JP2005209377A - Battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery with high capacity capable of improving battery characteristics like a cycle property. <P>SOLUTION: A negative electrode activator layer 12B includes at least one kind out of a group including single body, an alloy, and a compound of silicon or tin which can form an alloy with Li. The negative electrode activator layer 12B is alloyed with a negative electrode current collector 12A manufactured by a vapor phase method, a liquid phase method. A separator 15 is impregnated with an electrolyte liquid containing an anion expressed by [PF<SB>a</SB>(CH<SB>b</SB>F<SB>c</SB>(CF<SB>3</SB>)<SB>d</SB>)<SB>e</SB>]<SP>-</SP>. In the formula, a=1, 2, 3, 4, or 5; b=0, or 1; c=0, 2, or 3; d=0, 1, 2, or 3; e=1, 2, 3, or 4; a+e=6; b+c+d=3; and b+c≠0. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a battery including an electrolyte together with a positive electrode and a negative electrode.

  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 battery using a lithium alloy as a negative electrode has been developed (see, for example, Patent Documents 1 and 2).
JP-A-6-325765 JP-A-7-230800

  However, when the charge and discharge are repeated, the lithium alloy has a problem of being pulverized and refined due to severe expansion and contraction. Therefore, when this is used for the negative electrode, the electron conductivity is reduced due to the fineness due to particle cracking or the reduction of the contact area between the particles in the negative electrode, or the decomposition reaction of the solvent is promoted due to the increase in the surface area, There was a problem that the cycle characteristics were not sufficient.

  The present invention has been made in view of such problems, and an object thereof is to provide a battery that has a high capacity and can improve battery characteristics such as cycle characteristics.

A first battery according to the present invention is a battery provided with an electrolyte together with a positive electrode and a negative electrode. The negative electrode is provided in the negative electrode current collector and the negative electrode current collector, and is at least one of the interfaces with the negative electrode current collector. And the negative electrode active material layer alloyed with the negative electrode current collector, and the electrolyte contains an anion represented by Chemical Formula 1.
(Chemical formula 1)
[PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻
(In the formula, a, b, c, d and e are numbers satisfying the following formulas respectively: a = 1, 2, 3, 4 or 5, b = 0 or 1, c = 0, 1, 2 or 3, d = 0, 1, 2 or 3, e = 1, 2, 3 or 4, a + e = 6, b + c + d = 3, and b + c ≠ 0)

A second battery according to the present invention is a battery including an electrolyte together with a positive electrode and a negative electrode. The negative electrode includes a negative electrode current collector, and a gas phase method, a liquid phase method, and a sintering method for the negative electrode current collector. A negative electrode active material layer formed by at least one method of the group, and a part of the negative electrode active material alloyed with the negative electrode current collector, wherein the electrolyte is represented by chemical formula 2 It contains an anion.
(Chemical formula 2)
[PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻
(In the formula, a, b, c, d and e are numbers satisfying the following formulas respectively: a = 1, 2, 3, 4 or 5, b = 0 or 1, c = 0, 1, 2 or 3, d = 0, 1, 2 or 3, e = 1, 2, 3 or 4, a + e = 6, b + c + d = 3, and b + c ≠ 0)

  According to the first or second battery of the present invention, the negative electrode has a negative electrode active material layer alloyed with the negative electrode current collector at least at a part of the interface with the negative electrode current collector, or the negative electrode Has a negative electrode active material layer formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method and a sintering method, so that a high capacity can be obtained and a fine powder of the negative electrode can be obtained. Can be suppressed. In addition, since the electrolyte contains the anion represented by Chemical Formula 1 or Chemical Formula 2, the stability of the electrolyte can be improved and the decomposition reaction of the electrolyte can be suppressed. Therefore, high capacity can be obtained and battery characteristics such as cycle characteristics can be improved.

  In particular, when the negative electrode active material layer contains one or more of a group consisting of silicon, tin, an alloy, and a compound, a higher capacity can be obtained.

  Further, if the surface roughness of the negative electrode current collector is set to an arithmetic average roughness of 0.1 μm or more, higher cycle characteristics can be obtained.

  Further, if the electrolyte contains other anions in addition to the anion represented by Chemical Formula 1 or Chemical Formula 2, or if the electrolyte contains a derivative of a carbonate ester having a halogen atom, a higher effect can be obtained. Can be obtained.

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

(First embodiment)
FIG. 1 shows the configuration of the secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called coin-type battery, in which a negative electrode 12 accommodated in an exterior cup 11 and a positive electrode 14 accommodated in an exterior can 13 are laminated via a separator 15 impregnated with an electrolytic solution. Has been. The peripheral portions of the outer cup 11 and the outer can 13 are sealed by caulking through an insulating gasket 16. The exterior cup 11 and the exterior can 13 are each comprised by metals, such as stainless steel or aluminum, for example.

  The negative electrode 12 includes, for example, a negative electrode current collector 12A and a negative electrode active material layer 12B provided on the negative electrode current collector 12A. The negative electrode active material layer 12B may be formed on both surfaces of the negative electrode current collector 12A, or may be formed on one surface.

