JP2006221972A - Electrolyte and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte and a battery capable of obtaining high cycle characteristics even at a high battery voltage. <P>SOLUTION: A wound electrode body 20 formed by winding a positive electrode 21 and a negative electrode 22 through a separator 23 is housed in a battery can. The separator is impregnated with an electrolyte. The electrolyte contains phosphate ester such as tripropyl phosphate, triallyl phosphate, or triphenyl phosphate. Thereby, the decomposition reaction of the electrolyte in the positive electrode 21 is suppressed even at a high battery voltage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolytic solution to which an additive for preventing oxidation and a battery using the same.

  In recent years, many portable electronic devices such as notebook portable computers, cellular phones, and camera-integrated VTRs (video tape recorders) have appeared, and their size and weight have been reduced. Accordingly, as a power source for these portable electronic devices, development of a secondary battery that is lightweight and capable of obtaining a high energy density is in progress. As a secondary battery capable of obtaining a high energy density, for example, a lithium secondary battery is known.

In this lithium secondary battery, the electrolytic solution is decomposed by a strong oxidizing action at the positive electrode. Then, in order to suppress the decomposition reaction of electrolyte solution and to improve battery characteristics, such as a cycle characteristic, adding an antioxidant to electrolyte solution is proposed (for example, refer patent documents 1-4).
Japanese Patent Laid-Open No. 10-247517 JP 2001-283906 A JP 2001-338684 A JP 2003-123837 A

  However, when the discharge capacity is improved by increasing the battery voltage, the oxidation action at the positive electrode becomes stronger, so that sufficient cycle characteristics could not be obtained with the electrolyte added with the above-described antioxidant. .

  The present invention has been made in view of such a problem, and an object thereof is to improve the oxidation resistance, and to use an electrolytic solution capable of obtaining excellent cycle characteristics even when the battery voltage is increased. It is to provide a battery that has been.

  The electrolytic solution according to the present invention contains the phosphate ester shown in Chemical formula 1.

（式中、Ｒ１，Ｒ２およびＲ３は、アルキル基，アルキレン基，アルキニル基，アリール基，アルキルエーテル基、またはこれらの少なくとも一部の水素を置換基で置換した基を表す。）

(Wherein R1, R2 and R3 represent an alkyl group, an alkylene group, an alkynyl group, an aryl group, an alkyl ether group, or a group obtained by substituting at least a part of these hydrogens with a substituent.)

  The battery according to the present invention includes an electrolyte solution together with a positive electrode and a negative electrode, and the electrolyte solution contains a phosphate ester shown in Chemical Formula 2.

（式中、Ｒ１，Ｒ２およびＲ３は、アルキル基，アルキレン基，アルキニル基，アリール基，アルキルエーテル基、またはこれらの少なくとも一部の水素を置換基で置換した基を表す。）

(Wherein R1, R2 and R3 represent an alkyl group, an alkylene group, an alkynyl group, an aryl group, an alkyl ether group, or a group obtained by substituting at least a part of these hydrogens with a substituent.)

  According to the electrolytic solution and the battery of the present invention, since the phosphate ester shown in Chemical Formula 1 or Chemical Formula 2 is included, for example, even when the battery voltage is set to a high voltage of 4.25 V or higher, the electrolytic solution is decomposed at the positive electrode. The reaction can be suppressed, and excellent cycle characteristics can be obtained.

  In particular, if the content of the phosphate ester in the electrolytic solution is 20% by mass or less, a higher effect can be obtained.

  Furthermore, if the electrolytic solution contains vinylene carbonate, the cycle characteristics can be further improved. In particular, if the content of vinylene carbonate in the electrolytic solution is 10% by mass or less, a higher effect can be obtained. Obtainable.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 illustrates a cross-sectional configuration of the secondary battery according to the present embodiment. This secondary battery is a so-called cylindrical type, and is a wound electrode in which a strip-like positive electrode 21 and a negative electrode 22 are laminated and wound inside a substantially hollow cylindrical battery can 11 via a separator 23. It has a body 20. 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 pair of insulating plates 12, 13 are arranged 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 resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and 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.

  For example, a center pin 24 is inserted in the center of the wound electrode body 20. 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.

  FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces or one surface of a positive electrode current collector 21A having a pair of opposed surfaces. The positive electrode current collector 21A is made of, for example, a metal material such as an aluminum foil.

