JP2011129352A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for suppressing degradation of battery capacity while suppressing an increase in viscosity of electrolyte in a nonaqueous electrolyte secondary battery that uses a carbon-based negative electrode. <P>SOLUTION: The nonaqueous electrolyte secondary battery includes a positive electrode where a positive electrode active material layer is formed on the surface of a collector, a negative electrode where a negative electrode active material layer containing a negative electrode active material of carbon material is formed on the surface of collector, and an electrolyte layer. The electrolyte layer includes an ion liquid containing a cation component and an anion component, and an organic solvent containing a phosphorus atom or a fluorine atom whose viscosity is lower than the ion liquid. The negative electrode active material layer includes a lithium ion selective transmission part which selectively allows the lithium ion to be transmitted than the cation component. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, hybrid vehicles, electric vehicles, and fuel cell vehicles have been manufactured and sold from the viewpoints of environment and fuel efficiency, and new developments are continuing. In these so-called electric vehicles, it is indispensable to use a power supply device capable of discharging and charging. As the power supply device, a secondary battery such as a lithium ion battery or a nickel metal hydride battery, an electric double layer capacitor, or the like is used. In particular, lithium ion secondary batteries are considered suitable for electric vehicles because of their high energy density and high durability against repeated charging and discharging, and various developments have been intensively advanced.

Conventionally, as an electrolyte constituting an electrolyte layer of a lithium ion secondary battery, generally, an electrolytic solution in which a lithium salt (for example, LiPF ₆ or the like) is dissolved in a volatile flammable organic solvent (for example, ethylene carbonate or the like) is used. Are known.

  On the other hand, it has been attempted to use an ionic liquid as an electrolyte for the purpose of further improving the heat resistance and safety of the above-described conventional electrolytic solution. An ionic liquid is a general term for ionic substances that are liquid even at room temperature, and has excellent characteristics such as non-volatility and flame retardancy. By utilizing this feature and applying an electrolytic solution composed of a lithium salt and an ionic liquid as an electrolyte layer, a highly safe lithium ion secondary battery can be expected.

  As such a technique, Patent Document 1 reports a technique for adding a flame-retardant fluorine-based organic solvent to an ionic liquid and reducing the viscosity of the electrolyte in a battery using a lithium titanate-based negative electrode. (Patent Document 1). In this method, by reducing the viscosity of the electrolytic solution, the impregnation property of the electrolytic solution into the electrode, that is, the contact property between the electrode and the electrolytic solution is improved, thereby improving the charge / discharge performance.

Japanese Patent Laid-Open No. 2004-362872

  However, in a battery using a carbon-based negative electrode, the fluorine-based organic solvent has a strong tendency to solvate lithium ions. Therefore, a phenomenon occurs in which the cation constituting the ionic liquid is preferentially intercalated into the negative electrode during the charging reaction. Since this intercalation is irreversible, there is a problem in that the battery capacity is reduced.

  Therefore, an object of the present invention is to provide a means capable of suppressing a decrease in battery capacity while suppressing an increase in the viscosity of an electrolytic solution in a nonaqueous electrolyte secondary battery using a carbon-based negative electrode.

  The present inventors have intensively studied to solve the above problems. As a result, it has been found that the above problem can be solved by disposing a lithium ion selective transmission part in the negative electrode active material layer, and the present invention has been completed.

  That is, the nonaqueous electrolyte secondary battery of the present invention includes a positive electrode in which a positive electrode active material layer is formed on the surface of a current collector, and a negative electrode active material layer that includes a negative electrode active material made of a carbon material on the surface of the current collector. And a negative electrode formed with an electrolyte layer. The electrolyte layer includes an ionic liquid having a cation component and an anion component, and an organic solvent containing a fluorine atom or a phosphorus atom having a viscosity lower than that of the ionic liquid. In addition, the negative electrode active material layer has a lithium ion selective permeation portion that allows lithium ions to permeate more selectively than the cation component.

  According to the present invention, in a non-aqueous electrolyte secondary battery using a carbon-based negative electrode, lithium ions can selectively move on the negative electrode interface. For this reason, the preferential intercalation to the negative electrode of the cation component of an ionic liquid is suppressed. As a result, a decrease in battery capacity can be suppressed.

It is the cross-sectional schematic which represented the outline | summary of the laminated battery which is one Embodiment of the battery of this invention typically. It is the cross-sectional schematic diagram which represented typically the specific arrangement | positioning form of the lithium ion selective transmission part which the negative electrode has in one Embodiment of the battery of this invention. FIG. 2A shows a form in which a lithium ion selective transmission portion is disposed on the surface of the negative electrode active material layer main body. FIG. 2B shows a form in which the surface of the negative electrode active material particles is covered with a lithium ion selective transmission part. FIG. 2C illustrates a form in which a lithium ion selective transmission portion is present inside the negative electrode active material layer.

  Hereinafter, embodiments of the present invention will be described, but the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following forms. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

[Nonaqueous electrolyte secondary battery]
FIG. 1 is a schematic cross-sectional view schematically showing an outline of a stacked battery as an embodiment of the battery of the present invention. In the present specification, the laminated lithium ion secondary battery shown in FIG. 1 will be described in detail as an example, but the technical scope of the present invention is not limited to such a form.

