JP2005339900A - Electrolyte and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte capable of enhancing charge/discharge efficiency and load characteristics and to provide a battery using this electrolyte. <P>SOLUTION: A positive electrode 21 and a negative electrode 22 are laminated through a separator 23. The electrolyte is impregnated in the separator 23. A silane coupling agent and an oxalate are contained in the electrolyte. Since the reduction of the oxalate is conducted prior to the reduction of the silane coupling agent, a film is formed on the surface of the negative electrode 22, and then a film is formed by reaction of the silane coupling agent, increase of the film amount caused by the silane coupling agent can be suppressed. Increase in film resistance is suppressed, and at the same time reaction in the negative electrode 2 can be suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolytic solution containing a silane coupling agent and a battery using the electrolytic solution.

  In recent years, mobile electronic devices such as mobile phones, PDAs (personal digital assistants) or notebook computers have been energetically reduced in size and weight, and as part of these efforts, Improvement of the energy density of a battery as a driving power source, particularly a secondary battery is strongly desired.

  As a secondary battery capable of obtaining a high energy density, for example, a secondary battery using lithium (Li) as an electrode reactant is known. Among these, lithium ion secondary batteries using a material capable of inserting and extracting lithium such as a carbon material in the negative electrode are widely put into practical use. In order to further increase the capacity, the use of a material capable of forming an alloy with lithium for the negative electrode has been studied, and further, a material capable of inserting and extracting lithium is used for the negative electrode. Secondary batteries have also been developed in which lithium is deposited on the negative electrode during charging by making the charge capacity smaller than the charge capacity of the positive electrode (see, for example, Patent Document 1).

By the way, in these secondary batteries, in order to improve battery characteristics, such as cycling characteristics, adding various additives to electrolyte solution is examined. For example, Patent Document 2 describes that a silane coupling agent is added to improve high-temperature storage characteristics and cycle characteristics.
International Publication No. WO 01/22519 A1 Pamphlet JP 2002-42864 A

  However, although the charge / discharge efficiency can be improved by adding a silane coupling agent, there is a problem that the film resistance due to the silane coupling agent increases and the load characteristics deteriorate.

  The present invention has been made in view of such problems, and an object thereof is to provide an electrolytic solution capable of improving both charge / discharge efficiency and load characteristics, and a battery using the same.

  The electrolytic solution according to the present invention contains a silane coupling agent and an oxalate ester.

  The battery according to the present invention includes an electrolyte solution together with a positive electrode and a negative electrode, and the electrolyte solution includes a silane coupling agent and an oxalate ester.

  According to the electrolytic solution of the present invention, since the silane coupling agent and the oxalic acid ester are included, for example, when used in a battery, the oxalic acid ester is reduced prior to the silane coupling agent and the negative electrode A film can be formed on the film, and the amount of the film formed by the silane coupling agent can be reduced. Therefore, the side reaction in the negative electrode can be suppressed by the coating while suppressing increase in the coating resistance. Therefore, both charge / discharge efficiency and load characteristics can be improved.

  In particular, if the content of the silane coupling agent is 0.5% by mass or more and 2% by mass or less and the content of the oxalate ester is 0.2% by mass or more and 5% by mass or less, a higher effect is obtained. Can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, a so-called lithium ion secondary battery that uses insertion and extraction of lithium will be described.

[First Embodiment]
FIG. 1 shows a cross-sectional structure of a secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called cylindrical type, and a wound electrode body 20 in which a belt-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. 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 and 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 of a positive electrode current collector 21A having a pair of opposed surfaces. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil.

The positive electrode active material layer 21B includes a positive electrode material capable of inserting and extracting lithium, which is an electrode reactant, for example, as a positive electrode active material. As a positive electrode material capable of inserting and extracting lithium, for example, lithium-containing compounds such as lithium oxide, lithium phosphorus oxide, lithium sulfide, or an intercalation compound containing lithium are suitable, and two or more kinds are mixed. May be used. In particular, in order to increase the energy density, a lithium composite oxide or lithium phosphorus oxide represented by the general formula Li _x MIO ₂ or Li _y MIIPO ₄ is preferable. In the formula, MI and MII represent one or more transition metals, for example, at least one of cobalt (Co), nickel, manganese (Mn), iron, vanadium (V), and titanium (Ti) is preferable. The values of x and y vary depending on the charge / discharge state of the battery, and are usually values in the range of 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10. Specific examples of the lithium composite oxide represented by Li _x MIO ₂ include lithium cobalt composite oxide (LiCoO ₂ ), lithium nickel composite oxide (LiNiO ₂ ), and lithium nickel cobalt composite oxide (Li _z Ni _v Co). _1-v O ₂ ; z and v are, for example, 0 <z <1, 0.7 <v <1.02, or a lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel crystal structure Can be mentioned. A specific example of the lithium phosphorus oxide represented by Li _y MIIPO ₄ is LiFePO ₄ .

