JPH02172162A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To obtain a battery having high voltage, high energy density, and long charge-discharge cycle life by using a nonaqueous electrolyte prepared by dissolving LiPF6 in a nonaqueous mixed solvent containing cyclic carbonate and noncyclic carbonate. CONSTITUTION:A nonaqueous electrolyte prepared by dissolving LiPF6 in a nonaqueous mixed solvent containing cyclic carbonate and noncyclic carbonate is used. As the cyclic carbonate, ethylene carbonate or propylene carbonate is usually used. As the noncyclic carbonate, dialkyl carbonate such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, and methylethyl carbonate is used. The contents of the cyclic carbonate and the noncyclic carbonate in the nonaqueous mixed solvent is 20wt.% or more each. The ratio of the cyclic carbonate to the noncyclic carbonate is 5/1-1/5 by weight. The total amount of both carbonates is 80% or more of the whole solvent.

Description

[Detailed Description of the Invention] Industrial * The present invention relates to a non-aqueous electrolyte secondary battery using an organic conductive polymer material such as polyaniline as a positive electrode active material and lithium or a lithium alloy as a negative electrode active material. More specifically, the present invention relates to a nonaqueous electrolyte secondary battery that has high voltage, high energy density, long charge/discharge cycle life, and excellent stability and reliability.

Organic conductive polymer materials such as polyaniline, polyacetylene, polypyrrole, and polythiophene have been used as battery electrode materials because they are lightweight and highly flexible, and have the ability to incorporate ionic species. It has been proposed that
It is known that a secondary battery using these as electrode active materials can be a battery with good charging/discharging efficiency and high energy density. In particular, polyaniline is superior to other organic conductive polymer materials as an electrode material in terms of performance such as cycle life and self-discharge, and some of it has reached the stage of commercialization.

In such non-aqueous electrolyte batteries that use polyaniline as the positive electrode active material, it is preferable to use lithium metal as the negative electrode active material from the point of view of energy density, but if only lithium metal is used as the negative electrode material, charging and discharging As the cycle is repeated, dendrites form on the lithium negative electrode.
of lithium is generated, penetrating the separator between the positive and negative electrodes and causing a short circuit, and lithium precipitates in the form of fine powder and falls off or becomes passivated, resulting in problems such as a significant reduction in cycle life.

Conventionally, in order to solve these drawbacks, it has been proposed to use an alloy of lithium and aluminum, lead, indium, etc. for the negative electrode, but various problems still remain. In other words, when a lithium-aluminum alloy is used as the negative electrode active material, dendrites are not generated, but repeated charging and discharging may cause atomization and collapse of the negative electrode, and lithium diffusion in the α phase of the alloy may occur. Coulombic efficiency may be insufficient due to slow speed. When a lithium-lead alloy is used, the electrode collapses more severely than a lithium-aluminum alloy due to repeated charging and discharging, and alloys with a low lithium concentration have problems such as poor coulombic efficiency. When a lithium-indium alloy is used, the coulombic efficiency is good, but it is not practical because indium is expensive.

Furthermore, when these alloy negative electrodes are used, the electrode potential is about 0.3 to 0.8 V higher than that of lithium, and the weight of the negative electrode increases, which is disadvantageous in terms of energy density.

The present invention was made in view of the above-mentioned circumstances, and addresses the above-mentioned problems of a non-aqueous electrolyte secondary battery using an organic conductive polymer material such as polyaniline as a positive electrode active material and lithium or a lithium alloy as a negative electrode active material. The purpose of the present invention is to provide a nonaqueous electrolyte secondary battery that has high voltage, high energy density, long charge/discharge cycle life, and excellent stability and reliability.

In order to achieve the above object, the inventors of the present invention have conducted intensive studies and found that the electrolyte solution is By using LiPF dissolved in a non-aqueous mixed solvent containing a cyclic carbonate and an acyclic carbonate, the generation of dendrites can be prevented even when only lithium metal is used as the negative electrode active material. In addition, when a lithium alloy is used as the negative electrode active material, it is possible to prevent electrode collapse and decrease in coulombic efficiency, and it is possible to prevent the collapse of the electrode and reduce the Coulombic efficiency. The present invention was completed based on the finding that the following can be obtained.

Therefore, the present invention provides a secondary battery comprising a positive electrode using an organic conductive polymer material as an active material, a negative electrode using lithium or a lithium alloy as an active material, and a non-aqueous electrolyte. As LiPF.

The present invention provides a non-aqueous electrolyte secondary battery using a non-aqueous mixed solvent containing a cyclic carbonate and an acyclic carbonate.

The present invention will be explained in more detail below.