  First, the overall structure of the lithium ion secondary battery of the present invention will be described with reference to the drawings.

[Battery overall structure]
As shown in FIG. 1, the laminated lithium ion secondary battery 10 of this embodiment has a configuration in which a power generation element 17 is housed and sealed using a battery exterior material 22. Here, the power generation element 17 includes a negative electrode in which the negative electrode active material layer 12 is formed on both surfaces of the negative electrode current collector 11 (one surface for the lowermost layer and the uppermost layer of the power generation element), the electrolyte layer 13, and the positive electrode current collector 14. The positive electrode with the positive electrode active material layer 15 formed on both sides is laminated. During lamination, the negative electrode active material layer 12 on one negative electrode surface and the positive electrode active material layer 15 on one positive electrode surface adjacent to the one negative electrode face each other with the electrolyte layer 13 therebetween. A plurality of layers are stacked in the order of the positive electrode.

  Thus, the adjacent negative electrode active material layer 12, electrolyte layer 13, and positive electrode active material layer 15 constitute one single cell layer 16. Therefore, it can be said that the lithium ion secondary battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in parallel. Note that the negative electrode active material layer 12 is formed on only one side of the outermost negative electrode current collector 11 a located in both outermost layers of the power generation element 17. Note that the arrangement of the negative electrode plate and the positive electrode plate in FIG. 1 may be interchanged. In that case, the outermost layer positive electrode current collector (not shown) is positioned on both outermost layers of the power generation element 17, and also in the case of the outermost layer positive electrode current collector, the positive electrode active material layer 15 is formed only on one side. To be.

  Further, the negative electrode current collector plate 18 and the positive electrode current collector plate 19 connected to the respective electrodes (positive electrode and negative electrode) are connected to the negative electrode current collector 11 of each electrode and the negative electrode current collector 11 via the negative electrode terminal lead 20 and the positive electrode terminal lead 21, respectively. It is attached to the positive electrode current collector 14 by ultrasonic welding or resistance welding. Thus, the negative electrode current collector plate 18 and the positive electrode current collector plate 19 electrically connected to the negative electrode current collector 11 and the positive electrode current collector 14 have a structure exposed to the outside of the battery exterior material 22. .

  Next, each member which comprises the lithium secondary battery of this embodiment is demonstrated.

[Negative electrode]
The negative electrode has a configuration in which the negative electrode active material layer 12 is formed on the surface of the negative electrode current collector 11.

  The negative electrode current collector 11 is made of a conductive material. The conductive material constituting the current collector is not particularly limited as long as it has conductivity. For example, conventionally known materials such as metals and conductive polymers can be appropriately used. Specifically, at least one selected from the group consisting of Fe, Cr, Ni, Mn, Ti, Mo, V, Nb, Al, Cu, Ag, Au, Pt, and carbon, for example, two or more The current collector material such as stainless steel made of the above alloy can be preferably used. In the present embodiment, a Ni / Al clad material, a Cu / Al clad material, or a plating material obtained by combining these current collector materials can be preferably used. The current collector may be a current collector in which the surface of a metal (excluding Al) as the current collector material is coated with Al as the other current collector material. Moreover, you may use the electrical power collector which bonded together the metal foil which is two or more said electrical power collector materials depending on the case.

  The thickness of the current collector is not particularly limited, but any current collector is usually about 1 to 100 μm, preferably about 1 to 50 μm.

  The negative electrode active material layer 12 includes a negative electrode active material, and may further include a conductive aid, a binder, an electrolyte, and the like for increasing electrical conductivity as necessary.

(Negative electrode active material)
The negative electrode active material used in the present embodiment is a carbon-based conductive material (carbon material) capable of reversibly occluding and releasing lithium ions. Examples of such a carbon material include ketjen black, vulcan, acetylene black, black pearl, carbon support preliminarily heat-treated at high temperature, carbon particles including carbon nanotubes, carbon nanohorns, carbon fibers, and the like.

In some cases, as a negative electrode active material, a metal material such as lithium metal, a lithium-transition metal composite oxide such as lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ), and other conventionally known materials A negative electrode active material may be used in combination.

  The average particle size of the negative electrode active material contained in the negative electrode active material layer is not particularly limited, but is preferably 1 to 20 μm, more preferably 1 to 5 μm from the viewpoint of increasing the output. In the present specification, the “particle diameter” means the maximum distance L among the distances between any two points on the contour line of the active material. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted. The particle diameters and average particle diameters of other components can be defined in the same manner.

(Conductive aid)
A conductive assistant means the additive mix | blended in order to improve electroconductivity. The conductive auxiliary agent that can be used in the present embodiment is not particularly limited, and conventionally known forms can be appropriately referred to. Examples thereof include carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery. In addition, although the carbon material used as a negative electrode active material in this embodiment may have electroconductivity itself, in such a case, use of a conductive support agent is not necessarily required.

(binder)
The binder is added to the active material layer for the purpose of maintaining the electrode structure (three-dimensional network) by binding the active materials to each other or the active material and the current collector or conductive additive.