  The positive electrode active material layer 21B also contains, for example, a conductive agent, and may further contain a binder as necessary. Examples of the conductive agent include carbon materials such as graphite, carbon black, and ketjen black, and one kind or a mixture of two or more kinds is used. In addition to the carbon material, a metal material or a conductive polymer material may be used as long as it is a conductive material. Examples of the binder include synthetic rubber such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene rubber, or a polymer material such as polyvinylidene fluoride, and one or two or more kinds are used in combination. It is done.

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

  The negative electrode active material layer 22B includes, for example, one or more negative electrode materials capable of inserting and extracting lithium, which is an electrode reactant, as a negative electrode active material. For example, the binder similar to the positive electrode active material layer 13B may be included.

  Examples of the negative electrode material capable of inserting and extracting lithium include carbon materials such as graphite, non-graphitizable carbon, and graphitizable carbon. These carbon materials are preferable because the change in crystal structure that occurs during charge / discharge is very small, a high charge / discharge capacity can be obtained, and good charge / discharge cycle characteristics can be obtained. In particular, graphite is preferable because it has a high electrochemical equivalent and can provide a high energy density. The graphite may be artificial graphite or natural graphite.

  As a negative electrode material capable of inserting and extracting lithium, a simple substance, alloy or compound of a metal element capable of forming an alloy with lithium, or a simple substance, alloy or compound of a metalloid element capable of forming an alloy with lithium Is mentioned. These are preferable because a high energy density can be obtained. In particular, when used together with a carbon material, a high energy density can be obtained and excellent charge / discharge cycle characteristics can be obtained. Note that in this specification, alloys include those composed of one or more metal elements and one or more metalloid elements in addition to those composed of two or more metal elements. There are structures in which a solid solution, a eutectic (eutectic mixture), an intermetallic compound, or two or more of them coexist.

Examples of such metal elements or metalloid elements include tin (Sn), lead (Pb), aluminum, indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), and cadmium. (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y) or hafnium (Hf). It is done. These alloys or compounds, for example, those represented by a chemical formula Ma _s Mb _t. Ma represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, and Mb represents at least one of elements other than Ma. The values of s and t are s> 0 and t ≧ 0, respectively.

  Among them, a simple substance, alloy or compound of a group 14 metal element or metalloid element in the long-period periodic table is preferable, and silicon or tin, or an alloy or compound thereof is particularly preferable. These may be crystalline or amorphous.

Examples of the negative electrode material capable of inserting and extracting lithium further include other metal compounds or polymer materials. Examples of the other metal compounds include oxides such as iron oxide, ruthenium oxide, and molybdenum oxide, and LiN _3. Examples of the polymer material include polyacetylene.

  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 composed of, for example, a porous film made of a synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. The porous film may be laminated.

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

  Solvents include ethylene carbonate, propylene carbonate, vinylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, γ-valerolactone, tetrahydrofuran, 2 -Methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetate ester, butyrate ester, propionate ester, fluorobenzene, etc. Non-aqueous solvents are mentioned. As the solvent, one kind may be used alone, or two or more kinds may be mixed and used.

  Among them, the solvent preferably contains a cyclic carbonate and a chain carbonate, for example, at least one of ethylene carbonate, propylene carbonate, and vinylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. It is preferable to include at least one of them. This is because excellent charge / discharge capacity and charge / discharge cycle characteristics can be obtained.

Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB (C ₆ H ₅ ) ₄ , CH _3. Examples thereof include lithium salts such as SO ₃ Li, CF ₃ SO ₃ Li, LiCl, and LiBr. As the electrolyte salt, one kind may be used alone, or two or more kinds may be mixed and used.

