JPH09251851A - Lithium battery and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong a charging/discharging cycle lifetime by forming the surface of a negative electrode base plate out of metal copper or stainless steel. SOLUTION: A negative electrode 30 made of metal lithium containing carbonate ions is electrically deposited on a negative electrode base plate 20 made of copper or stainless steel. A separator 60 impregnated with an electrolyte is interposed between a positive electrode 40 made of polypyrrole and the negative electrode 30. These elements are housed inside a negative electrode cover 10 and a positive electrode container 50 in a sealed manner. Consequently, it is possible to provide a lithium secondary battery having a long-term cycle lifetime.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a battery of a type in which carbonate ion is contained in negative electrode lithium and a method for producing the same, and more particularly to a negative electrode carrying negative electrode lithium containing carbonate ion. It is about improving the board.

[0002]

2. Description of the Related Art In recent years, batteries using lithium as a negative electrode active material have been attracting attention as high energy density batteries. These high energy density batteries are used as backup power sources for VTRs, communication devices, and computer memories, but further miniaturization and higher performance are required.

In these secondary batteries, lithium is used for the negative electrode, and the lithium is formed on the negative electrode substrate material by the electrode from the electrolytic solution. Propylene carbonate (PC), 1,2-dimethoxyethane (DM) as electrolyte
E), γ-butyrolactone (γ-BL), tetrahydrofuran (THF), dimethyl sulfoxide (DMS)
O), ethylene carbonate (EC) or the like non-aqueous solvent or a mixed solution of the above non-aqueous solvents, LiClO ₄ , LiB
It is composed of a solution of an electrolyte containing lithium ions such as F ₄ , LiAsF ₆ , LiPF ₆ , and LiCF ₃ SO ₃ .

It is considered that the deterioration of the charge and discharge characteristics of the lithium battery is due to the fact that the light metal of the negative electrode is consumed during charge and discharge because the efficiency of light metal deposition and elution is not 100%. For this reason, it is known that it is effective to fill the negative electrode with more lithium than the positive electrode capacity.

Although lithium metal itself reacts with almost all non-aqueous solvents, it is apparently stable because a thin protective film which is a reaction product substance formed on the surface of lithium suppresses the reaction. In the battery, the charge / discharge reaction takes place in the presence of this protective film, and therefore has a great influence on the battery characteristics. However, sufficient studies have not yet been made on this protective film, and it is considered that it is a film that has lithium ion conductivity because it can be charged and discharged and has no electron conductivity because the electrolytic solution is not reduced. Impurities in the electrolytic solution have a great influence on the protective film, and conversely, investigations using additives have been attempted from the same viewpoint. For example, "battery Handbook" 1989 May 20, 1995 by Maruzen Co., Ltd. issued # 328 pages, O _2, N ₂ LiI, together with a quinone imine dyes such as a charge-discharge efficiency increasing effect as an additive for the electrolyte solution, CO ₂ is being raised.

There have been many studies on the negative electrode substrate material used for this lithium battery, but in the case of adding carbon dioxide gas to the electrolytic solution, the inventors of the present invention published 1994 Vol. In the paper reported on pages 5,451-452, nickel is used as the negative electrode substrate material. Similarly, the inventors
As reported at the 6th battery discussion meeting (Abstracts, page 157), ordinary copper foil and buffed copper with a mirror-finished surface did not give good characteristics, so expensive titanium is preferable. Was known.

Until today, the charge / discharge cycle life, which is an important characteristic of the battery, is greatly affected by the influence of water mixed into the battery system, and therefore a stable and inexpensive battery can be supplied. It was difficult.

[0008]

SUMMARY OF THE INVENTION The present invention has been made under these circumstances, and provides an excellent lithium battery having a long charge / discharge cycle life and a method for manufacturing the same.