  The anode current collector 12A is preferably made of a metal material containing at least one metal element that does not form an intermetallic compound with lithium. When lithium and an intermetallic compound are formed, they expand and contract with charge / discharge, structural breakdown occurs, current collection performance decreases, and the ability to support the negative electrode active material layer 12B decreases, so that the negative electrode active material layer 12B becomes a negative electrode. This is because it is easy to drop off from the current collector 12A. Note that in this specification, the metal material includes not only a single metal element but also an alloy composed of two or more metal elements or one or more metal elements and one or more metalloid elements. Examples of the metal element that does not form an intermetallic compound with lithium include copper (Cu), nickel (Ni), titanium (Ti), iron (Fe), and chromium (Cr).

  Among these, a metal element that is alloyed with the negative electrode active material layer 12B is preferable. As will be described later, when the negative electrode active material layer 12B includes at least one member selected from the group consisting of simple substances, alloys, and compounds such as silicon or tin alloyed with lithium, the negative electrode active material layer 12B accompanies charging / discharging. Is greatly expanded / contracted and easily falls off from the negative electrode current collector 12A. However, the negative electrode active material layer 12B and the negative electrode current collector 12A are alloyed and firmly bonded to each other, so that the dropout can be suppressed. It is. As a metal element that does not form an intermetallic compound with lithium and forms an alloy with the negative electrode active material layer 12B, for example, a metal element that forms an alloy with at least one of the group consisting of a simple substance, an alloy, and a compound such as silicon or tin. Examples include copper, nickel, and iron. In particular, copper, nickel, or iron is preferable from the viewpoint of alloying with the negative electrode active material layer 12B, strength, and conductivity.

  The negative electrode current collector 12A may be composed of a single layer, but may be composed of a plurality of layers. In that case, the layer in contact with the negative electrode active material layer 12B is made of a metal material that forms an alloy with at least one of the group consisting of a simple substance such as silicon or tin, an alloy, and a compound, and the other layer is made of another metal material. You may make it comprise. The negative electrode current collector 12A is preferably composed of a metal material made of at least one metal element that does not form an intermetallic compound with lithium, except for the interface with the negative electrode active material layer 12B.

  The surface roughness of the negative electrode current collector 12A is preferably 0.1 μm or more in terms of arithmetic average roughness Ra. Thus, as described later, when the negative electrode active material layer 12B is formed by a vapor phase method, a liquid phase method, a sintering method, or a combination thereof, or alloyed at least at a part of the interface with the negative electrode active material layer 12B. In this case, the shape of cracks generated by the expansion and contraction of the negative electrode active material layer 22 during charge / discharge can be controlled, and the stress can be dispersed to suppress the structural breakdown of the negative electrode 22. It is.

  The negative electrode active material layer 12B includes, for example, a group consisting of simple elements, alloys and compounds of metal elements capable of forming an alloy with lithium, and simple elements, alloys and compounds of metalloid elements capable of forming an alloy with lithium as the negative electrode active material. Of at least one of them. Thereby, the capacity | capacitance of the negative electrode 12 contains the capacity | capacitance component by this negative electrode active material inserting and extracting lithium, and can obtain a high energy density. Among these, the negative electrode active material preferably contains at least one member selected from the group consisting of a simple substance, an alloy, and a compound of silicon or tin. This is because a higher energy density can be obtained.

Examples of silicon alloys or compounds include SiB ₄ , SiB ₆ , Mg ₂ Si, 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) or LiSiO. Examples of tin compounds or alloys include alloys of tin and elements included in groups 4 to 11 of the long-period periodic table. In addition, Mg ₂ Sn, SnO _w (0 <w ≦ 2), SnSiO _3, or LiSnO can be used.

  The negative electrode active material layer 12B is preferably formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method. The negative electrode active material layer 12B can be prevented from being destroyed due to expansion / contraction due to charging / discharging, and the negative electrode current collector 12A and the negative electrode active material layer 12B can be integrated, and electrons in the negative electrode active material layer 12B can be integrated. This is because the conductivity can be improved. Moreover, it is because a binder, a space | gap, etc. can be reduced or eliminated and the negative electrode 12 can also be thinned. As used herein, “forming an active material layer by a sintering method” means that a layer formed by mixing a powder containing an active material and a binder is heat-treated in a non-oxidizing atmosphere or the like, This means that a denser layer having a higher volume density than before the heat treatment is formed.

  The negative electrode active material layer 12B is preferably alloyed with the negative electrode current collector 12A at least at a part of the interface with the negative electrode current collector 12A so that the negative electrode active material layer 12B does not fall off from the negative electrode current collector 12A due to expansion and contraction. . Specifically, the constituent elements of the negative electrode current collector 12A are diffused into the negative electrode active material layer 12B, the constituent elements of the negative electrode active material layer 12B are diffused into the negative electrode current collector 12A, or they are mutually diffused at the interface. preferable. This alloying often occurs at the same time when the anode active material layer 12B is formed by a vapor phase method, a liquid phase method or a sintering method, but is caused by further heat treatment or during initial charging. But you can. Note that in this specification, the above-described element diffusion is also included in one form of alloying.