  The electrolytic solution further contains a silane coupling agent and an oxalate ester as additives. This is because a side reaction in the negative electrode 22 can be suppressed by the coating formed with the silane coupling agent, and the increase in coating resistance with the silane coupling agent alone can be suppressed with the oxalate ester. . In the present embodiment, these silane coupling agents and oxalic acid esters will be described as additives focusing on their functions, but they may function as solvents.

  Examples of the silane coupling agent include vinyltrimethoxysilane, vinyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, and 3-methacryloxy. Examples thereof include propyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, and p-styryltrimethoxysilane. A silane coupling agent may be used alone or in combination of two or more. In particular, those having a polymerizable group such as a vinyl group, an acrylate group, a methacrylate group, or an epoxy group are preferable. This is because a more stable coating is considered to be formed, and even when propylene carbonate or the like that is easily decomposed into a solvent is used, a high effect can be obtained.

  Examples of the oxalate ester include chain oxalate esters such as dimethyl oxalate, diethyl oxalate, dipropyl oxalate, and dibutyl oxalate. One oxalate ester may be used alone, or two or more oxalate esters may be mixed and used.

  These contents in the electrolytic solution are within the range of 0.5 mass% to 2.0 mass% for the silane coupling agent and within the range of 0.2 mass% to 5 mass% for the oxalate ester. Is preferred. This is because a higher 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 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 obtained. Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 21A and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like, and the positive electrode 21 is manufactured.

  Next, 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-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry. And Subsequently, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, and the solvent is dried. Then, the negative electrode active material layer 22B is formed by compression molding using a roll press or the like, and 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. After that, 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.

  This secondary battery operates as follows.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode active material layer 21B and inserted into the negative electrode active material layer 22B through the electrolytic solution. At that time, in the negative electrode 22, the oxalate ester is first reduced at a more noble potential than the silane coupling agent to form a film on the surface of the negative electrode 22, and then the silane coupling agent reacts to form a film. Thereby, reaction of a silane coupling agent is suppressed and the quantity of the film formed with a silane coupling agent decreases. Next, when discharging is performed, for example, lithium ions are separated from the negative electrode active material layer 22B and inserted into the positive electrode active material layer 21B through the electrolytic solution. Therefore, the irreversible reaction generated between the negative electrode 22 and the electrolytic solution by the coating is suppressed, and the increase in coating resistance is also suppressed.

  As described above, according to the present embodiment, since the silane coupling agent and the oxalic acid ester are included, the negative electrode is coated with the silane coupling agent while suppressing the reaction of the silane coupling agent with the oxalic acid ester. 22 can be formed. Therefore, the side reaction in the negative electrode 22 can be suppressed by the coating while suppressing increase in the coating resistance. Therefore, both charge / discharge efficiency and load characteristics can be improved.

  In particular, if the content of the silane coupling agent is in the range of 0.5% by mass to 2% by mass and the content of the oxalate ester is in the range of 0.2% by mass to 5% by mass. Higher effects can be obtained.

[Second Embodiment]
FIG. 3 shows the configuration of the secondary battery according to the second embodiment of the present invention. This secondary battery is a so-called laminate film type, and has a wound electrode body 30 to which a positive electrode lead 31 and a negative electrode lead 32 are attached accommodated in a film-shaped exterior member 40. According to this secondary battery, it is possible to reduce the size, weight, and thickness as compared with the so-called cylindrical type described in the first embodiment.

  The positive electrode lead 31 and the negative electrode lead 32 are led out, for example, in the same direction from the inside of the exterior member 40 to the outside, and are each made of a metal material such as aluminum, copper, nickel, or stainless steel.

  The exterior member 40 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. For example, the exterior member 40 is disposed so that the polyethylene film side and the wound electrode body 30 face each other, and the outer edge portions are in close contact with each other by fusion bonding or an adhesive. An adhesive film 41 is inserted between the exterior member 40 and the positive electrode lead 31 and the negative electrode lead 32 to prevent intrusion of outside air. The adhesion film 41 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 may be made of a laminated film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminated film.

  FIG. 4 shows an enlarged part of the spirally wound electrode body 30 shown in FIG. The wound electrode body 30 is obtained by stacking and winding a positive electrode 33 and a negative electrode 34 with a separator 35 and an electrolyte layer 36 interposed therebetween.

