WO2012017520A1 - Lithium secondary battery - Google Patents

Lithium secondary battery Download PDF

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Publication number
WO2012017520A1
WO2012017520A1 PCT/JP2010/063119 JP2010063119W WO2012017520A1 WO 2012017520 A1 WO2012017520 A1 WO 2012017520A1 JP 2010063119 W JP2010063119 W JP 2010063119W WO 2012017520 A1 WO2012017520 A1 WO 2012017520A1
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Prior art keywords
lithium
cation
positive electrode
secondary battery
negative electrode
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PCT/JP2010/063119
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French (fr)
Japanese (ja)
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博文 中本
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トヨタ自動車株式会社
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Priority to PCT/JP2010/063119 priority Critical patent/WO2012017520A1/en
Publication of WO2012017520A1 publication Critical patent/WO2012017520A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a lithium secondary battery capable of suppressing lithium deposition.
  • the secondary battery can convert the decrease in chemical energy associated with the chemical reaction into electrical energy and perform discharge.
  • the secondary battery converts electrical energy into chemical energy by flowing current in the opposite direction to that during discharge.
  • the battery can be stored (charged).
  • lithium secondary batteries are widely used as power sources for notebook personal computers, mobile phones, and the like because of their high energy density.
  • lithium cobaltate Li 1-x CoO 2
  • Li 1-x CoO 2 + xLi + + xe ⁇ ⁇ LiCoO 2 (II) (In the above formula (II), 0 ⁇ x ⁇ 1.)
  • reverse reactions of the above formulas (I) and (II) proceed in the negative electrode and the positive electrode, respectively, and in the negative electrode, graphite (Li x C) containing lithium by graphite intercalation is Since lithium cobaltate (Li 1-x CoO 2 ) is regenerated, re-discharge is possible.
  • Patent Document 1 discloses a non-aqueous electrolyte for a lithium secondary battery characterized by containing a hydroxy sultone compound.
  • the lithium secondary battery of the present invention is a lithium secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode, wherein the negative electrode contains lithium metal,
  • the electrolytic solution contains an ionic liquid containing a cation and its counter anion, and a lithium salt, and the cation has one or more ether groups in its structure, and the counter anion is inert to lithium metal. It is characterized by.
  • the cation is an ammonium cation further having a heterocyclic structure closed by a nitrogen atom and an alkyl chain having 2 to 10 carbon atoms, and an ammonium having one or more chain alkyl groups having 1 to 10 carbon atoms.
  • a cation selected from the group consisting of cations is preferred.
  • the cation is preferably a cation represented by the following general formula (1) or (2).
  • R 1 to R 6 each independently represents a substituent selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 10 carbon atoms. And r is an integer of 1 or more.
  • the cation is a group consisting of N- (2-methoxyethyl) -N-methylpiperidinium cation and N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation. It is preferable that it is a cation chosen from these.
  • the ether group of the cation interacts with lithium ions, so that lithium ions can be easily supplied to the positive electrode, and as a result, precipitation of lithium metal in the battery can be suppressed. Further, according to the present invention, by using a counter anion that is inactive with respect to lithium metal, it is possible to suppress the decomposition of the ionic liquid and to extend the battery life.
  • FIG. 1 It is a figure which shows an example of the layer structure of the lithium secondary battery which concerns on this invention, Comprising: It is the figure which showed typically the cross section cut
  • FIG. 1 shows an example of the layer structure of the lithium secondary battery which concerns on this invention, Comprising: It is the figure which showed typically the cross section cut
  • the lithium secondary battery of the present invention is a lithium secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode, wherein the negative electrode contains lithium metal,
  • the electrolytic solution contains an ionic liquid containing a cation and its counter anion, and a lithium salt, and the cation has one or more ether groups in its structure, and the counter anion is inert to lithium metal. It is characterized by.
  • ionic liquids have low volatility and flammability, and can be easily adjusted in physical properties during synthesis by changing substituents on the cation center.
  • the present inventor uses a cation having at least one ether group in the structure and an ionic liquid having a counter anion inert to lithium metal in the electrolyte solution, thereby allowing a cation having no ether group in the structure. It was found that lithium can be deposited more uniformly than in the case of using an ionic liquid having the present invention, and the present invention has been completed.
  • the electrolyte solutions (Example 1 and Example 2) having a cation having one or more ether groups in the structure are the electrolyte solutions (Comparative Examples 1 and 2) having a cation having no ether group in the structure. It can be seen that the uniform deposition time of lithium is several times longer than in Example 2). Further, in the present invention, by using a counter anion that is inactive with respect to lithium metal, the decomposition of the ionic liquid can be suppressed and the battery life can be extended.
  • the cation used in the present invention is an ammonium cation further having a heterocyclic structure closed by a nitrogen atom and an alkyl chain having 2 to 10 carbon atoms, or a chain shape having 1 to 10 carbon atoms. It is preferably a cation selected from the group consisting of ammonium cations further having one or more alkyl groups. Specifically, such a cation is more preferably a cation represented by the following general formula (1) or (2).
  • R 1 to R 6 each independently represents a substituent selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 10 carbon atoms. And r is an integer of 1 or more.
  • Examples of the cation represented by the general formula (1) include N- (2-methoxyethyl) -N-methylpiperidinium cation, N- (2-methoxypropyl) -N-methylpiperidinium cation, N- (2-Methoxyethyl) -N-methylpyrrolidinium cation or N- (2-methoxypropyl) -N-methylpyrrolidinium cation is more preferred.
  • Examples of the cation represented by the general formula (2) include N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation, N-ethyl-N, N-dimethyl-N- ( 2-methoxyethyl) ammonium cation, N, N-diethyl-N-methyl-N- (2-methoxypropyl) ammonium cation or N-ethyl-N, N-dimethyl-N- (2-methoxypropyl) ammonium cation More preferred.
  • N- (2-methoxyethyl) -N-methylpiperidinium cation or N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation it is further possible to use N- (2-methoxyethyl) -N-methylpiperidinium cation or N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation. preferable.
  • the counter anion used for this invention will not be specifically limited if it is inactive with respect to lithium metal, What is normally used as anion seed
  • the anion inactive to the lithium metal herein refers to a stable anion that does not change its chemical structure even when the lithium metal is immersed in an electrolytic solution containing the anion for 100 minutes.
  • an anion active against lithium metal refers to an anion that decomposes by immersing lithium metal in an electrolyte containing the anion for 100 minutes.
  • counter anions used in the present invention are [N (CF 3 ) 2 ] ⁇ , [N (SO 2 CF 3 ) 2 ] ⁇ , [N (SO 2 C 2 F 5 ) 2 ] ⁇ .
  • Imide anions such as RSO 3 ⁇ (hereinafter R represents an aliphatic hydrocarbon group or aromatic hydrocarbon group), RSO 4 ⁇ , R f SO 3 ⁇ (hereinafter R f is a fluorine-containing halogenated hydrocarbon group) the point), R f SO 4 -, etc.
  • the counter anion used in the present invention is preferably a bis (trifluoromethanesulfonyl) imide ion ([N (SO 2 CF 3 ) 2 ] ⁇ ).
  • the electrolytic solution used in the present invention further contains a lithium salt as a supporting salt.
  • the lithium salt include inorganic lithium salts such as LiPF 6 , LiBF 4 , LiClO 4, and LiAsF 6 ; LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 (Li-TFSI), LiN (SO 2 C 2 F 5 ) 2 and organic lithium salts such as LiC (SO 2 CF 3 ) 3 . Two or more such lithium salts may be used in combination.
  • the amount of lithium salt added to the ionic liquid is not particularly limited, but is preferably about 0.1 to 1.5 mol / kg.
  • the electrolytic solution used in the present invention may contain a non-aqueous electrolyte in addition to the ionic liquid and the lithium salt.
  • a non-aqueous electrolyte solution and a non-aqueous gel electrolyte can be used as the non-aqueous electrolyte.
  • the nonaqueous electrolytic solution used in the present invention usually contains the above-described lithium salt and nonaqueous solvent.
  • the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl carbonate, butylene carbonate, ⁇ -butyrolactone, sulfolane.
  • the non-aqueous solvent is preferably a solvent having high oxygen solubility.
  • the concentration of the lithium salt in the nonaqueous electrolytic solution is, for example, in the range of 0.5 mol / L to 3 mol / L.
  • the non-aqueous gel electrolyte used in the present invention is usually a gel obtained by adding a polymer to a non-aqueous electrolyte solution.
  • a polymer such as polyethylene oxide (PEO), polyacrylonitrile (PAN), or polymethyl methacrylate (PMMA)
  • PEO polyethylene oxide
  • PAN polyacrylonitrile
  • PMMA polymethyl methacrylate
  • FIG. 1 is a diagram showing an example of a layer configuration of a lithium secondary battery according to the present invention, and is a diagram schematically showing a cross section cut in a stacking direction.
  • the lithium secondary battery according to the present invention is not necessarily limited to this example.
  • the lithium secondary battery 100 is sandwiched between the positive electrode 6 including the positive electrode active material layer 2 and the positive electrode current collector 4, the negative electrode 7 including the negative electrode active material layer 3 and the negative electrode current collector 5, and the positive electrode 6 and the negative electrode 7.
  • An electrolytic solution 1 is included.
  • the electrolytic solution is as described above.
  • the positive electrode, the negative electrode, the separator, and the battery case, which are components of the lithium secondary battery according to the present invention, will be described in detail.
  • the positive electrode of the lithium secondary battery according to the present invention preferably has a positive electrode active material layer having a positive electrode active material, and is usually connected to the positive electrode current collector and the positive electrode current collector. It has a positive electrode lead.
  • the lithium secondary battery which concerns on this invention is a lithium air battery, it has an air electrode containing an air electrode layer instead of the said positive electrode.
