JP4945074B2 - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having improved reflow heat resistance properties, cycle characteristics, and withstand voltage retaining characteristics by using silicon oxide, or the like for a negative electrode. <P>SOLUTION: The nonaqueous electrolyte secondary battery comprises a positive electrode; the negative electrode; a separator for separating the positive electrode from the negative one; an electrolyte containing a nonaqueous solvent and a supporting salt; and an ionic liquid added to the electrolyte at a ratio of 5-40 wt.%. The electrolyte containing a 5-40 wt.% ionic liquid is used as the nonaqueous electrolyte of an electrolyte. <P>COPYRIGHT: (C)2006,JPO&amp;NCIPI

Description

  The present invention relates to a reflow solderable non-aqueous electrolyte secondary battery.

  Non-aqueous electrolyte secondary batteries are increasingly used as backup power sources for equipment due to their high energy density and light weight.

  However, since the conventional non-aqueous electrolyte secondary battery does not use a material considering heat resistance, there is a drawback that the function as a battery is easily impaired when reflow soldering is performed. Furthermore, the material of the solder used for reflow is also required to be lead-free from the viewpoint of environmental load, and the demand for reflow at higher temperatures is increasing.

An ionic liquid is a salt that exists as a liquid at room temperature, that is, a salt that exists in a molten state at room temperature, and is also called a room temperature molten salt. Since ionic liquids are ionic volatile and nonflammable and have ionic conductivity, they are attracting attention as heat-stable ionic conductive liquids. For this reason, the application as a solvent of a chemical synthesis reaction and as an electrolyte of an electric double layer capacitor is expected (see, for example, Patent Document 1).
Japanese Patent Application Laid-Open No. 2004-146346 (Items 2 to 3)

  Conventional coin-type (button-type) non-aqueous electrolyte secondary batteries have low heat resistance and cause expansion of battery cans and deterioration of charge / discharge characteristics.

In coin-type (button-type) non-aqueous electrolyte secondary batteries having a 3V-class lithium-containing manganese oxide Li ₄ Mn ₅ O ₁₂ as a positive electrode and a lithium-aluminum alloy as a negative electrode, most combinations of electrolysis are available with reflow soldering. In a liquid or heat-resistant battery member, the electrolytic solution and the lithium alloy react to cause rapid expansion and deterioration of characteristics, which is a problem.

  In particular, lithium, a lithium alloy, a carbonaceous material that has a potential close to that of lithium and can be doped / undoped with lithium ions, or a general formula LixMySi1-yOz, tends to react with the electrolytic solution and cause rapid expansion. It was. Since these negative electrode active materials that have a low potential and are doped with a large amount of lithium cannot be used, reflow solderable coin-type (button-type) non-aqueous electrolyte secondary batteries must be produced with high output potential and high capacity. I could not.

  Even when there is no sudden bulging or rupture, large capacity deterioration is likely to occur before and after reflow, and large deterioration in cycle characteristics and storage characteristics is likely to occur.

  On the other hand, a non-aqueous electrolyte secondary battery using only an ionic liquid as an electrolyte was developed for the purpose of improving heat resistance, but the internal resistance increases and the capacity deteriorates greatly when stored in a voltage applied state after reflow. was there. Further, since the ionic liquid has a high viscosity, the electrode hardly penetrates into the electrode, and a battery using the ionic liquid as an electrolyte cannot obtain stable characteristics. Furthermore, the non-aqueous electrolyte secondary battery using the ionic liquid has not obtained good cycle characteristics.

  An object of the present invention is to provide a secondary battery that solves the above problems and has high heat resistance and excellent charge / discharge characteristics.

  The non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator separating the positive electrode and the negative electrode, an electrolytic solution containing a non-aqueous solvent and a supporting salt, and 5 to 40 weights relative to the electrolytic solution. % Of ionic liquid added at a rate of%. Furthermore, the present invention uses an electrolytic solution containing 5 to 40% by weight of an ionic liquid in order to solve the above problems.

  Moreover, the cation which comprises this ionic liquid used the single or composite selected from at least one of an imidazolium cation and a pyridium cation.

Furthermore, at least one of BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , CF ₃ CO ₂ ⁻ and CF ₃ SO ₃ ⁻ was used as an anion constituting the ionic liquid.

