JP6480140B2 - Secondary battery - Google Patents

Description

  The present invention relates to a secondary battery. More specifically, the present invention relates to a technique for suppressing deterioration of an electrolytic solution when a negative electrode active material containing silicon is used.

  In recent years, the development of electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV) has been promoted against the background of the increasing environmental protection movement. A secondary battery that can be repeatedly charged and discharged is suitable as a power source for driving these motors, and a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery that can be expected to have a high capacity and a high output is attracting attention.

The lithium ion secondary battery has a positive electrode active material layer containing a positive electrode active material (for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _2, etc.) formed on the current collector surface. In addition, the non-aqueous electrolyte secondary battery includes a negative electrode active material formed on the surface of the current collector (for example, carbonaceous materials such as metallic lithium, coke and natural / artificial graphite, metals such as silicon and tin, and oxide materials thereof) Etc.).

  In a lithium ion secondary battery, generally, a separator is provided as a partition wall for preventing a short circuit between the positive electrode active material layer and the negative electrode active material layer described above. Then, the power generation element configured as described above is sealed in the exterior body, and the battery is completed by pouring and sealing the electrolyte.

Here, as the electrolytic solution, a solution obtained by dissolving a lithium salt in an organic solvent such as ethylene carbonate or diethyl carbonate has been conventionally used. In the lithium ion secondary battery using such an electrolytic solution, for example, there is a problem that battery characteristics deteriorate when exposed to a high temperature of 200 ° C. or higher. In order to solve such a problem, flame retardant and extremely low volatility glyme (symmetric glycol diether; R—O (CH ₂ CH ₂ O) _n —R) is used as a solvent, and an alkali as a solute is used. There has been proposed a technique for forming an electrolytic solution by dissolving a metal salt (MX). For example, Patent Document 1 discloses an electrolyte solution for a lithium ion secondary battery including a glyme mixture composed of methyltriglyme and methyltetraglyme and a glyme complex composed of lithium ions. According to Patent Document 1, due to the eutectic effect produced by mixing methyltriglyme and methyltetraglyme, oxidative decomposition of the ethylene oxide chain during the charge / discharge reaction is suppressed, and the cycle characteristics of the secondary battery can be improved. It is said that.

JP 2010-287481 A

  However, according to the study by the present inventors, sufficient cycle characteristics cannot be obtained when a secondary battery is configured by combining the electrolytic solution described in Patent Document 1 and a negative electrode active material containing silicon. It has been found that this problem occurs.

  Therefore, an object of the present invention is to provide a means capable of improving cycle characteristics in a secondary battery having a negative electrode active material containing silicon.

  The present inventors have intensively studied to solve the above problems. As a result, the inventors found that the above problem can be solved by setting the ratio of the number of moles of alkali metal salt to the total number of moles of methyltriglyme and methyltetraglyme as a solvent to complete the present invention. I came to let you.

That is, according to one embodiment of the present invention, a positive electrode in which a positive electrode active material layer containing a positive electrode active material capable of occluding and releasing alkali metal ions is formed on the surface of the positive electrode current collector, and silicon on the surface of the negative electrode current collector. There is provided a secondary battery including a power generation element having a negative electrode formed with a negative electrode active material layer containing a negative electrode active material containing, and a separator for holding an electrolytic solution. The electrolytic solution is obtained by dissolving an alkali metal salt (MX) as a solute in methyltriglyme and methyltetraglyme as a solvent. The ratio (M _G / M _x ) between the total number of moles of methyltriglyme and methyltetraglyme (M _G ) and the number of moles of alkali metal (X) (M _x ) in the alkali metal salt (MX) is It is more than 0.9 and less than 1.1.

  According to the present invention, the electrical stability of the electrolytic solution during the charge / discharge reaction can be improved. As a result, it becomes possible to improve the cycle characteristics of the secondary battery.

1 is a schematic cross-sectional view showing a basic configuration of a lithium ion secondary battery that is not a flat type (stacked type) bipolar type according to an embodiment of the present invention.

According to one embodiment of the present invention, a positive electrode in which a positive electrode active material layer containing a positive electrode active material capable of occluding and releasing alkali metal ions is formed on the surface of the positive electrode current collector, and silicon is contained on the surface of the negative electrode current collector Provided is a secondary battery including a power generation element having a negative electrode on which a negative electrode active material layer containing a negative electrode active material is formed and a separator for holding an electrolytic solution. The electrolytic solution is obtained by dissolving an alkali metal salt (MX) as a solute in methyltriglyme and methyltetraglyme as a solvent. The ratio (M _G / M _x ) between the total number of moles of methyltriglyme and methyltetraglyme (M _G ) and the number of moles of alkali metal (X) (M _x ) in the alkali metal salt (MX) is It is more than 0.9 and less than 1.1. Hereinafter, constituent components of the electrolytic solution according to the present embodiment will be described first, and then an embodiment according to a secondary battery that is an application of the electrolytic solution will be described.

<Electrolyte>
The electrolytic solution is formed by dissolving an alkali metal salt (MX) as a solute in methyltriglyme and methyltetraglyme as a solvent.

