JP2005317446A - Electrolyte and battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery and an electrolyte used for the battery in which cycle characteristics can be improved. <P>SOLUTION: The battery is provided with a wound electrode body 20 in which a positive electrode 21 and a negative electrode 22 are wound through a separator 23. The separator 23 is impregnated with an electrolyte liquid in which an electrolyte salt is dissolved in a solvent. For the solvent, carbonic acid ester expressed by R31CFX31COOR32 is used. For the electrolyte salt, a light metal salt such as difluoro[oxolato-O,O'] lithium borate, tetrafluoro[oxolato-O,O'] lithium phosphate or difluoro-bis[oxolato-O,O'] lithium phosphate is used. Thereby, decomposition reaction of the electrolyte in the negative electrode 22 can be suppressed and cycle characteristics can be improved. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrolyte containing a carboxylic acid ester having a fluorine atom, and a battery using the same.

  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, a lithium-ion secondary battery using a material capable of inserting and extracting lithium (Li) such as a carbon material into the negative electrode has been commercialized, and the market has expanded. doing.

As a secondary battery capable of obtaining a high energy density, there is a lithium metal secondary battery that uses lithium metal for the negative electrode and uses only precipitation and dissolution reactions of lithium metal for the negative electrode reaction. Lithium metal secondary batteries have a large theoretical electrochemical equivalent of 2054 mAh / cm ^{3 of} lithium metal, which is equivalent to 2.5 times that of graphite used in lithium ion secondary batteries, so it is higher than lithium ion secondary batteries. The energy density is expected to be obtained. Until now, research and development regarding practical application of lithium metal secondary batteries has been made by many researchers and the like (for example, see Non-Patent Document 1).

  Further, recently, a secondary battery has been developed in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is represented by the sum thereof (for example, Patent Documents). 1). In this method, a carbon material capable of inserting and extracting lithium is used for the negative electrode, and lithium is deposited on the surface of the carbon material during charging. According to this secondary battery, it can be expected to achieve a high energy density as in the case of the lithium metal secondary battery.

By the way, in these secondary batteries, in order to improve various characteristics such as cycle characteristics, it has been conventionally studied to add various additives to the electrolyte (see, for example, Patent Documents 2 and 3).
Edited by Jean-Paul Gabano, "Lithium Batteries", London, New York, Academic Press, 1983 International Publication No. 01/22519 Pamphlet JP 2002-110235 A Japanese Patent Laid-Open No. 11-86901

  However, in a lithium metal secondary battery or a secondary battery in which the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium and is expressed by the sum thereof, the lithium ion secondary battery The cycle characteristics are low as compared with the secondary battery, and the improvement is desired. Further, in the lithium ion secondary battery, further improvement in cycle characteristics is demanded with the recent demand for extending the battery life.

  The present invention has been made in view of such problems, and an object thereof is to provide an electrolyte capable of improving cycle characteristics and a battery using the electrolyte.

  The electrolyte according to the present invention includes a compound represented by Chemical Formula 1 and a light metal salt represented by Chemical Formula 2.

（式中、Ｒ３１は水素基，フッ素基，または炭素数が１〜３のアルキル基あるいはその少なくとも一部の水素をフッ素で置換した基を表し、Ｘ３１は水素基またはフッ素基を表し、Ｒ３２は炭素数が１または２のアルキル基を表す。）

(Wherein R31 represents a hydrogen group, a fluorine group, an alkyl group having 1 to 3 carbon atoms, or a group obtained by substituting at least a part of hydrogen with fluorine, X31 represents a hydrogen group or a fluorine group, and R32 represents Represents an alkyl group having 1 or 2 carbon atoms.)

（式中、Ｒ１１は−Ｃ（＝Ｏ）−Ｒ２１−Ｃ（＝Ｏ）−基（Ｒ２１はアルキレン基，ハロゲン化アルキレン基，アリーレン基またはハロゲン化アリーレン基を表す。）または−Ｃ（＝Ｏ）−Ｃ（＝Ｏ）−基を表し、Ｒ１２はハロゲン基，アルキル基，ハロゲン化アルキル基，アリール基またはハロゲン化アリール基を表し、Ｘ１１およびＸ１２は酸素（Ｏ）または硫黄（Ｓ）をそれぞれ表し、Ｍ１１は遷移金属元素または短周期型周期表における３Ｂ族元素，４Ｂ族元素あるいは５Ｂ族元素を表し、Ｍ２１は短周期型周期表における１Ａ族元素あるいは２Ａ族元素またはアルミニウム（Ａｌ）を表し、ａは１〜４の整数であり、ｂは０〜８の整数であり、ｃ，ｄ，ｅおよびｆはそれぞれ１〜３の整数である。）

(Wherein R11 represents a —C (═O) —R21—C (═O) — group (R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group) or —C (═O ) —C (═O) — group, R12 represents a halogen group, an alkyl group, a halogenated alkyl group, an aryl group or a halogenated aryl group, and X11 and X12 represent oxygen (O) or sulfur (S), respectively. M11 represents a transition metal element or a group 3B element, a group 4B element or a group 5B element in the short periodic table, and M21 represents a group 1A element, a group 2A element or aluminum (Al) in the short period periodic table. A is an integer of 1 to 4, b is an integer of 0 to 8, and c, d, e and f are each an integer of 1 to 3.)

  The battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the electrolyte includes a compound represented by Chemical Formula 3 and a light metal salt represented by Chemical Formula 4.

（式中、Ｒ３１は水素基，フッ素基，または炭素数が１〜３のアルキル基あるいはその少なくとも一部の水素をフッ素で置換した基を表し、Ｘ３１は水素基またはフッ素基を表し、Ｒ３２は炭素数が１または２のアルキル基を表す。）

(Wherein R31 represents a hydrogen group, a fluorine group, an alkyl group having 1 to 3 carbon atoms, or a group obtained by substituting at least a part of hydrogen with fluorine, X31 represents a hydrogen group or a fluorine group, and R32 represents Represents an alkyl group having 1 or 2 carbon atoms.)