The non-aqueous electrolyte secondary battery of the present invention uses an organic conductive polymer material as a positive electrode active material as described above.
The organic conductive polymer material is not particularly limited, and various conductive polymers such as polyaniline, polyacetylene, polypyrrole, polythiophene, polyparaphenylene, and polyacene can be used, but polyaniline is particularly preferably used. In addition, as polyaniline, (NH
4) zSzO*-FeCQ, Cr, 07. KMn
Polyaniline polymerized by chemical oxidation polymerization using a chemical oxidizing agent such as O4, polyaniline polymerized electrochemically by electrolytic oxidation polymerization, etc. can be used, but the aniline concentration is usually 0.01 to 5 mol/12. Especially 0.5 to 3 mol/1
2. Acid concentration 0.02 to 10 mol/Q, especially 1 to 6 mol/Q
Those obtained by polymerization using an electrolytic solution containing Q are suitable. The acids used in the electrolytic solution for the above electrolytic polymerization include hydrofluoric acid, hydrochloric acid, sulfuric acid, nitric acid, perchloric acid,
Fluoroboric acid.

Examples include acetic acid, especially perchloric acid.

Hydrofluoroboric acid is preferably used.

The positive electrode constituting the battery of the present invention uses the above-mentioned organic conductive polymer material as an active material. , conductive materials with excellent corrosion resistance are preferably used. Among these, stainless steel is preferred from the viewpoint of corrosion resistance, cost, etc., and ferritic stainless steel is particularly preferred.

Next, as the negative electrode of the secondary battery of the present invention, it is desirable to use only lithium metal because it is advantageous in terms of energy density, but alloys of lithium and other metals can also be used. In this case, the lithium alloys include (a), (b), and (ma) containing lithium.

IVa, Va group metals or alloys of two or more thereof can be used, especially AQ, In containing lithium.

Sn, Pb, Bi, Cd, Zn, or alloys of two or more of these are preferably used.

The secondary battery of the present invention includes LiPF between the positive and negative electrodes.

It is constructed by interposing an electrolytic solution formed by dissolving as a solute in a non-aqueous mixed solvent containing a cyclic carbonate and an acyclic carbonate.

Ethylene carbonate and propylene carbonate are the most common cyclic carbonates blended into the non-aqueous mixed solvent constituting the electrolyte, but other carbonates have a five-membered ring with a carbonate group in their molecular structure. Any cyclic carbonate may be used as long as it has a high dielectric constant, and promotes the dissociation of LiPF, which is a solute. On the other hand, examples of acyclic carbonates include dialkyl carbonates such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, and methylethyl carbonate. Although these acyclic carbonates have a low dielectric constant, their low viscosity facilitates the diffusion of ions in the solution and contributes to improving the electrical conductivity. In addition, acyclic carbonate has a characteristic that it is difficult to decompose at high potential, and can keep the solvent stable even when charging and discharging at a high voltage of 3 V or more.

In addition, the non-aqueous mixed solvent may be a mixed solvent consisting of only two components, the above-mentioned acyclic carbonate and cyclic carbonate, or a mixed solvent consisting of three or more components in which other non-aqueous solvents are added. You can. In this case, other nonaqueous solvents include benzene, toluene, xylene, and ethylbenzene.

Aromatic compounds such as chlorobenzene, nitrobenzene, naphthalene, etc. 5 Hexane, heptane, octane.

Nonane, decane, inhexane, 2-methylhexane,
Hexene, hexadienecyclohexane.

Saturated and unsaturated alkyl compounds such as cyclopentene, cyclohexene, cyclohexadiene, cyclopentadiene, nitrile compounds such as acetonitrile, benzonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane.

Ether compounds such as jetoxyethane, as well as dimethylformamide and dimethylsulfoxide.

Examples include γ-butyrolactone, sulfolane, 3-methylsulfolane, N-methyl-2-oxazolidinone, etc.
One or more of these may be used, but the invention is not limited thereto. Here, the content of cyclic carbonate and acyclic carbonate in the above-mentioned non-aqueous mixed solvent is not particularly limited, but each should be 20% (wt%, same hereinafter) or more, especially 30 to 70%. Preferably, if the content of cyclic carbonate and acyclic carbonate is less than 20% each, it may not only be impossible to effectively prevent the deterioration of the electrode active material, but also the stability of the electrolyte at high potential may be affected. problems may occur, and sufficient performance may not be obtained in terms of cycle characteristics, float charging characteristics, self-discharge characteristics, etc. as a secondary battery. The weight ratio of cyclic carbonate to acyclic carbonate is 5/1 to 115 (cyclic carbonate/acyclic carbonate), particularly 3/1 to 1.
/3 is preferable. Further, the total amount of cyclic carbonate and acyclic carbonate is preferably 80% or more, particularly 90% or more of the entire solvent.

As described above, the electrolytic solution constituting the secondary battery of the present invention is one in which LiPF is dissolved in the above-mentioned non-aqueous mixed solvent. In this case, the content of LiPF is not particularly limited, but is usually about 0.2 to 5 mol/Q.