  • the positive electrode active material layer As a positive electrode is employ
  • adopted Specific examples of the positive electrode active material used in the present invention include LiCoO 2 , LiNi 1/3 Mn 1/3 Co 1/3 O 2 , LiNiPO 4 , LiMnPO 4 , LiNiO 2 , LiMn 2 O 4 , LiCoMnO 4. , Li 2 NiMn 3 O 8 , Li 3 Fe 2 (PO 4 ) 3 and Li 3 V 2 (PO 4 ) 3 .
  • LiCoO 2 is preferably used as the positive electrode active material.
  • the thickness of the positive electrode active material layer used in the present invention varies depending on the intended use of the lithium secondary battery, but is preferably in the range of 10 ⁇ m to 250 ⁇ m, and in the range of 20 ⁇ m to 200 ⁇ m. It is particularly preferred that it is in the range of 30 ⁇ m to 150 ⁇ m.
  • the average particle diameter of the positive electrode active material is, for example, preferably in the range of 1 ⁇ m to 50 ⁇ m, more preferably in the range of 1 ⁇ m to 20 ⁇ m, and particularly preferably in the range of 3 ⁇ m to 5 ⁇ m. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Because.
  • the average particle diameter of the positive electrode active material can be determined by measuring and averaging the particle diameter of the active material carrier observed with, for example, a scanning electron microscope (SEM).
  • the positive electrode active material layer may contain a conductive material, a binder, and the like as necessary.
  • the conductive material included in the positive electrode active material layer used in the present invention is not particularly limited as long as the conductivity of the positive electrode active material layer can be improved.
  • carbon black such as acetylene black and ketjen black Etc.
  • the content of the conductive material in the positive electrode active material layer varies depending on the type of the conductive material, but is usually in the range of 1% by mass to 10% by mass.
  • binder contained in the positive electrode active material layer used in the present invention examples include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Further, the content of the binder in the positive electrode active material layer may be an amount that can fix the positive electrode active material or the like, and is preferably smaller. The content of the binder is usually in the range of 1% by mass to 10% by mass.
  • the positive electrode current collector used in the present invention has a function of collecting the positive electrode active material layer.
  • Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Of these, aluminum and SUS are preferable.
  • As a shape of a positive electrode electrical power collector foil shape, plate shape, mesh shape etc. can be mentioned, for example, Foil shape is preferable.
  • the electrode active material layer of at least one of the positive electrode and the negative electrode can also be configured to contain at least an electrode active material and an electrode electrolyte.
  • an electrode electrolyte a solid electrolyte such as a solid oxide electrolyte or a solid sulfide electrolyte, the above-described polymer electrolyte, gel electrolyte, or the like can be used.
  • the method for producing the positive electrode used in the present invention is not particularly limited as long as it is a method capable of obtaining the positive electrode.
  • Air electrode layer Hereinafter, the case where the air electrode which has an air electrode layer as a positive electrode is employ
  • the air electrode layer used in the present invention contains at least a conductive material. Furthermore, you may contain at least one of a catalyst and a binder as needed.
  • the conductive material used for the air electrode layer used in the present invention is not particularly limited as long as it has conductivity, and examples thereof include a carbon material.
  • the carbon material may have a porous structure or may not have a porous structure.
  • the carbon material preferably has a porous structure. This is because the specific surface area is large and many reaction fields can be provided.
  • Specific examples of the carbon material having a porous structure include mesoporous carbon.
  • specific examples of the carbon material having no porous structure include graphite, acetylene black, carbon nanotube, and carbon fiber.
  • the content of the conductive material in the air electrode layer is, for example, preferably in the range of 65% by mass to 99% by mass, and more preferably in the range of 75% by mass to 95% by mass. If the content of the conductive material is too small, the reaction field may decrease and the battery capacity may be reduced. If the content of the conductive material is too large, the content of the catalyst is relatively reduced and sufficient. This is because it may not be possible to exert a proper catalytic function.
  • the catalyst used for the air electrode layer used in the present invention examples include cobalt phthalocyanine and manganese dioxide.
  • the catalyst content in the air electrode layer is, for example, preferably in the range of 1% by mass to 30% by mass, and more preferably in the range of 5% by mass to 20% by mass. If the catalyst content is too low, sufficient catalytic function may not be achieved. If the catalyst content is too high, the content of the conductive material is relatively reduced, the reaction field is reduced, and the battery capacity is reduced. This is because there is a possibility that a decrease in the number of times will occur. From the viewpoint that the electrode reaction is performed more smoothly, the conductive material described above preferably supports a catalyst.
  • the air electrode layer may contain at least a conductive material, but preferably further contains a binder for fixing the conductive material.
  • a binder for fixing the conductive material As the specific binder, those described in the above-mentioned “positive electrode active material layer” can be used.
  • the content of the binder in the air electrode layer is not particularly limited. For example, it is preferably 30% by mass or less, and more preferably in the range of 1% by mass to 10% by mass.
  • the thickness of the air electrode layer varies depending on the use of the air battery, but is preferably in the range of 2 ⁇ m to 500 ⁇ m, and more preferably in the range of 5 ⁇ m to 300 ⁇ m.
  • the air electrode current collector used in the present invention collects current in the air electrode layer.
  • the material for the air electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include stainless steel, nickel, aluminum, iron, titanium, and carbon.
  • Examples of the shape of the air electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape.
  • the shape of an air electrode electrical power collector is a mesh form. This is because the current collection efficiency is excellent.
  • a mesh-shaped air electrode current collector is disposed inside the air electrode layer.
  • the secondary battery of the present invention may have another air electrode current collector (for example, a foil-shaped current collector) that collects electric charges collected by the mesh-shaped air electrode current collector. good.
  • a battery case to be described later may also have the function of an air electrode current collector.
  • the thickness of the air electrode current collector is preferably, for example, in the range of 10 ⁇ m to 1000 ⁇ m, and more preferably in the range of 20 ⁇ m to 400 ⁇ m.
  • the negative electrode in the lithium secondary battery according to the present invention preferably has a negative electrode active material layer containing a negative electrode active material, and is usually connected to the negative electrode current collector and the negative electrode current collector in addition to this.
  • the negative electrode lead is provided.
  • the negative electrode layer in the lithium secondary battery according to the present invention contains a negative electrode active material.
  • the negative electrode active material used for the negative electrode active material layer is not particularly limited as long as it can occlude / release lithium ions.
  • metal lithium, lithium alloy, metal oxide, metal sulfide, metal nitride, and Examples thereof include carbon materials such as graphite.
  • the negative electrode active material may be in the form of a powder or a thin film.
  • the alloy having a lithium element include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy.
  • a metal oxide which has a lithium element lithium titanium oxide etc. can be mentioned, for example.
  • metal nitride containing a lithium element examples include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. Further, lithium coated with a solid electrolyte can also be used for the negative electrode layer.
  • the negative electrode layer may contain only a negative electrode active material, or may contain at least one of a conductive material and a binder in addition to the negative electrode active material.
  • a negative electrode layer containing only the negative electrode active material can be obtained.
  • a negative electrode layer having a negative electrode active material and a binder can be obtained.
  • the conductive material and the binder are the same as those described in the section “Air electrode” described above, and thus the description thereof is omitted here.
  • the thickness of the negative electrode active material layer is not particularly limited, but is preferably in the range of 10 ⁇ m to 100 ⁇ m, and more preferably in the range of 10 ⁇ m to 50 ⁇ m.
  • negative electrode current collector As the material and shape of the negative electrode current collector, the same materials and shapes as those of the positive electrode current collector described above can be employed.
  • the battery according to the present invention has a structure in which a laminate in which the order of positive electrode-electrolyte-negative electrode is repeatedly stacked, from the viewpoint of safety, the positive electrode and the negative electrode belonging to different laminates are stacked. It is preferable to have a separator in between.
  • the separator include porous films such as polyethylene and polypropylene; and nonwoven fabrics such as a resin nonwoven fabric and a glass fiber nonwoven fabric. These materials that can be used for the separator can also be used as a support material for the electrolytic solution by impregnating the above-described electrolytic solution.
  • the lithium secondary battery according to the present invention usually has a battery case that houses a positive electrode, an electrolytic solution, a negative electrode, and the like.
  • the shape of the battery case include a coin type, a flat plate type, a cylindrical type, and a laminate type.
  • the battery case may be an open-air battery case or a sealed battery case.
  • An open-air battery case is a battery case having a structure in which at least the air electrode layer can sufficiently come into contact with the atmosphere.
  • the battery case is a sealed battery case, it is preferable to provide a gas (air) introduction pipe and an exhaust pipe in the sealed battery case.
  • the gas to be introduced / exhausted preferably has a high oxygen concentration, and more preferably pure oxygen.
  • Example 1 N- (2-methoxyethyl) -N-methylpiperidinium bis (trifluoromethanesulfonyl) imide represented by the following formula (3) is mixed with lithium bis (trifluoromethanesulfonyl) imide at a concentration of 0.5 mol / kg. Thus, the electrolyte solution of Example 1 was prepared.
  • Example 2 N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide represented by the following formula (4) is mixed with 0.5 mol / liter of lithium bis (trifluoromethanesulfonyl) imide.
  • the electrolyte solution of Example 2 was prepared by dissolving to a concentration of kg.
  • FIG. 2 is a bar graph comparing the time during which lithium was deposited uniformly in the case where the electrolytic solutions of Examples 1 and 2 and Comparative Examples 1 and 2 were used.
  • the vertical axis of FIG. 2 represents the logarithm of the time during which lithium was deposited uniformly.
  • Example 1 and Comparative Example 1 which are electrolytic solutions having cations having a piperidine ring structure, are compared. From FIG. 2, in the electrolytic solution of Example 1 having one ether group in the side chain, the time for which lithium was uniformly deposited was 4200 seconds. On the other hand, in the electrolytic solution of Comparative Example 1 that does not have an ether group in the cation structure, the time during which lithium is uniformly deposited is 600 seconds.
  • Example 1 the time during which lithium was uniformly deposited was 7 times longer than that in Comparative Example 1.