（式中、Ｒ１１は−Ｃ（＝Ｏ）−Ｒ２１−Ｃ（＝Ｏ）−基（Ｒ２１はアルキレン基，ハロゲン化アルキレン基，アリーレン基またはハロゲン化アリーレン基を表す。）または−Ｃ（＝Ｏ）−Ｃ（＝Ｏ）−基を表し、Ｒ１２はハロゲン基，アルキル基，ハロゲン化アルキル基，アリール基またはハロゲン化アリール基を表し、Ｘ１１およびＸ１２は酸素または硫黄をそれぞれ表し、Ｍ１１は遷移金属元素または短周期型周期表における３Ｂ族元素，４Ｂ族元素あるいは５Ｂ族元素を表し、Ｍ２１は短周期型周期表における１Ａ族元素あるいは２Ａ族元素またはアルミニウムを表し、ａは１〜４の整数であり、ｂは０〜８の整数であり、ｃ，ｄ，ｅおよびｆはそれぞれ１〜３の整数である。）

(Wherein R11 represents a —C (═O) —R21—C (═O) — group (R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group) or —C (═O ) -C (= O)-group, R12 represents a halogen group, an alkyl group, a halogenated alkyl group, an aryl group or a halogenated aryl group, X11 and X12 each represent oxygen or sulfur, and M11 represents a transition metal Represents an element or a group 3B element, a group 4B element or a group 5B element in the short-period type periodic table, M21 represents a group 1A element or a group 2A element or aluminum in the short-period type periodic table, and a is an integer of 1 to 4 Yes, b is an integer from 0 to 8, and c, d, e, and f are each an integer from 1 to 3.)

  According to the electrolyte of the present invention, since the compound represented by Chemical Formula 1 and the light metal salt represented by Chemical Formula 2 are included, high stability can be obtained.

  Further, according to the battery of the present invention, since the electrolyte of the present invention is used, the decomposition reaction of the electrolyte in the negative electrode can be suppressed. Therefore, the efficiency in the negative electrode is improved, and the cycle characteristics can be improved.

  In particular, if a light metal salt other than the light metal salt represented by Chemical Formula 2 is included, a higher effect can be obtained.

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

  The electrolyte according to an embodiment of the present invention contains a so-called liquid electrolyte solution including, for example, a solvent and an electrolyte salt dissolved in the solvent.

  As the solvent, for example, a nonaqueous solvent such as an organic solvent is preferable, and a compound represented by Chemical formula 5 is preferable. For example, when used in a battery, the decomposition reaction of the electrolyte in the negative electrode can be suppressed, cycle characteristics can be improved, and high stability can be obtained.

（式中、Ｒ３１は水素基，フッ素基，または炭素数が１〜３のアルキル基あるいはその少なくとも一部の水素をフッ素で置換した基を表し、Ｘ３１は水素基またはフッ素基を表し、Ｒ３２は炭素数が１または２のアルキル基を表す。）

(Wherein R31 represents a hydrogen group, a fluorine group, an alkyl group having 1 to 3 carbon atoms, or a group obtained by substituting at least a part of hydrogen with fluorine, X31 represents a hydrogen group or a fluorine group, and R32 represents Represents an alkyl group having 1 or 2 carbon atoms.)

Specific examples of the compound represented by Chemical formula 5 include CF ₃ CF ₂ COOCH ₃ , CF ₃ CF ₂ COOC ₂ H ₅ , CF ₃ CHFCOOCH ₃ , CF ₃ CHFCOOC ₂ H ₅ , CH ₂ FCOOCH ₃ , and CHF ₂ COOC. ₂ H ₅ , CF ₃ COOCH ₃ , CF ₃ COOC ₂ H ₅ , CH ₃ CF ₂ COOCH ₃ , CH ₃ CF ₂ COOC ₂ H ₅ , CHF ₂ COOCH ₃ , CF ₃ CF ₂ CF ₂ COOCH ₃ , CF ₃ CF ₂ CF ₂ CF ₂ COOCH ₃ and the like.

  The compound represented by Chemical formula 5 may also be used by mixing with various conventionally used non-aqueous solvents. Specific examples of such a non-aqueous solvent include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, vinyl esters such as vinylene carbonate, vinyl ethylene carbonate, or γ-butyrolactone, sulfolane, 2-methyl. And ethers such as tetrahydrofuran or dimethoxyethane. These may be used alone or in combination of two or more. In particular, from the viewpoint of oxidation stability, a carbonic acid ester is preferable, and among them, it is preferable to include a cyclic carbonic acid ester of an unsaturated compound such as vinylene carbonate or vinyl ethylene carbonate. This is because the cycle characteristics and heavy load characteristics can be improved.

  The electrolyte salt preferably includes a light metal salt represented by Chemical Formula 6. When the light metal salt represented by Chemical formula 6 is used in, for example, a battery, a stable coating can be formed on the surface of the negative electrode and the decomposition reaction of the solvent can be suppressed, so that the stability of the electrolyte can be improved. Because.

（式中、Ｒ１１は化７または化８に示した基を表し、Ｒ１２はハロゲン基，アルキル基，ハロゲン化アルキル基，アリール基またはハロゲン化アリール基を表し、Ｘ１１およびＸ１２は酸素または硫黄をそれぞれ表し、Ｍ１１は遷移金属元素または短周期型周期表における３Ｂ族元素，４Ｂ族元素あるいは５Ｂ族元素を表し、Ｍ２１は短周期型周期表における１Ａ族元素あるいは２Ａ族元素またはアルミニウムを表し、ａは１〜４の整数であり、ｂは０〜８の整数であり、ｃ，ｄ，ｅおよびｆはそれぞれ１〜３の整数である。）

(Wherein R11 represents the group shown in Chemical Formula 7 or Chemical Formula 8, R12 represents a halogen group, an alkyl group, a halogenated alkyl group, an aryl group or a halogenated aryl group, and X11 and X12 each represent oxygen or sulfur. M11 represents a transition metal element or a 3B group element, a 4B group element or a 5B group element in the short periodic table, M21 represents a 1A group element, a 2A group element or aluminum in the short periodic table, and a is (It is an integer of 1-4, b is an integer of 0-8, c, d, e, and f are integers of 1-3, respectively.)

（Ｒ２１は、アルキレン基，ハロゲン化アルキレン基，アリーレン基またはハロゲン化アリーレン基を表す。）

(R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group.)

  As a light metal salt represented by Chemical formula 6, for example, a compound represented by Chemical formula 9 is preferable.

（式中、Ｒ１１は化１０または化１１に示した基を表し、Ｒ１３はハロゲン基を表し、Ｍ１２はリン（Ｐ）またはホウ素（Ｂ）を表し、Ｍ２１は短周期型周期表における１Ａ族元素あるいは２Ａ族元素またはアルミニウムを表し、ａ１は１〜３の整数であり、ｂ１は０，２または４であり、ｃ，ｄ，ｅおよびｆはそれぞれ１〜３の整数である。）

(Wherein R11 represents a group shown in Chemical Formula 10 or Chemical Formula 11, R13 represents a halogen group, M12 represents phosphorus (P) or boron (B), M21 represents a group 1A element in the short-period periodic table) Alternatively, it represents a group 2A element or aluminum, a1 is an integer of 1 to 3, b1 is 0, 2 or 4, and c, d, e and f are each an integer of 1 to 3.)