  Examples of the binder include, but are not limited to, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer, hexafluoride Heat such as propylene / vinylidene fluoride copolymer, tetrafluoroethylene / perfluorovinyl ether copolymer, thermoplastic resin such as polyvinyl acetate, polyimide, and acrylic resin, epoxy resin, polyurethane resin, and urea resin Examples thereof include curable resins and rubber materials such as styrene butadiene rubber (SBR). These may be used alone or in combination of two or more. In addition, these binders can also use what was melt | dissolved in the organic solvent in which binders are soluble, such as N-methyl-2-pyrrolidone (NMP), in a manufacture process.

(Electrolytes)
Since the specific form of the electrolyte that can be included in the negative electrode active material layer 12 is the same as that described in the section of [Electrolyte layer] described later, detailed description thereof is omitted here.

(Additive)
Examples of other additives that can be included in the negative electrode active material layer 12 of the present embodiment include an ion conductive polymer.

  The compounding ratio of the above components that can be included in the negative electrode active material layer 12 is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about the nonaqueous electrolyte secondary battery. There is no restriction | limiting in particular also about the thickness of a negative electrode active material layer, The conventionally well-known knowledge about a battery can be referred suitably. For example, the thickness of the negative electrode active material layer is about 2 to 100 μm.

(Lithium ion selective transmission part)
In the lithium ion secondary battery 10 of this embodiment, the negative electrode active material layer 12 has a lithium ion selective transmission part.

  A lithium ion selective transmission part is a film which can permeate | transmit lithium ion selectively. Here, “selectively permeate lithium ions” means that lithium ions are selectively permeated over the cation component of the ionic liquid constituting the electrolyte. Thereby, prior to the cation component of the ionic liquid constituting the electrolyte, lithium ions can preferentially permeate the lithium ion selective permeation portion and be intercalated to the negative electrode during the charging reaction. Since the intercalation of lithium ions into the negative electrode in a lithium ion secondary battery is reversible, the battery capacity can be maintained by employing the above-described configuration.

  In the present embodiment, the specific arrangement form of the lithium ion selective transmission unit is not particularly limited, but the form shown in FIG. 2 is exemplified. As shown in FIG. 2, the negative electrode 1 has a configuration in which a negative electrode active material layer 12 is formed on the surface of a negative electrode current collector 11. In the present invention, as the form of the lithium ion selective permeation part, for example, a form in which the lithium ion selective permeation part 2 is arranged on the surface of the negative electrode active material layer main body (FIG. 2A) can be mentioned. Moreover, the form (FIG. 2 (B)) by which the surface of the negative electrode active material particle 3 was coat | covered with the lithium ion selective permeation | transmission part 2 can also be employ | adopted. Furthermore, the form (FIG.2 (C)) in which the lithium ion selective permeable part 2 exists in the negative electrode active material layer 12 may be sufficient. From the viewpoint of enhancing the selectivity of lithium ions, preferably, a form in which a lithium ion selective transmission part is disposed on the surface of the negative electrode active material layer body, or a form in which the surface of the negative electrode active material particles is covered with a lithium ion selective transmission part It is. More preferably, the surface of the negative electrode active material particles is covered with a lithium ion selective permeation part.

  In this embodiment, the lithium ion selective permeation part is formed from an inorganic solid electrolyte containing an inorganic oxide or an inorganic sulfide, or a polymer solid electrolyte containing a polyalkylene oxide structure. Such a form is preferable because a lithium ion selective permeation portion can be easily formed and the lithium ion selectivity is excellent. However, it is not necessarily limited to such a form.

As an inorganic oxide as an inorganic solid electrolyte used for forming a lithium ion selective permeation part in the present embodiment, for example, B ₂ O ₃ —LiO, LiPON (Li _2.9 PO _3.3 N _{0. 46), Li 2 O-V} 2 O 5 -SiO 2, Li 1.3 Al 0.3 Ti 1.7 (PO 4) 3, etc. _{Li 0.35 La} 0.55 TiO ₃ and the like. Preferably, Li ₂ O—V ₂ O ₅ —SiO ₂ , Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li _0.35 La _0.55 TiO ₃ , particularly preferably Li _{0 .35} La _0.55 TiO ₃ . The inorganic sulfide as the inorganic solid _electrolyte, the _{Li 2 S-P 2 S 5} , Li 2 S-B 2 S 3, Li 2 S-SiS 2, Li 2 S-GeS 2 -P 2 S 5 Can be mentioned. From the viewpoint of easy preparation of the lithium ion selective permeation part and lithium ion selectivity, preferably Li ₂ S—B ₂ S ₃ , Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ —P ₂ S ₅ , Particularly preferred is Li ₂ S—GeS ₂ —P ₂ S ₅ .

  Examples of the polymer solid electrolyte used for forming the lithium ion selective permeation portion in the present embodiment include a polyalkylene oxide compound having a weight average molecular weight of 5,000 to 1,000,000. From the viewpoint of easy preparation of the lithium ion selective permeation part and lithium ion selectivity, the weight average molecular weight of the polyalkylene oxide compound is preferably 10,000 to 500,000, particularly preferably 100,000 to 500,000. is there. The alkylene group of the polyalkylene oxide compound is an alkylene group having 2 to 5 carbon atoms, preferably 2 to 3 carbon atoms, and particularly preferably 2 carbon atoms.

  Examples of the polyalkylene oxide compound include polyethylene oxide, polypropylene oxide, and polybutylene oxide. Also preferred are polyethylene oxide and polypropylene oxide, and particularly preferred is polyethylene oxide.

