JP6864033B2 - Dual ion battery - Google Patents

Description

The present invention relates to a dual ion battery.

Conventionally, electric double layer capacitors (EDLC: Electric double-layer capacitors) and lithium ion secondary batteries (LIB: lithium-ion battery) are known as storage devices for storing electric energy. The electric double layer capacitor is superior to the lithium ion secondary battery in that it has a long cycle life, a high charging speed, and a high output density. On the other hand, the lithium ion secondary battery has an advantage that the energy density (volume energy density) is higher than that of the electric double layer capacitor.

Recently, a non-aqueous solvent containing an electrolyte salt is used as an electrolytic solution, a substance capable of occluding and releasing anions of an electrolyte salt is used as a positive electrode active material, and a cation of an electrolyte salt is occluded and released as a negative electrode active material. A power storage device using a releaseable substance is being studied. This power storage device is called a dual ion battery because it occludes and discharges two ions, an anion and a cation of an electrolyte salt, into a positive electrode active material and a negative electrode active material, respectively, to charge and discharge the battery. Dual-ion batteries are attracting attention because they have excellent characteristics such as cycle life, charging speed, and output density as well as electric double layer capacitors, and their energy density is as high as that of lithium-ion secondary batteries.

Patent Document 1 discloses a dual ion battery using a mixed solvent containing ethyl methyl carbonate and cyclic carbonate as a non-aqueous solvent. In the examples of Patent Document 1, graphite is used as the positive electrode active material, lithium titanate is used as the negative electrode active material, and LiPF ₆ is 1.8 mol / L and LiBF ₄ is 0.2 mol / L as the electrolytic solution. Dual ion batteries using a mixed solvent containing in a proportion of L are described.

Japanese Unexamined Patent Publication No. 2018-41636

By the way, the power storage device is generally required to have a high charge / discharge capacity and a long cycle life. Further, in a power storage device used outdoors such as a power storage device for an automobile, it is required that the charge / discharge capacity and the cycle life fluctuate little depending on the environmental temperature.
However, in the conventional dual ion battery, the electrolyte solution and the electrolyte salt are easily decomposed in a high temperature environment in summer, and the cycle life may be shortened. On the other hand, in a low temperature environment in winter, the ionic conductivity of anions and cations may decrease, resulting in a decrease in charge / discharge capacity.

The present invention has been made in view of the above circumstances, and a dual ion battery having a high charge / discharge capacity and a long cycle life, particularly a dual ion battery having a long cycle life in a high temperature environment and a decrease in the charge / discharge capacity in a low temperature environment. It is an object of the present invention to provide a suppressed dual ion battery.

The inventor of the present invention uses graphite as a positive electrode active material and _{spinel-type lithium titanium oxide having a general formula represented by Li 4} Ti ₅ O ₁₂ as a negative electrode active material as an electrolytic solution in a dual ion battery. When a non-aqueous solvent containing lithium hexafluoride phosphate and borate tetrafluoride in a predetermined ratio is used, the cycle life in a high temperature environment is extended, and the decrease in charge / discharge capacity in a low temperature environment is suppressed. The present invention was completed by finding that it was done.

Therefore, in order to solve the above problems, the following means are provided.
[1] An electrolytic solution containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, a positive electrode containing a positive electrode active material capable of storing and releasing anions of the electrolyte salt, and a cation of the electrolyte salt are stored and stored. A dual ion battery including a negative electrode containing a dischargeable negative electrode active material, wherein the positive electrode active material contains graphite, and the negative electrode active material is a spinel type represented by a _{general formula of Li 4} Ti ₅ O _12. The electrolyte salt contains lithium titanium oxide, the electrolyte salt contains lithium hexafluorophosphate and borate tetrafluoride, and the content of the borate tetrafluoride is 1 mol of the lithium hexafluoride phosphate. A dual ion battery characterized in that it is in the range of 0.15 mol or more and 0.60 mol or less.

[2] The tetrafluoroborate is lithium borate tetrafluorate, tetraethylammonium borate tetrafluoride, triethylmethylammonium borate tetrafluorate, spirobipyrrolidinium tetrafluoride, and tetrafluoride. The dual ion battery according to [1], which comprises at least one compound selected from the group consisting of 1-ethyl borate-3-methylimidazolium borate.
[3] The dual ion battery according to [1] or [2], wherein the electrolyte salt further contains at least one of bisoxalatoborate and difluorooxalatoborate.

[4] The dual ion battery according to any one of [1] to [3], wherein the non-aqueous solvent contains at least one compound selected from the group consisting of cyclic carbonate and chain carbonate.
[5] The dual ion battery according to [4], wherein the cyclic carbonate contains at least one compound selected from the group consisting of propylene carbonate and ethylene carbonate.
[6] The dual ion battery according to [4], wherein the chain carbonate contains at least one compound selected from the group consisting of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[7] The positive electrode has a positive electrode current collector, the negative electrode has a negative electrode current collector, and the positive electrode current collector and the negative electrode current collector are plain aluminum material, etched aluminum material, and The dual ion battery according to any one of [1] to [6], which is an aluminum-containing member selected from the group consisting of an aluminum material coated with an amorphous carbon film.

According to the present invention, there is provided a dual ion battery having a high charge / discharge capacity and a long cycle life, particularly a dual ion battery having a long cycle life in a high temperature environment and suppressing a decrease in the charge / discharge capacity in a low temperature environment. It becomes possible to do.

