JPH07220752A - Lithium battery - Google Patents

Abstract

PURPOSE:To provide a lithium battery improving particularly a low temperature characteristic in a high discharge characteristic by forming lithium salt, constituting an electrolyte, of a plurality of lithium salts, and forming one of the lithium salts of mixed salt which is naphthalenesulfonate. CONSTITUTION:In a positive electrode active material, cobalt acid lithium as the first component, polypyrrole of doping 2,6-naphthalenesulfonate as the second component ad a compound positive pole 2, comprising an organic compound of mixing diacrylic ester of ethylene oxide with monoacrylic ester of polyethylene glycol, as a binding agent are formed on a stainless steel-made positive electrode collector plate 1. On the other hand, a negative electrode 4 formed of lithium metal is press attached to a stainless steel-made negative electrode collector plate 5. The organic compound, trigluoromethanesulfonic acid lithium, ethylene carbonate, gamma-butyrolactone, etc., are mixed and used in an electrolyte 3.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to improvements in lithium batteries.

[0002]

2. Description of the Related Art In recent years, electronic devices have been miniaturized with the development of the electronics field, and batteries as well as the devices have been desired to be miniaturized. In particular, a battery using lithium as the negative electrode active material can be expected to have a high energy density, and is therefore a very suitable battery for making it small and thin. Examples of the positive electrode used in the conventional lithium battery include a pyropolymer system obtained by firing a transition metal oxide, a conductive polymer compound, carbon, graphite, polyacrylonitrile, or the like at a high temperature.

Further, in recent years, since the development in the field of conductive polymer compounds has progressed, lithium secondary batteries using conductive polymer compounds have also been actively researched and developed by the batteries using polyacetylene of Mcdiarmid et al. As a result, lithium secondary batteries using polyaniline as a positive electrode have been industrialized. However, as a feature of the lithium battery using the conductive polymer compound, since the energy density depends on the doping / dedoping amount of the polymer, one dopant may be contained in 3 to 5 units of pyrrole such as polypyrrole. This type of polymer has a low energy density with respect to volume.
In addition, even in the case of a polymer such as polyaniline which theoretically contains one dopant per unit of monomer, the energy density in volume calculation is not high, and the intended use of the obtained battery is limited to memory backup, etc. Therefore, there is a problem that it is not suitable as a small-sized, thin, large-capacity battery.

Further, as a problem when the conductive polymer compound is used as a battery and a device related to electronics, it is mentioned that the conductive polymer compound is insoluble or infusible. The solution to this problem is to introduce a long-chain alkyl chain into the monomer, or to incorporate a sulfonic acid group or a methoxy group into the molecule, thereby making it soluble in polar solvents, general-purpose organic solvents, and water. Things have come to be synthesized. Further, a method of synthesizing a soluble precursor and heating it after casting to form a necessary insoluble / infusible conductive polymer compound has been studied for practical use. However, in industrialization, no suitable synthetic method has been found in terms of cost. Since polypyrrole, polyaniline and the like are inexpensive raw materials, it is even more preferable to use them without chemical modification such as a substituent.

Further, there is a problem of ion diffusion as a problem that occurs when a conductive polymer compound is used as an electrode. As widely discussed at academic conferences, the anion diffusion into the positive electrode system differs greatly depending on the polymer morphology, and also depends on the molecular size of the lithium salt. In particular, since the diffusion rate of anions is slow with respect to lithium cations, recently, complexing anions having a macromolecular structure has been combined with positive electrode conductive polymer compounds to allow doping / dedoping in the film system to be intrinsic. A method has been studied in which an anion having an existing macromolecular structure is used and ion compensation of the anion is performed using a lithium cation having a high diffusion rate. Further, the same effect can be expected with respect to the naphthalene sulfonate described in the claims of the present patent application, and therefore research is actively conducted. However, in the method of complexing anions having a macromolecular structure, there is a problem that the cations that have entered anion compensation cannot be removed, so that it is difficult to industrialize them under the present circumstances. Further, regarding the naphthalene sulfonate, the performance that can be expected cannot be exhibited due to the precipitation of the salt, particularly at low temperature characteristics, due to problems such as solubility of the salt.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a lithium battery having high discharge characteristics and particularly good low temperature characteristics.