[0009]

According to the present invention, such an object is to provide a negative electrode containing metallic lithium as a main component, a positive electrode which reversibly electrochemically reacts with the lithium ion, and a movement of lithium ion. In a battery provided with an electrolyte, a lithium battery characterized in that the negative electrode metallic lithium contains carbonate ions and the surface of the negative electrode substrate is metallic copper or stainless steel. Here, when the negative electrode substrate is metallic copper, the surface thereof is not sufficient by ordinary buffing, and an extremely clean surface achieved by etching or the like is required. On the other hand, when the surface of the negative electrode substrate is stainless steel, etching is not essential and a clean surface may be used, but etching is more preferable.

The object of the present invention is also to manufacture a battery provided with a negative electrode containing metallic lithium as a main component, a positive electrode which reversibly carries out an electrochemical reaction with the lithium ion, and an electrolyte which is responsible for the movement of lithium ions. In the method, after removing the oxide film at the outermost surface by etching the negative electrode substrate containing copper as a main component for supporting the negative electrode metallic lithium,
This is achieved by a method for manufacturing a lithium battery, characterized in that the negative electrode lithium is electrodeposited in an organic solvent containing carbon dioxide gas.

When the negative electrode substrate is mainly composed of stainless steel, etching is not necessary, and a negative electrode mainly composed of metallic lithium, a positive electrode which reversibly electrochemically reacts with the lithium ion, and a lithium ion The object of the present invention is achieved by a method for producing a lithium battery, characterized in that the negative electrode lithium is electrodeposited in an organic solvent containing carbon dioxide gas in a battery provided with an electrolyte responsible for the transfer of

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a specific configuration of the present invention will be described in detail. The lithium battery of the present invention comprises a negative electrode formed by electrodepositing metallic lithium on a negative electrode substrate, a positive electrode that reversibly performs an electrochemical reaction with the lithium ion, and an electrolyte that is responsible for lithium ion transfer. There is.

The lithium negative electrode is formed on the negative electrode substrate material by electrodeposition from a non-aqueous solvent electrolyte. As this electrolytic solution, various conventionally known non-aqueous solvents or mixed solutions of these non-aqueous solvents can be used, but it is important to dissolve carbon dioxide gas. To dissolve carbon dioxide in the electrolytic solution, high purity carbon dioxide, for example, 99.99% purity
By flowing the above carbon dioxide gas into the electrolytic solution for a long time, for example, for 30 minutes or more, it is possible to produce an electrolytic solution in a substantially saturated state. Regarding the lower limit of the carbon dioxide concentration in the electrolytic solution, when bubbling 5 liter / min of carbon dioxide into 1 liter of the electrolytic solution, the effect can be obtained in 1 minute or more.
The actual amount of dissolution is preferably about 1.2 × 10 ² mol / m ³ , and the upper limit is the saturated solubility.

By depositing lithium from an electrolytic solution in which carbon dioxide gas is dissolved, carbonate ions are incorporated into the formed lithium film. It is still unclear in what form it is contained. The carbonate ions taken into the lithium film form a film of lithium carbonate on the surface of the negative electrode, which significantly improves the charge / discharge characteristics of the battery. In particular, the effect of suppressing dendrite growth on the electrode surface is remarkable.

High performance can be obtained by using copper or stainless steel instead of aluminum, titanium, nickel or the like which has been conventionally used as the negative electrode substrate material.
Copper or stainless steel is cheaper than conventional materials,
The industrial advantages are great.

However, in the case of copper, the charge and discharge characteristics are not good in a normal copper foil and a substrate whose surface is mirror-finished by bubbling. This is because the oxide film formed on the surface substantially contributes to the characteristics. Therefore, in addition to the usual buffing, surface etching treatment with an acid solution or the like is required. By etching treatment, the surface oxide film is removed, and lithium is electrodeposited with metallic copper on the surface to obtain high characteristics. The etching can be performed by dipping in a dilute aqueous acid solution having no oxidizing power, for example, a dilute sulfuric acid aqueous solution. It is also possible to ionize and remove the tetraamine copper ion with aqueous ammonia. Drying after etching is very important and is performed quickly in a non-oxidizing atmosphere so that the oxide film is not reformed. Since it is very difficult to obtain a perfect metal surface and it is costly from an industrial point of view, the metal state in the present invention means that when treated in a dilute acid aqueous solution as described above and quickly dried. Refers to the surface condition. High-sensitivity surface analysis such as photoelectron spectroscopy reveals a small amount of oxides, but to a much lesser extent than untreated surfaces. The copper substrate is preferably 99% or more in purity, and particularly preferably 99.9% or more in purity because it is influenced by impurities.