  The positive electrode 14 includes, for example, a positive electrode current collector 14A and a positive electrode active material layer 14B provided on the positive electrode current collector 14A so that the positive electrode active material layer 14B side faces the negative electrode active material layer 12B. Is arranged. The positive electrode current collector 14A is made of, for example, aluminum, nickel, stainless steel, or the like.

The positive electrode active material layer 14B includes, for example, any one or two or more positive electrode materials capable of inserting and extracting lithium as a positive electrode active material, and a conductive material such as a carbon material and the like as necessary. A binder such as polyvinylidene fluoride may be included. As the positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing metal composite oxide represented by the general formula Li _x MIO ₂ is preferable. This is because the lithium-containing metal composite oxide can generate a high voltage and has a high density, so that the capacity of the secondary battery can be further increased. MI is one or more kinds of transition metals, and for example, at least one of cobalt and nickel is preferable. x varies depending on the charge / discharge state of the battery and is usually a value in the range of 0.05 ≦ x ≦ 1.10. Specific examples of such a lithium-containing metal composite oxide include LiCoO _{2 and} LiNiO ₂ .

  The separator 15 separates the negative electrode 12 and the positive electrode 14 and allows lithium ions to pass through while preventing a short circuit of current due to contact between both electrodes. The separator 15 is made of, for example, polyethylene or polypropylene.

  The electrolyte solution impregnated in the separator 15, that is, the liquid electrolyte contains, for example, a solvent and an electrolyte salt dissolved in the solvent, and may contain an additive as necessary. The solvent is preferably a non-aqueous solvent, and examples thereof include organic solvents represented by carbonate esters such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Any one of the solvents may be used alone, or two or more of them may be mixed and used. For example, if a high dielectric constant solvent such as ethylene carbonate or propylene carbonate is mixed with a low boiling point solvent such as dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate, high ionic conductivity can be obtained. preferable. In particular, the high dielectric constant solvent preferably contains ethylene carbonate.

  Examples of the solvent or additive include a cyclic carbonate having an unsaturated bond or a derivative of a carbonate having a halogen atom, and preferably contains at least one of these. It is because higher cycle characteristics can be obtained by containing these. Examples of the cyclic carbonate having an unsaturated bond include vinylene carbonate and vinyl ethylene carbonate. Examples of the derivative of a carbonic acid ester having a halogen atom include monofluoroethylene carbonate, monochloroethylene carbonate, monobromoethylene carbonate, difluorodiethylene carbonate, and the like.

As the electrolyte salt, one or more of light metal salts having a structure represented by Chemical Formula 3 are included. This light metal salt is at least partially ionized in the electrolytic solution, that is, the electrolytic solution contains an anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ . Thereby, the stability of the electrolytic solution is increased, and the decomposition reaction is suppressed. Specifically, for example, [PF ₃ (C ₂ F ₅ ) ₃ ] ⁻ , [PF ₄ (C ₂ F ₅ ) ₂ ] ⁻ or [PF ₃ (C ₄ F ₉₎ ) _3] ^- there is. The light metal salt is preferably a lithium salt, but is not necessarily a lithium salt, and other light metal salts such as a sodium salt, potassium salt, magnesium salt, calcium salt, or aluminum salt may be used. This is because lithium that contributes to the charge / discharge reaction may be supplied from the positive electrode 14.

(Chemical formula 3)
_{- [PF a (CH b F} c (CF 3) d) e]
(In the formula, a, b, c, d and e are numbers satisfying the following formulas respectively: a = 1, 2, 3, 4 or 5, b = 0 or 1, c = 0, 1, 2 or 3, d = 0, 1, 2 or 3, e = 1, 2, 3 or 4, a + e = 6, b + c + d = 3, and b + c ≠ 0)

The content of the anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ is preferably 0.01 mol / kg or more and 2.0 mol / kg or less with respect to the solvent. It is the sky which can obtain a higher effect within this range.

In addition to the light metal salt having the structure represented by Chemical Formula 3, it is preferable that the electrolyte salt includes other light metal salts. That is, the electrolyte preferably contains another anion in addition to the anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ . This is because a higher effect can be obtained. Examples of other anions include PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , an anion represented by Chemical Formula 4, or an anion represented by Chemical Formula 5. Other anions may be included alone or in combination of two or more, but it is preferable to include PF ₆ ⁻ because higher effects can be obtained.

(Chemical formula 4)
_{N (C m F 2m + 1} SO 2) (C n F 2n + 1 SO 2) -
(In the formula, m and n are integers of 1 or more.)

(Chemical formula 5)
C (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ) (C _r F _{2r + 1} SO ₂ ) ⁻
(In the formula, p, q and r are integers of 1 or more.)