The positive electrode active material layer 21B includes, for example, one or more of positive electrode materials capable of occluding and releasing lithium, which is an electrode reactant, as the positive electrode active material. A binder such as a material and polyvinylidene fluoride may be included. As a positive electrode material capable of inserting and extracting lithium, for example, lithium-containing compounds such as lithium oxide, lithium sulfide, or an intercalation compound containing lithium are suitable, and a mixture of two or more of these is used. May be. In order to increase the energy density, a lithium-containing compound containing lithium, a transition metal element, and oxygen (O) is preferable. Among them, the transition metal element includes cobalt (Co), nickel, manganese (Mn), and iron. It is more preferable if it contains at least one of them. Specifically, Li _f CoO ₂ (f≈1), Li _g NiO ₂ (g≈1), Li _h Ni _j Co _1-j O ₂ (h≈1, 0 <j <1), spinel structure Li _k Mn ₂ O ₄ (k≈1) or Li _m FePO ₄ (m≈1) having an olivine structure.

  The negative electrode 22 has, for example, a structure in which a negative electrode active material layer 22B is provided on both surfaces or one surface of a negative electrode current collector 22A having a pair of opposed surfaces. The negative electrode current collector 22B is made of a metal material such as a copper foil, for example.

  The negative electrode active material layer 22B includes, for example, any one or more of negative electrode materials capable of occluding and releasing lithium, which is an electrode reactant, as a negative electrode active material, and polyvinylidene fluoride as necessary. The binder may be included.

  Examples of the negative electrode material capable of inserting and extracting lithium include non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, and fired organic polymer compounds , Carbon materials such as carbon fiber or activated carbon. Among these, examples of coke include pitch coke, needle coke, and petroleum coke. An organic polymer compound fired body is a carbonized material obtained by firing a polymer material such as a phenol resin or a furan resin at an appropriate temperature, and part of it is non-graphitizable carbon or graphitizable carbon. Some are classified as: These carbon materials are preferable because the change in crystal structure that occurs during charge and discharge is very small, a high charge and discharge capacity can be obtained, and good cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. Further, non-graphitizable carbon is preferable because excellent cycle characteristics can be obtained. Furthermore, those having a low charge / discharge potential, specifically, those having a charge / discharge potential close to that of lithium metal are preferable because a high energy density of the battery can be easily realized.

  Examples of the negative electrode material capable of inserting and extracting lithium include materials capable of inserting and extracting lithium and containing at least one of a metal element and a metalloid element as a constituent element. . This is because a high energy density can be obtained by using such a material. In particular, the use with a carbon material is more preferable because a high energy density can be obtained and excellent cycle characteristics can be obtained. The negative electrode material may be a single element, alloy or compound of a metal element or metalloid element, or may have at least a part of one or more of these phases. In the present invention, alloys include those containing one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. Moreover, the nonmetallic element may be included. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

  Examples of metal elements or metalloid elements constituting the negative electrode material include magnesium (Mg), boron (B), aluminum, gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin ( Sn), lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd) or platinum ( Pt). These may be crystalline or amorphous.

  Among these, as the negative electrode material, a material containing a 4B group metal element or a semimetal element in the short-period type periodic table as a constituent element is preferable, and at least one of silicon and tin is particularly preferable as a constituent element. This is because silicon and tin have a large ability to occlude and release lithium, and a high energy density can be obtained.

  As an alloy of tin, for example, as a second constituent element other than tin, silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony (Sb), And those containing at least one member selected from the group consisting of chromium (Cr). As an alloy of silicon, for example, as a second constituent element other than silicon, among the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium The thing containing at least 1 sort (s) of these is mentioned.

  Examples of the tin compound or silicon compound include those containing oxygen or carbon (C), and may contain the second constituent element described above in addition to tin or silicon.

Examples of the negative electrode material capable of inserting and extracting lithium further include other metal compounds and polymer materials. Examples of other metal compounds include oxides such as MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ ), sulfides such as NiS and MoS, and lithium nitrides such as LiN _3. Examples include polyacetylene and polypyrrole.

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 23 is made of, for example, a porous film made of synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene or the like, or a multi-hard film made of ceramic, and these two or more kinds of porous films are laminated. It may be made the structure.

  The separator 23 is impregnated with an electrolytic solution that is a liquid electrolyte. This electrolytic solution contains a solvent and an electrolyte salt dissolved in the solvent.