  • Example 2 and Comparative Example 2 which are electrolytes having an alkylammonium cation will be compared. From FIG. 2, in the electrolytic solution of Example 2 having one ether group in the side chain, the time during which lithium was uniformly deposited was 60 seconds. On the other hand, in the electrolyte solution of Comparative Example 2 that does not have an ether group in the cation structure, the time during which lithium is uniformly deposited is 30 seconds. Therefore, in Example 2, the time during which lithium was uniformly deposited was twice as long as that in Comparative Example 2. From these results, the electrolyte solution having a cation having one or more ether groups in the structure is several times longer than the electrolyte solution having a cation having no ether group in the structure. I understand that
  • Example 1 compared with Example 2, the time during which lithium was uniformly deposited was 70 times longer. Therefore, it can be seen that the ammonium cation having a cyclic structure has a longer time for uniformly depositing lithium than the ammonium cation having only a linear alkyl group. Further, when the comparison results of Example 1 and Comparative Example 1 and the comparison results of Example 2 and Comparative Example 2 are further compared, the ammonium cation having a cyclic structure is more than the ammonium cation having only a linear alkyl group. However, it can be seen that the effect of uniform precipitation of lithium by introducing an ether group is more remarkable.

Abstract

The present invention provides a lithium secondary battery capable of minimizing precipitation of lithium. The lithium secondary battery is provided with at least a positive electrode, a negative electrode, and a liquid electrolyte disposed between the positive electrode and the negative electrode, and is characterized in that the negative electrode contains a lithium metal, and the electrolyte contains an ionic liquid and a lithium salt, the ionic liquid including cations and counter anions thereof. The cations have one or more ether groups in the structure thereof, and the counter anions are inert with respect to the lithium metal.

Description

リチウム二次電池Lithium secondary battery
　本発明は、リチウム析出を抑制できるリチウム二次電池に関する。 The present invention relates to a lithium secondary battery capable of suppressing lithium deposition.
　二次電池は、化学反応に伴う化学エネルギーの減少分を電気エネルギーに変換し、放電を行うことができる他に、放電時と逆方向に電流を流すことにより、電気エネルギーを化学エネルギーに変換して蓄積（充電）することが可能な電池である。二次電池の中でも、リチウム二次電池は、エネルギー密度が高いため、ノート型のパーソナルコンピューターや、携帯電話機等の電源として幅広く応用されている。 The secondary battery can convert the decrease in chemical energy associated with the chemical reaction into electrical energy and perform discharge. In addition, the secondary battery converts electrical energy into chemical energy by flowing current in the opposite direction to that during discharge. The battery can be stored (charged). Among secondary batteries, lithium secondary batteries are widely used as power sources for notebook personal computers, mobile phones, and the like because of their high energy density.
　リチウム二次電池においては、負極活物質としてグラファイト（Ｃと表現する）を用いた場合、放電時において、負極では式（Ｉ）の反応が進行する。
　ＬｉｘＣ→Ｃ＋ｘＬｉ＋＋ｘｅ－　　　（Ｉ）
（上記式（Ｉ）中、０＜ｘ＜１である。）
　上記式（Ｉ）で生じる電子は、外部回路を経由し、外部の負荷で仕事をした後、正極に到達する。そして、式（Ｉ）で生じたリチウムイオン（Ｌｉ＋）は、負極と正極に挟持された電解質内を、負極側から正極側に電気浸透により移動する。 In the lithium secondary battery, when graphite (expressed as C) is used as the negative electrode active material, the reaction of formula (I) proceeds at the negative electrode during discharge.
Li x C → C + xLi + + xe − (I)
(In the above formula (I), 0 <x <1.)
The electrons generated in the above formula (I) reach the positive electrode after working with an external load via an external circuit. Then, lithium ions (Li + ) generated in the formula (I) move by electroosmosis from the negative electrode side to the positive electrode side in the electrolyte sandwiched between the negative electrode and the positive electrode.
　また、正極活物質としてコバルト酸リチウム（Ｌｉ１－ｘＣｏＯ２）を用いた場合、放電時において、正極では式（ＩＩ）の反応が進行する。
　Ｌｉ１－ｘＣｏＯ２＋ｘＬｉ＋＋ｘｅ－→ＬｉＣｏＯ２　　　（ＩＩ）
（上記式（ＩＩ）中、０＜ｘ＜１である。）
　充電時においては、負極及び正極において、それぞれ上記式（Ｉ）及び式（ＩＩ）の逆反応が進行し、負極においてはグラファイトインターカレーションによりリチウムが入り込んだグラファイト（ＬｉｘＣ）が、正極においてはコバルト酸リチウム（Ｌｉ１－ｘＣｏＯ２）が再生するため、再放電が可能となる。 When lithium cobaltate (Li 1-x CoO 2 ) is used as the positive electrode active material, the reaction of formula (II) proceeds at the positive electrode during discharge.
Li 1-x CoO 2 + xLi + + xe − → LiCoO 2 (II)
(In the above formula (II), 0 <x <1.)
At the time of charging, reverse reactions of the above formulas (I) and (II) proceed in the negative electrode and the positive electrode, respectively, and in the negative electrode, graphite (Li x C) containing lithium by graphite intercalation is Since lithium cobaltate (Li 1-x CoO 2 ) is regenerated, re-discharge is possible.
　リチウムを活物質とする二次電池において、充放電の反復に伴い負極表面に局部的に析出するデンドライトは、二次電池の安全性、サイクル寿命、容量特性等に大きな影響を及ぼす。リチウムデンドライトによるこのようなデメリットの解決を目的とした発明として、特許文献１には、ヒドロキシスルトン化合物を含有することを特徴とするリチウム二次電池用非水系電解液が開示されている。 In a secondary battery using lithium as an active material, dendrite that locally deposits on the negative electrode surface with repeated charging and discharging greatly affects the safety, cycle life, capacity characteristics, etc. of the secondary battery. As an invention aimed at solving such disadvantages by lithium dendrite, Patent Document 1 discloses a non-aqueous electrolyte for a lithium secondary battery characterized by containing a hydroxy sultone compound.
特開２００６－４８１３号公報JP 2006-4813 A
　特許文献１の段落［００５９］には、当該文献に記載されたヒドロキシプロパンスルトンの効果として、ヒドロキシ基と負極表面の金属リチウムとの間に反応が起こった後に、当該プロパンスルトンが充放電により還元され開環し、Ｌｉ２ＣＯ３、ＬｉＦなどとともに有効な表面薄膜を負極表面上に形成できる効果が記載されている。しかし、このような効果は電解液の分解により生ずる効果であるため、デンドライト抑制効果は一時的なものであり、電池出力の長期安定性は望めない。
　本発明は、上記実状を鑑みて成し遂げられたものであり、リチウム析出を抑制できるリチウム二次電池を提供することを目的とする。 In paragraph [0059] of Patent Document 1, as an effect of the hydroxypropane sultone described in the document, after the reaction between the hydroxy group and the metal lithium on the negative electrode surface, the propane sultone is reduced by charging and discharging. The effect of opening the ring and forming an effective surface thin film on the negative electrode surface together with Li 2 CO 3 , LiF and the like is described. However, since such an effect is an effect caused by the decomposition of the electrolytic solution, the dendrite suppression effect is temporary and long-term stability of the battery output cannot be expected.
The present invention has been accomplished in view of the above circumstances, and an object thereof is to provide a lithium secondary battery capable of suppressing lithium deposition.
　本発明のリチウム二次電池は、少なくとも正極と、負極と、当該正極と当該負極との間に介在する電解液とを備えるリチウム二次電池であって、前記負極はリチウム金属を含有し、前記電解液は、カチオン及びそのカウンターアニオンを含むイオン液体、並びにリチウム塩を含有し、前記カチオンは、構造中にエーテル基を１以上有し、前記カウンターアニオンはリチウム金属に対して不活性であることを特徴とする。 The lithium secondary battery of the present invention is a lithium secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode, wherein the negative electrode contains lithium metal, The electrolytic solution contains an ionic liquid containing a cation and its counter anion, and a lithium salt, and the cation has one or more ether groups in its structure, and the counter anion is inert to lithium metal. It is characterized by.
　本発明においては、前記カチオンは、窒素原子及び炭素数２～１０のアルキル鎖により閉じたヘテロ環構造をさらに有するアンモニウムカチオン、並びに、炭素数１～１０の鎖状アルキル基をさらに１以上有するアンモニウムカチオンからなる群から選ばれるカチオンであることが好ましい。 In the present invention, the cation is an ammonium cation further having a heterocyclic structure closed by a nitrogen atom and an alkyl chain having 2 to 10 carbon atoms, and an ammonium having one or more chain alkyl groups having 1 to 10 carbon atoms. A cation selected from the group consisting of cations is preferred.
　本発明においては、前記カチオンは、下記一般式（１）又は（２）で表されるカチオンであることが好ましい。 In the present invention, the cation is preferably a cation represented by the following general formula (1) or (2).
Figure JPOXMLDOC01-appb-C000003
Figure JPOXMLDOC01-appb-C000003
Figure JPOXMLDOC01-appb-C000004
 （上記一般式（１）及び（２）中、Ｒ１～Ｒ６は各々独立に、水素原子及び炭素数１～１０のアルキル基からなる群から選ばれる置換基を表す。また、ｐ、ｑ及びｒは１以上の整数である。）
Figure JPOXMLDOC01-appb-C000004
 (In the general formulas (1) and (2), R 1 to R 6 each independently represents a substituent selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 10 carbon atoms. And r is an integer of 1 or more.)
　本発明においては、前記カチオンは、Ｎ－（２－メトキシエチル）－Ｎ－メチルピペリジニウムカチオン、及びＮ，Ｎ－ジエチル－Ｎ－メチル－Ｎ－（２－メトキシエチル）アンモニウムカチオンからなる群から選ばれるカチオンであることが好ましい。 In the present invention, the cation is a group consisting of N- (2-methoxyethyl) -N-methylpiperidinium cation and N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation. It is preferable that it is a cation chosen from these.
