JP2009117081A - Electrolyte solution for lithium-ion secondary battery and lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrolyte solution for a lithium-ion secondary battery with generating risk of micro short circuiting remarkably reduced. <P>SOLUTION: The electrolyte solution for the lithium-ion secondary battery contains one kind or two or more kinds of compounds selected from a group consisting of bathocuproine, bathocuproine sulfonate, 4, 7-diphenyl-1, 10-phenanthroline disulfonic acid, thiadiazole kinds, 2-(5-bromo-2-pyridylazo)-5-(N-propyl-3-sulfopropylamino) phenol, 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino) aniline, 4-(2-pyridylazo) resorcin, salicylaldoxime, α-benzoin oxime, dimethyl glyoxime, aluminon, 8-hydroxyquinoline and their derivatives, and a nonaqueous electrolyte solution. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrolyte for a lithium ion secondary battery and a lithium ion secondary battery including the electrolyte for a lithium ion secondary battery.

  With the recent development of electronic technology, mobile communication devices and portable computers have become widespread. As a power source for these portable devices, a high energy density secondary battery is considered promising. In particular, a lithium ion secondary battery, which is a nonaqueous electrolyte secondary battery, can be expected to have a high voltage, and thus can contribute to downsizing and weight reduction of equipment. In addition, lithium ion secondary batteries are also promising as hybrid automobile batteries that have been attracting attention in recent years as countermeasures for environmental problems, and their development has been accelerated.

A lithium ion secondary battery has a configuration in which a positive electrode and a negative electrode including an active material capable of inserting and extracting lithium are arranged via a separator. The positive electrode is a positive electrode mixture in which LiCoO ₂ as a positive electrode active material, LiNiO ₂ , LiMn ₂ O ₄ or the like, carbon black or graphite as a conductive agent, polyvinylidene fluoride as a binder, latex, rubber or the like is mixed. It is formed by coating on a positive electrode current collector made of aluminum or the like. On the other hand, the negative electrode is formed by coating a negative electrode current collector made of copper or the like with a negative electrode mixture obtained by mixing polyvinylidene fluoride, latex, rubber, or the like as a binder with coke or graphite as a negative electrode active material. Is done. The separator is made of porous polyethylene, porous polypropylene, or the like, and has a very thin thickness of several μm to several hundred μm. And the said positive electrode, a negative electrode, and a separator are impregnated with electrolyte solution. As the electrolytic solution, an electrolytic solution in which a lithium salt such as LiPF ₆ is dissolved in an aprotic solvent such as propylene carbonate or ethylene carbonate or a polymer such as polyethylene oxide is used.

  In such a lithium ion battery, a short circuit called a micro short circuit may occur as described in Patent Document 1. As a cause of this micro short circuit, when a minute amount of metal impurities in the manufacturing process, particularly due to copper contamination, and the deterioration of the positive electrode and the current collector gradually progress, copper, cobalt, nickel, In some cases, metal ions such as manganese are eluted in the battery, and the metal is deposited on the electrode by repeated charge and discharge.

In order to solve the above problem, for example, Patent Document 2 discloses that as a means for capturing a manganese component eluted from the positive electrode, lithium phosphate, lithium tungstate, lithium silicate, aluminite, lithium borate, molybdate acid in the positive electrode A method of adding a scavenger selected from the group of lithium and cation exchange resins is disclosed.
Patent Document 3 discloses a method in which a functional group comprising a hydroxyl group, a carboxylic acid group, a sulfonic acid group, or a salt thereof is imparted to the surface of a separator made of a nonwoven fabric.
Furthermore, Patent Document 4 discloses a method of modifying the separator surface with a cation exchange resin such as carboxylic acid or sulfonic acid for the purpose of capturing manganese eluted from the manganese-based positive electrode. However, a large amount of lithium ions are present in the electrolyte, and lithium has a very low electronegativity, so even if there is a cation exchange group as described above, it is eluted in a trace amount. It is difficult to efficiently capture heavy metals such as copper.

On the other hand, as a method for selectively capturing heavy metals, a method using a chelate functional group that coordinately binds heavy metal ions has been studied. For example, Patent Document 5 discloses a method of containing a chelate polymer in at least one of a positive electrode, a negative electrode, and a separator.
Patent Document 6 describes a method of adding a chelating agent or a chelating resin to a positive electrode or a negative electrode in a secondary battery using a manganese-based positive electrode.
Furthermore, Patent Document 7 discloses a method of adding a chelating agent to a binder, a separator, and an electrolyte.

