JP2007335170A - Nonaqueous electrolyte, and nonaqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte and a nonaqueous electrolyte battery capable of improving a discharge capacity maintenance rate in a charging/discharging cycle by selecting an additive suitable for a saturated chain carboxylic acid ester. <P>SOLUTION: The nonaqueous electrolyte contains at least one kind of saturated chain carboxylic acid ester expressed by the formula and at least one kind of unsaturated chain carboxylic acid ester. The discharge capacity maintenance rate in the charge/discharge cycle can be improved thereby. R<SB>1</SB>and R<SB>2</SB>in the formula are each hydrocarbon group having a carbon number of not less than one and not more than 3. Either R<SB>1</SB>or R<SB>2</SB>, or both of them can have an unsaturated bond. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte battery. More specifically, the present invention relates to a non-aqueous electrolyte having a lithium salt and a non-aqueous electrolyte battery using the same.

  In recent years, portable information terminals such as mobile phone devices and notebook personal computers have been rapidly reduced in size and weight, and research and development have been actively conducted to reduce the weight and increase the output power of driving power sources. Lithium ion secondary batteries use lithium compounds as active materials, have characteristics such as light weight, high voltage, and high energy density, and are widely put into practical use as power sources for portable terminals.

  A cyclic carbonate organic solvent such as ethylene carbonate (EC) or propylene carbonate (PC) is often used for the electrolyte of the lithium ion secondary battery. 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 high potentials specific to lithium ion secondary batteries, There is a problem in that the viscosity of the solution is high and efficient ion transfer is hindered. 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 electrolytic solution because the choice of solvent is narrow with only carbonate esters. In addition, since some carbonates have a high melting point and solidify at a low temperature, for example, the discharge characteristics at a low temperature in a battery in which the electrode active material is thickly applied and the energy density is improved still has problems to be improved. ing. Furthermore, it is difficult to obtain high electrical conductivity for more effective ion transfer only with a carbonate ester mixture.

Thus, for example, as described in Patent Document 1, methyl acetate (CH ₃ COOCH ₃ ), methyl propionate (CH ₃ CH ₂ ) having a lower melting point and lower viscosity than carbonic acid esters and high electrical conductivity. A method of adding a saturated chain carboxylic acid ester such as COOCH ₃ ) to the electrolytic solution has been proposed. The saturated chain carboxylic acid ester can increase the electric conductivity of the electrolyte and can improve the low-temperature characteristics of the battery.

JP 2004-319212 A

  However, the saturated chain carboxylic acid ester has a narrow potential window as compared with the carbonate ester, and therefore decomposes during the charge / discharge process of the lithium ion secondary battery. For this reason, the fall of the discharge capacity maintenance factor when repeating a charging / discharging cycle has been a problem.

  In order to suppress decomposition of the solvent during the charge / discharge process, conventionally, a method of adding a cyclic carbonate having an unsaturated bond such as vinylene carbonate (VC) or vinyl ethylene carbonate (VEC) to the electrolytic solution has been proposed. . This method is considered to be able to suppress decomposition of the solvent by reducing and decomposing the unsaturated cyclic carbonate during the initial charge of the battery, thereby forming a film and preventing contact between the electrode and the solvent molecule.

  In addition to the cyclic carbonate, for example, as described in Patent Document 2, there is a technique for improving battery characteristics by adding an unsaturated carboxylic acid ester such as a carboxylic acid vinyl ester as an additive to the electrolytic solution. Proposed.

Japanese Patent No. 3633269

  However, cyclic carbonates having an unsaturated bond, such as vinylene carbonate (VC), are widely used as additives for suppressing the decomposition of the solvent, but are optimal additives for electrolytes containing saturated chain carboxylic acid esters. Not necessarily. In addition, there is no systematic index for selecting the most suitable additive for electrolytes containing saturated chain carboxylic acid esters, and we are currently searching for the most suitable additive through trial and error. It is.

  Further, Patent Document 2 is directed to an electrolytic solution using only carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) as a solvent, and is an electrolysis having a high electrical conductivity containing a saturated chain carboxylic acid ester. There is no description or suggestion regarding the effect on the liquid.

  Accordingly, an object of the present invention is to provide a non-aqueous electrolyte and a non-aqueous electrolyte battery that can improve the discharge capacity maintenance rate in the charge / discharge cycle by selecting an additive suitable for the saturated chain carboxylic acid ester. It is in.

（式中、Ｒ₁およびＲ₂は、炭素数１以上３以下の炭化水素基である。Ｒ₁およびＲ₂のいずれか、または両方に不飽和結合を有していてもよい。） In order to solve the above-described problem, the first invention includes at least one saturated chain carboxylic acid ester represented by Chemical Formula 1 and at least one unsaturated chain carboxylic acid ester. It is a non-aqueous electrolyte.

(In the formula, R ₁ and R ₂ are each a hydrocarbon group having 1 to 3 carbon atoms. Either or both of R ₁ and R ₂ may have an unsaturated bond.)

（式中、Ｒ₁およびＲ₂は、炭素数１以上３以下の炭化水素基である。Ｒ₁およびＲ₂のいずれか、または両方に不飽和結合を有していてもよい。） The second invention comprises a positive electrode and a negative electrode, and a non-aqueous electrolyte,
Non-aqueous electrolyte
A non-aqueous electrolyte battery comprising at least one saturated chain carboxylic acid ester represented by Chemical Formula 2 and at least one unsaturated chain carboxylic acid ester.

