JP2004063156A - Nonaqueous solution electrolyte secondary cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a manufacturing problem of a battery short life by decomposing an electrolyte when a coating film is damaged by water infiltrating in a middle of a manufacturing process because in the case of Al usually used for a positive electrode current collection of a Li secondary cell, anticorrosion is not enough because of reaction of the coating film of an Al surface with acid and alkali. <P>SOLUTION: Based on two features found that a precise surface coating film of an Hf is effective in restraining decomposition of an electrolyte in an organic electrolyte including fluorine anion and is an anticorrosion coating film strong against a water solution system, influence of moisture is reduced by covering a good conductive Al metal surface or the like with Hf or its alloy and a Li secondary cell is manufactured with a stable manufacturing condition. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a non-aqueous electrolyte secondary battery. In particular, the present invention relates to a non-aqueous electrolyte lithium ion secondary battery using a lithium composite oxide containing a transition metal or a typical metal as a positive electrode active material.
[0002]
[Prior art]
Lithium rechargeable batteries, especially lithium ion rechargeable batteries, are one of the newest batteries among the many batteries known so far, and since lithium rechargeable batteries were first proposed to this day The speed of development, commercialization, dissemination, and growth during this period is outstanding and impressive. Now, the position as an indispensable power source for mobile phones and new electronic devices is becoming established. In fact, it is clear from various statistics that the production volume of mobile phones has shown a rapid increase with the spread of mobile phones, and this momentum is also in line with the social needs for diversification and leveling of electricity. In addition, it is expected that it will continue to develop in the future, but will not decline. In other words, it is expected that its role as a power storage device will be widely established in society and its role will be further increased.
[0003]
Almost all lithium-ion secondary batteries currently in practical use use an aluminum foil as a positive electrode current collector, and a lithium composite oxide such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₂ is used for the aluminum foil. A paste obtained by mixing a positive electrode active material powder selected from a mixture with a binder / solvent into a paste is applied to an appropriate thickness and dried to obtain a positive electrode. The negative electrode is obtained by coating and drying. The two electrodes thus obtained are superposed in the order of a negative electrode, a separator (polymer microporous membrane), a positive electrode, and a separator, and are wound into a cylindrical shape and housed in a cylindrical or prismatic battery can. In addition, various devices such as a non-aqueous electrolyte and a switch mechanism for interrupting a current for safety such as prevention of temperature rise, elements and the like are incorporated as a battery.
[0004]
Here, the non-aqueous electrolyte used for the lithium ion secondary battery has an electrolyte serving as a lithium ion source dissolved in a high dielectric constant solvent. Examples of the high dielectric constant solvent include DEC (Diethyl carbonate), DMC (Dimethyl carbonate), DME (1,2-Dimethyoxyethane), EC (Ethylene carbonate), EMC (Ethyl methyl carbonate-NMP-Nylon-Nylon-Nepoxide-Nylon-Nylon-Nylon-Nepoxide-Nylon-Nylon-Nepoxide-Nylon-N-Methoxy-N-Ethyl Carbonate-Nylon-N-Ethyl Carbonate) ), PC (Propylene carbonate), GBL (γ-Butyrolactone) and the like are used alone or, for example, in EC / DEC (1: 1) V / V%, EC / DMC (1: 1) V / V% is used by mixing at an appropriate mixing ratio.
[0005]
As an electrolyte serving as a lithium ion source, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , Et ₄ NBF ₄ , Et _{4 having} high solubility in an organic solvent are used. NPF ₆ , LiN (SO ₂ C ₂ F ₅ ) _{2 and the} like are known and used. These materials are not necessarily uniform in terms of ionic conductivity, temperature characteristics, cycle characteristics, and the like.Either of them is selected according to the battery characteristics to be set or the type of solvent to be combined. Since the liquid properties change, they are determined in total.
[0006]
As a separator for a lithium ion secondary battery, a microporous polyolefin membrane is used. That is, polyethylene, polypropylene or a combination thereof is used. As a function of this separator, it has been required to selectively transmit only ions during charge and discharge while preventing electrical contact between the positive electrode and the negative electrode. In order to prevent abnormal short-circuiting or overcharging and discharging between the electrodes in order to prevent the battery from being heated to a high temperature, ions can be transmitted when the battery reaches a certain heating temperature. There has also been developed and provided one designed to melt the hole to be spontaneously, thereby closing the hole, interrupting the flow of ions, and also acting as a so-called thermal fuse for interrupting the current.