[solvent]
In this embodiment, a mixed solution of methyltriglyme (hereinafter sometimes abbreviated as “G3”) and methyltetraglyme (hereinafter abbreviated as “G4”) is used as a solvent.

  Methyl triglyme and methyl tetraglyme have the following chemical structures, respectively.

  Thus, by using a mixed solution of methyltriglyme and methyltetraglyme as a solvent, cycle characteristics are significantly improved as compared with the case where either methyltriglyme or methyltetraglyme is used alone. sell. In particular, the effect of improving the cycle characteristics becomes more remarkable when the number of cycles is increased. More specifically, by using a mixed solution of methyltriglyme and methyltetraglyme as a solvent, cycle characteristics can be remarkably improved after 50 cycles, further after 60 cycles, particularly after 80 cycles. Although the mechanism by which the cycle characteristics are improved by using a mixed liquid is not clear, the present inventors presume as follows. According to the study by the present inventors, when attention is paid to the charging process of alkali metal ions (for example, lithium ions) to the silicon-based negative electrode, the case of using methyltetraglyme alone rather than the case of using methyltriglyme alone Gave better results. On the other hand, paying attention to the discharge process, better results were obtained when methyltriglyme was used alone than when methyltetraglyme was used alone. Therefore, when using a mixture of methyltriglyme and methyltetraglyme, it is possible to use active species superior in reaction in each process of charging or discharging, and it is considered that cycle characteristics and battery capacity are improved. .

  The mixing ratio of methyltriglyme and methyltetraglyme is not particularly limited. However, from the viewpoint of further improving the cycle characteristics, the ratio of the number of moles of methyltetraglyme to the total number of moles of methyltriglyme and methyltetraglyme is preferably 10 to 90 mol%, and 20 to 80 mol. % Is more preferable, 30 to 70 mol% is further preferable, 40 to 60 mol% is particularly preferable, and 45 to 55 mol% is most preferable. By setting such a ratio, the cycle characteristics can be further improved. As will be described later, it is also preferable to appropriately set the optimum range of the mixing ratio of methyltriglyme and methyltetraglyme according to the type of alkali metal salt (MX).

[Solute]
In this embodiment, an alkali metal salt (MX) is used as a solute.

The alkali metal (M) in the alkali metal salt (MX) is not particularly limited, and is lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr). Either can be used.
Among these, from the viewpoint of practical use and the abundance of elements, it is preferable to include at least one selected from the group consisting of lithium (Li), sodium (Na), and potassium (K). It is more preferable to contain. These alkali metals (M) may be used alone or in combination of two or more. In the electrolytic solution, the oxygen atom of glyme can coordinate to an alkali metal ion (M ⁺ ) and exist as a complex (complex salt).

On the other hand, X in the alkali metal salt (MX) is not particularly limited, but Cl, Br, I, BF ₄ , and PF _{6 are used} from the viewpoint of the melting point, viscosity, and ionic conductivity of the electrolytic solution that forms a complex structure with glyme. , CF ₃ SO ₃ , ClO ₄ , CF ₃ CO ₂ , AsF ₆ , SbF ₆ , AlCl ₄ , N (FSO ₂ ) ₂ , N (CF ₃ SO ₂ ) ₂ and N (CF ₃ CF ₂ SO ₂ ) ₂ It is preferable to include at least one selected from the group consisting of: Among these, N (CF ₃ SO ₂ ) ₂ and N (FSO ₂ ) ₂ are low in viscosity of the resulting complex structure, have an ionic conductivity exceeding ¹ mS · cm ⁻¹ , and are practical in terms of battery electrolytes. It is particularly suitable because it can sufficiently withstand use. These X may be used individually by 1 type, and may be used in combination of 2 or more type.

Specific examples of the alkali metal salt (MX), for _{example, LiCl, LiBr, LiI, LiBF} 4, LiPF 6, LiCF 3 SO 3, LiClO 4, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, LiN ( FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ and LiN (CF ₃ CF ₂ SO ₂ ) ₂ , NaN (FSO ₂ ) ₂ , NaN (CF ₃ SO ₂ ) ₂ , NaN (CF ₃ CF ₂ SO ₂ ) ₂ , KN (FSO ₂ ) ₂ , KN (CF ₃ SO ₂ ) ₂ , KN (CF ₃ CF ₂ SO ₂ ) _{2, and the} like, but are not limited thereto.

  Note that even an alkali metal salt (MX) developed after the filing of the present application can be included in the technical scope of the present application as long as the claims are satisfied.