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

  First, for example, a negative electrode current collector 12A made of a metal foil is prepared, and a negative electrode active material layer 12B is formed on the negative electrode current collector 12A by depositing a negative electrode active material by a vapor phase method or a liquid phase method. . Further, after forming a precursor layer containing a particulate negative electrode active material on the current collector 12A, the negative electrode active material layer 12B may be formed by a sintering method in which the current layer is sintered. The negative electrode active material layer 12B may be formed by combining two or three of the phase method and the sintering method. Thus, by using at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method, in some cases, at least part of the interface with the negative electrode current collector 12A, the negative electrode current collector A negative electrode active material layer 12B alloyed with 12A is formed. In order to further alloy the interface between the negative electrode current collector 12A and the negative electrode active material layer 12B, heat treatment may be further performed in a vacuum atmosphere or a non-oxidizing atmosphere. In particular, when the negative electrode active material layer 12B is formed by plating, it may be difficult to form an alloy. Therefore, it is preferable to perform this heat treatment as necessary. In addition, even in the case of forming a film by a vapor phase method, characteristics may be improved by further alloying the interface between the negative electrode current collector 12A and the negative electrode active material layer 12B. It is preferable to perform this heat treatment.

  Examples of the vapor phase method include a physical deposition method and a chemical deposition method. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a CVD (Chemical Vapor Deposition; Phase growth) method. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. As for the sintering method, a known method can be used, for example, an atmosphere sintering method, a reaction sintering method, or a hot press sintering method can be used.

  Next, the positive electrode 14 is prepared, for example, by mixing a positive electrode active material, a conductive material, and a binder to prepare a mixture, and this is dispersed in a dispersion medium such as N-methylpyrrolidone to form a positive electrode current collector 14A as a mixture slurry. The positive electrode active material layer 14 </ b> B is formed by applying and compression molding.

  Subsequently, for example, the negative electrode 12, the separator 15 impregnated with the electrolytic solution, and the positive electrode 14 are stacked, put into the outer cup 11 and the outer can 13, and caulked. Thereby, the secondary battery shown in FIG. 1 is obtained.

  In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 14 and inserted in the negative electrode 12 through the electrolytic solution. When the discharge is performed, for example, lithium ions are released from the negative electrode 12 and inserted in the positive electrode 14 through the electrolytic solution. At that time, since the anion represented by Chemical formula 4 is contained in the electrolytic solution, the stability of the electrolytic solution is high, and the decomposition reaction of the electrolytic solution is suppressed. Therefore, excellent charge / discharge cycle characteristics can be obtained.

Thus, in the present embodiment, the negative electrode active material layer 12B alloyed with the negative electrode current collector 12A, or at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method is used. In addition, since the negative electrode active material layer 12B is provided, a high capacity can be obtained and pulverization of the negative electrode can be suppressed. In addition, since the electrolyte contains an anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ , the stability of the electrolyte can be improved and the decomposition reaction of the electrolyte can be improved. Can be suppressed. Therefore, high capacity can be obtained and battery characteristics such as cycle characteristics can be improved.

  In particular, if the negative electrode active material layer 12B includes one kind of the group consisting of a simple substance, an alloy and a compound of silicon or tin, a higher capacity can be obtained.

  Further, if the surface roughness of the negative electrode current collector 12A is set to 0.1 μm or more in terms of arithmetic average roughness Ra, higher cycle characteristics can be obtained.

Further, if the electrolyte contains other anions in addition to the anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ , or the carbonate has a halogen atom. If the derivative is included, a higher effect can be obtained.

(Second Embodiment)
FIG. 2 shows the configuration of the secondary battery according to the second embodiment of the present invention. In this secondary battery, the wound electrode body 30 to which the leads 21 and 22 are attached is housed inside the film-like exterior members 40A and 40B, and can be reduced in size, weight, and thickness. Yes.

  The leads 21 and 22 are led out, for example, in the same direction from the inside of the exterior members 40A and 40B to the outside. The lead 21 and the lead 22 are each made of a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior members 40A and 40B are made of, for example, a rectangular aluminum laminate film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior members 40A and 40B are disposed, for example, so that the polyethylene film side and the electrode winding body 30 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesion film 41 for preventing the entry of outside air is inserted between the exterior members 40A and 40B and the leads 21 and 22. The adhesion film 41 is made of a material having adhesion to the leads 21 and 22, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior members 40A and 40B may be made of a laminate film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminate film.

  FIG. 3 shows a cross-sectional structure taken along line II of the electrode winding body 30 shown in FIG. The electrode winding body 30 is obtained by stacking and winding a negative electrode 31 and a positive electrode 32 via a separator 33 and an electrolyte layer 34, and the outermost peripheral portion is protected by a protective tape 35.

  The negative electrode 31 has a structure in which a negative electrode active material layer 31B is provided on one surface or both surfaces of a negative electrode current collector 31A. The positive electrode 32 also has a structure in which a positive electrode active material layer 32B is provided on one surface or both surfaces of the positive electrode current collector 32A, and the positive electrode active material layer 32B side is disposed so as to face the negative electrode active material layer 31B. Yes. The specific configurations of the negative electrode current collector 31A, the negative electrode active material layer 31B, the positive electrode current collector 32A, the positive electrode active material layer 32B, and the separator 33 are the same as those of the negative electrode current collector 12A, the negative electrode active material layer in the first embodiment. 12B, the same as the positive electrode current collector 14A, the positive electrode active material layer 14B, and the separator 15.