[0007]
The outline of the lithium ion secondary battery as the non-aqueous electrolyte secondary battery has been described above. As described above, aluminum is used as the positive electrode current collector of this secondary battery. That is, a metal that withstands anodic polarization of 3 V or more during charging, reduces the weight of the battery, shows corrosion resistance to the organic electrolyte, and forms an insulating film that protects the organic electrolyte from decomposition. Aluminum has been widely used (JP-B 4-52592).
[0008]
In particular, in order to maintain stable battery performance, it is required that the current collector and the organic electrolyte are materially stable and do not react with each other or deteriorate.
For this purpose, the current collector forms a stable and dense passive film on its surface, which shows corrosion resistance to the organic electrolyte and protects the organic electrolyte from decomposition by an insulating film. Must be formed metal.
[0009]
[Problem to be solved]
However, aluminum is an amphoteric metal and is easily attacked by acids and alkalis. Therefore, when the insulating film is damaged in the process of manufacturing the positive electrode current collector, there is a troublesome problem that the decomposition of the organic electrolyte is promoted and the life of the lithium secondary battery is shortened. There are many restrictions on the drugs used in solvation and the like. For example, at the stage of purchasing aluminum, rolling oil is attached to the surface of the aluminum, and cannot be used as an electrode material as it is. That is, when this is used as an electrode material, it must be degreased. Alkali is used to degrease the rolling oil, but the alkali treatment may create pinhole defects that cannot be removed from the aluminum surface film, and may impair the insulation performance of the positive electrode current collector. In addition, in the step of applying the positive electrode mixture to the positive electrode current collector, the aluminum surface film changes to a hydroxide or the like depending on the moisture concentration of the solvent of the binder of the positive electrode mixture slurry and the solvent drying conditions. The insulation performance of the current collector may be impaired. The present invention has many problems as described above in using aluminum as a positive electrode current collector. Therefore, the present invention provides a positive electrode current collector material that does not cause such problems, and a non-aqueous solution that does not have any problem due to the material design. It is intended to provide an electrolyte secondary battery.
[0010]
[Means for Solving the Problems]
In order to solve the above problem, the present inventors have conducted intensive studies and found that a dense surface film of hafnium suppresses decomposition of an electrolyte in an organic electrolyte containing a fluorine anion (LiPF ₆ / PC + DME, LiBF ₄ / PC + DME, etc.). It has been found that it has the two features that it is effective for water and that it is a corrosion-resistant film that is strong against aqueous solutions.
That is, the first is, (1) LiMnO the battery positive electrode active material _{2, LiMn 2 O 4, LiNiO} 2, LiCoO 2, LiVO 2, LiV 2 O 4, LiCrO 2, LiFeO 2, LiTiO 2, LiScO 2, LiYO _In a non-aqueous solution secondary battery using a lithium composite oxide containing a transition metal or a typical metal such as _2, and a lithium salt of an anion containing fluorine such as LiPF ₆ or LiBF ₄ as an electrolyte, at least as a positive electrode current collector, The problem is solved by forming a non-aqueous electrolyte secondary battery characterized by being a positive electrode current collector whose outer surface is made of a material made of hafnium or a hafnium-based alloy.
[0011]
The second feature is that (2) the positive electrode current collector has a metal substrate, and hafnium or a hafnium alloy is deposited, sprayed or plated on the substrate. This problem is solved by configuring a non-aqueous electrolyte secondary battery.
[0012]
Thirdly, (3) the non-aqueous electrolyte secondary battery according to the above (1) or (2), wherein the metal base is made of a base material made of aluminum. Is to be solved.
[0013]
Its fourth, (4) a lithium complex oxide as a positive electrode active material is _{LiMnO 4, LiMn 2 O 4,} LiNiO 2, LiCoO 2, LiV0 2, LiV 2 O 4, LiCrO 2, LiFeO 2, LiTiO 2, LiScO ₂ , a lithium composite oxide containing at least one transition metal or a typical metal selected from LiYO ₂ , which is solved by configuring the non-aqueous electrolyte secondary battery according to the above item (1). Is what you do.