In the case of stainless steel, since the surface oxide film is extremely thin, it can be used as it is, but it is more preferable to perform etching treatment. The stainless steel here refers to an alloy in which nickel or chromium is added to iron to improve corrosion resistance, and in particular, corrosion-resistant austenitic steel, namely J
It is preferably selected from SUS301 to SUS385 by the symbol according to IS.

In the negative electrode substrate material that has been known so far, lithium ions diffuse inside the substrate to form a β-LiAl alloy in the case of aluminum, for example, and lithium ions diffuse well in this β-LiAl alloy. As a result, high charge / discharge characteristics were obtained. On the other hand, the substrate material of the present invention is characterized by using a material that does not form an alloy with lithium.

Why the combination of carbon dioxide effect and substrate material
It has not yet been clarified whether or not high characteristics can be obtained specifically. However, the inventors have found that the reduction reaction of the electrolytic solution component occurs before the lithium electrodeposition reaction occurs, but it is important that the reduction reaction is unlikely to occur. I think this is due to the large influence that the physical action has.

It is also possible to similarly use a substrate in which another material is used as the substrate base material and a thin film of copper or stainless steel is formed on the surface by a sputtering method or the like. The substantial behavior when using these thin film metals is exactly the same as when using bulk materials. Further, as the negative electrode substrate material, an alloy containing the above metal as a main component can also be used. In addition, the negative electrode is Li / containing lithium as a main component in addition to metallic lithium.
Al alloy or Li / Wood metal alloy may be used.

Further, it is particularly preferable to use a solid electrolyte as the electrolyte. As a solid electrolyte, an organic polymer composite containing a lithium salt, in particular, a polyethylene oxide (PEO) polymer compound in which lithium ions dissociated in an amorphous phase are conducted by interaction with ether oxygen is widely known. In addition, using a conductive polymer having a π-conjugated system such as polypyrrole or polyaniline in the molecular chain for the positive electrode and integrating the electrolyte and the electrode is also a preferable form from the viewpoint of adding new functions such as downsizing and weight reduction and thinning. There is one.

[0022]