(In the formula, R ₁ and R ₂ are each a hydrocarbon group having 1 to 3 carbon atoms. Either or both of R ₁ and R ₂ may have an unsaturated bond.)

  In the first invention, since the saturated chain carboxylic acid ester represented by Chemical Formula 1 and the unsaturated chain carboxylic acid ester represented by Chemical Formula 1 are included, decomposition of the electrolyte solvent can be suppressed.

  In the second invention, since the electrolytic solution containing the saturated chain carboxylic acid ester represented by Chemical Formula 2 and the unsaturated chain carboxylic acid ester represented by Chemical Formula 2 is used, the discharge capacity is maintained in the charge / discharge cycle. The rate can be improved.

  According to this invention, the discharge capacity maintenance rate in the charge / discharge cycle can be improved.

  Embodiments of the present invention will be described below with reference to the drawings. The nonaqueous electrolytic solution according to an embodiment of the present invention includes, for example, a solvent and an electrolyte salt dissolved in the solvent.

  As the solvent, a solvent containing at least one saturated chain carboxylic acid ester represented by Chemical Formula 3 and at least one unsaturated chain carboxylic acid ester represented by Chemical Formula 3 is used. By including the saturated chain carboxylic acid ester represented by Chemical Formula 3, the electrical conductivity of the electrolytic solution can be improved. Moreover, the unsaturated chain carboxylic acid ester represented by Chemical Formula 3 can be added as an additive, and by containing this, decomposition of the solvent can be suppressed.

（式中、Ｒ₁およびＲ₂は、炭素数１以上３以下の炭化水素基である。Ｒ₁およびＲ₂のいずれか、または両方に不飽和結合を有していてもよい。）

(In the formula, R ₁ and R ₂ are each a hydrocarbon group having 1 to 3 carbon atoms. Either or both of R ₁ and R ₂ may have an unsaturated bond.)

More specifically, examples of the saturated chain carboxylic acid ester include methyl acetate (CH ₃ COOCH ₃ ), ethyl acetate (CH ₃ COOCH ₂ CH ₃ ), methyl propionate (CH ₃ CH ₂ COOCH ₃ ), and propion. And compounds such as ethyl acetate (CH ₃ CH ₂ COOCH ₂ CH ₃ ).

  More specific examples of the unsaturated chain carboxylic acid ester include methyl acrylate, ethyl acrylate, vinyl acetate, and vinyl crotonate.

From that we can obtain a more excellent charge-discharge cycle characteristics, and R ₁ a saturated chain carboxylate, it is more preferable that the difference of the number of carbon atoms of the unsaturated chain carboxylate R ₁ is 1 or less . Also, as R ₂ of saturated chain carboxylate, it is more preferable that the difference of the number of carbon atoms of the unsaturated chain carboxylate R ₂ is 1 or less.

Further, from the viewpoint of capable of obtaining a particularly excellent charge-discharge cycle characteristics, and R ₁ a saturated chain carboxylate, the difference of the number of carbon atoms of the unsaturated chain carboxylate R ₁ is 1 or less, The difference in carbon number between R ₂ of the saturated chain carboxylic acid ester and R ₂ of the unsaturated chain carboxylic acid ester is particularly preferably 1 or less.

Specifically, for example, when the saturated chain carboxylic acid ester is methyl propionate (R ₁ = ethyl group, R ₂ = methyl group), it is unsaturated with the same number of carbon atoms as the straight chain hydrocarbon group of methyl propionate. A methyl acrylate having a bond (R ₁ = vinyl group, R ₂ = methyl group) is preferred.

Further, for example, when the saturated chain carboxylic acid ester is methyl acetate (R ₁ = R ₂ = methyl group), vinyl acetate (R ₁ = methyl) in which the carbon number of the linear hydrocarbon group is extended within ₁ Groups, R ₂ = vinyl group) and unsaturated chain carboxylic acid esters such as vinyl acrylate (R ₁ = R ₂ = vinyl group) are preferred.

  The total concentration of the saturated and unsaturated chain carboxylic acid ester is preferably in the range of 10% by weight to 30% by weight with respect to the electrolytic solution. This is because more excellent charge / discharge cycle characteristics can be obtained.

  The concentration of the saturated chain carboxylic acid ester is more preferably in the range of 10% by weight to 30% by weight in order to impart high electrical conductivity to the electrolytic solution, and is preferably in the range of 10% by weight to 20% by weight. It is particularly preferable that it is within the range. By increasing the concentration of the saturated chain carboxylic acid ester, high electrical conductivity can be obtained. However, if the concentration exceeds 30% by weight, the influence of decomposition of the saturated chain carboxylic acid ester becomes large in the charge / discharge cycle. This is because the discharge capacity retention rate is reduced. Further, when the concentration is less than 10% by weight, the electric conductivity is reduced.

  The concentration of the unsaturated chain carboxylic acid ester is more preferably 1% by weight or less from the viewpoint that if it is too high, an excessive film may be formed on the electrode and the charge / discharge cycle may be deteriorated.

  Moreover, as a solvent, you may mix and use the conventionally used various solvent. Examples of such a solvent include carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

Examples of lithium salts that are electrolyte salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), and trifluoromethane. Lithium sulfonate (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), etc. Can be used. Any one of these may be used, but two or more may be used in combination.