[0006]

In order to achieve the above object, the present invention provides a lithium battery using a positive electrode, an electrolyte and a lithium metal or a lithium alloy or a compound capable of being doped with lithium as the negative electrode, and an electrolyte constituting the electrolyte. A battery characterized in that a lithium salt, which is a salt, uses a mixed salt of a lithium salt different from naphthalene sulfonate and naphthalene sulfonate, wherein the conductive polymer compound or the metal oxide and a conductive salt are used. It is characterized in that it is a positive electrode composite material containing a hydrophilic polymer compound as a main component. When the conductive polymer compound is a p-type conductive polymer and the synthesized conductive polymer compound is in a doped state, the dopant is the same as or different from the anion species of the electrolyte salt. May be. In addition, the positive electrode mixture containing a metal oxide and a conductive polymer compound as a main component has a compounding ratio of the conductive polymer compound of 5 to the metal oxide.
50% by weight is preferable, and naphthalene sulfonate which is an electrolyte salt constituting the electrolyte is 1,5- or 2,6-
The lithium salt is naphthalene sulfonate, and the lithium salt different from the naphthalene sulfonate is trifluoromethane sulfonate lithium salt.

[0007]

[Function] A battery using only the same salt as an electrolyte salt could not exhibit its performance in a low temperature region due to a problem such as the solubility of a conventional naphthalene sulfonate, but a salt having a good low temperature characteristic, for example, trifluoride. By mixing with lithium methanesulfonate, high characteristics can be exhibited as an effect of the naphthalene sulfonate at room temperature and high temperature, and high characteristics can be exhibited even at low temperature. Further, by using a mixed positive electrode of a metal oxide and a conductive polymer compound as the positive electrode, it is possible to reduce the influence on the discharge due to the rate limiting of the anion diffusion of the conductive polymer compound in the low temperature region. .

[0008]

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

(Example) A sheet-like battery of Example 1 of the present invention was manufactured according to the following procedure. a) 2,6-obtained by electrolytic polymerization of lithium cobalt oxide as the first component of the positive electrode active material of the battery and electrolytic polymerization as the second component
Using polypyrrole doped with naphthalene sulfonate anion, and diacrylate of ethylene oxide (molecular weight: 4000) and monoacrylate of polyethylene glycol (molecular weight: 400) 7: 3.
A mixture of the organic compound mixed with the above was used as a composite positive electrode. The method for producing this composite positive electrode is as follows. That is, a mixture of lithium cobalt oxide and the polypyrrole in a weight ratio of 10: 1 was added to 10 parts by weight of the organic compound, 1 part by weight of lithium trifluoromethanesulfonate, 0.05 part by weight of azobisisobutyronitrile, and ethylene. A mixture of 10 parts by weight of carbonate and 10 parts by weight of γ-butyrolactone was mixed in a dry inert gas atmosphere at a weight ratio of 10: 3. These mixtures were cast on a current collector having a conductive carbon film formed on the surface of a positive electrode current collector plate made of stainless steel. Then, it was hardened by leaving it for 1 hour at 100 ° C. in an inert gas atmosphere. b) Lithium metal was used as the negative electrode active material of the battery, and this was pressed onto a negative electrode current collector plate made of stainless steel. Then, to form an electrolyte layer on the lithium metal,
30 parts by weight of the above organic compound, 6 parts by weight of lithium trifluoromethanesulfonate, benzyl dimethyl ketal.
05 parts by weight, 32 parts by weight of ethylene carbonate and γ
A mixture of 32 parts by weight of butyrolactone was cast on the above lithium metal and cured by irradiation with ultraviolet rays in an inert gas atmosphere. c) Similarly, after forming an electrolyte layer on the positive electrode obtained in a), it is laminated with the current collector / lithium / electrolyte prepared in b) and the sealing portion is heat-sealed with a heat sealer to form a sheet-like battery. Was produced.