[0014]
Fifthly, (5) Lithium salt of fluorine-containing anion, LiPF ₆ or LiBF ₄ is used as the lithium salt, which is solved by configuring the non-aqueous solution secondary battery according to the above (1). It is.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described based on experiments described below.
According to the present invention, as described above, the dense surface film of hafnium is effective in suppressing the decomposition of an electrolytic solution in an organic electrolytic solution containing a fluorine anion (LiPF ₆ / PC + DME, LiBF ₄ / PC + DME, etc.), and an aqueous solution Lithium secondary battery, which has two features of being a corrosion resistant film that is highly resistant to corrosion, is made by plating hafnium or a hafnium alloy on a metal surface with good conductivity such as hafnium, a hafnium alloy, or aluminum by vapor deposition, thermal spraying, or deposition. Of this positive electrode current collector.
Hafnium is a valve metal like aluminum, and forms a dense film on the surface in an organic electrolytic solution containing a fluorinated anion such as LiPF ₆ or LiBF ₄ . Further, the film has a high insulating property and an extremely low electron conductivity. This can also be confirmed from the voltammogram of hafnium in LiPF ₆ / PC + DME shown in FIG.
[0016]
As can be seen in FIG. 1, when a sweep potential is applied between hafnium and silver electrodes facing each other in the organic electrolyte LiPF ₆ / PC + DME with hafnium as the positive electrode, the current flowing between the electrodes from about 1.5 V in the first cycle. Rapidly increases, and thereafter becomes a substantially constant current. This current acts to form a coating on the surface of the hafnium electrode. When the potential applied to the electrodes reaches 5 V and then is swept so that the potential decreases, the current sharply decreases. When a film is formed on the surface of the hafnium electrode in this way, almost no current flows in the potential sweep after the second cycle.
This indicates that hafnium is one of the few metals having an effect on corrosion resistance and suppression of electrolytic solution decomposition in LiPF ₆ / PC + DME.
[0017]
Therefore, if hafnium is used as a positive electrode current collector of a lithium secondary battery, it is extremely effective in suppressing decomposition of an electrolytic solution. Furthermore, unlike aluminum, hafnium has a property that it is hardly soluble in acids and does not react even when heated with an aqueous alkaline solution. Thus, by using hafnium for the positive electrode current collector of the lithium secondary battery, the current collector does not corrode even if the slurry becomes alkaline using an aqueous solution of the solvent of the positive electrode mixture slurry. There is also a method of using a positive electrode current collector in which hafnium metal is plated on the surface of an aluminum base material in order to reduce the cost of hafnium and improve mechanical workability.
For this reason, the influence of moisture taken in during the manufacturing process of the positive electrode current collector is reduced, and a lithium secondary battery can be manufactured under stable manufacturing conditions.
[0018]
In the above, the gist of the present invention has been referred to exclusively based on the positive electrode current collector material.However, the present invention is merely a non-aqueous electrolyte secondary battery, and is naturally provided with elements other than the positive electrode current collector. That is. However, the disclosure is entirely left to the prior art. The following experiments were performed to disclose the present invention so that it can be understood and put into practice. This experiment replaces the embodiment.
[0019]
【Example】
The embodiment of the present invention is based on the following experiment as described above.
Experiment;
(Preparation of electrolyte solution);
First, an electrolytic solution was prepared. As the electrolyte, LiPF ₆ and LiBF ₄ are used as the electrolyte, and this is dissolved in a mixed solvent (1: 1 vol ratio) of DME (1,2-dimethyloxyethane) and PC (Propylene carbonate) to have a concentration of 1 mol. Was prepared. To 300 ml of the prepared electrolyte, 30 g of molecular sieve 4A (4 to 12 mesh) heated and dehydrated for 4 hours in a stream of 400 ° C. Ar was added, and the mixture was shaken in a Teflon (registered trademark) bottle for about 30 minutes to remove water. The water content was kept at 50 ppm or less by adsorption dehydration. The moisture concentration in the electrolyte was measured by a Karl Fischer moisture meter (Hiranuma automatic moisture meter AQV-200).