  As the solvent, cyclic carbonates such as ethylene carbonate or propylene carbonate can be used, and it is preferable to use one of ethylene carbonate and propylene carbonate, particularly a mixture of both. This is because the cycle characteristics can be improved. 20 mass% or more is preferable with respect to the whole solvent, and, as for content of cyclic carbonate, it is more preferable if it is 90 mass% or less. This is because a higher effect can be obtained within this range.

  As the solvent, in addition to these cyclic carbonates, it is preferable to use a mixture of chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate or methylpropyl carbonate. It is more preferable to use a mixture of dimethyl or ethyl methyl carbonate. This is because high ionic conductivity can be obtained. The content of the chain carbonate is preferably 10% by mass or more and more preferably 50% by mass or less with respect to the entire solvent. This is because a higher effect can be obtained within this range.

  It is preferable that the solvent further contains 2,4-difluoroanisole. This is because the discharge capacity can be improved.

  In addition to these, examples of the solvent include butylene carbonate, γ-butyrolactone, γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3- Dioxolane, methyl acetate, methyl propionate, acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropironitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N-dimethyl Examples include imidazolidinone, nitromethane, nitroethane, sulfolane, and dimethyl sulfoxide.

  A compound in which at least a part of hydrogen in these solvents is substituted with fluorine may be preferable depending on the type of electrode to be combined because the reversibility of the electrode reaction may be improved.

  In addition, the solvent preferably contains vinylene carbonate. This is because the cycle characteristics can be improved. The content of vinylene carbonate is preferably 10% by mass or less, particularly preferably in the range of 0.5% by mass or more and 5% by mass or less with respect to the entire electrolytic solution. This is because a higher effect can be obtained within this range.

As electrolyte salt, lithium salt is mentioned, for example, 1 type may be used independently, and 2 or more types may be mixed and used for it. Lithium salts include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, difluoro [oxolato-O, O ′] lithium borate, lithium bisoxalate borate, or LiBr. Among them, LiPF ₆ is preferable because it can obtain high ion conductivity and can improve cycle characteristics.

  This electrolytic solution also contains the phosphate ester shown in Chemical formula 3. As a result, even when the battery voltage is set to a high voltage of 4.25 V or higher, the decomposition reaction of the electrolytic solution in the positive electrode 21 is suppressed, and excellent cycle characteristics can be obtained.

  In Chemical Formula 3, R1, R2 and R3 represent an alkyl group, an alkylene group, an alkynyl group, an aryl group, an alkyl ether group, or a group obtained by substituting at least a part of these hydrogens with a substituent. Substituents include fluorine, chlorine, bromine or iodine. Further, the alkyl ether group refers to a group in which at least a part of hydrogen of the alkyl group is substituted with an ether group. At least one of R1, R2 and R3 preferably has 1 to 15 carbon atoms, more preferably 1 to 10 carbon atoms, and particularly preferably 3 to 6 carbon atoms. This is because when the number of carbon atoms is large, the viscosity of the electrolytic solution increases. R1, R2 and R3 may be the same or different.

  Specific examples of such phosphate esters include trimethyl phosphate, triethyl phosphate, methyl diethyl phosphate, ethyl dimethyl phosphate, propyl dimethyl phosphate, tripropyl phosphate, triallyl phosphate, butyl phosphate. Dimethyl, tripentyl phosphate, pentyl dimethyl phosphate, tri-n-octyl phosphate, tri (2-ethylhexyl) phosphate, triphenyl phosphate, tricresyl phosphate, tri (2-n-butoxyethyl) phosphate, phosphorus Examples include tri (2-chloroethyl) acid and tri (1H, 1H, 5H-octafluoro-n-pentyl). Among these, tripropyl phosphate, triallyl phosphate, tripentyl phosphate, triphenyl phosphate, or tri (2-n-butoxyethyl) phosphate is preferable.

  The content of the phosphate ester is preferably 20% by mass or less, more preferably 2% by mass or more and 10% by mass or less with respect to the entire electrolytic solution. This is because a high effect can be obtained within this range.

  For example, the secondary battery can be manufactured as follows.

  First, for example, a positive electrode active material, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and then this positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone. A slurry is obtained. Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 21A, dried, and compression-molded by a roll press machine or the like to form the positive electrode active material layer 21B, whereby the positive electrode 21 is manufactured.