FIG. 1 is a sectional view of a sheet-shaped battery of Example 1 of the present invention. In the figure, 1 is a positive electrode current collector plate made of stainless steel, 2 is a composite positive electrode, and lithium cobalt oxide is used as the first component and 2,6-
Naphthalene sulfonate doped polypyrrole was used as a binder, an organic compound obtained by mixing a diacrylate ester of ethylene oxide and a monoacrylate ester of polyethylene glycol. Also. 4 is metallic lithium, 5 is a negative electrode current collector plate made of stainless steel, which also serves as an exterior. 6 is a sealing material made of modified polypropylene.

Comparative Example 1 a) Lithium cobalt oxide was used as the positive electrode active material of the battery, acetylene black was used as the conductive agent, and the diacrylate ester of ethylene oxide (molecular weight: 4000).
A mixture of a monoacrylic acid ester of polyethylene glycol (molecular weight: 400) and an organic compound obtained by mixing it in a ratio of 7: 3 was used as a composite positive electrode. The method for producing this composite positive electrode is as follows. That is, in a mixture of lithium cobalt oxide and acetylene black in a weight ratio of 10: 1, 10 parts by weight of the above organic compound, 1 part by weight of lithium trifluoromethanesulfonate, 0.05 part by weight of azobisisobutyronitrile, A mixture of 10 parts by weight of ethylene carbonate and 10 parts by weight of γ-butyrolactone was mixed in a dry inert gas atmosphere at a weight ratio of 10: 3. These mixtures were cast on a current collector having a conductive carbon film formed on the surface of a positive electrode current collector plate made of stainless steel. Then, it was hardened by leaving it for 1 hour at 100 ° C. in an inert gas atmosphere. b) Lithium metal was used as the negative electrode active material of the battery, and this was pressed onto a negative electrode current collector plate made of stainless steel. Next, 30 parts by weight of the organic compound, 1 part by weight of lithium trifluoromethanesulfonate, 0.05 part by weight of benzyl dimethyl ketal, 32 parts by weight of ethylene carbonate and A mixture of 32 parts by weight of γ-butyrolactone was cast on the lithium metal and cured by irradiation with ultraviolet rays in an inert gas atmosphere. c) the electrolyte / lithium / negative electrode current collector obtained in b),
The positive electrode current collector / composite positive electrode obtained in a) was brought into contact, and the sealing portion was heat-sealed with a heat sealer to seal the sheet-shaped battery.

