JP5487442B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery excellent in rate characteristics and safety.

2. Description of the Related Art In power storage devices such as lithium primary batteries and lithium secondary batteries that have been widely used in recent years, charging and discharging are performed by movement of lithium ions.
Accompanying the miniaturization and high performance of portable devices in which these electricity storage devices are used, energy storage devices are required to have higher energy density and higher output.

Currently, there are many positive electrode active materials for lithium secondary batteries, but the most commonly known one is a lithium cobalt oxide whose operating voltage is around 4 V (vs. Li / Li ⁺ ). It is a lithium-containing transition metal oxide based on (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganese oxide having a spinel structure (LiMn ₂ O ₄ ), or the like. Widely adopted as a positive electrode active material because of its excellent charge / discharge characteristics and energy density.
As the negative electrode active material, carbon materials such as hard carbon, soft carbon, and graphite are widely used, and an electrolytic solution in which LiPF ₆ is dissolved in cyclic and chain carbonates is used.

 However, considering the future expansion to medium-sized and large-sized vehicles, especially HEVs (Hybrid Electric Vehicles), which are expected to have a large demand, the safety and input required for HEV applications in the current small specification The output characteristics cannot be satisfied.

In Patent Document 1, olivine-based lithium iron phosphate (LiFePO ₄ ) having an operating voltage of 4 V (vs. Li / Li ⁺ ) or less is used for the positive electrode active material, and insertion / extraction of Li ions to the negative electrode active material is 1. A battery using lithium titanate performed near 4 to 1.7 V (vs. Li / Li ⁺ ) and using a gel electrolyte as an electrolyte has been reported.

Patent Document 2 discloses that a positive electrode including olivine-based lithium iron phosphate (LiFePO ₄ ) and porous carbon, a negative electrode including lithium titanate and porous carbon, and using a room temperature molten salt as an electrolyte, Devices that combine the characteristics of an ion battery and an electric double layer capacitor have been reported.

JP 2006-179237 A JP 2005-158719 A

However, in the battery described in Patent Document 1, according to the additional test by the present inventors, rate characteristics are inferior to those of carbonate-based electrolytes that are mainly used as electrolytes, and satisfactory rate characteristics are obtained. There wasn't.
In the case of the device described in Patent Document 2, satisfactory rate characteristics were not obtained when the present inventors made additional trials.

  An object of this invention is to provide the lithium ion secondary battery which shows the rate characteristic superior to the lithium ion battery using the carbonate type electrolyte solution generally used.

  As a result of intensive studies to solve the above problems, the inventors of the present invention contain a positive electrode active material whose working potential is lower than 4 V with respect to the metallic lithium potential as the positive electrode, and whose working potential is the metallic lithium potential as the negative electrode. When a mixed solvent of an ether compound having a specific structure and an ion conductive salt is used as an electrolyte in a lithium ion secondary battery containing a negative electrode active material nobler than 1 V, lithium using a conventional electrolyte The present inventors have found that the battery characteristics are superior to those of ion batteries and have completed the present invention.

(1) Lithium comprising a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode comprising a negative electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte In ion secondary batteries,
The positive electrode contains a positive electrode active material whose operating potential is lower than 4 V with respect to the metallic lithium potential;
The negative electrode contains a negative electrode active material having an operating potential nobler than 1 V with respect to a metal lithium potential, and the non-aqueous electrolyte contains at least one ether compound and at least one ion conductive salt, The lithium ion secondary battery, wherein the mixing molar ratio A / B of the ether compound (A) and the ion conductive salt (B) is 0.8 ≦ (A / B) ≦ 5.

(2) The lithium ion secondary battery according to (1), wherein the positive electrode active material is an olivine type lithium iron phosphate represented by a composition formula LiFePO ₄ .

(3) The lithium ion secondary battery according to (1) or (2), wherein the negative electrode active material is spinel type lithium titanate represented by a composition formula Li ₄ Ti ₅ O ₁₂ .

(4) The lithium ion secondary battery according to any one of (1) to (3), wherein the ether compound is an ether compound represented by the following general formula (I).

