal Foil & Powder Co., Ltd., which was pre-dried at 85 ° C., and further dried under vacuum at 85 ° C. to remove NMP. A positive electrode was prepared. Using this positive electrode, a battery K was constructed in the same manner as in Example 2.
The charge corresponding to 200 mAh / g was performed with respect to the apparent weight of the positive electrode active material calculated from the weight of the positive electrode mixture, and the charge / discharge characteristics were evaluated. FIG. 14 shows that 0.6 mA (current density;
15 mA / cm 2)
The charge / discharge pattern in 0 to 15 cycles is shown. FIG. 15 shows the cycle characteristics at 1 to 100 cycles.
It was shown to. The discharge pattern of this battery was flat and the potential rapidly decreased at the end of discharge. Further, as shown in FIG. 15, except for the initial 10 cycles, the Coulomb efficiency was stable at almost 100% for at least 100 cycles.

Comparative Example 1 Same as Example 11 except that the phosphor bronze foil of the positive electrode current collector used in Example 11 was a nickel foil (thickness: 10 μm) of Soekawa Rikagaku Co., Ltd. The battery L was constructed in the process described above. Battery L could be charged only at the beginning. However, when the discharge was performed, the potential immediately decreased to the threshold value of 2 V, and the discharge capacity was almost zero.

Comparative Example 2 The same procedure as in Example 11 was performed except that the phosphor bronze foil of the positive electrode current collector used in Example 11 was a titanium foil (thickness, 50 μm) of Furuuchi Chemical Co., Ltd. The battery M was constructed in the process described above. Battery M was also chargeable only at the beginning. However, when the discharge was performed, the potential immediately decreased to the threshold value of 2 V, and the discharge capacity was almost 0.

In the batteries shown in Examples 1 to 11, deterioration of the positive electrode current collector was recognized to some degree as the cycle progressed. This is considered to be because in other words, the dissolution-precipitation of the electrode metal is locally uneven. Examples 2 to 4 and 9 to 1 using alloy foil containing tin
1 and Examples 5 to 8 using copper foil, the former significantly suppressed the degree of deterioration of the current collector even when the difference in foil thickness was subtracted. In addition, as a result of comparative study using various copper alloy foils, good results were obtained with a copper alloy containing tin.

[0029]

As described above, according to the present invention, a positive electrode current collector containing an electrochemically active metal as a main component and an organic compound capable of forming a complex with the metal ion are used as main components of the positive electrode active material. By assembling a lithium secondary battery characterized by performing the above, a secondary battery exhibiting good charge / discharge characteristics can be configured.

[Brief description of the drawings]

FIG. 1 is a view showing a structure of a secondary battery according to the present invention.

FIG. 2 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 3 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 4 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 5 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 6 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 7 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 8 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 9 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 10 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 11 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 12 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 13 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 14 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

FIG. 15 shows a charge / discharge pattern when the secondary battery according to the present invention is charged / discharged in a constant charge / constant current discharge mode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass support 2 Stainless steel lead 3 Positive electrode collector 4 Positive electrode mixture 5 Polymer gel electrolyte 6 Lithium foil

Claims (13)

[Claims] 1. A lithium secondary battery comprising, as main components of a positive electrode, a positive electrode current collector containing at least an electrochemically active metal as a main component and an organic compound capable of forming a complex with the metal ion. battery. 2. A positive electrode, comprising a positive electrode current collector containing at least an electrochemically active metal as a main component, and an organic compound having an ability to form a complex with the metal ion, an organic solvent and a lithium salt. A lithium secondary battery comprising, as constituents, a polyacrylonitrile-based gel electrolyte, a lithium metal negative electrode and a negative electrode current collector. 3. A positive electrode comprising a positive electrode current collector containing at least an electrochemically active metal as a main component, and a mixture of an organic compound having a complex forming ability with the metal ion and a conductive polymer. A lithium secondary battery characterized by the following. 4. A mixture comprising an organic compound having at least an electrochemically active metal as a main component and an organic compound capable of forming a complex with the metal ion and a conductive polymer as a main component. A lithium secondary battery comprising, as constituent elements, a positive electrode, a polyacrylonitrile-based gel electrolyte containing an organic solvent and a lithium salt, a lithium metal negative electrode and a negative electrode current collector. 5. A positive electrode current collector containing copper or silver as a main component, wherein the main component of the positive electrode is dithizone. 3. The secondary battery according to claim 1, which is a derivative thereof. 6. The secondary battery according to claim 3, wherein the positive electrode current collector comprises copper or silver as a main component, and a main component of the positive electrode is a mixture of dithizone or a derivative thereof and polyaniline. 7. A positive electrode current collector containing copper as a main component, and a main component of the positive electrode is 8-oxyquinoline. 3. The secondary battery according to claim 1, which is a derivative thereof. 8. The secondary battery according to claim 3, wherein the secondary battery is a positive electrode current collector containing copper as a main component, and a main component of the positive electrode is a mixture of 8-oxyquinoline or a derivative thereof and polyaniline. 9. A positive electrode current collector containing copper as a main component, and a main component of the positive electrode is 1- (2-pyridylazo) -2.
-Naphthol 3. The secondary battery according to claim 1, which is a derivative thereof. 10. A positive electrode current collector containing copper as a main component, wherein a main component of the positive electrode is 1- (2-pyridylazo)-
5. The secondary battery according to claim 3, which is a mixture of 2-naphthol or a derivative thereof and polyaniline. 11. A positive electrode current collector containing copper as a main component, wherein a main component of the positive electrode is N-benzoyl-N-phenylhydroxyamine. 3. The secondary battery according to claim 1, which is a derivative thereof. 12. A secondary current collector according to claim 3, wherein said positive electrode current collector comprises copper as a main component, and a main component of said positive electrode is a mixture of N-benzoyl-N-phenylhydroxyamine or a derivative thereof and polyaniline. battery. 13. A tin-copper alloy or phosphor bronze foil having a tin content of 10% or less for the positive electrode current collector.
6, 7, 8, 9, 10, 11, and 12 secondary batteries.