₆ is a graph showing the relationship between the concentration of LiPF 6 and the relative energy density of the electrolytic solution of the coin-type dual ion battery produced in Examples 1 and 9 to 12.

Hereinafter, the dual ion battery according to the embodiment of the present invention will be described. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

The dual ion battery according to the present embodiment includes an electrolytic solution containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, a positive electrode containing a positive electrode active material capable of storing and releasing anions of the electrolyte salt, and an electrolyte salt. It is provided with a negative electrode containing a negative electrode active material capable of storing and releasing the cations of the above.

<Electrolytic solution>
The electrolytic solution contains a non-aqueous solvent and an electrolyte salt. In the dual ion battery of the present embodiment, the anion of the electrolyte salt in the electrolytic solution is stored in the positive electrode active material during charging, the cation of the electrolyte salt in the electrolytic solution is stored in the negative electrode active material, and in the positive electrode active material during discharging. The anion of the above is released into the electrolytic solution, and the cation in the negative electrode active material is released into the electrolytic solution.

[Non-aqueous solvent]
As the non-aqueous solvent, an organic solvent capable of dissolving the electrolyte salt is used. The non-aqueous solvent preferably contains at least one compound selected from the group consisting of cyclic carbonates and chain carbonates. As the cyclic carbonate, propylene carbonate (PC) and ethylene carbonate (EC) can be used. As the chain carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) can be used. These cyclic carbonates and chain carbonates may be used alone or in combination of two or more.

The non-aqueous solvent is preferably one kind or two or more kinds of chain carbonates, or a mixture of chain carbonates and cyclic carbonates, and particularly preferably one kind of chain carbonates. One type of chain carbonate is preferably EMC. The mixture of the chain carbonate and the cyclic carbonate is preferably in the range of 70:30 to 95: 5 (the former: the latter) in terms of mass ratio.

[Electrolyte salt]
In this embodiment, the electrolyte salt comprises lithium hexafluorophosphate (LiPF ₆ ) and borate tetrafluoride (XBF ₄ , X represents a cation).
Lithium hexafluorophosphate is mainly used in the charge / discharge reaction of a dual ion battery. That is, in the dual ion battery of the present embodiment, hexafluoride phosphate ion (PF ₆ ⁻ ) is used as an anion, and lithium ion (Li ⁺ ) is used as a cation. However, according to the study of the present inventor, when lithium hexafluorophosphate is used as the electrolyte salt, gas tends to be easily generated during charging. This is because the water remaining in the positive electrode active material or the water contained in the separator, the electrolytic solution, the negative electrode, etc. and the hexafluoride when charging, that is, when the anionic hexafluorophosphate ion is stored in the positive electrode active material. It is considered that this is because hydrogen fluoride is generated by reacting with phosphate ions, and the hydrogen fluoride generated on the positive electrode side moves to the negative electrode side and decomposes on the negative electrode active material to generate hydrogen gas. ..

On the other hand, borate tetrafluoride has the effect of suppressing the generation of gas during charging. The mechanism by which borate tetrafluoride suppresses the generation of gas is that borate tetrafluoride suppresses the reaction between water and hexafluoride phosphate ions, reducing the amount of hydrogen fluoride generated. it is conceivable that. In order to obtain the effect of suppressing the generation of gas during charging, in the present embodiment, the content of borate tetrafluoride is set to 0.15 mol or more with respect to 1 mol of lithium hexafluoride. It is set within the range of 60 mol or less. The content of borate tetrafluoride with respect to 1 mol of lithium hexafluorophosphate is preferably in the range of 0.2 mol or more and 0.50 mol or less.

The cation of borate tetrafluoride is preferably a monovalent cation. The cation of borate tetrafluoride is particularly preferably lithium ion or quaternary ammonium ion.

The quaternary ammonium ion is preferably represented by the following general formula (1).
N ⁺ R ¹ R ² R ³ R ⁴ ... (1)
In the above general formula (1), R ¹ , R ² , R ³ and R ⁴ independently represent hydrocarbon groups having 1 to 10 carbon atoms. The hydrocarbon group is preferably an alkyl group having 1 to 6 carbon atoms or an aralkyl group having 7 to 10 carbon atoms. The alkyl group may be linear or branched. Further, the two hydrocarbon groups may be bonded to each other via a nitrogen atom which may have a single bond or a substituent to form a ring.

Examples of borate tetrafluoroate are lithium borate tetrafluorate, tetraethylammonium borate tetrafluoride, triethylmethylammonium borate tetrafluoride, spirobipyrrolidinium borate tetrafluoride, and borate tetrafluoride. Examples thereof include 1-ethyl-3-methylimidazolium acid. These tetrafluoride borates may be used alone or in combination of two or more.