  The thickness of the lithium ion selective transmission part is preferably 5 to 2,000 nm, more preferably 10 to 1,000 nm, and particularly preferably 20 to 500 nm.

[Electrolyte layer]
The electrolyte layer 13 functions as a spatial partition (spacer) between the negative electrode active material layer 12 and the positive electrode active material layer 15. In addition, it also has a function of holding an electrolyte that is a lithium ion transfer medium between the positive and negative electrodes during charging and discharging. In the present embodiment, the electrolyte layer 13 includes an ionic liquid, a lithium salt, and an organic solvent.

(Ionic liquid)
The ionic liquid is a salt composed of a cation component and an anion component, which is also called a room temperature molten salt, and shows a liquid state at room temperature. The ionic liquid itself is a well-known material, and a great number of documents are distributed. Examples of ionic liquids preferably used for constituting the electrolyte layer in the present embodiment include, for example, ammonium (imidazolium, pyridinium, aliphatic quaternary ammonium [piperidinium]. , Pyrrolidinium, quaternary alkyl ammonium, quaternary alkyl ammonium having an alkoxy group]), phosphonium cation and sulfonium cation. Specific examples of the imidazolium cation include 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1-propyl-3-methylimidazolium, and 1-butyl-3. -Methylimidazolium, 1-hexyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium. Specific examples of the pyridinium cation include N-ethyl-N-methylpyridinium, N-methyl-N-propylpyridinium, N-butyl-N-methylpyridinium, and N-hexyl-N-methylpyridinium. Specific examples of the pyrrolidinium cation include N-ethyl-N-methylpyrrolidinium, N-methyl-N-propylpyrrolidinium, N-butyl-N-methylpyrrolidinium, N-hexyl-N-methyl. Pyrrolidinium is mentioned. Specific examples of piperidinium include N-ethyl-N-methylpiperidinium, N-methyl-N-propylpiperidinium, N-butyl-N-methylpiperidinium, N-hexyl-N-methylpiperidinium Is mentioned. Specific examples of the pyrrolidinium cation include N-ethyl-N-methylpyrrolidinium, N-methyl-N-propylpyrrolidinium, N-butyl-N-methylpyrrolidinium, N-hexyl-N-methyl. Pyrrolidinium is mentioned. Specific examples of the quaternary alkyl ammonium include N, N, N-trimethyl-N-ethylammonium, N, N, N-trimethyl-N-propylammonium, N, N, N-trimethyl-N-butylammonium, N, N, N-trimethyl-N-hexylammonium, N, N, N-triethyl-N-methylammonium may be mentioned. Specific examples of the quaternary alkyl ammonium having an alkoxy group include N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium. Specific examples of the phosphonium cation include triethylmethylphosphonium and triethylhexylphosphonium. Specific examples of the sulfonium cation include triethylmethylsulfonium and triethylhexylsulfonium.

Examples of the anionic component constituting the ionic liquid include BF ₄ ⁻ , AlF ₄ −, PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , ClO ₄ ⁻ , AlCl ₄ ⁻ , CF ₃ SO ₃ ⁻ , and C _2. F ₅ SO ₃ ⁻ _, CF ₇ SO ₃ ⁻ _, C ₄ F ₉ SO ₃ ⁻ _, CH ₃ SO ₃ ⁻ _, C ₂ H ₅ SO ₃ ⁻ _, CH ₃ OSO ₃ ⁻ _, C ₂ H ₅ OSO ₃ ⁻ _, (FO ^{_{2 S) 2 N - (FSI}} ), (CF 3 SO 2) 2 N - (TFSI), CF 3 CO 2 -, (C 2 F 5 SO 2) 2 N - (BETI), (C 4 F 9 SO ^{_{2) 2 N -, (CF}} 3 SO 2) 3 C -, (C 2 F 5 SO 2) 3 C -, (CN) 2 N -, (CF 3) 3 PF 3 -, (C 2 F 5) ^{_{3 PF 3 -, (C 3}} F 7) 3 PF 3 - Contact Beauty _{(C 4 F 9) 3 PF} 3 - , etc. are exemplified. In addition, as for these cation components and anion components, only 1 type may respectively be used independently and 2 or more types may be used. Among these, ionic liquids are N-ethyl-N-methylpiperidinium, N-methyl-N-propylpiperidinium, N-butyl-N from the viewpoint of low viscosity and excellent oxidation resistance and reduction resistance. -Methylpiperidinium, N-hexyl-N-methylpiperidinium, N-ethyl-N-methylpyrrolidinium, N-methyl-N-propylpyrrolidinium, N-butyl-N-methylpyrrolidinium, N-hexyl-N-methylpyrrolidinium, N, N, N-trimethyl-N-ethylammonium, N, N, N-trimethyl-N-propylammonium, N, N, N-trimethyl-N-butylammonium, N, N, N-trimethyl-N-hexylammonium, N, N, N-triethyl-N-methylammonium, N, N-diethyl-N-methyl-N One or more selected from the group consisting of (2-methoxyethyl) ammonim, and the anion constituting the ionic liquid is one or more selected from the group consisting of FSI, TFSI, and BETI It is preferable that

  There is no restriction | limiting in particular about content of the ionic liquid in an electrolyte layer, A conventionally well-known knowledge can be referred suitably.