（一般式（Ｉ）中、Ｒ_１及びＲ_３は、置換基を有していてもよい総炭素数１〜４のアルキル基を示し、Ｒ_１及びＲ_３が同時に同じ基となることはない。Ｒ_２は、主鎖を構成する炭素数が２〜４である総炭素数２〜４のアルキレン基を示し、置換基を有していてもよい。ｎは２〜６の整数である。）

(In general formula (I), R ₁ and R ₃ represent an alkyl group having 1 to 4 carbon atoms which may have a substituent, and R ₁ and R ₃ are not the same group at the same time. R ₂ represents a C 2-4 alkylene group having 2 to 4 carbon atoms constituting the main chain, and may have a substituent, and n is an integer of 2 to 6. )

(5) The ion conductive salt is a lithium salt, and the lithium salt is lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium Bis (trifluoromethanesulfonyl) amide (LiN (SO ₂ CF ₃ ) ₂ ), lithium bis (pentafluoroethanesulfonyl) amide (LiN (SO ₂ C ₂ F ₅ ) ₂ ), and lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) The lithium ion secondary battery according to any one of (1) to (4), which is one or a mixture of two or more selected from the group consisting of.

(6) The lithium ion secondary battery according to (5), wherein the lithium salt is lithium bis (trifluoromethanesulfonyl) amide (LiN (SO ₂ CF ₃ ) ₂ ).

(7) In any one of the above (1) to (6), n in the general formula (I) is 4, R ₁ and R ₃ are methyl groups, and R ₂ is an ethylene group The lithium ion secondary battery as described.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which shows the rate characteristic superior to the secondary battery using the conventional electrolyte solution can be provided.

The lithium ion secondary battery of the present invention includes a positive electrode having a positive electrode active material capable of occluding and releasing lithium ions as a constituent, a negative electrode having a negative electrode active material capable of occluding and releasing lithium ions as a constituent, and non-aqueous In the lithium ion secondary battery comprising an electrolyte, the positive electrode contains a positive electrode active material whose operating potential is lower than 4 V with respect to the metallic lithium potential, and the negative electrode has an operating potential with respect to the metallic lithium potential. A negative electrode active material nobler than 1 V, and the non-aqueous electrolyte contains at least one ether compound and at least one ion conductive salt, the ether compound (A) and the ion conductive salt (B ), The mixing molar ratio A / B is 0.8 ≦ (A / B) ≦ 5.
Below, each element of the lithium ion secondary battery of this invention is demonstrated sequentially.

（一般式（Ｉ）中、Ｒ_１及びＲ_３は、置換基を有していてもよい総炭素数１〜４のアルキル基を示し、Ｒ_１及びＲ_３が同時に同じ基となることはない。Ｒ_２は、主鎖を構成する炭素数が２〜４である総炭素数２〜４のアルキレン基を示し、置換基を有していてもよい。ｎは２〜６の整数である。） [Non-aqueous electrolyte]
(Ether compound)
Examples of the ether compound include dibutyl ether, 1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, glycol ethers (ethyl). Chain ethers such as cellosolve, ethyl carbitol, butyl cellosolve, butyl carbitol); cyclics such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4,4-dimethyl-1,3-dioxane Although ethers are mentioned, Among these, it is preferable that it is a chain | strand-shaped ether compound shown by the following general formula (I).

(In general formula (I), R ₁ and R ₃ represent an alkyl group having 1 to 4 carbon atoms which may have a substituent, and R ₁ and R ₃ are not the same group at the same time. R ₂ represents a C 2-4 alkylene group having 2 to 4 carbon atoms constituting the main chain, and may have a substituent, and n is an integer of 2 to 6. )

In the general formula (I) as the ether compound used in the present invention, R ₁ and R ₃ each represents an alkyl group having 1 to 4 carbon atoms which may have a substituent, and at the same time, Never become. Examples of the substituent include a halogenon group such as fluorine and chlorine, a nitrile group, a ketone group, and an alkenyl group.

Specific examples of the optionally substituted alkyl group having 1 to 4 carbon atoms represented by R ₁ or R ₃ include a methyl group, an ethyl group, an n-propyl group, a sec-propyl group, n -Unsubstituted alkyl group such as butyl group, sec-butyl group, tert-butyl group; fluoroalkyl group such as monofluoromethyl group, trifluoromethyl group, pentafluoroethyl group; trichloromethyl group, 2-chloroethyl group, penta A chloroalkyl group such as a chloroethyl group;

Since the viscosity tends to increase as the number of carbon atoms increases, the ionic conductivity of the alkyl group in which R ₁ or R ₃ is 5 or more is low, which is also an object of the present invention, and is good ion conduction. It becomes difficult to obtain the degree. Therefore, R ₁ and R ₃ are preferably a methyl group or an ethyl group, and more preferably a methyl group.