  For example, secondary batteries such as lithium batteries having various shapes and sizes can be manufactured using the nonaqueous electrolytic solution according to the embodiment of the present invention.

  A first example of a battery using a nonaqueous electrolytic solution according to one embodiment of the present invention will be described below. FIG. 1 shows a configuration example of a nonaqueous electrolyte battery according to an embodiment of the present invention. This nonaqueous electrolyte battery is, for example, a lithium ion secondary battery having a coin shape.

  As shown in FIG. 1, the nonaqueous electrolyte battery 1 includes a positive electrode 2, a positive electrode can 3 that accommodates the positive electrode 2, a negative electrode 4, a negative electrode can 5 that accommodates the negative electrode 4, and the positive electrode 2 and the negative electrode 4. A separator 6 disposed therebetween, an insulating gasket 7 that insulates between the positive electrode can 3 and the negative electrode can 5, and a non-aqueous electrolyte 8 are included.

In the positive electrode 2, a positive electrode mixture layer 10 containing, for example, a positive electrode active material, a binder, a conductive agent, and the like is formed on a positive electrode current collector 9. 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 among transition metals). lithium composite _{oxides, TiS 2, M O S 2} , NbSe 2, V 2 O metal sulfide not containing lithium (Li) such as _5, a metal oxide, or may employ certain polymers. Any one or a combination of these lithium composite oxides, metal sulfides, metal oxides, and the like may be used.

Examples of the lithium composite oxide include LiCoO ₂ , LiNiO ₂ , Li _x Ni _y Co _1-y O ₂ (x and y differ depending on the charge / discharge state of the battery, and generally 0 <x <1, 0.7 <y <1.02), and spinel type lithium / manganese composite oxides represented by LiMn ₂ O _{4 and the} like.

  As the positive electrode current collector 9, for example, net-like or foil-like aluminum (Al) or the like can be used. As the binder, a known resin material usually used for this type of non-aqueous electrolyte battery can be used. More specifically, for example, polyvinylidene fluoride (PVdF) can be used. Moreover, as a electrically conductive agent, the well-known thing normally used for this kind of nonaqueous electrolyte battery can be used. More specifically, for example, carbon black, graphite or the like can be used as the conductive agent.

  The positive electrode can 3 is a container made of a conductive metal having a shallow bottom, ie, a petri dish, that accommodates the positive electrode 2, and serves as an external positive electrode of the nonaqueous electrolyte battery 1. Specifically, in the positive electrode can 3, when the positive electrode 2 is accommodated, for example, aluminum (Al), stainless steel (SUS), and nickel (Ni) are sequentially accumulated in the thickness direction from the positive electrode 2. Use a container.

  In the negative electrode 4, a negative electrode mixture layer 12 containing a negative electrode active material is formed on a negative electrode current collector 11. Examples of the negative electrode active material include metals, alloys, elements, and compounds thereof that can be combined with lithium (Li).

Specifically, for example, when M is an element that can be combined with lithium (Li), M _x M ′ _y Li _z (M ′ is a Li element and a metal element other than the M element, and x is a numerical value greater than 0. And y and z are numerical values of 0 or more).

  In this chemical formula, for example, boron (B), silicon (Si), arsenic (As), and the like, which are semiconductor elements, are also mentioned as metal elements. More specifically, for example, magnesium (Mg), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), lead (Pb) ), Antimony (Sb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), arsenic (As), and the like Compounds containing these elements, Li—Al, Li—Al—M (M is one or more of 2A group, 3B group, 4B group transition metal elements), AlSb, CuMgSb, etc. Can be mentioned.

In particular, the element that can be combined with lithium (Li) is preferably a group 4B typical element. Among these, silicon (Si) and tin (Sn) are preferable, and silicon (Si) is more preferable. Specifically, for example, it is represented by a chemical formula of M _x Si, M _x Sn (M is one or more elements other than silicon (Si) and tin (Sn), and x is a numerical value of 0 or more)). A silicon compound and a tin compound are mentioned. More specifically, examples of the silicon compound include 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, and FeSi _2. , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi _2, etc., and any one or a mixture of these may be used.

Furthermore, as the negative electrode active material, a group 4B element compound other than carbon containing one or more nonmetallic elements can also be used. 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 lithium (Li) is doped into a compound or the like used as the negative electrode active material, for example, the lithium (Li) is supplied from a positive electrode 5 or a lithium (Li) source other than the positive electrode 5 before or after manufacturing the battery to perform electrochemical For example, by doping or by adding lithium (Li) during the synthesis of the negative electrode active material.

  As the negative electrode active material contained in the negative electrode 4, for example, a carbonaceous material capable of doping and dedoping lithium ions can be used in addition to the above-described compounds. Examples of the carbonaceous material 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, and phenolic resin. Organic polymer compound fired bodies, carbon fibers, activated carbon, carbon blacks, etc., which are carbonized by firing at a suitable temperature or furan resin, etc., and any one or more of these may be mixed Use. When these carbonaceous materials are contained in the negative electrode mixture layer 12, they also function as a conductive agent that improves the conductivity of the negative electrode mixture layer 12.

  In the negative electrode 4, the negative electrode mixture layer 12 can be formed by adding the above-described negative electrode active material to, for example, a binder made of a known resin material commonly used in this type of nonaqueous electrolyte battery. . Specifically, for example, polyvinylidene fluoride or styrene butadiene rubber is used as the binder.

