JP2008108454A - Nonaqueous electrolyte, and nonaqueous electrolyte battery including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte having a high impregnating ability and charge-discharge cycle characteristics, and a nonaqueous electrolyte battery including the same. <P>SOLUTION: A negative electrode 21 and a positive electrode 22 are wound through a separator 23 impregnated with nonaqueous electrolyte. The nonaqueous electrolyte includes fluorinated ether represented by the following equation (1); and one kind of carboxylate ester represented by the following equation (2) and nitrile compound represented by the following equation (3). This improves the impregnating ability and the electrical conductivity of the nonaqueous electrolyte to thereby improve the charge-discharge cycle characteristics of the nonaqueous electrolyte battery. C<SB>n</SB>H<SB>2n+1</SB>-O-C<SB>m</SB>F<SB>2m+1</SB>(1), R<SP>1</SP>-COO-R<SP>2</SP>(2), and R<SP>3</SP>-CN (3), where each of R<SP>1</SP>, R<SP>2</SP>, and R<SP>3</SP>represents a hydrocarbon radical. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention aims to improve cycle characteristics and safety in a non-aqueous electrolyte battery using a non-aqueous electrolyte having a low viscosity, a high electrical conductivity, and a high flash point, and to improve the impregnation property of the non-aqueous electrolyte. The present invention relates to an improvement of a non-aqueous electrolyte for use in a non-aqueous electrolyte battery.

  In recent years, portable information terminals such as mobile phones and notebook PCs have been rapidly reduced in size and weight, and research and development for reducing the power and driving power of the driving power source has been actively conducted. Among these, non-aqueous electrolyte batteries using a lithium compound as an active material have features such as light weight, high voltage, and high energy density, and are widely put into practical use as power sources for portable information terminals.

  In such a nonaqueous electrolyte battery, a cyclic carbonate organic solvent such as ethylene carbonate (EC) or propylene carbonate (PC) is often used. Since these solvents are high dielectric constant solvents, they can dissolve the lithium salt that is the supporting electrolyte, and because they have a wide potential window, they have the advantage of being stable even at the high potential peculiar to nonaqueous electrolyte batteries. There exists a problem that the viscosity of a solution is high and the efficient ion transfer is prevented. For this reason, usually, low-viscosity chain carbonates such as dimethyl carbonate (DMC) are often mixed and used.

  However, it is difficult to change the physical properties of the non-aqueous electrolyte due to the narrow selection of solvents with only carbonate esters. For example, in a non-aqueous electrolyte battery in which the electrode active material is thickly applied and the energy density is improved, the viscosity of the non-aqueous electrolyte is high with only carbonate esters, and the impregnation property of the non-aqueous electrolyte into the active material is insufficient. Become. In addition, since some carbonates have a high melting point and solidify at a low temperature, problems still remain in improving the low-temperature characteristics. In addition, it is difficult to obtain high electrical conductivity for more effective ion transfer only with a carbonate ester mixture.

  To compensate for these drawbacks, cyclic carboxylic acid esters γ-butyrolactone (GBL), γ-valerolactone (GVL), etc., which have a lower melting point and lower viscosity than carbonic acid esters and have high electrical conductivity, are used as solvents. It has been proposed. In addition, a technique of adding a chain carboxylic acid ester such as methyl acetate (MA) or methyl propionate (MP) having a viscosity lower than that of GBL to a non-aqueous electrolyte has been reported. Carboxylic acid esters have been reported to improve the electrical conductivity of non-aqueous electrolytes and improve the low-temperature characteristics of non-aqueous electrolyte batteries (Patent Documents 1 and 2).

  Similarly to carboxylic acid esters, nitrile compounds such as acetonitrile are known to be effective solvents for reducing the viscosity of non-aqueous electrolytes and improving electrical conductivity (Patent Documents 3 and 4). However, carboxylic acid esters and nitrile compounds have a narrow potential window compared to carbonate esters and decompose in the charge / discharge process of non-aqueous electrolyte batteries. End up. Decomposition of these solvents can be prevented by forming a film on the electrode with an unsaturated carbonate such as vinylene carbonate (VC).