  The positive electrode 33 has a structure in which a positive electrode active material layer 33B is provided on one side or both sides of a positive electrode current collector 33A, and the negative electrode 34 also has a negative electrode active material layer 34B on one side or both sides of the negative electrode current collector 34A. It has a provided structure. The positive electrode 33 and the negative electrode 34 are disposed so that the positive electrode active material layer 33B and the negative electrode active material layer 34B face each other. The specific configurations of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, the negative electrode active material layer 34B, and the separator 35 are the same as those of the positive electrode current collector 21A, the positive electrode active material layer in the first embodiment. This is the same as 21B, the negative electrode current collector 22A, the negative electrode active material layer 22B, and the separator 23.

  The electrolyte layer 36 is configured by a so-called gel electrolyte in which an electrolytic solution is held in a holding body. A gel electrolyte is preferable because it can obtain high ionic conductivity and prevent leakage. The configuration of the electrolytic solution (that is, the solvent, the electrolyte salt, and the additive) is the same as that in the first embodiment.

  The holding body is made of, for example, a polymer material. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, polypropylene oxide, polyphosphazene, polysiloxane, polyvinyl acetate, polyvinyl Examples thereof include alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene, and polycarbonate. In particular, from the viewpoint of electrochemical stability, it is desirable to use polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, or a polymer compound having a polyethylene oxide structure. The amount of the polymer compound added to the electrolytic solution varies depending on the compatibility between the two, but is usually preferably about 5% by mass to 50% by mass of the electrolytic solution.

  The electrolyte layer 36 may be made of an inorganic conductor or a mixture of a polymer compound and an inorganic conductor for the holding body. Examples of inorganic conductors include polycrystals of lithium nitride, lithium iodide or lithium hydroxide, a mixture of lithium iodide and dichromium trioxide, or a mixture of lithium iodide, thilium sulfide and diphosphorous subsulfide. The thing containing is mentioned.

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

  First, after forming the positive electrode 33 and the negative electrode 34 in the same manner as in the first embodiment, an electrolyte layer 36 in which an electrolytic solution is held in a holding body is formed on each of the positive electrode 33 and the negative electrode 34. Next, the positive electrode lead 31 is attached to the end portion of the positive electrode current collector 33A, and the negative electrode lead 32 is attached to the end portion of the negative electrode current collector 34A. Subsequently, the positive electrode 33 and the negative electrode 34 on which the electrolyte layer 36 is formed are stacked via the separator 35, and then wound in the longitudinal direction to form the wound electrode body 30. After that, for example, the wound electrode body 30 is sandwiched between the exterior members 40, and the outer edge portions of the exterior members 40 are sealed and sealed by thermal fusion or the like. At that time, the adhesion film 41 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 3 and 4 is completed.

  Further, in this secondary battery, the positive electrode 33 and the negative electrode 34 are laminated and wound via the separator 35 and sandwiched between the exterior members 40, and then the electrolytic solution and the polymer compound are opened from the opening of the exterior member 40. The electrolyte layer 36 may be formed by injecting an electrolyte composition containing a monomer as a raw material and polymerizing the monomer.

  This secondary battery operates in the same manner as in the first embodiment, and has the same effect as in the first embodiment.

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

(Examples 1-1 to 1-3)
The laminate film type secondary battery shown in FIGS. 3 and 4 was produced. First, lithium-cobalt composite oxide (LiCoO ₂ ) is used as a positive electrode active material, and the lithium-cobalt composite oxide, graphite as a conductive agent, and polyvinylidene fluoride as a binder are mixed to form a positive electrode composite. An agent was prepared. Next, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, and then uniformly applied to the positive electrode current collector 33A made of aluminum foil and dried, and a roll press machine The positive electrode active material layer 33B was formed by compression molding to produce a positive electrode 33 of 50 mm × 350 mm.

  Further, artificial graphite was prepared as a negative electrode active material, and this negative graphite was mixed with polyvinylidene fluoride as a binder to prepare a negative electrode mixture. Next, this negative electrode mixture was dispersed in N-methyl-2-pyrrolidone as a solvent to form a negative electrode mixture slurry, and then uniformly applied to the negative electrode current collector 34A made of copper foil and dried, and a roll press machine The negative electrode active material layer 34B was formed by compression molding to produce a negative electrode 34 of 52 mm × 370 mm.