（Ｒ２１は、アルキレン基，ハロゲン化アルキレン基，アリーレン基またはハロゲン化アリーレン基を表す。）

(R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group.)

  More specifically, it is represented by lithium difluoro [oxolato-O, O ′] lithium borate represented by Chemical formula 12, lithium tetrafluoro [oxolato-O, O ′] lithium phosphate represented by Chemical formula 13 or Chemical formula 14. More preferred is difluorobis [oxolato-O, O ′] lithium phosphate. A higher effect can be obtained when a B—O bond or a P—O bond is provided, and a higher effect is obtained particularly when an O—B—O bond or an O—P—O bond is provided. Because it can.

In addition to the light metal salt represented by Chemical Formula 6, any one or more of other light metal salts are preferably mixed and used as the electrolyte salt. For example, in a battery, battery characteristics such as storage characteristics can be improved and internal resistance can be reduced. Examples of other light metal salts include LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, LiBr, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) _2, LiN (C ₄ F ₉ SO ₂ ) (CF ₃ SO ₂ ) or other lithium salt represented by Chemical Formula 15 or LiC (CF ₃ SO ₂ ) _{3 and the} like, and lithium salts represented by the chemical formula 16 are mentioned.

（式中、ｍおよびｎは１以上の整数である。）

(In the formula, m and n are integers of 1 or more.)

（式中、ｐ，ｑおよびｒは１以上の整数である。）

(In the formula, p, q and r are integers of 1 or more.)

Among them, if LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , a lithium salt represented by Chemical formula 15 and a lithium salt represented by Chemical formula 16 are used in combination or two or more, It is preferable because a higher effect can be obtained and a higher conductivity can be obtained. LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , a lithium salt represented by Chemical formula 15 and a lithium represented by Chemical formula 16 It is more preferable to use a mixture of at least one member selected from the group consisting of salts.

  The content (concentration) of the electrolyte salt is preferably in the range of 0.3 mol / kg or more and 3.0 mol / kg or less with respect to the solvent. Outside this range, there is a risk that sufficient battery characteristics may not be obtained due to an extreme decrease in ionic conductivity. Among them, the content of the light metal salt represented by Chemical Formula 6 is preferably in the range of 0.01 mol / kg to 2.0 mol / kg with respect to the solvent. This is because a higher effect can be obtained within this range.

  The electrolyte may be gelled by containing a polymer compound that holds a so-called electrolytic solution containing these solvents and an electrolyte salt. The gel electrolyte is not particularly limited as long as the ion conductivity is 1 mS / cm or more at room temperature, and the composition and the structure of the polymer compound are not particularly limited. The electrolyte solution (that is, liquid solvent and electrolyte salt) is as described above. Examples of the polymer compound include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, polypropylene oxide, polyphosphazene, and polysiloxane. , Polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene or polycarbonate. In particular, from the viewpoint of electrochemical stability, it is desirable to use a polymer compound having a polyacrylonitrile, polyvinylidene fluoride, polyhexafluoropropylene or polyethylene oxide structure. The amount of the polymer compound added to the electrolytic solution varies depending on the compatibility between the two, but it is usually preferable to add a polymer compound corresponding to 5% by mass to 50% by mass of the electrolytic solution.

  This electrolyte can be produced, for example, by dissolving a light metal salt represented by Chemical Formula 6 in a solvent containing a compound represented by Chemical Formula 5. Moreover, when setting it as a gel form, it can manufacture, for example by mixing this electrolyte solution with a high molecular compound and a dilution solvent, and drying. Alternatively, for example, the electrolytic solution can be mixed with a monomer that is a starting material of the polymer compound, and the monomer can be polymerized.

  This electrolyte is used in the first secondary battery as follows, for example.

(First secondary battery)
FIG. 1 shows a cross-sectional structure of the first secondary battery. This secondary battery is a so-called lithium ion secondary battery in which the capacity of the negative electrode is represented by a capacity component due to insertion and extraction of lithium as an electrode reactant. This secondary battery is a so-called cylindrical type, and is a wound electrode in which a strip-shaped positive electrode 21 and a strip-shaped negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. 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 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.

  The wound electrode body 20 is wound around a center pin 24, for example. A positive electrode lead 25 made of aluminum 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 has, for example, a thickness of about 5 μm to 50 μm and is made of a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode active material layer 21B includes, for example, one or more positive electrode materials capable of inserting and extracting lithium, which is an electrode reactant, as a positive electrode active material. It is configured to contain a binder. That is, the capacity of the positive electrode 21 includes a capacity component due to insertion and extraction of lithium as an electrode reactant. The thickness of the positive electrode active material layer 21B is 60 μm to 250 μm. The thickness of the positive electrode active material layer 21B is the total thickness when the positive electrode active material layer 21B is provided on both surfaces of the positive electrode current collector 21A.

As the positive electrode material capable of inserting and extracting lithium, for example, in order to increase the energy density, it is preferable to contain a lithium-containing compound containing lithium, a transition metal element, and oxygen. It is more preferable to contain at least one selected from the group consisting of cobalt (Co), nickel, manganese (Mn) and iron. Examples of such a lithium-containing compound include LiCoO ₂ , LiNi _0.5 Co _0.5 O ₂ , LiMn ₂ O _{4, and} LiFePO ₄ .

  Such a positive electrode material is prepared by, for example, mixing lithium carbonate, nitrate, oxide or hydroxide with transition metal carbonate, nitrate, oxide or hydroxide so as to have a desired composition. And then pulverized and then fired at a temperature in the range of 600 ° C. to 1000 ° C. in an oxygen atmosphere.

  Examples of the conductive agent include carbon materials such as graphite, carbon black, and ketjen black, and one or more of them are used in combination. 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 more of them are mixed. Used. For example, when the positive electrode 21 and the negative electrode 22 are wound as shown in FIG. 1, it is preferable to use styrene butadiene rubber or fluorine rubber having high flexibility as the binder.