The concentration of lithium hexafluorophosphate in the electrolytic solution is preferably in the range of 1.5 mol / L or more and 3.5 mol / L or less, and 2.0 mol / L or more and 3.0 mol / L or less. It is particularly preferable that it is within the following range. By setting the concentration of lithium hexafluorophosphate within the above range, it is possible to further suppress the generation of gas during charging. This is because the anion (PF ₆ ⁻ ) of the electrolyte salt and the cation (Li ⁺ ) form a stable solvation, which reduces the amount of non-aqueous solvent that exists free of charge, which results in the fluoride generated on the positive electrode side. This is considered to be because it becomes difficult for hydrogen to move to the negative electrode side. The concentration of lithium tetrafluoroborate in the electrolytic solution is preferably in the range of 0.23 mol / L or more and 2.0 mol / L or less, and 0.3 mol / L or more and 1.5 mol. It is particularly preferable that it is within the range of / L or less. Further, the total concentration of lithium hexafluorophosphate and lithium tetrafluoroborate in the electrolytic solution is preferably in the range of 1.7 mol / L or more and 5.0 mol / L or less, 2.2. It is particularly preferable that the concentration is in the range of molar / L or more and 4.0 molar / L or less. The concentrations of lithium hexafluorophosphate and lithium tetrafluoroborate are the concentrations in the discharged state. The optimum value of the concentration depends on the type of solvent that dissolves the electrolyte salt.

The electrolyte salt may further contain at least one of bisoxalatoborate and difluorooxalatoborate. These borates have the effect of further suppressing the generation of gas during charging. The cations of bisoxalatoborate and difluorooxalatoborate are preferably monovalent cations. The cation of borate tetrafluoride is particularly preferably lithium ion or quaternary ammonium ion. Examples of quaternary ammonium ions are the same as for borate tetrafluoride.

As the bisoxalatoborate and difluorooxalatoborate, one type may be used alone, or two or more types may be used in combination. The total content of bisoxalate borate and difluorooxalate borate is preferably in the range of 0.01 mol or more and 0.50 mol or less with respect to 1 mol of lithium hexafluorophosphate, and is 0. It is particularly preferable that the amount is in the range of 0.02 mol or more and 0.20 mol or less.

<Positive electrode>
The positive electrode preferably has a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector. The positive electrode active material is contained in the positive electrode active material layer.

[Positive current collector]
As the material of the positive electrode current collector, for example, aluminum, aluminum alloy, copper, copper alloy, stainless steel, nickel, titanium and the like can be used. The shape of the positive electrode current collector may be a foil, a sheet, a film, a mesh, or the like. The thickness of the positive electrode current collector is not particularly limited, but is preferably in the range of 10 μm or more and 40 μm or less. When the thickness of the positive electrode current collector is less than 10 μm, the strength of the positive electrode current collector decreases. On the other hand, when the thickness of the positive electrode current collector exceeds 40 μm, it is necessary to make the thickness of the positive electrode active material layer relatively thin in order to accommodate the battery in a battery case having a predetermined shape, and the dual ion battery is charged and discharged. The capacity may decrease. Further, when the current collector is housed in the battery case, it is desirable that the current collector that does not contribute to the development of battery capacity is thin because it is desired to contain as much active material as possible that contributes to the battery reaction. However, since the strength differs depending on the type of metal, it is preferably within the range of 15 μm or more and 30 μm or less in the case of aluminum or aluminum alloy, and 10 μm or more and 20 μm or less in the case of copper, copper alloy, stainless steel, nickel, or titanium. It is preferable that it is within the range of.

The positive electrode current collector is preferably an aluminum-containing member containing aluminum or an aluminum alloy. As the aluminum-containing member, a plain aluminum material, an etched aluminum material, and an aluminum material coated with an amorphous carbon film can be used.

The plain aluminum material is an aluminum material that has not been subjected to a treatment such as etching. A passivation film, which is a natural oxide film, may be formed on the surface of the plain aluminum material. The passivation membrane itself has the advantage of being less susceptible to erosion by the electrolyte. On the other hand, since the passivation film leads to an increase in the resistance of the current collector, it is preferable not to reduce the resistance of the current collector. The passivation membrane can be removed, for example, by argon sputtering.

The etched aluminum material is roughened by etching. As the etching method, a method of immersing in an acid solution such as hydrochloric acid (chemical etching), a method of electrolyzing aluminum as an anode in an acid solution such as hydrochloric acid (electrochemical etching), and the like are used.

In the aluminum material coated with the amorphous carbon film, a plain aluminum material and an etched aluminum material can be used as the aluminum material as the base material. The aluminum material of the base material is preferably aluminum foil.

The amorphous carbon film that coats the aluminum material has a function of preventing corrosion of the aluminum material during charging and discharging. The amorphous carbon film is preferably an amorphous carbon film or a hydrogenated carbon film. Specific examples of the amorphous carbon film include a diamond-like carbon (DLC) film, a carbon hard film, an amorphous carbon (a-C) film, a hydride amorphous carbon (a-C: H) film, and the like. .. As a method for forming the amorphous carbon film, a known method such as a plasma CVD method using a hydrocarbon gas, a sputtering vapor deposition method, an ion plating method, or a vacuum arc vapor deposition method can be used. The amorphous carbon film preferably has enough conductivity to function as a current collector.

The DLC film is a material having an amorphous structure in which both a diamond bond (sp ³ ) and a graphite bond (sp ² ) are mixed, and is preferable in that it has high chemical resistance. The DLC membrane may be doped with boron or nitrogen to increase conductivity.

The film thickness of the amorphous carbon film is preferably 100 nm or more and 300 nm or less. If the film thickness of the amorphous carbon film is less than 100 nm, the coating effect of the amorphous carbon film may not be sufficiently obtained. If the film thickness of the amorphous carbon film exceeds 300 nm, the amorphous carbon film may become a resistor and the resistance between the aluminum material and the positive electrode active material layer may increase. The thickness of the amorphous carbon film is more preferably in the range of 120 nm or more and 300 nm or less, and further preferably in the range of 150 nm or more and 300 nm or less.