  In the negative electrode 4, a lithium (Li) doped or dedopeable metal or the like is formed on the negative electrode current collector 11 by sputtering or vapor deposition, and then annealed to thereby form lithium (Li) on the negative electrode current collector 11. A material in which a metal capable of being doped and dedoped with Li) may be used.

  The negative electrode can 5 is a container made of a petri dish-like conductive metal that accommodates the negative electrode 4, and serves as an external negative electrode of the nonaqueous electrolyte battery 1. Specifically, for the negative electrode can 5, for example, a metal container made of aluminum (Al), stainless steel, iron (Fe) with nickel (Ni) plating on the surface, or the like is used.

  The separator 6 separates the positive electrode 2 and the negative electrode 4 and allows lithium ions in the non-aqueous electrolyte 8 to pass through while preventing a short circuit of current due to contact between both electrodes. The separator 6 is made of a microporous membrane having a large number of minute pores. 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 the separator 6, what has been used for the conventional battery as a material can be used. Among these, a microporous film made of polypropylene, polyolefin, or the like that is excellent in short-circuit prevention effect and can improve battery safety by a shutdown effect is used.

  For example, the separator 6 has a thickness in the range of 5 μm or more and 50 μm or less, and a porosity representing a ratio of the void volume in the entire volume thereof is in the range of 20% or more and 60% or less. With the separator 6 meeting such conditions, it is possible to obtain the nonaqueous electrolyte battery 1 excellent in manufacturing yield, output characteristics, cycle characteristics, and safety.

  The insulating gasket 7 is integrated and integrated in the negative electrode can 5 and is formed of an organic resin such as polypropylene, for example. The insulating gasket 7 insulates the positive electrode can 3 serving as an external positive electrode and the negative electrode can 5 serving as an external negative electrode, and prevents leakage of the nonaqueous electrolyte 8 filled in the positive electrode can 3 and the negative electrode can 5. Will function.

  Next, a method for manufacturing the nonaqueous electrolyte battery 1 will be described.

  The positive electrode 2 is produced, for example, as described below. First, for example, a positive electrode active material, a conductive agent, and a binder are dispersed in a non-aqueous solvent or the like to prepare a positive electrode mixture coating solution. Next, this positive electrode mixture coating solution is uniformly applied to a metal foil-like positive electrode current collector 9 such as an aluminum (Al) foil, dried, and then compression molded to form the positive electrode mixture layer 10. Form. Thereby, the positive electrode 2 is obtained.

  The negative electrode 4 is produced, for example, as described below. First, for example, a negative electrode active material and a binder are dispersed in a non-aqueous solvent or the like to prepare a negative electrode mixture coating liquid. The negative electrode mixture coating liquid is uniformly applied to a metal foil-like negative electrode current collector 11 such as a copper (Cu) foil, dried, and then compressed to form the negative electrode mixture layer 12. Thereby, the negative electrode 4 is obtained.

  Next, the positive electrode 2 is accommodated in the positive electrode can 3, the negative electrode 4 is accommodated in the negative electrode can 5, and a separator 6 made of a polypropylene porous film or the like is disposed between the positive electrode 2 and the negative electrode 4. Thereby, the non-aqueous electrolyte battery 1 has an internal structure in which the positive electrode 2, the separator 6, and the negative electrode 4 are sequentially laminated.

  Next, the nonaqueous electrolytic solution 8 is poured into the positive electrode can 3 and the negative electrode can 5, and the positive electrode can 3 and the negative electrode can 5 are fixed via the insulating gasket 7. As described above, the coin-type non-aqueous electrolyte battery 1 is manufactured.

  Next, a second example of the non-aqueous electrolyte battery using the non-aqueous electrolyte according to one embodiment of the present invention will be described. FIG. 2 is a cross-sectional view showing a configuration of a second example of the nonaqueous electrolyte battery.

  This non-aqueous electrolyte battery is a so-called cylindrical type, and a pair of strip-like positive electrode 31 and strip-like negative electrode 32 are wound through a separator 33 inside a substantially hollow cylindrical battery can 21. A wound electrode body 30 is provided. The separator 33 is impregnated with an electrolytic solution that is a liquid electrolyte. The battery can 21 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 21, a pair of insulating plates 22 and 23 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 30.

  At the open end of the battery can 21, a battery lid 24, a safety valve mechanism 25 and a thermal resistance element (PTC element) 26 provided inside the battery lid 24 are interposed via a gasket 27. It is attached by caulking, and the inside of the battery can 21 is sealed.

  The battery lid 24 is made of the same material as the battery can 21, for example. The safety valve mechanism 25 is electrically connected to the battery lid 24 via the heat sensitive resistance element 26, and the disk plate 25A 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 24 and the wound electrode body 30 is cut off. When the temperature rises, the heat-sensitive resistor element 26 limits the current by increasing the resistance value, and prevents abnormal heat generation due to a large current. The gasket 27 is made of, for example, an insulating material, and asphalt is applied to the surface.

  The wound electrode body 30 is wound around a center pin 34, for example. A positive electrode lead 35 made of aluminum (Al) or the like is connected to the positive electrode 31 of the spirally wound electrode body 30, and a negative electrode lead 36 made of nickel or the like is connected to the negative electrode 32. The positive electrode lead 35 is welded to the safety valve mechanism 25 to be electrically connected to the battery lid 24, and the negative electrode lead 36 is welded to and electrically connected to the battery can 21.