JP 2005-209528 A JP 2000-11996 A JP 2000-268799 A JP 2002-25527 A Japanese Patent Laid-Open No. H11-121021 JP 2000-195553 A JP 2004-63123 A

  However, even if a low molecular weight compound such as a chelating agent is added, diffusion easily occurs in the battery, and the chelated heavy metal ion is reduced on the active electrode, resulting in a micro short circuit. End up. The binder is generally composed of a polymer such as polyvinylidene fluoride (PVDF) or a styrene butadiene copolymer, while the separator is composed of a polyolefin such as polyethylene or polypropylene. The polymers that make up such binders and separators have very poor adhesion to polymers with polar groups such as chelate groups and are also very poor in compatibility, so they can be mixed uniformly. It is accompanied by peeling from the interface and a decrease in strength of the binder and separator.

  In addition, as a reagent for precipitating metal ions in water, a metal gravimetric reagent is generally known. As a result of the study by the present inventors, in an organic solvent-based non-aqueous electrolyte, a metal such as Cu is used. It has been found that there are compounds capable of effectively precipitating ions and compounds that are not.

  In view of the above circumstances, an object of the present invention is to provide an electrolytic solution for a lithium ion secondary battery that significantly reduces the risk of occurrence of micro shorts.

  As a result of intensive studies to solve the above problems, the present inventors have found that a lithium ion secondary battery electrolyte containing a specific compound and a non-aqueous electrolyte can significantly reduce the risk of micro short-circuit occurrence. The present invention has been completed.

That is, the present invention is as follows.
[1]
Bathocuproin, sulfonated bascuproin, 4,7-diphenyl-1,10-phenanthroline disulfonic acid, thiadiazoles, 2- (5-bromo-2-pyridylazo) -5- (N-propyl-3-sulfopropylamino) phenol 2- (5-bromo-2-pyridylazo) -5- (N-propyl-N-sulfopropylamino) aniline, 4- (2-pyridylazo) resorcin, salicylaldoxime, α-benzoin oxime, dimethylglyoxime, An electrolytic solution for a lithium ion secondary battery, comprising one or two or more compounds selected from the group consisting of aluminone, 8-hydroxyquinoline, and derivatives thereof, and a nonaqueous electrolytic solution.
[2]
Content of the said compound is 0.0001 mass%-10 mass% electrolyte solution for lithium ion secondary batteries of said [1] description.
[3]
The thiadiazole is selected from the group consisting of 2,5-dimercapto-1,3,4-thiadiazole, 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione, and alkali metal salts thereof. The electrolyte solution for lithium ion secondary batteries according to the above [1] or [2], which is one kind or two or more kinds.
[4]
It is a lithium ion secondary battery provided with a positive electrode, a negative electrode, and the separator interposed between the said positive electrode and the said negative electrode, Comprising: The said lithium ion secondary battery is any one of said [1]-[3]. A lithium ion secondary battery comprising an electrolyte for a lithium ion secondary battery.

  ADVANTAGE OF THE INVENTION According to this invention, the electrolyte solution for lithium ion secondary batteries which reduced notably the generation | occurrence | production risk of a micro short circuit can be provided.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as the present embodiment) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

[Electrolyte for lithium ion secondary battery]
The electrolyte for the lithium ion secondary battery of this embodiment includes bathocuproin, sulfonated bascuproin, 4,7-diphenyl-1,10-phenanthroline disulfonic acid, thiadiazoles, 2- (5-bromo-2-pyridylazo ) -5- (N-propyl-3-sulfopropylamino) phenol, 2- (5-bromo-2-pyridylazo) -5- (N-propyl-N-sulfopropylamino) aniline, 4- (2-pyridylazo) ) One or more compounds selected from the group consisting of resorcin, salicylaldoxime, α-benzoin oxime, dimethylglyoxime, aluminone, 8-hydroxyquinoline, and derivatives thereof; a non-aqueous electrolyte; including.

  The said specific compound contained in the electrolyte solution of this Embodiment is 1 type of what is called the gravimetric analysis reagent for metals. The gravimetric reagent for metals forms a sparingly soluble precipitate with heavy metals such as iron, lead, gold, platinum, copper, chromium, cadmium, zinc, arsenic, manganese, cobalt, molybdenum, tungsten, tin, and bismuth. In this embodiment, the specific metal gravimetric analysis reagent is contained in the electrolytic solution.

  The specific compound has a very low solubility product of a complex with a heavy metal ion. Therefore, even in an organic solvent-based non-aqueous electrolyte, metal ions (eg, Ni ion, Cu ion, Co ion) eluted from an electrode or the like. And the like) efficiently to generate precipitates, it is possible to effectively prevent the occurrence of micro-shorts caused by crystal growth of the eluted metal ions and straddling between the electrodes.