The electrolytic solution of this embodiment has a ratio (M _G / M) of the total number of moles (M _G ) of methyltriglyme and methyltetraglyme to the number of moles (M _x ) of alkali metal (X) in the alkali metal salt (MX). It is essential that M _x ) is greater than 0.9 and less than 1.1. Outside this range, the cycle characteristics can be significantly degraded. The reason why the cycle characteristics are lowered when M _G / M _x is out of the above range is not clear, but the present inventors presume as follows. That is, when M _G / M _x is 0.9 or less, an excessive alkali metal salt (MX) that cannot form a complex with glyme is generated in the electrolytic solution, and a strong reducing power is exerted during the charge / discharge reaction. It can be reduced and decomposed into a negative electrode active material made of a silicon-based material. It can be considered that by-products generated at this time gradually accumulate on the surface of the negative electrode, the charge / discharge reaction is hindered, and the cycle characteristics (particularly the long-term cycle characteristics) deteriorate. On the other hand, when _MG / _Mx is 1.1 or more, excessive glyme that cannot form a complex with the alkali metal salt (MX) is generated in the electrolytic solution, and the ethylene oxide chain of the glyme undergoes charge / discharge reaction. It can be oxidatively decomposed. By-products generated by this oxidative decomposition also gradually accumulate in the electrolytic solution, and it is considered that the cycle characteristics are deteriorated by adversely affecting the charge / discharge reaction. In fact, the inventors prepared electrolytes with M _G / M _x = 0.9, 1.0, and 1.1, respectively, and performed each electrolysis by cyclic voltammetry using Li electrodes for both the working electrode and the counter electrode. When the electrochemical stability test of the liquid was performed, the electrolyte solution with M _G / M _x = 0.9 was reduced at a higher potential than the electrolyte solution with M _G / M _x = 1.0. I know it will happen. In addition, a large oxidation peak was observed in the electrolyte solution with M _G / M _x = 1.1, whereas no oxidation peak was observed in the electrolyte solution with M _G / M _x = 1.0. From the above results, it is considered that by making M _G / M _x more than 0.9 and less than 1.1, the electrochemical stability of the electrolytic solution is improved, and as a result, the cycle characteristics in the battery are improved. It was.

As described above, an object of the present invention is to improve cycle characteristics in a secondary battery when a negative electrode active material containing silicon is used. Since the silicon-based negative electrode has a higher reactivity than a conventional carbon-based negative electrode such as graphite, a carbon-based negative electrode is formed when a secondary battery including the silicon-based negative electrode is configured using the electrolytic solution described in Patent Document 1. It is presumed that reductive decomposition of the alkali metal salt that did not occur in this case occurred and sufficient cycle characteristics could not be obtained. In the secondary battery of the present embodiment, it is considered that such reductive decomposition is suppressed and cycle characteristics are improved by setting M _G / M _x of the electrolyte to be more than 0.9 and less than 1.1.

In the electrolytic solution of this embodiment, when X in the alkali metal salt (MX) is N (CF ₃ SO ₂ ) ₂ (for example, when the alkali metal salt (MX) is LiN (CF ₃ SO ₂ ) ₂ ), The ratio of the number of moles of methyltetraglyme (G4) to the total number of moles of methyltriglyme (G3) and methyltetraglyme (G4) is preferably 30 to 70 mol%, and 40 to 60 mol% It is more preferable that When X in the alkali metal salt (MX) is N (FSO ₂ ) ₂ (for example, when the alkali metal salt (MX) is LiN (FSO ₂ ) ₂ ), methyltriglyme (G3) The ratio of the number of moles of methyltetraglyme (G4) to the total number of moles of methyltetraglyme (G4) is preferably 10 to 70% by mole, and more preferably 30 to 60% by mole. By setting it as such a range, cycling characteristics and a battery capacity can be improved further.

  There is no restriction | limiting in particular in the manufacturing method of electrolyte solution (glyme complex), It can manufacture by mixing methyltriglyme, methyltetraglyme, and an alkali metal salt suitably. For example, a method of producing an electrolyte by adding an alkali metal salt to a glyme mixture in which methyltriglyme and methyltetraglyme are previously mixed; a mixture obtained by mixing lithium salt in methyltriglyme, and methyltetraglyme A method for producing an electrolytic solution by mixing a mixture obtained by mixing a lithium salt with methyl tetraglyme and a mixture obtained by mixing a lithium salt with methyltriglyme to produce an electrolytic solution Method: A method in which a mixture obtained by mixing lithium salt with methyltetraglyme and methyltriglyme are mixed to produce an electrolytic solution. The electrolytic solution of this embodiment (glyme complex) can be mentioned by any method. ) Is obtained.

  The conditions for mixing are not particularly limited, but it is preferable to stir and mix as necessary at a temperature of 20 to 80 ° C. until it is homogeneous. Moreover, it is preferable to prepare electrolyte solution in inert gas atmosphere, such as argon, nitrogen, and helium.

  Since moisture in the electrolyte affects the battery reaction, it is important to keep moisture in the inert gas as low as possible, and it is preferable to work at a dew point of −60 ° C. or lower. In particular, the dew point is more preferably −70 ° C. or lower.