  Further, as the cation constituting the ionic liquid, a single compound or a composite selected from at least one of N, N′-dialkylimidazolium cation and N-alkylpyridinium cation was used.

  Furthermore, as the cation constituting the ionic liquid, a single compound or a composite selected from at least one of 1-ethyl-3-methylimidazolim cation and N-alkylimidazolium cation was used.

  As a non-aqueous solvent for the electrolytic solution, a mixed solution of γ-butyrolactone (γBL) and ethylene carbonate (EC) at a volume ratio of 1: 1 was used.

As the negative electrode active material, one or more active materials selected from SiO, Si, WO ₂ , WO ₃ and a Li—Al alloy were used. As a result, a non-aqueous electrolyte secondary battery compatible with reflow soldering having improved thermal stability, good cycle characteristics, and excellent storage characteristics has become possible.

  According to the present invention, the heat resistance of the non-aqueous electrolyte secondary battery is improved, and even if reflow soldering is performed, the battery can does not expand, the internal resistance rises, or the capacity decreases. Further, by adding an ionic liquid, the conductivity of the electrolytic solution is improved, and a non-aqueous electrolyte secondary battery having excellent charge / discharge characteristics and storage characteristics can be realized.

  FIG. 1 shows a cross-sectional view of the structure of the battery of the present invention. A positive electrode 101 formed from a positive electrode mixture, a positive electrode case 102, a negative electrode 103 formed from a negative electrode mixture, a negative electrode case 104, a lithium foil 105, a separator 106 that separates the positive electrode from the negative electrode, a gasket 107, and an electrolyte solution 108.

  Lithium, lithium alloy or lithium-doped carbon, metal, or metal oxide is brought into contact with an electrolyte that is a non-aqueous electrolyte containing a supporting salt, and a rapid chemical reaction occurs when the temperature is raised to 200 ° C or higher. . This reaction is more severe as the boiling point of the organic solvent constituting the non-aqueous electrolyte is lower, and as the negative electrode active material is lower in potential and the lithium doping amount is larger.

  The supporting salt used in the present invention is solid at room temperature and is dissolved in a non-aqueous solvent and used as an electrolytic solution. As the supporting salt, the chlorine-based salt is more suitable because it is more thermally stable than the fluorine-based salt.

  The non-aqueous solvent used in the electrolytic solution has a low boiling point, and the pressure inside the battery is increased during reflow soldering, resulting in a problem of leakage.

  It has been found that the heat resistance of the secondary battery is improved by adding an ionic liquid having a very high boiling point and excellent heat resistance to the electrolyte. The ionic liquid is a liquid composed only of ions. By adding the ionic liquid, the conductivity of the electrolytic solution is improved and the internal resistance is reduced.

  By adding an ionic liquid having high conductivity and a wider potential window to the non-aqueous electrolyte, it was possible to obtain a non-aqueous electrolyte with excellent battery characteristics.

  An ionic liquid is an ion-binding substance that has a low melting point and is liquid at room temperature. The ionic liquid has very low volatility, is nonflammable, and has excellent conductivity and heat resistance.

  Examples of the cation constituting the ionic liquid include N, N'-dialkylimidazolium cation and N-alkylpyridinium cation. Specific examples of the N, N′-dialkylimidazolium cation include 1,3-dimethylimidazolium cation, 1,3,4-trimethylimidazolium cation, and 1-ethyl-3-methylimidazolium cation. The 1-ethyl-3 methyl imidazolium cation is preferred. Of the N-alkylpyridinium cations, 1-butylpyridinium cation is particularly desirable. An ionic liquid composed of these cations is excellent in ion conductivity, chemical stability, and electrochemical stability.

The anion constituting the ionic liquid may be selected from at least one of BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , CF ₃ CO ₂ ⁻ , and CF ₃ SO ₃ ^−. desirable. Ionic liquids composed of these fluoride anions have high thermal stability and are difficult to decompose even at high temperatures. In particular, the combination of 1-ethyl-3methylimidazolium cation and (CF ₃ SO ₂ ) ₂ N ^— is stable at the highest temperature.