In the general formula (I), R ₂ is the total number of carbon atoms which may have a substituent is an alkylene group having 2 to 4 carbon atoms constituting the main chain is 2 to 4. The compound having 1 carbon in the main chain in R ₂ has a low stability and tends not to be obtained as a stable compound near room temperature. On the other hand, when the number of carbon atoms in the main chain is 5 or more, not only the chemical stability is lowered but also the ionic conductivity tends to be lowered. R ₂ is particularly preferably one having 2 carbon atoms constituting the main chain.

R ₂ may be substituted if the total carbon number is 2 to 4 (the total carbon number is the number including the carbon atom of the substituent when it has a substituent). If the total number of carbon atoms is 5 or more, the ionic conductivity tends to be insufficient. Examples of the substituent include a halogen group such as an alkyl group, fluorine, and chlorine, an allyl group, an aryl group, an ether group, an ester group, a carboxyl group, and a nitrile group.

R ₂ is preferably an unsubstituted alkylene group such as an ethylene group, trimethylene group or tetramethylene group; an alkyl-substituted alkylene group such as an isopropylene group or isobutylene group, a tetrafluoroethylene group or a 1,1-difluoroethylene group. And fluoroalkylene groups such as hexafluorotrimethylene group; chloroalkylene groups such as tetrachloroethylene group, 1,2-dichloroethylene group and 1,1-dichloroethylene group.

  In the said general formula (I), n shows the integer of 2-6. When n is 1, the flame retardancy effect tends to be hardly obtained. Moreover, when n exceeds 6, there exists a tendency for the viscosity of a nonaqueous electrolyte to become high, and there exists a tendency for the permeability to the electrode of a nonaqueous electrolyte to fall. In addition, the ionic conductivity tends to be low and the rate characteristics tend to decrease. By setting n to an integer of 2 to 6, the number of oxygen atoms in the ether that can interact with the ion conductive salt increases, so that there is a tendency that a flame-retardant effect is easily obtained.

  Specific examples of the ether compound used in the present invention include ethylene such as diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, triethylene glycol dimethyl ether, triethylene glycol ethyl methyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, and hexaethylene glycol dimethyl ether. Examples include glycols, ethylene glycol bis (propiotolyl), diethylene glycol monoethyl ether acetate, 2-ethoxyethyl isobutyrate, and 2- (2-ethoxyethoxy) ethyl acrylate.

  The higher the boiling point or flash point of the ether compound constituting the non-aqueous electrolyte is preferable because the risk of ignition when used as a lithium battery or a lithium ion battery tends to decrease. Therefore, the ether compound used in the present invention preferably has a boiling point of 100 ° C. or higher, and more preferably 200 ° C. or higher. Examples of the ether having a boiling point of 100 ° C. or higher include diethylene glycol dimethyl ether, and examples of the ether having a boiling point of 200 ° C. or higher include triethylene glycol dimethyl ether.

(Ionic conductive salt)
Examples of the ionic conductive salt include a lithium salt, and there is no particular limitation as long as the lithium salt is stable in the operating voltage range of the lithium battery or the lithium ion battery.

Specific examples of the lithium salt used in the present invention include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), and lithium bis (trifluoromethane). Sulfonyl) amide (LiN (SO ₂ CF ₃ ) ₂ ), lithium bis (pentafluoroethanesulfonyl) amide (LiN (SO ₂ C ₂ F ₅ ) ₂ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), and the like. .
These lithium salts can be used singly or in combination of two or more.

  Among these, use of lithium bis (trifluoromethanesulfonyl) amide is desirable because the viscosity of the electrolytic solution is low and the solubility in ether is high.

When the melting point of the mixture of the ether compound and the ion conductive salt is higher than room temperature and is a solid at room temperature (about 25 ° C.), it can be used by dissolving in an organic solvent.
Further, even if the mixture of the ether compound and the ion conductive salt is liquid at room temperature, an organic solvent may be added for the purpose of lowering the viscosity and improving the lithium battery characteristics.