  Subsequently, specific embodiments of the secondary battery of the present embodiment in which the above-described electrolyte is used will be described by taking a lithium ion secondary battery as an example. However, the present invention is not limited only to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a cross-sectional view schematically showing a basic configuration of a lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) that is not a flat (stacked) bipolar type according to an embodiment of the present invention. FIG. As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery exterior material 29 that is an exterior body. Have. Here, the power generation element 21 has a configuration in which a positive electrode, a separator 17, and a negative electrode are stacked. In addition, the electrolyte solution mentioned above is injected into the inside of the battery exterior material including the separator 17. The positive electrode has a structure in which the positive electrode active material layers 15 are disposed on both surfaces of the positive electrode current collector 12. The negative electrode has a structure in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 15 and the negative electrode active material layer 13 adjacent thereto face each other with a separator 17 therebetween. Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the stacked battery 10 shown in FIG. 1 has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel.

  In addition, although the negative electrode active material layer 13 is arrange | positioned only in the single side | surface at all the outermost layer negative electrode collectors located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost positive electrode current collector is positioned on both outermost layers of the power generation element 21, and the outermost positive electrode current collector is disposed on one or both surfaces of the outermost layer positive electrode current collector. A positive electrode active material layer may be disposed.

  The positive electrode current collector 12 and the negative electrode current collector 11 are each provided with a positive electrode current collector plate (tab) 27 and a negative electrode current collector plate (tab) 25 that are electrically connected to the respective electrodes (positive electrode and negative electrode). It has the structure led out of the battery exterior material 29 so that it may be pinched | interposed into the edge part. The positive electrode current collector 27 and the negative electrode current collector 25 are ultrasonically welded to the positive electrode current collector 12 and the negative electrode current collector 11 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

  Note that FIG. 1 shows a flat battery (stacked battery) that is not a bipolar battery, but a positive electrode active material layer that is electrically coupled to one surface of the current collector and the opposite side of the current collector. And a bipolar battery including a bipolar electrode having a negative electrode active material layer electrically coupled to the surface. In this case, one current collector also serves as a positive electrode current collector and a negative electrode current collector. Hereinafter, each member will be described in more detail.

[Negative electrode active material layer]
The negative electrode active material layer includes a negative electrode active material. As the negative electrode active material, a silicon-based material (a material containing silicon and capable of functioning as a negative electrode active material by occluding and releasing lithium ions) is essential.

There is no restriction | limiting in particular as a silicon-type material used as a negative electrode active material, A conventionally well-known knowledge can be referred suitably. For example, silicon (Si) single addition, and a silicon oxide such as S iO. One type of negative electrode active material may be sufficient and 2 or more types may be used together.

  In a more preferred embodiment, the negative electrode active material contains silicon (Si) as a main component. In this specification, the “main component” means that the single silicon (Si) capacity in the total capacity of the negative electrode active material contained in the negative electrode active material layer is 50% or more. In other words, it means that the mass of silicon (Si) alone is 10% by mass or more. From the viewpoint that a larger theoretical capacity can be achieved, the mass is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 80% by mass or more, and particularly preferably. It is 90 mass% or more, Most preferably, it is 100 mass%.

In some cases, carbon materials such as graphite (graphite), soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), and metal materials other than silicon-based materials (for example, tin) (Sn) etc.) and other negative electrode active materials other than silicon-based materials may be used in combination.

  The thickness in the stacking direction of the negative electrode active material layer is not particularly limited. However, from the viewpoint of providing a battery having excellent battery characteristics, the thickness is preferably 50 nm to 100 μm, more preferably 100 nm to 100 μm, and still more preferably 100 nm to 50 μm. The negative electrode active material layer can be a thin film made of a silicon-based material. Such a thin film can be formed by vapor-depositing a silicon-based material (for example, silicon alone) as a negative electrode active material on a current collector by a gas phase film forming process. There is no restriction | limiting in particular about the specific form of such a vapor-phase film-forming process, A conventionally well-known method can be employ | adopted suitably. As an example, a vacuum deposition method, a sputtering method (for example, RF sputtering method), a chemical vapor deposition (CVD) method, etc. can be illustrated. According to such a method, the negative electrode active material layer having a uniform thickness can be formed by a simple method.

  Alternatively, the negative electrode active material layer may have the same shape as a conventional general active material layer. That is, the negative electrode active material layer may be in the form of a mixture layer in which a negative electrode active material containing a silicon-based material and additives such as a binder and a conductive additive that are added as necessary are mixed. Thereby, it is possible to create an active material layer by a method similar to a conventional general active material layer creation process. In such a form, there is no restriction | limiting in particular about the size of the negative electrode active material particle which is a particulate active material. For example, from the viewpoint of providing a battery having excellent battery characteristics, the average particle diameter of the particulate negative electrode active material is preferably 1 nm to 100 μm, more preferably 1 nm to 10 μm, and still more preferably. Is 1 to 500 nm. In addition, the negative electrode active material layer of such a form can be produced by the same liquid phase process as a negative electrode active material layer in the form of a conventionally known mixture layer. For example, first, each component (particulate active material and, if necessary, a binder and a conductive aid) constituting the negative electrode active material layer is dispersed in an appropriate amount of solvent (N-methyl-2-pyrrolidone, etc.) Adjust. Subsequently, the negative electrode active material layer can be produced by applying the slurry to a current collector and drying the slurry.