  The negative electrode 22 has, for example, a structure 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. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A. 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 having good electrochemical stability, electrical conductivity, and mechanical strength. In particular, copper foil is most preferable because it has high electrical conductivity. The thickness of the anode current collector 22A is preferably about 5 to 40 μm, for example. If the thickness is less than 5 μm, the mechanical strength decreases, and the negative electrode current collector 22A is easily torn in the manufacturing process, resulting in a decrease in production efficiency. If the thickness is larger than 40 μm, the negative electrode current collector 22A in the battery This is because the volume ratio becomes larger than necessary and it is difficult to increase the energy density.

  The negative electrode active material layer 22B includes one or more negative electrode materials capable of inserting and extracting lithium as the negative electrode active material, and the positive electrode active material layer 21B as necessary. It is comprised including the binder similar to. That is, the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium as an electrode reactant. The thickness of the negative electrode active material layer 22B is, for example, 40 μm to 250 μm. This thickness is the total thickness when the negative electrode active material layer 22B is provided on both surfaces of the negative electrode current collector 22A.

  In this secondary battery, the charge capacity of the negative electrode material capable of inserting and extracting lithium is larger than the charge capacity of the positive electrode 21. That is, in this secondary battery, lithium metal does not deposit on the negative electrode 22 during charging.

  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 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.

As the graphite, for example, the true density is preferably 2.10 g / cm ³ or more, and more preferably 2.18 g / cm ³ or more. In order to obtain such a true density, it is necessary that the (002) plane C-axis crystallite thickness is 14.0 nm or more. Further, the (002) plane spacing is preferably less than 0.340 nm, and more preferably in the range of 0.335 nm to 0.337 nm.

As non-graphitizable carbon, (002) plane spacing is 0.37 nm or more, true density is less than 1.70 g / cm ³ , and in differential thermal analysis (DTA) in air What does not show an exothermic peak at 700 ° C. or higher is preferable.

  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, and in particular, when used together with a carbon material, a high energy density can be obtained and excellent cycle characteristics can be obtained, and therefore, it is more preferable. 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. The structures include solid solutions, eutectics (eutectic mixtures), intermetallic compounds, or those in which 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. Examples of these alloys or compounds include those represented by the chemical formula Mα _s1 Mβ _s2 Li _s3 or the chemical formula Mα _s4 Mγ _s5 Mδ _s6 . In these chemical formulas, Mα represents at least one of a metal element and a metalloid element capable of forming an alloy with lithium, Mβ represents at least one of a metal element and a metalloid element other than lithium and Mα, Mγ represents at least one of nonmetallic elements, and Mδ represents at least one of metallic elements and metalloid elements other than Mα. The values of s1, s2, s3, s4, s5, and s6 are s1> 0, s2 ≧ 0, s3 ≧ 0, s4> 0, s5> 0, and s6 ≧ 0, respectively. Among these, a simple substance, alloy or compound of the group 4B metal element or metalloid element in the short periodic table is preferable, and silicon or tin, or an alloy or compound thereof is particularly preferable. These may be crystalline or amorphous.

Specific examples of such alloys or compounds include LiAl, AlSb, CuMgSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi _{2. , CaSi 2, CrSi 2, Cu} 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 < _{v ≦ 2), SnO w (} 0 <w ≦ 2), there is such SnSiO _3, LiSiO or LiSnO.

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

  The separator 23 is made of, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramic, and has a structure in which two or more kinds of porous films are laminated. May be. Among these, a porous film made of polyolefin is preferable because it is excellent in short-circuit preventing effect and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because a shutdown effect can be obtained within a range of 100 ° C. or higher and 160 ° C. or lower and the electrochemical stability is excellent. Polypropylene is also preferable, and any other resin having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  The separator 23 is impregnated with the electrolyte according to the present embodiment. Thereby, the decomposition reaction of the electrolyte in the negative electrode 22 can be suppressed, and battery characteristics such as cycle characteristics can be improved. The electrolyte salt is preferably a lithium salt, but may not be a lithium salt. This is because lithium ions that contribute to charging and discharging need only be supplied from the positive electrode or the like.

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

  First, for example, a positive electrode material capable of inserting and extracting lithium, a conductive agent, and a binder are mixed to prepare a positive electrode mixture, and this positive electrode mixture is mixed with N-methyl-2-pyrrolidone or the like. To make a paste-like positive electrode mixture slurry. Next, 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.

  Also, for example, a negative electrode material capable of inserting and extracting lithium 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. Thus, a paste-like negative electrode mixture slurry is obtained. Next, 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.

  Subsequently, 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, 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, an electrolyte 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 the gasket 17. Thereby, the secondary battery shown in FIG. 1 is formed.

  In this secondary battery, when charged, lithium ions are released from the positive electrode active material layer 21B, and first, the lithium contained in the negative electrode active material layer 22B is occluded and released through the electrolyte impregnated in the separator 23. Can be occluded by the negative electrode material. Next, when discharge is performed, lithium ions occluded in the negative electrode material capable of inserting and extracting lithium in the negative electrode active material layer 22B are released and inserted into the positive electrode active material layer 21B through the electrolyte. Here, since the electrolyte contains a light metal salt represented by Chemical Formula 6, a stable film is formed on the surface of the negative electrode 22, and the decomposition reaction of the solvent is suppressed. Moreover, since the compound represented by Chemical formula 5 is included, the decomposition reaction of the electrolyte in the negative electrode 22 is suppressed. Therefore, the synergistic action of these improves the efficiency of the negative electrode 22.

  As described above, in this embodiment, since the electrolyte includes the compound represented by Chemical Formula 5 and the light metal salt represented by Chemical Formula 6, the decomposition reaction of the electrolyte in the negative electrode 22 can be suppressed. Therefore, the efficiency in the negative electrode 22 is improved, and the cycle characteristics can be improved.

  In particular, if a light metal salt other than the light metal salt represented by Chemical Formula 6 is also included, a higher effect can be obtained.

(Secondary secondary battery)
The electrolyte of the present embodiment is also used for the second secondary battery as follows.

  The second secondary battery is a so-called lithium metal secondary battery in which the capacity of the negative electrode is represented by a capacity component due to precipitation and dissolution of lithium as an electrode reactant.

  This secondary battery has the same configuration and effects as those of the first secondary battery except that the configuration of the negative electrode active material layer is different. Therefore, here, description will be made with reference to FIGS. 1 and 2 using the same reference numerals. Detailed descriptions of the same parts are omitted.

  The negative electrode active material layer 22B is made of lithium metal deposited during charging, does not exist during assembly, and dissolves during discharge. That is, in this secondary battery, lithium metal is used as the negative electrode active material, and thereby a high energy density can be obtained.