Comparative Example 2 a) Lithium cobalt oxide was used as the positive electrode active material of the battery, acetylene black was used as the conductive agent, and the diacrylate ester of ethylene oxide (molecular weight: 4000).
A mixture of a monoacrylic acid ester of polyethylene glycol (molecular weight: 400) and an organic compound obtained by mixing it in a ratio of 7: 3 was used as a composite positive electrode. The method for producing this composite positive electrode is as follows. That is, a mixture of lithium cobalt oxide and acetylene black in a weight ratio of 10: 1, 10 parts by weight of the above organic compound, 2,6-
A mixture of 1 part by weight of lithium naphthalene sulfonate, 0.05 part by weight of azobisisobutyronitrile, 10 parts by weight of ethylene carbonate and 10 parts by weight of γ-butyrolactone was mixed in a dry inert gas atmosphere at 10: 3. Mixed in weight ratio. These mixtures were cast on a current collector having a conductive carbon film formed on the surface of a positive electrode current collector plate made of stainless steel. Then, it was hardened by leaving it for 1 hour at 100 ° C. in an inert gas atmosphere. b) Lithium metal was used as the negative electrode active material of the battery, and this was pressed onto a negative electrode current collector plate made of stainless steel. Next, in order to form an ion conductive polymer compound layer on the lithium metal, 30 parts by weight of the organic compound, 1 part by weight of lithium 2,6-naphthalenesulfonate, 0.05 parts by weight of benzyl dimethyl ketal, and 32 parts of ethylene carbonate. A mixture of 32 parts by weight of γ-butyrolactone and 32 parts by weight of γ-butyrolactone was cast on the lithium metal and cured by irradiation with ultraviolet rays in an inert gas atmosphere. c) the electrolyte / lithium / negative electrode current collector obtained in b),
The positive electrode current collector / composite positive electrode obtained in a) was brought into contact, and the sealing portion was heat-sealed with a heat sealer to seal the sheet-shaped battery. The electrode area of the sheet-shaped batteries of Examples and Comparative Examples can be variously changed by the manufacturing process, but in the present Example and Comparative Example, the electrode area was 33 cm ² . Using this sheet-shaped battery, a constant current charge / discharge of 6.6 mA was performed at 25 ° C and -20 ° C at a final charge voltage of 4.2V and a final discharge voltage of 3.7V at 25 ° C. FIG. 2 is a charge / discharge curve. As can be seen from FIG. 2, the sheet-shaped battery using the polymer solid electrolyte of the present invention has excellent charge / discharge characteristics at 20 ° C. as compared with the sheet-shaped battery of Comparative Example 1. Further, even at −20 ° C., the charge / discharge characteristics of the example are superior to those of the comparative example 2. That is, 20 ° C
In the batteries of Example and Comparative Example 2 in which lithium naphthalene sulfonate was blended in Comparative Example 1, the conductive polymer compound could be rapidly doped at the time of charging, so that the discharge capacity was Comparative Example 1.
It is considered that it has become larger than. Also, -20
In the charge / discharge test at ℃, since the battery of Comparative Example 2 uses only naphthalene sulfonate having a low low temperature solubility, the internal impedance is increased.
It is considered that the IR drop increased and the discharge capacity up to the specified cut voltage decreased. However, the discharge capacity of the battery of Example 1 of the present invention did not decrease even at low temperatures. It is considered that the trifluorosulfonic acid salt, which is effective for low-temperature characteristics, is contained in the metal oxide, so that the metal oxide, cobalt oxide, can enter and exit without problems.

[0012]

As is apparent from the above description, in a lithium battery using a positive electrode, an electrolyte, and a lithium metal or a lithium alloy or a compound capable of being doped with lithium as a negative electrode, a lithium salt that is an electrolyte salt constituting the electrolyte is Batteries that are characterized by using a mixed salt of naphthalene sulfonate and a lithium salt different from naphthalene sulfonate have higher characteristics as the effect of naphthalene sulfonate at room temperature and high temperature range compared to conventional batteries. It is possible to exhibit high characteristics even in a low temperature region. From these things, there is an effect that the performance of the battery can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a sheet-shaped battery of the present invention.

FIG. 2 is a graph showing discharge curves at 10th cycle of the sheet-shaped batteries of Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode current collector 2 Composite positive electrode, 3 Electrolyte 4 Metallic lithium, 5 Negative electrode current collector 6 Sealing material

Claims (7)

[Claims] 1. In a lithium battery using a positive electrode, an electrolyte, and a compound capable of being doped with lithium metal, a lithium alloy, or lithium as a negative electrode, a lithium salt that is an electrolyte salt constituting the electrolyte is composed of a plurality of lithium salts. A lithium battery comprising a mixed salt of naphthalene sulfonate. 2. The lithium battery according to claim 1, wherein the positive electrode is a conductive polymer compound. 3. The lithium battery according to claim 1, wherein the positive electrode is a positive electrode mixture containing a metal oxide and a conductive polymer compound as main components. 4. When the conductive polymer compound is a p-type conductive polymer and the synthesized conductive polymer compound is in a doped state, the dopant is the same as the anion species of the electrolyte salt or The lithium battery according to claim 2 or 3, which is of a different type. 5. The lithium battery according to claim 3, wherein the compounding ratio of the conductive polymer compound is 5 to 50% by weight with respect to the metal oxide. 6. The lithium battery according to claim 1, wherein the naphthalene sulfonate which is an electrolyte salt constituting the electrolyte is 1,5- or 2,6-naphthalene sulfonate lithium. 7. The lithium battery according to claim 1, wherein, in the plurality of lithium salts forming the electrolyte, the other lithium salt is a lithium trifluoromethanesulfonate salt.