　本発明によれば、カチオンが有するエーテル基がリチウムイオンと相互作用することにより、正極へリチウムイオンを供給しやすくなり、その結果、電池内におけるリチウム金属の析出を抑制することができる。また、本発明によれば、リチウム金属に対して不活性なカウンターアニオンを使用することにより、イオン液体の分解を抑制し、電池の長寿命化を達成することができる。 According to the present invention, the ether group of the cation interacts with lithium ions, so that lithium ions can be easily supplied to the positive electrode, and as a result, precipitation of lithium metal in the battery can be suppressed. Further, according to the present invention, by using a counter anion that is inactive with respect to lithium metal, it is possible to suppress the decomposition of the ionic liquid and to extend the battery life.
本発明に係るリチウム二次電池の層構成の一例を示す図であって、積層方向に切断した断面を模式的に示した図である。It is a figure which shows an example of the layer structure of the lithium secondary battery which concerns on this invention, Comprising: It is the figure which showed typically the cross section cut | disconnected in the lamination direction. 実施例１及び実施例２、並びに比較例１及び比較例２の電解液を使用した場合において、リチウムが均一に析出した時間を比較した棒グラフである。It is the bar graph which compared the time when lithium precipitated uniformly, when using the electrolyte solution of Example 1 and Example 2, and Comparative Example 1 and Comparative Example 2. FIG.
　本発明のリチウム二次電池は、少なくとも正極と、負極と、当該正極と当該負極との間に介在する電解液とを備えるリチウム二次電池であって、前記負極はリチウム金属を含有し、前記電解液は、カチオン及びそのカウンターアニオンを含むイオン液体、並びにリチウム塩を含有し、前記カチオンは、構造中にエーテル基を１以上有し、前記カウンターアニオンはリチウム金属に対して不活性であることを特徴とする。 The lithium secondary battery of the present invention is a lithium secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode, wherein the negative electrode contains lithium metal, The electrolytic solution contains an ionic liquid containing a cation and its counter anion, and a lithium salt, and the cation has one or more ether groups in its structure, and the counter anion is inert to lithium metal. It is characterized by.
　イオン液体は、有機溶媒と比較して、揮発性及び可燃性が低く、且つ、カチオン中心上の置換基を変えることにより、合成時においてその物性を容易に調整できることから、近年、電解液の候補として新たに注目を集めている。
　本発明者は、構造中にエーテル基を１以上有するカチオン、及びリチウム金属に対して不活性なカウンターアニオンを有するイオン液体を電解液に使用することによって、構造中にエーテル基を有しないカチオンを有するイオン液体を使用した場合よりもリチウムを均一に析出できることを見出し、本発明を完成させた。 In recent years, ionic liquids have low volatility and flammability, and can be easily adjusted in physical properties during synthesis by changing substituents on the cation center. Has attracted new attention as.
The present inventor uses a cation having at least one ether group in the structure and an ionic liquid having a counter anion inert to lithium metal in the electrolyte solution, thereby allowing a cation having no ether group in the structure. It was found that lithium can be deposited more uniformly than in the case of using an ionic liquid having the present invention, and the present invention has been completed.
　本発明においては、カチオンが有するエーテル基がリチウムイオンと相互作用することにより、正極へリチウムイオンを供給しやすくなり、その結果、電池内におけるリチウム金属の析出を抑制することができる。
　このような効果は、後述する実施例に支持されている。実施例の結果より、構造中にエーテル基を１以上有するカチオンを有する電解液（実施例１及び実施例２）は、構造中にエーテル基を有しないカチオンを有する電解液（比較例１及び比較例２）と比較して、リチウムの均一析出時間が数倍長くなることが分かる。
　また、本発明においては、リチウム金属に対して不活性なカウンターアニオンを使用することにより、イオン液体の分解を抑制し、電池の長寿命化を達成することができる。 In this invention, when the ether group which a cation has interacts with lithium ion, it becomes easy to supply lithium ion to a positive electrode, As a result, precipitation of lithium metal in a battery can be suppressed.
Such an effect is supported by Examples described later. From the results of the examples, the electrolyte solutions (Example 1 and Example 2) having a cation having one or more ether groups in the structure are the electrolyte solutions (Comparative Examples 1 and 2) having a cation having no ether group in the structure. It can be seen that the uniform deposition time of lithium is several times longer than in Example 2).
Further, in the present invention, by using a counter anion that is inactive with respect to lithium metal, the decomposition of the ionic liquid can be suppressed and the battery life can be extended.
　本発明に使用されるカチオンは、上述したエーテル基の他に、窒素原子及び炭素数２～１０のアルキル鎖により閉じたヘテロ環構造をさらに有するアンモニウムカチオン、又は、炭素数１～１０の鎖状アルキル基をさらに１以上有するアンモニウムカチオンからなる群から選ばれるカチオンであることが好ましい。このようなカチオンとしては、具体的には、下記一般式（１）又は（２）で表されるカチオンであることがさらに好ましい。 In addition to the ether group described above, the cation used in the present invention is an ammonium cation further having a heterocyclic structure closed by a nitrogen atom and an alkyl chain having 2 to 10 carbon atoms, or a chain shape having 1 to 10 carbon atoms. It is preferably a cation selected from the group consisting of ammonium cations further having one or more alkyl groups. Specifically, such a cation is more preferably a cation represented by the following general formula (1) or (2).
Figure JPOXMLDOC01-appb-C000005
Figure JPOXMLDOC01-appb-C000005
Figure JPOXMLDOC01-appb-C000006
 （上記一般式（１）及び（２）中、Ｒ１～Ｒ６は各々独立に、水素原子及び炭素数１～１０のアルキル基からなる群から選ばれる置換基を表す。また、ｐ、ｑ及びｒは１以上の整数である。）
Figure JPOXMLDOC01-appb-C000006
 (In the general formulas (1) and (2), R 1 to R 6 each independently represents a substituent selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 10 carbon atoms. And r is an integer of 1 or more.)
　上記一般式（１）で表されるカチオンとしては、Ｎ－（２－メトキシエチル）－Ｎ－メチルピペリジニウムカチオン、Ｎ－（２－メトキシプロピル）－Ｎ－メチルピペリジニウムカチオン、Ｎ－（２－メトキシエチル）－Ｎ－メチルピロリジニウムカチオン又はＮ－（２－メトキシプロピル）－Ｎ－メチルピロリジニウムカチオンがより好ましい。また、上記一般式（２）で表されるカチオンとしては、Ｎ，Ｎ－ジエチル－Ｎ－メチル－Ｎ－（２－メトキシエチル）アンモニウムカチオン、Ｎ－エチル－Ｎ，Ｎ－ジメチル－Ｎ－（２－メトキシエチル）アンモニウムカチオン、Ｎ，Ｎ－ジエチル－Ｎ－メチル－Ｎ－（２－メトキシプロピル）アンモニウムカチオン又はＮ－エチル－Ｎ，Ｎ－ジメチル－Ｎ－（２－メトキシプロピル）アンモニウムカチオンがより好ましい。
　これらのカチオンの中でも、Ｎ－（２－メトキシエチル）－Ｎ－メチルピペリジニウムカチオン、又はＮ，Ｎ－ジエチル－Ｎ－メチル－Ｎ－（２－メトキシエチル）アンモニウムカチオンを使用することがさらに好ましい。 Examples of the cation represented by the general formula (1) include N- (2-methoxyethyl) -N-methylpiperidinium cation, N- (2-methoxypropyl) -N-methylpiperidinium cation, N- (2-Methoxyethyl) -N-methylpyrrolidinium cation or N- (2-methoxypropyl) -N-methylpyrrolidinium cation is more preferred. Examples of the cation represented by the general formula (2) include N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation, N-ethyl-N, N-dimethyl-N- ( 2-methoxyethyl) ammonium cation, N, N-diethyl-N-methyl-N- (2-methoxypropyl) ammonium cation or N-ethyl-N, N-dimethyl-N- (2-methoxypropyl) ammonium cation More preferred.
Among these cations, it is further possible to use N- (2-methoxyethyl) -N-methylpiperidinium cation or N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation. preferable.
　本発明に使用されるカウンターアニオンは、リチウム金属に対して不活性であれば特に限定されず、通常イオン液体のアニオン種として使用されるものが挙げられる。
　ここでいうリチウム金属に対して不活性なアニオンとは、当該アニオンを含む電解液にリチウム金属を１００分間浸漬させても化学構造が変化せず、安定なアニオンをいう。一方、リチウム金属に対して活性なアニオンとは、当該アニオンを含む電解液にリチウム金属を１００分間浸漬させることによって分解するアニオンをいう。
　本発明に使用されるカウンターアニオンは、具体的には、［Ｎ（ＣＦ３）２］－、［Ｎ（ＳＯ２ＣＦ３）２］－、［Ｎ（ＳＯ２Ｃ２Ｆ５）２］－等のイミドアニオン；ＲＳＯ３ －（以下、Ｒは脂肪族炭化水素基又は芳香族炭化水素基を指す）、ＲＳＯ４ －、ＲｆＳＯ３ －（以下、Ｒｆは含フッ素ハロゲン化炭化水素基を指す）、ＲｆＳＯ４ －等のスルフェートアニオン又はスルフォネートアニオン；Ｒｆ ２Ｐ（Ｏ）Ｏ－、Ｒｆ ３ＰＦ３ －等のリン酸アニオン；その他、ラクテート、トリフルオロアセテート等が挙げられる。
　これらのアニオンのうち、本発明に使用されるカウンターアニオンは、ビス（トリフルオロメタンスルホニル）イミドイオン（［Ｎ（ＳＯ２ＣＦ３）２］－）であることが好ましい。 The counter anion used for this invention will not be specifically limited if it is inactive with respect to lithium metal, What is normally used as anion seed | species of an ionic liquid is mentioned.