  The electrolyte layer 34 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 can prevent battery leakage or swelling at high temperatures. The configuration of the electrolytic solution (that is, the solvent and the electrolyte salt) is the same as that in the first embodiment. The holding body is made of, for example, a polymer material. Examples of the polymer material include polyacrylonitrile, polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, or polyethylene oxide.

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

  First, on each of the negative electrode 31 and the positive electrode 32, an electrolyte layer 123 in which an electrolytic solution is held in a holding body is formed. After that, the lead 21 is attached to the end of the negative electrode current collector 31A by welding, and the lead 22 is attached to the end of the positive electrode current collector 32A by welding. Next, the negative electrode 31 and the positive electrode 32 on which the electrolyte layer 34 is formed are laminated via a separator 33 to form a laminated body, and then the laminated body is wound in the longitudinal direction to attach the protective tape 35 to the outermost peripheral portion. Thus, the electrode winding body 30 is formed. Finally, for example, the electrode winding body 30 is sandwiched between the exterior members 40A and 40B, and the outer edges of the exterior members 40A and 40B are sealed and sealed by thermal fusion or the like. At that time, the adhesive film 41 is inserted between the leads 21 and 22 and the exterior members 40A and 40B. Thereby, the secondary battery shown in FIGS. 2 and 3 is completed.

  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 with reference to the drawings.

(Examples 1-1 to 1-11)
The coin-type secondary battery shown in FIG. 1 was produced. First, an electrolytic copper foil having an arithmetic average roughness Ra of 0.5 μm and a thickness of 35 μm is prepared as a negative electrode current collector 12A, and this negative electrode current collector 12A has a thickness of 4 μm made of silicon as a negative electrode active material by a vapor deposition method. After forming the negative electrode active material layer 12B, heat treatment was performed to form the negative electrode 12. When the obtained negative electrode 12 was analyzed by XPS (X-ray Photoelectron Spectroscopy) and AES (Auger Electron Spectroscopy), the negative electrode active material layer 12B and the negative electrode current collector 12A It was confirmed that at least a part of the interface was alloyed with the negative electrode current collector 12A.

Next, a lithium-cobalt (LiCoO ₂ ) composite oxide powder having an average particle diameter of 5 μm as a positive electrode active material, carbon black as a conductive agent, and polyvinylidene fluoride as a binder are combined with lithium-cobalt composite oxide. The mixture was prepared by mixing at a mass ratio of product: carbon black: polyvinylidene fluoride = 92: 3: 5. Next, the mixture is dispersed in N-methyl-2-pyrrolidone as a dispersion medium to form a mixture slurry, which is applied to a positive electrode current collector 14A made of an aluminum foil having a thickness of 20 μm, dried, and pressurized to form a positive electrode. The active material layer 14B was formed, and the positive electrode 14 was produced.

Subsequently, a negative electrode 12 and a separator 15 made of polypropylene having a thickness of 25 μm are sequentially laminated at the center of the outer cup 11, and after injecting an electrolyte, the outer can 13 containing the positive electrode 14 is covered and caulked through the gasket 16. A coin-type secondary battery having a diameter of 20 mm and a height of 1.6 mm was produced. In the electrolyte, a solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 1 is mixed with Li [PF ₃ (C ₂ F ₅ ) ₃ ] or Li [PF ₃ (C ₂ F) as an electrolyte salt. _{5) 3]} and was used by dissolving and LiPF _6. At that time, the content of the electrolyte salt was changed as shown in Table 1 in Examples 1-1 to 1-11 with respect to the solvent.

In addition, as Comparative Examples 1-1 to 1-6 with respect to Examples 1-1 to 1-11, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ or LiC (CF ₃ SO ₂ ) ₃ was used, and the secondary battery was prepared in the same manner as in Examples 1-1 to 1-11 except that the content was 1.0 mol / kg with respect to the solvent. Produced.

Further, as Comparative Examples 1-7 and 1-8 for Examples 1-1 to 1-11, Example 1-1 or Comparative Example 1 was otherwise used except that a negative electrode was produced using graphite as the negative electrode active material. A secondary battery was produced in the same manner as in Example-1. For the negative electrode, 90 parts by weight of graphite powder and 10 parts by weight of polyvinylidene fluoride as a binder were mixed and dispersed in N-methyl-2-pyrrolidone as a dispersion medium, and then this was a copper foil having a thickness of 10 μm. It was produced by applying to a negative electrode current collector comprising the above, drying, and applying pressure to form a negative electrode active material layer. As the electrolyte salt, Li [PF ₃ (C ₂ F ₅ ) ₃ ] was used in Comparative Example 1-7, and LiPF ₆ was used in Comparative Example 1-8. The content of the electrolyte salt was 1.0 mol / kg with respect to the solvent.