  On the other hand, in recent years, it has been reported that a flame retardant fluorine compound is added to a non-aqueous electrolyte for the purpose of increasing the flash point of the non-aqueous electrolyte and improving safety (Patent Document 5). ).

Japanese Patent Laid-Open No. 2001-23684 JP 2004-319212 A JP 2001-196073 A JP 2004-303437 A JP 2005-340223 A

  Many carboxylic acid esters and nitrile compounds have low boiling points and flash points, and non-aqueous electrolytes containing these solvents are accompanied by a decrease in safety. It is rare. In addition, many fluorine compounds generally have a small dipole moment and thus have low solubility in non-aqueous electrolytes, and some may phase separate without mixing. Some of the fluorine compounds described in Patent Document 5 increase the viscosity of the non-aqueous electrolyte when added to the non-aqueous electrolyte, and the cycle of the non-aqueous electrolyte battery is caused by the accompanying decrease in the electrical conductivity of the non-aqueous electrolyte. May adversely affect properties. An increase in the viscosity of the non-aqueous electrolyte deteriorates the impregnation of the non-aqueous electrolyte into the non-aqueous electrolyte battery, prolongs the time for injecting the non-aqueous electrolyte, and increases the manufacturability of the non-aqueous electrolyte battery. make worse.

  The present invention has been made in view of such problems, and provides a non-aqueous electrolyte having high safety, low viscosity, high electrical conductivity, high impregnation, and a non-aqueous electrolyte battery using the same. The purpose is to do.

  The present inventors have found that the above object can be achieved by adding a fluorinated ether and at least one of a carboxylic acid ester and a nitrile compound to the nonaqueous electrolytic solution. The present invention has been made based on this finding, and is represented by a fluorinated ether represented by the following formula (1), a carboxylic acid ester represented by the following formula (2), and the following formula (3). By adding at least one of the nitrile compounds to constitute the non-aqueous electrolyte, the impregnation and electrical conductivity of the non-aqueous electrolyte are improved, and the charge / discharge cycle characteristics of the non-aqueous electrolyte battery are improved. Can be planned.

_{C n H 2n + 1 -O-} C m F 2m + 1 (1)
[In Formula (1), n represents 1-4, m represents the integer of 1-6. ]

R ¹ —COO—R ² (2)
[In Formula (2), R ¹ and R ² are hydrocarbon groups, and either or both of R ¹ and R ² may have a halogen atom or an unsaturated bond. R ¹ and R ² may be bonded to each other to have a cyclic structure. ]

R ³ -CN (3)
[In Formula (3), R ³ is a hydrocarbon group and may have a halogen atom. ]

  According to the present invention, by adding a fluorinated ether and at least one of a carboxylic acid ester and a nitrile compound to the non-aqueous electrolyte, the electrical conductivity is improved and the impregnation property to the non-aqueous electrolyte battery is increased. The productivity of the nonaqueous electrolyte battery can be improved. That is, according to the present invention, a non-aqueous electrolyte having high safety, low viscosity, high electrical conductivity, and high impregnation property, and a non-aqueous electrolyte battery having excellent charge / discharge cycle characteristics using the non-aqueous electrolyte are provided. be able to.

  Specific embodiments of the present invention will be described below.

  The nonaqueous electrolytic solution of the present invention is configured to contain a nonaqueous solvent and an electrolyte salt. The nonaqueous electrolytic solution of the present invention contains a fluorinated ether and at least one of a carboxylic acid ester and a nitrile compound in a nonaqueous solvent.

  As the fluorinated ether, one represented by the following formula (1) is used. By adding fluorinated ether to the non-aqueous electrolyte, the impregnation of the non-aqueous electrolyte is improved, the time required for injecting the non-aqueous electrolyte is shortened, and the flash point is increased to improve safety. Can do.

_{C n H 2n + 1 -O-} C m F 2m + 1 (1)
N in Formula (1) represents an integer of 1 to 4, and m represents an integer of 1 to 6.