  FIG. 3 is an enlarged cross-sectional view showing a part of the spirally wound electrode body 30 shown in FIG. Hereinafter, the positive electrode 31, the negative electrode 32, and the separator 33 which comprise a nonaqueous electrolyte battery are demonstrated sequentially, referring FIG.

  The positive electrode 31 has, for example, a structure in which a positive electrode mixture layer 31B is provided on both surfaces of a positive electrode current collector 31A having a pair of opposed surfaces. Although not shown, the positive electrode current collector 31A may have a region where the positive electrode mixture layer 31B is provided only on one surface. The positive electrode current collector 31A is made of, for example, a metal foil such as an aluminum foil.

  The positive electrode mixture layer 31B includes, for example, a positive electrode active material capable of inserting and extracting lithium (Li), and a conductive agent such as graphite and polyvinylidene fluoride (PVDF) as necessary. The binder is included. The positive electrode active material is the same as the positive electrode active material described in the first example.

  The negative electrode 32 has, for example, a structure in which a negative electrode mixture layer 32B is provided on both surfaces of a negative electrode current collector 32A having a pair of opposed surfaces. In addition, although not illustrated, you may make it have the area | region where the negative mix layer 32B was provided only in the single side | surface of 32 A of negative electrode collectors. The negative electrode current collector 32A is made of, for example, a metal foil such as a copper foil.

  The negative electrode mixture layer 32B includes, for example, a negative electrode active material capable of inserting and extracting lithium (Li), and includes a binder similar to that of the positive electrode mixture layer 31B as necessary. It consists of The negative electrode active material is the same as the negative electrode active material described in the first example.

  The separator 33 is the same as the separator 6 described in the second example.

  Next, an example of the manufacturing method of the 2nd example of a nonaqueous electrolyte battery is demonstrated. First, 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-methyl-2-pyrrolidone to obtain a paste-like material. A positive electrode mixture slurry is prepared. Next, this positive electrode mixture slurry is applied to the positive electrode current collector 31A, the solvent is dried, and the positive electrode mixture layer 31B is formed by compression molding using a roll press or the like. Thereby, the positive electrode 31 is obtained.

  Further, for example, a negative electrode active material and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry Is made. Next, the negative electrode mixture slurry is applied to the negative electrode current collector 32A, the solvent is dried, and the negative electrode mixture layer 32B is formed by compression molding using a roll press or the like. Thereby, the negative electrode 32 is obtained. The negative electrode mixture layer 32B may be formed, for example, by any of a vapor phase method, a liquid phase method, and a firing method, or a combination of two or more thereof. As the vapor phase method, for example, a physical deposition method or a chemical deposition method can be used. Specifically, a vacuum vapor deposition method, a sputtering method, an ion plating method, a laser application method, a thermal CVC (Chemical Vapor Deposition). A chemical vapor deposition method) or a plasma CVD method can be used. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. A known method can also be used for the firing method, and for example, an atmosphere firing method, a reaction firing method, or a hot press firing method can be used.

  Next, the positive electrode lead 35 is attached to the positive electrode current collector 31A by welding or the like, and the negative electrode lead 36 is attached to the negative electrode current collector 32A by welding or the like. After that, the positive electrode 31 and the negative electrode 32 are wound through the separator 33, the front end portion of the positive electrode lead 35 is welded to the safety valve mechanism 25, and the front end portion of the negative electrode lead 36 is welded to the battery can 21. The positive electrode 31 and the negative electrode 32 are sandwiched between a pair of insulating plates 22 and 23 and stored in the battery can 21. After the positive electrode 31 and the negative electrode 32 are accommodated in the battery can 21, the electrolytic solution is injected into the battery can 21 and impregnated in the separator 33. After that, the battery lid 24, the safety valve mechanism 25, and the heat sensitive resistance element 26 are fixed to the opening end portion of the battery can 21 by caulking through the gasket 27. Thereby, the nonaqueous electrolyte battery shown in FIG. 2 is obtained.

  In this nonaqueous electrolyte battery, for example, when charged, lithium ions are released from the positive electrode mixture layer 31B, and lithium contained in the negative electrode mixture layer 32B can be inserted and released through the electrolyte solution. Occluded by a negative electrode material. Next, when discharging is performed, lithium ions stored in the negative electrode material capable of inserting and extracting lithium in the negative electrode mixture layer 32B are released and inserted into the positive electrode mixture layer 31B through the electrolytic solution. .

  According to one embodiment of the present invention, excellent cycle characteristics can be obtained by using an electrolytic solution containing at least one saturated chain carboxylic acid ester represented by Chemical Formula 3 and at least one unsaturated chain carboxylic acid ester. Is obtained.

  Furthermore, more excellent charge / discharge cycle characteristics can be obtained when the total content of the saturated chain carboxylic acid ester and the unsaturated chain carboxylic acid ester represented by Chemical Formula 3 is in the range of 10 wt% to 30 wt%.

  Furthermore, by optimizing the combination of the saturated chain carboxylic acid ester and the unsaturated chain carboxylic acid ester represented by Chemical Formula 3 from the number of carbon atoms of the linear hydrocarbon group of the molecular structure, particularly excellent cycle characteristics Can be obtained. The reason why the excellent cycle characteristics can be obtained by optimizing the carbon number is not clear, but the existence state of each carboxylic acid ester in the electrolyte takes a specific structure due to the similarity of the molecular structure. The possibility is considered to be a factor.

  Hereinafter, the present invention will be specifically described with reference to FIG. Note that the present invention is not limited to these examples.