For the fabricated secondary batteries of Examples 1-1 to 1-11 and Comparative examples 1-1 to 1-8, a charge / discharge test was performed to examine the initial capacity and the cycle characteristics. Charging is performed at a constant current density of 1 mA / cm ² until the battery voltage reaches 4.2 V, and then at a constant voltage of 4.2 V until the current density reaches 0.02 mA / cm ² , and discharging is performed at 1 mA. This was performed until the battery voltage reached 2.5 V at a constant current density of / cm ² . When charging / discharging, based on the charge / discharge capacities of the positive electrode 14 and the negative electrode 12 obtained in advance, the negative electrode utilization rate in the first charge is set to 90%, and metallic lithium is deposited on the negative electrode 12. I tried not to. As the cycle characteristics, the capacity retention ratio at the 20th cycle relative to the initial capacity (capacity at the 20th cycle / initial capacity) × 100 was determined. The obtained results are shown in Table 1.

As shown in Table 1, according to Examples 1-1 to 1-11 using Li [PF ₃ (C ₂ F ₅ ) ₃ ] as an electrolyte salt, the capacity was higher than that of Comparative Example 1-6 which was not used. The maintenance rate could be improved, and in some cases the initial capacity could be improved. On the other hand, in Comparative Examples 1-7 and 1-8 using graphite as the negative electrode, Comparative Example 1-7 using Li [PF ₃ (C ₂ F ₅ ) ₃ ] as the electrolyte salt is not used. Although the characteristics were slightly improved as compared with Example 1-8, the degree was smaller than those of Examples 1-1 to 1-11.

That is, when the negative electrode active material layer 12B is formed by a vapor phase method or the like, or when the negative electrode active material layer 12B is alloyed with the negative electrode current collector 12A, [PF _a (CH _b F _c (CF ₃ It was found that the cycle characteristics can be effectively improved by including an anion represented by _d ) _e ] ^- ).

As can be seen from a comparison between Example 1-1 and Examples 1-2 to 1-11, it is better to use a mixture of Li [PF ₃ (C ₂ F ₅ ) ₃ ] and LiPF _6. Depending on the content, the initial capacity and capacity retention rate could be further improved. That is, if the electrolyte contains other anions in addition to the anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ , cycle characteristics can be further improved. I understood.

Furthermore, as can be seen from Examples 1-1 to 1-11, the content of Li [PF ₃ (C ₂ F ₅ ) ₃ ] should be 0.01 mol / kg or more and 2.0 mol / kg or less with respect to the solvent. It was confirmed that the cycle characteristics could be improved. That is, the content of the anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ is preferably in the range of 0.01 mol / kg to 2.0 mol / kg with respect to the solvent. I also understood that.

(Examples 1-12 to 1-21)
Other light metal salt, in place of LiPF _6, or in addition to LiPF _6, as shown in Table _{2 LiBF 4, LiClO 4, LiAsF} 6, LiN (CF 3 SO 2) 2 or LiC (CF ₃ SO ₂ ) A secondary battery was fabricated in the same manner as in Example 1-3 except that ₃ . At that time, the content of Li [PF ₃ (C ₂ F ₅ ) ₃ ] is 0.8 mol / kg with respect to the solvent, and the content of other light metal salts is 0.2 mol with respect to the solvent in the case of one kind. In the case of 2 types / kg, the amount was 1 mol / kg with respect to the solvent.

  For Examples 1-12 to 1-21, a charge / discharge test was performed in the same manner as in Example 1-3, and the initial capacity and cycle characteristics were examined. The results are shown in Table 2 together with the results of Example 1-3 and Comparative Examples 1-1 to 1-6.

As shown in Table 2, even when used together with other light metal salts other than LiPF ₆ , if Li [PF ₃ (C ₂ F ₅ ) ₃ ] is included, the capacity retention rate can be improved. did it. Also in that case, the capacity retention rate could be further improved by further including LiPF ₆ . That is, if the electrolyte contains PF ₆ ⁻ as another anion in addition to the anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ , the cycle characteristics are further improved. I found out that I could do it.

(Examples 1-22 to 1-25)
As an electrolyte salt, instead of Li [PF ₃ (C ₂ F ₅ ) ₃ ], as shown in Table 3 or Table 4, Li [PF ₄ (C ₂ F ₅ ) ₂ ] or Li [PF ₄ ( Other than using C ₂ F ₅ ) ₂ ] and LiPF ₆ , or Li [PF ₃ (C ₄ F ₉ ) ₃ ], or Li [PF ₃ (C ₄ F ₉ ) ₃ ] and LiPF ₆ A secondary battery was fabricated in the same manner as in Example 1-1 or Example 1-3. At that time, the content of the electrolyte salt was changed as shown in Table 3 or Table 4 with respect to the solvent.

  For Examples 1-22 to 1-25, charge and discharge tests were conducted in the same manner as in Examples 1-1 and 1-3, and the initial capacity and cycle characteristics were examined. The results are shown in Table 3 or Table 4 together with the results of Comparative Examples 1-1 to 1-6.