  Examples of the fluorinated ether represented by the formula (1) include methyl nonafluorobutyl ether (MnFBE) and ethyl nonafluorobutyl ether (EnFBE). Any one of these may be used alone, or a plurality of these may be used in combination.

  The concentration of the fluorinated ether is preferably in the range of 0.5 to 20% by mass and more preferably in the range of 5 to 20% by mass in the non-aqueous electrolyte. If the concentration is lower than this, the flame retardancy effect of the fluorinated ether is lowered, and if it is higher than this, the effect of increasing the viscosity by the fluorinated ether is increased, and the impregnation property of the nonaqueous electrolyte is lowered. Because there is a risk of doing.

  As the carboxylic acid ester, one represented by the following formula (2) is used. By adding a carboxylic acid ester to the non-aqueous electrolyte, the viscosity of the non-aqueous electrolyte can be reduced and the electrical conductivity can be improved.

R ¹ —COO—R ² (2)
R ¹ and R ² in the formula (2) are hydrocarbon groups, and either or both of R ¹ and R ² may have a halogen atom or an unsaturated bond. R ¹ and R ² may be bonded to each other to have a cyclic structure. Examples of the hydrocarbon group include a methyl group, an ethyl group, a propyl group, and a butyl group. The halogen atom may be any of a fluorine atom, a bromine atom, an iodine atom, and a chlorine atom. As an unsaturated bond, a carbon-carbon unsaturated bond is mentioned, for example.

  Examples of the carboxylic acid ester represented by the formula (2) include methyl acetate (MA), ethyl acetate (EA), propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and butyric acid. Chain carboxylates such as methyl, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone (GBL), γ-valerolactone (GVL), α-acetyl-butyrolactone, α-methyl-γ-butyrolactone, β-methyl Examples include cyclic carboxylic acid esters such as -γ-butyrolactone, α-angelicalactone, α-methylene-γ-butyrolactone, γ-hexanolactone, γ-nonanolactone, γ-octanolactone, and γ-methyl-γ-decanolactone. . Any one of these may be used alone, or a plurality of these may be used in combination. Among these, it is particularly preferable to use at least one selected from the group consisting of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone and γ-valerolactone.

  The concentration of the carboxylic acid ester is preferably in the range of 0.5 to 30% by mass, and more preferably in the range of 5 to 30% by mass in the nonaqueous electrolytic solution. If the concentration is lower than this, the effect of high electrical conductivity due to the carboxylic acid ester is lowered, and if the concentration is higher than this, the influence of decomposition of the carboxylic acid ester is increased.

  As the nitrile compound, one represented by the following formula (3) is used. By adding the nitrile compound to the non-aqueous electrolyte, the viscosity of the non-aqueous electrolyte can be reduced and the electrical conductivity of the non-aqueous electrolyte can be improved.

R ³ -CN (3)
R ³ in Formula (3) is a hydrocarbon group and may have a halogen atom. Examples of the hydrocarbon group include a methyl group, an ethyl group, a propyl group, and a butyl group. The halogen atom may be any of a fluorine atom, a bromine atom, an iodine atom, and a chlorine atom.

  Examples of the nitrile compound represented by the formula (3) include acetonitrile (AN), propionitrile (PN), butyronitrile, isobutyronitrile, valeronitrile, hexanenitrile, octanenitrile, undecanenitrile, decanenitrile, and cyclohexanecarbox. Examples include nitrile, benzonitrile, phenylacetonitrile, acrylonitrile, trimethylacetonitrile, and crotonnitrile. Any one of these may be used alone, or a plurality of these may be used in combination. Among these, it is particularly preferable to use at least one selected from acetonitrile and propionitrile.

  The concentration of the nitrile compound is preferably in the range of 0.5 to 20% by mass and more preferably in the range of 5 to 20% by mass in the non-aqueous electrolyte. This is because if the concentration is lower than this, the effect of high electrical conductivity by the nitrile compound is lowered, and if the concentration is higher than this, the influence of decomposition of the nitrile compound is increased.