  By adding the ionic liquid to the non-aqueous electrolyte containing the supporting salt, deterioration of battery characteristics due to reflow is suppressed by increasing the boiling point due to the addition of the ionic liquid, dissociating ions of the supporting salt in the non-aqueous electrolyte. This is considered to be due to the fact that the dissociation of the dissociated ions of the supporting salt due to the presence of ions of the ionic liquid was suppressed.

  The content of the ionic liquid in the electrolytic solution is preferably 5 to 40% by weight. If it is less than 5% by weight, it will not work effectively in terms of heat resistance. On the other hand, when the content is more than 40% by weight, the viscosity of the electrolytic solution becomes high, and it becomes difficult to impregnate the electrode with the electrolytic solution, which makes it difficult to manufacture a secondary battery. In addition, when the viscosity of the electrolytic solution increases, the internal resistance increases.

  Furthermore, the high-temperature storage characteristic by voltage application deteriorates. High-temperature storage characteristics due to voltage application in a battery are widely recognized as an accelerated test at room temperature use, and there is a concern that if this characteristic is poor, the life due to room temperature use is short. Moreover, it is desirable that it is 40% or less also from the surface of the ion concentration in electrolyte solution at the time of voltage application. In particular, it is preferably 25 to 35%.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 is a case where Nb ₂ O ₅ is used as the positive electrode active material and SiO is used as the negative electrode active material. A positive electrode, a negative electrode, and an electrolytic solution prepared as described below were used. The size of the battery was 5 mm in outer diameter and 1.5 mm in thickness.

As the positive electrode active material, commercially available niobic acid (Nb ₂ O ₅ .nH ₂ O) was heated in the atmosphere at 800 ° C. for 8 hours to obtain Nb ₂ O ₅ . The Nb ₂ O ₅ pulverized powder is mixed with graphite as a conductive agent and polyacrylic acid as a binder at a weight ratio of Nb ₂ O ₅ : graphite: polyacrylic acid = 75: 20: 5. Next, 5 mg of this positive electrode mixture was pressed into 2 mm / cm @ 2 pellets having a diameter of 2.0 mm. Thereafter, the positive electrode 101 thus obtained was bonded and integrated with the positive electrode case 102 using an electrode current collector made of a conductive resin adhesive containing carbon (made into a positive electrode unit), and then at 250 ° C. for 8 hours. Heat-treated in the atmosphere.

The negative electrode was produced as follows. A commercially available SiO pulverized material was used as the active electrode active material. This active material was mixed with graphite as a conductive agent and polyacrylic acid as a binder at a weight ratio of 45:40:15 to obtain a negative electrode mixture. 1.5 mg of the mixture was pressed into pellets having a diameter of 2.0 mm at ² ton / cm ² and used. Thereafter, the negative electrode 103 obtained in this manner was bonded and integrated to the negative electrode case 104 using an electrode current collector made of a conductive resin adhesive containing carbon as a conductive filler (negative electrode unitization). It heat-processed in air | atmosphere at 250 degreeC for 8 hours. Further, a lithium foil 105 punched out to a diameter of 2.0 mm and a thickness of 0.3 mm was pressure-bonded on the pellet to obtain a lithium-negative electrode pellet laminated electrode.

  A non-woven fabric made of glass fiber having a thickness of 0.2 mm was dried and punched out to a diameter of 3.0 mm to form a separator 106. The gasket 107 made of PEEK was used.

First, as the electrolytic solution 108, a solvent was prepared by mixing ethylene carbonate (EC): γ-butyllactone (γBL) at a volume ratio of 1: 1. Thereafter, a mixed solution was prepared in which the ratio of 1-ethyl-3methylimidazolium tetrafluoroborate (MEI · BF ₄ ) was 7: 3 in this solvent, and lithium borofluoride (LiBF ₄ ) was prepared there. Was dissolved at 2.0 mol / l to prepare an electrolytic solution. The positive electrode unit and the negative electrode unit, in which 5 μL of the electrolytic solution was placed in a battery can, were overlapped and sealed to produce a battery.

In the same manner as in Example 1, an electrolytic solution in which the anions of the ionic liquid in the electrolyte were PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , CF ₃ CO ₂ ⁻ , and CF ₃ SO ₃ ⁻ was produced. A battery was produced.