<Example 1>
The positive electrode 2 was produced as described below. First, 94 wt% lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 3 wt% graphite as a conductive agent, and 3 wt% polyvinylidene fluoride (PVDF) as a binder, N-methylpyrrolidone (NMP) as a non-aqueous solvent To prepare a positive electrode mixture coating solution. This positive electrode mixture coating solution was uniformly applied to a positive electrode current collector 9 made of an aluminum (Al) foil having a thickness of 20 μm, dried, and then compression molded to form the positive electrode mixture layer 10.

  The negative electrode 4 was produced as described below. A negative electrode mixture coating liquid was prepared by dispersing 95 wt% of graphite as a negative electrode active material and 5 wt% of polyvinylidene fluoride (PVDF) as a binder in N-methylpyrrolidone (NMP) as a nonaqueous solvent. This negative electrode mixture coating solution was uniformly applied to a negative electrode current collector 11 made of a copper (Cu) foil having a thickness of 15 μm, dried, and then compressed to form a negative electrode mixture layer 12.

  Next, after the positive electrode 2 was accommodated in the positive electrode can 3, the negative electrode 4 was accommodated in the negative electrode can 5, and a separator 6 made of a polypropylene porous film was disposed between the positive electrode 2 and the negative electrode 4. Next, the nonaqueous electrolytic solution 8 was poured into the positive electrode can 3 and the negative electrode can 5, and the positive electrode can 3 and the negative electrode can 5 were fixed via the insulating gasket 7.

As a solvent for the non-aqueous electrolyte 8, ethylene carbonate (EC), dimethyl carbonate (DMC), methyl acetate (CH ₃ COOCH ₃ ), and vinyl acrylate (CH ₂ = CHCOOCH = CH ₂ ) as an additive Were mixed at a weight ratio (EC: DMC: methyl acetate: vinyl acrylate) of 33: 46: 20: 1, and the electrolyte salt was prepared to contain 1 mol / kg of LiPF ₆ . Thus, a coin-type battery of Example 1 was produced.

<Example 2>
As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (CH ₃ COOCH _3), methyl acrylate as an additive (CH ₂ = CHCOOCH ₃₎ a weight ratio (EC: DMC: A coin-type battery of Example 2 was fabricated in the same manner as in Example 1 except that the mixture was mixed at 33: 46: 20: 1 with (methyl acetate: methyl acrylate).

<Example 3>
As a solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), methyl propionate (CH ₃ CH ₂ COOCH ₃ ), and methyl acrylate as an additive are in a weight ratio (EC: DMC: methyl propionate: A coin-type battery of Example 3 was fabricated in the same manner as in Example 1 except that the mixture was mixed with methyl acrylate (33: 46: 20: 1).

<Example 4>
As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl propionate _{(CH 3 CH 2 COOCH 2 CH} 3), and ethyl acrylate as an additive _{(CH 2 = CHCOOCH 2 CH 3} ) A coin-type battery of Example 4 was produced in the same manner as in Example 1 except that mixing was performed at a weight ratio (EC: DMC: ethyl propionate: ethyl acrylate) of 33: 46: 20: 1. did.

<Example 5>
As a solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), methyl acetate (CH ₃ COOCH ₃ ), and vinyl crotonate as an additive are in a weight ratio (EC: DMC: methyl acetate: vinyl crotonate). A coin-type battery of Example 5 was produced in the same manner as in Example 1 except that the mixing was performed so that the ratio was 33: 46: 20: 1.

<Example 6>
As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (CH ₃ COOCH _3), methyl acrylate as an additive (CH ₂ = CHCOOCH ₃₎ a weight ratio (EC: DMC: A coin-type battery of Example 6 was fabricated in the same manner as Example 1 except that the mixture was mixed with methyl acetate: methyl acrylate) to be 33: 61: 5: 1.

<Example 7>
As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (CH ₃ COOCH _3), methyl acrylate as an additive (CH ₂ = CHCOOCH ₃₎ a weight ratio (EC: DMC: A coin-type battery of Example 7 was fabricated in the same manner as in Example 1 except that the mixture was mixed at 33: 56: 10: 1 with (methyl acetate: methyl acrylate).

<Example 8>
As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (CH ₃ COOCH _3), methyl acrylate as an additive (CH ₂ = CHCOOCH ₃₎ a weight ratio (EC: DMC: A coin-type battery of Example 8 was fabricated in the same manner as in Example 1 except that the mixture was mixed with methyl acetate: methyl acrylate) to be 33: 37: 29: 1.

<Example 9>
As the solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (CH ₃ COOCH _3), methyl acrylate as an additive (CH ₂ = CHCOOCH ₃₎ a weight ratio (EC: DMC: A coin-type battery of Example 9 was produced in the same manner as in Example 1 except that the mixture was mixed at 33: 26: 40: 1 with (methyl acetate: methyl acrylate).

<Comparative Example 1>
As a solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl acetate (CH ₃ COOCH ₃ ) were mixed at a weight ratio (EC: DMC: methyl acetate) of 33:47:20. A coin-type battery of Comparative Example 1 was produced in the same manner as Example 1 except for the above.

<Comparative example 2>
As a solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), methyl propionate (CH ₃ CH ₂ COOCH ₃ ), and vinyl sorbate as an additive are in a weight ratio (EC: DMC: methyl propionate: sorbine). A coin-type battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the mixture was mixed at 33: 46: 20: 1 with vinyl acid).