  Mixing ratio of fluorinated ether and at least one selected from carboxylic acid ester and nitrile compound (fluorinated ether compound: at least one selected from carboxylic acid ester and nitrile compound) (mass ratio) is 1 to It is preferably within the range of 20: 20-1.

  The non-aqueous solvent described above can be used in combination with other non-aqueous solvents. Examples of non-aqueous solvents that can be used in combination include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and vinylene carbonate (VC). Etc. The concentration of the carbonate ester in the non-aqueous electrolyte is preferably in the range of 60 to 95% by mass. Moreover, it is preferable that the density | concentration of vinylene carbonate in a nonaqueous electrolyte solution exists in the range of 0.5-5 mass%.

A conventionally well-known thing can be used as electrolyte salt dissolved in said nonaqueous solvent. Specific examples include lithium salts. Examples include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF). ₆ ), lithium trifluoromethanesulfonate (CF ₃ SO ₃ Li), bis (trifluoromethanesulfonyl) imido lithium ((CF ₃ SO ₂ ) ₂ NLi), tris (trifluoromethanesulfonyl) methyl lithium ((CF ₃ SO ₂ ) ₃ CLi). Any one of these may be used alone, or a plurality of these may be used in combination. The concentration of the electrolyte salt in the non-aqueous electrolyte is preferably in the range of 0.5 to 2.0 mol / kg, regardless of which electrolyte salt is used.

  As a positive electrode and a negative electrode of a non-aqueous electrolyte battery using the non-aqueous electrolyte of the present invention, those normally used for this type of non-aqueous electrolyte battery can be used. FIG. 1 shows a configuration example of a lithium ion secondary battery (hereinafter also referred to as a battery) as a nonaqueous electrolyte battery to which the present invention is applied.

  The lithium ion secondary battery shown in FIG. 1 is a so-called cylindrical type, and a strip-shaped positive electrode 21 and a strip-shaped negative electrode 22 are interposed in a substantially hollow cylindrical battery can 11 via a separator 23. The wound electrode body 20 is wound. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a non-aqueous electrolyte, which is a liquid electrolyte, is injected and impregnated in the separator 23. In addition, a pair of insulating plates 12 and 13 are respectively disposed perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14, and a heat sensitive resistor (PTC element) 16 are caulked through a gasket 17. The inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  The positive electrode 21 has, for example, a structure in which a positive electrode mixture layer is provided on both surfaces or one surface of a positive electrode current collector having a pair of opposed surfaces, although not shown. The positive electrode current collector is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode mixture layer includes, for example, a positive electrode active material, and may include a conductive agent such as a carbon material and a binder such as polyvinylidene fluoride as necessary.

Examples of the positive electrode active material include a chemical formula Li _x MO ₂ (x is in the range of 0.5 to 1.1, and M is one or more compounds of transition metals). And lithium-containing metal oxides such as TiS ₂ , MoS ₂ , NbSe ₂ , and V ₂ O ₅ , metal oxides, and specific polymers. Among these, as the lithium composite oxide, for example, LiCoO ₂ , LiNiO ₂ , Li _x Ni _y Co _1-y O ₂ (x and y are different depending on the charge / discharge state of the battery, and usually 0 <x <1, 0. 7 <y <1.02), and spinel type lithium / manganese composite oxide represented by LiMn ₂ O ₄ or the like. And in the positive electrode 2, it is also possible to mix and use any 1 type or multiple types among the metal sulfide mentioned above, a metal oxide, lithium composite oxide, etc. as a positive electrode active material.

  Although not shown, the negative electrode 22 has, for example, a structure in which a negative electrode mixture layer is provided on both surfaces or one surface of a negative electrode current collector having a pair of opposed surfaces, similarly to the positive electrode 21. The negative electrode 22 is formed by sputtering or vapor deposition of a metal capable of doping / dedoping lithium on the negative electrode current collector, and then annealed to form a doped / undoped lithium on the negative electrode current collector. You may use what formed the metal of possible film. The negative electrode current collector is made of metal foil such as copper foil, nickel foil, and stainless steel foil. The negative electrode mixture layer includes, for example, a negative electrode active material, and may include a binder such as polyvinylidene fluoride as necessary.