In the same manner as in Example 1, the anion of the ionic liquid in the electrolyte was (CF ₃ SO ₂ ) ₂ N ^— and the cations were 1-ethyl-3 methylimidazolium cation and 1-butylpyridinium cation, respectively. An electrolyte was prepared to prepare a battery.

The same manner as in Example 1. As a anion of the ionic liquid in the electrolyte _{(CF 3 SO 2) 2 N} - and then, to prepare an ionic percentage of the liquid 5% by weight, the electrolyte solution was 40 wt% A battery was produced.

Comparative Examples 1-4

  As Comparative Examples 1 to 4, batteries in which the ratio of the ionic liquid in the electrolytic solution in Example 1 was 0 wt%, 3 wt%, 45 wt%, and 100 wt% were produced.

  In order to investigate whether or not each of the 10 batteries produced as described above can withstand the reflow temperature, a reflow test was performed by overheating at preheating 180 ° C. for 10 minutes and heating at 260 ° C. for 1 minute. The sample after heating was subjected to measurement of battery height, internal resistance, battery capacity, and cycle characteristics in order to examine swelling. Also, the reflowed battery was connected to a 2V power source, held in a high-temperature bath at 60 ° C. for 20 days, and then taken out and measured for battery height measurement, internal resistance measurement, battery capacity, and withstand voltage storage characteristics. . Charging / discharging conditions in the battery capacity and cycle characteristics are as follows. Charging is performed with a constant current low voltage method with a maximum current of 25 μA, a constant voltage of 2.0 V, and a charging time of 48 hours, and discharging is performed with a constant current of 5 μA and a final voltage of 1.0 V. It was.

  The production conditions and experimental results of Examples 1 to 12 and Comparative Examples 1 to 4 are shown in Table 1.

表１において、◎は良好な特性を示すもの、○は実用上問題ないもの、△は電池のわずかなふくらみや容量の若干の劣化等多少の問題があるもの、×は特性上問題があり実用レベルにないものである。表１において陽イオンＡは１―エチル―３メチルイミダゾリウム、陽イオンＢは１―エチル―３メチルイミダゾリウムクロリド、陽イオンＣは１−ブチルピリジニウムクロリド、陰イオンＡはＢＦ_４ ⁻、陰イオンＢはＰＦ_６ ⁻、陰イオンＣは（ＣＦ_３ＳＯ_２）Ｎ⁻、陰イオンＤはＣＦ_３ＣＯ_２ ⁻、陰イオンＥはＣＦ_３ＳＯ_３ ⁻である。

In Table 1, ◎ shows good characteristics, ○ shows no problem in practical use, △ shows some problems such as slight swelling of battery and slight deterioration of capacity, × shows problem in characteristics and practical use It is not in the level. In Table 1, cation A is 1-ethyl-3methylimidazolium, cation B is 1-ethyl-3methylimidazolium chloride, cation C is 1-butylpyridinium chloride, anion A is BF ₄ ⁻ , anion B is PF ₆ ⁻ , the anion C is (CF ₃ SO ₂ ) N ⁻ , the anion D is CF ₃ CO ₂ ⁻ , and the anion E is CF ₃ SO ₃ ⁻ .

As shown in Table 1, when the ratio of the ionic liquid was 30% by weight, no increase in internal resistance or deterioration in capacity due to reflow was observed in any combination of cation and anion. Also, with respect to the withstand voltage storage characteristics, good characteristics were obtained with almost no deterioration in capacity and the like. In particular cation 1-ethyl-3-methyl imidazolium cation in the ionic liquid, the anion _{(CF 3 SO 2) 2 N} - is one, the capacity deterioration after storage is 10% or less, most good Characteristics were obtained. Further, the swelling of the batteries was 0.03 mm or less, which was a problem-free level. As for the cycle characteristics, the capacity reduction amount was 20% or less at 100 times for any sample, and excellent characteristics were obtained. Similarly good results were obtained when the ionic liquid content was 5 wt% and 40 wt%.