  Among these compounds, thiadiazoles that form a heterocyclic ring composed of nitrogen and sulfur are preferred in order to form a complex that takes a bridge structure with heavy metal ions, and 2,5-dimercapto-1,3,4-thiadiazole is preferred. 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione, and alkali metal salts thereof are more preferable. When supplied in the form of an alkali metal salt, for example, it is supplied in the form of a lithium salt, potassium salt, sodium salt or the like. Here, 2,5-dimercapto-1,3,4-thiadiazole is “bismuthiol I”, and potassium salt of 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione is “bismuthiol”. II ".

  As content of the said compound, Preferably it is 0.0001 mass%-10 mass% with respect to the electrolyte solution for lithium ion secondary batteries, More preferably, it is 0.0001 mass%-5 mass%, More preferably, it is 0.00. 001 mass% to 5 mass%. When the content of the compound is 0.0001% by mass or more, the effect of preventing a micro short circuit tends to be remarkable, and when the content is 10% by mass or less, even when a lithium ion secondary battery is used for a long time. The possibility of causing deterioration of the constituent members is reduced.

  Examples of the non-aqueous electrolyte contained in the lithium ion secondary battery electrolyte of the present embodiment include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate; Examples include lactones such as gamma butyl lactone; ethers such as dimethyl ether; cyclic ethers such as tetrahydrofuran and dioxane; acetonitrile and the like. Among these, from the viewpoint of ensuring high ion conductivity, in particular, cyclic carbonate and chain carbonate A mixture is preferred, and a mixture of ethylene carbonate and methyl ethyl carbonate is more preferred.

  When a mixture of ethylene carbonate and methyl ethyl carbonate is used, the mixing ratio between the two is preferably (ethylene carbonate) / (methyl ethyl carbonate) (mass ratio), preferably 1/9 to 9/1, more preferably 3 / 7-7 / 3.

  As the non-aqueous electrolyte, one modified with fluorine, silicon or the like may be used for the purpose of reducing the decomposition of the non-aqueous electrolyte in the battery.

In addition to the specific compound and non-aqueous electrolyte described above, the electrolyte for a lithium ion secondary battery of the present embodiment can further include various lithium salts. Examples of such lithium salts include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , and LiAsF ₆ ; LiN (SO ₂ CF ₂ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CHF _{2) 2} and lithium imide salts such are preferably used. The concentration of the lithium salt in the electrolytic solution is preferably 0.1 to 2 mol / L.

[Lithium ion secondary battery]
The lithium ion secondary battery of the present embodiment has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the lithium ion secondary battery is included in the secondary battery. Including secondary battery electrolyte.

A metal oxide active material can be used as the positive electrode. As the metal oxide-based active material, for _{example, LiCoO 2, LiMn 2 O 4} , LiNiO 2, LiNi 1/3 Mn 1/3 Co 1/3 O 2, LiNi x Co 1-x O 2, LiFePO 4 or the like Can be mentioned. The metal oxide active material may be used alone, or a plurality of metal oxide active materials may be mixed and used.

  The average particle diameter of the metal oxide active material is preferably 0.1 μm to 100 μm, more preferably 1 μm to 10 μm. In the present embodiment, the “average particle diameter” means a 50% cumulative diameter value in measurement using a laser diffraction particle size distribution method.

  For example, a positive electrode mixture-containing paste is prepared by dispersing, in a solvent, a positive electrode mixture obtained by adding a conductive additive, a binder, or the like to the above active material as necessary. Next, this positive electrode mixture-containing paste is applied to a positive electrode current collector made of an aluminum foil or the like, dried to form a positive electrode mixture layer, and pressurized as necessary to adjust the thickness.

  Here, the solid content concentration in the positive electrode mixture-containing paste is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass.

  On the other hand, as the negative electrode, a carbonaceous material is suitably used as the active material. More specifically, for example, graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, graphite, carbon colloid, etc. are preferably used. It is done. The carbonaceous material may be used alone, or a plurality of carbonaceous materials may be mixed and used.

  The average particle size of such a carbonaceous material is preferably 0.1 μm to 100 μm, more preferably 1 μm to 10 μm.

  The negative electrode is prepared by, for example, preparing a negative electrode mixture-containing paste by dispersing, in a solvent, a negative electrode mixture prepared by adding a conductive additive or a binder as necessary to the negative electrode active material made of the carbonaceous material. Next, the negative electrode mixture-containing paste is applied to a negative electrode current collector, dried to form a negative electrode mixture layer, and pressurized as necessary to adjust the thickness.

  Here, the solid content concentration in the negative electrode mixture-containing paste is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass.