Subsequently, the positive electrode lead 31 was attached to the positive electrode current collector 33A, the negative electrode lead 32 was attached to the negative electrode current collector 34A, and the electrolyte layer 36 was formed on the positive electrode active material layer 33B and the negative electrode active material layer 34B. The electrolyte layer 36 is an electrolyte prepared by mixing ethylene carbonate and propylene carbonate in a mass ratio of 6: 4, and adding a silane coupling agent, an oxalate ester, and LiPF _{6 as} an electrolyte salt thereto. The gel electrolyte was held in a copolymer of hexafluoropropylene and vinylidene fluoride.

At that time, any one of vinyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, and 3-methacryloxypropyltriethoxysilane is used as the silane coupling agent, and the content thereof in the electrolyte is 1% by mass. did. Diethyl oxalate was used as the oxalate ester, and its content in the electrolyte was 1% by mass. The LiPF ₆ content was 0.7 mol / kg, and the ratio of hexafluoropropylene in the copolymer was 6.9% by mass.

  Next, the separator 35, the positive electrode 33, the separator 35, and the negative electrode 34 were stacked and wound in this order to form the wound electrode body 30, and then the wound electrode body 30 was sealed between the exterior members 40. This obtained the secondary battery of Examples 1-1 to 1-3.

  As Comparative Examples 1-1 to 1-3 with respect to Examples 1-1 to 1-3, except that diethyl oxalate was not added to the electrolyte, the same procedure as in Examples 1-1 to 1-3 was performed. A secondary battery was produced. Comparative Example 1-1 corresponds to Example 1-1, Comparative Example 1-2 corresponds to Example 1-2, and Comparative Example 1-3 corresponds to Example 1-3.

  The fabricated secondary batteries of Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 were subjected to a charge / discharge test to examine the initial charge / discharge efficiency and load characteristics. At that time, charging was performed at 23 ° C. with constant current and constant voltage charging at 0.1 C up to an upper limit of 4.2 V with a total charging time of 12 hours. In the first cycle discharge, a constant current discharge with a load of 0.2 C was performed to a final voltage of 3.0 V, and for the second cycle, a constant current discharge with a load of 2.0 C was performed to a final voltage of 3.0 V. Note that 0.1 C is a current value at which the theoretical capacity can be discharged in 10 hours, 0.2 C is a current value at which the theoretical capacity can be discharged in 5 hours, and 2.0 C is a current value at which the theoretical capacity can be discharged in 30 minutes. It is.

  The initial charge / discharge efficiency is obtained from the ratio of the discharge capacity to the charge capacity of the first cycle, that is, (discharge capacity of the first cycle / charge capacity of the first cycle) × 100, and the load characteristic is the first cycle (load 0. The ratio of the discharge capacity at the second cycle (load 2.0 C) to the discharge capacity at 2C), that is, (discharge capacity at the second cycle / discharge capacity at the first cycle) × 100. The obtained results are shown in Table 1.

  As shown in Table 1, according to Examples 1-1 to 1-3 in which a silane coupling agent and an oxalate ester were added, compared with Comparative Examples 1-1 to 1-3 in which no oxalate ester was added. Thus, the load characteristics can be greatly improved, and the same value for the initial charge / discharge efficiency was obtained. That is, it was found that if the silane coupling agent and the oxalate ester are included in the electrolytic solution, both the charge / discharge efficiency and the load characteristics can be improved.

(Example 2-1)
A secondary battery was fabricated in the same manner as in Example 1-1 except that dimethyl oxalate was used in place of diethyl oxalate as the oxalate ester. For the secondary battery of Example 2-1, the initial charge and discharge efficiency and load characteristics were examined in the same manner as in Example 1-1. The results are shown in Table 2 together with the results of Example 1-1 and Comparative example 1-1.

  As shown in Table 2, according to Example 2-1 to which dimethyl oxalate was added, as in Example 1-1 to which diethyl oxalate was added, in Comparative Example 1-1 to which no oxalate was added In comparison, the load characteristics could be greatly improved, and the same value for the initial charge / discharge efficiency could be obtained. That is, it was found that the same effect can be obtained not only with diethyl oxalate but also with other oxalate esters.