Examples of the negative electrode active material include metals, alloys, elements, and compounds thereof that can be combined with lithium. As the negative electrode active material, for example, when M is an element that can be combined with lithium, M _x M ′ _y Li _z (M ′ is a Li element and a metal element other than the M element, and x is a value larger than 0) , Y and z are numerical values of 0 or more). In this chemical formula, for example, B, Si, As, etc., which are semiconductor elements, are also mentioned as metal elements. Specifically, for example, elements such as Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, Y, B, Si, As, and the like Compounds containing these elements, Li-Al, Li-Al-M (M is one or more of 2A, 3B, 4B transition metal elements), AlSb, CuMgSb, etc. Can be mentioned.

As an element capable of combining with lithium, for example, a group 4B typical element is preferable, among which Si and Sn are more preferable, and Si is particularly preferable. Specifically, as the Si compound and Sn compound represented by the chemical formula of M _x Si, M _x Sn (M is one or more elements other than Si and Sn, and x is a numerical value of 0 or more) For example, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi _2, etc., and any one or a combination of these may be used.

Furthermore, examples of the negative electrode active material also include 4B group element compounds other than carbon containing one or more kinds of nonmetallic elements. This compound may contain a plurality of 4B group elements. Specifically, for example, SiC, Si ₃ N ₄ , Si ₂ N ₂ O, Ge ₂ N ₂ O, SiO _x (0 <x ≦ 2), SnO _x (0 <x ≦ 2), LiSiO, LiSnO, etc. Any one or a combination of these may be used.

  The compound used as the negative electrode active material is synthesized, for example, by subjecting the raw material of the compound to heat treatment at a predetermined temperature for a predetermined time in an inert gas atmosphere or a reducing gas atmosphere. Without being limited, they may be synthesized by various methods. Specifically, it is synthesized by, for example, a mechanical alloying method, a melt spinning method, a gas atomizing method, a water atomizing method, or the like. And although the compound synthesize | combined by these methods may be grind | pulverized and made into a powder, it can also be used with a solid substance, without grind | pulverizing. In addition, when doping a compound or the like used as the negative electrode active material with lithium, for example, lithium is supplied from a positive electrode 5 or a lithium source other than the positive electrode 5 before or after manufacturing the battery and electrochemically doped. It is performed by including lithium during the synthesis of the substance.

  Examples of the negative electrode active material include a carbonaceous material that can be doped / undoped with lithium ions in addition to the above-described compounds. Examples of such carbonaceous materials include graphites such as artificial graphite and natural graphite, non-graphitizable carbon, pyrolytic carbons, cokes such as pitch coke, needle coke, and petroleum coke, glassy carbon fiber, phenol Examples include organic polymer compound fired bodies, carbon fibers, activated carbon, carbon blacks, etc., which are carbonized by firing resin or furan resin at an appropriate temperature, and any one or more of these are mixed. And use. When these carbonaceous materials are contained in the negative electrode active material layer, they also function as a conductive material that improves the conductivity of the negative electrode active material layer.

  The separator separates the positive electrode and the negative electrode, and allows lithium ions in the non-aqueous electrolyte to pass through while preventing a short circuit of current due to contact between both electrodes. A separator consists of a microporous film | membrane which has many micropores. Here, the microporous membrane is a resin membrane having a large number of micropores having an average pore diameter of about 5 μm or less. Moreover, as a separator, what has been used for the conventional battery as a material can be utilized. Among these, it is preferable to use a microporous film made of polyolefin such as polypropylene or polyethylene, which is excellent in short-circuit prevention effect and can improve battery safety by a shutdown effect.

  The separator has a thickness in the range of 5 μm or more and 50 μm or less, and a porosity that represents the ratio of the void volume in the entire volume in the range of 20% or more and 60% or less. By using a separator that meets such conditions, it is possible to obtain a battery having excellent manufacturing yield, output characteristics, cycle characteristics, and safety.