[0020]
(Cyclic voltammogram = film insulation, corrosion resistance test);
Prepare as many beakers as the number of test specimens, put the above-mentioned electrolyte solution into each beaker, immerse the hafnium (hereinafter referred to as metal sample) to be measured in each electrolyte solution, and use this as one electrode (sample electrode). A platinum electrode was set on the other electrode (counter electrode). A silver electrode was set as a potential measurement reference (reference electrode). A current was applied to the counter electrode so that the voltage between the sample electrode and the reference electrode became a predetermined voltage, and the voltage and current at that time were measured. The potential sweep speed was 0.1 V / s.
[0021]
At the time of this measurement, a sample metal sample (0.5 mmφ) was used, which was sufficiently degreased by alkali treatment or the like, and this was cut off from the atmosphere in a glove box, that is, the metal was Alternatively, a sample which had been sufficiently dried so as not to be degraded by nitrogen and was directly sandwiched between stainless steel lead screws and fixed was used as a sample electrode.
[0022]
The result was as shown in FIG. That is, FIG. 1 shows a cyclic voltammogram of hafnium in LiPF ₆ / PC + DME (applied voltage: 3 V, standard electrode Ag). According to this experiment, a flat current was observed in the first cycle due to the potential sweep at a constant speed, and this behavior was characteristic of the high electric field mechanism where the film formation current was exponentially proportional to the electric field strength inside the film. It was found that a dense barrier film was formed on the hafnium surface.
[0023]
From the above results, hafnium is a metal that exhibits corrosion resistance in LiPF ₆ / PC + DME and is effective in suppressing the decomposition of the electrolytic solution. Therefore, the lithium composite oxide is used as the positive electrode active material, and the electrolytic solution is made of fluorine. In a non-aqueous electrolyte secondary battery containing a lithium salt of an anion containing hafnium, by using hafnium as a positive electrode current collector material, the disadvantages of the conventional method using aluminum metal are eliminated, and in non-aqueous secondary battery technology, It is thought that he was able to cross one wall.
[0024]
The hafnium used was of high purity (99.99%). However, as an embodiment of the invention, there is no adverse effect as a positive electrode current collector, and a charge / discharge cycle is started, and the battery characteristics are not affected. As far as possible, setting and using a hafnium-based alloy is included as an embodiment of the present invention without any problem.
[0025]
The electrolyte to be used is a non-aqueous electrolyte containing a lithium salt of an anion containing fluorine, which is a requirement, but the composition of the solution actually prepared includes various stabilizers including other electrolytes, The use of additives, and the addition and blending of such additives, may be included in the embodiments of the present invention.
[0026]
【The invention's effect】
The present invention provides that the use of hafnium having a corrosion resistance to aluminum from aqueous as a positive electrode current collector, of aluminum, the pretreatment agent and for the choice of aqueous solvent of the slurry becomes wider, the upper LiPF ₆ This is extremely significant because an electrolytic solution containing a lithium salt of a fluorine-containing anion, such as LiCl or LiBF _4, can form an insulating film that exhibits corrosion resistance and protects the electrolytic solution from decomposition.
[Brief description of the drawings]
FIG. 1 is a voltammogram of hafnium in LiPF6 / PC + DME.

Claims (5)

In a non-aqueous electrolyte secondary battery in which a lithium composite oxide is used as a positive electrode active material and the electrolyte contains a lithium salt of an anion containing fluorine, at least the outer surface of the positive electrode current collector is made of hafnium or a hafnium-based alloy. A non-aqueous electrolyte secondary battery characterized by being a positive electrode current collector made of a material comprising: The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode current collector has a metal substrate, and hafnium or a hafnium alloy is deposited, sprayed or plated on the substrate. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein said metal base is made of a base material made of aluminum. At least a lithium composite oxide as a positive electrode active material is selected from _{LiMnO 4, LiMn 2 O 4,} LiNiO 2, LiCoO 2, LiV0 2, LiV 2 O 4, LiCrO 2, LiFeO 2, LiTiO 2, LiScO 2, LiYO 2 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is a lithium composite oxide containing one kind of transition metal or typical metal. Non aqueous secondary battery according to claim 1, wherein the LiPF _6, LiBF ₄ is used as the lithium salt of the anion containing fluorine.

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