(Examples 3 to 5)
A secondary battery was produced in the same manner as in Examples 1-1 to 1-3 except that the contents of the silane coupling agent and oxalate ester in the electrolyte were changed. Efficiency and load characteristics were investigated. In Example 3, the silane coupling agent is vinyltriethoxysilane, in Example 4, the silane coupling agent is 3-acryloxypropyltrimethoxysilane, and in Example 5, the silane coupling agent is 3-methacryloxypropyltriethoxy. Silane was used, and the oxalate ester was diethyl oxalate in any of Examples 3 to 5. The results are shown in FIGS.

  5 to 8 show the results of Example 3, FIGS. 5 and 6 show the content of vinyltriethoxysilane on the horizontal axis, and FIGS. 7 and 8 show the content of diethyl oxalate on the horizontal axis. Yes. 9 to 12 show the results of Example 4. FIGS. 9 and 10 show the content of 3-acryloxypropyltrimethoxysilane on the horizontal axis, and FIGS. 11 and 12 show the content of diethyl oxalate on the horizontal axis. The axis. 13 to 16 show the results of Example 5. FIGS. 13 and 14 show the content of 3-methacryloxypropyltriethoxysilane on the horizontal axis, and FIGS. 15 and 16 show the content of diethyl oxalate on the horizontal axis. The axis.

  As shown in FIGS. 5 and 6, when the content of vinyltriethoxysilane is increased, the initial charge / discharge efficiency is improved and tends to decrease after showing the maximum value, and the load characteristic tends to gradually decrease. It was observed. In addition, as shown in FIGS. 7 and 8, when the content of diethyl oxalate is increased, the initial charge / discharge efficiency tends to gradually decrease after showing a maximum value at 1% by mass or less, and the load characteristic is After improving to about 1% by mass, there was a tendency to level off or gradually decrease. In Examples 4 and 5 using other silane coupling agents, substantially the same results were obtained as shown in FIGS.

  That is, the content of the silane coupling agent is preferably 0.5% by mass or more and 2% by mass or less, and the content of the oxalate ester is preferably 0.2% by mass or more and 5% by mass or less. I understood.

(Example 6-1)
The cylindrical secondary battery shown in FIGS. 1 and 2 was produced. At that time, a secondary battery was fabricated in the same manner as in Example 1-3 except that the electrolytic solution was used as it was without being held by the holder. That is, 3-methacryloxypropyltriethoxysilane was used for the silane coupling agent, diethyl oxalate was used for the oxalate ester, and the content in the electrolyte was 1% by mass. Moreover, as Comparative Example 6-1 with respect to Example 6-1, a secondary battery was fabricated in the same manner as Example 6-1 except that oxalate was not added. For the secondary batteries of Example 6-1 and Comparative Example 6-1, the initial efficiency and load characteristics were examined in the same manner as in Example 1-3. The results are shown in Table 3 together with the results of Example 1-3.

  As shown in Table 3, also in Example 6-1 using an electrolytic solution instead of the gel electrolyte, as in Example 1-3, compared to Comparative Example 6-1 in which no oxalate was added Thus, the load characteristics can be greatly improved, and the same value for the initial charge / discharge efficiency was obtained. That is, it can be seen that both the charge and discharge efficiency and the load characteristics can be improved by using the electrolyte solution as it is or by holding it in a holding body so as to contain a silane coupling agent and an oxalate ester. It was.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the embodiments and examples described above, the case where the positive electrodes 21 and 33 and the negative electrodes 22 and 34 are wound has been described, but the positive and negative electrodes may be folded or stacked. Further, in the above embodiments and examples, a cylindrical or laminated film type secondary battery has been described. For example, other types such as an elliptical type, a polygonal type, a coin type, a button type, a square type, or a large type are described. The present invention can also be applied to a secondary battery having a shape. Furthermore, not only the secondary battery but also the primary battery can be applied.

  In addition, in the above-described embodiments and examples, a so-called lithium ion secondary battery, that is, a secondary battery in which the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium has been described. The present invention can be similarly applied to the used battery. As a battery using another electrode reaction, for example, a battery in which the capacity of the negative electrode is represented by the sum of the capacity component due to insertion and extraction of lithium and the capacity component due to precipitation and dissolution of lithium, or the capacity of the negative electrode is A so-called lithium metal battery represented by a capacity component due to precipitation and dissolution of lithium is exemplified.