The anion inactive to the lithium metal herein refers to a stable anion that does not change its chemical structure even when the lithium metal is immersed in an electrolytic solution containing the anion for 100 minutes. On the other hand, an anion active against lithium metal refers to an anion that decomposes by immersing lithium metal in an electrolyte containing the anion for 100 minutes.
Specifically, counter anions used in the present invention are [N (CF 3 ) 2 ] − , [N (SO 2 CF 3 ) 2 ] − , [N (SO 2 C 2 F 5 ) 2 ] −. Imide anions such as RSO 3 − (hereinafter R represents an aliphatic hydrocarbon group or aromatic hydrocarbon group), RSO 4 − , R f SO 3 − (hereinafter R f is a fluorine-containing halogenated hydrocarbon group) the point), R f SO 4 -, etc. sulfate anion or sulfonate anion; R f 2 P (O) O -, R f 3 PF 3 - phosphoric acid such as anions like; lactate, trifluoroacetate, etc. Is mentioned.
Of these anions, the counter anion used in the present invention is preferably a bis (trifluoromethanesulfonyl) imide ion ([N (SO 2 CF 3 ) 2 ] − ).
　本発明に使用される電解液は、さらに支持塩としてリチウム塩を含有する。リチウム塩としては、例えばＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣｌＯ４及びＬｉＡｓＦ６等の無機リチウム塩；ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＳＯ２ＣＦ３）２（Ｌｉ－ＴＦＳＩ）、ＬｉＮ（ＳＯ２Ｃ２Ｆ５）２及びＬｉＣ（ＳＯ２ＣＦ３）３等の有機リチウム塩が挙げられる。このようなリチウム塩を２種以上組み合わせて用いてもよい。また、イオン液体に対するリチウム塩の添加量は特に限定されないが、０．１～１．５ｍｏｌ／ｋｇ程度とすることが好ましい。 The electrolytic solution used in the present invention further contains a lithium salt as a supporting salt. Examples of the lithium salt include inorganic lithium salts such as LiPF 6 , LiBF 4 , LiClO 4, and LiAsF 6 ; LiCF 3 SO 3 , LiN (SO 2 CF 3 ) 2 (Li-TFSI), LiN (SO 2 C 2 F 5 ) 2 and organic lithium salts such as LiC (SO 2 CF 3 ) 3 . Two or more such lithium salts may be used in combination. The amount of lithium salt added to the ionic liquid is not particularly limited, but is preferably about 0.1 to 1.5 mol / kg.
　本発明に使用される電解液は、上記イオン液体及びリチウム塩の他に、非水系電解質を含んでいてもよい。
　非水系電解質としては、非水系電解液及び非水ゲル電解質を用いることができる。
　本発明に使用される非水系電解液は、通常、上述したリチウム塩および非水溶媒を含有する。上記非水溶媒としては、例えばエチレンカーボネート（ＥＣ）、プロピレンカーボネート（ＰＣ）、ジメチルカーボネート（ＤＭＣ）、ジエチルカーボネート（ＤＥＣ）、エチルメチルカーボネート（ＥＭＣ）、エチルカーボネート、ブチレンカーボネート、γ－ブチロラクトン、スルホラン、アセトニトリル、１，２－ジメトキシメタン、１，３－ジメトキシプロパン、ジエチルエーテル、テトラヒドロフラン、２－メチルテトラヒドロフランおよびこれらの混合物等を挙げることができる。また、溶存した酸素を効率良く反応に用いることができるという観点から、上記非水溶媒は、酸素溶解性が高い溶媒であることが好ましい。非水系電解液におけるリチウム塩の濃度は、例えば０．５ｍｏｌ／Ｌ～３ｍｏｌ／Ｌの範囲内である。 The electrolytic solution used in the present invention may contain a non-aqueous electrolyte in addition to the ionic liquid and the lithium salt.
As the non-aqueous electrolyte, a non-aqueous electrolyte solution and a non-aqueous gel electrolyte can be used.
The nonaqueous electrolytic solution used in the present invention usually contains the above-described lithium salt and nonaqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl carbonate, butylene carbonate, γ-butyrolactone, sulfolane. , Acetonitrile, 1,2-dimethoxymethane, 1,3-dimethoxypropane, diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and mixtures thereof. Further, from the viewpoint that dissolved oxygen can be efficiently used for the reaction, the non-aqueous solvent is preferably a solvent having high oxygen solubility. The concentration of the lithium salt in the nonaqueous electrolytic solution is, for example, in the range of 0.5 mol / L to 3 mol / L.
　また、本発明に用いられる非水ゲル電解質は、通常、非水系電解液にポリマーを添加してゲル化したものである。例えば、上述した非水系電解液に、ポリエチレンオキシド（ＰＥＯ）、ポリアクリルニトリル（ＰＡＮ）またはポリメチルメタクリレート（ＰＭＭＡ）等のポリマーを添加し、ゲル化することにより、得ることができる。本発明においては、ＬｉＴＦＳＩ（ＬｉＮ（ＣＦ３ＳＯ２）２）－ＰＥＯ系の非水ゲル電解質を用いることが好ましい。 Further, the non-aqueous gel electrolyte used in the present invention is usually a gel obtained by adding a polymer to a non-aqueous electrolyte solution. For example, it can be obtained by adding a polymer such as polyethylene oxide (PEO), polyacrylonitrile (PAN), or polymethyl methacrylate (PMMA) to the non-aqueous electrolyte solution described above and gelling. In the present invention, it is preferable to use a LiTFSI (LiN (CF 3 SO 2 ) 2 ) -PEO-based non-aqueous gel electrolyte.
　図１は、本発明に係るリチウム二次電池の層構成の一例を示す図であって、積層方向に切断した断面を模式的に示した図である。なお、本発明に係るリチウム二次電池は、必ずしもこの例のみに限定されるものではない。
　リチウム二次電池１００は、正極活物質層２及び正極集電体４を備える正極６と、負極活物質層３及び負極集電体５を備える負極７と、正極６及び負極７に挟持される電解液１を有する。
　本発明に係るリチウム二次電池のうち、電解液については上述した通りである。以下、本発明に係るリチウム二次電池の構成要素である、正極、負極、セパレータ、電池ケースについて、詳細に説明する。 FIG. 1 is a diagram showing an example of a layer configuration of a lithium secondary battery according to the present invention, and is a diagram schematically showing a cross section cut in a stacking direction. The lithium secondary battery according to the present invention is not necessarily limited to this example.
The lithium secondary battery 100 is sandwiched between the positive electrode 6 including the positive electrode active material layer 2 and the positive electrode current collector 4, the negative electrode 7 including the negative electrode active material layer 3 and the negative electrode current collector 5, and the positive electrode 6 and the negative electrode 7. An electrolytic solution 1 is included.
Among the lithium secondary batteries according to the present invention, the electrolytic solution is as described above. Hereinafter, the positive electrode, the negative electrode, the separator, and the battery case, which are components of the lithium secondary battery according to the present invention, will be described in detail.
　（正極）
　本発明に係るリチウム二次電池の正極は、好ましくは正極活物質を有する正極活物質層を有するものであり、通常、これに加えて、正極集電体、及び当該正極集電体に接続された正極リードを有するものである。なお、本発明に係るリチウム二次電池がリチウム空気電池である場合には、上記正極の替わりに、空気極層を含む空気極を有する。 (Positive electrode)
The positive electrode of the lithium secondary battery according to the present invention preferably has a positive electrode active material layer having a positive electrode active material, and is usually connected to the positive electrode current collector and the positive electrode current collector. It has a positive electrode lead. In addition, when the lithium secondary battery which concerns on this invention is a lithium air battery, it has an air electrode containing an air electrode layer instead of the said positive electrode.
　（正極活物質層）
　以下、正極として、正極活物質層を有する正極を採用した場合について説明する。
　本発明に用いられる正極活物質としては、具体的には、ＬｉＣｏＯ２、ＬｉＮｉ１／３Ｍｎ１／３Ｃｏ１／３Ｏ２、ＬｉＮｉＰＯ４、ＬｉＭｎＰＯ４、ＬｉＮｉＯ２、ＬｉＭｎ２Ｏ４、ＬｉＣｏＭｎＯ４、Ｌｉ２ＮｉＭｎ３Ｏ８、Ｌｉ３Ｆｅ２（ＰＯ４）３及びＬｉ３Ｖ２（ＰＯ４）３等を挙げることができる。これらの中でも、本発明においては、ＬｉＣｏＯ２を正極活物質として用いることが好ましい。 (Positive electrode active material layer)
Hereinafter, the case where the positive electrode which has a positive electrode active material layer as a positive electrode is employ | adopted is demonstrated.
Specific examples of the positive electrode active material used in the present invention include LiCoO 2 , LiNi 1/3 Mn 1/3 Co 1/3 O 2 , LiNiPO 4 , LiMnPO 4 , LiNiO 2 , LiMn 2 O 4 , LiCoMnO 4. , Li 2 NiMn 3 O 8 , Li 3 Fe 2 (PO 4 ) 3 and Li 3 V 2 (PO 4 ) 3 . Among these, in the present invention, LiCoO 2 is preferably used as the positive electrode active material.
　本発明に用いられる正極活物質層の厚さは、目的とするリチウム二次電池の用途等により異なるものであるが、１０μｍ～２５０μｍの範囲内であるのが好ましく、２０μｍ～２００μｍの範囲内であるのが特に好ましく、特に３０μｍ～１５０μｍの範囲内であることが最も好ましい。 The thickness of the positive electrode active material layer used in the present invention varies depending on the intended use of the lithium secondary battery, but is preferably in the range of 10 μm to 250 μm, and in the range of 20 μm to 200 μm. It is particularly preferred that it is in the range of 30 μm to 150 μm.