  Examples of the conductive aid used as necessary in the production of the positive electrode and the negative electrode include graphite, acetylene black, carbon black, ketjen black, and carbon fiber. Examples of the binder include PVDF, PTFE, polyacrylic acid, styrene butadiene rubber, and fluorine rubber.

  The average particle size of such a conductive assistant is preferably 0.1 μm to 100 μm, more preferably 1 μm to 10 μm.

  As the separator, for example, a woven fabric, a nonwoven fabric, a synthetic resin microporous material, or the like can be used, and among them, a synthetic resin porous membrane can be preferably used. As the synthetic resin porous membrane, a polyolefin-based microporous membrane such as a microporous membrane made of polyethylene and polypropylene, or a microporous membrane obtained by combining these is preferably used.

  The positive electrode and the negative electrode can be formed as a battery by being wound with a separator interposed therebetween to obtain a laminated structure of a wound structure, or by forming a laminated body by bending or laminating a plurality of layers. The lithium ion secondary battery of this embodiment can be manufactured by pouring the electrolyte of this embodiment into the interior and sealing it. The battery form of the lithium ion secondary battery of the present embodiment is not limited to a specific one, and a cylindrical shape, an elliptical shape, a rectangular tube shape, a button shape, a coin shape, a flat shape, a laminate shape, and the like are preferably used. .

Next, the present embodiment will be described more specifically with reference to examples and comparative examples. However, the present embodiment is not limited to the following examples unless it exceeds the gist. In addition, the physical property in an Example was measured with the following method.
(1) Copper ion concentration (ppm) in the supernatant
The measurement of the copper ion concentration in the supernatant was performed using an ICP emission analyzer (Optima 5300 DV) manufactured by PerkinElmer.
(I) Preparation of solution Bismuthiol II (manufactured by Dojin Chemical Co., Ltd .: trade name Bismuthiol-II) was added to a nonaqueous electrolytic solution (ethylene carbonate / methyl ethyl carbonate = 1/2) containing 1 mol / L LiBF ₄ in the table below. A predetermined amount shown in 1 was dissolved to prepare an electrolyte for a lithium ion secondary battery.
A predetermined amount of Cu (BF ₄ ) ₂ shown in Table 1 below was added to this electrolytic solution and allowed to stand overnight at room temperature. Subsequently, this solution was centrifuged at 12,000 rpm for 20 minutes, and the following pretreatment was performed in order to measure the copper ion concentration in the sample supernatant by ICP-luminescence analysis.
(Ii) Preparation of ICP-luminescence analysis sample 1 mL of the sample supernatant was added to a platinum crucible and dried on a 260 ° C. hot plate for 1 hour, followed by ashing at 450 ° C. for 3 hours in an electric furnace. 1 mL of concentrated hydrochloric acid (30%) was added to a platinum crucible and dissolved, and the volume was made up to 50 mL with water to obtain a sample for ICP-luminescence analysis.
(Iii) Measurement conditions and calculation method As a standard sample, a commercially available Cu standard solution (Kanto Chemical Cu1000) was diluted with dilute hydrochloric acid (0.6% HCl) to obtain a predetermined concentration. Calibration curves of 0.01 to 0.1 ppm and 0.1 to 1 ppm were prepared and used for measurement.

(2) Measurement of stripping voltammetry The stripping voltammetry of the solution was measured using NanoDetector of TraceDetect.
(I) Preparation of solution Bismuthiol II (manufactured by Dojin Chemical Co., Ltd .: trade name Bismuthiol-II) was added to a nonaqueous electrolytic solution (ethylene carbonate / methyl ethyl carbonate = 1/2) containing 1 mol / L LiBF ₄ in the table below. A predetermined amount shown in 1 was dissolved to prepare an electrolyte for a lithium ion secondary battery. A predetermined amount of Cu (BF ₄ ) ₂ was added to the electrolytic solution and the measurement was immediately performed as shown in Table 1 below.
(Ii) Adjustment of the device Pre-measurement is performed 0-5 times in a copper ion solution of a predetermined concentration containing 3% nitric acid, and after stabilizing the electrode, the electrode is directly inserted into the electrolyte and the potential is inserted. Then, precipitation of copper ions contained in the solution and subsequent dissolution signals were evaluated. A silver / silver chloride electrode was used as a reference electrode.
In stripping voltammetry, the copper ion contained in the electrolyte is reduced once on the electrode surface, and the current when the copper deposited on the electrode surface is changed to copper ion by inserting the electrode potential to the oxidation side is measured. did. In this system, the potential when copper was deposited as copper ions was about 800 mV (vs. silver / silver chloride electrode).