EXAMPLES AND COMPARATIVE EXAMPLES The present invention will be described below with reference to specific examples and comparative examples. Examples 1 and 2 and Comparative Examples 1, 2 and 3 Using an electrolytic solution prepared by dissolving 1 mol of LiClO ₄ in 1 liter of propylene carbonate (PC), the purity was 99.9.
9% or more carbon dioxide gas was flowed in the electrolytic solution for 1 hour to obtain a carbon dioxide gas-dissolved electrolytic solution. Various negative electrode substrate materials shown in Table 1 were used. The substrate was buffed and then etched in an acid solution. The etching was carried out by immersing the substrate in a 10% by volume sulfuric acid aqueous solution at room temperature for 1 minute and then immediately drying it.
For comparison, a substrate without buffing and without etching was also used. As the initial electrodeposition, the electrodeposited at 1.0 C / cm ² at a current density of 1.0 mA / cm ² was used as the negative electrode. Further, for comparison, electrodeposition under the condition that carbon dioxide gas was not dissolved during electrolysis was also performed under the same conditions. A coin-type lithium secondary battery was manufactured by using the negative electrode thus manufactured, polypyrrole as the positive electrode, and propylene carbonate in which 1 molar equivalent of lithium perchlorate was dissolved in the electrolytic solution together with the polypropylene separator. A schematic diagram of this coin type lithium battery is shown in FIG. In the figure, a negative electrode 30 made of metallic lithium containing carbonate ions of the present invention is electrodeposited on a negative electrode substrate 20 made of copper or stainless steel, and a separator 60 impregnated with an electrolytic solution is interposed between the negative electrode substrate 20 made of copper or stainless steel and a positive electrode 40 made of polypyrrole. Intervenes. And these elements are the negative electrode lid 1.
0 and the positive electrode container 50 are housed and hermetically sealed. In the present coin-type lithium battery, the place where the amount of lithium charged in the negative electrode (the amount of initial electrodeposition) is usually excessive is used. To evaluate the characteristics of the negative electrode, the electrical capacity of the polypyrrole used for the positive electrode is determined by the surface area of the negative electrode. It is a large excess. The above experiment was naturally performed in a glove box filled with high-purity argon gas. The charging / discharging test was performed with a charging / discharging electricity quantity of 0.2 C / cm ² , and the termination condition was set when the battery potential reached 2.0V. The charge / discharge characteristics of Example 1 are shown in FIG. Table 1 shows the evaluation results. In addition,
When the initial electrodeposition was carried out at 10 C / cm ² in a sufficiently excessive amount, Comparative Examples 2 and 3 also exhibited charge / discharge life characteristics of 3000 times or more, and in Examples, further characteristics were exhibited. This indicates that the charge / discharge life depends largely on the amount of initial electrodeposition. Therefore, it is difficult to compare the cycle life test results by the absolute value, and it should be noted that the effect of the present invention can be confirmed only by the relative value by comparison with the reference sample. In this Example and Comparative Example, the experiment was carried out under relatively short initial electrodeposition conditions in order to improve the efficiency of the experiment.
Needless to say, it is desirable to exhibit a high cycle life with a smaller amount of initial electrodeposition.

[0023]

[Table 1]

From these results, it is found that the lithium battery of the present invention has excellent charge / discharge characteristics, and the effect of the present invention is clear. Further, although the coin type non-aqueous solvent battery has been described in the above-mentioned embodiment, the present invention is not limited to this, and the same can be applied to a cylindrical non-aqueous solvent battery and a rectangular non-aqueous solvent battery.

[0025]

The lithium battery of the present invention provides a lithium secondary battery having excellent charge / discharge characteristics, that is, a long cycle life.

[Brief description of drawings]

FIG. 1 is a schematic view showing the structure of a coin-type lithium secondary battery of the present invention.

FIG. 2 is a diagram showing charge / discharge characteristics of Example 1 of the present invention.

[Explanation of symbols]

 10 Negative Lid 20 Negative Substrate 30 Negative Electrode (Lithium) 40 Positive Electrode 50 Positive Electrode Container 60 Separator

Claims (3)

[Claims] 1. A negative electrode containing metallic lithium as a main component, and a positive electrode that reversibly undergoes an electrochemical reaction with the lithium ions,
And a battery provided with an electrolyte responsible for the transfer of lithium ions, wherein the lithium metal of the negative electrode contains carbonate ions, and the substrate surface is selected from metallic copper and stainless steel. . 2. A negative electrode containing metallic lithium as a main component, and a positive electrode that reversibly undergoes an electrochemical reaction with the lithium ions.
Further, in a battery provided with an electrolyte that is responsible for the transfer of lithium ions, in a lithium battery in which the negative electrode metallic lithium base body is mainly composed of copper, the negative electrode base body is etched to remove the oxide film on the outermost surface portion of the negative electrode lithium A method for producing a lithium battery, which comprises performing electrodeposition in an organic solvent containing carbon dioxide gas. 3. A negative electrode containing metallic lithium as a main component, and a positive electrode that reversibly electrochemically reacts with the lithium ions,
In addition, in a battery provided with an electrolyte that is responsible for the transfer of lithium ions, in a lithium battery in which the metallic lithium base material of the negative electrode is mainly composed of stainless steel, the negative electrode lithium is electrodeposited in an organic solvent containing carbon dioxide gas. A method for manufacturing a featured lithium battery.