　正極活物質の平均粒径としては、例えば１μｍ～５０μｍの範囲内、中でも１μｍ～２０μｍの範囲内、特に３μｍ～５μｍの範囲内であることが好ましい。正極活物質の平均粒径が小さすぎると、取り扱い性が悪くなる可能性があり、正極活物質の平均粒径が大きすぎると、平坦な正極活物質層を得るのが困難になる場合があるからである。なお、正極活物質の平均粒径は、例えば走査型電子顕微鏡（ＳＥＭ）により観察される活物質担体の粒径を測定して、平均することにより求めることができる。 The average particle diameter of the positive electrode active material is, for example, preferably in the range of 1 μm to 50 μm, more preferably in the range of 1 μm to 20 μm, and particularly preferably in the range of 3 μm to 5 μm. If the average particle size of the positive electrode active material is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material is too large, it may be difficult to obtain a flat positive electrode active material layer. Because. The average particle diameter of the positive electrode active material can be determined by measuring and averaging the particle diameter of the active material carrier observed with, for example, a scanning electron microscope (SEM).
　正極活物質層は、必要に応じて導電化材および結着材等を含有していても良い。
　本発明において用いられる正極活物質層が有する導電化材としては、正極活物質層の導電性を向上させることができれば特に限定されるものではないが、例えばアセチレンブラック、ケッチェンブラック等のカーボンブラック等を挙げることができる。また、正極活物質層における導電化材の含有量は、導電化材の種類によって異なるものであるが、通常１質量％～１０質量％の範囲内である。 The positive electrode active material layer may contain a conductive material, a binder, and the like as necessary.
The conductive material included in the positive electrode active material layer used in the present invention is not particularly limited as long as the conductivity of the positive electrode active material layer can be improved. For example, carbon black such as acetylene black and ketjen black Etc. The content of the conductive material in the positive electrode active material layer varies depending on the type of the conductive material, but is usually in the range of 1% by mass to 10% by mass.
　本発明において用いられる正極活物質層が有する結着材としては、例えばポリビニリデンフロライド（ＰＶＤＦ）、ポリテトラフルオロエチレン（ＰＴＦＥ）等を挙げることができる。また、正極活物質層における結着材の含有量は、正極活物質等を固定化できる程度の量であれば良く、より少ないことが好ましい。結着材の含有量は、通常１質量％～１０質量％の範囲内である。 Examples of the binder contained in the positive electrode active material layer used in the present invention include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Further, the content of the binder in the positive electrode active material layer may be an amount that can fix the positive electrode active material or the like, and is preferably smaller. The content of the binder is usually in the range of 1% by mass to 10% by mass.
　（正極集電体）
　本発明において用いられる正極集電体は、上記の正極活物質層の集電を行う機能を有するものである。上記正極集電体の材料としては、例えばアルミニウム、ＳＵＳ、ニッケル、鉄およびチタン等を挙げることができ、中でもアルミニウムおよびＳＵＳが好ましい。また、正極集電体の形状としては、例えば、箔状、板状、メッシュ状等を挙げることができ、中でも箔状が好ましい。 (Positive electrode current collector)
The positive electrode current collector used in the present invention has a function of collecting the positive electrode active material layer. Examples of the material for the positive electrode current collector include aluminum, SUS, nickel, iron, and titanium. Of these, aluminum and SUS are preferable. Moreover, as a shape of a positive electrode electrical power collector, foil shape, plate shape, mesh shape etc. can be mentioned, for example, Foil shape is preferable.
　前記正極及び前記負極のうち少なくとも一方の電極の電極活物質層が、少なくとも電極活物質及び電極用電解質を含有するという構成をとることもできる。この場合、電極用電解質としては、固体酸化物電解質、固体硫化物電解質等の固体電解質や、上述したポリマー電解質、ゲル電解質等を用いることができる。 The electrode active material layer of at least one of the positive electrode and the negative electrode can also be configured to contain at least an electrode active material and an electrode electrolyte. In this case, as the electrode electrolyte, a solid electrolyte such as a solid oxide electrolyte or a solid sulfide electrolyte, the above-described polymer electrolyte, gel electrolyte, or the like can be used.
　本発明に用いられる正極を製造する方法は、上記の正極を得ることができる方法であれば特に限定されるものではない。なお、正極活物質層を形成した後、電極密度を向上させるために、正極活物質層をプレスしても良い。 The method for producing the positive electrode used in the present invention is not particularly limited as long as it is a method capable of obtaining the positive electrode. In addition, after forming a positive electrode active material layer, in order to improve an electrode density, you may press a positive electrode active material layer.
　（空気極層）
　以下、正極として、空気極層を有する空気極を採用した場合について説明する。本発明に用いられる空気極層は、少なくとも導電性材料を含有するものである。さらに、必要に応じて、触媒および結着材の少なくとも一方を含有していても良い。 (Air electrode layer)
Hereinafter, the case where the air electrode which has an air electrode layer as a positive electrode is employ | adopted is demonstrated. The air electrode layer used in the present invention contains at least a conductive material. Furthermore, you may contain at least one of a catalyst and a binder as needed.
　本発明に用いられる空気極層に用いられる導電性材料としては、導電性を有するものであれば特に限定されるものではないが、例えば炭素材料等を挙げることができる。さらに、炭素材料は、多孔質構造を有するものであっても良く、多孔質構造を有しないものであっても良いが、本発明においては、多孔質構造を有するものであることが好ましい。比表面積が大きく、多くの反応場を提供することができるからである。多孔質構造を有する炭素材料としては、具体的にはメソポーラスカーボン等を挙げることができる。一方、多孔質構造を有しない炭素材料としては、具体的にはグラファイト、アセチレンブラック、カーボンナノチューブおよびカーボンファイバー等を挙げることができる。空気極層における導電性材料の含有量としては、例えば６５質量％～９９質量％の範囲内、中でも７５質量％～９５質量％の範囲内であることが好ましい。導電性材料の含有量が少なすぎると、反応場が減少し、電池容量の低下が生じる可能性があり、導電性材料の含有量が多すぎると、相対的に触媒の含有量が減り、充分な触媒機能を発揮できない可能性があるからである。 The conductive material used for the air electrode layer used in the present invention is not particularly limited as long as it has conductivity, and examples thereof include a carbon material. Furthermore, the carbon material may have a porous structure or may not have a porous structure. However, in the present invention, the carbon material preferably has a porous structure. This is because the specific surface area is large and many reaction fields can be provided. Specific examples of the carbon material having a porous structure include mesoporous carbon. On the other hand, specific examples of the carbon material having no porous structure include graphite, acetylene black, carbon nanotube, and carbon fiber. The content of the conductive material in the air electrode layer is, for example, preferably in the range of 65% by mass to 99% by mass, and more preferably in the range of 75% by mass to 95% by mass. If the content of the conductive material is too small, the reaction field may decrease and the battery capacity may be reduced. If the content of the conductive material is too large, the content of the catalyst is relatively reduced and sufficient. This is because it may not be possible to exert a proper catalytic function.
　本発明に用いられる空気極層に用いられる触媒としては、例えばコバルトフタロシアニンおよび二酸化マンガン等を挙げることができる。空気極層における触媒の含有量としては、例えば１質量％～３０質量％の範囲内、中でも５質量％～２０質量％の範囲内であることが好ましい。触媒の含有量が少なすぎると、充分な触媒機能を発揮できない可能性があり、触媒の含有量が多すぎると、相対的に導電性材料の含有量が減り、反応場が減少し、電池容量の低下が生じる可能性があるからである。
　電極反応がよりスムーズに行われるという観点から、上述した導電性材料は触媒を担持していることが好ましい。 Examples of the catalyst used for the air electrode layer used in the present invention include cobalt phthalocyanine and manganese dioxide. The catalyst content in the air electrode layer is, for example, preferably in the range of 1% by mass to 30% by mass, and more preferably in the range of 5% by mass to 20% by mass. If the catalyst content is too low, sufficient catalytic function may not be achieved. If the catalyst content is too high, the content of the conductive material is relatively reduced, the reaction field is reduced, and the battery capacity is reduced. This is because there is a possibility that a decrease in the number of times will occur.
From the viewpoint that the electrode reaction is performed more smoothly, the conductive material described above preferably supports a catalyst.
　上記空気極層は、少なくとも導電性材料を含有してれば良いが、さらに、導電性材料を固定化する結着材を含有することが好ましい。具体的な結着材としては、上述した「正極活物質層」の項に記載したものを用いることができる。空気極層における結着材の含有量としては、特に限定されるものではないが、例えば３０質量％以下、中でも１質量％～１０質量％の範囲内であることが好ましい。 The air electrode layer may contain at least a conductive material, but preferably further contains a binder for fixing the conductive material. As the specific binder, those described in the above-mentioned “positive electrode active material layer” can be used. The content of the binder in the air electrode layer is not particularly limited. For example, it is preferably 30% by mass or less, and more preferably in the range of 1% by mass to 10% by mass.
　上記空気極層の厚さは、空気電池の用途等により異なるものであるが、例えば２μｍ～５００μｍの範囲内、中でも５μｍ～３００μｍの範囲内であることが好ましい。 The thickness of the air electrode layer varies depending on the use of the air battery, but is preferably in the range of 2 μm to 500 μm, and more preferably in the range of 5 μm to 300 μm.