The organic solvent is not particularly limited as long as it can dissolve the ion conductive salt and is stable in the operating voltage range of the lithium battery or the lithium ion battery.
Specific examples of the organic solvent include lactones such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, 3-methyl-1,3-oxazolin-2-one; N-methylformamide, N, N-dimethyl Amides such as formamide, N-methylacetamide, N-methylpyrrolidinone; carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, styrene carbonate, vinylene carbonate; 1,3-dimethyl-2- Examples thereof include imidazolidinones such as imidazolidinone or fluorine-based solvents in which hydrogen atoms or alkyl groups of these various organic solvents are substituted with fluoroalkyl groups.
These non-aqueous organic solvents may be used individually by 1 type, and may be used in mixture of 2 or more types.

  Among them, those having a large dielectric constant, wide electrochemical stability range and use temperature range, and excellent safety are preferable, for example, a mixed solvent containing ethylene carbonate or propylene carbonate as a main component, ethylene carbonate, propylene carbonate, It is preferable to use at least one solvent selected from vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, fluorinated propylene carbonate, fluorinated ethylene carbonate, and fluorinated γ-butyrolactone.

  The method for producing the non-aqueous electrolyte according to the present invention is not particularly limited, but the method for producing the mixture by reacting the ether compound and the ion conductive salt at a specific mixing ratio to facilitate the reaction. To preferred.

  In the present invention, the mixing molar ratio A / B of the ether compound (A) and the ion conductive salt (B) is 0.8 ≦ (A / B) ≦ 5, but 1 ≦ (A / B) ≦ 4. Is preferred. If this ratio is less than 0.8, the viscosity becomes high, the impregnation property to the separator and the electrode is lowered, and the battery performance may not be sufficiently exhibited. If this ratio exceeds 5, the concentration of the ion conductive salt is lowered, the ion conductivity is lowered, the battery performance is lowered, or the ether compound is easily decomposed, although details are unknown, and charging / discharging. Efficiency may be reduced.

In the production of the non-aqueous electrolyte, the reaction temperature and time are not particularly limited. In general, an ether compound, an ion conductive salt, and if necessary an organic solvent are mixed at a temperature below the boiling point of the starting ether compound to be used with stirring, and the reaction is completed in several minutes to several hours. In the invention, the reaction time and the reaction temperature may be adjusted as appropriate.
In addition, in order to confirm that the reaction is completed and a mixture is obtained, the viscosity is confirmed. This can be confirmed by the fact that the viscosity does not change after a certain time.

  The non-aqueous electrolyte preferably has a viscosity of 200000 mPa · s or less, and more preferably 3000 mPa · s. Here, the viscosity refers to a viscosity at 25 ° C. measured using an E-type viscometer (“ELD” manufactured by Tokimec Co., Ltd. (manufactured by Tokyo Keiki Co., Ltd.)). In order to make the viscosity within the above range, it can be achieved by appropriately selecting an ether compound or an ion conductive salt, adjusting a mixing ratio of the ether compound and the ion conductive salt, or adding an organic solvent to the electrolytic solution.

  The above non-aqueous electrolyte is not known in detail as compared with the conventional electrolytes using carbonate-based electrolyte solvents or ambient temperature molten salts as electrolyte solvents, but the battery characteristics at high current density are not known. Especially excellent.

[Positive electrode active material]
In the present invention, as the positive electrode active material contained in the positive electrode, a positive electrode active material capable of occluding and releasing lithium ions and having an operating potential lower than 4 V with respect to the metallic lithium potential is used.