  When the negative electrode active material layer contains a binder, it is preferable to contain an aqueous binder. In addition to the easy procurement of water as a raw material, water-based binders can be greatly reduced in capital investment on the production line and reduced environmental load because it is water vapor that occurs during drying. There is an advantage.

  The water-based binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder using water as a dispersion medium refers to a polymer that includes all expressed as latex or emulsion and is emulsified or suspended in water. For example, a polymer latex that is emulsion-polymerized in a system that self-emulsifies. Kind.

  Specific examples of water-based binders include styrene polymers (styrene-butadiene rubber, styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, (meta ) Acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, polyhexyl acrylate , Polyhexyl methacrylate, polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylauryl meta Relate, etc.), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer , Polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, and saponification degree is preferably 80. Mol% or more, more preferably 90 mol% or more) and a modified product thereof (saponified product of 1 to 80 mol% of vinyl acetate units of a copolymer of ethylene / vinyl acetate = 2/98 to 30/70 mol ratio) The 1 to 50 mol% partially acetalized vinyl alcohol), starch and modified products thereof (oxidized starch, phosphated starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, And their salts), polyvinylpyrrolidone, polyacrylic acid (salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) acrylamide- (Meth) acrylate copolymer, alkyl (meth) acrylate (1 to 4 carbon atoms) ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, polyacrylamide Mannich Denatured body , Formalin condensation type resins (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine or dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soybean protein, synthetic protein, and mannangalactan derivatives Etc. These aqueous binders may be used alone or in combination of two or more.

  The water-based binder may contain at least one rubber-based binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. preferable. Furthermore, it is preferable that the water-based binder contains a styrene-butadiene rubber because the binding property is good.

  When styrene-butadiene rubber is used as the water-based binder, it is preferable to use the water-soluble polymer in combination from the viewpoint of improving coatability. Water-soluble polymers suitable for use in combination with styrene-butadiene rubber include polyvinyl alcohol and modified products thereof, starch and modified products thereof, cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and salts thereof), polyvinyl Examples include pyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Among them, it is preferable to combine styrene-butadiene rubber and carboxymethyl cellulose as a binder. The mass ratio of the styrene-butadiene rubber and the water-soluble polymer is not particularly limited, but is preferably styrene-butadiene rubber: water-soluble polymer = 1: 0.3 to 0.7. .

  When a negative electrode active material layer contains a binder, it is preferable that content of an aqueous binder is 80-100 mass% among the binders used for a negative electrode active material layer, and it is preferable that it is 90-100 mass%, 100 It is preferable that it is mass%. Examples of the binder other than the water-based binder include binders used in the following positive electrode active material layer.

  The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0 with respect to 100% by mass of the total amount of the negative electrode active material layer. It is 0.5-15 mass%, More preferably, it is 1-10 mass%, More preferably, it is 2-4 mass%, Most preferably, it is 2.5-3.5 mass%. Since the water-based binder has high binding power, the active material layer can be formed with a small amount of addition as compared with the organic solvent-based binder.

  The negative electrode active material layer further includes a conductive additive, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and other additives such as a lithium salt for increasing ion conductivity, as necessary.

  The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive auxiliary agent 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.

  Electrolyte salt (lithium salt) will be contained in a negative electrode active material layer because the electrolyte solution mentioned above osmose | permeates a negative electrode active material layer. Therefore, the specific form of the lithium salt that can be contained in the negative electrode active material layer is the same as the lithium salt that constitutes the electrolyte described above.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the negative electrode active material layer and the positive electrode active material layer described later is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

[Positive electrode active material layer]
The positive electrode active material layer contains an active material and, if necessary, other additives such as a conductive additive, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.), and a lithium salt for increasing ionic conductivity. An agent is further included.

The positive electrode active material layer includes a positive electrode active material. Examples of the positive electrode active material include LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and lithium-such as those obtained by replacing some of these transition metals with other elements. Examples include transition metal composite oxides, lithium-transition metal phosphate compounds, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, a lithium-transition metal composite oxide is used as the positive electrode active material from the viewpoint of capacity and output characteristics. More preferably, Li (Ni—Mn—Co) O ₂ and those in which some of these transition metals are substituted with other elements (hereinafter, also simply referred to as “NMC composite oxide”) are used. The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are stacked alternately via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained.

  As described above, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

  As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable that it is excellent in balance between capacity and durability.

  Of course, positive electrode active materials other than those described above may be used.

  The average particle size of the active material contained in the positive electrode active material layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 20 μm from the viewpoint of increasing the output.

  Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (F P), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesin such as polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFP) -TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene Fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine Examples thereof include vinylidene fluoride fluorine rubber such as rubber (VDF-CTFE fluorine rubber), epoxy resin, and the like. These binders may be used independently and may use 2 or more types together.

  The amount of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0.5 to 15% by mass with respect to the active material layer. More preferably, it is 1-10 mass%.

  About other additives other than a binder, the thing similar to the column of the said negative electrode active material layer can be used.