  This secondary battery can be manufactured in the same manner as the above-described lithium ion secondary battery except that the negative electrode active material layer 22B is formed by charging.

  In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 21 and deposited as lithium metal on the surface of the negative electrode current collector 22A via the electrolyte, as shown in FIG. Then, the negative electrode active material layer 22B is formed. When the discharge is performed, for example, lithium metal is eluted as lithium ions from the negative electrode active material layer 22B, and is occluded in the positive electrode 21 through the electrolyte. Here, since the electrolyte contains a light metal salt represented by Chemical Formula 6, a stable coating is formed on the surface of the negative electrode 22, and the reaction between the lithium metal deposited on the negative electrode 22 and the solvent is suppressed. Moreover, since the compound represented by Chemical formula 5 is included, the decomposition reaction of the electrolyte in the negative electrode 22 is suppressed. Therefore, the synergistic action of these improves the lithium deposition / dissolution efficiency in the negative electrode 22.

  Thus, in this embodiment, since the electrolyte contains the compound represented by Chemical Formula 5 and the light metal salt represented by Chemical Formula 6, the decomposition reaction of the electrolyte by the lithium metal deposited on the negative electrode 22 is suppressed. be able to. Therefore, the efficiency in the negative electrode 22 is improved, and battery characteristics such as cycle characteristics can be improved. Further, since lithium metal is used as the negative electrode active material and the capacity of the negative electrode 22 is expressed by the capacity component due to the precipitation and dissolution of lithium, a high energy density can be obtained.

  In particular, if a light metal salt other than the light metal salt represented by Chemical Formula 6 is also included, a higher effect can be obtained.

  In the secondary battery, the case where the negative electrode active material layer 22B is formed at the time of charging has been described. However, the negative electrode active material layer 22B may already be provided when the battery is assembled. In this case, similarly to the lithium ion secondary battery, the negative electrode active material layer 22B may be provided on the negative electrode current collector 22A, but the negative electrode active material layer 22B is also used as a current collector, The layer 22B may be deleted.

(Third secondary battery)
The electrolyte of the present embodiment is further used for the third secondary battery as follows.

  In the third secondary battery, the capacity of the negative electrode includes a capacity component due to insertion and extraction of lithium, which is an electrode reactant, and a capacity component due to precipitation and dissolution of lithium, and is represented by the sum thereof.

  This secondary battery has the same configuration and effects as the first secondary battery except that the configuration of the negative electrode active material layer is different, and can be manufactured in the same manner. Therefore, here, description will be made with reference to FIGS. 1 and 2 using the same reference numerals. Detailed description of the same part is omitted.

  For example, the negative electrode active material layer 22B has an open circuit voltage (that is, a battery voltage) in the charging process by making the charge capacity of the negative electrode material capable of occluding and releasing lithium smaller than the charge capacity of the positive electrode 21. Lithium metal begins to be deposited on the negative electrode 22 at a time point when the voltage is lower than the overcharge voltage. The capacity of the negative electrode 22 includes the capacity component due to insertion and extraction of lithium and the precipitation and dissolution of lithium as described above. And is represented by the sum thereof. Therefore, in this secondary battery, both the negative electrode material capable of inserting and extracting lithium and lithium metal function as a negative electrode active material, and the negative electrode material capable of inserting and extracting lithium is lithium metal. It is a base material for precipitation.

  In the present specification, occlusion and release of the electrode reactant means that the ions of the electrode reactant are electrochemically occluded and released without losing its ionicity. This includes not only the case where the occluded electrode reactant is present in a complete ionic state, but also the case where it is present in a state that is not a complete ionic state. As a case corresponding to these, for example, occlusion by an electrochemical intercalation reaction of ions of an electrode reactant to graphite. Further, occlusion of the electrode reactant into the alloy containing the intermetallic compound, or occlusion of the electrode reactant due to the formation of the alloy can also be mentioned.

  The overcharge voltage refers to the open circuit voltage when the battery is overcharged. For example, the “lithium secondary battery” is one of the guidelines established by the Japan Storage Battery Industry Association (Battery Industry Association). Refers to a voltage that is higher than the open circuit voltage of a “fully charged” battery as defined and defined in the “Safety Evaluation Criteria Guidelines” (SBA G1101). In other words, it refers to a voltage higher than the open circuit voltage after charging using the charging method, standard charging method, or recommended charging method used when determining the nominal capacity of each battery. Specifically, in this secondary battery, for example, when the open circuit voltage is 4.2 V, the battery is fully charged, and lithium is occluded and released in a part of the open circuit voltage in the range of 0 V to 4.2 V. Lithium metal is deposited on the surface of the possible negative electrode material.

  Thereby, in this secondary battery, it is possible to obtain a high energy density and to improve cycle characteristics and quick charge characteristics. This secondary battery is the same as the conventional lithium ion secondary battery in that a negative electrode material capable of inserting and extracting lithium is used for the negative electrode 22, and lithium metal is deposited on the negative electrode 22. However, although it is the same as that of a conventional lithium metal secondary battery, the following advantages are obtained by depositing lithium metal on a negative electrode material capable of inserting and extracting lithium.

  First, in the conventional lithium metal secondary battery, it was difficult to deposit lithium metal uniformly, which was a cause of deterioration of cycle characteristics. However, negative electrode materials capable of inserting and extracting lithium are as follows. Since the surface area is generally large, this secondary battery can deposit lithium metal uniformly. Secondly, in the conventional lithium metal secondary battery, the volume change accompanying the precipitation and dissolution of lithium metal is large, which has also caused the cycle characteristics to deteriorate, but in this secondary battery, lithium is occluded and released. This is because the volumetric change is small because lithium metal is deposited also in the gaps between the particles of the negative electrode material. Thirdly, the larger the amount of lithium metal deposited / dissolved in a conventional lithium metal secondary battery, the greater the above problem. In this secondary battery, however, it depends on the negative electrode material capable of inserting and extracting lithium. Since insertion and extraction of lithium also contribute to the charge / discharge capacity, the amount of lithium metal deposited / dissolved is small although the battery capacity is large. Fourthly, in a conventional lithium metal secondary battery, if rapid charging is performed, lithium metal is deposited more unevenly, resulting in further deterioration in cycle characteristics. Lithium is occluded in the anode material that can be occluded and released, so that rapid charging becomes possible.