  The battery configured as described above is manufactured as follows.

  First, the positive electrode is manufactured as follows, for example. A positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methylpyrrolidone to obtain a positive electrode mixture coating solution. Next, the positive electrode mixture coating liquid is applied to the positive electrode current collector and dried, and then compression molded to form a positive electrode mixture layer, whereby the positive electrode 21 is produced.

  Moreover, a negative electrode is produced as follows, for example. A negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent such as N-methylpyrrolidone to obtain a negative electrode mixture coating solution. Next, the negative electrode mixture coating liquid is applied to the negative electrode current collector and dried, and then compression molded to form a negative electrode mixture layer, whereby the negative electrode 22 is produced.

  Subsequently, the positive electrode lead 25 is attached to the positive electrode current collector by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector by welding or the like. Thereafter, the positive electrode 21 and the negative electrode 22 were wound through the separator 23, and the tip portion of the positive electrode lead 25 was welded to the safety valve mechanism 15, and the tip portion of the negative electrode lead 26 was welded to the battery can 11 and wound. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and housed in the battery can 11. Next, a non-aqueous electrolyte is injected into the battery can 11. Thereafter, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through the gasket 17.

  As described above, the lithium ion secondary battery shown in FIG. 1 is completed. In this lithium ion secondary battery, when charged, for example, lithium ions are detached from the positive electrode 21 and inserted in the negative electrode 22 through the electrolyte. When discharging is performed, for example, lithium ions are separated from the negative electrode 22 and inserted into the positive electrode 21 through the electrolyte.

  In the above description, the lithium ion secondary battery has been described as an example. However, the present invention is not limited to this, and the nonaqueous electrolytic solution of the present invention can also be applied to a primary battery. In addition, the above description is about a cylindrical secondary battery. However, the non-aqueous electrolyte of the present invention can be applied to an exterior material such as a coin battery, a square battery, a button battery, etc. The present invention can be applied to non-aqueous electrolyte batteries having any shape and size, such as batteries using a battery and batteries using a laminate film as an exterior material such as a thin battery.

  Further, specific embodiments of the present invention will be described in detail.

<Battery manufacturing method>
As Examples 1 to 21 and Comparative Examples 1 to 11, lithium ion secondary batteries described in the above-described embodiment were manufactured. First, 94 parts by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 3 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder are mixed uniformly. N-methylpyrrolidone was added to obtain a positive electrode mixture coating solution. Next, the obtained positive electrode mixture coating liquid was uniformly applied to a positive electrode current collector made of an aluminum foil having a width of 56 mm, a length of 550 mm, and a thickness of 20 μm and dried to form a positive electrode mixture layer having a thickness of 70 μm. Similarly, a positive electrode mixture layer having a thickness of 70 μm was also formed on the back surface of the positive electrode current collector. Thereafter, a positive electrode lead 25 made of aluminum was attached to one end of the positive electrode current collector.

  Further, 94 parts by mass of graphite as a negative electrode active material and 6 parts by mass of polyvinylidene fluoride as a binder were uniformly mixed, and then N-methylpyrrolidone was added to obtain a negative electrode mixture coating solution. Next, the obtained negative electrode mixture coating liquid was uniformly applied to a negative electrode current collector made of a copper foil having a width of 58 mm, a length of 600 mm, and a thickness of 15 μm, and dried to form a negative electrode mixture layer having a thickness of 70 μm. Similarly, a negative electrode mixture layer having a thickness of 70 μm was also formed on the back surface of the negative electrode current collector. Thereafter, a nickel negative electrode lead 26 was attached to one end of the negative electrode current collector.

  Subsequently, after laminating the positive electrode 21 and the negative electrode 22 with a separator 23 made of a microporous polypropylene film having a thickness of 25 μm, the wound electrode body 20 is formed by winding it with a winder. The battery can 11 was housed in a stainless steel can 11 made of 18 mm and 65 mm long. The capacity of this battery was 2400 mAh.