[Separator (electrolyte layer)]
The separator has a function of holding the electrolytic solution to ensure lithium ion conductivity between the positive electrode and the negative electrode, and a function as a partition wall between the positive electrode and the negative electrode.

  Examples of the separator include a porous sheet separator or a nonwoven fabric separator made of a polymer or fiber that absorbs and holds the electrolyte solution.

  As a separator for a porous sheet made of a polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it may be 4 to 60 μm in a single layer or multiple layers. desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

  As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated electrolyte. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  Here, the separator may be a separator in which a heat-resistant insulating layer is laminated on at least one surface of the resin porous substrate. The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the electrical device manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength.

  As described above, in a separator having a structure in which ceramic layers as heat-resistant insulating layers are laminated, the ceramic layer serves as a gas release means for releasing the gas generated inside the power generation element to the outside of the power generation element. Also works.

  Moreover, in this invention, the electrolyte solution mentioned above is hold | maintained in a separator. The above-mentioned electrolytic solution held in the separator may be in the form of a liquid electrolyte or a gel polymer electrolyte. Here, the gel polymer electrolyte has a configuration in which the above-described electrolytic solution is injected into a matrix polymer (host polymer) made of an ion conductive polymer. Using a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block the ion conductivity between the layers. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such polyalkylene oxide polymers, electrolyte salts such as lithium salts can be well dissolved.

  The matrix polymer of gel electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

[Current collector]
There is no particular limitation on the material constituting the current collector, but a metal is preferably used.

  Specifically, examples of the metal include aluminum, nickel, iron, stainless steel, titanium, copper, and other alloys. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. There is no particular limitation on the thickness of the current collector. The thickness of the current collector is usually about 1 to 100 μm.

[Positive electrode current collector and negative electrode current collector]
The material which comprises a current collector plate (25, 27) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. In addition, the same material may be used for the positive electrode current collecting plate 27 and the negative electrode current collecting plate 25, and different materials may be used.

[Positive lead and negative lead]
Moreover, although illustration is abbreviate | omitted, you may electrically connect between the collector 11 and the current collector plates (25, 27) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a tube or the like.

[Battery exterior]
The battery outer body 29 is a member that encloses the power generation element therein, and a bag-like case using a laminate film containing aluminum that can cover the power generation element can be used. As the laminate film, for example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used, but is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV. Moreover, since the group pressure to the electric power generation element applied from the outside can be adjusted easily, the exterior body is more preferably a laminate film containing aluminum.

  The secondary battery such as the lithium ion secondary battery described above can exhibit excellent cycle characteristics by using the electrolytic solution of this embodiment. Therefore, the secondary battery to which the electrolytic solution of this embodiment is applied is suitable as a power supply device for an electric vehicle.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example and a comparative example, this invention is not necessarily limited only to a following example.

<Preparation of electrolyte>
[Comparative Example 1]
Lithium bis (trifluoromethylsulfonyl) imide ([Li] ⁺ [N (CF ₃ SO ₂ ) ₂ ] ⁻ , hereinafter also referred to as “LiTFSI”) as a solute is added to methyltriglyme (G3) as a solvent, The mixture was stirred using a stirrer at 60 ° C. for 24 hours or longer to prepare an electrolytic solution. In this case, to adjust the number of moles _{(M G3)} and the number of moles of Li in LiTFSI _{(M Li)} ratio of _(M G3 _/ M _Li) is the amount added to a 1 methyl triglyme. A series of operations were all performed in a glove box under an argon atmosphere with a dew point of −60 ° C. or lower.

[Comparative Example 2]
An electrolytic solution was prepared in the same manner as in Example 1 except that methyltetraglyme (G4) was used in place of the solvent methyltriglyme (G3). In this case, to adjust the number of moles _{(M G4)} and the number of moles of Li in LiTFSI _{(M Li)} ratio of _(M G4 _/ M _Li) is the amount added to a 1-methyl tetraglyme.

[Comparative Example 3]
The same as Example 1 except that lithium bis (fluorosulfonyl) imide ([Li] ⁺ [N (FSO ₂ ) ₂ ] ⁻ , hereinafter also referred to as “LiFSI”) was used instead of LiTFSI as a solute. The electrolyte solution was prepared by the method. In this case, to adjust the number of moles _{(M G3)} and the number of moles of Li in LiFSI _{(M Li)} ratio of _(M G3 _/ M _Li) is the amount added to a 1 methyl triglyme.

[Comparative Example 4]
An electrolyte solution was prepared in the same manner as in Example 3 except that methyltetraglyme (G4) was used in place of the solvent methyltriglyme (G3). In this case, to adjust the number of moles _{(M G4)} and the number of moles of Li in LiFSI _{(M Li)} ratio of _(M G4 _/ M _Li) is the amount added to a 1-methyl tetraglyme.

[Comparative Example 5]
Except that the number of moles of methyl triglyme _{(M G3)} and the number of moles of Li in LiTFSI _{(M Li)} and a ratio of _(M G3 _/ M _Li) was adjusted the amount so that the 0.9, implemented An electrolyte solution was prepared in the same manner as in Example 1.