[Examples 1 to 4]
An electrolytic solution containing copper ions and Bismuthiol II having the composition shown in Table 1 was prepared. In either case, a precipitate was formed as soon as Cu (BF ₄ ) ₂ was added. When the supernatant liquid after centrifugation was analyzed by ICP emission, no copper ions were detected.

[Comparative Example 1]
An electrolyte solution containing only copper ions and not bismuthiol II was prepared. The electrolyte was uniform and no precipitate was formed. This was centrifuged in the same manner as in Example 1, and ICP emission analysis was performed using the supernatant. As a result, 20 ppm of copper ion, which was the same as the charged copper ion concentration, was detected.

[Examples 5 and 6]
An electrolytic solution containing copper ions and Bismuthiol II having the composition shown in Table 1 was prepared. Stripping voltammetry was measured after adding copper ions. No peak was observed near 800 mV, and it was found that the copper ions added to the electrolyte were electrochemically inactive.

[Comparative Example 2]
An electrolytic solution containing only copper ions and not bismuthiol II was prepared, and stripping voltammetry was measured in the same manner as in Examples 5 and 6. A large peak was observed at about 800 mV, and it was found that the copper ions added to the electrolyte were electrochemically active and caused microshorts.
[Comparative Examples 3 and 4]
Except for using “N-benzoylphenylhydroxylamine” (manufactured by Dojin Chemical Co., Ltd .: trade name BPA) or “diantipyrylmethane” (manufactured by Dojin Chemical Co., Ltd .: trade name Diantipyrylmethane) instead of Bistimol II, An electrolytic solution for a lithium ion secondary battery was prepared in the same manner as in Example 1. In any case, no precipitate was formed even when Cu (BF ₄ ) ₂ was added. Moreover, when the supernatant liquid after centrifuging on the same conditions as Example 1 was analyzed by ICP emission, 20 ppm copper ion same as the prepared copper ion concentration was detected.

As is clear from the results in Table 1, the electrolytes of Examples 1 to 4 using Bismuthiol II as a metal gravimetric reagent were obtained from the supernatant after centrifuging after adding Cu (BF ₄ ) _2. Copper ions were not detected, and Bismuthiol II and copper ions reacted efficiently to produce precipitates.
In addition, in the electrolyte solutions of Examples 5 and 6, no peak near 800 mV was observed in the stripping voltammetry measurement results after adding copper ions, and the copper ions added to the electrolyte solutions were electrochemically inactive. It was in a state. When the electrolytic solution of this embodiment is used as an electrolytic solution for a lithium ion secondary battery, it has been demonstrated that the occurrence of micro-shorts due to crystal growth of the eluted metal ions and straddling between the electrodes can be effectively prevented. It was done.
On the other hand, in Comparative Examples 1 and 2, which do not contain a metal gravimetric reagent, and in Comparative Examples 3, 4 using N-benzoylphenylhydroxylamine or diantipyrylmethane as a metal gravimetric reagent, copper ions Was in an electrochemically active state. Among the compounds classified as gravimetric reagents for metals, it was confirmed that there were those that could or might not inactivate copper ions in this example.

  The electrolyte for a lithium ion secondary battery of the present invention can remarkably reduce the risk of occurrence of micro shorts, and is industrially used as an electrolyte for a lithium ion secondary battery used in a power source of a portable device. Has availability.

Claims (4)

Bathocuproin, sulfonated bascuproin, 4,7-diphenyl-1,10-phenanthroline disulfonic acid, thiadiazoles, 2- (5-bromo-2-pyridylazo) -5- (N-propyl-3-sulfopropylamino) phenol 2- (5-bromo-2-pyridylazo) -5- (N-propyl-N-sulfopropylamino) aniline, 4- (2-pyridylazo) resorcin, salicylaldoxime, α-benzoin oxime, dimethylglyoxime, One or more compounds selected from the group consisting of aluminone, 8-hydroxyquinoline, and derivatives thereof;
A non-aqueous electrolyte,
An electrolyte for a lithium ion secondary battery.   The electrolyte solution for a lithium ion secondary battery according to claim 1, wherein the content of the compound is 0.0001 mass% to 10 mass%.   The thiadiazole is selected from the group consisting of 2,5-dimercapto-1,3,4-thiadiazole, 5-mercapto-3-phenyl-1,3,4-thiadiazole-2-thione, and alkali metal salts thereof. The electrolyte solution for lithium ion secondary batteries of Claim 1 or 2 which is 1 type, or 2 or more types. A lithium ion secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,
The said lithium ion secondary battery is a lithium ion secondary battery containing the electrolyte solution for lithium ion secondary batteries of any one of Claims 1-3.