  The charge / discharge curves of Example 3, Comparative Example 1 and Comparative Example 2 are shown in FIG. When the ionic liquid was added at 0 wt% and 3 wt% (Comparative Example 2), the internal resistance increased by about 100Ω after the reflow, and the capacity was only about half that before the reflow. In addition, when the addition amount of the ionic liquid was 45% by weight (Comparative Example 3), the capacity deterioration after reflow was slightly suppressed, but the variation was large, and the deterioration in the withstand voltage storage characteristic was 40% or more. . Although the details are unknown, it is considered that the viscosity and ion concentration of the electrolytic solution are increased. In addition, regarding the ionic liquid of 100% by weight, the deterioration of the cycle characteristics was severe. Thus, the present invention is effective when the addition amount of the ionic liquid is 5% or more and 40% or less.

In the same manner as in Example 1, the anion of the ionic liquid in the electrolyte was (CF ₃ SO ₂ ) ₂ N ^— , and the positive electrode active material was Li ₄ Mn ₅ O ₁₂ , Li ₄ Ti ₅ O ₁₂ , MoO _3. A battery was produced.
Reflow was performed in the same manner as in Example 1 and the capacity and the like were evaluated. However, the charge / discharge conditions were as follows.

For Li ₄ Mn ₅ O ₁₂ , the charging voltage was 3.3 V, the discharge starting voltage was 1.8 V, and other conditions were the same as those for Nb ₂ O ₅ . For Li ₄ Ti ₅ O ₁₂ , the charging voltage was 1.6 V, the discharge starting voltage was 0.9 V, and other conditions were the same as those for Nb ₂ O ₅ . For MoO ₃ , the charging voltage was 3 V, the discharge starting voltage was 1.2 V, and other conditions were the same as those for Nb ₂ O ₅ .

As shown in Table 1, even when the type of the positive electrode active material was changed, good results similar to those obtained when the positive electrode active material was Nb ₂ O ₅ were obtained.

  As for the electrolytic solution other than the portion constituting the ionic liquid, the following is preferable.

  As the electrolytic solution, organic solvents such as γ-butyrolactone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, 1,2-dimethoxyethane, tetrahydrofuran, dioxolane, dimethylformamide, etc. These may be used alone or as a mixed solvent.

  In order to perform reflow soldering, it is stable at the reflow temperature to use a nonaqueous solvent having a boiling point of 200 ° C. or higher at normal pressure as the electrolytic solution. In combination with the positive and negative electrodes, ethylene carbonate (EC) or γ-butyrolactone (γBL) was used alone or in combination.

  In addition to the organic solvent, a polymer can be used. Examples of the polymer include polyethylene oxide (PEO), polypropylene oxide, crosslinked polyethylene glycol diacrylate, polyvinylidene fluoride, crosslinked polyphosphazene, crosslinked polypropylene glycol diacrylate, crosslinked polyethylene glycol methyl ether acrylate, and polypropylene glycol methyl. Ether acrylate crosslinked products are preferred.

  Examples of main impurities present in the electrolytic solution (nonaqueous solvent) include moisture and organic peroxides (for example, glycols, alcohols, carboxylic acids). Each of the impurities is considered to form an insulating film on the surface of the active material and increase the interface resistance of the electrode. Therefore, the cycle life and capacity may be affected. In addition, self-discharge during storage at high temperatures (60 ° C. or higher) may increase. Room temperature molten salt is particularly greatly deteriorated by moisture. For this reason, it is preferable to reduce the impurities as much as possible in the electrolyte solution containing the non-aqueous solvent. Specifically, the moisture is preferably 50 ppm or less and the organic peroxide is preferably 1000 ppm or less.

Supported salts include lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorometasulfonate (LiCF) ₃ SO ₃ ), bistrifluoromethylsulfonylimide lithium [LiN (CF ₃ SO ₂ ) ₂ ], lithium salts (electrolytes) such as thiocyanate and aluminum fluoride can be used.

In performing reflow soldering, lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium trifluorometasulfonate, which are fluorine-containing supporting salts from chlorine-based materials such as LiClO ₄ (LiCF ₃ SO ₃ ) is stable both thermally and electrically. The amount dissolved in the non-aqueous solvent is preferably 0.5 to 3.0 mol / 1.