  In order to obtain these advantages more effectively, for example, the maximum deposition capacity of lithium metal deposited on the negative electrode 22 at the maximum voltage before the open circuit voltage becomes the overcharge voltage is to occlude and release lithium. It is preferable that it is 0.05 times or more and 3.0 times or less of the charge capacity capacity of the negative electrode material which can carry out. This is because when the amount of deposited lithium metal is too large, the same problem as that of the conventional lithium secondary battery occurs, and when the amount is too small, the charge / discharge capacity cannot be sufficiently increased. Further, for example, the discharge capacity capability of the negative electrode material capable of inserting and extracting lithium is preferably 150 mAh / g or more. This is because the amount of lithium metal deposited becomes relatively smaller as the ability to occlude and release lithium increases. The charge capacity capability of the negative electrode material can be obtained, for example, from the amount of electricity when a negative electrode using lithium metal as a counter electrode and the negative electrode material as a negative electrode active material is charged to 0 V by a constant current / constant voltage method. The discharge capacity capability of the negative electrode material is obtained, for example, from the amount of electricity when the current is discharged to 2.5 V over 10 hours or more by the constant current method.

  In this secondary battery, when charged, lithium ions are released from the positive electrode 21 and are first inserted into the negative electrode material capable of inserting and extracting lithium contained in the negative electrode 22 through the electrolyte. When charging is further continued, lithium metal begins to deposit on the surface of the negative electrode material capable of inserting and extracting lithium in a state where the open circuit voltage is lower than the overcharge voltage. After that, lithium metal continues to deposit on the negative electrode 22 until charging is completed. Next, when discharging is performed, first, lithium metal deposited on the negative electrode 22 is eluted as ions, and is inserted in the positive electrode 21 through the electrolyte. When the discharge is further continued, lithium ions occluded in the negative electrode material capable of inserting and extracting lithium in the negative electrode 22 are released and inserted into the positive electrode 21 through the electrolyte. Here, since the light metal salt represented by Chemical formula 6 is included, a stable film is formed on the surface of the negative electrode 22, and the decomposition reaction of the solvent in the negative electrode 22 is suppressed. Moreover, since the compound represented by Chemical formula 5 is included, the decomposition reaction of the electrolyte in the negative electrode 22 is suppressed. Therefore, the synergistic action of these improves lithium deposition / dissolution efficiency and efficiency of occluding and releasing lithium ions.

  Thus, in this embodiment, since the electrolyte contains the compound represented by Chemical Formula 5 and the light metal salt represented by Chemical Formula 6, the decomposition reaction of the electrolyte in the negative electrode 22 can be suppressed. Therefore, the efficiency in the negative electrode 22 is improved, and the cycle characteristics can be improved. Further, since the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium as an electrode reactant and a capacity component due to precipitation and dissolution of lithium, and is expressed by the sum thereof, a high energy density is obtained. Can be obtained.

  In particular, if a light metal salt other than the light metal salt represented by Chemical Formula 6 is also included, a higher effect can be obtained.

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

(Examples 1-1 to 1-11)
A battery was fabricated in which the capacity of the negative electrode 22 was represented by a capacity component due to insertion and extraction of lithium.

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 material was obtained. Next, 91 parts by mass of this lithium / cobalt composite oxide, 6 parts by mass of graphite as a conductive agent, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a positive electrode mixture slurry, which is uniformly applied to both surfaces of a positive electrode current collector 21A made of a strip-shaped aluminum foil having a thickness of 20 μm and dried. Then, the cathode active material layer 21B was formed by compression molding with a roll press machine, and the cathode 21 was produced. After that, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

  Further, an artificial graphite powder was prepared as a negative electrode material, and 90 parts by mass of the artificial graphite powder and 10 parts by mass of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture. Next, the 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 both surfaces of the negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 15 μm. The negative electrode 22 was produced by drying and compression molding with a roll press to form the negative electrode active material layer 22B. Subsequently, a negative electrode lead 26 made of nickel was attached to one end of the negative electrode current collector 22A. In Examples 1-1 to 1-11, the area density ratio between the positive electrode 21 and the negative electrode 22 was designed so that the capacity of the negative electrode 22 was represented by a capacity component due to insertion and extraction of lithium.

  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 by a reduced pressure method.

  In the electrolytic solution, lithium difluoro [oxolato-O, O ′] lithium borate represented by chemical formula 12 is used as an electrolyte salt in a solvent in which 21 vol% ethylene carbonate and 79 vol% compound represented by chemical formula 5 are mixed. What was dissolved so that it might become 1 mol / kg with respect to electrolyte solution was used. At that time, the type of the compound represented by Chemical Formula 5 used in Examples 1-1 to 1-11 was changed as shown in Table 1.

  After injecting the electrolyte into the battery can 11, the battery lid 14 was caulked to the battery can 11 through the gasket 17 having the surface coated with asphalt. A cylindrical secondary battery having a height of 65 mm was obtained.

As Comparative Examples 1-1 to 1-6 with respect to Examples 1-1 to 1-11, only LiPF ₆ was dissolved as an electrolyte salt in a solvent in which 21% by volume of ethylene carbonate and 79% by volume of the compound shown in Table 1 were mixed. A battery was fabricated in the same manner as in Examples 1-1 to 1-11 except that the electrolyte solution used was used.

  For the obtained secondary batteries of Examples 1-1 to 1-11 and Comparative Examples 1-1 to 1-6, constant-current charging was performed until the battery voltage reached 4.2 V at a constant current of 600 mA. A constant voltage charge was performed until the current reached 1 mA at a constant voltage of 4.2 V, and then a constant current discharge was performed until the battery voltage reached 3.0 V at a constant current of 400 mA, and the cycle characteristics were examined. As the cycle characteristics, the capacity retention rate at the 200th cycle (capacity at the 200th cycle / initial capacity) × 100 (%) with respect to the initial capacity (the capacity at the first cycle) was determined. The obtained results are shown in Table 1.

  As can be seen from Table 1, according to Examples 1-1 to 1-11 using the compound represented by Chemical formula 5 and the light metal salt represented by Chemical formula 12, the light metal salt represented by Chemical formula 12 was used. The cycle characteristics were improved as compared with Comparative Examples 1-5 and 1-6 in which the compound represented by Comparative Examples 1-1 to 1-4 or Chemical Formula 5 and the light metal salt represented by Chemical Formula 12 were not used.

  That is, if the electrolyte represented by the compound represented by Chemical Formula 5 and the light metal salt represented by Chemical Formula 12 are used, the capacity of the negative electrode 22 is used in a battery represented by a capacity component due to insertion and extraction of lithium. In addition, it was found that the cycle characteristics can be improved.