The secondary battery of the present invention is constructed by interposing the above-mentioned electrolyte between the positive and negative electrodes, but in this case, a separator may be interposed between the positive and negative electrodes to prevent short circuits of current due to contact between the two electrodes. can.

As a separator, it is porous and allows the electrolyte to pass through.

For example, woven fabrics, nonwoven fabrics, porous bodies, etc. of synthetic resins such as polypropylene, polyethylene, and polytetrafluoroethylene can be used.

The form of the nonaqueous electrolyte secondary battery of the present invention is not particularly limited, and may be a coin type, two cylindrical type, or two box type.

It can be made into various shapes such as paper type.

As explained above, the non-aqueous electrolyte secondary battery of the present invention includes:
In a non-aqueous electrolyte secondary battery in which an organic conductive polymer material is used as a positive electrode active material and lithium or a lithium alloy is used as a negative electrode active material, LiPF is dissolved in a non-aqueous mixed solvent containing a cyclic carbonate and an acyclic carbonate. By using a non-aqueous electrolyte, it is possible to put into practical use a secondary battery that has a high energy density and a long cycle life even when used at a high discharge capacity.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example 1] A coin-shaped secondary battery shown in FIG. 1 was manufactured by the following method. In addition, in the coin type secondary battery shown in Fig. 1,
In the figure, 1a is a positive electrode can, and 1b is a negative electrode can.

2 is a gasket, 3 is a positive electrode, 4 is a positive electrode current collector, 5 is a negative electrode, 6 is a negative electrode current collector, and 7 is a separator.

1 mol/Q aniline and 2 mol/Q HB as polymerization liquid
Using an aqueous solution containing F4, polyaniline was polymerized on a stainless steel mesh at a constant current with a current density of 6 mA/d. After washing this polyaniline with water and thoroughly drying it, 15n
A positive electrode 3 having a weight of 50 .mu.m was punched out to a size of mφ. Also, at this time, stainless steel is used as the positive electrode current collector 4 and the positive electrode can 1 is
It was joined to a. On the other hand, a lithium metal with a thickness of 300I1m was punched out to a size of 13mφ, which was used as the negative electrode 5, and LiPF with a concentration of 1.5 mol/Q was used as an electrolyte in a mixed solvent of ethylene carbonate and dimethyl carbonate (mixing ratio 50:50). A coin-type secondary battery (diameter 20+m+) shown in FIG.

A film with a thickness of 1.6 nm was fabricated.

[Example 2] Example 1 except that a mixed solvent of equal amounts of propylene carbonate and diethyl carbonate was used as the solvent for the electrolytic solution.
A battery was prepared in the same manner as the battery.

[Example 3] Example 1 except that a solvent in which benzene was added to a mixed solvent of equal amounts of ethylene carbonate and dimethyl carbonate (mixing ratio 45:45:10) was used as the solvent for the electrolytic solution.
A battery was prepared in the same manner as the battery.

[Comparative example]

Furthermore, for comparison, a battery was prepared in the same manner as in Example 1, except that an electrolytic solution having a concentration of 165 mol/Q in which LiBF was dissolved in a mixed solvent of equal amounts of propylene carbonate and dimethoxyethane was used as the electrolytic solution. Created.

A total of four batteries of Examples 1, 2.3 and Comparative Example above were charged to an upper limit voltage of 3.5■ with a constant current of 0.5 mA, and then charged with a constant current of 0.3 mA to a lower limit voltage of 2. , repeat the charge/discharge cycle of discharging to OV,
A charge/discharge test was conducted to measure the discharge capacity for each cycle. The results are shown in Figure 2.

From the results shown in Figure 2, the batteries of Examples 1 and 2.3 using nonaqueous electrolytes in which LiPF is dissolved in a mixed solvent of cyclic carbonate and acyclic carbonate can be charged and discharged for 200 cycles. It is recognized that the discharge capacity with an efficiency of approximately 60 to 70% of the initial discharge capacity is maintained even after repeated use.

On the other hand, in the battery of Comparative Example 1 using LiBF4, the discharge capacity rapidly decreased from approximately the 30th cycle, and the capacity was almost 0 at the 50th cycle.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of a coin-type secondary battery, and FIG. 2 is a graph showing changes in discharge capacity with respect to repeated charging and discharging of a secondary battery according to the present invention and a secondary battery of a comparative example. . 1a...Positive electrode can 2...Gasket 4...Positive electrode current collector 6...Negative electrode current collector 1b...Negative electrode can 3...Positive electrode 5...Negative electrode Applicant Brideston Co., Ltd. Agent Patent attorney Takashi Kojima

Claims (1)

[Claims] 1. In a secondary battery comprising a positive electrode using an organic conductive polymer material as an active material, a negative electrode using lithium or a lithium alloy as an active material, and a non-aqueous electrolyte, LiPF_6 is used as the non-aqueous electrolyte in a ring shape. A non-aqueous electrolyte secondary battery characterized by using a non-aqueous mixed solvent containing carbonate and acyclic carbonate.