(Lithium salt)
Examples of the lithium salt contained in the electrolyte layer in the present embodiment include Li (FSO ₂ ) ₂ N), Li (CF ₃ SO ₂ ) ₂ N), Li (C ₂ F ₅ SO ₂ ) ₂ N), and LiPF. ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₂ F ₅ SO _3, LiClO ₄ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (C ₃ F _{7) 3, LiPF 3 (C} 4 F 9) 3 and the like. As for these lithium salts, only 1 type may be used independently and 2 or more types may be used together. There is no restriction | limiting in particular also about the quantity of lithium salt in an electrolyte layer, A conventionally well-known knowledge can be referred suitably.

(Organic solvent)
In the present embodiment, the electrolyte layer includes an organic solvent containing a fluorine atom or a phosphorus atom. The organic solvent containing fluorine atoms or phosphorus atoms contained in the electrolyte layer has a viscosity lower than that of the ionic liquid described above. Thereby, even if it is a case where an ionic liquid is used, the viscosity increase of electrolyte can be suppressed.

  In the present invention, the organic solvent containing a fluorine atom or a phosphorus atom is preferably flame retardant. This is because a flame retardant effect can be imparted to the lithium ion secondary battery by using a flame retardant organic solvent in the electrolyte layer.

  The organic solvent containing a fluorine atom or a phosphorus atom may be an organic solvent composed of an organic compound having one or more fluorine atoms or phosphorus atoms per molecule. Such an organic solvent may be substantially composed of one kind of fluorine compound or phosphorus compound, or may be a mixture containing two or more kinds of fluorine compounds or phosphorus compounds. The fluorine compound or phosphorus compound constituting the organic solvent may be either cyclic or chain-like, or a mixture thereof.

  As a fluorine compound, all the hydrocarbon groups may be substituted with a fluoroalkyl group, or may be partially substituted with a fluoroalkyl group. In the present application, those in which all hydrocarbon groups are fluoroalkyl groups are referred to as “perfluoro compounds”, and those in which hydrocarbon groups remain are referred to as “hydrofluoro compounds”.

Specific examples of the organic solvent containing a fluorine atom include CF ₃ OCOOCH ₃ , CF ₃ OCOOCF ₃ , CF ₃ CH ₂ OCOOCH ₃ , C ₂ F ₅ OCOOCH ₃ , C ₂ F ₅ OCOOC ₂ H ₅ , and C ₂ F. _{5 OCOOC 2 F 5, C 3} F 7 OCOOCH 3, C 3 F 7 OCOOCF 3, C 3 F 7 OCOOC 2 H 5, C 3 F 7 OCOOC 2 F 5, C 4 F 9 OCOOCH 3, C 4 F 9 OCOOC ₂ H ₅ , C ₄ F ₉ OCOOC ₃ F ₇ , C ₄ F ₉ OCOOC ₄ H _{9 and the} like chain-like perfluoro or hydrofluorocarbonates having 2 to 10 carbon atoms, fluorine-substituted ethylene carbonate, fluorine-substituted methylethylene carbonate , Fluorine-substituted 1,1-dimethyl-1 ′, 1′-diethylethylene carbonate Perfluoro or hydrofluorocarbons carbonates annular 2-10 carbon atoms such _{bets, CF 3 OCH 3, CF 3} OCF 3, CF 3 CH 2 OCH 3, C 2 F 5 OCH 3, C 2 F 5 OCF 3, _{CF 3 CH 2 OC 2 H 5} , C 2 F 5 OC 2 H 5, C 2 F 5 OC 2 F 5, C 3 F 7 OCH 3, C 3 F 7 OC 2 H 5, C 3 F 7 OC 3 H ₇ , C ₄ F ₉ OCH ₃ , C ₄ F ₉ OC ₂ H ₅ , C ₄ F ₉ OC ₃ H ₇ , C ₄ F ₉ OC ₄ H ₉ , C ₅ F ₁₁ OCH ₃ , C ₅ F ₁₁ OC ₂ H ₂ , C ₆ F ₁₃ OCH ₃ , C ₆ F ₁₃ OC ₂ H ₅ , C ₆ F ₁₃ OC ₃ H ₇ , C ₆ F ₁₃ OC ₄ F _{9 and} other perfluoro or hydrofluoroethers having 2 to 10 carbon atoms Is mentioned . These hydrocarbon group and fluoroalkyl group may have a linear structure or a branched structure.

Specific examples of the organic solvent containing a phosphorus atom include phosphoric acid ester organic solvents such as trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, and tolyl phosphate, triphenylphosphine (Ph ₃ P ) -Based phosphine organic solvents.