[Comparative Example 6]
Except that the number of moles of methyl triglyme _{(M G3)} and the number of moles of Li in LiTFSI _{(M Li)} and a ratio of _(M G3 _/ M _Li) was adjusted to amount to 1.1, performed An electrolyte solution was prepared in the same manner as in Example 1.

[Comparative Example 7]
Except that the number of moles of methyl tetraglyme _{(M G4)} and the number of moles of Li in LiTFSI _{(M Li)} and a ratio of _(M G4 _/ M _Li) was adjusted the amount so that the 0.9, implemented An electrolyte solution was prepared in the same manner as in Example 2.

[Comparative Example 8]
Except that the number of moles of methyl tetraglyme _{(M G4)} and the number of moles of Li in LiTFSI _{(M Li)} and a ratio of _(M G4 _/ M _Li) was adjusted to amount to 1.1, performed An electrolyte solution was prepared in the same manner as in Example 2.

[Example 1]
In the same manner as in Comparative Example 1, solute LiTFSI was added to the solvent methyltriglyme (G3), mixed and stirred using a stirrer for 24 hours or more at 60 ° C., and lithium salt methyltriglyme solvated ion A liquid (Li (G3) TFSI) was prepared. In this case, to adjust the number of moles _{(M G3)} and the number of moles of Li in LiTFSI _{(M Li)} ratio of _(M G3 _/ M _Li) is the amount added to a 1 methyl triglyme. Further, in the same manner as in Comparative Example 2, LiTFSI as a solute was added to methyltetraglyme (G4) as a solvent, and mixed and stirred using a stirrer for 24 hours or more at 60 ° C., and a lithium salt methyltetraglyme solvent. A ionic liquid (Li (G4) TFSI) was prepared. In this case, to adjust the number of moles _{(M G4)} and the number of moles of Li in LiTFSI _{(M Li)} ratio of _(M G4 _/ M _Li) is the amount added to a 1-methyl tetraglyme.

  And the ratio of the number of moles of Li (G3) TFSI is 30 mole% with respect to the total number of moles of Li (G3) TFSI and Li (G4) TFSI, with Li (G3) TFSI and Li (G4) TFSI. The mixture was weighed and mixed and stirred at 60 ° C. for 24 hours or more using a stirrer to prepare an electrolytic solution. A series of operations were all performed in a glove box under an argon atmosphere with a dew point of −60 ° C. or lower.

[Example 2]
An electrolytic solution was prepared in the same manner as in Example 1 except that the ratio of the number of moles of Li (G3) TFSI to the total number of moles of Li (G3) TFSI and Li (G4) TFSI was 50 mole%. .

[Example 3]
An electrolyte solution was prepared in the same manner as in Example 1 except that the ratio of the number of moles of Li (G3) TFSI to the total number of moles of Li (G3) TFSI and Li (G4) TFSI was 70 mole%. .

[Example 4]
In the same manner as in Comparative Example 3, LiFSI as a solute was added to methyltriglyme (G3) as a solvent, mixed and stirred using a stirrer for 24 hours or more at 60 ° C., and lithium salt methyltriglyme solvated ion A liquid (Li (G3) FSI) was prepared. In this case, to adjust the number of moles _{(M G3)} and the number of moles of Li in LiFSI _{(M Li)} ratio of _(M G3 _/ M _Li) is the amount added to a 1 methyl triglyme. Further, in the same manner as in Comparative Example 4, LiFSI as a solute was added to methyltetraglyme (G4) as a solvent, and mixed and stirred using a stirrer for 24 hours or more at 60 ° C., and a lithium salt methyltetraglyme solvent. A ionic liquid (Li (G4) FSI) was prepared. In this case, to adjust the number of moles _{(M G4)} and the number of moles of Li in LiFSI _{(M Li)} ratio of _(M G4 _/ M _Li) is the amount added to a 1-methyl tetraglyme.

  And the ratio of the number of moles of Li (G3) FSI is 10 mol% with respect to the total number of moles of Li (G3) FSI and Li (G4) FSI. The mixture was weighed and mixed and stirred at 60 ° C. for 24 hours or more using a stirrer to prepare an electrolytic solution. A series of operations were all performed in a glove box under an argon atmosphere with a dew point of −60 ° C. or lower.

[Example 5]
An electrolytic solution was prepared in the same manner as in Example 4 except that the ratio of the number of moles of Li (G3) FSI to the total number of moles of Li (G3) FSI and Li (G4) FSI was 30 mol%. .

[Example 6]
An electrolytic solution was prepared in the same manner as in Example 4 except that the ratio of the number of moles of Li (G3) FSI to the total number of moles of Li (G3) FSI and Li (G4) FSI was 50 mol%. .

[Example 7]
An electrolyte solution was prepared in the same manner as in Example 4 except that the ratio of the number of moles of Li (G3) FSI to the total number of moles of Li (G3) FSI and Li (G4) FSI was set to 70 mol%. .