Further, the present invention does not select the type of the negative electrode active material, but as the negative electrode, lithium alloys such as lithium-aluminum, carbon doped with lithium, metal oxide doped with lithium (for example, SiO, WO ₂ , WO ₃ etc.), Si doped with lithium, etc. are effective.

  In particular, the use of a silicon oxide represented by SiOy (2> y> 0) such as SiO or Si as the negative electrode active material minimizes the deterioration of the negative electrode due to charge / discharge, and the battery has very good charge / discharge cycle characteristics. Can be created. In addition, when a battery is made using a metal oxide such as SiO as a negative electrode, a lithium-containing silicon oxide represented by LixSiOy (x ≧ 0, 2> y> 0) is prepared by previously storing movable lithium ions in SiO. There is a need to. In this case, by increasing the lithium content, the potential on the negative electrode side decreases, and the charge / discharge curve tilts. At the same time, it can be charged at a high voltage, and can be charged in a wide voltage range. When too much lithium is added, lithium metal is deposited on the electrode during charging, and therefore x is particularly preferably in the range of 4.0 ≦ x ≦ 4.5. In this way, even if silicon oxide that is contacted or electrochemically doped with lithium is used for the negative electrode, an ionic liquid is contained in the electrolyte, so that a rapid reaction occurs even at a reflow temperature exceeding 200 ° C. Is gone.

  The present invention does not select a positive electrode active material, but as a positive electrode active material, titanium oxide, lithium-containing titanium oxide, molybdenum oxide, manganese oxide, lithium-containing manganese oxide, lithium-containing cobalt oxide, niobium oxide And lithium-containing niobium oxide can be used.

  As the separator, an insulating film having a large ion permeability and a predetermined mechanical strength is used. As the pore diameter of the separator, a range generally used for batteries is used. For example, 0.01 to 10 μm is used. The thickness of the separator is generally used in the battery range, for example, 5 to 300 μm is used.

  As the gasket, polypropylene or the like is usually used.

  When performing reflow soldering, polyphenylene sulfide, polyethylene terephthalate, polyamide, liquid crystal polymer (LCP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), polyether ether ketone resin (PEEK), polyether nitrile resin (PEN), polyetherketone resin (PEK), polyamideimide, polyarylate resin, polybutylene terephthalate resin, polycyclohexanedimethylene terephthalate resin, polyethersulfone resin, polyaminobismaleimide resin, polyetherimide resin, fluorine resin reflow There was no rupture at temperature, and there was no problem of leakage due to deformation of the gasket even during storage after reflow.

  In particular, resins having a heat distortion temperature of 230 ° C. or higher, polyphenylene sulfide, liquid crystal polymer (LCP), polyetheretherketone resin (PEEK), polyethernitrile resin (PEN), polyamideimide resin, or tetrafluoroethylene-perfluoroalkyl The vinyl ether copolymer resin was excellent in terms of leakage resistance.

  Moreover, what added glass fiber, my cow whisker, ceramic fine powder, ceramic whisker, etc. with the addition amount of about 40 weight% or less to this material can be used. In particular, those using potassium titanate whiskers were good.

  As a method for manufacturing the gasket, there are an injection molding method, a thermal compression method, and the like.

  The thermal compression method is a method for obtaining a final molded product by performing thermal compression molding at a temperature equal to or lower than the melting point using a plate material having a thickness larger than the gasket shape of the molded product as a material molded product.

  In general, when a temperature is applied to a thermoplastic resin molded product molded by hot compression molding at a temperature below the melting point from the material molded product, there is a property of returning to the shape of the original material molded product. As a result, a non-aqueous electrolyte is supposed to have a gap between the outer can and the inner can (metal) and the gasket (resin), or a stress sufficient for sealing cannot be obtained between the can and the gasket. By using this gasket for the next battery, there is no gap between the outer can and can (metal) and gasket (resin) due to expansion of the gasket due to heat treatment (reflow soldering, etc.) or sealing between the can and gasket. Sufficient stress can be obtained.

  Further, it has a property of returning to the shape of the original material molded product over time, and is effective in batteries other than reflow soldering.