[Positive electrode active material layer]
The positive electrode active material layer preferably contains a positive electrode active material, a binder, and a conductive material. The content of the positive electrode active material, the binder and the conductive material in the positive electrode active material layer is preferably in the range of 70% by mass or more and 95% by mass or less for the positive electrode active material, and 2% by mass or more and 25% by mass or less for the binder. It is within the range, and the conductive material is within the range of 2% by mass or more and 25% by mass or less.

The positive electrode active material used in this embodiment contains graphite.
The graphite may be natural graphite or artificial graphite. One type of graphite may be used alone, or two or more types may be used in combination. As the natural graphite, scaly natural graphite and earth-like natural graphite can be used. As the artificial graphite, scaly artificial graphite, massive artificial graphite, and spherical artificial graphite can be used. Further, graphite may be coated with a carbon material.

The crystal structure of graphite is roughly divided into hexagonal crystals having a layered structure made of ABAB and rhombohedral crystals having a layered structure made of ABCABC. In this embodiment, both graphite having hexagonal crystals and graphite having rhombohedral crystals can be used. For example, as graphite having hexagonal crystals, mesocarbon microbeads (MCMB) manufactured by Osaka Gas Chemical Co., Ltd. can be mentioned. Examples of graphite having rhombohedral crystals include KS-6 (trade name) manufactured by Imerys GC Japan Co., Ltd.

As the binder, for example, fluororesin, rubber, acrylic resin, olefin resin, carboxymethyl cellulose (CMC) resin, and natural polymer can be used. Examples of the fluororesin include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Examples of rubber include fluororubber, ethylene propylene diene rubber, and styrene butadiene rubber. Examples of natural polymers include gelatin, chitosan and alginic acid. These binders may be used alone or in combination of two or more.

As the conductive material, for example, carbon black or carbon fiber can be used. Examples of carbon fibers include carbon nanotubes (CNT) and VGCF®. The carbon nanotubes may be single-walled carbon nanotubes or multi-walled carbon nanotubes. These conductive materials may be used alone or in combination of two or more.

[Cathode manufacturing method]
The positive electrode can be produced, for example, by applying a paste for forming a positive electrode active material layer in which a positive electrode active material, a binder, and a conductive material are dispersed in a solvent to the surface of a positive electrode current collector and drying the positive electrode. As the solvent for the paste for forming the positive electrode active material layer, an organic solvent such as N-methylpyrrolidone or dimethyl sulfoxide can be used. The method for applying the paste for forming the positive electrode active material layer is not particularly limited, and for example, it can be applied using a coating device such as a doctor blade, a die coater, a bar coater, or a roll coater.

<Negative electrode>
The negative electrode preferably has a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector. The negative electrode active material is contained in the negative electrode active material layer.

[Negative electrode current collector]
As the negative electrode current collector, those exemplified by the positive electrode current collector can be used.

[Negative electrode active material layer]
The negative electrode active material layer preferably contains a negative electrode active material, a binder, and a conductive material. The content of the negative electrode active material, the binder and the conductive material in the negative electrode active material layer is preferably in the range of 70% by mass or more and 95% by mass or less for the negative electrode active material, and 2% by mass or more and 25% by mass or less for the binder. It is within the range, and the conductive material is within the range of 2% by mass or more and 25% by mass or less.

The negative electrode active material used in this embodiment contains a spinel-type lithium titanium oxide whose _{general formula is represented by Li 4} Ti ₅ O _12.

As the binder, for example, fluororesin, rubber, acrylic resin, olefin resin, carboxymethyl cellulose (CMC) resin, and natural polymer can be used. Examples of fluororesin, rubber, and natural polymer are the same as in the case of a cathode binder.

As the conductive material, for example, carbon black or carbon fiber can be used. The example of carbon fiber is the same as that of the conductive material of the positive electrode.

[Manufacturing method of negative electrode]
The negative electrode can be manufactured, for example, by applying a paste for forming a negative electrode active material layer in which a negative electrode active material, a binder, and a conductive material are dispersed in a solvent to the surface of a negative electrode current collector and drying the negative electrode. The example of the solvent of the paste for forming the negative electrode active material layer is the same as that of the paste for forming the positive electrode active material layer. The example of the method of applying the paste for forming the negative electrode active material layer is the same as that of the paste for forming the positive electrode active material layer.

<Dual-ion battery configuration>
The configuration of the dual ion battery of the present embodiment is not particularly limited, and may be a known configuration adopted as a configuration of a power storage device such as a coin type, a button type, a sheet type, a cylindrical type, or a square type.

In the coin-type, button-type, and sheet-type dual-ion batteries, a laminate in which a positive electrode and a negative electrode are laminated with a separator so that the positive electrode active material layer and the negative electrode active material layer face each other is formed together with an electrolytic solution. It is a battery having a configuration in which it is housed in a battery case and sealed. As the separator, for example, a porous membrane, a non-woven fabric, or paper can be used. As the porous membrane, a porous membrane made of polyolefin such as polyethylene or polypropylene or a porous membrane made of fluororesin can be used. As the non-woven fabric, a polypropylene non-woven fabric, a cellulose non-woven fabric, or a glass fiber non-woven fabric can be used.