(Examples 2-1 and 2-2)
Except for using lithium tetrafluoro [oxolato-O, O ′] lithium phosphate represented by Chemical Formula 13 or difluorobis [oxolato-O, O ′] lithium phosphate represented by Chemical Formula 14 as the electrolyte salt, Otherwise, the batteries of Examples 2-1 and 2-2 were fabricated in the same manner as Example 1-11.

  For the obtained secondary batteries of Examples 2-1 and 2-2, the discharge capacity maintenance ratio at the 200th cycle was obtained in the same manner as in Example 1-11. The obtained results are shown in Table 2 together with the results of Example 1-11.

  As can be seen from Table 2, according to Examples 2-1 and 2-2, the same results as in Example 1-11 were obtained. That is, it was found that cycle characteristics can be improved even when a compound represented by Chemical Formula 5 and a light metal represented by Chemical Formula 6 having another composition are used.

(Example 3-1)
Except that lithium difluoro [oxolato-O, O ′] lithium borate represented by Chemical Formula 12 and LiPF ₆ as electrolyte salts are contained in the electrolyte solution at the contents shown in Table 3. Produced a secondary battery in the same manner as in Example 1-11.

  With respect to the obtained secondary battery of Example 3-1, the discharge capacity retention ratio at the 200th cycle was obtained in the same manner as in Example 1-11. The obtained results are shown in Table 3 together with the results of Example 1-11.

  As can be seen from Table 3, according to Example 3-1, the cycle characteristics were improved as compared with Example 1-11 using only the light metal salt represented by Chemical Formula 6. That is, it was found that a higher effect can be obtained if a light metal salt represented by Chemical Formula 6 and another light metal salt are included as the electrolyte salt.

(Example 4-1)
A battery in which the capacity of the negative electrode 22 is represented by a capacity component due to precipitation and dissolution of lithium was produced. At that time, a battery was manufactured in the same manner as in Example 3-1, except that the negative electrode 22 prepared by attaching lithium metal to the negative electrode current collector 22A made of a strip-shaped copper foil having a thickness of 15 μm was used. did.

Moreover, as Comparative Example 4-1 with respect to Example 4-1, an electrolyte solution in which only LiPF ₆ was dissolved as an electrolyte salt in a solvent in which 21% by volume of ethylene carbonate and 79% by volume of dimethyl carbonate were mixed was used. Except for the above, a battery was made in the same manner as in Example 4-1.

  For the obtained secondary batteries of Example 4-1 and Comparative Example 4-1, constant current charging and constant voltage discharging were performed under the same conditions as in Example 3-1, and the cycle characteristics were examined. As the cycle characteristics, the capacity retention ratio at the 100th cycle relative to the initial capacity (capacity at the 100th cycle / initial capacity) × 100 was determined. Table 4 shows the obtained results.

In addition, the batteries of Example 4-1 and Comparative Example 4-1 were charged and discharged for one cycle under the above-described conditions, and then completely charged again, and disassembled, and visually and by ⁷ Li nuclear magnetic resonance spectroscopy. Whether or not lithium metal and lithium ions are present in the negative electrode 22 was examined. Furthermore, two cycles of charge and discharge were performed under the above-described conditions, and the completely discharged one was disassembled, and similarly, it was examined whether or not lithium metal and lithium ions were present in the negative electrode 22.

As a result of ⁷ Li nuclear magnetic resonance spectroscopy, in both batteries of Example 4-1 and Comparative Example 4-1, a peak attributed to lithium metal was confirmed around 265 ppm in the fully charged state and the fully discharged state. On the other hand, a peak around 44 ppm attributed to lithium ions was not confirmed. These peak positions are values relative to external standard lithium chloride. Moreover, lithium metal was also confirmed visually. That is, it was confirmed that the capacity of the negative electrode 22 is represented by a capacity component due to precipitation and dissolution of lithium.

  As can be seen from Table 4, according to Example 4-1 using the compound represented by Chemical Formula 5 and the light metal salt represented by Chemical Formula 6, the cycle characteristics were higher than those of Comparative Example 4-1 not using these compounds. Improved.

  That is, if the electrolyte is a compound represented by Chemical Formula 5 and a light metal salt represented by Chemical Formula 6, when the negative electrode capacity is used in a battery represented by a capacity component due to lithium deposition and dissolution, It was also found that the cycle characteristics can be improved.

(Example 5-1)
A battery in which the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is represented by the sum thereof, was produced. At that time, the area density ratio between the positive electrode 21 and the negative electrode 22 is expressed by the sum of the capacity of the negative electrode 22 including the capacity component due to insertion and extraction of lithium and the capacity component due to precipitation and dissolution of lithium. A battery was fabricated in the same manner as in Example 3-1, except that it was designed as described above.

As Comparative Examples 5-1 and 5-2 with respect to Example 5-1, batteries were fabricated in the same manner as in Example 5-1, except that only LiPF ₆ or LiBF ₄ was used as the electrolyte salt. Furthermore, as Comparative Examples 5-3 and 5-4, an electrolytic solution in which only LiPF ₆ or LiBF ₄ was dissolved as an electrolyte salt in a solvent in which 21% by volume of ethylene carbonate and 79% by volume of dimethyl carbonate were mixed was used. A secondary battery was fabricated in the same manner as in Example 5-1, except for.

  For the obtained secondary batteries of Example 5-1 and Comparative Examples 5-1 to 5-4, constant current charging and constant voltage discharging were performed under the same conditions as in Example 3-1, and the cycle characteristics were examined. As the cycle characteristics, the capacity retention ratio at the 100th cycle relative to the initial capacity (capacity at the 100th cycle / initial capacity) × 100 was determined. The results obtained are shown in Table 5.

  Further, for the batteries of Example 5-1 and Comparative Examples 5-1 to 5-4, whether or not lithium metal and lithium ions were present in the negative electrode 22 was examined in the same manner as in Example 4-1.

As a result of ⁷ Li nuclear magnetic resonance spectroscopy, in the batteries of Example 5-1 and Comparative Examples 5-1 to 5-4, a peak attributed to lithium metal was confirmed around 265 ppm in the fully charged state, and around 44 ppm The peak attributed to lithium ion was confirmed. These peak positions are values relative to external standard lithium chloride. On the other hand, no peak attributed to lithium metal was observed in the fully discharged state. Moreover, the lithium metal was also confirmed by visual inspection only in the fully charged state. That is, it was confirmed that the capacity of the negative electrode 22 includes a capacity component due to insertion and extraction of lithium and a capacity component due to precipitation and dissolution of lithium, and is expressed by the sum thereof.