  Next, a nonaqueous electrolytic solution having the composition shown in Table 1 was injected into the battery can 11 with a liquid injector. As the electrolyte salt, lithium hexafluorophosphate was used at a concentration of 1.3 mol / kg. Each non-aqueous electrolyte contained 1% by weight of vinylene carbonate. The liquid injection was performed by placing the battery in a dedicated liquid injection machine and then injecting 4 g of the non-aqueous electrolyte at 2 atm. Thereafter, the battery lid 14 was caulked to the battery can 11 via the gasket 17 to obtain the cylindrical lithium ion secondary battery shown in FIG.

<Evaluation of electrolyte and battery>
(1) Liquid injection test The impregnation property of the non-aqueous electrolyte into the lithium ion secondary battery was examined by a liquid injection test. 4 g of the non-aqueous electrolyte having the composition shown in Table 1 was injected into the battery at 2 atm using a liquid injector, and the time until the non-aqueous electrolyte was completely injected into the battery was defined as the injection time. did. Based on the injection time of EC / DMC (30:70 mass ratio) with a non-aqueous electrolyte (Comparative Example 1), the shortening rate of the injection time with each non-aqueous electrolyte was calculated as a percentage. The results are shown in Table 1.
(2) Charging / discharging test The characteristic of the lithium ion secondary battery was investigated by the charging / discharging test. The lithium ion secondary battery obtained by the above manufacturing method was charged with a constant current and a constant voltage for 3.5 hours at 23 ° C. with a maximum of 4.2 V at 2.4 A, and then rested for 30 minutes and then 3 V at 2.4 A. The cycle of discharging until the value reached was repeated. After 100 cycles, the discharge capacity retention rate (%) was calculated with the discharge capacity at the first cycle as 100. The results are shown in Table 1.

  As can be seen from Table 1, in Examples 1 to 21 in which a fluorinated ether and a carboxylic acid ester or a nitrile compound or a mixture thereof were added to the non-aqueous electrolyte, these solvents were not added to the non-aqueous electrolyte. Compared with the comparative example 1, it showed a high discharge capacity maintenance rate and the injection time was shortened. For example, on the basis of Comparative Example 1, in Example 4, the injection time was shortened by 22%.

  Further, as can be seen from Table 1, when the concentration of the fluorinated ether, carboxylic acid ester, and nitrile compound in the nonaqueous electrolytic solution is 0.5% by mass or more, a higher effect of shortening the injection time is shown. It was. However, in Comparative Example 4 in which the concentration of the fluorinated ether in the nonaqueous electrolytic solution was 30% by mass, the fluorinated ether was not dissolved in the nonaqueous electrolytic solution and phase-separated, so that the liquid injection test and the battery characteristic test could not be performed. It was. And in the comparative example 5 which made the density | concentration of the carboxylic acid ester in a nonaqueous electrolyte solution 40 mass%, and the comparative example 6 which made the density | concentration of the nitrile compound in a nonaqueous electrolyte solution 30 mass%, a carboxylic acid ester or a nitrile compound As a result, the effect of the decomposition became large, and a high discharge capacity retention rate could not be obtained.

  Furthermore, Comparative Examples 2 and 3 in which fluorinated ether was added alone to the non-aqueous electrolyte resulted in a long injection time although the discharge capacity retention rate was high. Moreover, in Comparative Examples 7 to 11 in which the carboxylic acid ester and the nitrile compound were each added to the nonaqueous electrolytic solution alone, the discharge capacity retention rate was high, but the injection time was long, or the discharge capacity retention rate was higher than in the examples. The result was low.

  That is, it has been found that the coexistence of fluorinated ether and at least one of carboxylic acid ester and nitrile compound in the non-aqueous electrolyte exhibits a high discharge capacity maintenance rate and an effect of shortening the injection time. In addition, the concentration of the fluorinated ether is in the range of 0.5 to 20% by mass in the non-aqueous electrolyte, and the concentration of the carboxylic acid ester is in the range of 0.5 to 30% by mass in the non-aqueous electrolyte. It was found that a higher effect can be obtained if the concentration of the nitrile compound is set within the range of 0.5 to 20% by mass in the nonaqueous electrolytic solution.