A cylindrical or square dual-ion battery is a battery in which a winding body in which a positive electrode and a negative electrode are wound with a separator so that a positive electrode active material layer and a negative electrode active material layer face each other is wound together with an electrolytic solution. It is a battery that is housed in a case and sealed. As the separator, a porous membrane, a non-woven fabric, or paper can be used.

According to the dual ion battery of the present embodiment, the electrolyte salt contains lithium hexafluorophosphate and borate tetrafluoride, and the content of borate tetrafluoride is lithium hexafluorophosphate 1. Since it is in the range of 0.15 mol or more and 0.60 mol or less with respect to the molar, gas generation during charging is suppressed. By suppressing the generation of gas during charging, the cycle life of the dual ion battery, particularly the cycle life in a high temperature environment, is improved. Further, since the concentration of the electrolyte salt is high and the ratio of the solvent in the electrolytic solution is relatively low, the influence of solvation of anions and cations is reduced. This facilitates the movement of anions and cations in the electrolytic solution even at low temperatures. Further, LiBF ₄ forms a film containing boron on the surface of the negative electrode active material (Li ₄ Ti ₅ O ₁₂ ), and the negative electrode active material easily occludes and releases lithium ions even at a low temperature through this film. .. As a result, a decrease in charge / discharge capacity in a low temperature environment is suppressed.

In particular, in the dual ion battery of the present embodiment, the electrolyte salt further contains at least one of bisoxalatoborate and difluorooxalatoborate, so that the generation of gas during charging is further suppressed. This further improves the cycle life of the dual ion battery, especially in high temperature environments.

<Example 1>
[Cathode preparation]
80 parts by mass of graphite powder (KS-6 manufactured by Imeris GC Japan Co., Ltd.) as the positive electrode active material, 10 parts by mass of acetylene black as the conductive material, and 10 parts by mass of polyvinylidene fluoride as the binder. Mixed. The obtained mixture was put into 280 parts by mass of N-methylpyrrolidone and stirred and mixed to prepare a paste for forming a positive electrode active material layer.

As the positive electrode current collector, a DLC-coated aluminum foil in which an aluminum foil (thickness: 20 μm, purity: 99.99%) was coated with a DLC film (thickness: 160 nm) was prepared. The above-mentioned paste for forming a positive electrode active material layer is applied to the surface of this DLC-coated aluminum foil using a doctor blade and dried to prepare a positive electrode having a positive electrode active material layer formed on the surface of a positive electrode current collector. did. The thickness of the obtained positive electrode was measured using a micrometer and found to be 62 μm.

[Preparation of negative electrode]
_{80 parts by mass of Li 4} Ti ₅ O ₁₂ (spinel-type lithium titanium oxide) was mixed as the negative electrode active material, 10 parts by mass of acetylene black was mixed as the conductive material, and 10 parts by mass of polyvinylidene fluoride was mixed as the binder. .. The obtained mixture was put into 230 parts by mass of N-methylpyrrolidone and mixed by stirring to prepare a paste for forming a negative electrode active material layer. In Li ₄ Ti ₅ O ₁₂ , lithium carbonate and anatase-type titanium oxide were mixed at a ratio of lithium and titanium in a chemical quantity theory ratio of 4: 5, and then the obtained mixture was used in a muffle furnace. The temperature was raised to 800 ° C. at a heating rate of 10 ° C./min, held at this temperature for 5 hours, and then naturally cooled to room temperature for synthesis.

An aluminum foil (thickness: 20 μm, purity: 99.99%) was prepared as a negative electrode current collector. The above-mentioned paste for forming a negative electrode active material layer was applied to the surface of this aluminum foil using a doctor blade and dried to prepare a negative electrode having a negative electrode active material layer formed on the surface of a negative electrode current collector. The thickness of the obtained negative electrode was measured using a micrometer and found to be 48 μm.

[Preparation of electrolyte]
Ethyl methyl carbonate (EMC) was prepared as a non-aqueous solvent. _{Lithium hexafluorophosphate (LIPF 6} ) and lithium tetrafluoroboate (LiBF ₄ ) are added to this EMC as electrolyte salts, _{the concentration of LIPF 6} is 2 mol / L, and _{the concentration of LiBF 4} is 1 mol / mol. An electrolytic solution was prepared by dissolving the mixture so as to be L.

[Manufacturing a coin-type dual-ion battery]
The obtained positive electrode was punched into a disk shape having a diameter of 16 mm and the obtained negative electrode having a diameter of 14 mm, and vacuum dried at 150 ° C. for 24 hours. After that, it was moved to the argon glove box. The dried positive electrode and negative electrode were laminated via a paper separator (trade name: TF4425) manufactured by Nippon Kodoshi Paper Industry Co., Ltd. so that the positive electrode active material layer and the negative electrode active material layer face each other. The obtained laminate and the above electrolytic solution were housed in a coin-type battery case and sealed to prepare a coin-type dual-ion battery.