　（空気極集電体）
　本発明に用いられる空気極集電体は、空気極層の集電を行うものである。空気極集電体の材料としては、導電性を有するものであれば特に限定されるものではないが、例えばステンレス、ニッケル、アルミニウム、鉄、チタン、カーボン等を挙げることができる。空気極集電体の形状としては、例えば箔状、板状およびメッシュ（グリッド）状等を挙げることができる。中でも、本発明においては、空気極集電体の形状がメッシュ状であることが好ましい。集電効率に優れているからである。この場合、通常、空気極層の内部にメッシュ状の空気極集電体が配置される。さらに、本発明の二次電池は、メッシュ状の空気極集電体により集電された電荷を集電する別の空気極集電体（例えば箔状の集電体）を有していても良い。また、本発明においては、後述する電池ケースが空気極集電体の機能を兼ね備えていても良い。
　空気極集電体の厚さは、例えば１０μｍ～１０００μｍの範囲内、中でも２０μｍ～４００μｍの範囲内であることが好ましい。 (Air current collector)
The air electrode current collector used in the present invention collects current in the air electrode layer. The material for the air electrode current collector is not particularly limited as long as it has conductivity, and examples thereof include stainless steel, nickel, aluminum, iron, titanium, and carbon. Examples of the shape of the air electrode current collector include a foil shape, a plate shape, and a mesh (grid) shape. Especially, in this invention, it is preferable that the shape of an air electrode electrical power collector is a mesh form. This is because the current collection efficiency is excellent. In this case, usually, a mesh-shaped air electrode current collector is disposed inside the air electrode layer. Furthermore, the secondary battery of the present invention may have another air electrode current collector (for example, a foil-shaped current collector) that collects electric charges collected by the mesh-shaped air electrode current collector. good. In the present invention, a battery case to be described later may also have the function of an air electrode current collector.
The thickness of the air electrode current collector is preferably, for example, in the range of 10 μm to 1000 μm, and more preferably in the range of 20 μm to 400 μm.
　（負極）
　本発明に係るリチウム二次電池中の負極は、好ましくは負極活物質を含有する負極活物質層を有するものであり、通常、これに加えて負極集電体、及び当該負極集電体に接続された負極リードを有するものである。 (Negative electrode)
The negative electrode in the lithium secondary battery according to the present invention preferably has a negative electrode active material layer containing a negative electrode active material, and is usually connected to the negative electrode current collector and the negative electrode current collector in addition to this. The negative electrode lead is provided.
　（負極活物質層）
　本発明に係るリチウム二次電池中の負極層は、負極活物質を含有する。負極活物質層に用いられる負極活物質は、リチウムイオンを吸蔵・放出可能なものであれば特に限定されないが、例えば、金属リチウム、リチウム合金、金属酸化物、金属硫化物、金属窒化物、およびグラファイト等の炭素材料等を挙げることができる。また、負極活物質は、粉末状であっても良く、薄膜状であっても良い。
　リチウム元素を有する合金としては、例えばリチウムアルミニウム合金、リチウムスズ合金、リチウム鉛合金、リチウムケイ素合金等を挙げることができる。また、リチウム元素を有する金属酸化物としては、例えばリチウムチタン酸化物等を挙げることができる。また、リチウム元素を含有する金属窒化物としては、例えばリチウムコバルト窒化物、リチウム鉄窒化物、リチウムマンガン窒化物等を挙げることができる。また、負極層には、固体電解質をコートしたリチウムを用いることもできる。 (Negative electrode active material layer)
The negative electrode layer in the lithium secondary battery according to the present invention contains a negative electrode active material. The negative electrode active material used for the negative electrode active material layer is not particularly limited as long as it can occlude / release lithium ions. For example, metal lithium, lithium alloy, metal oxide, metal sulfide, metal nitride, and Examples thereof include carbon materials such as graphite. The negative electrode active material may be in the form of a powder or a thin film.
Examples of the alloy having a lithium element include a lithium aluminum alloy, a lithium tin alloy, a lithium lead alloy, and a lithium silicon alloy. Moreover, as a metal oxide which has a lithium element, lithium titanium oxide etc. can be mentioned, for example. Examples of the metal nitride containing a lithium element include lithium cobalt nitride, lithium iron nitride, and lithium manganese nitride. Further, lithium coated with a solid electrolyte can also be used for the negative electrode layer.
　また、上記負極層は、負極活物質のみを含有するものであっても良く、負極活物質の他に、導電性材料および結着剤の少なくとも一方を含有するものであっても良い。例えば、負極活物質が箔状である場合は、負極活物質のみを含有する負極層とすることができる。一方、負極活物質が粉末状である場合は、負極活物質および結着剤を有する負極層とすることができる。なお、導電性材料および結着剤については、上述した「空気極」の項に記載した内容と同様であるので、ここでの説明は省略する。
　負極活物質層の膜厚としては、特に限定されるものではないが、例えば１０μｍ～１００μｍの範囲内、中でも１０μｍ～５０μｍの範囲内であることが好ましい。 The negative electrode layer may contain only a negative electrode active material, or may contain at least one of a conductive material and a binder in addition to the negative electrode active material. For example, when the negative electrode active material is in the form of a foil, a negative electrode layer containing only the negative electrode active material can be obtained. On the other hand, when the negative electrode active material is in a powder form, a negative electrode layer having a negative electrode active material and a binder can be obtained. Note that the conductive material and the binder are the same as those described in the section “Air electrode” described above, and thus the description thereof is omitted here.
The thickness of the negative electrode active material layer is not particularly limited, but is preferably in the range of 10 μm to 100 μm, and more preferably in the range of 10 μm to 50 μm.
　（負極集電体）
　負極集電体の材料及び形状としては、上述した正極集電体の材料及び形状と同様のものを採用することができる。 (Negative electrode current collector)
As the material and shape of the negative electrode current collector, the same materials and shapes as those of the positive electrode current collector described above can be employed.
　（セパレータ）
　本発明に係る電池が、正極－電解質－負極の順番で配置されている積層体を、繰り返し何層も重ねる構造を取る場合には、安全性の観点から、異なる積層体に属する正極および負極の間に、セパレータを有することが好ましい。上記セパレータとしては、例えばポリエチレン、ポリプロピレン等の多孔膜；および樹脂不織布、ガラス繊維不織布等の不織布等を挙げることができる。
　セパレータに使用できるこれらの材料は、上述した電解液を含浸させることにより、電解液の支持材として使用することもできる。 (Separator)
When the battery according to the present invention has a structure in which a laminate in which the order of positive electrode-electrolyte-negative electrode is repeatedly stacked, from the viewpoint of safety, the positive electrode and the negative electrode belonging to different laminates are stacked. It is preferable to have a separator in between. Examples of the separator include porous films such as polyethylene and polypropylene; and nonwoven fabrics such as a resin nonwoven fabric and a glass fiber nonwoven fabric.
These materials that can be used for the separator can also be used as a support material for the electrolytic solution by impregnating the above-described electrolytic solution.
　（電池ケース）
　本発明に係るリチウム二次電池は、通常、正極、電解液及び負極等を収納する電池ケースを有する。電池ケースの形状としては、具体的にはコイン型、平板型、円筒型、ラミネート型等を挙げることができる。
　本発明に係る電池がリチウム空気電池である場合には、電池ケースは、大気開放型の電池ケースであっても良く、密閉型の電池ケースであっても良い。大気開放型の電池ケースは、少なくとも空気極層が十分に大気と接触可能な構造を有する電池ケースである。一方、電池ケースが密閉型電池ケースである場合は、密閉型電池ケースに、気体（空気）の導入管および排気管を設けることが好ましい。この場合、導入・排気する気体は、酸素濃度が高いことが好ましく、純酸素であることがより好ましい。また、放電時には酸素濃度を高くし、充電時には酸素濃度を低くすることが好ましい。 (Battery case)
The lithium secondary battery according to the present invention usually has a battery case that houses a positive electrode, an electrolytic solution, a negative electrode, and the like. Specific examples of the shape of the battery case include a coin type, a flat plate type, a cylindrical type, and a laminate type.
When the battery according to the present invention is a lithium-air battery, the battery case may be an open-air battery case or a sealed battery case. An open-air battery case is a battery case having a structure in which at least the air electrode layer can sufficiently come into contact with the atmosphere. On the other hand, when the battery case is a sealed battery case, it is preferable to provide a gas (air) introduction pipe and an exhaust pipe in the sealed battery case. In this case, the gas to be introduced / exhausted preferably has a high oxygen concentration, and more preferably pure oxygen. In addition, it is preferable to increase the oxygen concentration during discharging and decrease the oxygen concentration during charging.
　以下に、実施例及び比較例を挙げて、本発明をさらに具体的に説明するが、本発明は、これらの実施例のみに限定されるものではない。 Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to only these examples.
　１．電解液の調製
　［実施例１］
　下記式（３）で表されるＮ－（２－メトキシエチル）－Ｎ－メチルピペリジニウム　ビス（トリフルオロメタンスルホニル）イミドに、リチウムビス（トリフルオロメタンスルホニル）イミドを０．５ｍｏｌ／ｋｇの濃度となるように溶解させ、実施例１の電解液を調製した。 1. Preparation of electrolyte [Example 1]
N- (2-methoxyethyl) -N-methylpiperidinium bis (trifluoromethanesulfonyl) imide represented by the following formula (3) is mixed with lithium bis (trifluoromethanesulfonyl) imide at a concentration of 0.5 mol / kg. Thus, the electrolyte solution of Example 1 was prepared.
Figure JPOXMLDOC01-appb-C000007
Figure JPOXMLDOC01-appb-C000007
　［実施例２］
　下記式（４）で表されるＮ，Ｎ－ジエチル－Ｎ－メチル－Ｎ－（２－メトキシエチル）アンモニウム　ビス（トリフルオロメタンスルホニル）イミドに、リチウムビス（トリフルオロメタンスルホニル）イミドを０．５ｍｏｌ／ｋｇの濃度となるように溶解させ、実施例２の電解液を調製した。 [Example 2]
N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide represented by the following formula (4) is mixed with 0.5 mol / liter of lithium bis (trifluoromethanesulfonyl) imide. The electrolyte solution of Example 2 was prepared by dissolving to a concentration of kg.
Figure JPOXMLDOC01-appb-C000008
Figure JPOXMLDOC01-appb-C000008
　［比較例１］
　下記式（５）で表されるＮ－メチル－Ｎ－プロピルピペリジニウム　ビス（トリフルオロメタンスルホニル）イミドに、リチウムビス（トリフルオロメタンスルホニル）イミドを０．５ｍｏｌ／ｋｇの濃度となるように溶解させ、比較例１の電解液を調製した。 [Comparative Example 1]
Lithium bis (trifluoromethanesulfonyl) imide is dissolved in N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide represented by the following formula (5) to a concentration of 0.5 mol / kg. Then, an electrolytic solution of Comparative Example 1 was prepared.