Examples of the positive electrode active material include group I metal compounds such as CuO, Cu ₂ O, Ag ₂ O, CuS and CuSO ₄ , group IV metal compounds such as TiS ₂ , SiO ₂ and SnO, V ₂ O ₅ and V ₆ O. Group V metal compounds such as ₁₂ , VO _x , Nb ₂ O ₅ , Bi ₂ O ₃ and Sb ₂ O ₃ , Group VI metals such as CrO ₃ , Cr ₂ O ₃ , MoO ₃ , MoS ₂ , WO ₃ and SeO ₂ Compound, group VII metal compound such as MnO ₂ , Mn ₂ O ₃ , group VIII metal compound such as Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , CoO, or the general formula Li _x MX ₂ , Li _x MN _y X ₂ (M and N are metals of Group I to VIII, X is a chalcogen compound such as oxygen and sulfur. Further, 0.1 ≦ x ≦ 2, 0 ≦ y ≦ 1 1 ≦ z ≦ 4)), and the like, for example, lithium-cobalt composite oxide and lithium Beam - lithium-containing transition metal oxides such as manganese-based composite oxide, Li _x FePO ₄ and Li _x FeSO ₄ having an olivine structure (0.1 ≦ x ≦ 2), further, disulfide, polypyrrole, polyaniline, polyparaphenylene Examples thereof include, but are not limited to, conductive polymer compounds such as polyacetylene and polyacene-based materials, and pseudo-graphite-structured carbon materials. Among these, a lithium-containing transition metal oxide, Li _x FePO ₄ having an olivine structure is a positive electrode active material having a high operating voltage and capable of releasing lithium, so that a negative electrode capable of occluding lithium at the time of assembly. Easy to combine with active material. Furthermore, Li _x FePO ₄ having an olivine structure is preferable because it has the ability to release lithium even when the end-of-charge voltage is 3.6 V or less.

Li _x FePO ₄ does not release oxygen even at a high temperature, and is preferable from the viewpoint of ensuring safety when the battery reaches an abnormal temperature.

[Negative electrode active material]
In the present invention, the negative electrode uses an electrode composed of a negative electrode active material having an operating potential nobler than 1 V with respect to the metallic lithium potential.

Examples of the negative electrode active material include Group I metal compounds such as CuO, Cu ₂ O, Ag ₂ O, CuS and CuSO ₄ , Group IV metal compounds such as TiS ₂ , SiO ₂ and SnO, V ₂ O ₅ and V ₆ O. Group V metal compounds such as ₁₂ , VO _x , Nb ₂ O ₅ , Bi ₂ O ₃ and Sb ₂ O ₃ , Group VI metals such as CrO ₃ , Cr ₂ O ₃ , MoO ₃ , MoS ₂ , WO ₃ and SeO ₂ Compound, group VII metal compound such as MnO ₂ , Mn ₂ O ₃ , group VIII metal compound such as Fe ₂ O ₃ , FeO, Fe ₃ O ₄ , Ni ₂ O ₃ , NiO, CoO ₃ , CoO, or the general formula Li _x MX ₂ , Li _x MN _y X ₂ (M and N are metals of Group I to VIII, X is a chalcogen compound such as oxygen and sulfur. Further, 0.1 ≦ x ≦ 2, 0 ≦ y ≦ 1 1 is ≦ z ≦ 4.)) represented by like, for example, _{Li y TiO 2, Li 4 +} y Ti 5 O 12, lithium titanate, such as _{i 4 + y Ti 11 O 20} , further disulfide, polypyrrole, polyaniline, polyparaphenylene, polyacetylene, conductive polymer compounds such as polyacene-based material, but pseudo-graphite structure carbon material and the like However, it is not limited to these. Among these, Li _{4 + y} Ti ₅ O ₁₂ has a flat potential of 1.4 to 1.6 V with respect to the lithium potential. Furthermore, most lithium can be occluded at 1.2 V or more with respect to the lithium potential, and the negative electrode active material is suitable for detecting the end-of-charge potential at 1.2 V or more. Li _{4 + y} Ti ₅ O ₁₂ is preferable because, unlike graphite, the crystal distortion associated with insertion and extraction of lithium is small, so that the life of the lithium ion secondary battery can be improved.

The positive electrode active material of the lithium ion secondary battery of the present invention is olivine type lithium iron phosphate represented by the composition formula LiFePO ₄ , and the negative electrode active material is the spinel type titanium represented by the composition formula Li ₄ Ti ₅ O _12. Lithium acid is preferably used.

When producing an electrode for a charging device using an electrode active material, it is preferable to use a conductive aid together with a binder. Examples of the conductive aid used include carbon black such as acetylene black and ketjen black, natural graphite, and the like. Further, metal fibers such as thermally expanded graphite, carbon fiber, conductive carbon, ruthenium oxide, titanium oxide, aluminum, and nickel are used. Among these, acetylene black and ketjen black that can ensure desired conductivity with a small amount of blend are preferable.
In addition, although a conductive support agent is normally mix | blended about 0.5-50 mass% with respect to an electrode active material, it is more preferable to mix | blend 1-30 mass%.