[Manufacturing of laminated dual-ion battery]
The obtained positive electrode and negative electrode were cut into a width of 30 mm and a length of 60 mm, and aluminum tabs were welded to each of the positive electrode and the negative electrode by ultrasonic welding, and then dried at 120 ° C. for 12 hours in a vacuum dryer. The dried positive electrode and negative electrode are laminated in a dry room with a dew point of −45 ° C. via a paper separator (trade name: TF4425) manufactured by Nippon Kodoshi Paper Industry Co., Ltd., and the positive electrode, separator and negative electrode are arranged in this order. A laminated electrode group was obtained. At this time, it was fastened with Kapton (registered trademark) tape so that the separator would not come loose. This was placed in a bag-shaped container made of a laminated film having a width of 50 mm and a height of 80 mm, and 1.5 mL of an electrolytic solution was injected. Finally, a bag-shaped container was sealed using a sealer T-230K manufactured by Fuji Impulse Co., Ltd. to prepare a laminated dual-ion battery.

<Example 2>
A coin-type dual-ion battery and a laminated-type dual-ion battery were produced in the same manner as in Example 1 except that the concentration of LiBF _{4 in the electrolytic solution was 0.4 mol / L.}
<Example 3>
The coin-type dual-ion battery and the laminated-type dual-ion battery were further dissolved in the electrolytic solution in the same manner as in Example 1 except that lithium bisoxalateborate (LiBOB) was further dissolved so as to have a concentration of 0.1 mol / L. A battery was made.

<Example 4>
A coin-type dual-ion battery and a laminated-type dual were further dissolved in the electrolytic solution in the same manner as in Example 1 except that lithium difluorooxalateborate (LiDFOB) was further dissolved so as to have a concentration of 0.1 mol / L. An ion battery was manufactured.

<Example 5>
The same method as in Example 1 was used except that a mixed solvent containing ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) in a volume ratio of 70:30 was used as the non-aqueous solvent of the electrolytic solution. A coin-type dual-ion battery and a laminated-type dual-ion battery were manufactured.

<Example 6>
The same method as in Example 1 was used except that a mixed solvent containing ethyl methyl carbonate (EMC) and propylene carbonate (PC) in a volume ratio of 90:10 was used as the non-aqueous solvent of the electrolytic solution. A coin-type dual-ion battery and a laminated-type dual-ion battery were manufactured.

<Example 7>
The same method as in Example 1 was used except that a mixed solvent containing ethyl methyl carbonate (EMC) and ethylene carbonate (EC) in a volume ratio of 90:10 was used as the non-aqueous solvent of the electrolytic solution. A coin-type dual-ion battery and a laminated-type dual-ion battery were manufactured.

<Comparative example 1>
A coin-type dual-ion battery and a laminated-type dual-ion battery were produced in the same manner as in Example 1 except that the concentration of LIPF _{6 in} the electrolytic solution was 3 mol / L and LiBF _{4 was not used.}

<Comparative example 2>
A coin-type dual ion battery and a laminated dual type dual in the same manner as in Example 1 except that _{the concentration of LIPF 6} of the electrolytic solution was set to 1.8 mol / L and _{the concentration of LiBF 4 was set to 0.2 mol / L.} An ion battery was manufactured.

<Evaluation>
The following items were evaluated for the coin-type dual-ion battery or the laminated-type dual-ion battery produced in Examples 1 to 7 and Comparative Examples 1 and 2. The results are shown in Table 1 together with the composition of the electrolytic solution used for manufacturing the coin-type dual ion battery, the type of the positive electrode active material, and the type of the negative electrode active material.

[Gas generation amount]
Using the produced laminated dual-ion battery, the volume A was measured using an electronic hydrometer MDS-300 manufactured by Alpha Mirage Co., Ltd. Subsequently, a TOSCAT 3300 manufactured by Toyo System Co., Ltd. was used to ^{charge the battery at a constant current constant voltage of 1.0 mA / cm 2} and a voltage of 3.5 V for 24 hours, and then the volume B was charged using the electronic specific gravity meter MDS-300. It was measured. Volume B-volume A was calculated and used as the amount of gas generated.
This result is shown in Table 1 as a relative value with the amount of gas generated by the laminated dual-ion battery of Comparative Example 1 as 100.

[25 ° C cycle life]
Using the manufactured coin-type dual-ion battery, using TOSCAT3300 manufactured by Toyo System Co., Ltd., constant current and constant voltage charging with a current density of ^{1.0 mA / cm 2 and a voltage of 3.5 V in a constant temperature bath at 25 ° C.} After that, a charge / discharge test was conducted in which a discharge current value of ^{1.0 mA / cm 2 was used to discharge to a final voltage of 2.0 V.} Charging and discharging were repeated until the discharge capacity became 80% or less of the discharge capacity in the first cycle. The number of cycles when the discharge capacity became 80% or less was defined as the cycle life.
This result is shown in Table 1 as a relative value with the cycle life of the coin-type dual-ion battery of Comparative Example 1 as 100.

[55 ° C cycle life]
Using the manufactured coin-type dual-ion battery, using TOSCAT3300 manufactured by Toyo System Co., Ltd., constant current and constant voltage charging with a current density of ^{1.0 mA / cm 2 and a voltage of 3.5 V in a constant temperature bath at 55 ° C.} After that, a charge / discharge test was conducted in which a discharge current value of ^{1.0 mA / cm 2 was used to discharge to a final voltage of 2.0 V.} Charging and discharging were repeated until the discharge capacity became 80% or less of the discharge capacity in the first cycle. The number of cycles when the discharge capacity became 80% or less was defined as the cycle life.
This result is shown in Table 1 as a relative value with the cycle life of the coin-type dual-ion battery of Comparative Example 1 as 100.