<Comparative Example 3>
As a solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl propionate (CH ₃ CH ₂ COOCH ₂ CH ₃ ), and vinylene carbonate (VC) as an additive were in a weight ratio (EC: DMC: A coin-type battery of Comparative Example 3 was produced in the same manner as in Example 1 except that the mixture was mixed with methyl propionate (VC) at 33: 46: 20: 1.

Next, with respect to the coin-type batteries of Examples 1 to 9 and Comparative Examples 1 to 3 manufactured, first, constant current and constant voltage charging of 1.77 mA was performed up to an upper limit of 4.2 V, and then 1.77 mA. The charge / discharge was performed by performing a constant current discharge to a final voltage of 3.0V. Moreover, this charging / discharging operation was repeated 30 times. The discharge capacity retention ratio was obtained by calculating the ratio of the discharge capacity at the 30th cycle to the discharge capacity at the 2nd cycle by the following formula 1.
(Formula 1)
Discharge capacity retention rate (%) = (“Discharge capacity at 30th cycle” / “Discharge capacity at 2nd cycle”) × 100 (%)

  Table 1 shows the discharge capacity retention rates of Examples 1 to 9 and Comparative Examples 1 to 3.

As shown in Table 1, in Example 1 to Example 2, the discharge capacity retention rate was improved as compared with Comparative Example 1 in which an electrolytic solution differing only in not containing an unsaturated chain carboxylic acid ester was used. In Example 3, the discharge capacity retention rate was improved as compared with Comparative Example 2 in which an electrolyte solution differing only in that it contained vinyl sorbate having a hydrocarbon group R ₁ having a carbon number greater than 3 instead of methyl acrylate. In Example 4, the discharge capacity retention rate was improved over Comparative Example 3 in which an electrolytic solution differing only in containing vinylene carbonate of an unsaturated cyclic carboxylic acid ester instead of ethyl acrylate was used.

  That is, it was found that by using an electrolytic solution containing one kind of saturated chain carboxylic acid ester and one kind of unsaturated chain carboxylic acid ester represented by Chemical Formula 3, excellent charge / discharge cycle characteristics can be obtained.

  Moreover, in Example 1-Example 2, the discharge capacity maintenance factor improved from Example 5. FIG.

That is, the hydrocarbon group R _{1 of the} saturated chain carboxylic acid ester, which includes one kind of saturated chain carboxylic acid ester and one kind of unsaturated chain carboxylic acid ester represented by Chemical Formula 3, and the unsaturated chain carboxylic acid It has been found that by using an electrolytic solution having a carbon number difference of 1 or less from the ester hydrocarbon group R ₁ , more excellent charge / discharge cycle characteristics can be obtained.

Further, the hydrocarbon group R ₂ of the saturated chain carboxylic acid ester and the unsaturated chain carboxylic acid ester include one saturated chain carboxylic acid ester and one unsaturated chain carboxylic acid ester represented by Chemical Formula 3 Even when an electrolyte solution having a carbon number difference of 1 or less from that of the hydrocarbon group R ₂ is used, the charge / discharge cycle characteristics are more likely to be obtained. Further, the hydrocarbon group R _{1 of} the saturated chain carboxylic acid ester, which includes one saturated chain carboxylic acid ester and one unsaturated chain carboxylic acid ester represented by Chemical Formula 3, and the unsaturated chain carboxylic acid ester The difference in carbon number from the hydrocarbon group R ₁ of the acid ester is 1 or less, and the hydrocarbon group R ₂ of the saturated chain carboxylic acid ester and the hydrocarbon group R ₂ of the unsaturated chain carboxylic acid ester When an electrolytic solution having a carbon number difference of 1 or less is used, particularly excellent charge / discharge cycle characteristics tend to be obtained.

  Furthermore, in Example 2 and Examples 6 to 9, a high discharge capacity retention rate was obtained when the total content of methyl acetate and methyl acrylate was in the range of 10 wt% to 30 wt%. That is, more excellent charge / discharge cycle characteristics when the total content of one kind of saturated chain carboxylic acid ester and one kind of unsaturated chain carboxylic acid ester represented by Chemical Formula 3 is in the range of 10 wt% to 30 wt%. I found out that

  Furthermore, although the example mentioned above demonstrated the case where only 1 type of saturated chain carboxylic acid ester represented by Chemical formula 3 and 1 type of unsaturated chain carboxylic acid ester were included, the saturation represented by Chemical formula 3 was demonstrated. When using an electrolytic solution containing only one chain carboxylic acid ester and two or more unsaturated chain carboxylic acid esters represented by Chemical Formula 3, two or more saturated chain carboxylic acid esters represented by Chemical Formula 3 are used. And two or more saturated chain carboxylic acid esters represented by Chemical Formula 3 and Chemical Formula 3, when using an electrolyte solution containing only one type of unsaturated chain carboxylic acid ester represented by Chemical Formula 3 Similar results tend to be obtained when using an electrolytic solution containing two or more unsaturated chain carboxylic acid esters.

  The present invention is not limited to the above-described embodiments of the present invention, and various modifications and applications are possible without departing from the spirit of the present invention. For example, in the above-described embodiment, the coin-type battery and the cylindrical battery have been described as examples. However, the present invention is not limited to this, and for example, a metal for an exterior material such as a square battery or a button battery. Various shapes and sizes such as a battery using a container or the like, a battery using a laminate film or the like as an exterior material such as a thin battery can be used.