  For example, after preparing a negative electrode mixture by mixing a negative electrode active material and a binder, the negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a negative electrode mixture slurry. . Subsequently, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, dried, and compression-molded by a roll press or the like to form the negative electrode active material layer 22B, whereby the negative electrode 22 is manufactured.

  Next, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. Subsequently, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, 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 a gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.

  In the secondary battery, when charged, for example, lithium ions are extracted from the positive electrode 21 and inserted in the negative electrode 22 through the electrolytic solution. On the other hand, when discharging is performed, for example, lithium ions are extracted from the negative electrode 22 and inserted in the positive electrode 21 through the electrolytic solution. At that time, since the electrolytic solution contains the phosphate ester shown in Chemical Formula 3, even when the battery voltage is set to a high voltage of 4.25 V or higher, the decomposition reaction of the electrolytic solution in the positive electrode 21 is suppressed, and the cycle The characteristics are improved.

  Thus, according to the present embodiment, since the phosphoric acid ester shown in Chemical Formula 3 is included, for example, even when the battery voltage is set to a high voltage of 4.25 V or higher, the decomposition reaction of the electrolytic solution in the positive electrode 21 is performed. Can be suppressed, and excellent cycle characteristics can be obtained.

  In particular, if the content of the phosphate ester in the electrolytic solution is 20% by mass or less, a higher effect can be obtained.

  Furthermore, if the electrolytic solution contains vinylene carbonate, the cycle characteristics can be further improved. In particular, if the content of vinylene carbonate in the electrolytic solution is 10% by mass or less, a higher effect can be obtained. Obtainable.

  Further, specific embodiments of the present invention will be described in detail with reference to the drawings.

(Examples 1-1 to 1-12, 2-1 to 2-12)
First, lithium carbonate (Li ₂ CO ₃ ) and cobalt carbonate (CoCO ₃ ) are mixed at a ratio of Li ₂ CO ₃ : CoCO ₃ = 0.5: 1 (molar ratio), and 5 ° C. at 900 ° C. in the air. After firing for a time, lithium-cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material was obtained. Next, 90 parts by mass of this lithium-cobalt composite oxide, 5 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were prepared, and then a positive electrode mixture was prepared. A positive electrode mixture slurry was prepared by dispersing in some N-methyl-2-pyrrolidone. Subsequently, the positive electrode mixture slurry was applied to a positive electrode current collector 21A made of an aluminum foil having a thickness of 20 μm and dried, and then compression-molded by a roll press machine to form the positive electrode active material layer 21B, whereby the positive electrode 21 was produced. . After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

  Further, artificial graphite was used as the negative electrode active material, and 90 parts by mass of the artificial graphite and 10 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, and then N-methyl- A negative electrode mixture slurry was prepared by dispersing in 2-pyrrolidone. Subsequently, the negative electrode mixture slurry was uniformly applied to both surfaces of the negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 10 μm, dried, and then compression molded by a roll press to form the negative electrode active material layer 22B. A negative electrode 22 was produced. After that, a nickel negative electrode lead 26 was attached to one end of the negative electrode current collector 22A.

  After preparing the positive electrode 21 and the negative electrode 22, a separator 23 made of a microporous polypropylene film having a thickness of 25 μm is prepared, and the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 are stacked in this order to form a spiral structure. The wound electrode body 20 was produced by winding a number of times.

  After producing the wound electrode body 20, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, the negative electrode lead 26 is welded to the battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. The wound electrode body 20 was housed inside a nickel-plated iron battery can 11. After that, an electrolytic solution was injected into the battery can 11.

To the electrolytic solution, the phosphate ester shown in Chemical Formula 3 is added to a solvent obtained by mixing ethylene carbonate and dimethyl carbonate, which are solvents, in a mass ratio of ethylene carbonate: dimethyl carbonate = 70: 25. A solution in which LiPF ₆ was dissolved was used. At that time, in Examples 1-1 to 1-12 and 2-1 to 2-12, the phosphoric acid ester represented by Chemical Formula 3 was trimethyl phosphate, triethyl phosphate, ethyldimethyl phosphate, tripropyl phosphate, Triallyl phosphate, tripentyl phosphate, tri (2-ethylhexyl) phosphate, triphenyl phosphate, tricresyl phosphate, tri (2-n-butoxyethyl) phosphate, tri (2-chloroethyl) phosphate, or phosphoric acid Tri (1H, 1H, 5H-octafluoro-n-pentyl) was used. Moreover, content of these phosphate ester in electrolyte solution was 5 mass%, respectively.