It is a schematic sectional drawing which shows the internal structure of the lithium ion secondary battery which concerns on one embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Battery can, 12, 13 ... Insulation board, 14 ... Battery cover, 15 ... Safety valve mechanism, 15A ... Disc board, 16 ... Heat sensitive resistance element, 17 ... Gasket, 20 ... Winding electrode body, 21 ... Positive electrode, 22 ... Negative electrode, 23 ... Separator, 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead

Claims (14)

A non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent,
The non-aqueous solvent is at least one selected from a fluorinated ether represented by the following formula (1), a carboxylic acid ester represented by the following formula (2), and a nitrile compound represented by the following formula (3). A non-aqueous electrolyte characterized by containing a seed.
_{C n H 2n + 1 -O-} C m F 2m + 1 (1)
[In Formula (1), n represents 1-4, m represents the integer of 1-6. ]
R ¹ —COO—R ² (2)
[In Formula (2), R ¹ and R ² are hydrocarbon groups, and either or both of R ¹ and R ² may have a halogen atom or an unsaturated bond. R ¹ and R ² may be bonded to each other to have a cyclic structure. ]
R ³ -CN (3)
[In Formula (3), R ³ is a hydrocarbon group and may have a halogen atom. ]   The non-aqueous electrolyte according to claim 1, wherein the fluorinated ether is at least one selected from methyl nonafluorobutyl ether and ethyl nonafluorobutyl ether.   The carboxylic acid ester is at least one selected from the group consisting of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and γ-valerolactone. Non-aqueous electrolyte.   The non-aqueous electrolyte according to claim 1, wherein the nitrile compound is at least one selected from acetonitrile and propionitrile.   The non-aqueous electrolyte according to claim 1, wherein the concentration of the fluorinated ether is 0.5 to 20% by mass in the non-aqueous electrolyte.   The nonaqueous electrolytic solution according to claim 1, wherein the concentration of the carboxylic acid ester is 0.5 to 30% by mass in the nonaqueous electrolytic solution.   The non-aqueous electrolyte according to claim 1, wherein the concentration of the nitrile compound is 0.5 to 20% by mass in the non-aqueous electrolyte. A nonaqueous electrolyte battery comprising a positive electrode and a negative electrode, and a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent,
The non-aqueous solvent is at least one selected from a fluorinated ether represented by the following formula (1), a carboxylic acid ester represented by the following formula (2), and a nitrile compound represented by the following formula (3). A non-aqueous electrolyte battery comprising a seed.
_{C n H 2n + 1 -O-} C m F 2m + 1 (1)
[In said formula (1), n represents 1-4, m represents the integer of 1-6. ]
R ¹ —COO—R ² (2)
[In the above formula (2), R ¹ and R ² are hydrocarbon groups, and either one or both of R ¹ and R ² may have a halogen atom or an unsaturated bond. R ¹ and R ² may be bonded to each other to have a cyclic structure. ]
R ³ -CN (3)
[In the above formula (3), R ³ is a hydrocarbon group and may have a halogen atom. ]   9. The nonaqueous electrolyte battery according to claim 8, wherein the fluorinated ether is at least one selected from methyl nonafluorobutyl ether and ethyl nonafluorobutyl ether.   The carboxylic acid ester is at least one selected from the group consisting of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and γ-valerolactone. Non-aqueous electrolyte battery.   The non-aqueous electrolyte battery according to claim 8, wherein the nitrile compound is at least one selected from acetonitrile and propionitrile.   The non-aqueous electrolyte battery according to claim 8, wherein the concentration of the fluorinated ether is 0.5 to 20% by mass in the non-aqueous electrolyte.   The nonaqueous electrolyte battery according to claim 8, wherein the concentration of the carboxylic acid ester is 0.5 to 30% by mass in the nonaqueous electrolyte.   The non-aqueous electrolyte battery according to claim 8, wherein the concentration of the nitrile compound is 0.5 to 20% by mass in the non-aqueous electrolyte.

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