  In particular, in a gasket using tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA), a heat compression molded one produced by heating and pressing a sheet-like material is more sealed than one produced by injection molding. The property was good. This is because the PFA has rubber elasticity, and the injection molded product shrinks at the reflow temperature, whereas the hot compression molded product tries to return to the thickness of the sheet before molding at the reflow temperature. This is because the internal pressure of the gas increases and further sealing and airtightness can be achieved.

  On the other hand, the injection molding method is the most common gasket molding method. However, when the molding accuracy is sacrificed due to cost reduction or the like, it is essential to supplement the airtightness using a liquid sealant.

  In the case of coins and button batteries, one or a mixture of liquid sealants such as asphalt pitch, butyl rubber, fluorinated oil, chlorosulfonated polyethylene, and epoxy resin is used between the gasket and the positive and negative electrode cans. When the liquid sealant is transparent, it is colored to clarify the presence or absence of application. Examples of the method for applying the sealant include injection of the sealant into the gasket, application to the positive / negative electrode can, and dipping of the gasket into the sealant solution.

  When the battery shape is a coin or a button, the electrode shape is used by compressing a mixture of a positive electrode active material and a negative electrode active material into a pellet shape. In the case of a thin coin or button, an electrode formed in a sheet shape may be punched out. The thickness and diameter of the pellet are determined by the size of the battery.

  As the pellet pressing method, a generally adopted method can be used, but a die pressing method is particularly preferable. The pressing pressure is not particularly limited, but is preferably 0.2 to 5 t / cm2. The pressing temperature is preferably room temperature to 200 ° C.

  A conductive agent, a binder, a filler, or the like can be added to the electrode mixture. The kind of the conductive agent is not particularly limited and may be a metal powder, but a carbon-based one is particularly preferable. Carbon materials are the most common, and natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, channel black, thermal black, furnace black, acetylene black, carbon fiber, etc. are used. As the metal, metal powder such as copper, nickel, silver, or metal fiber is used. Conductive polymers are also used.

  The amount of carbon added varies depending on the electrical conductivity of the active material, the electrode shape, etc., and is not particularly limited. However, in the case of the negative electrode, it is preferably 1 to 50% by weight, particularly preferably 2 to 40% by weight.

  When the carbon particle size is in the range of 0.5 to 50 μm, preferably in the range of 0.5 to 15 μm, more preferably in the range of 0.5 to 6 μm, the contact between the active materials becomes good. Electron conduction network formation is improved, and active materials that are not involved in electrochemical reactions are reduced.

The binder is preferably insoluble in the electrolytic solution.
Polyacrylic acid and neutralized polyacrylic acid, polyvinyl alcohol, carboxymethylcellulose, starch, hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, polyvinylchloride, polyvinylpyrrolidone, tetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, ethylene-propylene -Diene polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, polybutadiene, fluoro rubber, polyethylene oxide, polyimide, epoxy resin, phenol resin and other polysaccharides, thermoplastic resin, thermosetting resin, rubber elastic polymer, etc. Are used as one or a mixture thereof. The addition amount of the binder is preferably 1 to 50% by weight.

By using a water-soluble binder, the burden on the environment can be reduced. In the preparation of the positive electrode mixture, when water-soluble polyacrylic acid and polyacrylic acid neutralized product, polyvinyl alcohol, carboxymethyl cellulose, starch, etc. are used, Nb ₂ O ₅ absorbs water, It is necessary to heat-treat the pellet formed with the positive electrode mixture.

  Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. In the present invention, fibers such as carbon and glass are used. Although the addition amount of a filler is not specifically limited, 0 to 30 weight% is preferable.

  It is desirable to use a metal plate having a low electrical resistance as a can that also serves as a current collector for the electrode active material. For example, in addition to stainless steel, nickel, aluminum, titanium, tungsten, gold, platinum, baked carbon, etc., the positive electrode has a surface of aluminum or stainless steel treated with carbon, nickel, titanium or silver. Used. As for stainless steel, duplex stainless steel is effective against corrosion. In the case of a coin or button battery, nickel plating is performed on the outside of the battery. Examples of the treatment method include wet plating, dry plating, CVD, PVD, clad formation by pressure bonding, coating, and the like.