Various publicly known binders can be used as the binder used together with the conductive aid when producing the electrode for the charging device.
For example, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, fluoroolefin copolymer crosslinked polymer, styrene-butadiene copolymer, polyacrylonitrile, polyvinyl alcohol, polyacrylic acid, polyimide, petroleum pitch, coal pitch, phenol resin, etc. Is mentioned.
In the production of the charging device electrode, it is also preferable to use a coating solvent such as N-methylpyrrolidone, N, N-dimethylformamide, dimethylacetamide, water, and alcohols.

  Although the structure of the lithium ion secondary battery of the present invention is not particularly limited, usually, a positive electrode and a negative electrode, and a separator provided as necessary, are wound into a flat spiral to form a wound electrode group, In general, these are laminated as a flat plate to form a laminated electrode plate group, or the electrode plate group is enclosed in an exterior body.

  As the separator, for example, a nonwoven fabric mainly composed of polyolefin such as polyethylene and polypropylene, cloth, microporous film, or a combination thereof can be used. In addition, when it is set as the structure where the positive electrode and negative electrode of the lithium ion secondary battery to produce are not in direct contact, it is not necessary to use a separator.

  Various known separators can also be used as the separator used in the charging device. Specific examples include paper, polypropylene, polyethylene, glass fiber separators, and the like.

  However, when the electrolyte solution has a high viscosity, the use of polypropylene or polyethylene may deteriorate the wettability, so the surface of the polypropylene or polyethylene porous body is made of silane and a pulling agent or resin. By using the treated separator, the wettability to the separator can be improved.

  The lithium ion secondary battery of the present invention is not particularly limited, but is used as a paper-type battery, a button-type battery, a coin-type battery, a laminated battery, a cylindrical battery, a rectangular battery, or the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Example 1]
(Preparation of positive electrode for lithium ion secondary battery)
The positive electrode active material of lithium iron phosphate LiFePO ₄ (Honjo Chemical Co., Ltd., "SLFP-PD 60") and carbon black (Denki Kagaku Kogyo Co., Ltd., "HS-100") and polyvinylidene fluoride as a binder (“PVDF # 1120” manufactured by Kureha Co., Ltd.) and N-methylpyrrolidone (hereinafter, NMP) as a coating solvent, positive electrode active material: carbon black: binder: NMP = 90: 5: 5: 90 (mass) Ratio, however, the binder was mixed at a ratio of solid content) to form a paste, applied to an aluminum current collector foil (manufactured by Nippon Electric Power Industry Co., Ltd., “20CB”), dried at 80 ° C. for 4 hours, It rolled and the positive electrode for lithium ion secondary batteries was obtained. The density of the positive electrode active material layer after rolling was 2.0 g / cm ³ . Note that lithium iron phosphate, which is a positive electrode active material, is a substance having an operating potential of 3.8 V noble with respect to the metallic lithium potential.

(Preparation of negative electrode for lithium ion secondary battery)
30 ml of a 9 mol / L aqueous ammonia solution and 15 ml of pure water were placed in a reaction vessel and cooled with ice so that the temperature of the solution would be 10 to 15 ° C. while stirring. An aqueous titanium chloride solution (45 ml) was added over 2 hours, followed by aging for 1 hour, and the resulting precipitate was filtered and washed with 2 liters of pure water to obtain a titanate compound.

1 mL of 3.7 mol / L lithium hydroxide aqueous solution in a slurry in which 1.5 g of the titanate compound is dispersed in 20 mL of pure water in terms of spray-dried TiO ₂ of a slurry containing a titanate compound and a lithium compound Then, using a mobile minor type spray dryer (manufactured by Niro Co., Ltd.), spray drying was performed under conditions of an inlet temperature of 250 ° C. and an outlet temperature of 110 ° C. to obtain a granulated dried product. The obtained granulated dried product was heat treated in the atmosphere at 725 ° C. for 2 hours to obtain lithium titanate Li ₄ Ti ₅ O ₁₂ as the negative electrode furniture material according to the present invention.