Figure JPOXMLDOC01-appb-C000009
Figure JPOXMLDOC01-appb-C000009
　［比較例２］
　下記式（６）で表されるＮ，Ｎ－ジエチル－Ｎ－メチル－Ｎ－プロピルアンモニウム　ビス（トリフルオロメタンスルホニル）イミドに、リチウムビス（トリフルオロメタンスルホニル）イミドを０．５ｍｏｌ／ｋｇの濃度となるように溶解させ、比較例２の電解液を調製した。 [Comparative Example 2]
N, N-diethyl-N-methyl-N-propylammonium bis (trifluoromethanesulfonyl) imide represented by the following formula (6) is mixed with lithium bis (trifluoromethanesulfonyl) imide at a concentration of 0.5 mol / kg. The electrolyte solution of Comparative Example 2 was prepared.
Figure JPOXMLDOC01-appb-C000010
Figure JPOXMLDOC01-appb-C000010
　２．リチウムが均一に析出した時間の比較
　実施例１及び２、並びに比較例１及び２の電解液を、それぞれリチウム／リチウム対称セルに導入し、電流密度０．２ｍＡ／ｃｍ２の条件で、一定時間定電流保持した。一定時間経過後、セル内の正極を取り出し、当該正極表面に析出したリチウム固体の表面を光学顕微鏡にて観察した。同一条件で複数回、一定時間ごとに正極表面の観察を繰り返し、正極表面において均一にリチウムが析出する時間を、その電解液においてリチウムが均一に析出した時間とした。これらの操作は、全てアルゴン雰囲気下で行った。 2. Comparison of time during which lithium was deposited uniformly The electrolytes of Examples 1 and 2 and Comparative Examples 1 and 2 were introduced into a lithium / lithium symmetrical cell, respectively, and the current density was 0.2 mA / cm 2 for a certain period of time. Constant current was maintained. After a certain period of time, the positive electrode in the cell was taken out, and the surface of the lithium solid deposited on the positive electrode surface was observed with an optical microscope. The observation of the positive electrode surface was repeated several times under the same conditions at regular intervals, and the time during which lithium was uniformly deposited on the positive electrode surface was defined as the time during which lithium was uniformly deposited in the electrolyte. All of these operations were performed under an argon atmosphere.
　図２は、実施例１及び実施例２、並びに比較例１及び比較例２の電解液を使用した場合において、リチウムが均一に析出した時間を比較した棒グラフである。図２の縦軸には、リチウムが均一に析出した時間の対数をとった。
　まず、ピペリジン環構造を有するカチオンを有する電解液である実施例１及び比較例１を比較する。図２より、側鎖にエーテル基を１つ有する実施例１の電解液において、リチウムが均一に析出した時間は４２００秒である。これに対し、カチオン構造中にエーテル基を有しない比較例１の電解液において、リチウムが均一に析出した時間は６００秒である。したがって、実施例１は比較例１と比べて、リチウムが均一に析出した時間が７倍長い。
　次に、アルキルアンモニウムカチオンを有する電解液である実施例２及び比較例２を比較する。図２より、側鎖にエーテル基を１つ有する実施例２の電解液において、リチウムが均一に析出した時間は６０秒である。これに対し、カチオン構造中にエーテル基を有しない比較例２の電解液において、リチウムが均一に析出した時間は３０秒である。したがって、実施例２は比較例２と比べて、リチウムが均一に析出した時間が２倍長い。
　これらの結果から、構造中にエーテル基を１以上有するカチオンを有する電解液は、構造中にエーテル基を有しないカチオンを有する電解液と比較して、リチウムが均一に析出した時間が数倍長くなることが分かる。 FIG. 2 is a bar graph comparing the time during which lithium was deposited uniformly in the case where the electrolytic solutions of Examples 1 and 2 and Comparative Examples 1 and 2 were used. The vertical axis of FIG. 2 represents the logarithm of the time during which lithium was deposited uniformly.
First, Example 1 and Comparative Example 1, which are electrolytic solutions having cations having a piperidine ring structure, are compared. From FIG. 2, in the electrolytic solution of Example 1 having one ether group in the side chain, the time for which lithium was uniformly deposited was 4200 seconds. On the other hand, in the electrolytic solution of Comparative Example 1 that does not have an ether group in the cation structure, the time during which lithium is uniformly deposited is 600 seconds. Therefore, in Example 1, the time during which lithium was uniformly deposited was 7 times longer than that in Comparative Example 1.
Next, Example 2 and Comparative Example 2 which are electrolytes having an alkylammonium cation will be compared. From FIG. 2, in the electrolytic solution of Example 2 having one ether group in the side chain, the time during which lithium was uniformly deposited was 60 seconds. On the other hand, in the electrolyte solution of Comparative Example 2 that does not have an ether group in the cation structure, the time during which lithium is uniformly deposited is 30 seconds. Therefore, in Example 2, the time during which lithium was uniformly deposited was twice as long as that in Comparative Example 2.
From these results, the electrolyte solution having a cation having one or more ether groups in the structure is several times longer than the electrolyte solution having a cation having no ether group in the structure. I understand that
　さらに、実施例１は実施例２と比べて、リチウムが均一に析出した時間が７０倍長い。したがって、直鎖のアルキル基のみを有するアンモニウムカチオンよりも、環状構造を有するアンモニウムカチオンの方が、リチウムが均一に析出した時間が長いことが分かる。また、実施例１及び比較例１の比較結果、並びに実施例２及び比較例２の比較結果をさらに比較すると、直鎖のアルキル基のみを有するアンモニウムカチオンよりも、環状構造を有するアンモニウムカチオンの方が、エーテル基を導入することによるリチウムの均一析出の効果が、より著しいことが分かる。 Furthermore, in Example 1, compared with Example 2, the time during which lithium was uniformly deposited was 70 times longer. Therefore, it can be seen that the ammonium cation having a cyclic structure has a longer time for uniformly depositing lithium than the ammonium cation having only a linear alkyl group. Further, when the comparison results of Example 1 and Comparative Example 1 and the comparison results of Example 2 and Comparative Example 2 are further compared, the ammonium cation having a cyclic structure is more than the ammonium cation having only a linear alkyl group. However, it can be seen that the effect of uniform precipitation of lithium by introducing an ether group is more remarkable.
１　電解液
２　正極活物質層
３　負極活物質層
４　正極集電体
５　負極集電体
６　正極
７　負極
１００　リチウム二次電池 DESCRIPTION OF SYMBOLS 1 Electrolytic solution 2 Positive electrode active material layer 3 Negative electrode active material layer 4 Positive electrode collector 5 Negative electrode collector 6 Positive electrode 7 Negative electrode 100 Lithium secondary battery

Claims (4)

  1. 　少なくとも正極と、負極と、当該正極と当該負極との間に介在する電解液とを備えるリチウム二次電池であって、
    　前記負極はリチウム金属を含有し、
    　前記電解液は、カチオン及びそのカウンターアニオンを含むイオン液体、並びにリチウム塩を含有し、
    　前記カチオンは、構造中にエーテル基を１以上有し、
    　前記カウンターアニオンはリチウム金属に対して不活性であることを特徴とする、リチウム二次電池。     A lithium secondary battery comprising at least a positive electrode, a negative electrode, and an electrolyte solution interposed between the positive electrode and the negative electrode,
    The negative electrode contains lithium metal;
    The electrolytic solution contains an ionic liquid containing a cation and its counter anion, and a lithium salt,
    The cation has one or more ether groups in the structure,
    The lithium secondary battery, wherein the counter anion is inert to lithium metal.
  2. 　前記カチオンは、窒素原子及び炭素数２～１０のアルキル鎖により閉じたヘテロ環構造をさらに有するアンモニウムカチオン、並びに、炭素数１～１０の鎖状アルキル基をさらに１以上有するアンモニウムカチオンからなる群から選ばれるカチオンである、請求の範囲第１項に記載のリチウム二次電池。 The cation is selected from the group consisting of an ammonium cation further having a heterocyclic structure closed by a nitrogen atom and an alkyl chain having 2 to 10 carbon atoms, and an ammonium cation further having one or more chain alkyl groups having 1 to 10 carbon atoms. The lithium secondary battery according to claim 1, which is a selected cation.
  3. 　前記カチオンは、下記一般式（１）又は（２）で表されるカチオンである、請求の範囲第１項又は第２項に記載のリチウム二次電池。
    Figure JPOXMLDOC01-appb-C000001
    Figure JPOXMLDOC01-appb-C000002
     （上記一般式（１）及び（２）中、Ｒ１～Ｒ６は各々独立に、水素原子及び炭素数１～１０のアルキル基からなる群から選ばれる置換基を表す。また、ｐ、ｑ及びｒは１以上の整数である。）     The lithium secondary battery according to claim 1 or 2, wherein the cation is a cation represented by the following general formula (1) or (2).
    Figure JPOXMLDOC01-appb-C000001
    Figure JPOXMLDOC01-appb-C000002
     (In the general formulas (1) and (2), R 1 to R 6 each independently represents a substituent selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 10 carbon atoms. And r is an integer of 1 or more.)
  4. 　前記カチオンは、Ｎ－（２－メトキシエチル）－Ｎ－メチルピペリジニウムカチオン、及びＮ，Ｎ－ジエチル－Ｎ－メチル－Ｎ－（２－メトキシエチル）アンモニウムカチオンからなる群から選ばれるカチオンである、請求の範囲第１項乃至第３項のいずれか一項に記載のリチウム二次電池。 The cation is a cation selected from the group consisting of N- (2-methoxyethyl) -N-methylpiperidinium cation and N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium cation. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is any one of claims 1 to 3.
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