  In addition to stainless steel, nickel, copper, titanium, aluminum, tungsten, gold, platinum, calcined carbon, etc., the negative electrode can has carbon, nickel, titanium or silver treated on the surface of copper or stainless steel. Al-Cd alloy or the like is used. Examples of the treatment method include wet plating, dry plating, CVD, PVD, clad formation by pressure bonding, coating, and the like.

  It is also possible to fix the electrode active material and the current collector can with a conductive adhesive. As the conductive adhesive, a resin in which carbon or metal powder or fiber is added to a resin dissolved in a solvent, or a conductive polymer dissolved therein is used.

  In the case of a pellet-shaped electrode, the electrode is fixed by applying between the current collector and the electrode pellet. The conductive adhesive in this case often includes a thermosetting resin.

  The application of the non-aqueous electrolyte secondary battery of the present invention is not particularly limited, but is optimal for backup power supplies such as mobile phones and pagers.

  The battery of the present invention is preferably assembled in a dehumidified atmosphere or an inert gas atmosphere. Moreover, it is preferable that the parts to be assembled are also dried in advance. As a method for drying or dehydrating pellets, sheets and other parts, it is preferable to use hot air, vacuum, infrared rays, far infrared rays, electron beams and low-humidity air alone or in combination. The temperature is preferably in the range of 80 to 350 ° C, particularly preferably in the range of 100 to 300 ° C. The water content is preferably 2000 ppm or less for the entire battery, and preferably 50 ppm or less for each of the positive electrode mixture, the negative electrode mixture and the electrolyte from the viewpoint of improving charge / discharge cycle performance.

Sectional view of coin-type lithium secondary battery of the present invention Charge / discharge curves of Example 3 and Comparative Examples 1 and 2 Charge and discharge curves before and after withstanding voltage storage in Example 3 Charge / discharge curve before and after withstand voltage storage of Comparative Example 2 Cycle characteristics of Example 3 and Comparative Example 3

Explanation of symbols

101 Positive electrode 102 Positive electrode case 103 Negative electrode 104 Negative electrode case 105 Lithium foil 106 Separator 107 Gasket 108 Electrolyte

Claims (9)

A non-aqueous secondary battery capable of reflow soldering comprising a positive electrode, a negative electrode, a gasket, a separator separating the positive electrode and the negative electrode, and an electrolyte containing a non-aqueous solvent and a supporting salt,
The gasket is made of a resin having a heat deformation temperature of 230 ° C. or higher ,
The non-aqueous solvent has a boiling point of 200 ° C. or higher at normal pressure,
The negative electrode comprises a silicon oxide represented by SiOy (2>y> 0) or a negative electrode containing one or more active materials selected from Si, WO ₂ , WO ₃ and a Li—Al alloy,
The electrolyte solution is characterized in that an ionic liquid is added in a ratio of 5 to 40% by weight with respect to the electrolyte solution, and the electrolyte solution is impregnated in the positive electrode and the negative electrode. Next battery. The ionic liquid includes a cation containing at least one of an imidazolium cation and a pyridinium cation, BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , CF ₃ CO ₂ ⁻ , and CF ₃ SO. _2. The nonaqueous electrolyte secondary battery according to claim 1, comprising both or one of anions containing at least one of ₃ ⁻ .   The nonaqueous electrolyte secondary battery according to claim 2, wherein the cation is an N, N′-dialkylimidazolium cation.   The nonaqueous electrolyte secondary battery according to claim 2, wherein the cation is a 1-ethyl-3-methylimidazolium cation.   The nonaqueous electrolyte secondary battery according to claim 2, wherein the cation is an N-alkylpyridinium cation.   The nonaqueous electrolyte secondary battery according to claim 2, wherein the cation is a 1-butylpyridinium cation.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous solvent is a nonaqueous solvent having a volume ratio of γ-butyrolactone (γBL) and ethylene carbonate (EC) of 1: 1. The gasket is any one of polyphenylene sulfide, liquid crystal polymer (LCP), polyetheretherketone resin (PEEK), polyethernitrile resin (PEN), polyamideimide resin, or tetrafluoroethylene-perfluoroalkylvinylether copolymer resin. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7 , wherein The nonaqueous electrolyte secondary battery according to claim 8 , wherein the gasket includes at least one of glass fiber, My Cowisker, ceramic fine powder, and ceramic whisker.

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