As shown in Table 3 or Table 4, according to Examples 1-22 to 1-25, the capacity was maintained more than Comparative Examples 1-1 to 1-6, as in Examples 1-1 and 1-3. The rate could be improved. Further, Examples 1-23 and 1-25 used together with LiPF ₆ were able to further improve the capacity retention rate compared to Examples 1-22 and 1-24 used alone. That is, it was found that even if the electrolyte contains another anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ , the cycle characteristics can be effectively improved.

(Example 1-26)
A secondary battery was fabricated in the same manner as in Example 1-1 except that fluoroethylene carbonate (4-fluoro-1,3-dioxolan-2-one) was used instead of the solvent ethylene carbonate. For Example 1-26, a charge / discharge test was conducted in the same manner as in Example 1-1, and the initial capacity and cycle characteristics were examined. The results are shown in Table 5 together with the results of Example 1-1.

  As shown in Table 5, Example 1-26 using fluoroethylene carbonate was able to further improve the capacity retention rate than Example 1-1 not using it. That is, it was found that a higher effect can be obtained if a carbonic acid ester derivative having a halogen atom such as fluoroethylene carbonate is contained in the electrolyte.

(Examples 2-1 to 2-11)
Tin is used as the negative electrode active material, and a negative electrode active material layer 12B having a thickness of 4 μm made of tin is formed by electrolytic plating on a negative electrode current collector 12A made of an electrolytic copper foil having an arithmetic average roughness Ra of 0.5 μm and a thickness of 25 μm. After that, the coin-type secondary battery shown in FIG. 1 was produced in the same manner as in Examples 1-1 to 1-25 except that the negative electrode 12 was produced by heat treatment. At that time, the type and content of the electrolyte salt were changed as shown in Tables 6 and 7.

Of these, Example 2-1 uses Li [PF ₃ (C ₂ F ₅ ) ₃ ] as an electrolyte salt, and Examples 2-2 to 2-7 show Li [PF ₃ (C ₂ F ₅ ) A mixture of ₃ ] and other light metal salts. In Example 2-8, Li [PF ₄ (C ₂ F ₅ ) ₂ ] was used as the electrolyte salt. In Example 2-9, Li [PF ₄ (C ₂ F ₅ ) ₂ ] and others were used. It was used by mixing with a light metal salt. In Example 2-10, Li [PF ₃ (C ₄ F ₉ ) ₃ ] was used as the electrolyte salt. In Example 2-11, Li [PF ₃ (C ₄ F ₉ ) ₃ ] and others were used. It was used by mixing with a light metal salt.

  In Examples 2-1 to 2-11 as well, when the obtained negative electrode 12 was analyzed by XPS and AES, the negative electrode active material layer 12B was found to be at least part of the interface with the negative electrode current collector 12A. It was confirmed that it was alloyed with the electric body 12A.

Further, as Comparative Examples 2-1 to 2-6 with respect to Examples 2-1 to 2-11, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ or LiC (CF ₃ SO ₂ ) ₃ is used, and the secondary battery is manufactured in the same manner as in Examples 2-1 to 2-11 except that the content is 1.0 mol / kg with respect to the solvent. Produced.

  For the fabricated secondary batteries of Examples 2-1 to 2-11 and Comparative Examples 2-1 to 2-6, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-26. The capacity retention rate at the 20th cycle was examined. The obtained results are shown in Tables 6 and 7.

As shown in Tables 6 and 7, Li [PF ₃ (C ₂ F ₅ ) ₃ ], Li [PF ₄ (C ₂ F ₅ ) ₂ ] or Li [PF ₃ (C ₄ F ₉ ) _{3 is used} as the electrolyte salt. According to Examples 2-1 to 2-11 using the above, the capacity retention rate can be improved as compared with comparative examples 2-1 to 2-6 which are not used, and in some cases, the initial capacity can also be improved. I was able to. In addition, Examples 2-2, 2-9, and 2-11 using a mixture of these light metal salts and LiPF ₆ were able to obtain higher effects.

That is, not only when silicon is used as the negative electrode active material but also when tin is used, or when the negative electrode active material layer 12B is formed not only by the vapor phase method but also by the liquid phase method, [PF _a It was found that if the anion represented by (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ is included, the cycle characteristics can be effectively improved.

In the above embodiment, the anion represented by [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻ has been described with some specific examples, but [PF _a (CH _b Similar results can be obtained by including other anions represented by F _c (CF ₃ ) _d ) _e ] ⁻ . Similar results can be obtained even when other negative electrode active materials are used, the negative electrode active material layer is formed by a sintering method, or a gel electrolyte is used instead of the electrolytic solution.

  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, a secondary battery using a gel electrolyte, which is one of an electrolytic solution or a solid electrolyte, has been described. However, the present invention provides a secondary battery using another electrolyte. The same applies to batteries. Other electrolytes include, for example, an ion conductive inorganic compound composed of a polymer solid electrolyte in which an electrolyte salt is dispersed in a polymer compound having ion conductivity, ion conductive ceramics, ion conductive glass, or ionic crystals. The thing which mixed electrolyte solution, or the thing which mixed these ion conductive inorganic compounds, gel electrolyte, or polymer solid electrolyte is mentioned.