[-30 ° C / 25 ° C volume ratio]
Using the manufactured coin-type dual-ion battery, using TOSCAT3300 manufactured by Toyo System Co., Ltd., constant current and constant voltage charging with a current density of ^{1.0 mA / cm 2 and a voltage of 3.5 V in a constant temperature bath at 25 ° C.} After that, the discharge capacity A was calculated by discharging to a final voltage of 2.0 V with a discharge current value of a current density of 1.0 mA / cm ^{2. Next, constant current and constant voltage charging is performed at a current density of 1.0 mA / cm 2} and a voltage of 3.5 V in a constant temperature bath at 25 ° C., and then the temperature of the constant temperature bath is changed to −30 ° C. 5 After standing for a while, the discharge capacity B was calculated by discharging to a final voltage of 2.0 V with a discharge current value of a current density of 1.0 mA / cm ^2. The discharge capacity B divided by the discharge capacity A was defined as the volume ratio of −30 ° C./25 ° C.
This result is shown in Table 1 as a relative value with the capacity ratio of −30 ° C./25 ° C. of the coin-type dual ion battery of Comparative Example 1 as 100.

All of the dual ion batteries of Examples 1 to 7 containing _{LiPF 6} and LiBF ₄ as electrolyte salts within the scope of the present invention are duals of Comparative Example 1 containing _{only LiPF 6 as an electrolyte salt and not LiBF 4.} Compared with the ion battery, the amount of gas generated was reduced, the cycle life at 25 ° C. and 55 ° C. was extended, and the capacity ratio of −30 ° C./25 ° C. was increased. It is considered that the decrease in the amount of gas generated is due to the suppression of the reaction between the _{water content and LiPF 6 during charging.} It is considered that the cycle life at 25 ° C. and 55 ° C. was extended because the gas generation was suppressed. The reason why the volume ratio of -30 ° C / 25 ° C became large was that a film containing boron was formed on the surface of the negative electrode active material (Li ₄ Ti ₅ O _{12 ) by LiBF 4, LiBOB, and LiDFOB containing boron, and this film was formed.} It is considered that this is because the negative electrode active material easily releases lithium ions even at a low temperature.

Further, the dual ion batteries of Examples 1 to 5 using only the chain carbonate as the non-aqueous solvent of the electrolytic solution are the dual ion batteries of Examples 6 to 7 using the mixed solvent of the chain carbonate and the cyclic carbonate. In comparison, the -30 ° C / 25 ° C volume ratio was larger. This is because the chain carbonate has a lower viscosity than the cyclic carbonate, so that the dual ion batteries of Examples 1 to 5 using only the chain carbonate use the mixed solvent of the chain carbonate and the cyclic carbonate. It is considered that the electric resistance of the electrolytic solution at low temperature was lower than that of the dual ion batteries of 6 to 7.

In particular, the dual ion batteries of Examples 1 to 4 using EMC alone as the non-aqueous solvent of the electrolytic solution generate more gas than the dual ion batteries of Example 5 using EMC and DEC. Reduced and longer cycle life at 25 ° C and 55 ° C. This is because EMC has a higher conductivity than DEC, so when the temperature is raised to 25 ° C or even 55 ° C, the mobility of electrolyte ions in the electrolyte is improved, and when the cycle is repeated. It is considered that this is due to the effect that the resistance increase of the electrolytic solution of the above is reduced. The effect of reducing gas generation is not clear, but I think it is because the stability of DEC is lower than that of EMC. The dual ion battery of Example 5 has a larger capacity ratio of −30 ° C./25 ° C. than that of the dual ion battery of Example 1. It is considered that this is because DEC has an advantage of having a lower melting point than EMC and has an effect of improving discharge characteristics at low temperatures.

Further, in the battery of Example 3 containing LiBOB and the battery of Example 4 containing LiBFOB as the electrolyte salt, gas generation was further reduced and the cycle life at 25 ° C. and 55 ° C. was further extended. It is considered that this is because LiBOB and LiBFOB have an effect of further suppressing the reaction between water and LiPF _{6 by coexisting with LiBF 4.}

The battery of Comparative Example 2 having a LiBF ₄ content lower than the range of the present invention has a reduced gas generation amount and a longer cycle life of 25 ° C. and 55 ° C. as compared with Comparative Example 1 containing no _{LiBF 4.} The volume ratio of -30 ° C / 25 ° C also increased. However, when the same EMC as in Comparative Example 2 was used as the solvent for the electrolytic solution, the LiBF ₄ content was lower than that in Examples 1 and 2 which are within the range of the present invention. It is considered that Comparative Example 2 is because _{the content of LiBF 4} was low and the effect of adding LiBF 4 was not sufficient.

<Example 8>
A coin-type dual-ion battery and a laminated-type dual-ion battery were produced in the same manner as in Example 1 except that mesocarbon microbeads (MCMB) manufactured by Osaka Gas Chemical Co., Ltd. were used as the positive electrode active material.