In the present embodiment, the organic solvent containing a fluorine atom or a phosphorus atom is preferably CF ₃ OCOOCH ₃ , CF ₃ OCOOCF ₃ , CF ₃ CH ₂ OCOOCH, from the viewpoint of reducing the viscosity of the electrolyte and flame retardancy. ₃ , chain perfluoro or hydrofluorocarbonate such as C ₂ F ₅ OCOOCH ₃ , C ₂ F ₅ OCOOC ₂ H ₅ , C ₂ F ₅ OCOOC ₂ F ₅ , fluorine-substituted ethylene carbonate, fluorine-substituted methyl ethylene carbonate, etc. cyclic perfluoro or hydrofluoroether _{carbonate, C 4 F 9 OCH 3,} C 4 F 9 OC 2 H 5, C 4 F 9 OC 3 H 7, C 6 F 13 OCH 3, C 6 F 13 OC 2 H 5, hydrofluoroethers, such as _{C 6 F 13 OC 3 H 7} , trimethylene phosphate , Triethyl phosphate, tributyl phosphate, triphenylphosphine. Particularly preferred are hydrofluoroethers represented by C ₄ F ₉ OC ₂ H ₅ , trimethyl phosphate, triethyl phosphate, and triphenylphosphine.

  Two or more of the organic solvents described above may be used in combination. This combination can be appropriately selected depending on the physical properties of each organic solvent.

  In the present embodiment, the content of the organic solvent described above in the electrolyte layer is preferably 0.1 to 15% by mass with respect to 100% by mass of the ionic liquid from the viewpoint of lowering the viscosity of the electrolytic solution. More preferably, it is 0.5-10 mass%, Most preferably, it is 1-7 mass%. If content of the said organic solvent is 0.1 mass% or more, the viscosity of an ionic liquid can be reduced, without inhibiting the lithium ion conductivity of an ionic liquid. In addition, when the content of the organic solvent is 15% by mass or less, it is possible to improve the rate characteristics and the capacity retention rate sufficiently efficiently. Note that an organic solvent other than the organic solvents described above may be included in the electrolyte layer as long as the effects of the present embodiment are not adversely affected.

[Positive electrode]
The positive electrode has a configuration in which the positive electrode active material layer 15 is formed on the surface of the positive electrode current collector 14.

  The positive electrode current collector 14 is made of a conductive material. About the kind and the thickness of the electroconductive material which comprise a positive electrode collector, since the form similar to having mentioned above about the negative electrode collector 11 can be employ | adopted, detailed description is abbreviate | omitted here.

  The positive electrode active material layer 15 includes a positive electrode active material, and may further include a conductive additive, a binder, an electrolyte, and the like for increasing electrical conductivity as necessary. In addition, about components other than a positive electrode active material, the form similar to having mentioned above about the negative electrode active material layer 12 can be employ | adopted.

The positive electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium, and a positive electrode active material usually used for a lithium ion secondary battery can be used. Specifically, a lithium-transition metal composite oxide is preferable. For example, a Li—Mn composite oxide such as LiMn ₂ O _4, a Li—Ni composite oxide such as LiNiO ₂ , LiNi _0.5 Mn _0. A Li—Ni—Mn based composite oxide such as ₅ O ₂ can be given. In some cases, two or more positive electrode active materials may be used in combination.

  The compounding ratio of the above components contained in the positive electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about non-aqueous electrolytic secondary batteries. Moreover, there is no restriction | limiting in particular also about the thickness of a positive electrode active material layer, The conventionally well-known knowledge about a battery can be referred suitably. For example, the thickness of the positive electrode active material layer is about 2 to 100 μm.

[Current collector]
As the material of the current collector plates (the positive electrode current collector plate 18 and the negative electrode current collector plate 19), aluminum, copper, nickel, stainless steel, alloys thereof, or the like can be used. These are not particularly limited, and known materials conventionally used as current collector plates can be used.

[Battery exterior materials]
In the lithium ion secondary battery 10 of the present embodiment, the entire power generation element 17 is accommodated inside the battery exterior member 22 in order to prevent external impact and environmental degradation during use. A laminate sheet can be used as the battery exterior material 22. For example, the laminate sheet may be configured as a three-layer structure in which polypropylene, aluminum, and nylon are laminated in this order. In some cases, a conventionally known metal can case can also be used as an exterior.

[Method for producing non-aqueous electrolyte secondary battery]
The lithium ion secondary battery 10 of this embodiment can be manufactured by a conventionally known manufacturing method. Hereinafter, a method for manufacturing a lithium ion selective transmission unit, which is a characteristic configuration of the present embodiment, will be briefly described.

  As described above, the preferred form of the battery of the present embodiment is a form in which the lithium ion selective transmission part is disposed on the surface of the negative electrode active material layer body, or the surface of the negative electrode active material particles is covered with the lithium ion selective transmission part. It is a form. Hereinafter, a method for producing each of these forms will be described as an example.

  First, a component for forming a lithium ion selective permeation portion (that is, a polymer solid electrolyte or an inorganic solid electrolyte) is dissolved or dispersed in an appropriate solvent to obtain a solution.

  Next, separately prepared negative electrode active material particles are added to the solution and mixed. Then, after removing a solution by filtration, a lithium ion selective permeation | transmission part can be produced on the surface of negative electrode active material particle | grains by making it dry.

  Alternatively, a solution in which a polymer solid electrolyte or an inorganic solid electrolyte is dissolved or dispersed is sprayed on the surface of the negative electrode active material particles and dried to produce a lithium ion selective permeation portion on the surface of the negative electrode active material particles. Good.