<Production of negative electrode>
First, a nickel foil (thickness 20 μm) was prepared as a negative electrode current collector. Next, an amorphous silicon thin film (thickness: 100 nm) as a negative electrode active material layer was formed on the surface of the nickel foil by RF sputtering to produce a negative electrode.

<Production of evaluation cell>
Two separators (25 μm thick polypropylene porous membrane) were sandwiched between the negative electrode prepared above and a lithium foil as a counter electrode, and the electrolytic solution prepared above was injected into the separator. These laminated bodies were housed in a commercially available HS cell (manufactured by Hosen Co., Ltd.) and sealed with screws to complete an evaluation cell. A series of operations were all performed in a glove box under an argon atmosphere with a dew point of −60 ° C. or lower.

<Evaluation of battery (cycle test)>
A cycle test was evaluated for the evaluation cells prepared using the electrolyte solutions prepared in Examples 1 to 7 and Comparative Examples 1 to 8. Specifically, a cycle test was performed by repeating charging and discharging by energizing a current at a constant rate of 0.5C. Charging was performed by flowing a predetermined current from the open circuit voltage state until the potential difference between the electrodes reached 5 mV. In addition, discharging was performed by flowing a constant current until the potential difference between the electrodes reached 2 V while maintaining a constant current value of 0.5 C rate as in the case of charging. The above evaluation was carried out in a thermostatic chamber kept constant at 30 ° C. Both the charge capacity and the discharge capacity were obtained by integrating the total energization amount in each of the charge process and the discharge process. The cycle test was performed by repeating this charging process and discharging process a predetermined number of times. And the ratio (discharge capacity maintenance ratio%) of the discharge capacity in each cycle when the discharge capacity in the fifth cycle was 100% was calculated. The results are shown in Table 1.

From the results in Table 1, Examples 1 to 7 using a mixed solvent of methyltriglyme and methyltetraglyme and M _G / M _x exceeding 0.9 and less than 1.1 are Comparative Examples 1 to It was shown that the discharge capacity retention rate was higher than 8. When Example 1 is compared with Comparative Example 2, the discharge capacity retention rate of Comparative Example 2 is slightly higher after 30 cycles, but that of Example 2 is significantly higher after 50 cycles. It was shown that.

When Examples 1 to 3 and Comparative Examples 1 and 2 are compared, even if M _G / M _x is constant at 1.0, it is significant that the solvent is a mixed solvent of methyl triglyme and methyltetraglyme. It was found that the discharge capacity retention rate was improved. In particular, when Example 2 and Comparative Examples 1 and 2 are compared, in Comparative Examples 1 and 2, the discharge capacity retention rate decreases significantly as the number of cycles increases, whereas in Example 2, extremely high discharge capacity is maintained. Rukoto has been shown.

Further, from the comparison between Comparative Example 5-8 and Comparative Example _1-2, when the M G / _{M x} 0.9 or 1.1, found that the discharge capacity retention rate after 30 cycles is significantly reduced It was. This was presumed to be caused by a decrease in the electrical stability of the electrolytic solution due to an excess of alkali metal salt or glyme in the electrolytic solution.

10 Lithium ion secondary battery (stacked battery),
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 separator,
19 cell layer,
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 Battery exterior material.

Claims (5)

A positive electrode formed by forming a positive electrode active material layer containing a positive electrode active material capable of occluding and releasing alkali metal ions on the surface of the positive electrode current collector;
A negative electrode in which a negative electrode active material layer containing a negative electrode active material containing silicon alone is formed on the surface of the negative electrode current collector;
A separator for holding an electrolyte solution;
A power generation element having
The electrolytic solution is obtained by dissolving an alkali metal salt (MX) as a solute in methyltriglyme and methyltetraglyme as a solvent,
The ratio (M _G / M _x ) of the total number of moles (M _G ) of methyltriglyme and methyltetraglyme to the number of moles (M _x ) of alkali metal (X) in the alkali metal salt (MX) is: A secondary battery that is greater than 0.9 and less than 1.1. X in the alkali metal salt (MX) is Cl, Br, I, BF ₄ , PF ₆ , CF ₃ SO ₃ , ClO ₄ , CF ₃ CO ₂ , AsF ₆ , SbF ₆ , AlCl ₄ , N (FSO ₂ ). _{2. The} secondary battery according to claim 1, which is at least one selected from the group consisting of ₂ , N (CF ₃ SO ₂ ) ₂ and N (CF ₃ CF ₂ SO ₂ ) ₂ . X in the alkali metal salt (MX) is N (CF ₃ SO ₂ ) ₂ ;
The secondary battery according to claim 1, wherein a ratio of the number of moles of methyltetraglyme to the total number of moles of methyltriglyme and methyltetraglyme is 30 to 70 mol%. X in the alkali metal salt (MX) is N (FSO ₂ ) ₂ ;
The secondary battery according to claim 1, wherein a ratio of the number of moles of methyltetraglyme to the total number of moles of methyltriglyme and methyltetraglyme is 10 to 70 mol%.   The secondary battery according to any one of claims 1 to 4, wherein the alkali metal (M) in the alkali metal salt (MX) is at least one selected from the group consisting of Li, Na, and K.