  Among these, a battery in which the capacity of the negative electrode is represented by the sum of the capacity component due to insertion and extraction of lithium and the capacity component due to precipitation and dissolution of lithium has, for example, a charge capacity of a negative electrode material capable of inserting and extracting lithium. The lithium ion secondary battery has the same configuration as the above-described lithium ion secondary battery except that lithium metal is deposited on the negative electrode during charging by being adjusted to be smaller than the charging capacity of the positive electrode. (For example, refer to Patent Document 1). In addition, the lithium metal battery has the same configuration as the lithium ion secondary battery described above except that the negative electrode is made of lithium metal and the like, and the precipitation and dissolution reaction of lithium is used in the negative electrode. Yes.

  Furthermore, in the above-described embodiments and examples, the case where lithium is used as the electrode reactant has been described. However, other alkali metals such as sodium (Na) or potassium (K), magnesium or calcium (Ca), etc. The present invention can also be applied to the case of using other light metals such as alkaline earth metals or aluminum.

It is sectional drawing showing the structure of the secondary battery which concerns on the 1st 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. It is a partial exploded perspective view showing the structure of the secondary battery which concerns on the 2nd 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. It is a characteristic view showing the relationship between initial charge and discharge efficiency and content of vinyltriethoxysilane. It is a characteristic view showing the relationship between a load characteristic and content of vinyltriethoxysilane. It is a characteristic view showing the relationship between initial charge / discharge efficiency and content of diethyl oxalate. It is a characteristic view showing the relationship between a load characteristic and content of diethyl oxalate. It is a characteristic view showing the relationship between the initial charge and discharge efficiency and the content of 3-acryloxypropyltrimethoxysilane. It is a characteristic view showing the relationship between load characteristics and the content of 3-acryloxypropyltrimethoxysilane. It is a characteristic view showing the relationship between initial charge / discharge efficiency and content of diethyl oxalate. It is a characteristic view showing the relationship between a load characteristic and content of diethyl oxalate. It is a characteristic view showing the relationship between the initial charge and discharge efficiency and the content of 3-methacryloxypropyltriethoxysilane. It is a characteristic view showing the relationship between a load characteristic and content of 3-methacryloxypropyl triethoxysilane. It is a characteristic view showing the relationship between initial charge / discharge efficiency and content of diethyl oxalate. It is a characteristic view showing the relationship between a load characteristic and content of diethyl oxalate.

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, 30 ... Winding electrode body, 21, 33 ... Positive electrode, 21A, 33A ... Positive electrode current collector, 21B, 33B ... Positive electrode active material layer, 22, 34 ... Negative electrode, 22A, 34A ... Negative electrode current collector, 22B, 34B ... Negative electrode active material layer, 23, 35 ... Separator , 24 ... center pin, 25, 31 ... positive electrode lead, 26, 32 ... negative electrode lead, 36 ... electrolyte layer, 40 ... exterior member, 41 ... adhesion film.

Claims (8)

  An electrolytic solution comprising a silane coupling agent and an oxalate ester.   The said silane coupling agent contains at least 1 sort (s) of the group which consists of vinyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, and 3-methacryloxypropyltriethoxysilane, The said 1st aspect is characterized by the above-mentioned. Electrolytic solution.   The electrolytic solution according to claim 1, wherein the oxalate ester includes at least one of dimethyl oxalate and diethyl oxalate.   The content of the silane coupling agent is 0.5% by mass or more and 2% by mass or less, and the content of the oxalate ester is 0.2% by mass or more and 5% by mass or less. The electrolytic solution described. A battery comprising an electrolyte solution together with a positive electrode and a negative electrode,
The battery, wherein the electrolytic solution contains a silane coupling agent and an oxalate ester.   The said silane coupling agent contains at least 1 sort (s) of the group which consists of vinyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, and 3-methacryloxypropyltriethoxysilane of Claim 5 characterized by the above-mentioned. battery.   The battery according to claim 5, wherein the oxalate ester includes at least one of dimethyl oxalate and diethyl oxalate. The content of the silane coupling agent in the electrolytic solution is 0.5% by mass or more and 2% by mass or less, and the content of the oxalate ester in the electrolytic solution is 0.2% by mass or more and 5% by mass or less. The battery according to claim 5.

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