  The solvent used in this case is not particularly limited as long as it can dissolve or disperse the polymer solid electrolyte or the inorganic solid electrolyte. For example, alcohol solvents such as methanol, ethanol, 1-propanol: acetone, methyl ethyl ketone Ketone solvents such as acetonitrile; hydrocarbon solvents such as acetonitrile; n-hexane, 2-methylpentane, and cyclopentane; ether solvents such as tetrahydrofuran and diisopropyl ether can be used. Even if these solvents remain in the electrolyte after the production of the battery, they are preferable because they are inactive to other components such as electrodes and separators.

  Drying can be performed by a conventionally known method such as vacuum drying or drying by a flow of nitrogen or the like. The drying temperature is preferably from 60 to 170 ° C, more preferably from 80 to 120 ° C, although it depends on the type of solvent. At such a temperature, the coated negative electrode active material particles are quickly dried without melting lithium at a high temperature.

  Through the above procedure, negative electrode active material particles having a lithium ion selective permeation portion on the surface are obtained. By forming such a negative electrode active material layer on the surface of the current collector using such negative electrode active material particles, a negative electrode active material layer having a lithium ion selective transmission part can be produced.

  In order to produce another form of the negative electrode active material layer, first, a solution in which a polymer solid electrolyte or an inorganic solid electrolyte is dissolved or dispersed is prepared in the same manner as described above.

  On the other hand, a negative electrode active material layer is formed on the surface of the current collector by a conventionally known method. And the solution prepared above is apply | coated or sprayed on the surface of this negative electrode active material layer, and it is made to dry. Thereby, the lithium ion selective transmission part is in a form covering the surface of the negative electrode active material layer.

  The effect of this invention is demonstrated using a following example and a comparative example. However, the technical scope of the present invention is not limited only to the following examples. Below, after adjusting the negative electrode active material layer which has a lithium ion selective permeation | transmission part, the lithium ion secondary battery using this negative electrode active material layer was produced. And the charge / discharge characteristic test of this lithium ion secondary battery was done.

[Example 1]
(1) Preparation of positive electrode slurry and preparation of positive electrode LiNiO ₂ (average particle size: 5 μm) as a positive electrode active material 85% by mass, acetylene black (average particle size: 0.1 μm) as a conductive auxiliary agent 5% by mass, and as a binder A solid content consisting of 10% by mass of PVDF was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content to prepare a positive electrode slurry. The obtained positive electrode slurry was applied on both sides of an Al foil (thickness: 15 μm) as a current collector, dried and pressed to prepare a positive electrode.

(2) Preparation of negative electrode slurry and preparation of negative electrode First, as a negative electrode active material, a graphite (average particle size: 5 μm) surface of 95% by mass, polyethylene glycol (PEO solution, Aldrich) having a weight average molecular weight of 500,000 5 mass % (Solid content conversion) was used to coat with a thickness of 100 nm. This obtained the negative electrode active material by which the lithium ion selective permeation | transmission part was provided in the surface. When coating the active material with PEO, 100 g of the PEO solution diluted 10-fold with acetonitrile and 50 g of the negative electrode active material were mixed and then filtered to remove excess PEO active material and acetonitrile. The mass was measured and the above operation was repeated until the target mass of PEO was coated. After the target mass of PEO was coated, vacuum drying was performed at 80 ° C. for 8 hours.

  A solid content consisting of 90% by mass of the negative electrode active material coating obtained above and 10% by mass of PVdF as a binder was prepared. An appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, was added to the solid content to prepare a negative electrode slurry. The obtained negative electrode slurry was applied to both surfaces of a Cu foil (thickness: 10 μm) as a current collector, dried and pressed to prepare a negative electrode.

(3) Preparation of electrolytic solution 1.0 mol / L bistrifluorosulfonylimide lithium (LiTFSI) was dissolved in 1-methyl-1-propylpyrrolidinium bisfluorosulfonylimide to prepare a lithium-containing ionic liquid. An electrolyte was prepared by mixing 5% by mass of hydrofluoroether (C ₄ F ₉ OC ₂ H ₅ ) as an organic solvent with 100% by mass of this lithium-containing ionic liquid.

(4) Production of battery The positive electrode produced above, a separator (a polyethylene microporous membrane in which silica particles are dispersed), and the negative electrode produced above are laminated in this order, and placed in an aluminum laminate molded body, so that the electrolyte is not deposited. An impregnation cell was prepared. Thereafter, the electrolyte prepared above was vacuum-impregnated and then sealed and molded to produce a stacked lithium ion secondary battery.

[Example 2]
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that 12% by mass of hydrofluoroether (C ₄ F ₉ OC ₂ H ₅ ) was mixed as an organic solvent with respect to 100% by mass of the lithium-containing ionic liquid. Produced.

[Example 3]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 3% by mass of triphenylphosphine was mixed as an organic solvent with respect to 100% by mass of the lithium-containing ionic liquid.

[Example 4]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 15% by mass of triphenylphosphine as an organic solvent was mixed with 100% by mass of the lithium-containing ionic liquid.

[Example 5]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that 5% by mass of triethyl phosphate as an organic solvent was mixed with 100% by mass of the lithium-containing ionic liquid.

[Example 6]
A lithium ion secondary battery was carried out in the same manner as in Example 1 except that a negative electrode active material in which lithium lanthanum titanate (Li _0.35 La _0.55 TiO ₃ ) was coated on the surface of graphite to a thickness of 50 nm was used. Was made.