<Comparative example 3>
A coin-type dual-ion battery and a laminated-type dual-ion battery were produced in the same manner as in Example 8 except that the concentration of LIPF _{6 in} the electrolytic solution was 3 mol / L and LiBF _{4 was not used.}

<Evaluation>
For the coin-type dual-ion battery and the laminated-type dual-ion battery produced in Example 8 and Comparative Example 3, the amount of gas generated, the cycle life of 25 ° C. and 55 ° C., and the volume ratio of −30 ° C./25 ° C. were measured by the above methods. did. This result is shown in Table 2 as a relative value with the result measured for the coin-type dual-ion battery and the laminated-type dual-ion battery of Comparative Example 3 as 100. In addition, Table 2 shows the composition of the electrolytic solution used for producing the coin-type dual-ion battery and the laminated-type dual-ion battery, the type of the positive electrode active material, and the type of the negative electrode active material.

Even when MCMB having hexagonal crystals is used as the positive electrode active material, the dual ion battery of Example 8 containing _{LiPF 6} and LiBF ₄ as the electrolyte salt within the scope of the present invention has only _{LiPF 6 as the electrolyte salt.} Compared with the dual ion battery of Comparative Example 3 containing and not containing LiBF ₄ , the amount of gas generated was reduced, the cycle life at 25 ° C. and 55 ° C. was extended, and the capacity ratio at -30 ° C./25 ° C. was increased. ..

<Example 9>
A coin-type dual-ion battery was produced in the same manner as in Example 1 except that the concentration of LiPF _{6 in the electrolytic solution was 2.5 mol / L.}

<Example 10>
A coin-type dual-ion battery was produced in the same manner as in Example 1 except that the concentration of LiPF _{6 in the electrolytic solution was 1.5 mol / L.}

<Example 11>
A coin-type dual-ion battery was produced in the same manner as in Example 1 except that the concentration of LiPF _{6 in the electrolytic solution was 1.0 mol / L.}

<Example 12>
A coin-type dual-ion battery was produced in the same manner as in Example 1 except that the concentration of LiPF _{6 in the electrolytic solution was 0.5 mol / L.}

<Evaluation>
For the coin-type dual-ion batteries manufactured in Examples 9 to 12, a TOSCAT3300 manufactured by Toyo System Co., Ltd. was used in a constant temperature bath at 25 ° C. at ^{a current density of 1.0 mA / cm 2} and a voltage of 3.5 V. Constant current and constant voltage charging was performed, and then ^{discharge was performed at a discharge current value of a current density of 1.0 mA / cm 2 to} a final voltage of 2.0 V to obtain a discharge capacity of 25 ° C. The obtained discharge capacity was calculated as a relative energy density which is a relative value with the discharge capacity at 25 ° C. of the coin-type dual ion battery of Example 1 as 100%.

FIG. 1 is a graph showing the relationship between the concentration _{of LiPF 6} and the relative energy density of the electrolytic solution of the coin-type dual ion battery produced in Examples 1 and 9 to 12. In FIG. 1, the horizontal axis represents _{the concentration of LiPF 6 in} the electrolytic solution, and the vertical axis represents the relative energy density. As shown in FIG. 1, in the range of 2 mol / L concentration of LiPF ₆ in the electrolytic solution is from 0.5 mol / L, the energy density becomes higher with increasing concentrations of LiPF _6, 2 molar concentration of LiPF ₆ It can be seen that the energy density becomes almost constant when it becomes / L or more. Therefore, from this result, _{it was confirmed that the concentration of LiPF 6 in} the electrolytic solution is preferably in the range of 2.0 mol / L or more and 2.5 mol / L or less.

Claims (7)

An electrolytic solution containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, a positive electrode containing a positive electrode active material capable of storing and releasing anions of the electrolyte salt, and a cation of the electrolyte salt capable of storing and releasing. A dual-ion battery including a negative electrode containing a negative electrode active material.
The positive electrode active material contains graphite and contains graphite.
The negative electrode active material contains a spinel-type lithium titanium oxide whose _{general formula is represented by Li 4} Ti ₅ O _12.
The electrolyte salt contains lithium hexafluorophosphate and borate tetrafluorophosphate, and the content of the borate tetrafluoride is 0.15 mol with respect to 1 mol of the lithium hexafluorophosphate. A dual ion battery characterized in that it is within the range of 0.60 mol or less. The tetrafluoroborate is lithium tetrafluoroborate, tetraethylammonium tetrafluoroborate, triethylmethylammonium borate tetrafluoride, spirobipyrrolidinium borate tetrafluorate, and boric acid tetrafluoride 1. The dual ion battery according to claim 1, which comprises at least one compound selected from the group consisting of −ethyl-3-methylimidazolium. The dual ion battery according to claim 1 or 2, wherein the electrolyte salt further comprises at least one of bisoxalatoborate and difluorooxalatoborate. The dual ion battery according to any one of claims 1 to 3, wherein the non-aqueous solvent contains at least one compound selected from the group consisting of cyclic carbonate and chain carbonate. The dual ion battery according to claim 4, wherein the cyclic carbonate contains at least one compound selected from the group consisting of propylene carbonate and ethylene carbonate. The dual ion battery according to claim 4, wherein the chain carbonate contains at least one compound selected from the group consisting of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. The positive electrode has a positive electrode current collector, the negative electrode has a negative electrode current collector, and the positive electrode current collector and the negative electrode current collector are plain aluminum material, etched aluminum material, and amorphous material. The dual ion battery according to any one of claims 1 to 6, which is an aluminum-containing member selected from the group consisting of an aluminum material coated with a carbon film.

Images