Lithium titanate Li ₄ Ti ₅ O ₁₂ as a negative electrode active material, carbon black, polyvinylidene fluoride as a binder, and N-methylpyrrolidone as a coating solvent: active material: carbon black: binder: NMP = 85: 5: 10 : 90 (mass ratio, but the binder is converted into solid content) into a paste, coated on an aluminum current collector foil, dried at 80 ° C. for 4 hours, rolled and used for lithium ion secondary batteries A negative electrode was obtained. The density of the negative electrode active material after rolling was 1.7 g / cm ³ . Note that lithium titanate, which is a negative electrode active material, is a substance having an operating potential of 1.2 V noble with respect to the lithium metal potential.

(Preparation of non-aqueous electrolyte)
100 g of tetraethylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd.) was distilled under reduced pressure at 90 ° C. Next, 3.77 g (17 mmol) of tetraethylene glycol dimethyl ether was added to 4.85 g (17 mmol) of lithium bis (trifluoromethanesulfonyl) amide (manufactured by Kishida Chemical Co., Ltd.) and stirred at room temperature for 24 hours under an argon atmosphere. A colorless transparent liquid was obtained, and this was designated as non-aqueous electrolyte 1. The reaction was completed and a mixture was obtained by confirming the viscosity. That is, it was confirmed that the viscosity did not change after a certain time.

(Production of lithium ion secondary battery)
Using the positive electrode and the negative electrode, both electrodes were opposed to each other via a separator (“Hypore N8416” manufactured by Asahi Kasei Co., Ltd.). Using the non-aqueous electrolyte 1, a 2016 coin battery having a design capacity of 1 mAh was produced.

(Evaluation of initial battery characteristics)
Charging was performed at a constant current of 0.1 mA and then increased to 2.8 V, and then charged at a constant voltage of 2.8 V. When the current value decreased to 0.01 mA, the charging was terminated. The charge capacity at this time was defined as the initial charge capacity.
Discharging was performed at a constant current of 0.1 mA up to 0.5 V, and the initial charge / discharge capacity was measured. A value obtained by dividing the initial discharge capacity by the initial charge capacity was calculated as the initial charge / discharge efficiency (%). The results are shown in Table 1.

(Evaluation of battery characteristics at 1 mAh)
When charging was performed at a constant current of 0.1 mA and the voltage increased to 2.8 V, charging was performed at a constant voltage of 2.8 V, and charging was terminated when the current value decreased to 0.01 mA.
Discharging was performed at a constant current of 1 mA up to 0.5 V, and the charge / discharge capacity at 1 mA was measured. Further, a value obtained by dividing the discharge capacity at 1 mA by the initial charge capacity was calculated as the capacity maintenance rate (%) at 1 mA. The results are shown in Table 1.

[Example 2]
The same procedure as in Example 1 was performed except that a mixture of 10.1 g (35 mmol) of lithium bis (trifluoromethanesulfonyl) amide and 11.8 g (53 mmol) of tetraethylene glycol dimethyl ether was used as the non-aqueous electrolyte.

[Example 3]
As in Example 1, except that 1.15 g (4.0 mmol) of lithium bis (trifluoromethanesulfonyl) amide and 3.65 g (16.4 mmol) of tetraethylene glycol dimethyl ether were used as the non-aqueous electrolyte. did.

[Example 4]
As a non-aqueous electrolyte, a mixture of 0.60 g (3.95 mmol) of lithium fluorophosphate LiPF ₆ (manufactured by Kishida Chemical Co., Ltd.) and 4.2 g (18.8 mmol) of tetraethylene glycol dimethyl ether was used. Was the same as in Example 1.

[Comparative Example 1]
As the non-aqueous electrolyte, an ethylene carbonate / diethyl carbonate / dimethyl carbonate (volume ratio: 1/1/1) solution (manufactured by Kishida Chemical Co., Ltd.) in which lithium fluoride phosphate LiPF ₆ having a concentration of 1M was dissolved was used. Except for this, the procedure was the same as in Example 1.

[Comparative Example 2]
Nonaqueous electrolysis in which lithium bis (trifluoromethanesulfonyl) amide having a concentration of 0.4 M was dissolved in N-methyl-N-propylpyrrolidinium (manufactured by Kanto Chemical Co., Inc.), which is a room temperature molten salt, as a nonaqueous electrolyte. The procedure was the same as Example 1 except that the liquid was used.

[Comparative Example 3]
The same procedure as in Example 1 was performed except that a mixture of 10.1 g (35 mmol) of lithium bis (trifluoromethanesulfonyl) amide and 5.66 g (25 mmol) of tetraethylene glycol dimethyl ether was used as the non-aqueous electrolyte.