[Example 7]
A lithium ion secondary battery was produced in the same manner as in Example 6 except that 5% by mass of triphenylphosphine was mixed as an organic solvent with respect to 100% by mass of the lithium-containing ionic liquid.

[Example 8]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that LiMnO ₄ was used as the positive electrode active material.

[Example 9]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that LiFePO ₄ was used as the positive electrode active material.

[Example 10]
Instead of hydrofluoroether (C ₄ F ₉ OC ₂ H ₅ ), a mixed solvent of terminal fluorine-substituted diethyl carbonate (CF ₃ CH ₂ OCOOC ₂ H ₅ ) and fluoroethylene carbonate (F—C ₃ H ₃ O ₃ ) A lithium ion secondary battery was produced in the same manner as in Example 1 except that was used.

[Comparative Example 1]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the electrolytic solution did not contain hydrofluoroether (C ₄ F ₉ OC ₂ H ₅ ).

[Comparative Example 2]
A lithium ion secondary battery was produced in the same manner as in Example 6 except that the electrolytic solution did not contain hydrofluoroether (C ₄ F ₉ OC ₂ H ₅ ).

[Comparative Example 3]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode active material was not coated with PEO.

[Comparative Example 4]
A lithium ion secondary battery was produced in the same manner as in Example 7 except that the negative electrode active material was not coated with lithium lanthanum titanate.

[Comparative Example 5]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the electrolytic solution did not contain hydrofluoroether (C ₄ F ₉ OC ₂ H ₅ ) and the negative electrode active material was not coated with PEO. did.

<Charge / discharge characteristics test>
A charge / discharge test was performed on the lithium ion secondary batteries produced in the above-described Examples and Comparative Examples. The charge / discharge test was performed as follows.
(1) Constant current charging (charging to a predetermined voltage with a predetermined current. After that, the voltage is held so that the total charging time is 7 hours.)
(2) Pause (pause for 30 minutes)
(3) Constant current discharge (discharge to a predetermined voltage with a predetermined current)
In addition, charging current: 0.2 C, charging voltage: 2.5 V (1.5 V in Examples 1 to 4), discharging current: 0.2 C, discharging voltage: 1 V (0.5 V in Examples 1 to 4) is there. Here, 1C is a current value at which the battery is fully charged (100% charged) when charged at that current value for 1 hour. For example, 0.2 C is a current value that is 0.2 times that of 1 C, and is a current value that can fully charge the battery in 5 hours.

  The 1C rate characteristic is a ratio of 1C discharge capacity when the 0.2C discharge capacity is 100%, that is, 1C rate characteristic (%) = {(1C discharge capacity) / (0.2C discharge capacity)} X100.

  The discharge capacity maintenance ratio is the ratio of the discharge capacity when the initial discharge capacity is 100%, that is, the discharge capacity maintenance ratio (%) = {(discharge capacity after 100 cycles) / (initial discharge capacity)} X100. The results are shown in Table 1.

  As described above, in Comparative Examples 1 and 2, the lithium ion selective permeation portion is provided in the negative electrode active material layer, but the electrolytic solution does not contain a predetermined organic solvent. On the contrary, in Comparative Examples 3 and 4, although the electrolytic solution contains a predetermined organic solvent, the negative electrode active material layer is not provided with a lithium ion selective transmission part. Compared with these comparative examples, Examples 1 to 10 showed excellent rate characteristics and capacity retention.

1 negative electrode,
2 Lithium ion selective transmission part,
3 negative electrode active material particles,
10 Multilayer secondary battery,
11 negative electrode current collector,
11a The outermost layer current collector on the negative electrode side,
12 negative electrode active material layer,
13 electrolyte layer,
14 positive electrode current collector,
15 positive electrode active material layer,
16 cell layer,
17 Power generation elements,
18 negative electrode current collector plate,
19 positive current collector,
20 Negative terminal lead,
21 positive terminal lead,
22 Battery exterior material.

Claims (6)

A positive electrode in which a positive electrode active material layer is formed on the surface of the current collector;
A negative electrode in which a negative electrode active material layer including a negative electrode active material made of a carbon material is formed on the surface of a current collector;
An electrolyte layer comprising an ionic liquid having a cationic component and an anionic component and an organic solvent containing a fluorine atom or a phosphorus atom having a viscosity lower than that of the ionic liquid, and a non-aqueous electrolyte secondary battery comprising:
The non-aqueous electrolyte secondary battery, wherein the negative electrode active material layer has a lithium ion selective permeation part that allows lithium ions to selectively permeate through the cation component.   The nonaqueous electrolyte secondary battery according to claim 1, wherein negative electrode active material particles are coated with the lithium ion selective permeation part.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the organic solvent is flame retardant.   The lithium ion selective permeation portion is formed of an inorganic solid electrolyte containing an inorganic oxide or an inorganic sulfide, or a polymer solid electrolyte containing a polyalkylene oxide structure. The nonaqueous electrolyte secondary battery according to one item.   5. The non-aqueous electrolyte 2 according to claim 1, wherein the organic solvent is at least one selected from the group consisting of hydrofluoroethers, phosphate esters, and phosphine compounds. Next battery.   The nonaqueous electrolyte secondary according to any one of claims 1 to 5, wherein a content of the organic solvent is 0.1 to 15% by mass with respect to 100% by mass of the ionic liquid. battery.

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