It is a schematic sectional drawing which shows the internal structure of the 1st example of the nonaqueous electrolyte battery using the electrolyte solution by one Embodiment of this invention. It is sectional drawing showing the structure of the 2nd example of the nonaqueous electrolyte battery using the electrolyte solution by one Embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Non-aqueous electrolyte battery 2 ... Positive electrode 3 ... Positive electrode can 4 ... Negative electrode 5 ... Negative electrode can 6 ... Separator 7 ... Insulating gasket 8 ... Non-aqueous electrolyte DESCRIPTION OF SYMBOLS 9 ... Positive electrode collector 10 ... Positive electrode mixture layer 11 ... Negative electrode collector 12 ... Negative electrode mixture layer 21 ... Battery can 22, 23 ... Insulating plate 24 ... Battery cover 25 ... Safety valve mechanism 25A ... Disc plate 26 ... Heat sensitive resistor 27 ... Gasket 30 ... Winding electrode body 31 ... Positive electrode 31A ... Positive electrode current collector 31B .... Positive electrode mixture layer 32 ... Negative electrode 32A ... Negative electrode current collector 32B ... Negative electrode mixture layer 33 ... Separator 34 ... Center pin 35 ... Positive electrode lead 36 ... Negative electrode lead

Claims (14)

A nonaqueous electrolytic solution comprising at least one saturated chain carboxylic acid ester represented by Chemical Formula 1 and at least one unsaturated chain carboxylic acid ester.

(In the formula, R ₁ and R ₂ are each a hydrocarbon group having 1 to 3 carbon atoms. Either or both of R ₁ and R ₂ may have an unsaturated bond.) A hydrocarbon radical R ₁ of the saturated chain carboxylate, the unsaturated chain carboxylic acid esters difference in the number of carbon atoms in the hydrocarbon radical R ₁ is as claimed in claim 1, wherein a is 1 or less Non-aqueous electrolyte. _2. The difference in carbon number between the hydrocarbon group R ₂ of the saturated chain carboxylic acid ester and the hydrocarbon group R ₂ of the unsaturated chain carboxylic acid ester is 1 or less. Non-aqueous electrolyte. A hydrocarbon radical R ₁ of the saturated chain carboxylate, the difference between the number of carbon atoms of the hydrocarbon group R ₁ in the unsaturated chain carboxylic acid ester is 1 or less,
And the hydrocarbon group R ₂ of saturated chain carboxylate, according to claim 1, wherein the difference in the number of carbon atoms of the hydrocarbon group R ₂ of the unsaturated chain carboxylic acid ester is characterized in that 1 or less Non-aqueous electrolyte. 2. The total content of the saturated chain carboxylic acid ester and the unsaturated chain carboxylic acid ester is within a range of 10% by weight to 30% by weight with respect to the nonaqueous electrolytic solution. The non-aqueous electrolyte described. The non-aqueous electrolyte according to claim 1, wherein the unsaturated chain carboxylic acid ester is at least one selected from the group consisting of vinyl acrylate, methyl acrylate, and ethyl acrylate. The non-aqueous electrolyte according to claim 1, wherein the saturated chain carboxylic acid ester is at least one selected from the group consisting of methyl acetate, methyl propionate, and ethyl propionate. A positive electrode and a negative electrode, and a non-aqueous electrolyte,
The non-aqueous electrolyte is
A non-aqueous electrolyte battery comprising at least one saturated chain carboxylic acid ester represented by Chemical Formula 2 and at least one unsaturated chain carboxylic acid ester.

(In the formula, R ₁ and R ₂ are each a hydrocarbon group having 1 to 3 carbon atoms. Either or both of R ₁ and R ₂ may have an unsaturated bond.) A hydrocarbon radical R ₁ of the saturated chain carboxylate, the unsaturated chain carboxylic acid esters difference in the number of carbon atoms in the hydrocarbon radical R ₁ is as claimed in claim 8, wherein a is 1 or less Non-aqueous electrolyte battery. A hydrocarbon radical R ₂ of the saturated chain carboxylate, the unsaturated chain carboxylic acid esters difference in the number of carbon atoms of the hydrocarbon group R ₂ is as claimed in claim 8, wherein a is 1 or less Non-aqueous electrolyte battery. A hydrocarbon radical R ₁ of the saturated chain carboxylate, the difference between the number of carbon atoms of the hydrocarbon group R ₁ in the unsaturated chain carboxylic acid ester is 1 or less,
And the hydrocarbon group R ₂ of saturated chain carboxylate, according to claim 8, wherein the difference in the number of carbon atoms of the hydrocarbon group R ₂ of the unsaturated chain carboxylic acid ester is characterized in that 1 or less Non-aqueous electrolyte battery. The total content of the saturated chain carboxylic acid ester and the unsaturated chain carboxylic acid ester is in the range of 10 wt% to 30 wt% with respect to the non-aqueous electrolyte. 8. The nonaqueous electrolyte battery according to 8. The non-aqueous electrolyte battery according to claim 8, wherein the unsaturated chain carboxylic acid ester is at least one selected from the group consisting of vinyl acrylate, methyl acrylate, and ethyl acrylate. The non-aqueous electrolyte battery according to claim 8, wherein the saturated chain carboxylic acid ester is at least one selected from the group consisting of methyl acetate, methyl propionate, and ethyl propionate.

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