[Comparative Example 4]
The same procedure as in Example 1 was performed except that 1.37 g (4.76 mmol) of lithium bis (trifluoromethanesulfonyl) amide and 5.66 g (25 mmol) of tetraethylene glycol dimethyl ether were used as the non-aqueous electrolyte.

[Comparative Example 5]
Example except that lithium cobalt phosphate LiCoO ₂ (Honjo Chemical Co., Ltd., “Cellseed-10N”) was used instead of lithium iron phosphate LiFePO ₄ as the positive electrode active material, and the operating voltage range of the battery was set to 1 to 3 V. Same as 1. Note that lithium cobaltate, which is a positive electrode active material, is a substance having an operating potential of 4.2 V noble with respect to the lithium metal potential.

[Comparative Example 6]
Example 1 except that lithium manganate LiMn ₂ O ₄ (Honjo Chemical Co., Ltd.) was used instead of lithium iron phosphate LiFePO ₄ as the positive electrode active material, and the operating voltage range of the battery was 1 to 3 V. did. Note that lithium manganate, which is a positive electrode active material, is a substance having an operating potential of 4.2 V noble with respect to the lithium metal potential.

[Comparative Example 7]
A ternary positive electrode material LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ (Honjo Chemical Co., Ltd.) is used instead of lithium iron phosphate LiFePO ₄ as the positive electrode active material, and the operating voltage range of the battery is 1 Same as Example 1 except that it was set to ~ 3V. Note that the ternary positive electrode material, which is a positive electrode active material, is a substance having an operating potential of 4.2 V noble with respect to the lithium metal potential.

[Comparative Example 8]
As in Example 1, except that graphite material MAG-D (manufactured by Hitachi Chemical Co., Ltd.) was used instead of lithium titanate as the negative electrode active material, and the battery operating voltage range was 2.4 to 3.8V. did. In addition, the graphite material which is a negative electrode active material is a substance whose operating potential is 0.02 V noble with respect to the lithium metal potential.

  As shown in Table 1, the lithium ion secondary batteries of the examples have high initial charge and discharge efficiency and excellent initial battery characteristics, and also have excellent battery characteristics in terms of 1 mA discharge rate (discharge capacity retention rate), that is, rate characteristics. Indicated.

Claims (4)

A lithium ion secondary comprising a positive electrode comprising a positive electrode active material capable of occluding and releasing lithium ions, a negative electrode comprising a negative electrode active material capable of occluding and releasing lithium ions, and a non-aqueous electrolyte In batteries,
The positive electrode contains a positive electrode active material that is olivine-type lithium iron phosphate represented by a composition formula LiFePO ₄ ;
The negative electrode contains a negative electrode active material that is a spinel type lithium titanate represented by a composition formula Li ₄ Ti ₅ O ₁₂ , and the non-aqueous electrolyte is at least one of the following general formula (I) It contains an ether compound and at least one ion conductive salt, and the mixing molar ratio A / B of the ether compound (A) and the ion conductive salt (B) is 0.8 ≦ (A / B) ≦ 5. A lithium ion secondary battery characterized by being.

(In General Formula (I), R ₁ and R ₃ represent an alkyl group having 1 to 4 carbon atoms which may have a substituent. R ₂ represents ₂ to 2 carbon atoms constituting the main chain. 4 represents an alkylene group having 2 to 4 carbon atoms in total and may have a substituent. N is an integer of 2 to 6.) The ion conductive salt is a lithium salt, and the lithium salt is lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium bis (trifluoro) From lomethanesulfonyl) amide (LiN (SO ₂ CF ₃ ) ₂ ), lithium bis (pentafluoroethanesulfonyl) amide (LiN (SO ₂ C ₂ F ₅ ) ₂ ), and lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) The lithium ion secondary battery according to claim 1, wherein the lithium ion secondary battery is one or a mixture of two or more selected from the group consisting of: The lithium ion secondary battery according to claim 2 , wherein the lithium salt is lithium bis (trifluoromethanesulfonyl) amide (LiN (SO ₂ CF ₃ ) ₂ ). The lithium ion according to any one of claims 1 to 3 , wherein n in the general formula (I) is 4, R ₁ and R ₃ are methyl groups, and R ₂ is an ethylene group. Secondary battery.