  In the above embodiments and examples, a coin-type or wound laminate-type secondary battery has been described. The present invention can be similarly applied to a secondary battery having a folded or stacked structure. Moreover, not only a secondary battery but a primary battery is applicable.

  Further, in the above embodiments and examples, the case where lithium is used as the electrode reactive species has been described. However, other alkali metals such as sodium (Na) or potassium (K), or alkalis such as magnesium or calcium (Ca) are used. The present invention can also be applied to the case where an earth metal or other light metal such as aluminum is used, and the same effect can be obtained. In this case, the negative electrode active material includes a simple substance, an alloy and a compound of a metal element capable of forming an alloy with the light metal, and a simple metal alloy, an alloy and a compound of a metalloid element capable of forming an alloy with the light metal. At least one kind is used. For example, at least one kind selected from the group consisting of the above-described simple substance, alloy, and compound of silicon or tin can be used. As the positive electrode active material, a positive electrode material capable of inserting and extracting the light metal is used.

It is sectional drawing showing the structure of the secondary battery which concerns on the 1st Embodiment of this invention. It is a disassembled perspective view showing the structure of the secondary battery which concerns on the 2nd Embodiment of this invention. It is sectional drawing showing the structure along the II line | wire of the electrode winding body shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Exterior cup, 12, 31 ... Negative electrode, 12A, 31A ... Negative electrode collector, 12B, 31B ... Negative electrode active material layer, 13 ... Outer can, 14, 32 ... Positive electrode, 14A, 32A ... Positive electrode collector, 14B , 32B ... positive electrode active material layer, 15, 33 ... separator, 16 ... gasket, 21, 22 ... lead, 30 ... electrode winding body, 34 ... electrolyte layer, 35 ... protective tape

Claims (12)

A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode has a negative electrode current collector, and a negative electrode active material layer provided on the negative electrode current collector and alloyed with the negative electrode current collector at least at a part of the interface with the negative electrode current collector,
The battery, wherein the electrolyte includes an anion represented by Chemical Formula 1.
(Chemical formula 1)
[PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻
(In the formula, a, b, c, d and e are numbers satisfying the following formulas respectively: a = 1, 2, 3, 4 or 5, b = 0 or 1, c = 0, 1, 2 or 3, d = 0, 1, 2 or 3, e = 1, 2, 3 or 4, a + e = 6, b + c + d = 3, and b + c ≠ 0) A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode has a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector by at least one method selected from the group consisting of a gas phase method, a liquid phase method, and a sintering method,
The battery includes an anion represented by Chemical Formula 2:
(Chemical formula 2)
[PF _a (CH _b F _c (CF ₃ ) _d ) _e ] ⁻
(In the formula, a, b, c, d and e are numbers satisfying the following formulas respectively: a = 1, 2, 3, 4 or 5, b = 0 or 1, c = 0, 1, 2 or 3, d = 0, 1, 2 or 3, e = 1, 2, 3 or 4, a + e = 6, b + c + d = 3, and b + c ≠ 0)   The battery according to claim 2, wherein the negative electrode active material layer is alloyed with the negative electrode current collector at least at a part of the interface with the negative electrode current collector.   3. The battery according to claim 2, wherein the negative electrode active material layer includes at least one selected from the group consisting of a simple substance, an alloy, and a compound of silicon (Si) or tin (Sn).   The battery according to claim 2, wherein the surface roughness of the negative electrode current collector is an arithmetic average roughness of 0.1 μm or more.   The electrolyte further contains a solvent, and the content of the anion represented by Chemical Formula 2 is 0.01 mol / kg or more and 2.0 mol / kg or less with respect to the solvent. Battery.   The battery according to claim 2, wherein the electrolyte further contains an anion other than the anion represented by Chemical Formula 2. The electrolyte further includes at least one member selected from the group consisting of PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , an anion represented by Chemical Formula 3, and an anion represented by Chemical Formula 4. The battery according to claim 2.
(Chemical formula 3)
_{N (C m F 2m + 1} SO 2) (C n F 2n + 1 SO 2) -
(In the formula, m and n are integers of 1 or more.)
(Chemical formula 4)
C (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ) (C _r F _{2r + 1} SO ₂ ) ⁻
(In the formula, p, q and r are integers of 1 or more.)   The battery according to claim 2, wherein the electrolyte includes ethylene carbonate.   The battery according to claim 2, wherein the electrolyte contains a derivative of a carbonic ester having a halogen atom.   The battery according to claim 2, wherein the electrolyte includes a polymer compound. The electrolyte has [PF ₃ (C ₂ F ₅ ) ₃ ] ⁻ , [PF ₄ (C ₂ F ₅ ) ₂ ] ⁻ and [PF ₃ (C ₄ F ₉ ) ₃ as anions represented by the chemical formula ₂ . ^- battery according to claim 2, characterized in that it comprises at least one selected from the group consisting of.

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