  After injecting the electrolytic solution into the battery can 11, the battery lid 14 is caulked to the battery can 11 through the gasket 17 whose surface is coated with asphalt, whereby a cylindrical secondary battery having a diameter of 14 mm and a height of 65 mm is obtained. Obtained.

  As Comparative Examples 1-1 and 2-1 to Examples 1-1 to 1-12 and 2-1 to 2-12, except that the phosphate ester shown in Chemical Formula 3 was not added, the other examples Secondary batteries were fabricated in the same manner as 1-1 to 1-12 and 2-1 to 2-12.

  For the fabricated secondary batteries of Examples 1-1 to 1-12, 2-1 to 2-12 and Comparative Examples 1-1 and 2-1, the cycle characteristics were examined as follows. First, in a 23 ° C. environment, after constant current charging at a constant current of 600 mA until the battery voltage reaches 4.5 V or 4.25 V, the current reaches 20 mA at a constant voltage of 4.5 V or 4.25 V. The battery was charged at a constant voltage until reaching a voltage, and then discharged at a constant current of 300 mA until the battery voltage reached 3.0 V to measure the discharge capacity. Subsequently, under a 23 ° C. environment, constant current / constant voltage charging was performed to 4.5 V or 4.25 V under the same conditions, and left in a constant temperature bath at 80 ° C. for 10 days. After that, in a 23 ° C. environment, constant current discharge is performed at a constant current of 300 mA until the battery voltage reaches 3.5 V, and then, at a constant current of 600 mA, the battery voltage reaches 4.5 V or 4.25 V. After performing constant current charging, charging / discharging with constant voltage charging is repeated until the current reaches 20 mA at a constant voltage of 4.5 V or 4.25 V, and the discharge capacity is The number of cycles up to 50 was measured. The results are shown in Tables 1 and 2.

  As can be seen from Tables 1 and 2, according to Examples 1-1 to 1-12 and 2-1 to 2-12 in which the phosphoric acid ester shown in Chemical Formula 3 was added to the electrolyte, this was not added. The number of cycles until the discharge capacity was halved was larger than those of Comparative Examples 1-1 and 2-1, respectively. Further, Examples 1-4 to 1-6, 1-8, 1-10, 1-12, 2-4 to 3 in which R1, R2, and R3 in the phosphate ester shown in Chemical Formula 3 have 3 to 6 carbon atoms. In 2-6, 2-8, 2-10, and 2-12, the number of cycles was particularly large.

  That is, it has been found that if the phosphate ester shown in Chemical Formula 3 is included in the electrolytic solution, the cycle characteristics can be improved even when the battery voltage is set to 4.25 V or higher. Moreover, it turned out that the number of carbons of at least one of R1, R2 and R3 in the phosphoric acid ester shown in Chemical formula 3 is preferably 3-6.

(Examples 3-1 to 3-5, 4-1 to 4-3)
Except that the content of tripropyl phosphate in the electrolytic solution was changed within the range of 2% by mass to 25% by mass as shown in Tables 3 and 4, Examples 1-4 and 2-4 were otherwise used. A secondary battery was fabricated in the same manner as described above.

  For the fabricated secondary batteries of Examples 3-1 to 3-5 and 4-1 to 4-3, cycle characteristics were measured in the same manner as in Examples 1-1 to 1-12 and 2-1 to 2-12. did. The results are shown in Tables 3 and 4 together with the results of Examples 1-4 and 2-4 and Comparative Examples 1-1 and 2-1.

  As can be seen from Tables 3 and 4, the number of cycles until the discharge capacity was reduced by half increased as the tripropyl phosphate content increased and then decreased.

  That is, it was found that the content of the phosphate ester in the electrolytic solution is preferably 20% by mass or less, and more preferably in the range of 2% by mass to 10% by mass.

(Examples 5-1 to 5-5, 6-1 to 6-5)
In addition to ethylene carbonate and dimethyl carbonate as a solvent, vinylene carbonate was mixed, and the contents of vinylene carbonate in the electrolyte were changed as shown in Tables 5 and 6. Secondary batteries were fabricated in the same manner as in 1-8, 2-5, and 2-8.