  As can be seen from Table 5, according to Example 5-1, the compounds represented by Chemical Formula 5 and Comparative Examples 5-1 and 5-2 not using the light metal salt represented by Chemical Formula 6 and The cycle characteristics were improved as compared with Comparative Examples 5-3 and 5-4 in which the light metal salt represented by Chemical Formula 6 was not used.

  That is, when the compound represented by Chemical Formula 5 and the light metal salt represented by Chemical Formula 6 are used in the electrolyte, the negative electrode capacity has a capacity component due to insertion and extraction of lithium, and a capacity component due to precipitation and dissolution of lithium. It was also found that the cycle characteristics can be improved even when used in a battery that is expressed by the sum thereof.

  In the above-described examples, the case where the compound represented by Chemical formula 5 and the light metal salt represented by Chemical formula 6 are used has been described with specific examples. It is thought that it originates in the structure of the light metal salt represented by Chemical formula 6. Therefore, similar results can be obtained using other compounds represented by Chemical Formula 5 and other light metal salts represented by Chemical Formula 6. Moreover, although the case where the electrolytic solution is used has been described in the above embodiment, the same result can be obtained even when a gel electrolyte is used.

  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 above embodiments and examples, the case where lithium is used as the electrode reactant has been described. However, other Group 1A elements such as sodium (Na) or potassium (K), or magnesium or calcium (Ca), etc. The present invention can also be applied to the case of using the 2A group element, other light metals such as aluminum, lithium, or alloys thereof, and the same effects can be obtained. At that time, a negative electrode material or a positive electrode material capable of occluding and releasing light metals is selected according to the electrode reactant.

  Moreover, in the said embodiment and Example, although the case where the gel electrolyte which is 1 type of electrolyte solution or solid electrolyte was used, you may make it use another electrolyte. Other electrolytes include, for example, a mixture of an ion conductive inorganic compound made of ion conductive ceramics, ion conductive glass or ionic crystal and an electrolyte, or an ion conductive inorganic compound and a gel electrolyte. Can be mentioned.

  Furthermore, in the above embodiments and examples, a cylindrical secondary battery having a winding structure has been described. However, the present invention can be applied to an elliptical or polygonal secondary battery having a winding structure, or a positive electrode. The present invention can be similarly applied to a secondary battery having a structure in which the negative electrode is folded or stacked. In addition, the present invention can also be applied to a so-called coin type, button type, or square type secondary battery. Moreover, not only a secondary battery but a primary battery is applicable.

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 comprising a compound represented by Chemical Formula 1 and a light metal salt represented by Chemical Formula 2.

(Wherein R31 represents a hydrogen group, a fluorine group, an alkyl group having 1 to 3 carbon atoms, or a group obtained by substituting at least a part of hydrogen with fluorine, X31 represents a hydrogen group or a fluorine group, and R32 represents Represents an alkyl group having 1 or 2 carbon atoms.)

(Wherein R11 represents a —C (═O) —R21—C (═O) — group (R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group) or —C (═O ) —C (═O) — group, R12 represents a halogen group, an alkyl group, a halogenated alkyl group, an aryl group or a halogenated aryl group, and X11 and X12 represent oxygen (O) or sulfur (S), respectively. M11 represents a transition metal element or a group 3B element, a group 4B element or a group 5B element in the short periodic table, and M21 represents a group 1A element, a group 2A element or aluminum (Al) in the short period periodic table. A is an integer of 1 to 4, b is an integer of 0 to 8, and c, d, e and f are each an integer of 1 to 3.) The electrolyte according to claim 1, wherein the light metal salt includes a compound represented by Chemical Formula 3.

(Wherein R11 represents a —C (═O) —R21—C (═O) — group (R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group) or —C (═O ) —C (═O) — group, R13 represents a halogen group, M12 represents phosphorus (P) or boron (B), M21 represents a group 1A element or a group 2A element or aluminum in the short-period periodic table A1 is an integer of 1 to 3, b1 is 0, 2 or 4, and c, d, e and f are each an integer of 1 to 3.) As the light metal salt, difluoro [oxolato-O, O ′] lithium borate represented by Chemical formula 4, tetrafluoro [oxolato-O, O ′] lithium phosphate represented by Chemical formula 5, or Chemical formula 6 2. The electrolyte according to claim 1, further comprising lithium difluorobis [oxolato-O, O ′] lithium phosphate.

  The electrolyte according to claim 1, further comprising a light metal salt other than the light metal salt. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The battery, wherein the electrolyte includes a compound represented by Chemical Formula 7 and a light metal salt represented by Chemical Formula 8.

(Wherein R31 represents a hydrogen group, a fluorine group, an alkyl group having 1 to 3 carbon atoms, or a group obtained by substituting at least a part of hydrogen with fluorine, X31 represents a hydrogen group or a fluorine group, and R32 represents Represents an alkyl group having 1 or 2 carbon atoms.)

(Wherein R11 represents a —C (═O) —R21—C (═O) — group (R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group) or —C (═O ) —C (═O) — group, R12 represents a halogen group, an alkyl group, a halogenated alkyl group, an aryl group or a halogenated aryl group, and X11 and X12 represent oxygen (O) or sulfur (S), respectively. M11 represents a transition metal element or a 3B group element, a 4B group element or a 5B group element in the short periodic table, M21 represents a 1A group element, a 2A group element or aluminum in the short periodic table, and a is (It is an integer of 1-4, b is an integer of 0-8, c, d, e, and f are integers of 1-3, respectively.) The battery according to claim 5, wherein the light metal salt includes a compound represented by Chemical Formula 9.

(Wherein R11 represents a —C (═O) —R21—C (═O) — group (R21 represents an alkylene group, a halogenated alkylene group, an arylene group or a halogenated arylene group) or —C (═O ) —C (═O) — group, R13 represents a halogen group, M12 represents phosphorus (P) or boron (B), M21 represents a group 1A element or a group 2A element or aluminum in the short-period periodic table A1 is an integer of 1 to 3, b1 is 0, 2 or 4, and c, d, e and f are each an integer of 1 to 3.) As the light metal salt, difluoro [oxolato-O, O ′] lithium borate represented by the chemical formula 10, tetrafluoro [oxolato-O, O ′] lithium phosphate represented by the chemical formula 11, or chemical formula 12 The battery according to claim 5, comprising lithium difluorobis [oxolato-O, O ′] lithium phosphate.

The battery according to claim 5, further comprising a light metal salt other than the light metal salt.

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