  For the fabricated secondary batteries of Examples 5-1 to 5-5, 6-1 to 6-5, cycle characteristics were measured in the same manner as in Examples 1-1 to 1-12 and 2-1 to 2-12. did. The results are shown in Tables 5 and 6 together with the results of Examples 1-5, 1-8, 2-5, and 2-8.

  As can be seen from Tables 5 and 6, according to Examples 5-1 to 5-5, 6-1 to 6-5 mixed with vinylene carbonate, Examples 1-5, 1- not mixed with vinylene carbonate The number of cycles until the discharge capacity was halved was larger than that of 8, 2-5 and 2-8. Moreover, the number of cycles until the discharge capacity was reduced by half increased as the vinylene carbonate content increased, and then decreased.

  That is, if vinylene carbonate is included, cycle characteristics can be further improved. In particular, the content of vinylene carbonate in the electrolytic solution is 10% by mass or less, particularly 0.5% by mass or more and 5% by mass or less. It was found that the range was preferable.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, a cylindrical secondary battery having a winding structure has been specifically described, but the present invention can be applied to an exterior such as a coin type, a sheet type, a button type, or a square type. The present invention can be similarly applied to secondary batteries having other shapes using members, or secondary batteries having a laminated structure in which a plurality of positive and negative electrodes are laminated.

  Moreover, although the case where electrolyte solution was used was demonstrated in the said embodiment and Example, it may replace with electrolyte solution and may use gel electrolyte. The gel electrolyte is obtained, for example, by holding an electrolytic solution in a polymer compound. The electrolytic solution is as described above. As the polymer compound, for example, any polymer that absorbs an electrolytic solution and gels can be used. Examples of such a polymer compound include polyacrylonitrile, polyvinylidene fluoride, vinylidene fluoride, and hexafluoropropylene. Copolymer, Polytetrafluoroethylene, Polyhexafluoropropylene, Polyethylene oxide, Polypropylene oxide, Polyphosphazene, Polysiloxane, Polyvinyl acetate, Polyvinyl alcohol, Polymethyl methacrylate, Polyacrylic acid, Polymethacrylic acid, Styrene-butadiene Examples thereof include rubber, nitrile-butadiene rubber, polystyrene, and polycarbonate. In particular, from the viewpoint of electrochemical stability, polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene, or polyethylene oxide is preferable.

  In the above embodiments and examples, a battery using lithium as an electrode reactant has been described. However, another alkali metal such as sodium (Na) or potassium (K), or an alkali such as magnesium or calcium (Ca) is used. The present invention can also be applied to the case of using an earth metal or another light metal such as aluminum. In that case, as a negative electrode active material, the thing similar to the said embodiment etc. can be used, for example.

It is sectional drawing showing the structure of the secondary battery which concerns on one embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the secondary battery shown in FIG.

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, 21A DESCRIPTION OF SYMBOLS ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode active material layer, 23 ... Separator, 24 ... Center pin, 25 ... Positive electrode lead, 26 ... Negative electrode lead.

Claims (8)

An electrolyte solution comprising the phosphate ester shown in Chemical Formula 1.

(Wherein R1, R2 and R3 represent an alkyl group, an alkylene group, an alkynyl group, an aryl group, an alkyl ether group, or a group obtained by substituting at least a part of these hydrogens with a substituent.)   2. The electrolytic solution according to claim 1, wherein a content of the phosphate ester is 20% by mass or less.   The electrolytic solution according to claim 1, further comprising vinylene carbonate.   The electrolytic solution according to claim 3, wherein the content of the vinylene carbonate is 10% by mass or less. A battery comprising an electrolyte solution together with a positive electrode and a negative electrode,
The battery, wherein the electrolyte contains a phosphate ester shown in Chemical Formula 2.

(Wherein R1, R2 and R3 represent an alkyl group, an alkylene group, an alkynyl group, an aryl group, an alkyl ether group, or a group obtained by substituting at least a part of these hydrogens with a substituent.)   The battery according to claim 5, wherein a content of the phosphate ester in the electrolytic solution is 20% by mass or less.   The battery according to claim 5, wherein the electrolytic solution further contains vinylene carbonate. The battery according to claim 7, wherein the content of the vinylene carbonate in the electrolytic solution is 10% by mass or less.

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